A Thin Composite Polymer Electrolyte Functionalized by a Novel Antihydrolysis Additive to Enable All‐Solid‐State Lithium Battery with Excellent Rate and Cycle Performance

Abstract Composite solid‐state electrolyte (CSE) incorporated with fluorine‐containing functional additives usually endows the assembled cell with improved electrochemical performance by forming stable electrode/electrolyte interfaces. However, most of fluorine‐containing additives are prone to hydrolysis, which is not suitable for the large‐scale preparation of CSEs. In this work, an antihydrolysis and fluorine‐containing additive of magnesium 2,3,4,5,6‐pentafluorophenylacetate (MgPFPAA) is successfully synthesized and then used to regulate the properties of the electrode/electrolyte interfaces of the all‐solid‐state lithium batteries (ASSLBs). The antihydrolysis property of MgPFPAA facilitates the large‐scale preparation of the ultrathin CSEs in atmospheric environment. Both theoretical calculations and experimental results indicate that MgPFPAA can effectively improve the composition and structure of the generated solid electrolyte interface film by providing rich F sources and Mg 2+ , thus leading to a stable CSE/Li interface. Furthermore, an ultrathin PEO/PVDF‐based CSE (≈30 µm) functionalized by this novel MgPFPAA additive enables the assembled LiFePO 4 ‐based ASSLB with greatly enhanced electrochemical performances, with high discharge specific capacity of 93.7 mAh g −1 at 10 C and a high capacity retention of 74.9% after 1500 cycles at 5.0 C. Also, this MgPFPAA functionalized CSE can be compatible with the high‐areal‐capacity LiFePO 4 and the high‐voltage LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathodes.