We present an investigation of the phase stability, electrochemical stability and Li+ conductivity of the Li10±1MP2X12 (M = Ge, Si, Sn, Al or P, and X = O, S or Se) family of superionic conductors using first principles calculations. The Li10GeP2S12 (LGPS) superionic conductor has the highest Li+ conductivity reported to date, with excellent electrochemical performance demonstrated in a Li-ion rechargeable battery. Our results show that isovalent cation substitutions of Ge4+ have a small effect on the relevant intrinsic properties, with Li10SiP2S12 and Li10SnP2S12 having similar phase stability, electrochemical stability and Li+ conductivity as LGPS. Aliovalent cation substitutions (M = Al or P) with compensating changes in the Li+ concentration also have a small effect on the Li+ conductivity in this structure. Anion substitutions, however, have a much larger effect on these properties. The oxygen-substituted Li10MP2O12 compounds are predicted not to be stable (with equilibrium decomposition energies >90 meV per atom) and have much lower Li+ conductivities than their sulfide counterparts. The selenium-substituted Li10MP2Se12 compounds, on the other hand, show a marginal improvement in conductivity, but at the expense of reduced electrochemical stability. We also studied the effect of lattice parameter changes on the Li+ conductivity and found the same asymmetry in behavior between increases and decreases in the lattice parameters, i.e., decreases in the lattice parameters lower the Li+ conductivity significantly, while increases in the lattice parameters increase the Li+ conductivity only marginally. Based on these results, we conclude that the size of the S2− is near optimal for Li+ conduction in this structural framework.

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Phase stability, electrochemical stability and ionic conductivity of the Li10±1MP2X12 (M = Ge, Si, Sn, Al or P, and X = O, S or Se) family of superionic conductors

Due to their high ionic conductivity and adeciduate mechanical features for lamination, sulfide composites have received increasing attention as solid electrolyte in all-solid-state batteries. Their smaller electronegativity and binding energy to Li ions and bigger atomic radius provide high ionic conductivity and make them attractive for practical applications. In recent years, noticeable efforts have been made to develop high-performance sulfide solid-state electrolytes. However, sulfide solid-state electrolytes still face numerous challenges including: 1) the need for a higher stability voltage window, 2) a better electrode-electrolyte interface and air stability, and 3) a cost-effective approach for large-scale manufacturing. Herein, a comprehensive update on the properties (structural and chemical), synthesis of sulfide solid-state electrolytes, and the development of sulfide-based all-solid-state batteries is provided, including electrochemical and chemical stability, interface stabilization, and their applications in high performance and safe energy storage.

Sulfide-Based Solid-State Electrolytes: Synthesis, Stability, and Potential for All-Solid-State Batteries.

Crystal structure and phase transitions of the lithium ionic conductor Li3PS4

Motivated by the high lithium ion conductivities of lithium thiophosphate glasses, a detailed study is performed on the local chemical nature of the thiophosphate building units within these materials. Using Raman and 31P MAS NMR (Magic Angle Spinning – Nuclear Magnetic Resonance) spectroscopy, the continuous change from dominant P2S74− (di-tetrahedral) anions to PS43− (mono-tetrahedral) anions with increasing Li2S fraction in the (Li2S)x(P2S5)(100−x) glasses is observed. In addition, synchrotron pair distribution function analysis (PDF) of synchrotron X-ray total scattering data is employed to monitor in situ crystallization and phase evolution in this class of materials. Depending on the composition, different crystalline phases evolve, which possess different decomposition temperatures into less conducting phases. The results highlight the critical influence of the local anionic building units on the cation mobility and thermal stability, with PS43− tetrahedra forming the most thermally robust glass ceramics with the highest ionic conductivity.

Lithium ion conductivity in Li2S–P2S5 glasses – building units and local structure evolution during the crystallization of superionic conductors Li3PS4, Li7P3S11 and Li4P2S7

Numerous channel- or tunnel-structured compounds are interesting materials in which lithium intercalation occurs primarily without destruction of the host lattice assuming a complete charge transfer. In many cases, the rigid-band model (RBM) is a useful first approximation for describing the changes in electronic properties of the host material with intercalation. The applicability of the rigid-band model is taken as a test for the properties most desirable in a good intercalation material. This review paper presents experimental results, namely optical and electrical measurements, obtained on various intercalation materials such as dichalcogenides, trichalcogenides and oxides to probe the validity of the RBM. The impact of the lithium intercalation is discussed for various structural forms, from well-crystallised to amorphous compounds. We observed, nevertheless, that the rigid-band model is not applicable to all of the layered intercalation materials. This needs yet to be more extensively documented for their promising application as insertion electrode in rechargeable lithium batteries. Compounds such as TiS 2 , TaS 2 , MoS 2 , NiPS 3 , MoO 3 , V 2 O 5 , V 6 O 13 , LiCoO 2 , LiNiO 2 , LiMn 2 O 4 and LiNiVO 4 are tested in this work. Some guidelines are established for improving the performances of these materials in their most eminent applications.

J. Douglande

Papers

Synthese, structure cristalline et analyse vibrationnelle de l'hexathiohypodiphosphate de lithium Li4P2S6