Differentiating the Rate Capabilities of Lithium-Nickel-Manganese Oxide Li[Ni 1/2 Mn 3/2 ]O 4 Insertion Materials and Electrodes Using Diluted Electrode Methods

Development of high-power lithium-ion batteries requires the optimization of the electrode kinetics of lithium-insertion materials to improve the rate capability of these devices. The rate capability of lithium-insertion electrodes is controlled by the concentration overvoltages that arise from changes in the Li + concentration at the electrode/electrolyte interface. Two distinct rate-capability behaviors prevail depending on whether charge transport is limited by Li-ion mass transfer within the solid particles or within the interstitial spaces of the electrode. In this study, the diluted electrode method is employed to characterize the two types of rate-capability behavior exhibited by Li[Ni 1/2 Mn 3/2 ]O 4 (LiNiMO) electrodes. Low-LiNiMO electrodes exhibit better rate capabilities than high-LiNiMO electrodes indicating that lithium-ion transport is more effective (i.e., much faster) in the solid active material than in liquid electrolyte within the electrode pore. The results provide useful insights for understanding the electrode kinetics of lithium-insertion materials and designing electrodes for high-power lithium-ion batteries.