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The Advent of the Sealed Nickel Cadmium CellWilliam FarrellListed below are the “Basic Chemistry 101” reactions inside a Nickel Cadmium Cell on Charge or Discharge. The “true facts” are that these formula only satisfy those folks who like to see equations nicely balanced on each side. They also like to see recognizable compounds. What is really going on inside the cells is much harder than this and most of it is still unknown. This is true for all battery systems. Charge, Overcharge and Discharge Equations for the Nickel Cadmium Cell Charge, Positive Plate 2Ni(OH)2 + 2(OH) yield 2NiOOH + 2H2O + 2e (Nickel Hydroxide) yield Nickel Oxy Hydroxide Overcharge, Positive Plate 2(OH) yield 1/202 + H2O + 2e Charge, Negative Plate Cd(OH)2 + 2e yield Cd + 2(OH) Cadmium Hydroxide yield Cadmium Metal Overcharge, Negative Plate 2H20 + 2e yield H2 = 2(OH) Discharge, Positive Plate 2NiOOH + 2H2O + 2e yield 2NI(OH)2 + 2(OH) Nickel Oxy Hydroxide yield Nickel Hydroxide Discharge, Negative Plate Cd + 2(OH) yields Cd(OH)2 + 2e Please note the General Fuzziness around the (OH)’s, These General Equations whetted the appetites of the entire electrochemical community when the Nickel Cadmium system was first investigated, back in the early 1900’s. There was the hint that the Nickel Cadmium Cell could be sealed to be maintenance free. In the pre-war era things settled down to making Nickel Cadmium Cells for Traction, Miner’s Lamps, Railway Signal, and Car Lighting Batteries. The Great Depression slowed the pace of research, and companies concentrated on “staying alive” with profitable products. I don’t want anyone to write to me about pre-WW-II, during-WW-II, or post-WW-II German or Swedish or Czech searches for the Sealed Nickel Cadmium Cell and/or Battery. I know all about those efforts. The Standard Schoolbook Formula shouts out that there should be ways to effect an equilibrium between energy, gas, and material that would allow “sealing up” the Nickel Cadmium cell to stop the consumption of the water, in the electrolyte. The Neuman Cell The Facts of the matter were that the only available sealed Nickel Cadmium cell (during the ‘30’s) was the “Neumann” cell, available in Czechoslovakia. This particular type of cell was made with a sort of fine wire “Brillo pad” made of a compressed mat of fine Nickel wire for the positive and a compressed mat of fine Cadmium wire for the negative plates with plenty of liquid potassium hydroxide electrolyte. The separator appeared to be a strong filter paper of some sort. Sometimes they used sodium hydroxide for the electrolyte. The active Hydrates, of the two metals were “formed” using the outer surface of the “Brillo”-like wires. The “Neumann” cell was available for flashlights. This type of cell was used because Manganese Dioxide Ore (the positive electrode for the LeClanche’ cell) was not available. The “Neumann” cell had a serious problem. Typical internal gas pressure at the End Of Charge was about 800 to 1,200 psig. Can you imagine installing a pair of these explosive beauties in a hand held flashlight to be used by your Mom? Call me Lefty. Swedish Patents Basic International Patents, that looked as though a real breakthrough was coming, were developed and issued to the Swedes. Nothing came of them. I always felt that the Swedes left the lab and disappeared into a shot glass of Akaavit while resting on their Patent Papers. They seemed to just forget the whole thing as being of little interest and no commercial value in Sweden. Sweden didn’t have enough of the Nickel and Cadmium raw materials to worry about, anyway. In the late 40’s and 50’s the Swedes woke up and found that they could collect sums of money for licensing these patents. They still do. Germany In Germany, lead became a critical item during and after the Blitzkreig days, and Lead Acid engine starting batteries were high on the critical list for both ground equipment and aircraft. Many of the most sophisticated German aircraft were still equipped with the old “hand cranked inertia” starters using a mechanical flywheel for the energy to start the engines. These devices became extremely heavy as engine horsepower got larger and larger. Carts were built with the flywheel mounted on the cart with a spline fitting that fit into a hole in the aircraft. The Germans developed and built Nickel Cadmium Aircraft Batteries using thick plates of a base sinter made of copper granules. This sintering process was already well understood from the sintered bronze or copper “Oilite” bearings. These flat sintered copper plaques were nickel plated after sintering. The supposition was that the plating would eliminate the formation of sharp dendrites at the negatives that would short out the cell. Unfortunately, the nickel plating of the copper particles doesn’t reach deep into the matrix of the sintered mass. These batteries had the unfortunate problem that Copper was not noble enough to be used for the Negative plates. Once the active materials had been impregnated into the sintered copper matrix and a cell assembled, the Negative plates grew little copper dendrites (spikes) through the separator materials and shorted out the cells. This dendrite growth also contributes to the short life of the Silver-Zinc and the Nickel-Zinc cell systems, today. I felt that one of the GE Chemists was very close to making satisfactory Nickel Zinc cells back in the late 60’s. He called them Zinkels. This dendritic mode of failure was not well understood back in the 40’s. This sintered copper plaque type of Nickel Cadmium Battery was made for use in German Pursuit Aircraft. Pursuit Aircraft must be ready to “scramble” on short notice. There can’t be any waiting around for the Inertia Start Cart to show up. The Dendrite Failure mode was accentuated and accelerated by long continuous overcharge at “trickle” rates. This was the normal mode while the planes were resting on the ground. Post War At the end of WW II, the Americans “liberated” a couple of German engineers from the German Nickel Cadmium facility. They were shipped off to the USA. Like “our” early rocket scientists, they developed the technique for sintering Carbonyl Nickel Powder into porous sheets on a nickel plated steel screen. These very thin flat plate sintered “plaques” were impregnated with Nickel and Cadmium salts and were used in the first USA Nickel Cadmium cells. In the Government’s infinite wisdom, they assigned the Commercial and Military development of this exciting new electro-chemical product to Sonotone Corp, a manufacturer of Hearing Aids and Sub-miniature Vacuum Tubes. The Vacuum Tubes were to disappear to the onslaught of Bell Labs and the introduction of the Transistor. As a matter of fact, the Sonotone hearing aid went the way of the Dodo also. The factory where this work was done is now a paper weight. The factory where the first Military Sintered Plate Nickel Cadmium cells and batteries were produced has been razed by the EPA and the Superfund. Grass has been planted where the 130,000 sq ft factory once stood, in Cold Spring, New York, adjacent to the Mighty Hudson River. The site is now free from any and all Cadmium pollution. In France, SAFT is an acronym, it stands for “Societe Accumulators Fixes et Traction”, which is why I abbreviate the name to an acronym (SAFT). SAFT has been manufacturing conventional Tubular and Pocket Plate Nickel Cadmium Cells for the Power Station, Mining, Traction and Railway Industries for almost 75 years. They also manufacture some Nickel Iron Cells. At the conclusion of WW-II, as a part of the War Reparations, they managed to secrete one of the top German Nickel Cadmium Manufacturing Engineers out of war torn Germany. With the awarded War Damage Reparations they also got some equipment from the German facility. All this stuff, and the engineer went to work at the SAFT factory at Bordeaux. This engineer’s job was to learn/teach how to sinter metals other than copper and bronze. He especially concentrated on sintering Nickel particles generated from the Oxidation of Atomized Nickel Carbonyl. This particular nickel particle exhibits extremely high surface area to weight ratios. These particles are extremely difficult to examine with a conventional optical microscope. It wasn’t until the advent of the Scanning Electron Beam Microscope (ca. 1970) that the inferred shape (an airy Christmas Tree) was confirmed. The inferred shape had been painstakingly developed by embedding the particle in a plastic matrix and then polishing away the upper surface of the particle and matrix in tiny layers. Photos were taken at each “slice”. It amounted to a sort of a mechanical MRI. When all the “slice” photos were assembled the shape “sort of” revealed itself. In due time these Nickel particles were successfully sintered into thin sheets, using a support structure of either perforated nickel plated steel, electro-formed nickel sheet, or nickel plated wire screen. The sintering temperatures were very high and difficult to control to the degree of precision necessary. Later developments of high current Silicon Controlled Rectifiers simplified the temperature control problems. The finished sintered plaques were about twice as thick as a matchbook cover. The porosity of this material was unbelievable, it was well into the 80% porous range, or beyond. The technique used to examine the porosity was Mercury infusion into the porous mass under very high pressure. This method was not entirely satisfactory as the Mercury had a tendency to amalgamate with the nickel particles, if the nickel surfaces were very clean. As a point of interest, common window screen is about 50% open. The rest is wire. Active material in the form of slightly acidic concentrated Nickel Nitrate was used for the Positive Plates and concentrated Cadmium Nitrate was used for the Negative plates. These materials were forced into the interstices (interstices are the spaces between the potatoes in a basket of potatoes. You can pour in a lot of shelled peas or corn into the interstices, even though the basket appears to be full of potatoes). The Nitrates were converted to Hydrates by soaking the plates in Lye after impregnating. The process (for the positives) is very touchy and is somewhat akin to kissing a duck in the hind end without touching the feathers. At the conclusion there were useful Positive and Negative cell plates. After this chemical processing, the plates were “formed” by alternately charging and discharging in a lye bath. This formation is usually done using only a negative or positive with a plain metal “dummy” plate as the other polarity. The awful truth was that these plates weren’t very good. The products didn’t measure up to the nominal electro-chemical capacity of the standard SAFT industrial product or even the Nickel Iron Edison Cells. The other problem was that the cells absolutely refused any attempt made to seal them up. The Lighter at the End of the Tunnel As Paul Harvey has been known to say, “Here’s is the rest of the story.” SAFT, is a part of Cie. General Electrique. SAFT answers to CGE for all its business practices, expenditures, and product development money. In 1948 one of the high muckity-muck Directors of CGE went to Bordeaux to visit the President (Pierre Jacquier, by name) for a friendly chat, a nice lunch, and for a fresh bottle of Beaujolais. After lunch the Director of CGE produced a cigarette and a cigarette lighter and lit his cigarette. The President of SAFT was startled to see that there was no flame involved with the lighting of the cigarette. He assumed that it was one of those catalytic Platinum/Alcohol jobs. It was not. The Director of CGE waved the lighter in front of the President of SAFT and taunted him with the fact that it was an “Electric” cigarette lighter with a Lead Acid Battery made by VARTA (a German battery manufacturer). He took the lighter (“Zippo” sized), removed the top and exposed the battery down in the metal holder, the cell was enclosed in a polyethylene cell container. There was some moderately nasty repartee concerning SAFT’s inability to keep up with the times, etc,. This moderate nastiness galvanized Mssr Jacquier into action. The President of SAFT called in his best model makers, technicians and engineers. He removed the offending Lead Acid battery from the lighter and told them to make a cell, from the sintered Nickel Plates of the German Engineer. The cell must fit in the Lighter to replace the offending Lead Acid Battery. The cell was to be assembled into a welded steel cell container, charged and ready to placed into the lighter. At SAFT, when Mssr l’President has spoken, he has spoken. Even if he has spoken softly, those within hearing, hear it very loud, indeed. After a flurry of dizzying activity, and a very short time, the lighter was returned to the Director of CGE, with the new sintered plate Nickel Cadmium cell assembled. The offending Lead Acid battery was put aside. The lighter was tried out and found to be in working order. After touring the factory and some casual talk with other members of the staff, the Director went back to Paris. About a month (or so) later the Director was back in Bordeaux and during the course of a very nice lunch and bottle of wine he complained that the Nickel Cadmium battery in his cigarette lighter was not as good as the old Lead Acid battery. It didn’t give as many “lights per charge” as the Lead Acid battery. The President called in his merry men (again) and asked if they had any of the original plate assemblies left over from the last time the Director was in Bordeaux. He was given a couple of dozen, or so. He handed them back to the waiting Technicians and Engineers. He told them that they were to put twice as much electrical capacity into the same cell size as the original. He sent them off to a new “Mission Impossible”. You can imagine the arm waving and cursing once they were out of earshot of the President. How the heck do you get 20 pounds of Oatmeal in a 10 lb bag? The Solution to this enigma came by a piece of luck. One of the Technicians took two of the offending plate assemblies (complete with the separator inserted) and placed them (one on top of the other) in a very large hydraulic press. He squeezed them down with enormous pressure, to one half their original thickness (remember that the nickel particles in the sinter were very porous and that not all the interstices were totally filled with active material). The sintered Nickel particle were also very ductile, so that most of the sintered bonds were not broken. He then put these squashed down plate assemblies into a metal cell container with electrolyte (Potassium Hydroxide) and welded the thing up. These cells did not accept much electrolyte as the plates were very dense, because of the squeezing. The cell was equipped with a little rubber safety vent on the top of the cell, just in case. All told, he made about 15 of these squashed down cells. The other technicians were typically French, and ridiculed what he was doing. When the cells were subjected to cursory testing, 11 of the cell were electrically ok (not shorted out). There were several that were short circuited by particles between the plates penetrating the separator. Some of the plate material had crumbled during the squeezing and lodged between the plates. Over the objection of some of the other technicians, these cells were given to the President. After all, they didn’t have anything else. One of these cells was inserted in the Director’s cigarette lighter. It worked. Later in the afternoon the Director left to go back to Paris, and civilization as he knew it. The President tossed the balance of the cells into the back of the top drawer of his desk and promptly forgot about them. About two months later the Director of CGE was there again and conversation drifted to the electric cigarette lighter. The director said that the new battery was working fine, but there was one thing that was odd about the little cigarette lighter battery, it never needed water. The President (of SAFT) was very competent about battery technology and to say that he was stunned by this revelation, would be an understatement. He never let on (to the Director) that something had been said that really set the hairs up on the back of his neck. Later, he dug out the spare squashed cells from his desk drawer, called in the Technicians and set them to work testing the little beauties. It was found that the internal pressure (at the end of charge) did not exceed 20 or 25 psig. Later it was learned that the cells never produced hydrogen during charge. Instead, the oxygen that was formed at the Positive Plate migrated to the Negative plate (across the very thin porous separator) and the oxygen with part of the OH radical (from the electrolyte) partially discharged the Negative Plate. The active material of the Negative Plate, at the end of charge, contains quite a bit of finely divided metallic Cadmium. The reaction was assisted by the limited amount of electrolyte in the cells, allowing a typical three phase reaction to take place. This partial discharge prevented the Negative Plate from producing hydrogen as the Negative plates never came up to full charge. If the cell doesn’t produce hydrogen, along with the oxygen (produced at the Positive Plates), it doesn’t consume water (the ultimate source of the hydrogen and oxygen) and so the cell can be maintenance free and sealed up. These 10 or 12 cells represented the World’s supply of Sealed Nickel Cadmium Sintered Plate Cells. Many experiments later, SAFT established some parameters that would allow replication of these “accidental” cells. The plates were thinned down, more porous separators were found, the proper amount of electrolyte/water was established that produced the right degree of “dryness/wetness” to allow the recombination of the hydrogen to take place. Because SAFT knew how to make flat plates, the first commercial products for these sintered Nickel Cadmium cells were Batteries for Miner’s Lamps and Railway Signal Lanterns. The cells were in the 4 to 9 ampere hour capacity range. The sealed batteries were much appreciated by the miners who were using leaky cells with construction that resembled the old Edison (Tubular Plate) battery with lots of “free” electrolyte. This free electrolyte could leak out and eat up everything in sight, including the Miner’s pants and rear end. Environmental Factors A whole new industry was about to be born in late 1948. In 1996, the manufacture of this battery system is now a pollution target for rampant ecologists. Manufacture of the Nickel Cadmium Battery is about to go down the toilet, here in the USA. The manufacturing process to produce Nickel Cadmium Cells is difficult to keep ecologically clean, especially when examining the receding mirage target given by the Courts and EPA for acceptable levels of Cadmium pollution. There is one other thing about these Sealed Nickel Cadmium Cells. They appeared fully developed in the 50’s at an energy level of about 14 watt hours per pound. This is about the same energy level as common Lead Acid cells. Other than minor improvements in capacity these sealed Nickel Cadmium Cells are still about the same as they were in way back in the very beginning. It is now more than 40 years since the commercial introduction. The “One Order Of Magnitude” improvement levels every ten years, typical to the integrated electronics industry, has never materialized with this cell system. The thin plate Nickel Cadmium system offered very good performance at extremely high rates of discharge and good performance at low temperatures but lagged far behind the Silver-Zinc system for capacity per pound and volume. Other electro-chemical energy systems are now slowly walking uphill away from the energy levels of the Nickel Cadmium system. The Nickel Cadmium system stands there and watches the improving capacity of other systems go bye-bye and seems powerless to effect a significant improvement. The highly touted “Metal Hydride” system appears to offer substantially higher capacity per cube per weight. The ultimate cycle life of the Metal Hydride system is somewhat suspect as current marketing statements have quite a bit of Snake Oil in them. Dr. Carson (GE Labs, Schenectady back in the 50’s) determined that the ultimate energy retrieval from Nickel Cadmium cells could be about 85–90 watt hours per pound. This has never been achieved as a manufacturing possibility, or even in the laboratory. After almost fifty years of intense research the Sealed Nickel Cadmium cells have improved to about 16 watt hours per pound, and still have the same inherent problems seen in the first cells. When are the cells charged? The easiest answer is, “When they are warm to the touch while they are still on charge.” What's Wrong with Them “How can I measure the “State of Charge?” You can’t. There are a lot of people who have promoted a lot of devices that purport to indicate the state of charge, all have come to naught. If you really want to know the state of charge, discharge the battery and measure the energy you get out of the blasted thing. “Why do my cells fade away and poop out?” There are a whole raft of answers for this one. The length of the explanation would make all of us old. “Why can’t I make a battery of more than 6 volts that will be reliable?” Even six volts is a lot for the typical sealed cell battery. There is always one weak sister in the pack that winds up being reverse charged at the end of the battery discharge. There is no way to recombine the Hydrogen generated when the cell is reverse charged, ergo the cell dries out a little each time the battery is discharged. More volts in a battery equals more cells being driven into the reverse charge mode at the end of battery discharge. I can only offer this friendly advice concerning the use of Sealed Nickel Cadmium Cells: • Charge them when they are dead. • Discharge them however you want. • Throw them in the recycling bin when they are really dead. Don’t foul the world with indiscriminate disposal of these things. World wide manufacturers make about 200,000,000 of these cells per year, I hope they don’t get in the rivers and streams. Look forward to accusations and condemnation of the performance and pollution from the so called “metal hydride” cell. Sooner or later some company is really going to make a commercial product in metal hydride cells. When that happens, someone will certainly find something objectionable about this new and highly touted cell system. The metal hydride cell is not a panacea for the ills of the Nickel Cadmium, or the sealed battery business, in general. As Paul Harvey has said, “Now you know the rest of the story about the discovery of the Sealed Nickel Cadmium Cell.” Access Author: William C. Farrell, 1 Kennedy Court, New Milford, CT 06776 • Phone & FAX 203-355-87311 Farrell, William C. "The Advent of the Sealed Nickel Cadmium Cell." Home Power Magazine. #52. Apr. - May 1996. 34-38. |