Preparation And Performance Studies Of Oxygen Catalytic Electrode With Three-dimensional Architecutre

In recent years,the lithium-oxygen（Li-O₂）batteries with ultra-high energy densities have emerged as a research hotspot for next generation energy storage systems,however their practical applications still face critical issues such as large polarization,short cycle life and low energy efficiency.These problems are mainly due to the sluggish kinetic of oxygen electrode and the reaction mechanism involving the accumulation of insoluble discharge products Li₂O₂.Therefore,rationally designed porous architecture is very important for oxygen electrode to fully expose the active sites of the catalyst,maintain the mass diffusion routes,and consequently enhance the performance of Li-O₂ batteries.Herein,this thesis designed a novel three-dimensional architecture of Co₃O₄ nanosheet arrays supported by carbon nanosheets.This architecture provides abundant conductive network,fully exposes the active sites of Co₃O₄,and achieve the high surface capacity and low polarization of oxygen electrode.In addition,previous researches have demonstrated that replacing organic electrolyte by solid polymer electrolyte（SPE）is an effective method to improve the safety of Li-O₂ batteries.However,the high impedance of electrode/solid electrolyte interface is the main obstacle to solid-state Li-O₂ batteries.This thesis utilized the novel design of electrode architecture to prepare an integrated array electrode-SPE structure on three-dimensional oxygen electrode.This structure realizes the efficient contact between the array electrode and the SPE at three-dimensional interface,provides a large number of reaction active sites,and improves the capacity and cycling performance of solid-state Li-O₂batteries.The main research contents and conclusions of the thesis are listed as following:（1）As an electrode substrate,carbon nanoflake arrays（CNF@CC）were prepared on carbon cloth（CC）by polydopamine coating and metal oxide template.Then,a novel hybrid three-dimensional oxygen electrode（Co₃O₄-CNF@CC）was prepared via electrodeposition method followed by heat treatment.SEM,TEM,XPS,and XRD studies confirm the successful preparation of the Co₃O₄-CNF hybrid structure.OER catalytic activity test characterizations prove that CNF@CC as three-dimensional conductive substrate not only enhance the conductivity of the entire electrode,but also induce uniform growth of ultrafine Co₃O₄ nanosheet arrays in the three-dimensional structure that improves the utilization of Co₃O₄ catalyst.As the oxygen electrode in Li-O₂ batteries,Co₃O₄-CNF@CC exhibits an ultra-high surface capacity of 3.14 mA h cm^-2,a low charge-discharge overpotential as 0.84 V,and 86 stable cycles with a curtailed capacity of 0.15 mA h cm^-2.The SEM and XPS characterizations of the Co₃O₄-CNF@CC electrode after discharge and recharge further confirm that the three-dimensional architecture expose more catalytic active sites to decompose the discharge product Li₂O₂ efficiently.This work provides a new strategy for improving the performances of nanoarray oxygen electrodes via the hybrid nanoarray architecture that integrates intrinsic properties of each component and induces three-dimensional distribution of TMO catalysts.（2）Enlighted by the previous electrode architecture design and the structural advantages of three-dimensional oxygen electrode,an integrated electrode-electrolyte structure was prepared by loading solid polymer electrolyte（SPE）on Co₃O₄@CC nanoarray as a simple three-dimensional oxygen electrode.The optical photos and SEM characterization show that SPE and nanoarray electrode are mutually intercalated in three-dimensional structure,which effectively reduces the solid-solid interface impedance and provides more catalytic reaction sites.The solid-state Li-O₂ batteries with integrated structure have almost the same discharge trend as the aprotic Li-O₂ batteries,and can stably operate for 25 cycles at a cut-off capacity of 0.15 mA h cm^-2.As a preliminary investigation of solid-state Li-O₂batteries,this work provides valuable experience for optimizing the interface contact method between oxygen electrode and solid electrolyte and the structural design of all-solid-state Li-O₂ batteries.