Beyond Imperfect Match: Silicon/Graphite Hybrid Anodes for High-Energy–Density Lithium-Ion Batteries

Silicon/graphite (Si/Gr) anodes, integrating Si's ultrahigh specific capacity with Gr's structural stability and electrical conductivity, have emerged as the most promising high-capacity systems for next-generation lithium-ion batteries (LIBs). The synergy between Si and Gr enables a balance between energy density, cycling stability, and manufacturability, already demonstrated in commercial cells. However, Si undergoes a large volume expansion of up to 300% during lithiation/delithiation, causing particle fracture, pulverization, electrode collapse, and unstable solid–electrolyte interface formation, which accelerates capacity fading. Although Gr can alleviate stress and maintain conductivity, mismatched electrochemical kinetics and mechanical properties between Si and Gr lead to heterogeneous lithiation and complex interfacial evolution, posing major engineering challenges. This review highlights recent advances in the mechanistic understanding and engineering optimization of Si/Gr anodes, emphasizing failure modes originating from both individual component degradation and interfacial coupling. The roles of advanced characterization and multiscale modeling in revealing volume effects and interfacial dynamics are discussed. Building on these insights, optimization strategies such as nanoscale structuring, interfacial engineering, buffered conductive frameworks, gradient architectures, electrode design, and pre-lithiation are summarized. A comprehensive understanding of expansion, fracture, and pulverization mechanisms is crucial for designing durable, high-energy–density Si/Gr anodes for long-life LIBs.