Fig. 1

The diagram of material preparation processes"

Fig. 2

SEM images of Bi-MOF/G (a) and TEM images at different magnifications (b), (c). SEM image (d) of Bi-C/G, TEM images (e)—(g) at different magnification. (h) HAADF-TEM image (i) of Bi-C/G and corresponding element distribution images of C(ii), O(iii), N(iv), Bi(v)"

Fig. 3

(a) XRD patterns of Bi-MOF and Bi-C/G, (b) Nitrogen absorption and desorption test curve of Bi-C/G, (c) TG curve of Bi-C/G, XRD pattern(d), SEM(e) and TEM(f) images of Bi without carbon coating"

Fig. 4

(a) XPS spectra and O 1s spectra of Bi-C/G and graphene (GNS), The spectra of C1s (c), N1s and Bi 4f (e) of Bi-C/G"

Fig. 5

(a) The first three CV curves of the Bi-C/G electrode at a scanning rate of 0.1 mV/s with a voltage window of 0.2—1.8 V, (b) The first three charge and discharge curves of the Bi-C/G electrode at 0.1 A/g, Cyclic (c) and rate (d) performance of Bi and Bi-C/G electrodes at 0.1 A/g, (e) Ultra-long cycle performance of Bi-C/G electrodes at 1 A/g, 2 A/g, 5 A/g, 10 A/g, respectively, (f) Comparison of rate properties with the bismuth-based composite anodes and hard carbon anode. XPS spectra(g) and O 1s spectra (h) of Bi electrode after two cycles at 0.1 A/g"

Fig. 6

CV curves (a) obtained by Bi-C/G electrode at different scanning rates (0.1—2 mV/s), and linear relationship (b) between scanning rate log(v) and peak current log(i) corresponding to different REDOX peaks, (c) Comparison of capacity contributions of diffusion control and pseudocapacitance control in Bi-C/G, (d) CV controlled by pseudocapacitance and original CV curve with a scan rate of 2 mV/s, (e) The linear relationship between the peak current i and the square root of the scanning rate v1/2 and the calculated diffusion coefficient of sodium ions. The AC impedance (f) of the Bi-C/G at 10 A/g, and the variation rule between the fitted Rct value and the cycle order (g), (h) Schematic diagram of the electrochemical reaction of a sodium ion battery and the transport path of sodium ions"

Fig. 7

(a) CV curves obtained by Bi electrode at different scanning rates (0.1—2 mV/s), (b) CV curve controlled by pseudocapacitance and original CV curve with a scan rate of 2 mV/s, (c) Comparison of capacity contributions of diffusion control and pseudocapacitance control in Bi, (d) The AC impedance of the Bi electrode cycled at 10 A/g for once"