Lithium-Ion-Conducting Argyrodite-Type Li₆PS₅X (X = Cl, Br, I) Solid Electrolytes Prepared by a Liquid-Phase Technique Using Ethanol as a Solvent

Argyrodite-type crystals, Li₆PS₅X (X = Cl, Br, I), are promising solid electrolytes (SEs) for bulk-type all-solid-state lithium-ion batteries with excellent safety and high energy densities because of their high ionic conductivities and electrochemical stabilities. However, these advantageous features alone are not sufficient to achieve good cell performance. It is also critically important to have a simple and effective synthetic route to SEs and techniques for forming favorable solid–solid interfaces with large contact areas between the electrode and electrolyte particles. Here, we report an effective route for the preparation of argyrodite-type crystals using a liquid-phase technique via a homogeneous ethanol solution to improve cell performance using an SE-coating on the active material. The preparation conditions, such as appropriate halogen species and alcohol solvents, dissolution time, and drying temperature, are examined, finally resulting in Li₆PS₅Br with a lithium-ion conductivity of 1.9 × 10^–4 S cm^–1. Importantly, the obtained solution forms a favorable solid–solid electrode–electrolyte interface with a large contact area in the all-solid-state cells, resulting in a higher capacity than conventional techniques such as hand mixing using a mortar

Crystallization behavior of the Li2S–P2S5 glass electrolyte in the LiNi1/3Mn1/3Co1/3O2 positive electrode layer

Abstract Sulfide-based all-solid-state lithium batteries are a next-generation power source composed of the inorganic solid electrolytes which are incombustible and have high ionic conductivity. Positive electrode composites comprising LiNi1/3Mn1/3Co1/3O2 (NMC) and 75Li2S·25P2S5 (LPS) glass electrolytes exhibit excellent charge–discharge cycle performance and are promising candidates for realizing all-solid-state batteries. The thermal stabilities of NMC–LPS composites have been investigated by transmission electron microscopy (TEM), which indicated that an exothermal reaction could be attributed to the crystallization of the LPS glass. To further understand the origin of the exothermic reaction, in this study, the precipitated crystalline phase of LPS glass in the NMC–LPS composite was examined. In situ TEM observations revealed that the β-Li3PS4 precipitated at approximately 200 °C, and then Li4P2S6 and Li2S precipitated at approximately 400 °C. Because the Li4P2S6 and Li2S crystalline phases do not precipitate in the single LPS glass, the interfacial contact between LPS and NMC has a significant influence on both the LPS crystallization behavior and the exothermal reaction in the NMC–LPS composites

Oxide-Based Composite Electrolytes Using Na₃Zr₂Si₂PO₁₂/Na₃PS₄ Interfacial Ion Transfer

All-solid-state sodium batteries using Na₃Zr₂Si₂PO₁₂ (NASICON) solid electrolytes are promising candidates for safe and low-cost advanced rechargeable battery systems. Although NASICON electrolytes have intrinsically high sodium-ion conductivities, their high sintering temperatures interfere with the immediate development of high-performance batteries. In this work, sintering-free NASICON-based composites with Na₃PS₄ (NPS) glass ceramics were prepared to combine the high grain-bulk conductivity of NASICON and the interfacial formation ability of NPS. Before the composite preparation, the NASICON/NPS interfacial resistance was investigated by modeling the interface between the NASICON sintered ceramic and the NPS glass thin film. The interfacial ion-transfer resistance was very small above room temperature; the area-specific resistances at 25 and 100 °C were 15.8 and 0.40 Ω cm², respectively. On the basis of this smooth ion transfer, NASICON-rich (70–90 wt %) NASICON–NPS composite powders were prepared by ball-milling fine powders of each component. The composite powders were well-densified by pressing at room temperature. Scanning electron microscopy observation showed highly dispersed sub-micrometer NASICON grains in a dense NPS matrix to form closed interfaces between the oxide and sulfide solid electrolytes. The composite green (unfired) compacts with 70 and 80 wt % NASICON exhibited high total conductivities at 100 °C of 1.1 × 10^–3 and 6.8 × 10^–4 S cm^–1, respectively. An all-solid-state Na₁₅Sn₄/TiS₂ cell was constructed using the 70 wt % NASICON composite electrolyte by the uniaxial pressing of the powder materials, and its discharge properties were evaluated at 100 °C. The cell showed the reversible capacities of about 120 mAh g^–1 under the current density of 640 μA cm^–2. The prepared oxide-based composite electrolytes were thus successfully applied in all-solid-state sodium rechargeable batteries without sintering

Mechanochemical Synthesis and Characterization of Metastable Hexagonal Li₄SnS₄ Solid Electrolyte

A new crystalline lithium-ion conducting material, Li₄SnS₄ with an <i>ortho</i>-composition, was prepared by a mechanochemical technique and subsequent heat treatment. Synchrotron X-ray powder diffraction was used to analyze the crystal structure, revealing a space group of <i>P</i>6₃/<i>mmc</i> and cell parameters of <i>a</i> = 4.01254(4) Å and <i>c</i> = 6.39076(8) Å. Analysis of a heat-treated hexagonal Li₄SnS₄ sample revealed that both lithium and tin occupied either of two adjacent tetrahedral sites, resulting in fractional occupation of the tetrahedral site (Li, 0.375; Sn, 0.125). The heat-treated hexagonal Li₄SnS₄ had an ionic conductivity of 1.1 × 10^–4 S cm^–1 at room temperature and a conduction activation energy of 32 kJ mol^–1. Moreover, the heat-treated Li₄SnS₄ exhibited a higher chemical stability in air than the Li₃PS₄ glass-ceramic