Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Patent
1996-03-21
1997-12-02
Maples, John S.
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
252 622, H01M 1038, H01M 1036
Patent
active
056934335
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The subject invention relates to ionically conductive solid polymer electrolytes and their method of preparation. More specifically, the subject invention relates to lithium-ion conductive solid polymer electrolytes comprising a substantially solvent-free electrolyte including an amorphous polyacrylonitrile copolymer and an ionizable lithium salt.
BACKGROUND OF THE INVENTION
There has been considerable interest in recent years in developing solid polymer electrolytes (SPE's) that may be used in electrochemical devices, for example, in fuel cells, supercapacitors, electrochromic devices and sensors. Such devices typically include an anode, a cathode and an electrolyte that has high ionic conductivity. Although the potential advantages offered by solid polymer electrolytes in such devices have been recognized for several years, D. F. Shriver et al., "Solid Ionic Conductors", Chem. & Eng. News, May 20, 1985, attempts to exploit these advantages in practical electrochemical devices have been limited by the physical properties of the SPE's.
A large number of polymer electrolytes are known at present. One of their characteristic features is formation of a complex between a lithium salt and an organic polymer (matrix) having an electron donor atom such as O or N. The complex is stabilized by the X.sup.- anion, which usually has a large size.
For example, such a complex formed from a soluble salt of an alkali metal (MX) and polyethylene oxide (PEO) is known to form an SPE, French Patent No. 7832978. Unfortunately, the conductivity of the SPE based on PEO attains conductivity values of 10.sup.-4 to 10.sup.-3 Ohm.sup.-1 cm.sup.-1 only at temperatures higher than about 100 .degree. C. These temperatures are considerably higher than the melting temperature of the polymer. The low values of the ionic conductivity at ambient temperature (10.sup.-6 to 10.sup.-7 Ohm.sup.-1 cm.sup.-1), which are caused by crystallinity of the polymer structure, is a major disadvantage for SPE's based on PEO and limits practical use of such electrolytes.
Therefore, in recent years attempts are being made to improve the electrical properties by means of modifying the composition of known SPE's, e.g., U.S. Pat. No. 5,102,751 to Narang and references cited therein. Narang is directed at providing plasticizers that enhance the ionic conductivity and mechanical properties. The highest ionic conductivity disclosed by Narang, 3.8.times.10.sup.-4 Ohm.sup.-1 cm.sup.-1, is not as high as is desired for SPE's having practical value. SPE's containing plasticizers have the further disadvantage of requiring additional materials that may make the SPE's more complicated and more expensive to manufacture.
The above-mentioned references include SPE's that are known as "solvent free". However, preparation of SPE's consisting of a liquid electrolyte held by a polymer has also been reported in the recent scientific and patent literature. Such jelly-like or solvent-swollen electrolytes exhibit higher ionic conductivity.
Solid polymer electrolytes based on the combination of a thermally cross-linked polyacrylonitrile (PAN) polymer (15-85 mole %), LiClO.sub.4 (4-21 mole %) and an organic solvent (10-75 mole %) with a high dielectric constant, such as ethylene carbonate, propylenecarbonate and dimethylformamide, are known which have higher conductivity at ambient temperature, M. Watanabe, M. Kanba, N. Nagaoka and I. Shinohara, J. Appl. Polymer Sci., vol. 27, 4191 (1982). Such polymer electrolytes may be prepared by dissolving the polymer and the lithium salt in one of the high-dielectric solvents and then coating the polymer as a thin film, for example, on a polytetrafluoroethylene (Teflon.TM.) substrate. Such thin films may be referred to as hybrid systems having a solid polymeric structure with a liquid phase dispersed therein. In such thin films the PAN polymer forms a three-dimensional network (jelly) containing stable solvate complexes formed by the lithium salt and the organic solvent.
Since the quantity of liquid phase stored in a
REFERENCES:
patent: 4654279 (1987-03-01), Bauer et al.
Animitsa Irina Evgenievna
Bushkova Olga Victorovna
Krasnobaev Yaroslav Arturovitch
Kruglyashoy Andrey Leonidovitch
Suvorova Anna Isaakovna
Maples John S.
Technology Resources International, Inc.
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