Impact of metallic interlayers at the lithium-Li6PS5Cl solid electrolyte interface
Souhardh Kotakadi, Jack Aspinall, Matthew Burton, Yi Liang, Yûichi Aihara, Mauro Pasta
Abstract
Solid-state batteries promise higher energy density than current lithium-ion technology. To achieve this and address challenges associated with metallic lithium, zero-excess lithium configurations are required. Metallic interlayers at the negative electrode-electrolyte interface present a route to control plating morphology and improve lithium cycling efficiency, but their underlying mechanism remains unclear. Here, we systematically investigate the lithiation dynamics of bismuth, indium, silver, and magnesium interlayers using operando scanning electron microscopy . Solid solution-forming interlayers promote uniform plating and maintain structural integrity, while intermetallic-forming interlayers undergo mechanical failure due to volumetric changes. Heterogeneous lithiation arises from lithium diffusivity differences between phases. Three-electrode impedance spectroscopy and coulometric titration time analysis reveal that interlayer deposition onto the solid electrolyte maximizes electrochemically active contact with the current collector, reducing effective current density but increasing solid electrolyte interphase growth. Overall, plating morphology, mechanical stability, and cycling efficiency are governed by alloy nucleation behavior and lithium diffusivity.