The Effect of Pressure during Sintering on the Interface between Oxide Solid Electrolyte and Cathode in Solid State Lithium Batteries

Conventional Li-ion batteries (LIBs), which have been widely used as main power sources for various electronic devices, are facing huge challenges with the explosive growth of electric vehicles (EVs) market. The safety problems of LIBs in EVs causing fire incident mainly result from the use of liquid electrolytes which provide fuel for combustion. Therefore, solid state lithium batteries using a solid electrolyte are widely accepted as promising candidates for next generation energy storage devices with superior safety performances. However, solid state batteries have limitations that originate from solid-solid interfaces between electrode and solid electrolyte, hindering practical development of solid state batteries. Especially, compared to sulfide based solid electrolyte, oxide based solid electrolyte is rigid, resulting in difficulty in forming intimate contact between solid electrolyte and electrode materials. In this study, using lithium vanadium phosphate (Li3V2(PO4)3, LVP) and lithium aluminum germanium phosphate (Li1.5Al0.5Ge1.5(PO4)3, LAGP) as cathode material and oxide solid electrolyte model system, we demonstrate the effect of pressure during sintering on the contact between LVP and LAGP, and concomitant cell performance. In addition, we found that the crystallinity of solid electrolyte and the content of carbon conducting agent critically affect the contact. Without any complicated interfacial modification, we successfully made decent cathode-solid electrolyte interface with simple method for superior solid state lithium batteries.