1 research outputs found
Nanostructured Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> for Hybrid Sodium-Ion Capacitors with Excellent Rate Capability
Herein, we report
a new Na-insertion electrode material, Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub>, as a potential candidate for Na-ion hybrid capacitors.
We study the structural properties of nanostructured Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub>, synthesized by a hydrothermal technique,
upon electrochemical cycling vs Na. Average and local structures of
Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> are elucidated from neutron
Rietveld refinement and pair distribution function (PDF), respectively,
to investigate the initial discharge and charge events. Rietveld refinement
reveals electrochemical cycling of Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> is driven by single-phase solid solution reaction during
(de)Âsodiation without any major structural deterioration, keeping
the average structure intact. Unit cell volume and lattice evolution
on discharge process is inherently related to TiO<sub>6</sub> distortion
and Na ion perturbations, while the PDF reveals the deviation in the
local structure after sodiation. Raman spectroscopy and X-ray photoelectron
spectroscopy studies further corroborate the average and local structural
behavior derived from neutron diffraction measurements. Also, Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> shows excellent Na-ion kinetics
with a capacitve nature of 86% at 1.0 mV s<sup>–1</sup>, indicating
that the material is a good anode candidate for a sodium-ion hybrid
capacitor. A full cell hybrid Na-ion capacitor is fabricated by using
Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> as anode and activated
porous carbon as cathode, which exhibits excellent electrochemical
properties, with a maximum energy density of 54 Wh kg<sup>–1</sup> and a maximum power density of 5 kW kg<sup>–1</sup>. Both
structural insights and electrochemical investigation suggest that
Na<sub>2</sub>Ti<sub>9</sub>O<sub>19</sub> is a promising negative
electrode for sodium-ion batteries and hybrid capacitors