Department of Chemistry, Bar-Ilan University , Ramat-Gan 52900, Israel.
INM - Leibniz Institute for New Materials , 66123 Saarbrücken, Germany.
ACS Appl Mater Interfaces. 2017 Aug 23;9(33):27664-27675. doi: 10.1021/acsami.7b06243. Epub 2017 Aug 10.
Intercalation-induced dimensional changes in a composite battery electrode (comprising a polymeric binder) are one of the major factors limiting electrode cycling performance. Since electrode performance is expressed by the quantities averaged over its entire surface area (e.g., capacity retention, Faradaic efficiency, rate capability), significant efforts have been made to develop a methodology allowing its facile mechanical diagnostics at the same areal scale. Herein we introduce such a generic methodology for a highly sensitive in situ monitoring of intrinsic mechanical properties of composite battery electrodes. The gravimetric, dimensional, viscoelastic, and adhesive changes in the composite electrodes caused by Li-ions intercalation are assessed noninvasively and in real time by electrochemical quartz-crystal microbalance with dissipation monitoring (EQCM-D). Multiharmonic acoustic waves generated by EQCM-D penetrate into thin porous electrodes comprising either rigid or a soft binder resulting in frequency and dissipation changes quantified by analytical acoustic load impedance models. As a first demonstration, we used a composite LiFePO (LFP) electrode containing either polyvinylidene dichloride (PVdF) or Na carboximethyl cellulose (NaCMC) as rigid and viscoelastic binders, respectively, in aqueous electrolytes. The intercalation-induced volume changes of LFP electrode were evaluated from a hydrodynamic correction to the mass effect of the intercalated ions for PVdF, and both components of the effective complex shear modulus (i.e., storage and loss moduli) in case of NaCMC binder have been extracted. The sliding friction coefficients for large particles bound at their bottom to the quartz crystal surface (a measure of the adhesion strength of binders) has also been evaluated. Tracking the mechanical properties of the composite electrodes in different environments and charging/cycling conditions in a self-consistent manner provides all necessary conditions for an optimal selection of the polymeric binders resistant to intercalation-induced volume changes of intercalation particles.
层间诱导的复合电池电极（包含聚合物粘结剂）的尺寸变化是限制电极循环性能的主要因素之一。由于电极性能是通过其整个表面积上的平均值来表示的（例如，容量保持率、法拉第效率、倍率性能），因此人们已经做出了很大的努力来开发一种允许在相同的面积尺度上对其进行方便的机械诊断的方法。在此，我们介绍了一种通用的方法，用于高灵敏度原位监测复合电池电极的固有机械性能。通过电化学石英晶体微天平与耗散监测（EQCM-D），非侵入性和实时评估复合电极中锂离子嵌入引起的重量、尺寸、粘弹性和粘附变化。由 EQCM-D 产生的多谐声波穿透由刚性或软粘结剂组成的薄多孔电极，导致通过分析声负载阻抗模型量化的频率和耗散变化。作为第一个演示，我们使用了包含聚偏二氟乙烯（PVdF）或羧甲基纤维素钠（NaCMC）作为刚性和粘弹性粘结剂的复合 LiFePO4（LFP）电极，分别在水性电解液中。从对嵌入离子质量效应的流体动力校正评估 LFP 电极的嵌入诱导体积变化对于 PVdF，以及对于 NaCMC 粘结剂提取有效复剪切模量的两个分量（即存储和损耗模量）。还评估了固定在石英晶体表面底部的大颗粒的滑动摩擦系数（粘结剂粘附强度的一种衡量标准）。以一致的方式跟踪复合电极在不同环境和充电/循环条件下的机械性能，为选择耐嵌入粒子嵌入诱导体积变化的聚合物粘结剂提供了所有必要的条件。
