Flexible Sub-Micro Carbon Fiber@CNTs as Anodes for Potassium-Ion Batteries

Potassium-ion batteries (KIBs) with potential cost benefits are a promising alternative to lithium-ion batteries (LIBs). However, because of the large radius of K⁺, current anode materials usually undergo large volumetric expansion and structural collapse during the charge-discharge process. Self-supporting carbon nanotubes encapsulated in sub-micro carbon fiber (SMCF@CNTs) are utilized as the KIB anode in this study. The SMCF@CNT anode exhibits high specific capacity, good rate performance, and cycling stability. The SMCF@CNT electrode has specific capacities of 236 mAh g^-1 at 0.1 C and 108 mAh g^-1 at 5 C and maintains over 193 mAh g^-1 after 300 cycles at 1 C. Furthermore, a combined capacitive and diffusion-controlled K⁺ storage mechanism is proposed on the basis of the investigation using in situ Raman and quantitative analyses. By coupling the SMCF@CNT anode with the K_0.3MnO₂ cathode, a pouch cell with good flexibility delivers a capacity of 74.0 mAh g^-1 at 20 mA g^-1. This work is expected to promote the application of KIBs in wearable electronics.