Structural Investigations, Visualization, and Electrolyte Properties of Silver Halide-Doped Li₇P₃S₁₁ Lithium Superionic Conductors

Abstract

A new silver halide-doped Li 7 P 3 S 11 (7Li 2 S−3P 2 S 5 ) solid electrolyte with increasing ionic conductivity and stability was prepared by the wet ball milling process. Detailed structural investigations were carried out after the doping process. First, AgI was added to a Li 7 P 3 S 11 solid electrolyte to achieve a novel composite/phase. The highest ionic conductivity of the composite was optimized by changing the AgI concentration (0.05, 0.10, and 0.25) and the sintering temperature (240, 270, and 300 °C). The selected Li 7 Ag 0.1 P 3 S 11 I 0.1 solid electrolyte displayed a high ionic conductivity of 1.35 × 10 −3 S cm −1 at room temperature, which is higher than the prepared pristine Li 7 P 3 S 11 solid electrolyte. High-power X-ray diffraction analysis is used to analyze the crystalline nature of the electrolyte. The surface morphology of the electrolyte was studied by the field-emission microscopy technique. The surface functional group of the Li 7 Ag 0.1 P 3 S 11 I 0.1 solid electrolyte was analyzed by the X-ray photoelectron spectroscopy technique. The electrochemical behavior of the selected electrolyte was analyzed by cyclic voltammetry, DC polarization, and impedance spectroscopy techniques. Cyclic voltammetry and DC polarization showed that the synthesized Li 7 Ag 0.1 P 3 S 11 I 0.1 solid electrolyte is highly stable up to 5 V potential window and has charge−discharge stability of more than 100 cycles against Li metal.

Li4.1P0.9Sn0.1S4I Solid Electrolyte with Favorable Air Stability for All-Solid-State Lithium Batteries

“…Among various types of solid electrolytes, sulfide electrolytes are particularly attractive due to their high room-temperature ionic conductivity. − The favorable ionic conductivity of sulfide electrolytes is attributed to their polarizable and deformable sulfur-based frameworks (e.g., PS 4 3– and P 2 S 7 4– ) and weak interaction of Li + and S 2– , making the Li ion more mobile. , However, P–S bonds of sulfides are fragile, and the combination of P–O and S–H is preferred when exposed to humid air. − As a result, air-exposed sulfide electrolytes not only suffer from low ionic conductivity and deteriorated electrochemical performance but also generate toxic H 2 S gas. The partial substitution of P 5+ with soft acids (e.g., Sb 5+ , As 5+ , and Sn 4+ ) provides a feasible route for sulfide electrolytes to improve tolerance toward humid air because of the stronger combination of soft acids and S 2– .…”

Preparation of Metal-Oxide-Doped Li7P2S8Br0.25I0.75 Solid Electrolytes for All-Solid-State Lithium Batteries

“…On the other hand, the addition of a metal oxide to the Li 2 S–P 2 S 5 solid electrolyte system suppresses the formation of H 2 S gas in an air atmosphere according to the HSAB theory. Further, the addition of metal oxide also decreases the interfacial resistance between the electrolyte and oxide active materials. − Although it is proven in few studies that metal/semimetal oxides doping improves the performance of sulfide based solid electrolytes, however, it is important to study the effect of various metal/semimetal oxide doping on sulfide based solid electrolytes. Thus, a detailed investigation of various metal-/semimetal-oxide-doped sulfide-based solid electrolytes should be carried out because the metal/semimetal oxides have different characteristics based on the metal/semimetal cation’s oxidation state and the electronic structure.…”