Fig. 1

Schematic illustration of the main classifications and modification strategies of tin-based anodes for Na-ion batteries"

Fig. 2

(a) Schematic illustration of the structural evolution of tin particles during sodiation[12]; (b) Schematic comparison of the chemical composition, structure and mechanical response to volume expansion of the SEI layer formed from NaBF4/EC/DMC and NaBF4/diglyme[11]; (c) Modeling of the alloying reaction, comparison of the cycling behavior of the anode in a compatible electrolyte (top panel) and an incompatible electrolyte (bottom panel)[8]; (d) Basic mechanism of electrochemical performance enhancement by remodeling the solvated structure of 15-Crown-5[16]; (e) Comparative cycling plots of a standard electrolyte (BE) and a modified electrolyte (BE+15-C-5) with the addition of 15-Crown-5[16]"

Fig. 3

(a) Simplified description of the growth mechanism of tin nanofibres by cathodic electrodeposition[17], (b) Electrochemical properties of tin powder: 3 μm graphite∶PANa = 8∶1∶1 electrodes; the left panel shows the charge-discharge curves of the nano-Sn powder electrodes, and the right panel shows the charge-discharge curves of the micron-tin powder electrodes; the inset shows the corresponding scanning electron microscope (SEM) images of the powders[19], (c) Synthesis process of SnNGnP and charge-discharge curves[20], (d) Cycling comparison of α-Sn and β-Sn anode electrodes; the corresponding structures of the two tin crystals are shown in the inset[25], (e) Schematic illustration of the similarity between the high temperature sintering process and the self-healing of tin particles during electrochemical cycling[26], (f) Schematic representation of the cross-linking reaction of PAA and GLY to enhance the mechanical properties of the electrode[28], (g) Comparison of the cycling of micron tin anode electrodes at 0.01—1 V and 0.01—0.62 V, the crystal structures corresponding to different cycling voltage intervals are shown in the inset[29], (h) Volume capacity versus anode electrode volume expansion curves for different volume percentages of active materials in the anode electrode, where the vertical dashed lines indicate the maximum expansion rates of graphite (Gr), aluminum (Al) and silicon (Si), respectively[30], (i) Charge-discharge curves of tin foil anode for a representative number of cycles in 100 cycles of 0.1C cycling[31]"

Fig. 4

(a) Schematic illustration of the preparation of MWNTs@SnO2@C composites[39]; (b) Cycling performance of MWNTs@SnO2@C composites at 50 mAh/g and 150 mAh/g current densities[39]; (c) Schematic flow illustration of the preparation of SnO2@SnS2@NG[41]; (d) Cycling performance of SnO2@SnS2@NG, SnO2@SnS2, SnO2@NG and SnS2@NG at 3 A/g[41]; (e) Schematic illustration of the synthesis process of SnO2-x /C nanofibres (upper panel) and SEM images of the morphology (lower panel)[37]; (f) Schematic of the reaction mechanism of SnO2 (upper panel) and SnO2-x /C (lower panel) electrodes during charging/discharging[37]; (g) Schematic illustration of the structural changes that occur in tin oxide nano spiral arrays fabricated directly on copper substrates after discharging and charging processes[46]; (h) Comparison of the cycling performance of electrodes made of amorphous SnO x nano spiral arrays, crystalline SnO2 nanoparticles and crystalline SnO nanoparticles[46]"

Fig. 5

(a) Schematic of the synthesis steps of SnS2/C nanospheres, nanosphere morphology, and cycling performance at 50 mA/g current density[47], (b) SEM images of SnS2 ultrathin nanosheets[48], (c) Rate performance of SnS2 ultrathin nanosheets.[48], (d) Schematic diagram of SnS2/rGO[49], (e) Rate performance of SnS2/rGO[49], (f) The upper panel shows the schematic of the synthesis of SnS@SnCF, the lower left figure shows the cycling performance of SnS@SnCF at 100 mA/g current density, the lower right figure shows the microstructure of SnS@SnCF[50]"

Fig. 6

(a) Cycling performance diagram of SnSe/C[51], (b) Transmission electron microscope (TEM) images of SnSe/C nanocomposites with corresponding as well as EDS elemental mapping of carbon, tin and selenium in the materials[52], (c) Comparison of the cycling performance of SnSe/C and unmodified SnSe at 0.5 A/g current density[52], (d) Schematic diagram of SnSe2 ⊂3DC buffered porous structure[53], (e) Cycling test of SnSe2 ⊂3DC at 2.5 A/g, where the initial activation was 0.13 A/g for 2 cycles[53], (f) Schematic diagram of the synthesis process of SnSe2@Se-C and SEM, TEM, high-Aangle annular dark field scanning transmission electron microscopy (HAADF-STEM) images and corresponding elemental mapping of SnSe2@Se-C[54], (g) Cycling performance of SnSe2@Se-C[54]"

Fig. 7

(a) Comparison of cycling performance of Sn4P3 and Sn anode. TEM image of Sn4P3 in the background[56], (b) Synthesis of the Sn4P3@C yolk-shell nanocube and its structural advantages over other anode materials. Schematic diagram of the synthesis of Sn4P3@C yolk-shell nanocube. Structural advantages of the Sn4P3@C yolk-shell nanocube over Sn4P3/C and bare Sn4P3 in the process of sodation/desodation[57], (c) Long-term cycling performance of the Sn4P3@C yolk-shell nanocube electrode at 1.0 A/g and 2.0 A/g and the corresponding Coulombic efficiency[57], the long-term cycling performance of Sn4P3@HC at NaClO4/EC:PC (orange inverted triangles), NaClO4/EC:PC:FEC (red diamonds), NaPF6/EC:PC (dark cyan hexagons), NaPF6/EC:PC:FEC (green circles), NaPF6/DEGDME (black squares) and NaPF6/DEGDME:FEC (dark gray star) electrolytes in (d) cycling and (e) rate performance[58], (f) Schematic of the synthetic pathway of Sn4P3/NHC[59], (g) cycling performance of Sn4P3@HC at 1 A/g current density[60]"