Dilute electrolyte with chaotropic anion addition for enhanced Zn-Ion storage performance in MXenes

Optimizing electrolytes is essential for improving the electrochemical stability window (ESW) and energy storage capacity of aqueous energy storage devices. High-concentration electrolytes improve performance but face solubility, conductivity, and stability issues. Here, a strong chaotropic anion, ClO₄⁻, is introduced into 1 M ZnSO₄ to expand the ESW and boost performance in dilute electrolytes. Theoretical simulation and experimental results provide that perchlorate not only significantly enhances ionic conductivity, leading to faster ion diffusion, but also weakens hydrogen bonds formation, reduces free water at the electrode surface, and promote the desolvation of hydrated zinc ions. Collectively, these factors lead to an improvement in the ESW and enhance overall device performance. Therefore, in the mixed electrolyte of 0.005 M Zn(ClO₄)₂ and 1 M ZnSO₄, the Zn//Mo₂ScC₂T_z aqueous zinc-ion hybrid supercapacitor (ZHSC) achieves a voltage window expansion from 1.0 to 1.3 V, delivering a high specific capacitance of 692.3 F g⁻¹ at 0.2 A g⁻¹. Furthermore, an asymmetric supercapacitor with the same electrolyte operates at 1.8 V, delivering an energy density of 98.1 Wh kg⁻¹ at 180 W kg⁻¹ and maintaining 17 Wh kg⁻¹ at 9000 W kg⁻¹. Notably, this electrolyte design strategy is universally applicable for enhancing Zn-ion storage performance of MXene-based materials.