A Li.sub.7P.sub.2S.sub.8I electrolyte for a battery is disclosed. The electrolyte can be a single phase of Li.sub.7P.sub.2S.sub.8I. A battery having a Li.sub.7P.sub.2S.sub.8I electrolyte is disclosed. A method of making a battery including a Li.sub.7P.sub.2S.sub.8I electrolyte is also disclosed.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
 This invention was made with government support under contract No. DE-AC05-00OR22725 awarded by the U.S. Department of Energy. The government has certain rights in this invention.