Solvent-Engineered Design of Argyrodite Li₆PS₅X (X = Cl, Br, I) Solid Electrolytes with High Ionic Conductivity

Abstract

Argyrodites, Li6PS5X (X = Cl, Br), are considered to be one of the most promising solid-state electrolytes for solid-state batteries. However, while traditional ball-mill approaches to prepare these materials do not promote scale-up, solution-based preparative methods have resulted in poor ionic conductivity. Herein, we report a solution-engineered, scalable approach to these materials, including the new argyrodite solid solution phase Li6–y PS5–y Cl1+y (y = 0–0.5), that shows very high ionic conductivities (up to 3.9 mS·cm–1) and negligible electronic conductivities. These properties are almost the same as their analogues prepared by solid-state methods, owing to a lack of amorphous contributions and low impurity contents ranging from 3 to 10%. Electrochemical performance is demonstrated for Li6PS5Cl in a prototype solid-state battery and compared to that of the same solid electrolyte derived from classic ball-milling processing.

Boosting Solid‐State Diffusivity and Conductivity in Lithium Superionic Argyrodites by Halide Substitution

“…Zuschriften boundary contributions could not be deconvoluted, [23] and hence the conductivity represents the total. While Li 6 PS 5 Cl exhibits aconductivity of s i = 2.5 mS cm À1 at 298 K, consistent with the literature (1.1-3.15 mS cm À1 ), [8,14,16] substitution of S 2À for Cl À results in an almost exponential increase with x ( Figure 3d). Theh ighest ionic conductivity of 9.4 AE 0.1 mS cm À1 is reached for Li 5.5 PS 4.5 Cl 1.5 ,a lmost af our-fold increase vis av is Li 6 PS 5 Cl.…”

“…[7] While room-temperature Li-ion conductivities initially reported for the Cl (1.9 mS cm À1 ) [8] and Br phases (0.7 mS cm À1 ), [9] were within practical ranges,r ecent values are even higher and comparable to those of liquid electrolytes.T otal ionic conductivities are heavily influenced by the synthesis method, grain boundary contributions,and methods used for conductivity measurements,i ncluding sintering cold-pressed pellets. [10] Solution-based Li 6 PS 5 Xs ynthesis routes typically give lower ion conductivities (10 À5 -10 À4 mS cm À1 ) [11][12][13] owing to phase impurities although recent studies using this method report high values for Li 6 PS 5 Cl and mixed anion Li 6 PS 5 (Cl,Br) argyrodites of 2.4 and 3.9 mS cm À1 ,r espectively; [14] and 3.1 mS cm À1 for Li 6 PS 5 Br. [15] Ac onductivity of 3.15 mS cm À1 for Li 6 PS 5 Cl was reported prepared by ar apid solid-state route [16] and av alue of 5mScm À1 was recently achieved upon long-term annealing,a lbeit using pellets pressed at eight tons.…”

Boosting Solid‐State Diffusivity and Conductivity in Lithium Superionic Argyrodites by Halide Substitution

“…EIS was also performed at 195 K for Li 5.5 PS 4.5 Cl 1.5 (Figure c, inset, see Tables S2, S3, Supporting Information for details) but bulk and grain boundary contributions could not be deconvoluted, and hence the conductivity represents the total. While Li 6 PS 5 Cl exhibits a conductivity of σ i =2.5 mS cm −1 at 298 K, consistent with the literature (1.1–3.15 mS cm −1 ), substitution of S 2− for Cl − results in an almost exponential increase with x (Figure d). The highest ionic conductivity of 9.4±0.1 mS cm −1 is reached for Li 5.5 PS 4.5 Cl 1.5 , almost a four‐fold increase vis a vis Li 6 PS 5 Cl.…”

“…Total ionic conductivities are heavily influenced by the synthesis method, grain boundary contributions, and methods used for conductivity measurements, including sintering cold‐pressed pellets . Solution‐based Li 6 PS 5 X synthesis routes typically give lower ion conductivities (10 −5 –10 −4 mS cm −1 ) owing to phase impurities although recent studies using this method report high values for Li 6 PS 5 Cl and mixed anion Li 6 PS 5 (Cl,Br) argyrodites of 2.4 and 3.9 mS cm −1 , respectively; and 3.1 mS cm −1 for Li 6 PS 5 Br . A conductivity of 3.15 mS cm −1 for Li 6 PS 5 Cl was reported prepared by a rapid solid‐state route and a value of 5 mS cm −1 was recently achieved upon long‐term annealing, albeit using pellets pressed at eight tons .…”

Tailoring Li6PS5Br ionic conductivity and understanding of its role in cathode mixtures for high performance all-solid-state Li–S batteries

“…8 To address these challenges, the wet chemical synthesis route based on a dissolution-reprecipitation process was proposed. [14][15][16][17][18][19] Although this solution route provides a more homogeneous electrolyte with higher repeatability compared with the mechanical milling route, it still has other issues, such as the low ionic conductivity of the final sample [18][19] and/or the application of high-toxicity solvents during the preparation process [16][17] .…”