JP3311597B2 - Secondary battery and its positive electrode - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery capable of reversible charging and discharging a plurality of times and a positive electrode thereof , and more particularly to a secondary battery using a non-aqueous electrolyte and a positive electrode thereof .

[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 provide a secondary battery capable of achieving a high energy density and a high output density, and a positive electrode thereof.
Ru near to provide.

[0008]

Means for Solving the Problems The secondary battery of the present invention and
The positive electrode has a negative electrode, a positive electrode, and a non-aqueous electrolyte containing a lithium salt, and relates to a secondary battery that can be charged and discharged a plurality of times. There characterized containing Mukoto the graphite 400 ~1027Å. Examples of the graphite used in the present invention include artificial graphite, natural graphite, lump graphite, flake graphite, expanded graphite, specially treated graphite, pitch graphite, coke graphite and the like.
Of these graphites, the ash content is 0.08% or less and L
a is set to 400 to 1027 ° . Preferably, the ash content is 0.05% or less and La is 500% or more, and most preferably, the ash content is 0.02% or less and La is 60%.
0 ° or more. If the ash content is more than 0.08%,
Since these impurities react with lithium in the positive electrode active material to reduce the amount of lithium, 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. Also, L
When a is larger than 1027 °, if there is much ash,
The power density decreases.

[0009] secondary battery and the positive electrode of the present invention, in including a conductive agent, and the black <br/> lead aforementioned ash at 0.08% or less, and a specific surface area of more than carbon black 50 m ² / g 5% by weight
It is characterized in that a mixture of 75% by weight or less is used. The carbon black used in the present invention includes acetylene black, Ketjen black, furnace black and the like. Of these carbon blacks, ash content is not more than 0.08%, and the ratio is preferably not less than 50 m ² / g surface area, more preferably at ash 0.05% or less, and a specific surface area of 200 meters ² /
g or more, most preferably 0.02% or less of ash content, and a specific surface area of 350 m ² / g or more. Ash content is 0.08
When the content is more than%, these impurities react with lithium in the positive electrode active material to reduce 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. Specific surface area is 50m ²
If it is less than / g, 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. Carbon black to be added, the graphite
5 wt% or more for the entire conductive agent containing, it is preferable to use those obtained by mixing in a range of 75 wt% or less as a conductive agent. Electrode resistance can not be reduced in the case the mixing amount of carbon black is less than 5 wt%, the effect of mixing the carbon black is not less. Further, when the mixing amount of carbon black is more than 75 wt% reduces the binding force of the binder active material is separated from the substrate, the mixing effect of carbon black is not less.

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 Co _0.2 O ₂ was used as a positive electrode material, and an ash content was 0.01% and La was 537 °, 0.1% as a conductive agent.
005%, La is 1027%, 0.08%, and La is 423%, 0.05%, and La is 651%.
Then, polyvinylidene fluoride was weighed at a weight ratio of 88: 7: 5 using graphite as a binder, and the mixture was kneaded with a grinder for 30 minutes, and then 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 used.
μ was coated on both sides of a copper foil. 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. The electrolyte contains 1 mol of LiPF ₆
Was dissolved in 1 liter of a mixed solution of ethylene carbonate and diethyl carbonate, and the solution was injected into a 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. As shown in Table 1, the ash and La of the present invention
High energy by using graphite
It can be seen that the density and power density are obtained.

[0016]

[Table 1]

(Comparative Example 1) LiNi _0.8 Co _0.2 O ₂ was used as a positive electrode material, and polyvinylidene fluoride was used as a conductive agent in a weight ratio of polyvinylidene fluoride having a ash content of 0.1% and La of 371 as a binder. 88:
After weighing so as to be 7: 5 and kneading for 30 minutes with a mill,
It was 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. 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 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 having 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 50:50, 5:95,
75:25, a mixture was used. 88% by weight of polyvinylidene fluoride as a positive electrode material, a conductive agent and a binder.
After weighing so as to be 7: 5 and kneading for 30 minutes with a mill,
It was applied to both sides 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. As shown in Table 1, the ash content and L
The use of graphite with a
It can be seen that the energy density and the power density can be obtained.

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]

According to the present invention, the energy density and the power
It is possible to provide a secondary battery with high power density and its positive electrode.
In addition, it is possible to provide a secondary battery capable of realizing a compact and lightweight system and good high-rate characteristics and a positive electrode thereof.
Things .

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shuko Yamauchi 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Masanori Yoshikawa 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 In Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-8-222206 (JP, A) JP-A-4-215252 (JP, A) JP-A-54-87821 (JP, A) Toshihisa Ishikawa , Shin Carbon Industry, Japan, Modern Editor, Co., Ltd., July 1, 1986, revised edition, P25 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/00-4/62 H01M 10/40

Claims (3)

(57) [Claims] 1. A negative electrode, a secondary battery having a non-aqueous electrolyte comprising a positive electrode and a lithium salt, prior Kiseikyoku the positive electrode active material,
A conductive agent and a binder, wherein the conductive agent has an ash content of 0.0
Graphite 8% or less, and La is 400 ~1027 Å
The secondary battery characterized by containing Mukoto. 2. A method according to claim 1, wherein the positive electrode, ash content is not more than 0.08%, and a specific surface area of 50 m ² / g or more der
Carbon black in the conductive agent that, from 5 to 75 wt%
A secondary battery comprising : 3. A positive electrode active material, a conductive agent and a binder, wherein the conductive agent has an ash content of 0.08% or less and a La of 40% or less.
A positive electrode for a secondary battery, comprising graphite having a size of 0 to 1027 °.