We've talked before about integrating significant amounts of analog functionality on to a silicon chip. That part is getting easier. In medical implant applications, this sort of integration is great, but what about the power source? It turns out that can be integrated, too.
Harvard University's Wyss Institute for Biologically Inspired Engineering recently described a method for making batteries with 3D printing. (The institute is an alliance among Harvard's Schools of Medicine, Engineering, and Arts & Sciences.) These are lithium-ion chemistry devices that can be as small as a few hundred micrometers on a side.
The proof-of-concept devices were fabricated by two teams of researchers — one at Harvard and one at the University of Illinois at Urbana-Champaign. They used a 30-micron nozzle operating at 105 psi and standard 3D printing techniques to print precisely interlaced electrodes. Since printing just one pair of interwoven electrodes would not create a battery with sufficient capacity, the researchers stacked one cell on top of another. They could do this because the extruded material would harden almost immediately. The stacking technique gave them the capacity they needed.
A battery requires two separate metallic compounds — one to make an anode (the cell's negative terminal) and one to make a cathode. Various metal pairs will work electrochemically. For anodes, lithium nickel cobalt aluminum oxide and lithium titanate will work. For cathodes, lithium iron phosphate, lithium manganese oxide, and lithium nickel manganese cobalt oxide will work. These were extruded on to two tiny gold combs.
The researchers put the comb assembly into a container and added an electrolyte solution. Voila — a battery.
This Wyss Institute video (running as twice the actual speed) shows a battery being made.
Even using this stacking method, the capacity is pretty low — on the order of tens of microamp-hours — but it's sufficient for some medical implants. It's important to keep in mind that for any design work on ICs for medical implant devices, the IC must be very low power.
Do you have any applications where a battery like this would be useful? Have you used a method like this already?