Preparation And Electrochemical Properties Of Two-dimensional Layers Ti₃C₂-based Composites

As a new kind of clean energy storage device,supercapacitor had attracted much attention in the field of new energy.The electrode material was the one of important factors affecting the electrochemical properties.The two-dimensional layered Ti₃C₂ in MXene family had a special two-demensional layered structure and a large surface area,low working voltage and good wettability with electrolyte.The layered structure of Ti₃C₂ was very suitable for the embedding and de-embedding of ions,but the lamination was easy to stack,leading to a great reduction in the transfer efficiency of electrolyte,resulting in its low specific capacity and limiting its electrochemical utilization rate.Based on the above problems,this paper combines Ti₃C₂ with carbon materials,metal oxides and conductive polymers to improve the electrochemical properties of materials.Its structure and phase were characterized and electrochemical properties had been studied.The main conclusions are as follows:?1?With titanium sulfate Ti?SO₄?₂ as Ti source,TiO₂/Ti₃C₂ composites were prepared by hydrothermal method.TiO₂ nanoparticles were evenly distributed on the surface and between layers of Ti₃C₂ and closely integrated with the laminates,preventing the stacking between Ti₃C₂ layers and improving the structural stability,expanding the interval between layers was conducive to improving the specific surface area of the composite,thus improving the charge transfer efficiency and further improving the energy storage efficiency of the composite.The specific capacitance of TiO₂/Ti₃C₂ was 117 F?g^-11 at the scan rate of 5mV?s^-1,and the capacitance retention is 94.8%after 10,000 cycles.?2?TiO₂/Ti₃C₂ composites were prepared by oxidation treatment of Ti₃C₂.The electrochemical performance of TiO₂/Ti₃C₂ under different oxidation time was studied.When the oxidation time was 12h,the scan rate was 5 mV?s^-1,and the maximum specific capacity of TiO₂/Ti₃C₂ composite was 127 F?g^-1.Too long oxidation time or too short oxidation time was not conducive to improving the electrochemical performance of the composite.The preparation process of TiO₂/Ti₃C₂ by in-situ oxidation was simpler and easier to operate than that by adding Ti source,and the in-situ synthesis had the superiority of uniform nucleation and stable interface combination,therefore,TiO₂/Ti₃C₂ prepared by this method has better electrochemical performance.?3?The hierarchical structure carbon microspheres/TiO₂/Ti₃C₂ composites were prepared by hydrothermal method.The glucose were hydrolyzed and attached to TiO₂/Ti₃C₂ sheets for nucleation and growth.The rich oxygen-containing groups on the surface of carbon microspheres improved the hydrophilicity of the composite material,improved the wettability of electrode material and electrolyte,and TiO₂ expanded the layer spacing of the composite material,which was more conducive to the interlayer of negative and cation,and further improved the electrochemical performance of the composite material through mutual coordination between different components.The specific capacity of carbon microspheres/TiO₂/Ti₃C₂ composites was 156 F?g^-11 at scanning rate of 5 mV?s^-1,the cyclic test results also show that the material has good cycling stability.?4?Pyrrole monomer and 2-D layered Ti₃C₂ were used as raw materials to prepare PPy/Ti₃C₂ composites under the condition of ice bath.A large number of dendritic polypyrrole successfully attached to the layer and surface of two-dimensional Ti₃C₂,Ti₃C₂ effectively prevented the dense accumulation in the process of polypyrrole polymerization,and the porous structure promoted the infiltration of electrolyte.The tight interconnection between PPy and Ti₃C₂provided a fast channel for carrier transport,which greatly promoted the formation of pseudocapacitance.Therefore,the PPy/Ti₃C₂ composite material had an enhanced capacity..PPy/Ti₃C₂ composites had a specific capacitance of137 F?g^-11 at the scan rate of 5mV?s^-1.?5?In order to further improve the specific capacitancethe TiO₂/Ti₃C₂composites,this part prepared PPy/TiO₂/Ti₃C₂ and MoO₃/TiO₂/Ti₃C₂ composites through in situ polymerization and hydrothermal method.The loading of TiO₂nanoparticles and polypyrrole increased the specific surface area of the composite,and improved the wettability between electrode materials and electrolyte.TiO₂ nanoparticles could provide channels for ion transfer.PPy is closely combined with the laminates of composite materials,ensuring the good electricalconductivityofPPy/TiO₂/Ti₃C₂.Thespecificcapacityof PPy/TiO₂/Ti₃C₂ was further improved by the cooperation of different components.In the MoO₃/TiO₂/Ti₃C₂ composites,the especially layered structureofMoO₃couldprovideenoughspaceforion intercalation/deintercalation,TiO₂ nanoparticles provide more active sites for ion attractive could further improve the electrochemical performance of the composites.The specific capacity of PPy/TiO₂/Ti₃C₂ and MoO₃/TiO₂/Ti₃C₂composites were 159 F?g^-11 and 168F?g^-11 at a scanning speed of 5mV?s^-1,the capacitance retention were 96%and 93%after 10000 galvanized charge/discharge.The two kinds of materials showed better high-rate performance and cycling stability.Comprehensive comparison showed that the electrochemical performance of the hierarchical structure composites based on TiO₂/Ti₃C₂ were significantly improved compared with the pure Ti₃C₂ and binary composites.The specific capacity of MoO₃/TiO₂/Ti₃C₂ electrode material was better than that of PPy/TiO₂/Ti₃C₂,which has better cycling stability.