Direct Imaging of Space Charges Around the Interface between Solid Electrolyte and Electrode of Solid-State Batteries

Solid-state batteries (SSBs) are a major focus for next-generation energy storage that is safe and has high energy density. In recent years, ion conductivity of solid-state electrolytes (SSEs) has developed to a level comparable to liquid electrolytes. However, great challenges are encountered at SSE/electrode interfaces when integrating the SSE into SSB cells. In addition to stability of the interface, which has been discussed extensively in the literature, a space-charge region around the electrode/SSE interface should exist and it can significantly affect Li-ion transport cross the interface [1]. Fermi-level alignment requires an ion charge transfer across the interface between the ion conductors that build an electric field around the interface. This space-charge region has been proposed theoretically,1 but direct measurement of the electric field or electrical potential has not been reported. On the other hand, the electric field in the semiconductor space-charge region has been studied extensively and directly measured and imaged; furthermore, the charge depletion and extension of the electric field into the semiconductor bulk have all been well documented. In fact, operations of many semiconductor micro-devices rely on the non-Ohmic current-voltage (I-V) characteristic across the space-charge region. And this makes the fundamental study and engineering of the semiconductor space charge among the farthest