Lithium Batteries 101: Electrical Modeling 2: Energy and Dynamics

With the simple voltage source and resistor model, we can now determine the charge and discharge current capability of a battery as a function of SOC. We can then determine the power availability vs SOC as well. As discharge power levels increase, the cell delivers less energy both due to thermal dissipation, as well as inaccessible energy stuck at low SOC. High power pulse loads such as racecars and EVTOL aircraft are often limited by high power availability at low SOC and have to carry increased energy accordingly.

After exploring additional graphical viewpoints, we consider the dynamic response of cells. Our one R model does not capture the dynamics in the cell and therefor struggles to predict the voltage in response to a current pulse or step. By adding RC pairs to the cell model we can capture dynamics more accurately. These RC pairs can be estimated or model fit by collected step response data and calculating the contribution of various terms over time.

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