Construction of Cu₂O@CuO Sea-Urchin-Like Heterojunction Materials for Enhancing Zinc Storage

Aqueous zinc-ion batteries (AZIBs), characterized by excellent safety, cost-effectiveness, and environmental friendliness, have emerged as a research focus in metal batteries. However, their low capacity and poor temperature adaptability hinder their practical application. Herein, deep eutectic solvents (DESs) are used as solvents, morphology assistants, and reducing agents to synthesize a sea-urchin-like Cu₂O@CuO heterojunction composite. This unique interfacial structure significantly accelerates ion diffusion and generates additional active sites. Characterization and theoretical calculations indicate that the heterojunction interface provides additional electromotive force, effectively promoting electron migration. The scanning electrochemical cell microscope (SECCM) has the capability to visually map heterogeneous interfaces and identify Zn²⁺ storage sites, and thus allows for their visualization. Furthermore, a gel electrolyte is prepared by dissolving PVA in one of the DES components. Notably, the flexible AZIB assembled using the prepared Cu₂O@CuO and gel electrolyte displays a specific discharge capacity of 337.1 mAh g^-1 and demonstrates broad temperature applicability within the range of -25-60 °C. In this study, the functionalization of DES is utilized to prepare Cu₂O@CuO, which paves a novel route for the synthesis of more metal oxide heterostructure electrode materials.