Carboxymethyl chitosan modified double-skeleton hydrogel electrolyte enables high performance for flexible zinc-air batteries

Flexible Zn-air batteries (FZABs) are regarded as promising energy storage devices for wearable electronics because of their intrinsic safety and high energy densities. However, the low water absorption, low ionic conductivity, and poor water retention of hydrogel electrolytes lead to serious charge/discharge polarization, low discharge capacity, and a short lifespan of FZABs. A novel hydrogel, named polyvinyl alcohol-polyacrylamide-carboxymethyl chitosan (PVA-PAM-CMCS), is developed to address the aforementioned issues. Through the hydrogen bonds and electrostatic interactions, CMCS is connected with the PAM-PVA backbone, which induces a denser and finer porous structure in the hydrogel. Taking advantage of the structural modification, the PVA-PAM-CMCS hydrogel electrolyte shows enhanced ionic conductivity (108.65 mS cm −1 ) and improved tensile stress (244.1 kPa) and strain (410.7 %). 2D fabric FZABs with PVA-PAM-CMCS hydrogel electrolyte exhibit long cycle life (118 h), impressive discharge capacity (805.3 mAh g −1 ), and maximum power density (91.04 mW cm −2 ). Furthermore, 1D yarn FZABs with PVA-PAM-CMCS electrolyte are continuously produced in an integrated manner by the yarn-wrapping technique. These yarn batteries can maintain stable electrochemical performance under both bending and stretching conditions. The combined design methodology of PVA-PAM-CMCS hydrogel electrolyte and yarn-wrapping technique for 1D yarn FZABs opens a new avenue to power various portable electronics.