Environmentally-Friendly Liquid Battery

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Photo: Xiaoli Dong, Jingyuan Liu & Yonggang Wang

A new liquid battery that is more environmentally friendly than its existing counterparts could help lead to safe, inexpensive storage of renewable energy for power grids, researchers in Shanghai say.

The new battery also has a much longer cycle life and much greater power than any current rechargeable battery, the scientists add.

The sun and wind are variable sources of power. As such, utility companies want massive rechargeable battery farms that can store the surplus energy from these renewable power sources for use when the sun goes down and the wind does not blow.

However, one concern with many current rechargeable batteries is safety. For instance, many of these devices contain corrosive, toxic, or flammable components, or require searing-hot operating temperatures.

In addition, today’s rechargeable batteries are often too expensive for use in large-scale energy storage. Most offer too few total charge-discharge cycles, which requires their regular replacement, increasing costs. Many also depend on metals from rare ores, driving up costs.

Now researchers have created a battery that uses environmentally-friendly liquids to store and release energy.

The new battery possesses a cathode made of: water-soluble iodide and triiodide ions; a watery electrolyte containing either lithium or sulfur ions that the cathode is dissolved in; a solid anode made of polyimide; and a polymer membrane that separates the anode and the cathode and allows ions to diffuse across it. When the battery is charging, the iodide oxidizes to form triiodide, and lithium or sodium ions flow across the membrane to chemically react with the polyimide. When the battery is discharging electricity, this process reverses. The scientists detailed their findings online in the 22 January edition of the journal Science Advances.

The researchers note that the cathode, anode, and electrolyte do not rely on metals. Furthermore, they calculated that sodium-ion and lithium-ion versions of this battery had energy densities of roughly 63.8 and 65.3 watt-hours per kilogram, respectively, comparable with other liquid batteries used for grid-level energy storage.

Moreover, this new battery has a super-long life of 50,000 cycles, much better than any other rechargeable battery, the researchers say. “The super-long cycling life potentially reduces battery cost,” says study co-author Yonggang Wang, an electrochemist at Fudan University in Shanghai.

Just as important, say the researchers, is that the battery can be charged or discharged in only 6.6 seconds—a level of power much greater than current rechargeable batteries and close to supercapacitors in capability. “High power is important for fast-rate energy storage,” Wang says.

The next steps for this research are larger batteries and better energy density, Wang says.

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