Metal-organic Framework Materials As Cathode Catalysts For Lithium-oxide Batteries And Their Electrochemical Performance Analysis

In recent years,environmental pollution and the energy crisis have intensified,making humans pay more and more attention to the research and development of green energy.The replacement of traditional fuel vehicles with electric vehicles using green energy can greatly reduce environmental pollution and alleviate the energy crisis.However,the current conventional power systems,such as lead-acid batteries,nickel-metal hydride batteries,and lithium-ion batteries,are difficult to support the long-distance driving of electric vehicles.Therefore,lithium-oxygen batteries with higher theoretical specific energy are considered to be suitable for the power system of the new generation of electric vehicles.However,it was found that lithium-oxygen batteries still have many problems that hinder their commercialization in the research.For example,in the non-aqueous electrolyte system,discharge products accumulate in the air electrode and block the oxygen diffusion channel.The discharge products of the bonds cause low battery cycle efficiency and the like.Therefore,finding effective oxygen reduction（ORR）and oxygen precipitation（OER）catalysts to accelerate the electrochemical reaction kinetics and promote the stability of the air electrode has very important practical significance for the practical application of lithium-oxide batteries.In this paper,manganese-based metal organic framework materials（Mn-MOFs）,Cobalt-based metal organic framework materials（Co-MOFs）,Manganese-cobalt composite-based metal-organic framework materials（Mn/Co-MOFs）and manganese-nickel composite-based metal-organic framework materials（Mn/Ni-MOFs）were prepared by solvothermal method.Analyzing the influence of the above materials as catalysts on the electrochemical performance of lithium-oxygen batteries.Manganese-based metal organic framework materials（Mn-MOFs）,Select three kinds of ligands:manganese acetate and terephthalic acid（the molar ratio was 1.2:1,1.3:1,1.5:1）.Prepared at 80°C and used as a catalyst for air electrode of lithium-oxygen batteries.The results show that Mn-MOFs with a molar ratio of 1.3:1 have higher crystallinity and orientation,and show obvious cluster structure;The lithium-oxygen battery assembled with this molar ratio Mn-MOF has very good cycle performance,After 35charge-discharge cycles,the discharge capacity remains at 500 mAh·g^-1.Cobalt-based metal organic framework materials（Co-MOFs）,Select two kinds of ligands:cobalt acetate and terephthalic acid（the molar ratio was 1:1,1.1:1,1.3:1,2:1）.Prepared at 80°C and used as a catalyst for air electrode of lithium-oxygen batteries.The results show that Co-MOFs with a molar ratio of 1.3:1 have a better crystal structure and molecular orientation and exhibit a leaf-like structure.The lithium-oxygen batteries assembled with this molar ratio Co-MOFs can reach 6000 mAh·g^-1’s high specific capacitance and low capacity attenuation under high rate discharge.（capacity attenuation is less than 50%when the current density is increased by 10 times）.Manganese-cobalt-based metal-organic framework materials（Mn/Co-MOFs）,first select Co-MOFs with a molar ratio of 1.3:1,and add Mn-MOFs with a prepared molar ratio of 1.3:1 to it,the ratio of manganese to cobalt is 1:1,1.2:1,1.5:1,1.7:1,2:1.Prepared at 80°C by the solvothermal method which is used as a lithium-oxygen battery air electrode catalyst.The results show that Mn/Co-MOFs with a manganese-cobalt ratio of 1.5:1 have good crystal structure and surface morphology.Mn and Co in Mn/Co-MOFs at this ratio show excellent synergy,and the assembled lithium-oxygen battery not only has a lower capacity attenuation under a large rate current density（Capacity attenuation is less than 50%when current density is increased by 10times）,but the cycle performance has also been significantly improved（the number of cycles at high rate current density is more than five times the number of cycles at low rate current density）.Manganese-nickel composite metal-organic framework materials（Mn/Ni-MOFs）,Select three kinds of ligands:manganese acetate,nickel acetate and terephthalic acid.Under the condition that the molar ratio of the cobalt metal ligand to the acid ligand is 1.3:1,adding 0.001 mol of the nickel metal ligand.prepared at 80°C by a solvothermal method as a lithium-oxygen battery air electrode catalyst.The results of electrochemical tests on lithium-oxygen batteries assembled using this catalyst show that although the discharge capacity is higher than Mn-MOFs at large rate current density,the cycle performance is inferior to Mn-MOFs.