Appropriate methods for evaluating the efficiency and capacitive behavior of different types of supercapacitors

The development of new brands of supercapacitors (SCs) has led to a variety of energy storage mechanisms and frequently to performance overestimation or erroneous presentation of the capacitive behavior through applying mathematical relations valid only for electrical double-layer capacitors (EDLCs). This paper addresses a realistic evaluation of capacitive performance and efficiency of SCs based on carbon electrodes. The presented examples of imprecise data processing include misleading information, such as seeming discharge capacitance increase during SC aging and coulombic efficiencies of 90% for SCs involving redox processes whilst energy efficiency is only 50%. Even in typical EDLCs, energy efficiency is 5–10% lower than coulombic efficiency.