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

Table 1. Various parameters (volume expansion, average voltage, and theoretical capacity) for sodiation reactions of alloy-based
materials
Average voltage
Volume expansion + Theoretical capacity
Metal Alloyed compositions (vs. Na/Na ) -1
(%) (V) (mAh g )
Si NaSi/Na 0.75 Si 114 ~0.50 954/725
Sn Na Sn 420 ~0.20 847
15 4
Ge NaGe 205 ~0.30 576
Sb Na Sb 390 ~0.60 660
3
Bi Na Bi 250 ~0.55 385
3
P Na P > 300 ~0.40 2,596
3

ALLOY-BASED ANODES FOR SIBS
Tin-based anodes for siBs
Tin (Sn) is an incredible choice as an anode material in SIBs because of its high theoretical capacity
-1
-1
(847 mAh g ), good electrochemical performance, high electric conductivity (9.17 × 10 Scm ),
4
environment friendliness, and relative abundance. In SIBs, varying alloying constitution ability of Sn has
been reported. The number of sodium ions participating in the alloying reaction can reach 3.75 to form
Na Sn in a multistep sodiation process. Moreover, the high affinity of Sn-based materials with Na ions has
+
15
4
motivated researchers to investigate other Sn-based materials such as their oxides, sulfides, selenides,
phosphides, and composites [24,60,61] . Despite their high theoretical capacity, Sn anodes face serious challenges.
The foremost problem is the pulverization of active material due to colossal volume expansion (420%)
during the alloying/dealloying process that, along with unstable SEI formation, can reduce the initial
Coulombic efficiency (ICE) and overall capacity [62,63] . Spontaneous particle aggravation during (de)sodiation
[64]
+
can induce large Na migration paths, further hindering Na transfer kinetics . To address these
+
drawbacks, researchers have adopted various strategies to present Sn-based materials as alternative SIB
anodes, including nanosizing, mixing with conductive matrixes, heteroatom doping, and heterostructuring
with additional modifications in selecting suitable electrolytes and additives [28,65-68] . The most common
modification is formation of an Sn-C nanocomposite by introducing a C matrix, such as the recently
prepared freestanding Sn-based electrode comprising spherical Sn particles ingrained in carbon nanofibers
(CNFs). When electrochemical performances of carbonate and ether-based electrolytes were compared,
poor rate performance was observed when carbonate electrolytes were used. An outstanding cycling
performance of 30,000 cycles with a capacity of 662 mAh g at 0.5 C has been achieved by utilizing dimethyl
-1
ether (DME) electrolyte . A µ-Sn anode for SIBs has recently been evaluated using operando scanning
[69]
electron microscopy (SEM) and X-ray absorption spectroscopy (XAS) to reveal volume variations and
structural evolutions during initial and extended cycling. Although some voids and volume expansion were
formed, using ether-based electrolytes could overcome these drawbacks to achieve a high ICE of 91.3% with
-1
[70]
a capacity above 400 mAh g after 20 cycles . Many other ways have been proposed to improve the
performance of Sn anodes for SIBs. For example, inclusion of K in the electrolyte can highly improve the
+
performance of Sn alloying anodes, yielding an energy of 565 mAh g over 3,000 cycles at 2 A g -1[71] .
-1
Similarly, the utilization of a cross-linked binder has been proposed in a µ-Sn anode for SIB to ensure a high
ICE and an extra-long cycle life with an improved capacity . Other approaches include presodiation and
[72]
intermetallic formulations with potential to uplift the capacity of Sn anodes in SIBs [61,73,74] .

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