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Page 32 of 64 Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06

Bismuth-based anodes for SIBs
Bismuth (Bi) has been regarded as a “green” choice for energy storage materials because of its non-toxicity,
good electronic properties, and layered structure with a larger interlayer distance of 0.395 nm to
accommodate Na that can reversibly give Na Bi an optimal gravimetric capacity of 385 mAh g -1[17,187] .
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Although Bi suffers low volume expansion (250%) (lower than 290% and 430% in Sb and Sn, respectively)
compared to other alloying anodes, it still has commercial real-time performance potential [188,189] . Many
modifications of Bi have been proposed for stabilized performance, mostly through C compositing.
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However, C compositing mostly limits the capacity (less than 200 mAh g ) by imposing an additional
barrier layer for ion diffusion [188,190,191] . Although other derivatives, including intermetallics , oxides ,
[30]
[192]
[194]
[195]
sulfides , selenides , tellurides , and others, have also been reported for high Na affinity as SIB
[193]
+
anodes [196-198] .
Both bulk and nanosized Bi anodes employing various synthetic and structural modifications have been
explored widely in recent years to delimit their capacity. However, they have posed considerable
bottlenecks. Mechanistic pathways during sodiation in bulk and nanoscale have not been well understood
yet [199,200] . Previously, Sottmann et al. have excellently addressed the impact of crystallite size in Bi SIB anodes
using synchrotron XRD and XAS . Ball-milled C composited Bi samples for 20 min (Bi/C-20 min) and
[200]
24 h (Bi/C-24 h) having crystallite sizes of 129.6 and 34 nm, respectively, showed different capacity
retainability. At the same time, the nanocrystalline- Bi/C-24 h sample sustained much higher capacity
(about 80% of the theoretical capacity) than the Bi/C-20 min sample (20% of theoretical capacity retention).
The metastable Na Bi cubic and hexagonal polymorphs generated during sodiation in Bi/C-24 h and Bi/C-
3
20 min samples, respectively, had varying degrees of volume expansions responsible for the difference in
sodiation capacity. Ex-situ XRD revealed high pulverization in the sample (Bi/C-20 min), whereby the
original particle size reduced to about one-third (with inactive role). However, the particle size in the Bi/C-
24 h sample did not effectively change.

Bi nanosphere-based SB anode has been recently updated by Zhang et al. . It showed an ultrahigh and
[201]
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stable capacity with an impressive longevity (10,000 cycles) at a high current density (i.e., 2 A g ). Although
it delivered an unimpressive ICE (53.4%, 422.4/790.3 mAh g , C/D), the electrode’s high CEs of above 99%
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and a good capacity retention of 333.4 mAh g were sustained at an exceedingly high ampere density of
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100 A g . An ultrafast (dis)charging SIB anode consisting of MOF-derived nanospherical Bi@C with hard C
[202]
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has been reported recently by Liang et al. . After an initial cycle capacity of 347.8 mAh g (CE 52.4%), the
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composite showed a high CE of about 99% in subsequent cycles. Even at an ampere density of 80 A g , it
can provide a capacity of 308.8 mAh g , leading to full (dis)charging in 15 s.
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A potential Bi nanosheet array on CNTs for an SIB anode has been recently reported by Liu et al. . It
[203]
delivered a stable capacity of 311.68 mAh g over 1,000 cycles at 1 A g . Importantly, the material showed
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an equally admired performance when it was applied in full cell configuration with Na (VOPO )F@rGO
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cathodic material, where an operating voltage of above 4 V was achieved with an overall energy density of
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221.99 Wh kg .
To minimize volume expansion and subsequent pulverization effects in Bi-contained SIB anodes, a novel
galvanic replacement (with iodine ion assisted) synthesis of Bi NTs for anodes has been presented
[Figure 16A] . It surpassed the currently reported performance of Bi alloying anodes in SIBs
[204]
[Figure 16B]. The anode lived for 65,000 cycles (capacity of 241 mAh g , 74% CE) at 50 A g . It also
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furnished 355 mAh g over 15,000 cycles at 20 A g . In-situ TEM [Figure 16C] and in-situ XRD
[Figure 16D] provided conclusive evidence of Bi NT stability during sodiation along with species evolution