Charge and energy storage properties of NiO-AC composites in organic electrolyte using operando Raman and distributed capacitance analyses in the time domain

Pursuing pseudocapacitive materials with higher energy densities for future electrochemical energy storage systems requires a comprehensive understanding of material and electrochemical properties. In addition to charge-storage mechanisms in the active material, the electrolyte medium plays an important role in energy density. Organic solvent electrolytes exhibit a wider operating voltage window in comparison to aqueous-based electrolytes, yet the investigation of pseudocapacitive active materials in supercapacitor electrodes remains underexplored. Here, we report a facile and scalable synthesis of the pseudocapacitive composite material NiO-activated carbon (AC) as a supercapacitor electrode. A comprehensive electrochemical study in the organic solvent medium is presented, elucidating the pseudocapacitive properties of NiO-AC, assessing the stable working voltage window in an organic solvent medium, and investigating ion dynamics during charge via operando Raman. Using electrochemical characterization techniques, such as single-step chronoamperometry (SSC), and the in-situ Raman results we showed that the synthesized material (NiO-AC) is stable for operation at 2.6 V. NiO-AC, presenting specific power of 23.7 kW kg −1 and specific energy of 21.4 W h kg −1 , with a capacitance increase due to the contribution of the NiO species, highlighting the potential of the study of pseudocapacitive materials in organic electrolyte systems. • Raman operando revealed increased solvation degree with applied voltage. • In-situ Raman indicated organic electrolyte stability at voltages as high as 3 V. • Determining voltage window for pseudocapacitive electrodes in organic electrolytes. • NiO-AC yielded power density of 23.7 kW/kg and an energy density of 21.4 Wh/kg.