Preparation method of garnet-type oxide solid electrolyte that can improve bulk density

Abstract

This invention relates to novel solid-state battery materials technology, aiming to provide a method for preparing garnet-type oxide solid electrolytes that can improve bulk density. The method includes: preparing LLZO precursor powder, the main crystalline phase of which is cubic Li7La3Zr2O. 12 It also contains La2Zr2O7 pyrochlore impurities, with the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO between 3.2% and 8.9%. The LLZO precursor powder is uniformly mixed with lithium salt, pressed into shape, and then sintered to obtain a garnet-type oxide solid electrolyte bulk with increased density. This invention can prepare ultra-high density LLZO ceramic bulk at a significantly lower sintering temperature than traditional methods, greatly suppressing lithium volatilization and impurity phase formation. The electrolyte bulk exhibits excellent comprehensive electrochemical performance. The technical principle of this invention is clear, the process is controllable, and it is applicable to various garnet-type oxide electrolyte systems doped with Ta, Al, Nb, etc., showing good versatility and industrialization prospects.

Description

Technical Field

[0001] This invention relates to the field of new materials technology for solid-state batteries, specifically to a method for preparing garnet-type oxide solid electrolytes that can improve bulk density. Background Technology

[0002] Garnet-type oxide solid electrolytes, especially lithium lanthanum zirconium oxide (Li7La3Zr2O) 12 Materials represented by LLZO are widely recognized as one of the core materials for realizing next-generation high-energy-density, high-safety all-solid-state lithium metal batteries due to their extremely high lithium-ion conductivity, excellent chemical stability to lithium metal, and wide electrochemical window. In the various applications of this material, highly dense, low-porosity sintered ceramic bulk materials play an irreplaceable role.

[0003] The density of bulk materials is the physical foundation and primary prerequisite for all their functional applications. Firstly, from an electrical performance perspective, high density minimizes open pores and closed voids, ensuring the continuity and effectiveness of lithium-ion conduction pathways. Any residual pores, especially interconnected pores, become insulating barriers to ion transport, significantly increasing bulk resistance and leading to uneven local current distribution. Secondly, from a mechanical and failure mechanism perspective, density directly determines the material's mechanical strength and toughness. A porous, loose ceramic body is highly susceptible to cracking and even fragmentation under battery assembly pressure or stress generated by volume changes in electrode materials during charging and discharging, leading to short-circuit failure. More importantly, in combating lithium dendrites—the most severe challenge in solid-state batteries—density is the first and most crucial physical defense. Theoretical research and experiments have confirmed that lithium dendrites preferentially nucleate at defects such as pores and cracks and propagate through these low-density regions. Therefore, obtaining LLZO ceramic bulk with near-theoretical density and uniform, defect-free microstructure is the fundamental guarantee for suppressing the physical penetration of lithium dendrites and improving the cycle stability and safety of batteries.

[0004] However, the preparation of high-density garnet-type oxide ceramic bulks presents significant technological challenges. Traditional sintering of LLZO typically requires prolonged holding at temperatures exceeding 1150°C, a process inherently contradictory: while high temperatures facilitate material diffusion and grain boundary migration for densification, they also induce severe lithium volatilization. Lithium loss not only leads to non-stoichiometry and the formation of low-conductivity impurity phases (such as La₂Zr₂O₇), but also leaves numerous vacancies and pores within the material due to component loss, ultimately undermining the densification goal. To lower the sintering temperature, researchers in this field commonly employ the introduction of various sintering aids or the formation of a eutectic liquid phase through solid-state reactions to promote densification. However, existing methods often face two levels of problems: firstly, at the precursor powder level, most studies directly use powders synthesized via solid-state methods followed by simple ball milling. These powders often exhibit problems such as wide particle size distribution, irregular morphology, severe hard agglomeration, and high crystallinity. As the "starting point" for sintering, the green blank formed by this powder accumulation has low density and poor uniformity, and its high crystallinity leads to insufficient sintering activity. Even with the addition of flux, higher temperatures or longer times are required to drive densification, which exacerbates lithium volatilization and easily forms an uneven microstructure with poor local density. Secondly, at the flux and grain boundary engineering level, common sintering strategies (such as adding Al2O3, Li3BO3, etc.) can promote grain growth and porosity removal to a certain extent, but often lack precise design of the final grain boundary phase state. During the cooling process after sintering, these fluxing components easily crystallize at the grain boundaries to form a second phase. The mismatch in thermal expansion coefficients between these crystalline phases and LLZO grains, as well as their own brittleness, introduces micro-stress or even micro-cracks at the grain boundaries, microscopically destroying the density and continuity of the grain boundary region, forming potential mechanical weak points and mass transport barriers. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the shortcomings of existing technologies and provide a method for preparing garnet-type oxide solid electrolytes that can improve bulk density. This method addresses both the intrinsic properties of precursor powders and the design of grain boundary structures, achieving simultaneous optimization of microstructure and improvement of performance.

[0006] To solve the technical problem, the solution of the present invention is:

[0007] A method for preparing garnet-type oxide solid electrolytes that can improve bulk density is provided, comprising:

[0008] (1) Preparation of LLZO precursor powder, the main crystalline phase of which is cubic phase Li7La3Zr2O 12 It also contains La2Zr2O7 pyrochlore impurities, and the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO is between 3.2% and 8.9%.

[0009] (2) After the LLZO precursor powder is mixed evenly with lithium salt, it is pressed into shape and then sintered to obtain a garnet-type oxide solid electrolyte block with increased density.

[0010] As a preferred embodiment of the present invention, the LLZO precursor powder particles are nearly spherical or weakly plate-like, and the particle size is in the submicron range.

[0011] As a preferred embodiment of the present invention, the LLZO precursor powder is prepared by sol-gel method, spray pyrolysis method or solvent-assisted sand milling-pre-calcination method.

[0012] As a preferred embodiment of the present invention, the lithium salt is one or any combination of lithium hydroxide, lithium iodide, and lithium nitrate; the lithium salt accounts for 5-15% of the mass fraction of the LLZO precursor powder.

[0013] As a preferred embodiment of the present invention, the pressing molding refers to dry pressing in a mold and then demolding to obtain a blank, or further includes isostatic pressing of the blank.

[0014] As a preferred embodiment of the present invention, the sintering is divided into two steps: first, the temperature is increased to 250-350°C at a heating rate of 10°C / min and held for 1-12 hours; then, the temperature is increased to 950-1050°C at a heating rate of 5°C / min and held for 10-240 minutes.

[0015] As a preferred embodiment of the present invention, the method further includes polishing the surface of the sintered block.

[0016] As a preferred embodiment of the present invention, the garnet-type oxide solid electrolyte bulk has a relative density ≥97% and an ionic conductivity at room temperature exceeding 1×10⁻⁶. -3 Scm -1 .

[0017] Description of the invention principle:

[0018] To address the various problems existing in the prior art, this invention provides a novel systematic solution. The core idea lies in simultaneously optimizing the "raw material basis" and "process control" of sintering, thereby fundamentally improving the sintering density of garnet-type electrolyte blocks.

[0019] Firstly, this invention, through precise design of the synthesis route, prepares precursor powders with specific particle sizes, regular morphologies, and suitable crystallinity. These powders possess high packing density and high sintering activity, providing an ideal starting point for low-temperature, efficient densification. Precise control of the precursor powders ensures extremely high surface energy and sintering driving force through submicron-level size; the near-spherical or weakly lamellar morphology facilitates maximizing powder packing density and reduces macropores in the green body. This lays the foundation for achieving highly uniform densification at lower temperatures, reducing lithium volatilization and abnormal grain growth caused by high-temperature, long-term sintering.

[0020] Secondly, this invention innovatively obtains a precursor powder containing La2Zr2O7 through process control and mixes it with a low-melting-point lithium salt system as a flux. The purpose is not only to provide an effective mass transfer medium to promote the removal of pores during sintering, but more importantly, to ensure that the flux exists in the final material in the form of LLZO phase through composition and process control.

[0021] The reaction pathway between La₂O₃ and ZrO₂ is shorter, making the formation of the binary compound La₂Zr₂O₇ kinetically much easier than simultaneously coordinating the four ions (lithium, lanthanum, zirconium, and tantalum) to form a complex three-dimensional garnet network. Generally, La₂Zr₂O₇ begins to form above 600℃, and LLZO begins to form above 800℃. Therefore, through proper process control, the ratio of La₂Zr₂O₇ to LLZO can be controlled within a specific range.

[0022] Thirdly, this invention, by adding a low-melting-point lithium salt and synergizing with the small amount of La2Zr2O7 already present in the precursor powder, forms an integrated and stable LLZO bulk. This approach, which does not introduce additional phase structures into the final material and achieves continuous densification and seamless connectivity, enables the preparation of ultra-high density, strongly grain-bound, and uniformly microstructured garnet-type oxide ceramic bulks at temperatures significantly lower than conventional methods, laying a solid physical foundation for the subsequent construction of high-performance solid-state batteries.

[0023] The low-melting-point lithium salt selected in this invention has a composition and ratio designed to achieve two functions: (a) providing an effective transient liquid phase in the early stages of sintering, significantly reducing the densification energy barrier; and (b) in the final sintering stage, through a combination of thermodynamics (compositional design to form the glass-forming region) and kinetics (precise control of T2 temperature and time in the two-step sintering method), preventing abnormal grain growth. This bulk structure, by greatly avoiding pores and voids, exhibits a high room-temperature total ionic conductivity (>1×10⁻⁶). -3 Scm -1 ).

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

[0025] 1. This invention can prepare LLZO ceramic bulk with ultra-high density (≥97%) at a sintering temperature significantly lower than that of traditional methods (by more than 100°C), which greatly suppresses lithium volatilization and impurity phase formation.

[0026] 2. The bulk electrolyte prepared by this invention has excellent comprehensive electrochemical performance: high total ionic conductivity (>1.0×10⁻⁶). -3 Scm -1 ).

[0027] 3. The technical principle of this invention is clear and the process is controllable. It is applicable to various garnet-type oxide electrolyte systems doped with Ta, Al, Nb, etc., and has good universality and industrialization prospects. Attached Figure Description

[0028] Figure 1 The XRD patterns of the precursor powders of Example 1, Comparative Examples 1 and 2 are shown (the strongest peak ratio in Example 1 is 441 / 4962=8.9%, and the strongest peak ratio in Comparative Example 1 is 669 / 6825=9.8%).

[0029] Figure 2 Microstructure of precursor powder in Example 1 (mostly particle size 500~800nm).

[0030] Figure 3 SEM of the block cross-section prepared in Example 1.

[0031] Figure 4 Microstructure of the precursor powder in Comparative Example 2 (mostly with particle size of 1~2μm).

[0032] Figure 5 SEM of the block cross-section prepared in Comparative Example 2. Detailed Implementation

[0033] Part 1 Overview of the Implementation Scheme of this Invention

[0034] This invention provides a method for preparing garnet-type oxide solid electrolytes that can improve bulk density, comprising the following steps:

[0035] (i) Preparation of garnet-type oxide precursor powder with specific morphology, size and crystallization state.

[0036] This invention utilizes existing technologies (such as sol-gel method, spray pyrolysis method, or solvent-assisted milling-pre-calcination method) to prepare LLZO precursor powder. Typically, due to insufficient pre-calcination temperature, lithium source volatilization, or uneven raw material mixing during the preparation process, some La2O3 and ZrO2 do not fully participate in the LLZO synthesis reaction, preferentially forming the thermodynamically stable La2Zr2O7 impurity phase, ultimately resulting in a phase composition of "main crystalline phase LLZO + impurity phase La2Zr2O7". In this invention, technicians can control the reaction conditions using conventional operating methods to synthesize precursor powder with nearly spherical or weakly lamellar primary particles containing a small amount of La2Zr2O7 phase (the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder is between 3.2% and 8.9%), and the primary particle grain size can reach submicron level. This control scheme only requires technicians to repeat the experiment multiple times and compare the results with the test data to find the optimal, highly reproducible reaction conditions, without requiring any creative effort. Since the morphology, size, crystallization state and other parameters of the product itself are the core content defined by this invention, and the control technology in the preparation process is not the focus, they are only given examples in the embodiments and will not be elaborated further.

[0037] (ii) Design and addition of low melting point lithium salts.

[0038] The prepared precursor powder is uniformly mixed with a low-melting-point lithium salt, wherein the mass ratio of the low-melting-point lithium salt (such as lithium hydroxide, lithium iodide, lithium nitrate, etc.) to the precursor powder is 5%–15%. The low-melting-point lithium salt melts in the early stage of sintering, providing a liquid phase to promote particle rearrangement and densification. At the same time, an appropriate amount of residual La2Zr2O7 phase will react with excess lithium to form continuous and stable LLZO.

[0039] (III) Preparation of dense bulk material by two-step sintering method.

[0040] After the mixed powder is dry-pressed or cold isostatically pressed into shape, it is sintered. The pressure acting on the dense bulk is generally not less than 200 MPa. First, the temperature is raised to the first temperature T1 at a relatively fast heating rate (at least 50°C higher than the melting point of low-melting-point lithium salts, and generally not exceeding 200°C), and held for 1 to 12 hours to allow the liquid phase to be evenly distributed and achieve initial densification. Then, the temperature is raised to the second temperature T2 (T2>T1, but more than 100°C lower than the traditional pure-phase LLZO sintering temperature), and held for a short time (10 to 240 minutes) to promote appropriate grain growth, close pores, and ensure that the grain boundary phase remains amorphous and does not crystallize.

[0041] (iv) After sintering, the surface of the bulk material is polished to obtain LLZO ceramic sheets with a relative density ≥97%, no obvious pores or voids, and a room temperature ionic conductivity exceeding 1×10⁻⁶. -3 Scm -1 .

[0042] Part Two: Examples and Comparative Cases

[0043] Example 1:

[0044] (I) Preparation of garnet-type solid electrolyte Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Precursor (sol-gel method)

[0045] According to Li 6.5 La3Zr 1.5 Ta 0.5 O 12 4.718 g of lithium acetate, 12.990 g of lanthanum nitrate hexahydrate, 5.088 g of zirconium nitrate hexahydrate, and 1.105 g of tantalum pentoxide were weighed according to stoichiometry. The powders were dissolved in 300 ml of 3M nitric acid solution at 40 °C with continuous stirring using a mechanical stirrer. After the precursor powders were completely dissolved, citric acid monohydrate was added as a chelating agent, and stirring was continued for 4 hours. The amount of citric acid used was 47.282 g. The solution was then evaporated on a 90 °C hot plate to form a transparent orange gel. The gel was dried in a 300 °C oven for 8 hours. The resulting brown precursor powder was ground in a mortar and calcined in a muffle furnace at 550 °C for 4 hours to remove organic matter and nitrates. Sintering at 650 °C for 6 hours yielded an LLZO precursor containing the La₂Zr₂O₇ phase.

[0046] from Figure 1 It can be seen that the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder is 8.9%. Figure 2 It can be seen that the grain size of the primary particles is 500~800nm ​​and is nearly spherical.

[0047] (ii) Selection and addition of low melting point lithium salts

[0048] The aforementioned precursor powder was collected in total to 8.254g. A mixture of lithium hydroxide and lithium nitrate (1.238g by mass fraction) was added and thoroughly mixed using a small high-speed mixer.

[0049] (III) Preparation of dense bulk material by two-step sintering method

[0050] Take 2g of the mixed powder and place it into a stainless steel mold with a diameter of 16mm. Press it into shape under a pressure of 300MPa. After molding, demold to obtain a green blank, and then sinter it. Heat the green blank to 250℃ at a heating rate of 10℃ / min and hold for 12h. Then heat it to 1000℃ at a heating rate of 5℃ / min and hold for 240 minutes.

[0051] (iv) After sintering, the surface of the block is polished to obtain a relative density of 97.4%. The cross-sectional SEM of the block is shown in the figure. Figure 3 As shown, the LLZO ceramic sheet without obvious pores and voids has an ionic conductivity of 1.81 × 10⁻⁶ at room temperature. -3 Scm -1 .

[0052] Example 2:

[0053] (I) Preparation of garnet-type solid electrolyte Li 6.4 Ga 0.2 La3Zr2O 12 Precursor (spray pyrolysis)

[0054] According to Li 6.4 Ga 0.2 La3Zr2O 12 5.148 g of lithium nitrate, 14.434 g of lanthanum nitrate hydrate, 7.161 g of zirconium oxychloride octahydrate, and 0.928 g of gallium nitrate nonahydrate were weighed according to stoichiometry. A certain amount of pure water was added to dissolve them and form a stable aqueous solution (0.3 mol / L). This aqueous solution was then sprayed into the pyrolysis chamber of a spray pyrolysis device. The spray feed rate was controlled at 3 mol / min, the nozzle pressure at 0.5 MPa, the inlet air temperature at 700℃, and the outlet air temperature at 600℃. Particles with an average particle size of 0.9 μm and a main crystalline phase structure of Li were collected. 6.4 Ga 0.2 La3Zr2O 12 Solid electrolyte precursor.

[0055] Analysis showed that the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder was 3.2%, and the grain size of the primary particles was 0.8~1.0μm, and they were nearly spherical.

[0056] (ii) Design and addition of low melting point lithium salts.

[0057] The aforementioned precursor powder was collected in total to 9.286g. A mixture of lithium hydroxide and lithium iodide with a mass fraction of 5% (0.464g) was added (the molar ratio of lithium hydroxide to lithium iodide was 2:1), and the mixture was thoroughly mixed using an airflow mixer.

[0058] (III) Two-step sintering method for preparing dense bulk materials:

[0059] Take 2g of the mixed powder and place it into a 16mm diameter stainless steel mold. Apply pressure of 100MPa. After preliminary molding, demold to obtain a green blank, which is then subjected to isostatic pressing at a pressure of 500MPa. Sinter the green blank by heating it to 350℃ at a rate of 10℃ / min and holding for 1 hour. Then, heat it to 950℃ at a rate of 5℃ / min and hold for 10 minutes.

[0060] (iv) After sintering, the surface of the bulk material is polished to obtain an LLZO ceramic sheet with a relative density of 98.6%, no obvious pores or voids, and a room temperature ionic conductivity of 2.52 × 10⁻⁶. -3 Scm -1 .

[0061] Example 3:

[0062] (I) Preparation of garnet-type solid electrolyte Li 6.4 La3Zr 1.4 Nb 0.6 O 12 Precursor (solvent-assisted milling-pre-calcination method)

[0063] According to Li 6.4 La3Zr 1.4 Nb 0.6 O 12 26.854 g of lithium hydroxide, 48.876 g of lanthanum oxide, 17.251 g of zirconium oxide, and 7.974 g of niobium oxide were weighed according to stoichiometry and 230 ml of ethanol was added as a solvent. A sand milling method was used to reduce the specific surface area of ​​the precursors while improving the uniformity of the mixture. The sand mill speed was set to 2500 rpm, the solid content was 35%, and the milling time was 2 hours. After centrifugation, the mixture was dried in an oven at 80℃ for 24 hours. Li was then heat-treated in a muffle furnace at 700℃ for 4 hours to obtain Li. 6.4 La3Zr 1.4 Nb 0.6 O 12 Precursor powder.

[0064] Analysis showed that the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder was 6.6%, the grain size of the primary particles was 1 μm, and they were weakly lamellar.

[0065] (ii) Design and addition of low melting point lithium salts.

[0066] The precursor powder was collected in total, totaling 79.459g. Lithium hydroxide with a mass fraction of 10% (7.946g) was added and then thoroughly mixed using a mixer.

[0067] (III) Two-step sintering method for preparing dense bulk materials:

[0068] Take 2g of the mixed powder and place it into a 16mm diameter stainless steel mold for pressing. Apply a pressure of 100MPa. After preliminary molding, demold to obtain a green blank, which is then subjected to isostatic pressing at a molding pressure of 400MPa. Sinter the green blank by heating it to 300℃ at a rate of 10℃ / min and holding it for 6 hours. Then, heat it to 1050℃ at a rate of 5℃ / min and hold it for 90 minutes.

[0069] (iv) After sintering, the surface of the bulk material is polished to obtain an LLZO ceramic sheet with a relative density of 97.5%, no obvious pores or voids, and a room temperature ionic conductivity of 1.93 × 10⁻⁶. -3 Scm -1 .

[0070] Comparative Example 1:

[0071] (a) Garnet-type solid electrolyte Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Preparation of precursors

[0072] In Example 1, the statement "LLZO precursor containing La2Zr2O7 phase can be obtained by sintering at 650℃ for 6 hours" is changed to "LLZO precursor containing La2Zr2O7 phase can be obtained by sintering at 650℃ for 2 hours," while keeping other conditions unchanged. Figure 1 It can be seen that in Comparative Example 1, the ratio of the strongest peak of La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder is 9.8%, the grain size of the primary particles is 500~800nm, and they are nearly spherical.

[0073] The operation content of (ii) and (iii) is the same as that of Example 1.

[0074] (iv) After sintering, the surface of the bulk material is polished to obtain an LLZO ceramic sheet with a relative density of 91.8%, obvious pores and voids, and abnormal grain growth. The room temperature ionic conductivity is 0.87 × 10⁻⁶. -3 Scm -1 .

[0075] Comparative Example 2:

[0076] (a) Garnet-type solid electrolyte Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Preparation of precursors

[0077] In Example 1, the statement "sintering at 650℃ for 6 hours yields an LLZO precursor containing the La2Zr2O7 phase" is changed to "sintering at 850℃ for 6 hours yields an LLZO precursor containing the La2Zr2O7 phase," while other conditions remain unchanged. Figure 1 It can be seen that the La2Zr2O7 phase disappeared in the precursor powder of Comparative Example 2. Figure 4 It can be seen that the grain size of the primary particles is 1-2 μm and they are nearly spherical.

[0078] The operation content of (ii) and (iii) is the same as that of Example 1.

[0079] (iv) After sintering, the surface of the block is polished to obtain a relative density of 92.3%. The SEM image of the block cross-section is shown below. Figure 5 As shown, the LLZO ceramic sheet exhibits obvious pores and voids, and abnormal grain growth. Its room temperature ionic conductivity is 0.72 × 10⁻⁶. -3 Scm -1 .

[0080] Comparative Example 3:

[0081] (a) Garnet-type solid electrolyte Li 6.4 Ga 0.2 La3Zr2O 12 Preparation of precursors

[0082] In Example 2, the phrase "controlling the inlet air temperature to 700℃ and the outlet air temperature to 600℃" was changed to "controlling the inlet air temperature to 900℃ and the outlet air temperature to 750℃". This resulted in the collection of samples with an average particle size of 2 μm and a main crystalline phase structure of Li. 6.4 Ga 0.2 La3Zr2O 12 Solid electrolyte precursor.

[0083] The ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the precursor powder is 2.2%, and the grain size of the primary particles is 0.8~1.0μm, and they are nearly spherical.

[0084] The operation content of (ii) and (iii) is the same as that of Example 1.

[0085] (iv) After sintering, the surface of the bulk material is polished to obtain an LLZO ceramic sheet with a relative density of 93.6%, obvious pores and voids, and abnormal grain growth. The room temperature ionic conductivity is 0.83 × 10⁻⁶. -3 Scm -1 .

[0086] The main structures and properties of the samples in each comparative example and embodiment are compared in Table 1.

[0087] Table 1

[0088] ;

[0089] As can be seen from the data in Table 1, the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO in the XRD of Examples 1-3 is between 3.2% and 8.9%, and the primary grain size can reach the submicron level. Figure 2 The corresponding relative densities all exceed 97% ( Figure 3 The room temperature ionic conductivity exceeds 1×10⁻⁶. -3 S / cm.

[0090] In the XRD patterns of Comparative Examples 1-3, the ratios of the strongest peaks of the La2Zr2O7 phase and the strongest peaks of LLZO were not between 3.2% and 8.9%, indicating that the primary grain size was in the micrometer range. Figure 4 The corresponding relative density does not exceed 95%, and the room temperature ionic conductivity is less than 1×10⁻⁶. -3 S / cm.

[0091] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing garnet-type oxide solid electrolytes that can improve bulk density, characterized in that, include: (1) Preparation of LLZO precursor powder, the main crystalline phase of which is cubic phase Li7La3Zr2O 12 It also contains La2Zr2O7 pyrochlore impurities, and the ratio of the strongest peak of the La2Zr2O7 phase to the strongest peak of LLZO is between 3.2% and 8.9%. (2) After the LLZO precursor powder is mixed evenly with lithium salt, it is pressed into shape and then sintered to obtain a garnet-type oxide solid electrolyte block with increased density.

2. The method according to claim 1, characterized in that, The LLZO precursor powder particles are nearly spherical or weakly plate-like, with a particle size in the submicron range.

3. The method according to claim 1, characterized in that, The LLZO precursor powder is prepared by sol-gel method, spray pyrolysis method or solvent-assisted sand milling-pre-calcination method.

4. The method according to claim 1, characterized in that, The lithium salt is one or any combination of lithium hydroxide, lithium iodide, and lithium nitrate; the lithium salt accounts for 5-15% of the mass fraction of the LLZO precursor powder.

5. The method according to claim 1, characterized in that, The pressing and molding refers to dry pressing in a mold and then demolding to obtain a blank, or further includes isostatic pressing of the blank.

6. The method according to claim 1, characterized in that, The sintering process consists of two steps: first, the temperature is increased to 250–350°C at a rate of 10°C / min and held for 1–12 hours; then, the temperature is increased to 950–1050°C at a rate of 5°C / min and held for 10–240 minutes.

7. The method according to claim 1, characterized in that, Further steps include polishing the surface of the sintered block.

8. The method according to claim 1, characterized in that, The relative density of the garnet-type oxide solid electrolyte mass is ≥97%, and the ionic conductivity at room temperature exceeds 1×10⁻⁶. -3 S cm -1 .

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