Original URL: A zinc battery that could compete with your favorite rechargeables
Lithium batteries are currently the belle of the battery ball. They have a lot going for them, including high energy storage for their weight and the ability to charge and recharge many times before losing much capacity.
But we're all familiar with the drawbacks, too. Lithium-ion batteries pose a fire risk, and the lithium and cobalt used in them aren't the most abundant elements, which makes things more expensive.
Plenty of other possible battery chemistries could compete with lithium, but getting them to live up to their theoretical potential is difficult. Zinc, for example, performs admirably in your non-rechargeable alkaline batteries, and it could theoretically make a safer and cheaper rechargeable one—with a water-based electrolyte rather than a flammable organic one. This hasn't happened, though, and the reason becomes apparent if you throw the batteries under a microscope.
Zinc anodes are typically made by binding together particles of zinc powder. Over cycles of charging and recharging, these develop a zinc oxide coating, which is less-conductive and effectively walls off some of the zinc. Branching needles of zinc can also start to grow as a result of this uneven charge distribution. These will eventually pierce through the thin barrier that separates anode from cathode and fatally short-circuit the battery.
A group at the US Naval Research Laboratory has been working on a different way to put together the zinc anode in order to avoid this problem. (The work was funded by a Department of Energy ARPA-E grant—a program the Trump administration has threatened and recently frozen.) In a paper published recently in Science, the team describes how the structure of the zinc anode is more like a sponge, in that the zinc is continuously connected throughout but peppered with tiny pockets of open space. In some ways, it's like a photo-negative of the zinc powder granules.
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Arndt Remhof's team has developed a solid electrolyte that facilitates good mobility of sodium ions at 20 degrees. This last point is crucial: ions require a source of heat in order to move, and inducing a reaction at room temperature poses a technical challenge. The electrolyte is also non-flammable and is chemically stable up to 300 degrees, which addresses the various safety concerns associated with lithium-ion batteries. Hans Hagemann's team at the University of Geneva has been working in parallel to develop cheaper technology for the production of this new solid electrolyte.
Unlike lithium, there are huge reserves of sodium: it's one of the two components of table salt. "Availability is our key argument", says Léo Duchêne of Empa and first author of the research paper. "However, it stores less energy than the equivalent mass of lithium and thus could prove to be a good solution if the size of the battery isn't a factor for its application."
Magnesium: the perfect but complex material
The same team has also developed a solid magnesium-based electrolyte. Until now, very little research had been done in this field. The fact that it is much more difficult to set this element in motion doesn't mean that it is any less attractive: it's available in abundance, it's light, and there's no risk of it exploding. But more importantly, a magnesium ion has two positive charges, whereas lithium only has one. Essentially, this means that it stores almost twice as much energy in the same volume.
Some experimental electrolytes have already been used to stimulate magnesium ions to move, but at temperatures in excess of 400 degrees. The electrolytes used by the Swiss scientists have already recorded similar conductivities at 70 degrees. "This is pioneering research and a proof of concept," says Elsa Roedern of Empa, who led the experiments. "We are still a long way from having a complete and functional prototype, but we have taken the first important step towards achieving our goal."
The energy density of a magnesium electrolyte would solve the EV range problem, if it is double lithium's.
(Score: 0, Funny) by Anonymous Coward on Saturday May 06 2017, @06:44AM (1 child)
We don't need no stinkin zinc! Lithium batteries are so yuuuge they're on fire.
(Score: 0) by Anonymous Coward on Saturday May 06 2017, @01:27PM
I want to see COAL batteries!! MOAR COAL MOAR JARBS!!