JP2002270175A - Secondary power source - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a secondary power source having a large capacity and excellent rapid charge and discharge cycle reliability. SOLUTION: This secondary power source is provided with a positive electrode containing activated carbon, a negative electrode containing Li4 Ti5 O12 or a mixture of a carbon material capable of storing and separating a lithium ion and Li4 Ti5 O12 , and an organic electrolyte containing lithium salt. The carbon material of the negative electrode has a surface space of 0.3335 to 0.410 nm at a (002) face measured by X-ray wide angle analysis. The mixture contains 20 to 50 mass % of Li4 Ti5 O12 and 80 to 50 mass % of the carbon material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a high discharge capacity,
The present invention relates to a secondary power supply having excellent charge / discharge cycle reliability at a large current.

[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 3.0 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 is 0.338 to 0.356 in X-ray diffraction.
A secondary power supply with an upper limit voltage of 3.0 V has been proposed in which an electrode obtained by previously absorbing lithium ions in a carbon material having a thickness of nm is used as a negative electrode. Japanese Patent Application Laid-Open No. Hei 8-107048 proposes a battery using, as a negative electrode, a carbon material which can occlude and desorb lithium ions by absorbing lithium ions in advance by a chemical method or an electrochemical method. I have. Japanese Unexamined Patent Publication No. 9-55342 proposes a secondary power supply having an upper limit voltage of 4.0 V, which has a negative electrode in which a carbon material capable of absorbing and desorbing lithium ions is supported on a porous current collector that does not form an alloy with lithium. Have been.

A secondary power supply using activated carbon for the positive electrode and a carbon material capable of inserting and extracting lithium ions for the negative electrode can operate at a higher voltage than conventional electric double layer capacitors using activated carbon for both the positive electrode and the negative electrode. High capacity can be achieved. In addition to the electric double layer capacitor and the above-mentioned secondary power source, a high-performance secondary power source includes a lithium ion secondary battery using a lithium-containing oxide for a positive electrode and a carbon material for a negative electrode. Lithium-ion secondary batteries can operate at higher voltages and have higher capacities than electric double-layer capacitors, but have the problem of high resistance and a significantly shorter life due to rapid charge / discharge cycles than electric double-layer capacitors. . Although the upper limit operating voltage of each of the secondary power supplies other than the electric double layer capacitor and the lithium ion secondary battery reaches 4.0 V or more, an effective capacity is obtained only from the upper limit voltage of 2.7 V.
The voltage range is around V. At a voltage of 2.7 V or less, almost no capacity can be obtained, so that it cannot be used at an operating voltage of 2.7 V or less.

[0005]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a secondary power supply which is capable of rapid charging and discharging, has a high energy density, and has a high charge and discharge cycle reliability.

[0006]

According to the present invention, there is provided a positive electrode containing activated carbon, and lithium titanate (hereinafter referred to as Li) as a first embodiment.
₄ Ti ₅ O ₁₂ ) as an active material or
A secondary power supply comprising: a negative electrode containing a carbon material capable of inserting and extracting lithium ions and Li ₄ Ti ₅ O ₁₂ as a mixed active material; and an organic electrolyte containing a lithium salt. I will provide a. In the present specification, a negative electrode body in which a negative electrode containing Li ₄ Ti ₅ O ₁₂ capable of inserting and extracting lithium ions and a current collector are joined and integrated is referred to as a negative electrode body. A positive electrode body is formed by joining and integrating a positive electrode containing activated carbon and a current collector. Although secondary batteries are electric double layer capacitor also one of the secondary power supply, in this specification and include activated carbon in the positive electrode, occluding lithium ions in the negative electrode, can desorb Li ₄ Ti ₅ O ₁₂ and / Alternatively, a secondary power supply having a specific configuration including a carbon material is simply referred to as a secondary power supply.

Li ₄ Ti ₅ having a spinel type crystal structure
The lithium titanate material represented by O ₁₂ has a charge / discharge potential of about 1.5 V with respect to Li ⁺ / Li potential, while
The activated carbon of the positive electrode has a potential of 4.0 V or higher with respect to the Li ⁺ / Li potential.
Since polarization up to 4.2 V is possible, the activated carbon cathode and Li
The upper limit operating voltage of the new secondary power supply system combining the ₄ Ti ₅ O ₁₂ negative electrode is in the range of 2.5 V to 2.7 V, and the lower limit is 1.
5V. The occlusion and elimination reactions of lithium ions into and from the carbon material occur mainly in the range of 1.0 to 0 V with respect to the Li ⁺ / Li potential, and at 1.0 V or higher, the capacity is hardly attained. On the other hand, in the case of an electric double layer capacitor, both the positive and negative electrodes are activated carbon, and when charged to 2.7 V, the discharge capacity per activated carbon mass of the positive and negative electrodes is about 30 mAh / g.
It is. On the other hand, the discharge capacity per Li ₄ Ti ₅ O ₁₂ mass is about 150 mAh / g, which is almost five times that of activated carbon. In addition, Li ₄ Ti ₅ O ₁₂ has a very flat potential change during charge and discharge and can maximize the capacity of the secondary power supply, so that a higher energy density can be obtained than an electric double layer capacitor.

As described above, the activated carbon of the positive electrode is Li ⁺ / L
Since polarization is possible up to 4.2 V with respect to the i potential, the effective operating voltage range is 4.2 to 2.5 V when an activated carbon positive electrode and a negative electrode made of a carbon material alone are combined. A new secondary power source using a mixed material of a carbon material and Li ₄ Ti ₅ O ₁₂ as a negative electrode and combining with a positive electrode of activated carbon is 4.2.
It can operate in a wide voltage range of up to 1.5 V, and both the conventional positive and negative electrodes can have a higher voltage and higher capacity than an electric double layer capacitor using activated carbon.

In 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. Is released from the lithium-containing transition metal oxide, and is stored in a carbon material capable of storing and releasing lithium ions of the negative electrode. The lithium ions are released from the negative electrode by discharge, and the 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 anions in the electrolyte are adsorbed on the activated carbon of the positive electrode by charging, and the lithium ions in the electrolyte are stored in lithium titanate, which can occlude and desorb the lithium ions of the negative electrode. Is done. Then, lithium ions are desorbed from the negative electrode by discharge, and anions are desorbed from 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. Unlike the lithium ion secondary battery, the positive electrode active material itself does not occlude and desorb lithium ions, and the deterioration of the positive electrode due to occlusion and desorption of lithium ions does not occur.

In addition, in the case of a lithium ion secondary battery, when charging and discharging are performed, the dimensional change of the carbon crystal in the Lc direction occurs as lithium ions are absorbed and desorbed between layers of the carbon material of the negative electrode. This dimensional change causes problems such as destruction of the coating on the carbon surface and loosening of the bonding between the carbon particles, which causes a reduction in cell capacity and an increase in resistance. Therefore, the first aspect of the present invention can prevent deterioration caused by the carbon negative electrode by using, for the negative electrode, lithium titanate having a spinel-type crystal structure with almost no dimensional change due to insertion and extraction of lithium. . The secondary power supply of the present invention has very little deterioration due to charge / discharge cycles and has excellent long-term reliability.

In order to obtain stable cycle characteristics, it is necessary to maintain the operating potential of the negative electrode at around 1.5 V with respect to the Li ⁺ / Li potential. This is because, when the negative electrode is overcharged, the potential drops to 1.5 V or lower, and when the potential becomes lower than 1.0 V, the electrolyte is decomposed and the capacity is reduced. In order to prevent overcharging of the negative electrode, it is necessary to set the capacity of the negative electrode larger than the capacity of the positive electrode. Specifically, the capacity ratio of the negative electrode to the positive electrode (capacity of the negative electrode / capacity of the positive electrode) is 1.05 to
It is preferred to be in the range of 1.3. When the capacity ratio is 1.
05, the Li ₄ Ti ₅ O ₁₂
If the diffusion of Li ions in the negative electrode cannot keep up with the current, the potential near the negative electrode drops, causing the decomposition of the electrolytic solution. If the capacitance ratio is larger than 1.30, the energy density of the entire secondary power supply will be reduced. As described above, activated carbon and Li ₄ Ti ₅ O ₁₂ discharge capacity per mass in the better of Li ₄ Ti ₅ O ₁₂ approximately five times greater because of the activated carbon in the amount and the negative electrode in the positive electrode so that the capacitance ratio Li ₄ T
The amount of i ₅ O ₁₂ may be adjusted.

In the second aspect of the present invention, the present inventors have made intensive studies and have found that when a mixed system of a carbon material and Li ₄ Ti ₅ O ₁₂ is used as a negative electrode, deterioration by the negative electrode can be minimized, It has been found that the charge / discharge cycle characteristics are improved as compared with the case of a negative electrode using either a carbon material or Li ₄ Ti ₅ O ₁₂ alone. Although the mechanism is not yet clear, the potential at which the respective occlusion and desorption reactions of the carbon material and Li ₄ Ti ₅ O ₁₂ occur are within a potential range where an irreversible reaction can occur with respect to the partner material. It is considered that the charge-discharge cycle characteristics were improved by improving the coulomb efficiency of the entire negative electrode.

In the second embodiment of the present invention, the ratio of Li ₄ Ti ₅ O _{12 in} the active material of the mixed negative electrode is preferably 20 to 50% by mass. The theoretical capacity of the mass unit of Li ₄ Ti ₅ O ₁₂ is about 150 mAh / g, which is less than half of the theoretical mass unit of the carbon material (> 300 mAh / g). If more than 50% by mass of Li ₄ Ti ₅ O ₁₂ is mixed, the overall capacity is adversely affected. If the amount is less than 20% by mass, the effect of improving the cycle characteristics by the mixed system is less likely to appear. The carbon material in the mixed negative electrode is not particularly limited, and the (002) plane spacing d00 by X-ray wide-angle diffraction method.
2 is preferably a carbon material having a thickness of 0.335 to 0.410 nm. In particular, since the dimensional change due to charge and discharge is small and the electrolyte mainly containing propylene carbonate (hereinafter, abbreviated as PC) is stable, d002 is 0.345 to 0.345.
A carbon material having a thickness of 0.390 nm is preferable.
002 is preferably 0.370 to 0.380 nm.

In the present invention, the solvent of the electrolytic solution is
Is PC, ethylene carbonate (hereinafter abbreviated as EC),
Butylene carbonate, dimethyl carbonate, ethyl
Methyl carbonate, diethyl carbonate, sulfora
And dimethoxyethane, and the like.
Alternatively, it can be used as a mixed solvent of two or more kinds. Above all,
Compatibility with the activated carbon of the positive electrode, withstand voltage stability and low-temperature characteristics
In terms of properties and the like, PC is preferred as the main solvent. Li
_FourTi_FiveO₁₂Negative electrode or non-graphitizable carbon and Li _FourTi_Five
O₁₂When using a mixed anode with
Typical PC electrolysis on graphitized carbon anode
Is stable, even in the electrolyte of PC main solvent.
The cycle characteristics are obtained.

Lithium contained in the organic electrolytic solution of the present invention
Um salt is LiPF₆, LiBF_Four, LiClO_Four, L
iN (SO_TwoCF_Three)_Two, CF_ThreeSO_ThreeLi, LiC
(SO _TwoCF_Three)_Three, LiAsF₆And LiSbF₆Or
One or more selected from the group consisting of is preferred. In the electrolyte
The concentration of the lithium salt is 0.1 to 2.5 mol / L,
Is preferably 0.5 to 2 mol / L.

The activated carbon contained in the positive electrode of the present invention is:
The specific surface area is preferably from 800 to 3000 m ² / g. The raw material and the activation conditions of the activated carbon are not limited. For example, the raw material includes coconut, phenolic resin, petroleum coke, and the like, and the activation method includes a steam activation method and a molten alkali activation method. Activated carbon obtained by activating steam from coconut or phenolic resin is particularly preferred. 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.
It is preferably contained in an amount of 1 to 20% by mass.

As a method for manufacturing a positive electrode body, for example, a mixture of activated carbon powder and a conductive material is mixed with polytetrafluoroethylene as a binder, kneaded, and then formed into a sheet to form a positive electrode. There is a method of fixing using a conductive adhesive. In addition, the activated carbon powder and the conductive material powder are dispersed in a varnish in which polyvinylidene fluoride, polyamideimide, polyimide, etc. are dissolved as a binder, and this liquid is coated on a current collector by a doctor blade method or the like, and dried to obtain a powder. You may. The amount of the binder contained in the positive electrode is preferably 1 to 20% by mass in view of the balance between the strength of the positive electrode body and characteristics such as capacity.

In the present invention, Li ₄ Ti used for the negative electrode is used.
₅ O ₁₂ may be obtained by mixing LiOH and TiO ₂ at a molar ratio of 4: 5, and baking the mixture at a temperature of 700 ° C. to 900 ° C. in an oxygen atmosphere for 10 hours. The specific surface area of Li ₄ Ti ₅ O ₁₂ is 1.0 to 3.
Those having 0 m ² / g are preferred. If it is less than 1.0 m ² / g, the effective area contributing to the electrode reaction is small, and it may not be possible to cope with charging and discharging with a large current. On the other hand, 3.
When it is larger than 0 m ² / g, the active surface becomes large,
Coulomb efficiency may be reduced due to decomposition of the organic electrolyte on the surface. The negative electrode body of the present invention is formed by mixing Li ₄ Ti ₅ O ₁₂ with a conductive material such as carbon black or a vapor-grown carbon fiber material as in the positive electrode, kneading polytetrafluoroethylene as a binder, and forming a sheet. It can be obtained by forming a negative electrode and bonding it to a current collector using a conductive adhesive.

The negative electrode body according to the second aspect of the present invention is obtained by kneading a carbon material, Li ₄ Ti ₅ O ₁₂ and a conductive material used as required, using polytetrafluoroethylene as a binder, similarly to the positive electrode, and forming the mixture into a sheet. To form a negative electrode, and adhere to a current collector using a conductive adhesive. Further, polyvinylidene fluoride, polyamide imide or polyimide as a binder, the carbon material and Li ₄ Ti ₅ O ₁₂ and a conductive material used as necessary in a solution in which a resin serving as a binder or a precursor thereof is dissolved in an organic solvent. There is also a method of dispersing, applying to a current collector, and drying. Among these methods, the method of coating the current collector is more preferable.

In the method of obtaining the negative electrode body by applying the solution to the current collector, 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 can be easily prepared. N-methyl-2-pyrrolidone (hereinafter, referred to as NMP) is preferable because it can be dissolved and is easily available. Here, the precursor of polyvinylidene fluoride, the precursor of polyamideimide, or the precursor of polyimide refers to those which are polymerized by heating to become polyvinylidene fluoride, polyamideimide, or polyimide, respectively. In the present invention, the mass ratio of the mixed active material of the carbon material and Li ₄ Ti ₅ O ₁₂ in the negative electrode to the binder is preferably 70:30 to 96: 4. 30 binder
When it is more than mass%, the negative electrode capacity becomes small. When the amount of the binder is less than 4% by mass, the effect as the binder is weakened, and the separation between the negative electrode and the current collector is increased.

[0022]

Now, the present invention will be described in further detail with reference to Examples 1 to 8.
However, the present invention is not limited to these.
The production and measurement of the devices of Examples 1 to 8 were all performed at the dew point.
Performed in an argon glove box below -60 ° C
Was. [Example 1] LiOH and TiO_TwoIn a molar ratio of 4: 5
At 800 ° C. in an oxygen atmosphere for 10 hours.
Baked for a specific surface area of 2.0 m^Two/ G Li
_FourTi_FiveO₁₂80% by mass of powder, vapor grown carbon fiber 10
%, And polytetrafluoroethylene as a binder
A mixture consisting of 10% by mass is kneaded by adding ethanol.
Rolled and vacuum dried at 150 ° C. for 2 hours to a thickness of 15
A 0 μm electrode sheet was obtained. Roll press this further
Press, the area of the negative electrode is 1cm x 1cm, thickness is 5
Conductivity with polyamideimide as binder as 0μm
Bonded to copper foil using adhesive, 10 hours at 150 ° C under reduced pressure
During the heat treatment, a negative electrode body was obtained.

Next, the phenol resin is used as a raw material for steam.
Specific surface area 2000m obtained by activation method^Two/ G activity
80% by mass of charcoal, 10% by mass of conductive carbon black,
And polytetrafluoroethylene 10 as binder
% Of the mixture is kneaded with ethanol.
After spreading, vacuum drying at 200 ° C for 2 hours to a thickness of 200μ
m electrode sheets were obtained. 1cm x 1 from this electrode sheet
cm × 200 μm electrode, and
Use an electrically conductive adhesive to make contact with the aluminum foil
And heat-treated at 260 ° C. for 10 hours under reduced pressure to obtain a positive electrode body.
Was. The positive electrode body and the negative electrode body are
The respective electrode surfaces face each other through the
To produce a device. PC and ethyl methyl carb
LiBF and a mixed solvent of (mass ratio 1: 1)
_FourIs dissolved at a concentration of 1 mol / L as an electrolyte,
Fully impregnate the device to allow 2.8V to 1.0V
The initial capacity was measured in the range of. Then, charge and discharge current 1
0mA / cm ^TwoIn the range from 2.7V to 1.5V
Perform a charge / discharge cycle and measure the capacity after 2000 cycles.
And the rate of change of capacity was calculated. Table 1 shows the results.

[Example 2] LiOH and TiO_TwoIn a molar ratio of 4:
And mixing the mixture at 850 ° C. in an oxygen atmosphere.
Fired in an atmosphere for 10 hours and the synthesized specific surface area is 1.5 m
^Two/ G Li _FourTi_FiveO₁₂Same as Example 1 except that powder was obtained
Then, a negative electrode body and a positive electrode body were prepared and evaluated in the same manner as in Example 1. Conclusion
The results are shown in Table 1. [Example 3] LiOH and TiO_TwoIn a molar ratio of 4: 5
At 650 ° C. in an oxygen atmosphere for 10 hours.
During firing, the synthesized specific surface area is 6.0m^Two/ G Li
_FourTi_FiveO₁₂Except for obtaining the powder, the anode body was
A polar body was prepared and evaluated in the same manner as in Example 1. The results are shown in Table 1.
You.

Example 4 LiOH and TiO_TwoIn a molar ratio of 4:
And the mixture was heated at 650 ° C. in an oxygen atmosphere.
Fired in an atmosphere for 10 hours and the synthesized specific surface area is 0.6m
^Two/ G Li _FourTi_FiveO₁₂Same as Example 1 except that powder was obtained
Then, a negative electrode body and a positive electrode body were prepared and evaluated in the same manner as in Example 1. Conclusion
The results are shown in Table 1. [Example 5 (Comparative Example)]
The same negative electrode body and positive electrode body as in the composition and manufacturing method of the positive electrode
Was prepared and evaluated in the same manner as in Example 1. Table 1 shows the results.

Example 6 LiOH and TiO_TwoIn a molar ratio of 4:
5 and the mixture was heated at 800 ° C. in an oxygen atmosphere.
Fired in an atmosphere for 10 hours and synthesized specific surface area is 2.0m
^Two/ G Li _FourTi_FiveO₁₂30 parts by mass of powder and spacing d0
02 is 40 mass parts of the non-graphitizable carbon material having 0.380 nm.
Mixing of 10 parts by mass of vapor grown carbon fiber as conductive material
Dissolve 20 parts by mass of polyvinylidene fluoride in NMP
Disperse in the solution, apply to a current collector made of copper, and dry.
After drying, a negative electrode was formed on the current collector. Roll this further
Press with a press machine, the area of the negative electrode is 1cm x 1cm, thickness
Heat treatment at 150 ° C under reduced pressure for 10 hours
Thus, a negative electrode body was obtained. Next, using phenolic resin as a raw material
Specific surface area 2000m obtained by steam activation method^Two/
g activated carbon 80% by mass, conductive carbon black 10
%, And polytetrafluoroethylene as a binder
A mixture consisting of 10% by mass is mixed with ethanol
After rolling, vacuum drying at 200 ° C. for 2 hours
A 00 μm electrode sheet was obtained. 1c from this electrode sheet
After obtaining an electrode of mx 1 cm x 200 μm,
Aluminum using conductive adhesive with binder as binder
Bonded to foil, heat-treated under reduced pressure at 260 ° C for 10 hours,
Body.

The positive electrode body and the negative electrode body are
The respective electrode surfaces face each other with a ren separator
Then, the device was sandwiched by a sandwiching plate to produce an element. PC and ethylme
Use a mixed solvent of tilcarbonate and (mass ratio 1: 1)
Yes, LiBF_FourIs dissolved at a concentration of 1 mol / L
As an electrolytic solution, fully impregnate the device with 4.2V
The initial capacity was measured in the range from 1.0 V to 1.0 V. afterwards,
Charge / discharge current 10mA / cm ^TwoFrom 4.0V to 1.5V
Charge / discharge cycles up to 2000 cycles
The subsequent capacity was measured and the rate of change of capacity was calculated. Table of results
It is shown in FIG.

[Example 7 (Comparative Example)] Spacing 0.337 nm
A mixture of 70 parts by mass of graphite (carbon material) and 10 parts by mass of vapor-grown carbon fiber as a conductive material is dispersed in a solution in which 20 parts by mass of polyvinylidene fluoride is dissolved in NMP. The initial capacity was measured from 4.2 V to 2.2 V except that the negative electrode was formed on the current collector after being coated on the body and dried.
A device was prepared and evaluated in the same manner as in Example 6, except that the charge / discharge cycle was performed in a voltage range of up to 75 V and a charge / discharge current of 10 mA / cm ² in a range from 4.0 V to 2.75 V. Table 1 shows the results.

Example 8 Li ₄ having a specific surface area of 2.0 m ² / g
A mixture obtained by mixing 40 parts by mass of Ti ₅ O ₁₂ powder, 30 parts by mass of a non-graphitizable carbon material having a plane spacing of 0.380 nm, and 10 parts by mass of vapor-grown carbon fiber as a conductive material was converted into 20 parts by mass of polyvinylidene fluoride to NMP. A device was prepared and evaluated in the same manner as in Example 6, except that the element was dispersed in a dissolved solution, applied to a current collector made of copper, dried, and a negative electrode was formed on the current collector. Table 1 shows the results.

[0030]

[0031]

According to the first aspect of the present invention, it is possible to provide a 2.7V class secondary power supply having a large capacity and a high reliability of a rapid charge / discharge cycle. According to a second aspect of the present invention,
A secondary power supply having a wide operating voltage range, a large capacity, a high withstand voltage, and high reliability in rapid charge / discharge cycles can be provided.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Manabu Tsushima 1150 Hazawa-cho, Kanagawa-ku, Yokohama-shi, Kanagawa Prefecture F-term within Asahi Glass Co., Ltd. 5H029 AJ03 AJ05 AK08 AL03 AL06 AL07 AL18 AM02 AM03 AM04 AM05 AM07 DJ17 HJ01 HJ02 HJ07 HJ13 HJ19 5H050 AA07 AA08 BA17 CA16 CB03 CB07 CB08 CB29 FA19 HA02 HA07 HA13 HA19

Claims (6)

[Claims] 1. A secondary power supply comprising: a positive electrode containing activated carbon; a negative electrode containing lithium titanate (Li ₄ Ti ₅ O ₁₂ ); and an organic electrolyte containing a lithium salt. 2. A positive electrode containing activated carbon, a negative electrode containing lithium titanate (Li ₄ Ti ₅ O ₁₂ ) and a carbon material capable of occluding and releasing lithium ions, and an organic electrolyte containing a lithium salt. A secondary power supply, characterized in that: 3. The secondary power supply according to claim 2, wherein the carbon material of the negative electrode has a (002) plane spacing d002 of 0.335 nm or more and 0.410 nm or less as measured by X-ray wide-angle diffraction. 4. A lithium titanate (Li ₄ T) in the negative electrode.
4. The secondary power supply according to claim 2, wherein the ratio of i ₅ O ₁₂ ) is 20 to 50% by mass, and the ratio of the carbon material is 80 to 50% by mass. 5. An electric capacity ratio of said negative electrode to said positive electrode is 1.
The secondary power supply according to any one of claims 1 to 4, wherein the secondary power supply is in a range of 0.5 to 1.3. 6. The negative electrode of lithium titanate (Li ₄ Ti
The secondary power source according to any one of claims 1 to 5 specific surface area of 1.0~3.0m ² / g of ₅ O _12).