In-situ measurements of electrochemical stress/strain fields and stress analysis during an electrochemical process

The importance of electrochemical stress has been widely recognized because it determines the lifetime of lithium-ion (Li+) batteries. Herein, we propose an in-situ method to visually measure the electrochemical stress fields associated with strain and Li+ concentration along the diffusion path. Three important links are established successively; namely, an electrochemical stress model, visual observation, and in-situ collaborative measurements of core mechano-electrochemical parameters. The strain field and Li+ concentration distribution in a graphite electrode are measured in situ using a dual optical system. The electrochemical stress field considering Li+ concentration, strain and Li+-dependent stiffening is obtained. The spatiotemporal evolution of the experimental parameters is evaluated. The experimental results demonstrate that the electrode experiences compressive stress and tensile strain. The strain and electrochemical stress exhibit gradient distributions along the Li+ diffusion path and increase with the electrochemical process. Furthermore, the mechano-electrochemical interrelation of tensile strain, compressive stress and Li+ concentration is considered. It is demonstrated that compressive stress (tensile strain) evolves linearly (nonlinearly) with Li+ concentration. Mechanical constraint-induced stress (i.e., strain) and Li+ concentration-induced stress show opposing positive and negative states, making them competitive contributions to electrochemical stress. This study increases understanding of the mechano-electrochemical interrelation in electrodes, which will help to improve electrode performance.