電場誘導高導電度TiO_2奈米陶瓷高分子複合電解質

Electric Field Poling of TiO_2 and Polymer Composite Electrolytes for Lithium Ion Battery

鄭兆軒(Zhao-Xuan Zheng) ； 諸柏仁(Peter Po-Jen Chu)

《化學》 76卷3期 (2018/09) Pp. 175-192

https://doi.org/10.6623/chem.201809_76(3).008

摘要

鋰離子電池廣泛使用在電子產品當中的電池，是重要的儲能裝置之一。固態高分子電解質薄膜改善安全性及耐用性成為下是代鋰電池發展的關鍵材料之一。雖具有諸多的優點，但在離子導電性以及與電極之間的界面相容性還是比傳統的液體電解質差，因此提升離子導電度以及改善界面相容性就成為固態高分子電解質首要發展的目標。本研究中，我們開發一新穎的無揮發性固態電解質展現高離子導電度及與電極展現良好的介面接合。此材料是利用離子液體[EMIM]^+[FSI]^-和TiO_2奈米顆粒添加到PVDF-HFP及PMMA混摻高分子薄膜中，並且浸泡離子液體。經電場極化後，橢圓的TiO_2奈米顆粒在高分子非結晶區被誘導產生有序順向排列，形成有利離子更直接傳導的機制。此外高介電TiO_2奈米顆粒可以有效的減弱離子液體的鍵結，釋放出鋰離子提供更高的電荷運輸。因此室溫下導電度達到1.16 × 10^(-3) S/cm，在TiO_2奈米顆粒添加至3%並且在80 °C下導電度可到達4.52 × 10^(-3) S/cm。此外由於PVDF/PMMA與電極的黏合性能，降低了電極電解質介面電阻有利於充放電。使用包含離子液體和TiO_2顆粒的固態高分子電解質以及磷酸鋰鐵作為陰極的鋰半電池，展現了優異且穩定的循環容量；在100圈充電和放電循環後在0.2C下仍然保持在140 mAh/g。

關鍵字

固態高分子電解質 ； 電場極化 ； 全固態鋰電池 ； 離子傳導機制 ； 介面電阻 ； 循環壽命

並列摘要

Lithium-ion battery is an important energy storage device, widely used in electronic products. In order to improve the durability and safety, solvent free polymer electrolyte becomes one of the critical components to meet the growing challenge. Although with many promising material advantages, solid polymer electrolyte is far inferior to the liquid electrolyte in ionic conductivity. A second drawback is the huge interface resistance between the electrolyte and the electrodes, due to the voids created by incomplete adhesion of the two solids. In this paper, we report novel solid polymer electrolytes where ionic liquid [EMIM]^+ [FSI]^- and TiO_2 nanoparticles were impregnated with polymer blends of PVDF-HFP and PMMA. Under electric field poling, the oval shape TiO_2 nano-particles is re-oriented with preferentially ordered arrangement in non-crystalline regions of the polymer blends which served to facilitate fluent ion migration induced in more straight forward manner. Furthermore, high dielectric constant of TiO_2 nanoparticles weakens the ionic force within ionic liquid which liberates lithium ion for better transport. Both factors contribute to appreciable increase of ionic conductivity of 1.16 × 10^(-3) S/cm at room temperature. In the composite electrolyte samples, ionic conductivity of 4.52 × 10^(-3) S/cm at 80 °C can be achieved with the addition of 3% TiO_2 nanoparticles. Although the mobility of the polymer is still not high at room temperature, the ordered arrangement created by electric field poling, and the high dielectric constants originated from the nano particles establishes favorable ionic liquid conduction mechanism. In combination with the superb PVDF/PMMA adhesion properties with the electrodes, the interface resistance is substantially reduced. Lithium battery half cells using the solid polymer electrolytes containing ionic liquids and TiO_2 particles, with lithium iron phosphate as a cathode, show stable cyclic capacity maintain at 140 mAh/gat 0.2 C discharge rate, after 100 charge and discharge cycles.

並列關鍵字

Solid polymer electrolyte ； Electric field polarization ； All solid state lithium battery ； Ion conucting mechanism ； Interface resistance ； Cycle life