Preparation of bio-polyelectrolyte complex membrane from carboxymethylcellulose and chitosan as a selective alternative zinc-ion battery separator

Zinc-ion batteries (ZIBs) are gaining recognition as eco-friendly and easy-to-process energy storage solutions. Separators, which are crucial for performance, have received less attention. Separators play a vital role in facilitating efficient zinc-ion transfer and ensuring uniform ion distribution to minimize dendrite formation. Polyelectrolyte complexes (PECs), with their charged functional groups, show promise as separators. This study developed bio-polyelectrolyte complex (b-PEC) membranes using carboxymethylcellulose (CMC) and chitosan through the hot-press method. Adding NaCl during preparation activated functional groups and enhancing structural integrity. Without chemical crosslinking, the b-PEC membranes retained the original properties of the constituent polyelectrolytes. Chitosan functional groups reduced Zn²⁺ diffusion and immobilized SO₄²⁻, while CMC facilitated Zn²⁺ transport, promoting uniform ion distribution and reducing dendrite formation. The optimized b-PEC (0.5)-ZnSO₄ membrane achieved an ionic conductivity of 9.29 × 10⁻³ S cm⁻¹ and a zinc-ion transference number of 0.68, highlighting its potential as a ZIB separator.