Penn State Team Devises New Control Strategy to Enhance EV Battery Performance when Driving in Cold Temperatures

Researchers at Penn State, with a colleague from EC Power, have devised a new control strategy that can rapidly restore EV battery power and permit full regeneration while driving at temperatures as low as −40 °C.  The strategy involves heating the battery internally during regenerative braking and rest periods of driving.

In a paper in the Journal of Power Sources, they report that this technique fully restores room-temperature battery power and regeneration in 13, 33, 46, 56 and 112 seconds into uninterrupted driving in 0, −10, −20, −30 and −40 °C environments, respectively.  Correspondingly, the strategy significantly increases cruise range of a vehicle operated at cold temperatures—49% at −40 °C in simulated US06 driving cycle tests.  Based on their findings, the team suggests that smart batteries with embedded sensing/actuation can significantly improve their performance compared to more conventionally controlled counterparts.

Drastically reduced driving range is a major challenge for electric vehicles (EVs) operating at subzero temperatures as it exacerbate drivers’ range anxiety.  Two technical problems of Li-ion batteries are particularly long-standing.  First, regenerative braking is restricted or completely turned off at cold temperatures due to the phenomena of lithium plating that could severely reduce battery life and increase safety hazards.  Second, there is significant power loss, up to 10 fold at −30 °C, due to sluggish reaction kinetics, slow diffusion, reduced electrolyte conductivity, and increased solid-electrolyte interface (SEI) resistance at low temperatures.

Great efforts have been made to increase battery power at cold temperatures, notably reformulating electrolytes, hybridizing batteries with high-power supercapacitors, and preheating batteries before driving.  Among these approaches, battery preheating has been extensively investigated due to its relatively simple implementation.  But preheating is slow, typically tens of minutes, and inconvenient, prohibiting instantaneous mobility of EVs.

Here we demonstrate an active control strategy that can rapidly restore EV battery power while driving, which eliminates any need to wait for preheating.  This control strategy represents a new paradigm allowing batteries to be actively controlled and manipulated.  We also demonstrate, through simulated US06 driving cycle tests and an energy balance analysis, that power restoration while driving could significantly increase EV driving range by fully recuperating braking energy and significantly increasing utilization of energy stored.

—Zhang et al.

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