Impact of particle size of lithium manganese oxide on charge transfer resistance and contact resistance evaluated by electrochemical impedance analysis

To achieve high-power lithium-ion batteries, resistances of both positive and negative electrodes must be reduced, because these are the main sources of internal resistance of the batteries. It is necessary to elucidate the impact of physicochemical properties of lithium insertion materials on the resistance of electrodes, to reduce the internal resistance of the batteries. The resistance of electrodes consists of charge transfer resistance, R-ct, and contact resistance, R-cont. The diluted electrode method, in which the amount of active material in an electrode varies but retains the factors related to electrode structure, can distinguish the two resistances, R-ct and R-cont. As this method does not alter the electrode structure, it is possible to elucidate the relationship between the two resistances and the physicochemical properties of lithium insertion materials. In this study, the impact of the particle size of Li[Li0.1Mn1.9]O-4 (LMO) on the R-ct and R-cont is revealed using the electrochemical impedance analysis by applying the diluted electrode method. As the particle size of LMO increases, R-cont slightly decreases. The R-ct more strongly depends on the LMO particle size because of the change in specific surface area as a function of the particle size, although the charge transfer resistance per LMO surface area is constant. From the two resistances determined by the electrochemical impedance spectroscopy, the optimum particle morphology and electrode structure is discussed. (C) 2020 Elsevier Ltd. All rights reserved.