1 research outputs found
Fast Diffusivity of PF<sub>6</sub><sup>β</sup> Anions in Graphitic Carbon for a Dual-Carbon Rechargeable Battery with Superior Rate Property
The
diffusivity of PF<sub>6</sub><sup>β</sup> intercalated
into graphitic carbon is investigated using the galvanostatic intermittent
titration technique (GITT) and electrochemical impedance spectroscopy
(EIS). The chemical diffusion constant <i>D</i> of PF<sub>6</sub><sup>β</sup> is estimated by the GITT and EIS to be
around 10<sup>β12</sup> cm<sup>2</sup>/s. The diffusivity of
PF<sub>6</sub><sup>β</sup> in graphitic carbon is comparable
to or slightly higher than that of Li<sup>+</sup> in oxide cathode
materials such as LiFePO<sub>4</sub> or LiCoO<sub>2</sub> for Li ion
batteries. The activation energy for PF<sub>6</sub><sup>β</sup> diffusion is also estimated using EIS and found to be around 0.366
eV. The diffusion route of PF<sub>6</sub><sup>β</sup> in graphitic
carbon is probed using density functional theory (DFT), and diffusion
is found to be slightly easier along the β¨100β© direction
than along the β¨110β© direction. The estimated activation
energy for PF<sub>6</sub><sup>β</sup> diffusion obtained by
DFT calculation was about 0.23 eV, which is lower than that estimated
using EIS. However, both the experimentally measured and theoretically
calculated low activation barrier values confirm the fast diffusivity
of PF<sub>6</sub><sup>β</sup> along the β¨100β©
family of directions in graphitic carbon, which is an interesting
phenomenon in light of its large ionic size. This result also suggests
that a superior rate property can reasonably be achieved in dual-carbon
battery applications