Ultrastable and high-capacity carbon nanofiber anodes derived from pitch/polyacrylonitrile for flexible sodium-ion batteries

Free-standing flexible sodium-ion battery anodes are fabricated by NH3 treating coal tar pitch/polyacrylonitrile based electrospun nanofibers. The carbon nanofiber films (NCFs) consist of disordered carbon matrix with well distributed graphitic microdomains. The disordered carbon matrix with enlarged interlay distance greatly enhances Na+ transfer kinetics. And the graphitic microdomains distributed throughout the entire matrix as a result of the addition of pitch form conductive network, which facilitates electron transfer. Micro/mesopores resulting from the NH3 treatment combined with interconnected network structure facilitate the access of electrolyte to the electrode and Na+ diffusion. Benefiting from these structural features, NCFs achieve a high reversible capacity of 341 mA h g−1 at 0.1 A g−1 in the half sodium-ion cells. Even after an ultralong cycling of 10 000 times, specific capacities of 235 and 217 mA h g−1 can still be retained at 1 and 2 A g−1, respectively. Furthermore, the flexible sodium-ion full batteries which consist of NCFs anode and Na3V2(PO4)3@C cathode show excellent rate performance and good cycling capability, with a stable discharge plateau of 3.3–2.2 V under different flexing angles. This novel high-performance carbon nanofiber film anode holds great potential in future flexible and wearable sodium-ion batteries.