what is super capacitor
Electrochemical Double Layer Capacitor – also called super capacitor or electrochemical capacitor that have high capacitance and high energy density when compared to common capacitors, and higher power density when compared to batteries.
Most super capacitor are constructed from two carbon based electrodes, an electrolyte (aqueous or organic) and a separator (that allows the transfer of ions, but provides electronic insulation between the electrodes). As voltage is applied, ions in the electrolyte solution diffuse across the separator into the pores of the electrode of opposite charge. Charge accumulates at the interface between the electrodes and the electrolyte (the double layer phenomenon that occurs between a conductive solid and a liquid solution interface), and forms two charged layers with a separation of several angstroms – the distance from the electrode surface to the center of the ion layer in Fig. The double layer capacitance is the result of charge separation in the interface. Since capacitance is proportional to the surface area and the reciprocal of the distance between the two layers, high capacitance values are achieved.
super capacitor‘s store electrical charge electrostatically, and almost no reaction occurs between the electrodes and the electrolyte. Consequently, electrochemical capacitors can undergo hundreds of thousands of charge and discharge cycles.
The first super capacitorbased device made in 1957 by General Electric. the developed by the Standard Oil Company of Ohio (SOHIO), who patented a device that shaped the format commonly used today. In 1978, NEC was the first to introduce supercapacitors commercially as low voltage devices with high ESR, primarily designed for backup applications. Since then, EDLC’s have evolved: high voltage and very high capacitance (thousands of Farads) on the one hand, and low ESR pulse supercapacitors with a capacitance range of few mili-Farads, up to 1- 2 Farads, on the other hand.
Significant improvements in materials, design and the process of production of pulse supercapacitors has lead to low profile prismatic devices that can supply high peak currents of up to 2 – 3 A. These devicesare suited to meet the peak power demands of many battery-powered electronics and other consumer and industrial devices with current-limited energy sources.
Storage principles of super capacitor
In conventional capacitors electric energy is stored in a static electric field .. The electric field originates by the separation of charge carriers.
Conventional capacitors are called static capacitors. The potential of a charged capacitor decreases linearly between the electrodes.. The electrolyte as cathode may be a little bit resistive so that for “wet” electrolytic capacitors a small amount of the potential decreases by electrolyte. For electrolytic capacitors with high conductive solid polymer electrolyte this voltage drop is negligible. They do not have a solid dielectric which separates the electrical charge. The capacitance value of an electrochemical capacitor is determined by two high-capacity different storage principles:
- Electrostatic storage of the electrical energy achieved by separation of charge in a Helmholtz double layer at the interface between the surface of a conductor electrode and an electrolytic solution electrolyte. This capacitance is called double-layer capacitance and is static in origin.
- Electrochemical storage of the electrical energy, achieved by redox reactions with specifically adsorbed ions from the electrolyte, intercalation of atoms in the layer lattice or electrosorption, underpotential deposition of hydrogen or metal adatoms in surface lattice sites that results in a reversible faradaic charge-transfer on the electrode. This capacitance is called pseudocapacitance and is faradaic in origin.
Because each super capacitor have two electrodes the potential of the capacitor decreases symmetrically over both Helmholtz layers .Both the electrostatic storage of energy in the Helmholtz double layer and the storage of electrochemical energy with the faradaic charge transfer. Due to this linear behavior of storage of electric energy in a super capacitor the voltage across the capacitor linear to the of stored energy.
Why use super capacitor for energy storage
Super capacitor are unique electrical storage devices that can store much more energy , and offer higher power density .
Batteries are widely used for energy storage because of their high energy density, but are limited in their power density. its limited power the battery often cannot supply the required power while retaining open circuit voltage. The larger voltage drop of the battery larger the load on the battery. when a battery needs to supply high power at small pulse widths, the voltage drop may be large, causing lower voltage than required. The large load decreases the energy stored in battery, harming its life-span.
When high power is require in battery operated devices, the combination of the super capacitor connected in parallel to the battery gives the advantages of both, enhancing the performance of the battery and extending its life, exploiting the batteries to its maximum potential. The super capacitor connected to the battery in parallel produces a voltage damping effect – low impedance super capacitor can be charged in seconds with a low current during standby times between high current pulses. Adding the super capacitor to the battery in parallel decreases the voltage drop, leading to:
- Better energy and power management
- Battery life and operational range extension
- Superior energy density in the battery
- Power to be produced by both the super capacitor and the battery, each supplying power inversely to its own ESR
- Fewer battery replacements in some of the applications
Batteries are very inefficient at low temperatures. Their internal resistance increases due to the slower kinetics of the chemical reaction within the battery. The internal resistance is reduced by incorporating a super capacitor into the system with the battery. The internal resistance of pulse type super capacitor is much lower than that of batteries, even at low temperatures down to -40C.
Why choose Cellergy Super capacitor
- Cellergy’s efficient automated manufacturing process lowers the cost of each super capacitor, making using super capacitor affordable applications
- Cellergy Super capacitor’s ESR performs well at low temperature down to – 40C
- Environmentally friendly product
- Smallest Super capacitor available commercially in the world
- No need to worry about polarity
- Shape and dimension flexibility
- Wide range of voltages, from 1.4V up to 18V
- No dry or clean room needed during production
Advantages and limitations of super capacitor
Virtually unlimited cycle life; can be cycled millions of time High specific power; low resistance enables high load currentsCharges in seconds; no end-of-charge termination required Simple charging; draws only what it needs; not subject to overcharge Super capacitor do not explode even if overcharged Excellent low-temperature charge and discharge performance
Low specific energy; holds a fraction of a regular battery Linear discharge voltage prevents using the full energy spectrum High self-discharge; higher than most batteries Low cell voltage; requires serial connections with voltage balancing. High cost per watt.In super capacitor Serial connections are needed to obtain higher voltages