The Research On The Effects Of Ga-based Liquid Metal Functionalized Cathode On The Performance Of Lithium Oxygen Battery

Lithium-oxygen battery has a high theoretical specific energy density(3500 Wh kg^-1),much higher than that of commercial lithium-ion batteries,which has potential application prospects in electric vehicles,grid energy storage systems,etc.,and has attracted much attention.However,poor cycling stability and safety problems limit the practical application of lithium-oxygen batteries.During the discharge process of lithium-oxygen battery,oxygen reduction reaction occurs at the cathode to generate solid product Li₂O₂,and the Li₂O₂ is decomposed during charging process.Incomplete decomposition of Li₂O₂ and side reactions during charging and discharging process will lead to cathode passivation and lead to the poor the cycling stability.In this paper,liquid metal（LM）with fluidity and self-repairing properties was adopted to solve the problem of cathode passivation.MWNTs and Ga-SnLM/Ga-InLM composite were loaded on the carbon paper to change the surface properties of the cathode,which promoted the formation and decomposition efficiency of Li₂O₂.Cathode passivation was alleviated and the discharge capacity of lithium oxygen battery was increased.Meanwhile,the cyclic stability of lithium-oxygen battery was improved.Specifically,it includes the following parts:Ga-SnLM and Ga-InLM were obtained through the melting method with the mass ratios of 88:12 for Ga-Sn and 75:25 for Ga-In liquid metals,and four kinds of electrodes were prepared by compounding with MWNTs.The surface performance of the LM was tested,the results showed that an oxide film was formed on the surface of the LM to protect the internal metal from further oxidation and LM droplets could recover after being squeezed.The functionalized cathode was characterized by SEM,EDS,and XRD,and it was found that the size of Ga-SnLM and Ga-InLM particles were approximately 210 nm and 350 nm.Ga-SnLM and Ga-InLM have good stability in the electrolyte since their structure maintained even after soaking soaked in Li Cl O₄-DMSO electrolyte about four days.The cycle life,rate performance,and discharge capacity of lithium-oxygen battery with Ga-SnLM/MWNTs composite as cathode were measured.When the composite of LM loading on MWNTs was used as the cathode,the morphology of the discharge product was small-sized flakes.On the contrary,precipitation of sheet-like and flower-like products can be observed on the MWNTs cathode.The structure of the cathode was tested by XRD and Raman spectroscopy,which demonstrated that the discharge product was Li₂O₂.In situ optical microscope found that the discharge products can flow on the surface of Ga-SnLM.Ga-SnLM maintains its original shape during the cycling,and the LM/MWNTs cathode promoted the decomposition of Li₂O₂,the passivation rate of the cathode was slowed down.Meanwhile,the corrosion of the lithium anode was alleviated.The battery cycle number was increased to 200 times（50 times for MWNTs cathode）,the battery capacity was increased to2.14 m Ah（0.29 m Ah for MWNTs cathode）,and the rate performance of the lithium-oxygen battery ware effectively improved.The cycle life,rate performance,and discharge capacity of lithium-oxygen battery with Ga-SnLM/MWNTs composite as cathode were investigated.Unlike the cathode with Ga-SnLM,the discharge products of LMI/MWNTs cathodes ware mainly ring-shaped and spherical（average size was about 600 nm）.XRD results indicated that the discharge products ware Li₂O₂.The discharge capacity of the cathode of LMI/MWNTs was increased to 3.42 m Ah,and the battery was stably cycled for 310 cycles.LMI/MWNTs battery showed the lowest overpotential（0.7 V in the first cycle）,which effectively alleviated the cathodes passivation speed,as well as the lithium corrosion.