• Bong, Jia Hui
• Adams, Stefan

Abstract

<jats:p> While LiFePO<jats:sub>4</jats:sub> found wide applications as a high-performance Li-ion battery cathode material, its sodium analog, crystalline NaFePO<jats:sub>4</jats:sub>, cannot deliver its attractive theoretical capacity of 154 mAh ⋅ g[Formula: see text] at practical (dis)charge rates due to the low ionic conductivity of the stable Maricite phase of NaFePO<jats:sub>4</jats:sub>. Recently, it was found that amorphization greatly enhances the rate capability of NaFePO<jats:sub>4</jats:sub> turning it into an attractive Na-ion battery cathode material. Here, we study the effect of amorphization on the rate-limiting ionic conductivity. To this end, structure models of amorphous NaFePO<jats:sub>4</jats:sub> are produced by simulated melt-quenching of Maricite. Ion transport pathways in the resulting glass structure are then compared to those in crystalline Maricite to provide a more in-depth understanding of the mechanism behind the significantly enhanced rate performance. Static bond valence site energy landscape analyses reveal a considerable reduction of the sodium migration energy for crystalline Maricite from about 1.6 eV to 0.65(11) eV for 1D paths and 0.77(15) eV for 2D paths in amorphous NaFePO<jats:sub>4</jats:sub>. Detailed molecular dynamics simulations then reveal that the first local Na[Formula: see text] redistributions can even occur with the extremely low migration energy of 0.12 eV. </jats:p>

Topics

• amorphous
• simulation
• melt
• glass
• glass
• molecular dynamics
• Sodium
• quenching