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Page 14 of 64 Rehman et al. Energy Mater 2024;4:400068 https://dx.doi.org/10.20517/energymater.2024.06

Figure 6. (A) TEM imaging studies showing (a) SnO microspheres, (b) SnO /SiO microspheres, (c) hollow microspheres of SnO @C,
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and (d) hollow microspheres of Sn P @C. (e-h) Elemental mapping images of Sn P @C, (i) HRTEM image of Sn P with (j) SAED
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pattern of Sn P @C. (B) (a) Discharge/charge profiles of hollow Sn P @C electrodes at different current densities, (b) Comparison of
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cyclic performance of hollow Sn P @C with pure Sn P electrodes at a current density of 0.2 A g , and (c) Extended cycling of Sn P @C
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hollow microsphere anode at high ampere densities of 2 and 5 A g , respectively. Reproduced with permission from [103] . Copyright ©
2019 American Chemical Society.
Initially sodiated states formed included the irreversible formation of Na Sn and Na P in the first cathodic
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scan (at 0.03 V). The anodic scan showed two consistent peaks at 0.55 and 0.68 V that corroborated the
desodiation of Na Sn and Na P to form Sn and P, respectively. This evidence was further proved by ex-situ
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[105]
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XRD and TEM . An interesting multiphase Sn P /rGO nanohybrid with pronounced Na storage
x y
characteristics has been reported. The multiphasic structure with Sn in the form of Sn P and SnP was
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protected by graphene, which, together with the multiphase Sn structure, enabled high volume shuttering
along with an excellent structural reversibility as evidenced by ex-situ XRD, SEM, and HRTEM studies
where both Sn P and SnP were detected in disassembled electrodes. The SnxPy/rGO electrode afforded
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an improved capacitive-dominated Na storage capacity of 421.8 mAh g over 100 (dis)charge cycles at a
current density of 500 mA g , resulting in a capacity retention of 84.7%. Additionally, a capacity of about
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200 mAh g was conserved over 200 cycles at 2.0 A g , which was superior to many other phosphide SIB
[101]
anodes with unimpressive capacity retention at high current rates .
Fan et al. have recently fabricated template-assisted growth of Sn P hollow nanospheres (HS) dually
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protected by multifunctional conductive MXene sheeted shells . The highly controlled methodology
[106]
ensured optimum morphological benefits for Na transport assisted by MXene encapsulation, as shown in
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Figure 7A. The role of conductive shell extends to maintaining the homogeneous ionic flux on the MXenes
surface, which upon interaction with the electrolyte ensures a highly thin and stable SEI. The SEI
composition in the cycled cells was traced using ex-situ X-ray photoelectron spectroscopy (XPS). In
addition to other electrolyte decomposition products, species contributing to SEI stabilization and structural
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stability that ensured an ICE of about 84% along with a capacity of 390.5 mAh g at 1 A g after 500 cycles
in the full cell taking the Sn P HS@MXene anode coupled with the commonly used SIB cathode, NVP, were
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traced, as demonstrated in Figure 7B.
Fan et al. have reported a method of transforming 2D MXene to the highly conductive 3D conductive
network by sandwiching Sn and Sn P nanoparticles between MXene sheets . Due to covalent interaction
[107]
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with Sn P nanoparticles, the uniformly distributed ultra-small Sn nanoparticles (≈ 4 nm) contributed to
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