Study on the performance of electric double-layer capacitors based on lignocellulose gel polymer electrolytes with different pH values for Zn2+-lignocellulose coordination mechanism

Developing sustainable gel polymer electrolyte (GPE) for electric double-layer capacitor (EDLC) using renewable natural polymers garners significant attention. Lignocellulose (LC), with its excellent mechanical strength and wettability, is an ideal material for polymer matrices. However, the abundant hydroxyl (-OH) groups in LC form extensive hydrogen bonding networks, resulting in a dense structure that severely limits electrolyte uptake and hinders electrochemical performances. Herein, we propose a straightforward strategy by coordinating zinc ions (Zn2+) with the -OH groups in LC, effectively disrupting the hydrogen bond network to form a porous structure, exposing more active sites to remove the solvation of water molecules and provide migration channels for active ions. Moreover, ionic concentration and conductivity of the electrolyte affect EDLC performances. LC-based GPEs are prepared through 1 M Li2SO4, 1 M H2SO4 and 6 M KOH aqueous electrolytes to assemble EDLCs for performance inspection and comparison. The results show that all acidic GPEs exhibit superior double-layer capacitance performance, with ZLG-15 having a high ionic conductivity (48.9 mS cm- 1), lower activation energy (1.32 KJ mol- 1), and retaining 90.7 % of its initial capacity after 30,000 cycles. Impressively, in both acidic and alkaline GPEs, the coordination bonds between Zn2+ and -OH groups are partly broken, allowing Zn2+ to participate in the migration process of the electrolyte ions.