Two-dimensional NiCl2 monolayers as a promising multifunctional anchoring material in sodium–sulfur batteries

Abstract

Room-temperature sodium–sulfur (Na–S) batteries hold great potential for next-generation energy storage devices due to their high theoretical energy density and low cost. However, the shuttling effect of sodium polysulfide (Na₂S_n) species and the sluggish kinetics of the electrochemical conversion reaction greatly hamper the practical application of Na–S batteries. To address these challenges, by means of density functional theory (DFT) computations, we proposed two-dimensional metal chloride (MCl₂, M = Mg and Ni) monolayers as multifunctional anchoring materials, including immobilizing soluble Na₂S_n intermediates, boosting the reduction reaction of Na₂S_n and the decomposition of Na₂S species. Our results revealed that the NiCl₂ monolayer can effectively immobilize the higher-order Na₂S_n species with a stronger binding strength than the common electrolytes to prevent their dissolution. In particular, the NiCl₂ substrate exhibits excellent electrocatalytic activity for the sulfur reduction reaction with a low free energy barrier (0.37 eV) and the Na₂S decomposition reaction with a small kinetic barrier (0.45 eV), greatly lowering the energy barriers of Na₂S_n conversions during discharge and charge and thus guaranteeing the fast redox kinetics and high sulfur utilization of Na–S batteries. Therefore, we predicted that NiCl₂ monolayers can be utilized as a highly efficient multifunctional anchoring material for Na–S batteries.