Mild and Sustainable Synthesis of Li₁₅Si₄ as Lithium-Compensation Additive for High-Energy Lithium-Ion Batteries

Lithium-compensation is critically important for high-energy and long-life lithium-ion batteries. As promising lithium-compensation additives, lithium silicides (Li_xSi) suffer from energy-intensive synthesis or expensive precursors. Herein, we develop a mild and sustainable lithium-arene complex (LAC)-mediated strategy to directly convert industrial-grade micro-sized silicon (µSi) into fine-grained Li₁₅Si₄ at ambient temperature. By regulating the redox chemistry and solvation environment of LAC, rapid and spontaneous lithiation of µSi accompanied by in situ self-fragmentation is achieved. When integrated as a prelithiation layer on Si/graphite anodes, the Li₁₅Si₄ additive increases the initial Coulombic efficiency (ICE) from 76.04% to 98.40%. In NCM523||Si/Gr, NCM622||Si/Gr, and LFP||Si/Gr full cells, the prelithiation strategy markedly improves ICE and raises energy density by 27.0%, 31.0%, and 32.6%, respectively. The prelithiated cells also show improved rate capability and cycling stability. This work establishes a practical route for upgrading low-cost micro-sized silicon into high-value lithium-compensation additives for high-energy-density silicon-based LIBs.