Not All Lithium–Indium Counter Electrodes Are Made Equal: Probing the Inhomogeneities and Kinetics of Uniaxially Pressed Li–In Counter Electrodes in All Solid-State Batteries

Lithium indium alloys are commonly used as counterelectrodes in all-solid-state batteries. However, the method ofpreparation varies from research groups, including ball milling, rollpressing, and uniaxial pressing of the two metals. While the latter is acommon approach used in the literature, it is not entirely clear howhomogeneous uniaxially pressed counter electrodes are and whetherthe differences can be observed electrochemically. In this work, in thefirst section, two distinct Li sources, one from the chemical Li−In alloyand the other from the electrochemical Li−In alloy formed duringcycling, are electrochemically probed and investigated as a function ofthe temperature, indium foil thickness, and Li area. In the secondsection, the kinetics of electrochemically alloyed Li−In ($e-Li_xIn$) areinvestigated using Butler-Volmer kinetics to extrapolate exchange current densities in combination with time and temperature-dependent distribution of relaxation time (DRT) analyses to better understand the alloying and dealloying process. These findingsunderscore the considerable influence that counter electrode preparation has on the kinetics and electrochemical performance of twoelectrode half-cells.