JPH02199778A - Overcharge preventing element - Google Patents

Abstract

PURPOSE:To prevent the overcharge of a battery by forming one of a pair of facing electrodes by a high molecular material revealing conductivity by the doping of ions, and making the both electrodes into the electrically connected state. CONSTITUTION:A base electrode 6 bonded to a base electrode terminal plate 2 through a collector 5 consisting of stainless net, a counter electrode 7 consisting of a high molecular material revealing conductivity by the doping of ions which electrode is bonded to a counter electrode terminal plate 3, and a conductive separator provided between the both electrodes 6, 7 are mounted in the state dipped in an electrolyte in the inside of a case 1 of an overcharge preventing element D. Thus, by connecting the overcharge preventing element D in parallel to a battery, the voltage increase exceeding a charge terminating voltage regulated at the time of charging can be prevented in a secondary battery, and also the overcharge state by a reverse applied voltage exceeding an allowable value is prevented in a primary battery. Hence, the performance deterioration and battery breakdown accompanied by overcharge can be prevented without changing the constitution and structure of the battery itself.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is useful for maintaining the end-of-charge voltage of a secondary battery at a specified value, an element connected in parallel to a battery to prevent overcharging of the battery, and particularly for maintaining the end-of-charge voltage of a secondary battery at a specified value. The present invention relates to an overcharge prevention element.

[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 of battery destruction due to the gas pressure generated due to 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 since all of these effects are irreversible, there are limits to the degree and frequency of overcharging, and there are limits to the degree and frequency of overcharging. Attaching a battery or an explosion-proof device will complicate the battery configuration and increase costs. On the other hand, if the generated gas is absorbed on the negative electrode side, the negative electrode component must be in large excess of the positive electrode component, making the battery larger. There was a problem.

In view of the above-mentioned circumstances, it is an object of the present invention to provide an overcharge prevention element that can reliably prevent performance deterioration of a battery due to overcharging and does not impose any structural or structural restrictions on the battery itself.

[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 found that the transition between an insulator and a conductor occurs rapidly and reversibly due to changes in the amount of ion doping in such polymeric materials, and by applying this property, the above voltage value can be adjusted. It is possible to construct an independent element that opens and closes the circuit as a boundary, and when this element is connected in parallel with a battery, when a voltage exceeding the allowable value is applied to the battery, the element itself switches to a conductive state, thereby preventing overcharging of the battery. The inventors have discovered that this can be prevented, and have come up with this invention.

That is, the present invention is characterized in that one of a pair of electrodes arranged opposite to each other with an electrolyte interposed therebetween is made of a polymer material that exhibits conductivity by doping with ions, and the two electrodes are electrically connected. The present invention relates to an overcharge prevention element.

[Structure and operation of the invention]

In the overcharge prevention element of the present invention, the above-mentioned polymeric substance constituting one electrode sharply switches from one of an insulator and a conductor to the other after a certain voltage value, so that the potential difference between the two electrodes is as described above. It becomes conductive when the voltage is greater than the voltage value, and becomes non-conductive when it is smaller than the voltage value. When incorporated into an electric circuit, it exhibits a sensitive switching action that opens and closes the circuit at the voltage value. The voltage that causes the above conversion takes a specific fixed value depending on the combination of the type of polymer substance, the constituent material of the other electrode, and the electrolyte that provides doping ions, and can be arbitrarily set by changing this combination.

Therefore, if the conversion voltage of this element is set to almost match the end-of-charge voltage specified for the secondary battery, and the secondary battery is charged with this element connected in parallel, the voltage applied to the battery will be reduced. When the voltage becomes higher than the end-of-charge voltage, the element switches to a conductive state and functions as an overcharge prevention element that prevents the battery voltage from rising above the allowable value.

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 connecting overcharge prevention elements set to a certain voltage in parallel, it is possible to prevent the elements from becoming conductive when a high reverse voltage is applied in the same way as described above, and thereby preventing the battery from becoming overcharged.

In addition, since the change between the conductive state and the non-conductive state of this overcharge prevention element is reversible based on the change in the amount of ion doping in the polymeric substance that constitutes one electrode, the connection with the battery described above is possible. Even if high voltage is frequently applied in the current state, the overcharge prevention function is maintained without any change each time.

Although such an overcharge prevention element can be handled as an independent electronic component by itself, it can be incorporated into a device for charging a secondary battery or an electric device using a secondary battery and a primary battery.

Zener diodes are known as voltage-sensitive switching elements, but since they do not perform switching functions at low voltages like batteries, and the conversion voltage cannot be precisely selected, they are not used as overcharge prevention elements for batteries. Not suitable.

FIG. 1 shows an example of the structure of the overcharge prevention element of the present invention in the form of a button-type battery.

In the figure, l is an element case, in which a reference electrode terminal plate 2 and a counter electrode terminal plate 3, both of which are dish-shaped, are placed facing each other.
A flat airtight container is constructed by fitting and press-bonding the peripheral edges of both with an annular gasket 4 made of an elastic insulating material such as synthetic rubber or synthetic resin interposed therebetween. This case 1
Inside, there is a reference electrode 6 bonded to the reference electrode terminal plate 2 via a current collector 5 made of stainless steel net, etc., and a polymer material that develops conductivity by doping with ions bonded to the counter electrode terminal plate 3. A counter electrode 7 and a conductive separator 8 interposed between the two electrodes 6.7 are loaded in a state of being immersed in an electrolytic solution.

Figure 2 is a wiring diagram when charging the secondary battery C using this overcharge prevention element, and the battery C and the element are connected in parallel to the circuit of the charging power source S. .

As the polymer material constituting the counter electrode 7, any material can be used as long as it exhibits conductivity through ion doping. Specific examples include polyaniline, polyacetylene, polyparaphenylene, polythiophene,
Examples include polypyrrole. In order to form the counter electrode 7 using such polymeric substances, powders of these polymeric substances alone or as a mixture with a binder may be pressure-molded, or the powders may be molded onto a non-conductive substrate such as a non-woven polypropylene fabric. The molded body may be formed into a molded body having a desired thickness and size by an appropriate means such as pressure bonding.

The electrode material for the reference electrode 6 is a conductive material with a stable constant potential, such as various conductive metals and alloys, carbon-based conductive substances such as activated carbon fibers, and alkali salts of conductive metal oxides and sulfides. In particular, various electrode materials in which lithium is intercalated such as LiMo□, materials containing lithium such as metallic lithium, and lithium alloys are suitable.

As the conductive separator 8, a porous sheet having conductivity and capable of impregnating and retaining an electrolytic solution, such as activated carbon fiber cloth, is used.

As the electrolyte, L i B F 4 % L i C
I Oa, LiBΦ4 (Φ is phenyl group), LiBF
4. A lithium ion conductive electrolytic solution prepared by dissolving a lithium salt such as LiAsF6 in a non-aqueous solvent such as propion carbonate, γ-butyrolactone, dimethoxyethane, dioxolane, etc. is preferable, but it is not limited to lithium ions and can be used with any of the above-mentioned polymeric substances. Electrolytes containing various electrolytes that produce ions that can be doped to impart conductivity can also be used. Moreover, instead of such an electrolytic solution, a solid electrolyte that can provide similar doping ions can also be used.

Note that the electrode material of the reference electrode 6 and the polymer substance and electrolyte of the counter electrode 7 are selected so that the conversion voltage is approximately equal to the end-of-charge voltage of the secondary battery or the allowable voltage of the primary battery, which is the target of overcharging prevention. It goes without saying that they should be selected and combined so that

Further, since the overcharge prevention element of the present invention can maintain electrical connection between the electrode made of the polymeric substance and the other electrode with an electrolyte interposed therebetween, the overcharge prevention element of the present invention can be configured as illustrated in FIG. 1, for example. By using an electrode material capable of holding an electrolyte such as activated carbon fiber as the reference electrode 6, the conductive separator 8 is omitted and the reference electrode 6 and the counter electrode 7 are in direct contact with each other, or Conversely, it is also possible to adopt a structure in which the reference electrode 6 is omitted and the reference electrode terminal plate 2 itself is used as an electrode.

Furthermore, the overcharge prevention element of the present invention is not limited to the button type battery as illustrated in FIG. Can be formed into any structure and size.

〔Effect of the invention〕

According to the overcharge prevention element of the present invention, by connecting the overcharge prevention element in parallel with a battery, it is possible to prevent a voltage rise exceeding the end-of-charge voltage specified during charging in a secondary battery, and it is also permissible in a secondary battery. This prevents overcharging due to reverse applied voltage exceeding the specified value, thereby preventing performance deterioration and battery destruction due to overcharging and improving lifespan and safety without changing the configuration or structure of these batteries themselves. becomes possible. Moreover, this overcharge prevention effect is based on reversible switching between a conductive state and a non-conductive state due to the potential difference between the two electrodes of the element, so there is almost no decline in the effect due to the number of operations, and it is stable and reliable over a long period of time. be done.

In addition, this element is structurally extremely simple and easy to miniaturize, and can be configured into various forms of independent electronic components, as well as being easily integrated into charging equipment and various electrical devices that use batteries. It is possible.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 Lithium foil with a thickness of 0.24 tm and a thickness of 0 as a reference electrode
3 Diameter 7 formed by crimping with On+ aluminum foil,
A 75W Li-Al crimped body, a polyaniline molded body with a diameter lOw and a thickness of 0.3T obtained by pressure molding polyaniline powder 30IIv as a counter electrode, and a separator with a diameter of 9Fl and a thickness of 0.2**. A sheet of activated carbon fiber and propylene carbonate containing 1 molar LiBF as an electrolyte were used to form a sheet with a diameter of 1) as shown in FIG. 6 cranes, total thickness 2. An ON button-type overcharge prevention element D1 was manufactured. Note that stainless steel plates were used as the terminal plates of the reference electrode and the counter electrode.

Regarding this element, when we measured the relationship between the voltage applied between both poles and the resistance between both ends of the element using an alternating current of 10t (z), we obtained the results shown by curve D1 in Figure 3. It has been found that the element D1 becomes conductive on the high voltage side and non-conductive on the low voltage side with a boundary of 2.7 V, and has a sensitive switching function with the above voltage value as the operating point.

By the way, for example, L i A 12 / T i S
For Z series lithium secondary batteries, the end-of-charge voltage is 2.7■
It is said that it is preferable to maintain it at a certain level. Therefore, when charging the secondary battery, by connecting the element in parallel with the battery, the battery voltage will not rise above 2°7cm, and overcharging will be reliably prevented.

Example 2 As a reference electrode, a diameter of 7.75 m is made of Li Mo O2 in which lithium is intercalated with Mo O□.
.

A button-shaped overcharge prevention element D2 was produced in the same manner as in Example 1, except that a thin plate with a thickness of 0.50 m was used and propylene carbonate containing 1 molar concentration of Li CIO was used as the electrolyte. did.

Regarding this element Dt, the relationship between the applied voltage and the resistance was measured in the same manner as in Example 1, and the results shown by the curve in FIG. 3 were obtained. From this result, this element D2 is
It is clear that it exhibits a switching function with an operating point of 1.8V, and therefore the end-of-charge voltage of Ni/Cd secondary batteries, Ni/M(H) secondary batteries, etc. is 1.8V. It can be seen that the present invention is useful as an overcharge prevention element for secondary batteries of a certain level.

Example 3 Lithium foil with a thickness of 0.24 mm and a thickness of 0 as a reference electrode
, a diameter of 7゜7 made by crimping 401m of indium foil.
A 5 mm Li-In crimped body is used, and 1 molar concentration of Li Cj! is used as the electrolyte. A button-shaped overcharge prevention element was produced in the same manner as in Example 1, except that T-butyrolactone containing 04 was used.

Regarding this device, the relationship between applied voltage and resistance was measured in the same manner as in Example 1, and the results shown by curve D3 in FIG. 3 were obtained. From this result, this element is
It is clear that it has a switching function with an operating point of 2.1■, and therefore it is useful as an overcharge prevention element for secondary batteries such as lead batteries whose end-of-charge voltage is about 2.1■. It turns out that there is something.

[Brief explanation of the drawing]

Fig. 1 is a vertical cross-sectional view showing an example of the structure of the overcharge prevention element of the present invention, Fig. 2 is a wiring diagram when charging a secondary battery using the above element, and Fig. 3 is a diagram showing a structure obtained in an embodiment of the invention. FIG. 3 is a correlation characteristic diagram between the applied voltage of the element and the resistance across the element. D: Overcharge prevention element, 6: Reference electrode, 7: Counter electrode (polymer material), 8: Conductive separator Patent applicant Hitachi Maxell, Ltd.

Claims (1)

[Claims] (1) One of the pair of electrodes arranged opposite to each other with an electrolyte interposed therebetween is made of a polymer material that exhibits conductivity through ion doping, and the two electrodes are electrically connected. Overcharge prevention element.