Changes in the cation ordering of layered O3 Lix̳Ni₀.₅Mn₀.₅O₂ during electrochemical cycling to high voltages

Selected area electron diffraction patterns were collected from a pristine LiNi₀.₅Mn₀.₅O₂ sample and cycled Lix̳Ni₀.₅Mn₀.₅O₂ samples to 4.5 V and 5.3 V in the charged and discharged states. In the pristine sample, the single-crystal diffraction patterns clearly revealed superlattice reflections consistent with a ... supercell that is characteristic of cation ordering in the transition metal layer. Furthermore, these superlattice reflections were found to have considerably weakened or completely disappeared in the charged samples. Comparing the 4.5 V and 5.3 V charged samples, fewer crystals in the 5.3 V charged sample were found to exhibit these superlattice reflections. Another difference is that additional superlattice reflections consistent with the 01 phase with hexagonal-close-packed oxygen array were detected in the 5.3 V but not in the 4.5 V charged sample. Therefore, electron diffraction evidence was found to support the concept of Ni migration from the Li to the transition metal layer, and to confirm the increased Ni occupancy in the transition metal layer upon charging. In addition, electron diffraction data showed that Ni migration was in part reversible upon discharge as demonstrated by the increase in the fractions of crystals exhibiting the ... superlattice reflections from the charged to the discharged samples.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Mechanical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Li, Hayley Han

Advisor dc:contributor.advisor

• Yang Shao-Horn.

• Mechanical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/38706

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/38706