A Low-Cost Liquid-Phase Method of Synthesizing High-Performance Li₆PS₅Cl Solid-Electrolyte

Abstract

Li 6 PS 5 Cl is an extensively studied sulfide-solidelectrolyte for developing all-solid-state lithium batteries. However, its practical application is hindered by the high cost of its raw material lithium sulfide (Li 2 S), the difficulty in its massive production, and its substandard performance. Herein we report an economically viable and scalable method, denoted as "de novo liquid phase method", which enables in synthesizing highperformance Li 6 PS 5 Cl without using commercial Li 2 S but instead in situ making Li 2 S from cheap materials of lithium chloride (LiCl) and sodium sulfide. LiCl, a raw material needed for making both Li 2 S and Li 6 PS 5 Cl, can be added at a full-scale in the beginning and unrequired to separate when making the intermediate Li 3 PS 4 . Such a consecutive feature makes this method time-efficient; and the excess amount of LiCl in the step of making Li 2 S also facilitates removing the byproduct of sodium chloride via the common ion effect. The materials cost of this method for Li 6 PS 5 Cl is ∼ $55/kg, comparable with the practical need of $50/kg. Moreover, the obtained Li 6 PS 5 Cl shows high ionic conductivity and outstanding cyclability in full battery tests, that is, ∼2 mS/cm and >99.8% retention for 400+ cycles at 1 C, respectively. Thus, this innovative method is expected to pave the way to develop practical sulfide-solid-electrolytes for all-solid-state lithium batteries.

Green Synthesis for Battery Materials: A Case Study of Making Lithium Sulfide via Metathetic Precipitation

“…Li 6 PS 5 Cl is a prime candidate among all SEs and has made remarkable progress toward practical applications. − Its synthesis herein adapted the liquid-phase approach we have recently developed, and please refer to the Supporting Information for details including its XRD characterization (Figure S7). Based on electrochemical impedance spectra (Figure a), the room-temperature ionic conductivity (σ) for Li 6 PS 5 Cl made from s-Li 2 S was 2.52 mS/cm, slightly higher than that of the c-Li 2 S counterpart (2.38 mS/cm). The temperature-dependent electrochemical impedance spectra in the range of 30–110 °C were also measured to understand the temperature dependence of σ.…”

Synthesis of Deliquescent Lithium Sulfide in Air

“…On the basis of electrochemical impedance spectroscopy (Figure a) and chronoamperometry (Figure b), the ionic conductivity and electronic conductivity for c-Li 6 PS 5 Cl (h-Li 6 PS 5 Cl) can be extracted as 2.90 mS/cm and 1.27 × 10 –6 mS/cm (4.45 mS/cm and 4.89 × 10 –6 mS/cm), respectively. These values are in the acceptable range for a typical Li 6 PS 5 Cl . Their cycling performances (Figure c) were also similar.…”

“…These values are in the acceptable range for a typical Li 6 PS 5 Cl. 45 Their cycling performances (Figure 11c) were also similar. For c-Li 6 PS 5 Cl, its charge/discharge capacities were initially 202 and 153 mA h/g, respectively, and became 82.8 and 82.7 mA h/g after 200 cycles.…”

Chemically Understanding the Liquid-Phase Synthesis of Argyrodite Solid Electrolyte Li6PS5Cl with the Highest Ionic Conductivity for All-Solid-State Batteries

“…The high-energy mechanical ball-milling causes a serious obstacle to scale-up due to much energy consumption. In contrast, liquid-phase synthesis is more suitable for large-scale manufacturing because of the low cost and high scalability. − The wet chemical reaction relies on the nature of organic solvents, which plays an important role in the solubility and reactivity of lithium thiophosphates. , The argyrodite-type Li 6 PS 5 Cl SEs were synthesized using ethyl diamine, anisole, and ethanol (EtOH) solvents. − Ethanol has a high dielectric constant and low boiling point, which facilitate the dissolution of argyrodite-type SE precursors. However, the use of ethanol results in detrimental effects: the formation of Li 3 PO 4 and enhancement of decomposition kinetics of the anion unit in the precursor solution. ,− The combination of tetrahydrofuran (THF) and EtOH still leads to the formation of Li 3 PO 4 in argyrodite-type Li 6 PS 5 Cl SEs. , This highlights that Li 3 PO 4 is produced through an anionic ring-opening reaction of THF in the wet chemical reaction.…”