A llzto / pvdf composite solid electrolyte membrane modified by a surface organic layer, and a preparation method and application thereof

Abstract

The application discloses a kind of LLZTO / PVDF composite solid electrolyte membrane modified by surface organic layer and preparation method and application thereof, the LLZTO / PVDF composite solid electrolyte membrane is made of LLZTO, PVDF and lithium salt, the lithium salt includes LiTFSI and LiDFOB;The surface of the LLZTO is formed with organic modification layer;The organic modification layer at least includes the passivation layer formed by the reaction of GA and LLZTO surface residual basic component, and the polyether type flexible conductive layer formed by DOL at interface.This application uses LLZTO as inorganic filler, PVDF as polymer matrix, uses LiTFSI and LiDFOB as lithium salt, by introducing GA and DOL to the surface of LLZTO in situ organic layer modification, to inhibit its basicity induced decomposition to PVDF, improve inorganic / organic interface compatibility, and improve the mechanical properties and ionic conduction performance of composite membrane.

Description

Technical Field

[0001] This invention belongs to the field of solid-state battery technology and relates to a polyvinylidene fluoride (PVDF)-based composite solid-state electrolyte membrane and its preparation method. Specifically, it relates to a composite solid-state electrolyte membrane prepared by pretreatment with glutaric anhydride (GA) combined with in-situ polymerization of 1,3-dioxolane (DOL) to modify LLZTO filler, thereby inhibiting PVDF dehydrofluorination, improving interfacial compatibility and enhancing mechanical properties, as well as its preparation method and application. Background Technology

[0002] PVDF-based solid electrolyte membranes have potential applications in all-solid-state lithium batteries due to their good chemical stability and certain mechanical properties. However, when LLZTO ceramic filler is combined with PVDF in polar solvents such as DMF to form a membrane, residual lithium components such as Li2CO3 and LiOH are easily generated on the LLZTO surface. Furthermore, due to the Lewis acid-base properties of the surface, the surface becomes locally alkaline, which in turn induces the dehydrofluorination reaction of PVDF.

[0003] Specifically, the strongly basic sites on the LLZTO surface attack the -CH2-CF2- structure in the PVDF molecular chain, inducing the removal of HF and the formation of carbon-carbon double bonds (-C=C-). This leads to PVDF molecular chain breakage, increased conjugated structures, and the slurry may rapidly change from white to yellow or even black, resulting in significantly increased brittleness after film formation. These interfacial side reactions not only reduce the mechanical strength of the composite film but also cause deterioration of interfacial stability, localized agglomeration, and discontinuity in ion transport channels. Existing physical mixing methods are insufficient to eliminate these interfacial side reactions; therefore, chemical passivation and interfacial control based on the LLZTO surface are necessary.

[0004] In the prior art, if LLZTO is not surface-treated, the LLZTO dispersion in PVDF-based electrolyte membranes is poor and the interfacial compatibility is limited, making it difficult to form a stable composite electrolyte structure.

[0005] Therefore, there is an urgent need for a composite solid electrolyte membrane preparation scheme that can simultaneously achieve LLZTO surface passivation, enhance compatibility with PVDF, and improve the overall performance of the composite membrane. Summary of the Invention

[0006] This invention provides an LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer, its preparation method, and its application. The method uses LLZTO as an inorganic filler, PVDF as a polymer matrix, and LiTFSI and LiDFOB as lithium salts. By introducing GA and DOL into the NMP system to modify the LLZTO surface with an in-situ organic layer, the alkaline-induced decomposition of PVDF is inhibited, the inorganic / organic interface compatibility is improved, and the mechanical and ion conduction properties of the composite membrane are enhanced.

[0007] The objective of this invention is achieved through the following technical solution:

[0008] An LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer is made of LLZTO inorganic filler, PVDF polymer matrix and lithium salt, wherein:

[0009] The lithium salts include LiTFSI and LiDFOB;

[0010] The LLZTO is Li 6.4~6.75 La3Zr 1.4~1.75 Ta 0.25~0.6 O 12 The particle size is 0.1~5 μm;

[0011] An organic modification layer is formed on the surface of the LLZTO;

[0012] The organic modification layer includes at least a passivation layer formed by the reaction of GA and residual alkaline components on the LLZTO surface, and a polyether-type flexible conductive layer formed by DOL at the interface.

[0013] The LLZTO accounts for 5-20% of the PVDF mass, the mass ratio of GA to LLZTO is 0.3:1 to 3:1, the mass ratio of DOL to LLZTO is 0.1:1 to 2:1, the mass ratio of LiTFSI to PVDF is 0.3:1 to 1.0:1, and the mass ratio of LiDFOB to LiTFSI is 0.05:1 to 0.3:1.

[0014] In this invention, the organic modification layer is used to isolate the alkaline sites on the LLZTO surface from direct contact with the PVDF matrix, thereby inhibiting the dehydrofluorination reaction of PVDF. Specifically, GA can preferentially neutralize the alkaline lithium residue on the LLZTO surface and form a surface passivation layer, while DOL can further form a flexible conductive layer rich in ether oxygen in the interfacial environment, thereby isolating the unfavorable contact between LLZTO and PVDF, reducing the tendency for dehydrofluorination, improving slurry stability, and improving the toughness and electrochemical performance of the final film.

[0015] A method for preparing the above-mentioned LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer includes the following steps:

[0016] Step 1: Add LLZTO to an anhydrous organic solvent and disperse it by ultrasonication to obtain a uniform LLZTO suspension, wherein: the anhydrous organic solvent is one or more of DMF, NMP, DMAc and THF;

[0017] Step 2: Add GA and DOL to the LLZTO suspension, heat and stir, so that GA reacts preferentially with the alkaline components on the LLZTO surface, and DOL undergoes preliminary activation or in-situ modification in the interfacial environment, thereby obtaining an LLZTO dispersion system with a modified organic layer on the surface.

[0018] Step 3: Add LiTFSI and LiDFOB to the system obtained in Step 2, and continue heating and stirring to fully dissolve the lithium salt and further stabilize the interfacial ionic environment in the system;

[0019] Step 4: Add PVDF to the system obtained in Step 3 and continue stirring to fully dissolve the PVDF and form a homogeneous composite slurry with the modified LLZTO, lithium salt and organic modification layer;

[0020] Step 5: Coat the composite slurry obtained in Step 4 onto the substrate, and then dry it to remove the solvent, thereby obtaining an LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer. The drying process can be carried out under vacuum or inert atmosphere at a temperature of 60-80°C for 12-48 hours. The LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer can be used in all-solid-state lithium batteries, especially suitable for lithium metal anode systems and high-energy-density cathode systems, to improve interface stability and enhance cycle performance.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. GA effectively passivates the Li2CO3 alkalinity on the LLZTO surface, and the DOL polymer layer provides a flexible buffer, improving the interfacial compatibility between LLZTO and PVDF.

[0023] 2. The organic layer is rich in ether oxygen, which promotes Li + Conduction reduces interface impedance.

[0024] 3. The process is mild and does not require high temperatures, making it suitable for large-scale production.

[0025] 4. This invention passivates the alkaline residual lithium layer on the LLZTO surface with glutaric anhydride and then uses DOL in-situ polymerization to form a polyether buffer layer. This method effectively inhibits the LLZTO-induced dehydrofluorination reaction of PVDF, solving the industry problems of slurry discoloration and membrane brittleness.

[0026] 5. Experiments have shown that the modified composite membrane has an increased ionic conductivity of 0.5 mS / cm and a tensile strength of 12 MPa, which significantly improves the interface stability and cycle life of the all-solid-state lithium battery. Attached Figure Description

[0027] Figure 1 Schematic diagrams of the appearance of the LLZTO-modified solution before and after mixing with PVDF;

[0028] Figure 2 Comparison diagrams of composite solid electrolyte membranes with different components, including PVDF+lithium salt membrane, PVDF+LLZTO+lithium salt membrane and PVDF+modified LLZTO+lithium salt membrane;

[0029] Figure 3 The tensile strength test results are for the unmodified LLZTO composite film.

[0030] Figure 4 The tensile strength test results are for the modified LLZTO composite film.

[0031] Figure 5 The battery cycle performance curves are shown for the LLZTO / PVDF composite solid electrolyte membrane before and after modification. Detailed Implementation

[0032] The technical solution of the present invention will be further described below with reference to the embodiments, but it is not limited thereto. Any modifications or equivalent substitutions to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention should be covered within the protection scope of the present invention.

[0033] Example 1

[0034] 0.5 g of LLZTO powder was weighed and added to 40 mL of anhydrous DMF. The mixture was ultrasonically dispersed for 15 min to ensure uniform suspension of LLZTO in the solvent. Then, 0.1 g of glutaric anhydride and 0.4 g of DOL were added to the dispersion system, and the mixture was stirred at 70 °C for 30 min. This process allowed the glutaric anhydride to preferentially passivate residual alkaline sites on the LLZTO surface and enabled the DOL to undergo initial activation and organic layer construction in the interfacial environment. Next, 3.3 g of LiTFSI and 0.3 g of LiDFOB were added, and the mixture was stirred at 70 °C for another 30 min to ensure complete dissolution of the lithium salt and a stable ionic environment. Finally, 5 g of PVDF was added, and the mixture was stirred continuously for 12 h until the PVDF was completely dissolved and a homogeneous and stable composite slurry was formed. The resulting composite slurry was coated onto a substrate and vacuum dried at 80 °C for 12 h to obtain an LLZTO / PVDF composite solid electrolyte membrane with an organic surface layer.

[0035] Compared with the unmodified LLZTO system, the composite slurry prepared in this embodiment has a more stable color and does not show obvious yellowing or blackening, indicating that GA and DOL have a good passivation effect on the alkaline sites on the LLZTO surface.

[0036] Example 2

[0037] Weigh 0.5 g of LLZTO powder and add it to 40 mL of anhydrous DMF. Disperse the mixture ultrasonically for 15 min. Then add 0.08 g of glutaric anhydride and 0.3 g of DOL to the system and stir at 70 °C for 30 min to form an organic modification layer on the LLZTO surface. Next, add 3.3 g of LiTFSI and 0.3 g of LiDFOB and continue stirring for 30 min to ensure that the lithium salt is fully dissolved. Then add 5 g of PVDF and continue stirring for 12 h until the PVDF is completely dissolved. Coat the resulting slurry into a film and dry it under vacuum at 80 °C for 12 h to obtain a composite solid electrolyte membrane.

[0038] The membrane prepared in this embodiment has good uniformity, indicating that appropriate treatment with GA and DOL can effectively improve the dispersibility and interfacial compatibility between LLZTO and PVDF.

[0039] Example 3

[0040] Weigh 0.5 g LLZTO powder and add it to 40 mL anhydrous DMF, then ultrasonically disperse for 15 min. Next, add 0.05 g glutaric anhydride and 0.2 g DOL to the system and stir at 70 °C for 30 min. Then add 3.3 g LiTFSI and 0.3 g LiDFOB, and continue stirring for 30 min. Afterward, add 5 g PVDF and continue stirring for 12 h until completely dissolved. Coat the slurry into a film and vacuum dry at 80 °C for 12 h to obtain a composite solid electrolyte membrane.

[0041] This example was used to investigate the effect of lower GA / DOL addition on membrane stability. The results showed that the interface modification effect was weaker than that of Example 1, but still better than the unmodified LLZTO system.

[0042] Comparative Example 1

[0043] Weigh 0.5 g of LLZTO powder and add it directly to 40 mL of anhydrous DMF. Disperse the powder by ultrasonication for 15 min without adding GA or DOL. Then add 3.3 g of LiTFSI and 0.3 g of LiDFOB and stir for 30 min. Add 5 g of PVDF and continue stirring for 12 h until the powder is completely dissolved. After forming a film by coating, dry the film under vacuum at 80 °C for 12 h to obtain an unmodified LLZTO / PVDF composite solid electrolyte membrane.

[0044] This comparative example is mainly used to compare with Examples 1-3 to verify the effects of GA and DOL on LLZTO surface modification and film performance improvement.

[0045] Figure 1The figures show the appearance of the LLZTO-modified solution mixed with PVDF before and after modification. As can be seen from the figures, the unmodified LLZTO will trigger the dehydrofluorination reaction of PVDF, causing the solution to turn yellow; while the modified solution is a normal milky white, indicating that the surface modification has the effect of inhibiting side reactions.

[0046] Figure 2 The images show a comparison of solid electrolyte membranes with different components. The color differences of the membranes can further verify the effectiveness of the modification.

[0047] Figure 3 and Figure 4 The tensile strength test results are shown for unmodified and modified LLZTO composite films, respectively. The comparison shows that LLZTO surface modification helps to improve the tensile strength of the composite film.

[0048] Figure 5 The battery cycle performance curves of the LLZTO / PVDF composite solid electrolyte membrane before and after modification are shown. The results indicate that the modification treatment significantly improves the battery cycle performance.

Claims

1. A LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer, characterized in that... The LLZTO / PVDF composite solid electrolyte membrane is made of LLZTO inorganic filler, PVDF polymer matrix and lithium salt, wherein: An organic modification layer is formed on the surface of the LLZTO; The organic modification layer includes at least a passivation layer formed by the reaction of GA and residual alkaline components on the LLZTO surface, and a polyether-type flexible conductive layer formed by DOL at the interface.

2. The LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 1, characterized in that... The LLZTO is Li 6.4~6.75 La3Zr 1.4~1.75 Ta 0.25~0.6 O 12 .

3. The LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 1 or 2, characterized in that... The particle size of the LLZTO is 0.1~5 μm.

4. The LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 1, characterized in that... The lithium salt includes LiTFSI and LiDFOB; LLZTO accounts for 5-20% of the mass of PVDF, the mass ratio of GA to LLZTO is 0.3:1 to 3:1, the mass ratio of DOL to LLZTO is 0.1:1 to 2:1, the mass ratio of LiTFSI to PVDF is 0.3:1 to 1.0:1, and the mass ratio of LiDFOB to LiTFSI is 0.05:1 to 0.3:

1.

5. A method for preparing an LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer as described in any one of claims 1-4, characterized in that... The method includes the following steps: Step 1: Add LLZTO to an anhydrous organic solvent and disperse it using ultrasonication to obtain a uniform LLZTO suspension; Step 2: Add GA and DOL to the LLZTO suspension, heat and stir, so that GA reacts preferentially with the alkaline components on the LLZTO surface, and DOL undergoes preliminary activation or in-situ modification in the interfacial environment, thereby obtaining an LLZTO dispersion system with a modified organic layer on the surface. Step 3: Add LiTFSI and LiDFOB to the system obtained in Step 2, and continue heating and stirring to fully dissolve the lithium salt and further stabilize the interfacial ionic environment in the system; Step 4: Add PVDF to the system obtained in Step 3 and continue stirring to fully dissolve the PVDF and form a homogeneous composite slurry with the modified LLZTO, lithium salt and organic modification layer; Step 5: Coat the composite slurry obtained in Step 4 onto the substrate, and then dry it to remove the solvent, to obtain an LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer.

6. The method for preparing the LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 5, characterized in that... The anhydrous organic solvent is one or more of DMF, NMP, DMAc, and THF.

7. The method for preparing the LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 5, characterized in that... The drying process is carried out under a vacuum or inert atmosphere.

8. The method for preparing an LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer according to claim 5 or 7, characterized in that... The drying temperature is 60–80°C, and the drying time is 12–48 h.

9. The application of the LLZTO / PVDF composite solid electrolyte membrane modified with a surface organic layer as described in any one of claims 1-4 in an all-solid-state lithium battery.

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