Synthesis And Electrochemical Performances Of MXene-based High-Energy-Density Electrode Materials For Secondary Batteries

Motivated by the escalating demands for advanced technologies and energy,rechargeable batteries with high energy and power density,inner safety,long service life,satisfying Coulombic efficiency and low cost are key enablers for large scale grid energy storage systems,electric vehicles,and portable electrical devices.Electrode materials have important influence on the electrochemical performance of a battery.Developing high-energy-density,safe,long-life,and low-cost electrode materials is vital for the next-generation secondary rechargeable batteries.However,several key scientific challenges hinder their practical application:(1)Huge volume change during cycling processes causes particles to fracture and lose electrical contact.Moreover,volume change can destroy the SEI layer,leading to continuous electrolyte decomposition,loss of Li,increasing cell impedance and low Coulombic efficiency.The electrochemical performance of battery is severely degraded.(2)Low-electrical conductivity causes sluggish ions diffusion kinetics,resulting in poor rate performance.(3)For some metal anodes(e.g.,Li metal anode and Zn metal anode),the uncontrollable dendrite growth degrades the electrochemical performance and brings severe safety concerns.Therefore,in this thesis,we design a series of high-performance MXene-based electrode materials for Li/Zn/K ion batteries via electrodeposition approach,heat treatment approach,and vacuum filtration.1.Flexible,free-standing and binder-free Mxene@Si paper is fabricated via vacuum filtration and directly used as anodes for LIBs.Highly conductive MXene networks can supply a rigid current collector,enhance the conductivity of MXene@Si electrode,accommodate the large volume expansion.offer additional active sites,and facilitate the efficient ion transport.Meanwhile,the Si nanospheres can prevent the restack of MXene sheets.Thus,MXene@Si anode achieves superior electrochemical performance,which maintains 1672 mAh g-1 at 1000 mA g-1 after 200 cycles.The performance enhanced mechanism is investigated,revealing the relationship between microstructure,volume effect and reaction kinectics.This work may shed lights on the development of silicon-based anodes for LIBs.2.The growth behaviors of metallic Sb,Sn and Bi on Ti3C2Tx MXene paper are systematically investigated via a facile electrodeposition approach.Robust,flexible,free-standing and binder-free Ti3C2Tx MXene@Sb paper is employed as anode for potassium-ion batteries,achieving improved electrochemical performance.The hierarchical structure provides a short diffusion distance for potassium ions and buffer volume change during the potassiation/depotassiation process.Highly conductive and flexible MXene paper serves as elastic current collector providing an electronic highway to facilitate electron transport and accommodating volume change during the cycling process.MXene@Sb delivers a high reversible capacity of 516.8 mAh g-1 and a high rate capacity of 270 mAh g-1 at 500 mA g-1.Moreover,the improvement mechanism of potassium storage performance is comprehensively investigated.The relationship between material structure,volume effect and interface is revealed.This work may also be interesting in relation to research on other rechargeable batteries,catalysts,sensors,etc.3.The growth behavior of metallic Zn on Ti3C2Tx MXene is explored.Flexible freestanding three-dimensional layered Ti3C2Tx MXene@Zn paper is designed via electrodeposition approach and employed as both zinc metal anode and lithium metal anode host.The crystal growth mechanism of Zn metal on Zn foil and T13C2Tx MXene@Zn paper was studied.It is found that the Ti3C2Tx MXene@Zn paper can effectively suppress the dendrite growth of Zn,enabling reversible and fast Zn plating/stripping kinetic in aqueous electrolyte.Moreover,the Ti3C2Tx MXene@Zn paper can be used as a 3D host for lithium metal anode.In this host,Zn is utilized as a nucleation agent to suppress the Li dendrite growth.These findings may be useful for the design of dendrite-free metal-based energy storage systems.4.The thermal stability behavior of V2CTx MXene in air atmosphere is studied by heat treatment.The effects of annealing conditions on crystallinity and microstructure of V2CTx are systematically probed.Morphology-tunable micron-sized nanoporous V2O5 arrays are synthesized from V2CTx.The rationally designed V2O5 possesses special porous architecture,2D structure,and pseudocapacitive effect,which ensures high ion accessibility,excellent structure stability,and fast charge transport.Consequently,the optimal V2O5 cathode for gel zinc-ion batteries exhibits high capacity(358.7 mAh g-1 at 200 mA g"1 after 400 cycles),superior rate performance(250.4 mAh g-1 at 8 A g-1),and stable long-term cyclability(279 mAh g-1 at 2 A g-1 over 3500 cycles).The zinc storage enhancing mechanism is assessed by quantitative kinetics analysis.Furthermore,the V2O5 cathode also delivers an improved potassium storage performance.This work may provide a universal avenue to fabricate high-performance electrodes from MXene-based materials for next generation battery systems.5.The thermal stability behavior of Ti3C2Tx MXene in CO2 atmosphere is studied by heat treatment.The microstructure and components evolution of MXene with varied annealing temperature are probed.Ultrafine TiO2 confined in 3D freestanding carbon paper is constructed by one-step green in-situ oxidation of MXene paper with CO2.The flexible C/TiO2 paper is employed as anodic host for Li metal batteries.The growth process of metallic Li on C/TiO2 is also systematically investigated,revealing the internal mechanism of dendrite suppression.The lithiophilic TiO2 seeds and freestanding 3D carbon matrix can synergistically induce uniform Li deposition and buffer the volume changes during lithium stripping and deposition,which ensure improved electrochemical performance with high Coulombic efficiency and low overpotential,etc.This work may be useful for both the design of dendrite-free lithium metal batteries and the sustainable utilizing of CO2.