| Not only polymerized ionic liquid (PIL) electrolytes have the merits of ionic liquid electrolytes, such as non-volatile, non-flammable and high ionic conductivity, but also they have the characteristics of polymer electrolytes including dimensional stability, high mechanical strength, free-leakage, easy processing etc. PIL electrolytes are new sorts of safety electrolytes. In this paper, a new series of solid and gel PIL electrolytes based on guanidinium cations have been synthesized, and their thermal and electrochemical properties including thermal decomposition temperature, Tg, ionic conductivity, lithium redox in the electrolytes and electrochemical stability have been characterized. Furthermore, three gel PIL electrolytes have been used as new polymer electrolytes in lithium secondary batteries.Gel polymer electrolytes composed of PVdF-HFP microporous membrane incorporating a guanidinium-based ionic liquid with 0.8 mol kg?1 lithium bis(trifluoromethanesulfonylimide) are characterized as the electrolytes in Li/LiFePO4 batteries. The ionic conductivity of these gel polymer electrolytes is 3.16×10-4 and 8.32×10-4 S cm-1 at 25 and 50℃, respectively. The electrolytes show good interfacial stability toward lithium metal and high oxidation stability, and the decomposition potential reaches 5.3 and 4.6 V (vs. Li/Li+) at 25 and 50℃, respectively. Li/LiFePO4 cells using the PVdF-HFP/1g13TFSI-LiTFSI electrolytes show good discharge capacity and cycle stability, and no significant loss in discharge capacity of the battery is observed over 100 cycles. The cells discharge the capacity of 142 and 150 mAh g-1 at the 100th cycling at 25 and 50℃, respectively.A series of guanidinium PIL electrolytes combining different anions, such as BF4-, PF6-, ClO4- and N(CF3SO2)2-, were synthesized through copolymerization and anion exchange reaction as new promising solid polymer electrolytes. The PILs present different decomposition temperature and glass transition temperature (Tg) , and their thermal properties strongly depend on the sort of anions. The 1g2-MA-BF4 possesses the better thermal stability and it decomposes at 353℃. The 1g2-MA-TFSI shows the lower Tg and it is below -60℃. The ionic conductivity of the PIL electrolytes depends on the lithium salts used and its content. The best ionic conductivity of the PILs electrolyte 1g2-MA-BF4/LiBF4 (30 wt %) was 1.35×10-4 S cm-1 at 30℃. The electrochemical properties of solvent-free, quaternary polymer electrolytes based on a novel PIL, 1g3-MA-TFSI as polymer host and incorporating 1g13TFSI ionic liquid, LiTFSI salt and nano-scale silica are reported. The PIL-LiTFSI-1g13TFSI-SiO2 electrolyte membranes are found to be chemically stable even at 80℃in contact with lithium anode and thermally stable up to 320℃. Particularly, the quaternary polymer electrolytes exhibit high lithium ion conductivity at high temperature, wide electrochemical stability window, time-stable interfacial resistance values and good lithium stripping/plating performance. Batteries assembled with the quaternary polymer electrolyte at 80℃are capable to deliver 140 mAh g-1 at 0.1C rates with very good capacity retention.PILs having cyclic guanidinium cations with different counter anions, such as PF6- and TFSI-, were synthesized by copolymerization of a guanidinium ionic liquid monomer with methyl acrylate, and an anion exchange reaction afterwards. Furthermore, incorporating a guanidinium ionic liquid, LiTFSI salt and nano-size SiO2, a quaternary gel polymer electrolyte based on one of the PILs as the polymer host was prepared. The quaternary gel polymer electrolyte was chemically stable even at a higher temperature of 80℃in contact with lithium anode. Particularly, the electrolyte exhibited high lithium ion conductivity, wide electrochemical stability window and good lithium stripping/plating performance. Li/LiFePO4 Batteries with the quaternary gel polymer electrolyte at 80℃had capacities of 140 and 130 mAh g-1 at 0.1 and 0.2 C current rates, respectively.
|
PDF Full Text Request