LONG-TERM STRUCTURAL STABILITY OF PMMA-BASED GEL POLYMER ELECTROLYTES

Gel-based SPEs are promising candidates as polymer electrolytes in ele ctrochemical devices such as Li-ion batteries. In particular, PMMA-bas ed gel electrolytes have shown electrical conductivity at room tempera ture as high as 10(-3) Scm(-1). One of the most important drawbacks of these gels is their lack of long-term structural stability, which det ermines a reduction of the contact area with the electrode and causes drops in conductance. We have observed macroscopic volume reductions ( > 5%) in gels made of PMMA, ethylene carbonate (EC), dimethyl carbonat e (DMC) and LiN(CF3SO2)(2). The timescale of this phenomenon depends o n the ratio EC/DMC. In this paper we investigate the structural modifi cations induced in the above mentioned system by annealing for several months at room temperature. We show that a crystalline phase grows in a matter of weeks with a kinetics controlled by the ratio EC/DMC and disappears for longer annealings. (C) 1998 Published by Elsevier Scien ce Ltd. All rights reserved.