磷酸鋰鐵水系漿料製程中黏結劑對於電化學性能的影響之研究

Effect of Binder Additions on the Electrochemical Performances of Water-based LiFePO4 Cathodes

林育生(Yu-Sheng Lin)

指導教授 ： 李嘉甄

國立臺北科技大學/工程學院/材料科學與工程研究所/碩士(2011年)

https://doi.org/10.6841/NTUT.2011.00015

摘要

本研究使用磷酸鋰鐵作為水系漿料中的活物，並以羧甲基纖維素鈉(SCMC,sodium carboxymethyl cellulose)和苯乙烯丁二烯橡膠(SBR, styrene butadiene rubber)作為水系漿料的增稠劑與黏結劑，以不同羧甲基取代度(DS)之SCMC及兩種不同水系漿料製程的黏結劑添加順序來討論正極極板的物理及電化學效應。首先由流變實驗、表面電位及黏結劑吸附曲線確認SCMC和SBR之間有競爭吸附的關係，且先添加SCMC所配製之漿料其分散性質比較好，並隨著添加DS值較低的SCMC，其漿料的分散性越好。接著，利用研究黏結劑之遷移率的實驗，可發現DS值較低的SCMC有助於減少極板內部中黏結劑的遷移量以及提升極板的黏附效果。而藉由測量AC頻譜阻抗所得到的數據結果可推知，黏結劑之遷移率較低的極板有增加電解液在極板表面潤濕的效果，故有較低的鋰離子阻抗之表現。另一方面，由CV曲線比較兩種不同水系製程之極板的電性品質，可觀察到同時添加SBR和SCMC所配製之漿料，其製備的極板雖然具有較佳之黏附強度，但極板當中的SBR黏結劑之分佈行為會阻礙鋰離子的擴散而造成最終之電化學性質較差。
進一步比較加壓處理前後之極板的電化學性質，則優先添加SCMC之極板因分散性質佳而較不易受到輾壓的影響；而同時添加SBR和SCMC之極板其分散性質較差，電性循環壽命容易衰退，但其經輾壓後，則因為活物粉末排列較緊密而可以提升電容保持率。因此由實驗結果可以知道不同的黏結劑的添加順序會造成不同的電性表現，且極板的分散性質是主導電化學性質表現的關鍵。

關鍵字

鋰離子電池 ； 正極 ； 磷酸鋰鐵鹽 ； 羧甲基纖維素鈉 ； 苯乙烯丁二烯橡膠 ； 分散性質

並列摘要

It has been known that the blend of sodium carboxymethyl cellulose (SCMC) and styrene butadiene rubber (SBR) has been primarily used as the water-based binder for aqueous LiFePO4 cathode slurries. In this investigation, effects of the substitution degree (DS) of SCMC and the slurry-preparation process on physical and electrochemical properties of as-prepared cathodes were studied. The competitive adsorptions between SCMC and SBR on inorganic powders of LiFePO4 cathodes were characterized and clarified by the measuring techniques of zeta-potential, rheology and adsorption isotherms. The results show that the dispersion properties of as-prepared cathode slurries closely correlate with the slurry-preparation processes and the DS value of SCMC. Preparing the slurry with process of adding SCMC prior to SBR helps the dispersion of LiFePO4 in aqueous slurry. Using SCMC with lower DS value as the thickening agent also improves the dispersion properties. In the analyses of electrochemical properties, it was found that the use of SCMC with low DS can improve the distribution homogeneity of binder and adhesion strength of dried electrode sheets. Moreover, uniform distribution of binder in the electrode sheet facilitates the wetting of electrolyte solution on the surface of electrode, which decreases the impedance of Li ions.
Furthermore, the electrochemical properties of compressed and uncompressed electrodes were compared. The cathode prepared by the process of adding SCMC prior to SBR showed that its electrochemical properties were not affected by the step of compression. However, they were greatly affected when the cathode was prepared via the process of adding SCMC and SBR simultaneously.

並列關鍵字

Li-ion battery ； cathode ； LiFePO4 ； SCMC ； SBR ； dispersion

參考文獻

[16] 林月微，「高性能電池正極材料介紹」，工業材料，157， 152。

[3] F. Croce, A.D. Epifanio, J. Hassoun, A. Deptula, T. Olczac, B. Scrosati, Electrochem. Solid State Lett., 5(3), 2002, A47.

State Commun., 129, 2004, 311.

[7] A. Yamada, S.C. Chung, K. Hinokuma, J. Electrochem. Soc., 148(3), 2001, A224.

[9] Z. Chen, J.R. Dahn, J. Electrochem. Soc., 149(9), 2002, A1184.