Preparation Of NiCo₂O₄@NiO@FNi Cathode Catalyst And Its Application In Lithium-air Battery

Lithium-air battery is one of the most promising electrochemical energy storage batteries.In the past five years,due to its potential in electric vehicles,it has attracted great attention.However,the current research on lithium-air batteries is still in its infancy,and there are many problems that need to be solved,such as higher charge-discharge overpotential,shorter cycle life,and lower energy efficiency.To improve the above problems,the air cathode plays an important role,and the use of transition metal oxides to construct a non-carbon air cathode can not only reduce the side reactions caused by carbon materials and binders,but also have better oxygen.Catalytic performance of reduction reaction（ORR）and oxygen evolution reaction（OER）.In this work,NiO nanosheets and NiCo₂O₄ nanowires were successively constructed on the nickel foam collector by secondary hydrothermal method to prepare NiCo₂O₄@NiO@FNi composite non-carbon positive electrode.The construction of this composite structure,on the one hand,can increase the reactive site by increasing the specific surface area,on the other hand,combines the catalytic ability of NiCo₂O₄ to ORR/OER and NiO to decompose carbonate products,and finally improves the overall performance of lithium-air battery.The main research contents are as follows:（1）In this experiment,by changing the ratio of water to ethanol in the hydrothermal process,NiO nanosheets of different sizes were obtained.The materials were characterized by FESEM,XRD,BET and other methods,which proved the successful preparation of porous NiO nanosheets.When the solvent volume ratio of water to ethanol is 1:1,the specific surface area of the generated NiO nanosheets is the largest,reaching 6.9635 m² g^-1,and the catalytic performance of OER/ORR is the best.（2）In this experiment,by varying the solvent ratio and hydrothermal time,NiCo₂O₄nanoarray structures with different morphologies,such as nanosheets and nanowires,were obtained.Using FESEM,XRD,BET and other methods to characterize the material,and assemble it into a battery for electrochemical performance testing.At a current density of 200m A g^-1 and a limited discharge capacity of 500 m A h g^-1,the number of battery cycles with NiCo₂O₄ nanowires as the positive electrode is 52 times,which is better than NiCo₂O₄nanosheets.This is closely related to the larger specific surface area and better pore structure of NiCo₂O₄ nanowires,which is beneficial to the formation and decomposition of discharge products.（3）Combined with the aforementioned research,the NiCo₂O₄ nanowires were compounded to the NiO nanosheets by secondary hydrothermal method to prepare the nanosheet-nanowire structure NiCo₂O₄@NiO@FNi composite cathode.Using FESEM,XRD,BET and other means to characterize and analyze the material,and assemble it into a battery for electrochemical performance testing.When the current density is 200 m A g^-1,the specific capacity of the NiCo₂O₄@NiO@FNi electrode is 7667 m A h g^-1.At a current density of 200m A g^-1 and a discharge capacity of 500 m A h g^-1,the number of NiCo₂O₄@NiO@FNi electrode cycles can reach 176 cycles.Through the performance comparison and charge and discharge product analysis,the charge-discharge reaction mechanism of lithium-air battery was further analyzed in depth.In the end,it is believed that this kind of positive electrode with composite structure not only retains the ability of NiO to decompose lithium carbonate products,but also can fully exert the bidirectional catalytic effect of NiCo₂O₄ on ORR/OER.In summary,this paper first constructs a NiO nanosheet substrate;then prepares NiCo₂O₄nanoarrays with excellent properties;and finally combines NiO nanosheets and NiCo₂O₄nanoarrays by hydrothermal method to obtain a special structure of NiCo₂O₄@NiO@FNiComposite positive electrode.Comparing the difference between the performance of the composite positive electrode and the NiO and NiCo₂O₄ positive electrodes in the lithium-air battery,combined with the characterization of their discharge products,the catalytic mechanism of the composite catalyst in the lithium-air battery was thoroughly explored.