Enabling Fast Interfacial Desolvation Kinetics in Hard Carbon Anodes via Boric Acid-Crosslinked Binder Network

As a key auxiliary component for electrode fabrication, the binder not only serves as the macroscopic scaffold that holds electrode constituents together, but also acts as a bridge governing electrode−electrolyte contact. While hard carbon (HC) offers efficient sodium storage capacity and superior cycling stability due to its unique hybrid ordered-disordered structure, its rate performance is often constrained by sluggish sodium-ion desolvation kinetics at the interface. To achieve uniform regulation of desolvation rates, we designed a crosslinked multifunctional binder, NaPAB, by incorporating boron centers with vacant orbitals into a sodium polyacrylic acid backbone. This creates a 3D network with Lewis acidic sites that uniformly cover the electrode interface, aligning with the desolvation region. These boron sites coordinate with solvent molecules via Lewis acid−base interactions, weakening Na + −solvent binding and thereby lowering the desolvation energy barrier, accelerating interfacial kinetics, and reducing in-plane heterogeneity. The improved uniformity alleviates local ionic flux disparities and suppresses kinetically driven sodium plating, enabling rapid and stable Na + insertion. Meanwhile, the crosslinked network enhances mechanical integrity by connecting hard-carbon particles and mitigating stress. The sodium-salt moieties offer partial Na + compensation to reduce first-cycle irreversibility. Additionally, boron sites facilitate the formation of a robust solid−electrolyte interphase (SEI), suppressing side reactions and ensuring long-term transport stability. Consequently, the NaPAB-based hard carbon anode exhibits a high initial Coulombic efficiency (ICE) of 89.06% and significantly enhanced rate capability in half-cells, with sodium plating effectively mitigated even after high-rate cycling. This work demonstrates that precisely regulating the interfacial microenvironment via a functionalized binder network is a promising strategy, offering a new perspective for optimizing the electrochemical performance of hard carbon.