Abstract:

LiNi_0.5Mn_1.5O₄(LNMO) is a promising cathode material for the next generation of high energy density lithium ion batteries. However, the serious manganese ion dissolution and rapid capacity degradation impede their practical application. Here, ternary spinel type high voltage cathode material LiNi_0.4Co_0.1Mn_1.5O₄(LNCMO) was synthesized by hydrothermal-calcination method. The calcination temperature and heating rate were optimized and investigated. The sample was uniform rhomboid-like morphology feature with pure structure. The specific surface area of the sample was 3.72m²/g and the average pore size was 11.60nm. The discharge voltage of LNCMO was close to 4.75V, and the initial specific capacity was about 143.90mAh/g, which was close to the theoretical specific capacity of LNCMO(146.70mAh/g). According to the XRD and XPS results, the proportion of Mn⁴⁺ was higher than that of Mn³⁺ in this sample. At the same time, appropriate calcination temperature and heating rate could avoid the formation of Li _x Ni_1-x O impurity phase, and thus the structural stability was higher, the charge transfer resistance was lower and the electrical performance was better of this sample. Comparing the XRD and SEM results of cathode materials before and after the cycle, the phase was basically the same, but the morphology and structure collapse was serious under high current density, which limited the cycle stability. This paper provided an effective strategy for preparing ternary high voltage materials for higher capacity and discharge voltage.

Key words: lithium ion battery, cathode, composites, high voltage, LiNi_0.4Co_0.1Mn_1.5O₄

摘要：

LiNi_0.5Mn_1.5O₄（LNMO）是一种有前景的下一代高能密度锂离子电池正极材料，但其中的锰离子溶解严重、容量衰减严重，阻碍了其应用。本工作通过水热-煅烧合成了LiNi_0.4Co_0.1Mn_1.5O₄（LNCMO）三元尖晶石型高电压复合材料，探究了煅烧温度和升温速率等制备条件对样品形貌和结构的影响。本文合成的LNCMO样品微观形貌呈类菱形结构，物相纯净，比表面积为3.72m²/g，平均孔径为11.60nm，放电电压接近4.75V，在20mA/g下初始放电比容量达143.90mAh/g，和LNCMO的理论比容量（146.71mAh/g）的比值达98%。根据XRD和XPS等表征分析可知，复合材料中的Mn⁴⁺比例较大，Mn³⁺较少，且合适的煅烧温度和升温速率避免了Li _x Ni_1-x O杂质相的生成，因此本文制备的材料相比LNMO材料结构稳定性增强，电荷转移阻力低，电性能尤其是比容量大幅提升。本文还对比了循环前后的样品，发现其物相基本一致，但高电流密度下形貌结构坍塌严重，影响了循环稳定性。本研究提供了一种有效制备三元高电压材料的策略。

关键词: 锂离子电池, 正极, 复合材料, 高电压, LiNi_0.4Co_0.1Mn_1.5O₄