JP7215004B2 - Positive electrode active material for lithium ion secondary battery and manufacturing method thereof, positive electrode mixture paste for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

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

In recent years, with the spread of small information terminals such as smart phones and tablet PCs, there is a demand for the development of small and lightweight secondary batteries with high energy density. There is also a demand for the development of high-output secondary batteries as secondary batteries for electric vehicles such as hybrid vehicles. As a secondary battery that satisfies such requirements, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, and the like, and a material capable of desorbing and intercalating lithium is used as an active material for the negative electrode and the positive electrode.

Such lithium-ion secondary batteries are still being actively researched and developed. Since the secondary battery can obtain a voltage as high as 4V class, it is being put to practical use as a battery having a high energy density. Materials that have been mainly proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, lithium-nickel composite oxide (LiNiO ₂ ), which uses nickel, which is cheaper than cobalt, and lithium-nickel oxide. Cobalt-manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), lithium-manganese composite oxide (LiMn ₂ O ₄ ) using manganese, and the like can be mentioned.

Of these, batteries using lithium-cobalt composite oxide have been extensively developed to obtain excellent initial capacity characteristics and cycle characteristics, and various results have already been obtained. However, since lithium-cobalt composite oxide uses an expensive cobalt compound as a raw material, the unit price per capacity of a battery using this lithium-cobalt composite oxide is significantly higher than that of a nickel-metal hydride secondary battery. is quite limited. Therefore, not only for small secondary batteries for portable electronic devices, but also for large secondary batteries for power storage, electric vehicles, etc., the cost of positive electrode active materials can be reduced to manufacture cheaper lithium ion secondary batteries. There are great expectations for making it possible, and it can be said that its realization has great industrial significance.

As a new active material for lithium-ion secondary batteries, a lithium-nickel composite oxide using nickel, which is cheaper than cobalt, can be mentioned. Since it exhibits a low electrochemical potential, decomposition due to oxidation of the electrolyte is less likely to be a problem, and a higher capacity can be expected. It is being actively developed as a material.

By the way, the positive electrode of a lithium ion secondary battery is prepared by mixing a positive electrode active material, a binder such as polyvinylidene fluoride (PVDF), and a solvent such as N-methyl-2-pyrrolidone (NMP), for example. It is formed by making a paste and applying it to a current collector such as aluminum foil. At this time, if lithium is liberated from the positive electrode active material in the positive electrode mixture paste, it may react with moisture contained in the binder or the like to generate lithium hydroxide. The produced lithium hydroxide and the binder may react to cause gelation of the positive electrode material mixture paste. Gelation of the positive electrode material mixture paste causes poor operability in the manufacturing process and deterioration of yield. This tendency is remarkable when the lithium-transition metal composite oxide, which is the positive electrode active material, has excess lithium relative to the transition metal in excess of the stoichiometric ratio and nickel accounts for a high proportion of the transition metal.

In order to further improve charge-discharge cycle characteristics, it is effective, for example, to contain lithium in excess of the stoichiometric composition with respect to metal elements such as nickel, cobalt, and manganese. It has also been proposed to improve the battery characteristics by adding a boron-containing compound to the lithium-nickel-cobalt composite oxide.

Patent Document 1 discloses a positive electrode active material for a non-aqueous electrolyte secondary battery having at least a lithium-transition metal composite oxide having a layered crystal structure, wherein the lithium-transition metal composite oxide is a particle and at least A positive electrode active material for a non-aqueous electrolyte secondary battery has been proposed, which has lithium borate on the surface of the particles. According to Patent Document 1, the presence of lithium borate on the surface of the particles can improve the thermal stability while maintaining the same initial discharge capacity and initial efficiency.

In Patent Document 2, composite oxide particles containing lithium (Li) and at least one of nickel (Ni) and cobalt (Co) are coated with at least one of a sulfate salt and a boric acid compound. and heat-treating the composite oxide particles coated with at least one of the sulfate and borate compounds in an oxidizing atmosphere. Proposed. According to Patent Literature 2, it is possible to manufacture a positive electrode active material capable of increasing the capacity of a secondary battery and improving the charge/discharge efficiency.

Several attempts have been made to suppress the gelation of the positive electrode mixture paste. For example, Patent Document 3 proposes a positive electrode composition for a non-aqueous electrolyte secondary battery containing a positive electrode active material made of a lithium transition metal composite oxide and additive particles made of acidic oxide particles. In this positive electrode composition, the lithium hydroxide generated by reacting with the moisture contained in the binder preferentially reacts with the acidic oxide, suppressing the reaction between the generated lithium hydroxide and the binder, resulting in a positive electrode mixture paste. It is said that it suppresses gelation. In addition, the acidic oxide plays a role as a conductive agent in the positive electrode, lowers the resistance of the entire positive electrode, and contributes to the improvement of the output characteristics of the battery.

In addition, Patent Document 4 describes a method for manufacturing a lithium ion secondary battery, in which a lithium transition metal oxide containing LiOH outside the composition is prepared as a positive electrode active material; LiOH contained per 1 g of the positive electrode active material Grasping the molar amount P; preparing 0.05 mol or more of tungsten oxide in terms of tungsten atoms per 1 mol of LiOH with respect to the molar amount P of LiOH; kneading with an organic solvent together with a material and a binder to prepare a positive electrode paste;

JP-A-2004-335278 JP 2009-146739 A JP 2012-028313 A JP 2013-084395 A

In the proposals of Patent Documents 1 and 2, it is said that both battery characteristics such as output characteristics are improved, but the addition of the boron compound causes the problem of gelation of the positive electrode mixture paste during electrode production. There is Therefore, it is desired to improve battery characteristics such as output characteristics and battery capacity, and further improve gelation.

Further, according to the proposal of Patent Document 3, the acid oxide particles remaining in the positive electrode composition may cause breakage of the separator and, accordingly, deterioration of the thermal stability of the battery. In addition, further suppression of gelation in the positive electrode mixture paste is required. It is thought that gelation can be further suppressed by increasing the amount of the acidic oxide added, but the increase in the amount of addition increases the cost of raw materials, and the addition of the acidic oxide increases the amount of charge and discharge that does not contribute to charging and discharging. An increase in the weight ratio may reduce the battery capacity per unit mass.

Also, in the proposal of Patent Document 4, the separator may be damaged due to residual tungsten oxide. In addition, further suppression of gelation in the positive electrode mixture paste is required. In addition, the addition of tungsten, which is a heavy element that does not contribute to charging and discharging, causes a problem of a decrease in battery capacity per unit weight.

In view of the above problems, the present invention suppresses deterioration of battery capacity and output characteristics when used in a lithium ion secondary battery, and has an effect of suppressing gelation of a positive electrode mixture paste during electrode production. An object of the present invention is to provide a large positive electrode active material. Another object of the present invention is to provide a method for easily producing such a positive electrode active material on an industrial scale.

In a first aspect of the present invention, a lithium-nickel composite oxide and amorphous LiBO ₂ are included, the lithium-nickel composite oxide includes lithium, nickel, cobalt, and an element M, and each The ratio (molar ratio) of the substance amounts of the elements is Li: Ni: Co: M = a: (1-xy): x: y (where 0.95 ≤ a ≤ 1.10, 0.05 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.10, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al), lithium At least part of the surface of the nickel composite oxide is coated with amorphous LiBO2, and the boron content is 0.01% by mass or more and 0.1% by mass or less with respect to the entire positive electrode active material. A positive electrode active material for an ionic secondary battery is provided.

In a second aspect of the present invention, a lithium-nickel composite oxide and a boron compound are mixed to obtain a mixture, and the mixture is heat-treated at a temperature of 300° C. or higher and 500° C. or lower in an oxygen atmosphere. and reacting the boron compound with lithium in the lithium-nickel composite oxide to form amorphous LiBO ₂ on at least a portion of the surface of the lithium-nickel composite oxide, wherein the lithium-nickel composite oxide comprises The substance contains lithium, nickel, cobalt, and the element M, and the ratio (molar ratio) of the amount of each element is Li:Ni:Co:M=a:(1-xy):x : y (where 0.95 ≤ a ≤ 1.10, 0.05 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.10, M is Mn, V, Mg, Mo, Nb, Ti, W, Zr and at least one element selected from Al), and the mixture contains 0.01% by mass or more and 0.1% by mass or less of boron in the boron compound with respect to the entire mixture, lithium ion A method for manufacturing a positive electrode active material for a secondary battery is provided.

Also, the boron compound preferably contains at least one selected from H ₃ BO ₃ and B ₂ O ₃ . Moreover, it is preferable that the lithium compound contains lithium hydroxide. Moreover, it is preferable that LiBO ₂ covers at least part of the surface of the lithium-nickel composite oxide.

In addition, the boron compound has an amount of lithium hydroxide eluted when the positive electrode active material is dispersed in water, which is measured by a neutralization titration method, with respect to the entire positive electrode active material, and is 0.01% by mass or more. It is preferable to adjust the content to be less than 2% by mass.

A third aspect of the present invention provides a positive electrode mixture paste for a lithium ion secondary battery containing the positive electrode active material for a lithium ion secondary battery.

A fourth aspect of the present invention provides a lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, and having a positive electrode containing the positive electrode active material for a lithium ion secondary battery.

ADVANTAGE OF THE INVENTION According to the present invention, it is possible to obtain a positive electrode mixture slurry that suppresses deterioration in battery capacity and output characteristics when used in a lithium ion secondary battery, and that suppresses gelation and has high stability. Substances can be provided. Furthermore, the production method thereof is easy and suitable for production on an industrial scale, and its industrial value is extremely high.

FIG. 1 is a diagram showing an example of a positive electrode active material for lithium ion secondary batteries according to an embodiment. FIG. 2A is a diagram showing an example of a method for producing a positive electrode active material for lithium ion secondary batteries according to an embodiment. FIG. 2B is an explanatory diagram of the reaction between lithium contained in the lithium-nickel composite oxide (raw material) and the boron compound. FIG. 3 is a schematic explanatory diagram of an example of measurement of impedance evaluation and an equivalent circuit used for analysis. FIG. 4 is a schematic diagram of a coin-type battery used for battery evaluation.

Hereinafter, a positive electrode active material for lithium ion secondary batteries, a method for producing the same, a positive electrode mixture paste for lithium ion secondary batteries, and a lithium ion secondary battery according to an embodiment of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following detailed description.

1. 1. Positive Electrode Active Material for Lithium Ion Secondary Battery FIG. 1 is a diagram showing an example of a positive electrode active material 100 for a lithium ion secondary battery (hereinafter also referred to as "positive electrode active material 100") according to the present embodiment. As shown in FIG. 1, the positive electrode active material 100 includes a lithium-nickel composite oxide 10 and amorphous LiBO ₂ (indicated by the symbol “LB” in FIG. 1, hereinafter also referred to as “amorphous LiBO ₂ ”). ), and at least part of the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ . That is, the positive electrode active material 100 includes a coating layer (also referred to as a LiBO ₂ layer) in which at least part of the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ .

As a result of intensive research, the present inventors have found that the presence of amorphous LiBO ₂ on the particle surface of the lithium-nickel composite oxide 10 results in the battery capacity and output characteristics of a secondary battery using this positive electrode active material 100 as the positive electrode. It has been found that it is possible to achieve both suppression of the decrease in the s and suppression of gelation of the positive electrode mixture paste. Each configuration of the positive electrode active material 100 will be described below.

(lithium nickel composite oxide)
The lithium-nickel composite oxide 10 contains lithium, nickel, cobalt, and an element M, and the ratio (molar ratio) of the amounts of these elements is Li:Ni:Co:M=a:(1 -xy): x: y (where 0.95 ≤ a ≤ 1.10, 0.05 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.10, M is Mn, V, Mg, Mo , Nb, Ti, W, Zr, and Al) and forms a layered crystal structure. Moreover, the lithium-nickel composite oxide 10 includes secondary particles in which a plurality of primary particles are aggregated. In addition, the ratio of the substance amount of each element (the content of each element) can be measured by ICP emission spectroscopy.

In the above molar ratio, the value of a indicates the ratio of the amount of Li substance (Li/Me) to the total amount of substance (Me) of Ni, Co, and M, and 0.95 ≤ a ≤ 1.10. be. The value of a is a value including the amount of Li contained in amorphous LiBO ₂ . As will be described later, the amorphous LiBO ₂ is produced by a reaction between the boron compound B and lithium contained in the lithium-nickel composite oxide 10a (raw material) in the heat treatment step (step S2, see FIG. 2A). (See FIG. 2B). Therefore, considering the amount of Li contained in LiBO ₂ , the value of a may be 1 or more, or may exceed 1.

In the above molar ratio, (1-xy), which indicates the amount of nickel, satisfies 0.55≦(1-xy)≦0.95. Lithium-nickel composite oxides (positive electrode active materials) containing a large amount of nickel usually tend to cause gelation of the positive electrode mixture paste. By coating the surface of the lithium-nickel composite oxide 10 with amorphous LiBO ₂ , it is possible to suppress the gelation of the positive electrode mixture paste during electrode fabrication.

In the above molar ratio, x indicating the amount of cobalt satisfies 0.05≦x≦0.35. When the amount of cobalt is within the above range, excellent cycle characteristics are obtained while maintaining a high battery capacity.

In the above molar ratio, M is at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al, and the thermal stability of the positive electrode active material is improved. From a viewpoint, it is preferable to contain Al. The value of y, which indicates the amount of M, satisfies 0≤y≤0.10, preferably 0.01≤y≤0.10.

Further, the lithium-nickel composite oxide 10 has a general formula (1): Li _a Ni _1-xy Co _x M _y O _2+α (where 0.05≦x≦0.35, 0≦y≦0.10 , 0.95 ≤ a ≤ 1.10, 0 ≤ α ≤ 0.2, M is at least one element selected from Mn, V, Mg, Mo, Nb, Ti, W, Zr, and Al) may be represented by Note that the technical significance and preferred range of each element in the general formula (1) are the same as in the explanation of the molar ratio above, so the description is omitted.

(Amorphous LiBO ₂ )
At least a part of the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ in the positive electrode active material 100, so that when the positive electrode active material 100 is used in a secondary battery, the battery capacity decreases and It is possible to achieve both suppression of deterioration in output characteristics due to an increase in positive electrode resistance and suppression of gelling of the positive electrode mixture paste during electrode production.

Generally, when the surface of the lithium _- nickel composite oxide 10 is coated with a different compound, the battery characteristics such as the reaction resistance of the positive electrode (positive electrode resistance) may decrease. Therefore, when the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ , it is possible not only to suppress deterioration of the battery characteristics (e.g., battery capacity) in the secondary battery, but also to reduce the positive electrode resistance. can do.

In addition, the lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ can suppress gelation of the positive electrode mixture paste. Although the details of the mechanism by which paste gelation is suppressed in the lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ are unknown, for example, the manufacturing process of the positive electrode active material 100 (see FIG. ), as shown in FIG. 2B, the boron compound B used as a raw material is the surplus lithium present on the surface of the lithium-nickel metal composite oxide 10a used as a raw material (e.g., unreacted lithium compound, It is believed that gelation of the paste is suppressed by reacting with lithium in the crystals) to form amorphous LiBO ₂ .

The positive electrode active material 100 may contain lithium borate other than amorphous LiBO ₂ , but preferably contains amorphous LiBO ₂ alone. The lithium borate covering the surface of the lithium-nickel composite oxide 10 may be amorphous LiBO ₂ alone, or may contain lithium borate other than amorphous LiBO ₂ . More preferably, the surface of oxide 10 is covered substantially only by amorphous LiBO ₂ . Examples of lithium borate other than amorphous LiBO ₂ include crystalline LiB(OH) _{4 , LiBO 2} and Li ₃ BO ₃ . It is preferably free of _BO3 .

The presence of lithium borate on the surface of the lithium-nickel composite oxide 10 and the crystallinity can be confirmed by Raman spectroscopy. Note that "substantially amorphous LiBO ₂ only covers" means a state in which only a broad peak of LiBO ₂ is detected as a peak other than the peak derived from the lithium-nickel composite oxide 10 in Raman spectroscopy. and may contain small amounts of other lithium borate below the detection limit.

When the surface of the lithium-nickel composite oxide 10 is coated with amorphous LiBO ₂ alone, the positive electrode resistance can be further reduced and gelling of the positive electrode mixture paste can be suppressed. The surface of the lithium-nickel composite oxide 10 can be coated with amorphous LiBO ₂ , for example, by a method for producing a positive electrode active material (see FIG. 2A), which will be described later.

(boron content)
The content of boron (B) contained in the positive electrode active material 100 is 0.01% by mass or more and 0.1% by mass or less, preferably 0.03% by mass or more and 0.06% by mass, with respect to the entire positive electrode active material. % by mass or less. When the content of boron is within the above range, when the positive electrode active material 100 is used in a secondary battery, it suppresses deterioration of battery capacity and output characteristics, and suppresses gelation of the positive electrode mixture paste during electrode production. It is possible to be compatible with

On the other hand, if the boron content is less than 0.01% by mass, the effect of suppressing gelation of the positive electrode mixture paste during electrode production cannot be sufficiently obtained. The reason for this is thought to be that the lithium hydroxide remaining on the surface of the lithium-nickel composite oxide 10 cannot be sufficiently removed. Moreover, when the boron content exceeds 0.1% by mass, the battery characteristics of the secondary battery may deteriorate. Although the details of the reason for this are unknown, it is believed that the amorphous LiBO ₂ layer formed on the surface of the lithium-nickel composite oxide 10 is too thick, increasing the reaction resistance of the positive electrode.

(Elution amount of lithium hydroxide)

A water-soluble lithium compound containing lithium hydroxide (LiOH) (hereinafter collectively referred to as “surplus lithium”) is present on the surface of a normal lithium-nickel composite oxide (eg, symbol “10a” in FIG. 2(B)). exist. When manufacturing a secondary battery, the positive electrode mixture paste may gel. The reason for this is that surplus lithium is eluted into the water contained in the positive electrode mixture paste, which raises the pH value of the paste. It is believed that this is because

1) Among the surplus lithium remaining in the normal lithium-nickel composite oxide 10a, the present inventors found that lithium eluted as lithium hydroxide (LiOH) in the positive electrode mixture paste in particular is the gel of the positive electrode mixture paste. 2) When the amount of lithium eluted as lithium hydroxide (LiOH) when the positive electrode active material 100 is dispersed in water is controlled within a specific range, the positive electrode mixture paste It was found that gelation can be suppressed.

When the lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ is dispersed in water, the amount of lithium hydroxide eluted (hereinafter also referred to as “excess lithium hydroxide amount”) is It is preferably less than 0.2% by mass, more preferably 0.15% by mass or less, and more preferably 0.1% by mass or less with respect to the entire substance 100 . When the amount of surplus lithium hydroxide is within the above range, gelation of the positive electrode mixture paste can be suppressed, and deterioration of battery characteristics can be suppressed.

On the other hand, when the amount of excess lithium hydroxide is 0.2% by mass or more, the effect of suppressing gelation of the paste may not be sufficiently obtained. The reason for this is thought to be that there is a large amount of surplus lithium hydroxide, which promotes gelation. Further, the lower limit of the surplus lithium hydroxide amount is, for example, 0.01% by mass or more, may be 0.05% by mass or more, or is 0.09% by mass or more with respect to the entire positive electrode active material 100. may

In this specification, the surplus lithium hydroxide amount refers to the amount of acid used up to the first neutralization point by neutralization titration among the lithium compounds eluted by dispersing the positive electrode active material 100 in water. Refers to the amount of Li to be measured, and the lithium compound neutralized to the first neutralization point when the carbonate is once precipitated by adding an aqueous solution of barium chloride to the slurry in which the positive electrode active material 100 is dispersed. It is a calculated value assuming that all are derived from lithium hydroxide (LiOH).

Specifically, the surplus lithium hydroxide amount can be measured by the following method. First, 15 g of the positive electrode active material is sufficiently dispersed in 75 ml of pure water, left to stand for 10 minutes, and then the supernatant is diluted with 50 ml of pure water to obtain an aqueous solution. Then, 5 mL of 10% barium chloride aqueous solution is added to the aqueous solution. The amount of Li eluted in the aqueous solution thus obtained is measured by a neutralization titration method using an acid such as hydrochloric acid. During the neutralization titration, the pH of the aqueous solution obtained by diluting the supernatant drops in two stages. The first stage indicates the pH that decreases due to the neutralization of lithium hydroxide. Therefore, by neutralization titration, the surplus lithium hydroxide amount is calculated assuming that the Li amount calculated from the amount of acid used up to the first neutralization point is entirely derived from lithium hydroxide (LiOH). At the first neutralization point, for example, Li ₃ BO ₃ is also eluted, so the amount of excess lithium hydroxide may include lithium derived from Li ₃ BO ₃ .

The amount of excess lithium hydroxide in the lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ can be obtained, for example, in the production process of the lithium-nickel composite oxide 10 described later (see FIG. 2(A)). The above range can be controlled by appropriately adjusting the amount of the boron compound added in the mixing step (step S1) and the heat treatment temperature in the heat treatment step (step S2).

2. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery Next, with reference to FIGS. Also referred to as a “method for producing a positive electrode active material”) will be described. FIG. 2A is a diagram showing an example of a method for manufacturing a positive electrode active material according to this embodiment. FIG. 2B is an explanatory diagram of the reaction between lithium contained in the lithium-nickel composite oxide 10a (raw material) and the boron compound B. FIG. By the method for producing a positive electrode active material according to the present embodiment, the positive electrode active material 100 containing the lithium-nickel composite oxide 10 having at least a portion of the surface coated with amorphous LiBO ₂ as described above can be produced on an industrial scale. It can be manufactured with good productivity.

The method for producing a positive electrode active material of the present embodiment includes mixing the lithium-nickel composite oxide 10a (raw material) and a boron compound B to obtain a boron mixture (step S1); and heat-treating at a temperature of 300° C. or more and 500° C. or less to obtain a lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ (step S2). Each step will be described below.

[Mixing step (step S1)]
In the manufacturing method of the positive electrode active material of the present embodiment, first, the boron compound B and the lithium-nickel composite oxide 10a (raw material) are mixed to obtain a boron mixture (step S1).

As the _boron compound _{B ,} a compound containing _boron capable of reacting with lithium can be used. (NH ₄ )2B ₄ O _{7.4H 2} O), ammonium pentaborate octahydrate ((NH ₄ ) ₂ O.5B _{2 O 3.8H 2 O )} , and the like. These compounds are highly reactive with lithium salts, and are considered to form amorphous LiBO ₂ after the heat treatment step (step S2) described later. Among these compounds, it is preferable to use at least one selected from H ₃ BO and B ₂ O ₃ . H ₃ BO ₃ and B ₂ O ₃ are preferred as the above boron compound B because they exhibit acidity and are more reactive with Li.

In the boron compound B, boron (B) in the boron compound B is 0.01% by mass or more and 0.1% by mass or less, preferably 0.03% by mass or more and 0.06% by mass with respect to the entire positive electrode active material to be obtained. It is mixed in an amount that is equal to or less than mass %.

The lithium _{- nickel} composite _{oxide 10a (} raw material) is not particularly limited, and a known one can be used. 0.95≦a≦1.10, 0.05≦x≦0.35, 0≦y≦0.10, 0≦α≦0.2, M is Mn, V, Mg, Mo, Nb, Ti , W, Zr, and Al) can be used.

The surplus lithium hydroxide amount of the lithium-nickel composite oxide 10a (raw material) is, for example, 0.15% by mass or more and 0.25% by mass or less, preferably 0, with respect to the entire lithium-nickel composite oxide 10a as the raw material. 0.15% by mass or more and 0.21% by mass or less.

The amount of the boron compound B to be mixed is such that the upper limit of the amount of surplus lithium hydroxide in the finally obtained positive electrode active material 100 is preferably less than 0.2% by mass, more preferably 0% with respect to the entire positive electrode active material 100. It is preferable to adjust the amount to 0.1% by mass or less, more preferably 0.1% by mass or less. Moreover, it is preferable that the lower limit of the amount of the boron compound B to be mixed is set to be, for example, 0.01% by mass or more with respect to the entire positive electrode active material 100 .

That is, in the manufacturing method of the present embodiment, the amount of lithium hydroxide ( The amount of lithium-nickel composite oxide 10a (raw material) is mixed so that the amount of excess lithium hydroxide) is in the range of 0.01% by mass or more and less than 0.2% by mass with respect to the entire positive electrode active material 100. Preferably, the amount of boron compound B is adjusted. As a result, the obtained positive electrode active material 100 can further suppress the gelation of the positive electrode mixture paste, and can suppress deterioration of battery characteristics.

In the mixing step (step S1), the boron compound B and the lithium-nickel composite oxide 10a are preferably thoroughly mixed. For mixing, a general mixer can be used, for example, a shaker mixer, Loedige mixer, Julia mixer, V blender, etc. can be used, and the shape of the lithium nickel composite oxide particles is not destroyed. is sufficiently mixed with the boron compound B.

[Heat treatment step (step S2)]
Next, the boron mixture is heat-treated in an oxygen atmosphere at a temperature of 300° C. or more and 500° C. or less to obtain a lithium-nickel composite oxide 10 coated with amorphous LiBO ₂ (step S2). By heat-treating the lithium-nickel composite oxide 10 containing the boron compound B, as shown in FIG. high-quality LiBO ₂ can be produced. Since boron is difficult to form a solid solution in the lithium-nickel composite oxide 10, most of the boron added as the boron compound B is considered to form _LiBO2 .

The heat treatment temperature is 300° C. or higher and 500° C. or lower, preferably 300° C. or higher and 450° C. or lower. When the firing temperature is within the above range, the surface of the lithium-nickel composite oxide 10 can be uniformly coated with the LiBO ₂ layer in an amorphous state. When the firing temperature is 300° C. or higher, the hydroxyl groups in LiB(OH) ₄ produced by the reaction between the boron compound B and the lithium hydroxide remaining on the surface of the lithium nickel composite oxide 10 are removed to form amorphous LiBO. ₂ can be generated. Thereby, the surface of the lithium-nickel composite oxide 10 can be uniformly coated with the LiBO ₂ layer.

On the other hand, if the calcination temperature is less than 300° C., the removal of hydroxyl groups from LiB(OH) ₄ is insufficient, resulting in low lithium ion conductivity and further deterioration of battery characteristics. In addition, when the firing temperature exceeds 500 ° C., LiBO ₂ extracts lithium from the lithium-nickel composite oxide 10 and Li ₃ BO ₃ is generated, so that the reaction resistance of the lithium-nickel composite oxide 10 increases, and the battery It is not preferable because the characteristics deteriorate.

The holding time at the heat treatment temperature is, for example, 0.5 hours or more and 5 hours or less, preferably 1 hour or more and 3 hours or less, and may be, for example, 1 hour or more and 2 hours or less. Moreover, the atmosphere during the heat treatment is an oxygen atmosphere, and for example, an atmosphere having an oxygen concentration of 100% by volume is preferable.

The lithium-nickel composite oxide 10 (positive electrode active material 100) according to the present embodiment can be obtained by the manufacturing method described above. In the lithium-nickel composite oxide 10 (positive electrode active material 100) coated with amorphous LiBO ₂ obtained in the present embodiment, the amount of excess lithium hydroxide measured by the neutralization titration method, as described above, is It is preferably less than 0.2% by mass, more preferably 0.15% by mass or less, and more preferably 0.1% by mass or less with respect to the entire active material 100 . When the excess lithium hydroxide amount is within the above range, gelation of the positive electrode mixture paste can be suppressed. In addition, it is preferable that the lower limit of the excess lithium hydroxide amount is, for example, 0.01% by mass or more with respect to the entire positive electrode active material 100 .

Further, for example, the surplus lithium hydroxide amount (mass%) of the lithium-nickel composite oxide 10 with respect to the entire positive electrode active material 100 is the surplus lithium hydroxide amount (mass%) of the lithium-nickel composite oxide 10a (raw material) used as a raw material. %) may be 0.01% by mass or more, 0.02% by mass or more, or 0.05% by mass or more. As shown in FIG. 2(B), surplus lithium in the raw material is considered to be used as a Li source when amorphous LiBO ₂ is formed, and as a result, the amount of surplus lithium hydroxide is reduced. Therefore, the difference in the amount of excess lithium hydroxide between the lithium nickel composite oxide 10 and the raw material is considered to reflect the reaction and the degree of coating of amorphous LiBO ₂ , and the difference in the amount of excess lithium is within the above range. , it can be said that amorphous LiBO ₂ is sufficiently formed on the surface of the lithium-nickel composite oxide 10 . Although the upper limit of the above difference is not particularly limited, it is, for example, 0.15% by mass or less.

3. Positive electrode mixture paste for non-aqueous secondary battery Next, a method for producing the positive electrode mixture paste for lithium-ion secondary batteries (hereinafter also referred to as “positive electrode mixture paste” or “paste”) according to the present embodiment will be described. do. The paste of this embodiment contains a lithium-nickel composite oxide 10 (positive electrode active material 100) coated with amorphous LiBO ₂ . Therefore, elution of lithium from the lithium-nickel composite oxide 10 (positive electrode active material 100) in the paste is reduced, and gelation of the paste is suppressed. Therefore, even when the paste is stored for a long period of time, the viscosity of the paste changes little and the paste can have high stability. When a positive electrode is produced using such a paste, it is possible to stably obtain a positive electrode having excellent characteristics, and to stably improve the characteristics of the finally obtained secondary battery.

The constituent materials of the positive electrode mixture paste are not particularly limited except for the lithium-nickel composite oxide 10 described above, and materials equivalent to known positive electrode mixture pastes can be used. The positive electrode material mixture paste contains, for example, the lithium-nickel composite oxide 10, a conductive material, and a binder. The positive electrode mixture paste may further contain a solvent. In the positive electrode mixture paste, when the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, for example, the content of the positive electrode active material is 60 to 95 parts by mass, and the content of the conductive material is 1 to 95 parts by mass. 20 parts by mass, and the content of the binder can be 1 to 20 parts by mass.

Examples of conductive agents that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black-based materials such as acetylene black and ketjen black.

Binders (binders) play a role in binding active material particles, and examples thereof include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, and cellulose resin. , polyacrylic acid, etc. can be used.

A conductive material and activated carbon may be dispersed in the positive electrode active material 100, and a solvent for dissolving a binder (binding agent) may be added as necessary. As the solvent, specifically, an organic solvent such as N-methyl-2-pyrrolidone (NMP) can be used. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity. The positive electrode mixture paste is prepared by, for example, mixing the above-described powdery oxide, conductive material, and binder, adding activated carbon and a solvent for the purpose of viscosity adjustment, if necessary, and kneading the mixture. can be made.

4. Lithium Ion Secondary Battery A lithium ion secondary battery (hereinafter also referred to as a “secondary battery”) according to the present embodiment includes a positive electrode containing the above-described positive electrode active material as a positive electrode material. A lithium ion secondary battery can be composed of the same components as conventionally known lithium ion secondary batteries, and includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte. A secondary battery may also include, for example, a positive electrode, a negative electrode, and a solid electrolyte. In addition, the secondary battery may be a secondary battery that charges and discharges by desorption and insertion of lithium ions. For example, it may be a non-aqueous electrolyte secondary battery, or an all-solid lithium secondary battery. There may be. It should be noted that the embodiments described below are merely examples, and the lithium ion secondary battery of the present embodiment can be modified based on the knowledge of those skilled in the art based on the embodiments described herein. It can be implemented in improved form. Moreover, the lithium-ion secondary battery of this embodiment is not particularly limited in its application.

[Components]
(positive electrode)
First, the positive electrode active material 100, a conductive material, and a binder are mixed, and if necessary, activated carbon and a solvent for viscosity adjustment are added, and the mixture is kneaded to prepare a positive electrode mixture paste. . As the positive electrode mixture paste, the positive electrode mixture paste of the present embodiment described above can be used.

The obtained positive electrode material mixture paste is applied, for example, to the surface of a current collector made of aluminum foil and dried to scatter the solvent. If necessary, pressure may be applied by a roll press or the like in order to increase the electrode density. Thus, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size depending on the intended battery, and used for manufacturing the battery. The method for producing the positive electrode is not limited to the method described above, and other methods may be used.

(negative electrode)
Metallic lithium, a lithium alloy, or the like may be used as the negative electrode. In addition, as a negative electrode, a negative electrode active material capable of intercalating and deintercalating lithium ions is mixed with a binder, and an appropriate solvent is added to form a paste. It may be applied to the surface, dried, and compressed to increase the electrode density as necessary.

As the negative electrode active material, for example, natural graphite, artificial graphite, sintered organic compounds such as phenol resin, and powdery carbon substances such as coke can be used. In this case, a fluorine-containing resin such as PVDF can be used as the binder for the negative electrode in the same manner as the binder for the positive electrode. Solvents can be used.

(separator)
Between the positive electrode and the negative electrode, a separator is interposed and arranged as necessary. The separator separates the positive electrode from the negative electrode and holds the electrolyte, and may be a thin film of polyethylene, polypropylene, or the like, having a large number of minute pores.

(Non-aqueous electrolyte)
A non-aqueous electrolytic solution can be used as the non-aqueous electrolyte. The non-aqueous electrolytic solution may be, for example, one obtained by dissolving a lithium salt as a supporting salt in an organic solvent. Further, as the non-aqueous electrolytic solution, an ionic liquid in which a lithium salt is dissolved may be used. The ionic liquid refers to a salt composed of cations and anions other than lithium ions and exhibiting a liquid state even at room temperature.

Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate and dipropyl carbonate; One selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butane sultone, and phosphorus compounds such as triethyl phosphate and trioctyl phosphate may be used alone, or two or more may be mixed. can be used as

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN(CF ₃ SO ₂ ) ₂ , composite salts thereof, and the like can be used. Furthermore, the non-aqueous electrolytic solution may contain radical scavengers, surfactants, flame retardants, and the like.

A solid electrolyte may be used as the non-aqueous electrolyte. Solid electrolytes have the property of withstanding high voltages. Solid electrolytes 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 is used.

The oxide-based solid electrolyte is not particularly limited, and can be used as long as it contains oxygen (O) and has lithium ion conductivity and electronic insulation. Examples of oxide-based solid electrolytes include lithium phosphate (Li ₃ PO ₄ ), Li ₃ PO ₄ N _x , LiBO ₂ N _x , LiNbO ₃ , LiTaO ₃ , Li ₂ SiO ₃ , Li ₄ SiO ₄ -Li ₃ PO4, _{Li4SiO4 - Li3VO4} , Li2O _{- B2O3 - P2O5 ,} Li2O _{- SiO2} , Li2O _{- B2O3 -} ZnO, _{Li1 + X AlXTi 2-X} (PO ₄ ) ₃ (0≦X≦1), Li _1+X Al _X Ge _2-X (PO ₄ ) ₃ (0≦X≦1), LiTi ₂ (PO ₄ ) ₃ , Li _3X La _{2/ 3-X} TiO ₃ (0≦X≦2/3), Li ₅ La ₃ Ta ₂ O ₁₂ , Li ₇ La ₃ Zr ₂ O ₁₂ , Li ₆ BaLa ₂ Ta ₂ O ₁₂ , Li _3.6 Si _0.6 P _0.4 O ₄ and the like.

The sulfide-based solid electrolyte is not particularly limited, and any solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be used. Examples of sulfide solid electrolytes include Li ₂ SP ₂ S ₅ , Li ₂ S—SiS ₂ , LiI—Li ₂ S—SiS ₂ , LiI—Li ₂ SP ₂ S ₅ , LiI—Li ₂ S—B ₂ S ₃ , Li ₃ PO ₄ —Li ₂ S—Si ₂ S, Li ₃ PO ₄ —Li ₂ S—SiS ₂ , LiPO ₄ —Li ₂ S—SiS, LiI—Li ₂ S—P ₂ O ₅ , LiI—Li ₃ PO ₄ —P ₂ S ₅ and the like.

Inorganic solid electrolytes other than those described above may be used, such as Li ₃ N, LiI, Li ₃ N--LiI--LiOH, and the like.

The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ion conductivity. For example, polyethylene oxide, polypropylene oxide, copolymers thereof, and the like can be used. Moreover, the organic solid electrolyte may contain a supporting salt (lithium salt). When a solid electrolyte is used, the solid electrolyte may also be mixed in the positive electrode material in order to ensure contact between the electrolyte and the positive electrode active material.

(Battery shape and configuration)
The configuration of the secondary battery is not particularly limited, and may be composed of a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, etc. as described above, or may be composed of a positive electrode, a negative electrode, a solid electrolyte, etc. Moreover, the shape of the secondary battery is not particularly limited, and various shapes such as a cylindrical shape and a laminated shape can be used.

For example, when the secondary battery is a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are laminated with a separator interposed to form an electrode body, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode collection is performed. A current collecting lead or the like is used to connect between a current collector and a positive electrode terminal that communicates with the outside, and between a negative electrode current collector and a negative electrode terminal that communicates with the outside, and the secondary battery is sealed in a battery case. complete the

(Characteristic)
For the initial discharge capacity, the coin-type battery CBA used in the example was left for about 24 hours after it was manufactured, and after the open circuit voltage OCV (Open Circuit Voltage) was stabilized, the current density for the positive electrode was set to 0.1 mA/cm ² . It is a value obtained by charging to a cut-off voltage of 4.3 V, discharging to a cut-off voltage of 3.0 V after resting for 1 hour, and measuring the capacity.

The method for measuring the positive electrode resistance in this embodiment is exemplified as follows. When the frequency dependence of the battery reaction is measured by the AC impedance method, which is commonly used as an electrochemical evaluation method, the Nyquist plot based on the solution resistance, negative electrode resistance and negative electrode capacity, and positive electrode resistance and positive electrode capacity is shown in Fig. 3. obtained in The battery reaction at the electrodes consists of a resistance component associated with charge transfer and a capacity component due to the electric double layer. Expressing these in an electric circuit results in a parallel circuit of resistance and capacity. It is represented by an equivalent circuit in which circuits are connected in series. Using this equivalent circuit, a fitting calculation can be performed on the measured Nyquist diagram, and each resistance component and capacitance component can be estimated. The positive electrode resistance is equal to the diameter of the lower frequency semicircle of the resulting Nyquist plot. Therefore, the positive electrode resistance can be estimated by performing AC impedance measurement on the produced secondary battery and performing fitting calculation with an equivalent circuit to the obtained Nyquist diagram.

EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. The examples and comparative examples were evaluated based on the measurement results using the following apparatus and method.

[Composition of entire positive electrode active material]
After dissolving the obtained positive electrode active material in nitric acid, it was measured with an ICP emission spectrometer (ICPS-8100 manufactured by Shimadzu Corporation).

[Compound species identification]
The obtained positive electrode active material was evaluated by an X-ray diffraction device (trade name: X'Pert PRO, manufactured by Panalytical) and a Raman spectrometer (trade name: DXR2, manufactured by Thermo Fisher Scientific).

[Viscosity stability of positive electrode mixture paste]
25.0 g of the positive electrode active material, 1.5 g of conductive carbon powder, 2.9 g of polyvinylidene fluoride (PVDF), and N-methyl-2-pyrrolidone (NMP) are mixed by a planetary kneader to form a positive electrode mixture. got a paste. The amount of N-methyl-2-pyrrolidone (NMP) added was adjusted so that the viscosity was 1.5 to 2.5 Pa·s according to the viscosity measurement method using a vibration viscometer specified in JIS Z 8803:2011. The obtained positive electrode material mixture paste was stored for 76 hours, and the occurrence of gelation was visually evaluated.

[Measurement of surplus lithium hydroxide amount]
After dispersing 15 g of the obtained positive electrode active material in 75 ml of pure water, let stand for 10 minutes, dilute 10 ml of the supernatant liquid with 50 ml of pure water, add 5 mL of 10% barium chloride aqueous solution to the diluted liquid, and The amount of Li dissolved in the aqueous solution was measured by a neutralization titration method in which 1 mol/liter of hydrochloric acid was added. In the neutralization titration, the pH of the supernatant aqueous solution is lowered in two stages. Assuming that the decrease in pH in the first step indicates the amount of excess lithium hydroxide (first neutralization point), the amount of eluted Li (excess lithium hydroxide amount) is calculated from the amount of hydrochloric acid up to the first neutralization point. bottom. The amount of excess lithium hydroxide is the amount of Li measured from the amount of hydrochloric acid up to the first neutralization point when carbonate is once precipitated by adding an aqueous solution of barium chloride to the slurry in which the positive electrode active material 100 is dispersed. were all derived from lithium hydroxide (LiOH).

[Evaluation of battery characteristics]
(Preparation of coin-type battery for evaluation)
20% by mass of acetylene black and 10% by mass of PTFE were mixed with 70% by mass of the obtained positive electrode active material, and 150 mg of the mixture was taken out to prepare pellets and used as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as the supporting electrolyte (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte, and the dew point was −80 ° C. A 2032-type coin-type battery CBA as shown in FIG. The performance of the manufactured coin-type battery CBA was evaluated based on the initial discharge capacity and the like.

(initial discharge capacity)
For the initial discharge capacity, the coin-type battery CBA was left for about 24 hours after it was manufactured, and after the open circuit voltage OCV (open circuit voltage) was stabilized, the current density for the positive electrode was 0.1 mA / cm ² and the cutoff voltage was 4. The battery was charged to 3 V, rested for 1 hour, and discharged to a cut-off voltage of 3.0 V. The discharge capacity was measured and taken as the initial discharge capacity before exposure to the atmosphere.

(positive electrode resistance)
When the coin-type battery CBA was charged at a charging potential of 4.1 V and the internal resistance was measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (manufactured by Solartron, 1255B), the Nyquist plot shown in FIG. 3 was obtained. can get. The Nyquist plot is a sum of characteristic curves representing solution resistance, negative electrode resistance and capacity, and positive electrode resistance and capacity. A fitting calculation was performed using an equivalent circuit based on the obtained Nyquist plot to calculate the value of the positive electrode resistance.

(Example 1)
Boron compound H ₃ BO ₃ (manufactured by Wako Pure Chemical Industries, Ltd.) is added to lithium-nickel composite oxide particles having an average particle diameter of 13 μm so that the amount of boron is 0.03% by mass with respect to the positive electrode active material, A boron mixture was formed. Mixing was performed using a shaker mixer device (TURBULA Type T2C manufactured by Willie & Bacchofen (WAB)). The resulting mixture was sintered (heat treated) in an oxygen stream (oxygen: 100% by volume) at 300° C. (heat treatment temperature) for 1 hour, cooled and sieved to obtain a positive electrode active material. The resulting positive electrode active material contained _0.03 % by mass of boron relative to the positive electrode active material _, and was lithium nickel represented by the composition _{formula Li1.03Ni0.82Co0.15Al0.03O2 .} It was a composite oxide.

When the obtained positive electrode active material was analyzed with a Raman spectrometer (trade name DXR2, manufactured by Thermo Fisher Scientific), a broad peak of _LiBO2 was detected, indicating that _LiBO2 was amorphous on the surface of the lithium-nickel composite oxide. was confirmed to exist. Tables 1 and 2 show the evaluation results of the obtained positive electrode active materials and the like.

(Example 2)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.06% by mass relative to the positive electrode active material. Evaluation results are shown in Tables 1 and 2.

(Example 3)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the heat treatment temperature was 450°C. Evaluation results are shown in Tables 1 and 2.

(Example 4)
A positive electrode active material and the like were obtained in the same manner as in Example 1 except that H ₃ BO ₃ was added so that the boron content was 0.06% by mass relative to the positive electrode active material, and the heat treatment temperature was 450 ° C. evaluated. Evaluation results are shown in Tables 1 and 2.

(Example 5)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the boron compound B ₂ O ₃ was added so that the boron content was 0.06% by mass relative to the positive electrode active material. Evaluation results are shown in Tables 1 and 2.

(Comparative example 1)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1 except that boric acid (boron compound) was not added. Evaluation results are shown in Tables 1 and 2.

(Comparative example 2)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.005% by mass relative to the positive electrode active material. Evaluation results are shown in Tables 1 and 2.

(Comparative Example 3)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the heat treatment temperature was 600°C. Evaluation results are shown in Tables 1 and 2.

(Comparative Example 4)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that the heat treatment temperature was 200°C. Evaluation results are shown in Tables 1 and 2.

(Comparative Example 5)
A positive electrode active material and the like were obtained and evaluated in the same manner as in Example 1, except that H ₃ BO ₃ was added so that the boron content was 0.2% by mass relative to the positive electrode active material. Evaluation results are shown in Tables 1 and 2.

(Evaluation results)
When X-ray diffraction of the positive electrode active materials obtained in Examples 1-5 and Comparative Examples 1-5 was measured, a peak of lithium-nickel composite oxide was detected. Moreover, in Comparative Example 3, a peak of Li ₃ BO ₃ was also detected in addition to the peak of the lithium-nickel composite oxide. Further, when the positive electrode active materials obtained in Examples 1 to 5 and Comparative Examples 2 and 5 were analyzed with a Raman spectrometer, a broad peak of LiBO ₂ was detected.

In Examples 1 to 5, amorphous LiBO ₂ was uniformly coated on the surface, and compared to Comparative Examples 1 to 5, when used as the positive electrode of a secondary battery, any increase in positive electrode resistance was suppressed. and a high battery capacity was obtained. Moreover, gelation of the paste was suppressed in all of the positive electrode active materials obtained in Examples 1 to 5. In Comparative Example 1, the excessive amount of lithium hydroxide was large, and the paste gelled. On the other hand, in Comparative Example 2, since the amount of boron was small, the amount of surplus lithium hydroxide was not sufficiently reduced, and the paste gelled. In Comparative Example 3, the formation of Li ₃ BO ₃ is thought to extract lithium from the surface of the lithium-nickel composite oxide, increasing the positive electrode resistance. Further, in Comparative Example 4, LiBO ₂ was not generated and sufficient lithium ion conductivity was not obtained, so that the positive electrode resistance increased. In addition, in Comparative Example 5, the coating layer of LiBO ₂ was thick, and it is considered that the initial discharge capacity decreased and the positive electrode resistance increased.

From the above results, the positive electrode active material of the present embodiment has good output characteristics due to reduced positive electrode resistance, high battery capacity, and It is clear that a positive electrode active material can be obtained that is compatible with suppressing paste gelation during electrode production.

ADVANTAGE OF THE INVENTION The positive electrode active material for lithium ion secondary batteries of this invention suppresses gelation of positive electrode mixture paste, and can exhibit stable battery performance at low cost. Therefore, it is particularly suitable as a positive electrode active material for lithium ion batteries used as power sources for hybrid vehicles and electric vehicles.

100: Positive electrode active material 10: Lithium-nickel composite oxide 10a: Lithium-nickel composite oxide (raw material)
LB: Amorphous _LiBO2
B... Boron compound CBA... Coin type battery CA... Case PC... Positive electrode can NC... Negative electrode can GA... Gasket PE... Positive electrode NE... Negative electrode SE... Separator

Claims (7)

A lithium-nickel composite oxide and a coating layer covering at least part of the surface of the lithium-nickel composite oxide ,
The lithium-nickel composite oxide contains lithium, nickel, cobalt, and an element M, and the ratio (molar ratio) of the amount of each element is Li:Ni:Co:M=a:(1−x -y): x: y (where 0.95 ≤ a ≤ 1.10, 0.05 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.10, M is Mn, V, Mg, Mo, Nb , Ti, W, Zr, and at least one element selected from Al),
the coating layer is composed of lithium borate, the lithium borate comprising amorphous LiBO 2 _;
The content of boron is 0.01% by mass or more and 0.1% by mass or less with respect to the entire positive electrode active material.
Positive electrode active material for lithium ion secondary batteries. mixing a lithium-nickel composite oxide and a boron compound to obtain a mixture;
The mixture is heat-treated in an oxygen atmosphere at a temperature of 300° C. or higher and 500° C. or lower to react the boron compound with lithium in the lithium-nickel composite oxide, thereby obtaining the surface of the lithium-nickel composite oxide. forming a coating layer covering at least a portion of
The lithium-nickel composite oxide contains lithium, nickel, cobalt, and an element M, and the ratio (molar ratio) of the amount of each element is Li:Ni:Co:M=a:(1−x -y): x: y (where 0.95 ≤ a ≤ 1.10, 0.05 ≤ x ≤ 0.35, 0 ≤ y ≤ 0.10, M is Mn, V, Mg, Mo, Nb , Ti, W, Zr, and at least one element selected from Al),
the coating layer is composed of lithium borate, the lithium borate comprising amorphous LiBO ₂ ;
The mixture contains 0.01% by mass or more and 0.1% by mass or less of boron in the boron compound with respect to the entire mixture.
A method for producing a positive electrode active material for a lithium ion secondary battery. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim ₂ , wherein the boron compound contains at _least one selected from _H3BO3 and _B2O3 . 4. The method for producing a positive electrode active material for a lithium ion secondary battery according to claim 2 or 3, wherein at least part of the surface of said lithium nickel composite oxide is coated with amorphous _LiBO2 . The amount of lithium hydroxide measured by a neutralization titration method, which is eluted when the positive electrode active material obtained after the heat treatment is dispersed in water, is 0.01% by mass or more and 0.2% with respect to the entire positive electrode active material. 5. The method for producing a positive electrode active material for a lithium ion secondary battery according to any one of claims 2 to 4, wherein the content is adjusted to be less than % by mass. A positive electrode mixture paste for lithium ion secondary batteries, comprising the positive electrode active material for lithium ion secondary batteries according to claim 1 . A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte, wherein the positive electrode comprises the positive electrode active material according to claim 1 .

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