Rechargeable sealed batteries require apparatus and methods for rapid recharging. In general, a rapid charge is considered to be any current equal to, or in excess of, the nominal one-hour current rating of the battery or cell. The nominal one-hour rating is generally referred to as the "capacity" (C). Capacity is more specifically defined as the nominal rate of discharge current for one hour, to a selected voltage, such as one volt per cell. For example, a cell normally rated at 1.5 ampere-hours has a C rating of 1.5 amps. Thus, any charging current applied to the cell which is in excess of 1.5 amps is considered to be a rapid charging current. In contrast, slow or trickle charging is generally considered to be any currents less than C, typically in the neighborhood of 0.1 C to 0.5 C.
Rechargeable batteries may be charged at many rates varying from trickle charging rates such as 0.1 C to extremely rapid charging rates as high as 10 C. Users of rechargeable batteries would prefer that the battery provide maximum capacity and minimum recharge time. To this extent, high rates of charging batteries are desirable. Unfortunately, the deliverable capacity of a battery cell is reduced as the charging rate is increased. FIG. 1 shows the relationship between deliverable capacity and charging rate.
As a result, a compromise is typically struck between the deliverable capacity of a battery and the recharging rate. Typically, this compromise results in charge rates of 0.2 C-1.0 C in order to provide the highest possible usable capacity while still maintaining a reasonable recharge time. A method of providing high deliverable capacity and very short recharging times, that is, recharge rates greater than C, would be highly desirable and a significant contribution to the art. Users of rechargeable batteries would find such a method to be a significant improvement over the prior art.