Effect of hydration level on zinc electrolyte properties

Abstract

We study zinc (Zn) plating and stripping in zinc cells using various compositions of hydrated zinc chloride (ZnCl₂·nH₂O) electrolyte (n = 10, n = 2.33, n = 1.5) at temperatures from −10 °C to 40 °C. The effect of deposition temperature on nuclei size, nucleation density, and growth of deposited Zn metal is studied by ex-situ microscopy investigations. Lowering the deposition temperature leads to smaller nuclei, higher nucleation density, and smoother zinc growth, forming a dendrite-free electrode surface. Compact and smooth zinc deposits contribute to long-term stability. There is no change in overpotential for the cell at −10 °C for more than 400 h. Long-term Zn deposition in Zn/Cu cells achieves an average coulombic efficiency (CE) of 99.2 % in the last 50 cycles using ZnCl₂·10H₂O electrolyte. The performance of electrolytes is evaluated in zinc-ion batteries with (zinc hexacyanoferrate) ZnHCF cathodes. The electrochemical studies show that the capacity of our zinc-ion battery in molten hydrated electrolytes increases from 17 mAh g⁻¹ at −10 °C to 72 mAh g⁻¹ at 40 °C, using n = 10 and n = 1.5 compositions of molten ZnCl₂ electrolyte. Increasing the temperature to 40 °C yields a high capacity and long-life zinc-ion battery. This research advances understanding of temperature-dependent molten hydrated electrolyte systems for zinc batteries.