P(VdF-HFP)-基离子液体复合聚合物电解质的阴极稳定性及热稳定性

以聚偏氟乙烯-六氟丙烯P(VdF-HFP)聚合物为基体, 制备了含离子液体1-甲基-3-乙基咪唑六氟磷酸盐(EMIPF6)、用于锂离子电池的离子液体复合聚合物电解质P(VdF-HFP)/LiPF₆/EMIPF₆/EC(碳酸乙烯酯)-PC(碳酸丙烯酯)]. 采用热重分析法以及燃烧实验测试了复合聚合物电解质的热稳定性. 离子电导率测试表明, 离子液体的存在显著改善了复合聚合物电解质的离子传输; 循环伏安测试表明, 添加剂EC和PC的加入提高了复合电解质的阴极稳定性, 制得的离子液体复合聚合物电解质在0.3-4.3 V 电压范围内稳定存在. Li₄Ti₅O₁₂ 和LiCoO₂为电极材料、P(VdF-HFP)/LiPF₆/EMIPF₆/EC-PC 为电解质的半电池表现出优良的循环性能, 0.1C充放电倍率下, Li/LiCoO₂和Li/Li₄Ti₅O₁₂半电池的可逆容量分别为130和144 mAh·g^-1. 但EC、PC在一定程度上降低了离子液体复合聚合物电解质的热稳定性.

Cathodic and Thermal Stabilities of the P(VdF-HFP)-Based Ionic Liquid Composite Polymer Electrolyte

We report on a composite polymer electrolyte containing the ionic liquid 1-ethyl-3 methylimidazolium hexafluorophosphate (EMIPF6). This composite polymer electrolyte is based on the poly(vinylidene fluoride-co-hexafluoropropylene) (P(VdF-HFP)) polymer matrix and is a potential electrolyte for use in lithium ion batteries. The ionic conductivity of the composite polymer electrolyte was measured by electrochemical impedance spectroscopy (EIS). Linear sweep voltammetry (LSV) was performed to investigate the electrochemical stability window of the polymer electrolyte. The thermal properties for the composite polymer electrolyte were also characterized by thermogravimetry (TG) and by a flammability test. The results show that the presence of the EMIPF6 ionic liquid increases the ion transport properties greatly but a better cathodic stability is only obtained by the addition of organic additives such as ethylene carbonate-propylene carbonate (EC-PC), which extends the cathodic stability to 0.3 V. This corresponds to an electrochemical stability window of 0.3-4.3 V. The selected Li4Ti5O12 anode and LiCoO2 cathode materials exhibit acceptable electrochemical performance in combination with the prepared P(VdF-HFP)/LiPF6/EMIPF6/EC-PC composite polymer electrolyte. At a charge-discharge rate of 0.1C, Li/LiCoO2 and Li/Li4Ti5O2 have reversible capacities of 130 and 144 mAh·g-1, respectively. However, the corresponding thermal performance is suppressed because of the presence of organic additives.