JPH10233213A - Manufacture of secondary battery positive electrode active material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method by which a secondary battery positive electrode active material is manufactured at low costs and with high efficiency in which quality is uniform, sizes are fine, and filling density can be heightened. SOLUTION: In a manufacturing method for positive electrode active material shown by a general formula LiMx O2x (where M is an element of Ni, Mn, Co, Cr, Fe, or V, and (x) is 1 or 2), organic amine is added to mixture solution containing Li<+> and M<n+> (where (n) is the ion valence of M element) so as to precipitate M(OH)n , and hydrogen peroxide is added to M(OH)n formation solution so as to convert the M(OH)n into MOOH so as to precipitate Li2 O2 on MOOH particle surfaces. Li2 O2 -precipitated MOOH particles are dried, and MOOH powder is mixed into Li and M composite fatty acid metal salt compound solution. Thereafter, the same is dried so as to coat the surface of the powder by the Li and M composite fatty acid metal salt compound, and the coated powder is heat treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a compound of the general formula LiM _x O
_2x (where M is at least one element selected from Ni, Mn, Co, Cr, Fe and V, x is 1 or 2
The present invention relates to a method for producing a positive electrode active material for a secondary battery represented by

[0002]

2. Description of the Related Art Conventionally, the following method has been proposed as a method for producing a positive electrode active material for a secondary battery.

(1) Powders of carbonates or oxides of metal element ions constituting the positive electrode active material for secondary batteries are separately weighed, mixed and pulverized, and calcined at a temperature of 700 ° C. or more. A desired positive electrode active material for a secondary battery is obtained.

(2) A positive electrode active material for a secondary battery is obtained by a sol-gel method using an alkoxide.

(3) A precipitant for forming a precipitate is added to a mixed solution of metal element ions constituting the positive electrode active material for a secondary battery to cause a reaction, and the obtained precipitate is calcined to obtain a desired positive electrode for a secondary battery. Obtain the active material.

[0006]

However, each of the above-described manufacturing methods has the following problems.

In the method (1), since a carbonate or oxide powder is used as a starting material, it is impossible to uniformly mix each powder at a molecular level. For this reason,
Local composition deviation occurs, and a uniform positive electrode active material cannot be obtained.

[0008] Incidentally. Each powder as a starting material can be synthesized by a wet method and then calcined to precipitate. However, even if the precipitate during synthesis is fine,
When used, a treatment such as drying is performed to agglomerate and coarsen particles, resulting in poor surface activity. Therefore, in order to obtain a positive electrode active material for a secondary battery, it is necessary to calcine at a high temperature of 700 ° C. or more. is there. The calcined powder obtained by calcining at a high temperature in this way has a low packing density and a small surface area because the particles are strongly agglomerated and coarse, and when used as a positive electrode active material of a secondary battery. , Can not take out enough electricity.

In the method (2), the desired cathode active material for a secondary battery can be synthesized at a low temperature, and the obtained cathode active material powder has a fine particle size, a large specific surface area, and a high packing density. Therefore, when used as a positive electrode active material of a secondary battery, there is an advantage that a sufficient amount of electricity can be taken out.
However, although the alkoxide as a starting material is a material suitable for a laboratory, it is too expensive for industrial use and cannot be used.

Further, alkoxides are very sensitive to water and are easily hydrolyzed. Therefore, a reactor is required which is not affected by water in the air, which increases equipment costs and causes cost increase.

As the method (3), for example, there is a method in which a precipitate is formed as an oxalate and then calcined to obtain a desired cathode active material for a secondary battery. In this method, the dispersibility of the constituent elements is significantly improved as compared with the method (1).

However, oxalate precipitates have low solubility in some compounds, but generally have rather high solubility in water. Therefore, there is a problem that a difference occurs in the solubility of the oxalate compound of each element constituting the positive electrode active material for a secondary battery, and the constituent element ratio of the precipitate after washing and dehydration is different from that at the time of preparation. I have.

Another problem is that there is no precipitation-forming agent for simultaneously obtaining a precipitate of Li and other constituent elements. For example, the constituent elements other than Li can form a precipitate of a hardly soluble hydroxide or carbonate by using caustic alkali carbonate as a precipitation-forming agent, but the hydroxide or carbonate of Li is Since it is easily soluble in water, it cannot be obtained as a precipitate.

Accordingly, an object of the present invention is to provide a method for efficiently and inexpensively producing a positive electrode active material for a secondary battery which solves the above-mentioned problems and is homogeneous, fine and capable of increasing the packing density. Is to provide.

[0015]

In order to achieve the above object, a method for producing a positive electrode active material for a secondary battery according to the present invention comprises a general formula LiM _x O _2x (where M is Ni, Mn, Co, Cr,
At least one element selected from Fe and V,
x is 1 or 2), wherein an organic amine is added to a mixed solution containing Li ⁺ and M ^{n +} (where n represents the ionic valence of M element). In addition, a step of precipitating M (OH) _n (where n represents the ionic valence of the M element), and adding hydrogen peroxide to the M (OH) _n producing solution to convert M (OH) _n to MOOH. And depositing Li ₂ O ₂ on the surface of the MOOH particles, drying the MOOH particles having the Li ₂ O ₂ deposited thereon, and dissolving the MOOH powder in a solution of a complex fatty acid metal salt compound of Li and M. And a step of drying and coating the surface of the powder with a complex fatty acid metal salt compound of Li and M, and a step of heat-treating the coated powder.

Further, the ion source of the element M is a water-soluble compound or a compound soluble in nitric acid or acetic acid.

When the amine is added, the pH is adjusted to 9 to
It is characterized in that it is adjusted to 9.5.

The heat treatment temperature of the powder coated with the complex fatty acid metal salt compound is 450 to 650 ° C.

Further, the complex fatty acid metal salt compound is
It is obtained by reacting a linear saturated fatty acid or monoene unsaturated fatty acid having 5 to 30 carbon atoms with an acetate of Li and M elements.

Here, examples of the raw material of Li ⁺ include lithium hydroxide, lithium acetate, lithium carbonate, lithium nitrate and the like, but are not limited to these compounds. A compound that is water-soluble or soluble in acetic acid or nitric acid can be used as appropriate.

The raw materials of M ^{n +} include hydroxides, acetates, carbonates, nitrates and the like as in the case of Li, but are not limited to these compounds. A compound that is water-soluble or soluble in acetic acid or nitric acid can be used as appropriate.

The straight-chain saturated fatty acids used for obtaining the complex fatty acid metal salt compound include hexanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, and the like.
Examples include tetradecanoic acid, hexadecanoic acid, octadecanoic acid, eicosanoic acid, docosanoic acid, tetracosanoic acid, hexacosanoic acid, octacosanoic acid, and triaconic acid.

Further, as the monoene unsaturated fatty acid,
cis-4-decenoic acid, 9-decenoic acid, cis-4-dodecenoic acid, 10-undecenoic acid, cis-4-tetradecenoic acid, cis-5-teradedecenoic acid, cis-9-tetradecenoic acid, cis-6-hexadecene Acid, cis-
9-hexadecenoic acid, cis-6-octadecenoic acid, c
is-9-octadecenoic acid, trans-9-octadecenoic acid, cis-11-octadecenoic acid, trans-
11-octadecenoic acid, cis-9-eicosenoic acid, c
is-11-docosenoic acid, cis-13-docosenoic acid,
trans-13-docosenoic acid, cis-15-tetracosenoic acid, cis-17-hexacosenic acid, cis-2
1-triacontenic acid and the like.

As described above, the present invention employs a method of forming precipitated particles having a double structure in which water-insoluble Li ₂ O ₂ is deposited on the surface of hydroxy oxide precipitated particles of MOOH. I have. For this reason, the constituent element ratio does not differ from that at the time of preparation due to dissolution of the Li compound. In addition, since the element compounds constituting the positive electrode active material are in direct contact with each other and the constituent elements are at the shortest distance, the mutual reaction tends to proceed smoothly. As a result, a positive electrode active material for a secondary battery can be obtained at a lower temperature of 450 to 650 ° C. than the conventional solid phase method. And the positive electrode active material for secondary batteries which is excellent in dispersibility can be obtained.

The surface of the MOOH precipitated particles has Li ₂ O ₂
The double-structured powder deposited with
There is a disadvantage that i ₂ O ₂ absorbs moisture and the powder itself becomes wet, resulting in poor handling. The Li as a countermeasure for preventing hygroscopic ₂ O _2, it is conceivable to cover the Li ₂ O ₂ surface with a compound of the water-repellent higher fatty acid. However, higher fatty acids themselves are not preferable because they react with Li ₂ O ₂ to form a fatty acid salt of Li and dissolve Li ₂ O ₂ . In the present invention, by covering with a complex fatty acid metal salt compound of Li and M constituting the positive electrode active material, the reaction with Li ₂ O ₂ is prevented and the hygroscopicity is prevented. In addition, the ratio of Li and M of the complex fatty acid metal salt compound to be coated for imparting water repellency is determined by comparing Li ₂ O ₂ and MO
By matching the OH i.e. LiM _x O _2x of Li and the ratio of M of interest, rather than generating a material of a different composition, it is possible to obtain a stable cathode active material for a secondary battery was homogeneous properties.

The thermal decomposition temperature of the complex fatty acid metal salt compound itself is 450 to 500 ° C. However, MO
When OH and Li ₂ O ₂ coexist, MOOH and Li ₂
Combustion of the complex fatty acid metal salt compound is promoted by the action of nascent oxygen released at the time of thermal decomposition of O _{2, and} the temperature is 250 to 270 ° C., which is 200 ° C. or more lower than that of the case of thermal decomposition alone
Decomposition combustion occurs at such a temperature. Then, the heat of combustion of the complex fatty acid metal salt compound causes the LiM
_x O _2x is produced.

In addition, since a water-soluble compound or a hydroxide, acetate, carbonate, nitrate or the like soluble in nitric acid or acetic acid is used as a starting material of the positive electrode active material for a secondary battery, an inexpensive secondary battery is used. The positive electrode active material for use can be obtained.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the method for producing a positive electrode active material for a secondary battery according to the present invention will be described below based on examples.

(Example) First, lithium acetate, manganese acetate and cobalt acetate were prepared as starting materials. Next, after accurately weighing and dispensing the prepared starting materials so that the ratios of Li, Mn and Co are as shown in Sample Nos. 1 to 3 in Table 1, dissolve them in pure water by stirring at high speed. Let L
A mixed solution containing i ⁺ and M ^{n +} (where M is Mn or Co) was prepared. The concentration of the mixed solution was adjusted to 0.1 mol / L in terms of the target positive electrode active material.
Thereafter, while the mixed solution was stirred at a high speed, an aqueous dimethylamine solution was added to adjust the pH to 9 to 9.5.
(OH) _n precipitated particles were formed. Furthermore, (Li ⁺
+ M ^{n +} ) was slowly added with high-speed stirring to the same equivalent of H ₂ O ₂ water (30% concentration) to obtain M (OH)
_n is oxidized to MOOH and Li ⁺ is converted to Li ₂ O ₂
Was deposited on the surface of the MOOH precipitated particles. Thereafter, the reaction solution having the precipitated product was transferred to a rotary evaporator, and the solvent was removed under the conditions of a reduced pressure of 50 mmHg and a heating temperature of 60 ° C. to obtain a dry powder.

[0030]

[Table 1]

Next, the obtained dried powder is mixed with 1
A water-repellent complex fatty acid metal salt compound in an amount corresponding to 2.5 wt% was placed in a benzene solution in which it was dissolved and mixed. Thereafter, excess benzene was removed by heating and evaporating, and the surface of the dried powder was covered with a complex fatty acid metal salt compound.

The complex aliphatic metal salt compound is prepared by converting lithium acetate, manganese acetate and cobalt acetate into Li, Mn.
And Co were collected so as to have the ratios shown in Sample Nos. 1 to 3 in Table 1, and octadecanoic acid as a linear saturated fatty acid was added thereto and reacted while dispersing and heating in a benzene solution. What was done was used.

Next, powder obtained by coating the surface of the MOOH particles on which Li ₂ O ₂ is deposited with a complex fatty acid metal salt compound
Heat treatment was performed at a temperature of ７００700 ° C. for 2 hours.

Thereafter, the obtained heat-treated powder was analyzed by X-ray diffraction (XRD) to identify the product, and the particle size was determined by observation with a scanning electron microscope (SEM). Table 2 shows the results. In Table 2, LM ₁ represents LiMnO ₂ , LC represents LiCoO ₂ , and LM ₂ represents LiMn ₂
Represents O ₄ . Then, L _x C _y represents an oxide of Li-Co-based _{non-x / y = 1.00, LM 1} #, LM 2 # and L
C _# represents sweet LM _1, LM ₂ and LC-crystalline immediately after generation starts.

[0035]

[Table 2]

(Comparative Example) Lithium carbonate and cobalt oxide powders were accurately weighed and weighed and placed in a polyethylene pot, and ethanol was added and mixed so that the ratio of Li and Co was as shown in the comparative example in Table 1. After pulverization, heat treatment was performed at 550 to 750 ° C. for 2 hours to obtain a heat-treated powder.

Thereafter, the obtained heat-treated powder was subjected to XRD analysis to identify the product. Table 2 shows the results.

As is clear from the results in Table 2, in the comparative example, the LiCoO ₂
Whereas a single-layer powder of
At 0 ° C., a single-layer powder of LiCoO _{2 has} already been obtained, and the desired positive electrode active material for a secondary battery has been obtained at a temperature lower by 300 ° C. than the conventional method. Also, LiMnO ₂ or L
Also for iMn ₂ O ₄ , a single layer compound was obtained at a heat treatment temperature as low as 450 ° C. The average particle size of the powder of the positive electrode active material for a secondary battery obtained in this example was about 0.3.
It is as fine as μm and submicron order.

From the above results, according to the method of the present invention,
LiCoO ₂ , which is homogeneous and fine and can increase the packing density when used as a positive electrode active material of a secondary battery,
Powders of LiMnO ₂ and LiMn ₂ O ₄ can be obtained.

In the above embodiment, the case where the starting material is an acetate is described, but the present invention is not limited to this. Hydroxides, acetates, carbonates,
A water-soluble compound such as a nitrate or a compound soluble in nitric acid or acetic acid can be used as appropriate.

The complex fatty acid metal salt compound was obtained by reacting an acetate with octadecanoic acid, which is a kind of linear saturated fatty acid. It can also be obtained by reacting a saturated fatty acid with an acetate.

Further, in the above embodiment, the case where the positive electrode active material is LiCoO ₂ , LiMnO ₂ or LiMn ₂ O ₄ has been described, but the present invention is not limited to this. General formula LiM _x O _2x (where M is N
i, Mn, Co, Cr, Fe and V, and at least one element selected from x, and x is 1 or 2). Obtainable.

[0043]

As is clear from the above description, according to the present invention, a homogeneous cathode active material for a secondary battery can be synthesized at a low temperature. The obtained positive electrode active material has a submicron particle size.

Therefore, by using the positive electrode active material obtained by the present invention in a secondary battery, the packing density of the positive electrode active material can be increased and the electric capacity can be increased.

Further, the use of an inexpensive inorganic acid salt as a starting material and the elimination of a pulverizing step and the like make it possible to industrially produce a positive electrode active material for a secondary battery at low cost.

Claims (5)

[Claims] 1. The general formula LiM _x O _2x (where M is Ni,
Mn, Co, Cr, at least one element selected from Fe and V, x in the positive electrode active material manufacturing method of the secondary battery represented by 1 or 2), Li ⁺ and M
^An organic amine is added to a mixed solution containing ^{n +} (where n represents the ionic valence of M element) to form M (OH) _n (where n is M
Precipitating the ionic valence of the element);
Hydrogen peroxide is added to the (OH) _n producing solution to form M (OH) _n
To MOOH, and Li ₂
The step of depositing O ₂ and the MO on which the Li ₂ O ₂ is deposited.
Drying the OH particles;
And after mixing with the solution of the complex fatty acid metal salt compound of M
A step of drying and coating the surface of the powder with a complex fatty acid metal salt compound of Li and M; and a step of heat-treating the coated powder. The method of manufacturing the substance. 2. The method according to claim 1, wherein the ion source of the element M is a water-soluble compound or a compound soluble in nitric acid or acetic acid. 3. When the amine is added, the pH is adjusted to 9 to 9.
The method for producing a positive electrode active material for a secondary battery according to claim 1, wherein the method is adjusted to 9.5. 4. The method according to claim 1, wherein the heat treatment temperature of the powder coated with the complex fatty acid metal salt compound is 450 to 650 ° C. 5. The complex fatty acid metal salt compound is obtained by reacting a linear saturated fatty acid having 5 to 30 carbon atoms or a monoene unsaturated fatty acid with acetates of Li and M elements. The method for producing a positive electrode active material for a secondary battery according to claim 1.