A Dilatometric Study of Graphite Electrodes during Cycling with X-Ray Computed Tomography

Abstract

Since the 1970s, electrochemical dilatometry (ECD) has been used to investigate the dilation of layered host materials due to the intercalation of guest ions, atoms or molecules , but to date has not been extensively applied to Li-ion batteries (LiBs) [1][2]. Understanding how commonly adopted anodes dilate and degrade in LiBs using ECD can be of critical value in improving the battery. Cathode materials also undergo volume changes during cycling, the extent of which is dependent on their stoichiometry and structure. However, the influence of cathode material dilation and contraction on battery performance, and overall cell dilation is often neglected [3].Graphite is the mostly widely used commercial anode material in LiBs because of its high coulombic efficiency and cycling performance. However, prolonged cycling of LiBs has a deleterious effect on the graphite electrode’s durability. The present study uses correlative ECD to reveal the thickness changes of the electrode during cycling, alongside X-ray Computed Tomography (X-ray CT). X-ray CT provides additional visual corroborative evidence of the morphological changes that occur during cycling and explains changes in dilatometric measurements. X-ray CT is also used to acquire images of cycled and uncycled graphite electrodes for simulations exploring how continuous dilation and contraction impact electrode porosity and tortuosity.To date, there is no research to our knowledge combining in-situ ECD with X-ray CT and image-based modelling. In this presentation, the structural changes that graphite undergoes during dilation and contraction will be explored, and the consequences that continuous dilation and contraction has on morphological properties, namely porosity and tortuosity will be explained.