JP7272052B2 - Positive electrode active material for lithium ion secondary battery and method for producing the same - Google Patents

Description

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

In recent years, with the spread of mobile electronic devices such as smartphones, tablet terminals, digital cameras, and notebook computers, the demand for lithium-ion secondary batteries, which have high energy density and can be made smaller and lighter, is increasing. In addition, there is an increasing demand for high-output lithium-ion secondary batteries as batteries for driving electric vehicles such as hybrid vehicles or for auxiliary devices. Furthermore, the practical application of an all-solid battery in which the positive electrode, the negative electrode, and the electrolyte are all solid is expected.

A lithium-ion secondary battery having the above characteristics is mainly composed of a negative electrode, a positive electrode, and an electrolyte. Materials have been proposed, and research and development are still actively carried out. In particular, lithium-ion secondary batteries using a layered or spinel-type lithium metal composite oxide as a positive electrode material can obtain a high voltage of 4V class, and are already being put to practical use.

The main lithium-metal composite oxide materials proposed so far include lithium-cobalt composite oxide (LiCoO ₂ ), which is relatively easy to synthesize, and lithium-nickel composite oxide (LiNiO 2 ), which uses nickel, which is cheaper than cobalt. ₂ ), lithium-manganese composite oxide ( _LiMn2O4 ) using manganese _, lithium-nickel-manganese-cobalt composite oxide (LiNi1 _{/3Mn1 /3Co1 / 3O2} ) using both nickel and manganese, etc. can be mentioned. Of these, lithium-nickel-based composite oxides such as lithium-nickel composite oxides containing nickel, lithium-nickel-manganese-cobalt composite oxides, and lithium-nickel-cobalt-aluminum composite oxides in which nickel is partially replaced with cobalt or aluminum are It is attracting attention as a material that can provide high capacity, and research continues with the aim of reducing resistance, which is necessary for even higher output.

By the way, in the above lithium-nickel-based composite oxide in the form of powder particles, the particle surfaces thereof are coated in order to improve the battery characteristics. For example, in Patent Document 1, a lithium-nickel-based composite oxide powder and a lithium-free tungsten compound powder are mixed and subjected to heat treatment to remove the hydroxide contained in the surface of each lithium-nickel-based composite oxide particle. A technique of reacting lithium with a tungsten compound to produce lithium transition metal compound particles coated with a tungsten-containing coating layer has been proposed.

It is described that this makes it possible to produce coated lithium-transition metal-based compound particles for lithium secondary battery positive electrode material easily and with high productivity, thereby enabling production on an industrial scale. Patent document 1 mentions two kinds of tungsten compounds, Li ₄ WO ₅ and Li ₂ WO ₄ , as the tungsten compound contained in the surface portion of the lithium-nickel-based composite oxide particles.

JP 2017-134996 A

As described above, in lithium-ion secondary batteries, as the use of lithium-ion secondary batteries expands to use in environmentally friendly vehicles, etc., positive electrodes containing positive electrode active materials are being developed with the aim of improving battery performance, such as further increasing output and lowering resistance. There is a need to further improve the properties of materials. However, in the conventional coated lithium-nickel-based composite oxide particles and the method for producing the same as disclosed in Patent Document 1, variations in output performance may occur. The present invention has been made in view of the problems associated with such conventional coated lithium-nickel-based composite oxide particles. Intended to provide substance.

In order to solve the above problems, the present inventors have extensively studied the powder characteristics of lithium-nickel-based composite oxides used as positive electrode active materials for lithium-ion secondary batteries, and the effects on the positive electrode resistance of batteries. , After mixing a base material powder made of a lithium nickel-based composite oxide that does not contain tungsten and a tungsten compound powder, when coating the surface of each particle of the base material powder with a lithium tungsten compound, the base material powder contains The inventors have found that the ratio of the molar amount of tungsten contained in the tungsten compound powder to the molar amount of lithium hydroxide affects the morphology of the coating layer made of the tungsten compound after coating, and have completed the present invention.

That is, the method for producing a positive electrode active material for a lithium ion secondary battery of the present invention is represented by the general formula Li _d Ni _1-abc Co _a W _{b Mc} O ₂ (where 0≦a≦0.35, 0.01≤b≤0.30, 0≤c≤0.35, 0.97≤d≤1.15, M is at least one selected from Mn, Ca, V, Mg, Mo, Nb, Ti and Al A method for producing a positive electrode active material comprising a coated lithium-nickel-based composite oxide powder represented by a seed element), comprising a base material powder made of a lithium-nickel-based composite oxide containing no tungsten, and a tungsten compound powder. and a heat treatment step of heat-treating the mixture to obtain a lithium-nickel-based composite oxide powder coated with a lithium-tungsten compound, wherein in the mixing step, the base material powder The ratio y/x of the molar amount y of tungsten contained in the tungsten compound powder to the molar amount x of lithium hydroxide contained in the powder is more than 0.2 and less than 1.8.

Further, the positive electrode active material for lithium ion secondary batteries of the present invention has the general formula Li _d Ni _1-ab-c Co _a W _b M _c O ₂ (where 0 ≤ a ≤ 0.35, 0.01 ≤b≤0.30, 0≤c≤0.35, 0.97≤d≤1.15, M is at least one element selected from Mn, Ca, V, Mg, Mo, Nb, Ti and Al ), which is attributed to the diffraction pattern of _Li4WO5 together with the lithium-nickel- _based composite oxide when identified by an X-ray diffraction method. It is characterized by being coated with the coating layer showing only the peak of

ADVANTAGE OF THE INVENTION According to this invention, the positive electrode active material for lithium ion secondary batteries of higher output than before can be easily provided on an industrial scale.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic explanatory drawing of the equivalent circuit used for the measurement example of the impedance evaluation of a battery, and the analysis. 1 is a perspective view and a longitudinal sectional view of a coin-type battery used for battery evaluation in Examples of the present invention. FIG.

Hereinafter, positive electrode active materials for lithium ion secondary batteries and methods for producing the same according to embodiments of the present invention will be described in the following order. It should be noted that the present invention is not limited to the contents of the following description, and can include various modifications and alternative examples without departing from the scope of the present invention.
1. Method for producing positive electrode active material for lithium ion secondary battery2. Positive electrode active material for lithium ion secondary battery3. battery rating

1. Method for Producing Positive Electrode Active Material for Lithium Ion Secondary Battery Hereinafter, each step of a method for producing a positive electrode active material according to an embodiment of the present invention will be described in detail. The present invention is not limited to the following embodiments, and any method other than the manufacturing method described below may be used as long as the positive electrode active material of the embodiment of the present invention described later can be produced. A method for producing a positive electrode active material for a lithium ion secondary battery according to an embodiment of the present invention is represented by the general formula (1): Li _d Ni _1-ab-c Co _a W _b M _c O ₂ (where 0≦a ≤0.35, 0.01≤b≤0.30, 0≤c≤0.35, 0.97≤d≤1.15, M is Mn, Ca, V, Mg, Mo, Nb, Ti and Al A method for producing a positive electrode active material for a lithium-ion secondary battery comprising a coated lithium-nickel-based composite oxide powder represented by at least one element selected from

The method for producing the coated lithium-nickel-based composite oxide powder includes a mixing step of obtaining a mixture by mixing a base material powder made of a lithium-nickel-based composite oxide containing no tungsten with a tungsten compound powder; and a heat treatment step of coating the surface of each particle of the base material powder with a coating layer made of a lithium tungsten compound to obtain a lithium nickel-based composite oxide powder coated with a lithium tungsten compound. In the mixing step, the ratio y/x of the molar amount y of tungsten contained in the tungsten compound powder to the molar amount x of lithium hydroxide contained in the base material powder is more than 0.2 and less than 1.8. is. Each of these mixing step and heat treatment step will be specifically described below.

[Mixing process]
In the mixing step, a tungsten compound powder is added to a lithium-nickel-based composite oxide powder composed of primary particles or secondary particles formed by agglomeration of the primary particles, or a mixture of these primary particles and secondary particles. It is a step of mixing by hand. The lithium-nickel-based composite oxide powder may consist of primary particles and/or secondary particles formed by agglomeration of the primary particles as described above, and may be produced using a known technique. can be done. For example, a nickel composite oxide obtained by coprecipitating metal elements constituting a lithium-nickel-based composite oxide to form a nickel composite hydroxide and then heat-treating the nickel composite hydroxide in an oxidizing atmosphere, and lithium Lithium-nickel-based composite oxide particles can be obtained by mixing with a compound and firing.

Since this lithium-nickel-based composite oxide particle will be the base material of the finally obtained positive electrode active material, its composition has the same general formula (2) as that of the base material: Li _d Ni _{1-ab CoaMcO2} (where 0≤a≤0.35, 0≤c≤0.35 _, 0.97≤d≤1.15, M is _Mn , Ca, V, Mg, Mo, Nb, Ti and at least one element selected from Al). As a method of adding the tungsten compound powder to the lithium nickel composite oxide powder as the base material, a method of adding the tungsten compound powder to the lithium metal composite oxide particles in a wet state containing water and mixing them is used. be able to. By this method, the tungsten compound dissolves in the moisture contained in the lithium-nickel-based composite oxide and permeates the lithium-nickel-based composite oxide powder, thereby making contact with the electrolyte that constitutes the lithium-nickel-based composite oxide powder. Tungsten (W) can be dispersed on possible primary particle surfaces.

In the method for producing a positive electrode active material according to the embodiment of the present invention, in order to improve the quality of the positive electrode active material, the lithium-nickel-based composite oxide powder as the base material is washed with water in advance before the mixing step. is preferred. The washing method is not particularly limited, and known methods and conditions may be used. However, excessive washing with water may result in elution of lithium from the lithium metal composite oxide powder, resulting in deterioration of battery characteristics. Therefore, it is preferable to wash sufficiently to the extent that such deterioration does not occur. A tungsten compound powder is mixed with the wet washed cake obtained by the water washing treatment in this way, or the wet powder obtained by simply adding water to the base material powder, to obtain a lithium nickel-based A mixture of composite oxide particles and tungsten compound powder (also referred to as a tungsten mixture) is obtained.

Since this tungsten compound penetrates to the surface of the primary particles inside the secondary particles, it is desirable that the tungsten compound is water-soluble and dissolves in water contained in the mixture. Also, since the water in the mixture becomes alkaline due to the elution of lithium, it may be a compound that is soluble in alkali. In addition, since the mixture is heated in the heat treatment step of the post-process, even if it is difficult to dissolve in water at room temperature, it can be dissolved in water by heating during the heat treatment step, or lithium nickel-based composite oxidation can be performed. Preferably, it reacts with the lithium compound on the surface of each particle of the solid powder to form lithium tungstate and dissolve it. Furthermore, the dissolved tungsten compound only needs to be in an amount that can penetrate to the surface of the primary particles inside the secondary particles. may be

As described above, the tungsten compound only needs to be in a state of being soluble in water during heating in the heat treatment step, and examples of such tungsten compounds include tungsten oxide, tungstic acid, ammonium tungstate, and sodium tungstate. , lithium tungstate, and the like. Among these, tungsten oxide (WO ₃ ) or monohydrate tungstic acid (WO ₃ ·H ₂ O), which is less likely to be contaminated with impurities, is preferable.

The mixing of the base material powder in the wet state and the tungsten compound is preferably carried out at an ambient temperature of 50° C. or less. If the ambient temperature exceeds 50° C., the amount of water in the mixture required to promote the reaction between the lithium compound and the tungsten compound may not be obtained due to drying during mixing. A general mixer can be used for mixing the wet state lithium-nickel-based composite oxide powder and the tungsten compound powder. For example, shaker mixers, Loedige mixers, Julia mixers, V-blenders, etc. are preferably used. At that time, it is preferable to sufficiently mix the particles under conditions that do not destroy the outline of the lithium-nickel-based composite oxide particles.

In the step of mixing the wet state lithium-nickel-based composite oxide powder and the tungsten compound powder in the manufacturing method of the embodiment of the present invention, the amount of tungsten added is the amount of tungsten contained in the finally obtained positive electrode active material. matches Therefore, the mixing ratio of the base material powder and the tungsten compound in this mixing step is the ratio y of the molar amount y of tungsten in the tungsten compound powder to the molar amount x of lithium hydroxide contained in the lithium nickel-based composite oxide powder /x is adjusted to be more than 0.2 and less than 1.8.

As a result, excessive elution of Li from the lithium-nickel-based composite oxide powder can be suppressed, and formation of lithium tungstate, which is highly effective in promoting movement of Li ions, can be promoted. As a result, the form of the coating layer made of the tungsten compound formed on the surface of the primary particles constituting the base material powder can be made into Li _{WO 5} with high ion conductivity, and as a result, the positive electrode active material has a high output. become possible.

If the molar ratio y/x is 0.2 or less, the amount of tungsten added is not sufficient, and the effect of the lithium-tungsten compound produced cannot be sufficiently exhibited, and the resistance increases and the output decreases. I don't like it. Conversely, when the molar ratio y/x is 1.8 or more, the amount of tungsten added becomes excessive, and Li ₂ WO ₄ and Li ₆ W ₂ O ₉ , which are inferior in ionic conductivity to Li ₄ WO ₅ , are produced. , unreacted tungsten compound remains, which is not preferable because the effect of reducing the resistance is limited.

The amount of lithium hydroxide contained in the lithium-nickel-based composite oxide powder can be obtained by performing a preliminary test using a tungsten-free lithium-nickel-based composite oxide powder. That is, a lithium-nickel-based composite oxide powder containing no tungsten is dispersed in a solution, and the obtained slurry is neutralized with at least one acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid and organic acids. Titrate. By converting the alkali content determined by this neutralization titration into the amount of lithium hydroxide, the amount of lithium hydroxide that can react with tungsten to form a tungsten compound can be determined.

[Heat treatment process]
The heat treatment step is a step of drying the lithium-nickel-based composite oxide powder in which tungsten (W) is dispersed in the mixing step and forming a coating layer. That is, a compound containing W and Li is formed from tungsten (W) supplied from the tungsten compound and lithium (Li) dissolved in the moisture in the wet lithium-nickel-based composite oxide powder after mixing. A coating layer having a compound containing W and Li is formed on the surface of each primary particle of the lithium-nickel-based composite oxide powder. Thereby, a positive electrode active material for a lithium ion secondary battery is obtained. This heat treatment method is not particularly limited, but in order to prevent deterioration of electrical properties when used as a positive electrode active material for lithium ion secondary batteries, heat treatment in an oxidizing atmosphere at an ambient temperature of 100 to 250 ° C. or in a vacuum atmosphere. preferably.

If the ambient temperature is less than 100° C., the moisture may not evaporate sufficiently and the compound may not be sufficiently formed. Conversely, if the ambient temperature exceeds 250° C., not only will drying take a long time, but also the scale of the production equipment will increase, making it unsuitable for production on an industrial scale. The reason why the atmosphere during the heat treatment is an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is to avoid reaction with moisture and carbonic acid in the atmosphere.

The heat treatment time is also not particularly limited, but in order to sufficiently evaporate the water content of the wet lithium-nickel composite oxide powder to form a compound, the maximum temperature of the temperature profile of the ambient temperature in the heat treatment step is 0.5. It is preferably maintained for at least an hour. In addition, if the temperature is raised in the presence of moisture, Li may be eluted from the lithium-nickel-based composite oxide powder too much. It is desirable that the ambient temperature does not exceed °C.

2. Positive electrode active material for lithium ion secondary batteries The positive electrode active material for lithium ion secondary batteries according to the present invention has the general formula Li _d Ni _1-abc Co _a W _b Mc _{O 2} (where 0 ≤ a ≤ 0.35, 0.01 ≤ b ≤ 0.30, 0 ≤ c ≤ 0.35, 0.97 ≤ d ≤ 1.15, M is Mn, Ca, V, Mg, Mo, Nb, Ti and _at least one element selected from Al). It is characterized as being _WO5 . Li ₄ WO ₅ is preferable because it has higher lithium ion conductivity than other lithium-tungsten compounds and has a high resistance-reducing effect when the surface of the lithium-nickel-based composite oxide is coated with Li 4 WO 5 .

3. Battery Evaluation The positive electrode active material of the embodiment of the present invention can be suitably evaluated by using it as a positive electrode material for a 2032-type coin battery 1 (hereinafter referred to as a coin battery) as shown in FIG. This coin-type battery 1 is composed of a case 2 and an electrode 3 housed in the case 2 . The case 2 comprises a cylindrical positive electrode can 2a with an open upper end, and a cylindrical positive electrode can 2a with an outer diameter slightly smaller than the positive electrode can 2a and with an open lower end. It is configured by fitting them in such a manner that they face each other. An electrode 3 is accommodated in a space formed by the positive electrode can 2a and the negative electrode can 2b. The electrode 3 has a structure in which a positive electrode 3a, a separator 3c, and a negative electrode 3b are stacked in this order from bottom to top. in contact with the inner surface.

Gaskets 2c are provided on both peripheral edge portions of the positive electrode can 2a and the negative electrode can 2b so as to keep them out of contact with each other. The gasket 2c serves to fix the positive electrode can 2a and the negative electrode can 2b so that they do not move relative to each other. The gasket 2c also has the function of sealing the gap between the positive electrode can 2a and the negative electrode can 2b to seal off the inside of the case 2 from the outside in an airtight and liquid-tight manner.

The coin-type battery 1 shown in FIG. 2 can be manufactured, for example, as follows. First, 52.5 mg of a positive electrode active material for a lithium ion secondary battery, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene resin (PTFE) were mixed and press-molded at a pressure of 100 MPa to form a disk having a diameter of 11 mm and a thickness of 100 μm. A positive electrode 3a having a shape is produced. The obtained positive electrode 3a is put into a vacuum dryer and dried at an atmospheric temperature of 120° C. for 12 hours.

As the negative electrode 3b, a negative electrode sheet is prepared by applying graphite powder having an average particle size of about 20 μm and polyvinylidene fluoride to one side of a copper foil punched into a disk shape of 14 mm in diameter. A polyethylene porous film having a film thickness of 25 μm is prepared as the separator 3c. As an electrolytic solution, an equal mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) with 1 M LiClO ₄ as a supporting electrolyte (manufactured by Tomiyama Pharmaceutical Co., Ltd.) is prepared. Using the positive electrode 3a, the negative electrode 3b, the separator 3c, and the electrolytic solution, the above-described coin-type battery 1 is assembled in an Ar atmosphere glove box in which the dew point is controlled at -80°C.

The positive electrode resistance, which indicates the performance of the manufactured coin-type battery 1, was evaluated as follows. When the coin-type battery 1 is charged at a charging potential of 4.1 V and measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (1255B manufactured by Solartron), the Nyquist plot shown in FIG. 1 is obtained. Since this Nyquist plot is represented as the sum of characteristic curves showing solution resistance, negative electrode resistance and its capacity, and positive electrode resistance and its capacity, fitting calculations are performed using an equivalent circuit based on this Nyquist plot, A positive electrode resistance value can be calculated. EXAMPLES The present invention will be specifically described below with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
With respect to nickel composite hydroxide particles (composition formula Ni _0.91 Co _0.045 Al _0.045 (OH) ₂ ) having an average particle size of 12 μm, hydration is performed so that Li / (Ni + Co + Al) = 1.015 mixed with lithium. The resulting mixture was fired in an oxygen stream at 745° C. for 8 hours, cooled and pulverized. 1 L of water was added to 1250 g of the pulverized powder to prepare a slurry, and the slurry was washed with water by stirring. Then, it was filtered and dried to obtain a lithium-nickel-based composite oxide powder (water-washed powder).

A portion of this water-washed powder was sampled, water was added to make a slurry, and neutralization titration with hydrochloric acid was performed to determine the alkaline content, thereby determining the amount of lithium hydroxide contained in the powder. Based on the amount of lithium hydroxide thus obtained, the washing powder and Tungsten oxide was compounded and mixed. This mixture was heat-treated in a vacuum dryer at an atmospheric temperature of 190° C. to prepare a positive electrode active material comprising a tungsten-coated lithium-nickel-based composite oxide powder.

When the obtained tungsten-coated lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, a peak attributed to the diffraction pattern of Li ₄ WO ₅ was confirmed together with the lithium-nickel-based composite oxide. Finally, the powder was pulverized through a sieve with an opening of 38 μm to obtain a positive electrode active material having a lithium tungstate compound on the surface of the primary particles.

The tungsten content and Li/Me of the obtained positive electrode active material were analyzed by the ICP method. was confirmed and its Li/Me was 0.973. The positive electrode resistance of the coin-shaped battery 1 shown in FIG. For Example 2 , Reference Example , and Comparative Examples 1 to 3, only materials and conditions changed from Example 1 are shown below. Table 1 shows the positive electrode resistance evaluation values of Examples 1 and 2, Reference Examples , and Comparative Examples 1 and 3.

[Example 2]
Tungsten-coated lithium nickel system was prepared in the same manner as in Example 1 except that the ratio of the molar amount of tungsten contained in tungsten oxide to the molar amount of lithium hydroxide contained in the water-washed powder was changed from 0.85 to 0.25. A positive electrode active material composed of a composite oxide powder was produced. When the obtained tungsten-coated lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, a peak attributed to the diffraction pattern of Li ₄ WO ₅ was confirmed together with the lithium-nickel-based composite oxide. Further, when the tungsten content was analyzed by the ICP method, the tungsten content was 0.02 atomic % with respect to the total number of atoms of Ni, Co and M.

[ Reference example ]
Tungsten-coated lithium nickel system was prepared in the same manner as in Example 1 except that the ratio of the molar amount of tungsten contained in tungsten oxide to the molar amount of lithium hydroxide contained in the water-washed powder was changed from 0.85 to 1.77. A positive electrode active material composed of a composite oxide powder was produced. When the obtained tungsten-coated lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, the diffraction of Li ₄ WO ₅ and (Li ₂ WO ₄ ) ₇ (H ₂ O) ₄ along with the lithium-nickel-based composite oxide. A peak assigned to the pattern was confirmed. Also, when the tungsten content was analyzed by the ICP method, the tungsten content was 0.16 atomic % with respect to the total number of atoms of Ni, Co and M.

[Comparative Example 1]
Tungsten-coated lithium nickel system was prepared in the same manner as in Example 1 except that the ratio of the molar amount of tungsten contained in tungsten oxide to the molar amount of lithium hydroxide contained in the water-washed powder was changed from 0.85 to 1.85. A positive electrode active material composed of a composite oxide powder was produced. When the obtained tungsten-coated lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, the diffraction patterns of (Li ₂ WO ₄ ) ₇ (H ₂ O) ₄ and WO ₃ along with the lithium-nickel-based composite oxide were observed. Assigned peaks were confirmed. Further, when the tungsten content was analyzed by the ICP method, the tungsten content was 0.17 atomic % with respect to the total number of atoms of Ni, Co and M.
Table 1 shows the results.

[Comparative Example 2]
Tungsten-coated lithium nickel system was prepared in the same manner as in Example 1 except that the ratio of the molar amount of tungsten contained in tungsten oxide to the molar amount of lithium hydroxide contained in the water-washed powder was changed from 0.85 to 0.11. A positive electrode active material composed of a composite oxide powder was produced. When the obtained tungsten-coated lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, a peak attributed to the diffraction pattern of Li ₄ WO ₅ was confirmed together with the lithium-nickel-based composite oxide. Further, when the tungsten content was analyzed by the ICP method, the tungsten content was 0.009 atomic % with respect to the total number of atoms of Ni, Co and M.

[Comparative Example 3]
A positive electrode active material composed of a tungsten-coated lithium-nickel-based composite oxide powder was prepared in the same manner as in Example 1, except that tungsten was not added. When the obtained lithium-nickel-based composite oxide powder was identified by an X-ray diffraction method, only peaks attributed to the lithium-nickel-based composite oxide were confirmed. Also, when the tungsten content was analyzed by the ICP method, no tungsten was detected. The results of Examples 1 and 2, Reference Examples and Comparative Examples 1 and 3 are summarized in Table 1 below.

[evaluation]
As is clear from Table 1 above, the positive electrode active materials of Examples 1 and 2 , which were produced according to the present invention, had a lower positive electrode resistance than the comparative examples, and the batteries had excellent characteristics. It's becoming In Comparative Example 1, since the amount of tungsten oxide charged was excessive, Li ₂ WO ₄ having a lower lithium ion conductivity than Li ₄ WO ₅ was generated, and there was tungsten oxide that remained without being able to react with lithium. Therefore, the resistance has increased.

In Comparative Example 2, although Li ₄ WO ₅ was generated, the amount of tungsten introduced was less than 0.01 atomic %, so the resistance reduction effect of the lithium tungsten compound was not sufficiently obtained, and the resistance increased. It's gone. In Comparative Example 3, since tungsten was not added, the effect of reducing resistance by forming a lithium-tungsten compound was not obtained at all, and the resistance was increased.

The lithium ion secondary battery of the present invention is suitable for electric vehicle batteries that require high output. In addition, the lithium ion secondary battery of the present invention has excellent safety and can be made smaller and higher in output, so it is suitable as a power source for electric vehicles that are limited in mounting space. The present invention can be used not only as a power source for electric vehicles that are driven purely by electric energy, but also as a power source for so-called hybrid vehicles that use a combustion engine such as a gasoline engine or a diesel engine.

REFERENCE SIGNS LIST 1 coin-type battery 2 case 2a positive can 2b negative can 2c gasket 3 electrode 3a positive 3b negative 3c separator

Claims (4)

General formula Li _d Ni _{1-abc CoaWbMcO2 (} where 0≤a≤0.35 _, 0.01≤b≤0.30 _, 0≤c≤0.35, 0 .97 ≤ d ≤ 1.15, M is at least one element selected from Mn, Ca, V, Mg, Mo, Nb, Ti and Al) from coated lithium nickel composite oxide powder A method for producing a positive electrode active material comprising: a mixing step of mixing a base material powder made of a lithium-nickel-based composite oxide containing no tungsten and a tungsten compound powder to obtain a mixture; and heat-treating the mixture to obtain lithium and a heat treatment step of obtaining a lithium-nickel-based composite oxide powder coated with a tungsten compound, wherein in the mixing step, tungsten contained in the tungsten compound powder with respect to the molar amount x of lithium hydroxide contained in the base material powder A method for producing a positive electrode active material for a lithium ion secondary battery, wherein the ratio y/x of the molar amount y of is more than 0.2 and less than 1.8. 2. The lithium ion secondary battery according to claim 1, wherein the base material powder is composed of primary particles, secondary particles obtained by agglomeration of the primary particles, or a mixture of these primary particles and secondary particles. A method for producing a positive electrode active material for The molar amount x of lithium hydroxide contained in the base material powder is obtained by adding water to the base material powder to form a slurry, and then separating the slurry into solid and liquid phases to obtain the liquid phase, and the amount of hydrochloric acid, sulfuric acid, and 3. The lithium according to claim 1 or 2, wherein the alkaline content is determined by neutralization titration with at least one acid selected from the group consisting of nitric acid and organic acids, and converted into the amount of lithium hydroxide. A method for producing a positive electrode active material for an ion secondary battery. General formula Li _d Ni _{1-abc CoaWbMcO2 (} where 0≤a≤0.35 _, 0.01≤b≤0.30 _, 0≤c≤0.35, 0 .97 ≤ d ≤ 1.15, M is at least one element selected from Mn, Ca, V, Mg, Mo, Nb, Ti and Al) from coated lithium nickel composite oxide powder characterized by being coated with a coating layer that exhibits only peaks attributed to the diffraction pattern of Li _{WO 5} together with the lithium-nickel-based composite oxide when identified by an X-ray diffraction method. A positive electrode active material for lithium ion secondary batteries.

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