Development of Surface‐Engineered Tape‐Casting Method for Fabricating Freestanding Carbon Nanotube Sheets Containing Fe₂O₃ Nanoparticles for Flexible Batteries

Abstract

Chemical vapor deposition and filtration are commonly used to fabricate freestanding multiwalled carbon nanotube sheets containing iron(III) oxide (Fe 2 O 3 ) (MWCNT–Fe 2 O 3 sheets). However, the former is relatively expensive, and the latter suffers from poor scalability. Here, the authors develop an inexpensive, scalable, high‐throughput, tunable tape‐casting method for fabricating flexible, foldable freestanding MWCNT–Fe 2 O 3 sheets. When tested as electrodes in lithium‐ion batteries, the sheets perform better than conventional graphite on copper foil (681 mAh g −1 after 20 cycles at 100.5 mA g −1 /0.1 C‐rate vs. 72.5 mAh g −1 after 20 cycles at 37.2 mA g −1 /0.1 C‐rate). Sheets prepared at Fe 2 O 3 :MWCNT mass ratios ranging from 1/4 to 2/1 are flexible and easy to be separated from the substrate, but a sheet prepared at a 9/1 ratio is not. The ratio can be tuned to suit various applications. Sheets with high (low) Fe 2 O 3 :MWCNT mass ratios has high (low) charge‐transfer resistance and are suitable for applications requiring high energy density (high power density). Mechanical compression of the sheets flattens them and increase their density from 0.449 to 0.771 g cm −3 , which in turn increases their electrical conductivity from 3.56 × 10 3 to 5.73 × 10 3 S m −1 .