Investigation of lithium ion kinetics through LiMn2O4 electrode in aqueous Li2SO4 electrolyte

Spinel LiMn2O4 was prepared by sol-gel method and characterized by Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscope. Cyclic voltammogram, galvanostatic charge/discharge testing, and electrochemical impedance spectroscopy (EIS) techniques were employed to evaluate the electrochemical behaviors of LiMn2O4 in 1 M Li2SO4 aqueous solution. Two redox couples at E-SCE = 0.78/0.73 and 0.91/0.85 V were observed, corresponding to those found at E-Li/Li(+) = 4.05/3.95 and 4.06/4.18 V in organic electrolyte. The discharge capacity of pristine LiMn2O4 in aqueous electrolyte was 57.57 mAh g(-1), and the capacity retention of the electrode is 53.7 % after 60 cycles. Only one semicircle emerged in EIS at different potentials in aqueous electrolyte, while three semicircles were observed in organic electrolytes. There was no solid electrolyte interface film on the surface of spinel LiMn2O4 electrode in aqueous electrolyte. The change of kinetic parameters of lithium ion insertion in spinel LiMn2O4 with potential in aqueous electrolyte for initial charge process was discussed in detail, and a suitable model was proposed to explain the impedance response of the insertion materials of lithium ion batteries in different electrolytes.