阅读说明：本技术 锂二次电池用正极活性物质、锂二次电池用正极和锂二次电池 (Positive electrode active material for lithium secondary battery, positive electrode for lithium secondary battery, and lithium secondary battery ) 是由 中山哲理 高森健二 堂前京介 北本隆志 于 2015-01-26 设计创作，主要内容包括：本发明要解决的课题是提供在高电流倍率下显示出高输出的锂二次电池用正极活性物质。本发明的锂二次电池用正极活性物质在包含二次粒子的含锂复合金属氧化物的表面具备覆盖层,所述二次粒子是可以掺杂和脱掺杂锂离子的一次粒子聚集而成,所述锂二次电池用正极活性物质满足下述条件(1)～(3)：(1)所述含锂复合金属氧化物具有式(A)所示的α-NaFeO<Sub>2</Sub>型晶体结构,Li<Sub>a</Sub>(Ni<Sub>b</Sub>Co<Sub>c</Sub>M<Sup>1</Sup><Sub>1-b-c</Sub>)O<Sub>2</Sub>…(A)；(2)所述覆盖层包含Li与M<Sup>2</Sup>的金属复合氧化物；(3)所述锂二次电池用正极活性物质的平均二次粒径为2μm以上且20μm以下,BET比表面积为0.1m<Sup>2</Sup>/g以上且2.5m<Sup>2</Sup>/g以下,夯实密度除以未夯实密度得到的值为1.0以上且2.0以下。(The positive electrode active material for a lithium secondary battery of the present invention comprises a coating layer on the surface of a lithium-containing composite metal oxide containing secondary particles formed by aggregating times particles capable of being doped and dedoped with lithium ions, wherein the secondary particles are formed by aggregating times particles, and the positive electrode active material for a lithium secondary battery satisfies the following conditions (1) to (3), wherein (1) the lithium-containing composite metal oxide has α -NaFeO represented by the formula (A) 2 Crystal structure of type, Li a (Ni b Co c M 1 1‑b‑c )O 2 … (A); (2) the capping layer comprises Li and M 2 The metal composite oxide of (3); (3) the positive electrode active material for a lithium secondary battery has an average secondary particle diameter of 2 to 20 [ mu ] m and a BET specific surface area of 0.1m 2 2.5 m/g or more 2 (iv) a value obtained by dividing the tamped density by the untampered density of 1.0 or more and 2.0 or less.)

A positive electrode active material for lithium secondary batteries, which is characterized by having a coating layer on the surface of a lithium-containing composite metal oxide containing secondary particles formed by aggregating secondary particles capable of doping and dedoping lithium ions, and which satisfies the following conditions (1) to (3):

(1) the lithium-containing composite metal oxide has α -NaFeO represented by the formula (A)₂A crystal structure of a crystal form of the crystal form,

Li_a(Ni_bCo_cM¹ _1-b-c)O₂…(A)

in the formula, a is more than or equal to 0.9 and less than or equal to 1.2, b is more than or equal to 0.9 and less than or equal to 1, c is more than 0 and less than or equal to 0.1, b + c is more than 0.9 and less than or equal to 1,

M¹represents at least kinds of arbitrary metals selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn,

(2) the capping layer comprises Li and M²Metal composite oxide of, M²Represents at least kinds of arbitrary metals selected from Al, Ti, Zr and W,

(3) the positive electrode active material for a lithium secondary battery has an average secondary particle diameter of 2 to 20 [ mu ] m and a BET specific surface area of 0.1m²2.5 m/g or more²(iv) a value obtained by dividing the tamped density by the untampered density of 1.0 or more and 2.0 or less.

2. The positive electrode active material for lithium secondary batteries according to claim 1, wherein M is M¹Is at least selected from Mg, Al, Ca, Ti, Mn, Zn, Ga, Zr and Sn.

3. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, wherein M is M¹Is at least selected from Mg, Al, Mn, Zn and Sn.

4. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, wherein the tamped density is 1.0g/cm³Above and 3.5g/cm³The following.

5. The positive electrode active material for a lithium secondary battery according to claim 1 or 2, wherein the 90% cumulative particle size distribution is obtained from the measured particle size distributionParticle size (D)₉₀) 10% cumulative particle diameter (D)₁₀) The value of (A) is 1 to 5 inclusive.

6. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, wherein M is M²Relative to the atomic ratio of Ni, Co and M¹The sum of the atomic ratios of (A) to (B) is 0.1 to 5 mol%.

7. The positive electrode active material for lithium secondary batteries according to claim 1 or 2, wherein M is M²Is Al.

8. The positive electrode active material for a lithium secondary battery according to claim 7, wherein the coating layer is lithium aluminate.

9, kinds of positive electrodes for lithium secondary batteries, characterized in that, it has the lithium secondary battery of any of of claims 1-8 positive electrode active material.

10, kinds of lithium secondary batteries, characterized in that, it has the lithium secondary battery positive electrode of claim 9.

Technical Field

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

The present application is based on the priority claim of Japanese application No. 2014-012835, which was filed in Japan on 27.1.2014, and the content thereof is incorporated herein by reference.

Background

Lithium secondary batteries have been put into practical use as small-sized power sources for mobile applications, notebook-sized computer applications, and the like, and further , application to medium-and large-sized power sources for automobile applications, electric storage applications, and the like has been attempted.

Therefore, as a conventional positive electrode active material for a lithium secondary battery, for example, patent document 1 describes the following technique: a coating layer of a lithium manganese composite oxide or the like having a different composition depending on the site is formed on the surface of the lithium nickel composite oxide, thereby improving thermal stability during charging.

Disclosure of Invention

Problems to be solved by the invention

However, a lithium secondary battery obtained by using the conventional lithium-containing composite metal oxide as a positive electrode active material for a lithium secondary battery as described above cannot achieve a required high output in applications requiring a high output at a high current rate, that is, in applications for automobiles, power tools such as electric tools, and the like.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a positive electrode active material for a lithium secondary battery having a higher current rate and a higher output than conventional ones by controlling the composition and particle form of a lithium-containing composite metal oxide and further forming a coating layer .

Means for solving the problems

In order to solve the above problems, aspects of the present invention provide a positive electrode active material for a lithium secondary battery, comprising a coating layer on the surface of a lithium-containing composite metal oxide containing secondary particles, wherein the secondary particles are formed by aggregating secondary particles capable of doping and dedoping lithium ions, and the positive electrode active material for a lithium secondary battery satisfies the following conditions (1) to (3):

(1) the lithium-containing composite metal oxide has α -NaFeO represented by the formula (A)₂A crystal structure of a crystal form of the crystal form,

Li_a(Ni_bCo_cM¹ _1-b-c)O₂…(A)

in the formula, a is more than or equal to 0.9 and less than or equal to 1.2, b is more than or equal to 0.9 and less than or equal to 1, c is more than 0 and less than or equal to 0.1, b + c is more than 0.9 and less than or equal to 1,

M¹represents at least 1 arbitrary metal selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn,

(2) the capping layer comprises Li and M²Wherein M is²Represents any 1 or more of any metals selected from Al, Ti, Zr and W,

(3) the positive electrode active material for a lithium secondary battery has an average secondary particle diameter of 2 to 20 [ mu ] m and a BET specific surface area of 0.1m²2.5 m/g or more²(iv) a value obtained by dividing the tamped density by the untampered density of 1.0 or more and 2.0 or less.

In modes of the invention, M¹Preferably at least 1 selected from the group consisting of Mg, Al, Ca, Ti, Mn, Zn, Ga, Zr and Sn, and more preferably at least 1 selected from the group consisting of Mg, Al, Mn, Zn and Sn.

In the modes of the invention, the tamped density is preferably 1.0g/cm³Above and 3.5g/cm³The following.

In modes of the present invention, the 90% cumulative particle diameter (D) was determined from the particle size distribution measurement value₉₀) 10% cumulative particle diameter (D)₁₀) The value of (c) is preferably 1 or more and 5 or less.

In modes of the invention, M²Relative to the atomic ratio of Ni, Co and M¹The sum of the atomic ratios of (A) and (B) is preferably 0.1 to 5 mol%.

In modes of the invention, M²Preferably Al.

In modes of the invention, the capping layer is preferably lithium aluminate.

In addition, aspects of the present invention provide a positive electrode for a lithium secondary battery, which has the above-described positive electrode active material for a lithium secondary battery.

In addition, embodiments of the present invention provide a lithium secondary battery having a negative electrode and the positive electrode for a lithium secondary battery described above.

Effects of the invention

According to the present invention, a positive electrode active material for a lithium secondary battery, which is useful for a lithium secondary battery exhibiting high output at a higher current rate than conventional ones, can be provided. Further, a positive electrode for a lithium secondary battery and a lithium secondary battery obtained using such a positive electrode active material for a lithium secondary battery can be provided.

Drawings

Fig. 1A is a schematic configuration diagram showing an example of a lithium secondary battery.

Fig. 1B is a schematic configuration diagram showing an example of a lithium secondary battery.

Detailed Description

[ Positive electrode active Material for lithium Secondary batteries ]

The positive electrode active material for a lithium secondary battery of the present embodiment includes a coating layer on the surface of a lithium-containing composite metal oxide containing secondary particles formed by aggregating -th-order particles capable of being doped and dedoped with lithium ions, and satisfies the following conditions (1) to (3),

(1) the lithium-containing composite metal oxide has α -NaFeO represented by the formula (A)₂A crystal structure of a crystal form of the crystal form,

Li_a(Ni_bCo_cM¹ _1-b-c)O₂…(A)

in the formula, a is more than or equal to 0.9 and less than or equal to 1.2, b is more than or equal to 0.9 and less than or equal to 1, c is more than 0 and less than or equal to 0.1, b + c is more than 0.9 and less than or equal to 1,

M¹represents at least 1 arbitrary metal selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn,

(2) the capping layer comprises Li and M²Wherein M is²Represents any 1 or more of any metals selected from Al, Ti, Zr and W,

(3) the positive electrode active material for lithium secondary batteriesHas an average secondary particle diameter of 2 to 20 μm and a BET specific surface area of 0.1m²2.5 m/g or more²(iv) a value obtained by dividing the tamped density by the untampered density of 1.0 or more and 2.0 or less.

The positive electrode active material for a lithium secondary battery of the present embodiment will be described in detail below.

(lithium-containing composite Metal oxide)

The positive electrode active material for a lithium secondary battery of the present embodiment includes a lithium-containing composite metal oxide of a core portion and a covering layer covering the core portion.

First, the crystal structure of the lithium-containing composite metal oxide in the present embodiment is α -NaFeO₂A layered structure of form (la), more preferably a crystal structure of hexagonal form or a crystal structure of monoclinic form.

The crystal structure of the hexagonal crystal form is selected from P3 and P3₁、P3₂、R3、P-3、R-3、P312、P321、P3₁12、P3₁21、P3₂12、P3₂21、R32、P3m1、P31m、P3c1、P31c、R3m、R3c、P-31m、P-31c、P-3m1、P-3c1、R-3m、R-3c、P6、P6₁、P6₅、P6₂、P6₄、P6₃、P-6、P6/m、P6₃/m、P622、P6₁22、P6₅22、P6₂22、P6₄22、P6₃22、P6mm、P6cc、P6₃cm、P6₃mc、P-6m2、P-6c2、P-62m、P-62c、P6/mmm、P6/mcc、P6₃/mcm、P6₃Any space groups in/mmc.

In addition, the monoclinic crystal structure is selected from P2 and P2₁、C2、Pm、Pc、Cm、Cc、P2/m、P2₁/m、C2/m、P2/c、P2₁Any space groups of/C and C2/C.

Among these, the crystal structure of the positive electrode active material for a lithium secondary battery is particularly preferably a hexagonal crystal structure belonging to the space group R-3m or a monoclinic crystal structure belonging to C2/m, because the discharge capacity of the obtained lithium secondary battery is increased.

In the present embodiment, the space group of the lithium-containing composite metal oxide can be identified as follows.

First, a powder X-ray diffraction measurement is performed on a positive electrode active material for a lithium secondary battery using Cu — K α as a radiation source and with a measurement range of a diffraction angle 2 θ of 10 ° or more and 90 ° or less, and then, based on the result, Rietveld analysis is performed to identify a crystal structure of a lithium-containing composite metal oxide and a space group for the crystal structure, the Rietveld analysis being a method of analyzing the crystal structure of a material using data (diffraction peak intensity, diffraction angle 2 θ) of a diffraction peak in the powder X-ray diffraction measurement of the material, and being a means used up to (for example, refer to "experimental example - リ トべルト method in" published by the method of powder X-ray analysis ", published by the japanese society for analytical chemistry, X-ray analysis, which was published by the society of japan 10 months of 2002).

α -NaFeO shown in formula (A)₂In the crystal structure of the form, a is in the range of 0.9. ltoreq. a.ltoreq.1.2 from the viewpoint of enhancing the effect of the present invention, a is preferably in the range of 0.95. ltoreq. a.ltoreq.1.2, more preferably in the range of 0.96. ltoreq. a.ltoreq.1.15, further preferably in the range of 0.97. ltoreq. a.ltoreq.1.1 in the step , and most preferably in the range of 0.98. ltoreq. a.ltoreq.1.05.

α -NaFeO shown in formula (A)₂In the crystal structure of the form, b is in the range of 0.9. ltoreq. b < 1. from the viewpoint of enhancing the effect of the present invention, b is preferably in the range of 0.9. ltoreq. b.ltoreq.0.98, more preferably in the range of 0.9. ltoreq. b.ltoreq.0.95, and further in the range of 0.9. ltoreq. b.ltoreq.0.92 in step .

α -NaFeO shown in formula (A)₂In the crystal structure of the type (A), c is in the range of 0< c.ltoreq.0.1. from the viewpoint of enhancing the effect of the present invention, c is preferably in the range of 0< c.ltoreq.0.09, more preferably in the range of 0.01. ltoreq.c.ltoreq.0.08, further in the range of 0.02. ltoreq.c.ltoreq.0.07 in steps, and most preferably in the range of 0.03. ltoreq.c.ltoreq.0.06.

Further, b + c is in the range of 0.9< b + c.ltoreq.1, preferably in the range of 0.9< b + c.ltoreq.1, more preferably in the range of 0.92. ltoreq. b + c.ltoreq.1, and further is preferably in the range of 0.93. ltoreq. b + c.ltoreq.1.

In the positive electrode active material for a lithium secondary battery of the present embodiment, M is¹Is selected from Mg,At least 1 arbitrary metal selected from the group consisting of Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In and Sn, preferably at least 1 metal selected from the group consisting of Mg, Al, Ca, Ti, Mn, Zn, Ga, Zr and Sn, more preferably at least 1 metal selected from the group consisting of Mg, Al, Mn, Zn and Sn, and further steps are preferably at least 1 or more metal selected from the group consisting of Mg, Al and Mn.

(cover layer)

The capping layer comprises Li and M²The metal composite oxide of (3). M²Is at least 1 selected from the group consisting of Al, Ti, Zr and W, preferably Al. further steps, the capping layer is preferably lithium aluminate, more preferably α -lithium aluminate.

In this embodiment, the capping layer may further include at least 1 metal selected from Mn, Fe, Co, and Ni.

M in the coating layer from the viewpoint of improving the effect of the present invention²Relative to Ni, Co and M in the lithium-containing composite metal oxide¹The ratio of the sum of atomic ratios of (a ratio of atomic ratio of M2/(an atomic ratio of Ni + an atomic ratio of Co + an atomic ratio of M1) × 100) is preferably 0.1 to 5 mol%, more preferably 0.1 to 3 mol%, and further is preferably 1 to 3 mol%.

In the present embodiment, the composition of the coating layer can be confirmed by STEM-EDX elemental line analysis using a secondary particle cross section, inductively coupled plasma emission spectroscopy, electron probe microanalyzer analysis, or the like. The confirmation of the crystal structure of the covering layer can be performed using powder X-ray diffraction, electron diffraction.

(particle diameter)

In the present embodiment, from the viewpoint of improving the effect of the present invention, the average -th-order particle size is preferably 0.1 μm or more and 2.0 μm or less, more preferably 0.1 μm or more and 1.5 μm or less, and further is preferably 0.1 μm or more and 1.0 μm or less, and the average -th-order particle size can be measured by SEM observation.

The average secondary particle size of the secondary particles formed by the -time particle aggregation is 2 μm or more and 20 μm or less, more preferably 2 μm or more and 15 μm or less, and further preferably 5 μm or more and 15 μm or less in the step, from the viewpoint of improving the effect of the present invention.

In the present embodiment, the "average secondary particle diameter" of the positive electrode active material for a lithium secondary battery is a value measured by the following method (laser diffraction scattering method).

First, 0.1g of a powder of a positive electrode active material for a lithium secondary battery was put into 50ml of a 0.2 mass% aqueous solution of sodium hexametaphosphate to obtain a dispersion liquid in which the powder was dispersed. The particle size distribution of the obtained dispersion was measured using a MASTERSIZER2000 (laser diffraction scattering particle size distribution measuring apparatus) manufactured by Malvern instruments ltd, and a volume-based cumulative particle size distribution curve was obtained. In the cumulative particle size distribution curve obtained, the particle diameter (D) observed from the fine particle side at 50% accumulation₅₀) The value is defined as the average secondary particle diameter of the positive electrode active material for a lithium secondary battery. Further, in the same manner, the particle diameter (D) observed from the fine particle side at 10% accumulation was₁₀) As the 10% cumulative particle diameter, the particle diameter (D) observed from the fine particle side at the time of cumulative 90% was measured₉₀) As a 90% cumulative particle size.

(BET specific surface area)

The BET specific surface area of the positive electrode active material for a lithium secondary battery of the present embodiment is 0.1m²2.5 m/g or more²The ratio of the carbon atoms to the carbon atoms is less than g. From the viewpoint of improving energy density, 0.1m is preferable²1.5 m/g or more²A ratio of the total amount of the components to the total amount of the components is 0.2m or less²0.6m or more per g²The ratio of the carbon atoms to the carbon atoms is less than g.

(compacted density, untamped density)

The value obtained by dividing the tamped density by the untampered density of the positive electrode active material for a lithium secondary battery of the present embodiment is 1.0 or more and 2.0 or less, and from the viewpoint of improving the effect of the present invention, it is preferably 1.1 or more and less than 2, more preferably 1.2 or more and 1.9 or less, and further is preferably 1.2 or more and 1.8 or less.

The tamped density is preferably 1.0g/cm³Above and 3.5g/cm³The followingMore preferably 2.0g/cm³Above and 3.0g/cm³Hereinafter, the amount of steps is preferably 2.2g/cm³Above and 2.7g/cm³The following.

The untamped density is preferably 0.5g/cm³Above and 2.4g/cm³Hereinafter, more preferably 1.4g/cm³Above and 2.2g/cm³Hereinafter, the amount of steps is preferably 1.5g/cm³Above and 2.1g/cm³The concentration is preferably 1.6g/cm³Above and 2.0g/cm³The following.

Here, the tamped density corresponds to the tapped bulk density in JIS R1628-.

(particle size distribution)

From the viewpoint of enhancing the effect of the present invention, the particle size distribution of the positive electrode active material for a lithium secondary battery of the present embodiment has a 90% cumulative particle diameter (D) obtained from the measured value of the particle size distribution₉₀) 10% cumulative particle diameter (D)₁₀) The value of (b) is preferably 1 or more and 5 or less, more preferably more than 1 and 4 or less, further preferably 1.1 or more and 3 or less, particularly preferably 1.3 or more and 2.5 or less, and most preferably 1.5 or more and 2.3 or less in the step .

(intensity ratio of diffraction Peak)

In the positive electrode active material for a lithium secondary battery of the present embodiment, from the viewpoint of enhancing the effect of the present invention, the intensity ratio of the (003) diffraction peak to the (104) diffraction peak when the diffraction peaks are assigned to the space group R3-m in the powder X-ray diffraction pattern is preferably 1 or more and 10 or less, more preferably 1.2 or more and 5 or less, and further preferably 1.6 or more and 3 or less in the step.

In addition, other active materials may be mixed with the positive electrode active material for a lithium secondary battery of the present embodiment within a range in which the effects of the present embodiment are not impaired.

[ Process for producing lithium-containing Complex Metal oxide ]

In the present embodiment, it is preferable that, In producing the lithium-containing composite metal oxide, a metal composite compound containing metals other than lithium, that is, Ni and Co, and at least 1 arbitrary metal selected from Mg, Al, Ca, Sc, Ti, V, Cr, Mn, Fe, Cu, Zn, Ga, Ge, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, and Sn is first prepared, and the metal composite compound is calcined with an appropriate lithium salt.

(Process for producing Metal Compound)

The metal composite compound can be produced by a generally known batch method or coprecipitation method. Hereinafter, the production method of the metal will be described in detail by taking a metal composite hydroxide containing nickel, cobalt and manganese as an example of the metal.

First, Ni salt solution, cobalt salt solution, manganese salt solution and complexing agent are reacted by a coprecipitation method, particularly a continuous method described in Japanese patent application laid-open No. 2002-201028_xCo_yMn_z(OH)₂(wherein x + y + z is 1).

The nickel salt as the solute of the nickel salt solution is not particularly limited, and for example, kinds of nickel sulfate, nickel nitrate, nickel chloride and nickel acetate may be used, kinds of cobalt salt as the solute of the cobalt salt solution may be used, and kinds of manganese sulfate, manganese nitrate and manganese chloride may be used as the manganese salt as the solute of the manganese salt solution_xCo_yMn_z(OH)₂The composition ratio of (b) is used. In addition, water is used as a solvent.

The complexing agent is a complexing agent capable of forming a complex with nickel, cobalt and manganese ions in an aqueous solution, and examples thereof include ammonium ion donors (ammonium sulfate, ammonium chloride, ammonium carbonate, ammonium fluoride, etc.), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracil diacetic acid (ウラシル diacetic acid) and glycine.

In the precipitation, an alkali metal hydroxide (e.g., sodium hydroxide or potassium hydroxide) is added if necessary in order to adjust the pH of the aqueous solution.

When the above-mentioned nickel salt solution, cobalt salt solution and manganese salt solution and the other complexing agent are continuously supplied to the reaction vessel, nickel, cobalt and manganese react with each other to produce Ni_xCo_yMn_z(OH)₂. During the reaction, the temperature of the reaction tank is controlled to be, for example, 10 ℃ or higher and 60 ℃ or lower, preferably 20 ℃ or higher and 60 ℃ or lower, the pH value in the reaction tank is controlled to be, for example, pH9 or higher and 13 or lower, preferably pH10 or higher and 13 or lower, and the contents of the reaction tank are appropriately stirred. As the reaction tank, in order to separate the formed reaction precipitate, a type of reaction tank which overflows it may be used.

After the above reaction, the obtained reaction precipitate is washed with water, then dried, and the nickel-cobalt-manganese composite hydroxide as a nickel-cobalt-manganese composite compound is separated. Further, if necessary, washing may be performed with weak acid water. Note that although the nickel-cobalt-manganese composite hydroxide was produced in the above example, a nickel-cobalt-manganese composite oxide may be produced.

In order to achieve a more desirable particle form, can be given as a method of bubbling through inert gas such as nitrogen, argon, carbon dioxide, or the like, air, oxygen, or the like, in addition to the above conditions, and in order to achieve the reaction conditions, the reaction conditions can be optimized by monitoring various physical properties of the finally obtained positive electrode active material for a lithium secondary battery in consideration of the above conditions.

(Process for producing lithium-containing Complex Metal oxide)

The metal composite oxide or metal composite hydroxide is dried and then mixed with a lithium salt.

The drying conditions are not particularly limited, and examples thereof include conditions such as conditions under which the metal composite oxide or the metal composite hydroxide is not oxidized and reduced (oxide → oxide, hydroxide → hydroxide), conditions under which the metal composite hydroxide is oxidized (hydroxide → oxide), and conditions at which the metal composite oxide is reduced (oxide → hydroxide). In order to avoid the conditions under which the metal composite hydroxide is not oxidized and reduced, inert gases such as nitrogen, helium, and rare gases such as argon may be used, and in the conditions under which the metal composite hydroxide is oxidized, the drying may be performed in an atmosphere of oxygen or air.

After the metal composite oxide or the metal composite hydroxide is dried, classification may be appropriately performed. The above-mentioned lithium salt and the metal composite oxide or the metal composite hydroxide may be used in consideration of the composition ratio of the final object. For example, when a nickel-cobalt-manganese composite hydroxide is used, a lithium salt and the metal composite hydroxide correspond to LiNi_xCo_yMn_zO₂(in the formula, x + y + z is 1) is used. The lithium-nickel cobalt manganese composite oxide can be obtained by calcining a mixture of the nickel cobalt manganese composite hydroxide and the lithium salt. Namely, a lithium-containing composite metal oxide can be obtained. In addition, for the calcination, dry air, an oxygen atmosphere, an inert atmosphere, or the like may be used depending on a desired composition, and if necessary, a plurality of heating steps may be performed.

The mixing may be carried out by any of types of dry mixing and wet mixing, dry mixing is preferable for the sake of simplicity, and examples of the mixing device include a stirring mixer, a V-type mixer, a W-type mixer, a ribbon mixer, a drum mixer, a ball mill, and the like.

The calcination temperature of the metal composite oxide or metal composite hydroxide and a lithium compound such as lithium hydroxide or lithium carbonate is not particularly limited, but is preferably 650 ℃ or higher and 850 ℃ or lower, and more preferably 700 ℃ or higher and 850 ℃ or lower. If the calcination temperature is less than 650 ℃, there is a problem that the energy density (discharge capacity) and high-rate discharge performance are liable to be lowered. In the region below this, there is a possibility that a structural factor that hinders Li movement is grown.

Further , if the firing temperature exceeds 850 ℃, it is easy to cause problems in production such as difficulty in obtaining a lithium-containing composite metal oxide of the target composition due to volatilization of Li, and in lowering of battery performance due to densification of the particles, this is because if it exceeds 850 ℃, the particle growth rate is increased times, and the crystal particles of the lithium-containing composite metal oxide become too large, but besides, it is considered that local Li deficiency increases, and the structure is unstable, and it is likely to be the cause, then , the higher the temperature, the more element substitution between the sites occupied by the Li element and the sites occupied by the transition metal element occurs, and Li conduction paths are suppressed, and thereby the discharge capacity is lowered, and by setting the firing temperature to a range of 700 ℃ or more and 850 ℃ or less, it is possible to produce a battery exhibiting particularly high energy density (discharge capacity) and excellent charge-discharge cycle performance, the firing time is preferably 3 to 20 hours, if it exceeds 20 hours, there is a case where the firing time is substantially deteriorated due to volatilization of Li, and it is preferable to proceed to the pre-firing temperature of 300 ℃.

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

The lithium-containing composite metal oxide can be used to obtain a positive electrode active material for a lithium secondary battery as described below. For example, a raw material of the covering material is mixed with the lithium-containing composite metal oxide, and a heat treatment is performed as necessary, thereby forming a covering layer on the surface of the secondary particles of the lithium-containing composite metal oxide, and obtaining a positive electrode active material for a lithium secondary battery.

As a raw material of the covering material, an oxide, a hydroxide, a carbonate, a nitrate, a sulfate, a halide, an oxalate, or an alkoxide can be used, and preferably, an oxide is used.

In order to coat the surface of the lithium-containing composite metal oxide with the raw material of the covering material more efficiently, the raw material of the covering material is preferably fine particles as compared with the secondary particles of the lithium-containing composite metal oxide. Specifically, the average secondary particle size of the raw material of the covering material is preferably 1 μm or less, and more preferably 0.1 μm or less.

The mixing of the raw material of the covering material and the lithium-containing composite metal oxide may be performed in the same manner as the mixing in the production of the lithium-containing composite metal oxide. The mixing is preferably performed by a method using a mixing device which does not include a mixing medium such as balls and does not involve strong pulverization, such as a method of mixing by using a powder mixer having an agitating blade therein. Further, by keeping it in an atmosphere containing water after mixing, the covering layer can be more firmly attached to the surface of the lithium-containing composite metal oxide.

The heat treatment conditions (temperature, holding time) in the heat treatment performed as needed after mixing the raw material of the covering material with the lithium-containing composite metal oxide may vary depending on the kind of the raw material of the covering material. The heat treatment temperature is preferably set in the range of 300 to 850 ℃, and is preferably a temperature equal to or lower than the calcination temperature of the lithium-containing composite metal oxide. For example, the temperature of the heat treatment is preferably 0 to 550 ℃ lower than the calcination temperature, and more preferably 50 to 400 ℃ lower. If the temperature is higher than the calcination temperature of the lithium-containing composite metal oxide, the raw material of the covering material and the lithium-containing composite metal oxide may be solid-dissolved without forming a covering layer. The holding time in the heat treatment is preferably set to be shorter than the holding time in the calcination. For example, the time of the heat treatment is preferably 0.5 to 10 hours, more preferably 1 to 8 hours shorter than the calcination temperature. The atmosphere in the heat treatment may be the same atmosphere as that in the above-mentioned calcination.

The positive electrode active material for a lithium secondary battery may be obtained by forming a coating layer on the surface of the lithium-containing composite metal oxide by means of sputtering, CVD, vapor deposition, or the like.

In addition, a positive electrode active material for a lithium secondary battery may be obtained by mixing and calcining the above-described raw materials with a lithium salt and a covering material.

The obtained lithium-containing composite metal oxide having a covering layer is appropriately crushed and classified to prepare a positive electrode active material for a lithium secondary battery.

[ lithium Secondary Battery ]

Next, the structure of a lithium secondary battery will be described, and a positive electrode for a lithium secondary battery obtained by using the lithium-containing composite metal oxide as a positive electrode active material for a lithium secondary battery, and a lithium secondary battery having the positive electrode for a lithium secondary battery will be described.

An example of the lithium secondary battery of the present embodiment includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte solution disposed between the positive electrode and the negative electrode.

Fig. 1A and 1B are schematic diagrams showing examples of the lithium secondary battery of the present embodiment, and the cylindrical lithium secondary battery 10 of the present embodiment is manufactured as follows.

First, as shown in fig. 1A, in a band shape was laminated and wound on a band-shaped positive electrode 2 having a positive electrode lead 21 at the end of the separator 1 or , and a band-shaped negative electrode 3 having a negative electrode lead 31 at the end of in the order of separator 1, positive electrode 2, separator 1, and negative electrode 3 to form an electrode group 4.

Next, as shown in fig. 1B, after the electrode group 4 and an insulator not shown are accommodated in the battery can 5, the can bottom is sealed, the electrode group 4 is impregnated with the electrolyte solution 6, and the electrolyte is disposed between the positive electrode 2 and the negative electrode 3, and further , the upper portion of the battery can 5 is sealed with the top insulator 7 and the sealing member 8, whereby the lithium secondary battery 10 can be manufactured.

Examples of the shape of the electrode group 4 include a columnar shape having a cross-sectional shape when the electrode group 4 is cut in a direction perpendicular to the winding axis, such as a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

As the shape of the lithium secondary battery having such an electrode group 4, a shape defined by IEC60086, which is a standard for batteries specified by the international electrical standards Institute (IEC), or a shape defined by JIS C8500 can be adopted. Examples of the shape include a cylindrical shape and a rectangular shape.

Further , the lithium secondary battery is not limited to the above-mentioned wound-type configuration, and may be a laminated-type configuration in which a laminated structure of a positive electrode, a separator, a negative electrode, and a separator is repeatedly laminated.

Hereinafter, each configuration will be described in turn.

(Positive electrode)

The positive electrode for a lithium secondary battery of the present embodiment can be produced by the following method: first, a positive electrode mixture containing a positive electrode active material for a lithium secondary battery, a conductive material, and a binder is prepared, and the positive electrode mixture is supported on a positive electrode current collector.

(conductive Material)

As the conductive material of the positive electrode for a lithium secondary battery of the present embodiment, a carbon material can be used. Examples of the carbon material include graphite powder, carbon black (e.g., acetylene black), and fibrous carbon materials. Since carbon black is fine particles and has a large surface area, addition of a small amount of carbon black to the positive electrode mixture can improve the electrical conductivity inside the positive electrode for a lithium secondary battery, and improve the charge/discharge efficiency and the output characteristics, but if the amount of carbon black is too large, the adhesion between the positive electrode mixture and the positive electrode current collector by the binder and the adhesion inside the positive electrode mixture are both reduced, which may cause an increase in internal resistance.

The proportion of the conductive material in the positive electrode mixture is preferably 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the positive electrode active material for a lithium secondary battery. When a fibrous carbon material such as graphitized carbon fiber or carbon nanotube is used as the conductive material, the ratio can be reduced.

(Binder)

As the binder included in the positive electrode for a lithium secondary battery of the present embodiment, a thermoplastic resin can be used. Examples of the thermoplastic resin include fluorine resins such as polyvinylidene fluoride (hereinafter, may be referred to as PVdF), polytetrafluoroethylene (hereinafter, may be referred to as PTFE), tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymers, tetrafluoroethylene-perfluorovinyl ether copolymers, and the like; polyolefin resins such as polyethylene and polypropylene.

These thermoplastic resins may be used in combination of 2 or more. By using a fluororesin and a polyolefin resin as a binder, the proportion of the fluororesin is 1 mass% or more and 10 mass% or less and the proportion of the polyolefin resin is 0.1 mass% or more and 2 mass% or less with respect to the entire positive electrode mixture, and thus a positive electrode mixture having high adhesion to the positive electrode current collector and high bonding force inside the positive electrode mixture can be obtained.

(Positive electrode Current collector)

As the positive electrode current collector included in the positive electrode for a lithium secondary battery according to the present embodiment, a strip-shaped member made of a metal material such as Al, Ni, or stainless steel can be used. Among them, from the viewpoint of easy processing and low cost, a current collector obtained by processing Al as a forming material into a thin film is preferable.

The positive electrode mixture may be supported on the positive electrode current collector by pasting the positive electrode mixture with an organic solvent, applying the obtained paste of the positive electrode mixture on at least the surface side of the positive electrode current collector, drying the paste, and pressurizing and solidifying the paste.

Examples of the organic solvent that can be used when the positive electrode mixture is formed into a paste include amine solvents such as N, N-dimethylaminopropylamine and diethylenetriamine; ether solvents such as tetrahydrofuran; ketone solvents such as methyl ethyl ketone; ester solvents such as methyl acetate; amide solvents such as dimethylacetamide and N-methyl-2-pyrrolidone (hereinafter, sometimes referred to as NMP).

Examples of the method of applying the positive electrode mixture paste to the positive electrode current collector include a slit die coating method, a screen coating method, a curtain coating method, a knife coating method, a gravure coating method, and an electrostatic spray method.

By the above-mentioned method, a positive electrode for a lithium secondary battery can be produced.

(cathode)

The negative electrode of the lithium secondary battery of the present embodiment may be doped or dedoped with lithium ions at a potential lower than that of the positive electrode for the lithium secondary battery, and examples thereof include an electrode in which a negative electrode mixture containing a negative electrode active material is supported on a negative electrode current collector, and an electrode composed of a negative electrode active material alone.

(negative electrode active Material)

Examples of the negative electrode active material of the negative electrode include a carbon material, a chalcogenide compound (oxide, sulfide, or the like), a nitride, a metal, or an alloy, and a material capable of doping and dedoping lithium ions at a potential lower than that of the positive electrode for a lithium secondary battery.

Examples of carbon materials that can be used as the negative electrode active material include graphite such as natural graphite and artificial graphite, coke-based materials, carbon black, pyrolytic carbon-based materials, carbon fibers, and calcined organic polymer compounds.

Examples of the oxide that can be used as the negative electrode active material include SiO₂SiO, etc. of the general formula_x(here, x is a positive real number); TiO 2₂TiO, or the like of the general formula_x(here, x is a positive real number); v₂O₅、VO₂VO of the same general formula_x(here, x is a positive real number); fe₃O₄、Fe₂O₃FeO, etc. of the general formula FeO_x(here, x is a positive real number); SnO₂SnO, and the like_x(here, x is a positive real number); WO₃、WO₂General formula WO_x(here, x is a true solidNumber) of tungsten oxide; li₄Ti₅O₁₂、LiVO₂And the like metal composite oxides containing lithium and titanium or vanadium.

Examples of the sulfide that can be used as the negative electrode active material include Ti₂S₃、TiS₂TiS, etc. formula TiS_xA sulfide of titanium (here, x is a positive real number); v₃S₄、VS₂VS, etc. of the general formula VS_x(here, x is a positive real number); fe₃S₄、FeS₂FeS, etc. of the general formula_x(here, x is a positive real number); mo₂S₃、MoS₂MoS of the same general formula_xA sulfide of molybdenum (here, x is a positive real number); SnS₂SnS, etc. formula_x(here, x is a positive real number); WS₂Of the general formula WS_x(here, x is a positive real number); sb₂S₃Of the general formula SbS_x(here, x is a positive real number); se₅S₃、SeS₂SeS, etc. general formula SeS_x(here, x is a positive real number) and a sulfide of selenium.

Examples of the nitride that can be used as the negative electrode active material include Li₃N、Li_3-xA_xAnd a lithium-containing nitride such as N (wherein A represents or both of Ni and Co, and 0< x < 3).

These carbon materials, oxides, sulfides, and nitrides may be used in only 1 kind, or in combination with and 2 or more kinds, and these carbon materials, oxides, sulfides, and nitrides may be either crystalline or amorphous .

Examples of the metal that can be used as the negative electrode active material include lithium metal, silicon metal, and tin metal.

Examples of the alloy that can be used as the negative electrode active material include lithium alloys such as Li-Al, Li-Ni, Li-Si, Li-Sn, and Li-Sn-Ni; silicon alloys such as Si-Zn; tin alloys such as Sn-Mn, Sn-Co, Sn-Ni, Sn-Cu, and Sn-La; cu₂Sb、La₃Ni₂Sn₇And the like.

These metals and alloys can be used as electrodes, for example, after being processed into a foil shape.

Among the above negative electrode active materials, a carbon material mainly composed of graphite such as natural graphite or artificial graphite is preferably used for reasons such as a low average discharge potential and a high capacity retention rate (good cycle characteristics) during repeated charge and discharge, because the potential of the negative electrode is almost unchanged from an uncharged state to a fully charged state during charge (good potential flatness), and the shape of the carbon material may be any of such as a sheet such as natural graphite, a spherical such as mesocarbon microbeads, a fibrous such as graphitized carbon fibers, or an aggregate of fine particles.

The negative electrode mixture may contain a binder if necessary. Examples of the binder include thermoplastic resins, and specifically, PVdF, thermoplastic polyimide, carboxymethyl cellulose, polyethylene, and polypropylene.

(negative current collector)

Examples of the negative electrode current collector of the negative electrode include a belt-like member made of a metal material such as Cu, Ni, or stainless steel. Among them, from the viewpoint of difficulty in forming an alloy with lithium and easiness in processing, a current collector obtained by processing Cu as a forming material into a thin film is preferable.

As a method for supporting the negative electrode mixture on such a negative electrode current collector, as in the case of a positive electrode for a lithium secondary battery, a method by pressure molding; a method of pasting the paste with a solvent or the like, applying the paste on a negative electrode current collector, drying the paste, and then pressing the paste under pressure.

(isolation film)

As the separator included in the lithium secondary battery of the present embodiment, for example, a material having a form of a porous film, a nonwoven fabric, a woven fabric, or the like, which is made of a material such as a polyolefin resin such as polyethylene or polypropylene, a fluororesin, or a nitrogen-containing aromatic polymer, can be used. The separator may be formed using 2 or more of these materials, or may be formed by stacking these materials.

Examples of the isolation film include those described in Japanese patent laid-open Nos. 2000-30686 and 10-324758. From the viewpoint of improving the volumetric energy density of the battery and reducing the internal resistance, the thickness of the separator is preferably as thin as possible within the limit of maintaining the mechanical strength, and is preferably about 5 to 200 μm, and more preferably about 5 to 40 μm.

(electrolyte)

The electrolyte solution included in the lithium secondary battery of the present embodiment includes an electrolyte and an organic solvent.

As the electrolyte contained in the electrolytic solution, LiClO may be mentioned₄、LiPF₆、LiAsF₆、LiSbF₆、LiBF₄、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiN(SO₂C₂F₅)₂、LiN(SO₂CF₃)(COCF₃)、Li(C₄F₉SO₃)、LiC(SO₂CF₃)₃、Li₂B₁₀Cl₁₀LiBOB (here, BOB refers to bis (oxalato) borate, bis (oxalato) borate), LiFSI (here, FSI refers to bis (fluorosulfonyl) imide), lithium lower aliphatic carboxylate, LiAlCl₄Lithium salts, etc., and mixtures of 2 or more of them may also be used. Among them, as the electrolyte, it is preferable to use a composition containing LiPF selected from fluorine-containing₆、LiAsF₆、LiSbF₆、LiBF₄、LiCF₃SO₃、LiN(SO₂CF₃)₂And LiC (SO)₂CF₃)₃At least 1 kind of electrolyte in (1).

Examples of the organic solvent contained in the electrolyte solution include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, 4-trifluoromethyl-1, 3-dioxolan-2-one, and 1, 2-bis (methoxycarbonyloxy) ethane, ethers such as 1, 2-dimethoxyethane, 1, 3-dimethoxypropane, pentafluoropropylmethyl ether, 2, 3, 3-tetrafluoropropyldifluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran, esters such as methyl formate, methyl acetate, and γ -butyrolactone, nitriles such as acetonitrile and butyronitrile, amides such as N, N-dimethylformamide and N, N-dimethylacetamide, carbamates such as 3-methyl-2-oxazolinone, sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1, 3-propanesultone, and solvents obtained by introducing fluorine groups into these organic solvents in steps (solvents obtained by substituting 1 or more of hydrogen atoms contained in the organic solvents with fluorine atoms).

Among these, a mixed solvent containing carbonate esters is preferable, and a mixed solvent containing cyclic carbonate and acyclic carbonate, and a mixed solvent containing cyclic carbonate and ethers is preferable at step .

In addition, as the electrolyte, in order to improve the thermal stability of the obtained lithium secondary battery, it is preferable to use a lithium secondary battery containing LiPF₆And an electrolyte solution containing a fluorine-containing lithium salt and an organic solvent having a fluorine substituent, wherein a mixed solvent containing dimethyl carbonate and an ether having a fluorine substituent such as pentafluoropropylmethyl ether and 2, 2, 3, 3-tetrafluoropropyldifluoromethyl ether has a high capacity retention rate even when charged and discharged at a high current rate, and is therefore preferred in step .

As the solid electrolyte, for example, an organic polymer electrolyte such as a polyoxyethylene-based polymer compound, a polymer compound containing at least kinds or more of polyorganosiloxane chains or polyoxyalkylene chains, or the like can be usedSo-called gel-type electrolytes obtained from the compounds. Furthermore, Li may be mentioned₂S-SiS₂、Li₂S-GeS₂、Li₂S-P₂S₅、Li₂S-B₂S₃、Li₂S-SiS₂-Li₃PO₄、Li₂S-SiS₂-Li₂SO₄、Li₂S-GeS₂-P₂S₅And the like, and a mixture of 2 or more of them may be used, and by using these solid electrolytes, the thermal stability of the lithium secondary battery may be further improved in some cases.

In the lithium secondary battery of the present embodiment, when a solid electrolyte is used, the solid electrolyte may function as a separator, and in this case, the separator may not be necessary.

The positive electrode active material for a lithium secondary battery having the above-described configuration uses the lithium-containing composite metal oxide provided with the coating layer, and therefore, the lithium secondary battery can exhibit a high output at a current rate higher than that of the conventional one.

In addition, since the positive electrode for a lithium secondary battery having the above-described configuration includes the positive electrode active material for a lithium secondary battery obtained using the lithium-containing composite metal oxide of the present embodiment, the lithium secondary battery can exhibit a high output at a current rate higher than that of a conventional lithium secondary battery.

Further , since the lithium secondary battery having the above-described configuration has the above-described positive electrode for a lithium secondary battery, it can be a lithium secondary battery that exhibits a high output at a current magnification higher than that of the conventional one.