Sodium plating on hard carbon anodes in sodium-ion batteries: mechanisms, detection methods, and mitigation strategies.

Due to sodium's abundance and cost advantages, sodium-ion batteries (SIBs) are promising alternatives to lithium-ion batteries. The commercial adoption of hard carbon (HC) as an anode material-attributed to its low sodiation potential, high Na⁺ storage capacity, and extensive availability-further reinforces the potential of SIBs. Nevertheless, the inherent thermodynamic instability of HC anodes predisposes them to irreversible Na plating during operation. This phenomenon not only poses considerable safety hazards due to dendrite-induced short circuits but also accelerates capacity degradation, thereby undermining the feasibility of large-scale SIB deployment. This review comprehensively delineates the mechanisms underlying Na plating on HC anodes by examining internal factors-such as the electrode structure, the N/P ratio, and the electrolyte composition-and external factors including the state of charge, low temperature, and fast charging conditions. It further details various detection methods, encompassing both electrochemical techniques and physical characterization techniques, and outlines mitigation strategies such as electrode structure design, surface engineering, and electrolyte regulation to suppress plating. By synthesizing current understanding, the review posits future directions for developing safer, high-performance SIB anodes. Addressing Na plating is thus critical for advancing SIB technology toward large-scale applications.