Material Design of Dimensionally Invariable Positive Electrode Material for Solid-State Batteries

A lithium-excess vanadium oxide, Li8/7Ti2/7V4/7O2, with a cation-disordered structure is synthesized and proposed as potential high-capacity, high-power, long-life, and safe positive electrode materials. Li8/7Ti2/7V4/7O2 delivers a large reversible capacity of ~ 300 mA h g–1 based on two-electron cationic redox, V3+/V5+. Moreover, Li8/7Ti2/7V4/7O2 has a unique character as electrode materials, i.e., a dimensionally invariable character, which originates from reversible V migration on electrochemical cycles. This character is effective to solve the key issue of solid-state batteries related to interfacial connection loss between electrode materials and solid electrolytes. An all-solid-state cell with Li8/7Ti2/7V4/7O2 and Li6PS5Cl, which is a sulfide-based solid electrolyte with an argyrodite-type structure, shows excellent capacity retention without degradation, coupled with superior rate-capability, and this system is potentially used for practical battery applications without huge external pressure in the future.