Single-side coated diaphragm as well as preparation method and application thereof

Abstract

The invention provides a single-side coated diaphragm as well as a preparation method and application thereof, and belongs to the technical field of diaphragms, the single-side coated diaphragm comprises a base membrane and an inherent microporous polymer coating arranged on the surface of one side of the base membrane; the surface characteristic parameter R of the single-side coated diaphragm is equal to RA / RB, and R is 0.5-30; wherein the roughness of one surface, far away from the base membrane, of the inherent microporous polymer coating is RA; the roughness RB of the non-coated surface of the base film is 0.005 to 0.150 [mu] m. According to the single-sided coated diaphragm provided by the invention, the range of the surface characteristic parameter R is controlled within a specific range, so that the microporous structure of the coated surface can be kept stable, and the overall ventilation value, the surface resistance and the transition metal ion blocking efficiency of the single-sided coated diaphragm are balanced; the high air permeability and low surface resistance of the diaphragm can be maintained while the enough transition metal ion barrier effect is guaranteed, and the uniformity of the load of the single-side coated diaphragm is improved.

Description

Technical Field

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

[0002] As an efficient energy storage device, the performance and safety of lithium-ion batteries highly depend on the functionality of the diaphragm. The diaphragm in a lithium-ion battery plays a core role of blocking electron conduction and allowing lithium ions to migrate freely, but its long-term stability is often limited by the dissolution and diffusion problems of transition metal ions (such as nickel, iron, manganese) in the positive electrode. During the battery cycling process, transition metal ions in the positive electrode active material will migrate through the electrolyte to deposit on the negative electrode surface, triggering the destruction of the SEI film, the growth of lithium dendrites and capacity attenuation, and even leading to safety hazards such as thermal runaway.

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

[0004] The above technical solutions still have the problem of lack of ion blocking mechanism in practical applications. Existing coating layer materials (such as conventional ceramic / polymer composite coatings) lack specific adsorption or size sieving ability for transition metal ions (Ni, Fe, Mn), and cannot effectively block their transmembrane diffusion, resulting in continuous destruction of the SEI film and loss of lithium inventory; residual moisture in the aqueous coating system (>600 ppm) will catalyze the migration of transition metal ions, and the oily system is prone to form local weak bonding areas due to incomplete solvent volatilization, and the coating is easy to peel off from the base film after cycling (peeling force <0.5 N / cm); while nano single-ion conductor materials (such as LLTO) are expensive, and the existing process requires multiple coating-drying steps (energy consumption >3 kWh / m²), restricting large-scale application.

[0005] Therefore, in this field, there is a desire to develop a diaphragm that has excellent ion selectivity, high heat resistance, and a simple process. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the purpose of the present invention is to provide a single-sided coated separator and its preparation method and application, specifically to provide a single-sided coated separator with ion selectivity and its preparation method and application. Through the optimization of material components, the innovation of coating processes, and the design of interfacial structures, the present invention specifically solves the problems in the prior art such as low barrier efficiency of the separator against transition metal ions, poor coating uniformity, and insufficient interfacial durability.

[0007] To achieve the purpose of this invention, the following technical solutions are adopted:

[0008] In the first aspect, the present invention provides a single-sided coated separator, which includes a base film and an intrinsically microporous polymer (PIM) coating provided on one side surface of the base film; the surface characteristic parameter R of the single-sided coated separator is R A / R B , where R is 0.5 to 30, for example, it can be 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 the range composed of any two of them;

[0009] Among them, the roughness of the side of the intrinsically microporous polymer coating away from the base film is R A ;

[0010] The roughness of the non-coated surface of the base film (that is, the side of the base film away from the intrinsically microporous polymer coating) is R B , R B is 0.005 to 0.150 μm, for example, it can be 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 the range composed of any two of them, preferably 0.010 to 0.100 μm.

[0011] For the single-sided coated separator provided by the present invention, by controlling the range of the surface characteristic parameter R within a specific range, the microporous structure of the coated surface can be maintained stable, so that the overall air permeability value, surface resistance, and barrier efficiency against transition metal ions of the single-sided coated separator reach a balance, while ensuring sufficient barrier effect against transition metal ions, maintaining high air permeability and low surface resistance (≤2.5 Ω·cm 2 ) of the separator, which is beneficial to improving the uniformity of the load of the single-sided coated separator. In addition, due to the strong internal molecular stress of the formed PIM polymer coating, it also has an inhibitory effect on the thermal shrinkage of the separator 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 twisted structures within the molecule, the polymer cannot be effectively stacked when forming a close packing, resulting in a large number of nano-scale microporous structures (most of the pore sizes are below 2 nm). These micropores provide sufficient lithium-ion channels, which can selectively allow lithium ions to pass through while blocking the passage of other transition metal (manganese, iron, nickel) ions, providing a very good channel for the smooth transmission of lithium ions and the blocking of transition metal ions. The PIM polymer realizes dynamic capture of transition metal ions through a dual mechanism of self-assembled pore sieving and chemical chelation, greatly reducing the pollution of transition metal ions to the negative electrode of the battery and improving the cycle life and safety of the battery.

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

[0014] Preferably, the roughness R of the side of the inherently microporous polymer coating away from the base film A is 0.05 to 0.20 μm, for example, it can be 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 the range composed of any two of them. The value of R can be controlled within the range of 0.05 to 0.20 μm by adjusting the coating process and the types and parameters of raw materials. A Within the range of 0.05 to 0.20 μm, the value of R A will directly affect the ion conduction efficiency and interfacial contact resistance of the single-sided coated separator.

[0015] Preferably, the difference in roughness between the two sides of the base film, that is, the coated side and the non-coated side, is 0.005 to 0.100 μm, for example, it can be 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 the range composed of any two of them. The coated side of the base film refers to the side of the base film in contact with the inherently microporous polymer coating.

[0016] The roughness of the two sides of the base film affects the pore connectivity and load uniformity of the base film.

[0017] Preferably, the inherently microporous polymer may include the polymers 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-oriented synthesis of polymer membranes with ion solvation cages. Nature, Volume 592, Issue 7853, pp. 225 - 231. doi: 10.1038 / s41586-021-03377-7. Published online 7 April 2021. PMID: 33828319);

[0018] McKeown, N.B., Budd, P.M., Msayib, K., Ghanem, B., Microporous Polymer Material, US7690514B2, 2010.. (McKeown, N.B., Budd, P.M., Msayib, K., Ghanem, B., Microporous Polymer Material, US Patent No. US7690514B2, 2010.)

[0019] Preferably, the inherently microporous polymer comprises repeating units (R AB ) represented by the following formula (I):

[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] wherein each R 10 is independently selected from (C 1-6 ) alkyl or H;

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

[0027] each R 12 is 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, a 3- to 8-membered heterocyclic group, (a 3- to 8-membered heterocyclic group)-C 1-20 alkyl, a 5- to 8-membered heteroaryl, heteroaryl-C 1-20alkyl; alternatively, each R1 and R2 is optionally and independently substituted by one or more Z1; alternatively, each alkyl, alkenyl, and alkynyl 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 in an oxidized form, such as C=O, C=S, N=O, N=S, S=O, or S(O2); alternatively, R1 and R2 together with the nitrogen atom to which they are attached form a 3- to 8-membered heterocyclic group or a 5- to 8-membered heteroaryl group, 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 heterocyclic group, 3- to 8-membered heteroaryl group, (C 3-8 cycloalkyl)-C 1-20 alkyl, (3- to 8-membered heterocyclic group)-C 1-20 alkyl, (5- to 8-membered heteroaryl group)-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 heterocyclic group, (3- to 8-membered heterocyclic group)-C 1-20 alkyl, 5- to 8-membered heteroaryl group, or (5- to 8-membered heteroaryl group)-C 1-20 alkyl; specifically, R4 and R5 may together form (C 4-8), cycloalkyl, (C 6-12 ), aryl, 4- to 8-membered heterocyclic group or 5- to 8-membered heteroaryl; specifically, R6 and R7 together form a 4- to 8-membered heterocyclic group or 5- to 8-membered heteroaryl; specifically, R7 and R8 together form a 4- to 8-membered heterocyclic group or 5- to 8-membered heteroaryl.

[0031] Each R 13 is independently H, (C 1-20 ), alkyl or (C 3-8 ), cycloalkyl, wherein the alkyl and cycloalkyl are optionally and independently substituted by 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 heterocyclic group, 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 is independently H, (C 1-20 ), alkyl or (C 3-8 ), cycloalkyl.

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

[0035] Preferably, the thickness of the intrinsically microporous polymer coating is 0.1 - 3 μm, for example, it can be 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 the range composed of any two of them, preferably 0.5 - 1.5 μm.

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

[0037] Preferably, the porous polyolefin base film comprises a PE (polyethylene) porous film, a PP (polypropylene) porous film, a PE-PP multi-layer composite porous film, preferably a PE porous film.

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

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

[0040] Preferably, the intrinsically 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 needs to be fully soluble in the solvent system of the coating slurry. The second polymer and the PIM polymer form a composite coating, which can further enhance the adhesion between the separator and the electrode sheet or the heat resistance performance, etc.

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

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

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

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

[0046] Preferably, after the single-sided coated separator is placed at 130 °C for 1 h, the thermal shrinkage rates in the MD direction (longitudinal direction) and TD direction (transverse direction) are both lower 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 composed of any two of them, preferably 0.5% - 2.8%.

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

[0048] Preferably, the diffusion coefficient of the single-sided coated separator for Mn 3+ 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 composed of any two of them.

[0049] Preferably, the diffusion coefficient of the single-sided coated separator for Fe 3+ 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 composed of any two of them.

[0050] Preferably, the diffusion coefficient of the single-sided coated separator for Ni 3+ 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 composed of any two of them.

[0051] In a second aspect, the present invention provides a method for preparing a single-sided coated separator as described in the first aspect, and the preparation method includes the following steps:

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

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

[0054] (3) Coat the coating slurry on the side of the base film to be coated, and dry it to form an intrinsically microporous polymer coating with a surface roughness of R A , and obtain the single-sided coated separator. The surface characteristic parameter R of the single-sided coated separator is R = R A / R B , where R is 0.5 - 30.

[0055] Preferably, the organic solvent includes any one or a combination of at least two of dichloromethane, tetrahydrofuran, acetone, toluene, N,N-dimethylformamide, and dimethyl carbonate, and preferably any one or a combination of at least two of dichloromethane, tetrahydrofuran, and acetone. These three solvents, dichloromethane, tetrahydrofuran, and acetone, are highly volatile organic solvents. The advantage of using these three solvents is the convenience of production and the relatively small impact on the performance of the separator. Of course, other solvents can also be used, but longer drying time or higher temperature is required.

[0056] Preferably, the mass ratio of the intrinsically microporous polymer in the coating slurry is 0.5% - 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 a range composed of any two of them, and preferably 1% - 2.5%.

[0057] Optionally, the diaphragm with a specific roughness provided in step (2) can be a base film with a selected specific roughness, or the base film can be pretreated before coating. For example, when it is necessary to increase the surface roughness of the film, chemical etching can be used. Specifically, before coating, the non-treated surface of the base film is covered with a corrosion-resistant thin film, and the etching solution is evenly sprayed on the surface to be treated by spraying. After staying for a period of time, it is rinsed with deionized water to remove the residual acid and dried thoroughly. Or both sides of the base film are treated by this method to control different roughnesses on both sides of the base film. If it is necessary to reduce the surface roughness of the film, heat treatment of the film surface can also be used for control. For example, the surface to be treated is heat-treated with a hot roller at 60 - 90°C for 5 - 25 s, and then cooled with a quenching roller (3 - 15°C) for 5 - 15 s. If the roughness still cannot be reduced to the ideal range, the above process can be repeated for the surface of the film to be treated until the appropriate roughness is obtained.

[0058] Optionally, the etching solution for the chemical etching can be, for example, 30% H2SO4 at 60°C, and the staying time is 5 - 30 s, such as 5 s, 10 s, 15 s, 20 s, 25 s, 30 s or the range composed of any two of them.

[0059] Preferably, the coating in step (3) includes coating with a gravure roll. The number of lines of the engraving pattern of the gravure roll is selected as 120L - 260L according to the coating requirement, such as 120L, 140L, 160L, 180L, 200L, 220L, 240L, 260L or the range composed of any two of them.

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

[0061] Preferably, the surface temperature of the wet pressing roll is controlled at 10 - 25°C, such as 10°C, 15°C, 18°C, 20°C, 22°C, 23°C, 25°C or the range composed of any two of them. By using the wet pressing roll to perform surface pretreatment on the wet film (the surface is covered with the undried film) after coating, the shrinkage of the composite film after entering the oven can be avoided, and at the same time, the surface roughness can be controlled, and the coating uniformity can be improved, thereby affecting the surface morphology of the composite film. It can be understood that the wet pressing roll in the present invention refers to a roll or a set of rolls with a smooth roll surface that can perform low-temperature rolling on the undried film surface to control the flatness.

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

[0063] Preferably, the temperature of the oven is 20~80°C, for example, it can be 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or the range composed of any two of them, preferably 35~48°C. By limiting the temperature of the oven within a specific range, it helps to control the roughness of both sides of the single-sided coated separator within the range defined in the present invention. The coated film surface stays in the oven for 3~30 seconds according to different solvents to ensure sufficient volatilization of the solvent.

[0064] The surface coating of the single-sided coated separator after coating is uniform, and the film surface is completely covered by the PIM polymer, forming a dense polymer coating. At the same time, the surface topography of the coated surface and the non-coated surface of the base film is controlled by process and technical means, and then the surface characteristic parameter R is controlled within a certain specific range, so that the overall performance of the single-sided coated separator is significantly improved.

[0065] It should be noted that other implementation manners such as slit coating or spraying can also be used for the coating of the present invention.

[0066] Selecting a base film with a specific roughness can optimize the air permeability effect of the coated separator and greatly reduce the influence of the dense coating on the air permeability of the separator; by controlling process means such as thickness, areal density increment and slurry solid content, the surface topography of the coated surface and the base film surface is changed, and the surface characteristic parameters of the coated separator are controlled within a certain range, which is beneficial to increasing the contact area between the coated surface and the electrolyte, providing a sufficient aggregation place for lithium ions in the electrolyte, improving the wettability and water content of the coated separator, and then improving the lithium ion transmission efficiency; and it helps to relieve the internal stress of the coated surface and improve the overall heat resistance of the coated separator. Preferably, by controlling the roughness of the coated surface and the non-coated surface of the base film, it is beneficial to further enhance the above effects.

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

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

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

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

[0071] The single-sided coated separator provided by the present invention can keep the microporous structure of the coating layer stable by controlling the range of the surface feature parameter R within a specific range, so that the overall air permeability value, surface resistance and transition metal ion barrier efficiency of the single-sided coated separator reach an equilibrium. While ensuring sufficient transition metal ion barrier effect, it can also maintain the high air permeability and low surface resistance of the separator, which is beneficial to improving the uniformity of the load of the single-sided coated separator. In addition, due to the strong intramolecular stress of the formed PIM polymer coating, it also has an inhibitory effect on the thermal shrinkage of the separator at high temperatures. Description of the Drawings

[0072] Figure 1 It is a schematic structural diagram of the single-sided coated separator provided in Embodiment 1 of the present invention;

[0073] Figure 2 It is a SEM image of the surface of the intrinsic microporous polymer coating of the single-sided coated separator provided in Embodiment 1 of the present invention.

[0074] Among them, 1 - base film, 2 - intrinsic microporous polymer coating. Detailed Embodiments

[0075] The technical solutions of the present invention will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present invention and should not be regarded as specific limitations on the present invention.

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

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

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

[0079] Original base film (i.e., the base film whose roughness on one or both sides is not controlled by chemical etching or heat treatment): Select the polyethylene base film of Xingyuan Material, model: SW809I, porosity 48%, thickness 9μm, surface density 4.5g / m 2 , and the roughness of both sides is 0.040μm; as described in the above invention content part, it can be processed on one or both sides by chemical etching or heat treatment to control the roughness of both sides to reach the target values of the embodiments and comparative examples.

[0080] Embodiment 1

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

[0082] The preparation method comprises the following steps:

[0083] (1) dissolving an intrinsic microporous polymer (PIM-C1) in an organic solvent (tetrahydrofuran), stirring sufficiently 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, whose specific roughness data is shown in Table 1;

[0085] (3) At room temperature of 25°C, the coating slurry is coated on 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. The coated diaphragm is then placed 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] The base film is made of Xingyuan 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 R of the non-coated surface of the base film B , the coating surface roughness of the base film, the preparation conditions of the single-sided coated diaphragm, etc. are different, as shown in Tables 1 and 2. For the contents not shown in Tables 1 and 2, they are deemed 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) is provided, 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, the double-sided coated diaphragm 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), stirring sufficiently 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 coated on both sides of the base film by micro-concave roller coating, the line number of the roller was selected as 240L, and the slurry was coated on 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 was formed; the slurry was continuously coated on the other side of the base film by 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 was formed, and a double-sided coated diaphragm was obtained, wherein the single-sided coating thickness was 0.7 μm.

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

[0098] The performance test of the diaphragms provided in the embodiments of the present invention and the comparative examples is carried out in the following manner:

[0099] (1) Air permeability value: The air permeability value of the single-sided coated diaphragm is obtained according 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 reagent consumed and the titration degree.

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

[0102] (4) Thermal shrinkage rate: Refer to the method specified in the national standard GB / T 36363-2018 "Polyolefin Separator for Lithium-ion Batteries" to obtain the thermal shrinkage rates in the MD direction (longitudinal direction) and TD direction (transverse direction) of the separator, and take the average value as the thermal shrinkage rate of the separator; among them, the heat treatment temperature of the oven is 130 °C and the heat treatment time is 1 h.

[0103] (5) Roughness: Use a confocal microscope (model OLYMPUS OLS5100) with a magnification of 10 times to select 3 equally spaced positions horizontally and 3 equally spaced positions vertically on the surface of the sample film to be measured. The reference length interval is 3 cm, and there are a total of 9 positions. The average value of the surface roughness Sa is calculated separately by the Analysis application software, and then the average value of the data at 9 positions is further taken as the roughness.

[0104] (6) Surface resistance: Cut a total of 4 separator samples with a diameter of 45 mm at a flat position, immerse the samples in the electrolyte (1 mol / L LiPF6 electrolyte, and the solvent is EC, EMC, and DMC with a volume ratio of 1:1:1) and seal them for 30 min; pour the above electrolyte into the surface resistance test fixture; place 1, 2, 3, and 4 separators in the fixture for testing respectively; make a linear fit with the number of separator layers as the abscissa and the separator resistance as the ordinate, and find the slope and goodness of fit of the straight line. When the goodness of fit is greater than 0.999, the slope at this time is the surface resistance of the separator, and the unit is ohm Ω·cm 2 。

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

[0106] In the glove box, use a glass H-type electrolytic cell. The left side is the high-concentration side (simulating the positive electrode side), connected to the counter electrode (Pt wire), and the right side is the low-concentration side (simulating the negative electrode side) and connected to the working electrode (glassy carbon) and the reference electrode (lithium wire). The middle is separated by a 1-layer circular separator sample with a diameter of 10 cm, and the orientation of the separator is the same as that in the battery; equal amounts of electrolyte (1 mol / L LiPF6 electrolyte, and the solvent is EC, EMC, and DMC with a volume ratio of 1:1:1) are added to both sides. Before the test, add the transition metal salt solution to the left side and stir to dissolve it so that the concentration of the transition metal ions on the left side is 50 mmol / L, and then add LiPF6 to the right side and stir to dissolve it so that Li +The concentration is 150mmol / L. The transition metal salt solutions are independently acetylacetonate manganese (III) salt, acetylacetonate nickel and acetylacetonate iron. The above three electrodes are connected to the electrochemical workstation, and the CV test is performed at a rate of 0.2V / s in the range of 4.0V~1.5V. 5mL of liquid sample is taken from the right side 1 hour after the test starts, and the corresponding transition metal ion concentration is tested by ICP after acid digestion. Ion diffusion coefficient = transition metal ion concentration × diaphragm area ÷ 3600s.

[0107] (8) Cycle life

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

[0109] The specific battery preparation and assembly method is as follows:

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

[0111] 2) Add active material artificial graphite, conductive agent acetylene black and binder CMC / SBR (mass ratio of 1:1) into water in a mass ratio of 90:5:5 and disperse evenly to form negative electrode slurry, which is then coated on a copper foil current collector with a thickness of 10 μm, 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 <-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, and heat at 2.5 g / m 2 The electrolyte (Xinzhoubang, LBC3008A) was injected in a proportion of 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 separator provided by the present invention has high air permeability, low surface resistance, and high barrier efficiency for transition metal ions, enabling these three properties to reach a balance, and having good heat resistance.

[0120] Compared with Example 1, the surface resistance of the single-sided coated separator provided by Comparative Example 1 increases significantly, and the barrier efficiency for transition metal ions decreases; the base film provided by Comparative Example 2 has significantly lower barrier efficiency for transition metal ions; the surface resistance of the double-sided coated separator provided by Comparative Example 3 increases significantly, and the air permeability becomes significantly worse.

[0121] The applicant declares that the present invention uses the above embodiments to illustrate the single-sided coated separator of the present invention, its preparation method and application, but the present invention is not limited to the above embodiments, that is, it does not mean that the present invention must rely on the above embodiments to be implemented. Those skilled in the art should understand that any improvement to the present invention, the equivalent substitution of the raw materials selected for the present invention, the addition of auxiliary components, and the selection of specific methods, etc., all fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A single-sided coated separator, characterized in that, The single-sided coated separator includes a base film and an inherent microporous polymer coating provided on one surface of the base film; the surface characteristic parameter R of the single-sided coated separator is R A / R B , where R is 0.5 to 30; Among them, the roughness of the side of the inherently microporous polymer coating away from the base film is R A ; the roughness of the non-coated surface of the base film is R B , and R B is 0.005 to 0.150 μm.

2. The single-sided coated separator according to claim 1, characterized in that, The surface characteristic parameter R of the single-sided coated separator is 1 to 14; The roughness R of the side of the inherently microporous polymer coating away from the base film A is 0.05 to 0.20 μm; The difference in roughness between the coated surface and the non-coated surface of the base film is 0.005 to 0.100 μm.

3. The single-sided coated separator according to claim 1, wherein The inherently microporous polymer comprises repeating units 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): ； wherein each R 10 is independently selected from (C 1-6 )alkyl or H; Each R 11 is independently selected from -CH2NR1R2 or H; Each R 12 is independently selected from -C(NOR 13 ), N(R 14 ), 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 haloalkyl), (C 1-20 haloalkoxy), a 3- to 8-membered heterocyclic group, (3- to 8-membered heterocyclic group)-C 1-20 alkyl, a 5- to 8-membered heteroaryl, heteroaryl-C 1-20 alkyl; or, each of R1 and R2 is optionally and independently substituted with one or more Z1; or, each alkyl, alkenyl, and alkynyl 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 in an oxidized form; or, R1 and R2 together with the nitrogen atom to which they are attached form a 3- to 8-membered heterocyclic group or a 5- to 8-membered heteroaryl, each of which is optionally substituted with 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 heterocyclic group, 3- to 8-membered heteroaryl, (C 3-8 cycloalkyl)-C 1-20 alkyl, (3- to 8-membered heterocyclic group)-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; 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 heterocyclic group, (3- to 8-membered heterocyclic group)-C 1-20 alkyl, 5- to 8-membered heteroaryl, or (5- to 8-membered heteroaryl)-C 1-20 alkyl; Each R 13 is independently H, (C 1-20 )alkyl or (C 3-8 )cycloalkyl, where the alkyl and cycloalkyl are optionally and independently substituted by one or more Z3; Each Z3 is independently a 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 heterocyclic group, 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; Each R 14 is independently H, (C 1-20 )alkyl or (C 3-8 )cycloalkyl.

4. The single-sided coated separator according to claim 3, wherein The inherently microporous polymer includes any one or a combination of at least two of PIM-1, PIM-2, PIM-C1, and PIM-py.

5. The single-sided coated separator according to claim 1, wherein, The thickness of the inherently microporous polymer coating is 0.1 to 3 μm.

6. The single-sided coated separator according to claim 1, wherein The base film includes a porous polyolefin base film; The thickness of the base film is 3 to 20 μm; The porosity of the base film is 33% to 55%.

7. The single-sided coated separator according to claim 1, wherein The areal density increment of the single-sided coated separator compared to the base film is 0.08 to 1 g / m 2 ; The air permeability value of the single-sided coated separator is 100 to 10,000 sec / 100 mL; The moisture content of the single-sided coated separator is 270 to 480 ppm; The electrolyte infiltration area of the single-sided coated separator is 72~95 mm 2 ; After the single-sided coated separator is placed at 130 °C for 1 h, the thermal shrinkage rates in the MD direction and the TD direction are both less than 3%; The surface resistance of the single-sided coated separator at room temperature is ≤2.8 Ω·cm 2 ; The diffusion coefficient of the single-sided coated separator for Mn 3+ is 1×10 -10 ~1×10 -8 cm 2 / s; The diffusion coefficient of the single-sided coated separator for Fe 3+ is 1×10 -11 ~4×10 -9 cm 2 / s; The diffusion coefficient of the single-sided coated separator to Ni 3+ is 1×10 -11 ~1×10 -9 cm 2 / s.

8. A method for preparing a single-sided coated separator according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Dissolve the inherently microporous polymer in an organic solvent to obtain a coating slurry; (2) Provide a base film, and the roughness R of the non-coated surface of the base film B is 0.005 to 0.150 μm; (3) Coating the coating slurry on the side of the base film to be coated, and drying to form an inherently microporous polymer coating with a surface roughness of R A to obtain the single-sided coated separator, where the surface characteristic parameter R of the single-sided coated separator is R A / R B , and R ranges from 0.5 to 30.

9. The preparation method according to claim 8, wherein 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 ratio of the inherently microporous polymer in the coating slurry is 0.5% to 8%; The coating in step (3) includes coating with a microgravure roll; The drying is carried out in an oven; The temperature of the oven is 20 to 80 °C.

10. A battery, characterized in that, The battery includes the single-sided coated separator according to any one of claims 1-7; The battery includes a lithium-ion battery.

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