JP2000058053A - Manufacture of positive-electrode active material for nonaqueous-electrolyte secondary battery, positive- electrode active material for nonaqueous-electrolyte secondary battery, and nonaqueous-electrolyte secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, at a low cost, a large-capacity positive electrode for a nonaqueous-electrolyte secondary battery by reducing the amount of gaseous carbon dioxide and water contained in air at synthesis. SOLUTION: A manufacturing method of a cobalt-lithium solid solution compound nickel oxide expressed by the general formula, LixNi(1-y)CoyO2, (0.9<=x<=1.2, 2.0<=y<0.5) as a positive-electrode active material for a nonaqueous- electrolyte secondary battery, has a first-stage baking process for baking within the range of 300 to 700 deg.C for 2 hours or more in air from which gaseous carbon dioxide and water are removed, followed by a pulverizing process at 100 deg.C or under, and a second-stage baking process for baking a product obtained in the processes within the range of 700 to 900 deg.C for 2 hours or more. A process for pulverizing active material is performed in an atmosphere of 0.01 vol.% or less of gaseous carbon dioxide and a water dew point of 0 deg.C or under.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to an improvement in a method for producing a positive electrode active material thereof.

[0002]

2. Description of the Related Art In recent years, portable and portable electronic devices have been rapidly advanced, and there is a demand for a small, lightweight, and high energy density secondary battery as a power source for these devices.
In particular, non-aqueous electrolyte secondary batteries, especially lithium secondary batteries,
It is attracting attention as a battery having high density and high energy. Conventionally, lithium cobalt oxide (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn) have been used as a positive electrode active material of a lithium secondary battery.
₂ O ₄ ) is known, and secondary batteries using lithium cobalt oxide have already been commercialized. However, lithium cobalt oxide has problems of resources and cost of cobalt, and lithium nickel oxide and the like are attracting attention as a positive electrode active material instead, and development of cobalt solid solution lithium composite nickel oxide and the like is being promoted. . This lithium nickelate is lower cost than lithium cobaltate,
Due to its high capacity, research and development is actively pursued.

Heretofore, lithium nickel oxide has greatly different charge / discharge characteristics depending on the synthesis method, and it has been considered difficult to synthesize lithium nickel oxide exhibiting a large charge / discharge capacity. However, recently, in studying synthesis conditions, a method for synthesizing lithium nickelate exhibiting a large charge / discharge capacity has been reported. For example, a method of synthesizing lithium nickelate using nickel hydroxide and lithium hydroxide as raw materials (Japanese Patent Laid-Open No. 5-290851), pulverization, mixing, and crystallization after the first baking for uniform baking. A method of performing a second-stage baking to promote the treatment (Japanese Unexamined Patent Publication No. 9-251
No. 854).

[0004]

However, in any of the synthesizing methods, it is a method of obtaining a lithium-containing composite oxide by reacting cobalt-containing nickel hydroxide and lithium hydroxide as raw materials in the air. Lithium is excessively used. Also, in the stage of mixing and baking cobalt-containing nickel hydroxide and lithium hydroxide, a large amount of an oxidizing agent, mainly oxygen gas, is required to oxidize the valence of nickel and cobalt from divalent to trivalent. And consume. Therefore, since it is necessary to maintain the oxygen partial pressure in the air at a certain level or more for the synthesis, it is necessary to introduce air or oxygen gas into the firing furnace.

However, when the air is used as it is, about 0.03% by volume of carbon dioxide gas is contained in the air, and the carbon dioxide gas is used as a raw material for synthesizing the lithium-containing composite oxide. Reacts easily with lithium oxide,
This produces lithium carbonate.

The produced lithium carbonate and the cobalt-containing nickel hydroxide do not react and the synthesis is not performed uniformly, so that the produced active material contains 3% or more of carbonate ions in the produced active material.
There is a problem that the average oxidation number of nickel does not reach trivalence. In addition, when a lithium ion secondary battery is manufactured using such a material having a low average valence of nickel as a positive electrode active material, there is a problem that the charge / discharge capacity is reduced.
For this reason, conventionally, since the reaction is performed without lowering the oxygen partial pressure,
A method using pure oxygen has been adopted.

However, the use of pure oxygen in the reaction atmosphere avoids the production of lithium carbonate, but the introduction of pure oxygen requires expensive liquid oxygen cylinders and membrane-separated oxygen generators, which is costly for synthesis. Had.

Further, the produced cobalt-solid-solution lithium composite nickel oxide and the raw material lithium hydroxide have a high hygroscopicity, and the carbon dioxide gas is more easily absorbed under the hygroscopic condition, so that the active material is deteriorated. Had.

On the other hand, under the condition that the water content of the active material measured by the Karl Fischer method is 1500 ppm or more, the cobalt-solid-solution lithium composite nickel oxide is liable to agglomerate, and the yield upon classification by aggregation is reduced. It had the drawback of lowering.

An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide an inexpensive and high-performance cobalt-solid-solution lithium composite nickel oxide.

[0011]

Means for Solving the Problems In order to solve the above-mentioned problems, a synthesis method according to the present invention comprises a method in which a mixture of at least nickel hydroxide or nickel hydroxide in which cobalt is dissolved as a solid and a lithium salt is used as a raw material. In a temperature range of 700 ° C., 0.01% by volume or less of carbon dioxide gas and a moisture dew point of 0
A first-stage baking step of baking for 2 hours or more in an air atmosphere at a temperature of not more than 100 ° C., a step of pulverizing at 100 ° C. or less, and further baking the mixture obtained in the above step in a temperature range of 700 to 900 ° C. for 2 hours or more. It has a second firing step. Further, after firing in the second stage, the method includes a step of pulverizing and classifying the active material in an air atmosphere having a carbon dioxide gas content of 0.01% by volume or less and a moisture dew point of 0 ° C. or less.

By synthesizing by the above-mentioned method, oxygen in the air can be effectively used, and a less expensive cobalt-dissolved lithium composite nickel oxide can be provided. Further, a less expensive non-aqueous electrolyte secondary battery can be provided. Can be manufactured. In addition, by reducing the amount of carbon dioxide gas, it is possible to prevent the raw material from being altered and deactivated due to the reaction between lithium hydroxide and carbon dioxide gas, which are unnecessary reactions, and a non-aqueous electrolyte capable of producing a higher capacity. A secondary battery can be manufactured.

Further, by performing the pulverizing and classifying steps in a dry atmosphere, it is possible to prevent moisture absorption of the positive electrode active material, prevent deterioration of the positive electrode active material due to moisture absorption, and improve the yield.

According to the present invention, there is also provided a positive electrode active material synthesized by the above-described production method, and a carbon-based conductive material kneaded with an N-methylpyrrolidone solution containing a binder of a fluorine-based compound,
By using a sheet that has been made into a paste, applied to an aluminum foil, and dried as a positive electrode plate, a high-capacity nonaqueous electrolyte secondary battery can be provided at lower cost.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The manufacturing method of the present invention will be described with reference to the flowchart shown in FIG. In the present invention, the raw materials of cobalt-solid-solution nickel hydroxide and lithium hydroxide are mixed, and as a first-stage calcination step, carbon dioxide gas is 0.01% by volume or less at a temperature range of 300 to 700 ° C., and a moisture dew point is 0%.
Baking for 2 hours or more in an air atmosphere at a temperature of
It has a step of pulverizing at a temperature of 0 ° C. or lower, and further, as a second-step firing step, firing at a temperature in a range of 700 to 900 ° C. for 2 hours or more.

In the synthesis of the positive electrode active material, a basic structure of crystals of the cobalt solid solution lithium composite nickel oxide is formed by the first-stage firing step. In the first stage, if the calcination temperature is less than 300 ° C. or the calcination time is less than 2 hours, the synthesis reaction of the cobalt-dissolved lithium composite nickel oxide does not proceed sufficiently.
The temperature must be at least 0 ° C. and the firing time must be at least 2 hours. In the first stage, if the firing atmosphere contains more than 0.01% by volume of carbon dioxide gas, the raw materials lithium hydroxide and carbon dioxide gas react with each other to produce lithium carbonate. Lithium does not react any more and the synthesis cannot be performed uniformly. Therefore, the content of carbon dioxide gas in the firing atmosphere is set to 0.01% by volume or less.

Further, in the second stage firing, if the firing temperature is less than 700 ° C. or the firing time is less than 2 hours, the crystal growth of the cobalt-dissolved lithium composite nickel oxide becomes insufficient. For this reason, the firing temperature is 700 ° C.
As described above, the firing time must be 2 hours or more.

By grinding after the first-stage firing step, the segregated lithium salt of the cobalt-solid-solution lithium composite nickel oxide formed by the first-stage firing can be ground and dispersed. These lithium salts react sufficiently, and the utilization rate per active material weight increases. Further, by pulverizing and dispersing the segregated lithium salt of the cobalt solid solution lithium composite nickel oxide, when the segregated lithium salt is fired at a high temperature of about 700 ° C. or more, it is strongly sintered with the cobalt solid solution lithium composite oxide. Sintering can be prevented, and a uniform positive electrode active material can be obtained. In addition, when pulverization is performed at the completion of the synthesis, variation in the particle size distribution is reduced, and the classification efficiency is improved.

Further, according to the present invention, the positive electrode active material synthesized in the second-stage calcination step is treated with carbon dioxide gas at 0.01% by volume.
In the following, there is a step of pulverizing and separating in an atmosphere having a moisture dew point of 0 ° C. or less. Cobalt-dissolved lithium composite nickel oxide is liable to agglomerate due to moisture absorption, and the classification efficiency is improved by drying during classification.

When a positive electrode active material for a non-aqueous electrolyte secondary battery is obtained by the method of the present invention, the content of a carbonate compound having a positive ion of either lithium, cobalt or nickel is less than 2%, and Water content is 1500ppm
, And the discharge capacity when a battery is formed is large.

When the cobalt solid solution lithium composite nickel oxide is handled under the dry conditions as described above, a dry and uniform material can be obtained. On the other hand, if the paste is prepared under the condition of absorbing moisture, the quality of the binder is changed, which hinders the paste coating. Therefore, the concentration of carbon dioxide gas in the atmosphere is desirably 0.01% by volume or less, and the humidity is desirably a moisture dew point of 0 ° C. or less.

In order to remove carbon dioxide in the atmosphere gas of the present invention, there is a method of passing the atmosphere gas through a column filled with lithium hydroxide, barium hydroxide and sodium hydroxide.

In order to remove moisture in the atmospheric gas, a method of passing through a column filled with phosphorus pentoxide,
There is a method using a cooling and reheating air dryer.

[0024]

Embodiments of the present invention will be described below.

Example 1 Lithium hydroxide and cobalt solid solution nickel hydroxide were mixed such that the atomic ratio of lithium, nickel and cobalt was 1.0: 0.8: 0.2.
In an air atmosphere having a carbon dioxide gas content of 0.01% by volume or less and a moisture dew point of 0 ° C. or less, the temperature was raised to 500 ° C. at a rate of 5 ° C./min, and calcination was carried out at the same temperature for 7 hours (the first stage calcination step). ). The calcined product was cooled to 100 ° C. or lower and pulverized by a grinding pulverizer.

The carbon dioxide gas in the atmosphere gas was removed by passing through a column filled with lithium hydroxide, barium hydroxide and sodium hydroxide. The water was removed by passing through a column filled with diphosphorus pentoxide. Next, the pulverized product was heated to 800 ° C. at a rate of 5 ° C./min, and fired at the same temperature for 15 hours (second stage firing step). The calcined product is cooled to 100 ° C. or less,
In an air atmosphere of 1% by volume or less and a moisture dew point of 0 ° C. or less, pulverization was performed by a grinding pulverizer. After pulverization under the same atmosphere, the mixture was classified using a sieve shaker. The compound obtained in this synthesis was used as active material 1
And

Next, a positive electrode plate is prepared using the active material 1,
A cylindrical battery having the structure shown in FIG. 2 was assembled. The structure of this battery will be described with reference to FIG. An electrode plate group 3 in which a positive electrode plate and a negative electrode plate are spirally wound via a separator is accommodated in a stainless steel battery case 6 with insulating plates 4 and 5 arranged vertically. The opening of the case 6 is closed by an assembly sealing plate 7 having a safety valve and an insulating packing 8. The positive electrode plate and the negative electrode plate were produced as follows.

For the positive electrode, 4 parts by weight of acetylene black as a conductive agent and 4 parts by weight of polyvinylidene fluoride as a binder were dissolved with respect to 100 parts by weight of a cobalt-solid-solution lithium composite nickel oxide as active material 1. A methylpyrrolidone solution was added and kneaded to form a paste. This paste was applied on both sides of an aluminum foil, dried, and then rolled to obtain a positive electrode plate having a thickness of 0.144 mm, a width of 37 mm, and a length of 250 mm.

On the other hand, as the negative electrode, one obtained by graphitizing mesophase small spheres (hereinafter referred to as mesophase graphite) was used. 100 parts by weight of the mesophase graphite was mixed with 3 parts by weight of styrene / butadiene rubber as a binder, and an aqueous carboxymethyl cellulose solution was added and kneaded to form a paste. The paste is applied to both sides of a copper foil, dried, and then rolled to a thickness of 0.21 mm, a width of 39 mm, and a length of 2 mm.
An 80 mm negative electrode plate was used.

A positive electrode lead 1 made of aluminum is attached to the positive electrode plate, and a negative electrode lead 2 made of nickel is attached to the negative electrode plate. The separator is made of a polyethylene separator having a thickness of 0.025 mm, a width of 45 mm, and a length of 740 mm. A spirally wound electrode plate group 3 having a diameter of 14.0 mm and a height of 5
It was stored in a 0 mm battery case.

As the electrolytic solution, a solution prepared by dissolving 1 mol / L lithium hexafluorophosphate in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 20:80 was used. After injecting this electrolytic solution, sealing it,
And

The active material 1 was prepared in the same manner as above except that the amount of carbon dioxide and the amount of water in the first-stage sintering atmosphere were changed to the conditions shown in Table 1.
Active materials 2 to 7 were synthesized in the same manner as in the above method.

Active materials 8 to 11 were synthesized in the same manner as in the above-mentioned active material 1, except that the amount of carbon dioxide and the amount of water in the atmosphere in the pulverizing and classifying step after the second step were changed to the conditions shown in Table 1.

With respect to the active materials 1 to 11, the yield, the content of carbonic acid traces, and the content of water were measured, and the results are shown in Table 1.

Further, active materials 2 to 11 are used in place of active material 1.
A cylindrical battery was prepared in the same manner as the battery 1 except that was used, and batteries 2 to 11 were obtained.

A charge / discharge test was performed on each of the batteries 1 to 11 under the following conditions. Charging is performed at 4.2V for 2 hours at a constant voltage, and until the battery voltage reaches 4.2V, 42 hours.
It was set so as to be a constant current charge of 0 mA. Discharge is 61
The discharge was performed at a constant current of 0 mA, the charge end voltage was set to 3.0 V, and the charge / discharge environment was set to 20 ° C. Table 1 shows the discharge capacity of the battery after repeating the charge and discharge five times.

[0037]

[Table 1]

A comparison between the battery 1 and the batteries 2 to 7 shows that the lower the carbon dioxide gas and moisture concentration in the first stage firing atmosphere, the higher the charge / discharge capacity. However, when the carbon dioxide gas content is 0.01% by volume or less, the difference in the discharge capacity of the battery is not large,
It is good that it is 1 volume% or less. It was also found that changing the amount of water in the firing atmosphere in the first stage did not significantly affect the classification efficiency.

On the other hand, a comparison between the battery 1 and the batteries 8 to 11 showed that the amount of water in the treatment atmosphere had a great effect on the classification efficiency in the pulverization and classification steps. It is considered that these are directly due to the fact that the active material absorbs moisture in the air and agglomerates to lower the classification efficiency.

Further, a comparison between the battery 1 and the batteries 8 to 11 shows that the charge / discharge capacity was remarkably reduced under the condition that moisture and carbon dioxide gas coexist. This indicates that the absorption of carbon dioxide gas was promoted by the presence of water.

As described above, the present invention has the effect of preventing generation of impurities in the synthesis process by removing moisture and carbon dioxide gas from the atmosphere in the synthesis of the positive electrode active material. An excellent positive electrode active material can be provided.

In the above embodiment, LiNi
_0.8 Co _0.2 O ₂ was explained, but Li _x Ni _(1-y) C
similar effect on _{o y O 2 (0.95 ≦ x} ≦ 1.2,2.0 ≦ y <0.5) the compounds represented by is obtained.

Further, in the above embodiment, LiNi
Lithium hydroxide, nickel hydroxide, and cobalt hydroxide were used as raw materials for _0.8 Co _0.2 O ₂ , but cobalt salts such as cobalt oxide represented by lithium oxide, CoO, Co ₂ O ₃ , and Co ₃ O ₄ ; The same effect can be obtained by using nickel hydroxide in which Co and Co are dissolved.

Further, in the above-mentioned embodiment, the pulverization was carried out by a grinding pulverizer. The same effect can be obtained by using a pin mill, a jet mill, or the like.

In the above embodiment, the classification was carried out by a sieve shaker. However, other classifiers such as a sonic sieve, a centrifugal sieve, an inertial classifier, a cyclone, and a centroid classifier were used. A similar effect was obtained.

In the above embodiment, evaluation was made using a cylindrical battery, but the same effect can be obtained even when the battery shape is different, such as a square battery.

Further, in the above embodiment, a mixed solvent of ethylene carbonate and ethyl methyl carbonate was used as a solvent for the electrolyte. However, other non-aqueous solvents, for example, cyclic ethers such as propylene carbonate and chain ethers such as dimethoxyethane were used. The same effect can be obtained by using a non-aqueous solvent such as a chain ester such as methyl propionate or a multi-component mixed solvent thereof.

[0048]

As described above, according to the present invention, in the synthesis of the cobalt-solid-solution lithium composite nickel oxide, the air atmosphere in the synthesis and classification and pulverization step is reduced to 0.02 g of carbon dioxide gas.
By setting the content to 1% by volume or less and the water dew point to 0 ° C. or less, a positive electrode active material having excellent charge / discharge characteristics can be provided.

[Brief description of the drawings]

FIG. 1 is a flowchart of synthesis according to an embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of a cylindrical battery according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode lead 2 Negative electrode lead 3 Electrode group 4,5 Insulating plate 6 Battery case 7 Sealing plate 8 Insulating packing

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Kunio Ito 1006 Kadoma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Terms (reference) 4G048 AA04 AB04 AB05 AB08 AC06 AE05 AE08 5H003 AA02 AA04 BA01 BA03 BA04 BB05 BC01 BD00 BD01 BD03 BD04 5H014 AA02 BB00 BB01 BB06 BB08 EE05 HH00 HH01 HH08 5H029 AJ03 C07 AJ05 BJ03 C07 EJ01 HJ00 HJ02 HJ14

Claims (4)

[Claims] 1. Using a mixture of at least nickel hydroxide or nickel hydroxide having a solid solution of cobalt and a lithium salt as a raw material, a general formula Li _x Ni _(1-y) Co _y O ₂ (0.95
≦ x ≦ 1.2, 0 ≦ y <0.5) A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, which obtains a cobalt solid solution lithium composite nickel oxide represented by the following formula: ° C
In a first stage firing step of firing for 2 hours or more in an air atmosphere having a carbon dioxide gas content of 0.01% by volume or less and a moisture dew point of 0 ° C. or less in the temperature range of Pulverizing the resulting mixture;
A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising a second-stage sintering step of sintering in a temperature range of 00 to 900 ° C. for 2 hours or more. 2. The method according to claim 1, wherein the positive electrode active material synthesized in the second step is 0.01% by volume or less of carbon dioxide gas and has a moisture dew point of 0%.
The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, further comprising a step of pulverizing and classifying in an air atmosphere at a temperature of not more than ° C. 3. A positive electrode active material synthesized by the production method according to claim 1 or 2, wherein the total content of carbonates whose positive ions are lithium, cobalt, or nickel is less than 2%. Yes, and the water content is 150
A positive electrode active material for a non-aqueous electrolyte secondary battery which is less than 0 ppm. 4. A positive electrode active material and a carbon-based conductive material synthesized by the production method according to claim 1 or 2 are kneaded together with a binder of a fluorine-based compound and an N-methylpyrrolidone solution to form a paste into aluminum. A non-aqueous electrolyte secondary battery using a sheet coated and dried on a foil as a positive electrode plate for a non-aqueous electrolyte secondary battery.