Effect of introducing interlayers into electrode/electrolyte interface in all-solid-state battery using sulfide electrolyte

Introduction of an interlayer between a cathode and a sulfide solid electrolyte is a well-known method for reducing the interfacial resistance and improving the performance of all-solid-state batteries. However, the mechanism responsible for the interlayer remains unclear because it is difficult to observe the reactions at the nanometer-scale range. In this study, thin-film model interface of LiCoO2/80Li2S·20P2S5 and LiCoO2/Li3PO4/80Li2S·20P2S5 are fabricated by pulsed-laser deposition. The model interfaces are investigated by performing electrochemical measurements and depth-resolved X-ray absorption spectroscopy to clarify the effect of the Li3PO4 interlayer. The results indicate that a reaction product layer forms between the LiCoO2 cathode and the 80Li2S·20P2S5 electrolyte during charge/discharge processes, resulting in high interfacial resistance. Meanwhile, the formation of the reaction product layer can be suppressed by the introduction of a Li3PO4 interlayer.