Over the past years, supercapacitors have emerged as high-performance energy storage devices for long operating lifetimes and high power densities. Gel electrolyte is the key technical material. An ideal gel electrolyte usually requires a combination of advantages of high ion migration rate, reasonable mechanical strength and robust water retention ability at the solid state. However, there are still difficulties in constructing ordered ion channels and the inner electrochemical mechanism remains to be explored.

Breakthrough was made by Prof. XIE Yi’s group from the University of Science and Technology of China of Chinese Academy of Sciences, in cooperation with adjunct Prof. LIU Guangming’s team from the Chemistry Department. They fabricated a zwitterionic gel electrolyte that successfully brings the synergic advantages of robust water retention ability and ion migration channels, manifesting in superior electrochemical performance.

Prof. WU and his research team obtained graphene from the chemical reduction of graphene oxides and used it to fabricate working electrodes. They then coated PPDP/LiCl gel electrolyte on the parallel region filling the channel between two working electrodes. After the gel electrolyte became solid state, the graphene-based solid-state supercapacitor was fabricated and ready for electrochemical tests. Researchers also repeated the experiment under exactly the same situation with PPDP replaced by polyvinyl alcohol (PVA) so that the electrochemical behavior between PVA and PPDP gel electrolytes can be compared fairly.

The zwitterionic nature of PPDP not only offers this gel electrolyte robust water retention ability at the solid-state through a combination of about eight water molecules around the charged groups, but also brings ion migration channels to the electrolyte ions, leading to better electrochemical performance. Results indicate that when applying PPDP as a gel electrolyte, the as-fabricated graphene-based solid-state supercapacitor reaches a volume capacitance of 300.8 F cm⁻³ at 0.8 A cm⁻³, with a rate capacity of only 14.9% capacitance loss when the current density increases from 0.8 to 20 A cm⁻³, recording the best value among the previously reported graphene-based solid-state supercapacitors.

It was anticipated that zwitterionic gel electrolyte will be a promising gel electrolyte for the next generation of solid-state supercapacitors. The work entitled A zwitterionic gel electrolyte for efficient solid-state supercapacitors was published on Nature Communications.

The work was financially supported by the National Basic Research Program of China, the National Natural Science Foundation of China , National Program for Support of Top-notch Young Professionals, etc.

Figure: A zwitterionic gel electrolyte that successfully brings the synergic advantages of robust water retention ability and ion migration channels. (Image by the research group)