Enhanced Cycling Stability in Zn-Ion Batteries Using Aqueous-Organic Electrolyte Solvent Blends

Zinc-ion batteries (ZIBs) have emerged as a promising candidate for safe and affordable energy storage. This is particularly true for ZIBs using aqueous electrolytes, but unfortunately, they suffer from severe degradation issues that have not been resolved despite of extensive research efforts in this field. Hybrid electrolytes using both water and dimethyl sulfoxide (DMSO) as a solvent are proposed, which combine the non-flammable properties of water-based electrolytes with the stability of solvent-based electrolytes. Further, this hybrid electrolyte allows for using tetrafluoroborate (Zn(BF₄)₂) as a salt, which readily corrodes Zn in aqueous formulations, but also contributes to a more stable SEI in the hybrid solvent system. These results are corroborated using Density Functional Theory (DFT) simulations to show how DMSO modifies the solvation structure, as well as HRTEM to analyze the SEI structure and composition. Finally, it is demonstrated that the hybrid electrolyte suppresses the dissolution of NVO cathodes, allowing Zn||NVO full cells to operate stably for over 2000 cycles with ≈80% capacity retention. Overall, this work illustrates how mixed solvent-water based electrolytes have the potential to retain the safety and cost advantages of aqueous electrolytes, while at the same time suppressing degradation mechanisms.