Abstract
The study involves a bottom-up approach, from bottom cells to large supercapacitor pouch cells, encompassing the design, modelling and fabrication stages of the cells leading to a 12 V transient start–stop (TSS) power system for automotive applications. More specifically, the design of a large composite supercapacitor is presented, consisting of a high power density component and a high energy density component, hybridised at material level. The composition of the composite supercapacitor is optimised to be application-specific so that it satisfies a specified energy-to-maximum power ratio for the 12 V TSS system. The testing of the large composite supercapacitor pouch cells and the 12 V TSS system proves the validity of the bottom-up approach, validates the design and the proposed electric circuit model and its parameters, fitted according to experimental data of small laboratory cells and applied successfully to the large cells, and proves the high quality of the scaled-up fabrication processes. The 12 V TSS power system of seven large composite supercapacitor cells satisfies the set criteria of energy and maximum power for the specified duration, 15 Wh and 4.2 kW respectively, at a total mass of 3.94 kg, below the original set limit of 5 kg.
Highlights
A transient start–stop (TSS) power system aims at conserving the energy of a vehicle, provided by an internal combustion (IC) engine or a battery, reducing harmful emissions to the environment, especially in the case of an IC engine
The present study describes the development of the 12 V TSS power system following a bottom-up approach across modelling, design and experimental scaling up stages, from small 2–4 cm[2] laboratory scale cells of each type of electrode material, small high energy electrochemical double layer capacitors (EDLCs) and small high power EDLC, to large composite EDLC pouch cells of over 0.5 kg each
An electrical circuit (EEC) model was suggested for each type of EDLC part in the composite EDLC, namely the high energy density EDLC part and the high power density EDLC part
Summary
A transient start–stop (TSS) power system aims at conserving the energy of a vehicle, provided by an internal combustion (IC) engine or a battery, reducing harmful emissions to the environment, especially in the case of an IC engine. As the above design of each composite EDLC in the 12 V TSS power system, the modelling starts from the small laboratory cells of the ACF-based high energy density EDLC (4 cm[2] cells), EDLCe, and the coating-based high power density EDLC (2 cm[2] cells), EDPCp, the experimental data of which is presented in Fields et al.[8] Figure 2(a) presents the equivalent electrical circuit (EEC) model used in this study for each small laboratory cell, EDLCe or EDLCp, consisting of an inductor, L1, connected in series with a resistor, R1, a Voigt circuit, and a constant phase element, CPE3. Increasing the coating thickness above this value increased the cell resistance; the coating thickness value of 150 mm was selected Based on these data, the application-specific design of the composite supercapacitor in the ‘Modelling and design’ section yielded a required area of high power EDLC-equivalent of AP 1⁄4 2880 cm[2] with coating-type electrode material of mass mP 1⁄4 46.1 g at coating areal density of 8 mg cm–2. The voltage of the EDLC system was measured at the end of the five consecutive engine start tests
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