Boosting Zn Anode Utilization by Trace Iodine Ions in Organic-Water Hybrid Electrolytes through Formation of Anion-rich Adsorbing Layers

Aqueous Zn batteries are attracting extensive attentions, but their application is still hindered by H2O-induced Zn-corrosion and hydrogen evolution reactions. Addition of organic solvents into aqueous electrolytes to limit the H2O activity is a promising solution, but at the cost of greatly reduced Zn anode kinetics. Here we propose a simple strategy for this challenge by adding 50 mM iodine ions into an organic-water (1,2-dimethoxyethane (DME)+water) hybrid electrolyte, which enables the electrolyte simultaneously owns the advantages of low H2O activity and accelerated Zn kinetics. We demonstrate that the DME breaks the H2O hydrogen-bond network and exclude H2O from Zn2+ solvation shell. And the I- is firmly adsorbed on the Zn anode, reducing the Zn2+ de-solvation barrier from 74.33 kJ mol(-1) to 32.26 kJ mol(-1) and inducing homogeneous nucleation behavior. With such electrolyte, the Zn//Zn symmetric cell exhibits a record high cycling lifetime (14.5 months) and achieves high Zn anode utilization (75.5 %). In particular, the Zn//VS2@SS full cell with the optimized electrolyte stably cycles for 170 cycles at a low N : P ratio (3.64). Even with the cathode mass-loading of 16.7 mg cm(-2), the full cell maintains the areal capacity of 0.96 mAh cm(-2) after 1600 cycles.

Automated summary

Aqueous Zn batteries still face challenges due to Zn-corrosion and hydrogen evolution reactions. Adding organic solvents and iodine ions to the electrolyte provides a solution by reducing activity of water and improving Zn kinetics. The study demonstrates enhanced performance and high cycling lifetime of Zn anodes in both symmetric cells and full cells.