Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1994-10-18
1997-08-19
Skapars, Anthony
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
429212, 429218, 296231, H01M 618
Patent
active
056586876
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a battery operating reversibly at room temperature, comprising an improved cathode, electrolyte and anode, and a method for manufacturing such a battery.
With a recent tendency to design various electric equipment in a micro-electronic form, batteries have been housed in an electric apparatus and integrated with the electronic elements and the circuit, such as in power sources for memory back-up of various electric devices. For this reason, the demand for minimizing the size, weight and thickness of batteries and the need for a battery having a high energy density have been increasing. In the field of primary batteries, a small-sized and light-weight battery such as a lithium battery has already been put to practical use, however, its application is limited. Under these circumstances, in the field of secondary batteries, a battery utilizing a nonaqueous electrolyte, which can be made smaller in size and weight, attracts public attention at present as an alternate battery to replace the conventional lead battery and nickel-cadmium battery. However, in battery utilizing a nonaqueous electrolyte, an electrode active material which satisfies practical physical properties, such as cycle characteristics and self-discharge characteristics, has not yet been found. Therefore, investigations are still being carried on in many research organizations.
In order to develop a small-sized and light-weight battery having a high energy density and a high reliability, it is necessary to examine the following problem areas (1) and (2):
As for problem area (1), the inventor examined a film type battery, that is, a battery having cell units with a thicknesses of 100 to 500 .mu.m, also called a "sheet-shaped" battery. With this kind of battery, however, the problem arose that the manufacture of metallic lithium foil having a desirable performance was somewhat difficult from a technical point of view and that therefore, the manufacturing process of such a battery became complicated. Further, in the secondary battery, the problem of lithium dendrite formation and passivation of the interface took place so that use of the metallic lithium was restricted. Therefore, investigations on alloys including lithium metals such as lithium-aluminum, lithium-lead and lithium-tin, have been actively carried out. However, during testing, the electrode cracked or broke into fine pieces due to repeated charging and discharging so that the cycle characteristic was not improved when these alloys were used, because these alloys, such as the lithium-aluminum alloy, have little strength. As an alternate way of restricting the formation of lithium dendrite, investigations on the selection of an electrolyte salt and improvement in separators have been examined. As for the separator, it has been attempted to restrict the formation of lithium dendrite by laminating non-woven fabrics made of polypropylene or glass fiber. However, a substantial solution has not yet been found.
Currently electrode active materials utilizing intercalation or a doping phenomenon of a layer compound are being specially studied in many research organizations. These materials are expected to have extremely excellent charge/discharge cycle characteristics, because a theoretically complicated chemical reaction does not occur at the time of the electrochemical reaction in charging and discharging. Use of carbon material as the electrode active material is a method which was developed, during the studies mentioned above, as a solution for problems of cycle characteristics and self-discharge characteristics of the electrode active material. Features of this carbon material are a high doping capacity, a low self-discharge rate and an excellent cycle characteristic. A special feature to mention is that it has a base-potential very close to that of metallic lithium.
On the other hand, problem area (2) is described below. A liquid electrolyte, especially prepared by dissolving an ionic compound in an organic electrolyte, has so far be
REFERENCES:
patent: 5237031 (1993-08-01), Kubota et al.
Izuchi Syuichi
Takeda Kazunari
Skapars Anthony
Yusasa Corporation
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