Tailoring the mesoporous ZnMn₂O₄ spheres as anode materials with excellent cycle stability for sodium-ion batteries

Mesoporous spinel ZnMn₂O₄ (ZMO) microspheres as potential anode materials for sodium-ion batteries are prepared using the polyvinyl pyrrolidone (PVP)-assisted solvothermal technique. A one-step heat treatment process with heating varying from 1 to 5 °C min⁻¹ is used to reveal the crystal phase purity and tuning of porosity of the as-prepared materials. The ZnMn₂O₄ synthesized by heating rate of 1 °C min⁻¹ exhibits the highest specific surface area (47.016 m² g⁻¹) and pore size (23.342 nm). The slow heating rate sample exhibited better capacity and rate capability compared with the sample with the fast heating rate. The electrochemical reaction mechanism is epitomized by ex-situ X-ray powder diffraction/X-ray photoelectron spectroscopy analyses that revealed the conversion mechanism of the ZnMn₂O₄ electrode during charge and discharge processes. The results indicate that PVP-assisted approach provide porous microspheres of ZnMn₂O₄ demonstrates enhanced electrochemical performance due to a larger surface area and porosity to facilitate faster Na⁺ diffusion kinetics.