Background

Mechano-electro-chemical coupling during the ion diffusion process is a core factor to determine the electrochemical performance of electrodes. However, relationship between the mechanics and the electrochemistry has not been clarified by experiments.

Objective

In this work, we conduct an in situ, visual, comprehensive characterization of strain field and Li concentration distribution to further explore the mechano-electro-chemical relationship.

Methods

The digital image correlation characterized by fluorescent speckle and active optical imaging is developed. Combined with electrochromic-based Li concentration detection, the spatiotemporal evolution of in-plane strain and Li concentration of a graphite electrode during the lithiation and delithiation processes are measured and displayed visually via a dual optical path acquisition system.

Results

The visual results show that in-plane strain and Li concentration possess a spatially non-uniform gradient distribution along the radial direction (i.e., diffusion path) with large values outside and small values inside, and that both present obvious temporal segmentation. And mechano-electro-chemical coupling analysis reveals that the in-plane strain is not always linearly related to the concentration and infers that a high strain limits the diffusion and lithiation. The strain–concentration evolution exhibits obvious asymmetric differences between lithiation and delithiation, wherein three equations are fitted to approximately represent the evolution process between in-plane strain and concentration during the lithiation and delithiation processes

Conclusions

This work overcomes the difficulties of fine strain measurements and collaborative concentration characterization during the electrochemical process, and provides an effective experimental method and data support for further exploration of mechano-electro-chemical coupling.

中文翻译：

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通过荧光数字图像相关对石墨电极进行原位应变场测量和机械电化学分析

背景

离子扩散过程中的机电耦合是决定电极电化学性能的核心因素。然而，力学与电化学之间的关系尚未通过实验阐明。

客观的

在这项工作中，我们对应变场和锂浓度分布进行了原位、视觉、综合表征，以进一步探索机电-化学关系。

方法

开发了以荧光散斑和主动光学成像为特征的数字图像相关性。结合基于电致变色的锂浓度检测，通过双光路采集系统测量并可视化显示在锂化和脱锂过程中石墨电极的面内应变和锂浓度的时空演变。

结果

视觉结果表明，面内应变和锂浓度沿径向（即扩散路径）具有空间非均匀梯度分布，外大内小，且均呈现明显的时间分割。机械-电化学耦合分析表明，面内应变并不总是与浓度呈线性相关，并推断高应变限制了扩散和锂化。应变-浓度演化在锂化和脱锂过程中表现出明显的不对称差异，其中拟合三个方程来近似表示锂化和脱锂过程中面内应变和浓度的演化过程

结论

这项工作克服了电化学过程中精细应变测量和协同浓度表征的困难，为进一步探索机电化学耦合提供了有效的实验方法和数据支持。