Application Of Heterostructure Ni/La_0.9Mn_0.6Ni_0.4O_3-δ Nanofibers As Cathode Catalyst For Lithium-air Battery

With the depletion of traditional fossil energy,the new energy industry has been vigorously developed worldwide.How to realize the efficient use of energy is the most important issue,so it is urgent to develop more efficient technology of energy storage.Lithium-air batteries（LABs）has become an emerging research topic due to their ultra-high specific capacity.However,high overpotentials and reduced cycling stability of LABs limit their practical applications.Among the component of LABs,the performance of cathode plays a crucial role that recognized as the place that oxygen reduction reaction（ORR）/oxygen evolution reaction（OER）occur.Thus,promoting the kinetics of ORR and OER is a straighthood method to improve the charge/discharge performance of the battery.Therefore,the development of high-performance bifunctional cathode catalysts is significance for the development of lithium-air batteries.The perovskite oxide that have advantages of good ORR/OER activity,tuned structure and low cost is considered to be one of the high-performance catalysts for the replacement of precious metals.In this work,La_0.9Mn_0.6Ni_0.4O_3-δperovskite oxide is selected as cathode catalyst in aqueous lithium-air batteries to improve the capacity and cycling stability.In order to enhance the O₂ transportation during the cathode and increase the reaction active sites,porous La_0.9Mn_0.6Ni_0.4O_3-δnanofibers are prepared and compared with La_0.9Mn_0.6Ni_0.4O_3-δnanoparticles to investigate the effect of morphology on catalytic performance.Moreover,to improve electronic transmission of the catalysts and fabricate abundant oxygen vacancies,La_0.9Mn_0.6Ni_0.4O_3-δnanofibers were calcined in a reducing atmosphere,and then the Ni nanoparticles are in situ growth on the surface.A series of characterization and electrochemical performance of the materials were performed to determine the importance of this optimization.The main research results of this article are shown:（1）Perovskite oxide La_0.9Mn_0.6Ni_0.4O_3-δnanofibers（LMN NFs）with a wrinkled morphology have been synthesized by the electrospinning technique,which was as the cathode catalyst for Li-air batteries.Compared with La_0.9Mn_0.6Ni_0.4O_3-δnanoparticles（LMN NPs）synthesized by traditional sol-gel method,LMN NFs exhibit a special pore structure that can provide numerous reaction active sites,promote transport of O₂ and provide more storage area for discharge products.The lithium-air battery with LMN NFs delivers a larger discharge capacity(9397 m Ah g^-1),better cycling stability（100 cycles）and a lower first-cycle overpotential（1.111 V）at a current density of 300 m A g^-1 with fixed specific capacity of 500 m Ah g^-1.（2）Perovskite oxide La_0.9Mn_0.6Ni_0.4O_3-δnanofibers with in-situ Ni nanoparticles（H-LMN NFs）have been synthesized by the electrospinning followed reduced at 650℃in 5%H₂/N₂.After reduction,a large number of Ni nanoparticles are in-situ exsolved and oxygen vacancies are formed on the surface of the H-LMN NFs,which further improves the electronic conductivity of the catalyst and the concentration of reactive sites,optimizes the adsorption capacity of O₂,and promotes the first step of Li₂O₂ generation（O₂+e^-→O₂!）,greatly improve the ORR/OER.With the enhanced ORR/OER kinetics,at a current density of 400 m A g^-1,the lithium-air batteries with H-LMN NFs can deliver larger discharge capacity of 16656 m Ah g^-1 and better cycle stability of 95 cycles.