Boston Power Swing Li-Ion Battery

Boston Power is looking to build a new battery manufacturing facility here in the states, and they’ve applied for the DOE’s ABC (advanced battery and cell) funds from the stimulus package. They made waves when they introduced the eco-battery for HP’s laptops, what will their automotive batteries have to offer?

The Boston Power Swing 4400 series of batteries is specifically designed for automotive applications, and the battery specifications match up just about perfectly, as long as its going into a large E-REV or BEV due to the comparatively low specific power rates.  It is assumed that the battery uses a nickel-manganese-cobalt cathode.

The high specific energy and high cycle counts would lead to lower amounts of “excess” battery capacity. A 16kW battery pack could be only 115kg (with about 90kg of actual battery mass), however its continual power would only be about 40kW (53HP). The pulse power would be over 120kW, however their specifications indicate this is a 2s pulse (most other manufacturers I’ve seen post 10s pulse rates).

To maintain 65mph, a Volt with a coefficient of drag of 0.3 would have a rolling resistance of 5kW and an aerodynamic resistance of 13kW, for a total of 18kW. This seems low compared to the 120kW electric motor, but remember its only to maintain a constant speed on a flat surface, and it ignores any inefficiencies between the battery pack and the wheels (inverter, motor, transmission). Acceleration times are very dependent on how much pulse power the pack can generate, and for how long.

The specifications also state very high cycle counts at 60% – 7,000 cycles, or far more than would ever be needed by an automotive battery in an E-REV configuration – it would represent over 450,000 miles in a 40-mile pack configuration (7,000 cycles / 60% * 40 miles per charge). Even at higher depth of discharge rates (90%) for BEVs, 2,000 cycles is 150,000 miles in a 75-mile pack configuration.

It seems after much musing and math, the weakest point is specific power, which could be an issue for E-REVs depending on how the numbers work out for maximum speed and acceleration. Though it isn’t an issue with BEVs. In fact these numbers pencil out really well for the proposed Ford Focus BEV – 75 miles/charge, 22kWh battery pack (150kg, less than the Volt pack), 90% DoD for 150,000 miles on the battery before 80%, tiny volume (420W/L is only 52.4L).