MXene-based materials for electrochemical energy storage

Rechargeable batteries and supercapacitors are widely investigated as the most important electrochemical energy storage devices nowadays due to the booming energy demand for electric vehicles and hand-held electronics. The large surface-area-to-volume ratio and internal surface areas endow two-dimensional（2D） materials with high mobility and high energy density; therefore, 2D materials are very promising candidates for Li ion batteries and supercapacitors with comprehensive investigations. In 2011, a new kind of 2D transition metal carbides, nitrides and carbonitrides, MXene, were successfully obtained from MAX phases. Since then about 20 different kinds of MXene have been prepared. Other precursors besides MAX phases and even other methods such as chemical vapor deposition（CVD） were also applied to prepare MXene, opening new doors for the preparation of new MXene. Their 2D nature and good electronic properties ensure the inherent advantages as electrode materials for electrochemical energy storage. In this review, we summarize the recent progress in the development of MXene with emphasis on the applications to electrochemical energy storage. Also, future perspective and challenges of MXene-based materials are briefly discussed regrading electrochemical energy storage.

Recent progress and prospective on layered anode materials for potassium-ion batteries

Potassium-ion batteries(PIBs),also known as“novel post-lithium-ion batteries,”have promising energy storage and utilization prospects due to their abundant and inexpensive raw materials.Appropriate anode materials are critical for realizing high-performance PIBs because they are an important component determining the energy and power densities.Two-dimensional(2D)layered anode materials with increased interlayer distances,specific surface areas,and more active sites are promising candidates for PIBs,which have a high reversible capacity in the energetic pathway.In this review,we briefly summarize K+storage behaviors in 2D layered carbon,transition metal chalcogenides,and MXene materials and provide some suggestions on how to select and optimize appropriate 2D anode materials to achieve ideal electrochemical performance.

Recent progress in 2D materials for flexible supercapacitors

High performance supercapacitors coupled with mechanical flexibility are needed to drive flexible and wearable electronics that have anesthetic appeal and multi-functionality. Two dimensional（2D） materials have attracted attention owing to their unique physicochemical and electrochemical properties, in addition to their ability to form hetero-structures with other nanomaterials further improving mechanical and electrochemical properties. After a brief introduction of supercapacitors and 2D materials, recent progress on flexible supercapacitors using 2D materials is reviewed. Here we provide insights into the structure–property relationships of flexible electrodes, in particular free-standing films. We also present our perspectives on the development of flexible supercapacitors.

阳离子辅助自组装制备二维Ti_(3)C_(2)T_(x)/rGO复合纳米材料及其在高性能锂离子电容器中的应用

二维(2D)材料MXenes由于具有金属导电性以及种类丰富的表面终止基团,在储能材料领域得到广泛研究.MXenes片层之间存在空隙,能够提供快速的离子传输通道,实现高倍率性能,并且进一步剥离的MXenes能够提供更多的离子储存位点.然而,剥离的MXenes纳米片存在着严重的重新堆叠情况,导致电化学性能降低.为了解决该问题,本文提出了一种借助四丁基铵离子(TBA+)修饰,使均带负电的剥离Ti_(3)C_(2)T_(x)(MXenes)和氧化石墨烯(GO)纳米片通过静电自组装再退火的策略,制备结构稳定的Ti_(3)C_(2)T_(x)/rGO复合纳米材料.Ti_(3)C_(2)T_(x)与rGO纳米片以面对面的结构排布,分散均匀且能够缓解MXenes纳米片重新堆叠的情况,增大了电极材料的电化学活性面积,因此能够提供高的可逆比容量(1394 mAh g^(-1))和优越的倍率性能.同时与活性碳作为正极组装成锂离子电容器,能量密度最高可达145 Wh kg^(-1),循环5000次后的容量保持率>80%,充分证明了Ti_(3)C_(2)T_(x)/rGO作为锂离子电容器电极材料的潜力.