Nickel-Iron Battery
This page is currently under construction and might undergo drastic changes within a short span of time.
http://en.wikipedia.org/wiki/Nickel_iron_battery
Basic Concepts Behind Construction
The electrochemistry of a Nickel iron battery is similar to a NiCd or NiMH battery in that nickel oxyhydroxide is used as an anode, but iron is used instead of the toxic metal complexes in NiCd and NiMH batteries. During discharge, both metals turn into their hydroxide forms: Ni(OH)2 and Fe(OH)2. (see the wikipedia article under electrochemistry). Given the resilience and rechargeability of the NiFe battery, it should be possible to build it in a discharged state, combining the appropriate hydroxides of Nickel and Iron. Alternatively, the battery could be constructed out of metallic nickel and iron, and the nickel should mostly convert to an NiOOH form after the first discharge-charge cycle.
First test
A sample concrete cell was tested, but no practical benefit is achieved using concrete as an electrolyte, as to be effective, the entire cell must be submerged, and the electrical conductivity of cement is far too high when submerged. A new design is in the works for a cell which would use raw glycerine (glycerol) as a byproduct of biodiesel production, thus improving the ecologies of both systems. The rationale is that the lye (KOH or NaOH) which 'contaminates' the glycerine should prove to be an effective electrolyte, and the glycerine itself should support a more stable cell. (Glycerine will evaporate much more slowly than water, and due to higher viscosity, should even further improve vibration-resistance of the cell. Ideally, this design could even be adapted to portable units.
Preliminary Figures for a 12V, 1kWh pile
NiFe cells produce a working potential of 1.2V, and charge at 1.4V. A 12V battery would then consist of 10 cells, and charge at 14V which is typical for most "12V" batteries. To achieve 1kWh capacity, we will need 1000W/12V = ~85Ah. This means that each cell will need to provide 85Ah capacity. This corresponds to 306,000C, which is approximately 3.17 moles of electrons. Sheet steel will form a base material for the electrodes, so iron is not a limiting factor. Nickel's electrochemistry in an NiFe battery indicates a 1:1 molar ratio, so 3.17 moles of nickel will be required. This is about 185g of Ni at a molar mass of 58.69g/mole. For a 'safety' margin, we will round up to 200g. At 200g Ni per cell, a total of 2kg of nickel will be needed for a 1kWh unit. The actual capacity of this cell based on the rounded values above would be 1095.8kWh.
Related pages
http://openfarmtech.org/wiki/Nickel-Iron_Batter/Research (the page was accidentally created with the lack of y typo, don't know how to change that)
Environmental Aspects
All batteries (at least the ones in common use) are toxic to a greater or lesser extent. The NiFe Battery isn't an exception, but it is far less toxic than Cadmium-based batteries.
- Iron is non-toxic and commonly available.
- Nickel Oxide is toxic. The Appropriate Technology Collaborative is investigating toxicity [1].
- The lye electrolyte is caustic and corrosive, but perhaps could be used in small amounts.
- Suspending the lye in glycerin also mitigates effects.
- Glycerin is a by-product of creating bio-diesel, thus using a waste of a different process.
Sources
FusionBeads [2] 3"x3" 24 gauge nickel sheet is $3.25.
Metric: 76.2x76.2mm and 0.5mm thick. The density of nickel is 8.902 g/cm3. 2903.22 mm3 which is 2.90 cm3. Thus, each sheet weights 25.84g. 2000g (2kg required as above) is 77.38 sheets. $251.50 is the cost of 2kg of nickel. Actually, it can be gotten cheaper in these quantities, but this is an outside number.