Identifying the anionic redox activity in cation-disordered Li1.25Nb0.25Fe0.50O2/C oxide cathodes for Li-ion batteries

Mingzeng Luo; Shiyao Zheng; Jue Wu; Ke Zhou; Wenhua Zuo; Min Feng; Huajin He; Rui Liu; Jianping Zhu; Gang Zhao; Shijian Chen; Wanli Yang; Zhangquan Peng; Qihui Wu; Yong Yang

doi:10.1039/C9TA11739C

Identifying the anionic redox activity in cation-disordered Li_1.25Nb_0.25Fe_0.50O₂/C oxide cathodes for Li-ion batteries†

Mingzeng Luo,

^a Shiyao Zheng,^a Jue Wu,^ab Ke Zhou,^a Wenhua Zuo,^a Min Feng,^c Huajin He,^a Rui Liu,

^ad Jianping Zhu,^a Gang Zhao,^e Shijian Chen,^a Wanli Yang,

^b Zhangquan Peng,^f Qihui Wu^g and Yong Yang*^ae

Author affiliations

* Corresponding authors

^a State Key Laboratory for Physical Chemistry of Solid Surfaces, Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, China
E-mail: yyang@xmu.edu.cn

^b Advanced Light Source, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, California 94720, USA

^c Department of Chemical Engineering and Materials Science, College of Engineering, Michigan State University, East Lansing, Michigan 48824, USA

^d School of Materials Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China

^e School of Energy, Xiamen University, Xiamen 361005, China

^f State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Science, Changchun 130022, China

^g College of Mechanical and Energy Engineering, Jimei University, Xiamen 361021, China

Abstract

Li-excess cation-disordered cathodes for Li-ion batteries have attracted much interest due to their high capacity. However, issues regarding anionic redox activity and capacity degradation still need to be clarified for their performance improvement. In this work, a newly designed cation-disordered Li_1.25Nb_0.25Fe_0.50O₂/C cathode is investigated. The mapping of resonant inelastic X-ray scattering (mRIXS) reveals direct evidence of reversible anionic redox during cycling for the first time and defines the voltage range. Furthermore, differential electrochemical mass spectroscopy (DEMS) finds that oxygen release is involved during high voltage charging with electrolyte decomposition. A surface densified layer induced by excessive oxygen oxidation is also identified by in/ex situ X-ray diffraction (XRD). In the densified layer, lithium ion diffusion is blocked due to the reduced amount of percolating 0-TM (transition metal) network. Besides, irreversible oxygen loss during cycling leads to the sustained growth of the densified layer and results in larger lattice volume variations. Therefore, the performance degradation of the material is largely due to oxygen loss, surface densification, and large volume variation upon electrochemical operation.

This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers

Journal of Materials Chemistry A

Identifying the anionic redox activity in cation-disordered Li_1.25Nb_0.25Fe_0.50O₂/C oxide cathodes for Li-ion batteries†

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Identifying the anionic redox activity in cation-disordered Li_1.25Nb_0.25Fe_0.50O₂/C oxide cathodes for Li-ion batteries

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Journal of Materials Chemistry A