## 3 Results and Discussion
These results were in good conformity to the SEM and TEM measurements. In the bore diameters distribution graphs shown in Figure 4b,d, the CNF sample had a main peak at 2 nm and the adsorption capacity was mainly derived from micropores. However, plenty of mesopores in the range of 2-100 nm were observed in the PCNF sample. For electrode, the mesopore structure in the PCNF sample could be more suitable for rapid charge and discharge, due to a greater wettability  
Figure 2: The XRD and Raman images of CNF (black) and PCNF (red) samples: (**a**) XRD pattern; (**b**) Raman pattern. and accessibility of electrolyte, quicken lithium ion diffusion and transport from the bath solution to the surface of the electrode, in comparison with the micropore feature. Therefore, the presence of a large proportion of mesopore in PCNF could be expected to lead to an improved electrochemical performance in LiBs. Figure 4: (**a**) N\({}_{2}\) adsorption-desorption isotherms of the CNF; (**b**) pore diameter distribution of the CNF; (**c**) N\({}_{2}\) adsorption-desorption isotherms of the PCNF; (**d**) pore diameter distributions of the PCNF. Figure 3: SEM and TEM measurements (images) of PVP, CNF and PCNF nanofibers: (**a,d,g**) PVP nanofibers; (**b,e,h**) CNF nanofibers; (**c,f,i**) PCNF nanofibers. To assess the electrochemical properties, the CNF and PCNF samples were used as anodes without adding any binder or conductive additive for button cell. In the coin cells, metallic lithium and Celgard 2300 film were employed as the counter electrode and separator, respectively. Figure 5a displays the first charge-discharge images of the CNF and PCNF materials at 0.1 C at a working potential from 0.01 to 3.0 V (vs. Li/Li\({}^{+}\)). For the maiden charge and discharge cycle, the PCNF showed a high discharge capacity of 2070 mAh g\({}^{-1}\), which was much better than the CNF (1391 mAh g\({}^{-1}\)). Nevertheless, the invertible discharge capacities decreased to 1138 and 785 mAh g\({}^{-1}\). In the initial charge-discharge curve, both of CNF and PCNF sample had an obvious irreversible capacity loss, their initial coulombic efficiency was only around 55% and 56%. This large irreversible capacity loss was an inherent defect for almost all carbon electrodes, mainly due to the blemished structure of samples that showed irreversibly depleted extra lithium ions [43; 44] and the appearance of solid-state electrolyte interphase (SEI) film [43; 44; 45; 46; 47]. It also irreversibly consumed an abundance of electrolyte and lithium ions. Interestingly, comparing with graphite materials [26; 48], the PCNF sample shows a much higher invertible capacity up to 1138 mAh g\({}^{-1}\), which will be helpful to obtain high energy anode materials of LIBs. Good rate performance had a significant impact on the application of LIBs in the energy storage field. The rate capabilities of the CNF and PCNF anode materials were further evaluated under different C-rates and the results were seen in Figure 5b. The cells with CNF anode displayed invertible specific capacities of 785, 322.8, 234.5, 170.7, 98.9, 60, 48.7, 39.1 mAh g\({}^{-1}\) at 0.1 C, 0.5 C, 1 C, 2 C, 5 C, 8 C, 10 C and 15 C, respectively. Meantime, the homologous specific discharge capacities of the PCNF sample were 1138, 609.8, 450.4, 401.9, 303.8, 201.3, 151 and 101.2 mAh g\({}^{-1}\), far more than that of the CNF anode. Furthermore, after cycling for 80 times at different C-rates, the discharge capacity recovered to 449.4 mAh g\({}^{-1}\) while the ampere density was returned to 1 C, following a high capacity retention of 99%, implying the positive performance rates of the PCNF sample. In addition, the long circulation measurements were conducted under a high C-rate of 5 C of the CNF and PCNF electrode were displayed in Figure 5c.