Tag Archives: Supercapacitors

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.

Seaweed For Making Superconductors and Supercapacitors

Seaweed, a kind of algae, and a part of cuisines in many parts of the world could be worked to supply power to electronics and other devices. Researchers have developed a material from seaweed to produce better superconductors, batteries, and fuel cells.

The research has been presented at a meeting of the American Chemical Society (ACS) on April 5, 2017.

Dongjiang Yang, PhD, a team member explains that carbon rich materials offer the most efficient energy storage solutions. Since the team wanted to use a green method for making superconductors, they chose seaweed, which is highly renewable as the base material. The scientists have intended to use seaweed extract as a template for fabricating a chain of porous materials that could be used to build the superconductors and energy storage solutions.

Although conventional carbon materials like graphite and graphene dominate the prevalent energy scenario, upcoming advances in storage devices could call for more sustainable materials. Yang, who is at Qingdao University in China, says that abundantly available seaweed could provide a more lasting solution in this regard. He has worked with colleagues in Griffith University in Australia and in Los Alamos National Laboratory in the US to devise a special kind of structure from the algae.

Egg-Box Structure

The scientists drew out porous carbon nanofibers from the seaweed extract by the process of chelating or binding. This process involved attaching cobalt ions to the alginate molecules of the seaweed. These molecules enveloped the cobalt metallic ions, which resulted in the formation of the nanofibers with a special structure resembling an egg-box. This structure contributes to the stability of the material so that the synthesis can be controlled.

Wide Range of Functions

Tests performed on the material showed that its reversible capacity is very high, around 625 mA hours per gram. This is much more than 372 mA hours per gram, which is the corresponding value for that of traditional graphite anodes used in lithium ion batteries.

Furthermore, the material performed as an efficient superconductor with a capacitance as high as 197 Farads per gram. This could be exploited in supercapacitors and zinc-air batteries. Tests also revealed that the performance of these egg-box nanofibers is as good as platinum-based catalysts used in fuel cells.

The scientists had first made public their findings on the egg-box structure in 2015. Since then they have been upgrading the technology involved. It is expected that there would be further improvements of the material.

For instance, the researchers explain that they have worked on the egg-box structure to reduce certain flaws in the seaweed structure that increased the motion of lithium ions. This helped to fabricate improved cathodes used in lithium ion batteries enhancing the performance.

In a more recent development, the researchers have forwarded a technique by which they have combined carrageenann, a variety derived from red algae with iron to prepare a carbon aerogel doped with sulfur. It has a very porous surface making for an extremely large surface area. The researchers say that this could be used very effectively in supercapacitors and in lithium sulfur batteries.

The researchers are now working towards commercial production of the seaweed-based devices.