Research On Preparation And Modification Of Biomass Carbon Materials And The Electrochemical Properties Of Them

As society has progressed,the utilization of fossil fuels and their detrimental effects on the environment have prompted individuals to increasingly prioritize alternative energy sources and delve into extensive research Commercial lithium-ion batteries exhibit flaws such as limited energy density and inadequate cycling capabilities.,while lithium sulfur batteries(Li-S)is a new type of energy storage element with great development prospects and it has great advantages in theoretical capacity and energy density.But there are also certain problems faced in the research of lithium-sulfur batteries.Although the sulfur element as its cathode material is rich in nature and low in price,its own conductivity is poor.In addition,the lithium sulfur battery will produce a series of problems The positive active substance of the battery is the elemental sulfur,which has the disadvantage of poor conductivity.In the process of redox reaction inside the battery,polysulfide will dissolve and diffuse in the electrolyte,which is the so-called "shuttle effect".Porous carbon materials have ultra-high specific surface area and rich pore diameter,can be loaded with more active substances,and have a certain binding effect on by-products,effectively alleviate the "shuttle effect" and volume strain in the battery reaction process to improve the cycling performance and capacity of the battery.In this thesis,inexpensive and readily available biomass waste is chosen as the carbon source,and activated carbon material with multiple pores is obtained through high-temperature activation treatment,which has higher economic benefits and alleviates the environmental pollution caused by biomass waste to a certain extent.Waste utilization is in line with the concept of green development.The main work contents are as follows:(1)The rice husk was selected as the carbon source to prepare the non activated biomass carbon material(N-RBC(Not activated rice husk based biomass carbon))and the surface active carbon material(O-RBC(Once activated rice husk based biomass carbon))using KOH as the activator by two-step carbonization method.The surface active carbon material(O-RBC)using KOH as the activator has high specific surface area and rich pores.The melting method was used to cover sulfur on two kinds of biomass carbon materials.The electrochemical properties of composite materials S/N-RBC and S/O-RBC were tested.The test results show that O-RBC has higher capacity and cycle performance.(2)The surface active carbon prepared by two-step carbonization method with rice husk as carbon source and KOH as activator was doped with Fe and Co respectively to prepare composite materials Fe-O-RBC as well as Co-O-RBC,The electrochemical performance of the composite materials obtained from the sulfur coating operation of the two composite materials as the cathode of the lithium sulfur battery was tested.The conclusion explain that the O-RBC doped with Fe and Co has higher capacity and cycling performance than the undoped surface active carbon.(3)Cobalt and iron salts were added into the surface activated carbon prepared by two-step carbonization method with rice husk as carbon source and KOH as activator,and the composite containing cobalt iron alloy and O-RBC was prepared by high temperature nitrogen annealing CoFe-O-RBC,S is obtained after sulfur coating/ CoFeO-RBC The composite material is used as the cathode material of lithium sulfur battery for the electrochemical performance test,cycle,magnification,impedance,polarization and other tests.S/ CoFe-O-RBC.Compared with single Co doping or Fe doping,it has better initial capacity and cycling performance.