A Localized Weak‐Solvation Electrolyte Enables Stable Cycling of High‐Mass‐Loading Li|LiFe 0.3 Mn 0.7 PO ₄ Batteries at Elevated Temperature

LiFe y Mn 1−y PO 4 (LFMP) has been regarded as one of the most promising cathode materials for lithium‐ion batteries owing to its higher energy density compared to LiFePO 4 (LFP). However, induced by the Jahn‐Teller effect of Mn 3+ , the interfacial side reactions and unstable cathode‐electrolyte interphase (CEI) of LFMP severely limit the full realization of its high energy density advantage. To address these challenges, we develop a localized weak‐solvation electrolyte consisting of 1.0 M lithium bis(oxalato)borate (LiBOB) in a mixture of tetrahydropyran (THP) and triethyl phosphate (TEP). In this electrolyte, the high HOMO level of LiBOB promotes its preferential interfacial oxidation, while the weak solvation ability of THP weakens the Li +– TEP coordination, creating a localized weak‐solvation environment that facilitates the formation of an anion‐derived CEI layer on LFMP. Consequently, a thin boron/phosphorus‐rich CEI effectively suppresses parasitic side reactions and markedly enhances the cycling stability of LFMP. Moreover, even with a high mass loading of 11.8 mg cm −2 , this electrolyte enables the LFMP cell to achieve a high‐capacity retention of 95.0% after 300 cycles at 25°C and 85.9% after 150 cycles at 55°C.