Determination of the chemical diffusion coefficient of lithium ions in spherical Li[Ni0.5Mn0.3Co0.2]O2

Abstract

The chemical diffusion coefficients of lithium ions (DLi) in spherical Li[Ni0.5Mn0.3Co0.2]O2 are systematically determined by galvanostatic intermittent titration technique (GITT) and electrochemical impedance spectroscopy (EIS). The DLi obtained from GITT are greatly dependent on the lithium content and cell potential. In the charge process, the DLi values are in the range of 9.0 × 10−11 to 3.3 × 10−9 cm2 s−1. In the discharge process, the DLi values are in the range of 1.9 × 10−11 to 3.9 × 10−9 cm2 s−1. In addition, the minimum values in the DLi are observed at the stoichiometry x ≈ 0.25 for Li1−x[Ni0.5Mn0.3Co0.2]O2, which coincide with the voltage-plateau region at about 3.75 V. The DLi obtained from EIS are in the range of 1.7 × 10−11 to 6.5 × 10−9 cm2 s−1 and the variation tendency with cell potential is consistent with the results obtained from GITT during the charge process.