Nanoconfinement-induced high-rate performance of hard carbon for densified sodium clusters storage

Abstract

Hard carbon is recognized as a promising anode material for sodium-ion batteries, but its practical application is constrained by low initial Coulombic efficiency (ICE), insufficient reversible capacity, and poor rate performance, which are rooted in inadequate pseudo-graphitic domains structure and uncontrolled sodium cluster formation. Herein, we propose a nanoconfinement strategy via graphene orientation-guided graphitization to achieve high-rate performance of cellulose-derived hard carbon. The oxygen-functional groups of graphene form stable cross-linking structure with cellulose to suppress disordered defects, while the sp2-hybridized carbon skeleton guides directional arrangement of carbon layers, synergistically constructing confined structure with abundant pseudo-graphitic domains and size-tunable closed pores. Benefiting from this optimized structure, the resultant electrode achieves a high specific capacity of 323.9 mAh g-1, an ICE of 89.9%, and excellent rate performance (226.8 mAh g-1 at 3.0 A g-1). More importantly, the sodium metal clusters are for the first time observed via nanoconfinement induction with the filling stage achieving their controllable densification by enhancing micropore confinement. This further validates and reinforces the new adsorption-intercalation-pore filling mechanism for sodium clusters densification. This work highlights nanoconfinement induction for high-rate hard carbon anodes, promoting the application of sodium-ion batteries in large-scale energy storage systems