In-situ experimental measurements of lithium concentration distribution and strain field of graphite electrodes during electrochemical process

The decay and lifetime of the graphite electrodes in lithium ion batteries are determined by coupling of deformation and lithium concentration. In this paper, lithium concentration and strain in graphite electrodes are investigated in-situ during an electrochemical process. We propose an experimental method to simultaneously measure the electrode concentration field and strain field in real time. A visual electrochemical simulation cell is developed, and a dual optical experimental system for in-situ image acquisition during electrochemical cycling is designed and built. On the basis of the relationship between the lithium concentration and color, we combine a color imaging technique to measure the concentration distribution. We also apply an improved digital image correlation technology to measure the strain field, and realize real time simultaneous measurements of the lithium concentration and strain distribution of graphite electrodes during the electrochemical lithiation process. It is founded that lithium concentration and strain in the graphite electrode show a nonlinear distribution along the direction of diffusion, and higher concentrations are associated with greater strain. This paper proposes a new experimental method to quantify the coupling relationship between the lithium concentration and strain, which provides an important experimental means for analyzing mechano-electrochemical coupling mechanisms.