【Research Background】

     2D nanomaterials generally have a high surface area and therefore generally have excellent physicochemical properties, so the full potential of a single nanosheet is achieved by assembling 2D nanoscale blocks into 3D porous structures such as aerogels and porous foams. It is crucial in practical applications. MXene is a new class of 2D transition metal carbides and nitrides with the formula Mn+1XnTx, where M is the transition metal (Ti, V, Mo, Nb, etc.) and X is carbon or nitrogen (n = 1, 2 or 3) , T represents a functional group containing an oxy group, a hydroxyl group, a fluorine group or the like. It is made by etching and extracting an element A (III A or IVA) layer from a layered MAX phase precursor. Due to its unique structure and surface chemistry, MXenes has metal conductivity, excellent hydrophilicity and good mechanical stability. It is used in many fields such as energy storage, electromagnetic interference shielding, electrocatalytic hydrogen evolution, piezoresistive sensors and diaphragms. Shows promising prospects.

[Introduction]

     Prof. Xu Bin from Beijing University of Chemical Technology published the flexible 3D Porous MXene Foam for High-Performance Lithium-Ion Batteries in Small, and prepared a flexible 3D porous MXene film with S as a sacrificial template. It has excellent capacity and cycle performance.

     Two-dimensional transition metal carbides and nitrides are promising energy storage materials, but the aggregation and stacking of two-dimensional nanosheets limits their electrochemical performance. In order to overcome this problem and make full use of the potential of MXene nanosheets, a 3D MXene membrane with porous structure was prepared by a simple sulfur template method. The membrane is free-standing, flexible and highly conductive, and can be directly used as a lithium ion battery. electrode. The three-dimensional porous structure of the MXene membrane provides a large number of active sites to enhance lithium storage capacity. The 3D porous structure facilitates electrolyte penetration and rapid Li+ transfer. Therefore, this flexible three-dimensional porous MXene exhibits a capacity of 455.5 mAh g−1 at 50 mA g−1, excellent rate performance (101 mAh g−1 at 18 A g−1), and extremely long period stability. Sex (expressed at 1 A g−1 after 3500 cycles, exhibiting 220 mAh g−1). This work not only proves the great superiority of three-dimensional porous MXene, but also proposes a sulfur template method for constructing three-dimensional foam with two-dimensional nanosheets at relatively low temperature.

Figure 1 3DMXene synthesis flow chart

Figure 2 a, b) is an SEM image of 3dMXene. It can be seen that the 3dMXen film is thicker than the conventional MXene film. c) for p-MXen-71 flexible test d) for 3dMXene pore size analysis e) XRD analysis f-h) for XPS analysis

Figure 3 a-d) CV curve at 0.1 mV s-1 scan rate e-h) 50 mA g-1 charge and discharge curve at current density. (a,e) Stacking MXene (b,f) p-MXene-35, (c,g) p-MXene-48 (d,h) p-MXene-71

Figure 4 Electrochemical performance test a) Cyclic performance at 50 mA g-1 current density b) Rate performance c) Ultra long cycle stability test d, e) 300 cycles before and after impedance

[Summary of this article]
   Three-dimensional MXene with controlled pore structure was prepared by sulfur template method. The material has good flexibility and can be directly used as anode of lithium ion battery. At a relatively low temperature of 300 ° C, the sulfur template can be easily removed and an s-doped group with enhanced electrolyte wettability is produced. The three-dimensional porous MXene not only retains the excellent conductivity and flexibility of the MXene film, but also exposes more active sites from the increased surface area for Li+ storage, resulting in high capacity. In addition, MXene‘s porous structure provides a large number of electrolyte channels for ion transfer and provides a fast surface Faraday redox reaction, which means good rate performance. 3 d MXene‘s most developed porous structure (p-MXene-71) exhibits a current density of 50 mA g-1 and a high capacity of 455.5 mAh g-1, excellent rate capacity of 101 mAh g−1 even at an ultra-high current density of 18A G−1, and excellent long-term cycling stability (220 mAh g−1 at 1 A g-1 current density after 3500 laps). Excellent electrochemical lithium storage properties demonstrate the importance of three-dimensional porous structures in the full utilization of MXene nanosheets. The unique microstructure makes the 3D MXene also suitable for pressure sensors and has broad application prospects. In addition, the sulfur template method provides a new idea for constructing a three-dimensional porous foam structure from two-dimensional nanosheets, which can be extended to other two-dimensional materials.

Literature link:

DOI: 10.1002/smll.201904293

Source：WeChat public number  MXene Frontier