A new sodium storage mechanism of chemisorption-ion implantation in hard carbon anodes mediated by C–N–B dynamic covalent bonds

Hard carbon was regarded as one of the most promising anode materials for sodium-ion batteries, yet its sodium storage mechanism, particularly the plateau region, has long been oversimplified as a physical pore-filling process, limiting further exploration of anode materials with high performance. Herein, a novel perspective for understanding the sodium storage was proposed through molecularly designed carbon–nitrogen–boron (C–N–B) dynamic covalent bond centers in phenolic resin‑based hard carbon. We have revealed that the sodium storage at C–N–B sites involved the reversible bond reconstruction coupled with strong electron transfer between B sites and Na+, which can be understood as a hybrid “dynamic chemisorption-ion implantation” process and a chemical supplement to the conventional pore-filling mechanism. The optimized material (NBHC‑10) delivered an excellent reversible capacity of 438 mAh g−1 and an initial Coulombic efficiency of 87.1% in half‑cells, along with a capacity retention over 90% after 500 charge/discharge cycles at 0.3 A g−1. This work gave new insight into sodium storage in hard carbons at the level of chemical bond and provided a new perspective for the rational design of high-performance anode materials for energy storage.