A cathode
material based on polyphosphazene with pyrene-4,5,9,10-tetraone
(PTO) units as electroactive groups with a high specific capacity
in the side chain, poly[(bis(2-amino-4,5,9,10-pyrenetetraone)]phosphazene (PPAPT), is synthesized. The structural characterization of PPAPT is carried out by using appropriate standard spectroscopic
methods such as 31P NMR spectroscopy, FT-IR, DSC, and TGA.
The material is found to be an insoluble and halogen-free flame retardant
in accordance with the results of the simple flame test and solubility
control in electrolyte solutions accompanied by UV–vis analysis.
The electrochemical performance of PPAPT is evaluated
as a Li–ion battery cathode material. The fabricated cells
demonstrate immensely good capacity retention with 72% after 500 discharge–charge
cycles at a high current density of 20 C. In comparison with the pristine
PTO, introducing a PTO unit into the side chain of the polyphosphazene
leads to substantially improved performance because of the lowered
LUMO energy levels of PPAPT. In order to investigate
the reversibility of carbonyl groups as an electroactive side with
respect to their chemical composition, complementary chemical post-mortem
analyses are performed by FT-IR, X-ray photoelectron spectroscopy
(XPS) analysis. Density functional theory (DFT) calculations are also
proposed to determine HOMO–LUMO levels and investigate the
lithiation mechanism of PPAPT.
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