Theoretical Simulation Of The Catalytic Reaction Mechanism Of Ni Catalyst Surface In Lithium Air Battery

Driven by the growing demand of energy storage devices,rechargeable lithium–air batteries,especially non–aqueous ones,are considered as one of the most promising next–generation batteries technologies due to their ultrahigh energy density.The net the positive discharging reaction is oxygen reduction reaction?ORR?,and the reverse charging reaction is oxygen evolution reaction?OER?.However,this new battery technology has several problems such as low power density,low coulomb efficiency,short cycle life,and electrolyte instability.All these problems are related to the sluggish kinetics of OER and ORR,especially the decomposition of discharge products.Compared with lithium peroxide,lithium oxide is considered to be a more benign discharge product.As a catalyst for the cathode of lithium–air battery,Ni is conducive to the four–electron reaction to generate lithium oxide.In order to obtain the mechanism of the initial oxygen reduction and oxygen evolution reactions on the Ni surface,this thesis adopts first–principles calculations to systematically study the adsorption performance of oxygen molecules and lithium atoms on the Ni?111?surface,as well as the initial ORR and OER reaction processes.The main content of this article is divided into the following two parts:The first part of the research:The Ni?111?surface was constructed,and the adsorption of oxygen molecules and lithium atoms on the surface was studied respectively.The results show that the adsorption of oxygen molecules adsorbed on the Ni surface at the most stable hcp site,while the lithium atoms adsorbed on the Ni surface is also the most stable at the hcp site.Then,this thesis studies two possible reaction paths for the first step of the initial ORR reaction on the Ni?111?surface to generate lithium peroxide.Subsequently,the second step of the initial ORR reaction was studied,which is the process of lithium peroxide disproportionation to generate lithium oxide and release oxygen,as well as the energy changes of the reaction intermediates and products in this path.Based on the results of the above calculations and simulations,this thesis proposes the most likely reaction path for the molecular lithium oxide to grow on the Ni surface at the beginning of the discharge.After that,there will be many cluster–like Li₂O molecular growing on the Ni?111?surface with this reaction path.As the depth of discharge increases,Li₂O crystals gradually grow on the top and edges of these molecular clusters until the surface is completely covered.The second part of the research:The reverse process of the ORR reaction mentioned above,that is,the decomposition process of Li₂O crystals,was studied.Since Li₂O₂ is an intermediate species,the decomposition of Li₂O must be accompanied by the decomposition of Li₂O₂.Therefore,this part constructed and optimized the Li₂O surface slab model,Li₂O₂/Ni and Li₂O/Ni interface models,explored the self–decomposition process of Li₂O surface,the decomposition process of Li₂O₂ on the Ni surface from the top lithium atom layer,and the decomposition process of Li₂O on the Li₂O/Ni interface.Finally,the initial OER reaction mechanism of Li₂O on Ni?111?surface was summarized.This thesis studies the mechanism of Li₂O oxygen reduction and oxygen evolution reaction on Ni?111?surface,which will help to develop higher performance lithium–air batteries.