Understanding electrolyte chemistry under extreme battery operating conditions

Simultaneous high-voltage (≥4.5 V vs Li+/Li) and fast-charging (≥4C, sub-15 min) operation drives liquid electrolytes into a nonequilibrium state in which cathode reactivity, Li+ redistribution, and interfacial polarization evolve on comparable timescales. The local electrolyte environment established during charging consequently differs substantially from its bulk-averaged state, altering both Li+ transfer and oxidative decomposition near the electrode surfaces. This review presents a mechanistic perspective that connects these processes through the dynamic evolution of solvation structures and electrode–electrolyte interphases. Within this framework, electrolyte design is directed toward sustaining Li+ flux through exchangeable coordination environments while controlling the interfacial availability and decomposition of reactive species. Molecular structure and composition influence performance by changing solvent activity, ion association, coordination-shell reorganization, and the selectivity of interphase-forming reactions. These molecular mechanisms must persist throughout charge cycles, accommodating the concurrent evolution of concentration gradients, surface reconstruction, and impedance growth. Emerging approaches that organize solvation environments across molecular and spatial scales offer new opportunities to regulate this dynamic response. Establishing transferable design principles will require operando characterization and practical-cell evaluation that directly connect local electrolyte chemistry with charge-transfer kinetics, degradation, and long-term high-voltage fast-charging performance.