A water-based binder for improved adhesion and reversibility of the graphite cathode for sodium dual-ion batteries

Due to the high voltage (>4.5 V) and dual-ion intercalation in dual-ion batteries (DIBs), the selection of a suitable binder becomes crucial. Polyvinylidene fluoride (PVDF), a commonly used binder for most cathodes, has been found to be ineffective in binding graphite cathodes. This study introduces a water-based binder composed of carboxymethyl cellulose (CMC) and sodium lignosulfonate (LgSA), which exhibits excellent adhesion to the current collector and remains stable under high-voltage conditions during repeated charge/discharge cycles. LgSA, a lignin-derived binder containing sulfonate groups, not only provides oxidative stability at elevated voltages but also synergistically enhances dispersion, electrochemical stability, and mechanical integrity when combined with CMC. Beyond binding, the CMC-LgSA is identified to maintain the integrity of the graphite framework during repeated PF₆^- intercalation and deintercalation. A dual-ion cell employing the proposed binder operates reversibly for over 500 cycles, maintaining a high coulombic efficiency of ∼87%. This study presents a fluorine-free binder that outperforms PVDF in high-voltage graphite cathodes, paving the way for scalable and high-performance sodium-based dual-ion battery technology.