Composite electrolyte membrane and preparation method and application thereof

Abstract

The invention provides a composite electrolyte membrane and a preparation method and application thereof. The preparation method comprises the following steps: preparing a polymer premixed solution, and then mixing the polymer premixed solution with a solid electrolyte to obtain a semi-solid slurry with the solid content of more than or equal to 80%; carrying out compression molding on the semi-solid slurry to obtain a solid electrolyte membrane; and compounding the solid electrolyte membrane and a porous support membrane, and then carrying out hot pressing to obtain the composite electrolyte membrane. According to the method, the dosage of the organic solvent is reduced, the problems of sagging, shrinkage defects and the like of the traditional low-solid-content slurry can be avoided, the drying time is shortened, the energy consumption is reduced, the production efficiency and the product yield are improved, and the method has remarkable production consistency and cost advantages; according to the process, the composite performance of the solid electrolyte membrane and the porous supporting membrane is optimized, the room-temperature ionic conductivity, the tensile strength and the interface impedance performance are all improved, high ionic conduction and dendrite penetration resistance are both considered, and the commercial potential is outstanding.

Description

Technical Field

[0001] This invention belongs to the field of electrolyte materials technology, specifically relating to a composite electrolyte membrane, its preparation method, and its application. Background Technology

[0002] Solid-state rechargeable batteries (such as solid-state lithium-ion batteries and solid-state sodium-ion batteries) and their hybrid capacitor forms (such as lithium / sodium-ion capacitors), as next-generation energy storage devices, need to possess both high energy density and high power density characteristics. Their performance largely depends on the ionic conductivity, interfacial stability, and mechanical strength of the composite electrolyte membrane.

[0003] In existing technologies, composite electrolyte membranes are mostly prepared using a wet molding process: polymers (such as polyvinylidene fluoride, polyethylene oxide, etc.), oxide solid electrolytes (such as lithium lanthanum zirconium titanium oxide, etc.), plasticizers, etc., are dissolved in a large amount of organic solvent (such as N-methylpyrrolidone, etc.) to form a low-solids content (usually 40-60%) slurry, which is then prepared through coating, drying, and pressing steps. However, the use of large amounts of organic solvents leads to high VOC emissions during the production process, resulting in significant environmental pressure. Solvent residues also increase interfacial impedance and reduce device cycle stability. Furthermore, the low-solids content slurry requires a long drying time (e.g., 8-12 hours) to remove the solvent, extending the production cycle, increasing energy consumption, and the drying process can easily lead to membrane shrinkage and cracking, reducing product yield (usually <80%).

[0004] In addition, some solutions introduce mesh support materials to enhance mechanical strength. However, the pore size and thickness of the support material are not designed properly, making it difficult to balance ion conduction and mechanical properties. Furthermore, due to the excessive fluidity of traditional pastes, uneven filling is likely to occur when they are combined with support materials, resulting in a film thickness deviation of >10%, which affects the consistency of the device.

[0005] Therefore, how to significantly reduce solvent usage, shorten drying time, improve production efficiency and product yield, and optimize the composite performance of electrolyte membrane and support material are urgent technical problems to be solved. Summary of the Invention

[0006] To address the shortcomings of existing technologies, the present invention aims to provide a composite electrolyte membrane, its preparation method, and its applications. This invention is based on a semi-solid slurry with a solid content ≥80%, significantly reducing the amount of organic solvents used, thus solving environmental and residue problems at the source. Furthermore, this semi-solid slurry exhibits excellent plasticity, avoiding problems such as sagging and shrinkage defects common with traditional low-solid-content slurries. It also significantly shortens drying time, reduces energy consumption, and improves production efficiency and product yield, demonstrating significant production consistency and cost advantages, thus meeting the needs of large-scale green production. Simultaneously, this process optimizes the composite performance of the solid electrolyte membrane and the porous support membrane, improving the room-temperature ionic conductivity, tensile strength, and interfacial impedance properties of the composite electrolyte membrane, while maintaining both high ion conductivity and resistance to dendrite penetration, demonstrating significant commercial potential.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a method for preparing a composite electrolyte membrane, the method comprising the following steps:

[0009] A polymer premix is ​​prepared, and then the polymer premix is ​​mixed with a solid electrolyte to obtain a semi-solid slurry with a solid content of ≥80%.

[0010] The semi-solid slurry is pressed into shape to obtain a solid electrolyte membrane.

[0011] The solid electrolyte membrane and the porous support membrane are combined and then hot-pressed to obtain the composite electrolyte membrane.

[0012] This invention uses a semi-solid slurry with a solid content of ≥80% as the core molding raw material, significantly reducing the amount of organic solvents used and blocking the main emission pathways of VOCs at the source. This solves the environmental pressure and solvent residue problems caused by excessive organic solvent use in traditional processes. Simultaneously, the semi-solid slurry, with its excellent plasticity and morphological stability, effectively avoids defects such as sagging during the coating process and shrinkage cracking during the drying stage of traditional low-solid-content slurries, increasing product yield to over 90%. In terms of production efficiency, the high solid content of the semi-solid slurry shortens drying time, significantly reduces energy consumption in the drying process, greatly improves production cycle time, adapts to the needs of large-scale continuous production, has significant cost advantages, is compatible with existing secondary battery production lines, and has outstanding commercial potential.

[0013] This invention enhances the interfacial bonding and pore filling uniformity between the solid electrolyte membrane and the porous support membrane through process optimization, thereby synergistically improving the overall performance of the composite electrolyte membrane. It achieves dual optimization of "ion conduction and mechanical strength", ensuring efficient ion conduction while suppressing dendrite penetration through mechanical strength, and has good application prospects in solid-state secondary batteries.

[0014] In this invention, the solid content is ≥80%, for example, it can be 80%, 82%, 84%, 86%, 88%, 90%, etc.

[0015] Preferably, the method for preparing the polymer premix includes:

[0016] The polymer and an organic solvent are mixed, and then a plasticizer is added for blending to obtain the polymer premix. For example, the organic solvent may be any one or a combination of two of N-methylpyrrolidone, dimethylformamide, dimethyl sulfoxide, etc.

[0017] Preferably, the polymer comprises polyvinylidene fluoride and modified polyethylene oxide.

[0018] Preferably, the modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide.

[0019] In this invention, maleic anhydride is used to graft and modify polyethylene oxide, which helps to improve its viscosity, polarity and compatibility with other polymers.

[0020] Preferably, the grafting rate of the modified polyethylene oxide is 12-15%, for example, it can be 12%, 13%, 14% or 15%, etc.

[0021] Preferably, the molecular weight of the modified polyethylene oxide is 50,000-500,000 g / mol, for example, it can be 50,000 g / mol, 100,000 g / mol, 200,000 g / mol or 300,000 g / mol.

[0022] Preferably, the mass ratio of polyvinylidene fluoride to modified polyethylene oxide is (15-25):(30-50), wherein the polyvinylidene fluoride is selected in the range of "15-25", for example, 15, 17, 20, 22 or 25, and the modified polyethylene oxide is selected in the range of "30-50", for example, 30, 35, 40, 45 or 50.

[0023] Preferably, the mass ratio of the polymer to the organic solvent is (45-75):(50-70), wherein the polymer range of "45-75" can be, for example, 45, 50, 55, 60 or 75, and the organic solvent range of "50-70" can be, for example, 50, 55, 60, 65 or 70.

[0024] This invention optimizes the mass ratio of polymer and organic solvent, enabling the preparation of semi-solid slurry with a solid content of ≥80%, significantly reducing the use of organic solvents and solving environmental and solvent residue problems from the source. The resulting dough-like slurry has excellent plasticity and avoids problems such as sagging and shrinkage defects of traditional low-solid-content slurries.

[0025] Preferably, the organic solvent includes any one or a combination of at least two of N-methylpyrrolidone, dimethylformamide, or dimethyl sulfoxide.

[0026] Preferably, the plasticizer includes any one or a combination of at least two of poly(ethylene glycol dimethyl ether), polyethylene glycol, or di-n-butyl phthalate.

[0027] Preferably, the mass ratio of the polymer to the plasticizer is (45-75):(1-15), wherein the polymer selection range "45-75" can be, for example, 45, 50, 65, 70 or 75, and the plasticizer selection range "1-15" can be, for example, 1, 2, 4, 6, 8, 10, 12 or 15.

[0028] Preferably, the solid content of the polymer premix is ​​45-65 wt%, for example, it can be 45 wt%, 50 wt%, 55 wt%, 60 wt%, or 65 wt%.

[0029] Preferably, the working temperature during the preparation of the polymer premix is ​​60-80℃, for example, 60℃, 70℃ or 80℃.

[0030] Preferably, the solid electrolyte is an oxide solid electrolyte.

[0031] Preferably, the oxide solid electrolyte comprises any one or a combination of at least two of LLTO (lithium lanthanum titanate), LLZTO (lithium lanthanum zirconium titanate), LLZO (lithium lanthanum zirconium titanate), LATP (lithium aluminum titanium phosphate), or NZSP (lithium sodium zirconium phosphate).

[0032] Preferably, the particle size D50 of the solid electrolyte is 1-5 μm, for example, it can be 1 μm, 2 μm, 3 μm or 5 μm.

[0033] Preferably, the mass ratio of the polymer premix to the solid electrolyte is (40-50):(50-75), wherein the polymer in the polymer premix is ​​selected from the range of "40-50", for example, 40, 42, 44, 45 or 50, and the solid electrolyte is selected from the range of "50-75", for example, 50, 55, 60, 65 or 75.

[0034] In this invention, a suitable mass ratio of polymer to solid electrolyte can fully leverage their synergistic effect. The polymer promotes ion interface migration and buffers brittleness, while the solid electrolyte inhibits polymer crystallization and enhances conductivity, thereby improving electrical conductivity and mechanical strength. An improper ratio will lead to insufficient conductivity, decreased strength, or particle agglomeration and a sharp increase in interfacial impedance, failing to meet application requirements.

[0035] Preferably, the solid content of the semi-solid slurry is 80-90 wt%, for example, it can be 80 wt%, 82 wt%, 84 wt%, 86 wt%, 88 wt%, 89 wt%, or 90 wt%.

[0036] In this invention, a semi-solid slurry with an appropriate solid content has excellent plasticity, which is beneficial for the uniform dispersion of polymer matrix and solid electrolyte particles during the rolling process. It can fill the fine gaps in the mold or network structure with moderate fluidity, and maintain morphological stability under pressure. This avoids component sedimentation due to excessive thinness or film breakage caused by excessive thickness, and finally obtains a solid electrolyte membrane with uniform thickness and no voids, ensuring the continuity of ion conduction path and the reliability of mechanical properties.

[0037] Preferably, the pressing method includes roll forming.

[0038] Preferably, during the rolling process, the working temperature is 60-80℃, for example, 60℃, 70℃ or 80℃, the linear pressure is 10-20kN / m, for example, 10kN / m, 12kN / m, 14kN / m, 16kN / m, 18kN / m or 20kN / m, and the rolling speed is 5-15m / min, for example, 5m / min, 8m / min, 10m / min, 12m / min or 15m / min.

[0039] Preferably, the thickness of the solid electrolyte membrane is 40-100 μm, for example, it can be 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm or 100 μm.

[0040] Preferably, the flatness deviation of the solid electrolyte membrane is <5%, for example, it can be 4.5%, 4%, 3.5%, 3%, 2.5%, 2% or 1%, etc.

[0041] Preferably, the porous support membrane is made of any one of polypropylene porous mesh material, polyethylene porous mesh material, or metal mesh.

[0042] Preferably, the pore size of the porous support membrane is 1-45 mesh, for example, it can be 1 mesh, 5 mesh, 10 mesh, 20 mesh, 30 mesh, 40 mesh or 45 mesh, etc.

[0043] Preferably, the thickness of the porous support membrane is 30-100μm, for example, it can be 30μm, 40μm, 50μm, 60μm, 70μm, 80μm, 90μm or 100μm.

[0044] In this invention, a porous support membrane with a specific pore size and thickness can ensure rapid ion conduction while providing sufficient mechanical support, thereby improving the mechanical strength of the composite electrolyte membrane.

[0045] Preferably, the hot pressing is a step-by-step hot pressing, which includes a first-step hot pressing, drying and a second-step hot pressing performed sequentially.

[0046] This invention utilizes the synergy of a porous support membrane and a stepwise hot-pressing process to achieve a balanced optimization of ion conductivity and mechanical strength. Furthermore, it improves production consistency, material utilization, and simplifies the process, resulting in a significant cost reduction.

[0047] Preferably, the temperature of the hot pressing step is 80-110℃, for example, it can be 80℃, 90℃, 100℃ or 110℃.

[0048] Preferably, the pressure of the hot pressing step is 5-15 MPa, for example, it can be 5 MPa, 10 MPa or 15 MPa.

[0049] Preferably, the hot pressing time is 5-15 minutes, for example, 5 minutes, 10 minutes or 15 minutes.

[0050] Preferably, the temperature of the two-step hot pressing is 90-120℃, for example, it can be 90℃, 100℃, 110℃ or 120℃.

[0051] Preferably, the pressure of the two-step hot pressing is 15-25 MPa, for example, it can be 15 MPa, 20 MPa or 25 MPa.

[0052] Preferably, the two-step hot pressing time is 3-10 minutes, for example, it can be 3 minutes, 5 minutes, 7 minutes or 10 minutes.

[0053] Preferably, the drying temperature is 50-80°C, for example, it can be 50°C, 60°C, 70°C or 80°C.

[0054] Preferably, the drying time is 1-6 hours, for example, it can be 1 hour, 2 hours, 4 hours or 6 hours.

[0055] In this invention, the drying time is significantly shortened compared to traditional technologies, greatly reducing energy consumption, improving material utilization, and meeting the needs of large-scale green production.

[0056] Preferably, the drying method includes vacuum drying and / or hot air circulation drying.

[0057] Preferably, the preparation method includes the following steps:

[0058] (1) Preparation of polymer premix:

[0059] The polymer is added to an organic solvent and stirred at 60-80°C (e.g., 60°C, 70°C, or 80°C) for 2-8 hours (e.g., 2 hours, 4 hours, 6 hours, or 8 hours). Then, a plasticizer is added and stirred to obtain the polymer premix.

[0060] The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of (15-25):(30-50), wherein the modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 12-15%; the mass ratio of the polymer to the organic solvent is (45-75):(50-70); the mass ratio of the polymer to the plasticizer is (45-75):(1-15); and the solid content of the polymer premix is ​​45-65 wt%.

[0061] (2) Add the oxide solid electrolyte with a particle size D50 of 1-5 μm to the polymer premix and disperse it at a speed of 800-1200 rpm (e.g., 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm, etc.) for 2-8 hours (e.g., 2 hours, 3 hours, 4 hours, 6 hours or 8 hours, etc.) to obtain a semi-solid slurry with a solid content of 80-90 wt% and a dough-like consistency.

[0062] The mass ratio of the polymer premix to the oxide solid electrolyte is (40-50):(50-75); based on the mass of the semi-solid slurry, the mass content of the organic solvent is 10-20%.

[0063] (3) The semi-solid slurry is rolled at 60-80℃, with a linear pressure of 10-20kN / m and a rolling speed of 5-15m / min to obtain a solid electrolyte membrane with a thickness of 40-100μm and a flatness deviation of <5%.

[0064] (4) The solid electrolyte membrane and the porous support membrane are stacked, and then hot-pressed for 5-15 minutes at 80-110℃ and 5-15MPa to fill the mesh of the porous support membrane with the solid electrolyte membrane. Then, the membrane is vacuum dried at 50-80℃ for 1-6 hours to obtain the dried composite membrane.

[0065] The dried composite membrane is placed in a mold with a built-in release membrane and subjected to a two-step hot pressing at 90-120℃ and 15-25MPa for 3-10 minutes to obtain a composite electrolyte membrane with a thickness of 35-90μm and a relative density ≥92% (e.g., 92%, 94% / 95%, 96%, 97% or 98%).

[0066] It should be noted that after obtaining the solid electrolyte membrane in step (3), the solid electrolyte membrane can be cut into sheets of 100mm×100mm-200mm×200mm. The purpose is to provide a substrate of suitable size for the subsequent composite process with the porous support membrane. This size range not only retains sufficient operating space to facilitate the alignment and stacking of the membrane material and the support membrane by manual or automated equipment, avoiding edge misalignment during stacking due to excessively small size, but also reduces redundant membrane material and lowers material loss in the subsequent composite process. At the same time, the cutting operation can simultaneously remove burrs, warping, and other defects formed on the edges of the membrane material due to coating and drying, ensuring that the contact surface of the two membranes is flat during composite, laying the foundation for the uniformity of the mesh filling during subsequent hot pressing.

[0067] It should be noted that before placing the dried composite film into the mold with the built-in release film, the film is first cut into sheets of 50mm×50mm-150mm×150mm to match the dimensions of the mold cavity. This operation can prevent the composite film from wrinkling or stacking in the mold due to being too large, or from being too small, causing pressure to concentrate in the edge area during hot pressing. At the same time, uniformly cut sheets ensure consistent placement within the mold, resulting in even stress distribution across the film during the secondary hot pressing process, thus ensuring that the thickness tolerance of the final product is controlled within the preset range (±3μm).

[0068] It should be noted that after obtaining the composite electrolyte membrane, it can be cut into circular pieces or square pieces of the corresponding size with a diameter of 10-25mm (e.g., 10mm, 15mm, 20mm or 25mm) according to the electrode size in the solid secondary battery capacitor.

[0069] It should be noted that release film is a functional film with low adhesion (easy peeling). Its principle is to coat the surface of the base film with a release agent (such as silicone, fluorine compounds, etc.) to reduce surface tension, allowing the composite electrolyte membrane to form only a weak bond with it. Therefore, it will not leave residue or damage the contacted material during peeling. For example, it could be a PET (polyethylene terephthalate) release film.

[0070] It should be noted that relative density refers to the ratio of the actual density of the composite electrolyte membrane to its theoretical maximum density.

[0071] In a second aspect, the present invention provides a composite electrolyte membrane, which is prepared by the preparation method described in the first aspect.

[0072] Thirdly, the present invention provides an application of the composite electrolyte membrane as described in the second aspect in the field of secondary batteries.

[0073] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0074] Compared with the prior art, the present invention has the following beneficial effects:

[0075] (1) This invention uses a semi-solid slurry with a solid content of ≥80% as the core molding raw material, which greatly reduces the amount of organic solvent used (more than 60% less than the traditional wet process), blocks the main emission path of VOCs from the source, and solves the environmental pressure and solvent residue problems caused by excessive use of organic solvents in the traditional process. At the same time, the semi-solid slurry, with its excellent plasticity and morphological stability, can effectively avoid the defects of traditional low solid content slurry in coating process such as sagging and shrinkage cracking in drying stage, so as to improve the product yield to more than 90%.

[0076] (2) In terms of production efficiency, the high solid content of semi-solid slurry shortens the drying time, significantly reduces the energy consumption of the drying process, greatly improves the production cycle, reduces the production cycle by 50% compared with traditional processes, increases the material utilization rate to over 90%, adapts to the needs of large-scale continuous production, has significant cost advantages, is compatible with existing secondary battery production lines, and has outstanding commercial potential.

[0077] (3) This invention enhances the interface bonding and mesh filling uniformity between the solid electrolyte membrane and the porous support membrane through process optimization, thereby synergistically improving the overall performance of the composite electrolyte membrane and achieving dual optimization of "ion conduction-mechanical strength". That is, the room temperature ion conductivity and tensile strength are both improved, and the interface impedance between it and the electrode is reduced. Therefore, it can ensure efficient ion conduction and suppress dendrite penetration through mechanical strength, and has good application prospects in solid secondary batteries. Detailed Implementation

[0078] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0079] Example 1

[0080] This embodiment provides a method for preparing a composite electrolyte membrane, the method comprising the following steps:

[0081] (1) Preparation of polymer premix:

[0082] The polymer was added to an organic solvent and stirred at 70°C for 4 hours. Then, a plasticizer was added and stirred to obtain the polymer premix.

[0083] The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of 16:40. The modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 13% and a molecular weight of 300,000 g / mol. The mass ratio of the polymer to the organic solvent is 56:54. The mass ratio of the polymer to the plasticizer is 56:8. The solid content of the polymer premix is ​​54 wt%. The plasticizer is poly(ethylene glycol dimethyl ether). The organic solvent is a mixture of N-methylpyrrolidone and dimethyl sulfoxide in a mass ratio of 8:2.

[0084] (2) An oxide solid electrolyte with a particle size D50 of 1.5 μm was added to the polymer premix and dispersed in a twin-screw mixer at a speed of 1000 rpm for 6 hours to obtain a semi-solid slurry with a solid content of 81 wt% and a dough-like consistency.

[0085] The oxide solid electrolyte is LLZTO solid electrolyte; the mass ratio of the polymer premix to the oxide solid electrolyte is 45:61; and the organic solvent content is 19% based on the mass of the semi-solid slurry.

[0086] (3) Under the conditions of 75℃, linear pressure of 15kN / m and rolling speed of 6m / min, the semi-solid slurry is rolled by a double roller press to obtain a solid electrolyte membrane with a thickness of 45μm and a flatness deviation of <5%. Then the membrane is cut into 100mm×100mm sheets.

[0087] (4) The cut solid electrolyte membrane and the porous support membrane are aligned and stacked, and then a hot press is used to perform a one-step hot pressing at 95°C and 10MPa for 10 minutes, so that the solid electrolyte membrane fills the mesh of the porous support membrane. Then, the membrane is vacuum dried at 70°C for 3 hours to obtain the dried composite membrane. The porous support membrane is made of polypropylene with a pore size of 10 mesh and a thickness of 38μm.

[0088] (5) Remove the edge defects of the dried composite film, then cut the film into 50mm×50mm sheets, and then place them in a mold with a built-in PET release film. Perform two-step hot pressing at 110℃ and 25MPa for 5 minutes to obtain a composite electrolyte membrane with a thickness of 35μm and a relative density of 94%.

[0089] Example 2

[0090] This embodiment provides a method for preparing a composite electrolyte membrane, the method comprising the following steps:

[0091] (1) Preparation of polymer premix:

[0092] The polymer was added to an organic solvent and stirred at 80°C for 6 hours. Then, a plasticizer was added and stirred to obtain the polymer premix.

[0093] The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of 18:36, wherein the modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 12% and a molecular weight of 400,000 g / mol; the mass ratio of the polymer to the organic solvent is 54:54; the solid content of the polymer premix is ​​53 wt%; the mass ratio of the polymer to the plasticizer is 54:6; the plasticizer is poly(ethylene glycol dimethyl ether); and the organic solvent is N-methylpyrrolidone.

[0094] (2) An oxide solid electrolyte with a particle size D50 of 2.5 μm was added to the polymer premix and dispersed in a twin-screw mixer at a speed of 800 rpm for 6 hours to obtain a semi-solid slurry with a solid content of 83 wt% and a dough-like consistency.

[0095] The oxide solid electrolyte comprises LLZTO and LLZO in a mass ratio of 1:1; the mass ratio of the polymer premix to the oxide solid electrolyte is 40:70; and the organic solvent content is 17% based on the mass of the semi-solid slurry.

[0096] (3) Under the conditions of 75℃, linear pressure of 20kN / m and rolling speed of 8m / min, the semi-solid slurry is rolled by a double roller press to obtain a solid electrolyte membrane with a thickness of 42μm and a flatness deviation of <5%. Then the membrane is cut into 100mm×100mm sheets.

[0097] (4) The cut solid electrolyte membrane and the porous support membrane are aligned and stacked, and then a hot press is used to perform a one-step hot pressing at 100°C and 10MPa for 6 minutes, so that the solid electrolyte membrane fills the mesh of the porous support membrane. Then, the membrane is vacuum dried at 80°C for 4 hours to obtain the dried composite membrane. The porous support membrane is made of polypropylene with a pore size of 5 mesh and a thickness of 40μm.

[0098] (5) Remove the edge defects of the dried composite film, then cut the film into 50mm×50mm sheets, and then place them in a mold with a built-in PET release film. Perform two-step hot pressing at 120℃ and 25MPa for 3 minutes to obtain a composite electrolyte membrane with a thickness of 38μm and a relative density of 92%.

[0099] Example 3

[0100] This embodiment provides a method for preparing a composite electrolyte membrane, the method comprising the following steps:

[0101] (1) Preparation of polymer premix:

[0102] The polymer was added to an organic solvent and stirred at 70°C for 4 hours. Then, a plasticizer was added and stirred to obtain the polymer premix.

[0103] The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of 18:50. The modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 15% and a molecular weight of 200,000 g / mol. The mass ratio of the polymer to the organic solvent is 68:54. The mass ratio of the polymer to the plasticizer is 68:10. The solid content of the polymer premix is ​​59 wt%. The plasticizer is di-n-butyl phthalate, and the organic solvent is N-methylpyrrolidone.

[0104] (2) An oxide solid electrolyte with a particle size D50 of 1.5 μm was added to the polymer premix and dispersed in a twin-screw mixer at a speed of 1200 rpm for 5 hours to obtain a semi-solid slurry with a solid content of 86 wt% and a dough-like consistency.

[0105] The oxide solid electrolyte comprises LLZTO and LLZO in a mass ratio of 1:1; the mass ratio of the polymer premix to the oxide solid electrolyte is 40:75; and the organic solvent content is 14% based on the mass of the semi-solid slurry.

[0106] (3) Under the conditions of 70℃, linear pressure of 20kN / m and rolling speed of 6m / min, the semi-solid slurry is rolled by a double roller press to obtain a solid electrolyte membrane with a thickness of 48μm and a flatness deviation of <5%. Then the membrane is cut into 100mm×100mm sheets.

[0107] (4) The cut solid electrolyte membrane and the porous support membrane are aligned and stacked, and then a hot press is used to perform a one-step hot pressing at 110°C and 15MPa for 8 minutes, so that the solid electrolyte membrane fills the mesh of the porous support membrane. Then, the membrane is vacuum dried at 80°C for 2 hours to obtain the dried composite membrane. The porous support membrane is made of polypropylene with a pore size of 30 mesh and a thickness of 40μm.

[0108] (5) Remove the edge defects of the dried composite film, then cut the film into 50mm×50mm sheets, and then place them in a mold with a built-in PET release film. Perform two-step hot pressing at 120℃ and 20MPa for 10 minutes to obtain a composite electrolyte membrane with a thickness of 36μm and a relative density of 93%.

[0109] Example 4

[0110] The difference between this embodiment and Embodiment 1 is that the modified polyethylene oxide in step (1) is replaced with unmodified polyethylene oxide.

[0111] The remaining preparation methods and parameters are consistent with those in Example 1.

[0112] Example 5

[0113] The difference between this embodiment and Embodiment 1 is that, based on the mass of the semi-solid slurry, the mass content of the organic solvent is adjusted to 20%, and the total mass content of the oxide solid electrolyte is adaptively adjusted to 70%, so that the solid content of the semi-solid slurry is 80%.

[0114] The remaining preparation methods and parameters are consistent with those in Example 1.

[0115] Example 6

[0116] The difference between this embodiment and Embodiment 1 is that the mass ratio of the polymer premix to the organic solvent is 40:70.

[0117] The remaining preparation methods and parameters are consistent with those in Example 1.

[0118] Example 7

[0119] The difference between this embodiment and Embodiment 1 is that the mass ratio of the polymer to the organic solvent is 75:45.

[0120] The remaining preparation methods and parameters are consistent with those in Example 1.

[0121] Example 8

[0122] The difference between this embodiment and Embodiment 1 is that the pore size of the porous support membrane is 50 mesh.

[0123] The remaining preparation methods and parameters are consistent with those in Example 1.

[0124] Example 9

[0125] The difference between this embodiment and embodiment 1 is that the vacuum drying temperature in step (4) is 45°C.

[0126] The remaining preparation methods and parameters are consistent with those in Example 1.

[0127] Example 10

[0128] The difference between this embodiment and embodiment 1 is that the vacuum drying temperature in step (4) is 85°C.

[0129] The remaining preparation methods and parameters are consistent with those in Example 1.

[0130] Example 11

[0131] The difference between this embodiment and embodiment 1 is that the vacuum drying time in step (4) is 8 hours.

[0132] The remaining preparation methods and parameters are consistent with those in Example 1.

[0133] Example 12

[0134] The difference between this embodiment and embodiment 1 is that the two-step hot pressing described in step (4) is not performed.

[0135] The remaining preparation methods and parameters are consistent with those in Example 1.

[0136] Comparative Example 1

[0137] This comparative example provides a method for preparing a composite electrolyte membrane, the method comprising the following steps:

[0138] (1) The polymer is added to an organic solvent and stirred at 60°C for 6 hours. Then, a plasticizer is added and stirred to obtain the polymer premix.

[0139] The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of 7:18. The modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 13% and a molecular weight of 350,000 g / mol. The mass ratio of the polymer to the organic solvent is 1:3. The mass ratio of the polymer to the plasticizer is 25:4. The plasticizer is poly(ethylene glycol dimethyl ether), and the organic solvent is N-methylpyrrolidone.

[0140] (2) Add the oxide solid electrolyte with a particle size D50 of 2 μm to the polymer premix, disperse it at a speed of 3500 rpm for 4 hours using a high shear disperser, add solvent to adjust the viscosity, and obtain a fluid slurry with a solid content of 58% and a viscosity of 5000 cP.

[0141] The oxide solid electrolyte is a lithium lanthanum zirconium titanium oxide solid electrolyte; the mass ratio of the polymer premix to the oxide solid electrolyte is 7:5.

[0142] (3) The fluid slurry is coated onto the PET film by a scraper with a coating gap of 150 μm and a coating speed of 5 m / min. After coating, it is dried in a hot air oven at 60°C for 8 hours to form a solid electrolyte film with a thickness of 60 μm and a flatness deviation of <10%. Then the film is cut into 100 mm × 100 mm sheets.

[0143] (4) The cut solid electrolyte membrane is hot-pressed at 95°C and 15MPa for 12 minutes to peel off the PET film and obtain a composite electrolyte membrane with a thickness of 55μm.

[0144] The membrane shrinkage rate of the dried membranes in Example 1 and Comparative Example 1 was tested. It was found that the membrane shrinkage rate of the dried membrane in Example 1 was <2%, while the membrane shrinkage rate of the dried membrane in Comparative Example 1 was 9%, indicating that the membrane structure of the present invention is more stable.

[0145] Comparative Example 2

[0146] The difference between this comparative example and Example 1 is that a porous support membrane was not used, i.e., step (4) was not performed.

[0147] The remaining preparation methods and parameters are consistent with those in Example 1.

[0148] Performance testing

[0149] The composite electrolyte membranes provided in the above embodiments and comparative examples were tested for ionic conductivity, tensile strength, interfacial impedance and thickness deviation.

[0150] Methods for testing ionic conductivity:

[0151] The electrochemical impedance spectroscopy (EIS) method was used to assemble a symmetrical battery consisting of a composite electrolyte membrane sandwiched between two stainless steel electrodes, forming a "stainless steel | composite electrolyte membrane | stainless steel" structure. The test was conducted at room temperature (25℃) with a frequency range of 1Hz to 1MHz and an amplitude of 10mV. The electrolyte bulk resistance (R) was read from the intersection of the high-frequency region and the real axis in the impedance spectrum. The ionic conductivity (σ) was calculated using the formula σ = L / (R × S), where L is the thickness of the composite electrolyte membrane (cm) and S is the effective area of ​​the electrode (cm²). 2 ).

[0152] Methods for testing tensile strength:

[0153] According to GB / T1040.3-2006 standard, the composite electrolyte membrane was cut into dumbbell-shaped specimens with a width of 10 mm and a length of 50 mm, and tested using a universal testing machine. The test environment temperature was 25℃, the relative humidity was 50% ± 5%, the tensile rate was 5 mm / min, and the maximum load at which the specimen broke was recorded. The tensile strength (σ) was calculated according to the formula σ=F / (b×d), where F is the maximum load (N), b is the specimen width (mm), and d is the specimen thickness (mm).

[0154] Methods for testing interfacial impedance:

[0155] An electrochemical impedance spectroscopy (EIS) method was used to assemble a symmetrical lithium-ion battery ("lithium|composite electrolyte membrane|lithium") using lithium metal as the electrode. The test was conducted at room temperature (25°C) with a frequency range of 0.1 Hz to 1 MHz and an amplitude of 10 mV. The interfacial impedance value was read from the semicircle diameter in the low-frequency region of the impedance spectrum; this value reflects the interfacial charge transfer resistance between the composite electrolyte membrane and the lithium electrode.

[0156] Test method for thickness deviation:

[0157] Ten test points were randomly selected on the composite electrolyte membrane using a high-precision micrometer (accuracy 0.001 mm) (avoiding the 10 mm edge area), and the thickness values ​​were measured at each point. The average thickness (davg) of the ten points was calculated, and the deviation value was calculated according to the formula: thickness deviation = [(dmax - dmin) / davg] × 100%, where dmax is the maximum thickness and dmin is the minimum thickness.

[0158] The test results are shown in Table 1.

[0159] Table 1

[0160]

[0161] analyze:

[0162] As shown in Table 1, this invention enhances the interfacial bonding and pore filling uniformity between the solid electrolyte membrane and the porous support membrane through process optimization, resulting in a synergistic improvement in the overall performance of the composite electrolyte membrane. This achieves dual optimization of "ion conductivity and mechanical strength": the room temperature ionic conductivity is increased to 1.0 × 10⁻⁶. -4 -1.6×10 -4 The tensile strength is increased to 20-23 MPa, and the interfacial resistance with the electrode is reduced to 240-310 Ω·cm. 2 It can ensure efficient ion conduction and suppress dendrite penetration through mechanical strength, and has good application prospects in solid-state secondary batteries.

[0163] A comparison of Examples 1 and 4 shows that if the modified polyethylene oxide is replaced with unmodified polyethylene oxide, it is detrimental to the compatibility of the polymer with other components and the continuity of the ion conduction pathway, resulting in a decrease in the ionic conductivity of the composite electrolyte membrane of approximately 56% (from 1.6 × 10⁻⁶). -4 S / cm decreased to 7.0×10 -5 The interfacial impedance increased to 385 Ω·cm (S / cm). 2 The tensile strength decreased to 16 MPa.

[0164] A comparison of Examples 1 and 5 shows that if the mass content of the organic solvent is 20%, that is, the solid content of the semi-solid slurry is 80%, then due to the slightly higher solvent content, the membrane density is slightly worse, and the ionic conductivity drops to 1.4 × 10⁻⁶. -4 S / cm, interface impedance rises to 260Ω·cm 2 Its overall performance is poor.

[0165] A comparison of Examples 1 and 6-7 shows that if the mass ratio of polymer to organic solvent is too small (e.g., 40:70), the excessive solvent leads to excessive slurry fluidity, making it prone to uneven filling during rolling, increasing the thickness deviation to 4.8%, and reducing the electrical conductivity to 9.0 × 10⁻⁶. -5 S / cm; if the ratio is too high (e.g., 75:45), insufficient solvent will result in poor slurry flowability, uneven dispersion of solid electrolyte particles, and a decrease in conductivity to 8.5 × 10⁻⁶. -5 S / cm, the interfacial impedance increases to 370Ω·cm 2 .

[0166] A comparison between Example 1 and Example 8 shows that if the pore size of the porous support membrane is too small, the continuity of the ion conduction path is weakened, resulting in a decrease in ionic conductivity to 8.0 × 10⁻⁶. -5 Although the tensile strength increased slightly to 24 MPa, the overall performance decreased.

[0167] A comparison of Example 1 and Examples 9-10 shows that if the vacuum drying temperature is too low, the solvent residue increases, and the interfacial impedance rises to 320 Ω·cm. 2 If the temperature of vacuum drying is too high, the plasticizer will easily volatilize, causing the tensile strength to drop to 20 MPa and the flexibility of the film to decrease.

[0168] A comparison of Example 1 and Example 11 shows that if the vacuum drying time is too long (e.g., 8 hours), the plasticizer will volatilize excessively, the film will become more brittle, the tensile strength will drop to 19 MPa, and the interfacial resistance will rise to 280 Ω·cm. 2 .

[0169] A comparison between Example 1 and Example 12 shows that if the two-step hot pressing described in step (4) is not performed, the film will lack sufficient density, its relative density will decrease, and its ionic conductivity will drop to 6.0 × 10⁻⁶. -5 S / cm, interface impedance increased to 380Ω·cm 2 The thickness deviation reached 7%, which failed to meet the performance requirements.

[0170] As can be seen from the comparison between Example 1 and Comparative Example 1, the process route provided by the present invention significantly reduces the amount of solvent used, the semi-solid slurry has strong plasticity and no sagging phenomenon; VOCs emissions are greatly reduced; the drying time is reduced from 8h to 3h, and the production efficiency is improved; the ionic conductivity of the obtained composite electrolyte membrane is 1.7 times that of Comparative Example 1, the tensile strength is increased by 156%, and the overall performance is better.

[0171] As can be seen from the comparison between Example 1 and Comparative Example 2, if a porous support membrane is not used, the composite electrolyte membrane loses its mechanical support, and the tensile strength drops sharply to 8 MPa (only 35% of that in Example 1), with a thickness deviation of 10.2%. Although the ionic conductivity is similar, the mechanical properties cannot meet the requirements for dendrite resistance.

[0172] It should be noted that the ionic conductivity data for Comparative Example 1 (9.6 × 10⁻⁶) -5 The S / cm ratio is slightly higher than in some embodiments, presumably because solvent residue in traditional processes has a certain auxiliary effect on ion conduction. However, this advantage cannot make up for its poor mechanical properties and large thickness deviation, and solvent residue will lead to a decrease in long-term cycle stability.

[0173] It should be noted that the present invention is illustrated through the above embodiments, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a composite electrolyte membrane, characterized in that, The preparation method includes the following steps: A polymer premix is ​​prepared, and then the polymer premix is ​​mixed with a solid electrolyte to obtain a semi-solid slurry with a solid content ≥80%. The semi-solid slurry is pressed into shape to obtain a solid electrolyte membrane; The solid electrolyte membrane and the porous support membrane are combined and then hot-pressed to obtain the composite electrolyte membrane.

2. The preparation method according to claim 1, characterized in that, The preparation method of the polymer premix includes: The polymer and organic solvent are mixed, and then a plasticizer is added for blending to obtain the polymer premix; Preferably, the polymer comprises polyvinylidene fluoride and modified polyethylene oxide; Preferably, the modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide; Preferably, the grafting rate of the modified polyethylene oxide is 12-15%; Preferably, the mass ratio of polyvinylidene fluoride to modified polyethylene oxide is (15-25):(30-50); Preferably, the mass ratio of the polymer to the organic solvent is (45-75):(50-70); Preferably, the organic solvent includes any one or a combination of at least two of N-methylpyrrolidone, dimethylformamide, or dimethyl sulfoxide; Preferably, the plasticizer comprises any one or a combination of at least two of poly(ethylene glycol dimethyl ether), polyethylene glycol, or di-n-butyl phthalate; Preferably, the mass ratio of the polymer to the plasticizer is (45-75):(1-15); Preferably, the solid content of the polymer premix is ​​45-65 wt%. Preferably, the working temperature during the preparation of the polymer premix is ​​60-80℃.

3. The preparation method according to claim 1 or 2, characterized in that, The solid electrolyte is an oxide solid electrolyte; Preferably, the oxide solid electrolyte includes any one or a combination of at least two of LLTO, LLZTO, LLZO, LATP, or NZSP; Preferably, the particle size D50 of the solid electrolyte is 1-5 μm; Preferably, the mass ratio of the polymer premix to the oxide solid electrolyte is (40-50):(50-75); Preferably, the solid content of the semi-solid slurry is 80-90 wt%.

4. The preparation method according to any one of claims 1-3, characterized in that, The pressing and forming method includes roll forming; Preferably, during the rolling process, the working temperature is 60-80℃, the linear pressure is 10-20kN / m, and the rolling speed is 5-15m / min; Preferably, the thickness of the solid electrolyte membrane is 40-100 μm; Preferably, the flatness deviation of the solid electrolyte membrane is <5%.

5. The preparation method according to any one of claims 1-4, characterized in that, The porous support membrane is made of any one of polypropylene porous mesh material, polyethylene porous mesh material, or metal mesh. Preferably, the porous support membrane has a pore size of 1-45 mesh; Preferably, the thickness of the porous support membrane is 30-100 μm; Preferably, the hot pressing is a step-by-step hot pressing, which includes a first-step hot pressing, drying and a second-step hot pressing performed sequentially.

6. The preparation method according to claim 5, characterized in that, The temperature of the hot pressing step is 80-110℃; Preferably, the pressure of the hot pressing step is 5-15 MPa; Preferably, the hot pressing time for the first step is 5-15 minutes; Preferably, the temperature of the two-step hot pressing is 90-120℃; Preferably, the pressure of the two-step hot pressing is 15-25 MPa; Preferably, the two-step hot pressing time is 3-10 minutes.

7. The preparation method according to claim 5 or 6, characterized in that, The drying temperature is 50-80℃; Preferably, the drying time is 1-6 hours; Preferably, the drying method includes vacuum drying and / or hot air circulation drying.

8. The preparation method according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Preparation of polymer premix: The polymer is added to an organic solvent and stirred at 60-80°C for 2-8 hours. Then, a plasticizer is added and stirred to obtain the polymer premix. The polymer comprises polyvinylidene fluoride and modified polyethylene oxide in a mass ratio of (15-25):(30-50), wherein the modified polyethylene oxide is maleic anhydride-grafted polyethylene oxide with a grafting rate of 12-15%; the mass ratio of the polymer to the organic solvent is (45-75):(50-70); the mass ratio of the polymer to the plasticizer is (45-75):(1-15); and the solid content of the polymer premix is ​​45-65 wt%. (2) Add the oxide solid electrolyte with a particle size D50 of 1-5 μm to the polymer premix and disperse it at a speed of 800-1200 rpm for 2-8 hours to obtain a semi-solid slurry with a solid content of 80-90 wt% and a dough-like consistency. The mass ratio of the polymer premix to the oxide solid electrolyte is (40-50):(50-75); based on the mass of the semi-solid slurry, the mass content of the organic solvent is 10-20%. (3) The semi-solid slurry is rolled at 60-80℃, with a linear pressure of 10-20kN / m and a rolling speed of 5-15m / min to obtain a solid electrolyte membrane with a thickness of 40-100μm and a flatness deviation of <5%. (4) The solid electrolyte membrane and the porous support membrane are stacked, and then hot-pressed for 5-15 minutes at 80-110℃ and 5-15MPa to fill the mesh of the porous support membrane with the solid electrolyte membrane. Then, the membrane is vacuum dried at 50-80℃ for 1-6 hours to obtain the dried composite membrane. The dried composite membrane is placed in a mold with a built-in release film and subjected to a two-step hot pressing at 90-120℃ and 15-25MPa for 3-10 minutes to obtain a composite electrolyte membrane with a thickness of 35-90μm and a relative density ≥92%.

9. A composite electrolyte membrane, characterized in that, The composite electrolyte membrane is prepared using the preparation method described in any one of claims 1-8.

10. The application of the composite electrolyte membrane as described in claim 9 in the field of secondary batteries.

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