Preparation And Performance Study Of Iron Phthalocyanine/carbon Nanocomposites Based On Lithium-Sulfur Battery Cathodes

The rapid development of electronic devices and new energy vehicles has led to a surge in demand for energy storage devices.Traditional lithium-ion batteries,with their limited energy density,can no longer meet this demand.As a result,lithium-sulfur(Li-S)batteries have gained significant attention due to their high energy density,cost-effectiveness,and eco-friendliness.Nonetheless,the electrical conductivity of sulfur(S)and its discharge product,lithium sulfide(Li2S),is very low,resulting in a sluggish reaction kinetics.Moreover,the reaction involves a large volume change of up to 79%,which can damage the electrode structure.The "shuttle effect" is caused by the high solubility of the intermediate product,lithium polysulfides(LiPSs),in the electrolyte.This subsequently results in an irreversible loss of capacity and corrosion and dendrite of lithium anode.Researchers have been exploring the use of highly efficient catalytic materials for cathodes and separator in order to solve these problems.Transition metal phthalocyanine complexes(MPc)have been shown to possess strong adsorption properties with respect to LiPSs and promote their conversion,while their nanoscale structural design can effectively enhance their surface activity.Additionally,the conjugation effect of MPc substituted by electron-absorbing groups is significantly amplified.However,agglomeration and low intrinsic conductivity remain as issues during long-term charging and discharging.Therefore,a common solution strategy has been to compound MPc with a high specific surface area,high conductivity carbon substrate material and employ it as a host material for S.This alleviates the low electrical conductivity and bulk effect of S,while also inhibiting the agglomeration of the catalytic material and enhancing the electron exchange efficiency between the catalytic material and LiPSs.This thesis is aimed at constructing iron hexadecafluorophthalocyanine(FePcF16)composite with carbon nanomaterials for improving the electrochemical performance of Li-S batteries by designing the compounding method and optimizing the compounding process.The main content is as follows:(1)Employing carboxylated multi-walled carbon nanotubes(F-MWCNTs)as the substrate material,FePcF16 nanoparticles were nucleated and their active sites fully exposed,while the carbon nanotubes served as a conductive network framework to facilitate intermolecular charge exchange.The Li2S generation potential of the FePcF16/F-MWCNTs positive electrode was 2.083 V with increase of 0.05 V,thus catalyzing rapid Li2S nucleation.The Li2S activation potential was observed to be 2.298 V with decrease of 0.06 V compared to F-MWCNTs,significantly reducing the Li2S decomposition potential.The high specific capacity of 784 mAh g-1 was achieved after 500 full cycles of charging and discharging at a current density of 1 C.(2)Using apple pomace as a biomass carbon source,the effects of alkali etching and oxidation processes on the carbon skeleton morphology were studied to obtain high-quality hard carbon substrates.Solid-phase synthesis of the FePcF16/OAPC composites in situ as a Li-S battery cathode host material was conducted,and its electrochemical performance was then evaluated.After 500 cycles,the FePcF16/OAPC composite cathode,with a current density of 2 C,the FePcF]6/OAPC composite cathode displayed a capacity of 698 mAh g-1 after 500 cycles,with a capacity retention of 71.8%.When tested at a higher current density of 3 C,the initial discharge capacity was 920 mAh g-1 and remained above 682 mAh g-1 after 500 charge/discharge cycles,with a capacity decay rate of 0.052%per cycle.(3)The FePcF16/GO nanocomposite was synthesized by preform method and solid-phase method.Graphene oxide,exfoliated,not only yielded a greater quantity of nucleation sites for FePcF 16,but also augmented the charge transfer between the molecules.The FePcF16/GO composite’s enhanced onset potential of 2.47 V in the transformation of S monomers to LiPSs demonstrates its considerable influence on the solid-liquid conversion between S monomers and LiPSs,as well as a heightened catalytic effect on the conversion of Li2S2 to Li2S in the solid state.