Effect of Film Thickness on the Kinetics of Lithium Insertion in LiMn2O4 Films Made by Multilayer Pulsed Laser Deposition for Thin-Film All-Solid-State Battery Cathode Materials

Multi-layer pulsed laser deposition is a promising technique for producing LiMn2O4 thin films for solid-state batteries. In this work, thin films are deposited with different numbers of pulses, leading to different thicknesses and grain sizes. We investigated "in operando" the kinetics of the Li thorn transfer into LiMn2O4 films by means of dynamic impedance spectroscopy. This technique allowed us to resolve the contributions of the reaction mechanism and of the transport phenomena, as well as to quantify their equivalent resistances. Surprisingly, with increasing film thickness, the charge transfer resistance increases while the apparent diffusion coefficient of lithium increases, leading to a decrease of the mass transport resistance. It appears that both these effects are related to the dimension of the crystals in the LiMn2O4 thin films. These results provide new insights for an optimal tuning of the materials' preparation in view of maximizing their electrochemical performances.