Fig. 1

The scheme of construction of biomass derived carbon-based materials and its sodium storage mechanism"

Fig. 2

(a) XRD patterns of RHHC-1100, RHHC-1300 and RHHC-1500; (b) Raman spectra; (c)—(e) HRTEM images (inset is the corresponding SAED image)[24]; SEM image of (f) PWT-1000; (g) PWT-1200; (h)PWT1400; (i) PWT-1600 (inset shows enlarged image)[52]"

Fig. 3

(a) SEM images of CPP; (b) TEM images of CPP[53]; (c) SEM image of cross section of CRC-900; (d) SEM image of longitudinal section of CRC-900[54]"

Fig. 4

(a) N2 adsorption and desorption isotherm of porous carbon material generated by H3PO4 activation of pomelo peel (the inset shows the pore size distribution)[61]; (b) Pore size distribution of HPC-1-1, HPC-1-2, HPC-2-2 and HPC-2-4[62]; (c)—(d) SEM image of PC-3 and its corresponding element distribution; (e) XPS map of PC-3; (f) High rate XPS map of P element[64]"

Fig. 5

(a)—(b) SEM images of NOMC at different rates; (c)—(d) TEM images of NOMC at different rates (inset is the corresponding HRTEM image)[65]; (e) Preparation principle schematic diagram of N and O co-doping uniform ultraporous porous carbon (NOPC-UM)[66]"

Fig. 6

(a)—(c) FESEM image of MCMS-K; (d) Particle size distribution of MCMS-K; (e) TEM image of MCMS-K; (f) HRTEM image of MCMS-K; (g) Rate performance of MCMS-K; (h) Long cycle curve of MCMS-K[73]"

Fig. 7

(a) Schematic preparation of (Ni0.5Co0.5)S2@NPCS; (b) Cycling performance of (Ni0.5Co0.5)S2@NPCS at 100 mA/g; (c) Rate performance of (Ni0.5Co0.5)S2@NPCS[75]"

Fig. 8

(a) SEM image of FeS/ CFS-1; (b) EDSelement distribution of C, Fe and S elements of FeS/CFs-1; (c) Cyclic performance of CFs, FeS/CFs, FeS/ CFS-1 and FeS/ CFS-2 at 1 A/g[78]"

Fig. 9

(a) TEM image of FeS/CAN; (b) EDS mapping of C, Fe and S elements of FeS/CAN; (c) Cycling performance of FeS/CAN at 2 A/g; (d) Rate performance of FeS/CAN[80]"

Fig. 10

(a) XRD patterns of HC-900, HC-1000 and HC-1100; (b) N2 adsorption-analytic isotherms of HC-900, HC-1000 and HC-1100[84]"

Fig. 11

(a) CV curve of AC700 at 0.1 mV/s; (b) AC700 at 100 mA/g at 1st, 2nd, Constant-current charge-discharge curves for the 50th and 150th cycles; (c) Rate performance of AC600, AC700, and AC800;(d) Cycle performance of AC700 at 100 mA/g[87]"

Fig. 12

(a) TEM image of NDCS; (b) HRTEM image of NDCS; (c) Charge and discharge curves of NDCS at different cycles at 0.15 C (1 C= 375 mA/g) [40]"

Fig. 13

(a) Rate performance curve of CP; (b) Constant current charge-discharge cycle curve of CP[34]"

Fig. 14

(a) CV images of LC at 0.01—3 V and scan rate of 0.1 mV/s; (b) CV images of BC at 0.01—3 V and scan rate of 0.1 mV/s; (c) Rate performance of LC and BC[99]"

Fig. 15

(a)—(b) HRTEM images of APCs at different rate; (c) Pore size distribution of APCs; (D) Charge-discharge curve of APCs at constant current[106]"

Fig. 16

High-resolution TEM and SAED images of (a) CC-Pre-800, (b) CC-1200, and (c) CC-1600; (d)Size distribution from a mercury intrusion porosimetry (inset: relation curve of total intrusion volume and carbonization temperature); (e) NLDFT pore size distribution (inset: nitrogen adsorption/desorption isotherms); (f) Cyclic capability of CCs at a current rate of 0.1 C; (g) SAXS patterns (inset: relation curve of the diameters of the closed pores and carbonization temperature); (h) Sectional SEM images of pristine, first discharged and 200th dis-charged CC-1600 electrodes; (i) Pore structure comparison between low and high temperature samples including BET surface area and closed pore volume (obtained from true density tests)[108]"