Melt-formable block copolymer electrolytes for lithium rechargeable batteries

Microphase separated block copolymers consisting of an amorphous poly(ethyl ene oxide) (PEO)-based polymer covalently bound to a second polymer offer a highly attractive avenue to achieving both dimensional stability and high ionic conductivity in polymer electrolytes for solid-state rechargeable lit hium batteries. However, due to the strong thermodynamic incompatibility ty pically found for most polymer pairs, the disordered, liquid state of the c opolymer can rarely be achieved without the incorporation of a solvent, whi ch complicates processing. Herein, we report the design of new block copoly mer electrolytes based on poly(methyl methacrylate), PMMA, and poly(oligo o xyethylene methacrylate), POEM, which are segmentally mixed at elevated tem peratures appropriate for melt processing, while exhibiting a microphase se parated (ordered) morphology at ambient temperature. Although pure PMMA-b-P OEM is segmentally mixed at all temperatures, it is shown that microphase s eparation in these materials can be induced in a controlled manner by the i ncorporation of even limited amounts of lithium trifluoromethane sulfonate (LiCF3SO3), a salt commonly employed to render PEO ionically conductive. Su ch "salt-induced'' microphase separation suggests a simple method for desig ning new solid polymer electrolytes combining high ionic conductivities wit h excellent dimensional stability and improved processing flexibility. (C) 2001 The Electrochemical Society.