Long-circulation heat-stable lithium supplementing diaphragm, preparation method and application thereof, and lithium ion battery

Abstract

The application discloses a long-circulation heat-stable lithium supplement diaphragm and a preparation method and application thereof and a lithium ion battery, and belongs to the technical field of lithium ion battery diaphragms. The diaphragm comprises a polymer base film, a heat-stable coating layer which is compounded on the surface of the polymer base film, and a lithium supplement coating layer which is compounded on the surface of the heat-stable coating layer; the heat-stable coating layer is a mixture layer which is compounded by ceramic powder, polystyrene butadiene copolymer and sodium carboxymethyl cellulose; and the lithium supplement coating layer is a mixture layer which is compounded by an aminated lithium supplement compound, a conductive agent and polyvinylidene fluoride. The diaphragm has the characteristics of high electrolyte infiltration degree, high liquid retention coefficient, good heat stability and high tensile strength, and the coating layer is not easy to fall off in the battery charging and discharging process, the interface impedance of the contact interface with the pole piece is low, and the degree of side reaction with the electrolyte is low; and the battery made of the diaphragm can achieve the effects of high capacity, high initial efficiency and excellent cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator technology, specifically relating to a long-cycle thermally stable lithium replenishment separator, its preparation method, and its application in lithium-ion batteries. Background Technology

[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.

[0003] With the development of the new energy industry, people's requirements for the energy density of lithium-ion batteries are constantly increasing. The reversible capacity of cathode materials, which is closely related to energy density, has begun to receive attention. The key factor affecting the reversible capacity of cathode materials is that during the battery formation process, lithium ions form an SEI film on the surface of the anode material. Some lithium ions participate in the reaction, which prevents these lithium ions from returning to the cathode to participate in the cycle. Since the consumption of these lithium ions is a one-time event, people have begun to use the method of adding lithium replenishing agents to make up for the consumed lithium ions. As a result, various lithium replenishing materials and methods have been developed.

[0004] Lithium replenishment via separator has become one of the most promising lithium replenishment methods in the lithium-ion battery industry due to its advantages such as simple process, low requirements for preparation environment, high safety of lithium replenishment materials, and outstanding lithium replenishment effect. Patent CN111816822A proposes a functionalized lithium replenishment separator, which consists of a lithium replenishment layer and a base film layer. The lithium replenishment layer comprises a lithium-containing compound, a polymer substrate, and a toughening agent, while the base film layer includes a polymer substrate. However, this lithium replenishment separator has an overly simple structure, resulting in poor compatibility between the lithium replenishment layer and the electrolyte, low utilization efficiency of the lithium replenishment material in the lithium replenishment layer, high interfacial impedance between the lithium replenishment layer, electrolyte, and electrode, and easy pulverization and detachment during cycling. This leads to poor capacity performance, cycle performance, and polarization after battery fabrication, and it does not take into account the physical advantages of conventional ceramic-coated separators. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a long-cycle thermally stable lithium-ion separator, its preparation method, and its application in lithium-ion batteries. The lithium-ion separator provided by the present invention features high electrolyte wetting degree, high electrolyte retention coefficient, good thermal stability, and high tensile strength. At the same time, during battery charging and discharging, the coating in the lithium-ion separator is not easily detached, the interfacial impedance at the interface with the electrode is low, and the degree of side reaction with the electrolyte is low. Batteries made with this lithium-ion separator can achieve high capacity, high initial efficiency, and excellent cycle performance.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] In one aspect, a long-cycle thermally stable lithium replenishment separator is provided, comprising a polymer base film, a thermally stable coating compounded on the surface of the polymer base film, and a lithium replenishment coating compounded on the surface of the thermally stable coating.

[0008] The heat-stabilized coating is a mixture layer formed by ceramic powder, polystyrene-butadiene copolymer (SBR), and sodium carboxymethyl cellulose (CMC); the lithium-supplementing coating is a mixture layer formed by aminated lithium-supplementing compound, conductive agent, and polyvinylidene fluoride (PVDF).

[0009] In some embodiments of the present invention, the surface of the heat-stabilized coating is provided with grooves, and the lithium replenishing coating is composited with the heat-stabilized coating by fitting into the grooves.

[0010] In some embodiments of the present invention, the thickness of the thermally stabilized coating at its highest point is 1.5 to 2.5 μm, the depth of the grooves on its surface is 0.5 to 1 μm, and the width of the grooves and the spacing between each groove are both 0.5 to 1.5 mm.

[0011] In some embodiments of the present invention, the total thickness of the thermally stabilized coating and the lithium replenishment coating is 4 to 5 μm.

[0012] In some embodiments of the present invention, the polymer base film includes, but is not limited to, any one of polyethylene (PE), polypropylene (PP), thermoplastic polyurethane elastomer (TPU), polyetheretherketone (PEEK), polyethylene terephthalate (PET), poly(m-phenylene isophthalamide) (PMIA), poly(m-phenylene isophthalamide)-polyurethane (PMIA-PU), polystyrene strut material (PBO), polyvinylidene fluoride (PVDF), polybenzimidazole (PBI), polyphenylene sulfide (PPS), and polyimide (PI).

[0013] It should be noted that the present invention does not limit the thickness of the polymer base film, and a thickness conventional in the art can be used. For example, the thickness of the polymer base film can be 7 to 12 μm, specifically 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, etc.

[0014] In some embodiments of the present invention, the ceramic powder includes, but is not limited to, any one of boehmite, aluminum oxide, zirconium dioxide, tin oxide, silicon dioxide, magnesium oxide, and beryllium oxide.

[0015] It should be noted that the present invention does not impose requirements on the particle size of the ceramic powder; particle sizes commonly used in the field of lithium-ion battery separator preparation can be used, such as micrometer-scale and near-nanometer-scale.

[0016] In some embodiments of the present invention, the conductive agent includes, but is not limited to, any one or more of SP, carbon nanotubes (CNT), vapor-grown carbon fibers (VGCF), ECP, reduced graphene oxide (rGO), acetylene black, and Carbon ECP.

[0017] In some embodiments of the present invention, the aminated lithium-supplementing compound is obtained by reacting 3-aminopropyltriethoxysilane with a lithium-containing compound, wherein the lithium-containing compound is a lithium-containing metal oxide or lithium-ion salt with a theoretical specific capacity >170 mAh / g; preferably, the lithium-containing compound includes, but is not limited to, any one or more of Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li2C2O4, Li2SO4, and Li2SiO3.

[0018] In some embodiments of the present invention, the mass ratio of the ceramic powder, polystyrene-butadiene copolymer, and sodium carboxymethyl cellulose is (22-23):1.5:1. At this ratio, the heat-stabilized coating exhibits excellent performance.

[0019] In some embodiments of the present invention, the mass ratio of the aminated lithium-supplementing compound, the conductive agent, and polyvinylidene fluoride is (6.5–8):(0.5–1):(3–1). At this ratio, the lithium-supplementing coating exhibits excellent performance.

[0020] A second aspect of the present invention provides a method for preparing the above-mentioned long-cycle thermally stable lithium-supplementing separator, comprising:

[0021] Ceramic powder, polystyrene-butadiene copolymer, and sodium carboxymethyl cellulose are added to a first solvent and mixed to obtain coating A; coating A is coated on the surface of a polymer base film and dried to obtain a single-layer coated diaphragm.

[0022] An aminated lithium-supplementing compound, a conductive agent, and polyvinylidene fluoride are added to a second solvent and mixed to obtain coating B. Coating B is then applied to the single-layer coated membrane and dried to obtain a long-cycle thermally stable lithium-supplementing membrane.

[0023] It should be noted that, to ensure uniform coating, a deaerator can be used to mix and disperse the mixture of raw materials and solvent. For example, ceramic powder, polystyrene-butadiene copolymer, and sodium carboxymethyl cellulose are added to a first solvent to obtain mixed solution A. Mixed solution A is then mixed and dispersed in a deaerator for 15–25 minutes to obtain coating A. The deaerator speed is 1500–2500 rpm / min. Alternatively, an aminated lithium-supplementing compound, a conductive agent, and polyvinylidene fluoride are added to a second solvent to obtain mixed solution B. Mixed solution B is then mixed and dispersed in a deaerator for 15–25 minutes, repeated 2–4 times to obtain coating B. The deaerator speed is 1500–2500 rpm / min.

[0024] In some embodiments of the present invention, the first solvent is water, and the second solvent is an organic solvent, including any one of N-methylpyrrolidone, chloroform, dichloromethane and petroleum ether, preferably N-methylpyrrolidone.

[0025] It should be noted that the lithium-replenishing compounds selected in this invention react with water to varying degrees. During the aqueous homogenization process, they can damage the lithium-replenishing material, leading to its deactivation and thus affecting the lithium-replenishing effect of the membrane. Using an organic solvent as a second solvent can prevent the lithium-replenishing compound from deactivating, ensure stable adhesion of the coating, and effectively improve the cycle life of the lithium-replenishing membrane.

[0026] In some embodiments of the present invention, the mass ratio of the ceramic powder, polystyrene-butadiene copolymer and sodium carboxymethyl cellulose is (22-23):1.5:1.

[0027] In some embodiments of the present invention, the mass ratio of the aminated lithium-supplementing compound, the conductive agent, and the polyvinylidene fluoride is (6.5–8):(0.5–1):(3–1).

[0028] In some embodiments of the present invention, the preparation method includes: selecting a coating blade with grooves to coat a coating A onto a polymer base film, and then vacuum drying at 40-50°C for 8-12 hours to obtain a single-layer coated diaphragm with grooves; preferably, the solid content of coating A is 60%-75%; preferably, the coating rate is 2-5 mm / s when coating coating A.

[0029] In some embodiments of the present invention, the preparation method includes: applying coating B to the side with the grooved coating using a flat-edged coating blade, and then vacuum drying at 40-50°C for 4-6 hours to obtain a long-cycle thermally stable lithium-replenishing separator; preferably, the solid content of the coating B is 60%-75%; preferably, the coating rate is 2-5 mm / s when coating B.

[0030] It should be noted that, in order to improve efficiency, accuracy and save costs, a vacuum automatic coating machine can be used to coat coating A and coating B.

[0031] In some embodiments of the present invention, the preparation method of the aminated lithium-supplementing compound includes: dispersing the lithium-supplementing compound in methanol, sonicating, adding 3-aminopropyltriethoxysilane, reacting at room temperature for 1.5 to 2.5 h, centrifuging the product and washing it with methanol, and drying it under vacuum at 105 to 115 °C for 10 to 12 h to obtain the aminated lithium-supplementing compound.

[0032] In some embodiments of the present invention, the molar ratio of the lithium supplementation compound and 3-aminopropyltriethoxysilane is 1:1.1 to 1.3.

[0033] A third aspect of the present invention provides the application of the above-described long-cycle thermally stable lithium-replenishing separator or the long-cycle thermally stable lithium-replenishing separator prepared by the above-described preparation method in a lithium-ion battery.

[0034] A fourth aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrode solution;

[0035] The separator includes the long-cycle thermally stable lithium-replenishing separator described above or the long-cycle thermally stable lithium-replenishing separator prepared by the above preparation method.

[0036] The beneficial effects of this invention are as follows:

[0037] To address the problems of poor thermal stability, poor electrolyte wettability, low liquid retention coefficient, poor lithium replenishment effect, high battery polarization, and poor cycle performance in lithium-ion battery separators, this invention provides a long-cycle thermally stable lithium-ion battery separator. This separator consists of a polymer base film, an inner thermally stable coating, and an outer aminated lithium-ion coating. The thermally stable coating is composed of SBR, CMC, and ceramic materials, while the aminated lithium-ion coating is composed of an aminated lithium-ion compound, a conductive agent, and PVDF. The thermally stable coating and the aminated lithium-ion coating are combined in a grooved interlocking manner. The resulting grooved interlocking composite coating lithium-ion battery separator exhibits high electrolyte wettability, high liquid retention coefficient, good thermal stability, and high tensile strength. Furthermore, during battery charging and discharging, the separator coating is less prone to detachment, has low interfacial impedance at the electrode contact interface, and exhibits a low degree of side reactions with the electrolyte. Batteries made with this separator can achieve high capacity, high initial efficiency, and excellent cycle performance.

[0038] Specifically, this invention uses an aminated lithium-replenishing coating composed of an aminated lithium-replenishing compound, a conductive agent, and PVDF as the outer coating of the lithium-replenishing separator. The surface of the aminated lithium-replenishing compound particles contains amino groups. Since amino groups are highly compatible with polar electrolyte solutions, the coating surface exhibits significantly improved wettability to the electrolyte, resulting in better electrolyte absorption and retention, thereby enhancing ionic conductivity and reducing the concentration of Li in the lithium-replenishing compound. + The extraction is more complete, and the aminated lithium-replenishing compounds are all lithium-containing metal oxides or lithium-ion salts. + The transmission rate and electronic conductivity of this coating are far superior to those of conventional boehmite membrane coatings. Therefore, it exhibits lower electrochemical impedance and reduced interfacial impedance at the electrode contact interface when used in batteries. The presence of conductive agents in the coating effectively reduces the interfacial impedance at the electrode contact interface. The high conductivity of the conductive agents promotes the migration of lithium ions at the electrode-electrolyte interface during repeated cycles. Furthermore, due to its carbon-based lamellar and porous structure, the composite coating membrane's electrolyte absorption and retention effects are further enhanced. The choice of PVDF, an oil-based auxiliary material, is based on coating processing considerations. The lithium-replenishing compounds selected in this invention react to water to varying degrees, which can damage the lithium-replenishing materials during aqueous homogenization, leading to their deactivation and affecting the lithium-replenishing effect of the membrane. Simultaneously, PVDF, as an excellent toughening agent and binder, ensures stable coating adhesion, preventing pulverization and detachment during cycling, effectively improving the cycle life of the lithium-replenishing membrane.

[0039] Using a thermally stable coating composed of CMC, SBR, and ceramic materials as the inner coating of the lithium-ion replenishing separator ensures its thermal stability. During actual application, the aminated lithium-ion replenishing coating may gradually thin with cycling. The presence of the inner thermally stable coating ensures that the thermal stability and mechanical properties of the lithium-ion replenishing separator remain almost identical to their initial state during battery cycling. Furthermore, the aqueous auxiliary material system of CMC and SBR is used because, compared to other binders such as PVDF and PMMA, the elastomer SBR has higher flexibility, stronger bonding force, and higher heat resistance. CMC, with its carboxylic acid anion and hydroxyl functional groups, effectively disperses the ceramic powder uniformly in the slurry. The coating applied under this system exhibits higher thermal stability, mitigating the thermal shrinkage of the outer aminated lithium-ion replenishing coating, while also possessing good tensile, bending, and needle-puncture resistance.

[0040] By using a groove-fitting method to bond the inner and outer coatings together, the adhesion between the aminated lithium-supplementing coating and the heat-stabilized coating becomes tighter and stronger. This maximizes the complementary advantages of the two coatings, significantly mitigating thermal shrinkage and cyclic shedding of the lithium-supplementing coating under high-temperature conditions. It also reduces Li-related losses during cycling. +The resistance to transport between the aminated lithium-supplementing coating and the thermally stabilized coating phases is reduced, thereby decreasing the Li + Electrochemical polarization during transmission enhances battery capacity utilization and cycle performance.

[0041] The presence of a dual-layer composite coating can more effectively adsorb trace impurities in the electrolyte, such as water and HF, thereby reducing side reactions in the battery system, improving interface stability, and enhancing the cycle performance of lithium batteries. Attached Figure Description

[0042] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0043] Figure 1 This is a schematic diagram of the structure of the long-cycle thermally stable lithium replenishment separator according to an embodiment of the present invention;

[0044] Figure 2 This is a diagram showing the electrolyte contact angle of the long-cycle thermally stable lithium-filling separator obtained in Example 1 of the present invention;

[0045] Figure 3 The LFP button cell 0.1C charge / discharge curve is shown for the long-cycle thermally stable lithium-ion separator obtained in Example 1 of this invention.

[0046] Among them, 1-polymer base film, 2-thermal stable coating, 3-lithium replenishment coating. Detailed Implementation

[0047] To improve the problems of poor thermal stability, poor electrolyte wettability, low liquid retention coefficient, poor lithium replenishment effect, large polarization of the battery after it is made, and poor cycle performance of lithium replenishment membrane, this invention provides a long-cycle thermally stable lithium replenishment membrane, its preparation method and lithium-ion battery.

[0048] like Figure 1 As shown, the long-cycle thermally stable lithium replenishing membrane is composed of a polymer base film 1, an inner thermally stable coating 2, and an outer lithium replenishing coating 3. The thermally stable coating 2 is composed of SBR, CMC, and ceramic powder, and the lithium replenishing coating 3 is composed of an aminated lithium replenishing compound, a conductive agent, and PVDF. The surface of the thermally stable coating 2 is provided with grooves, and the lithium replenishing coating 3 is composited on the surface of the thermally stable coating 2 by interlocking with the grooves.

[0049] This invention also provides a method for preparing a long-cycle thermally stable lithium-supplementing separator, comprising the following steps:

[0050] 1. Add ceramic, SBR, and CMC to water in a ratio of (22-23):1.5:1 to obtain mixture A. Mix and disperse the mixture A in a degassing machine for 15-25 minutes to obtain water-based coating A. Use a polymer membrane as the base membrane and place it in a vacuum automatic coating machine. Select a coating blade with grooves to coat the water-based coating A onto the base membrane. Vacuum dry at 40-50℃ for 8-12 hours to obtain a single-layer coated membrane with grooves. The solid content of the mixture A is 60%–75%, the degassing machine speed is 1500–2500 rpm / min, and the coating rate of the vacuum automatic coating machine is 2–5 mm / s; the ceramic is one or more of metal oxide ceramics, including but not limited to boehmite, aluminum oxide, zirconium dioxide, tin oxide, silicon dioxide, magnesium oxide, beryllium oxide, etc.; the polymer separator is one of PE, PP, TPU, PEEK, PET, PMIA, PMIA-PU, PBO, PVDF, PBI, PPS, and PI with a thickness of 7–12 μm; the thickness of the grooved coating at its highest point is 1.5–2.5 μm, the height difference between the lowest and highest points of the scraper groove is 0.5–1 μm, and the groove width and the spacing between each groove are 0.5–1.5 mm.

[0051] 2. Disperse the lithium-replenishing compound powder in methanol and sonicate for 25-35 minutes. Then add 3-aminopropyltriethoxysilane and react at room temperature for 1.5-2.5 hours. Centrifuge the product and wash it several times with methanol. Dry it under vacuum at 105-115°C for 10-12 hours to obtain powdered N-lithium-replenishing compound particles. The lithium-replenishing compound is a lithium-containing metal oxide or lithium-ion salt with a theoretical specific capacity >170 mAh / g, including but not limited to Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li2C2O4, Li2SO4, and Li2SiO3.

[0052] 3. N-lithium-supplementing compound, conductive agent, and PVDF are added to NMP in a ratio of (6.5–8):(0.5–1):(3–1) to obtain mixture B. Mixture B is then dispersed in a degassing machine for 15–25 min, repeated 2–4 times to obtain oil-based coating B. A grooved single-layer coated diaphragm is placed in a vacuum automatic coating machine, and a flat-tipped coating blade is used to coat the grooved coating side. Finally, the diaphragm is vacuum-dried at 40–50°C for 4–6 h to obtain a grooved interlocking composite coating lithium-supplementing diaphragm. The solid content of mixture B is 60%–75%, the degassing machine speed is 1500–2500 rpm / min, the vacuum automatic coating machine coating rate is 2–5 mm / s, and the conductive agent is one or more of SP, CNT, VGCF, ECP, rGO, acetylene black, and Carbon ECP. The total thickness of the two coating layers of the lithium-supplementing diaphragm is 4–5 μm.

[0053] The long-cycle thermally stable lithium-replenishing separator prepared by this invention has the characteristics of high electrolyte wetting degree, high liquid retention coefficient, good thermal stability and high tensile strength. At the same time, the coating of the separator is not easy to fall off during battery charging and discharging, the interfacial impedance at the interface with the electrode is low, and the degree of side reaction with the electrolyte is low. Batteries made with this separator can achieve high capacity, high first efficiency and excellent cycle performance.

[0054] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0055] The raw materials used in this invention are not particularly limited in their source; they can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0056] The purity of all raw materials used in this invention is not particularly limited, but analytical grade or conventional purity used in the field of lithium-ion battery separator preparation is preferred.

[0057] Example 1

[0058] A method for preparing a long-cycle thermally stable lithium-supplementing separator includes the following steps:

[0059] 1. Boehmite, SBR, and CMC were added to DI water at a mass ratio of 22.5:1.5:1 to obtain mixture A. The solid content of mixture A was controlled at 65%, and the mixture A was mixed and dispersed in a deaerator at a speed of 1800 rpm / min for 17 min to obtain water-based coating A. A PE membrane with a thickness of 12 μm was used as the base film and placed in a vacuum automatic coating machine. A coating blade with a groove width and a spacing of 0.5 mm between each groove and a height difference of 1 μm between the lowest and highest points was selected to coat the water-based coating A onto the base film at a coating rate of 2 mm / s. The coating was vacuum dried at 48℃ for 10 h to obtain a single-layer coated membrane with grooves. The thickness of the grooved coating at its highest point was 2 μm.

[0060] 2. Disperse Li5FeO4 powder in methanol and sonicate for 30 min. Then add 3-aminopropyltriethoxysilane. The molar ratio of Li5FeO4 to 3-aminopropyltriethoxysilane is 1:1.3. After reacting at room temperature for 2 h, centrifuge the product and wash it several times with methanol. After vacuum drying at 110 °C for 12 h, obtain powdered N-Li5FeO4 particles.

[0061] 3. N-Li5FeO4, SP, and PVDF were added to NMP at a mass ratio of 8:1:1 to obtain mixture B. The solid content of mixture B was controlled at 65%, and the mixture B was mixed and dispersed in a degassing machine at a speed of 2000 rpm / min for 17 min. This process was repeated 3 times to obtain oil-based coating B. The single-layer coated diaphragm with grooves obtained in step 1 was then placed in a vacuum automatic coating machine. A flat-tipped coating blade was selected to coat the oil-based coating B onto the side with the grooved coating at a coating rate of 2 mm / s. Finally, the diaphragm was vacuum dried at 50℃ for 6 h to obtain a grooved interlocking composite coating lithium-supplementing diaphragm, i.e., a long-cycle thermally stable lithium-supplementing diaphragm. The total thickness of the two coating layers coated on the base film was 4.5 μm.

[0062] Example 2

[0063] A method for preparing a long-cycle thermally stable lithium-supplementing membrane, which differs from Example 1 in that the lithium-supplementing compound in step 2 is Li2C2O4, while the remaining steps are the same as in Example 1.

[0064] Example 3

[0065] A method for preparing a long-cycle thermally stable lithium-filling separator differs from Example 1 in that the thickness of the coating with grooves at its highest point in step 1 is 1.5 μm, and the total thickness of the two coating layers in step 3 is 5 μm. The remaining steps are the same as in Example 1.

[0066] Example 4

[0067] A method for preparing a long-cycle thermally stable lithium-filling separator differs from Example 1 in that the thickness of the coating with grooves at its highest point is 2.5 μm in step 1, and the total thickness of the two coating layers is 4 μm in step 3. The remaining steps are the same as in Example 1.

[0068] Comparative Example 1

[0069] A method for preparing a lithium-supplemented separator includes the following steps:

[0070] 1. Boehmite, SBR, and CMC were added to DI water at a mass ratio of 22.5:1.5:1 to obtain a mixture. The solid content of the mixture was controlled to be 65%. The mixture was then mixed and dispersed in a deaerator at a speed of 1800 rpm / min for 17 min to obtain a water-based coating. A PE membrane with a thickness of 12 μm was used as the base membrane and placed in a vacuum automatic coating machine. A flat-edged coating blade was selected to coat the water-based coating onto the base membrane at a coating rate of 2 mm / s. The membrane was then vacuum dried at 48℃ for 10 h to obtain a ceramic single-layer coated membrane with a coating thickness of 4.5 μm.

[0071] Comparative Example 2

[0072] A method for preparing a lithium-supplemented separator includes the following steps:

[0073] Li5FeO4 and PVDF were added to NMP at a mass ratio of 8.5:1.5 to obtain a mixture. The solid content of the mixture was controlled at 65%, and the mixture was mixed and dispersed in a degassing machine at a speed of 2000 rpm / min for 17 min. This process was repeated 3 times to obtain an oil-based coating. A PE membrane with a thickness of 12 μm was used as the base membrane and placed in a vacuum automatic coating machine. A flat-edged coating blade was selected to coat the oil-based coating onto the base membrane at a coating rate of 2 mm / s. Finally, the membrane was vacuum dried at 50 °C for 6 h to obtain a lithium-replenishing coated membrane with a coating thickness of 4.5 μm.

[0074] Comparative Example 3

[0075] A method for preparing a lithium-supplemented separator includes the following steps:

[0076] 1. Boehmite, SBR, and CMC were added to DI water at a mass ratio of 22.5:1.5:1 to obtain mixture A. The solid content of mixture A was controlled to be 65%. The mixture A was then mixed and dispersed in a deaerator at a speed of 1800 rpm / min for 17 min to obtain water-based coating A. A PE membrane with a thickness of 12 μm was used as the base membrane and placed in a vacuum automatic coating machine. A flat-edged coating blade was selected to coat the coating A onto the base membrane at a coating rate of 2 mm / s. The membrane was then vacuum dried at 48℃ for 10 h to obtain a single-layer coated membrane with a coating thickness of 2 μm.

[0077] Steps 2 and 3 are the same as in Example 1.

[0078] Comparative Example 4

[0079] A method for preparing a lithium-supplemented separator includes the following steps:

[0080] 1. Boehmite, SBR, and CMC were added to DI water at a mass ratio of 22.5:1.5:1 to obtain mixture A. The solid content of mixture A was controlled to be 65%. The mixture A was then mixed and dispersed in a deaerator at a speed of 1800 rpm / min for 17 min to obtain water-based coating A. A PE membrane with a thickness of 12 μm was used as the base film and placed in a vacuum automatic coating machine. A coating blade with a groove width and a spacing of 0.5 mm between grooves and a height difference of 1 μm between the lowest and highest points was selected to coat the water-based coating A onto the base film at a coating rate of 2 mm / s. The coating was then vacuum dried at 48℃ for 10 h to obtain a single-layer coated membrane with grooves. The thickness of the grooved coating at its highest point was 2 μm.

[0081] 2. Li5FeO4 and PVDF were added to NMP at a mass ratio of 8.5:1.5 to obtain mixture B. The solid content of mixture B was controlled at 65%, and the mixture B was mixed and dispersed in a degassing machine at a speed of 2000 rpm / min for 17 min. This process was repeated 3 times to obtain oil-based coating B. The single-layer coated diaphragm with grooves obtained in step 1 was then placed in a vacuum automatic coating machine. A flat-blade coating blade was selected to coat the oil-based coating B onto the side with the grooved coating at a coating rate of 2 mm / s. Finally, the diaphragm was vacuum dried at 50℃ for 6 h to obtain a grooved interlocking composite coating lithium-supplementing diaphragm. The total thickness of the two coatings coated on the base film was 4.5 μm.

[0082] Performance testing

[0083] Heat shrinkage rate test: Cut three 10cm×10cm samples, draw cross lines along the longitudinal shrinkage rate (MD) and transverse shrinkage rate (TD) directions, and mark the MD and TD directions. Place the samples between two A4 sheets of paper (one on top and one on the bottom). After heating at the set temperature for 1 hour, measure the length of the cross lines to calculate the shrinkage rate. Shrinkage rate % = (L0-L1) / L0*100% (L0: initial cross line length of the sample, L1: cross line measurement length after heating). Take the average of the three points as the sample heat shrinkage rate.

[0084] Tensile strength test: Sample size: 200mm × 10mm, with no burrs or tears on the edges. Thickness value is the average of actual test results. Clamp spacing: 100mm. Speed: 200mm / min. Result is the average of 3 points. (GB / T1040.3-2006)

[0085] Button battery preparation: Conductive carbon black was added to a polyvinylidene fluoride (PVDF) NMP solution, followed by lithium iron phosphate powder. The mixture was stirred until homogeneous, and the slurry was evenly coated onto aluminum foil using a coating machine to form electrode sheets. The coated electrode sheets were then placed in a vacuum drying oven at 120°C and vacuum dried for 6 hours. After drying, the electrode sheets were rolled on a roller press for later use. Button battery assembly was performed in a glove box under an argon atmosphere. The electrolyte was 1M LiPF6 + EC:DEC:DMC = 1:1:1 (volume ratio). Lithium metal sheets were used as the counter electrode, and the separator was the separator prepared in the embodiments or comparative examples of this invention. Capacity testing was conducted using an Arbin BT2000 battery tester (USA), with a charge / discharge voltage range of 2 to 4.2V and charge / discharge rates of 0.1C and 1C, respectively.

[0086] The test results are shown in Tables 1 and 2.

[0087] Table 1 Comparison of diaphragm properties obtained from the examples and comparative examples.

[0088]

[0089] As shown in Table 1, the lithium-supplementing separator prepared in the examples has slightly lower contact angle and tensile strength, and slightly higher thermal shrinkage rate compared to the lithium-supplementing separator prepared in Comparative Example 1, but the overall physical properties are not significantly different. Compared to Comparative Example 2, the lithium-supplementing layer in the lithium-supplementing separator prepared in Example 1 underwent an amino functionalization reaction, which significantly improved the wettability of the coating surface to the electrolyte and greatly reduced the contact angle. Furthermore, due to the presence of the inner thermally stable coating and the grooved interlocking coating scheme, the separator has better thermal stability and mechanical properties, resulting in significantly higher tensile strength and significantly lower thermal shrinkage rate. Compared to Comparative Example 3, Example 1 did not use the grooved interlocking coating scheme, so the tensile strength of the comparative example was reduced, and the thermal shrinkage rate increased to some extent. Compared to Comparative Example 4, Example 1 included an amino functionalization step, which significantly improved the wettability of the coating surface to the electrolyte, thus significantly reducing the contact angle.

[0090] Table 2. Electrical properties of LFP coin cells prepared with diaphragms from the examples and comparative examples.

[0091]

[0092] As shown in Table 2, the coin cell made with the separator in Example 1 showed an increase of approximately 10 mAh / g in 0.1C charging capacity compared to the coin cell in Comparative Example 1, while the initial efficiency decreased significantly. This indicates that the lithium replenishment component has been charged to the negative electrode to form a film or be stored, effectively playing a lithium replenishment role. Furthermore, the initial discharge capacity at 1C and the capacity retention rate after 50 cycles at 1C were both significantly improved. Compared to Comparative Example 2, the lithium replenishment coating in Example 1 underwent amino functionalization and the addition of conductive agents, resulting in a higher concentration of Li in the coating. +The more complete extraction and faster transmission rate result in higher 0.1C charging capacity and lower initial efficiency. Furthermore, due to the coating's lower electrochemical impedance, reduced interfacial impedance at the electrode contact interface, and the synergistic effect of the grooved composite coating, the 1C initial charge capacity and capacity retention after 50 cycles are also higher, resulting in better cycle performance. Compared to Comparative Example 3, the Example 3 lacks the grooved coating scheme, leading to a significant difference in cycle performance. The Example 3 exhibits higher capacity retention after 50 cycles at 1C and slightly higher initial charge capacity at 1C. Compared to Comparative Example 4, the Example 4 lacks the amino functionalization of the lithium replenishment coating and the addition of a conductive agent. Therefore, the Example 4 has significantly higher 0.1C charging capacity and lower initial efficiency, while also exhibiting higher 1C initial discharge capacity and capacity retention after 50 cycles at 1C, resulting in superior overall electrical performance. Comparative Examples 3 and 4, as well as all the embodiments, employed composite coatings, resulting in fewer side reactions and higher interface stability during the cycling process. Consequently, they exhibited higher capacity retention and better cycling performance after 1C50 cycles compared to Comparative Examples 1 and 2.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. 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 long cycle, thermally stable lithium supplementing separator, characterized by, The lithium supplement coating is a mixture layer of an aminated lithium supplement compound, a conductive agent and polyvinylidene fluoride. The surface of the heat-stable coating is provided with grooves, and the lithium supplement coating is combined with the heat-stable coating in a manner of being fitted into the grooves.

2. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The maximum thickness of the heat-stable coating is 1.5-2.5 μm, the depth of the grooves on the surface of the heat-stable coating is 0.5-1 μm, and the width of the grooves and the interval distance between the grooves are both 0.5-1.5 mm.

3. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The total thickness of the heat-stable coating and the lithium supplement coating is 4-5 μm.

4. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The polymer base film comprises any one of polyethylene, polypropylene, thermoplastic polyurethane elastomer, polyether ether ketone, polyethylene terephthalate, poly-m-phenylene isophthalamide, poly-m-phenylene isophthalamide-polyurethane, polystyrene rod material, polyvinylidene fluoride, polybenzimidazole, polyphenylene sulfide and polyimide.

5. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The ceramic powder comprises any one of boehmite, aluminum oxide, zirconium dioxide, tin oxide, silicon dioxide, magnesium oxide and beryllium oxide.

6. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The conductive agent comprises any one or more of SP, carbon nanotube, vapor-grown carbon fiber, ECP, reduced graphene oxide, acetylene black and Carbon ECP.

7. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The aminated lithium supplement compound is obtained by the reaction of 3-aminopropyl triethoxysilane and a lithium-containing compound, and the lithium-containing compound is a lithium-containing metal oxide or a lithium ion salt with a theoretical specific capacity of >170 mAh / g.

8. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The lithium-containing compound comprises any one or more of Li5FeO4, Li5Fe5O8, Li6CoO4, Li2NiO2, Li2O, Li2O2, Li2C2O4, Li2SO4 and Li2SiO3.

9. The long cycle, thermally stable, lithium supplementing separator of claim 8, wherein, The mass ratio of the ceramic powder, polystyrene butadiene copolymer and sodium carboxymethyl cellulose is (22-23):1.5:

1.

10. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The mass ratio of the aminated lithium supplement compound, conductive agent and polyvinylidene fluoride is (6.5-8):(0.5-1):(3-1).

11. The long cycle, thermally stable, lithium supplementing separator of claim 1, wherein, The lithium supplement coating is a mixture layer of an aminated lithium supplement compound, a conductive agent and polyvinylidene fluoride.

12. A process for the preparation of the long-cycling, thermally stable lithium supplementing separator of claim 1, characterized in that, The ceramic powder, polystyrene butadiene copolymer and sodium carboxymethyl cellulose are added into a first solvent, uniformly mixed to obtain coating A; the coating A is coated on the surface of the polymer base film and dried to obtain a single-layer coated separator; The aminated lithium supplement compound, conductive agent and polyvinylidene fluoride are added into a second solvent, uniformly mixed to obtain coating B; the coating B is coated on the single-layer coated separator and dried to obtain a long-cycle heat-stable lithium supplement separator. The first solvent is water, and the second solvent is an organic solvent comprising any one of N-methyl pyrrolidone, chloroform, dichloromethane and petroleum ether.

13. The production method according to claim 12, wherein The second solvent is N-methyl pyrrolidone.

14. The production method according to claim 13, wherein The mass ratio of the ceramic powder, polystyrene butadiene copolymer and sodium carboxymethyl cellulose is (22-23):1.5:

1.

15. The production method according to claim 12, wherein ​ 16. The production method according to claim 12, wherein The mass ratio of the aminated lithium supplement compound, the conductive agent and the polyvinylidene fluoride is (6.5-8):(0.5-1):(3-1).

17. The production method according to claim 12, wherein The preparation method comprises: selecting a coating doctor blade with grooves to coat coating A on the polymer base film, and then vacuum drying at 40-50 DEG C for 8-12 h to obtain a single-layer coated separator with grooves.

18. The production method according to claim 17, wherein The solid content of coating A is 60%-75%.

19. The production method according to claim 17, wherein When coating coating A, the coating speed is 2-5 mm / s.

20. The production method according to claim 17, wherein The preparation method comprises: selecting a flat-coated doctor blade to coat coating B on the side with the grooved coating, and then vacuum drying at 40-50 DEG C for 4-6 h to obtain a long-cycle thermal stable lithium supplement separator.

21. The production method according to claim 20, wherein The solid content of coating B is 60%-75%.

22. The production method according to claim 20, wherein When coating coating B, the coating speed is 2-5 mm / s.

23. The production method according to claim 12, wherein The preparation method of the aminated lithium supplement compound comprises: dispersing the lithium supplement compound in methanol, ultrasonicating, then adding 3-aminopropyl triethoxysilane, reacting at room temperature for 1.5-2.5 h, centrifuging the product and washing with methanol, and vacuum drying at 105-115 DEG C for 10-12 h to obtain the aminated lithium supplement compound.

24. The production method according to claim 23, wherein The molar ratio of the lithium supplement compound and 3-aminopropyl triethoxysilane is 1:1.1-1.

3.

25. The long-cycle thermal stable lithium supplement separator of any one of claims 1-11 or prepared by the preparation method of any one of claims 12-24 is applied in a lithium ion battery.

26. A lithium-ion battery, characterized by, It comprises a positive electrode, a negative electrode, a separator and an electrode liquid. The separator comprises the long-cycle thermal stable lithium supplement separator of any one of claims 1-11 or prepared by the preparation method of any one of claims 12-24. The separator comprises the long-cycle thermal stable lithium supplement separator of any one of claims 1-11 or prepared by the preparation method of any one of claims 12-24.

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