阅读说明：本技术 锂离子二次电池用正极活性物质的制造方法、锂离子二次电池用正极活性物质、锂离子二次电池 (Method for producing positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery ) 是由 铃木淳 于 2020-02-18 设计创作，主要内容包括：本发明提供一种锂离子二次电池用正极活性物质的制造方法,其包括：混合工序,对作为起始原料的锂镍复合氧化物及不含锂的钨化合物粉末加热的同时进行混合而获得钨混合物；热处理工序,对钨混合物进行热处理,其中,锂镍复合氧化物包含Li、Ni及元素M,起始原料中的钨原子数相对于锂镍复合氧化物包含的镍及所述元素M的合计原子数的比率为0.05原子％以上3.00原子％以下,起始原料中的作为在水与锂镍复合氧化物中所述水所占的比率的水分率为3.0质量％以上,混合工序的温度为30℃以上65℃以下。(The present invention provides a method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a mixing step of mixing a lithium-nickel composite oxide as a starting material and a tungsten compound powder containing no lithium while heating the mixture to obtain a tungsten mixture; and a heat treatment step of heat-treating the tungsten mixture, wherein the lithium-nickel composite oxide contains Li, Ni and an element M, the ratio of the number of tungsten atoms in the starting material to the total number of nickel atoms and the element M contained in the lithium-nickel composite oxide is 0.05 at% or more and 3.00 at% or less, the water content ratio of the starting material, which is the ratio of water to the lithium-nickel composite oxide, is 3.0 mass% or more, and the temperature in the mixing step is 30 ℃ or more and 65 ℃ or less.)

1. A method for producing a positive electrode active material for a lithium ion secondary battery, comprising:

a mixing step of mixing a lithium-nickel composite oxide as a starting material and a tungsten compound powder containing no lithium while heating the starting materials to obtain a tungsten mixture; and

a heat treatment step of heat-treating the tungsten mixture,

the lithium nickel composite oxide comprises lithium (Li), nickel (Ni) and an element M (M), wherein the element M is at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co and Al,

in the starting material, the ratio of the number of tungsten atoms to the total number of atoms of nickel and the element M contained in the lithium-nickel composite oxide is 0.05 atomic% or more and 3.00 atomic% or less,

a water content ratio of the starting material, which is a ratio of water to the lithium nickel composite oxide in which the water is present, is 3.0 mass% or more,

the temperature in the mixing step is 30 ℃ to 65 ℃.

2. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1, wherein,

the lithium nickel composite oxide is a lithium nickel composite oxide in which: ni: m ═ y: 1-x: the material mass ratio of x comprises a layered compound of lithium (Li), nickel (Ni) and the element M (M), wherein x is more than or equal to 0 and less than or equal to 0.70, and y is more than or equal to 0.95 and less than or equal to 1.20.

3. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2, wherein,

the water content is 3.0 mass% to 7.0 mass%.

4. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 3,

the water content is 4.0 mass% or more and 6.0 mass% or less.

5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 4,

the heat treatment temperature in the heat treatment step is 100 ℃ to 200 ℃.

6. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 5,

the atmosphere in the mixing step is either decarbonated air or an inert gas.

7. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 6, wherein,

the charging speed of the lithium nickel composite oxide in the mixing step is 1 kg/min and is 0.15m³More than 0.30 m/min³Discharging the atmosphere in the mixing step at a rate of less than or equal to one minute, and supplying the decarbonated air or the inert gas within a range in which the atmosphere in the mixing step is not at a negative pressure.

8. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 7,

the atmosphere in the heat treatment step is either decarbonated air or an inert gas.

9. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 8,

the lithium-free tungsten compound is selected from tungsten oxide (WO)₃) And tungstic acid (WO)₃·H₂O) at least one kind selected from the group consisting of (1) and (2).

10. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 1 to 9,

in the heat treatment step, lithium tungstate is fixed to the surface of the lithium nickel composite oxide particles.

11. A positive electrode active material for a lithium ion secondary battery,

the positive electrode active material for a lithium ion secondary battery comprises a plurality of composite particles,

the composite particle comprises:

taking the mass ratio as Li: ni: m ═ y: 1-x: x is particles of a lithium-nickel composite oxide containing lithium (Li), nickel (Ni) and an element M (M), wherein x is 0. ltoreq. x.ltoreq.0.70, y is 0.95. ltoreq. y.ltoreq.1.20, and the element M is at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co and Al; and

a compound containing tungsten and lithium disposed on the surface of the lithium nickel composite oxide particles,

the ratio of segregated particles, in which the compound containing tungsten and lithium disposed on the surfaces of the lithium nickel composite oxide particles is greater than the other composite particles, is 0.1% or less by number,

the ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of atoms of nickel and the element M contained in the lithium-nickel composite oxide is 0.05 at% or more and 3.0 at% or less.

12. A lithium ion secondary battery having a lithium ion secondary battery,

the positive electrode for a lithium ion secondary battery, which comprises the positive electrode active material according to claim 11.

Technical Field

The present invention relates to a method for producing a positive electrode active material for a lithium ion secondary battery, and a lithium ion secondary battery.

Background

In recent years, with the spread of portable electronic devices such as mobile phones and portable computers, there has been an increasing demand for the development of small and lightweight secondary batteries having high energy density. In addition, there is an increasing demand for development of high-output secondary batteries as batteries for electric vehicles such as hybrid vehicles.

As a secondary battery that can satisfy such a demand, there is a lithium ion secondary battery. The lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and active materials of the negative electrode and the positive electrode are materials capable of releasing and inserting lithium.

Among them, lithium ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material have been actively researched and developed, and have been put into practical use as batteries having a high energy density because they can obtain a high voltage of 4V class.

Examples of materials mainly proposed so far include lithium cobalt composite oxide (LiCoO) which is relatively easy to synthesize₂) Lithium nickel composite oxide (LiNiO) using nickel having a lower price than cobalt₂) Lithium nickel cobalt manganese composite oxide (LiNi)_{1/ 3}Co_1/3Mn_1/3O₂) Lithium manganese complex oxide (LiMn) using manganese₂O₄) And the like.

Among them, lithium nickel composite oxides have drawn attention as materials that can realize low resistance and high output because of their good cycle characteristics. In addition, in recent years, attention has been paid to a low resistance for obtaining a high output when a lithium ion secondary battery is produced as a positive electrode active material for a lithium ion secondary battery.

As a method for achieving the low resistance, it is considered useful to use a method of adding different elements, particularly, transition metals such as W, Mo, Nb, Ta, and Re, which can obtain a high valence number.

For example, patent document 1 proposes a lithium transition metal compound powder for a positive electrode material of a lithium secondary battery, which satisfies a predetermined composition formula, and in which the ratio of 1 or more elements selected from Mo, W, Nb, Ta, and Re to the total molar amount of Mn, Ni, and Co in the composition formula is 0.1 mol% or more and 5 mol% or less. Patent document 1 also discloses a method for producing a lithium transition metal compound powder for a positive electrode material of a lithium secondary battery, the method comprising: a spray drying step of pulverizing lithium carbonate, a Ni compound, a Mn compound, a Co compound, and a metal compound containing at least 1 or more elements selected from Mo, W, Nb, Ta, and Re in a liquid medium, and spray drying a slurry in which these are uniformly dispersed; and a firing step of firing the obtained spray-dried product.

According to patent document 1, it is possible to achieve both the cost reduction, the high safety, the high load characteristic, and the improvement in handling property of the lithium transition metal compound powder used for the positive electrode material of the lithium secondary battery.

However, according to the above-mentioned production method disclosed in patent document 1, the above-mentioned lithium transition metal compound powder is obtained by pulverizing raw materials in a liquid medium, spray-drying a slurry in which these raw materials are uniformly dispersed, and firing the obtained spray-dried body. Therefore, a part of different elements such as Mo, W, Nb, Ta, and Re is substituted with Ni arranged in a layered manner, and there is a problem that battery characteristics such as battery capacity and cycle characteristics are degraded.

Patent document 2 proposes a positive electrode active material for a nonaqueous electrolyte secondary battery, which has at least a lithium transition metal composite oxide having a layered structure, wherein the lithium transition metal composite oxide is present in the form of particles composed of one or both of primary particles (grains) and secondary particles as aggregates thereof, and at least the surface of the particles has a compound containing at least 1 element selected from the group consisting of molybdenum, vanadium, tungsten, boron and fluorine. Patent document 2 discloses a method of producing the positive electrode active material for a nonaqueous electrolyte secondary battery, in which a mixture of an additive element compound such as a molybdenum compound, a lithium compound, and a compound obtained by coprecipitation (coprecipitation) of cobalt or the like and heat treatment is used as a raw material mixture, and the raw material mixture is fired and pulverized.

According to the positive electrode active material for a nonaqueous electrolyte secondary battery disclosed in patent document 2, in particular, when the particle surface has a compound containing at least 1 selected from the group consisting of molybdenum, vanadium, tungsten, boron, and fluorine, the initial characteristics can be improved without impairing the improvement of thermal stability, load characteristics, and output characteristics.

However, the effect obtained in patent document 2 by selecting at least 1 additive element from the group consisting of molybdenum, vanadium, tungsten, boron, and fluorine is to improve the initial characteristics, i.e., the initial discharge capacity and the initial efficiency, and not to improve the output characteristics. Further, according to the production method disclosed in patent document 2, since a raw material mixture, which is a mixture of an additive element compound such as a molybdenum compound, a lithium compound, and a compound obtained by coprecipitating cobalt or the like and then performing heat treatment, is fired, a part of the additive element is substituted with nickel disposed in a layered state, and thus, there is a problem that battery characteristics are degraded.

Patent document 3 proposes a positive electrode active material obtained by coating composite oxide particles having a predetermined composition with a tungstic acid compound and heating the coated particles, wherein the carbonate ion content is 0.15 mass% or less. Patent document 3 discloses a method for producing a positive electrode active material, which includes a coating step of coating a tungstic acid compound on complex oxide particles containing lithium (Li) and nickel (Ni), and a heating step of heating the complex oxide particles coated with the tungstic acid compound.

The technique of patent document 3 is considered to be capable of suppressing gas generation due to decomposition of a nonaqueous electrolytic solution or the like, or suppressing gas generation originating from itself in a positive electrode active material. However, the output characteristics are not improved.

Further, improvement has been made in terms of high output of the lithium nickel composite oxide.

For example, patent document 4 proposes a positive electrode active material for a nonaqueous electrolyte secondary battery, which is a lithium metal composite oxide composed of primary particles and secondary particles in which the primary particles are aggregated, and has a surface containing Li on the surface of the lithium metal composite oxide₂WO₄、Li₄WO₅、Li₆W₂O₉The fine particles of lithium tungstate represented by any one of (1) above are considered to be capable of obtaining a high output while obtaining a high capacity.

However, while it is possible to achieve high output while maintaining high capacity, the demand for higher capacity has further increased.

Patent document 5 proposes a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, which includes: a mixing step of mixing lithium-nickel composite oxide particles, a lithium-free tungsten compound powder, and water to obtain a tungsten mixture; and a heat treatment step of heat-treating the tungsten mixture. The heat treatment process includes: a first heat treatment step (1) of heat-treating the tungsten mixture to cause a reaction between the lithium compound present on the primary particle surface of the lithium nickel composite oxide particles and the tungsten compound particles and dissolve the tungsten compound particles, thereby forming lithium nickel composite oxide particles in which tungsten is dispersed on the primary particle surface; and a 2 nd heat treatment step of performing heat treatment at a temperature higher than that in the 1 st heat treatment step after the 1 st heat treatment step to form lithium nickel composite oxide particles having a compound containing tungsten and lithium on the surfaces of primary particles of the lithium nickel composite oxide particles.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2009 and 289726

Patent document 2: japanese patent laid-open publication No. 2005-251716

Patent document 3: japanese patent laid-open No. 2010-40383

Patent document 4: japanese patent laid-open publication No. 2013-125732

Patent document 5: japanese patent laid-open publication No. 2017-063003

Disclosure of Invention

Problems to be solved by the invention

However, in the example of patent document 5, only an example in which the mixed powder of the tungsten mixture is placed in an aluminum bag and purged with nitrogen gas in the 1 st heat treatment step is disclosed, and mass production by this method has a problem of extremely high cost.

In patent document 5, the mixing step, the 1 st heat treatment step and the 2 nd heat treatment step are required, and the number of steps is large, which also increases the production cost. Further, since the aluminum bag and the vacuum dryer are used, the mixing and the heat treatment cannot be continuously performed, which is not advantageous in terms of cost.

In view of the above-described problems of the prior art, an object of the present invention is to provide a method for producing a positive electrode active material for a lithium ion secondary battery, which is low in cost and can achieve high capacity and high output when used for a positive electrode of a lithium ion secondary battery.

Means for solving the problems

In order to solve the above problems, one aspect of the present invention provides a method for producing a positive electrode active material for a lithium ion secondary battery, comprising: a mixing step of mixing lithium-nickel composite oxide as a starting material and tungsten compound powder containing no lithium while heating the starting material to obtain a tungsten mixture; a heat treatment step of heating the tungsten mixture. The lithium-nickel composite oxide contains lithium (Li), nickel (Ni), and an element M (M) (wherein the element M is at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al), the ratio of the number of tungsten atoms in the starting material to the total number of atoms of nickel and the element M contained in the lithium-nickel composite oxide is 0.05 at% or more and 3.00 at% or less, the water content ratio in the starting material, which is the ratio of water to the water in the lithium-nickel composite oxide, is 3.0 mass% or more, and the temperature in the mixing step is 30 ℃ or more and 65 ℃ or less.

Efficacy of the invention

According to one aspect of the present invention, a method for producing a positive electrode active material for a lithium ion secondary battery, which is low in cost and can achieve high capacity and high output when used for a positive electrode of a lithium ion secondary battery, can be provided.

Drawings

Fig. 1 is an example of SEM images when measuring segregation particles.

FIG. 2 is an SEM photograph of segregated particles.

FIG. 3 is an SEM photograph of segregated particles.

Fig. 4 is an explanatory view of a cross-sectional structure of the button cell manufactured in the examples and comparative examples.

Fig. 5A shows an example of impedance evaluation.

Fig. 5B is a schematic explanatory view of an equivalent circuit used for analysis.

Detailed Description

The embodiments for carrying out the present invention will be described below with reference to the drawings, but the present invention is not limited to the embodiments described below, and various changes and substitutions may be made to the embodiments described below without departing from the scope of the present invention.

[ method for producing Positive electrode active Material for lithium ion Secondary Battery ]

The method for producing a positive electrode active material for a lithium ion secondary battery according to the present embodiment (hereinafter, also simply referred to as "method for producing a positive electrode active material") may include the following steps.

And a mixing step of mixing the lithium nickel composite oxide as a starting material and the tungsten compound powder containing no lithium while heating to obtain a tungsten mixture.

And a heat treatment step of heating the tungsten mixture.

Further, the lithium nickel composite oxide may include lithium (Li), nickel (Ni), and an element m (m). The element M is preferably at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co and Al.

The ratio of the number of tungsten atoms in the starting material to the total number of nickel and element M contained in the lithium nickel composite oxide may be 0.05 at% or more and 3.00 at% or less. The water content of the starting material, which is the ratio of water to the lithium nickel composite oxide, is 3.0 mass% or more, and the temperature in the mixing step is preferably 30 ℃ to 65 ℃.

Hereinafter, the method for producing the positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described in detail for each step.

(mixing Process)

In the mixing step, the lithium nickel composite oxide and the tungsten compound containing no lithium (hereinafter, also simply referred to as "tungsten compound") as the starting materials may be mixed while heating. Thus, a tungsten mixture as a mixture of the lithium nickel composite oxide and the tungsten compound containing no lithium can be obtained through the mixing process. As described later, it is considered that at least a part of the tungsten compound reacts with the remaining lithium compound present on the surface of the primary particles of the lithium nickel composite oxide in the mixing step to generate a compound containing tungsten and lithium. Thus, the tungsten mixture can also comprise compounds containing tungsten and lithium in place of or in addition to the tungsten compound.

The starting material supplied to the mixing step preferably contains water, and for example, in the case where the lithium nickel composite oxide and the lithium-free tungsten compound as the starting materials do not contain water, water may be added in the mixing step. In addition, when at least one of the lithium nickel composite oxide and the lithium-free tungsten compound contains sufficient moisture, it is not necessary to separately add water in the mixing step.

When the starting raw material contains water, the remaining lithium compound present on the surface of the primary particles of the lithium nickel composite oxide dissolves, and therefore, when a tungsten compound that can be dissolved in a water-soluble or alkaline solution is used, the dissolution of the tungsten compound and the dispersion of the tungsten component can be enhanced in the mixing step.

The mixing step is preferably performed without placing the mixture in a sealed container such as an aluminum bag.

By mixing the lithium nickel composite oxide and the tungsten compound while heating, the remaining lithium compound present on the surface of the primary particles of the lithium nickel composite oxide can be reacted with the tungsten compound. Then, the compound containing tungsten and lithium obtained by reacting the remaining lithium compound present on the surface of the primary particle of the lithium nickel composite oxide with the tungsten compound is dissolved in water, whereby the compound containing tungsten and lithium can be dispersed on the surface of the primary particle of the lithium nickel composite oxide.

The composition of the lithium nickel composite oxide to be supplied to the mixing step is not particularly limited, and for example, lithium (Li), nickel (Ni), and an element m (m) are preferably contained in such a manner that the ratio of the amounts of substances is Li: ni: m ═ y: 1-x: x (wherein x is more than or equal to 0 and less than or equal to 0.70, and y is more than or equal to 0.95 and less than or equal to 1.20). Here, the element M may be at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co, and Al. Further, y is more preferably 0.97. ltoreq. y.ltoreq.1.15. The lithium nickel composite oxide is preferably a compound having a layered structure, i.e., a layered compound.

The lithium nickel composite oxide can be represented by the general formula Li_yNi_1-xM_xO_2+αAnd (4) showing. The description of x, y, and M is omitted here. Alpha is preferably, for example, -0.2. ltoreq. alpha.ltoreq.0.2.

The lithium nickel composite oxide may have a powder form including primary particles and secondary particles in which the primary particles are aggregated, for example.

For example, a lithium nickel composite oxide can be prepared for the mixing step by firing a mixture of a nickel composite compound such as a nickel composite oxide or a nickel composite hydroxide and a lithium compound. Further, for example, the lithium nickel composite oxide obtained after firing may be further washed with water to reduce the amount of residual lithium components and the like adhering to the surfaces of the lithium nickel composite oxide particles, thereby forming a washed cake, and then the washed cake may be supplied to the mixing step. Here, in the case where the lithium nickel composite oxide is supplied to the mixing step after being formed into a cake, since the cake contains moisture, it is not necessary to add moisture in the mixing step as described above depending on the content of the moisture and the like.

However, the lithium nickel composite oxide to be supplied to the mixing step is preferably added in a state after firing, that is, without being washed with water. The lithium nickel composite oxide in the fired state, i.e., without being washed with water, has a particularly sufficient amount of lithium compound on the surface of its primary particles for reaction with the tungsten compound. Therefore, by using the lithium nickel composite oxide in a fired state, it is possible to reduce lithium extracted from the interior of the lithium nickel composite oxide particles when reacting with the tungsten compound in a mixing step or the like, and to suppress the formation of a deteriorated layer on the surface of the primary particles of the lithium nickel composite oxide.

The tungsten compound used is preferably water-soluble and soluble in moisture contained in the starting material so as to permeate the surface of the primary particles inside the secondary particles of the lithium nickel composite oxide. Since the moisture in the starting material becomes alkaline by elution of lithium, the tungsten compound may be a compound soluble under alkaline conditions. Further, since the starting material is heated in the mixing step, a material which is hardly soluble in water at normal temperature but is soluble in water after being heated in the mixing step or a material which is soluble in water after reacting with a lithium compound on the surface of the lithium nickel composite oxide particle to form a compound containing tungsten and lithium is suitably used as the tungsten compound.

In addition, since the amount of the dissolved tungsten compound is only required to be an amount that can penetrate the surface of the primary particles in the secondary particles of the lithium nickel composite oxide, for example, when an excessive amount of the tungsten compound is added, it may be possible that a part of the tungsten compound is in a solid state after mixing and heating.

As described above, the tungsten compound preferably does not contain lithium and is soluble in water when heated in a mixing step or the like. The lithium-free tungsten compound to be supplied to the mixing step is not particularly limited, and for example, 1 or more selected from tungsten oxide, tungstic acid, ammonium tungstate, sodium tungstate and the like is preferable, and tungsten oxide having a low possibility of being contaminated with impurities is more preferably used (WO)₃) And tungstic acid (WO)₃·H₂O) at least one kind selected from the group consisting of (1) and (2).

The amount of tungsten contained in the starting material is not particularly limited, and for example, the tungsten compound is added by adding the tungsten compound in such a manner that the number of tungsten atoms is preferably 0.05 atomic% or more and 3.00 atomic% or less, more preferably 0.05 atomic% or more and 2.00 atomic% or less, further preferably 0.10 atomic% or more and 1.00 atomic% or less, and particularly preferably 0.10 atomic% or more and 0.50 atomic% or less, relative to the total number of atoms of nickel and the element M contained in the lithium nickel composite oxide in the starting material.

When the tungsten compound is added so that the amount of tungsten in the starting material satisfies the above range, the amount of tungsten in the compound containing tungsten and lithium formed on the particle surface of the lithium nickel composite oxide in the obtained positive electrode active material may satisfy a preferred range. Therefore, when the positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, the charge/discharge capacity and the output characteristics can be improved, and both can be achieved.

After the mixing step and the heat treatment step, the ratio of the number of tungsten atoms to the total number of atoms of nickel and the element M contained in the product does not change. Therefore, the tungsten atomic number ratio to the total atomic number of nickel and the element M in the tungsten mixture obtained after the mixing step or the positive electrode active material obtained after the heat treatment step preferably satisfies the same range as the above-mentioned starting material.

The moisture content, which is the ratio of water in the starting material and the lithium nickel composite oxide to water, is not particularly limited, and is, for example, preferably 3.0 mass% or more, more preferably 3.0 mass% or more and 7.0 mass% or less, and still more preferably 4.0 mass% or more and 6.0 mass% or less.

By setting the water content to 3.0 mass% or more, the starting material can contain a sufficient amount of water, and the tungsten compound can be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide. This enables the tungsten compound to react sufficiently with the lithium compound on the surface of the lithium nickel composite oxide particle. Further, by setting the water content to 7.0 mass% or less, excessive elution of lithium from the lithium nickel composite oxide can be suppressed.

In the mixing step, the remaining lithium compound present on the surface of the primary particles of the lithium nickel composite oxide is reacted with the tungsten compound, and therefore, it is preferable to mix the lithium nickel composite oxide while heating the mixture. Here, by mixing while heating, the tungsten compound or the compound containing tungsten and lithium can be sufficiently dispersed on the surface of the primary particles of the lithium nickel composite oxide.

The temperature to be heated in the mixing step, i.e., the mixing temperature, is not particularly limited. The mixing temperature in the mixing step is, for example, preferably 30 ℃ to 65 ℃, more preferably 45 ℃ to 60 ℃, and still more preferably 50 ℃ to 60 ℃.

In the mixing, the temperature of the tungsten mixture is slightly increased by the reaction between the lithium compound and the tungsten compound present on the surface of the lithium nickel composite oxide particles, and by setting the mixing temperature to 65 ℃ or lower, the tungsten compound can be uniformly dispersed in the particles of the lithium nickel composite oxide while suppressing the decrease in the amount of water in the tungsten mixture between the mixing steps. In addition, by uniformly dispersing the tungsten compound, the tungsten compound can be sufficiently reacted with the remaining lithium compound present on the surface of the primary particles of the lithium nickel composite oxide. However, when the mixing temperature is a temperature exceeding 65 ℃, the moisture amount necessary for promoting the reaction of the lithium compound and the tungsten compound may not be obtained due to the drying of the tungsten mixture.

By setting the mixing temperature to 30 ℃ or higher, the dispersion of the tungsten compound can be particularly promoted, and particularly, the reaction of the tungsten compound with the remaining lithium compound can be promoted.

The time for carrying out the mixing step is not particularly limited, and may be arbitrarily selected depending on the mixing temperature and the like. The mixing step is preferably performed for a time period of, for example, 15 minutes to 60 minutes, and more preferably 25 minutes to 45 minutes. By setting the mixing time to 15 minutes or more, the dispersion of the tungsten compound and the reaction between the tungsten compound and the remaining lithium compound can be promoted. Further, even if the mixing time is excessively prolonged, there is no great difference in the dispersion of the tungsten compound or the degree of reaction between the tungsten compound and the remaining lithium compound, and therefore, from the viewpoint of improving productivity and reducing cost, the mixing time is preferably 60 minutes or less.

The atmosphere in the mixing step is not particularly limited, but in order to avoid reaction between carbon dioxide in the atmosphere and the lithium component on the surface of the lithium nickel composite oxide particle, the atmosphere in the mixing step is preferably decarbonated air or an inert gas. Here, decarbonating air means that air in which carbonic acid in air, that is, carbon dioxide is reduced is used as an atmosphere. The inert gas is 1 or more kinds of gas selected from rare gas and nitrogen gas as an atmosphere.

In addition, in order to discharge moisture released from the lithium nickel composite oxide, it is preferable to exhaust the atmosphere of the mixing step. The exhaust rate is not particularly limited, but is preferably 0.15m relative to the charging rate (charging amount) of 1 kg/min for charging the lithium nickel composite oxide into the mixing step³More than 0.30 m/min³The atmosphere in the mixing step is exhausted at a rate of less than or equal to one minute. When the atmosphere in the mixing step is exhausted, the decarbonated air or the inert gas is supplied within a range not to make the atmosphere in the mixing step a negative pressure, that is, the flow rate of the decarbonated air or the inert gas is preferably adjusted. When the atmosphere in the mixing step is at a negative pressure, air may flow into the atmosphere in the mixing step, and the lithium component may react with carbon dioxide. In contrast, by controlling the atmosphere in the mixing step to prevent the negative pressure, the reaction of the lithium component with carbon dioxide can be suppressed, and in particular, the characteristic degradation of the finally produced positive electrode active material can be prevented.

When the lithium nickel composite oxide and the lithium-free tungsten compound are mixed, a general mixer can be used. For example, a vibration stirrer, a ledige (Lodige) stirrer, a Julia (Julia) stirrer, a V-type mixer, or the like may be used to sufficiently mix the lithium nickel composite oxide so as not to damage the morphology of the lithium nickel composite oxide.

(Heat treatment Process)

In the heat treatment process, the tungsten mixture may be heat-treated. In the heat treatment step, moisture in the tungsten mixture can be sufficiently evaporated, and the compound containing tungsten and lithium can be fixed to the surface of the primary particles of the lithium-nickel composite oxide particles.

The heat treatment temperature in the heat treatment step is not particularly limited, and is preferably 100 ℃ to 200 ℃. The reason for this is that by setting the heat treatment temperature to 100 ℃ or higher, the moisture in the tungsten mixture can be sufficiently evaporated, and the compound containing tungsten and lithium can be sufficiently fixed to the particle surface of the lithium nickel composite oxide.

Further, by setting the heat treatment temperature to 200 ℃ or lower, it is possible to suppress a problem that necking (necking) of the particles of the lithium nickel composite oxide by the compound containing tungsten and lithium is caused, and the specific surface area of the particles of the lithium nickel composite oxide is reduced. Thus, when the obtained positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, the battery characteristics can be particularly improved.

The heat treatment time in the heat treatment step is not particularly limited, and is preferably 1 hour to 5 hours in order to sufficiently evaporate water and fix the compound containing tungsten and lithium.

In order to avoid the reaction of carbon dioxide in the atmosphere with lithium on the particle surface of the lithium nickel composite oxide, the atmosphere in the heat treatment step is preferably decarbonated air or an inert gas.

According to the method for producing a positive electrode active material of the present embodiment described above, the tungsten compound can be uniformly dispersed in the particles of the lithium nickel composite oxide by mixing while heating in the mixing step. In addition, the remaining lithium compound present on the particle surface of the lithium nickel composite oxide can be reacted with the tungsten compound to form a compound containing tungsten and lithium, and the compound can be uniformly dispersed. In addition, by sufficiently evaporating moisture in the heat treatment step, a compound containing tungsten and lithium, for example, lithium tungstate can be uniformly fixed to the particle surface of the lithium nickel composite oxide. This can suppress the ratio of segregated particles containing more tungsten and lithium compounds than other particles deposited on the particle surfaces of the lithium nickel composite oxide. By suppressing the ratio of the segregated particles, the cycle characteristics can be improved and the positive electrode resistance can be suppressed.

Further, by making the amount of tungsten in the tungsten mixture formed in the mixing step satisfy a predetermined range, the amount of tungsten contained in the compound containing tungsten and lithium formed on the particle surface of the lithium nickel composite oxide in the obtained positive electrode active material can be made to be a preferable range. Thus, when the positive electrode active material produced by the method for producing a positive electrode active material according to the present embodiment is used as a positive electrode material for a lithium ion secondary battery, it is possible to improve the charge/discharge capacity and the output characteristics in particular, and to achieve both of them. That is, high output can be obtained while high capacity is obtained.

In addition, according to the method for producing a positive electrode active material of the present embodiment, a desired positive electrode active material can be produced through the mixing step and the heat treatment step described above without performing an operation such as sealing in an aluminum container or the like. Therefore, the positive electrode active material can be obtained at low cost, and has a high capacity and a high output as described above.

[ Positive electrode active Material for lithium ion Secondary batteries ]

Hereinafter, a description will be given of a structural example of the positive electrode active material for a lithium ion secondary battery (hereinafter, also simply referred to as "positive electrode active material") according to the present embodiment. Here, for example, the positive electrode active material for a lithium-ion secondary battery of the present embodiment can be produced by the above-described method for producing a positive electrode active material, and therefore, the description of the parts already described will be omitted.

The positive electrode active material for a lithium ion secondary battery of the present embodiment may include a plurality of composite particles including: taking the mass ratio as Li: ni: m ═ y: 1-x: particles of a lithium-nickel composite oxide in which x comprises lithium (Li), nickel (Ni), and an element m (m); and a compound containing tungsten and lithium disposed on the particle surface of the lithium-nickel composite oxide.

Here, x and y preferably satisfy 0. ltoreq. x.ltoreq.0.70 and 0.95. ltoreq. y.ltoreq.1.20, and the element M may be at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti, Co and Al. More preferably, y is 0.97. ltoreq. y.ltoreq.1.15.

The ratio of the compound containing tungsten and lithium disposed on the particle surface of the lithium nickel composite oxide among the plurality of composite particles to the segregated particles of the other composite particles may be 0.1% or less by number ratio. The ratio of the number of tungsten atoms in the compound containing tungsten and lithium to the total number of atoms of nickel and the element M contained in the lithium-nickel composite oxide is preferably 0.05 at% or more and 3.0 at% or less.

The positive electrode active material according to the present embodiment may include a plurality of composite particles including the lithium nickel composite oxide particles and a compound including tungsten and lithium disposed on the surfaces of the lithium nickel composite oxide particles. Here, the positive electrode active material of the present embodiment may be composed of the composite particles.

The lithium nickel composite oxide may be represented by the general formula Li_yNi_1-xM_xO_2+αAnd (4) showing. The description of x, y and M is omitted herein. Alpha is preferably, for example, -0.2. ltoreq. alpha.ltoreq.0.2. The lithium nickel composite oxide may have a layered structure, for example. Namely, it may be a layered compound.

The particles of the lithium nickel composite oxide may have primary particles and secondary particles in which the primary particles are aggregated.

By using such a lithium nickel composite oxide, a higher charge/discharge capacity can be obtained.

As described above, the lithium nickel composite oxide may have a structure in which a compound containing tungsten and lithium, for example, lithium tungstate, is disposed on the particle surface of the lithium nickel composite oxide.

In general, it is considered that when the surface of the positive electrode active material is completely covered with the different compound, the movement (intercalation) of lithium ions is greatly restricted, and as a result, the high capacity advantage of the lithium nickel composite oxide is lost. However, in the positive electrode active material of the present embodiment, although a compound containing tungsten and lithium is formed on the particle surface of the lithium nickel composite oxide, such a compound containing tungsten and lithium has good lithium ion conductivity and has an effect of promoting lithium ion transfer. Therefore, by disposing a compound containing tungsten and lithium on the particle surface of the lithium nickel composite oxide, a lithium conduction path can be formed at the interface with the electrolyte, and the reaction resistance of the positive electrode active material (hereinafter, sometimes referred to as "positive electrode resistance") can be reduced, thereby improving the output characteristics.

That is, by reducing the positive electrode resistance, the voltage lost in the battery is reduced, and the voltage actually applied to the load side is relatively increased, so that high output can be obtained. Further, since the applied voltage on the load side is increased, lithium can be sufficiently inserted into and extracted from the positive electrode, and thus the battery capacity is also increased. Further, as the reaction resistance decreases, the load of the active material during charge and discharge also decreases, and therefore, the cycle characteristics can be improved.

Such a compound containing tungsten and lithium can have good lithium ion conductivity and an effect of promoting lithium ion transfer by containing tungsten and lithium, and the specific composition thereof is not particularly limited. However, lithium tungstate is preferred, and for example, 50% or more of tungsten contained in the compound containing tungsten and lithium is preferably represented by Li in terms of the ratio of the number of atoms₄WO₅Exist in the form of (1).

The reason for this is that, in the compound containing tungsten and lithium, Li₄WO₅Has many lithium ion conductive channels and a high effect of promoting lithium ion transfer, and therefore, W is Li in an atomic number ratio of 50% or more₄WO₅When the form (2) is present, a more significant effect of reducing the reaction resistance can be obtained.

Here, since the electrolyte and the lithium nickel composite oxide are in contact with each other on the surface of the primary particles of the lithium nickel composite oxide, it is preferable that a compound containing tungsten and lithium is formed on the surface of the primary particles of the lithium nickel composite oxide.

The surface of the primary particle of the lithium nickel composite oxide in the present embodiment includes the following portions: the surface of the primary particles exposed to the outside of the secondary particles of the lithium-nickel composite oxide; a vicinity of a surface of the secondary particle which is in communication with an outside of the secondary particle and is permeable to an electrolyte; and the surface of the primary particles exposed in the internal voids. In addition, even at the grain boundaries between the primary particles, the primary particles are included in the surfaces of the primary particles if the primary particles are not completely bonded and are in an electrolyte-permeable state.

That is, the contact between the lithium nickel composite oxide and the electrolyte is not limited to the outer surface of the secondary particles in which the primary particles of the lithium nickel composite oxide are aggregated, and voids occur near the surface and in the interior of the secondary particles, and even at the incomplete grain boundaries. Therefore, it is preferable to form and arrange a compound containing tungsten and lithium on the surface of the primary particles to promote the movement of lithium ions.

Therefore, by forming a compound containing tungsten and lithium on a large portion of the surface of the primary particles of the lithium nickel composite oxide that can be in contact with the electrolyte, the reaction resistance of the lithium nickel composite oxide particles can be further reduced.

Here, the compound containing tungsten and lithium need not be formed on the entire surface of the primary particles that can be in contact with the electrolyte, and may be in a partially coated state or a dispersed state. Even in a state of being partially coated or dispersed, if a compound containing tungsten and lithium is formed on the surface of the primary particles that can come into contact with the electrolyte, the effect of reducing the positive electrode resistance can be obtained.

The lithium nickel composite oxide particles contained in the positive electrode active material of the present embodiment preferably have a compound containing tungsten and lithium uniformly formed on the surface thereof.

Here, the positive electrode active material includes a plurality of composite particles including particles of a lithium nickel composite oxide and a compound including tungsten and lithium disposed on the surfaces of the particles of the lithium nickel composite oxide. The particles of the lithium nickel composite oxide may include primary particles containing the lithium nickel composite oxide and secondary particles formed by aggregating the primary particles.

In addition, when the compound containing tungsten and lithium is unevenly formed between the composite particles on the particle surface of the lithium nickel composite oxide, lithium ions between the composite particles move unevenly, and a load is applied to specific composite particles, which may deteriorate the cycle characteristics over a long period of time and increase the positive electrode resistance.

When the positive electrode active material of the present embodiment contains segregated particles, the segregated particles are white relative to the gray (gray) color exhibited by other composite particles when the positive electrode active material is observed with a Scanning Electron Microscope (SEM). Here, the segregated particles are particles in which more compounds including tungsten and lithium are unevenly deposited and arranged on the particle surface of the lithium nickel composite oxide than other composite particles.

Therefore, the presence or absence of the segregated particles, the calculation of the number ratio of the segregated particles, and the like can be seen by observing the positive electrode active material of the present embodiment with a scanning electron microscope.

In the positive electrode active material according to the present embodiment, as described above, among the plurality of composite particles, the segregated particles in which the compound containing tungsten and lithium is disposed on the particle surface of the lithium nickel composite oxide more than the other composite particles are preferably 0.1% or less, more preferably 0.01% or less in terms of the number ratio. When the ratio of the segregated particles in the plurality of composite particles is 0.1% or less, the cycle characteristics can be improved and the positive electrode resistance can be suppressed.

The lower limit of the ratio of the segregated particles in the plurality of composite particles is not particularly limited, and is preferably set to 0% or more because the segregated particles are not present.

The method of calculating the ratio of segregated particles in the plurality of composite particles contained in the positive electrode active material of the present embodiment is not particularly limited, and for example, the positive electrode active material can be observed in a range of 3 to 20 fields of view at a magnification of 10 to 1000 times using a scanning electron microscope, and the ratio of segregated particles in the composite particles in the obtained plurality of field-of-view images can be calculated. The observation conditions of the scanning electron microscope are not particularly limited, and the acceleration voltage is preferably 1kV or more and 20kV or less, for example.

Regarding the uniformity of the compound containing tungsten and lithium in the obtained composite particles, for example, a sample of the composite particles may be extracted from the positive electrode active material a plurality of times, the tungsten content may be analyzed, and evaluation and confirmation may be performed based on the variation of the tungsten content.

The ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of atoms of nickel and the element M contained in the nickel composite oxide (hereinafter, also referred to as "tungsten amount") is preferably 0.05 at% or more and 3.00 at% or less, more preferably 0.05 at% or more and 2.00 at% or less, further preferably 0.10 at% or more and 1.00 at% or less, and particularly preferably 0.10 at% or more and 0.50 at% or less. When the amount of tungsten is set to the above range, the positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, and high charge/discharge capacity and output characteristics can be achieved at the same time.

In the positive electrode active material of the present embodiment, for example, tungsten is derived from a compound containing tungsten and lithium disposed on the particle surface of the lithium nickel composite oxide, and nickel and the element M are derived from the lithium nickel composite oxide. Therefore, the above-mentioned amount of tungsten can be said to be different, that is, in the positive electrode active material of the present embodiment, the ratio of the number of tungsten atoms to the total number of atoms of nickel and the element M is preferably 0.05 at% or more and 3.00 at% or less, as described above.

When the amount of tungsten is 0.05 atomic% or more, the output characteristics can be particularly improved, which is preferable.

When the amount of tungsten is 3.00 atomic% or less, the occurrence of segregated particles can be particularly suppressed. When the amount of tungsten is 3.00 atomic% or less, lithium conductivity between the lithium nickel composite oxide and the electrolyte can be improved, and charge/discharge capacity can be improved.

The form of the compound containing tungsten and lithium disposed on the particle surface of the lithium nickel composite oxide is not particularly limited. However, in the case where the particle surface of the lithium nickel composite oxide is covered with a layer as a thick film of a compound containing tungsten and lithium, the grain boundaries of the lithium nickel composite oxide particles are filled with the thick film, possibly resulting in a reduction in specific surface area. In addition, when a layer is formed as a thick film of a compound containing tungsten and lithium, the compound containing tungsten and lithium may be intensively formed on the particle surface of a specific lithium nickel composite oxide, but not on the particle surfaces of other plural lithium nickel composite oxides. Here, the intervention of a compound containing tungsten and lithium may reduce the contact area between the lithium nickel composite oxide and the electrolyte.

Therefore, in order to obtain higher effects, the compound containing tungsten and lithium is preferably present on the particle surface of the lithium nickel composite oxide as particles having a particle diameter of 1nm to 300 nm.

When the particle size of the compound containing tungsten and lithium is 1nm or more, particularly sufficient lithium ion conductivity can be exhibited. In addition, when the particle diameter of the compound containing tungsten and lithium is 300nm or less, the compound particles containing tungsten and lithium can be particularly uniformly formed on the particle surface of the lithium nickel composite oxide, and particularly, the reaction resistance can be reduced.

By adopting the above-described form of the particles containing the compound of tungsten and lithium, a sufficient contact area with the electrolyte is obtained, and lithium ion conductivity can be effectively improved, so that the charge/discharge capacity can be particularly improved, and the reaction resistance can be more effectively reduced.

However, it is not necessary that all particles containing a compound of tungsten and lithium are particles having a particle diameter of 1nm to 300 nm. For example, it is preferable that 50% or more of the number of particles of the compound containing tungsten and lithium formed on the particle surface of the lithium nickel composite oxide satisfy the above range because particularly high effects can be obtained.

On the other hand, when the particle surface of the lithium nickel composite oxide is covered with a thin film containing a compound of tungsten and lithium, a Li conduction channel is formed at the interface with the electrolyte while suppressing a decrease in the specific surface area, and the effects of further improving the charge/discharge capacity and reducing the reaction resistance can be obtained. When the surface of the primary particle is covered with such a thin-film compound containing tungsten and lithium, the compound containing tungsten and lithium is preferably present on the surface of the primary particle of the lithium nickel composite oxide in the form of a coating film having a thickness of 1nm to 200 nm.

When the film thickness of the thin film containing a compound of tungsten and lithium is 1nm or more, the thin film can have particularly sufficient lithium ion conductivity. Further, when the film thickness of the thin film containing a compound of tungsten and lithium is 200nm or less, lithium ion conductivity can be particularly improved and reaction resistance can be particularly reduced, which is preferable.

The thin film containing the compound of tungsten and lithium does not need to be formed on the entire particle of the lithium nickel composite oxide, for example, a part of the surface of the particle of the lithium nickel composite oxide, and it is not required that the film thickness of the coating film all satisfies the range of 1nm to 200 nm. The above-mentioned high effect can be obtained when a thin film containing a compound of tungsten and lithium is formed on at least a part of the surface of the primary particles to a thickness of 1nm to 200 nm. Here, for example, when a compound containing tungsten and lithium is formed as a coating film, a sufficient film thickness of 1nm to 200nm can be formed by controlling the amount of tungsten contained in the compound to fall within the above range, which is necessary to obtain the effect.

In addition, in the case where a compound containing tungsten and lithium is formed on the particle surface of the lithium nickel composite oxide in which the particle form and the thin film form are mixed, a high effect can be obtained in terms of battery characteristics.

The amount of lithium in the entire positive electrode active material is not particularly limited, and the ratio of the sum of the numbers of atoms (Me) of nickel and element M to the number of lithium atoms (Li) "Li/Me ratio" in the positive electrode active material is preferably 0.95 to 1.20, and more preferably 0.97 to 1.15.

When the Li/Me ratio is 0.95 or more, when the obtained positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, the reaction resistance of the positive electrode can be particularly suppressed, and the output of the battery can be improved. When the Li/Me ratio is 1.20 or less, the excess lithium component on the particle surface of the lithium nickel composite oxide can be suppressed, and therefore, when the positive electrode active material is used as a positive electrode material for a lithium ion secondary battery, the initial discharge capacity can be particularly improved, and the reaction resistance of the positive electrode can be suppressed.

Here, since the lithium component in the compound containing tungsten and lithium is lithium provided by the lithium nickel composite oxide as the matrix, the lithium amount of the entire positive electrode active material does not change before and after the formation of the compound containing tungsten and lithium.

That is, after the compound containing tungsten and lithium is formed, the Li/Me ratio of the lithium nickel composite oxide particles as the base material (core material) is reduced from that before the formation. Therefore, by setting the Li/Me ratio to 0.97 or more, more favorable charge/discharge capacity and reaction resistance can be obtained.

Accordingly, the Li/Me ratio of the entire positive electrode active material is more preferably 0.97 to 1.15.

In the positive electrode active material of the present embodiment, since the output characteristics and the cycle characteristics are improved by disposing the compound containing tungsten and lithium on the secondary particle surface and the primary particle surface of the lithium nickel composite oxide particle, the powder characteristics such as the particle diameter and tap density (tap density) as the positive electrode active material are not particularly limited, and may be within the range of a commonly used positive electrode active material, for example.

The effects that can be achieved by providing a compound containing tungsten and lithium on the surfaces of the secondary particles and the primary particles of the lithium-nickel composite oxide are not limited to the powders of lithium-cobalt composite oxide, lithium-manganese composite oxide, lithium-nickel-cobalt-manganese composite oxide, and the like, and the positive electrode active material disclosed in the present invention, but can also be applied to a positive electrode active material for a lithium secondary battery that is generally used.

[ lithium ion Secondary Battery ]

The lithium ion secondary battery (hereinafter, also referred to as "secondary battery") according to the present embodiment may have a positive electrode containing the positive electrode active material.

Hereinafter, a description will be given of a configuration example of the secondary battery according to the present embodiment for each component. The secondary battery of the present embodiment includes, for example, a positive electrode, a negative electrode, and a nonaqueous electrolyte, and may be configured with the same components as those of a conventional lithium ion secondary battery. The embodiments described below are merely examples, and the lithium-ion secondary battery according to the present embodiment is based on the embodiments described below, and can be implemented in various modified and improved forms by those skilled in the art based on the knowledge thereof. The use of the secondary battery is not particularly limited.

(Positive electrode)

The positive electrode provided in the secondary battery of the present embodiment may contain the positive electrode active material.

An example of the method for producing the positive electrode will be described below. First, the positive electrode active material (powder), the conductive material, and the binder (binder) are mixed to prepare a positive electrode mixture, and if necessary, activated carbon and a solvent for the purpose of viscosity adjustment or the like are added thereto and kneaded to prepare a positive electrode mixture paste.

The mixing ratio of the materials in the positive electrode mixture is an element that determines the performance of the lithium ion secondary battery, and therefore, can be adjusted according to the application. The mixing ratio of the materials may be the same as that of a known positive electrode for a lithium ion secondary battery, and for example, when the total mass of the solid components of the positive electrode mixture excluding the solvent is 100 mass%, the content ratio of each portion may be 60 mass% to 95 mass% of the positive electrode active material, 1 mass% to 20 mass% of the conductive material, and 1 mass% to 20 mass% of the binder.

The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, aluminum foil, and dried to scatter the solvent, thereby producing a sheet (sheet) like positive electrode. If necessary, the electrode density may be increased by applying pressure using a roll press or the like. The sheet-like positive electrode thus obtained is cut or the like to have a size corresponding to the target battery, and is supplied to a battery production process.

Examples of the conductive material include graphite (natural graphite, artificial graphite, expanded graphite, and the like), and carbon black-based materials such as acetylene black and Ketjen black (registered trademark).

As the binder (binder), one or more selected from polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), Fluorine rubber (Fluorine rubber), Ethylene propylene diene rubber (Ethylene propylene diene rubber), Styrene butadiene (Styrene butadiene), cellulose resin (cellulose resin), Polyacrylic acid (Polyacrylic acid), and the like can be used to exert an effect of binding the active material particles.

If necessary, a solvent for dispersing the positive electrode active material, the conductive material, and the like and dissolving the binder may be added to the positive electrode mixture. Specific examples of the solvent include organic solvents such as N-methyl-2-pyrrolidone. In addition, activated carbon may be added to the positive electrode mixture in order to increase the electric double layer capacity.

The method of manufacturing the positive electrode is not limited to the above-described exemplary method, and other methods may be employed. For example, the positive electrode mixture may be pressure-molded and then dried in a vacuum atmosphere to prepare a positive electrode.

(cathode)

The negative electrode may use metallic lithium, lithium alloy, or the like. In addition, the negative electrode may be formed by mixing a binder with a negative electrode active material capable of occluding (occluding) and releasing lithium ions, adding an appropriate solvent to obtain a paste-like negative electrode mixture, coating the surface of a metal foil current collector such as copper with the negative electrode mixture, drying the coating, and compressing the coating as necessary to increase the electrode density.

Examples of the negative electrode active material include a fired organic compound such as natural graphite, artificial graphite, and phenol resin, and a powdered carbon material such as coke. In this case, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as in the positive electrode, and as a solvent for dispersing these active materials and the binder, an organic solvent such as N-methyl-2-pyrrolidone can be used.

(diaphragm)

A separator may be interposed between the positive electrode and the negative electrode as needed. The separator is used to separate the positive electrode and the negative electrode and hold the electrolyte, and a known separator, for example, a film having a large number of micropores such as polyethylene or polypropylene may be used.

(nonaqueous electrolyte)

As the nonaqueous electrolyte, for example, a nonaqueous electrolytic solution can be used.

As the nonaqueous electrolytic solution, for example, a nonaqueous electrolytic solution in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. Further, as the nonaqueous electrolytic solution, a nonaqueous electrolytic solution in which a lithium salt is dissolved in an ionic liquid may be used. The ionic liquid is a salt that is composed of a cation other than lithium ions and an anion and is liquid at room temperature.

As the organic solvent, cyclic carbonates such as Ethylene carbonate (Ethylene carbonate), Propylene carbonate (Propylene carbonate), Butylene carbonate (Butylene carbonate), and trifluoropropylene carbonate (Trifluoro Propylene carbonate) can be used alone; chain carbonates (Chain carbonates) such as Diethyl carbonate (Diethyl carbonate), Dimethyl carbonate (Dimethyl carbonate), Ethyl methyl carbonate (Ethyl methyl carbonate), and Dipropyl carbonate (Dipropyl carbonate); ether compounds such as Tetrahydrofuran (Tetrahydrofuran), 2-methyltetrahydrofuran (2-methyltetrahydrofuran), and Dimethoxyethane (Dimethoxyethane); sulfur compounds such as Ethyl methyl sulfone (Ethyl methyl sulfone) and Butane sultone (Butane sultone); 1 kind selected from phosphorus compounds such as Triethyl phosphate (Triethyl phosphate) and Trioctyl phosphate (Trioctyl phosphate), or mixture of more than 2 kinds.

As supporting salt, LiPF may be used₆、LiBF₄、LiClO₄、LiAsF₆、LiN(CF₃SO₂)₂And complex salts thereof, and the like. The nonaqueous electrolyte solution may further contain a radical scavenger, a surfactant, a flame retardant, and the like.

In addition, as the nonaqueous electrolyte, a solid electrolyte may be used. The solid electrolyte has high voltage resistance. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

Examples of the inorganic solid electrolyte include an oxide solid electrolyte and a sulfide solid electrolyte.

The oxide solid electrolyte is not particularly limited, and for example, an oxide solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be preferably used. As the oxide-based solid electrolyte, for example, lithium phosphate (Li) can be used₃PO₄)、Li₃PO₄N_X、LiBO₂N_X、LiNbO₃、LiTaO₃、Li₂SiO₃、Li₄SiO₄-Li₃PO₄、Li₄SiO₄-Li₃VO₄、Li₂O-B₂O₃-P₂O₅、Li₂O-SiO₂、Li₂O-B₂O₃-ZnO、Li_1+XAl_XTi_2-X(PO₄)₃(0≤X≤1)、Li_{1+ X}Al_XGe_2-X(PO₄)₃(0≤X≤1)、LiTi₂(PO₄)₃、Li_3XLa_2/3-XTiO₃(0≤X≤2/3)、Li₅La₃Ta₂O₁₂、Li₇La₃Zr₂O₁₂、Li₆BAla₂Ta₂O₁₂、Li_3.6Si_0.6P_0.4O₄And the like, and 1 or more selected from the group.

The sulfide solid electrolyte is not particularly limited, and for example, a sulfide solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation properties can be preferably used. As the sulfide-based solid electrolyte, for example, Li (lithium) can be used₂S-P₂S₅、Li₂S-SiS₂、LiI-Li₂S-SiS₂、LiI-Li₂S-P₂S₅、LiI-Li₂S-B₂S₃、Li₃PO₄-Li₂S-Si₂S、Li₃PO₄-Li₂S-SiS₂、LiPO₄-Li₂S-SiS、LiI-Li₂S-P₂O₅、LiI-Li₃PO₄-P₂S₅And the like, and 1 or more selected from the group.

In addition, as the inorganic solid electrolyte, other substances than those described above can be used, and for example, Li can be used₃N、LiI、Li₃N-LiI-LiOH and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound having ion conductivity, and for example, polyethylene oxide, polypropylene oxide, a copolymer thereof, or the like can be used. In addition, the organic solid electrolyte may further contain a supporting salt (lithium salt).

(shape and Structure of Secondary Battery)

The lithium-ion secondary battery of the present embodiment described above may have various shapes such as a cylindrical shape and a stacked shape. In any of the shapes, in the case where a nonaqueous electrolyte solution is used as the nonaqueous electrolyte in the secondary battery of the present embodiment, a separator may be interposed between the positive electrode and the negative electrode to form an electrode body, and the obtained electrode body may be immersed in the nonaqueous electrolyte solution to connect the positive electrode collector and the positive electrode terminal leading to the outside and the negative electrode collector and the negative electrode terminal leading to the outside by using a current collecting lead or the like, thereby sealing the electrode body to the battery case.

As described above, the secondary battery of the present embodiment is not limited to the form in which the nonaqueous electrolytic solution is used as the nonaqueous electrolyte, and may be, for example, a secondary battery using a solid nonaqueous electrolyte, that is, an all-solid battery. When forming an all-solid battery, the structure other than the positive electrode active material may be changed as necessary.

In the secondary battery of the present embodiment, since the positive electrode active material is used as a material of the positive electrode, a high capacity and a high output can be obtained.

In particular, when a lithium ion secondary battery using the positive electrode active material is used as a positive electrode of, for example, a 2032-type coin battery, the lithium ion secondary battery can have characteristics of high initial discharge capacity of, for example, 210mAh/g or more, that is, high capacity, low positive electrode resistance, and higher output, depending on the composition. In addition, the thermal stability is high, and the safety is excellent.

The secondary battery of the present embodiment is applicable to various applications, but is a secondary battery having a high capacity and a high output, and is therefore preferably applied to a power supply for small portable electronic devices (portable computers, mobile phone terminals, etc.) that generally require a high capacity, and also to a power supply for electric vehicles that require a high output, for example.

Further, the secondary battery of the present embodiment can be reduced in size and increased in output, and is therefore preferably used as a power supply for an electric vehicle in which the installation space is limited. The secondary battery of the present embodiment can be used not only as a power source for an electric vehicle that is driven purely by electric energy, but also as a power source for a so-called hybrid vehicle that is used together with an internal combustion engine such as a gasoline engine or a diesel engine.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples. Here, various evaluation methods of the positive electrode active material and the battery in the examples and comparative examples are as follows.

(evaluation of Positive electrode active Material)

(a) Ratio of segregated particles

The following measurement method was used to calculate the segregation particle ratio contained in the composite particles in the positive electrode active material. First, scanning electron microscopy was performed on any 10 positions of the positive electrode active material powder at an applied voltage of 5kV and a magnification of 100 times. Namely, observation was performed in 10 fields. Among them, in 1 field, for example, a scanning electron microscope photograph as shown in fig. 1 can be obtained. Then, the number of segregated particles reflected as white particles in the 10 SEM photographs was counted, and the segregated particle ratio in the composite particles included in the 10 SEM photographs was calculated.

As shown in fig. 2 and 3, the segregation particles a are white particles, and the other composite particles B are gray particles.

(production and evaluation of Battery)

(a) Manufacture of batteries

For evaluation of the positive electrode active material, a 2032-type coin cell 11 (hereinafter, referred to as coin cell) as shown in fig. 4 was used.

As shown in fig. 4, the button cell 11 includes a case 12 and an electrode 13 housed in the case 12.

The case 12 includes a hollow positive electrode can 12a having one open end and a negative electrode can 12b disposed in an opening of the positive electrode can 12a, and the negative electrode can 12b is disposed in the opening of the positive electrode can 12a, thereby forming a space for accommodating the electrode 13 between the negative electrode can 12b and the positive electrode can 12 a.

The electrode 13 is composed of a positive electrode 13a, a separator 13c, and a negative electrode 13b, which are stacked in this order, and is housed in the case 12 such that the positive electrode 13a contacts the inner surface of the positive electrode can 12a via the current collector 14, and the negative electrode 13b contacts the inner surface of the negative electrode can 12b via the current collector 14. A current collector 14 is also disposed between the positive electrode 13a and the separator 13 c.

Further, case 12 includes gasket 12c, and this gasket 12c realizes relative movement inherent between positive electrode can 12a and negative electrode can 12b to maintain the non-contact state therebetween. Gasket 12c also has a function of sealing the gap between positive electrode can 12a and negative electrode can 12b, and sealing the space between the inside and the outside of case 12 in a gas-tight and liquid-tight manner.

The button cell 11 shown in fig. 4 was produced in the following manner.

First, 52.5mg of the positive electrode active material for lithium ion secondary batteries prepared in examples and comparative examples, 15mg of acetylene black, and 7.5mg of Polytetrafluoroethylene (PTFE) resin were mixed and press-molded under a pressure of 100MPa to prepare a positive electrode 13a having a diameter of 11mm and a thickness of 100 μm. The fabricated positive electrode 13a was dried in a vacuum dryer at 120 ℃ for 12 hours.

The button cell 11 was produced in an Ar atmosphere glove box with a dew point (dew point) of-80 ℃ using the positive electrode 13a, the negative electrode 13b, the separator 13c, and the electrolyte.

Here, as the negative electrode 13b, a negative electrode sheet was used which was punched out into a disk shape having a diameter of 14mm and was formed by coating graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride on a copper foil.

The separator 13c used a polyethylene porous membrane having a thickness of 25 μm. The electrolyte used 1M LiClO₄An equal amount of a mixed solution of Ethylene Carbonate (EC) and diethyl carbonate (DEC) as a supporting electrolyte (manufactured by fushan chemical industries co., ltd.).

(b) Evaluation of

After the production of the coin cell 11, the initial discharge capacity, the positive electrode resistance, and the cycle characteristics, which indicate the performance, were evaluated as follows.

(b1) Initial discharge capacity

Regarding the initial discharge capacity, the button cell 11 was left to stand for approximately 24 hours after it was manufactured, and after the open Circuit voltage ocv (open Circuit voltage) was stabilized, the current density to the positive electrode was set to 0.1mA/cm²Charging to cut-off voltage of 4.3V, pausing for 1 hour, and discharging to cut-offThe voltage was 3.0V, and the capacity at this time was used as the initial discharge capacity.

(b2) Positive electrode resistance

As for the positive electrode resistance, the coin cell 11 was charged at a charging potential of 4.1V, and then measured by an ac impedance method using a frequency response analyzer and a constant-potential constant current meter (manufactured by solartron, 1255B), and a Nyquist diagram (Nyquist plot) shown in fig. 5A was obtained.

The nyquist diagram represents the sum of characteristic curves of the solution resistance, the negative electrode resistance and the capacity thereof, and the positive electrode resistance and the capacity thereof.

The battery reaction of the electrode is composed of a resistance component that moves with electric charge and a capacity component of the electric double layer, and when these are represented by circuits, they are parallel circuits of resistance and capacitance, and as the whole battery, they are represented by an equivalent circuit in which parallel circuits of solution resistance, negative electrode, and positive electrode are connected in series.

Therefore, based on the nyquist diagram shown in fig. 5A, fitting (fitting) calculation was performed using the equivalent circuit shown in fig. 5B, and the value of the positive electrode resistance was calculated. Here, table 1 shows the results of the positive electrode resistance before cycling.

(b3) Cyclic character

The cycle characteristics were evaluated based on the capacity retention rate after the cycle test. After the initial discharge capacity was measured by the cycle test, the operation was suspended for 10 minutes, and the charge and discharge cycle was repeated 500 times (charge and discharge) in the same manner as the initial discharge capacity measurement. The discharge capacity at 500 th cycle was measured, and the percentage of the discharge capacity at 500 th cycle to the discharge capacity at 1 st cycle (initial discharge capacity) was calculated as a capacity retention rate (%).

(b4) Carbon content

The carbon content was measured using a carbon sulfur analyzer (model: CS-600, manufactured by LECO Co.).

In the present example, unless otherwise specified, various samples of reagent grade manufactured by Wako pure chemical industries, Ltd were used for the production of the positive electrode active material and the secondary battery.

[ example 1]

The positive electrode active material and the lithium ion secondary battery were produced and evaluated according to the following procedures.

(mixing Process)

Li is obtained by using an oxide containing Ni as a main component and lithium hydroxide by a known technique_0.98Ni_0.91Co_0.06Al_0.03O₂The powder of lithium nickel composite oxide particles as a layered compound of (1) as a matrix. In other examples and comparative examples described below, a lithium nickel composite oxide of a layered compound was also used as a matrix. Then, water was added to the base material, and the water content (hereinafter, also simply referred to as "water content") of the starting material supplied to the mixing step, which was the ratio of the lithium nickel composite oxide to the water, was 3.2 mass%.

The base material added with water was put into a paddle type mixing device, and tungsten oxide (WO) was put into the base material so that the ratio of the number of W atoms to the total number of Ni, Co, and Al atoms in the base material became 0.12 atom%₃) These starting materials were mixed at 60 ℃ for 30 minutes to obtain a tungsten mixture.

In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.20m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate.

The ratio of the number of W atoms in the starting material to the total number of atoms of Ni and the element M of the base material is shown as "W amount" in table 1.

(Heat treatment Process)

Then, heat treatment was performed at 190 ℃ for 120 minutes using a steam tube dryer, and furnace cooling was performed.

Here, the atmosphere in the mixing step and the heat treatment step is decarbonated air.

Finally, the resultant was pulverized and passed through a sieve having a mesh size of 38 μm, thereby obtaining a positive electrode active material having compound particles containing tungsten and lithium on the surfaces of primary particles of the lithium-nickel composite oxide.

For the obtained positive electrode active material, the ratio of segregated particles was calculated.

The obtained positive electrode active material was evaluated for the amount of tungsten as the ratio of the number of W atoms to the total number of atoms of Ni, Co, and Al using ICP. As a result, it was confirmed that the W amount of the obtained positive electrode active material was equal to the ratio of the W number in the starting material supplied to the mixing step to the total number of atoms of Ni, Co, and Al in the base material, that is, the W amount.

In the following other examples and comparative examples, it was also confirmed that the amount of tungsten, which is the ratio of the number of W atoms to the total number of atoms of Ni and the element M in the obtained positive electrode active material, was equal to the ratio of the number of W atoms in the starting material to the total number of atoms of Ni and the element M in the base material (W amount).

Here, the tungsten contained in the obtained positive electrode active material is derived from a compound containing tungsten and lithium disposed on the particle surface of the lithium nickel composite oxide, and the nickel and the element M are derived from the lithium nickel composite oxide. Therefore, the amount of tungsten in the positive electrode active material corresponds to the ratio of the number of tungsten atoms contained in the compound containing tungsten and lithium to the total number of nickel atoms and the element M contained in the lithium nickel composite oxide in the positive electrode active material.

A coin cell 11 as shown in fig. 4, which was equipped with a positive electrode made using the obtained positive electrode active material, was subjected to battery characteristic evaluation. Here, as the evaluation value of the positive electrode resistance before the cycle test (positive electrode resistance before the cycle test), the relative value of example 1 as 1.00 was used.

The carbon content was measured by the above-described measurement method.

The test conditions and the evaluation results are shown in table 1.

[ example 2]

A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1, except that the water content was 3.4 mass%, and the temperature during mixing was 55 ℃.

The test conditions and the evaluation results are shown in table 1.

[ example 3]

The water content was 5.7 mass%, and WO was added so that the ratio of the number of W atoms to the total number of Ni, Co and Al atoms in the base material became 0.24 atom%₃The temperature during mixing was 50 ℃, the temperature for heat treatment was 150 ℃ and the heat treatment time was 180 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 4]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 6.9 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.06 atom%₃. In the mixing step, decarbonated air is supplied while exhausting the gas from the mixing device. Specifically, the amount of the base material added with water was 0.15m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 5]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 4.1 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.27 atom%₃. In the mixing step, decarbonated air is supplied while exhausting the gas from the mixing device. Specifically, the amount of the base material added with water was 0.15m at a rate of 1 kg/min³The mixing was controlled by venting at a rate of one minute and supplying decarbonated air at the same flow rateNo negative pressure is created within the device. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 6]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 5.5 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.15 atom%₃The temperature during mixing was 45 ℃ and the mixing time was 45 minutes. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.25m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 7]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 4.9 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃The temperature at the time of mixing was 30 ℃, the mixing time was 60 minutes, the heat treatment temperature was 175 ℃, and the heat treatment time was 150 minutes. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.30m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 8]

The composition of the parent material is Li_0.98Ni_0.88Co_0.09Al_0.03O₂The moisture content was 4.3 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 9]

The composition of the parent material is Li_0.98Ni_0.88Co_0.09Al_0.03O₂The moisture content was 3.6 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.30 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 10]

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The moisture content was 6.4 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.15 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 11]

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The moisture content was 5.8 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.30 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the input speed of the base material added with water is 1 kg/minClock, at 0.15m³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 12]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 8.6 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 13]

The composition of the parent material is Li_0.98Ni_0.88Co_0.09Al_0.03O₂The moisture content was 7.9 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.15 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 14]

Adding water to the base material and WO₃Continuously feeding the mixture into a continuous paddle type mixing device, continuously supplying the mixture from the continuous paddle type mixing device to a continuous steam type dryer, and continuously discharging the dried mixture from the continuous steam type dryer. That is, the mixing step and the heat treatment step are continuously performed. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 15]

Will addWater-added base material and WO₃Continuously feeding the mixture into a continuous paddle type mixing device, continuously supplying the mixture from the continuous paddle type mixing device to a continuous steam type dryer, and continuously discharging the dried mixture from the continuous steam type dryer. That is, the mixing step and the heat treatment step are continuously performed. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 5.

The test conditions and the evaluation results are shown in table 1.

[ example 16]

The composition of the parent material is Li_0.98Ni_0.55Co_0.20Mn_0.25O₂Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 17]

The water content was 4.9 mass%, and WO was added so that the percentage of W atoms to the total number of Ni, Co and Mn atoms in the matrix became 0.18 atom%₃A positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 16, except that the temperature during mixing was 55 ℃.

The test conditions and the evaluation results are shown in table 1.

[ example 18]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 5.2 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.15 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.10m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced in the same manner as in example 1, andand (6) evaluating.

The test conditions and the evaluation results are shown in table 1.

[ example 19]

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 5.5 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.19 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.35m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 20]

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The moisture content was 4.9 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.10m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

[ example 21]

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The moisture content was 5.3 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃. In the mixing step, the mixing apparatus is exhaustedDecarbonated air is provided. Specifically, the amount of the base material added with water was 0.35m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

[ example 22]

The composition of the parent material is Li_0.98Ni_0.55Co_0.20Mn_0.25O₂The moisture content was 5.3 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.19 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.10m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

[ example 23]

The composition of the parent material is Li_0.98Ni_0.55Co_0.20Mn_0.25O₂The moisture content was 4.8 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.17 atom%₃. In the mixing step, decarbonated air is supplied while exhausting gas from the mixing device. Specifically, the amount of the base material added with water was 0.35m at a rate of 1 kg/min³The inside of the mixing device was controlled not to be negative pressure by exhausting air at a rate of one minute and supplying decarbonated air at the same flow rate. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 1

The composition of the parent material is Li_0.97Ni_0.91Co_0.04Al_0.05O₂The moisture content was 5.2 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.03 atom%₃Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 2

The water content was 2.7 mass%, and WO was added so that the percentage of W atoms to the total number of Ni, Co and Al atoms in the base material became 0.15 atom%₃Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 3

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The moisture content was 2.8 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.15 atom%₃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 4

The composition of the parent material is Li_0.98Ni_0.91Co_0.06Al_0.03O₂The moisture content was 4.5 mass%, and WO was added so that the percentage of W atoms to the total number of atoms of Ni, Co and Al in the base material became 0.18 atom%₃The temperature at the time of mixing was 25 ℃ and the mixing time was 90 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 5

The composition of the parent material is Li_0.98Ni_0.91Co_0.06Al_0.03O₂The water content was 4.4% by mass, the W atom number ratio relative to the total atom number of Ni, Co and Al in the base material was 0.15% by atom, the temperature at the time of mixing was 70 ℃ and the mixing time was 30 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 6

The composition of the parent material is Li_0.98Ni_0.88Co_0.09Al_0.03O₂The water content was 4.5% by mass, the W atom number ratio relative to the total atom number of Ni, Co and Al in the base material was 0.18 atom%, the temperature at the time of mixing was 70 ℃, and the mixing time was 30 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 7

The composition of the parent material is Li_0.97Ni_0.88Co_0.07Al_0.05O₂The water content was 4.2% by mass, the W atom number ratio relative to the total atom number of Ni, Co and Al in the base material was 0.18 atom%, the temperature at the time of mixing was 75 ℃ and the mixing time was 30 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 1.

The test conditions and the evaluation results are shown in table 1.

Comparative example 8

The water content was 3.4 mass%, the ratio of the number of W atoms to the total number of atoms of Ni, Co and Mn in the matrix was 0.13 atomic%, and the temperature at the time of mixing was 70 ℃. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 16.

The test conditions and the evaluation results are shown in table 1.

Comparative example 9

The water content was 3.9% by mass, the W atom number ratio relative to the total atom number of Ni, Co and Mn in the matrix was 0.14 atom%, the temperature at the time of mixing was 25 ℃ and the mixing time was 90 minutes. Except for this, a positive electrode active material and a secondary battery were produced and evaluated in the same manner as in example 16.

The test conditions and the evaluation results are shown in table 1.

[ Table 1]

[ evaluation ]

As is clear from table 1, the positive electrode active materials of examples 1 to 17 had high initial discharge capacity, low positive electrode resistance, high capacity retention rate, and a small proportion of segregated particles, compared with comparative examples corresponding to the base material composition, and formed batteries having excellent characteristics.

In examples 1, 2, 9, 14 and 16, since the water content ratio, which is the ratio of water in the starting material supplied to the mixing step to the water in the lithium nickel composite oxide, was less than 4.0 mass%, the amount of WO was very small₃Failure to disperse completely, resulting in unreacted WO₃Easily remain in the solution. And thus may result in a slightly higher ratio of segregated particles than the other embodiments, and slightly inferior battery characteristics compared to the other embodiments.

In examples 4, 12, and 13, the moisture content greatly exceeded 6.0%, lithium in the lithium nickel composite oxide eluted into the excess moisture, and in the part where lithium locally increased, the reaction with tungsten increased, resulting in the generation of segregated particles. Therefore, the number of segregated particles is larger than that of the other examples, and the battery characteristics are slightly inferior to that of the other examples.

In examples 6 and 7, the temperature during mixing was low, and therefore, a longer mixing time was required than in the other examples, but the evaluation results were good.

In examples 18, 20 and 22, although the carbon content was not so high, the carbon content was higher than that in the other examples. The reason for this is that the carbonation of the lithium component in the lithium nickel composite oxide is promoted because the concentration of carbonic acid gas in the atmosphere in the mixing step is high due to the small exhaust rate and the small flow rate of decarbonated air. The carbonic acid component may become a gas in the battery, resulting in a decrease in characteristics. Therefore, it is preferable to reduce carbonation as much as possible.

In examples 19, 21 and 23, the exhaust rate and the flow rate of decarbonated air were large, so that the lithium component of the lithium-nickel composite oxide was less carbonated, but the air flow slightly promoted drying, and the unreacted WO was found to be a little harmful degree₃More are.

In contrast, in comparative example 1, since the ratio of the number of W atoms to the total number of atoms of Ni, Co, and Al in the base material was less than 0.05 atom%, a compound including tungsten and lithium could not be sufficiently formed, and as a result, the battery characteristics were significantly degraded.

In comparative examples 2 and 3, WO could not be added due to the low water content₃Fully dispersed and a large amount of unreacted WO remains₃Therefore, a large amount of residual lithium component remains, resulting in deterioration of battery characteristics.

In comparative examples 4 and 9, the mixing temperature was less than 30 ℃ and WO could not be applied₃Fully dispersed and a large amount of unreacted WO remains₃And thus, a remaining lithium component also remains in a large amount, resulting in deterioration of battery characteristics.

In comparative examples 5 to 8, the mixing temperature exceeded 65 ℃ and the moisture in the tungsten mixture rapidly decreased, and WO could not be maintained₃The water required for dispersion of (A) results in a large amount of unreacted WO₃And thus a large amount of remaining lithium components remain, deteriorating battery characteristics.

In comparative examples 2 to 9, WO could not be applied as described above₃Since the dispersion was sufficient, the segregation particle ratio was increased, and it was confirmed that the battery characteristics were deteriorated.

As is clear from the above, the positive electrode active material of the present embodiment is low in cost, and has high capacity and high output. It is noted that in examples 14 and 15, the continuous treatment was carried out, and the evaluation results were good, and the productivity was high, and it is obvious that further cost reduction is expected.

The method for producing the positive electrode active material for a lithium ion secondary battery, and the lithium ion secondary battery have been described above with reference to the embodiments, examples, and the like, but the present invention is not limited to the embodiments, examples, and the like. Various modifications and changes can be made within the scope of the gist of the present invention described in the claims.

The present application claims priority based on patent application No. 2019-.