| As a kind of secondary battery,sodium ion battery?SIBs?is expected to replace lithium ion battery due to its abundant resources and low cost.However,the larger ionic radius of sodium ions in the process of repeatedly inserting and extracting the electrode material causes a problem of volume expansion of the material,which causes a problem of battery capacity attenuation and cycle performance degradation.MXene,as a kind of two-dimensional material,has excellent charge transfer capability and unique two-dimensional structure.Its capacitive behavior-controlled energy storage method allows sodium ions to be inserted primarily into the layers of MXene rather than into the crystal lattice of the material.The above characteristics make MXene ideal candidate for solving the problem of poor cycle stability of SIBs.However,MXene will agglomerate and self-stack,which will affect the electrochemical performance of the material.In order to avoid this phenomenon,the Graphene conductive skeleton plays a supporting role to prevent the agglomeration of the MXene sheet,thereby achieving the purpose of improving the electrochemical performance of the material.In this work,MXene was prepared by wet chemical method,and Graphene was prepared by chemical oxidation.The GO/MXene film prepared by vacuum-assisted method showed a three-dimensional porous morphology after reduction,and Graphene formed a conductive skeleton to effectively avoid the agglomeration of MXene.After assembling rGO/MXene film into SIBs,it is verified that the energy storage mode of the material is mainly controlled by capacitive behavior.The battery still has a capacitance contribution of up to 71%at a high sweep speed of 10 mV·s-1.As the Graphene content increases,the specific capacity of the battery was also imporoved.When the content of Graphene was 5 Mass%,the battery had a specific capacity of 89 mAh·g-1after 500 cycles at a current density of 20 mA·g-1.In this process,the layer spacing of the material was only increased by 0.84?,showing excellent structural stability.When the current density is increased to 500 mA·g-1,the battery still has a specific capacity of 60 mAh·g-1and exhibits excellent rate performance.Based on the satisfactory performance exhibited by Graphene and MXene,the work then explores the application of two materials to flexible energy storage devices.Two kinds of two-dimensional materials were prepared into rGO/MXene fibers by wet spinning and chemical reduction,and the fibers exhibited good flexibility and tensile properties and the electrical properties of the fibers after reduction were also greatly improved.The rGO/MXene fibers were assembled into a fiber-type SIBs with a specific capacity of up to 118 mAh·g-1and a first week Coulomb efficiency of 62%at a current density of 33 mA·g-1.During the 40 cycles,the battery exhibited an average discharge specific capacity of 105.6 mAh·g-1.The fiber-type battery has the potential to be applied to flexible wearable devices due to its fine electrochemical performance. |
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