Enhanced electrostatic shielding effect through incorporation of trace amounts of highly chelating anions for establishing a more stable electric double layer†

Electrolyte engineering is seen as a straightforward and efficient approach to optimize the cycling performance of aqueous zinc-ion batteries (ZIBs), but most of the studies tend to focus on the role of a single functional group or molecule, ignoring the intra and intermolecular interactions. This study focuses on tetrasodium iminodisuccinate (IDHA) and analyzes the coexistence and interaction of anions and cations in the electrolyte. It is found that the IDHA anion, with its strong chelating ability, strongly adheres to the Zn anode surface, while also participating in the solvation structure of Zn²⁺ and Na⁺. As a result of the influence of IDHA anions, Na⁺ also acquires a more robust and stable solvation sheath, achieving a combination of electrostatic shielding effect and steric hindrance effect. Based on the joint action of these effects, the Zn anode/electrolyte electric double layer is reshaped, which inhibits the occurrence of growth of dendrites and various side reactions. With a trace amount of IDHA (0.02 mol L⁻¹), a high cumulative capacity density of 6860 mA h cm⁻² at 4 mA cm⁻² has been achieved for Zn//Zn symmetric cells, and a high coulombic efficiency of 99.879% and a stable voltage distribution in more than 2800 cycles have been achieved for the Zn//Cu asymmetric batteries. Besides, it demonstrates exceptional long-term cycling and rate performance when assembled with various cathode materials. In summary, we can propose a principle for the selection of electrolyte additives—molecules composed of anions with strong chelating ability and cations with the electrostatic shielding effect will become a class of key directions for selection of ideal additives in the future, and this kind of targeted modification idea will play a certain role in promoting the interfacial regulation strategies for aqueous metal batteries.