Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, USA.
Nano Lett. 2013 Feb 13;13(2):758-64. doi: 10.1021/nl3044508. Epub 2013 Jan 17.
To utilize high-capacity Si anodes in next-generation Li-ion batteries, the physical and chemical transformations during the Li-Si reaction must be better understood. Here, in situ transmission electron microscopy is used to observe the lithiation/delithiation of amorphous Si nanospheres; amorphous Si is an important anode material that has been less studied than crystalline Si. Unexpectedly, the experiments reveal that the first lithiation occurs via a two-phase mechanism, which is contrary to previous understanding and has important consequences for mechanical stress evolution during lithiation. On the basis of kinetics measurements, this behavior is suggested to be due to the rate-limiting effect of Si-Si bond breaking. In addition, the results show that amorphous Si has more favorable kinetics and fracture behavior when reacting with Li than does crystalline Si, making it advantageous to use in battery electrodes. Amorphous spheres up to 870 nm in diameter do not fracture upon lithiation; this is much larger than the 150 nm critical fracture diameter previously identified for crystalline Si spheres.
为了在下一代锂离子电池中使用高容量硅阳极，必须更好地理解硅-锂反应过程中的物理和化学转化。在这里，我们使用原位透射电子显微镜来观察非晶硅纳米球的锂化/脱锂过程；非晶硅是一种重要的阳极材料，其研究不如晶体硅充分。出乎意料的是，实验表明首次锂化是通过两相机制发生的，这与之前的理解相矛盾，并且对锂化过程中机械应力的演化有重要影响。基于动力学测量，这种行为被认为是由于 Si-Si 键断裂的限速效应。此外，结果表明，与晶体硅相比，非晶硅与锂反应时具有更有利的动力学和断裂行为，因此有利于用作电池电极。直径高达 870nm 的非晶硅纳米球在锂化过程中不会断裂；这远大于之前为晶体硅纳米球确定的 150nm 临界断裂直径。
