For the first time, researchers at the U.S. Army Research Laboratory and the University of Maryland have developed a lithium-ion battery using a water-salt solution as its electrolyte. It can reach the stuy4.0-volt mark desired for electronics like laptop computers, minus the fire and explosive risks associated with some commercially available non-aqueous lithium-ion batteries.
This technology will provide the soldiers a “completely safe and flexible Li-ion battery that provides identical energy density as the SOA Li-ion batteries”.
“The batteries will remain safe – without fire and explosion – even under severe mechanical abuses,” says co-senior author Dr. Kang Xu, ARL fellow specializing in electrochemistry and materials science.
“In the past, if you wanted high energy, you would choose a non-aqueous lithium-ion battery, but you would have to compromise on safety. If you preferred safety, you could use an aqueous battery such as nickel/metal hydride, but you would have to settle for lower energy,” said Dr. Xu. “Now, we are showing that you can simultaneously have access to both high energy and high safety.”
The research followed a 2015 study in the U.S. that produced a similar 3.0-volt battery with an aqueous electrolyte but was prevented from achieving higher voltages by the so-called “cathodic challenge”, in which one end of the battery, made from either graphite or lithium metal, is degraded by the aqueous electrolyte. To fix the problem and make the leap from three volts to four, the researchers designed a new gel polymer that can be applied to the graphite or lithium anode.
This interphase can further protect the anode from debilitating side reactions, allowing the battery to use desirable anode materials and achieve better energy density and cycling ability.
“The key innovation here is making the right gel that can block water contact with the anode so that the water doesn’t decompose and can also form the right interphase to support high battery performance,” said co-senior author Chunseng Wang, Professor of Chemical & Biomolecular Engineering at the University of Maryland’s A. James Clark School of Engineering.
The addition of the gel coating 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 non-flammability 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 layers is damaged, it reacts slowly with the lithium or lithiated graphite anode, preventing the smoking, fire, or explosion that could otherwise occur if a damaged battery brought the metal into direct contact with the electrolyte.
The researchers plan to increase the number of full performance cycles that the battery can complete and to reduce material expenses where possible.
“Right now, we are talking about 50-100 cycles, but to compare with organic electrolyte batteries, we want to get to 500 or more,” said Prof. Wang.
Dr. Xu said the interphase chemistry should be perfected before it can be commercialized. He also said more work needs to be done on scaling up the technology in big cells for testing. With enough funding, the 4-volt chemistry could be ready for commercializing in about five years.