Study Of Electrolyte Systems For Non-aqueous Lithium-oxygen Batteries

Combining with the advantages of both ultrahigh theoretical specific energy and environmental friendly electrochemical behavior,the lithium air batteries are regarded as promising energy storage devices for applications on electric vehicles and smart power grids.However,there still come with many challenges in their way to practical use including low capacity,high over potential,electrolyte decomposition,lithium dendrite formation,limited cycle life and so on.In this article,novel electrolyte systems were developed for non-aqueous Li-O₂ batteries and their interface properties and electrochemical performance were investigated.Firstly,a misxed solvent?TEGDME-DX?with lithium salt?LiFSI?was applied to prepare a effective organic electrolyte.The results show that lithium anode and the proposed electrolyte possess good compatibility with the formation of high quality SEI film,which contributes to the lower interface resistance and enhanced cycling stability.Even after long cycling operation of 850 h,the over potential is still as low as 0.15 V.Moreover,the synergistic effect of LiFSI and DX benefits to form a well-distributed Li deposition layer and mitigate the dendrite formation,resulting in smooth and uniform size particle morphology.Furthermore,the wide electrochemical window?4.94 vs.Li/Li⁺?,high coulombic efficiency?94.1%?and successful operation with a typical oxygen cathode indicate the feasibility for employing this new electrolyte in high-energy Li-O₂batteries.Liquid electrolytes suffer from leakage,evaporation and decomposition in the open system of lithium air batteries.To avoid such problems,a novel polymer electrolyte was developed based on the lithiated perfluorinated sulfonic acid?PFSA-Li?ionomer and poly?tetrafluoroethylene??PTFE?with DMSO as placitisizer.The as-prepared PFSA-Li/PTFE polymer electrolyte showed high ionic conductivity(1.5×10^-4 S cm^-1)at room temperature and high lithium transference number?0.84?.Its use in a lithium-oxygen battery demonstrated excellent compatibility to lithium anode with stable interface property and dendrite-free Li deposition.A good cycling stability over 90 cycles at 1000 mAh g^-1 and rate capability up to 2 A g^-1 were obtained suggesting a feasible strategy for developing large-scale Li-O₂ battery systems towards high energy and high power application.Finally,attempts were made to modified the DMSO solvent and a bis?methoxy ethyl?sulfonic acid ester?OS2?with high boiling point was synthesized.A good solubility to lithium salts and stability to lithium anode make OS2 a promising solvent for lithium battery applications.However,the Li-O₂ cell with 1 M LiTFSI/OS2 electrolyte appears two obvious charge-discharge plateaus indicating a newly formation of redox reaction,which might results from the decomposition of electrolyte.What's more,a heavy polarization phenomenon was observed with large charge voltage suggesting unsuitability to apply such an electrolyte with limited electrochemical window?4.3 V vs.Li/Li⁺?.