JPH1092434A - Battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the energy density and the output density of secondary battery positive electrode material by containing at least one kind of graphite which has ash portion of specified percentage or less and has La of specified Åor more as a conductive agent. SOLUTION: In a battery which is composed of a negative electrode, a positive electrode, and lithium salt-containing nonaqueous electrolyte and can be reversibly charged and discharged plural times, the positive electrode contains at least one kind of graphite which has ash portion of 0.08% or less and has La of 400Å or more as a conductive agent. When the ash portion is more than 0.08%, impurities react with lithium in positive electrode active material to reduce lithium amount so that the energy density of the positive electrode active material is decreased and output density is reduced since a reaction product is an insulating substance. When the La is less than 400Å, the electron conductivity is deteriorated so that the energy density is decreased. Thereby, the energy density and the output density of secondary battery positive electrode material are enhanced.

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 and lightweight because of the high power consumed by the backlight and drawing control of the liquid crystal display panel, and the fact that the capacity of the secondary battery is still insufficient at present. It is in.

[0004] Further, with the increase of global environmental problems, electric vehicles that do not emit exhaust gas and noise have attracted attention.
However, current batteries have problems such as short running distance, poor acceleration, small space in the vehicle, and poor stability of the vehicle body due to low energy density and low output density.

[0005] Among secondary batteries, lithium secondary batteries using a non-aqueous electrolyte are particularly attracting attention because of their high voltage, light weight, and high energy density. The cathode material of this secondary battery is made of a conductive polymer such as polyaniline, polyacene, polyparaphenylene, Li _x CoO ₂ ,
Representative examples include Li _x NiO ₂ , Li _x Mn ₂ O ₄ , complex oxides obtained by substituting these transition metals with other transition metals, alkaline earth metals, metalloids, etc., and chalcogenite compounds such as TiS ₂ and MoS _2. It is. However, all of them have a disadvantage that the resistance of the material itself is high. Therefore, by adding a conductive agent to the positive electrode active material, electron conductivity is increased, and characteristics as the positive electrode active material are developed. Conventionally,
In order to achieve higher energy density or higher output density of a lithium secondary battery using a non-aqueous electrolyte, attempts have been made to improve the conductive agent of the positive electrode. For example, graphite having a porosity of 5 to 40% is used as a conductive agent (Japanese Patent Application Laid-Open No. 7-1303).
No. 96), using a material having a d (002) of greater than 3.358% (Japanese Patent Laid-Open No. 7-192718), having an oil absorption of 50 ml.
/ 100 g or more and less than 300 ml / 100 g of carbon black (JP-A-7-288140).

[0006]

By using graphite having a porosity of 5 to 40% as a conductive agent, the resistance of the electrode can be reduced without exfoliating the active material from the substrate. However, the reason why the resistance of the electrode can be reduced is that the binder is absorbed into the pores of the graphite and does not cover the surface of the active material, and the electrode resistance is reduced by controlling the distribution of the binder in the electrode. Has its own limitations. The same applies to the case where a material having d (002) larger than 3.358 ° is used. When d (002) is large, the binder penetrates between the layers, so that the electrode resistance is reduced. Oil absorption 50ml / 100
The same applies when using carbon black in an amount of at least 300 g / 100 g. In these conventional methods, by controlling the distribution of the binder in the electrode, the resistance of the electrode is reduced without the active material peeling from the substrate, and the resistance is not drastically reduced. Effective methods for increasing the energy density or the output density of the semiconductor have not been found.

An object of the present invention is to increase the energy density and the output density of a positive electrode material for a secondary battery.

[0008]

The battery and the positive electrode of the present invention relate to 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. And at least one kind of graphite having an ash content of 0.08% or less and a La of 400 ° or more. The graphite used in the present invention is artificial graphite, natural graphite,
Various graphites such as massive graphite, flaky graphite, expanded graphite, specially treated graphite, pitch-based graphite, and coke-based graphite are exemplified. Of these graphites, those having an ash content of 0.08% or less and La of 400% or more are preferred, more preferably 0.05% or less of ash content and 500% or more of La, and most preferably an ash content of 0.5% or more. Not more than 02% and La
Is 600 ° or more. When the ash content is more than 0.08%, these impurities react with lithium in the positive electrode active material to decrease the amount of lithium, so that the energy density of the positive electrode active material decreases. In addition, since the reaction product of the impurity and lithium is an insulating substance, the resistance of the electrode increases and the output density decreases. When La is smaller than 400 °, the electron conductivity of graphite decreases, so that the electrode resistance cannot be reduced, and the energy density and the output density also decrease.

In the battery and the positive electrode of the present invention, a conductive agent containing at least one kind of graphite contains carbon black having an ash content of not more than 0.08% and a specific surface area of not less than 50 m ² / g in an amount of from 5% by weight to 75% by weight. % Is used. The carbon black used in the present invention includes acetylene black, Ketjen black, furnace black and the like. Of these carbon blacks, those having an ash content of not more than 0.08% and a specific surface area of not less than 50 m ² / g are preferable, and more preferably having an ash content of not more than 0.05% and a specific surface area of 200 m ² / g.
As described above, most preferably, the ash content is 0.02% or less, and the specific surface area is 350 m ² / g or more. Ash content is 0.08%
If the amount is larger, these impurities react with lithium in the positive electrode active material to decrease the amount of lithium, so that the energy density of the positive electrode active material decreases. In addition, since the reaction product of the impurity and lithium is an insulating substance, the resistance of the electrode increases and the output density decreases. The specific surface area is 50 m ² / g
If it is smaller, the binder covers the surface of the positive electrode active material, so that the electrode resistance cannot be reduced and the mixing effect of carbon black cannot be obtained, so that both the energy density and the output density decrease. It is preferable to use, as the conductive agent, a mixture of carbon black and a conductive agent containing at least one kind of graphite in a range of 5% by weight or more and 75% by weight or less. If the mixing amount of carbon black is less than 5% by weight, the electrode resistance cannot be reduced and the mixing effect of carbon black cannot be obtained. On the other hand, if the mixing amount of carbon black is more than 75% by weight, the binding force of the binder is reduced and the active material is peeled off from the substrate, so that the effect of mixing carbon black cannot be obtained.

The positive electrode active material used in the present invention may be a transition metal oxide, a transition metal sulfide, or a conductive polymer capable of reversibly inserting and releasing lithium ions, and particularly preferably a lithium-containing transition metal oxide. The preferred lithium-containing transition metal oxide used in the present invention is Ti, C
Lithium-containing oxides containing r, V, Fe, Mn, Mo, W, Cu, Ni, and Co may be mentioned. More preferred lithium-containing transition metal oxide cathode active materials used in the present invention are semi-metals such as Al, Ga, In, Ge, besides transition metals.
Sn, Pb, Sb, Bi and the like may be mixed. Also,
It is more preferable to mix an alkali metal or alkaline earth metal other than lithium. More preferred lithium-containing cathode active material used in the present invention is Li _x Co _a O
₂ , Li _x Co _{(ab) Mb} O ₂ (M is Ti, Cr,
V, Fe, Mn, Mo, W, Cu, Ni, Al, Ga,
In, Ge, Sn, Pb, Sb, Bi, at least one of alkali metals and alkaline earth metals other than lithium), Li _x Ni _a O ₂ , Li _x Ni _(ab) M _b O ₂ (M
Are Ti, Cr, V, Fe, Mn, Mo, W, Cu, C
o, Al, Ga, In, Ge, Sn, Pb, Sb, B
i, at least one of alkali metals other than lithium and alkaline earth metals), Li _x Mn _2a O ₄ , Li _x Mn
_{(2a-b) M b O} 4 (M is Ti, Cr, V, Fe, Mo, W,
Cu, Co, Al, Ga, In, Ge, Sn, Pb, S
b, Bi, at least one of alkali metals other than lithium and alkaline earth metals), Li _x V _2a O ₅ , Li _x V
_{2 (ab) M b O 5} (M is Ti, Cr, Co, Ni, Fe, M
n, Mo, W, Cu, Ni, Al, Ga, In, Ge,
Sn, Pb, Sb, Bi, at least one of alkali metals other than lithium and alkaline earth metals), Li _{x
Fe a O 2, Li x Fe} (ab) M b O 2 (M is Ti, Cr,
V, Co, Mn, Mo, W, Cu, Ni, Al, Ga,
In, Ge, Sn, Pb, Sb, Bi, at least one of alkali metals other than lithium and alkaline earth metals), Li _x Cu _a O ₂ , Li _x Cu _(ab) M _b O
₂ (M is Ti, Cr, V, Co, Mn, Mo, W, F
e, Ni, Al, Ga, In, Ge, Sn, Pb, S
b, Bi, at least one of an alkali metal other than lithium and an alkaline earth metal), Li _x C _a O ₂ ,
Li _x Cr _(ab) M _b O ₂ (M is Ti, Cu, V, Co, M
n, Mo, W, Fe, Ni, Al, Ga, In, Ge,
Sn, Pb, Sb, Bi, at least one of alkali metals other than lithium and alkaline earth metals), Li _{x
Fe (MoO 4) O 3,} Li x Fe (Mo (1-b) M b O 4) O 3 (M
Are Ti, Cu, V, Co, Mn, W, Fe, Ni, A
l, Ga, In, Ge, Sn, Pb, Sb, Bi, at least one of alkali metals other than lithium and alkaline earth metals), Li _x Fe (SO ₄ ) _a (MoO ₄ ) _(3-a) , L
_{i x Fe (SO 4) a} (Mo (1-b) M b O 4) (3-a) (M is Ti,
Cu, V, Co, Mn, W, Fe, Ni, Al, Ga,
In, Ge, Sn, Pb, Sb, Bi, at least one of alkali metals and alkaline earth metals other than lithium (where a = 1.5 to 0.5, b = 0.5 to 0.000)
5). Here, the x value increases or decreases due to charging and discharging.

The electrolyte may be, for example, propylene carbonate, a propylene carbonate derivative, ethylene carbonate, butylene carbonate, vinylene carbonate,
Gamma-butyl lactone, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, 1,2
-Dimethoxyethane, 2-methyltetrahydrofuran,
Dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, gisanemethyl, methyl acetate, methyl propionate, ethyl propionate, phosphoric acid triester, trimethoxymethane, dioxolane derivative, diethyl ether, At least one selected from the group consisting of 1,3-propanesultone, sulfolane, 3-methyl-2-oxazolidinone, tetrahydrofuran, tetrahydrofuran derivative, dioxolan, 1,2-diethoxyethane, and halides thereof. A non-aqueous solvent and a lithium salt such as LiClO ₄ , LiBF ₄ ,
LiPF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAs
F ₆ , LiSbF ₆ , LiB ₁₀ Cl ₁₀ , LiAlCl ₄ , L
By using a mixed solution with at least one salt selected from the group consisting of iCl, LiBr, LiI, lithium lower aliphatic carboxylate, lithium chloroborane, lithium tetraphenylborate, and the like, the positive electrode of the present invention has good characteristics. Is shown.

The use of the reversibly chargeable / dischargeable battery of the present invention is not particularly limited. For example, notebook personal computers, pen input personal computers, pocket personal computers, notebook word processors, pocket word processors, electronic book players, mobile phones, cordless phones Phone handset, pager, handy terminal, portable copy, electronic organizer, calculator, LCD TV, electric shaver, power tool, electronic translator, car phone, transceiver, voice input device, memory card, backup power supply, tape recorder, radio, Headphone stereo,
Portable printer, Handy cleaner, Portable CD,
Power supplies for equipment such as video movies and navigation systems, refrigerators, air conditioners, televisions, stereos, water heaters, microwave ovens, dishwashers, washing machines, dryers, game machines, lighting equipment, toys, road conditioners, medical care It can be used as a power source for equipment, 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 conductive agent of the present invention, the positive electrode resistance can be reduced without the active material peeling off from the substrate.
The energy density of the positive electrode active material can be improved. At the same time, the output density can be improved. By using the electrode of the present invention and a battery using the same in various systems, the size and weight of the system can be reduced. In addition, it can be applied to a system that requires charging and discharging at a high rate.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in more detail with reference to specific examples.

Example 1 LiNi _0.8 as a positive electrode material
Using Co _0.2 O ₂ and 0.01% ash as conductive agent
And La is 537%, 0.005%, La is 1027%, 0.08%, and La is 423%, 0.0%.
5% and La of 651% of graphite was used as a binder, polyvinylidene fluoride was weighed in a weight ratio of 88: 7: 5, mixed with a grinder for 30 minutes, and then 20 μm thick aluminum foil. Coated on both sides. 93 artificial graphite as negative electrode material
7% by weight, polyvinylidene fluoride as binder
The prepared mixture was applied to both surfaces of a copper foil having a thickness of 30 μm. 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.
The battery was charged at 280 mA to 4.2 V and then charged and discharged at a constant current of 280 mA to 2.7 V, and the output density and energy density were evaluated. Table 1 shows the results.

[0016]

[Table 1]

Comparative Example 1 LiNi _0.8 as a positive electrode material
Using Co _0.2 O ₂ , ash content is 0.1% as conductive agent,
Polyvinylidene fluoride was weighed at a weight ratio of 88: 7: 5 using graphite having La of 371 as a binder, kneaded with a triturator for 30 minutes, and applied to both sides of a 20 μm thick aluminum foil. . A mixture prepared by preparing 93% by weight of artificial graphite as a negative electrode material and 7% by weight of polyvinylidene fluoride as a binder was applied to both surfaces of a copper foil having a thickness of 30μ. Example 1
In the same manner as in the above, a battery was produced. Table 1 shows the results of the power density and the energy density. Both the output density and the energy density are lower than in the first embodiment. (Example 2) LiNi _0.8 Co _0.2 O ₂ was used as a positive electrode material, graphite having an ash content of 0.01%, La of 537 ° and ash content of 0.05%, and a specific surface area of 65 m ² were used as a conductive agent. / G of acetylene black in a weight ratio of 50: 5
A mixture of 0,5: 95,75: 25 was used. A positive electrode material, a conductive agent, and polyvinylidene fluoride as a binder were weighed at a weight ratio of 88: 7: 5, kneaded with a trimmer for 30 minutes, and applied to both surfaces of a 20 μm thick aluminum foil. A battery was manufactured in the same manner as in Example 1. Table 1 shows the results of the power density and the energy density.

Comparative Example 2 LiNi _0.8 as a positive electrode material
Using Co _0.2 O ₂ and 0.01% ash as conductive agent
A mixture of graphite having an La content of 537 ° and acetylene black having an ash content of 0.1% and a specific surface area of 25 m ² / g in a weight ratio of 50:50 was used. A positive electrode material, a conductive agent, and polyvinylidene fluoride as a binder were weighed at a weight ratio of 88: 7: 5, kneaded with a trimmer for 30 minutes, and applied to both surfaces of a 20 μm thick aluminum foil. A battery was manufactured in the same manner as in Example 1. Table 1 shows the results of the power density and the energy density. Both the output density and the energy density are lower than in the second embodiment.

[0019]

As described above, the battery and the system can be made compact and lightweight, and good high-rate characteristics can be realized.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuko Yamauchi 7-1-1, Omikacho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Masanori Yoshikawa 7-1, Omikamachi, Hitachi City, Ibaraki Prefecture No. 1 Inside the 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, wherein the conductive material of the positive electrode has an ash content of 0.08% or less and La Contains at least one kind of graphite of 400 ° or more. 2. The battery according to claim 1, wherein carbon black having an ash content of 0.08% or less and a specific surface area of 50 m ² / g or more is mixed in a range of 5% by weight or more and 75% by weight or less. 3. A battery-using system using the positive electrode or the battery according to claim 1.