Construction And Energy Storage Properties Of Titanium/Vanadium MXene Composites

2D MXenes have attracted extensive attention for energy storage applications owing to their high electronic conductivity,excellent redox activity,and remarkable mechanical property.Nevertheless,the inadequate capacity performance and the self-stacking phenomenon during the energy storage process which caused sluggish electrochemical kinetics and inferior cycling stability motivates the development of MXene composites.Herein,Ti/V-based MXene(Ti₃C₂T_x,V₂CT_x,Ti_2-yV_yCT_x)is used as the research object.Flexible V₂CT_x/Ti₃C₂T_x composite films and Ti O₂/MXene heterostructure were constructed through pillar supporting and select oxidation,respectively,and separately served as electrode materials of supercapacitor and lithium ion battery.The main research achievements include:（1）Flexible V₂CT_x/Ti₃C₂T_x composite films have been successfully assembled to improve the sluggish electrochemical kinetics and inferior cycling stability caused by self-restacking problem of d-Ti₃C₂T_x.The delaminated Ti₃C₂T_x matrix guarantees the predominant electronic conductivity and high Young’s modulus of the flexible electrode.Meanwhile,pillared ml-V₂CT_x spacers embedded in d-Ti₃C₂T_x layers efficiently restrain their self-restacking and consequently result in enriched ion channels for electrolyte ion accessibility.Benefiting from this elaborately designed vertical-liked pillar structure,the composite electrode containing 30%mass percentage ml-V₂CT_x exhibits a maximum gravimetric capacitance of 365 F g^-1 at 1 A g^-1,and out-standing cycling stability without capacitance loss after 10,000 cycles.Moreover,the assembled V₂CT_x/Ti₃C₂T_x based symmetric supercapacitor shows a high energy density of 5.4 m Wh g^-1 at a power density of 357.8 m W g^-1.This work provides an effective way to realize the construction of flexible MXene composite films with different morphologies and compositions to synergistically improve the performance of supercapacitors.（2）Due to the various oxidation tendency of Ti and V,double transition metal Ti/V MXenes(Ti_2-yV_yCT_x)act as precursors to engineer Ti O₂/MXene heterostructure with improved lithium storage properties.During the oxidation of Ti_2-yV_yCT_x,vanadium atoms with higher oxidative tolerance can maintain the 2D lamella morphology and high electronic conductivity while titanium atoms can be selectively oxidized to well-dispersed Ti O₂ nanoparticles.The content and dispersity of derived Ti O₂ nanoparticles can be well controlled by adjusting the molar ratio of Ti/V in the Ti_2-yV_yCT_x precursors.The intensive interfacial interaction between derived Ti O₂ and vanadium dominated MXene layers protects Ti O₂ nanoparticles from pulverization and detachment from 2D MXene as well as the restacking of MXene layers during charge/discharge cycles.Benefiting from the synergistic effects,the Ti O₂@Ti VCT_x anode delivers a superior specific capacity of 741.2 m Ah g^-1 at 0.1 A g^-1,which shows prominent advantage in current MXene-derived anode materials.This work innovatively realizes atomically selective oxidation of double metal transition MXenes and regulate the structure of derivatives for superior lithium storage properties.