Preparation Of Two Dimensional Ti₃C₂T_x And Metal Compound Composites And Study On Performance Of Supercapacitors

The wide operating temperature range,high power density,and good stability of Supercapacitors(SCs)make them an efficient and environmentally friendly energy storage device with great potential for use in electric vehicles,smart grids,and many other fields.However,with the continuous expansion of downstream application scenarios,the demand for SCs with better performance is also growing.The production of electrode materials with greater specific capacitance,energy density,and stability is essential for the enhancement of supercapacitors and the advancement of new ones.Ti3C2Tx MXenes has become an excellent twodimensional conductive substrate for electrode materials of supercapacitors(SCs),with outstanding physical and chemical characteristics.However,due to the low theoretical specific capacitance of Ti3C2Tx and its easy agglomeration between layers,its electrochemical performance and practical application are seriously limited.Theoretically-capacitive,with plentiful raw materials and a variety of structures,transition metals such as Ni,Mn,and Co,which possess pseudocapacitance properties,have been extensively researched as electrode materials for supercapacitors.This thesis improves the electrochemical performance through the structural design or composite modification of Ti3C2Tx Mxenes and Ni,Mn,Co oxygen/sulfide materials.The main work includes:(1)By employing a straightforward hydrothermal synthesis approach,we created a three-dimensional Ni(OH)2-MnO2 nanoflower between the Ti3C2Tx sheets,resulting in a unique 3D pillared structure.This not only solved the issue of easy agglomeration between the Ti3C2Tx layers,but also highlighted the benefits of Ni(OH)2 and MnO2 as transition metal compounds with high specific capacitance.The Ni(OH)2-MnO2@Ti3C2Tx yielded a synergistic effect between components.The advanced hierarchical pillared structure shows excellent structural stability and pseudo-capacitor high capacity characteristics.By comparing the composites with different proportions of Ti3C2Tx,we found that when the molar ratio of Ni(OH)2,MnO2 and Ti3C2Tx is 4:5:1.5,the maximum specific capacitance of 2523 F/g at 2 mV/s is about 25 times of Ti3C2Tx and 5.8 times of Ni(OH)2-MnO2.After 10000 charge-discharge cycles,the capacitance retention rate reaches 88.1%at a current density of 10 A/g.This electrode’s assembly of the SSC yields a remarkable 421.5 W/kg power density when the energy density is 36.3 Wh/kg.The strategy of constructing hierarchical structure provides application prospects for pseudo-capacitor metal electrode.(2)The polyhedral transition metal sulfide Ni3S2 and layered carbon-based material Ti3C2Tx were directly synthesized by electrostatic assembly,and successfully prepared Ni3S2@Ti3C2Tx compound material.The layered Ti3C2Tx,as a conductive network,shows excellent conductivity and low volume expansion,while the small polyhedral transition metal sulfide Ni3S2,provides higher charge storage capacity.Ni3S2@Ti3C2Tx,a two-phase composite,has an impressive multiplicity performance of up to 98%after 5000 cycles at a current density of 2 A/g.The SSC devices,when assembled,have a wide potential window of 0-1.6 V,a remarkable multiplicative performance of 93%,a high power density of 792.1 W/kg,and an energy density of 71.7 Wh/kg.The solid polyhedral Ni3S2@laminated Ti3C2Tx composite has a good synergistic effect,synergistically reducing the expansion and collapse of the material through its own excellent electrochemical properties,achieving a strong enhancement of its multiplicative properties,energy density and other electrochemical properties,which may offer potential application prospects for high energy density SSCs.(3)Derived from metal-organic framework(MOF),the yolk-shell NiCO2S4@Co3S4 nano-cage(YSN)is anchored on the surface of Ti3C2Tx through ion exchange reaction and electrostatic attraction,forming a unique layered structure.NiCo2S4@Co3S4 YSN has a large void space,which can be regarded as a limited reactor.It not only provides a buffer for volume changes,but also establishes a stable structure during charging and discharging,and also provides rich active sites,flexible charge transfer paths,short ion diffusion channels,and inhibits the aggregation of Ti3C2Tx nanosheets.Benefiting from the above advantages,NiCo2S4@Co3S4/Ti3C2Tx electrode shows a significant specific capacitance(1872 F/g,2 mV/s),and still shows a significant magnification capability,low resistance and excellent pseudocapacitance at high current density.The ASC,a NiCo2S4@Co3S4/Ti3C2Tx and AC-assembled water system asymmetric supercapacitor,boasts an energy density of 241.9 Wh/kg and a power density of 1125 W/kg,allowing it to illuminate 10 LEDs at once.This reasonable design method can provide a meaningful prospect for MXenes and MOF derivative composites to be used in high-performance ASCs.