High-performance flexible and self-healable quasi-solid-state zinc-ion hybrid supercapacitor based on borax-crosslinked polyvinyl alcohol/nanocellulose hydrogel electrolyte

With the rapid development of wearable electronics, there arises an urgent need to exploit flexible, bendable, and even self-reparative energy storage devices. In order to realize this goal, one should construct suitable gel electrolytes. Herein, a zinc-salt-containing borax-crosslinked polyvinyl alcohol/nanocellulose hydrogel electrolyte is developed, and shows great mechanical properties, intriguing self-healing feature, and high ionic conductivity. To demonstrate the feasibility of this hydrogel electrolyte, a flexible quasi-solid-state zinc-ion hybrid supercapacitor is assembled from the hydrogel electrolyte, cellulose paper cathode, and zinc metal anode. This device can combine the advantages of both zinc-ion batteries and supercapacitors. It exhibits high capacity (56.1 mA h g(-1), 504.9 mF cm(-2), and 224.4 mu A h cm(-2) at 0.5 mA cm(-2)), great rate capability (22.1 mA h g(-1) at 10 mA cm(-2)), and excellent cyclability (95.3% capacity retention over 5000 cycles). It can also be folded, bent, compressed, and even self-healed while sacrificing only a small portion of its capacity. This work opens the door to new possibilities in flexible energy storage.