lighter, but there are issues of safety, primarily because of lithium’s reactivity with water, and regeneration or recharging needs to be developed. Solid polymer Li-ion electrolyte batteries offer higher energy densities and more stability than Li-ion batteries, but safety and operational challenges (such as achieving acceptable current density at ambient temperatures) will be difficult to meet. There do not appear to be any other radically new battery technologies on the horizon (the lithium metal-air battery concept has been around for many years) that could economically provide the enhanced performance needed, but the vibrant research and development programs world-wide may produce a technology that will overcome these barriers.

Also, totally different approaches are being considered. Swapping battery packs at stations that charge them for the next vehicle is one possibility, but it is not clear if pack and vehicle design will be sufficiently standardized to make this widely practical. Battery leasing is another proposal. Leasing could lower the initial cost to the consumer and perhaps provide some reassurance about durability, but it would not necessarily lower overall costs.

It should also be noted that higher CAFE standards or high oil prices will improve the competitiveness of PHEVs. Conversely, HEV cost and performance characteristics will continue to improve, reducing the fuel-saving advantage of PHEVs. Although HEVs will be more expensive than nonhybrid vehicles, PHEVs will be significantly more expensive than HEVs. However, the low fuel consumption of PHEVs, especially the PHEV-40 type, will be advantageous in helping the United States reduce its dependence on imported oil. Also, once the carbon intensity of grid electricity is reduced, PHEVs will be able to significantly reduce greenhouse gas (GHG) emissions from the light-duty vehicle sector.

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