Lithium lanthanum zirconium oxide nano-powder, preparation method thereof and application of lithium lanthanum zirconium oxide nano-powder in solid electrolyte

Abstract

The invention belongs to the technical field of electrolyte materials, and provides lithium lanthanum zirconium oxide nano powder, a preparation method of the lithium lanthanum zirconium oxide nano powder and application of the lithium lanthanum zirconium oxide nano powder in solid electrolyte. ZrO2, La2O3 and water are mixed and then dried, the mixture is melted, quenched and smashed at the temperature of 1300-1600 DEG C to obtain glass powder, then the glass powder is mixed with a Li source, dried and calcined at the temperature of 600-750 DEG C to obtain the LLZO nano-powder, the particle size is small, LLZO nano-crystalline grains are complete, after calcination, crushing and refining do not need to depend on post-treatment procedures such as ball milling or sand milling, crystal lattice distortion of the crystalline grains is avoided, and the prepared LLZO nano-powder is uniform in particle size and good in stability. And the calcination temperature is low, Li volatilization is low, and an electrolyte sheet further prepared from the LLZO nano-powder has high ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of electrolyte materials technology, and more specifically, to a lithium lanthanum zirconium oxide nanopowder, its preparation method, and its application in solid electrolytes. Background Technology

[0002] With the rapid development of electrochemical energy storage technology, the requirements for battery system safety and energy density are increasing. Against this backdrop, solid-state electrolytes, due to their non-flammability, high-temperature resistance, and good chemical stability, are becoming key materials driving the evolution of battery technology. Currently, solid-state electrolytes have shown broad application prospects in both semi-solid-state and all-solid-state battery technologies. In semi-solid-state battery systems, solid-state electrolytes are introduced as functional additives or composite matrices to improve the intrinsic safety of the battery, suppress lithium dendrite growth, and enhance the stability of the electrode / electrolyte interface. In all-solid-state battery systems, solid-state electrolytes completely replace traditional organic electrolytes, undertaking the dual role of lithium-ion transport and physical separator. Among many solid-state electrolyte materials, garnet-type lithium lanthanum zirconium oxide (LLZO) exhibits excellent comprehensive performance due to its unique crystal structure: its cubic phase has abundant lithium-ion vacancies, achieving up to 10... -3 It exhibits ionic conductivity on the order of S / cm; a high electrochemical window that allows it to be matched with various high-voltage cathode materials; and excellent stability against lithium metal anodes.

[0003] However, LLZO powder is typically prepared using a solid-state method. During its preparation and further processing into dense electrolyte sheets, high-temperature calcination (>1000℃) is usually required to ensure complete incorporation of the oxides and maintain a cubic phase, thereby achieving high ionic conductivity. However, Li is highly volatile at high temperatures (>850℃), and this volatility increases with increasing calcination temperature. Therefore, currently, the main approach is to add an excess of 10-30 wt% Li source to reduce the impact of Li volatilization on LLZO synthesis and sintering. However, the high cost of Li sources significantly increases the manufacturing cost of LLZO, limiting its large-scale industrial application. Furthermore, in semi-solid-state batteries, solid electrolytes are often used for separator coating, cathode material mixing, or coating, which places high demands on the particle size of the LLZO powder, typically requiring a particle size ≤300 nm. However, LLZO powder prepared by conventional solid-state methods has large particles (usually with a particle size Dv50 greater than 2 μm), which need to be crushed and refined by ball milling or sand milling. However, the intense mechanical force will introduce a large number of crystal defects into the LLZO lattice. These defects may become scattering centers for lithium ion migration, reduce the ionic conductivity of the electrolyte sheet prepared from it, and may become the starting point for preferential growth of lithium dendrites.

[0004] Therefore, there is an urgent need to develop a method for preparing low-Li volatilization LLZO nanoparticles, with the obtained LLZO nanoparticles having a particle size Dv50≤200nm, and which can be further used to prepare electrolyte sheets with high ionic conductivity. Summary of the Invention

[0005] This invention aims to solve at least one of the technical problems existing in the prior art. To this end, this invention proposes a lithium lanthanum zirconium oxide (LLZO) nanopowder, its preparation method, and its application in solid-state electrolytes. The LLZO nanopowder provided by this invention has a small particle size (Dv50 particle size is 55-86 nm), and the LLZO nanocrystals are intact. It eliminates the need for post-processing steps such as ball milling or sand milling after powder calcination, avoiding lattice distortion of the grains. Furthermore, it has low Li volatility, thus reducing Li loss and lowering costs. The electrolyte sheet further prepared from the LLZO nanopowder has high ionic conductivity (e.g., reaching (0.81-1.55) × 10⁻⁶). -3 ).

[0006] The first aspect of the present invention provides a method for preparing lithium lanthanum zirconium oxide nanopowder.

[0007] Specifically, a method for preparing lithium lanthanum zirconium oxide (LLZO) nanoparticles includes the following steps:

[0008] (1) ZrO2, La2O3 and water are mixed and dried to obtain a first mixed powder; (2) First, heat the mixture to 1300-1600℃, then keep the first mixed powder at 1300-1600℃ for 1-5 hours to melt it. After the melting is completed, quench it to obtain the glass precursor. After crushing, glass powder is obtained. (3) The Li source and the glass powder are mixed to obtain a Li source mixture, which is then dried to obtain a second mixed powder. After calcination at 600-750℃, the lithium lanthanum zirconium oxide nanopowder is obtained.

[0009] This invention uses ZrO2 and La2O3 as main raw materials. After high-temperature melting, the mixture is quenched to obtain glass recrystallization. After pulverization, a Li source is added, and the mixture is reacted at a low temperature (600-750℃). This process not only yields LLZO nanoparticles with small particle size (particle size Dv50≤200nm), but also effectively reduces Li volatilization. Furthermore, based on the fragile and easily ball-milled nature of glass, this invention pulverizes and refines the glass precursor at the glass precursor stage to obtain glass powder. This is followed by low-temperature calcination and recrystallization to obtain LLZO nanoparticles with intact grains and small particle size. This eliminates the need for further pulverization (ball milling or sand milling) of the LLZO nanoparticles, avoiding the adverse effects of grain breakage and improving the ionic conductivity of electrolyte sheets further prepared from the LLZO nanoparticles. Moreover, this process is faster, consumes less energy, and reduces costs.

[0010] Preferably, in step (3), the chemical formula of the lithium lanthanum zirconium oxide nanoparticles is Li 7-3x M x La3Zr2O 12 The formula is given, where M is the doped metal and x = 0-0.5.

[0011] Preferably, in step (1), according to Li 7-3x M x La3Zr2O 12 Calculate and weigh ZrO2 and La2O3, where M is the dopant metal and x = 0-0.5. The dopant metal can stabilize the cubic phase of LLZO and improve its ionic conductivity.

[0012] Preferably, step (1) further includes mixing the dopant with ZrO2, La2O3 and water, wherein the dopant is an oxide, hydroxide or salt of a doped metal.

[0013] Preferably, the doped metal is one of Al, Ga, Ba, and Sb.

[0014] Preferably, in step (1), the dopant is one of the following: an oxide of Al or its hydroxide (such as Al2O3 or Al(OH)3), an oxide of Ga (such as Ga2O3), a metal salt of Ba (such as BaCO3), or an oxide of Sb (such as Sb2O3).

[0015] Preferably, in step (1), the added weight of water is 1-2 times the total weight of ZrO2, La2O3 and dopants.

[0016] Preferably, in step (1), after mixing ZrO2, La2O3, dopant and water, the mixture is milled at 1000-3000 rpm for 3-8 hours to obtain a mixed slurry, and then the mixed slurry is subjected to a first drying.

[0017] Preferably, in step (1), the first drying is spray drying.

[0018] Preferably, in step (1), the temperature of the first drying is 120-200℃.

[0019] Preferably, in step (1), ZrO2, La2O3, dopant and water are mixed and a first organic acid is added.

[0020] Preferably, in step (1), ZrO2, La2O3, dopant and water are mixed and a first dispersant is added.

[0021] More preferably, in step (1), ZrO2, La2O3, dopant and water are mixed, and a first organic acid and a first dispersant are added in sequence.

[0022] Preferably, the first organic acid and the second organic acid are each independently selected from at least one of oxalic acid, citric acid, and malic acid.

[0023] The first and second organic acids react with each raw material, increasing the number of defects on the powder surface, thereby improving the reactivity and lowering the melting temperature of the mixture. The organic acids can also react with glass powder, which can improve its activity and lower its reaction temperature with the Li source and its crystallization temperature.

[0024] Preferably, the first dispersant and the second dispersant are each independently selected from at least one of polyvinylpyrrolidone (PVP), polyacrylamide, polyammonium methacrylate, and polyethylene glycol.

[0025] The first and second dispersants can prevent powder agglomeration during mixing and milling, adjust the viscosity of the slurry, and enable the components to be mixed more evenly and improve milling efficiency.

[0026] Preferably, in step (2), the heating rate is 3-10℃ / min.

[0027] Preferably, in step (2), the quenching is done by pouring the liquid into water.

[0028] More preferably, in step (2), the quenching is done by pouring the solution into room temperature water.

[0029] After quenching, a glass precursor is obtained. Since the mixture is in a molten state at high temperature, the ion mass transfer is relatively fast, which makes the doped metal M distributed very evenly in the precursor.

[0030] Preferably, in step (2), the crushing is performed by sand milling.

[0031] Preferably, in step (2), the grinding time is 3-6 hours.

[0032] Because glass is more brittle than ceramics, it is easier to grind and crush.

[0033] Preferably, in step (2), the Dv50 of the glass powder is ≤50nm.

[0034] Preferably, in step (3), the Li source is at least one of lithium carbonate, lithium hydroxide, and lithium chloride.

[0035] Preferably, in step (3), the added weight of the Li source is 0.5-2 wt% excess of the theoretical weight of the LLZO chemical formula.

[0036] More preferably, in step (3), the added weight of the Li source is 0.5-1 wt% excess of the theoretical weight of the LLZO chemical formula.

[0037] Preferably, in step (3), the second drying is spray drying.

[0038] Preferably, in step (3), the calcination temperature is 650-700℃, and / or the calcination time is 3-10h.

[0039] Preferably, in step (3), the Dv50 of the LLZO nanoparticles is ≤200nm.

[0040] More preferably, in step (3), the Dv50 of the LLZO nanoparticles is ≤100nm.

[0041] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention first mixes ZrO2, La2O3, and water, then dries the mixture, melts it at 1300-1600℃, quenches it to obtain a glass precursor, pulverizes it to obtain glass powder, then mixes it with a Li source, dries it, and finally calcines it at a low temperature of 600-750℃ to obtain LLZO nanoparticles. These nanoparticles not only have small particle sizes (e.g., the Dv50 particle size of LLZO nanoparticles can reach 55-86nm) and intact LLZO nanocrystals, but also avoid lattice distortion of the grains because there is no need for further processing such as ball milling or sand milling after calcination. Furthermore, the low calcination temperature of this invention results in low Li volatilization, thus reducing Li loss and lowering costs. Additionally, the electrolyte sheet made from the LLZO nanoparticles of this invention has high ionic conductivity (e.g., reaching (0.81-1.55) × 10⁻⁶). -3 ). Attached Figure Description

[0042] Figure 1 The X-ray diffraction (XRD) spectra of the LLZO nanoparticles prepared in Examples 1-3 of this invention are shown below. Figure 2The images are scanning electron microscope (SEM) images of the LLZO nanoparticles prepared in Examples 1-3 of this invention. Detailed Implementation

[0043] To enable those skilled in the art to more clearly understand the technical solutions described in this invention, the following embodiments are provided for illustration. It should be noted that the following embodiments do not constitute a limitation on the scope of protection claimed by this invention.

[0044] Unless otherwise specified, the raw materials, reagents or devices used in the following examples are available from conventional commercial sources or can be obtained by existing known methods.

[0045] The purity of the raw material components used in all embodiments and comparative examples of the present invention is 3N or higher, and the Dv50 of the raw material powder is less than 5μm.

[0046] Example 1 A method for preparing LLZO nanopowder includes the following steps: (1) Weigh the raw materials (i.e. ZrO2, La2O3 and doped alumina) and place them in a mixer. Then add deionized water at a total weight of 1.5 times that of ZrO2, La2O3 and doped alumina. Mix them in a mixer at a speed of 800 rpm. Then add organic acid (oxalic acid) at a total mass of 2 wt% of the raw materials and dispersant (PVP) at a total mass of 0.5 wt% of the raw materials. After stirring for 2 h, transfer it to a sand mill and sand mill at a speed of 2500 rpm for 6 h to obtain a uniformly mixed slurry. Spray dry at 160 °C to obtain the first mixed powder. (2) Place the crucible in a glass melting furnace and heat it to the melting temperature of 1500℃ at a rate of 5℃ / min. Then add the first mixed powder and keep it at that temperature for 2 hours. During the holding process, stir the melt with an alumina rod to make it melt more evenly. After the holding period, quickly pour the melt in the crucible into deionized water at room temperature for quenching to obtain the quenched La2O3-ZrO2-MO. x The glass precursor was milled in a sand mill for 5 hours to obtain glass powder with Dv50 < 50 nm. (3) Preparation of LLZO nanopowder: Li source (lithium carbonate) and glass powder were mixed to obtain a Li source mixture, wherein the weight of the Li source was 1 wt% more than the theoretical weight of the LLZO chemical formula. Then, an organic acid solution (oxalic acid) with a mass concentration of 0.5 wt% was added to promote the dissolution of the Li source, and a dispersant (PVP) of 0.5 wt% of the weight of the Li source mixture was added. The weight of the organic acid solution was 1.2 times the weight of the Li source mixture. The mixture was stirred thoroughly and stirred at 1800 rpm for 5 h in a mixer. Then, it was spray dried to obtain a second mixed powder. Finally, it was calcined at a low temperature (680℃) for 5 h to obtain LLZO nanopowder with uniform particle size.

[0047] Examples 2-9 Examples 2-9 provide a method for preparing LLZO nanopowder. The difference between this method and Example 1 is that the raw materials in step (1), the melting temperature in step (2), and the calcination temperature in step (3) are different, as shown in Table 1.

[0048] Comparative Example 1 An LLZO nanopowder, wherein the weight of the Li source (lithium carbonate) is 10 wt% in excess of the theoretical weight of LLZO according to the chemical formula, is prepared by a conventional solid-state method, specifically including the following steps: Lithium carbonate, ZrO2, La2O3, and dopants were weighed and mixed to obtain a mixture. Then, 1.5 times the total weight of deionized water was added to the mixture, and the mixture was stirred in a mixer at 800 rpm. Then, 0.5 wt% of dispersant (PVP) was added to the mixture, and the mixture was stirred for 2 hours. The mixture was then transferred to a sand mill and milled at 2500 rpm for 6 hours to obtain a uniformly mixed slurry. The slurry was spray-dried at 160℃ and calcined at 1100℃ for 10 hours to obtain LLZO powder with a Dv50 particle size of 3-5 μm. After cooling, the powder was milled for 12 hours. The milled powder was then spray-dried to obtain secondary nanoparticles, and their Dv50 values ​​are shown in Table 1.

[0049] Comparative Example 2 An LLZO nanopowder was prepared by a conventional solid-state method. The only difference between the preparation method and Comparative Example 1 is that the weight of the Li source (lithium carbonate) is 20 wt% more than the theoretical weight of the LLZO chemical formula.

[0050] Product effectiveness test 1. Testing Method (1) Particle size of LLZO nanoparticles: The particle size of LLZO nanoparticles prepared in each example and comparative example was characterized using a laser particle size analyzer.

[0051] (2) Preparation of electrolyte sheets and testing of their ionic conductivity: The LLZO nanoparticles prepared in each example and comparative example were pressed into discs with a thickness of approximately 0.20 mm under a pressure of 100 MPa. They were then held in a muffle furnace at 800 °C for 5 h and cooled with the furnace to obtain electrolyte sheets. Then, each electrolyte sheet was polished, coated with conductive silver electrodes on both sides, cured (held at a heating platform at 350 °C for 1 h), and its ionic conductivity was tested using an electrochemical workstation.

[0052] The test results are shown in the table below.

[0053] 2. Test Results Table 1. Key process parameters, LLZO powder particle size, and ionic conductivity of electrolyte sheets for each embodiment and comparative example.

[0054] As shown in the table above, the Dv50 particle size of the LLZO nanoparticles prepared in Examples 1-9 of this invention is 55-86 nm, and the ionic conductivity of the electrolyte sheets prepared from them can reach (0.91-1.55) × 10⁻⁶. -3 This indicates that the glass precursor is more brittle and easier to ball mill, resulting in electrolyte sheets with less Li volatility, higher sintering density, and a more complete structure.

[0055] The XRD patterns of the LLZO nanopowders prepared in Examples 1-3 are as follows: Figure 1 As shown in the figure, it can be seen that all LLZO nanoparticles are cubic phase.

[0056] The SEM image of the LLZO nanopowder prepared in Example 2 is shown below. Figure 2 As shown in the figure, the LLZO nanocrystals are intact.

[0057] Examples 10-13 compare the effects of melting temperature and calcination conditions with Example 2. In Examples 10-11, the melting temperature is changed compared to Example 2. If the melting temperature is too high, it will lead to increased volatilization of some elements and increased defects; if it is too low, it will lead to uneven mixing. In Examples 12-13, the calcination temperature is changed compared to Example 2. If the calcination temperature is too low, the reaction between the Li source and the glass powder will be insufficient, resulting in more grain defects in the powder and uneven distribution of elements, thereby weakening the ionic conductivity; if the calcination temperature is too high, the grain growth will be faster, the lattice distortion and abnormal growth will increase, and the ionic conductivity will be reduced.

[0058] Comparative Examples 1 and 2 prepared LLZO using a conventional solid-state method. The LLZO obtained after calcination had a large particle size, so it was necessary to further pulverize (mill) the LLZO to obtain nanoparticles. However, even after this process, the final LLZO nanoparticles still had a relatively large particle size (158-165 nm, much larger than the LLZO nanoparticles of this invention). Furthermore, the intense mechanical force during direct milling of LLZO introduced numerous crystal defects into the LLZO lattice, which could potentially lead to lithium ionization. The scattering centers of lithium migration reduce the ionic conductivity of the electrolyte sheet and may become the starting point for preferential growth of lithium dendrites (while the preparation method of the present invention can directly produce nanoscale LLZO products with a particle size <100nm, without the need for ball milling or sand milling of the LLZO products); in addition, the amount of Li source added in Comparative Examples 1 and 2 is 10% and 20% excess, respectively, which requires far more Li source than the present invention, but the ionic conductivity of the electrolyte sheet prepared by them is still lower than that of Examples 1-9 of the present invention, indicating that Li volatilization is serious.

[0059] This invention only requires adding 0.5-2 wt% excess Li source to the theoretical Li content of LLZO powder (far less than the 10-30 wt% excess Li source required by conventional solid-state methods). Compared with conventional solid-state methods (which require first obtaining LLZO powder and then calcining it, relying on post-processing steps such as ball milling or sand milling for crushing and refining, which leads to lattice distortion of the grains), the method of this invention can obtain LLZO nanopowder with more complete grains, and the prepared electrolyte sheet also has higher ionic conductivity.

Claims

1. A method for preparing lithium lanthanum zirconium oxide nanopowder, characterized in that, Includes the following steps: (1) ZrO2, La2O3 and water are mixed and dried to obtain a first mixed powder; (2) First, heat the mixture to 1300-1600℃, then keep the first mixed powder at 1300-1600℃ for 1-5 hours to melt it. After the melting is completed, quench it to obtain the glass precursor. After crushing, glass powder is obtained. (3) The Li source and the glass powder are mixed to obtain a Li source mixture, which is then dried to obtain a second mixed powder. After calcination at 600-750℃, the lithium lanthanum zirconium oxide nanopowder is obtained.

2. The preparation method according to claim 1, characterized in that, In step (1), according to Li 7-3x M x La3Zr2O 12 Calculate and weigh ZrO2 and La2O3, where M is the doped metal and x = 0-0.

5.

3. The preparation method according to claim 1, characterized in that, Step (1) also includes mixing the dopant with ZrO2, La2O3 and water, wherein the dopant is an oxide, hydroxide or salt of a doped metal.

4. The preparation method according to claim 3, characterized in that, In step (1), ZrO2, La2O3, dopant and water are mixed and a first organic acid is added, and / or, in step (1), ZrO2, La2O3, dopant and water are mixed and a first dispersant is added.

5. The preparation method according to claim 4, characterized in that, The first organic acid and the second organic acid are each independently selected from at least one of oxalic acid, citric acid, and malic acid.

6. The preparation method according to claim 4, characterized in that, The first dispersant and the second dispersant are each independently selected from at least one of polyvinylpyrrolidone, polyacrylamide, polyammonium methacrylate, and polyethylene glycol.

7. The preparation method according to claim 1, characterized in that, In step (2), the quenching is done by pouring the liquid into water.

8. The preparation method according to claim 1, characterized in that, In step (2), the Dv50 of the glass powder is ≤50nm.

9. The preparation method according to claim 1, characterized in that, In step (3), the calcination temperature is 650-700℃, and / or the calcination time is 3-10h.

10. The preparation method according to claim 1, characterized in that, In step (3), the Dv50 of the LLZO nanopowder is ≤200nm.

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