Charge-discharge rate of spinel lithium manganese oxide and olivine lithium iron phosphate in ionic liquid-based electrolytes

摘要

Rate capability of Li/spinel LiMn_2O_4 or olivine LiFePO_4 positive electrode cells containing mixed imi-dazolium ionic liquids electrolytes has been investigated under comparison with conventional organic solvent electrolyte and piperidinium ionic liquid. The LiMn_2O_4 electrode provides variation of rate capabilities among the ionic liquid electrolytes, while ionic liquid electrolytes provide similar extent of capacity degradation under high rate compared with organic solvent electrolyte for LiFePO_4 electrode. Such differences in electrolyte dependences of the rate capabilities can be explained in relation to parameters in the high frequency resistances on AC impedance, assumed as interfacial resistances. The rate capability of LiMn_2O_4 is somewhat related to the activation energy of the high frequency resistance, while for LiFePO_4 the resistance value appears to contribute to the rate capability.