A DFT Investigation on the Origins of Solvent-Dependent Polysulfide Reduction Mechanism in Rechargeable Li-S Batteries

Abstract

The lithium-sulfur (Li-S) battery is one of the promising energy storage alternatives because of its high theoretical capacity and energy density. Factors governing the stability of polysulfide intermediates in Li-S batteries are complex and are strongly affected by the solvent used. Herein, the polysulfide reduction and the bond cleavage reactions are calculated in different solvent environments by the density functional theory (DFT) methods. We investigate the relationship between the donor numbers (DN) as well as the dielectric constants (ε) of the solvent system and the relative stability of different polysulfide intermediates. Our results show that the polysulfide reduction mechanism is dominated by its tendency to form the ion-pair with Li+ in different organic solvents.

Packing Sulfur Species by Phosphorene‐Derived Catalytic Interface for Electrolyte‐Lean Lithium–Sulfur Batteries

“…The structures of Li 2 S x ( x = 1, 2, 4, 6, 8) and their adsorption energy on graphene is comparable to previously reported studies. [ 46,47 ] In comparison with pristine graphene, both the EBP and the EBP/EGr showed stronger adhesion towards LiPS, suggesting that the polarity of EBP plays a major role in immobilizing LiPS, consistent with the above experimental findings. Moreover, the stronger binding between Li 2 S and EBP/EGr heterostructure is due to the charge relocations between EGr and EBP and the abundant adsorption sites, rendering the EBP/EGr heterostructure with sulfiphilicity to realize effectively and fast electrocatalytic transformation of LiPS.…”

Liquid electrolyte design for metal‐sulfur batteries: Mechanistic understanding and perspective

“… 42,79 Instead, S 4 2− was stabilized as the main intermediate in low donicity solvent 15,80 (Figure 3(B)). The preferential stabilization of S 3 • − and S 4 2− respectively in high and low donicity solvent, which is further confirmed by DFT calculation, 81 lead to significantly distinct reaction pathways (Figure 3(E)) and cell behaviors. According to the cyclic voltammetry (CV) test (Figure 3(D)), with S 3 • − as dominant intermediate, in high donicity solvent like DMSO, sulfur redox reaction shows two independent reduction peaks with three oxidation peaks 15,77,78,82 .…”

A Perspective on Li/S Battery Design: Modeling and Development Approaches

“…Researchers have also applied ab initio molecular dynamics (AIMD) within the frame-work of DFT to describe the time-dependent interatomic interactions between multiple species, thus allowing more dynamic and complex models to be developed [60]. DFT models have largely been used to develop electrode and separator materials by providing insights into the PS reaction mechanisms [61][62][63], structure [64], and binding/adsorption energy [65][66][67].…”

“…These catalysts lower the overpotential and Li 2 S energy barrier, which in turn accelerates the reaction kinetics and improves sulfur utilization, rate capability, and cycle life [75]. DFT and AIMD simulations have also been used to elucidate the Li 2 S/Li metal surface interactions, the nucleation and growth of a Li 2 S film at the lithium surface [61], and the reaction phenomena occurring at the sulfur electrode [62]. Additionally, DFT and AIMD have been used to discover a layer-by-layer reaction pattern during lithiation and delithiation [63] and to explain the impact of electrolyte chemistry on precipitation and electrocatalytic transformation of Li-PS in electrolytes [64].…”

“…However, DFT/AIMD simulations have provided useful insights for rational design [13], including Li-PS binding properties of potential electrode structures [65,[68][69][70][71][72]74], dopants [34,[65][66][67], and electrocatalysts [68,69,73,77,78]. Furthermore, these models have been used to elucidate the impact of electrolyte chemistry on the structure and behavior of Li-PS in solution [64] and to describe reaction phenomena occurring at the electrodes during lithiation and delithiation [61][62][63]. A comprehensive analysis of Li-PS binding through chemical and mechanical properties at the cathode may help researchers improve cycle life by confining the Li-PS shuttle effect to the cathode.…”