US Scientists at Rice University have used a seamless graphene-carbon nanotube (GCNT) electrode to create a rechargeable lithium metal battery with three times the capacity of commercial lithium-ion batteries. It stores lithium metal reversibly and with complete suppression of dendrite formation. Dendrites are lithium deposits that grow into the battery’s electrolyte and can pose a risk of failure, fire or even explosion, if they form a short circuit between the anode and cathode.
In a paper published in the journal ACS Nano, the team led by Dr. James Tour reports that a full battery based on GCNT-Li/sulfurised carbon (SC) exhibits high energy density, high capacity, good cycle stability and is free of Li polysulfides and dendrites that would cause severe capacity fade.
The anode of the Rice battery is a unique hybrid of graphene and carbon nanotubes, with a low density of nanotubes forming a carpet-like surface. This surface provides abundant area for lithium to inhabit and lithium can coat all the way down to the substrate. It can accommodate large amounts of metal homogeneously distributed as a thin coating over CNT bundles. The structure suppresses dendrite formation during reversible cycles of plating and stripping the lithium coating.
Post-Li-ion batteries, such as Li-S and Li-air batteries, require high gravimetric capacity anodes and cathodes. Ideally, during the charging of a battery, the maximum gravimetric capacity would be achieved if Li is deposited on the anode directly as pure Li metal rather than stored in intercalation compounds such as graphite as in Li-ion batteries (LIBs). The theoretical capacity based on lithiated graphite LiC6 is ~ 339 mAh g-1 while pure Li metal can theoretically deliver 3860 mAh g-1 assuming 100% of Li usage in the discharge operation.
This enormous capacity compared to commercial Li-ion anodes explain the revisiting of Li metal after more than 30 years of the first attempts to incorporate this low density metal in high energy density batteries. However, Li metal problematically forms dendrites and related unstable structures during battery operation. This results in low coulombic efficiency (CE) and cycle life and poses serious safety concerns as the dendrites can cause short circuits.—Raji et al.