Theoretical Simulation Of The Catalytic Mechanism On The Surface Of Transition Metal Oxygen Group Compounds In Lithium-Air Batteries

In a non-aqueous lithium-air battery,the known electrochemical pathway is 2Li⁺+2e^-+O₂?Li₂O₂or 4Li⁺+4e^-+O₂?2Li₂O.Calculations show that the theoretical energy density of this type of battery is several times higher than that of ordinary lithium-ion batteries.Therefore,it has great application prospects in electric vehicles and other mobile high energy consumption equipment.However,non-aqueous lithium-air batteries face serious problems such as slow reaction kinetics,high charge/discharge overpotential,and short cycle life,where the high overpotential during ORR（Oxygen Reduction Reaction）and OER（Oxygen Evolution Reaction）leads to low coulomb efficiency,which is one of the biggest problems hindering the commercial use of lithium-air batteries.The use of efficient catalysts in the positive electrode to improve the actual performance of the battery is considered an effective way to solve this type of problem.In search of a catalyst with better optimisation and understand its catalytic nature and mechanism.In this paper,the pathways of ORR and OER reactions occurring on different catalyst surfaces are investigated using the first-principles caculations.In the first part:the Ni（111）surface is first constructed and the distribution of individual O atoms on the Ni（111）surface is analysed.The findings of the analysis show that single oxygen atoms tend to adsorb more readily to the hcp sites on the Ni surface.Next the formation energy of the Ni（111）surface was calculated for different oxygen coverages and a stable 100%oxygen covered Ni（111）surface was determined.The rationality of the oxidized Ni（111）surface is explained by comparing the surface energy of the oxidized Ni（111）surface with that of the pure Ni（111）surface.Then the two-electrons and four-electrons paths of the ORR process were simulated on the identified O-100%-Ni（111）surface,and the equilibrium voltage,discharge voltage and overpotential of the reaction were obtained,which had lower overpotential and better catalytic effect than the pure nickel catalyst.By calculating the Gibbs free energy under these two reaction paths,it was concluded that the O-100%-Ni（111）surface ORR reaction tends to four-electrons process and produces the product Li₂O.The underlying reason for following the four-electrons reaction pathway was analyzed by the detailed electronic structure of the ORR.Finally,the reasonableness of this model growth was analysed by means of density of states.The second part of the research:Due to the high lattice match of the four-electrons discharge product Li₂O to the Mo S₂catalyst,this part first constructs the Li₂O（111）and Mo S₂（111）interface and obtains the most stable Li₂O（111）/Mo S₂（111）interface model by adjusting the distance between them.Then the mechanism of the OER reaction of the discharge product Li₂O at the Li₂O（111）/Mo S₂（111）interface was studied,and the charging voltage and overpotential of the four paths were calculated,thus identifying“path II”--Li/-Li/-O₂/-Li/-Li as the most suitable dissociation path.Finally,the overpotential and charging voltage of Li₂O undergoing self-decomposition according to path II were calculated,and it was found that Mo S₂catalyst can effectively reduce the overpotential of Li₂O,indicating that Mo S₂catalyst has good catalytic activity.In this paper,the ORR and OER reaction mechanisms of Li₂O on different transition metal oxygen group compounds catalyst surfaces are investigated and the underlying causes are analyzed,which will provide an effective theoretical basis for the future development of Li-air batteries.