Mild and Sustainable Synthesis of Li ₁₅ Si ₄ 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 x Si) 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 ( µ Si) into fine‐grained Li 15 Si 4 at ambient temperature. By regulating the redox chemistry and solvation environment of LAC, rapid and spontaneous lithiation of µ Si accompanied by in situ self‐fragmentation is achieved. When integrated as a prelithiation layer on Si/graphite anodes, the Li 15 Si 4 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.