Study of Microstructure Change of Carbon Nanofibers as Binder-Free Anode for High-Performance Lithium-Ion Batteries

Flexible and binder-free film of N, O-doped carbon nanofibers (CNFs) is the ideal anode for high-energy-density batteries. Here, CNFs flexible films which the N, O dopant give defect in graphite structure results in high specific surface area more than 500 m² g^-1. A flexible film of CNF800 carbonized at 800 °C delivers initial capacities of 2000 and 755 mAh g^-1 at the current densities of 5 and 10 A g^-1, respectively. After 500 cycles, CNF800 remains the capacities of 1251, 865, 702, and 305 mAh g^-1 at 0.5, 1, 5, and 10 A g^-1, respectively. The microstructures of CNFs under various state of charge are studied by HRTEM, XPS, ¹³C NMR, and so forth. The lithiation/delithiation mainly happens to the interlayer of graphite domain of CNFs. The dopants of nitrogen and oxygen involve in lithiation, but much of Li-N is irreversible. The excellent performances of CNFs film can be attributed to the N, O doped structure of graphite domain that has increased the conductivity and lithium storage ability. Further development of N, O doped CNFs may enable practical applications as flexible anode in high-performance lithium-ion batteries.