Elucidating Interfacial Phenomena between Solid-State Electrolytes and the Sulfur-Cathode of Lithium–Sulfur Batteries

Abstract

Sulfide solid-state electrolytes are promising materials to be used in Li–S batteries because they have the potential to mitigate some of the challenges currently faced by this technology such as the dissolution of polysulfide species and the flammability of conventional organic-based electrolytes. Nevertheless, the electrode/electrolyte interfaces are not well-understood yet. In this study, we use density functional theory and ab initio molecular dynamics simulations to investigate the formation of the cathode–electrolyte interface at two limiting states of charge: S8 and Li2S. β-Li3PS4 and two lithium halide-doped sulfides (Li6PS5Cl and Li7P2S8I) were selected because of their Li-ion superionic conductivity and compatibility with sulfur electrodes. The work of adhesion and interfacial energy of the interfaces were calculated as descriptors of the interfacial properties, and then the mechanisms of the interfacial reactions taking place were characterized. Finally, a charge transfer analysis is presented, suggesting that, overall, the S8 electrode will oxidize the electrolyte, whereas the fully discharged Li2S cathode will reduce it at different extents depending on the reactivity of the exposed facet.

Sulfide and Oxide Inorganic Solid Electrolytes for All-Solid-State Li Batteries: A Review

“…The reported diffusion coefficient value of Li 6 PS 5 Cl was reported to be two orders of magnitude lower than that determined using 7 Li nuclear magnetic resonance (NMR) (7.7 × 10 −8 cm 2 s −1 at 40 • C) [179]. According to Camacho-Forero and Balbuena [184], the ionic conductivity of Li 6 PS 5 I was significantly lower than those of Li 6 PS 5 Cl and Li 6 PS 5 Br. (iii) Argyrodite electrolytes can be synthesized using different methods [169,, such as the conventional sealed tube solid-state reaction [169], ball milling [181,183,187], and solution-based methods [189,208].…”

“…Owing to their high Li + ion conductivity at room temperature, sulfide-based materials are more promising electrolytes than oxide-based ones [ 159 , 160 , 161 , 162 , 163 , 164 , 165 , 166 , 167 , 168 , 169 , 170 , 171 , 172 , 173 , 174 , 175 , 176 , 177 , 178 , 179 , 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 , 188 , 189 , 190 , 191 , 192 , 193 , 194 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 , 206 , 207 , 208 ,…”

“…This work opened the avenue for the further understanding of the structural and physical properties of solid-state electrolytes and facilitated the development of ASSBs. Argyrodite presents high conductivity; moreover, argyrodite-based batteries are easier to fabricate than those featuring oxide-based solid electrolytes, and therefore, below, we summarize a series of reports on the synthesis, fabrication, and interfacial properties of argyrodite electrolytes [ 179 , 180 , 181 , 182 , 183 , 184 , 185 , 186 , 187 , 188 , 189 , 190 , 191 , 192 , 193 , 194 , 195 , 196 , 197 , 198 , 199 , 200 , 201 , 202 , 203 , 204 , 205 ].…”

“…They reported the presence of a three-dimensional (3D) pathway network for the long-range ion conduction of all Li 6 PS 5 X ( X = Cl, Br, I) phases, which consisted of interconnected low-energy local pathway cages [ 180 ]. The experimentally measured ionic conductivity at 25 °C of Li 6 PS 5 Cl, Li 6 PS 5 Br, and Li 6 PS 5 I prepared by ball milling followed by heating at 550 °C in inert atmosphere are in the range 1.9 × 10 −4 –7.0 × 10 −3 S cm −1 and calculated activation energies in the range 0.26–0.41 eV ( Table 1 ) [ 180 , 181 , 182 , 183 , 184 , 185 , 186 ]. Further, Boulineau et al [ 183 ] reported the effect of enhancement of the conductivity of Li 6 PS 5 Cl from 2× 10 −4 S cm −1 to 1.33 × 10 −3 S cm −1 when the ball milling time varies from 1 h to 10 h. Rao and Adams [ 181 ] compared the values of E a determined by both experimental and computational method for Li 6 PS 5 X with X = Cl, Br, I in the range 0.25–0.38 eV.…”

“…Further, Boulineau et al [ 183 ] reported the effect of enhancement of the conductivity of Li 6 PS 5 Cl from 2× 10 −4 S cm −1 to 1.33 × 10 −3 S cm −1 when the ball milling time varies from 1 h to 10 h. Rao and Adams [ 181 ] compared the values of E a determined by both experimental and computational method for Li 6 PS 5 X with X = Cl, Br, I in the range 0.25–0.38 eV. Camacho-Forero and Balbuena [ 184 ] performed ab initio calculations and determined that conductivity, activation energy, and the diffusion coefficient of Li + ions at 27 °C were 0.17 × 10 −3 S cm −1 , 0.37 eV, and 1.2 × 10 −9 cm 2 s −1 for Li 6 PS 5 Cl and 6.07 × 10 −3 S cm −1 , 0.27 eV, and 5.8 × 10 −9 cm 2 s −1 for Li 6 PS 5 I, respectively. The reported diffusion coefficient value of Li 6 PS 5 Cl was reported to be two orders of magnitude lower than that determined using 7 Li nuclear magnetic resonance (NMR) (7.7 × 10 −8 cm 2 s −1 at 40 °C) [ 179 ].…”