VRLA BATTERIES: THE BEGINNING
Batteries International spoke to John Devitt who, now 91, recalls how he conceived of the first absorbent glass mat battery and the challenges that he and Don McLelland had to overcome to create prototypes that could be manufactured.
Patent no 3,862,861: the key that opened up VRLA
It all started with a memo. A nine page memorandum to George Jenkins, head of research at Gates Rubber Company. The memo subject line? Lead-Acid Sealed Cells. Moreover, the author, John Devitt, a battery research manager, had only fledgling knowl-edge of lead batteries.
Not exactly the stuff of legend. But those nine pages were to create the largest shake-up to the lead battery industry since 1881 and the days of Camille Faure.
It was April 1965. Devitt has started working for Gates just three months beforehand. And half a century later the world is still coming to terms with the consequences.
“This memo didn’t just come out of the woodwork,” recalls Devitt. “For most of the preceding 15 years I’d managed two battery factories in succession; both of them supplied a number of different silver-zinc batteries to the US Department of Defense.
“All were destined to be used in either missiles or torpedoes. One of the factories was the principal source of batteries for the main electrical power of the Minuteman, Polaris and Poseidon ICBM missiles. I also directed the development of these products.”
At the time Gates was the largest manufacturer of rubber belts and hoses in the world.
In 1965 it was privately held by the Gates family: “Charlie Gates was CEO, and he ran the company his way,” says Devitt. “That included an unusual willingness to experiment with new types of products, and even completely diverse enterprises.
“The local grapevine one day yielded the news that Gates was interested in going into the battery business. I had for some time wished to become involved with non-military batteries — even lead batteries, then by far the largest portion of the overall battery business, including dry cells and the rest.
“A very unusual environment greeted me at Gates. Charlie could decide a new idea was a good one in the morning and by afternoon someone’s work was going in a new direction. And it turned out that Jenkins, my new VP, was very skilled in finding new R&D areas to whet Charlie’s appetite.
Jenkins was also an expert at summarizing for Gates (both were engineers) the technical intrigues involved with a possible new enterprise.
“Perhaps best of all, only Jenkins stood between me and Charlie Gates. In retrospect, the whole thing was too good to be true. No more bureaucrats. No more waiting for an unpredictable board meeting.”
Gates’ interest in battery manufacturing was based on advice from a consultant who had been charged with the task of finding diversification opportunities. Work on nickel-cadmi-um and nickel-zinc battery systems was recommended. One result was that Devitt began a serious nickel-zinc sealed-cell development project in 1965.
“But only a small feasibility study was authorized for the lead acid cell,” he says. “This latter opportunity, however, was exploited unmercifully. Vendor contacts were established and much library work was done. Grids were planned to be made of longitudinally expanded lead sheet purchased from vendors. This decision was based upon Devitt’s only previous battery experience: 12 years in the development and manufacture of silver oxide zinc primary and secondary batteries.
Expanded silver and copper sheet materials were used in those batteries. Grid material and oxides were procured in 1965, but used only in relatively few preliminary experiments.
About two years passed after that April memo, during which Gates’ management thought about the idea of lead batteries – which would have been a major departure from the tra-ditional rubber manufacturing business.
“That 24-month delay gave us priceless time in which many contacts with sources of materials and information could be used to permit plans to be made,” he says.
By mid-1967 a clear go-ahead had finally been received and Devitt’s team moved rapidly. The team itself was an unusual one and more characteristic of Devitt’s thought processes than traditional hiring or interviewing techniques.
“Some chemical background was an obvious plus but I was more interested in how an answer was arrived at than in its accuracy,” he says. “Some interviews lasted well over an hour. It must be mentioned that the team which developed the battery consisted, for the period beginning with the first experiments and ending with sales to customers, of only four people with a relevant technical degree – the rest having wholly diverse backgrounds.
“These latter folk were classified as technicians. Not one had ever worked in an activity similar to the one they were about to enter, and no-one ever quit the project while I was there.”
Here it is worth introducing co-patentee Don McLelland, who had given a paper on silver zinc batteries at a Electrochemical Society meeting in 1965. Devitt had met him there, liked him and thought he fitted the bill perfectly for his research plans. When he learned that McLelland’s wife’s par-ents lived near the battery project he said: “It was a simple matter to entice them from their residence in California.”
At the beginning McLelland investigated some electrochemical details of other battery types being considered, but for the final three years of the total of seven invested in lead acid cells, he directed the work on the D- and X-cells while Devitt became involved with business plans and other details for the future.
(It is fascinating to note that the original D-cell development was car-ried out by McClelland and Devitt, neither of whom had any previous experience with lead-acid cells, together with some technicians who had no battery background!)
But to go back to Devitt’s first plans. He had been particularly fascinated by investigations into sealed nickel-cadmium cells, which he had heard described at the 1960 meeting of the Electrochemical Society. The oxygen cycle employed in these was, he reck-oned, one of the major breakthroughs in battery science.
In these cells, advantage is taken of the fact that, in electrode reactions, no electrolyte is consumed. The liquid needs to be present only in sufficient amount to transport ions from one electrode to the other. So if there is a wettable, fibrous separator between the electrodes, it can be merely damp, or ‘starved’ of liquid.
During overcharge, if the negative cadmium plate is of substantially larger coulombic capacity than the positive, there will be oxygen evolution within the cell before hydrogen gassing begins.
Oxygen diffuses through the separa-tor pores to the cadmium surfaces and reacts to form water, and this situa-tion can continue indefinitely without either hydrogen or oxygen escaping from the cell. Practical Ni-Cd cells are made using thin, spirally-wound plates in the cylindrical units and are capable of high-rate discharges and charges.
Another object of his preliminary work was to find, if available, more or less maintenance-free lead acid batteries. The only ones worth studying, Devitt reckoned, were those made by Sonnenschein in Germany and, at that time, imported by Globe Union (later Johnson Controls). These were called gel cells because of the silicaceous addition to the acid which turned it into a stiff jelly and kept it from running out of the battery when it was in a spillable position. Unlike the Ni-Cd cells, this battery did not use oxygen recombination. It was basically designed and made as a flooded battery with non-spillable acid electrolyte.
“The batteries I purchased were shipped with full charging instructions which cautioned against using voltages above the gassing potential. In addition, the gas exit of the battery contained a rubber umbrella valve, used simply as a check valve, allowing gas exit but not entry,” says Devitt. “On testing it held no measurable internal pressure; so there is no question that it was not an early VRLA battery. Particularly when new, its negative plates were buried in acid gel. This material also tended to slow down the electrode kinetics to such a degree that true high-rate performance was not available.
“With this background it was not difficult to suppose that an extremely attractive objective might be the devel-opment of a small lead acid cell with as many of the characteristics of the sealed Ni-Cd cell as could be achieved. “Our new, future product would be high rate, as sealed as possible, non-spillable of course, and quite inexpen-sive because of the much lower materials cost.”
“All of the early work was devoted to learning ‘The Art of Lead Batteries’, almost none of it being recognizable in terms of silver-zinc technology,” says Devitt. “Valuable advice was ob-tained from Everett Ritchie of Eagle Picher and John Nees of National Lead. Both oxide vendors were then valuable sources of battery design and processing information.”
Everett had been working on an ILZRO contract which resulted in probably the most complete data on paste formulations, curing and so on published anywhere. The recommendations from this source resulted in both positive and negative recipes, which found their way into the finished products.
The first D-cells which cycled well were made in October 1967 by Marvin Walker, a technician, and Devitt. They were housed in polystyrene pill containers. Their design included expanded lead calcium grids and paste recipes based upon Ritchie’s recommendations. The separators were a special pheno-lictreated cellulosic paper which was flexible enough to wind up. The cells were sealed as well as tape and glue would permit.
As sometimes happens, their perfor-mance was not significantly exceeded by cells made during most of the following year. Also in 1967 the team became aware of the unspillable miners’ lamp batteries which used a latex-bound diatomaceous earth separator. It proved a dead end — design did not yield usable ideas.
But by the end of 1967 the D-cell capacity specification had been established at 2.5 Ah, a value still used today. Devitt had also conducted the first exploration of the market for this product, with a very positive result.
1968 was occupied with work in optimizing formulations, processing parameters and mechanical details. A 960-cell computerized cell-cycling and data-recording installation was planned and implemented. Every cell could be cycled individually. “Our pilot plant began operating in early 1969,” says Devitt. “It could, on short notice, transform an idea into enough test cells to be placed on the big tester to give a meaningful answer. This combination of pilot plant and large tester was a key factor in our realizing the relatively short total D-cell development time of less than four years.”
But the separator was still a problem. A large number of synthetic non-wovens and treated papers were tried, in many combinations. Drip coffee filters were even tried at one point.
By the end of 1968 McClelland was directing the D-cell project on a full-time basis.
During the first half of 1969, D-cell cycle life was still limited by water loss. Further design optimization was done, including grid alloy experiments. “Because of our use of expanded grids, alloy choices depended more on their successful passage through the expanding machine, and our ability to paste and wind the electrodes, than on such important considerations as corrosion and growth in the positive,” says Devitt.
“In the middle of 1969, the scene began to change fast. Some cells containing a layer of treated cellulose paper and a layer of Whatman GF83 filter paper (microfiber glass) began to exhibit abnormally low water loss. As 1970 proceeded it became obvious that we were at last on the road to a true starved electrolyte, recombination design.
A company Devitt had used as a supplier of absorbent cellulose paper for silver-zinc cells (tea-bag paper!), CH Dexter Company, had mentioned its expertise in making various types of fiberglass paper, including those grades made of microfibers. “Enquiries led to their furnishing us with a Type 225 which, as was our habit, was first used in combination with other materials,” he says.
“At last it was used alone. Many test cells later it was apparent that our cells now failed, at a life of hundreds of cycles, from grid corrosion and growth, with little or no readily-measurable water loss.
Final design optimization included many plate compression experiments. In the 1960s it was commonly said that ‘lead-calcium batteries do not cycle well’. But the batteries in question did not typically incorporate any significant retention of the posi-tive active material.
Early in the project Devitt started to conclude that an abnor-mally large pressure applied to the active material surface might accomplish two things. First, it might reduce the electronic resistance in the interface between the grid and lead dioxide to such a level that there would be no inclination for a sulfate or oxide layer to form.
And second, at the same time, ‘shedding’ of material would be impossible, and, again, electronic contact between particles of active material might prevent their becoming either detached or inactive.
“Accordingly, we employed that most ideal of dimensionally-stable structures, the cylinder, as our retention device,” he says. “One has only to vary the length of the spiral electrodes and separators to obtain any degree of initial compression desired.”
This technique proved to be a vital element in the design of a long-lived cell. As experience was gained in pilot plant production of the D-cell, a number of processing difficulties were recognized. The element winder was a persistent mechanical problem. “It is no exaggeration to say that the formation of a starved cell was by far the most troublesome operation.”
Deliveries to customers started going well in 1971 and larger cell sizes were introduced. In the early 1970s the grid form was changed to the use of a punched configuration. This avoided the dimensional instability of the expanded grid, which passed through the machinery only with great difficulty, says Devitt.
The punched grid could also be made of pure lead, or a low-tin alloy, without losing its ability to be processed, as the punched configuration is inherently mechanically stable. Lastly, the plate lugs could be made solid, for much improved terminal connections.
The basic patent was filed in 1972 and awarded in 1975 on the Gates’ recombination technology, US Patent No 3 862 861 to D.H. McClelland and J.L. Devitt, was licensed throughout the world, and forms the basis for AGM technology.