Rice University researchers have made use of graphene and carbon nanotubes to create a rechargeable lithium metal battery with three times more power than those in existence.
The new battery anode – which is made up of a seamless graphene-nanotube hybrid – is said to resist the formation of damaging dendrites or mossy deposits.
Dendrites have always been a bane for battery manufacturers. It has squashed attempts to replace lithium-ion with advanced lithium metal batteries that last longer and charge faster. Due to their lithium deposits that grow into the battery’s electrolyte, they often bridge the anode and cathode and create a short circuit – resulting in battery failure, fires or even explosions.
The researchers led by Rice chemist James Tour found that when the new batteries are charged, lithium metal evenly coats the highly conductive carbon hybrid in which nanotubes are covalently bonded to the graphene surface.
“Lithium-ion batteries have changed the world, no doubt,” Tour said, “but they’re about as good as they’re going to get. Your cellphone’s battery won’t last any longer until new technology comes along.”
Tour contends that the anode’s nanotube forest, with its low density and high surface area, has plenty of space for lithium particles to slip in and out as the battery charges and discharges. The lithium is evenly distributed, spreading out the current carried by ions in the electrolyte and suppressing the growth of dendrites.
Though the prototype battery’s capacity is limited by the cathode, the anode material achieves a lithium storage capacity of 3,351 milliamp hours per gram, close to the theoretical maximum and 10 times that of lithium-ion batteries, Tour said.
Because of the low density of the nanotube carpet, the ability of lithium to coat all the way down to the substrate ensures maximum use of the available volume, Tour stated further.
To test the anode, the Rice lab built full batteries with sulfur-based cathodes that retained 80 percent capacity after more than 500 charge-discharge cycles, approximately two years’ worth of use for a normal cellphone user, Tour said.
Electron microscope images of the anodes after testing showed no sign of dendrites or the moss-like structures that have been observed on flat anodes. To the naked eye, anodes within the quarter-sized batteries were dark when empty of lithium metal and silver when full, the researchers reported.
Image credits and content: Tour Group/Rice University