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Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06 Page 23 of 64

conversion and alloying reactions for Sb Se can be written as follows:
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-
Sb Se + 6Na 6e ↔ 3Na Se + 2Sb (Conversion)
+
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2
+
Sb + 3Na + 3e ↔ Na Sb (Alloying)
-
3
The persistence of volume changes and sluggish diffusion kinetics in these Sb-based materials are real
bottlenecks to achieving high reversible capacities. Recently, many modifications have been reported. They
are dominated by those adapting heterostructuring approaches that often utilize carbonaceous compounds.
[141]
A 2D Sb Se layered anode has been investigated with a focus on mechanistic understandings . Compared
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to a bare Sb Se electrode with a huge capacity loss, an amorphous carbon composited Sb Se anode retained
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3
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-1
high gravimetric and volumetric capacities of 378 mAh g and 688 mAh cm , respectively, after 50 cycles.
-3
The electrode also offered superior rate performance behavior with gravimetric and volumetric rates of
-1
-3
about 270 mAh g and 492 mAh cm , respectively, at 2C. The capacity drop of the bare Sb Se electrode was
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related to the formation of Na Sb accompanied by huge volume expansion, causing large capacity losses
3
after ten cycles. An encapsulated structured Sb Se by rGO has been proposed to achieve high reversibility
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[139]
for the de(sodiation) process . This Sb Se /rGO was able to preserve promising capacities (448 and
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386 mAh g ) at high ampere rates (1.0 and 2.0 A g , respectively). Besides their long-term stability for 500
-1
-1
cycles, composited nanorods of Sb Se in the rGO matrix showed high structural endurance. The detailed
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reaction mechanism was investigated using in-situ XRD, ex-situ TEM, and SAED studies. It was verified
+
that the multistage process involved initial intercalation of Sb Se with Na , followed by conversion and
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(de)alloying with good reversibility [Figure 11].
Sluggish sodium diffusion has been one of the limiting factors for the low capacity of Sb Se -based SIB
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anodes. Wang et al. have enhanced the capacity by achieving higher Na -diffusion in their N-doped
+
C-coated ZnSe/Sb Se with superior pseudocapacitive dominated Na storage . The micro-spherical
+
[142]
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porous ZnSe/Sb Se @NC anode exhibited a higher capacity than corresponding Zn or Sb selenide even with
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C compositing. Over 120 cycles, the multimetallic ZnSe/Sb Se @NC anode could sustain a capacity of
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438 mAh g at 0.2 A g with a rate storage capacity of 316 mAh g at 10 A g of ampere density. Multiple
-1
-1
-1
-1
factors, including superior robust hollow morphology offering fast diffusion kinetics ensured by the
synergistic influence of ZnSe and Sb Se , N-doped C (for volume buffering and conductivity enhancement),
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and ether-based electrolyte with superior wettability, all coherently enhanced the stability to enable the
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-1
electrode for an extended cyclic performance over 250 cycles (with a capacity of 295 mAh g at 2 A g ).
A detailed and conceptual representation of the improved performance of the Sb Se @CNT hybrid has been
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reported recently by Ihsan-ul-Haq et al. . The as-synthesized composite could attain a stable rate
[143]
-1
-1
capability of 454 mAh g at 12.8 A g with 62% capacity retention over 200 cycles at 10 A g . Moreover, a
-1
power density of 175 Wh kg (at 0.5 C) and an energy density of 5,784 W kg have been achieved in full-cell
-1
-1
configuration. Detailed theoretical (ab initio) and experimental investigations were performed along with
ex-situ cryo-TEM, CV, and XPS. The CV of the prepared electrode showed highly preserved peaks at
potentials of 0.78, 1.36, 1.58, and 1.88 V, proving it reversible desodiation and favorable kinetics. In contrast,
the CV of commercial Sb Se signaled highly thick SEI with more electrolyte degradations. Subsequent
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cycling CV curves showed erratic behavior, signaling unstable SEI and poor reversibility. The cryo-TEM
utilization of frozen (-175 °C) electrodes showed a highly thin SEI of about 35.7 nm with a high uniformity
in the synthesized Sb Se @CNT electrode. Interestingly, the commercially used anode showed a highly
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2
irregular and thicker SEI with a thickness of 71.8 nm, which was about double the thickness of the as-
prepared electrode.