- Charging battery from a standard house outlet

- What defines a PHEV is that it operates primarily in electric mode operating by battery power only. For longer travel, it switches over to operate in HEV mode.

Image source United States Department of Energy

Plug-In HEV concept is to have a long range of Electric Vehicle Mode combined with regular gasoline engine. Over 70% of Americans drive less than 30 miles per day. PHEV concept is to cover the daily commuting distance by battery power. Therefore, only  in those situations where the driver needs to drive further than the average daily commuting distance, would the gasoline engine be required to power the vehicle, and charge the battery back up, when the battery is drained. The PHEV user will charge the battery once a day (typically at night).

Various versions of PHEVs, PHEV-10, PHEV-20, PHEV-40, etc., are under development and under consideration. PHEV-10 signifies that the vehicle’s battery supports up to 10 miles of electric mode driving. With longer driving distance requirements, the user will need bigger (higher capacity) batteries.

Since the bigger battery will function as a HEV battery after its EV mode, the power density requirements are less than those required in the regular HEV. But, the driving distance using the battery (EV mode) is important, which means that energy density plays a much more important role. Thus for the PHEV application, we need medium levels of power performance and energy density performance. The capability of rapid charging would also be very favorable.