A multifunctional ionic liquid additive providing a solvation structure and electrostatic shielding layer for highly stable aqueous zinc ion batteries

Abstract

The growth of dendrites and water-induced side reactions on the zinc (Zn) metal anode surface present significant challenges to the practical application of aqueous zinc ion batteries (AZIBs). To address these challenges, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF₆) was employed as a multifunctional ionic liquid additive. First-principles calculations and molecular dynamics simulations reveal that [BMIM]⁺ cations preferentially adsorb onto the protrusions of the Zn metal anode surface due to its high adsorption energy, promoting homogeneous Zn²⁺ ion deposition and effectively mitigating the “tip effect”. Simultaneously, the PF₆⁻ anions participate in the solvation structure of hydrated Zn²⁺ ions to minimize the solvation effect by reducing the number of surrounding water (H₂O) molecules. This suppresses unexpected side reactions caused by active H₂O molecules entering the Helmholtz Plane (HP), thereby optimizing the diffusion and nucleation behaviour of Zn²⁺ ions. Therefore, the Zn//Zn symmetric cell achieved an extended cycle lifetime of over 1000 h at a high current density of 4 mA cm⁻² and a capacity of 0.5 mA h cm⁻². Meanwhile, even after 3000 cycles at a high current density of 10 A g⁻¹, the Zn//NH₄V₄O₁₀ full cell exhibited an impressive capacity retention of 92.7%. The practical application of flexibility further demonstrates that the designed AZIBs exhibit promising potential for large-scale energy storage and provide valuable insights for future studies.