JPH06163046A - Manufacture of positive electrode active material for nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To reduce manufacturing cost by eliminating capacity degradation caused by a charge and discharge cycle of a nonaqueous electrolyte battery formed by using a positive electrode active material mainly composed of LiCoO2, manufacturing the positive electrode active material having large discharge capacity, and manufacturing the positive electrode active material for the nonaqueous electrolyte battery by low temperature and short time baking. CONSTITUTION:Mixture of a coprecipitation body or a single compound composed of carbonate, basic carbonate, hydroxide or oxide of respective elements to constitute a positive electrode active material, is reacted with citric acid in aqueous solution or organic solvent, and created composite citric acid salt composed of lithium, cobalt and boron is baked at a temperature of 400-950 deg.C in an oxidation atmosphere.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for producing a positive electrode active material for a non-aqueous electrolyte battery, and provides a method for producing a positive electrode active material having a high utilization rate and a long charge / discharge cycle life. is there.

[0002]

2. Description of the Related Art In recent years, with the miniaturization of various electronic devices, there has been a demand for secondary batteries with higher energy density. Secondary batteries using non-aqueous electrolytes have energy densities several times higher than those of conventional batteries using aqueous electrolytes, and therefore practical application is awaited. The non-aqueous electrolyte is
It is a solution of a metal salt serving as an electrolyte in an aprotic organic solvent. For example, for lithium salts, LiC
propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyrolactone, dioxolane, 2-O ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiCF ₃ SO ₃ etc.
A single solvent such as methyltetrahydrofuran, diethylcarbonate, dimethylcarbonate, sulfolane or the like or a mixture of these dissolved in a solvent is used. These non-aqueous electrolytes are used by injecting into a battery container, but impregnated into a porous separator, added high molecular weight resin to make it highly viscous, or gelated to lose fluidity. It is sometimes used in the state. Further, a polymer electrolyte represented by polyethylene oxide is also being studied as an electrolyte for a non-aqueous electrolyte secondary battery.

As a positive electrode active material for a non-aqueous electrolyte secondary battery,
As shown in JP-A-55-136131, research on lithium cobalt composite oxide (LiCoO ₂ ) has been actively conducted in recent years. Batteries using this active material have an average operating voltage of about 3.6 V, which is about three times higher than 1.2 V for nickel-cadmium batteries. Is possible. However, the non-aqueous electrolyte secondary battery using this LiCoO ₂ as a positive electrode active material has a drawback that the capacity deterioration due to charge / discharge cycles is extremely large, and in order to eliminate this drawback, JP-A-62-2
56371 and Japanese Patent Laid-Open No. 63-211565 use LiCoO _{2 as} a positive electrode active material.
It has been proposed to add Ni, V, Cr, Fe.

Conventionally, each of these composite oxides is produced by a solid phase method in which a mixture of a lithium carbonate and a transition metal carbonate or two or more coprecipitated carbonates is fired at a temperature of around 900 ° C. is doing. However, the positive electrode active materials produced by these solid phase methods have the disadvantages that the composition is non-uniform, the growth of crystals is insufficient, the utilization rate is low, and the capacity deterioration with charge / discharge cycles is large. It has been insufficient in terms of providing a good positive electrode active material for a non-aqueous electrolyte secondary battery.

[0005]

Lithium-cobalt composite oxide LiCoO ₂ is originally a stable substance, but when it is used as a positive electrode active material of a non-aqueous electrolyte battery, the capacity is greatly deteriorated with charge / discharge cycles. was there. LiC
oO ₂ has the property that when Li is released by charging, it becomes unstable in its crystal structure, separates oxygen, and gradually changes to Co ₂ O ₃ . Co ₂ O ₃ remains LiCoO
Do not return to ₂ . When charging and discharging are repeated, the capacity decreases,
There is a drawback that the charge / discharge cycle is short. In addition, an increase in battery internal pressure due to gas generation is also recognized.

The conventionally reported lithium cobalt composite oxide and the composite oxide in which a part of cobalt is replaced with another transition metal are produced by the solid phase method, and the composition is not uniform and the crystal growth is The deterioration was promoted because it was insufficient.

[0007]

Means for Solving the Problems The present invention eliminates capacity deterioration due to charge / discharge cycles of a non-aqueous electrolyte battery using a positive electrode active material containing LiCoO ₂ as a main component, and has a large discharge capacity. The present invention provides a manufacturing method of. When synthesizing a positive electrode active material for a non-aqueous electrolyte battery that is substantially composed of oxides of lithium, cobalt, and boron, carbonates, basic carbonates, hydroxides, or oxides of each element that constitutes the positive electrode active material are synthesized. A coprecipitate consisting of a compound or a mixture of single compounds is reacted with citric acid in an aqueous solution or an organic solvent, and the formed complex citrate composed of lithium, cobalt and boron is heated in an oxidizing atmosphere at a temperature of 400 to 950 ° C. A method for producing a positive electrode active material for a non-aqueous electrolyte battery, which comprises firing.

[0008]

[Function] The complex citrate composed of lithium, cobalt, and boron is uniformly mixed at the molecular level, and by firing, a complex oxide with high crystallinity can be easily obtained. . Citrate does not generate harmful gases such as nitrate and acetate in the heat treatment process and can be operated safely.

The optimum composition of the lithium-boron-cobalt composite oxide produced by the method of the present invention is as follows:
Cobalt has 0.75 to 0.999 atoms and boron has 0.001 to 0.25 atoms. For convenience, it is represented by LiBxCo (1-x) O ₂ , but the exact chemical formula is unknown.

The lithium-boron-cobalt composite oxide has a hexagonal crystal structure like the conventional lithium-cobalt composite oxide. However, since the diffraction peak of the crystal according to the X-ray diffraction pattern is sharper than that of the conventional product, it is considered to have a crystal structure with a high degree of crystallization and with few lattice defects. Lithium boron cobalt composite oxide
The stability is high in a charged state, that is, a state in which a part of lithium ions is removed from the crystal structure, the capacity does not decrease much even if charging and discharging are repeated, and oxygen gas is less generated by decomposition.

At a relatively lower temperature than conventional LiCoO ₂ ,
It is characterized in that it can be manufactured by heat treatment for a short time. Conventionally, heat treatment at about 900 ° C or higher was required for the synthesis of complex oxides, but complex oxides containing boron are
The synthesis was possible even at about 400 ° C. Although the reason is not clear, it seems that a mixture phase having a low melting point is generated during the heating process, and crystal growth is facilitated. Heat treatment temperature is 400
C. to 950.degree. C., preferably 500 to 900.degree.

It was confirmed that the effect of boron was not affected by the type of boron raw material. There is no limitation on the raw materials of lithium, cobalt, and boron as long as they are oxides by heat treatment. The most advantageous raw material can be used in terms of manufacturing process and raw material cost.

By using a calcined product of fine-particle composite citrate obtained by the reaction with citrate as a positive electrode active material of a non-aqueous electrolyte secondary battery, the capacity deterioration due to charge / discharge cycles is extremely effective. To suppress. The positive electrode active material produced by the production method of the present invention has high crystallinity, so that it is less likely to decompose or change in structure, and has a characteristic of high capacity and less capacity deterioration due to charge / discharge cycles.

[0014]

【Example】

[Example 1] Lithium carbonate (40.44% as Li ₂ O) 7
Disperse 3.9 parts of boric acid (61.81% as B ₂ O ₃ ) 1.1 parts and 243 parts of basic cobalt carbonate (61.04% as CoO) in 1000 parts of pure water, warm to 50-60 ° C, and add citric acid. Add 433 parts and stir. The resulting citric acid slurry was dried at 120 ° C, calcined at 500 ° C, and then hydrated at 680 ° C for 3 hours.
Burned for hours. The obtained fired product was pulverized with a ball mill for 30 minutes. The composition of the obtained lithium-boron-cobalt composite oxide corresponds to LiB _x Co _y O ₂ (x = 0.01, y = 0.99). When the crystal structure was examined by powder X-ray diffraction, L
The same hexagonal diffraction peak as iCoO ₂ was shown, and it was confirmed that a composite oxide was formed.

FIG. 2 shows a powder X-ray diffraction pattern. The intensity of the diffractive surface corresponding to the d ₀₀₃ plane of the crystal structure is high, indicating that the crystal structure is particularly well developed. It was observed by an electron microscope that the crystal grain size of the composite oxide was 2 to 4 μm. This positive electrode active material material is designated as A. [Comparative Example 1] LiCoO ₂ was prepared by a conventional method. 73.9 parts of lithium carbonate and 245.5 parts of basic cobalt carbonate are pulverized and mixed in a ball mill and calcined at 500 ° C. for 1 hour, then 90
It heat-processed at 0 degreeC for 24 hours. The obtained fired product was pulverized with a ball mill for 30 minutes. When the crystal structure was examined by powder X-ray diffraction, a diffraction peak of LiCoO ₂ was shown.

FIG. 3 shows a powder X-ray diffraction pattern. Despite firing at high temperature for a long time, the diffraction peak on the d ₀₀₃ plane did not rise. When observed with an electron microscope,
The particle size was observed to be 2 to 4 μm, and it was confirmed that the particle shape was almost the same as that for the positive electrode active material source A of the present invention. This positive electrode active material raw material is designated as B.

85 parts of each of the composite oxides of A and B, 8 parts of acetylene black as a conductive agent, and 34 parts of a PTFE dispersion aqueous solution (containing 15% of polytetrafluoroethylene resin) as a binder were kneaded. Was passed between a pair of rolls to form a sheet, and then pressure-bonded to both surfaces of an expanded metal core material made of aluminum to produce a positive electrode substrate having a thickness of about 0.6 mm. This substrate was punched out to prepare a strip-shaped positive electrode having a width of 14 mm and a length of 52 mm, and the electrode characteristics were measured by a beaker test cell.

FIG. 1 shows the structure of a beaker test cell.
Reference numeral 1 denotes a beaker for a glass container, which holds a non-aqueous electrolyte solution 2 therein and whose opening is covered with a polypropylene lid 3. 4 is a positive electrode of the test electrode, and 5 and 5'are counter electrodes. 6 is a reference electrode, and lithium was used. Using lithium as the counter electrode, a single electrode charge / discharge cycle test was performed in an equal volume mixture of ethylene carbonate and diethyl carbonate in which 1 molar LiPF ₆ was dissolved. The test was carried out in a dry box in an argon atmosphere to prevent adverse effects of water and oxygen. After charging up to 4.1V against the lithium potential with a current of 20mA, repeat the cycle of discharging up to 2.75V against the lithium potential with the same current of 20mA.
The change in discharge capacity per unit weight of the composite oxide was observed.

FIG. 4 shows the result of the cycle test. The positive electrode using the raw material A produced by the production method of the present invention had a large discharge capacity and excellent cycle characteristics. It is considered that the positive electrode active material produced by the present invention has a uniform composition and is highly stable because the crystal structure is not easily broken, and that the capacity deterioration due to charge / discharge cycles is extremely small. [Comparative Example 2] 73.9 parts of lithium carbonate and basic cobalt carbonate
245.5 parts were pulverized and mixed in a ball mill, calcined at 500 ° C for 1 hour, and then heat-treated at 680 ° C for 3 hours. The obtained fired product was pulverized with a ball mill for 30 minutes. When the crystal structure was examined by powder X-ray diffraction, a slight diffraction peak of LiCoO ₂ was observed. Observation with an electron microscope revealed that the grain size was 0.1 μm or less and no crystals were grown at all. As a result of the beaker test cell, almost no discharge was possible. In order to prepare a complex oxide that can be used as an active material in a conventional solid-state reaction without using citric acid and boron, 90
A firing temperature of 0 ° C is required. [Comparative Example 3] 73.9 parts of lithium carbonate, 1.1 parts of boric acid, and 243 parts of basic cobalt carbonate were pulverized and mixed in a ball mill to obtain 500
After calcination at ℃ for 1 hour, heat treatment at 680 ℃ for 3 hours.
The obtained fired product was pulverized with a ball mill for 30 minutes. Powder X
When the crystal structure was examined by line diffraction, a diffraction peak of LiCoO ₂ was detected, but the peak intensity was weak, indicating that crystallization did not proceed. When observed by an electron microscope, the grain size was 0.5 μm or less, and the crystal growth did not proceed. The beaker test cell showed a discharge capacity of 80 mAh / g. In order to grow crystals by the conventional solid-state reaction without using citric acid, it was necessary to raise the temperature to 700 ℃ or more, or to heat treatment for 5 hours or more. [Example 2] Lithium hydroxide (35.62% as Li ₂ O)
83.9 parts of boron oxide (99.0% as B ₂ O ₃ ) 0.7 parts and cobalt oxide (98.8% as CoO) 150.2 parts of pure water 750
Dispersed in 1 part, heated to 70-80 ° C, and then citric acid 652.
Add 5 g and stir. The resulting citric acid slurry was 12
It was dried at 0 ° C., calcined at 350 ° C., and then calcined at 650 ° C. for 1 hour. The obtained fired product was pulverized with a ball mill for 30 minutes. The composition of the obtained lithium-boron-cobalt composite oxide corresponds to LiB _x Co _y O ₂ (x = 0.01, y = 0.99).
The crystal structure, the crystal grain size, and the discharge characteristics were measured in the same manner as in Example 1. The crystal structure shows the same diffraction peak as LiCoO ₂ ,
The crystal grain size was 1 to 3 μm. The discharge capacity at the first cycle was 151 mAh / g. [Example 3] 73.9 parts of lithium carbonate, 11.3 parts of boric acid and 221.0 parts of basic cobalt carbonate were dispersed in 1000 parts of pure water to obtain 50 parts.
After heating to ~ 60 ° C, add 435 parts of citric acid and stir. The resulting citric acid slurry was dried at 120 ° C and
It was calcined at 0 ° C for 1 hour. The mixture after calcination was fired at different temperatures and times. The firing temperature is 400 ℃, 450 ℃, 500
℃, 600 ℃, 700 ℃, 800 ℃, 900 ℃, and 950 ℃, and fired for 1 hour, 3 hours, 9 hours, and 24 hours, respectively. The obtained fired product was pulverized with a ball mill for 30 minutes. The composition of the lithium-boron-cobalt composite oxide after firing is LiB _x Co
_{It corresponds to y} O ₂ (x = 0.1, y = 0.9).

When the crystal structure was examined by powder X-ray diffraction, it was confirmed that all showed the same hexagonal diffraction peak as LiCoO ₂ and that a complex oxide was formed.

Table 1 shows the crystal grain size of the composite oxide under various firing conditions and the discharge capacity at the first cycle measured in the same manner as in Example 1. The crystal grain size is measured by an electron micrograph.

[0022]

[Table 1] No clear crystal growth was observed at a low temperature of 400 to 450 ° C, but large crystal growth was observed at 500 ° C or higher. Although the discharge capacity of the calcined product at a low temperature was small, it was considered that all were capable of discharging and that a uniform composite oxide was formed.

[0023]

According to the present invention, in synthesizing a positive electrode active material of a non-aqueous electrolyte battery which is substantially composed of oxides of lithium, cobalt and boron, a raw material mixture of each element constituting the positive electrode active material is quenched. By reacting with an acid and calcining the formed complex citrate composed of lithium, cobalt and boron, it is possible to manufacture a positive electrode active material for a non-aqueous electrolyte battery by calcining at low temperature for a short time. Therefore, it is extremely effective in reducing the manufacturing cost.

In the non-aqueous electrolyte secondary battery, by using a composite oxide of the composition LiB _x Co _(1-x) O ₂ containing boron as the positive electrode active material, despite the fact that the composite oxide is fired at a low temperature, The charge / discharge cycle characteristics of the non-aqueous electrolyte secondary battery have been improved, and it has become possible to provide a long-life secondary battery.

As a raw material of each element constituting the positive electrode active material, a carbonate, a basic carbonate, a hydroxide, or a coprecipitate or a mixture of oxides can be used. In both cases, at least a part of the components becomes citric acid salt by addition of citric acid, and they are uniformly mixed in a molecular state. As a component of boron, compounds containing most of boron such as boron, boron oxide, boric acid, ammonium borate, lithium borate and the like can be used.

In the present invention, a part of cobalt is further converted into Ni, Mn,
The effect of firing at low temperature was also confirmed for those substituted with transition metals such as Fe and Ti and metals such as Mg, Ca, Sr, Ba and Al. The composite oxide consisting essentially of lithium and cobalt is a hexagonal crystal, and the citrate salt of these elements containing boron is easily decomposed at low temperatures, resulting in a hexagonal system with a high single-phase conversion rate. It is thought to produce the crystals of.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a beaker test cell.

FIG. 2 shows X of a positive electrode active material manufactured according to an embodiment of the present invention.
Line diffraction diagram.

FIG. 3 is an X-ray diffraction diagram of a positive electrode active material manufactured according to a comparative example.

FIG. 4 is a diagram showing charge / discharge cycle characteristics of positive electrode active materials according to the manufacturing methods of Examples and Comparative Examples of the present invention.

[Explanation of symbols]

 1 Beaker 2 Non-Aqueous Electrolyte 3 Lid 4 Positive Electrode 5, 5'Counter Electrode 6 Reference Electrode A Cycle characteristics of positive electrode active material according to the production method of the present invention B Cycle characteristics of positive electrode active material according to production method of Comparative Example

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Minor Mizutani No. 1 Nishinosho-Inaba Babacho, Kichijoin, Minami-ku, Kyoto City, Japan Battery Co., Ltd. (72) Inventor Susumu Hiyama 3-2-10 Chigasaki, Chigasaki City Within Mical Corporation

Claims (2)

[Claims] 1. When synthesizing a positive electrode active material of a non-aqueous electrolyte battery which is substantially composed of oxides of lithium, cobalt and boron, a carbonate or a basic carbonate of each element constituting the positive electrode active material, Characterized by reacting a hydroxide or a coprecipitate of oxides or a mixture of single compounds with citric acid in an aqueous solution or an organic solvent to calcine the produced complex citrate composed of lithium, cobalt, and boron And a method for producing a positive electrode active material for a non-aqueous electrolyte battery. 2. A positive electrode active material for a non-aqueous electrolyte battery according to claim 1, wherein the composite citrate composed of lithium, cobalt and boron is fired at a temperature of 400 to 950 ° C. in an oxidizing atmosphere. Manufacturing method.