Preparation And Properties Of Porous Carbon/metal Nanoparticle Hybrid Materials

In recent years,lithium-sulfur battery has received extensive attention from researchers because of their low cost,rich sulfur resources,environmental friendliness,and high energy density(2600 Wh kg-1).They are considered to be the most promising next-generation rechargeable battery.However,there are still a series of problems in the commercial application of lithium-sulfur battery,such as low electronic and ionic conductivity of the sulfur,the "shuttle effect" of poly sulfides,and large volume change during charging and discharging.Among these problems,the "shuttle effect" of polysulfides is the most critical obstacle to be solved.The key to developing a high-performance lithium-sulfur battery is to build an effective sulfur-loaded matrix to suppress the "shuttle effect" of polysulfides,and then form a composite sulfur cathode with excellent performance.This thesis focuses on the composite design of the sulfur-loaded matrix of the cathode material of lithium-sulfur batteries.With the goal of achieving excellent cycle stability and excellent rate performance of lithium-sulfur batteries,a simple and effective synthesis method is used to design the sulfur-loaded matrix to achieve excellent electrochemical performance.The main research contents are concluded as follow:(1)The PP nonwoven fabric is used as the matrix,and the technology of UV-induced graft polymerization is used to graft the PAA gel network to the surface,and then immersed in an aqueous solution of cobalt acetate tetrahydrate,adjusted to neutrality and water treatment.Finally,carry out high temperature carbonization after drying treatment,the carbon hollow carbon fiber/cobalt nanoparticles hybrid material was obtained.In the process of PP carbonization at high temperature,PP non-woven fabrics act as a sacrificial template,which causes the PAA hydrogels network grafted on the surface of PP fibers to form a hollow structure after carbonization,and Co2+is reduced to Co nanoparticles due to the carbothermal reduction reaction.By controlling the time of light time and the content of cross-linking agent,the grafting status of the PP nonwoven fabric surface can be effectively controlled,such as the porous structure of the surface,the thickness of the hydrogels layer,the loading of metal cobalt ions,etc.And then change the porous structure of the prepared hollow carbon fiber,the loading of metal cobalt nanoparticles,etc.The porous structure of the prepared hollow carbon fiber will provide more active sites for Co nanoparticles,thereby improving the active utilization rate of Co.(2)A preparation method of nitrogen-doped carbon foams which contain hierarchically porous structure and are decorated with zinc nanodots(Zn@NCFs)is proposed.This method uses acrylamide as monomer,ammonium persulfate as initiator,ZnCl2 as activator and the precursor of zinc nanodots is prepared by thermally initiated polymerization of PAM hydrogel containing ZnCl2,which is obtained by freeze-drying and high-temperature carbonization.The obtained Zn@NCFs integrate graded pore structure of micropores,mesopores,macropores on the carbon foams conductive network and have a specific surface area of up to 242.9m2g-1.These carbon foams,which serve as hosts for sulfur in lithium battery,can provide a conducting network and shorter diffusion length for Li-ions.Specially,the zinc nanodots derived from the carbothermal reaction of ZnCl2 at high temperature can interact with sulfur/polysulfides by strong chemisorption.In addition,the zinc nanodots can also facilitate the conversion reaction between Li2SX(2<x<8)and Li2S/Li2S2.Therefore,Zn@NCFs/S cathode presents high sulfur utility and large capacity.