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Submicron Ti2CTx MXene as a high-rate intercalation anode material for Li-ion batteries

First author: Cui Cong

Corresponding author: Wang Xiaohui*

Units: Institute of Metal Research, Chinese Academy of Sciences, University of Science and Technology of China, Zhengzhou University



Research Background

The development of lithium-ion batteries with high rate capability is of great significance for realizing fast charging and discharging of portable electronic devices and electric vehicles. The rate capability of lithium-ion batteries mainly depends on the rate capability of electrode materials.

For cathode materials, LiFePO4, Li(Fe0.5Mn0.5)PO4, Li1.2Ni0.13Mn0.54Co0.13O2, etc. all have good rate capability. However, the most widely used anode materials, graphite and silicon, have poor rate performance. Although Li4Ti5O12 has high rate capability, its theoretical specific capacity is low and the discharge potential is high. Therefore, it is of great significance to develop a new generation of anode materials with high rate performance, high specific capacity and high cycle stability.



Introduction to the article

Based on this, Researcher Wang Xiaohui from the Institute of Metal Research, Chinese Academy of Sciences and Associate Professor Fan Bingbing from Zhengzhou University published a paper entitled "Submicron Ti2CTx MXene Particulates as High-Rate Intercalation Anode Materials for Li-Ion Batteries" in the internationally renowned Journal of Materials Chemistry A. article. This article reports a method for obtaining submicron Ti2CTx MXenes by etching Ti2AlC synthesized by molten salt method. In this paper, the formation mechanism of Ti2AlC in molten salt and the high-rate performance mechanism of submicron Ti2CTx MXene are analyzed, and a high-rate self-supporting flexible electrode based on Ti2CTx is prepared, which lays the foundation for its application in flexible electronic devices.



Figure 1. Schematic illustration of TiH2, Al and nanocarbon black forming Ti2AlC MAX phase in equimolar KCl/NaCl molten salt. The metal elements are continuously dissolved in the molten salt, and finally diffuse into the nano-carbon black to form Ti2AlC



Figure 2. (a) Scanning photo of Ti2AlC synthesized by molten salt method, (b) Scanning photo of submicron Ti2CTx, (c) Transmission photo of submicron Ti2CTx, (d) XRD patterns of Ti2AlC and submicron Ti2CTx, (e) Nitrogen adsorption/desorption isotherm curves of Ti2AlC and submicron Ti2CTx



Figure 3. XPS spectrum of submicron Ti2CTx. (a) Ti 2p, (b) O 1s, (c) F 1s, (d) Cl 2p



Figure 4. Electrochemical performance characterization of submicron Ti2CTx. (a) Galvanostatic charge-discharge curves at different current densities, (b) comparison of electrochemical properties, (c) characterization of cycling stability at high current densities



Fig. 5. Comparative study of electrochemical behaviors of micron-scale large-scale Ti2CTx (l-Ti2CTx) and sub-micron small-scale Ti2CTx (s-Ti2CTx). (a) Cyclic voltammetry curves of s-Ti2CTx at 0.1 mV s-1 scan rate, (b) s-Ti2CTx and (c) l-Ti2CTx cyclic voltammetry curves at different scan rates, (d) capacitance behavior versus capacity Contribution ratio, (e) galvanostatic intermittent titration curve, (f) lithium ion diffusion coefficient measured at different potentials



Figure 6. AC impedance spectra of s-Ti2CTx at different potentials. (a) Uncycled fresh battery, (b) 3.0 V, (c) 2.25 V, (d) 1.5 V, (e) 0.75 V, (f) 0.05 V, (g) fresh battery and measured at 3.0 V AC impedance spectrum fitting circuit obtained, (h) AC impedance spectrum fitting circuit measured at 2.25~0.05 V



Figure 7. (a) Voltage curve and corresponding ex-situ XRD pattern, (b) DFT-calculated voltage curve of Ti2CO2Lix during lithiation, (c) (002) diffraction peak of s-Ti2CTx and corresponding interlayer spacing with charge and discharge Voltage evolution process



Figure 8. Characterization of s-Ti2CTx/SWCNTs self-supporting flexible electrodes. (a) Optical photograph, (b) Scanned photograph, (c) Magnification performance, (d) Cycling performance



Key points of this article

Point 1: Formation mechanism of Ti2AlC in molten salt environment

By analyzing the results of XRD patterns, Raman spectra, scanning morphologies and corresponding energy spectrum element surface distributions at different temperatures, the formation mechanism of Ti2AlC due to the diffusion of metal elements to carbon elements in molten salts was determined. The plausibility of this reaction mechanism was further confirmed by comparative studies using micron-scale carbon sources.



Point 2: Submicron Ti2CTx achieves high-rate performance mechanism

The specific capacity of submicron Ti2CTx can still reach 155 mAh g-1 at a current density of 10 A g-1, such a high rate capability exceeds that of most unmodified MXenes, even partially modified MXenes. By comparing the electrochemical behaviors of submicron Ti2CTx and micron-scale Ti2CTx, it is determined that higher lithiation/delithiation activity at low potential is the key to achieving high rate performance of submicron Ti2CTx.



Point 3: Design, preparation and application exploration of stack-based Ti2CTx flexible electrodes

In addition to its high rate capability, submicron TiCTx can also be fabricated into a self-supporting thin-film electrode with good flexibility by compounding with single-walled carbon nanotubes, which can achieve 173 mAh g-1 at a current density of 5 A g-1. 1 and exhibited good cycling stability. This method can be further extended to the preparation of lithium iron phosphate flexible cathode, and then combined with the pre-lithiated Ti2CTx flexible anode to form a flexible electrode full battery with high first Coulomb efficiency, which lays a good foundation for the application of Ti2CTx in flexible electronic devices.



About the corresponding author

Introduction to Researcher Wang Xiaohui: Graduated from the Department of Chemistry of Zhengzhou University in 1997 with a Ph.D. at the Institute of Metal Research, Chinese Academy of Sciences, under the tutelage of Researcher Zhou Yanchun, and then worked in the National Institute of Materials Science (NIMS) and the Institute of Multi-Material Science, Tohoku University, Japan Postdoctoral researcher, joined the Institute of Metal Research, Chinese Academy of Sciences in 2007. He has been engaged in the research and development of structural ceramics and energy storage materials for a long time. As the corresponding author, he has published dozens of research papers in academic journals such as Chemical Society Reviews, Nano Letters, and ACS Nano. So far, more than 130 papers have been published, which have been cited more than 8,000 times, and the H-factor is 45.



Introduction to the subject group

Researcher Wang Xiaohuis research group has long been engaged in the research and development of structural ceramic materials and electrochemical energy storage materials, such as MAX phase ceramics, MXene, LiFePO4, etc.



Article link

Submicron Ti2CTx MXene Particulates as High-Rate Intercalation Anode Materials for Li-Ion Batteries

https://pubs.rsc.org/en/content/articlepdf/2022/ta/d2ta03050k