A Solid Polymer Electrolyte with Inorganic‐Enriched Cathode Electrolyte Interphases Enabling 5.1 V Solid‐State Lithium‐Ion Batteries

Abstract Manufacturing solid polymer electrolytes (SPEs) is an effective strategy for pursuing safe, energy‐dense solid‐state lithium‐ion batteries (SSLIBs). However, the challenges lie in obtaining high‐voltage SSLIBs due to the lack of an electrochemically stable SPE and the degradation of the high‐voltage cathode beyond 5 V. Hence, we employed quantum chemical calculations to screen a poly(vinylidene fluoride‐co‐trifluoroethylene‐co‐chlorotrifluoroethylene) (PVDF‐TrFE‐CFE, designated as PVTF) polymer with strong antioxidant capability to fabricate stable SPEs for high‐voltage SSLIBs. Furthermore, a sacrificial additive (lithium difluorophosphate, LiDFP) was introduced in PVTF SPE to build a high‐quality cathode electrolyte interphase (CEI) layer to stabilize the LiNi 0.5 Mn 1.5 O 4 (LNMO) cathode, which is denoted as PVTF1.0@LiDFP. The Li|PVTF1.0@LiDFP|LiNi 0.5 Mn 1.5 O 4 (LNMO) cell operating at 5.1 V sustains excellent cycling performance and remarkable rate performance, maintaining a long cycle life of over 200 cycles and achieving a high‐rate capability of up to 2 C. Complementary characterization methods were utilized to dynamically observe the cathode structure and interphase evolution, revealing that the high antioxidant stability of the polymeric PVTF framework and the incorporation of LiDFP additive to form a high‐quality CEI enriched with inorganic components realize the superior performance of Li|PVTF1.0@LiDFP|LNMO cell. Overall, the insights gained from our study provide a solid foundation for the development of high‐voltage SSLIBs.