Excluding the Trouble from Interfacial Water by Covalent Organic Polymer to Realize Extremely Reversible Zn Anode

Abstract

The side reactions related to water are the major issue hindering practical application of Zn metal batteries. To exclude the trouble from interfacial water, a covalent organic polymer (COP) layer with N, N′-Bis(salicylidene)ethylenediamine structure is designed, whose strong coordination ability with Zn2+ enhances the de-solvation kinetics of solvated Zn2+ which is conducive to interfacial water removal thus alleviating the side reactions related to water. This function has been certified by density functional theory along with molecular dynamics analysis. Moreover, measurements including in situ electrochemical gas chromatography, in situ optical microscopy, in situ X-ray diffraction and in situ Raman spectroscopy verify the weakened side reactions (including hydrogen evolution and corrosion) along with homogenous Zn deposition contributed from the covalent organic polymer layer. Benefiting from these merits, when assemble into cells based on common ZnSO4-based aqueous electrolyte, the COP layer-decorated anode exhibits excellent electrochemical performance of a high average Coulombic efficiency value 99.5% at a high capacity of 5.0 mA h cm−2. What's more, the symmetric cells can operate at −20 °C and the full cell with N/P ratio as low as 1.2 can cycle stably for 100 cycles, which would carry forward the promising practical application of Zn metal batteries.