Batteries for Plug-in Hybrid Electric Vehicles (PHEVs): Goals and the State of Technology circa 2008

This report discusses the development of advanced batteries for plug-in hybrid electric vehicle (PHEV) applications. We discuss the basic design concepts of PHEVs, compare three sets of influential technical goals, and explain the inherent trade-offs in PHEV battery design. We then discuss the current state of several battery chemistries, including nickel-metal hydride (NiMH) and lithium-ion (Li-Ion), comparing their abilities to meet PHEV goals, and potential trajectories for further improvement. Four important conclusions are highlighted. First, PHEV battery “goals” vary according to differing assumptions of PHEV design, performance, use patterns and consumer demand. Second, battery development is constrained by inherent tradeoffs among five main battery attributes: power, energy, longevity, safety and cost. Third, Li-Ion battery designs are better suited to meet the demands of more aggressive PHEV goals than the NiMH batteries currently used for HEVs. Fourth, the flexible nature of Li-Ion technology, as well as concerns over safety, has prompted several alternate paths of continued technological development. Due to the differences among these development paths, the attributes of one type of Li-Ion battery cannot necessarily be generalized to other types. This paper is not intended to be a definitive analysis of technologies; instead, it is more of a primer for battery non-experts, providing the perspective and tools to help understand and critically review research on PHEV batteries.