| In future,artificial intelligence and digital transportation electrification will continue to develop with electricity as the medium.The scientific development of new energy requires the utilization of wind power,hydropower,geothermal and solar photovoltaic as clean energy.In order to meet the power supply of electric vehicle,portable mobile electronic devices,the rapid development of high-quality and highperformance electrochemical energy storage system is urgently needed.The research and development of electrode materials,the optimization of electrode functions and the study of electrode energy storage mechanism are the foundation for building an electrochemical energy storage system to meet the futuredemands.MXenes,as a new two-dimensional transition metal carbon,nitrogen or carbonitride,contain two-dimensional lamellar carbon atom layer.Thus,it exhibits good conductivity similar to graphene.The transition metal layer exposed on the surface has the physical and chemical properties similar to the transition metal oxide.The surface can be linked to a variety of functional groups to achieve the hydrophilic,adsorption and regulate other interfacial properties.In addition,it has a two-dimensional interlayer to facilitate ion storage and transportation.The integration of these unique performances unlocks the potential of MXene and its composites in many energy storage fields,such as super capacitor,lithium/sodium/magnesium ion secondary battery,lithium sulfur battery,zincair battery and hydrogen storage.In this dissertation,surface chemical regulation,inner layer space regulation and structure electrode design were employed to enhance the electrochemical performance as electrode active materials.The main research contents are as follows:1.Compared with pristine Ti3C2 electrodes,Ti3C2 annealed under H2 offers a route for tailored surface functionalization,exhibiting a knockdown-F content.When the low-F Ti3C2 was employed as anodes materials of lithium-ion batteries,an enhanced volumetric specific capacity of ~123.7 m Ah/cm3(the c-discharge current density is ~100 m A/cm3)and an excellent cycling stability(above 75% remain after 100 cycles)were obtained.The improvement is attributed to the lower terminal group-F concentration at the Ti3C2 layer,which leads to a faster ion transport and increases of more active sites exposed to the electrolyte.Empolying high temperature hydrogen to remove the F terminal optimizes the kinetics of ion transport.Thus,it may be a way to meet the increasing demands of high power and high energy storage devices.2.Improved Li storage capacity and cycling performance were realized for Ti3C2 Tx MXene-based lithium ion battery,as a delicate design of high-valence cation Al3+ preintercalation.The high-valence cation Al3+ offers constructing of an effective interspace of MXenes to allow for more Li+ intercalation reaction,and accelarte the ion transport.Since the Al3+ pre-intercalation provided a charge compensation during the charge/ discharge process,the Li ion transfer channels were broadened at a state of full lithiation,responsible for the suppressed microstrucutural deformation upon cycling.These findings may be generally applicable to other 2D and layered materials.It is worth mentioning that by carefully selecting intercalation cations as ?Tents-Pitching?,it should be possible to realize a general atomic-level match between intercalants and intercalated compounds.3.We constructed a DIB with Fe pre-intercalated ML Ti3C2 Tx as anodes,graphite as cathodes and [EMIm][PF6] ionic liquid as electrolyte.Benefited from intercalation behaviors in both anodes and cathodes,the fabricated DIBs exhibit an energy density of 76 W h kg-1 at the power density of 360 W kg-1,delivering a capacity retention of 94% after 50 charge–discharge cycles.The electrochemical pre-intercalation technology offers an approach to precise control the interlayer environment.The knockdown content of pre-intercalated ions has a huge impact on the electrochemical performance.This work provides new sights into the future development of the electrode modification.In addition,the more kinds of ions may be pre-intercalated via this technology and the electrodes can achieve a higher electrochemical performance.4.A simple method by changing the filter membrane to obtain an anti-T MXene film electrode is proposed.Our proof-of-concept of anti-T design affords a significant increase in the electrochemical performance of supercapacitors via accelerating the ion diffusion rate.The anti-T Ti3C2 Tx film electrode can obtain a higher capacitance under diffusion-controlled and capacitive mechanisms than that of flat Ti3C2 Tx.Moreover,our assembled anti-T Ti3C2 Tx symmetric supercapacitor exhibited an energy density of 11.27 Wh kg-1 at the power density of 699.9 W kg-1.This convenient and feasible method combining the vacuum filtration approach may offer a possibility for the preparation of the large-area film electrodes.The filter membrane with designed geometry may motivate the new architectured electrodes.To sum up,high-performance Ti3C2 Tx MXenes based electrochemical electrodes were obtained by exploring the electrochemical energy storage mechanism of Ti3C2 Tx MXenes based electrodes and optimizing the ion transport and electron transport ability.Understanding the energy storage mechanism of Ti3C2 Tx MXenes based electrochemical electrode and constructing the theoretical system of electrode design are of great significance for the development of high-energy density energy storage devices. |
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