Method for improving interfacial compatibility of filler and polymer matrix in polyvinylidene fluoride-based composite solid electrolyte

Abstract

The invention discloses a method for improving interfacial compatibility of filler in polyvinylidene fluoride-based composite solid electrolyte and a polymer matrix, which comprises the following steps: mixing isocyanate fatty ester with a siloxane coupling agent APTES, and carrying out hydrolysis reaction in a weakly acidic solvent to obtain an acylation modified APTES organic solution; the preparation method comprises the following steps: adding inorganic filler LLZTO particles into an acylation-modified APTES organic solution, carrying out surface modification, separating, washing and drying to obtain surface-modified LLZTO particles; adding a lithium salt, polyvinylidene fluoride and the surface-modified LLZTO particles into an organic solvent, and uniformly stirring and dispersing to obtain composite electrolyte slurry; and carrying out casting molding on the composite electrolyte slurry, and carrying out drying treatment to obtain the PVDF-based composite solid electrolyte membrane. The preparation method is simple, and the composite solid electrolyte with high ionic conductivity can be prepared through a solution pouring method.

Description

A method for improving the interfacial compatibility between polyvinylidene fluoride composite solid electrolyte filler and polymer matrix Technical Field

[0001] This invention belongs to the field of composite solid electrolyte technology, specifically relating to a method for optimizing the interfacial compatibility between the filler and the polymer matrix in a polyvinylidene fluoride composite solid electrolyte. Background Technology

[0002] With the introduction of the dual-carbon strategy, new energy sources have ushered in development opportunities while also facing new challenges. The expanding market for electric vehicles, electronic products, and storage devices for intermittent renewable energy sources places higher demands on the energy density, cycle life, and safety of energy storage devices. However, the most widely used lithium-ion batteries currently suffer from poor safety performance due to the presence of flammable organic electrolytes, which can easily lead to fires or explosions. Furthermore, the energy density of existing systems is nearing its theoretical limit, still unable to meet the demands for extended range in electric vehicles. High mechanical strength and non-flammability allow solid-state electrolytes to suppress lithium dendrite growth at its source, mitigating the risk of battery thermal runaway and achieving intrinsic safety. Meanwhile, lithium metal possesses a high theoretical capacity (3860 mAh g−1), low density (0.59 g cm−3), and the most negative electrode potential (-3.040 V vs. standard hydrogen electrode), making it an ideal anode material for achieving high-energy-density batteries. Therefore, all-solid-state lithium metal batteries (ASSLMB), composed of a high-capacity transition metal-based cathode, a lithium metal anode, and a solid electrolyte (SE), are expected to simultaneously solve the two core bottlenecks of energy density and safety, representing the hope for next-generation batteries.

[0003] Currently, solid-state electrolytes (SPEs) can be broadly classified into three categories: inorganic ceramic electrolytes (ICEs), solid polymer electrolytes (SPEs), and ceramic-polymer composite electrolytes (CPEs). ICEs possess high ionic conductivity and excellent mechanical strength; however, they are unstable in air, and the rigid contact between particles leads to poor interfacial contact between the electrode and the electrolyte. Conversely, SPEs exhibit good flexibility and interfacial compatibility with the electrode, but show poor ionic conductivity (<10−5 S cm−1) and low lithium-ion transference number (<0.5) at room temperature. Therefore, CPEs, combining the advantages of ICEs and SPEs, exhibit excellent ionic conductivity, flexibility, and good interfacial contact. However, the heterogeneity of different materials can cause interfacial incompatibility and high interfacial lithium-ion transport barriers. When the loading of inorganic fillers is high, particles naturally tend to aggregate, forming discontinuous lithium-ion conduction pathways in the polymer matrix, resulting in higher energy barriers that lithium-ion migration must overcome. Therefore, designing and constructing an intermediate layer that can stabilize the interface between the inorganic filler and the polymer matrix remains a key requirement for improving the performance of SSLMBs. Summary of the Invention

[0004] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of the invention, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0005] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0006] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the interfacial compatibility between the filler in a polyvinylidene fluoride composite solid electrolyte and the polymer matrix.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: It includes mixing isocyanate fatty esters with siloxane coupling agent APTES, and hydrolyzing them in a weakly acidic solvent to obtain an acylated APTES organic solution; adding inorganic filler LLZTO particles to the acylated APTES organic solution for surface modification, followed by separation, washing, and drying to obtain surface-modified LLZTO particles; adding lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles to an organic solvent, stirring and dispersing them evenly to obtain a composite electrolyte slurry; and casting the composite electrolyte slurry into a mold and drying it to obtain a PVDF-based composite solid electrolyte membrane.

[0008] In a preferred embodiment of the method described in this invention, the hydrolysis reaction in a weakly acidic solvent is wherein the weakly acidic solvent is a mixture of anhydrous ethanol, deionized water, and acetic acid.

[0009] In a preferred embodiment of the method described in this invention, the hydrolysis reaction is carried out at a temperature of 60-80°C for 2-4 hours.

[0010] In a preferred embodiment of the method described in this invention, the surface modification is performed at a temperature of 50-70°C for 6-12 hours.

[0011] In a preferred embodiment of the method described in this invention, the surface-modified LLZTO particles contain 1.36 to 1.56 wt% acylated APTES.

[0012] In a preferred embodiment of the method described in this invention, the lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles are added to an organic solvent, wherein the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, bis(trifluoromethane)sulfonylimide, and lithium difluorooxalateborate.

[0013] In a preferred embodiment of the method described in this invention, the amount of surface-modified LLZTO particles added relative to polyvinylidene fluoride is 10-20 wt%.

[0014] In a preferred embodiment of the method described in this invention, the mass ratio of the lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles is 5~8:10:1~4.

[0015] In a preferred embodiment of the method described in this invention, the total solids to organic solvent in the composite electrolyte slurry have a mass-to-volume ratio of 4.8~5.5 g:100 mL.

[0016] In a preferred embodiment of the method described in this invention, the composite electrolyte slurry is cast into a mold and then dried to obtain a PVDF-based composite solid electrolyte membrane, wherein the drying includes forced-air drying and vacuum drying.

[0017] The beneficial effects of the present invention are as follows: (1) In the present invention, the siloxane coupling agent reacts with the isocyanate fatty ester to generate urea group (-NH-CO-NH-) to obtain N-APTES. N-APTES combines with the hydroxyl group (-OH) on the surface of LLZTO through silicon-oxygen bond (Si-O) to form a uniform coating layer. The urea group in N-APTES can form hydrogen bond with the polymer matrix PVDF, promote the uniform dispersion of inorganic filler in the polymer matrix and prevent agglomeration, reduce the generation of by-products, and at the same time reduce the crystallinity of PVDF, further improve the ionic conductivity of the composite solid electrolyte, and buffer and disperse the stress generated during charging and discharging, and reduce the generation and propagation of cracks.

[0018] (2) In this invention, LLZTO@N-APTES is used as an inorganic filler to form a composite solid electrolyte with PVDF. The inorganic filler improves the overall electrochemical window and mechanical properties.

[0019] (3) The preparation method of the composite solid electrolyte of the present invention is simple. The composite solid electrolyte with high ionic conductivity can be prepared by solution casting. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 is an elemental mapping image of LLZTO@N-APTES powder in Example 1 of the present invention.

[0022] Figure 2 shows HRTEM images of pure LLZTO powder (a) in Comparative Example 1 and LLZTO@N-APTES powder (b) in Example 1 of the present invention.

[0023] Figure 3 shows the XRD patterns of pure LLZTO powder in Comparative Example 1 and LLZTO@N-APTES powder in Example 1 of this invention.

[0024] Figure 4 shows the TGA images of pure LLZTO powder in Comparative Example 1 and LLZTO@N-APTES powder in Example 1 of this invention.

[0025] Figure 5 shows physical images of the pure PVDF polymer solid electrolyte membrane prepared in Comparative Example 2, the PVDF-LLZTO composite solid electrolyte membrane prepared in Comparative Example 1, and the PVDF-LLZTO@N-APTES composite solid electrolyte membrane prepared in Example 1.

[0026] Figure 6 shows the SEM images of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 of this invention.

[0027] Figure 7 shows the XRD patterns of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 of this invention. Detailed Implementation

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0029] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0030] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0031] The LLZTO particles used in this invention are tantalum-doped garnet-type solid electrolytes (Li) prepared by high-temperature solid-state sintering. 6.5 La3Zr 1.5 Ta 0.5 O 12(LLZTO), with an ionic conductivity of 3.0 × 10⁻⁶. -4 S·cm -1 Up to 5.0×10 -4 S·cm -1 .

[0032] The method for testing the ionic conductivity of the solid electrolyte membrane in this invention is as follows: A stainless steel plate|solid electrolyte|stainless steel plate button cell is assembled in a glove box filled with argon gas, and the electrochemical impedance is measured at 25°C. This invention uses a frequency range of 7 MHz to 100 mHz and a voltage amplitude of 10 mV. The ionic conductivity σ is calculated using the formula σ = L / (R·S), where σ is the ionic conductivity (mS / cm), L is the electrolyte thickness (μm), R is the electrolyte impedance (Ω), and S is the effective contact area between the electrolyte and the stainless steel plate.

[0033] Example 1 This example provides a method for improving the interfacial compatibility between the filler and the polymer matrix of polyvinylidene fluoride composite solid electrolyte, specifically: (1) Mixing isocyanate fatty ester and siloxane coupling agent APTES in a 1:1 molar ratio, and hydrolyzing them in a weakly acidic solvent at 70°C for 4 hours to obtain an acylated modified APTES organic solution (N-APTES), wherein the weakly acidic solvent is composed of anhydrous ethanol, deionized water and acetic acid in a volume ratio of 90:6:2.5; (2) Adding inorganic filler LLZTO particles to N-APTES, stirring at 70°C for 12 hours for surface modification, centrifuging, washing with anhydrous ethanol 3 times, and drying at 75°C for 12 hours to obtain surface-modified LLZTO particles (LLZTO@N-APTES), wherein the amount of N-APTES modified onto LLZTO is 1.56 wt%; (3) Lithium bis(fluorosulfonyl)imide (LiFSI) and polyvinylidene fluoride (PVDF, Arkema, Kynar) are mixed. 761, Mw = 300000, powder), LLZTO@N-APTES were added to organic solvent DMF and stirred at 23℃ for 7h to disperse evenly, to obtain composite electrolyte slurry; among which, the amount of LLZTO@N-APTES added compared to PVDF was 15 wt%, the mass ratio of LiFSI, PVDF and LLZTO@N-APTES was 267:400:60, and the ratio of total solid mass to solvent DMF volume was 727 mg:15 mL; (4) The composite electrolyte slurry was poured onto a glass culture dish mold, dried at 80℃ for 1 h, and then dried under vacuum at 120℃ for 14h to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@N-APTES) with a thickness of 130 μm.

[0034] The elemental mapping image of the LLZTO@N-APTES powder in Test Example 1 is shown in Figure 1. It can be seen that N-APTES is uniformly distributed on the surface of LLZTO. C and N signals were detected on the outer layer of LLTO@N-APTES, which is due to the modification of N-APTES coupling agent.

[0035] Comparative Example 1 This comparative example provides a method for preparing a composite solid electrolyte. The difference from Example 1 is that LLZTO is not modified with N-APTES. The other preparation methods are the same as those in Example 1. Specifically, (1) Lithium salt LiFSI, polyvinylidene fluoride (PVDF, Arkema, Kynar 761, Mw = 300000, powder) and pure LLZTO are added to DMF solvent and stirred at 23°C for 7 hours to disperse evenly to obtain a composite electrolyte slurry. The amount of pure LLZTO added is 15 wt% compared to PVDF. The mass ratio of LiFSI, PVDF and pure LLZTO is 267:400:60, and the ratio of total solid mass to DMF volume is 727:15. (2) The composite electrolyte slurry is cast onto a glass culture dish mold, dried at 80°C for 1 hour, and then dried under vacuum at 120°C for 14 hours to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO) with a thickness of 100 μm.

[0036] The HRTEM images of pure LLZTO powder (a) in Comparative Example 1 and LLZTO@N-APTES powder (b) in Example 1 were tested, and the results are shown in Figure 2. The figure shows that the pure LLZTO powder has obvious lattice fringes, verifying the existence of the LLZTO (422) and (400) crystal planes. In addition to the lattice fringes, the HRTEM image of the LLZTO@N-APTES powder clearly shows an amorphous N-APTES coating layer on the crystal surface, with a thickness of approximately 5.7 nm.

[0037] The XRD patterns of pure LLZTO powder in Comparative Example 1 and LLZTO@N-APTES powder in Example 1 are shown in Figure 3. As can be seen from Figure 3, the XRD pattern of pure LLZTO powder is consistent with the standard card for LLZTO (PDF #45-0109), proving that LLZTO is a pure cubic phase, and that coating it with a layer of N-APTES does not change the cubic crystal phase of LLZTO.

[0038] The XRD patterns of pure LLZTO powder in Comparative Example 1 and LLZTO@N-APTES powder in Example 1 are shown in Figure 3. As can be seen from the figure, the XRD pattern of pure LLZTO powder is consistent with the standard card for LLZTO (PDF #45-0109), proving that LLZTO is a pure cubic phase, and that coating it with a layer of N-APTES does not change the cubic crystal phase of LLZTO.

[0039] The TGA graphs of pure LLZTO powder in Comparative Example 1 and LLZTO@N-APTES powder in Example 1 are shown in Figure 4. Comparing the two curves in Figure 4, it can be seen that the N-APTES content in the prepared LLZTO@N-APTES particles is 1.56 wt%.

[0040] Comparative Example 2 differs from Comparative Example 1 in that pure LLZTO is not added, while the rest of the preparation methods are the same as those in Comparative Example 1, resulting in a PVDF-based solid electrolyte membrane with a thickness of 80 μm.

[0041] Figure 5 shows, from left to right, the pure PVDF polymer solid electrolyte membrane prepared in Comparative Example 2, the PVDF-LLZTO composite solid electrolyte membrane prepared in Comparative Example 1, and the PVDF-LLZTO@N-APTES composite solid electrolyte membrane prepared in Example 1.

[0042] SEM images of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 are shown in Figure 6. (a) and (d) are the pure PVDF polymer solid electrolyte membrane prepared in Comparative Example 2; (b) and (e) are the PVDF-LLZTO composite solid electrolyte membrane prepared in Comparative Example 1; and (c) and (f) are the PVDF-LLZTO@N-APTES composite solid electrolyte membrane prepared in Example 1. It can be seen that the pure PVDF membrane (Figure 6a) exhibits a typical spherulite morphology and forms large interconnected pores (Figure 6d). After adding LLZTO (Figure 6b), the spherulite structure begins to break down, the pore size decreases, but obvious LLZTO agglomeration occurs (Figure 6e). In contrast, the LLZTO@N-APTES composite membrane modified with N-APTES (Figure 6c) further refines the structure, the spherulite morphology tends to disappear, the pores are more dense, and the uniformity of filler distribution is significantly improved, greatly reducing agglomeration (Figure 6f).

[0043] The XRD patterns of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 are shown in Figure 7. Comparing the three curves in the figure, it can be seen that both PVDF-LLZTO and PVDF-LLZTO@N-APTES show characteristic peaks similar to those of the original LLZTO powder, which is consistent with the standard card of LLZTO (PDF #45-0109), proving that both membranes contain LLZTO. The characteristic peaks of the original PVDF weakened after the addition of LLZTO and LLZTO@N-APTES, which may be due to the increase in disorder and decrease in crystallinity within the PVDF after the addition of LLZTO and LLZTO@N-APTES.

[0044] The ionic conductivity of the solid electrolyte membranes prepared in Example 1 and Comparative Examples 1-2 was tested, and the results are shown in Table 1.

[0045] Table 1. Effect of filler on the ionic conductivity of solid electrolyte membranes

[0046] Comparing Example 1 and Comparative Examples 1-2 in Table 1, it can be seen that the ionic conductivity of PVDF-LLZTO and pure PVDF membranes is significantly lower than that of PVDF-LLZTO@N-APTES, indicating that the modification of LLZTO by N-APTES significantly improves the ion migration rate.

[0047] Example 2 This example provides a method for improving the interfacial compatibility between the filler and the polymer matrix of polyvinylidene fluoride composite solid electrolyte, specifically: (1) Mixing isocyanate fatty ester and siloxane coupling agent APTES in a 1:1 molar ratio, and hydrolyzing them in a weakly acidic solvent at 70°C for 4 hours to obtain an acylated modified APTES organic solution (N-APTES), wherein the weakly acidic solvent is composed of anhydrous ethanol, deionized water and acetic acid in a volume ratio of 90:6:2.5; (2) Adding inorganic filler LLZTO particles to N-APTES, stirring at 70°C for 12 hours for surface modification, centrifuging, washing with anhydrous ethanol 3 times, and drying at 75°C for 12 hours to obtain surface-modified LLZTO particles (LLZTO@N-APTES), wherein the amount of N-APTES coupled to LLZTO is 1.56 wt%; (3) Mixing lithium salt LiFSI and polyvinylidene fluoride (PVDF, Arkema, Kynar) 761, Mw = 300000, powder), LLZTO@N-APTES were added to DMF-THF co-solvent (DMF:THF volume ratio = 1:2), stirred at 24℃ for 7h to disperse evenly, and a composite electrolyte slurry was obtained; among which, the amount of LLZTO@N-APTES added to PVDF was 10 wt%, the mass ratio of LiFSI, PVDF and LLZTO@N-APTES was 200:300:30, and the ratio of total solid mass to co-solvent DMF-THF volume was 530 mg:10 mL; (4) The composite electrolyte slurry was poured onto a glass culture dish mold, dried at 55℃ for 0.5 h, and then dried under vacuum at 80℃ for 36h to remove the solvent, and a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@N-APTES) with a thickness of 83 μm was obtained.

[0048] Example 3 This example provides a method for improving the interfacial compatibility between the filler and the polymer matrix of polyvinylidene fluoride composite solid electrolyte, specifically: (1) Mixing isocyanate fatty ester and siloxane coupling agent APTES in a 1:1 molar ratio, and hydrolyzing them in a weakly acidic solvent at 70°C for 4 hours to obtain an acylated modified APTES organic solution (N-APTES), wherein the weakly acidic solvent is composed of anhydrous ethanol, deionized water and acetic acid in a volume ratio of 90:6:2.5; (2) Adding inorganic filler LLZTO particles to N-APTES, stirring at 70°C for 12 hours for surface modification, centrifuging, washing with anhydrous ethanol 3 times, and drying at 75°C for 12 hours to obtain surface-modified LLZTO particles (LLZTO@N-APTES), wherein the amount of N-APTES coupled to LLZTO is 1.56 wt%; (3) Mixing lithium salt LiFSI and polyvinylidene fluoride (PVDF, Arkema, Kynar) 761, Mw = 300000, powder), LLZTO@N-APTES were added to organic solvent DMF and stirred at 23℃ for 7h to disperse evenly, to obtain composite electrolyte slurry; among which, the amount of LLZTO@N-APTES added compared to PVDF was 20 wt%, the mass ratio of LiFSI, PVDF and LLZTO@N-APTES was 267:400:80, and the ratio of total solid mass to solvent DMF volume was 747 mg:15 mL; (4) The composite electrolyte slurry was poured onto a glass culture dish mold, dried at 80℃ for 1 h, and then dried under vacuum at 120℃ for 14h to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@N-APTES) with a thickness of 80 μm.

[0049] Example 4 This example provides a method for improving the interfacial compatibility between the filler and the polymer matrix of polyvinylidene fluoride composite solid electrolyte, specifically: (1) Mix isocyanate fatty ester and siloxane coupling agent APTES in a 1:1 molar ratio, and hydrolyze in a weakly acidic solvent at 70°C for 4 h to obtain an acylated modified APTES organic solution (N-APTES), wherein the weakly acidic solvent is composed of anhydrous ethanol, deionized water and acetic acid in a volume ratio of 90:6:2.5; (2) Add inorganic filler LLZTO particles to N-APTES, stir at 70°C for 6 h for surface modification, centrifuge, wash three times with anhydrous ethanol, and dry at 75°C for 12 h to obtain surface-modified LLZTO particles (LLZTO@N-APTES), wherein the amount of N-APTES coupled to LLZTO is 1.36 wt%; (3) Mix lithium salt LiFSI and polyvinylidene fluoride (PVDF, Arkema, Kynar 761, Mw = 300000 (powdered) LLZTO@N-APTES was added to the organic solvent DMF and stirred at 23℃ for 7h to disperse evenly, thus obtaining a composite electrolyte slurry; wherein, the amount of LLZTO@N-APTES added compared to PVDF was 15 wt%, the mass ratio of LiFSI, PVDF, and LLZTO@N-APTES was 267:400:60, and the ratio of total solid mass to solvent DMF volume was 727 mg:15 mL; the composite electrolyte slurry was poured onto a glass petri dish mold, first dried at 80℃ for 1 h by forced air, and then dried under vacuum at 120℃ for 14 h to remove the solvent, thus obtaining a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@N-APTES) with a thickness of 81 μm.

[0050] The impedance and ionic conductivity of the PVDF-based composite solid electrolyte membranes prepared in Examples 1-4 and Comparative Example 1 at 25°C were tested, and the results are shown in Table 2.

[0051] Table 2 Performance Comparison of PVDF-based Composite Solid Electrolyte Membranes

[0052] From Table 2, Examples 1-3 and Comparative Example 1, it can be seen that by changing the amount of filler LLZTO@N-APTES added to 10-20 wt%, composite solid electrolyte membranes with high ionic conductivity can be prepared. Comparing Examples 1 and 4, it can be seen that when the amount of N-APTES coupled to LLZTO is reduced to 1.36 wt%, the ion migration rate decreases slightly, but is still significantly higher than that of the unmodified PVDF-LLZTO membrane.

[0053] The difference between Comparative Example 3 and Comparative Example 1 is that only the amount of pure LLZTO added relative to PVDF was adjusted to 20 wt%, and the rest of the preparation methods were the same as those in Comparative Example 1. Specifically: (1) Lithium salt LiFSI, polyvinylidene fluoride (PVDF, Arkema, Kynar 761, Mw = 300000, powder) and pure LLZTO were added to DMF solvent and stirred at 23°C for 7 h to disperse evenly to obtain a composite electrolyte slurry; wherein, the amount of pure LLZTO added relative to PVDF was 20 wt%, the mass ratio of LiFSI, PVDF and pure LLZTO was 267:400:80, and the ratio of total solid mass to DMF volume was 747:15; (2) The composite electrolyte slurry was cast onto a glass culture dish mold, dried at 80°C for 1 h, and then dried under vacuum at 120°C for 14 h to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO) with a thickness of 170 μm.

[0054] The difference between Comparative Example 4 and Example 1 is that step (1) acylation modification of APTES was not performed. Instead, inorganic filler LLZTO particles were directly added to APTES for modification. The rest of the preparation methods were the same as in Example 1. Specifically: (1) Inorganic filler LLZTO particles were added to APTES and stirred at 70°C for 12 h for surface modification. After centrifugation, washing with anhydrous ethanol three times, and drying at 75°C for 12 h, surface-modified LLZTO particles (LLZTO@APTES) were obtained. The amount of APTES coupled to LLZTO was 1.56 wt%. (2) Lithium salt LiFSI, polyvinylidene fluoride (PVDF, Arkema, Kynar 761, Mw = 300000, powder), and LLZTO@APTES were added to organic solvent DMF and stirred at 23°C for 7 h to disperse evenly, thus obtaining a composite electrolyte slurry. The amount of LLZTO@APTES added was 15% of that added to PVDF. wt%, the mass ratio of LiFSI, PVDF, and LLZTO@APTES is 267:400:60, and the ratio of total solid mass to solvent DMF volume is 727 mg:15 mL; (3) The composite electrolyte slurry is poured onto a glass culture dish mold, dried at 80℃ for 1 h, and then dried under vacuum at 120℃ for 14 h to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@APTES) with a thickness of 90 μm.

[0055] The difference between Comparative Example 5 and Comparative Example 4 is that only the amount of LLZTO@APTES added relative to PVDF was adjusted to 20wt%. The rest of the preparation methods are the same as those of Comparative Example 1. Specifically: (1) Inorganic filler LLZTO particles were added to APTES and stirred at 70℃ for 12h for surface modification. After centrifugation, washing with anhydrous ethanol three times, and drying at 75℃ for 12h, surface-modified LLZTO particles (LLZTO@APTES) were obtained. The amount of APTES coupled to LLZTO was 1.56wt%. (2) Lithium salt LiFSI, polyvinylidene fluoride (PVDF, Arkema, Kynar 761, Mw = 300000, powder), and LLZTO@APTES were added to organic solvent DMF and stirred at 23℃ for 7h to disperse evenly to obtain composite electrolyte slurry. The amount of LLZTO@APTES added relative to PVDF was 20wt%. wt%, the mass ratio of LiFSI, PVDF, and LLZTO@APTES is 267:400:80, and the ratio of total solid mass to solvent DMF volume is 747 mg:15 mL; (3) The composite electrolyte slurry is poured onto a glass culture dish mold, dried at 80℃ for 1 h, and then dried under vacuum at 120℃ for 14 h to remove the solvent, to obtain a PVDF-based composite solid electrolyte membrane (PVDF-LLZTO@APTES) with a thickness of 90 μm.

[0056] The impedance and ionic conductivity of the PVDF-based composite solid electrolyte membranes prepared in Comparative Examples 3-5 were tested at 25℃, and the results are shown in Table 3.

[0057] Table 3 Performance Comparison of PVDF-based Composite Solid Electrolyte Membranes

[0058] Comparing Comparative Examples 1 and 3 in Table 3, it can be seen that increasing the amount of LLZTO compared to PVDF actually reduces the ionic conductivity. Comparing Example 1 and Comparative Examples 4-5, it can be seen that directly adding inorganic filler LLZTO particles to APTES for modification cannot significantly improve the membrane ionic conductivity. Even increasing the amount of LLZTO@APTES cannot achieve the effect of Example 1. Only by modifying LLZTO particles with acylated APTES can the ionic conductivity be effectively improved.

[0059] In summary, the LLZTO active filler used in this invention, modified with an acylated siloxane coupling agent, has the following advantages: First, the modified N-APTES with an amphiphilic structure can act as a bridge to promote lithium-ion transport at the polymer-filler interface, reducing the energy barrier that needs to be overcome for interfacial ion migration. Second, it can reduce the crystallinity of PVDF, change its spherulite morphology, reduce pore size, and make the composite solid electrolyte membrane more compact. Third, it can protect LLZTO from direct contact with humid air, reducing the formation of byproducts such as LiOH and Li2CO3. Fourth, it prevents LLZTO from directly contacting PVDF, alleviating the side reaction of defluorination of PVDF induced by the alkaline atmosphere on the LLZTO surface. Fifth, it can form a modulus gradient transition layer, alleviating the huge modulus difference between the hard LLZTO and the relatively flexible PVDF, buffering and dispersing the stress generated during charging and discharging, and reducing the generation and propagation of cracks.

[0060] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for improving the interfacial compatibility between the filler in a polyvinylidene fluoride composite solid electrolyte and the polymer matrix, characterized in that: The process includes: mixing isocyanate fatty esters with siloxane coupling agent APTES and hydrolyzing them in a weakly acidic solvent to obtain an acylated APTES organic solution; adding inorganic filler LLZTO particles to the acylated APTES organic solution for surface modification, followed by separation, washing, and drying to obtain surface-modified LLZTO particles; adding lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles to an organic solvent and stirring to disperse them evenly to obtain a composite electrolyte slurry; and casting the composite electrolyte slurry into a mold and drying it to obtain a PVDF-based composite solid electrolyte membrane.

2. The method as described in claim 1, characterized in that: The hydrolysis reaction is carried out in a weakly acidic solvent, wherein the weakly acidic solvent is a mixture of anhydrous ethanol, deionized water, and acetic acid.

3. The method as described in claim 2, characterized in that: The hydrolysis reaction is carried out at a temperature of 60-80℃ for 2-4 hours.

4. The method as described in claim 1, characterized in that: The surface modification is performed at a temperature of 50-70°C for 6-12 hours.

5. The method as described in claim 1, characterized in that: The surface-modified LLZTO particles, wherein the amount of acylated APTES modified onto the LLZTO particles is 1.36~1.56 wt%.

6. The method as described in claim 1, characterized in that: The process involves adding lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles to an organic solvent. The lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, bis(trifluoromethane)sulfonylimide, and lithium difluorooxalate borate.

7. The method as described in claim 6, characterized in that: The amount of surface-modified LLZTO particles added is 10-20 wt% compared to polyvinylidene fluoride.

8. The method as described in claim 6, characterized in that: The mass ratio of lithium salt, polyvinylidene fluoride, and surface-modified LLZTO particles is 5~8:10:1~4.

9. The method as described in claim 6, characterized in that: In the composite electrolyte slurry, the mass-to-volume ratio of total solids to organic solvent is 4.8~5.5 g:100 mL.

10. The method as described in claim 6, characterized in that: The process involves casting the composite electrolyte slurry into a mold and then drying it to obtain a PVDF-based composite solid electrolyte membrane. The drying process includes forced-air drying and vacuum drying.

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