JPS61239562A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To prevent fluctuation of charge/discharge curve even upon overdischarge by containing specific conductive macromolecules in the positive electrode. CONSTITUTION:Any one of pyrrole, thiophene or conductive macromolecules to be synthesized from their inducers is contained in the positive electrode. When discharging such a cell, positive electrode active substance such as V2O5, MoO3, MnO2, etc. is reduced. When employing V2O5 and Li respectively for the positive and the negative electride, discharge will advance on the basis of the formula (2) and upon droppage of the potential of the positive electrode to the lower limit of reversibility of positive electrode active substance or about 2V (against Li/Li<+>), reaction shown on the formula (3) will occur. Consequently, the macromolecules (M)n in the positive electrode discharged of ClO4<-> will loss the conductivity thus to become an insulator. Thereby, the resistance in the positive electrode will increase abruptly to promote polarization thus to drop the cell voltage. In other word, the positive electrode substance will be hard to discharge in the over-discharge region to eliminate transfer to non-reversible structure. Consequently, the charge/discharge characteristic of cell is never sacrificed even upon further discharge than the reversible lower limit voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, particularly to improvements in its positive electrode.

Conventional technology currently uses alkali metals such as Li and Na as negative electrode active materials, and Lick○4°LiBF4. L
So-called non-aqueous electrolysis in which iCl etc. are dissolved 27, - 1'''''', s = *i, tomi'''; Utr b, h
r @ ko I However, this type of secondary battery is 1
It has not yet been put into practical use. The reason for this is that the lifespan of charging and discharging cycles is short, and the charging and discharging efficiency during charging and discharging is low. The cause of this performance deterioration is mainly the active material of the positive and negative electrodes.

Charge, 1, 1, 1, 1, 1. 1
It is a decline.

As for positive electrode active materials, Ti, V, C
r, □Oxides and chalcogen compounds having a layered structure or tunnel structure such as MO are known. □This is Rano Naka T I S2
, V S e2 and other chalcogen compounds
: has excellent reversibility during charging and discharging. but,[
Chalcogen compounds have a low density, so the
Dori's density is small. On the other hand, oxides have a high density and a metal element with a high oxidation number.
, ! ``It is preferable to use an oxide as the positive electrode active material rather than a chalcogen compound because it can provide a higher energy density.

Oxides such as v2051MOQ39Mno2 are being considered as positive electrode active materials having the above-mentioned high voltage, high V charge/discharge capacity, that is, high energy density. Indeed, even in cycle characteristics, these exhibit good reversibility at a constant discharge voltage. However, when discharging to a voltage lower than this, that is, overdischarging,
These oxides transform into irreversible structures. Even if the battery is discharged again after this, the charging and discharging behavior is completely different from that before overdischarging, and in particular, the discharge curve is not flat and monotonically decreases as the battery discharges, which is extremely inconvenient for the battery.

Furthermore, the charge/discharge capacity rapidly decreases with cycles when overdischarge is performed. In order to maintain good reversibility of the oxide as described above, it is necessary to set the lower limit of the discharge potential to about 2■ with respect to Li/Li+.

When discharging is performed at a potential 1 lower than this, the subsequent charging/discharging behavior changes significantly.

Traditionally, as a means to avoid overdischarge of the positive electrode active material,
When assembling the battery, a negative electrode limited type battery was constructed in which the discharge capacity of the negative electrode active material was lower than that of the positive electrode active material. However, in secondary batteries that use alkali metals such as Li as the negative electrode active material, due to the low charge and discharge efficiency of the negative electrode active material, a positive electrode limited type battery must be constructed that conversely reduces the discharge capacity of the positive electrode active material. . Therefore, in this type of battery, even if the positive electrode active material reaches the lower limit of reversibility due to discharge, the negative electrode active material remains, resulting in further overdischarge, which causes problems in subsequent charging and discharging.

Problems to be Solved by the Invention As described above, non-aqueous electrolyte secondary batteries using oxides such as V2O6, MoO2, MnO2, etc. as positive electrode active materials have poor charging and discharging behavior only under the condition that the discharge voltage is controlled. Although it is possible to maintain a high energy density and a high energy density, there is a problem in that it deteriorates when over-discharged.

The present invention eliminates these conventional drawbacks, and provides a highly reliable battery with high energy density and excellent charge/discharge behavior with no change in the charge/discharge curve even when overdischarged. The purpose is to provide a non-aqueous electrolyte secondary battery.

5,-7 Means for solving the problem The nonaqueous electrolyte secondary battery of the present invention contains pyrrole, pyrrole,
It is characterized by containing any one of conductive polymers synthesized from thiophene and derivatives thereof.

, i ′''6°4%t'6Kf+-f-1ri,,
;hb″゛°“゛11 Solutes include pyrrole, thiophene,
Alternatively, it can be easily synthesized into the positive electrode by melting a derivative of Cholera and, after assembling the battery, passing an anode current to the positive electrode side of the battery. The solute in the electrolyte is L IC704
In this case, the reaction becomes:

nM + nxclo-nee CM” (ClO,i),]
. 18. (1) M: monomer suspension of pyrrole, thiophene, etc. The effect of this technical means is as follows.

When a battery containing a conductive polymer as described above in its positive electrode plate is discharged, positive electrodes such as V2O5, MoO2, MnO2, etc.
．． The active material is reduced according to the following equation. When the positive electrode is V2O5 and the negative electrode is Ll, 6, -V2O3+ y L 1 +- → V2O5 (L 1 y
)...(2). The same applies to other oxides. According to equation (2), the discharge further progresses, and when the potential of the positive electrode decreases to about 2V (i/Li), which is the lower limit of reversibility of the positive electrode active material, the following reaction occurs.

CM”(CnO,−)x], −+ (M), + x
cOo4. ,, (3) According to equation (3), the polymer (M)n in the positive electrode that has released CIO loses its conductivity and becomes an insulator. Therefore, the resistance value within the positive electrode increases rapidly, the polarization becomes weaker, and the battery voltage decreases. That is, the overdischarge region of the positive electrode active material becomes difficult to discharge, and the positive electrode active material does not transition to an irreversible structure. Therefore, if the battery of the present invention is used, the charge/discharge characteristics of the battery will not be impaired even if the battery is further discharged below the voltage that is the lower limit of reversibility.

Example Hereinafter, the present invention will be explained in detail with reference to Examples.

(Example 1) ■205 was used as the positive electrode active material. This ■20. ．． Carbon black and tetrafluoroethylene resin at a weight ratio of 100
They were mixed at a ratio of 5:1Q. 400 mg of mixture 2
This was molded and crimped onto a titanium expanded metal current collector measuring cm x 2 cTn, used as a positive electrode plate, and a titanium lead wire was spot welded. The negative electrode used was a metal lithium plate pressure-bonded to a nickel expanded metal current collector with a nickel lead attached. A metal lithium plate was also used for the reference electrode, and it was constructed in the same manner as the negative electrode. The electrolyte was a mixture of equal volumes of glopylene carbonate and methoxyethane, and LiCl was added at a rate of 1 mol/l.
O4 was dissolved and pyrrole was added thereto at a concentration of 0.05 mol/l. These were assembled into a glass cell.

To this battery, an anode current of 1 mA was applied to the positive electrode side for 30 minutes. The positive electrode voltage at this time!
The voltage was 3.8v. Analysis revealed that polypyrrole, a conductive polymer, was formed on the conductive agent carbon black. Using this battery, charging and discharging were performed at a constant current of 2 mA in a potential range of 1.6 to 3.5 V.

As a comparative example, a battery was similarly constructed and charged and discharged under the same conditions except that polypyrrole was not produced in the positive electrode.

FIG. 1 is a diagram depicting the discharge curves of the first cycle and the second cycle of the battery of the present invention. From this, it can be seen that even if the v205 positive electrode is over-discharged, there is no change in the discharge curve.

FIG. 2 is a diagram depicting the discharge curves of the first cycle and the second cycle of the battery of the comparative example. From this, if the positive electrode does not contain polypyrrole, which is a conductive polymer, the discharge will continue even if v205 becomes 2■ or less, and it will transition to an irreversible structure, so after overdischarge. It can be seen that a significant change appears in the discharge curve.

(Example 2) A test was conducted using a flat battery using MnO2 as a positive electrode active material. MnO2, carbon black, and tetrafluoroethylene resin were prepared in the same manner as in Example 1.

9 ... mixture 200 tng (theoretical capacity 53.6 mAh
) was molded and crimped into a battery case to which a titanium expanded metal current collector was spot welded. The diameter of the positive electrode plate is 1
It is 7.5M. Metallic lithium with a thickness of 0.38 M was used as the negative electrode, and was pressure-bonded to a sealing plate to which a nickel expanded metal current collector was spot-welded. The electrolyte contains
Add L I C7 at a rate of 1 mol/l to a mixture of equal volumes of glopylene carbonate and dimethoxyethane.
04 was dissolved, and 0.05 mol/l of thiophene was added to it.
The mixture was added at a ratio of . In addition, a polypropylene nonwoven fabric was used for the separator to prevent internal short circuits caused by dendrites that occur in the metal lithium electrode.

Note that a battery used as a comparative example was constructed in the same manner except that thiophene was not added to the electrolyte.

First, an anode current of 0.5 mA was applied to the positive electrode side of the battery configured in this manner until the battery voltage reached 4.5V. As a result of the analysis, it was found that polythiophenylene was formed in the carbon 0A-5 particles in the battery of the present invention, as in Example 1.

Next, using the above batteries, at a constant current of 2 mA,
Charging and discharging were performed within a voltage range of 3.8 .

FIG. 3 shows the discharge curves in the second cycle of the example of the present invention and the comparative example, where the solid line is the battery of the present invention and the broken line is the battery of the comparative example.

From this, it can be seen that the discharge curve of the battery of the comparative example was monotonically downward, lacked flatness, and was inconvenient as a battery.

FIG. 4 is a diagram plotting the discharge capacity at each cycle of the batteries of the present example (solid line) and the comparative example (broken line). From this, the battery of this example has a lower discharge capacity than the comparative example at the beginning of the number of cycles, but the discharge capacity for each cycle is almost constant, and the cycle life is long, making it a highly reliable battery. You can see that

Note that similar results were obtained using conductive polymers obtained from derivatives such as N-methylpyrrole and 3-methylthiophene in addition to pyrrole and thiophene.

Effects of the Invention As described above, according to the present invention, at high energy density,
Furthermore, a non-aqueous electrolyte secondary battery with excellent layer charge-discharge behavior without any change in the charge-discharge curve even when over-discharged is obtained.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the discharge curves of the first cycle and the second cycle in the non-aqueous electrolyte secondary battery of Example 1 of the present invention, and FIG. 2 is a diagram showing the discharge curve in each cycle of the comparative example battery. 3 is a diagram depicting the discharge curve of the second cycle in Example 2 of the present invention and the comparative example, and FIG. 4 is a diagram depicting the discharge capacity in each cycle of the battery of Example 2 and the comparative example. FIG. Name of agent: Patent attorney Toshio Nakao and 1 other person ^1
1^

Claims (1)

[Claims] The components include a positive electrode, a non-aqueous electrolyte that conducts alkali metal ions, and a negative electrode containing an alkali metal as an active material. A non-aqueous electrolyte secondary battery characterized by containing any of the above.