Pulse Discharge Power Availability of a Lithium-Ion Hybrid Vehicle Battery Pack

A previously validated 1-D electrochemical model of a 72 cell, 6 Ah, 276 V nominal lithium-ion hybrid vehicle battery pack is used to predict maximum discharge current for discharge pulses ranging from zero to twenty seconds in duration from various state of charge (SOC) initial conditions. Ohmic drop from open-circuit potential limits instantaneous pulse power capability (83 kW from 50% SOC) while Li⁺ diffusion inside negative electrode active material solid particles limits long-time capability (28 kW for a 20 second pulse from 50% SOC).

A simple lumped negative electrode solid diffusion model is derived to dynamically describe electrode-averaged solid phase concentration distribution inside of active material particles as a function of measured current time history. Based on the assumption that depleted negative electrode surface concentrations cause end of discharge (EOD) at the minimum voltage limit, the model explicitly estimates maximum available pulse current for pulses of 10 seconds or longer to within 5% accuracy.