The charge density differences in different charge states reflect the contributions of each transition-metal atom to the electron transfer process, fundamentally revealing the formation mechanism of the three pairs of redox peaks shown by NCHCF.
Cathode materials play a decisive
role in the building of high
energy density sodium-ion batteries. Among them, Na3V2(PO4)2O2F (NVPOF) is receiving
active attention due to its high structural integrity, satisfactory
work voltage, and outstanding energy density. However, its practical
application is still impeded by the poor rate performance related
to its low intrinsic electronic conductivity. Herein, Na3V2(PO4)2O2F grown on
the surface of the core carbon sphere (CS@NVPOF) was initially synthesized
via a one-step hydrothermal method. Subsequently, by carbonization
of polydopamine, the above particles coated with a uniform N-doped
carbon layer (CS@NVPOF@NC) were successfully fabricated. This sandwiched
structure built by a core carbon sphere and carbon layer can significantly
improve the electronic conductivity, boost sodium-ion diffusion kinetics,
and mitigate volume change of the electrode upon the cycling process.
As a result, the as-prepared electrode exhibits a desirable specific
capacity of 119.8 mA h g–1 with an attractive capacity
retention of 96% after 100 cycles at a current density of 1 C. Even
at a high current density of 10 C, the capacity can retain 103.9 mA
h g–1, and the capacity decay per cycle is only
0.032% during 500 cycles, indicating outstanding electrochemical performance.
All the analyses demonstrate that CS@NVPOF@NC has enormous potential
as an applicable cathode for sodium-ion batteries.
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