Unraveling the Technology behind the Frontrunner LIC ULTIMO to Serve as a Guideline for Optimum Lithium‐Ion Capacitor Design, Assembly, and Characterization

Abstract The fast growth experienced by the field of lithium‐ion capacitors (LICs) in the last five years led to tremendous progress in this technology. However, the authors have observed some parallelism with its ultracapacitor (UC) sister technology, where an over‐rapid growth in the last decade resulted in a loss of focus and the need of several tutorials for reconducting incorrect reporting habits. In the light of what may be coming, the authors aim to set this work as a direction to the scientific community and the new researchers in the field to serve as i) a retrospective analysis of the original target for LICs to prevent focus deviation and ii) a guideline for proper LIC design and assembly toward high energy, high power, and long cycle life, as well as for correct electrochemical characterization and reporting. The underlying thread throughout this report is the technology behind the frontrunner LIC ULTIMO, a reference device in the market that presents 3–4 times the energy density of an UC and can stand over 1 million cycles, unraveled by means of ante‐mortem analysis.