New 'Water Batteries' Are Cheaper, Recyclable, And Won't Explode

Clare Watson reports via ScienceAlert: By replacing the hazardous chemical electrolytes used in commercial batteries with water, scientists have developed a recyclable 'water battery' -- and solved key issues with the emerging technology, which could be a safer and greener alternative. 'Water batteries' are formally known as aqueous metal-ion batteries. These devices use metals such as magnesium or zinc, which are cheaper to assemble and less toxic than the materials currently used in other kinds of batteries.

Batteries store energy by creating a flow of electrons that move from the positive end of the battery (the cathode) to the negative end (the anode). They expend energy when electrons flow the opposite way. The fluid in the battery is there to shuttle electrons back and forth between both ends. In a water battery, the electrolytic fluid is water with a few added salts, instead of something like sulfuric acid or lithium salt. Crucially, the team behind this latest advancement came up with a way to prevent these water batteries from short-circuiting. This happens when tiny spiky metallic growths called dendrites form on the metal anode inside a battery, busting through battery compartments.

To inhibit this, the researchers coated the zinc anode of the battery with bismuth metal, which oxidizes to form rust. This creates a protective layer that stops dendrites from forming. The feature also helps the prototype water batteries last longer, retaining more than 85 percent of their capacity after 500 cycles, the researchers' experiments showed. According to Royce Kurmelovs at The Guardian, the team has so far developed water-based prototypes of coin-sized batteries used in clocks, as well as cylindrical batteries similar to AA or AAA batteries. The team is working to improve the energy density of their water batteries, to make them comparable to the compact lithium-ion batteries found inside pocket-sized devices. Magnesium is their preferred material, lighter than zinc with a greater potential energy density. [I]f magnesium-ion batteries can be commercialized, the technology could replace bulky lead-acid batteries within a few years. The study has been published in the journal Advanced Materials.

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