Ionic liquids-assisted electrolytes in aqueous zinc ion batteries

In the quest for safer and low-cost batteries, zinc ion batteries have remarkable potential in various energy storage applications. However, selecting suitable electrolytes for zinc electrochemistry is challenging due to zinc's passivation and dendritic growth hindering long-term stability. Moreover, the synergy between newly developed electrode materials and electrolytes remains challenging for commercial applications. Therefore, in this study fifty (50) combinations of ionic liquids (ILs) were screened using COSMO-RS simulation to identify suitable ILs for aqueous electrolytes with ZnSO4 salt by comparing activity coefficients at infinite dilution, selectivity, and capacity of ILs to dissolve ZnSO4 salt in the aqueous phase. Further, calcium vanadate (CaV2O6) was synthesized using a modified molten salt method and characterized using a Scanning Electron Microscope and X-ray diffraction to confirm its successful synthesis. Afterwards, the performance of calcium vanadate in aqueous zinc batteries having ILs-assisted electrolytes were also evaluated and compared with conventional electrolyte (aqueous 1 M ZnSO4). Results revealed that ILs based on tetramethyl ammonium cation were suitable for electrolyte applications with ZnSO4 salt. Furthermore, Tetramethylammonium hydrogen sulfate was compared with conventional ZnSO4 electrolyte and an initial discharge capacity of 330 mAh/g for calcium vanadate electrode with ILs-assisted electrolyte was observed as compared to 230 mAh/g with 1 M ZnSO4 aqueous electrolyte. Electrochemical impedance spectroscopy (EIS) measurements showed that ILs-assisted electrolyte's charge transfer and surface film resistance were lower than the conventional electrolyte. However, additional advancement in electrode and electrolytes, i.e. synthesis of electrode materials, and formulation of ILs-assisted electrolytes, may further improve the performance of aqueous zinc ion batteries.