Thick Architected Silicon Composite Battery Electrodes Using Honeycomb Patterned Carbon Nanotube Forests

Abstract

To meet the growing performance demands for personal electronics and electric vehicles the energy density of lithium-ion batteries can be increased by incorporating thicker electrodes. We present thick “honeycomb” electrodes based on patterned, vertically aligned carbon nanotubes (CNTs) on Cu foils. Thick electrodes are created by Si deposition on >100 μm tall honeycomb patterned CNTs. Si-CNT electrodes are cycled in half-cells, demonstrating electronic connection between the Si and Cu foil via the aligned CNTs. For ~4.7 mAh cm−2 capacity the honeycomb patterning improves capacity retention (78%) over 30 cycles compared to non-patterned electrodes (58%). We attribute this improvement to the honeycomb’s ability to accommodate Si expansion, thereby reducing cracking that causes active material loss and solid electrolyte interphase instability, and to provide pathways for Li-ion transport into the electrode. The Si-CNT electrode capacity is further increased to 20 mAh cm−2 by increasing the Si loading. Finally, a fluoroethylene carbonate containing electrolyte is used to increase cell lifetime. Here, the honeycomb electrodes have a higher areal (~10.2 mAh cm−2) and retained (65%) capacity over 180 cycles, and exhibit superior rate performance to their non-patterned counterparts. Our work demonstrates the role of patterning in enabling aligned CNTs as a robust template for thick battery electrodes.