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NCSU researchers discover new insight into energy storage capacitors

A team of physicists at the North Carolina State University (NCSU) have reported new insights into the ability of capacitors to store and deliver electric charge. Their findings could accelerate the development of the so called ultra capacitors that can be used in conjunction with batteries in electric cars of the future. The Lithium ion battery in an electric car is good for storage of energy but is not capable of delivering the quick bursts of energy needed for fast acceleration. The chemical reactions that enable energy storage in batteries are slow. In contrast, a capacitor stores and discharges electric charge in milliseconds. The capacitor can, however, only store limited amounts of energy which makes it logical to use it in combination with a battery.

Mechanism Behind Capacitor’s High-Speed Energy Storage Discovered.

Combining a battery with a capacitor is already used, for example, in the flash gun of a camera. Energy from the camera battery charges a capacitor that is fed to the light bulb to produce a high intensity flash. It is also used in a medical defibrillator that delivers short duration electric shocks to the heart.

Earlier in 2007, another team from the same university had discovered that using Polyviylidne Fluoride (PVDF) as the dielectric increases energy storage in capacitors seven times compared to previously used materials like polypropylene or Mylar. Following this finding, PVDF based capacitors are now being made and used in applications needing high energy storage. However, the reason for this property of higher energy storage had not been investigated.

The NCSU team led by Dr. Vivek Ranjan applied computer simulation to the new dielectric material and discovered that when an electric charge is applied, all the atoms in the PVDF get polarized and instantly align in one direction. This is different from other materials where the atoms in contact with the electrodes polarize first and then cause adjacent atoms to polarize in an outward dispersal pattern. This dispersal process uses up some of the energy applied to the capacitor. This finding unlocks the physics behind the PVDF capacitor and will lead to the creation of even better dielectric materials, perhaps using nanotechnology.

Better capacitor storage could help electric cars not just in fast acceleration, but also in improved energy recovery from regenerative braking during stop go city driving. An efficient capacitor could also help in right sizing the car battery for driving range; using the capacitor to provide the additional energy needed for overtaking or hill climbing.

Via: ncsunews

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