A highly stable and high ionic conductivity solid oxide electrolyte, a preparation method thereof, and an oxide electrolyte sheet for solid-state batteries

Abstract

This invention discloses a highly stable, high-ionic-conductivity solid oxide electrolyte, its preparation method, and an oxide electrolyte sheet for solid-state batteries. The preparation method of the highly stable, high-ionic-conductivity solid oxide electrolyte provided by this invention includes: preparing a solid oxide electrolyte precursor using a composite solvent of organic solvent and water as the ball milling medium; and then processing the solid oxide electrolyte precursor to obtain the solid oxide electrolyte. The volume ratio of the organic solvent to water in the composite solvent is (9:1)–(2:8), and the organic solvent includes at least one of aliphatic hydrocarbon solvents and alcohol solvents. The above-mentioned use of a composite solvent of organic solvent and water as the ball milling medium to prepare the solid oxide electrolyte precursor can optimize the microstructure of the solid oxide electrolyte, increase its relative density, and reduce the surface Li₂CO₃ content, thereby improving the ionic conductivity of the solid oxide electrolyte.

Description

Technical Field

[0001] This invention relates to the field of solid electrolyte technology, and more specifically, to a highly stable, high ionic conductivity solid oxide electrolyte, its preparation method, and an oxide electrolyte sheet for solid batteries. Background Technology

[0002] In the current pursuit of high energy density, solid-state lithium batteries have attracted much attention due to their potential for high energy density. Garnet-type LLZO solid electrolyte materials have advantages such as a wide electrochemical window, high room-temperature ionic conductivity, and chemical stability to metallic lithium, making them one of the most promising solid electrolyte materials. Despite a series of advances in LLZO-based research, the preparation and production of practical LLZO-based solid-state lithium batteries still face many challenges.

[0003] LLZO readily reacts in humid air, forming substances such as Li₂CO₃, which not only affects its electrochemical performance but may also lead to interfacial contact problems. To improve the air stability of LLZO, researchers have adopted various strategies, such as surface modification, doping, and atmosphere control. For example, forming a stable passivation layer on the LLZO surface can reduce reactions with moisture and CO₂ in the air. Although the ionic conductivity of LLZO is already relatively high among oxide solid electrolytes, further improvements in its ionic conductivity and stability are necessary to meet the demands of practical applications. Summary of the Invention

[0004] The purpose of this invention is to overcome the defects of the prior art and provide a highly stable, high ionic conductivity solid oxide electrolyte, its preparation method, and an oxide electrolyte sheet for solid batteries.

[0005] The technical problem solved by this invention is achieved by the following technical solution.

[0006] This invention provides a method for preparing a highly stable, high ionic conductivity solid oxide electrolyte, comprising: using a composite solvent of organic solvent and water as a ball milling medium to prepare a solid oxide electrolyte precursor, and then processing the solid oxide electrolyte precursor to obtain a solid oxide electrolyte, wherein: the volume ratio of organic solvent to water in the composite solvent is (9:1)-(2:8), and the organic solvent includes at least one of aliphatic hydrocarbon solvents and alcohol solvents.

[0007] This invention provides a highly stable, high ionic conductivity solid oxide electrolyte prepared according to the above-described preparation method. The composition of the solid oxide electrolyte is M1. x M2 y-LLZTO, wherein: M1 includes at least one of Al and Ga, M2 includes at least one of Mg, Nb and Sb, 0 < x ≤ 0.2, 0 < y ≤ 0.2.

[0008] The present invention provides a method for preparing an oxide electrolyte sheet for solid-state batteries, comprising: mixing the above-mentioned solid oxide electrolyte with a binder solution and grinding until the solvent evaporates completely, then pressing to obtain a green blank; and then sintering the green blank a second time to obtain an oxide electrolyte sheet for solid-state batteries.

[0009] The present invention provides a solid-state battery having the above-described oxide electrolyte sheet for solid-state batteries.

[0010] The present invention has the following beneficial effects:

[0011] This invention provides a highly stable, high-ionic-conductivity solid oxide electrolyte, its preparation method, and an oxide electrolyte sheet for solid-state batteries. The preparation method of the highly stable, high-ionic-conductivity solid oxide electrolyte provided by this invention includes: preparing a solid oxide electrolyte precursor using a composite solvent of organic solvent and water as the ball milling medium; and then processing the solid oxide electrolyte precursor to obtain the solid oxide electrolyte. The ratio of organic solvent to water in the composite solvent is (9:1)-(2:8), and the organic solvent includes at least one of aliphatic hydrocarbon solvents and alcohol solvents. In the above preparation method, the composite solution of organic solvent and water is used as the ball milling medium for the oxide solid electrolyte precursor. By adjusting the ratio of organic solvent to water, the morphology of the oxide solid electrolyte is controlled. By optimizing the microstructure of the oxide solid electrolyte, the effects of reducing grain boundary resistance and improving ionic conductivity are achieved. Attached Figure Description

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0013] Figure 1 SEM image of the solid oxide electrolyte prepared in Comparative Example 4;

[0014] Figure 2 SEM image of the solid oxide electrolyte prepared in Comparative Example 5;

[0015] Figure 3 SEM image of the solid oxide electrolyte prepared in Example 7;

[0016] Figure 4SEM image of the solid oxide electrolyte prepared in Example 1;

[0017] Figure 5 SEM image of an electrolyte sheet made from the solid oxide electrolyte prepared in Example 1;

[0018] Figure 6 The image shows the XRD pattern of an electrolyte sheet made from the solid oxide electrolyte prepared in Example 1. Detailed Implementation

[0019] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0020] The following is a detailed description of a highly stable, high-ionic-conductivity solid oxide electrolyte, its preparation method, and an oxide electrolyte sheet for solid-state batteries provided by embodiments of the present invention.

[0021] In a first aspect, embodiments of the present invention provide a method for preparing a highly stable, highly ionicly conductive solid oxide electrolyte, comprising: using a composite solvent of an organic solvent and water as a ball milling medium to prepare a solid oxide electrolyte precursor, and then processing the solid oxide electrolyte precursor to obtain a solid oxide electrolyte, wherein: the volume ratio of the organic solvent to water in the composite solvent is (9:1)-(2:8), and the organic solvent includes at least one of aliphatic hydrocarbon solvents and alcohol solvents.

[0022] This invention provides a method for preparing a highly stable, high-ionic-conductivity solid oxide electrolyte. A composite solvent of organic solvent and water is used as the ball milling medium to prepare the solid oxide electrolyte precursor. Ball milling improves the uniformity and reaction rate of the mixture, lowers the reaction temperature, and promotes the formation of a stable cubic phase structure under low-temperature conditions during single-pass sintering. Furthermore, the low temperature reduces Li₂CO₃ on the surface of the solid oxide electrolyte particles, lowering the residual alkali content on the particle surface. In addition, using the composite solvent of organic solvent and water as the ball milling medium can optimize the microstructure of the solid oxide electrolyte, resulting in uniform and dispersed particle size, which is beneficial for the success rate of tableting, producing high-density tablets and improving the overall lithium-ion conductivity of the electrolyte tablets.

[0023] In some alternative embodiments, the aliphatic hydrocarbon solvent includes at least one of n-hexane and acetone, and the alcohol solvent includes at least one of methanol, ethanol, and isopropanol.

[0024] In some optional embodiments, the following steps are included: dry mixing of La source, Zr source, Ta source, M1 source and M2 source and pre-calcination to remove impurities; ball milling and drying of the mixture obtained by mixing the pre-calcined material with Li source to obtain a solid oxide electrolyte precursor, wherein: the ball milling medium is a composite solvent of organic solvent and water; and then the solid oxide electrolyte precursor is sintered once and dry ball milled to obtain a solid oxide electrolyte.

[0025] In some optional embodiments, the La source, Zr source, Ta source, M1 source and M2 source include one or more of the oxides, nitrates and sulfates of La, Zr, Ta, M1 and M2 elements, and the pre-calcination temperature is 850-950°C and the time is 8-12 hours.

[0026] In some alternative embodiments, the Li source in the mixture includes one or more of lithium carbonate and lithium nitrate, and the Li source needs to be in excess by 15%.

[0027] In some alternative embodiments, the solid content of the mixture after adding the milling media is 20-30%, and then it is continuously ball-milled for 10-14 hours using a planetary ball mill at a ball-to-material mass ratio of 5-7:1. Here, the ball-to-material mass ratio refers to the mass ratio of zirconia balls to the mixture.

[0028] In some alternative embodiments, the sintering temperature is 850℃-950℃ and the time is 9-15h. If the sintering temperature is too low, lithium will not fully enter, the raw materials will not react, the LLZTO crystal structure will be poor, and it will not be able to fully exert its potential. If the sintering temperature is too high, Li will overflow from the LLZTO crystal structure, resulting in a lithium-depleted structure in LLZTO, which will hinder lithium ion migration and reduce ionic conductivity.

[0029] Secondly, embodiments of the present invention provide a highly stable, high ionic conductivity solid oxide electrolyte prepared according to the above preparation method, wherein the composition of the solid oxide electrolyte is M1. x M2 y -LLZTO, wherein: M1 includes at least one of Al and Ga, M2 includes at least one of Mg, Nb and Sb, 0 < x ≤ 0.2, 0 < y ≤ 0.2.

[0030] Thirdly, embodiments of the present invention provide a method for preparing an oxide electrolyte sheet for solid-state batteries, comprising: mixing the above-mentioned solid oxide electrolyte with a liquid adhesive and grinding until the solvent evaporates completely, then pressing to obtain a green blank; and then sintering the green blank a second time to obtain an oxide electrolyte sheet for solid-state batteries.

[0031] In some alternative implementations, the following conditions are met:

[0032] (1) The adhesive is selected from at least one of PVA and PVB, and the concentration of the adhesive solution is 4-8 wt%; the amount of adhesive solution added is 3-6 wt% of the mass of the solid oxide electrolyte;

[0033] (2) Press the powder obtained by grinding at 14-16 MPa for 2-5 min to obtain a green body;

[0034] (3) Place the green blank into a corundum crucible and cover it with solid oxide electrolyte, and then sinter it at 1100-1200℃ for 3-8 hours to obtain oxide electrolyte sheet for solid battery.

[0035] Fourthly, embodiments of the present invention provide a solid-state battery having the aforementioned oxide electrolyte sheet for solid-state batteries.

[0036] The present invention will be further described below with reference to embodiments.

[0037] Example 1

[0038] A method for preparing a highly stable, high ionic conductivity solid oxide electrolyte sheet, wherein the solid oxide electrolyte is composed of Al 0.1 Sb 0.12 -LLZO; includes the following steps:

[0039] Step 1, based on AI 0.1 Sb 0.12 -Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Stoichiometric ratio of La2O3, ZrO2, and Al2O 3、 Ta2O5 and Sb2O3 were calcined at 850℃ for 10 hours.

[0040] Step 2: Mix Li₂CO₃ with the pre-calcined La₂O₃, ZrO₂, Al₂O₃, Ta₂O₅, and Sb₂O₃ from Step 1 according to stoichiometric ratios, with Li₂CO₃ in 15% excess to compensate for lithium volatilization during sintering. The mixture is then continuously ball-milled for 12 hours using a planetary ball mill at a ball-to-material mass ratio of 5:1. The milling medium is a composite solvent of organic solvent and water. After milling, the sample is dried to obtain a solid oxide electrolyte precursor. The ratio of organic solvent to water in the mixed solution is 6:4, and the organic solvent is anhydrous ethanol.

[0041] Step 3: The solid oxide electrolyte precursor is sintered once at a temperature of 900℃ for 10 hours; then the sintered powder is dry ball-milled until there are no particles, thus obtaining the solid oxide electrolyte.

[0042] Step 4: Weigh an appropriate amount of solid oxide electrolyte, add 5 wt% PVB adhesive (solvent is NMP), and grind until the solvent evaporates completely. Pour the ground powder into a mold through weighing paper, and press it under a pressure of 15 MPa for 3 minutes to obtain a green body.

[0043] Step 5: Place the green blank into a corundum crucible and cover it with solid oxide electrolyte. Then, perform secondary sintering in a high-temperature muffle furnace at 1150°C for 5 hours to obtain oxide electrolyte sheets for solid-state batteries.

[0044] Example 2

[0045] The steps are similar to those in Example 1, except that in step 1, M1: Al content is 0.05 and M2: Sb content is 0.05.

[0046] Example 3

[0047] The steps are similar to those in Example 1, except that in step 1, M1: Al content is 0.2 and M2: Sb content is 0.2.

[0048] Example 4

[0049] The steps are similar to those in Example 1, except that in step 1, M1: Ga content is 0.1 and M2: Mg content is 0.18.

[0050] Example 5

[0051] The steps are similar to those in Example 1, except that in step 1, M1: Al content is 0.08 and M2: Nb content is 0.1.

[0052] Example 6

[0053] The steps are similar to those in Example 1, except that in step 2, the volume ratio of anhydrous ethanol to water is 9:1.

[0054] Example 7

[0055] The steps are similar to those in Example 1, except that in step 2, the volume ratio of anhydrous ethanol to water is 2:8.

[0056] Example 8

[0057] The steps are similar to those in Example 1, except that in step 2, the volume ratio of anhydrous ethanol to water is 5:5.

[0058] Example 9

[0059] The steps are similar to those in Example 1, except that in step 3, the sintering is carried out at 850°C for 8 hours.

[0060] Example 10

[0061] The steps are similar to those in Example 1, except that in step 3, the sintering is carried out at 950°C for 12 hours.

[0062] Example 11

[0063] The steps are similar to those in Example 1, except that in step 5, the sintering temperature is 1100℃ for 3 hours.

[0064] Example 12

[0065] The steps are similar to those in Example 1, except that in step 5, the sintering temperature is 1200℃ for 8 hours.

[0066] Comparative Example 1

[0067] The steps are similar to those in Example 1, except that in step 1, there are no sources M1 and M2.

[0068] Comparative Example 2

[0069] The steps are similar to those in Example 1, except that in step 1, there is no source M1.

[0070] Comparative Example 3

[0071] The steps are similar to those in Example 1, except that in step 1, there is no M2 source.

[0072] Comparative Example 4

[0073] The steps are similar to those in Example 1, except that in step 2, the grinding medium is water.

[0074] Comparative Example 5

[0075] Similar to the steps in Example 1, except that in step 2, the grinding medium is anhydrous ethanol.

[0076] Comparative Example 6

[0077] The steps are similar to those in Example 1, except that in step 3, the sintering is carried out at 700℃ for 10 hours.

[0078] Comparative Example 7

[0079] The steps are similar to those in Example 1, except that in step 3, the sintering is carried out at 1000℃ for 10 hours.

[0080] Comparative Example 8

[0081] The steps are similar to those in Example 1, except that in step 5, the sintering is carried out at 1250℃ for 5 hours.

[0082] Comparative Example 9

[0083] The steps are similar to those in Example 1, except that in step 5, the sintering is carried out at 1050℃ for 5 hours.

[0084] Test results

[0085] 1. After preparing the solid oxide electrolytes of Examples 1, 7, 4, and 5, they were subjected to scanning electron microscopy (SEM) tests.

[0086] In the preparation of solid oxide electrolytes, the preparation of the solid oxide electrolyte precursor is crucial. Due to the differences in polarity and molecular structure between water and anhydrous ethanol, the grinding effect and distribution of each raw material vary during ball milling. Water and anhydrous ethanol affect the particle morphology and distribution of subsequent materials. Specifically: if water is used as the ball milling medium, particles tend to clump together, resulting in poor dispersibility (see Comparative Example 4). Figure 1 If pure anhydrous ethanol is used as the ball milling medium, the particle size in the mixture is smaller and the dispersibility is improved (see Comparative Example 5 as an example). Figure 2 With the addition of water to the milling media, small particles combine to form larger particles (see Example 7). Figure 3 As the amount of water added gradually increases, the proportion of large particles gradually increases, eventually forming a block. When the volume ratio of anhydrous ethanol to water is 6:4, the particles are round and uniform in size (see Example 1). Figure 4 For further details, the SEM and XRD patterns of the electrolyte sheet fabricated using the solid oxide electrolyte prepared in Example 1 are shown in [reference 1]. Figure 5 and Figure 6 As can be seen from the figure, the oxide electrolyte particles are densely packed and have high density. The diffraction peaks in the electrolyte diffraction pattern are clearly sharp, indicating that the synthesized electrolyte has high crystallinity. In addition, compared with the standard card, the electrolyte is cubic phase, which is beneficial to the performance of lithium-ion conductivity.

[0087] 2. Li2CO3 test:

[0088] A high-frequency infrared carbon-sulfur analyzer was used to "burn" the carbon and sulfur components in the sample into CO2 and SO2 using a high-frequency induction furnace, thus separating them from the matrix elements. Then, an infrared detector was used to measure the energy decay law of CO2 and SO2 after selective absorption of infrared light. After computer data processing, the carbon and sulfur content in the sample was analyzed. Finally, the Li2CO3 content W was calculated using the following formula.

[0089] W = W0 * M1 / ​​M0

[0090] Where: W0 is the tested CO2 content (%), M1 is the molecular weight of Li2CO3 (g / mol), and M0 is the molecular weight of CO2 (g / mol).

[0091] 3. Relative density test:

[0092] The actual density of the solid electrolyte sheet was determined by the Archimedes method in anhydrous ethanol, and the calculation formula is as follows:

[0093]

[0094] Where: w0 is the mass (g) of the dried sample in air, w1 is the mass (g) of the sample in anhydrous ethanol after being fully immersed in anhydrous ethanol, w2 is the mass (g) of the sample in air after being fully immersed in anhydrous ethanol, ρ w The density of anhydrous ethanol is 0.789 g / cm³. 3 The relative density ρ of electrolytes r The calculation formula is:

[0095]

[0096] In the above formula: ρ0 is the theoretical density of the electrolyte (g / cm³). 3 ), can be calculated from the formula

[0097]

[0098] In the formula: M is the molecular weight (g / mol) of the electrolyte chemical formula, and NA is Avogadro's constant (mol). -1 V is the theoretical unit cell volume of the electrolyte (cm³). 3 )

[0099] 4. Lithium-ion conductivity test:

[0100] The sintered solid electrolyte sheet was mirror-polished using 800, 1200, 1500, and 2000 grit silicon carbide abrasive paper on a polishing machine. The polished solid electrolyte was then cleaned with ethanol, ultrasonically removed to remove surface impurities, and dried. Next, high-temperature silver paste was coated onto the top and bottom surfaces of the solid electrolyte sheet, dried at 150℃ for 10 minutes, and then sintered at 850℃ for 10 minutes. Electrochemical impedance spectroscopy (EIS) testing was then performed. The AC voltage amplitude was 5 mV, and the frequency range was 1 Hz–2 MHz. The ionic conductivity of the ceramic sample can be obtained using the following formula:

[0101]

[0102] In the formula: d is the sample thickness (cm), and S is the electrode area (cm²). 2 ), where R is the sample resistance (Ω).

[0103] The table below shows the test results of the oxide electrolyte sheets for solid-state batteries prepared in the examples and comparative examples.

[0104]

[0105] As can be seen from the table above:

[0106] (1) The results of Examples 1-5 and Comparative Examples 1-3 show that both elements M1 and M2 have an impact on oxide solid electrolytes. When elements M1 and M2 are incorporated into Li sites and Zr sites respectively, they affect the distribution of lithium ions in the material. Some lithium ions overflow and generate Li2CO3, which hinders lithium ion migration and reduces lithium ion conductivity.

[0107] (2) The results from Examples 1, 6-8, and Comparative Examples 4-5 show that particle size and size distribution affect the density of the oxide electrolyte sheet. Furthermore, water and anhydrous ethanol differ in polarity and molecular structure; therefore, their contents affect the distribution of raw materials during ball milling, thus influencing the surface Li2CO3 content. Density and lithium carbonate both affect lithium-ion conductivity.

[0108] (3) The results of Examples 9-10 and Comparative Examples 6-7 show that the first sintering temperature has a significant impact on the Li2CO3 content. At low temperatures, some Li2CO3 does not participate in the reaction. As the first sintering temperature increases, almost all Li2CO3 participates in the reaction and enters the crystal structure. However, if the first sintering temperature is too high, the sintered material will be too hard, which is not conducive to subsequent dry ball milling and tableting, and increases the difficulty of the process.

[0109] (4) The results of Examples 11-12 and Comparative Examples 8-9 show that the secondary temperature is mainly related to the density of the electrolyte sheet. If the sintering temperature is too low, there are pores between the particles, resulting in low density and a longer lithium ion migration path, which affects the lithium ion conductivity. If the sintering temperature is too high, the lithium ions in the crystal migrate to the surface to form Li2CO3, which is not conducive to the performance of lithium ion conductivity.

[0110] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a highly stable, high ionic conductivity solid oxide electrolyte, characterized in that, It includes: A solid oxide electrolyte precursor is prepared by using a composite solvent of organic solvent and water as a ball milling medium, and then the solid oxide electrolyte precursor is post-processed to obtain a solid oxide electrolyte. The volume ratio of organic solvent to water in the composite solvent is (9:1)-(2:8), and the organic solvent includes at least one of aliphatic hydrocarbon solvent and alcohol solvent. The composition of the solid oxide electrolyte is M1 x M2 y -LLZTO, wherein: M1 includes at least one of Al and Ga, M2 includes at least one of Mg, Nb and Sb, 0 < x ≤ 0.2, 0 < y ≤ 0.

2.

2. The preparation method according to claim 1, characterized in that, The aliphatic hydrocarbon solvent includes one or more of hexane and acetone, and the alcohol solvent includes one of methanol, ethanol, and isopropanol.

3. The preparation method according to claim 1, characterized in that, Includes the following steps: The La, Zr, Ta, M1, and M2 sources are dry-mixed and pre-calcined to remove impurities. The pre-calcined material is then mixed with the Li source to obtain a mixture, which is ball-milled and dried to obtain a solid oxide electrolyte precursor. The ball-milling medium is a composite solvent of organic solvent and water. The solid oxide electrolyte precursor is then sintered once and dry-milled to obtain a solid oxide electrolyte.

4. The preparation method according to claim 3, characterized in that, The La source, Zr source, Ta source, M1 source, and M2 source include one or more of the oxides, nitrates, and sulfates of La, Zr, Ta, M1, and M2 elements, with a pre-calcination temperature of 850-950℃ and a time of 8-12 hours; the Li source includes one or more of lithium carbonate and lithium nitrate, and the Li source needs to be in excess by 15%.

5. The preparation method according to claim 3, characterized in that, The solid content of the mixture after adding the ball milling media is 20-30%, and then it is continuously ball milled for 10-14 hours using a planetary ball mill at a ball-to-material mass ratio of 5-7:

1.

6. The preparation method according to claim 3, characterized in that, The temperature for the first sintering is 850℃-950℃, and the time is 9-15h.

7. A method for preparing an oxide electrolyte sheet for solid-state batteries, characterized in that, It includes: mixing the solid oxide electrolyte of any one of claims 1-6 with a binder and grinding until the solvent evaporates completely, then pressing to obtain a green blank; and then sintering the green blank a second time to obtain an oxide electrolyte sheet for solid-state batteries.

8. The preparation method according to claim 7, characterized in that, The following conditions must be met: (1) The adhesive is selected from at least one of PVA and PVB, and the concentration of the adhesive solution is 4-8 wt%; the amount of adhesive solution added is 3-6 wt% of the mass of the solid oxide electrolyte; (2) Press the powder obtained by grinding at 14-16 MPa for 2-5 min to obtain a green body; (3) The green blank is placed in a corundum crucible and buried with the solid oxide electrolyte, and then sintered at 1100-1200℃ for 3-8 hours to obtain an oxide electrolyte sheet for solid batteries.

9. A solid-state battery, characterized in that, It has an oxide electrolyte sheet for solid-state batteries as described in any one of claims 7-8.

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