Organic pH Buffer for Dendrite-Free and Shuttle-Free Zn-I2 Batteries

Aqueous Zn-Iodine (I-2) batteries are attractive for large-scale energy storage. However, drawbacks include, Zn dendrites, hydrogen evolution reaction (HER), corrosion and, cathode shuttle of polyiodines. Here we report a class of N-containing heterocyclic compounds as organic pH buffers to obviate these. We evidence that addition of pyridine /imidazole regulates electrolyte pH, and inhibits HER and anode corrosion. In addition, pyridine and imidazole preferentially absorb on Zn metal, regulating non-dendritic Zn plating /stripping, and achieving a high Coulombic efficiency of 99.6 % and long-term cycling stability of 3200 h at 2 mA cm(-2), 2 mAh cm(-2). It is also confirmed that pyridine inhibits polyiodines shuttling and boosts conversion kinetics for I-/I-2. As a result, the Zn-I-2 full battery exhibits long cycle stability of >25 000 cycles and high specific capacity of 105.5 mAh g(-1) at 10 A g(-1). We conclude organic pH buffer engineering is practical for dendrite-free and shuttle-free Zn-I-2 batteries.

Automated summary

A class of N-containing heterocyclic compounds acts as organic pH buffers in aqueous Zn-Iodine (I-2) batteries to mitigate issues such as Zn dendrites, hydrogen evolution reaction (HER), corrosion, and polyiodines shuttle. These compounds regulate electrolyte pH, inhibit HER and anode corrosion, and preferentially absorb on Zn metal, achieving non-dendritic Zn plating/stripping. The batteries with these buffers exhibit high Coulombic efficiency, long-term cycling stability, and improved conversion kinetics.