Ceramic solid electrolyte film and preparation method therefor

Abstract

A ceramic solid electrolyte film and a preparation method therefor. The preparation method comprises the following steps: (1) mixing a solid electrolyte blank with a fibrillatable polymer, so that the polymer is fibrillated and is uniformly mixed with the solid electrolyte blank; (2) carrying out hot pressing treatment on the mixture obtained in step (1) to a preset thickness, so as to obtain a solid electrolyte intermediate film; (3) carrying out high-temperature sintering on the solid electrolyte intermediate film obtained in step (2) to obtain a solid electrolyte film. The preparation method of the solid electrolyte film simplifies the preparation process, and the prepared solid electrolyte film has a high ceramic content, a compact structure and a high ionic conductivity.

Description

Ceramic solid electrolyte film and preparation method thereof Technical Field

[0001] The present invention relates to a ceramic solid electrolyte film and a preparation method thereof, application of the ceramic solid electrolyte film in a solid-state battery, and a solid-state lithium metal battery comprising the ceramic solid electrolyte film. Background Art

[0002] Solid-state lithium metal batteries are a new type of battery technology that uses solid electrolytes instead of traditional liquid electrolytes. Their advantages include enhanced safety, higher energy density, and extended cycle life, which give them enormous potential in battery technology and are expected to drive innovation and development.

[0003] Currently, solid electrolyte materials primarily include sulfides, oxides, polymers, halides, and composite solid electrolytes. Oxide solid electrolytes, among others, offer advantages such as excellent ionic conductivity, thermal stability, and a wide electrochemical window, and can be prepared in air, making them a current research hotspot. Known oxide solid electrolytes in the art include lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium aluminum oxide (LLAZO), lithium lanthanum zirconium gallium oxide (LLGZO), lithium lanthanum titanate oxide (LLTO), lithium aluminum germanium phosphate (LAGP), and lithium aluminum titanium phosphate (LATP). Thin-film preparation of oxide solid electrolytes is a key factor influencing their industrial production and application. Currently, the mainstream method for producing solid electrolyte thin films is through tape casting and sintering. However, the tape casting and sintering process is complex, requiring slurry preparation, film formation, binder removal, and sintering. This process results in a long production cycle, low efficiency, high energy consumption, poor uniformity, and low yield. Therefore, simplifying the production process for solid electrolyte thin films and improving production efficiency are key to achieving large-scale production.

[0004] Summary of the Invention

[0005] The technical problem to be solved by the present invention is that the current solid electrolyte film has the disadvantages of complicated production process, poor product uniformity, low density, low ion conductivity, etc.

[0006] To address the above technical problems, the present invention provides a method for preparing a solid electrolyte film. This method simplifies the preparation process, eliminating the use of solvents, wet casting, and additives such as binders and plasticizers. It also reduces the amount of polymer used and eliminates the need for a complex debinding process. A dense electrolyte membrane can be obtained through a single sintering step, saving time and energy. The solid electrolyte film produced by this method has a high ceramic content, a dense structure, and high ionic conductivity.

[0007] A first aspect of the present invention provides a method for preparing a solid electrolyte film, characterized in that the preparation method comprises the following steps:

[0008] (1) mixing a solid electrolyte blank with a fibrillable polymer, fibrillating the polymer and uniformly mixing the solid electrolyte blank;

[0009] (2) hot pressing the mixture obtained in step (1) to a predetermined thickness to obtain a solid electrolyte green film;

[0010] (3) Sintering the solid electrolyte green film obtained in step (2) at high temperature to obtain a solid electrolyte thin film.

[0011] In some specific embodiments, the solid electrolyte is an oxide solid electrolyte.

[0012] In some specific embodiments, the solid electrolyte is selected from lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium aluminum oxide (LLAZO), lithium lanthanum zirconium gallium oxide (LLGZO), lithium lanthanum titanate oxide (LLTO), lithium aluminum germanium phosphate (LAGP) or lithium aluminum titanium phosphate (LATP).

[0013] In some specific embodiments, the fiberizable polymer includes at least one of polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carboxymethyl cellulose (CMC) and polyimide (PI). In the most preferred embodiment, the fiberizable polymer is polytetrafluoroethylene.

[0014] In some specific embodiments, in step (1), the solid electrolyte blank has a content of 80-99.9 wt%, preferably 90-99 wt%, and more preferably 95-99 wt%.

[0015] In some specific embodiments, in step (1), the content of the fiberizable polymer is 0.1-20 wt%, preferably 1-10 wt%, and more preferably 1-5 wt%.

[0016] In some embodiments, the method for fiberizing the polymer in step (1) is selected from at least one of the following:

[0017] (1) grinding the polymer and the solid electrolyte blank together;

[0018] (2) shearing the polymer and the solid electrolyte blank together at high speed;

[0019] (3) heating and stretching the polymer;

[0020] (4) The polymer and the solid electrolyte blank are subjected to air flow pulverization.

[0021] It should be understood that the present invention has no particular limitation on the method for fiberizing the polymer, and any method capable of fiberizing the fiberizable polymer is included within the scope of the present invention.

[0022] In some specific embodiments, the hot pressing treatment in step (2) is performed by using a roller press to perform hot rolling one or more times.

[0023] In some specific embodiments, the preset thickness in step (2) is 50-300 μm. According to specific embodiments, the preset thickness of the solid electrolyte film can be 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, or any thickness within the above range.

[0024] In some specific embodiments, the step (3) causes the polymer in the solid electrolyte film to decompose, preferably completely decompose.

[0025] In some embodiments, the sintering temperature in step (3) is 800-1200°C. The sintering temperature depends on the chemical composition of the solid electrolyte. For example, for LLZO, LLZTO, LLAZO, and LLGZO, the sintering temperature is preferably 1050-1200°C; for LLTO, the sintering temperature is preferably 1100-1200°C; for LAGP, the sintering temperature is preferably 800-900°C; and for LATP, the sintering temperature is preferably 900-1000°C.

[0026] In some specific embodiments, in step (3), the heating rate is 5 to 20° C. / min, preferably 10° C. / min; and the sintering time is 6 to 24 hours, preferably 12 hours.

[0027] In some specific embodiments, when the solid electrolyte blank is mixed with the fiberizable polymer in step (1), an excess amount of a lithium element precursor is additionally added, wherein the lithium element precursor is selected from LiOH·H2O and Li3PO4.

[0028] In some specific embodiments, the excess molar ratio of the lithium element precursor in step (1) is 1% to 50%, wherein

[0029] When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanate oxide, the precursor of the lithium element is LiOH·H2O, and the excess ratio of the molar number thereof is 20% to 50%, preferably 30% to 50%;

[0030] When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the excess ratio of the molar number thereof is 1% to 20%, preferably 5% to 15%.

[0031] In some specific embodiments, the method for preparing the solid electrolyte blank in step (1) comprises the following steps:

[0032] (a1) mixing precursors of each element and an excess lithium precursor with a solvent according to the chemical composition of the solid electrolyte, and then ball milling the mixture, followed by drying. The lithium precursor is selected from LiOH·H2O and Li3PO4;

[0033] (a2) pre-calcining the mixture obtained in step (a1) to obtain the solid electrolyte blank.

[0034] In some specific embodiments, the excess molar ratio of the lithium element precursor in step (a1) is 1% to 50%, wherein

[0035] When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanate oxide, the precursor of the lithium element is LiOH·H2O, and the excess ratio of the molar number thereof is 20% to 50%, preferably 30% to 50%;

[0036] When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the excess ratio of the molar number thereof is 1% to 20%, preferably 5% to 15%.

[0037] In some specific embodiments, the method for preparing a solid electrolyte film includes adding an excess amount of a precursor of the lithium element in step (a1) and also adding an excess amount of a precursor of the lithium element in step (1), wherein the total excess ratio of the molar number of the precursor of the lithium element in step (a1) and step (1) is 1% to 50%, wherein

[0038] When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanate oxide, the precursor of the lithium element is LiOH·H2O, and the total excess ratio of the molar number thereof is 20% to 50%, preferably 30% to 50%;

[0039] When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the total excess ratio of the molar number thereof is 1% to 20%, preferably 5% to 15%.

[0040] A second aspect of the present invention provides a solid electrolyte film, which is prepared by the preparation method of the first aspect of the present invention.

[0041] The third aspect of the present invention provides the use of the solid electrolyte film according to the second aspect of the present invention in a solid-state lithium metal battery.

[0042] A fourth aspect of the invention provides a solid-state lithium metal battery, which includes the solid-state electrolyte film according to the second aspect of the invention.

[0043] The preparation method of the solid electrolyte film of the present invention has a simple process, a small amount of auxiliary agents, low time and energy consumption, and the polymer components can be completely decomposed during the sintering step to form a solid electrolyte film that is close to 100% ceramic, with a dense structure and high ionic conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic diagram showing the preparation process of the ceramic solid electrolyte film of the present invention.

[0045] FIG2 shows a physical picture of the solid electrolyte film of Example 1 of the present invention.

[0046] FIG3 shows a SEM image of the solid electrolyte film of Example 1 of the present invention.

[0047] FIG4 is a physical picture showing a solid electrolyte film of Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0048] The present invention will be further described below by way of specific embodiments. Unless otherwise specified, the terms used herein have the same meanings as those generally understood by those of ordinary skill in the art. The numerical limits or ranges set forth herein include endpoints, specifically all values ​​and subranges within the numerical limits or ranges.

[0049] A first aspect of the present invention provides a method for preparing a solid electrolyte film, characterized in that the preparation method comprises the following steps:

[0050] (1) mixing a solid electrolyte blank with a fibrillable polymer, fibrillating the polymer and uniformly mixing the solid electrolyte blank;

[0051] (2) hot pressing the mixture obtained in step (1) to a predetermined thickness to obtain a solid electrolyte green film;

[0052] (3) Sintering the solid electrolyte green film obtained in step (2) at high temperature to obtain a solid electrolyte thin film.

[0053] The basic process of the method for preparing the ceramic solid electrolyte film of the present invention is shown in FIG1 .

[0054] In some specific embodiments, the solid electrolyte is an oxide solid electrolyte. The method for preparing the solid electrolyte film of the present invention has no particular limitation on the chemical composition of the solid electrolyte, as long as it is a ceramic solid electrolyte that can be prepared by high-temperature sintering.

[0055] In some specific embodiments, the solid electrolyte is selected from lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium aluminum oxide (LLAZO), lithium lanthanum zirconium gallium oxide (LLGZO), lithium lanthanum titanate oxide (LLTO), lithium aluminum germanium phosphate (LAGP) or lithium aluminum titanium phosphate (LATP).

[0056] In a specific embodiment, the chemical formula of lithium lanthanum zirconium oxide (LLZO) is Li7La3Zr2O 12 ;

[0057] The chemical formula of lithium lanthanum zirconium tantalum oxide (LLZTO) is Li 7-x La3Zr 2-x Ta x O 12 For example, when x=0.5, the chemical formula is Li 6.5 La3Zr 1.5 Ta 0.5 O 12 , when x=0.6, the chemical formula is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 ;

[0058] The chemical formula of lithium lanthanum zirconium aluminum oxide (LLAZO) is Li 7-3x La3Al x Zr2O 12 For example, when x=0.1, the chemical formula is Li 6.7 La3Al 0.1 Zr2O 12 , when x=0.2, the chemical formula is Li 6.4 La3Al 0.2 Zr2O 12 ;

[0059] The chemical formula of lithium lanthanum zirconium gallium oxide (LLGZO) is Li 7-3x La3Ga x Zr2O 12 For example, when x=0.2, the chemical formula is Li 6.4 La3Ga 0.2 Zr2O 12 , when x=0.3, the chemical formula is Li 6.1 La3Ga 0.3 Zr2O 12 ;

[0060] The chemical formula of lithium lanthanum titanate (LLTO) is Li 2-3x La x TiO3, for example, when x = 0.4, the chemical formula is Li 0.8 La 0.4 TiO3, when x = 0.5, the chemical formula is Li 0.5 La 0.5 TiO3;

[0061] The chemical formula of lithium aluminum germanium phosphate (LAGP) is Li 1.5 Al 0.5 Ge 1.5 (PO4)3;

[0062] The chemical formula of lithium aluminum titanium phosphate (LATP) is Li 1.3 Al 0.3 Ti 1.7 (PO4)3.

[0063] Those skilled in the art will appreciate that the solid electrolytes listed above are for illustrative purposes only and the scope of the present invention is not limited thereto. For example, electrolytes such as LLZTO and LLAZO are element-doped forms of the garnet-type solid electrolyte LLZO, and have similar properties in certain aspects. They can all be prepared into solid electrolyte films using the methods of the present invention. Other element-doped forms of the listed solid electrolytes, as well as other solid electrolytes not listed, can also be prepared into films using the methods of the present invention.

[0064] In some specific embodiments, the fibrosifiable polymer includes at least one of polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), carboxymethyl cellulose (CMC) and polyimide (PI). In the present invention, there is no particular limitation for fibrosifiable polymer, as long as it is a polymer that can be fibrosified and can decompose at high temperatures. In the most preferred embodiment, the fibrosifiable polymer is polytetrafluoroethylene (PTFE). The advantage of using polytetrafluoroethylene is that the polymer molecular weight is larger, longer fibrils can be formed in the fibrosizing process, and polymer networks are easily formed when hot pressing, which is conducive to the aggregation of electrolyte powder and the formation of dense electrolyte membrane. Similarly, when using other polymers, it is advantageous to use a polymer with a larger molecular weight.

[0065] In some specific embodiments, in the step (1), the content of the solid electrolyte stock is 80-99.9wt%, preferably 90-99wt%, and more preferably 95-99wt%. For example, the content of the solid electrolyte stock can be 80wt%, 85wt%, 88wt%, 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 95.5wt%, 96wt%, 96.5wt%, 97wt%, 97.5wt%, 98wt%, 98.5wt%, 99wt%, 99.5wt%, 99.9wt%, etc. According to the preparation method of the present invention, the higher the content of the solid electrolyte stock, the easier it is to sinter into a dense ceramic membrane.

[0066] In some specific embodiments, in step (1), the content of the fibrillating polymer is 0.1-20wt%, preferably 1-10wt%, and more preferably 1-5wt%. For example, the content of the fibrillating polymer can be 0.1wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 12wt%, 15wt%, 20wt%, etc. According to the preparation method of the present invention, the content of the fibrillating polymer is small, and a complicated debinding process is not required. A dense solid electrolyte film can be obtained by sintering in one step.

[0067] In some specific embodiments, in step (1), the total content of the solid electrolyte blank and the fiberizable polymer is 100 wt%.

[0068] In some embodiments, the method for fiberizing the polymer in step (1) is selected from at least one of the following:

[0069] (1) grinding the polymer and the solid electrolyte blank together;

[0070] (2) shearing the polymer and the solid electrolyte blank together at high speed;

[0071] (3) heating and stretching the polymer;

[0072] (4) The polymer and the solid electrolyte blank are subjected to air flow pulverization.

[0073] It should be understood that the present invention has no particular limitation on the method for fiberizing the polymer, and any method capable of fiberizing the fiberizable polymer is included within the scope of the present invention.

[0074] In some specific embodiments, the hot pressing treatment in step (2) is performed using a roller press for one or more hot rolling. In some preferred embodiments, in step (2), the mixture obtained in step (1) is rolled multiple times under heating conditions using a roller press to gradually reduce the thickness of the green film, thereby obtaining a solid electrolyte green film with a predetermined thickness. The temperature of the hot rolling is not particularly limited, as long as it is a temperature that is conducive to processing, for example, 50-150°C, 60-120°C, 70-100°C, 75-90°C, etc.

[0075] In some specific embodiments, the preset thickness in step (2) is 50-300 μm. According to the specific embodiment, the preset thickness of the solid electrolyte green film can be 50 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, or any thickness within the above range. In the preparation method of the present invention, the thickness of the electrolyte green film is directly related to the thickness of the final electrolyte film, thereby affecting the battery energy density. Generally speaking, the smaller the thickness of the electrolyte film, the greater the energy density. The preset thickness of the electrolyte green film can be selected within the above range according to the actual application.

[0076] In some specific embodiments, step (3) decomposes the polymer in the solid electrolyte green film, preferably completely decomposing it. Through the high-temperature sintering in step (3), the polymer components in the solid electrolyte green film can be substantially completely decomposed, forming a solid electrolyte film that is nearly 100% ceramic. This preparation method results in a dense structure and high ionic conductivity for the solid electrolyte film of the present invention.

[0077] In some embodiments, the sintering temperature in step (3) is 800-1200°C. The sintering temperature depends on the chemical composition of the solid electrolyte. For example, for LLZO, LLZTO, LLAZO, and LLGZO, the sintering temperature is preferably 1050-1200°C; for LLTO, the sintering temperature is preferably 1100-1200°C; for LAGP, the sintering temperature is preferably 800-900°C; and for LATP, the sintering temperature is preferably 900-1000°C.

[0078] In some specific embodiments, in step (3), the heating rate is 5 to 20° C. / min, preferably 5 to 10° C. / min; and the sintering time is 6 to 24 hours, preferably 12 hours.

[0079] Since lithium in the solid electrolyte blank volatilizes at high temperatures, in order to obtain a solid electrolyte film with the desired stoichiometric ratio, it is preferred that the mixture to be sintered contains a portion of excess lithium. For example, the excess lithium can be contained in the solid electrolyte blank. Alternatively, the excess lithium can be added additionally when the solid electrolyte blank is mixed with the fiberizable polymer in step (1).

[0080] Therefore, in some specific embodiments, when the solid electrolyte blank is mixed with the fiberizable polymer in step (1), an excess amount of a lithium element precursor is additionally added, wherein the lithium element precursor is selected from LiOH·H2O and Li3PO4.

[0081] In addition, in some specific embodiments, the method for preparing the solid electrolyte blank in step (1) comprises the following steps:

[0082] (a1) mixing precursors of each element and an excess lithium precursor with a solvent according to the chemical composition of the solid electrolyte, and then ball milling the mixture, followed by drying. The lithium precursor is selected from LiOH·H2O and Li3PO4;

[0083] (a2) pre-calcining the mixture obtained in step (a1) to obtain the solid electrolyte blank.

[0084] In addition, in some specific embodiments, the method for preparing a solid electrolyte film includes adding an excess amount of a lithium precursor in step (a1) and also includes adding an excess amount of a lithium precursor in step (1). In this case, the excess molar ratio of the lithium precursor in step (a1) and step (1) should be calculated together.

[0085] In the context of the present invention, “excess” refers to the fact that the number of moles of lithium element precursor added during the preparation process is greater than the molar content of lithium element in the solid electrolyte calculated based on the moles of other element precursors (such as lanthanum source, zirconium source, tantalum source, etc.) according to the chemical composition of the solid electrolyte. For example, when the preparation chemical formula is Li 7-x La3Zr 2-x Ta x O 12 When using an LLZTO solid electrolyte, if the molar ratio of lithium, lanthanum, zirconium and tantalum elements in the lithium source, lanthanum source, zirconium source and tantalum source is Li:La:Zr:Ta=M:3:2-x:x, then the molar ratio M of the lithium element in the lithium source is greater than 7-x; the excess percentage is calculated as (M-(7-x)) / (7-x).

[0086] In a specific embodiment of the present invention, no matter the precursor of the lithium element is added in step (a1), in step (1), or in both step (a1) and step (1), the excess ratio (or total excess ratio) of the number of moles thereof is 1% to 50%. According to a specific embodiment, the excess ratio of the number of moles of the precursor of the lithium element can be 1%, 3%, 5%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, 22%, 24%, 25%, 26%, 28%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 48%, 50%, or any ratio within the above range. Specifically, when the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanium oxide, the precursor of the lithium element is LiOH·H2O, and its molar excess ratio (or total excess ratio) is 20% to 50%, preferably 30% to 50%; when the solid electrolyte is selected from lithium germanium aluminum phosphate or lithium titanium aluminum phosphate, the precursor of the lithium element is Li3PO4, and its molar excess ratio (or total excess ratio) is 1% to 20%, preferably 5% to 15%. After research, the inventors found that excess lithium can be added during the preparation of solid electrolyte blanks and green membranes. When the total amount of excess ratio is kept constant, the timing of adding the excess lithium source has basically no effect on the technical effect.

[0087] Because the Li in the lattice evaporates during high-temperature heating, causing the crystalline phase to change, generating a second phase that does not contain lithium ions, which reduces ionic conductivity. The excessive provision of a lithium source can prevent the crystalline phase from changing, thereby improving the ionic conductivity of the prepared solid electrolyte membrane. The inventors have confirmed through experiments that after the pre-burning of the solid electrolyte blank and the sintering of the solid electrolyte green membrane, the above-mentioned excessive lithium source does not affect the physical structure of the solid electrolyte. On the one hand, due to the inclusion of two high-temperature treatment processes, the volatilization of the lithium element is relatively large, and the excessive lithium source added can compensate for the amount of lithium volatilization. On the other hand, a small amount of lithium residue can form a lithium-rich phase at the grain boundary, thereby better connecting the solid electrolyte grains and increasing the compactness after sintering.

[0088] A second aspect of the present invention provides a solid electrolyte film, which is prepared by the preparation method of the first aspect of the present invention.

[0089] The third aspect of the present invention provides the use of the solid electrolyte film according to the second aspect of the present invention in a solid-state lithium metal battery.

[0090] A fourth aspect of the present invention provides a solid-state lithium metal battery, which includes the solid-state electrolyte film according to the second aspect of the present invention.

[0091] Example

[0092] The present invention is described in detail below by way of examples, which are not intended to limit the present invention. The experimental methods in the following examples are all conventional methods unless otherwise specified.

[0093] In the following examples, the PTFE used was purchased from Kejing, with a weight average molecular weight of 10 6 g / mol, and the median particle size is 0.3 μm.

[0094] Preparation of LLZTO solid electrolyte blank

[0095] To prepare the chemical formula Li 6.4 La3Zr 1.4 Ta 0.6 O 12 The LLZTO solid electrolyte is prepared by weighing the following raw materials in a molar ratio according to a stoichiometric ratio and a certain proportion of excess lithium source: lithium hydroxide monohydrate (LiOH·H2O), lanthanum oxide (La2O3), zirconium oxide (ZrO2) and tantalum oxide (Ta2O5).

[0096] Place the weighed precursor powders of each element into a zirconia ball mill. Add five times the weight of the raw materials in zirconia ball milling beads and an equal amount of isopropyl alcohol. Wet mill at 500 rpm for 3 hours to obtain a mixed powder. The mixed powder is then dried in an oven to completely remove the isopropyl alcohol solvent.

[0097] The dried powder was placed in a muffle furnace and calcined at 900°C for 12 h, with a heating and cooling rate of 5°C / min. After cooling, the LLZTO solid electrolyte powder blank was obtained.

[0098] Unless otherwise specified, the LLZTO solid electrolyte powder blank prepared above was used as the starting material when preparing LLZTO solid electrolyte films in subsequent examples.

[0099] Preparation of LLZO solid electrolyte blank

[0100] To prepare the chemical formula Li7La3Zr2O 12 The LLTO solid electrolyte is prepared by weighing the following raw materials in a molar ratio according to a stoichiometric ratio and a certain proportion of excess lithium source: lithium hydroxide monohydrate (LiOH·H2O), lanthanum oxide (La2O3) and zirconium oxide (ZrO2).

[0101] Place the weighed precursor powders of each element into a zirconia ball mill. Add five times the weight of the raw materials in zirconia ball milling beads and an equal amount of isopropyl alcohol. Wet mill at 500 rpm for 3 hours to obtain a mixed powder. The mixed powder is then dried in an oven to completely remove the isopropyl alcohol solvent.

[0102] The dried powder was placed in a muffle furnace and calcined at 900°C for 12 hours with a heating and cooling rate of 5°C / min. After cooling, the LLZO solid electrolyte powder blank was obtained.

[0103] Unless otherwise specified, the LLZO solid electrolyte powder blank prepared above was used as the starting material when preparing LLZO solid electrolyte films in subsequent examples.

[0104] LATP, LAGP solid electrolyte blanks

[0105] In the subsequent examples, LATP or LAGP solid electrolyte films were prepared using LATP or LAGP solid electrolyte powder purchased from Kejing as the starting material.

[0106] Example 1: Preparation of LLZTO solid electrolyte film

[0107] 95 parts by mass of LLZTO powder blank (LiOH·H2O is in excess of 40% during blank preparation) and 5 parts by mass of PTFE powder were weighed, mixed evenly, and placed in a grinder. The mixture was fully ground at 200 rpm for 30 min to fiberize the PTFE and fully mix it with the LLZTO powder to obtain a fiberized PTFE and LLZTO mixed block.

[0108] The mixed block was rolled several times at 80° C. using a roller press to gradually reduce the thickness of the green membrane, and finally an electrolyte green membrane with a thickness of 300 μm was obtained.

[0109] The electrolyte film was placed in a magnesium oxide crucible and placed in a muffle furnace for high-temperature sintering in air. The sintering conditions were: a heating rate of 10°C / min, a holding temperature of 1150°C for 12 hours, and a cooling rate of 5°C / min. After cooling, the LLZTO solid electrolyte film was obtained.

[0110] Example 2: Preparation of LLZTO solid electrolyte film

[0111] In this example, the LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the LLZTO powder stock was increased to 97 parts by mass and the PTFE powder was reduced to 3 parts by mass.

[0112] Example 3: Preparation of LLZTO solid electrolyte film

[0113] In this example, the LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the LLZTO powder stock was increased to 99 parts by mass and the PTFE powder was reduced to 1 part by mass.

[0114] Example 4: Preparation of LLZTO solid electrolyte film

[0115] In this example, an LLZTO solid electrolyte thin film was obtained by the same steps and conditions as in Example 1, except that the thickness of the electrolyte green film obtained by roller pressing was reduced to 200 μm.

[0116] Example 5: Preparation of LLZTO solid electrolyte film

[0117] In this example, an LLZTO solid electrolyte thin film was obtained by the same steps and conditions as in Example 1, except that the thickness of the electrolyte green film obtained by roller pressing was reduced to 100 μm.

[0118] Example 6: Preparation of LLZTO solid electrolyte film

[0119] In this example, an LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the thickness of the electrolyte green film obtained by roller pressing was reduced to 50 μm.

[0120] Example 7: Preparation of LATP solid electrolyte film

[0121] In this embodiment, in addition to replacing the LLZTO powder blank with LATP (Li 1.3 Al 0.3 Ti 1.7 (PO4)3) and the sintering holding temperature was adjusted to 950°C, the same steps and conditions as in Example 1 were followed to obtain a LATP solid electrolyte film.

[0122] Example 8: Preparation of LAGP solid electrolyte film

[0123] In this embodiment, in addition to replacing the LLZTO powder blank with LAGP (Li 1.5 Al 0.5 Ge 1.5 (PO4) 3) and the sintering holding temperature was adjusted to 850 ° C., the LAGP solid electrolyte film was obtained by the same steps and conditions as in Example 1.

[0124] Example 9: Preparation of LLZO solid electrolyte film

[0125] In this embodiment, the LLZO solid electrolyte film was obtained by following the same steps and conditions as in Example 1, except that the LLZTO powder stock was replaced by the LLZO powder stock.

[0126] Example 10: Preparation of LLZTO solid electrolyte film

[0127] In this example, the LLZTO solid electrolyte film was obtained by following the same steps and conditions as in Example 1, except that the PTFE powder was replaced with ethylene-tetrafluoroethylene copolymer (ETFE).

[0128] Example 11: Preparation of LLZTO solid electrolyte film

[0129] In this embodiment, the LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the excess ratio of LiOH·H 2 O in the preparation of the LLZTO blank was adjusted to 20%.

[0130] Example 12: Preparation of LLZTO solid electrolyte film

[0131] In this example, the LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the excess ratio of LiOH·H 2 O was adjusted to 30% during the preparation of the LLZTO powder blank.

[0132] Example 13: Preparation of LLZTO solid electrolyte film

[0133] In this example, the LLZTO solid electrolyte film was obtained by the same steps and conditions as in Example 1, except that the excess ratio of LiOH·H 2 O was adjusted to 50% during the preparation of the LLZTO powder blank.

[0134] Comparative Example 1: Preparation of LLZTO solid electrolyte by traditional tape casting sintering method

[0135] Step 1 (slurry preparation): According to the mass ratio of LLZTO powder blank: isopropyl alcohol (solvent): triethanolamine (dispersant): PVB (binder): BBP (plasticizer) = 50.5:36.5:1.8:5.5:5.8, the corresponding materials were weighed and added to a zirconia ball mill at 300 rpm for 12 hours, and kept under negative pressure for 60 minutes to remove bubbles to obtain a casting slurry;

[0136] Step 2: Use a doctor blade method to apply the cast slurry onto a PET film. After drying the solvent, peel off the film and perform isostatic pressing at a pressure of 200 MPa for 10 minutes to obtain an electrolyte green film with a thickness of 300 μm.

[0137] Step 3: Place the above electrolyte green film in a muffle furnace, heat it to 650°C at a heating rate of 1°C / min, and keep it at this temperature for 12 hours for debinding treatment;

[0138] Step 4: Place the debinding electrolyte film in a magnesium oxide crucible, place it in a muffle furnace, and sinter it in air at high temperature. The sintering conditions are: heating rate 10°C / min; holding temperature: 1150°C for 12 hours; cooling rate 5°C / min. After cooling, the LLZTO solid electrolyte produced by the tape-cast sintering method is obtained.

[0139] Characterization of solid electrolytes

[0140] The solid electrolyte films prepared according to the above examples and comparative examples were visually observed to evaluate the film formation. Actual images of the solid electrolyte films of Example 1 and Comparative Example 1 are shown in FIG2 and FIG4 , respectively.

[0141] The diameter and thickness of the solid electrolyte film were measured using a micrometer.

[0142] The solid electrolyte film was subjected to SEM testing, including surface SEM and cross-sectional SEM. The SEM testing instrument was a Zeiss Sigma 300, and the sintered solid electrolyte was directly tested. The cross-sectional SEM of the solid electrolyte film of Example 1 is shown in Figure 3.

[0143] To test the ionic conductivity of the solid electrolyte film, a conductive layer of Ag was deposited on both sides using a thermal evaporation coating apparatus. The film was then encapsulated with a button cell battery. AC impedance measurements were then performed using a Metrohm Autolab electrochemical workstation at an AC voltage of 10 mV and a frequency of 10 MHz–1 Hz. After measuring the AC impedance of the solid electrolyte film, the ionic conductivity σ was calculated using the formula σ = L / RS, where L is the thickness of the electrolyte film, R is the AC impedance of the electrolyte film, and S is the surface area of ​​a single surface of the electrolyte film.

[0144] The characterization results of the solid electrolytes of Examples 1-8 and Comparative Example 1 are summarized in Table 1.

[0145] Table 1 Characterization data of solid electrolyte films

[0146] Results and evaluation

[0147] As shown in Figure 2, the LLZTO solid electrolyte film prepared in Example 1 is flat and translucent, indicating a thin and dense electrolyte film. The thickness of the electrolyte film is significantly reduced compared to the thickness of the raw electrolyte film, indicating the formation of a dense crystalline structure. As shown in Figure 3, the electrolyte grains in the LLZTO solid electrolyte film prepared in Example 1 grow uniformly and densely, with no apparent pores.

[0148] Similarly, the solid electrolyte films prepared in Examples 2-13 also have a smooth appearance and a dense texture, indicating that the electrolyte film preparation method of the present invention is applicable to the preparation of oxide solid electrolyte films with different chemical compositions and can obtain a dense electrolyte membrane.

[0149] The ionic conductivity data in Table 1 show that increasing the ceramic content in the electrolyte green film improves the ionic conductivity of the electrolyte membrane, as seen in Examples 1-3. Furthermore, Examples 1 and 4-6 show that decreasing the thickness of the electrolyte membrane also leads to a certain decrease in ionic conductivity, likely due to increased lithium loss during the sintering process. Therefore, when mixing the solid electrolyte green material with the fiberizable polymer, an excess of LiOH·H2O or Li3PO4 can be added to compensate for lithium volatilization losses.

[0150] By comparing Examples 1 and 11-13, it can be seen that as the lithium excess ratio increases, the ionic conductivity of the solid electrolyte membrane continues to rise, and the ionic conductivity is the highest when the lithium excess ratio is 40%. If the lithium excess ratio is further increased, the ionic conductivity decreases slightly, which may be due to the increase of lithium-containing impurity phases (such as LiOH·H2O, LiOH, Li2O, etc.). Therefore, in the present invention, the most preferred lithium excess ratio is 40%. In addition, as shown in the SEM image of Figure 3, when the lithium excess is 40%, the LLZTO grains in the solid electrolyte film are large and the grain boundaries are few, indicating that it is basically free of impurities, verifying that the excess lithium source can compensate for the volatilization of the lithium component during the high-temperature sintering process.

[0151] Relatively speaking, it can be seen from Figure 4 that in Comparative Example 1, which does not adopt the method of the present invention, the electrolyte film obtained by sintering by tape casting is loose and porous, with obvious warping / ripples, easy to crack, and uneven color. Through measurement, it was found that the thickness of the solid electrolyte in Comparative Example 1 did not change much compared with that before sintering. That is, compared with the preparation process of the present invention, the tape casting sintering method is difficult to form a dense electrolyte membrane under the same conditions even after debinding. Moreover, due to the fragmentation of the electrolyte membrane of Comparative Example 1, the ionic conductivity test could not be carried out. The mechanical properties of the electrolyte film prepared in Comparative Example 1 cannot meet the application in battery preparation.

[0152] The above examples are used to describe exemplary embodiments of the present invention, but the present invention is not limited thereto. It should be understood by those skilled in the art that the above examples are for illustrative purposes only, and the specific embodiments and examples of the present invention should not be construed as limiting the scope of the present invention. The embodiments can be changed and modified within the scope of the present invention, and such changes and modifications should fall within the scope of protection of the present invention.

Claims

1. A method for preparing a ceramic solid electrolyte film, characterized in that: The preparation method comprises the following steps: (1) mixing a solid electrolyte stock with a fibrillable polymer, so that the polymer is fibrillated and uniformly mixed with the solid electrolyte stock; (2) hot pressing the mixture obtained in step (1) to a preset thickness to obtain a solid electrolyte green film; (3) Sintering the solid electrolyte green film obtained in step (2) at high temperature to obtain a solid electrolyte thin film.

2. The preparation method according to claim 1, characterized in that: The solid electrolyte is an oxide solid electrolyte.

3. The preparation method according to claim 2, characterized in that: The solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide, lithium lanthanum titanium oxide, lithium aluminum germanium phosphate or lithium aluminum titanium phosphate.

4. The preparation method according to any one of claims 1 to 3, characterized in that The fiberizable polymer includes at least one of polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, polyvinylidene fluoride, styrene-butadiene rubber, polyacrylic acid, carboxymethyl cellulose and polyimide.

5. The preparation method according to claim 4, characterized in that: The fiberizable polymer is polytetrafluoroethylene.

6. The preparation method according to any one of claims 1 to 5, characterized in that: In the step (1), the content of the solid electrolyte blank is 80-99.9wt%; and / or the content of the fiberizable polymer is 0.1-20wt%.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The method for fiberizing the polymer in step (1) is selected from at least one of the following: (1) grinding the polymer and the solid electrolyte blank together; (2) shearing the polymer and the solid electrolyte blank together at high speed; (3) heating and stretching the polymer; (4) The polymer and the solid electrolyte blank are subjected to air flow pulverization.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The hot pressing treatment in step (2) is performed by using a roller press to perform hot rolling once or multiple times; and / or The preset thickness in step (2) is 50-300 μm.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The step (3) completely decomposes the polymer in the solid electrolyte film; and / or The sintering temperature in the step (3) is 800-1200°C.

10. The preparation method according to any one of claims 1 to 9, characterized in that: When the solid electrolyte blank is mixed with the fiberizable polymer in step (1), an excess amount of a lithium element precursor is additionally added, wherein the lithium element precursor is selected from LiOH·H2O and Li3PO4; Preferably, the molar excess ratio of the lithium precursor in step (1) is 1% to 50%, wherein When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanium oxide, the precursor of the lithium element is LiOH·H2O, and the excess ratio of the molar number thereof is 20% to 50%; When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the excess ratio of the molar number thereof is 1% to 20%.

11. The preparation method according to any one of claims 1 to 10, characterized in that: The method for preparing the solid electrolyte blank in step (1) comprises the following steps: (a1) according to the chemical composition of the solid electrolyte, the precursors of each element and the precursor of an excess lithium element are mixed with a solvent, and then ball-milled, and then dried, wherein the precursor of the lithium element is selected from LiOH·H2O and Li3PO4; (a2) pre-calcining the mixture obtained in step (a1) to obtain the solid electrolyte blank; Preferably, the molar excess ratio of the lithium precursor in step (a1) is 1% to 50%, wherein When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanium oxide, the precursor of the lithium element is LiOH·H2O, and the excess ratio of the molar number thereof is 20% to 50%; When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the excess ratio of the molar number thereof is 1% to 20%.

12. The preparation method according to claim 11, characterized in that: When the solid electrolyte blank is mixed with the fiberizable polymer in step (1), an excess amount of lithium element precursor is additionally added, wherein the total excess ratio of the molar number of the lithium element precursor in step (a1) and step (1) is 1% to 50%, wherein When the solid electrolyte is selected from lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium aluminum oxide, lithium lanthanum zirconium gallium oxide or lithium lanthanum titanium oxide, the precursor of the lithium element is LiOH·H2O, and the total excess ratio of the molar number thereof is 20% to 50%; When the solid electrolyte is selected from lithium aluminum germanium phosphate or lithium aluminum titanium phosphate, the precursor of the lithium element is Li3PO4, and the total excess ratio of the molar number thereof is 1% to 20%. 13 . A ceramic solid electrolyte film, wherein the ceramic solid electrolyte film is prepared by the preparation method according to any one of claims 1 to 12.

14. Use of the ceramic solid electrolyte film according to claim 13 in a solid-state lithium metal battery.

15. A solid-state lithium metal battery, comprising the ceramic solid electrolyte film according to claim 13.

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