Sun Gang, Yin Xucai, Yang Wu, Song Ailing, Jia Chenxiao, Yang Wang, Du Qinghua, Ma Zhipeng, Shao Guangjie
State Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinhuangdao 066004, China.
Phys Chem Chem Phys. 2017 Nov 15;19(44):29886-29894. doi: 10.1039/c7cp05530g.
Lithium cathode materials have been considered as promising candidates for energy storage applications because of their high power/energy densities, low cost, and low toxicity. However, the Li/Ni cation mixing limits their application as practical electrode materials. The cation mixing of lithium transition-metal oxides, which was first considered only as the origin of performance degeneration, has recently been reconsidered as a way to stabilize the structure of active materials. Here we find that as the duration of the post-synthesis thermal treatment (at 500 °C) of LiNiCoMnO (NCM) was increased, the Li/Ni molar ratio in the final product was found to decrease, and this was attributed to the reduction in nickel occupying lithium sites; the cation mixing subtly changed; and those subtle variations remarkably influence their cycling performance. The cathode material with appropriate cation mixing exhibits a much slower voltage decay and capacity fade during long-term cycling. Combining X-ray diffraction, Rietveld analysis, the Fourier transform infrared technique, field-emission scanning electron microscopy, and electrochemical measurements, we demonstrate that an optimal degree of Ni occupancy in the lithium layer enhances the electrochemical performance of layered NMC materials and that this occurs through a "pillaring" effect. The results provide new insights into "cation mixing" as a new concept for material design utilization of layered cathodes for lithium-ion batteries, thereby promoting their further application in lithium-ion batteries with new functions and properties.
锂阴极材料因其高功率/能量密度、低成本和低毒性，被视为储能应用的有前景的候选材料。然而，锂/镍阳离子混合限制了它们作为实用电极材料的应用。锂过渡金属氧化物的阳离子混合，最初仅被视为性能退化的根源，最近又被重新视为稳定活性材料结构的一种方式。在这里，我们发现，随着LiNiCoMnO（NCM）合成后热处理（在500°C）时间的增加，最终产物中的锂/镍摩尔比降低，这归因于占据锂位点的镍的减少；阳离子混合发生了微妙变化；而这些微妙变化显著影响了它们的循环性能。具有适当阳离子混合的阴极材料在长期循环过程中表现出慢得多的电压衰减和容量衰减。结合X射线衍射、Rietveld分析、傅里叶变换红外技术、场发射扫描电子显微镜和电化学测量，我们证明锂层中镍的最佳占据程度通过“支柱”效应增强了层状NMC材料的电化学性能。这些结果为“阳离子混合”提供了新的见解，“阳离子混合”是一种用于锂离子电池层状阴极材料设计利用的新概念，从而促进它们在具有新功能和特性的锂离子电池中的进一步应用。
