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 a cathode, but iron is used instead of the toxic metal complexes in NiCd and most NiMH batteries as the anode. During discharge, both metals turn into their hydroxide forms: Ni(OH)2 and Fe(OH)2. (see the wikipedia article under electrochemistry). 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 could be converted to NiOOH or Ni(OH)2 in situ through oxidization with ozone or peroxide and UV or some other means. (We will definitely need someone who knows some chemistry and is willing to put in some time at at least several stages in this development process.)

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.

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.

We need to look into purchasing in bulk as it is far cheaper than this sheet, although sheet could be used for electrode material. Those guys must be making generous profit to say the least.

Price of Nickel and Iron

http://www.indexmundi.com/commodities/?commodity=nickel price is very roughly $23 per kg. Pretty good really. http://www.steelonthenet.com/commodity_prices.html price $0.60 per kg for scrap steel, presumably pure iron would be in that range.

From the electrochemistry figures above for a 1 kWh unit, that would be $48 or so on metals. So 20 Wh per $ ($0.05 per Wh). Even the cheapest lead acid batteries are 7 Wh per $. In reality they are more like 4. So the good news it that materials cost should not sink the ship anyway, although I'm sure all the other costs for the perforated pocket, assembly etc. will add up plenty fast.

Toxicity

Nickel itself that is the concern rather than any particular compound. Water soluble compounds are unsurprisingly much more of a concern than metal that is bound in solid objects like nickel plating or some types of stainless steel, since it is more bioavailable and can be spread and spilled more easily. At low levels of exposure talking in terms of nickel content is done. But of course the exact solubility and other factors has a substantial effect on the exact toxicity at higher levels of different water soluble compounds too, note the ld50 is 10x lower for nickel chloride as for nickel oxyhydroxide according to the documents below, so the expedient of speaking in terms of nickel content doesn't always work that well.

Still all metals are toxic to some degree including iron and we need some numbers to make an informed decision. Preferably a solid evaluation of dose response relationship, and if the batteries are to be widely adopted now is the time to factor in chronic exposure too. It needs to be considered not in a vacuum but relative to other options available.

This is one of the benefits of batteries with non aqueous electrolytes apparently - the compounds involved in such batteries are less soluble in water since most compounds trend towards being soluble in aqueous or nonaqueous solvents but not both.

higher quality : http://jas.fass.org/cgi/content/abstract/28/5/620 http://www.annclinlabsci.org/cgi/content/abstract/11/2/119 http://www.hpa.org.uk/web/HPAwebFile/HPAweb_C/1236757324101 looks better but didn't read msot of it http://www.epa.gov/iris/subst/0271.htm https://fscimage.fishersci.com/msds/53189.htm http://www.nickelinstitute.org/index.cfm/ci_id/13029/la_id/safe_use_guide_5.cfm.htm

unkown due to lack of acess: http://www.ncbi.nlm.nih.gov/pubmed/19888907 http://www.annclinlabsci.org/cgi/content/abstract/7/5/377 Low quality: http://www.crios.be/Nickel/toxicology.htm material safety datasheets with information regarding nickel oxyhydroxide, clearly it is sometimes used as anode material in NiMH, in fact most of the hits are datasheets for such batteries rather than the material itsself: http://www.rdbatteries.net/Data/Panasonic_NiMH_Info.pdf http://www.chiefsupply.com/resources/msds/Moto-NiCd.pdf http://www.batteriesplus.com/msds/Duracell_Nickel_Oxyhydroxide_%20Batteries_NorthAmericaMSDS.pdf (as if companies would give accurate information on their own products) http://www.it.pg.com/productsafety/msds/fabric_and_homecare/duracell/Duracell_Nickel_Oxyhydroxide_Batteries_(North_America_MSDS).pdf

Note that the permissible exposure limits (PEL) for the material is about a fifth that of graphite, which we know is not too toxic though it might accumulate in the lungs I guess. Still there are a lot of variables there as most particles inhaled are not retained, depends on size etc etc.

Obviously the LD50 is quite low at 1000 mg/kg range. But that means little in terms of what happens at lower levels. For Chloride it seems to be in the 100 mg/kg range.

http://www.osha.gov/SLTC/healthguidelines/nickelsolublecompounds/recognition.html They fail to say dosages in critical places, this information is actually low quality

nickel chloride: http://www.sciencelab.com/xMSDS-Nickel_chloride-9926213

oxide:http://www.inchem.org/documents/ukpids/ukpids/ukpid70.htm

From Dietary information perspective: http://iom.edu/Activities/Nutrition/SummaryDRIs/~/media/Files/Activity%20Files/Nutrition/DRIs/ULs%20for%20Vitamins%20and%20Elements.pdf

"A Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects to almost all individuals in the general population. Unless otherwise specified, the UL represents total intake from food, water, and supplements."

1 milligram per day for nickel, 40 for iron. Well that's to totally zero adverse effect level and there's probably plenty of room for more there. Nickel is probably available as a dietary supplement, I wonder what happens when people take too much.

http://www.eoearth.org/article/Public_Health_Statement_for_Nickel case report little more than half way down of people drinking 250 mg/liter (250 ppm) nickel welding, relevant to pocket production: http://www.crios.be/Welding/toxicology.htm Maybe it woudl be better to make the pockets without welding. Folding perforated sheets cleverly, sewing with nickel wire etc. plenty of other options that shoud lbe fine .

As usual it is difficult to obtain quality information on a health issue and it is very time consuming to wade through the crap and get some answers. Case reports, vague qualitative statements, condtradictions, paywalls, are the norm. Ideally a table of dose-response relationships for a range of different people over a wide range of doses would be obtained but whatever.

In summary it looks like it is certainly less problematic than lead or mercury, gloves, ladling or scooping rather than pouring dry materials, and working outside would more than suffice for me personally. Spills of solutions should be prevented.

Future Prototypes

If nickel hydroxide is produced in situ a high surface area metallic nickel cathode would be needed. (Note that in electrochemistry the cathode is the electrode to which cations are attracted. In other words the positive electrode, when when talking about the exterior of the battery could be called the anode. This is due to historical reasons.) Sponge, sintered powder, and nickel fabric cloth like material have been used. Nickel wool might do as well.

A high surface area solid iron electrode or powdered iron may be used. More reading of the references on the research page is needed to determine if plain powder will do. The appropriate surface area of both electrodes which will give a reasonably low internal resistance needs to be calculated.

If powdered iron is attractive it can either be sintered into a porous block or converted to sponge (open cell metal foam although technically so is the sintered block) as described in patents in the research page or it may be possible to just have it loose. In the case of loose powder the conductivity between powder particles due to physical contact and the electrolyte needs to be determined. It may be sufficient.

 In at least one of the Edison batteries he chose to use mercury to increase the conductivity between particles but that may have been a battery intended for Starting and lighting (SLI) in cars, which requires a very low internal resistance as discharge rates can exceed 20C during starting.  We need no more than 1C or at most 2C (lithium ion are 2C or so usually) for general use and short term load leveling, and 0.3 may do for solar power system energy storage.  If we did need high currents sintered electrodes would be more sensible.

It needs to be determined how the changing shape of the electrode goes. For the cathode it is not a problem as the nickel oxyhydroxide can be caused to accumulate on a nickel substrate whose shape does not change. For the anode either another nickel substrate might work or an excess or iron could be used in the sintered block or powder bed. In the latter case the iron that remains at the point of deepest discharge forms the scaffold for the following charging period. But over time the electrode shape could change in undesirable ways, reducing surface area and increasing the battery's internal resistance to an excessive value. This is one of the reasons deep discharging of lead acid is a problem. Although there are many different types of lead acid battery there is sometimes an alloy of antimony and lead used to form the electrode scaffold for one or both electrodes, which reacts more slowly than the lead that is supposed to cover it. But if discharged too deeply the scaffold can react too, and it cannot be reformed in the shape it was, rendering the battery damaged. Similarly during recharge some battery types form dendrites from one electrode to another - thin shafts of metal. As the finger of metal protrudes towards the opposing electrode the resistance between the tip of the finger and the opposing electrode gets lower, resulting in a higher current at the tip of the dendrite, causing metal to be preferentially deposited at the tip of it, lengthening it until it touches the opposite electrode, shorting the battery. Clearly over many charge/discharge cycles the cumulative effects that result from the relative effect size of these processes can cause substantial changes in electrode shape if they are not understood and accounted for.

At a smaller scale the electric field at a surface is higher if the radius of curvature is higher. This can result in either the sharpest parts of an electrode having slightly higher current densities than the rest resulting in higher reaction rates there and smoothing of the electrode (an effect leveraged in electropolishing). Or in reverse surface roughening, which is known in electroplating. Clearly more information is needed on these processes relating to this specific chemistry, and they need to be factored in to electrode design.

Related pages

http://openfarmtech.org/wiki/Batteries http://openfarmtech.org/wiki/Nickel-Iron_Battery/Research