FAQ Supercapacitor Construction EDLC Saftey safe Supercapacitors super capacitor Ultracapacitor spel graphene

EDLC Supercapacitors

What is Supercapacitor..?

Supercapacitor also reffered to as Ultracapacitor or Electric double-layer capacitors or Electrochemical double layer capacitors (EDLC) is a electrochemical capacitor with extremly high charge storage capacity when compared to normal capacitors of same physical dimension and weight. In brief Supercapacitor is a high-capacity capacitor with a capacitance value much higher than normal capacitors, but with lower voltage limits, typically maximum single cell voltage rating upto 3.0 Volts DC. But due to high capacitance in given volume/weight Supercapacitors typically stores 10 to 100 times more energy per unit volume or mass than electrolytic capacitors.

To summarize Supercapacitor is similar to the basic capacitor in the sense that it stores energy in an electric field, but with a huge leap over a common capacitor when it comes to energy storage capacity in given size. As such, it can quickly deliver and store energy because there is no chemical reaction involved. It can also survive thousands of charge and discharge cycles.

Unlike convectional capacitors, supercapacitors do not use the conventional solid dielectric, but rather, they use electrostatic double-layer capacitance, and electrochemical pseudocapacitance, both of which contribute to the total capacitance of the capacitor.

Are there any Types or Classifications in Supercapacitors..?

Supercapacitors can be defined or Classified into different types on basis of storage mechanisim which translates into capacity or a capacitance of supercapacitors, which can be defined as below.

Electrostatic double layer capacitance (EDLC), by virtue of charge stored at electrode surface.
Electrochemical pseudocapacitance resulting from reversible reduction and oxidation (redox) reactions or intercalation effect.
A supercapacitor which uses both mechanisms simultaneously is called a hybrid supercapacitor.

Supercapacitor Types — **Types and Classification of Supercapacitors based on Storage mechanisim**

What is storage mechanism and Construction of EDLC Supercapacitor..?

Capacitor: Capacitor construction consist of a dielectric placed between two electrodes. In a conventional capacitor, energy is stored by the removal of charge carriers, typically electrons from one metal plate and depositing them on another. This charge separation creates a potential between the two plates, which can be harnessed in an external circuit. The total energy stored in capacitor is directly proportional to surface area of electrodes, and inversly proportional to distance between these two plates, which is thickness of dielectric in practical capacitor. The dielectric constant value is multiplying factor in final capacitance value of capacitors.
Various Insulating materials with different dielectric constant can be inserted between the plates to allow higher voltages to be stored, leading to higher energy densities for any given size. For example aluminum electrolytic and tantalum electrolytic capacitors, use an aluminum oxide film and a tantalum oxide film as the dielectric, respectively.

Supercapacitor: Supercapacitor construction consist of separtor sandwitch in between porous electrode, and this is soaked in electrolyte. Supercapacitor do not have any dielectric in general, but rather utilize the phenomena of charge separtion at interface area of porous electrode and ions in electrolyte medium, giving rise to two seperate capacitor each at one porous electrode, which electrically gets connected in series, typically referred to as the electric double layer a Helmhozlt Model . In the double layer, the effective thickness of the “dielectric” is exceedingly thin, and because of the porous nature of the carbon the surface area is extremely high, which translates to a very high capacitance. The charge in this is stored at the interface by changing electric field between anode and cathodes.

Supercapacitor Storage — **Storage Mechanism of Supercapacitor**

What are various Carbons (Electrode) Materials for EDLC..?

Carbon Aerogel: Carbon aerogels are nanoscale particles made by pyrolyzing polymeric aerogels, and resin derived carbons. Carbon areogels are activated carbons prepared from polymers, and were widely popular choice for EDLC supercapacitors in past, but they have been largely supplanted by activated coconut shell carbon due reduction of cost of coconut shell carbon over a period of time.

Coconut Shell Carbon: Coconunt shell carbon used in EDLC Supercapacitor is a premium grade activated carbon of purified grade. This Activated carbon is made by charring a precursor, then oxidizing the charred body using an agent such as steam or carbon dioxide to create nanoscopic pores. This is most popular electrode material used in almost all commercially available EDL Supercapacitors.

Carbon Nanotubes: Carbon nanotubes have been extensively studied as supercapacitor electrode materials, the single-walled nanotubes remain prohibitively expensive, while multi-walled nanotubes offer comparable performance to activated carbon but at a higher cost.

Carbide Derived Carbon: Carbon nanotubes have been extensively studied as supercapacitor electrode materials, the single-walled nanotubes remain prohibitively expensive, while multi-walled nanotubes offer comparable performance to activated carbon but at a higher cost.

Graphene: Graphene is a thin layer of pure carbon, tightly packed and bonded together in a hexagonal honeycomb lattice. It is widely regarded as a wonder material it is the thinnest compound known to man at one atom thick, as well as the best known conductor.
Reduced Graphene Oxide (rGO) is eligible electrode material which can replace present activated carbon in supercapacitors, in part due to its high relative surface area (which is even more substantial than that of activated carbon).
Therotically Graphene-based supercapacitors can store almost as much energy as lithium-ion batteries, charge and discharge in seconds and maintain all this over tens of thousands of charging cycles.

How Supercapacitor differs from Battery..?

Supercapacitors can be described as high-capacity capacitors. They have higher capacitance and lower voltage limits than regular convectional capacitors. Functionally Supercapacitors lie somewhere in between electrolytic capacitors and rechargeable batteries in terms of energy storage capacity. Supercapacitors score over convectional Supercapacitors on energy density, and score over power density when compared with battery.

Typically Supercapacitors in present state of development are 20times plus power dense when compared with convectional battery.

The unique default features of Supercapacitors is that they get Charged much faster than batteries, and have over million charge/discharge cycle as compared to lithium-ion batteries which ranges between 500 and 10,000 cycles.

Are Supercapacitors Safe..?

Supercapacitors are absoultely safe device unlike batteries when mistreated/abused they do not explode. Unlike Lithium-Ion batteries there is no thermal runaway issues. Above all Supercapacitors are Environment friendly product as no hazardous material is used.

What if Supercapacitor polarity is interchanged..?

At the basic level Supercapacitors are originally non-polar device. The desiganated anode and cathode are similar or symmetrical type. It is not advisable to change designated pre-defined polarity of these capacitors, there will not be any saftey issues, but would this act will result in increase in ESR of Supercapacitor and would also reduce service life.

What if a charged Supercapacitor is directly shorted...?

In case of Supercapacitors the ESR is of order of milli-Ohms, wheras in case of batteries the ESR is in Kilo-Ohms, due to this batteries when subjected to short circuit or excess current drawing tends to explode due to excessive heating in this scenario, but in case of Supercapacitor due to low ESR maximum drop will occur on load side, resulting in lesser temperature rise in Supercapacitor, moreover construction of supercapacitors incorporate saftey vent, which breaks open when interrnal pressure exceeds 12 bar.

What if Supercapacitor service/operating voltage or temperature exceeds the max rated value ...?

The maximum voltage rating of single cell Supercapacitor is indicated on product, which would normally be like 2.7V/ 2.85V/ 3.0 V per cell. This max rating ofvoltage is mainly derived from the electrochemical stability of the electrolyte and electrode materials.
Utmost care should be taken to "Not to exceed the indicated maximum voltage across Supercapacitor".

Please note if cells are operated above their rated voltage for a long period of time, the life is reduced. This is because of electrolyte breakdown with exposure to high voltage. The amount of damage varies based on the voltage and the amount of time the cell is exposed to the over-voltage condition.

SPEL Supercapacitors are designed to endure temporary high temperature for few minutes, but this would shorten product life. Please note if the product is expose to high temperature over for certain period of time, product shape may get deformed. It is strongly recommend to use product within the specified or indicated maximum temperature limits.

What is end of life and failure mode for Supercapacitors capacitor..?

In general failure mode in Supercapacitor is open circuit. In service life Supercapacitors do not have a hard end of life failure similar to batteries. Their end of life is defined as when the capacitance drop is 20% and/or 100% increase in ESR.

How change in Temperature & Voltage affects performance of Supercapacitor....?

By using Arrhenius plots method, logarithim of the chemical kinetics reaction rate constant is plotted against reciprocal of the temperature change to analyze the effect of temperature on the rates of chemical reactions. It is observrd that for every 10℃ drop of operational temperature, the product life becomes approximately double if all other conditions being equal. Likewise for every 0.1 V drop, the product life extends about double.

FAQ-Supercapacitors

EDLC Supercapacitors