Scalable Pore Size Tuning Process for Seeking Better Cathode of Lithium Ion Capacitor and Development of High-Performance Full Cell Device through It
Authors: Won Jong Ho , Kang Jeung Ku 
Published: February 2020

With the development of the industry, the need for better energy storage devices that can be used in various devices continues to grow, but the pace at which practical alternatives are developed is very slow. Many prior studies have succeeded in increasing the energy density of lithium-ion batteries to a significant level, but they have not been able to lead to actual production due to battery instability, life problems, production and price issues. Many battery manufacturers currently faced the limit capacity of the cathode and are aiming to improve the energy density by developing an anode with a capacity of 430 mAh / g by mixing graphite with a high capacity active materials. However, in such a method, it is difficult to satisfy the high power density due to the difference in charge/discharge speed between the graphite and the high capacity active material. So, in reality, current access and pricing policies are not able to create a significant gap in the lithium-ion battery platform. For this reason, the study of lithium-ion capacitors satisfying both energy density and power density has received much attention due to its high versatility. Lithium-ion capacitors can use conventional lithium-ion anodes and use carbon materials instead of heavy metal alloys as cathodes. Initial lithium-ion capacitor research was concentrated on an anode capable of high capacity such as a lithium-ion battery. In fact, the main factor that determines the capacity per mass/volume of lithium-ion capacitors is the capacity of the cathode. As the cathode of the lithium-ion capacitor, a porous carbon material which has been used as the electrode material of the electric double layer capacitor has been widely used. However, the electrode of the EDLC stores OH- ions, while the cathode of the lithium-ion capacitor should adsorb and store much larger ions such as PF6- ions. Thus, the electrode material originally used in the EDLC may be unsuitable for storing larger ions due to the small pore size. Here we have found improvements that can improve the capacity of lithium-ion capacitors. We intend to develop a cathode material for lithium-ion capacitors that can store larger ions such as PF6- ions in this work. We have developed seven cathode materials that composed of concentrate pores with a certain size using graphene and a template that is vaporized below 100 degrees of Celsius. The size of the pores ranges from less than 5 nm to 150 nm. Although the effects of the number of Angstrom pores have been addressed in the meantime, the impact of macro size pores has not been addressed in the lithium-ion capacitor research. We evaluated the capacity and characteristics of the developed cathode using PF6-, TFSI-, BF4-, ClO4-, and so on. In the experimental results, we confirmed that macro-sized pores have a profound effect on the adsorption and storage of ions and their obvious tendency. To put it briefly, the TFSI- and PF6- ions are significantly different in size, and thus the cathode with the highest capacity is different from each other, which is revealed by the tendency. Additionally, the full cell lithium-ion capacitor with developed cathodes and a commercial MCMB anode recorded the highest energy density of up to 145 Wh/kg and an energy density over 70 Wh/kg at a power density of 7200 W/kg. We have demonstrated the effect of macro-sized pores on the cathode of a lithium-ion capacitor and succeeded in developing a cathode material for an excellent lithium ion capacitor.