Preparation And Performance Research Of Soluble Polyimide Based Single Ion Gel Polymer Electrolyte

The reduction of reserves of fossil energy and environmental pollution requires more kinds of energy and energy storage devices.However,the traditional liquid electrolyte lithium-ion battery working will occur leakage,electrolyte oxidation,dendrite,short circuit and other hidden dangers,which seriously menace the safety of lives and property of people.Solid state lithium batteries（SLIBs）have thus become the research focus owing to their large energy density,low space requirements and less polluting.Therefore,it is very significant for the development of SLIBS to design single ion polymer electrolyte to limit the growth of lithium dendrite.In this paper,two kinds of single ion gel polymer electrolytes based on polyimide were prepared by thiol-olefin click chemical crosslinking and Williamson reaction,and their physical and electrochemical properties were studied.The first single ion gel polymer electrolyte was based on polyimide with double bond（DPI）.First,4-styrene sulfonamide lithium（Li SSPSI）was designed and synthesized as lithium single ion monomer,and DPI had excellent thermal stability.The structures were characterized and confirmed via ¹H NMR and FTIR.The molecular weight of DPI was measured via gel permeation chromatograph（GPC）,which was 1.7×10⁴ g mol^-1.The DPI crosslinked single ion polymer electrolyte（DPI-SIPE）was prepared via UV irradiation of Li SSPSI and DPI in the presence of crosslinker pentaerythritol tetra（2-mercaptoacetate）and photoinitiator 2,2-dihydroxymethylpropionic acid and polyethylene oxide（PEO）.The dense and smooth morphology of the DPI-SIPE was observed via SEM.DPI-SIPE was immersed in plasticizer EC/DMC=（V:V=1:1）to obtain single ion gel polymer electrolyte（DPI-SIGPE）.The results showed that the ionic conductivity of DPI-SIGPE was 2.1×10^-4 S cm^-1,the lithium ion transfer number was 0.87.The electrochemical window was stable at 4.4 V（vs Li⁺/Li）at 30℃.The first discharge capacity of Li/DPI-SIGPE/Li Fe PO₄ battery was102 m Ah g^-1 at 0.2 C,and the discharge capacity was 98 m Ah g^-1 after 270 cycles.The results of charge/discharge tests at different rates showed that DPI-SIGPE had good electrochemical stability.Furthermore,hydroxyl-containing polyimide（PI-OH）based single ion gel polymer electrolyte was prepared.Firstly,PI-OH with high thermal stability and lithium salt 3-chloropropyl three-fluoromethylsulfonimide lithium（Li CPSI）were designed and synthesized.The structures of PI-OH and Li CPSI were measured by ¹H-NMR and FTIR.The PI-OH was analyzed by thermogravimetric analyzer（TGA）and GPC,T₅=412℃,Mn=2.46×10⁴ g mol^-1.Polyimide single ion gel polymer electrolyte（PI-SIPE）was prepared by Williamson reaction of PI-OH and Li CPSI.PI-SIPE was prepared via blending with PVDF-HFP and casting solution.PI-SIPE kept at 200℃for 0.5 h was without obvious shrinkage,which had excellent thermostability.SEM showed that the PI-SIPE had a dense morphology.Polyimide based single ion gel polymer electrolyte（PI-SIGPE）was obtained,after PI-SIPE was infiltrated by plasticizer EC:DMC（V:V=1:1）,The ionic conductivity of PI-SIPE was 1.4×10^-4 S cm^-1 at 30℃.The lithium ion transfer number arrived 0.97,and the electrochemical window stability was 5.2 V（vs Li⁺/Li）.The initial discharge capacity of Li/PI-SIPE/Li Fe PO₄ battery was about 161 m Ah g^-1 at 0.2 C,and the capacity retention rate was more than 90%after 320 cycles.The rate test results showed that PI-SIGPE had good electrochemical stability.