Electrode thickness control: Precondition for quite different functions of graphene conductive additives in LiFePO4 electrode
Electrode thickness control: Precondition for quite different functions of graphene conductive additives in LiFePO4 electrode
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电极厚度控制：LiFePO4电极石墨烯导电添加剂功能差异较大的前提
DOI：
10.1016/j.carbon.2015.04.064
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发表时间：
2015-10
期刊：
影响因子：
10.9
通讯作者：
Kang, Feiyu
中科院分区：
文献类型：
--
作者：
Li, Baohua;Li, Zhengjie;Yang, Quan-Hong;Kang, Feiyu
由于石墨烯具有高导电性，因此作为锂离子电池中的导电添加剂得到了广泛的研究。然而，研究发现，石墨烯在不同的评价系统中，如商业软包装电池和硬币半电池，对速率性能有很大不同的影响。研究表明，随着石墨烯含量的增加，纽扣电池的高倍率性能得到改善，而商用电池的高倍率性能则相反。在正常情况下，纽扣电池的电极厚度比商业电池的电极厚度小得多。在此，发现电极厚度对其中使用石墨烯作为导电添加剂的LiFePO4电极的高倍率性能具有相当大的影响。较厚的电极导致较长的锂离子扩散路径，因此石墨烯可能阻碍锂离子扩散的空间效应被放大，导致高得多的极化和在高速率下的较差性能。相比之下，这种现象在较薄的电极中并不明显。因此，当在厚电极中引入更多石墨烯时，功率性能大大减弱，如在商业电池中观察到的。这一发现对于设计具有石墨烯添加剂的高性能商用锂离子电池具有重要意义。
Because of high electrical conductivity, graphene has been widely investigated as conductive additive in lithium-ion batteries. Whereas, it is found that graphene has quite different influences on the rate performance in diverse evaluation systems, such as commercial soft-packed cells and coin half-cells. It has been proved that the coin cells show better high-rate performance with the increase of graphene content, while it is of the opposite trend in commercial cells. In normal cases, the electrode thickness of coin cells is much smaller than that of commercial cells. Herein, it is found that the electrode thickness has a considerable effect on the high-rate performance of LiFePO4electrode in which graphene is used as the conductive additive. Thicker electrode results in a longer Li-ion diffusion path, and thus the steric effect that graphene could hinder the Li-ion diffusion is amplified, inducing much higher polarization and poorer performance at high rate. Comparatively, this phenomenon is not obvious in thinner electrode. Thus, when more graphene is introduced in thick electrode, the power performance is greatly weakened as is observed in the commercial cells. This finding is of great importance for designing a high-performance commercial lithium-ion battery with graphene additives.
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