Constructing Continuously-Distributed and Crystalline-NaF-Rich SEI on Hard Carbon Anode Through Binder Chemistry for High-Performance Sodium-Ion Batteries

Abstract

Constructing the continuously-distributed and crystalline-NaF-rich solid electrolyte interface (CC-NaF-SEI) is expected to greatly promote the sodium storage performance of hard carbon (HC) anodes. However, such an impressive concept remains extremely intractable to achieve and lacks an efficiently cost-less strategy. Herein, the application of the commercially available LA133 binder is pioneered to engineer such a CC-NaF-SEI. Through comparative analysis of representative binders with distinct functional groups, reveals the critical role of binder chemistry on SEI regulation. Specifically, the LA133 binder demonstrates a dual-regulation mechanism for CC-NaF-SEI formation. The anion-coordination preferred ─CN bonds induce an anion-enriched interfacial solvation structure, and the ─CONH/─CN groups catalytically cleave P─F bond dissociation in PF₆⁻, synergistically promoting anion decomposition kinetics to form crystalline NaF. Furthermore, robust hydrogen bonds between multiple polar groups in LA133 and HC surface create the spatially anion-confined microenvironments to guide orderly anion decomposition and facilitate continuous NaF growth into a mechanically integrated SEI. The optimized CC-NaF-SEI endows HC anodes with exceptional sodium storage performance: an ultrahigh initial Coulombic efficiency (95.9%), remarkable reversible capacity (356.6 mAh g⁻¹), and stable cycling under extreme conditions (−20–60 °C). This work provides fundamental insights into binder-SEI correlations, establishing a novel paradigm for interfacial optimization in sodium-ion batteries.