Diaphragm, composite electrolyte membrane and semi-solid-state battery

Abstract

Disclosed is a separator comprising: a base film; the surfaces of the two sides of the base membrane are coated with the first composite coatings, the first composite coatings comprise first high-temperature-resistant fibers and first ceramic particles dispersed in the first high-temperature-resistant fibers, and the first ceramic particles have the first D50 particle size; the outer side surface of the first composite coating is coated with the second composite coating, the second composite coating comprises second high-temperature-resistant fibers and second ceramic particles dispersed in the second high-temperature-resistant fibers, and the second ceramic particles have the second D50 particle size. Wherein the first D50 particle size is smaller than the second D50 particle size. According to the diaphragm disclosed by the invention, the temperature resistance and the ionic conductivity of the diaphragm are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and particularly to a separator, composite electrolyte membrane, and semi-solid battery for lithium-ion batteries. Background Technology

[0002] Solid-state batteries, which replace traditional liquid electrolytes with solid-state electrolyte systems, hold the promise of fundamentally solving the thermal runaway problem of commercial lithium-ion batteries, thus becoming a research hotspot in the energy storage field. Among various solid-state electrolytes, organic-inorganic composite solid-state electrolytes combine the flexibility of polymer materials with the high ionic conductivity of inorganic solid-state electrolytes, and are considered one of the most promising technologies for industrialization. However, existing organic-inorganic composite solid-state electrolytes still face several technical bottlenecks: First, it is difficult to achieve synergistic optimization between high ionic conductivity, ultra-thin thickness, and high strength; second, there is a significant solid-solid interface contact problem between the electrode and the electrolyte, resulting in high interfacial impedance and low ion transport efficiency; in addition, existing solid-state battery manufacturing processes have poor compatibility with traditional lithium-ion battery production lines, often requiring the reconstruction of production lines, which significantly increases manufacturing costs.

[0003] To promote the large-scale application of solid-state batteries and improve interfacial contact, researchers have proposed a solid-state technology based on in-situ polymerization. Although this technology can construct a continuous and compact electrode-electrolyte interface inside the battery, it still faces many challenges: the mechanical strength of gel electrolytes is generally low, making lithium salt dissociation difficult in solvent-poor systems; at the same time, the viscosity of the polymerization precursor solution is much higher than that of conventional electrolytes, resulting in poor wettability in porous electrodes and separators, leading to uneven distribution of the electrode-electrolyte interface and seriously affecting the consistency of battery performance.

[0004] To address the aforementioned issues, several improved solutions have been proposed in existing patented technologies, but significant limitations remain. For example, CN116344917A proposes coating the membrane surface with inorganic solid electrolyte particles and then thermally initiating in-situ polymerization via the injection of a precursor solution to form an organic-inorganic composite electrolyte. However, in this solution, the inorganic coating has weak adhesion to the base membrane, resulting in limited effectiveness in suppressing membrane thermal shrinkage, and the wettability of the precursor solution within the coating remains unsatisfactory. CN105789539A and CN1115099168A improve heat resistance and safety by coating the polyolefin membrane surface with inactive ceramic particles such as alumina and boehmite, but the ceramic layer is too dense, leading to a reduction in electrolyte retention, an increase in battery internal resistance, and consequently affecting rate performance and cycle life. CN107799696A uses high-temperature resistant polymer fibers as the skeleton structure and introduces inorganic nanoparticles to enhance stability. Although it improves the dimensional retention of the membrane at high temperatures to some extent, the heat resistance limit of polymer materials is still lower than that of pure ceramic materials. Furthermore, the inorganic particles used do not have lithium-ion conduction capabilities and cannot effectively improve the overall ionic conductivity of the system. Summary of the Invention

[0005] A first aspect of the present invention aims to provide a diaphragm, comprising: a base membrane; a first composite coating coated on both sides of the base membrane, comprising a first high-temperature resistant fiber and first ceramic particles dispersed in the first high-temperature resistant fiber, wherein the first ceramic particles have a first D50 particle size; and a second composite coating coated on the outer surface of the first composite coating, comprising a second high-temperature resistant fiber and second ceramic particles dispersed in the second high-temperature resistant fiber, wherein the second ceramic particles have a second D50 particle size. The first D50 particle size is smaller than the second D50 particle size.

[0006] In some embodiments, the first D50 particle size is in the range of 10 to 500 nm, and the second D50 particle size is in the range of 500 nm to 1.5 μm.

[0007] In some embodiments, the thickness of the base film is in the range of 1 to 15 μm, the thickness of the first composite coating is in the range of 0.5 to 1.5 μm, and the thickness of the second composite coating is in the range of 0.8 to 2.5 μm.

[0008] In some embodiments, in the first composite coating, the mass ratio of the first high-temperature resistant fiber to the first ceramic particle is in the range of (0.01-0.50):1; and in the second composite coating, the mass ratio of the second high-temperature resistant fiber to the second ceramic particle is in the range of (0.01-0.50):1.

[0009] In some embodiments, the base film is a single-layer polyethylene film, a single-layer polypropylene film, or a PP / PE / PP multilayer composite film.

[0010] In some embodiments, the materials of the first high-temperature resistant fiber and the second high-temperature resistant fiber are each selected from one or more of the group consisting of polyimide, fluorinated polyimide, para-aramid, meta-aramid, polyvinylidene fluoride, or polymethyl methacrylate.

[0011] In some embodiments, the diameter of the first high-temperature resistant fiber and the second high-temperature resistant fiber are in the range of 50 to 1000 nm, and the length is in the range of 1 to 300 μm.

[0012] In some embodiments, the materials of the first ceramic particles and the second ceramic particles are each selected from one or more of the group consisting of alumina, boehmite, silicon dioxide, magnesium hydroxide, or oxide solid electrolytes, wherein the oxide solid electrolytes are selected from one or more of the group consisting of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum titanium tantalum oxide, oxylithium lanthanum titanium niobium oxide, or oxychloride anti-perovskite.

[0013] In some embodiments, the separator further includes an adhesive layer coated on the outer surface of the second composite coating to maintain good adhesion to the electrode during cell assembly.

[0014] Another aspect of the present invention aims to provide a composite electrolyte membrane, which is obtained by in-situ polymerization of any of the above-mentioned separators and a precursor electrolyte at 10 to 80°C.

[0015] In some embodiments, the in-situ polymerization precursor electrolyte comprises a polymerizing monomer, a lithium salt, a solvent, and an additive, wherein the solid-liquid interface contact angle between the precursor electrolyte and the first composite coating and the second composite coating is in the range of 0 to 10°.

[0016] In some embodiments, the polymerizing monomer may be selected from one or more of the group consisting of methyl methacrylate, 1,3-dioxolane, vinylene carbonate or ethylene ethylene carbonate. The lithium salt can be selected from one or more of the group consisting of LiPF6, LiFSI, LiTFSI, LiClO4, LiBF4, LiBOB or LiDFOB; The solvent can be selected from one or more of the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether; The additives may be selected from one or more of the group consisting of fluoroethylene carbonate, dimethyl sulfate, ethylene sulfate, or diethyl oxalate.

[0017] Another aspect of the present invention aims to provide a semi-solid battery comprising any of the above-mentioned composite electrolyte membranes.

[0018] This invention provides a gradient organic-inorganic composite coating membrane. By constructing a dense coating of "high-temperature resistant fiber / small-diameter ceramic particles" in the inner layer closely adhering to both sides of the base membrane, the thermal stability and dimensional integrity of the membrane are effectively improved. By constructing a porous coating of "high-temperature resistant fiber / large-diameter ceramic particles" in the outermost layer of the dense coating, high porosity and excellent electrolyte retention capability are achieved, thereby improving the temperature resistance and ionic conductivity of the membrane. Attached Figure Description

[0019] Figure 1 A schematic structural diagram of a diaphragm according to some embodiments of the present invention is shown. Detailed Implementation

[0020] The separator, composite electrolyte membrane, and semi-solid-state battery disclosed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following detailed description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, and are only used for the purpose of conveniently and clearly illustrating the embodiments of this invention.

[0021] Reference Figure 1 The diaphragm 10 is described according to this disclosure.

[0022] The diaphragm 10 may include a base membrane 1, a first composite coating 2 (inner layer) coated on both sides of the base membrane 1, a second composite coating 3 (outer layer) coated on the outer side of the first composite coating 2, and an optional adhesive layer 4. That is, the diaphragm 10 according to the present disclosure forms a multilayer structure consisting of a base membrane 1, a first composite coating 2, a second composite coating 3, and an adhesive layer 4 from the inside out.

[0023] The base film 1 can be a single-layer polyethylene film, a single-layer polypropylene film, or a PP / PE / PP multilayer composite film, and its thickness can be in the range of 1 to 15 μm or 5 to 10 μm. The base film 1 can have a porous structure.

[0024] The first composite coating 2 is distributed on both sides of the base film 1, forming a sandwich structure with the base film 1. The first composite coating 2 may contain a first high-temperature resistant fiber and first ceramic particles dispersed in the first high-temperature resistant fiber. The first high-temperature resistant fiber may be constructed as a three-dimensional network skeleton, and the first ceramic particles are dispersed in the network.

[0025] The second composite coating 3 is distributed on the outer surface of the first composite coating 2. The second composite coating 3 may contain a second high-temperature resistant fiber and first ceramic particles dispersed in the second high-temperature resistant fiber. The second high-temperature resistant fiber may be constructed as a three-dimensional network skeleton, and the second ceramic particles are dispersed in the network.

[0026] The thickness of the first composite coating 2 can be in the range of 0.5 to 1.5 μm, or 0.7 to 1.3 μm, or 0.9 to 1.1 μm. The thickness of the second composite coating 3 can be in the range of 0.8 to 2.5 μm, or 1 to 2.3 μm, or 1.2 to 2.1 μm, or 1.4 to 1.9 μm, or 1.6 to 2.8 μm.

[0027] In the first composite coating 2, the mass ratio of the first high-temperature resistant fiber to the first ceramic particle can be in the range of (0.01-0.50):1; and in the second composite coating 3, the mass ratio of the second high-temperature resistant fiber to the second ceramic particle can also be in the range of (0.01-0.50):1.

[0028] As used herein, the term “inner side” refers to the side facing or close to the basement membrane, and the term “outer side” refers to the side facing away from or away from the basement membrane.

[0029] As used in this article, the term "high-temperature resistant fiber" refers to chemical fibers that can maintain their original physical and mechanical properties when subjected to high temperatures (such as 200°C and above) for a relatively long period of time.

[0030] The first and second high-temperature resistant fibers can be made of the same or different materials, each of which can be selected from one or more of the group consisting of polyimide, fluorinated polyimide, para-aramid, meta-aramid, polyvinylidene fluoride, or polymethyl methacrylate.

[0031] The diameters of the first and second high-temperature resistant fibers can be in the range of 50 to 1000 nm, or 100 to 950 nm, or 150 to 900 nm, or 200 to 850 nm, or 250 to 800 nm, or 300 to 750 nm, or 350 to 700 nm, or 400 to 650 nm, or 450 to 600 nm, or 500 to 550 nm; the lengths can be in the range of 1 to 300 μm, or 50 to 250 μm, or 100 to 200 μm.

[0032] The first and second high-temperature resistant fibers are randomly distributed and overlap each other in the corresponding coatings to form a three-dimensional network skeleton, which strengthens the ceramic particles and thereby enhances the bonding strength and toughness of the first and second composite coatings 2 and 3, and further improves their heat resistance and dimensional stability.

[0033] The first ceramic particle and the second ceramic particle can be made of the same or different materials, each of which can be selected from one or more of the group consisting of polyalumina, boehmite, silicon dioxide, magnesium hydroxide, or oxide solid electrolytes, wherein the oxide solid electrolyte is selected from one or more of the group consisting of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum titanium tantalum oxide, oxylithium lanthanum titanium niobium oxide, or oxychloride anti-perovskite.

[0034] The first ceramic particle may have a first D50 particle size, and the second ceramic particle may have a second D50 particle size.

[0035] According to the present invention, the first D50 particle size is smaller than the second D50 particle size, so that the second composite coating 3 forms a high porosity structure, which enhances the electrolyte retention capacity and ionic conductivity of the diaphragm 10.

[0036] Specifically, the first D50 particle size is in the range of 10 to 500 nm, or 50 to 450 nm, or 100 to 400 nm, or 150 to 350 nm, or 200 to 300 nm; the second D50 particle size is in the range of 500 nm to 1.5 μm, or 550 to 1.45 μm, or 600 to 1.4 μm, or 650 to 1.35 μm, or 700 to 1.3 μm, or 750 to 1.25 μm, or 800 to 1.2 μm, or 850 to 1.15 μm, or 900 to 1.1 μm, or 950 to 1.05 μm. Thus, the diaphragm according to the present invention forms an organic-inorganic composite coating diaphragm with a gradient (ceramic particle size). By constructing a dense coating of "high-temperature resistant fiber / small-diameter ceramic particles" (i.e., the first composite coating 2) in the inner layer closely attached to both sides of the base membrane 1, the thermal stability and dimensional integrity of the diaphragm are effectively improved. By constructing a porous coating of "high-temperature resistant fiber / large-diameter ceramic particles" (i.e., the second composite coating 3) in the outermost layer of the dense coating, high porosity and excellent electrolyte retention capacity are achieved, providing an efficient channel for ion migration and solving the contradiction of difficulty in simultaneously achieving "thermal stability", "wetting properties" and "ion conductivity".

[0037] The adhesive layer 4 is coated on the outer surface of the second composite coating 3 to maintain good adhesion to the electrode during cell assembly.

[0038] In another aspect, the present invention provides a composite electrolyte membrane, which is obtained by in-situ polymerization of any of the above-mentioned separators 10 and a precursor electrolyte at 10 to 80°C. Specifically, the precursor electrolyte is injected into the battery equipped with the separator 10, and an in-situ polymerization reaction is carried out at 10 to 80°C for 6 to 72 hours, so that the electrolyte solidifies inside the battery to form a composite solid electrolyte membrane.

[0039] The precursor electrolyte may contain polymeric monomers, lithium salts, solvents, and additives. In particular, the precursor electrolyte contains 1 to 90 wt% (preferably 1 to 50 wt%) of polymeric monomers, 3 to 60 wt% of lithium salts, 0 to 95 wt% of solvents, and 0 to 5 wt% (preferably 0 to 1 wt%) of additives.

[0040] The solid-liquid interface contact angle between the precursor electrolyte and the first composite coating 2 and the second composite coating 3 is within the range of 0 to 10°, enabling the electrolyte to diffuse rapidly and achieve uniform wetting after injection, thereby significantly improving injection efficiency and production speed. Specifically, the large-diameter ceramic particles of the outer second composite coating constitute a macroscopic porous structure, serving as a low-resistance inlet and storage area for the electrolyte; the small-diameter ceramic particles of the inner first composite coating form a nanoscale porous network, generating strong capillary force, which acts as a power pump to continuously draw and uniformly deliver the electrolyte from the outer layer to the electrode interface. This synergistic transport mechanism ensures the formation of a dense and uniform electrode-electrolyte interface after in-situ solidification, effectively eliminating local dry areas and reducing interfacial impedance.

[0041] By utilizing the gradient structure design of the membrane 10, rapid and uniform wetting of the precursor electrolyte onto the membrane 10 is achieved. Furthermore, in-situ polymerization is used to form a composite solid electrolyte membrane with excellent interfacial contact and a stable structure. This not only physically ensures the uniformity of the interface but also chemically reduces the risk of side reactions.

[0042] This electrolyte membrane exhibits excellent thermal shrinkage properties, significantly improving battery thermal safety. Furthermore, this structure ensures thorough wetting of the electrodes by the precursor electrolyte, and the composite solid electrolyte membrane formed after in-situ polymerization maintains close contact with the electrodes, effectively reducing interfacial impedance and forming a protective layer at the interface to inhibit the continuous erosion of the electrode materials by the electrolyte.

[0043] In some embodiments, the polymerization monomers may be selected from one or more of the group consisting of methyl methacrylate, 1,3-dioxolane, vinylene carbonate, or ethylene ethylene carbonate. Polymerization of 1,3-dioxolane with monomers such as methyl methacrylate and vinylene carbonate at 10 to 80°C avoids the negative impact of traditional thermal initiator residues on battery cycle performance, while also providing interface protection.

[0044] The lithium salt can be selected from one or more of the group consisting of LiPF6, LiFSI, LiTFSI, LiClO4, LiBF4, LiBOB or LiDFOB.

[0045] The solvent can be selected from one or more of the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether.

[0046] The additives may be selected from one or more of the group consisting of fluoroethylene carbonate, dimethyl sulfate, ethylene sulfate, or diethyl oxalate.

[0047] In another aspect, this invention provides a semi-solid-state battery comprising any of the aforementioned composite electrolyte membranes. The semi-solid-state battery using this composite electrolyte membrane exhibits excellent cycle performance and safety performance. The aforementioned uniform and stable electrode-electrolyte interface effectively suppresses side reactions and lithium dendrite growth, thereby improving the battery's cycle life and safety performance. The outer layer's large-pore structure acts as an electrolyte reservoir, replenishing the interface with electrolyte during cycling; the inner layer's small-particle-size structure ensures sufficient contact between the electrolyte and the active material. Ultimately, the combination of this gradient separator and in-situ solidification technology results in a composite solid electrolyte membrane that simultaneously possesses ultra-thin characteristics, high mechanical strength, and high heat resistance, achieving a comprehensive improvement in the electrochemical and safety performance of the semi-solid-state battery.

[0048] To better understand the technical solution provided by the present invention, the following specific examples illustrate the specific preparation process and application of semi-solid-state batteries according to the present invention.

[0049] Example 1 This example uses LiNi 0.88 Co 0.08 Mn 0.04 O2 was used as the positive electrode material, and silicon-carbon was used as the negative electrode material. The electrolyte composition was ethylene carbonate (16.6 wt%), fluoroethylene carbonate (16.5 wt%), methyl methacrylate (49.9 wt%), LiPF6 (11 wt%), LiFSI (2.2%), trimethyl phosphate (2.5%), trimethylsilyl phosphate (0.5 wt%), and ethylene sulfate (0.8%). The polymer monomer 1,3-dioxolane (DOL) accounted for 2% of the total electrolyte mass. After electrolyte injection, the battery was encapsulated and cured at room temperature for 48 hours, thus completing the preparation of a 20 Ah semi-solid-state battery.

[0050] In this example, the diaphragm is a PI / LATP composite coated diaphragm with a PI / LATP weight ratio of 0.1:1. The thickness of the first composite coating is 1 μm, and the thickness of the second composite coating is 1 μm. The first D50 particle size is 300 nm, and the second D50 particle size is 700 nm. A dispensing process is used on both sides.

[0051] Example 2 The difference from Example 1 is that the high-temperature resistant organic fiber is para-aramid.

[0052] Example 3 The difference from Example 1 is that the ceramic is lithium lanthanum zirconium tantalum oxide.

[0053] Example 4 The difference from Example 1 is that the ceramic is lithium lanthanum titanium tantalum oxide. Example 5 The difference from Example 1 is that the ceramic is boehmite.

[0054] Example 6 The difference from Example 1 is that the ceramic is Al2O3.

[0055] Example 7 The difference from Example 1 is that the weight ratio of PI / LATP is 0.01:1.

[0056] Example 8 The difference from Example 1 is that the weight ratio of PI / LATP is 0.5:1.

[0057] Example 9 The difference from Example 1 is that the thickness of the first composite coating is 0.5 μm and the thickness of the second composite coating is 0.8 μm.

[0058] Example 10 The difference from Example 1 is that the thickness of the first composite coating is 1.5 μm and the thickness of the second composite coating is 2.5 μm.

[0059] Comparative Example 1 The difference from Example 1 is that no polymer monomers were added to complete the preparation of the 20Ah liquid battery.

[0060] Comparative Example 2 The difference from Example 1 is that the first composite coating is on the inside, and the second composite coating is on the inside.

[0061] Characterization test Diaphragm property testing: The test method shall be performed in accordance with GB / T 36363-2018.

[0062] Cycle life test: Cycle test at a charge / discharge rate of 0.5C / 1C for a total of 1000 cycles within the operating voltage range of 2.5–4.25V to evaluate the battery’s capacity retention capability.

[0063] Rate charge / discharge test: Hot chamber test: The battery was charged to 100% SOC at a rate of 0.33C, and then placed in a temperature chamber. The temperature was increased from room temperature to 130℃±2℃ at a rate of 5℃ / min and held for 30 minutes. The temperature was then increased to 150℃±2℃ at the same rate and held for 30 minutes. Finally, the temperature was increased to 180℃±2℃ and held for another 30 minutes. The thermal stability and safety performance of the battery were observed.

[0064] Test data The basic physical properties of the membranes prepared in Examples 1-10 and Comparative Example 2 are shown in Table 1.

[0065] Table 1. Physical properties of the coated diaphragms in each example and comparative example.

[0066] As shown in Table 1, compared with Comparative Example 2, the coated diaphragm prepared in this patent embodiment shows comprehensive advantages in key performance parameters such as electrolyte contact angle, air permeability and ionic conductivity.

[0067] The coated separators from Examples 1 and 2 were matched with NCM811 cathodes, silicon-carbon anodes, and gel electrolytes, respectively, to assemble soft-pack semi-solid-state lithium-ion batteries with a nominal capacity of 20 Ah. Meanwhile, the soft-pack liquid lithium-ion battery assembled in Comparative Example 1, with a capacity of 20 Ah, was used as a reference system. Subsequently, according to the GB / T 31485 standard method, all battery samples underwent rate charge-discharge tests and cycle life tests. The specific results are listed in Table 2.

[0068] As shown in Table 2, the examples are comparable to Comparative Example 1 in terms of capacity retention and rate performance, but significantly outperform Comparative Example 1, which uses a liquid electrolyte, in terms of hot box safety and needle penetration safety. Meanwhile, compared to Comparative Example 2, which uses a conventional separator, the pouch cells prepared in the examples demonstrate superior performance in capacity retention, rate performance, and hot box testing. In summary, the gradient structure composite electrolyte membrane provided by this invention offers significant advantages in comprehensively improving the overall electrical and safety performance of lithium-ion batteries.

[0069] Table 2. Battery performance indicators of coated separators in examples and comparative cases.

[0070] The separator, composite electrolyte membrane, and battery of the present invention achieve the following effects through the synergistic effect of the separator gradient structure design and the organic-inorganic composite system:

[0071] Improved structural stability and thermal safety: The inner layer of the diaphragm is composed of high-temperature resistant fibers and small-diameter ceramic particles, giving the diaphragm excellent thermal stability and mechanical strength; the outer layer is composed of high-temperature resistant fibers and large-diameter ceramic particles, which, while maintaining structural integrity, forms a high-porosity structure, significantly enhancing electrolyte retention capacity and ionic conductivity.

[0072] Enhanced mechanical and thermal properties of the coating: High-temperature resistant organic fibers are randomly distributed and overlapped in the coating to form a three-dimensional network framework, which plays a reinforcing role on the inorganic ceramic particles; This composite structure not only improves the bonding strength and toughness of the coating, but also further improves its heat resistance and dimensional stability.

[0073] Optimization of interface wettability and uniformity: This gradient composite coating exhibits excellent affinity with the in-situ polymerization precursor electrolyte, resulting in an extremely low solid-liquid interface contact angle, thereby significantly accelerating the electrolyte wetting process. Specifically, the outer large-particle-size coating forms a macroporous structure, serving as a low-resistance inlet and reservoir for the electrolyte; the inner small-particle-size coating forms a nanoscale pore network, generating strong capillary forces that act as a pump to continuously draw and uniformly deliver the electrolyte from the outer layer to the electrode interface. This synergistic transport mechanism ensures the formation of a dense and uniform electrode-electrolyte interface after in-situ curing, effectively eliminating localized dry areas and reducing interfacial impedance.

[0074] Enhanced overall battery performance: The aforementioned uniform and stable interface effectively suppresses side reactions and lithium dendrite growth, thereby improving the battery's cycle life and safety performance. The outer layer's large-pore structure acts as an electrolyte reservoir, replenishing the interface with electrolyte during cycling; the inner layer's small-particle structure ensures sufficient contact between the electrolyte and the active material. Ultimately, this gradient separator, combined with in-situ solidification technology, produces a composite solid electrolyte membrane that simultaneously possesses ultra-thin characteristics, high mechanical strength, and high heat resistance, achieving a comprehensive improvement in the electrochemical and safety performance of the semi-solid-state battery.

[0075] In the description of this invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0076] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0077] The singular forms “a,” “the,” and “the” used in this disclosure and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0078] Obviously, those skilled in the art can make various modifications and variations to the diaphragm disclosed in this invention without departing from the spirit and scope of this invention. Therefore, if these modifications and variations of this invention fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A diaphragm, characterized in that, include: Base film; The first composite coating applied to both sides of the base film comprises a first high-temperature resistant fiber and first ceramic particles dispersed in the first high-temperature resistant fiber, wherein the first ceramic particles have a first D50 particle size. as well as The second composite coating, applied to the outer surface of the first composite coating, comprises a second high-temperature resistant fiber and second ceramic particles dispersed in the second high-temperature resistant fiber, wherein the second ceramic particles have a second D50 particle size. Wherein, the first D50 particle size is smaller than the second D50 particle size.

2. The diaphragm according to claim 1, characterized in that, The first D50 particle size is in the range of 10 to 500 nm, and the second D50 particle size is in the range of 500 nm to 1.5 μm.

3. The diaphragm according to claim 1, characterized in that, The thickness of the base film is in the range of 1 to 15 μm, the thickness of the first composite coating is in the range of 0.5 to 1.5 μm, and the thickness of the second composite coating is in the range of 0.8 to 2.5 μm.

4. The diaphragm according to claim 1, characterized in that: In the first composite coating, the mass ratio of the first high-temperature resistant fiber to the first ceramic particles is in the range of (0.01-0.50):1; and In the second composite coating, the mass ratio of the second high-temperature resistant fiber to the second ceramic particles is in the range of (0.01-0.50):

1.

5. The diaphragm according to claim 1, characterized in that, The base film is a single-layer polyethylene film, a single-layer polypropylene film, or a PP / PE / PP multilayer composite film.

6. The diaphragm according to claim 1, characterized in that, The materials of the first high-temperature resistant fiber and the second high-temperature resistant fiber are each selected from one or more of the group consisting of polyimide, fluorinated polyimide, para-aramid, meta-aramid, polyvinylidene fluoride, or polymethyl methacrylate.

7. The diaphragm according to claim 6, characterized in that, The diameters of the first and second high-temperature resistant fibers are in the range of 50 to 1000 nm, and the lengths are in the range of 1 to 300 μm.

8. The diaphragm according to claim 1, characterized in that, The materials of the first ceramic particle and the second ceramic particle are each selected from one or more of the group consisting of alumina, boehmite, silicon dioxide, magnesium hydroxide, or oxide solid electrolytes, wherein the oxide solid electrolyte is selected from one or more of the group consisting of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium aluminum lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium lanthanum titanium tantalum oxide, oxylithium lanthanum titanium niobium oxide, or oxychloride anti-perovskite.

9. The diaphragm according to claim 1, characterized in that, The diaphragm also includes an adhesive layer coated on the outer surface of the second composite coating.

10. A composite electrolyte membrane, characterized in that, The composite electrolyte membrane is obtained by in-situ polymerization of the diaphragm and the precursor electrolyte according to any one of claims 1 to 9 at 10 to 80°C.

11. The composite electrolyte membrane according to claim 10, characterized in that, The precursor electrolyte comprises polymeric monomers, lithium salts, solvents, and additives, wherein the solid-liquid interface contact angle between the precursor electrolyte and the first composite coating and the second composite coating is in the range of 0 to 10°.

12. The composite electrolyte membrane according to claim 11, characterized in that: The polymeric monomer is selected from one or more of the group consisting of methyl methacrylate, 1,3-dioxolane, vinylene carbonate, or ethylene ethylene carbonate. The lithium salt is selected from one or more of the group consisting of LiPF6, LiFSI, LiTFSI, LiClO4, LiBF4, LiBOB or LiDFOB; The solvent is selected from one or more of the group consisting of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether. The additive is selected from one or more of the group consisting of fluoroethylene carbonate, dimethyl sulfate, ethylene sulfate, or diethyl oxalate.

13. A semi-solid-state battery comprising a composite electrolyte membrane according to any one of claims 10 to 12.

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