Facile Fabrication of Flexible Carbon Nanofiber Electrodes with Both High Packing Density and Capacity for Li‐Ion Batteries

Freestanding carbon nanofiber (CNF) films are promising flexible battery electrodes because of their rich functionalities and the avoidance of the unnecessary usage of conductive additives and binders, which introduce additional interfacial resistance. However, most reported freestanding CNF electrodes have lower energy density than the metrics of practical usage. Herein, an in situ welding strategy is proposed to fabricate flexible CNF electrodes with both high packing density (0.343 g cm−3) and capacity (832.4 mA h g−1 @0.1 C) by electrospinning of a polyacrylonitrile (PAN) and poly(vinyl‐butyral) (PVB) sol followed by pyrolysis. The addition of 20 wt% of low‐thermal‐stability PVB into PAN carbon precursors endows the CNFs with mixed amorphous/graphitic carbon domains and welded structures. The former enhances the capacity and long‐cycling stability, and the latter improves the flexibility and packing density of the anodes. As a result, these flexible anodes display stable reversible capacities of 430 mA h g−1 @1 C over 1000 cycles and excellent rate performance from 0.1 to 5 C. The successful fabrication of high‐capacity CNF anodes at commercial‐level density opens a new avenue for their practical application.