9/16" * 3" brass tube with holes drilled in it. Later I electroplated it with nickel, then
jammed it with "positive electrode mix" of various formulations using
the steel rod with a hammer to drive it in. Finally it was filled with
55mm depth of good, highly conductive powder and a lead was attached: ready
to test in a battery.
The Monel Powder Ratio Experiment:
Fine monel powder seems to be THE way to make battery Electrodes!
I'll start with the conclusion: Adding fine monel powder appears to be a far superior system to current
electrode making techniques. Fine monel powder has
turned out to be the key ingredient for electrode conductivity.
Where others strive to coax a bit more feeble
their very thin electrodes (1mm and thinner), I now simply add monel
powder to the mix
until the exact desired very high conductivity is attained in an
electrode perhaps 3 to 9mm thick. Across this thickness range, battery
resistance rises and current
capacity decreases regardless of electrode conductivities, as the
electrolyte has farther to go and has a harder time penetrating into
3mm: Thin, very high current battery electrode
for rapid charging and discharging, slightly lower energy density.
6mm: Medium, "good" current capacity batteries.
9mm: Thick, lower current, slightly higher energy density batteries.
To get greater current capacity, eg for hybrid cars that
need to take very rapid charging from regenerative braking and
discharging from "pedal to the metal" acceleration, the usual present
technique is to make batteries with very thin nickel electrodes, eg 0.3mm.
This makes for batteries with very low amp-hours capacity for their
size that won't take a car very far.
The very thick, highly conductive electrodes with monel can
handle such high currents while storing far more energy than a
(Lithium battery electrodes
are even worse: they're often deposited as a thin film, small fractions of a millimeter, on a thin substrate.
To compensate, big area electrodes are rolled or folded into the
Monel is an alloy
of nickel and copper, perhaps around 2/3
nickel. It is very hard and extremely corrosion resistant. It was
popular for marine use until stainless steel - "good enough" and
cheaper - came along. In a battery with a salt electrolyte, monel is
probably the best there is. Fine nickel powder might also work well,
and graphite has been used with often workable results. (Eg, it's used
in the "standard" dry cell.) But I'm sticking with the monel - it's
In this experiment I started with an electrode powder
mixture having a small amount of monel, poured the mix into the
electrode tube through a funnel, and pounded it with a hammer and steel rod until it essentially
stopped compressing further. Then I measured the resistance between the
rather solid "sandstone" electrode powder and the tube metal. Then I dug out the electrode (with
a small screwdriver a little at a time), and poured the grit back into
the original container, and mixed a bit more monel powder into it for the next trial.
There appears to be a "critical ratio" of monel powder to
(in this electrode) nickel hydroxide, very close to 1 to 1 by weight.
If there's less monel than 45%, the conduction is poor to nil, then
over the next 10% increase it goes from being mediocre to fair to good
to excellent. By 55% or so the electrode is amazingly conductive by battery electrode standards,
eg, reading 5-15 ohms with the ohmmeter. No doubt I can drop the
somewhat pricey "typical" cobalt oxide conductivity additive - it's
replaced by a minute amount of extra monel.
Probably each electrode
substance will have its own best ratio with monel. What probably
happens is that at the critical level of monel, with compaction the
grains of monel start to press against each other and form metal
connection paths throughout the electrode. Of course, they also press
on the active material everywhere, connecting it all to the terminal.
Here's a table derived from the actual results. Consistent
ohmmeter readings are not be had - every spot, every reading is
different, and the harder you jab in the test probe, to a point, the
lower the resistance reading. Hence the vague, yet telling, resistance
The original powder mix that the monel was added to was
5.00g Ni(OH)2, 0.50g MnO2 (+10%), 0.10g Co2O3 (+2%): 5.60g.
A lot of powder puffed out the tiny side holes in the tube
on the first test. This decreased with each successive test. Not much
was coming out by test 7. Evidently the consistency of the powder
changed markedly with the increase of monel. (or perhaps it was because
more and more of the powder had been previously compacted?)
|Total Monel (grams)
|Off Scale (>20 Megohms)
|various readings: 100s to millions
|upper 10's (eg 50) to low 100's
|5.70 (intended 5.60)
|mid 10s (eg 40)
|upper 1s (eg 6.8) to lower 10s (eg 14)
Result 4 might be an okay low current battery, 5 is quite good (and with just
2% more monel), 6 is excellent and 7 is a fantastically conductive
electrode. Of course, it is disappointing that half the weight of the
electrode is non-active filler --- but it will provide very high currents!
The monel powder I used was some I ground myself from solid
monel with a 220 grit grinding wheel, coarser than what I bought from
AEE/Micron Metals. (That was 300 mesh IIRC.) It may well be that the
finer powder will produce the same or better results with a somewhat
lower percentage of powder.
(Also, for the record: in fact a little powder was lost
with each test, but as only 1/4 or so of the powder was utilized each
time, the loss of "a little of 1/4" was ignored. But it may be that the
"% monel" is actually a bit higher in the later tests, eg the 56% might
actually be 57-58%.)
For a comparison, the nickel electrode of the Ni-MH "AA"
battery I disassembled seems to read 10,000s of ohms, eg 40,000. That may be
typical, or not. And yet that small battery put out 10 amps when short circuited.
In a rougher experiment just previous to the one above, small
filings of brass, added even to twice the weight of the hydroxide (ie, 67% brass), didn't
make the electrode notably conductive without the monel powder. But after adding
enough monel, I got readings around one ohm. That should be good for
exceptional current - extremely rapid charging and discharging - but
the brass filings added a lot of extra weight. I expect that more monel
powder, eg 60% or more by weight, would make it similar or even better
with less weight.
On the other hand, a battery with such phenomenal current
capacity might make incredible fireworks - or even explode - if it was
short circuited, without really adding anything to normal operational
performance. There can be too much of a good thing! Perhaps tens of
ohms, or at least upper ones, should be the limit to conductance.
It's very significant that the ~1:1 ratio is by weight.
The copper, nickel, and hence monel, are density of about 8.9 g/cc.
Compacted nickel hydroxide is about 2 g/cc, about a quarter as dense.
Thus by volume, a 5mm thick electrode would separate into 4mm of
compacted nickel hydroxide and only 1mm of compacted monel. The battery
is heavier, but not much larger, and the gain in current capacity -
"power density" - is
critical to allowing such thick electrodes to exist at all: it would
be as much as three orders of magnitude. Without the monel, many very
thin electrodes would have to be used, which would have its own
overhead of non-contributing material. So it may be that a battery with
monel will in fact have comparable energy density - and in a superior
The perforated tube construction isn't my ideal, but it
may prove to be the most practical way to make batteries at home. You
can hammer a rod into a small tube with good crushing pressure, whereas
to compact powder across an entire large flat plate as I would like to
do would require a steel mold (easy enough to make) and might be
problematic without a "mega" hydraulic press. A filled tube would
certainly last "forever", as Edison's batteries have. A sticky point is
that it seems hard to make the holes in the metal tubes. I'm wondering
if a nickel mesh, held in a steel square profile container while the
powder is compacted, might not be suitable. Fabric insulating wraps or
pockets would cover the conducting materials.
With square tubes, there'd be little wasted space,
and the electrodes would be butted together, in close proximity for good ion transfer.
In the first operating test, I threw the electrode in an
alkaline cell with a prior made negative electrode (Last month's
nickel-iron). Results were about the same as with that battery before
(crappy), which I attribute to using the same ferric oxide negative
electrode and not to the new and presumably much superior positive.
Next I paired it with a zinc electrode of the same new
type construction. Negative electrodes generally have much better
conductance than positives, as it charges to the pure metal. In
addition, zinc oxide itself is more conductive than nickel hydroxide.
However, adding the monel ensured super conductivity at any state of
In this case, the electrode material is much denser than
the nickel and it took 15 grams of it, plus the monel, to fill the
electrode. I mixed "X" grams of monel into 5.0 grams of powder of 98%
ZnO and 2% Co2O3 three times. I obtained these conductance figures:
|Total Monel (grams)
|% Monel (weight%)
| - none -
|around 6 Megohms
|around 6 megohms
|3 to 5 ohms
|3 to 6 ohms
Notwithstanding the "critical ratio" point of monel
evident with the nickel electrode, I am suspicious that I
didn't get a proper reading on "mix 2". In "mix 3" I also got megohm
readings at first, then suddenly (and seemingly inexplicably) the
extremely low resistances.
I put the two electrodes together in KOH solution. The
open circuit voltage seems surprisingly low, about 1.45V where the
listed reaction voltages of +0.52 and -1.24 say it should be 1.66.
Perhaps that comes from buying the zinc oxide at a ceramics supply
instead of a supplier that guarantees the purity. (Or maybe I just haven't charged it long enough.)
Unlike all my previous batteries, this one seems to take a good charge, and to hold it. It doesn't seem to perform very
well currentwise, but indications are that the culprit is poor electrolyte/ion connection
between electrodes. This makes sense with the small number of tiny holes in the tubes give
little interface area, plus there's a wide distance separating most of those few, tiny
interface points between the two round electrodes.
As the electron conductivity of
both electrodes is now amazing, I expect square tubes touching each
other (but insulated) with thousands of
holes would yield entirely different results. (I wonder how many holes
were in Edison's battery tubes, and how big those holes were?)
In salt solution, the voltage should be somewhat higher
than 1.66: I'm estimating about +1.0 volts from nickel and -1.0 volts
from the zinc, for two volt cells.
Note that the two electrodes are mismatched:
Ni(OH)2 is: 289 mAH/g * 5g = 1445 mAH. (but it's only about 3/4 full.)
ZnO is: 659 mAH/g * 15g = 9885 mAH. (full.)
Thus, notwithstanding that there seem to be additives
to promote further oxidation of the nickel compound and get "extra" amp
hours from it, the zinc electrodes can really be made much smaller than
nickel ones. I'll be trying other promising substances besides nickel
hydroxide for the positive electrode, including of course the
illustrious lanthanum hydroxide with monel powder in burned bean sauce.
Some other possibilities were mentioned in previous newsletters.
It's not quite there yet, but with this, in combination
with previously mentioned techniques and materials, a very small, very
battery that can start your car engine and excellent for
electric transportation, is looking quite doable.