Silicon-based anodes for lithium and sodium-ion batteries: nanoparticle design, composite engineering, failure mechanisms, and practical challenges

The development of high-performance anode materials is crucial for improving the energy density and cycle life of lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Silicon (Si) is a promising anode candidate because of its high theoretical capacity (~3579 mAh/g), far exceeding that of conventional carbonaceous anodes. However, its practical application is hindered by severe volume expansion during cycling, which triggers mechanical fracture, unstable interphase formation, loss of electrical contact, and rapid capacity fading. This review provides an integrated assessment of Si-based anodes for both LIBs and SIBs by linking synthesis and structural design with ion-storage mechanisms, failure behaviour, and mitigation strategies. Particular emphasis is placed on the synergies and trade-offs among carbon modification, polymer encapsulation, nanostructured/porous Si architectures, and electrolyte/interfacial engineering in simultaneously addressing mechanical, electrical, and interfacial degradation. The distinct challenges associated with Li and Na storage are critically compared, highlighting the substantially less developed understanding of Si-based anodes for SIBs. Rather than evaluating individual modification strategies in isolation, this review establishes relationships among material architecture, conductive networks, mechanical stability, and interphase chemistry and discusses their implications for practical electrode design. Finally, remaining challenges and research priorities are identified toward scalable, high-loading, interfacial stable, and sustainable Si-based anodes for next-generation energy-storage systems.