November 24, 2015 | By Barbara Vergetis Lundin

Researchers from the University of Maryland (UMD) and the U.S. Army Research Laboratory (ARL) have found a solution to better, safer batteries for use in safety-critical, automotive and grid storage applications.

The groundbreaking discovery is a "Water-in-Salt" aqueous (water-based) Lithium-ion (Li-on) battery technology that could provide power, efficiency and longevity comparable to today's Lithium-ion batteries -- without the fire risk, poisonous chemicals and environmental hazards.

This work demonstrates a major advance in the long history of water-based batteries by doubling the voltage, or power, of an aqueous battery.

The technology holds promise, especially in applications that involve large energies at kilowatt or megawatt levels, such as electric vehicles or grid-storage devices for energy harvest systems, and in applications where battery safety and toxicity are primary concerns, such as safe, non-flammable batteries for airplanes, naval vessels or spaceships.

According to Lt. Col. (Retired) Edward Shaffer, who heads the Army Research Laboratory's Energy and Power Division, the significant potential advantages this new approach has over current batteries "could lead to thermally, chemically and environmentally safer batteries carried and worn by soldiers; safe, reduced-footprint energy storage for confined spaces, particularly submarines; and novel hybrid power solutions for military platforms and systems."

The key to the breakthrough was the use of a type of water-based electrolyte containing ultrahigh concentrations of a carefully selected Lithium salt, which transformed the battery's chemistry, resulting in the formation of a thin protective film on the anode electrode for the very first time in a water-based battery. Known in battery science as a "Solid Electrolyte Interphase (SEI)," such a protective and stabilizing film is essential to the high performance characteristics of state-of-the-art Li-ion batteries, but has only been achieved in non-aqueous electrolytes.

The UMD and ARL team compared the performance of their new "Water-in-Salt" battery with that of other aqueous battery systems, demonstrating that the high stability of other aqueous batteries was achieved only at the expense of voltage and energy density and vice versa. However, the formation of an anode/electrolyte interphase allowed them to break this inverse relationship between cycling stability and high voltage and to achieve both simultaneously.

"Researchers in the Li-ion battery field have recently found that previously "useless" solvents could be made functional in Li-ion cells through the addition of high concentrations of salts. The work by Suo et al., extends this idea to the case of the solvent, water.  By extending the operational voltage window to approximately 3 Volts, it is possible that a new generation of safer and possibly less expensive Li-ion cells could result," said Dalhousie University (Nova Scotia) Professor Jeff Dahn, a leading battery researcher, who was not involved in the study. "Only further R&D efforts will be able to verify the practicality of this discovery, so prudence is needed in assessing the potential of this, or any basic research advance."

The research could lead to advances in other aqueous electrochemical devices like supercapacitors and electroplating devices.

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