Preparation Of Transition Metal Iron And Molybdenum Carbide Materials And Study On Their Electrochemical Energy Storage Behavior

The development of high conversion efficiency,multi-purpose lithium ion energy storage device is crucial.However,the contradiction between the limited reserves in the earths crust and the huge demand hinders future applications on a larger scale.The development of high-performance sodium ion batteries may be one of the solutions to solve the above contradiction for the urgent large-scale energy storage devices in the future.At present,lithium/sodium ion batteries still need to be concerned about energy density and poor conductivity.The research work of this paper mainly improves the ion diffusion ability and electronic conductivity of Fe₃C and Mo₂C as anode materials of lithium/sodium ion batteries,and then significantly improve the electrochemical performance of transition metal carbide as anode materials.The main research work is summarized as follows:?1?Defect-rich carbon encapsulated Fe₃C nanoparticle?Fe₃C@DRC?was obtained via a modified sol-gel method,the defect-rich structure on the surface of carbon can be produced by sintering the gel precursor,to significantly increase more Li⁺active reaction sites and improve the high-rate performance.The Fe₃C@DRC displays a stable capacity of 215 mAh g^-1 at a current density of 1 A g^-1 and an excellent rate capability(128.8 mAh g^-1 even at 10 A g^-1).The Fe₃C@DRC//AC LIC delivers a high energy density of 187.78 Wh kg^-1 at 200 W kg^-1.The above excellent electrochemical performance is mainly attributed to the defect-rich nanostructure provides plenty of ion-accessible reaction sites on the surface and efficiently shortens the diffusion pathway of Li⁺in the bulk materials,which demonstrates the remarkable capacity and high-rate performance in LIBs.?2?Lamellar Mo₂C nanosheet materials assembled by Mo₂C nanoparticles were synthesized from ammonium molybdate and 4-chlor-o-phenediamine by simple hydrolysis and subsequent calcination process.The lamellar Mo₂C nanostructures assembled by Mo₂C nanoparticles provide more ion-accessible sites with an increase in sodium transport kinetics because of interconnected high electron conductivity,which mitigates the volume expansion and maintain the carefully designed electrode structure.The lamellar Mo₂C nanosheet electrode shows a high cycle stability at 0.5 A g^-1 over1200 cycles.After coupling with a commercial activated carbon cathode,Mo₂C//AC SIC demonstrates a high energy and power density of 76.1 Wh kg^-1 at 112 W kg^-1 and an excellent cycle life with 83%of the capacity retained after 4000 cycles.Together with these results,lamellar Mo₂C nanosheet is a very promising sodium ion energy storage material.?3?Mo₂C nanoparticles uniformly anchored into cross-linked hierarchical porous carbon?HPC-Mo₂C?have been produced by a water-soluble NaCl template strategy as sodium storage anode material.The problem of low utilization of active sites and slow ion diffusion in electrode materials was solved.On the other hand,the cross-linked hierarchically porous network also provides efficient channels of the Na⁺to the electrode surface.More importantly,the porous carbon will effectively improve the electrical conductivity.The as-obtained HPC-Mo₂C shows excellent sodium ions storage performance including a large specific capacity(190.6 mAh g^-1 at 1 A g^-1 after2500 cycles)in half cell.Galvanostatic intermittent titration technique and consecutive cyclic voltammetry results illustrate that the Mo₂C nanoparticles uniformly anchored into cross-linked hierarchical porous structure can accelerate fast Na⁺diffusion kinetics for the redox reaction.The SIC composed of HPC-Mo₂C as anode and activated carbon?AC?as cathode delivers an unprecedented cycling stability of 88.9%retention after10000 cycles.,as well as an impressive energy density of 130.2 Wh kg^-1 and ultra-high power density of 30000.0 W kg^-1.This work may provide a new direction for high-performance sodium storage anode materials.