Functional Polymer Thin Films for Establishing an Effective Electrode Interface in Sulfide‐Based Solid‐State Batteries

Abstract

Sulfide solid electrolytes (SSEs) have garnered significant attention for their high ionic conductivity in the development of all‐solid‐state batteries (ASSBs). However, SSEs face challenges due to poor chemical and electrochemical stability, leading to SE decomposition at the anode, which in turn increases internal resistance and reduces cycle performance. Herein, to address this issue, thin polymer layers are applied to prevent direct contact between the SSE and anode using the initiated chemical vapor deposition process. This method facilitates the uniform coating of eight types of polymers with polar functionalities on indium (In) anodes. Half‐cell tests and X‐ray photoelectron spectroscopy analysis reveals that poly(acrylic acid) and poly((perfluorohexyl)ethyl acrylate), containing ─COOH and C─F bonds respectively, effectively stabilized the In/SSE interface. In full cells assembled with polymer‐coated In and LiNi0.8Co0.1Mn0.1O2 (NCM811), capacity retention show remarkable improvement, achieving 64.8% for In@pAA and 50.7% for In@pC6FA after 100 cycles, compared to 29.0% for bare In. This study provides insights into the interaction between polar bonds in polymers and SSEs, potentially bridging a significant knowledge gap resulting from the significant lack of research investigating the relationship between polymers, one of the primary materials commonly used in ASSBs.