Compression-Assisted Improvement of Electrochemical Performances of Carbon Nanotube in Symmetric Supercapacitors

The unique geometry of carbon nanotubes (CNTs) contributes to their excellent rate capability when used as electrode materials for supercapacitors (SCs). However, the practical application of low-cost commercial CNTs is limited by their moderate specific capacitance due to the relatively low surface area which is around 220 m² g⁻¹. This limitation can be addressed by applying proper compressive stress to the CNTs, resulting in improved capacitance. The effects of compression on capacitance vary depending on the length and inner diameter of the CNTs, which have been systematically investigated. It has been found that longer and narrower CNTs exhibit more significant improvements in capacitance due to compression. Specifically, under 12 MPa, there is an ≈135% increase in specific capacitance compared to that under 1 MPa, with the optimum value of 68.2 F g⁻¹ at 1 A g⁻¹. An excellent rate capability of 93.5% at 40 A g⁻¹ is also obtained by compression. Furthermore, when an light emitting diode light is powered by a compressed CNT-based SC, both brightness and lasting time are dramatically enhanced compared to the case without compression. This cost-efficient strategy for improving the energy storage performance of CNTs may facilitate their practical application as electrode materials for ultrafast supercapacitors.