Utilization method of garnet type oxide solid electrolyte invalid mother powder

Abstract

The invention discloses a utilization method of garnet type oxide solid electrolyte spent mother powder, and belongs to the technical field of secondary resource recycling. The garnet type oxide solid electrolyte failure mother powder comes from excessive garnet type oxide solid electrolyte raw material powder used for supplementing a lithium source in the garnet type oxide solid electrolyte sintering process; preparing an electrolyte green body by adjusting the proportion and granularity of the failure mother powder and the garnet type oxide solid electrolyte raw material powder and changing the pressure in the forming process; and preparing the oxide solid electrolyte sheet from the green body through a two-stage heating method. The prepared garnet type oxide solid electrolyte sheet is of a pure-phase structure, the lithium element is evenly distributed, the ionic conductivity is larger than or equal to 3.3 * 10 <-4 > S / cm, and the density is larger than or equal to 96.4%. The preparation method realizes recycling of the invalid mother powder, reduces the cost of raw materials, improves the resource utilization rate, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to a method for utilizing a failed mother powder of garnet-type oxide solid electrolyte, belonging to the technical field of secondary resource recycling. Background Art

[0002] Solid-state lithium batteries have become a popular direction for the next-generation battery technology due to their non-flammability and high safety, and by combining with high-voltage cathodes and lithium anodes, the energy density can be significantly improved. Among them, garnet-type oxide solid electrolyte Li7La3Zr2O 12 (LLZO) and its doped derivatives are promising candidates for next-generation solid electrolyte materials due to their high lithium ion conductivity (10 -3 ~10 -4 S / cm), high Young's modulus, non-reactivity with lithium metal, and good chemical stability in air.

[0003] Currently, due to its relatively simple synthesis process and low requirements for preparation conditions, the traditional high-temperature solid-state method has become the main process for preparing garnet-type oxide solid electrolyte sheets. During the sintering process of the traditional high-temperature solid-state method, it is necessary to convert the crystal structure of the tetragonal phase (10 -6 ~10 -5 S / cm) into the crystal structure of the cubic phase (10 -4 ~10 -3 S / cm) under a long-term lithium-rich atmosphere to obtain a higher ionic conductivity. In order to obtain a solid electrolyte with excellent electrochemical performance, it is usually necessary to add sintering aids (such as Al2O3, LiF, Li3PO4, etc.) to the green body and carry out high-temperature sintering (>1100°C) for a long time (>5h) to promote the densification of the solid electrolyte sheet, stabilize the crystal structure, and improve the ionic conductivity. However, the long-term high-temperature sintering results in the sublimation and loss of a large amount of Li2O in the electrolyte sheet. In order to compensate for the lithium loss, during the sintering process, the electrolyte green body usually needs to be covered with mother powder several times its own weight. The mother powder is an electrolyte powder with the same composition as the electrolyte green body. Due to the long-term high-temperature sintering, a large amount of active lithium in the mother powder is lost, and even a La2Zr2O7 (LZO) heterophase is formed, resulting in the mother powder being unable to be used again and becoming a failed mother powder.

[0004] The existing patent application proposes a method for recycling a failed mother powder of garnet-type oxide solid electrolyte, application number: 202410472942.3, which proposes a method for regenerating the failed mother powder by supplementing the lost lithium, realizing the recovery and recycling of the failed mother powder. However, this method requires two calcinations, which not only increases the complexity of the recovery process, but also increases the lithium loss during the two high-temperature calcinations, and additional lithium addition is required.

[0005] Therefore, it is urgent to simplify the method for recycling the failed mother powder of garnet-type oxide solid electrolyte through reasonable process design. Summary of the Invention

[0006] In order to solve the problems of the failed mother powder of garnet-type oxide solid electrolyte losing "active lithium" and generating impurities La2Zr2O7 (LZO), the present invention proposes a method for utilizing the failed mother powder of garnet-type oxide solid electrolyte, and the method includes the following steps:

[0007] (1) Add the failed mother powder of garnet-type oxide solid electrolyte and the raw material powder of garnet-type oxide solid electrolyte into a solvent (the solvent is used as a wet grinding medium and does not participate in the reaction, and there is no special requirement for the dosage), mix evenly, and wet grind and refine to prepare a mixed slurry.

[0008] (2) Dry the mixed slurry obtained in step (1), press it into a sheet, and then carry out two-stage sintering. The first-stage sintering temperature is 900 - 1100 °C; the second-stage sintering temperature is 1100 °C - 1400 °C, and finally a regenerated garnet-type oxide solid electrolyte sheet is obtained.

[0009] Preferably, the chemical general formula of the garnet-type oxide solid electrolyte powder is Li 7-x La3Zr 2-x A x O 12 , where A is one of Ta, Nb, Sn, Hf, Sc, Ge elements, and 0 ≤ x ≤ 0.75.

[0010] More preferably, the chemical general formula of the raw material powder of garnet-type oxide solid electrolyte is Li 6.5 La3Zr 1.5 Ta 0.5 O 12 .

[0011] Preferably, the mass ratio of the failed mother powder of garnet-type oxide solid electrolyte to the raw material powder of garnet-type oxide solid electrolyte in step (1) is (0.5 - 2):1.

[0012] Preferably, the solvent in step (1) is one or more of water, ethanol, propanol, ethylene glycol, propylene glycol, allyl alcohol, isopropanol, dimethyl carbonate, diethyl carbonate, propylene carbonate, ethylene carbonate, and is mixed in any ratio.

[0013] Preferably, the wet grinding speed in step (1) is 300 - 3000 r / min, and the wet grinding time is 1 - 20 h.

[0014] Preferably, in step (2), a vacuum drying oven or a blast drying oven is used for drying, the drying temperature is 40-100°C, and the drying time is 1-20 h.

[0015] Preferably, in step (2), the pressure for tabletting is 5 MPa - 80 MPa, and the pressure holding time is 10 - 300 s.

[0016] Preferably, in step (2), the garnet-type oxide solid electrolyte sheet has a diameter of 10 - 20 mm and a thickness of 0.5 - 4 mm.

[0017] Preferably, in step (2), the heat preservation time for the first-stage sintering is 1 - 10 h, and the heating rate is 2 - 15°C / min; the heat preservation time for the second-stage sintering is 0.5 - 10 h, and the heating rate is 2 - 15°C / min.

[0018] The garnet-type oxide solid electrolyte failure master powder comes from the excessive garnet-type oxide solid electrolyte raw material powder added to supplement the lithium source during the sintering process of the garnet-type oxide solid electrolyte. The excessive garnet-type oxide solid electrolyte raw material powder becomes the garnet-type oxide solid electrolyte failure master powder due to the problems of a large loss of active lithium, the formation of a heterophase La2Zr2O7, and the growth and agglomeration of crystal grains during the high-temperature sintering process.

[0019] Principle of the present invention: The garnet-type oxide solid electrolyte failure master powder used in the present invention is a powder with a large loss of active lithium, the formation of a heterophase La2Zr2O7, and the growth and agglomeration of crystal grains. To ensure that the garnet-type oxide solid electrolyte raw material powder can fully supplement the "active lithium" to the garnet-type oxide solid electrolyte failure master powder during the calcination process, it is necessary to grind the mixed particles to the nanoscale, adjust the reaction and sintering temperature and sintering time in a two-stage manner, and finally synthesize a pure cubic-phase oxide electrolyte sheet through high-temperature calcination.

[0020] In the present invention, the failure master powder is the abbreviation of the garnet-type oxide solid electrolyte failure master powder.

[0021] Technical effects of the present invention:

[0022] (1) The present invention ingeniously adopts a two-stage sintering process, uses the "active lithium" in the garnet-type oxide solid electrolyte raw material powder to compensate for the "lithium loss" in the garnet-type oxide solid electrolyte failed mother powder, and uses the impurity lanthanum zirconate in the garnet-type oxide solid electrolyte failed mother powder as a sintering aid. For the first time, it realizes the direct preparation of an electrolyte sheet with high ionic conductivity by adding the garnet-type oxide solid electrolyte raw material powder to the garnet-type oxide solid electrolyte failed mother powder, promotes the recycling of waste resources, does not require additional addition of the garnet-type oxide solid electrolyte raw material powder for embedding during the sintering process, and no new garnet-type oxide solid electrolyte failed mother powder will be generated during the sintering process.

[0023] (2) The method of the present invention not only effectively utilizes waste resources but also saves the use of the garnet-type oxide solid electrolyte mother powder.

[0024] (3) The ionic conductivity of the regenerated garnet-type oxide solid electrolyte sheet prepared by the present invention is greater than or equal to 3.3×10 -4 S / cm, the relative density is greater than or equal to 96.4%, and the electrochemical stability window is 0 - 6V.

[0025] (4) This direct recycling method can greatly reduce lithium loss, has simple operation and is easy to repeat, is suitable for large-scale commercial production, and the prepared oxide electrolyte sheet has excellent electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the reuse process of the garnet-type oxide solid electrolyte failed mother powder in Examples 1, 2 and 3 of the present invention: adding the garnet-type oxide solid electrolyte raw material powder to the garnet-type oxide solid electrolyte failed mother powder, pressing into tablets and sintering to prepare the regenerated garnet-type oxide solid electrolyte sheet.

[0027] Figure 2 X-ray diffraction (XRD) patterns of the garnet-type oxide solid electrolyte failed mother powder used in the examples and Comparative Example 1 of the present invention, and the regenerated garnet-type oxide solid electrolyte sheet prepared by sintering in Example 1 of the present invention.

[0028] Figure 3 Scanning electron microscope (SEM) image of the garnet-type oxide solid electrolyte failed mother powder used in the examples of the present invention.

[0029] Figure 4 Scanning electron microscope (SEM) image of the regenerated garnet-type oxide solid electrolyte sheet prepared by sintering in Example 1 of the present invention.

[0030] Figure 5Room temperature impedance (EIS) diagram of the regenerated garnet-type oxide solid electrolyte sheet obtained by sintering in Example 1 of the present invention.

[0031] Figure 6 Arrhenius curve diagram of the regenerated garnet-type oxide solid electrolyte sheet obtained by sintering in Example 1 of the present invention.

[0032] Figure 7 Scanning electron microscope (SEM) diagram of the regenerated garnet-type oxide solid electrolyte sheet obtained by sintering in Comparative Example 1 of the present invention. Detailed implementation manners

[0033] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the content described. Unless otherwise specified, the reagents used in the present invention are all conventional commercially available analytical pure reagents.

[0034] The garnet-type oxide solid electrolyte matrix powder in the embodiment of the present invention takes Li 6.5 La3Zr 1.5 Ta 0.5 O 12 (LLZTO) as an example for analysis and description. The garnet-type oxide solid electrolyte failed matrix powder is the powder generated after the garnet-type oxide solid electrolyte matrix powder undergoes high-temperature sintering, with a large amount of active lithium loss, formation of a heterophase La2Zr2O7, and grain growth and agglomeration. The garnet-type oxide solid electrolyte failed matrix powder is characterized and analyzed. The XRD diffraction pattern is shown in Figure 2 , and the SEM pattern is shown in Figure 3 . It can be seen from Figure 2 that when the garnet-type oxide solid electrolyte failed matrix powder is compared with the standard card, lanthanum zirconate (La2Zr2O7) impurities are generated; it can be seen from Figure 3 that the grains are irregular, with large voids and fragmentation.

[0035] Example 1

[0036] This example provides a method for utilizing the garnet-type oxide solid electrolyte failed matrix powder. The preparation method includes the following steps:

[0037] (1) Mix the garnet-type oxide solid electrolyte failed matrix powder (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) and the garnet-type oxide solid electrolyte matrix powder (Li 6.5 La3Zr 1.5 Ta 0.5 O 12Mix them in a mass ratio of 0.5:1, add isopropanol, place them in a zirconia ball milling jar, grind and mix evenly. The wet milling speed is 1000 r / min and the wet milling time is 4 h to obtain a mixed slurry.

[0038] (2) Dry the mixed slurry obtained in step (1) using a vacuum drying oven at a drying temperature of 80 °C and a drying time of 4 h. Press the dried powder into tablets under a pressure of 5 Mpa for 300 s, and then perform sintering. The reaction conditions are as follows: heat up at a heating rate of 15 °C / min to 900 °C, hold for 10 h for the first-stage sintering; then heat up at a heating rate of 5 °C / min to 1200 °C, hold for 10 h for the second-stage sintering, and naturally cool to 25 °C to prepare a regenerated garnet-type oxide solid electrolyte sheet (LLZTO solid electrolyte sheet).

[0039] Perform characterization and analysis. The XRD diffraction pattern is shown in Figure 2 , the SEM image is shown in Figure 4 , the EIS impedance is shown in Figure 5 , the Arrhenius curve is shown in Figure 6 . From Figure 2 's XRD diffraction pattern, it can be seen that the peak positions of the regenerated garnet-type oxide solid electrolyte sheet are exactly the same as those of the standard card, which is a pure cubic-phase LLZTO structure without obvious impurity peaks. From Figure 4 's SEM scanning electron microscope image, it can be seen that the grains of the regenerated garnet-type oxide solid electrolyte sheet prepared in Example 1 are cubic-phase, with uniform size and closely arranged. From Figure 5 At room temperature, from the EIS spectrum, the ionic conductivity of the regenerated garnet-type oxide solid electrolyte sheet prepared in Example 1 is 3.3×10 -4 S / cm after fitting calculation. From Figure 6 's Arrhenius curve graph, it can be seen that the activation energy of the regenerated garnet-type oxide solid electrolyte sheet prepared in Example 1 is 0.325 eV after fitting and calculation, and the measured relative density is 96.4%

[0040] Example 2

[0041] This example provides a method for utilizing the failed mother powder of garnet-type oxide solid electrolyte. The preparation method includes the following steps:

[0042] (1) Mix the failed mother powder of garnet-type oxide solid electrolyte (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) and the mother powder of garnet-type oxide solid electrolyte (Li 6.5 La3Zr 1.5 Ta 0.5 O12 ) Mix them in a mass ratio of 1:1, add isopropanol, place them in a zirconia ball milling jar, grind and mix evenly. The wet milling speed is 1000 r / min and the wet milling time is 10 h to obtain a mixed slurry.

[0043] (2) Dry the mixed slurry obtained in step (1) using a vacuum drying oven at a drying temperature of 40 °C for 20 h. Press the dried powder into tablets under a pressure of 40 Mpa for 100 s, and then sinter. The reaction conditions are as follows: heat up at a heating rate of 3 °C / min to 1000 °C, hold for 1 h for the first-stage sintering; then heat up at a heating rate of 3 °C / min to 1300 °C, hold for 1 h for the second-stage sintering, and cool naturally to 25 °C to prepare a regenerated garnet-type oxide solid electrolyte sheet (LLZTO solid electrolyte sheet). Its structure and performance are similar to those of Example 1, and its ionic conductivity is 2.9×10 -4 S / cm, and the measured relative density is 95.6%.

[0044] Example 3

[0045] This example provides a method for utilizing the failed mother powder of garnet-type oxide solid electrolyte. The preparation method includes the following steps:

[0046] (1) Mix the failed mother powder of garnet-type oxide solid electrolyte (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) and the mother powder of garnet-type oxide solid electrolyte (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) in a mass ratio of 2:1, add isopropanol, place them in a zirconia ball milling jar, grind and mix evenly. The wet milling speed is 800 r / min and the wet milling time is 20 h to obtain a mixed slurry.

[0047] (2) Dry the mixed slurry obtained in step (1) using a vacuum drying oven at a drying temperature of 100 °C for 1 h. Press the dried powder into tablets under a pressure of 80 Mpa for 10 s, and then sinter. The reaction conditions are as follows: heat up at a heating rate of 2 °C / min to 1100 °C, hold for 6 h for the first-stage sintering; then heat up at a heating rate of 5 °C / min to 1400 °C, hold for 0.5 h for the second-stage sintering, and cool naturally to 25 °C to prepare a regenerated garnet-type oxide solid electrolyte sheet (LLZTO solid electrolyte sheet). Its structure and performance are similar to those of Example 1. Its structure and performance are similar to those of Example 1, and its ionic conductivity is 3.0×10 -4 S / cm, and the measured relative density is 96.2% Comparative Example 1

[0048] Compared with Example 1, the difference in this comparative example is that the sintering method is to continuously heat up to the highest temperature for heat preservation, and other steps and reagents used are the same as those in Example 1. The specific steps are as follows:

[0049] (1) Mix garnet-type oxide solid electrolyte failed master powder (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) and garnet-type oxide solid electrolyte master powder (Li 6.5 La3Zr 1.5 Ta 0.5 O 12 ) in a mass ratio of 0.5:1, using isopropanol as the solvent, placing them in a zirconia ball milling tank and grinding and mixing evenly. The wet grinding speed is 800 r / min, and the wet grinding time is 6 h to obtain a mixed slurry.

[0050] (2) Dry the mixed slurry obtained in step (1) using a vacuum drying oven. The drying temperature is 80°C, and the drying time is 4 h. Press the dried powder into tablets under a pressure of 5 Mpa for 300 s, and then sinter. The reaction conditions are to heat up to 1200°C at a heating rate of 10°C / min and keep the temperature for 10 h to prepare a regenerated garnet-type oxide solid electrolyte sheet (LLZTO solid electrolyte sheet).

[0051] Perform characterization and analysis. The SEM scanning electron micrograph is shown in Figure 7 . It can be seen that there are a large number of pores in the LLZTO solid electrolyte sheet, and abnormal grain growth exists. The measured density is 86.2%.

Claims

1. A method for utilizing spent mother powder of garnet-type oxide solid electrolyte, characterized in that: The steps include: (1) adding garnet-type oxide solid electrolyte spent mother powder and garnet-type oxide solid electrolyte raw material powder to a solvent, mixing them evenly, and wet-grinding them to prepare a mixed slurry; (2) drying the mixed slurry obtained in step (1), pressing into a sheet, and then sintering in two stages, wherein the first stage sintering temperature is 900-1100° C.; and the second stage sintering temperature is 1100° C.-1400° C., and finally obtaining a regenerated garnet-type oxide solid electrolyte sheet.

2. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: The chemical formula of the garnet-type oxide solid electrolyte raw material powder is Li 7-x Ln3Z 2-x A x O 12 , wherein A is one of Ta, Nb, Sn, Hf, Sc, and Ge, and 0≤x≤0.

75.

3. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: In step (1), the mass ratio of the failed mother powder of garnet-type oxide solid electrolyte to the raw material powder of garnet-type oxide solid electrolyte is (0.5-2):

1.

4. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: The solvent in step (1) is one or more of water, ethanol, propanol, ethylene glycol, propylene glycol, allyl alcohol, isopropanol, dimethyl carbonate, diethyl carbonate, propylene carbonate, and vinyl carbonate mixed in any ratio.

5. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: In step (1), the wet grinding speed is 300 to 3000 r / min, and the wet grinding time is 1 to 20 h.

6. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: In step (2), the drying is performed in a vacuum drying oven or a blast drying oven at a temperature of 40 to 100° C. for a drying time of 1 to 20 hours.

7. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: The tableting pressure in step (2) is 5 MPa to 80 MPa, and the holding time is 10 to 300 s.

8. The method for utilizing the spent mother powder of garnet-type oxide solid electrolyte according to claim 1, characterized in that: In step (2), the holding time of the first sintering stage is 1 to 10 hours, and the heating rate is 2 to 15°C / min; the holding time of the second sintering stage is 0.5 to 10 hours, and the heating rate is 2 to 15°C / min.

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