Electrochemical and solid-state NMR studies on LiCoO2 coated with Al2O3 derived from carboxylate-alumoxane |
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| Affiliation: | 1. Department of Chemical and Materials Engineering, National Central University, Chung-Li, Taiwan, ROC;2. Department of Chemistry, National Central University, Chung-Li, Taiwan, ROC;1. School of Materials Science and Engineering, Nanjing University of Science and Technology, Nanjing 210094, China;2. Herbert Gleiter Institute of Nanoscience, Nanjing University of Science and Technology, Nanjing 210094, China;3. Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China;1. College of Material Science and Engineering, China Jiliang University, Hangzhou, 310018, Zhejiang, China;2. Zhejiang Zhenlong Battery Co., Ltd, Huzhou, 313100, China;1. Materials Genome Institute, Shanghai University, Shanghai, 200444, China;2. Tianmu Lake Institute of Advanced Energy Storage Technologies, Changzhou, 213300, China;1. School of Metallurgy and Environment, Central South University, Changsha 410083, China;2. Ningde Amperex Technology Ltd, Ningde 352100, China |
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| Abstract: | The surface of LiCoO2 cathodes was coated with various wt.% of Al2O3 derived from methoxyethoxy acetate-alumoxane (MEA-alumoxane) by a mechano-thermal coating procedure, followed by calcination at 723 K in air for 10 h. The structure and morphology of the surface modified LiCoO2 samples have been characterized with XRD, SEM, EDS, TEM, BET, XPS/ESCA and solid-state 27Al magic angle spinning (MAS) NMR techniques. The Al2O3 coating forms a thin layer on the surface of the core material with an average thickness of 20 nm. The corresponding 27Al MAS NMR spectrum basically exhibited the same characteristics as the spectrum for pristine Al2O3 derived from MEA-alumoxane, indicating that the local environment of aluminum atoms was not significantly changed at coating levels below 1 wt.%. This provides direct evidence that Al2O3 was on the surface of the core materials. The LiCoO2 coated with 1 wt.% Al2O3 sustained continuous cycle stability 13 times longer than pristine LiCoO2. A comparison of the electrochemical impedance behavior of the pristine and coated materials revealed that the failure of pristine cathode performance is associated with an increase in the particle–particle resistance upon continuous cycling. Coating improved the cathode performance by suppressing the characteristic structural phase transitions (hexagonal to monoclinic to hexagonal) that occur in pristine LiCoO2 during the charge–discharge processes. |
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