Lignin-containing cellulose nanofibril separators: Tailoring microstructure and surface wettability via hydrothermal...

To develop a green, renewable, and low-cost biomass-based separator used in sodium ion batteries (SIBs), an eco-friendly and efficient combination of hydrothermal pretreatment, mechanical grinding, and non-thermal plasma activation were performed using renewable bamboo to produce lignin-containing cellulose nanofibrils (LCNFs) for the separator of SIBs. The anode of SIBs installed with the optimal LCNF separator (S-200/60-P), with hydrothermal pretreatment at 200 °C for 60 min and oxygen (O₂) plasma activation, achieved an initial charge capacity of 328.2 mAh g^-1 at 20 mAh g^-1 and an exceptional capacity retention rate of 98.22% after 500 cycles. The reduction of hydrogen bonding among nanofibrils, resulting from lignin retaining, formed a loose porous microstructure with an improved specific surface area (93.212 m² g^-1) and median pore size (10.269 nm). The abundant carbonyl, carboxylate, and pyridinic nitrogen groups on the LCNF separator introduced by plasma treatment enhanced electrolyte affinity and promoted uniform ion flux. Theoretical calculations revealed that lignin exhibited a lower dissociation energy (0.544 eV) for sodium perchlorate compared to cellulose (0.653 eV), indicating that lignin promoted the desolvation of sodium ions from the solvent coordination layer, thereby facilitating their transportation into the electrolyte.