Molecular-Level Insight into the Interfacial Reactivity and Ionic Conductivity of a Li-Argyrodite Li₆PS₅Cl Solid Electrolyte at Bare and Coated Li-Metal Anodes

Abstract

Sulfide glasses, with high room-temperature Li-ion conductivities, are a promising class of solid-state electrolytes for all-solid-state batteries. Yet, when in contact with Li metal, our current understanding of important interfacial phenomena such as electrolyte reduction and Li-ion transport is still quite limited, especially at the atomic scale. Here, using first-principles molecular dynamics simulations, we tackle these open questions head-on and examine key interfacial properties of Li-argyrodite Li6PS5Cl electrolyte at bare and coated Li-metal anodes. Specifically, we investigate the role of the interfacial composition and morphology in a number of Li-metal surfaces, including surfaces coated with thin films of Li2Sn5, MoS2, LiF, and Li3P. Our materials models are designed to gain insights into the early stages of interface formation and structural evolution. In addition, by employing a novel topological analysis of procrystal electron density distribution as applied to interfacial solid-state ionics, we thoroughly assess Li-ion conductivity through the investigated interfaces. Our results provide evidence of progressive breaking of P–S bonds in PS4 3– groups and eventual P–P recombination of intermediate species as the main reaction mechanisms of Li6PS5Cl reduction by Li metal. We also predict Li2Sn5 as the most suitable coating to partially prevent the electrolyte degradation while keeping a relatively low interfacial resistance. These findings shed light on the interface chemistry of sulfide-based electrolytes in contact with Li metal and pave the way for rationalizing further computational and experimental studies in the field.

From symmetry breaking in the bulk to phase transitions at the surface: a quantum-mechanical exploration of Li6PS5Cl argyrodite superionic conductor

“…According to their results, the fully relaxed P 1 structure deviates only marginally from the high symmetry one (much less than 10%) and is more stable by 0.65 eV per formula unit (0.05 eV per atom); that is in very good agreement with our predictions. In addition, metastability of cubic Li 6 PS 5 Cl was briefly mentioned in the paper by Carrasco et al 48…”

“…According to their results, the fully relaxed P1 structure deviates only marginally from the high symmetry one (much less than 10 %) and is more stable by 0.65 eV per formula unit (0.05 eV per atom); that is in very good agreement with our predictions. In addition, metastability of cubic 48 Instead of Model 1, let us now consider cells with Li + ion occupying the Wyckoff 48h site, we observe the following: upon optimization, the symmetry degradation leads to two stable minima, one monoclinic in a Pm space group (Model 4) and a structure with a P1 symmetry (Model 3). In the latter case, the crystalline positions of the atoms and the total energy are very close to our Model 2 just described.…”

In Situ Formed Protective Layer: Toward a More Stable Interface between the Lithium Metal Anode and Li6PS5Cl Solid Electrolyte

“…17,37 The decomposition mechanisms by P−P bond recombination are possible in less densely packed interface structures, whereas more densely packed interfaces prefer to proceed by the stepwise breaking of P−S bonds until formation of new Li−S, Li−P, and Li−Cl bonds. 38 These decomposition products, acting as an unstable SEI, will lead to increased interfacial resistance and promote Li dendrite growth To further demonstrate that the in situ formed SEI membrane has the ability to inhibit dendrite growth in solidstate Li batteries, the NCM613/solid electrolyte/Li batteries using Li 6 PS 5 Cl and Li 6 PS 5 Cl with the incorporation of Li(G4)TFSI as the electrolyte material were evaluated, as shown in Figure 5. The NCM613/Li(G4)TFSI-assisted Li 6 PS 5 Cl/Li battery has an initial specific discharge capacity of 132.3 mAh/g at 0.05 C. After three cycles at 0.05C, the current density was increased to 0.1C in the subsequent cycles.…”

“…No characteristic peak of P 2p is found in the XPS spectrum, and the spectral features of Li 2 S and the reduction product of Li 6 PS 5 Cl do not appear in the peak at 160.0 eV in the S 2p spectra . The thermodynamic instability of Li 6 PS 5 Cl in contact with Li metal has been widely investigated. , The decomposition mechanisms by P–P bond recombination are possible in less densely packed interface structures, whereas more densely packed interfaces prefer to proceed by the stepwise breaking of P–S bonds until formation of new Li–S, Li–P, and Li–Cl bonds . These decomposition products, acting as an unstable SEI, will lead to increased interfacial resistance and promote Li dendrite growth in the Li 6 PS 5 Cl electrolyte.…”

Computational Investigation of Lithium-Ion Transport Mechanisms in Perfluoropolyether Polymers

“…Notably, in all-solid-state batteries, battery cell structures can be simplified by stacking SSEs in alternating layers, and bipolar electrodes can double the gravimetric energy density of cells with conventional liquid electrolytes. , However, some drawbacks exist with SSEs, which limit their applications, including poor compatibility between the electrode and the solid inorganic electrolyte, , thermodynamic instability against Li metal, , and high interfacial resistance. , Polymer electrolytes, which possess shape versatility, flexibility, and the ability to form intimate electrolyte/electrode contact, , are known to be likely candidates for use in high-energy-density Li-ion batteries. Based on these advantages, polymer electrolytes are now widely being combined with inorganic fillers to synthesize polymer/inorganic composite electrolytes (CPEs). , …”