Electrochemical behavior of olivine-type LiMnPO4-based material in a mild aqueous electrolyte

Olivine-type pristine LiMnPO4 and nickel-substituted LiNi0.05Mn0.95PO4 electrode materials were synthesized via a sol-gel route, and characterized by X-ray diffraction (XRD), transmission electron microscopy, and X-ray fluorescence analysis techniques. Their electrochemical properties in 2 M Li2SO4 aqueous solution were investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge methods. Furthermore, X-ray absorption near edge structure analysis and XRD technique were employed to study the structural change of the pristine LiMnPO4 during the first charge/discharge cycle and the first-stage repeated charge/discharge activation cycles (increase in discharge capacity with increasing cycle number). The LiMnPO4-based electrodes were found to undergo a first-stage activation process with gradual increase in discharge capacity prior to capacity degradation in the experimental condition. Partial nickel substitution for manganese in LiMnPO4 can enhance the charge transfer reaction kinetics, and thereby increase the specific capacity of the LiMnPO4-based electrode.