Posted by Deliverator on March 6th, 2009
Whether you are talking Lead-Acid, Lithium ION, Lithium Polymer, NIMH or NiCd you are constantly confronted with a simply expressed truth. Batteries suck. Different formulations suck in different ways. How do I loathe thee, let me count the ways:
-Self Discharge (the tendency for batteries to drain themselves over time)
-Diminished capacity over time
-Operational lifetimes on the order of several hundred to a few thousand charge cycles. Even less in batteries that exhibit “Memory” when not charged/discharged in the correct way.
-Risk of fire and explosion
-Toxic, caustic or environmentally damaging components.
-Long charge times and poor ability to dump stored energy quickly
-Performance variation at low or high temperatures
New improved formulations and manufacturing techniques have offered incremental improvements in recent years, but not on a grand scale. Batteries still suck, they just suck slightly less.
There is one energy storage device which does not suffer from the various ills which afflict batteries, namely capacitors. Capacitors can be charged and discharged quickly, can be charged a near infinite number of times and offer relatively temperature invariant performance. The problem, historically, has been that capacitors of all types have only been able to store a near infinitesimal amount of energy compared to a battery. In recent years, there has been an increasing amount of interest in what are usually called Ultra or Super-Capacitors. Although underlying technologies vary, in the last few years capacitors with energy densities within an order of magnitude of the best batteries have hit the market and have found some niche uses due to their unique properties. There are super capacitors commercially available now with energy densities similar to lead acid batteries (~30 Watt Hours per Kilogram) and capacitors have been publicly demonstrated with energy densities of 3 times that amount. That is within spitting distance of the best batteries available today with almost none of the drawbacks! Companies like EEStor are promising even higher energy densities, but their claims have not undergone scientifically independent verification and duplication. If their claims prove true, it will spark a technological revolution on the same order as the advent of the microprocessor.
In the meantime, real honest to god super capacitors are starting to trickle onto the market in actual, purchasable consumer products. I recently purchased my first, a Coleman branded electric screwdriver. While Coleman doesn’t claim their product is able to sink as many screws in a row as a lithium ion powered counterpart, one can recharge their screwdriver in a mere 90 seconds and get right back to work. They claim they can sink far more screws / hour than a lithium on the premise that the lithium battery and a presumed spare in rotation will both be sitting idle needing a long recharge while you can just keep going till the cows come home with their super capacitor (they call it Flashcell for marketing purposes) powered unit. Ridiculously high replacement battery prices for cordless power tools make the near infinite cycle capacity of the super capacitor a very attractive proposition. It is quite possible that capacitor powered electronics could be passed down as geek heirlooms which far outlast their owner’s lifetime! I hope to have my unit soon and promise to put it to a thorough testing and report back with any personal observances.