The Preparation And Performance Study Of ROMP-type Imidazolium-Functionalized Norbornene Ionic Liquid Block Copolymer And Their Lithium Polyelectrolyte Membranes

Lithium-ion batteries have been attracted widespread attention by the virtue of their high energy density, high working voltage, good cycle performance and light quality. Lithium-ion batteries not only have a widely application in portable electronics, such as laptop, cell-phone and camera, but also occupy an important place in the field of electromobile, electric bicycle and aviation. Solid polymer electrolytes own the good film formation, superior safer performance and battery processability, it can overcome the leakage, deformation, firing and exploding which often caused by the traditional liquid electrolytes. Polymerized ionic liquid(PIL) electrolytes as a new type of solid polymer electrolytes, they have the properties of non-flammability, low vapor pressure, high conductivity and thermostability of ionic liquids, as well as the features of machinability and size controllability from polymers. PIL block copolymers have the properties of self-assembly and ionic conduction and become one of the research hotspots as solid polymer electrolytes, but have the issue of low ionic conductivity. In the text, considering the low ionic conductivity of solid polymer electrolytes, we designed the new norbornene ionic liquids with the imidazole functional group and the corresponding block copolymers via ring-opening metathesis polymerization(ROMP). The solid polymer electrolyte membranes were prepared by blending the block copolymers with lithium salt. Besides, adding nano-SiO2 can improve its conductivity. The details are as follows:(1) Imidazolium-functionalized norbornene ionic liquid block copolymers are synthesized via ring-opening metathesis polymerization(ROMP). The solid polyelectrolytes were prepared by blending the copolymers with various contents of lithium bis(trifluoromethanesulphonyl)imide. The effects of the polymerized ionic liquid(PILs) compositions on the properties, morphology, and ionic conductivity of the polyelectrolytes are investigated. The polymer with 50.7 mol% PIL displays a long-range ordered lamellar structure, and its corresponding polyelectrolyte achieves the best ionic conductivity with 7.44×10-6 S/cm at 30 oC and 4.68 ×10-4 S/cm at 100 oC, respectively. The ionic conductivity is enhanced by 1 order of magnitude compared to the polyelectrolytes with lower polymerized ionic liquid block compositions. In addition, the polyelectrolytes are electrochemically stability up to 4.2 V, indicating they have good electrochemical property.(2) To further improve the mechanical properties and conductivity of the copolymers, we designed and synthesized a benzene-functionalized norbornene, and copolymerized with the imidazolium-functionalized norbornene ionic liquid to afford diblock copolymers(P(NPh-b-NIm-TFSI)).(The different molar ratios of PIL block are 42.6%, 55.7%, and 64.9%). We prepared the P(NPh-b-NIm-TFSI)/LiTFSI electrolyte membrane and P(NPh-b-NIm-TFSI)/LiTFSI/SiO2 composite electrolyte membrane, discover that adding nano-SiO2 can improve the conductivity obviously. Then we studied the influence of SiO2 content on conductivity of polymer electrolyte. The best conductivity of P(NPh-b-NIm-TFSI)/20 wt.%LiTFSI/10 wt.%SiO2 composite polymer membrane with 7.7×10-5 S/cm at 30 oC and 1.3×10-3 S/cm at 100 oC was obtained,respectively.