Water-In-Salt Electrolyte Induced Fast Ion Diffusion and Moisture Driven Charging of CNT Inks Based Sustainable Flexible Microsupercapacitor.

In today's era, the rise of flexible, biodegradable, and micro-energy storage devices represents the next frontier of sustainable electronics. Despite promising conductivity, carbon nanotube (CNT)-based supercapacitors display modest capacitance and compromised rate performance due to densely packed layers or diffusion paths of ions. To make a promising and sustainable device, we synthesized CNT-inks with enhanced and improved intertubular spacing. Herein, we report improved ion diffusion paths and enhanced interwall spacing by insertion of ions. For the scalable production of microsupercapacitors (MSCs), the Li-ion modified CNT-ink was further processed via screen printing. Coupled with the engineered electrode architecture and wide electrochemical window of bis(trifluoromethane)sulfonamide lithium (LiTFSI) water-in-salt (WIS) electrolyte, the device with limited interdigitated-electrode (IDE) fingers achieved a high areal capacitance (42 mF/cm2) and excellent cyclic durability (∼95% after 20,000  cycles). Additionally, Kelvin-probe force microscopy (KPFM) revealed dynamic surface potential modulation, directly evidencing Fermi level tuning through Li+ ion adsorption. Notably, the MSC also performed with commendable electrochemical behavior even at ultra-low temperatures down to -60°C and demonstrated effective power generation at high humidity. Also, we tested device reproducibility with remarkable performance and excellent flexibility. These outstanding performances underscore their strong potential for next-generation wearable and environmentally adaptive electronics.