Bacterial Cellulose/Polyelectrolyte Complex Hydrogel Separator with Thermal and Dimensional Stabilities for Dendrite Suppression in Zinc Ion Battery

In this study, bacterial cellulose-polyelectrolyte complex (BC/PEC) composite hydrogels were prepared for an electrode separator. First, the poly(sodium 4-styrenesulfonate)/poly(dimethyl diallyl ammonium chloride) hydrogel was prepared using NaCl as a shielding agent and a dialysis tube to control the formation of the PEC hydrogel. BC was incorporated into the supporting skeleton. The 3D BC sponge was prepared by using an alkali swollen BC gel, followed by freeze–thaw cycles to develop the porous framework. The BC backbone was then cross-linked with glutaraldehyde (GA) under acidic conditions to obtain cross-linked BC (BC-GA), resulting in the improved dimensional stability of the BC skeleton in an alkali medium. Subsequently, the PEC was introduced into the BC-GA pores, resulting in the BC-GA/PEC composite hydrogel with improved mechanical and dimensional properties and thermal stability. Electrolyte permeability tests with 6 M KOH showed that BC/PEC had lower permeability (approximately 2 × 10^–2 cm²/min) compared to BC and BC-GA (1.0–1.5 × 10^–1 cm²/min) compared to the ionic conductivity of BC-GA/PEC with values of 30.9–55.9 mS/cm. The charge–discharge cycling performance of BC-GA/PEC hydrogels as a zinc battery separator was evaluated using plating/stripping tests, revealing that the zinc anode surface exhibited less corrosion and slower dendrite growth. This phenomenon was due to the decrease in Zn²⁺ crossover by either repulsion or attraction forces between Zn²⁺ and BC-GA/PEC hydrogels, making them an alternative for electrode separators in place of liquid electrolyte separators.