Graphene foam is a solid, open-cell foam made of single-layer sheets of graphene. It is a candidate substrate for the electrode of lithium-ion batteries.
Contents
GO-0.5BN
GO-0.5BN is a foam made of graphene oxide that self-assembles with the assistance of hexagonal boron nitride platelets and can be made in any size and shape. The foam is resilient, returning to its native shape after considerable deformation. Its density is .25% of graphite's.
Hexagonal boron nitride (h-BN), known as “white graphene,” looks like GO, with the same “chicken wire” array of atoms. It can form hybrids with graphene. Both the GO and BN were exfoliated from powders, mixed with catalysts and freeze-dried. The resulting foam takes the shape of its container.
The foam consists of self-assembled sheets of overlapping GO flakes. Cross-linking platelets of BN were uniformly distributed and bonded to the GO sheets. The platelets absorb stress from compression and stretching, preventing the GO floors from crumbling and increasing the foam's thermal stability. The platelets prevented the propagation of cracks that destroyed samples with less or no h-BN.
Construction
The foam is manufactured using vapor deposition to coat a metal foam, a three-dimensional mesh of metal filaments. The metal is then removed.
Electrode
A physically flexible battery was created using the foam for electrodes. The anode was made by coating the foam with a lithium-titanium compound (Li
4Ti
5O
12) and the cathode by coating the foam with LiFePO
4. Both electrodes were lightweight and their large surface area provided high energy density of 110 Wh/kg, comparable to commercial batteries.
Power density was much greater than a typical battery. At a rate that completely discharged the material in 18 seconds, power delivered was 80 percent of what it produced during an hour-long discharge. Performance remained stable through 500 charge/discharge cycles.
Support
In 2017 researchers used carbon nanotubes to reinforce a foam. The latter material supports 3,000 times its own weight and can return to its original shape when unweighted. Nanotubes, a powdered nickel catalyst and sugar were mixed. Dried pellets of the substance were then compressed in a steel die in the shape of a screw. The nickel was removed, leaving a screw-shaped piece of foam. The nanotubes' outer layers split and bonded with the graphene.