Stretchable Ti₃C₂T_xMXene microsupercapacitors with high areal capacitance and quasi-solid-state multivalent neutral electrolyte

Emerging wearable electronics require stretchable energy storage devices to achieve energy autonomy for future commercialization. Stretchable microsupercapacitors (SMSCs) with neutral multivalent electrolytes are desired to increase the specific capacitance while addressing the safety concerns of using acidic/organic electrolytes near the human body. Ti₃C₂T_xMXene nanosheets exhibit attractive electrochemical properties for various energy storage applications, yet few MXene SMSCs with neutral electrolytes were reported. Herein, a two-step contraction process was developed for fabrication of MXene SMSCs with high specific capacitance. After thermal shrinkage and solvent-induced contraction, an elastomer-infiltrated MXene (e-MXene) device with miniaturized dimensions and interdigitated electrodes was obtained. Upon incorporating an acidic gel electrolyte, the e-MXene SMSC demonstrated high areal capacitance (C_A, 127.9 mF cm⁻²), high rate performance (64.0% retention from 10 to 200 mV s⁻¹), and high mechanical stability under 50% strain for 3000 cycles (91.6% preservation). Furthermore, the e-MXene SMSC with neutral multivalent electrolyte demonstrated highC_Aof 61.4 and 51.7 mF cm⁻²under 0% and 50% strains, respectively. Compared with the literature, our e-MXene SMSC with acidic electrolyte showed superior energy density (5.4 μW h cm⁻²at 0.15 mW cm⁻²), and the SMSC with neutral multivalent electrolyte demonstrated high electrochemical performance (3.1 μW h cm⁻²at 0.03 mW cm⁻²) together with ensured user safety.