1D Nanostructured
Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) as High-Potential
and Superior-Performance Cathode Material for Sodium-Ion Batteries
- Publication date
- Publisher
Abstract
Tailoring
materials into nanostructure offers unprecedented opportunities
in the utilization of their functional properties. High-purity Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) with 1D nanostructure is prepared as a cathode material
for rechargeable Na-ion batteries. An efficient synthetic approach
is developed by carefully controlling the crystal growth in the molten
sodium phosphate. Based on the XRD, XPS, TG, and morphological characterization,
a molten-salt assisted mechanism for nanoarchitecture formation is
revealed. The prepared Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) nanorod has rectangle sides
and preferential [001] growth orientation. GITT evaluation indicates
that the sodium de/intercalation of Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) nanorod involves
V<sup>3+</sup>/V<sup>4+</sup> redox reaction and Na<sub>5</sub>V<sup>3.5+</sup><sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) as intermediate phase, which results in two pairs of potential
plateaus at the equilibrium potentials of 3.8713 V (V<sup>3+</sup>/V<sup>3.5+</sup>) and 3.8879 V (V<sup>3.5+</sup>/V<sup>4+</sup>),
respectively. The unique nanoarchitecture of the phase-pure Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) facilitates its reversible sodium de/intercalation, which
is beneficial to the high-rate capability and the cycling stability.
The Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) cathode delivers 80% of the capacity (obtained at
C/20) at the 10 C rate and 95% of the initial capacity after 200 cycles.
Therefore, it is feasible to design and fabricate an advanced rechargeable
sodium-ion battery by employment of 1D nanostructured Na<sub>7</sub>V<sub>4</sub>(P<sub>2</sub>O<sub>7</sub>)<sub>4</sub>(PO<sub>4</sub>) as the cathode material