“Water-in-salt” electrolyte enables high-voltage aqueous lithium-ion chemistries

Lithium-ion batteries raise safety, environmental, and cost concerns, which mostly arise from their nonaqueous electrolytes. The use of aqueous alternatives is limited by their narrow electrochemical stability window (1.23 volts), which sets an intrinsic limit on the practical voltage and energy output. We report a highly concentrated aqueous electrolyte whose window was expanded to ~3.0 volts with the formation of an electrode-electrolyte interphase. A full lithium-ion battery of 2.3 volts using such an aqueous electrolyte was demonstrated to cycle up to 1000 times, with nearly 100% coulombic efficiency at both low (0.15 coulomb) and high (4.5 coulombs) discharge and charge rates.

Science 20 November 2015:
Vol. 350 no. 6263 pp. 938-943
DOI: 10.1126/science.aab1595

http://www.sciencemag.org/content/350/6263/938

Opening the window for aqueous electrolytes

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.

Science 20 November 2015:
Vol. 350 no. 6263 p. 918
DOI: 10.1126/science.aad5575

http://www.sciencemag.org/content/350/6263/918.short