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Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06 Page 25 of 64

Recently, Wu et al. have successfully recognized asymmetric phase transformational characteristics during
+
[147]
(de)sodiation of Sb Se nanowires . The multistep mechanism involved in sodiation includes Na
3
2
intercalation, conversion, and sequential alloying involving Na Sb intermediate phases. An incomplete
x
desodiation process has been tracked. It originated from an irreversible capacity fading. The authors were
able to trace lateral and surface Na diffusion, whereby a fast Na surface diffusion was found with radial
+
+
volume expansions. Moreover, the use of in-situ HRTEM and corresponding fast Fourier transformation
(FFT) patterns reflected the tracing of Na Sb Se , Na Se, Sb, NaSb, Na Sb, and Na Sb phases showing
2
3
x
3
2
2
conversion/alloying transformations.
Phosphorous-based anodes for SIBs
Phosphorous (P) is deemed to be a potential candidate due to its unique properties such as low potential
(0.5 V) and ultrahigh theoretical capacity (2,596 mAh g ). In addition, it is cheap and benign similar to red
-1
Phosphorous (RP). Among various allotropes of P, RP has the most optimistic performance characters. In
-1
the amorphous phase, it can store high Na . However, it has a low conductivity (10-14 Scm ). It also suffers
+
from huge volume changes (490%). The optimum alloying phase in P is Na P. Although white and layered
3
+
black P have also been reported to have alloying potential with Na , unfortunately, white P is toxic and the
black P is synthesized under harsh conditions. However, black P has a high conductivity of 300 Scm -1[148,149] .
A promising composite with nanoporous RP has been constructed by adding the rGO sheeted matrix to
yield the composite (NPRP@rGO). Such addition not only enhanced conductive features of the SIB anode,
-1
but also ensured high capacity storage parameters (capacity retainability of 1,249.7 mAh g at 173.26 mA g
-1
@ 150 cycles and rate performance of about 656.9 mAh g at 3.462 A g ) . The improved performance
-1 [150]
-1
was due to more interfacial contacts and effective electrolyte penetrability along with confinement of NPRP
nanoparticles on rGO sheets through P-C chemical bonding. Furthermore, electrochemical impedance
spectroscopy (EIS) highlighted the peculiar role of a highly conductive rGO network, which guaranteed
+
effective and quick Na /e transportation.
-
A durable phosphorus anode for SIBs with an extended cycle life span has been developed through coupling
of sulfurized Polyacrylonitrile (SPAN), RP, and C black . The hybrid has plenty of P-S bonds that could
[151]
help withstand large volume variations. It offers a high capacity of about 1,300 mAh g at a current density
-1
-1
of 520 mA g , with high CE (> 99%) and good cycling performance (i.e., CE = 91% for 100 cycles).
Capone et al. have utilized synergy of particle size of RP, its retainability in the C matrix, and its correlation
with the capacity . Through a two-step milling process using wet and dry ball milling to first reduce the
[152]
particle size and later composite it with the C (graphite), this methodology has impacted the performance of
the anode for SIBs application to achieve 1,354 mAh g as initial charging capacity along with an overall CE
-1
of 88% over 100 cycles. Xiao et al. have established a correlation between stability of the RP composite
electrode in ambient conditions and its performance . The composited electrode (derived from RP and C
[153]
black) showed a good initial performance (1,070 mAh g of capacity retention over 200 cycles at
-1
400 mAh g ). When exposed to air, the electrode showed a decrement in capacity retainability, while
-1
synchrotron-based XAS showed a concurrent appearance of phosphate species that passivated capacitive
reactions.

To optimize the SIB anode performance in the C compositing of RP, various modest synthetic
modifications have been adapted. For instance, Liu et al. have reported a controlled synthesis of RP-rGO
composite using ethylenediamine additive to get ultra-small and well-dispersed RP particles on the surface
[154]
of rGO . The composite showed highly admiring performance with a storage capacity of 2,057 mAh g at
-1