Investigation of LiMn2O4 cathodes in liquid and in gel electrolyte by electrochemical impedance spectroscopy

LiMn2O4 has been electrochemically investigated in gel electrolyte (24 wt% PMMA in 1 M LiBF4/1:1 EC:DEC) at various temperatures. At all temperatures tested, at least three time-constants could be distinguished, i.e. two semicircles and a sloping line at low frequencies. It was found that the high-to-medium frequency semicircle is close to constant with temperature, whereas the medium-to-low frequency semicircle shows a strong dependence on the temperature. It was demonstrated that the high-to-medium frequencies semicircle is related to the contact between the current collector and the active electrode material and the medium-to-low frequencies to the kinetics of the active electrode material. Moreover, fitting a mathematical model to the experimental data measured in gel and in liquid electrolyte indicated that the presence of 24 wt% PMMA does not have a significant impact on the kinetics of LiMn2O4.