JPH02216771A - Method of manufacturing a rechargeable electrochemical device - Google Patents

Abstract

PURPOSE:To manufacture an even Li alloy for negative electrode easily and to improve the preservative property in a high temperature ambiance by carrying out a transformation discharge at a temperature scope 40-70 deg.C after assembling the device. CONSTITUTION:This dischargeable electrochemical device consists of a case 1 being a positive electrode terminal concurrently, a sealing plate 2 being a negative electrode terminal, a gasket 3 made of propylene, a positive electrode 4, a positive electrode collector 5, a separator 6, a negative electrode 7, a nickel net 8, a negative electrode Li 9, and an electrolyte made by solving lithium borofluoride in a mixture solvent of the same volumes of propylene carbonate and gamma-butyrolactone at the ratio 1mol per l. The positive electrode 4 is formed by mixing and kneading 40 wt.pt. of active carbon particles, 10 wt.pt. of acetylene black, and 20 wt.pt. of solid component of the water dispersion of a fluorine resin, and transferring to a titanium plate after making in a sheet form by passing through two rolls. After the device is assembled, a transformation discharge is carried out at the temperature scope 40-70 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a rechargeable electrochemical device used as a mobile DC power source, a backup power source, or the like.

BACKGROUND ART As a rechargeable electrochemical device, a device is known that uses activated carbon mainly using an electric double layer as a positive electrode, a lithium alloy as a negative electrode, and a non-aqueous organic solvent as an electrolyte. The method for preparing the lithium alloy used for the negative electrode of this device is (
1) Metal and lithium are melted and alloyed in an inert atmosphere. (2) Perform electrochemical reduction in an organic electrolyte to occlude lithium in the metal. (3) After the metal and lithium sheet are brought into close contact.

It constitutes an electrochemical device in which lithium is naturally absorbed into metal. Of these (1).

Although method (2) allows the preparation of a uniform alloy of metal and lithium, method (3) is mainly adopted because it has drawbacks such as increased man-hours and higher cost.

Problems to be Solved by the Invention However, while method 3) has many advantages in terms of process, such as ease of production, it has the following disadvantages. The negative electrode is a sheet of lithium crimped onto one side of the metal, so after the device is assembled, a large amount of lithium is naturally absorbed into the metal from one side of the metal and alloying progresses. Curving may occur, and lithium may be unevenly distributed in the alloy, making it impossible to produce a uniform negative electrode alloy. Furthermore, negative ff1l
c If a large amount of lithium is present, there is a possibility that lithium and the electrolyte will react and form an insulating film on the lithium surface. These results have caused problems such as variations in internal resistance or an abnormal increase in internal resistance during high-temperature storage. As a solution to this problem, the amount of lithium is reduced because the above-mentioned problem hardly occurs if the amount of lithium is small. Alternatively, attempts were made to prevent lithium from being suddenly absorbed into the metal by crimping a very thin metal lithium sheet to the entire surface of the metal, and to obtain a uniform lithium alloy, but if the amount of lithium was reduced, the capacity decreases. Another drawback is that thin metal sheets are extremely difficult to handle during the process, so they have not been a concrete solution.

The present invention aims to solve the above-mentioned conventional problems, easily produce a uniform lithium alloy for negative electrodes, and improve storage performance in a high-temperature atmosphere.

Means for Solving the Problems In order to solve the above-mentioned problems, 5 the present invention brings a metal and a lithium sheet into close contact with each other by pressure bonding, etc., configures an electrochemical device using this as a negative electrode, and after assembling the device, the electrochemical device is heated at 40°C to 70°C. C
Chemical discharge is performed in an atmosphere at a temperature of .

Function: According to this manufacturing method, after assembling the device, a portion of the lithium that has been brought into close contact with the metal is discharged in an atmosphere at a high temperature, for example, 400 to 70°C, so that a portion of the lithium is transferred to the positive electrode side. The amount of lithium on the negative electrode side is reduced, and a large amount of lithium is not suddenly added.

Therefore, it is possible to prevent the formation of a non-uniform lithium alloy in which lithium is unevenly distributed or the alloy to be curved during alloying. This seems to be because the reaction is activated at high temperatures and the entire electrode plate reacts uniformly. As a result, variations in internal resistance are reduced, and the alloy is prevented from bending, resulting in better contact between each component within the device.
Increase in internal resistance due to high temperature storage can be suppressed. In addition, since the amount of lithium present in the negative electrode in the discharged state is very small,
It is possible to significantly suppress the increase in internal resistance in high temperature and high humidity environments, which is thought to be caused by deterioration of lithium in the negative electrode due to moisture.

The metal alloyed with lithium is preferably lead, cadmium, tin, bismuth, etc. alone, or an alloy of two or more of these. Of course, metals other than those mentioned above may also be used as long as they can be alloyed with lithium.

Further, the above-mentioned discharge is effective whether it is a constant current discharge or a constant resistance discharge. Furthermore, regarding the temperature atmosphere, the higher the temperature, the more effective the effect will be, but if the temperature exceeds aOC, the temperature approaches the boiling point of the electrolyte, and there is a risk that the electrolyte will decompose.

Therefore, the temperature should be kept within 70C.

EXAMPLE Hereinafter, an example of the present invention will be explained using FIGS. 1 and 2.

FIG. 1 shows a rechargeable electrochemical device using activated carbon as a positive electrode and a lithium alloy as a negative electrode. In the figure, 1 is a case that also serves as a positive electrode terminal, 2 is a sealing plate that is punched out of the same material as the case and serves as a negative electrode terminal, 3 is a polypropylene gasket that insulates the case and the sealing plate, and 4 is a positive electrode. 7 parts by weight of activated carbon powder bed, 10 parts by weight of acetylene black as a conductive material, and 20 parts by weight of aqueous dispersion type (solid content ratio 60%) of fluororesin as a binder were kneaded in two parts. After forming it into a sheet by passing it between rolls, it was transferred to a titanium lath plate having a thickness of 0.4 o+m and forming the positive electrode current collector 5. After drying for 12 hours under reduced pressure at 160℃, the thickness was adjusted to Q, 8au++, and the diameter was 15mm.
A pellet was punched out, a part of the mixture was peeled off, and the current collector 5 was welded to the case 1.

6 is a separator made of polypropylene fabric. γ is a negative electrode, which is an alloy with lithium storage capacity, made by melting and alloying 50 parts by weight of lead and 60 parts by weight of cadmium in an argon atmosphere, rolling it to a thickness of 0jfffffl, transferring it to a nickel net 8, and then rolling it to a diameter of 15+ nm. Punch it out and weld it to the back of the sealing plate 2.

9 is negative electrode lithium, thickness 0.1 mff + diameter IQff1
It is made of a metal lithium sheet having a thickness of m and is pressure-bonded to one side of the negative electrode alloy 7. The electrolytic solution used is one in which lithium fluoroborate is dissolved in an equivolumic mixed solvent of propylene carbonate and γ-butyrolactone at a ratio of 1 mo/L/111.

Figure 1 is a cross-sectional view of the device immediately after it is assembled using the above parts, and the size of the device is 2offIm in diameter and 2m in thickness.
mm and the capacity is 1 mm h per 1 volt.

Next, immediately after assembling this device, chemical discharge was performed in an atmosphere at each temperature for 20 minutes at a constant current of smm. These electrochemical devices are referred to as Mu-1 to Mu-7, and after being stored for one month at a temperature of 60°C and a relative humidity of 90% after assembly, AC wave 1
The internal resistance at KHz was measured. The results are shown in FIG. Note that Mu-1 is a conventional example at a normal temperature of 20°C.

The result is that as the ambient temperature increases, the internal resistance decreases.
It is stabilizing. However, when it reaches 80C, it increases, but this is presumed to be due to fluctuations due to the high temperature of the electrolyte. From these things, the chemical discharge temperature is 40
It can be said that the range of C to 70C is preferable.

Effects of the Invention As described above, according to the present invention, it is possible to provide a stable chargeable electrochemical device with low internal resistance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a rechargeable electrochemical device according to the present invention, and FIG. 2 is a diagram showing changes in internal resistance due to chemical discharge under various temperature atmospheres. 1... Case, 2... Sealing plate, 4...
...Positive electrode, 7...Negative electrode, 9...Lithium.

Claims (1)

[Claims] An electrochemical device consisting of a positive electrode made of activated carbon, a negative electrode made of a lithium alloy, and an electrolytic solution made of a non-aqueous solvent in which lithium salt is dissolved.
A method for manufacturing a rechargeable electrochemical device, characterized in that chemical discharge is performed in a temperature range of 70° C. or less.