Dynamic analysis of bi-material cathode in lithium-ion battery capacitors by DRT method

Lithium-ion battery capacitor with bi-material cathode containing battery and capacitor materials combines the characteristics of lithium-ion battery and supercapacitor, filling the gap in meeting application needs for both high power and energy density. However, research on the operating mechanisms of bi-material cathode in lithium-ion battery capacitor is still in its infancy, particularly lacking in dynamic analysis. Distribution of relaxation times method allows for efficient analysis of dynamic characteristics by deconvolving electrochemical impedance spectroscopy. This study applies this method to lithium-ion battery capacitor for the first time, systematically analyzing relaxation times and impedances of various electrochemical processes in activated carbon, LiNi 1/3 Co 1/3 Mn 1/3 O 2 , and bi-material cathodes at different states of charge. The polarization dynamics of the bi-material cathodes reveal the synergistic effect of the two materials. Ohmic impedance remains stable, while interfacial and charge transfer impedances decrease with increasing voltage, and diffusion impedance first decreases and then increases. In-situ electrochemical impedance spectroscopy further indicates that the addition of activated carbon improves the rate performance of the bi-material cathode and the increase in temperature accelerates the reaction dynamics of the bi-material cathode. Additionally, dynamic analysis is conducted on soft carbon anode and full-cell, showing good compatibility between the bi-material cathode and anode. These findings enhance the understanding of the dynamics in bi-material cathodes and guide the development of high-performance and safe lithium-ion battery capacitors.