The performance of Li-ion batteries relies heavily on the capacity and stability of constituent electrodes. Recently synthesized 2D silicene has demonstrated excellent Li-ion capacity with high charging rates. To explore the external influences for battery performance, in this work, first-principles calculations are employed to investigate the effect of external strain on the adsorption and diffusion of Li on silicene monolayers. It was found that tensile strain could enhance Li binding on silicene. The diffusion barrier is also calculated and the results show that Li diffusion through silicene is facilitated by tensile strain, whereas the strain has a limited effect on the energy barrier of diffusion parallel to the plane of pristine silicene. Our results suggest that silicene could be a promising electrode material for lithium ion batteries.