Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
1999-12-14
2002-09-03
Ryan, Patrick (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C429S189000
Reexamination Certificate
active
06444359
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrolyte solution, a secondary battery using the electrolyte solution, and a secondary battery using a plastisol as a liquid electrolyte.
2. Description of the Related Art
As the market for notebook personal computer, portable telephone, etc. has expanded rapidly, the requirement for batteries used therein, having a high output and excellent stability has increased. To respond to the requirement, there have been developed secondary batteries which use an alkali metal ion (e.g. lithium ion) as a charge carrier and utilize an electrochemical reaction associated with the donation and acceptance of the above ion.
Such batteries using an alkali metal ion need to use a non-aqueous electrolyte solution and, therefore, have had a possibility of reduced battery properties caused by liquid leakage and vaporization. Hence, there have been used, as the solvent for the electrolyte solution, high-boiling basic solvents such as ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, &ggr;-butyrolactone and the like, singly or in combination. With these solvents, however, it has been impossible to completely eliminate the possibility of reduced battery properties caused by liquid leakage and/or vaporization. A stable and highly safe electrolyte solution has been required also for electrochemical apparatuses such as electric double layer capacitor, electrolytic capacitor, various sensors and the like; however, no completely satisfactory electrolyte solution has been developed.
Secondary batteries using a liquid electrolyte have, in some cases, a structure in which an active material layer for positive electrode and an active material layer for negative electrode are separated by a separator made of a porous film and the resulting combination of two electrodes and a separator is wound a plurality of times or piled in a plurality of layers. A liquid electrolyte is introduced between the positive electrode and the negative electrode. In such batteries, the film-shaped separator has functions of (1) preventing the contact of two electrode active materials with each other and (2), when, for example, an abnormally large current flows and Joule's heat is generated, melting and plugging the pores which are the passages of ion. In recent years, as electronic appliances have become smaller and come to possess a higher performance, the secondary batteries used therein have become smaller and come to possess a higher output and a higher capacity; therefore, when short-circuiting arises in the batteries, a large current may be generated and may break the film-shaped separator of battery. In recent years, in response to the requirement for smaller battery, there has come to be often employed a thin battery having such a structure that a combination of a positive electrode active material layer, a negative electrode active material layer and a separator is wound a plurality of times and then crushed. In such a battery, however, the separator receives a large pressure and breaks very easily. The breakage of separator may invite short-circuiting and make charging impossible, or may produce firing or fuming. Therefore, in such a battery, it has been necessary as a measure for possible short-circuiting, to provide a protective circuit or a fuse at the outside of the battery. Thus, in secondary batteries which use a liquid electrolyte and wherein a positive electrode and a negative electrode are separated from each other by a separator film, there have been rooms for improvement, as mentioned above.
Meanwhile, it has been investigated to use a solvent-free polymer solid electrolyte or a polymer gel electrolyte low in solvent content, in order to prevent the reduction in battery properties caused by liquid leakage and vaporization and further prevent the occurrence of short-circuiting and the firing or fuming caused by heat generation. In such a battery constitution, no separator film is required and, therefore, the breakage of separator film and resultant occurrence of short-circuiting, etc. can be eliminated. As the polymer solid electrolyte, there are known those obtained by dissolving a metal salt in a polymer having a polyether segment (e.g. polyethylene oxide) or in a crosslinking product of the polymer.
In U.S. Pat. No. 4,303,748 is disclosed an electricity-generating device of charge and discharge type, which uses, as the electrolyte, a solid solution obtained by dissolving an ionic substance in a polymer having an ethylene oxide main chain. In JP-A-8-7924 is disclosed an ion-conductive polymer obtained by crosslinking a polymer having a polyether segment, with acryloyl group or the like. Further, investigations have been made on polymer gel electrolytes wherein a polymer is allowed to contain an organic solvent for improved ionic conductivity. For example, in JP-B-61-23947 is disclosed a polymer gel electrolyte comprising a polymer (e.g. polyvinylidene fluoride), a group I or II metal salt and an organic solvent having solubility for both the polymer and the metal salt. In U.S. Pat. No. 5,296,318 is disclosed a polymer gel electrolyte obtained by impregnating a hexafluoropropylene-vinylidene fluoride copolymer film with a solution (an organic solvent containing a lithium salt). Also in JP-A-5-109310 is disclosed a method for producing a complex wherein an alkali metal-containing solution is infiltrated into the inside of a crosslinked polymer, by mixing a polymer having a crosslinkable polyether segment, an alkali metal salt and a solvent capable of dissolving the metal salt, molding the mixture, and applying a light, a radiation or the like to the molded material to give rise to crosslinking. Investigations have also been made on polymer gel electrolytes using a combination of two or more kinds of polymers. For example, in JP-A-58-75779 is disclosed a battery constituted by at least one kind of polymer selected from a polyvinylidene fluoride, a polymethyl methacrylate and other particular polymers, a lithium salt, a particular organic solvent, a metal lithium negative electrode and a positive electrode consisting of a particular inorganic compound. In JP-A-9-971618 is disclosed a polymer gel electrolyte obtained by preparing a mixture or solution of a polymer sparingly soluble in an organic electrolytic solution and a polymer soluble in the organic electrolytic solution, making the mixture or solution into a polymer alloy film, and impregnating the film with the organic electrolytic solution to give rise to gelation. Therein are shown, as an example of the polymer sparingly soluble in the organic electrolytic solution, a polyvinylidene fluoride and, as an example of the polymer soluble in the organic electrolytic solution, a polyethylene oxide. In these polymer solid electrolytes and polymer gel electrolytes, however, as compared with liquid electrolytes, ionic conductivity is low and it is difficult to obtain a high output.
As mentioned above, with a liquid electrolyte, although a high ionic conductivity is obtained, it is difficult to completely eliminate the possible liquid leakage and vaporization from the very small flaws of sealed container. Therefore, in batteries which use an alkali metal ion as a charge carrier and wherein a positive electrode and a negative electrode are adjacent via an electrolytic solution, it has been impossible to completely eliminate the possible reduction in battery properties, caused by liquid leakage and vaporization; further, there has been a risk that the separator film breaks easily and short-circuiting takes place between the positive electrode and the negative electrode, making charging impossible and inducing firing or fuming.
Meanwhile, with polymer solid electrolytes containing no solvent or with polymer gel electrolytes containing a solvent in a low concentration, although the risk of short-circuiting is low, no sufficiently high ionic conductivity is obtained, making it difficult to obtain a secondary battery of high output.
In view of the
Bannai Yutaka
Kumeuchi Tomokazu
Ohyama Norihide
Satoh Masaharu
Shirakata Masato
Ruthkosky Mark
Ryan Patrick
Young & Thompson
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