Luo Langli, Liu Bin, Song Shidong, Xu Wu, Zhang Ji-Guang, Wang Chongmin
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Energy and Environment Directorate, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99352, USA.
Nat Nanotechnol. 2017 Jul;12(6):535-539. doi: 10.1038/nnano.2017.27. Epub 2017 Mar 27.
The performances of a Li-O battery depend on a complex interplay between the reaction mechanism at the cathode, the chemical structure and the morphology of the reaction products, and their spatial and temporal evolution; all parameters that, in turn, are dependent on the choice of the electrolyte. In an aprotic cell, for example, the discharge product, LiO forms through a combination of solution and surface chemistries that results in the formation of a baffling toroidal morphology. In a solid electrolyte, neither the reaction mechanism at the cathode nor the nature of the reaction product is known. Here we report the full-cycle reaction pathway for Li-O batteries and show how this correlates with the morphology of the reaction products. Using aberration-corrected environmental transmission electron microscopy (TEM) under an oxygen environment, we image the product morphology evolution on a carbon nanotube (CNT) cathode of a working solid-state Li-O nanobattery and correlate these features with the electrochemical reaction at the electrode. We find that the oxygen-reduction reaction (ORR) on CNTs initially produces LiO, which subsequently disproportionates into LiO and O. The release of O creates a hollow nanostructure with LiO outer-shell and LiO inner-shell surfaces. Our findings show that, in general, the way the released O is accommodated is linked to lithium-ion diffusion and electron-transport paths across both spatial and temporal scales; in turn, this interplay governs the morphology of the discharging/charging products in Li-O cells.
锂氧电池的性能取决于阴极反应机制、反应产物的化学结构和形态及其时空演化之间的复杂相互作用；而所有这些参数又反过来取决于电解质的选择。例如，在非质子电池中，放电产物LiO通过溶液化学和表面化学的结合形成，这导致了一种令人困惑的环形形态的形成。在固体电解质中，阴极的反应机制和反应产物的性质均未知。在此，我们报告了锂氧电池的全循环反应途径，并展示了其与反应产物形态的相关性。利用在氧气环境下的像差校正环境透射电子显微镜（TEM），我们对工作中的固态锂氧纳米电池的碳纳米管（CNT）阴极上的产物形态演变进行成像，并将这些特征与电极处的电化学反应相关联。我们发现，碳纳米管上的氧还原反应（ORR）最初产生LiO，随后LiO歧化为LiO和O。O的释放形成了一种具有LiO外壳和LiO内壳表面的中空纳米结构。我们的研究结果表明，一般来说，释放的O的容纳方式与跨时空尺度的锂离子扩散和电子传输路径有关；反过来，这种相互作用控制着锂氧电池中放电/充电产物的形态。
