Rubbery Block Copolymer Electrolytes for Solid‐State Rechargeable Lithium Batteries

Abstract

For nearly 20 years, poly(ethylene oxide)‐based materials have been researched for use as electrolytes in solid‐state rechargeable lithium batteries. Technical obstacles to commercialization derive from the inability to satisfy simultaneously the electrical and mechanical performance requirements: high ionic conductivity along with resistance to flow. Herein, the synthesis and characterization of a series of poly(lauryl methacrylate)‐ b ‐poly[oligo(oxyethylene) methacrylate]‐based block copolymer electrolytes (BCEs) are reported. With both blocks in the rubbery state (i.e., having glass transition temperatures well below room temperature) these materials exhibit improved conductivities over those of glassy‐rubbery block copolymer systems. Dynamic rheological testing verifies that these materials are dimensionally stable, whereas cyclic voltammetry shows them to be electrochemically stable over a wide potential window, i.e., up to 5 V at 55°C. A solid‐state rechargeable lithium battery was constructed by laminating lithium metal, BCE, and a composite cathode composed of particles of (monoclinic), carbon black, and graphite in a BCE binder. Cycle testing showed the battery to have a high reversible capacity and good capacity retention. Li/BCE/Al cells have been cycled at temperatures as low as −20°C. © 1999 The Electrochemical Society. All rights reserved.