Zheng Jiaxin, Teng Gaofeng, Xin Chao, Zhuo Zengqing, Liu Jiajie, Li Qinghao, Hu Zongxiang, Xu Ming, Yan Shishen, Yang Wanli, Pan Feng
School of Advanced Materials, Peking University, Shenzhen Graduate School , Shenzhen 518055, People's Republic of China.
Advanced Light Source, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
J Phys Chem Lett. 2017 Nov 16;8(22):5537-5542. doi: 10.1021/acs.jpclett.7b02498. Epub 2017 Nov 1.
Ni/Li exchange (disordering) usually happens in layered Li(NiMnCo)O (NMC) materials and affects the performance of the material in lithium-ion batteries. Most of previous studies attributed this phenomenon to the similar size of Ni and Li, which implies that Ni should be more favorable than Ni to be located at Li 3b sites in the Li slab. However, this theory cannot explain why in Ni-rich NMC materials where most Ni cations are Ni, Ni/Li exchange happens even more frequently. Using extensive ab initio calculations combined with experiments, here we report that a superexchange interaction between transition metals plays a dominating role in tuning the Ni/Li disordering in NMC materials. Under this scheme, we also propose a new charge compensation mechanism that describes that after Ni/Li exchange the nearest Co transforms to Co in Ni-rich NMC materials. On the basis of this theory, the existence of Co in the initial Ni-rich NMC samples was predicted for the first time, which was further confirmed by our synchrotron-based soft X-ray absorption spectroscopy.
镍/锂交换（无序化）通常发生在层状Li(NiMnCo)O（NMC）材料中，并影响锂离子电池中该材料的性能。先前的大多数研究将这种现象归因于镍和锂的尺寸相似，这意味着在锂层中，镍比锂更倾向于占据Li 3b位点。然而，该理论无法解释为什么在富镍NMC材料中，大多数镍阳离子为Ni时，镍/锂交换反而更频繁地发生。结合实验，通过广泛的从头算计算，我们在此报告，过渡金属之间的超交换相互作用在调节NMC材料中的镍/锂无序化方面起主导作用。在此框架下，我们还提出了一种新的电荷补偿机制，该机制描述了在镍/锂交换后，富镍NMC材料中最近的钴会转变为Co。基于该理论，首次预测了初始富镍NMC样品中Co的存在，这通过我们基于同步加速器的软X射线吸收光谱进一步得到证实。
