Rational design of Janus MXene monolayers as promising frameworks for high-performance sodium metal anodes†

Abstract

MXenes represent a novel class of two-dimensional materials that have been extensively utilized as frameworks in sodium (Na) metal anodes due to their high electrical conductivity, large specific surface area, and diverse surface terminations. Although MXenes offer numerous advantages, there is still room for improvement regarding sodiophilicity. Various modification approaches have been proposed to augment the sodiophilicity of MXene frameworks, thus facilitating the uniform deposition of Na. Nevertheless, the function of innovative Janus modification approaches in regulating Na deposition remains unclear. To address this issue, six Janus MXene monolayers with distinct transition metals on opposing sides were designed to evaluate their potential as Na metal anode frameworks. The deposition and diffusion behavior of Na on the surfaces of these six Janus MXenes was investigated using first-principles calculations and ab initio molecular dynamics simulations. The computational results indicate that these Janus MXenes exhibit superior performance compared to the pristine single transition metal MXenes, attributed to the alterations in charge state resulting from the asymmetric surface structure. Specifically, HfTiCS₂ and VTaCO₂ exhibit significant sodiophilicity and possess large critical current densities, enhancing the cycling stability of Na metal batteries. Consequently, Janus MXenes demonstrate their superiority as framework materials for Na metal anodes and will drive further breakthroughs in Na metal battery technology.