Design And Application Of Transition Metal Oxides Cathodes For Metal Batteries With High Energy Density

Currently,the rechargeable batteries with high energy density and low cost have gained increasing attention owing to the vigorous development of portable electronic devices and electric vehicles.Both of Na(1160 m Ah g^-1)and Zn(820 m Ah g^-1)metals have high specific energy densities,richer reserves and lower cost,rendering more promising application.Despite these advantages of Na and Zn based metal batteries,finding a proper cathode material with high energy density is still challengeable before commercialization.Considering the rich elemental valence,high electrochemical reactivity,strong reversibility,and environmental friendliness,transition metal oxides are more suitable to be applied as cathode material for rechargeable metal batteries.In this dissertation,Ni,Co,Mnbased transition metal oxides are designed and modified to enhance the structural stability and electrochemical activity.They all demonstrate excellent cycling stability when applied as cathode materials in different metal batteries,including N?-O₂,hybrid Zn-O₂,and Zn-ion batteries.The main research contents and conclusions are listed as follows:?1?C@Ni Co₂O₄-NAs based N?-O₂ batteries:a vertically self-standing C@Ni Co₂O₄nanoneedle arrays?C@Ni Co₂O₄-NAs?has been fabricated by a facile hydrothermal method.It shows spinel structure with good crystallinity.The Ni Co₂O₄ nanoneedles are in-situ grown on the carbon paper,forming unique urchin-like structure.This self-standing material has excellent electron-conductivity.The as-prepared C@Ni Co₂O₄-NAs is directly used as cathode without any polymer binders or conductive additives to avoid side reaction during the charge-discharge process.Owing to the numerous catalytic sites and high electron mobility,the N?-O₂ battery containing C@Ni Co₂O₄-NAs cathode demonstrates a high initial discharge capacity of 6500 m Ah g^-1 and low over-potential of 0.6 V under a current density of 50 m A g^-1.Meanwhile,the cyclability has been improved to be over 120 cycles at a capacity cut-off of 800 m Ah g^-1.?2?h-Co₃O₄@MnCo₂O_4.5 Ns based N?-O₂ batteries:hierarchical Co₃O₄@MnCo₂O_4.5nanocubes(h-Co₃O₄@MnCo₂O_4.5 Ns)with yolk-shell structure are synthesized via a template-assisted method.It is demonstrated to be helpful in creating high specific surface area of 130.4 m² g^-1,hierarchical macro-and mesopore structure,and synergistic yolk-shelled Co₃O₄@MnCo₂O_4.5active sites.These unique structural properties render h-Co₃O₄@MnCo₂O_4.5 Ns remarkably enhanced electrocatalytic activity towards both ORR and OER.The N?-O₂ battery based on h-Co₃O₄@MnCo₂O_4.5 Ns displays ultrahigh initial discharge capacity of 8400 m Ah g^-1 and ultralow charge-discharge overpotential of 0.45 V under a current density of50 m A g^-1.The battery also exhibits impressive cycling performance with stable cycling up to 135 cycles at a capacity cut-off of 1000 m Ah g^-1.Based on the FTIR and XPS results,it can be concluded that the discharge products are Na₂O₂ and Na2-x O2.?3?Co₃O₄ Ns based hybrid Zn-O₂ batteries:Co₃O₄nano-cubes?Co₃O₄ Ns?with superb dispersion are fabricated from metal-organic frameworks.Then,a novel hybrid Zn-O₂ battery is assembled with Co₃O₄ Ns cathode and Zn anode.It combines the superiority of Zn-O₂ battery and Zn-ion battery,achieving a high discharge plateau of1.85 V in the Zn-ion battery region and a high specific energy density of 13.8 m Ah cm^-2 at a current density of 100?A cm^-2.Besides,the hybrid Zn-O₂ battery demonstrates good rate capability and long-term cycling stability up to 1000 h at a capacity cut-off of 300?Ah cm^-2.Furthermore,a flexible hybrid Zn-O₂ battery is constructed with PAM gel electrolyte.The battery demonstrates high flexibility and works well under both anaerobic or aerobic conditions.?4??-MnO₂/CNT HMs based Zn-ion batteries:?-MnO₂ nanofibers/carbon nanotubes hierarchically assembled microspheres??-MnO₂/CNT HMs?are synthesized by a facile yet scalable chemical precipitation/spray-granulation combined methodology.The nanofibrous?-MnO₂ is uniformly anchored to the CNTs-based framework,forming a three-dimensional charge-transfer channel.The close-packed network structure is capable of remarkably increasing the tap density and improving electron-transfer capability.When utilized as a high-performance cathode for Zn-ion batteries,the as-synthesized?-MnO₂/CNT HMs delivers a prominent specific capacity of 296 m Ah g^-1,and excellent rate capability.A high areal energy density of 0.98 Wh cm^–2 at 0.2 A g^–1and a record cycling stability with96%capacity retention over 10000 cycles at 3 A g^–1 are achieved.Zn²⁺and H⁺co-insertion reaction mechanism with high reversibility is further revealed.