The ideal electrolyte material for a solid-state battery would have the ionic conductivity of a liquid, the mechanical properties of a solid, and the formability of a commodity thermoplastic. If system energy densities >300 Wh/kg are to be achieved, the electrolyte must be light and thin, yet act as a reliable physical separator for the electrodes. In this laboratory it has been shown that this challenge can be met with several classes of microphase-separating polymers, specifically, block and graft copolymers. The attributes and performance limitations of each are described along with the prognosis for their deployment in a solid-state battery. (C) 2003 Elsevier B.V. All rights reserved.