TRANSPORT PROPERTY MEASUREMENTS OF POLYMER ELECTROLYTES

Straightforward electrochemical methods for determining the transport properties (bulk ionic conductivity, salt diffusion coefficient, and c ation transference number) of polymer electrolytes are described herei n. The new technique for measuring t(+)(0) is:based on concentrated so lution theory, and requires no assumptions to be made concerning ideal ity of the solution. The experimental methods are described and result s on representative polymer electrolyte systems are presented in this paper. Cation transference numbers are found to be salt-concentration; dependent and considerably less than unity or even negative over a wi de concentration range. This implies that the cationic current is main ly carried by complexed ions. The presence of associated ionic species in the present systems is confirmed by Raman spectroscopic evidence. Finally, the practical effects of a negative t(+)(0) on cell operation and implications for device design are discussed. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.