Controlled Crystallization Preparation And Anion & Cation Co-dopant For LiMn₂O₄

Spinel LiMn₂O₄ is one kind of cathode materials for Li-ion batteries (LIB), which is quite cheap and benign to environment, but the Jahn-Teller Effects caused by Mn³⁺ during the process of charge-and-discharge make the material very bad cycle performances, especially at high temperature. Spinel LiMn₂O₄ will play an important role in the two application fields of handy electrical source and batteries for electric vehicle (EV) if its capacity retention can be strengthened. Based on the mechanism of capacity fading, in this paper dopant was selected and shape controlling of LiMn₂O₄ particles was optimized aiming to improve its integrative performance.Spinel LiMn₂O₄ was synthesized by Solid-State reaction at 800 °C with electrolytic manganese oxide and Li₂CO₃ as precursors. It was demonstrated that the synthesized material had good electrochemical performance. Its initial reversible capacity was up to 122.04mAh/g, and the capacity retention was still about 80% after 100 cycles.Spinel LiMn₂O₄ were synthesized, into which F^- anion was co-doped together with each of Co³⁺, Cr(3+), Al(3+), Mg²⁺. It was showed that the materials co-doped by Al & F, Mg & F had better electrochemical performance, and their reversible capacities and capacity retentions were 118.07mAh/g, 117.57mAh/g and 91.77%, 99.04%, respectively, after 20 cycles. These two kinds of materials also displayed better high-temperature performance compared with pure LiMn₂O₄. The (LiMn₂O₄)_x (MgAl₂O₄)_1-x (x=0, 0.025, 0.050, 0.075) compounds were synthesized by Solid-State Reaction and studied firstly in this paper. The compound exhibited standard spinel structure and good electrochemical performance when x was 0.025, whose initial reversible capacity was up to 120.07mAh/g keeping the high capacity retention of 93.93% after 30 cycles.Controlled Crystallization Method was firstly put forward to synthesize the spherical LiMn₂O₄ in order to improve the integrative performance. The factors which would affect the shape of spherical MnCO₃, such as concentrations, stirring intensity, deposition agents, themode of adding reagent, were systematically studied based on the principle of preparation of single dispersed particle. The suitable conditions were obtained, in which spherical and uniformly dispersed MnCO3 were available.MnCC>3 pretreated was mixed uniformly with Li2CO3 in agate mortar, followed by calcinations at high temperature, and then spherical or sphere-like spinel LiMn2O4 was attained. The Stoichiometric sphere-like spinel LiMn2O4 had obviously excellent electrochemical performance, whose initial reversible capacity was 129.40mAh/g with high capacity retention of 95.28% after 100 cycles, than those synthesized by traditional Solid-State Reaction. Li-riched spherical LiMn2O4 had the reversible capacity of 112.95mAh/g after 150 cycles, and the capacity fading was just 2.86%, that is to say, only 0.019% capacity fading each cycle.Kinetics of Li intercalation/de-intercalation into/from LiMn2O4 was analyzed by cycle voltammetry (CV) measurement. In the CV the two sharp and symmetrical redox apexes were observed. Moreover, it was demonstrated that the material had very good reversible Li intercalation and de-intercalation reaction.