Aerospace Battery Simulation: New Frontier

We did have the challenge of doing many simulations because one of the items is that this is a new technology, and one of the critical parts is that there are two parts to the simulation. One of the uses profiled is the drive cycle and the flight profile. We had to learn and understand that and then get into our upfront simulation activities to see how it didn't respond.

Thermally for an aircraft, we need to look at the entire system response in terms of accuracy of state of charge, which is different from a ground vehicle where you have a certain amount of peak and continuous power. A ground vehicle can open the throttle to get your 0 to 60 or 60 or 100, and then you come back down to low power. However, aerospace is about continuous high power, medium higher power, and high power. Most of our simulation activities were done on the thermal side before we built anything.

The primary aerospace concern, inherently an issue with any lithium-ion battery, is thermal runaway. We optimized our battery cassette design from the beginning of the project to look at a single-cell or dual-cell runaway of the cell without propagation. That means in traditional automotive production designs, we prevent thermal runaway with any method in the pack design.

Nevertheless, we cannot entirely prevent it. The design objective in automotive is to prolong that event so you have enough time. We're talking minutes, tens of minutes, for the operator, the driver to get alerted and move out of there. For the aircraft application, we couldn't do that. We have to stop the propagation.

To come up with the right design for the mechanical system, we did many simulations and individual cell testing, then took the learnings or the data, the actual data of the energy, the release of the energy over time, and how it then spreads within the cassette and spreads within the entire system to then do the simulation and optimize and change materials.

We changed the construction of the units to come to a simulation result that gives us confidence that the thermal event will not spread. It will have two or three unusable cells, and an entire cassette is inoperable, but the whole battery system is still fully functional with a minor degradation, and the airplane can still fly.

Physical testing validated all the simulation activities and was translated into actual tests and results.