Emergency Li-ion Battery Discharge using Nonlinear Model Predictive Control with Temperature and Venting Pressure Constraints

Because thermal events in battery systems can evolve quickly, any response to prevent thermal runaway propagation and re-ignition will need to be fast, including an emergency fast discharge. However, a fast discharge can create internal heat generation and lead to high temperatures where gas generation and venting of the flammable electrolyte can occur. This work formulates the fast discharge as a multi-objective, nonlinear model predictive control problem that leverages an electro-thermo-mechanical model. Constraints are placed on temperature and pressure to avoid cell venting. The controller is applied to simulate a fast discharge of a fully-charged, 4.6 Ah pouch cell under three constraint scenarios. When the maximum temperature is set to 45°C, representative of an upper limit during normal operation, discharging down to 60%SOC took 13 minutes. When the constraint was increased to 80°C, discharging to 60%SOC was four times faster, but the cell vented after 14 minutes. Adding a pressure constraint to the latter case allowed the cell to discharge to 60%SOC equally as fast while also avoiding cell venting in the future, achieving a safe emergency discharge. This is the first work that applies a nonlinear controller with venting considerations to manage abnormal battery behavior for mitigating thermal runaway in a Li-ion battery.