The Preparation Of Poly(ethylene Oxide)-based Electrolyte And The Study Of Its Performance For Solid-state Li-S Battery

All-solid-state lithium sulfur（Li-S）battery has the advantages of high energy density and high safety and its key component is solid electrolyte.At present,the performance of solid electrolyte is unsatisfactory and limits the application of solid-state Li-S battery.Therefore,it is important to develop high performance electrolyte to improve the performance of all-solid-state Li-S battery.Poly（ethylene oxide）（PEO）,which has electrochemical stability to sulfur cathode and lithium anode,satisfactory mechanical property and high dissociation ability to lithium salts,is appropriately employed as electrolyte for all-solid-state Li-S battery.However,the ionic conductivity at the room temperature of PEO is low and intermediate polysulfide is soluble in the PEO polymer leading to the shuttle of polysulfide during discharge and charge process,which results in capacity attenuation and battery failure.From the perspective of ion transport channel construction and polysulfide adsorption,Nb₂CT_x nanosheet composite PEO electrolyte and Mn-based nanowires/Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）composite PEO electrolyte were prepared by taking advantage of one-dimensional/two-dimensional nanomaterial properties.The detailed research is as follow:（1）The effects of the content and sheet size of Nb₂CT_x nanosheets on the performance of composite electrolyte and solid-state Li-S battery were investigated,and the mechanism of improved performance by Nb₂CT_x nanosheets was analyzed.Nb₂CT_x MXene with sheet sizes of 500nm-300 nm,300 nm-100 nm and below 100 nm was prepared by etching,intercalation and sonication in vacuum.The Nb₂CT_x MXene composite PEO electrolytes were prepared by solvent casting.The lithium ion（Li⁺）conductivity of PEO integrated 3%Nb₂CT_xMXene with sheet size of below 100 nm reaches 0.97×10^-4 S cm^-1,which is 5.4 times higher compared with PEO at 60°C.A high capacity of 1149 m Ah g^-1 at 0.5C and a cycle life of 200 cycles are obtained for all-solid-state Li-S battery.The promoted performance attributes to（1）Nb₂CT_x MXene facilitates the dissociation of lithium salts,looses the interaction between PEO and lithium salts and improves ionic conductivity;（2）polysulfide is effectively adsorbed with Nb₂CT_x MXene by forming Nb-S bonding.（2）In order to further improve the ionic conductivity,the Mn-based nanowires and LLZTO were introduced to construct a three-dimensional Li⁺transport network.Mn-based nanowires were prepared by hydrothermal method.Mn-based nanowires/LLZTO composite PEO electrolyte was prepared by solvent casting,and the effects of content of Mn-based nanowires and interaction between Mn-based nanowires and LLZTO on the performance of composite electrolyte and solid-state Li-S battery were investigated.PEO-based electrolyte with 5%Mn-based nanowires and 10%LLZTO have highest Li⁺conductivity of 0.35×10^-4 S cm^-1 at 55°C.A preferable capacity of 1524 m Ah g^-1 under 0.2C is obtained for all-solid-state Li-S battery at 55°C.The cycling life of all-solid-state Li-S battery is improved from below 10 cycles using PEO electrolyte to 100 cycles using composite electrolyte.The improved performance ascribes to（1）The dissociation of lithium salt is further promoted by polar group on the surface of Mn-based nanowires leading to the enhancive Li⁺concentration in the electrolyte,and the rapid conduction of Li⁺is promoted by LLZTO.（2）Mn-S bonding are formed between the Mn-based nanowires and soluble polysulfide,resulting in the inhibition of shuttle effect.