While batteries make most of the headlines when it comes to the energy storage requirements of electric cars, the capacitor could be an exciting and viable alternative. Unlike batteries, which store chemical energy and make it available for use as electrical energy, capacitors store energy in the electric field between a pair of conductors. Supercapacitors, or ultracapacitors, are currently being developed which could rival batteries in the amount of energy that they can store. Whether capacitors see use as part of a hybrid drivetrain or as the sole source of electricity for a pure electric vehicle, we expect to see them make a dent in the automotive sector as the future unfolds. Then again, we've been expecting some news on this front for a while (EESTOR, anyone?), so we might have to keep waiting.

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In a recent article in Popular Mechanics, editor Mike Allen declared himself a fan of ultracapacitors for hybrid cars. He explains how he visited Honda's development facilities 15 years ago and found himself testing a mild hybrid that used an ultracapacitor to store energy. However, we all know that current hybrids don't use ultracapacitors. Instead, they have powerful batteries, which have a higher power density and a price that is going down.

Nevertheless, Allen predicts that once ultracapacitors can be made successfully at a competitive price point, conventional hybrids will use them because of the "capacitor's longer life span and lower internal resistance, as well as its deep-discharge tolerance. While a battery pack can be damaged by being discharged completely, capacitors simply don't care." On the other hand, he foresees that plug-in hybrids will always need batteries for their main battery pack, while using capacitors to reclaim energy while slowing down and to provide high-current acceleration. EESTOR must be happy.

[Source: Popular Mechanics]

One of the means that electrically powered vehicles used to maximize their range is regenerative braking where the kinetic energy of the vehicle is recaptured during deceleration and than released during acceleration. The problem is that most batteries can't absorb energy quickly enough to capture all the available energy. This is where capacitors have an advantage since they can absorb energy a lot faster than batteries and do it a lot more times. Unfortunately the total energy capacity is limited, which also limits their usefulness. While a lithium ion battery pack could contain enough energy to drive a vehicle a couple of hundred miles, an ultra-capacitor pack would be lucky to get a few miles.

Now a team of physicists at North Carolina State University have developed a new capacitor material that can contain up to seven times as much energy as existing capacitors. Vivek Ranjan, Liping Yu, Marco Buongiorno Nardelli and Jerry Bernholc figured adding a polymer called CTFE as an impurity to another polymer, polyvinylidene fluoride (PVDF) make for a much better capacitor dielectric greatly enhanced the latter's energy absorption. Perhaps if the cost of this material can be reduced a capacitor of this type could be combined with a battery to produce an energy system that can absorb and release energy quickly and still provide decent range.

[Source: PhysOrg]