Multifunctional Electrolyte Additive Enabling Enhanced High‐Rate Performance With Interfacial Stability for LiMn _0.6 Fe _0.4 PO ₄ Cathodes

Among the olivine‐based cathode materials, LiMn _0.6 Fe _0.4 PO ₄ (LMFP64) has recently been considered the most promising because of its high working electrochemical potential. Nonetheless, its parasitic reactions observed at the LMFP64 interface limit their widespread adoption in conventional batteries as a result of fading during cycling. In this regard, diethyl[difluoro(trimethylsilyl)methyl]phosphonate (DFSP) is proposed as a multifunctional additive to mitigate the unstable interfacial behavior, which is expected to form the Li ⁺ ‐affinitive cathode–electrolyte interphase (CEI) via electrochemical oxidation. In practice, thin LiF‐ and Li ₃ PO ₄ ‐rich CEI layers are formed at the LMFP64 interface, which makes the interphase more Li ⁺ ‐conductive and durable under prolonged cycling. Further ex situ analyses indicate that the residual DFSP additive in the electrolyte effectively decreases the F ⁻ concentration via chemical trapping, thereby suppressing transition‐metal dissolution and delaying the deterioration of the LMFP64 cathodes. As a result, the DFSP‐containing electrolyte exhibits stable cycling retention (75.2%) at a 3.0 C rate, whereas the bare electrolyte only shows apparent fading behavior (51.2%) after 150 cycles.