利用化學分析電子能譜及自製真空系統來探討LiTFSI, NaTFSI, KTFSI 三種離子液體電擴散及固態電解質介面層

Abstract

鋰電池在現今不只要求要高效能，更重要的是安全。離子液體以熱穩定性佳，因此在最近十年提升了許多研究興趣。除了選擇更好的電解液，固態電解質介面層的生成也是離電池安全的關鍵之一，由於可以避免鋰金屬滲入電極而短路。因此，可以藉由電擴散來理解表面之間的作用力。當今鋰電池，鈉和鉀電池的討論也日益上升因此我們選用 LiTFSI, NaTFSI, KTFSI 並以 EmimTFSI 當作溶劑來配置。藉由這些離子液體在一個真空的腔體內進行電化學，最後利用光學顯微鏡同步看到電擴散的現象。電擴散的能力會因為鹼金族離子而增強，前提是未加到飽和濃度。我們利用化學分析電子能譜去釐清經由電擴散後表面的離子的分布，利用陰陽離子的比例發現 KTFSI 的液珠邊緣富含陰離子，相較於 EmimTFSI, LiTFSI, NaTFSI 的液珠邊緣富含陽離子。最後固態電解質介面層可以利用化學分析電子能譜中的氮、硫以及深層頗析來說明其組成方式。我們的實驗可以幫助了解藉由 EmimTFSI, LiTFSI, NaTFSI 和 KTFSI 之間的電擴散差異及生成的固態電解質介面層。

Nowadays, Li-ion battery aims for not only high performance but also safety. Therefore, ionic liquids due to its thermal stability has raise interest in the past decade. Furthermore, the formation of SEI is crucial for the safety and prevents short circuit from lithium dendrite. Hence, the interaction between electrode and IL can be analyze with electrowetting. Due to the increase interest of Na-ion and K-ion battery, we select LiTFSI, NaTFSI, KTFSI with EmimTFSI as solvent to conduct electrochemical experiment in a vacuum chamber, therefore, observing the electrowetting in-situ with the optical microscope. The electrowetting ability will increase by adding alkali ion before critical concentration. We use XPS to determine the distribution of the interface after electrowetting with the ratio of cation/anion, and KTFSI has more anion on the electrowetting edge, where EmimTFSI, LiTFSI, NaTFSI have more cation. At last, we find out the SEI formation by compare the XPS signal of N, S and depth profile. Our work helps the understanding of electrowetting and the formation of SEI for EmimTFSI, LiTFSI, NaTFSI and KTFSI.