Study of structural and electrochemical characteristics of LiNi0.33Mn0.33Co0.33O2 electrode at lithium content variation

Abstract

In this paper, we present the results of a joint analysis of the structural, morphological, and electrochemical (thermodynamic and kinetic) characteristics of the LiNi0.33Co0.33Mn0.33O2 electrode. In the present study we applied following methods: scanning electron microscopy (SEM) with energy-dispersive elemental microanalysis (EDS), X-ray diffraction (XRD) in the operando mode during reversible lithiation/delithiation of the electrode, constant current chronopotentiometry (galvanostatic charge/discharge), galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). Using the material morphology analysis, the geometry of the space for the diffusion of lithium ions within its particles was determined. Structural studies made it possible to track the nature of the change in the unit cell parameters of the crystal structure of the material during the reversible lithiation/delithiation of the electrode. Electrochemical methods made it possible to determine the dependencies of the thermodynamic and kinetic parameters of the intercalation process on the electrode potential (the concentration of lithium ions in the intercalate). It was found that the lithium ions diffusion coefficient increases with the growth of the electrode potential (decreasing of the concentration of lithium ions), passes through a smooth maximum, and decreases gradually. The variation of D occurs in the range of 10−13–2 · 10−12 cm2·s−1. Synchronously with D, the structural parameter c changes in the range of 14.2–14.5 Å, which determines the diffusion limitations in the material. The existence of a significant and unavoidable hysteresis of the dependencies of the kinetic, thermodynamic and structural parameters on the electrode potential as well as the dependencies of the relaxed potential on the concentration of lithium ions in the intercalate has been established.