A new strategy for accelerating redox kinetics in lithium-ion batteries: Highly porous poly(ethylene glycol)/nanocellulose separators

Nanocellulose has garnered attention in energy storage as an environmentally friendly and stable separator for lithium-ion batteries (LIBs). However, cellulose nanofibers (CNF) form a dense network that impedes Li-ion migration and limits electrolyte uptake. To develop an efficient LIB separator, polyethylene glycol (PEG) was incorporated with CNF to promote hydrogen bonding, leading to a stable PEG/CNF composite that enhances ionic conductivity. Additionally, polystyrene (PS) was used as a porogen to create a highly porous structure with uniform pore distribution. The PEG/CNF-based separators exhibited superior electrolyte compatibility, uptake capacity, and thermal stability compared to polypropylene (PP)-based commercial separators. The porous PEG/ CNF separator demonstrated significantly higher ionic conductivity than the PP separator, with values of 2.0672 and 1.3272 mS cm-1, respectively. The cell paired with the PEG/CNF separator, LiFePO4, and Li metal (PEG/CNF cell) exhibited improved mass transfer kinetics under high current density. At a current density of 10C, the PEG/ CNF cell achieved a specific capacity of 108 mAh g-1. After 300 cycles at a current density of 5C, the capacity retention of cells with the PEG/CNF separator was 80 %, compared to only 25 % with the PP separator. These findings highlight the superior Li-ion transport capacity of the porous PEG/CNF separator.