Opening the window for aqueous electrolytes

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Science  20 Nov 2015:
Vol. 350, Issue 6263, pp. 918
DOI: 10.1126/science.aad5575

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By facilitating ion motion between electrodes, electrolytes help to harness the chemical energy in a battery to produce a current and supply usable electric power. Among liquid electrolytes, there are traditional solutions of salt dissolved in solvents (aqueous or organic) and ionic liquids. Lithium-ion batteries, whether for consumer electronics or electric vehicles, have used nonaqueous liquid electrolytes because of their higher voltage stability. Although aqueous electrolytes would be safer and more environmentally benign, the electrochemical voltage window (1.23 V) precludes the use of high-voltage electrode couples that enable the high energy density of lithium-ion batteries. On page 938 of this issue, Suo et al. (1) change this perception by demonstrating an operating window of 3 V created by increasing the salt concentration to form “water-in-salt” electrolytes.