JPH02199769A - Battery with overcharge preventing function - Google Patents

Abstract

PURPOSE:To prevent a deterioration of the performance and the breakdown due to overcharge and achieve the prolongation of life and an improvement of the safety by disposing a separator containing a high molecular material revealing conductivity by the doping of ions between a positive electrode and a negative electrode. CONSTITUTION:In the inside of a battery case 1, a negative electrode 6 bonded to a negative terminal plate 2 through a collector 5 consisting of stainless net, a positive electrode 7 bonded to a positive terminal plate 3, and a separator 8 containing a high molecular material revealing conductivity by the doping of ions present between the both electrodes 6, 7 are mounted in the state dipped in an electrolyte. The combination of each kind of the electrode material of the both electrodes 6, 7, the high molecular material of the separator 8, and the electrolyte is selected in such a manner that the conversion voltage of the high molecular material is slightly higher than the charge terminating voltage in a secondary battery and nearly the same as the allowable voltage in a primary battery. Hence, a stable overcharge preventing function is given to the battery itself, and the prolongation of life and an improvement in safety can be achieved.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a battery that itself has an overcharge prevention function, and in particular, the present invention relates to a battery that itself has an overcharge prevention function, and in particular, a battery that has a voltage rise above the end-of-charge voltage specified when charging as a secondary battery. Useful to prevent.

[Conventional technology]

In order to properly maintain battery performance in secondary batteries, it is necessary to strictly adhere to the final voltage during charging, but during actual use, there are many opportunities for high voltage to be applied due to accidents or misuse. In addition to causing deterioration, there is a risk that the battery may be destroyed due to the gas pressure caused by excessive reaction.

Conventionally, measures to deal with such overcharging include installing safety valves and explosion-proof devices for degassing in lithium batteries, and absorbing gas generated on the positive electrode side in nickel-cadmium and lead-acid batteries on the negative electrode side. A structure that causes cyclical self-discharge is adopted (document unknown).

[Problem to be solved by the invention]

However, the above measures do not have a sufficient effect on performance deterioration due to overcharging, and all of these effects become irreversible when the current value increases, so there is a permissible limit on the degree and frequency of overcharging. In addition, adding safety valves and explosion-proof devices complicates the battery configuration and increases costs, while if the generated gas is to be absorbed on the negative electrode side, the negative electrode component must be in large excess of the positive electrode component. There was a problem that the battery became larger.

In view of the above-mentioned circumstances, this invention provides a stable overcharge prevention function to the battery itself without changing the basic structure of the battery or impairing the battery characteristics, thereby achieving long life and excellent safety. The aim is to provide batteries with improved performance.

[Means to solve the problem]

In the course of intensive studies to achieve the above object, the inventors focused on polymeric substances that can be used as electrode materials for polymer batteries. In other words, organic polymeric substances are generally nonconducting, but some polymeric substances, such as those used as electrode materials, have the property of exhibiting conductivity through ion doping, and the polymer battery described above has the property of exhibiting conductivity in this conductive region. It utilizes changes in electrode potential due to changes in doping amount.

The inventors have proposed that these polymer materials can be used as positive and negative electrodes in a battery, since the transition between an insulator and a conductor is rapid and reversible due to changes in the amount of ion doping in polymer materials. By interposing it between the two electrodes, it is possible to prevent overcharging by converting from an insulator to a conductor and causing an internal short circuit between the two electrodes when the battery voltage exceeds the allowable value during charging. They discovered this and came up with this invention.

That is, the present invention relates to a battery with an overcharge prevention function, in which a separator is interposed between a positive electrode and a negative electrode and includes a polymer substance that is in contact with these electrodes and exhibits conductivity by doping with ions.

[Structure and operation of the invention]

The above-mentioned polymeric substance contained in the separator of the battery of the present invention is characterized in that when a voltage is applied in the presence of an electrolyte that provides doping ions, the amount of ion doping increases rapidly after a certain value of this voltage. Based on this doping amount, there is a sharp transition between an insulator on the low voltage side and a conductor on the high voltage side at the voltage value. and,
This conversion voltage takes a fixed fixed value depending on the combination of the polymer substance, the positive and negative electrode materials, and the electrolyte, and can be arbitrarily set by changing this combination.

Therefore, the electrolyte used should be one that can provide doping ions to the polymeric substance as well as the original battery reaction, and the conversion voltage of the polymeric substance should be set slightly higher than the end-of-charge voltage specified for the secondary battery. As a result, when the potential difference between both electrodes during charging exceeds the above conversion voltage, the separator becomes conductive and short-circuits both electrodes, so the battery voltage does not rise above the allowable value and overcharging is avoided. Ru. When the potential difference is below the conversion voltage, the separator maintains a non-conducting state and performs its original insulating function, and there is no adverse effect on battery characteristics such as discharge characteristics.

The reason why the conversion voltage is set slightly higher than the end-of-charge voltage is to increase the insulation properties of the separator in a steady state and to minimize self-discharge through the separator.

On the other hand, reverse applied voltage exceeding the allowable value may be applied to negative batteries due to various factors such as accidents or misuse, resulting in overcharging, resulting in performance deterioration or destruction. By using a separator containing the polymer material set to a voltage, it is possible to avoid the separator becoming conductive when a high reverse voltage is applied in the same manner as described above, and the battery being overcharged.

In addition, since the change in the conducting state and non-conducting state of the separator is reversible based on the change in the amount of ion doping in the polymer material, high voltage may not be applied due to misuse, accident, etc. Even if there are many occasions, the overcharging prevention function will be exhibited without any change each time.

As the above-mentioned polymeric substance contained in such a separator, any substance can be used as long as it exhibits conductivity through ion doping. However, the ion species differ depending on the type of battery; for example, in lithium batteries, those that are doped with anions to develop conductivity are used. Specific examples include polyaniline,
Examples include polyacetylene, polyparaphenylene, polythiophene, and polypyrrole. To form a separator containing such a polymeric substance, a high-performance method such as chemical oxidation polymerization, melt dipping, coating, or powder compression is usually applied to the surface of an insulating porous substrate such as a nonwoven polypropylene fabric. The cough polymer material layer may be formed by any appropriate means depending on the type and properties of the molecular material. Note that if these polymeric substances themselves can form a porous film capable of holding an electrolyte, it is also possible to use this as it is as a separator.

FIG. 1 shows an example of the structure of a battery C with an overcharge prevention function according to the present invention applied to a button type battery.

In the figure, 1 is a battery case, in which a negative electrode terminal plate 2 and a positive electrode terminal plate 3, both of which are plate-shaped, face each other, and a ring-shaped gasket 4 made of an elastic insulating material such as synthetic rubber or synthetic resin is attached to the peripheral edges of the two. A flat airtight container is constructed by intervening and fitting and crimping. Inside this case 1, there is a negative electrode 6 connected to the negative electrode terminal plate 2 via a current collector 5 made of stainless steel net, a positive electrode 7 connected to the positive electrode terminal plate 3, and an electrode interposed between the two electrodes 6 and 7. The separator 8 containing the above-mentioned polymeric substance is loaded in a state of being immersed in an electrolytic solution.

Various electrode materials are selected and used for the negative electrode 6 and the positive electrode 7 depending on the type of battery. For example, in lithium secondary and primary batteries, lithium or a lithium alloy is generally used as the negative electrode 6, and transition metal oxide or sulfide, activated carbon fiber, conductive polymer material, etc. are used as the positive electrode 7.

The electrolytic solution used is one in which an electrolyte that causes a battery reaction and provides ions that can be doped into the polymeric substance of the separator is dissolved in a solvent. selected. For example, in a lithium battery, L 1BFa,
L i Cl0a , LiBΦ4 (Φ is a phenyl group)
A lithium ion conductive electrolytic solution prepared by dissolving a lithium salt such as , LiPF, or LiAsFa in a nonaqueous solvent such as propion carbonate, γ-butyrolactone, dimethoxyethane, or dioxolane is suitable. Moreover, instead of such an electrolytic solution, a solid electrolyte that can provide similar doping ions can also be used.

The combinations of the electrode materials of the bipolar electrodes 6.7 and the polymer substances and electrolytes of the separator 8 as described above are as follows:
The conversion voltage of the polymer material is selected so that it is slightly higher than the end-of-charge voltage for secondary batteries, and approximately equal to the allowable voltage for secondary batteries.

Note that the battery with an overcharge prevention function of the present invention is not limited to the button type battery as illustrated in FIG. 1, but can be formed into various external shapes, structures, and sizes.

〔Effect of the invention〕

According to this invention, since a separator that is interposed in contact between the positive electrode and the negative electrode contains a polymeric substance that exhibits conductivity through ion doping, the potential difference between the two electrodes is greater than a permissible value. It has an overcharge prevention function that prevents the battery voltage from rising above the specified value due to an internal short circuit between the two electrodes. It is possible to provide a highly safe battery with a long life and no performance deterioration or destruction. Moreover, this overcharge prevention function is based on the reversible change in the amount of ion doping due to the voltage of the polymer material (
Therefore, when the potential difference between the two electrodes becomes less than the conversion voltage, the separator returns to its original non-conducting state and does not cause internal discharge, and there is almost no functional deterioration due to repeated conversion or functional deterioration over time, and it can be used for a long period of time. Reliable overcharging prevention function is demonstrated throughout the battery life.

In addition, the battery of this invention has no difference in basic configuration and structure from existing batteries, except for the use of a separator containing the above-mentioned polymer substance to provide an overcharge prevention function, so it can be easily assembled and manufactured. There is no need to modify conventional processes, parts used, equipment used, etc., and therefore it has the advantage of being able to be manufactured at low cost.

〔Example〕

Examples of the present invention will be described in detail below.

Example negative electrode: Lithium foil with a thickness of 0.24 m and a thickness of 0°30
Diameter 7゜75sn made by crimping with Tsuru's aluminum foil
37cm TiS as the negative electrode, a compact formed by pressure molding the powder into a disc shape with a diameter of 7.75fi, and as the separator polyaniline was applied to the fiber surface of a polypropylene nonwoven fabric using a chemical oxidation polymerization method on the entire separator. A sheet with a diameter of 9 squares and a thickness of 0.3 squares was deposited so as to account for 5% by weight of the electrolyte, and a 1 molar concentration of Li (:l!O,
A button-type lithium battery having a diameter of 11.5 mm and a total thickness of 2.0 cm was fabricated using each of propylene carbonate containing the following.

When this battery was charged with a constant current of 1 mA, it was confirmed that the battery voltage did not rise above 2.7V. From this result, in the battery of the above example, when the potential difference between the two electrodes becomes 2.7 μm, the polyaniline in the separator converts from an insulator to a conductor, and the separator becomes electrically conductive, causing the internal space between the two electrodes to become conductive. It can be seen that a short circuit occurs. Also,
After this charging, the battery voltage drops to 2.5V relatively quickly, but it was also found that at this 2.5V, the separator becomes an insulator and self-discharge becomes extremely small.

By the way, Li-A1 alloy is generally used for the negative electrode, and Ti is used for the positive electrode.
A battery using Sz has a power rating of 1.5 to 2. It is said that it can be used as a secondary battery in the voltage range of 1 V, and in this case, it is preferable to set the end-of-charge voltage to about 2.7 V.

Therefore, the battery of the above embodiment is most suitable as the above-mentioned secondary battery with an overcharge prevention function.

Comparative Example A lithium battery was produced in the same manner as in the example except that a sheet of polypropylene nonwoven fabric not coated with polyaniline was used as a separator. When this battery was charged with a constant current of 1 mA as in the example, the battery voltage rose to 4.2 V, and it was found that if maintained in this state, performance would deteriorate in a short period of time due to decomposition of the electrolyte. did.

Next, the batteries of the above example and comparative example were connected to a constant voltage power supply of 3 cm through a resistor of IKΩ, respectively.
After 3 hours of constant voltage charging, 0.5 mA, 2
When the end-of-discharge voltage was measured for each cycle in which a constant amount of electricity of 1 mAh was taken out during discharge for an hour, the results shown in FIG. 2 were obtained. From this result, it can be seen that in the battery of the comparative example with the conventional configuration, a large voltage drop occurs almost in proportion to the increase in the number of charge/discharge cycles, whereas in the battery of the example according to the present invention, the voltage decreases due to the increase in the number of charge/discharge cycles. It can be seen that the battery has an extremely long life as a secondary battery with almost no lag.

In addition, for the batteries of the above examples and comparative examples, IKΩ
After performing a floating test at various voltages through the resistor, the discharge capacity was measured at 0.5 mA with a final voltage of 1.5V, and the results shown in the table below were obtained.

Discharge capacity after floating (mAh) > A vertical cross-sectional view showing a structural example, and FIG. 2 is a chart of charge-discharge cycle characteristics of each battery of an example of the present invention and a comparative example.

C... Battery, 6... Negative electrode, 7... Positive electrode, 8...
Sebaleta

Claims (1)

[Claims] (1) A battery with an overcharge prevention function, in which a separator is interposed between a positive electrode and a negative electrode and includes a polymer substance that is in contact with these electrodes and exhibits conductivity through ion doping.