Preparation And Application Of Porous Carbon/Molybdenum Oxide Composites For Lithium Sulfur Batteries

Lithium-sulfur?Li-S?battery has become one of the most potential energy storage systems due to the advantages of high energy density(2600 W h kg^-1),environmental friendliness and abundant sulfur.However,the active material sulfur and intermediate products of Li-S battery have poor conductivity.Besides,the high order intermediate products are easy to dissolve into the electrolyte,referred to as the“shuttle effect”,which leads to low utilization and poor cycling performance.In order to solve these problems,the MoO₂-rGO-S material with three-dimensional?3D?structure,the MoO₂-CMK-3-S material with catalytic effect and the Mo₄O₁₁-AC?active carbon?interlayer were designed and prepared from the perspective of cathode material and the whole battery structure of Li-S battery.Firstly,the MoO₂-rGO-S hybrid with three-dimensional structure was prepared by an in-situ reduction.The MoO₂ particles wih size<10 nm are evenly distributed in the three dimensional rGO matrix.The nano MoO₂ particles can improve the utilization of the active materials in the Li-S battery and prevent the"shuttle effect"of the polysulfide.The MoO₂-rGO-S hybrid electrode showed good conductivity and electrochemical performance.The discharge capacity of the first cycle was 1236 mA h g^-1 at 0.1C,and the Coulombic efficiency remained at 99.6%even after 100 cycles.Secondly,as porous carbon materials have weak adsorption with soluble polysulfide in Li-S battery,MoO₂-CMK-3-S hybrid with catalytic effect was prepared.In this hybrid,mesoporous carbon material CMK-3 can prevent the migration of polysulfide by physical adsorption,provide channels for ion transmission and space for the load of active materials.MoO₂ particles with a size of about 15 nm attached to the surface of CMK-3,can prevent the"shuttle effect"of polysulfide by chemical adsorption with polysulfide,promote the conversion of long chain polysulfide to short chain polysulfide by catalytic effect,and improve the Coulombic efficiency of Li-S battery as a stable supporting active material.After 1000 cycles at 0.5C,the specific capacity of the electrode is still 533 mA h g^-1,and the capacity fade per cycle is only0.04%from the second cycle.Finally,from the view of the overall battery structure,the Mo₄O₁₁-AC?active carbon?interlayer was prepared by a simple method.The microporous active carbon in the interlayer could provide physical adsorption sites and additional electron transport channels for the active material sulfur and polysulfides,and reactivate the captured active material sulfur and polysulfide,then improve the utilization ratio of the active materials in Li-S battery.The Mo₄O₁₁ material can inhibit the"shuttle effect"of the polysulfide by chemical adsorption and imcrease the Coulombic efficiency of Li-S battery.For Li-S battery with Mo₄O₁₁-AC interlayer,the discharge capacity of the first cycle is as high as 1389 mA h g^-1.From the 109^th to 350^th cycle,the capacity fade per circle is only 0.036%.