Correlating Macro and Atomic Structure with Elastic Properties and Ionic Transport of Glassy Li₂S‐P₂S₅ (LPS) Solid Electrolyte for Solid‐State Li Metal Batteries

Abstract

all-solid-state batteries (ASSBs). [1] ASSBs have garnered interest since they offer the potential for improved safety and energy density compared to lithium-ion batteries. To realize these advantages, the nonflammable solid electrolyte would replace the flammable liquid electrolyte and Li metal would replace carbon anodes to reduce cell volume and weight. [2] As a result, about 100% higher energy densities could be achieved compared to conventional Li-ion batteries. [3,4] Sulfide-based electrolytes with adequate ionic conductivity, low interfacial resistance against electrodes, and low processing cost make them one of the most promising inorganic solid electrolyte materials that could enable ASSBs. [5] However, despite the development of different compositions through different synthesis techniques in the Li 2 S-P 2 S 5 (LPS) family, [6][7][8][9][10] the successful transition to Li metal with relevant charging rates (≥3 mA cm −2 at room temperature) has not been realized. It has been reported that microstructural defects, such as grain boundaries and/or pores can play a role in determining the maximum charging rate (or critical current density, CCD) a solid electrolyte can withstand without Li penetration. [11,12] Thus, a glassy, dense microstructure may be preferred for ASSB applications. In previous work, [13] the densification behavior or LPS 75-25 was studied as a function of temperature (25-300 °C) at fixed pressure (47 MPa). It was determined that crystallization of the thio-LiSICON III analog phase occurred between 170 and 250 °C. Moreover, the relative density was more or less invariant of densification temperature (≈80% RD; calculated dividing the geometrical density by its theoretical density in the amorphous phase: 1.88 g cm −3 ). [14] While in our previous study, the maximum hot-pressing pressure (47 MPa) was limited by the mechanical integrity of the molding die, we recently developed capabilities to increase pressure to achieve 360 MPa. With this new capability, the current study compliments our previous study by investigating the densification behavior of LPS 75-25 as a function of pressure at fixed temperature. The pressure ranged between 47 and 360 MPa and the temperature was fixed at the glass transition temperature (T glass ). We hypothesize that by increasing the molding pressure the relative density will increase. Furthermore, the simultaneous application of A combination of high ionic conductivity and facile processing suggest that sulfide-based materials are promising solid electrolytes that have the potential to enable Li metal batteries. Although the Li 2 S-P 2 S 5 (LPS) family of compounds exhibit desirable characteristics, it is known that Li metal preferentially propagates through microstructural defects, such as particle boundaries and/ or pores. Herein, it is demonstrated that a near theoretical density (98% relative density) LPS 75-25 glassy electrolyte exhibiting high ionic conductivity can be achieved by optimizing the molding pressure and temperature. The optimal molding pressur...

Under Pressure: Mechanochemical Effects on Structure and Ion Conduction in the Sodium-Ion Solid Electrolyte Na3PS4

“…Similar observations of increased conductivity upon pressing were found from recent variable-pressure conductivity measurements on the isostructural Na3SbS4 44 . These observations are analogous to variations of measured ionic conductivity as a function of pellet preparation which has been reported for several solid electrolytes [64][65][66] , including ball-milled Na3PS4 56 . We attribute this to extrinsic effects on macroscopic ionic percolation through the consolidation of the pellet, improving particle-particle and pellet-electrode contact.…”

Sulfide and Oxide Inorganic Solid Electrolytes for All-Solid-State Li Batteries: A Review

“…Subsequently, many research groups explored the composition of LPS, to elucidate the crystal structure, ionic conductivity, and fabrication of LPS-based ASSBs. Garcia-Mendez et al [219] reported the effect of molding pressure on mechanical and ionic conductivity values of LPS electrolyte, and recently, Ohno et al [220] summarized various other factors which influence the electrical properties of sulfate electrolytes.…”

“…red the composition of LPS, to elucidate the crystal structure, ionic conductivity, ation of LPS-based ASSBs. Garcia-Mendez et al [219] reported the effect of molding pres echanical and ionic conductivity values of LPS electrolyte, and recently, Ohno et al arized various other factors which influence the electrical properties of sulfate electrolyte ii) Homma et al [221] studied the crystal structure and phase transitions of temperature synchrotron XRD and thermal studies were used to determine that LPS exhi phase transitions at different temperatures. The γ, β, and α phases were present at um (300−450 °C), and high (473 °C) temperature.…”

“…The lithium phosphorus sulfide (Li 3 PS 4 , LPS) electrolyte was derived from the (100 − x )Li 2 S– x P 2 S 5 binary system for x = 25 [ 203 , 204 , 209 , 210 , 211 , 212 , 213 , 214 , 215 , 216 , 217 , 218 , 219 , 220 , 221 , 222 , 223 , 224 , 225 , 226 , 227 , 228 , 229 , 230 , 231 , 232 , 233 , 234 , 235 , 236 , 237 , 238 ]. The first report on LPS was published by Tachez et al [ 212 ] in 1984; later on, Eckert et al [ 213 ] performed solid NMR studies on these systems.…”

Hybrid Li‐S pouch cell with a reinforced sulfide glass solid‐state electrolyte film separator

“…To circumvent these challenges, hot pressing can be used to consolidate sulfide-based SSE separators. [22][23][24][25][26] Hot pressing involves heating sulfide glass above its glass transition temperature so that applied pressure can effect densification through sintering and viscoplastic flow. Depending on composition, the glass transition temperature of sulfide-based SSEs ranges from about 200-350°C, which is a fraction of the temperature required to sinter oxide ceramics.…”