JP6599209B2 - Positive electrode active material for lithium ion battery, positive electrode for lithium ion battery and lithium ion battery - Google Patents

Description

  The present invention relates to a positive electrode active material for a lithium ion battery, a positive electrode for a lithium ion battery, and a lithium ion battery.

Lithium-containing transition metal oxides are generally used as positive electrode active materials for lithium ion batteries. Specifically, lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc., improved characteristics (higher capacity, cycle characteristics, storage characteristics, reduced internal resistance) In order to improve the rate characteristics and safety, it is underway to combine them. Lithium ion batteries for large-scale applications such as in-vehicle use and load leveling are required to have different characteristics from those of conventional mobile phones and personal computers.

One of the techniques used for the positive electrode active material for lithium ion batteries is surface modification. This is mainly based on the following three technologies (a) to (c).
(A): The side reaction which decomposes | disassembles electrolyte solution on the surface of an active material is suppressed as much as possible. In the past, oxides of single elements such as Al ₂ O ₃ and ZrO ₂ were mainly used, but if the entire surface of the active material is modified with this, Li ions cannot be inserted or desorbed. Is mainly based on the technique of partially modifying the surface or modifying the surface with a Li ion conductor or an active material.
(B): The transition metal (particularly Mn) is prevented from being eluted from the active material by the hydrogen fluoride impurity in the electrolytic solution. In this case as well, the entire surface of the active material cannot be modified in the same manner as in (a), so there is currently a technology for suppressing Mn elution by reacting hydrogen fluoride impurities in the electrolytic solution by blending with a Ni-based active material. It is the subject. The reason why Mn is particularly targeted for elution suppression is that it easily reacts with carbon of the negative electrode, and when the positive electrode is a Mn-based active material and the negative electrode is a graphite-based active material, charging and discharging are repeated. Depending on the design, only 10 times the initial discharge capacity is lost in 10 cycles.
(C): There is a technique for coating a material with high electron conductivity on an active material with low electron conductivity. This technology has been established as a technology for coating carbon materials on phosphate-based, silicate-based, and lithium-titanium-based active materials, and is easy to manufacture. Has been.

  When considering the technologies (a), (b), and (c) above, the surface modification technology does not inhibit lithium ion conduction and also suppresses electrolyte decomposition, and further improves battery characteristics. It can be said that is demanded.

JP 2009-087647 A

Here, as a surface modification technique of the positive electrode active material, for example, in Patent Document 1, an additive that does not work as an active material such as a Zr ⁴⁺ compound and an electrolyte solution additive such as a tertiary carbonate are combined. In addition, the overcharge safety at the time of high rate has been improved compared to the conventional case. In this way, there have been many technologies that have been studied as countermeasures in consideration of the effect of the decomposition of ethylene carbonate and dialkyl carbonate, which were the main components of the electrolyte, on the cycle characteristics. In some cases, the reaction between the material and the substitution element of the positive electrode material is considered. Therefore, consideration of the structure and state of the surface is even more important. However, as in the case of focusing on the decomposition of the main component of the electrolytic solution, there is no technology that focuses on the reaction mechanism and the reaction point so far. Therefore, as for the technique of the electrolytic solution additive, there are still many contents that prevent the electrolytic solution main component from being decomposed on the positive electrode by decomposing before the electrolytic solution main component. However, when considering further improvement of the battery, it is very important to consider the compatibility between the positive electrode material additive element and the electrolyte additive.

  In general, it has been found that when a battery is manufactured and a charging operation is performed at an appropriate current, a compound formed by the decomposition of the electrolytic solution is formed on the positive electrode surface and the negative electrode surface. A film made of this compound is called a Solid Electrolyte Interface (SEI: solid electrolyte interface). Regarding SEI, although there are some reports on what the compound is, no conclusion has been reached. Therefore, it is also unclear whether it is a decomposition product of only the electrolytic solution or a product in which both the electrode and the electrolytic solution react and are altered. However, it can be easily predicted that the lithium ions have passed through the SEI and are desorbed. Therefore, if the movement of lithium ions is stopped by this SEI, or if the movement of lithium ions is slow in SEI, battery characteristics will be greatly affected. In this regard, it is known that the decomposition product of the electrolytic solution has a smooth conduction of lithium ions. However, if the electrolytic solution is decomposed, the risk of liquid drainage increases. In addition, a compound similar to an electrolytic solution that decomposes at a high potential (for example, vinylene carbonate) is added as an electrolytic solution additive. On the other hand, addition of sulfolane to the positive electrode is considered to be effective, but since a uniform SEI is not formed, the addition amount must be increased, and the melting point is near room temperature, resulting in an increase in viscosity.

  Accordingly, the present invention provides a positive electrode active material for a lithium ion battery that can produce a lithium ion battery with better cycle characteristics and better storage characteristics at high temperatures in a non-aqueous electrolyte battery with a small amount of sulfolane added. The issue is to provide.

  As a result of various studies to solve such problems, the present inventor formed an oxide containing Li, Zr, and W on the surface of lithium composite oxide particles having a predetermined composition for the positive electrode active material. In the non-aqueous electrolyte battery to which a small amount of sulfolane is added, by controlling the space group of the oxide structure containing Li, Zr, and W to have a portion that is P213 at room temperature, the cycle characteristics are good, It was also found that a battery having good storage characteristics at high temperatures can be produced.

In one aspect, the present invention completed on the basis of the above knowledge has a composition formula: Li _x Ni _a Co _b Mn _c O ₂
(In the above formula, 1.01 ≦ x ≦ 1.05, a ≧ 0.5, 0 <b ≦ 0.25, 0 <c ≦ 0.35)
The positive electrode active for lithium ion batteries which has the oxide B which contains Li, Zr, and W on the surface of the particle | grains represented by these, and the space group of the structure of the said oxide B has a part which is P213 at normal temperature It is a substance.

In the positive electrode active material in one embodiment for a lithium ion battery of the present invention, the mass ratio of the said B A B: A is from 1: 99 to 5: 95.

  In another embodiment of the positive electrode active material for a lithium ion battery of the present invention, the composition of B is 1: 2 to 2: 1 in terms of a molar ratio of Zr: W, and is based on the total amount of Zr and W. The amount of Li is 1.

  In another aspect, the present invention is a lithium ion battery positive electrode having the lithium ion battery positive electrode active material of the present invention.

  In still another aspect, the present invention is a lithium ion battery having the positive electrode for a lithium ion battery of the present invention, a negative electrode, and an electrolyte containing sulfolane.

  According to the present invention, in a non-aqueous electrolyte battery with a small amount of sulfolane added, a positive electrode active material for a lithium ion battery capable of producing a lithium ion battery having better cycle characteristics and good storage characteristics at high temperatures is provided. Can be provided.

It is the graph which plotted the nuclear quadrupole parameter (delta) concerning an Example and a comparative example with respect to temperature.

(Configuration of positive electrode active material for lithium ion battery)
The positive electrode active material for a lithium ion battery of the present invention has a composition formula: Li _x Ni _a Co _b Mn _c O ₂
(In the above formula, 1.01 ≦ x ≦ 1.05, a ≧ 0.5, 0 <b ≦ 0.25, 0 <c ≦ 0.35)
A portion where the space group of the oxide structure containing Li, Zr, and W has an oxide B containing Li, Zr, and W on the surface of the particle A represented by A positive electrode active material for a lithium ion battery. The surface-modified oxide is in the P213 phase at room temperature, but when it reaches a temperature of about 400 to 500 K or higher, it becomes the Pa-3 phase. (The same applies hereinafter.)

As described above, the core lithium composite oxide particles that are surface-modified with an oxide containing Li, Zr, and W have a composition formula: Li _x Ni _a Co _b Mn _c O ₂
(In the above formula, 1.01 ≦ x ≦ 1.05, a ≧ 0.5, 0 <b ≦ 0.25, 0 <c ≦ 0.35)
It is represented by Here, the ratio of lithium is 1.01 to 1.05. However, if the ratio is less than 1.01, it is difficult to maintain a stable crystal structure, and if it exceeds 1.05, the high capacity of the battery may not be secured. Because there is. Moreover, since the composition of nickel is 0.5 or more, the capacity, output, and safety of the lithium ion battery using the positive electrode active material for lithium ion battery are improved in a well-balanced manner. The composition of nickel in the positive electrode active material for lithium ion batteries is preferably 0.5 to 0.9, more preferably 0.7 to 0.9, and even more preferably 0.8 to 0.9.

The oxide (shell) containing Li, Zr, and W that modifies the surface of the lithium composite oxide particles that form the core has a portion in which the space group of the structure of the oxide is P213 at room temperature. The oxide containing Li, Zr, and W may be formed in a layered manner on the surface of the lithium composite oxide particle as the core, or may be formed so as to partially adhere to the particle surface. .
The reason why the cycle efficiency and the storage rate are improved by the above configuration is unknown at present, but the present invention assumes as follows. That is, when the carbon-sulfur bond in the sulfolane weakly adsorbed by the transition metal of Zr or W is decomposed and heat is generated, the rolling of Zr-OW based on the structure of P213 or Pa-3 occurs. Then, it is considered that the adsorbed sulfolane is detached and further decomposition is suppressed. Conventionally, there are many techniques in which Zr or W is added to the positive electrode active material, but the structure is not based on the structure of P213 or Pa-3, but approximately Li ₂ ZrO ₃ (space group C2 / C) or Li ₂ WO ₄ Mostly due to the structure of (space group I41 / amd). Therefore, even when a conventional positive electrode active material is applied to a sulfolane-added battery, Zr—O—W based on the structure of P213 or Pa-3 does not roll, and decomposition beyond sulfolane is inevitable. As a result, sulfolane is decomposed at random in the initial stage, and SEI has thick and thin portions. Although the cycle characteristics are improved, the width is considered to be small. On the other hand, the positive electrode active material of the present invention is an oxide containing Li, Zr, and W that modifies the surface of the lithium composite oxide particles that are the core, and the space group of the structure of the oxide has a room temperature. Therefore, the positive electrode active material decomposes sulfolane more uniformly in the lithium ion battery and uniforms the thickness of SEI, so that the cycle characteristics are remarkably improved. Further, since lithium is contained in the oxide (shell) containing Li, Zr, and W which are modifiers on the core particle surface, the SEI produced as a result of the decomposition reaction of sulfolane contains lithium. As a result, the storage characteristics at high temperatures are improved together with the cycle characteristics.

The mass ratio B of the said B A: A is 1: 99 to 5: is preferably 95. If B is 1% or less of the whole, it may be difficult to satisfy the required cycle characteristics, and if it exceeds 5% of the total of A and B, the capacity may be reduced.

  Preferably, the composition of B is 1: 2 to 2: 1 in terms of a molar ratio of Zr: W, and the amount of Li is 1 with respect to the total amount of Zr and W. In the composition of B, when the amount of Li is large, impurities such as lithium carbonate and lithium hydroxide are generated on the surface, and when the amount is small, a side reaction between the P213 phase and the electrolytic solution may occur. In this case, if the amount of the P213 phase itself is large, the side effect can be suppressed because the rolling effect is increased. However, if the P213 phase is small and the amount of Li in the phase is small, the side reaction occurs and the cycle characteristics deteriorate. May lead to Further, when the ratio of Zr and W is outside the range of 1: 2 to 2: 1, another phase may be generated, and the capacity or cycle characteristics may be deteriorated.

(Configuration of positive electrode for lithium ion battery and lithium ion battery having the same)
The positive electrode for a lithium ion battery according to an embodiment of the present invention includes, for example, a positive electrode mixture prepared by mixing a positive electrode active material for a lithium ion battery having the above-described configuration, a conductive additive, and a binder from an aluminum foil or the like. The current collector has a structure provided on one side or both sides. Moreover, the lithium ion battery which concerns on embodiment of this invention has the positive electrode for lithium ion batteries of such a structure, a negative electrode, and the electrolyte containing a sulfolane.

(Method for producing positive electrode active material for lithium ion battery)
Next, the manufacturing method of the positive electrode active material for lithium ion batteries which concerns on embodiment of this invention is demonstrated in detail.

-Synthesis | combination of the oxide (modifier) containing Li, Zr, and W The oxide containing Li, Zr, and W which modifies the surface of the particle | grains of lithium composite oxide is produced as follows.
First, Li alkoxide, Zr alkoxide-containing alcohol solution, W alkoxide-containing alcohol solution, and acetylacetone are mixed so that the molar ratio of Li: Zr: W: acetylacetone becomes a predetermined value, and then water is added. To make a gel.
Next, the gel is calcined, for example, at 400 to 500 ° C. for 1 to 20 hours (this temperature and time can be appropriately changed as long as those skilled in the art can remove organic substances). Subsequently, the powder produced by calcining is filled in a mold, and is 585 to 612 ° C. at a press pressure of 30 to 250 MPa and a temperature increase rate of 70 to 500 ° C./min in an inert gas atmosphere by a discharge plasma sintering apparatus. The temperature is rapidly raised to 1 and kept for 1 to 20 minutes, and then poured into a large amount of water kept at 4 to 40 ° C. and rapidly cooled.
After rapid cooling, coarsely pulverized by a roll mill, filled in a suitable pot together with zirconia beads having a diameter of about 2 mm, Solmix A-7, and finely pulverized by a vibration mill. The weight ratio of powder, beads and solmix is, for example, 1: 0.5 to 7: 0.001 to 0.005, and the pulverization time is 30 to 120 minutes.
After pulverization, the extracted powder was classified with an appropriate sieve, and the substance under the sieve was used as a modifying substance.

Synthesis of core lithium composite oxide For lithium composite oxide, the techniques described in a number of prior patents (for example, Japanese Patent Application Laid-Open No. 2003-168428) can be used. Is described below.
First, nickel sulfate, manganese sulfate, and cobalt sulfate are dissolved in pure water at a predetermined molar ratio of about 40 ° C., and an aqueous solution A of about 40 ° C. with a concentration of (Ni + Co + Mn) of 1 to 2 mol / kg is obtained. Make it. The aqueous solution A is substantially free of components other than Ni, Co, Mn, SO ₄ and H ₂ O.
Separately from the aqueous solution A, NaOH is dissolved in pure water to prepare a 1.5 to 3 mol / kg NaOH aqueous solution B.
Separately from the aqueous solutions A and B, the ammonia aqueous solution is diluted with pure water to produce an ammonia aqueous solution C of 0.001 mol% or more. About this C, the thing of the saturation density | concentration in the temperature to handle can be used.
Next, the temperature of the aqueous solutions B and C is heated to about 40 ° C., and nitrogen is passed through each of the separately prepared reaction tanks and the aqueous solutions A, B, and C to drive out air.
Next, after the aqueous solutions A and B are fed to the reaction vessel for about 10 minutes at 1 to 2 L per minute with a tube pump or the like to form seed crystals (at this time, C is added simultaneously with the feeding of the aqueous solutions A and B). The aqueous solutions A, B and C may be fed by 0.5 to 1 L per minute by a tube pump. The produced slurry is subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrack), and all liquid feeding is stopped when the average particle size (D50) reaches a desired value. This is filtered and washed with water, and then heated at 320 to 600 ° C. for 0.5 to 15 hours to obtain a precursor. The firing temperature and firing time can be appropriately changed as long as those skilled in the art consider that a hydroxide can be converted into an oxide.

Next, the contents of nickel, manganese and cobalt contained in the precursor are analyzed by ICP-MS, and LiOH.H ₂ O is adjusted so that Li / (Ni + Co + Mn) is 1.00 to 1.2 in molar ratio. Determine the amount. The molar ratio can be appropriately changed as long as those skilled in the art ultimately believe that the residual alkali content can be sufficiently suppressed. Analysis of ICP-MS is performed by a conventional method. LiOH · H ₂ O is pulverized with a jet mill, and then the precursor and LiOH · H ₂ O are put into a Henschel mixer container in this order, and the lid is closed and mixed for 1 to 10 minutes. After taking out the mixed powder, it is heated to about 500 ° C. at 15 ° C./min or less, and further to 750 to 1000 ° C. at about 5 ° C./min. Next, hold at 750 to 1000 ° C. for 1 to 20 hours, cool to about 400 ° C. at about 5 ° C./min, then remove from the furnace and crush using a roll mill, pulverizer, etc., and lithium composite oxidation that becomes the core Get things.

Synthesis of positive electrode active material Lithium composite oxide which is an oxide (modifier) containing Li, Zr and W, prepared by the above-described method, and a core powder prepared by the above-described method. At the same time, the positive electrode active material is obtained by putting the particles in a dry particle compounding apparatus at a predetermined weight ratio and compositing the particles.
Thereafter, if necessary, the positive electrode active material is pulverized using, for example, a pulverizer to obtain a positive electrode active material powder.

  Examples for better understanding of the present invention and its advantages are provided below, but the present invention is not limited to these examples.

(Comparative Example 1)
Synthesis of core lithium composite oxide First, nickel sulfate, manganese sulfate, and cobalt sulfate were dissolved in pure water at 40 ° C., the concentration of (Ni + Co + Mn) was 1.15 mol / kg, and Ni: Co: Mn A 40 ° C. aqueous solution A having a molar ratio of 8: 1: 1 was prepared. The aqueous solution A is substantially free of components other than Ni, Co, Mn, SO ₄ and H ₂ O. Separately from the aqueous solution A, NaOH was dissolved in pure water to prepare a 1.85 mol / kg NaOH aqueous solution B. In addition, a commercially available about 29 wt% ammonia aqueous solution (Kanto Chemical) was diluted with pure water to obtain a 0.1 mol% ammonia aqueous solution C. The temperature of the aqueous solutions B and C was set to 40 ° C. by heating, and nitrogen was passed through each of the separately prepared reaction tanks and aqueous solutions A, B, and C to expel the air. Then, after the aqueous solutions A and B are sent to the reaction tank by 1.5 L per minute to the reaction tank for about 10 minutes to form seed crystals, the aqueous solutions A, B and C are sent 0.8 L per minute by the tube pump. Liquid. The produced slurry was subjected to particle size distribution measurement with a laser diffraction / scattering type particle size distribution meter (Microtrac), and when the average particle diameter (D50) exceeded 15 μm, all liquid feeding was stopped. This was filtered and washed with water, and then heated in air at 400 ° C. for 3 hours to obtain a precursor.
Next, the contents of nickel, manganese and cobalt contained in the precursor were analyzed by ICP-MS, and the amount of LiOH.H ₂ O was determined so that Li / (Ni + Co + Mn) was 1.01 in terms of molar ratio. . ICP-MS was analyzed by a conventional method. LiOH · H ₂ O was pulverized with a jet mill, and then the precursor and LiOH · H ₂ O were put into the Henschel mixer vessel in that order, and the lid was closed and mixed for 5 minutes. After taking out the mixed powder, it is heated to 500 ° C. at 10 ° C./min, heated to 780 ° C. at 5 ° C./min, held at 780 ° C. for 10 hours, cooled to 400 ° C. at 5 ° C./min, and then the furnace door Was gradually opened, cooled to room temperature, and pulverized to obtain a lithium composite oxide as a core.

Example 1
Synthesis of oxide (modifier) containing Li, Zr and W Lithium isopropoxide, zirconium (IV) isopropoxide in isopropanol solution, tungsten (VI) isopropoxide in isopropanol solution, acetylacetone in Li: Zr: W: acetylacetone was mixed in nitrogen so that the molar ratio was 3: 1: 2: 6, and then total water of 1 mol for Li, 4 mol for Zr, and 6 mol for W Was added to form a gel. Next, the gel was calcined at 450 ° C. for 12 hours. The calcined powder is filled in a graphite mold (jig diameter: 20 mmφ), and the temperature is raised to 600 ° C. at a pressurization pressure of 50 MPa and a heating rate of 100 ° C./min in an argon gas atmosphere of 1 atm by a discharge plasma sintering apparatus. The mixture was warmed, held for 10 minutes, and then poured into a large amount of water held at 20 ° C. for rapid cooling. After rapid cooling, the mixture was coarsely pulverized with a roll mill, filled into a pot together with φ2 mm zirconia beads and Solmix A-7, and finely pulverized with a vibration mill. The weight ratio of powder, beads and solmix was 1: 2: 0.0002 and the grinding time was 46.06 minutes. After pulverization, the taken-out powder was passed through a sieve having an eye size of 22 μm at room temperature, and the substance under the sieve was used as a modifying substance. When XRD of this modifier was measured at room temperature, it was identified as P213.

-Synthesis | combination of positive electrode active material Next, the powder under a sieve which is an oxide (modifier) containing Li, Zr, and W, together with a lithium composite oxide serving as a core produced in the same manner as in Comparative Example 1, The positive electrode active material was obtained by putting in the dry particle compounding apparatus so that the weight ratio of the powder under the sieve: lithium composite oxide as the core was 1:99 and compositing the particles. This was designated Example 1.

(Example 2)
A positive electrode active material was produced in the same manner as in Example 1 except that the composition of Ni: Co: Mn in the core was changed to 5: 2: 3, and Example 2 was obtained.

(Comparative Example 2)
A positive electrode active material was prepared in the same manner as in Comparative Example 1 except that the composition of Ni: Co: Mn in the core was changed to 5: 2: 3, and Comparative Example 2 was obtained.

(Example 3)
A positive electrode active material was prepared in the same manner as in Example 1 except that the modifying material Li: Zr: W: acetylacetone was used in a molar ratio of 3: 2: 1: 6.

Example 4
A positive electrode active material was prepared in the same manner as in Example 1 except that the weight ratio of the powdered powder: core lithium composite oxide was 5:95 during the synthesis of the modifying material. It was set to 4.

(Example 5)
A positive electrode active material was prepared in the same manner as in Example 1 except that the composition of Ni: Co: Mn in the core was set to 85: 7.5: 7.5.

(Comparative Example 3)
A positive electrode active material was produced in the same manner as in Comparative Example 1 except that the composition of Ni: Co: Mn in the core was set to 85: 7.5: 7.5.

(Example 6)
A positive electrode active material was produced in the same manner as in Example 1 except that the molar ratio of Li / (Ni + Co + Mn) of the core was 1.05, and Example 6 was obtained.

(Comparative Example 4)
Synthesis of oxide (modifier) containing Li and Zr Commercially available Li ₂ CO ₃ and ZrO ₂ were mixed so that the molar ratio of Li: Zr was 2: 1, and then placed in a firing furnace. Heated to 500 ° C. at 500 ° C./min to 900 ° C. at 5 ° C./min, held at 900 ° C. for 10 hours, cooled to 400 ° C. at 5 ° C./min, and then cooled to room temperature by opening the furnace door. After taking out from the firing furnace, it was coarsely pulverized with a roll mill, filled into a pot together with φ2 mm zirconia beads and Solmix A-7, and finely pulverized with a vibration mill. The weight ratio of powder, beads and solmix was 1: 2: 0.0002 and the grinding time was 46.06 minutes. After pulverization, the taken-out powder was passed through a sieve having an eye size of 22 μm at room temperature, and the substance under the sieve was used as a modifying substance. When XRD of this modifier was measured at room temperature, it was identified as space group C2 / C (Li ₂ ZrO ₃ ).
Synthesis of positive electrode active material Next, the powder under the sieve, which is an oxide (modifier) containing Li and Zr, together with the lithium composite oxide that becomes the core produced in the same manner as in Comparative Example 1 The positive electrode active material was obtained by putting the powder in the dry particle composite apparatus so that the weight ratio of the powder: core lithium composite oxide was 1:99 and compositing the particles. This was designated as Comparative Example 4.

(Comparative Example 5)
Synthesis of oxide (modifier) containing Li and W After mixing commercially available Li ₂ CO ₃ and WO _{3 so} that the molar ratio of Li: W is 2: 1, the mixture is put in a firing furnace. Heated to 500 ° C. at 500 ° C./min to 900 ° C. at 5 ° C./min, held at 900 ° C. for 10 hours, cooled to 400 ° C. at 5 ° C./min, and then cooled to room temperature by opening the furnace door. After taking out from the firing furnace, it was coarsely pulverized with a roll mill, filled into a pot together with φ2 mm zirconia beads and Solmix A-7, and finely pulverized with a vibration mill. The weight ratio of powder, beads and solmix was 1: 2: 0.0002 and the grinding time was 46.06 minutes. After pulverization, the taken-out powder was passed through a sieve having an eye size of 22 μm at room temperature, and the substance under the sieve was used as a modifying substance. When XRD of this modifying substance was measured at room temperature, it was identified as space group I41 / amd (Li ₂ WO ₄ ).
Synthesis of positive electrode active material Next, the powder under the sieve, which is an oxide (modifier) containing Li and W, together with the lithium composite oxide that becomes the core produced in the same manner as in Comparative Example 2 The positive electrode active material was obtained by putting the powder in the dry particle composite apparatus so that the weight ratio of the powder: core lithium composite oxide was 1:99 and compositing the particles. This was designated as Comparative Example 5.

(Comparative Example 6)
Synthesis of mixed phase (modifier) of oxide containing Li and Zr and oxide containing Li and W Commercially available Li ₂ CO ₃ , ZrO _2, and WO ₃ are in a molar ratio of Li: Zr: W. 6: 1: 2 and then put into a firing furnace, heated to 500 ° C. at 10 ° C./min, heated to 900 ° C. at 5 ° C./min, held at 900 ° C. for 10 hours, and kept at 5 ° C. / It cooled to 400 degreeC by min. Then, the furnace door was opened and it cooled to room temperature. After taking out from the firing furnace, it was coarsely pulverized with a roll mill, filled into a pot together with φ2 mm zirconia beads and Solmix A-7, and finely pulverized with a vibration mill. The weight ratio of powder, beads and solmix was 1: 2: 0.0002 and the grinding time was 46.06 minutes. After pulverization, the taken-out powder was passed through a sieve having an eye size of 22 μm at room temperature, and the substance under the sieve was used as a modifying substance. When XRD of this modifying substance was measured at room temperature, it was identified as a mixed phase of space group C2 / C (Li ₂ ZrO ₃ ) and space group I41 / amd (Li ₂ WO ₄ ).
-Synthesis | combination of positive electrode active material Next, the powder under a sieve which is a mixed phase (modifier) of the oxide containing Li and Zr, and the oxide containing Li and W is used similarly to the comparative example 1. Along with the prepared lithium composite oxide as a core, the powder is put into a dry particle composite apparatus so that the weight ratio of the powder under the sieve: lithium composite oxide as a core is 5:95, and the particles are composited. Thus, a positive electrode active material was obtained. This was designated as Comparative Example 6.

(Comparative Example 7)
Synthesis of amorphous oxide (modified substance) containing Li, Zr, and W Commercially available Li ₂ CO ₃ , ZrO _2, and WO ₃ have a molar ratio of Li: Zr: W of 6: 1: 2. After mixing in such a manner, it is put in a firing furnace, heated to 500 ° C. at 10 ° C./min, heated to 900 ° C. at 5 ° C./min, held at 900 ° C. for 10 hours, opened the furnace door, and taken out the fired product. Quenched until. After quenching, it was coarsely pulverized with a hammer mill, filled into a pot together with φ2 mm zirconia beads and Solmix A-7, and finely pulverized with a vibration mill. The weight ratio of powder, beads and solmix was 1: 5: 0.0002 and the grinding time was 46.06 minutes. After pulverization, the taken-out powder was passed through a sieve having an eye size of 22 μm at room temperature, and the substance under the sieve was used as a modifying substance. When the XRD of this modifying substance was measured at room temperature, no peak was detected and it was determined that the substance was amorphous.
Synthesis of positive electrode active material Next, a lithium composite oxide serving as a core prepared by producing a powder under a sieve, which is an amorphous oxide (modifier) containing Li, Zr, and W, in the same manner as in Comparative Example 1. In addition to the powder, the powder under the sieve: the lithium composite oxide serving as the core is put into a dry particle composite device so that the weight ratio of the lithium composite oxide is 5:95, and the particles are composited to obtain a positive electrode active material. It was. This was designated as Comparative Example 7.

(Evaluation)
Each evaluation was carried out under the following conditions using the samples of Examples and Comparative Examples thus prepared.
-Evaluation of composition of positive electrode material-
About the coating layer, it analyzed by EPMA and the molar ratio of each metal was computed. The metal content in each positive electrode material was measured with an inductively coupled plasma optical emission spectrometer (ICP-OES), and the composition ratio (molar ratio) of each metal was calculated. Further, the oxygen content was measured by the LECO method, and it was confirmed that all were “O ₂ ” in the composition formula.

-Space group of oxide (modifier) structure containing Li, Zr and W-
The space group of the structure of the oxide (modifier) containing Li, Zr and W was evaluated by time-resolved perturbed angular correlation spectroscopy using a 497.5-72.0 keV γ-γ cascade. Specifically, Z. Natureforsch. 55a, 301-310 (2000). According to the method of Experimental.
First, thermal neutron capture was performed on ¹⁸⁶ W in the active material to generate ¹⁸⁷ W (half-life 23.72 hours). This ¹⁸⁷ W generates ¹⁸⁷ Re (half-life 555.3 nanoseconds) by β decay. At this time, γ rays are emitted at the same time, but γ ₁ (497.5 keV) and γ ₂ (72.0 keV) are continuously emitted. The time t from the release of γ ₁ to the release of γ ₂ was measured, and the nuclear quadrupole parameter δ due to γ ₂ was calculated. This measurement was performed at three or more points within a temperature range of about 17 to 403 K, and the nuclear quadrupole parameter δ was plotted against temperature (FIG. 1). In the graph shown in FIG. 1, if the curve is convex downward, the modifying substance has a P213 space group at room temperature.

-Evaluation of battery characteristics-
A mixture of 80 g of a positive electrode active material, 15 g of acetylene black, 50 g of PVdF (polyvinylidene difluoride) dissolved in NMP (N-methyl-2-pyrrolidone) at a concentration of 10 wt%, and 50 g of pure NMP, It apply | coated on foil and dried at 200 degreeC, it pressurized with the line load of 10 kN / cm, and it was set as the positive electrode. Similarly, 90 g of graphite and 100 g of PVdF dissolved in NMP at a concentration of 10 wt% were mixed, applied onto a copper foil, dried at 200 ° C., and pressurized at a line load of 10 kN / cm to obtain a negative electrode. Using a 1: 1 mixed solvent of ethylene carbonate and dimethyl carbonate containing 1 mol / L LiPF ₆ to which 0.005 wt% of sulfolane was added as an electrolyte, the above positive electrode, A negative electrode and a commercially available separator were cut out and placed in an argon glove box, the separator was impregnated with the electrolyte, and the electrolyte was also dropped and soaked into the positive electrode and the negative electrode. These were caulked in combination with a 2032 type coin cell member to produce a 2032 type coin cell. This was charged and discharged at room temperature at 0.2 C and 3.0 to 4.3 V, and the initial discharge capacity and the discharge capacity after 300 cycles were measured. (Discharge capacity after 300 cycles) / (Initial discharge capacity) Was defined as cycle efficiency. In addition, a coin cell that is charged and discharged only once for each sample is prepared, and this coin cell is held at 4.3 C for one week at 0.2 C, 40 ° C., and then 0.2 C, 3. Charging / discharging was performed at 0 to 4.3 V, and the discharge capacity after storage was measured. Then, (discharge capacity after storage) / (initial discharge capacity) was defined as the storage rate.
These results are shown in Table 1.

Claims (5)

Composition _{formula: Li x Ni a Co b Mn} c O 2
(In the above formula, 1.01 ≦ x ≦ 1.05, a ≧ 0.5, 0 <b ≦ 0.25, 0 <c ≦ 0.35)
The positive electrode active for lithium ion batteries which has the oxide B which contains Li, Zr, and W on the surface of the particle | grains represented by these, and the space group of the structure of the said oxide B is P213 at normal temperature material. The mass ratio B of the said B A: A is 1: 99 to 5: cathode active material for a lithium ion battery according to claim 1 which is 95.   3. The lithium ion according to claim 1, wherein the composition of B is 1: 2 to 2: 1 in a molar ratio of Zr: W, and the amount of Li is 1 with respect to the total amount of Zr and W. 4. Positive electrode active material for batteries.   The positive electrode for lithium ion batteries which has the positive electrode active material for lithium ion batteries as described in any one of Claims 1-3.   The lithium ion battery which has a positive electrode for lithium ion batteries of Claim 4, a negative electrode, and the electrolyte containing a sulfolane.

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