Construction Of RuO₂/MnO₂@NC Array Electrode And Its Application As A High Performance Lithium Oxygen Battery Cathode

Although lithium-oxygen batteries（Li-O₂）have attracted more and more attention due to their higher energy density.The accumulation of insoluble products Li₂O₂ and Li₂CO₃ during the discharge process,as well as the electrolyte decomposition caused by the high overpotential during the charging process,and the corrosion of carbon materials have severely restricted the further improvement of battery life and commercial applications.The space structure of the positive electrode material and its catalytic activity for charge and discharge reactions are the key to solving the above problems.A suitable cathode material should have an excellent void structure to store insoluble products,and should have a large specific surface area and excellent oxygen reduction/oxygen evolution catalytic activity to promote the efficient and reversible formation and decomposition of Li₂O₂,reduce battery overpotential,and able to maintain a long cycle life.Taking into account the importance of the structure,composition and function of the catalyst,by using methods such as electropolymerization,calcination,hydrothermal method,and low-temperature adsorption,a nitrogen-doped nano-carbon array is grown in situ on the surface of carbon paper.RuO₂/MnO₂ is loaded on the surface of the carbon array to form the high-efficiency composite cathode catalyst（RuO₂/MnO₂@NC）for Li-O₂ battery.It has a unique three-dimensional hierarchical array structure,which helps electrode wetting and oxygen transportation,and provides a larger space for the deposition of Li₂O₂.This in-situ growth structure avoids the use of binder and reduces the occurrence of side reactions.The growth of MnO₂ nanosheets on the surface of the carbon array can change the surface roughness and provide attachment points for the subsequent loading of catalyst nanoparticles.In addition,the introduction of RuO₂ induces the formation of Mn3+on the surface of MnO₂,which not only improves the electrode conductivity,but also enhances the catalytic activity for ORR/OER.Electrochemical tests and subsequent characterization show that batteries based on RuO₂/MnO₂@NC cathodes can guide the conformal growth of Li₂O₂ as a thin layer on the electrode surface and the reversible decomposition of Li₂O₂ during long-term cycling.Compared with the cathode material without carbon array structure or catalyst,the Li-O₂ battery with RuO₂/MnO₂@NC cathode has significantly improved performance and high discharge capacity（approximately 10000 mAh g-1 at a current density of 100 mA g-1）and longer cycle life（252 cycles at 200 mA g-1,with a limited capacity of 500 mAh g-1）.Although the cathode catalyst material with excellent spatial structure can greatly alleviate the accumulation of Li₂O₂ and improve the decomposition efficiency of Li₂O₂,the solid-solid contact between Li₂O₂ and the solid catalyst in lithium-oxygen batteries is not tight.The decomposition efficiency of Li₂O₂ far away from the catalyst is limited.During long-term cycling,lithium electrode is easily corroded by by-products in the battery system such as water molecules and positive electrode oxygen molecules shuttle to the negative electrode,and the corrosion is irreversible.The corrosion products such as lithium carbonate and lithium hydroxide are solid and cannot be dissolved,eliminated,and accumulated on the surface of the lithium sheet,causing the battery resistance to increase,and the battery to expand in volume.Additives dissolved in the electrolyte such as redox media can be in close contact with Li₂O₂,and suitable additives can promote the formation of a stable SEI film on the surface of lithium metal,which is an effective way to solve the above problems.For this reason,on the basis of the first chapter,this article adds Ruc,LiI,InI3,LiNO3 to the electrolyte to achieve further optimization of the battery’s long-term cycle life,through various aspects such as Li₂O₂ decomposition efficiency and lithium anode protection.It has been verified that the addition of Ruc and LiNO3 can significantly improve the battery life.Among them,Ruc can be used as a redox medium and has a certain lithium protection effect,while the role of LiNO3 is mainly concentrated on the formation of the stable SEI film and the protection of the lithium anode.However,limited by its flying shuttle effect,LiI has a limited effect on improving cycle performance,and when the flying shuttle effect is more serious,the stability of lithium tablets becomes a key factor affecting cycle stability.