In-situ imaging of Li intercalation in graphite particles in an Li-ion battery.

This paper presents the imaging of the expansion and contraction of graphite particles at the anode of a lithium-ion battery. The intercalation and deintercalation of Li ions in the graphite particles induced by charging and discharging lead to expansion and contraction of the layered materials. These changes in volume were imaged through current collectors using scanning probe microscopy, which permitted in-situ observation of the Li ion shift with high resolutions. We were able to evaluate the properties of each individual graphite particle. Here, we present variations in the images obtained by two methods of charging/discharging. In one method, the applied fields are changed, forcing the ions to move back into the graphite particles. Images showing detailed structures were obtained, allowing us to investigate the fine structures of the graphite particles. In the other method, the amount of ions is periodically injected into the graphite, which did not reveal the detailed structure but clearly distinguished inactive from active particles.