Effects of MgO Coating on the Structural and Electrochemical Characteristics of LiCoO2 as Cathode Materials for Lithium Ion Battery
Effects of MgO Coating on the Structural and Electrochemical Characteristics of LiCoO2 as Cathode Materials for Lithium Ion Battery
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DOI：
10.1021/cm403846a
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发表时间：
2014-04-22
影响因子：
8.6
通讯作者：
Park, Sung Soo
中科院分区：
文献类型：
--
作者：
Shim, Jae-Hyun;Lee, Sanghun;Park, Sung Soo
为了了解MgO包覆LiCoO 2作为锂离子电池正极材料的电化学性能增强的原因，我们在纳米尺度上研究了材料的内部结构。MgO包覆的LiCoO 2在750-810 ℃的各种温度下退火，以找到最佳的热处理条件。用SEM、TEM、EELS、XRD等手段对薄膜的表面形貌和晶体结构进行了表征。电化学测试结果表明，MgO包覆的LiCoO 2具有较高的容量和良好的保持性能。特别地，在810摄氏度退火的样品，其在Li位点中具有高掺杂水平的Me 2+离子，表现出最高的保持容量，而在循环期间在MgO涂层和本体LiCoO 2之间的界面中不经历相变。通过TEM测量监测脱锂状态下的锂和空位有序。与裸LiCoO 2相比，我们发现MgO涂层在近界面处起到了阻止锂和空位有序化的作用，这与在810 ℃退火的MgO涂层样品的优异电化学循环性能一致。结果表明，随着热处理温度的升高，MgO层中的Mg 2+离子竞争性地向LiCoO 2中的Co和Li位扩散，影响LiCoO 2的结构稳定性和电化学性能。
To understand the origin of enhanced electrochemical performances of MgO-coated LiCoO2 as cathode materials for lithium ion battery, we investigate the internal structures of the materials at the nanometer scale. The MgO-coated LiCoO2 are annealed at various temperatures of 750-810 degrees C so as to find the optimized heat-treatment condition. The surface morphologies and crystalline structures are characterized by SEM, TEM, EELS, and XRD. The electrochemical results show that the MgO-coated LiCoO2 delivers a high capacity with excellent retention property. In particular, the sample annealed at 810 degrees C, which possesses the high doping level of Me2+ ion in the Li sites, exhibits the highest retention capacity without undergoing phase transformation in the interfaces between the MgO-coating layer and the bulk LiCoO2 during cycling. Lithium and vacancy ordering in the delithiated state is monitored by TEM measurements. comparison with the bare LiCoO2, we reveal that the MgO-coating layer plays a role in the prevention of lithium and vacancy ordering in the near-interfaces, which is in agreement with the excellent electrochemical cycling performances of the MgO-coated sample annealed at 810 degrees C. As a result, depending on the thermal treatment temperature, the Mg2+ ions from MgO layer diffuse into Co and Li sites in LiCoO2, competitively, and affect the structural stability and electrochemical performances.