Observation of partial reduction of manganese in the lithium rich layered oxides, 0.4Li 2 MnO 3 -0.6LiNi 1/3 Co 1/3 Mn 1/3 O 2 , during the first charge.

Autor:	Shim HC; Department of Nano-Mechanics, Korea Institute of Machinery & Materials (KIMM), 156, Gajeongbuk-ro, Yuseong-gu, Daejeon, 34103, Republic of Korea., Kim D; Energy Material Lab., Material Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Co., Ltd., 130, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16678, Republic of Korea. taehwan.yu@samsung.com., Shin D; Energy Material Lab., Material Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Co., Ltd., 130, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16678, Republic of Korea. taehwan.yu@samsung.com., Hyun S; Department of Nano-Mechanics, Korea Institute of Machinery & Materials (KIMM), 156, Gajeongbuk-ro, Yuseong-gu, Daejeon, 34103, Republic of Korea., Woo CS; Department of Nano-Mechanics, Korea Institute of Machinery & Materials (KIMM), 156, Gajeongbuk-ro, Yuseong-gu, Daejeon, 34103, Republic of Korea., Yu T; Energy Material Lab., Material Research Center, Samsung Advanced Institute of Technology, Samsung Electronics, Co., Ltd., 130, Samsung-ro, Yeongtong-gu, Suwon-si, Gyeonggi-do 16678, Republic of Korea. taehwan.yu@samsung.com., Ahn JP; Advanced Analysis Center (AAC), Korea Institute of Science and Technology (KIST), 5, Hwarang-ro, 14-gil, Seongbuk-guSeoul, 02792, Republic of Korea. jpahn@kist.re.kr.
Jazyk:	angličtina
Zdroj:	Physical chemistry chemical physics : PCCP [Phys Chem Chem Phys] 2017 Jan 04; Vol. 19 (2), pp. 1268-1275.
DOI:	10.1039/c6cp07574f
Abstrakt:	Lithium-rich layered oxides show promise as high-energy harvesting materials due to their large capacities. However, questions remain regarding the large irreversible loss in capacities for the first charge-discharge cycle due to oxygen removal in lattices related to layered Li 2 MnO 3 . Herein we present detailed studies on Li-rich Mn-based layered oxides of 0.4Li 2 MnO 3 -0.6LiNi 1/3 Co 1/3 Mn 1/3 O 2 (Li-rich NCM) electrochemically activated between 2.5 V and 4.3 or 4.7 V vs. Li + /Li. Electron energy loss spectroscopy (EELS) and X-ray absorption spectroscopy (XAS) revealed unusual manganese reduction after the first charge up to a high voltage of 4.7 V. Moreover, the electronic structure did not fully recover to the original pristine of Mn 4+ state after discharge. Interestingly, these phenomena were not limited to a single particle, but were observed across the entire electrode. High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and electron dispersive spectra (EDS) also showed a dramatic decline in oxygen content with highly porous morphologies, associated with oxygen vacancy formation following oxidation of O 2- ions to O 2 . Our analysis suggests that an unstable manganese valence state with severe defects due to oxygen vacancies may lead to large irreversible capacity loss during the first charge-discharge cycle of Li-rich layered oxides.
Databáze:	MEDLINE
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