All-Solid-State Capacitor with Oxide Solid Electrolyte

In order to realize a carbon–neutral society, all-solid-state energy storage devices with high safety and long cycle life are required. In addition to all-solid-state rechargeable batteries, the development of all-solid-state capacitors (ASSCs) using inorganic solid electrolytes (SEs) is desired. However, the previously reported ASSCs suffer from lower capacity and rate performance than conventional electric double-layer capacitors (EDLCs), which use aqueous solutions or organic liquid electrolytes. Here, we show that highly deformable Li-ion conducting oxide SEs improve the electrochemical performance of ASSCs. Bulk-type symmetric ASSCs with a 33Li3BO3·33Li2SO4·33Li2CO3 (LBSCO) SE layer between two electrode layers of an LBSCO-CNT composite, operated at 100–300 °C. Furthermore, they achieved the highest capacitance at the highest current density of any ASSCs reported to date. The highly deformable SE facilitates the design of ASSCs and expands the potential application range of EDLCs.