Journal
CHEMISTRY OF MATERIALS
Volume 23, Issue 24, Pages 5415-5424Publisher
AMER CHEMICAL SOC
DOI: 10.1021/cm2026703
Keywords
EXAFS; XANES; lithium-ion batteries; composite; cathode; lithium-nickel-phosphate; Li2MnO3
Funding
- Office of Vehicle Technologies of the U.S. Department of Energy (DOE)
- Center for Electrical Energy Storage: Tailored Interfaces, an Energy Frontier Research Center
- U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences
- U.S. DOE, Basic Energy Sciences
- National Sciences and Engineering Research Council of Canada
- U.S. Department of Energy Office of Science laboratory [DE-AC02-06CH11357]
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We have taken advantage of the element specific nature of X-ray absorption spectroscopy to elucidate the chemical and structural details of a surface treatment intended for the protection of high-capacity cathode materials. Electrochemical data have shown that surface treatments of 0.5Li(2)MnO(3)center dot 0.5LiCoO(2) (Li1.2Mn0.4Co0.4O2) with an acidic solution of lithium nickel-phosphate significantly improves electrode capacity, rate, and cycling stability. XAS data reveal that the surface treatment results in a modification of the composite structure itself, where Ni2+ cations, intended to be present in a lithium nickel-phosphate coating, have instead displaced lithium in the transition metal layers of Li2MnO3-like domains within the 0.5Li(2)MnO(3)center dot 0.5LiCoO(2) structure. X-ray diffraction data show the presence of Li3PO4, suggesting that phosphate ions from the acidic solution are responsible for lithium extraction and nickel insertion with the formation of vacancies and/or manganese reduction for charge compensation. Furthermore, we show that the above effects are not limited to lithium-nickel-phosphate treatments. The studies described are consistent with a novel approach for synthesizing and tailoring the structures of high-capacity cathode materials whereby a Li2MnO3 framework is used as a precursor for synthesizing a wide variety of composite metal oxide insertion electrodes for Li-ion battery applications.
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