JPH08138649A - Non-aqueous secondary battery - Google Patents

Abstract

PURPOSE: To provide a secondary battery with large capacity by making a positive electrode, at least the part of which is coated with an electrolytic oxide film, have a specified value of a bulk density of higher. CONSTITUTION: About 0.01-5.0mol/liter concentration of a substance (e.g. acrylonitrile, phenol, aniline, pyrrole, etc.) which can form an electrolytic oxide film is added to an electrolytic liquid and after the assembly of a battery, the battery is charged and discharged one time. As a result, the initial capacity loss of the negative electrode is solved and a secondary battery with high energy can be obtained. The weight ratio of the electrolytic oxide film in the positive electrode is preferably 5-10 pts. by wt. and in the case the weight ratio is less than 1 pts. by wt., the conpensating effect is too small and in the case the weight ratio is more than 20 pts. by wt., the positive material may be cracked at the time of polymerization and peeled out of an electric collector. The bulk density of the positive electrode should be 2.2g/cm<3> or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous secondary battery.

[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.

Such carbonaceous material may be used in any form such as powder, carbon fiber or carbon fiber structure.

Further, recently, in order to meet the demand for higher energy density, the search and development of active materials exhibiting high capacity have been promoted, and transition metal oxides containing alkali metals and inorganic compounds such as transition metal chalcogens have been known. Has been. Among them, 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) is a high potential,
We believe that it is the most promising in terms of 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, and the discharge capacity is smaller, and it is known that it is particularly large when a carbonaceous material is used as the negative electrode active material. ing. The reason for this is that when charging,
It is considered that side reactions such as decomposition of the electrolytic solution, electrolysis of residual moisture, and that part of lithium ions stored in the negative electrode active material during charging do not come out during discharging.

As measures against this initial capacity loss, reforming of the negative electrode active material and increase of the lithium concentration in the positive electrode active material have been studied in addition to the above-mentioned increase of the positive electrode active material. In particular, with respect to the increase of the lithium concentration, an excessive amount of a lithium salt is added at the time of adjusting the raw material, and for example, Li _x CoO ₂ (x> 1),
Attempts have been made to synthesize Li _x NiO ₂ (x> 1) and the like to deal with it. However, the lithium composite oxide synthesized in this manner is unstable to moisture in the atmosphere, and LiC
Since it decomposes into oO ₂ , LiNiO ₂ and LiOH, there is a problem that a dry atmosphere must be used in a post-process such as crushing. Further, 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 to obtain Li _x CoO ₂ (x> 1), Li.
A method of synthesizing _x NiO ₂ (x> 1) and the like is disclosed.

However, in the method of increasing the lithium concentration in the positive electrode active material described above, the lithium composite oxide is unstable in water, the treatment (immersion) time is long, the effect of the remaining lithium-forming agent, and the compensating capacity is positive. There was a problem that it could not be increased due to the structural stability of the active material.

Here, as an example in which aniline, polyaniline, polypyrrole or the like is blended in the positive electrode active material of a non-aqueous secondary battery, JP-A-5-258772, JP-A-5-114399, and JP-A-6-1999 are cited. There is a publication of -68866.

In Japanese Unexamined Patent Publication (Kokai) No. 5-258772, amorphous FeOOH synthesized by reacting iron oxychloride and aniline is used as a positive electrode active material, and a part of the remaining organic material is overcharged. It is described as expressing a buffering action (oxidation reaction). This residual organic substance is considered to be polyaniline from the synthetic method, but there is a problem that the capacity is low because the dispersed state in the positive electrode is a mixed state.

In both JP-A-5-114399 and JP-A-6-68866, conductive polymers such as polyaniline and polypyrrole are added to the positive electrode. However, also in this case, since the dispersed state in the positive electrode is a mixed state, there is the same problem as described above. Further, in JP-A-5-114399, the positive electrode has a bulk density of 0.
It is characterized by 6 to 2.0 g / cm ³ ,
Also in this case, there is a problem that the capacity is low.

[0012]

SUMMARY OF THE INVENTION The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to provide a high capacity secondary battery.

[0013]

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

"A non-aqueous secondary battery using a positive electrode at least a part of which is covered with an electrolytic oxide film, and the bulk density of the positive electrode is 2.2 g / cm ³ or more. Secondary Battery. ”As described above, the secondary battery of the present invention is preferably used as a secondary battery using a nonaqueous electrolytic solution containing an alkali metal salt. Therefore, the lithium ion secondary battery will be described below as an example and will be described in detail with specific examples.

As a result of intensive studies on the above-mentioned measures for reducing the initial capacity loss, the present inventors have found that the initial capacity loss is reduced when pyrrole is added to the electrolytic solution. In addition to pyrrole, it was found that acrylonitrile, phenol, aniline, thiophene, etc. also have an initial capacity loss reducing effect. This loss reduction is
It is considered that this is because the above-mentioned monomer is oxidized on the surface of the positive electrode and the electrolytic oxide film is polymerized. That is, it is effective for reducing the initial capacity loss that a polymerized thin film of acrylonitrile polymer, phenol polymer, polypyrrole, polyaniline, polythiophene or the like is formed on the electrode surface during the initial charge.

During charging, a side reaction occurs with the rise of the positive electrode potential, lithium ions are released from the positive electrode active material into the electrolytic solution, and a monomer (pyrrole or the like) in the electrolytic solution gives electrons to the positive electrode. As a result, an electrolytic oxidative polymerization reaction of the monomer in the electrolytic solution occurs. At this time, on the negative electrode side, lithium ions are inserted into the negative electrode active material from the electrolytic solution. Therefore, the lithium ion concentration in the electrolytic solution is reduced, but the lithium salt concentration in the commonly used electrolytic solution is a large excess of 1 mol or more, and there is no problem. Furthermore, when the polymerized electrolytic oxide film is a conductive film such as polypyrrole, polyaniline, or thiophene, it is suitable because it contributes to the reduction of the electrode resistance. Generally, in such an electrolytic oxidation reaction, hydrogen gas is generated, but most of it dissolves in the electrolytic solution and there is no problem. It is advisable to place a hydrogen storage material.

Substances capable of forming an electrolytic oxide film (acrylonitrile, phenol and its derivatives, aniline, pyrrole, thiophene, paraphenylene, phenylenevinylene and the like) having a concentration of about 0.01 to 5.0 mol / liter in an electrolytic solution. (Derivatives thereof, etc.) are added and the battery is assembled and then charged and discharged once to eliminate the initial capacity loss of the negative electrode and obtain a high energy secondary battery. Here, since the dispersion state in the positive electrode is different from that in which a polymer of a substance capable of forming an electrolytic oxide film (for example, polyaniline) is dispersed and mixed, it can be clearly distinguished. That is, in the case of the present invention, electrolytic oxidative polymerization uniformly occurs everywhere in the positive electrode, and an electrolytic oxide film is formed, whereas the one obtained by dispersing and mixing the polymer in the positive electrode is
Since it is a mixture to the last, it does not exist in the form of a film because the polymer mass is dispersed. If the current during electrolytic oxidation is too large, there may be a relatively large amount of electrolytic oxide film near the surface of the positive electrode, but in this case as well, the state of dispersion of polymer lumps is quite different.

In the present invention, the weight ratio of the electrolytic oxide film to the positive electrode is preferably 1 to 20 parts by weight,
Further, it is preferably 5 to 10 parts by weight. If it is less than 1 part by weight, the compensation effect is too small, and if it exceeds 20 parts by weight, the positive electrode material is cracked or peeled off from the current collector during electrolytic oxidation polymerization. By adjusting the amount to 1 to 20 parts by weight, a compensating effect effective for eliminating the initial loss can be obtained, and
Stable positive electrode performance such as cycle life characteristics can be obtained. That is, when expressed in bulk density, it must be 2.2 g / cm ³ or more.

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. The positive electrode used in can be mentioned. Among these, in the case of a secondary battery using a non-aqueous electrolyte containing a lithium salt, cobalt, manganese, molybdenum, vanadium, chromium, iron,
Transition metal oxides such as copper and titanium and transition metal chalcogens are preferably used. In particular, as mentioned above, Li _x Co
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.

A carbonaceous material is preferably used for the negative electrode of the present invention. The carbonaceous material is not particularly limited, and a material obtained by firing an organic material is generally used. When the electron conductivity of the carbonaceous material is sufficiently high for the purpose of collecting electricity, it is not necessary to add a conductive agent.

When a carbon fiber is used as the counter electrode of the electrode of the present invention, it may have any form, but it is preferably arranged in a uniaxial direction or a fabric-like or felt-like structure. Becomes

The electrolytic solution of the secondary battery using the electrode of the present invention is not particularly limited, and a conventional electrolytic solution may be used, and examples thereof include an acid or alkaline aqueous solution or a non-aqueous solvent. Among them, as an electrolyte solution of a secondary battery composed of the above-mentioned non-aqueous electrolyte 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.

The secondary battery using the electrode of the present invention can be used as 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.

[0024]

EXAMPLES Specific embodiments of the present invention will be described below with reference to examples, but the present invention is not limited thereto. It should be noted that the judgment of a high capacity (high energy) secondary battery is based on a commercially available AA lithium ion secondary battery (US61 #
14500; manufactured by Sony Energy Tech Co., Ltd.) with a capacity of 350 mAh.

Example 1 Commercially available lithium carbonate (Li ₂ CO ₃ ) and basic cobalt carbonate (2CoCO ₃ .3Co (OH) ₂ were used in a molar ratio of Li.
/ Co = 1/1, weighed with a zirconia ball mill (we use ethanol as a grinding solvent), and then 90
LiCoO ₂ was synthesized by heat treatment at 0 ° C. for 20 hours. This was crushed with the above ball mill to obtain LiCoO ₂ powder. To this powder, acetylene black was added as a conductive agent, and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder was added in an amount of 4 parts by weight and 7 parts by weight, respectively.
The viscosity was adjusted with MP to obtain a paste. This is applied on an aluminum foil having a thickness of 13 μm whose surface has been degreased in advance with n-hexane, dried and further heat-treated at 200 ° C. for 15 minutes to form a Li electrode having a width of 50 mm and a length of 200 mm.
A CoO ₂ electrode sheet was prepared. The electrode sheet was roller-pressed at a linear pressure of about 100 kgf / cm to be pressure-bonded to an aluminum current collector, and then cut to obtain a discharge capacity measurement sample. Further, the bulk density was calculated from the thickness, area and weight of the positive electrode material and was found to be 3.15 g / cm ³ .

A commercially available PAN-based carbon fiber (“Torayca” T-300, manufactured by Toray Industries, Inc.) 3 strands (3K: 3000 pieces) was used as a negative electrode on the LiCoO ₂ positive electrode thus prepared, and a porous polypropylene film (Celguard # 25
No. 00, manufactured by Daicel Chemical Industries, Ltd., and the glass cell secondary battery was manufactured by stacking them via a separator. The electrolyte is 1M LiBF ₄ containing EC and DEC (volume ratio 1: 1).
And pyrrole having a concentration of 0.1 mol / liter was added. Using the secondary battery produced in this way, LiC
3. With constant current of 30 mA / g of current density per oO ₂ .
It was charged to 3V (vs. Li ⁺ / Li). 30 mA / g after charging
At a constant current of 3.0 V (vs. Li ⁺ / Li). At this time, the charge capacity per battery calculated from the charge amount is
The discharge capacity was 6.7 mAh and the discharge capacity was 5.5 mAh. Further, the charge capacity of the second charge / discharge is 5.
At 5 mAh, the discharge capacity was 5.5 mAh. This is a high-capacity (high-energy) secondary battery with an AA battery conversion of about 500 mAh. After measuring the battery capacity,
The glass cell is disassembled and the Fourier transform infrared spectroscope (FT
-IR510; manufactured by Nicolet Analytical Instruments)
When the total reflection spectrum of the positive electrode surface was measured using, the formation of polypyrrole was confirmed.

Comparative Example 1 A glass cell secondary battery was prepared in the same manner as in Example 1 except that pyrrole was not added, and charge / discharge evaluation was performed.
The first charge capacity is 5.5 mAh and the discharge capacity is 3.
It was 1 mAh. Furthermore, regarding the capacity in the second charge / discharge, the charge capacity is 3.2 mAh and the discharge capacity is 3.1 m.
It was Ah. This is approximately 280 mAh in terms of AA batteries
Becomes

Example 2 Basic nickel carbonate (NiCO ₃ .2Ni (OH) ₂ .4H ₂ O) was used in place of basic cobalt carbonate,
A glass cell secondary battery was produced in the same manner as in Example 1 except that LiNiO ₂ was synthesized by heat treatment in an atmosphere of 100% oxygen. The bulk density of the positive electrode material used at this time was 3.2.
It was 0 g / cm ³ . Next, using the glass cell secondary battery thus produced, the charging potential was 4.2 V (vs. Li ⁺
Charge / discharge evaluation was performed by adding a predetermined amount of pyrrole to the electrolytic solution in the same manner as in Example 1 except that / Li) was used. 1 at this time
The charge capacity of the first time is 7.6 mAh and the discharge capacity is 6.5.
It was mAh. Further, regarding the capacity in the second charge / discharge, the charge capacity is 6.5 mAh and the discharge capacity is 6.5 mA.
It was h. This is approximately 590 mAh in terms of AA batteries.
It is a high capacity (high energy) secondary battery.

After measuring the battery capacity, the total reflection spectrum on the surface of the positive electrode was measured by using a Fourier transform infrared spectroscope in the same manner as in Example 1, and it was confirmed that polypyrrole was produced.

Comparative Example 2 A glass cell was prepared in the same manner as in Example 2 except that pyrrole was not added, and charge / discharge evaluation was performed. At this time, the first charge capacity is 6.5 mAh and the discharge capacity is 3.7 m.
It was Ah. Furthermore, regarding the second charge / discharge capacity, the charge capacity was 3.8 mAh and the discharge capacity was 3.7 mA.
It was h. This is about 340 mAh in terms of AA batteries.

Example 3 The electrode active material raw materials used in Examples 1 and 2 were weighed and mixed to obtain Li _1.0 (Co _0.5 Ni _0.5 ) O _{2 in} terms of oxide. A positive electrode was produced in the same manner as in 1. The bulk density of the positive electrode material used at this time was 3.1.
It was 8 g / cm ³ . Next, using the positive electrode thus manufactured, charge and discharge evaluation was performed in the same manner as in Example 1 except that aniline having a concentration of 0.1 mol / liter was added to the electrolytic solution. The first charge capacity at this time is 7.2 mAh.
The discharge capacity was 6.0 mAh. Furthermore, the capacity in the second charge and discharge is 6.3 mAh,
The discharge capacity was 6.0 mAh. This is a secondary battery of high capacity (high energy), which is about 550 mAh in terms of AA battery.

After measuring the battery capacity, the total reflection spectrum of the positive electrode surface was measured using a Fourier transform infrared spectroscope in the same manner as in Example 1, and it was confirmed that polyaniline was produced.

Comparative Example 3 The same Li as in Example 3 except that aniline was not added.
_1.0 using _{(Co 0.5 Ni 0. 5) O} 2, was prepared in the same manner as the glass cell secondary battery as in Example 3, it was subjected to a charge and discharge evaluation. At this time, the first charge capacity was 6.2 mAh and the discharge capacity was 3.3 mAh. Further, regarding the capacity in the second charge / discharge, the charge capacity was 3.3 mAh and the discharge capacity was 3.3 mAh. This is about 300 mAh in terms of AA batteries.

Example 4 A commercially available pitch coke was used as the negative electrode active material, and 90 parts by weight of the pitch coke and 10 parts by weight of PVDF were weighed and mixed, and then the viscosity was adjusted with NMP to form a paste. A glass cell secondary battery was prepared in the same manner as in Example 1 except that a negative electrode prepared by drying and pressing the same as the positive electrode after spreading on a foil was used, and charge / discharge evaluation was performed.
At this time, the first charge capacity was 5.6 mAh and the discharge capacity was 4.3 mAh. Further, regarding the capacities in the second charge and discharge, the charge capacity was 4.4 mAh and the discharge capacity was 4.3 mAh. This is about 3 AA batteries.
The rechargeable battery has a high capacity (high energy) of 90 mAh.

After measuring the battery capacity, the total reflection spectrum of the positive electrode surface was measured by using a Fourier transform infrared spectroscope in the same manner as in Example 1, and it was confirmed that polypyrrole was produced.

Comparative Example 4 A glass cell secondary battery was prepared in the same manner as in Example 4 except that pyrrole was not added, and charge / discharge evaluation was performed.
The first charge capacity is 4.3 mAh and the discharge capacity is 2.
It was 3 mAh. Furthermore, regarding the capacity in the second charge / discharge, the charge capacity is 2.4 mAh and the discharge capacity is 2.3 m.
It was Ah. This is approximately 210 mAh in terms of AA batteries.
Becomes

[0037]

According to the present invention, high capacity (high energy)
The secondary battery can be manufactured.

Claims (10)

[Claims] 1. A non-aqueous secondary battery using a positive electrode, at least a portion of which is covered with an electrolytic oxide film, wherein the positive electrode has a bulk density of 2.2 g / cm ³ or more. Aqueous secondary battery. 2. The non-aqueous secondary battery according to claim 1, wherein the electrolytic oxide film is a polymer film. 3. The non-aqueous secondary battery according to claim 2, wherein the polymer is selected from an acrylonitrile polymer, a phenol polymer and a derivative thereof. 4. The non-aqueous secondary battery according to claim 2, wherein the polymer film is a conductive polymer film. 5. The conductive polymer film is selected from a conjugated polymer selected from polyaniline, polypyrrole, polythiophene, polyparaphenylene and polyphenylenevinylene, and a derivative thereof. The non-aqueous secondary battery according to claim 4. 6. The non-aqueous secondary battery according to claim 5, wherein a hydrogen storage material is arranged in the battery can. 7. The non-aqueous secondary battery according to claim 1, wherein the positive electrode active material is a lithium composite oxide. 8. 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.
The non-aqueous secondary battery according to claim 7, wherein the non-aqueous secondary battery is selected from the group consisting of 0, 0 <y ≤ 1.0). 9. The non-aqueous secondary battery according to claim 1, wherein a carbonaceous material is used as the negative electrode active material. 10. The non-aqueous secondary battery according to claim 9, wherein the carbonaceous material is carbon fiber.