JPH08195199A - Electrode for battery and secondary battery using it - Google Patents

Abstract

PURPOSE: To compensate the initial capacity loss and attain a high capacity by containing an electron donating compound capable of generating anions and cation radical salt in an electrolyte. CONSTITUTION: An electron donating compound forming anions and cation radical salt in an electrolyte is added to a positive electrode or the electrolyte to prevent the reduction of ion conduction of the electrolyte. When a battery is charged and discharged once after it is assembled, the initial capacity loss of a negative electrode is resolved, and high energy is attained. A condensation polycyclic aromatic compound or a heterocyclic compound is used for the electron donating compound. An inorganic compound such as a transition metal oxide containing an alkaline metal or transition metal chalcogen, or a conjugate polymer such as polyparaphenylene is used for a positive electrode active material. When a nonaqueous electrolyte containing lithium salt is used, a transition metal oxide such as cobalt or manganese or transition metal chalcogen is used. The initial charge capacity of a positive electrode is increased, and the capacity of the battery is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery using a material that absorbs and releases lithium as a positive electrode and a negative electrode.

[0002]

2. Description of the Related Art In recent years, with the widespread use of portable devices such as video cameras and notebook computers, demand for small and high capacity secondary batteries has increased. Most of the secondary batteries currently used are nickel-cadmium batteries using an alkaline electrolyte, but the battery voltage is low at about 1.2 V, and it is difficult to improve the energy density. Therefore, a lithium secondary battery using lithium metal for the negative electrode has been studied.

However, in a secondary battery in which lithium metal is used as the negative electrode, lithium tends to grow into dendrites due to repeated charging / discharging, resulting in short circuits and shortened life. Therefore, there has been proposed a secondary battery in which various carbonaceous materials are used for the negative electrode and used by doping and dedoping with lithium ions. Further, such various carbonaceous materials can be used as a positive electrode after being doped with anions. Secondary batteries using electrodes made by doping lithium ions or anions into the above carbonaceous materials are disclosed in JP-A-57-208079 and JP-A-58.
-93176, JP-A-58-192266, JP-A-62-90863, and JP-A-62-12.
Japanese Laid-Open Patent Publication No. 2066 and Japanese Laid-Open Patent Publication No. 2-66856 are known.

Further, recently, in order to meet the demand for higher energy density, a battery voltage of around 4V has appeared and has been attracting attention. Higher battery voltage has been pursued by searching for and developing an active material exhibiting a high potential in the positive electrode, and inorganic compounds such as transition metal oxides and transition metal chalcogens containing alkali metals are known. Among them, Li _X C
O ₂ (0 <x ≦ 1.0), Li _X NiO ₂ (0 <x ≦
1.0) and Li _X Co _Y Ni _1-Y O ₂ (0 <x ≦
1.0, 0 <y ≦ 1.0) and the like are considered to be the most promising in terms of high potential, stability, and long life.

However, in the conventional secondary battery as described above, in order to compensate for the capacity decrease due to the initial capacity loss of the negative electrode active material, the positive electrode active material must be overfilled, which lowers the energy density. It was a factor. Here, the initial capacity loss of the negative electrode active material refers to the difference between the initial charge capacity and the discharge capacity, the discharge capacity is smaller than the charge capacity, especially when a carbonaceous material is used for the negative electrode active material,
It is known that this difference is large. This is caused by (1) side reactions such as decomposition of the electrolytic solution during charging, (2) electrolysis of residual water, and (3) part of the lithium ions stored in the negative electrode active material during charging. , It does not come out at the time of discharge, but it is not concluded.

As measures against this initial capacity loss, in addition to the above-mentioned increase in the amount of the positive electrode active material, (1) conditions for synthesizing the negative electrode active material,
Studies have been conducted on (2) surface treatment of the negative electrode active material, and (3) increasing the lithium concentration in the positive electrode active material. In particular,
Regarding (3), for example, Li _X CoO ₂ (1 <x) or Li _X Ni was added by adding an excessive lithium salt when adjusting the raw materials.
Attempts have been made to synthesize O ₂ (1 <x) and the like, but the lithium composite oxide synthesized in this manner is unstable with respect to moisture in the atmosphere, and thus LiCoO ₂ , LiN
Since it decomposes into iO ₂ and LiOH, there is a problem that a dry atmosphere has to be used in a post-process such as crushing. On the other hand, in JP-A-5-135760, the positive electrode is immersed in a solution containing a lithiating agent such as butyllithium, phenyllithium, naphthyllithium, or lithium iodide, and Li _x CoO ₂ (1 <x). , Li
A method for synthesizing _X NiO ₂ (1 <x) and the like is disclosed.

[0007]

However, even in the above method, the capacity to be compensated cannot be increased because the treatment (immersion) time is long, the adverse effect of the residual lithium-imparting agent and the lithium composition in the positive electrode active material are limited. , And so on.

SUMMARY OF THE INVENTION The present invention is intended to solve such a conventional defect, and an object thereof is to provide a high capacity secondary battery and a battery electrode used therefor by compensating for an initial capacity loss.

[0009]

The present invention has the following constitution in order to solve the above problems.

"(1) A battery electrode containing an anion in an electrolytic solution and an electron-donating compound capable of forming a cation radical salt.

(2) A secondary battery using the above battery electrode.

(3) A secondary battery using an electrolytic solution containing an anion and an electron-donating compound capable of forming a cation radical salt. As a particularly preferable secondary battery in the present invention, a secondary battery using a non-aqueous electrolytic solution containing an alkali metal salt as described above can be mentioned. Therefore, the lithium ion secondary battery will be described below as an example and will be described in detail with specific examples. In the present invention, since the positive electrode or the electrolytic solution contains an electron-donating compound, the positive electrode potential increases during charging, and the electron-donating compound is electrolytically oxidized at the positive electrode to become a cation radical, resulting in electrolysis. It forms a salt with the anion in the liquid. At this time, on the negative electrode side, lithium ions are inserted into the negative electrode active material from the electrolytic solution, so that the initial capacity loss of the negative electrode is compensated by the lithium ions. At this time, the lithium ion concentration in the electrolytic solution decreases, but in order to prevent the decrease in the ionic conductivity of the electrolytic solution, it may be added in advance in excess. The initial capacity loss of the negative electrode is eliminated by adding an electron-donating compound that forms a salt with the anion in the electrolytic solution to the positive electrode or the electrolytic solution, and then assembling the battery and charging and discharging once. A high energy secondary battery can be obtained.

The electron donating compound in the present invention may be used without limitation as long as it has an oxidation potential higher than the charging potential of the positive electrode active material. As such an electron-donating compound, a condensed polycyclic aromatic compound or a heterocyclic compound is used. As the substance, hydrocarbons such as anthracene, tetracene, pyrene, perylene, coronene, phenothiazine, acridine, aromatics containing a hetero element such as dithiopyrene, tetrathiafulvalene, tetraselenafulvalene, bisethylenedithiotetrathiafulvalene, tetrathia Heterocycle-containing compounds such as tetracene can be mentioned. Further, these compounds may have a substituent such as an alkyl group, an amino group, a halogen element and a hydroxy group. More preferred are pyrene, phenothiazine, ethylenedithiotetrathiafulvalene and the like.

As the positive electrode active material used in the present invention,
Inorganic compounds such as transition metal oxides and chalcogens containing alkali metals, conjugated polymers such as polyparaphenylene, polyphenylene vinylene, polyaniline, polypyrrole and polythiophene, crosslinked polymers with disulfide bonds, etc. Examples of the positive electrode active material used in. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, cobalt, manganese, molybdenum, vanadium, chromium,
Transition metal oxides such as iron, copper and titanium and transition metal chalcogens are preferably used. Especially as mentioned above, Li _X
CoO ₂ (0 <x ≦ 1.0), Li _X NiO ₂ (0 <x
≦ 1.0) and Li _X Co _Y Ni _1-Y O ₂ (0 <x ≦
1.0, 0 <y ≦ 1.0) and the like are considered to be the most promising in terms of high potential, stability, and long life.

The electrode of the present invention is preferably used as a positive electrode. At this time, the negative electrode is not particularly limited, but a carbonaceous material is preferably used. The carbonaceous material is not particularly limited, and a material obtained by firing an organic material is generally used. The form of the carbonaceous material may be powder, fibrous, short fibers having an average length of 5 mm or less, and the like. Here, in such short fibers, the average length is, for example, by observation with a microscope such as SEM,
It is determined by measuring the length in the orientation direction of 20 or more short fibers.

When the carbon fiber is used as an electrode, it may have any form, but it is preferably arranged uniaxially or made into a fabric-like or felt-like structure. . Examples of fabric-like or felt-like structures include woven fabrics, knitted fabrics, braids, laces, nets,
Examples thereof include felt, paper, non-woven fabric, and mat. Among them, woven fabric and felt are preferable from the viewpoint of properties of carbon fiber and electrode characteristics. Further, by shortening the carbon fiber, an electrode can be easily manufactured by the same means as for powder carbon.

Specific examples of the carbon fibers include PAN-based carbon fibers obtained from polyacrylonitrile (PAN), pitch-based carbon fibers obtained from pitch of coal or petroleum, cellulose-based carbon fibers obtained from cellulose, Vapor grown carbon fibers obtained from a gas of a molecular weight organic substance are preferably used. In addition, carbon fibers obtained by firing polyvinyl alcohol, lignin, polyvinyl chloride, polyamide, polyimide, phenol resin, furfuryl alcohol, etc. can be used without particular limitation.

The electrolytic solution of the secondary battery using the electrode of the present invention is not particularly limited, and a conventional electrolytic solution is used, and examples thereof include an acid or alkaline aqueous solution or a non-aqueous solvent. Among these, as the electrolytic solution of the secondary battery composed of the above-mentioned non-aqueous electrolytic solution containing an alkali metal salt, propylene carbonate (PC), ethylene carbonate (EC), γ-butyrolactone (BL), N-methylpyrrolidone ( MP), acetonitrile (AN), N, N-
Dimethylformamide, dimethylsulfoxide, tetrahydrofuran (THF), 1,3-dioxolane, methyl formate, sulfolane (SL), oxazolidone, thionyl chloride, 1,2-dimethoxyethane (DME), diethylene carbonate (DEC), dimethyl carbonate. (DMC) and derivatives and mixtures of these are preferably used. As the electrolyte contained in the electrolytic solution, alkali metal, particularly lithium halide, perchlorate, thiocyanate, borofluoride, phosphorus fluoride, arsenic fluoride, aluminum fluoride, trifluoromethyl sulfate, etc. Is preferably used.

In the present invention, if necessary, these active materials may be mixed with acetylene black, Ketjen black,
A conductive agent such as carbon black, and a positive electrode mixture by kneading with a binder such as polyvinylidene fluoride, methyl cellulose, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl butyral, polyethylene, polyvinyl alcohol, and polytetrafluoroethylene to form a positive electrode mixture. Coating on a collector such as Ni,
An electrode can be obtained by drying, pressing and forming into a sheet.

The secondary battery using the electrode of the present invention can be used for a video camera, a personal computer, a word processor, a radio-cassette, by utilizing the features of light weight, high capacity and high energy density.
It is widely applicable to portable small electronic devices such as mobile phones.

[0021]

【Example】

Example 1 5.13 g of LiCoO ₂ and 0.19 g of acetylene black as a conductive agent, and an oxirane ring-containing compound as a binder (trade name “Denacol EX- manufactured by Nagase Kasei Co., Ltd.”
861 ") 0.06 g, m-phenylenediamine 0.0
08 g, carboxymethyl cellulose sodium (manufactured by Daicel Chemical Industries, Ltd., "CMC Daicel product number 129"
0 ") 2% aqueous solution (2.58 g) and pyrene (0.27 g) as an electron donating compound were added, and water as a solvent was added and kneaded to form a paste. This was degreased on the surface with n-hexane in advance. Apply it on an aluminum foil with a thickness of 13 μm
Dry at 30 ℃ for 1 hour, the electrode part width 50mm, length 20
A 0 mm LiCoO ₂ electrode sheet was prepared. The electrode sheet was roller-pressed at a linear pressure of about 100 kg / cm to be pressure-bonded to an aluminum current collector, and then cut to obtain a positive electrode for measuring discharge capacity.

A commercially available PAN-based carbon fiber (“Torayca” T-300, manufactured by Toray Industries, Inc.) 17 was added to the positive electrode thus prepared.
mg was used as a negative electrode, and the glass cell secondary battery was manufactured by stacking the films with a porous polypropylene film (Celguard # 2500, manufactured by Daicel Chemical Industries, Ltd.) interposed therebetween. As the electrolytic solution, EC and DMC (volume ratio 3: 7) containing 1M LiBF ₄ were used.

Using the secondary battery thus produced, it was charged to 4.3 V (vs. Li ⁺ / Li) with a constant current of 55 mA / g per LiCoO ₂ . 2 after charging
It was discharged to 3.0 V (vs. Li ⁺ / Li) at a constant current of 7.5 mA / g. The amount of charge per battery at this time is 10.0 mA
At h, the discharge amount was 6.6 mAh.

Example 2 A positive electrode was prepared in the same manner as in Example 1 except that 1.95 g of phenothiazine was used instead of pyrene. PC and DME containing 1M LiBF ₄ as an electrolyte (volume ratio 1:
Using the glass cell secondary battery prepared in the same manner as in Example 1 using 1), charge / discharge evaluation was performed under the same conditions as in Example 1.
The charge amount was 10.3 mAh and the discharge amount was 6.8 mAh.

Example 3 2.54 g of LiCoO ₂ and 0.21 g of acetylene black as a conductive agent, 1.78 g of a 10% NMP solution of polyvinylidene fluoride as a binder, and bisethylenedithiotetrathiafulvalene as an electron donating compound 0 .21 g
Was added, and the viscosity was adjusted with NMP as a solvent to form a paste. This was applied on an aluminum foil having a thickness of 13 μm, the surface of which was degreased with n-hexane in advance, and dried at 90 ° C. for 1 hour, and the width of the electrode portion was 50 mm and the length of LiCo was 200 mm.
An O ₂ electrode sheet was prepared. The electrode sheet was roller-pressed at a linear pressure of about 100 kg / cm to be pressure-bonded to an aluminum current collector, and then cut to obtain a positive electrode for measuring discharge capacity.

Commercially available short PAN-based carbon fibers ("Torayca" M
LD-30, fiber length 30 μm, manufactured by Toray Industries, Inc., 8.5 g
0.49 g of acetylene black as a conductive agent and a 10% NMP solution of polyvinylidene fluoride as a binder.
87 g was added and the viscosity was adjusted with NMP as a solvent to form a paste. This was applied on a copper foil having a thickness of 13 μm, the surface of which was degreased with n-hexane in advance, and dried at 90 ° C. for 1 hour to prepare a negative electrode sheet having an electrode portion width of 50 mm and a length of 200 mm. Apply this electrode sheet to a linear pressure of about 100 kg /
After being roller-pressed at 10 cm and press-bonded to a copper current collector, it was cut to obtain a negative electrode for measuring discharge capacity.

Using the positive electrode and the negative electrode, the same evaluation was performed in the same cell as in Example 1, and as a result, the charging capacity was 9.5 mA.
h, the discharge capacity was 6.4 mAh.

Example 4 A positive electrode was prepared in the same manner as in Example 1 except that pyrene was not added, and PC containing 1M LiBF ₄ as an electrolytic solution was used.
And DMC (volume ratio 3: 7) 50 ml, pyrene 6.0 mg
Using a glass cell secondary battery prepared in the same manner as in Example 1 by using the melted material of Example 1, charge / discharge evaluation was performed under the same conditions as in Example 1. Charge amount 9.6mAh, discharge amount 6.6mAh /
g.

Example 5 Charge / discharge evaluation was carried out in the same manner as in Example 4 except that 65.5 mg of phenothiazine was used instead of pyrene. The charge amount was 9.9 mAh and the discharge amount was 6.5 mAh.

Comparative Example 1 Charge / discharge evaluation was carried out in the same manner as in Example 1 except that pyrene was not added. Charge capacity 8.4 mAh, discharge capacity 5.
It was 2 mAh

[0031]

According to the present invention, the initial charge capacity of the positive electrode is increased, the initial capacity loss of the negative electrode can be compensated, and a high capacity (high energy) secondary battery can be manufactured.

Claims (18)

[Claims] 1. A battery electrode containing an anion in an electrolytic solution and an electron-donating compound capable of forming a cation radical salt. 2. The battery electrode according to claim 1, wherein the electron-donating compound is a condensed polycyclic aromatic and / or heterocyclic ring-containing compound. 3. The battery electrode according to claim 1, wherein the electron-donating compound is at least one selected from pyrene, phenothiazine and bisethylenedithiotetrathiafulvalene. 4. The battery electrode according to claim 1, wherein the positive electrode active material is a lithium composite oxide. 5. The lithium composite oxide is Li _x CoO ₂
(0 <x ≦ 1.0), Li _x NiO ₂ (0 <x ≦ 1.
0) and Li _x Co _Y Ni _1-Y O ₂ (0 <x ≦ 1.
0, 0 <y ≤ 1.0).
The battery electrode described. 6. The battery electrode according to claim 1, which is used for a positive electrode. 7. The battery electrode according to claim 6, wherein the negative electrode active material is a carbonaceous material. 8. The battery electrode according to claim 7, wherein the carbonaceous material is carbon fiber. 9. The battery electrode according to claim 8, wherein the carbonaceous material is a short fiber having an average length of 5 mm or less. 10. A secondary battery using the battery electrode according to claim 1. 11. A secondary battery using an electrolytic solution containing an anion and an electron-donating compound capable of forming a cation radical salt. 12. The secondary battery according to claim 11, wherein the electron donating compound is a condensed polycyclic aromatic and / or heterocyclic ring-containing compound. 13. The electron donating compound is at least one selected from pyrene, phenothiazine and bisethylenedithiotetrathiafulvalene.
The secondary battery according to any one of 1. 14. The secondary battery according to claim 11, wherein the positive electrode active material is a lithium composite oxide. 15. The lithium composite oxide is Li _x CoO.
₂ (0 <x ≦ 1.0), Li _x NiO ₂ (0 <x ≦ 1.
0) and Li _x Co _Y Ni _1-Y O ₂ (0 <x ≦ 1.
15. The secondary battery according to claim 14, wherein the secondary battery is selected from 0, 0 <y ≦ 1.0). 16. The secondary battery according to claim 11, wherein the negative electrode active material is a carbonaceous material. 17. The carbonaceous material is carbon fiber.
The secondary battery according to item 6. 18. The secondary battery according to claim 16, wherein the carbonaceous material is a short fiber having an average length of 5 mm or less.