a composite electrolyte material having increased ionic conductivity and suppressed electronic conductivity is provided . the composite electrolyte includes a first material exhibiting both ionic conductivity and electronic conductivity and a second material having electron trapping sites on the outer surface thereof . the first material is coated on the second material , or the second material is dispersed within the first material , and an electron depletion zone is created at interfaces between the first and second materials . the electrons trapped in the electron depletion zone do not contribute to the electronic conductivity of the composite electrolyte , and the ratio of ionic conductivity to electronic conductivity of the composite electrolyte is higher than that of the first material alone .