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Nat Commun. 2018 Aug 16;9(1):3285. doi: 10.1038/s41467-018-05802-4.

Understanding voltage decay in lithium-excess layered cathode materials through oxygen-centred structural arrangement.

Author information

1
Department of Energy Engineering and School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea.
2
Beamline Research Division, Pohang Accelerator Laboratory (PAL), Pohang, Kyungbuk, 37673, Republic of Korea. mgkim@postech.ac.kr.
3
Department of Energy Engineering and School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology (UNIST), Ulsan, 689-798, South Korea. jpcho@unist.ac.kr.

Abstract

Lithium-excess 3d-transition-metal layered oxides (Li1+xNiyCozMn1-x-y-zO2, >250 mAh g-1) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

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