JP2000228222A - Secondary power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high breakdown voltage lower than the natural potential at the end of discharging and a good charging-discharging cycle characteristic by using a mixture obtained by mixing a specified quantity of activated carbon with carbon material and an organic electrolyte containing a specified metal salt in a negative electrode. SOLUTION: Material containing activated carbon is used in a positive electrode, and an organic electrolytic solution containing quaternary onium salt and lithium salt is used as an electrolytic solution. The negative electrode is formed of a mixture obtained by mixing activated carbon 10-80 wt.% of the total quantity with carbon material which stores and desorbs lithium ion. At the time of charging, at the negative electrode, lithium ion and quaternary onium ion are adsorbed to activated carbon, lithium ions are stored in the carbon material, and at the time of discharging, some of lithium ions remain in the activated carbon. At the end of discharge, the potential at the negative electrode becomes base potential lower than the natural potential before charging, and at the time of re-charging, charging is performed in the base potential lower than the natural potential. At the time of charging and discharging with a large current, lowering of capacity due to repetition is inhibited by physical reaction such as ion adsorption and desorption to/from the activated carbon.

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. Increasing the voltage is most effective for improving the energy density of the electric double layer capacitor. However, increasing the voltage causes decomposition of the electrolytic solution and greatly affects the life.

[0004]

SUMMARY OF THE INVENTION An object of the present invention is to provide a secondary power supply having a high withstand voltage, a high capacity, a high energy density and a high charge / discharge cycle reliability.

[0005]

SUMMARY OF THE INVENTION The present invention provides a positive electrode containing activated carbon, a negative electrode containing activated carbon and a carbon material capable of absorbing and desorbing lithium ions, and an organic electrolysis containing a quaternary onium salt and a lithium salt. And a liquid.

[0006] In the present specification, a positive electrode body is obtained by joining and integrating a positive electrode containing activated carbon or activated carbon, a lithium-containing transition metal oxide, and a current collector. The same definition applies to the negative electrode body. In addition, although both secondary batteries and electric double layer capacitors are one type of secondary power supply, in this specification, a specific electrode containing a carbon material capable of absorbing and desorbing activated carbon and lithium ions in a negative electrode contains activated carbon in a positive electrode. The secondary power supply having the configuration is simply referred to as a secondary power supply.

In the secondary power supply of the present invention, during charging, anions in the electrolytic solution are adsorbed on the activated carbon at the positive electrode, and lithium ions and quaternary onium ions are adsorbed on the activated carbon at the negative electrode, and occlude and desorb lithium ions. Lithium ions are stored in the resulting carbon material. Note that, in this specification, the term “adsorption” refers to the adsorption of ions to activated carbon due to the formation of an electric double layer during charging, and the term “occlusion” refers to a reaction accompanied by charge transfer at the same time that ions are taken into the electrode. The separation of ions from the activated carbon during discharge is called desorption, and the separation of ions with charge transfer at the same time as the separation of ions is called desorption.

At the time of discharge of the secondary power supply, desorption of anions adsorbed on activated carbon occurs at the positive electrode, and lithium ions and quaternary onium ions adsorbed on the activated carbon desorb at the negative electrode. The quaternary onium ions are easily desorbed from the activated carbon, but all of the lithium ions are not desorbed but remain partially on the activated carbon. Therefore, the potential of the negative electrode at the end of discharging becomes lower than the natural potential of the negative electrode before the first charge.

Then, when the activated carbon is charged again, quaternary onium ions are adsorbed on the activated carbon from a potential lower than the natural potential of the activated carbon. That is, since the negative electrode can be charged at a potential lower than the natural potential, the withstand voltage of the secondary power supply can be increased.

When a carbon material capable of absorbing and desorbing lithium ions is generally used as a negative electrode active material, a large capacity can be obtained by an electrochemical reaction in which lithium ions are absorbed and desorbed from the carbon material. Significant decrease in capacity. However, the carbon material capable of occluding and desorbing lithium ions of the negative electrode according to the present invention stores and desorbs lithium ions at the time of charging and discharging with a relatively small current, respectively. no response. In the secondary power supply of the present invention, in the case of charging and discharging with a large current, a physical reaction of adsorption and desorption of ions to activated carbon occurs. In the case of a physical reaction, the capacity is small, but the capacity is not reduced even after repeated charging and discharging of a large current.

That is, in the present invention, a mixture of a carbon material capable of occluding and desorbing high-capacity lithium ions and activated carbon having a low capacity but having a small capacity reduction with respect to large-current charge / discharge is used for the negative electrode. It can be a negative electrode having a high capacity and a small decrease in capacity due to a large current discharge.

The amount of activated carbon contained in the negative electrode is preferably 10 to 80% by weight based on the total amount of activated carbon and a carbon material capable of occluding and desorbing lithium ions. If it is less than 10% by weight, the capacity of the secondary power supply is significantly reduced due to the large current discharge. If it exceeds 80% by weight, the capacity of the negative electrode itself becomes small, and the capacity of the secondary power supply cannot be increased. The amount of activated carbon is especially 30 to 70
% By weight is preferred.

In the present invention, a cation is contained in the organic electrolyte.
Contains quaternary onium ions and lithium ions
You. As quaternary onium ions, quaternary ammonium
And quaternary phosphonium ions are preferred.
To (C_TwoH_Five)_FourP⁺Ion, (C _TwoH_Five)_FourN⁺Ion, (C
_TwoH_Five)_Three(CH_Three) N⁺Ions and the like are preferred.

The anions of the quaternary onium salt and the lithium salt, which are contained in the organic electrolyte, are
PF ₆ ⁻ , BF ₄ ⁻ , ClO ₄ ⁻ , N (CF ₃ SO ₂ ) ₂ ⁻ , CF
^{_{3 SO 3 -, C (SO}} 2 CF 3) 3 -, AsF 6 - and SbF ₆ ^-
At least one member selected from the group consisting of
F ₄ ^- is preferred. In addition, the anion of the quaternary onium salt and the anion of the lithium salt may be the same or different.

[0015] The concentration of the quaternary onium salt and the lithium salt contained in the organic electrolyte is 0.5 to 0.5%.
2.5mol / L, lithium salt 0.5 ~ 2.0mol
/ L, especially when the lithium salt is 0.8 to
1.5 mol / L, lithium salt 0.8-1.5 mol
/ L is preferable.

The solvent of the organic electrolyte is ethylene carbonate, propylene carbonate, butylene carbonate,
One or more selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, sulfolane and dimethoxyethane are preferred.

The activated carbon contained in the positive electrode and the negative electrode may be the same or different, but each has a specific surface area of 300 to 3
Preferably, it is 000 m ² / g. Raw material of activated carbon,
The activation conditions are not particularly limited. For example, the raw materials include bean, phenol resin, petroleum coke and the like, and the activation methods include a steam activation method and a molten alkali activation method.

In order to increase the capacity of the secondary power supply of the present invention, the positive electrode preferably contains a lithium-containing transition metal oxide. A lithium-containing transition metal oxide of lithium and at least one selected from the group consisting of V, Fe, Co, Mn, Ni, W and Zn is preferred, and Li _x Co _y Ni _1-y is particularly preferred.
O ₂ or Li _z Mn ₂ O ₄ (provided that 0 <x <2, 0 ≦ y ≦
1, 0 <z <2. Is preferred. By including the lithium-containing transition metal oxide, the capacity of the positive electrode is increased. If the amount of the carbon material capable of occluding and releasing lithium ions of the negative electrode is accordingly increased, the secondary power supply can have a higher capacity.

The amount of the lithium-containing transition metal oxide in the positive electrode is 5 to 5 of the total amount of the activated carbon and the lithium-containing transition metal oxide.
80% by weight is preferred. When the content is less than 5% by weight, the effect of the lithium-containing transition metal oxide being contained in the positive electrode is small,
The voltage of the secondary power supply cannot be increased. If it exceeds 80% by weight, the amount of activated carbon in the positive electrode becomes relatively small, so that the capacity is significantly reduced in the charge / discharge cycle. More preferably, it is 10 to 60% by weight.

In order to reduce the resistance of the positive electrode, it is preferable that the positive electrode contains conductive carbon black or graphite as a conductive material. At this time, the conductive material is preferably contained in the positive electrode in an amount of 0.1 to 20% by weight.

In the present invention, the carbon material capable of inserting and extracting lithium ions contained in the negative electrode preferably has a [002] plane spacing of 0.335 to 0.410 nm as measured by X-ray diffraction. A carbon material having a plane spacing of more than 0.410 nm is liable to be deteriorated in a charge / discharge cycle. 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.

As a method of manufacturing a positive electrode body, for example, a mixture of activated carbon powder, carbon black as a conductive material, and polytetrafluoroethylene as a binder is kneaded, and then formed into a sheet to form a positive electrode. There is a method of fixing to an electric body using a conductive adhesive. Further, as a binder, polyvinylidene fluoride, polyamide imide,
Activated carbon powder and carbon black may be dispersed in a varnish in which polyimide or the like has been dissolved, and this may be obtained by applying the powder on a current collector by a doctor blade method or the like and drying. When the positive electrode contains a lithium-containing transition metal oxide, it can be similarly prepared using a mixture of activated carbon powder and lithium-containing transition metal oxide powder instead of the above-mentioned activated carbon powder.

The amount of the binder contained in the positive electrode is preferably 1 to 20% by weight in view of the balance between the strength of the positive electrode body and characteristics such as capacity. Further, the negative electrode body is preferably produced in the same manner as the positive electrode body, and the amount of the binder contained in the negative electrode body is also preferably 1 to 20% by weight.

[0024]

EXAMPLES Next, the present invention will be described more specifically with reference to Examples (Examples 1 to 4) and Comparative Examples (Example 5), but the present invention is not limited thereto. The production and measurement of the cells in Examples 1 to 5 were all performed in an argon glove box having a dew point of −60 ° C. or less.

Example 1 80% by weight of activated carbon having a specific surface area of 2000 m ² / g obtained by a steam activation method using a phenol resin as a raw material, 10% by weight of conductive carbon black, and 10% by weight of polytetrafluoroethylene as a binder % By weight, kneaded with ethanol, rolled, and vacuum dried at 200 ° C. for 2 hours to form a mixture having a thickness of 1%.
An electrode sheet of 50 μm was obtained. This sheet was bonded to an aluminum foil using a conductive adhesive having polyamideimide as a binder, and heat-treated under reduced pressure at 300 ° C. for 2 hours.
A positive electrode body was obtained. The electrode area was 24 cm ² .

The activated carbon used for the positive electrode body is obtained by heat-treating 70% by weight of petroleum coke.
2] A mixture of 10% by weight of a carbon material capable of absorbing and desorbing lithium ions having a plane spacing of 0.344 nm, 10% by weight of carbon black, and 10% by weight of polytetrafluoroethylene as a binder is ethanol. Is added and kneaded, and the thickness is 150 μm in the same manner as for the positive electrode.
Was prepared. This sheet was bonded to a copper foil using a conductive adhesive having polyamideimide as a binder, similarly to the positive electrode, and heat-treated at 300 ° C. for 2 hours under reduced pressure to obtain a negative electrode body. The electrode area was 24 cm ² .

The positive electrode body and the negative electrode body are
Opposed and sandwiched by a non-woven fabric separator made of ren
Was prepared. 1 mol / L of propylene carbonate
(C _TwoH_Five)_Three(CH_Three) NBF_FourAnd 1 mol / L LiB
F_FourIs used as an electrolyte, and the element is added to the electrolyte.
, Fully charged at 3.2V for 24 hours,
Thereafter, the battery was discharged to 1V. Next, from 3.2V to 1V
The initial capacity was measured in the range. Thereafter, the charge / discharge current 240
Charge / discharge cycle in the range of 3.2V to 1V at mA
Perform a test and measure the capacity after 2000 cycles.
The rate of change was calculated. Table 1 shows the results.

[Example 2] The mixing ratio of the negative electrode sheet was 40% by weight of activated carbon, 40% by weight of a carbon material capable of absorbing and desorbing lithium ions, 10% by weight of carbon black, and polytetrafluorocarbon as a binder. A negative electrode body was obtained in the same manner as in Example 1 except that ethylene was changed to 10% by weight. A device was prepared in the same manner as in Example 1 except that this negative electrode body was used, and was impregnated with an electrolytic solution in the same manner as in Example 1. Evaluation was performed in the same manner as in Example 1 using this device. Table 1 shows the results.

Example 3 Instead of a mixture of 80% by weight of activated carbon, 10% by weight of conductive carbon black and 10% by weight of polytetrafluoroethylene, 60% by weight of activated carbon, 20% by weight of LiCoO ₂ , 10% by weight of conductive carbon black and 1% of polytetrafluoroethylene
A positive electrode body was obtained in the same manner as in Example 1 except that a mixture of 0% by weight was used.

An element was prepared in the same manner as in Example 1 except that the above-mentioned positive electrode body was used, and evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 4 Instead of LiCoO ₂ , LiCo
_A positive electrode body was obtained in the same manner as in Example 3, except that _0.2 Ni _0.8 O ₂ was used. An element was prepared in the same manner as in Example 1 except that this positive electrode body was used, and evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 5 An element was prepared in the same manner as in Example 1 except that the positive electrode body obtained in Example 1 was used for both the positive electrode body and the negative electrode body, and the capacity was measured in the same manner as in Example 1. Evaluation was performed in the same manner as in Example 1. Table 1 shows the results.

[0033]

[Table 1]

[0034]

According to the secondary power supply of the present invention, the quaternary onium ions are adsorbed and desorbed in the negative electrode during charging and discharging with a relatively large current, and the lithium ions are absorbed and discharged in the charging and discharging with a relatively small current. Lithium ions are absorbed and desorbed in the desorbable carbon material. Therefore, the carbon material capable of occluding and desorbing lithium ions due to charging and discharging with a large current is hardly deteriorated and has excellent rapid charging and discharging characteristics.

Since the potential of the activated carbon contained in the negative electrode is lower than the natural potential, the secondary power supply of the present invention has a high withstand voltage. Further, since the negative electrode contains a carbon material capable of inserting and extracting lithium ions, the capacity is high.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 4/02 H01G 9/00 301D 4/58 301A F-term (Reference) 5H003 AA01 AA02 AA04 AA10 BB01 BB05 BD00 BD04 BD06 5H014 AA02 EE08 EE10 HH00 HH01 HH08 5H029 AJ02 AJ03 AJ05 AJ12 AK03 AL06 AM03 AM04 AM07 DJ09 HJ10

Claims (6)

[Claims] A positive electrode containing activated carbon; a negative electrode containing activated carbon and a carbon material capable of absorbing and desorbing lithium ions;
A secondary power supply, comprising: an organic electrolyte containing a graded onium salt and a lithium salt. 2. The secondary power source according to claim 1, wherein the active carbon is contained in the negative electrode in an amount of 10 to 80% by weight in the total amount of the activated carbon and the carbon material. 3. The organic electrolyte contains a quaternary onium salt in an amount of 0.1%.
5 to 2.5 mol / L, lithium salt is 0.5 to 2.0 m
The secondary power source according to claim 1, wherein the secondary power source includes ol / L. 4. The cathode has V, Fe, Co, Mn, Ni,
4. The secondary power supply according to claim 1, wherein the secondary power supply includes a lithium-containing transition metal oxide containing lithium and at least one selected from the group consisting of W and Zn. 5. 5. The method according to claim 1, wherein the lithium-containing transition metal oxide is Li _x C
o _y Ni _1-y O ₂ or Li _z Mn ₂ O ₄ (where 0 <x <
2, 0 ≦ y ≦ 1, 0 <z <2. The secondary power supply according to claim 4, wherein 6. The secondary power supply according to claim 4, wherein the lithium-containing transition metal oxide is contained in the positive electrode in an amount of 5 to 80% by weight.