Reflex Charging for Anion-Derived Solid Electrolyte Interphase Formation

Lithium (Li) metal offers exceptional energy density but suffers from unstable interphases that lead to dendrite growth and poor reversibility. Because the interphase is established during the earliest stages of operation, controlling its formation is critical for stabilizing Li metal electrodes. Here, we demonstrate that a reflex charging strategy, in which short discharge pulses are introduced during charging, dynamically reprograms the interfacial environment. This approach sustains anion enrichment near the electrode surface and shifts Li⁺ solvation from solvent-dominated structures toward anion-coordinated structures, thereby promoting the formation of an inorganic-rich interphase. The resulting interphase reduces interfacial resistance and enables dense and uniform Li deposition. Consequently, the reflex charging-based formation protocol exhibits markedly improved Li deposition/stripping reversibility, and greater resistance to degradation during cycling and calendar aging. In full cells paired with LiFePO₄ (LFP) cathodes, the system retains 73% capacity after 500 cycles, demonstrating practical performance benefits. These findings establish formation protocol as an effective operation-driven lever for controlling interfacial chemistry, offering a practical route that complements conventional materials-based strategies for stabilizing Li metal batteries (LMBs).