Spray-Printed and Self-Assembled Honeycomb Electrodes of Silicon-Decorated Carbon Nanofibers for Li-Ion Batteries.

Directional, micron-scale honeycomb pores in Li-ion battery electrodes were fabricated using a layer-by-layer, self-assembly approach based on spray printing of carbon nanofibers. By controlling the drying behavior of each printed electrode layer through optimization of (i) the volume ratio of fugitive bi-solvent carriers in the suspension, and (ii) the substrate temperature during printing, self-assembled, honeycomb pore channels through the electrode were created spontaneously and reliably on current collector areas larger than 20 cm × 15 cm. The honeycomb pore structure promoted efficient Li-ion dynamics at high charge/discharge current densities. Incorporating an optimum fraction (2.5 wt%) of high energy density Si particulate into the honeycomb electrodes provided a four-fold increase in deliverable discharge capacity at 8000 mA/g. The spray printed, honeycomb pore electrodes were then investigated as negative electrodes coupled with similar spray printed LiFePO4 positive electrodes in a full Li-ion cell configuration, providing an approximately 50 % improvement in rate capacity retention over half-cell configurations of identical electrodes at 4000 mA/g.