<scp>UV</scp> Grafting of Novel Copolymer on Polyolefin Nonwoven Separator for Rechargeable Alkaline Nickel‐Zinc Battery

ABSTRACT Polyolefin nonwoven separators have been widely used in alkaline batteries. However, their hydrophobic nature limits wettability and electrolyte absorption, resulting in suboptimal battery performance. To address this, hydrophilic polymer such as polyacrylic acid is commonly grafted onto the polyolefin membranes. Despite this, alkaline zinc batteries with such separators often experience premature failure during cycling. This study aims to enhance the cycling stability of alkaline nickel‐zinc (NiZn) batteries by UV‐grafting novel copolymers of acrylic acid, styrene, and divinylbenzene onto nonwoven polyolefin membranes. The grafting was confirmed by FTIR, TGA, and FESEM‐EDX analyses. Wettability improvements were assessed through electrolyte absorption, retention, and contact angle measurements. NiZn coin cell test showed a 10‐fold improvement in cycle life with the copolymer‐grafted separator compared to the polyacrylic acid‐grafted separator and achieved a discharge capacity of 346 mAh/g at a charge/discharge rate of 0.3 C. Failure analysis revealed that the polyacrylic acid‐grafted separator led to excessive ZnO adhesion on the separator, contributing to early cell failure. In contrast, the copolymer‐grafted separator showed reduced ZnO adherence, contributing to enhanced cycling performance. This study demonstrates a simple yet effective modification of polyolefin separators with novel copolymer grafts, resulting in a significant improvement in the cycling performance of NiZn batteries.