阅读说明：本技术 非水系电解质二次电池用正极活性物质和其制造方法、非水系电解质二次电池用正极复合材料糊剂和非水系电解质二次电池 (Positive electrode active material for nonaqueous electrolyte secondary battery, method for producing same, positive electrode composite material paste for nonaqueous electrolyte secondary battery, an) 是由 渔师一臣 大塚良广 大下宽子 于 2018-05-31 设计创作，主要内容包括：提供：用于二次电池的正极的情况下具有高的电池容量、且能抑制正极复合材料糊剂的凝胶化的非水系电解质二次电池用正极活性物质。一种非水系电解质二次电池用正极活性物质,其包含：锂镍复合氧化物和硼化合物,所述锂镍复合氧化物用通式：Li<Sub>a</Sub>Ni<Sub>1-x-y</Sub>Co<Sub>x</Sub>M<Sub>y</Sub>O<Sub>2+α</Sub>(其中,0.01≤x≤0.35、0≤y≤0.10、0.95≤a≤1.10、0≤α≤0.2,M为选自Mn、V、Mg、Mo、Nb、Ti和Al中的至少1种元素)表示,硼化合物的至少一部分以Li<Sub>3</Sub>BO<Sub>3</Sub>和LiBO<Sub>2</Sub>的形态存在于锂镍复合氧化物的表面,Li<Sub>3</Sub>BO<Sub>3</Sub>与LiBO<Sub>2</Sub>的质量比(Li<Sub>3</Sub>BO<Sub>3</Sub>/LiBO<Sub>2</Sub>)为0.005以上且10以下,包含相对于正极活性物质总量为0.011质量％以上且0.6质量％以下的硼。(Providing: a positive electrode active material for a nonaqueous electrolyte secondary battery, which has a high battery capacity when used for a positive electrode of a secondary battery and can suppress gelation of a positive electrode composite paste. A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising: lithium nickel composite oxide and boron compound, the lithium nickel composite oxideThe general formula for the compounds: li a Ni 1‑x‑y Co x M y O 2+α (wherein, x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, a is 0.95. ltoreq. a.ltoreq.1.10, and α is 0. ltoreq. α.ltoreq.0.2; and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti and Al), and at least a part of the boron compound is represented by Li 3 BO 3 And LiBO 2 Is present on the surface of the lithium nickel composite oxide, Li 3 BO 3 With LiBO 2 Mass ratio of (Li) 3 BO 3 /LiBO 2 ) 0.005 to 10 inclusive, and 0.011 to 0.6 mass% of boron based on the total amount of the positive electrode active material.)

1. A positive electrode active material for a nonaqueous electrolyte secondary battery, comprising: a lithium nickel composite oxide and a boron compound, the lithium nickel composite oxide being represented by the general formula: li_aNi_1-x-yCo_xM_yO_2+αWherein x is 0.01-0.35, y is 0-0.10, a is 0.95-1.10, alpha is 0-0.2, M is at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti and Al,

at least a part of the boron compound is represented by Li₃BO₃And LiBO₂Is present on the surface of the lithium nickel composite oxide, Li₃BO₃With LiBO₂Mass ratio of (i) Li₃BO₃/LiBO₂Is 0.005 to 10 inclusive,

contains boron in an amount of 0.011 mass% or more and 0.6 mass% or less based on the total amount of the positive electrode active material.

2. A method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, comprising the steps of:

mixing a nickel composite hydroxide or a nickel composite oxide, a lithium compound, and a 1 st boron compound capable of reacting with lithium, such that the amount of boron a in the 1 st boron compound is 0.001 to 0.1 mass% inclusive with respect to the total amount of the positive electrode active material, to obtain a lithium mixture;

roasting the lithium mixture at a temperature of 700 ℃ to 800 ℃ in an oxygen atmosphere to obtain a 1 st lithium-nickel composite oxide; and the combination of (a) and (b),

mixing a 1 st lithium nickel composite oxide with a 2 nd boron compound capable of reacting with lithium so that the amount of boron B in the 2 nd boron compound is 0.01 to 0.5 mass% relative to the total amount of a positive electrode active material and the ratio A/B of the amount of boron A in the 1 st boron compound to the amount of boron B in the 2 nd boron compound is 0.005 to 10 inclusive to obtain a 2 nd lithium nickel composite oxide,

the 1 st boron compound and the 2 nd boron compound are the same or different compounds,

the general formula Li for the 2 nd lithium nickel composite oxide_aNi_1-x-yCo_xM_yO_2+αWherein x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, a is 0.95. ltoreq. a.ltoreq.1.10, and α is 0. ltoreq. α.ltoreq.0.2, M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti and Al, and Li is present on the surface thereof₃BO₃And LiBO₂。

3. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 2, wherein the 1 st boron compound contains H₃BO₃、B₂O₃And LiBO₂At least one of (a).

4. The method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 2 or 3, wherein the 2 nd boron compound contains H₃BO₃And B₂O₃One or both of them.

5. A positive electrode composite paste for a nonaqueous electrolyte secondary battery, comprising the positive electrode active material for a nonaqueous electrolyte secondary battery according to claim 1.

6. A nonaqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode comprises the positive electrode active material according to claim 1.

Technical Field

The present invention relates to a positive electrode active material for a nonaqueous electrolyte secondary battery, a method for producing the same, a positive electrode composite material paste for a nonaqueous electrolyte secondary battery, and a nonaqueous electrolyte secondary battery.

Background

In recent years, with the spread of mobile electronic devices such as mobile phones and notebook-size personal computers, development of small and lightweight nonaqueous electrolyte secondary batteries having high energy density has been demanded. In addition, as a battery for an electric vehicle represented by a hybrid vehicle, development of a secondary battery having a high output has been demanded. As a nonaqueous electrolyte secondary battery that satisfies such a demand, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte solution, and the like, and a material capable of inserting and extracting lithium is used as an active material of the negative electrode and the positive electrode.

Research and development of such lithium ion secondary batteries, in which a layered or spinel type lithium ion secondary battery is used, are actively ongoingLithium ion secondary batteries using a lithium metal composite oxide as a positive electrode active material have been put to practical use as batteries having a high energy density because they can obtain a high voltage of 4V class. As a material mainly proposed so far, lithium cobalt composite oxide (for example, LiCoO) which is relatively easy to synthesize can be cited₂) Lithium nickel composite oxide (LiNiO) using nickel which is less expensive than cobalt₂) Lithium nickel cobalt manganese composite oxide (LiNi)_1/3Co_1/3Mn_1/3O₂) Lithium manganese composite oxide (LiMn) using manganese₂O₄) And the like.

Among them, in batteries using a lithium cobalt composite oxide, a large number of developments have been made so far for obtaining excellent initial capacity characteristics and cycle characteristics, and various results have been obtained. However, since the lithium cobalt composite oxide uses an expensive cobalt compound as a raw material, the unit price per unit capacity of a battery using the lithium cobalt composite oxide is significantly higher than that of a nickel-metal hydride battery, and the applicable use is very limited. Therefore, not only small-sized secondary batteries for mobile devices but also large-sized secondary batteries for power storage, electric vehicles, and the like are expected to be industrially significant for reducing the cost of the positive electrode active material and producing lithium ion secondary batteries at a lower cost.

As a new material of an active material for a lithium ion secondary battery, there is a lithium nickel composite oxide using nickel which is less expensive than cobalt, and this lithium nickel composite oxide exhibits an electrochemical potential lower than that of a lithium cobalt composite oxide, so that decomposition by oxidation of an electrolytic solution is not likely to be a problem, and a higher capacity can be expected, and a high battery voltage is exhibited as in the cobalt system, and therefore, development of an electric vehicle in particular is actively underway. However, in an electric vehicle mounted with a battery produced using a lithium nickel composite oxide as disclosed in patent document 1 or the like, it is difficult to achieve a cruising distance comparable to that of a gasoline car, and a further increase in capacity is demanded.

Further, as a disadvantage of the lithium nickel composite oxide, there is a disadvantage that gelation of the positive electrode composite paste is easily caused. The positive electrode of the nonaqueous electrolyte secondary battery may be formed, for example, as follows: the positive electrode active material is mixed with a binder such as polyvinylidene fluoride (PVDF) and a solvent such as N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode composite material paste, and the paste is applied to a current collector such as an aluminum foil. In this case, when lithium is released from the positive electrode active material in the positive electrode composite material paste, lithium hydroxide may be generated by reaction with moisture contained in the binder or the like. The lithium hydroxide thus produced reacts with the binder, and is thought to cause gelation of the positive electrode composite paste. The gelation of the positive electrode composite paste causes deterioration in workability and deterioration in yield. This tendency becomes remarkable when the ratio of lithium in the positive electrode active material exceeds the stoichiometric ratio and the ratio of nickel is high.

Several attempts have been made to inhibit gelation of the positive electrode composite paste. For example, patent document 2 proposes a positive electrode composition for a nonaqueous electrolyte secondary battery, which contains: a positive electrode active material composed of a lithium transition metal composite oxide; and, an additive particle composed of an acidic oxide particle. In the positive electrode composition, the moisture contained in the binder reacts with lithium released from the positive electrode active material to generate lithium hydroxide, the generated lithium hydroxide preferentially reacts with the acid oxide, and the reaction between the generated lithium hydroxide and the binder is suppressed, thereby suppressing gelation of the positive electrode composite paste. The acidic oxide functions as a conductive agent in the positive electrode, and it is said that the acidic oxide reduces the resistance of the entire positive electrode and contributes to improvement of the power characteristics of the battery.

Further, patent document 3 proposes a method for manufacturing a lithium ion secondary battery, which includes the steps of: preparing a lithium transition metal composite oxide containing LiOH except for the components as a positive electrode active material; grasping a molar amount P of LiOH contained in 1g of the positive electrode active material; preparing tungsten oxide in an amount of 0.05 mol or more in terms of tungsten atoms per 1 mol of LiOH with respect to the molar amount P of LiOH; and kneading the positive electrode active material and tungsten oxide together with the conductive material and the binder in an organic solvent to prepare a positive electrode paste.

Patent document 4 discloses the following technique: an electrode using a lithium transition metal composite oxide or the like contains boric acid or the like as an inorganic acid, and prevents gelation of an electrode paste. Lithium nickelate is disclosed as a specific example of the lithium transition metal composite oxide.

Disclosure of Invention

Problems to be solved by the invention

However, when the positive electrode active material described in patent document 1 is used, it is insufficient as a secondary battery for an electric vehicle, and a further increase in capacity is demanded. In the proposal of patent document 2, there is a concern that the separator may be broken due to the remaining acidic oxide particles and the thermal stability may be reduced. In addition, the positive electrode composite paste is not sufficiently inhibited from gelling. Further, although the inhibition of gelation can be improved by increasing the amount of the acid oxide to be added, the battery capacity per unit mass is deteriorated due to an increase in the cost of raw materials caused by the addition of the acid oxide and an increase in the weight caused by the addition of the acid oxide.

In addition, the proposal of patent document 3 cannot be said to eliminate the problem related to the damage of the separator and the suppression of gelation caused by the residue of the acidic oxide. Further, tungsten, which is a heavy element unfavorable for charge and discharge, is added, so that the battery capacity per unit weight is greatly reduced.

In addition, patent document 4 proposes a method in which a positive electrode active material, a conductive agent, and a binder are added to a solvent containing boric acid or the like and mixed with stirring, but in this method, there is a concern that gelation may occur locally until the positive electrode active material is sufficiently dispersed.

In view of the above problem, an object of the present invention is to provide: a positive electrode active material for a nonaqueous electrolyte secondary battery, which has a high battery capacity when used as a positive electrode active material and can suppress gelation of a positive electrode composite paste.

Means for solving the problems

In order to solve the above problems, the present inventors have made extensive studies on a lithium metal composite oxide used as a positive electrode active material for a nonaqueous electrolyte secondary battery and a method for producing the same, and as a result, have obtained the following findings: the present inventors have found that a positive electrode active material which is improved in battery capacity and can suppress gelation of a positive electrode composite paste can be obtained by allowing two boron compounds to be present on the surface of a lithium nickel composite oxide at a specific content ratio, and have completed the present invention.

In the 1 st aspect of the present invention, there is provided a positive electrode active material for a nonaqueous electrolyte secondary battery, comprising: a lithium nickel composite oxide and a boron compound, the lithium nickel composite oxide being represented by the general formula: li_aNi_1-x-yCo_xM_yO_2+α(wherein, x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, a is 0.95. ltoreq. a.ltoreq.1.10, and α is 0. ltoreq. α.ltoreq.0.2; and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti and Al), and at least a part of the boron compound is represented by Li₃BO₃And LiBO₂Is present on the surface of the lithium nickel composite oxide, Li₃BO₃With LiBO₂Mass ratio of (Li)₃BO₃/LiBO₂) 0.005 to 10 inclusive, and 0.011 to 0.6 mass% of boron based on the total amount of the positive electrode active material.

In the 2 nd aspect of the present invention, there is provided a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery, comprising the steps of: mixing a nickel composite hydroxide or nickel composite oxide, a lithium compound, and a 1 st boron compound capable of reacting with lithium, such that the amount of boron a in the 1 st boron compound is 0.001 to 0.1 mass% inclusive with respect to the total amount of the positive electrode active material, to obtain a lithium mixture; roasting the lithium mixture at 700-800 deg.c in oxygen atmosphere to obtain the 1 st composite lithium-nickel oxideA compound; and mixing the 1 st lithium nickel composite oxide with a 2 nd boron compound capable of reacting with lithium so that the boron amount B in the 2 nd boron compound is 0.01 to 0.5 mass% relative to the total amount of the positive electrode active material and the ratio (A/B) of the boron amount A of the 1 st boron compound to the boron amount B of the 2 nd boron compound is 0.005 to 10, to obtain the 2 nd lithium nickel composite oxide, wherein the 1 st boron compound and the 2 nd boron compound are the same or different compounds, and the 2 nd lithium nickel composite oxide is formed by the general formula Li for the 2 nd lithium nickel composite oxide_aNi_1-x-yCo_xM_yO_2+α(wherein 0.05. ltoreq. x.ltoreq.0.35, 0. ltoreq. y.ltoreq.0.10, 0.95. ltoreq. a.ltoreq.1.10, 0. ltoreq. alpha.ltoreq.0.2, and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti and Al), and Li is present on the surface thereof₃BO₃And LiBO₂。

In addition, the 1 st boron compound preferably contains H₃BO₃、B₂O₃And LiBO₂At least one of (a). In addition, the 2 nd boron compound preferably contains H₃BO₃And B₂O₃One or both of them.

In claim 3 of the present invention, there is provided a positive electrode composite paste for a nonaqueous electrolyte secondary battery, which contains a positive electrode active material for a nonaqueous electrolyte secondary battery.

In the 4 th aspect of the present invention, there is provided a nonaqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, wherein the positive electrode contains the positive electrode active material.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a positive electrode active material for a nonaqueous electrolyte secondary battery can be obtained which has a high battery capacity when used as a positive electrode material for a secondary battery and can suppress gelation of a positive electrode composite paste. Further, the production method is easy and suitable for industrial scale production, and is extremely industrially valuable.

Drawings

Fig. 1 is a view showing an example of a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery according to an embodiment.

Fig. 2 is a schematic sectional view of a coin-type battery used in battery evaluation.

Detailed Description

The positive electrode active material for a nonaqueous electrolyte secondary battery, the method for producing the same, the positive electrode composite paste, and the nonaqueous electrolyte secondary battery of the present invention will be described below. The present invention is not limited to the following detailed description unless otherwise specified.

1. Positive electrode active material for nonaqueous electrolyte secondary battery

The positive electrode active material for a nonaqueous electrolyte secondary battery (hereinafter, also referred to as "positive electrode active material") according to the present embodiment includes: a lithium nickel composite oxide and a boron compound, the lithium nickel composite oxide being represented by general formula (1): li_aNi_1-x-yCo_xM_yO_2+α(wherein x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, a is 0.95. ltoreq. a.ltoreq.1.10, and α is 0. ltoreq. α.ltoreq.0.2, and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, and Al). The boron compound means a compound containing boron. The content of each element can be measured by ICP emission spectrometry.

In the general formula (1), x representing the content of cobalt (Co) is 0.01. ltoreq. x.ltoreq.0.35, and preferably 0.01. ltoreq. x.ltoreq.0.20 from the viewpoint of further improving the battery capacity (charge/discharge capacity) of a secondary battery using a positive electrode active material. In addition, x may be 0.05. ltoreq. x.ltoreq.0.35, or 0.05. ltoreq. x.ltoreq.0.20.

In the above general formula (1), M is at least 1 element selected from Mn, V, Mg, Mo, Nb, Ti and Al. M is an additive element and may be selected from a variety of elements depending on the desired characteristics. M may comprise Al, for example. In addition, y representing the content of M is 0. ltoreq. y.ltoreq.0.10, and from the viewpoint of further improving the battery capacity (charge-discharge capacity) of a secondary battery using the positive electrode active material, 0. ltoreq. y.ltoreq.0.07 is preferable, and 0. ltoreq. y.ltoreq.0.05 is more preferable.

In the general formula (1), (1-x-y) representing the content of nickel (Ni) is 0.55. ltoreq. 1-x-y. ltoreq.0.95, and from the viewpoint of further improving the battery capacity of a secondary battery using a positive electrode active material, 0.6. ltoreq. 1-x-y. ltoreq.0.95, and more preferably 0.65. ltoreq. 1-x-y. ltoreq.0.95.

In the general formula (1), a representing the content of lithium (Li) is in the range of 0.95. ltoreq. a.ltoreq.1.10. For example, in the general formula (1), when a representing the content of lithium (Li) is 1< a, and when the content of nickel (Ni) is high, the positive electrode composite paste tends to be more likely to be gelled. However, the positive electrode active material of the present embodiment contains a specific boron compound at a specific ratio, and thus can suppress gelation of the positive electrode composite paste and has a high battery capacity even with a composition that is likely to undergo gelation.

At least a part of the boron compound is represented by Li₃BO₃And LiBO₂Is present on the surface of the lithium nickel composite oxide. In the positive electrode active material of the embodiment, Li is present on the surface of the lithium nickel composite oxide₃BO₃And LiBO₂The two lithium boron compounds shown have high battery capacity and can suppress gelation of the positive electrode composite paste when used in a positive electrode of a secondary battery. The presence form of the boron compound can be confirmed by XRD diffraction. The positive electrode active material of the present embodiment is detected by Li by XRD diffraction, for example₃BO₃And LiBO₂The boron compound formed.

In the positive electrode active material, Li₃BO₃With LiBO₂Mass ratio of (Li)₃BO₃/LiBO₂) Is 0.005 to 10 inclusive, preferably 0.01 to 5 inclusive. Mass ratio (Li)₃BO₃/LiBO₂) If the amount is less than 0.005, it is necessary to add a large amount of the 2 nd boron compound to the 1 st lithium nickel composite oxide in the later-described process for producing a positive electrode active material, and lithium in the crystal of the lithium nickel composite oxide is likely to react with boron in the 2 nd boron compound to decrease, and the battery capacity may be decreased. On the other hand, mass ratio (Li)₃BO₃/LiBO₂) When the amount is more than 10, the amount of the 1 st boron compound or the 2 nd boron compound added exceeds a suitable range in the process for producing a positive electrode active material to be described laterTherefore, the battery characteristics sometimes deteriorate. Note that the mass ratio (Li)₃BO₃/LiBO₂) Can be calculated from the ratio of Li to B obtained by chemical analysis.

In addition, the positive electrode active material has a mass ratio (Li) from the viewpoint of satisfying both the battery capacity and the gelation inhibition at a higher level₃BO₃/LiBO₂) Preferably 0.05 or more and 2 or less, and more preferably 0.05 or more and 1 or less.

The positive electrode active material of the present embodiment contains 0.011 mass% or more and 0.6 mass% or less of boron with respect to the total amount of the positive electrode active material. When the amount of boron contained in the positive electrode active material is less than 0.011 mass% based on the total amount of the positive electrode active material, it is difficult to achieve both the discharge capacity improving effect and the gelation inhibiting effect. When the amount exceeds 0.6 mass%, a large amount of Li is formed on the surface of the lithium nickel composite oxide₃BO₃And LiBO₂This is not preferable because the resistance increases and the battery capacity decreases.

From the viewpoint of achieving both the battery capacity and the suppression of gelation at a higher level, the positive electrode active material preferably contains 0.05 mass% or more of boron with respect to the total amount of the positive electrode active material, preferably contains 0.055 mass% or more of boron with respect to the total amount of the positive electrode active material, and more preferably contains 0.1 mass% or more of boron with respect to the total amount of the positive electrode active material.

2. Method for producing positive electrode active material

Fig. 1 is a view showing an example of a method for producing a positive electrode active material for a nonaqueous electrolyte secondary battery (hereinafter, also referred to as a "method for producing a positive electrode active material") according to the present embodiment. Hereinafter, a method for producing a positive electrode active material according to the present embodiment will be described with reference to fig. 1. The method for producing a positive electrode active material can produce a positive electrode active material containing the lithium nickel composite oxide and the boron compound as described above on an industrial scale with good productivity.

The manufacturing method of the present embodiment includes the steps of: mixing a nickel composite hydroxide or nickel composite oxide with a lithium compound and with a 1 st boron compoundSynthesizing a lithium mixture (step S10); calcining the obtained lithium mixture at 700 ℃ to 800 ℃ in an oxygen atmosphere to obtain a 1 st lithium-nickel composite oxide (step S20); and mixing the obtained 1 st lithium nickel composite oxide with the 2 nd boron compound to obtain a 2 nd lithium nickel composite oxide (step S30). Li is present on the surface of the obtained 2 nd lithium nickel composite oxide₃BO₃And LiBO₂。

First, a nickel composite hydroxide or a nickel composite oxide is mixed with a lithium compound and a 1 st boron compound to obtain a lithium mixture (step S10).

As the 1 st boron compound, a boron compound which can react with lithium can be used, and for example, boron oxide (B)₂O₃) Boric acid (H)₃BO₃) Ammonium tetraborate tetrahydrate ((NH)₄)₂B₄O₇·4H₂O), ammonium pentaborate octahydrate ((NH)₄)₂O·5B₂O₃·8H₂O)、LiBO₂And the like. Among them, preferred is the use of a compound selected from H₃BO₃、B₂O₃And LiBO₂More preferably, H is used₃BO₃And B₂O₃At least one of (a). It is considered that these boron compounds have high reactivity with lithium salts, and that the lithium salts react with lithium derived from the lithium compound used as the raw material to form mainly Li after the firing step (step S20) described later₃BO₃. In the mixing step (step S10), in addition to the lithium compound which is advantageous for forming the lithium nickel composite oxide, the boron in the 1 st boron compound added may be added simultaneously so as to sufficiently generate Li so as not to reduce the amount of lithium contained in the crystal of the positive electrode active material₃BO₃A lithium salt of lithium in an amount of.

The 1 st boron compound is mixed so that the amount a of boron in the 1 st boron compound is preferably 0.001 mass% or more and 0.1 mass% or less, more preferably 0.003 mass% or more and 0.08 mass% or less, and still more preferably 0.01 mass% or more and 0.08 mass% or less, with respect to the total amount of the positive electrode active material. In the case where the amount a of boron is within the above range,when the obtained positive electrode active material is used in a secondary battery, the battery capacity (discharge capacity) can be improved. When the boron amount a is less than 0.001 mass%, the flux effect described later becomes insufficient, and the effect of improving the battery capacity cannot be exhibited. On the other hand, when the boron content a exceeds 0.08 mass%, Li in the obtained positive electrode active material₃BO₃A large amount of the metal oxide is not preferable because it causes resistance and lowers capacity.

When the boron amount a of the 1 st boron compound is mixed in the above range and the obtained lithium mixture is calcined (step S20), boron derived from the 1 st boron compound reacts with Li present on the surface of the 1 st lithium nickel composite oxide to produce Li₃BO₃. It is considered that in the firing step (step S20), Li is formed on the surface of the 1 st lithium-nickel composite oxide₃BO₃The flux effect is exerted on the 1 st lithium nickel composite oxide, and the crystal growth is promoted, so that the crystal structure of the lithium nickel composite oxide can be more complete. The positive electrode active material of the present embodiment contains Li₃BO₃And thus exhibits an effect of improving discharge capacity when used as a positive electrode material for a secondary battery.

The nickel composite hydroxide or nickel composite oxide is not particularly limited, and known ones can be used, and for example: a nickel composite hydroxide obtained by a crystallization method, and/or a nickel composite oxide obtained by subjecting the nickel composite hydroxide to oxidation baking (heat treatment). As the method for producing the nickel composite hydroxide, either a batch method or a continuous method can be applied. From the viewpoint of cost and filling property, a continuous method of continuously recovering nickel composite hydroxide particles overflowing from the reaction vessel is preferable. In addition, a batch method is preferable from the viewpoint of obtaining particles with higher uniformity.

In addition, for the nickel composite hydroxide or nickel composite oxide, for example, the mass ratio (molar ratio) of nickel (Ni), cobalt (Co), and element M may be represented by Ni: co: m ═ (1-x-y): x: y (wherein, x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti and Al). Since the molar ratio of each element in the nickel composite hydroxide or nickel composite oxide is maintained in the obtained positive electrode active material, the preferred range of the molar ratio of each element is the same as the range of each element in the general formula (1) in the positive electrode active material.

As the lithium compound, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and the like can be used, and among them, lithium hydroxide and lithium carbonate are preferable, and lithium hydroxide is more preferable from the viewpoint of reactivity with a boron compound.

The lithium compound is mixed in such an amount that the ratio (Li/Me) of the number of atoms of lithium (Li) to the total number of atoms (Me) of the metal elements other than lithium is 0.95 to 1.10. When Li/Me is less than 0.95, the reaction resistance of the positive electrode in the secondary battery using the obtained positive electrode active material increases, and therefore, the power of the battery decreases. When Li/Me exceeds 1.10, the initial discharge capacity of the obtained positive electrode active material decreases, and the reaction resistance of the positive electrode also increases.

In the mixing step (step S10), the 1 st boron compound, the nickel composite hydroxide and/or the nickel composite oxide, and the lithium compound are preferably mixed thoroughly. The mixing may be carried out by using a conventional mixer, for example, a swing mixer, a Ladige mixer, a Julia mixer, a V-type mixer, or the like, as long as the lithium compound is sufficiently mixed to such an extent that the skeleton of the composite hydroxide particles is not broken.

Next, the obtained lithium mixture is fired at 700 ℃ to 800 ℃ in an oxygen atmosphere to obtain a 1 st lithium nickel composite oxide (step S20). Calcining the lithium mixture containing the 1 st boron compound to form the 1 st lithium nickel composite oxide while forming Li on the surface thereof₃BO₃。

The firing temperature is preferably 700 ℃ to 800 ℃, and more preferably 720 ℃ to 780 ℃. In the case where the firing temperature is less than 700 deg.c, the crystals of the 1 st lithium nickel composite oxide do not grow sufficiently. If the firing temperature exceeds 800 ℃, the 1 st lithium nickel composite oxide is decomposed, and the battery characteristics are undesirably degraded.

The holding time at the firing temperature is, for example, 5 hours or more and 20 hours or less, preferably 5 hours or more and 10 hours or less. The atmosphere during firing is an oxygen atmosphere, and for example, an atmosphere having an oxygen concentration of 100% by volume is preferable.

The conditions in the mixing step (step S10) and the firing step (step S20) may be adjusted within the above-mentioned ranges so that most of the boron added in the form of the 1 st boron compound forms Li₃BO₃. A part of boron may be dissolved in the 1 st lithium nickel composite oxide to a degree that does not impair the effects of the present invention.

Note that the composition of the 1 st lithium nickel composite oxide may be represented by the general formula (2) in addition to boron: li_aNi_{1-x- y}Co_xM_yO_2+α(wherein x is 0.01. ltoreq. x.ltoreq.0.35, y is 0. ltoreq. y.ltoreq.0.10, a is 0.95. ltoreq. a.ltoreq.1.10, and α is 0. ltoreq. α.ltoreq.0.2, and M is at least 1 element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, and Al). In addition, M in the general formula may contain Al, for example. In the case where the 1 st lithium nickel composite oxide has the above composition, a higher battery capacity can be obtained. Since the molar ratio of each element of the 1 st lithium nickel composite hydroxide is maintained in the obtained positive electrode active material, the preferable range of the molar ratio of each element is the same as the range of each element in the general formula (1) in the positive electrode active material.

Next, the 1 st lithium nickel composite oxide and the 2 nd boron compound are mixed to obtain a 2 nd lithium nickel composite oxide (step S30). In this step, the 1 st lithium nickel composite oxide and the 2 nd boron compound are mixed in a dry manner, and excess lithium in the 1 st lithium nickel composite oxide reacts with the 2 nd boron compound to form LiBO₂. Thus, the positive electrode active material of the present embodiment can be obtained more easily and with good productivity on an industrial scale. The composition of the 2 nd lithium nickel composite hydroxide (positive electrode active material) and the molar ratio of each element are shown by the general formula (1).

As the 2 nd boron compound, a boron compound which can react with lithium other than a lithium compound can be used, and for example, a boron compound which can react with lithium other than a lithium compoundTo give boron oxide (B)₂O₃) Boric acid (H)₃BO₃) Ammonium tetraborate tetrahydrate ((NH)₄)₂B₄O₇·4H₂O), ammonium pentaborate octahydrate ((NH)₄)₂O·5B₂O₃·8H₂O), and the like. Among them, H is more preferably used₃BO₃And B₂O₃At least one of (1), further preferably H₃BO₃. These boron compounds have high reactivity with lithium hydroxide, and can rapidly react with excess lithium such as lithium hydroxide present on the surface of the 1 st lithium nickel composite oxide when added. The 2 nd boron compound may be the same as or different from the 1 st boron compound.

The 2 nd boron compound is preferably a powder, and the average particle diameter is preferably 5 μm or more and 40 μm or less. This makes the distribution of boron in the obtained positive electrode active material uniform, and further promotes the reaction between the excess lithium in the 1 st lithium-nickel composite oxide and the 2 nd boron compound B, thereby enabling the formation of more LiBO₂。

The 2 nd boron compound is mixed in an amount such that the amount of boron B in the 2 nd boron compound is 0.01 to 0.5 mass%, preferably 0.03 to 0.4 mass%, based on the total amount of the positive electrode active material. When the boron amount B is within the above range, it reacts with lithium hydroxide (excess lithium) present on the surface of the 1 st lithium-nickel composite oxide and causing gelation to form LiBO₂Thereby, gelation of the paste can be suppressed.

When the boron amount B of the 2 nd boron compound is less than 0.01 mass%, the addition amount is too small, and excess lithium including lithium hydroxide remains on the surface of the 2 nd lithium-nickel composite oxide, and gelation cannot be suppressed. When the boron amount B of the 2 nd boron compound exceeds 0.5 mass%, lithium in the crystal interior of the lithium nickel composite oxide is abstracted and reacts with the 2 nd boron compound to produce LiBO₂Therefore, the amount of lithium in the lithium nickel composite oxide may decrease to lower the capacity.

Further, the 2 nd boron compound is mixed so that the ratio A/B of the boron amount A of the 1 st boron compound to the boron amount B of the 2 nd boron compound (hereinafter, also referred to as "B")Referred to as "boron mass ratio a/B") of 0.005 or more and 10 or less, preferably 0.01 or more and 5 or less. When the boron mass ratio A/B is in the above range, it is possible to obtain a boron alloy having Li at an appropriate ratio on the surface thereof₃BO₃And LiBO₂The 2 nd lithium nickel composite oxide. As described above, it is considered that the 1 st boron compound forms Li₃BO₃The growth of the crystal structure of the lithium nickel composite oxide is facilitated, and the 2 nd boron compound B forms LiBO₂This is advantageous in suppressing gelation of the positive electrode composite paste due to excess lithium such as lithium hydroxide present on the surface of the 1 st lithium nickel composite oxide.

When the boron mass ratio a/B is less than 0.005, a large amount of the 2 nd boron compound B is added (mixed) to the 1 st lithium nickel composite oxide in which the crystal structure is not sufficiently grown, and lithium in the crystal of the 1 st lithium nickel composite oxide is likely to react with boron to decrease, and the battery capacity may be decreased. On the other hand, when the boron mass ratio A/B exceeds 10, the amount of the 1 st boron compound or the 2 nd boron compound added is not preferably in the above range.

In the mixing step (step S30), the 1 st lithium nickel composite oxide and the 2 nd boron compound are sufficiently mixed to such an extent that the skeleton of the 1 st lithium nickel composite oxide is not broken. The remaining lithium containing lithium hydroxide in the 1 st lithium nickel composite oxide in the mixture reacts with the 2 nd boron compound to form LiBO₂. As a result, Li formed in the firing step (step S20) was present on the surface of the obtained 2 nd lithium nickel composite oxide₃BO₃And LiBO formed in the mixing step (step S30)₂。

The mixing can be carried out by a conventional mixer, for example, a swing mixer, a Ladige mixer, a Julia mixer, a V-type mixer, etc. The mixing time is not particularly limited, as long as the 1 st lithium nickel composite oxide and the 2 nd boron compound are sufficiently mixed to form LiBO₂For example, the time may be 3 minutes or more and 1 hour or less.

In the mixing step (step S30), LiBO is added₂The formation of (b) can be confirmed by, for example, X-ray diffraction. In addition, the mixing is preferably such thatIn the obtained positive electrode active material, when observed by a Scanning Electron Microscope (SEM), the mixture was mixed to such an extent that no powder showing the shape of the 2 nd boron compound B was observed.

The obtained positive electrode active material of the present embodiment has a high battery capacity when used in a secondary battery, and can suppress gelation of the positive electrode composite paste. The positive electrode active material of the present embodiment can have a higher initial discharge capacity than, for example, a positive electrode active material that does not contain a boron compound and has the same composition except for boron. The positive electrode active material of the present embodiment can suppress gelation of the positive electrode composite paste in the stability evaluation described in examples, for example.

3. Nonaqueous electrolyte secondary battery

The nonaqueous electrolyte secondary battery (hereinafter, also referred to as "secondary battery") according to the present embodiment includes a positive electrode containing the positive electrode active material as a positive electrode material. The nonaqueous electrolyte secondary battery may be constituted by the same components as those of conventionally known nonaqueous electrolyte secondary batteries, and includes, for example, a positive electrode, a negative electrode, and a nonaqueous electrolytic solution. The secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte solution.

The embodiments described below are merely examples, and the nonaqueous electrolyte secondary battery according to the present embodiment can be implemented in various modified and improved forms based on the embodiments described in the present specification based on the common general knowledge of those skilled in the art. The nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited in its application.

(Positive electrode)

The positive electrode of the nonaqueous electrolyte secondary battery is produced, for example, as follows, using the positive electrode active material for a nonaqueous electrolyte secondary battery obtained as described above.

First, a powdery positive electrode active material, a conductive material, and a binder are mixed, and further, if necessary, activated carbon, a target solvent for viscosity adjustment, and the like are added and kneaded to prepare a positive electrode composite paste. In this case, the mixing ratio of each positive electrode composite paste is also an important factor for determining the performance of the nonaqueous electrolyte secondary battery. When the solid content of the positive electrode composite material excluding the solvent is set to 100 parts by mass, it is desirable that the content of the positive electrode active material is 60 to 95 parts by mass, the content of the conductive material is 1 to 20 parts by mass, and the content of the binder is 1 to 20 parts by mass, as in the case of a positive electrode of a general nonaqueous electrolyte secondary battery.

The obtained positive electrode composite material paste is applied to the surface of a current collector made of, for example, aluminum foil, dried, and a solvent is scattered. If necessary, the electrode density may be increased by pressing with a roll press or the like. Thus, a sheet-like positive electrode can be produced. The sheet-shaped positive electrode may be cut into an appropriate size according to a target battery, and the cut positive electrode may be used for manufacturing the battery. The method for manufacturing the positive electrode is not limited to the above example, and may be based on other methods.

In the case of producing the positive electrode, as the conductive material, for example, a carbon black-based material such as graphite (natural graphite, artificial graphite, expanded graphite, or the like), acetylene black, ketjen black, or the like can be used.

The binder plays a role of fixing and linking the active material particles, and for example, polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene monomer, styrene butadiene, cellulose-based resin, and polyacrylic acid can be used.

The positive electrode active material, the conductive material, and the activated carbon are dispersed as necessary, and a solvent for dissolving the binder is added to the positive electrode composite material. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, activated carbon may be added to the positive electrode composite material in order to increase the electric double layer capacity.

(cathode)

The negative electrode used were: a negative electrode formed by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, such as metallic lithium or a lithium alloy, adding an appropriate solvent to form a paste, coating the surface of a metal foil current collector such as copper with the obtained negative electrode composite material, drying the coating, and compressing the coating to increase the electrode density as necessary.

Examples of the negative electrode active material include calcined organic compounds such as natural graphite, artificial graphite, and phenol resin, and powdered carbon materials such as coke. In the above 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.

(spacer)

The positive electrode and the negative electrode are disposed with a separator interposed therebetween as necessary. The separator is used to separate the positive electrode from the negative electrode and to hold the electrolyte, and a film of polyethylene, polypropylene, or the like having a large number of fine pores may be used.

(nonaqueous electrolyte)

As the nonaqueous electrolyte, a nonaqueous electrolytic solution can be used. The nonaqueous electrolyte solution may be one in which a lithium salt as a supporting salt is dissolved in an organic solvent, for example. In addition, as the nonaqueous electrolytic solution, one in which a lithium salt is dissolved in an ionic liquid can be used. The ionic liquid means: a salt which is composed of a cation other than lithium ion and an anion and is liquid at ordinary temperature.

As the organic solvent, 1 kind selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and propylene trifluorocarbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfides such as ethylmethylsulfone and butylsultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more kinds may be mixed and used.

As supporting salt, LiPF may be used₆、LiBF₄、LiClO₄、LiAsF₆、LiN(CF₃SO₂)₂And double salts thereof, and the like. The nonaqueous electrolytic 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 a property of withstanding high voltage. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, or the like can be used.

The oxide-based solid electrolyte is not particularly limited, and any oxide-based solid electrolyte can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation properties. Examples of the oxide-based solid electrolyte include lithium phosphate (Li)₃PO₄)、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+XAl_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.

The sulfide-based solid electrolyte is not particularly limited, and any sulfide-based solid electrolyte can be used as long as it contains sulfur (S) and has lithium ion conductivity and electronic insulation properties. Examples of the sulfide-based solid electrolyte include Li₂S-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.

In addition to the above, for example, Li can be used as the inorganic solid electrolyte₃N、LiI、Li₃N-LiI-LiOH and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting 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 contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may be mixed with the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(shape and constitution of Battery)

The nonaqueous electrolyte secondary battery of the present embodiment, which is composed of the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte or the positive electrode, the negative electrode, and the solid electrolyte as described above, may be formed in various shapes such as a cylindrical shape and a laminated shape.

When a nonaqueous electrolyte solution is used as the nonaqueous electrolyte, an electrode body is formed by laminating a positive electrode and a negative electrode with a separator interposed therebetween, the electrode body is impregnated with the nonaqueous electrolyte solution, and a positive electrode current collector and a positive electrode terminal communicating with the outside and a negative electrode current collector and a negative electrode terminal communicating with the outside are connected by a current collecting lead or the like and sealed in a battery case to complete a nonaqueous electrolyte secondary battery.