CHEMICAL SCIENCE

The latest research on lithium-ion batteries! Two-dimensional molybdenum carbide vacancy regulation strategy enhances Faraday reaction!


On July 28, 2022, Professor Liu Xiaosong, Associate Researcher Chen Shuangming, and Associate Researcher Wang Changda of the University of Science and Technology of China hosted an energy journal at Tsinghua University, Nano Research Energy (https://www.sciopen.com/journal/2790-8119) on the publication title“Vacancy manipulating of molybdenum carbide MXenes to enhance faraday reaction for high performance lithium-ion batteries”Latest research results.

Figure 1 (a) Schematic diagram of the lithium storage process of the Mo1.33CTx electrode material; (b) STEM diagram of the ordered vacancy Mo1.33CTx; and (c) Mo atomic valence fitting based on XAFS; (d) Mo K-side EXAFS spectra of the Fourier transform.

There are inherent defects such as point defects, line defects, and surface defects in nanomaterials, and the local electronic structure and atomic coordination environment are adjusted by manipulating defects to regulate the physicochemical properties of the material, which is called the “intrinsic” strategy. The energy distortion caused by the vacancy defect is relatively small, which will significantly affect the electronic structure of the electrode material, introduce impurity energy levels, effectively improve the electronic conductance, and then accelerate the charge transfer process of the electrode redox reaction. At the same time, the ion vacancies themselves can be used as additional active sites for adsorption and transmission, enhancing the storage capacity of Li+. The vacancy defect also reduces the diffusion barrier of alkali metal ions, which facilitates reversible embedding and shedding. MXenes has a unique layered structure, rich surface groups, and excellent physico-chemical properties, but limited intercalation pseudocapacitor processes and insufficient active sites inhibit its storage performance. Therefore, the development of vacancy-regulated MXenes high-capacity electrode materials, taking into account cycle stability, is the key to achieving high-performance lithium-ion batteries.

In this paper, a quaternary (Mo2/3Y1/3)2AlC i-MAX phase with an in-plane chemically ordered structure is designed by M-bit alloying strategy. Subsequently, Y and Al atoms were removed by hydrofluoric acid etching, forming Mo1.33CTx i-MXene nanosheets with alternating ordered cation vacancies. Compared to Mo2CTx, Mo1.33CTx has a special flower-like topography and a larger specific surface area. Synchrotron radiation-based X-rays indicate that the introduction of ordered vacancies causes the average valence state of the Mo atom to increase to +4.44. Thanks to the introduction of atomically active sites and mo in the high valence state, Mo1.33CTx exhibits improved pseudo-capacitance and enhanced Faraday reactions, which greatly increase specific capacitance. At 0.2 A·g–1, the Mo1.33CTx has a storage capacity of 603.7 mAh·g–1, which is superior to most original MXenes. Li+ storage kinetic analysis and DFT simulation results show that the improved performance compared to Mo2CTx stems from the addition of more charge compensation during charge-discharge, which enhances the Faraday reaction. Vacancy regulation provides an effective strategy for the application of MXenes in lithium-ion batteries.

Related paper information:

Guo, X.; Wang, C. D.; Wang, W. J.; Zhou, Q.; Xu, W. J.; Zhang, P. J.; Wei, S. Q.; Cao, Y. Y.; Zhu, K. F.; Liu, Z. F.; Yang, X. Y.; Wang, Y. X.; Wu, X. J.; Song, L.; Chen, S. M.; Liu, X. S. Vacancy manipulating of molybdenum carbide MXenes to enhance faraday reaction for high performance lithium-ion batteries. Nano Res. Energy 2022, 1: e9120026. DOI: 10.26599/NRE.2022.9120026. https://doi.org/10.26599/NRE.2022.9120026 .

As a sister journal of Nano Research, Nano Research Energy (ISSN: 2791-0091; e-ISSN: 2790-8119; Official website: https://www.sciopen.com/journal/2790-8119It was launched in March 2022 and is co-edited by Professor Qu Liangti of Tsinghua University and Professor Chunyi Zhi of the City University of Hong Kong. Nano Research Energy is an international multidisciplinary, all-English open access journal, focusing on the cutting-edge research and application of nanomaterials and nanoscience technology in new energy-related fields, benchmarking against the top international energy journals, and committed to publishing high-level original research and review papers. This journal is open access until 2023No APC feesTeachers are welcome to submit articles. Please contact: NanoResearchEnergy@tup.tsinghua.edu.cn.

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