E-Mobility Engineering | September/October 2023 29 Nyobolt EV | Dossier instance, you need a 400 kW input, or around 1000 A to test that battery at 10C, which is what our cyclers are capable of. “We can stack more modules together in series to hit the 400 V input that the cycler has at 1000 A. But in general, current has been the bottleneck, as it isn’t incredibly high in most EV networks. It’s usually below 200-400 A, with voltages getting higher and higher to prevent the need for high currents and the potential losses that follow in conventional highenergy batteries, so that’s what most testers are designed for. “On the discharge side though, getting all the power we’ve used back into the grid is a little more challenging, so we had to do some clever things with the cabling infrastructure for that. Some test regimes would see a couple of megawatts going in and out of our test facility, and in future we’ll be manufacturing batteries and using power at around 20 MW, so that brought some important lessons for the factory design we’ll need one day.” Cell-level mechanics In seeking to encapsulate its battery materials in ideal packaging, Nyobolt has taken two main approaches to cell design. Richard Ward, head of mechanical engineering at Nyobolt, says, “First, there is the cylindrical cell format, as popularised by Tesla and now widespread throughout the EV world. We also have a pouch cell battery, which is available as a small design as well as a larger version. “The small pouch cell is what we’re primarily using at the moment; it’s effectively the first stage for initial manufacturing and road-testing the chemistry inside our modules and packs,” he adds. “But we’ve also manufactured larger pouch cells, because there will be end-user applications in which storing a given amount of energy in a smaller number of larger cells will be more efficient than using a larger number of the smaller cells. For instance, larger commercial EVs will still need bigger packs than the 35 kWh on our demonstrator EV. “And when I say using larger cells is more efficient, I particularly mean the weight and cost saved via the reduced number of welding and connection points, sensors and so on that comes with fewer cells per module and pack. Ultimately, having a large number of individual cells will come with those and similar overheads, which will conflict with maximising Wh/kg or Wh/litre one way or another – and even if we’re heavily focused on maximising charging times while keeping lifespans long, volumetric and gravimetric energy density are still going to be major targets for us as well.” The company adds that its use of cylindrical cells was primarily in the prototyping stages, through its partnership with Prof Alex Roberts at Coventry University, who has access to a pilot line for cylindrical cell assembly. Nyobolt has since moved away from these to pouch cells for production though. Nyobolt cites various advantages of pouch cells for commercial products. The format maximises the amount of active material that can be packaged in a given volume, and the shape, surface area and lack of a hard case enable effective heat extraction from each cell and hence high thermal efficiency for the overall module. The modules in the EV’s demonstrator pack use Nyobolt’s small pouch cell format, mounted in an aluminium frame for fastening and coolant flow (Courtesy of Elan PR) Creating the embedded systems for the EV and battery required some reference studies of highcurrent PCBs in megawatt-level vehicles across rail, marine and mining (Courtesy of Elan PR)
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