Silicon is one of the most promising anode materials for next-generation lithium-ion batteries because of its very high theoretical capacity and natural abundance, yet its practical use is limited by severe volume expansion, structural degradation, unstable solid electrolyte interphase formation, and capacity fading. Beyond these known issues, a critical but underexplored degradation feature is the Coulombic efficiency trough, a transient but universal dip in efficiency that appears during early-to-mid cycling. This trough is generally associated with silicon volume change that generates sponge-like porous structures, repeated interfacial rupture, continued SEI renewal, and irreversible lithium loss. This review analyzes the mechanistic origin of the CE trough and highlights it as a diagnostic framework that links the fundamental cause of volume change to consequences that include new surface generation, interfacial instability, and declining lithium inventory. We also evaluate major suppression strategies, including LiF-rich SEI formation through electrolyte design, mechanically adaptive binders that accommodate expansion, and voltage window optimization to limit interfacial stress. Together these approaches reduce irreversible reactions, stabilize the SEI, and improve cycling stability. Treating the CE trough as a quantitative performance indicator provides a unified basis for comparing mitigation strategies and advancing durable, high-capacity silicon anodes.
Silicon anodes in lithium-ion batteries suffer from severe volume change and sluggish through-plane ion transport in stacked graphene hosts. Here we report a dual-modulation strategy that couples thermal reduction with controlled H2O2 etching to build a holey reduced graphene oxide (HRGO) framework around silicon. Reduction restores a continuous graphitic network while maintaining a compact interlayer structure; subsequent oxidative etching perforates the basal planes and modestly expands the interplanar galleries relative to reduced graphene oxide (RGO), creating short, wide Li⁺ pathways. Across various silicon-graphene composite materials, multi-modal characterization verifies defect/porosity tuning and etching-driven spacing expansion, consistent with enhanced battery performance. Electrochemically, Si–HRGO delivers stable cycling (1659 mAh g−1 after 300 cycles, 72.6% retention at 0.5 C) with suppressed swelling, higher capacitive contribution, faster Li⁺ diffusion, and reduced impedance growth. XPS depth profiling reveals an inorganic-rich solid electrolyte interphase (Li2O/LiF/lithium silicates) and deeper lithium retention within HRGO matrices, supporting durable interfacial chemistry. The combined interplanar-spacing modulation and holey architecture co-optimize ion transport, mechanical compliance, and interfacial stability via a scalable process. This framework is generalizable to other 2D material hosts and beyond-Li chemistries where through-plane flux and structural resilience are concurrently required.
Advancing lithium-sulfur batteries (LSBs) toward practical commercialization necessitates separator designs that effectively balance pore structure with interfacial chemical functionality. In this study, a unique separator architecture featuring hierarchical carbon microspheres, comprising multiscale porous carbon (MPC) cores encapsulated within functionalized reduced graphene oxide (rGO) shells, is proposed. This structure systematically optimizes pore distribution and surface chemistry to improve lithium polysulfide (LiPS) retention, electrolyte penetration, and electrochemical stability under high sulfur loading and lean electrolyte conditions. Compared to traditional porous separators, the rGO/MPC-coated separator demonstrates significantly enhanced LiPS trapping capability and superior cycling stability, achieving a high initial discharge capacity of 1532 mAh g−1 at 0.1C, sustained capacity retention (decay of only 0.13% per cycle over 300 cycles), and excellent rate capability (944 mAh g−1 at 4C). These results point out the critical role of synergistically tuning porosity and chemical functionalities, establishing a new benchmark for separator engineering in high-performance LSBs.
