JPH0636372B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a non-aqueous electrolyte secondary battery using a conductive polymer as an electrode material.

(B) Conventional technology As a conventional non-aqueous electrolyte secondary battery, a negative electrode made of a light metal such as lithium, a positive electrode made of a metal compound such as molybdenum trioxide or vanadium pentoxide, and lithium perchlorate ( LiClO ₄ ), lithium borohydride (L
iBF ₄ ) and a non-aqueous electrolyte in which a salt such as iBF ₄ ) was dissolved.

In recent years, for example, JP-A-56-136469.
As disclosed in the publication, a secondary battery using a conductive polymer typified by polyacetylene as an electrode material has been proposed.

Normally, organic polymers show almost no conductivity,
A conductive polymer which is an electrode material of a secondary battery of this kind has a feature that it can be doped and the conductivity is remarkably increased by the doping. Moreover, the doping can be performed electrochemically.The conductive polymer doped with anions can be used as the positive electrode of the battery, and the conductive polymer doped with cations can be used as the negative electrode. A rechargeable battery can be constructed by reversibly performing doping.

(C) Problems to be Solved by the Invention The present invention aims to improve the charge / discharge efficiency, charge / discharge cycle characteristics and storage characteristics of a non-aqueous electrolyte secondary battery using a conductive polymer for at least one electrode. .

In order to measure the increase in capacity in a battery using a conductive polymer electrode, it is necessary to increase the amount of conductive polymer in the battery. For that purpose, it is advantageous to press-mold a powdery polymer into a high-density electrode rather than using a film-shaped polymer as the conductive polymer. However, the conductive polymer itself is generally not well molded, and even if only the conductive polymer is pressure-molded, the mechanical strength will be low, and the electrode will collapse due to charge / discharge reaction or long-term storage. There was a problem with cycle characteristics and storage characteristics.

As a countermeasure against this, for example, a binder such as polytetrafluoroethylene is mixed. However, if the binder is mixed, the capacity per unit volume is inevitably reduced by that amount. The electrodeposit mixed with the binder has a bad "wetting" with the electrolytic solution, which adversely affects the battery performance.

(D) Means for Solving Problems A non-aqueous electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte, and uses a conductive polymer electrode as at least one electrode. That is, the conductive polymer electrode has a polymer electrolyte layer on its surface.

The polymer electrolyte used here is a polymer having a special structure and usable as an electrolyte, for example, a complex of a polymer having a helical structure and an alkali metal salt or an ion exchange resin ion-exchanged with an alkali ion. Is mentioned.

As a specific example of the former, a complex of a polymer such as polyethylene oxide, polymethylmethacrylate, or polyvinylpyrrolidone and a lithium salt such as lithium perchlorate or lithium borofluoride is known.

(E) Operation When the polymer electrolyte layer is formed on the surface of the conductive polymer electrode, the mechanical strength is improved and the polymer electrolyte layer is less likely to be collapsed as compared with the case where the conductive polymer is used alone, and the polymer electrolyte layer does not dissolve the electrolytic solution. Since the electrolyte retains its function, the diffusion of the electrolytic solution from the electrode is suppressed and a stable battery capacity can be obtained, so that cycle characteristics, storage characteristics and charge / discharge efficiency can be improved.

(F) Example [Example 1] In producing a positive electrode, a polyacetylene powder having a diameter of 20.
A positive electrode made of a polyacetylene molded body having a thickness of about 0.7 mm is obtained by compression molding into a disk shape of 0 mmφ. Then, a solution in which polymethylmethacrylate and lithium perchlorate were dissolved in an appropriate amount of dimethylformamide in a weight ratio of 3: 1 to obtain a solution, and the positive electrode was immersed in this solution, taken out and dried to form a positive electrode on the surface of the positive electrode. A polymer electrolyte layer is formed. When immersed in the solution, care should be taken so that the solution does not adhere to the surface of the positive electrode in contact with the positive electrode can or the current collector.

The negative electrode used was a 0.3 mm thick lithium foil punched out to a diameter of 20.0 mmφ, and the electrolyte was propylene carbonate containing 1 mol / mol of lithium perchlorate and was impregnated into a polypropylene nonwoven separator. Then, the battery (A) of the present invention was prepared. FIG. 1 is a vertical cross-sectional view of the battery of the present invention, (1) is a polyacetylene positive electrode having a polymer electrolyte layer (2) formed on the surface thereof, and a positive electrode can (4) via a positive electrode current collector (3). Is pressed against the inner bottom surface of the. (5) is a lithium negative electrode, which is pressure-bonded to the inner bottom surface of the negative electrode can (7) via the negative electrode current collector (6). (8) is a separator and (9) is an insulating packing.

For comparison, a comparative battery similar to that of Example 1 except that a polyacetylene positive electrode having no polymer electrolyte layer on the surface was used.
Created (B).

2 and 3 are battery characteristic comparison diagrams of these batteries (A) and (B). In FIG. 2, the battery was charged at a current of 0.5 mA for a certain period of time and then discharged at a current of 0.5 mA. The relationship between the charge capacity and the discharge capacity under the condition that the discharge is terminated when the voltage reaches 2.0 V is shown in FIG.
The charge and discharge cycle characteristics are shown under the condition that the battery is charged with a current of A for 1 hour and then discharged with a current of 0.5 mA and the discharge end voltage is 2.0V.

[Example 2] The solution composition for forming the polymer electrolyte layer was one in which polyethylene oxide and lithium borohydride were dissolved in an appropriate amount of acetonitrile at a weight ratio of 3: 1, and the electrolytic solution composition was propylene. A battery (A) 'of the present invention was prepared in the same manner as in Example 1, except that 1 mol / mol of lithium borofluoride was dissolved in carbonate.

For comparison, a comparative battery (C) similar to that of Example 2 was prepared except that a polyacetylene positive electrode having no polymer electrolyte layer on the surface was used.

FIG. 4 is a charge / discharge cycle characteristic diagram of these batteries (A) '(C)', and the measurement conditions are the same as in the case of FIG.

Fig. 5 is a comparison diagram of the discharge characteristics of the battery (A) 'of the present invention and the comparative battery (C) after a predetermined cycle. The solid line shows that the battery was charged at 0.5 mA for 1 hour at the 100th cycle and immediately after charging. Discharge characteristics when discharged at 0.5 mA, and the broken line is 101
The discharge characteristics are shown when the battery was charged at 0.5 mA for 1 hour at the cycle cycle, stored for 1 week after charging, and then discharged at 0.5 mA.

Regarding the charging / discharging efficiency from FIG. 2, the cycle characteristics from FIGS. 3 and 4, and the storage characteristics from FIG. 5, the batteries (A) (A) ′ of the present invention are better than the comparative batteries (B) (C). The improvement of the characteristics can be seen.

Considering the reason for this, the conductive polymer is slightly swollen and becomes brittle when immersed in the electrolytic solution. Moreover, in the charged state, that is, in the doped state, it becomes more and more fragile and easily broken. Therefore, when the charging / discharging cycle is repeated, the charging / discharging efficiency tends to decrease, and in charging / discharging with a larger capacity, the efficiency decreases significantly. However, in the battery of the present invention, the surface of the conductive polymer electrode is coated with a polymer electrolyte layer, and the polymer electrolyte layer suppresses the collapse of the conductive polymer electrode, resulting in charge / discharge cycle characteristics and storage. It is considered that the characteristics are improved.

Further, it is considered that the polymer electrolyte layer suppresses the escape of the electrolytic solution from the conductive polymer electrode, and the abundant electrolytic solution is present in the vicinity of the electrode, so that the charge / discharge efficiency is improved.

In addition, although the case of polyacetylene was illustrated in the examples as an example of the conductive polymer, the present invention is not limited to this and, for example, polythiophene, polypyrrole, polyphenylene and the like can also be applied.

Furthermore, the conductive polymer electrode can be used only for the negative electrode, or can be used for both the positive and negative electrodes.

(G) Effect of the invention As described above, in the non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator and a non-aqueous electrolytic solution, using a conductive polymer electrode as at least one electrode, as the conductive polymer electrode By using the one having the polymer electrolyte layer on its surface, the charge / discharge efficiency, charge / discharge cycle characteristics and storage characteristics can be improved, and its industrial value is extremely large.

[Brief description of drawings]

FIG. 1 is a longitudinal sectional view of a battery according to an embodiment of the present invention, FIG.
5 to 5 are battery characteristic comparison diagrams, FIG. 2 is charge / discharge efficiency, FIGS. 3 and 4 are charge / discharge cycle characteristics, and FIG.
The figures show storage characteristics, respectively. (1) …… conductive polymer electrode, (2) …… polymer electrolyte layer,
(4) …… Positive electrode can, (5) …… Lithium negative electrode, (7) …… Negative electrode can, (8) …… Separator, (9) …… Insulating packing, (A)
(A ′) …… Invention battery, (B) (C) …… Comparison battery.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-111276 (JP, A) JP-A-59-873 (JP, A) JP-A-60-32258 (JP, A) JP-A 61- 8854 (JP, A) JP 59-132576 (JP, A) JP 58-100374 (JP, A) Physical Review B. , 30 [8] (1984) (US) P. 4846 ~ 4849

Claims (3)

[Claims] 1. A positive electrode, a negative electrode, a separator, and a nonaqueous electrolytic solution, wherein a conductive polymer electrode is used as at least one electrode, wherein the conductive polymer electrode is
A non-aqueous electrolyte secondary battery having a polymer electrolyte layer on its surface. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer electrolyte is an ionic conductor made of a composite of an organic polymer and a lithium salt. 3. The non-aqueous electrolyte secondary battery according to claim 2, wherein the organic polymer is selected from polyethylene oxide, polymethylmethacrylate, and polyvinylpyrrolidone.