JPH065286A - Manufacture of positive electrode material for lithium battery - Google Patents

Abstract

PURPOSE:To provide a large initial capacity and enhance charge/discharge cycle stability by pulverizing positive electrode active material composed mainly of a vanadium pentoxide in a planetary ball mill, then pulverizing it in a jet mill, and pulverizing it again in the planetaty ball mill. CONSTITUTION:Positive electrode active material composed mainly of a vanadium pentoxide is pulverized first in a planetaty ball mill, next in a jet mill, and again in the planetaty ball mill. Positive electrode material having a particle diameter of a submicron degree can be for the first time obtained by the three steps of pulverizing. In the positive electrode material thus obtained and having a small average particle diameter, a surface area is increased to increase an apparent diffusion coefficient of Li ion and an initial discharge capacity per weight. In this method, a positive electrode of high performance can be provided.

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 material used in a lithium battery.

[0002]

2. Description of the Related Art Various sulfides and oxides have been conventionally known as positive electrode materials for lithium batteries. Furthermore,
Techniques such as complex oxides and amorphization have also been proposed.
For example, a positive electrode active material made of a solid solution prepared by adding phosphorus pentoxide to vanadium pentoxide, firing it, and then rapidly cooling it (see Japanese Patent Application Laid-Open No. 59-134561), which is 30 mol% or less of vanadium pentoxide. A positive electrode body composed of an amorphous powder compact obtained by preparing a mixture to which phosphorus oxide is added by a melt quenching method (JP-A-2-3386).
No. 8 and No. 2-68868) are proposed.

[0003]

When producing a positive electrode material using these positive electrode active materials, it is necessary to make coarse powder into fine powder. Usually, wet milling or dry milling is performed using a ball mill or jet mill. It is being appreciated. However, in the case of wet grinding, the solvent used is a common water or alcohols, water soluble amorphous V ₂ O _5, also alcohols amorphous V ₂ O ₅
The initial capacity tends to decrease in reaction with. On the other hand, dry pulverization does not have such a problem, but the pulverization limit of the conventional pulverization method is on the order of microns. As the battery electrode, the utilization rate can be further improved by pulverizing to the submicron order, so that pulverization is not sufficient at present. As described above, even when these positive electrode materials are used, the problem that the initial capacity is insufficient or the capacity decreases when charging and discharging are repeated cannot be solved, and the initial discharge capacity is large, A positive electrode material with good cycle stability has not been obtained. The present invention has been made against the background of such problems of the prior art, and has a large initial discharge capacity per weight as a positive electrode material and good charge / discharge cycle stability, and is a vanadium pentoxide-based positive electrode material for lithium batteries. The purpose is to provide.

[0004]

The present invention is characterized in that a positive electrode active material containing vanadium pentoxide as a main component is pulverized by a planetary ball mill, pulverized by a jet mill, and then pulverized again by a planetary ball mill. A method for producing a positive electrode material for a lithium battery is provided.

The positive electrode active material that can be used in the present invention contains vanadium pentoxide as a main component, and a metal such as manganese, cobalt, chromium, molybdenum, tungsten, phosphorus pentoxide or calcium oxide, which is used alone or in combination. It is a mixture of oxides or sulfides. The content of vanadium pentoxide in the positive electrode active material is usually 64 mol% or more, preferably about 65 to 80 mol%. Specific examples of the composition of the positive electrode active material suitable for use in the present invention include, for example, Japanese Patent Application No.
74188.

This positive electrode active material is, for example, vanadium pentoxide, cobalt oxide, phosphorus pentoxide, and MO (however,
(M represents an alkaline earth metal element) and the like are mixed and melted at 500 to 800 ° C., preferably 560 to 740 ° C., and then dropped into water or pressed with a metal plate to form an amorphous V ₂ Obtained as O ₅ . Upon melting, it is preferable to hold at 200 to 500 ° C. for 30 minutes to 6 hours, and further to hold at 560 to 740 ° C. for 5 minutes to 1 hour.

The solid solution thus obtained is amorphous. Usually, rapid cooling is necessary to obtain an amorphous body, and generally, a twin roller made of copper at room temperature is used and rapidly cooled at about 10 ⁶ ° C / sec. In the present invention, a positive electrode active material containing V ₂ O ₅ as a main component is melt-mixed, and the mixture is dropped into water (quenching rate 10 ² to 10 ³ ° C / sec) with a small quenching rate or a metal plate pressing method (quenching rate). An amorphous body can be obtained by 10 to 10 ⁴ ° C / sec. Therefore, an amorphous body can be easily obtained without requiring a large-scale quenching device. Further, the obtained amorphous solid solution is very stable, and the amorphous solid solution can be mechanically pulverized to obtain an excellent positive electrode material.

In the present invention, the positive electrode active material thus obtained is first pulverized by a planetary ball mill. In this pulverization, the positive electrode active material is also pulverized into the submicron region, but the particle size distribution cannot be controlled and is usually in the range of about 0.1 to 70 μm. In this coarse grinding, the average particle size is 10 μm.
The following is appropriate. The conditions for grinding with a planetary ball mill are 1 to 20 G, preferably 5 to 5 G with grinding energy.
15G is good for about 5 to 120 minutes.

Next, in the present invention, the thus roughly crushed positive electrode active material is crushed by a jet mill to reduce the average particle size to about 2.0 μm. Milling with a jet mill is effective for milling several tens of μm, and the particle size distribution curve rises sharply. By this pulverization, the maximum particle size can be reduced to 10 μm or less, and the particles are pulverized to the micron order. However, the average particle size is 2.0 μm
Since the pulverization in the submicron region does not proceed, the planetary ball mill is pulverized again to pulverize in the submicron region to further reduce the average particle size. The average particle size of the positive electrode material thus obtained is usually 1.
It is 8 μm or less, preferably 1.5 μm or less, and more preferably 0.5 to 1.3 μm. The conditions for crushing with a jet mill are, for example, single track jet mill FS-
4 [manufactured by Seishin Enterprise Co., Ltd.], 0.5 to 3.0
Grind at a throughput of kg / hour. Moreover, the conditions of the pulverization in the planetary ball mill to be performed again may be the same as those in the first stage pulverization. It is preferable to carry out all pulverization by a dry method. Instead of crushing with a jet mill, a region having a large particle size may be removed by classification.

The positive electrode material obtained by the production method of the present invention as described above has an average particle size in the submicron region and is smaller than the conventional one, and has a larger specific surface area, so that the apparent Li ion diffusion coefficient is increased. Therefore, the initial discharge capacity per weight increases. By using the positive electrode material thus obtained, a high performance positive electrode can be produced. In this case, for these finely divided positive electrode materials,
A positive electrode can be produced by a method of adding and mixing a conductive agent such as acetylene black and a binder such as fluororesin powder, rolling with a roll, and drying. In addition,
The amount of the conductive agent mixed is 5 to 5 with respect to 100 parts by weight of the positive electrode material.
It can be 0 parts by weight, particularly 7 to 10 parts by weight, and in the present invention, the positive electrode material has good conductivity,
The amount of conductive agent used can be reduced. The amount of the binder compounded is 5 to 10 with respect to 100 parts by weight of the positive electrode material.
It is preferable to use parts by weight.

The non-aqueous electrolyte used in the battery using the positive electrode material of the present invention is chemically stable with respect to the positive electrode material and the negative electrode material, and lithium ions are electrochemically reacted with the positive electrode active material. even mentioned any non-aqueous material can be moved to the available, in particular compounds comprising a combination of a cation and an anion, PF ₆ examples of Li ^+, also anion as cation ^-, Halide anions of halogen elements of Va group elements such as AsF ₆ ⁻ and SbF ₆ ⁻ , I ⁻ (I
^{_{3 -), Br -, Cl}} - halogen anion, such as, C
perchlorate anion such as 10 ₄ ⁻ , HF ₂ ⁻ , CF ₃
SO ₃ ^-, SCN ^- and the like can be mentioned compounds having an anion such as, but not necessarily limited to these anions. Specific examples of the electrolyte having such cations and anions include LiPF ₆ and LiA
sF ₆ , LiSbF ₆ , LiBF ₄ , LiClO ₄ , L
iI, LiBr, LiCl, LiAlCl ₄ , LiHF
₂ , LiSCN, LiSO ₃ CF _{3 and the} like.
Of these, LiPF ₆ , LiAsF ₆ , L
iBF ₄ , LiClO ₄ , LiSbF ₆ , LiSO ₃ C
F ₃ is preferred.

The nonaqueous electrolyte is usually used in a state of being dissolved in a solvent. In this case, the solvent is not particularly limited, but a solvent having a relatively large polarity is preferably used. Specifically, propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, glymes such as diethylene glycol dimethyl ether, lactones such as γ-butyrolactone, phosphate esters such as triethyl phosphate, boro. One or more of boric acid esters such as acid triethyl, sulfur compounds such as sulfolane and dimethyl sulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, dimethyl sulfate, nitromethane, nitrobenzene and dichloroethane. Can be mentioned. Of these, ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran, 2
One or a mixture of two or more selected from -methyltetrahydrofuran, dimethoxyethane, dioxolane and γ-butyrolactone is suitable.

Further, as the non-aqueous electrolyte, the above non-aqueous electrolyte is impregnated with a polymer such as polyethylene oxide, polypropylene oxide, a cross-linked isocyanate of polyethylene oxide, or a polymer such as a phosphazene polymer having an ethylene oxide oligomer in a side chain. It is also possible to use a solid electrolyte, an inorganic ion derivative such as Li ₃ N or LiBCl ₄ , or an inorganic solid electrolyte such as lithium glass such as Li ₄ SiO ₄ or Li ₃ BO ₃ .

A lithium secondary battery using the positive electrode material of the present invention will be described in more detail with reference to the drawings. That is, the lithium secondary battery using the positive electrode material of the present invention,
As shown in FIG. 1, a button-shaped positive electrode case 10 having an opening 10a sealed with a negative electrode cover plate 20 is partitioned by a separator 30 having fine holes, and a positive electrode current collector 40 is provided in the partitioned positive electrode side space. While the positive electrode 50 arranged on the positive electrode case 10 side is stored, the negative electrode 70 in which the negative electrode current collector 60 is arranged on the negative electrode cover plate 20 side is stored in the negative electrode side space. As the negative electrode material used for the negative electrode 70, for example, lithium or a lithium alloy or carbon capable of inserting and extracting lithium is used. In this case, as a lithium alloy,
A group IIa, IIb, IIIa, IVa, Va group metal containing lithium or an alloy of two or more thereof can be used, and particularly Al, In, Sn, Pb, Bi, Cd containing lithium,
Zn or alloys of two or more of these are preferred. As the separator 30, for example, a non-woven fabric, a woven fabric or a knitted fabric made of a synthetic resin such as polytetrafluoroethylene, polypropylene or polyethylene, which is porous and capable of passing or containing an electrolytic solution, can be used. . Reference numeral 80 denotes a polyethylene insulating packing that is provided around the inner peripheral surface of the positive electrode case 10 to insulate and support the negative electrode cover plate 20.

[0015]

In the present invention, crushing is first carried out by a planetary ball mill. This pulverization can be performed from the bulk, and although the pulverization proceeds to the submicron region, the particle size distribution cannot be controlled and is in the range of 0.1 to 70 μm. Therefore, several tens of μ
It is effective for pulverizing m and has a maximum grain size of 50 μm or less and an average grain size of about 5.0 μm by pulverizing with a jet mill having a sharp rise in particle size distribution. However, since the crushing does not proceed to the submicron range in the jet mill, it is crushed again in the planetary ball mill. In this way, the positive electrode material having a particle size of submicron order can be obtained only by pulverizing in three steps while making the most of the features of each pulverizing method. The thus obtained positive electrode material having a small average particle size has an increased surface area, so that the apparent diffusion coefficient of Li ions increases and the initial discharge capacity per weight increases.

[0016]

EXAMPLES Examples of the present invention will be described below, but the present invention is not necessarily limited to these examples. Example 1 Molar ratio of V ₂ O ₅ : P ₂ O ₅ : CaO = 84: 8: 8
Each compound was weighed and mixed in a mortar so that After that, hold in an electric furnace at 740 ° C for 10 minutes to obtain V
It was obtained ₂ O ₅ -P ₂ molten salt of O ₅ -CaO. By sandwiching this between copper plates at room temperature, amorphous V ₂ O ₅ was obtained. This is a planetary ball mill (FRITSCH P-
5, agate 500ml container, agate crushing ball 20
(φ, 100 g, 10φ, 200 g), the motor was rotated at 1,240 rpm for 1 hour, and the average particle size was 1.
7 μm of coarsely crushed powder was obtained. A single track jet mill FS-4 [manufactured by Seishin Enterprise Co., Ltd.] was used for this coarsely pulverized powder, the nozzle pressure was 4 kg / cm ² , and the air volume used was 1.2 m.
^It was crushed 3 times at a throughput of 25 g / min at ³ / min. The average particle size of the obtained powder was 1.7 μm. This is again crushed with a planetary ball mill.
00g, 5φ; 100g, and other conditions were the same as the above. The average particle size of the obtained powder was 1.2 μm. The result of measuring the apparent Li ion diffusion coefficient of this positive electrode material powder was used to calculate the apparent L of various positive electrode materials having various particle sizes.
It is shown in FIG. 2 together with the diffusion coefficient of i ions.

80% by weight of the powder thus obtained,
After mixing 10% by weight of acetylene black as a conductive agent and 10% by weight of a fluororesin powder as an adhesive, the mixture was rolled to about 200 μm with a rolling roll, vacuum dried at 150 ° C., and then punched into a disk shape with a diameter of 20 mm. Was used as the positive electrode. For the negative electrode, an aluminum plate punched to a predetermined size was pressure-bonded with lithium and aluminum-lithium alloyed in an electrolytic solution was used, and propylene carbonate and diethylene glycol dimethyl ether (weight ratio =
A battery shown in FIG. 1 was assembled by using LiClO ₄ dissolved in a mixed solvent of 1: 1) at 1 mol / l as an electrolytic solution. Using this battery, the initial discharge capacity per weight was measured. The results are shown in FIG. 3 together with the initial discharge capacities per weight of the batteries obtained by similarly using the positive electrode materials having various particle sizes.

Example 2 As in Example 1, after pulverizing 3 times with a jet mill,
It was pulverized with a planetary ball mill under the same conditions as the first pulverization of Example 1. The average particle size was 1.5 μm. Comparative Example 1 In the same manner as in Example 1, the mixture was pulverized twice with a jet mill. The average particle size was 1.7 μm. Comparative Example 2 In the same manner as in Example 1, the particles were crushed once with a jet mill. The average particle size was 2.7 μm. Comparative Example 3 As in Example 1, the particles were pulverized with a planetary ball mill. The average particle size was 4.6 μm. Comparative Example 4 A bulk was crushed with a bee. The average particle size was 50 μm. The above results are shown in FIGS.

As is clear from FIGS. 2 and 3, the smaller the particle size, the larger the apparent Li ion diffusion coefficient,
The submicron region positive electrode material powder obtained by the method of the present invention has a very large apparent Li ion diffusion coefficient, and the initial discharge capacity per weight of the battery obtained using this is also large. On the other hand, the positive electrode material having a particle size in the micron range obtained by the method of the comparative example has a small apparent Li ion diffusion coefficient, and the initial discharge capacity per weight of the battery obtained therefrom is small.

[0020]

According to the present invention, it is possible to provide a vanadium pentoxide-based positive electrode material for lithium batteries, which has a large initial discharge capacity per weight and good charge / discharge cycle stability.

[Brief description of drawings]

FIG. 1 is a front view including a partial cross-sectional view of a lithium secondary battery using a positive electrode material for a lithium battery of the present invention.

FIG. 2 is a graph showing the relationship between the average particle diameter of positive electrode material powder and the apparent Li ion diffusion coefficient.

FIG. 3 is a graph showing the relationship between the average particle size of the positive electrode material powder and the initial discharge capacity of the obtained lithium secondary battery.

[Explanation of symbols]

 30 Separator 50 Positive electrode 70 Negative electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenji Sato, Inventor Kenji Sato, 4-1-1 Chuo, Wako-shi, Saitama Inside Honda R & D Co., Ltd. (72) Inventor, Koichi Miyashita 4-1-1, Chuo, Wako, Saitama No. Stock Company Honda Technical Research Institute

Claims (1)

[Claims] 1. A method for producing a positive electrode material for a lithium battery, which comprises crushing a positive electrode active material containing vanadium pentoxide as a main component with a planetary ball mill, crushing with a jet mill, and then crushing with a planetary ball mill again. Method.