Dissipative effects in nonideal supercapacitors and batteries

The literature is full of reports containing very high specific energy (E/W h g  1) and power (P/W g  1) values for different classes of electrochemical energy storage devices (EESD) based on distinct types of microstructured and nanosized advanced electrode materials (AEM), such as supercapacitors and batteries. In most cases, the eval-uation of energy and power characteristics for EESD is carried out based on classic theory for electrical systems (Esc = CU2/2 or Ebat = CU), where the charge carriers are assumed as massless point entities, i.e., electrons and holes. However, EESDs operate simultaneously with the transport of electronic and ionic charges involving massive/finite-sized charge carriers (e.g., anions and cations) with pronounced steric effects that control the overall charge transport in migration and/or diffusion phenomena in viscous media. To overcome the inherent theoretical difficulty in studying porous and redox-active electrode materials used in AEMs, and considering the typical case where a robust theoretical model is absent to represent the different classes of EEDs, we propose a phenomenological analysis where the use of an empirical correction parameter denoted as the deviation coefficient (& gamma;) representing the discrepancies from the classic electric predictions results in more reliable specific energy and power values. From the analysis of different experimental data obtained for laboratory-made devices, we verified that using Esc = CU2/2 and Ebat = CU equations can result in important discrepancies characterized by & gamma; =/ 1. Finally, we discussed the distinction between well-behaved supercapacitors and ill-defined EESD systems in light of & gamma;-values.

Automated summary

The literature reports high energy and power values for electrochemical energy storage devices based on advanced electrode materials. However, traditional theoretical models fail to accurately describe the transport of massive charge carriers, leading to the proposal of using an empirical correction parameter for reliable energy and power values.