The Sealed Cell: Catching the Gas Before It Leaves

**US 2,571,927**, Georges Neumann and Ulrich Gottesmann, Bureau Technique Gautrat, filed **29 January 1949**, granted **16 October 1951**, long expired. Title: *Electrolytic cell, and in particular alkaline cell*. The drawing on this page is its own sheet 1. The claim that matters describes a cell arranged for *the depolarization and recombination of a substantial amount of the gas developed at the electrode of the opposite polarity*. Read that slowly, because every word is doing work: - **developed at the electrode** — the gas is not a fault, it is what any cell does when the charging current outruns the chemistry it has left. - **of the opposite polarity** — oxygen is made at the positive and consumed at the negative. It has to physically travel between them. - **a substantial amount** — not all of it. The design does not promise perfection, it promises that the rate of consumption can keep up with a specified rate of production. Exceed that rate and the cell still vents. Write those three lines in your notebook before you go further. The rest of this rung is the engineering that each one forces, and every later thing in this batch — the pack, the charger, the balance board — exists because of the third one. Note what the claim does **not** say: it says nothing about a better chemistry. Jungner's nickel-cadmium couple from 1899 is used unchanged. What changed is the arrangement.

Take one **fully charged** sealed NiMH cell — NiMH runs the same oxygen cycle as the NiCd the patent describes, and is the cell you can actually buy. Put it in a holder, tape a thermocouple to the side of the can with a small piece of electrical tape, and record the starting temperature and terminal voltage. Set the bench supply to **constant current** at C/10 — for a 2,000 mAh cell that is 200 mA — and limit the voltage to 1.6 V so nothing can run away if a connection opens. Start it, start the stopwatch, and log voltage and can temperature every five minutes for an hour. What you are looking for is not dramatic and that is the point: - The **voltage rises**, flattens, and then falls very slightly. That small fall is the −ΔV signature, and it is the whole subject of rung 5. - The **temperature climbs steadily** and does not stop climbing. Step 2 computed why: the charging power has stopped storing anything and is being spent entirely on running the oxygen round the cell. - The **cell does not swell and does not hiss.** Compare that with what the arithmetic in step 2 said an uncatalysed cell would be doing by now. Stop at one hour, or sooner if the can passes about 45 °C. Do not leave it running unattended, and do not do this to a lithium cell — a lithium cell has no recombination cycle at all and overcharging one is the subject of rung 9.

Look at the positive end of a sealed cell under good light. The cap is not a single piece of steel: it is a crimped assembly with a rubber or plastic grommet and a spring-loaded disc under it. That is a **resealing safety vent**, and it is the thing the recombination cycle was supposed to make unnecessary. It is there because the claim said *a substantial amount*, not *all*. Push charge in faster than the negative can consume oxygen — a fast charger on a cold cell, a reversed cell in a series string, a short — and gas is produced quicker than it is eaten. The vent lifts at its set pressure, lets the excess out, and reseals. The cell survives; it just lost some water and some capacity permanently. Measure what you can from outside, without opening anything. Put the calipers on the can: a sub-C is nominally 22.2 mm across and 42.9 mm long. Weigh it. Divide the rated watt-hours by that mass and write the figure down — you will compare it against a lithium cell in rung 4 and the gap is the reason this whole ladder kept climbing. **Do not cut a cell open.** The electrolyte is concentrated potassium hydroxide, it is strongly caustic, and a NiCd additionally carries cadmium, which is a cumulative poison. Everything this rung needs is visible or measurable from the outside. Spent cells go to a battery collection point, never in household waste.

**Attribution.** US 2,571,927, *Electrolytic cell, and in particular alkaline cell*, Georges Neumann and Ulrich Gottesmann, assigned to the Bureau Technique Gautrat in France; filed 29 January 1949, granted 16 October 1951. The patent has long expired and its drawing is public domain, which is why it is the hero image here. **What it unlocked.** Waldemar Jungner had the nickel-cadmium chemistry in 1899 and Thomas Edison had his nickel-iron cell a few years later. Both were real, rechargeable and rugged, and both stayed in fixed installations — railway lighting, signalling, standby power — for half a century. A vented cell has to stand upright, has to be watered, and cannot be built into anything you carry. Sealing it is the single change that moves the whole chemistry from the plant room into your hand, and everything else in this batch follows from it. **Honest limits, and they are real.** The recombination cycle turns surplus charge into heat, so a sealed cell punishes fast charging with temperature, and that becomes the engineering problem of rung 5. It also gives the cell no way to tell you it is full except by those two faint signals, voltage and heat. And cadmium is genuinely toxic; the chemistry that made this possible has since been restricted in most consumer uses in Europe, which is why the cell you can buy today to repeat step 3 is nickel-metal-hydride — the same oxygen cycle, a different negative electrode. The sealed cell is also a good example of a pattern worth naming: the invention is not a new material, it is a **new arrangement of known materials that closes a loop**. The gas was always going to be made. The idea was to give it somewhere to go.