Design Of Li?Na??air Batteries Based On MnO₂ Catalytic Cathode And Fluorinated Carbon/Li?Na? Composite Anodes

Lithium–air batteries have been regarded as next-generation high energy density battery system due to their ultrahigh theoretical energy density.However,the sluggish kinetics during formation and decomposition of the insulated discharge product Li₂O₂,and inevitable dendrites issues because of the use of metallic Li restrict the development of lithium–air batteries.Developing high-performance cathode catalysts can accelerate battery reaction kinetics,and lithium dendrites issues require essential protection for Li anodes.In this dissertation,in the light of the demand for high-performance air battery catalytic cathode,we adopt a low-cost manganese-based catalyst with the decoration of noble metal oxides particles to enhance its activity.The application of manganese-based catalyst to Li–CO₂ battery can realize the capture of greenhouse gas CO₂.Considering the limited metallic Li resources,we utilize metallic Na with more abundant resources to study the performance of sodium–air batteries and employ protection methods for Na anodes.The main research contents and results are as lists:High-performance IrO₂/MnO₂ catalyst composed of MnO₂ nanosheets and IrO₂nanoparticles has been synthesized via a two-step hydrothermal method.After 200cycles at 800 mA g^-1 between 2 and 4.5 V,a discharge capacity of 1070 mAh g^-1 can be kept for the IrO₂/MnO₂-catalyzed Li–CO₂ cell in a full charge/discharge mode.When the load mass of IrO₂/MnO₂ boosts from 0.4 mg cm^–2 to 1 mg cm^–2,the cell can be stably cycled for 378 times at 400 mA g^-1 with a limited specific capacity of 1000 mAh g^-1,indicating outstanding electrochemical performance and rate capability.After 50cycles at 800 mA g^-1,IrO₂/MnO₂ catalytic cathode can still recover its pristine morphology,showing good cycling stability.A soft-pack cell was fabricated adopting a2 cm×2 cm IrO₂/MnO₂ catalytic cathode and can exhibit stable cycling at 400 mA g^-1with a limited specific capacity of 500 and 1000 mAh g^-1.Na/FCNTs composite anode has been obtained using metallic Na and fluorinated carbon nanotubes?FCNTs?by melting and mechanically mixing.The results of air exposure and symmetric cells tests tell the fact that Na/FCNTs electrode possesses better mechanical stability,electrochemical performance and cycling stability than bare Na electrode.From the in-situ optical observation images,the growth rate of Na dendrites on the surface of Na/FCNTs electrode is much slower than that of bare Na electrode.Na–O₂ cell with bare Na anode can only sustain 62 times stable cycling,while the cell with Na/FCNTs anode can stably cycle for 112 times at 400 mA g^?1 between1.5 and 4.5 V with a limited specific capacity of 1000 mAh g^?1.The performance improvement of Na/FCNTs electrode and the cell can be attributed to the formation of a FCNTs-incorporated,NaF-rich SEI layer on the surface of Na.XPS confirms the production of NaF on the surface of Na anode,and the reaction energy barrier between Na and FCNTs is calculated to be–3.8269 eV/Na atom by DFT method,which provides theoretical proof for the formation of NaF.Employing a similar mechanically hammering method,Na/FG composite anode has been prepared using metallic Na and fluorinated graphene?FG?.Na?CO₂ cell with Na/FG anode is able to sustain a stable cycling up to 391 times,while the cell with bare Na anode can merely stably cycle for 258 times at 200 mA g^?1 with a limited specific capacity of 1000 mAh g^?1.Air exposure test proves the ability of maintaining initial shape of Na/FG electrode is better than that of bare Na electrode.According to the results of symmetric cells test,Na/FG electrode bears much smaller polarization voltage and surface resistance than bare Na electrode.XPS spectra reveal that FG can react with Na to produce NaF and graphene during preparing and cycling,and the spontaneity of the above reaction is verified by DFT calculations.The in-situ constructed NaF-rich SEI layer can effectively suppress the growth of Na dendrites,thus extending the cycle life of electrode and cell.A unique core–shell MnO₂@NiCo₂O₄ catalytic cathode has been designed.MnO₂@NiCo₂O₄-catalyzed Li–O₂ cell can be stably cycled for 168 times at 400 mA g^-1 with a limited specific capacity of 500 mAh g^-1,showing good cycling stability.Ru nanoparticles-decorated knitted Co₃O₄ nanowires have been grown via a solution chemical method,which promotes the catalytic performance of pristine Co₃O₄.As a comparison,MnO₂-based catalyst possesses better catalytic performance.A Cu electrode with the co-deposition of Li,graphite and FCNTs?Li@GFCNTs@Cu?has been acquired by blade coating and electroplating.This electrode delivers a coulombic efficiency over 90%in the insertion/deinsertion of Li,a relatively small overpotential and a total specific capacity of 6 mAh cm^–2.Meanwhile,it exhibits a uniform and compact deposition layer as well as minimum lithium excess.Li–O₂ cell using Li@GFCNTs@Cu anode with limited lithium excess can sustain 9 times cycling at 0.05mA cm^–2 with a limited specific capacity of 0.5 mAh cm^–2,and 5 times cycling at 0.1mA cm^–2 with a limited specific capacity of 1 mAh cm^–2.