Journal
JOURNAL OF PHYSICAL CHEMISTRY LETTERS
Volume 8, Issue 22, Pages 5537-5542Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpclett.7b02498
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Funding
- National Materials Genome Project [2016YFB0700600]
- National Natural Science Foundation of China [21603007, 51672012]
- Shenzhen Science and Technology Research Grant [JCYJ20150729111733470, JCYJ20151015162256516]
- Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy [DE-AC02-05CH11231]
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Ni/Li exchange (disordering) usually happens in layered Li(NixMnyCoz)O-2 (NMC) materials and affects the performance of the material in lithium-ion batteries. Most of previous studies attributed this phenomenon to the similar size of Ni2+ and Lit, which implies that Ni2+ should be more favorable than Ni3+ to be located at Li 3b sites in the Li slab. However, this theory cannot explain why in Ni-rich NMC materials where most Ni cations are Ni3+, Ni/Li exchange happens even more frequently. Using extensive ab initio calculations combined with experiments, here we report that a superexchange interaction between transition metals plays a dominating role in tuning the Ni/Li disordering in NMC materials. Under this scheme, we also propose a new charge compensation mechanism that describes that after Ni3+/Li exchange the nearest Co3+ transforms to Co4+ in Ni-rich NMC materials. On the basis of this theory, the existence of Co4+ in the initial Ni-rich NMC samples was predicted for the first time, which was further confirmed by our synchrotron-based soft X-ray absorption spectroscopy.
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