Application Of Polymer Electrolyte Synthesis In Lithium Ion Batteries

Nowadays,lithium ion batteries?LIBs?have shown wide prospects and great economic benefits because of their high voltage,high specific energy,long cycle life,especially in the field of electric vehicles.However,the common commercial lithium ion batteries still have shortcomings.The current research are mainly focus on three directions:1)the desire for high energy density and fast charge discharge rate of LIBs;2)high voltage from 3 V to 5 V;3)safety.As we all known,traditional LIBs still bear the inherent safety issues from leakable and flammable liquid electrolytes made of organic ether solvents.It is promising for polymer electrolyte to replace conventional electrolyte although they exist problems which may hinder their practical applications.This thesis studies the application of polymer electrolyte in LIBs and the main contents of this thesis are as follows:First,we synthesized the comb shape single ion conducting polymers with poly?ether ether ketone?backbone and lithiated perfluoroalkylsulfonylimide and sulfonic acid side chains,which are thermal and electrochemically stable with high liquid retaining capability and flam retardancy.Ionic conductivities of SPEEK-PFSILi GPEs?room temperature?can reach 1.3×10^-4 and 4.4×10^-5 S·cm^-1 after swelling with propylene carbonate?PC?and tetra?ethylene glycol?dimethyl ether?G4?,respectively.In addition,it shows the high lithium-ion transference numbers?t+up to 0.90?since its anions are linked to the polymer chain and can not free to move.The Li/LiFePO₄battery assembled with SPEEK-PFSILi GPEs exhibited a stable charge-discharge behavior and good cycling performance.Therefore,GPE made of SPEEK-PFSILi may be useful for developing safer higher voltage LIBs.Secondly,we synthesized a new type of quaternary ammonium polymeric ionic liquid?PIL?by a simple and convenient method,and the composite solid electrolyte was prepared by combining PIL with LLZO and lithium salt.The new quaternary ammonium polymeric ionic liquid composite solid electrolyte has a very high electrochemical window,up to 5.5 V.For PIL has a poly-cationic structure,which can anchor TFSI anion and avoid migration and boundary polarization.The ionic conductivity of PIL/TFSILi/LLZO can reach 2.2×10^-4 S·cm^-1?50??.The Li/LiFePO₄battery assembled with PIL/TFSILi/LLZO solid electrolyte exhibited good cycling performance.It is worth noting that there is an activation process at the initial stage of circulation.The discharge capacity can be kept around 125 mAh·g^-1 after it is stable.And the efficiency of Kulun remains at around 100%.The solid electrolyte is expected to prepare high voltage solid state polymer lithium ion battery with high-voltage cathode materials.