Fig. 1

(a) Typical X-ray diffraction patterns; (b) Schematic of representative microstructures; (c) Charge-discharge curves at second cycle in sodium half cell of graphite, soft carbon, hard carbon and reduced graphene oxide (rGO)[12]"

Fig. 2

(a) Typical charge curves of hard carbon anodes carbonized at different temperatures[27]; (b) The relationship between the capacity from LPP and specific surface area obtained by N2 adsorption"

Fig. 3

(a) Schematic of carbon molecular sieve for N2/O2 separation; (b) Charge-discharge curves at first cycle of graphite, activated carbon and carbon molecular sieve; (c) SAXS patterns of porous carbon (PC) and (d) sieving carbon (SC) anodes before and after (dashed line) five full cycles at a current density of 50 mA/g. Inset: the relative location of the SEI to the nanopores. The SEI is a green irregular shape with yellow solid circles (sodium ions) inside[26]"

Fig. 4

Characterizing the sodium storage mechanism of SC (a) 23Na MAS ssNMR spectra of SC anodes at various states of charge in the first cycle. The spinning sideband is labeled with an asterisk (?); (b) Operando Raman spectra of SC anodes during the first charge/discharge at a current density of 50 mA/g[26]"

Fig. 5

Analysis of the local environment of stored sodium in SC using a smooth overlap of atomic positions kernel, as a structural similarity initially used for Gaussian approximation potential fitting. The most similar points are aggregated together with similar colors[26]"

Fig. 6

Rational design principles for sieving carbon anodes. (a) Relationship between the pore diameter, quasi-metallic Na peak shift and sample pyrolysis temperature[27]; (b) Ex-situ23Na 55 kHz ssNMR spectra of SCs at 0.005 V for the 10th discharge at 50 mA/g (solid curves). The dashed curves are the corresponding ssNMR spectra of SCs at 0.005 V for the first discharge[26]; (c) Relationship among the plateau capacity (0.1-0 V), true density, and EtOH content; (d) Charge capacity from the low-potential plateau versus SSA obtained by SAXS and N2 adsorption for the SC anodes[26]"