JP6390230B2 - Coated lithium-nickel composite oxide particles and method for producing coated lithium-nickel composite oxide particles - Google Patents

Description

  The present invention relates to a coated lithium-nickel composite oxide particle having a high nickel content, and relates to a coated lithium-nickel composite oxide particle having improved stability in the atmosphere and easy to handle, and a method for producing the same.

  In recent years, with the rapid expansion of small electronic devices such as mobile phones and notebook computers, the demand for lithium ion secondary batteries as a chargeable / dischargeable power source has increased rapidly. As a positive electrode active material that contributes to charging / discharging in the positive electrode of a lithium ion secondary battery, lithium-cobalt oxide (hereinafter sometimes referred to as cobalt-based) is widely used. However, by optimizing the battery design, the capacity of the cobalt-based positive electrode is improved to the same level as the theoretical capacity, and it is becoming difficult to further increase the capacity.

  Therefore, development of lithium-nickel composite oxide particles using lithium-nickel oxide having a theoretical capacity higher than that of conventional cobalt-based materials is in progress. However, pure lithium-nickel oxide has problems in safety, cycle characteristics, etc. due to its high reactivity with water, carbon dioxide and the like, and it has been difficult to use it as a practical battery. Accordingly, lithium-nickel composite oxide particles to which transition metal elements such as cobalt, manganese, iron or the like or aluminum are added have been developed as measures for improving the above problems.

  The lithium-nickel composite oxide is a composite oxide particle represented by a transition metal composition Ni0.33Co0.33Mn0.33 called a so-called ternary system in which equimolar amounts of nickel, manganese, and cobalt are added (hereinafter, referred to as “ternary system”). Ternary system) and so-called nickel-based lithium-nickel composite oxide particles (hereinafter sometimes referred to as nickel-based) having a nickel content exceeding 0.65 mol. From the viewpoint of capacity, the nickel system having a high nickel content has a great advantage over the ternary system.

However, nickel is more sensitive to the environment than cobalt and ternary because of its high reactivity with water and carbon dioxide, and has a feature that it absorbs moisture and carbon dioxide (CO ₂ ) in the air more easily. is there. It has been reported that moisture and carbon dioxide are deposited on the particle surface as impurities such as lithium hydroxide (LiOH) and lithium carbonate (Li ₂ CO ₃ ), respectively, and adversely affect the positive electrode manufacturing process and battery performance.

  By the way, in the manufacturing process of a positive electrode, it passes through the process of apply | coating and drying the positive mix slurry which mixed lithium- nickel composite oxide particle | grains, a conductive support agent, a binder, the organic solvent, etc. on collectors, such as aluminum. In general, lithium hydroxide may react with a binder to rapidly increase the slurry viscosity or cause the slurry to gel in the positive electrode mixture slurry manufacturing process. These phenomena can cause defects and defects, and a decrease in the yield of positive electrode manufacturing, resulting in a difference in product quality. In addition, during charging and discharging, these impurities may react with the electrolytic solution to generate gas, which may cause problems in battery stability.

  Therefore, when nickel-based material is used as the positive electrode active material, it is necessary to perform the positive electrode manufacturing process in a dry (low humidity) environment in a decarboxylation atmosphere in order to prevent the generation of impurities such as lithium hydroxide (LiOH). is there. Therefore, despite the high theoretical capacity of nickel-based materials, which is promising as a material for lithium ion secondary batteries, high installation costs are required to maintain the manufacturing environment, and this is a barrier to their spread. There is a problem.

In order to solve such a problem, a method of coating the surface of the lithium-nickel composite oxide particles by using a coating agent has been proposed. Such coating agents are broadly classified into inorganic coating agents and organic coating agents, and inorganic coating agents include fumed silica, titanium oxide, aluminum oxide, aluminum phosphate, cobalt phosphate, and fluoride. of materials such as lithium, as the coating agent of organic, carboxymethyl cellulose, the material such as a fluorine-containing polymer has been proposed.

  For example, Patent Document 1 discloses a method of forming a lithium fluoride (LiF) or fluorine-containing polymer layer on the surface of lithium-nickel composite oxide particles, and Patent Document 2 discloses a fluorine-containing polymer formed on lithium-nickel composite oxide particles. A method of forming a layer and adding a Lewis acid compound for further neutralizing impurities has been proposed. In both treatments, lithium-nickel composite oxide particles are modified to be hydrophobic by a coating layer containing a fluorine-based material, suppressing moisture adsorption and suppressing deposition of impurities such as lithium hydroxide (LiOH). Is possible.

  However, the coating layer containing the above-described fluorine-based material used in these coating methods is only attached to the lithium-nickel composite oxide particles only by electrostatic attraction. Therefore, the adhesion between the coating layer and the lithium-nickel composite oxide particles is low, and the coating layer is likely to be detached from the lithium-nickel composite oxide particles in a slurry manufacturing process or the like. As a result, it is not only possible to sufficiently suppress defects, defects, and yield reduction, which are problems in the nickel system, but it can substantially solve the problem of battery stability due to the generation of impurities. It was not a thing.

JP 2013-179063 A Special table 2011-511402 gazette

  In view of the above-described problems of the prior art, the present invention provides a coated lithium-nickel composite oxide that can be handled in an air atmosphere and that can provide a coating of lithium-nickel composite oxide particles that does not adversely affect battery characteristics. It is an object to provide product particles and a method for producing the same.

  As a result of intensive research in order to solve the above-described problems in the prior art, the present inventors have coated an organic sulfur compound having a high affinity with the nickel-based lithium-nickel composite oxide particles. It has been found that an integrated monomolecular film is formed. The coated lithium-nickel composite oxide in which a self-assembled monomolecular film is formed of such an organic sulfur compound is excellent in that the particles can suppress the permeation of moisture and carbon dioxide gas while having strong adhesion to the coating layer. As a result, the present invention was completed.

  Specifically, the present invention provides the following.

That is, in the first invention, the surface of the nickel-based lithium-nickel composite oxide particles is coated with an organic sulfur compound, and the coating amount of the organic sulfur compound is relative to the specific surface area of the lithium-nickel composite oxide particles. This is a coated lithium-nickel composite oxide particle for a positive electrode active material for a lithium ion battery that is 4.05 × 10 ⁻⁶ mol / m ² or more and 1.62 × 10 ⁻⁵ mol / m ² or less.

According to a second invention, the organic sulfur compound is a thiol group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring, or a disulfide group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring. The coated lithium-nickel composite oxide particles for the lithium ion battery positive electrode active material described.
A third invention is the coated lithium-nickel composite oxide particle according to the first or second invention, wherein the molecular orbital energy of the highest occupied orbit of the organic sulfur compound is less than -9.0 eV.

  A fourth invention is a coated lithium-nickel composite oxide particle according to any one of the first to third inventions, which is a disulfide group-containing molecule having a diphenyl disulfide skeleton or a thiol group-containing molecule having a triazine dithiol skeleton. .

  According to a fifth invention, the organic sulfur compound is diphenyl disulfide, 2-naphthalenethiol, 6- (dibutylamino) -1,3,5-triazine-2,4-dithiol and 6- (anilino) -1,3. , 5-triazine-2,4-dithiol. The coated lithium-nickel composite oxide particle according to any one of the first to fourth inventions, which is at least one compound selected from the group consisting of

A sixth invention is the coated lithium-nickel composite oxide particle according to any one of the first to fifth inventions, wherein the organic sulfur compound is represented by the following general formula (1).
_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
(Wherein x is 0.80 to 1.10, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.65, M represents at least one element selected from Co or Mn, and N represents at least one element selected from Al, In, or Sn.)

  A seventh invention is the coated lithium-nickel composite oxide particle according to any one of the first to sixth inventions, which is a spherical particle having an average particle diameter of 5 to 20 μm.

  The eighth invention is the coated lithium-nickel composite oxide according to any one of the first to seventh inventions, wherein the organic sulfur compound-containing layer formed on the coated lithium-nickel composite oxide particles is a monomolecular film. It is a physical particle.

  A ninth invention includes the steps of mixing the organic sulfur compound and the lithium-nickel composite oxide particles with a polar solvent within a temperature range from room temperature to immediately before the decomposition temperature of the molecule. The method for producing coated lithium-nickel composite oxide particles according to any one of the inventions.

  According to the present invention, coated lithium-nickel composite oxide particles in which the surface of nickel-based lithium-nickel composite oxide particles is coated with an organic sulfur compound absorbs moisture and carbon dioxide gas because of its high environmental stability. With the excellent lithium-nickel composite oxide particles that can suppress the generation of impurities due to the process, do not easily leave the coating layer, and are stable electrochemically, and a method for producing the same is there.

It is a correlation diagram of the value of the molecular orbital energy in HOMO computed from the oxidation potential of each molecular species and the molecular orbital calculation by MO method.

  The coated lithium-nickel composite oxide particles of the present invention and the production method thereof will be described in detail below. In addition, this invention is not limitedly interpreted by the following detailed description. In the present invention, secondary particles in which primary particles are aggregated may be referred to as lithium-nickel composite oxide particles.

[Nickel-based lithium-nickel composite oxide particles]
The nickel-based lithium-nickel composite oxide is spherical and preferably has an average particle size of 5 to 20 μm. By setting it as such a range, while having favorable battery performance as nickel-type lithium-nickel composite oxide particle, and being able to make compatible the lifetime (cycle characteristic) of a favorable battery, it is preferable.

  The nickel-based lithium-nickel composite oxide is preferably oxide particles represented by the following general formula (1).

_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
In the formula, x is 0.80 to 1.10, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.65, and M is Represents at least one element selected from Co or Mn, and N represents at least one element selected from Al, In, or Sn.

  Note that the value of 1-yz (nickel content) is preferably a value exceeding 0.70, and more preferably a value exceeding 0.80, from the viewpoint of capacity.

  The electrode energy densities (Wh / L) of cobalt-based (LCO), ternary (NCM), and nickel-based (NCA) are 2160 Wh / L (LiCoO 2) and 2018.6 Wh / L (LiNi 0.33 Co 0.33 Mn 0.33 Co 0, respectively. .33O2), 2376 Wh / L (LiNi0.8Co0.15Al0.05O2). Therefore, a high-capacity battery can be manufactured by using the nickel-based lithium-nickel composite oxide particles as a positive electrode active material of a lithium ion battery.

[Organic sulfur compounds]
The present invention is characterized in that lithium-nickel composite oxide particles are coated with an organic sulfur compound. The organic sulfur compound is, for example, a thiol group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring or a disulfide group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring. Since it is one of the adsorptive functional groups shown, it can be preferably coated on basic lithium-nickel composite oxide particles. Further, sulfur molecules in thiol groups and disulfide groups have high affinity with transition metals and can be preferably used because they are chemically adsorbed to lithium-nickel composite oxide particles.

  The predetermined organic sulfur compound is a thiol group-containing molecule (R-SH) molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring, or a disulfide group-containing molecule (RS-SR) having a cyclic skeleton that is an aromatic ring or a heterocyclic ring. It is. The reaction mechanism between the metal (M) and the organic sulfur compound can be represented by the formulas (2) and (3).

^{_{RS-H + M n 0 →}} RS-M + · M n-1 0 + 1 / 2H 2 ··· formula (2)

^{_{RS-SR + M n 0 →}} 2 (RS-M +) · M n-2 0 ··· formula (3)

  The arrangement has regular properties determined by the arrangement of atoms on the underlying metal surface and the interaction between the molecules of the adsorbed organic sulfur compound. Therefore, if the organic sulfur compound to be selected contains a hydrophobic group, the surface of the positive electrode material coated with these compounds becomes hydrophobic, preventing moisture absorption. Further, if the selected organic sulfur compound is electrochemically stable in the battery driving potential range, there is no influence on the battery characteristics.

The organic sulfur compound has a molecular orbital energy value of HOMO (highest occupied orbital molecular orbital ) of less than −9.0 eV, more preferably less than −9.3 eV, and contains a hydrophobic group. preferable. When the molecular orbital energy value in HOMO is less than −9.0 eV, more preferably less than −9.3 eV, the battery characteristics are not adversely affected as described later. In addition, the inclusion of a hydrophobic group in the organic sulfur compound is more favorable because it can further prevent moisture absorption of the lithium-nickel composite oxide particles.

Examples of such organic sulfur compounds include diphenyl disulfide having diphenyl disulfide as a basic skeleton, di-p-tolyl disulfide, bis (4-methoxyphenyl) disulfide, 2-naphthalenethiol, benzenethiol, benzyl mercaptan, and triazine skeleton. 6- (dibutylamino) 1,3,5-triazine-2,4-dithiol, 2-anilino-4,6 dimercapto-1,3,5-triazine, 6- (arinino) 1,3,5-triazine Preferred examples include organic sulfur compounds such as -2,4-dithiol .

<Redox potential>
The molecular species has a specific redox potential, and there is a correlation known as the Nernst equation between the logarithm of the concentration ratio of the oxidant and the reductant and the redox potential. That is, the lower the molecular orbital energy level of the molecular species HOMO, the more difficult it is to extract electrons, so the oxidation potential becomes higher (noble), and the molecular orbital energy level of LUMO (Lowest Unoccupied Molecular Orbital) is higher. The higher the value, the harder it is to give electrons, and the reduction potential increases in the negative (base) direction. FIG. 1 shows a correlation diagram between the oxidation potential of molecular species extracted from literature and the value of molecular orbital energy in HOMO calculated by MO method (Molecular Orbital method). As shown in FIG. 1, there is a linear relationship between the oxidation potential of molecular species and the value of molecular orbital energy in HOMO, and the potential for electrochemical oxidation can be estimated from the value of molecular orbital energy in HOMO of molecular species. . Here, since the lithium-nickel composite oxide-based lithium ion battery drive has an upper limit voltage of 4.0 to 4.3 V, the energy level of HOMO corresponding to this is −9.0 in terms of FIG. It corresponds to -9.3 eV. Therefore, if a molecule having a molecular orbital energy value of HOMO of less than −9.0 eV, more preferably less than −9.3 eV is selected as the organic sulfur compound of the present invention, within the driving voltage range of the lithium ion battery. The organic sulfur compound does not cause an oxidation reaction on the electrode, which is favorable. Therefore, more preferable coated lithium-nickel composite oxide particles can be obtained by coating an organic sulfur compound having a molecular orbital energy value of HOMO of less than −9.0 eV, more preferably less than −9.3 eV.

<SAM (Self-Integrated Monolayer)>
The organic sulfur compound in the coated lithium-nickel composite oxide particles of the present invention forms a SAM (self-assembled monolayer, Self-Assembly Monolayer) and is coated. As will be described later, the SAM forms an ultra-thin film, and the change given to the three-dimensional shape to be coated is extremely small even on the inner wall of the pores and the surface having the uneven shape.

  In general, microelements such as atoms, molecules, fine particles, and clusters may spontaneously assemble to form a regular arrangement. One of material processes using this self-assembly is the formation of a single layer film / multilayer film by self-assembly of organic molecules. The definition of such a self-assembled film is as follows: 1) a molecular aggregate formed when an organic molecule is chemisorbed on a solid surface, and 2) a molecule when the precursor molecule is in a liquid phase or gas phase. Compared with the aligned state, when it becomes an aggregate and forms a thin film, it becomes a molecular film in which molecular orientation and alignment regularity are remarkably improved.

  When a substrate made of a compound is immersed in a solution of a compound having affinity for a specific substance, the compound molecules are chemisorbed on the material surface to form a thin film. In this case, an aggregate is spontaneously formed by the interaction between adsorbed molecules during the adsorption process, and a molecular film in which the adsorbed molecules are densely aggregated and aligned is formed in some cases. In particular, when the adsorption molecular layer is a single layer, that is, when a monomolecular film is formed, it is called SAM.

  In the SAM formation process, since the reaction between the substrate and the molecule is a necessary condition for adsorption, the reactive functional group is adsorbed in the direction facing the substrate surface. The number of adsorbed molecules increases with time. Many molecules that self-assemble have long-chain alkyl groups and benzene nuclei. Between adjacent adsorbed molecules, van der Waals force and hydrophobic interaction occur between alkyl groups, and π-electron interaction acts between benzene nuclei. As a result, the aggregate of adsorbed molecules becomes thermodynamically stable, so that a monomolecular film in which molecules are densely integrated is formed.

  The formation of SAM is a self-stopping process in which film growth automatically stops when a monomolecular film is completed. In order to form a molecular level ultrathin film having a film thickness of 1 to 2 nm, film thickness control by precise process management is not required. If there is a gap through which the adsorbed molecules can enter, coating can be performed anywhere, and the change given to the three-dimensional shape of the coating target is so small that it can be ignored even on the inner wall of the pores or the surface with the uneven shape.

  The growth of SAM depends on the specific chemical reaction between the substrate and organic molecules, and a specific combination of substrate and molecules is required to form a SAM. Since the surface of the nickel-based lithium-nickel composite oxide particle is basic, it is effective to select an adsorption functional group that exhibits acidity, such as a thiol group-containing molecule.

[Method for producing coated lithium-nickel composite oxide particles]
Examples of a method for producing coated lithium-nickel composite oxide particles, that is, a method of coating lithium-nickel composite oxide particles with an organic sulfur compound include, for example, an organic sulfur compound from room temperature to immediately before the decomposition temperature of the molecule. The film can be coated by being directly mixed with the lithium-nickel composite oxide particles in a solution within a temperature range. In particular, heating is particularly preferred because the molecule can soften or melt and improve the uniformity of the coating.

  The mixing time is desirably determined according to the temperature in the solution. This is because the diffusion of molecules in the solution increases with temperature, and if the temperature is low, it is necessary to lengthen the mixing time. The mixing time range is 30 seconds to 10 hours, so that the organic sulfur compound can be coated. The solvent used for mixing is not particularly limited as long as it is a highly polar solvent, but it is particularly preferable to use water because it is excellent in cost and characteristics.

The amount of the organic sulfur compound used in the method according to the present invention is 4.05 × 10 ⁻⁶ mol / m ² to 1.62 × 10 ⁻⁵ mol / m ² per specific surface area of the lithium-nickel composite oxide particles. It is preferable that More preferably, it is from 8.10 × 10 ⁻⁶ mol / m ² to 1.62 × 10 ⁻⁵ mol / m ² . If it exceeds 1.62 × 10 ⁻⁵ mol / m ² , the excess organic sulfur compound may adversely affect the negative electrode, leading to a decrease in charge capacity / discharge capacity during cycling. Moreover, when it is less than 4.05 × 10 ⁻⁶ mol / m ² , the coating amount on the particles is small, and the effect tends to be difficult to obtain.

  Hereinafter, the present invention will be specifically described with reference to comparative examples. However, the present invention is not limited to the following examples.

[Example 1]
As nickel-based lithium-nickel composite oxide particles, 15 g of composite oxide particles having a transition metal composition represented by Li _1.03 Ni _0.82 Co _0.15 Al _0.03 are mixed with 20 ml of water and 0.0668 g of diphenyl disulfide ( 1.62 × 10 ⁻⁵ mol / m ² s) was mixed at room temperature. This mixing was performed using a homogenizer at a peripheral speed of 10.5 m / s and a stirring time of 1 minute. After mixing, water was separated by suction filtration and dried at 100 ° C. under reduced pressure for 2 hours to prepare coated lithium-nickel composite oxide particles, and the following evaluation was performed.

[Example 2]
The coated lithium-nickel composite oxide particles were similarly prepared except that the amount of diphenyl disulfide added to the coating material of Example 1 was changed to 0.0334 g (equivalent to 8.10 × 10 ⁻⁶ mol / m ² s), The following evaluation was performed.

[Example 3]
The coated lithium-nickel composite oxide particles were similarly prepared except that the amount of diphenyl disulfide added to the coating material of Example 1 was changed to 0.0167 g (equivalent to 4.05 × 10 ⁻⁶ mol / m ² s), The following evaluation was performed.

[Example 4]
The coated lithium-nickel composite oxide particles were prepared in the same manner except that 0.0490 g of 2-naphthalenethiol (equivalent to 1.62 × 10 ⁻⁵ mol / m ² s) was used as the coating material of Example 1, and the following: Was evaluated.

[Example 5]
The coated lithium-nickel composite oxide particles were prepared in the same manner except that 0.0245 g of 2-naphthalenethiol (equivalent to 8.10 × 10 ⁻⁶ mol / m ² s) was used as the coating material of Example 1. Was evaluated.

[Example 6]
The coated lithium-nickel composite oxide particles were prepared in the same manner except that 0.0123 g of 2-naphthalenethiol (equivalent to 4.05 × 10 ⁻⁶ mol / m ² s) was used as the coating material of Example 1. Was evaluated.

[Example 7]
Except for using 0.0833 g (corresponding to 1.62 × 10 ⁻⁵ mol / m ² s) of 6- (dibutylamino) -1,3,5 triazine-2,4-dithiol as the coating material of Example 1, the same Then, coated lithium-nickel composite oxide particles were prepared, and the following evaluation was performed.

[Example 8]
The same applies except that 0.0723 g of 6- (Alinino) 1,3,5-triazine-2,4-dithiol (equivalent to 1.62 × 10 ⁻⁵ mol / m ² s) was used as the coating material of Example 1. The coated lithium-nickel composite oxide particles were prepared and evaluated as follows.

[Comparative Example 1]
Evaluation was carried out as lithium-nickel composite oxide particles without performing the coating treatment of Example 1.

[Comparative Example 2]
The coated lithium-nickel composite oxide particles were prepared in the same manner except that the coating material of Example 1 was changed to 0.0083 g (corresponding to 2.03 × 10 ⁻⁶ mol / m ² s) of diphenyl disulfide. Evaluation was performed.

[Comparative Example 3]
The coated lithium-nickel composite oxide particles were similarly prepared except that 2-naphthalenethiol of the coating material of Example 1 was changed to 0.0061 g (equivalent to 2.03 × 10 ⁻⁶ mol / m ² s), The following evaluation was performed.

<Environmental stability test>
The environmental stability of each example and comparative example was evaluated by performing the weight change rate when exposed to a temperature of 30 ° C. and a humidity of 70% RH for one week. The increase in mass with respect to the initial mass of about 2.0 g of the particles of each Example and Comparative Example is shown in Table 1 in mass%.

  According to Table 1, the coated lithium-nickel composite oxide particles of Examples 1 to 8 according to the present invention have a mass change of less than 1.60%, and are lithium-nickel composite oxide particles with high environmental stability. I understand that there is. On the other hand, the lithium-nickel composite oxide particles of Comparative Examples 1 to 3 were confirmed to be lithium-nickel composite oxide particles having a large mass change as compared with Examples 1 to 8 and poor environmental stability.

<Stability test of positive electrode mixture slurry>
The weight ratio of the lithium-nickel composite oxide particles of each Example and Comparative Example was 45: 2.5: 2.5: 50 in a weight ratio of particles: acetylene black: PVdF: N-methylpyrrolidone (NMP). Then, 1.5% by weight of water was added, and the mixture was stirred with a rotation / revolution mixer to obtain a positive electrode mixture slurry. The obtained slurry was stored in an incubator at 25 ° C., and the change with time of 24 hours was stirred with a spatula to evaluate the viscosity increase and the degree of gelation for each of Examples and Comparative Examples, and are shown in Table 1. In addition, even if it left to stand for 24 hours, what was fluid in the positive mix slurry was set to "(circle)", and what gelatinized and gelatinized was set to "x".

  According to Table 1, none of the coated lithium-nickel composite oxide particles of Examples 1 to 8 according to the present invention caused gelation, and even when slurried, the coated lithium was good without peeling off the coating film. -It turns out that the nickel complex oxide particle is formed. On the other hand, since the lithium-nickel composite oxide particles of Comparative Example 1 were all evaluated as “x” when gelled, the coating was not sufficient, and the generation of impurities which is the object of the present invention It was confirmed that the lithium-nickel composite oxide particles could not be suppressed.

  Further, when the lithium-nickel composite oxide particles are coated with a fluorine compound, the fluorine compound is generally dissolved in N-methyl-2-pyrrolidone (NMP). Is believed to dissolve. Therefore, unlike the coated lithium-nickel composite oxide particles according to the examples, it is considered difficult to suppress the generation of impurities when the manufactured positive electrode is stored. Therefore, it is difficult to suppress the reaction with the electrolyte accompanying gas generation when the battery is driven due to impurities generated during positive electrode storage, and expensive storage equipment is required.

Moreover, the value of the energy level of the HOMO of the coated organic sulfur compounds of Examples 1 to 3 and Examples 7 and 8 is less than -9.0 eV. Therefore, even when the coated lithium-nickel composite oxide particles of Examples 1 to 3 and Examples 7 and 8 are used as the positive electrode active material of the lithium ion battery, the organic sulfur compound does not cause an oxidation reaction on the electrode. Therefore, it is presumed that the coated lithium-nickel composite oxide particles are better for the positive electrode active material of the lithium ion battery.

Claims (9)

The surface of nickel-based lithium-nickel composite oxide particles having a nickel content exceeding 0.65 mol is coated with an organic sulfur compound,
The coating amount of the organic sulfur compound, a lithium - Ri 1.62 × ¹⁰ -5 mol / ^{m 2} or less der 4.05 × ¹⁰ -6 mol / ^{m 2} or more with respect to the specific surface area of the nickel composite oxide particles,
The organic sulfur compound is diphenyl disulfide, di-p-tolyl disulfide, bis (4-methoxyphenyl) disulfide, 2-naphthalenethiol, benzenethiol, benzyl mercaptan, 6- (dibutylamino) 1,3,5-triazine- At least one selected from the group consisting of 2,4-dithiol, 2-anilino-4,6 dimercapto-1,3,5-triazine and 6- (arinino) 1,3,5-triazine-2,4-dithiol Coated lithium-nickel composite oxide particles for a lithium ion battery positive electrode active material , which are the above organic sulfur compounds .   The lithium ion battery positive electrode active according to claim 1, wherein the organic sulfur compound is a thiol group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring, or a disulfide group-containing molecule having a cyclic skeleton that is an aromatic ring or a heterocyclic ring. Coated lithium-nickel composite oxide particles for materials.   The coated lithium-nickel composite oxide particle according to claim 1 or 2, wherein the molecular orbital energy of the highest occupied orbit of the organic sulfur compound is less than -9.0 eV.   The coated lithium-nickel composite oxide particle according to any one of claims 1 to 3, wherein the organic sulfur compound is a disulfide group-containing molecule having a diphenyl disulfide skeleton or a thiol group-containing molecule having a triazine dithiol skeleton.   The organic sulfur compound is diphenyl disulfide, 2-naphthalenethiol, 6- (dibutylamino) -1,3,5-triazine-2,4-dithiol and 6- (anilino) -1,3,5-triazine-2. The coated lithium-nickel composite oxide particle according to claim 1, which is at least one compound selected from 1,4-dithiol. The coated lithium-nickel composite oxide particle according to any one of claims 1 to 5, wherein the organic sulfur compound is represented by the following general formula (1).
_{Li x Ni (1-y-} z) M y N z O 2 ··· (1)
(Wherein x is 0.80 to 1.10, y is 0.01 to 0.20, z is 0.01 to 0.15, 1-yz is a value exceeding 0.65, M represents at least one element selected from Co or Mn, and N represents at least one element selected from Al, In, or Sn.)   The coated lithium-nickel composite oxide particle according to any one of claims 1 to 6, which is a spherical particle having an average particle size of 5 to 20 µm.   The coated lithium-nickel composite oxide particle according to any one of claims 1 to 7, wherein the organic sulfur compound-containing layer formed on the coated lithium-nickel composite oxide particle is a monomolecular film. 9. The method according to claim 1, comprising a step of mixing the organic sulfur compound and the lithium-nickel composite oxide particles with a polar solvent within a temperature range from room temperature to immediately before the decomposition temperature of the molecule. A method for producing coated lithium-nickel composite oxide particles.

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