Constructing Quasi‐Localized High‐Concentration Solvation Structures to Stabilize Battery Interfaces in Nonflammable Phosphate‐Based Electrolyte

Abstract Flame‐retardant phosphate‐based electrolytes effectively enhance lithium‐ion battery safety but suffer from poor compatibility with graphite anodes and high‐voltage cathodes, hindering scalability. Fluorinated phosphates, though widely used, increase interfacial resistance at the anode, degrading performance. In this work, carbonate solvents with strong polarity are introduced to prevent tris(2,2,2‐trifluoroethyl) phosphate (TFEP) from participating in the solvation structure of lithium ions. This strategy forms a quasi‐localized high‐concentration solvation structure, thereby restricting the reduction of TFEP and its impact on the graphite anode. The LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NCM811) | Graphite (Gr) pouch cell with optimized electrolyte exhibits a capacity retention rate of 80.1% after 370 cycles at 0.5C, which is much more stable than the electrolyte with TFEP‐involved solvation structure (capacity retention rate: 47.1% after 300 cycles). The corresponding pouch cell with cut‐off voltage to 4.5 V exhibits a capacity retention rate of 82.8% after 125 cycles, significantly outperforming cells employing commercial carbonate electrolytes (capacity retention rate: 56.9% after 125 cycles). Thus, the developed quasi‐localized high‐concentration solvation structure can effectively stabilize the electrode interface, greatly enhancing the cycling performance of phosphate‐based flame‐retardant electrolytes.