JPS63105478A - Secondary battery - Google Patents

Abstract

PURPOSE:To improve cycle characteristic by using an organic solvent, a mixture of propylene carbonate and 1, 2 diethoxyethane, as a solvent for electrolyte. CONSTITUTION:An organic solvent mode of propylene carbonate mixed with 1, 2 dithozyethane in volume proportion of 1/9-4 is used as an electrolyte solvent for a secondary battery. In this case, a solvation of anion and 1, 2 diethoxyethane tends to become disconnected due to interaction between the 1, 2 diethoxyethane and a conductive polymer. This tendency becomes particularly conspicuous when what is easily be doped like poly aniline and poly pyrrole composed of 6-ring or 5-ring macro molecules including a nitrogen atoms is used as the conductive polymer. By this method, decomposition of an electrolyte, a dopant, or the conductive polymer, is inhibited, which results in the improved charge and discharge characteristic, and cycle characteristic, of a battery.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a secondary battery using a conductive polymer as an electrode.

<Prior Art> In recent years, secondary batteries using conductive polymers as electrodes have been proposed, as seen in, for example, Japanese Patent Application Laid-Open No. 56-136469.

The conductive polymer used for the electrodes of this secondary battery usually has a slight conductivity, but it can be doped with various dopants, and the conductivity can be dramatically increased by doping. do. And CJ20
Conductive polymers doped with anions such as 4- and BF4- are used as positive electrode materials, and conductive polymers doped with cations such as Ll and Na are used as negative electrode materials. A battery that can be charged and discharged is constructed by making the process reversible.

Such conductive polymers are generally made by chemical polymerization using an oxidizing agent or electrolytic polymerization, and conventionally known examples include polyacetylene, polypyrrole, polythiophene, polyaniline, and polyparaphenylene. If this polymer is obtained in powder form, it is pressure-molded into a shape that corresponds to the shape of the electrode, and if it is in film form, it is directly applied to the electrode dimensions, or it is pulverized to form a powder. It is used. Batteries using these conductive polymers are expected to be lightweight, have high energy density, and are non-polluting. In particular, the above-mentioned polypyrrole and polyaniline have good properties, and secondary batteries using these are considered promising as practical batteries.

The electrolyte for this type of secondary battery is usually the same as that used in existing non-aqueous batteries such as lithium batteries.
A solution prepared by dissolving an alkali metal salt such as a lithium salt such as lithium perchlorate LiCβ04 in an aprotic solvent such as propylene carbonate is used.

<Problems to be Solved by the Invention> However, secondary batteries using these conductive polymers as electrodes generally have a considerably higher electrode potential than existing non-aqueous batteries, making it difficult to use the conventional electrolyte described above. If a battery is configured using these materials, the battery voltage will become too high as charging progresses, and as a result, not only will the battery can and current collector be susceptible to corrosion, but also the electrolyte, dopant, and even conductive There are problems such as side reactions such as decomposition of the polymer, resulting in decreased charge/discharge efficiency, deterioration of storage characteristics, and shortened cycle life.

<Means for Solving the Problems> The present inventor conducted research to improve the charging/discharging characteristics and cycle characteristics of this type of secondary battery by improving the composition of the electrolyte used in this type of secondary battery. However, I learned that the desired purpose could be achieved by using the following methods.

That is, the secondary battery of the present invention is a secondary battery that uses a conductive polymer as at least one electrode, and uses an organic solvent prepared by mixing propylene carbonate and 1,2 diethoxyethane as a solvent for the electrolytic solution. The gist is that it was used.

<Function> By configuring a battery using a mixed solution of propylene carbonate and 1,2 diethoxyethane as an electrolyte solvent as described above, the rise in voltage during charging can be suppressed to a low level, and as a result, , prevents corrosion of battery cans and current collectors,
Furthermore, decomposition of the electrolyte, dopant, or conductive polymer is suppressed, and the charge/discharge characteristics and cycle characteristics of the battery are improved.

The reason why the properties are improved when propylene carbonate is mixed with 1,2-diethoxyethane is considered to be due to the following reason. In other words, for example, anions used as dopants in this type of battery exist as solvates with the solvent in which they are dissolved in an undoped state, but when a doping reaction occurs, this solvation is removed and the anions are dissolved. itself doped into the conductive polymer. At this time, the ease of desolvation and the ease of doping are greatly influenced by the interaction between the solvent in which the anion is solvated and the conductive polymer to which the anion is doped.

When an organic solvent containing 1,2 diethoxyethane is used as an electrolyte solvent as described above, anion and 1,
It is thought that the solvation with 2-diethoxyethane becomes easier to release due to the interaction between 1.2-diethoxyethane and the conductive polymer.

This tendency is particularly noticeable when a conductive polymer such as polyaniline or polypyrrole, which is composed of a six-membered ring or a five-membered ring polymer containing a nitrogen atom and is very easily doped, is used.

On the other hand, the structural formula of 1,2 diethoxyethane is and, for example, the structural formula of polypyrrole is. Therefore, in an electrode made of polypyrrole, the oxygen atom of 1,2 diethoxyethane approaches the carbon atoms at the 2nd and 5th positions of the polypyrrole unit, and this oxygen atom approaches the above carbon atoms of the polypyrrole along the polypyrrole chain. It is thought that a reaction may occur in which the oxygen atom of 1,2-diethoxyethane approaches the nitrogen atom of polypyrrole and the oxygen atom coordinates with the nitrogen atom of polypyrrole along the polypyrrole chain. It will be done.

On the other hand, the structural formula of polyaniline is 1.2 in an electrode using this polyaniline.
There is a possibility that a reaction occurs in which the oxygen atom of diethoxyethane approaches the carbon atoms at the 1st and 4th positions of the polyaniline unit, and this oxygen atom coordinates with the above carbon atoms of the polyaniline along the polyaniline chain. is possible.

By coordinating 1.2 diethoxyethane to a part of the conductive polymer in this way, the above-mentioned desorption from the solvation of the anion becomes smoother, and the doping of the anion into the conductive polymer becomes easier. It is conceivable that this will occur more easily.

As described above, according to the present invention, anion doping, which is a charging reaction of the battery, occurs very easily, so that an increase in charging voltage during charging is suppressed.

<Example> Pyrrole was assembled by electrolytic polymerization, and 1q of film-like polypyrrole was peeled off from the electrode and crushed to obtain polypyrrole powder. This polypyrrole powder was pressure-molded into a disk shape and used as a positive electrode. did. This positive electrode was combined with a disk-shaped lithium foil as a negative electrode. The electrolyte contains propylene carbonate (PC) and 1
, 2 diethoxyethane (1,2-DEE) at a volume ratio (
PC: 1.2-DEE), respectively 90:10 (Battery A>, 50:50 (Battery B), 20:80 (Battery C)
), add 1 liter of lithium perchlorate to an organic solvent mixed at a ratio of
Using a solution containing M, a battery A having the structure shown in FIG.
-C were produced respectively. In the figure, 1 is a positive electrode, 2 is a negative electrode, 3 is a separator, 4 is a positive electrode can, 5 is a negative electrode can, 6 is a positive electrode current collector, 7 is a negative electrode current collector, and 8 is an insulating gasket. In addition, a battery solution was prepared in the same manner except that a solution of 1M lithium perchlorate dissolved in an organic solvent consisting only of propylene carbonate was used as the electrolyte, and an organic solvent consisting only of 1,2 diethoxyethane was used as the electrolyte. Battery E was prepared in the same manner except that a solution containing 1M lithium perchlorate was used.

These batteries A-E were charged for 10 hours at a current of 1 mA, and the battery voltage was 2.5 at a current of 1 mA.
A charge/discharge cycle of discharging until the voltage reached V was repeated, and the cycle change in charge/discharge efficiency (%) of each battery was examined. Figure 2 shows the results. From FIG. 2, a battery A of the present invention using a mixture of propylene carbonate and 1,2 diethoxyethane as the electrolyte solvent is shown.
-C shows a very slight decrease in charge/discharge efficiency, showing a high rate of 95% or more even after the 150th cycle, and has good cycle characteristics. On the other hand, batteries using propylene carbonate or 1.2 diethoxyethane alone.

Battery E had poor cycle characteristics, and when the cycle life was defined as the time when the charge/discharge efficiency became 50% or less, the cycle life was 100 cycles and 120 cycles, respectively.

The characteristics of Batteries A-C are good because these batteries have a slow voltage rise during charging and a low end-of-charge voltage.
This is thought to be due to the fact that side reactions such as corrosion of the battery can and current collector or decomposition of the electrolyte, dopant, and polypyrrole of the positive electrode are less likely to occur. On the other hand, with battery E, the voltage rise during charging is large, so the side reactions mentioned above occur significantly, and as a result, as the charge/discharge cycle progresses, the charge/discharge efficiency rapidly decreases and the cycle characteristics deteriorate. It seems to have deteriorated. In addition, in the solvent of the electrolytic solution used in the present invention, the volume ratio of 1,2 diethoxyethane to propylene carbonate is 1/9 to 4.
It is preferable to mix at a ratio of .

Figure 3 shows battery A- during the 100th charge/discharge cycle.
Table 1 shows the changes over time in the battery voltage (V) of E.
The battery voltage (V) at the end of charging at the 0th cycle and the 100th cycle is shown.

From the above results, in batteries A to C of the present invention, the increase in battery voltage during charging is suppressed to a small extent, and the end-of-charge voltage is low not only at the beginning of the cycle but also at the time when the cycle progresses. Furthermore, it can be seen that the voltage drop during discharging is small and the charging/discharging efficiency is high.

The above examples are examples in which polypyrrole is used as the conductive polymer, lithium is used as the negative electrode, and lithium perchlorate is used as the electrolyte solute, but other conductive polymers such as polyaniline, polythiophene, or polyacetylene may be used as the positive electrode. Other lithium alloys such as lithium-aluminum alloys and lithium-boron alloys, light metals such as sodium and potassium, or alloys thereof may be used for the negative electrode, or L! BF4, L! PF6, L! ASF6, L! C.F.
3303, L! Of course, similar effects can be obtained when a lithium salt such as 2B1 (>Ci2.10) is used as the solute.

Additionally, although the above is an example in which the conductive polymer of the present invention is used only in the positive electrode, it is needless to say that similar results can be obtained when the conductive polymer of the present invention is used in the negative electrode or positive and negative electrodes. do not.

<Effects of the Invention> As detailed above, according to the secondary battery of the present invention, the rise in battery voltage during charging can be suppressed to a low level, so corrosion of the battery can and current collector can be prevented, and electrolytic The decomposition of the liquid, dopant, and conductive polymer is suppressed, and as a result, the charge/discharge efficiency is increased, and the cycle characteristics can be improved. .

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the structure of the battery of the example, Figure 2
The figure is a graph showing the cycle characteristics of the battery of the example, and FIG. 3 is a graph showing the change in battery voltage over time during the 100th charge/discharge cycle of the battery of the example. 1...Positive electrode, 2...Negative electrode, 3...Separator. Figure 1 Figure 2 Plui ri/shi ft (concave) Figure 3 Charging/discharging time (Sunny weather) Procedures Neho Seigen (Voluntary Submission) January 26, 1985

Claims (1)

[Claims] 1. A secondary battery using a conductive polymer as at least one electrode, which uses an organic solvent made of a mixture of propylene carbonate and 1,2-diethoxyethane as a solvent for the electrolyte. A secondary battery characterized by: 2. The secondary battery according to claim 1, wherein 1,2 diethoxyethane is mixed with propylene carbonate at a volume ratio of 1/9 to 4. 3. The secondary battery according to claim 1 or 2, wherein the conductive polymer is polypyrrole or polyaniline.