Novel, early-stage study reveals adding a small volume of the chemical lithium hexafluoro—hosphate to a dual salt, carbonate solvent-based electrolyte can make rechargeable lithium-metal batteries stable, high voltage and have a charge quickly.
“A good lithium-metal battery will have the similar lifespan as the lithium – ion batteries that power today’s electronic cars and consumer electric devices, but also gather more energy so we can drive longer in between charges,” says chemist Wu Xu of the Department of Energy’s Pacific Northwest National Laboratory.
Most of the rechargeable batteries employed today are lithium-ion batteries that have two electrodes – one that is positively charged and comprises lithium, and another negatively charges that is usually prepared of graphite. Electricity is generated when electrons flow through a wire that connects the two.
When lithium-based rechargeable batteries were first introduced in the 1970s, scientists employed lithium metal for the negative electrode, known as anode. Lithium was selected because it has ten times more energy storage capacity than graphite. Issue was, the lithium carrying electrolyte reacted with the lithium anode. This caused microscopic lithium nanoparticles and branches known as dendrites to grow on the anode surface and resulted in the early batteries to fail.
Next, they attempted adding tiny amounts of a salt that is already employed in lithium-ion batteries, lithium hexafluorophosphate, to their fast-charging electrolyte. They coupled the newly linked up electrolyte with a lithium anode and lithium nickel manganese cobalt oxide cathode. It turned out to be a winning combination, leading to a fast, effective and high-voltage battery.
The additive allowed a 4.3 volt battery that retained more than 97% of its initial charge after 500 repeated charges and discharges, while carrying 1.75 milliamps of electronic current per square centimetre of area. It took the battery about one hour to fully charge.
The battery performed well largely as the additive helps prepare a robust protective layer of carbonate polymers on the lithium anode battery. This sleek layer prevents lithium from being employed in unwanted side reactions, which can kill a battery. And, since the additive is already an established component of lithium-ion batteries, it is readily available and relatively cost-effective. The small volumes required is just 0.6% of the electrolyte by weight should also further lower the cost of electrolyte.
Xu and his group continue to evaluate numerous ways to make rechargeable lithium-metal batteries viable, comprising enhancing electrodes, electrolytes and separators. Specific next steps include making and testing bigger quantities of their electrolyte, further enhancing the capacity and efficacy retention of a lithium-metal battery using their electrolyte, boosting material loading on the cathode and trying a sleeker anode.
Filed Under: News