Defect Emission Energy and Particle Size Effects in Fe:ZnO Nanospheres Used in Li-Ion Batteries as Anode

Pure and Fe-doped ZnO (Fe_xZn_yV1−x−yO₂) nanostructures with varying iron mole percentages of 3%, 4.5%, and 6% were synthesized by co-precipitation without vacuum ambient. Structural, morphological, defect, and electrochemical properties, when serving as an anode in Li-ion batteries, were studied. All the samples have a wurtzite ZnO crystallinity, and a slight shift from the x-ray diffraction patterns of Fe:ZnO samples shows that Fe³⁺ ions were substituted by Zn²⁺ ions. As the percentage of the Fe mole increases from 3% to 4.5%, the size of the particles decreases from 12 nm to 9 nm, but increases to 14 nm with 6% Fe doping. Although all the samples have a spherical type, and porous surfaces are exhibited in the 4.5% Fe:ZnO nanospheres. The emission bands originate due to energy levels generated by ZnO intrinsic defects in all the samples with changing emission peaks by Fe doping. The 4.5% Fe:ZnO results substantially enhance the specific capacity of 400 mAh g⁻¹ during 100 cycles.