Flexible, Interdigitated Shape Memory Supercapacitor Based on Reduced Graphene Oxide/Nanocellulose Aqueous Ink

Flexible supercapacitors (SCs) enduring mechanical deformation without affecting electrochemical performance are crucial in the development of miniature wearable electronics. Integrating shape memory alloys (SMAs) into SC design is one of the promising approaches to enhance their flexibility and durability. The current work is the first-ever approach introducing the interdigitated structure of Nickel-Titanium (NiTi) SMA as the current collector for the shape memory SCs (SMSC). A water-based reduced graphene oxide (rGO) ink is developed using cellulose nanofiber (CNF) as a nanospacer and carboxymethyl cellulose sodium (CMC) as a binder. The finger width of the interdigitated structure (500 mu m), screen-printing mesh size (140), and number of printing passes (4) are optimized. The SCs are screen-printed on interdigitated NiTi and Cu current collectors using the rGO/CNF/CMC ink. NiTi SMSC with EMIM BF4 electrolyte exhibits a high areal capacitance of 52.90 mF cm-2 at a current density of 0.2 mA cm-2, and maximum energy density of 29.38 mu Wh cm-2 at a power density of 0.2 mW cm-2. The NiTi SMSC retains 81% of its initial capacitance at 180 degrees static bending and 60% at cyclic bending, with a shape recovery ratio of 97% after 1000 bending cycles, mainly attributed to its superelasticity and high mechanical strength. This study highlights the potential of superelastic NiTi SMA for flexible energy storage devices, offering enhanced durability and performance in applications requiring mechanical resilience.