Recently, a research team led by Prof. Tianshou Zhao at the Hong Kong University of Science and Technology comprehensively investigated the feasibility of using borophene, a newly synthesised 2D sheet of boron, as an anode material for sodium-based batteries via ab initio calculations.
The calculation results show that during charge, the maximum Na/B ratio can reach 0.5 (Na0.5B), corresponding to a capacity of as high as 1218 mAh·g-1. The unique buckling structure of borophene leads to an anisotropic diffusion behavior.
Along the valley direction of borophene, the diffusion energy barrier for sodium is as low as 0.0019 eV, corresponding to an ultrahigh sodium diffusivity, which is estimated to be more than a thousand times higher than that of conventional anode materials and one to seven magnitudes higher than other previously reported 2D materials.
This ultrahigh diffusivity is expected to revolutionise the rate capability of sodium-based batteries. During the charge and discharge process, the metallic feature and structural integrity of borophene is predicted to be well preserved, which ensures good electronic conductivity and stable cyclability.
The calculated average OCV is 0.53 V, which is an appropriate value for sodium-based batteries to maintain a high energy density while effectively suppressing the dendrite formation. Till now, compared with other reported sodium anode materials, borophene holds the highest sodium diffusivity.