Synthesis Of ZIF-67 Derivatives And Their Effects On Catalytic Performance Of Lithium-Oxygen Batteries

In recent years,with the rapid development of electric vehicles,artificial intelligence and electronic equipment,the demand for battery energy gets more and more urgent.Therefore,it is imperative to research and develop energy new storage systems with high specific energy density.Lithium-air batteries have attracted much attention due to their high specific energy density.However,the industrial development of lithium-air batteries still faces many problems,such as low rate capability,high polarization and low cycle life.As the main sites of ORR/OER and the mian transport channels for Li⁺,O₂ as well as e^-,the composition and structure of air electrodes have a profound impact on the morphology and deposition site of discharge products,thus further affect the electrochemical performance of batteries.Therefore,the well design and synthesis of carbon-based catalysts with specific morphology and composition is still one of the main methods to improve the performance of lithium-air batteries.In this paper,we took ZIF-67 as the precursor and prepared the active materials with special morphology and specific components through nitridation and sulfuration,respectively.The main contents include:1.ZIF-67 is formed in situ on the surface of graphene oxide by electrostatic attraction.The reduction of graphene oxide and the pyrolysis of ZIF-67 are simultaneously completed in the subsequent carbonization process,and Co-N-rGO with special morphology is obtained.The material serves as an electrode material for lithium-oxygen battery.It was found that prolonging the carbonization time can cause the ZIF-67 carbon skeleton to collapse to the plane of rGO.Electrochemical tests show that it has excellent ORR and OER catalytic activity,the discharge platform is about 2.75 V,and the charging platform is about 4.2 V.The carbonation time was studied to affect the morphology of the catalyst,which further affected the deposition and morphology of the discharge products.As the carbonization time increased,the active sites gradually increased,and the catalytic mechanism also changed from surface-mediated to solution-mediated.Effective control of the generation mechanism of discharge products.When the carbonization time was prolonged to 7hours,the battery exhibited the highest discharge specific capacity(3304 mAh g^-1)and best cycle performance.2.ZIF-67 was grown on CNTs by the same method above to form a network structure with ZIF-67 as knots.CoS₂/CNTs was achieved by subsequent sulfuration reaction,which was used for the preparation of air electrodes.CNTs through the ZIF-67 derivative skeleton serve good transport channels for electron,thus the battery exhibits good electrochemical performance.A discharge specific capacity of 2569 mAh g^-1 was obtained at a current density of 0.05 mA cm^-2.The catalyst can effectively decompose the discharge product Li2O2 during the charging process,and can decompose by-products such as lithium acetate and lithium formate.When controlling the discharge depth to 500 mAh g^-1,it can be cycled for 52 cycles,with the cutoff voltage keeping above 2.0 V.