High-strength and high-modulus silicon monoxide for high-energy-density and fast-charging lithium-ion batteries

Silicon-based negative electrodes suffer from severe mechanical degradation due to repetitive volumetric fluctuations and the resulting stress during cycling. Prevailing mitigation strategies enhance only elastic deformation resistance (via increased Young's modulus) while overlooking yield strength improvement-critical for suppressing plastic deformation and cyclic fatigue under high-rate conditions. Here, we fabricate high-strength, high-modulus silicon monoxide incorporating intraparticle domains of crystalline lithium fluoride. By exploiting the (inverse) Hall-Petch relationship and the rule of mixtures for composites, size engineering of crystalline lithium fluoride domains maximizes particle-level mechanical reinforcement. The particles are simultaneously encapsulated by ionically conductive amorphous lithium fluoride/electronically conductive fluorine-doped carbon sheaths. This mechanical/kinetic enhancement enables automotive-acceptable coin-type full-cell cycling for 1000 cycles at 2 C (10 mA cm^-2) with high-loading positive electrodes (5 mAh cm^-2). In addition, a 1.26 Ah pouch full cell delivers stable operation for 500 cycles at 2 C (2.52 A), attaining a specific energy of 402 Wh kg^-1 and an energy density of 1125 Wh L^-1. Whereas graphite, lithium metal, and conventional silicon-based negative electrodes face a trade-off between energy density and fast-charging capability, this approach satisfies both prerequisites, establishing a foundational guideline to realize the intrinsic promise of silicon-based negative electrodes.