Electrical Modeling and Impedance Spectra of Lithium-Ion Batteries and Supercapacitors

Abstract

In this study, electrical models for cylindrical/pouch-type lithium Li-ion batteries and supercapacitors were investigated, and the impedance spectra characteristics were studied. Cylindrical Li-ion batteries use Ni, Co, and Al as the main materials, while pouch-type Li-ion batteries use Ni, Co, and Mn as the main materials. Herein, 2600–3600 mAh 18650-type cylindrical Li-ion batteries, 5000 mAh 21700-type cylindrical Li-ion batteries, 37–50.5 Ah pouch-type Li-ion batteries, and a 2.7 V, 600 F supercapacitor are compared and analyzed. For a cylindrical Li-ion battery, the (Formula presented.) value of a battery with a protection device (circular thermal disc cap) is in the range of 14–38 mΩ. For the 18650-type cylindrical Li-ion battery with a protection device, the (Formula presented.) value of the battery is between 48 and 105 mΩ, and the protection device increases the (Formula presented.) value by at least 33 mΩ. A good Li-ion battery exhibits (Formula presented.). Moreover, it has small overall (Formula presented.) and (Formula presented.) values. For the 21700-type cylindrical Li-ion battery with a protection device, the (Formula presented.) value of the battery is 25 mΩ. For the pouch-type Li-ion battery, the (Formula presented.) value of the battery is between 0.86 and 1.04 mΩ. For the supercapacitor, the (Formula presented.) value of the battery is between 0.4779 and 0.5737 mΩ. A cylindrical Li-ion battery exhibits a semicircular shape in the impedance spectrum, due to the oxidation and reduction reactions of Li ions, and the impedance increases with a slope of 45° in the complex plane, due to the (Formula presented.) generated by Li ion diffusion. However, for a pouch-type Li-ion battery, the impedance spectrum exhibits a part of the semicircular shape, due to the oxidation and reduction reactions of Li ions, and the (Formula presented.) generated by Li ion diffusion does not appear. In a supercapacitor, the oxidation and reduction reactions of ions do not appear at all, and the (Formula presented.) generated by Li ion diffusion does not occur.