JP3169688B2 - Method for producing positive electrode material for lithium 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 material used in a lithium battery using lithium or a lithium alloy as a negative electrode material.

[0002]

2. Description of the Related Art Various sulfides, oxides and composite oxides have been known as cathode materials for lithium batteries.
Furthermore, techniques such as amorphization have been proposed,
As the method, for example, a method of adding phosphorus pentoxide to vanadium pentoxide, calcining and rapidly cooling to produce a solid solution (see JP-A-59-134561); A method in which a mixture containing phosphorus pentoxide is adjusted by a melt quenching method to obtain an amorphous powder (see JP-A-2-33868), a method in which phosphorus pentoxide and an oxide of an alkaline earth metal are added to vanadium pentoxide. A method in which a mixture added at a specific ratio is quenched to be amorphous (see Japanese Patent Application No. 3-74188), and an oxide of cobalt oxide, phosphorus pentoxide and alkaline earth metal is added to vanadium pentoxide. (See Japanese Patent Application No. 3-332799) has been proposed.

[0003]

Usually, rapid cooling is required to obtain an amorphous body. Generally, it is necessary to quench using a twin roller made of copper at room temperature. Requires equipment. Therefore, in order to solve this, a method of adding an oxide of an alkaline earth metal to a system of vanadium pentoxide-phosphorus pentoxide has been proposed. Thus, an amorphous body can be obtained with a simple device. However, phosphorus pentoxide and oxides of alkaline earth metals absorb moisture and carbon dioxide gas in the air, so that accurate weighing cannot be performed, causing variations in characteristics. In order to avoid this, weighing must be performed in a dry box in order to perform accurate weighing, and the operation is complicated. The present invention has been made in view of such problems of the related art, and provides a method for easily obtaining a stable vanadium pentoxide-based positive electrode material in an amorphous state having good charge / discharge cycle stability as a positive electrode material. The purpose is to do.

[0004]

According to the present invention, V ₂ O ₅ and an alkaline earth metal phosphate, and if necessary, CoO ₂
A method for producing a positive electrode material for a lithium battery, characterized in that the mixture is melted, dropped into water, and pulverized.

Further, the present invention is characterized in that a mixture of V ₂ O ₅ , an alkaline earth metal phosphate and, if necessary, CoO ₂ is further melted and then pressed by a metal plate and pulverized. It is intended to provide a method for producing a positive electrode material for a battery.

The alkaline earth metal phosphate used in producing the cathode material of the present invention includes, for example, M (H ₂
PO ₄ ) ₂ .nH ₂ 0 (M is an alkaline earth metal, n is 1
To 2), specifically, Ca (H ₂ PO
₄ ) ₂ · H ₂ O, Mg (H ₂ PO ₄ ) ₂ · 2H ₂ O and the like.

[0007] V ₂ O ₅ and the mixing ratio of phosphoric acid alkaline earth metal salt (molar ratio), V ₂ O ₅ is 64 to 92 mol%, preferably 65 to 80 mol%, alkaline earth metal phosphate Is 36 to 8 mol%, preferably 35 to 20 mol%.
If V ₂ O ₅ is less than 64 mol%, the discharge capacity of the obtained positive electrode material decreases, while if it exceeds 92 mol%, amorphization becomes difficult, which is not preferable.

When CoO ₂ is used, its amount is
V ₂ O ₅ to 10 mol%, preferably 1-6 mol%. If it is less than 1 mol%, the effect of adding it, that is, the cycle stability of the obtained cathode material cannot be further improved, while if it exceeds 10 mol%, both the initial capacity and the cycle stability decrease.

In the method of the present invention, such a mixture of vanadium pentoxide, alkaline earth metal phosphate and, if necessary, CoO ₂ is melted and then dropped into water or pressed with a metal plate. After quenching, a positive electrode material is obtained by pulverization. In 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.

[0010] The solid solution thus obtained is amorphous. Usually, in order to obtain an amorphous body, rapid cooling is required. Generally, a twin roller made of copper at room temperature is used and rapidly cooled at about 10 ⁶ ° C / sec. Since the alkaline earth metal acid salt is a good amorphizing aid, it is dropped in water having a low quenching speed (a quenching speed of 10 ²
-10 ³ ° C / sec) or metal plate pressing (rapid cooling rate 10-1)
0 ⁴ ° C. / sec) even it is possible to obtain an amorphous material, furthermore alkaline earth metal phosphate has no hygroscopicity, since it is accurate weighing in air, without requiring a large-scale quench unit An amorphous body can be easily obtained. The obtained amorphous solid solution is very stable, and the amorphous solid solution can be mechanically pulverized to obtain an excellent positive electrode material.

When a positive electrode is manufactured using this positive electrode material, the particle size of the positive electrode material is not necessarily limited, but a high-performance positive electrode can be manufactured by using an average particle size of 5 μm or less. In this case, for these powders,
A positive electrode can be manufactured by adding and mixing a conductive agent such as acetylene black or a binder such as a fluororesin powder, rolling with a roll, and drying. In addition,
The mixing amount of the conductive agent is 5 to 5 with respect to 100 parts by weight of the positive electrode material.
0 parts by weight, particularly 7 to 10 parts by weight, and in the present invention, since the conductivity of the positive electrode material is good,
The amount of conductive agent used can be reduced. The amount of the binder is 5 to 10 parts by weight based on 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 chemically reacted with the positive electrode active material. Any non-aqueous substance can be used as long as it can move to perform the reaction, in particular, a compound composed of a combination of a cation and an anion, wherein the cation is Li ⁺ , and the example of the anion is PF ₆ ⁻ , A halide anion of a halogen group element such as AsF ₆ ⁻ and SbF ₆ ⁻ , and I ⁻ (I
_{^{3 -), Br -, Cl}} - halogen anion, such as, C
lO ₄ ^- perchlorate anions such as, 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 a cation and an anion include LiPF ₆ , 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.
Among these, LiPF ₆ , LiAsF ₆ , L
iBF ₄ , LiClO ₄ , LiSbF ₆ , LiSO ₃ C
F ₃ is preferred.

The non-aqueous electrolyte is usually used in a state of being dissolved by a solvent. In this case, the solvent is not particularly limited, but a solvent having a relatively large polarity is preferably used. Specifically, glymes such as propylene carbonate, ethylene carbonate, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, dioxane, dimethoxyethane, diethylene glycol dimethyl ether, lactones such as r-butyrolactane, phosphates such as triethyl phosphate, borate Boric esters such as triethyl acid, sulfur compounds such as sulfolane and dimethylsulfoxide, nitriles such as acetonitrile, amides such as dimethylformamide and dimethylacetamide, and one or more kinds such as dimethyl sulfate, nitromethane, nitrobenzene and dichloroethane. And mixtures thereof. Of these, ethylene carbonate, propylene carbonate, butylene carbonate, tetrahydrofuran,
One or more mixed solvents selected from -methyltetrahydrofuran, dimethoxyethane, dioxolane and γ-butyrolactone are preferred.

Further, as the non-aqueous electrolyte, an organic material obtained by impregnating the above-mentioned non-aqueous electrolyte with a polymer such as polyethylene oxide, polypropylene oxide, a crosslinked isocyanate of polyethylene oxide, or a phosphazene polymer having an ethylene oxide oligomer in a side chain. Solid electrolytes, inorganic ion derivatives such as Li ₃ N and LiBCl _4, and inorganic solid electrolytes such as lithium glass such as Li ₄ SiO ₄ and Li ₃ BO ₃ can also be used.

A lithium secondary battery using the cathode 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 in which an opening 10 a is 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 placed in the partitioned positive electrode side space. The positive electrode 50 disposed on the positive electrode case 10 side is stored, while the negative electrode 70 having the negative electrode current collector 60 disposed 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 carbon and a lithium alloy capable of occluding and releasing lithium are used. In this case, as the lithium alloy, metals of Group IIa, IIb, IIIa, IVa, Va containing lithium or alloys of two or more of them can be used.
In particular, Al, In, Sn, Pb, Bi, C containing lithium
d, Zn or alloys of two or more of these are preferred. As the separator 30, a nonwoven fabric, a woven fabric, a knitted fabric, or the like made of a synthetic resin such as polytetrafluoroethylene, polypropylene, or polyethylene that can pass or contain an electrolyte can be used. . Reference numeral 80 denotes a polyethylene insulating packing which is provided around the inner peripheral surface of the positive electrode case 10 and insulates and supports the negative electrode cover plate 20.

[0016]

[Operation] In the present invention, in forming an amorphous state,
The use of alkaline earth metal phosphate with low hygroscopicity as an amorphization aid enables accurate weighing even in air, and eliminates the need for a large-scale apparatus for producing amorphous materials with little variation in performance. It can be obtained easily.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below, but the present invention is not necessarily limited to these embodiments. Example 1 V ₂ O ₅ : CoO ₂ : Ca (H ₂ PO ₄ ) _2.
H ₂ O = 86: 4: to be 10, the respective compounds were weighed in air and then mixed in a mortar. After that, after being kept at 400 ° C. for 30 minutes in an alumina crucible, 7
V ₂ O ₅ —CoO ₂ —Ca is maintained at 40 ° C. for 10 minutes.
A molten salt of (H ₂ PO ₄ ) ₂ .H ₂ O was obtained. This is dropped on a copper plate (40 cm square, 1 mm thick), and V ₂ O ₅ —CoO ₂ —P ₂ O ₅ —
A powder consisting of an amorphous solid solution of CaO was obtained.
FIG. 2 shows a TG─DTA curve of the obtained powder, and FIG. 4A shows an X-ray diffraction pattern.

After mixing 80% by weight of the obtained powder, 10% by weight of acetylene black as a conductive agent, and 10% by weight of a fluororesin powder as an adhesive, the mixture is rolled to about 200 μm with a rolling roll, and vacuumed at 80 ° C. After drying, it was punched into a disk having a diameter of 20 mm, and this was used as a positive electrode. The negative electrode was prepared by pressing lithium on an aluminum plate punched to a predetermined size and then forming an aluminum-lithium alloy in an electrolytic solution, and also dissolving LiClO ₄ at 1 mol / l in a solvent of propylene carbonate and diethylene glycol dimethyl ether. Is used as an electrolyte, and FIG.
Was assembled. Using this battery, the discharge end voltage was 2 V, the charge end voltage was +3.7 V, and the charge / discharge current density was 1.
The cycle stability was measured under the conditions of 6 mA / cm ² . The results are shown in FIG.

Reference Example 1 V ₂ O ₅ : CoO ₂ : P ₂ O ₅ : CaO = 7 in molar ratio
A powder was obtained in the same manner as described above, except that each compound was weighed in a dry box so that the ratio became 6: 4: 10: 10. FIG. 3 shows a TG 粉末 DTA curve of the obtained powder.
FIG. 4B shows an X-ray diffraction pattern. From FIG. 2, FIG. 3 and FIG. 4, P ₂ O _{5 is} added to V ₂ O ₅ and CoO _2.
5 and CaO are weighed in a dry box, and instead of being melt-mixed and quenched, Ca (H ₂ PO ₄ ) ₂ .H ₂ O
Be quenched by melt mixing were weighed in air, P ₂ O ₅
It can be seen that the same amorphous material as that obtained by quenching CaO and CaO is obtained, and further amorphization proceeds.

[0020]

According to the method of the present invention, it is possible to obtain a stable amorphous solid solution of V ₂ O ₅ -alkali earth metal phosphate easily by simplifying the steps. By using the solid solution obtained as a positive electrode material,
A lithium battery having excellent cycle stability can be obtained.

[Brief description of the 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 shows TG @ DTA of the powder obtained by the method of Example 1.
It is a curve.

FIG. 3 shows TG @ DTA of the powder obtained by the method of Reference Example 1.
It is a curve.

FIG. 4 is an X-ray diffraction pattern of the powder obtained by the method of Example 1 and Reference Example 1.

FIG. 5 is a graph showing the cycle stability of a lithium secondary battery using the powder obtained by the method of Example 1.

[Explanation of symbols]

 30 Separator 50 Positive electrode 70 Negative electrode

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenji Sato 1-4-1, Chuo, Wako, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Koichi Miyashita 1-4-1, Chuo, Wako, Saitama (56) References JP-A-2-158056 (JP, A) JP-A-61-116758 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/58 H01M 10/40

Claims (4)

(57) [Claims] 1. A method for producing a positive electrode material for a lithium battery, comprising: melting a mixture of V ₂ O ₅ and an alkaline earth metal phosphate, dropping the mixture in water, and pulverizing the mixture. 2. The method for producing a positive electrode material for a lithium battery according to claim 1, wherein the mixture further contains CoO ₂ . 3. A method for producing a positive electrode material for a lithium battery, comprising melting a mixture of V ₂ O ₅ and an alkaline earth metal phosphate, followed by pressing with a metal plate and pulverizing. 4. The method for producing a positive electrode material for a lithium battery according to claim 3, wherein the mixture further contains CoO ₂ .