Regulating Interfacial Nucleophilic Chemistry via Hybrid Electrolyte Enables Stable 4.8 V-Class Li-Rich||Li-Metal Batteries.

High-energy-density Li-rich layered oxide-based Li-metal batteries depend critically on the unique anionic redox. However, severe electrolyte decomposition and interfacial structural degradation hinder the longevity and stability of Li-rich||Li-metal batteries. Here, we show that a rational hybrid electrolyte design strategy can regulate interfacial chemistry through precise manipulation of cathode surface-exposed nucleophilic species. As a proof of concept, ethyl methyl sulfone is employed as the primary solvent due to its oxidative stability and resistance to nucleophilic attack, simultaneously strategically fabricating a fluorinated ether as a cosolvent that directs nucleophilic reaction toward its targeted functionality. Furthermore, this hybrid electrolyte design simultaneously facilitates the formation of a LiF-rich cathode electrolyte interphase (CEI) and reorganizes the solid electrolyte interphase on the Li metal from the preferential decomposition of cosolvents and anions. As a result, ultrahigh Coulombic efficiency (CE) (>99.4%) for Li-rich cathodes and enhanced Li-metal plating/stripping reversibility are achieved. Consequently, the optimized electrolyte demonstrates exceptional cycling stability, retaining 92% capacity over 100 cycles with ultrahigh average CE (>99.3%) under demanding conditions (limited Li supply, N/P = 2). Remarkably, this hybrid electrolyte enabled superior operation with anode-free cell architectures and enabled extreme temperatures (-30 to 55 °C) cycling. By effectively transforming detrimental nucleophilic attack into interfacial enhancement, this work establishes a new paradigm for electrolyte design in utilizing anionic redox chemistry.