E-Mobility Engineering 014 l InoBat Auto dossier l In Conversation: Brandon Fisher l Battery monitoring focus l Supercapacitor applications insight l Green-G ecarry digest l Lithium-sulphur batteries insight l Cell-to-pack batteries focus

Supercapacitors and batteries make an ideal team, reports Peter Donaldson , who looks at how they are used in EVs Perfect partners A lthough batteries and supercapacitors both store electrical energy, they do so in very different ways that bestow them with complementary characteristics. In a nutshell, batteries store energy chemically and offer high energy density (measured in Wh/litre) while supercapacitors store energy in electric fields and offer high power density, measured in kW/litre. That means supercapacitors can absorb and deliver a lot of power in short bursts, which is very useful in many EV applications but is something that batteries don’t do very well, and for which they suffer when forced into applications that require it. Supercapacitors are therefore a battery’s best friend, as one supplier puts it. Illustrating this relationship, they are teamed up increasingly with batteries as load smoothing, ‘shock absorbing’ devices that give the batteries easier lives and allow them to focus on what they do best, which is absorb and deliver large amounts of energy at relatively low rates. This perhaps becomes clearest when considered in terms of charge rates. Where a state-of-the art EV’s lithium- ion battery might accept a full charge in less than an hour, an equivalent supercapacitor could be fully charged in less than 10 seconds, assuming a sufficiently powerful charger could be found. Supercapacitors also typically discharge over time frames measured in seconds, while EV batteries discharge at rates that depend on how the vehicle is driven, often delivering modest amounts of power over several hours. Supercapacitors are much longer lived than batteries as well, withstanding orders of magnitude more charge-discharge cycles and greater extremes of temperature, so they can generally be expected to last at least as long as the host vehicle. Supercapacitor principles Sometimes referred to as ultracapacitors, supercapacitors are called that simply because they have far higher capacitance than ordinary capacitors. In an ordinary capacitor, the insulating layer is either air or a plastic film, while the electrodes can be rigid plates or flexible films coated with conductive materials such as carbon. As the capacitor is charged, electrons leave one electrode, where a positive charge builds up, and collect on the other, building a negative charge. The two opposing charges are kept apart by the insulator, creating the electric field that stores the energy. Connecting the positive and negative electrodes in an electric circuit allows current to flow, discharging the device. A 1 Farad (symbol F) capacitor holding a charge of 1 Coulomb (C) has a potential difference of 1 V between its electrodes, and takes 1 second to charge to 1 V when given a 1 A current. A Coulomb can be thought of as an astronomical number of electrons, and because all electrons carry a negative electric charge and therefore repel each other, forcing them together on one conductor by charging the capacitor is rather like compressing a spring. Lamborghini’s limited edition Sian coupe uses a combination of supercapacitors and an electric motor as a performance booster for its V12 engine (Courtesy of Lamborghini) 42 Summer 2022 | E-Mobility Engineering