A solid electrolyte sheet for solid-state battery and preparation method thereof

Abstract

The present invention discloses a solid electrolyte sheet for solid-state batteries and a preparation method thereof, comprising the following steps: step S1: calcining the raw material powders separately; step S2: weighing the calcined raw material powders according to the stoichiometric ratio in the chemical formula; step S3: mixing the weighed powders to obtain a mixed powder, adding a ball milling agent for ball milling to obtain a uniform mixed slurry, and drying to obtain a ball-milled mixed powder; step S4: sintering the ball-milled mixed powder once to obtain a solid electrolyte precursor powder, pressing the precursor powder into a sheet, and sintering it twice to obtain a solid electrolyte sheet; step S5: after polishing the solid electrolyte sheet, dripping a hydrofluoric acid solution on one bottom surface of the solid electrolyte sheet and drying it, dripping a hydrofluoric acid solution on the other opposite bottom surface of the solid electrolyte sheet and drying it to complete the preparation. The present invention improves the performance of lithium lanthanum zirconium tantalum oxide solid electrolyte.

Description

Technical Field

[0001] The present invention relates to the field of solid battery materials, and in particular to a solid electrolyte sheet for solid-state batteries and a preparation method thereof. Background Art

[0002] Currently, fossil fuels are facing a crisis and pose serious environmental risks. New alternative energy sources and efficient energy storage systems are gaining increasing attention. Since renewable energy sources like solar, wind, and hydropower are difficult to store, energy storage devices are particularly important in modern production and life. Among commercial portable electrochemical energy storage devices, lithium-ion batteries are the most widely used. Lithium batteries consist of a positive electrode, a separator, a negative electrode, an electrolyte, and a battery casing. Due to their high voltage and high specific energy, they are widely used in mobile phones and laptops. Traditional lithium-ion batteries generally use organic liquid electrolytes. While these have relatively low ionic resistance, the use of liquid electrolytes has many drawbacks, including safety hazards (electrolyte leakage, flammability, and explosion), short service life, high cost, and low energy density. Comparisons between solid-state and liquid electrolytes have shown that solid electrolytes are more stable, safe, and reliable than liquid electrolytes.

[0003] However, the theoretical energy density of solid electrolyte lithium-ion batteries is 350-400W·h / kg, while the actual energy density is only 100-220W·h / kg, which is difficult to meet the growing demand for energy density in advanced energy storage and power applications. To address the above problems, people have developed lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolytes, which improve the electrical conductivity of solid electrolytes. However, lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolytes still have the following problems:

[0004] (1) There is a huge interfacial impedance between lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte and lithium metal;

[0005] (2) Lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte is unstable in air and easily reacts with moisture and carbon dioxide in the air, thereby producing a large amount of lithium carbonate on the surface of LLZO;

[0006] (3) Lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolytes are prone to forming lithium dendrites, which can lead to short circuits;

[0007] (4) Lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte easily reacts with the electrolyte (LE), resulting in huge LLZTO / electrolyte (LE) interface impedance. Summary of the Invention

[0008] In order to overcome the shortcomings of the existing technology, the present invention provides a solid electrolyte sheet for solid-state batteries and a preparation method thereof, which solves the technical problems in the existing technology of lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte having huge interface impedance with lithium metal, easy generation of a large amount of lithium carbonate on the surface, easy formation of lithium dendrites, and easy reaction with the electrolyte, thereby achieving the purpose of improving the performance of lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte.

[0009] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0010] A method for preparing a solid electrolyte sheet for a solid-state battery comprises the following steps:

[0011] Step S1: calcining lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder and tantalum oxide powder respectively;

[0012] Step S2: According to the chemical formula Li 6.5 La3Zr 1.5 Ta 0.5 O 12 calcined lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder, and tantalum oxide powder according to the stoichiometric ratio, wherein the lithium hydroxide powder is weighed in excess of 2% to 40% by mass based on the stoichiometric ratio;

[0013] Step S3: All the powders weighed in step S2 are mixed to obtain a mixed powder, a ball milling agent is added to the mixed powder to obtain a uniform mixed slurry, and then the mixed powder is dried to obtain a ball-milled mixed powder;

[0014] Step S4: sintering the ball-milled mixed powder once to obtain a solid electrolyte precursor powder, pressing the solid electrolyte precursor powder into a sheet, and sintering it twice to obtain a solid electrolyte sheet;

[0015] Step S5: After the solid electrolyte sheet is polished, a hydrofluoric acid solution is dripped onto one bottom surface of the solid electrolyte sheet and dried, and a hydrofluoric acid solution is dripped onto the other opposite bottom surface of the solid electrolyte sheet and dried to complete the preparation.

[0016] As a preferred embodiment of the present invention, in step S5, the concentration of the hydrofluoric acid solution is 15% to 50% by mass, and the amount of the hydrofluoric acid solution added is 20 to 100 μL.

[0017] As a preferred embodiment of the present invention, the concentration of the hydrofluoric acid solution is 25% to 45% by mass.

[0018] As a preferred embodiment of the present invention, in step S5, the concentration of the hydrofluoric acid solution is 0.1% to 15% by mass, and the amount of the hydrofluoric acid solution added is 20 to 100 μL.

[0019] As a preferred embodiment of the present invention, the concentration of the hydrofluoric acid solution is 1% to 10% by mass.

[0020] As a preferred embodiment of the present invention, in step S5, the concentration of the hydrofluoric acid solution added to one bottom surface of the solid electrolyte sheet is 15% to 50% by mass, and the concentration of the hydrofluoric acid solution added to the other opposite bottom surface of the solid electrolyte sheet is 0.1% to 15%. The amount of the hydrofluoric acid solution added twice is 20 to 100 μL.

[0021] As a preferred embodiment of the present invention, the concentration of the hydrofluoric acid solution added to one bottom surface of the solid electrolyte sheet is 25% to 45% by mass, and the concentration of the hydrofluoric acid solution added to the other opposite bottom surface of the solid electrolyte sheet is 1% to 10% by mass.

[0022] As a preferred embodiment of the present invention, the calcination temperature in step S1 is 700-1000°C, and the time is 1-48 hours; in step S3, the ball milling agent is any one of ethanol, isopropanol, acetonitrile, ether, petroleum ether or acetone, the mass ratio of the mixed powder, the ball milling agent and the ball milling beads is mixed powder: ball milling agent: ball milling beads = 1:1-5:4-20, the ball milling time is 4-48 hours, the ball milling speed is 200-1200 r / min, the drying temperature is 50-150°C, and the drying time is 4-24 hours.

[0023] As a preferred embodiment of the present invention, in step S4, the primary sintering temperature is 700-1200° C., the time is 4-24 hours, and the secondary sintering temperature is 1050-1500° C., the time is 0.5-20 hours;

[0024] The drying temperature in step S5 is 50-100° C. and the drying time is 1-8 hours.

[0025] A solid electrolyte sheet for a solid-state battery is prepared by the above-mentioned preparation method.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The LLZTO solid electrolyte sheet treated with a high-solubility hydrofluoric acid solution has a very good effect in inhibiting the formation of lithium carbonate. No lithium carbonate is generated after being placed in air for 90 days.

[0028] (2) The interface impedance between the LLZTO solid electrolyte sheet and lithium metal after high concentration hydrofluoric acid solution is only 3Ω·cm 2 , it can stably cycle for more than 7000h at room temperature, solving the battery interface problem on the negative electrode side of the battery;

[0029] (3) After treatment with low-concentration hydrofluoric acid solution, the interface impedance between the LLZTO solid electrolyte sheet and the electrolyte is only 41Ω·cm 2 ,, used to assemble lithium symmetric batteries, at 0.5 mA·cm -1 It can stably cycle for more than 900 hours, solving the battery interface problem on the positive electrode side of the battery;

[0030] (4) The LLZTO solid electrolyte sheet treated with high-concentration hydrofluoric acid solution and low-concentration hydrofluoric acid solution was used to assemble the LFP full battery. After 900 cycles at 1C, the capacity retention rate could reach 85.6%. It was used to assemble the NCM811 full battery. After 200 cycles at 0.5C, the capacity retention rate could reach 89%, which gave the full battery excellent battery performance.

[0031] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 - is the impedance spectrum of the solid electrolyte sheet of the comparative example of the present invention;

[0033] Figure 2 - is the XRD diffraction pattern of the solid electrolyte sheet of the comparative example of the present invention;

[0034] Figure 3 - is a scanning electron microscope image of a solid electrolyte sheet of a comparative example of the present invention;

[0035] Figure 4 - is the impedance spectrum of the solid electrolyte sheet of Example 1 of the present invention;

[0036] Figure 5 - is the impedance spectrum of the solid electrolyte sheet of Example 2 of the present invention;

[0037] Figure 6 - is the impedance spectrum of the solid electrolyte sheet of Example 3 of the present invention;

[0038] Figure 7 - is the impedance spectrum of the solid electrolyte sheet of Example 4 of the present invention;

[0039] Figure 8 - is the XRD diffraction pattern of the solid electrolyte sheet of Example 4 of the present invention;

[0040] Figure 9- is a scanning electron microscope image of the solid electrolyte sheet of Example 4 of the present invention;

[0041] Figure 10 - is the interface impedance diagram of the assembled lithium symmetrical battery of Example 4 of the present invention;

[0042] Figure 11 - is a cycle test diagram of the assembled lithium symmetrical battery of Example 4 of the present invention;

[0043] Figure 12 - is a cycle test diagram of the assembled lithium symmetrical battery of the comparative example of the present invention;

[0044] Figure 13 - is the impedance spectrum of the solid electrolyte sheet of Example 5 of the present invention;

[0045] Figure 14 - is the impedance spectrum of the solid electrolyte sheet of Example 6 of the present invention;

[0046] Figure 15 - is the impedance spectrum of the solid electrolyte sheet of Example 7 of the present invention;

[0047] Figure 16 - is the XRD diffraction pattern of the solid electrolyte sheet of Example 7 of the present invention;

[0048] Figure 17 - is a scanning electron microscope image of the solid electrolyte sheet of Example 7 of the present invention;

[0049] Figure 18 - is a cycle test diagram of the assembled lithium symmetrical battery of Example 7 of the present invention;

[0050] Figure 19 - is the impedance spectrum of the solid electrolyte sheet of Example 8 of the present invention;

[0051] Figure 20 - is a cycle test diagram of the assembled LFP full cell of Example 9 of the present invention;

[0052] Figure 21 - is a cycle test chart of an NCM811 full battery assembled in Example 9 of the present invention;

[0053] Figure 22 - is a cycle test diagram of the hf-LLZTO solid electrolyte sheet of Example 9 of the present invention assembled into an LFP full battery. DETAILED DESCRIPTION

[0054] The method for preparing a solid electrolyte sheet for a solid-state battery provided by the present invention comprises the following steps:

[0055] Step S1: Lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder and tantalum oxide powder are placed in a muffle furnace respectively and calcined at 900° C. for 12 hours.

[0056] Step S2: According to the chemical formula Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The stoichiometric ratio of (lithium lanthanum zirconium tantalum oxide) is adopted, and calcined lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder and tantalum oxide powder are weighed. Among them, the lithium hydroxide powder is weighed in excess of 2% to 40% by mass on the basis of the stoichiometric ratio.

[0057] Preferably, the lithium hydroxide powder is weighed in excess of 7% to 20% by mass.

[0058] Step S3: All the weighed powders are mixed to obtain a mixed powder, the mixed powder is placed in a ball mill, a ball milling agent is added, and ball milling is performed to obtain a uniform mixed slurry, which is then dried at 50 to 150° C. for 4 to 24 hours to obtain a ball-milled mixed powder.

[0059] Preferably, the drying is carried out at 60-120° C. for 6-16 hours.

[0060] The ball milling conditions are as follows:

[0061] The grinding agent is any one of ethanol, isopropanol, acetonitrile, ether, petroleum ether and acetone;

[0062] The material of the ball milling beads is any one of agate, zirconia, stainless steel, and polyurethane;

[0063] The mass ratio of the mixed powder, the ball milling agent and the ball milling beads is mixed powder: ball milling agent: ball milling beads = 1:1-5:4-20;

[0064] The ball milling time is 4 to 48 hours, and the ball milling speed is 200 to 1200 r / min. Preferably, the ball milling time is 8 to 24 hours, and the speed is 400 to 800 r / min.

[0065] Step S4: The mixed powder after ball milling is transferred to a muffle furnace for primary sintering to obtain a solid electrolyte precursor powder. The solid electrolyte precursor powder is then pressed into The disc is sintered twice to obtain an LLZTO solid electrolyte sheet;

[0066] The specific conditions of the first sintering are: sintering at 700-1200° C. for 4-24 hours; the specific conditions of the second sintering are: sintering at 1050-1500° C. for 0.5-20 hours.

[0067] Preferably, the solid electrolyte precursor powder is pressed into of round pieces.

[0068] Preferably, the specific conditions of the primary sintering are: sintering at 850-1050° C. for 6-16 hours.

[0069] Preferably, the specific conditions of the secondary sintering are: sintering at 1150-1400° C. for 1-8 hours.

[0070] Step S5: After the solid electrolyte sheet is polished, a hydrofluoric acid solution is added to one bottom surface of the solid electrolyte sheet, which is then placed in an oven and dried at 50-100°C for 1-8 hours. A hydrofluoric acid solution is added to the other opposite bottom surface of the solid electrolyte sheet, which is then placed in an oven and dried at 50-100°C for 1-8 hours to complete the preparation.

[0071] When LLZTO (lithium lanthanum zirconium tantalum oxide) solid electrolyte sheets are exposed to air, a large amount of lithium carbonate (Li2CO3) is generated on the surface of the LLZTO solid electrolyte sheet, resulting in a significant interfacial impedance. However, treatment with a hydrofluoric acid solution can convert the lithium carbonate (Li2CO3) on the LLZTO surface into the lithiophilic LiF. The hydrofluoric acid solution further reacts with the LLZTO solid electrolyte sheet to form LiF-LaF3 on the LLZTO solid electrolyte sheet, thereby inhibiting the further formation of Li2CO3 on the LLZTO solid electrolyte sheet surface and improving the storage capacity of the LLZTO solid electrolyte sheet.

[0072] Preferably, after the hydrofluoric acid solution is added dropwise, the mixture is placed in an oven at 60-80° C. and dried for 2-4 hours.

[0073] Preferably, the concentration of the hydrofluoric acid solution is 15% to 50% by mass (defined as a high concentration in the present invention), and the amount of the hydrofluoric acid solution added is 20 to 100 μL. The LL ZTO solid electrolyte sheet treated with the high-solubility hydrofluoric acid solution is named HF-LLZTO solid electrolyte sheet.

[0074] The purpose of the treatment with a high-concentration hydrofluoric acid solution is to utilize the high solubility of the high-concentration hydrofluoric acid solution to generate a specific three-dimensional burr microsphere structure composed of LiF-LaF3 on the surface of the LLZTO solid electrolyte sheet, thereby improving interfacial compatibility and inhibiting the growth of lithium dendrites. The three-dimensional burr microspheres have a large specific surface area, which is conducive to the infiltration and diffusion of molten lithium. As a result, a three-dimensional lithium ion transport channel is formed between the LLZTO solid electrolyte and lithium metal, which greatly reduces the interfacial impedance and improves the lithium ion transport capacity at the interface.

[0075] More preferably, the concentration of the hydrofluoric acid solution is 25% to 45% by mass.

[0076] Preferably, the concentration of the hydrofluoric acid solution is 0.1% to 15% by mass (defined as low concentration in the present invention), and the amount of the hydrofluoric acid solution added is 20 to 100 μL. The LL ZTO solid electrolyte sheet treated with the low-concentration hydrofluoric acid solution is named hf-LLZTO solid electrolyte sheet.

[0077] Using a low-concentration hydrofluoric acid solution to treat the LLZTO solid electrolyte sheet can form a strong, ultra-thin, and dense LiF-LaF3 layer structure on the surface. The strong structure greatly improves the interface's ability to inhibit dendrite growth, the ultra-thin structure greatly improves the transport capacity of lithium ions at the interface, and the dense structure effectively prevents electrolyte corrosion on the LLZTO solid electrolyte sheet, thereby greatly improving the interfacial performance between the LLZTO solid electrolyte sheet and the electrolyte.

[0078] More preferably, the concentration of the hydrofluoric acid solution is 1% to 10% by mass.

[0079] Preferably, the concentration of the hydrofluoric acid solution added to one bottom surface of the solid electrolyte sheet is 15% to 50% by mass, and the concentration of the hydrofluoric acid solution added to the opposite bottom surface of the solid electrolyte sheet is 0.1% to 15%. The amount of hydrofluoric acid solution added in both additions is 20 to 100 μL. The LLZTO solid electrolyte sheet treated with the high- and low-solubility hydrofluoric acid solutions is designated as HF-LLZTO-hf solid electrolyte sheet.

[0080] The LLZTO solid electrolyte sheet was treated with high-concentration hydrofluoric acid solution and low-concentration hydrofluoric acid solution. After the high-concentration hydrofluoric acid solution was used on one side of the LLZTO solid electrolyte sheet, a LiF-LaF3 three-dimensional burr microsphere structure protective layer was formed on the surface of that side, isolating the LLZTO solid electrolyte sheet from the air. After the low-concentration hydrofluoric acid solution was used on the other side of the LLZTO solid electrolyte sheet, a LiF-LaF3 layer structure was formed on the surface of that side, which improved the ability of the interface to inhibit dendrite growth.

[0081] More preferably, the concentration of the hydrofluoric acid solution added dropwise to one bottom surface of the solid electrolyte sheet is 25% to 45% by mass, and the concentration of the hydrofluoric acid solution added dropwise to the other opposite bottom surface of the solid electrolyte sheet is 1% to 10% by mass.

[0082] The solid electrolyte sheet for solid-state batteries provided by the present invention is prepared by the above-mentioned preparation method.

[0083] The following examples are provided to further illustrate the present invention, but the scope of the present invention is not limited thereto.

[0084] Comparative Example

[0085] Preparation of LLZTO solid electrolyte sheet:

[0086] According to the stoichiometric ratio of Li 6.5 La3Zr 1.5 Ta 0.5 O 12 4.5045g lithium hydroxide (lithium hydroxide is weighed in excess of 10%), 7.3305g lanthanum oxide, 2.772g zirconium oxide and 1.6575g tantalum oxide were weighed and placed in an agate ball mill jar, 15g isopropyl alcohol was added as a ball milling agent, and the ball milling was carried out at a speed of 350r / min for 24h. After that, the mixed slurry was dried in a 60℃ oven for 15h to obtain a dry mixed powder. The mixed powder was then sintered at 900℃ for 12h to obtain LLZO precursor powder, which was then pressed into a diameter of The disc was sintered at 1250℃ for 6h to obtain LLZTO solid electrolyte sheet. After polishing, its impedance and XRD were tested. The results are as follows Figure 1 and Figure 2 As shown, the conductivity of lithium ions is calculated to be 8.4x10 -4 S / cm.

[0087] The LLZTO solid electrolyte sheet of the comparative example was tested by scanning electron microscope (SEM), and the results are as follows: Figure 3 As shown by Figure 3 It can be seen that the grains in the LLZTO solid electrolyte sheet are closely arranged, and the grain size is about 3 μm, indicating that the density of the prepared LLZTO solid electrolyte sheet is very good.

[0088] Example 1

[0089] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 15% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 20 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 15% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 20 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain a HF-LLZTO solid electrolyte sheet. The impedance of the sheet was tested, and the impedance spectrum was shown as follows: Figure 4 As shown, the conductivity of lithium ions is calculated to be 6.65x10 -4 S / cm. By comparing the conductivity with that of the control example, it can be seen that the conductivity is decreasing, indicating that the hydrofluoric acid solution with a concentration of 15% corrodes the surface of the LLZTO solid electrolyte sheet, thereby forming a three-dimensional burr microsphere structure on the surface.

[0090] No diffraction peak of Li2CO3 was found in the XRD spectra before and after being placed in the air for 90 days, indicating that the treated HF-LLZTO solid electrolyte sheet has very good air stability.

[0091] Scanning electron microscopy (SEM) testing of the surface of the HF-LLZTO solid electrolyte sheet revealed that the surface of the treated HF-LLZTO solid electrolyte sheet was a three-dimensional burr microsphere. The HF-LL ZTO solid electrolyte was assembled into a lithium symmetrical battery, and the interface impedance between it and lithium metal was tested, which showed low interface impedance. The assembled lithium symmetrical battery was subjected to a cycle stability test, which showed that it could stably cycle for more than 7000 hours, demonstrating very good interface performance. This indicates that the structure formed by the LLZTO solid electrolyte sheet after treatment with a 15% hydrofluoric acid solution can solve the battery interface problem on the negative electrode side of the battery.

[0092] Example 2

[0093] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 20% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 40 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 20% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 40 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain an HF-LLZTO solid electrolyte sheet. The impedance of the sheet was tested, and the impedance spectrum was shown in FIG. Figure 5 As shown, the conductivity of lithium ions is calculated to be 6.5x10 -4 S / cm. By comparing the conductivity with that of Example 1, it can be seen that the conductivity continues to decrease, indicating that the hydrofluoric acid solution with a concentration of 20% further corrodes the surface of the LLZTO solid electrolyte sheet, and a three-dimensional burr microsphere structure continues to form on the surface.

[0094] No diffraction peak of Li2CO3 was found in the XRD spectra before and after being placed in the air for 90 days, indicating that the treated HF-LLZTO solid electrolyte sheet has very good air stability.

[0095] Scanning electron microscopy (SEM) testing of the surface of the HF-LLZTO solid electrolyte sheet revealed that the surface of the treated HF-LLZTO solid electrolyte sheet was a three-dimensional burr microsphere. The HF-LL ZTO solid electrolyte was assembled into a lithium symmetrical battery, and the interface impedance between it and lithium metal was tested, which showed low interface impedance. The assembled lithium symmetrical battery was subjected to a cycle stability test, which showed that it could stably cycle for more than 7000 hours, demonstrating very good interface performance. This indicates that the structure formed by the LLZTO solid electrolyte sheet after treatment with a 20% hydrofluoric acid solution can solve the battery interface problem on the negative electrode side of the battery.

[0096] Example 3

[0097] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 30% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 50 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 30% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 50 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain an HF-LLZTO solid electrolyte sheet. The impedance of the sheet was tested, and the impedance spectrum was shown in FIG. Figure 6 As shown, the conductivity of lithium ions is calculated to be 5.8x10 -4 S / cm. By comparing the conductivity with that of Example 2, it can be seen that the conductivity continues to decrease, indicating that the hydrofluoric acid solution with a concentration of 30% further corrodes the surface of the LLZTO solid electrolyte sheet, and a three-dimensional burr microsphere structure continues to form on the surface.

[0098] No diffraction peak of Li2CO3 was found in the XRD spectra before and after being placed in the air for 90 days, indicating that the treated HF-LLZTO solid electrolyte sheet has very good air stability.

[0099] Scanning electron microscopy (SEM) testing of the surface of the HF-LLZTO solid electrolyte sheet revealed that the surface of the treated HF-LLZTO solid electrolyte sheet was a three-dimensional burr microsphere. The HF-LL ZTO solid electrolyte was assembled into a lithium symmetrical battery, and the interface impedance between it and lithium metal was tested, which showed low interface impedance. The assembled lithium symmetrical battery was subjected to a cycle stability test, which showed that it could stably cycle for more than 7000 hours, demonstrating very good interface performance. This indicates that the structure formed by the LLZTO solid electrolyte sheet after treatment with a 30% hydrofluoric acid solution can solve the battery interface problem on the negative electrode side of the battery.

[0100] Example 4

[0101] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 40% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 80 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 40% hydrofluoric acid solution was added dropwise to the other bottom surface opposite to the LLZTO solid electrolyte sheet in an amount of 80 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain a HF-L LZTO solid electrolyte sheet. The impedance of the sheet was tested, and the impedance spectrum was shown as follows: Figure 7 As shown, the conductivity of lithium ions is calculated to be 4.7x10 -4 S / cm. By comparing the conductivity with that of Example 3, it can be seen that the conductivity continues to decrease, indicating that the hydrofluoric acid solution with a concentration of 40% further corrodes the surface of the LLZTO solid electrolyte sheet, and a three-dimensional burr microsphere structure continues to form on the surface.

[0102] Figure 8 The XRD patterns of the HF-LLZTO solid electrolyte sheet before placement and after 90 days in air are shown in Figure 2. Figure 8 It can be seen that no diffraction peak of Li2CO3 was found in the XRD spectra before and after being placed in the air for 90 days, indicating that the treated HF-LLZTO solid electrolyte sheet has very good air stability.

[0103] Figure 9 is the SEM image of the HF-LLZTO surface. Figure 9 It can be seen that the surface of the HF-LLZTO solid electrolyte sheet treated with a hydrofluoric acid solution with a concentration of 40% is a three-dimensional burr microsphere.

[0104] The HF-LLZTO solid electrolyte was assembled into a lithium symmetric battery, such as Figure 10 As shown, the interface impedance is only 3Ω·cm 2 ,like Figure 11 As shown, the lithium symmetrical battery can be stably cycled for more than 7000 hours, showing very good interface performance, indicating that the structure formed by the LLZTO solid electrolyte sheet after being treated with a hydrofluoric acid solution with a concentration of 40% can solve the battery interface problem on the negative electrode side of the battery.

[0105] The LLZTO solid electrolyte sheet in the comparative example was assembled into a lithium symmetric battery, and the impedance of the lithium symmetric battery was tested. Figure 10 As shown, its interface impedance is as high as 1989563Ω·cm 2 , further, as Figure 12 As shown, the lithium symmetric battery cycle is 0.1mA·cm -2 A short circuit occurs at a current density of 0.1 GHz, indicating very poor interfacial performance.

[0106] Example 5

[0107] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 50% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 100 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 50% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 100 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain an HF-LLZTO solid electrolyte sheet. The impedance of the sheet was tested, and the impedance spectrum was shown in FIG. Figure 13 As shown, the conductivity of lithium ions is calculated to be 4.58x10 -4 S / cm. By comparing the conductivity with that of Example 4, it can be seen that the treatment effect is almost the same as that of the hydrofluoric acid solution with a concentration of 40%, indicating that the hydrofluoric acid solution with a concentration of 50% no longer causes further corrosion to the LLZTO solid electrolyte sheet.

[0108] No diffraction peak of Li2CO3 was found in the XRD spectra before and after being placed in the air for 90 days, indicating that the treated HF-LLZTO solid electrolyte sheet has very good air stability.

[0109] Scanning electron microscopy (SEM) testing of the surface of the HF-LLZTO solid electrolyte sheet revealed that the surface of the treated HF-LLZTO solid electrolyte sheet was a three-dimensional burr microsphere. The HF-LL ZTO solid electrolyte was assembled into a lithium symmetrical battery, and the interface impedance between it and lithium metal was tested, which showed low interface impedance. Cycling stability testing of the assembled lithium symmetrical battery showed that it could stably cycle for more than 7000 hours, demonstrating very good interface performance. This indicates that the structure formed by treating the LLZTO solid electrolyte sheet with a 50% hydrofluoric acid solution can solve the battery interface problem on the negative electrode side of the battery.

[0110] Example 6

[0111] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 0.1% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 25 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 0.1% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 25 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain an hf-LLZTO solid electrolyte sheet. The impedance spectrum of the sheet is shown in FIG. Figure 14 As shown, its lithium ion conductivity is calculated to be 8.4x10 -4S / cm, indicating that the hydrofluoric acid solution with a concentration of 0.1% has almost no effect on the surface of the LLZTO solid electrolyte sheet, and a layered structure is formed on the surface of the LLZTO solid electrolyte sheet.

[0112] XRD pattern analysis of the LLZTO solid electrolyte sheet after being treated with a 0.1% hydrofluoric acid solution shows that a 0.1% hydrofluoric acid solution can effectively remove Li2CO3 on the surface of the LLZTO solid electrolyte sheet.

[0113] Scanning electron microscopy (SEM) tests showed that the surface of the hf-LLZTO solid electrolyte sheet treated with a 0.1% hydrofluoric acid solution showed a strong, ultra-thin and dense layered structure.

[0114] The hf-LLZTO solid electrolyte sheet treated with a 0.1% hydrofluoric acid solution was subjected to a cycle test by assembling a lithium symmetric battery. The symmetric battery modified with a 0.1% hydrofluoric acid solution can be stably cycled for more than 900 hours, indicating that the structure formed by the LLZTO solid electrolyte sheet treated with a 0.1% hydrofluoric acid solution can solve the battery interface problem on the positive electrode side of the battery.

[0115] Example 7

[0116] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 1% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 40 μL. The sheet was then placed in an oven at 60°C for drying for 4 h. A 1% hydrofluoric acid solution was added dropwise to the other bottom surface of the LLZTO solid electrolyte sheet in an amount of 40 μL. The sheet was then placed in an oven at 60°C for drying for 4 h to obtain an hf-LLZTO solid electrolyte sheet. The impedance spectrum of the sheet is shown in FIG. Figure 15 As shown, its conductivity is calculated to be 8.4x10 -4 S / cm, and its conductivity did not show a significant decrease, and a layered structure was formed on the surface of the LLZTO solid electrolyte sheet.

[0117] The XRD pattern analysis was performed, such as Figure 16 As shown by Figure 16 It can be seen that a hydrofluoric acid solution with a concentration of 1% can also effectively remove Li2CO3 on the surface of the LLZTO solid electrolyte sheet.

[0118] Scanning electron microscope (SEM) test was performed on it, and the results were as follows Figure 17 As shown by Figure 17 It can be seen that the surface of the hf-LLZTO solid electrolyte sheet treated with a 1% hydrofluoric acid solution presents a strong, ultra-thin and dense layered structure.

[0119] The hf-LLZTO solid electrolyte sheet treated with 1% hydrofluoric acid solution and the comparative L LZTO solid electrolyte sheet were assembled into lithium symmetric batteries for cycle testing. The results are shown in Figure 2. Figure 18 As shown by Figure 18 It can be seen that after modification with 1% hydrofluoric acid solution, the symmetrical battery can be stably cycled for more than 900 hours, while the symmetrical battery of the comparative example generates a huge polarization voltage after 480 hours of cycling, which makes the battery unable to continue normal operation. This shows that the structure formed by treating the LLZTO solid electrolyte sheet with a concentration of 1% hydrofluoric acid solution can solve the battery interface problem on the positive electrode side of the battery.

[0120] Example 8

[0121] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 10% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 45 μL. The sheet was then placed in an oven at 60°C for drying for 4 hours. A 10% hydrofluoric acid solution was added dropwise to the other bottom surface opposite to the LLZTO solid electrolyte sheet in an amount of 45 μL. The sheet was then placed in an oven at 60°C for drying for 4 hours to obtain an hf-LL ZTO solid electrolyte sheet. The conductivity of the sheet was tested as follows: Figure 19 As shown, its conductivity is calculated to be 7.4x10 -4 S / cm, and its conductivity also did not show a significant decrease, and a layered structure was formed on the surface of the LLZTO solid electrolyte sheet.

[0122] XRD pattern analysis of the LLZTO solid electrolyte sheet after being treated with a 10% hydrofluoric acid solution shows that the 10% hydrofluoric acid solution can effectively remove Li2CO3 on the surface of the LLZTO solid electrolyte sheet.

[0123] Scanning electron microscopy (SEM) tests showed that the surface of the hf-LLZTO solid electrolyte sheet treated with a 10% hydrofluoric acid solution exhibited a strong, ultra-thin and dense layered structure.

[0124] The hf-LLZTO solid electrolyte sheet treated with a 10% hydrofluoric acid solution was subjected to a cycle test by assembling a lithium symmetric battery. The symmetric battery modified with a 10% hydrofluoric acid solution can be stably cycled for more than 900 hours, indicating that the structure formed by the LLZTO solid electrolyte sheet treated with a 10% hydrofluoric acid solution can solve the battery interface problem on the positive electrode side of the battery.

[0125] Example 9

[0126] The LLZTO solid electrolyte sheet prepared in the comparative example was placed in a fume hood, and a 40% hydrofluoric acid solution was added dropwise to one bottom surface of the LLZTO solid electrolyte sheet in an amount of 80 μL. The sheet was then placed in an oven at 60°C for drying for 4 hours. A 1% hydrofluoric acid solution was added dropwise to the other opposite bottom surface of the LLZTO solid electrolyte sheet in an amount of 40 μL. The sheet was then placed in an oven at 60°C for drying for 4 hours to obtain a non-sandwich structured HF-LLZTO-hf solid electrolyte sheet.

[0127] The full battery was assembled and tested, with LFP (lithium iron phosphate) and NCM811 as the positive electrodes, and the results are shown in Figures 20 and 21. Figure 20 It can be seen that after 900 cycles of LFP full battery at 1C, the capacity retention rate can reach 85.6%. Figure 21 It can be seen that after 200 cycles at 0.5C, the capacity retention rate of the NCM811 full battery can reach 89%. This shows that the structure formed by treating the LLZTO solid electrolyte sheet with a 40% hydrofluoric acid solution and a 1% hydrofluoric acid solution gives the full battery excellent battery performance.

[0128] An LFP full cell assembled with hf-LLZTO solid electrolyte sheets was cycled at 1C for 900 cycles. As shown in Figure 22, its capacity retention was only 19.4%, demonstrating very poor cycling performance. An NCM811 full cell assembled with hf-LLZTO solid electrolyte sheets also exhibited low capacity retention after 200 cycles at 0.5C.

[0129] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A method for preparing a solid electrolyte sheet for a solid-state battery, characterized in that: The following steps are involved: Step S1: calcining lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder and tantalum oxide powder respectively; Step S2: According to the chemical formula Li 6.5 La3Zr 1.5 Ta 0.5 O 12 calcined lithium hydroxide powder, lanthanum oxide powder, zirconium oxide powder, and tantalum oxide powder according to the stoichiometric ratio, wherein the lithium hydroxide powder is weighed in excess of 2% to 40% by mass based on the stoichiometric ratio; Step S3: All the powders weighed in step S2 are mixed to obtain a mixed powder, a ball milling agent is added to the mixed powder to obtain a uniform mixed slurry, and then the mixed powder is dried to obtain a ball-milled mixed powder; Step S4: sintering the ball-milled mixed powder once to obtain a solid electrolyte precursor powder, pressing the solid electrolyte precursor powder into a sheet, and sintering it twice to obtain a solid electrolyte sheet; Step S5: After polishing the solid electrolyte sheet, a hydrofluoric acid solution is added dropwise to one bottom surface of the solid electrolyte sheet and dried, and a hydrofluoric acid solution is added dropwise to the other opposite bottom surface of the solid electrolyte sheet and dried to complete the preparation; wherein, the concentration of the hydrofluoric acid solution is 15% to 50% or 0.1% to 15% by mass.

2. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 1, wherein: In step S5, the amount of the hydrofluoric acid solution added is 20-100 μL.

3. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 2, wherein: Calculated by mass percentage, the concentration of the hydrofluoric acid solution is 25% to 45%.

4. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 1, wherein: Calculated by mass percentage, the concentration of the hydrofluoric acid solution is 1% to 10%.

5. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 1, wherein: In step S5, a hydrofluoric acid solution having a concentration of 15% to 50% by mass is added to one bottom surface of the solid electrolyte sheet, and a hydrofluoric acid solution having a concentration of 0.1% to 15% is added to the other opposite bottom surface of the solid electrolyte sheet. The amount of the hydrofluoric acid solution added twice is 20 to 100 μL.

6. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 5, characterized in that: The concentration of the hydrofluoric acid solution added dropwise to one bottom surface of the solid electrolyte sheet is 25% to 45% by mass, and the concentration of the hydrofluoric acid solution added dropwise to the other opposite bottom surface of the solid electrolyte sheet is 1% to 10% by mass.

7. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 1, wherein: The calcination temperature in step S1 is 700-1000° C., and the time is 1-48 hours. In step S3, the ball milling agent is any one of ethanol, isopropanol, acetonitrile, ether, petroleum ether, or acetone. The mass ratio of the mixed powder, the ball milling agent, and the ball milling beads is mixed powder: ball milling agent: ball milling beads = 1:1-5:4-20. The ball milling time is 4-48 hours, the ball milling speed is 200-1200 r / min, the drying temperature is 50-150° C., and the drying time is 4-24 hours.

8. The method for preparing a solid electrolyte sheet for a solid-state battery according to claim 1, wherein: In step S4, the primary sintering temperature is 700-1200° C. and the time is 4-24 hours, and the secondary sintering temperature is 1050-1500° C. and the time is 0.5-20 hours; in step S5, the drying temperature is 50-100° C. and the time is 1-8 hours.

9. A solid electrolyte sheet for a solid-state battery, characterized in that: Prepared by the preparation method according to any one of claims 1 to 8.

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