Tikalon Blog by Dev Gualtieri

Edison Battery

May 3, 2021

Electric batteries have been used for more than two centuries. The first battery, called the voltaic pile, was invented by Alessandro Volta in 1800, and our voltage unit, the volt, is named in his honor. The voltaic pile was a stack of alternating copper and zinc disks separated by blotting paper soaked in brine. Brine is a highly concentrated salt water solution that acts as an electrolyte.

The voltaic pile is a primary battery; that is, it is not rechargeable. The zinc anode is converted into doubly-charged zinc cations (Zn²⁺) with two electrons injected into the zinc electrode.

Zn -> Zn²⁺ + 2e^-

The zinc cations are balanced by the production of hydrogen at the copper cathode. Electrons obtained from the closed electric circuit combine with the hydrogen cations to form hydrogen gas.

2H⁺ + 2e^- -> H₂

The hydrogen gas bubbles into the air at the copper cathode. The copper electrode is not chemically involved in the electrochemical reaction, which is

Zn + 2H⁺ -> Zn²⁺ + H₂

The voltaic pile was Volta's most important, but not his only, discovery. He isolated methane in 1778; and, after the invention of the voltaic pile, he was able to ignite a methane-air mixture with an electric spark.

An electrochemical cell with a penny anode, a dime cathode, and an acetic acid electrolyte

An electrochemical cell, one element of a voltaic pile, with a penny anode, a dime cathode, and a vinegar (acetic acid, CH₃CO₂H) electrolyte. When I conducted this experiment (millivolt reading on the right), I thought that a US dime was still mostly silver. This shows my age, since the composition of a dime changed from (90% silver, 10% copper), to (91.67% copper, 8.33% nickel) in 1965. A US penny is copper-plated zinc.

My experiment revealed some important hints if you want to build a voltaic pile from coins. First, coins have a ridge around their circumference that requires the blotter paper to be cut to a smaller size. Second, the blotter paper should be thick enough that the coins don't touch under applied pressure. I used a few layers of paper towel material.

(Diagram created using Inkscape.)

Despite our present aversion to lead, the rechargeable battery workhorse since the early 20th century has been the lead-acid battery, invented in 1859. Although this battery type has low energy-to-volume and energy-to-weight ratios, it has qualities, such as low cost and long lifetime, that make them suitable for many applications that include automotive batteries in non-electric vehicles. It's based on the reaction of lead with sulfuric acid; viz,

Pb^(s) + PbO₂^(s) + 2H₂SO₄^(aq) -> 2PbSO₄^(s) + 2H₂O^(l)

The cell voltage is about 2.05 volts, so six cells are series connected in an automobile battery to give the putative 12 volt battery voltage. A typical automobile battery has a capacity of a little more than a hundred amp-hours. For comparison, a standard zinc-carbon D-size battery has a capacity of 8 amp-hours.

A nickel–iron battery was commercialized by Thomas Edison more than a century ago. In true Edison style, this battery wasn't invented by Edison. That honor goes to Swedish inventor, Waldemar Jungner, but Edison made money by selling it. He created the Edison Storage Battery Company in East Orange, New Jersey that operated from 1903 to 1975. Edison promoted this battery as a power source for electric vehicles and home appliances. I wrote about the Edison battery in an earlier article (Edison's Nickel-Iron Battery Modernized, July 9, 2012).

Fig. 4 of US Patent No. 692,507, 'Reversible Galvanic Battery,' by Thomas Alva Edison, February 4, 1902

Thomas Edison with his nickel iron battery in 1910, and fig. 4 of US patent No. 692,507, "Reversible Galvanic Battery," by Thomas Alva Edison, February 4, 1902. (Left image, via Wikimedia Commons. Right image, via Google Patents.[1] Click for larger image.)

The nickel–iron battery has a nickel oxide-hydroxide cathode and an iron anode. The electrolyte is potassium hydroxide, often with an addition of lithium hydroxide. The electrolyte acts merely as a reservoir of mobile hydroxide ions, and it is not part of the reaction.

Cathode Reaction:
2NiOOH + 2H₂O + 2e⁻ <--> 2Ni(OH)₂ + 2OH⁻
Anode Reaction:
Fe + 2OH⁻ <--> Fe(OH)₂ + 2e⁻

Edison's nickel-iron batteries had a somewhat higher energy density than lead-acid batteries (up to 50 Wh/kg vs 35-40 Wh/kg).[2] Nickel-iron batteries can be charged twice as fast as lead-acid batteries, and they can endure many charge/discharge cycles.[2] However, nickel has become an expensive material, selling for about $16/kg as compared with lead's price of about $2/kg.

The open-circuit voltage of a nickel-iron battery is 1.4 volts, dropping to 1.2 volts during discharge.[2] These cells are typically charged at 1.65 volts, but they have the property that once they're fully charged, continued application of voltage causes the cells to perform water electrolysis; that is, the electrolyte water is split into hydrogen and oxygen. This is a problem for batteries; but, as the management slogan goes, there are no problems, just opportunities. A research team from the Technische Universiteit Delft (Delft University of Technology, Delft, The Netherlands) has turned this effect into a method for production of hydrogen as a carbon-free fuel.[3-4]

The Delft researchers call their device a battolyser, a combination of the words, battery and electrolyser, and it solves the problem of intermittent production of energy by renewable energy sources such as wind and solar.[3-4] Conventional batteries can store such intermittent energy; but. when they're fully charged, additional available energy is lost. When the nickel-iron battolyser is fully charged, it can be used to make hydrogen fuel, instead.[4] When the instantaneous electric price is high, the battolyser can feed power into the electrical grid, and when it's low, the same device can make hydrogen.[4]

Solar photovoltaic and wind power. Left, a 19 megawatt peak photovoltaic system near Thüngen, Bavaria, Germany. Right, the 40 megawatt Middelgrunden offshore wind farm at Øresund strait near Copenhagen, Denmark. (Left image by Oh Weh, and right image by Kim Hansen, both from Wikimedia Commons. Click for larger image.)

In operation as an electrolyser, nanostructured NiO(OH) and Fe coat the electrode surfaces, and these act as good catalysts for oxygen and hydrogen production.[3] The battolyser electrodes are robust in electrolysis, while electrodes in traditional batteries are degraded, and their energy conversion efficiency is in the range of 80-90%.[4] Aside from hydrogen, such cells can be designed to generate ammonia or methanol, two fuels that are easier to store than hydrogen.[4]

At this time, the researchers have produced a 15 kW/15 kWh battolyser which has storage potential for powering one and a half households. They are making a 30 kW/30 kWh battolyser for the Magnum power station in Eemshaven, Netherlands.[4] Scaling to gigawatts would solve the storage needs of a wind farm, but smaller units can serve rural areas away from the main power grids.[4] Areas for further research are reduction in the cell internal resistance to improve efficiency.[4]

Edison Battery

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