A Spin-polarized DFT study of functionalized MXenes as effective anchor materials in lithium-sulfur batteries

Abstract

Lithium-sulfur (Li-S) batteries have attracted great enthusiasm in recent years due to ultra-high theoretical energy densities, abundant sulfur electrode resources and low price. Despite the severe shuttle effect of lithium polysulfides (LiPSs), the poor conductivity of S₈ and its intermediate products, and the relatively slow dynamics, pose significant challenges for the commercial application of Li-S batteries. Here, functionalized MXenes M₂CT₂ (M = V, Cr, Mn, and Mo; T = F and O) used as the sulfur host are studied to build multifunctional cathodes via spin-polarized first-principles calculation. Through analyzing the adsorption energy and configuration of S₈/Li₂S_n adsorbed M₂CT₂, it is found that spin polarization is indispensable to the Li-S battery calculation of MXenes with transition metals. With the spin polarization calculation, the M₂CT₂ exhibit moderate anchoring strengths and stable adsorption structures, which effectively mitigates the polysulfide shuttle phenomenon. The low decomposition barriers of Li₂S (0.27–1.00 eV) and low diffusion barriers of Li⁺ (0.11–0.44 eV) of M₂CT₂ are observed, which effectively improve the rate performance of batteries. Among the studied MXenes, V₂CO₂ and Mo₂CO₂ are the best choices of host materials for LiPSs with metallic characteristics, outstanding electrocatalysis performance, low decomposition barriers of Li₂S, and diffusion barriers of Li⁺. This work provides important insights into spin-polarized electrode materials for enhanced energy storage capabilities by investigating the application of intrinsic magnetic MXene compounds.