Supersalty Water Boosts Battery Safety | Chemical & Engineering News
Volume 93 Issue 46 | p. 26 | Concentrates
Issue Date: November 23, 2015

Supersalty Water Boosts Battery Safety

Energy Delivery: Highly concentrated aqueous electrolyte solutions could replace hazardous organic solvents in lithium-ion batteries
Department: Science & Technology
News Channels: Materials SCENE
Keywords: lithium-ion battery, battery safety
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PENNY FOR YOUR WATTS
This small test device showed that water-in-salt batteries can provide power and voltages closer to those achieved with standard batteries that use flammable solvents.
Credit: Liumin Suo
A photograph shows a battery about the size of a penny.
 
PENNY FOR YOUR WATTS
This small test device showed that water-in-salt batteries can provide power and voltages closer to those achieved with standard batteries that use flammable solvents.
Credit: Liumin Suo

Flammable solvents currently used in lithium-ion batteries, such as ethylene carbonate, can turn the devices into chemical volcanoes if they fail. Aqueous electrolytes are a safe alternative, but water breaks down at the voltages required by electric cars and other power hogs. That may change thanks to a team led by Liumin Suo and Chunsheng Wang from the University of Maryland, College Park, and Kang Xu from the Army Research Laboratory. To boost the stability of water in a battery, the team cranked up the concentration of the aqueous electrolyte (Science 2015, DOI: 10.1126/science.aab1595). Typical batteries use electrolytes with salt concentrations of about 6 M or less, Xu and Wang tell C&EN. They instead used lithium bis(trifluoromethane sulfonyl)imide solutions at better than 20 M. The salty solution roughly doubled water’s useful voltage range in batteries. In these concentrated electrolytes, the salt’s anions reduce before water starts breaking down electrochemically. A lithium fluoride film then forms at the anode, the team speculates, protecting against the decomposition of water at elevated voltages. This is the first report of such a protective barrier in a battery using aqueous chemistry, the team says.

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WATER-IN-SALT
The electrolyte used in a new battery is so concentrated it behaves more like a water-in-salt than salt-in-water solution, which improves water’s electrochemical stability.
Credit: Science
A figure compares conventional battery electrolytes with a new electrolyte.
 
WATER-IN-SALT
The electrolyte used in a new battery is so concentrated it behaves more like a water-in-salt than salt-in-water solution, which improves water’s electrochemical stability.
Credit: Science
 
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