Improved Mechanical Characterization of LiCoO2 Cathode Material by Ab-Initio Calculations Using Density Functional Theory

In the application of density functional theory (DFT) calculations to LiCoO2 (LCO) cathode material of lithium-ion batteries, this study investigates the differences between the obtained values for lattice constants, elastic constants, and stress-strain curves using different calculation condition such as exchange-correlation energy functionals; additionally, it attempts to improve the accuracy of the mechanical characterization of the DFT calculation. The results reveal that the adoption of Perdew-Wang (PW91) functional with dispersion corrections is better in the structural optimization of the DFT calculation for the LCO cathode compared with other calculation conditions, such as the adoption of Perdew-Burke-Ernzerhof (PBE) and revised PBE for solids (PBE-solid), which have been used in previous studies. The high accuracy of the lattice constant calculations in the structural optimization using PW91 results in a relatively high evaluation accuracy of the mechanical properties of these cathode materials. Additionally, a strong correlation between the lattice (or lattice volumes) and elastic constants is observed; evidently, a slight deviation in the lattice constants causes a relatively significant change in the elastic constants. In some of the calculation results for stress-strain curves, differences in the elastic limits (elastic regions) dependent on the selected exchange-correlation functionals are clearly observed. In the ab-initio calculations using density functional theory, we estimate the mechanical properties of LiCoO2 (LCO) cathode material and seek better exchange-correlation functionals. Our study reveals that the Perdew-Wang (PW91) functional is better in the structural optimization and estimation of mechanical properties of LCO compared with other functionals.