Research On Reactive Oxygen Species Of The Lithium-air Battery By Electron Paramagnetic Resonance

Lithium-air batteries have become a hot spot for researchers because of their extremely high energy density.However,lithium-air batteries still face many dilemmas in practical applications:the insulated discharge products lead to a higher charging potential,resulting in a decreased coulomb efficiency;the highly reactive singlet oxygen（~1O₂）in the battery reaction is easy to react with electrolyte and electrode materials,resulting in attenuation of battery performance;non-oxygen components in the air cause the complex reaction mechanism of lithium-air batteries so that most lithium-air batteries can only work in pure O₂environment.To address the actual problems faced by lithium-air batteries,elucidate the side reaction mechanism and improve the performance of the battery,this paper successfully prepared highly efficient metal oxide catalysts and explored the role of CO₂gas in lithium-air batteries.In the experiment,the electronic paramagnetic resonance（EPR）technology was used to monitor the generation of ~1O₂in lithium-air batteries by building operando/ex-situ battery test systems,which provided theoretical basis for studying the side reaction mechanism of lithium-air batteries and electrode material design.The following results were achieved:1)Through a simple and easy preparation method,three transition metal oxide catalysts Co₃O₄,Ni Co₂O₄,Ni_xCo_3-xO₄were successfully synthesized and applied to lithium-air batteries.After evaluating their electrochemical properties,Co₃O₄catalyst was selected as a representative to delve into the reasons for the improvement in battery performance.By comparing the charge and discharge curves of carbon nanotube（CNT）cathodes with Co₃O₄/CNT cathode,the discharge products on the electrodes and the corresponding decomposition process,we found that the catalyst Co₃O₄could reduce the charging overpotential and inhibit the reactive oxygen species intermediate ~1O₂in the battery reaction,and the Li O₂-like species in the discharge products play a key role in the formation of ~1O₂in the initial charging stage.2)With carbon nanotubes as cathode materials,the effect of CO₂concentration on lithium-air batteries was explored by regulating the O₂/CO₂ratio.In the experiment,we found that a small amount of CO₂gas helps to improve the discharge capacity and cycle performance of the battery.With the help of Raman and SEM techniques,the influence of O₂/CO₂ratio on product morphology and composition was clarified,and it was found that Li₂CO₃was the main component of the discharge product of Li-O₂/CO₂batteries.Based on the changes of lithium anode after discharge and the results of ex-situ EPR experiments,it is that the improvement of the stability of lithium anode and the reduction of ~1O₂during charging could be the reasons for the performance improvement of Li-O₂/CO₂batteries.