Facile Method for the Formation of Intimate Interfaces in Sulfide-Based All-Solid-State Batteries.

Sulfide-based inorganic solid electrolytes have been considered promising candidates for all-solid-state batteries owing to their high ionic conductivity. Compared with oxide-based inorganic solid electrolytes which require high-temperature sintering, the intrinsic deformability of sulfide electrolytes enables the fabrication of all-solid-state batteries by a simple cold pressing method. Nevertheless, the performance of sulfide-based all-solid-state batteries is still unsatisfactory, owing to the insufficient interfacial properties within the composite electrodes. Using cold pressing alone, it is challenging to form intimate contacts with rigid oxide-based cathode materials. Here, we demonstrate a mild-temperature pressing (MP) method for the fabrication of all-solid-state batteries. The mild temperature (85 °C) increases the deformability of the sulfide and therefore helps to form more enhanced interfacial contacts in the composite cathode without side reactions. Compared with the conventional cold pressing cell, the MP cell possesses more favorable contacts, resulting in higher capacity, cyclability, and rate capability. In addition, we demonstrate that the charge-transfer resistance in composite cathodes dominates the electrochemical performance of all-solid-state batteries.

Functionalized Sulfide Solid Electrolyte with Air-Stable and Chemical-Resistant Oxysulfide Nanolayer for All-Solid-State Batteries.

Sulfide solid electrolytes (SEs) with high Li-ion conductivities (σion) and soft mechanical properties have limited applications in wet casting processes for commercial all-solid-state batteries (ASSBs) because of their inherent atmospheric and chemical instabilities. In this study, we fabricated sulfide SEs with a novel core-shell structure via environmental mechanical alloying, while providing sufficient control of the partial pressure of oxygen. This powder possesses notable atmospheric stability and chemical resistance because it is covered with a stable oxysulfide nanolayer that prevents deterioration of the bulk region. The core-shell SEs showed a σion of more than 2.50 mS cm-1 after air exposure (for 30 min) and reaction with slurry chemicals (mixing and drying for 31 min), which was approximately 82.8% of the initial σion. The ASSB cell fabricated through wet casting provided an initial discharge capacity of 125.6 mAh g-1. The core-shell SEs thus exhibited improved powder stability and reliability in the presence of chemicals used in various wet casting processes for commercial ASSBs.

Superionic Halogen-Rich Li-Argyrodites Using In Situ Nanocrystal Nucleation and Rapid Crystal Growth.

Although several crystalline materials have been developed as Li-ion conductors for use as solid electrolytes in all-solid-state batteries (ASSBs), producing materials with high Li-ion conductivities is time-consuming and cost-intensive. Herein, we introduce a superionic halogen-rich Li-argyrodite (HRLA) and demonstrate its innovative synthesis using ultimate-energy mechanical alloying (UMA) and rapid thermal annealing (RTA). UMA with a 49 G-force milling energy provides a one-pot process that includes mixing, glassification, and crystallization, to produce as-milled HRLA powder that is ∼70% crystallized; subsequent RTA using an infrared lamp increases this crystallinity to ∼82% within 25 min. Surprisingly, this HRLA exhibits the highest Li-ion conductivity among Li-argyrodites (10.2 mS cm-1 at 25 °C, cold-pressed powder compact) reported so far. Furthermore, we confirm that this superionic HRLA works well as a promising solid electrolyte without a decreased intrinsic electrochemical window in various electrode configurations and delivers impressive cell performance (114.2 mAh g-1 at 0.5 C).

Atomistic Assessments of Lithium-Ion Conduction Behavior in Glass-Ceramic Lithium Thiophosphates.

We determined the interatomic potentials of the Li-[PS43-] building block in (Li2S)0.75(P2S5)0.25 (LPS) and predicted the Li-ion conductivity (σLi) of glass-ceramic LPS from molecular dynamics. The Li-ion conduction characteristics in the crystalline/interfacial/glassy structure were decomposed by considering the structural ordering differences. The superior σLi of the glassy LPS could be attributed to the fact that ∼40% of its structure consists of the short-ranged cubic S-sublattice instead of the hexagonally close-packed γ-phase. This glassy LPS has a σLi of 4.08 × 10-1 mS cm-1, an improvement of ∼100 times relative to that of the γ-phase, which is in agreement with the experiments.

Thermally Induced S-Sublattice Transition of Li3PS4 for Fast Lithium-Ion Conduction.

The ion-transport phenomenon, determined by the interaction of strain and electrostatic energy, is one of the most important examples that confirms the effects of the polymorphism and atomic morphology. We investigated the correlation between the structural morphology and Li-ion conduction characteristics in α-Li3PS4, a high-temperature phase of the Li3PS4, using ab initio molecular dynamics (AIMD) calculations. We successfully reproduced the thermal disorder and partial occupancy observed at high temperatures by AIMD and confirmed the Li-ion sites and its migration pathways. The activation energy and Li-ion conductivity of α-Li3PS4 at room temperature were predicted to be about 0.18 eV and 80 mS cm-1, respectively, indicating that α-Li3PS4 is one of the fastest Li-ion conductors known so far. The fast Li-ion conduction in α-Li3PS4 is mainly caused by the BCC S-sublattice and tetrahedron-tetrahedron pathway with fully occupied Li-ion sites. Therefore, α-Li3PS4 having a BCC S-sublattice offers a promising structural morphology for effective Li-ion conduction.

Quantitative Analysis of Microstructures and Reaction Interfaces on Composite Cathodes in All-Solid-State Batteries Using a Three-Dimensional Reconstruction Technique.

The composite cathode of an all-solid-state battery composed of various solid-state components requires a dense microstructure and a highly percolated solid-state interface different from that of a conventional liquid-electrolyte-based Li-ion battery. Indeed, the preparation of such a system is particularly challenging. In this study, quantitative analyses of composite cathodes by three-dimensional reconstruction analysis were performed beyond the existing qualitative analysis, and their microstructures and reaction interfaces were successfully analyzed. Interestingly, various quantitative values of structure properties (such as the volume ratio, connectivity, tortuosity, and pore formation) associated with material optimization and process development were predicted, and they were found to result in limited electrochemical charge/discharge performances. We also verified that the effective two-phase boundaries were significantly suppressed to ∼23% of the total volume because of component dispersion and packing issues.