Preparation And Properties Of Fluorinated Ether Polymer Gel Electrolytes

Solid-state lithium metal batteries（SSLMBs）have attracted a lot ofattention due to their excellent performance in terms of energy density and thermal safety.Solid-state electrolytes（SSEs）are of significance in SSLMBs,which should meet the requirements of wide electrochemical window,high ionic conductivity and excellent stability with lithium metal anode.Solid polymer electrolytes（SPEs）are becoming a hot research topic in SSEs because of their processability,plasticity and stable interfacial contact with electrodes.However,low ionic conductivity at room temperature hindered their further development.The ionic conductivity of SPEs can be effectively improved by preparing gel polymer electrolytes（GPEs）,but they still have problems such as narrow electrochemical window.When the polymer matrix contains fluorine atoms,the electrochemical window of which can be improved,and the formation of a dense and homogeneous solid electrolyte interface（SEI）layer is conducive to improving the stability of the electrolyte with lithium anode.This paper mainly focuses on GPEs as the main research subject.Firstly,the effect of fluorine introduction on the GPEs is investigated by comparing the performance of structurally similar fluorinated GPEs with that of non-fluorinated GPEs.Secondly,glycidyl 2,2,3,3-tetrafluoropropyl ether（TFP）was copolymerized with 1,2-epoxybutane（EOB）to prepare TFPx-EOB（x=0.05,0.10,0.15）fluorinated GPEs to investigate the effects of copolymerization and fluorine content on the properties of fluorinated GPEs.The following conclusions were obtained from the study:（1）The introduction of fluorine is beneficial to improve the degree of polymerization,thermal stability,and electrochemical window of GPEs.The formation of lithium fluoride SEI layer between electrolyte and lithium metal interface allows the stability of GPEs with lithium anode to be enhanced.However,the introduction of fluorine leads to a decrease in the ionic conductivity of GPEs.（2）The relative content of fluorine in fluorinated GPEs is too much or too little,which is not conducive to its performance improvement.TFP0.05-EOB and TFP0.15-EOB have lower thermal stability,ionic conductivity and stability with lithium anode than TFP0.10-EOB.（3）Copolymerization can improve the polymerization degree,thermal stability and ionic conductivity of fluorinated GPEs.TFP0.10-EOB prepared by copolymerization exhibits well thermal stability,ionic conductivity of 2.92×10^-5 S cm^-1 at room temperature,electrochemical window of 4.7 V,and excellent stability with lithium metal anode.TFP0.10-EOB based Li Fe PO₄/Li battery shows stable charge/discharge cycling performance.