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292 results on '"Kong, Weijin"'

30. Adjusting the Redox Coupling Effect via Li/Co Anti‐Site Defect for Stable High‐Voltage LiCoO2 Cathode.

Author

Kong, Weijin, Zhou, Dong, Zhang, Qinghua, Wong, Deniz, An, Ke, Schulz, Christian, Zhang, Nian, Zhang, Jicheng, and Liu, Xiangfeng

Subjects
*ANTISITE defects, *OXIDATION-reduction reaction, *CATHODES, *STRUCTURAL stability, *OXYGEN reduction, *TRANSITION metals, *CHARGE transfer
Abstract

High‐voltage LiCoO2 (LCO) is pressingly required for the portable electronics. But the O→Co charge transfer and the oxygen redox at high delithiation induce the issues of irreversible Co reduction, oxygen release, and unfavored phase transformation. Herein, it is proposed to tune the O→Co charge transfer via regulating Li/Co anti‐site defect with Mg2+ and (PO4)3− co‐doping to achieve a stable high‐voltage LiCoO2 cathode. The appropriately regulated Li/Co anti‐site defect enhances the redox activity of the Co‐ions, and inhibits the irreversibility of the oxygen redox and the coupled Co reduction. The increase of the formation energy of oxygen vacancies in the modified cathode at deep delithiation inhibits oxygen escape. Moreover, (PO4)3− doping also stabilizes oxygen‐packed framework due to its strong bond energy with transition metal. These functions enhance the structural stability and the reversible Co/O redox ability. The improved cathode delivers a high capacity and long‐cycle capacity retention on both 4.5 and 4.6 V. This study provides some insights into adjusting the redox coupling effect and enhancing the oxygen redox reversibility by Li/Co anti‐site regulation. [ABSTRACT FROM AUTHOR]

Published
2023
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33. Stabilizing Lattice Oxygen in a P2-Na0.67Mn0.5Fe0.5O2Cathode via an Integrated Strategy for High-Performance Na-Ion Batteries

Author

Shao, Guangzheng, Kong, Weijin, Yu, Yang, Zhang, Jicheng, Yang, Wenyun, Yang, Jinbo, Li, Yanchao, and Liu, Xiangfeng

Abstract

P2-type Na0.67Mn0.5Fe0.5O2(MF) has attracted great interest as a promising cathode material for sodium-ion batteries (SIBs) due to its high specific capacity and low cost. However, its poor cyclic stability and rate performance hinder its practical applications, which is largely related to lattice oxygen instability. Here, we propose to coat the cathode of SIBs with Li2ZrO3, which realizes the “three-in-one” modification of Li2ZrO3coating and Li+, Zr4+co-doping. The synergy of Li2ZrO3coating and Li+/Zr4+doping improves both the cycle stability and rate performance, and the underlying modification mechanism is revealed by a series of characterization methods. The doping of Zr4+increases the interlayer spacing of MF, reduces the diffusion barrier of Na+, and reduces the ratio of Mn3+/Mn4+, thus inhibiting the Jahn–Teller effect. The Li2ZrO3coating layer inhibits the side reaction between the cathode and the electrolyte. The synergy of Li2ZrO3coating and Li+, Zr4+co-doping enhances the stability of lattice oxygen and the reversibility of anionic redox, which improves the cycle stability and rate performance. This study provides some insights into stabilizing the lattice oxygen in layered oxide cathodes for high-performance SIBs.

Published
2023
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35. Hollow CoS/C Structures for High-Performance Li, Na, K Ion Batteries

Author

Liu, Yan, primary, Li, Xiangkun, additional, Zhang, Fengling, additional, Zhang, Leqing, additional, Zhang, Tao, additional, Li, Changshuan, additional, Jin, Zhicheng, additional, Wu, Yueying, additional, Du, Zhongyu, additional, Jiao, Huiwen, additional, Jiang, Ying, additional, Yan, Yuliang, additional, Li, Qiang, additional, and Kong, Weijin, additional

Published
2022
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43. Effect of OH– on fluorescence properties in 1.5–1.6 μm for Er:Yb:YCOB crystal

Author

Chen Hu, Bing Teng, Jianhong Li, Hui Xu, Fei You, Kong Weijin, Dongjuan Wang, Shijia Sun, Zhenghe Yu, Shakir Ullah, Degao Zhong, and Jie Tang

Subjects
Materials science, Absorption spectroscopy, Band gap, Analytical chemistry, 02 engineering and technology, General Chemistry, Crystal structure, 010402 general chemistry, 021001 nanoscience & nanotechnology, 01 natural sciences, Fluorescence, 0104 chemical sciences, Ion, Crystal, Geochemistry and Petrology, Absorption (chemistry), Fourier transform infrared spectroscopy, 0210 nano-technology
Abstract

FTIR absorption spectra indicate that H+ can easily enter the crystal structure and form OH– centers in Er:Yb:YCOB and O H bonds prefer to lie in the a-c plane. Within our current studied concentration level, crystal samples with higher OH– absorption coefficients demonstrate stronger fluorescence intensity and longer fluorescence lifetime at 1535 nm. As the stretching vibration energy of OH– group approximately corresponds to the energy gap between the 4I11/2 and 4I13/2 levels of Er3+, and thus, OH– ions can shorten the fluorescence lifetime of Er3+-4I11/2 level by the phonon-assisted cross-relaxation process between the Er3+ and OH– ions. Our current results confirm that a certain content of OH– ions can enhance the energy transfer process from Yb3+ to Er3+ and subsequently promote fluorescence output in 1.5–1.6 μm.

Published
2019

49. Stabilizing the Anionic Redox in 4.6 V LiCoO2 Cathode through Adjusting Oxygen Magnetic Moment.

Author

Kong, Weijin, Wong, Deniz, An, Ke, Zhang, Jicheng, Chen, Zhenhua, Schulz, Christian, Xu, Zijian, and Liu, Xiangfeng

Subjects
*MAGNETIC moments, *PHASE transitions, *OXIDATION-reduction reaction, *OXYGEN, *ACTIVATION energy
Abstract

The irreversible oxygen redox and the resulting structure degradation of LiCoO2 at a high voltage cause very poor cycling performance. Herein, the anionic redox chemistry in 4.6 V LiCoO2 cathode material through manipulating the oxygen magnetic moment (OMM) with oxygen vacancy and V doping is proposed to stabilize, and the relationship between OMM and the oxidation degree of oxygen is revealed. Oxygen vacancy induces the generation of OMM, and the synergy of oxygen vacancy and V doping reduces the change of OMM during charge/discharge processes. This mitigates the oxidation degree of oxygen and improves the reversibility of oxygen redox, which greatly inhibits the irreversible oxygen escape. The oxygen vacancies can further reduce the overlap of the electron clouds and lower the O 2p band center thus decreasing the oxygen redox activity. Moreover, the introduced V also increases the energy barrier of the phase transition and suppresses the irreversible phase transition and Co migration. The irreversible O2 release is significantly inhibited and the cycling stability at 4.6 V is largely enhanced. This study presents the relationship between OMM and the oxidation degree of oxygen and provides some insights into improving the anion redox reversibility through adjusting the oxygen magnetic moment. [ABSTRACT FROM AUTHOR]

Published
2022
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