Alanine-assisted low-temperature combustion synthesis of nanocrystalline LiMn2O4 for lithium-ion batteries

Nanocrystalline LiMn2O4 powders have been synthesized by combustion process in a single step using a novel fuel, l-alanine. Thermogravimetric analysis and differential thermal analysis of the gel indicate a sharp combustion at a temperature as low as 149 °C. Quantitative phase analysis of X-ray diffraction data shows about 97% of phase purity in the as-synthesized powder, which on further calcination at 700 °C becomes single phase LiMn2O4. High Brunauer, Emmett, and Teller surface area values obtained for ash (53 m2/g) and calcined powder (23 m2/g) indicate the ultrafine nature of the powder. Average crystallite size is found to be ∼60–70 nm from X-ray diffraction analysis and transmission electron microscopy. Fourier transformed infra-red spectrum shows two strong bands at 615 and 511 cm−1 originating from asymmetrical stretching of MnO6 octahedra. A nominal composition of Li0.88 Mn2O4 is calculated from the inductive coupled plasma analysis. From UV–vis spectroscopy, an optical band gap of 1.43 eV is estimated which is assigned to a transition between t2g and eg bands of Mn 3d. Electrochemical charge–discharge profiles show typical LiMn2O4 behavior with a specific capacity of 76 mAh/g.