A DFT study on the mechanical properties of Co 9 S 8 during the lithiation/sodiation process

Cobalt sulphides, including CoS, CoS 2 , Co 3 S 4 and Co 9 S 8 , have been studied as potential anode materials for Li- and Na-ion batteries. However, the mechanical properties of the cobalt sulphides have not been intensively investigated. In this work, density functional theory (DFT) calculation was employed to study the mechanical properties of the cobalt sulphides mentioned above. Besides, the mechanical properties of final products of lithiation/sodiation of Co 9 S 8 have been calculated, including the bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio. This work provides an insight into understanding the electrochemical performance of Co 9 S 8 material as anode material for Li- and Na-storage during the cycling process.