Electrocapacitive Properties of MnFe2O4 Electrodes in Aqueous LiNO3 Electrolyte with Surfactants

The electrocapacitive properties of MnFe2O4 hollow spheres and colloidal nanocrystal clusters in electrolyte LiNO3 containing surfactants were studied. Electrochemical performances of supercapacitors were evaluated by cyclic voltammetry (CV), galvanostatic charge-discharge, self-discharge, cycle stability and electrochemical impedance spectroscopy (EIS). Results showed that the MnFe2O4 colloidal nanocrystal clusters electrode displayed a higher capacitance than that of MnFe2O4 hollow sphere. Anionic surfactant sodium dodecyl sulphate (SDS) and non-ionic surfactant p-t-octylophenol (Triton-X-100) and poly(ethylene glycol)-block-poly(propylene glycol)-block-Poly(ethylene glycol) (P123) were added respectively to LiNO3 electrolyte to investigate capacitive features of MnFe2O4-nanocrystal-based supercapacitors. It was found that lowering the interfacial tension between the electrode and electrolyte favoured the diffusion of lithium ions. For example, surfactant SDS enhanced 36.8% capacitance with an energy density of 14.5 Wh/Kg at the current density of 0.05 A/g, and the capacitive retention was 82% after 1000 cycles. However, the capacitance improves about 22.8% and 12.8% after the addition of Triton-X-100 and P123, respectively. Based on the experimental results, the enhancement mechanism of surfactants on the electrochemical performances of the as-prepared supercapacitors was proposed.