Printing method for air batteries and more efficient solar cells : THE PALO Alto Research Centre has demonstrated a new technology which could see batteries and fuel cell electrodes made by printing. The co-extrusion printing technology from PARC promises higher energy/power density through low-cost printed structures, and is a method with potential for making advanced battery and fuel cell electrodes, particularly air cathodes.
Air batteries derive power by oxidising metals using oxygen from the air. Metal air batteries and fuel cells have the potential to surpass the storage capability of lithium ion batteries.
Successful implementation depends on developing air cathodes that support the power density, particularly for vehicle applications. The current density in an air-breathing electrode is proportional to the amount of electro-catalytic surface area that is exposed to air.
PARC therefore developed a non-contact, high-throughput, mask-less technology for direct-printing high aspect ratio functional materials onto substrates. This technology produces up to 10 times the exposed electro-catalytic surface area than possible with conventional electrode manufacturing methods. The electrode material coating method extrudes pastes in a ribbon of interdigitated stripes of functional materials. The pastes can contain hydrophobic air transport materials such as Teflon interleaved with hydrophilic electro-catalyst material.
Processing after the deposition dries and sinters the deposit into the final electrode structure. The stripes can be as narrow as several microns wide and as tall as several hundred microns for increased exposure to air.
The technique has already been used for silver gridlines on the front surface of solar cells. Compared to screen-printed gridlines, the narrower and taller front gridlines created by this technique covered less solar cell surface area, resulting in increased absolute cell efficiency. The non-contact nature of the technology also increases the yield due to reduced breakage and supports cost reduction by enabling thinner wafers.
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