Synthesis And Investigation Of New Solid Polysiloxane Electrolytes For Lithium-Ion Batteries

All-solid-state lithium-ion batteries have high safety performance due to using solid polymer electrolyte(SPE)instead of the traditional liquid electrolyte,and it can fundamentally solve the potential safety hazards of traditional lithium-ion batteries.in collision,overcharge,and with long time use.However,most of SPEs exhibit low ionic conductivity at room temperature that prevent them from application in lithium batteries.Polysiloxane has an extremely low glass transition temperature,high segment motion and better chemical stability.Therefore,polysiloxane has become a promising polymer electrolyte material.In this thesis,polysiloxane-based solid polymer electrolytes are prepared through graft modification for polysiloxane molecules,which have excellent comprehensive properties and can be used in lithium batteries at room temperature.A bifunctional polysiloxane(PZ-PMHS)was synthesized based on flexible polysiloxane with pendant sulfobetaine zwitterion(ZI)and poly(ethylene oxide)(PEO)via hydrosilylation.Subsequently,PZ-PMHS was blended with tri(ethylene glycol)divinyl ether cross-linker and LiTFSI,cured by heating and cross-linking to obtain PZ-PMHS polymer electrolyte membrane.The conductivity of the SPE effects by zwitterion and lithium salt concentration is investigated via electrochemical impedance spectroscopy(EIS),a high ionic conductivity of 3.39×10-4S/cm is obtained when ZI/PEO=1/10,EO/Li+=20:1 at room temperature.The electrochemical stability window of SPE is up to 5.0 V(vs.Li+/Li)at room temperature by linear sweep voltammetry(LSV),which indicats that the zwitterion pendant groups play an important role in increasing the comprehensive performance of SPE.Li/LiFePO4 battery based on this SPE presents a superior cycle life of 100 times with an initial discharge capacity of 155 mAh g-1 at 0.1?,and the Coulombic efficiency is nearly 99%for the whole cycles at 30 ?.In order to further design more excellent comprehensive properties of polysiloxane-based solid polymer electrolytes,combining the advantage of ionic liquid and nitrile groups,a novel polymer electrolyte(PIN-PMHS)was prepared by the same method as the substitution of nitrile-imidazole ionic liquid(IL-CN)for ZI.The SPE with excellent ionic conductivity of 3.56×10-4 S cm-1,wide electrochemical stable window of 5.4 V(vs.Li+/Li),high lithium ion transference number of 0.29 at room temperature.These results indicate that the IL-CN plays a significant role in the improvement of SPE performance.The interfacial stability test of SPE and lithium metal anode shows that the introduction of IL-CN can enhance the interfacial compatibility of SPE and lithium electrode,reduce the interface resistance and improve the cycle stability of the battery.High voltage Li/LiNi0.5Mn1.5O4 batteries with this SPE present an initial discharge capacity of 128.8 mAh g-1 at 0.1 C,and the discharge capacity of the cell is reached to 115.6 mAh g-1 after 100 cycles,which keeps 89.7%of its original capacity.Moreover,the Coulombic efficiency is maintained about 99%during the whole cycle,and the cell exhibit excellent cycling performance at 30 ?.