Preparation And Performance Of Transition Metal Compound/N-CNTA In Lithium-Air Battery

The rechargeable lithium-air battery has attracted people’s wide attention due to its high theoretical energy density(11400 Wh·kg^-1,excluding the mass of oxygen in the air),high theoretical specific capacity(3828 m Ah·g^-1,relative to the metal lithium anode)and environmental benign.Unfortunately,there is a long way away from being truly commercialized because of its terrible cycle performance.Due to the positive electrode material of lithium-air battery plays a crucial role in the complex gas-liquid-solid three-phase reaction,it is particularly important to develop efficient air electrode materials.Carbon nanotubes（CNTs）are widely used in many energy storage systems,because of their excellent electronic conductivity and easy modification.In the field of lithium-air batteries,the modification of CNTs with N atom doping can improve oxygen adsorption.Nitrogen-doped carbon nanotube array（N-CNTA）has unique pore structure and excellent oxygen reduction reaction（ORR）catalytic activity,which can provide sufficient reaction space and oxygen conversion rate for lithium air batteries.However,the current composite ability of N-CNTA and catalyst materials is weak.It has low catalytic activity for oxygen evolution reaction（OER）of lithium air batteries,which limits cycle life of lithium-air batteries.In this paper,chemical vapor deposition is used to grow N-CNTA on the side of conductive carbon paper.By oxidizing it and then chemically hybridizing Co₃O₄ and MoS₂ nanoparticles with different proportions.And test the electrochemical performance of the two in lithium air battery.The main content of this paper:（1）N-CNTA is oxidized and functionalized by high-temperature heat treatment.Scanning electron microscope,X-ray photoelectron spectroscopy,etc.were used to characterize the morphology and structure of the material,and combined with electrochemical performance test of three-electrode system and battery.The results show:the surface of N-CNTA oxidized at 420℃formed defects and introduced oxygen-containing functional groups to make it have excellent ORR catalytic activity.Lithium-air battery can be circulated 25 times under the condition of limited capacity of 500 m Ah·g^-1.However,the catalytic activity of OER is low,which is manifested as a high charging voltage and poor cycle stability.（2）Co₃O₄/N-CNTA with different carbon-cobalt ratios was prepared by reflow method based on the oxidation of N-CNTA.We combined with physical characterization and battery electrochemical performance test.The results show:when C:Co=20:1,the lithium-air battery exhibits a better charging and discharging platform（discharge voltage 2.75 V,charge voltage 3.28 V）and cycle performance,under the premise of limiting the capacity to 500 m Ah·g^-1,it can maintain 40 cycles without attenuation,which effectively reduces its reaction overpotential and improves the cycle performance of lithium-air batteries.（3）MoS₂/N-CNTA with different carbon-molybdenum ratio was prepared by one-step solvothermal and subsequent calcination methods.We combined with physical characterization and battery electrochemical performance test.The results show:hybridization of MoS₂ nanoparticles in the form of chemical bonds on the surface of N-CNTA.It improves the stability of the air electrode material and optimizes the ORR/OER catalytic activity to promote the decomposition of the discharge product Li₂O₂ and reduce its accumulation on the surface of the positive electrode.And when C:Mo=30:1,ORR/OER has the highest catalytic activity,which is mainly manifested in higher discharge voltage（2.82 V）and lower charging voltage（3.52 V）.Under the premise of limiting the capacity of500 m Ah·g^-1,it can maintain 30 cycles without attenuation,greatly reduce the internal ohmic resistance and charge transfer resistance of the battery,ensure the efficiency of matter and charge transfer,and improve the cycle stability.