Regulation of ligand-induced solvation structure for stable aqueous Zn-ion batteries

The practical application of aqueous zinc batteries (AZBs) is plagued by the limited reversibility of the electrodes, which is closely related to the Zn2+ primary solvation sheath (PSS). Ligand additives with a strong coordination ability are commonly preferred to tailor the Zn2+ PSS, but most of them are used at the expense of a higher desolvation energy barrier and sluggish charge-transfer kinetics. Herein, we investigated the relationship between additives' coordination ability with Zn2+ and performance of AZBs through three ligand additives, namely, BDM (1,3-benzenedimethanol), PDM (2,6-pyridinedimethanol) and PDMA (2,6-pyridinedimethanamine). As revealed by experimental and theoretical characterizations, both coordination strength and configuration of the additive with Zn2+ are determining factors in the Zn2+ desolvation process and lifespan of AZBs. PDM additives with a moderate coordination strength and delicate coordination configuration can effectively stabilize zinc anodes with a negligible effect on the Zn2+ charge-transfer kinetics. PDM can preferentially adsorb, exclude H2O and include SO42- in the PSS and promote the formation of a ZnS-modified solid-electrolyte interface (SEI). Therefore, with a trace amount of PDM (1.39 mg mL-1), a highly reversible Zn anode was demonstrated. Together with PDM's significant effect on inhibiting V2O5 dissolution and structural collapse and decreasing electrostatic repulsion between Zn2+ and the host material, Zn//V2O5 full cells can achieve high capacity and cycling stability.