Modified lithium lanthanum zirconium tantalum oxide solid electrolyte and preparation method thereof

Abstract

The present invention provides a modified lithium lanthanum zirconium tantalum oxide solid electrolyte and a preparation method thereof. The preparation method comprises: pre-sintering a potassium source, tantalum pentoxide and an excess strontium source to obtain a strontium-doped K2SrTa2O7 precursor; and sequentially doping and sintering a mixture of a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide and a strontium-doped K2SrTa2O7 precursor to obtain a strontium-doped K2SrTa2O7-coated modified lithium lanthanum zirconium tantalum oxide solid electrolyte. The solid electrolyte prepared by the method provided in the present application has higher ionic conductivity, lower surface lithium carbonate content and better processing performance; it also has lower electrolyte activation energy, which is more conducive to the transmission of lithium ions and improves the comprehensive performance of the material. In addition, the method is simple and easy to implement, which is conducive to industrial production.

Description

Technical Field

[0001] The present invention relates to the field of solid electrolyte preparation, and in particular to a modified lithium lanthanum zirconium tantalum oxide solid electrolyte and a preparation method thereof. Background Art

[0002] Compared to liquid lithium-ion batteries, solid-state lithium-ion batteries offer advantages such as higher packaging efficiency, improved safety, the ability to manufacture high-voltage cells, and higher energy density. Current solid-state electrolytes primarily include inorganic solid electrolytes, polymer solid electrolytes, and organic-inorganic solid electrolytes. All-solid-state lithium-ion batteries share a similar structure to traditional lithium batteries, replacing the liquid electrolyte with a solid-state electrolyte. This not only addresses the capacity degradation of traditional lithium-ion batteries but also has the potential to address key battery material safety issues.

[0003] Among the many inorganic solid electrolytes, sulfides have the highest conductivity, even higher than liquid electrolytes. However, sulfides are very sensitive to atmospheric humidity and have strict requirements on the environment. The second is oxide solid electrolytes, such as perovskite-type lithium niobium titanate, which has the advantages of stable metallic lithium and a wide electrochemical window. However, the surface of this material is very sensitive to moisture and easily forms a layer of lithium carbonate, which reduces the conductivity. Polymer solid electrolytes have significant advantages in mechanical properties, among which the most widely studied is polyethylene oxide (PEO). The ionic conductivity of the PEO group is very low at room temperature, but it can be increased to 10 by modification. -5 S / cm. The ionic conductivity of lithium lanthanum zirconium tantalum oxide (LLZTO) as a solid electrolyte material reported in the literature is 10 -5 ~10 -4 S / cm order of magnitude, and can be used as a solid electrolyte material.

[0004] However, the conductivity of solid electrolytes depends on the migration of conductive ions. The faster the ion migration rate, the better the conductivity of the electrolyte. The tightness of the crystal arrangement inside the lithium ion conductor has an important influence on the migration rate of ions inside the conductor. In order to better improve its ionic conductivity, improve polarization and LLZTO will cause Li + / H + The exchange surface generates Li2CO3, which will lead to problems such as reducing the wettability of LLZTO to Li and the ionic conductivity, limiting the further development of LLZTO.

[0005] In view of the existence of the above problems, it is necessary to provide a lithium lanthanum zirconium tantalum oxide solid electrolyte with high ionic conductivity. Summary of the Invention

[0006] The main purpose of the present invention is to provide a modified lithium lanthanum zirconium tantalum oxide solid electrolyte and a preparation method thereof, so as to solve the problems of low ionic conductivity and density of the existing lithium lanthanum zirconium tantalum oxide solid electrolyte.

[0007] In order to achieve the above-mentioned objectives, the present invention provides, on the one hand, a method for preparing a modified lithium lanthanum zirconium tantalum oxide solid electrolyte. The method for preparing the modified lithium lanthanum zirconium tantalum oxide solid electrolyte comprises: pre-sintering a potassium source, tantalum pentoxide and an excess strontium source to obtain a strontium-doped K2SrTa2O7 precursor; and sequentially doping and sintering a mixture of a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide and a strontium-doped K2SrTa2O7 precursor to obtain a strontium-doped K2SrTa2O7-coated modified lithium lanthanum zirconium tantalum oxide solid electrolyte.

[0008] Furthermore, before the pre-sintering process, the preparation method of the modified lithium lanthanum zirconium tantalum oxide solid electrolyte also includes: mixing the potassium source, tantalum pentoxide and strontium source with a first dispersing solvent and then performing a first ball milling treatment and a first drying treatment in sequence; preferably, the rotation speed of the first ball milling process is 300-600 rpm, and the time is 4-9 hours; the temperature of the first drying process is 60-95°C, and the time is 3-7 hours.

[0009] Furthermore, the molar ratio of potassium in the potassium source, tantalum in tantalum pentoxide, and strontium in the strontium source is 2:2:(1.002-1.01).

[0010] Furthermore, the temperature of the pre-sintering treatment is 300-500° C., and the sintering time is 4-10 hours.

[0011] Furthermore, the doping process includes: mixing a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide and a second dispersing solvent to form a dispersion; subjecting the dispersion and a strontium-doped K2SrTa2O7 precursor to a second ball milling treatment and a second drying treatment in sequence; preferably, the rotation speed of the second ball milling process is 400-800 rpm, and the time is 3-10 hours; the temperature of the second drying process is 70-90°C, and the time is 4-10 hours.

[0012] Furthermore, the stoichiometric ratio of lithium source, lanthanum source, zirconium source and tantalum pentoxide in the dispersion is Li:La:Zr:Ta, which is 6.75:3:1.75:0.25; the ratio of the total weight of the lithium source, lanthanum source, zirconium source and tantalum pentoxide to the weight of the second dispersion solvent is 1:(1-2), and the weight ratio of the strontium-doped K2SrTa2O7 precursor to the second dispersion is (1-5):100.

[0013] Furthermore, the temperature of the sintering process is 750-900° C., and the sintering time is 10-20 hours.

[0014] Furthermore, the potassium source is selected from one or more of the group consisting of potassium carbonate, potassium hydroxide and potassium nitrate; the strontium source is selected from one or more of the group consisting of strontium carbonate, strontium sulfate and strontium oxide; the lithium source is selected from one or more of the group consisting of lithium carbonate, lithium hydroxide and lithium nitrate; the lanthanum source is selected from one or more of the group consisting of lanthanum oxide, lanthanum hydroxide and lanthanum nitrate; and the zirconium source is selected from zirconium oxide and / or zirconium hydroxide.

[0015] Another aspect of the present application also provides a modified lithium lanthanum zirconium tantalum oxide solid electrolyte, including a core and a modified layer coated on the surface of the core, the core is a lithium lanthanum zirconium tantalum oxide solid electrolyte, and the modified layer is a K2SrTa2O7 layer; the modified lithium lanthanum zirconium tantalum oxide solid electrolyte is prepared by the preparation method of the lithium lanthanum zirconium tantalum oxide solid electrolyte provided in the present application.

[0016] Furthermore, in the modified lithium lanthanum zirconium tantalum oxide solid electrolyte, the doping amount of strontium element is 0.2-1 wt%, and the thickness of the modified layer is 2-10 nm.

[0017] The technical solution of the present invention is applied to pre-sintering K2SrTa2O7 (Sr is added in excess), which is then mixed with a lithium lanthanum zirconium tantalum oxide raw material to react and obtain a Sr-doped lithium lanthanum zirconium tantalum oxide material (LLZTO) with in-situ K2SrTa2O7 coating on the surface. Strontium doping can lower the crystallization temperature of LLZTO, inhibit lithium volatilization, reduce charge transfer resistance, and improve ionic conductivity. K2SrTa2O7 coating of LLZTO can effectively increase the density and ionic conductivity of the LLZTO material and reduce the content of lithium carbonate on the LLZTO surface due to reaction with water. The synergistic effect of Sr doping and K2SrTa2O7 coating of LLZTO results in higher ionic conductivity and lower surface lithium carbonate content than single modification of LLZTO, thereby improving the material's processing performance. The present invention also modifies LLZTO by doping it with strontium (Sr) and coating it in situ with K2SrTa2O7. This further reduces the activation energy of the LLZTO electrolyte, facilitates lithium ion transport, and improves the overall performance of the material. Furthermore, this method is simple and easy to implement, making it suitable for industrial production. DETAILED DESCRIPTION

[0018] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0019] As described in the background technology, the existing lithium lanthanum zirconium tantalum oxide solid electrolyte has the problems of low ionic conductivity and low density. In order to solve the above technical problems, the present application provides a method for preparing a modified lithium lanthanum zirconium tantalum oxide solid electrolyte, comprising: pre-sintering a potassium source, tantalum pentoxide and an excess strontium source to obtain a strontium-doped K2SrTa2O7 precursor; and sequentially doping and sintering a mixture of a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide and a strontium-doped K2SrTa2O7 precursor to obtain a strontium-doped K2SrTa2O7-coated modified lithium lanthanum zirconium tantalum oxide solid electrolyte.

[0020] K2SrTa2O7 is synthesized by pre-sintering (Sr is added in excess), which is then doped and sintered with lithium lanthanum zirconium tantalum oxide raw materials to produce Sr-doped lithium lanthanum zirconium tantalum oxide (LLZTO) with in-situ K2SrTa2O7 coating on the surface. Strontium doping can lower the crystallization temperature of LLZTO, inhibit lithium volatilization, reduce charge transfer resistance, and improve ionic conductivity. K2SrTa2O7 coating of LLZTO can effectively increase the density and ionic conductivity of the LLZTO material and reduce the content of lithium carbonate on the LLZTO surface due to reaction with water. The synergistic effect of Sr doping and K2SrTa2O7 coating of LLZTO results in higher ionic conductivity and lower surface lithium carbonate content than single modification of LLZTO, improving the material's processing performance. The present invention also modifies LLZTO by doping it with strontium (Sr) and coating it in situ with K2SrTa2O7. This further reduces the activation energy of the LLZTO electrolyte, facilitates lithium ion transport, and improves the overall performance of the material. Furthermore, this method is simple and easy to implement, making it suitable for industrial production.

[0021] In a preferred embodiment, before the pre-sintering process, the preparation method of the modified lithium lanthanum zirconium tantalum oxide solid electrolyte further includes: mixing the potassium source, tantalum pentoxide and strontium source with a first dispersing solvent, and then sequentially performing a first ball milling process and a first drying process. Under the action of the first dispersing solvent, the first ball milling process can make the above raw materials more evenly mixed and the particle size more uniform, which is conducive to making the reaction degree of the pre-sintering reaction more sufficient, and obtaining a strontium-doped K2SrTa2O7 precursor. The first dispersing solvent can be selected from the types commonly used in the art, including but not limited to anhydrous ethanol. The drying process can remove moisture from the surface of the product obtained after the first ball milling process, thereby shortening the time of the pre-sintering process.

[0022] Preferably, the speed of the first ball milling process is 300-600 rpm and the duration is 4-9 hours; the temperature of the first drying process is 60-95°C and the duration is 3-7 hours. The speed and duration of the first ball milling process include but are not limited to the above ranges, and limiting them to the above ranges can further improve the ball milling effect. Limiting the temperature and time of the first drying process to the above ranges can further improve the drying rate.

[0023] In a preferred embodiment, the molar ratio of potassium in the potassium source, tantalum in tantalum pentoxide, and strontium in the strontium source is 2:2:(1.002-1.01). Limiting the molar ratio of potassium in the potassium source, tantalum in tantalum pentoxide, and strontium in the strontium source to this range, compared to other ranges, allows for an excess of strontium, thereby further improving the conversion rate of the strontium-doped K2SrTa2O7 precursor.

[0024] In a preferred embodiment, the pre-sintering temperature is 300-500°C, and the sintering time is 4-10 hours. The pre-sintering temperature and sintering time include, but are not limited to, the above ranges, and limiting them to the above ranges is beneficial to improving the yield of the strontium-doped K2SrTa2O7 precursor.

[0025] In a preferred embodiment, the doping process includes: mixing a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide, and a second dispersing solvent to form a dispersion; and sequentially subjecting the dispersion to a second ball milling process and a second drying process with a strontium-doped K2SrTa2O7 precursor. Preferably, the speed of the second ball milling process is 400-800 rpm, and the time is 3-10 hours; the temperature of the second drying process is 70-90°C, and the time is 4-10 hours. The speed and time of the second ball milling process include, but are not limited to, the above-mentioned ranges. Limiting them to the above-mentioned ranges is beneficial to further improving the ball milling and strontium doping rate, thereby further improving the ionic conductivity of the solid electrolyte and reducing the lithium carbonate content on the surface of the lithium lanthanum zirconium tantalum oxide material; limiting the temperature and time of the second drying process to the above-mentioned ranges is beneficial to further improving its drying rate.

[0026] The weight ratio of the lithium source, lanthanum source, zirconium source, tantalum pentoxide, and second dispersing solvent to the strontium-doped K2SrTa2O7 precursor in the dispersion affects the doping amount of strontium in the lithium lanthanum zirconium tantalum oxide material and the coating amount of K2SrTa2O7. In a preferred embodiment, the weight ratio of the lithium source, lanthanum source, zirconium source, tantalum pentoxide, and second dispersing solvent to the strontium-doped K2SrTa2O7 precursor in the dispersion is 6.75:3:1.75:0.25 according to the stoichiometric ratio of Li:La:Zr:Ta. The ratio of the total weight of the lithium source, lanthanum source, zirconium source, and tantalum pentoxide to the weight of the second dispersing solvent is 1:(1-2), and the weight ratio of the strontium-doped K2SrTa2O7 precursor to the second dispersion is (1-5):100. Limiting the weight ratio of the above raw materials within the above range can obtain a suitable strontium doping amount and K2SrTa2O7 coating amount in the lithium lanthanum zirconium tantalum oxide material, thereby helping to further reduce the activation energy of the modified lithium lanthanum zirconium tantalum oxide solid electrolyte, making it more conducive to the transmission of lithium ions and improving the overall performance of the material.

[0027] In a preferred embodiment, the sintering temperature is 750-900°C and the sintering time is 10-20 hours. Compared with other sintering temperatures and times, limiting the sintering temperature and time within the above range is beneficial to further improve the overall performance of the LLZTO electrolyte, such as structural stability and specific capacity.

[0028] In the above preparation method, the potassium source, strontium source, lithium source, lanthanum source, and zirconium source can be selected from commonly used sources in the art. In a preferred embodiment, the potassium source includes, but is not limited to, one or more of the group consisting of potassium carbonate, potassium hydroxide, and potassium nitrate; the strontium source includes, but is not limited to, one or more of the group consisting of strontium carbonate, strontium sulfate, and strontium oxide; the lithium source includes, but is not limited to, one or more of the group consisting of lithium carbonate, lithium hydroxide, and lithium nitrate; the lanthanum source includes, but is not limited to, one or more of the group consisting of lanthanum oxide, lanthanum hydroxide, and lanthanum nitrate; and the zirconium source includes, but is not limited to, zirconium oxide and / or zirconium hydroxide.

[0029] Another aspect of the present application also provides a modified lithium lanthanum zirconium tantalum oxide solid electrolyte, including a core and a modified layer coated on the surface of the core, the core is a lithium lanthanum zirconium tantalum oxide solid electrolyte, and the modified layer is a K2SrTa2O7 layer; the modified lithium lanthanum zirconium tantalum oxide solid electrolyte is prepared by the preparation method of the lithium lanthanum zirconium tantalum oxide solid electrolyte provided in the present application.

[0030] K2SrTa2O7 is synthesized by pre-sintering (Sr is added in excess), which is then doped and sintered with lithium lanthanum zirconium tantalum oxide raw materials to produce Sr-doped lithium lanthanum zirconium tantalum oxide (LLZTO) with in-situ K2SrTa2O7 coating on the surface. Strontium doping can lower the crystallization temperature of LLZTO, inhibit lithium volatilization, reduce charge transfer resistance, and improve ionic conductivity. K2SrTa2O7 coating of LLZTO can effectively increase the density and ionic conductivity of the LLZTO material and reduce the content of lithium carbonate on the LLZTO surface due to reaction with water. The synergistic effect of Sr doping and K2SrTa2O7 coating of LLZTO results in higher ionic conductivity and lower surface lithium carbonate content than single modification of LLZTO, improving the material's processing performance. The present invention also modifies LLZTO by doping it with strontium (Sr) and coating it in situ with K2SrTa2O7. This further reduces the activation energy of the LLZTO electrolyte, facilitates lithium ion transport, and improves the overall performance of the material. Furthermore, this method is simple and easy to implement, making it suitable for industrial production.

[0031] In a preferred embodiment, the modified lithium lanthanum zirconium tantalum oxide solid electrolyte has a strontium doping amount of 0.2 to 1 wt%, and the thickness of the modified layer is 2 to 10 nm. Limiting the strontium doping amount within the aforementioned range helps improve the ionic conductivity of the modified lithium lanthanum zirconium tantalum oxide solid electrolyte while reducing the surface lithium carbonate content. Similarly, limiting the thickness of the K2SrTa2O7 coating layer within the aforementioned range helps improve the uniformity of the LLZTO material and suppress polarization.

[0032] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0033] Example 1

[0034] A solid electrolyte material, lithium lanthanum zirconium tantalum oxide material, comprises the following steps:

[0035] S1. Preparation of K2SrTa2O7 precursor: Weigh potassium carbonate, tantalum pentoxide, and strontium carbonate according to the stoichiometric ratio of K:Ta:Sr of 2:2:1.002, disperse them in anhydrous ethanol, and ball-mill at 300 rpm for 4 h; dry at 60°C for 3 h, and pre-calculate at 300°C for 4 h in an air atmosphere to obtain a K2SrTa2O7 precursor.

[0036] S2. Lithium carbonate, lanthanum oxide, zirconium oxide, and tantalum pentoxide are weighed according to the stoichiometric ratio of Li:La:Zr:Ta of 6.75:3:1.75:0.25, and dispersed in isopropyl alcohol to form a dispersion, wherein the ratio of the total mass of lithium carbonate, lanthanum oxide, zirconium oxide, and tantalum pentoxide to the mass of isopropyl alcohol is 1:1.

[0037] S3. Add the K2SrTa2O7 precursor in S1 to the dispersion of S2, ball mill at 400 rpm for 3 hours; dry at 70°C for 4 hours, and finally sinter at a constant temperature of 750°C for 10 hours in an air atmosphere and cool naturally to obtain a strontium-doped and K2SrTa2O7-coated lithium lanthanum zirconium tantalum oxide modified material, wherein the weight ratio of the K2SrTa2O7 precursor to the dispersion is 1:100, the strontium doping amount is 0.2% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 2 to 3 nm.

[0038] Example 2

[0039] A solid electrolyte material, lithium lanthanum zirconium tantalum oxide material, comprises the following steps:

[0040] S1. Preparation of K2SrTa2O7 precursor: Weigh potassium hydroxide, tantalum pentoxide, and strontium sulfate in anhydrous ethanol at a stoichiometric ratio of K:Ta:Sr of 2:2:1.003, disperse them, and ball-mill them at 400 rpm for 5 h. Dry them at 75°C for 5 h, and pre-calculate them at 350°C for 6 h in an air atmosphere to obtain a K2SrTa2O7 precursor.

[0041] S2. Lithium hydroxide, lanthanum hydroxide, zirconium hydroxide, and tantalum pentoxide are weighed according to the stoichiometric ratio of Li:La:Zr:Ta of 6.75:3:1.75:0.25, and dispersed in isopropyl alcohol to form a dispersion, wherein the ratio of the total mass of lithium hydroxide, lanthanum hydroxide, zirconium hydroxide, and tantalum pentoxide to the mass of isopropyl alcohol is 1:1.2.

[0042] S3. Add the K2SrTa2O7 precursor in S1 to the dispersion of S2, ball mill at 450rpm for 5h, dry at 70-90℃ for 6h, and finally sinter at 800℃ for 10-20h in an air atmosphere and naturally cool to obtain a strontium-doped and K2SrTa2O7-coated lithium lanthanum zirconium tantalum oxide modified material, wherein the weight ratio of the K2SrTa2O7 precursor to the dispersion is 2:100, the strontium doping amount is 0.3% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 3-4nm.

[0043] Example 3

[0044] A solid electrolyte material, lithium lanthanum zirconium tantalum oxide material, comprises the following steps:

[0045] S1. Preparation of K2SrTa2O7 precursor: Potassium hydroxide, tantalum pentoxide, and strontium oxide were weighed according to the stoichiometric ratio of K:Ta:Sr of 2:2:1.006, dispersed in anhydrous ethanol, and ball-milled at 450 rpm for 6.5 h; dried at 80°C for 5 h, and pre-calcined at 400°C for 7 h in an air atmosphere to obtain a K2SrTa2O7 precursor.

[0046] S2. Lithium hydroxide, lanthanum oxide, zirconium oxide, and tantalum pentoxide are weighed according to the stoichiometric ratio of Li:La:Zr:Ta of 6.75:3:1.75:0.25, and dispersed in isopropanol to form a dispersion, wherein the ratio of the total mass of lithium hydroxide, lanthanum oxide, zirconium oxide, and tantalum pentoxide to the mass of isopropanol is 1:1.5.

[0047] S3. Add the K2SrTa2O7 precursor in S1 to the dispersion of S2, ball mill at 600 rpm for 6.5 hours; dry at 80°C for 7 hours, and finally sinter at a constant temperature of 800°C for 15 hours in an air atmosphere and naturally cool to obtain a strontium-doped and K2SrTa2O7-coated lithium lanthanum zirconium tantalum oxide modified material, wherein the weight ratio of the K2SrTa2O7 precursor to the dispersion is 3:100, the strontium doping amount is 0.6% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 4 to 6 nm.

[0048] Example 4

[0049] A solid electrolyte material, lithium lanthanum zirconium tantalum oxide material, comprises the following steps:

[0050] S1. Preparation of K2SrTa2O7 precursor: Potassium nitrate, tantalum pentoxide, and strontium sulfate were weighed according to the stoichiometric ratio of K:Ta:Sr of 2:2:1.008, dispersed in anhydrous ethanol, and ball-milled at 500 rpm for 7 h; dried at 85°C for 3 h, and pre-calcined at 300°C for 4 h in an air atmosphere to obtain a K2SrTa2O7 precursor.

[0051] S2. Lithium nitrate, lanthanum hydroxide, zirconium oxide, and tantalum pentoxide are weighed according to the stoichiometric ratio of Li:La:Zr:Ta of 6.75:3:1.75:0.25, and dispersed in isopropyl alcohol to form a dispersion, wherein the ratio of the total mass of lithium nitrate, lanthanum hydroxide, zirconium oxide, and tantalum pentoxide to the mass of isopropyl alcohol is 1:1.1.

[0052] S3. Add the K2SrTa2O7 precursor in S1 to the dispersion of S2, ball mill at 600 rpm for 8 hours; dry at 80°C for 7 hours, and finally sinter at a constant temperature of 850°C for 16 hours in an air atmosphere and cool naturally to obtain a strontium-doped and K2SrTa2O7-coated lithium lanthanum zirconium tantalum oxide modified material, wherein the weight ratio of the K2SrTa2O7 precursor to the dispersion is 4:100, the strontium doping amount is 0.8% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 6 to 8 nm.

[0053] Example 5

[0054] A solid electrolyte material, lithium lanthanum zirconium tantalum oxide material, comprises the following steps:

[0055] S1. Preparation of K2SrTa2O7 precursor: Weigh potassium nitrate, tantalum pentoxide, and strontium oxide in a stoichiometric ratio of K:Ta:Sr of 2:2:1.01, disperse them in anhydrous ethanol, and ball-mill at 600 rpm for 9 h; dry at 95°C for 7 h, and pre-calculate at 500°C for 10 h in air atmosphere to obtain a K2SrTa2O7 precursor.

[0056] S2. Lithium nitrate, lanthanum nitrate, zirconium hydroxide, and tantalum pentoxide are weighed according to the stoichiometric ratio of Li:La:Zr:Ta of 6.75:3:1.75:0.25, and dispersed in isopropyl alcohol to form a dispersion, wherein the ratio of the total mass of lithium nitrate, lanthanum nitrate, zirconium hydroxide, and tantalum pentoxide to the mass of isopropyl alcohol is 1:2.

[0057] S3. Add the K2SrTa2O7 precursor in S1 to the dispersion of S2, ball mill at 800 rpm for 10 hours; dry at 90°C for 10 hours, and finally sinter at 900°C for 20 hours in an air atmosphere and naturally cool to obtain a strontium-doped and K2SrTa2O7-coated lithium lanthanum zirconium tantalum oxide modified material, wherein the weight ratio of the K2SrTa2O7 precursor to the dispersion is 5:100, the strontium doping amount is 1% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 8 to 10 nm.

[0058] Comparative Example 1

[0059] The difference from Example 3 is that no strontium element is doped and no K2SrTa2O7 layer is coated.

[0060] Comparative Example 2

[0061] The difference from Example 3 is that in step S1, during the preparation of the K2SrTa2O7 precursor, the stoichiometric ratio of K:Ta:Sr elements is 2:2:1.

[0062] Comparative Example 3

[0063] The only difference from Example 3 is that no K2SrTa2O7 coating was performed, and only strontium doping was performed. The strontium-doped lithium lanthanum zirconium tantalum oxide prepared had a strontium doping amount of 0.6% of the molar weight of the lithium lanthanum zirconium tantalum oxide.

[0064] Comparative Example 4

[0065] The only difference from Example 3 is that in step S1, during the preparation of the K2SrTa2O7 precursor, the stoichiometric ratio of K:Ta:Sr is 2:2:1.015, and a lithium lanthanum zirconium tantalum oxide modified material doped with strontium and coated with K2SrTa2O7 is obtained, wherein the doping amount of strontium element is 1.5% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 4 to 6 nm.

[0066] Comparative Example 5

[0067] The only difference from Example 3 is that in step S3, the weight ratio of the K2SrTa2O7 precursor to the dispersion is 8:100, and a lithium lanthanum zirconium tantalum oxide modified material doped with strontium and coated with K2SrTa2O7 is obtained, wherein the strontium doping amount is 0.6% of the molar weight of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 12 to 15 nm.

[0068] Comparative Example 6

[0069] The differences from Example 3 are: (1) in step S1, during the preparation of the K2SrTa2O7 precursor, the stoichiometric ratio of K:Ta:Sr elements is 2:2:1.001; (2) in step S3, the weight ratio of the K2SrTa2O7 precursor to the dispersion is 0.5:100, and a lithium lanthanum zirconium tantalum oxide modified material doped with strontium and coated with K2SrTa2O7 is obtained, wherein the doping amount of strontium element is 0.1% of the molar amount of lithium lanthanum zirconium tantalum oxide, and the coating layer thickness is about 0 to 1 nm.

[0070] Performance testing:

[0071] Density: The actual density of the sample is determined by calculating the volume using the Archimedes displacement method and measuring the mass before and after using an electronic balance.

[0072] Ionic conductivity: The solid electrolyte material is made into a wafer sample to be tested. Using an electrochemical workstation, the AC impedance at different response frequencies is recorded. Different electrode processes with different reaction time constants are analyzed, and the ionic conductivity of the material is obtained through fitting, analysis, and calculation.

[0073] Surface lithium carbonate content: Dissolve in deionized water, filter, neutralize the filtrate with acid and alkali, and measure with a potentiometric titrator.

[0074] Activation energy: Tested in accordance with GB / T33047.2 Plastic polymer thermogravimetry (TG) Part 2: Determination of activation energy.

[0075] Table 1

[0076] Density / % Ionic conductivity / S / cm Surface lithium carbonate content / % Activation energy / ev Example 1 88.92 <![CDATA[2.46×10 -4 ]]> 0.032 0.32 Example 2 89.21 <![CDATA[2.61×10 -4 ]]> 0.029 0.26 Example 3 89.78 <![CDATA[3.54×10 -4 ]]> 0.011 0.25 Example 4 87.02 <![CDATA[2.71×10 -4 ]]> 0.031 0.28 Example 5 85.87 <![CDATA[2.14×10 -4 ]]> 0.032 0.32 Example 6 84.32 <![CDATA[2.06×10 -4 ]]> 0.026 0.31 Comparative Example 1 70.14 <![CDATA[0.65×10 -4 ]]> 0.54 0.67 Comparative Example 2 76.41 <![CDATA[1.21×10 -4 ]]> 0.021 0.52 Comparative Example 3 78.24 <![CDATA[1.43×10 -4 ]]> 0.41 0.55 Comparative Example 4 79.18 <![CDATA[1.54×10 -4 ]]> 0.052 0.41 Comparative Example 5 80.53 <![CDATA[1.41×10 -4 ]]> 0.018 0.42 Comparative Example 6 79.24 <![CDATA[1.69×10 -4 ]]> 0.38 0.47

[0077] As can be seen from Table 1:

[0078] Example 3 The strontium doping amount is 0.6% of the molar amount of lithium lanthanum zirconium tantalum oxygen. The density of the LLZTO material with a coating thickness of about 4-6 nm is 89.78%, and the ionic conductivity is 3.54×10 -4 S / cm, surface lithium carbonate, activation energy is only 0.25ev. This application has obvious effects on improving density and ionic conductivity and reducing surface lithium carbonate content and activation energy.

[0079] Compared with the LLZTO materials of comparative example 1 (undoped and coated), comparative example 2 (undoped and uncoated), comparative example 4 (overdoped), comparative example 5 (overcoated), and comparative example 6 (doped and undercoated), the present invention demonstrates significant advantages. In other words, the dosage of doping and coating used in the solution of this application is carefully considered, and compared with the unmodified material, all aspects of comprehensive performance have been significantly improved.

[0080] It should be noted that the terms "first," "second," and the like in the specification and claims of this application are used to distinguish similar objects, and are not necessarily used to describe a specific order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments of the application described herein can, for example, be implemented in an order other than that described herein.

[0081] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for preparing a modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte, characterized in that: The preparation method of the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte comprises: The potassium source, tantalum pentoxide and an excess strontium source are pre-sintered to obtain a strontium-doped K2SrTa2O7 precursor; A mixture of a lithium source, a lanthanum source, a zirconium source, tantalum pentoxide and the strontium-doped K2SrTa2O7 precursor is sequentially doped and sintered to obtain a strontium-doped and K2SrTa2O7-coated modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte; The doping process includes: mixing the lithium source, the lanthanum source, the zirconium source, the tantalum pentoxide and a second dispersing solvent to form a dispersion; and sequentially subjecting the dispersion and the strontium-doped K2SrTa2O7 precursor to a second ball milling process and a second drying process.

2. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1, wherein: Before the pre-sintering process, the preparation method of the modified lithium lanthanum zirconium tantalum oxide LLZTO solid electrolyte further includes: mixing the potassium source, the tantalum pentoxide and the strontium source with a first dispersing solvent and then sequentially performing a first ball milling process and a first drying process.

3. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 2, wherein: The rotation speed of the first ball milling process is 300-600 rpm, and the time is 4-9 hours; the temperature of the first drying process is 60-95° C., and the time is 3-7 hours.

4. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1 or 2, characterized in that: The molar ratio of the potassium element in the potassium source, the tantalum element in the tantalum pentoxide, and the strontium element in the strontium source is 2:2:(1.002-1.01).

5. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1 or 2, characterized in that: The temperature of the pre-sintering treatment is 300-500° C., and the sintering time is 4-10 hours.

6. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1, wherein: The rotation speed of the second ball milling process is 400-800 rpm, and the time is 3-10 hours; the temperature of the second drying process is 70-90° C., and the time is 4-10 hours.

7. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1, wherein: The lithium source, the lanthanum source, the zirconium source, and the tantalum pentoxide in the dispersion have a stoichiometric ratio of Li: La: Zr: Ta of 6.75: 3: 1.75: 0.25; The weight ratio of the total weight of the lithium source, lanthanum source, zirconium source, and tantalum pentoxide to the weight of the second dispersion solvent is 1: (1-2), and the weight ratio of the strontium-doped K2SrTa2O7 precursor to the dispersion liquid is (1-5):

100.

8. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1, wherein: The temperature of the sintering process is 750-900° C., and the sintering time is 10-20 hours.

9. The method for preparing the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 1 or 2, characterized in that: The potassium source is selected from one or more of the group consisting of potassium carbonate, potassium hydroxide and potassium nitrate; The strontium source is selected from one or more of the group consisting of strontium carbonate, strontium sulfate and strontium oxide; The lithium source is selected from one or more of the group consisting of lithium carbonate, lithium hydroxide and lithium nitrate; The lanthanum source is selected from one or more of the group consisting of lanthanum oxide, lanthanum hydroxide and lanthanum nitrate; The zirconium source is selected from zirconium oxide and / or zirconium hydroxide.

10. A modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte, characterized in that: The invention comprises a core and a modified layer coated on the surface of the core, wherein the core is a strontium-doped lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte, and the modified layer is a K2SrTa2O7 layer; the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte is prepared by the preparation method of the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to any one of claims 1 to 9.

11. The modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte according to claim 10, characterized in that: In the modified lithium lanthanum zirconium tantalum oxide (LLZTO) solid electrolyte, the doping amount of strontium element is 0.2-1 wt %, and the thickness of the modified layer is 2-10 nm.