Toward Rapid-Charging Sodium-Ion Batteries using Hybrid-Phase Molybdenum Sulfide Selenide-Based Anodes

To attain both high energy density and power density in sodium-ion (Na⁺ ) batteries, the reaction kinetics and structural stability of anodes should be improved by materials optimization. In this work, few-layered molybdenum sulfide selenide (MoSSe) consisting of a mixture of 1T and 2H phases is designed to provide high ionic/electrical conductivities, low Na⁺ diffusion barrier, and stable Na⁺ storage. Reduced graphene oxide (rGO) is used as a conductive matrix to form 3D electron transfer paths. The resulting MoSSe@rGO anode exhibits high capacity and rate performance in both organic and solid-state electrolytes. The ultrafast Na⁺ storage kinetics of the MoSSe@rGO anode is attributed to the surface-dominant reaction process and broad Na⁺ channels. In situ and ex situ measurements are conducted to reveal the Na⁺ storage process in MoSSe@rGO. It is found that the MoS and MoSe bonds effectively limit the dissolution of the active materials. The favorable Na⁺ storage kinetics of the MoSSe@rGO electrode are ascribed to its low adsorption energy of -1.997 eV and low diffusion barrier of 0.087 eV. These results reveal that anion doping of metal sulfides is a feasible strategy to develop sodium-ion batteries with high energy and power densities and long life-span.