A Mechano‐Electrochemical Stable Hydrogel for Flexible Energy Storage and Motion Monitoring

Balancing mechanical toughness, environmental durability, sensing accuracy in hydrogel based flexible devices remains challenging. This paper reports a multifunctional hydrogel P(AM‐co‐SBMA)/CMCS‐IL, synthesized via free radical polymerization in [EMIM][BF 4 ]/H 2 O binary solvent system, natural polysaccharide CMCS as rigid reinforcing network, AM and zwitterionic SBMA for flexibility. The hydrogen bonds provide exceptional tensile properties, enduring 961% strain and 80% compressive strain without fracturing. It exhibits strong dehydration resistance, retaining 80% of its water content after 12 h in room temperature environment. When assembled into FSC, the device has high specific capacitance of 151.6 F g − 1 at 0.2 A g − 1 and energy density of 21.06 Wh kg − 1 at 200 W kg − 1 , while maintaining 76% capacitance retention after 8,000 cycles. Crucially, the FSC shows outstanding electrochemical stability across different bending (0° to 180°) and wide temperature range (−20°C to 60°C). Additionally, a flexible strain sensor based on the hydrogel features rapid electromechanical response (response and recovery times of 0.7 s and 0.6 s) and captures bending deformations and subtle muscle activities with high signal to noise ratios. This multifunctional electrolyte provides a key design strategy for integrating smart skins and flexible energy storage systems.