Rice University scientists have developed a new process to create conductive, 3D objects from graphene foam.
The process is an extension of the Tour lab’s breakthrough which produced the first laser-induced graphene (LIG) in 2014 by heating inexpensive polyimide plastic sheets with a laser.
According to the Tour group, the laser burns halfway through the plastic and turns the top into interconnected flakes of 2D carbon that remain attached to the bottom half.
This ensures that the laser-induced graphene can be made in macroscale patterns at room temperature.
The new method is based on laminated object manufacturing, in which layers of a material are assembled and then cut to shape. In this case, the bottom LIG layer remains attached to its polyimide base.
A second layer is coated with ethylene glycol and placed facedown on the first, like a jelly sandwich. Its polyimide top is then burned into graphene; the process is repeated until the block is complete.
The ethylene glycol binder is evaporated away on a hot plate, and any remaining polyimide can be removed in a furnace. This leaves a pristine, spongy carbon block, says co-lead author of the paper Duy Xuan Luong.
The Rice lab stacked up to five layers of foam and then used a custom-built fiber lasing system on a modified 3D printer to mill the block into complex shapes.
The lab assembled proof-of-concept lithium-ion capacitors that used 3D LIG as both anodes and cathodes. The anode’s gravimetric capacity of 354 milliamp hours per gram neared the theoretical limit of graphite, while the cathode’s capacity exceeded the average capacity of other carbon materials.
According to the Tour group, the full test cells retained about 70 percent of their capacity after 970 charge-discharge cycles.
The researchers also infused a block of 3D LIG with liquid polydimethylsiloxane through its 20- to 30-nanometer pores. This created a stronger, still-flexible, conductive material well suited for electronic sensor applications.
Image, video and content: The Tour Group/Rice University
