Power and thermal characterization of a lithium-ion battery pack for hybrid-electric vehicles

A 1 D electrochemical, lumped thermal model is used to explore pulse power limitations and thermal behavior of a 6 Ah, 72 cell, 276 V nominal Li-ion hybrid-electric vehicle (HEV) battery pack. Depleted/saturated active material Li surface concentrations in the negative/positive electrodes consistently cause end of high-rate (similar to 25 C) pulse discharge at the 2.7 V cell(-1) minimum limit, indicating solid-state diffusion is the limiting mechanism. The 3.9 V cell(-1) maximum limit, meant to protect the negative electrode from lithium deposition side reaction during charge, is overly conservative for high-rate (similar to 15 C) pulse charges initiated from states-of-charge (SOCs) less than 100%. Two-second maximum pulse charge rate from the 50% SOC initial condition can be increased by as much as 50% without risk of lithium deposition. Controlled to minimum/maximum voltage limits, the pack meets partnership for next generation vehicles (PNGV) power assist mode pulse power goals (at operating temperatures > 16 degrees C), but falls short of the available energy goal. In a vehicle simulation, the pack generates heat at a 320 W rate on a US06 driving cycle at 25 degrees C, with more heat generated at lower temperatures. Less aggressive FUDS and HWFET cycles generate 6-12 times less heat. Contact resistance ohmic heating dominates all other mechanisms, followed by electrolyte phase ohmic heating. Reaction and electronic phase ohmic heats are negligible. A convective heat transfer coefficient of h = 10.1 W m(-2) K-1 maintains cell temperature at or below the 52 degrees C PNGV operating limit under aggressive US06 driving. (c) 2006 Elsevier B.V All rights reserved.