Supercapacitors and rechargeable batteries, a tale of two technologies: Past, present and beyond

Supercapacitors and rechargeable batteries are energy storage devices where the performance strengths of one are traditionally the weaknesses of the other. Batteries benefit from superior energy storage capacity while supercapacitors possess higher power rates and longer cycle life. The rapid adoption of these devices in electric vehicles and grid energy storage applications is driving their further development and production. Accumulating and comprehending the current knowledge of both device technologies shall serve as a foundation for the progress in future research and development within these two distinct fields that share common goals. Therefore, in this review, we aggregate the supercapacitor and battery energy-power performance trends from over the last 18 years, to construct a projection of where the technologies could be heading in the coming decade. We specifically discuss the influence of each of these technologies in the energy storage landscape and their effect on hybridization research. Projections of the trends suggest that by 2040 the best-performing asymmetric and hybrid supercapacitors could be comparable to commercial battery technologies that are currently under development, in terms of energy density (ED). In terms of power density (PD), battery technology can achieve performance comparable to certain electrical double layer (EDL)-based supercapacitors. For some applications, we foresee that the two devices will continue to hybridize to fill the energy-power gap in a way that the penalty to PD for enhanced ED becomes insignificant. This expected improvement may eventually reach a saturation point, suggesting that once a certain level of ED is achieved, any further enhancements of the metric only lead to severe trade-offs with PD, and vice versa. The saturation observed in these technologies has also prompted an exploration of new pathways, with a notable emphasis on sustainability, to achieve high performance using renewable materials and methods.