Comparative study of 1,3-propane sultone, prop-1-ene-1,3-sultone and ethylene sulfate as film-forming additives for sodium ion batteries

Electrolyte additives play a pivotal role in improving the cyclability of the sodium-ion batteries (SIB) by modifying the composition of solid electrolyte interphase (SEI) film. Herein, we select three sulfur-based additives with similar molecular structure (1,3-propane sultone (1,3-PS), prop-1-ene-1,3-sultone (PES) and ethylene sulfate (DTD)), which is contrastively investigated using home-made Na(Ni0.4Mn0.4Cu0.1Ti0.1)0.999La0.001O2 (NMCT-La)/commercial hard carbon (HC) full-type cells within the voltage range of 1.2–4.4 V. It is shown that adding 2 wt% 1,3-PS or 2 wt% DTD in the base electrolyte (1 M NaPF6 in EC:DMC with 2 wt% FEC) can achieve an increasingly capacity retention rate from 58.7% to 82.0% and 79.4%, respectively, while PES has a negative effect. Electron microscopy characterizations (FESEM and TEM) and X-ray photoelectron spectroscopy (XPS) results confirm that 1,3-PS or DTD can generate a denser and more uniform SEI film on the HC electrode, meanwhile, be oxidized on the positive electrode to protect the NMCT-La material from the attack of the electrolyte during cycling. The formation of sulfates and sulfites (such as ROSO2Na and RSO3Na) through the decomposition of 1,3-PS and DTD can stabilize SEI film, resulting in a high-performance SIB with long lifespan.