A single-sided coated diaphragm and its preparation method and application

Abstract

The present invention provides a single-sided coated diaphragm and a preparation method and application thereof, which belongs to the field of diaphragm technology. The single-sided coated diaphragm comprises a base film and an inherent microporous polymer coating provided on one surface of the base film; the surface characteristic parameter R=R A / R B , R is 0.5~30; among them, the roughness of the side of the inherent microporous polymer coating away from the base film is R A ; Roughness R of the non-coated surface of the base film B The single-sided coated diaphragm provided by the present invention can maintain a stable microporous structure on the coated surface by controlling the range of the surface characteristic parameter R within a specific range, thereby achieving a balance between the overall air permeability, sheet resistance, and transition metal ion barrier efficiency of the single-sided coated diaphragm. While ensuring sufficient transition metal ion barrier effect, the high air permeability and low sheet resistance of the diaphragm can be maintained, which is conducive to improving the uniformity of the load of the single-sided coated diaphragm.

Description

Technical Field

[0001] The present invention belongs to the technical field of diaphragms, and relates to a single-sided coated diaphragm and a preparation method and application thereof, and in particular to a single-sided coated diaphragm with ion selectivity and a preparation method and application thereof. Background Art

[0002] As highly efficient energy storage devices, the performance and safety of lithium-ion batteries are highly dependent on the functionality of their separators. Lithium-ion battery separators play a key role in the battery, blocking electron conduction and allowing the free migration of lithium ions. However, their long-term stability is often limited by the dissolution and diffusion of transition metal ions (such as nickel, iron, and manganese) in the positive electrode. During battery cycling, transition metal ions in the positive electrode active material migrate through the electrolyte to the negative electrode surface, causing SEI film destruction, lithium dendrite growth, capacity decay, and even leading to safety hazards such as thermal runaway.

[0003] Existing coating methods for diaphragm safety include using inorganic ceramic particles (such as alumina, silica, boehmite) and matrix resins (such as PVDF, PMMA) to form a coating layer, using the high thermal stability of ceramic materials to enhance the high-temperature resistance of the diaphragm, and improving the electrolyte wettability through resin bonding; or by introducing single-ion conductor materials (such as lithium lanthanum titanium oxide compounds), nanofiber networks or polymers modified with functional groups (such as ionomers containing sulfonic acid groups), attempting to construct a coating structure with ion screening function to optimize the lithium ion transmission path.

[0004] In practical applications, the above-mentioned technical solutions still suffer from the problem of lack of ion barrier mechanism. Existing coating materials (such as conventional ceramic / polymer composite coatings) lack specific adsorption or size screening capabilities for transition metal ions (Ni, Fe, Mn), and cannot effectively block their cross-membrane diffusion, resulting in continuous damage to the SEI membrane and loss of lithium inventory. Residual moisture (>600ppm) in the water-based coating system will catalyze the migration of transition metal ions. The oil-based system is prone to forming local weak bonding areas due to incomplete solvent evaporation. After circulation, the coating is easily peeled off from the base film (peel force <0.5N / cm). Nano single-ion conductor materials (such as LLTO) are expensive, and the existing process requires multiple coating-drying steps (energy consumption >3kWh / m²), which restricts large-scale application.

[0005] Therefore, in the art, it is desired to develop a membrane that has excellent ion selectivity, high heat resistance, and simple process. Summary of the Invention

[0006] To address the shortcomings of the prior art, the present invention aims to provide a single-sided coated diaphragm, its preparation method, and its application. Specifically, it provides an ion-selective single-sided coated diaphragm, its preparation method, and its application. By optimizing material components, innovating the coating process, and designing the interface structure, the present invention specifically addresses the problems of low efficiency in barrier efficiency for transition metal ions, poor coating uniformity, and insufficient interface durability in prior art diaphragms.

[0007] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a single-sided coated diaphragm, comprising a base membrane and an intrinsically microporous polymer (PIM) coating disposed on one surface of the base membrane; the surface characteristic parameter R=R A / R B , R is 0.5 to 30, for example, 0.5, 0.6, 0.8, 1, 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 or a range consisting of any two thereof;

[0009] The roughness of the side of the inherent microporous polymer coating away from the base film is R A ;

[0010] The roughness of the non-coated surface of the base film (i.e., the side of the base film away from the intrinsic microporous polymer coating) is R B , R B The thickness of the nanostructured carbon fiber is 0.005 to 0.150 μm, for example, 0.005 μm, 0.006 μm, 0.008 μm, 0.010 μm, 0.020 μm, 0.030 μm, 0.040 μm, 0.050 μm, 0.060 μm, 0.070 μm, 0.080 μm, 0.100 μm, 0.120 μm, 0.130 μm, 0.150 μm or a range consisting of any two thereof, preferably 0.010 to 0.100 μm.

[0011] The single-sided coated diaphragm provided by the present invention can maintain a stable microporous structure on the coating surface by controlling the range of the surface characteristic parameter R within a specific range, so that the overall air permeability, surface resistance and transition metal ion barrier efficiency of the single-sided coated diaphragm are balanced, while ensuring sufficient transition metal ion barrier effect while maintaining high air permeability and low surface resistance (≤2.5Ω·cm 2 ), which helps improve the uniformity of the single-sided coated diaphragm load. In addition, since the formed PIM polymer coating has strong intramolecular stress, it also inhibits the thermal shrinkage of the diaphragm at high temperatures.

[0012] The PIM used in the present invention is a special type of polymer with a very high specific surface area (BET > 200 m 2 / g), due to the presence of various rigid and distorted structures within the molecules, the polymer cannot effectively stack when forming a dense packing, resulting in a large number of nanoscale micropores (most of which are below 2nm in size). These micropores provide ample lithium ion channels, selectively allowing lithium ions to pass through while also preventing the passage of other transition metal ions (manganese, iron, and nickel), creating an excellent channel for the smooth transmission of lithium ions and the isolation of transition metal ions. PIM polymers dynamically capture transition metal ions through the dual mechanisms of self-assembly pore screening and chemical chelation, significantly reducing transition metal ion contamination of the battery's negative electrode and improving the battery's cycle life and safety.

[0013] Preferably, the surface characteristic parameter R of the single-sided coated diaphragm is 1-14.

[0014] Preferably, the roughness R of the side of the intrinsically microporous polymer coating away from the base film is A The range of R can be 0.05 to 0.20 μm, for example, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.10 μm, 0.11 μm, 0.12 μm, 0.13 μm, 0.14 μm, 0.15 μm, 0.16 μm, 0.17 μm, 0.18 μm, 0.19 μm, 0.20 μm or any two thereof. R can be controlled by adjusting the coating process and the type and parameters of the raw materials. A In the range of 0.05~0.20μm, R A The value of will directly affect the ion conduction efficiency and interface contact resistance of the single-sided coated diaphragm.

[0015] Preferably, the difference in roughness between the two sides of the base film, i.e., the coated side and the non-coated side, is 0.005-0.100 μm, for example, 0.005 μm, 0.010 μm, 0.015 μm, 0.020 μm, 0.025 μm, 0.030 μm, 0.035 μm, 0.040 μm, 0.045 μm, 0.050 μm, 0.055 μm, 0.060 μm, 0.065 μm, 0.070 μm, 0.075 μm, 0.080 μm, 0.085 μm, 0.090 μm, 0.095 μm, 0.100 μm, or any two thereof. The coated side of the base film refers to the side of the base film in contact with the intrinsically microporous polymer coating.

[0016] The roughness of both sides of the basement membrane affects the pore connectivity and loading uniformity of the basement membrane.

[0017] Preferably, the inherently microporous polymer may include a polymer listed in the following literature: Baran MJ, Carrington ME, Sahu S, Baskin A, Song J, Baird MA, Han KS, Mueller KT, Teat SJ, Meckler SM, Fu C, Prendergast D, Helms BA. Diversity-oriented synthesis of polymer membranes with ion solvation cages. Nature. 2021 Apr;592(7853):225-231. doi: 10.1038 / s41586-021-03377-7. Epub 2021 Apr 7. PMID: 33828319.(Baran MJ, Carrington ME, Sahu S, Baskin A, Song J, Baird MA, Han KS, Mueller KT, Teat SJ, Meckler SM, Fu C, Prendergast D, Helms BA. Diversity-guided synthesis of ionic solvatable cage polymer membranes. Nature, 592(7853): 225–231. doi: 10.1038 / s41586-021-03377-7. Epub ahead of print April 7, 2021. PMID: 33828319.

[0018] McKeown, NB, Budd, PM, Msayib, K., Ghanem, B., Microporous Polymer Material, US7690514B2, 2010.

[0019] Preferably, the intrinsically microporous polymer comprises a repeating unit (R AB ):

[0020] Formula (I); wherein n is an integer between 5 and 10,000;

[0021] A is a monomer segment selected from any one of the following (A), (B), (C), (D), (E), (F), (G), (H), (I) or (j):

[0022] ;

[0023] B is a monomer segment selected from any one of the following (a), (b), (c), (d), (e), (f) or (g):

[0024] ;

[0025] Among them, each R 10 Each independently selected from (C 1-6 ) alkyl or H;

[0026] Each R 11 Each independently selected from -CH2NR1R2 or H;

[0027] Each R 12 Each independently selected from -C(NOR 13 )N(R 14 )2 or -CN;

[0028] R1 and R2 are each independently (C 1-20 ) alkyl, (C 2-20 ) alkenyl, (C 2-20 ) alkynyl, (C 6-12 ) aryl, (C 3-8 ) cycloalkyl, (C 6-12 aryl)-C 1-20 Alkyl, (C 3-8 Cycloalkyl)-C 1-20 Alkyl, (C 1-20 ) heteroalkyl, (C 1-20 ) haloalkyl, (C 1-20 ) haloalkoxy, 3 to 8 membered heterocyclyl, (3 to 8 membered heterocyclyl)-C 1-20 alkyl, 5- to 8-membered heteroaryl, heteroaryl-C 1-20alkyl; or, each R1 and R2 is optionally and independently substituted by one or more Z1; or, each alkyl, alkenyl and alkynyl group in R1 and R2 optionally and independently contains one or more heteroatoms independently selected from silicon, chalcogenides and pnictides, and one or more atoms in R1 and R2 are optionally and independently present in an oxidized form, such as C=O, C=S, N=O, N=S, S=O or S(O2); or, R1 and R2, together with the nitrogen atom to which they are attached, form a 3- to 8-membered heterocyclyl or a 5- to 8-membered heteroaryl, each of which is optionally substituted by one or more Z2;

[0029] Z1 and Z2 are each independently halogen, -OH, -NO2, -CN, (C 1-20 ) alkyl, (C 2-20 ) alkenyl, (C 2-20 ) alkynyl, (C 6-12 ) aryl, (C 3-8 ) cycloalkyl, (C 6-12 aryl)-C 1-20 Alkyl, (C 1-20 ) heteroalkyl, 3 to 8 membered heterocyclyl, 3 to 8 membered heteroaryl, (C 3-8 Cycloalkyl)-C 1-20 Alkyl, (3 to 8 membered heterocyclyl)-C 1-20 Alkyl, (5- to 8-membered heteroaryl)-C 1-20 Alkyl, (C 1-20 ) haloalkyl, (C 1-20 ) haloalkoxy, -OR6, -SR6, -S(O)R6, -S(O)2R6, SO2NR6NR7, NR6C(O)R7, NR6S(O)2R7, NR6C(O)NR7R8, NR6R7, CO2R6, -C(O)NR6R7 or -C(O)R6.

[0030] Preferably, R3, R4, R5, R6, R7 and R8 are each independently (C 1-20 ) alkyl, (C 2-20 ) alkenyl, (C 2-20 ) alkynyl, (C 6-12 ) aryl, (C 3-8 ) cycloalkyl, (C 6-12 aryl)-C 1-20 Alkyl, (C 3-8 Cycloalkyl)-C 1-20 Alkyl, (C 1-20 )heteroalkyl, 3 to 8 membered heterocyclyl, (3 to 8 membered heterocyclyl)-C 1-20 alkyl, 5- to 8-membered heteroaryl, or (5- to 8-membered heteroaryl)-C 1-20 Specifically, R4 and R5 can form together (C 4-8) cycloalkyl, (C 6-12 ) aryl, 4 to 8 membered heterocyclyl or 5 to 8 membered heteroaryl; specifically, R6 and R7 together form a 4 to 8 membered heterocyclyl or 5 to 8 membered heteroaryl; specifically, R7 and R8 together form a 4 to 8 membered heterocyclyl or 5 to 8 membered heteroaryl.

[0031] Each R 13 are independently H, (C 1-20 ) alkyl or (C 3-8 ) cycloalkyl, wherein alkyl and cycloalkyl are optionally and independently substituted with one or more Z3;

[0032] Each Z3 is independently halogen, -NO2, -CN, -OH, -SO3H, -NH2, (C 1-20 ) alkyl, (C 2-20 ) alkenyl, (C 2-20 ) alkynyl, (C 6-12 ) aryl, (C 3-8 ) cycloalkyl, (C 6-12 aryl)-C 1-20 Alkyl, (C 1–20 ) heteroalkyl, 3 to 8 membered heterocyclyl, 5 to 8 membered heteroaryl, (C 3-8 Cycloalkyl)-C 1–20 Alkyl, (5- to 8-membered heteroaryl)-C 1-20 Alkyl, (C 1-20 ) haloalkyl, (C 1-20 ) haloalkoxy, -OR6, -SR6, -S(O)R6, -S(O)2R6, SO2NR6NR7, NR6C(O)R7, NR6S(O)2R7, NR6C(O)NR7R8, NR6R7, CO2R6, -C(O)NR6R7 or -C(O)R6;

[0033] Each R 14 are independently H, (C 1-20 ) alkyl or (C 3-8 ) cycloalkyl.

[0034] Preferably, the inherent microporous polymer comprises PIM-1 (A unit is selected from (A) monomer segment, R 11 H, B unit is selected from (a) monomer segment, R 12 CN), PIM-2 (A unit is selected from (A) monomer segment, R 11 H, B unit is selected from (g) monomer segment), PIM-C1 (A unit is selected from (j) monomer segment, B unit is selected from (a) monomer segment, R 12 CN), PIM-py (A unit is selected from (A) monomer segment, R 11 H, B unit is selected from (b) monomer segment, R12 CN) or a combination of at least two thereof.

[0035] Preferably, the thickness of the inherently microporous polymer coating is 0.1 to 3 μm, for example, 0.1 μm, 0.2 μm, 0.3 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm or any two thereof, preferably 0.5 to 1.5 μm.

[0036] Preferably, the base film comprises a porous polyolefin base film.

[0037] Preferably, the porous polyolefin-based membrane includes a PE (polyethylene) porous membrane, a PP (polypropylene) porous membrane, or a PE-PP multilayer composite porous membrane, preferably a PE porous membrane.

[0038] Preferably, the thickness of the base film is 3~20μm, for example, it can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm or any two of them, preferably 5~11μm.

[0039] Preferably, the porosity of the base film is 33% to 55%, for example, it can be 33%, 35%, 37%, 38%, 40%, 42%, 44%, 46%, 48%, 49%, 50%, 51%, 53%, 54%, 55% or any two thereof, preferably 48% to 51%.

[0040] Preferably, the inherently microporous polymer coating further comprises a second polymer.

[0041] Preferably, the second polymer comprises any one or a combination of at least two of polyamide, aramid, poly(meth)acrylate, (meth)acrylic acid-(meth)acrylate copolymer, polyimide, polyacrylonitrile, cellulose, polyvinylidene fluoride, polytetrafluoroethylene, or vinylidene fluoride-hexafluoropropylene copolymer. The second polymer must be fully soluble in the solvent system of the coating slurry. The second polymer and the PIM polymer form a composite coating that further enhances the adhesion between the diaphragm and the electrode and heat resistance.

[0042] Preferably, the surface density increment of the single-sided coated diaphragm compared to the base film is 0.08-1 g / m 2 , for example, it can be 0.08g / m 2 , 0.1g / m2 , 0.2g / m 2 , 0.3g / m 2 , 0.4g / m 2 , 0.5g / m 2 , 0.6g / m 2 , 0.7g / m 2 , 0.8g / m 2 , 0.9g / m 2 , 1g / m 2 or a range consisting of any two of them.

[0043] Preferably, the air permeability of the single-sided coated diaphragm is 100~10000sec / 100mL, for example, it can be 100sec / 100mL, 200sec / 100mL, 300sec / 100mL, 400sec / 100mL, 500sec / 100mL, 600sec / 100mL, 700sec / 100mL, 800sec / 100mL, 900sec / 100mL, 1000sec / 100mL, 2000sec / 100mL, 3000sec / 100mL, 4000sec / 100mL, 4000sec / 100mL, 6000sec / 100mL, 7000sec / 100mL, 8000sec / 100mL, 9000sec / 100mL, 10000sec / 100mL or a range consisting of any two of them.

[0044] Preferably, the moisture content of the single-sided coated diaphragm is 270~480ppm, for example, it can be 270ppm, 280ppm, 300ppm, 320ppm, 330ppm, 350ppm, 360ppm, 380ppm, 400ppm, 420ppm, 440ppm, 460ppm, 480ppm or a range consisting of any two thereof.

[0045] Preferably, the electrolyte infiltration area of ​​the single-sided coated diaphragm is 72~95mm 2 , for example, it can be 72mm 2 , 73mm 2 , 74mm 2 , 76mm 2 , 78mm 2 , 80mm 2 , 82mm 2 , 84mm 2 , 86mm 2 , 88mm 2 , 90mm 2 , 92mm 2 , 94mm2 , 95mm 2 or a range consisting of any two of them.

[0046] Preferably, after the single-sided coated diaphragm is placed at 130°C for 1 hour, the thermal shrinkage rates in the MD direction (longitudinal direction) and the TD direction (transverse direction) are both less than 3%, for example, they can be 2.8%, 2.6%, 2.4%, 2.2%, 2%, 1.8%, 1.6%, 1.4%, 1.2%, 1%, 0.8%, 0.7%, 0.5%, 0.4%, 0.3% or a range of any two thereof, preferably 0.5% to 2.8%.

[0047] Preferably, the surface resistance of the single-sided coated diaphragm at room temperature is ≤2.8Ω·cm 2 , for example, it can be 2.8Ω·cm 2 , 2.7Ω·cm 2 , 2.6Ω·cm 2 , 2.5Ω·cm 2 , 2.3Ω·cm 2 , 2.2Ω·cm 2 , 2Ω·cm 2 , 1.8Ω·cm 2 , 1.6Ω·cm 2 , 1.4Ω·cm 2 , 1.2Ω·cm 2 , 1Ω·cm 2 , 0.8Ω·cm 2 or a range consisting of any two of them.

[0048] Preferably, the single-sided coated diaphragm has 3+ The diffusion coefficient is 1×10 -10 ~1×10 -8 cm 2 / s, for example, it can be 1×10 -10 cm 2 / s, 2×10 -10 cm 2 / s, 3×10 -10 cm 2 / s, 5×10 -10 cm 2 / s, 8×10 -10 cm 2 / s, 1×10 -9 cm 2 / s, 2×10 -9 cm 2 / s, 3×10 -9 cm 2 / s, 5×10 -9 cm2 / s, 8×10 -9 cm 2 / s, 1×10 -8 cm 2 / s or a range consisting of any two of them.

[0049] Preferably, the single-sided coated diaphragm is 3+ The diffusion coefficient is 1×10 -11 ~4×10 -9 cm 2 / s, for example, it can be 1×10 -11 cm 2 / s, 2×10 -11 cm 2 / s, 3×10 -11 cm 2 / s, 5×10 -11 cm 2 / s, 8×10 -11 cm 2 / s, 1×10 -10 cm 2 / s, 2×10 -10 cm 2 / s, 3×10 -10 cm 2 / s, 5×10 -10 cm 2 / s, 8×10 -10 cm 2 / s, 1×10 -9 cm 2 / s, 2×10 -9 cm 2 / s, 3×10 -9 cm 2 / s, 4×10 -9 cm 2 / s or a range consisting of any two of them.

[0050] Preferably, the single-sided coated diaphragm is 3+ The diffusion coefficient is 1×10 -11 ~1×10 -9 cm 2 / s, for example, it can be 1×10 -11 cm 2 / s, 2×10 -11 cm 2 / s, 3×10 -11 cm 2 / s, 5×10 -11 cm 2 / s, 8×10 -11 cm2 / s, 1×10 -10 cm 2 / s, 2×10 -10 cm 2 / s, 3×10 -10 cm 2 / s, 5×10 -10 cm 2 / s, 8×10 -10 cm 2 / s, 1×10 -9 cm 2 / s or a range consisting of any two of them.

[0051] In a second aspect, the present invention provides a method for preparing the single-sided coated diaphragm according to the first aspect, the preparation method comprising the following steps:

[0052] (1) dissolving the inherent microporous polymer in an organic solvent to obtain a coating slurry;

[0053] (2) Providing a base film, wherein the roughness R of the non-coated surface of the base film is B 0.005~0.150μm;

[0054] (3) Apply the coating slurry to the side of the base film to be coated and dry it to form a surface roughness of R A The inherent microporous polymer coating is obtained to obtain the single-sided coated diaphragm, and the surface characteristic parameter R=R A / R B , R is 0.5~30.

[0055] Preferably, the organic solvent comprises any one or a combination of at least two of dichloromethane, tetrahydrofuran, acetone, toluene, N,N-dimethylformamide, and dimethyl carbonate, with dichloromethane, tetrahydrofuran, and acetone being preferred. Dichloromethane, tetrahydrofuran, and acetone are highly volatile organic solvents. The advantages of using these three solvents are ease of production and minimal impact on the performance of the diaphragm. Other solvents may also be used, but they require longer drying times or higher temperatures.

[0056] Preferably, the mass proportion of the inherent microporous polymer in the coating slurry is 0.5% to 8%, for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8% or any two thereof, preferably 1% to 2.5%.

[0057] Optionally, the membrane with a specific roughness provided in step (2) can be a base membrane with a specific roughness, or the base membrane can be pretreated before coating. For example, when the roughness of the membrane surface needs to be improved, chemical etching can be used. Specifically, before coating, the non-treated surface of the base membrane is covered with a corrosion-resistant film, and the etching liquid is sprayed evenly on the surface to be treated. After a period of time, it is rinsed with deionized water to remove residual acid and fully dried. Alternatively, this method is used to treat both sides of the base membrane separately to control the two sides of the base membrane to have different roughness. If it is necessary to reduce the roughness of the membrane surface, the membrane surface can also be controlled by heat treatment. For example, the surface to be treated is treated with a hot roller at 60~90℃ for 5~25s, and then cooled with a rapid cooling roller (3~15℃) for 5~15s. If it still cannot be reduced to the ideal roughness range, the above process can be repeated on the surface to be treated until the appropriate roughness is obtained.

[0058] Optionally, the chemical etching solution may be, for example, 30% H2SO4 at 60°C, and the dwell time may be 5 to 30 seconds, such as 5 seconds, 10 seconds, 15 seconds, 20 seconds, 25 seconds, 30 seconds, or any two thereof.

[0059] Preferably, the coating in step (3) includes coating using a micro-concave roller. The number of lines of the micro-concave roller is selected from 120L to 260L according to the coating requirements, for example, it can be 120L, 140L, 160L, 180L, 200L, 220L, 240L, 260L or any two thereof.

[0060] Preferably, after the coating in step (3), the step of rolling with a wet pressing roller is also included.

[0061] Preferably, the surface temperature of the wet pressing roller is controlled between 10°C and 25°C, for example, within a range of 10°C, 15°C, 18°C, 20°C, 22°C, 23°C, 25°C, or any combination thereof. By pre-treating the wet film (surface covered with undried film) with the wet pressing roller after coating, shrinkage of the composite film after entering the drying oven is avoided. Surface roughness is also controlled, coating uniformity is improved, and thus the composite film surface morphology is affected. It should be understood that the wet pressing roller of the present invention refers to a roller or roller assembly with a smooth surface that can perform low-temperature rolling on the undried film surface to control flatness.

[0062] Preferably, the drying is carried out in an oven.

[0063] Preferably, the oven temperature is 20-80° C., for example, 20° C., 30° C., 40° C., 50° C., 60° C., 70° C., 80° C., or any two thereof, preferably 35-48° C. By limiting the oven temperature to a specific range, it is helpful to control the roughness of both sides of the single-sided coated separator within the range defined in the present invention. The coated membrane surface is kept in the oven for 3-30 seconds, depending on the solvent, to ensure sufficient evaporation of the solvent.

[0064] The surface coating of the single-sided coated diaphragm after coating is uniform, and the membrane surface is completely covered by the PIM polymer to form a dense polymer coating. At the same time, the surface morphology of the coating surface and the non-coated surface of the base membrane is controlled through process and technical means, and the surface characteristic parameter R is controlled within a specific range, which significantly improves the overall performance of the single-sided coated diaphragm.

[0065] It should be noted that the coating of the present invention may also be carried out by other methods such as slit coating or spray coating.

[0066] Selecting a base film with a specific roughness can optimize the air permeability of the coated diaphragm and greatly reduce the impact of the dense coating on the membrane's air permeability. By controlling the thickness, surface density increment, and slurry solid content, the surface morphology of the coating surface and the base film surface can be changed, and the surface characteristic parameters of the coated diaphragm can be controlled within a certain range. This helps increase the contact area between the coating surface and the electrolyte, providing a sufficient gathering place for lithium ions in the electrolyte, improving the wettability and water content of the coated diaphragm, and thus increasing the lithium ion transmission efficiency. It also helps to relieve the internal stress of the coating surface and improve the overall heat resistance of the coated diaphragm. Preferably, by controlling the roughness of the coated and uncoated surfaces of the base film, it is beneficial to further enhance the above effects.

[0067] Further preferably, the base film with a specific roughness, the high volatility solvent system and the low oven temperature selected in the present invention can provide the prerequisites for the formation of a dense PIM polymer coating and good physical properties of the single-sided coated separator.

[0068] In a third aspect, the present invention provides a battery comprising the single-sided coated separator as described in the first aspect.

[0069] Preferably, the battery comprises a lithium-ion battery.

[0070] Compared with the prior art, the present invention has the following beneficial effects:

[0071] The single-sided coated membrane provided by the present invention maintains a stable microporous structure on the coating surface by controlling the surface characteristic parameter R within a specific range. This balances the membrane's overall air permeability, sheet resistance, and transition metal ion barrier efficiency. While ensuring sufficient transition metal ion barrier performance, the membrane also maintains high air permeability and low sheet resistance, facilitating improved loading uniformity across the single-sided coated membrane. Furthermore, the resulting PIM polymer coating exhibits strong intramolecular stress, which inhibits thermal shrinkage of the membrane at high temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 This is a schematic structural diagram of the single-sided coated diaphragm provided in Example 1 of the present invention;

[0073] Figure 2 This is a SEM image of the surface of the inherent microporous polymer coating of the single-sided coated diaphragm provided in Example 1 of the present invention.

[0074] Among them, 1-base membrane, 2-inherent microporous polymer coating. DETAILED DESCRIPTION

[0075] The technical solution of the present invention is further described below by way of specific embodiments. It should be understood by those skilled in the art that the embodiments are merely to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0076] Unless otherwise specified, some of the raw material information involved in the following examples and comparative examples of the present invention are as follows:

[0077] PIM-C1: [C 32 H 20 N2O5] n , CAS:918776, purchased from Sigma-Aldrich;

[0078] PIM-1: brand HWG58338, purchased from Beijing Huawei Ruike Chemical Co., Ltd.;

[0079] Original base film (i.e., base film that has not been chemically etched or heat-treated to control the roughness on one or both sides): Xingyuan material polyethylene base film, model: SW809I, porosity 48%, thickness 9μm, surface density 4.5g / m 2 , the roughness of both sides is 0.040 μm; as described in the above invention content, one or both sides can be processed by chemical etching or heat treatment to control the roughness of both sides to reach the target value of the embodiment and the comparative example.

[0080] Example 1

[0081] In this embodiment, a single-sided coated diaphragm is provided, and its structural schematic diagram is as follows: Figure 1 As shown, the single-sided coated diaphragm includes a base film 1 and an inherent microporous polymer coating 2 provided on one surface of the base film;

[0082] The preparation method comprises the following steps:

[0083] (1) dissolving the intrinsic microporous polymer (PIM-C1) in an organic solvent (tetrahydrofuran) and stirring thoroughly until the solid is completely dissolved to obtain a coating slurry, wherein the mass proportion of PIM-C1 in the coating slurry is 1.5%;

[0084] (2) Providing a base film, the specific roughness data of which is shown in Table 1;

[0085] (3) At room temperature of 25°C, the coating slurry is applied to the side of the base film to be coated by micro-concave roller coating, and the number of roller lines is selected to be 160L. After coating, a wet pressing roller is added for rolling, wherein the surface temperature of the wet pressing roller is controlled at 16°C, and the coating surface is pretreated. Then, the coated diaphragm is kept in an oven at 40°C for 14 seconds for drying to form an inherent microporous polymer coating, thereby obtaining the single-sided coated diaphragm.

[0086] Among them, the base film is made of Xingyuan material polyethylene base film, model: SW809I, porosity 48%, thickness 9μm, surface density 4.5g / m 2 .

[0087] The surface SEM image of the inherent microporous polymer coating of the single-sided coated diaphragm provided in this embodiment is as follows: Figure 2 shown.

[0088] Example 2-Example 10, Comparative Example 1

[0089] The difference from Example 1 is that the type of intrinsic microporous polymer, the type of organic solvent, the roughness of the non-coated surface of the base film R B , the coating surface roughness of the base film, the preparation conditions of the single-sided coated diaphragm, etc. are different, as shown in Table 1 and Table 2. For the contents not shown in Table 1 and Table 2, they are all considered to be the same as those in Example 1.

[0090] Comparative Example 2

[0091] In this comparative example, a commercially available polyethylene wet-process membrane (purchased from Shenzhen Xingyuan Material Technology Co., Ltd., SW809I) with a porosity of 48%, a thickness of 9 μm, and an area density of 4.5 g / m 2 The roughness of both surfaces is 0.040μm.

[0092] Comparative Example 3

[0093] In this comparative example, a double-sided coated diaphragm is provided, comprising a base film and an inherent microporous polymer coating disposed on both sides of the base film;

[0094] The preparation method comprises the following steps:

[0095] (1) dissolving an intrinsic microporous polymer (PIM-1) in an organic solvent (tetrahydrofuran) and stirring thoroughly until the solid is completely dissolved to obtain a coating slurry, wherein the mass proportion of PIM-1 in the coating slurry is 10%;

[0096] (2) At room temperature of 25°C, the coating slurry was applied to both sides of the base film by means of a micro-concave roller coating method. The number of lines of the roller was selected as 240L. The slurry was applied to one side of the base film. After coating, it was dried at 50°C for 30 minutes, then heated to 80°C for drying for 40 minutes, and then heated to 100°C for drying for 30 minutes. After drying, a first coating layer was formed. The slurry was continuously applied to the other side of the base film using a micro-concave roller. After coating, it was dried at 50°C for 30 minutes, then heated to 80°C for drying for 40 minutes, and then heated to 100°C for drying for 30 minutes. After drying, a second coating layer was formed, and a double-sided coated diaphragm was obtained, wherein the thickness of the single-sided coating layer was 0.7 μm.

[0097] Among them, the base film is made of Xingyuan material polyethylene base film, model: SW809I, porosity 48%, thickness 9μm, surface density 4.5g / m 2 .

[0098] The performance tests of the diaphragms provided in the embodiments of the present invention and the comparative examples were conducted using the following test methods:

[0099] (1) Air permeability: The air permeability of the single-side coated diaphragm is obtained by referring to the method specified in the national standard GB / T 36363-2018 "Polyolefin diaphragms for lithium-ion batteries".

[0100] (2) Moisture content: The Karl Fischer method (volume method) is used to test the moisture content of the diaphragm. The moisture content is tested based on the volume of consumed reagents and the titer.

[0101] (3) Electrolyte wetting area: Cut the diaphragm into a 10 × 10 mm square, then place it on a glass slide and tape it tightly to keep the membrane surface flat. Use an injection needle to take 2 μL of propylene carbonate and drop it on the diaphragm sample. Measure the area of ​​the droplet after 5 minutes.

[0102] (4) Thermal shrinkage: The thermal shrinkage of the membrane in the MD direction (longitudinal direction) and TD direction (transverse direction) was obtained according to the method specified in the national standard GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries", and the average value was taken as the thermal shrinkage of the membrane; wherein, the heat treatment temperature of the oven was 130°C and the heat treatment time was 1 h.

[0103] (5) Roughness: Using a confocal microscope (OLYMPUS OLS5100) with a 10x magnification, select three equally spaced positions in the horizontal direction and three equally spaced positions in the vertical direction on the surface of the sample film to be tested. The reference length interval is 3 cm, for a total of 9 positions. The average value of the surface roughness Sa is calculated by the Analysis application software, and the average value of the data at the 9 positions is further taken as the roughness.

[0104] (6) Surface resistance: Cut 4 pieces of diaphragm samples with a diameter of 45 mm on a flat surface, soak the samples in an electrolyte (1 mol / L LiPF6 electrolyte, the solvent is EC, EMC and DMC with a volume ratio of 1:1:1) and seal and soak for 30 min; pour the above electrolyte into the surface resistance test fixture; place 1, 2, 3, and 4 diaphragms in the fixture for testing respectively; use the number of diaphragm layers as the horizontal axis and the diaphragm resistance as the vertical axis for linear fitting, and calculate the slope and fit of the straight line. When the fit is greater than 0.999, the slope is the surface resistance of the diaphragm, and the unit is ohm Ω·cm 2 .

[0105] (7) Mn 3+ 、Fe 3+ 、Ni 3+ Diffusion coefficient: the flow rate of a substance passing through a unit area per unit time. Specifically, an H-type electrolytic cell is used to test the diffusion coefficient of the corresponding transition metal ion after 1 hour. The specific test method includes the following steps:

[0106] In the glove box, a glass H-type electrolytic cell was used, in which the left side was for high concentration measurement (simulating positive electrode measurement) and connected to the counter electrode (Pt wire), the right side was for low concentration measurement (simulating negative electrode side) and connected to the working electrode (glass carbon) and the reference electrode (lithium wire), and the middle was separated by a 10cm diameter circular diaphragm sample, and the diaphragm was oriented in the same direction as in the battery; equal amounts of electrolyte (1mol / L LiPF6 electrolyte, solvents were EC, EMC and DMC with a volume ratio of 1:1:1) were added to both sides. Before the test, the transition metal salt solution was added to the left side and stirred to dissolve, so that the transition metal ion concentration on the left was 50mmol / L, and then LiPF6 was added to the right side and stirred to dissolve, so that Li +The concentration was 150 mmol / L. The transition metal salt solutions were independently composed of manganese (III) acetylacetonate, nickel acetylacetonate, and iron acetylacetonate. These three electrodes were connected to an electrochemical workstation and subjected to CV measurements at a rate of 0.2 V / s in the range of 4.0 V to 1.5 V. One hour after the start of the test, a 5 mL liquid sample was taken from the right side. After acid digestion, the corresponding transition metal ion concentration was measured using ICP. The ion diffusion coefficient = transition metal ion concentration × diaphragm area ÷ 3600 s.

[0107] (8) Cycle life

[0108] After preparing and assembling a battery using the single-sided coated diaphragms prepared in the embodiments and comparative examples of the present invention, the first-cycle discharge capacity was measured at 0.5C charge / 0.5C discharge at 25°C. The number of cycles was recorded under these conditions when the discharge capacity reached 70% of the first-cycle discharge capacity. 50 groups of parallel experiments were tested and the average value was taken.

[0109] The specific battery preparation and assembly methods are as follows:

[0110] 1) The positive electrode active material NCM811, conductive agent SP, conductive agent KS-6, and binder PVDF were added to the solvent NMP in a mass ratio of 90:2:1:3, mixed evenly, and prepared into a positive electrode slurry. The slurry was then coated onto a 10 μm aluminum foil current collector. The slurry was then dried in an oven at 95°C and rolled on a roller press for later use.

[0111] 2) Add the active material artificial graphite, the conductive agent acetylene black and the binder CMC / SBR (mass ratio of 1:1) into water at a mass ratio of 90:5:5 and disperse evenly to form a negative electrode slurry. The slurry is then coated on a 10μm thick copper foil current collector, dried in an oven at 85°C, and rolled on a roller press for later use.

[0112] 3) In a drying room with a dew point of less than -40°C, place the single-sided coated separator of the present invention between the positive electrode sheet and the negative electrode sheet for stacking and packaging. 2 The electrolyte (Xinzhoubang, LBC3008A) was injected in a ratio of 1.5 to obtain a battery.

[0113] The performance test results are shown in Table 1 and Table 2.

[0114] Table 1

[0115]

[0116] Table 2

[0117]

[0118] It should be noted that in Table 2, the ratio of the organic solvent tetrahydrofuran to dichloromethane is a mass ratio.

[0119] As can be seen from Table 1, the single-sided coated diaphragm provided by the present invention has high air permeability, low surface resistance and high transition metal ion barrier efficiency, can achieve a balance between these three properties, and has good heat resistance.

[0120] Compared with Example 1, the surface resistance of the single-sided coated diaphragm provided by Comparative Example 1 is significantly increased, and the barrier efficiency for transition metal ions is reduced; the barrier efficiency of the base membrane provided by Comparative Example 2 for transition metal ions is significantly lower; the surface resistance of the double-sided coated diaphragm provided by Comparative Example 3 is significantly increased, and the air permeability is significantly deteriorated.

[0121] The applicant declares that the present invention uses the above-described embodiments to illustrate the single-sided coated diaphragm, its preparation method, and its application. However, the present invention is not limited to the above-described embodiments, which does not necessarily mean that the present invention must rely on the above-described embodiments in order to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the raw materials used, addition of auxiliary components, and selection of specific methods, etc., fall within the scope of protection and disclosure of the present invention.

Claims

1. A single-sided coated diaphragm, characterized in that: The single-sided coated diaphragm comprises a base film and an inherent microporous polymer coating disposed on one surface of the base film; the surface characteristic parameter R of the single-sided coated diaphragm is R A / R B , R is 0.5~30; The roughness of the side of the inherent microporous polymer coating away from the base film is R A , R A The roughness of the non-coated surface of the base film is R B , R B 0.005~0.150μm.

2. The single-sided coated diaphragm according to claim 1, characterized in that The surface characteristic parameter R of the single-sided coated diaphragm is 1 to 14; The difference in roughness between the coated surface and the non-coated surface of the base film is 0.005-0.100 μm.

3. The single-sided coated diaphragm according to claim 1, characterized in that The intrinsically microporous polymer comprises a repeating unit represented by the following formula (I): Formula (I); Wherein, n is an integer between 5 and 10,000; A is a monomer segment selected from any one of the following (A), (B), (C), (D), (E), (F), (G), (H), (I) or (j): ； B is a monomer segment selected from any one of the following (a), (b), (c), (d), (e), (f) or (g): ； Among them, each R 10 Each independently selected from C 1-6 Alkyl or H; Each R 11 Each independently selected from -CH2NR1R2 or H; Each R 12 Each independently selected from -CNOR 13 N (R 14 )2 or -CN; R1 and R2 are each independently C 1-20 Alkyl, C 2-20 Alkenyl, C 2-20 Alkynyl, C 6-12 Aryl, C 3-8 Cycloalkyl, C 6-12 Aryl-C 1-20 Alkyl, C 3-8 Cycloalkyl-C 1-20 Alkyl, C 1-20 Heteroalkyl, C 1-20 Halogenated alkyl, C 1-20 Haloalkoxy, 3 to 8 membered heterocyclyl, 3 to 8 membered heterocyclyl-C 1-20 alkyl, 5- to 8-membered heteroaryl, heteroaryl-C 1-20 alkyl; or, each R1 and R2 is optionally and independently substituted by one or more Z1; or, each alkyl, alkenyl and alkynyl group in R1 and R2 optionally and independently contains one or more heteroatoms independently selected from silicon, chalcogenides and pnictides, and one or more atoms in R1 and R2 are optionally and independently present in an oxidized form; or, R1 and R2, together with the nitrogen atom to which they are attached, form a 3- to 8-membered heterocyclyl or a 5- to 8-membered heteroaryl, each of which is optionally substituted by one or more Z2; Z1 and Z2 are each independently halogen, -OH, -NO2, -CN, C 1-20 Alkyl, C 2-20 Alkenyl, C 2-20 Alkynyl, C 6-12 Aryl, C 3-8 Cycloalkyl, C 6-12 Aryl-C 1-20 Alkyl, C 1-20 heteroalkyl, 3 to 8 membered heterocyclyl, 3 to 8 membered heteroaryl, C 3-8 Cycloalkyl-C 1-20 Alkyl, 3 to 8 membered heterocyclyl-C 1-20 Alkyl, 5 to 8 membered heteroaryl-C 1-20 Alkyl, C 1-20 Halogenated alkyl, C 1-20 Haloalkoxy, -OR6, -SR6, -SOR6, -SO2R6, SO2NR6NR7, NR6COR7, NR6SO2R7, NR6CONR7R8, NR6R7, CO2R6, -CONR6R7 or -COR6; R3, R4, R5, R6, R7 and R8 are each independently C 1-20 Alkyl, C 2-20 Alkenyl, C 2-20 Alkynyl, C 6-12 Aryl, C 3-8 Cycloalkyl, C 6-12 Aryl-C 1-20 Alkyl, C 3-8 Cycloalkyl-C 1-20 Alkyl, C 1-20 heteroalkyl, 3 to 8 membered heterocyclyl, 3 to 8 membered heterocyclyl-C 1-20 alkyl, 5- to 8-membered heteroaryl, or 5- to 8-membered heteroaryl-C 1-20 alkyl; Each R 13 Independently H, C 1-20 Alkyl or C 3-8 Cycloalkyl, wherein alkyl and cycloalkyl are optionally and independently substituted with one or more Z3; Each Z3 is independently halogen, -NO2, -CN, -OH, -SO3H, -NH2, C 1-20 Alkyl, C 2-20 Alkenyl, C 2-20 Alkynyl, C 6-12 Aryl, C 3-8 Cycloalkyl, C 6-12 Aryl-C 1-20 Alkyl, C 1–20 heteroalkyl, 3 to 8 membered heterocyclyl, 5 to 8 membered heteroaryl, C 3-8 Cycloalkyl-C 1–20 Alkyl, 5 to 8 membered heteroaryl-C 1-20 Alkyl, C 1-20 Halogenated alkyl, C 1-20 Haloalkoxy, -OR6, -SR6, -SOR6, -SO2R6, SO2NR6NR7, NR6COR7, NR6SO2R7, NR6CONR7R8, NR6R7, CO2R6, -CONR6R7 or -COR6; Each R 14 Independently H, C 1-20 Alkyl or C 3-8 Cycloalkyl.

4. The single-sided coated diaphragm according to claim 3, characterized in that The intrinsic microporous polymer includes any one of PIM-1, PIM-2, PIM-C1, and PIM-py, or a combination of at least two thereof.

5. The single-sided coated diaphragm according to claim 1, characterized in that The thickness of the intrinsically microporous polymer coating is 0.1-3 μm.

6. The single-sided coated diaphragm according to claim 1, characterized in that The base film comprises a porous polyolefin base film; The thickness of the base film is 3-20 μm; The porosity of the base film is 33% to 55%.

7. The single-sided coated diaphragm according to claim 1, characterized in that The single-sided coated diaphragm has a surface density increment of 0.08 to 1 g / m2 compared to the base film. 2 ; The air permeability of the single-sided coated diaphragm is 100-10000 sec / 100 mL; The moisture content of the single-sided coated diaphragm is 270-480 ppm; The electrolyte infiltration area of ​​the single-sided coated diaphragm is 72~95mm 2 ; After the single-sided coated diaphragm is placed at 130°C for 1 hour, the thermal shrinkage in both the MD and TD directions is less than 3%; The surface resistance of the single-sided coated diaphragm at room temperature is ≤2.8Ω·cm 2 ; The single-sided coated diaphragm has a great influence on the Mn 3+ The diffusion coefficient is 1×10 -10 ~1×10 -8 cm 2 / s; The single-sided coated diaphragm has a great influence on the Fe 3+ The diffusion coefficient is 1×10 -11 ~4×10 -9 cm 2 / s; The single-sided coated diaphragm is Ni 3+ The diffusion coefficient is 1×10 -11 ~1×10 -9 cm 2 / s.

8. A method for preparing a single-sided coated diaphragm according to any one of claims 1 to 7, characterized in that: The preparation method comprises the following steps: (1) dissolving the inherent microporous polymer in an organic solvent to obtain a coating slurry; (2) Providing a base film, wherein the roughness R of the non-coated surface of the base film is B 0.005~0.150μm; (3) Apply the coating slurry to the side of the base film to be coated and dry it to form a surface roughness of R A The inherent microporous polymer coating is obtained to obtain the single-sided coated diaphragm, and the surface characteristic parameter R=R A / R B , R is 0.5~30, R A 0.06~0.19μm.

9. The preparation method according to claim 8, characterized in that The organic solvent includes any one or a combination of at least two of dichloromethane, tetrahydrofuran, acetone, toluene, N,N-dimethylformamide, and dimethyl carbonate; The mass proportion of the inherent microporous polymer in the coating slurry is 0.5% to 8%; The coating in step (3) includes coating with a micro-concave roller; The drying is carried out in an oven; The temperature of the oven is 20-80°C.

10. A battery, characterized in that: The battery comprises a single-sided coated separator as claimed in any one of claims 1 to 7; The battery comprises a lithium-ion battery.

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