From Charge Storage Mechanism to Performance: A Roadmap toward High Specific Energy Sodium‐Ion Batteries through Carbon Anode Optimization

TLDR

Sodium‑ion batteries are a low‑cost alternative to lithium‑ion batteries, yet challenges such as negligible sodium uptake in graphite and subpar performance of hard carbon remain, while other carbons show high capacities but suffer from high voltage and first‑cycle loss. The study aims to overcome the tradeoff between high capacity and high voltage/first‑cycle loss by deeply understanding charge‑storage mechanisms and their link to structure and microstructure. The authors review emerging routes to optimize carbon anodes for SIBs by surveying reported electrochemical performances and charge‑storage mechanisms. They find that although some carbons achieve capacities beyond graphite, their higher voltage and first‑cycle loss limit full‑cell specific energy gains.

Abstract

Abstract While sodium‐ion batteries (SIBs) represent a low‐cost substitute for Li‐ion batteries (LIBs), there are still several key issues that need to be addressed before SIBs become market‐ready. Among these, one of the most challenging is the negligible sodium uptake into graphite, which is the keystone of the present LIB technology. Although hard carbon has long been established as one of the best substitutes, its performance remains below that of graphite in LIBs and its sodium storage mechanism is still under debate. Many other carbons have been recently studied, some of which have presented capacities far beyond that of graphite. However, these also tend to exhibit larger voltage and high first cycle loss, leading to limited benefits in terms of full cell specific energy. Overcoming this concerning tradeoff necessitates a deep understanding of the charge storage mechanisms and the correlation between structure, microstructure, and performance. This review aims to address this by drawing a roadmap of the emerging routes to optimization of carbon materials for SIB anodes on the basis of a critical survey of the reported electrochemical performances and charge storage mechanisms.