A Function‐Oriented Binder with Exceptional Interface Ion Transport and Impurity Tolerance for Hard Carbon Anode

Abstract Hard carbon is the sole anode material employed in commercial sodium‐ion batteries. However, its intrinsic defects and impurities will lead to battery failure, diminishing further development of sodium batteries in energy storage. Here, an acrylonitrile copolymer and poly(ethylene oxide) (LA/PEO) composite binder is developed to address these challenges in biomass‐derived hard carbon. Typical commercial biomass‐derived hard carbon with this binder (HC‐LA/PEO) achieved an initial coulombic efficiency (ICE) of 91.1% and a reversible capacity of 341.12 mAh g −1 , superior to most of binders currently used. When transition metal ion impurities exist in hard carbon, the HC‐LA/PEO shows better tolerance and even shows a higher reversible capacity than its high purity counterpart. After function‐oriented design, due to hydrogen bonding and polar interaction, the HC‐LA/PEO demonstrated superior initial efficiency and reversible capacity while enhancing mechanical strength and reducing electrode brittleness. In addition, this composite binder induced a more uniform and stable SEI layer on hard carbon, improving interfacial stability and ion transport efficiency. The LA/PEO binder acts as an intelligent gatekeeper mitigating the adverse effects from intrinsic defects and impurities, consequently, gives full play to the biomass‐derived hard carbon in sodium batteries.