28 September/October 2023 | E-Mobility Engineering nuance there with regards to balancing the two electrodes in the cell, or trading off between capacities and C-rates with metal oxide additives or other approaches. “But they achieved incredible things, like batteries capable of discharging at 100C. In-house, we know how to exceed even 200C, it’s just that for now, that far exceeds what the commercial world needs.” Nyobolt’s research has therefore built on the contributions of its former motorsport engineers and gone beyond, particularly with regard to increasing charging speed and cycle life – tens of thousands of cycles are the target, including high transients and extremes of temperature without damaging the materials. Along the way it built a library of which materials to pick for a desired parameter increase, such as peak power, continuous power, range or thermal stability. “Perhaps most important from our point of view, we’ve tailored our anode for as low a resistance as possible for the amount of material in each cell, to enable more ions to flow in and out and at a high rate,” Dr Shivareddy says. “Broadly there are two ways to go about that: change the material or work from a blank sheet completely; or tune an existing chemistry using different particles, surface properties, ways of installing them into an electrode, processing conditions, binders and other additives, and so on. “All those things entail a cost structure which we need to bear in mind if our smaller packs are really to enable cost savings for OEMs and drivers, on top of giving drivers a good experience in which they have a smaller battery with less range, but can replenish that range in 5-6 minutes at a station.” He adds that high C-rates and the controllability enabled through Nyobolt’s anode material and other innovations can also feed into the discharge side. Optimising the battery’s high powerto-weight ratio can translate into fast acceleration and smooth control for drivers, assuming the downstream parts of the car such as gearboxes and SiC inverters are built to make use of the high power delivery. “The benefits of high power density don’t stop there either,” Dr Shivareddy says. “Thermal management requirements for instance are much lower across the board in our batteries and our EV, because the impedance is much lower, which of course means heat losses are inherently lower too. “As well as learning about high power densities and building our library of which materials improve certain properties, we learned a lot about what doesn’t work. Conventional anode materials like silicon oxides have problems at the atomic level and higher up at the electrical interface level, which interfere with our ability to maximise ionic and electrical conductivity, and we need to do that to easily get an electron out of the cell every time an ion goes in. “Each material has its own ionic conductivity, electrical conductivity and interfacial transfer properties. In essence, we found a way within the constraints of known materials and chemistries to engineer for maximising these properties without making mistakes like packing in so much material per cell that there’s no point of access for electrons or ions to enter.” Dr Shivareddy also notes that Nyobolt’s cell designs are largely agnostic regarding cathode materials, and can use whichever cathode is appropriate for a given application, such as NMC for automotive applications or LFP if avoiding nickel and cobalt or enhancing safety for industrial purposes are desired. Battery testing In the course of testing and maturing its cells for high power density applications, Nyobolt’s primary challenge was to achieve the high currents necessary for identifying the electrochemical limits of its battery designs. “The amount of external power available from the grid defines limits on things like how many batteries and test rigs you can run in parallel,” Dr Shivareddy explains. By and large, the company has used COTS equipment for testing, simulation, analysis and data recording, particularly for test cyclers and chambers for providing pack-level currents and conditions. “That said, we tend to do most of our testing at the module level,” Dr Shivareddy says. “If you’re working with a pack storing 100 Ah or 40 kWh for Although Nyobolt used cylindrical cells in its prototyping stages, it has since moved to pouch cells for production (Courtesy of Elan PR)
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