磷酸鋰鐵於SCMC/SBR漿料系統中之膠化機制研究

Gelation mechanisms of lithium iron phosphate in SCMC/SBR containing water-based slurries

蔡鋒諺(Feng-Yen Tsai)

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(2014年)

摘要

已知電極漿料系統中黏結劑、助導劑與其他正極材料間的相互作用會影響漿料的分散性質。本實驗以水系漿料系統搭配增稠劑─羧甲基纖維素鈉(SCMC)及黏結劑─苯乙烯丁二烯橡膠(SBR)做為複合式黏結劑，探討相同型號但不同批次之商用磷酸鋰鐵正極材料在水系漿料中進行膠化的反應機制。
為了解決磷酸鋰鐵導電性不佳之缺點，一般取得之商售粉末表面多已覆有碳層，然而當其碳覆層未能完整覆蓋磷酸鋰鐵表面時，裸露的磷酸鋰鐵表面將具有較高的極性，極性的粉體表面易因化學吸附反應而帶有羥基。當磷酸鋰鐵表面帶有羥基，則與SCMC表面所帶的羥基產生分子間氫鍵，並傾向形成三維結構造成漿料產生膠化現象。
本實驗乃藉由表面電位儀、傅立葉轉換紅外線光譜(FTIR)、與拉曼光譜比較不同批次粉體間的表面特性差異，並藉由測量表面電位的趨勢變化探討磷酸鋰鐵之溶解機制對於水系漿料分散性質的影響。此外，亦利用X-射線光電子能譜(XPS)分析不同批次之磷酸鋰鐵的化學組成差異(如磷酸鋰在粉體表面的含量)，最後以流變分析方法確認粉末表面之磷酸鋰含量對於磷酸鋰鐵於水系漿料中產生膠化機制的影響。

關鍵字

磷酸鋰鐵 ； 磷酸鋰 ； 水系漿料 ； 羥基 ； 氫鍵 ； 膠化

並列摘要

It has been understood the interaction between binders, conductive agents and other cathode materials makes impacts on the dispersibility of electrode slurry. In this research, the thickener of sodium carboxymethyl cellulose (SCMC) and the binder of
Styrene Butadience Rubber (SBR) were used as a complex binder to investigate the gelation mechanism of the same type but different lots of commercialized lithium iron phosphate (LFP) cathode material in water-based slurry.
Carbon coating technique has been widely used to overcome the drawback of intrinsic poor electronic conductivity of typical commercialized LFP cathode materials. However, once LFP particle surface is not covered by evenly distributed carbon coating, the exposed LFP particle surface will have higher polarity, as compared with uniformly carbon coated cases. The polarized LFP surface forms hydroxyl groups easily because of chemical absorption reaction. The hydroxyl groups attached on the surfaces of LFP and SCMC bond together to form intermolecular hydrogen bonding which leads to the formation of a 3-dimentional structure, causing the phenomenon of slurry gelation.
The discrepancy of surface characteristics between different lots of LFP powder were analyzed by Zeta potential, Fourier transform infrared spectroscopy(FTIR) and
Raman spectroscopy. The impacts of dissolution mechanism on the dispersibility of water-based slurry were studied by measuring the tendency of zeta potential.
Moreover, the differences of chemical compositions of several lots of LFP powder, e.g. the content of lithium phosphate on the surface of powder, were analyzed via X-ray photoelectron spectroscopy (XPS). Finally, the impact of lithium phosphate residues on powder surface on the gelation mechanism of water-based LFP was confirmed via rheological behavior measurement.

並列關鍵字

Lithium iron phosphate ； Lithium phosphate Water-based slurry ； Hydroxy groups ； Hydrogen bonding ； Gelation

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