Li Linze, Self Ethan C, Darbar Devendrasinh, Zou Lianfeng, Bhattacharya Indranil, Wang Donghai, Nanda Jagjit, Wang Chongmin
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, 902 Battelle Boulevard, Richland, Washington 99354, United States.
Chemical Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37830, United States.
Nano Lett. 2020 Apr 8;20(4):2756-2762. doi: 10.1021/acs.nanolett.0c00380. Epub 2020 Mar 4.
Structural transformations near surfaces of solid-state materials underpin functional mechanisms of a broad range of applications including catalysis, memory, and energy storage. It has been a long-standing notion that the outermost free surfaces, accompanied by broken translational symmetry and altered atomic configurations, are usually the birthplace for structural transformations. Here, in a layered oxide cathode for Li-ion batteries, we for the first time observe the incipient state of the well-documented layered-to-spinel-like structural transformation, which is surprisingly initiated from the subsurface layer, rather than the very surface. Coupling atomic level scanning transmission electron microscopy imaging with electron energy loss spectroscopy, we discover that the reconstructed subsurfaces, featuring a mix of discrete patches of layered and spinel-like structures, are associated with selective atomic species partition and consequent nanoscale nonuniform composition gradient distribution at the subsurface. Our findings provide fundamental insights on atomic-scale mechanisms of structural transformation in layered cathodes.
固态材料表面附近的结构转变是包括催化、记忆和能量存储在内的广泛应用功能机制的基础。长期以来的观点认为，伴随着平移对称性破坏和原子构型改变的最外层自由表面通常是结构转变的发源地。在此，在一种用于锂离子电池的层状氧化物阴极中，我们首次观察到了有充分记录的从层状到类尖晶石结构转变的初始状态，令人惊讶的是，这种转变是从次表层而非表面开始的。通过将原子级扫描透射电子显微镜成像与电子能量损失谱相结合，我们发现，重构的次表层具有层状和类尖晶石结构的离散斑块混合特征，与次表层选择性的原子种类分配以及随之而来的纳米级非均匀成分梯度分布有关。我们的发现为层状阴极中结构转变的原子尺度机制提供了基本见解。
