Rapid fabrication of thick spray-layer-by-layer carbon nanotube electrodes for high power and energy devices

Rapid fabrication of layer-by-layer (LbL) electrodes is essential to expand their utility in energy storage applications. Herein, we address challenges in developing thick LbL electrodes of multi-wall carbon nanotubes (MWNTs) using conventional dip- and spray-LbL processes, and present a solution to overcome these challenges. The vacuum-assisted spray-LbL process using porous carbon substrates enabled a linear growth of LbL-MWNT electrodes with a 600 time decrease in their fabrication time. This result was attributed to the enhanced surface interactions between MWNTs and substrate via increased surface areas, enhanced capillary forces, physical entrapment in pores, and changes in hydrodynamic drag forces. Scanning electron microscopy (SEM) revealed high surface area carbon nanotube networks comprised of individual MWNT's. The spray MWNT electrodes delivered a high gravimetric energy of 100 W h kg^-1 at high gravimetric power of 50 kW kg^-1, which is higher than those of most carbon nanotube electrodes reported. Moreover, the spray MWNT electrodes delivered the highest energy capacity per unit area (up to 300 μW h cm ^-2 at 0.4 mW cm^-2 among the LbL electrodes reported, and showed excellent retention of energy capacity up to 100 μW h cm^-2 at high power capacity of 200 mW cm^-2. These performance values are higher or comparable to the most advanced battery electrodes for high energy capacity per unit area.