The ionic conductivity of composite solid-state electrolytes (SSEs) can be tuned by introducing inorganic fillers, of which the mechanism remains elusive. Herein, ion conductivity of composite SSEs is characterized in an unprecedentedly wide frequency range of 10-2 -1010 Hz by combining chronoamperometry, electrochemical impedance spectrum, and dielectric spectrum. Using this method, it is unraveled that how the volume fraction v and surface fluorine content xF of TiO2 fillers tune the ionic conductivity of composite SSEs. It is identified that activation energy Ea is more important than carrier concentration c in this game. Specifically, c increases with v while Ea has the minimum value at v = 10% and increases at larger v. Moreover, Ea is further correlated with the dielectric constant of the SSE via the Marcus theory. A conductivity of 3.1×10-5 S cm-1 is obtained at 30 °C by tuning v and xF , which is 15 times higher than that of the original SSE. The present method can be used to understand ion conduction in various SSEs for solid-state batteries.
Keywords: electrical response; ionic conductivity; multiscale mechanism; solid state electrolytes.
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