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ULTRACAPACITORS
(A NEW REVOLUTIONARY TECHNOLOGY)
Abstract:
The science and technology of ultracapacitors are reviewed for a number of electrode materials, including carbon, mixed metal oxides, and conducting Polymers .More work has been done using microporous carbons than with the other materials and most of the commercially available devices use carbon electrodes and an organic electrolytes.
This paper reveals the importance and the urgent need for the evolution of ultra capacitors which is expected to bring a revolutionary and remarkable change in the replacement of the traditional batteries. The need for ultracapacitors is lucidly mentioned in this paper. The fundamental phenomena of capacitor charging is mentioned which serves as a foundation in further advancements. The role of Nanotubes in the development of ultra capacitor is dealt. The advantage of Nanotubes over conventional capacitors is explained. The main problem faced is the capacitor current is capacitor current is a function of both voltage change and capacitance change as a function of voltage. So the specifications are to be considered in the ultracapacitor. Using all these method of ultracapping a car is briefly dealt
INTRODUCTION:
A smattering of mass-transit vehicles and industrial machines may seem like one wimpy revolution, but revolutionary they are unlike most of their electric relatives, these vehicles all share one key attribute: they don't run on batteries. Instead, they are powered by ultracapacitors, which are souped-up versions of that tried-and-true workhorse of electrical engineering, the capacitor.
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. 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. What's more, rechargeable batteries usually degrade within a few thousand charge-discharge cycles. In a given year, a light-rail vehicle might go through as many as 300 000 charging cycles, which is far more than a battery can handle. The synergy between batteries and capacitors has been growing, to the point where ultracapacitors may soon be almost as indispensable to portable electricity as batteries are now.
Ultracapacitors are already all over the place. Millions of them provide backup power for the memory used in microcomputers and cell phones. Perhaps most exciting is could do for electric cars. 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. Most deadly to the life of a battery are the moments when it is subjected to high-current pulses and charged or discharged too quickly. Conveniently, delivering or accepting power during short-duration events is the ultracapacitors strongest suit. And because capacitors function well in temperatures as low as –40 ºC, they can give electric cars a boost in cold weather, when batteries are at their worst.
Reason behind developing Ultracapacitors:
The most common electrical energy storage device is the battery. Batteries have been the technology of choice for most applications, because they can store large amounts of energy in a relatively small volume and weight and provide suitable levels of power for many applications. In recent times, the power requirements in a number of applications have increased markedly and have exceeded the capability of batteries of standard design. This has led to the design of special high power, pulse batteries. Ultracapacitors are being developed as an alternative to pulse batteries. To be an attractive alternative, ultracapacitors must have much higher power and much longer shelf and cycle life than batteries. Ultracapacitors have much lower energy density than batteries and their low energy density is in most cases the factor that determines the feasibility of their use in a particular high power application. For ultracapacitors, the trade-off between the energy density and the RC time constant of the device is an important design consideration.
How do Ultracapacitors store energy?
The most common electrical energy storage devices are capacitors and batteries. Capacitors store energy by charge separation. The simplest capacitors store the energy in a thin layer of dielectric material that is supported by metal plates that act as the terminals for the device. The energy stored in a capacitor is given by 1/2 CV 2. The maximum voltage of the capacitor is dependent on the breakdown characteristics of the dielectric material.
An ultracapacitor, sometimes referred to as an electrochemical capacitor, is an electrical energy storage device that is constructed much like a battery. It has two electrodes immersed in an electrolyte with a separator between the electrodes. The electrodes are fabricated from high surface area, porous material having pores of diameter in the nanometer. Charge is stored in the micropores at or near the interface between the solid electrode material and the electrolyte. However, calculation of the capacitance of the ultracapacitor is much more difficult as it depends on complex phenomena occurring in the micropores of the electrode. It is convenient to discuss the mechanisms for energy storage in ultracapacitors in terms of double-layer and pseudo capacitance separately