Preparation Of Titanium And Vanadium Based Two-Dimensional Double Transition Metal Mxene Composite And Its Application In Energy Storage

Supercapacitors and lithium-ion batteries have been attracting much attention due to their higher power and energy density.The energy and power density,cycle stability and service life of electrochemical energy storage devices are largely determined by the choice of electrode materials.As the electrode materials are the key factor to determine the performance of supercapacitor and lithium-ion,the development of high-performance electrode materials is essential for the practical use of electrochemical energy storage devices.2D transition metal carbides,nitrides,and carbonitrides,also known as MXene with unique in-plane anisotropic layered structure,are versatile materials due to their adjustable element and structure,excellent hydrophilic,metallic conductivity.MXene materials are widely utilized in the field of energy storage due to their high surface to volume ratio,fast ion diffusion pathways,low ion transport barrier and unique physicochemical properties.However,MXene with a single metal component are difficult to have the advantages,such as high specific capacity,efficient ion/electron transport and stability,in the electrochemical environment.Novel Ti&V-based double transition-metal MXene（TiVCT_xand Ti₂VC₂T_x）were investigated in this thesis.Preparation and applications in supercapacitors and lithium-ion batteries are discussed.The main research contents are as following:（1）A new strategy of spontaneous transforming few-layered TiVCT_x MXene nanosheets directly into TiVCT_x/Poly-o-PD composites（N-TiVCT_x）with three-dimensional（3D）stable tremella-like architecture by utilizing o-phenylenediamine（oPD）as the monomer of oxidant-free polymerization is proposed.Characterizations were carried out to evaluate the morphology and structure by using XRD,TEM,SEM,XPS,TGA,BET and FTIR.Meanwhile,electrochemical performance of the supercapacitor using TiVCT_x and N-TiVCT_x in acidic and neutral electrolyte was examined for the first time.Notedly,N-TiVCT_x composites show outstanding electrochemical capacitance property with a high specific capacitance of 282 F g^-1 at 10m V s^-1.Compared with the pristine TiVCT_x,the capacitance was increased by 50%.Besides,the 3D N-TiVCT_x electrode exhibits stable pseudocapacitive charge storage with capacity up to 415.6 m Ah g^-1 at 0.1 A g^-1 and retains outstanding performance of224 m Ah g^-1 at 2 A g^-1 for lithium-ion storage.The N-TiVCT_x MXene greatly increases the stability including thermal,chemical,and electrochemical stability.（2）Ti₂VC₂T_x MXene was prepared by HCl/Li F etch agent for the first time,and the single layer Ti₂VC₂T_x（SL-Ti₂VC₂T_x）was successfully exfoliated after TMAOH intercalation.TEM,SEM,XRD,TGA,BET,UVs and XPS analysis were used to characterization of ML-Ti₂VC₂T_xand SL-Ti₂VC₂T_x.Furthermore,the electrochemical energy storage performance of Ti₂VC₂T_x was investigated as the electrode for supercapacitor and lithium-ion batteries for the first time.As the electrode of supercapacitor,the specific capacities of SL-Ti₂VC₂T_x at 5 m V s^-1 in 1 M H₂SO₄,1 M KOH,and 1 M Mg SO₄ are 270,170 and 163 F g^-1,respectively.The specific capacity of the lithium-ion battery based on SL-Ti₂VC₂T_x electrode can reach up to 260 m Ah g^-1 at 0.1 A g^-1 current density.After 2000 cycles at 1 A g^-1 current density,the capacity maintained at 140 m Ah g^-1 without any decay,and the specific capacity was increased by 10%during the process of charging and discharging.