Sulfur‑Containing Additives for Enhanced Kinetics and Interfacial Stability of Phosphorus Anodes in Li‑Ion Batteries

Red phosphorus offers ultrahigh theoretical capacity for lithium‐ion battery anodes but is fundamentally limited by poor electronic conductivity, sluggish lithium‐ion diffusion, and severe volume expansion that destabilizes the solid‐electrolyte interphase. Here, we introduce a synergistic strategy that simultaneously regulates reaction kinetics and interfacial stability using sulfur‐containing additives, lithium sulfide, and in situ generated lithium sulfate. Lithium sulfide confines lithium polyphosphide intermediates, enabling a direct and highly reversible conversion reaction, while lithium sulfate selectively absorbs solvent molecules and directs the formation of a uniform, lithium‐oxide‐dominated and mechanically adaptive interphase. Through this cooperative modulation, reaction kinetics are accelerated, structural integrity is preserved during cycling, and interfacial failure is effectively suppressed. As a result, the optimized red phosphorus anode retains 96.1% and 94.1% of its capacity after 450 and 1000 cycles at 1 and 4 C respectively, and still maintains 80% capacity retention after 1200 cycles at 6 C. This dual‐functional strategy establishes a coherent design principle for durable, high‐capacity conversion‐type anodes.