Super Capacitor

 The super capacitor, also known as ultra capacitor or double-layer capacitor, differs from a regular capacitor in that it has very high capacitance. 

C= q/V

where,
C= capacitance
q= amount of charge on either side of capacitor
V= potential difference between the conductor

Fig: Super Capacitors

Super capacitor is also known as “ultracapacitor”. It is rated in farads. The supercapacitor is used for energy storage undergoing frequent charge and discharge cycles at high current and short duration.

HISTORY

In 1957, the 1st super capacitor device was created by General Electrical Co., but there aren’t known commercial application. In 1966, standard oil accidentally discovered double layered capacitor while working on fuel cells, but it wasn’t until the late 1970s that the Japanese company, NEC began commercially offering the first “super capacitor” for computer memory backup. Companies like Maxwell Technologies, Murata & teacate generally dominate the super capacitor field.

STRUCTURE

The elementary structure of a supercapacitor consists of:

• Aluminum current collectors
• Electrodes (generally out of activated carbon impregnated in an organic or aqueous electrolyte) 
• A separator ( inserted between the two electrodes to insulate them)

The principle of operation of a super capacitor is based on the storage of energy by distribution of the ions coming from the electrolyte in the contact of the surface of the two electrodes. 

• Electrodes are the electrodes of the supercapacitor is made of Activated Carbon material. The electrodes have Porous nature which helps to store more charge carriers. And we know that if the electrodes are able to store more charge carriers then the capacitance will be increased. There are two electrodes one is the positive electrode and another is the negative electrode

• Current Collectors are the current collectors are used to connect the electrodes and the terminals of the capacitor. The current collectors are generally made up with foil metals. Mostly aluminum is used. There are two current collectors in the supercapacitor one for the positive electrode and another is the negative electrode.

• Separator is the separator is used to provide insulation or separate the electrodes to prevent the short-circuit. The separator mainly made up with Kapton material. The separator is very thin like paper. The separator provides insulation between the electrodes but it allows to the flowing of charge carrier through it.

• Electrolyte Solution is mainly the Acetonitrile or propylene carbonate as solvents are used as electrolytic in the supercapacitor. The electrolyte solution consists the charge carriers like positive cations and negative anions.

WORKING PRINCIPLE OF SUPER CAPACITOR

We already know that the positive and negative ions are present in the electrolyte solution with mixed in. So at first when we apply a voltage across the electrodes of the supercapacitor then it starts charging. The electrodes start to attract the Ions of opposite polarity. That means the positive electrode attracts the negative ions or charges and the negative electrode attracts the positive Ions or charges.

As a result, the positive ions or charges creates a layer near the negative electrode and the negative ions create a layer near the positive electrode. As there two layers is formed by the electrical charge carriers that is why it is called Electrical Double Layer Capacitor(EDLC).

APPLICATION

They have been found to have the biggest potential for application in hybrid transportation. TOYOTA, Peugeot-chiroen, Mazada and Lamborgini have all released models of vehicles that use combination of super capacitors and Li ion battery. Tesla invested more than $100 million in the purchase of Maxwell technology which uses super capacitor.

Some cars are using super capacitors for specific role. When the car is slowing down the energy generated from that action is tored in super capacitors on board and later use it for acceleration. It saves battery for other purpose than acceleration and deceleration. As of collected data Cellergy are at top in manufacturing the super capacitor whereas Maxwell Industries are in 3rd Position.

• Harvest power from regenerative braking systems and release power to help hybrid buses accelerate.
• Reliably crank semi-trucks in cold weather or when batteries are drained from repetitive starting or in-cab electric loads.
• Provide energy to data centers between power failures and initiation of backup power systems, such as diesel generators or fuel cells.

Some Differences Between Super Capacitor and Lithium ion Battery

	Super capacitor	Lithium ion battery
Charging time	1-10 sec	10-60 min
Cell voltage	2.3-2.7V	3.6V
Specific energy (Wh/kg)	5	120-240
Specific power (W/kg)	Upto 10,000	1000-3000
Cost per kWh	$10,000	$250-$1000
Service life (industrial)	10-15 yrs	5-10 yrs
Charge temperature	-40 °C to 65°C	0°C-45°C
Discharge temperature	-40°C-65°C	-20°C-60°C
Cycle life	1 million	500d higher

ADVANTAGES OF SUPER CAPACITOR

• Virtually unlimited cycle life. Can be used millions of times.
• High specific power due to low resistance which enables high load currents.
• Charges in seconds.
• Excellent low-temperature charge and discharge performance is shown.
• Safe to use.

DISADVANTAGES OF SUPER CAPACITOR

• It has very low specific energy.
• Linear discharge voltage prevents it from using the full energy.
• It has high high self discharge than most batteries.
• Individually have low cell voltage but can be used in parallel combinations to increase cell voltage.
• It has high cost per watt. So it is not practically preferable in daily life.