Design Of Cobalt Selenide Carbon Composite And Its Application In Lithium-ion Batteries

Lithium-ion batteries are considered as promising electrochemical energy storage devices due to their high mass specific capacity and low relative electrode potential.As the main host material for lithium-ion anode,graphite cannot meet the market demand for high energy/power density energy storage devices due to its low theoretical capacity.At present,transition metal chalcogenides have become an ideal choice for lithium-ion batteries anode materials due to their advantages such as high capacity,low toxicity,and simple synthesis process.However,the characteristics of transition metal chalcogenides,such as low electrical conductivity and volume change during cycling,severely restrict their application in the field of energy storage.In this paper,aiming at the existing defects,a series of cobalt selenide carbon-based composite electrode materials were designed and synthesized,and systematically studies the structure-efficiency relationship between the composition,microstructure and electrochemical properties of the obtained materials by different synthesis methods.The research contents are as follows:1.Using MOF（ZIF-67）as the precursor and mask paper as the substrate,a binder-free self-supporting Co_0.85Se@CP-CMF composite was prepared by a self-assembly,pyrolysis-selenization strategy at room temperature.Co_0.85Se carbon microplates are anchored on the mask fibers to serve as an anode for lithium-ion batteries.The study showed that the material has a three-dimensional conductive network,which accelerates the rapid transfer of electrons and ions The regular and orderly embedding of Co_0.85Se@CP on the surface of carbon fibers can effectively increase the contact between the electrode and the electrolyte,prevent the aggregation and fragmentation of Co_0.85Se@CP,and buffer the volume change during repeated charging and discharging,making the composite material with good rate performance and cycle stability.2.Similarly,MOF（ZIF-67）was used as precursor to construct MOF-derived in situ grown carbon nanotube composites(Co_0.85Se@CNT-CP)using a simple pyrolysis-selenization strategy,and it was used as an anode for lithium-ion batteries.This fluffy 3D hierarchical structure greatly can trigger the efficient interfacial transformation reaction kinetics,which helps to increase the efficient paths for electron and Li⁺entry,reduces the volume change effect during cycling,and simultaneously enhances the surface capacitance contribution.Moreover,the high specific surface area also helps to enhance the capacitance-dominated lithium storage mechanism,showing for ultrafast rate capability.Electrochemical test results show that Co_0.85Se@CNT-CP has good rate capability(449.4 m A h g^-1at 5 A g^-1)and stable cycle stability(701.0 m A h g^-1after 350 cycles at 0.5 A g^-1).3.Extending the urea-assisted and moderate pyrolysis-selenization treatment strategies,the in-situ growth Co_0.85Se@CNTs/C hierarchical structure assembled by carbon nanosheets was constructed,and its electrochemical properties as anode materials for lithium-ion batteries were investigated.The three-dimensional hierarchical structure can fully expose the Co_0.85Se active sites,and the Co_0.85Se is firmly anchored on the carbon nanosheets,while a small amount is also encapsulated in the carbon nanotubes,with strong structural stability.Under the highly conductive paths of one-dimensional（1D）carbon nanotubes,the nanocomposite electrode provides efficient electron/ion transport channels and shorts diffusion paths,and has high pseudocapacitance properties.The self-doping of abundant N atoms provides sufficient active sites for storing lithium ions,and enhances the capacitance-dominated Li-storage mechanism.The construction of carbon architectures with multi-scale structures by assembling different low-dimensional units is an effective means to improve the performance of lithium-ion batteries.Because of the synergistic contribution of each component,the initial capacity is1354.2 m A h g^-1at 0.1A g^-1,and even at 5A g^-1,reaches capacity of 596.6 m A h g^-1.At the same time,after 600 cycles at1A g^-1,the capacity still retains 701.2 m A h g^-1,and the capacity retention rate is 84.5%.