Effect of electrode design parameters on the rate performance of LiNi0.6Co0.2Mn0.2O2 cathodes using pulse measurements

Abstract

Enhancing the rate performance and energy density of Li-ion batteries is of significant importance for their widespread applications. Herein, we evaluate the rate capability of LiNi0.6Co0.2Mn0.2O2 cathodes by varying the electrode parameters, such as the electrode density and loading mass, and probe the limiting factors behind the electrochemical performance based on electrochemical impedance spectroscopy and pulse polarization measurements at constant currents. The rate properties for both charging and discharging at C-rates of 0.2C–20C are highly dependent on the electrode design parameters. The moderate electrode density of 2.7 g cc−1 affords a balance between electron conduction and ion transport in the electrode, leading to the best rate capability. The thicker electrodes suffer from larger concentration overpotentials upon high-rate charging and discharging due to the Li-ion concentration gradient developed at the interface between the electrolyte and active material. The pulse experiments at long pulse time reveal the limiting factors, including the Li-ion mass transfer kinetics, allowing differentiation of the kinetics arising from different electrode parameters upon charging and discharging. The trade-off relationship between the energy and power properties from the Ragone plots underlines the importance of a suitable electrode design for specific fields in terms of gravimetric and volumetric applications.