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

锂离子电池正极材料的开发对于满足便携式设备和未来电动汽车的使用等需求至关重要。在阴极中，LiMn_2O_4及其氧化物因其成本低、毒性低、能量密度高而受到广泛关注。特别是LiNi_<0.5>Mn_<1.5>O_4，由于其放电容量大，循环性能好，在4.7 V左右有优势平台，而其他材料在~ 4和5 V有两个平台，受到了广泛的关注。本研究尝试通过在尖晶石氧化物中引入缺陷来提高速率性能。此外，还从缺陷化学的角度揭示了影响速率性能的因素。在不同温度下合成了尖晶石型氧化物LiNi_<0.5>Mn_<1.5>O_4，并对其化学计量学、晶体结构和电化学性能进行了研究。在氧气环境下，恒温动物的非化学计量量在760℃左右突然增加。此外，红外光谱研究表明，Ni和Mn在八面体位置上的有序排列由于非化学计量量的增加而部分崩溃。研究了在760℃以上和低于760℃的氧气氛中淬火样品的电化学性能，发现760℃以上淬火样品的速率性能优于760℃以下淬火样品。因此，LiNi_<0.5>Mn_<1.5>O_4的合成温度是控制Ni和Mn排列、非化学计量和电化学性能的关键因素。

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.