A new class of cation conductors: polyphosphazene sulfonates

Abstract

Abstract : In recent years there has been considerable interest in the mechanism of charge transport in solvent-free polymer electrolytes and in the potential application of these electrolytes in electrochemical devices. Most attention has been paid to polymer electrolytes formed from linear-chain poly ethers, poly(ethylene oxide) or poly(propylene oxide) with alkali metal salts. Recently, polymer electrolytes based on phosphazene and siloxane comb polymers have been reported which exhibit better conductivity at room temperature than for the linear-chain polyether electrolytes. The high conductivity of these materials arises from their highly flexible polymer segments. A drawback for most polymer electrolytes is that the transference number for the cation lies in the range 0.3 to 0.5. In order to increase the fraction of the charge carried by the cation, we have experimented with polymers in which the anion is covalently attached to the polymer (polyelectrolytes). Conventional polyelectrolytes are rigid materials in the absence of solvent, however, we have shown that certain plasticizers greatly improve the conductivity of polymers such as sodium poly(styrene sulfonate), and we suggested that polyelectrolytes that incorporate flexible groups by covalent bonds would be a logical next step.