期刊
NANO LETTERS
卷 14, 期 8, 页码 4334-4341出版社
AMER CHEMICAL SOC
DOI: 10.1021/nl502090z
关键词
Li-ion battery; Li-Mn-rich NMC; X-ray nanotomography; XANES imaging
类别
资金
- U.S. Department of Energy [DE-AC05-00OR22725]
- Vehicle Technologies Program for the Office of Energy Efficiency and Renewable Energy
- NIH/NIBIB [5R01EB004321]
- NSFCScience Fund for Creative Research Groups, NSFC [11321503]
- National Basic Research Program of China [2012CB825801]
- Knowledge Innovation Program of the Chinese Academy of Sciences [KJCX2-YW-N42]
Understanding the evolution of chemical composition and morphology of battery materials during electrochemical cycling is fundamental to extending battery cycle life and ensuring safety. This is particularly true for the much debated high energy density (high voltage) lithium- manganese rich cathode material of composition Li-1 M-+ x(1) (-) O-x(2) (M = Mn, Co, Ni). In this study we combine full-field transmission X-ray microscopy (TXM) with X-ray absorption near edge structure (XANES) to spatially resolve changes in chemical phase, oxidation state, and morphology within a high voltage cathode having nominal composition Li1.2Mn0.525Ni0.175Co0.1O2. Nanoscale microscopy with chemical/elemental sensitivity provides direct quantitative visualization of the cathode, and insights into failure. Single-pixel (similar to 30 nm) TXM XANES revealed changes in Mn chemistry with cycling, possibly to a spinel conformation and likely including some Mn(II), starting at the particle surface and proceeding inward. Morphological analysis of the particles revealed, with high resolution and statistical sampling, that the majority of particles adopted nonspherical shapes after 200 cycles. Multiple-energy tomography showed a more homogeneous association of transition metals in the pristine particle, which segregate significantly with cycling. Depletion of transition metals at the cathode surface occurs after just one cycle, likely driven by electrochemical reactions at the surface.
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