Preparation And Electrochemical Performances Of MXene-Based Composites

Ti₃C₂T_x(MXene)is a burgeoning two-dimensional transition metal carbide.It is widely applied in supercapacitor and battery due to their ultrahigh electrical conductivity,outstanding mechanical strength and promising volumetric capacitance.However,the practical application of pure MXene nanosheet is limited.The monolayer MXene is easily self-restacking which will lead to low capacitance.Thus,it is a great challenge to restrain MXene self-restacking efficiently.To solve this problem,the main idea of this paper is to assemble MXene with other materials,specifically,including monolayer CoAl-LDH(Layered double hydroxide,LDH),oxygen vacancies-enriched Bi_2.88Fe₅O_12-x(BFO),Fe₂O₃and Carbon nanotubes(CNTs).To adjust the structure and propertie of the composite,the electrode materials are applied to supercapacitors and lithium-ion batteries.The specific contents are as follows:The monolayer CoAl-LDH was prepared by two-steps ion exchange and liquid phase exfoliation.Following these two procedures,the monolayer of negatively charged MXene nanosheets and the monolayer of positively charged CoAl-LDH nanosheets through electrostatic self-assembly to fabricate MXene/CoAl-LDH(ML-80)composite.Due to the excellent synergistic effects between MXene and CoAl-LDH nanosheets,CoAl-LDH could effectively hinder the irreversible self-restacking of MXene.Morever,MXene could provide conductivity for the materials.The ML-80 electrode has the ultrahigh volumetric capacity of2472 C?cm^-3.To assemble an asymmetric supercapacitor with MXene/rGO-5%(MG-5),it exhibited a high volumetric energy density of 85.4 Wh?L^-1 and an excellent cycling stability.Through the hydrothermal way,the ultrathin(7 nm),positively charged Bi_2.88Fe₅O_12-x(BFO)nanoparticles have been fabricated.Through the electrostatic self-assembly with the MXene nanosheets to prepare the MXene/Bi_2.88Fe₅O_12-x(MBFO)composite.The BFO nanoparticles could be uniformly immobilized on the surfaces of MXene nanosheets,which can efficiently eliminate the restacking of the MXene nanosheets,and increase electrical conductivity.Being benefited from the intimate interfacial contact,the MBFO nanocomposite exhibites an excellent gravimetric and volumetric specific capacity of 176m Ah?g^-1 and 476 m Ah?cm^-3.The rGO/Ni Co-LDH//MBFO asymmetric supercapacitor has a high volumetric energy density(177 Wh?L^-1)and cycling stability.In terms of the performance of lithium-ion battery,it also shows an excellent electrochemical performance.To prepare Fe₂O₃ nanoparticles through the thermal decomposition,we used a simple physical mixture with MXene nanosheets to obtain MXene/Fe₂O₃ composite.MXene could improve the conductivity of the composite hindering the volumetric change of Fe₂O₃ during the electrochemistry test.The MXene/Fe₂O₃ composite has an excellent specific capacity of526 C?g^-1.The assembled rGO/NiMn-LDH//MXene/Fe₂O₃ asymmetric supercapacitor has an ultrahight energy density(108 Wh?kg^-1)and cycling stability.The CNTs modified by the cationic surfactant PDDA solution with positively charged,then by electrostatically self-assembling with MXene nanosheets to prepare the MXene/CNTs-5%(MC-5)composite.The CNTs could build a three-dimensional network structure between the layers of MXene,increasing the interlayer spacing of MXene nanosheets.It helps improving the rate capability of the composite.Thus,the MC-5composite has an excellent specific capacitance(420 F?g^-1)and cycling perfprmance(after10000 cycles,the retention rate capacitance is 110.3%).The MC-50 electrode prepared by the same method also showed an excellent reversible specific capacity in lithium-ion battery testing.