Fabrication of Oxide-Based All-Solid-State Batteries by a Sintering Process Based on Function Sharing of Solid Electrolytes

Garnet-type Li7La3Zr2O12 (LLZ) has advantages of stability with Li metal and high Li+ ionic conductivity, achieving 1 × 10–3 S cm–1, but it is prone to react with electrode active materials during the sintering process. LISICON-type Li3.5Ge0.5V0.5O4 (LGVO) has the advantage of less reactivity with the electrode active material during the sintering process, but its ionic conductivity is on the order of 10–5 S cm–1. In this study, these two solid electrolytes are combined as a multilayer solid electrolyte sheet, where 2 μm thick LGVO films are coated on LLZ sheets to utilize the advantages of these two solid electrolytes. These two solid electrolytes adhere well through Ge diffusion without significant interfacial resistance. The LLZ–LGVO multilayer is combined with a LiCoO2 positive electrode and a lithium metal anode through annealing at 700 °C. The resultant all-solid-state battery can undergo repeated charge–discharge reactions for over 100 cycles at 25 or 60 °C. The LGVO coating suppresses the increases in the resistance from the solid electrolyte and interfacial resistance induced by annealing by ca. 1/40. As with sulfide-based all-solid-state batteries, function sharing of solid electrolytes will be a promising method for developing advanced oxide-based all-solid-state batteries through a sintering process.