Study On Cobalt-based Cathode Materials Design And Performance For Lithium-Oxygen Battery

Lithium-oxygen batteries(LOBs)are expected to be one of the most competitive energy storage devices for the next generation due to their high theoretical energy density(3500 Wh kg-1).However,the slow kinetics of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)in current LOBs lead to the actual energy density being much lower than the theoretical value and low cycling efficiency.Lithium peroxide,the product of discharge on the cathode side,has low electron/ion conductivity and is difficult to decompose during charging.Moreover,solid phase lithium peroxide is insoluble in organic electrolyte,which is easy to block material transfer and gas transmission channels.Therefore,to develop LOBs with high energy density and long life,it is necessary to reasonably design the cathode electrode material,accelerate the oxygen reduction/oxygen precipitation reaction on the cathode side,and promote the deposition and decomposition of lithium peroxide.From the perspective of the cathode materials to improve LOBs,this paper selects the transition metal cobalt-based material as the research focus.Based on the strategies of anion doping,bimetallic regulation,composite with oxides or single-atoms regulation,promoting ORR/OER catalytic activity,regulating the formation path,the morphology and crystalline of Li2O2.So the discharge/charge potential is reduced,the actual energy density and cycle lifespan of LOBs is improved.The specific content includes the following points:1.Nitrogen doped cobalt oxide as a cathode improved the electron/ion conductivity of the materials,optimized the adsorption of oxygen-containing intermediates,and promoted the formation of small-size amorphous lithium peroxide at the positive electrode ORR,reducing the overpotential(0.92 V).Meanwhile,the composite anode material based on nitrogen-doped cobalt oxide not only greatly alleviates the generation of dendrites and "dead lithium",but also enriches with lithium carbonate on the surface after cycling in LOBs,which enhances the corrosion resistance of water/oxygen and slows down the generation of LiOH.The full battery with cathode and anode electrodes assembled on the basis of nitrogen doped cobalt oxide can cycle 200 cycles stably at the current of 0.1 mA cm-2 and the capacity of 0.25 mAh cm-2.In this study,the strategy of introducing nitrogen doping into oxides for dual regulation of cathode and anode electrodes is helpful to improve LOBs performance as a whole.2.Nitrogen-doped bimetallic nickel-cobalt oxide nanoarrays(NNCO/CC)were prepared to improve the ORR/OER kinetics of LOBs.The NNCO/CC cathode promotes the production of amorphous lithium peroxide during discharging.Experimental characterization and theoretical calculation show that nitrogen doping has a significant effect on the electronic structure of bimetallic oxides,which is conducive to the adsorption and conversion of oxygen-containing intermediates,and nitrogen doping bimetallic oxides have a synergistic effect in the ORR/OER process.As a cathode of LOBs,the material still has a small overpotential(0.35V)after 200 cycles at a current density of 0.05 mA cm-2 and can maintain a stable cycle of 500 cycles.In this study,low overpotential and long-life LOBs can be achieved through the regulation of bimetallic electronic structure.3.Porous nitrogen-doped carbon nanocages(RuOx-CoOx-NC)loaded with ruthenium/cobalt oxides were prepared to promote the ORR/OER processes.CoOx and small-size RuOx nanoparticles jointly accelerated the ORR/OER process of the cathode and had a 1.06 V overpotential when the current density was 0.05 mA cm-2 and the capacity was 0.1 mAh cm-2 with a lifespan of 65 cycles.The porous nitrogen-doped carbon derived from ZIF-67 acts as a three-dimensional skeleton,providing deposition space for lithium peroxide.In addition,RuOx-CoOx-NC nanocages can induce the LOBs to produce nanosheet-like lithium peroxide during discharge and decompose completely during charging.In this study,the composite of cobalt oxide and other metal oxides to improve the performance of ORR/OER provides a new idea for expanding the application of cobalt-based materials in LOBs.4.Molybdenum disulfide/carbon cloth composite(SA Co-MoS2/CC)loaded with single atom cobalt was prepared to improve atomic utilization and LOBs performance.The molybdenum disulfide is used as a carrier to capture monatomic Co.Combined with the unsaturated coordination characteristics of highly dispersed monatomic cobalt,the electronic structure of the material is optimized.The improved discharge capacity(3.98 mAh cm-2)and more stable cycling performance(800 h)are obtained in 0.05 mA cm-2 in LOBs.In addition,the SA Co-MoS2/CC cathode induces LOBs to form a more uniform film-like of lithium peroxide during ORR process.This study provides a way to improve the performance of LOBs by improving the atom utilization rate through the defect anchor single-atom.