Preparation Of V₂O₅,Sulfur And Bio-Porous Carbon Composite Materials For High-performance Lithium Storage Batteries

The energy density of current commercial lithium-ion batteries has reached a bottleneck,and it is difficult to achieve breakthrough improvements.Therefore,in order to solve this problem,it is necessary to explore and develop new electrode materials with higher energy density,and through the rational design of the material and the overall electrode,to obtain high energy density and cycle performance stability under high rate charge and discharge conditions Lithium ion battery.Vanadium pentoxide and sulfur cathode materials are important ways to develop new lithium ion batteries with high energy density and stable electrochemical performance because of their advantages such as high specific capacity,low cost,and environmental friendliness.This thesis takes vanadium pentoxide and sulfur active materials as the research object.Through compounding them with bioporous carbon,it effectively solves the problems of poor conductivity of the active material,rapid decline in rate performance,and low utilization rate of the active material.The main research contents are as follows:1.By high temperature carbonization and hydrothermal method,a large scale carambola-like V₂O₅nanoflowers array were grown on the inner surface of reed carbon with periodic micropores.V₂O₅is evenly distributed on the surface of porous reed carbon,and each V₂O₅nanoflower is tightly bound to the carbon surface.The unique composite structure can not only improve the electronic conductivity of the entire electrode,but also prevent the V₂O₅nano-flowers from agglomerating during cycling.The composite material of V₂O₅nano-flower arrays and periodic microporous reed carbon stabilized at 273 mAhg^-1after 100 cycles of 0.2 C.And after cycling 500 cycles at a high current of 2.0 C,the capacity can still be maintained at 180 mAhg^-1,showing good cycle stability and rate performance.2.In order to solve the low conductivity of sulfur active materials in Li-S batteries,the high solubility of lithium polysulfide,and the resulting shuttle effect,highly conductive carbon nanotubes and vanadium-based precursors were added to the lotus root powder.After high-temperature carbonization treatment,the composite structure of porous lotus powder carbon coated with carbon nanotubes@vanadium pentoxide nanoparticles was successfully prepared.In this structure,the chemical adsorption of N-doped porous carbon and the chemical catalysis of V₂O₅nanoparticles are fully utilized to improve the cycle stability and rate performance of Li-S batteries.Using V₂O₅@MWCNTs/PSC-S as the positive electrode of lithium-sulfur battery,after 200 cycles of high current charge and discharge at 4.0 C,the reversible capacity of 869 mAhg^-1was maintained,and the capacity retention rate was stable at 86%.Even at 4.0 C current,the battery can still provide a capacity of784.5 mAhg^-1after 500 cycles.3.The surface of the traditional separator was coated with I and N co-doped graded mesoporous kelp porous carbon to modify the separator.Kelp porous carbon materials have micropore and mesoporous structure,and can have physical adsorption effect on lithium polysulfide dissolved in organic electrolyte.At the same time,the low electrochemically active sites caused by the co-doping of I and N elements in kelp carbon have a strong chemisorption effect on polysulfide lithium.The synergistic effect of physical and chemical adsorption is conducive to improving the utilization rate of sulfur active materials and improving the electrochemical performance stability of Li-S batteries.The experimental results show that the Li-S battery prepared by us had a sulfur load of up to 80%.When the sulfur load mass per unit area was 2.0 mg cm^-2,the specific capacity was stable at 760 mAhg^-1after 200 cycles at 0.5 C current.Moreover,after 500 cycles,it still had a high specific capacity of 498mAhg^-1,which is equivalent to a slight attenuation of 0.07%per cycle.