Investigation of the Electrochemical Performance of Supercapacitor Pouch Cells in Hybrid and Symmetric Configurations using Aqueous Electrolytes

This paper reports the electrochemical characteristics of supercapacitor pouch cells assembled on the basis of activated carbon YP80F and two types of aqueous electrolytes: 5 M LiTFSI + 0.5 M NaI (redox-active electrolyte) and 10 M LiTFSI (neat electrolyte). A comparative analysis was performed using cyclic voltammetry (CV) and galvanostatic charge-discharge (GCPL) methods in the voltage range from 0.6 to 1.5 V. It was found that the system with the addition of NaI demonstrates pronounced effects on overall performance due to reversible I⁻/I2 redox processes, which provides an increase in specific capacitance to 128 F/g and energy to 9.26 W·h/kg at a voltage of 1.5 V while maintaining high Coulombic efficiency (>97%). In contrast, the supercapacitor with 10 M LiTFSI electrolyte exhibits classic electric double layer (EDL) behavior and lower specific capacitance (64 F/g) but high stability and reversibility (efficiency >99%). A comparative analysis showed that the hybrid supercapacitor pouch cell with NaI is more promising for tasks requiring high energy density, while concentrated LiTFSI-based system is preferable for applications focused on durability and stability. The results obtained contribute to the understanding of charge accumulation mechanisms in aqueous supercapacitors and open up prospects for optimizing their characteristics depending on the target operating conditions. The results highlight that the 5 M LiTFSI + 0.5 M NaI electrolyte enhances energy density through I⁻/I2 redox reactions, while the 10 M LiTFSI system offers superior stability, demonstrating a trade-off between energy density and long-term performance.