Carbon-Cloth Supported ZnO Nanorods as Binder-Free Zinc-Ion Battery Anodes: An Investigation into the Electrode Formation Process

Abstract

Zinc-based batteries are emerging as promising alternatives to mainstream technologies due to their superior safety, cost-effectiveness, and abundance of raw materials. However, zinc anodes, exhibit insufficient cycle life and low utilization in aqueous electrolytes, mainly owing to shape change and passivation. While nanostructuring of Zn anodes has been explored for Zn-Ni rechargeable alkaline batteries, no explicit electrochemical studies have elucidated how nanostructures, fabricated in the oxidized state, are reduced during the initial formation step, yielding elemental Zn. In this work, a hydrothermal synthesis of freestanding electrodes is proposed, based on vertically aligned ZnO nanorods grown directly on carbon cloth (CC) (ZnO/CC). ZnO nanostructuring mitigates passivation, while the carbon cloth fiber network confines soluble Zn(II) intermediates, hindering diffusion into the electrolyte bulk. Moreover, the CC substrate provides optimal electronic contact to the active material, and acts as a built-in current collector. This work investigates the evolution of ZnO/CC during the first electrochemical reduction cycle, with emphasis on morphochemical nanostructure changes  rather than establishing a benchmark anode. Electrochemical measurements are combined with advanced characterization techniques,  high-resolution transmission electron microscopy (HRTEM), and X-ray absorption hyperspectral imaging via scanning transmission X-ray microscopy (STXM) and ptychography at the Zn L-edge. This multimodal approach offers unprecedented insights into the ZnO-to-Zn reduction to guide future Zn-ion anode design.