Zhang Ming-Jian, Teng Gaofeng, Chen-Wiegart Yu-Chen Karen, Duan Yandong, Ko Jun Young Peter, Zheng Jiaxin, Thieme Juergen, Dooryhee Eric, Chen Zonghai, Bai Jianming, Amine Khalil, Pan Feng, Wang Feng
Sustainable Energy Technologies Department , Brookhaven National Laboratory , Upton , New York 11973 , United States.
School of Advanced Materials , Peking University, Shenzhen Graduate School , Shenzhen 518055 , China.
J Am Chem Soc. 2018 Oct 3;140(39):12484-12492. doi: 10.1021/jacs.8b06150. Epub 2018 Sep 19.
Metal (M) oxides are one of the most interesting and widely used solids, and many of their properties can be directly correlated to the local structural ordering within basic building units (BBUs). One particular example is the high-Ni transition metal layered oxides, potential cathode materials for Li-ion batteries whose electrochemical activity is largely determined by the cationic ordering in octahedra (e.g., the BBUs in such systems). Yet to be firmly established is how the BBUs are inherited from precursors and subsequently evolve into the desired ordering during synthesis. Herein, a multimodal in situ X-ray characterization approach is employed to investigate the synthesis process in preparing LiNiMnCoO from its hydroxide counterpart, at scales varying from the long-range to local individual octahedral units. Real-time observation corroborated by first-principles calculations reveals a topotactic transformation throughout the entire process, during which the layered framework is retained; however, due to preferential oxidation of Co and Mn over Ni, significant changes happen locally within NiO octahedra. Specifically, oxygen loss and the associated symmetry breaking occur in NiO; as a consequence, Ni ions become highly mobile and tend to mix with Li, causing high cationic disordering upon formation of the layered oxides. Only through high-temperature heat treatment, Ni is further oxidized, thereby inducing symmetry reconstruction and, concomitantly, cationic ordering within NiO octahedra. Findings from this study shed light on designing high-Ni layered oxide cathodes and, more broadly, various functional materials through synthetic control of the constituent BBUs.
金属（M）氧化物是最有趣且应用广泛的固体材料之一，其许多性质都与基本结构单元（BBUs）内的局部结构有序性直接相关。一个特别的例子是高镍过渡金属层状氧化物，它是锂离子电池的潜在正极材料，其电化学活性很大程度上由八面体中的阳离子有序性决定（例如，此类体系中的BBUs）。然而，BBUs如何从前驱体继承并在合成过程中随后演变成所需的有序结构仍有待确定。在此，采用多模态原位X射线表征方法来研究从其氢氧化物对应物制备LiNiMnCoO的合成过程，研究范围从长程到局部单个八面体单元。第一性原理计算证实的实时观察揭示了整个过程中的拓扑转变，在此过程中保留了层状结构；然而，由于Co和Mn比Ni优先氧化，NiO八面体内局部发生了显著变化。具体而言，NiO中发生氧损失和相关的对称性破坏；结果，Ni离子变得高度可移动并倾向于与Li混合，在层状氧化物形成时导致高阳离子无序。只有通过高温热处理，Ni才会进一步氧化，从而诱导对称性重建，并随之在NiO八面体内产生阳离子有序。这项研究的结果为通过对组成BBUs的合成控制来设计高镍层状氧化物正极以及更广泛地设计各种功能材料提供了启示。
