Bifunctional Additive for Stable Lithium Manganese Iron Phosphate Operated Under High‐Temperature and High‐Voltage

ABSTRACT Lithium manganese iron phosphate (LMFP) cathodes are pivotal for next‐generation energy storage but are plagued by severe manganese dissolution and interfacial instability, particularly under high‐temperature or high‐voltage conditions. Herein, a bifunctional electrolyte engineering strategy is proposed utilizing trimethylsilyl borate (TMSB) to fortify the cathode–electrolyte interphase (CEI) and scavenge trace acidic species. Theoretical calculations and experimental characterizations reveal that TMSB integrates into the primary Li + solvation sheath, enabling preferential sacrificial oxidation to construct a thin, hermetic, and highly conductive boron/phosphorus‐enriched CEI. Moreover, the active trimethylsilyl functional groups of TMSB chemically scavenge corrosive hydrofluoric acid, effectively inhibiting lattice corrosion and transition metal dissolution by over 60%. Consequently, this bifunctional protection confers exceptional stability to LMFP half‐cells, which retain 86.4% capacity after 500 cycles at 4.3 V and demonstrate robust resilience under aggressive conditions (4.5 V cutoff and 60°C). Furthermore, the practical viability is validated in 1 Ah graphite||LMFP pouch cells, achieving an impressive 80.1% capacity retention after 200 cycles. This work provides critical insights into designing interface‐compatible electrolytes for high‐energy‐density batteries.