Ultrathin Carbon Nanotube Fibers with a Record High Ampacity Fabricated Using a Water Coagulation Bath

Abstract Ultrathin carbon nanotube fibers (CNTFs) with a high electrical conductivity and ampacity are needed for use in wearable electronic devices. However, it is very challenging to spin ultrathin CNTFs due to the core–shell structure formed in the normal acetone coagulation bath used during the wet spinning process, which limits the applicable draw ratio. Here, the breaking of this limitation is reported by using double‐wall CNTs with a high aspect ratio as the raw material and water as a coagulation bath, which permits a significant improvement of the draw ratio from 1.6 to 54.6. As a result, ultrathin CNT fibers (UCNTFs) with an equivalent diameter of 2.68 µm are first obtained, ≈6 times thinner than those spun in acetone coagulation (A‐CNTFs). The UCNTFs show a high Herman orientation factor of 0.99, low content of residual chlorosulfonic acid (CSA), excellent temperature stability, and a record high ampacity of 1.52 × 10 9 A m −2 . This superior electrical property stems from their ultrathin diameter and less CSA doping, which permits rapid heat dissipation upon Joule heating.