Local structure of LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] cathode material probed by in situ x-ray absorption spectroscopy
- SLAC
The layered nickel manganese oxide of LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} is a technologically important and promising cathode material for lithium-ion batteries. A study of the structural perturbation, charge compensation mechanism, and the valence of the constituent transition metal elements (Ni and Mn) during electrochemical cycling was performed using x-ray absorption spectroscopy (XAS) employing an in situ technique with an electrochemical cell designed for long term x-ray experiments. We present the changes in the oxidation state, bond distance, and coordination number of the Ni and Mn absorbers as a function of the state of charge of the material during electrochemical cycling at moderate rate through a typical Li-ion battery operating voltage range (2.9-4.7 V). The oxidation states of the transition metals in LiNi{sub 0.5}Mn{sub 0.5}O{sub 2} are Mn{sup 4+} and Ni{sup 2+}. The x-ray absorption near edge spectra reveal that on delithiation of Li{sub 1-x}Ni{sub 0.5}Mn{sub 0.5}O{sub 2} the Mn is electrochemically inactive and remains at Mn{sup 4+} whereas the Ni is oxidized from Ni{sup 2+} to almost Ni{sup 4+} through an intermediate stage of Ni{sup 3+}. A quantitative picture of the Ni valence during the charging process was obtained employing Faraday's law calculations in combination with the XAS results. The Faraday's law calculation indicated that at the end of the charge Ni is at Ni{sup 3.91+} in close agreement with the XAS results where Ni is found to be at Ni{sup 3.88+} at the end of the charge. Analysis of the extended x-ray absorption fine structure shows that during cycling the material retains its crystallographic symmetry and good structural short-range order which should lead to stable cycling.
- Research Organization:
- Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 1007762
- Journal Information:
- J. Appl. Phys., Vol. 99, Issue (6) ; 03, 2006; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- ENGLISH
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