JPH0821430B2 - Secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a secondary battery using a conductive aniline polymer as an electrode active material for a positive electrode.

[Prior art]

Numerous reports are known on the technology of batteries that can be charged and discharged, that is, secondary batteries.

As a typical secondary battery, there is one using a conductive polymer as an electrode active material, and it is known to use polyacetylene as an example of the conductive polymer. (For example, US Pat. Nos. 4,321,114 and 4,442,187).

JP-A-56-136469 discloses that polyacetylene is used as an electrode active material for a positive electrode and a negative electrode and is used as a positive electrode during charging.
_{^{ClO 4 -, PF 6 -,}} BF 4 - anion such as, also, a lithium ion as a negative _{electrode, (C 4 H 9) 4} p doped with cations such as N ⁺ type and n-type conductivity polyacetylene To form
Techniques for undoping these ions in discharge have been disclosed.

A secondary battery using polypyrrole as a positive electrode active material is also known, and a secondary battery using polythiophene or polyphenylquinoline as a positive or negative electrode active material is also known.

All of the publicly known secondary batteries described above use a non-aqueous solvent-based electrolytic solution.

The secondary batteries of the above-mentioned known examples have comparatively short cycle life and large self-discharge, so that they have not been put into practical use.

On the other hand, recently, the electrochemical behavior of polyaniline has been reported, and its application as an electrode active material for secondary batteries has been attempted. Polyaniline can be polymerized from an acidic aqueous solution of aniline by an electrolytic oxidation reaction, and the polymerized film formed on the electrode shows a reversible redox reaction in an acidic aqueous solution containing a supporting salt and is electrochemically active. It has been found that the electrical conductivity of polyaniline in the dry state varies from 10 ^-15 to 10 ^-1 S · cm ^-1 .

The electrolytically synthesized polyaniline was used as the electrode active material for the positive electrode, zinc was used as the negative electrode, and 1 mol of the electrolytic solution was used.
A battery using a ZnSO ₄ aqueous solution or a solution obtained by adding sulfuric acid to the aqueous solution to reduce the pH is rechargeable, and an open circuit voltage after charging is 1.2 to 1.6 V (Electrochemical Society No. 50.
Annual Conference Presentations, p123 (1983)].

However, as described above, this battery uses an aqueous solution as an electrolyte and the battery voltage is low, and dendritic deposition of zinc during charging is unavoidable, and there are electrode dropouts and short circuits between electrodes. It is very difficult to function as a secondary battery.

In addition, polyaniline was synthesized by potentiostatic electrolysis on platinum with 2M HClO ₂ aqueous solution containing aniline, which was used as an electrode active material in the positive electrode, and metal lithium was used as the negative electrode, and the electrolyte solution was 1 mol / perchloric lithium. It is also known to use a dissolved propylene carbonate solution. The open circuit voltage after charging of this secondary battery is 3.6 to 4.0 V,
A charge / discharge cycle test of 56% of the maximum capacity was performed, and Coulombic efficiency was 100% after 50 cycles [Proceedings of the 24th Battery Symposium, p197 (1983)]. This secondary battery has a high battery voltage and a high energy density as described above, but has a very short cycle life due to the phenomenon that metal lithium dendrites are precipitated during charging. Further, according to the research conducted by the present inventors, this secondary battery is often self-discharged.

[Problems to be solved by the invention]

The present invention is intended to solve the drawbacks (short charge / discharge life and many self-discharge) in the above-mentioned known secondary battery, and its object is to reduce self-discharge and charge / discharge life. It aims to provide long-lasting secondary batteries.

[Means for solving problems]

The above-mentioned object is a secondary battery in which a positive electrode having a conductive polymer as an electrode active material and a negative electrode made of a lithium alloy are opposed to each other with an electrolytic solution interposed therebetween, and the conductive polymer and the electrolytic solution are respectively described below ( a) (b) (a) The conductive polymer has the following structural formula (1) And the structure of the formula (1) includes a structure of the following formula (1 ′) as a modification, Moreover, the atomic number ratio of hydrogen and carbon constituting the polymer is 0.75.
~ 0.85, and the atomic ratio of nitrogen to carbon (average value) is 0.15
Consisting of ~ 0.18 polyaniline. In addition, (1)
In the formula (1 ′), X ⁻ is an anion, and n is the degree of polymerization.

(B) The electrolytic solution is a mixed solvent of polypropylene carbonate and an ether solvent in which a double salt of lithium is dissolved.

It is achieved by configuring as follows.

[Action]

In the secondary battery configured as described above, anions are doped by charging and undoped by discharging (that is, anions are released from polyaniline). Due to this phenomenon, the function as a secondary battery with little self-discharge and long cycle life can be fulfilled.

As the anion, ClO ₄ ⁻ , PF ₆ ⁻ , BF ₄ ⁻ , AsF ₆ ^−, etc. can be used.

The polyaniline is obtained, for example, by electrochemically oxidatively polymerizing an aqueous solution of HBF ₄ containing aniline (platinum is used as an electrode).

The polyaniline can also be obtained by chemically synthesizing an aqueous solution of HBF ₄ containing aniline by adding an oxidizing agent such as ammonium persulfate.

The general structural formula of the polyaniline is as shown in formula (1) below.

The component composition of this polyaniline is obtained by thermally decomposing the polyaniline and measuring N ₂ , CO ₂ , and H ₂ O by gas chromatography,
The amount of C and H can be calculated and obtained.

The structure of the above formula (1) includes a modified mode such as the formula (1 ′) which will be described below.

X ^{− in the above} formulas (1) and (1 ′) means an anion. The value of n is considered to be 20 or more as judged from the molecular weight of polyaniline soluble in dimethylformamide.
According to experiments conducted by the present inventor, good results are easily obtained when 20 <n.

The present inventor conducts elemental analysis on polyaniline obtained by electrolytic synthesis from a BHF ₄ aqueous solution containing aniline and polyaniline obtained by chemical synthesis, and has a structural formula as shown in the following formula (2). Was confirmed.

Using polyaniline having the structural formula of the equation (2) as an active material for the positive electrode, the anion BF ₄ in the charge ^- the BF ₄ in conjunction with discharge doping ^- the reaction at the time of the undoping, the following equation Represented.

The electric conductivity of the polyaniline having the structure of the above formula (2) shows 5 S · cm ⁻¹ in a dry state, and when undoped with an electrolytic solution, it changes as shown in FIG.
-It was cm ^-1 , but it was experimentally confirmed that the electrode active material exhibits excellent conductivity even in a discharged state.

The positive electrode is a mixture of an active material powder made of polyaniline (the structural formula is the above formula (1)) obtained by electrolytic synthesis or chemical synthesis, and a powder of a conductive material such as acetylene black. Then, it can be manufactured by mixing a binder such as polytetrafluoroethylene and pressure molding. In carrying out the present invention, the polyaniline having the structure of the above formula (1) is added to the active material 50
It is desirable to occupy 100% (% by weight). The polyaniline having a structure other than the structure of (1) has insufficient (or zero) properties for doping anions, resulting in poor performance.

In order to obtain the polyaniline represented by the structural formula (1), the molar ratio of hydrogen and carbon (the "molar ratio" in this specification means x when hydrogen atom is x mol and carbon atom is y mol). / y
I mean. Considering that Avogadro's number of atoms are included in 1 mol, x / y is equivalent to "atomic ratio". ) Is 0.75 to 0.85 (average value), and the molar ratio of nitrogen and carbon is 0.15 to 0.18 (average value).

The lithium alloy of the negative electrode is preferably an alloy of at least one of aluminum, silicon, and magnesium with lithium. Particularly, an alloy of aluminum and lithium is easy to obtain good results.

In any case, the lithium content is preferably 20 to 80% (atomic%).

JP-A-56-86463 discloses Al, Si, Pb, Mg, Sn, Na, Bi,
A lithium alloy containing Cd, Ca, Co, Cu, Ag, etc. is disclosed, and JP-A-57-98977 discloses a Li-Al-Mg alloy. It can be applied to the invention.

The use of an alloy in which these elements are added to lithium as an electrode has the effect of suppressing the deposition of lithium dendrites during charging, resulting in a longer cycle life.

As the electrolytic solution, a mixture of lithium salt as an electrolyte and propylene carbonate and an ether solvent is used.
As the lithium salt, it is preferable to use LiBF ₄ , LiPF ₆ , LiClO ₄ , LiAsF _6, or the like. Further, as the ether-based solvent, dimethoxyethane, dimethoxymethane and the like can be used, but it is preferable to use dimethoxyethane.

When an electrolyte solution containing no ether solvent is used, there is a risk that self-discharge may occur or the Coulombic efficiency may decrease. The cause of such a defect is considered to be that propylene carbonate decomposes during charging and the product deteriorates polyaniline. It was found that when propylene carbonate was mixed with ether, the amount of propylene carbonate decomposed during charging was suppressed to 1/4 or less. By suppressing the decomposition, the adverse effects of the decomposition products are significantly reduced.

By containing the ether solvent, the viscosity of the electrolytic solution is lowered and the electrolyte is easily diffused. This reduces the electric resistance of the electrolyte and improves the conductivity, so the charging voltage is set to 0.
Can be as low as 2 to 0.5 volts. By lowering the charging voltage, the electrolysis suppressing effect during charging of propylene carbonate can be further enhanced. FIG. 8 shows the relationship between the conductivity and the amount of propylene carbonate in a mixed solvent of propylene carbonate containing 1 mol of LiClO ₄ and dimethoxyethane.
The figure shows the relationship between the viscosity of the electrolytic solution and the amount of propylene carbonate. The temperature of the electrolyte is 25 ° C. From these figures, it is understood that the amount of propylene carbonate is preferably in the range of 20 to 80 vol%.

It is highly preferable that the polyaniline, which is the active material of the positive electrode, has a fibrous shape. When polyaniline is obtained by electrolytic synthesis, fibrous polyaniline is obtained. Further, even when polyaniline is obtained by chemical synthesis, fibrous polyaniline can be obtained by maintaining the temperature of the aqueous solution containing aniline at about 30 ° C or higher. The fibers obtained by these synthetic methods have a diameter of about 1000 to 3000 angstroms and a length of several μm to several tens of μm. When the temperature of the aniline-containing aqueous solution in the chemical synthesis is about 20 ° C or lower, the obtained polyaniline has a granular shape. It was confirmed that when fibrous polyaniline was used as the positive electrode active material, the anion doping ratio was significantly higher than when granular polyaniline was used, and the charging / discharging cycle life could be extended.

When assembling the secondary battery, it is preferable to use a porous separator and hold the electrolyte in the holes of the separator. It is preferable to use an electrically insulating material such as polypropylene carbonate or a glass filter for the separator.

〔Example〕

FIG. 1 is a characteristic diagram showing undope and electrical conductivity of electrochemically synthesized polyaniline.

Example 1 Platinum was used as a working electrode and a counter electrode in a 0.5M HBF ₄ aqueous solution containing 0.1 M aniline, and the potential of the working electrode was kept at 0.8 V with respect to a silver-silver chloride reference electrode, and electrolysis was performed. Polyaniline was produced on polar platinum. This was scraped off, washed with water, dried in vacuum, and powdered, and observed by an electron microscope to find that it was fibrous. In addition, as a result of performing elemental analysis of carbon, hydrogen and nitrogen to obtain the molar ratio, hydrogen and carbon are 0.75 to 0.85, nitrogen and carbon are 0.15 to 0.18, and the structural formula is (2) above. It was as the ceremony said.

The powder of polyaniline was made into pellets with a diameter of 9 mm at a pressure of 100 kg / cm ² , and the electrical conductivity was determined by measuring the resistance by the 4-terminal method. As a result, 3.8 to 5.0 S · cm ⁻¹ was obtained.

Using this polyaniline pellet as the working electrode and platinum as the counter electrode, cyclic voltammetry in propylene carbonate containing 1M LiBF ₄ and dimethoxyethane solvent
As shown in the figure, an oxidation current (shown by a chain line) and a reduction current (shown by a solid line) were observed.

The positive flowing current, that is, the oxidation current, is the doping of BF ₄ ^{− into} the polyaniline, and the negative flowing current, that is, the reducing current, is the doping from the BF ₄ ⁻ of polyaniline. When polyaniline is used as the electrode active material in the positive electrode, the former doping corresponds to charging and the latter undoping corresponds to discharging. The coulombic efficiency, that is, the ratio of the amount of electricity for doping and the amount of electricity for undoping, that is, about 100% was obtained.

(Example 2) 11% by weight of carbon (acetylene black) was added to the polyaniline synthesized in Example 1 and mixed, and polytetrafluoroethylene was added as a binder.
A positive electrode was obtained by molding at a pressure of 100 kg / cm ² and forming a pellet having a diameter of 9 mm. Using a mixed solvent of propylene carbonate containing 1 M LiBF ₄ and dimethoxyethane (1: 1 volume ratio) as the electrolyte,
A battery was constructed using a 0Li-20Al (atomic ratio) alloy for the negative electrode. The doping ratio of BF ₄ ⁻ to polyaniline was set to 20 mol% (to aniline) unit.

A indicated by a solid line in FIG. 3 shows a change in charging voltage during constant current charging and discharging after discharging 5 mA / cm ² until the battery voltage reached 1.5 V in Example 2. Similarly, A'in the figure shows the discharge voltage change. The open circuit voltage of this example was 3.0V.
The result of the charge / discharge cycle experiment under the above conditions is
Shown in Figure C. 630 cycles were obtained. After the 25th charge was completed, the battery was kept open and left for 24 hours. After that, the battery was discharged under the same conditions as for charging, and the self-discharge rate was calculated from the amount of electricity, resulting in 4.5% / day.

Comparative Example 1 The polyaniline obtained in Example 1 was immersed and stirred in a 1M KOH aqueous solution for 5 hours, then washed with water and dried in vacuum. This was molded at a pressure of 100 kg / cm ² , pelletized to have a diameter of 9 mm, and the resistance was measured by the four-terminal method to obtain the electric conductivity. The result was about 10 ⁻⁸ S · cm ⁻¹ . 11% by weight of carbon (acetylene black) was added to and mixed with the polyaniline powder, and the pellet was molded into a pellet having a diameter of 9 mm under the above-mentioned conditions. It was discharged, but could not be discharged.

In Comparative Example 1, it can be seen that polyaniline does not incorporate anions and does not function as a secondary battery.

The reason why the anion cannot be doped is that the structural formula of polyaniline is different from the above formula (1).

Example 3 A 1M HBF ₄ aqueous solution containing 0.2M aniline was kept at 40 ° C., ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₇ ) was added to 0.1M, and the mixture was left for 5 hours with stirring. . The precipitate was washed with water and vacuum dried to obtain powdery polyaniline, which was observed with an electron microscope, and as a result, it was found to be fibrous.

The powder was molded under a pressure of 100 kg / cm ² , and the resistance was measured as a 9 mm diameter pellet by the four-terminal method to obtain the electric conductivity, which was 2.6 S · cm ⁻¹ . Carbon and tetrafluoroethylene were added to the polyaniline powder thus obtained by chemical synthesis in the same manner as in Example 2 to form pellets.
A battery similar to that of Example 2 was assembled using this as a positive electrode, and a battery test was conducted under the same conditions. The number of charge / discharge cycles that could achieve 100% Coulombic efficiency was 720. The self-discharge rate of this battery was 4.8% / day.

Comparative Example 2 A battery was constructed using the same positive electrode and negative electrode as in Example 2 described above, and using a propylene carbonate solvent containing 1 M LiBF ₄ as the electrolytic solution. The battery test was performed under the same conditions as in Example 2. The voltage changes during constant current charging and discharging at a current density of 5 mA / cm ² are shown as B and B ′ in FIG. A broken line B shows a change in charging current when charging and discharging with a constant current in this comparative example 2, and a broken line B ′ shows a change in discharging voltage.

It can be seen that the voltage flatness of Comparative Example 2 of this example is inferior to that of the voltage change curves A and A ′ (solid line) in Example 2.

The Coulombic efficiency in Comparative Example 2 is shown in D of FIG.

The number of charge and discharge cycles was 183, which kept the Coulombic efficiency at 100%. The self-discharge rate in Comparative Example 2 was 8% / day.

From this Comparative Example 2, it was found that the secondary battery using only propylene carbonate as the electrolytic solution had poor durability and voltage characteristics. It is considered that the cause of such a defect is that the viscosity of propylene carbonate is high and the wetting of the electrode is poor.

(Comparative Example 3) A battery was constructed in the same manner as in Example 2 except that the negative electrode was omitted, and a metal lithium foil was used as the negative electrode. The battery test was performed under the same conditions as in Example 2. The open circuit voltage of the battery was almost the same as that of Example 2. However, the number of charge and discharge cycles was about 120 to 150.

From this Comparative Example 3, it was found that it was difficult to obtain sufficient durability when lithium pure metal was used as the negative electrode.

(Example 4) A battery similar to that of Example 2 was formed except that the negative electrode was omitted.
A lithium-aluminum alloy having the following composition was used for the negative electrode, and a battery was assembled in each.

(I) 20Li-80Al (atomic ratio) (ii) 40Li-60Al (atomic ratio) (iii) 50Li-50Al (atomic ratio) The battery test was conducted under the same conditions as in Example 2. The open circuit voltages of the batteries (i), (ii) and (iii) were 0.2 to 0.4 V lower than the open circuit voltage of the battery of Example 2. Obtained charge of Coulomb efficiency of almost 100%,
The number of discharge cycles and the self-discharge rate were as follows.

(I) Battery, 764 cycles, self-discharge rate 3.5% / day (ii) Battery, 1162 cycles, self-discharge rate 4.0% / day Battery (iii), 1320 cycles, self-discharge rate 4.4% / day Day (Example 5) A portion other than the negative electrode constituted the same battery as in Example 2, and the negative electrode used was a lithium alloy of 98Li-2Al (atomic ratio).
After discharging at a current density of 5 mA / cm ² , charging was performed so that the doping ratio of BF ₄ ⁻ to polyaniline was 20 mol%. Then, the battery was left open for 15 hours for discharging. This charging-open circuit-discharging was set as one cycle, and the number of cycles in which the Coulomb efficiency was 90% or more, which was subjected to the repeated test, was 428, and the self-discharge rate was 3.8% / day.

(Example 6) The same battery as in Example 2 was constructed except for the electrolytic solution. The electrolytic solution contains propylene carbonate containing 1M LiClO _4.
A mixed solvent of dimethoxyethane was used. The battery test was performed under the same conditions as in Example 2, and the number of charge / discharge cycles at which 100% Coulombic efficiency was obtained was 736. The self-discharge rate of this battery was excellent at 3.5% / day.

(Example 7) Platinum was used as a working electrode and a counter electrode in a 0.5M HBF ₄ aqueous solution containing 0.1 M aniline, the potential of the working electrode was kept at 0.9 V with respect to a silver-silver chloride reference electrode, and electrolytic oxidation was performed at room temperature. Then, polyaniline was synthesized on the working electrode. Polyaniline was taken from the electrode, washed with water, vacuum dried at 80 ° C., and atomized. The scanning electron micrograph of polyaniline thus obtained (magnification × 10.000) shows that polyaniline has a diameter of approximately
It was 1,500 angstrom fibrous.

To the polyaniline obtained as described above, 10% by weight of acetylene black was added and mixed, and polytetrafluoroethylene was further added and stirred to obtain 12 mg of the mixture.
Was molded into pellets with a diameter of 9 mm at a pressure of 300 kg / cm ² , and this was used as a positive electrode, propylene carbonate in which 1M LiBF ₄ was dissolved and dimethoxyethane (1: 1 volume ratio) were used as an electrolytic solution, and 50Li-50Al.
A battery was constructed using (atomic percent) alloy as the negative electrode and polypropylene as the separator between the electrodes. Once this battery is discharged, charge it at a current density of 1 mA / cm ² ,
The doping rate of BF ₄ ⁻ into polyaniline was 67 mol% / aniline unit. When this battery was charged at a doping rate of 30 mol% / aniline unit at a current density of 1 mA / cm ² and then discharged at the same current density until the battery voltage became 1 V, a charge / discharge cycle test was conducted.
Even at 730 cycles, the Coulombic efficiency (ratio of charge and discharge electricity) was 99% or more. The open circuit voltage of this battery after completion of charging was 3.5V.

Example 8 Electrolytic oxidation was performed in a 1 MH ₂ SO ₄ aqueous solution containing 0.1 M aniline under the same conditions as in Example 7, and a post-treatment was performed in the same manner to obtain a polyaniline powder. The scanning electron micrograph of this polyaniline powder was fibrous.

A battery similar to that of Example 7 was constructed using this polyaniline, and the doping ratio of BF ₄ ⁻ into the polyaniline was determined. As a result, 58 mol% / aniline unit was obtained. In the same charge / discharge cycle test, the number of cycles was 740 or more with a Coulomb efficiency of 99%.

Example 9 To a 0.5 M HBF ₄ aqueous solution containing 0.2 M aniline, a 0.1 M ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₇ ) solution was added for 1.5 hours while maintaining the temperature at 40 ° C., and polyaniline was added. Synthesized. The polyaniline was washed with water and vacuum dried at 80 ° C. to be atomized. The scanning electron micrograph (magnification: 10,000) of the polyaniline obtained by the chemical oxidation at high temperature had a fibrous structure, and the diameter of the fiber was about 1,500 angstroms.

A battery similar to that of Example 7 was constructed using this polyaniline, and the doping ratio of BF ₄ ⁻ to polyaniline was determined. As a result, 62 mol% / aniline unit was obtained. In the same charge / discharge cycle test, a cycle number of 680 or more was obtained with a Coulomb efficiency of 99%.

Example 10 Chemical oxidation was carried out in a 1 MH ₂ SO ₄ aqueous solution containing 0.1 M aniline under the same conditions as in Example 9, and a post-treatment was carried out in the same manner to obtain a polyaniline powder. The scanning electron micrograph of this polyaniline had a fibrous morphology and a diameter of 2000 angstroms.

A battery similar to that of Example 7 was constructed using this polyaniline, and the doping ratio of BF ₄ ⁻ to polyaniline was determined to be 60 mol% / aniline unit.
In the same charge / discharge cycle test as in Example 7, a cycle number of 665 or more was obtained with a Coulomb efficiency of 99%.

(Example 11) A 0.5 M HBF ₄ aqueous solution containing 0.2 M aniline was added with a 0.1 M ammonium persulfate solution at a temperature of 20 ° C.
It was added for a period of time to synthesize polyaniline. The polyaniline was washed with water and vacuum dried at 80 ° C. to be atomized. The scanning electron micrograph (magnification: 10,000) of the polyaniline thus obtained showed that the polyaniline had a fine morphology.

A battery similar to that of Example 7 was constructed using this polyaniline, and the doping ratio of BF ₄ ⁻ to polyaniline was determined to be 34 mol% / aniline unit.
In the same charge / discharge cycle test as in Example 7, the Coulombic efficiency began to decrease after 180 times.

(Example 12) FIG. 5 and FIG. 6 show a comparison of performances of secondary batteries using fibrous polyaniline and fibrous polyacetylene as conductive polymers, respectively.

The battery obtained in Example 7 was used as the positive electrode of the battery in this example. The structure of the battery is the same as that of the present invention and that of the comparative example using polyacetylene as the positive electrode active material, and has the structure shown in FIG. FIG. 7 shows a perspective view and a partial sectional view of the secondary battery. Reference numeral 1 is a positive electrode, 2 is a negative electrode, 3 is a positive electrode current collector, and 4 is a negative electrode current collector. The current collectors 3 and 4 are made of austenitic stainless steel, such as 18 wt% Cr-8 wt% Ni.
It is made of steel or expanded metal. In this embodiment, stainless steel is used. Reference numeral 5 is a separator, which is made of a porous electrically insulating material and holds the electrolytic solution in the pores. As the separator material, for example, polypropylene carbonate, glass filter or the like can be used. In this embodiment, polypropylene carbonate is used. Reference numeral 6 is a positive collector terminal, and 7 is a negative collector terminal. Austenitic stainless steel containing 18 wt% Cr and 8 wt% Ni was used for these collector terminals. Reference numeral 8 is a battery container, and 9 is a cap. The cap 9 has a male thread, and the inner surface of the battery case 8 has a female thread so as to mesh with the male thread. The positive electrode 1 is pressed against the negative electrode 2 side by screwing in the cap 9. The battery container and the cap were made of polytetrafluoroethylene.

The doping rate is 20 mol% / aniline unit, (3 mol% / carbon unit) for the battery using polyaniline, and 4 mol% / carbon unit for the battery using polyacetylene. Discharge time (h), self-discharge rate (%)
And E is a battery using polyaniline, and F is a battery using polyacetylene. In Fig. 6, the horizontal axis represents charge-1 hour rest-discharge (current density 5mA / cm
² ) is the number of cycles (cycles) in the cycle mode, the vertical axis is the Coulombic efficiency (%), E is the battery using polyaniline, and F is the battery using polyacetylene. ing. Batteries using polyacetylene have a high self-discharge rate, and Coulombic efficiency (%) is several tens.
In contrast, the battery using polyaniline has a low self-discharge rate of 4.5% / day at a discharge time of 90 hours, and the decrease in Coulombic efficiency (%) is recognized even after several hundred times. I couldn't do it.

〔The invention's effect〕

As described above in detail, the secondary battery to which the present invention is applied has an excellent practical effect that it has no self-discharge and has a long charge / discharge life.

[Brief description of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention,
FIG. 3 is a characteristic diagram showing the relationship between undoping and electrical conductivity of electrochemically synthesized polyaniline. FIG. 2 is a characteristic diagram showing a cyclic voltammgram of a polyaniline electrode in an electrolytic solution, and FIG. 3 is a characteristic diagram showing a charge / discharge curve of a battery using polyaniline as an electrode active material in a positive electrode and a lithium alloy as a negative electrode. FIG. 4 is a characteristic diagram showing Coulombic efficiency and the number of cycles, that is, cycle life. 5 and 6 are charts for explaining the effects of the present invention. FIG. 7 is a perspective view showing the structure of a secondary battery according to an embodiment of the present invention. FIG. 8 is a characteristic diagram showing the relationship between the electrical conductivity of the electrolytic solution and the amount of propylene carbonate, and FIG. 9 is a characteristic diagram showing the relationship between the viscosity of the electrolytic solution and the amount of propylene carbonate. 1 ... Positive electrode, 2 ... Positive electrode, 3 ... Positive electrode current collector, 4 ...
Negative electrode current collector, 5 ... Separator, 6,7 ... Current collector terminal, 9 ... Cap.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroyuki Sugimoto 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Hitate Works, Ltd., Hitachi Research Laboratory (72) Inventor Atsuko Toyama 4026 Kuji Town, Hitachi City, Ibaraki Prefecture Nitate Works Co., Ltd. Hitachi Research Laboratory (72) Inventor Noboru Ebado 4026 Kuji Town, Hitachi City, Hitachi, Ibaraki Prefecture Hitachi Research Institute Co., Ltd. (72) Inventor Shinpei Matsuda 4026 Kuji Town, Hitachi City, Ibaraki Hitachi Research Laboratory Co., Ltd. (56) References JP-A-61-68864 (JP, A)

Claims (7)

[Claims] 1. A secondary battery in which a positive electrode using a conductive polymer as an electrode active material and a negative electrode made of a lithium alloy are opposed to each other with an electrolytic solution interposed therebetween, and the conductive polymer and the electrolytic solution are respectively described below. A secondary battery having the structure as described in (a) and (b). (A) The conductive polymer has the following structural formula (1). And the structure of the formula (1) includes a structure of the following formula (1 ′) as a modification, Moreover, the atomic number ratio of hydrogen and carbon constituting the polymer is 0.75.
.About.0.85 and consisting of polyaniline having an atomic ratio of nitrogen to carbon of 0.15 to 0.18. In addition, in the formulas (1) and (1 ′), X ⁻
Is an anion, and n represents the degree of polymerization. (B) The electrolytic solution is a mixed solvent of polypropylene carbonate and an ether solvent in which a double salt of lithium is dissolved. 2. The secondary battery according to claim 1, wherein the conductive polymer has a fiber shape. 3. The secondary battery according to claim 2, wherein the polyaniline polymerization degree n> 20. 4. The positive electrode according to any one of claims 1 to 3, wherein the positive electrode is formed by binding polyaniline powder and carbon powder with a binder made of polytetrafluoroethylene. And a secondary battery. 5. A secondary battery according to any one of claims 1 to 4, wherein the electrolytic solution is impregnated and held in a porous electrically insulating separator. 6. The secondary battery according to claim 5, wherein the separator is polypropylene carbonate. 7. The fiber-shaped polyaniline according to claim 3, characterized in that its diameter is 1000 to 3000 angstroms and its length is several microns to several tens of microns. Next battery.