One-step in situ biosynthesis fabrication of double-network hydrogel electrolytes with satisfactory water retention capacity and excellent electrical conductivity for Zn-air batteries

• The BC-PVA composite hydrogel was successfully prepared by a one-step in situ biosynthesis method. • Benefiting from the double-network, the BC-PVA hydrogel had excellent water retention and electrical conductivity capacity. • The sandwich-type ZABs based on BC-PVA exhibited excellent electrochemical performance. In the semi-open environment of flexible Zn-air batteries, water in the electrolyte inevitably evaporates continuously leading to a drastic decrease in ionic conductivity. The development of novel electrolytes with excellent water retention capacity and superior electrochemical performance for long-term stability is the key to improve the life of Zn-Air batteries. In this paper, BC-PVA composite hydrogel was successfully prepared by adding polyvinyl alcohol (PVA) suspension to bacterial cellulose (BC) medium using a one-step in situ biosynthesis method. Benefiting from the double network structure, the hydrogel exhibited excellent performance. The experimental results showed that the BC-PVA-2 composite hydrogel had an excellent water retention rate of 97.90%. Compared with pure BC, the breaking strength and ionic conductivity of BC-PVA-2 containing 2 wt.% PVA were improved by about 42% and 600%, respectively. After assembling the sandwich-type Zn-air batteries (ZABs), the open circuit voltage was 1.32 V, the peak charge current density was 110 mA·cm -2 .