Synergistic Construction of Electrode–Electrolyte Interphases via Electrolyte Cosolvent and Additive Chemistry toward Ultrastable and Fast-Charging Li-Rich Batteries

Lithium-rich manganese oxide (LRMO) is a promising high-energy-density material for high-voltage lithium-ion batteries, but its performance is hindered by interfacial side reactions, transition metal dissolution, and oxygen release. To address these issues, we propose a high-voltage electrolyte strategy that utilizes cosolvent and additive synergy to create stable dual interphases at both the cathode and anode. Specifically, lithium difluoro(oxalato)borate (LiDFOB) additive sacrificially decomposes to form a uniform yet stable cathode-electrolyte interphase (CEI) layer, while cosolvent of bis(2,2,2-trifluoroethyl) carbonate (BTFEC) effectively adjusts the solvation structure and synergistically stabilizes the solid-electrolyte interphase (SEI) on the anode, ultimately achieving ultrahigh cycle stability and fast-charging feasibility. The presence of B-F, LiB_<i>x</i>O_<i>y</i> species derived from LiDFOB exceptionally stabilizes the fast-ion-transfer CEI layer, while the F-rich robust SEI layer inhibits the irregular growth of lithium dendrites. Our electrolyte enables Li||LRMO cells to maintain 95% capacity after 200 cycles at 4.8 V, with a specific capacity of 238 mAh g^-1 after 350 cycles at 3C. Importantly, a 5 Ah graphite||LRMO pouch cell achieves a high energy density of 323 Wh kg^-1 with 80.4% capacity retention after 150 cycles, demonstrating its practical application potential.