JP2979826B2 - Method for producing positive electrode active material for non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, portable and cordless electronic devices have been rapidly advancing, and there is a high demand for a small and lightweight secondary battery having a high energy density as a drive power source for these devices. In this respect, non-aqueous secondary batteries, especially lithium secondary batteries, are expected to have high voltage and high energy density.

Particularly recently, a Li-containing composite oxide (general formula L
A battery system using iMO ₂ or LiM ₂ O _{4 (} where M is a transition element) as a positive electrode active material and a carbon material as a negative electrode has attracted attention as a high energy density lithium secondary battery. The feature of this battery system is that both the positive and negative electrodes utilize an intercalation reaction. In particular, metal L
Since i is not used, safety can be expected without short circuit between electrodes due to precipitation of dendritic Li, and rapid charging can be expected.

Therefore, several materials have been proposed as such Li-containing positive electrode active materials for non-aqueous electrolyte secondary batteries. In particular, LiMO ₂ which is a Li-containing composite oxide having a layered structure and LiM ₂ O ₄ which is a Li-containing composite oxide having a spinel structure are said to be promising cathode active material materials. Among them, LiCoO ₂ , LiNiO ₂ , LiM
n ₂ O ₄ has been actively studied. Conventionally, general methods for producing LiMO ₂ or LiM ₂ O ₄ include (hydr) oxide or M salt (carbonate or nitrate) and lithium salt (carbonate, nitrate or hydroxide). And baking at a temperature of 400 ° C. to 1000 ° C. in an air atmosphere (method 1).

Further, a Li-containing composite oxide represented by LiMO ₂ is prepared by mixing an aqueous solution of a nitrate represented by the general formula M (NO ₃ ) ₂ and an aqueous solution of lithium hydroxide in advance containing M and lithium in approximately equimolar proportions. At 400 ℃ after drying.
There is a method (method 2) obtained by baking at 1000 ° C. Further, a method of mixing Li ₂ MO ₃ and MO in an equimolar ratio and baking at a temperature of 400 ° C. to 1000 ° C. in an inert gas atmosphere to obtain LiMO ₂ (method 3)
There is also.

In addition to these production methods, a transition metal oxide or a transition metal sulfide is reacted in an n-butyllithium-containing hexane solution or lithium iodide-containing acetonitrile solution to obtain a lithium-containing oxide or a lithium-iodide acetonitrile solution. There is also a method for obtaining Li-containing sulfide (method 4).

[0007]

The above-mentioned general production method (method 1) is used for producing LiCoO ₂ having a layered structure or LiMn ₂ O ₄ having a spinel structure.

[0008] The method 2 is generally used for producing LiNiO ₂ having a layered structure. When these are used as the positive electrode active material for a non-aqueous electrolyte secondary battery, good charge / discharge characteristics can be obtained. However, Co and Ni have limitations as resources and are expensive, which is disadvantageous because the cost increases when manufacturing a battery. On the other hand, LiMn ₂ O ₄ is advantageous because it uses abundant and inexpensive Mn as a resource, but the theoretical capacity is about half that of LiCoO ₂ and LiNiO ₂ , so a high energy density is required. It is disadvantageous to use such a battery.

[0009] Therefore, when using a resource enriched inexpensive Mn, the production of LiMnO ₂ is substantially equal to the theoretical capacity LiCoO ₂ and LiNiO _2, was performed as a method 3, LiMnO ₂ having a layered structure Is obtained. However, when the LiMnO ₂ thus produced is used as a positive electrode active material for a non-aqueous electrolyte secondary battery, good charge / discharge characteristics cannot be obtained.

The Li-containing oxide or Li-sulfide produced using the method 4 reacts with water to contain L
Since i is released, water cannot be used when manufacturing the electrode plate. In addition, when processing the electrode plate and when storing the electrode plate, water management is required, which is not practical in terms of difficulty in manufacturing the electrode plate and complicated processes.

The present invention solves the above-mentioned problems, and uses abundant and inexpensive Mn as a resource and has a theoretical capacity of L.
iCoO ₂ and LiNiO ₂ and LiMnO ₂ is substantially the same
The purpose of the present invention is to provide a manufacturing method.

[0012]

In order to achieve the above-mentioned object, the present invention relates to a method of producing a Li-containing oxide material represented by the formula LiMnO ₂ as a starting material (raw material).
And LiOH at a ratio containing approximately equimolar amounts, and then calcined in an inert gas atmosphere at a temperature range of 400 ° C. to 600 ° C. for 3 hours or more. More preferably, _x in the formula Li _x MnO ₂ is 0.9 <x <1.
MnOOH and LiOH are mixed so as to be 1. The inert gas is nitrogen, helium or argon,
The concentration of oxygen contained in the inert gas is 0.5% or less, and the baking treatment is performed at a temperature of 400 ° C or more and 600 ° C or less.
Baking is performed for 3 hours or more.

The characteristics of LiMnO ₂ obtained as described above are such that it does not react with water to release Li taken in the crystal lattice, is stable in water, and uses a carbon material for the negative electrode. When used as a positive electrode active material of an organic electrolyte secondary battery, a battery having a large discharge capacity is supplied.

[0014]

According to the above-mentioned production method, when MnOOH and LiOH are used as starting materials (raw materials), and when calcination is carried out under the above conditions, a dehydration reaction as shown in the following (formula 1) proceeds.

MnOOH + LiOH → LiMnO ₂ + H ₂ O Formula 1 LiMnO ₂ thus obtained has a theoretical capacity of LiC
It is almost equivalent to oO ₂ and LiNiO _2, and when used as a positive electrode active material for a non-aqueous electrolyte secondary battery, good charge / discharge characteristics can be obtained. Also, the LiMnO thus obtained is
₂ does not react with water and liberate Li. Therefore, it is practical also from the viewpoint of difficulty in manufacturing an electrode plate and complicated processes.

This is because MnOOH and L as starting raw materials
It is considered that the use of iOH facilitated the dehydration reaction to obtain such LiMnO ₂ .

[0017]

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 In this example, a positive electrode active material for a non-aqueous electrolyte secondary battery having a composition represented by the formula LiMnO ₂ , which is a Li-containing Mn oxide, was produced.

First, MnOOH and LiOH are used as raw materials.
And mixing such that the atomic ratio of Li and Mn is 1: 1. This was fired at a temperature of 500 ° C. for 5 hours in a nitrogen atmosphere.

A non-aqueous electrolyte secondary battery was constructed using the positive electrode active material manufactured according to the present embodiment and the positive electrode active material manufactured according to the conventional example (method 1), and their battery characteristics were compared.

FIG. 1 is a longitudinal sectional view of a coin-type battery used in an embodiment of the present invention. In FIG. 1, a positive electrode 1 is composed of an active material in which carbon powder as a conductive material is mixed in an amount of 5 wt% with respect to the active material, and a polytetrafluoroethylene resin powder as a binder is mixed in an amount of 7 wt% with respect to the active material. It is press-formed on a titanium net 3 fixed by spot welding inside the positive electrode case 2.

The negative electrode 4 is obtained by mixing a powder of a carbonaceous material (here, pitch-based spheroidal graphite is used) with a polyacrylic acid-based resin powder as a binder at 5 wt% with respect to the carbonaceous material. It is press-formed on a stainless steel net 6 fixed to the inside of the sealing plate 5 by spot welding. A separator 7 made of polypropylene is disposed between the positive and negative electrodes.
, A proper amount of electrolyte 8 was injected, and the sealing plate 5 was sealed with the case 2 via a gasket 9 made of polypropylene to obtain a completed battery having a diameter of 20 mm and a height of 1.6 mm. The electrolyte used was one in which 1 mol of lithium perchlorate was dissolved in 1 liter of a mixed solvent of propylene carbonate and ethylene carbonate. Note that, in this example, in order to mainly evaluate the characteristics of the positive electrode active material, a material in which the negative electrode capacity was increased in advance was used.

The curve shown by a broken line in FIG. 2 indicates a constant current charge / discharge of 2 mA in a battery using LiMnO ₂ produced as a positive electrode active material manufactured by the conventional example (method 1) at a charge end voltage of 4.1 V and a discharge end. It is a discharge voltage characteristic of the first cycle when the voltage is set to 2.0 V. For this battery,
The discharge capacity was 8.2 mAh. On the other hand, the discharge voltage characteristic of the battery using LiMnO ₂ produced according to the present invention as the positive electrode active material was 12.1 as shown by the solid line in FIG.
2 mAh, which is almost 50% larger than the conventional example.
This is because Li and Mn are mixed when the raw materials are mixed before firing.
Although the atomic ratio of 1 was 1: 1, it is considered that the amount of Li taken in the crystal lattice of the Mn oxide during firing was different, and the positive electrode active material produced by the present invention was larger.

Example 2 In order to increase the amount of Li incorporated into the crystal lattice of Mn oxide, the mixing ratio of MnOOH and LiOH as starting materials was changed to obtain Li _x MnO as a positive electrode active material. It was manufactured by changing the value of x in ₂ . First, for MnOOH and LiOH, x is 0.
5, 0.7, 0.8, 0.9, 1.0, 1.1, 1.
The mixture was mixed at 2, 1.3, 1.5 and baked at 500 ° C. for 5 hours under a nitrogen atmosphere. A non-aqueous electrolyte secondary battery was constructed using the positive electrode active material manufactured under each condition, and their battery characteristics were compared. FIG. 3 shows the discharge capacity with respect to each x when a charge / discharge test was performed under the conditions shown in Example 1. When x was 0.5, the discharge capacity was 5.1 mAh, and up to x, the discharge capacity increased as the value increased. However, when x was larger than 1.2, the discharge capacity was slightly reduced. From this, Li _x MnO ₂ which is a positive electrode active material
The value of x in the MnOO is set so that 0.9 <x <1.1.
It is desirable to mix H and LiOH. This is presumably because the amount of Li taken into the crystal lattice of the Mn oxide increases as x increases, which leads to an increase in the amount of Li that can move during charge and discharge, and the discharge capacity increases. However, if x is greater than 1,
L exceeds the amount of Li incorporated into the crystal lattice of the Mn oxide.
It is considered that because i exists, the discharge capacity did not increase, and conversely, excess Li was mixed in as an impurity, and the discharge capacity was reduced.

Example 3 In addition, Mn which is a positive electrode active material
In order for the amount of Li incorporated in the crystal lattice of the oxide to be 1, firing must be performed in an inert gas atmosphere. Therefore, the amount of oxygen contained in the inert gas was examined.

First, starting materials MnOOH and LiO
H is mixed so that the atomic ratio of Li and Mn is 1: 1. The oxygen contained in nitrogen is 5%, 2%,
It was fired at a temperature of 500 ° C. for 5 hours in a gas atmosphere mixed to be 10%, 0.5%, and 0.1%. A non-aqueous electrolyte secondary battery was constructed using the positive electrode active material manufactured under each condition, and their battery characteristics were compared. That is, FIG. 4 shows the discharge capacity for each oxygen concentration when the same charge / discharge test as in Example 1 was performed. When the oxygen concentration was 0.5% or less, the discharge capacity was 12 mAh or more, but as the oxygen concentration increased, the discharge capacity decreased. For this reason, it is desirable to perform firing in a gas atmosphere in which the oxygen concentration is 0.5% or less. This is presumably because when oxygen was present during firing, some Mn ions were oxidized from trivalent to tetravalent, and the amount of Li taken into the crystal lattice of the Mn oxide was reduced.

Example 4 Next, the positive electrode active material Li
Heat needs to be applied in order for the chemical reaction involved in the production of MnO ₂ to proceed. Therefore, the discharge capacity characteristics depending on the difference in the firing temperature were examined.

First, the starting materials MnOOH and LiO
H was mixed at an atomic ratio of Li: Mn of 1: 1 under a gas atmosphere in which the concentration of oxygen contained in nitrogen was 0.1% or less.
00 ° C, 300 ° C, 400 ° C, 500 ° C, 600 ° C, 7
The firing was performed at 00 ° C. and 800 ° C. for 5 hours. A non-aqueous electrolyte secondary battery was constructed using the positive electrode active material manufactured under each condition, and their battery characteristics were compared. Here, FIG. 5 shows the discharge capacity with respect to the firing temperature when the same charge / discharge test as in Example 1 was performed. When the firing temperature was 200 ° C., the discharge capacity showed a small value of 4.0 mAh, but as the temperature became higher, the discharge capacity became larger.
When fired at a temperature of 0 ° C., the discharge capacity shows a maximum value,
When the firing temperature was further increased, the discharge capacity decreased. For this reason, it is desirable to perform firing so that the firing temperature is 400 ° C. or higher and 600 ° C. or lower. This is because when the firing temperature is 400 ° C. or lower, LiOH and MnO
This is probably because the OH dehydration reaction did not proceed completely, and the amount of Li taken into the crystal lattice of the Mn oxide was small. Further, it is considered that when the sintering temperature is 700 ° C. or higher, a transition to another crystal phase occurs.

The positive electrode active material obtained by the method for producing a positive electrode of the present invention was tested on a cylindrical battery having a spiral structure, and as a result, almost the same effect as the result of the button battery used in the previous embodiment was obtained. I knew it could be done.

In this embodiment, lithium perchlorate is used as the solute of the electrolytic solution. However, other lithium-containing salts, for example, lithium borofluoride, lithium hexafluorophosphate, lithium hexafluoroarsenate and the like are used. The solvent for the electrolyte may be a mixed solvent of propylene carbonate and dimethoxyethane, or a single or mixed solvent of carbonates such as ethylene carbonate and butylene carbonate, and carbonates such as tetrahydrofuran. A similar effect was obtained.

[0031]

As described above, the Li-containing positive electrode active material obtained by the production method of the present invention is stable against water, and is incorporated into the crystal lattice by reacting with water. Will not be released. This is useful in battery production. A non-aqueous electrolyte battery using this positive electrode active material has the effect of increasing its discharge capacity.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a coin-type battery used in an embodiment of the present invention.

FIG. 2 is a diagram showing a comparison of discharge characteristics between a battery assembled using the positive electrode active material manufactured by the manufacturing method of the present invention and a battery assembled using the positive electrode active material manufactured by the conventional manufacturing method.

FIG. 3 is a diagram showing a discharge capacity difference when x in Li _x MnO ₂ is changed by changing a mixing ratio of LiOH and MnOOH in the manufacturing method of the present invention.

FIG. 4 is a diagram showing a difference in discharge capacity due to a difference in the concentration of oxygen contained in nitrogen in the production method of the present invention.

FIG. 5 is a view showing a difference in discharge capacity due to a difference in firing temperature in the manufacturing method of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Positive electrode case 3 Titanium net 4 Negative electrode 5 Sealing plate 6 Stainless steel net 7 Separator 8 Electrolyte 9 Gasket

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Sho Ota 1006 Kazuma Kadoma, Kadoma City, Osaka Inside Matsushita Electric Industrial Co., Ltd. (56) References JP-A-3-4445 (JP, A) JP-A-4- 181660 (JP, A) JP-A-3-98262 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01M 4/58 H01M 4/02

Claims (4)

(57) [Claims] 1. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprising a composite oxide of lithium and manganese having a composition represented by the formula Li _x MnO ₂ (x ≒ 1),
(A) the starting material serving as a manganese source is MnOOH;
(B) a starting material serving as a lithium source is LiOH, and a step of baking after mixing these raw materials at a ratio containing approximately equimolar amounts is carried out. A) a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery performed in a temperature range of 400 ° C. or more and 600 ° C. or less 2. The positive electrode active material for a non-aqueous electrolyte battery according to claim 1, wherein the two starting materials are mixed so that 0.9 <x <1.1 in a composition represented by the formula Li _x MnO _2. Manufacturing method. 3. The positive electrode active material for a non-aqueous electrolyte battery according to claim 1, wherein the inert gas is nitrogen, helium, or argon, and oxygen contained in the inert gas is 0.5% or less. Production method. 4. The method for producing a positive electrode active material for a non-aqueous electrolyte battery according to claim 1, wherein the sintering is carried out at a temperature of 400 ° C. to 600 ° C. for 5 hours or more.