| 학회 | 한국고분자학회 |
| 학술대회 | 2005년 가을 (10/13 ~ 10/14, 제주 ICC) |
| 권호 | 30권 2호 |
| 발표분야 | 기능성 고분자 |
| 제목 | Impedance and Lithium-7 NMR Studies of Solvent-Free Polymer Electrolytes Having Pores Filled with Viscous P(EO-EC)/LiCF3SO3 |
| 초록 | In previous studies1,2, the solvent-free polymer electrolytes based on porous poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)]/poly(ethylene oxide-co-ethylene carbonate) [P(EO-EC)] membranes filled with viscous P(EO-EC)/LiCF3SO3 were prepared. These polymer electrolytes showed relatively high ionic conductivity (ca. 3.7 × 10-5 S cm-1 at 25 °C) and wide electrochemical stability window (0.6 ~ 5.0 V). In this study, in order to study a better understanding of the Li-ion mobility in polymer electrolytes, we report on impedance and 7Li NMR measurements as a function of temperature in a series of polymer electrolytes with various P(EO-EC)/LiCF3SO3 contents. Ionic conductivity was determined by complex impedance measurements, using a Zahner Electrik IM6 impedance analyzer. The 7Li solid-sate NMR measurements were performed, using a modified Bruker CXP 300 NMR spectrometer operating at a 7Li resonance frequency of 155.4 MHz. The ionic conductivity of polymer electrolytes obeying Arrhenius behavior increased with increasing the P(EO-EC)/LiCF3SO3 content in polymer electrolytes. The Li-ion mobility was investigated by measuring the linewidth of 7Li NMR spectra (그림 1). At the lowest temperature, the linewidths were very broad. This implies that the Li-ion is essentially immobile and thus the observed linewidths are the result of increased quadrupolar or internuclear dipole-dipole interactions. As the temperature increased, the Li-ion mobility increased enough to average out dipolar interaction, thereby producing a line narrowing. Fig. 1. 7Li NMR spectra obtained for the polymer electrolyte with 40 wt% P(EO-EC)/LiCF3SO3 content. An estimation of the activation energy for polymer electrolytes can be obtained using Bloemvergeon-Purcell-Pound (BPP) theory. The temperature dependence of the correlation time is assumed to follow Arrhenius behavior, which activation energies for Li-ion mobility are determined3: The slope of the plot of ln τc against T-1 yields Ea. Interestingly, the Arrhenius plots of τc for all polymer electrolytes were composed of two different regions separated by low and high temperature range and each plot showed linear type. This result is well consistent with linear behavior observed from impedance experiments in the same temperature range. It means that there is an abrupt decrease of ion mobility with decreasing temperature near 275 - 280 K (denote hereafter as Tsc, temperature at slope change) corresponding to the rapid change in the slope of the correlation time. Therefore, it is noteworthy to determine Tsc related to the abrupt deterioration of characteristic parameters (e.g., activation energy and ionic conductivity). Overall results indicate that high Li-ion mobility contributes to high conductivity because it is related to the number of charge carriers and Li-ion mobility. 참고문헌 1. J.-D. Jeon, B. W. Cho, and S.-Y. Kwak, J. Power Sources, 143, 219 (2005). 2. J.-D. Jeon, S.-Y. Kwak, and B. W. Cho, J. Electrochem. Soc., 152, XXX (2005). 3. N. Bloembergen, E. M. Purcell, and R. V. Pound, Phys. Rev., 73, 679 (1948). |
| 저자 | 전재덕, 곽승엽 |
| 소속 | 서울대 |
| 키워드 | polymer electrolytes; porous membranes; lithium NMR |
