Graphene foam

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.

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 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.

Applications

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 Whrs/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, the total power delivered was 80 percent of what it produced during an hour-long discharge. Performance remained stable through 500 charge/discharge cycles.

See also

• Aerographene
• Lithium-ion battery
• Foam