Preparation And Research Of Cost-Effective Cathode Catalyst For Lithium-Oxygen Batteries

Limited by their energy density,conventional lithium-ion batteries(LIBs)could not satisfy our demands towards electric vehicles and electronic products.Recent years,rechargeable nonaqueous lithium-oxygen batteries(Li-O2 batteries,LOBs)have attracted enormous interests because of the high specific capability.However,the study of LOBs is still in its early stage,and it is faced with many challenges in terms of practical application.,such as poor cycling stability,high overpotential and side reaction problem.In order to solve above problems,proper cathode catalyst should be synthesized.In this paper,we prepared two types of catalyst(transition metal oxide and precious metal)by some facile methods.The composition and morphology of catalysts were characterized by many methods,and their battery performance were studied by electrochemical methods.At the same time,density functional theory(DFT)was employed to study the reaction mechanism.The specific research content is as follows:(1)Urchin-like NiO-NiCo2O4(NCO)microspheres were successfully synthesized through a facile hydrothermal method and presented favourable catalytic activity for nonaqueous Li-O2 batteries.The composition of NiO-NiCo2O4 varied as the thermal treatment changed,and the NiO-NiCo2O4 calcined under 500 ? exhibited the best performance.The Li-O2 batteries employing NCO-500 delivered a high discharge/charge capacity of 9231/8349 mAh g'1 under the current density of 100 mA g-1.which is better than that of Super P.Besides,NCO-500 also exhibited good rate capability and cycling stability.When the current density increased to 500 mA g-1,batteries could still achieve a discharge/charge capacityof 3711/2254 mAh g_'.When capacities were limited to 600 mAh g-1,Li-O2 batteries containing the NCO-500 electrode could be cycled for 80 cycles stably.This superior electrocatalytic performance resulted from the unique morphology of NiO-NiCo2O4,which can facilitate continuous oxygen flow and charge transport as well as promote Li2O2 deposition and decomposition.(2)g-C3N4 with different morphology were prepared through thermal treatment firstly.Then,single-atom Pt supported on CNHS(Pt-CNHS)was successfully prepared through a facile liquid phase method.Battery tests showed that the performance of Pt-CNHS was better than that of CNHS.Li-O2 batteries using Pt-CNHS as catalyst delivered a high discharge capacity of 17059 mAh g-1 under the current density of 100 mA g-1,while that of pure CNHS was only 5890 mAh g-1.When the current density increased to 800 mA g-1,Pt-CNHS still could achieve a discharge capacity of 5964 mAh g-1.Pt-CNHS cathode could be cycled for 100 times under the capacity of 600 mAh g-1 and current density of 100 mA g-1.Density functional theory showed that local electric field formed between Pt atom and CNHS enables the efficient electrons and ions transport in the electrode,resulting in superior specific capacity and cycling stability of the Pt-CNHS.At the same time,porous structure and large surface area of CNHS can facilitate the fast mass transportation and electrolyte wetting,as well as promote the accommodate Li2O2:single-atom Pt can improve the utilization effiency as well as serve as excellent reaction sites.