Preparation And Performance Of Novel Cross-linked Polymer Electrolytes

Solid-state batteries,as energy storage devices,play a key role in modern life.The development of solid-state electrolytes is of great significance to improve the safety and energy density of solid batteries.Polymer electrolytes has attracted much attention due to their low cost,non-toxic and relatively soft properties.The poly（ethylene oxide）（PEO）-based polymer electrolyte has been the subject of intensive research,but its low ionic conductivity,poor mechanical strength and interface instability limit its application in solid state batteries.However,inorganic electrolytes limit their large-scale applications due to their high brittleness,poor processability,and instability in air.Therefore,the preparation of polymer electrolytes with high ionic conductivity,good mechanical strength,interface stability,adjustable thickness and suitable for the current lithium-ion battery manufacturing process is an important way to realize the application in solid state batteries.In this thesis,a novel three-dimensional cross-linked network polymer electrolyte was synthesized,and on this basis,a cross-linked polymer electrolyte membrane with a sandwich structure of"external flexibility and internal rigidity"was designed.The effect of the cross-linked network on the electrochemical performance of the electrolyte was subsequently investigated.The main research process is as follows:1.A novel thioctic acid functionalized crosslinking network was synthesized by initiator-free ring-opening polymerization.Compared with the traditional crosslinking network electrolyte,the latent effect of the initiator on the performance of the solid state battery was eliminated by synthesizing without initiator.Thioctic acid functionalization included the synergistic effect of highly polarized sulfur atoms and ether oxygen segments,which accelerated the dissociation of lithium salts and provided a good transport path for lithium ions.The formation of the crosslinking network regulated the distribution of active sites of lithium deposition at the interface and made the process of lithium deposition more uniform.Based on the above reasonable design,the lithium ion conductivity of the polymer electrolyte reaches 0.11 m S cm^-1at 30℃,the activation energy is 0.21 e V,The Li⁺transference number is 0.47,the cycle of symmetrical Li cells is 1800 h,the assembled solid-state battery with Li Fe PO₄as anode and lithium metal as anode can circulate for 300cycles at 0.5 C with a capacity retention rate of 80%,and the pouch cell subsequently assembled has good safety performance.This work shows that the crosslinking network without initiator provides a new method for the preparation of high-performance polymer electrolytes.2.By adjusting the content of polymer electrolyte and using the infiltration coating method matching the manufacturing process of existing lithium ion batteries,the polymer electrolyte membrane with"external flexibility and internal rigidity"sandwich structure was prepared.The outer layer of the polymer electrolyte was used to ensure good interface contact with the electrode when circulating,and the inner layer was used to adopt rigid porous ultrathin separator,and the polymer was poured into the separator pores.The sandwich structure was designed to ensure the overall mechanical strength of the electrolyte and form a continuous lithium ion transport channel.The results show that the polymer electrolyte has excellent flexibility and high mechanical strength（16.8 MPa）,and the electrolyte film thickness is only 13μm.The cycle time of lithium symmetric battery reaches 3000 h.The solid-state battery assembled with Li Fe PO₄as anode and lithium metal as anode can be stably circulated for 200 cycles with a capacity retention rate of 83%.This work offers a promising strategy to realize ultrathinness,high strength,as well as safe solid electrolytes for solid-state lithium-metal batteries.