Heterogeneous Engineered Solid Electrolyte for Seamless and Stable Integration of Anode and Cathode

Abstract Solid‐state lithium metal batteries (LMBs) with high safety and energy density are the ultimate goal for energy storage systems. The bottleneck lies in the solid electrolytes, which must maintain perfect solid–solid contact and be electrochemically stable for both Li anode and high‐voltage cathode. Here, we develop an in situ polymerized hetero‐layered electrolyte that simultaneously broadens the electrochemical window and addresses interfacial issues between multiple components. The polyvinylidene fluoride (PVDF) layer toward the cathode improves high voltage compatibility to 4.8 V, while the boron nitride (BN) layer toward the anode provides sufficient mechanical strength, regulates Li‐ions transport and promotes the formation of an inorganic‐rich solid electrolyte interphase (SEI). The effect of the hetero‐layered structure is then verified in an easy‐to‐process in situ polymerized poly(1,3‐dioxane) (PDOL) electrolyte, that seamlessly integrates multiple interfaces, bridging cathode, PVDF, BN, and Li metal. This solid electrolyte is characterized by high room temperature (RT) ionic conductivity (2.1 × 10 −3 S cm −1 ), and high Li‐ions transference number (0.801). Most importantly, the Li|LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) full batteries show remarkable cycling performance with capacity retention of 90.3% over 200 cycles at 0.5 C. The hetero‐layered structure with a seamless in situ polymerized interface provides a new avenue for high‐energy, solid‐state LMBs.