Long cycle life and high rate capability of three dimensional CoSe2 grain-attached carbon nanofibers for flexible sodium-ion batteries

Abstract The flexible binderless films composed of cobalt selenide grains attached on carbon nanofibers (denoted as CoSe 2 /CNFs) are prepared by electrospinning to enhance the electronic conductivity, Na-ions diffusion and alleviate volume variation during charge/discharge process for high performance sodium-ion batteries (SIBs). The binderless and flexible CoSe 2 /CNFs electrode can obtain a high reversible capacity of 430 mAh g −1 after 400 cycles at a current density of 200 mA g −1 , an exceptional rate capability of 224 mAh g −1 at 15 A g −1 , even a capacity of 370 mAh g −1 at 2 A g −1 after 1000 cycles. The superior electrochemical performance can be ascribed to the synergistic effects of the homogeneous distribution of CoSe 2 grains attached to the carbon nanofibers and the high electronic conductivity framework of 3D interconnecting carbon nanofibers, which can alleviate the volume variation during charge-discharge process and sustain the high electrical conductivity and fast Na-ions diffusion throughout the electrode. This binderless flexible CoSe 2 /CNFs nanocomposite electrode may hold great application promising for high cycling performance SIBs.