Kinetic characteristics of mixed conductive electrodes for lithium ion batteries

The rate performances of four mixed conductive electrodes (Li4/3Ti5/3O4, LiFePO4, LiCoO2 and LiCo1/3Ni1/3Mn1/3O2) were investigated using galvanostatic charge/discharge, electrochemical impedance Spectroscopy (EIS) and galvanostatic intermittent titration (GITT). These four electrode materials can be roughly divided into two groups according to the structure change during Li intercalation/extraction, i.e. the phase transition materials (Li4/3Ti5/3O4 and LiFePO4) and mixed phase transformation and solid solution materials (LiNi1/3Mn1/3Co1/3O2 and LiCoO2). Both the ionic conductivity and phase transition kinetics have a strong impact on the rate capability of the electrode material in addition to the generally accepted factors such as particle size and electronic conductivity. The rate capabilities of Li4/3Ti5/3O4 and LiFePO4, which have an extended flat region in the charge/discharge curves, mainly depended on their phase transition kinetics. The rate performance of the solid solution materials were controlled by the ionic conductivity, with some influence from the electronic conductivity.