Comparison of rechargeable lithium and nickel/cadmium battery cells for implantable circulatory support devices

Size and weight constraints are critical areas in the design of implantable medical devices. For this reason, a study of different rechargeable lithium and nickel/cadmium (Ni/Cd) battery cell types was undertaken to determine which cell type, when assembled into a multicell battery pack, would provide the smallest and lightest power source for implantation. The discharge rate and cycle life characteristics of 2 different rectangular prismatic Ni/Cd cells and 5 different rechargeable lithium cells were determined at 37 degrees C by charge/discharge cycling, the cells using a constant discharge load of 0.87 A. Using the observed discharge rate and cycle life characteristics of the cells, along with the desired performance criteria of 30 min operating time at the end of a 1-year implant period, the projected weight and volume of the various 12-V battery packs were determined. These results showed that one of the rectangular prismatic Ni/Cd cells would yield the smallest (53 ml) and lightest (189 g) 12-V battery pack that met the performance criteria specified. The results also indicate that, for applications requiring long implant times, cycle life can be more important in the selection of cells for a small, lightweight battery pack than specific energy or energy density.