The identification of specific N-configuration responsible for Li-ion storage in N-doped porous carbon nanofibers: An ex-situ study

Nitrogen (N)-doped carbon is widely used as an anode material for Li-ion battery (LIB). However, the identification of a specific type of N-configuration responsible for Li-ion storage in N-doped carbon is an elusive topic for LIB. Herein, the N-doped porous carbon nanofibers (N-pCNFs) with various atomic percentages of N and different types of N-configurations are prepared by carbonization of polyacrylonitrile-Zeolitic imidazolate framework-8 fibres at 800, 900, and 1000 °C in N₂ atmosphere. The N content of pCNFs-800, N-pCNFs-900, and N-pCNFs-1000 samples are found to be 12.9, 9.4, and 4.8% atomic percentage, respectively. The free-standing/binder-free N-pCNFs-800, N-pCNFs-900, and N-pCNFs-1000 anode electrodes deliver the reversible Li storage capacity of 650, 805, and 520 mAh g⁻¹, respectively at 0.1 C-rate. The ex-situ X-ray diffraction, scanning electron, and transmission electron microscopic results of N-pCNFs-900 indicate the formation of the solid electrolyte interface (SEI) layer. Further, the ex-situ X-ray photoelectron spectroscopy (XPS) analysis of N-pCNFs-900 identifies the presence of LiF, Li_xPF_5-x, Li_xPOF_5-x, Li-O-C, and R-COOLi constituents of the SEI layer and the deconvoluted XPS N1s spectra confirms that the pyridinic-N is responsible for Li-ion storage sites in N-pCNFs.