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SLAC National Accelerator Laboratory

Mesoscale Phase Distribution in Li-ion Battery Electrode Materials
May 2013 SSRL Science Summary by Lori Ann White, SLAC Office of Communications

Figure 1a) Chemical phase map obtained by linear combination fitting of XANES data at each pixel acquired with FF TXM at Beam Line 6-2 for a particle with nominal composition of Li0.74FePO4. b) STEM image of a fully delithiated sample. Figure adapted from Boesenberg et al. 2013

Li-ion batteries are key devices in the effort to develop efficient chemical energy storage from sustainable energy sources. However, any effort to optimize battery performance requires a deeper understanding of the fundamental mechanisms of diffusion and phase transformation in battery electrodes. In this study supported by the Northeastern Center for Chemical Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, scientists from Lawrence Berkeley National Laboratory and SSRL used full-field transmission x-ray microscopy coupled with x-ray absorption near-edge spectroscopy (FF TXM-XANES) at SSRL Beam Line 6-2 to visualize the chemical phase transformations occurring in single crystals of electrode materials, such as LiFePO4, in Li-ion technologies.

In the study, the researchers used FF TXM-XANES to produce 30 nm chemical- and spatial-resolution maps of the distribution of chemical species involved in the transformation, in partially delithiated, micron-sized LiFePO4 plate-like crystals. They compared the maps to morphological information collected by scanning transmission electron microscopy (STEM), building a mesoscale picture of the interplay between crystal microstructure and redox reactions, and tying this complex delithiation behavior to a combination of kinetic limitations due to macroscopic defects in the crystals and thermodynamic effects. Stresses accompanying the delithiation process led to the cracking of the particles due to the buildup of strain at the phase boundaries.

The results stress the role of microstructure as a kinetic factor during redox transformations of a particle, especially when defects are considered, and provide clues to the design of electrode materials with enhanced utilization and durability. It also constitutes a highly representative example of the capabilities of TXM-XANES to study processes relevant to energy applications.


Primary Citations

U. Boesenberg, F. Meirer, Y. Liu, A. K. Shukla, R. Dell’Anna, T. Tyliszczak, G. Chen, J. C. Andrews, T. J. Richardson, R. M. Kostecki, J. Cabana, " Mesoscale Phase Distribution in Single Particles of LiFePO4 following Lithium Deintercalation", Chem. Mater. 25, 1664 (2013)

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Jordi Cabana, Lawrence Berkeley National Laboratory

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