First-Principles Study on Structural and Electronic Properties of α-S and Na–S Crystals

Abstract

Several Na-S solid phases have been considered to be produced in low-temperature Na/S batteries during chargedischarge reactions. We study structural and electronic properties of ¡-S and Na 2 S x (x = 1, 2, 4, and 5) crystals using first-principles calculations. Calculated structural properties are in good agreement with experiments, and the van der Waals interactions have an essential role on the cohesive properties in ¡-S. The results of energetics and electronic structures show that all the calculated Na-S crystal phases are insulating and are stable relative to the elemental Na and S phases. We estimate voltage curves as a function of the Na concentration in the S-cathode of all-solid Na/S batteries, showing mainly three voltage regions at 2.

Lattice thermal expansion and anisotropic displacements in 𝜶-sulfur from diffraction experiments and first-principles theory

“…The rather small asymmetric unit, the absence of strongly absorbing atom types and the dispersion-dominated intermolecular interactions make α-S8 a very well-suited candidate for calculations with dispersion-corrected DFT and concomitant experimental evaluation. There have been several DFT studies on α-sulfur so far, 34,35 including a recent application of the quasi-harmonic approximation (QHA) to calculate thermodynamic properties, 36 to which we will return below. In this work, we measure experimentally and calculate from first principles the lattice thermal expansion and ADPs of α-S8.…”

High and intermediate temperature sodium–sulfur batteries for energy storage: development, challenges and perspectives

“…Density functional theory (DFT) calculations predict Na 2 S 3 to be of C 2v symmetry with the coordination of the metal by the terminal sulfur atoms of the S 3 unit only. 46,60 The enthalpy of formation of Na 2 S 3 (À0.85 eV per atom) is greater than the one of Na 2 S 4 and Na 2 S 5 , respectively (À0.80 and À0.70 eV per atom). Beyond this point, sodium disulde (Na 2 S 2 , T m ¼ 475 C) is formed as corroborated by density functional calculations and the phase diagram of Fig.…”

“…45 a-S is composed of puckered S 8 rings organizing in an orthorhombic cell. 46 In its elemental form, it shows as an odorless, non-metallic, paleyellow solid. Sulfur is one of the chemical industry's most important raw materials, utilized as the derivative in numerous industrial processes including rubber processing, cosmetics and pharmaceuticals.…”

First‐Principles Study of Na‐Ion Battery Performance and Reaction Mechanism of Tin Sulfide as Negative Electrode

“…Based on the reaction formulae obtained from the theoretical ternary phase diagram, we study electrochemical properties of the Na/SnS battery system. Voltage values can be calculated by estimating the DFT total energy difference for a given reaction formula ,…”