JP2001236960A - Method of manufacturing secondary power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary power supply having high breakdown voltage, high capacity, and good quick charging and discharging cycle characteristics. SOLUTION: A secondary power supply has a negative electrode mainly containing a carbon material with an edge surface thereof increased by treating carbon material capable of absorbing and desorbing a lithium ion with a solution with aromatic hydrocarbon dissolved in an ether solvent, a positive electrode mainly containing activated carbon, and an organic electrolyte containing a lithium salt.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary power supply having a high withstand voltage, a large capacity, and a high rapid charge / discharge cycle reliability.

[0002]

2. Description of the Related Art Polarizable electrodes mainly composed of activated carbon are used for both positive and negative electrodes of conventional electric double layer capacitors. The withstand voltage of the electric double layer capacitor is 1.2 V when an aqueous electrolyte is used, and 2.5 to 3.3 V when an organic electrolyte is used. Since the energy of the electric double layer capacitor is proportional to the square of the withstand voltage, the organic electrolyte having a higher withstand voltage has higher energy than the aqueous electrolyte. However, even an electric double layer capacitor using an organic electrolyte has an energy density of 1/10 or less of a secondary battery such as a lead storage battery, and further improvement in energy density is required.

On the other hand, Japanese Patent Application Laid-Open No. 64-14882 discloses that an electrode mainly composed of activated carbon is used as a positive electrode, and the [002] plane spacing by X-ray diffraction is 0.338 to 0.356 nm.
A secondary power supply having an upper limit voltage of 3 V using an electrode in which lithium ions are previously absorbed in a carbon material as a negative electrode is described. Japanese Patent Application Laid-Open No. 8-107048 describes a battery in which a carbon material which can occlude and desorb lithium ions by absorbing lithium ions in advance by a chemical method or an electrochemical method is used as a negative electrode. Also,
Japanese Patent Application Laid-Open No. 9-55342 proposes a secondary power supply having an upper limit voltage of 4 V and having a negative electrode in which a carbon material capable of absorbing and releasing lithium ions is supported on a porous current collector that does not form an alloy with lithium. However, these secondary power supplies have a problem that a step of previously storing lithium ions in the carbon material of the negative electrode is required.

In addition to the electric double layer capacitor, a power source capable of charging and discharging a large current is a lithium ion secondary battery.
A lithium ion secondary battery has a higher voltage and a higher capacity than an electric double layer capacitor, but has a problem that it has a high resistance and has a significantly shorter life due to a rapid charge / discharge cycle than an electric double layer capacitor.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a method of manufacturing a secondary power supply capable of rapid charge / discharge, high withstand voltage, high capacity, high energy density, and high charge / discharge cycle reliability. Aim.

[0006]

SUMMARY OF THE INVENTION The present invention provides a secondary battery comprising a positive electrode mainly composed of activated carbon, a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions, and an organic electrolyte containing a lithium salt. In the method of manufacturing a power supply, the carbon material used as the main component of the negative electrode can occlude and desorb lithium ions by a solution obtained by reacting a solution obtained by dissolving an aromatic hydrocarbon in an ether solvent with lithium metal. Provided is a method for manufacturing a secondary power supply, which is obtained by processing a carbon material.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION In this specification, a negative electrode body is formed by joining and integrating a negative electrode mainly composed of a carbon material capable of inserting and extracting lithium ions with a current collector. The same definition applies to the positive electrode body. In addition, although both secondary batteries and electric double layer capacitors are one type of secondary power supply, in this specification, the positive electrode is mainly composed of activated carbon, and the negative electrode is mainly composed of a carbon material capable of absorbing and desorbing lithium ions. Is simply referred to as a secondary power supply.

[0008] Lithium metal can be dissolved in a solution in which an aromatic hydrocarbon is dissolved in an ether-based solvent. In this case, it is considered that the solution and the lithium metal react to form a complex between the aromatic hydrocarbon and the lithium ion.
When a carbon material capable of absorbing and desorbing lithium ions is added to this solution and stirred in an environment with sufficiently low moisture, it is considered that only lithium ions are absorbed by the carbon material from the complex. After adding the carbon material, preferably 1 to 24
When the solvent is removed by sufficiently stirring and reacting for about an hour, a carbon material having properties different from those of the carbon material before being added to the solution can be obtained. Hereinafter, in this specification, the carbon material before being added to the solution is referred to as untreated carbon, and the carbon material after reacting in the solution is referred to as treated carbon.

When the carbon after the treatment is measured by Raman spectroscopy,
Intensity intensity I ₁₃₆₀ and 1580 cm ^-1 in 1360 cm ^-1 I
_{The 1580} ratio R = I ₁₃₆₀ / I ₁₅₈₀ is larger than that of the untreated carbon, and a change in the surface structure is observed. As the intensity ratio R is larger, the edge surface of the graphite is relatively larger, and as the ratio is smaller, the basal surface is more, the edge surface of the graphite is increased by the above processing. Since the site where lithium ions are inserted and desorbed is an edge surface, it is considered that a carbon material suitable for large-current discharge is obtained by increasing the edge surface.

When the carbon after treatment obtained by the above treatment is used as the negative electrode carbon material of the present invention, the intensity I _{1360 at 1360} cm ^-1 in the Raman spectrum of the carbon after treatment.
Intensity I ₁₃₆₀ of 1360 cm ^-1 in the ratio R ¹ and Raman spectrum of the untreated carbon intensity I ₁₅₈₀ of 1580 cm ^-1
And the ratio R ² of the intensity I ₁₅₈₀ of ₁₅₈₀ cm ⁻¹ is the difference Δ
It is preferable that R = R ¹ -R ² is 0.05 to 0.6. When ΔR is less than 0.05, the processing effect is hardly exhibited, and the large current discharge characteristics are hardly improved. If it exceeds 0.6, the edge surface becomes too large and the capacity decreases. More preferably, ΔR is from 0.1 to 0.4.

The strength ratio R ² of the untreated carbon used in the present invention is 0.06 to 0.15, particularly 0.08 to 0.1.
It is preferably 2. When untreated carbon in this range is used for R ^{2 and the} treated carbon having R ¹ of 0.2 to 0.4 is obtained by the above treatment, the secondary power source using the treated carbon as the negative electrode is subjected to a large current discharge. Excellent characteristics and large capacity.

The ether solvent is not particularly restricted but includes tetrahydrofuran, 2-methyltetrahydrofuran,
2,5-dimethyltetrahydrofuran, dimethoxymethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dimethoxypropane, 1- It preferably contains at least one member selected from the group consisting of methoxybutane, diethyl ether, dimethyl ether and ethyl methyl ether.

As the aromatic hydrocarbon, a condensed polycyclic hydrocarbon is preferable, and at least one selected from the group consisting of naphthalene, pyrene, anthracene, naphthacene, phenanthrene, 1,2-benzopyrene and 4,5-benzopyrene is preferred. Is preferred. These aromatic hydrocarbons can be dissolved in the above ether solvent, and lithium metal can be dissolved in the obtained solution. When the untreated carbon is immersed in a solution in which lithium metal is dissolved, lithium ions can be easily inserted into the untreated carbon.

In general, in the case of a lithium ion secondary battery, the positive electrode is an electrode mainly composed of a transition metal oxide containing lithium, and the negative electrode is an electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions. Lithium ions are desorbed from the lithium-containing transition metal oxide of the positive electrode, are stored in a carbon material capable of occluding and desorbing lithium ions of the negative electrode, lithium ions are desorbed from the negative electrode by discharging, and lithium ions are stored in the positive electrode. Therefore, lithium ions in the electrolyte do not essentially participate in charging and discharging of the battery.

On the other hand, in the secondary power supply of the present invention, the anion in the electrolytic solution is adsorbed on the activated carbon of the positive electrode by charging, and the lithium ions in the electrolytic solution are stored in the carbon material capable of absorbing and desorbing the lithium ions of the negative electrode. You. Then, lithium ions are desorbed from the negative electrode by discharging, and the anions are desorbed in the positive electrode. That is, in the secondary power supply of the present invention, the solute of the electrolytic solution is essentially involved in the charging and discharging, and the charging and discharging mechanism is different from that of the lithium ion battery. Further, unlike the lithium ion secondary battery, since the lithium ion is not inserted or extracted from the positive electrode active material itself, the secondary power supply of the present invention has excellent charge / discharge cycle reliability.

In a secondary power supply using a positive electrode as activated carbon and a negative electrode mainly as a carbon material capable of absorbing and desorbing lithium ions, ions dissolved in the electrolyte participate in charging and discharging.
Therefore, when the solute concentration of the electrolytic solution is low, there is a possibility that the battery cannot be sufficiently charged. The solute concentration of the electrolyte is preferably 0.5 to 2.0 mol / L, particularly preferably 0.75 to 1.5 mol / L.

In the secondary power supply of the present invention, the cycle efficiency of the negative electrode in the first charge / discharge cycle is not necessarily 100%.
Instead, some occluded lithium ions do not desorb. In this case, since the lithium ion concentration in the electrolyte decreases and charging may not be sufficiently performed from the next charging, it is preferable to add a lithium-containing transition metal oxide to the positive electrode to prevent characteristic deterioration. By this method, lithium ions that cannot be eliminated from the negative electrode can be supplemented. In this case, the content of the lithium-containing transition metal oxide contained in the positive electrode is preferably 0.1 to 20%, more preferably 3 to 15% of the total weight of the positive electrode. If it is less than 0.1%, the effect is small.
If it exceeds 0%, the capacity of the lithium-containing transition metal oxide is large, so that the secondary power supply performance of high output and high reliability, which is a characteristic of the activated carbon electrode, cannot be obtained.

As the lithium-containing transition metal oxide, a composite oxide of lithium and one or more transition metals selected from the group consisting of V, Mn, Fe, Co, Ni, Zn and W is preferable. In particular, a composite oxide of lithium and at least one selected from the group consisting of Mn, Co, and Ni is preferable. Among them, Li _x Co _y Ni _(1-y) O ₂ or Li _z M
n ₂ O ₄ (however, 0 <x <2, 0 ≦ y ≦ 1, 0 <z <
2. ) Is preferred.

In the present invention, the activated carbon contained in the positive electrode preferably has a specific surface area of 800 to 3000 m ² / g. Activated carbon raw materials and activation conditions are not limited,
For example, as raw materials, coconut, phenolic resin, petroleum coke, and the like can be mentioned. As the activation method, a steam activation method,
A molten alkali activation method and the like can be mentioned. In the present invention,
Steam activated charcoal activated carbon or steam activated phenolic resin activated carbon is preferred. Further, in order to reduce the resistance of the positive electrode, it is preferable to include conductive carbon black or graphite as a conductive material in the positive electrode. In this case, the conductive material is included in 0.1 to 20% of the total mass of the positive electrode. Is preferred.

As a method for producing a positive electrode body, for example, polytetrafluoroethylene as a binder is mixed with activated carbon powder, kneaded and then formed into a sheet to form a positive electrode, which is then used as a current collector with a conductive adhesive. There is a way to fix. Further, using polyvinylidene fluoride, polyamide imide, polyimide or the like as a binder, the activated carbon powder is dispersed in a solution in which these are dissolved in a solvent, and this solution is coated on a current collector by a doctor blade method or the like, and dried. You may get it. The amount of the binder contained in the positive electrode may be 1 to 20 times the total weight of the positive electrode, based on the balance between the strength of the positive electrode body and characteristics such as capacity.
%.

The untreated carbon according to the present invention has a [002] plane spacing of 0.335 to 0.4 as measured by X-ray diffraction.
It is preferably 10 nm. 0.410n
Carbon materials with a length of more than m are liable to deteriorate in charge / discharge cycles. Specific examples include petroleum coke, a material obtained by heat-treating mesophase pitch-based carbon material or vapor-grown carbon fiber at 800 to 3000 ° C., natural graphite, artificial graphite, and non-graphitizable carbon material. In the present invention, any of these materials can be preferably used. Above all, the [002] plane is 0.335 to 0.337 nm, and the non-graphitizable carbon material or natural graphite or easily graphitic carbon is heat-treated at 2800 ° C. or more. A material having a thickness of about 0.337 nm is preferably low in the potential for inserting and extracting lithium ions.

The negative electrode body of the present invention is obtained by treating with polytetrafluoroethylene as a binder, kneading with carbon, forming a sheet, and adhering it to a current collector using a conductive adhesive. In addition, polyvinylidene fluoride, polyamideimide or polyimide as a binder,
There is also a method in which carbon is dispersed after treatment in a solution in which a resin serving as a binder or a precursor thereof is dissolved in an organic solvent, the resultant is coated on a current collector, and then dried.

In the method of applying the liquid to the current collector to obtain the negative electrode body, the solvent for dissolving the resin serving as the binder or the precursor thereof is not limited, but the resin constituting the binder or the precursor thereof is easily dissolved. N-methyl-2-pyrrolidone (hereinafter referred to as NMP)
Is preferred. Here, the term “polyamide imide precursor” or “polyimide precursor” refers to those which are polymerized by heating to form polyamide imide or polyimide, respectively.

The above-mentioned binders are cured by heating and are excellent in chemical resistance, mechanical properties and dimensional stability. The temperature of the heat treatment is preferably 200 ° C. or higher. If the temperature is 200 ° C. or higher, even if it is a polyamideimide precursor or a polyimide precursor, it is usually polymerized to be a polyamideimide or a polyimide, respectively. The atmosphere for the heat treatment is preferably an inert atmosphere such as nitrogen or argon or a reduced pressure of 133 Pa or less. Polyamide imide or polyimide is resistant to the organic electrolyte used in the present invention, and is used to remove water from the negative electrode.
It is sufficiently resistant to high temperature heating of about 00 ° C. or heating under reduced pressure.

The lithium contained in the organic electrolyte according to the present invention
Um salt is LiPF₆, LiBF_Four, LiClO_Four, Li
N (SO_TwoCF_Three)_Two, CF_ThreeSO_ThreeLi, LiC (SO_TwoC
F_Three) _Three, LiAsF₆And LiSbF₆Selected from the group consisting of
One or more types are preferred. Solvent is ethylene carbonate
G, propylene carbonate, butylene carbonate,
Dimethyl carbonate, ethyl methyl carbonate, di
Ethyl carbonate, sulfolane and 1,2-dimethoxy
One or more selected from the group consisting of cyethanes is preferred.
The electrolyte consisting of these lithium salts and solvents has a withstand voltage.
High electrical conductivity.

[0026]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples (Examples 1 to 5) and Comparative Examples (Examples 6 and 7), but the present invention is not limited thereto.

Example 1 A mass ratio of activated carbon having a specific surface area of 2000 m ² / g, conductive carbon black, and polytetrafluoroethylene as a binder obtained by a steam activation method using a phenol resin as a raw material is 8: 1: 1. The mixture was kneaded with ethanol and rolled.
Vacuum drying was performed at 0 ° C. for 2 hours to obtain an electrode sheet. An electrode having a size of 6 cm × 3 cm and a thickness of 150 μm was obtained from this electrode sheet, and bonded to an aluminum foil using a conductive adhesive having polyamideimide as a binder.
Heat treatment was performed at 2 ° C. for 2 hours to obtain a positive electrode body.

Next, 1,2-dimethoxyethane (20 mL) was placed in a glove box having a dew point of -60 ° C. in an argon atmosphere.
In this solution, 1.0 g of naphthalene was dissolved, and 100 mg of lithium metal foil was added to this solution, followed by stirring to dissolve lithium metal. Thereafter, mesocarbon microbeads (manufactured by Osaka Gas Co., Ltd .; hereinafter, referred to as MCMB) 5.0, which is a material capable of absorbing and desorbing lithium ions, heat-treated at 2800 ° C.
g was added and the mixture was stirred in a closed container for 24 hours. This was filtered in the air and dried at 200 ° C. The ratio R = I ₁₃₆₀ / I ₁₅₈₀ of the intensity I ₁₅₈₀ of the intensity I ₁₃₆₀ and 1580 cm ^-1 in 1360 cm ^-1 by Raman spectroscopy, the untreated carbon R ² =
In contrast to 0.14, the carbon after treatment was R ¹ = 0.1.
32. That is, ΔR = R ¹ −R ² = 0.18.

A graphitized carbon fiber (hereinafter, referred to as VGCF) obtained by vapor growth and the above-mentioned treated carbon were subjected to NMP.
Dispersed in a solution of polyvinylidene fluoride dissolved in
This liquid was applied to a current collector made of copper and dried to obtain a negative electrode body. The mass ratio of carbon: graphitized VGCF: polyvinylidene fluoride after treatment in the negative electrode was 8: 1: 1. When this negative electrode body was further pressed by a roll press, the obtained negative electrode had a size of 6 cm × 3 cm and a thickness of the negative electrode layer of 1 cm.
It was 5 μm.

In a argon glove box having a dew point of −60 ° C. or lower, the positive electrode body and the negative electrode body obtained as described above are opposed to each other via a polypropylene separator, and 1 mol / L of LiBF ₄ is mixed with ethylene carbonate. A secondary power source was obtained by impregnating a solution dissolved in a mixed solvent with diethyl carbonate (50:50 by volume) for a sufficient time. After measuring the initial capacity of this secondary power supply in an argon glove box having a dew point of −60 ° C. or less, a charge / discharge cycle was performed at a charge / discharge current of 180 mA in a range from 4.2 V to 2.75 V. After 3000 cycles, The capacity was measured and the rate of change in capacity was calculated. Table 1 shows the results.

Example 2 MCMB was treated in the same manner as in Example 1 except that 2-methyltetrahydrofuran was used as a solvent for a solution in which lithium was dissolved. The carbon after treatment is
Intensities I ₁₃₆₀ and 15 at ₁₃₆₀ cm ^-1 by Raman spectroscopy
The ratio R ¹ of the intensity I ₁₅₈₀ of 80 cm ⁻¹ was R 0.28.
That is, R = R ¹ −R ² = 0.14. Using this, a negative electrode body was manufactured in the same manner as in Example 1, a secondary power supply was manufactured in the same manner as in Example 1, and evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

Example 3 MCMB was treated in the same manner as in Example 1 except that diethyl ether was used as a solvent for a solution in which lithium was dissolved. It was R ¹ = 0.30. That is, ΔR = R ¹ −R ² = 0.16. Using this, a negative electrode body was manufactured in the same manner as in Example 1, a secondary power supply was manufactured in the same manner as in Example 1, and evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

Example 4 MCMB was treated in the same manner as in Example 1 except that tetrahydrofuran was used as a solvent for a solution in which lithium was dissolved. It was R ¹ = 0.31.
That is, ΔR = R ¹ −R ² = 0.17. Using this, a negative electrode body was manufactured in the same manner as in Example 1, a secondary power supply was manufactured in the same manner as in Example 1, and evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

[Example 5] Occlusion and desorption of lithium ions
Natural graphite (LB-CG, R ^Two= 0.1
3, manufactured by Nippon Graphite Co., Ltd.)
The carbon material was processed. R¹= 0.33. Sand
ΔR = R¹-R^Two= 0.16. Using this
A negative electrode body was prepared in the same manner as in Example 1, and was manufactured in the same manner as in Example 1.
A secondary power supply was manufactured and evaluated in the same manner as in Example 1. Table 1 shows the results
Shown in

Example 6 As a carbon material capable of inserting and extracting lithium ions, M was heat-treated at 2800 ° C. as in Example 1.
A negative electrode body was prepared in the same manner as in Example 1, except that CMB was used without being treated with a solution in which lithium metal was dissolved. Using this, a secondary power supply was produced in the same manner as in Example 1, and evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 7 A negative electrode was produced in the same manner as in Example 1 except that the same natural graphite as in Example 5 was used as a carbon material for absorbing and desorbing lithium ions without being treated with a solution in which lithium metal was dissolved. Was prepared. Using this, a secondary power supply was produced in the same manner as in Example 1, and evaluated in the same manner as in Example 1. Table 1 shows the results.

[0037]

[Table 1]

[0038]

According to the present invention, it is possible to provide a secondary power supply having a high withstand voltage, a large capacity, and a high reliability of a rapid charge / discharge cycle.

Continued on the front page F term (reference) 5H029 AJ02 AJ03 AJ05 AK08 AL06 AM02 CJ11 CJ15 HJ13 5H050 AA02 AA07 AA08 BA15 CA16 CB07 DA02 DA03 FA19 GA11 GA16 HA13

Claims (4)

[Claims] 1. A method of manufacturing a secondary power supply comprising: a positive electrode mainly composed of activated carbon; a negative electrode mainly composed of a carbon material capable of absorbing and desorbing lithium ions; and an organic electrolytic solution containing a lithium salt. The main carbon material is obtained by treating a carbon material capable of absorbing and desorbing lithium ions by a solution obtained by reacting a solution obtained by dissolving an aromatic hydrocarbon in an ether solvent with lithium metal. A method for manufacturing a secondary power supply, comprising: 2. The intensity I ₁₃₆₀ and 15 at ₁₃₆₀ cm ^-1 in the Raman spectrum of the carbon material used as the main component of the negative electrode.
The ratio of the intensity I _{1580 at} 80 cm ⁻¹ is R ¹ = I ₁₃₆₀ / I _1580, and the intensity I _{1360 at 1360} cm ⁻¹ and 1580 cm in the Raman spectrum of the carbon material before being treated with the solution.
_{Assuming that} the ratio of the intensity I ₁₅₈₀ of ^-1 is R ² = I ₁₃₆₀ / I ₁₅₈₀ , Δ
^{2. The} method of claim 1, wherein R = R ¹ −R ² is 0.05 to 0.6. 3. 3. The method according to claim 1, wherein R ¹ is 0.2 to 0.4 and R ² is 0.0 to 0.4.
3. The method for manufacturing a secondary power supply according to claim 2, wherein the number is 6 to 0.15. 4. The ether solvent is tetrahydrofuran, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, dimethoxymethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, 1,2-dimethoxyethane. , 1,2-diethoxyethane, 1,2-
At least one selected from the group consisting of dimethoxypropane, 1-methoxybutane, diethyl ether, dimethyl ether and ethyl methyl ether, wherein the aromatic hydrocarbon is naphthalene, pyrene, anthracene, naphthacene, phenanthrene, 1,2-benzopyrene And 4,5
The secondary power source according to claim 1, 2 or 3, which is at least one member selected from the group consisting of -benzopyrene.