Uncovering the Early-Stage Intercalation Mechanism in Graphite-Based Anode Materials.

Graphite and graphite derivatives, the standard anode materials for Li-ion batteries, are also of great interest for post-Li-ion technologies, such as potassium-ion batteries. However, certain aspects of the intercalation process in these systems, as well as the resulting consequences, still require a deeper understanding. In particular, the first steps of K intercalation in graphitic systems, i.e., at low concentrations, are fundamentally different from the case of Li. Herein, we use density functional theory to elucidate the early-stage intercalation of K in graphitic materials by seeking comparison to the behavior of Li and Na. Our results show the crucial role of the competition between the interlayer van der Waals interaction and the alkali metal-carbon bond formation for the initial stages of intercalation of large alkali metal atoms. As a consequence, and in contrast to the case of Li, K intercalation becomes energetically unfavorable at low concentrations. This is a significant finding, which can explain the origin of the differences observed for Li and K intercalation in graphitic materials. Hence, we identify the first steps of K intercalation as potential reasons for performance loss and battery failure and show that heteroatom doping can open pathways for solving these issues.