The effect of solvent on reactivity of the Li2S-P2S5 system in liquid-phase synthesis of Li7P3S11 solid electrolyte

Solution-Based Suspension Synthesis of Li2S-P2S5 Glass-Ceramic Systems as Solid-State Electrolytes: A Brief Review of Current Research

All-solid-state batteries are set to be the next generation of batteries offering improved performance and safety over current conventional lithium-ion batteries. Glass-ceramic Li2S-P2S5 solid-state sulfide electrolytes are promising contenders to achieve all-solid-state batteries with exceptional ionic conductivity on the order of 10-2 S cm-1. Solid-state processing techniques for synthesizing sulfide solid electrolytes are energetically and time consumptive. However, proposed solution processing techniques offer faster and lower temperature processes rendering them scalable. The chemistries that underly solution processing of sulfide solid electrolytes are still not well understood. This brief review highlights key aspects of current research into solution-based suspension synthesis processing techniques of Li2S-P2S5 sulfide solid electrolytes discussing precursor stoichiometries, solvent selectivity, reaction conditions, chemical impurities, and particle morphology with the intent of promoting further research into solution processing of sulfide solid-state electrolytes.

Rapid Solution Synthesis of Argyrodite-Type Li6PS5X (X = Cl, Br, and I) Solid Electrolytes Using Excess Sulfur

All-solid-state lithium-ion batteries (ASSLBs) have the potential to be the next-generation energy storage systems because of their high safety features. However, one of the major challenges to the commercialization of ASSLBs is the development of well-established large-scale manufacturing techniques for solid electrolytes (SEs). Herein, we synthesize Li₆PS₅X (X = Cl, Br, and I) SEs in a total of 4 h by a rapid solution synthesis method using excess elemental sulfur as a solubilizer and reasonable organic solvents. In the system, trisulfur radical anions stabilized by a highly polar solvent increase the solubility and reactivity of the precursor. Raman and UV-vis spectroscopies reveal the solvation behavior of halide ions in the precursor. This result demonstrates that the solvation structure modified by the halide ions determines the chemical stability, solubility, and reactivity of chemical species in the precursor. The prepared Li₆PS₅X (X = Cl, Br, and I) SEs show ionic conductivities of 2.1 × 10^-3, 1.0 × 10^-3, and 3.8 × 10^-6 S cm^-1 at 30 °C, respectively. Our study provides a rapid synthesis of argyrodite-type SEs with high ionic conductivity.

Artificial Intelligence-Aided Mapping of the Structure-Composition-Conductivity Relationships of Glass-Ceramic Lithium Thiophosphate Electrolytes

Lithium thiophosphates (LPSs) with the composition (Li₂S) _x (P₂S₅)_1-x are among the most promising prospective electrolyte materials for solid-state batteries (SSBs), owing to their superionic conductivity at room temperature (>10^-3 S cm^-1), soft mechanical properties, and low grain boundary resistance. Several glass-ceramic (gc) LPSs with different compositions and good Li conductivity have been previously reported, but the relationship among composition, atomic structure, stability, and Li conductivity remains unclear due to the challenges in characterizing noncrystalline phases in experiments or simulations. Here, we mapped the LPS phase diagram by combining first-principles and artificial intelligence (AI) methods, integrating density functional theory, artificial neural network potentials, genetic-algorithm sampling, and ab initio molecular dynamics simulations. By means of an unsupervised structure-similarity analysis, the glassy/ceramic phases were correlated with the local structural motifs in the known LPS crystal structures, showing that the energetically most favorable Li environment varies with the composition. Based on the discovered trends in the LPS phase diagram, we propose a candidate solid-state electrolyte composition, (Li₂S) _x (P₂S₅)_1-x (x ∼ 0.725), that exhibits high ionic conductivity (>10^-2 S cm^-1) in our simulations, thereby demonstrating a general design strategy for amorphous or glassy/ceramic solid electrolytes with enhanced conductivity and stability.

High Ionic Conductivity with Improved Lithium Stability of CaS- and CaI2-Doped Li7P3S11 Solid Electrolytes Synthesized by Liquid-Phase Synthesis

Li₇P₃S₁₁ solid electrolytes (SEs) subjected to liquid-phase synthesis with CaS or CaI₂ doping were investigated in terms of their ionic conductivity and stability toward lithium anodes. No peak shifts were observed in the XRD patterns of CaS- or CaI₂-doped Li₇P₃S₁₁, indicating that the doping element remained at the grain boundary. CaS- or CaI₂-doped Li₇P₃S₁₁ showed no internal short circuit, and the cycling continued, indicating that not only CaI₂ including I^- but also CaS could help increase the lithium stability. These results provide insights for the development of sulfide SEs for use in all-solid-state batteries in terms of their ionic conductivity and stability toward lithium anodes.