Traction batteries for hybrid and fuel cell vehicles must maintain temperatures within operational limits for longer battery lifetime and better performance. The uneven battery temperature due to improper heat transfer during discharging/charging could accumulate battery degradation on hot cells resulting in early failure of the battery pack. Current battery systems use a unidirectional coolant flow for battery thermal management. However, due to the nature of the cooling method, the unidirectional cooling systems are prone to show a largest temperature differential ΔTs between the battery cells at fixed flow boundaries, although sophisticated thermal/fluid designs are implemented to make the battery temperature uniform. Here, an innovative battery cooling method ([1]) using a reciprocating cooling flow is proposed. The reciprocating cooling system switches the coolant flow direction periodically by a valve-fan mechanism. By switching the flow direction periodically and thus the cold and hot boundaries of the battery cooling system, the battery cell temperatures are regulated with a very small fluctuation and the temperature differential ΔTs is drastically reduced. In hybrid electric vehicle and fuel cell vehicle applications, the cooling improvement using the new concept would set battery cooling system free of auxiliary air-conditioning system. Parametric study shows that using the reciprocating cooling system for a Li-Ion battery system, an optimum reciprocating period to minimize temperature differential ΔTs and maximum battery temperature Ts,max exists.

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