Composite diaphragm with high ionic conductivity, composite solid electrolyte and preparation method thereof

Abstract

The invention relates to a composite diaphragm with high ionic conductivity, a composite solid electrolyte and a preparation method thereof. The composite diaphragm is composed of a lithium lanthanum-based fluorine-doped solid electrolyte LLMOF and a base membrane, the chemical general formula of the LLMOF is Li < x > La < y > M < 1 > < z > M < 2 > < w > M < 3 > O < 6 > F, wherein M1 is a tetravalent cation, M2 is a pentavalent cation, and M3 is a hexavalent cation; 1 < x + 3y < 5, 0 < x < = 2, and 1 / 3 < y < 5 / 3; 0 < = z < = 2, 0 < = w < = 2, 0 < = u < = 2, z + w + u = 2; the base membrane is a large-aperture base membrane, and the aperture r is more than or equal to 200nm and less than or equal to 1mu m; the particle size D50 of the LLMOF is 50 nm to 1 [mu] m, and the particle size D50 of the LLMOF is less than or equal to the aperture r of the base film. According to the composite diaphragm disclosed by the invention, the LLMOF solid electrolyte with an ion channel function is introduced, so that efficient conduction of ions is realized; the particle size is matched with that of a large-aperture base membrane, the membrane can be uniformly embedded into membrane holes, a continuous conduction path is constructed, and the ionic conductivity is improved; meanwhile, the composite diaphragm has excellent thermal stability and interface wettability, interface impedance is effectively reduced, and growth of lithium dendrites is inhibited.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, and in particular to a composite membrane with high ionic conductivity, a composite solid electrolyte, and a method for preparing the same. Background Technology

[0002] In existing battery systems, traditional polyolefin separators (such as polyethylene (PE) membranes) or separators modified with inorganic oxides (such as Al2O3@PE) are widely used in liquid or gel electrolytes. These separators are essentially electronic insulators, and ion conduction depends entirely on the liquid electrolyte injected into their pores. However, these separators themselves have extremely low ionic conductivity (typically <10). -5 It has a low concentration of mS / cm and poor compatibility with polar solvents, making it difficult to form stable interfacial contacts. Especially in high-voltage systems, it is prone to interfacial dewetting and ion migration hindrance, which limits the development of high-performance electrolyte systems.

[0003] To improve safety and interfacial stability, various polymer-based in-situ solid-state or gel electrolyte systems have been developed, especially in-situ polymerization of ether polymers such as polyethylene oxide (PEO) and their monomers at the electrode interface. However, existing in-situ polymerization systems still face several problems: easy crystallization during polymerization, phase separation leading to structural inhomogeneity; and low ionic conductivity (<10). -4 The lithium-ion transference number is also low (approximately 0.2–0.3); the electrochemical window is limited, and most systems cannot withstand voltages higher than 3.8V; in addition, volume shrinkage during polymerization easily causes debonding at the electrode interface, and the mechanical strength of the film after deposition is insufficient to meet the requirements for structural stability or dendrite suppression, exhibiting a low critical current density (CCD < 1.6 mA / cm). 2 ).

[0004] On the other hand, some polymer electrolyte systems improve mechanical properties or ionic conductivity by adding inorganic fillers (such as oxide particles). However, improper particle size distribution often leads to membrane pore blockage, hindering the formation of ion migration pathways and reducing overall ionic conductivity. Furthermore, insufficient dispersion of the filler can easily cause agglomeration, resulting in structural inhomogeneity and local interfacial incompatibility. Meanwhile, commercially available polyolefin membranes and some polymer systems exhibit poor thermal stability, easily shrinking, deforming, or even melting at high temperatures (e.g., 200°C), posing serious safety hazards. Therefore, there is an urgent need to develop a novel composite membrane and polymer electrolyte system with high ionic conductivity, excellent interfacial wettability, and thermal stability. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a composite membrane with high ionic conductivity, a composite solid electrolyte, and a method for preparing the same.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a solution mainly composed of a lithium lanthanum-based fluorine-doped solid electrolyte LLMOF and a base film;

[0007] The general chemical formula of the LLMOF is Li x La y M1 z M2 w M3 u O6F; where M1 is a tetravalent cation, M2 is a pentavalent cation, and M3 is a hexavalent cation; 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3; 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2;

[0008] The base film is a large-pore base film, and the pore size r of the base film satisfies 200nm ≤ r ≤ 1μm; the particle size D50 of the LLMOF is 50nm. -1 μm, and the particle size D50 of the LLMOF is less than or equal to the pore size r of the base film.

[0009] Preferably, the macroporous base membrane is a base membrane formed of polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), or polyethylene terephthalate (PET), or a double-layer composite base membrane or a triple-layer composite base membrane formed by a combination of the above materials.

[0010] Preferably, M1 is one or more of Zr, Ti, Hf, Si, Ge, and Sn; M2 is one or more of Nb, Sb, Bi, V, and Ta; and M3 is one or more of W, Cr, Mo, and Mn.

[0011] Secondly, embodiments of the present invention provide a method for preparing the composite separator described in the first aspect above, the method comprising:

[0012] The inorganic filler lithium lanthanum-based fluorine-doped solid electrolyte LLMOF, dispersant and solvent were mixed in a mass ratio of [5-20]:[1-2]:[78-94] and stirred until homogeneous to obtain a mixed solution;

[0013] The base membrane is immersed in the mixed solution, ultrasonically treated under vacuum, and then vacuum dried in a vacuum oven to obtain the composite membrane.

[0014] Preferably, the dispersant comprises: polyvinylpyrrolidone (PVP) and / or 3-aminopropyltriethoxysilane (KH-550); the solvent comprises: one or more of ethanol, deionized water, N-methylpyrrolidone (NMP), and acetone;

[0015] During the ultrasonic treatment, the vacuum level is ≤0.5Pa, the frequency of the ultrasonic probe is 20-80kHz, and the ultrasonic time is 30-60min.

[0016] The temperature of the oven is 40-90℃.

[0017] Thirdly, embodiments of the present invention provide a composite solid electrolyte, comprising: the composite membrane described in the first aspect or the composite membrane prepared by the preparation method described in the second aspect, and a solid electrolyte obtained by in-situ polymerization.

[0018] Preferably, the preparation method includes:

[0019] The composite diaphragm is immersed in the prepared in-situ polymerization precursor solution for 0.5-10 hours.

[0020] The impregnated membrane is polymerized in situ under ultraviolet light to obtain a composite solid electrolyte; wherein the ultraviolet light is emitted by an ultraviolet lamp with an irradiation wavelength of 250-420nm and a power of 2-10W / cm. 2 The irradiation time is 0.5-6 hours.

[0021] Preferably, before immersing the composite membrane into the prepared in-situ polymerization precursor solution, the method further includes: preparing the in-situ polymerization precursor solution, specifically including:

[0022] A first mixture is prepared by mixing monomers, crosslinking agents, and octafluoropentyl acrylate (OFPA) in a mass ratio of [1-2]:[1-2]:[6-8]. An initiator, comprising 0.5-3 wt% of the mass of the first mixture, is added to the first mixture to form a first solution. The monomers include one or more of vinylene carbonate (VEC), tetrahydrofuran acrylate (THFA), and ethylene glycol phenyl ether acrylate (EPHA). The crosslinking agents include one or more of pentaerythritol triacrylate (PETA) and dipentaerythritol pentaacrylate (DPPA). The initiators include one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0023] A second solution is prepared by heating and mixing a linear dinitrile compound with a lithium salt at a mass ratio of 1:1 to 5:1 at 40-80°C; the linear dinitrile compound includes one or more of succinic anionyl, malononitrile, and glutaronitrile; the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium dioxalate borate.

[0024] The first solution and the second solution are mixed at a volume ratio of 1:1 to 1:3 to form the in-situ polymerization precursor solution.

[0025] More preferably, the amount of the initiator added is 1.5 wt% of the mass of the first mixture;

[0026] The mass ratio of the linear dinitrile compound to the lithium salt is 3:1;

[0027] The volume ratio of the first solution to the second solution is 1:2;

[0028] The ultraviolet lamp has an irradiation wavelength of 365nm and a power of 4-6W / cm². 2 The time is 3-5 hours.

[0029] Fourthly, embodiments of the present invention provide a solid-state battery, comprising the composite solid-state electrolyte described in the second aspect above, or comprising the composite solid-state electrolyte obtained by in-situ polymerization of the preparation method described in the third aspect above.

[0030] The composite separator provided in this invention achieves continuous and stable ion conduction channels within the separator by introducing lithium lanthanum-based fluorine-doped (LLMOF) material with a particle size D50 less than or equal to the membrane pore size into a macroporous base membrane, thereby improving the overall ion migration efficiency of the system. The LLMOF possesses a rigid framework structure with tunable composition. The introduction of diverse coordination environments through multivalent cation doping facilitates the formation of open channels conducive to lithium-ion transport. Simultaneously, fluorine doping further enhances the material's polarity and interfacial wettability, improving interfacial contact with the electrolyte and electrodes and reducing interfacial impedance. Furthermore, the particle size control of the LLMOF, matching that of the macroporous polymer base membrane, helps it to be uniformly embedded in the membrane pores without clogging micropores, thus maintaining the separator's mechanical support function while endowing it with excellent ion conductivity and interfacial stability. The composite separator proposed in this invention can significantly improve ion transport capacity, interfacial compatibility, and thermal stability in solid-state or gel electrolyte systems, providing strong support for high-performance battery systems. Attached Figure Description

[0031] Figure 1 A scanning electron microscope (SEM) image of a large-pore base film provided in an embodiment of the present invention;

[0032] Figure 2 The critical current density curves of Comparative Example 1 and Example 1 provided for embodiments of the present invention. Detailed Implementation

[0033] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0034] This invention provides a composite membrane with high ionic conductivity, a composite solid electrolyte, and a method for preparing the same.

[0035] The composite membrane proposed in this invention is mainly composed of lithium lanthanum-based fluorine-doped solid electrolyte LLMOF and a base membrane.

[0036] The general chemical formula of LLMOF is Li x La y M1 z M2 w M3 u O6F; where M1 is a tetravalent cation, M2 is a pentavalent cation, and M3 is a hexavalent cation; 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3; 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2.

[0037] In the optional scheme, M1, M2, and M3 in LLMOF must have at least two components at the same time, that is, two of z, w, and u are not simultaneously zero.

[0038] Specifically, M1 is one or more of Zr, Ti, Hf, Si, Ge, and Sn; M2 is one or more of Nb, Sb, Bi, V, and Ta; and M3 is one or more of W, Cr, Mo, and Mn.

[0039] The base membrane is a macroporous membrane, with a pore size r satisfying 200 nm ≤ r ≤ 1 μm; the particle size D50 of the LLMOF is 50 nm. -1 μm, and the particle size D50 of LLMOF is less than or equal to the pore size r of the base film.

[0040] The macroporous base membrane is specifically a base membrane formed of polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA) or polyethylene terephthalate (PET), or a double-layer composite base membrane or a triple-layer composite base membrane formed by a combination of the above materials.

[0041] The composite membrane of the present invention can be prepared by the following method. The main preparation steps include:

[0042] Step 110: Mix the inorganic filler lithium lanthanum-based fluorine-doped solid electrolyte LLMOF, dispersant and solvent in a mass ratio of [5-20]:[1-2]:[78-94] and stir until homogeneous to obtain a mixed solution;

[0043] LLMOF can be prepared by solid-state sintering. For example, it can be prepared by mixing Li2CO3, La2O3, oxides of M1, M2, and M3 with LiF according to the molar ratio of LLMOF elements, and then sintering at high temperature, which can be controlled between 800-1300℃.

[0044] The dispersants include: polyvinylpyrrolidone (PVP) and / or 3-aminopropyltriethoxysilane (KH-550).

[0045] Solvents include one or more of the following: ethanol, deionized water, N-methylpyrrolidone (NMP), and acetone.

[0046] Step 120: Immerse the base membrane in the mixed solution, perform ultrasonic treatment under vacuum, and then dry it in an oven to obtain the composite membrane.

[0047] The base membrane is the large-pore base membrane described above.

[0048] During ultrasonic treatment, the vacuum level is ≤0.5Pa, the frequency of the ultrasonic probe is 20-80kHz, and the ultrasonic time is 30-60min; the temperature of the oven is 40-90℃.

[0049] The ultrasound in this step is applied to the combined system of the base membrane and the mixed solution; that is, the ultrasound treatment is performed under vacuum. Under the action of ultrasound, the active components in the mixed solution can penetrate more fully into the membrane pores, while also breaking up air bubbles, improving the uniform distribution of the liquid within the membrane, and promoting uniform filling of the components in the membrane rather than aggregation.

[0050] A vacuum effectively removes air from the membrane pores, allowing the solution to more easily penetrate the micropores and improving filling efficiency. Appropriate heating reduces the viscosity of the mixture, making it easier to flow and enter the base membrane micropores, while also promoting a more stable bond between the active components and the base membrane material.

[0051] In a preferred embodiment, the base membrane can be immersed in a mixed solution, placed in a vacuum oven with an integrated ultrasonic probe, ultrasonically dried, removed from the solution, and then vacuum dried to obtain a composite diaphragm.

[0052] Specifically, the base film is immersed in the mixed solution and then placed together in a vacuum oven with an integrated ultrasonic probe. Both vacuum ultrasonication and drying are performed within the vacuum oven with the integrated ultrasonic probe, at a vacuum level ≤0.5 Pa, an ultrasonic probe frequency of 20-80 kHz, an ultrasonication time of 30-60 min, and an oven temperature of 40-90℃. Simultaneously, the oven temperature is used for heat preservation.

[0053] Under the combined effect of heating and vacuum, the active components can be more effectively and uniformly penetrate deep into the membrane pores, reducing residual bubbles, enhancing structural density and interfacial adhesion, and improving drying efficiency. Under these conditions, ultrasound, conducted through the liquid, promotes the full penetration and uniform distribution of the active components in the mixture within the membrane pore structure, and prevents the agglomeration of the filler, thereby improving the uniformity of the membrane structure and the quality of interfacial contact.

[0054] The composite separator proposed and prepared in this invention achieves continuous and stable ion conduction channels within the separator by introducing lithium lanthanum-based fluorine-doped (LLMOF) material with a particle size D50 less than or equal to the membrane pore size into a macroporous base membrane, thereby improving the overall ion migration efficiency of the system. The LLMOF possesses a rigid framework structure with tunable composition. The introduction of diverse coordination environments through multivalent cation doping facilitates the formation of open channels conducive to lithium-ion transport. Simultaneously, fluorine doping further enhances the material's polarity and interfacial wettability, improving interfacial contact with the electrolyte and electrodes and reducing interfacial impedance. Furthermore, the particle size control of LLMOF, matching the macroporous polymer base membrane, helps it to be uniformly embedded in the membrane pores without clogging micropores, thus endowing the separator with excellent ion conductivity and interfacial stability while maintaining its mechanical support function. The composite separator proposed in this invention can significantly improve ion transport capacity, interfacial compatibility, and thermal stability in solid-state or gel electrolyte systems, providing strong support for high-performance battery systems.

[0055] The composite membrane proposed above can be used together with a solid electrolyte prepared by in-situ polymerization of ionic liquid as electrolyte to construct a high-performance composite solid electrolyte.

[0056] Specific preparation methods include:

[0057] Step 210: Immerse the composite membrane in the prepared in-situ polymerization precursor solution for 0.5-10 hours.

[0058] The preparation method for the in-situ polymerization precursor solution used in this step is as follows:

[0059] A first mixture is prepared by mixing monomers, crosslinking agents, and octafluoropentyl acrylate (OFPA) in a mass ratio of [1-2]:[1-2]:[6-8]. An initiator, comprising 0.5-3 wt% of the mass of the first mixture, is added to the first mixture to prepare a first solution. The monomers include one or more of vinylene carbonate (VEC), tetrahydrofuran acrylate (THFA), and ethylene glycol phenyl ether acrylate (EPHA). The crosslinking agents include one or more of pentaerythritol triacrylate (PETA) and dipentaerythritol pentaacrylate (DPPA). The initiators include one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-hydroxy-2-methyl-1-phenyl-1-propanone.

[0060] A second solution is prepared by heating and mixing a linear dinitrile compound with a lithium salt at a mass ratio of 1:1 to 5:1 at 40-80°C; wherein the linear dinitrile compound includes one or more of butadionitrile, malononitrile, and glutaronitrile; and the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, and lithium dioxalate borate.

[0061] The first solution and the second solution are mixed at a volume ratio of 1:1 to 1:3 to form an in-situ polymerization precursor solution.

[0062] Step 220: The impregnated membrane is polymerized in situ under ultraviolet light to obtain a composite solid electrolyte;

[0063] The ultraviolet light is emitted by an ultraviolet lamp with an irradiation wavelength of 250-420nm and a power of 2-10W / cm². 2 The irradiation time is 0.5-6 hours.

[0064] In the above preparation method, more preferred parameters are: the amount of initiator added is 1.5 wt% of the mass of the first mixture; the mass ratio of the linear dinitrile compound to the lithium salt is 3:1; the volume ratio of the first solution to the second solution is 1:2; the irradiation wavelength of the ultraviolet lamp is 365 nm, and the power is 4-6 W / cm². 2 The time is 3-5 hours.

[0065] In the above preparation method, a dual-solvent in-situ polymerization precursor is constructed by combining a first solution of an organic polymer monomer / crosslinking agent system with a second solution of a lithium salt-containing linear dinitrile solvent system, thereby achieving synergistic optimization of electrochemical performance and structural uniformity.

[0066] The first solution contains octafluoroamyl acrylate (OFPA) with a high fluorine content. The introduction of multiple electronegative fluorine atoms into its molecular structure can significantly enhance the antioxidant capacity of the polymerized electrolyte, thereby significantly improving the oxidation stability voltage of the composite electrolyte.

[0067] In the second solution, the –C≡N group in the straight-chain dinitrile molecule can react with Li + It forms reversible coordination, effectively dissolves lithium salts and provides continuous lithium-ion migration channels, thereby forming a uniform, stable, and high-transfer-number lithium-ion transport network, improving the lithium-ion migration efficiency in the solid-state system.

[0068] This invention mixes two solutions in a volume ratio of 1:1–1:3 to construct a dual-solvent network with a "polymerizable structure + soluble lithium salt system". In-situ polymerization is achieved under ultraviolet light irradiation. The amorphous crosslinked network after polymerization solves the problem of uniformity during polymerization.

[0069] The fluorinated monomers in the composite electrolyte prepared by this invention possess strong electronegativity, enabling them to attract surrounding electron pairs and form stable covalent bonds. This strong electronegativity results in a more uniform distribution of fluorine atoms within the molecule, thereby reducing intermolecular forces, lowering surface energy, making the electrolyte easier to spread on the electrode surface, reducing microscopic voids at the solid-solid interface, and lowering surface impedance. Furthermore, the rigid LLMOF framework enhances the mechanical properties of the electrolyte and effectively inhibits the growth of lithium dendrites.

[0070] The composite solid electrolyte of the present invention can be applied in solid-state batteries, and has high ionic conductivity, wide electrochemical stability window and good interface compatibility, which helps to improve the energy density, cycle stability and safety of the battery.

[0071] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0072] Example 1

[0073] This embodiment prepares a composite solid electrolyte.

[0074] First, prepare solid electrolyte Li 1.25 La 0.58 Nb₂O₆F, denoted as LLNOF, includes the following steps:

[0075] Li₂CO₃, La₂O₃, Nb₂O₅, and LiF were mixed in a molar ratio of 0.625:0.29:1:1. After homogeneous mixing, the mixture was sintered in a tube furnace to produce the aforementioned LLNOF. The sintering conditions were: nitrogen atmosphere flow rate of 1 L / min, heating rate from room temperature to sintering temperature of 5 °C / min, sintering temperature of 1200 °C, and holding time of 6 hours.

[0076] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0077] The first step involves mixing inorganic filler (LLNOF): dispersant (PVP): solvent (ethanol, water content ≤100ppm) in a ratio of 15g:1g:84g, and then stirring at room temperature (25℃) for 500 rpm for 5 hours to obtain a uniformly mixed solution.

[0078] The second step is to pour the well-stirred mixture into a petri dish and then place a large-pore PP membrane (200nm≤r≤1μm, SEM image of the large-pore PP membrane used is shown below) onto the petri dish. Figure 1 (As shown.) Completely immersed in the solution, then transferred to a 50°C vacuum oven and evacuated to a vacuum level of 5 × 10⁻⁶. -3 Pa. The vacuum oven integrates a 40kHz ultrasonic probe (power density 0.5W / cm²). 2 This process breaks down agglomerates. Ultrasonication is maintained for 60 minutes under heating and vacuum conditions to ensure the inorganic filler fully fills the pores of the base membrane.

[0079] The third step involves removing the diaphragm from the petri dish and placing it in a drying container to dry it completely in an oven at 50°C, thus obtaining a macroporous diaphragm containing electrolyte material, which is the composite diaphragm.

[0080] Step 4: Prepare the first solution: Mix VEC:PETA:OFPA in a mass ratio of 2g:2g:8g to obtain a mixed solution. Add the UV initiator: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) at a concentration of 1.5 wt% of the total mass of the mixed solution to prepare the first solution.

[0081] Step 5: Prepare the second solution: Mix succinate (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at a mass ratio of 3g:1g under heating conditions at 60°C.

[0082] Step 6: Mix the first solution and the second solution at a volume ratio of 1:2 to form an in-situ polymerization precursor solution.

[0083] Step 7: Immerse the prepared composite membrane in the prepared in-situ polymerization precursor solution for 3 hours.

[0084] Step 8: Place the impregnated composite membrane under a UV lamp for photopolymerization. The UV lamp power is 6W / cm². 2 Irradiation was performed at 380 nm for 60 min to achieve the absorption peak.

[0085] The composite solid electrolyte required in this embodiment is obtained through the above steps.

[0086] Example 2

[0087] This embodiment prepares a composite solid electrolyte.

[0088] First, prepare solid electrolyte Li 1.25 La 0.58 Ta₂O₆F, denoted as LLTOF, includes the following steps:

[0089] Li₂CO₃, La₂O₃, Ta₂O₅, and LiF were mixed in a molar ratio of 0.625:0.29:1:1. After homogeneous mixing, the mixture was sintered in a tube furnace to produce the aforementioned LLTOF. The sintering conditions were: nitrogen atmosphere flow rate of 1 L / min, heating rate from room temperature to sintering temperature of 5 °C / min, sintering temperature of 1200 °C, and holding time of 6 hours.

[0090] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler. The method was the same as in Example 1 and will not be described in detail here.

[0091] Example 3

[0092] This embodiment prepares a composite solid electrolyte.

[0093] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0094] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0095] The first step involves mixing inorganic filler (LLNOF): dispersant (PVP): solvent (ethanol, water content ≤100ppm) in a ratio of 20g: 2g: 78g, and then stirring at room temperature (25℃) for 500 rpm for 5 hours to obtain a uniformly mixed solution.

[0096] The methods for steps two through eight are the same as in Example 1, and will not be described further.

[0097] Example 4

[0098] This embodiment prepares a composite solid electrolyte.

[0099] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0100] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0101] The first step involves mixing inorganic filler (LLNOF): dispersant (PVP): solvent (ethanol, water content ≤100ppm) in a ratio of 10g:1g:89g, and then stirring at room temperature (25℃) for 500 rpm for 5 hours to obtain a uniformly mixed solution.

[0102] The methods for steps two through eight are the same as in Example 1, and will not be described further.

[0103] Example 5

[0104] This embodiment prepares a composite solid electrolyte.

[0105] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0106] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0107] In the second step, the ultrasound is maintained under heating and vacuum conditions for 30 minutes. The remaining steps are the same as in Example 1 and will not be described in detail.

[0108] Example 6

[0109] This embodiment prepares a composite solid electrolyte.

[0110] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0111] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0112] The methods for steps one through three are the same as in Example 1, and will not be described further.

[0113] Step 4: Prepare the first solution: Mix VEC:PETA:OFPA in a mass ratio of 1.5g:1.5g:7g to obtain a mixed solution. Add the UV initiator: diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO) at a concentration of 1 wt% of the total mass of the mixed solution to prepare the first solution.

[0114] The methods for steps five through eight are the same as in Example 1, and will not be described further.

[0115] Example 7

[0116] This embodiment prepares a composite solid electrolyte.

[0117] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0118] The methods for steps one through four are the same as in Example 1, and will not be described further.

[0119] Step 5: Prepare the second solution: Mix succinate (SN) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) at a mass ratio of 3g:2g under heating conditions at 60°C.

[0120] The methods for steps six through eight are the same as in Example 1, and will not be described further.

[0121] Example 8

[0122] This embodiment prepares a composite solid electrolyte.

[0123] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0124] The methods for steps one through seven are the same as in Example 1, and will not be described further.

[0125] Step 8: Place the impregnated composite membrane under a UV lamp for photopolymerization. The UV lamp power is 6W / cm². 2 Irradiate the absorption peak at 300nm for 30 minutes.

[0126] Example 9

[0127] This embodiment prepares a composite solid electrolyte.

[0128] First, prepare solid electrolyte Li 0.5 La 1.17NbCrO6F, denoted as LLNCOF, includes the following steps:

[0129] Li₂CO₃, La₂O₃, Nb₂O₅, CrO₃, and LiF were mixed in a molar ratio of 0.25:0.585:0.5:1:1. After homogeneous mixing, the mixture was sintered in a tube furnace to produce the aforementioned LLNCOF. The sintering conditions were: nitrogen atmosphere flow rate of 1 L / min, heating rate from room temperature to sintering temperature of 5 °C / min, sintering temperature of 1200 °C, and holding time of 6 hours.

[0130] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler. The method was the same as in Example 1 and will not be described in detail here.

[0131] Example 10

[0132] This embodiment prepares a composite solid electrolyte.

[0133] First, the solid electrolyte LiLaNbTiO6F, denoted as LLNTOF, is prepared, including the following steps:

[0134] Li₂CO₃, La₂O₃, Nb₂O₅, TiO₂, and LiF were mixed in a molar ratio of 0.5:0.5:0.5:1:1. After homogeneous mixing, the mixture was sintered in a tube furnace to produce the aforementioned LLNCOF. The sintering conditions were: nitrogen atmosphere flow rate of 1 L / min, heating rate from room temperature to sintering temperature of 5 °C / min, sintering temperature of 1200 °C, and holding time of 6 hours.

[0135] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler. The method was the same as in Example 1 and will not be described in detail here.

[0136] Comparative Example 1

[0137] A composite solid electrolyte was prepared in this comparative example.

[0138] This comparative example uses a commercial PP membrane (pore size r≤100nm) to replace the large-pore PP base membrane in the preparation of the composite solid electrolyte.

[0139] The other methods and steps are the same as in Example 1, and will not be described in detail here.

[0140] Comparative Example 2

[0141] A semi-solid electrolyte was prepared in this comparative example.

[0142] This comparative example directly uses a commercial PE diaphragm with a 3:1 mixed solution of SN:LiTFSI as the electrolyte to obtain a semi-solid electrolyte.

[0143] Comparative Example 3

[0144] A composite solid electrolyte was prepared in this comparative example.

[0145] First, prepare solid electrolyte Li 1.25 La 0.58 The method for Nb2O6F (LLNOF) is the same as in Example 1, and will not be described further.

[0146] Next, a composite solid electrolyte was prepared using a solid electrolyte as an inorganic filler.

[0147] In the second step, simply pour the well-stirred mixture into a petri dish, completely immerse the large-pore PP base membrane in the solution, maintain immersion for 60 minutes, and do not perform ultrasonic treatment.

[0148] The remaining steps are the same as in Example 1, and will not be described in detail here.

[0149] The test methods and calculation methods for various parameters of the electrolytes prepared in Examples 1-8 and Comparative Examples 1-3, as well as the specific methods for coin cell assembly testing, are as follows:

[0150] Test Method 1: (1) The determination of ionic conductivity is performed by electrochemical impedance spectroscopy (EIS) on an electrochemical workstation. The specific steps are as follows: First, the electrolyte material is cut into small circular pieces and sandwiched between two stainless steel (SS) inert electrodes, and then the battery is installed for testing. To ensure the accuracy of the test, the test battery is placed in a constant temperature chamber for temperature control. In the EIS test, the frequency range is set to 0.01Hz to 1MHz, and the amplitude voltage is set to 10mV, in order to accurately measure the resistance of the electrolyte. Then, by analyzing the Nyquist impedance spectrum, the ionic conductivity of the electrolyte can be calculated using the corresponding formula as follows: In the process of determining ionic conductivity, d in the formula represents the thickness of the electrolyte (≈20μm±2), R is the volume resistance of the electrolyte read from the Nyquist impedance diagram of EIS, and S represents the effective contact area between the electrolyte and the stainless steel inert electrode. To ensure the accuracy of the measurement, when testing the ionic conductivity at different temperatures, the constant temperature chamber needs to be set to the target temperature and maintained for half an hour to allow the test battery to reach thermal equilibrium. This step ensures the stability of the test environment, thereby allowing accurate measurement of the ionic conductivity of the electrolyte at various temperatures. (2) Sheet resistance = impedance value × area.

[0151] Test Method 2: To determine the electrochemical window of the electrolyte, a lithium metal sheet was used as both the reference and counter electrode, while a stainless steel sheet (SS) was used as the working electrode. During the experiment, a lithium / stainless steel (Li|SS) battery was assembled in a glove box, and then linear sweep voltammetry (LSV) was performed in a constant temperature chamber at room temperature. The scan rate was set to 1 millivolt per second (mV / s), scanning from the open-circuit voltage to 6V.

[0152] Test Method 3: To test the mechanical strength of the electrolyte, a universal tensile testing machine was used. The electrolyte was cut into a 5×1cm rectangle, and the thickness of the electrolyte membrane was measured with vernier calipers. The cut electrolyte was then clamped onto the tensile testing machine, and the parameters were set for testing.

[0153] Test Method 4: To test the critical current density (CCD) of the battery, a lithium metal|electrolyte|lithium metal coin cell was assembled and subjected to cyclic testing at different current densities. Specifically, a constant current deposition / stripping method was used (1 hour per step), with increasing current density (0.1 mA / cm²). 2 Perform cyclic testing. Record the maximum current density during stable cycling as the critical current density.

[0154] Test Method 5: To test thermal stability, the electrolyte was placed in an oven with an increasing temperature gradient. Each temperature range was maintained for 10 minutes, and the critical temperature at which the electrolyte volume shrinkage occurred was recorded. The test temperature ranges included: 50℃, 80℃, 100℃, 120℃, 140℃, 160℃, 180℃, 200℃, 220℃, 240℃, 260℃, 280℃, and 300℃.

[0155] Test Method 6: The particle size D50 of the material refers to the median particle size of the material, which can be the median value sorted by volume, mass, or quantity. In the embodiments of this invention, the median particle size sorted by quantity is specifically used, representing the particle size of the porous carbon matrix that accounts for 50% of the total number of particles. Particle size D50 is a well-known concept in the art. The particle size D50 of the material provided in the embodiments of this invention can be determined by instruments and conventional methods known in the art. Specifically, in the embodiments of this invention, the Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK, is used to determine the particle size D50.

[0156] Test Method 7: In this invention, pore size refers to the diameter of the internal pores in a large-pore base film, a meaning known in the art. Pore size can be measured using instruments and conventional methods known in the art. In this example, the pore size of the base film can be directly measured using a scanning electron microscope (SEM).

[0157] The test results for each parameter are recorded in Table 1 below.

[0158]

[0159] Table 1

[0160] As can be seen from the data in Table 1, the ionic conductivity of Examples 1-8 is much higher than that of Comparative Examples 1-3, the electrochemical window of Examples 1-8 is significantly higher than that of Comparative Examples 1-3, the stress intensity of Examples 1-8 is significantly higher than that of Comparative Examples 1-3, and the heat shrinkage temperature of Examples 1-8 is significantly higher than that of Comparative Examples 1-3.

[0161] Comparative Example 1 used a commercially available PP membrane, which had very low ionic conductivity and electrochemical window, and a lower heat shrinkage temperature than the examples; and so on. Figure 2 As shown, the critical current density in Example 1 is 2.5 mA / cm². 2 The critical current density of Comparative Example 1 is 1.6 mA / cm². 2 This indicates that the electrolyte in Example 1 is more effective at suppressing lithium dendrite growth. Comparative Example 2 used a PE membrane without a polymerization solution, resulting in significantly reduced mechanical strength and heat shrinkage temperature. Comparative Example 3 prepared a composite membrane sample using only wetting without ultrasonic treatment. It was found that the ionic conductivity was significantly reduced, the sheet resistance increased, the electrochemical window narrowed, and the heat shrinkage temperature decreased. Because vacuum ultrasonic treatment was not performed, the mixed solution could not fully penetrate into the base membrane pores, leading to incomplete filling, poor interfacial bonding, and local agglomeration, thus affecting the continuity and interfacial stability of the ion channel structure. Comparative experiments show that vacuum ultrasonic treatment can effectively improve solution permeability and uniformity, while synergistic heating promotes deep filling and uniform distribution of active components within the pores, effectively improving the overall performance of the composite membrane.

[0162] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite diaphragm, characterized in that, The composite membrane is mainly composed of lithium lanthanum-based fluorine-doped solid electrolyte LLMOF and a base membrane; The general chemical formula of the LLMOF is Li x La y M1 z M2 w M3 u O6F; where M1 is a tetravalent cation, M2 is a pentavalent cation, and M3 is a hexavalent cation; 1 < x + 3y < 5, 0 < x ≤ 2, 1 / 3 < y < 5 / 3; 0 ≤ z ≤ 2, 0 ≤ w ≤ 2, 0 ≤ u ≤ 2, z + w + u = 2; The base film is a large-pore base film, and the pore size r of the base film satisfies 200nm ≤ r ≤ 1μm; the particle size D50 of the LLMOF is 50nm. -1 μm, and the particle size D50 of the LLMOF is less than or equal to the pore size r of the base film.

2. The composite diaphragm according to claim 1, characterized in that, The macroporous base membrane is a base membrane formed of polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), or polyethylene terephthalate (PET), or a double-layer composite base membrane or a triple-layer composite base membrane formed by a combination of the above materials.

3. The composite diaphragm according to claim 1, characterized in that, M1 is one or more of Zr, Ti, Hf, Si, Ge, and Sn; M2 is one or more of Nb, Sb, Bi, V, and Ta; and M3 is one or more of W, Cr, Mo, and Mn.

4. A method for preparing the composite separator as described in any one of claims 1-3, characterized in that, The preparation method includes: The inorganic filler lithium lanthanum-based fluorine-doped solid electrolyte LLMOF, dispersant and solvent were mixed in a mass ratio of [5-20]:[1-2]:[78-94] and stirred until homogeneous to obtain a mixed solution; The base membrane is immersed in the mixed solution, ultrasonically treated under vacuum, and then dried in an oven to obtain the composite membrane.

5. The method for preparing the composite diaphragm according to claim 4, characterized in that, The dispersant comprises: polyvinylpyrrolidone (PVP) and / or 3-aminopropyltriethoxysilane (KH-550); the solvent comprises: one or more of ethanol, deionized water, N-methylpyrrolidone (NMP), and acetone. During the ultrasonic treatment, the vacuum level is ≤0.5Pa, the frequency of the ultrasonic probe is 20-80kHz, and the ultrasonic time is 30-60min. The temperature of the oven is 40-90℃.

6. A composite solid electrolyte, characterized in that, include: The composite membrane described in claims 1-3 or the composite membrane prepared by the preparation method described in claims 4-5, and the solid electrolyte obtained by in-situ polymerization.

7. A method for preparing the composite solid electrolyte according to claim 6, characterized in that, The preparation method includes: The composite diaphragm is immersed in the prepared in-situ polymerization precursor solution for 0.5-10 hours. The impregnated membrane is polymerized in situ under ultraviolet light to obtain a composite solid electrolyte; wherein the ultraviolet light is emitted by an ultraviolet lamp with an irradiation wavelength of 250-420nm and a power of 2-10W / cm. 2 The irradiation time is 0.5-6 hours.

8. The method for preparing the composite solid electrolyte according to claim 7, characterized in that, Before immersing the composite membrane into the prepared in-situ polymerization precursor solution, the method further includes: preparing the in-situ polymerization precursor solution, specifically including: A first mixture is prepared by mixing monomers, crosslinking agents, and octafluoropentyl acrylate (OFPA) in a mass ratio of [1-2]:[1-2]:[6-8]. An initiator, comprising 0.5-3 wt% of the mass of the first mixture, is added to the first mixture to form a first solution. The monomers include one or more of vinylene carbonate (VEC), tetrahydrofuran acrylate (THFA), and ethylene glycol phenyl ether acrylate (EPHA). The crosslinking agents include one or more of pentaerythritol triacrylate (PETA) and dipentaerythritol pentaacrylate (DPPA). The initiators include one or more of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2-hydroxy-2-methyl-1-phenyl-1-propanone. A second solution is prepared by heating and mixing a linear dinitrile compound with a lithium salt at a mass ratio of 1:1 to 5:1 at 40-80°C; the linear dinitrile compound includes one or more of succinic anionyl, malononitrile, and glutaronitrile; the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium hexafluorophosphate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium dioxalate borate. The first solution and the second solution are mixed at a volume ratio of 1:1 to 1:3 to form the in-situ polymerization precursor solution.

9. The method for preparing the composite solid electrolyte according to claim 8, characterized in that, The amount of the initiator added is 1.5 wt% of the mass of the first mixture; The mass ratio of the linear dinitrile compound to the lithium salt is 3:1; The volume ratio of the first solution to the second solution is 1:2; The ultraviolet lamp has an irradiation wavelength of 365nm and a power of 4-6W / cm². 2 The time is 3-5 hours.

10. A solid-state battery, characterized in that, The solid-state battery includes the composite solid-state electrolyte as described in claim 6, or the composite solid-state electrolyte obtained by in-situ polymerization of the preparation method described in any one of claims 7-9.

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