In situ formation of a renewable cellulose hydrogel electrolyte for high-performance flexible all-solid-state asymmetric supercapacitors

All-solid-state supercapacitors using renewable and biodegradable hydrogel-based electrolytes are attractive where the close contact of the electrode and electrolyte will promote electron transfer. Here, we report an in situ low temperature cross-linking approach to prepare a new type of cellulose-based hydrogel electrolyte for application in flexible all-solid-state hydrogel supercapacitors where the as-prepared N-doped graphene (NG) hydrogel works as the electrode. When crosslinked using 3 mL epichlorohydrin, the optimized symmetric supercapacitor exhibited a high specific capacitance of 98.8 F g(-1) at 1 A g(-1), good rate capability of 89.5% at 16 A g(-1) and excellent capacitance retention of 93.9% after 5000 charges/discharge cycles. The interconnected cellulose chains acted as a framework that provided mechanical stability for supercapacitors to work normally in the bending state without electrochemical performance reduction. Then an asymmetric supercapacitor was fabricated using the cellulose hydrogel as the electrolyte, NG and cobalt carbonate hydroxide (CCH)/NG hydrogels as electrodes, and achieved a maximum energy density of 45.3 W h kg(-1) at a power density of 742.0 W kg(-1). These results confirm that the newly developed cellulose hydrogel electrolyte has great potential for use in various energy storage devices.