Super-compact ultracapacitors could come out of work now progressing at the Lawrence Livermore National Lab where researchers are extruding graphene aerogel on a special 3D printer.
The 3D-printing process LLNL developed is called direct-ink writing. It uses a graphene-oxide composite ink designed at the Lab. To make a supercapacitor, Lab researchers 3D-printed a lattice comprised of the graphene material. Graphene-based inks, the researchers said, have a distinct advantage over carbon-based materials due to their ultrahigh surface area, lightweight properties, elasticity and superior electrical conductivity. The graphene composite aerogel supercapacitors also are extremely stable, the researchers reported, capable of nearly fully retaining their energy capacity after 10,000 consecutive charging and discharging cycles. UC Santa Cruz professor Yat Li and grad student Tianyu Liu performed the electrochemical characterizations and optimized the materials used in the process.
A key factor in developing the super caps was the creation of an extrudable graphene oxide-based composite ink and coming up with a way to 3D-print the stuff. The graphene oxide (GO) inks are prepared by combining an aqueous GO suspension and silica filler to form a homogenous, highly viscous ink. These GO inks are then loaded into a syringe barrel and extruded through a micronozzle to pattern 3D structures.
The super caps using these 3D-GCA electrodes display exceptional capacitive retention (ca. 90% from 0.5 to 10 A/g) and power densities (>4 kW/kg). Researchers have not yet released energy density figures for the super caps, but the power densities they report are in the same ballpark as those for existing super caps and conventional capacitors.
In addition, the 3D-printed graphene aerogel microlattices show much better mass transport than conventional bulk graphene materials, researchers said.
Aerogel is a synthetic porous, ultralight material derived from a gel, in which the liquid component of the gel has been replaced with a gas. Previous attempts at creating bulk graphene aerogels produced a largely random pore structure. This structure thwarted efforts to tailor transport and other mechanical properties of the material for specific applications. 3D printing lets researchers design the pore structure of the aerogel so they can control mass transport (aerogels typically require high pressure gradients to drive mass transport through them due to small, tortuous pore structure) and optimize physical properties, such as stiffness.