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Page 48 of 64 Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06

poor capacity and low electronic conductivity known to hamper their utilization. Prussian blue analogs
(PBAs) suffer from lower tap density and the presence of water of crystallization in their structures known
to pose safety threats and thermal runaway issues. The most critical challenge for cell SIBs is the choice of
suitable anodes with a matching high capacity and stability cathode material that could offer a high voltage.
The potential of composited cathodes can also improve the overall performance of SIBs. This must be
considered for alloying-based anode counterparts [59,288] . Vast material, structural, and compositional options
for alloying anodes need immense experimental and theoretical screening using the latest machine-learning
tools to determine their compatibility with commercially successful cathodes to achieve high-performing
SIB cells ultimately.

Other optimization parameters
Alloying SIB anodes have been modified to entrap more (de)sodiation capacity using various strategies
including presodiation, dealloying, and so on. The presodiation strategy offers an excellent solution to
+
complement the Na concentration consumed and depleted in the SEI formation and side reactions.
Presodiation at a certain level in both anode and cathodes is known to augment the SIB performance. Some
recent studies have highlighted its importance [289,290] . Presodiation must be optimized to maximize benefits,
as in the Sn-C composite anode presented previously. The effectiveness of presodiation has been evident.
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An optimized presodiated anode can deliver a steady capacity of 130 mAh g without capacity losses for
60 cycles . In fact, a presodiated Sb anode presented by Liu et al. can improve ICE from 75% to 100%.
[291]
[292]
After 300 cycles, this presodiated anode maintained 85% of its capacity . Presodiation can be done by
adding sodiating agents with many standard methodologies. It has the potential to get the optimal design
architecture. Recently, the presodiation strategy has been employed by Shen et al. for Sn-based anodes .
[73]
They took a commercially available Sn powder and sodiating agents, such as sodium biphenyl, and so on,
and achieved a marvelous capacity of 602 mAh g after 7,500 cycles. This Sn-based anode kept 71% of its
-1
capacity in the full cell configuration. They extended their presodiation methodology for synthesizing other
porous alloying anodes such as Sb and Bi.

Various researchers have also adopted dealloying to achieve the optimized morphology for SIB alloying
electrode materials, although dealloying has not been explored extensively. In this strategy, some element
(sacrificial element) is often selectively removed to achieve the desired 3D porous/hollow/network structure.
Some reports have claimed to attain superior and stable capacities using a dealloying methodology. For
-1
example, Sb O @Sb proposed by Ma et al. could sustain 200 mAh g at a high current rate of 29.7 A g in
-1
3
2
[125]
rate capacity . It showed 99.8% cyclic capacity retention. Recently, a novel approach to improve the
performance of alloying SIB anode has been highlighted. In this approach, K incorporated into the
+
-1
electrolyte can highly improve the performance of Sn alloying anode, yielding an energy of 565 mAh g over
3,000 cycles at 2 A g -1[71] . Dimensional structure and electrode formulations can also be used for achieving
the optimized SIB performance using (a) tin; (b) antimony; (c) phosphorus; (d) germanium; (e) silicon; and
(f) bismuth-based anode materials. These are provided in Table 3.
SUMMARY AND FUTURE PROSPECTIVE
Recent trends in synthetic methodologies for robust structural design, material selection, and analysis tools
focusing on intermediate evolutions during (de)sodiation were highlighted in detail from a capacity-stability
aspect for SIB alloying anode materials. Moreover, challenges faced by the current generation of alloying
materials in terms of mechano-electrochemical changes incurred during cycling and strategies diversely
employed to overcome those challenges were summarized. Detailed remediation strategies diversely
employed to overcome the limitations were also highlighted. Conclusively, more focus on the latest
mechanistic-driven characterization tools is obligatory for the upcoming high energy-density SIBs based on
alloying anodes.