JPH1021913A - Battery that can be charged and discharged multiple times reversibly - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the energy density per unit volume and prevent occurrence of short circuit and ignition by utilizing as a negative electrode active material a material produced by coating the surface of a carbon based material, to and from which lithium is intercalated and released, with a specified oxide. SOLUTION: In a secondary battery containing a non-aqueous electrolytic solution, a material produced by coating the surface of a carbon-based material, to and from which lithium is intercalated and released, with an oxide containing one or more elements selected from Li, Ge, Sn, Pb, Sb, Bi, B, Al, Si, and In is used as a negative electrode active material. As the carbon based material, to and from which lithium is intercalated and released, natural graphite, artificial graphite, pitch coke, hollow carbon molecule, amorphous carbon, etc., may be usable. By using this battery, a system can be made compact. A battery in which short circuiting due to dendrite hardly occurs and which has a long life and high safeness is thus obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery that can be reversibly charged and discharged a plurality of times, and more particularly to a secondary battery using a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, secondary batteries have become one of the essential components that are indispensable as power sources for personal computers and mobile phones, or as power sources for electric vehicles and power storage.

A portable computer (including a pen computer) and a personal digital assistant (Personal Digita)
l Assistant or Personal Intelligent Communic
A demand for mobile communication (mobile computing) such as an ator or a hand-held communicator includes miniaturization and weight reduction. However, it is difficult to make the system compact because the power consumed by the backlight and the drawing control of the liquid crystal display panel is high, and the capacity of the secondary battery is still insufficient at present.

[0004] Further, with the increase of global environmental problems, electric vehicles that do not emit exhaust gas and noise have attracted attention.
However, since the battery occupies an extremely large volume with respect to the vehicle body and the total weight of the battery is extremely heavy, there are problems such as a small space inside the vehicle, poor stability of the vehicle body, and poor acceleration. I have. These are also caused by the low energy density of the secondary battery.

[0005] In order to reduce the size of a system using a secondary battery, it is necessary to further increase the energy density of the secondary battery compared to the present. As a negative electrode material for a secondary battery using a non-aqueous electrolyte, lithium metal, sodium metal, and alloys using these are typical.However, lithium metal or sodium metal precipitates in a dendritic manner during charge and discharge. It has the disadvantage of causing an internal short circuit or firing. On the other hand, a material mainly composed of carbon capable of reversibly inserting and releasing lithium has been put into practical use, which is advantageous in terms of safety since lithium metal and sodium metal do not precipitate in a dendritic manner. The disadvantage of this material is that the energy density per volume is low due to the low true density. In order to increase the energy density, it is necessary to increase the energy density per volume of the carbon material. For example,
In a negative electrode for a lithium secondary battery, a porous layer made of a lithium alloy is formed on the surface of a carbon layer (Japanese Patent Laid-Open No. 7-32).
No. 6342), a granular material having a laminated structure of a lithium-based metal layer and a carbon layer is used (JP-A-7-326345), and a mixture of graphite and a lithium-containing metal oxide is used (JP-A-8-7886). )and so on.

[0006]

In order to further increase the energy density of a secondary battery using a non-aqueous electrolyte, it is necessary to improve the volume energy density of a negative electrode material for a secondary battery. By forming a layer made of a lithium alloy having a high energy density per volume on the surface of the carbon layer, an improvement in energy density can be expected. However, lithium alloys tend to form dendritic precipitates,
There remain security issues. The same applies to the case where a granular material having a laminated structure of a lithium-based metal layer and a carbon layer is used. Also, when a mixture of graphite and a lithium-containing metal oxide is used, the energy density increases due to the presence of the lithium-containing metal oxide having a high energy density per volume. However, since the charging operation potential, that is, the lithium insertion potential, differs between graphite and the lithium-containing metal oxide, if the graphite and the lithium-containing metal oxide are not uniformly mixed, lithium locally precipitates as a metal and short-circuits. Accidents such as fire and fire.

As described above, few effective methods have been found for improving the volume energy density of the negative electrode material for a secondary battery.

[0008] It is an object of the present invention to provide a highly safe negative electrode material for a secondary battery which has a higher energy density per volume than conventional ones and is free from short-circuiting and ignition.

[0009]

A battery and a negative electrode according to the present invention comprise, as a negative electrode active material, Li, Ge, Sn, P
It is characterized by using a material coated with an oxide containing at least one selected from b, Sb, Bi, B, Al, Si and In. Materials mainly composed of carbon that inserts and releases lithium include natural graphite (phosphorous graphite, flaky graphite, earthy graphite, etc.), artificial graphite, petroleum pitch coke, coal pitch coke, hollow carbon molecules ( Fullerene), hollow carbon fiber (nanotube), amorphous carbon and the like. A material obtained by carrying or plating a metal such as silver, tin, copper, zinc, or lead on these carbons may be used. Li, Ge, Sn, P
An oxide containing at least one selected from b, Sb, Bi, B, Al, Si, and In is coated. As a method of coating, a method using a dry process of coating an oxide layer on a carbon surface by sputtering or the like using an oxide target, or electroplating or electroless plating of a metal, followed by heat treatment in an oxidizing atmosphere to form a coating on the surface. There are a method of coating an oxide film, and a method of forming an oxide layer on the carbon surface by mixing and mechanically fusing the oxides of fine particles on the carbon surface. Regarding the shape of the coating, the carbon surface may be coated in a film form, or a plurality of particles may be attached to the carbon surface in a granular form. The amount to be coated, expressed as a weight ratio of oxide to carbon, is preferably in the range of 80/20 to 20/80, more preferably in the range of 60/40 to 40/60, and most preferably 45/55. To 55/45. As this range, it is preferable to select a region in which the discharge capacity characteristics of carbon and the oxide are approximately equal. For example, when a discharge capacity of 200 mAh / g is used for carbon and a discharge capacity of 800 mAh / g is used for oxide, the weight ratio of oxide to carbon is 2%.
0/80. As a result, the discharge capacity characteristics of carbon and the discharge capacity characteristics of the oxide become substantially equal. By making the capacities of carbon and oxide almost equal, only one material will not be used extremely,
It is possible to obtain a composite negative electrode material in which dendrite is less likely to be generated and there is no danger such as short circuit or ignition. The discharge capacities of both materials should be such that the energy density per unit weight and the energy density per unit volume do not significantly decrease due to the mixture of the two, and there is no current concentration caused by the extreme use of only one of the materials. Use in the area where is equal. In addition, since the oxide is mixed by coating on the carbon surface, the oxide is more uniformly dispersed as compared with the ordinary mixing method, so that it is difficult to generate dendrites. According to the present invention, a high energy density and a long cycle life can be achieved by the synergistic effect of the advantages of both materials, and neither carbon alone nor oxide alone can be obtained.

Further, the present invention is characterized in that the oxide is amorphous. The charge reaction of the oxide as a negative electrode is
Li, Ge, Sn, P present in the oxygen matrix
Lithium is inserted in such a manner as to be randomly dissolved and alloyed with elements such as b, Sb, Bi, B, Al, Si, and In.
Therefore, the oxide after the insertion of lithium becomes amorphous. Therefore, the oxide used may be amorphous. Since the charge potential of this amorphous oxide is lower than the charge potential of carbon, the amorphous oxide layer is formed by coating the outer periphery of carbon without dendrite depositing lithium not taken into carbon. Can be taken in.

Examples of the electrolyte include propylene carbonate, propylene carbonate derivatives, ethylene carbonate, butylene carbonate, vinylene carbonate, gamma-butyl lactone, dimethyl carbonate,
Diethyl carbonate, methyl ethyl carbonate,
1,2-dimethoxyethane, 2-methyltetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, gisanmethyl, methyl acetate, methyl propionate, ethyl propionate,
Phosphate triester, trimethoxymethane, dioxolane derivative, diethyl ether, 1,3-propanesultone, sulfolane, 3-methyl-2-oxazolidinone,
At least one non-aqueous solvent selected from the group consisting of tetrahydrofuran, tetrahydrofuran derivative, dioxolan, 1,2-diethoxyethane, and halides thereof, and a lithium salt such as LiClO ₄ ,
LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ , LiC
_{F 3 CO 2, LiAsF 6,} LiSbF 6, LiB 10 C
l ₁₀ , LiAlCl ₄ , LiCl, LiBr, LiI,
By using a mixed solution with at least one salt selected from the group consisting of lithium lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate, and the like, the negative electrode active material of the present invention exhibits good characteristics. .

Any positive electrode active material may be used as long as it can insert and release lithium, and is preferably a lithium-containing transition metal oxide. For example, Li _x Mn ₂ O ₄ , Li _x C
oO ₂ , Li _x NiO ₂ , Li _x MnO ₂ , Li _x MaNi
(1-a) O ₂ (M is Co, V, Mn, Fe, B, Mg,
One or more elements selected from Al, Cu and Cr, a =
0.01-0.95).

The use of the reversibly chargeable / dischargeable battery of the present invention is not particularly limited. Phone handset, pager, handy terminal, portable copy, electronic organizer, calculator, LCD TV,
Electric shaver, power tool, electronic translator, car phone,
Power supplies for equipment such as transceivers, voice input devices, memory cards, backup power supplies, tape recorders, radios, headphone stereos, portable printers, handy cleaners, portable CDs, video movies, navigation systems, refrigerators, air conditioners, televisions,
Stereo, water heater, microwave oven, dishwasher,
It can be used as a power source for washing machines, dryers, game devices, lighting devices, toys, road conditioners, medical devices, automobiles, electric vehicles, golf carts, electric carts, power storage systems, and the like. It can be used not only for civilian purposes but also for military use and space.

By using the battery of the present invention, the energy density per volume can be improved. As a result, the system can be made compact. In addition, a dendrite short circuit hardly occurs, and a long-life and highly safe battery can be obtained.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the examples unless it exceeds the gist of the invention.

(Example 1) Artificial graphite as a negative electrode material,
(1) SnSiO ₃ (2)
Al ₂ O ₃ (3) SnO (4) SnO ₂ (5) PbO
(6) Sb ₂ O ₃ (7) LiBiO ₂ (8) GeO ₂ (9)
B ₂ O ₃ (10) In ₂ O ₃ was weighed so that the weight ratio was 1: 1. This was rotated for 15 hours in an Ar atmosphere at a rotation speed of 250 rpm using a planetary ball mill to coat the graphite material with the coating material. 93% by weight of this powder,
Using a mixture prepared by preparing 7% by weight of polyvinylidene fluoride as a binder, the mixture was kneaded with a triturator for 30 minutes, and then applied to both surfaces of a copper foil having a thickness of 30 microns. LiCoO ₂ powder was used for the positive electrode, a mixture prepared by preparing 87% by weight of this powder, 6% by weight of acetylene black as a conductive agent, and 7% by weight of polyvinylidene fluoride as a binder.
After mixing and mixing, it was applied to both sides of an aluminum foil having a thickness of 20 microns. The positive and negative electrodes were roll-formed by a press, and the terminals were spot-welded and then vacuum-dried at 150 ° C. for 5 hours. A positive electrode and a negative electrode were laminated with a microporous polypropylene separator interposed therebetween, spirally wound, and inserted into an aluminum battery can. The negative electrode terminal was welded to the battery can, and the positive electrode terminal was welded to the battery lid. As the electrolytic solution, a solution prepared by dissolving 1 mol of LiPF ₆ in 1 liter of a mixed solution of ethylene carbonate and diethyl carbonate was used, and the solution was injected into the battery can. The battery cover was swaged to produce a cylindrical battery having a capacity of 1400 mAh.
After charging the battery to 4.2 V at 280 mA, the battery was charged and discharged at a constant current of 280 mA to 2.7 V, and the cycle life and volume energy density were evaluated. Table 1 shows the results.

[0017]

[Table 1]

(Comparative Example 1) 9 artificial graphite was used as a negative electrode material.
A mixture prepared by preparing 3% by weight and 7% by weight of polyvinylidene fluoride as a binder was applied to both surfaces of a copper foil having a thickness of 30 microns. A battery was manufactured in the same manner as in Example 1. Table 1 shows the results of the cycle life and the volume energy density.
The volume energy density is lower than that of Example 1.

(Comparative Example 2) Artificial graphite was used as a negative electrode material.
Using a mixture prepared by preparing 7% by weight, 46% by weight of SnO, and 7% by weight of polyvinylidene fluoride as a binder, the mixture was kneaded for 30 minutes with a rake machine, and applied to both sides of a copper foil having a thickness of 30 microns. . A battery was manufactured in the same manner as in Example 1. Table 1 shows the results of the cycle life and the volume energy density. The life was shorter than that of Example 1, and after disassembly, dendritic deposits of lithium were observed on the negative electrode surface. (Comparative Example 3) As the negative electrode material, artificial graphite and SnO were weighed at a weight ratio of 85:15. This was coated on the graphite surface with SnO using a planetary ball mill under the same conditions as in Example 1. Using a mixture prepared by mixing 93% by weight and 10% by weight of this powder and 7% by weight of polyvinylidene fluoride as a binder, kneading the mixture for 30 minutes with a rake machine, and then applying the mixture to both sides of a 30 micron thick copper foil. did. A battery was manufactured in the same manner as in Example 1. Table 1 shows the results of the cycle life and the volume energy density. The life is shorter than that of Example 1, and after disassembly,
Dendritic deposits of lithium were observed on the negative electrode surface. Further, the volume energy density is lower than that of Example 1.

Example 2 Amorphous carbon carrying Ag as a negative electrode material and (1) SnSiO ₃ (2) Al ₂ O ₃ (3) SnO (4) as a coating material for coating the same
SnO ₂ (5) PbO (6) Sb ₂ O ₃ (7) LiBiO ₂
(8) GeO ₂ (9) B ₂ O ₃ (10) In ₂ O ₃ were weighed so as to have a weight ratio of 1: 1. The surface of the alloy was coated in the same manner as in Example 1, and a battery was produced using the alloy. Table 2 shows the results of the cycle life and the volume energy density.

[0021]

[Table 2]

[0022]

According to the present invention, since the volume energy density can be improved, the battery can be made compact.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shuko Yamauchi 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Toshinori Dozono 7-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 Hitachi, Ltd., Hitachi Research Laboratories (72) Inventor Ren Muranaka 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi, Ltd. Hitachi Research Laboratory (72) Inventor Masanori Yoshikawa Hitachi, Ibaraki Prefecture 7-1-1, Omikacho Inside Hitachi Research Laboratory, Hitachi, Ltd.

Claims (3)

[Claims] 1. A battery comprising a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt, which can be charged and discharged a plurality of times reversibly.
In the negative electrode active material of the negative electrode, around a material mainly composed of carbon that inserts and releases lithium, Li, Ge, S
A negative electrode and a battery using the negative electrode, which are coated with an oxide containing at least one selected from n, Pb, Sb, Bi, B, Al, Si, and In. 2. The negative electrode according to claim 1, wherein the oxide is amorphous, and a battery using the negative electrode. 3. A battery-using system using the negative electrode or the battery according to claim 1.