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Advance In Super/Ultra Capacitor Tech: High Voltage and High Capacity
fyngyrz writes: Ultracaps offer significantly faster charge and discharge rates as well as considerably longer life than batteries. Where they have uniformly fallen short is in the amount of energy they can store as compared to a battery, and also the engineering backflips required to get higher voltages (which is the key to higher energy storage because the energy stored in a cap scales with the square of the cap's voltage, whereas doubling the cap's actual capacitance only doubles the energy, or in other words, the energy increase is linear.) This new development addresses these shortcomings all at once: considerably higher voltage, smaller size, higher capacitance, and to top it off, utilizes less corrosive internals. The best news of all: This new technology looks to be easy, even trivial, to manufacture, and uses inexpensive materials — and that is something neither batteries or previous types of ultracaps have been able to claim. After the debacle of EEStor's claims and failure to meet them for so long, and the somewhat related very slow advance of other ultracap technology, it's difficult not to be cynical. But if you read TFA (yes, I know, but perhaps you'll do it anyway) you may decide some optimism might actually be called for.
You said it. We want a lot of energy in a hand-held format. But it's dangerous.
Do you have any comprehension of the amount of energy stored in a tank of gasoline? A lot of energy stored is not in and of itself dangerous. What matters is the means by which that energy can be released. Your body stores a huge amount of energy but there is no easy way to release that energy rapidly. Diesel has even more energy than gasoline but good luck igniting it. You can drop a lit match on diesel fuel and nothing will happen. Now do batteries and ultracaps have their own unique failure modes? Sure. But it's not hard to demonstrate that the chances of an explosion are pretty minimal.
That energy will get hacked for purposes both good and bad, and the bad purposes will include explosions.
Do you see a lot of exploding cars outside of fictional movies? Causing an explosion normally requires a criminal act typically involving external explosives. It's not actually a very easy thing to cause an explosion. (thank goodness) In most cases even if there is a catastrophic failure the car merely burns, it doesn't explode. I actually trust the engineers working on this stuff and I've worked with companies building battery packs for cars and other high energy applications over the years. They are pretty well aware of the possible failure modes and what to do about them. Explosions aren't something they are overly worried about.
Well, yes, the amount of energy stored goes up as the square of voltage for a given capacitance. However, for a given dielectric getting twice the voltage requires twice the thickness and cuts the charge in half -- so the energy per unit volume is unchanged.
Which shouldn't be surprising since the energy is stored in the dielectric by (e.g.) straining the molecular structure of the material.
The biggest reason for going to higher voltages is to reduce the interconnects, which get enormous at low voltages and high currents. (Cross-sectional area goes up inversely with the square of voltage for any acceptable IR loss, which is why long-distance power lines run at scary voltages.)
Lacking <sarcasm> tags,
Energy stored is C * V * V / 2. Telling us C without V is sort of like measuring the capacity of a gas tank by giving you the length, but leaving out the depth and width.
They report capacitances in the 1000 millifarads for a "centimeter scale" device.
If the maximum voltage is 1V, then we have an unimpressive energy storage of 0.5 J in their "centimeter scale" device.
AAA batteries can store about 5000 J, by contrast. To match that, these would need to be charged to 100V.
Without the V number this article is disappointingly uninformative.
--PM
If only somebody invented diodes and fuses
From here