Research Of Doped Carbon Materials To Suppress The Shuttling Effect In Lithium-Sulfur Battery

Lithium sulfur battery is one of the most promising new-generation energy storage systems.However,the shuttling effect of sulfur cathode and the growth of lithium dendrites hinder the commercial application of lithium sulfur batteries.Therefore,in view of the shuttling effect in lithium sulfur batteries,this paper prepared B,N codped graphene(BNG),Co,N co-doped hollow polyhedron embedded in three-dimensional conductive carbon fiber(HPTCF),and nanocrystalline niobium carbide(NbC)coated separator,which could inhibit the shuttling effect by forming strong chemical interaction with lithium polysulfides and improve the utilization rate of the active materials and cycling stability.In addition,the doped carbon materials can also induce uniform nucleation of lithium,thereby suppressing the growth of lithium dendrites and improving the safety of the battery.To this end,this paper mainly carried out the following three research works:1)The investigation of the non-metal doped carbon material in sulfur cathode.After introducing a polar group into the non-polar carbon-based materials,an interaction with lithium polysulfides is formed to suppress the shuttling effect and corresponding improved cycle stability is obtained.Based on this,the prepared B,N co-doped graphene(BNG)supported material was successfully synthesized.The BNG material with high content of B and N elements and good dispersibility,is rich in pyridine nitrogen and N-B/N=B bonds.After combining with sulfur to forming BNG@S cathode,the following assembled lithium-sulfur half-cell exhibits excellent electrochemical performance.After combining with the pre-lithiated nano-Ge anode to assembling Ge-S full cell,the energy density is as high as 350 Wh kg-1 based on the whole mass of the entire positive and negative electrodes.2)The research of the metal/non-metal groups co-doped carbon material in both sulfur cathode and lithium anode.Based on the non-metal doped carbon material,high conductivity metal was further introduced.And Co,N co-doped hollow polyhedron embedded in three-dimensional conductive carbon fiber(HPTCF)was developed.Thanks to its rich active interface,HPTCF can simultaneously inhibit the shuttling effect of the sulfur electrode and the dendrite problem of the lithium anode,thereby achieving excellent electrochemical performance in both the sulfur cathode and lithium anode.Moreover,the lithium sulfur full cell using HPTCF in both cathode and anode was assembled.When the sulfur loading is 4.0 mg cm-2 and the lithium excess is about 50%,the energy density can reach 836 Wh kg-1 based on the whole mass of the cathode and anode.3)The study of high conductivity and polar metallic carbide in the coating layer of the separator.Besides carbon materials,a lot of metallic carbides are high conductivity and polarity.Based on this,nanocrystalline niobium carbide(NbC)was developed by feasible high-pressure technology,and was first time used as an interlayer material for lithium sulfur batteries.Combining the advantages of the strong ability to anchor lithium polysulfides and high conductivity to transport electrons,NbC coated separator effectively inhibits the shuttling effect of lithium polysulfides and facilitates faster sulfur electrochemical reaction,thus achieving excellent cycle stability.The capacity decay rate is only 0.037%per cycle after 1500 cycles at the rate of 2 C.In addition,the coated separator was used to assemble a soft packaged lithium sulfur battery with an initial capacity of 1125 mAh g-1 and a stable cycling more than 95 cycles at 0.2 C.