Study Of Sulfur-containing Composites Based On The Catalytic Effects Of LiFePO₄ And VO₂ With High Redox Potential

Due to the high energy density,low cost and environmental friendliness,lithium-sulfur battery is considered to be one of the most research value and application prospects in the future.However,the poor conductivity,large volume change and"shuttle effect"of the sulfur cathodes seriously hinder the commercial application of the lithium-sulfur battery.In this study,based on the catalytic effect of LFP and VO₂ with high oxidation-reduction potential,sulfur-carrying holey graphene/lithium iron phosphate/sulfur?HG/LFP/S?and holey graphene/vanadium dioxide/sulfur?HG/VO₂/S?composites were prepared and constructed.And the physical properties of each composite were characterized by Scanning electron microscope?SEM?,X-ray diffraction?XRD?,etc.The electrochemical properties of the materials were tested by constant current charge-discharge test,etc.The energy storage mechanism of materials was studied though lithium sulfide deposition experiments,polysulfide adsorption experiments,symmetric battery tests and shuttle current tests,combined with theoretical calculations.This study is helpful for understanding the mechanism of polysulfide catalytic conversion and has certain reference significance for the design of sulfur-loaded composite materials in the future.Through an electrostatic attraction method coupled with high temperature treatment,HG/LFP sulfur-carrying matrix were prepared.After the sulfur impregnation and heat treatment process,the HG/LFP/S composite with a yolk-shell structure were obtained.The HG component could effectively suppress the agglomeration phenomenon of LFP microspheres,and thus,enhancing the contact area between LFP and LiPSs.On the other hand,the HG component could physically adsorb LiPSs to some extent inhibit the shuttle effect.In addition,the porous HG component also facilitates mass transport during cycling and guarantees good electronic conductivity of the sulfur positive electrode.The LFP microspheres with strong chemical polarity and high oxidation-reduction potential not only play a chemical adsorption role on polysulfides,but also accelerate the conversion process between soluble polysulfides and short-chain Li₂S₂/Li₂S,which effectively inhibiting the"shuttle effect"during charging and discharging.The as-prepared HG/LFP/S electrode has an initial specific capacity of 1615 mAh g^-1 at 0.1 C,a reversible specific capacity of 798 mAh g^-1 at a high rate of 5.0 C,1089 mAh g^-1after 200cycles at 0.2 C.and 831 mAh g^-1 after 500 cycles at 1.0 C.Employing hydrothermal in-situ assembly and heat treatment prepared HG/VO₂sulfur-carrying matrix,which has a unique three-dimensional aerogel structure.The VO₂component with strong chemical polarity and high electrochemical redox potential not only play the key roles for chemically adsorption of soluble polysulfide intermediates,but also accelerates the conversion process between soluble polysulfides and short-chain Li₂S₂/Li₂S,which could effectively suppress the"shuttle effect"during charge and discharge process.On the other hand,the three-dimensional interconnected graphene network structure can also physically adsorb polysulfide and ensure good electronic conductivity of the composite,thereby improving the electrochemical kinetics of the reaction.After sulfur impregnation and heat treatment,the HG/VO₂/S composite has an initial specific capacity of 1644 mAh g^-1 at 0.1 C,a reversible specific capacity of 804mAh g^-1 at a high rate of 5.0 C,994 mAh g^-1after 300 cycles at 0.2 C.and 863 mAh g^-1after 500 cycles at 1.0 C.