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Issue 22, 2015
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A comparative study on the oxidation state of lattice oxygen among Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3, LiNi0.5Co0.2Mn0.3O2 and LiCoO2 for the initial charge–discharge

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Abstract

The Li-rich layered oxides are attractive electrode materials due to their high reversible specific capacity (>250 mA h g−1); however, the origin of their abnormal capacity is still ambiguous. In order to elucidate this curious anomaly, we compare the lattice oxygen oxidation states among the Li-rich layered oxide Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3 and LiNi0.5Co0.2Mn0.3O2, the two components in Li-rich layered oxides, and the most common layered oxide LiCoO2 before and after initial charge–discharge. For simplicity, we employ chemical treatments of NO2BF4 and LiI acetonitrile solutions to simulate the electrochemical delithiation and lithiation processes. X-ray photoelectron spectroscopy (XPS) studies reveal that part of lattice oxygen in Li1.14Ni0.136Co0.136Mn0.544O2 and Li2MnO3 undergoes a reversible redox process (possibly O2− ↔ O22−), while this does not occur in LiNi0.5Co0.2Mn0.3O2 and LiCoO2. This indicates that the extra capacity of Li-rich layered oxides can be attributed to the reversible redox processes of oxygen in the Li2MnO3 component. Thermogravimetric analysis (TGA) further suggests that the formed O22− species in the delithiated Li1.14Ni0.136Co0.136Mn0.544O2 can decompose into O2 at about 210 °C. This phenomenon demonstrates a competitive relationship between extra capacity and thermal stability, which presents a big challenge for the practical applications of these materials.

Graphical abstract: A comparative study on the oxidation state of lattice oxygen among Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3, LiNi0.5Co0.2Mn0.3O2 and LiCoO2 for the initial charge–discharge

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Supplementary files

Article information


Submitted
24 Mar 2015
Accepted
27 Apr 2015
First published
27 Apr 2015

J. Mater. Chem. A, 2015,3, 11930-11939
Article type
Paper
Author version available

A comparative study on the oxidation state of lattice oxygen among Li1.14Ni0.136Co0.136Mn0.544O2, Li2MnO3, LiNi0.5Co0.2Mn0.3O2 and LiCoO2 for the initial charge–discharge

S. Han, Y. Xia, Z. Wei, B. Qiu, L. Pan, Q. Gu, Z. Liu and Z. Guo, J. Mater. Chem. A, 2015, 3, 11930
DOI: 10.1039/C5TA02161H

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