#689 1896 · National Carbon Company (E. M. Jewett, George Little) · Batteries / electrochemistry

Every dry cell wasted most of its interior on a plaster liner, so National Carbon swapped it for cardboard and packed the space with battery instead

问题

Dry cell batteries wasted most of their limited interior space on the separator

背景

By the 1880s, German scientist Carl Gassner had solved the core problem of the old wet-cell battery — a heavy, leak-prone jar of liquid electrolyte, unusable except sitting upright — by sealing everything inside a zinc container that also served as the battery's anode, creating the first true "dry cell." Gassner's design used a molded plaster-of-Paris lining as the separator, the layer that keeps the anode and cathode from touching and short-circuiting the cell.

Plaster of Paris did the separator's job reliably, and by the 1890s it was the established way every dry cell manufacturer built theirs. But plaster is bulky: molding a rigid plaster liner inside the cylindrical zinc can consumed a large share of the battery's limited interior volume, leaving only a small remaining space for the cathode — the active material that actually determines how much current the battery can deliver. Every manufacturer simply accepted that trade-off as how a dry cell was built.

换别人会怎么做

By the 1890s, every dry cell manufacturer built their battery Gassner's way: a molded plaster-of-Paris liner separating the anode from the cathode. Plaster was an established, reliable building material that reliably kept the two electrodes from touching, and nobody building a dry cell had reason to question using it or look for something thinner — the separator's job was simply to sit there and prevent a short circuit, and plaster did that job.

他们看到了什么

Jewett and Little saw that the separator's only real job was to keep the anode and cathode electrically apart, not to be structurally substantial — and a molded plaster liner was doing that job at an enormous cost in wasted interior space, space that could instead hold more of the cathode material that actually produced the battery's current. A thin cardboard tube, coiled to fit the can and coated to hold its shape, separated the electrodes just as reliably while giving back nearly all the volume plaster had been consuming.

那一手

At National Carbon Company's Cleveland-area lab in the mid-1890s, E. M. Jewett, working under George Little, replaced the molded plaster-of-Paris separator with a thin tube of cardboard, coiled to fit inside the can and coated with a paste of flour and potato starch. The cardboard did the same electrical-separation job the plaster had, at a fraction of the thickness.

为什么管用

Because the cardboard separator was dramatically thinner than a molded plaster liner while still fully preventing the anode and cathode from touching, the same size can could hold significantly more cathode material — the ingredient that actually determines how much current a battery can deliver — without changing the battery's exterior dimensions at all. That extra capacity, combined with cardboard being cheaper and far easier to roll into shape than casting plaster inside every individual unit, is what let the Columbia become the first dry cell genuinely practical to manufacture and sell at mass-market scale.

值了多少

Because the coiled-cardboard separator took up dramatically less interior volume than molded plaster, the Columbia dry cell — launched in 1896 as a sealed, six-inch, 1.5-volt battery — could pack far more cathode material into the same can, directly improving its capacity, while also being cheaper and simpler to assemble than casting plaster inside every unit. It became the first dry cell battery successfully manufactured and distributed at mass-market scale.

什么时候会失灵

This only works when the passive component's true function can be cleanly separated from the bulk it happens to carry — a separator only needs to block electrical contact and withstand the cell's internal chemistry, which cardboard could do; a component that is also load-bearing, or that needs its bulk for some other real physical reason such as structural support or heat absorption, can't simply be swapped for a thinner substitute without losing whatever that bulk was actually doing. It also depends on the thinner replacement being genuinely reliable over the product's working life, since a separator that fails and lets the electrodes touch destroys the whole battery.

后来呢

The Columbia found immediate demand in the rapidly expanding telephone and automobile industries and served as the design basis for dry cell batteries for roughly the next sixty years; National Carbon's later Eveready brand grew directly out of this line of business. The American Chemical Society designated the Columbia Dry Cell Battery a National Historic Chemical Landmark in 2005.

资料来源

[1]The Columbia Dry Cell Battery (National Historic Chemical Landmark)American Chemical Society, 2005acs.org
[2]National Carbon Co.Encyclopedia of Cleveland History, Case Western Reserve University, 2018case.edu