Enhanced structural description of sodium vanadium phosphate glasses: A combined experimental and molecular dynamics study

Abstract

Structural and bonding insights into sodium vanadium phosphate (NVP) glasses are crucial for optimizing their performance as cathode materials in sodium-ion batteries. This study quantitatively assesses the structural features and bonding characteristics of two NVP glass compositions: (Na${}_2$O)${}_{\alpha }$–(V${}_x$O$y$)${}_{(1-2\alpha )}$–(P${}_2$O${}_5$)${}_{\alpha }$ with $\alpha =$ 0.375, 0.285. We combine experimental characterization (differential scanning calorimetry, X-ray diffraction and X-ray photoelectron spectroscopy,) and atomistic modeling (classical molecular dynamics (CMD), and Born–Oppenheimer molecular dynamics (BOMD)). This work provides a quantitative analysis of the different VO${}_n$ units in the two NVP glass models, superseding previous knowledge based largely on CMD simulations. Our results show that the account of the electronic structure, inherent in BOMD simulations is essential for capturing the VO bonding environment. This includes the splitting of the VO peak in the pair distribution function due to both short VO and longer VO bonds, a higher degree of polymerization in the phosphate network and a more significant role for V${}^{5+}$ as a network former.