New insights into electrochemical anion intercalation into carbonaceous materials for dual-ion batteries: Impact of the graphitization degree

Within the past 5 years, dual-ion batteries and in particular their all-carbon/all-graphite versions, the dual-carbon or dual-graphite batteries, have received rising interest due to the use of carbonaceous active materials for both, the positive and the negative electrode. With regard to the capacity determining reactions at the positive electrode, related to the intercalation of anions, the influence of the carbon/graphite structure has been by far not fully understood. In this work, we present a comprehensive investigation on the structure – property relationship with special focus on the preparation and characterization of carbon materials with different degree of graphitization (DoG) and their electrochemical performance study as active material for the positive electrode in dual-ion batteries. We found that an increasing DoG directly leads to an enhanced specific discharge capacity, while the crystallite height exhibits only a negligible contribution to the capacity for the carbons examined in this work. A further observation is that the staging mechanism is a major step of the overall anion storage mechanism, even for carbons possessing a low DoG. Moreover, an increased DoG leads to a decreased voltage hysteresis between the charge and discharge step and, thus, to an enhanced voltage efficiency during charge/discharge cycling.