Modified garnet type solid electrolyte sheet as well as preparation method and application thereof

Abstract

The invention provides a modified garnet type solid electrolyte sheet and a preparation method and application thereof, and the preparation method comprises the following steps: arranging a metal layer on the surface of the garnet type solid electrolyte sheet, and then carrying out sintering oxidation to obtain the garnet type solid electrolyte sheet with a metal oxide layer on the surface; the garnet type solid electrolyte sheet with the metal oxide layer on the surface is immersed in molten lithium, a replacement reaction and an alloying reaction are sequentially carried out, the modified garnet type solid electrolyte sheet with an interface layer on the surface is obtained, and the interface layer comprises Li2O and a lithium-containing alloy. According to the preparation method, the interface layer in which Li2O and the lithium-containing alloy coexist is prepared, and the solid electrolyte sheet is protected inside, so that the conductivity can be ensured, direct contact between lithium metal and the garnet type solid electrolyte sheet can be reduced, the stability to lithium is improved, and the service life of the garnet type solid electrolyte sheet can be prolonged.

Description

Technical Field

[0001] The invention belongs to the technical field of batteries and relates to a modified garnet-type solid electrolyte sheet and a preparation method and application thereof. Background Art

[0002] Compared with other secondary batteries, lithium-ion batteries have the advantages of high energy, high output voltage, long cycle life, no memory effect, low self-discharge, and environmental friendliness. However, the traditional liquid electrolytes used in lithium-ion batteries have safety issues, mainly manifested in: thermal runaway, prone to dangerous situations such as combustion and explosion; in addition, the risk of liquid electrolyte leakage is high, and some uncontrollable side reactions may occur between the electrodes and the electrolyte. The existing technology has proposed using solid electrolytes instead of liquid electrolytes to improve the safety of lithium-ion batteries, such as Li7La3Zr2O 12 The garnet-type LLZO (lanthanum lithium zirconate) ceramic solid electrolyte has a cubic crystal structure and the room temperature lithium ion conductivity is increased to 3×10 -4 S cm -1 , its high lithium ion conductivity, high stability and great development potential have attracted more and more attention.

[0003] Garnet-type lithium-ion ceramic electrolytes represented by lanthanum zirconate lithium system were prepared by solid phase reaction method with a series of apparent molecular formula Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Ta-doped lithium lanthanum zirconate (LLZTO) electrolyte, and the room temperature lithium ion conductivity reached 1.0×10 -3 S cm -1 , which has higher ionic conductivity and more stable cubic orientation than LLZO, and is gradually used in lithium-ion batteries to replace liquid electrolytes.

[0004] When solid electrolytes such as LLZTO are used as electrolytes in lithium-ion batteries, they will inevitably come into contact with lithium sheets or lithium metal generated by cathode electrode reactions. If solid electrolytes such as LLZTO prepared by conventional solid-phase methods are used directly without any treatment, the Ta in LLZTO will 5+ and Zr 5+ It will be gradually reduced to Ta as it comes into contact with lithium metal. 3+ 、Ta 2+ and Zr 3+ etc., which destroys its own garnet structure, shortens the life of the ceramic piece, and thus greatly affects the life of the corresponding device.

[0005] Based on the above research, it is necessary to improve the stability of garnet-type solid electrolyte sheets to lithium without affecting the Li + Normal transportation ensures that it has high electrical conductivity. Summary of the Invention

[0006] The purpose of the present invention is to provide a modified garnet-type solid electrolyte sheet and its preparation method and application. The preparation method prepares a uniform interface layer on the surface of the garnet-type solid electrolyte sheet, in which Li2O and lithium-containing alloy coexist, which can protect the solid electrolyte sheet inside, not only allowing Li + By ensuring electrical conductivity, the direct contact between lithium metal and garnet-type solid electrolyte sheets can be reduced, thereby improving the stability of the garnet-type solid electrolyte sheets to lithium, thereby increasing their service life.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a modified garnet-type solid electrolyte sheet, the preparation method comprising the following steps:

[0009] S1: providing a metal layer on the surface of a garnet-type solid electrolyte sheet, and then sintering and oxidizing it to obtain a garnet-type solid electrolyte sheet having a metal oxide layer on the surface;

[0010] S2: Immersing the garnet-type solid electrolyte sheet having a metal oxide layer on its surface in step S1 into molten lithium, sequentially performing a replacement reaction and an alloying reaction to obtain the modified garnet-type solid electrolyte sheet having an interface layer on its surface, wherein the interface layer includes Li2O and a lithium-containing alloy.

[0011] Preferably, the thickness of the metal layer in step S1 is 3 μm-6 μm.

[0012] Preferably, the method of providing the metal layer in step S1 includes an evaporation method.

[0013] Preferably, the material of the metal layer in step S1 includes any one of Mg, Al or Ag, or a combination of at least two of them.

[0014] Preferably, the sintering oxidation in step S1 is performed in an oxygen-containing atmosphere, and the oxygen-containing atmosphere includes an air atmosphere.

[0015] Preferably, the sintering oxidation in step S1 is performed at a temperature of 650° C. to 750° C., for a time of 30 min to 60 min, and at a heating rate of 4° C. / min to 6° C. / min.

[0016] Preferably, the garnet-type solid electrolyte sheet in step S1 comprises an LLZO ceramic sheet or an LLZTO ceramic sheet.

[0017] Preferably, the alloying reaction time in step S2 is more than 48 hours.

[0018] Preferably, the temperature of the alloying reaction in step S2 is 350°C-400°C.

[0019] Preferably, the temperature of the replacement reaction in step S2 is 200°C-250°C.

[0020] Preferably, the replacement reaction time in step S2 is 20h-28h.

[0021] Preferably, the thickness of the interface layer in step S2 is 5 μm-11 μm.

[0022] In a second aspect, the present invention provides a modified garnet-type solid electrolyte sheet, which is prepared by the preparation method described in the first aspect.

[0023] In a third aspect, the present invention provides an application of the modified garnet-type solid electrolyte sheet as described in the second aspect, wherein the application includes use in a solid-state battery.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention provides a metal layer on the surface of a garnet-type solid electrolyte sheet, then oxidizes the metal layer into a corresponding metal oxide layer, and then immerses the sheet in molten lithium. The molten lithium and the metal oxide layer first undergo a replacement reaction to obtain Li2O and a corresponding metal. Then, an alloying reaction is performed, and the molten lithium and the replaced metal undergo an alloying reaction to obtain a lithium-containing alloy. Therefore, an interface layer in which Li2O and a lithium-containing alloy coexist is finally obtained on the surface of the garnet-type solid electrolyte sheet. This not only reduces the contact between the garnet-type solid electrolyte sheet and lithium metal during use, but also improves the stability of the garnet-type solid electrolyte sheet to lithium, especially the stability to lithium under high temperature conditions (250°C to 600°C), while not affecting the Li + Normal transport of lithium metal is ensured, ensuring high ionic conductivity. If the interface layer contains only lithium-containing alloy, although the conductivity is high, the lithium therein will react with the garnet-type solid electrolyte sheet. If the interface layer contains only Li2O, although it can isolate lithium metal, its ionic conductivity is low. Therefore, the interface layer of the present invention in which Li2O and lithium-containing alloy coexist can both isolate lithium metal and ensure ionic conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 These are fracture photos of the modified garnet solid electrolyte sheet obtained in Example 1 of the present invention after being immersed in molten lithium at 300° C. for different days.

[0027] Figure 2 These are fracture photos of the modified garnet solid electrolyte sheet obtained in Example 1 of the present invention after being immersed in molten lithium at 600° C. for different days.

[0028] Figure 3 These are fracture photos of the garnet-type solid electrolyte sheet obtained in Comparative Example 1 of the present invention after being immersed in molten lithium at 300° C. for different days.

[0029] Figure 4 This is an XPS test image of a partial cross-section of the internal ceramic sheet of the modified garnet-type solid electrolyte sheet obtained in Example 1 after being immersed in molten lithium at 300°C for 12 days.

[0030] Figure 5 This is an XPS test image of the blackened portion of the garnet solid electrolyte sheet obtained in Comparative Example 1 after being immersed in molten lithium at 300°C for 12 days. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0032] In a first aspect, a specific embodiment of the present invention provides a method for preparing a modified garnet-type solid electrolyte sheet, the preparation method comprising the following steps:

[0033] S1: providing a metal layer on the surface of a garnet-type solid electrolyte sheet, and then sintering and oxidizing it to obtain a garnet-type solid electrolyte sheet having a metal oxide layer on the surface;

[0034] S2: Immersing the garnet-type solid electrolyte sheet having a metal oxide layer on its surface in step S1 into molten lithium, sequentially performing a replacement reaction and an alloying reaction to obtain the modified garnet-type solid electrolyte sheet having an interface layer on its surface, wherein the interface layer includes Li2O and a lithium-containing alloy.

[0035] In order to solve the problem that the garnet-type solid electrolyte sheet is in long-term contact with lithium during use, the strong reducing property of lithium reduces the ions in the lattice of the garnet-type solid electrolyte sheet, causing the internal structure to change and shortening the life of the garnet-type solid electrolyte sheet. The present invention first provides a metal layer on the surface of the garnet-type solid electrolyte sheet (the entire surface of the garnet-type solid electrolyte sheet), then sintering and oxidizing the metal layer to oxidize it into a corresponding metal oxide layer, and then immersing it in molten lithium. The molten lithium and the metal oxide layer first undergo a replacement reaction to obtain Li2O and the corresponding metal, and the reaction formula is: 2Li+MO=Li2O+M (wherein M is the corresponding metal in the metal layer); then an alloying reaction is carried out, and the molten lithium and the replaced metal alloy react to obtain a lithium-containing alloy. Therefore, an interface layer in which Li2O and the lithium-containing alloy coexist is finally obtained on the surface of the garnet-type solid electrolyte sheet, which not only reduces the contact between the garnet-type solid electrolyte sheet and the lithium metal during use, but also does not affect the Li + Normal transport of lithium metal is ensured, ensuring high ionic conductivity. If the interface layer contains only lithium-containing alloy, although the conductivity is high, the lithium therein will react with the garnet-type solid electrolyte sheet. If the interface layer contains only Li2O, although it can isolate lithium metal, its ionic conductivity is low. Therefore, the interface layer in which Li2O and lithium-containing alloy coexist in the present invention can both isolate lithium metal and ensure ionic conductivity, and has high stability to lithium under high temperature conditions (250°C to 600°C).

[0036] In a specific embodiment, the thickness of the metal layer in step S1 is 3μm-6μm, for example, it can be 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm or 6μm, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0037] The thickness of the metal layer of the present invention will affect the thickness of the final interface layer. If the metal layer is too thin, the thickness of the final interface layer will be too thin, and it will not have an effective protection effect. If the metal layer is too thick, the final interface layer will be too thick, which will affect lithium ion conduction.

[0038] In a specific embodiment, the method of providing the metal layer in step S1 includes an evaporation method.

[0039] The present invention adopts the evaporation method to set the metal layer, and the present invention does not specifically limit the specific conditions of the evaporation; the growth rate of the coating during exemplary evaporation is 1-2nm / s, for example, it can be 1nm / s, 1.5nm / s or 2nm / s, but is not limited to the listed values, and other unlisted values ​​within the numerical range are also applicable.

[0040] In a specific embodiment, the material of the metal layer in step S1 includes any one of Mg, Al or Ag, or a combination of at least two of them.

[0041] The material of the metal layer in step S1 of the present invention includes Mg, Al or Ag. These metals can generate oxides under high temperature conditions in an oxygen-containing atmosphere and can react with lithium metal to form alloys. Therefore, the lithium-containing alloy in the interface layer finally obtained can be a lithium-magnesium alloy, a lithium-aluminum alloy or a lithium-silver alloy.

[0042] In a specific embodiment, the sintering oxidation in step S1 is performed in an oxygen-containing atmosphere, and the oxygen-containing atmosphere includes an air atmosphere.

[0043] In a specific embodiment, the sintering oxidation temperature in step S1 is 650°C-750°C, for example, it can be 650°C, 670°C, 690°C, 710°C, 730°C or 750°C, the time is 30min-60min, for example, it can be 30min, 40min, 50min or 60min, and the heating rate is 4°C / min-6°C / min, for example, it can be 4°C / min, 4.5°C / min, 5°C / min, 5.5°C / min or 6°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] The sintering and oxidation conditions of the present invention affect the stability and oxidation effect of the garnet-type solid electrolyte sheet. If the heating rate of the sintering and oxidation is too low, the oxidation efficiency will be affected, but if the heating rate is too high, the garnet-type solid electrolyte sheet will easily crack. If the sintering and oxidation temperature is too low and / or the time is too short, the oxidation will be incomplete. If the sintering and oxidation temperature is too high and / or the time is too long, the surface metal will volatilize.

[0045] In a specific embodiment, the garnet-type solid electrolyte sheet in step S1 includes an LLZO ceramic sheet or an LLZTO ceramic sheet.

[0046] The garnet-type solid electrolyte sheet of the present invention can be an LLZO ceramic sheet or an LLZTO ceramic sheet. The present invention does not specifically limit the preparation method of the garnet-type solid electrolyte sheet. If necessary, the surface thereof is polished (e.g., polished with 600 mesh or 1200 mesh diamond sandpaper) to obtain a ceramic sheet with a smooth surface.

[0047] In a specific embodiment, the alloying reaction time in step S2 is more than 48 hours, for example, it can be 48 hours, 60 hours, 72 hours, 84 hours, 96 hours or 108 hours, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0048] The time of the alloying reaction described in the present invention is related to the thickness of the metal layer described in step S1. For every 1.5 μm increase in the thickness of the metal layer, the time of the alloying reaction increases by at least 24 hours. If the alloying reaction time is too short, the alloying is incomplete, resulting in the presence of unalloyed elemental metal in the interface layer, resulting in a decrease in the lithium ion conductivity of the garnet-type solid electrolyte sheet.

[0049] In a specific embodiment, the temperature of the alloying reaction in step S2 is 350°C-400°C, for example, it can be 350°C, 360°C, 370°C, 380°C, 390°C or 400°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0050] After the replacement reaction is completed, the temperature is raised to carry out the alloying reaction. That is, after the replacement reaction is completed, the alloying reaction can be achieved by immersing the substrate in molten lithium and then directly raising the temperature to carry out annealing.

[0051] In one specific embodiment, the temperature of the replacement reaction in step S2 is 200°C-250°C, for example, it can be 200°C, 210°C, 220°C, 230°C, 240°C or 250°C, but is not limited to the listed values. Other values ​​not listed within the numerical range are also applicable.

[0052] In a specific embodiment, the replacement reaction time in step S2 is 20 h-28 h, for example, 20 h, 22 h, 24 h, 26 h or 28 h, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0053] In a specific embodiment, the thickness of the interface layer in step S2 is 5 μm-11 μm, for example, it can be 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or 11 μm, but is not limited to the listed values. Other unlisted values ​​within the numerical range are also applicable.

[0054] In a second aspect, a specific embodiment of the present invention provides a modified garnet-type solid electrolyte sheet, which is prepared by the preparation method described in the first aspect.

[0055] In a specific embodiment, the applicable temperature range of the modified garnet solid electrolyte sheet of the present invention is 250°C to 600°C.

[0056] In a third aspect, a specific embodiment of the present invention provides an application of the modified garnet-type solid electrolyte sheet as described in the second aspect, wherein the application includes use in a solid-state battery.

[0057] The technical solution of the present invention is further illustrated by specific examples. The preparation method of the LLZTO ceramic sheet used in the following examples and comparative examples includes the following steps:

[0058] Mix LLZTO pre-calcined powder and water in a mass ratio of 1:1 to obtain a slurry with a solid content of 50%. Pour the slurry into a sand mill and add 1% mass fraction of PVA. The sand mill speed is 2000rpm and the time is 100min. The powder is fully ground and mixed with PVA. The ground slurry is connected to the spray granulator, and the air inlet temperature is set to 160℃ and the air outlet temperature is set to 90℃. Start spray granulation. A 1% release agent was added to the mold and evenly applied. The powder obtained by spraying was then added. After smoothing the surface with a scraper, the press was started and the pressure was set to 100 MPa to produce the LLZTO ceramic electrolyte green body. 60 g of pre-fired, but unsanded, LLZTO pre-fired powder was added to the bottom of an Al2O3 crucible as a buried powder. After lightly flattening, the green body was placed on top of the buried powder. The sintering temperature range was set from 1220°C / 10 min to 1100°C / 600 min. After sintering, the LLZTO ceramic sheet was removed after cooling to room temperature.

[0059] The surface of the obtained LLZTO ceramic sheet was polished with 600 mesh and 1200 mesh diamond sandpaper to obtain an LLZTO ceramic sheet with a smooth surface.

[0060] The preparation method of the LLZTO ceramic sheet provided above is described for the completeness of the technical solution and should not be regarded as limiting the present invention.

[0061] Example 1

[0062] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet, the preparation method comprising the following steps:

[0063] S1: A magnesium metal layer with a thickness of 3 μm is uniformly deposited on the surface of the LLZTO ceramic sheet using a vacuum evaporation device.

[0064] The steps of vacuum evaporation are as follows: first, place the sample on the sample table, then put it into the evaporation coating instrument, and start the vacuum operation after it is completely sealed. When the vacuum degree reaches 1×10 -3 After Pa, start to increase the evaporation current, slowly increase the evaporation current until the metal liquefies and stops increasing, then observe the data of the film thickness meter, continue to slowly increase the evaporation current until the film thickness meter shows that the film growth rate reaches 1.5nm / s, stop increasing the evaporation current, 15min later, when the film thickness meter shows that the film thickness reaches 3μm, reduce the evaporation current to 0, turn off the evaporation coating instrument, and take out the sample after it is completely cooled.

[0065] S2: placing the evaporated LLZTO ceramic sheet obtained in step S1 in a box furnace, heating it to 700° C. at 5° C. / min in an air atmosphere and keeping the temperature for 30 min to oxidize the magnesium metal layer into a magnesium oxide layer.

[0066] S3: Immerse the LLZTO ceramic sheet with a magnesium oxide layer on the surface obtained in step S2 in molten metal lithium at 200° C. for 24 hours to perform a replacement reaction, where lithium reacts with magnesium oxide to obtain lithium oxide and magnesium.

[0067] S4: Continue heating to 350° C. and annealing for 48 hours to perform an alloying reaction. Lithium and magnesium react to form a lithium-magnesium alloy, thereby obtaining an LLZTO ceramic sheet including a lithium oxide and a lithium-magnesium alloy interface layer. The thickness of the interface layer is 5 μm.

[0068] Example 2

[0069] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet, the preparation method comprising the following steps:

[0070] S1: A vacuum evaporation device is used to uniformly deposit a 4.5 μm thick aluminum metal layer on the surface of the LLZTO ceramic sheet.

[0071] The steps of vacuum evaporation are as follows: first, place the sample on the sample table, then put it into the evaporation coating instrument, and start the vacuum operation after it is completely sealed. When the vacuum degree reaches 1×10 -3 After Pa, start to increase the evaporation current, slowly increase the evaporation current until the metal liquefies and stops increasing, then observe the data of the film thickness meter, continue to slowly increase the evaporation current until the film thickness meter shows that the film growth rate reaches 1nm / s, stop increasing the evaporation current, after 25 minutes, when the film thickness meter shows that the film thickness reaches 4.5μm, reduce the evaporation current to 0, turn off the evaporation coating instrument, and take out the sample after it is completely cooled.

[0072] S2: placing the evaporated LLZTO ceramic sheet obtained in step S1 in a box furnace, heating it to 650° C. at 4° C. / min in an air atmosphere and holding the temperature for 60 min to oxidize the aluminum metal layer into an aluminum oxide layer.

[0073] S3: Immerse the LLZTO ceramic sheet with an aluminum oxide layer on the surface obtained in step S2 in molten metal lithium at 250° C. for 20 hours to perform a replacement reaction, where lithium reacts with aluminum oxide to obtain lithium oxide and aluminum.

[0074] S4: Continue heating to 380° C. and annealing for 72 hours to perform an alloying reaction. Lithium reacts with aluminum to form a lithium-aluminum alloy, thereby obtaining an LLZTO ceramic sheet including a lithium oxide and a lithium-aluminum alloy interface layer. The thickness of the interface layer is 8 μm.

[0075] Example 3

[0076] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet, the preparation method comprising the following steps:

[0077] S1: A silver metal layer with a thickness of 6 μm is uniformly deposited on the surface of the LLZTO ceramic sheet using a vacuum evaporation device.

[0078] The steps of vacuum evaporation are as follows: first, place the sample on the sample table, then put it into the evaporation coating instrument, and start the vacuum operation after it is completely sealed. When the vacuum degree reaches 1×10 -3 After Pa, start to increase the evaporation current, slowly increase the evaporation current until the metal liquefies and stops increasing, then observe the data of the film thickness meter, continue to slowly increase the evaporation current until the film thickness meter shows that the film growth rate reaches 2nm / s, stop increasing the evaporation current, 30min later, when the film thickness meter shows that the film thickness reaches 6μm, reduce the evaporation current to 0, turn off the evaporation coating instrument, and take out the sample after it is completely cooled.

[0079] S2: The evaporated LLZTO ceramic sheet obtained in step S1 is placed in a box furnace, and the temperature is raised to 750° C. at 6° C. / min in an air atmosphere and kept at this temperature for 45 minutes to oxidize the silver metal layer into a silver oxide layer.

[0080] S3: Immerse the LLZTO ceramic sheet with a silver oxide layer on the surface obtained in step S2 in molten metal lithium at 250° C. for 28 hours to perform a replacement reaction, where lithium reacts with silver oxide to obtain lithium oxide and silver.

[0081] S4: Continue heating to 400° C. and annealing for 96 hours to perform an alloying reaction, where lithium reacts with silver to form a lithium-silver alloy, thereby obtaining an LLZTO ceramic sheet including a lithium oxide and lithium-silver alloy interface layer, wherein the thickness of the interface layer is 11 μm.

[0082] Example 4

[0083] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet. The preparation method is the same as that of Example 1, except that the thickness of the magnesium metal layer in step S1 is 2 μm and the adaptability of the obtained interface layer is changed.

[0084] Example 5

[0085] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet. The preparation method is the same as that of Example 1, except that the thickness of the magnesium metal layer in step S1 is 7.5 μm and the adaptability of the obtained interface layer is changed.

[0086] Example 6

[0087] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet. The preparation method is the same as that of Example 1, except that the thickness of the magnesium metal layer in step S1 is 7.5 μm and the annealing time in step S4 is 120 h.

[0088] Example 7

[0089] This embodiment provides a method for preparing a modified garnet-type solid electrolyte sheet. The preparation method is the same as that of Example 1 except that the annealing time in step S4 is 40 hours.

[0090] Comparative Example 1

[0091] This comparative example provides a garnet-type solid electrolyte sheet, which is a garnet-type solid electrolyte sheet that has not been processed by steps S1 to S4 of Example 1.

[0092] Comparative Example 2

[0093] This comparative example provides a method for preparing a garnet-type solid electrolyte sheet. The preparation method is the same as Example 1, except that step S2 and step S3 are not performed and the obtained interface layer does not contain lithium oxide.

[0094] Comparative Example 3

[0095] This comparative example provides a method for preparing a garnet-type solid electrolyte sheet. The preparation method is the same as that of Example 1, except that step S4 is not performed and the obtained interface layer does not contain lithium-magnesium alloy.

[0096] Multiple pieces of the modified garnet-type solid electrolyte sheets obtained in the above examples and the garnet-type solid electrolyte sheets obtained in the comparative example were immersed in molten lithium at 300°C (multiple pieces of the electrolyte sheets obtained in Examples 1-3 were immersed in molten lithium at 600°C). After taking out one piece every three days and breaking it, the fracture surface was photographed for archival analysis. The fracture surface photographs of the modified garnet-type solid electrolyte sheet obtained in Example 1 after being immersed in molten lithium at 300°C for different days are shown in FIG. Figure 1 As shown by Figure 1 It can be seen that after immersing in molten lithium at 300°C for 12 days, the interior of the ceramic piece of Example 1 is still its own light yellow color, and no other changes have occurred. The XPS test of the interior of the ceramic piece of the ceramic piece that has been immersed for 12 days is performed, and the test results are as follows: Figure 4 As shown, no change in the element valence state was observed. The fracture photos of the modified garnet solid electrolyte sheet obtained in Example 1 after being immersed in molten lithium at 600°C for different days are shown in FIG. Figure 2 As shown by Figure 2It can be seen that after immersing in molten lithium at 600°C for 12 days, the interior of the ceramic sheet of Example 1 is still its original light yellow color, and no other changes have occurred. The fracture photos of the garnet-type solid electrolyte sheet obtained in Comparative Example 1 after immersion for different days are as follows: Figure 3 As shown, after 3 days of immersion, the inside of the ceramic piece has become black to varying degrees. The longer the immersion time, the more serious the blackening. The blackened part of the ceramic piece was taken for XPS test, and the test results were Figure 5 As shown in the figure, the Ta element is no longer pure +5 valence, but has been reduced to various valence states from +1 to +4.

[0097] The modified garnet-type solid electrolyte sheet obtained in the above embodiment and the garnet-type solid electrolyte sheet obtained in the comparative example were immersed in molten lithium, and the changes in the internal structure of the ceramic sheet are shown in Table 1. The room temperature ionic conductivity of the modified garnet-type solid electrolyte sheet obtained in the above embodiment and the garnet-type solid electrolyte sheet obtained in the comparative example was tested by AC impedance spectroscopy, and the test results are shown in Table 1:

[0098] Table 1

[0099]

[0100]

[0101] From Table 1 we can see that:

[0102] (1) It can be seen from Example 1 and Comparative Example 1 that the interface layer prepared by the present invention can not only isolate lithium metal, so that the modified garnet-type solid electrolyte sheet has higher stability to lithium, but also ensure ionic conductivity; it can be seen from Example 1 and Comparative Example 2 that when step S2 and step S3 are not performed, the obtained interface layer does not contain lithium oxide, and the interface layer contains a separate lithium-containing alloy. The lithium in the lithium-containing alloy will react with LLZTO, thereby reducing the lithium stability of the garnet-type solid electrolyte sheet; it can be seen from Example 1 and Comparative Example 3 that when step S4 is not performed, the obtained interface layer does not contain a lithium-containing alloy, but contains lithium oxide and metal, thereby reducing the ionic conductivity of the garnet-type solid electrolyte sheet.

[0103] (2) It can be seen from Examples 1 and 4 that when the thickness of the metal layer is too thin, the thickness of the corresponding interface layer is too thin, the protective effect of the interface layer is reduced, and the stability of the garnet-type solid electrolyte sheet to lithium is reduced; it can be seen from Examples 1 and 5-6 that when the thickness of the metal layer is too thick, it will affect the transmission of lithium ions. Even if the alloying reaction time is increased to achieve complete alloying, the transmission of lithium ions will be affected; it can be seen from Examples 1 and 7 that the alloying reaction time will affect the degree of alloying. When the alloying reaction time is too short, the interface layer still contains unalloyed metal, which will affect the transmission of lithium ions and affect the ionic conductivity of the garnet-type solid electrolyte sheet.

[0104] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a modified garnet-type solid electrolyte sheet, characterized in that: The preparation method comprises the following steps: S1: providing a metal layer on the surface of a garnet-type solid electrolyte sheet, and then sintering and oxidizing it to obtain a garnet-type solid electrolyte sheet having a metal oxide layer on the surface; S2: Immersing the garnet-type solid electrolyte sheet having a metal oxide layer on its surface in step S1 into molten lithium, sequentially performing a replacement reaction and an alloying reaction to obtain the modified garnet-type solid electrolyte sheet having an interface layer on its surface, wherein the interface layer includes Li2O and a lithium-containing alloy.

2. The preparation method according to claim 1, characterized in that The thickness of the metal layer in step S1 is 3 μm-6 μm.

3. The preparation method according to claim 1 or 2, characterized in that The method of providing the metal layer in step S1 includes an evaporation method; And / or, the material of the metal layer in step S1 includes any one of Mg, Al or Ag, or a combination of at least two of them.

4. The preparation method according to claim 1 or 2, characterized in that The sintering oxidation in step S1 is performed in an oxygen-containing atmosphere, wherein the oxygen-containing atmosphere includes an air atmosphere; And / or, the sintering oxidation in step S1 is performed at a temperature of 650° C. to 750° C., for a time of 30 min to 60 min, and at a heating rate of 4° C. / min to 6° C. / min.

5. The preparation method according to claim 1 or 2, characterized in that The garnet-type solid electrolyte sheet in step S1 includes an LLZO ceramic sheet or an LLZTO ceramic sheet.

6. The preparation method according to claim 1 or 2, characterized in that The alloying reaction time in step S2 is more than 48 hours; And / or, the temperature of the alloying reaction in step S2 is 350°C-400°C.

7. The preparation method according to claim 1 or 2, characterized in that The temperature of the replacement reaction in step S2 is 200°C-250°C; And / or, the replacement reaction time in step S2 is 20h-28h.

8. The preparation method according to claim 1 or 2, characterized in that The thickness of the interface layer in step S2 is 5 μm-11 μm.

9. A modified garnet-type solid electrolyte sheet, characterized in that: The modified garnet-type solid electrolyte sheet is prepared by the preparation method according to any one of claims 1 to 8.

10. A use of the modified garnet-type solid electrolyte sheet according to claim 9, characterized in that: Such applications include use in solid-state batteries.

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