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

equivalent break-over for an aviation steady-state application,” he says. He explains that the silicon allows more of the active elements to be deposited on the anode in the formation process during cell manufacture, when it receives its first charge under carefully controlled conditions, becoming lithiated. “That is the potential energy that is being created, and then the ion exchange is what delivers the electrical performance,” he says. “Silicon allows an increase in that activity to take place.” He emphasises that the 622 and 811 chemistries have different pros and cons, with 622 better for stability and service life, and 811 for power density. Cells with 622 chemistry are lasting beyond 3000 cycles, whereas the capacity of cells with 811 chemistry fade on a steeper gradient. He adds that 811 cells are still good for 1500 cycles, but for vehicles where total cost of ownership is more important than ultimate performance, 622 is better. Wight emphasises the importance of the end-use requirement for the cell in the battery pack and the vehicle- to-chemistry selection, stressing that understanding the duty cycle is critical. “In the IC world you wouldn’t put an engine with a 12,000 rpm limit but only a 1500 rpm useable range in a commercial vehicle or family car, because it would be horrible to drive. Similarly, with batteries, it is important to make sure they are fit for the vehicle’s purpose.” Optimising chemistries Optimising chemistries for different applications involves extensive testing using small form factor coin cells to evaluate multiple combinations of materials against a number of performance parameters under various conditions, such as temperature extremes. “We look carefully at an electrochemical level, which allows us to target our questions and to make sure we are down-selecting based not just on the headline performance parameter, but also on secondary and tertiary parameters that are not immediately obvious but are necessary to optimise for,” MacAndrew says. “The data that comes out is so detailed that we spend many hours looking at one set of results. Their interactions are quite extensive, and the complexity of that data means it still has to be interpreted even though it has gone through a powerful computer using AI to pick out the information we need to see.” The process also helps in designing cells for safety, particularly with regard to finding electrode chemistries that are resistant to thermal runaway while also achieving the required performance in combination with the other components of the cell, MacAndrew explains. “We work with separator technology that can help reduce energy release under certain abuse conditions; we optimise electrolytes so they can mitigate for abusive situations or faults, and we implement quality processes to ensure we don’t induce conditions under which resistances can build,” he says. “Then we define how cells need to be operated at a system level to provide a sustainable performance without risking any of the severe reactions that can take place if you charge any cell too much, or if you completely discharge a cell then recharge it. Cells can’t compensate for that level of abuse. “What we define is a safe operating window and safe characterisation of the cell,” he adds. “Then we work with integrators and OEMs who know the importance of the part they play in vehicle safety.” Contrasting safety cases MacAndrew emphasises that the safety cases in aviation and automotive are different. “I would hesitate to say aviation is at a higher level, but it With external work on Volta 1 nearing completion, engineers are working on the internal layout of the plant, with its labs and production facilities Summer 2022 | E-Mobility Engineering 25 Dossier | InoBat Auto