Mechanical properties modeling of cathode materials for lithium-ion batteries based on bond valence model

To clarify electrochemical-mechanical relation of cathode materials for lithium-ion batteries, a series of empirical mechanical property models based on the bond valence model are applied to estimate the hardness, bulk, shear, and Young's moduli, Poisson's ratio and fracture toughness of typical cathode materials, such as LiCoO2, LiNi1-x-yCoxMnyO2, LiNi0.80Co0.15Al0.05O2, LiMn2O4, and LiFePO4. The calculated results are in agreement with experimental values. The mechanical properties have been predicted for low Ni compounds LiNixCo1–2xMnxO2 (0 ≤ x ≤ 0.5), high Ni compounds LiNi0.8Mn0.2-xCoxO2 (x = 0, 0.1, 0.2), and free Co compounds LiNixMn1-xCo0O2 (x = 0.5, 0.6, 0.8). For LiCoO2 during lithiation and delithiation processes, the hardness and bulk modulus of LixCoO2 decrease nearly linearly with the decrease of Li concentration. The effects of Al doping on the mechanical properties of LiAlxCo1-xO2 are also revealed from the insights into the chemical bonds. The models are powerful for extensively predicting and tuning electrochemical-mechanical properties of cathode materials.