Traction batteries made up of dissimilar cells

In this paper, the feasibility of a 2-part battery with separate `energy´ and `power´ modules is investigated. The battery is constructed of two parallel modules, each using a unique cell type. This type of battery has often been proposed as a solution to the absence of a cell optimised for both energy density and power density. In the energy-optimised module, the cell type is chosen for its specific energy, but will have limited power delivery ratings. In the power-optimised module, the cell type is chosen for its high power rating, but will have limited energy storage ability. A study has been made of the practicality of using such a two-part battery, initially with an intelligent charge management scheme between the two `halves´ of the pack, then without. The charge management brings better usage of the cells, but at a cost and weight disadvantage, hence the interest in an `unmanaged´ option, where dissimilar cells are directly connected. The evaluation is made theoretically, on the basis of weight and volume savings of the pack in meeting vehicle energy and maximum power targets and then the overall efficiency when exercised over typical drivecycles.