Yang Zhenzhong, Ong Phuong-Vu, He Yang, Wang Le, Bowden Mark E, Xu Wu, Droubay Timothy C, Wang Chongmin, Sushko Peter V, Du Yingge
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, Richland, WA, 99354, USA.
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, 99354, USA.
Small. 2018 Dec;14(52):e1803108. doi: 10.1002/smll.201803108. Epub 2018 Nov 6.
Nonuniform and highly localized Li dendrites are known to cause deleterious and, in many cases, catastrophic effects on the performance of rechargeable Li batteries. However, the mechanisms of cathode failures upon contact with Li metal are far from clear. In this study, using in situ transmission electron microscopy, the interaction of Li metal with well-defined, epitaxial thin films of LiCoO , the most widely used cathode material, is directly visualized at an atomic scale. It is shown that a spontaneous and prompt chemical reaction is triggered once Li contact is made, leading to expansion and pulverization of LiCoO and ending with the final reaction products of Li O and Co metal. A topotactic phase transition is identified close to the reaction front, resulting in the formation of CoO as a metastable intermediate. Dynamic structural and chemical imaging, in combination with ab initio simulations, reveal that a high density of grain and antiphase boundaries is formed at the reaction front, which are critical for enabling the short-range topotactic reactions and long-range Li propagation. The fundamental insights are of general importance in mitigating Li dendrites related issues and guiding the design principle for more robust energy materials.
众所周知，不均匀且高度局部化的锂枝晶会对可充电锂电池的性能产生有害影响，在许多情况下甚至会造成灾难性后果。然而，阴极与锂金属接触时发生失效的机制仍远未明确。在本研究中，利用原位透射电子显微镜，在原子尺度上直接观察了锂金属与使用最为广泛的阴极材料——外延LiCoO₂薄膜之间的相互作用。结果表明，一旦锂发生接触，就会引发自发且迅速的化学反应，导致LiCoO₂膨胀并粉碎，最终生成Li₂O和金属钴作为反应产物。在靠近反应前沿处识别出了一个拓扑化学反应，导致形成了亚稳态中间体CoO。动态结构和化学成像与从头算模拟相结合，揭示出在反应前沿形成了高密度的晶粒和反相边界，这对于实现短程拓扑化学反应和长程锂传输至关重要。这些基本见解对于缓解与锂枝晶相关的问题以及指导设计更坚固的能量材料的原则具有普遍重要意义。
