Lithium‐Metal Anode Instability of the Superionic Halide Solid Electrolytes and the Implications for Solid‐State Batteries

Abstract

Owing to high ionic conductivity and good oxidation stability, halide‐based solid electrolytes regain interest for application in solid‐state batteries. While stability at the cathode interface seems to be given, the stability against the lithium metal anode has not been explored yet. Herein, the formation of a reaction layer between Li ₃InCl ₆ (Li ₃YCl ₆) and lithium is studied by sputter deposition of lithium metal and subsequent in situ X‐ray photoelectron spectroscopy as well as by impedance spectroscopy. The interface is thermodynamically unstable and results in a continuously growing interphase resistance. Additionally, the interface between Li ₃InCl ₆ and Li ₆PS ₅Cl is characterized by impedance spectroscopy to discern whether a combined use as cathode electrolyte and separator electrolyte, respectively, might enable long‐term stable and low impedance operation. In fact, oxidation stable halide‐based lithium superionic conductors cannot be used against Li, but may be promising candidates as cathode electrolytes.

Abstract

Superionic halide solid electrolytes show excellent cathodic electrolyte properties in solid state batteries, but they are unstable in contact with the lithium metal anode. The forming solid electrolyte interphase is analyzed herein, using X‐ray photoelectron spectroscopy and impedance spectroscopy. Additionally, the hetero‐interface between Li ₃InCl ₆ and Li ₆PS ₅Cl is analyzed to highlight the concept of hybrid electrolyte cells.