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Shipitsyn et al. Energy Mater 2023;3:300038 https://dx.doi.org/10.20517/energymater.2023.22 Page 17 of 37

Figure 7. Electrochemical performance of cells with SbF additive. (A) Cross-sectional SEM and EDS mappings of cycled Na metal in the
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electrolyte with 1% SbF additive; (B) Testing in symmetric Na||Na cells. Nyquist plots for Na V (PO ) /Na cells with different
3 3 2 4 3
[84]
electrolytes after (C) three cycles and (D) 20 cycles. Reproduced from ref , Copyright 2020 Elsevier. EDS: Energy dispersive X-ray
spectroscopy; SEM: scanning electron microscopy.
Fullerene-containing additives
Fullerene (C60) cages have been reported to preferentially anchor on the sodium surface to induce uniform
Na deposition [86,87] . With the addition of special functional groups on the C60 cages, those additives are able
to further improve the reversibility of sodium metal anodes. Nitrofullerene [C (NO ) , Table 9] was first
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proposed as an additive for LIBs by Jiang et al. Recently, this additive was reported as a highly electrolyte
[86]
compatible additive for SIBs. Li et al. showed that C (NO ) is compatible with different solvents (PC,
[87]
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FEC, DEC, DMC, EMC, DME, triglyme, and diglyme). Moreover, the additive improves the stability of
sodium metal by maintaining a constant overpotential [Figure 8A] and reducing the interface resistance and
charge transfer resistance [Figure 8B] of symmetrical cells. XPS spectra [Figure 8C] showed that the
addition of C (NO ) forms three new species on the surface of the electrode: C , NaN O , and Na N, which
y
x
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can protect the electrolyte from further decomposition on the electrode surface. C (NO ) also can improve
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the Na V (PO ) /Na cell lifetime [Figure 8D].
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Trifluormethylfullerene [C (CF ) , Table 9] was described as a new additive for SIBs by Li et al. . They
[88]
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+
concluded that C (CF ) can enhance Na migration in the electrolyte, form a NaF-rich SEI, and improve
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the cycling performance and rate capabilities. Overpotential maintained a constant value within over