Impact of metallic interlayers at the lithium – Li6PS5Cl solid electrolyte interface

Solid-state batteries promise significant improvements in energy density over current lithium-ion technology. To achieve maximum energy density and overcome densification challenges associated with metallic lithium, cells must be assembled in a zero-excess lithium configuration. The addition of a metallic interlayer at the negative electrode–electrolyte interface has been proposed as a route to control plating morphology and improve lithium plating and stripping e!ciency, but the mechanism underlying its operation remains un- clear. Here, we deposit four interlayers—bismuth, indium, silver, and magnesium—and investigate their lithiation dynamics and effects on plating morphology using operando scanning electron microscopy. We use three-electrode impedance spectroscopy and current titration time analysis to show that depositing the interlayer directly onto the solid electrolyte maximises the electrochemically active contact area with the current collector, reducing the effective current density but promoting the growth of the solid electrolyte interphase. We demonstrate that the lithiation dynamics of the interlayers, and the result- ing lithium plating morphology, vary across the materials and are directly related to the physical properties of the alloy phases formed during lithiation.