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• Main Authors: Chen-pin Tuan, 段振斌
• Other Authors: 諸柏仁
• Format: Others
• Language: zh-TW
• Published: 2014
• Online Access: http://ndltd.ncl.edu.tw/handle/6jztm6

碩士 === 國立中央大學 === 化學學系 === 102 === The success in reaching the goals of high power high capacity lithium battery requires the use of electrolytes with sufficiently high ion conductivity that are nonvolatile, retardant to flame, highly electrochemical and highly thermally stable. Room temperature ionic liquid (RTIL) has been explored for this purpose due to its unique properties such as: low vapor pressure, high solubility in polar solvent, and most importantly, high electrochemical and thermal stable window. However, it’s high viscosity, and relatively low ion conductivity has hampered the full cell performance. Another approach widely explored over the past 20 year is the polymer electrolytes where enhancing salt dissociation and ion hopping motion are common goals that have been hampered largely by polymer inherent properties such as smaller free volume, higher chain viscosity, and low dielectric constant. Our previous works disclosed a composite polymer electrolyte using TiO2 nanotube to induce higher salt dissociation, and to provide a direct ion conducting pathway which shows ion conductivity approaching the order of 10-3 S/cm without the use of any volatile electrolyte. In present paper, we disclosed novel electrolyte systems which composed of ionic liquids and a high dielectric polymer PVdF with the addition of small amount of TiO2 nanotube. In this system, the ionic liquids and the lithium salt are completely dissociated and the mobility is raised in presence of TiO2 nanotube. As results, the lithium ion conductivity reached a value of S/cm (25C) and S/cm at 80C. This high ion conducting polymer electrolyte system is tolerating to high voltage, is highly thermally stable and chemical stable. Suitable applications can be found in high energy lithium battery using high voltage cathode, in Li/S, Li/Air or other systems using high capacity anode. Since there is no SEI formation, longer life cycle is expected. As the electrolyte is nonvolatile, higher safety can be guaranteed. Film forming property implies this electrolyte is suitable to be applied to thin film (flexible) battery. Here is the result that increases of ion conductivity with increasing temperature. Commercial electrolyte displayed a value in the order of 10-3 S/cm throughout the temperature measured, with a less temperature dependant property, reflecting lower activation energy in ion transport. In the IL/PVdF composite system, samples 10P10B and 10P20B representing 10 part (by weight) and 20 part of ionic liquids in 10 part of PVdF, which displayed higher ion conductivity than that of commercial liquid electrolyte throughout all temperature range measured. Furthermore, the addition of TiO2 has impacted ion conductivity. With initial increase of TiO2 nanotube to 5wt% (wt% relative to the amount of solvent), conductivity is raised, but it dropped quickly with further addition to 7% or 9 wt%. The improvement in ion conductivity at some optimized TiNT is related to the fact that it assisted in dissociating the salt which allows for more movable ion, and provided a more directed ion conducting channel. And the deteriorated performance at high TiNT content is possibly due to aggregation of inorganic moiety. In these cases with ionic liquids, a steeper slope in the arrheneous plot is found, indicating the ion transport is experiencing higher activation energy process compared to that in the volatile liquid electrolytes. Moreover, we displayed the battery performance using the IL/PVdF composite electrolytes with different IL composition. The capacity is close to that using volatile electrolyte (155mAh/g), and is found to increase continuously, and the interface resistance decrease with increasing of IL content. A capacity value of 147 mAh/g can be realized at 0.05C rate in sample 10P20B. However, the membrane becomes soft and lost it free-standing property when IL exceeds this composition.