Presently used experimental techniques for the characterization of tensile and compressive behavior of active layers in lithium-ion batteries have limitations of different kinds. This is particularly true for measurements of compressive properties. Furthermore, the characterizations of time-dependent stress-strain behavior are largely missing. In order to characterize the stress-strain relationship for a dry cathode active layer in lithium-ion batteries, a mechanical testing method is presented that previously has been applied to the testing of optical fibers. The method is based on U-shaped bending of single-side coated aluminum foils, which enables separate measurements of tensile and compressive properties. In particular, the method has clear advantages for measurements of compressive properties in comparison to previously reported techniques. Relaxation experiments are also conducted in order to characterize the time-dependent properties of the dry active layer and to check if these effects could explain the measured hysteresis. It is found that the elastic modulus in compression is significantly larger than the elastic modulus in tension and that the compressive modulus increases with strain level. Contrary, the tensile modulus is approximately independent of strain. Furthermore, hysteresis effects are present at loading-unloading measurements, both for tension and compression. The low values of the measured elastic moduli show that the electrode properties are largely controlled by the binder and carbon additives. It is concluded that the development of particle-particle contacts most likely is the reason for the higher modulus in compression in comparison to tension. The time-dependent effects are significant, primarily for shorter time scales, which explains the relaxation behavior, but they cannot fully explain the hysteresis effects. Most likely non-linear micro-mechanisms do contribute as well.

中文翻译：

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使用弯曲测试方法表征锂离子电池中阴极活性层的本构行为

目前用于表征锂离子电池活性层拉伸和压缩行为的实验技术具有不同种类的局限性。对于压缩特性的测量尤其如此。此外，随时间变化的应力应变行为的特征在很大程度上缺失。为了表征锂离子电池中干阴极活性层的应力-应变关系，提出了一种以前已应用于光纤测试的机械测试方法。该方法基于单面涂层铝箔的 U 形弯曲，可以分别测量拉伸和压缩性能。特别是，与以前报道的技术相比，该方法在测量压缩特性方面具有明显的优势。还进行了松弛实验，以表征干活性层的时间相关特性，并检查这些影响是否可以解释测量的滞后。发现压缩弹性模量明显大于拉伸弹性模量，并且压缩模量随着应变水平而增加。相反，拉伸模量几乎与应变无关。此外，在加载-卸载测量中，无论是拉伸还是压缩，都存在滞后效应。测得的弹性模量的低值表明电极性能在很大程度上受粘合剂和碳添加剂的控制。得出的结论是，颗粒-颗粒接触的发展最有可能是压缩模量高于拉伸模量的原因。时间依赖效应是显着的，主要是对于较短的时间尺度，这解释了松弛行为，但它们不能完全解释滞后效应。最有可能的非线性微机制也有贡献。