Fabrication of Li Metal-Sulfide Solid Electrolyte Interface Using Ultrasonic-Assisted Fusion Welding Process

Torealize all-solid-state Li metal batteries, developinga technologythat effectively joins Li metal with inorganic solid electrolytesis important. The ultrasonic-assisted fusion welding process, a novelprocess for joining Li metal and solid electrolytes, has the potentialto offer advantages that cannot be obtained by the conventional pressingprocess of solid-solid joining because it uses molten Li. Inthis study, to investigate the applicability of this process to thejoining of Li metal and sulfide solid electrolytes, amorphous Li3PS4 was used as an electrolyte, and the interfaceconditions and electrochemical properties were evaluated. Molten Lifilled the roughness of the surface of the pelletized electrolyte,and the fabricated Li-Li3PS4 interfacewas in close contact without voids. Impedance analysis, SEM observations,and XPS depth profile analysis did not detect high-resistive layers.In the Li symmetric cells prepared by this process, electrochemicalproperties such as critical current density and repeated Li stripping/platingfor 100 h were comparable or superior to the cells prepared by theconventional cold isostatic pressing process. Furthermore, this processachieved the joining of Li to the Li3PS4 thin-filmsheet without a short circuit. Repeated charge-discharge cycleshave been successfully demonstrated in the Li|Li3PS4|Li4Ti5O12 battery configuration.