On the drastically improved performance of Fe - Doped LiMn₂O₄ nanoparticles prepared by a facile solution - Gelation route

LiFe_xMn_2-xO₄ (x = 0.0, 0.1 and 0.2) with superior rate and cycling performance is synthesized using a sol - gel method by combining citric acid and glucose as the chelating agent. For the first time Fe is found to basically occupy the 16d site. Fe doping decreases the occupancies of Mn at the 8a site considerably, and reduces the variations of the lattice volume before and after charge significantly, and suppresses the formation of the lower valence manganese surface phases. The structure - related factors other than the conventional morphology and size lead to the drastically enhanced performance of the Fe - doped samples. The combination of the decreased occupancies of Mn on the 8a site, and the only occupation of Fe on the 16d site, and the suppression of the surface phases of manganese ions with the lower valences and the alleviation of the Jahn - Teller effect due to the partial replacement of Mn³⁺ by Fe³⁺ result in both the improved electronic and ionic conductivities, and thus the drastically enhanced performance. The capacity of 66 mAh g^-1 for x = 0.2 is delivered for 300C discharge with 1C charge. The capacity retentions after 1500 cycles for 100C discharge and 10C charge at room temperature (RT) and 60°C are 90% and 83%, respectively. The present study opens a feasible way to obtain the high performance manganese spinel cathode by controlling the lattice site occupation of an alien element and manganese and the formation of low valence manganese surface phases.