True Meaning of Pseudocapacitors and Their Performance Metrics: Asymmetric versus Hybrid Supercapacitors

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 16; no. 37; pp. e2002806 - n/a
• Main Authors: Chodankar, Nilesh R., Pham, Hong Duc, Nanjundan, Ashok Kumar, Fernando, Joseph F. S., Jayaramulu, Kolleboyina, Golberg, Dmitri, Han, Young‐Kyu, Dubal, Deepak P.
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 01-09-2020
• Subjects: asymmetric supercapacitors; Asymmetry; battery materials; Business metrics; Diffusion rate; Electrolytes; Energy storage; hybrid supercapacitors; Kinetics; Nanotechnology; Performance measurement; Polymer gels; pseudocapacitive materials; Rechargeable batteries; Signatures; Storage systems; Supercapacitors
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202002806

The development of pseudocapacitive materials for energy‐oriented applications has stimulated considerable interest in recent years due to their high energy‐storing capacity with high power outputs. Nevertheless, the utilization of nanosized active materials in batteries leads to fast redox kinetics due to the improved surface area and short diffusion pathways, which shifts their electrochemical signatures from battery‐like to the pseudocapacitive‐like behavior. As a result, it becomes challenging to distinguish “pseudocapacitive” and “battery” materials. Such misconceptions have further impacted on the final device configurations. This Review is an earnest effort to clarify the confusion between the battery and pseudocapacitive materials by providing their true meanings and correct performance metrics. A method to distinguish battery‐type and pseudocapacitive materials using the electrochemical signatures and quantitative kinetics analysis is outlined. Taking solid‐state supercapacitors (SSCs, only polymer gel electrolytes) as an example, the distinction between asymmetric and hybrid supercapacitors is discussed. The state‐of‐the‐art progress in the engineering of active materials is summarized, which will guide for the development of real‐pseudocapacitive energy storage systems.
Pseudocapacitive materials are in high demand due to their unique characteristic of high energy storing capacity with high rates for long periods of time. However, with the recent scientific advancements, the boundary between pseudocapacitive and battery materials is blurred. This Review provides a true meaning of pseudocapacitors and the distinction between asymmetric and hybrid supercapacitors based on electrode combinations.