Revisiting the Electrochemical Stability of Solid Electrolytes

The development of a high-performance bulk-type all-solid-state lithium battery requires a better understanding of the high interfacial resistance between the electrode and solid electrolyte. In this presentation, we propose that the electrochemical stability window of solid electrolyte was overestimated by the conventional experimental method, and the electrochemical decompositions of solid electrolyte could cause high interfacial resistance in the bulk-type solid-state battery depending on the conducting properties of the decomposition interphases. A novel experimental method using a Li/electrolyte/electrolyte-carbon cell was proposed to approach the intrinsic stability window of the most promising solid electrolytes, Li10GeP2S12 (LGPS) and garnet-type Li7La3Zr2O12 (LLZO). The results indicate that both of these solid electrolyte materials have much narrower electrochemical window than claimed. The decomposition products for both electrolytes were also characterized by XPS test. Suppressing the unwanted electrochemical decomposition of solid electrolyte at the interface is critical for achieving a high performance bulk-type solid-state battery. The idea is supported by our most recent experimental result. By introducing an (electro)chemically stable and ionically conductive interphase between LiCoO2 and garnet-type LLZO solid electrolyte, the electrochemical decomposition of LLZO at the LLZO/LiCoO2 interface could be suppressed, which enables a cycling-stable Li/LLZO/LiCoO2 cell with a full-ceramic cathode.