Research Of The Fluorinated Electrode And The Fluorinated Polymer Electrolyte For Lithium-Oxygen Battery

The rechargeable non-aqueous lithium-O₂?Li-O₂?batteries are recently attracting increasing research attention because of their higher specific energy density,environment friendly and low-cost advantages compared with conventional lithium-ion batteries?LIBs?.It is expected that Li-O₂batteries could be widely applied as new energy resources in electric vehicles?EVs?and other electric devices.Despite much research efforts have been devoted on Li-O₂ batteries,some significant barriers still limit the practical application of Li-O₂ batteries,such as electrode polarization,electrolyte decomposition,lithium metal corrosion and poor rechargeable performance.Hydrophobic fluoride materials with the great percentage of mesoporous used to store lithium ionhas been applied in the lithium ion battery.As the single-ion and stable conductor,perfluorinated sulfonic acid polymer has been got good application in lithium-ion batteries.Here we do the research of the fluorinated air-electrode and the foluorinated polymer electrolyte for lithium-oxygen batteries.A hybrid air-electrode composed of a mixture of fluorinated carbon?CF_x?and Ketjen black?KB?active carbon composite materials was prepared to improve performance of Li-O₂ battery.In the hybrid air-electrodes,four kinds of CF_x materials were utilized as lithium insertion materials.The physical properties and morphologies of the KB and CF_x materials were characterized by Brunauer-Emmett-Teller?BET?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?and Scanning electron microscopy?SEM?measurements.Compared with the conventional KB air-electrode,all the CF_x/KB hybrid air-electrodes in Li-O₂ batteries showed higher specific discharge capacity,especially at high current density.Among these CF_x/KB hybrid air-electrodes,the fluorinated graphite based electrode showed the best electrochemical performance in Li-O₂ battery due to its highest specific surface area,and the highest percentage of mesoporous.The electrochemical performance of Li-O₂ and Li-air batteries using the hybrid air-electrodes with the different fluorinated graphite:KB weight ratio,were systematically investigated.At a current density of 0.5 mA cm^-2,the fluorinated graphite based air-electrode delivered a high specific discharge capacity of 1138 mAh g^-1 in Li-O₂ batteries,which was more than four times than that of the conventional KB air-electrode(265 mAh g^-1)under same testing conditions.The battery assembled with the fluorinated graphite based air-electrode exhibited better cycling stability than that of the battery assembled with the conventional KB air-electrode.Another challenge of Li-air battery is the lack of stable electrolytes.Herein,new stable polymer electrolyte,lithiated perfluorinated sulfonic?PFSA-Li?ion exchange membrane swollen with non-aqueous solvent,was developed for Li-O₂ batteries.Test results show that the lithium ionic conductivity at room temperature can reach 6.4×10^-4 S/cm or 10^-3S/cm level under the high temperature and the lithium ion transference number is 0.93?45??.The Li-O₂ battery using the PFSA-Li membrane swollen with non-aqueous solvent as both electrolyte and separator shows good discharge specific capacity and better cycling stability.Fourier transform infrared?FTIR?and X-ray photoelectron spectroscopy?XPS?results proved that the PFSA-Li polymer electrolyte could be stable in Li-O₂ batteries.No additional adding lithium salt is another advantage of the Polymer electrolyte membrane.