Phenolized lignin binders inducing ultrathin SEI of hard carbon for advanced sodium storage

Abstract

Hard carbon (HC) has emerged as a preferred anode material of sodium-ion batteries (SIBs). However, its practical application is significantly hindered by low initial coulombic efficiency (ICE) and unsatisfactory reversible capacity. In this study, an interface modification strategy employing phenolized lignin (DpAKL) binders is demonstrated to enhance the sodium storage capability of HC. The DpAKL binders not only enable uniform dispersion of carbon black on the HC surface through π-π interactions and electrostatic adsorption-repulsion effects but also serve as physical barriers that cover surface defects and suppress electrolyte decomposition. This facilitates the formation of an ultrathin solid electrolyte interface (SEI) layer composed of an inorganic NaF-rich inner layer and a flexible organic outer layer, which reduces irreversible capacity loss and promotes efficient Na⁺ transport at the electrode–electrolyte interface. Consequently, the optimized HC anode delivers a high reversible capacity of 430 mAh g⁻¹, an outstanding ICE of 93.6%, and excellent cycling stability. Full-cell evaluations reveal strong compatibility between the DpAKL-modified HC anode and a commercial Na3V2(PO4)3 cathode, highlighting its promising potential for large-scale energy storage applications. This study offers a binder chemistry strategy for regulating the interfacial structure of HC for superior sodium storage.

Keywords: Phenolized lignin, hard carbon, Binder, solid electrolyte interface, Sodium ion battery