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Page 16 of 64 Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06

+
Sb + Na + e → NaSb

-
+
NaSb + 2Na + 2e → Na Sb
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However, detailed Mossbauer and solid-state nuclear magnetic resonance (NMR)-derived spectroscopic
evidence has proposed a multistep alloying with amorphous sodium depleted intermediates not in good
agreement with various studies [30,108] . Huge volume variations (390%) upon full sodiation have also impeded
the utility of Sb anodes. Among common routes of modifications, nanostructuring, intermetallic alloy
formations, and hybrid composite structural optimizations have been commonly chosen. Thin-walled,
heteroatom-doped 1D Sb nanotubes (NTs) reported by Liu et al. have shown formidable performance as an
SIB anode showing long cyclability with 342 mAh g capacity retaining ability at a current density of 1 A g
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over 6,000 cycles and a rate performance of 286 mAh g at a current density of 10 A g -1[109] . Manifestation of
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a high operational voltage (2.7 V) and a good energy density (252 Wh kg ) has also been demonstrated in a
full cell configuration when coupled with Na (VOPO ) F as a cathode.
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4 2
Several Sb composites have been presented to improve Na storage performances of SIB anodes with more
+
resilience for volume variations. In this regard, again, the favored choice was the utilization of C-based
heterogeneous matrices. Qian et al. have previously proposed Sb/C SIB anodes showing a capacity of
575 mAh g over 100 cycles at 0.1 A g -1[110] . Xu et al. have prepared Sb nanoparticles in a N-doped C matrix
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by pyrolysis. These Sb nanoparticles showed superior cyclic and rate performances than bare Sb anodes and
sustained a capacity of about 328 mAh g at 100 mA g (300 cycles) . The composite anode was also
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[111]
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tested at higher current densities, showing an optimum capacity storage of 237 mAh g at a current rate of
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5 A g . Moreover, in full cell assembly using NVP cathode, a capacity of 139 mAh g was achieved.
It has been reported that 0D Sb nanodots interconnected with 2D C nanosheet composite (Sb-NDs/CN)
have an optimum 3D network structure that provides a high surface area, short ion and electronic diffusion
paths, and well-dispersed Sb nanodots that could prevent their agglomeration and afford volume
buffering . As an SIB anode, the composite showed competing rate performance (271 mAh g at a current
[112]
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of 2 A g ) and good cyclic stability of about 380 mAh g at a current density of 0.3 A g . A thin filmed,
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porous self-supported Sb-C framework has been proposed previously. It sustained a capacity of 306 mAh g
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over 5,000 cycles at 2.34 A g and supplemented with a high rate performance of 200 mAh g at a high
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current rate of 7 A g -1[113] . The superb performance was due to thin patterning with well-dispersed Sb
nanodots (~3 nm size) ensured by a conductive C matrix for efficient Na and e transfer kinetics that
+
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ensured amorphous/crystalline phase reversibility.
Recently, we have tested an MOF-derived mesoporous carbon composite of Sb along with SiOC as an SIB
anode. It showed stable performance. Upon sodiation, it showed multiple plateaus corresponding to the
[114]
stepwise Sb transformation to Na Sb that mainly contributed to the capacity . After 200 cycles, a capacity
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of 403.81 mAh g was traced with 100% CE, while a rate performance of 366.83 mAh g at 5 A g was
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observed. Cycled electrodes were analyzed by SEM. They showed macro cracks after 200 cycles. SiOC layers
effectively buffered volume changes of Sb during sodiation-desodiation cycles. Liu et al. have recently
validated yolk-void-shell assembled antimony-graphdiyne (Sb@Void@GDY) nanocuboid structures for
classical performance of an SIB anode . They bear definite voids to nullify the volumetric expansion/
[115]
contraction of Sb during charge/discharge processes [Figure 8]. The unique synthetic strategy illustrated in
Figure 8A was validated by XPS and TEM studies [Figure 8B]. Although the ICE was deliberately low
(45.6%), the electrode showed more committed performance afterward and offered a capacity of
593 mAh g at 0.1 A g over 100 cycles, maintaining almost 100% of its capacity [Figure 8C]. The rate
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