A rechargeable lithium-ion cell capable of being discharged to deliver high power pulses sufficient for implantable defibrillation applications and the like, is described. The cell is housed in a casing having an external volume of 5 cm3, or less. Both the negative and positive electrodes are less than about 0.15 mm in total thickness. Negative and positive electrodes of a reduced thickness provide the cell with high electrode surface area relative to its volume. As such, the present cell is capable of providing pulses in excess of 30C with minimal voltage drop.