Polymer electrolytes

Abstract

This invention provides alkali ion conducting polymer electrolytes with high ionic conductivity and elastomeric properties suitable for use in high energy batteries. The polymer electrolytes are cyclic carbonate-containing polysiloxanes that can be modified with a cross linker or chain extender, and an alkali metal ion-containing material dissolved in the carbonate-containing polysiloxane. The cyclic carbonate-containing polysiloxanes may be prepared by reacting derivatized polysiloxanes with chain extending and/or crosslinking agents. The invention also provides batteries prepared by contacting an alkali metal anode with an alkali metal intercalating cathode and an alkali ion-conducting polymer electrolyte. As one example, polymers prepared from poly {3[2,3-(carbonyldioxy)propoxy]propyl]methyl siloxane, a polysiloxane with cyclic carbonate side chains, have shown promising results for battery applications. This polymer was crosslinked with methyltriacetoxy silane and incorporates lithium trifluoromethanesulfonate into the polymer matrix as the ion conductor. Polymers were prepared using various solvent systems and temperatures in order to produce a polymer film with the desired properties for this application. Each polymer made from the precursor poly {3[2,3-(carbonyldioxy)propoxy]propyl]methyl siloxane exhibits a glass transition temperature (T ) in the range of −100° C. to −70° C. and ionic conductivity of 6.5×10 at 25° C. and 5.3×10 at 60° C. which indicates that this material has distinct possibilities in lithium battery applications. Materials are flexible and readily adhere to the electrode surface. Polymers are synthesized by initially forming alkyl chains which include an ester carbonic acid group. The ester carbonic acid contains the ether oxygen within the single phase polymer matrix which facilitates the ionic dissociation of lithium salts. Ester carbonic acids groups are formed by the transesterification of alkyl diols such as 3-(allyloxy)-1,2-propanediol and 1,2 hexanediol with diethyl carbonate. This reaction produces ester carbonic acids with reactive end groups such as alkyls and alkanes which can then be further reacted to form dihalide end groups. Reactive groups on the ester carbonic acid are then reacted with various polymethyl siloxanes which serve as the polymer backbone for single phase elastomeric polymers which readily dissolve lithium salts.