JP2014022293A - Positive electrode active material for nonaqueous electrolyte secondary battery and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, for obtaining a nonaqueous electrolyte secondary battery high in capacity and high in safety, and a method for producing the positive electrode active material for a nonaqueous electrolyte secondary battery.SOLUTION: There are provided: a positive electrode active material for a nonaqueous electrolyte secondary battery, which is a particle of a lithium metal composite oxide mainly consisting of nickel or cobalt while the surface of the composite oxide particle is covered with a phosphate film and carbon, in this order; and a method for producing the positive electrode active material for a nonaqueous electrolyte secondary battery.

Description

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

In recent years, with the widespread use of portable electronic devices such as mobile phones and notebook computers, non-aqueous electrolyte secondary batteries having high energy density, small size and light weight are strongly desired. Furthermore, in the automobile industry, development of large-sized lithium secondary batteries to be mounted on electric vehicles (EV) and hybrid electric vehicles (HEV), which are expected to reduce greenhouse gas emissions, has been actively conducted.
Secondary batteries that satisfy such requirements include lithium ion secondary batteries, which are composed of a negative electrode, a positive electrode, an electrolyte, and the like. A material that can be detached and inserted is used.

  This lithium ion secondary battery is currently under active research and development. Among these, lithium ion secondary batteries using a layered lithium metal composite oxide or a spinel type lithium metal composite oxide as the positive electrode material are among them. Since a high voltage of 4V class can be obtained, practical use is progressing as a secondary battery having a high energy density.

Here, as materials proposed as the positive electrode active material, 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. ) And lithium / manganese composite oxide (LiMn ₂ O ₄ ) using manganese.
However, when the oxide is left in a high temperature environment in a charged state, oxygen is released due to decomposition, and there is a safety problem that the released oxygen and the organic electrolyte react to easily ignite. It was. For this reason, lithium ion secondary batteries currently in practical use are designed with multiple safety mechanisms such as strict voltage control and internal circuit innovation.

On the other hand, various studies have been made so far on methods for enhancing the safety of the layered or spinel type lithium metal composite oxide itself.
For example, in order to improve the thermal stability of the lithium ion secondary battery positive electrode material, the general _{formula: Li a M b Ni c Co} d O e ( where, M is, Al, Mn, Sn, In , Fe , V, Cu, Mg, Ti, Zn, and Mo, and a, b, c, d, and e are 0 <a <1.3 and 0.02 ≦ b. ≦ 0.5, 0.02 ≦ d / c + d ≦ 0.9, 1.8 <e <2.2, and b + c + d = 1.) A lithium metal composite oxide or the like has been proposed ( For example, see Patent Document 1).

  In this case, when, for example, aluminum is selected as the additive element M, it is confirmed that if the amount of substitution from nickel to aluminum is increased, the decomposition reaction of the positive electrode active material is suppressed and the thermal stability is improved. However, if nickel is replaced with an aluminum amount effective to ensure sufficient stability, the amount of nickel contributing to the oxidation-reduction reaction accompanying the charge / discharge reaction decreases, so the initial capacity is greatly reduced. Have.

As another method, a positive electrode material for a non-aqueous electrolyte lithium ion secondary battery in which a lithium compound is impregnated on the surface of lithium / nickel oxide particles has been proposed (for example, see Patent Document 2).
However, these proposals do not solve the fundamental problem that layered oxides and spinel oxides easily release oxygen when heated to a high temperature in a charged state (a state in which lithium is released). On the surface, further improvement was required.

In response to such a requirement, for example, an olivine-type lithium phosphate compound represented by a general formula: LiFePO ₄ or the like (see, for example, Patent Documents 3 and 4) has strong (PO ₄₎ due to a covalent bond between phosphorus and oxygen. ) Since ^3- polyanion is formed, there is little volume change due to charge / discharge, and oxygen is hardly released. For this reason, it is strong against overdischarge and overcharge that cause problems in safety, and has high stability at high temperatures. Furthermore, there is an advantage in cycle life and rapid charge / discharge.

However, since the electrical conductivity is as low as 10 ⁻⁸ S / cm 2 or less, a device on the process is required. At present, in most cases, the surface of LiFePO ₄ particles is coated with conductive carbon. Furthermore, since the diffusibility of Li is low and sufficient performance cannot be obtained as it is, fine particles are formed to a diameter of several tens of nm, the diffusion distance is shortened and the surface area is increased.
On the other hand, since the LiFePO ₄ particles are finely divided, it is difficult to fill them with high density, and the discharge capacity cannot be sufficiently improved.

Therefore, by developing a positive electrode material with high safety and high capacity by combining a positive electrode active material with large discharge capacity but poor safety and lithium iron phosphorus composite oxide (LiFePO ₄ ) with high safety but small capacity. Is underway.
In Patent Document 5, lithium-nickel composite oxide (Li _x Ni _1-y M _y O _z , 0.9 <x ≦ 1.1, 0 ≦ y ≦ 0.7, 1.9 ≦ z ≦ 2.1, M is a production method of firing lithium, iron, phosphorus composite oxide (LiFePO ₄ ) and a conductive carbon source, including at least one of Al, Co, and Mn, and has a high discharge capacity and excellent high-temperature storage characteristics. It is said that a non-aqueous electrolyte secondary battery can be obtained.

  However, in the method described in Patent Document 5, the lithium / iron / phosphorus composite oxide is mixed with the lithium / nickel composite oxide, and the coating of the lithium / iron / phosphorus composite oxide is incomplete, and the adhesion strength However, it may peel off due to a volume change caused by charging and discharging, and thermal stability may not be maintained.

In Patent Document 6, a composite of a first lithium compound represented by LiMPO ₄ (M has Fe) and a second lithium compound having a nobler potential than the first lithium compound is used as a positive electrode active material. The technique used is disclosed. According to this technique, it is said that a battery having excellent charge / discharge characteristics can be obtained.
However, this technique has a problem that the high-temperature storage characteristics are not sufficient.

In Patent Document 7, even when lithium iron phosphate, which is the main component of the mixture, repeatedly contracts and expands during charge and discharge by using a mixture of lithium iron phosphate and lithium cobaltate as the positive electrode active material, the positive electrode Since the active material contains lithium cobaltate having an electric conductivity of 10 ⁻⁶ S / cm or more, expanding lithium when releasing, and contracting when absorbing lithium, the positive electrode active material Even after the electron conduction path is maintained and the charge / discharge cycle is repeated, the discharge characteristics are excellent and the main component is iron phosphate / lithium having an olivine structure with high thermal stability. It is disclosed that it can be obtained.
However, only iron phosphate / lithium and lithium cobalt oxide are mixed, and iron phosphate / lithium is excellent in thermal stability, but the surface of lithium cobaltate is in contact with the electrolyte, improving overall thermal stability. Can't hope.

Japanese Patent Laid-Open No. 5-242891 JP-A-2005-190996 JP-A-9-134725 WO2005 / 041327 JP 2008-210701 A JP 2001-307730 A JP 2008-34218 A

  The present invention has been made to solve the above problems, and provides a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same for obtaining a non-aqueous electrolyte secondary battery having high capacity and high safety. It is to provide.

  In view of the above situation, the present inventor has prepared a lithium metal composite oxide particle surface by phosphoric acid treatment and coating with a phosphate film, so that the lithium metal composite oxide particles can be left in a high temperature environment in a charged state. It has been found that oxygen desorption due to decomposition of metal composite oxide particles is suppressed. Furthermore, it was also found that by covering the outside of the phosphate film with carbon, conductivity between particles was ensured, and a high capacity and high safety non-aqueous electrolyte secondary battery was obtained, and the present invention was completed. It has come. More specifically, the present invention provides the following.

  1st invention of this invention is lithium metal complex oxide particle | grains, Comprising: The metal which comprises nickel or cobalt as a main component, The complex oxide particle surface is coat | covered in order of the phosphate film and carbon. A positive electrode active material for a non-aqueous electrolyte secondary battery.

According to a second aspect of the present invention, the lithium metal composite oxide particles according to the first aspect have a general formula Li _x Ni _1-y M _y O ₂ (wherein 0.05 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.7, M is at least one selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr). A positive electrode active material for a non-aqueous electrolyte secondary battery, wherein the positive electrode active material is a lithium-nickel composite oxide particle.

According to a third aspect of the present invention, the lithium metal composite oxide particles according to the first aspect are represented by the general formula Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.1, M is one or more selected from the group consisting of Mg, Al, Ti, and Zr.) and lithium-cobalt composite oxide particles having a layered structure represented by It is a positive electrode active material for nonaqueous electrolyte secondary batteries.

  The fourth invention of the present invention is a step of coating the particle surface of the lithium metal composite oxide particles with a phosphate coating by phosphoric acid treatment, and a step of coating the particle surface coated with the phosphate coating with carbon It is a manufacturing method of the positive electrode active material for nonaqueous electrolyte secondary batteries characterized by including.

In a fifth aspect of the present invention, the lithium metal composite oxide particles in the fourth aspect are Li _x Ni _1-y M _y O ₂ (wherein 0.05 ≦ x ≦ 1.2. 0 ≦ y ≦ 0.7, and M is selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr. This is the manufacturing method of the positive electrode active material for a non-aqueous electrolyte secondary battery.

In a sixth aspect of the present invention, the lithium metal composite oxide particles in the fourth aspect are Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.2. In addition, 0 ≦ y ≦ 0.1, and M is one or more selected from the group consisting of Mg, Al, Ti and Zr.) Of the positive electrode active material for a non-aqueous electrolyte secondary battery It is a manufacturing method.

  According to the present invention, the surface of the lithium metal composite oxide particles is coated with a phosphate film, and the surface is further coated with carbon, thereby decomposing the lithium metal composite oxide particles in a high temperature environment during charging. A positive electrode active material for a non-aqueous electrolyte secondary battery having the characteristics of suppressing desorption of oxygen and maintaining conductivity between particles is obtained. By using this positive electrode active material, a high capacity and high safety can be obtained. A water electrolyte secondary battery can be obtained.

It is sectional drawing of the positive electrode active material for nonaqueous electrolyte secondary batteries concerning this invention. It is sectional drawing of a 2032 type coin battery produced for evaluation of a positive electrode active material.

The positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention has a structure in which the surface of the lithium metal composite oxide particles is treated with phosphoric acid and coated with a phosphate film, and further coated with carbon.
Here, the technical feature of the positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention is that the surface of the lithium metal composite oxide particles is treated with phosphoric acid and coated with a phosphate film, and further coated with carbon. Therefore, the positive electrode active material for a non-aqueous electrolyte secondary battery and the method for producing the same according to the present invention will be described in detail.

<1. Cathode active material>
The positive electrode active material for a non-aqueous electrolyte secondary battery of the present invention will be specifically described with reference to the drawings.
FIG. 1 is a cross-sectional view specifically showing an embodiment of a positive electrode active material for a non-aqueous electrolyte secondary battery according to the present invention.
As shown in FIG. 1, the positive electrode active material 11 for a nonaqueous electrolyte secondary battery according to the present invention has a phosphate film 2 formed by phosphoric acid treatment on the surface of a lithium metal composite oxide particle 3. The lithium metal composite oxide particles are characterized in that the carbon film 1 is formed on the surface of the phosphate film.

[Lithium metal composite oxide particles]
The lithium metal composite oxide particle 3 mainly constituting the positive electrode active material of the present invention contains Ni or Co as a main component, specifically, a general formula: Li _x Ni _1-y M _y O ₂ (wherein 0.05 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.7, M is from Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, Sr Or Li _x Co _1-y M _y O ₂ (wherein 0.9 ≦ x ≦ 1.2, 0 ≦ y ≦ 0.1, M is Mg, Al) Lithium metal composite oxide particles represented by the formula (1) or more selected from the group consisting of Ti and Zr.

[Phosphate film]
The phosphate coating 2 of the present invention may be any coating that covers the surface of the lithium metal composite oxide particles 3 and suppresses the desorption of oxygen when the temperature rises.
That is, when lithium metal composite oxide particles are used as the positive electrode, Li is extracted from the lithium metal composite oxide particles during charging, resulting in an unstable structure and bonding at the interface between the lithium metal composite oxide particles and the electrolyte. Desorption of weak oxygen occurs. Therefore, the release of oxygen is suppressed by coating the surface of the lithium metal composite oxide particles with a strong (PO ₄ ) ^3- polyanion by covalent bonding of phosphorus and oxygen.
Further, it is only necessary that the lithium metal composite oxide particles are continuously connected to the surface of the lithium metal composite oxide particles and are difficult to peel off, so that Li ions can be easily diffused.

[Carbon film]
The coating with the carbon coating 1 covers the surface of the lithium metal composite oxide particles coated with the phosphate coating 2 and improves the electron conductivity.
As the carbon source, organic acids such as acetic acid and citric acid, sugars such as cellulose, glucose, sucrose, lactose and maltose, polymers such as polyvinyl alcohol, and the like can be used. In addition, although the mass ratio of the carbon material with respect to the lithium metal composite oxide particle coat | covered with the phosphate membrane | film | coat is not limited, the amount of positive electrode active materials can be reduced, so that the mass ratio of a carbon material is low.

<2. Method for producing positive electrode active material>
[Method for producing lithium metal composite oxide particles]
The method for producing the lithium metal composite oxide particles is not particularly limited as long as it is a method in which at least one or more transition metal elements mainly composed of Ni and Co are dissolved in Li.
For example, Li ₂ CO ₃ (lithium carbonate), NiCO ₃ (nickel carbonate), and CoCO ₃ (cobalt carbonate) are mixed so that the molar ratio of Li, Ni, and Co is 1: 0.5: 0.5. After mixing in a mortar, this mixture is heat-treated in air at 850 ° C. for 20 hours to prepare lithium metal composite oxide particles composed of LiNi _0.5 Co _0.5 O ₂ .

[Method of coating with phosphate film]
As a coating method using a phosphate film, a method of grinding in an organic solvent in the presence of phosphoric acid can be used. According to this method, by adding phosphoric acid when the lithium metal composite oxide particles are pulverized by an attritor or the like, even if a new surface is generated in the aggregated particles by pulverization, the particles react instantaneously with phosphoric acid in the solvent. A stable phosphate film is formed on the surface. After that, even if the pulverized lithium metal composite oxide particles are aggregated, the contact surface is already stabilized, and an incomplete region of the coating does not occur due to crushing.

Moreover, the thickness of the phosphate film necessary for protecting the surface of the lithium metal composite oxide particles is usually 5 to 100 nm on average. If the average thickness of the phosphate film is less than 5 nm, sufficient oxygen desorption suppression cannot be obtained, and if it exceeds 100 nm, the battery characteristics deteriorate.
There is no restriction | limiting in particular as phosphoric acid used for formation of a phosphate membrane | film | coat, Commercially available normal phosphoric acid, for example, 85% concentration phosphoric acid aqueous solution can be used.

  Furthermore, the addition method of phosphoric acid is not specifically limited, For example, when grind | pulverizing lithium metal complex oxide particle | grains with an attritor etc., phosphoric acid is added to the organic solvent used as a solvent. Phosphoric acid only needs to finally have a desired phosphoric acid concentration, and may be added all at once before the start of pulverization or gradually during pulverization.

  The organic solvent is not particularly limited, and usually alcohols such as ethanol or isopropyl alcohol, ketones, lower hydrocarbons, aromatics, or a mixture thereof is used.

The amount of phosphoric acid added is generally unrelated since it is related to the particle size, surface area, etc. of the pulverized lithium metal composite oxide particles, but is usually 0.1 mol with respect to the lithium metal composite oxide particles to be pulverized. / Kg or more and less than 2 mol / kg, more preferably 0.15 to 1.5 mol / kg, still more preferably 0.2 to 0.4 mol / kg.
That is, when it is less than 0.1 mol / kg, the surface treatment of the lithium metal composite oxide particles is not sufficiently performed, so that the desorption of oxygen is not sufficient.

  Furthermore, it is preferable to heat-treat the lithium metal composite oxide particles coated with the phosphate film thus obtained at 100 ° C. or higher in an inert gas or in a vacuum. When the heat treatment is performed at less than 100 ° C., drying does not proceed sufficiently and formation of a stable surface film is inhibited.

[Method of coating with carbon film]
For example, a lithium metal composite oxide particle coated with a phosphate film is impregnated in a cellulose acetate solution dissolved in acetone. After drying, the temperature is raised and held in an argon atmosphere in a heating furnace. Subsequently, it cools in steps in argon atmosphere. Through this step, the surface of the lithium metal composite oxide particles coated with the phosphate film can be further coated with carbon.

<3. Production of secondary battery>
Using the positive electrode active material for a nonaqueous electrolyte secondary battery, for example, a positive electrode is produced as follows.
First, a powdered positive electrode active material, 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. Each mixing ratio in the positive electrode mixture paste is also an important factor that determines the performance of the secondary battery.
When the total mass of the solid content of the positive electrode mixture excluding the solvent is 100 parts by mass, the content of the positive electrode active material is 50 to 95 parts by mass as in the case of the positive electrode of a general non-aqueous electrolyte secondary battery, and the conductive material It is desirable to set the content of 1 to 30 parts by mass and the content of the binder to 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. This sheet-like positive electrode is cut into an appropriate size according to the target battery and used for the production of the battery. However, the method for manufacturing the positive electrode is not limited to the above-described examples, and other methods may be used.

Examples of the conductive agent used include graphite (natural graphite, artificial graphite, expanded graphite, etc.), carbon black materials such as acetylene black and ketjen black.
The binder to be used plays a role of anchoring the active material particles. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluoro rubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin, poly Acrylic acid or the like can be used.

  Furthermore, if necessary, a positive electrode active material, 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.

Next, components other than the positive electrode used in the secondary battery of the present invention will be described. However, the secondary battery of the present invention is characterized in that the positive electrode active material is used, and other components are not particularly limited.
As the negative electrode, for example, metallic lithium, lithium alloy, or the like, a negative electrode mixture made by mixing a binder with a negative electrode active material capable of occluding and releasing lithium ions, and adding a suitable solvent to form a paste, For example, a metal foil current collector such as a metal foil is applied and dried, and is 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 polyvinylidene fluoride can be used as in the case of the positive electrode, and the active material and the solvent for dispersing the binder include N-methyl-2-pyrrolidone. Organic solvents can be used.

  The separator is sandwiched between the positive electrode and the negative electrode. This separator separates a positive electrode and a negative electrode and retains an electrolyte. For example, a thin film of polyethylene, polypropylene or the like and a film having many minute holes can be used.

The nonaqueous electrolytic solution is obtained by dissolving a lithium salt as a supporting salt in an organic solvent.
Examples of the organic solvent to be used include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethylmethyl carbonate, and dipropyl carbonate, tetrahydrofuran, and 2-methyl. At least one selected from ether compounds such as tetrahydrofuran and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butane sultone, or phosphorus compounds such as triethyl phosphate and trioctyl phosphate can be used.

As the supporting salt to be used, for example, 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.

The lithium secondary battery according to the present invention composed of the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte solution has various shapes such as a cylindrical shape and a laminated shape.
In any case, the positive electrode and the negative electrode are laminated via a separator to form an electrode body, and the electrode body is impregnated with the non-aqueous electrolyte solution. The positive electrode current collector and the positive electrode terminal communicating with the outside, 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. The battery having the above configuration is sealed in a battery case to complete the battery.

  The surface of the lithium metal composite oxide particles of the present invention is treated with phosphoric acid, coated with a phosphate film, and further coated with carbon to form a lithium metal composite oxide by using a positive electrode active material for a non-aqueous electrolyte secondary battery. A high capacity can be obtained by physical particles, and a phosphate film can suppress the desorption of oxygen at the electrolyte solution interface at high temperatures, resulting in a highly safe nonaqueous electrolyte secondary battery.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further more concretely, this invention is not limited to a following example at all.

<Preparation of positive electrode active material>
[1. Preparation of lithium / nickel composite oxide particles]
First, Li ₂ CO ₃ (lithium carbonate), MnCO ₃ (manganese carbonate), NiCO ₃ (nickel carbonate), and CoCO ₃ (cobalt carbonate) have a molar ratio of Li, Ni, Co, and Mn of 1: 0.45. : 0.45: 0.1 After mixing in a mortar, the mixture was heat-treated in air at 850 ° C. for 20 hours to obtain lithium / lithium / LiNi _0.45 Co _0.45 Mn _0.1 O _2. Nickel composite oxide particles were prepared.

[2. Coating with phosphate film]
Next, 1 kg of lithium / nickel composite oxide particles were pulverized in 1.5 kg of isopropanol for 2 hours at 200 rpm with an attritor substituted with nitrogen inside the container to prepare lithium / nickel composite oxide particles. .

  During or after pulverization, a predetermined amount of 85% aqueous orthophosphoric acid solution was added to and mixed with the lithium / nickel composite oxide particles according to the description in Table 1. Thereafter, the lithium / nickel composite oxide particles were dried in vacuum at 120 ° C. for 4 hours to obtain lithium / nickel composite oxide particles coated with a phosphate film having a thickness of 12 nm.

[3. Carbon coating]
Lithium / nickel composite oxide particles coated with a phosphate film are impregnated in a solution of cellulose acetate (acetyl group content: 39.7 mass%, weight average molecular weight Mw 50000) dissolved in acetone. The amount of cellulose acetate added is 5% by mass of the lithium / nickel composite oxide particles coated with the treated phosphate film.
Utilization of the carbon precursor as a solution enables complete distribution onto the lithium / nickel composite oxide particles coated with the phosphate coating. After drying, the temperature is raised to 700 ° C. at 6 ° C./min in an argon atmosphere in a heating furnace and held for 1 hr. Subsequently, it cools in steps in argon atmosphere.

Through the steps 1 to 3, the surface of the lithium / nickel composite oxide particles was coated with a phosphate coating, and the surface coated with the phosphate coating could be coated with carbon.
FIG. 1 shows a cross-sectional view of lithium / nickel composite oxide particles 11a according to Example 1 coated with the carbon film 1 and the phosphate film 2. As shown in FIG. 3a is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

[Measurement of phosphate film thickness]
The phosphate film thickness of the obtained lithium / nickel composite oxide particles was monitored by P and O spectra by XPS. From the P profile of the film, the position where the maximum strength was reduced to 50% was defined as the interface position between the film and the base, and the sputtering time L (sec) from the surface to the interface position was read. This L was multiplied by a sputtering rate of 5 nm / min in the standard sample SiO ₂ to obtain a SiO ₂ equivalent film thickness. The results are shown in Table 1.

[Battery fabrication]
60 parts by mass of the positive electrode active material powder was mixed with 30 parts by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10 parts by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.). A pellet was prepared and used as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) using 1M LiPF ₆ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte.
Using these, a 2032 type coin battery was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

  In the produced 2032 type coin battery, as shown in FIG. 2, a separator 5 impregnated with the electrolytic solution is disposed between a positive electrode 6 as an evaluation electrode and a negative electrode 4 made of lithium metal. Is covered with a negative electrode can 8 from the negative electrode side and a positive electrode can 9 from the positive electrode side. A gasket 7 is disposed between the positive electrode can 9 and the negative electrode can 8 to prevent the positive electrode can 9 and the negative electrode can 8 from being short-circuited and to shield the inside of the 2032 type coin battery 10 from the outside.

[Discharge capacity evaluation]
The produced battery was left for about 24 hours, and after the OCV was stabilized, the initial discharge capacity was measured.
The initial discharge capacity was evaluated by conducting a charge / discharge test with a current density of 0.5 mA for the positive electrode and a cutoff voltage of 4.3-3.0 V. Table 1 shows the results.

[Thermal stability evaluation]
As evaluation of thermal stability, the heat generation behavior of the charged positive electrode mixture was examined using DSC (Differential Scanning Calorimeter) (manufactured by Rigaku Corporation: DSC-10A). Specifically, the exothermic peak intensity, the initial total calorific value, which is the total amount of heat generated by the positive electrode mixture after the first charge, and the total amount of heat generated by the positive electrode mixture at the 20th charge / discharge cycle. The total calorific value at the cycle was measured. The measurement results are shown in Table 1.

Details of the measurement method are as follows.
First, the 2032 type coin battery shown in FIG. 2 was allowed to stand for about 24 hours to stabilize the OCV. After that, the current density with respect to the positive electrode is set to 0.5 mA / cm ² and charged to a voltage of 4.3 V. When the current value becomes 0.01 mA or less according to the voltage regulation, the charging is terminated by the constant current constant voltage (CCCV) method. Went.

  Thereafter, the charged coin battery was disassembled, the internal positive electrode mixture was taken out, and the adhered electrolyte solution was removed as much as possible until the deposited electrolyte solution was 0.05 mg or less. Then, 3 mg of this positive electrode mixture and 1.3 mg of the electrolyte used for the coin battery were placed in an Al pan for DSC measurement, and the Al pan was caulked to seal it. After sealing, a small sample was made in the surface of the Al pan for degassing to complete a measurement sample. Further, 3 mg of alumina powder collected and caulked in an Al pan was completed as a measurement sample in the same manner as described above, and used as a reference sample.

  And about the produced sample, the range from room temperature to 305 degreeC was scanned with the temperature increase rate of 10 degree-C / min using DSC, the exothermic behavior was measured, and the exothermic peak intensity | strength and the initial total calorific value were measured.

The total calorific value after 20 cycles was charged and discharged at a cutoff voltage of 4.3 to 3.0 V with a current density of 0.5 mA / cm ² with respect to the positive electrode up to the 19th cycle. After charging to 4.3 V, CCCV was performed to complete charging when the current value was 0.01 mA or less by voltage regulation, and the coin battery was disassembled in the same manner as described above, and then evaluated by DSC.

  A 2032 type coin battery comprising a lithium / nickel composite oxide particle prepared in the same manner as in Example 1 except that the thickness of the phosphate coating was 22 nm, and a positive electrode plate using the lithium / nickel composite oxide particle. The battery characteristics were measured. The results are shown in Table 1.

  Except that the thickness of the phosphate coating was 69 nm, lithium-nickel composite oxide particles were prepared in the same manner as in Example 1, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 1.

(Comparative Example 1)
A 2032 type coin battery was manufactured in the same manner as in Example 1 except that the coating step with the phosphate coating was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior.
Table 1 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  As is clear from Table 1, the lithium / nickel composite oxide particles shown in Examples 1 to 3 in which a phosphate film and a carbon film were sequentially formed on the surface of the lithium / nickel composite oxide particles It can be seen that the thermal stability of the uncoated lithium / nickel composite oxide particles is improved while maintaining the high discharge capacity.

<Preparation of positive electrode active material>
[1. Preparation of lithium / nickel composite oxide particles]
First, Li ₂ CO ₃ (lithium carbonate), MnCO ₃ (manganese carbonate), NiCO ₃ (nickel carbonate), and CoCO ₃ (cobalt carbonate) have a molar ratio of Li, Ni, Co, and Mn of 1: 0.33. : 0.33: After coating with a carbon film and a phosphate film in the same manner as in Example 1 except that the mixture was mixed in a mortar so as to be 0.33, this mixture was heat-treated at 850 ° C. in air for 20 hours. LiNi _0.33 Co _0.33 Mn _0.33 O ₂ lithium / nickel composite oxide particles were prepared and used as the positive electrode active material.

[2. Coating with phosphate film]
Next, 1 kg of lithium / nickel composite oxide particles were pulverized in 1.5 kg of isopropanol for 2 hours at 200 rpm with an attritor substituted with nitrogen inside the container to prepare lithium / nickel composite oxide particles. .
During or after pulverization, a predetermined amount of 85% aqueous orthophosphoric acid solution was added to and mixed with the lithium / nickel composite oxide particles according to the description in Table 2. Thereafter, the lithium / nickel composite oxide particles were dried in vacuum at 120 ° C. for 4 hours to obtain lithium / nickel composite oxide particles coated with a phosphate film having a thickness of 12 nm.

[3. Carbon coating]
Lithium / nickel composite oxide particles coated with a phosphate film are impregnated in a solution of cellulose acetate (acetyl group content: 39.7 mass%, weight average molecular weight Mw 50000) dissolved in acetone. The amount of cellulose acetate added is 5% by mass of the lithium / nickel composite oxide particles coated with the treated phosphate film. Utilization of the carbon precursor as a solution enables complete distribution onto the lithium / nickel composite oxide particles coated with the phosphate coating.

  After drying, the temperature is raised to 700 ° C. at 6 ° C./min in an argon atmosphere in a heating furnace and held for 1 hr. Subsequently, it cools in steps in argon atmosphere.

Through the steps 1 to 3, the surface of the lithium / nickel composite oxide particles was coated with a phosphate coating, and the surface coated with the phosphate coating could be coated with carbon. FIG. 1 shows a cross-sectional view of lithium / nickel composite oxide particles 11b according to Example 4 coated with the carbon film 1 and the phosphate film 2. 3b is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

[Measurement of phosphate film thickness]
The phosphate film thickness of the obtained lithium / nickel composite oxide particles was monitored by P and O spectra by XPS. From the P profile of the film, the position where the maximum strength was reduced to 50% was defined as the interface position between the film and the base, and the sputtering time L (sec) from the surface to the interface position was read. This L was multiplied by a sputtering rate of 5 nm / min in the standard sample SiO ₂ to obtain a SiO ₂ equivalent film thickness. Table 2 shows the results.

[Battery fabrication]
60 parts by mass of the positive electrode active material powder was mixed with 30 parts by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10 parts by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.). A pellet was prepared and used as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) using 1M LiPF ₆ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte. Using these, a 2032 type coin battery was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

  The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior. Table 2 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  A 2032 type coin battery comprising a lithium / nickel composite oxide particle prepared in the same manner as in Example 4 except that the thickness of the phosphate coating was 22 nm, and a positive electrode plate using the lithium / nickel composite oxide particle. The battery characteristics were measured. The results are shown in Table 1.

  Except that the thickness of the phosphate coating was 69 nm, lithium-nickel composite oxide particles were produced in the same manner as in Example 4, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 1.

(Comparative Example 2)
A coin battery was manufactured in the same manner as in Example 4 except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 4, and the thermal stability was also evaluated using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 4. This was done by examining the heat generation behavior.
Table 2 shows the measurement results of the initial discharge capacity, the exothermic peak intensity, the initial total calorific value, and the total calorific value at the 20th cycle.

  As is clear from Table 2, the lithium / nickel composite oxide particles shown in Examples 4 to 6 in which the phosphate film and the carbon film were sequentially formed on the surface of the lithium / nickel composite oxide particles It can be seen that the thermal stability of the uncoated lithium / nickel composite oxide particles is improved while maintaining the high discharge capacity.

<Preparation of positive electrode active material>
[1. Preparation of lithium / nickel composite oxide particles]
First, Li ₂ CO ₃ (lithium carbonate), MnCO ₃ (manganese carbonate), NiCO ₃ (nickel carbonate), and CoCO ₃ (cobalt carbonate) are mixed at a molar ratio of Li, Ni, Co, and Mn of 1: 0.5. : After coating with a carbon film and a phosphate film in the same manner as in Examples 1 to 3 except that the mixture was mixed in a mortar so as to be 0.5: 0, the mixture was heat-treated at 850 ° C. in air for 20 hours. , LiNi _0.5 Co _0.5 O ₂ lithium-nickel composite oxide particles were prepared and used as the positive electrode active material.

[2. Coating with phosphate film]
Next, 1 kg of lithium / nickel composite oxide particles were pulverized in 1.5 kg of isopropanol for 2 hours at 200 rpm with an attritor substituted with nitrogen inside the container to prepare lithium / nickel composite oxide particles. .
During or after pulverization, a predetermined amount of 85% aqueous orthophosphoric acid solution was added to and mixed with the lithium / nickel composite oxide particles according to the description in Table 3. Thereafter, the lithium / nickel composite oxide particles were dried in vacuum at 120 ° C. for 4 hours to obtain lithium / nickel composite oxide particles coated with a phosphate film having a thickness of 12 nm.

[3. Carbon coating]
The lithium / nickel composite oxide particles coated with the phosphate film are impregnated in a solution of cellulose acetate (acetyl group content: 39.7 mass%, weight average molecular weight Mw 50000) dissolved in acetone. The amount of cellulose acetate added is 5% by mass of the lithium / nickel composite oxide particles coated with the treated phosphate film. Utilization of the carbon precursor as a solution enables complete distribution onto the lithium / nickel composite oxide particles coated with the phosphate coating.

  After drying, the temperature is raised to 700 ° C. at 6 ° C./min in an argon atmosphere in a heating furnace and held for 1 hr. Subsequently, it cools in steps in argon atmosphere.

Through the steps 1 to 3, the surface of the lithium / nickel composite oxide particles was coated with a phosphate coating, and the surface coated with the phosphate coating could be coated with carbon.
FIG. 1 shows a cross-sectional view of a lithium / nickel composite oxide particle 11 c according to Example 7 coated with the carbon film 1 and the phosphate film 2. 3c is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

[Measurement of phosphate film thickness]
The phosphate film thickness of the obtained lithium / nickel composite oxide particles was monitored by P and O spectra by XPS.
From the P profile of the film, the position where the maximum strength was reduced to 50% was defined as the interface position between the film and the base, and the sputtering time L (sec) from the surface to the interface position was read. This L was multiplied by a sputtering rate of 5 nm / min in the standard sample SiO ₂ to obtain a SiO ₂ equivalent film thickness.
Table 3 shows the results.

[Battery fabrication]
60 parts by mass of the positive electrode active material powder was mixed with 30 parts by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10 parts by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.). A pellet was prepared and used as a positive electrode.
Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) using 1M LiPF ₆ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte.
Using these, a 2032 type coin battery was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior.
Table 3 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  A 2032 type coin battery comprising a lithium / nickel composite oxide particle prepared in the same manner as in Example 7 except that the thickness of the phosphate coating was 22 nm, and a positive electrode plate using the lithium / nickel composite oxide particle. The battery characteristics were measured. The results are shown in Table 3.

  Except that the thickness of the phosphate coating was 69 nm, lithium-nickel composite oxide particles were prepared in the same manner as in Example 7, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 3.

(Comparative Example 3)
A coin battery was manufactured in the same manner as in Example 7, except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 7. The thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 7. This was done by examining the heat generation behavior.
Table 3 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  As can be seen from Table 3, the lithium / nickel composite oxide particles shown in Examples 7 to 9 in which the phosphate film and the carbon film were sequentially formed on the surface of the lithium / nickel composite oxide particles are shown in Comparative Example 3. It can be seen that the thermal stability of the uncoated lithium / nickel composite oxide particles is improved while maintaining a high discharge capacity.

<Preparation of positive electrode active material>
[1. Preparation of lithium / nickel composite oxide particles]
Except that nickel sulfate hexahydrate, cobalt sulfate heptahydrate, aluminum sulfate were mixed so that the molar ratio of Ni, Co, and Al was 0.8: 0.15: 0.05 to prepare an aqueous solution. In the same manner as in Example 1, it was coated with a carbon film and a phosphate film. This aqueous solution was dropped into an agitated reaction tank equipped with a discharge port with water kept at 50 ° C. simultaneously with aqueous ammonia and caustic soda. The pH was maintained at 11.5 and the residence time was controlled to be 11 hours.

  In this way, spherical Co · Al-containing nickel hydroxide in which primary particles were aggregated was produced by a reactive crystallization method. Lithium hydroxide monohydrate was mixed with the obtained Co · Al-containing nickel hydroxide in a V blender so as to have a desired composition, and this mixture was mixed in an electric furnace in an oxygen atmosphere at 500 ° C. for 3 hours. Calcination was performed under the conditions of 730 ° C. and 20 hours, followed by furnace cooling to room temperature. After the furnace was cooled, the lithium-nickel composite oxide with spherical or oval spherical secondary particles was prepared by crushing treatment.

Each mass of the raw materials used in the above steps was weighed so that the molar ratio of Li, Ni, Co, and Al was 1: 0.8: 0.15: 0.05, and LiNi _0.8 Co _0.15. Lithium / nickel composite oxide particles made of Al _0.05 O ₂ were prepared and used as a positive electrode active material.

[2. Coating with phosphate film]
Next, 1 kg of lithium / nickel composite oxide particles were pulverized in 1.5 kg of isopropanol for 2 hours at 200 rpm with an attritor substituted with nitrogen inside the container to prepare lithium / nickel composite oxide particles. .
During or after pulverization, a predetermined amount of 85% aqueous orthophosphoric acid solution was added to and mixed with the lithium / nickel composite oxide particles according to the description in Table 4. Thereafter, the lithium / nickel composite oxide particles were dried in vacuum at 120 ° C. for 4 hours to obtain lithium / nickel composite oxide particles coated with a phosphate film having a thickness of 12 nm.

[3. Carbon coating]
Lithium / nickel composite oxide particles coated with a phosphate film are impregnated in a solution of cellulose acetate (acetyl group content: 39.7 mass%, weight average molecular weight Mw 50000) dissolved in acetone. The amount of cellulose acetate added is 5% by mass of the lithium / nickel composite oxide particles coated with the treated phosphate film.
Utilization of the carbon precursor as a solution enables complete distribution onto the lithium / nickel composite oxide particles coated with the phosphate coating.

  After drying, the temperature is raised to 700 ° C. at 6 ° C./min in an argon atmosphere in a heating furnace and held for 1 hr. Subsequently, it cools in steps in argon atmosphere.

Through the steps 1 to 3, the surface of the lithium / nickel composite oxide particles was coated with a phosphate coating, and the surface coated with the phosphate coating could be coated with carbon.
FIG. 1 shows a cross-sectional view of a lithium / nickel composite oxide particle 11d according to Example 10 coated with the carbon film 1 and the phosphate film 2. 3d is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

[Measurement of phosphate film thickness]
The phosphate film thickness of the obtained lithium / nickel composite oxide particles was monitored by P and O spectra by XPS. From the P profile of the film, the position where the maximum strength was reduced to 50% was defined as the interface position between the film and the base, and the sputtering time L (sec) from the surface to the interface position was read.
This L was multiplied by a sputtering rate of 5 nm / min in the standard sample SiO ₂ to obtain a SiO ₂ equivalent film thickness. Table 4 shows the results.

[Battery fabrication]
60 parts by mass of the positive electrode active material powder was mixed with 30 parts by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10 parts by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.). A pellet was prepared and used as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) using 1M LiPF ₆ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte.
Using these, a 2032 type coin battery was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior.
Table 4 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  A 2032 type coin battery comprising a lithium / nickel composite oxide particle prepared in the same manner as in Example 10 except that the thickness of the phosphate coating was 22 nm, and a positive electrode plate using the lithium / nickel composite oxide particle. The battery characteristics were measured. The results are shown in Table 4.

  Except that the thickness of the phosphate coating was 69 nm, lithium-nickel composite oxide particles were produced in the same manner as in Example 10, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 4.

(Comparative Example 4)
A coin battery was manufactured in the same manner as in Example 10 except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 10, and the thermal stability was also evaluated using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 10. This was done by examining the heat generation behavior.
Table 4 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  As is clear from Table 4, the lithium / nickel composite oxide particles shown in Examples 10 to 12 in which the phosphate film was formed on the surface of the lithium / nickel composite oxide particles were in the uncoated state shown in Comparative Example 4. It can be seen that the thermal stability of the lithium / nickel composite oxide particles is improved while maintaining the high discharge capacity.

<Preparation of positive electrode active material>
[1. Preparation of lithium / nickel composite oxide particles]
First, Li ₂ CO ₃ (lithium carbonate), MnCO ₃ (manganese carbonate), NiCO ₃ (nickel carbonate), and CoCO ₃ (cobalt carbonate) are mixed in a molar ratio of Li, Ni, Co, and Mn of 1: 1: 0. : after the non-zero mixed in a mortar such that were coated with phosphate film and carbon film in the same manner as in example 1, the mixture was heat-treated for 20 hours at 850 ° C. in air, lithium consisting LiNiO ₂ Nickel composite oxide particles were prepared and used as positive electrode active materials.

[2. Coating with phosphate film]
Next, 1 kg of lithium / nickel composite oxide particles were pulverized in 1.5 kg of isopropanol for 2 hours at 200 rpm with an attritor substituted with nitrogen inside the container to prepare lithium / nickel composite oxide particles. .
A predetermined amount of 85% orthophosphoric acid aqueous solution was added to and mixed with the lithium / nickel composite oxide particles according to the description in Table 5 during or after pulverization.
Thereafter, the lithium / nickel composite oxide particles were dried in vacuum at 120 ° C. for 4 hours to obtain lithium / nickel composite oxide particles coated with a phosphate film having a thickness of 12 nm.

[3. Carbon coating]
Lithium / nickel composite oxide particles coated with a phosphate film are impregnated in a solution of cellulose acetate (acetyl group content: 39.7 mass%, weight average molecular weight Mw 50000) dissolved in acetone. The amount of cellulose acetate added is 5% by mass of the lithium / nickel composite oxide particles coated with the treated phosphate film. Utilization of the carbon precursor as a solution enables complete distribution onto the lithium / nickel composite oxide particles coated with the phosphate coating.

  After drying, the temperature is raised to 700 ° C. at 6 ° C./min in an argon atmosphere in a heating furnace and held for 1 hr. Subsequently, it cools in steps in argon atmosphere.

Through the steps 1 to 3, the surface of the lithium / nickel composite oxide particles was coated with a phosphate coating, and the surface coated with the phosphate coating could be coated with carbon.
FIG. 1 shows a cross-sectional view of lithium / nickel composite oxide particles 11e according to Example 13 coated with the carbon film 1 and the phosphate film 2. 3e is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

[Measurement of phosphate film thickness]
The thickness of the phosphate film of the obtained lithium / nickel composite oxide particles was monitored by XPS for P and O spectra. From the P profile of the film, the position where the maximum strength was reduced to 50% was defined as the interface position between the film and the base, and the sputtering time L (sec) from the surface to the interface position was read. This L was multiplied by a sputtering rate of 5 nm / min in the standard sample SiO ₂ to obtain a SiO ₂ equivalent film thickness.
Table 5 shows the results.

[Battery fabrication]
60 parts by mass of the positive electrode active material powder was mixed with 30 parts by mass of acetylene black (manufactured by Denki Kogyo Co., Ltd.) and 10 parts by mass of PTFE (manufactured by Daikin Kogyo Co., Ltd.). A pellet was prepared and used as a positive electrode. Lithium metal was used as the negative electrode, and an equivalent mixed solution of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) using 1M LiPF ₆ as a supporting salt (manufactured by Toyama Pharmaceutical Co., Ltd.) was used as the electrolyte. Using these, a 2032 type coin battery was produced in an Ar atmosphere glove box whose dew point was controlled at −80 ° C.

The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior.
Table 5 shows the measurement results of the initial discharge capacity of the battery, the size of the heat generation peak, the initial total heat generation amount, and the total heat generation amount at the 20th cycle.

  Except that the thickness of the phosphate coating was 22 nm, lithium-nickel composite oxide particles were produced in the same manner as in Example 13, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 5.

  Except that the thickness of the phosphate coating was 69 nm, lithium-nickel composite oxide particles were prepared in the same manner as in Example 13, and a 2032 type coin battery provided with a positive electrode plate using the lithium-nickel composite oxide particles The battery characteristics were measured. The results are shown in Table 5.

(Comparative Example 5)
A coin battery was manufactured in the same manner as in Example 13 except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 13, and the thermal stability was also evaluated using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 13. This was done by examining the heat generation behavior.
Table 5 shows the measurement results of the initial discharge capacity, the size of the heat generation peak, the initial total heat generation amount, and the total heat generation amount at the 20th cycle.

  As apparent from Table 5, the lithium / nickel composite oxide particles shown in Examples 13 to 15 in which the phosphate film and the carbon film were formed in this order on the surface of the lithium / nickel composite oxide particles were It can be seen that the thermal stability of the uncoated lithium / nickel composite oxide particles is improved while maintaining the high discharge capacity.

As a starting material, lithium carbonate (Li ₂ CO ₃ ) is co-precipitated as a lithium source, and magnesium (Mg) and aluminum (Al) as heterogeneous elements are co-precipitated in 1 mol% with respect to cobalt as a cobalt source. Using the different element-added tricobalt tetroxide ([Co _0.98 Al _0.01 Mg _0.01 ] ₃ O ₄ ) obtained by the above method, the molar ratio of these compounds to the total amount of lithium, cobalt, magnesium and aluminum A lithium / cobalt composite oxide particle having a 12 nm-thick phosphate film and a carbon film coated thereon was prepared in the same manner as in Example 1 except that the mixture was mixed so as to be 1: 1.
FIG. 1 shows a cross-sectional view of a lithium / nickel composite oxide particle 11f according to Example 16 coated with the carbon film 1 and the phosphate film 2. 3f is a lithium / nickel composite oxide particle before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.

A coin battery using the produced lithium / cobalt composite oxide particles as a positive electrode active material was produced.
The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated by using a DSC (differential scanning calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the heat generation behavior.
Table 6 shows the measurement results of the initial discharge capacity, the heat generation peak size, the initial total heat generation amount, and the 20th cycle total heat generation amount of the battery.

  A 2032 type coin battery comprising a lithium / cobalt composite oxide particle prepared in the same manner as in Example 16 except that the thickness of the phosphate coating was 22 nm, and a positive electrode plate using the lithium / cobalt composite oxide particle. The battery characteristics were measured. The results are shown in Table 6.

  Except that the thickness of the phosphate coating was 69 nm, lithium-cobalt composite oxide particles were produced in the same manner as in Example 16, and a 2032 type coin battery provided with a positive electrode plate using the lithium-cobalt composite oxide particles The battery characteristics were measured. The results are shown in Table 6.

(Comparative Example 6)
A coin battery was manufactured in the same manner as in Example 16 except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated using a DSC (Differential Scanning Calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the exothermic behavior.
Table 6 shows the measurement results of the initial discharge capacity, the heat generation peak size, the initial total heat generation amount, and the 20th cycle total heat generation amount of the battery.

  As is clear from Table 6, the lithium-cobalt composite oxide particles shown in Examples 16 to 18 in which a phosphate film and a carbon film were formed in this order on the surface of the lithium-cobalt composite oxide particles were It can be seen that the thermal stability of the uncoated lithium-cobalt composite oxide particles is improved while maintaining the high discharge capacity.

Lithium carbonate and cobalt oxide were coated with a 12 nm thick phosphate film and carbon film in the same manner as in Example 1 except that the molar ratio of lithium to cobalt was 1: 1. Cobalt composite oxide particles were prepared.
FIG. 1 shows a cross-sectional view of a lithium / nickel composite oxide particle 11g according to Example 19 coated with the carbon film 1 and the phosphate film 2. 3 g are lithium / nickel composite oxide particles before coating with phosphate and carbon.
This sample contains 1% by weight of carbon, which corresponds to a carbonization efficiency of cellulose acetate of 20%.
A coin battery was produced using the produced lithium-cobalt composite oxide particles as a positive electrode active material.

The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated using a DSC (Differential Scanning Calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the exothermic behavior.
Table 7 shows the measurement results of the initial discharge capacity of the battery, the size of the heat generation peak, the initial total heat generation amount, and the total heat generation amount at the 20th cycle.

  A 2032 type coin battery comprising a lithium / cobalt composite oxide particle prepared in the same manner as in Example 19 except that the thickness of the phosphate coating was 23 nm, and a positive electrode plate using the lithium / cobalt composite oxide particle. The battery characteristics were measured. The results are shown in Table 7.

  Except that the thickness of the phosphate coating was 67 nm, lithium-cobalt composite oxide particles were produced in the same manner as in Example 19, and a 2032 type coin battery provided with a positive electrode plate using the lithium-cobalt composite oxide particles The battery characteristics were measured. The results are shown in Table 7.

(Comparative Example 7)
A coin battery was manufactured in the same manner as in Example 19 except that the coating step with the phosphate film was omitted.
The initial discharge capacity of the produced battery was measured by the same method as in Example 1, and the thermal stability was also evaluated using a DSC (Differential Scanning Calorimeter) for the charged positive electrode mixture as in Example 1. This was done by examining the exothermic behavior.
Table 7 shows the measurement results of the initial discharge capacity, exothermic peak intensity, initial total calorific value, and 20th cycle total calorific value of the battery.

  As apparent from Table 7, the lithium-cobalt composite oxide particles shown in Examples 19 to 21 in which the phosphate film and the carbon film were formed in this order on the surface of the lithium-cobalt composite oxide particles were It can be seen that the thermal stability of the uncoated lithium-cobalt composite oxide particles is improved while maintaining the high discharge capacity.

1 Carbon film 2 Phosphate film 3 Lithium metal composite oxide particles 3a Lithium / nickel composite oxide particles 3b according to Example 1 Lithium / nickel composite oxide particles 3c according to Example 4 Lithium / nickel according to Example 7 Composite oxide particles 3d Lithium / nickel composite oxide particles 3e according to Example 10 Lithium / nickel composite oxide particles 3f according to Example 13 Lithium / nickel composite oxide particles 3g according to Example 16 Lithium according to Example 19 Nickel composite oxide particles 4 Lithium metal negative electrode 5 Separator (electrolyte impregnation)
6 Positive electrode (Evaluation electrode)
7 Gasket 8 Negative electrode can 9 Positive electrode can 10 2032 type coin battery 11 Lithium metal composite oxide particles having phosphate film and carbon film (non-aqueous electrolyte positive electrode active material of the present invention)
11a Lithium / nickel composite oxide particles 11b having a phosphate coating and a carbon coating according to Example 1 Lithium / nickel composite oxide particles 11c having a phosphate coating and a carbon coating according to Example 4 Lithium / nickel composite oxide particles 11d having phosphate film and carbon film Lithium / nickel composite oxide particles 11e having phosphate film and carbon film according to Example 10 Phosphate film and carbon according to Example 13 Lithium / nickel composite oxide particles 11f having a film 11f Lithium / nickel composite oxide particles having a phosphate film and a carbon film according to Example 16 Lithium / nickel having a phosphate film and a carbon film according to Example 19 Composite oxide particles

Claims (6)

Lithium metal composite oxide particles,
The metal is mainly composed of nickel or cobalt,
A cathode active material for a non-aqueous electrolyte secondary battery, wherein the particle surface of the composite oxide particles is coated in the order of a phosphate film and carbon. The lithium metal composite oxide particles are represented by the general formula Li _x Ni _1-y M _y O ₂ (where 0.05 ≦ x ≦ 1.2, and 0 ≦ y ≦ 0.7. , M is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr). The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is a nickel composite oxide particle. The lithium metal composite oxide particles have a general formula of Li _x Co _1-y M _y O ₂ (where 0.9 ≦ x ≦ 1.2, and 0 ≦ y ≦ 0.1. , M is one or more selected from the group consisting of Mg, Al, Ti and Zr.), And lithium-containing cobalt composite oxide particles having a layered structure represented by: Positive electrode active material for non-aqueous electrolyte secondary battery.   Non-water characterized by comprising a step of coating a particle surface of a lithium metal composite oxide particle with a phosphate coating by phosphoric acid treatment, and a step of coating the particle surface coated with the phosphate coating with carbon A method for producing a positive electrode active material for an electrolyte secondary battery. The lithium metal composite oxide particles are Li _x Ni _1-y M _y O ₂ (wherein 0.05 ≦ x ≦ 1.2, and 0 ≦ y ≦ 0.7. Is one or more selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, V, Ti, Mg, Ca, and Sr. Item 5. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to Item 4. The lithium metal composite oxide particles are Li _x Co _1-y M _y O ₂ (wherein 0.9 ≦ x ≦ 1.2 and 0 ≦ y ≦ 0.1. Is at least one selected from the group consisting of Mg, Al, Ti and Zr.) The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 4.

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