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

The flexible binderless films composed of cobalt selenide grains attached on carbon nanofibers (denoted as CoSe2/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 CoSe2/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 CoSe2 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 CoSe2/CNFs nanocomposite electrode may hold great application promising for high cycling performance SIBs.