Research On Preparation And Performance Of Aqueous Supercapacitors Based On MXene

In recent years,with the increasing demand for portable electronic products with long cycle life and fast charging,researchers began to study energy storage systems.Compared with lithium ion battery supercapacitors,they have low temperature resistance and high power density.MXene anode materials are emerging two-dimensional materials and one of large families of transition metal carbides,nitrides,or carbonitride known for their high capacity,conductivity,strong mechanical strength,and modifiable surface functional groups.Due to these excellent physical and chemical properties,MXene began to show great potential as an alternative to electrode materials for next-generation energy storage devices,especially in supercapacitors.Here we improve the performance of supercapacitors from three aspects:preparation,modification and assembly of MXene materials.The main contents and results are as follows:（1）Comparing the different synthesis temperatures（35℃,40℃,45℃,50℃and 55℃）of the etching process,the effect on the morphology and electrochemical performance of the MXene has been explored.40℃of the etching temperature allows the Al layer in the raw material to be fully etched,a stable MXene lamellar structure is obtained.During the etching process,increasing electrolyte concentration,increasing the concentration of H⁺can also increase the interlayer spacing.MXene can get 555 F g^-1 mass specific capacity at a sweep speed of 10 m V s^-1,as the sweep speed increases to 500m V s^-1,the capacity retention rate can reach more than 88%.At the same time,the influence of ultrasonic time on MXene performance has been explored,When the scan rate was 10 m V s^-1 and 500 m V s^-1,the specific capacity was kept as 466 F g^-1 and 411 F g^-1,respectively.The capacity retention rate is 88%,showed good rate performance.（2）Utilizing a simple PANI/MXene flexible electrode has been shown in this section,PANI/MXene composites were synthesized by electrostatic self-assembly of MXene and PANI nanoparticles.PANI/MXene with different mass ratios were prepared.Finally,the PANI_0.5/MXene composite with the best performance is selected.As a supercapacitor,at 5 m V s^-1,initial capacitance of the composite electrode is 610 F g^-1,maintained 565 F g^-1,at1000 m V s^-1 equivalent to 92.6%capacitance retention.At low temperatures,down to-30℃,at a low current density of 2 A g^-1with a specific capacity of76.5 m Ah g^-1,compared with room temperature,still has 93.2%capacitance retention,have a good low temperature resistance.（3）Using a porous MXene film as a negative electrode,PANI_0.5/MXene composite film as positive electrode,to design a fully pseudocapacitive asymmetric device(PANI_0.5/MXene//porous MXene),to increase the energy density of MXene based asymmetric supercapacitors.Asymmetric devices,electrochemical properties were tested.Broaden the voltage window to 1.3V.At 2 A g^-1 current density at room temperature,specific capacity was 32.8m Ah g^-1,as the current density increases to 200 A g^-1,capacity was 30.5 m Ah g^-1.The capacitance retention rate was 93%.And when the temperature drops to-60℃,the device still works,compared with normal temperature,81%of the total capacitance was maintained at-60℃.When a power density is 0.55KW Kg^-1,the energy density reaches maximum 19.25 Wh Kg^-1,when the temperature drops to minus 60℃,the maximum energy density is 12.07 Wh kg-1,which indicates that the device has good low temperature resistance and excellent magnification capability.It is superior to most of the previously reported MXene-based supercapacitors.