Optimizing Synthesis of Maghemite Nanoparticles as an Anode for Li-Ion Batteries by Exploiting Design of Experiment

The synthesis of iron oxide nanoparticles via coprecipitation was studied by exploiting a factorial design of experiment methodology to investigate the influence of pH, medium temperature, Fe 3+ /Fe 2+ ratio, and reaction time on the crystallite size. X-ray diffraction revealed that crystallite size decreased with increased pH and the Fe 3+ /Fe 2+ ratio more significantly. This approach enabled us to make a reliable and reproducible protocol for optimizing the synthesis of monodispersed maghemite nanoparticles. Fourier transform infrared spectra and simultaneous thermal analysis results suggested the coexistence of two kinds of binding energies between surfactant (oleic acid) molecules and the maghemite nanoparticles. Brunauer–Emmett–Teller surface area and high-resolution transmission electron microscope results disclosed that the average particle size of the optimized sample was around 8 nm. Galvanostatic charge–discharge cycling for the optimized sample, and the sample with average particle size of 19 nm showed reversible capacities of 430 mAh g −1 and 340 mAh g −1 at 500 mA g −1 , respectively, which is attributed to the narrower size distribution and smaller particle size of the optimized sample.