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

Abstract

Aqueous Zn-Iodine (I2) 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−/I2. As a result, the Zn-I2 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-I2 batteries.