Researchers have developed a lithium-ion battery that uses a water-salt solution as its electrolyte — reaching the 4.0- Volt mark for electronics such as laptops — without the fire and explosive risks associated with commercially available, non-aqueous lithium-ion batteries.

The hydrophobic gel polymer electrolyte coating expels water molecules from the vicinity of the electrode surface.

In the past, in order to obtain high energy, the choice was a non-aqueous lithium-ion battery, but the compromise would be safety. If safety was preferred, an aqueous battery such as nickel/metal hydride could be used, but with lower energy.

A gel polymer electrolyte coating was developed that can be applied to the graphite or lithium anode. This hydro-phobic coating expels water molecules from the vicinity of the electrode surface and then, upon charging for the first time, decomposes and forms a stable interphase — a thin mixture of breakdown products that separates the solid anode from the liquid electrolyte. This interphase, inspired by a layer generated within non-aqueous batteries, protects the anode from debilitating side reactions, allowing the battery to use desirable anode materials, such as graphite or lithium metal, and achieve better energy density and cycling ability.

The addition of the gel coating also boosts the safety advantages of the new battery when compared to standard non-aqueous lithium-ion batteries, and boosts the energy density when compared to any other proposed aqueous lithium-ion batteries. All aqueous lithium-ion batteries benefit from the nonflammability of water-based electrolytes as opposed to the highly flammable organic solvents used in their non-aqueous counterparts. Unique to this one, however, is that even when the interphase layer is damaged (if the battery casing were punctured, for instance), it reacts slowly with the lithium or lithiated graphite anode, preventing the smoke, fire, or explosion that could otherwise occur if a damaged battery brought the metal into direct contact with the electrolyte.

Though the power and energy density of the new battery are suitable for commercial applications currently served by more hazardous non-aqueous batteries, certain improvements would make it even more competitive. In particular, the researchers would like to increase the number of full-performance cycles that the battery can complete, and reduce material expenses where possible.

The electrochemical manipulations behind the jump to 4V have importance within battery technology and beyond, including sodium-ion batteries, lithium-sulfur batteries, multiple ion chemistries involving zinc and magnesium, or electroplating and electrochemical synthesis.

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