Manufacture Of Lithium Sulfur Battery Based On Biomass Carbon Materials

Lithium-sulfur batteries have attracted widespread attention due to their high theoretical energy density and low cost.However,for sulfur cathode,the low conductivity of active sulfur,volume expansion during cycling,the dissolution and shuttle effect of polysulfides hinder the commercial applications of lithium-sulfur batteries.As the conductive matrix of the positive electrode of lithium-sulfur battery,biomass carbon materials have huge specific surface area and abundant pore structure,which provide sufficient space for the loading and deposition of activel sulfur.Renewable biomass carbon materials provide a simple and feasible strategy for preparing carbonaceous materials,which have good mechanical properties and electrons transfer capacity.The method has the characteristics of low cost,high efficiency and environmental protection.In view of the superiorities of sustainable biomass sources,the biomass carbon materials are designed as hosts for active sulfur,which opens a new direction for the realization of high energy density lithium-sulfur batteries.In this dissertation,low-cost biomass materials are subjected to simple heat treatment to obtain heteroatom-doped porous carbon materials,which are used as the host of active sulfur in lithium-sulfur batteries.The morphology,composition and electrochemical properties are studied.1.Using the seed hairs of metaplexis japonica as the precursor,one-dimensional nitrogen-doped carbon hollow microfibers（NCHM）are obtained after a simple heat treatment and used as sulfur host.NCHM have unique hollow structure and a large specific surface area up to 474.21 m² g^-1,which are conducive to the infiltration of the electrolyte and can provide sufficient space for the active materials to achieve high sulfur loading.The continuity of NCHM accelerates the electron transfer and ion diffusion rate,so that the battery has good performance.The doping of nitrogen atoms provides sufficient anchoring sites and enhances the cycle stability of the battery.The NCHM/S cathode has a first discharge specific capacity of 1120 mAh g^-1 at 0.2 C,a reversible capacity of 715 mAh g^-1after 200 cycles and a capacity retention rate of 63.8%.2.Sunflower pith as a precursor is first activated with KOH and then calcined in an ammonia atmosphere to obtain a three-dimensional porous carbon material co-doped with nitrogen and sulfur,which is applied as host for sulfur in lithium-sulfur battery.The doping of nitrogen and sulfur atoms provides more anchoring sites for the adsorption of polysulfides and effectively inhibits the shuttle effect of lithium polysulfides.The three-dimensional porous carbon framework can not only increase the loading of active materials and increase the wettability of the electrolyte,but also shorten the transmission path of electrons and ions.Batteries assembled with this material have lower overpotential and faster reaction kinetics.The initial discharge specific capacity is 1082 mAh g^-1 at 0.1C.After 300 cycles,the discharge specific capacity is 650 mAh g^-1 and the average decay rate per cycle is 0.12%.The battery has good rate performance.3.A one-dimensional porous carbon material tri-doped with nitrogen,phosphorus and sulfur is obtained through simple heat treatment of seed hairs of Conyzabonariensis（L.）Cronq.as the precursor.The one-dimensional continuous carbon framework is beneficial to promote the electron transfer rate and the large specific surface area is favorable for the loading of active sulfur.The porous structure physically limits the diffusion of polysulfides and the doping of heteroatoms facilitates chemical adsorption of polysulfides to slow down the shuttle effect,thereby providing lithium-sulfur batteries with excellent cycle stability.The battery with this material as the cathode has a discharge capacity of 645 mAh g^-1 and a capacity retention rate of 65%after being cycled for 100 cycles at 0.05 C.