Synthesis And Electrochemical Performance Of Solid State Electrolytes Based On Polysiloxane Grafted Polyethylene Oxide

Electrolytes play a vital role in determining the energy density,charging/discharging cycling stability,safety property of the lithium ion battery.Conventional liquid electrolyte suffer from the leakage,volatilization,and flammability,which may cause severe safety issues.Solid state polymer electrolytes are proposed to be safer alternatives to the liquid electrolytes.However,solid-state polymer electrolytes display a low ionic conductivity and a low lithium ion transference number at ambient temperature.In this paper,solid state electrolytes based on polysiloxane grafted polyethylene oxide were prepared and studied about their electrochemical properties.A poly(ethylene oxide)-substituted polysiloxane was synthesized via hydrosilylation.The polymer electrolytes(SCPE)were prepared by cross-linking polysiloxane and α,ω-diallyl poly(ethylene glycol).The conductivity of the SCPE effected by lithium salt concentration was investigated by electrochemical impedance spectroscopy,a high conductivity of 1.74 × 10-4 S/cm at room temperature was obtained when EO:Li was 20:1.Electrochemical stability of SCPE was studied by linear scanning voltammetry,and a wide electrochemical window of 5.0 V(vs.Li+/Li)was observed.LiFePO4/Li battery based on this polymer electrolyte showed a discharge capacity of 130 mAh/g at 0.15 C after 30 cycles.Ionic conductivity and electrochemical window of SCPE were improved when succinonitrile(SN)was added.In order to improve the lithium ion transference number,a novel lithium 4-styrenesulfonyl(perfluorobutylsulfonyl)imide was synthesized,the highly delocalized anionic charges of-SO2-N(-)-SO2-C4F9-have a weak association with lithium ions,resulting in the increase of mobile lithium ions number.Then anion of lithium salt and poly(ethylene oxide)were grafted on polysiloxane via hydrosilylation and then cross-linked by α,ω-diallyl poly(ethylene glycol)to form single ion conducting polymer electrolyte(SPE).Chemical structure of lithium salt and polymer were characterized by FTIR and NMR.Thermal properties of SPE were studied by DSC and TG and it exhibited the designed polymer electrolytes possessed ultra-low glass transition temperature and good thermal stability.Electrochemical properties of SPE were investigated by EIS and LSV.A remarkably high conductivity of 3.7 × 10-5 S/cm at 30 ℃ was observed.Electrochemical window of SPE reached 5.2 V(vs.Li+/Li)and a high lithium ion transference number of 0.80 was also observed.