Preparation method and application of a garnet solid-state electrolyte

Abstract

This invention belongs to the field of solid electrolytes and discloses a method for preparing and applying a high-temperature, fast-sintering garnet-type solid electrolyte without embedded powder. By controlling the heating rate, using short sintering time, and adding sintering aids, lithium atmosphere volatilization is suppressed, thereby improving ionic conductivity and density. The garnet electrolyte prepared by this invention has an ionic conductivity ≥ 5.06 × 10⁻⁶. ‑4 With a relative density of ≥97.3% and a density of S / cm, this invention eliminates the need for powder embedding, requires low-lithium replenishment, has a short sintering time, consumes less energy, produces ceramics with better overall performance, and is efficient, simple, and can achieve industrial mass production.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolytes, and specifically relates to a method for preparing and applying a powder-free, high-temperature, fast-burning garnet-type solid electrolyte. Background Technology

[0002] Currently, with the development of smart grids, new energy power generation, pure electric vehicles and mobile equipment, lithium-ion batteries are developing rapidly in the field of energy storage and are receiving widespread application and attention due to their advantages such as high specific energy, operating voltage, long service life, wide operating temperature range and recyclability.

[0003] However, commercially available lithium-ion batteries also have some problems that urgently need to be solved, such as safety issues. Currently, lithium-ion batteries use liquid electrolytes, which are flammable, toxic, volatile, and explosive, posing certain safety hazards. Moreover, their energy density has already reached its upper limit of 280-320 Wh / kg. Therefore, the future development direction of lithium batteries is to solve battery safety issues while developing high-energy-density lithium batteries.

[0004] With the development of battery technology, all-solid-state batteries can effectively solve the problems of safety and energy density. Compared with traditional lithium-ion batteries, the electrolyte in solid-state batteries is solid, which can act as both a lithium-ion transport channel and a separator to isolate electrons, simplifying the battery structure and effectively improving safety and energy density. Therefore, the quality of the solid-state electrolyte is a key technology determining the development of lithium battery technology.

[0005] Currently, the development of solid-state electrolytes mainly falls into two categories: polymer solid-state electrolytes and inorganic solid-state electrolytes. Among them, polymer solid-state electrolytes cannot significantly improve the energy density of lithium batteries due to their low electrochemical window. Inorganic solid-state electrolytes are further divided into oxide solid-state electrolytes and sulfide solid-state electrolytes. Sulfide solid-state electrolytes have poor air stability and high preparation costs, which limit their application. Garnet-type oxide solid-state electrolytes, on the other hand, have the characteristics of high lithium-ion conductivity at room temperature, good air stability, and stability to lithium metal anodes, and are expected to be used as solid-state electrolytes in all-solid-state lithium batteries.

[0006] There are many studies on the preparation of garnet solid electrolytes. For example, patent publication CN113402271A discloses the effect of increasing the Ta doping amount on the synthesis of dense LLZTO. Its synthesis process requires powder embedding and sintering. Although the sintering time is short, it still reaches about 5 hours, and the relative density reaches about 95%, which needs to be improved.

[0007] Therefore, the synthesis of garnet-type solid electrolytes still faces the following challenges:

[0008] (1) It needs to be kept at a high temperature for a long time, exceeding 5 hours or even 24 hours, resulting in excessive energy consumption;

[0009] (2) A certain amount of buried powder is required for sintering, which consumes a large amount of lithium source, resulting in resource waste and environmental pollution (buried powder sintering: an essential process in traditional sintering methods, which involves evenly spreading the pre-burned powder after ball milling onto the pressed sheet to act as a lithium source and replenish the lithium volatilized from the sheet during long-term sintering).

[0010] (3) It is difficult to increase the relative density of ceramics. The relative density of traditional sintered ceramics is below 95%. Summary of the Invention

[0011] To overcome the shortcomings and deficiencies of the prior art, the primary objective of this invention is to provide a method for preparing a high-temperature, fast-firing garnet-type solid electrolyte without embedded powder and with low lithium supplementation. This invention employs a strategy combining rapid heating in a short time, ultra-short holding time, and the addition of sintering aids, which reduces lithium volatilization, promotes fine grain development, and thus densifies the ceramic, improving its overall performance.

[0012] Another objective of this invention is to provide a high-temperature fast-burning garnet-type solid electrolyte prepared by the above method. The obtained garnet-type solid electrolyte has high ionic conductivity, high relative density, simple preparation process, low cost, good repeatability and easy industrial production.

[0013] Another object of the present invention is to provide the application of the above-mentioned garnet-type solid electrolyte.

[0014] The objective of this invention is achieved through the following solution:

[0015] A method for preparing a garnet-type solid electrolyte includes the following steps:

[0016] 1) Weigh the lithium source compound, lanthanum source compound, zirconium source compound and M source compound in a certain stoichiometric ratio, and ball mill the resulting powder once and dry it in an oven to obtain a mixed raw material;

[0017] 2) The mixed raw materials are calcined to obtain garnet-type solid electrolyte pre-calcined powder;

[0018] 3) Mix the pre-fired powder and sintering aid SA, granulate, and press into shape to obtain a ceramic green body;

[0019] 4) Place the ceramic blank in a crucible and heat it at a rate of 12-50℃ / min to sinter at 1180℃-1340℃ for 1-10 min to finally obtain the garnet-type solid electrolyte material.

[0020] The heating rate of the sintering process is T1 when it is below 1000℃ and T2 when it is above 1000℃, where T1 > T2.

[0021] The solid electrolyte material has the general formula Li 7-x La3(Zr 2-x Mx)O 12 +ySA, where M is selected from a metallic element, preferably at least one selected from Al, Ga, Ti, Nb, and Ta; 0 < x < 1. SA represents a sintering aid, which can be at least one of CuO, La2Zr2O7, or Li3BO3; 0 wt% ≤ y ≤ 5 wt%, where y represents the proportion of the sintering aid SA in the solid electrolyte material (Li 7-x La3(Zr 2-x Mx)O 12 +ySA) mass percentage.

[0022] In one embodiment of the present invention, as a preferred embodiment, M is selected as Ta, where 0.2 < x < 0.8, and more preferably 0.4 ≤ x ≤ 0.7.

[0023] The lithium source compound mentioned in step (1) is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium hydroxide, lithium chloride, lithium sulfate, and lithium oxalate, preferably lithium hydroxide;

[0024] The lanthanum source compound mentioned in step (1) is at least one of lanthanum oxide, lanthanum hydroxide, etc., preferably lanthanum oxide;

[0025] The zirconium source compound mentioned in step (1) is at least one of zirconium dioxide and zirconium hydroxide;

[0026] The M source compound mentioned in step (1) is at least one of the metal oxides and hydroxides containing M; preferably, the M source compound is at least one of tantalum pentoxide, niobium pentoxide, gallium oxide, titanium dioxide, and aluminum oxide; more preferably, the M source compound is tantalum pentoxide; using Ta compounds can stabilize the cubic phase garnet structure, which is beneficial for synthesizing materials with higher ionic conductivity.

[0027] The mass of lithium source compound, lanthanum source compound, zirconium source compound, and M source compound in the mixed raw materials mentioned in step (1) are calculated according to the general structural formula Li 7-x La3(Zr 2-x Mx)O 12 The mass of the sintering agent SA in step (3) is calculated based on the atomic ratio of +ySA, while the mass of the sintering agent SA is calculated based on the mass percentage y, where 0.4≤x≤0.7; 0wt%≤y≤5wt%.

[0028] The lithium source compound used in step (1) is in excess of 0-8 wt%, where excess of 0-8 wt% means that the actual amount of lithium source compound used is 1-1.08 times the mass of lithium source compound weighed according to the general structural formula, preferably 5% wt, that is, the actual amount of lithium source compound used is 1.05 times the mass of lithium source compound weighed according to the general structural formula.

[0029] The ball milling in step (1) uses a planetary ball mill and the ball milling method is wet milling. Specifically, the raw materials, solvent and ball milling beads are mixed in a mass ratio of (1-3):(6-10):(9-14) and then ball milled at a speed of 300-600 rpm for 8-36 hours. The solvent is at least one of isopropanol, anhydrous ethanol and water, preferably isopropanol.

[0030] The drying process described in step (1) refers to placing the raw material in a forced-air drying oven at a temperature of 50-80℃ for 4-12 hours.

[0031] The calcination temperature in step (2) is 900℃~1000℃, the calcination time is 2h~6h, and the heating rate is 2℃ / min~8℃ / min; preferably, the calcination temperature is 950℃, the holding time is 4h, and the heating rate is 3℃ / min. The crucible used for calcination (pre-calcination) is an Al2O3 crucible, an MgO crucible, or a platinum crucible, preferably an MgO crucible;

[0032] The sintering aid SA mentioned in step (3) is at least one of copper oxide, lithium borate, lanthanum zirconate, etc.

[0033] Preferably, the sintering aid is La2Zr2O7; using La2Zr2O7 as the sintering aid SA can lower the sintering temperature, which is beneficial to grain development and inhibits the volatilization of lithium atmosphere.

[0034] The mixing described in step (3) is preferably carried out by secondary ball milling. The secondary ball milling refers to the ball milling of the mixed raw materials (pre-calcined powder and calcining aid SA), solvent and milling ball at a mass ratio of (1-2):(6-10):(9-14) at a ball milling speed of 300-500 rpm for 24-48 hours. The solvent is at least one of isopropanol, anhydrous ethanol and water. Preferably, the solvent is isopropanol.

[0035] The pressing and molding operation described in step (3) uses a mold radius The pressure is 5 MPa to 20 MPa, and the holding time is 10 s to 2 min. Pressing under this pressure and holding time helps to improve the density of the material during sintering.

[0036] In step (4), the heating rate of the sintering process is T1 when it is below 1000℃ and T2 when it is above 1000℃, with T1 > T2. At higher temperatures, the atomic diffusion rate is faster, and the grains are easier to form and grow. At this time, the sintering rate is 12-50℃ / min, which can complete the grain growth and ceramic densification process in a shorter time. When the sintering temperature is raised to 1000℃, the sintering aid produces a liquid phase. Reducing the heating rate is beneficial to the development of crystals and filling any possible pores.

[0037] Preferably, the sintering temperature is 1280℃~1340℃, and the heating rate T1 is 30℃ / min~50℃ / min when below 1000℃, and 12℃ / min~30℃ / min (excluding 30℃ / min) when above 1000℃. Heating at 30~50℃ / min in T1 helps avoid lithium volatilization, thus eliminating the need for powder-embedded sintering. Simultaneously, the rapid heating process promotes the formation of the garnet phase and grain growth. Heating at 12℃ / min~30℃ / min in T2 is beneficial for uniform grain size formation and for crystal development and filling of any potential pores. Furthermore, reducing the heating rate also reduces equipment wear and tear, achieving a green and environmentally friendly goal.

[0038] Preferably, the sintering temperature is 1320℃, the preferred holding time is 5min, the preferred heating rate for T1 is 30℃ / min, and the preferred heating rate for T2 is 15℃ / min.

[0039] A garnet-type solid electrolyte prepared by the above method satisfies one or more of the following (1) to (4):

[0040] (1) The structure is a pure cubic phase;

[0041] (2) Ionic conductivity at room temperature ≥ 5.06 × 10⁻⁶ -4 S / cm;

[0042] (3) Relative density ≥ 97.3%;

[0043] (4) Particle size D50 is 1-4μm;

[0044] Currently, commercial lithium-ion batteries mainly use organic electrolytes, which pose safety hazards such as leakage, combustion, and explosion under unconventional environments. The garnet-type solid electrolyte described above is of great significance in solving the safety problems of traditional liquid batteries. It possesses advantages such as high lithium-ion conductivity, a wide chemical window, high specific energy, long cycle life, low self-discharge, and strong designability, effectively improving the safety and low capacity issues of lithium-ion batteries.

[0045] A lithium-ion battery comprising the aforementioned garnet-type solid electrolyte.

[0046] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0047] 1. This application prepares garnet solid electrolyte by rapid heating and rapid sintering at high temperature, without the need for powder sintering. The excess lithium element in this application can be controlled to below 10%, and low lithium supplementation can save a lot of lithium source and reduce production costs.

[0048] 2. The method of the present invention can effectively suppress abnormal grain growth of garnet-type solid electrolytes, and effectively improve the relative density and ionic conductivity, wherein the relative density is ≥97.3% and the ionic conductivity is ≥5.06×10⁻⁶. -4 S / cm;

[0049] 3. This application utilizes wet ball milling to control the particle size D50 of the secondary ball milling slurry to remain within 1-4 μm. Simultaneously, the introduction of a small amount of sintering aid SA effectively reduces sintering time and temperature, resulting in finer ceramic grains with a D50 of 1-4 μm and good grain size uniformity. This effectively improves the material's density and electrical properties while reducing sintering energy loss.

[0050] 4. By introducing M element doping, the cubic structure of garnet at room temperature can be effectively stabilized, maintaining a high ionic conductivity. Attached Figure Description

[0051] Figure 1 This is the XRD pattern of Example 1.

[0052] Figure 2 This is the SEM image of Example 1.

[0053] Figure 3 This is a particle size distribution diagram of the secondary ball milling slurry from Example 1.

[0054] Figure 4 The impedance spectrum is shown in Example 1.

[0055] Figure 5 Impedance spectra for both the example and comparative models. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0057] Unless otherwise specified in the examples, the conditions should be performed according to standard conditions or the manufacturer's recommendations.

[0058] Unless otherwise specified, all reagents and instruments used are commercially available products. Unless otherwise specified, all reagents used in the examples are readily available from the market.

[0059] Example 1

[0060] Preparation of Li with x = 0.6 and y = 0. 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte

[0061] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill speed was 320 rpm / min, and mixing was carried out for 24 hours. After the raw materials were completely mixed, the mixture was heated to 80℃. The material was dried for 12 hours, then pre-fired at 950℃ with a heating rate of 3℃ / min for 4 hours. The resulting pre-fired powder was then subjected to a second ball milling process using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material-solvent-ball weight ratio was 1:8:10, and the milling time was 24 hours at a milling rate of 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process involved a die diameter of... The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible without adding pre-calcined powder. The temperature was rapidly increased to 1000℃ at 30℃ / min, then increased to 1320℃ at 15℃ / min and held for 5 min. After natural cooling to room temperature, the relative density and impedance spectrum were measured.

[0062] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 190 Ω, and the total ionic conductivity is 5.06 × 10⁻⁶. -4 S / cm, with a relative density of 98%.

[0063] Example 2

[0064] Preparation of Li with x = 0.6 and y = 1.5 wt% 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte with +1.5wt% La2Zr2O7

[0065] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill speed was 320 rpm / min, and mixing was carried out for 24 hours. After the raw materials were mixed, they were dried at 80℃ for 12 hours. The dried material was pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The pre-calcined powder was then obtained. This pre-calcined powder was further ball-milled with 1.5wt% La₂Zr₂O₇ using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing in original text]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible without adding pre-calcined powder. The temperature was rapidly increased to 1000℃ at 30℃ / min, then increased to 1280℃ at 15℃ / min and held for 5 min. After natural cooling to room temperature, the relative density and impedance spectrum were measured.

[0066] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 123.6 Ω, and the total ionic conductivity is 7.82 × 10⁻⁶. -4 S / cm, with a relative density of 99.5%.

[0067] Example 3

[0068] Preparation of Li with x = 0.6 and y = 1.5 wt% 6.4 La3Zr 1.4 Ti 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte with +1.5wt% La2Zr2O7

[0069] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and TiO2 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill speed was 320 rpm / min, and mixing was carried out for 24 hours. After the raw materials were mixed, they were dried at 80℃ for 12 hours. The dried material was pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The pre-calcined powder was then obtained. This pre-calcined powder was further ball-milled with 1.5wt% La₂Zr₂O₇ using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing in original text]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible without adding pre-calcined powder. The temperature was rapidly increased to 1000℃ at 30℃ / min, then increased to 1280℃ at 15℃ / min and held for 5 min. After natural cooling to room temperature, the relative density and impedance spectrum were measured.

[0070] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 191.4 Ω, and the total ionic conductivity is 5.16 × 10⁻⁶. -4 The density is 97.3% (S / cm).

[0071] Example 4

[0072] Preparation of Li with x = 0.6 and y = 1.5 wt% 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte with +1.5wt% La2Zr2O7

[0073] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill speed was 320 rpm / min, and mixing was carried out for 24 hours. After the raw materials were mixed, they were dried at 80℃ for 12 hours. The dried material was pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The pre-calcined powder was then obtained. This pre-calcined powder was further ball-milled with 1.5wt% La₂Zr₂O₇ using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing in original text]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible without adding pre-calcined powder. The temperature was rapidly increased to 1000℃ at 40℃ / min, then increased to 1280℃ at 15℃ / min and held for 5 min. After natural cooling to room temperature, the relative density and impedance spectrum were measured.

[0074] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 193.3 Ω, and the total ionic conductivity is 5.2 × 10⁻⁶. -4 S / cm, with a relative density of 98.5%.

[0075] Comparative Example 1

[0076] Preparation of Li with x = 0.6 and y = 1.5 wt% 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte with +1.5wt% La2Zr2O7

[0077] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill speed was 320 rpm / min, and mixing was carried out for 24 hours. After the raw materials were mixed, they were dried at 80℃ for 12 hours. The dried material was pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The pre-calcined powder was then obtained. This pre-calcined powder was further ball-milled with 1.5wt% La₂Zr₂O₇ using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing in original text]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible and rapidly heated to 1280 °C at 30 °C / min, held for 5 min, and then naturally cooled to room temperature to test the relative density and impedance spectrum.

[0078] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 311 Ω, and the total ionic conductivity is 3.09 × 10⁻⁶. -4 S / cm, with a relative density of 95%.

[0079] Comparative Example 2

[0080] Preparation of Li with x = 0.6 and y = 0. 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte

[0081] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill was operated at 320 rpm / min and mixed for 24 hours. After the raw materials were mixed, the mixture was heated at 80℃. The material was dried for 12 hours under the specified conditions. It was then pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The resulting pre-calcined powder was then subjected to a second ball milling process using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible, and 2 g of pre-calcined powder was added to embed the sheet. The temperature was increased to 1180℃ at 3℃ / min and held for 10 h. After naturally cooling to room temperature, the relative density and impedance spectrum were tested.

[0082] The total resistance of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 278 Ω, and the total ionic conductivity is 3.46 × 10⁻⁶. -4 S / cm, with a relative density of 94%.

[0083] Comparative Example 3

[0084] Preparation of Li with x = 0.6 and y = 0. 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte

[0085] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, with isopropanol as solvent and zirconium dioxide balls as milling mills. The weight ratio of material:solvent:balls was 2:7:10. The planetary ball mill was operated at 320 rpm / min and mixed for 24 hours. After the raw materials were mixed, the mixture was heated at 80℃. The material was dried for 12 hours under the specified conditions. It was then pre-calcined at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. The resulting pre-calcined powder was then subjected to a second ball milling process using isopropanol as the solvent and zirconium dioxide balls as the milling mills. The material:solvent:ball weight ratio was 1:8:10. The milling time was 24 hours, and the milling rate was 400 rpm / min. The second-milled material was then dried, granulated, and tableted. The tableting process was as follows: [Diameter of mold is missing]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible, and 2 g of pre-calcined powder was added to embed the sheet. The temperature was increased to 1180℃ at 3℃ / min and held for 5 min. After naturally cooling to room temperature, the relative density and impedance spectra were measured.

[0086] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 3180 Ω, and the total ionic conductivity is 3.03 × 10⁻⁶. -5 Its density is 87.6% (S / cm).

[0087] Comparative Example 4

[0088] Preparation of Li with x = 0.6 and y = 0. 6.4 La3Zr 1.4 Ta 0.6 O 12 Lithium lanthanum zirconium oxide solid electrolyte

[0089] Lithium source LiOH·H2O (purity 99.9%, lithium excess 5wt%), La2O3 (purity 99.9%), ZrO2 (purity 99%), and Ta2O5 (purity 99.9%) were used as raw materials, mixed according to stoichiometric ratio, and zirconia balls were used as milling mills. The weight ratio of raw materials to balls was 1:5. The planetary ball mill speed was 320 rpm / min, and the mixture was dry-mixed for 24 hours (the difference between dry ball milling and wet ball milling is whether a solvent is added). After the materials are mixed, they are dried at 80℃ for 12 hours. The dried materials are then pre-fired at 950℃ with a heating rate of 3℃ / min and a holding time of 4 hours. Pre-fired powder is obtained after pre-firing. This pre-fired powder is then subjected to secondary ball milling using zirconia balls. The material-to-ball weight ratio is 1:10, the milling time is 24 hours, and the milling rate is 400 rpm / min. The secondary milled material is then dried, granulated, and tableted. The tableting process is as follows: [Diameter of mold is missing]. The pressure was 10 MPa, and the holding time was 30 s. The formed sheet was placed in a magnesium oxide crucible without adding pre-calcined powder. The temperature was rapidly increased to 1000℃ at 30℃ / min, then increased to 1320℃ at 15℃ / min and held for 5 min. After natural cooling to room temperature, the relative density and impedance spectrum were measured.

[0090] The total resistivity of this garnet-type lithium lanthanum zirconium oxide solid electrolyte is 230 Ω, and the total ionic conductivity is 4.18 × 10⁻⁶. -4 S / cm, with a relative density of 95%.

[0091] Table 1 compares the experimental data of total ionic conductivity and relative density of the examples and comparative examples. Example 1 is a sintering regime without powder embedding, rapid heating, and short holding time. Example 2 is a comparison with the addition of sintering aids. It can be seen that adding sintering aids can lower the sintering temperature and increase ionic conductivity. Example 1 and Comparative Example 1 compare sintering with and without powder embedding. It can be seen that during high-temperature short-time sintering, powder embedding has little effect on the ionic conductivity and density of the sample. Powder-free sintering can also reduce costs and processes. Comparing Example 2 and Comparative Example 1, it can be seen that the sample with rapid heating followed by slow heating performs better than the sample with rapid heating alone. From Comparative Examples 2 and 3, it can be seen that low-temperature short-time sintering is not feasible in traditional sintering regimes, while long-time sintering not only wastes time but also increases energy consumption and costs, and the performance is also poor. From Example 1 and Comparative Example 4, it can be seen that wet ball milling has a shorter sintering time and higher ionic conductivity and density than dry ball milling. Short-duration, high-temperature rapid sintering yields performance 1-2 orders of magnitude better than long-duration sintering for the following reasons: 1. Rapid heating and shorter holding times significantly reduce lithium loss, allowing for more efficient lithium utilization; 2. Shorter holding times effectively inhibit secondary grain growth, thus increasing the relative density of the ceramic; 3. Adding sintering aids effectively lowers the sintering temperature, promoting grain development and reducing lithium atmosphere volatilization, resulting in higher density and lithium-ion conductivity; 4. Wet ball milling ensures more uniform mixing of raw materials, and secondary ball milling produces finer slurry particles with higher reactivity, leading to higher relative density and ionic conductivity of the material.

[0092] Table 1 Comparison of experimental data between the examples and comparative examples.

[0093]

[0094] from Figure 1 As can be seen from the XRD, the present invention has prepared a pure phase structure of garnet.

[0095] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a garnet-type solid state electrolyte, characterized by The method comprises the following steps: 1) A lithium source compound, a lanthanum source compound, a zirconium source compound, and an M source compound are weighed in stoichiometric proportions, and the obtained powder is mixed to obtain a mixed raw material; wherein M is selected from metal elements; 2) The mixed raw material is calcined to obtain a garnet-type solid electrolyte pre-sintered powder; 3) The pre-sintered powder and a sintering aid are mixed, granulated, and pressed to form a ceramic green body; 4) The ceramic green body is placed in a crucible and heated at a heating rate of 12-50 ℃ / min to 1180-1340 ℃ and sintered for 1-10 min, to finally obtain a garnet-type solid electrolyte material; wherein the heating rate of the sintering process is T1 below 1000 ℃ and T2 above 1000 ℃, T1>T2, T1 is 30-50 ℃ / min below 1000 ℃, and T2 is 12-30 ℃ / min above 1000 ℃.

2. The method for preparing a garnet-type solid electrolyte according to claim 1, characterized in that: The solid-state electrolyte material has a general formula Li 7-x La3(Zr 2-x , M x )O 12 +ySA, wherein M is selected from at least one of Al, Ga, Ti, Nb and Ta; 0 < x < 1; SA represents a sintering aid; y represents a percentage of the sintering aid SA in the mass of the solid-state electrolyte material, 0 wt% ≤ y ≤ 5 wt%.

3. The method for preparing a garnet-type solid electrolyte according to claim 1 or 2, characterized in that: the lithium source compound in step (1) is at least one of lithium carbonate, lithium hydroxide, lithium nitrate, lithium hydroxide, lithium chloride, lithium sulfate, and lithium oxalate; the lanthanum source compound in step (1) is at least one of lanthanum oxide and lanthanum hydroxide; the zirconium source compound in step (1) is at least one of zirconium dioxide and zirconium hydroxide; the M source compound in step (1) is at least one of a metal oxide and a hydroxide containing M.

4. The method for preparing a garnet-type solid electrolyte according to claim 3, characterized in that: the M source compound is at least one of tantalum pentoxide, niobium pentoxide, gallium oxide, titanium dioxide, and aluminum oxide.

5. The method for preparing a garnet-type solid electrolyte according to claim 1 or 2, characterized in that: the sintering aid SA in step (3) is at least one of copper oxide, lithium borate, and lanthanum zirconate.

6. The method of claim 5, wherein the method further comprises: the sintering aid in step (3) is La2Zr2O7.

7. The method for preparing a garnet-type solid electrolyte according to claim 1 or 2, characterized in that: the mixing in step (1) is ball milling, the ball milling is performed by a planetary ball mill, and the ball milling method is wet milling, specifically: the mixed raw material, a solvent, and ball milling beads are mixed in a mass ratio of (1-3):(6-10):(9-14), and then ball milling is performed at a ball milling speed of 300-600 rpm for 8-36 h, and the ball-milled product is dried and then calcined; and / or the mixing in step (3) is also ball milling, which refers to that the pre-sintered powder and the sintering aid SA, a solvent, and ball milling beads are mixed in a mass ratio of (1-2):(6-10):(9-14) and ball milling is performed at a ball milling speed of 300-500 rpm for 24-48 h, and the ball-milled product is dried and then granulated.

8. The method for preparing a garnet-type solid electrolyte according to claim 1 or 2, characterized in that: The temperature of the calcination in step (2) is 900-1000℃, the calcination time is 2-6h, and the heating rate is 2-8℃ / min.

9. The method for preparing the garnet solid-state electrolyte according to claim 1 or 2, characterized in that: The pressing operation in step (3) is performed using a mold radius of 13mm, a pressure of 5-20Mpa, and a pressure holding time of 10s-2min.

10. The method for preparing the garnet solid-state electrolyte according to claim 1 or 2, characterized in that: The sintering temperature in step (4) is 1280-1340℃, the heating rate is 30-50℃ / min below 1000℃ and 12-30℃ / min above 1000℃.

11. The method for preparing the garnet solid-state electrolyte according to claim 10, characterized in that: The sintering temperature in step (4) is 1320℃, the holding time is 5min, the heating rate below 1000℃ is 30℃ / min, and the heating rate above 1000℃ is 15℃ / min.

12. A garnet-type solid state electrolyte prepared according to the method of any one of claims 1-8, characterized in that, The garnet solid-state electrolyte satisfies one or more of the following (1)-(4): (1) the structure is pure cubic phase; (2) Ionic conductivity ≥ 5.06 x 10 -4 S / cm at room temperature; (3) the relative density is ≥97.3%; (4) the particle size D50 is 1-4μm.

13. A lithium-ion battery, characterized by The garnet solid-state electrolyte according to claim 12.

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