ULTRACAPACITORTECHNICAL DETAILS & APPLICATIONS

Report by:Vivek Nandan

Emtech Foundation

Table of contents

1.Introduction.2.Attractive Features.3.Advantages to conventional

Energy Storing Devices.4.Inside a

Supercapacitor/Ultracapacitor.5.Working.6.Applications.7.Drawbacks.

IntroductionWhat is a Ultracapacitor?A charge storing device(Capacitor) .Differ in constructional features with

respect to simple capacitors.Has ability to store tremendous charge.Capacitance ranges up to 5000F!Also called Super capacitor or Double-

layered capacitor.Invented by Engineers at Standard

Oil,1966.

Attractive Features Capacitance ranges to 5000 F. No chemical reaction involved. Much more effective at rapid, regenerative

energy storage than chemical batteries . Works even at low temperatures -40 degrees

Celsius. Ultracapacitors can store 5 percent as much energy

as a modern lithium-ion battery. 5000 farads measure about 5 centimeters by 5 cm

by 15 cm, which is an amazingly high capacitance relative to its volume.

Can effectively fulfill the requirement of High current pulses that can kill a battery if used instead.

Advantages to conventional energy storing devices.

Batteries: Degrade within a few thousand charge-discharge cycles. Ulracapacitors can

have more than 300 000 charging cycles, which is far more than a battery can handle.

Ultra capacitor charges within seconds whereas batteries takes hrs. Because no chemical reaction is involved, ultracapacitors--also known as

supercapacitors and double-layer capacitors--are much more effective at rapid, regenerative energy storage than chemical batteries are.

Batteries fail where high charging discharging takes place whereas ultracapacitor fares extremely well.

Ordinary Capacitors: Higher capacitance.

Put two ordinary capacitors the size of a D-cell battery in your flashlight, each charged to 1.5 volts, and the bulb will go out in less than a second, if it lights at all. An ultracapacitor of the same size, however, has a capacitance of about 350 farads and could light the bulb for about 2 minutes.

Ultra Capacitors are Expensive.

Inside a Super Capacitor

Two Electrodes coated with sponge like activated carbon. Electrolyte :Contains free mobile ions. Porous Seprator-:Prevents electrodes from shoritng out.

•The combination of enormous surface area and extremely small charge separation gives the ultracapacitor its outstanding capacitance relative to conventional capacitors.

Constructional Features Originally electrodes were made of aluminum.  Standard Oil engineers coated these aluminum with 100-

micrometer-thick layer of carbon. The carbon was first chemically etched to produce many holes that

extended through the material, as in a sponge, so that the interior surface area was about 100 000 times as large as the outside. (This process is said to ”activate” the carbon.)

They filled the interior with an electrolyte and used a porous insulator, one similar to paper, to keep the electrodes from shorting out.

carbon is inert and does not react chemically with the ions attached to it. Nor do the ions become oxidized or reduced, as they do at the higher voltages used in an electrolytic cell.

Working When a voltage is applied, the ions are attracted to

the electrode with the opposite charge, where they cling electrostatically to the pores in the carbon.

At the low voltages used in ultracapacitors, carbon is inert and does not react chemically with the ions attached to it. Nor do the ions become oxidized or reduced, as they do at the higher voltages used in an electrolytic cell.

As the effective area where ions are stuck is much larger, appreciably high value of capacitance is obtained.

Modern UltracapacitorsNanotechnology is being

employed in the design.The active carbon is replaced by

a thin layer of billions of Nanotubes .

Each Nanotube is like a uniform hollow cylinder with 5nm and 100 µm long.

These Nanotubes are verically grown over the conducting electrodes.

NANOTUBES STRUCTURES

Benefits of Nanotubes Several Advantages over Activated carbon. Limitations of Actiavated carbon are

The high porosity means there isn't much carbon material to carry current.

The material must be ”glued” to the aluminum current collector using a binder, which exhibits a somewhat high resistance.

• Carbon Nanotubes Depending on their geometry, can be excellent

conductors .Thus they can supply more power than ultracapacitors outfitted with activated carbon.

Their structure makes them less chemically reactive, so they can operate at a higher voltage.

Applications Military projects — for example, starting the engines of battle tanks

and submarines or replacing batteries in missiles. Common applications today include starting diesel trucks and

railroad locomotives, actuators, and in electric/hybrid-electric vehicles for transient load leveling and regenerating the energy of braking.

A bank of ultracapacitors releases a burst of energy to help a crane heave its load aloft; they then capture energy released during the descent to recharge.

They're being explored as replacements for the batteries in hybrid cars. 

In ordinary cars, they could help level the load on the battery by powering acceleration and recovering energy during braking.

Delivering or accepting power during short-duration events is the ultracapacitor's strongest suit.

ultracapacitors function well in temperatures as low as –40 C, they can give electric cars a boost in cold weather, when batteries are at their worst.

Drawbacks of UltracapacitorsLinear discharge voltage prevents use of the full

energy spectrumLow energy density - typically holds one-fifth to

one-tenth the energy of an electrochemical battery

Cells have low voltages - serial connections are needed to obtain higher voltages. Voltage balancing is required if more than three capacitors are connected in series

High self-discharge - the rate is considerably higher than that of an electrochemical battery.

Requires sophisticated electronic control and switching equipment

Questions?