Preparation And Performance Investigation Of P-NiO And MoSe₂-Ni_0.85Se@C Cathode Catalysts For Li-O₂ Batteries

As global industrialization and energy consumption continue to accelerate,so does,excessive use of fossil fuels would not only result in an irreversible decrease in global fossil energy reserves,but also lead to serious consequences such as global warming,ecological degradation,and natural disasters.The exploration of sustainable clean energy utilization and storage has become a hot topic of concern,among which,lithium-ion batteries have been used in various energy storage systems because of their excellent features such as no memory effect,environmentally friendly and low self-discharge.However,technological advancements have resulted in higher requirements for the range of electric vehicles and electronic products,and the lower energy density of lithium-ion batteries is hard to meet these requirements.Lithiumoxygen batteries have received a great attention because of their extremely high theoretical energy density(3505 Wh kg-1),which far exceeds that of the current state-of-the-art lithiumion batteries.However,owing to the slow oxygen reduction reaction and oxygen evolution reaction kinetics,lithium-oxygen batteries commonly exhibit limited specific capacities,unsatisfactory cycling capability,high overpotentials,and low energy conversion efficiency,which largely hinder the further development of lithium-oxygen battery technology.The development of high-efficiency cathode catalytic materials could aid in solving abovementioned issues and advance the application and development of lithium-oxygen batteries.In this project,different typical transition metal oxides,including the design and preparation of phosphorus-doped NiO microspheres(P-NiO)and the construction of spherical MoSe2Ni0.85Se@C heterostructures,have been investigated from different perspectives,which were applied as the cathode catalysts for lithium-oxygen batteries,and their performance and mechanism of action were investigated.The main contents in this paper are as follows:(1)NiO materials with different phosphorus doping contents were synthesized by hydrothermal and annealing methods and employed as cathode catalysts for lithium-oxygen batteries.It is demonstrated that the optimal doped P-NiO material achieves a high discharge/charge specific capacities of 16628/16490 mAh g-1 at 100 mA g-1 with low overpotentials of 0.29/1.05 V,as well as over 300 cycles at 500 mA g-1 with limiting specific capacity of 600 mAh g-1.Density functional theory calculations further show that the introduction of P heteroatoms effectively enabled the charge distribution on the P-NiO surfaces to generate large number of Ni-P coordination groups as emerging catalytic sites,which greatly reduced the Gibbs energy barrier during the cycling processes and led to a significant improvement in the reaction kinetics.(2)MoSe2-Ni0.85Se@C heterostructured hollow composites were successfully prepared using the simple hydrothermal and calcination methods and used as electrocatalytic cathode catalysts for lithium-oxygen batteries.The cross-aligned nanosheets avoid the constant accumulation between nanosheets,and the large gaps formed can provide enough space for storing the discharge products and accelerate the mass and charge transport.In addition,the built-in electric fields formed at the heterogeneous interfaces of MoSe2 and Ni0.85Se induced charge redistribution and promote interfacial charge transfer kinetics.the MoSe2-Ni0.85Se@C composite cathode could provide large specific capacities,excellent rate performance,and outstanding cycling stability.