Effect of Anions in Zn‐Based Aqueous Electrolyte on Electrochemical Performance of Prussian Blue Analogue

The solvation structure of the cation is significantly influenced by the nature of the surrounding anions and electrolyte concentration. Herein, different anions such as Cl⁻, SO₄ ²⁻, and NO₃ ⁻ is shown to influence Zn²⁺ solvation structure and other properties, consequently affecting the electrochemical performance of Prussian blue analogue as revealed by experimental and computational studies.

The effect of an anion from the electrolyte salt plays a crucial role in modulating the solvation structure of the cation and the electrochemical performances of the energy storage systems. Herein, the effect of different anions such as chlorides (Cl⁻), nitrates (NO₃ ⁻), sulfates (SO₄ ²⁻), and their influence on the solvation structure, diffusivity of Zn²⁺ cation, redox kinetics, and ion storing behavior of Zn-based Prussian blue analogue (PBA) electrodes are explored. Combining molecular dynamics simulations and experimental observations, the results divulge that different anions can significantly modulate the solvation shell and diffusivity of the cation, thereby influencing the electrochemical properties of the PBA electrodes. Further, increased anion concentration and its consequences on the aforementioned properties are investigated by employing 6 m water-in-salt electrolyte (WiSE). It is found that in ZnCl₂, a moderate Zn²⁺-Cl⁻ interaction offers higher ion diffusivity, thereby facilitating more efficient Zn²⁺ intercalation into the PBA electrode, resulting highest specific capacity of 56 mAh g⁻¹ at 2C-rate and the highest coulombic efficiency of 80% in 1 m ZnCl₂ and shows superior cycling stability in long-term cycling in 6 m-WiSE comparison to other anions. This work highlights the pivotal role of anions in tuning electrolyte molecular structure and its dynamics, ultimately governing cation transport and electrode kinetics in aqueous zinc-ion batteries.

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