正極多孔性極板結構對鋰離子二次電池的放電性能影響

The Effect of Porous Structure of Positive Electrode on Lithium Ion Battery

劉俊彥(Chun-Yen Liu)

指導教授 ： 萬其超 ； 王詠雲

國立清華大學/工學院/化學工程學系/碩士(2007年)

https://doi.org/10.6843/NTHU.2007.00052

摘要

藉由XRD、SEM、AC Impedance、Cyclic Voltammetry，以及毛細現象分析極板潤濕程度等五種分析技術，探討正極極板輾壓密度對鋰離子二次電池在不同放電速率下的影響。
實驗結果顯示，當電池放電速率小於1C時，極板密度越密的電池，其放電容量越高。然而，當電池放電速率高於2C時，最密極板結構的電池(3.6 g/cm3)，其放電容量將快速遞減。
這表示，極板輾壓將使鈷酸鋰活性顆粒物質推擠得更緊密並且降低電池內組抗，使反應動力學增快。因此，活性顆粒物質間的接觸品質，是電池在小於1C放電速率下的主要影響因素。此外，當電池放電速率超過2C時，電解液的離子導電度與對多孔性極板結構的潤濕程度，將會成為影響放電容量的主要因素。當然，此時活性顆粒物質間的接觸品質，仍然是重要的因素，並且極板密度至少要高於3.2 g/cm3。也就是說，在3C放電速率情況下，對於密度高於3.2 g/cm3的電池而言，其放電容量將受電解液的離子導電度與對多孔性極板結構的潤濕程度影響。

關鍵字

鋰離子電池 ； 鈷酸鋰極板密度 ； 放電速率 ； 粒子間接觸品質 ； 潤濕性 ； 離子導電度

並列摘要

The effect of rolling positive electrodes into different densities on the performance of lithium ion batteries discharged at different rates was studied by using X-ray diffraction, SEM, AC impedance, cyclic voltammetry, and gravimetrically measured capillary liquid movement.
The results show that, as the battery discharged at lower than 1C rate, the capacity increased as electrodes density increased. However, as the discharging rate increased over 2C, the capacity of the densest electrode, 3.6 g/cm3, would drop rapidly.
This suggests that rolling positive electrode would make the active particles (LiCoO2) be compacted more closely, resulting in decreased internal impedance and faster kinetics. Therefore, the inter-particle contact quality is the main factor to determine the discharge efficiency if the discharging rate is below 1C. Moreover, as the discharging rate increases over 2C, both liquid ionic conductivity and the contact area between active particles and electrolyte, that is to say “wettability”, would govern the discharge capacity. But, the inter-particle contact quality is still important and the density should be at least denser than 3.2 g/cm3. Namely, these two factors, ionic conductivity and wettability, would become more important for battery discharge at 3C with electrode denser than 3.2 g/cm3.

並列關鍵字

lithium ion battery ； LiCoO2 electrode density ； discharge rate ； inter-particle contact resistance ； wettability ； ionic conductivity

參考文獻

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