Investigation of Structural Dynamics in Lithium Layered Oxide Positive Electrodes Via Coherent Diffraction Imaging
Authors: Hy Sunny , Singer Andrej , Wingert James , Liu Haodong , Ulvestad Andrew , Harder Ross , Shpyrko Oleg , Meng Ying Shirley 
Published: February 2020

The need to increase energy density in the layered oxide positive electrode materials has lead to a push to higher voltages.1 However, as a consequence of these higher voltages, the cycle stability drops considerably due to lattice contraction, electrode surface reactions with the electrolyte, and related strain.  The lithium-excess layered oxides, a subset of layered oxide materials, exhibit one of the highest capacities in positive electrode materials due to the addition of anion redox pairs to compensate the charge mechanism2. While promising, this material also suffers from thermodynamic instabilities and surface transformations when charged to higher voltages, necessary to utilize its full capacity3. Operando coherent X-ray diffraction is an eloquent technique that has provided information in the nonequilibrium structural dynamics at the single particle level in lithium battery spinel positive electrode materials4. In addition, through phase retrieval algorithms, three-dimensional defect dynamics can also be determined to understand the nanoscale mechanisms during high voltage cycling5,6.   In this study, we apply the same principles to the lithium excess layered oxide, Li1.2Ni0.133Mn0.533Co0.133O2where a plateau can be observed for the Li-rich material at 4.5 V that correspond to a simultaneous extraction of lithium and oxygen. Figure (Left) illustrates powder diffraction at the (003) bragg peak during electrochemical cycling illuminating ~ 20 individual particles where they can be found at relatively high and low angles during the plateau region. Figure 2(right) is the corresponding single particle diffractive imaging for two different primary particles of the same material. Interestingly, an inhomogeneous structural evolution during the first charge occurs where some particles shows a delay before moving to lower angles. 

Acknowledgements

This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract DE-SC0001805. Y.S.M., S.H. and H.L. acknowledge the support by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-AC02-05CH11231, Subcontract No. 7073923, under the Advanced Battery Materials Research (BMR) Program. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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Figure 1