Impact of hydrogen bonding in succinonitrile and ethylene glycol on performance of DEE for supercapacitor

In this work, a highly stable deep eutectic gel polymer electrolyte (DEE) based on a novel deep eutectic solvent (DES) derived from succinonitrile (SN) and ethylene glycol (EG) has been developed for supercapacitor applications, addressing the growing demand for durable and adaptable energy storage solutions. The DES consists of different molar ratios of HBA (succinonitrile) and HBD (ethylene glycol), specifically 0.2:0.8, 0.4:0.6, 0.5:0.5, 0.6:0.4, and 0.8:0.2. Herein, it was found that the eutectic temperature of DES is approximately 30 °C. Typically, a DES exhibits a melting point lower than those of its individual components. In this study, the melting point of DES is lower than that of SN but higher than that of EG which is 58 °C and −12.9 °C, respectively. In the formulation of DEE, a fixed amount of propylene carbonate (PC) polyethylene oxide (PEO) and LiClO₄ were added to the system. The eutectic point of the electrolyte can be retained in a gel form with the addition of PC, accompanied by PEO. Furthermore, the ionic conductivity of the formulated DEE samples was found to range from 5.25 to 6.80 mS/cm, which supports efficient ion transport. Among the prepared DEE samples, DEE with a 0.5:0.5 ratio of SN and EG exhibited the best electrochemical performance, demonstrating a specific capacitance of 9.19F/g and a capacity retention of 77 % from GCD curve. Remarkably, after 40,000 charge–discharge cycles, the device exhibited a performance drop of only 13 % from the initial capacity, corresponding to a capacity retention of 87 %, indicating excellent cycle stability. These results highlight the potential of the developed DEE for use in next-generation flexible and wearable electrochemical energy storage systems, offering both high performance and mechanical adaptability.