Synergistic crosslinking effect of hydroxyethyl cellulose and montmorillonite on the improvement of mechanical and electrochemical properties of polyvinyl alcohol hydrogel

Flexible solid-state zinc-ion battery is promising energy technology with low cost, excellent performance, and safety. However, the mechanical properties of flexible electrolytes are severely limited. Here, hydroxyethyl cellulose (HEC) and montmorillonite (MMT) were introduced into a polyvinyl alcohol (PVA) matrix to prepare a novel composite hydrogel using a repeated freeze-thaw method. Both organic HEC and inorganic MMT could form hydrogen bonds with PVA molecular chains, acting as crosslinkers to construct a well-networked hydrogel structure. The synergistic effect of these two crosslinkers significantly enhanced the mechanical properties of the composite hydrogel. The composite hydrogel prepared with 3 wt% HEC and 2 wt% MMT (denoted as P–H3%-M2%) exhibited a 242.6% increase in tensile strength, 78.6% increase in elongation at break, and 970.1% increase in compressive strength compared to pure PVA hydrogel. P–H3%-M2% hydrogel also demonstrated a high electrolyte uptake rate (199.15%) and ion conductivity (24.6 mS cm−1). When assembled in a Zn symmetric battery, it maintained stable operation for 3000 h with a low polarization voltage of approximately 70 mV. Furthermore, P–H3%-M2% hydrogel assembled in a Zn//MnO2 battery exhibited a discharge specific capacity of 218 mAh g−1 at a current density of 0.15 A g−1, with 91% capacity retention after 450 cycles. At a higher current density of 1.5 A g−1, it showed a discharge specific capacity of 108 mAh g−1, which is 4.5 times higher than that of the PVA hydrogel battery, demonstrating excellent rate performance.