1 research outputs found
CuV<sub>2</sub>S<sub>4</sub>: A High Rate Capacity and Stable Anode Material for Sodium Ion Batteries
The
ternary compound CuV<sub>2</sub>S<sub>4</sub> exhibits an excellent
performance as anode material for sodium ion batteries with a high
reversible capacity of 580 mAh g<sup>–1</sup> at 0.7 A g<sup>–1</sup> after 300 cycles. A Coulombic efficiency of ≈99%
is achieved after the third cycle. Increase of the C-rate leads to
a drop of the capacity, but a full recovery is observed after switching
back to the initial C-rate. In the early stages of Na uptake first
Cu<sup>+</sup> is reduced and expelled from the electrode as nanocrystalline
metallic Cu. An increase of the Na content leads to a full conversion
of the material with nanocrystalline Cu particles and elemental V
embedded in a Na<sub>2</sub>S matrix. The formation of Na<sub>2</sub>S is evidenced by <sup>23</sup>Na MAS NMR spectra and X-ray powder
diffraction. During the charge process the nanocrystalline Cu particles
are retained, but no crystalline materials are formed. At later stages
of cycling the reaction mechanism changes which is accompanied by
the formation of copperÂ(I) sulfide. The presence of nanocrystalline
metallic Cu and/or Cu<sub>2</sub>S improves the electrical conductivity,
leading to superior cycling and rate capability