Evolution of Chemical and Morphological Changes of High Capacity Electrode Materials Across Multiple Lengths Scales

Abstract

Understanding and quantifying the changes in chemical composition as well as morphology of battery materials under electrochemical cycling is fundamental to their long cycle life and safety1-2. This is particularly true for high energy density lithium-manganese rich cathodes which transitions from a high voltage layered–layered phase to a defect type spinel phase under constant electrochemical cycling. In this study we combine the full-field transmission X-ray microscopy (TXM) and the X-ray absorption near edge structure (XANES) to spatially resolve and map the accompanying chemical phase change and morphology of a high voltage lithium-ion cathode composition, Li1.2Mn0.525Ni0.175Co0.1O2, (LMR-NMC)3 at a resolution down to 30 nm over a fields-of-view of several tens of microns. 2D TXM-XANES imaging was conducted on a series of samples recovered at different stages of the battery cycling, showing that the material experiences phase segregation of various transition metal species from the particle bulk to surface4. Energy-resolved 3D morphology and quantification analysis with elemental information suggested that the distribution of three transition metal is heterogeneous and the surface of material particle constantly evolves with electrochemical cycling with varied average concentration of Mn, Co and Ni compared to particle internal.These results will be compared with results obtained from confocal ex-situ Raman mapping for pristine and cycled LMR-NMC composite cathodes. Raman results provide important information regarding the chemical homogeneity of the electrodes with respect to active material, binder and carbon additive distribution and their changes under high voltage electrochemical cycling. Florian Meirer, Jordi Cabana, Yijin Liu, Apurva Mehta, Joy C. Andrews and Piero Pianetta, J. Synchrotron Rad,. 18, 773 (2011).Wen-Chin Chen, Yen-Fang Song, Chun-Chieh Wang, Yijin Liu, Darius T. Morris,Piero A. Pianetta, Joy C. Andrews, Hung-Chun Wud and Nae-Lih Wu, J. Mater. Chem. A 1, 10847. (2013).Surendra K. Martha, Jagjit Nanda, Gabriel Veith Nancy J. Dudney, J Power Sources 199, 220 (2012)Fei fei Yang et al. Under preparation (2014)