Preparation And Electrochemical Properties Of Flexible MXenes-Based Electrode Materials

Electrochemical energy storage refers to the use of chemical elements as an energy storage medium,and the charging and discharging process is accompanied by the chemical reaction or price change of the energy storage medium.At present,electrochemical energy storage mainly includes lead-acid battery,liquid flow battery,sodium sulfur battery,ion battery（lithium-ion battery,sodium ion battery,etc.）,and so on.At present,ion battery and supercapacitors are mainly used.In addition,with the development of science and technology,flexible wearable devices have gradually come into our lives,such as flexible folding mobile phones,wearable clothes,etc.In such flexible wearable devices,flexible batteries are an important component of which a crucial link is that the electrode materials need to be flexible and bendable.Currently,in commercial batteries or flexible batteries,electrode materials are often coated with active substances on the collector fluid.In this case,the flexible properties of the electrode are generated by the collector fluid.Although the electrode is flexible,the active substance often falls off from the collector in the process of repeated bending.Therefore,it is intuitive and important to develop flexible self-supporting electrode materials.At the same time,it is necessary to maintain high energy density and power density while maintaining the flexibility of electrode materials.In this paper,Ti₃C₂T_x,which is the most widely studied MXenes material,is the main research object.Firstly,different methods of preparing flexible MXene-based electrodes are explored,and the electrochemical performance of flexible electrodes is explored by studying the modification of electrodes.The research results are as follows:Firstly,we prepared a flexible binder-less freestanding thin film material by electrospinning technology,and obtained the final product Ti₃C₂T_x-Si@CNF flexible free-standing thin film by pre-oxidation and carbonization process in the later stage.Conductive carbon nanofibers provide an open three-dimensional network,which effectively slows down the volume expansion of silicon nanoparticles during the process of lithium/delithium.At the same time,the addition of MXene effectively improves the electronic conductivity of the composite material.This composite network structure is conducive to the highly reversible storage and rapid charge-discharge ability of lithium ions.Subsequently,the flexible freestanding Fe VO₄/Ti₃C₂T_x films were successfully prepared by vacuum assisted filtration method.Due to the synergic action of Fe VO₄and Ti₃C₂T_x,FVO/MX films show excellent electrochemical properties The structure can effectively inhibit the volume expansion during the kinetic reaction of Li⁺/Na⁺batteries.Meanwhile,the FVO/MX electrode also shows good electrochemical stability with rate performance in sodium ion batteries.Secondly,we introduced a simple method to control the surface morphology and chemical properties of MXene,and successfully prepared porous flexible materials with metal ions.We found the pore-making effect and layer-expanding effect of bivalent metal ions on the surface of MXene,and MXene-M can simultaneously increase the layer spacing between layers and form mesoporous structures in the layers.In-situ XRD is used to prove that Ti₃C₂T_x-Mn,the intercalated pseudocapacitor energy storage mechanism of MXene-M electrode,has excellent electrochemical performance.At the current density of 100 A/g,the mass specific capacity of Ti₃C₂T_x-Mn can still reach 248F/g after 100,000 cycles.Excellent bulk energy density of 52.4 m Wh/cm³ and ultra-high bulk power density of 55.3 W/cm³.In addition,Ti₃C₂T_x-Mn solid-state supercapacitor has excellent low temperature tolerance and low temperature multiplier performance.Ti₃C₂T_x-Mn-based supercapacitors have ultra-high low temperature surface capacity and low temperature cycle stability.The surface capacity is 807m F/cm² at-50℃and 658 m F/cm² at-60℃.Finally,Mo₂C/Mo O₃ heterostructures were prepared by in situ high temperature oxidation method.The thermal stability of Mo₂CT_x in air was determined by in-situ high temperature XRD technique.Mo₂C/Mo O₃ heterostructures in different proportions were prepared by in situ oxidation method,showing excellent electrochemical performance in water and all-solid systems.Mo₂C/Mo O₃ electrode has good electrochemical performance and low temperature tolerance（-60℃）and can reach up to 811 F/g specific capacity in water system.Mo20//Mo20 has a maximum energy density of 25 Wh/kg at a power density of 243 W/kg and a power density of 4320 W/kg,the energy density can still reach 6 Wh/kg.To sum up,the relevant research work in this round focuses on the design of flexible MXene-based electrode materials,explores different methods to prepare flexible MXene-based electrodes,studies electrochemical properties,flexibility and low temperature tolerance of electrode materials,and obtains good experimental results,providing theoretical and experimental basis for the design and application of flexible Mxenes-based materials.