Preparation Of PEO Based Composite Polymer Electrolytes And Study On Their Ion Conduction

In order to meet the growing energy demand and technical requirements,we have carried out in-depth research on lithium-ion batteries.However,the liquid electrolytes used in lithium-ion batteries have great safety risks,such as flammable explosion caused by electrolyte leakage,which hinders its large-scale application.In order to make up for the inherent defects of liquid electrolyte,the most effective method is to replace the liquid electrolyte with solid electrolyte.At present,most studied polymer electrolytes are PEO,PSS and other polymers combined with lithium ion salts(such as Li TFSI and Li Cl O₄),but the ionic conductivity of these materials is usually low,which is difficult to meet the practical application.Therefore,the design and preparation of new ionic conductive materials to achieve high ionic conductivity is on the stage and chanllenging in the global research..Polyoxometalates,are a class of materials with nano size and adjustable structures,which are composed of counteracting cations and heteropoly anions.Because of its abundant exchangable counter cations,it is expected to have great potential applications in ion conduction.In this paper,we studied a class of organic-inorganic composite polymer electrolytes based on polyoxometalates and studied its lithium ion conductivity,the specific work is as follows:(1)The PEO/PVDF/NENU-3(Li)electrolyte membrane was prepared by adding MOF-based material NENU-3(Li)to the PEO/PVDF blended polymer.NENU-3(Li)possess abundant,regular and orderly channels for Li⁺transmission to further improve ion conductivity.The highest ion conductivity is the material prepared when the NENU-3(Li)content is 20%.It has an ion conductivity of 1.83×10^-4S cm^-1and Li⁺migration number of0.4 at 60°C.(2)The small molecule compound succinonitrile(SN)and the polyoxometalates Li₆P₂Mo₁₈O₆₂(LPM)were added to the PEO/PVDF polymer matrix to prepare the PEO/PVDF/SN/LPM electrolyte membrane.The molecular size of SN matches the distance of the Li⁺binding site,which can build a continuous ion channel in the electrolyte that is beneficial to ion conduction.The ionic conductivity reaches the highest when the content of SN is 5%.The conductivity of PEO/PVDF/SN/LPM is 1.17×10^-4S cm^-1,and the Li+migration value is 0.46 at 60°C.In order to verify the feasibility of this method,we replaced the LPM with Li₆P₂W₁₈O₆₂(LPW)and prepared a PEO/PVDF/SN/LPW electrolyte membrane.The test results obtained are consistent with that of PEO/PVDF/SN/LPM electrolyte membrane.(3)LPM-IL composites with different molar ratios were prepared using PEG-based ionic liquid(IL)and polyoxometalates Li₆P₂Mo₁₈O₆₂(LPM).The optimal molar ratio of LPM-IL is incorporated into the PEO and PVDF blend polymer matrix to prepare the PEO/PVDF/LPM-IL electrolyte membrane.The ion conduction is best when the content of LPM-IL is 5%.The ionic conductivity is 1.17×10^-4S cm^-1(30?)and 4.26×10^-4S cm^-1(60?),respectively.Meanwhile,the number of Li⁺migration reaches 0.54.In order to prove the feasibility of this method,we replaced the LPM with Li₆P₂W₁₈O₆₂(LPW),and prepared the PEO/PVDF/LPW-IL electrolyte membrane in the same ratio.The test results are similar to that of PEO/PVDF/LPM-IL electrolyte membrane.