Comparison of Different Cathode-Solid Electrolyte Interface Solutiuons for High-Voltage All-Solid-State Sodium Batteries

The use of inorganic solid-state electrolytes in composite cathodes is challenging due to their rigid nature and poor interfacial contact with the active electrode material. Various cathode-solid electrolyte modifications have been proposed to minimize the interfacial resistance, but they vary in their high-voltage stability. We will present results on Na-solid-state batteries using a sodium super ionic conductor (NASICON)-type solid-state electrolyte and the high-voltage Na₃(VOPO₄)₂F cathode charged up to 4.3V. The high-voltage stability of three different interfacial engineering concepts is compared: 1) liquid electrolyte addition; 2) a cathode composite with solid-state polymer electrolyte; 3) or a layer of plastic-crystal electrolyte. We find that the addition of both liquid electrolyte and polymer electrolyte leads to a rapid capacity loss within 10 cycles due to their oxidation at high voltage. In contrast, the plastic-crystal interface exhibits a vastly improved electrochemical performance with more than 90% capacity retention after 200 cycles. In addition, the plastic-crystal interface maintains similarly good high-voltage cycling stability at both room temperature and elevated temperate (50°C), which demonstrates its compatibility for operating at high-voltage.