SODIUM/LITHIUM PHOSPHOROTHIOATES AS NOVEL SOLID-STATE ELECTROLYTE FOR SODIUM/LITHIUM BATTERY

Abstract

The disclosure relates to solid-phase and molten metal phosphorothioates useful as electrolytes, batteries comprising solid-phase and molten metal phosphorothioates, and methods of making solid-phase and molten metal phosphorothioates.

Claims

1. A solid-phase or molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

2. The solid-phase or molten electrolyte of claim 1, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is 1:1.

3. The solid-phase or molten electrode of claim 1, wherein x is an integer from 6 to 8.

4. The solid-phase or molten electrode of claim 3, wherein x is 8.

5. A solid-state battery comprising a cathode, an anode, and a solid-state electrolyte in contact with the cathode and the anode, wherein the cathode and/or anode comprise: an active material; optionally a conductive additive; and a solid-state qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex, wherein: the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:2 and 2:1; and x is an integer from 1 to 12; and wherein the solid-state electrolyte comprises a solid-phase mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and wherein x is an integer from 1 to 12.

6. The solid-state battery of claim 5, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is 1:1.

7. The solid-state battery of claim 5, wherein x of the solid-state qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 8.

8. The solid-state battery of claim 5, wherein the cathode and/or anode further comprise a molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:2 and 2:1; and y is an integer from 1 to 12.

9. The solid-state battery of claim 8, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is 1:1.

10. The solid-state battery of claim 8, wherein y is 8.

11. The solid-state battery of claim 8, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are the same and x and y are the same.

12. The solid-state battery of claim 11, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are different or x and y are different.

13. The solid-state battery of claim 8, wherein the cathode and/or the anode comprise a continuous interphase.

14. A method of manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises: mixing sodium sulfide (Na.sub.2S), phosphorus pentasulfide (P.sub.2S.sub.5), and sulfur powder (S) in an organic solvent to form a solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; and exposing the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex to less-than-atmospheric pressure to precipitate a solid-phase mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

15. The method of claim 14, wherein organic solvent is selected from the group consisting of diethylene glycol dimethyl ether (diglyme), 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, tetraethylene glycol dimethyl ether, and methyl acetate.

16. The method of claim 14, wherein organic solvent is diglyme.

17. The method of claim 14, wherein the concentration of solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is between about 0.5 M and about 2 M.

18. The method of claim 17, wherein the concentration of solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is about 1.5 M.

19. A method of manufacturing a molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises: manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex according to the method of claim 12; and heating the solid-phase electrolyte to form the molten electrolyte; wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

20. The method of claim 19, wherein the solid-phase electrolyte is heated at a temperature of from about 50 C. to about 120 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 is a schematic of the complexation and precipitation process to produce mP.sub.2S.sub.5-nNa.sub.2S.sub.x solids.

[0008] FIG. 2 is a set of photos of P.sub.2S.sub.5Na.sub.2S and P.sub.2S.sub.5Na.sub.2S.sub.8 in diglyme.

[0009] FIG. 3 is a set of photos of mP.sub.2S.sub.5-nNa.sub.2S.sub.8 (m:n=4:5, 2:3, 4:7 and 1:2) in diglyme.

[0010] FIG. 4 is a set of Raman profiles of P.sub.2S.sub.5Na.sub.2S.sub.x (x=1, 6, 8) and mP.sub.2S.sub.5-nNa.sub.2S.sub.8 (m:n=4:5, 2:3, 4:7, 1:2) in diglyme.

[0011] FIG. 5 is a photo of P.sub.2S.sub.5Na.sub.2S.sub.8 in 0.5 M, 1.0 M and 1.5 M concentrations in diglyme.

[0012] FIG. 6 is a set of Raman profiles of P.sub.2S.sub.5Na.sub.2S.sub.8 in diglyme at different concentrations (0.5, 1.0 and 1.5M correspond to 28, 55, 83 wt % solid-to-liquid ratios, respectively).

[0013] FIG. 7 is a set of Raman profiles of P.sub.2S.sub.5Na.sub.2S.sub.8 solids produced using different solvents.

[0014] FIG. 8A is a Raman profile of P.sub.2S.sub.5Na.sub.2S.sub.8 solids.

[0015] FIG. 8B is an X-ray diffraction profile of P.sub.2S.sub.5Na.sub.2S.sub.8 solids.

[0016] FIG. 8C is a Raman profile of P.sub.2S.sub.5Na.sub.2S solids.

[0017] FIG. 8D is an X-ray diffraction profile of P.sub.2S.sub.5Na.sub.2S solids.

[0018] FIG. 9 is a set of X-ray photoelectron spectroscopy profiles of P.sub.2S.sub.5Na.sub.2S.sub.8, P.sub.2S.sub.5Na.sub.2S.sub.6 and P.sub.2S.sub.5Na.sub.2S solids.

[0019] FIG. 10 is a graph depicting .sup.31P solid-state nuclear magnetic resonance of P.sub.2S.sub.5Na.sub.2S.sub.8 and P.sub.2S.sub.5Na.sub.2S solids.

[0020] FIG. 11A is a differential scanning calorimetry (DSC) curve of P.sub.2S.sub.5Na.sub.2S.sub.8 solid.

[0021] FIG. 11B is an enlarged DSC curve of P.sub.2S.sub.5Na.sub.2S.sub.8 solid.

[0022] FIG. 12A is a DSC curve of P.sub.2S.sub.5Na.sub.2S solid.

[0023] FIG. 12B is an enlarged DSC curve of P.sub.2S.sub.5Na.sub.2S solid.

[0024] FIG. 13 is a Ramen profile of melt phase (i.e., molten) P.sub.2S.sub.5Na.sub.2S.sub.8.

[0025] FIG. 14 is a depiction of the proposed molecular structure of P.sub.2S.sub.5Na.sub.2S.sub.8 solid/melt.

[0026] FIG. 15A is a schematic configuration of split cells for electrochemical impedance spectroscopy measurement.

[0027] FIG. 15B is a real set-up of split cells for electrochemical impedance spectroscopy measurement.

[0028] FIG. 16 is a set of electrochemical impedance spectroscopy curves of P.sub.2S.sub.5Na.sub.2S.sub.8, P.sub.2S.sub.5Na.sub.2S.sub.6 and 4P.sub.2S.sub.5-5Na.sub.2S.sub.8 solids.

[0029] FIG. 17 is a cyclic voltammetry curve of P.sub.2S.sub.5Na.sub.2S.sub.8 solid electrolyte.

[0030] FIG. 18 is a set of electrochemical impedance spectroscopy curves of P.sub.2S.sub.5Na.sub.2S.sub.8 melt after cooling for 10 minutes and 2 hours. No solidification was observed after cooling at 20 C. overnight.

[0031] FIG. 19 is a comparison of electrode preparation for solid-state batteries using the traditional method and using proposed method with molten P.sub.2S.sub.5Na.sub.2S.sub.8 in lieu of binder.

DETAILED DESCRIPTION

[0032] Unless defined otherwise, all technical and scientific terms used herein generally have the same meaning as commonly understood by one of ordinary skill in the art. Generally, the nomenclature used herein and the laboratory procedures in cell culture, molecular genetics, organic chemistry, and peptide chemistry are those well-known and commonly employed in the art.

[0033] As used herein, the articles a and an refer to one or to more than one (i.e., to at least one) of the grammatical object of the article. By way of example, an element means one element or more than one element. Furthermore, use of the term including as well as other forms, such as include, includes, and included, is not limiting.

[0034] As used herein, the term about will be understood by persons of ordinary skill in the art and will vary to some extent on the context in which it is used. As used herein when referring to a measurable value such as an amount, a temporal duration, and the like, the term about is meant to encompass variations of 20% or 10%, including 5%, 1%, and 0.1% from the specified value, as such variations are appropriate to perform the disclosed methods.

Solid-Phase and Molten Electrolytes

[0035] In one aspect, the present disclosure provides a solid-phase or molten electrolyte comprising an mP.sub.2S.sub.5-nM.sub.2S.sub.x complex, wherein: M is Li or Na; the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is between 1:2 and 2:1; and x is an integer from 1 to 12.

[0036] In some embodiments, M is Li. In some embodiments, M is Na.

[0037] The molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is between 1:2 and 2:1. Accordingly, by nonlimiting example, the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) may be 1:2, 4:7, 2:3, 4:5, 1:1, 5:4, 3:2, 7:4, or 2:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is between 1:1.5 and 1.5:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is between 1:1.25 and 1.25:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is between 1:1.1 and 1.1:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (m:n) is 1:1.

[0038] In some embodiments, x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. In some embodiments, x is an integer from 5 to 9. In some embodiments, x is an integer from 6 to 8. In some embodiments, x is 1. In some embodiments, x is 6. In some embodiments, x is 8.

[0039] In some embodiments, the electrolyte is a solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has an amorphous structure. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 100 C. higher, at least 110 C. higher, at least 120 C. higher, at least 130 C. higher, at least 140 C. higher, at least 150 C. higher, at least 160 C. higher, at least 170 C. higher, at least 180 C. higher, or at least 190 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 100 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 140 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 180 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte.

[0040] In some embodiment, the electrolyte is a molten electrolyte. In some embodiments, the molten electrolyte does not solidify at a temperature of 0 C., 10 C., 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., or 90 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 0 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 50 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 90 C.

[0041] Sodium (Na), as used in the present disclosure, possesses certain chemical/physical properties similar to Li, but Na also has several advantages over Li. By way of example, Na's first ionization energy of 495.8 kJ mol.sup.1 is lower than that of Li (520.2 kJ mol.sup.1), leading to improved kinetics in chemical reactions. As an earth-abundant element, Na is over 1000 times more abundant than Li in the earth crust. The cost of Na raw materials (carbonate salt) is more than 100 times less expensive than that of Li.

[0042] Accordingly, in another aspect, the present disclosure provides a solid-phase or molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein: the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1; and x is an integer from 1 to 12.

[0043] The molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1. Accordingly, by nonlimiting example, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) may be 1:2, 4:7, 2:3, 4:5, 1:1, 5:4, 3:2, 7:4, or 2:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:1.5 and 1.5:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:1.25 and 1.25:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:1.1 and 1.1:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is 1:1.

[0044] In some embodiments, x is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. In some embodiments, x is an integer from 5 to 9. In some embodiments, x is an integer from 6 to 8. In some embodiments, x is 1. In some embodiments, x is 6. In some embodiments, x is 8.

[0045] In some embodiments, the electrolyte is a solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has an amorphous structure. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 100 C. higher, at least 110 C. higher, at least 120 C. higher, at least 130 C. higher, at least 140 C. higher, at least 150 C. higher, at least 160 C. higher, at least 170 C. higher, at least 180 C. higher, or at least 190 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 100 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 140 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte. In some embodiments, the solid-phase electrolyte has a melting point (T.sub.m) that is at least 180 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase electrolyte.

[0046] In some embodiment, the electrolyte is a molten electrolyte. In some embodiments, the molten electrolyte does not solidify at a temperature of 0 C., 10 C., 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., or 90 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 0 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 50 C. In some embodiments, the molten electrolyte does not solidify at a temperature of 90 C.

Solid-State Batteries

[0047] In another aspect the present disclosure provides a solid-state battery comprising a cathode, an anode, and a solid-state electrolyte in contact with the cathode and the anode, wherein the cathode and/or the anode comprise an active material, optionally a conductive additive, and a solid-state qP.sub.2S.sub.5-rM.sub.2S.sub.x complex; wherein M is Li or Na; the molar ratio of P.sub.2S.sub.5 to M.sub.2S.sub.x (q:r) is between 1:2 and 2:1; and wherein x is an integer from 1 to 12; wherein the solid-state electrolyte comprises a solid-phase mP.sub.2S.sub.5-nM.sub.2S.sub.x complex; wherein M is Li or Na; the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1; and wherein x is an integer from 1 to 12.

[0048] In general, the solid-state batteries of the disclosure include two electrodes (an anode and a cathode) and a solid-state electrolyte, which is sandwiched between the anode and cathode. The electrodes of the solid-state battery may contain conductive additives (electronic conductivity), binders, active materials, and a solid-state electrolyte (ionic conductivity).

[0049] In some embodiments, the solid-phase qP.sub.2S.sub.5-rM.sub.2S.sub.x complex is a solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex, wherein: the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:2 and 2:1; and x is an integer from 1 to 12.

[0050] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:1.5 and 1.5:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:1.25 and 1.25:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:1.1 and 1.1:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is 1:1.

[0051] In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is an integer from 5 to 9. In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is an integer from 6 to 8. In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 1. In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 6. In some embodiments, x of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 8.

[0052] In some embodiments, the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex has an amorphous structure. In some embodiments, the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex has a melting point (T.sub.m) that is at least 100 C. higher, at least 110 C. higher, at least 120 C. higher, at least 130 C. higher, at least 140 C. higher, at least 150 C. higher, at least 160 C. higher, at least 170 C. higher, at least 180 C. higher, or at least 190 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex. In some embodiments, the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex has a melting point (T.sub.m) that is at least 100 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex. In some embodiments, the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex has a melting point (T.sub.m) that is at least 140 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex. In some embodiments, the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex has a melting point (T.sub.m) that is at least 180 C. higher than the freezing point (T.sub.f) of the molten form of the solid-phase qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex.

[0053] In some embodiments, the cathode and/or the anode further comprise one or more conductive additives.

[0054] In some embodiments, the cathode and/or the anode further comprise one or more active materials. By nonlimiting example, active materials suitable for inclusion in the anode include TiO.sub.2, Sn, Sb and P. By nonlimiting example, active materials suitable for inclusion in the cathode include Na.sub.3V.sub.2(PO.sub.4).sub.3, Na.sub.xCoO.sub.2, LiCoO.sub.2, Na.sub.xMnO.sub.2, LiMnO.sub.2, LFMP (lithium-iron-manganese-phosphate) and NCMA (nickel, cobalt, manganese, aluminum).

[0055] In some embodiments, the cathode and/or the anode further comprise a molten aP.sub.2S.sub.5-bM.sub.2S.sub.y complex, wherein: M is Li or Na; the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:2 and 2:1; and y is an integer from 1 to 12.

[0056] In some embodiments, the cathode and/or the anode further comprise a molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex, wherein: the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:2 and 2:1; and y is an integer from 1 to 12.

[0057] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:1.5 and 1.5:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:1.25 and 1.25:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:1.1 and 1.1:1. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is 1:1.

[0058] In some embodiments, y is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. In some embodiments, y is an integer from 5 to 9. In some embodiments, y is an integer from 6 to 8. In some embodiments, y is 1. In some embodiments, y is 6. In some embodiments, y is 8.

[0059] In some embodiments, the molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex does not solidify at a temperature of 0 C., 10 C., 20 C., 30 C., 40 C., 50 C., 60 C., 70 C., 80 C., or 90 C. In some embodiments, the molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex does not solidify at a temperature of 0 C. In some embodiments, the molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex does not solidify at a temperature of 50 C. In some embodiments, the molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex does not solidify at a temperature of 90 C.

[0060] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are the same. In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are the different.

[0061] In some embodiments, x and y are the same. In some embodiments, x and y are the different.

[0062] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are the same, and x and y are the same.

[0063] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are different, or x and y are different.

[0064] In some embodiments, the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are different, and x and y are different.

[0065] In some embodiments, the cathode and/or the anode comprise a continuous interphase.

[0066] An electrode (i.e., a cathode or anode) having a continuous interphase is one that lacks significant voids between the component parts of the electrode. Traditionally prepared electrodes employ the use of binders to form a closely packed structure. Typical binders, however, are poorly conductive as compared to the solid-phase electrolyte and cannot completely fill the interstitial spaces between the other components of the electrodes. Thus, traditional electrodes contain voids within their structure and are characterized as having a discontinuous interphase (FIG. 19). By employing molten aP.sub.2S.sub.5-bM.sub.2S.sub.y complexes (which possess high conductivity and are fluid in nature) as ion conductive interphases in lieu of traditional binders, the electrodes of the present disclosure are able to overcome certain disadvantages of traditional electrodes.

Fabrication of Solid-Phase and Molten Electrolytes

[0067] In contrast to traditional syntheses of solid sulfide electrolytes, which require high energy and temperature, the solid-phase and molten electrolytes of the present disclosure can be produced via a cost-effective, scalable process with low energy and temperature requirements. The process involves two main steps: complexation of precursors in a solvent, and solid precipitation of the complexes from the solution.

[0068] Accordingly, in an aspect, the present disclosure provides a method of manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises: mixing sodium sulfide (Na.sub.2S), phosphorus pentasulfide (P.sub.2S.sub.5), and sulfur powder (S) in an organic solvent to form a solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; and exposing the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex to less-than-atmospheric pressure to precipitate a solid-phase mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1, and x is an integer from 1 to 12.

[0069] Organic solvents suitable for use in the methods of the disclosure will be identifiable by those skilled in the art. By non-limiting example, the organic solvent may be diethylene glycol dimethyl ether (diglyme), 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, tetraethylene glycol dimethyl ether, or methyl acetate. In some embodiments, the organic solvent is diglyme, 1,2-dimethoxyethane, 1,3-dioxolane, or methyl acetate. In some embodiments, the organic solvent is diglyme.

[0070] The concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation may, by nonlimiting example, be between about 0.1 M and about 4 M. In some embodiments, the concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is between about 0.5 M and about 2 M. In some embodiments, the concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is between about 0.5 M and about 1.5 M. In some embodiments, the concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is about 0.5 M. In some embodiments, the concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is about 1 M. In some embodiments, the concentration of the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is about 1.5 M.

[0071] In some embodiments, the method further comprises transferring the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex to a quartz crucible prior to exposing the complex to less-than-atmospheric pressure. In some embodiments, the method further comprises sealing the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in a vacuum tube under an inert gas prior to exposing the complex to less-than-atmospheric pressure. In some embodiments, the inert gas is argon.

[0072] In some embodiments, the less-than-atmospheric pressure is between about 0.001 MPa and about 0.25 MPa. In some embodiments, the less-than-atmospheric pressure is between about 0.025 MPa and about 0.1 MPa. In some embodiments, the less-than-atmospheric pressure is about 0.05 MPa.

[0073] In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is heated while under less-than-atmospheric pressure. In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is heated at a temperature between about 100 C. and about 200 C. while under less-than-atmospheric pressure. In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is heated at a temperature of about 150 C. while under less-than-atmospheric pressure.

[0074] In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is exposed to less-than-atmospheric pressure for at least 0.5 hours, at least 1 hour, at least 1.5 hours, at least 2 hours, at least 2.5 hours, at least 3 hours, at least 3.5 hours, at least 4 hours, at least 4.5 hours, or at least 5 hours. In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is exposed to less-than-atmospheric pressure for between 2 hours and 4 hours. In some embodiments, the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex is exposed to less-than-atmospheric pressure for about 3 hours.

[0075] In another aspect, the disclosure provides a method of manufacturing a molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex according to the methods disclosed herein; and heating the solid-phase electrolyte to form the molten electrolyte; wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1; and x is an integer from 1 to 12.

[0076] In some embodiments, the solid-phase electrolyte is heated at a temperature above 50 C. In some embodiments, the solid-phase electrolyte is heated at a temperature from about 50 C. to about 120 C. In some embodiments, the solid-phase electrolyte is heated at a temperature of about 60 C.

[0077] This disclosure is further illustrated by the following Items:

[0078] 1. A solid-phase or molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

[0079] 2. The solid-phase or molten electrolyte of Item 1, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is 1:1.

[0080] 3. The solid-phase or molten electrode of any of preceding Items, wherein x is an integer from 6 to 8.

[0081] 4. The solid-phase or molten electrode of any of preceding Items, wherein x is 8.

[0082] 5. A solid-state battery comprising a cathode, an anode, and a solid-state electrolyte in contact with the cathode and the anode, wherein the cathode and/or anode comprise: [0083] an active material; [0084] optionally a conductive additive; and [0085] a solid-state qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex, wherein: [0086] the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is between 1:2 and 2:1; and [0087] x is an integer from 1 to 12;
and wherein the solid-state electrolyte comprises a solid-phase mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and wherein x is an integer from 1 to 12.

[0088] 6. The solid-state battery of Item 5, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) is 1:1.

[0089] 7. The solid-state battery of any of Items 5-6, wherein x of the solid-state qP.sub.2S.sub.5-rNa.sub.2S.sub.x complex is 8.

[0090] 8. The solid-state battery of Item 5, wherein the cathode and/or anode further comprise a molten aP.sub.2S.sub.5-bNa.sub.2S.sub.y complex, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is between 1:2 and 2:1; and y is an integer from 1 to 12.

[0091] 9. The solid-state battery of Item 8, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) is 1:1.

[0092] 10. The solid-state battery of any of Items 8-9, wherein y is 8.

[0093] 11. The solid-state battery of any of Items 8-10, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are the same and x and y are the same.

[0094] 12. The solid-state battery of any of Items 8-10, wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (q:r) and the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.y (a:b) are different or x and y are different.

[0095] 13. The solid-state battery of any of Items 8-12, wherein the cathode and/or the anode comprise a continuous interphase.

[0096] 14. A method of manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises: [0097] mixing sodium sulfide (Na.sub.2S), phosphorus pentasulfide (P.sub.2S.sub.5), and sulfur powder (S) in an organic solvent to form a solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; and [0098] exposing the solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex to less-than-atmospheric pressure to precipitate a solid-phase mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex; [0099] wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

[0100] 15. The method of Item 14, wherein organic solvent is selected from the group consisting of diethylene glycol dimethyl ether (diglyme), 1,2-dimethoxyethane, 1,3-dioxolane, tetrahydrofuran, tetraethylene glycol dimethyl ether, and methyl acetate.

[0101] 16. The method of Item 14, wherein organic solvent is diglyme.

[0102] 17. The method of any of Items 14-16, wherein the concentration of solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is between about 0.5 M and about 2 M.

[0103] 18. The method of Items 14-17, wherein the concentration of solvated mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex in the organic solvent prior to precipitation is about 1.5 M.

[0104] 19. A method of manufacturing a molten electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex, wherein the method comprises: [0105] manufacturing a solid-phase electrolyte comprising an mP.sub.2S.sub.5-nNa.sub.2S.sub.x complex according to the method of claim 12; and [0106] heating the solid-phase electrolyte to form the molten electrolyte; [0107] wherein the molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x (m:n) is between 1:2 and 2:1 and x is an integer from 1 to 12.

[0108] 20. The method of Item 19, wherein the solid-phase electrolyte is heated at a temperature of from about 50 C. to about 120 C.

EXAMPLES

Example 1: Preparation and Characterization of Sodium Phosphorothioates

[0109] Fabrication of mP.sub.2S.sub.5-nNa.sub.2S.sub.x solids via complexation and precipitation mP.sub.2S.sub.5-nNa.sub.2S.sub.x solids were produced via two main steps: complexation and precipitation (FIG. 1). During the complexation step, commercial sodium sulfide (Na.sub.2S), phosphorus pentasulfide (P.sub.2S.sub.5) and sulfur (S) powders were used as precursors for the synthesis of mP.sub.2S.sub.5-nNa.sub.2S.sub.x (1x8, molar ratio of P.sub.2S.sub.5 to Na.sub.2S.sub.x is m:n) in a solvent (e.g., diglyme). The mixture was stirred in an argon (Ar)-purged glove box at room temperature to form a solution up to a solid-to-liquid ratio of 83 wt %. During the precipitation process, the complexed solutions were then transferred to a high vacuum desiccator that is capable of pumping down to vacuum level of 0.1 bar through an external pump. The precipitation step was then proceeded under the vacuum with or without heating, where a yellow solid (e.g. P.sub.2S.sub.5Na.sub.2S.sub.8) could be obtained after the full evaporation of solvent.

Characterization Protocols

[0110] Laser Raman spectroscopy (LRS) used a Horiba labRAM HR Evolution operating at 532 nm wavelength with a double pass macro cuvette holder. Raman shifts were calibrated using the sharp characterization peak at 520 cm.sup.1 of the standard silicon sample. X-ray diffraction (XRD) was carried out using Rigaku (model no. 007) with a scanning angle 20 from 10 to 70. X-ray photoelectron spectroscopy (XPS) was conducted on a PHI Versaprobe II scanning XPS microprobe with a 0.47 eV system resolution using a monochromatic 1486.7 X-ray source. The samples were transferred into the XPS chamber via an Argon-filled, sealed vessel to avoid exposure to air. Differential scanning calorimetry (DSC) was performed using Netzsch DSC 204 F1 Phoenix. The temperature range of P.sub.2S.sub.5Na.sub.2S is 90 C. to 600 C. and the one of P.sub.2S.sub.5Na.sub.2S.sub.8 is 90 C. to 170 C. Both samples and reference were tested at a controlled rate of 10 C./min. .sup.31P solid-state nuclear magnetic resonance (ssNMR) was performed using a Bruker AVIII 500 MHz with a 4.0 mm HX probe.

Characterization of Sodium Phosphorothioates after Complexation

[0111] The mP.sub.2S.sub.5-nNa.sub.2S.sub.x family of materials can be tailored in two dimensions: the S.sub.x chain length (x) and the P.sub.2S.sub.5-to-Na.sub.2S.sub.x molar ratio (m:n). It was observed that both S.sub.x chain length and m:n molar ratio affect the nature and color of the prepared systems (FIG. 2 and FIG. 3).

[0112] Specifically, P.sub.2S.sub.5Na.sub.2S solution exhibits an orange color while the P.sub.2S.sub.5Na.sub.2S.sub.8 exhibits a yellow color. Unlike the transparency observed in two 1:1 systems, mP.sub.2S.sub.5-nNa.sub.2S.sub.8 (m:n=4:5, 2:3, 4:7 and 1:2) exhibits opacity to some extent, the colors of which become darker with the increase of Na.sub.2S.sub.8 (i.e., the decrease of m:n).

[0113] Raman spectroscopy was employed to identify the synthesized complexes and study the chemical bonding. As shown in FIG. 4, the Raman profile of P.sub.2S.sub.5Na.sub.2S shows distinctive and similar peak positions to those in P.sub.2S.sub.5Na.sub.2S.sub.x (x=6, 8), where the peaks at 388 and 418 cm.sup.1 indicate the presence of P.sup.2 while the peak at 482 cm.sup.1 is ascribed to the symmetric stretching modes of SS. The increase of the variable x leads to lower-energy shift of the SS mode. In P.sub.2S.sub.5Na.sub.2S.sub.x (x=6, 8) profiles, the band at 200215 cm.sup.1 suggests the presence of P.sup.2/P.sup.3 SROs while peaks at 386 and 493 cm.sup.1 reveal the modes in P.sup.2 SRO. The peak at 575 cm.sup.1 is assigned to T.sub.2 asymmetric stretching of tetrahedral structure.

[0114] Regarding the P.sub.2S.sub.5-to-Na.sub.2S.sub.x molar ratio (m:n), it was observed that the peak intensities become weaker with a higher content of Na.sub.2S.sub.8 (FIG. 4), possibly owing to the strong light absorption of the excess Na.sub.2S.sub.8.

Optimization and Investigation of Precipitation Step

[0115] It was determined that both solute concentration and solvent type affected the yield for the precipitation process and the efficiency of the complexation-precipitation approach. In diglyme, the concentration of P.sub.2S.sub.5Na.sub.2S.sub.8 could be prepared up to 1.5 M (83 wt % solid-to-liquid ratio), without exhibiting any obvious differences in appearance (FIG. 5) or molecular structure (FIG. 6) compared to those in 0.5 M (28 wt %) and 1.0 M (55 wt %). However, the preparation of concentrated P.sub.2S.sub.5Na.sub.2S.sub.8 in diglyme (1.5 M) required the assistance of heating (60 C.).

[0116] Besides diglyme, three other solvents1,2-dimethoxyethane (DME), 1,3-dioxolane (DOL) and methyl acetate (MA)were investigated with respect to the stability of the P.sub.2S.sub.5Na.sub.2S.sub.8 complex (FIG. 7). The precipitates from the four systems show similar Raman profiles (the solid from DOL shows an additional peak at 600700 cm.sup.1), indicating the P.sub.2S.sub.5Na.sub.2S.sub.8 complex is compatible with an array of solvents. Of the tested solvents, diglyme shows the highest solubility of P.sub.2S.sub.5Na.sub.2S.sub.8, confirming the practicality of the solvent to achieve high yield in the process.

[0117] A concentration of 1.5 M (83 wt %) in diglyme solvent was employed to produce the solid phase of P.sub.2S.sub.5Na.sub.2S.sub.8 for further characterization and electrochemical evaluation.

Characterization of the Structure and Composition of Solid P.sub.2S.sub.5Na.sub.2S.sub.8

[0118] To investigate the nature of solid P.sub.2S.sub.5Na.sub.2S.sub.8, both Raman spectroscopy and X-ray powder diffraction (XRD) were conducted using P.sub.2S.sub.5Na.sub.2S as a control. Almost no additional peak occurrence/disappearance can be observed in P.sub.2S.sub.5Na.sub.2S.sub.8 solid (FIG. 8A) as compared to the solvated complex, indicating the solid sample possesses similar composition and network structure as those in the corresponding solution sample (in diglyme). (Notably, the diglyme solvent peak (317 cm.sup.1) disappears in the solid phase spectrum). In contrast, solid P.sub.2S.sub.5Na.sub.2S (FIG. 8C) had a distinct profile from the corresponding solvated complex, suggesting a change in composition and/or structure following evaporation of the solvent. Both solids reveal amorphous phases as characterized in XRD (FIGS. 8B and 8D).

[0119] X-ray photoelectron spectroscopy (XPS) and .sup.31P solid-state nuclear magnetic resonance (ssNMR) were performed to further characterize the molecular structure of the solid P.sub.2S.sub.5Na.sub.2S.sub.8 complex. For XPS, the binding energies of all elements were calibrated with respect to C.sub.1s at 284.8 eV (FIG. 9). For the peak-fitting of S.sub.2p, the 2p.sub.3/2 to 2p.sub.1/2 area ratio is fixed at 2:1 according to the ratio of degeneracy, where 1.18 eV is employed as the doublet separation of 2p.sub.3/2 and 2p.sub.1/2. As to the peak-fitting of P.sub.2p, the 2p.sub.3/2 to 2p.sub.1/2 area ratio is fixed at 2:1 according to the ratio of degeneracy, where 0.87 eV is used as the doublet separation of 2p.sub.3/2 and 2p.sub.1/2. Studies regarding the solvated complex have revealed that long chain P.sub.2S.sub.5Na.sub.2S.sub.x (x=6, 8) possesses three main P.sup.n SROs, including P.sup.3, P.sup.2 and P.sup.2, while short chain P.sub.2S.sub.5Na.sub.2S has P.sup.2 and P.sup.0 SROs. Therefore, the peaks at 132.13, 133.50 and 134.63 eV (based on 2p.sub.3/2) in P.sub.2p can be assigned to P.sup.3, P.sup.2 and P.sup.2 in P.sub.2S.sub.5Na.sub.2S.sub.x (x=6, 8), respectively, while the ones at 133.70 and 134.42 eV can be ascribed to P.sup.2 and P.sup.0 in P.sub.2S.sub.5Na.sub.2S, respectively. As to S.sub.2p, the peaks at 162.10 and 163.75 eV are attributed to the presence of PS and SS, respectively. It was observed that samples with longer S.sub.x chain (x=6, 8) showed higher concentration of SS(bridging S in S.sub.x) over PS, compared to the short chain sample (P.sub.2S.sub.5Na.sub.2S).

[0120] The main narrow peak in the ssNMR spectrum of P.sub.2S.sub.5Na.sub.2S.sub.8 solid can be fitted with three peaks at 116.3, 115.5 and 114 ppm, representing the existence of P.sup.3, P.sup.2 and P.sup.2 (FIG. 10). In contrast, two different P sites of 118 ppm and 101.8 ppm in solid P.sub.2S.sub.5Na.sub.2S can be assigned to the presence of P.sup.2 and P.sup.0. The weak spinning sidebands are due to chemical shift anisotropy (CSA).

[0121] Differential scanning calorimetry (DSC) was carried out to investigate thermal behaviors of P.sub.2S.sub.5Na.sub.2S.sub.8 and P.sub.2S.sub.5Na.sub.2S solids (FIGS. 11A, 11B, 12A, and 12B). In particular, P.sub.2S.sub.5Na.sub.2S solid exhibited a glass transition point (T.sub.g) at 275.7 C. and an exothermic reaction at 400 C. The exothermic reaction is likely related to the crystallization process of the Na.sub.3PS.sub.4 phase. In contrast, P.sub.2S.sub.5Na.sub.2S.sub.8 solid showed a T.sub.g at 65.4 C. along with a melting point (T.sub.m) of 106.5 C. Surprisingly, it was observed that molten P.sub.2S.sub.5Na.sub.2S.sub.8 (denoted P.sub.2S.sub.5Na.sub.2S.sub.8 melt) did not solidify even after the temperature was lowered to 90 C. This observation confirms the irreversibility of T.sub.m in P.sub.2S.sub.5Na.sub.2S.sub.8. As shown in FIG. 13, the P.sub.2S.sub.5Na.sub.2S.sub.8 melt shows the same molecular structure as that of the corresponding solid.

Example 2: Ionic Conductivity and Electrochemical Stability of P.SUB.2.S.SUB.5.Na.SUB.2.S.SUB.8 .Solid

[0122] Based on the characterization data of Example 1, a molecular structure of a highly interconnected network has been proposed for P.sub.2S.sub.5Na.sub.2S.sub.8 solid/melt, which contains an open framework likely facilitating the diffusion of Na.sup.+ ions (FIG. 14).

[0123] To prepare the solid-state electrolyte for electrochemical evaluation, thin pellets were fabricated through cold-pressing process. The as-synthesized solid materials were accommodated in a dry pellet pressing die and further pressed through a cold isostatic press. The obtained pellets were then subjected to electrochemical impedance spectroscopy (EIS) measurement via split cells as depicted in FIGS. 15A and 15B.

[0124] The split cells loaded with the pellet sandwiches were pressed via the isostatic press to ensure a good contact. Electrochemical impedance spectroscopy (EIS) was conducted using an electrochemical workstation (VMP3, Bio-Logic Science Instruments) at a scanning frequency from 1 MHz to 0.1 Hz with an AC amplitude of 5 mV.

[0125] The ionic conductivity was calculated by analyzing the obtained Nyquist plot. The plot was fitted to an equivalent circuit in the form of (R.sub.bulk)(R.sub.gbQ.sub.gb)(Q.sub.electrode), where R.sub.bulk is bulk resistance, R.sub.gb is grain boundary resistance, Q.sub.gb is grain boundary capacitance, and Q.sub.electrode is double layer capacitance from the ion blocking electrodes. The bulk resistance was attributed to the end point of the semi-circle at the high-frequency zone. With the obtained bulk resistance, the ionic conductivity () could then be calculated using the equation of [=d/(R.sub.bulkA)], where d is the pellet thickness, and A is the pellet area contacting the copper pressing die. The calculated will be recorded in millisiemens per centimeter (mS/cm).

[0126] The Nyquist plot of P.sub.2S.sub.5Na.sub.2S.sub.8 solid was compared with the ones of P.sub.2S.sub.5Na.sub.2S.sub.6 solid and 4P.sub.2S.sub.5-5Na.sub.2S.sub.8 solid (FIG. 16). P.sub.2S.sub.5Na.sub.2S.sub.8 solid showed the smallest bulk resistance. After calculation, P.sub.2S.sub.5Na.sub.2S.sub.8 was determined to possess the ionic conductivity of 4.8610{circumflex over ()}(2) mS cm.sup.1 (Table 1), which is two orders of magnitude larger than that of P.sub.2S.sub.5Na.sub.2S.sub.6 and three orders of magnitude larger than that of P.sub.2S.sub.5-3Na.sub.2S (P.sub.2S.sub.5Na.sub.2S shows no conductivity). As for the m:n ratio, 4P.sub.2S.sub.5-5Na.sub.2S.sub.8 showed a much smaller value of 5.8710{circumflex over ()}(5) mS cm.sup.1 while 2P.sub.2S.sub.5-3Na.sub.2S.sub.8 was out of range. Surprisingly, the increase of Na.sub.2S.sub.8 does not improve the ionic conductivity of mP.sub.2S.sub.5-nNa.sub.2S.sub.8 even though the concentration of Na.sup.+ ions is enhanced in the bulk. Therefore, the maintenance of a highly interconnected network as depicted in FIG. 14 appears to be more critical in producing high conductivity.

[0127] The electrochemical stability of electrolytes is a key parameter affecting their utility and application. As shown in FIG. 17, the obtained P.sub.2S.sub.5Na.sub.2S.sub.8 solid electrolyte showed a stability window of 2.0 V to 4.2 V when sandwiched within two identical stainless steel current collectors.

TABLE-US-00001 TABLE 1 Summary of ionic conductivity results of mP.sub.2S.sub.5nNa.sub.2S.sub.x solids. Conductivity Conductivity (mS cm.sup.1) (mS cm.sup.1) Sample without calibration after calibration S.sub.x chain P.sub.2S.sub.5Na.sub.2S N/A N/A effect P.sub.2S.sub.5Na.sub.2S.sub.6 5.60 10{circumflex over ()}(4) 8.96 10{circumflex over ()}(4) P.sub.2S.sub.5Na.sub.2S.sub.8 3.04 10{circumflex over ()}(2) 4.86 10{circumflex over ()}(2) Ratio effect 4P.sub.2S.sub.55Na.sub.2S.sub.8 3.67 10{circumflex over ()}(5) 5.87 10{circumflex over ()}(5) 2P.sub.2S.sub.53Na.sub.2S.sub.8 Out of range Out of range Note: Commercial NASICON was used to calibrate the measured conductivity results (Measured value: 0.75 mS cm.sup.1; Reported value (from the company): 1.2 mS cm.sup.1). P.sub.2S.sub.53Na.sub.2S (stands for 2Na.sub.3PS.sub.4) shows 4.2 10{circumflex over ()}(5) mS cm.sup.1 without calibration. N/A indicates that the electrolyte system is not stable during EIS measurement.

Example 3: Novel Electrode Preparation for Solid-State Batteries Using P.SUB.2.S.SUB.5.Na.SUB.2.S.SUB.8 .Melt

[0128] The ionic conductivity and resistance of P.sub.2S.sub.5Na.sub.2S.sub.8 melt were also evaluated. The resistance of P.sub.2S.sub.5Na.sub.2S.sub.8 melt did not increase much even after cooling at 35 C. for 2 hours (FIG. 18). After calculation, the ionic conductivity of P.sub.2S.sub.5Na.sub.2S.sub.8 melt was found to be 9.1210{circumflex over ()}(3) mS cm.sup.1, only 5 times smaller than that of P.sub.2S.sub.5Na.sub.2S.sub.8 solid (Table 2).

[0129] Traditional preparation of the electrodes for solid-state batteries is a time-consuming process involves the mixing of solid electrolyte, conductive additive, binder, and active electrode materials. Furthermore, the production of voids and the formation of discontinuous interphase are issues that arise using the traditional method (FIG. 19). Consequently, the reaction kinetics and the full cell performance of traditionally prepared solid-state batteries are largely impeding.

[0130] A new approach for preparing the electrodes for solid-state batteries takes advantage of the ion-conducting property and fluidity of P.sub.2S.sub.5Na.sub.2S.sub.8 melt. Specifically, P.sub.2S.sub.5Na.sub.2S.sub.8 melt can not only provide an ionic path but also serve as binder. Therefore, the energy density and reaction kinetics of the solid-state battery can be dramatically improved by avoiding the need for heavy binder materials and by filling the voids and generating continuous interphase (FIG. 19).

TABLE-US-00002 TABLE 2 Comparison of ionic conductivity results of P.sub.2S.sub.5Na.sub.2S.sub.8 solid and melt. Conductivity (mS cm.sup.1) Conductivity (mS cm.sup.1) Sample without calibration after calibration P.sub.2S.sub.5Na.sub.2S.sub.8 solid 3.04 10{circumflex over ()}(2) 4.86 10{circumflex over ()}(2) P.sub.2S.sub.5Na.sub.2S.sub.8 melt 5.70 10{circumflex over ()}(3) 9.12 10{circumflex over ()}(3) Note: Commercial NASICON was used to calibrate the measured conductivity results (Measured value: 0.75 mS cm.sup.1; Reported value (from the company): 1.2 mS cm.sup.1).

REFERENCES

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