Ultrahigh line-capacity and flexible graphene/carbon nanotube/tin oxide fibers as sodium ion battery anodes

As one dimensional substrate, carbon based fibers have been paid sufficient attention and acquired extensive success in wearable energy storage devices due to fascinating characteristics, such as excellent conductivity, porous structure and outstanding flexibility. However, there is still a severe challenge to assemble fiber-shaped anode for flexible power devices with high line capacity. Herein, porous graphene/carbon nanotube/tin oxide (PP-GCS) fiber was successfully fabricated via wet spinning following freeze-dried and finally mechanical power derived rearrangement. The oriented structure by mechanical power provided a desired skeleton and endowed a flexible characteristic for fiber. The porous structure could form sufficient open channels to guarantee the fast diffusion of electrolyte, resulting in that PP-GCS fiber presented an excellent electrochemical performance, especially remarkable line capacity. The assembled fiber shaped sodium-ion batteries (SIBs) demonstrated a stable cycle performance in the discharge capacity increased from 290.9 to 309 mAh g−1 (4.8–5.1 mAh m−1) after 100 cycles at 0.05 A g−1 and reversible capacity of 164.1 mAh g−1 (2.71 mAh m−1) at 0.5 A g−1. Besides, with the increase of PP-GCS fiber's diameter, the highest line capacity of porous fiber reached 15.74 mAh m−1 at a current density of 0.05 A g−1. This work provided a promising preparation method for high energy device in next-generation wearable electronics.