Methods for manufacturing a thin solid electrolyte separator independent of or directly on the electrode for all-solid-state batteries

Abstract

Methods for making a dry electrode-solid electrolyte film and a freestanding electrolyte film are included herein. The first method includes providing an electrode layer having a working surface, applying dry solid electrolyte powder over the working surface to form an intermediate layered structure, and pressing the electrode layer and the dry solid electrolyte powder to mechanically bind them together into a dry electrode-solid electrolyte film. Here, the dry solid electrolyte powder is free of solvent and free of polytetrafluoroethylene. The second method includes providing a suspension comprising a solid electrolyte and a polymeric binder dissolved in a non polar organic solvent, milling the suspension with media to reduce the particle size of the solid electrolyte, applying a layer of the suspension, post-milling, to a substrate, drying the layer of the suspension to form a film, and delaminating the film from the substrate for a freestanding solid electrolyte separator film.

Description

Attorney Docket No. 24636.785WO1METHODS FOR MANUFACTURING A THIN SOLID ELECTROLYTE SEPARATOR INDEPENDENT OF OR DIRECTLY ON THE ELECTRODE FOR ALL-SOLID-STATE BATTERIESRELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Application No. 63 / 746,813, filed January 17, 2025, the entirety of which is incorporated herein by reference.STATEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under 2044465 awarded by the National Science Foundation. The government has certain rights in the invention.TECHNICAL FIELD

[0003] This Application relates generally to methods for manufacturing thin solid electrolyte separators, which may be described as films, more specifically, such films that are formed independent of the electrode (with a solvent) or are formed directly on the electrode (without solvent).BACKGROUND

[0004] All-solid-state batteries are constructed with a solid electrolyte, thereby providing a battery that has no liquid component. This provides an opportunity for enhanced safety eliminating the conventional liquid electrolyte, which are typically corrosive, and a strong potential for realizing a high-energy-density storage system. As such, the solid electrolyte is the cornerstone of all-solid-state battery technology and holds the key for unlocking its performance.

[0005] The bottleneck in commercializing such all-solid-state technology is the large-scale assembly of the different electrodes (e.g., cathode and anode) and the solid electrolyte separator, in particular methods that are scalable and environmentally friendly. Specifically, fabrication of the solid electrolyte separator typically involves using organic solvent, which is highly toxic and requires an energy-intensive recycling system. This can increase the production cost and environmental concerns with increasing battery demands. Moreover, Maxwell-type dry processing typically uses polytetrafluoroethylene (PTFE) as a binder, which is not electrochemically stable at low chemical potential and is difficult to form a thin (e.g., less than or equal to 200 pm) solid electrolyte film.

[0006] Some embodiments disclosed herein may address one or more of the above-noted problems by providing a manufacturing solid electrolyte separator, without binder, all-solid-state battery cell, and solid-state battery cell.SUMMARY

[0007] In some example embodiments, a method for manufacturing a thin solid electrolyte separator without binder and solvent for all-solid-state batteries is disclosed.Attorney Docket No. 24636.785WO1

[0008] In a first aspect, methods for making a dry electrode-solid electrolyte film are disclosed herein. The methods include providing an electrode layer having a working surface, applying dry solid electrolyte powder over the working surface of the electrode layer to form an intermediate layered structure, and pressing the electrode layer and the dry solid electrolyte powder to mechanically bind them together into a dry electrode-solid electrolyte film. The dry solid electrolyte powder is free of solvent and free of polytetrafluoroethylene. The electrode can be the anode or the cathode, either of which may be a composite material. In all embodiments, the dry solid electrolyte powder layer of the dry electrode-solid electrolyte film has a thickness in a range of about 30 pm to about 200 pm.

[0009] The pressing includes applying a pressure in a range of about 20 MPa to about 100 MPa to the intermediate layered structure. The pressing can be cold pressing at temperatures in a range of about 20 °C to about 120 °C, which can include passing the intermediate layered structure through a calendar machine or pressing in a mold / die.

[0010] In all embodiments, applying the dry solid electrolyte powder can include distributing the dry solid electrolyte powder over the working surface by a doctor blade or by electrospray deposit. The dry solid electrolyte powder can be selected from the group consisting of sodium closo-hydroborates (Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y), lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, NasPSe4), lithium sulfide-based (IJ3PS4, Lie-xPSsClx), lithium halide (LisZrCk, Li2YCle), and combinations thereof, wherein x and y are each in a range of 0 to 1.

[0011] Optionally, the methods can include the addition of a polymeric binder to the dry solid electrolyte powder to form an electrolyte composite. The polymeric binder can be selected from the group consisting of polyvinylidene fluorides (PVDF), polyvinyl alcohols (PVA), polyvinyl butyrals (PVB), styrene-ethylene-butylene- styrenes (SEBS), styrene-butadiene-styrenes (SBS), styrene-butadiene rubbers (SBR), and combinations thereof. In other embodiments, the dry solid electrolyte powder is free of all binders.

[0012] In some embodiments, the method can include milling the solid electrolyte powder in a non-polar organic solvent and removing the non-polar organic solvent before applying the dry solid electrolyte powder to the electrode.

[0013] In a second aspect, the dry electrode-solid electrolyte film made according to the above methods are disclosed, which results in a dry solid electrolyte powder mechanically bound to an electrode layer by cold pressing in the absence of a solvent and absence of polytetrafluoroethylene. The electrode can be the anode or the cathode, each of which can be a composite material.Attorney Docket No. 24636.785WO1

[0014] In a third aspect, methods for making a freestanding solid electrolyte separator film are disclosed herein. The methods include providing a suspension comprising a solid electrolyte and a polymeric binder dissolved in a non-polar organic solvent, milling the suspension with media to reduce the particle size of the solid electrolyte, applying a layer of the suspension, post-milling, to a substrate, drying the layer of the suspension to form a film, and delaminating the film from the substrate for a freestanding solid electrolyte separator film. The film has a thickness less than 100 pm. In all embodiments, the non-polar organic solvent is selected from the group consisting of toluene, xylene, benzene, hexane, cyclohexane heptane, octane, nonane, decane, diethyl ether, M-Cymene, 2,2,5,5-tetramethyloxolane (TMO), and combinations thereof.

[0015] The solid electrolyte powder is selected from the group consisting of sodium closo-hydroborates (Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y), lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, Na3PSe4), lithium sulfide-based (I 3PS4, Lie-xPSsCk), lithium halide (LisZrCk, Li2YCle), and combinations thereof, wherein x and y are each in a range of 0 to 1. The polymeric binder is selected from the group consisting of polyvinylidene fluorides (PVDF), polyvinyl alcohols (PVA), polyvinyl butyrals (PVB), styrene-ethylene-butylene- styrenes (SEBS), styrene-butadiene-styrenes (SBS), styrene-butadiene rubbers (SBR), and combinations thereof.

[0016] In a third aspect, all-solid-state batteries are disclosed herein that have a dry electrodesolid electrolyte film or a freestanding solid electrolyte separator film made according to any of the methods disclosed herein in operative arrangement with a primary and / or secondary electrode. These components of the al-solid-state battery are housed in a pouch cell, prismatic cell, coin cell, or cylindrical cell.

[0017] The details of one or more variations of the subject matter described herein are set forth in the accompanying drawings and the description below. Other features and advantages of the subject matter described herein will be apparent from the description and drawings, and from the claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings, which are incorporated in and constitute a part of this specification, show certain aspects of the subject matter disclosed herein and, together with the description, help explain some of the principles associated with the disclosed implementations. In the drawings,

[0019] FIG. lAis a photograph of one embodiment of a thin solid electrolyte made according to one of the methods disclosed herein, showing a solid electrolyte pre-pressed on an electrode.

[0020] FIG. IB is a photograph of a dry electrode-solid electrolyte film made according to one of the methods disclosed herein.Attorney Docket No. 24636.785WO1

[0021] FIG. 2 is an enlarged scanning electron microscope image of a cross-section of the film of FIG. 1, showing a 100 pm scale thereon, after pressing under, for example 250 MPa isostatic pressure.

[0022] FIG. 3 is a Nyquist plot of the impedance parameters Z' versus Z" for the powder and a pouch cell made therefrom, which shows minimal ionic conductivity changes after the process.

[0023] FIG. 4 is a graph of the potential profiles over three cycles of an all-solid-state battery (pouch cell) made with the thin solid electrolyte disclosed herein measured at room temperature.

[0024] FIG. 5 is a graph of the cycle number versus discharge capacity and efficiency (reversible discharge capacity) for an all-solid-state battery (pouch cell) made with the thin solid electrolyte disclosed herein, under 5 MPa isostatic pressurization at room temperature.

[0025] FIG. 6Ais a graph demonstrating the ionic conductivity of Na2(BioHio)o.5(Bi2Hi2)o.5 (NBH) before and after exposure to toluene.

[0026] FIG. 6B is a graph of X-ray diffraction measurements of NBH before and after exposure to toluene.

[0027] FIG. 7 is a series of scanning electron microscopy images of NBH particles before and after wet milling for various, sequential amounts of time.

[0028] FIG. 8 are photographs showing two embodiments of NBH films case onto polyethylene terephthalate (PET) substrates.

[0029] FIG. 9 is a photograph of freestanding NBH film after delamination from its PET substrate.

[0030] FIG. 10 is a graph of the ionic conductivity of the freestanding NBH film of FIG. 8.

[0031] FIG. 11 is a scanning electron microscopy image of a focused-ion, beam-milled, freestanding NBH film (the film of FIG. 9).

[0032] FIG. 12 is a simplistic representation of an all-solid state battery construction.DETAILED DESCRIPTION

[0033] To provide a technical solution, in some embodiments, the above and / or other aspects may be accomplished by the provision of solid electrolyte film for sodium-based or lithium based all-solid-state batteries. The electrode-solid electrolyte film may comprise a solid electrolyte cold-pressed onto the electrode below for example 100 MPa or via calendaring. After the compaction, the solid electrolyte forms a layer that adheres to the electrode for the assembly, the adhesive being a mechanical adhesion. In some embodiments, a dry-processing and powder compaction of the solid electrolyte onto the electrode is disclosed, which forms a compacted and adhered dry electrode-solid electrolyte film without a binder in the solid electrolyte layer. The adhesion is direct adhesion between the electrode and the dry solid electrolyte layer, so that the resultant architecture possesses excellent processibility for subsequent assembly in all-solid-stateAttorney Docket No. 24636.785WO1batteries. With respect to the effect of some of the embodiments, it relates to dry-processing a binder-free thin and highly ionic conductive electrolyte film for all-solid-state batteries, comprising for example lithium- or sodium-based chemistry. Some of the disclosed embodiments may thus provide a binder-free solid electrolyte film (e.g., 200 pm or less) for sodium -based all-solid-state pouch cells, which can be stably used for an electrochemical energy storage system ranging from for example 60 °C and below.

[0034] Unless otherwise indicated, all numbers expressing quantities or ingredients, measurement of properties and so forth used in the specification and embodiments are to be understood as being modified in all instances by the term "about." Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present specification and claims can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings of the present disclosure. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claimed embodiments, each numerical parameter and the word “about” as applied thereto should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques.

[0035] Referring to FIGS. 1 and 2, one embodiment of a dry electrode-solid electrolyte film 100 is shown made according to methods disclosed herein. The method includes providing an electrolyte-electrode layer 102 having a working surface 104, applying dry solid electrolyte powder 106 over the working surface 104 of the electrode layer 102 to form an intermediate layered structure, and pressing the electrolyte-electrode layer 102 and the dry solid electrolyte powder 106 of the intermediate layered structure to mechanically bind them together into a dry electrode-solid electrolyte film 100. In this dry processing method, no solvent is present, i.e., the dry solid electrolyte powder and the method steps are performed free of solvent. Additionally, the dry solid electrolyte powder is free of polytetrafluoroethylene (PTFE). Post-compaction, the dry solid electrolyte powder layer of the dry electrode-solid electrolyte film has a thickness in a range of about 30 pm to about 200 pm, preferably in a range of about 30 pm to about 150 pm, and more preferably 30 pm to about 100 pm.

[0036] The electrode can be an anode or a cathode, which can be a composite material. The anode composite material can consist of hard carbon, Sn, Sb, Bi, and Al with or without solid electrolyte, and combinations thereof. The cathode composite material can consist of NaCrO2, Na2 / 3MnC>2, Na2 / 3Nii-x-yFexMnyO2, wherein 0<x<0.5, and 0<y<0.5, with or without solid electrolyte and carbon additive, and combinations thereof.

[0037] In all embodiments, applying the dry solid electrolyte powder includes distributing the dry solid electrolyte powder over the working surface to form an evenly distributed layer thereover, such as a layer of uniform thickness of a preselected thickness. This may be achievedAttorney Docket No. 24636.785WO1by a doctor blade apparatus, by electrospray deposition, by brush, by spatula (or other spreader), or by a shaker, which are provided as a few non-limiting examples. The applied thickness can be adjusted by a setting on the respective equipment, by the operator of the equipment, or by a applying the dry solid electrolyte powder multiple times to provide multiple layers adding to provide a sufficient overall pre-compression thickness. A release film (e.g., Mylar film, silicone film, and / or other types of release film known or herein after developed) may be placed between a die or roller, and the solid electrolyte layer to prevent adhesion onto the die or roller.

[0038] The dry solid electrolyte powder is free of PTFE as noted above and can be, and is preferably free of a binder in the dry compaction method disclosed herein. The dry solid electrolyte suitable for the methods herein are inorganic materials with low mechanical modulus, in other words each can be densified at room temperature or slightly elevated temperatures between 40 °C and 120 °C (and high temperature sintering (>500 °C) is not necessary. The dry solid electrolyte powder can be selected from the group consisting of sodium closo-hydroborates (Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y), lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, NasPSe4), lithium sulfide-based (I 3PS4, Lie-xPSsClx), lithium halide (LisZrCk, Li2YCle), and combinations thereof. In these chemical formulas x and y are in a range of 0 to 1. In some embodiments, x = 0, x = 0.25, x=0.5, x=0.75, x=l, and in some embodiments, y = 0, y = 0.25, y=0.5, y=0.75, y=l.

[0039] The solid electrolyte is not NASICON type LiTi2(PC>3)3 based electrolyte, LiGe2(PC>3)3 based electrolyte, or Garnet type LiyLaiZ Oi 2 based electrolyte, more specifically it is not Ca / Ta co-doped Garnet type Li6.55 La2.95Cao.o5)(Zn.5Tao.5)Oi2, Ta-doped Lie.sLasZn.sTao.s O12, NASICON type Lii.4Alo.4Tii.6(P03)3-based electrolyte, NASICON type Lii.3Alo.3Tii.7(P03)3-based electrolyte, or NASICON Na3Zr2Si2POi2-based electrolyte. These solid electrolytes require high temperature sintering to densify the material.

[0040] The method includes pressing the intermediate layered structure to mechanically bind the layers together. The pressure can be in a range of about 20 MPa to about 250 MPa to the intermediate layered structure, preferably about 20 MPa to about 200 MPa, or even 20 MPa to about 100 MPa. The pressure can be an isostatic application of pressure. In one embodiment, the pressing is cold pressing at temperatures in a range of about 20 °C to about 120 °C, preferably about 20 °C to about 100 °C, more preferably about 20 °C to about 80 °C, even more preferably about 20 °C to about 60 °C, or even about 20 °C to about 40 °C. Cold pressing can include passing the intermediate layered structure through a calendar machine or pressing in a mold. In one embodiment, the compaction pressure is below 100 MPa.Attorney Docket No. 24636.785WO1

[0041] In an optional embodiment, the dry electrolyte powder can comprise a polymer binder (other than PTFE) as a mixture or electrolyte composite. The polymeric binder can be one or more of polyvinylidene fluorides (PVDF), polyvinyl alcohols (PVA), polyvinyl butyrals (PVB), styrene-ethylene-butylene-styrenes (SEBS), styrene-butadiene- styrenes (SBS), and styrenebutadiene rubbers (SBR). These polymers come in varying grades, monomer quantities, and polymer types, such as homopolymers, copolymers, linear, branched, cross-linked, block, network, side chain, etc. polymers and copolymers. The application of the polymeric binder containing dry electrolyte powder may be conducted at between 20 and 200 °C, preferably between 150 and 200 °C. The polymeric binder, if present, is mechanically mixed with the dry solid electrolyte powder before it is applied to the electrode substrate. Once applied, the method proceeds as described above to form a pressed, compacted and adhered dry electrode-solid electrolyte film, with binder but still without a solvent. The polymeric binder can increase the adhesive between the dry solid electrolyte powder and the electrode.

[0042] In some embodiment, when a polymeric binder is present, the pressing temperature may be higher than those expressed above. The temperature may be in a range of about 20 °C to about 200 °C, preferably about 50 °C to about 200 °C. In one embodiment, the temperature was in a range of about 150 °C to about 200 °C.

[0043] This method can also include reducing the particle size of the solid electrolyte powder. In some embodiments, the reduction in particle size can be accomplished by milling the solid electrolyte powder, for example in a ball mill apparatus. As described in more detail in Example 2, with respect to a second method of making disclosed herein, the solid electrolyte powder can be milled in a non-polar organic solvent, followed by removing the non-polar organic solvent before applying the dry solid electrolyte powder to the electrode.

[0044] Turning now to FIG. 12, in another aspect, all-solid state batteries, generally represented by reference number 200, are disclosed that include a dry electrode-solid electrolyte film 100 made as described above without a binder (i.e., it has a first electrode 102 as a substrate with a dry solid electrolyte powder layer 106 compacted thereto), and a secondary electrode 208 in operative arrangement relative to the dry electrode-solid electrolyte film. In one embodiment, the first electrode is a negative electrode (anode) and the secondary electrode is a positive electrode (cathode), and in another embodiment, it is the reverse with the first electrode being the cathode and the secondary electrode being the anode. The dry electrode-solid electrolyte film and the secondary electrode can be housed in a housing 210 such as a pouch cell, prismatic cell, coin cell, or cylindrical cell.Attorney Docket No. 24636.785WO1

[0045] In some embodiments, there is provided an all-solid-state battery structure comprising a positive electrode, an inorganic solid electrolyte, and at least one negative electrode layer. In some embodiments, a solid electrolyte film is provided for sodium-based all-solid-state batteries, and more particularly to the formation of the binder-free and highly ionic conductive solid electrolyte film (200 pm or less) on an electrode.

[0046] In another aspect, a second method, a solution-based process, is disclosed to create freestanding solid electrolyte separator films. The free standing film made will have a thickness of 100 pm or less. The solvent in this process must be compatible with the solid electrolyte material and has two main requirements: the solvent does not dissolve the solid electrolyte and the solvent does not react with the solid electrolyte. Non-polar organic solvents, such as toluene, xylene, benzene, hexane, cyclohexane heptane, octane, nonane, decane, diethyl ether, M-Cymene, and 2,2,5,5-tetramethyloxolane (TMO) are compatible with solid electrolyte powders.

[0047] The solid electrolyte powder can be selected from the same group of electrolyte powders identified above in the first method. Each are equally applicable here. Additional solid electrolyte powders include sodium oxychlorides (NaTaOCh, NaNbOCh), and Na2(BioHio)o.5(Bi2Hi2)o.5. In Example 2 below, the solid electrolyte was a sodium closo-hydroborates, more specifically Na2(BioHio)o.5(Bi2Hi2)o.5 powder. Turning to FIGS. 6A and 6B, respectively, show the ionic conductivity and X-ray diffraction, which demonstrate that the ionic conductivity is not significantly affected by exposure to a non-polar organic solvent, here toluene. The crystal structure is also unaffected. Similar results are expected for the other nonpolar organic solvents listed above.

[0048] An important parameter for processing films that have a thickness of 100 pm or less is the particle size of the solid electrolyte. Ideally, the solid electrolyte particles should be as small as possible. The method used here to reduce the size of the as-synthesized solid electrolyte is wet milling. This process involves dispersing the solid electrolyte in a solvent and using a ball mill with grinding media. The ball milling can be performed for 1 hour, 2 hours, 3 hours, 4 + y hours (wherein y is in 0.25 min, 0.5 min, 0.75 min, or 1 hour increments) up to 100 hours. Per the results shown in FIG. 7, each hour reduced the particle size further. Three hours of milling was used in Example 2, but 2 hours, and 1 hour can also provide suitable films. A 300 rpm milling speed was used in Example 2, but 200 rpm, 400 rpm, and 500 rpm can also be used. 1 mm diameter yttria-stabilized zirconia grinding media was used and a 30: 1 weight ratio of media:sample was used. A range of media:sample ratios from 10:1 up to 50:1 can be used. The amount of solvent can range from 5 mL / g of solid electrolyte to 20 mL / g.Attorney Docket No. 24636.785WO1

[0049] A polymeric binder can be present with the solid electrolyte in the non-polar organic solvent. The polymeric binder can be any of those discussed above for the dry processing method.

[0050] To fabricate freestanding solid electrolyte separator films a substrate is provided, such as a polyethylene terephthalate (PET) substrate. Other non-limiting examples of suitable substrates include silicone, polyethylene, polypropylene, polyester, and silica glass. One of the polymeric binders was selected and mixed with the solvent. In one embodiment, polystyrene-block-poly(ethylene-ran-butylene)-block-poly styrene (SEBS) polymer binder (formula (I) below) was dissolved in toluene.This SEBS is an ABA block copolymer and has a CAS Number of 66070-58-4. Then, solid electrolyte is added, followed by additional toluene solvent to achieve a desired viscosity, thereby placing the solid electrolyte in suspension therein. Next, the suspension is applied to the substrate.

[0051] In one embodiment, the suspension was cast onto the PET substrate using a doctor blade set to the desired separator film thickness. The thickness can range from 20-200 microns. Ideally, the thickness is less than 100 microns. The cast film was allowed to dry under vacuum. The drying temperature depends on the solvent used and should be higher than the boiling point of said solvent under vacuum. When toluene is used under a vacuum pressure of 1 mTorr, a temperature of 70 °C can be used. In one embodiment, the dry freestanding solid electrolyte film has 5% wt / wt polymeric binder and 95% wt / wt solid electrolyte. 5% wt / wt polymeric binder used in Example 2 provided adequate mechanical strength to the film. Polymeric binder content can range from 5% wt / wt to 20% wt / wt corresponding to a solid electrolyte content ranging from 95% wt / wt to 80% wt / wt respectively. The ratio of polymeric binder to solid electrolyte is fixed in the solution. The weight ratio of solvent to polymeric binder / solid electrolyte can range from 1:1 to 10:1.

[0052] A thin metal strip was used to delaminate the casted solid electrolyte film from the substrate. The result is a freestanding solid electrolyte separator film, see FIG. 9. The film was confirmed to retain a reasonable ionic conductivity after processing, see the graph presented as FIG. 10.Attorney Docket No. 24636.785WO1

[0053] The freestanding solid electrolyte film morphology was observed using focused-ion beam milling (FIG. 11). Porosity can be observed and can be used to optimize the casting thickness, as the solid electrolyte will be fully densified during typical solid-state battery fabrication pressing.Examples

[0054] Example 1

[0055] Tin (Sn) powder was cast onto an aluminum (Al) foil by a conventional doctor blade method, using N-Methyl-2-pyrrolidone (NMP) as the solvent and PVDF as the binder. The cast film was dried at 120 °C under vacuum overnight, then calendared to densify the Sn layer.

[0056] Approximately 24 mg / cm2of Na2(BioHio)o.5(Bi2Hi2)o.5 dry powder was evenly applied and spread on the dried densified Sn layer using a spatula. A release film made of mylar material was placed on top of the Na2(BioHio)o.5(Bi2Hi2)o.5 powder before transferring the stack to a die with two rubber sheets to ensure uniform pressure under a uniaxial load.

[0057] A uniaxial pressure of approximately 100 MPa was applied onto the Sn / Na2(BioHio)o.5(Bi2Hi2)o.5 stack for about 10 s between 20 °C and 30 °C (about room temperature) to compact the Na2(BioHio)o.5(Bi2Hi2)o.5 layer and secure it onto the surface of the dried densified Sn layer, forming the structure shown in FIG. 1 A, which is ready for subsequent battery assembly.

[0058] Example 2

[0059] Ball milling to reduce particle size: 1 g of Na2(BioHio)o.5(Bi2Hi2)o.5 powder (as-synthesized) was dispersed in 7 ml of toluene. This dispersion was placed in a Retsch Emax™ ball mill with 1 mm yttria-stabilized zirconia balls in a ratio of 30:1 (i.e., 30:1 is the ration of ball to powder ratio by weight, which means that for every 30 grams of grinding media, 1 gram of solid electrolyte powder is present). The ball mill was set at 300 rpm for preselected, sequential time increments, such as 1 hour, 2 hours, and 3 hours. See the decreased particle size in the scanning electron microscopy images in FIG. 7. The particle size was significantly reduced after 3 hours of milling. The particle size is clearly smaller than 10 pm, much smaller.

[0060] Fabricating freestanding solid electrolyte separator films: A thin film of PET was provided as a substrate. An amount of SEBS polymer binder was dissolved in toluene to provide a 5% wt of SEBS in the final film relative to the solid electrolyte powder. Here, 0.05 g of polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene was added to 1 ml of toluene with stirring. Then, 0.95 g of NBH having the reduced particle size after 3 hours of ball milling was added to the SEBS-toluene solution and additional toluene. Additional toluene was added until the solution was suitable for casting onto a substrate. This can be visually determined by one of ordinary skill in the art. The resulting dispersion of NBH was cast onto the PET substrateAttorney Docket No. 24636.785WO1using a doctor blade set to a film thickness of 80 gm. FIG. 8 has photographs comparing the post-doctor blade distribution of the dispersion according to this example to a similar suspension made with the as-synthesized NBH (the pristine NBH of FIG. 7).

[0061] After the NBH dried on the PET substrate, a thin metal strip was used to delaminate the NBH film from the PET substrate. A freestanding NBH film was produced, as shown in FIG.9, and this film retained its ionic conductivity, as shown in FIG. 10. Furthermore, with reference to FIG. 11, the freestanding NBH film morphology is shown, and porosity can be observed. This porosity can enable the NBH to be fully densified during the pressing typically used to fabricate solid-state batteries or all-solid-state batteries.

[0062] In view of the above-described implementations of subject matter this application discloses the following list of examples, wherein one feature of an example in isolation or more than one feature of said example taken in combination and, optionally, in combination with one or more features of one or more further examples are further examples also falling within the disclosure of this application:

[0063] The above examples and disclosure are intended to be illustrative and not exhaustive. These examples and description will suggest many variations and alternatives to one of ordinary skill in this art. All these alternatives and variations are intended to be included within the scope of the attached claims. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims attached hereto.

Claims

Attorney Docket No. 24636.785WO1What is claimed:

1. A method for making a dry electrode-solid electrolyte film, the method comprising: providing an electrode layer having a working surface;applying dry solid electrolyte powder over the working surface of the electrode layer to form an intermediate layered structure; andpressing the electrode layer and the dry solid electrolyte powder to mechanically bind them together into a dry electrode-solid electrolyte film;wherein the dry solid electrolyte powder is free of solvent and free ofpoly tetrafluoroethyl ene .

2. The method of claim 1, wherein pressing comprises applying a pressure in a range of about 20 MPa to about 100 MPa to the intermediate layered structure.

3. The method of claim 2, wherein pressing comprises cold pressing at temperatures in a range of about 20 °C to about 120 °C.

4. The method of claim 3, wherein cold pressing comprises passing the intermediate layered structure through a calendar machine or pressing in a mold.

5. The method of claim 1, wherein applying the dry solid electrolyte powder comprises distributing the dry solid electrolyte powder over the working surface by a doctor blade or by electrospray deposit.

6. The method of claim 1, wherein the electrode is a composite material.

7. The method of claim 1, further comprising adding a polymeric binder to the dry solid electrolyte powder to form an electrolyte composite, wherein the polymeric binder is selected from the group consisting of polyvinylidene fluorides (PVDF), polyvinyl alcohols (PVA), polyvinyl butyrals (PVB), styrene-ethylene-butylene-styrenes (SEBS), styrene-butadiene-styrenes (SBS), styrene-butadiene rubbers (SBR), and combinations thereof.

8. The method of claim 1, wherein the dry solid electrolyte powder is free of a binder.Attorney Docket No. 24636.785WO19. The method of claim 1, wherein the dry solid electrolyte powder layer of the dry electrode-solid electrolyte film has a thickness in a range of about 30 pm to about 200 pm.

10. The method of claim 1, wherein the dry solid electrolyte powder is selected from the group consisting of sodium closo-hydroborates (Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y), lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, Na3PSe4), lithium sulfide-based (I 3PS4, Lie-xPSsClx), lithium halide (LisZrCk, Li2YCle), and combinations thereof, wherein x and y are each in a range of 0 to 1.

11. The method of claim 1, further comprising milling a solid electrolyte powder in a nonpolar organic solvent and removing the non-polar organic solvent before applying the dry solid electrolyte powder.

12. A dry electrode-solid electrolyte film comprising:a dry solid electrolyte powder mechanically bound to an electrode layer by cold pressing in the absence of a solvent and absence of polytetrafluoroethylene.

13. The dry electrode-solid electrolyte film of claim 12, wherein the electrode is a composite material.

14. The dry electrode-solid electrolyte film of claim 12, wherein the dry solid electrolyte powder comprises a polymeric binder selected from the group consisting of polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), styrene-ethylene-butylene-styrene (SEBS), styrene-butadiene- styrene (SBS), styrene-butadiene rubber (SBR), and combinations thereof.

15. The dry electrode-solid electrolyte film of claim 12, wherein the dry solid electrolyte powder is free of a binder.

16. The dry electrode-solid electrolyte film of claim 12, wherein the dry solid electrolyte powder layer of the dry electrode-solid electrolyte film has a thickness in a range of about 30 pm to about 200 pm.Attorney Docket No. 24636.785WO117. The dry electrode-solid electrolyte film of claim 12, wherein the dry solid electrolyte powder is selected from the group consisting of sodium closo-hydroborates(Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y), lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, Na3PSe4), lithium sulfide-based (I 3PS4, Lie-xPSsCk), lithium halide (LisZrCk, Li2YCle), and combinations thereof, wherein x and y are each in a range of 0 to 1.

18. An all-solid-state battery comprising:a dry electrode-solid electrolyte film according any of claims 12 to 17; anda secondary electrode in operative arrangement relative to the dry electrode-solid electrolyte film.

19. The all-solid-state battery of claim 18, wherein the dry electrode-solid electrolyte and the secondary electrode are housed in a pouch cell, prismatic cell, coin cell, or cylindrical cell.

20. A method for making a freestanding solid electrolyte separator film, the method comprising:providing a suspension comprising a solid electrolyte and a polymeric binder dissolved in a non-polar organic solvent;milling the suspension with media to reduce the particle size of the solid electrolyte; applying a layer of the suspension, post-milling, to a substrate;drying the layer of the suspension to form a film; anddelaminating the film from the substrate for a freestanding solid electrolyte separator film.

21. The method of claim 20, wherein the film has a thickness less than 100 pm.

22. The method of claim 21, wherein the non-polar organic solvent is selected from the group consisting of toluene, xylene, benzene, hexane, cyclohexane heptane, octane, nonane, decane, diethyl ether, M-Cymene, 2,2,5,5-tetramethyloxolane (TMO), and combinations thereof.

23. The method of claim 21, wherein the solid electrolyte powder is selected from the group consisting of sodium closo-hydroborates (Na2(Bi2Hi2)i-x(Na2BioHio)x, Na2x+y(Bi2Hi2)x(BH4)y),Attorney Docket No. 24636.785WO1lithium closo-hydroborate (Li2(Bi2Hi2)i-x(Na2BioHio)x, Li2x+y(Bi2Hi2)x(BH4)y), sodium sulfide (NasPS4, Na3PSe4), lithium sulfide-based (I 3PS4, Lie-xPSsClx), lithium halide (LisZrCE, Li2YCle), and combinations thereof, wherein x and y are each in a range of 0 to 1.

24. The method of claim 20, wherein a polymeric binder is selected from the group consisting of polyvinylidene fluorides (PVDF), polyvinyl alcohols (PVA), polyvinyl butyrals (PVB), styrene-ethylene-butylene-styrenes (SEBS), styrene-butadiene- styrenes (SBS), styrene-butadiene rubbers (SBR), and combinations thereof.

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