原位聚合法制备凝胶型离子液体／PMMA聚合物电解质

Gelled Ionic Liquid/PMMA Polymer Electrolyte Prepared by Radical Polymerization

采用原位聚合法制备了含有N-甲基、丙基哌啶双三氟甲磺酰亚胺离子液体的凝胶型聚合物电解质．利用SEM和XPS测试了电解质膜与LiFePO4电极的界面状态，充放电循环后，在电解质膜与LiFePO4之间有一层薄膜，这层薄膜中含有N和S元素．结果表明，随着充放电的不断进行，凝胶型电解质中未聚合的甲基丙烯酸甲酯与电极表面的锂离子之间发生电子转移，形成SEI膜，至少要三个循环后才能形成稳定的SEI膜．随着SEI膜的增厚，放电容量增加，阻碍了电子转移，使系统更加的稳定．在不同倍率下测试了凝胶型离子液体／PMMA聚合物电解质电池性能，当充放电达到30个循环时，0．2、0．5和1C下电池比容量分别为132、128和120mAh／g．

The gel polymer electrolyte containing N-propyl, methylpyrrolidinium bis（（trifiuoromethyl） sulfonyl）imide （PYR13TFSI） with better performance is prepared by radical polymerization method. The interface status between the LiFePO4 electrode and the electrolyte is characterized by a scanning electron microscope and X-ray photoelectron spectroscopy （XPS）. There is a layer of membrane on the gel electrolyte and perfect shell membranes on the surface of active LiFePO4 cluster, on the other hand, N and S photoelectron signals are observed in XPS spectra after charge-discharge cycles. The results show that the ionic liquids and unpolymerized methyl methacrylate incorporate into the electrode surface and form the SEI membrane with Li ion and electrons while the gel electrolyte contacts with the electrode. The formation process of the SEI membrane needs at least three cycles, the discharge capacity increases as the SEI membrane becomes sufficiently thick, which blocks further electron transfer, and the system may approach steady state. The performance of cell with ionic liquid gel polymer electrolyte is measured at different rate. The cells retain 132 mAh/g at 0.2 C, 128 mAh/g at 0.5 C, and 120 mAh/g at 1.0 C after 30 cycles with charge-discharge efficiency of ca. 98% at every rate.