Synthesis And Performance Of A New Cathode Material For Lithium Air Batteries

After decades of research,great progress has been made in the research of lithium-air batteries,but there are still some problems that are difficult to overcome,which have become a stumbling block in the development of lithium-air batteries.Among them,poor performance of air cathode and low catalytic activity of ORR and OER lead to low energy conversion rate,poor cycle performance and serious life degradation of battery.It was found that the design of a porous cathode can effectively improve the specific surface area and increase the active sites of the catalytic reaction.On this basis,the introduction of electrocatalysts into the porous cathode can further improve the catalytic activity of the electrode and greatly improve the performance of the battery.Carbon-based materials are widely used in lithium air batteries due to their unique physical and chemical properties.Natural biopolymer is widely found on the earth surface.It is an ideal precursor for the synthesis of carbon-based materials because of its low price and high yield.Alginate,as a common natural polymer,can be chelated with various metal ions to form alginate gel.Groups containing oxygen are decomposed into carbon dioxide and water during the process of high temperature carbonization,resulting in microporous structure,and then metal/carbon composite porous materials containing metal nanostructures are formed.In this paper,an amorphous porous carbon supporting transition metal cathode catalyst material for lithium air batteries will be synthesized by a new method.The structure and composition of the cathode catalyst material will be analyzed in detail.On this basis,the electrochemical performance of the cathode catalyst will be further studied.The work of this paper includes three section.Section one:The background of lithium air batteries is briefly reviewed.The development history and classification of lithium air batteries are introduced.The structure and working principle of non-aqueous lithium air batteries are introduced in detail.The optimization of lithium air batteries is elaborated in three directions,including optimizing air cathode,protecting metal lithium anode and improving electrolyte.Section two:The preparation of nickel nanoparticles/amorphous carbon porous composites was introduced in detail.In the process of preparing alginate gel,surfactant?CTAB?was used as micelle template to change the pore structure of the material.nickel nanoparticles/amorphous carbon porous composites were prepared by carbonization at different temperatures.The change of carbonization temperature and the introduction of micelle template have different effects on the morphology,structure,composition and electrochemical properties of the materials.The structure tests showed that the samples without micelle template carbonized at 600 centigrade had high specific surface area(185 m²g^-1)and multi-stage pore?including microporous,mesoporous and macropore?.Component analysis showed that the sample had good conductivity.As a cathode material for lithium air batteries,the electrochemical performance tests showed that the sample exhibited good OER catalytic activity?charging equilibrium voltage 4.2 V?,better energy conversion rate?62%?,higher discharge specific capacity(1950 mAhg^-1)and better rate performance.Section three:The gel of manganese alginate was prepared by ion exchange,and micelle template was used to change the pore structure of the material.Manganese oxide nanoparticles/amorphous carbon porous composites were prepared by drying and carbonization.As cathode catalyst of lithium air battery,impedance test showed that the sample had good impedance performance.It was found that the impedance performance was related to carbonization temperature.The higher the temperature,the greater the graphitization degree,and the smaller the impedance.Constant current of charge-discharge tests showed that the sample exhibited better OER catalytic activity?charge equilibrium voltage was 4.15 V?,better energy conversion?62.7%?and higher specific discharge capacity(2500 mAhg^-1).