Solvent mediated sodium storage enhancement in van der Waals layered materials

Layered materials with weak van der Waals interactions between interlayers are able to provide adequate spaces for sodium ion intercalation and expressways for ion diffusion. Ether solvents are proved capable to facilitate the transport of ions and electrons transport in electrodes in virtue of their flexible one-dimensional chain structure. The combination of layered graphite and ether-based electrolytes even contributes to the revival of graphite as a promising anode material for sodium ion batteries via solvent co-intercalation. Lighted by these findings, in this work, we choose a quasi-layered vanadium sulfide (VS4) as the electrode material and diglyme (DGM) as a multifunctional electrolyte solvent, to investigate the synergetic effects of solid material structure and electrolyte solvent on the electrochemical performances. Contrast to a drastically decay of capacity in electrolytes with ethylene carbonate/dimethyl carbonate, the capacity of VS4/RGO composites in DGM could maintain a value of near 400 mAh·g− 1 at a current density of 100 mA·g− 1 over 30 cycles and a capacity about 300 mAh·g− 1 at a quite high current density of 800 mA·g− 1. The performance enhancement could be ascribed to the solvent co-intercalation into the van der Waals gaps and the resulting facilitated ion diffusion in electrode, which was later proved by TEM characterization and EIS measurements. To further prove the role of DGM, the electrochemical performances of another typical layered material WS2 in these two electrolytes were measured and DGM solvent was found to contribute to greatly promoted performances as well.