Ce(NO3)4: A dual-functional electrolyte additive for room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur batteries face enormous challenges in the coulombic efficiency, capacity retention, and rate performance, which are seriously related to the solid electrolyte interface film, the shuttle effect of polysulfide, and the sodium-sulfur reaction kinetics. Adjusting the electrolyte composition by additives can significantly improve the battery performance and is attracting tremendous attention. However, the reported additives mainly focus on one of the two electrodes. It is still a considerable challenge to balance both aspects. This work proposes a novel dual-functional additive, Ce(NO3)4, and studies its comprehensive influence on the battery performance by X-ray diffraction (XRD), Fourier transforms infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), and electrochemical techniques. The results show that Ce(NO3)4 generates NaCeO2 and NaNO3 to deposit on the Na surface. This inert deposition layer inhibits the side reactions between Na and polysulfides and optimizes the Na dissolution/deposition process, thereby improving the cycle stability of the battery. In addition, Ce4+ has a strong adsorption effect on capturing and evenly depositing polysulfides on the S cathode to inhibit the shuttle effect. In short, the Ce(NO3)4 additive plays a dual function of protecting the Na anode and optimizing the S cathode reaction.