Study On Preparation And Energy Storage Characteristics Of Supercapacitors Based On Nickel/Cobalt Composite For MXene Two Dimensional Materials

With the rapid development of electric vehicles,much attention is being paid to batteries with outstanding performance.Although the presently commercialized batteries have relatively high energy density,they still have some shortcomings,such as low power density,poor cycle life and environment unfriendly issues,which largely hinder the large-scale deployment of electric vehicles.Supercapacitors(SCs),as a novel energy storage device,show great prospects for resolving the above issues because of their higher power density,longer cycling life,wider working potential window and environment friendly.One of the key factors determining the electrochemical performance of SCs is the electrode materials.MXenes,a new type of two-dimensional(2D)carbonitrides or transition metal carbides similar to graphene,have excellent electrical conductivity and high redox activity,exhibiting great prospects as electrode materials for supercapacitors.Nickel-cobalt based electrode materials has attracted renewed and great attention from researchers due to its high theoretical capacitance,low cost,favorable stability and environmentally benign nature.In this paper,we designed layer MXene and enlarged the layer space.Based NF,we prepared ?-Ni(OH)2 arrays,Nickel-cobalt-LDH and their compounds.The effects of different treatments and morphologies of NF based electrode materials on the properties of supercapacitors were comprehensive analyzed.The main results and research works are as follows:1.This work employed a two-step procedure to obtain a highly opened layer structure for Ti3C2.Firstly,the mild NH4HF2 etching agent is used to prepare the regular Ti3C2 MXene.Secondly,KOH is added into the obtained solution for K+to intercalate the MXene.The K+intercalation is found to greatly increase the(002)crystal planar spacing of the Ti3C2 from 10.8 A to 12.4 A.To investigate their electrochemical capacitance properties,the regular and K+intercalated Ti3C2 MXenes are used to fabricate binder-free electrodes on nickel foams by an electrophoretic deposition method.The K+intercalated MXene based electrode is found to have twice higher specific capacitance more than the regular MXene(690.9 and 333.3 F g-1 for the K-MXene and MXene,respectively,at a current density of 1 A g-1).Furthermore,the K+intercalated Ti3C2 MXene based electrode exhibits an excellent cyclic stability.2.The as-prepared ?-Ni(OH)2@NF integrated electrode does not involve the usage of any extra binders or conductors,and it exhibits high electrochemical properties(3.68 mAh cm-2 at the current density of 2 mA cm-2,and the areal capacity reached 115.8%of the initial value after 2000 cycles at a current density of 15 mA cm-2).Furthermore,we employed the integrated electrode and AC to assemble an ASC device,which is found to deliver a high energy density of 74.2 Wh kg-1 at the power density of 776.9 W kg-1.The ASC device easily lights up 8 light-emitting diodes(LEDs).Furthermore,it has an excellent cycling stability(89.9%after 10000 cycles).3.NiCo-LDH@NF cathode material with high specific capacitance was first synthesized by in-situ growth method,with a specific capacity of 10.04 C cm-2 at a current density of 2 mA cm-2.The best performance is obtained when the atomic ratio of NiCo is 1:1.6.In addition,we have assembled NiCo-LDH@NF//AC@NF hybrid supercapacitors with a wide voltage window of 0-1.8V,using PVA solid electrolyte to study its flexible performance,and the electrochemical performance without loss after bending 900 and 180°.When the energy density is 56.5 Wh kg-1,the power density can reach 937.3 W kg-1,and the cycle performance will reach 97.1%after 10,000 charge and discharge cycles.4.Compound NiCo-LDH and K-MXene in two different ways.The first is NiCo-LDH doped K-MXene through in-situ growth method under alkaline environment.At the same time,the three-electrode test also showed excellent electrochemical performance with a specific capacity of 11.2 C cm-2 at 2 mA cm-2 current density.The second is use NiCo-LDH and K-MXene as the positive and negative electrodes of a solid-state hybrid capacitor,respectively.It is found that it has a voltage window of 0-1.4 V and the energy density is 40.5 Wh kg-1,while power density is 729 W kg-1,means great prospect of practical application.The research of this subject is to design electric double-layer capacitor electrodes and high-capacity battery-type electrodes for the development of high-performance supercapacitor.Reveals its growth mechanism,performance principle and provides guidance for future practical applications.