Good practice guide for papers on supercapacitors and related hybrid capacitors for the Journal of Power Sources

The term supercapacitor (or ultracapacitor) [1] is used to indicate an electrochemical capacitor capable of storing charge through a capacitive process occurring in the electrical double layer formed at the interface between an electronic conductor (i.e., the electrode) and an electrolytic solution (e.g., non-aqueous electrolyte) [2,3]. The increasing demand for improved electrochemical energy storage systems continually boosts research efforts toward new materials, configurations and production processes, both for batteries and supercapacitors. The development of hybrid devices (e.g., where one electrode stores charge through a faradaic process and the other through a non-faradaic process) has also exploited progress in both the battery and supercapacitor fields. However, not all investigated materials are promising or industry-relevant, contrary to the claims in many research works. For example, complications related to the upscaling of lab-scale experiments hamper the exploitation at industrial scale. For these reasons, it is essential to define the best-practice methods to obtain reasonable predictions for supercapacitor materials and device testing. Also, many battery electrode materials are explored as supercapacitor electrode materials. However, not all battery materials can be considered as candidate electrode materials for hybrid devices. Only those materials with a suitable crystal structure for high rate capability and good cycling stability are appropriate.