Batteries and Supercapacitors

In the past, only mission-critical devices had them. Now, a wide range of electronic applications demands backup power solutions. These applications include consumer, commercial, and industrial end-products. Of the several options available, the most energy-dense solution is that offered by supercapacitors, acting as energy reservoirs during interruptions of the main supply. Typically, this occurs during an outage of the mains power, or during swapping out batteries.

Although they are versatile, supercapacitors present challenges in design. This is due to their capacity to provide only 2.7 VDC. Potentially, this means adding multiple supercapacitors, along with the necessary cell-balancing circuitry, and voltage converters for step-up and step-down for supplying regulated power to the power rail operating at 5VDC. The solution is a nuanced and complex circuit, which not only takes up excessive board space but is also relatively expensive.

Comparing them with batteries can explain why supercapacitors offer many technical advantages for compact, low-voltage electronic applications. Supercapacitors help in designing simple, elegant solutions for powering a rail operating at 5VDC using only a single capacitor in combination with a buck/boost reversible voltage converter.

Modern electronic devices often need uninterruptible power as a critical element to provide a satisfactory user experience. The absence of a constant power source can not only stop the electronic product from operating, but it can also lead to vital information loss as well. For instance, a personal computer operating from mains power will lose the information contained in its volatile RAM during a power outage. Similarly, important blood glucose readings in the volatile memory of an insulin pump may be lost while replacing its batteries.

It is possible to prevent this from happening by including a backup battery. Not only will the battery store energy, but it can also release it during the failure of the main source of power. Currently, devices typically use lithium-ion batteries, as these are mature technology, offering very good energy density. This allows relatively compact devices to offer considerable backup power for relatively extended periods.

Irrespective of their base chemistries, batteries offer distinctive problematic characteristics under specific circumstances. Not only are they relatively heavy, but they also take relatively long times to recharge, which may be problematic in areas with frequent power outages. Moreover, it is possible to recharge the cells only a limited number of times, thereby increasing maintenance costs. In addition, batteries often include chemicals that can introduce environmental and safety hazards.

The supercapacitor, or ultracapacitor, offers an alternative solution. Technically, the supercapacitor is a capacitor with an electric double layer. Manufacturers construct supercapacitors using electrochemically stable, symmetric positive and negative carbon electrodes. They separate the electrodes by an ion-permeable separator that is insulating and use a container that they fill with an organic salt/solvent electrolyte.

Supercapacitor manufacturers design the electrolyte to maximize electrode wetting and iconic conductivity. The combination of the minuscule charge separation and high surface area of activated carbon electrodes results in the very high capacitance of the supercapacitor, as compared to the capacitance of regular capacitors.

The reliance on electrostatic mechanisms to store energy makes the electrical performance of supercapacitors more predictable than those of batteries.