Synthesis Of PEO-based Polymer Electrolyte And Its Application To All-solid-state Lithium Sulfur Battery

In recent years,research on lithium-sulfur(Li-S)batteries has received much attention.This is because the sulfur positive electrode and the lithium metal negative electrode have a high theoretical specific capacity(lithium metal-3800 mAh g-1,sulfur?1675 mAh g-1).Also,sulfur is considered to be the most promising cathode material for secondary lithium batteries,due to its advantages of low price and environmental friendly,However,the practical application of conventional liquid Li-S batteries is still obstructed by several critical issues,such as lithium ploysulfides shuttle effect,long-term stability of lithium metal anode with organic liquid electrolytes and the safety concerns related to the lithium anode and liquid electrolyte.All-solid-state Li-S batteries using solid state electrolytes are considered as one of the most promising techniques to address the safety challenges of lithium ion batteries.Herein poly(ethylene oxide)(PEO)-based solid polymer electrolytes are prepared and investigated as electrolyte membranes for all-solid-state Li-S batteries.PEO/LiTFSI polymer electrolytes with different[EO]/[Li+]were prepared and applied to lithium sulfur batteries.It is found that although the PEO/LiTFSI(EO/Li+=8)electrolyte has higher ionic conductivity,the PEO/LiTFSI(EO/Li+=20)electrolyte shows lower interfacial resistance and higher interfacial stability with lithium anode.Li|PEO/LiTFSI(EO/Li+=20)|Li symmetric cells exhibits very stable evolutions of voltage w:ithout obvious erratic values or Li infiltration even over 300 h at 60 ? and current density of 0.1 mA cm-2.However,the PEO/LiTFSI(EO/Li+=8)based one fails due to intern short circuit after being cycled for less than 75 h.The polymer Li-S cells comprising PEO/LiTFSI(EO/Li+=20)electrolyte delivers a high first discharge capacity of 934 mAh/g and good cycling stability with a capacity retention of 917 mAh/g after 16 cycles at 60 ?.In contrast,the PEO/LiTFSI(EO/Li+=8)electrolyte based cells are not able to charged normally with severe overcharge even at the first cycle,due to the poor interfacial stability of PEO/LiTFSI(EO/Li+=8)electrolyte with lithium anodeTo further improve the electorchemical performance of PEO/LiTFSI(EO/Li+=20)electrolyte,composite polymer electrolyte membranes are fabricated by incorporation of Li10SnP2S12 into PEO matrix using a solution casting method.The incorporation of Li10SnP2S12 plays a positive role on Li-ionic conductivity,mechanical property and interfacial stability of the composite electrolyte,thus significantly enhances the electrochemical performance of solid state Li-S battery.The optimal PEO-1%LiIOSnP2Si2 electrolyte presents a maximum ionic conductivity of 1.69×10-4 S cm-1 at 50 ? and highest mechanical strength.The possible mechanism for the enhanced electrochemical performance and mechanical property is analyzed.The uniform distribution of Li 10SnP2S12 in PEO matrix inhibits crystallization and weakens the interactions among the PEO chains.The PEO-1%Li10SnP2S12 electrolyte exhibits lower interfacial resistance and higher interfacial stability with lithium anode than pure PEO/LiTFSI electrolyte.The Li-S cell comprising PEO-1%Li10SnP2S12 electrolyte exhibits outstanding electrochemical performance with high discharge capacity(ca.1000 mAh g-1),high coulombic efficiency and good cycling stability at 60 ?.Most importantly,PEO-1%Li10SnP2S12 based cell still possesses attractive performance with high specific capacity(ca.800 mAh g-1)and good cycling stability even at 50 ?,where the PEO/LiTFSI based cell can't be successfully discharged due to the low ionic conductivity and high interfacial resistance of PEO/LiTFSI electrolyte.