Method for preparing a direct-write formed polyvinylidene fluoride / strontium titanate solid electrolyte membrane

Abstract

This invention provides a method for preparing a direct-write molding polyvinylidene fluoride (PVDF) / strontium titanate (SLT) solid electrolyte membrane. The method uses PVDF as a matrix, dissolves it in a polar solvent, adds lithium / magnesium salts and SLT fillers to obtain a printing slurry, and then uses 3D printing to form a layer-by-layer structure followed by hot pressing to obtain a composite solid electrolyte membrane with controllable structure. 3D printing technology can precisely construct complex structures such as three-dimensional meshes and porous structures. By controlling parameters such as the printing path, layer height, and filler density, the directional design of ion transport channels and mechanical structures can be achieved. It also offers advantages such as integrated molding, high material utilization, and no need for molds. The high dielectric constant of the SLT filler synergistically enhances the dielectric properties and interfacial stability of the membrane, giving it a controllable porous structure, high dielectric constant, and excellent energy storage performance, making it promising for applications in solid-state batteries, flexible sensors, and micro-energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of polymer capacitor film technology, and specifically to a method for preparing a direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte film. Background Technology

[0002] Dielectric capacitors, as crucial electronic components, are widely used in high-power energy storage fields such as new energy vehicles and aerospace power systems. They possess significant advantages in terms of rapid charging and discharging speeds and ultra-high power density, making them one of the core components for realizing advanced power systems and energy management technologies. Polymer dielectrics, due to their light weight, good processability, high dielectric strength, and low cost, have become the preferred material for these energy storage devices. Among them, polyvinylidene fluoride (PVDF)-based polymers exhibit unique advantages in the field of flexible energy storage due to their high intrinsic dielectric constant and good ferroelectric and piezoelectric properties.

[0003] However, pure PVDF-based solid electrolyte membranes still face several technical bottlenecks in practical applications. First, the high crystallinity of PVDF and the limited proportion of amorphous regions restrict the effective migration of ions between polymer segments, resulting in low room-temperature ionic conductivity. Second, although its dielectric constant is superior to that of traditional polypropylene materials, it still falls short of meeting the further dielectric performance requirements of high-energy-density energy storage devices. Furthermore, the poor interfacial compatibility between PVDF and electrode materials easily leads to increased interfacial impedance and decreased cycle stability. PVDF films prepared by traditional casting and coating processes have a simple structure, making it difficult to achieve precise control over the micropore structure and ion transport channels, thus limiting their application in high-efficiency energy storage devices.

[0004] To improve the dielectric properties and energy storage density of polyvinylidene fluoride (PVDF)-based composites, high-dielectric ceramic fillers such as strontium titanate (STO) are often introduced to construct polymer-ceramic composite systems. STO has advantages such as high dielectric constant, good chemical stability, and excellent compatibility with PVDF, which can significantly enhance the dielectric properties of composite systems. However, in composite films prepared by traditional casting and coating processes, STO fillers are prone to agglomeration and uneven dispersion, making it difficult to precisely control the microstructure and limiting further performance improvements. To address this, this application employs 3D printing technology combined with STO fillers. By flexibly controlling parameters such as printing path and layer height, uniform distribution of the filler and controllable construction of the microstructure are achieved, effectively improving dielectric properties, interface stability, and processing accuracy, thus meeting the urgent demand for comprehensive performance in high-energy-density energy storage devices. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane. By utilizing the high dielectric constant, good chemical stability, and excellent compatibility between strontium titanate (STO) ceramic filler and the polyvinylidene fluoride (PVDF) matrix, combined with the programmability of microstructures through 3D printing technology, the dielectric properties, ion transport efficiency, and interfacial stability of the composite solid electrolyte membrane are significantly improved, enabling it to maintain excellent energy storage characteristics and electrochemical performance in the range from room temperature to high temperature.

[0006] This invention provides a method for preparing a polyvinylidene fluoride (PVDF) / strontium titanate (STO) composite solid electrolyte membrane based on 3D printing. Using PVDF as the matrix, STO filler is added after dissolution in a polar solvent, and a uniform printing slurry is obtained through ultrasonic or mechanical stirring. Direct-write 3D printing technology is employed, with layer-by-layer deposition following a preset path. By adjusting parameters such as the printing path, layer height, and filler density, controllable microstructures such as three-dimensional meshes or porous structures are constructed. Hot-pressing is then used to achieve densification and interlayer fusion, resulting in a composite solid electrolyte membrane with high dielectric constant, good flexibility, and efficient ion transport. This method utilizes the precise control of microstructure through 3D printing technology, overcoming the limitations of traditional processes with their single structural design. Furthermore, the uniform dispersion and synergistic enhancement of STO filler significantly improves dielectric properties, energy storage density, and interface stability, making it widely applicable in solid-state batteries, flexible sensors, and micro-energy storage devices.

[0007] As a further improvement to the present invention, the specific steps include: (1) Add a polar solvent to polyvinylidene fluoride and stir magnetically at 80 °C to fully dissolve the polymer matrix. Then add lithium salt or magnesium salt and continue stirring until complete dissociation to form a uniform polymer-salt composite solution. (2) Add a certain amount of strontium titanate ceramic filler to the polysulfone solution, stir at room temperature for 12 to 15 hours to mix thoroughly and make the components uniformly mixed to obtain a printing paste with suitable rheological properties; (3) The printing paste is prepared by direct writing 3D printing, and is precisely deposited layer by layer on the glass substrate according to the preset digital model path. The core advantage of 3D printing technology lies in its programmability: by independently controlling the printing speed, layer height, filling density and path spacing and other process parameters, the customized design of the electrolyte membrane microstructure can be realized, and complex geometric features such as three-dimensional mesh, porous structure and gradient pore distribution can be flexibly constructed, providing technical possibilities for the synergistic optimization of ion transport channels and mechanical bearing structures. After printing, the resulting nascent membrane is placed in a vacuum drying oven and vacuum dried at room temperature or a set temperature to completely remove the polar solvent and obtain a nascent membrane with controllable microstructure and stable forming accuracy; (4) The nascent membrane after vacuum drying is placed in a hot press and subjected to hot pressing under preset temperature and pressure conditions. This step, while preserving the precision of the microstructure constructed by 3D printing, further densifies the membrane layer through hot pressing, while optimizing the interlayer interface bonding formed by layer-by-layer printing, eliminating microscopic defects, and improving the overall density and ion transport continuity of the electrolyte membrane. During the hot pressing process, the use of intermediate layer materials such as polytetrafluoroethylene plates and PET films ensures uniform pressure transmission and maintains the flatness of the membrane surface, which is beneficial to the uniform distribution of ceramic fillers in the polymer matrix and interfacial compatibility. After hot pressing, the membrane is naturally cooled to room temperature, resulting in a composite solid polymer electrolyte membrane with controllable structure, dense interface, and stable performance, which fully leverages the advantages of 3D printing in terms of microstructure designability and the role of ceramic fillers in enhancing dielectric properties.

[0008] The polymer matrix is ​​selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (PVDF-TrFE-CTFE), with a molecular weight of 100,000 to 500,000. Among them, PVDF has good film-forming properties and chemical stability, PVDF-TrFE has higher piezoelectric response and crystallization control ability due to the introduction of trifluoroethylene segments, and PVDF-TrFE-CTFE further significantly reduces crystallinity and increases the proportion of amorphous phase through ternary copolymer structure, providing more low-energy-barrier channels for ion migration, while giving the material better flexibility and interfacial compatibility. The lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the magnesium salt is selected from at least one of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) and magnesium perchlorate (Mg(ClO4)2); the magnesium salt and lithium salt constitute a composite salt system, which effectively improves ion transport kinetics and electrode / electrolyte interface stability by synergistically regulating ion dissociation and migration behavior.

[0009] The polar solvent in step 2 is selected from N,N-dimethylacetamide, N,N-dimethylformamide, or dimethyl sulfoxide, and the solid-liquid ratio of the polymer matrix to the polar solvent is 1 g / 5 mL to 1 g / 15 mL. This type of solvent has strong polarity and good dissolving ability, which can fully dissolve the PVDF matrix and promote the uniform dispersion of STO filler, ensuring the stability and rheological properties of the printing paste. Its suitable evaporation rate can balance the molding accuracy and interlayer bonding during the 3D printing process, while being easily and completely removed during the drying stage, avoiding the influence of solvent residue on dielectric properties. Furthermore, the solvent has good compatibility with PVDF and STO, effectively inhibiting filler agglomeration and fully leveraging the high dielectric constant of STO to enhance the dielectric properties of the composite system.

[0010] Raw materials comprising the following percentage by weight: Polymer matrix 20 wt%–50 wt%; lithium or magnesium salt 10 wt%–35 wt%; ceramic filler 0 wt%–20 wt%.

[0011] The 3D printing density is 40–60, and the printing thickness is 0.17–0.23 mm. By adjusting the printing density, precise control can be achieved over the porosity and pore connectivity within the electrolyte membrane, constructing gradient distribution or multi-level pore structures to provide continuous and efficient migration channels for ion transport. By adjusting the printing thickness and layered printing strategy, multi-scale design of the membrane structure can be achieved, optimizing interlayer interface bonding and mechanical load-bearing capacity.

[0012] When adding a polar solvent to the polymer matrix, the heating and magnetic stirring temperature is 70–80°C, and the stirring time is 10–12 h.

[0013] In step S3, a hot press is used for hot pressing at a temperature of 150–200°C, a pressure of 4–5 MPa, and a pressing time of 5–10 min. During the hot pressing process, a 1 mm thick polytetrafluoroethylene (PTFE) sheet and a 100 μm thick polyethylene terephthalate (PET) film are used as intermediate layer materials to achieve good demolding performance and uniform pressure transmission, respectively. This hot pressing process, while preserving the precision of the microstructure constructed by 3D printing, further densifies the layer-by-layer film by applying appropriate temperature and pressure. Simultaneously, it optimizes the interlayer interface bonding, eliminates microscopic defects that may occur during printing, and ensures the uniform distribution and interfacial compatibility of the ceramic filler in the polymer matrix. This fully leverages the core advantage of 3D printing technology in terms of microstructure programmability, resulting in a composite solid polymer electrolyte membrane with controllable structure, dense interface, and efficient ion transport.

[0014] After hot pressing, the nonwoven fabric-like spindle is naturally cooled to room temperature and then removed.

[0015] The beneficial effects of this invention are: (1) The present invention prepares a polyvinylidene fluoride-strontium titanate composite solid electrolyte membrane based on 3D printing. The preparation method is simple, low cost, and has low requirements for environmental humidity.

[0016] (2) The composite solid polymer electrolyte membrane prepared by the present invention improves the interfacial compatibility by adding ceramic filler.

[0017] (3) By introducing strontium titanate (STO) ceramic filler, the present invention utilizes the synergistic enhancement effect between its high dielectric constant (ε > 300) and polyvinylidene fluoride (PVDF) matrix to significantly improve the dielectric properties and polarization response of the composite solid electrolyte membrane. At the same time, by combining the precise control of microstructure through 3D printing technology, controllable configurations such as three-dimensional mesh and porous structure are designed to provide continuous and efficient migration channels for ion transport, effectively overcoming the technical bottlenecks of easy agglomeration of filler and difficulty in precise control of microstructure in traditional processes.

[0018] (4) The 3D-printed polyvinylidene fluoride / strontium titanate composite solid electrolyte membrane provided by this invention exhibits a significantly improved dielectric constant at room temperature, while maintaining a low dielectric loss and a significantly higher energy storage density compared to the pure PVDF system. Simultaneously, the uniform dispersion of the strontium titanate filler and the good interfacial bonding with the polymer matrix ensure that the composite membrane maintains excellent flexibility and film-forming processability while also possessing good electrochemical stability and interfacial compatibility. Through a non-equilibrium process combining 3D printing and hot pressing, the microstructure of the electrolyte membrane can be customized as needed, with controllable production costs and strong process adaptability. This meets the application requirements of flexible electronics, wearable devices, and micro energy storage devices for personalized structures and adjustable performance, demonstrating broad application prospects. Attached Figure Description

[0019] Figure 1 Scanning electron microscope image of the surface of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane prepared for Example 1 above without salt addition; Figure 2 Scanning electron microscope image of the surface of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane prepared for Example 2 above without salt addition; Figure 3 Scanning electron microscope image of the surface of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane prepared for Example 3 above without salt addition; Figure 4 The dielectric real part test diagrams of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes prepared in Examples 1, 2, and 3 above are shown. Figure 5 The dielectric loss test diagrams are for the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes prepared in Examples 1, 2, and 3 above. Figure 6 The conductivity diagrams are for the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes prepared in Examples 1, 2, and 3 above. Figure 7 Electrochemical window diagrams of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes prepared in Examples 1, 2, and 3 above; Figure 8The above-described direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes are shown in the ion transfer number diagrams. Figure 9 The XRD patterns are of the direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membranes prepared in Examples 1, 2, and 3 above. Detailed Implementation

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings required in the description of the embodiments or the prior art will be briefly introduced below.

[0021] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0022] Example 1: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Example 1 includes the following steps: (1) Add 20 mL of DMF to 2 g of PVDF and stir at 80 °C for 12 h until fully dissolved. Then add 4 g of LiTFSI and stir at 80 °C for 1 h. Add 1 g of SrTiO3 and continue stirring at 80 °C for 1 h. Then stir at room temperature for 12 h and let stand for 30 min to obtain a uniform 3D printing slurry.

[0023] (2) The slurry was injected into the 3D printer, and the film diameter was set to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Three layers were stacked one after another (the first layer was 0.05 mm, and the last two layers were 0.06 mm each). After printing, the film was vacuum dried at 80 °C for 12 h to obtain the nascent film.

[0024] (3) The nascent membrane is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled to room temperature in the furnace to obtain a composite solid polymer electrolyte membrane containing PVDF, SrTiO3 and LiTFSI.

[0025] This invention provides a 3D-printed PVDF, SrTiO3, and LiTFSI solid electrolyte system. By introducing nano-strontium titanate filler into the PVDF matrix and combining this with the precise microstructure control capabilities of 3D printing, a synergistic improvement in ionic conductivity, dielectric properties, and interfacial stability is achieved. The system achieves a room-temperature ionic conductivity of up to 10-1. ⁻4 The S / cm scale represents an improvement of 1-2 orders compared to a pure PVDF system. Figure 6 While maintaining the excellent flexibility, film-forming properties, and thermal stability (>350°C) of PVDF, the core mechanism for performance improvement lies in the high dielectric constant of STO nanoparticles. Figure 4, Figure 5 This creates localized high-dielectric microregions in the polymer matrix, effectively promoting the dissociation of LiTFSI and significantly increasing the free carrier concentration. Figure 1 , Figure 8 The introduction of STO disrupts the regular arrangement of PVDF segments, reduces crystallinity, and increases ion transport channels in amorphous regions; simultaneously, STO acts as a rigid filler to enhance mechanical strength, and its chemical inertness suppresses side reactions between lithium salt and electrodes, improving interfacial stability. Figure 7 Furthermore, 3D printing technology, by controlling parameters such as printing path, layer height, and infill density, can construct controllable microstructures such as three-dimensional meshes and porous structures, enabling the directional design of ion transport channels and fully leveraging the synergistic enhancement effect of STO filler and PVDF matrix. This composite solid electrolyte membrane possesses high ionic conductivity, excellent dielectric properties, good mechanical flexibility, and interfacial stability, showing broad application prospects in fields such as solid-state batteries, flexible sensors, and micro energy storage devices.

[0026] Example 2: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Example 2 includes the following steps: (1) Add 20 mL of DMF to 2 g of PVDF-TrFE and stir at 80 °C for 12 h until fully dissolved. Then add 4 g of LiTFSI and stir at 80 °C for 1 h. Add 1 g of SrTiO3 and continue stirring at 80 °C for 1 h. Then stir at room temperature for 12 h and let stand for 30 min to obtain a uniform 3D printing slurry.

[0027] (2) The slurry was injected into the 3D printer, and the film diameter was set to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Three layers were stacked one after another (the first layer was 0.05 mm, and the last two layers were 0.06 mm each). After printing, the film was vacuum dried at 80 °C for 12 h to obtain the nascent film.

[0028] (3) The nascent membrane is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled to room temperature in the furnace to obtain a composite solid polymer electrolyte membrane with PVDF-TrFE, SrTiO3 and LiTFSI.

[0029] The PVDF-TrFE, SrTiO3, and LiTFSI system, while inheriting the high ionic conductivity, thermal stability, and 3D printing process advantages of the PVDF, SrTiO3, and LiTFSI system, further enhances the β-phase content by introducing TrFE segments. Figure 9 ), piezoelectric response, dielectric constant ( Figure 4 , Figure 5With its high dielectric properties and flexibility, it is more suitable for applications requiring high piezoelectric performance and flexible adaptability, such as self-powered sensors and wearable energy harvesting. Both systems leverage the high dielectric properties of STO fillers and the precise microstructure control achieved through 3D printing. Figure 2 This enables the preparation of composite solid electrolyte membranes with controllable structure and adjustable performance, which can meet the performance requirements of different application scenarios.

[0030] Example 3: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Example 3 includes the following steps: (1) Add 20 mL of DMF to 2 g of PVDF-TrFE-CTFE and stir at 80 °C for 12 h until fully dissolved. Then add 4 g of LiTFSI and stir at 80 °C for 1 h. Add 1 g of SrTiO3 and continue stirring at 80 °C for 1 h. Then stir at room temperature for 12 h and let stand for 30 min to obtain a uniform 3D printing slurry.

[0031] (2) The slurry was injected into the 3D printer, and the film diameter was set to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Three layers were stacked one after another (the first layer was 0.05 mm, and the last two layers were 0.06 mm each). After printing, the film was vacuum dried at 80 °C for 12 h to obtain the nascent film.

[0032] (3) The nascent membrane is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled to room temperature in the furnace to obtain a composite solid polymer electrolyte membrane with PVDF-TrFE-CTFE, SrTiO3 and LiTFSI.

[0033] The PVDF-TrFE-CTFE, SrTiO3, and LiTFSI system introduces CTFE as a third monomer into the PVDF-TrFE binary copolymer, further optimizing the matrix microstructure and achieving the lowest crystallinity. Figure 9 The structure features the highest proportion of amorphous phase and the richest ion transport channels. Figure 3 Its room-temperature ionic conductivity, flexibility, interfacial compatibility, and dielectric properties are superior to those of PVDF-TrFE and PVDF-based systems. This system significantly improves dielectric properties and polarization response by leveraging the high dielectric properties of SrTiO3 (STO) filler and synergistic reinforcement with the PVDF matrix. Figure 4 By combining 3D printing technology with precise control of microstructures, it is possible to achieve directional design of ion transport channels and multi-scale structural optimization, which is suitable for high-end energy storage devices such as high-energy-density solid-state batteries, flexible self-powered sensors and wearable energy harvesters, showing broad application prospects.

[0034] Example 4: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Example 4 includes the following steps: (1) Add 20 mL of DMF to 2 g of PVDF and stir at 80 °C for 12 h until fully dissolved. Then add 4 g of Mg(TFSI)2 and stir at 80 °C for 1 h. Add 1 g of SrTiO3 and continue stirring at 80 °C for 1 h. Then stir at room temperature for 12 h and let stand for 30 min to obtain a uniform 3D printing slurry.

[0035] (2) The slurry was injected into the 3D printer, and the film diameter was set to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Three layers were stacked one by one (the first layer was 0.05 mm, and the last two layers were 0.06 mm each). After printing, the film was vacuum dried at 80 °C for 12 h to obtain the nascent film.

[0036] (3) The nascent membrane is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled to room temperature in the furnace to obtain a composite solid polymer electrolyte membrane containing PVDF, SrTiO3 and Mg(TFSI)2.

[0037] The composite solid electrolyte system based on 3D-printed PVDF, SrTiO3, and Mg(TFSI)2 provided by this invention achieves programmability of microstructure through 3D printing technology, enabling precise construction of controllable ion transport channels such as three-dimensional meshes and porous structures, and significantly reducing Mg content. 2+ The system mitigates energy barriers and optimizes interfacial contact. Simultaneously, the introduction of high-dielectric-constant STO filler promotes Mg(TFSI)₂ dissociation, increasing free carrier concentration. Combined with the unique advantages of Mg(TFSI)₂ magnesium salt's high dissociation degree, wide electrochemical window, and the formation of a stable MgF₂-rich SEI layer, it effectively suppresses magnesium dendrite growth and interfacial side reactions. This system also exhibits excellent flexibility, thermal stability, and wide temperature range adaptability, demonstrating broad application prospects in solid-state magnesium batteries, flexible sensors, and high-safety energy storage devices.

[0038] Example 5: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Example 5 includes the following steps: (1) Add 20 mL of DMF to 2 g of PVDF and stir at 80 °C for 12 h until fully dissolved. Then add 4 g of Mg(ClO4)2 and stir at 80 °C for 1 h. Add 1 g of SrTiO3 and continue stirring at 80 °C for 1 h. Then stir at room temperature for 12 h and let stand for 30 min to obtain a uniform 3D printing slurry.

[0039] (2) The slurry was injected into the 3D printer, and the film diameter was set to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Three layers were stacked one by one (the first layer was 0.05 mm, and the last two layers were 0.06 mm each). After printing, the film was vacuum dried at 80 °C for 12 h to obtain the nascent film.

[0040] (3) The nascent membrane is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled to room temperature in the furnace to obtain a composite solid polymer electrolyte membrane containing PVDF, SrTiO3 and Mg(ClO4)2.

[0041] This invention relates to a composite solid polymer electrolyte system of PVDF, SrTiO3, and Mg(ClO4)2 constructed using 3D printing. Leveraging the flexible controllability of microstructure achieved by 3D printing technology, controllable ion channels such as three-dimensional meshes and porous structures can be constructed, effectively reducing the Mg content. 2+ STO filler reduces migration resistance and optimizes interfacial contact; its high dielectric constant creates a local high dielectric region in the matrix, promoting Mg(ClO4)2 dissociation and increasing the concentration of free ions. At the same time, as a rigid component, it reduces the crystallinity of PVDF and enhances mechanical properties. Mg(ClO4)2 magnesium salt has the advantages of low cost, high dissociation efficiency, and good thermal stability. It can form a dense passivation layer on the surface of magnesium anode, effectively suppressing dendrite growth. It has important application potential in solid-state magnesium batteries, flexible sensing, and low-cost energy storage.

[0042] Comparative example: The method for preparing the direct-write molding polyvinylidene fluoride / strontium titanate solid electrolyte membrane provided in Comparative Example 1 includes the following steps: (1) Weigh 3g of PVDF and dissolve it in 20mL of DMF. Stir at 80 °C for 12 h until fully dissolved. Add 5g of LiTFSI and continue stirring for 1 h. Let stand for 30 min to obtain a uniform printing paste.

[0043] (2) Inject the slurry into the 3D printer, set the film diameter to 21 mm, the printing density to 40, and the total thickness to 0.17 mm. Stack the three layers one by one (the first layer is 0.05 mm, and the last two layers are 0.06 mm each). After printing, vacuum dry at 80 °C for 12 h.

[0044] (3) After drying, the film is hot-pressed at 150 °C and 5 MPa for 0.5 h with a 1 mm thick polytetrafluoroethylene plate and a 100 μm thick PET film as the intermediate layer, and then cooled in the furnace to obtain pure PVDF and LiTFSI solid electrolyte membrane.

[0045] The 3D-printed PVDF and LiTFSI composite solid electrolyte system has significant shortcomings in terms of ionic conductivity, interfacial stability, dielectric properties, mechanical flexibility, and cost control. Simply relying on 3D printing to modify the structure cannot compensate for the core defects of PVDF matrix, such as its limited intrinsic ionic conductivity and poor interfacial compatibility with lithium anodes. Therefore, this system typically requires modification through the introduction of high dielectric constant fillers, functional additives, or the use of copolymer matrices to achieve comprehensive optimization of ion transport, interfacial stability, and mechanical properties.

[0046] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane, characterized in that, A polar solvent is added to polyvinylidene fluoride (PVDF), followed by strontium titanate ceramic filler. The filler is then uniformly dispersed by mechanical stirring to form a 3D printing slurry with suitable rheological properties. Direct writing 3D printing technology is used to form the slurry layer by layer. By controlling parameters such as printing path, layer height, and filler density, an electrolyte membrane preform with a controllable microstructure is constructed. Then, hot pressing is used to densify and fuse the interface, thus preparing a PVDF-strontium titanate composite solid electrolyte membrane with high dielectric properties, good mechanical flexibility, and ion transport efficiency.

2. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to claim 1, characterized in that, Specifically, the following steps are included: (1) Add a polar solvent to polyvinylidene fluoride and stir magnetically at 80°C to fully dissolve the polymer matrix. Then add lithium salt or magnesium salt and continue stirring until complete dissociation to form a uniform polymer-salt composite solution. (2) Add a certain amount of strontium titanate ceramic filler to the composite solution, stir at room temperature for 12-15 hours to mix thoroughly and make the components uniformly mixed to obtain a printing paste with suitable rheological properties; (3) The printing paste is prepared by direct writing 3D printing method, and is precisely deposited layer by layer on the glass substrate according to the preset digital model path; the core advantage of 3D printing technology lies in its structural programmability: by independently controlling the printing speed, layer height, filling density and path spacing and other process parameters, the customized design of the electrolyte membrane microstructure can be realized, and complex geometric features such as three-dimensional mesh, porous structure and gradient pore distribution can be flexibly constructed, providing technical possibility for the synergistic optimization of ion transport channels and mechanical bearing structure; After printing, the resulting nascent film is placed in a vacuum drying oven and dried under vacuum at room temperature or a set temperature to completely remove the polar solvent and obtain a nascent film with a controllable microstructure and stable molding precision. (4) The nascent membrane after vacuum drying is placed in a hot press and hot-pressed under preset temperature and pressure conditions. This step, while preserving the accuracy of the microstructure constructed by 3D printing, further densifies the membrane layer through hot pressing, while optimizing the interlayer interface bonding formed by layer-by-layer printing, eliminating micro-defects, and improving the overall density and ion transport continuity of the electrolyte membrane. During the hot pressing process, the pressure is uniformly transmitted and the membrane surface is kept flat by using intermediate layer materials such as polytetrafluoroethylene plates and PET films, which is conducive to the uniform distribution of ceramic fillers in the polymer matrix and the interfacial compatibility. After the hot pressing is completed, the membrane is naturally cooled to room temperature, and a composite solid polymer electrolyte membrane with controllable structure, dense interface, and stable performance is obtained. This fully leverages the advantages of 3D printing in terms of microstructure designability and the role of ceramic fillers in enhancing dielectric properties.

3. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to claim 2, characterized in that, The polymer matrix is ​​selected from at least one of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-trifluoroethylene copolymer (PVDF-TrFE), and polyvinylidene fluoride-trifluoroethylene-trifluorochloroethylene terpolymer (PVDF-TrFE-CTFE), with a molecular weight of 100,000 to 500,000. PVDF exhibits good film-forming properties and chemical stability, while PVDF-TrFE, due to the introduction of trifluoroethylene segments, possesses higher piezoelectric response and crystallization control capabilities. PVDF-TrFE-CTFE further enhances these properties through the introduction of trifluoroethylene segments. The meta-copolymer structure significantly reduces crystallinity and increases the proportion of amorphous phase, providing more low-barrier channels for ion migration, while also endowing the material with superior flexibility and interfacial compatibility; the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); the magnesium salt is selected from at least one of magnesium bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) and magnesium perchlorate (Mg(ClO4)2); the magnesium salt and lithium salt constitute a composite salt system, which effectively improves ion transport kinetics and electrode / electrolyte interface stability by synergistically regulating ion dissociation and migration behavior.

4. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to claim 2, characterized in that, The polar solvent in step 2 is selected from N,N-dimethylacetamide, N,N-dimethylformamide, or dimethyl sulfoxide, and the solid-liquid ratio of the polymer matrix to the polar solvent is 1g / 5 mL to 1g / 15 mL.

5. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to claim 2, characterized in that, Raw materials comprising the following percentage by weight: Polymer matrix 20 wt%–50 wt%; lithium or magnesium salt 10 wt%–35 wt%; ceramic filler 0 wt%–20 wt%.

6. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane as described in claim 2, characterized in that, In step (1), the heating magnetic stirring temperature when adding polar solvent to polymer matrix is ​​70-80°C and the stirring time is 10-12h.

7. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane as described in claim 2, characterized in that, In step (2), the 3D printing density is 40-60 and the printing thickness is 0.17-0.23 mm. By adjusting the printing density, the porosity and pore connectivity inside the electrolyte membrane can be precisely controlled, and a gradient distribution or multi-level pore structure can be constructed to provide a continuous and efficient migration channel for ion transport. By adjusting the printing thickness and the layered printing strategy, the multi-scale design of the membrane structure can be realized, and the interlayer interface bonding and mechanical load-bearing capacity can be optimized.

8. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane as described in claim 2, characterized in that, In step S3, a hot press is used for hot pressing at a temperature of 150–200°C, a pressure of 4–5 MPa, and a pressing time of 5–10 min. During the hot pressing process, a 1 mm thick polytetrafluoroethylene sheet and a 100 μm thick polyethylene terephthalate film are used as intermediate layer materials to achieve good demolding performance and uniform pressure transmission, respectively. This hot pressing process, while preserving the accuracy of the microstructure constructed by 3D printing, further densifies the layered film by applying appropriate temperature and pressure, while optimizing the interlayer interface bonding, eliminating microscopic defects that may occur during the printing process, and ensuring the uniform distribution and interfacial compatibility of the ceramic filler in the polymer matrix. This fully leverages the core advantages of 3D printing technology in terms of microstructure programmability to obtain a composite solid polymer electrolyte membrane with controllable structure, dense interface, and efficient ion transport.

9. The method for preparing a direct-write molded polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to claim 2, characterized in that, After hot pressing, the nonwoven fabric-like spindle is naturally cooled to room temperature and then removed.

10. The application of the composite solid polymer electrolyte membrane prepared by the direct-write molding method for preparing polyvinylidene fluoride / strontium titanate solid electrolyte membrane according to any one of claims 1-9 in dielectric capacitors.

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