Garnet type composite solid electrolyte and preparation method and application thereof

Abstract

The invention discloses garnet type composite solid electrolyte as well as a preparation method and application thereof. The garnet type composite solid electrolyte is a test block which is prepared by mixing LLZO powder and LLZOF powder, pressing and sintering, the chemical general formula of the LLZO is Li7-3x-yGaxLa3Zr2-yTayO12, x is greater than or equal to 0 and less than or equal to 0.3, y is greater than or equal to 0 and less than or equal to 0.6, and 7-3x-y is greater than or equal to 6.1 and less than or equal to 6.8; the chemical general formula of the LLZOF is Li < 7-3x-y-z > GaxLa3Zr2-yTayO12-zFz, x is greater than or equal to 0 and less than or equal to 0.3, y is greater than or equal to 0 and less than or equal to 0.6, and z is greater than or equal to 0.1 and less than or equal to 0.4. The prepared novel garnet type composite solid electrolyte has high ionic conductivity and low electronic conductivity, and meanwhile, the preparation method is simple and easy to implement and suitable for industrial production.

Description

Technical Field

[0001] This invention belongs to the field of solid electrolyte technology, and particularly relates to a garnet-type composite solid electrolyte, its preparation method, and its application. Background Technology

[0002] Compared to traditional lithium-ion batteries, all-solid-state lithium batteries use solid electrolytes instead of organic electrolytes, which is expected to fundamentally eliminate safety hazards while improving energy density. Among many solid lithium-ion electrolytes, Li7La3Zr2O with a garnet structure is particularly promising. 12 (LLZO) is due to its high room temperature ionic conductivity (>10). -4 Its high S / cm, wide electrochemical window (≥ 5 V / Li), and stability in contact with lithium metal make it one of the most promising solid electrolytes. However, its high electronic conductivity (>10 S / cm) is a concern. -8 S / cm is the key reason for the growth of lithium dendrites ( Nat. Energy, 2019, 4: 187-196 ).

[0003] To reduce the electronic conductivity of LLZO, researchers introduced a low-electronic-conductivity second phase into LLZO to prepare a composite solid electrolyte to block electron migration. Experimental results show that the introduction of the second phase can effectively reduce the electronic conductivity of LLZO, thereby suppressing lithium dendrite formation. However, the low-electronic-conductivity second-phase modified material usually does not possess high ionic conductivity, which hinders the rapid migration of lithium ions. Furthermore, during high-temperature sintering, elemental interdiffusion deteriorates the interface structure between the second-phase material and LLZO, further worsening lithium-ion transport performance and electron blocking performance. J. Adv. Ceram. 2022, 11 (10), 1530 1541 , Chem. Rev. 2020, 120 (10), 4257 4300，J. Alloys Compd. 2024, 1003, 175769 ).

[0004] In conclusion, developing composite solid electrolytes that combine high ionic conductivity with low electronic conductivity has become an urgent task. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a garnet-type composite solid electrolyte, its preparation method, and its applications. LLZOF, which has high ionic conductivity and low electronic conductivity, is combined with LLZO, which has high ionic conductivity and high electronic conductivity. The mixture is then sintered at high temperature for a short time. A small amount of F from the LLZOF diffuses into the LLZO, but due to the short sintering time, only a gradient of F concentration is formed on the surface of the LLZO particles. xLLZOF can conduct lithium ions relatively quickly while blocking electron migration, while LLZO with F diffusion has a surface layer of LLZOF. x With the same capability, LLZO can conduct lithium ions faster, thus enabling the prepared novel garnet-type composite solid electrolyte to have both high ionic conductivity and low electronic conductivity.

[0006] The objective of this invention is achieved through the following technical solution: A garnet-type composite solid electrolyte is a test block formed by mixing LLZO powder and LLZOF powder, and then pressing and sintering it. The general chemical formula of the LLZO is: Li 7-3x-y Ga x La3Zr 2-y Ta y O 12 , 0≤x≤0.3, 0≤y≤0.6, and 6.1≤7-3x-y≤6.8; The general chemical formula of the LLZOF is: Li 7-3x-y-z Ga x La3Zr 2-y Ta y O 12-z F z , 0≤x≤0.3, 0≤y≤0.6, 0.1≤z≤0.4.

[0007] Preferably, the mass of the LLZOF powder is 1 to 25 wt% of the mass of the LLZO powder.

[0008] Preferably, the particle size of the LLZOF powder is 0.1~10μm, the particle size of the LLZO powder is 1~20μm, and the particle size of the LLZOF powder is less than or equal to the particle size of the LLZO powder.

[0009] The preparation method of the above-mentioned garnet-type composite solid electrolyte includes the following steps: S1. According to the general chemical formula of LLZOF, weigh out lithium source, lanthanum source, zirconium source, gallium source, tantalum source and fluorine source, mix them, ball mill and dry them, and ball mill them again after the first pre-calcination treatment to obtain LLZOF powder. S2. According to the general chemical formula of LLZO, weigh out lithium source, lanthanum source, zirconium source, gallium source and tantalum source, mix them, ball mill and dry them, and ball mill them again after a second pre-calcination treatment to obtain LLZO powder. S3. The LLZOF powder and LLZO powder are mixed, ball-milled, dried and pressed into shape, and finally sintered to obtain the garnet-type composite solid electrolyte.

[0010] Preferably, the lithium source in steps S1 and S2 is selected from at least one of lithium oxide, lithium carbonate, lithium nitrate and lithium hydroxide.

[0011] Preferably, the lanthanum source in steps S1 and S2 is selected from at least one of lanthanum oxide, lanthanum carbonate, lanthanum nitrate, and lanthanum hydroxide.

[0012] Preferably, the zirconium source in steps S1 and S2 is selected from at least one of zirconium oxide, zirconium carbonate, zirconium nitrate, and zirconium hydroxide.

[0013] Preferably, the gallium source in steps S1 and S2 is selected from at least one of gallium oxide, gallium carbonate, gallium nitrate, and gallium hydroxide.

[0014] Preferably, the tantalum source in steps S1 and S2 is selected from at least one of tantalum oxide, tantalum carbonate, tantalum nitrate, and tantalum hydroxide.

[0015] Preferably, the fluorine source in step S1 is lithium fluoride. In actual production, lithium fluoride is used as both a fluorine source and a lithium source.

[0016] Preferably, the mass ratio of LLZOF powder to LLZO powder in step S3 is 1~25:100.

[0017] Preferably, in step S1, the temperature of the first pre-firing treatment is 700~1100℃ and the time is 0.5~12h.

[0018] Preferably, the temperature of the second pre-firing treatment in step S2 is 700~1100℃ and the time is 0.5~12h.

[0019] Preferably, the sintering temperature in step S2 is 1250~1450℃, and the sintering time is 5~25 min.

[0020] The above-mentioned garnet-type composite solid electrolyte is used in the preparation of lithium-ion battery electrolytes.

[0021] Compared with the prior art, the beneficial effects of the present invention include: (1) The novel garnet-type composite solid electrolyte prepared by the present invention has both high ionic conductivity and low electronic conductivity, and its performance is superior to both LLZO and LLZOF.

[0022] (2) The novel garnet-type composite solid electrolyte prepared by the present invention combines the advantages of LLZTO and LLZTOF while avoiding their disadvantages, thus exhibiting a stronger ability to suppress lithium dendrites.

[0023] (3) The preparation method of the present invention is simple and easy to implement, and is suitable for industrial production. Attached Figure Description

[0024] Figure 1 TEM image and F element line scan image of the garnet-type composite solid electrolyte prepared in Example 1, where (a) is the TEM image and (b) is the F element line scan image.

[0025] Figure 2 X-ray diffraction patterns of the garnet-type composite solid electrolytes prepared in Examples 1, 3, 5 and 6.

[0026] Figure 3 Electron paramagnetic resonance spectra of the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 are shown, where LLZTOF-LLZTO corresponds to Example 1, LLZTO corresponds to Example 1, and LLZTO corresponds to LLZTOF. 0.1 The response ratio is 2.

[0027] Figure 4 The AC impedance curves, DC polarization curves, and Arrhenius curves of the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 are shown at room temperature. (a) is the AC impedance curve, (b) is the DC polarization curve, and (c) is the Arrhenius curve. LLZTOF-LLZTO corresponds to Example 1, LLZTO corresponds to Comparative Example 1, and LLZTOF corresponds to Comparative Example 2.

[0028] Figure 5 The critical current density test curves of the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 are shown, where (a) corresponds to Comparative Example 1, (b) corresponds to Comparative Example 2, and (c) corresponds to Example 1.

[0029] Figure 6 Photographs showing the contact stability of garnet-type solid electrolytes with lithium metal prepared in Example 1 and Comparative Example 2, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 1.

[0030] Figure 7 The lithium-symmetric battery assembled from the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 was tested at room temperature and 0.3 mA / cm². 2 The following is a comparison chart of the cycle performance, where (a) corresponds to Example 1, (b) corresponds to Example 2, and (c) corresponds to Example 1. Detailed Implementation

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0032] Example 1 A method for preparing a garnet-type composite solid electrolyte, the specific steps of which are as follows: S1, according to Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Lithium hydroxide monohydrate (LiOH·H₂O), lanthanum oxide (La₂O₃), zirconium oxide (ZrO₂), and tantalum oxide (Ta₂O₅) powders were weighed according to stoichiometry (10% excess lithium source to compensate for lithium loss during high-temperature sintering). 15g of the above mixed powder was placed in a ball mill jar, and 30g (200% by mass) of isopropanol and an appropriate amount of zirconium oxide balls were added for ball milling at 400 r / min for 10 h. After ball milling, the mixture was placed in a drying oven and dried at 80℃ for 10 h, then pre-calcined at 950℃ for 6 h, and then ball-milled and dried again to obtain Li. 6.5 La3Zr 1.5 Ta 0.5 O 12 Powder; S2, according to Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Lithium hydroxide monohydrate (LiOH·H2O), lanthanum oxide (La2O3), zirconium oxide (ZrO2), tantalum oxide (Ta2O5) powder, and lithium fluoride (LiF) were weighed according to stoichiometry (10% excess lithium source to compensate for lithium loss during high-temperature sintering). 15g of the above mixed powder was placed in a ball mill jar, and 30g (200% by mass) of isopropanol and an appropriate amount of zirconium oxide balls were added for ball milling at 400 r / min for 10 h. After ball milling, the mixture was placed in a drying oven and dried at 80℃ for 10 h, then pre-calcined at 950℃ for 6 h, and then ball-milled and dried again to obtain Li. 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder; S3, Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12The powders were mixed at a mass ratio of 2:98 (denoted as 2LLZOF-LLZO), and then the mixture was placed in a mortar and ground for 30 minutes. The mixture was then placed in a steel mold and pressed at 250 MPa for 5 minutes to obtain a green body. The green body was heated to 1320°C at a heating rate of 5°C / min, held for 15 minutes, and then cooled in the furnace to obtain the garnet-type composite solid electrolyte.

[0033] Figure 1 TEM images and F element line scans of the garnet-type composite solid electrolyte prepared in Example 1 are shown, where (a) is the TEM image and (b) is the F element line scan. Figure 1 We can see that during short-time sintering at high temperature, a small amount of F in LLZOF diffuses into LLZO. However, due to the short sintering time, only a concentration gradient of F is formed on the surface of the LLZO particles. x (as shown in (b)), its surface layer LLZOF x It can conduct lithium ions relatively quickly while blocking electron migration, and LLZO can conduct lithium ions even faster. Example 2 Example 2 provides a method for preparing a garnet-type composite solid electrolyte. The only difference from Example 1 is that Li... 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powders were mixed at a mass ratio of 5:95, and the remaining steps were the same as in Example 1.

[0034] Example 3 Example 3 provides a method for preparing a garnet-type composite solid electrolyte, which differs from Example 1 only in that Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powders were mixed at a mass ratio of 10:90, and the remaining steps were the same as in Example 1. The final product was designated as 10LLZOF-LLZO.

[0035] Example 4 Example 4 provides a method for preparing a garnet-type composite solid electrolyte. The only difference from Example 1 is that Li... 6.4La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powders were mixed at a mass ratio of 15:85, and the remaining steps were the same as in Example 1.

[0036] Example 5 Example 5 provides a method for preparing a garnet-type composite solid electrolyte, which differs from Example 1 only in that Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powders were mixed at a mass ratio of 20:80, and the remaining steps were the same as in Example 1. The final product was designated as 20LLZOF-LLZO.

[0037] Example 6 Example 6 provides a method for preparing a garnet-type composite solid electrolyte. The only difference from Example 1 is that Li was prepared. 6.4 Ga 0.2 La3Zr2O 12 Powder and Li 6.3 Ga 0.2 La3Zr2O 11.9 F 0.1 Powder, and Li 6.3 Ga 0.2 La3Zr2O 11.9 F 0.1 Powder and Li 6.4 Ga 0.2 La3Zr2O 12 The powders were mixed at a mass ratio of 1:99, and the remaining steps were the same as in Example 1. The final product was designated as 1LLZOF-LGLZO.

[0038] Figure 2 X-ray diffraction patterns of the garnet-type composite solid electrolytes prepared in Examples 1, 3, 5, and 6. From... Figure 2 It can be seen that the X-ray diffraction peaks of the novel garnet-type composite solid electrolyte match well with the PDF card (45-0109) of cubic LLZO, indicating that the novel garnet-type composite solid electrolyte is still cubic LLZO.

[0039] Comparative Example 1 Comparative Example 1 provides a garnet-type solid electrolyte, which differs from Example 1 only in that it only prepares Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Powder, not involving Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 The powder is processed using the same steps as in Example 1.

[0040] Comparative Example 2 Comparative Example 2 provides a garnet-type solid electrolyte, which differs from Example 1 only in that it only prepares Li 6.4 La3Zr 1.5 Ta 0.5 O 11.9 F 0.1 Powder, not involving Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powder is processed using the same steps as in Example 1.

[0041] Figure 3 Electron paramagnetic resonance spectra of the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 are shown, where LLZTOF-LLZTO corresponds to Example 1, LLZTO corresponds to Example 1, and LLZTO corresponds to LLZTOF. 0.1 Response ratio 2. From Figure 3 We can see that the incorporation of F leads to an increase in oxygen vacancies, which will facilitate the transition of lithium ions and also inhibit electron transport by binding with electrons.

[0042] AC impedance testing at different temperatures and DC polarization testing at room temperature were performed using an electrochemical workstation. The test results are as follows: Figure 4 As shown. Figure 4 The AC impedance curves, DC polarization curves, and Arrhenius curves at room temperature are shown for the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2. (a) is the AC impedance curve, (b) is the DC polarization curve, and (c) is the Arrhenius curve. LLZTOF-LLZTO corresponds to Example 1, LLZTO corresponds to Comparative Example 1, and LLZTOF corresponds to Comparative Example 2. Figure 4 We can see that, compared to LLZTO, the novel garnet-type composite solid electrolyte prepared in Example 1 benefits from the increased number of oxygen vacancies, which facilitates lithium-ion transitions while also inhibiting electron transport through binding with electrons. Therefore, the prepared novel garnet-type composite solid electrolyte possesses both high ionic conductivity and low electronic conductivity.

[0043] Figure 5 The critical current density test curves are shown for the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2, where (a) corresponds to Comparative Example 1, (b) corresponds to Comparative Example 2, and (c) corresponds to Example 1. Figure 5 We can see that Example 1 exhibits a higher critical current density than Comparative Example 1 and Comparative Example 2.

[0044] Figure 6 Photographs showing the contact stability of garnet-type solid electrolytes with lithium metal prepared in Example 1 and Comparative Example 2, where (a) corresponds to Comparative Example 2 and (b) corresponds to Example 1. Figure 6 We can see that the garnet-type solid electrolyte prepared in Example 1 is stable in contact with molten lithium metal, and no lithium metal penetrates the solid electrolyte sheet, while lithium metal penetration occurs in Comparative Example 2.

[0045] Figure 7 The lithium-symmetric battery assembled from the garnet-type solid electrolytes prepared in Example 1 and Comparative Examples 1-2 was tested at room temperature and 0.3 mA / cm². 2 The following is a comparison chart of cycle performance, where (a) corresponds to Example 1, (b) corresponds to Example 2, and (c) corresponds to Example 1. From Figure 7 We can see that the lithium symmetric battery assembled in Example 1 can stably cycle 3000 times at room temperature.

[0046] Comparative Example 3 Comparative Example 3 provides a garnet-type solid electrolyte, which differs from Example 6 only in that it only prepares Li 6.4 Ga 0.2 La3Zr2O 12 Powder, not involving Li 6.3 Ga 0.2 La3Zr2O 11.9 F 0.1 The powder is processed using the same steps as in Example 6.

[0047] Comparative Example 4 Comparative Example 4 provides a garnet-type solid electrolyte, which differs from Example 1 only in that it only prepares Li 6.5 La3Zr 1.5 Ta 0.5 O 12 Powder, and in step S3, LiF and Li 6.5 La3Zr 1.5 Ta 0.5 O 12 The powder was mixed at a ratio of 1:99, and the remaining steps were the same as in Example 1.

[0048] The ionic conductivity and electronic conductivity of the garnet-type solid electrolytes prepared in Examples 1-6 and Comparative Examples 1-4 at room temperature (25°C) are statistically shown in Table 1.

[0049] Table 1 Ionic and electronic conductivity of the examples and comparative examples

[0050] Referring to Table 1, we can see that the garnet-type composite solid electrolytes prepared in Examples 1-6 of this invention have lower electronic conductivity and higher ionic conductivity than the comparative examples. Further comparing Example 1 and Comparative Example 1, the ionic conductivity of the novel garnet-type composite solid electrolyte sample prepared in Example 1 can reach 8.15 × 10⁻⁶ at room temperature. -4 The energy density is S / cm, the activation energy is 0.32 eV, and the electronic conductivity is only 2.73 × 10⁻⁶. -9 S / cm, compared to Comparative Example 1 (1.64 × 10⁻⁶) -8 The electronic conductivity decreased by an order of magnitude (S / cm), indicating that combining LLZOF with LLZO not only maintains good lithium-ion conductivity but also blocks electron migration and provides stable contact with lithium metal.

[0051] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A garnet-type composite solid electrolyte, characterized in that, It is a test block made by mixing LLZO powder and LLZOF powder, pressing and sintering. The general chemical formula of the LLZO is: Li 7-3x-y Ga x La3Zr 2-y Ta y O 12 , 0≤x≤0.3, 0≤y≤0.6, and 6.1≤7-3x-y≤6.8; The general chemical formula of the LLZOF is: Li 7-3x-y-z Ga x La3Zr 2-y Ta y O 12-z F z , 0≤x≤0.3, 0≤y≤0.6, 0.1≤z≤0.

4.

2. The garnet-type composite solid electrolyte according to claim 1, characterized in that, The mass of the LLZOF powder is 1 to 25 wt% of the mass of the LLZO powder.

3. The garnet-type composite solid electrolyte according to claim 1, characterized in that, The particle size of the LLZOF powder is 0.1~10μm, the particle size of the LLZO powder is 1~20μm, and the particle size of the LLZOF powder is less than or equal to the particle size of the LLZO powder.

4. The method for preparing the garnet-type composite solid electrolyte according to any one of claims 1 to 3, characterized in that, Includes the following steps: S1. According to the general chemical formula of LLZOF, weigh out lithium source, lanthanum source, zirconium source, gallium source, tantalum source and fluorine source, mix them, ball mill and dry them, and ball mill them again after the first pre-calcination treatment to obtain LLZOF powder. S2. According to the general chemical formula of LLZO, weigh out lithium source, lanthanum source, zirconium source, gallium source and tantalum source, mix them, ball mill and dry them, and ball mill them again after a second pre-calcination treatment to obtain LLZO powder. S3. The LLZOF powder and LLZO powder are mixed, ball-milled, dried and pressed into shape, and finally sintered to obtain the garnet-type composite solid electrolyte.

5. The method for preparing the garnet-type composite solid electrolyte according to claim 4, characterized in that, The lithium source in steps S1 and S2 is selected from at least one of lithium oxide, lithium carbonate, lithium nitrate, and lithium hydroxide; and / or The lanthanum source in steps S1 and S2 is selected from at least one of lanthanum oxide, lanthanum carbonate, lanthanum nitrate, and lanthanum hydroxide; and / or The zirconium source in steps S1 and S2 is selected from at least one of zirconium oxide, zirconium carbonate, zirconium nitrate, and zirconium hydroxide; and / or The gallium source in steps S1 and S2 is selected from at least one of gallium oxide, gallium carbonate, gallium nitrate, and gallium hydroxide; and / or The tantalum source in steps S1 and S2 is selected from at least one of tantalum oxide, tantalum carbonate, tantalum nitrate, and tantalum hydroxide; and / or The fluorine source in step S1 is lithium fluoride.

6. The method for preparing the garnet-type composite solid electrolyte according to claim 4, characterized in that, The mass ratio of LLZOF powder to LLZO powder in step S3 is 1~25:

100.

7. The method for preparing the garnet-type composite solid electrolyte according to claim 4, characterized in that, In step S1, the temperature of the first pre-firing treatment is 700~1100℃, and the time is 0.5~12h.

8. The method for preparing the garnet-type composite solid electrolyte according to claim 4, characterized in that, In step S2, the temperature of the second pre-firing treatment is 700~1100℃, and the time is 0.5~12h.

9. The method for preparing the garnet-type composite solid electrolyte according to claim 4, characterized in that, The sintering temperature in step S2 is 1250~1450℃, and the sintering time is 5~25 min.

10. The application of the garnet-type composite solid electrolyte according to any one of claims 1 to 3 in the preparation of lithium-ion battery electrolytes.

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