Analyses of capacity loss and improvement of cycle performance for a high-voltage hybrid electrochemical capacitor
Analyses of capacity loss and improvement of cycle performance for a high-voltage hybrid electrochemical capacitor
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DOI：
10.1149/1.2746562
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发表时间：
2007-01-01
影响因子：
3.9
通讯作者：
Morita, Masayuki
中科院分区：
文献类型：
--
作者：
Aida, Taira;Murayama, Ichiro;Morita, Masayuki
高压混合电化学电容器（HEC）采用不可石墨化碳作为负极，活性炭作为正极，并以锂盐作为电解质。在高电压条件下，当正极在相对于 Li/Li+ 的电位超过 4 V 时高度极化时，在充放电循环过程中观察到较大的容量损失。这种容量损失是由负极界面电阻的增加引起的。充放电循环后，负极表面观察到大量氟化锂（LiF）。据认为，LiF是通过六氟磷酸根阴离子（PF6-）分解产生的氢氟酸（HF）与负极表面的烷基碳酸锂（半碳酸盐，ROCOOLi）或碳酸锂（Li2CO3）反应而生成的。通过在正极和负极之间设置锂金属，抑制了LiF的生成和容量损失。由此证实，活性炭正极的高极化引起的LiF生成的抑制可以实现具有良好循环性的高电压HEC。 (c) 2007 年电化学协会。
A high-voltage hybrid electrochemical capacitor (HEC) which uses nongraphitizable carbon for a negative electrode and activated carbon for a positive electrode has been constructed with lithium salt for the electrolyte. Under high-voltage conditions, large capacity loss during charge-discharge cycling was observed when the positive electrode was highly polarized at a potential over 4 V vs Li/Li+. This capacity loss was induced by the increase of the interfacial resistance at the negative electrode. A large amount of lithium fluoride (LiF) was observed on the surface of the negative electrode after charge-discharge cycling. It is considered that the LiF was generated by a reaction of hydrofluoric acid (HF), generated by the decomposition of hexafluorophosphate anion (PF6-), with lithium alkyl carbonate (semicarbonate, ROCOOLi) or lithium carbonate (Li2CO3) on the surface of the negative electrode. The generation of LiF and the capacity loss were suppressed by providing lithium metal between the positive electrode and the negative electrode. It was thus confirmed that the suppression of LiF generation, caused by high polarization of activated carbon positive electrode, can realize a high-voltage HEC with good cycleability. (c) 2007 The Electrochemical Society.