電漿改質隔離膜以提升鋰離子電池之效能

Performance Improvement of Lithium-Ion Batteries Using Plasma-Modified Separators

林紀呈(Chi-Cheng Lin)

指導教授 ： 莊瑞鑫

元智大學/工程學院/化學工程與材料科學學系/碩士(2012年)

https://doi.org/10.6838/YZU.2012.00162

摘要

本研究主要係探討鋰離子電池元件之商購隔離膜透過電漿表面改質後，其表面物化性、電池電性表現之情形。本文主要分為三部份，首先第一部份為使用氣旋式常壓電漿反應器進行表面改質，探討在純氬氣電漿系統下最適化條件。發現系統參數於處理時間90 s、功率100 W、氣體流率10 slm及基材至氣體噴頭距離10 mm時，隔離膜表面有最佳活化之效果；並以老化實驗探討電漿活化對膜材表面之時效性。
第二部份為使用前者推估之最佳參數，以丙烯酸(Acrylic acid)為單體，使用常壓氬氣電漿誘導接枝於隔離膜上，以不同濃度、溫度及反應時間作為參數，並以重量法測定接枝率；並可由FTIR上波數1710 cm-1之C=O特性峰可確認膜材已成功接上具有羧基之丙烯酸單體，透過XPS分析膜材，結果顯示其表面氧碳元素含量比例皆有明顯上升之情形，再DSC分析改質前後之隔離膜，發現膜材不因接枝程序造成熱穩定性偏差；從SEM觀測改質前後之膜材，其表面差異並不大，因此我們亦使用多孔性材料孔洞分析儀(CFP)分析隔離膜內部孔徑之變化，發現改質後隔離膜平均孔徑有增大的現象，並隨接枝率上升膜材內孔洞減小；另外，我們也以電解液1 M LiPF6, EC/EMC/DMC; 1:1:1 (wt%)對隔離膜進行濕潤性之測試， 其中接枝率0.54%與未改質隔離膜相比有4.5倍吸附量之差距。
第三部份則是利用交流阻抗分析儀與充放電儀對鈕扣型鋰離子電池進行電性測試。結果顯示，電池內阻抗從未改質之52 ohm降至電漿活化之37 ohm，接枝率0.54%則降至29 ohm，代表常壓氬氣電漿活化與接枝處理可有效降低電池內阻抗；而在電容量表現方面，電漿活化與接枝0.54%處理之膜材在鋰電池電容量表現上分別從83.4 mAh/g提升至91.3 mAh/g與95.4 mAh/g，在5C、50次循環充放電下未改質之衰退率達13.7%，改質後膜材則可減緩至2.1%，以上皆證明改質隔離膜能夠提高電池效能及改善循環壽命。

關鍵字

隔離膜 ； 鋰離子電池 ； 電漿改質 ； 接枝

並列摘要

In this study, cyclonic atmospheric-pressure plasma was employed to modify the separator surfaces of lithium ion battery to improve the performance of battery. Physical and chemical properties, thermal stability, wettability were analyzed. The surface of separator became highly hydrophilic when it exposed to the cyclonic atmospheric-pressure plasma at 100 W, 10 slm for 90 s. This optical activation could maintain for 24 h.
The acrylic acid (AA) was used as the grafting monomer for the surface grafting on separator surface. The C=O peak at 1710 cm-1 of plasma modified separator was found from FTIR analysis, indicating that acrylic acid was grafted on the separator. In the XPS analysis, the amount of O/C obviously increases. The temperature melt of the grafting modified separator analyzed by DSC slightly since that the thermal stability couldn't be affected by the modification of AA grafting. Surface morphological changes on the plasma modified separator were characterized by FESEM. The mean pore size of modified separator increased analyzing by CFP. The wettability of 0.54% AA modified separator dipping in 1 M LiPF6, EC/EMC/DMC; 1:1:1 (wt%) electrolyte were 4.5 times higher than the untreated one.
The electric properties of modified separator were analyzed by the AC impedance and charging-discharging equipments. The results showed that the impedance reduced from 52 ohm to 37 ohm and 29 ohm. The capacity increased from 83.4 mAh/g to 95.4 mAh/g. The declining rates of both unmodified and modified separator were 13.7% and 2.1% after 50 cycles at 5C. Both results proved that the plasma and modified AA grafting of separator could improve the performance of lithium ion secondary battery.

並列關鍵字

separator ； lithium ion batteries ； plasma modification ； graft

參考文獻

Arora, P.; Zhang, Z., Battery separators, Chemical Reviews, 104 (2004) 4419-4462.

Ciszewski, A.; Gancarz, I.; Kunicki, J.; Bryjak, M., Plasma-modified polypropylene membranes as separators in high-power alkaline batteries, Surface and Coatings Technology, 201 (2006) 3676-3684.

Croce, F.; Appetecchi, G. B.; Persi, L.; Scrosati, B., Nanocomposite polymer electrolytes for lithium batteries, Nature, 394 (1998) 456-458.

Delmas, C., Alkali metal intercalation in layered oxides, Materials Science and Engineering: B, 3 (1989) 97-101.

Gao, K.; Hu, X.; Yi, T.; Dai, C., PE-g-MMA polymer electrolyte membrane for lithium polymer battery, Electrochimica Acta, 52 (2006) 443-449.