Aqueous Na-ion batteries are among the most discussed
alternatives
to the currently dominating Li-ion battery technology, in the area
of stationary storage systems because of their sustainability, safety,
stability, and environmental friendliness. The electrochemical properties
such as ion insertion kinetics, practical capacity, cycling stability,
or Coulombic efficiency are strongly dependent on the structure, morphology,
and purity of an electrode material. The selection and optimization
of materials synthesis route in many cases allows researchers to engineer
materials with desired properties. In this work, we present a comprehensive
study on size- and shape-controlled hydro(solvo)thermal synthesis
of NaTi2(PO4)3 nanoparticles. The
effects of different alcohol/water synthesis media on nanoparticle
phase purity, morphology, and size distribution are analyzed. Water
activity in the synthesis media of different alcohol solutions is
identified as the key parameter governing the nanoparticle phase purity,
size, and shape. The careful engineering of NaTi2(PO4)3 nanoparticle morphology allows control of the
electrochemical performance and degradation of these materials as
aqueous Na-ion battery electrodes.
Due to their stability
and structural freedom, NASICON-structured
materials such as NaTi2(PO4)3 show
a lot of promise as active electrode materials for aqueous batteries
and deionization cells. However, due to their low intrinsic electronic
conductivity, they must usually be composited with carbon to form
suitable electrodes for power applications. In this work, two series
of NaTi2(PO4)3–carbon composite
structures were successfully prepared by different approaches: postsynthetic
pyrolytic treatment of citric acid and surface polymerized dopamine.
The latter route allows for a superior carbon loading control and
yields more uniform and continuous particle coatings. The homogeneity
of the polydopamine derived core–shell carbon layer is supported
by FTIR, TEM, and XPS analysis. Combustion elemental analysis also
indicates significant nitrogen doping in the final carbonaceous structure.
The galvanostatic charge and discharge cycling results show similar
initial capacities and their retention, but at only half of the carbon
loading in polydopamine derived samples. The overall results indicate
that careful nanostructure engineering could yield materials with
superior properties and stability suitable for various electrochemical
applications such as aqueous Na-ion batteries and deionization cells.
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