Bacterial cellulose hydrogel: A promising electrolyte for flexible zinc-air batteries

Flexible zinc-air battery is a promising energy source for wearable electronic devices. However, few studies have focused on solid-state electrolyte which determines the servicing life and energy efficiency of zinc-air batteries. Herein, we propose a facile method to prepare a solid-state electrolyte based on bacterial cellulose (BC) hydrogel. Benefiting from the three-dimensional network structure, excellent hydrophilicity and stable chemical properties of BC, the prepared electrolyte bacterial cellulose-potassium hydroxide-potassium iodide (BC-KOH-KI) exhibits ultra-high mechanical strength of 2.1 MPa and excellent ionic conductivity of 54 mS cm−1. Moreover, the KI is introduced to drive a more energy-efficient path for charging reaction. The flexible zinc-air battery based on BC-KOH-KI displays a narrow charge-discharge voltage gap of 0.46 V at 5 mA cm−2 (energy efficiency: 73%), a high power density of 129 mW cm−2, a high capacity of 794 mAh g−1 and a large cycling number of over 100. The battery also keeps stable output at various bending angle, indicating a great potential for wearable applications.