Fig 1

Schematic of the composition for sodium-ion battery system 9."

Fig 2

Schematic of mechanism illustration for sodium-ion battery 11."

Fig 3

Operation voltages versus specific capacities of sodium-ion battery anode materials 12."

Fig 4

Operation voltages versus specific capacities of sodium-ion battery cathode materials 12."

Fig 5

Schematic derivation of the energy diagram of iron-based mixed polyanion cathode materials for sodium-ion batteries 18."

Fig 6

Crystal structures of (a) Maricite-type and (b) Triphylite-type NaFePO4."

Fig 7

(a) In situ synchrotron Fe K-edge XANES and (b)ex situ XRD studies of the NaFePO4 during initial cycles 25."

Fig 8

(a) Schematic illustration of the preparation process, (b) SEM image, and (c) long-term cycling performance of the NaFePO4@C 35."

Fig 9

(a) Crystal structure and (b) ion migration paths of Na3V2(PO4)3 45."

Fig 10

(a) In-situ XRD patterns of the Na3V2(PO4)3/Na cell, ? Na3V2(PO4)3, ? Na3V2(PO4)3 46; STEM ABF images of (b) Na3V2(PO4)3 and (c) Na3V2(PO4)3 along the [1${\rm{\bar 1}}$${\rm{\bar 1}}$] projection 47; Line profiles along in the ABF images of (d) Na3V2(PO4)3 and (e) Na3V2(PO4)3 47."

Fig 11

Morphological evolution process and rate performance of Na3V2(PO4)3 hierarchical microspheres prepared by hydrothermal reaction 55."

Fig 12

(a) Schematic illustration of the fabrication, (b) ultralong-life cycling performance, and (c) sodium-ion full-cell performance of 3D graphene capped Na3V2(PO4)3 nanoflakes 52."

Fig 13

XRD patterns and crystal structures of (a) Na4MnV(PO4)3 61 and (b) Na3MnZr(PO4)3 62."

Fig 14

Schematic representation of alkali-ions (Li/Na/K) insertion in crystalline and amorphous FePO4 electrode hosts 72."

Fig 15

Crystal structures of VOPO4 and NaVOPO4."

Fig 16

Crystal structures of (a) monoclinic and (b) tetragonal NaVPO4F, (c) charge-discharge curve and (d) in situ XRD pattern of NaVPO4F 96."

Fig 17

(a) The TGA/DSC curves of raw materials upon heating in Ar flow; (b) The corresponding specific compositional changes calculated by semiquantitative calculation of in situ XRD patterns 106."

Fig 18

Crystal structures of (a) Na3V2(PO4)2F3 and (b) Na3(VOPO4)2F."

Fig 19

(a) Potential-composition electrochemical curves obtained upon Na+ extraction from Na3V2(PO4)2F3 110. (b) Trigger the activity of the third sodium electrochemically via the formation of a disordered NaxV2(PO4)2F3 phase 111. (c) Sodium distribution obtained from Rietveld refinement of the different phases upon sodium extraction from Na3V2(PO4)2F3 110."

Fig 20

(a) Voltage–composition curves for the Nay(VO1?xPO4)2F1+2x (0 ≤ x ≤ 1; 0 ≤ y ≤ 3) electrodes from first-principles calculations 114. (b) Comparison of the voltage profiles of NaxV2(PO4)2M with different anion (M) substitutions 116."

Fig 21

Preparation procedure of Na3V2(PO4)2F3 microcubes/graphene composite and its long cycling performance at 20C rate 117."

Fig 22

Crystal structures and corresponding charge-discharge curves of (a, d) Na2FePO4F, (b, e) Na2MnPO4F, and (c, f) Na2CoPO4F 131, 137, 138."

Fig 23

(a) In situ XRD patterns and (b) cycling performance of the Na2FePO4F 131."

Fig 24

Crystal structures of (a) NaFeP2O7-I, (b) NaFeP2O7-II, and (c) NaVP2O7/NaTiP2O7."

Fig 25

Crystal structures of (a) Na2MP2O7-I (M = Fe, Mn) and (b) Na2MnP2O7-II. Charge-discharge curves of (c) Na2FeP2O7 150 and (d) Na2MnP2O7 159."

Fig 26

(a) Crystal structure and (b) charge-discharge curves of Na3.12Fe2.44(P2O7)2 163."

Fig 27

(a) Crystal structure and (b) charge-discharge curves of Na7V3(P2O7)4 170."

Fig 28

(a) Crystal structures of Na4M3(PO4)2(P2O7) (M = Fe, Mn, Co, Ni). (b) in situ XRD patterns and (c) charge-discharge curves of Na4Fe3(PO4)2(P2O7) 179. Charge-discharge curves of (d) Na4Co3(PO4)2(P2O7) 183, (e) Na4Mn3(PO4)2(P2O7) 185, and (f) Na4Ni3(PO4)2(P2O7) 186."

Fig 29

Crystal structures and corresponding charge-discharge curves of (a, c) Na7V4(P2O7)4PO4 187 and (b, d) Na3MnCO3PO4 191."