Atomic-Scale Structure of Intercalated/De-Intercalated Electrode Materials in Lithium/Sodium Ion Batteries Via Aberration-Corrected Annular-Bright-Field Electron Microscopy

To satisfy ever-demanding inquires upon energy storage for applications in portable electronics, electric vehicles and smart grid etc., lithium ion batteries have been proved to be one of the ideal candidates in terms of energy density and power density. However, limited understanding for the structural evolution of electrode materials at atomic scale amid electrochemical process  substantially hinders their further performance optimization. The recent success of annular-bright-field (ABF) imaging method erected on aberration-corrected scanning transmission electron microscopy (STEM) has been demonstrated to be a powerful technique to directly visualize individual light atoms, in particular the lithium ions, probing the nearly-equilibrated local structure of lithiated/delithiated electrodes under electrochemical cycling at atomic resolution.  Compared to the high-angle annular-dark-field (HAADF) image, it is clearly demonstrated that not only heavy elements are revealed in ABF image, but also the atomic columns of O and Li. The ABF contrast tends to minimize the variance of the atomic number (Z) by following a Z1/3 dependency. With the unique ABF method, we have further studied possible electrochemical reaction mechanisms and detailed microstructure for (partially) lithiated/delithiated 1D-LiFePO4, 2D-LiCoO2, Li2MnO3 and 3D-Li4Ti5O12 and other lithium-based active materials with atomic resolution, which are essential for basic understanding and further performance optimization. These achievements provide new insight into the lithium/sodium storage mechanism in important cathode materials for lithium/sodium ion batteries.

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