組成及分散均勻性對LiCoO2正電極性能的影響之研究

Effects of compositional homogeneity on the cell performance of LiCoO2 cathodes

王雅慧(Ya-Hui Wang)

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(2012年)

https://doi.org/10.6841/NTUT.2012.00428

摘要

對於鋰離子電池正極，電極漿料的分散性以及乾燥程序後的生胚均勻性，皆是影響電極最終電化學及物理性質的重要因素。漿料系統中所添加的黏結劑種類、添加量將會左右漿料的分散性及電極內的組成均勻性。本實驗研究添加不同黏結劑對LiCoO2電極性質之比較，水系系統漿料以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；有機系統方面則採用聚二氟乙烯(PVDF)做為黏結劑，針對黏結劑對漿料的分散穩定性、乾燥後的黏結劑均勻性、孔隙率、電化學性質等進行比較。
高分子黏結劑與正極漿料的分散穩定性間具有極高的相關性，當黏結劑吸附於粉體表面時，粉體間具有立體障礙而可避免漿料內團聚情形產生，使漿料得到較高的分散穩定性。高分散穩定性的漿料經塗佈後可得到較緻密的電極生胚，有助於降低電極阻抗及提高電化學性質，因此添加的高分子對於漿料粉體的分散性亦為混漿時考量的因素之一。並且電極漿料經過乾燥程序時，未吸附於粉體上的黏結劑將隨著蒸發的溶劑遷移到生胚的表面，此一結果致使生胚內產生黏結劑的濃度差。另一方面，當黏結劑的遷移率較大，將會降低電極粉體彼此間的黏附及電極對於鋁箔的黏附力，使得電極的電化學表現較差。因此漿料乾燥時，在乾燥速率曲線中固定速率區間的長短與吸附於粉體表面的黏結劑多寡會是影響生胚內組成均勻性的關鍵因素。
本實驗藉由比較水系電極中添加不同SBR和SCMC相對比例，進行電極物理及電化學性質的比較，以研究和拮取最佳的水系黏結劑配比。並利用最佳的水系黏結劑比例和有機系統間的黏結劑進行比較，探討不同系統間的黏結劑對電極之物理及電化學性質上的差異。實驗利用表面電位儀及流變儀，探討電極粉體與黏結劑混合後的表面電位以及混漿後之流變曲線，以進行漿料分散性的分析。並藉由熱重分析儀及掃描式電子顯微鏡得到電極生胚內的組成分佈情形，最後進行電極板加壓前後之黏附強度、電極阻抗、充放電性質等進行分析。從漿料之分散性質及乾燥時所造成的遷移情形與正電極物理、電化學性質間的關聯性，以了解生胚組成均勻性及漿料分散性，對於電極物理及電化學表現的影響。

關鍵字

鋰離子二次電池 ； 正極 ； 羧甲基纖維素鈉 ； 苯乙烯丁二烯橡膠 ； 均勻性

並列摘要

The fabrication of Li-ion battery has been discussed by wet mixing process is this investigation. Dispersion property and drying conditions will change the homogeneity of the resulted cathode sheets to affect the physical and electrochemical properties. This investigation studied effects of binder compositions on the homogeneity and electrochemical performances, in which the binder used including the aqueous-based composited of SBR & SCMC and the organic-based PVDF.
It has been known that binder plays an important role in the powder dispersion system. When binder can be to adsorbed on the surface of particles, steric hindrance will be generated between particles, and the slurry will reveals a very stable condition. Cathode sheets manufactured by the well dispersed slurries can exhibit better electrochemical performances. The electrochemical properties of cathode sheets with containing composite different ratios of SBR and SCMC were discussed in this investigation. Where cathode particles are adsorbed by the binder molecules, the steric hindrance in cathode slurries due to the adsorptions may have them being cell stabilized.
It was fond that the binder that is free and not adsorbed on powder could migrate with solvent up to evaporation the surface of the cathode tape during drying, resulting in an inhomogeneous distribution of binder content in the dried electrode sheet. When binder shows larger migration, the adhesion force between particles will decrease, and so does the adhesions between the cathode sheet and the aluminum foil could become poorer, and so does the electrochemical performance.
Based on the theoretical calculations, it can be understand that the non-uniform distribution of binder in the cathode sheet are dominated by the migration control theory mechanism.
The dispersion homogeneity of cathode slurries were practical examined in the measurements of zeta potential and rheology. The physical & electrochemical properties of the dried cathode sheets were assessed on the measurements of adhesion force, electrical resistance, AC-Impedance and rate capabilities.

並列關鍵字

Li-ion battery ； Cathode ； Sodium carboxymethyl cellulose ； Styrene-butadiene rubber ； Uniformity

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