Cathode Interface Construction by Rapid Sintering in Solid‐State Batteries

Solid‐state batteries (SSBs) are poised to replace traditional organic liquid‐electrolyte lithium‐ion batteries due to their higher safety and energy density. Oxide‐based solid electrolytes (SEs) are particularly attractive for their stability in air and inability to ignite during thermal runaway. However, achieving high‐performance in oxide‐based SSBs requires the development of an intimate and robust SE–cathode interface to overcome typically large interfacial resistances. The transition interphase should be both physically and chemically active. This study presents a thin, conductive interphase constructed between lithium aluminum titanium phosphate and lithium cobalt oxide using a rapid sintering method that modifies the interphase within 10 s. The rapid heating and cooling rates restrict side reactions and interdiffusion on the interface. SSBs with thick composite cathodes demonstrate a high initial capacity of ≈120 mAh g−1 over 200 cycles at room temperature. Furthermore, the rapid sintering method can be extended to other cathode systems under similar conditions. These findings highlight the importance of constructing an appropriate SE–cathode interface and provide insight into designing practical SSBs. Using a 10 s rapid sintering method, a thin conductive interphase is constructed between lithium aluminum titanium phosphate and lithium cobalt oxide. This method is used to make solid‐state batteries with thick composite cathodes that demonstrate a high initial capacity of ≈120 mAh g−1 over 200 cycles at room temperature.