VARTA Microbattery has developed innovations in the construction of lithium coin cells, which have increased their energy density to the point where standard coin cells (VARTA Microbattery CoinPower) can now replace custom battery packs. These cells feature a coiled electrode construction, which makes more efficient use of the space inside the casing, while providing a greater surface area of electrode per cubic centimeter than conventional stacked or layered electrode constructions.
VARTA Microbattery has also invented and patented the ILoc casing construction in which precisely engineered upper and lower casings slide together securely, eliminating the requirement for a bulky rim and separate sealing material. This design also enables the cell to operate as a current interruption device when the pressure inside the cell exceeds a certain level – for example, when the cell is charged at an excessive current or voltage – the upper and lower casings separate by a small, controlled amount sufficient to break the circuit and shut down the battery.
While CoinPower’s electrode design plays a crucial part in producing a cell with a high energy density, it is also important to note the supporting electronic circuit is also small. A CoinPower cell requires only a standard circuit protection IC, widely available at low cost from dozens of manufacturers (including the ZSPM4551 from ZMDI and several models from Skyworks including the AAT3681, AAT3681A, AAT3688 and AAT3688A), plus two miniature passives. The footprint of this circuitry can be considerably smaller than the complex PCB generally implemented in custom battery packs.
Device manufacturers can now avoid the cost and risk associated with custom engineered battery packs while achieving high energy capacity in a small footprint. Additionally, CoinPower’s hard metal case enables products to be assembled using automated equipment, lowering production costs and eliminating risks of manufacturing defects.