Extending the Range of Electric Vehicles Through the Use of a Dual-Chemistry Battery System

Electric vehicle range and charging time are two factors which limit the acceptability of the electric powertrain as a practical replacement for those customers who need a vehicle for longer distance driving. The electric vehicle range is directly proportional to the useful energy available within the energy storage system. The useful energy can be increased by combining two complementary battery chemistries which operate in a parallel configuration. The dual chemistries combined with the appropriate supervisory controls are ratioed to allow the energy storage system to operate more efficiently, regardless of the driver demand. The energy transfer of the dual chemistry system is enhanced in both discharging and charging due to a reduction of I²R losses. This reduction in power losses while fast charging has the benefit of reducing the overall charging time and increasing the available state-of-charge (SOC). Simulation of the system indicated additional benefits such as reduced stress, less internal heating, and increased electrical power availability during cold battery operation. These enhancements can be realized through the proper matching and ratioing of the battery chemistries, so that the two battery chemistries complement each other. These benefits have been validated in vehicle level testing.