Assessment of Li-ion capacitor for using in BEV and HEV applications

In hybrid electric vehicle (HEV) and battery electric vehicle (BEV) applications, the energy storage unit can be considered as a key issue. The energy storage system should be able to have good performances in the terms of peak powers and energy density. However, in the most BEV applications, the battery is dimensioned as a high energy system. This yields that the battery is not applicable to provide high peak current. In order to enhance the power capabilities of such batteries, EDLCs could be used. But, the energy density of this system is a limitation factor. In the last few years a new energy storage technology has been developed, which is called Asymmetric Lithium-Ion Capacitors. Based on the performed tests, we observe that the energy density of such systems is few times higher than EDLCs and the power performances exceed few times the best lithium-ion battery capabilities.
In the framework of this study the general characteristics of Li-Cap are analyzed. The focus lies on the power density, energy density, and the performances at different temperature conditions. Furthermore, the capabilities in terms of life cycle and electrochemical impedance spectroscopy are investigated.
In addition, in this report a new model developed in Matlab/Simulink is proposed. This model can estimate the Li-Cap behavior under all conditions such as state of charge, temperature and life cycle as well. Based on the developed model, we will be able to classify this new rechargeable energy storage system. Finally, a detailed comparison between the conventional EDLCs, Li-Cap and lithium-ion batteries will be done.

Publication year:2012

Keywords:Lithium, EDLC, Model