Theoretical Simulation Of Catalytic Reaction Mechanism Of Manganese Oxide Stepped Surface In Lithium-Air Battery

The rapid development of society and the great challenges faced by the environment are constantly demanding the capacity of energy storage devices,and lithium-air batteries with only a very high theoretical energy density has attracted people’s attention.However,despite the very attractive potential applications of lithium-air batteries,there are still many basic scientific and engineering problems that need to be solved,including high overpotential,low energy efficiency,unstable electrolyte,poor cycle reversibility,etc.,and there is still a great distance from the practicalization of lithium-air batteries.Researchers had done a lot of experimental and theoretical simulations on the essential sources of these problems,but the understanding is still very inadequate,especially on the slow kinetics of the Oxygen Reduction Reaction（ORR）and Oxygen Evolution Reaction（OER）in non-aqueous lithium-air batteries,and the catalytic mechanism of the catalyst are in urgent need of a deeper understanding.In order to understand the mode of action and the nature of the catalyst from the molecular-atomic level and reduce the charging overpotential,this paper adopted a first-principles calculation method to construct an interface structure model between the discharge product Li₂O₂and the catalystα-MnO₂,and to conduct a study of the OER catalytic reaction path on the stepped surface.The first part of the research:Firstly,we selected the catalystα-MnO₂（100）surface and the discharge product Li₂O₂（001）surface for lattice matching,obtained the interface structure ofα-MnO₂（100）surface and Li₂O₂（001）surface,continuously adjusted the distance between the Li₂O₂（001）surface and theα-MnO₂（100）surface which is optimized to find the most stable interface structure ofα-MnO₂（100）-Li₂O₂（001）.The density of states（DOS）of the most stable interface structure was analyzed.It is found that the first layer exposed to the vacuum and the Li₂O₂single layer near the interface are metallic,but the Li₂O₂layer in the middle is still insulating.The second part of the research:On the basis of the most stable interface structure that has been determined,the stepped surface was structured.Because the stepped surface has good conductivity,it connects the conductive channel between the top surface of Li₂O₂and the interface;Then the mechanism of the OER reaction on the surface of the step with three different reaction paths was studied.By calculating the equilibrium voltage,charging voltage and overpotential of these three different reaction paths,influences of the good catalytic activity ofα-MnO₂and different factors such as defects and doping on the catalytic activity ofα-MnO₂catalyst are compared.The results show thatα-MnO₂as a good catalyst for lithium air battery can enhance the catalytic effect ofα-MnO₂when it is combined with Li₂O₂step surface.In addition,the presence of O defects has little effect on the inability to improve the catalytic performance ofα-MnO₂,and the effect of Co doping is related to the specific decomposition path.This paper found the most stable interface structure betweenα-MnO₂（100）surface and Li₂O₂（001）surface,proposed a novel step surface model,and explored the oxygen evolution reaction path of Li₂O₂charging on the step surface with lower overpotential.This work will help develop higher performance lithium-air batteries.