JP2019192512A - Positive electrode active material for non-aqueous electrolyte secondary battery and method of manufacturing the same - Google Patents

Abstract

To provide a positive electrode active material capable of manufacturing a non-aqueous electrolyte secondary battery with high capacity while suppressing gelation of a positive electrode mixture paste when used as a positive electrode active material for a secondary battery.SOLUTION: The positive electrode active material for a non-aqueous electrolyte secondary battery includes: lithium-nickel composite oxide particles containing boron; and a coating layer, attached to at least a portion of a surface of the particles, containing a compound containing one or more of silicon (Si), zinc (Zn), and aluminum (Al).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same.

  In recent years, with the spread of portable information terminals such as smartphones and tablet PCs, development of small and lightweight secondary batteries having high energy density is required. In addition, as a battery for electric vehicles such as hybrid vehicles, development of a high output secondary battery is also required. As a secondary battery satisfying such a requirement, there is a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery. A lithium ion secondary battery includes a negative electrode, a positive electrode, an electrolytic solution, and the like, and a material capable of detaching and inserting lithium is used as an active material for the negative electrode and the positive electrode.

Non-aqueous electrolyte secondary batteries are currently being actively researched and developed. Among these, non-aqueous electrolyte secondary batteries using a lithium metal composite oxide having a layered structure or a spinel structure as a positive electrode active material Since a high voltage of 4V class can be obtained, practical use is progressing as a battery having a high energy density. As positive electrode active materials that have been mainly proposed so far, lithium cobalt composite oxide (LiCoO ₂ ) that is relatively easy to synthesize, lithium nickel composite oxide (LiNiO ₂ ) using nickel that is cheaper than cobalt, Examples thereof include lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) and lithium manganese composite oxide (LiMn ₂ O ₄ ) using manganese.

  Among these, since lithium cobalt complex oxide uses an expensive cobalt compound as a raw material, the unit price per capacity of the battery is significantly higher than that of a conventional nickel-metal hydride battery, and applicable applications are considerably limited. Expectations are high not only for small secondary batteries, but also for large-sized secondary batteries for electric vehicles and power storage applications, which can reduce the cost of the cathode active material and enable the manufacture of cheaper non-aqueous electrolyte secondary batteries. The realization of this is industrially significant.

  A candidate for a positive electrode active material for a non-aqueous electrolyte secondary battery that is cheaper and applicable to a wide range of applications includes a lithium nickel composite oxide using nickel that is cheaper than cobalt. Lithium-nickel composite oxide shows high battery voltage like lithium-cobalt composite oxide, but has lower electrochemical potential than lithium-cobalt composite oxide. It is expected to be developed especially for electric vehicles.

  However, even in an electric vehicle equipped with a battery manufactured using a conventional lithium nickel composite oxide, it is difficult to realize a cruising distance comparable to that of a gasoline vehicle (see, for example, Patent Document 1), and an even higher capacity There was a need to make it.

  Another drawback of the lithium nickel composite oxide is that the positive electrode mixture paste is easily gelled. The positive electrode of the nonaqueous electrolyte secondary battery is, for example, a positive electrode mixture paste 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). Is formed and applied to a current collector such as an aluminum foil, followed by drying and pressure bonding. At this time, when lithium is desorbed from the positive electrode active material in the positive electrode mixture paste, it may react with moisture contained in the paste to increase the pH of the paste. The binder and solvent in the paste may be polymerized due to an increase in pH, and the positive electrode mixture paste may be gelled. When the positive electrode mixture paste is gelled, the coating property to the current collector is deteriorated and the yield of battery production is also deteriorated. This tendency is particularly remarkable when the lithium contained in the positive electrode active material is in excess of the stoichiometric composition of the lithium nickel composite oxide and the nickel ratio in the transition metal other than lithium is high.

  Several attempts have been made to suppress such gelation of the positive electrode mixture paste. For example, Patent Document 2 proposes a positive electrode composition for a secondary battery that includes a positive electrode active material made of a lithium transition metal composite oxide and an additive made of acidic oxide particles. In this positive electrode composition, lithium hydroxide generated by reacting lithium desorbed from the positive electrode active material with moisture contained in the binder causes a neutralization reaction with the acidic oxide, and suppresses an increase in pH of the positive electrode mixture paste. , Trying to suppress gelation. In addition, the acidic oxide plays a role as a conductive agent in the positive electrode, lowers the resistance of the whole positive electrode, and contributes to the improvement of the output characteristics of the battery.

  In Patent Document 3, excess lithium hydroxide is calculated with respect to the stoichiometric composition of the lithium transition metal composite oxide, and 0.05 mol or more of tungsten oxide per 1 mol of the excess lithium hydroxide is used as the positive electrode active material. A method for producing a non-aqueous electrolyte secondary battery is proposed in which a positive electrode mixture paste is mixed with a conductive additive and a binder to obtain a secondary battery having high battery characteristics while suppressing gelation. Yes.

  Patent Document 4 discloses a technique for containing boric acid or the like as an inorganic acid in a positive electrode using a lithium transition metal composite oxide or the like and preventing gelation of the electrode paste. As a specific example of the oxide, lithium nickelate is disclosed.

Japanese Laid-Open Patent Publication No. 04-300153 JP 2012-28313 A JP 2013-84395 A JP-A-10-79244

  However, even when the positive electrode active material described in Patent Document 1 is used, it is not sufficient for electric vehicles, and a further increase in capacity is required.

  Moreover, in the proposal of the above-mentioned patent document 2, there is a fear that the separator is damaged and the safety is lowered due to the remaining acidic oxide particles. Moreover, it cannot be said that gelation suppression is sufficient. Although the suppression of gelation can be improved by increasing the addition amount of the acidic oxide, the battery capacity per unit weight deteriorates due to the increase in raw material cost due to the addition and the increase in weight due to the addition.

  Even in the proposal of Patent Document 3, it cannot be said that the problem regarding the breakage of the separator due to the remaining acidic oxide and the suppression of gelation are not solved. Further, the addition of tungsten, which is a heavy element that does not contribute to charging / discharging, greatly reduces the battery capacity per weight.

  Furthermore, in the proposal of Patent Document 4, a positive electrode active material, a conductive agent, and a binder are added and mixed in a solvent to which boric acid or the like is added. In this method, the positive electrode active material is sufficiently dispersed. There is a risk that gelation will occur locally until this occurs.

  In view of the above problems, the object of the present invention is to produce a high-capacity non-aqueous electrolyte secondary battery while suppressing gelation of the positive electrode mixture paste when used as a positive electrode active material for a secondary battery. An object of the present invention is to provide a positive electrode active material.

  In order to solve the above-mentioned problems, the present inventor conducted extensive research on a lithium metal composite oxide used as a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, and as a result, a lithium nickel composite containing boron By using a positive electrode active material in which a film of a compound containing at least one of silicon (Si), zinc (Zn), and aluminum (Al) is formed on the oxide particle surface, a positive electrode mixture paste and The present invention has been completed by obtaining the knowledge that a secondary battery having a large battery capacity can be obtained while gelling is suppressed.

  According to the first aspect of the present invention, boron-containing lithium nickel composite oxide particles, and silicon (Si), zinc (Zn), and aluminum (attached to at least a part of the surface of the particles) There is provided a positive electrode active material for a non-aqueous electrolyte secondary battery having a coating layer containing a compound containing at least one of Al).

  Moreover, it is preferable that content of boron is 0.002 mass% or more and 0.15 mass% or less with respect to the whole positive electrode active material. The total content of silicon (Si), zinc (Zn), and aluminum (Al) in the coating layer is 0.01% by mass or more and 0.15% or less with respect to the whole positive electrode active material. It is preferable. Further, in the particles of the lithium nickel composite oxide, the substance amount (mole) ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = s :( 1-xy): x: y (where 0.95 ≦ s ≦ 1.30, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.1, M is Mn, V, Mg, It is preferably represented by at least one element selected from Mo, Nb, Ti and Al. The lithium nickel composite oxide particles may include secondary particles formed by agglomerating a plurality of primary particles, and at least a part of the boron may be dissolved in the lithium nickel composite oxide particles. preferable. Moreover, it is preferable that a coating layer contains the hydrolysis product of the organometallic compound which has an alkoxy group.

  According to the second aspect of the present invention, there is provided a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising mixing a nickel compound, a boron compound and a lithium compound, and firing the mixture obtained by the mixing. And dissolving an organometallic compound containing at least one of silicon (Si), zinc (Zn), and aluminum (Al) in a solvent on the particle surface of the lithium nickel composite oxide obtained by firing. Adhering the coating liquid obtained in the above, and drying the lithium nickel composite oxide to which the coating liquid has adhered, wherein the organometallic compound comprises a metal alkoxide having an alkoxy group, and the metal alkoxide. Metal chelates in which at least one of the alkoxy groups is substituted with acetylacetonate or alkyl acetoacetate It is at least one of Gobutsu method for producing a positive active material for non-aqueous electrolyte secondary battery is provided.

Moreover, it is preferable that a coating liquid contains the product obtained by hydrolyzing an alkoxy group. The hydrolysis is preferably performed by adding pure water to the coating solution and stirring at room temperature. The nickel compound is preferably at least one of nickel hydroxide and nickel oxide. The lithium compound is preferably at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium nitrate, lithium chloride, and lithium sulfate. The boron compound is preferably at least one of boric acid (H ₃ BO ₃ ), boron oxide (B ₂ O ₃ ), and lithium metaborate (LiBO ₂ ). Moreover, it is preferable that an organometallic compound contains an acetylacetonate metal complex. Further, it is preferable that the firing is performed in an oxygen atmosphere at a maximum firing temperature of 700 ° C. or higher and 800 ° C. or lower.

  According to the positive electrode active material of the present invention, when used as a positive electrode active material of a battery, gelation of the positive electrode mixture paste during battery production is suppressed, and a non-aqueous electrolyte secondary battery having a high charge / discharge capacity Can be obtained. Moreover, the manufacturing method of the positive electrode active material of this invention can produce said positive electrode active material easily on an industrial scale, The industrial value is very large.

FIG. 1A is a diagram illustrating an example of a positive electrode active material according to this embodiment, and FIG. 1B is a diagram illustrating an example of a structure of a lithium nickel composite oxide. FIG. 2 is a diagram illustrating an example of a method for producing a positive electrode active material according to the present embodiment. 3A and 3B are diagrams illustrating an example of a method for manufacturing a material used in the mixing step. 4 (A) and 4 (B) are diagrams showing an example of a method for producing a coating liquid used in the attaching step. FIG. 5 is a diagram showing another example of a method for producing a positive electrode active material. FIG. 6 is a schematic cross-sectional view of a coin-type battery used for battery evaluation.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Further, in the drawings, in order to make each configuration easy to understand, a part of the structure is emphasized or a part of the structure is simplified, and an actual structure, shape, scale, or the like may be different. In addition, this embodiment described below does not unduly limit the content of the present invention described in the claims, and can be modified without departing from the gist of the present invention.

1. Cathode Active Material for Nonaqueous Electrolyte Secondary Battery FIG. 1A is also referred to as a cathode active material for a nonaqueous electrolyte secondary battery according to this embodiment (hereinafter, “cathode active material”, “cathode active material 100”). ). As shown in FIG. 1A, the positive electrode active material 100 includes a lithium-nickel composite oxide particle 10 containing boron, and silicon (Si) and zinc (Zn) adhering to at least a part of the surface of the particle. And a coating layer 20 containing a compound containing one or more of aluminum (Al).

  FIG. 1B is a diagram showing an example of the structure of the lithium nickel composite oxide particles 10. As shown in FIG. 1B, the lithium nickel composite oxide particles 10 are oxide particles containing lithium and nickel, and include secondary particles 2 composed of a plurality of primary particles 1. The lithium nickel composite oxide particles 10 are mainly composed of the secondary particles 2, but may contain a small amount of the primary particles 1 in addition to the secondary particles 2.

(Composition of lithium nickel composite oxide)
The lithium nickel composite oxide may contain only nickel as a metal component other than lithium, but may contain other elements other than nickel, and preferably contains other metal elements. Examples of other metal elements include Co, Mn, V, Mg, Mo, Nb, Ti, and Al. The lithium nickel composite oxide includes various known metal elements according to required characteristics. be able to. For example, the lithium nickel composite oxide preferably contains cobalt from the viewpoint of improving cycle characteristics and improving thermal stability during charging.

  The lithium nickel composite oxide preferably has a layered crystal structure, and preferably has a crystal structure in which a part of nickel is substituted with an arbitrary metal containing cobalt. The lithium-nickel composite oxide particles 10 contain boron, but at least a part of boron is preferably in solid solution, and a part of nickel has a crystal structure substituted with boron. Is preferred.

  When the lithium-nickel composite oxide has nickel and cobalt as metal elements other than lithium, for example, the substance amount (mole) ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = s: (1-xy): x: y (where 0.95 ≦ s ≦ 1.30, 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0. 1, M may be represented by at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al. Note that the lithium nickel composite oxide represented by the above-mentioned substance amount ratio may contain a small amount of an element other than the above element M.

(lithium)
In the substance ratio, s indicating the lithium content is preferably 0.95 or more and 1.30 or less, and more preferably 1.0 or more and 1.10 or less. When the substance amount ratio of lithium is less than 0.95, the site where lithium should occupy in the crystal of the lithium nickel composite oxide may be occupied by other elements, and the charge / discharge capacity may decrease. On the other hand, if the mass ratio exceeds 1.30, there will be an excess of lithium compound that does not contribute to charging / discharging together with the lithium nickel composite oxide, resulting in an increase in battery resistance or a decrease in charging / discharging capacity. There are things to do.

(nickel)
In the substance ratio, (1-xy) indicating nickel content is preferably 0.55 or more and 0.95 or less. From the viewpoint of improving the battery capacity of the secondary battery, the nickel content is preferably larger within the above range. On the other hand, when the content of nickel is large, gelation of the positive electrode mixture paste is likely to occur, but the positive electrode active material according to the present embodiment includes silicon (Si), zinc (Zn), and aluminum (Al) described later. By having the coating layer 20 containing a compound containing one or more of them, it has a high charge / discharge capacity (battery capacity) and can suppress gelation of the positive electrode mixture paste.

(cobalt)
In the substance ratio, x indicating the cobalt content is preferably 0.05 or more and 0.35 or less. When the amount ratio of cobalt is in the above range, the cycle characteristics when charging / discharging is repeated and the thermal stability during charging can be improved while maintaining the high charge / discharge capacity of the lithium nickel composite oxide. .

(Element M)
In the substance amount ratio, the element M is at least one selected from Mn, V, Mg, Mo, Nb, Ti, and Al, and y indicating the content of the element M is 0 or more and 0.1 or less. It is preferable. In addition, when the element M is included (when M exceeds 0), characteristics are improved in various ways such as improvement of cycle characteristics and thermal stability, improvement of rate characteristics, and reduction of battery resistance depending on the kind of element to be added. be able to. On the other hand, when the substance amount ratio of the element M exceeds 0.10, the nickel content in the particles 10 of the lithium nickel composite oxide decreases, and the charge / discharge capacity tends to decrease.

(Boron)
The lithium nickel composite oxide particles 10 contain boron (B). In the lithium nickel composite oxide particles 10, it is preferable that at least a part of boron is dissolved in the crystal structure. The solid solution in the crystal structure and the presence of the boron compound can be confirmed by powder X-ray diffraction or the like. For example, when the lithium nickel composite oxide contains boron and no boron compound is detected as a different phase by powder X-ray diffraction, it is assumed that boron is in solid solution. When boron is dissolved in the crystal structure, a part of nickel is considered to be substituted with boron. A part of boron may be present as a compound containing boron on the surface or crystal grain boundary of the primary particle 1 and / or the secondary particle 2, but from the viewpoint of improving the charge / discharge capacity in the secondary battery, It is preferable to dissolve in the crystal structure.

  When boron dissolves in the crystal structure of the lithium nickel composite oxide particles 10, the charge / discharge capacity of the positive electrode active material 100 can be improved. Although details of this mechanism are unknown, for example, it is presumed as follows. As described above, the lithium nickel composite oxide particles 10 include secondary particles 2 in which primary particles 1 composed of fine single crystals are aggregated. For example, between single crystals or between primary particles 1 (boundary surface) is a discontinuous surface in terms of crystal even when there is no void, which hinders the movement of lithium ions during charging and discharging. . The larger the area of this boundary surface, the larger the battery resistance of the secondary battery, mainly the positive electrode resistance, and the charge / discharge capacity is reduced. When compared with the secondary particles 2 having the same size, it can be said that the total area of the boundary surface decreases as the size of the single crystal and the primary particle 1 increases. Here, when a part of the transition metal (eg, nickel) is replaced with boron, the crystal growth is facilitated, so that the single crystal and the primary particle 1 are increased, and the charge / discharge capacity of the positive electrode active material 100 is improved. It is done.

  The content of boron is not particularly limited as long as it has the above effect, but is preferably 0.002% by mass or more and 0.15% by mass or less, and 0.005% by mass or more with respect to the whole positive electrode active material. It is preferable that it is 0.1 mass% or less, and 0.01 mass% or more and 0.05 mass% or less may be sufficient. In addition, when there is too little content of boron, the said effect may not fully be expressed. In addition, when the boron content is excessive, the ratio of nickel to metal other than lithium is decreased, and the ratio of nickel in the positive electrode active material 100 is decreased, so that the charge / discharge capacity may be decreased. Moreover, when there is much content of boron, the ratio which exists as a compound containing boron in the surface or the crystal grain boundary of the primary particle 1 and / or the secondary particle 2 may become high, and battery capacity may fall.

Furthermore, particles 10 of the lithium nickel composite oxide, as a composition formula, except for boron, the formula _{(1): Li s Ni 1} -x-y Co x M y O 2 + α ( although, 0.05 ≦ x ≦ 0. 35, 0 ≦ y ≦ 0.10, 0.95 ≦ s ≦ 1.30, −0.5 <α <0.5, M is selected from Mn, V, Mg, Mo, Nb, Ti and Al At least one element). A preferable range of each element in the general formula (1) is the same as the above atomic ratio.

(Coating layer)
The positive electrode active material 100 is a compound containing at least one of silicon (Si), zinc (Zn), and aluminum (Al) attached to at least a part of the surface of the particles 10 of the lithium nickel composite oxide. The coating layer 20 contains. When the surface of the particles 10 of the lithium nickel composite oxide is covered with the coating layer 20, gelation of the positive electrode mixture slurry can be extremely suppressed. In addition, the compound containing 1 or more types of silicon (Si), zinc (Zn), and aluminum (Al) may contain silicon, zinc, and aluminum independently, and may contain each in combination. Further, this compound may be an oxide containing one or more of silicon, zinc, and aluminum.

  Generally, a positive electrode mixture slurry is a mixture of a positive electrode active material such as lithium nickel composite oxide, a conductive auxiliary agent such as acetylene black, a binder such as PVDF, and other additives together with a solvent such as N-methylpyrrolidone. Prepared. The positive electrode mixture slurry is applied to a current collector (eg, an aluminum thin plate), dried, and then press-compressed as necessary to produce a positive electrode. During the production of the positive electrode, the viscosity of the positive electrode mixture slurry increases with time, and application to the current collector may be difficult. Although the details of this reason are unknown, lithium ions are eluted from the lithium transition metal composite oxide particles 10 into the solvent, the pH of the positive electrode mixture slurry is increased, and a part of the solvent is polymerized and gelled. It is considered because.

  On the other hand, in the positive electrode active material 100 of the present embodiment, the presence of the coating layer 20 on the surfaces of the lithium nickel composite oxide particles 10 suppresses the elution of lithium ions into the positive electrode mixture slurry, and the positive electrode mixture. It is considered that the pH increase of the agent slurry is less likely to occur, and gelation is suppressed. Further, when the coating layer 20 contains a compound containing at least one of silicon, zinc, and aluminum, the lithium elution suppression effect is large and the lithium ion conductivity can be secured during the charge / discharge reaction. A high charge / discharge capacity can be maintained while suppressing the gelation of the agent slurry.

  The coating layer 20 is a contact surface between the lithium nickel composite oxide particles 10 and the electrolyte constituting the secondary battery (eg, the surface of the secondary particles 2 and the surface of the primary particles 1 in contact with the voids in the secondary particles 2). Etc.). Further, the content (total amount) of silicon, zinc, and aluminum in the coating layer 20 is preferably 0.01% by mass or more and 0.15% by mass or less, more preferably, with respect to the entire positive electrode active material. It is 0.01 mass% or more and 0.10 mass% or less. When the content (total amount) of silicon, zinc, and aluminum is less than 0.01% by mass, the surface of the lithium nickel composite oxide particles 10 by the coating layer 20 is not sufficiently covered and partly exposed. Lithium ions may be eluted from the surface of the lithium-nickel composite oxide particles 10, and a sufficient gelation suppressing effect may not be obtained. On the other hand, when the content (total amount) of silicon, zinc, and aluminum exceeds 0.15% by mass, the thickness of the coating layer 20 is increased, and the gelling suppression effect can be sufficiently obtained. Resistance may increase, battery resistance of the secondary battery may increase, and charge / discharge capacity may decrease.

  As the compound containing at least one of silicon, zinc, and aluminum contained in the coating layer 20, a hydrolysis product obtained by hydrolyzing an organometallic compound having an alkoxy group is preferable, and silicon, zinc, and It may be an oxide containing at least one of aluminum. It is preferable to coat the surface of the lithium nickel composite oxide with a compound containing at least one of silicon, zinc, and aluminum by a method that can easily and uniformly coat the entire surface. As described later, when a solution containing an organometallic compound having an alkoxy group is used as a coating solution, a compound containing at least one of silicon, zinc, and aluminum is uniformly and evenly distributed on the surface of the secondary particles. Is easy. Moreover, the coating liquid containing an organometallic compound becomes a compound containing at least one of solid phase silicon, zinc, and aluminum by hydrolysis or thermal decomposition. Lithium nickel composite oxide particles 10 to which a coating layer 20 containing a compound containing at least one of silicon, zinc, and aluminum is attached can be obtained by drying or heat treatment after coating the coating liquid. .

  The positive electrode active material 100 is not particularly limited as long as it has the above characteristics, but can be easily manufactured by a manufacturing method described later.

2. 2. Method for Producing Positive Electrode Active Material FIG. 2 is a diagram showing an example of a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present embodiment (hereinafter also referred to as “a method for producing a positive electrode active material”). . The positive electrode active material 100 described above can be easily manufactured with high productivity by the positive electrode active material manufacturing method of the present embodiment. In addition, the manufacturing method of this embodiment may manufacture positive electrode active materials other than said positive electrode active material 100. FIG. Hereinafter, a method for producing the positive electrode active material according to the present embodiment will be described.

[Mixing step (Step S10)]
First, a nickel compound, a boron compound, and a lithium compound are mixed (step S10). By baking the mixture obtained by this process (step S20), a lithium nickel composite oxide can be obtained. Hereinafter, the material used for this process is demonstrated.

(Nickel compounds)
As the nickel compound, a known compound can be used as long as it is a compound containing nickel. The nickel compound may contain an element other than nickel, and preferably contains a metal element. Examples of the metal element include Co, Mn, V, Mg, Mo, Nb, Ti, and Al, and various metal elements can be included depending on required characteristics. The nickel compound preferably contains Co, for example, from the viewpoint of improving cycle characteristics and improving thermal stability during charging.

  The nickel compound can have the same composition as that of the lithium nickel composite oxide particles 10 except for lithium and boron. The nickel compound has, for example, a ratio of nickel (Ni), cobalt (Co), and element M (molar amount) of Ni: Co: M = (1-xy): x: y (however, 0 0.05 ≦ x ≦ 0.35, 0 ≦ y ≦ 0.35, and M may be represented by at least one element selected from Mn, V, Mg, Mo, Nb, Ti, and Al). In addition, since the preferable range of substance amount ratio of each metal is the same as the range mentioned above, description is abbreviate | omitted.

  Further, the nickel compound may be a hydroxide containing nickel (nickel hydroxide), oxide (nickel oxide), carbonate (nickel carbonate), sulfate, chloride, and the like. From the viewpoint of reducing the reactivity with the lithium compound and the anion that becomes an impurity, it is preferably at least one of nickel hydroxide, nickel oxide, and nickel carbonate, more preferably nickel water. It is at least one of oxide and nickel oxide. For example, when nickel oxide is used as the nickel compound, variation in composition of the obtained positive electrode active material can be reduced. In the obtained positive electrode active material, boron derived from the boron compound is dissolved in the primary particles. And it can distribute uniformly in the whole secondary particle. In addition, you may use a nickel compound individually by 1 type or in mixture of 2 or more types.

  In addition, the manufacturing method of a nickel compound will not be specifically limited if it has the said composition, A well-known method can be used. FIGS. 3A and 3B are diagrams showing an example of a method for producing a nickel compound used in the mixing step (step S10). For example, as shown in FIG. 3A, nickel hydroxide is produced by crystallization (step S1) using an aqueous solution containing Ni and optionally Co and element M, and nickel hydroxide is obtained. May be used in the mixing step (step S10). Further, for example, as shown in FIG. 3B, the nickel hydroxide obtained after crystallization (step S1) is heat-treated (step S2), and at least part of the nickel hydroxide is changed to nickel oxide, followed by a mixing step. You may use for (step S10). When a positive electrode active material is produced using a precursor (nickel hydroxide / nickel oxide) obtained by crystallization (step S1), a positive electrode active material having a more uniform composition, physical properties, etc. among particles is obtained. Can do.

  When the nickel hydroxide is heat-treated (step S2), the temperature of the heat treatment can be, for example, 105 ° C. or higher and 750 ° C. or lower. When all the nickel hydroxide is converted to nickel oxide, the temperature is 400 ° C. or higher. It is preferable. Although heat processing time is not specifically limited, For example, it is 1 hour or more, and 5 hours or more and 15 hours or less are preferable. Moreover, the atmosphere which heat-processes is not specifically limited, What is necessary is just a non-reducing atmosphere, but you may carry out in the airflow which can be performed easily.

(Lithium compound)
As long as the lithium compound is a compound containing lithium, a known compound can be used. For example, at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium nitrate, lithium chloride, and lithium sulfate may be used. . As the lithium compound, lithium hydroxide, lithium oxide, and lithium carbonate are preferable, and lithium hydroxide is more preferable from the viewpoint of reactivity with the nickel compound and reduction of impurities. In addition, you may use a lithium compound individually by 1 type or in mixture of 2 or more types.

For example, when nickel oxide (NiO) and lithium hydroxide (LiOH) are mixed and reacted at 700 ° C. or higher and 800 ° C. or lower, a lithium nickel composite oxide is generated by the reaction of the following formula (1).
Formula (1): NiO + LiOH + 1 / 4O ₂ → LiNiO ₂ + 1 / 2H ₂ O

  The nickel oxide may contain other metal elements such as cobalt and the element M as described above, and may contain boron (B) as described later. Further, when nickel oxide is used as the material used in the mixing step (step S10), boron can be easily dissolved in the lithium nickel composite oxide in the subsequent firing step (step S20).

(Boron compound)
The boron compound is a compound containing boron, and a known compound can be used. As the boron compound, at least one of boric acid (H ₃ BO ₃ ), boron oxide (B ₂ O ₃ ), and lithium metaborate (LiBO ₂ ) is used from the viewpoint of availability and reduction of impurities. Preferably, at least one of boric acid and boron oxide is more preferable. In addition, you may use a boron compound individually by 1 type or in mixture of 2 or more types.

(Mixing method)
It is preferable that the nickel compound, the lithium compound, and the niobium compound are sufficiently mixed so that no fine powder is generated. When mixing is insufficient, Li / Me varies among individual particles of the obtained positive electrode active material, and sufficient battery characteristics may not be obtained. In addition, a general mixer can be used for mixing. As the mixer, for example, a shaker mixer, a Laedige mixer, a Julia mixer, a V blender, or the like can be used.

[Baking process (step S20)]
Next, the mixture obtained by the above mixing process (step S10) is baked (step S20). By firing the nickel compound and the lithium compound together with the boron compound, particles of the lithium nickel composite oxide containing the boron compound can be obtained. Moreover, it is preferable that at least a part of boron is solid-dissolved in the particles of the lithium nickel composite oxide.

  The firing temperature is preferably 700 ° C. or higher and 800 ° C. or lower. When the calcination temperature is less than 700 ° C., the rate of the calcination reaction is slow, which may be industrially disadvantageous. In addition, when the firing temperature exceeds 800 ° C., the generated lithium nickel composite oxide undergoes a decomposition reaction, the yield of the lithium nickel composite oxide decreases, and excessive crystal growth occurs, resulting in battery characteristics, particularly cycle characteristics. May be reduced.

  The firing time is not particularly limited as long as the firing reaction is sufficiently performed. For example, the firing time is 3 hours to 20 hours, preferably 5 hours to 10 hours. The atmosphere during firing is preferably an oxygen atmosphere, and may be an atmosphere having an oxygen concentration of 100% by volume.

[Adhesion Step (Step S30)]
Next, an organometallic compound containing one or more of silicon (Si), zinc (Zn), and aluminum (Al) is dissolved in a solvent on the particle surface of the lithium nickel composite oxide obtained by firing. The applied coating solution is attached (attachment step: step S30). The manufacturing method and the adhesion method of the coating liquid are not particularly limited, and a known method can be used, but the following method is preferable.

(Coating solution)
The coating liquid is obtained by dissolving the organometallic compound in a solvent (FIG. 2, step S31). The organometallic compound is at least one of a metal alkoxide having an alkoxy group and a metal chelate compound in which at least one of the alkoxy groups of the metal alkoxide is substituted with acetylacetonate or alkyl acetoacetate.

Examples of the organometallic compound include one or more alkoxides of silicon, zinc, and aluminum (hereinafter, these are collectively referred to as “metal alkoxide”). As the metal alkoxide, for example, selected from ethoxide (M ′ (OC ₂ H ₅ ) _n ), tetrapropoxide (M ′ (OC ₃ H ₇ ) _n ), and tetrabutoxide (M ′ (OC ₄ H ₉ ) _n ) 1 type or 2 types or more are preferable (however, M 'shows 1 or more types in silicon, zinc, and aluminum). In addition, you may use an organometallic compound individually by 1 type or in mixture of 2 or more types.

In addition, as the organometallic compound, at least one of the alkoxide groups of the metal alkoxide may be acetylacetonate or a compound (metal complex) substituted with alkylacetoacetate, and all the alkoxide groups may be acetylacetonate. Alternatively, it may be an acetylacetonate metal complex substituted with an alkyl acetoacetate or an alkyl acetoacetate metal complex. Examples of the acetylacetonate metal complex include compounds represented by the general formula: M ′ (C ₅ H ₇ O ₂ ) _n or M ′ (CH ₃ C (O) CHC (O) CH ₃ ) _n. Examples of the alkyl acetoacetate metal complex include compounds represented by the general formula: M ′ (C ₆ H ₉ O ₃ ) _n or M ′ (CH ₃ C (O) CHC (O) OC ₂ H ₅ ) _n. It is done.

  For example, in the case of an organometallic compound containing zinc, an acetylacetonate metal complex is preferably used. In the case of an organometallic compound containing aluminum, a metal chelate compound in which a part of the alkoxide group is substituted with ethyl acetoacetonate is preferable.

  When these organometallic compounds are used, since they are composed of only metal M ′ and oxygen, carbon, and hydrogen, the surfaces of the lithium nickel composite oxide particles include at least one of silicon, zinc, and aluminum. When a coating film (coating layer) containing a compound is formed, the formation of anions that inhibit charge / discharge reactions in secondary batteries is suppressed, and because it is soluble in various organic solvents, the coating solution can be prepared. Easy.

  The solvent for preparing the coating liquid is not particularly limited, and a known solvent can be used, but a lower alcohol having 4 or less carbon atoms is preferable from the viewpoint of ease of adjustment. Examples of the lower alcohol include ethyl alcohol (ethanol), n-propyl alcohol, isopropyl alcohol, tetrabutyl alcohol and the like. When a lower alcohol is used, the solubility of the alkoxide is high and the viscosity is low, so that it can be easily applied to the surface of the lithium nickel composite oxide particles. In addition, when higher alcohol is used, the viscosity may be high and spraying may be difficult.

  Further, the viscosity of the solution is adjusted by adding an organic solvent other than alcohol such as acetylacetone, and a compound solution containing at least one of silicon, zinc, and aluminum suitable for spraying can be obtained. In addition, acetylacetone can chelate (modify) a part of alkoxy group which an organometallic compound has, and can adjust the rate of hydrolysis.

  FIG. 4A and FIG. 4B are diagrams showing an example of a method for adjusting the coating liquid. As shown in FIG. 4A, after mixing the solvent and the organometallic compound (step S31), at least a part of the organometallic compound may be hydrolyzed (step S32) by adding water, for example. . When a coating liquid obtained by hydrolyzing at least a part of the organometallic compound is used, the bond between the surface of the lithium nickel composite oxide particles and the compound containing at least one of silicon, zinc, and aluminum is strengthened. A coating layer can be formed more reliably. This is because the polymer produced by hydrolysis of the organometallic compound tends to form a film (eg, silicon oxide, zinc oxide, aluminum oxide) on the surface of the lithium nickel composite oxide, and the oxygen-hydrogen bond of the hydrolyzate This is probably because (—OH) can be easily combined with oxygen on the surface of the lithium nickel composite oxide. The amount of water mixed is preferably 10 parts by weight or more and 50 parts by weight or less with respect to 100 parts by weight of the added organometallic compound. In addition, for example, the amount of water mixed may be 0.5 mol times or more and 2 mol times or less with respect to the alkoxy group contained in the organometallic compound. It may be 0 times or more.

  The solution obtained after hydrolysis (step S32) may be used as it is as a coating solution, or may be further diluted with a solvent so as to have a concentration suitable for coating. Moreover, the addition amount (mixing amount) of the organometallic compound in the coating solution may be, for example, 0.2% by mass or more and 10% by mass or less, and 0.5% by mass or more and 5% by mass or less with respect to the entire coating solution. The mass% or less may be sufficient.

  Further, as shown in FIG. 4B, a chelating agent may be mixed when the solvent and the organometallic compound are mixed (step S31). As the chelating agent, for example, acetylacetone can be used. Alternatively, the solution obtained after hydrolysis (step S32) may be diluted by mixing a solvent and glycols (step S33). As the glycol, it is preferable to use one or more selected from polyethylene glycol, polypropylene glycol, and hexylene glycol. Among these, polyethylene glycol that is easily soluble in water or lower alcohol from the viewpoint of low cost and easy handling. And / or polypropylene glycol is more preferred. By adding a small amount of water-soluble glycol together with the solvent and diluting (step S33), it is possible to improve the film uniformity during coating and to avoid the occurrence of film cracking and peeling during drying. The addition amount of glycols is, for example, 2 to 20 parts by mass with respect to 100 parts by mass of the organometallic compound.

(Adhesion method)
As a method for adhering the coating liquid to the particle surface of the lithium nickel composite oxide, a known method can be used as long as the coating liquid uniformly adheres to the particle surface. For example, lithium nickel The composite oxide and the coating liquid may be mixed and adhered. Further, from the viewpoint of more uniformly attaching the coating liquid, a method of spraying the organometallic compound solution in droplets while stirring and mixing the particles of the lithium nickel composite oxide is preferable.

  The mixing amount (addition amount) of the coating liquid includes the amount of the compound containing at least one of silicon, zinc, and aluminum to be deposited, and at least one of silicon, zinc, and aluminum in the coating liquid to be added. Although it can adjust suitably with the density | concentration of a compound (the organometallic compound / hydrolyzate of an organometallic compound), Preferably it is 5 to 25 mass% with respect to the whole lithium nickel composite oxide. When the mixing amount of the coating liquid exceeds the above range, the mixture may become a paste and the subsequent handling may be extremely difficult.

[Drying Step (Step S40)]
Next, the lithium nickel composite oxide to which the coating liquid is attached is dried (step S40). Unnecessary solvent components can be removed by drying (step S40). Further, during the drying step (step S40), the organometallic compound / organometallic compound hydrolyzate in the coating solution is adsorbed and bonded to the surface of the lithium nickel composite oxide particles. In addition, a drying process (step S40) may be performed simultaneously with said adhesion process (step S30), and may be performed separately.

  Although a drying temperature is not specifically limited, For example, they are 50 degreeC or more and 200 degrees C or less. When alcohol is used as the solvent, the drying temperature may be 50 ° C. or higher and 150 ° C. or lower. Moreover, after performing hydrolysis (step S32), when aqueous solvents, such as water, are used as a solvent of dilution (step S34), 100 degreeC or more and 200 degrees C or less may be sufficient as drying temperature.

  The drying time is not particularly limited as long as the solvent evaporates and adhesion between particles does not occur. For example, the drying time is 1 hour or more and 5 hours or less. The drying atmosphere is not particularly limited, but may be an acidic atmosphere (for example, an air atmosphere) from the viewpoint of ease of handling and cost.

  As shown in FIG. 5, the lithium nickel composite oxide containing boron may be added as a compound containing boron (a salt containing boron) during crystallization (step S1 '). Thereby, boron can be uniformly contained in the obtained nickel compound. Next, a nickel compound containing boron and a lithium compound are mixed (step S10 ') and fired (step S20), whereby a lithium nickel composite oxide containing boron can be obtained. In the above-described mixing step (step S10), when a boron compound is mixed, the obtained lithium nickel composite oxide can be easily adjusted to the targeted boron addition amount.

3. Non-aqueous electrolyte secondary battery The positive electrode active material 10 obtained by the manufacturing method of this embodiment described above can be suitably used for the positive electrode of a non-aqueous electrolyte secondary battery (hereinafter also referred to as “secondary battery”). . The secondary battery includes, for example, a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator. In addition, the secondary battery may include, for example, a positive electrode, a negative electrode, and a solid electrolyte. Further, the secondary battery may be composed of the same components as those of a general non-aqueous electrolyte secondary battery.

  Hereinafter, a secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator will be described. The embodiment described below is merely an example, and the nonaqueous electrolyte secondary battery of the present invention can be variously modified based on the knowledge of those skilled in the art based on the embodiment described in the present specification. It can be implemented in an improved form. Further, the use of the nonaqueous electrolyte secondary battery of the present embodiment is not particularly limited.

(A) Positive electrode Using the positive electrode active material 100 described above, for example, a positive electrode of a non-aqueous electrolyte secondary battery can be produced as follows.

  First, a powdered positive electrode active material 100, a conductive material, and a binder are mixed, and if necessary, a target solvent such as activated carbon and viscosity adjustment is added and kneaded to prepare a positive electrode mixture paste. . In the positive electrode mixture pace produced using the positive electrode active material 100 according to this embodiment, the occurrence of gelation is greatly suppressed.

  Each mixing ratio in the positive electrode mixture paste is not particularly limited. For example, when the total solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the positive electrode active material 100 is 60 to 95 masses. The conductive material is preferably 1 to 20 parts by mass, and the binder is preferably 1 to 20 parts by mass.

  The obtained positive electrode mixture paste is applied to the surface of a current collector made of, for example, an aluminum foil and dried to disperse the solvent. If necessary, pressurization may be performed by a roll press or the like to increase the electrode density. In this way, a sheet-like positive electrode can be produced. The sheet-like positive electrode can be cut into an appropriate size or the like according to the target battery and used for battery production. However, the method for manufacturing the positive electrode is not limited to the illustrated one, and other methods may be used.

  In producing the positive electrode, as the conductive agent, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black, ketjen black, and the like can be used.

  The binder plays a role of holding the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluorine rubber, ethylene propylene diene rubber, styrene butadiene, cellulosic resin, polyacrylic. An acid or the like can be used.

  If necessary, a positive electrode active material 100, a conductive material, and activated carbon are dispersed, and a solvent that dissolves the binder is added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode mixture in order to increase the electric double layer capacity.

(B) Negative electrode For the negative electrode, metallic lithium, lithium alloy, or the like, or a negative electrode mixture in which a binder is mixed with a negative electrode active material capable of inserting and extracting lithium ions, and an appropriate solvent is added. Is applied to the surface of a metal foil current collector such as copper, dried, and compressed to increase the electrode density as necessary.

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

(C) Separator A separator is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode and retains the electrolyte, and a thin film such as polyethylene or polypropylene and a film having many minute holes can be used.

(D) Non-aqueous electrolyte The non-aqueous electrolyte is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.

  Examples of the organic solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; and tetrahydrofuran, 2- One kind selected from ether compounds such as methyltetrahydrofuran and dimethoxyethane, sulfur compounds such as ethylmethylsulfone and butanesultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. are used alone or in admixture of two or more. be able to.

As the supporting salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , or a composite salt thereof can be used.

  Furthermore, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, and the like.

(E) Shape and configuration of secondary battery The shape of the secondary battery can be various, such as a cylindrical type and a stacked type. In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the obtained electrode body is impregnated with a non-aqueous electrolyte and communicated with the positive electrode current collector and the outside. The positive electrode terminal and the negative electrode current collector and the negative electrode terminal communicating with the outside are connected using a current collecting lead or the like and sealed in a battery case to complete a non-aqueous electrolyte secondary battery. .

(F) Characteristics The nonaqueous electrolyte secondary battery using the positive electrode active material 100 obtained by the manufacturing method according to the present embodiment can have a high capacity and a low positive electrode resistance. The non-aqueous electrolyte secondary battery using the positive electrode active material 100 obtained in a particularly preferred form is, for example, 190 mAh / g or more, preferably when used for the positive electrode of a 2032 type coin battery as shown in the examples described later. A high initial discharge capacity of 200 mAh / g or more can be obtained.

  Next, the positive electrode active material for a non-aqueous electrolyte secondary battery, the method for producing the positive electrode active material for a non-aqueous electrolyte secondary battery, and the non-aqueous electrolyte secondary battery according to an embodiment of the present invention will be described in detail with reference to examples. . The present invention is not limited to these examples. In addition, the analysis method of the metal contained in the positive electrode active material in an Example and a comparative example and the various evaluation methods of a positive electrode active material are as follows.

[Whole particle composition]
The positive electrode active material was dissolved in nitric acid, and then measured with an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation, ICPS-8100).

[Identification of compound species]
The positive electrode active material was evaluated with an X-ray diffractometer (manufactured by PANALYTICAL, X′Pert, PROMRD).

[Evaluation of battery characteristics]
(Coin battery structure)
For the evaluation of the capacity of the positive electrode active material, a 2032 type coin battery CBA (hereinafter referred to as “coin type battery CBA”) having the structure shown in FIG. 6 was used. The coin-type battery CBA includes a case CA, an electrode EL housed in the case, and a wave washer WW.

  The case has a positive electrode can PC that is hollow and open at one end, and a negative electrode can NC that is disposed in the opening of the positive electrode can PC. When the negative electrode can NC is disposed in the opening of the positive electrode can PC, A space for accommodating the electrode EL is formed between the negative electrode can NC and the positive electrode can PC.

  The electrode is composed of a positive electrode PC, a separator SE, and a negative electrode NC, which are stacked in this order. The positive electrode PE contacts the inner surface of the positive electrode can PC, and the negative electrode NE contacts the inner surface of the negative electrode can NC. It is accommodated in the case CA. The case CA includes a gasket GA, and the gasket GA is fixed so as to maintain a non-contact state between the positive electrode can PC and the negative electrode can NC.

  Further, the gasket GA also has a function of sealing the gap between the positive electrode can PC and the negative electrode can NC so as to block the inside and the outside of the case CA in an airtight and liquid tight manner. The coin-type battery CBA was produced as follows.

(Production of coin-type battery)
First, a slurry in which 20.0 g of the obtained positive electrode active material, 2.35 g of acetylene black, and 1.18 g of polyvinylidene fluoride were dispersed in N-methyl-2-pyrrolidone (NMP) was placed on an Al foil per 1 cm 2. After coating so that 5.0 mg of the positive electrode active material was present, it was dried in the air at 120 ° C. for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into a strip shape having a width of 66 mm, and roll-pressed with a load of 1.2 t to prepare the positive electrode 2. The positive electrode 2 was punched into a circle having a diameter of 13 mm and dried at 120 ° C. for 12 hours in a vacuum dryer.
Next, using the positive electrode 2, the coin-type battery 1 was produced in a glove box in an Ar atmosphere in which the dew point was controlled at −80 ° C. At this time, a lithium foil punched into a disk shape having a diameter of 14 mm was used for the negative electrode 3.

The initial discharge capacity is left for about 24 hours after the coin-type battery 10 is manufactured. After the open circuit voltage OCV (open circuit voltage) is stabilized, the current density with respect to the positive electrode is set to 0.1 mA / cm ² and the cut-off voltage 4 The battery was charged to 3 V, and after a pause of 1 hour, the discharge capacity when discharged to a cutoff voltage of 3.0 V was measured and used as the initial discharge capacity.

[Method of evaluating positive electrode mixture paste stability]
The positive electrode mixture paste was 20.0 g of a positive electrode active material for a non-aqueous electrolyte secondary battery, 2.35 g of carbon powder as a conductive additive, 14.7 g of KF polymer L # 7208 (solid content 8 mass%) as a binder, As a solvent, 5.1 g of N-methyl-2-pyrrolidone (NMP) was prepared by kneading for 15 minutes using a rotating and rotating mixer. The stability of the positive electrode mixture paste was evaluated by observing the prepared positive electrode mixture paste in a sealed polypropylene container and storing the tube at room temperature for 7 days. Viscosity was confirmed by visual check and a glass rod, and those that maintained fluidity and did not gel were evaluated as ◯, and those that gelled and could not be stirred even when trying to stir with a glass rod were evaluated as x.

(Example 1)
[Lithium nickel composite oxide]
Using a 106 μm sieve, a portion of 106 μm or less was fractionated into 3000 g of a nickel composite oxide (composition formula: Ni _0.87 Co _0.09 Al _0.04 O ₂ ) having an average particle diameter of 13.0 μm prepared by a known technique. 7.46 g of the boric acid powder (H ₃ BO ₃ , manufactured by Wako Pure Chemical Industries, Ltd.) was added, and then 1005.15 g of lithium hydroxide (LiOH) was added and mixed. Mixing was performed using a shaker mixer apparatus (TURBULA Type T2C manufactured by Willy et Bacofen (WAB)). In addition, the said nickel composite oxide was obtained by heat-processing the nickel composite hydroxide produced using the crystallization method. The obtained mixture was calcined at 750 ° C. for 8 hours in an oxygen stream (oxygen: 100% by volume), cooled and then crushed with a hammer mill to obtain a calcined powder.

The fired powder obtained was 0.03% by mass of boron (B), 7.39% by mass of lithium (Li), 52.3% by mass of nickel (Ni), and cobalt (Co) by ICP emission spectroscopic analysis. 5.75% by mass and 1.07% by mass of aluminum (Al) were confirmed, and the substance ratio of Ni: Co: Al was 0.87: 0.09: 0.04. The mass ratio of lithium to Co, Al was 1.03. Further, in X-ray diffraction, only a peak corresponding to lithium nickelate (LiNiO ₂ ) is observed, no peak similar to a boron compound is observed, and added boron is dissolved in the lithium nickel composite oxide crystal. Was confirmed.

[Preparation of coating liquid containing silicon]
Ethyl alcohol diluted to 19.42 g of ethyl alcohol 0.22 g of tetraethoxysilane (Si (OC ₂ H ₅ ) ₄ , manufactured by Tokyo Chemical Industry Co., Ltd.), 0.21 g of acetylacetone, and a pure water concentration of 10% by mass After adding 0.37 g of solution and mixing, it heated and stirred at 60 degreeC, and obtained the coating liquid containing the hydrolyzate of tetraethoxysilane.

[Coating]
100 g of lithium nickel composite oxide containing 0.03% by mass of boron is charged into a tumbling fluidized coating apparatus (manufactured by Paulek, MP-01), and the hydrolyzate of tetraethoxylane is mixed with mixing. The coating layer forming solution contained was sprayed and coated. After the completion of spraying, it was dried at 110 ° C. for 4 hours to obtain a boron-containing lithium nickel composite oxide coated with a silicon compound as a positive electrode active material.

  The obtained positive electrode active material for a lithium ion secondary battery was confirmed to contain 0.03% by mass of silicon by ICP emission spectroscopic analysis. In addition, after embedding in an epoxy resin and preparing a sample that was cross-polished to expose the cross section of the particles, the state of silicon distribution was confirmed by energy dispersive X-ray analysis (EDS). The positive electrode active material detected and detected was confirmed to have a film containing tetraethoxysilane and its hydrolyzate formed on the surface of lithium nickel composite oxide particles containing a small amount of boron. It was done.

  Using the obtained positive electrode active material, a coin cell for evaluation was prepared by the above-described method, and the initial discharge capacity was measured by the above-described evaluation method, which showed 200 mAh / g. Further, when the stability of the positive electrode mixture paste was evaluated by the above-described method, the positive electrode mixture paste after storage maintained fluidity, and the stability evaluation result was ◯.

(Example 2)
A boron-containing lithium nickel composite oxide coated with a zinc compound was synthesized in the same manner as in Example 1 except that the following solution was used as the coating solution.
[Coating solution containing zinc]
Ethyl diluted to 19.81 g of ethyl alcohol with 0.27 g of zinc (II) acetylacetonate (Zn (C ₅ H ₇ O ₂ ) ₂ , manufactured by Tokyo Chemical Industry Co., Ltd.) and a pure water concentration of 10% by mass After adding and mixing the alcohol solution 0.19g, it heated and stirred at 60 degreeC, and obtained the solution for coating layer formation containing the hydrolyzate of diethoxy zinc.

  The obtained positive electrode active material was confirmed to contain 0.07% by mass of zinc by ICP emission spectroscopic analysis. Further, when the zinc distribution state was confirmed by the same method as in Example 1, zinc was detected only in the vicinity of the particle surface, and the obtained positive electrode active material was particles of lithium nickel composite oxide containing a small amount of boron. It was confirmed that a coating containing diethoxyzinc and its hydrolyzate was formed on the surface.

  Using the positive electrode active material, a coin cell for evaluation was prepared by the above-described method, and the initial discharge capacity was measured by the above-described evaluation method. As a result, it was 201 mAh / g. Further, when the stability of the positive electrode mixture paste was evaluated by the above-described method, the positive electrode mixture paste after storage maintained fluidity, and the stability evaluation result was ◯.

(Example 3)
A boron-containing lithium nickel composite oxide coated with an aluminum compound was synthesized in the same manner as in Example 1 except that the following solution was used as the coating solution.
[Aluminum compound coating solution]
To 19.63 g of ethyl alcohol, 0.28 g of aluminum ethyl acetoacetate diisopropylate (Al (OC ₃ H ₇ ) ₂ (C ₆ H ₉ O ₃ ), manufactured by Kawaken Fine Chemical Co., Ltd.) and a pure water concentration of 10% by mass After adding 0.37 g of the diluted ethyl alcohol solution and mixing, the mixture was heated to 60 ° C. and stirred to obtain a coating layer forming solution containing a hydrolyzate of aluminum ethyl acetoacetate diisopropylate.

  The obtained positive electrode active material was confirmed to contain 0.02% by mass of aluminum by ICP emission spectroscopic analysis. Further, when the aluminum distribution state was confirmed by the same method as in Example 1, aluminum was detected only in the vicinity of the particle surface, and the obtained positive electrode active material was lithium nickel composite oxide particles containing a small amount of boron. It was confirmed that a film containing aluminum ethyl acetoacetate diisopropylate and its hydrolyzate was formed on the surface.

  Using the positive electrode active material, a coin cell for evaluation was prepared by the above-described method, and the initial discharge capacity was measured by the above-described evaluation method. As a result, it was 202 mAh / g. Further, when the stability of the positive electrode mixture paste was evaluated by the above-described method, the positive electrode mixture paste after storage maintained fluidity, and the stability evaluation result was ◯.

Example 4
Under the same conditions as in Example 3, except that the amount of boric acid powder added was adjusted so that the boron (B) content in the obtained fired powder (lithium nickel composite oxide) was 0.10% by mass. The positive electrode active material was manufactured and evaluated. The evaluation results are shown in Table 1.

(Example 5)
The positive electrode active material was produced and evaluated under the same conditions as in Example 3 except that the coating amount of the aluminum compound was adjusted so that the aluminum content in the obtained positive electrode active material was 0.10% by mass. did. The evaluation results are shown in Table 1.

(Comparative Example 1)
Similarly to Example 1, 3000 g of nickel composite oxide (composition formula: Ni _0.87 Co _0.09 Al _0.04 O ₂ ) prepared by a known technique and having an average particle diameter of 13.0 μm was added to lithium hydroxide ( LiOH) 1005.15 g was added and mixed. Mixing was performed using a shaker mixer apparatus (TURBULA Type T2C manufactured by Willy et Bacofen (WAB)). The obtained mixture was calcined at 750 ° C. for 8 hours in an oxygen stream (oxygen: 100% by volume), cooled and then crushed with a hammer mill to obtain a calcined powder.

The obtained calcined powder was measured by ICP emission spectroscopic analysis. Lithium (Li) 7.40% by mass, Nickel (Ni) 52.3% by mass, Cobalt (Co) 5.76% by mass, Aluminum (Al) 1.08% by mass was confirmed, and the substance amount ratio of Ni: Co: Al was 0.87: 0.09: 0.04, and the substance amount of lithium with respect to the moles of Ni, Co, and Al. The ratio was 1.03. Further, in X-ray diffraction, only a peak corresponding to lithium nickelate (LiNiO ₂ ) was observed, and it was confirmed that the lithium nickel composite oxide had the above composition.

  Using the lithium nickel composite oxide, the battery characteristic evaluation and the positive electrode mixture paste stability evaluation were performed in the same manner as in Example 1. The initial discharge capacity was 201 mAh / g, the positive electrode mixture paste after storage was gelled so that it could not be deformed with a glass rod, and the stability evaluation result was x.

(Comparative Example 2)
The boron-containing lithium nickel composite oxide prepared in the same manner as in Example 1 is not coated with a compound containing at least one of silicon, zinc, and aluminum, and at least the silicon, zinc, and aluminum are used on the particle surface. As a positive electrode active material in which a compound film containing one kind was not formed, battery characteristics evaluation and positive electrode mixture paste stability evaluation were performed in the same manner as in Example 1. The evaluation results are shown in Table 1.

(Comparative Example 3)
Using the lithium nickel composite oxide not containing boron synthesized in Comparative Example 1 and using the lithium nickel composite oxide not containing boron coated with the compound containing aluminum in the same manner as in Example 3, as the positive electrode active material Obtained. The evaluation results are shown in Table 1.

(Comparative Example 4)
A positive electrode active material was produced under the same conditions as in Example 3 except that pure water was not added when obtaining the coating layer forming solution. When the aluminum content of the obtained positive electrode active material for a non-aqueous electrolyte secondary battery was analyzed by ICP emission spectroscopic analysis, the content was significantly lower than the target aluminum content, and the positive electrode active material was not evaluated. .

  The results of measuring the initial discharge capacity using the positive electrode active materials obtained in Examples and Comparative Examples and the results of evaluating the stability of the positive electrode mixture paste are summarized in Table 1.

(Evaluation results)
A film containing a partial hydrolysis product of silicon (Si), zinc (Zn), aluminum (Al) alkoxide or chelate compound was formed on the surface of the particles of lithium nickel composite oxide containing a small amount of boron in the example. The positive electrode active material for lithium ion secondary batteries was able to suppress gelation of the positive electrode mixture paste, and a high initial discharge capacity exceeding 200 mAh / g was obtained. On the other hand, neither of the positive electrode active materials having a film formed on the particle surfaces of the lithium nickel composite oxides of Comparative Examples 1 and 2 could suppress the gelation of the positive electrode mixture paste. In addition, the positive electrode active material for a non-aqueous electrolyte secondary battery in which a film was formed on the surface of particles of lithium nickel composite oxide not containing boron in Comparative Example 3 can suppress gelation of the positive electrode mixture paste, but Example 1 In comparison, the initial discharge capacity decreased. In Comparative Example 4 where the aluminum compound was not hydrolyzed, the coating layer was not sufficiently formed.

  The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention increases the capacity of the battery when used as a positive electrode material of a battery, and can suppress gelation of a positive electrode mixture paste, particularly for hybrid vehicles and electric vehicles. It is suitable as a positive electrode active material of a lithium ion battery used as a power source.

DESCRIPTION OF SYMBOLS 100 ... Positive electrode active material 10 ... Lithium nickel composite oxide particle 1 ... Primary particle 2 ... Secondary particle 20 ... Coating layer CBA ... Coin type battery CA ... Case PE ... Positive electrode NE ... Negative electrode GA ... Gasket PE ... Positive electrode NE ... Negative electrode SE ... Separator

Claims (14)

  A lithium nickel composite oxide particle containing boron, and a compound containing at least one of silicon (Si), zinc (Zn), and aluminum (Al) attached to at least a part of the surface of the particle. A positive electrode active material for a non-aqueous electrolyte secondary battery, comprising: a coating layer including the coating layer.   2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein a content of the boron is 0.002% by mass or more and 0.15% by mass or less with respect to the entire positive electrode active material.   The total content of silicon (Si), zinc (Zn), and aluminum (Al) in the coating layer is 0.01% by mass or more and 0.15% or less with respect to the whole positive electrode active material, The positive electrode active material for non-aqueous electrolyte secondary batteries according to claim 1 or 2.   In the lithium-nickel composite oxide particles, the mass (molar) ratio of lithium (Li), nickel (Ni), cobalt (Co), and element M is Li: Ni: Co: M = s: (1 -Xy): x: y (where 0.95≤s≤1.30, 0.05≤x≤0.35, 0≤y≤0.1, M is Mn, V, Mg, Mo) 4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, represented by: at least one element selected from Nb, Ti, and Al).   The lithium nickel composite oxide particles include secondary particles formed by aggregating a plurality of primary particles, and at least a part of the boron is dissolved in the lithium nickel composite oxide particles. The positive electrode active material for nonaqueous electrolyte secondary batteries as described in any one of Claims 1-4.   The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the coating layer contains a hydrolysis product of an organometallic compound having an alkoxy group. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising:
Mixing a nickel compound, a boron compound and a lithium compound;
Firing the mixture obtained by the mixing;
It is obtained by dissolving an organometallic compound containing at least one of silicon (Si), zinc (Zn), and aluminum (Al) in a solvent on the particle surface of the lithium nickel composite oxide obtained by the firing. Depositing the coating liquid,
Drying the lithium nickel composite oxide to which the coating liquid is attached;
With
The organometallic compound is at least one of a metal alkoxide having an alkoxy group and a metal chelate compound in which at least one of the alkoxy groups of the metal alkoxide is substituted with acetylacetonate or alkyl acetoacetate,
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery.   The said coating liquid is a manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries of Claim 7 containing the product obtained by hydrolyzing the said organometallic compound.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8, wherein the hydrolysis is performed by adding pure water to the coating solution and stirring at room temperature.   The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 9, wherein the nickel compound is at least one of nickel hydroxide and nickel oxide.   The nonaqueous system according to any one of claims 7 to 10, wherein the lithium compound is at least one of lithium hydroxide, lithium carbonate, lithium oxide, lithium nitrate, lithium chloride, and lithium sulfate. A method for producing a positive electrode active material for an electrolyte secondary battery. The boron compound is boric acid _(H 3 _BO 3), at least one of boron oxide _(B 2 _{O 3)} or lithium metaborate (LiBO _2), one of the claims 7 to claim 11 one The manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries as described in claim | item.   The manufacturing method of the positive electrode active material for non-aqueous electrolyte secondary batteries as described in any one of Claims 7-12 whose said organometallic compound is an acetylacetonate metal complex. The positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 7 to 13, wherein the baking is performed in an oxygen atmosphere at a maximum baking temperature of 700 ° C or higher and 800 ° C or lower. Production method.

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