Influences on Reliable Capacity Measurements of Hard Carbon in Highly Loaded Electrodes

Abstract For the development of a full‐cell battery system, typically appropriate cathodes and anodes are characterized within a half‐cell setup where a metal counter electrode is installed to gather data about the employed electrodes. Ultimately, the individual capacity loadings allow for suitable balancing of the anode to cathode capacity in the full‐cell. This approach seems rather unproblematic for lithium‐ion batteries. For sodium‐ion batteries, however, we show that the high reactivity of sodium metal strongly influences hard carbon‐based electrode measurements within sodium‐ion half‐cells. As hard carbon is considered state‐of‐the‐art anode material, the presented results have high impact on the development of sodium ion batteries. Specifically, we show that the type of electrolyte, as well as cell‐ and measurement‐setup are key factors for reliable sodium half‐cell measurements of hard carbon. The investigated hard carbon electrodes have a high active material loading of 7.2 mg/cm² (with 93 % active material content) resulting in an areal capacity of 2.4 mAh/cm², which represent application‐relevant conditions.