Synthesis of spherical nanostructured LiMxMn2−xO4 (M = Ni2+, Co3+, and Ti4+; 0 ≤ x ≤ 0.2) via a single-step ultrasonic spray pyrolysis method and their high rate charge–discharge performances

LiMxMn2−xO4 (M = Ni2+, Co3+, and Ti4+; 0 ≤ x ≤ 0.2) spinels were prepared via a single-step ultrasonic spray pyrolysis method. Comparative studies on powder properties and high rate charge–discharge electrochemical performances (from 1 to 15 C) were performed. XRD identified that pure spinel phase was obtained and M was successfully substituted for Mn in spinel lattice. SEM and TEM studies confirmed that powders had a feature of ‘spherical nanostructural’, that is, powders consisted of spherical secondary particles with the size of about 1 μm, which were developed from close-packed primary particles with several tens of nanometers. Substitutions enhanced density of second particles to different extents, depending on M and its content. Charge–discharge tests showed that as-prepared LiMn2O4 could deliver excellent rate performance (around 100 mAh/g at 10 C). Ni substitution contributed to improving electrochemical performances. In the voltage range of 4.95–3.5 V, the materials showed much better electrochemical performances than LiMn2O4 in terms of capacity, cycleability and rate capability.