High power performance by defect introduction into spinel oxides for the usage of large-scale lithium ion battery

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Development of the cathode materials for Li ion battery is vital to meet the demands of portable devices, future usages of electric vehicles and so on. Among the cathodes, LiMn_2O_4 and related oxides has gained much attention because of its low cost, low toxicity, and relatively high energy density. Especially, LiNi_<0.5>Mn_<1.5>O_4 has received much attention because of its high discharge capacity, good cyclability, and dominant plateau at around 4.7 V, whereas other materials showed two plateaus at 〜4 and 5 V. In this study, the improvement of rate performance was attempted by introducing defects into spinel oxides. In addition, it was aimed to reveal the factors affecting rate performance from the viewpoint of defect chemistry. Spinel type oxide, LiNi_<0.5>Mn_<1.5>O_4 was synthesized with various temperatures and investigated their stoichiometry, crystal structures and electrochemical properties. Under oxygen atmosphere, a sudden increase of nonstoichiometry occurred with endothermes at around 760℃. In addition, infrared spectroscopic study revealed that ordered arrangement of Ni and Mn in octahedral sites was partially collapsed by the increase of nonstoichiometry. The electrochemical performance for the samples quenched from above and below 760℃ in oxygen atmosphere were investigated, and the samples quenched above 760℃ showed better rate-performance than those quenched below 760℃ Accordingly, the synthesis temperature of LiNi_<0.5>Mn_<1.5>O_4 was the key factor for controlling the arrangement of Ni and Mn, nonstoichiometry and electrochemical properties.