Preparation And Properties Of Cathode Materials For Lithium-Air Batteries

Lithium-air battery is a new renewable energy storage technology,which has a high theoretical energy density（11400Wh/kg）,which can effectively realize large-capacity,low-cost and high-efficiency energy storage.It is expected to be used in many fields,such as aerospace,military equipment and electric vehicles.However,due to its low actual specific capacity,poor cycle stability and high charge-discharge overpotential,its commercial development is hindered.This thesis mainly aims at the technical problems faced by the development of lithium-air batteries,namely low discharge specific capacity,poor cycle stability and high overpotential,combined with the working principle of lithium-air batteries,and proposes solutions.That is,cathode materials with high specific surface area,microscopic porous channels,many catalytic active sites and excellent conductivity are designed.Therefore,this thesis mainly explores the preparation and electrochemical performance of cathode materials for lithium-air batteries.The research is as follows:（1）Natural Balsa wood was selected as the biomass substrate,a certain amount of thiourea was added,and under the condition of molten salt Ni Cl₂/Na Cl medium,calcined at high temperature to obtain a three-dimensional self-supporting carbon material co-doped with Ni/N/S.Characterization tests such as SEM show that in the environment of molten salt medium,it can promote the formation of a large number of pores in biocarbon materials,which is conducive to the efficient transport of reactants during the discharge reaction,and then improve the discharge specific capacity.XPS and element mapping maps indicate the formation of Ni/N/S doping sites,thereby providing more catalytic active sites and effectively reducing overpotential.The prepared S₂-wd-700°C was applied to the positive electrode of lithium-air battery and electrochemical performance test,and the discharge specific capacity reached 24.07m Ah cm^-2 under the condition of current density of 0.1 m A cm^-2,and it could cycle 108cycles under the limited capacity condition of 0.5 m Ah cm^-2,and S₂-wd-700°C showed excellent ORR/OER activity.（2）The natural Balsa wood was impregnated in Fe Cl₃/Li Cl solution,and after drying,it was mixed with a certain amount of sodium hypophosphite and carbonized at a high temperature of 900°C to prepare Fe3C-modified phosphorus-doped self-supporting carbon materials.Through the test and analysis of characterization technology,it is confirmed that the mixed molten salts Fe Cl₃ and Li Cl melt into nanodroplets at high temperature and penetrate into the carbon skeleton,resulting in etching effect,creating more pores for carbonized wood,thereby increasing the specific surface area of the cathode.At the same time,under the catalytic action of iron,phosphorus is successfully introduced into the carbon backbone,so that the charge density is redistributed,thereby improving the electrocatalytic performance of the cathode material.The prepared P_0.5-wd-MS was directly applied to the electrochemical test of the positive electrode of lithium-air battery,and the discharge specific capacity could reach 37.1 m Ah cm^-2 under the condition of current density of 0.05 m A cm^-2,and it could cycle 172 cycles under the limit condition of 0.5 m Ah cm^-2.It is verified that P_0.5-wd-MS has excellent catalytic performance as a cathode material.Due to the simple preparation process,low material cost and environmental friendliness,a new method is provided for the design of the cathode of lithium-air batteries.