期刊
NATURE MATERIALS
卷 13, 期 12, 页码 1149-1156出版社
NATURE PUBLISHING GROUP
DOI: 10.1038/NMAT4084
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资金
- Samsung Advanced Institute of Technology Global Research Outreach Program
- Stanford School of Engineering and Precourt Institute for Energy
- Samsung-MIT Program for Materials Design in Energy Applications
- Office of Basic Energy Sciences, Division of Materials and Engineering Sciences, US Department of Energy [DE-AC04-94AL85000]
- US Department of Energy through the Sandia Laboratory Directed Research and Development program [DE-AC04-94AL85000]
- Office of Science, Office of Basic Energy Sciences, of the US Department of Energy [DE-AC02-05CH11231]
- King Abdullah University of Science and Technology
- National Science Foundation Graduate Research Fellowship [DGE-114747]
Many battery electrodes contain ensembles of nanoparticles that phase-separate on (de) intercalation. In such electrodes, the fraction of actively intercalating particles directly impacts cycle life: a vanishing population concentrates the current in a small number of particles, leading to current hotspots. Reports of the active particle population in the phase-separating electrode lithium iron phosphate (LiFePO4; LFP) vary widely, ranging from near 0% (particle-by-particle) to 100% (concurrent intercalation). Using synchrotron-based X-ray microscopy, we probed the individual state-of-charge for over 3,000 LFP particles. We observed that the active population depends strongly on the cycling current, exhibiting particle-by-particle-like behaviour at low rates and increasingly concurrent behaviour at high rates, consistent with our phase-field porous electrode simulations. Contrary to intuition, the current density, or current per active internal surface area, is nearly invariant with the global electrode cycling rate. Rather, the electrode accommodates higher current by increasing the active particle population. This behaviour results from thermodynamic transformation barriers in LFP, and such a phenomenon probably extends to other phase-separating battery materials. We propose that modifying the transformation barrier and exchange current density can increase the active population and thus the current homogeneity. This could introduce new paradigms to enhance the cycle life of phase-separating battery electrodes.
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