Strain-engineered two-dimensional MoS 2 as anode material for performance enhancement of Li/Na-ion batteries

Recent years have witnessed a surge of research in two-dimensional (2D) nanostructures for development of new rechargeable Li/Na-ion battery systems. Herein, via first-principles calculations we demonstrate strain-engineered Li/Na adsorption and storage in 2D MoS2 as anode material, aiming to enhance the operating performance of Li/Na-ion batteries. Our results show that tensile strain greatly increases the adsorption of Li/Na atoms on MoS2, and a modest strain of 6% increases Li (Na) adsorption energy by over 70%, which originates from the strain-induced upshift of Mo d states towards Fermi level that interact strongly with Li/Na s states, in analogy with the d-band model in metal catalyst. Significant narrowing of the n-doped semiconducting gap of MoS2 suggests the improved electric conductivity that may benefit charge carrier transport. By mapping out the potential energy surfaces, we show shallow energy barriers of ion diffusion with ~0.2 eV for Li and 0.1 eV for Na. Furthermore, the strain-steered competition between chemical bonding and coulomb repulsion results in high Li/Na storage capability and relatively low average operating voltage. We believe that the fundamental principle underlying the use of strain to enhance performance of renewable ion battery is applicable to other stretchable low-dimensional nanomaterials.