Modification, Preparation Of Carboxylated Acrylonitrile Butadiene Rubber Based Polymer Electrolytes And Their Ion Transport Property

In recent decades, much attention was focused on rechargeable lithium batteries due to their characteristic of high specific energy, longer lifespan, environmentally friendly, safety. Liquid electrolytes, existing the danger of solvents leakage, volatilication and flammability, easily cause safety accidents. Gel polymer electrolytes can lower the risk to some extent, but they can not still avoid the use of organic solvents. Solid polymer electrolytes(SPEs), being the most suitable substitutes because of the absent of solvent to address these problems, have been attracted much attention.In this work, a novel kind of borate ester grafted carboxylated acrylonitrile butadiene rubber XNBR(XNBR-B) was synthesized. The chemical structure of XNBR-B were confirmed by FTIR and NMR. DSC indicated that XNBR and XNBR-B were amorphous at room temperature. Both XNBR and XNBR-B had excellent thermal stability, which were verified by TG.Two kinds of rubber-based(XNBR and XNBR) polymer electrolytes(RSPEs) were prepared after doping with bistrifluoromethanesulfonimide lithium salt(Li TFSI). The formation of coordination bonds – C≡N…Li+ in favor of salts dissolving in RSPEs, which was confirmed by FTIR. The effect of the Lewis acidity of borate ester groups grafted into the XNBR on the ionic conductivities and lithium transference numbers has been investigated by comparing XNBR-B/Li TFSI systems with that XNBR/Li TFSI. Although the conductivities of the XNBR-B/Li TFSI electrolytes(3.667×10-8 S/cm) were approximately one order of magnitude lower than that system of XNBR/Li TFSI(2.048×10-7 S/cm) for the enhancement of Tg confirmed by DSC. The maximum of lithium transference number(TLi+) is 0.65 for XNBR-B and 0.54 for XNBR, respectively. Therefore, this result indicated that such borate ester grafted XNBR realize the enhancement of TLi+, which could improve cell performance. The temperature dependence on ionic conductivities of RSPEs obeyed VTF rule. The electrochemical stability of XNBR-B/Li TFSI was up to 4.2 V, which was greater than XNBR/Li TFSI(3.7 V). A passivation layer was formed between a lithium metal electrode and RSPEs by the study of the evolution of the interface resistance over storage times.Composite polymer electrolytes(CPEs) were prepared by adding ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethyl)sulfonyl(BMIMTFSI). The conductivities of CPEs raised with the addition of the BMIMTFSI due to the increase of charge carriers and the reduction of Tg which was confirmed by DSC. It can not obtained a free-standing polymer electrolyte film when the contents of BMIMTFSI exceeded 23%, So the composite polymer electrolyte matrixs was prepared with 23% mass fraction of BMIMTFSI, named as XNBR-B-BMI23 and XNBR-BMI23. The conductivities descended with the increased of the Li TFSI, The conductivities of XNBR-B-BMI23 and XNBR-B-BMI23-Li16.0 were 1.742×10-6 S/cm, 0.903×10-6 S/cm at 30 ℃, respectively. But the TLi+ raised with the addition of the Li TFSI. The maximum of TLi+ was 0.27 for XNBR-B-BMI23-Li16.0 and 0.21 for XNBR-BMI23-Li16.0. This result further indicated that such borate ester grafted XNBR realize the enhancement of TLi+. The temperature dependence on ionic conductivities of CPEs obeyed VTF rule. The electrochemical stability of CPEs was up to 4.2 V. A passivation layer was formed between a lithium metal electrode and CPEs by the study of the evolution of the interface resistance over storage times.