SURFACE TREATMENT OF A SULFIDE GLASS SOLID ELECTROLYTE LAYER

Abstract

Chemically treating ionically conductive sulfide glass solid electrolyte separators or separator layers can improve performance. In particular, treatment involving chemically etching a surface or surface region of the sulfide glass separator to blunt, lessen or remove edge defects or surface flaws, and/or to enhance surface smoothness is cost effective, reliable and well suited for high production environments compared to physical methods of removing scratches or smoothing surfaces, such as mechanical grinding and polishing.

Claims

1. A method for treating a surface of an ion conductive sulfide glass solid electrolyte, the method comprising exposing a surface or surface region of the sulfide glass solid electrolyte to an etching media.

2. The method of claim 1 wherein the etching media is a liquid etching solution comprising water and a carrier solvent that is inert in direct contact with the sulfide glass.

3. The method of claim 1 wherein water is the etching media active etching species.

4. The method of claim 2 wherein the inert carrier solvent is acetonitrile.

5. The method of claim 2 wherein the inert carrier solvent is a glyme.

6. The method of claim 2 wherein the concentration of water in the etching solution is between 0.01 to 2 Molar.

7. The method of claim 2 wherein the concentration of water in the etching solution is between 0.01 to 0.1 Molar.

8. A method for treating a sulfide glass solid electrolyte, the method comprising contacting the sulfide glass solid electrolyte with an etching solution comprising an organic carbonic acid that serves as an active etchant in the etching solution.

9. The method of claim 8 wherein organic carbonic acid is selected from the group consisting of formic acid, acetic acid, propionic acid, butyric acid, oxalic acid, and malonic acid.

10. The method of claim 8 wherein the etching solution comprises a carrier solvent that is inert in direct contact with the sulfide glass.

11. The method of claim 10 wherein the carrier solvent is an aprotic solvent.

12. The method of claim 11 wherein the carrier solvent is selected from the group consisting of glymes and organic carbonates.

13. The method of claim 10 wherein the organic carbonic acid is a solid at standard temperature and pressure and soluble in the carrier solvent.

14. The method of claim 13 wherein the solid organic carbonic acid is oxalic acid or malonic acid.

15. The method of claim 8 wherein the concentration of the organic carbonic acid in the etching solution is between 0.1 to 2 Molar.

16. The method of claim 8 wherein the concentration of the organic carbonic acid in the etching solution is between 0.1 to 0.01 Molar.

17. The method of any of claim 1, wherein i) the lithium ion conducting sulfide glass solid electrolyte has first and second major opposing and substantially parallel surfaces and peripheral edge surfaces, and at least one of said surfaces includes a defect that degrades the mechanical strength of the sulfide glass solid electrolyte; and ii) the mechanical strengthen of the sulfide glass solid electrolyte is increased by contacting the defect with an etching solution.

18. The method of claim 17 wherein the etching solution comprises water as an active etchant and further comprises a carrier solvent that is inert in direct contact with the sulfide glass sheet.

19. A method for treating a sulfide glass solid electrolyte, the method comprising: i) providing a lithium ion conducting sulfide glass solid electrolyte having a first and second surface region; ii) providing an etching media; iii) providing an etching mask having first and second opposing surfaces; iii) positioning the etching mask to cover the first surface region of the sulfide glass solid electrolyte, wherein the mask first surface adjacently opposes the sulfide glass solid electrolyte first surface region; iv) exposing the sulfide glass solid electrolyte to the etching media; wherein the etching media directly contacts the mask second surface; and further wherein the mask prevents contact between the first surface region and the etching media.

20. The method of claim 19 wherein the etching media comprises water as an active etchant and further comprises a carrier solvent that is inert in direct contact with the sulfide glass electrolyte.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0013] FIG. 1 illustrates sulfide glass sheet/membranes having various useful edge shapes in accordance with embodiments.

DETAILED DESCRIPTION

[0014] Reference will now be made in detail to specific embodiments. Examples of the specific embodiments are illustrated in the accompanying drawings. While the disclosure will be described in conjunction with these specific embodiments, it will be understood that it is not intended to limit the disclosure to such specific embodiments. On the contrary, it is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the disclosure as defined by the appended claims. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present disclosure. Embodiments described in the present disclosure may be practiced without some or all of these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present disclosure.

[0015] When used in combination with “comprising,” “a method comprising,” “a device comprising” or similar language in this specification and the appended claims, the singular forms “a,” “an,” and “the” include plural reference unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs.

[0016] In one aspect the present disclosure provides methods for chemically strengthening a Li ion conducting sulfide glass solid electrolyte. In various embodiments the sulfide glass solid electrolyte is in the form of a sheet as described in U.S. Pat. No. 10,164,289, hereby incorporated by reference for its disclosure relating to sulfide glass solid electrolyte structure, fabrication and composition. Non-limiting examples of sulfide glass solid electrolyte compositions that may be fabricated into a glass sheet separator include lithium phosphorous sulfide, lithium phosphorous oxysulfide, lithium boron sulfide, lithium boron oxysulfide, lithium boron phosphorous oxysulfide, lithium silicon sulfide, lithium silicon oxysulfide, lithium germanium sulfide, lithium germanium oxysulfide, lithium arsenic sulfide, lithium arsenic oxysulfide, lithium selenium sulfide, lithium selenium oxysulfide, lithium aluminum sulfide, lithium aluminum oxysulfide, and combinations thereof.

[0017] The present disclosure is not limited to any particular sulfide glass composition. However, it is particularly useful for sulfide glasses that are highly sensitive to water, and decompose in the presence of excess water. For this reason it is somewhat counter intuitive that in various embodiments the active etchant is water (i.e., water molecules). Indeed, conventional etching solutions which may be used to textualize or strengthen structural silicate glasses are aqueous acids that are chemically incompatible in contact with sulfide glass solid electrolytes and therefore entirely unsuitable for use herein as an etching media.

[0018] In accordance with the present disclosure, in various embodiments the chemical etching process is a hydrolytic etch that involves hydrolysis at the sulfide glass solid electrolyte surface, the etching media including water molecules as the active etchant (e.g., liquid phase or vapor phase). In the presence of water or its vapor, ionically conductive sulfide glasses generally undergo rapid hydrolysis followed by evolution of hydrogen gas. In various embodiments the hydrolysis rate may be reduced and controlled by mixing water with one or more non-aqueous solvents as the etching media. For instance, using non-aqueous solvents mixed with a low concentration of water as the chemical etchant. In various embodiments the concentration of water in the etching solution is between 0.01 to 2 Molar, and in particular embodiments, the etching solution is between 0.01 to 0.1 Molar or between 0.1 to 0.2 Molar or between 0.2 to 0.5 Molar. For example, such mixtures of water with acetonitrile or glymes, such as monoglyme (DME), may be used to decrease the rate of glass etching via hydrolysis. In other embodiments a gaseous mixture of water vapor and a carrier gas for which the glass sheet is inert may be used for controlling the etching rate. For example, the gaseous etching media may be a mixture of water vapor (as the active etchant) with nitrogen or argon as the carrier gas.

[0019] In various embodiments hydrolytic etching of the sulfide glass sheet produces a hydrolysis product, such as a salt, that is poorly soluble in water and the other non-aqueous solvents which are used in the etching media as an inert carrier. The presence of insoluble products can lead to the formation of a solid precipitate on the glass surface and a progressive reduction in the rate of surface etching. For instance, hydrolysis of Li2S-P2S5 glasses leads to formation of lithium orthophosphate having low solubility in water. To mitigate solid precipitation taking place during the etching process, in various embodiments the etching media includes a solid product dissolving additive that is able to dissolve otherwise insoluble products resulting from the hydrolytic etch. In various embodiments the dissolving additive is an inorganic acid such as hydrochloric acid or sulfuric acid. In various embodiments the acid is dissolved in the carrier solvent. For instance, a nitrile such as acetonitrile is a particular suitable carrier solvent as it is inert in contact with the sulfide glass solid electrolyte and miscible with inorganic acids. For instance, concentrations of the dissolving additive may be in the range of 0.1 to 5 vol %. In a particular embodiment the etching media is a mixture of acetonitrile, water, and hydrochloric acid (e.g., having a hydrochloric acid concentration in the range of 0.1 to 5 vol % and a concentration of water in the range of 0.01 to 2 Molar). Because some inorganic acids are soluble in acetonitrile, it is contemplated to use low concentrations of hydrochloric or sulfuric acid in acetonitrile as the etching media. In various embodiments the process involves etching a surface or surface region of the sulfide glass solid electrolyte followed by rinsing the surface with an excess of acetonitrile, which does not react with sulfide glasses.

[0020] In various embodiments organic carbonic acids are used as the etchant, and, in particular, formic, acetic, propionic, butyric, oxalic, and malonic acids.

[0021] Liquid formic, acetic, propionic and butyric acids are miscible with aprotic solvents that are not reactive with sulfide glasses, and in particular glymes and organic carbonates. The solid carbonic acids such as oxalic and malonic acids have significant solubility in these solvents. In various embodiments, to control the rate of glass hydrolysis (or completely eliminate it), mixtures of formic, acetic, propionic and butyric acids with glymes, in particular dimethyl ether (DME), diglyme and triglyme may be used as carrier solvent, and/or organic carbonates, in particular, dimethyl carbonate (DMC).

[0022] The carbonic acid based etching media may be used in liquid phase. It is also contemplated to use a vapor of carbonic acids or their mixtures with carrier gases (e.g., nitrogen or argon). Regulation of the acid vapor pressure may be achieved by controlling the temperature and/or adjusting the ratio between the acid in the vapor phase and the carrier gas.

[0023] In various embodiments, the extent of etching may be controlled, in part, by modifying the composition of the etching media, as described above, as well as the duration of etching. Etching times may vary from seconds to minutes depending on the type of flaw or defect and more generally on the amount of material to be removed. In various embodiments these parameters are selected to remove an equivalent thickness of glass of about 0.1, 0.3, 0.5, 1.0, or about 5.0 microns, and in some embodiments, it is contemplated to remove more than 5 microns (e.g., between 5 to 10 microns) of glass.

[0024] In various embodiments the chemical etching process involves multiple etching steps. For instance, an initial controlled hydrolysis step using a water-based etchant followed by applying an acidic solution onto the etched surface to dissolve insoluble products formed during the hydrolytic etch, and especially those precipitates with low solubility in water. Once any surface precipitates or sludge has been removed by acid dissolution, a final rinsing may be applied to remove any residual products (water and acids) using aprotic solvent(s), such as glymes and organic carbonates.

[0025] In various embodiments a mask may be used to limit exposure of the etching media to only those areas intended for etching and material/defect removal. For instance, in various embodiments it is particularly important to etch the edges of the glass sheet or web in order to remove flaws that may result from trimming the edges during glass sheet manufacturing. In such embodiments the mask is positioned to cover the major opposing surfaces of the glass sheet while only exposing a narrow width along the sheet edge (e.g., the exposed width of about 10 um to 1 mm wide).

[0026] The material makeup of the mask depends, in part, on the composition of the etching media. In various embodiments the masks may be fabricated from metal and/or plastic layers.

[0027] For wet etching using a liquid solution of carbonic acid, as described, particularly useful masks may be made from chromium, titanium, aluminum, and nickel, for example. Titanium masks are particularly suitable for etching media based on acetic, formic, malonic, butyric and propionic acids. Nickel masks are particularly suitable for use with malonic, oxalic, and formic acids. And aluminum masks for use with propionic and butyric acid.

[0028] In various embodiments, a liquid mask may be employed. For instance mineral oil may be applied onto the surfaces of the sulfide glass solid electrolyte sheet or membrane and thereon serve as a masking overlayer. Methods for applying a mineral oil liquid mask include coating and printing techniques. In accordance with the present disclosure, in various embodiments the etching process may be incorporated as an inline station when fabricating a sulfide glass solid electrolyte sheet (e.g., using a drawdown process) and in particular for web and roll to roll manufacture. U.S. Pat. No. 10,164,289 describes manufacturing methods for making a web of sulfide glass solid electrolyte sheet (e.g., in line with drawing the sheet and trimming the edges to a certain width). In accordance with the present disclosure, wet etching processes, as disclosed herein, may be incorporated as an inline station for the web manufacture after the drawn down or otherwise processed sheet has been trimmed (e.g., mechanically sliced or laser cut).

[0029] In various embodiments the chemical etching processes described herein may be applied to the edge surfaces of a sulfide glass solid electrolyte sheet to modify the edge shape for sealing the glass electrolyte when incorporated in a battery cell. In particular shaping the edges may be used to optimize edge sealing of the glass separator to an adjacent electrode (e.g., cathode or anode) or some other component in the battery cell. In FIG. 1 sulfide glass sheet/membranes 101a/b/c having various useful edge shapes, for example for facilitating sealing to adjacent battery cell components, are illustrated in cross sectional depiction. This approach is particularly useful for edge sealing in battery cells that include a liquid electrolyte that should be prevented from contacting the electroactive material of one of the electrodes.

CONCLUSION

[0030] Although the foregoing has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing both the process and compositions of the present disclosure. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.

[0031] All references cited herein are incorporated by reference for all purposes.