A method for preparing a composite solid electrolyte membrane that suppresses interfacial reactions
By introducing a bicarbonate buffer into a fluorinated polymer/garnet composite solid electrolyte, the interfacial reaction was controlled, the gelation problem of the composite electrolyte membrane was solved, and high ionic conductivity and excellent cycling performance were achieved, thus preparing a high-performance composite solid electrolyte membrane.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHEAST UNIV
- Filing Date
- 2023-06-08
- Publication Date
- 2026-07-03
AI Technical Summary
Existing fluorinated polymer/garnet composite solid electrolytes exhibit severe side reactions at the interface, leading to material structure damage and decreased ion transport performance. Current methods struggle to effectively suppress these reactions while maintaining the material structure and excellent ion transport performance.
By introducing bicarbonate as a buffer during the mixing process of fluorinated polymer and garnet solid electrolyte, the interfacial reaction environment is regulated. The H2CO3/HCO3- buffer pair is used to weaken the strong alkalinity of garnet and inhibit the defluorination reaction of fluorinated polymer segments, thus preparing a composite solid electrolyte membrane.
A composite solid electrolyte membrane with high ionic conductivity and long cycling performance was achieved. The room temperature ionic conductivity reached 10⁻³ S cm⁻¹, and the capacity retention rate after 250 cycles was over 90%, which significantly improved the overall performance of the material.
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Figure CN116632363B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for preparing an electrolyte membrane, specifically a method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions. Background Technology
[0002] Fluoropolymers, such as polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF–HFP), and poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-TrFE)), not only possess excellent mechanical properties and thermal stability but also contain a large number of polar electron-withdrawing –F functional groups, giving them high dielectric constants and promoting lithium salt dissociation, making them ideal matrix materials for preparing polymer solid electrolytes. However, fluoropolymers still suffer from drawbacks such as low ionic conductivity and weak mechanical strength. Garnet solid electrolytes exhibit excellent ionic conductivity and good mechanical strength. Adding garnet solid electrolytes can not only solve the aforementioned problems of fluoropolymer solid electrolytes but also reduce polymer crystallinity, broaden the electrochemical voltage window, increase lithium stability, and provide additional ion transport channels. Therefore, preparing a composite system of fluoropolymers / garnet solid electrolytes is an effective strategy for preparing high-performance solid electrolytes. However, this type of composite solid electrolyte suffers from severe interfacial side reactions, specifically, the alkaline environment of garnet attacks the fluoropolymer backbone, inducing defluorination and resulting in discoloration or even gelation reactions. These side reactions severely affect the processing and electrochemical performance of composite solid electrolytes. Therefore, it is necessary to develop a simple and efficient strategy to inhibit gelation and prepare high-performance composite solid electrolytes.
[0003] For example, patent CN113644312A discloses a surface modification method and application based on garnet-type solid electrolytes. This involves heating and drying the garnet solid electrolyte in a lithium salt solution, then rinsing it with a dimethyl carbonate solution to improve the alkaline environment of the garnet solid electrolyte. The treated garnet solid electrolyte, when mixed with a fluorinated polymer, does not exhibit gelation. However, this method is inefficient and can damage the material's structure. Another example is patent CN115832412A, which discloses a composite solid electrolyte comprising garnet electrolyte, a fluorinated polymer, and a lithium salt. In this method, a dispersion of the garnet solid electrolyte is mixed with an organic acid to improve the alkaline environment of the garnet solid electrolyte, effectively preventing the defluorination of hydrogen from the fluorinated polymer chains. The assembled solid-state lithium battery exhibits excellent cycle performance. However, this method introduces new organic impurities, increases the interface, and makes it difficult to fully utilize the electrolyte's lithium-ion transport capability.
[0004] In summary, existing suppression methods struggle to effectively suppress interfacial side reactions while maintaining the material's structure and excellent ion transport performance. Summary of the Invention
[0005] Purpose of the invention: In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing a composite solid electrolyte membrane with excellent ion transport performance, good cycle performance and inhibition of interfacial reactions.
[0006] Technical solution: The present invention provides a method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions.
[0007] Step 1: Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide and stir until homogeneous at 45-55°C to obtain solution A;
[0008] Step 2: Ball mill the garnet solid electrolyte to obtain a uniform dispersion, then add bicarbonate and stir until uniform to obtain solution B. The mass ratio of fluorinated polymer, lithium salt, garnet solid electrolyte, and bicarbonate is 0.4:0.6:1:0.15-0.25.
[0009] Step 3: Add solution B to solution A and stir to obtain a uniform electrolyte slurry;
[0010] Step four: Transfer the material obtained in step three to a glass petri dish, dry it first at 45-50°C with forced air, and then dry it under vacuum at 110-120°C to obtain a composite solid electrolyte membrane.
[0011] Further, in step one, the fluorinated polymer is poly(vinylidene fluoride-co-hexafluoropropylene), polyvinylidene fluoride, or poly(vinylidene fluoride-co-trifluoroethylene), preferably poly(vinylidene fluoride-co-hexafluoropropylene) (Maclean, Mw~455000). The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.
[0012] Furthermore, in step two, the garnet solid electrolyte is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.4 Ga 0.2 La3Zr2O 12 Or Li 6.28 La3Zr2Al 0.24 O 12 Li is preferred 6.4 La3Zr 1.4 Ta 0.6 O 12 The average particle size of the garnet solid electrolyte is 5–8 μm. The bicarbonate is one or more of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate; the bicarbonate, preferably ammonium bicarbonate, is used as a buffer to regulate the degree of interfacial reaction.
[0013] Furthermore, in step three, the stirring speed is 450–500 r / min, and the time is 12–16 h.
[0014] Furthermore, in step four, the drying time is 2-4 hours by forced air drying and 16-20 hours by vacuum drying.
[0015] Furthermore, the thickness of the composite solid electrolyte membrane is 100–300 μm.
[0016] Preparation Principle: Garnet solid electrolytes are dispersed in a polar solvent. The presence of residual alkali on the surface and the interaction with the polar solvent create an alkaline environment, which attacks the fluorinated polymer backbone, inducing dehydrofluorination of the fluorinated polymer segments. This dehydrofluorination reaction forms numerous unsaturated carbon bonds, resulting in discoloration and even gelation. This invention utilizes the H₂CO₃ / HCO₃ combination by introducing bicarbonate. - The buffer pair weakens the strongly alkaline environment of garnet, alleviates the attack of alkaline substances on the fluorinated polymer chain segments, thereby inhibiting gelation and improving the overall performance of the fluorinated polymer / garnet composite electrolyte.
[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant features:
[0018] 1. By introducing bicarbonate to improve the alkaline environment of the garnet solid electrolyte, the interfacial reaction between the fluorinated polymer and the garnet solid electrolyte can be quantitatively controlled. When the mass ratio of garnet solid electrolyte to ammonium bicarbonate is 1:0.15, the ionic conductivity of the composite solid electrolyte at room temperature (25°C) is increased to 10. -3 S cm -1 ;
[0019] 2. The solid-state battery assembled with the prepared composite solid-state electrolyte exhibits excellent long-cycle performance, with a capacity retention of over 90% after 250 cycles at 1C rate. Attached Figure Description
[0020] Figure 1 This is a diagram showing the effect of different amounts of bicarbonate added to inhibit interfacial reactions according to the present invention;
[0021] Figure 2 This is a graph showing the change in ionic conductivity of the composite solid electrolyte as a function of temperature in Example 1 of the present invention.
[0022] Figure 3 This is a scanning electron microscope image of the composite solid electrolyte of Embodiment 1 of the present invention;
[0023] Figure 4 This is a comparison chart of the rate performance of solid-state batteries using composite solid-state electrolytes from Embodiment 1 and Comparative Example 3 of the present invention.
[0024] Figure 5 This is the cycling curve of the solid-state battery assembled with the composite solid-state electrolyte of Embodiment 1 of the present invention at a 1C rate. Detailed Implementation
[0025] In the following embodiments, the average particle size of the garnet solid electrolyte is 5–8 μm. Poly(vinylidene fluoride-co-hexafluoropropylene), McLean, Mw–455000.
[0026] Example 1
[0027] A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions includes the following steps:
[0028] (1) Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide solvent at a mass ratio of 0.4:0.6. The fluorinated polymer is PVDF-HFP and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LITFSI). Stir at 50°C to obtain solution A.
[0029] (2) According to the garnet solid electrolyte Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) and fluorinated polymer were mixed in a mass ratio of 1:0.4. Garnet solid electrolyte was ball-milled, and bicarbonate was added in a mass ratio of 1:0.15 between garnet solid electrolyte and bicarbonate. The bicarbonate was NH4HCO3, and solution B was obtained.
[0030] (3) Add solution B to solution A and stir at room temperature and 500 r / min for 12 h to obtain a uniform electrolyte slurry;
[0031] (4) Use a pipette to transfer the product obtained in step (3) into a glass culture dish, dry it in a forced-air drying oven at 50°C for 2 hours, and then transfer it to a vacuum oven to dry it at 120°C for 16 hours to remove the solvent and obtain a composite solid electrolyte membrane with a thickness of 200 μm.
[0032] Example 2
[0033] A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions includes the following steps:
[0034] (1) Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide solvent at a mass ratio of 0.4:0.6. The fluorinated polymer is PVDF-HFP and the lithium salt is LITFSI. Stir at 50°C to obtain solution A.
[0035] (2) According to the garnet solid electrolyte Li 6.4 La3Zr 1.4 Ta0.6 O 12 (LLZTO) and fluorinated polymer were mixed in a mass ratio of 1:0.4. Garnet solid electrolyte was ball-milled, and bicarbonate was added at a mass ratio of 1:0.2 between garnet solid electrolyte and bicarbonate. The bicarbonate was NH4HCO3, resulting in solution B.
[0036] (3) Add solution B to solution A and stir at room temperature and 500 r / min for 12 h to obtain a uniform electrolyte slurry;
[0037] (4) Use a pipette to transfer the product obtained in step (3) into a glass culture dish, dry it in a forced-air drying oven at 50°C for 2 hours, and then transfer it to a vacuum oven to dry it at 120°C for 16 hours to remove the solvent and obtain a composite solid electrolyte membrane with a thickness of 200 μm.
[0038] Example 3
[0039] A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions includes the following steps:
[0040] (1) Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide solvent at a mass ratio of 0.4:0.6. The fluorinated polymer is PVDF-HFP and the lithium salt is LITFSI. Stir at 50°C to obtain solution A.
[0041] (2) According to the garnet solid electrolyte Li 6.4 La3Zr 1.4 Ta 0.6 O 12 (LLZTO) and fluorinated polymer were mixed in a mass ratio of 1:0.4. Garnet solid electrolyte was ball-milled, and bicarbonate was added in a mass ratio of 1:0.25 between garnet solid electrolyte and bicarbonate. The bicarbonate was NH4HCO3, and solution B was obtained.
[0042] (3) Add solution B to solution A and stir at room temperature and 500 r / min for 12 h to obtain a uniform electrolyte slurry;
[0043] (4) Use a pipette to transfer the product obtained in step (3) into a glass culture dish, dry it in a forced-air drying oven at 50°C for 2 hours, and then transfer it to a vacuum oven to dry it at 120°C for 16 hours to remove the solvent and obtain a composite solid electrolyte membrane with a thickness of 200 μm.
[0044] Comparative Example 1
[0045] A method for preparing a solid electrolyte membrane includes the following steps:
[0046] (1) Dissolve PVDF–HFP and LITFSI in DMF solvent at a mass ratio of 0.4:0.6 and stir at 50°C to obtain solution A;
[0047] (2) Ball mill LLZTO with a mass ratio of LLZTO to PVDF–HFP of 1:0.4 without adding bicarbonate to obtain solution B;
[0048] (3) When solution B is added to solution A and stirred at 500 r / min at room temperature, an interfacial gelation reaction occurs, and a solid electrolyte membrane cannot be prepared.
[0049] Comparative Example 2
[0050] A method for preparing a solid electrolyte membrane includes the following steps:
[0051] (1) Dissolve PVDF–HFP and LITFSI in DMF solvent at a mass ratio of 0.4:0.6 and stir at 50°C to obtain solution A;
[0052] (2) Ball mill LLZTO at a mass ratio of LLZTO to PVDF–HFP of 1:0.4, and add bicarbonate at a mass ratio of LLZTO to bicarbonate of 1:0.1 to obtain solution B;
[0053] (3) When solution B is added to solution A and stirred at 500 r / min at room temperature, interfacial gelation reaction still occurs, and a solid electrolyte membrane cannot be prepared.
[0054] Comparative Example 3
[0055] A method for preparing a solid polymer electrolyte membrane includes the following steps:
[0056] PVDF–HFP and LITFSI were dissolved in DMF solvent at a mass ratio of 0.4:0.6 and stirred at 50°C to obtain a homogeneous solution. The solution was then placed in a forced-air drying oven and dried at 50°C for 2 hours. After that, it was transferred to a vacuum oven and dried at 120°C for 16 hours to remove the solvent, thus obtaining a solid polymer electrolyte membrane.
[0057] Relevant tests for composite solid electrolytes:
[0058] The solid electrolyte membranes prepared in Examples 1-3 and Comparative Examples 1-3 were assembled with lithium iron phosphate cathodes and lithium metal anodes to form solid-state batteries. Impedance analysis of the battery cycle performance was performed using an electrochemical workstation. The calculated ionic conductivity data of each solid electrolyte at room temperature are shown in Table 1 below.
[0059] Table 1 Ionic conductivity of solid electrolyte membranes
[0060] <![CDATA[Polymer: Lithium salt: LLZTO: NH4HCO3]]> Ionic conductivity σ (S / cm) Comparative Example 1 0.4:0.6:1:0.00 \ Comparative Example 2 0.4:0.6:1:0.10 \ Example 1 0.4:0.6:1:0.15 <![CDATA[1.19×10 -3 ]]> Example 2 0.4:0.6:1:0.20 <![CDATA[0.75×10 -3 ]]> Example 3 0.4:0.6:1:0.25 <![CDATA[0.62×10 -3 ]]> Comparative Example 3 0.4:0.6:0:0.00 <![CDATA[0.48×10 -3 ]]>
[0061] Through Table 1 and Figure 1 It is known that when the mass ratio of NH4HCO3 to LLZTO is less than 0.15, a composite solid electrolyte membrane cannot be successfully prepared. With the addition of NH4HCO3, the mass ratio to LLZTO reaches 0.15, effectively inhibiting interfacial gelation and successfully preparing the composite solid electrolyte. At a mass ratio of LLZTO to NH4HCO3 of 1:0.15, its ionic conductivity reaches 1.19 mS / cm. -1 When the content of NH4HCO3 is further increased, the ionic conductivity and mechanical properties of the composite solid electrolyte membrane both decrease.
[0062] like Figure 2 As can be seen, the composite solid electrolyte membrane obtained in Example 1 has an ionic conductivity of 1.19 mS / cm at room temperature. -1 With an activation energy of only 0.21 eV, it indicates that its ionic conductivity is less sensitive to temperature and has the potential to be used over a wide temperature range.
[0063] Figure 3 The image shown is a scanning electron microscope (SEM) image of the composite solid electrolyte membrane obtained in Example 1. Figure 1 As can be seen, the granular LLZTO is uniformly dispersed in the polymer matrix, and its overall morphology is relatively dense.
[0064] The solid electrolyte membranes prepared in Example 1 and Comparative Example 3 were respectively assembled into solid-state batteries with lithium iron phosphate cathode and lithium metal anode, and their rate performance was tested at 25°C. The results are as follows. Figure 4 As shown, when the LLZTO:NH4HCO3 ratio is 1:0.15, the composite solid electrolyte has a higher capacity than the solid polymer electrolyte at all rate functions, and still maintains a capacity of 81.9 mAh g at 3C rate. -1 The specific capacity of the battery is significantly higher than that of the battery assembled with a solid polymer electrolyte membrane, while the specific capacity of the battery at 3C rate is only 48.1 mAh g. -1 Specific capacity.
[0065] Figure 5 The cycling curve of the battery assembled in Example 1 at 25°C and 1C is shown. Figure 5 It can be seen that the specific capacity is 134mAh g. -1 Furthermore, the capacity retention rate reached 90.8% after 250 cycles, indicating that after appropriately suppressing the interfacial side reactions between the fluorinated polymer and garnet electrolyte, the composite solid electrolyte membrane exhibits superior overall performance compared to the solid polymer electrolyte membrane.
[0066] Example 4
[0067] A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions includes the following steps:
[0068] (1) Dissolve fluoropolymer and lithium salt in N,N-dimethylformamide solvent at a mass ratio of 0.4:0.6. The fluoropolymer is PVDF and the lithium salt is lithium bis(trifluoromethanesulfonyl)imide. Stir at 45°C to obtain solution A.
[0069] (2) According to the garnet solid electrolyte Li 6.4 Ga 0.2 La3Zr2O 12 (LGLZO) and fluorinated polymer were mixed in a mass ratio of 1:0.4. Garnet solid electrolyte was ball-milled, and sodium bicarbonate was added at a mass ratio of 1:0.15 to garnet solid electrolyte. Solution B was obtained.
[0070] (3) Add solution B to solution A and stir at room temperature and 450 r / min for 16 h to obtain a uniform electrolyte slurry;
[0071] (4) Use a pipette to transfer the product obtained in step (3) into a glass culture dish, dry it in a forced-air drying oven at 45°C for 4 hours, and then transfer it to a vacuum oven to dry it at 110°C for 20 hours to remove the solvent and obtain a composite solid electrolyte membrane with a thickness of 100 μm.
[0072] Example 5
[0073] A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions includes the following steps:
[0074] (1) Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide solvent at a mass ratio of 0.4:0.6. The fluorinated polymer is poly(vinylidene fluoride-co-trifluoroethylene), and the lithium salt is lithium bis(trifluoromethanesulfonylimide). Stir at 55°C until homogeneous to obtain solution A.
[0075] (2) According to the garnet solid electrolyte Li 6.28 La3Zr2Al 0.24 O 12 (LLZAO) and fluorinated polymer were mixed in a mass ratio of 1:0.4. Garnet solid electrolyte was ball-milled, and potassium bicarbonate was added at a mass ratio of 1:0.15 to 0.20 to garnet solid electrolyte and bicarbonate to obtain solution B.
[0076] (3) Add solution B to solution A and stir at room temperature and 480 r / min for 14 h to obtain a uniform electrolyte slurry;
[0077] (4) Use a pipette to transfer the product obtained in step (3) into a glass culture dish, dry it in a forced-air drying oven at 48°C for 3 hours, and then transfer it to a vacuum oven to dry it at 115°C for 18 hours to remove the solvent and obtain a composite solid electrolyte membrane with a thickness of 300 μm.
Claims
1. A method for preparing a composite solid electrolyte membrane that inhibits interfacial reactions, characterized in that, Includes the following steps: Step 1: Dissolve the fluorinated polymer and lithium salt in N,N-dimethylformamide and stir until homogeneous at 45-55°C to obtain solution A; the fluorinated polymer is poly(vinylidene fluoride-) co -hexafluoropropylene), polyvinylidene fluoride or poly(vinylidene fluoride- co -trifluoroethylene); the lithium salt is lithium bis(trifluoromethanesulfonylimide); Step 2: Ball mill the garnet solid electrolyte to obtain a uniform dispersion, then add bicarbonate and stir until uniform to obtain solution B. The bicarbonate is one or more of ammonium bicarbonate, sodium bicarbonate, and potassium bicarbonate. Step 3: Add solution B to solution A and stir to obtain a uniform electrolyte slurry; the mass ratio of fluorinated polymer, lithium salt, garnet solid electrolyte, and bicarbonate is 0.4 : 0.6 : 1 : 0.15~0.
25. Step four: Transfer the material obtained in step three to a glass petri dish, dry it first at 45~50℃ with forced air, and then dry it under vacuum at 110~120℃ to obtain a composite solid electrolyte membrane.
2. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: In step two, the garnet solid electrolyte is Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.4 Ga 0.2 La3Zr2O 12 Or Li 6.28 La3Zr2Al 0.24 O 12 .
3. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: In step two, the average particle size of the garnet solid electrolyte is 5~8 μm.
4. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: The bicarbonate is ammonium bicarbonate.
5. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: In step three, the stirring speed is 450~500 r / min, and the time is 12~16 h.
6. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: In step four, the drying time is 2-4 hours by forced air drying and 16-20 hours by vacuum drying.
7. The method for preparing a composite solid electrolyte membrane for inhibiting interfacial reactions according to claim 1, characterized in that: The thickness of the composite solid electrolyte membrane is 100~300 μm.