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Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06 Page 43 of 64

on [252,254-256] . These binders have very little volume swelling effects in organic electrolytes, which is beneficial
for inducing solvent-binder interactive effects that can marginalize the capacity. The 3D cross-linkage
connectivity between the binder and the alloying anode material can highly ameliorate adhesion in
electrode components, involving greater interaction with the metallic current collector to ensure high
electrical conductivity and integrity. Feng et al. have reported that their Sb@C anode shows capacities of 553
[257]
-1
-1
and 435 mAh g over 50 cycles at 50 mA g using sodium alginate and PVDF binders, respectively .
Performance influence of binder modifications has very recently been detailed for alloy-type SIB anodes by
Yao et al. in a comprehensive study focusing on the cross-linking effect of glycerin (GLY) on
poly(acrylic acid) (PAA) binders . They also optimized cross-linking conditions, particularly the cross-
[72]
linking temperature. They tested the cross-linking influence on microsized Sn, Bi, and Sb electrodes. The
cross-linking not only enhanced mechanical properties, but also promoted electrolyte diffusion and
wettability and lessened the electrode presodiation step. The cross-linked binder in µ-Sn anodes furnished a
-1
high capacity of 668.5 mAh g at 2 A g after cycling 500 times. Afterward, the capacity dropped to
-1
457.8 mAh g with extended cycling of 2,000 times. Rendering to the electrolyte’s effective percolation, an
-1
initial CE of just above 90% was obtained with a final capacity retention of 68.5%. In comparison, electrodes
fabricated with the same µ-Sn but with different binders, such as PVDF or PAA, showed inferior
performances. Thick electrodes with high mass loading have also been fabricated to further broaden the
scope of the cross-linking effect. It has been successfully demonstrated that electrodes with mass loading
-2
-2
from 1.6 to 8.3 mg cm all show linear increase in areal capacity from 1.3 to 6.8 mAh cm . Another
[258]
conclusive evidence of an optimized multifunctional binder has been presented by Patra et al. .
SnO @CMK (C mesostructured by KAIST) conversion-alloying SIB anodes fabricated using different
2
binders such as PVDF, sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and
NaCMC/NaPAA have shown capacities of 460, 530, 560, and 650 mAh g , respectively, under a current of
-1
100 mA g over 300 cycles. The uplifted performance of NaCMC/NaPAA mixed binder effectively
-1
increased the strength, binding characteristics, and volumetric forbearance during expansion/contraction
with excellent wettability, all coherently stabilized the SEI and capacity. These results highlight the
imperative role of binders in screening and optimizing performances of next-generation SIBs.

Some recent studies have focused on binder-free electrodes where C-fiber often hosts the active material
assembly either in the form of a support on which the active material is grown or embedded inside the C
matrix. Another approach is to use C foam as a binder-free support [120,259] . A binder-free SIB alloying anode
constructed from MOF-derived C and Bi nanodots has shown a higher performance than the bare
electrode . The electrode sustained a high ICE and maintained a capacity of 550 mAh g at 100 mA g ,
[260]
-1
-1
coupled with a specific rate capacity of 110 mAh g at 2.4 A g . The excellent volume buffering with
-1
-1
efficient diffusion kinetics of Na ensured resilience with SIB potential. Another binder-free Sb/NiSb
+
-1
-1
alloying anode has been tested. It achieved a capacity of 521 mAh g over 100 cycles at 200 mA g , with an
[117]
excellent rate performance and a high ICE .
Reducing voltage hysteresis
Many recent efforts in reducing voltage hysteresis have shown improved cyclic performance. A recent
attempt has been made to identify the role of phase transformations and hysteresis using Na-Sb and Na-P
systems with electrode materials having stable phases to minimize polarization effects and have better
cyclability . Similarly, the Sb Bi alloy anode in SIBs has been recently selected for delivering a high ICE of
[261]
8
1
87.1% at 0.1 A g . The electrode exhibited low polarization effects. It could furnish a high capacity of
-1
625 mAh g after 100 cycles at 1 A g -1[42] . Selecting suitable interfaces can mitigate the voltage hysteresis
-1
issue, as recently reported in Co-Sn alloy, where dually functioning active/inactive phases can reduce
dendrite growth in sodium metal batteries . Although roles of structural modifications, electrolyte
[262]