Preparation Of Transition Metal Phosphides And Study On The Performance Of The Li-O₂ Batteries

Due to the increasingly serious problems of energy shortage and environmental pollution,the research on green and sustainable energy is progressing rapidly,and the development of energy storage equipment is also advancing.Li-ion batteries have become the mainstream of the current battery market due to their unique properties such as environmental protection and high energy density.However,the energy density of traditional Li-ion batteries is difficult to meet the requirements of current electric vehicles and portable electronic products.Li-O2 batteries came into being,and they have become a hot research topic in the energy industry.At this stage,there are still severe challenges for Li-O2 batteries from laboratory research to practical applications:the cycle stability,overpotentials,energy conversion efficiency,rate performance,electrolyte volatilization and safety issue.Progress is still needed in other areas.For Li-O2 batteries,the most effective and direct way to solve the above problems is to develop an efficient bifunctional catalyst to promote the effective and rapid progress on the cathode towards the oxygen reduction reaction(ORR)and oxygen evolution reaction(OER).Among many cathode catalysts for Li-O2 batteries,precious metal materials,such as Pt and so on,show the best catalytic effect.However,the high cost of precious metals has severely restricted their large-scale application.Transition metal phosphides have become important candidates to replace precious metal materials due to their high electrical conductivity(close to those of metals),excellent electrochemical activity,environmental protection and low price.This topic introduces a simple synthesis method for the universal synthesis of a variety of transition metal phosphides and carbon composite materials(MP@NPC),including but not limited to FeP@NPC,Co2P@NPC,Ni2P@NPC,Cu3P@NPC and MoP@NPC materials.Their catalytic mechanisms were also explored.In this project,a variety of MP@NPC composite materials were successfully prepared by a one-step pyrolysis method,and their catalytic effects and mechanisms in the OER and ORR processes of Li-O2 batteries,were explored,and the performance advantages and disadvantages of several MP@NPC cathodes were compared.Therefore,this topic is mainly carried out from the following two aspects:(1)One-step pyrolysis method was employed to synthesize MP@NPC composite materials,of which structure and morphology were characterize,and their electrochemical performance of composite material cathodes were investigated in Li-O2 batteries;(2)By comparing reaction products at different stages of MP@NPC cathodes,the critical roles in promoting the formation and decomposition of Li2O2 in the charge and discharge processes were explored.The research significance of this topic lies in:(1)A simple,environmentally friendly,low-cost and large-scale synthesis scheme was designed for the preparation of MP@NPC composite materials;(2)The effective combination of transition metal phosphides and carbon materials was realized,and by applying synergistic effect,bifunctional catalytic effect was boosted;(3)Based on the reaction mechanisms,the excellent performance of MP@NPC cathodes was researched,providing the future research direction of phosphides.