Solid-state electrolyte and method for preparing the same

Abstract

The application relates to the technical field of lithium ion batteries, in particular to a solid-state electrolyte and a preparation method thereof. The preparation method comprises the following steps: preparing a precursor solution by using CeF3 particles coated with SiO2, LiTFSi, DMF and PVDF-HFP powder, drying the precursor solution into a film, and obtaining the solid-state electrolyte. The preparation method takes PVDF-HFP as a polymer electrolyte matrix, coats high specific surface area SiO2 on the surface of the filler CeF3 to increase the surface active sites, increases the interaction with the fluorine-containing groups in the polymer phase, reduces the crystallinity of the composite polymer electrolyte as a whole, improves the ion conductivity, improves the ion transference number, and improves the interface compatibility of the filler phase and the polymer phase.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a solid electrolyte and its preparation method. Background Technology

[0002] Traditional liquid batteries are prone to safety issues during use, and the use of non-flowing solid electrolytes is the future trend. Polymer solid electrolytes are low in cost and easy to process, but have low conductivity. Doping with fillers is an effective way to improve the ionic conductivity of electrolytes and has made great progress. However, the poor compatibility between the filler and the polymer two-phase interface can affect ion transport efficiency.

[0003] Therefore, patent CN 117913357 A proposes a method for preparing a composite quasi-solid-state polymer electrolyte for solid-state lithium metal batteries by adding LATP (lithium aluminum titanium phosphate) ceramic particles to improve interfacial reactions and increase ionic conductivity. However, this preparation method requires the addition of LATP ceramic particles, which have high processing requirements, are difficult to control in terms of particle size, and large-sized LATP particles are prone to agglomeration, affecting ionic conductivity. Furthermore, the LATP ceramic phase has poor compatibility with the polymer phase, has few surface active sites, and exhibits an ion concentration difference on both sides of the phase boundary. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a solid electrolyte with high ionic conductivity and good interface compatibility, and a method for preparing the same.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a method for preparing a solid electrolyte, comprising the following steps: preparing a precursor liquid using CeF3 particles coated with SiO2, LiTFSi (lithium bis(trifluoromethanesulfonylimide)), DMF (N,N-dimethylformamide) and PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer) powder, drying the precursor liquid into a film to obtain a solid electrolyte.

[0006] Another technical solution adopted in this invention is: a solid electrolyte prepared by the above-mentioned solid electrolyte preparation method.

[0007] The beneficial effects of the present invention are as follows: The preparation method of the present invention uses PVDF-HFP as the polymer electrolyte matrix, and increases the surface active sites by coating the surface of filler CeF3 with SiO2 with high specific surface area, thereby increasing the interaction with fluorine-containing groups in the polymer phase, reducing the overall crystallinity of the composite polymer electrolyte, improving ionic conductivity, increasing ion transference number, and improving the interfacial compatibility between the filler phase and the polymer phase. Detailed Implementation

[0008] To explain in detail the technical content, objectives, and effects of the present invention, the following description is provided in conjunction with the embodiments.

[0009] A method for preparing a solid electrolyte includes the following steps: preparing a precursor solution using CeF3 particles coated with SiO2, LiTFSi, DMF and PVDF-HFP powder, drying the precursor solution into a film, and obtaining a solid electrolyte.

[0010] As can be seen from the above description, the beneficial effects of the present invention are as follows: The present invention uses CeF3 particles coated with SiO2 as fillers. These fillers have a high specific surface area, and the surface of the SiO2 coating layer has abundant active sites, such as hydroxyl groups and silicate groups. These active sites will interact with the fluorine-containing groups in the PVDF-HFP polymer phase, reduce the crystallinity of the polymer chain structure, improve the interfacial compatibility between the filler phase and the polymer phase, and increase the lithium-ion transport efficiency after the amorphous region is increased.

[0011] The active sites on the surface of the SiO2 coating can adsorb large anion clusters in the polymer matrix, which restricts the disordered migration of anion clusters during charging and discharging and can improve the ion transference number.

[0012] This invention uses LiTFSI as the lithium source, which has better conductivity, solubility, and the quality of the SEI film formed.

[0013] Furthermore, the mass ratio of CeF3 particles coated with SiO2, LiTFSi, and 20g of PVDF-HFP powder is 3:2.5~3:20.

[0014] Furthermore, the preparation method of CeF3 particles with SiO2 coating includes: dispersing CeF3 powder in deionized water, adding a dispersant to form a suspension, then ultrasonically dispersing, heating to 80~100℃ and adding Na2SiO3 solution, then centrifuging and aging, and drying to obtain CeF3 particles with SiO2 coating.

[0015] As can be seen from the above description, compared with adding SiO2 and CeF3 alone, CeF3 particles coated with SiO2 have better uniformity in size, which can improve the uniformity of the material; the particles on the surface of the coating layer can be smaller, which is beneficial to increasing the specific surface area, and the particle dispersion is better compared with SiO2 and CeF3 of the same size.

[0016] CeF3 particles coated with SiO2 have the following advantages: 1. They have abundant active sites, which can reduce the crystallinity of polymer chain segments and improve the interfacial compatibility between the filler phase and the polymer phase; 2. CeF3 is a fluorine-containing compound that can form compounds that facilitate lithium conduction at the SEI interface, thereby improving interfacial compatibility; 3. Due to the extremely strong electronegativity of fluorine, CeF3 can increase the degree of dissociation of lithium salts in polymer electrolytes and increase the number of migratable ions.

[0017] Furthermore, the dispersant is a sodium hexafluoromethphosphate solution.

[0018] Furthermore, the amount of sodium hexafluoromethphosphate solution added is 40~50 g / L.

[0019] As can be seen from the above description, adding too much dispersant will reduce the performance of the electrolyte, while adding too little will result in poor electrolyte uniformity.

[0020] Furthermore, the aging time is 110-130 minutes.

[0021] As can be seen from the above description, aging makes the particle size distribution of CeF3 particles coated with SiO2 on the surface more uniform.

[0022] Furthermore, the drying temperature is 110~130℃.

[0023] Furthermore, the preparation method of CeF3 powder includes: dissolving Ce(NO3)3·6H2O in deionized water, then adding NH4F aqueous solution to react, and after the reaction is completed, centrifuging, washing and drying are performed in sequence to obtain CeF3 powder.

[0024] Furthermore, the mass ratio of Ce(NO3)3·6H2O to NH4F in the aqueous solution is 40~45:11~12.

[0025] Furthermore, the specific conditions for the reaction are: the reaction is carried out at 100~120℃.

[0026] The specific steps for obtaining CeF3 powder by drying are as follows: drying at 75~85℃ in a vacuum environment.

[0027] Another technical solution adopted in this invention is: a solid electrolyte prepared by the above-mentioned solid electrolyte preparation method.

[0028] As can be seen from the above description, the solid electrolyte of the present invention has high ionic conductivity and ion transference number, and good interface compatibility.

[0029] Embodiment 1 of the present invention is a method for preparing a solid electrolyte, comprising the following steps:

[0030] S1: Weigh 11.2g of NH4F and 43.4g of Ce(NO3)3·6H2O using an analytical balance, and prepare a 15wt% NH4F aqueous solution. Place the Ce(NO3)3·6H2O into a beaker containing 30mL of deionized water and stir for 10min at a speed of 120r / min to obtain a Ce(NO3)3·6H2O aqueous solution. Slowly add the NH4F aqueous solution to the stirred Ce(NO3)3·6H2O aqueous solution, and continue stirring for 40min. Then transfer the mixture to a 100mL reactor for reaction at a temperature of 110℃ for 16h. After the reaction is complete, centrifuge the product, wash it with deionized water and anhydrous ethanol in sequence, transfer it to a vacuum oven and dry it at 80℃ for 8h. Then grind the product and pass it through 400 and 600 mesh sieves to obtain CeF3 powder.

[0031] S2: CeF3 powder was dispersed in 300 mL of deionized water, and 2 mL of sodium hexafluoromethphosphate solution with a concentration of 45 g / L was added to form a suspension. The suspension was then ultrasonically dispersed for 20 min. The ultrasonically dispersed mixture was placed in a 90 °C water bath and stirred at a stirring speed of 120 r / min. During the stirring process, 250 mL of Na2SiO3 solution with a concentration of 20 g / L was slowly added. The mixture was then centrifuged and aged for 120 min. Finally, it was dried at 120 °C for 20 h to obtain CeF3 particles with SiO2 coating on the surface.

[0032] S3: Add 3g of CeF3 particles coated with SiO2 and 2.7g of LiTFSi to a beaker containing 50g of DMF and stir until homogeneous. Weigh 20g of PVDF-HFP powder and slowly add it to the beaker while stirring. Stir at 120r / min for 8 hours to obtain a uniform precursor solution. Place the beaker in a vacuum degassing machine to remove the gas mixed in during stirring. Then, use a 2000um scraper to uniformly coat the precursor solution onto a polytetrafluoroethylene plate. Place the plate in a vacuum drying oven at 60℃ for 24 hours to obtain a solid electrolyte.

[0033] Comparative Example 1 of the present invention is: replacing the CeF3 particles with SiO2 coating on the surface with an equal mass of CeF3.

[0034] Comparative Example 2 of the present invention is: replacing CeF3 particles coated with SiO2 on the surface with an equal mass of SiO2.

[0035] The solid electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 were subjected to the following tests:

[0036] 1. The ion transference number of the solid electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 was determined using the following method: A symmetrical Li | SSEs | Li battery was assembled, and the lithium ion transference number (tLi+) of the sample film was measured using electrochemical impedance spectroscopy (EIS) and direct current (DC) polarization method. It can be calculated using the following formula:

[0037]

[0038] Where ΔV represents the applied polarization voltage (unit: V), which is 10 mV. I0 and R0 represent the initial current and battery interface resistance, respectively. s and R s These represent the steady-state current and the battery interface resistance, respectively; the test results are shown in Table 1.

[0039] Table 1

[0040]

[0041] As shown in Table 1, the addition of CeF3 particles coated with SiO2 can adsorb large anion clusters in the polymer matrix, restricting the disordered migration of anion clusters during the charging and discharging process and increasing the ion transference number.

[0042] 2. The ionic conductivity of the solid electrolytes prepared in Example 1, Comparative Example 1, and Comparative Example 2 was tested using the following method: Symmetrical stainless steel (SS) | SSEs | SS cells were assembled, and the ionic conductivity of the electrolytes was measured using electrochemical impedance spectroscopy (EIS). Open-circuit voltage was used, and the test frequency range was 0.01 Hz to 1000 kHz. The conductivity value can be calculated using the following formula:

[0043]

[0044] Where σ represents the ionic conductivity of the sample membrane, in units of S·cm. -1 R, l, and S represent the bulk resistance (Ω), thickness (cm), and area (cm²) of the measured electrolyte membrane, respectively. 2 The test results are shown in Table 2.

[0045] Table 2

[0046]

[0047] As shown in Tables 1 and 2, the present invention improves the interfacial compatibility between the filler and the polymer phase by adding CeF3 particles with SiO2 coating on the surface, providing more ion pathways, thereby increasing the ion transference number and ion conductivity.

[0048] Embodiment 2 of the present invention is a method for preparing a solid electrolyte, comprising the following steps:

[0049] S1: Weigh 11g of NH4F and 40g of Ce(NO3)3·6H2O using an analytical balance, and prepare a 15wt% NH4F aqueous solution. Place the Ce(NO3)3·6H2O into a beaker containing 30mL of deionized water and stir for 10min at a speed of 120r / min to obtain a Ce(NO3)3·6H2O aqueous solution. Slowly add the NH4F aqueous solution to the stirred Ce(NO3)3·6H2O aqueous solution, and continue stirring for 40min. Then transfer the mixture to a 100mL reactor for reaction at 100℃ for 16h. After the reaction is complete, centrifuge the product, wash it with deionized water and anhydrous ethanol in sequence, transfer it to a vacuum oven and dry it at 75℃ for 8h. Then grind the product and pass it through 400 and 600 mesh sieves to obtain CeF3 powder.

[0050] S2: CeF3 powder was dispersed in 300 mL of deionized water, and 2 mL of sodium hexafluoromethphosphate solution with a concentration of 40 g / L was added to form a suspension. The suspension was then ultrasonically dispersed for 20 min. The ultrasonically dispersed mixture was placed in a 90 °C water bath and stirred at a stirring speed of 120 r / min. During the stirring process, 250 mL of Na2SiO3 solution with a concentration of 20 g / L was slowly added. The mixture was then centrifuged and aged for 110 min. Finally, it was dried at 110 °C for 20 h to obtain CeF3 particles with SiO2 coating on the surface.

[0051] S3: Add 3g of CeF3 particles coated with SiO2 and 2.5g of LiTFSi to a beaker containing 50g of DMF and stir until homogeneous. Weigh 20g of PVDF-HFP powder and slowly add it to the beaker while stirring. Stir at 120r / min for 8 hours to obtain a uniform precursor solution. Place the beaker in a vacuum degassing machine to remove the gas mixed in during stirring. Then, use a 2000um scraper to uniformly coat the precursor solution onto a polytetrafluoroethylene plate. Place the plate in a vacuum drying oven at 60℃ for 24 hours to obtain a solid electrolyte.

[0052] Embodiment 3 of the present invention is a method for preparing a solid electrolyte, comprising the following steps:

[0053] S1: Weigh 12g of NH4F and 45g of Ce(NO3)3·6H2O using an analytical balance, and prepare a 15wt% NH4F aqueous solution. Place the Ce(NO3)3·6H2O into a beaker containing 30mL of deionized water and stir for 10min at a speed of 120r / min to obtain a Ce(NO3)3·6H2O aqueous solution. Slowly add the NH4F aqueous solution to the stirred Ce(NO3)3·6H2O aqueous solution, and continue stirring for 40min. Then transfer the mixture to a 100mL reactor for reaction at a temperature of 120℃ for 16h. After the reaction is complete, centrifuge the product, wash it with deionized water and anhydrous ethanol in sequence, transfer it to a vacuum oven and dry it at 85℃ for 8h. Then grind the product and pass it through 400 and 600 mesh sieves to obtain CeF3 powder.

[0054] S2: CeF3 powder was dispersed in 300 mL of deionized water, and 2 mL of 50 g / L sodium hexafluoromethphosphate solution was added to form a suspension. The suspension was then ultrasonically dispersed for 20 min. The ultrasonically dispersed mixture was placed in a 90 °C water bath and stirred at a speed of 120 r / min. During the stirring process, 250 mL of 20 g / L Na2SiO3 solution was slowly added. The mixture was then centrifuged and aged for 130 min. Finally, it was dried at 130 °C for 20 h to obtain CeF3 particles with SiO2 coating on the surface.

[0055] S3: Add 3g of CeF3 particles coated with SiO2 and 3g of LiTFSi to a beaker containing 50g of DMF and stir until homogeneous. Weigh 20g of PVDF-HFP powder and slowly add it to the beaker while stirring. Stir at 120r / min for 8 hours to obtain a uniform precursor solution. Place the beaker in a vacuum degassing machine to remove the gas mixed in during stirring. Then, use a 2000um scraper to uniformly coat the precursor solution onto a polytetrafluoroethylene plate. Place the plate in a vacuum drying oven at 60℃ for 24 hours to obtain a solid electrolyte.

[0056] Example 4 of the present invention is a solid electrolyte prepared using the preparation method of Example 1.

[0057] In summary, the method for preparing solid electrolytes provided by this invention has the following advantages:

[0058] 1. Using CeF3 particles coated with SiO2 as fillers can increase the active sites for interaction with PVDF-HFP, improve the interfacial compatibility between the filler phase and the polymer phase, and improve lithium-ion transport efficiency and ion transference number.

[0059] 2. Using LiTFSI as the lithium source, it exhibits excellent conductivity, solubility, and SEI film quality;

[0060] 3. Solid electrolytes have good uniformity and dispersibility.

[0061] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent modifications made using the present invention specification, or direct or indirect applications in related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a solid electrolyte, characterized in that, Includes the following steps: A precursor solution was prepared using CeF3 particles coated with SiO2, LiTFSi, DMF solution, and PVDF-HFP powder. The precursor solution was dried to form a film to obtain a solid electrolyte. The mass ratio of CeF3 particles coated with SiO2, LiTFSi and 20g of PVDF-HFP powder is 3:2.5~3:20; The method for preparing CeF3 particles with SiO2 coating includes: dispersing CeF3 powder in deionized water, adding a dispersant to form a suspension, then ultrasonically dispersing, heating to 80~100℃ and adding Na2SiO3 solution, then centrifuging and aging, and drying to obtain CeF3 particles with SiO2 coating.

2. The method for preparing a solid electrolyte according to claim 1, characterized in that, The dispersant is a sodium hexafluoromethphosphate solution.

3. The method for preparing a solid electrolyte according to claim 2, characterized in that, The amount of sodium hexafluoromethphosphate solution added is 40~50 g / L.

4. The method for preparing a solid electrolyte according to claim 1, characterized in that, The aging time is 110-130 minutes.

5. The method for preparing a solid electrolyte according to claim 1, characterized in that, The drying temperature is 110~130℃.

6. The method for preparing a solid electrolyte according to claim 1, characterized in that, The method for preparing CeF3 powder includes: dissolving Ce(NO3)3·6H2O in deionized water, then adding NH4F aqueous solution to react, and after the reaction is completed, centrifuging, washing and drying are performed sequentially to obtain CeF3 powder.

7. The method for preparing a solid electrolyte according to claim 6, characterized in that, The mass ratio of Ce(NO3)3·6H2O to NH4F in the aqueous solution is 40~45:11~12.

8. The method for preparing a solid electrolyte according to claim 6, characterized in that, The specific conditions for the reaction are: the reaction is carried out at 100~120℃.

9. A solid electrolyte prepared by any of the solid electrolyte preparation methods according to claims 1-8.

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