Controllable Preparation And Performance Of Self-Supporting Lithium-Oxygen Battery Cathode Materials

Lithium-oxygen?Li-O₂?batteries have received extensive attention due to their ultra-high theoretical energy density,but its commercial application is limited by low actual energy density,poor round-trip efficiency,high overpotential and less desirable cycle life.These problems are mainly related to the oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?kinetics of the cathode material,and the wide band gap?4-5 eV?of the discharge product?Li₂O₂?forces it to be decomposed at a high potential,resulting the cycle stability and energy efficiency of the battery.High-efficiency catalysts have significant effects on improving ORR and OER kinetics,cathode materials suitable for framework structures can accommodate more discharge products and are an effective means of improve battery performance.At present,researches on these problems mainly focus on the development of reasonably structures positive materials and highly active catalysts.In this paper,a series of Li-O₂ battery metal sulfides self-supporting cathodes were synthesized on the skeleton of nickel foam?Ni?as the substrate by hydrothermal method,the carbon cloth was also used as the substrate material for nitrogen doping by magnetic sputtering,and the self-supporting cathode of nitrogen doped CC composite metallic phosphides was prepared by hydrothermal synthesis and high-temperature annealing.The phase and microstructure of the electrode were characterized by X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,scanning electron microscopy?SEM?and transmission electron microscopy?TEM?.The electrochemical properties of the battery were examined by cyclic voltammetry and constant current charge-discharge method.The results show that:?1?honeycomb-like nickel sulfide composite nickel foam?H-Ni₃S₂@Ni?with controllable morphology was prepared with nickel foam as the skeleton by the hydrothermal method.This carbon-free and binder-free electrode effectively reduces the overpotential of the battery?0.74 V?and enhances the stability of the cycle?more than 116 stable cycles?.The significant improvement of battery performance can be attributed to the self-supporting electrode structure and unique morphology of Ni₃S₂,avoiding side reactions caused by conductive agents and adhesives.At the same time,the high specific surface area of honeycomb-like Ni3S2 can accommodate more discharge products,further improving the discharge capacity of the battery.On the other hand,good conductivity of nickel foam substrate contributes to electron transport,porous network structure is beneficial to oxygen?O₂?diffusion,and highly catalytic Ni₃S₂ can effectively improve ORR and OER reaction kinetics,thus improving the redox reaction rate inside the battery.?2?hydrothermal preparation of spinel structured ternary copper cobalt sulfur?CuCo₂S₄?materials were used as a positive catalyst for Li-O₂ batteries.Compared with binary metal sulfide,the discharge capacity of the battery was significantly improved,and the synergistic effect of Cu²⁺and Co³⁺effectively improved the reaction kinetics of ORR and OER.Based on excellent catalytic activity of CuCo₂S₄,the CuCo₂S₄@Ni composite with three-dimensional nanosheet array was further synthesized by hydrothermal method as the self-supporting positive electrode of Li-O₂battery.The test results show that CuCo₂S₄@Ni electrode has a good bifunctional catalytic activity,improving the cycle stability of the battery(stable cycle 164 th under the condition of 200 mA g^-1,500 mA h g^-1)and service life(83 cycles under the condition of 500 mA g^-1,1000 mA h g^-1).The excellent electrochemical performance of the battery can be attributed to:CuCo₂S₄ nanosheet array grows on the nickel foam skeleton in situ,forming a special three-dimensional open structure,which can not only promote the electron and O₂ transmission,but also effectively reduce the polarization effect of the battery.Self-supporting positive pole structure without the use of conductive agent and adhesive to prevent the occurrence of side reactions.Excellent bifunctional catalytic activity of CuCo2S4 facilitates the deposition and decomposition of discharge products and improves the reaction kinetics of ORR and OER.The large-area CuCo2S4@Ni electrode was set by the same process and successfully applied to the soft-pack battery.With 5 mA(100 mA g^-1),the discharge capacity of about 509 mA h(about 9000 mA h g^-1)and the energy density of 536 Wh kg^-1 was obtained,which was about twice as much as that of the traditional lithium-ion battery.?3?the ternary transition metal sulfide composite foam nickel?McCo₂S₄@Ni,M=Zn,Fe?was prepared by hydrothermal method to be used as the self-supporting positive electrode of lithium-oxygen battery,so as to study the influence of positive electrode material on the growth mechanism of Li2O2 in the discharge process.The results showed that the flower-like ZnCo₂S₄@Ni electrode could induce Li₂O₂ to deposit on the electrode surface in solution growth model,and the excellent catalytic activity of ZnCo₂S₄@Ni was conducive to the decomposition of Li₂O₂ in the charging reaction,thus effectively reducing the overpotential of the battery?0.78 V?and improving the battery cycle life?500 stable cycles without attenuation?.The cascade pore structure of FeCo₂S₄@Ni exposes a large number of edge active sites,promotes the reversible generation and decomposition of Li₂O₂,improves the reaction rate of ORR and OER,effectively improves the stability of battery cycle?109 cycles of stable cycle?,and enhances the battery multiple performance(4401 mA h g^-1 high discharge capacity at 500 mA g^-1).?4?N doped by magnetron sputtering on carbon cloth and as basal material,using the hydrothermal method and annealing treatment on the surface preparation of transition metal phosphide and hetero atoms doped carbon fabric composite material,the preparation of the crimp nano structure of phosphating cobalt composite nitrogen doped carbon cloth?CoP@N-CC?and umbrella skeleton structure of the cobalt nickel doped phosphate compound nitrogen doped carbon cloth?Co-Ni₂P@N-CC?and used as lithium-oxygen battery self-supporting cathode.Both CoP@N-CC and Co-Ni₂P@N-CC exhibit comparable performance to precious metals?CoP@N-CC overpotential of 0.76 V and Co-Ni₂P@N-CC overpotential of 0.73 V?,and shows excellent cycle stability during long-term cycling?CoP@N-CC stable cycle exceeds134 th,Co-Ni₂P@N-CC stabilizes over 147 cycles?,which effectively improves the cycle life of the battery?both>500 th?.