常壓電漿技術表面改質磷酸鋰鐵電極於鋰離子電池效能提升之研究

能源議題在近十幾年來不斷地被提出發展新技術，其中電動車發展被全球各國重視，而鋰離子電池由於能量密度高被視為適用於電動車之儲能。而磷酸鋰鐵（LiFePO_4）為廣為使用之正極材料，然而其導電度及高溫性能仍具改善之空間，因此為近年來之主要研究重點。本研究主旨為以利用常壓射頻電漿對LiFePO_4正極材料進行表面改質，藉由接枝親水官能基於正極材料表面，並形成非晶質含碳化合物相，以期達成在高溫下對磷酸鋰鐵正極材料之保護性提升，同時避免Fe離子自結構中釋出以改善電容量衰退之情形。由光放射光譜（Optical Emission Spectroscopy; OES）所獲取之電漿物種分析結果得知電漿內部物種含有氫氧官能基、氧自由基與激發態氬氣等。從水接觸角實驗結果顯示，LiFePO_4電極經電漿處理後接觸角126.8°大幅降低至電漿改質掃描次數3次（PA3）的55.1°，其中經過電漿改質次數6次的試片（PA6），具有最親水之水接觸角角度（18.9°）。從Raman分析中可得知，此電極的石墨化比例些微下降，故確認常壓射頻電漿處理6次的LiFePO_4具有較多之親水官能基之接枝於正極表面。高溫（55℃）電性測試結果得知，在電容量之提升首圈放電電容量：original，161.4 mAh/g；PA6，165.9mAh/g及經高溫充放電35迴圈電容量：original，149.7 mAh/g；PA6，158.6mAh/g，衰退率為：original，7.24%；PA6，4.40%，本研究確實有效改善磷酸鋰鐵正極材料應用於鋰離子電池之高溫操作環境電池性能。

關鍵字

鋰離子電池；正極材料；磷酸鋰鐵；常壓電漿

並列摘要

The development of electric vehicle (EV) attracts lots of attention in the world due to the energy issue in recent decades. Lithium ion battery is considered as an alternative storage on EV because of its high energy density. LiFePO_4 is one of the most popular cathode materials that applies to EV regarding several advantages, such as the low price, long cycle life, environmental safety and high specific energy, respectively. However, LiFePO_4 is limited to its application on EV according to the low electric conductivity at room temperature and low cyclic stability at high temperature operation. In order to ovecome those drawbacks, many efforts have been made to improve the electrochemical performance at high temperature and the electric conductivity of this material. This research is to demonstrate the LiFePO_4 is treated by radio frequency atmospheric pressure plasma jet (APPJ) for improving the electrical performance and cyclic stability at high temperature. From the result of optical emission spectroscopy, the generated plasma species composed of hydroxyl radicals, oxygen-related radicals and excited argon atoms, which were proved to alter the surface properties of the materials. Furthermore, APPJ treatment results in the plasma-induced grafting of hydrophilic functional groups and formed a core-shell structure of LiFePO_4, which the shell presents an amorphous layer. The original LiFePO_4 sample has a discharge capacity of 149.7 mAh g^(1) and decay rate of 7.24% at high temperature operation of 55°C. For the plasma-treated LiFePO_4 for 6 times (PA6) samples, the higher discharge capacity (165.9 mAh g^(-1)) and better cyclic stability (decay rate of 4.40%) at high temperature of 55°C were evidently achieved. It can be contributed that the functional layer grafted on LiFePO_4 electrode processed the suppressing iron dissolution from the structure.

並列關鍵字

Lithium-ion batteries ； cathode material ； lithium iron phosphate ； Atmospheric Pressure Plasma Jet

國際替代計量

常壓電漿技術表面改質磷酸鋰鐵電極於鋰離子電池效能提升之研究

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