Most lithium-ion batteries on the market come in cylindrical or rectangular shapes. Theoretically, 3D-printing technologies can fabricate an entire device, including the battery and structural and electronic components, in almost any shape. However, the polymers used for 3D printing, such as poly(lactic acid) (PLA), are not ionic conductors, creating a major hurdle for printing batteries.
So Christopher Reyes, Benjamin Wiley and colleagues at Duke University in Texas wanted to develop a process to print complete lithium-ion batteries with an inexpensive 3D printer.
The PLA was infused with a mixture of ethyl methyl carbonate, propylene carbonate, and LiClO 4 to obtain an ionic conductivity of 0.085 mS/cm, comparable to that of polymer and hybrid electrolytes. Different electrically conductive materials such as Super P, graphene and multiwall carbon nanotubes, and other active materials such as lithium titanate and lithium manganese oxide were blended into PLA to determine the relationships among filler loading, conductivity, charge storage capacity, and printability.
Up to 30 percent of the solids could be mixed into PLA without degrading its printability, and an 80:20 ratio of conductive to active material maximized the charge storage capacity. The highest capacity was obtained with lithium titanate and graphene nanoplatelets in the anode, and lithium manganese oxide and multiwall carbon nanotubes in the cathode.
To demonstrate the battery's potential, the team 3D printed an LED bangle bracelet with an integrated lithium-ion battery. The bangle battery could power a green LED for about 60 seconds. However, they say that they have several ideas for increasing the capacity, such as replacing the PLA-based materials with 3D-printable pastes.