Stanford boosts century-old battery tech A group of Stanford University scientists is claiming a breakthrough using graphene that would bring nickel-iron batteries into the modern world. Originally an invention of Thomas Edison, nickel-iron batteries are durable but slow, both for charging and discharging. Although they only lasted in their original application – …
Flock Kroes is perfectly correct, Martin 71 got it wrong. The voltage/charge relationship is indeed linear, far more so than a battery. The logarithmic capacitor behaviour is voltage/time when connected across a constant resistance, in which case the current (charge moved per unit time) is no longer a constant but varies lineally as the voltage across the capacitor varies.
OK, so they are boosting the charge/discharge rate by boosting the electrode surface area through use of clever materials to stick nickel and iron particles to. But how much of an improvement is this to the obvious first pass solution to using iron wire wool and nickle plated iron wire wool for the electrodes?
And what about the battery longevity? The key advantage of NiFe batteries is that they are capable of surviving many thousands of recharge cycles, unlike other battery technologies. Does the use of nano-scale electrode wires impact how quickly the batteries wear out? If it does then this technology scores a massive own-goal.
Real world capacitors often have capacities that are voltage dependent, frequency dependent, temperature dependent, ... . Hence the statement that a linear relation Q = CU defines a capacitor and a non-linear relation indicates a battery does not really hold.
The battery stores electrical energy via an electrochemical reaction, hence charge storage does not require charge-separation and the voltage only increases weakly (logarithmically) with the charge.
But things can get messy with modern batteries: The Li-ion battery moves ions from one host lattice to another without ever truly reducing the charged ions to neutral metal. (That's a good thing, considering that lithium metal has a tendency to burn or explode in contact with air or water). So is that a capacitor or a battery?
I used a NiFe battery in a research lab from 1947 to the early 1950s.
I think it had seven cells to give a nominal 12 V . I cannot remember what we did with it.
It came as a scruffy wooden box like frame holding encrusted white metal cells. It was explained that it was much better than lead acid and could withstand a short circuit or high current charge, but suffered from decrease of voltage as the charge was consumed.
Discussion was that this was the future of stored power. They were proud of it.
I calculated the power to weight ratio was the same for lead acid and NiFe, NiFe was more expensive.
The Edison cell was an incredible feat of technology. By 1905, Edison had perfected the design of the Nickel-Iron cell to the point where the design remained virtually unchanged until the end of production, somewhere around 1972.They had a number of advantages over lead-acid cells. They were robust, having nickel plated steel cases. They were tolerant of over charging and discharging. Deep discharging had no effec ton the cells capacity. They could be left fully discharged for long periods without loss of capacity. They were incredibly long lived. I hav e a few miners lamps which are over sixty years old, which still retain more than two thirds of their original capacity. When your modern laptop battery runs out after an hour or so, think on this. On the other hand, they did have some problems. They were difficult and labour intensive to manufacture, and therefore more expensive than the cheap, short lived lead acid equivalent.The electrolyte was potassium hydroxide, which does really nasty things to organic materials, like skin. They tended to self discharge, over long periods, and their charge/discharge efficiency was lower than lead-acid, and therefore gassed off more and required more frequent topping up. The electolyte, exposed to the atmosphere, absorbed carbon dioxide and became ineffective. These problem were answered, in part, by sealing the cell with one way vents, and providing the cell with ample electrolyte capacity.. The voltage of the battery, by the way, was 1.2 volts per cell. and the discharge voltage was relativlely flat over much of the range.
Where we are in the UK, we have our own power supply, using
1.Lister startamatic 6kva sr2 running on bio diesel some of the time
2. an Outback charger/controller/inverter to give 230v ac
3. 3 tons of alcad in wooden crates 316 stainess cased alkaline cells.,tho only use 1 ton as of now.
These are in 2 banks giving between 60v dc when fully charged to 48v when down to 85% of capacity.
4. The other 2 tons will be inluded in our system when we can afford solar panels.
Im sure they are nickel cadmium with potassium hydroxide electrolite.
In the 3v yrs weve been using them, they havnt used any water.
Acad quoted us a replacement cost of over £25000 per ton, tho they dont make this type any more.
Certainly the voltage is 1.2 v per cell when low, 1.5v when fully charged.
Are we confusing nickel iron with nickel cadmium?
Not the rechargeable cells one uses in torches or CE products.
Can some one elucidate? the difference if any? between these 2 types?
The Register 
Biting the hand that feeds IT
Copyright. All rights reserved © 1998–2024
