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

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 (Na2Sn) 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 Na2Sn intermediates, boosting the reduction reaction of Na2Sn and the decomposition of Na2S species. Our results revealed that the NiCl2 monolayer can effectively immobilize the higher-order Na2Sn 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 Na2Sn 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.

Automated summary

Room-temperature sodium-sulfur (Na-S) batteries have great potential for next-generation energy storage devices, but face challenges of sodium polysulfide shuttle effect and sluggish reaction kinetics. This study proposes 2D metal chloride monolayers as multifunctional anchoring materials to address these challenges and enhance the battery performance.