Lee Sang-Young, Yong Hyun Hang, Lee Young Joo, Kim Seok Koo, Ahn Soonho
Batteries R and D and Corporate R and D, LG Chem, 104-1, Moonji-dong, Yusong-gu, Daejon 305-380, South Korea.
J Phys Chem B. 2005 Jul 21;109(28):13663-7. doi: 10.1021/jp051974m.
It is a common observation that when ionic liquids are added to electrolytes the performances of lithium ion cells become poor, while the thermal safeties of the electrolytes might be improved. In this study, this behavior is investigated based on the kinetics of ionic diffusion. As a model ionic liquid, we chose butyldimethylimidazolium hexafluorophosphate (BDMIPF(6)). The common solvent was propylene carbonate (PC), and lithium hexafluorophosphate (LiPF(6)) was selected as the lithium conducting salt. Ionic diffusion coefficients are estimated by using a pulsed field gradient NMR technique. From a basic study on the model electrolytes (BDMIPF(6) in PC, LiPF(6) in PC, and BDMIPF(6) + LiPF(6) in PC), it was found that the BDMI(+) from BDMIPF(6) shows larger diffusion coefficients than the Li(+) from LiPF(6). However, the anionic (PF(6)(-)) diffusion coefficients present little difference between the model electrolytes. The higher diffusion coefficient of BDMI(+) than that of Li(+) suggests that the poor C-rate performance of lithium ion cells containing ionic liquids as an electrolyte component can be attributed to the two-cation competition between Li(+) and BDMI(+).
一个常见的现象是，当将离子液体添加到电解质中时，锂离子电池的性能会变差，而电解质的热安全性可能会提高。在本研究中，基于离子扩散动力学对这种行为进行了研究。作为模型离子液体，我们选择了六氟磷酸丁基二甲基咪唑鎓（BDMIPF₆）。常用溶剂为碳酸丙烯酯（PC），并选择六氟磷酸锂（LiPF₆）作为锂导电盐。通过使用脉冲场梯度核磁共振技术估算离子扩散系数。通过对模型电解质（PC中的BDMIPF₆、PC中的LiPF₆以及PC中的BDMIPF₆ + LiPF₆）的基础研究发现，BDMIPF₆中的BDMI⁺显示出比LiPF₆中的Li⁺更大的扩散系数。然而，模型电解质之间的阴离子（PF₆⁻）扩散系数几乎没有差异。BDMI⁺比Li⁺更高的扩散系数表明，含有离子液体作为电解质成分的锂离子电池的C倍率性能较差可归因于Li⁺和BDMI⁺之间的双阳离子竞争。
