Fig. 1

Schematic crystal structures of PB and PBAs framework (a) an intact Na2MII[FeII(CN)6] framework without structural defects, (b) an ideally defective NaMII[-FeII(CN)6]0.75· □ 0.25 framework with 25% Fe(CN)6 vacancies existing in each unit cell"

Fig. 2

(a) The optimized migration paths of Na+ ions for NiCoFe-PB, and (b) the energy barrier profiles of four samples; (c) (A—D) The total density of state patterns, and (E—H) the partial density of state patterns of four Ni-PB species; (d) (A, B) The initial charge/discharge profiles at 20 mA/g and 100 mA/g of four samples, (C, D) corresponding cycle performance, and (E, F) long cycle performance and initial charge/discharge profiles at 1 A/g of four samples, (G) Long cycle performance of NiCoFe-PB at 2 A/g"

Fig. 3

A schematic of the crystal structures for layered materials (Na x TMO2) for (a) P2-type, (b) O2-type, (c) O3-type and (d) P3-type materials. The blue balls represent the transition metal and the yellow balls represent the Na ions"

Fig. 4

(a) The XRD patterns of the P2-NaNM; (b) Voltage-specifific capacity profifile for the Na/P2-NaNM half-cell; (c) The structural schematics of the P2-O2 phase transition and stacking sequence of oxygen layers; (d) The charge/discharge profifiles of P2-Na2/3Ni1/3Mn1/3Ti1/3O2 at 0.1C in 2.5—4.15 V; (e) Diagrammatic presentation of the P2-type structures of the Na x MO2 phases; (f) Cycling performance of the NaMF and NaMFN cathodes at 0.05C; (g) Calculated total density of states (DOS) for β-NaMnO2 and β-NaCu1/8Mn7/8O2"

Fig. 5

(a) The crystal structures of phosphate; (b) The structures of pyrophosphate cathodes for SIBs; (c) The structures of NASICON-type phosphate cathodes for SIBs"

Fig. 6

(a) The electrochemical performance for Na3Mn2-x Fe x P3O11@C (0≤ x ≤0.5) samples: (a) cycling performance at 0.1 C over 100 cycles; (b) rate performance from 0.1 C to 5 C; (c) Nyquist plots before cycling in the frequency range from 0.01 Hz to 100 kHz (equivalent circuit inserted); (d) the relationship between Z ’ and ω-1/2 in the low-frequency range"

Fig. 7

(a) Schematic diagram of graphite crystal structure; (b) Typical XRD and microstructure diagrams of graphite, soft carbon, and hard carbon"

Fig. 8

Schematics of (a) fabrication procedure and (b) cross-sectional view of the structural evolution of the flexible NiS2-PCF. (c) Photos of knotted NiS2-PCF bundles"

Fig. 9

(a) Schematic illustration of the preparation process of Fe0.95S1.05@C-rGO and SEM images at different synthesis stages; (b) illustration of the reversible breathing of Fe0.95S1.05@C-rGO; (c) illustration of the impaired breathing of Fe0.95S1.05@C"

Fig. 10

(a) Charge/discharge profiles of Fe3O4 anodes in the voltage window 0.04—3.0 V vs Na+/Na (Inset: cycle stability); (b) Electrochemical charge/discharge profiles of Co3O4 anodes in the voltage range between 0.01 and 2.5 V vs Na+/Na; (c) Charge/discharge curves of CuO anodes in the voltage window 0.01—3.0 V vs Na+/Na"