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

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.