A lot of hype has been given lately to ultra capacitors. They are a new type of capacitor that can theoretically achieve energy densities similar to or even surpassing lithium ion batteries.

The creators of these capacitors hope to replace chemical batteries in everything from laptops to cellphones to electric vehicles. Electric vehicles in particular they claim will benefit because they say ultra capacitors can charge and discharge at higher rates thus allowing more effective regenerative braking.

It is my opinion that much of this hype is overblown. There are issues that I think will severely limit ultra capacitors applications. Chemical batteries maintain a relative constant voltage across the majority of their discharge curve. A lithium ion cell using a graphite anode is typically just under 4 volts fully charged and just over 3 volts fully discharged.

If you had a 4 volt ultracapacitor, it would be 4 volts fully charged but 0 volts fully discharged. At 3volts, you’d only have used 44% of it’s capacity. So to use an ultracapacitors full capacity you have to have equipment that can operate over a wide voltage and current range (because the current will have to increase as the voltage decreases to maintain the same power level).

The advantages of ultra capacitors, their high charge and discharge rate capability has been duplicated in advanced nano-particle based lithium ion batteries. There are lithium ion batteries in production today that can be fully charged in 3 minutes and charged to 80% of their capacity in one.

Present day ultra capacitors do not have the longevity one would expect from a capacitor, down to about 80% of their initial capacity after 1000 charge / discharge cycles.

I’m not saying ultra capacitors aren’t a useful technology, but I do not believe they will displace chemical batteries in all applications like their manufacturers would like to suggest. Rather I think the hype is mostly “investors give us your money” crapola.