JPH0415585B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an improvement in the manufacturing method of an organic electrolyte battery using lithium as a negative electrode active material and manganese dioxide as a positive electrode active material, and aims to provide an organic electrolyte battery with low internal resistance and good storage performance. . In organic electrolyte batteries that use lithium as the negative electrode active material and an organic electrolyte in which solutes such as perchlorate and borofluoride salts are dissolved in various organic solvents, lithium is used as the positive electrode active material during storage. Manganese dioxide, which has low dissolution and high monopolar potential, is preferably used, but organic electrolyte batteries using this manganese dioxide as a positive electrode active material have a problem in that internal resistance increases during storage. Therefore, the inventors of the present invention conducted various studies to investigate the cause, and found that the increase in internal resistance during storage is due to the high potential part of manganese dioxide that appears at the beginning of discharge oxidizing the electrolyte. It turned out to be triggered. Therefore, the present inventors have conducted extensive research to eliminate such high potential parts of manganese dioxide, and
When predischarging at a constant current of 10 to 25 mA/cm ² after battery assembly, the high potential part of the manganese dioxide is erased, suppressing the increase in internal resistance during storage, and also removing the oxide film on the lithium surface. Been,
It was discovered that an organic electrolyte battery with low internal resistance and good storage performance could be obtained, and a patent application (Japanese Patent Application No. 167759, 1983) was filed for this, but as a result of further research, it was found that an organic electrolyte battery with low internal resistance and good storage performance could be obtained. When pre-discharging is performed by superimposing an alternating current with a larger amplitude than the constant current value, the above effect is achieved with a smaller current and with a smaller amount of pre-discharge electricity than when pre-discharging with only direct current. In addition, the inventors have discovered that heavy load discharge performance is also improved, leading to the completion of the present invention. That is, in manufacturing an organic electrolyte battery in which lithium is used as a negative electrode active material and manganese dioxide is used as a positive electrode active material, the present invention provides 5 to 5 steps after battery assembly.
The present invention relates to a method for producing an organic electrolyte battery, characterized in that preliminary discharge is carried out by superimposing an alternating current having an amplitude larger than the constant current value on a direct current constant current of 25 mA/cm ² . By superimposing an alternating current with a larger amplitude than the constant current value on a constant DC current, the internal resistance is small and the storage performance is reduced with a smaller current and a smaller amount of discharged electricity than when pre-discharging with only a constant DC current. The reason why an organic electrolyte battery with good performance can be obtained is not entirely clear at present, but since the current is periodically strengthened and weakened by superimposing alternating current, the oxide film on the lithium surface can be easily removed, and the manganese dioxide This is thought to be due to the reduction occurring deep within the powder. It is thought that the reason why the heavy load discharge performance is improved is that lithium is deposited at the current reversal part, that is, the part where the current becomes negative, and the surface becomes dendrite-like and the reaction area increases. The frequency of the superimposed alternating current varies depending on the size and shape of the battery, the composition of the positive electrode, the type of electrolyte, etc., but is preferably in the range of 0.5 to 100 Hz. Furthermore, if the amplitude of the superimposed alternating current is too large, the electrodeposited lithium will fall off, which will reduce the reaction area and lower the closed circuit voltage, so it must be larger than the constant DC current value and less than 2.5 times the constant DC current value. is preferred. In the present invention, the range of DC constant current is 5 to 5.
The reason why the DC current is set at 25 mA/cm ² is because if the DC current is larger than the above range, side reactions such as oxidation of the electrolyte will occur in addition to the battery reaction, and if it is smaller than the above range, it will be difficult to remove the oxide film on the lithium surface. It is not done from all over the surface, but only partially,
This is because although the open circuit voltage decreases, the internal resistance does not become sufficiently small due to the remaining oxide film. In the present invention, the constant current value of 5 to 25 mA/cm ² is based on the area of the negative electrode lithium facing the positive electrode side. In the present invention, the pre-discharge electricity amount is equal to the positive electrode capacity.
It is preferably 1.5 to 5%. This is because pre-discharging to this extent can sufficiently erase the high potential portion of manganese dioxide and sufficiently prevent oxidation of the electrolyte, and this pre-discharging can also allow the battery to maintain a practically acceptable discharge capacity. It is from.
That is, according to the research of the present inventors, the lower limit of the potential at which manganese dioxide oxidizes the electrolyte is around 3.08V, and if the amount of pre-discharge electricity is less than the above range, the voltage will not drop to around 3.08V. Therefore, there is a risk that the electrolytic solution will be oxidized, and if the amount of electricity for preliminary discharge exceeds the above range, the loss of discharge capacity will increase. In the present invention, the electrolytic solution includes, for example, a solvent such as propylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,2-dimethoxyethane, dioxolane, etc. alone or a mixture of two or more thereof, and an electrolyte such as lithium perchlorate or lithium borofluoride. A dissolved solution is used. Next, the present invention will be explained with reference to Examples. Mixture 290 consisting of 100 parts of manganese dioxide (parts by weight, the same applies hereinafter), 10 parts of phosphorous graphite, and 2 parts of polytetrafluoroethylene, heat-treated at 400°C for 4 hours.
After filling mg into a mold and preforming at 1t/ ^cm2 ,
placing a stainless steel mesh on the preform;
Pressure molded at 7t/cm ² to a diameter of 16mm and thickness of 0.5mm, and use this as the positive electrode. The above positive electrode, a negative electrode made of a lithium plate with a diameter of 14 mm and a thickness of 0.2 mm, and 0.5 mole of lithium perchlorate were dissolved in a mixed solvent of propylene carbonate and 1,2-dimethoxyethane in a volume ratio of 1:1. using an electrolyte with a diameter of 20 mm using the configuration shown in Figure 1.
A flat organic electrolyte battery with a diameter of 1.6 mm and a thickness of 1.6 mm was assembled using a conventional method. In addition, in FIG. 1, 1 is the above-mentioned positive electrode, 2 is a stainless steel mesh, and 3 is a stainless steel positive electrode can. 4 is a separator made of polypropylene nonwoven fabric, and 5 is a negative electrode can made of stainless steel. 6 is a stainless steel mesh spot welded to the inner surface of the negative electrode can 5; 7 is the negative electrode, which is crimped to the mesh 6; 8 is an annular gasket made of polypropylene. The battery assembled as described above is pre-discharged to 3.5% of the positive electrode capacity by superimposing an alternating current of 1.5 times the amplitude at a frequency of 5 Hz on the constant DC current shown in Table 1 using a galvanostat and a function generator. The internal resistance (internal resistance at 20°C, hereinafter the same) of the battery initially after discharge and after storage at 60°C for a predetermined period was measured. The results are shown in Table 1. For comparison, Table 1 also shows the results obtained when preliminary discharge was performed using the method of the prior application, that is, using only a constant DC current.

[Table] As shown in Table 1, when alternating current is superimposed, the internal resistance is small when the direct current is in the range of 5 to 25 mA/cm ² , and the increase in internal resistance due to storage is small.
Note that the earlier application method, which pre-discharges only with direct current, also exhibits good effects, but in the earlier application method, the internal resistance is small in the range of 10 to 25 mA/cm ² , and the increase in internal resistance due to storage is small, so it is good. The lower limit of the current value that exhibits this effect is slightly higher than that of the method of the present invention. Next, the organic electrolyte battery assembled in the same manner as above was subjected to a constant DC current of 17 mA/cm ² with an amplitude of 5 Hz.
A 1.5 times as much alternating current was superimposed to pre-discharge the amount of electricity shown in Table 2. Table 2 shows the results of measuring the internal resistance of the battery initially after preliminary discharge and after storage at 60° C. for a predetermined period. Note that the pre-discharged electricity amount in Table 2 is indicated by the percentage of the positive electrode capacity that the discharged electricity amount corresponds to. For comparison, Table 2 also shows the results obtained when preliminary discharge was performed using only a constant DC current of 17 mA/cm ² according to the method of the prior application.

[Table] As shown in Table 2, when alternating current is superimposed, if the positive electrode capacity is pre-discharged by 1.5% or more, the internal resistance will be small and the increase in internal resistance due to storage will be sufficiently small. Note that the first application method also exhibits a good effect, but in the case of the first application method, the increase in internal resistance is particularly small when the amount of pre-discharge electricity is 2% or more, and the lower limit of the amount of pre-discharge electricity that exhibits a good effect. is slightly higher than that of the method of the present invention. Next, the organic electrolyte battery assembled in the same manner as above was subjected to a constant DC current of 17 mA/cm ² at a frequency of 5 Hz.
The positive electrode capacity is calculated by superimposing alternating current with the amplitude shown in the table.
3.5% pre-discharge. -10℃, load at 80% discharge of battery after pre-discharge
The closed circuit voltage was measured after discharging at 300Ω for 5 seconds. The results are shown in Table 3. For comparison, Table 3 also shows the results obtained when preliminary discharge was performed using only a constant DC current of 17 mA/cm ² according to the method of the prior application.

【table】

【table】 [Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the organic electrolyte battery of the present invention. 1...Positive electrode, 7...Negative electrode.

Claims (1)

[Scope of Claims] 1. Lithium is used as a negative electrode active material and manganese dioxide is used as a positive electrode active material, and after battery assembly, an alternating current with an amplitude larger than the constant current value is applied to a constant current of 5 to 25 mA/cm ² . A method for manufacturing an organic electrolyte battery characterized by superimposed preliminary discharge. 2. The method for manufacturing an organic electrolyte battery according to claim 1, wherein the pre-discharge amount of electricity is 1.5 to 5% of the positive electrode capacity.