Tuning fermi level and band gap in Li4Ti5O12 by doping and vacancy for ultrafast Li+ insertion/extraction |
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Authors: | Zhenya Wang Hao Guo De Ning Xiaobai Ma Lirong Zheng Dmitry Smirnov Kai Sun Dongfeng Chen Limei Sun Xiangfeng Liu |
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Affiliation: | 1. Center of Materials Science and Optoelectronics Engineering, College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences, Beijing, China;2. Department of Nuclear Physics, China Institute of Atomic Energy, Beijing, China;3. Helmholtz-Center Berlin for Materials and Energy, Berlin, Germany;4. Beijing Synchrotron Radiation Facility, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, China |
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Abstract: | Li4Ti5O12 (LTO) attracts great interest due to the “zero strain” during cycles but the poor electronic and ionic conductivity critically impede the practical application. Herein, we report a synergy strategy of tuning localized electrons to shift Fermi level and band gap by Mg/Zr co-doping and oxygen vacancy incorporation, which significantly improves Li+ and electronic transport. More importantly, the intrinsic synergistic mechanism has been revealed by neutron diffraction, X-ray absorption spectra, and first-principles calculations. The “elastic effect” of lattice induced by Mg/Zr co-doping allows LTO to accommodate more oxygen vacancies to a certain degree without a severe lattice distortion, which largely improves the electronic conductivity. Mg/Zr co-doping and oxygen vacancy incorporation effectively enhanced the dynamic characteristics of LTO electrode, achieving the excellent rate performance (90 mAh/g at 20C) and cycle stability (96.9% after 500 cycles at 10C). First-principles calculations confirm Fermi level shifts to the conduction band, and the band gap becomes narrowed due to the synergistic modulation, and the intrinsic mechanism of the enhanced electronic and Li-ion conductivity is clarified. This study offers some insights into achieving the fast Li+ insertion/extraction by tuning the crystal and electronic structure with lattice doping and oxygen vacancy engineering. |
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Keywords: | anode material band gap Fermi level Li4Ti5O12 synergistic mechanism |
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