Constructing High-Performance Zn-Iodine Batteries with CuI-PVP Composite Layer Coated Zn Anodes

Abstract

Aqueous zinc-iodine (Zn-I₂) batteries featuring abundant raw materials, inherent safety, excellent cost competitiveness and environmental benignity have been identified as one kind of important electrochemical energy storage devices. However, these batteries always suffer from inferior electrochemical performance, because of dendrite growth and corrosion/passivation of the anodes. Herein, a copper iodide-polyvinylpyrrolidone (CuI-PVP) composite layer is proposed to suppress the parasitic reactions and protect the Zn anodes. In this layer, the CuI can spontaneously react with metallic Zn and convert into Cu and Cu₅Zn₈ (2CuI+Zn→2Cu+ZnI₂; 5Cu+8Zn→Cu₅Zn₈). The highly zincophilic Cu and Cu₅Zn₈, as heterogeneous seeds, can guide the uniform Zn nucleation and deposition, while alleviating corrosion of the Zn anodes. At the same time, the iodide species releasing from the composite layer can be oxidized and deposited on the cathodes, contributing additional capacity. As a result, the symmetric cell prepared with the CuI-PVP@Zn anodes demonstrates a long cycling lifetime of 1400 hours at 1 mA cm⁻² and 1 mAh cm⁻². Under an even higher current density of 5 mA cm⁻², the CuI-PVP@Zn cell can still stably work for more than 660 hours. The practical application of this CuI-PVP@Zn electrode has been further demonstrated in Zn-I₂ full batteries, which achieve 60 % higher specific capacity than the untreated ones (251.4 vs. 157.1 mAh g⁻¹ after 2800 cycles).