Two Dimensional Materials

Energy Storage and Application for 2D Nano-material MXenes Article

ZHENG Wei, YANG Li, ZHANG Peigen, CHEN Jian, TIAN Wubian, ZHANG Yamei, SUN Zhengming

Materials Reports 2018,32(15 ):2513 -2537. DOI:10.11896/j.issn.1005-023X.2018.15.001

Abstract （1599）

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Save Energy storage and conversion devices are one of the indispensable bases for the modern society. The demands for high performance energy storage and conversion devices are becoming more and more urgent with the rapid development of portable electronic devices and electric vehicles. The performance of energy storage and conversion devices strongly depends on the development and utilization of energy storage materials. Generally, the requirements for energy storage materials are as follows: being capable of reversible redox reactions; having excellent ionic accessibility; providing plenty of redox active sites; having high electronic conductivity.
Recently, two dimensional materials have shown great advantages in energy storage area for their large surface area and short ion transmission path. Two dimensional materials, possessing only atomic layer thickness and large number of surface active sites, good mechanical properties, exactly fit the role of energy storage and conversion devices. MXenes are a new type of two-dimensional materials, generally represented as M_n+1X_nT_x, where M is the transition metal elements, X is carbon and/or nitrogen, T represents functional groups (-F,-OH,-O, etc.) produced in the MXenes preparation process, and n is usually 1—4. Since being discovered in 2011, they have been highly expected for energy-related technology applications. MXenes exhibit good conductivity, fast charge response, pseudocapacitance and stable cycle life. The carbon layers in MXenes lead to good conductivity; the transition metal (M) layers render MXenes similar properties of transition metal oxides; whereas the functional groups enable MXenes hydrophilic surface. Such unique structure and properties perfectly match the requirements for energy storage materials and thus drive the research on MXenes a hot topic. In addition, portable energy storage and conversion devices demand high volumetric capacity and volumetric energy density. Compared with carbon-based electrode materials, MXenes have high accumulation density, which can effectively reduce the volume of energy storage devices and thus widen its application spectrum.
MXenes and their composites have already shown practical application in supercapacitors, lithium/sodium/magnesium ion se-condary batteries, lithium-sulphur batteries, zinc-air batteries, hydrogen storage and other energy storages. However, pristine MXenes are prone to collapse and restack during preparation and service, compromising their performance as electrode material. Much work, such as intercalating, modification, doping, compositing with other materials, has been done to reduce the ion diffusion resistance and increase the ion adsorption sites, resulting in the prevention of MXene restacking and electrochemical properties improvement. Moreover, different energy storage and conversion devices have different requirements for the synthesis processes and structural features of MXenes. Given that the research papers on MXene-related energy materials exponentially expand, it is necessary to comprehensively summarize and analyze it in order to promote their development in the field of energy storage and conversion.
This article reviews the latest progress on the synthesis, structure, properties and energy storage applications of MXenes and also discusses the research directions and challenges for MXenes for the years to come.

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