Coating diaphragm for lithium ion battery, preparation method and lithium ion battery

Abstract

The invention provides a coated diaphragm for a lithium ion battery, a preparation method of the coated diaphragm and the lithium ion battery. The coated diaphragm is composed of a porous polyolefin middle layer, and a first skin layer and a second skin layer which are positioned on two sides of the porous polyolefin middle layer, the first skin layer is composed of nanofibers and nano ceramic particles; the second skin layer is composed of an intrinsic microporous polymer (PIM) and / or a modified intrinsic microporous polymer; the first skin layer and the second skin layer are respectively arranged on the upper surface and the lower surface of the porous polyolefin middle layer to form a sandwich structure, the diffusion coefficient of the obtained coated diaphragm to nickel ions is 3.21 * 10 <-9 >-4.65 * 10 <-9 > cm < 2 > / s, and the diffusion coefficient of the obtained coated diaphragm to manganese ions is 5.75 * 10 <-10 >-6.88 * 10 <-10 > cm < 2 > / s; the mechanical property and the heat resistance of the diaphragm are improved, meanwhile, the permeability of the diaphragm to nickel and manganese ions is greatly reduced, the situation that metal ions such as nickel and manganese in an existing lithium ion battery positive electrode material are dissolved out to pollute a negative electrode of a battery during operation of the battery is effectively avoided, and the service life of the battery can be effectively prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion battery separators, and particularly to a coated separator for lithium-ion batteries, a preparation method and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are widely used in new energy vehicles, electrochemical energy storage, electronic digital products and other fields due to their advantages such as high energy density, long cycle life, excellent rate performance and low self-discharge rate. With the rapid development of new energy vehicles, higher requirements are put forward for the energy density and safety performance of batteries.

[0003] In lithium-ion batteries, the separator is a key component. Its main function is to isolate the positive and negative electrodes to prevent short circuits, while allowing lithium ions to migrate freely in the electrolyte, thereby realizing the normal charge and discharge of the battery. An ideal separator should only allow lithium ions to migrate between the positive and negative electrodes. However, currently widely used polyethylene, polypropylene separators and their modified or coated products still cannot achieve single-selective conduction for lithium ions. As the battery operates, metal ions such as nickel ions (Ni²⁺) and manganese ions (Mn²⁺) in the positive electrode material will pass through the separator, resulting in a gradual decline in battery capacity. Therefore, the performance of traditional lithium-ion batteries will significantly decline after 2 - 3 years of use or after multiple cycles. Although existing modified or coated separators have improved in heat resistance and mechanical properties, they still cannot achieve selective permeation of lithium ions.

[0004] Therefore, developing a separator that can only conduct lithium ions and prevent the migration of metal ions such as nickel and manganese is of great significance for improving the performance of lithium-ion batteries and extending their service life. Summary of the Invention

[0005] In view of the above problems existing in the prior art, the present invention provides a coated separator for lithium-ion batteries, a preparation method and an application. The specific content of the invention is as follows: In the first aspect, the present invention provides a coated separator for lithium-ion batteries. The coated separator is composed of a porous polyolefin intermediate layer, and a first skin layer and a second skin layer located on both sides of the porous polyolefin intermediate layer; the composition of the first skin layer includes nanofibers and nano-ceramic particles; The composition of the second skin layer includes intrinsic microporous polymer PIM or modified intrinsic microporous polymer PIM.

[0006] Optionally, the intrinsic microporous polymer PIM is selected from PIM-1 or PIM-2; the modified intrinsic microporous polymer PIM is selected from one or more of PIM-PI, PIM-CA, PIM-EN, PIM-EA-TB, PIM-Trip-TB and PIM-TOT. The structural formulas are as follows: , , , , , , , ; In the structural formula, the value of n satisfies that the molecular weight of the intrinsic microporous polymer PIM or the modified intrinsic microporous polymer PIM is between 50,000 and 100,000.

[0007] Optionally, the nanofibers are selected from one or more of Kevlar aramid nanofibers, bacterial cellulose, nanocellulose, and cotton nanofibers, and the nanoceramic particles are selected from one or more of alumina, boehmite, barium titanate, magnesium oxide, silicon oxide, and magnesium hydroxide.

[0008] Optionally, the thickness T of the first skin layer 2 is 1 μm to 2 μm; The thickness T of the porous polyolefin intermediate layer 3 is 5 to 15 μm; The thickness T of the second skin layer 1 is 0.5 to 1.5 μm.

[0009] Optionally, the thickness T of the first skin layer 2 , the thickness T of the porous polyolefin intermediate layer 3 and the thickness T of the second skin layer 1 satisfy (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0010] Optionally, the average length L of the nanofibers is 10 to 30 μm, and the diameter D 0 is 30 to 50 nm.

[0011] Optionally, the particle size of the nanoceramic particles includes the first particle size nanoceramic particle D 1 , the second particle size nanoceramic particle D 2 and the third particle size nanoceramic particle D 3 , and the particle size range of the first particle size nanoceramic particle D 1 is 100 to 300 nm, and the mass ratio is 5% to 10%; The particle size range of the second particle size nanoceramic particle D 2 is 500 to 700 nm, and the mass ratio is 85 - 90%, The particle size range of the third particle size nanoceramic particle D 3The particle size range is 900 to 1000 nm, and the mass ratio is 1% to 6%.

[0012] Optionally, the first particle size nano-ceramic particles D 1 , the second particle size nano-ceramic particles D 2 and the third particle size nano-ceramic particles D 3 satisfy the following mass ratio relationship: (D 2 ) 0.5 ≤D 1 +D 3 ≤(D 2 ) 0.61 , and D 3 ≤D 1 .

[0013] Optionally, the composition of the porous polyolefin intermediate layer is selected from polyethylene and / or polypropylene, and the porosity is 40% to 50%.

[0014] Optionally, the moisture content of the coated separator is 500 to 560 ppm; and / or the electrolyte wetting area of the coated separator is 84.3 to 93.2 mm 2 ; and / or the areal density of the coated separator is 8.59 to 8.92 g / m 2 .

[0015] Optionally, the diffusion coefficient of the coated separator for nickel ions is 3.21×10 -9 ~ 4.65×10 -9 cm 2 / s; and / or the diffusion coefficient of the coated separator for manganese ions is 5.75×10 -10 ~ 6.88×10 -10 cm 2 / s.

[0016] In a second aspect, the present invention provides a method for preparing the coated separator for a lithium-ion battery according to the first aspect above. The preparation method includes: Mixing nanofibers, nano-ceramic particles, a dispersant, and a binder uniformly to form a first slurry; dissolving an intrinsically microporous polymer and / or a modified intrinsically microporous polymer in an organic solvent to form a second slurry; Coating the first slurry on one side of the porous polyolefin intermediate layer, and drying to form a first skin layer on one side of the porous polyolefin intermediate layer; Continuing to coat the second slurry on the other side of the porous polyolefin intermediate layer, and drying to form a second skin layer on the other side of the porous polyolefin intermediate layer, and completing the preparation of the coated separator.

[0017] Optionally, in the first slurry, the mass ratio of the nanofibers is 3.8% to 10%; the mass ratio of the nano-ceramic particles is 75.9% to 86.6%; the mass ratio of the dispersant is 5.9 to 11.7%; the mass ratio of the binder is 2% to 6%.

[0018] Optionally, the dispersant is selected from sodium acrylate and / or ammonium polyacrylate.

[0019] Optionally, the binder is selected from acrylamide monomers.

[0020] Optionally, the acrylamide monomers are selected from acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, N,N-methylenebisacrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxypropyl)acrylamide, and acrylate monomers: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, and 3-hydroxypropyl methacrylate, and any combination of two of them, with a mass ratio of 1.5 to 9.

[0021] Optionally, in the second slurry, the mass ratio of the intrinsic microporous polymer PIM or the modified intrinsic microporous polymer PIM is 20% to 30%.

[0022] Optionally, in the second slurry, the organic solvent is selected from one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, and chloroform.

[0023] In a third aspect, the present invention provides a lithium-ion battery, which includes the coated separator described in the first aspect above.

[0024] Compared with the prior art, the present invention has the following advantages: The present invention provides a coated separator for a lithium-ion battery. The coated separator is composed of a porous polyolefin intermediate layer, and a first skin layer and a second skin layer located on both sides of the porous polyolefin intermediate layer. The composition of the first skin layer includes nanofibers and nano-ceramic particles. The composition of the second skin layer includes an intrinsic microporous polymer PIM or a modified intrinsic microporous polymer PIM. By respectively arranging the first skin layer and the second skin layer on the upper and lower surfaces of the porous polyolefin intermediate layer to form a sandwich structure, the water content of the obtained coated separator is 500 to 560 ppm; the electrolyte wetting area of the coated separator is 84.3 to 93.2 mm 2 ; the areal density of the coated separator is 8.59 to 8.92 g / m 2; The diffusion coefficient of the coated separator for nickel ions is 3.21×10 -9 ~ 4.65×10 -9 cm 2 / s, and the diffusion coefficient for manganese ions is 5.75×10 -10 ~6.88×10 -10 cm 2 / s; moreover, the thermal shrinkage rate of the coated separator under the condition of being kept at 150°C for 1 hour is 1.8% - 4.3%; while improving the mechanical properties and heat resistance of the separator, the permeability of the separator to nickel and manganese ions is greatly reduced, effectively avoiding the contamination of the negative electrode of the battery by metal ions such as nickel and manganese in the existing cathode materials of lithium-ion batteries during battery operation, and effectively extending the battery life. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 shows a schematic cross-sectional structure diagram of the coated separator for lithium-ion batteries provided by the embodiments of the present invention; Figure 2 shows a flowchart of the method for the coated separator for lithium-ion batteries provided by the embodiments of the present invention; Figure 3 shows a physical diagram of the coated separator for lithium-ion batteries provided by the embodiments of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features and being the same as or similar to the present invention falls within the protection scope of the present invention. And all other embodiments obtained by those of ordinary skill in the art without creative efforts also belong to the protection scope of the present invention.

[0028] In the embodiments, if the specific experimental procedures or conditions are not specified, the operations or conditions of the conventional experimental procedures described in the existing technologies in this field can be followed. For the reagents and other instruments whose manufacturers are not specified, they are all conventional reagent products that can be obtained through commercial purchases. In addition, the attached drawings are only schematic diagrams of the embodiments of the present invention and are not necessarily drawn to scale. The same reference numerals in the drawings represent the same or similar parts, and thus the repeated descriptions thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities and do not necessarily correspond to physically or logically independent entities.

[0029] Technologies, methods, and devices known to those of ordinary skill in the relevant fields may not be discussed in detail, but where appropriate, the said technologies, methods, and devices should be regarded as part of the specification of the present invention.

[0030] In the description of the present invention, it should be understood that the use of terms such as "first" and "second" to limit the components is only for the convenience of differentiating the corresponding components. Without further statement, the above terms have no special meaning, and thus should not be construed as limiting the protection scope of the present invention.

[0031] In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0032] It should be noted that in the intrinsic microporous polymer PIM involved in the embodiments of the present invention, PIM-1 is specifically polymerized from 5,5',6,6'-tetrahydroxy-3,3,3,3'-tetramethyl-1,1'-spirobifluorene (TTSBI) and 2,3,5,6-tetrafluorohydroquinone (TFTPN); the reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-1 is between 50,000 and 100,000.

[0033] PIM-2 is polymerized from TTSBI and perfluorobiphenyl (DFBP), and the reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-2 is between 50,000 and 100,000.

[0034] In the modified intrinsic microporous polymer PIM involved in the embodiments of the present invention, PIM-PI is formed by using pyromellitic dianhydride (PMDA) and spirobifluorenediamine (SBF) as monomers through a polycondensation reaction to form a polyimide precursor (polyamic acid), and then imidization; the reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-PI is between 50,000 and 100,000.

[0035] PIM-CA is a carboxylated derivative of PIM-1, and its structural formula is: , where the value of n satisfies that the molecular weight of PIM-CA is between 50,000 and 100,000.

[0036] PIM-EN is formed by copolymerization of 2.4 2',3',6',7'-tetrahydroxyfluorene derivative [fluorene-9,9'-anthracene-10',9'-fluorene] (EN), TTSBI and TFTPN, and the reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-EN is between 50,000 and 100,000.

[0037] PIM-EA-TB is formed by alternating polymerization of ethylenediamine anthracene (EA) and tellurium oxide (TB), and PIM-Trip-TB is formed by alternating polymerization of triptycene diamine (Trip) and tellurium oxide (TB) The reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-EA-TB is between 50,000 and 100,000.

[0038] , where the value of n satisfies that the molecular weight of PIM-Trip-TB is between 50,000 and 100,000.

[0039] PIM-TOT is formed by polycondensation of 5,5',6,6'-tetrahydroxy-3,3,3,3'-tetramethyl-1,1'-spiro nitrile (TTSBI) and 2,3,7,8-tetrafluoro-5,5',10,10'-tetrasulfur dioxide anthracene (TOT) monomers, and the reaction formula is as follows: , where the value of n satisfies that the molecular weight of PIM-TOT is between 50,000 and 100,000.

[0040] The present invention provides a coated separator for a lithium ion battery, Figure 1 shows a schematic cross-sectional structure diagram of the coated separator for a lithium ion battery provided by an embodiment of the present invention, as Figure 1 shown, the coated separator is composed of a porous polyolefin intermediate layer 101, and a first skin layer 102 and a second skin layer 103 located on both sides of the porous polyolefin intermediate layer 101; the composition of the first skin layer 102 includes nanofibers and nanoceramic particles; the composition of the second skin layer 103 includes an intrinsically microporous polymer PIM and / or a modified intrinsically microporous polymer PIM; wherein, the intrinsically microporous polymer PIM is selected from PIM-1 or PIM-2; the modified intrinsically microporous polymer PIM is selected from one or more of PIM-PI, PIM-CA, PIM-EN, PIM-EA-TB, PIM-Trip-TB and PIM-TOT.

[0041] In specific implementation, the nanofibers and nano-ceramic particles have high thermal stability, chemical stability and mechanical strength, and the PIM-based materials have a high specific surface area, a rich microporous structure and good electrolyte affinity. Based on this, in the present invention, an intrinsic microporous polymer PIM or a modified intrinsic microporous polymer PIM is deposited on one side of the porous polyolefin intermediate layer (forming a first skin layer), and the PIM-based material is deposited on the other side of the porous polyolefin intermediate layer (forming a second skin layer). Without affecting the wettability and lithium ion permeability of the porous polyolefin intermediate layer, the mechanical properties and heat resistance of the entire separator are improved. At the same time, the permeability of the separator to metal ions such as Mn, Ni, and Fe is also greatly reduced, effectively avoiding the contamination of the negative electrode of the battery by the dissolution of metal ions such as Mn, Ni, and Fe in the cathode material of the lithium ion battery using the existing separator (without a skin layer) during battery operation, and effectively extending the battery life.

[0042] The structural formulas of the intrinsic microporous polymer PIM or the modified intrinsic microporous polymer PIM used in this embodiment are shown below: , , , , , , , .

[0043] In some embodiments, the nanofibers are selected from one or more of Kevlar aramid nanofibers, bacterial cellulose, nanocellulose, and cotton nanofibers. The average length L of the nanofibers is 10 - 30 μm, and the diameter D 0 is 30 - 50 nm; the nano-ceramic particles are selected from one or more of alumina, boehmite, barium titanate, magnesium oxide, silicon oxide, and magnesium hydroxide.

[0044] It should be noted that the present invention further refines the particle size of the selected nano-ceramic particles. The present invention selects three different particle size ranges of nano-ceramic particles, namely the first particle size nano-ceramic particle D 1 , the second particle size nano-ceramic particle D 2 and the third particle size nano-ceramic particle D 3 . And the particle size range of the first particle size nano-ceramic particle D 1 is 100 - 300 nm, the particle size range of the second particle size nano-ceramic particle D 2 is 500 - 700 nm, and the particle size range of the third particle size nano-ceramic particle D 3 is 900 - 1000 nm; the mass ratios of the above three different particle size nano-ceramic particles are respectively: the first particle size nano-ceramic particle D1 The mass ratio of the first particle size of the nanoceramic particles D is 5-10%, and the second particle size of the nanoceramic particles D 2 The mass ratio is 85-90%, and the third particle size of the nanoceramic particles D 3 The mass ratio is 1-6%. When specifically taking values, the first particle size of the nanoceramic particles D 1 , the second particle size of the nanoceramic particles D 2 And the mass ratio relationship of the third particle size of the nanoceramic particles D 3 Satisfies the following formula: (D 2 ) 0.5 ≤D 1 +D 3 ≤(D 2 ) 0.61 , and D 3 ≤D 1 .

[0045] In some embodiments, the composition of the porous polyolefin intermediate layer is selected from polyethylene and / or polypropylene, and the porosity is 40% to 50%.

[0046] Furthermore, in order to ensure that the polyolefin-coated separator has good wettability, lithium ion permeability, and reduce the permeability of metal ions such as Mn, Ni, and Fe, in the embodiments of the present invention, a porous polyolefin membrane is used as the intermediate layer for coating preparation of the first skin layer and the second skin layer. Among them, the thickness T 2 Of the first skin layer is 1 μm to 2 μm; the thickness T 3 Of the porous polyolefin intermediate layer is 5 to 15 μm; the thickness T 1 Of the second skin layer is 0.5 to 1.5 μm. When specifically taking values, through a large number of performance test measurements, it is found that the thickness T 2 Of the first skin layer, the thickness T 3 Of the porous polyolefin intermediate layer and the thickness T 1 Of the second skin layer satisfy (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2, the performance of the coated separator has obvious advantages.

[0047] The present invention forms a sandwich structure by respectively arranging a first skin layer and a second skin layer on the upper and lower surfaces of the porous polyolefin intermediate layer. The water content of the obtained coated separator is 500-560 ppm; the electrolyte wetting area of the coated separator is 84.3-93.2; the areal density of the coated separator is 8.59-8.92 g / m 2 ; the diffusion coefficient of the coated separator for nickel ions is 3.21×10 -9 ~ 4.65×10 -9 cm2 / s, the diffusion coefficient of manganese ions is 5.75×10 -10 ~ 6.88×10 -10 cm 2 / s; and, the thermal shrinkage rate of the coated separator under the condition of keeping warm at 150°C for 1 hour is 1.8% - 4.3%; while improving the mechanical properties and heat resistance of the separator, the diffusion coefficients of nickel and manganese ions in the separator are greatly reduced, effectively avoiding the pollution of the negative electrode of the battery by metal ions such as nickel and manganese in the existing lithium-ion battery cathode material during battery operation, and can effectively extend the battery life. The present invention also provides a preparation method of a coated separator for a lithium-ion battery. Figure 2 The flowchart of the preparation method of the coated separator for a lithium-ion battery provided by the embodiment of the present invention is shown. As Figure 2 shown, the preparation method includes the following steps: S1. Mix nanofibers, nano-ceramic particles, a dispersant, and a binder evenly to form a first slurry; dissolve an intrinsically microporous polymer and / or a modified intrinsically microporous polymer in an organic solvent to form a second slurry. S2. Coat the first slurry on one side of a porous polyolefin intermediate layer, and after drying, form a first skin layer on one side of the porous polyolefin intermediate layer. S3. Continuously coat the second slurry on the other side of the porous polyolefin intermediate layer, and after drying, form a second skin layer on the other side of the porous polyolefin intermediate layer, and complete the preparation of the coated separator.

[0048] In the embodiment of the present invention, skin layers are prepared on both sides of a porous polyolefin intermediate layer by means of slurry coating. The composition of the porous polyolefin intermediate layer can be polyethylene or polypropylene, or a mixture of polyethylene and polypropylene. The porosity of the porous polyolefin intermediate layer is 40% - 50%. Specifically, in the first slurry, the mass ratio of nanofibers is 3.8% - 10%, the mass ratio of nano-ceramic particles is 75.9% - 86.6%, the dispersant is selected from sodium acrylate and / or ammonium polyacrylate, and the mass ratio is 5.9 - 11.7%; the binder is selected from acrylamide monomers, and the mass ratio is 2% - 6%; including any two combinations of acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, N,N-methylenebisacrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxypropyl)acrylamide, and acrylate monomers: 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, 3-hydroxypropyl methacrylate, and the mass ratio is 1.5 - 9.

[0049] Further, to ensure good bonding between the nano-ceramic particles and the nano-fibers in the first slurry, avoid delamination, consider the influence of the nano-ceramic particles and the nano-fibers on thermal stability, and reduce the coating difficulty of the first slurry, in the embodiment of the present invention, according to the average length L of the selected nano-fibers being 10 - 30 μm and the diameter D 0 being 30 - 50 nm, the confirmation of the mass ratio S of the nano-fibers in the first slurry is associated with the average length L and the diameter D of the nano-fibers 0 ; the three satisfy: S = k * (L / D 0 ) 3 , and the mass ratio R of the nano-ceramic particles and the mass ratio S of the nano-fibers satisfy: R = x * (S 1 / 2 ) * 2.5, where x is a correction coefficient with a value range of 1 - 1.8; k is also a correction coefficient with a value range of 0.1 - 5; to clarify the specific value of the mass percentage S of the nano-fibers within 4% - 10% according to the characteristics of the selected nano-fibers, to obtain a better mass ratio of the nano-fibers, and further confirm the specific mass ratio R of the nano-ceramic particles according to the mass ratio S of the nano-fibers.

[0050] As an example, when the average length of the selected nano-fibers is 20 μm and the diameter is 50 nm, the mass ratio S of the nano-fibers is confirmed to be 6.4% (k takes 1) according to S = k * (L / D 0 ) 3 , and the mass ratio R of the nano-ceramic particles is confirmed to be 75.9% (x takes 1.2) according to the relationship R = x * (S 1 / 2 ) * 2.5.

[0051] As another example, when the average length of the selected nano-fibers is 10 μm and the diameter is 30 nm, the mass ratio S of the nano-fibers is confirmed to be 3.8% (k takes 1) according to S = k * (L / D 0 ) 3 , and the mass ratio R of the nano-ceramic particles is confirmed to be 86.6% (x takes 1.8) according to the relationship R = x * (S 1 / 2 ) * 2.5.

[0052] As another example, when the average length of the selected nano-fibers is 30 μm and the diameter is 50 nm, the mass ratio S of the nano-fibers is confirmed to be 8.6% (k takes 0.4) according to S = k * (L / D 0 ) 3 , and the mass ratio R of the nano-ceramic particles is confirmed to be 80.8% (x takes 1.1) according to the relationship R = x * (S 1 / 2 ) * 2.5.

[0053] As another example, when the average length of the selected nanofibers is 10 μm and the diameter is 50 nm, the mass fraction S of the nanofibers is determined according to S = k*(L / D 0 ) 3 to be 4% (k = 5), and the mass fraction R of the nanoceramic particles is determined to be 85% (x = 1.7) according to the relationship R = x*(S 1 / 2 )*2.5

[0054] As another example, when the average length of the selected nanofibers is 30 μm and the diameter is 30 nm, the mass fraction S of the nanofibers is determined according to S = k*(L / D 0 ) 3 to be 10% (k = 0.1), and the mass fraction R of the nanoceramic particles is determined to be 79.1% (x = 1) according to the relationship R = x*(S 1 / 2 )*2.5

[0055] Furthermore, to avoid the problem of uneven thickness of the second skin layer formed by coating due to the rapid volatilization of the solvent, when preparing the second slurry, an organic solvent with moderate volatility needs to be selected. The organic solvent used in this embodiment can be selected from one or more of N-methylpyrrolidone (NMP), dimethyl sulfoxide (DMSO), N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and chloroform.

[0056] In this embodiment, by controlling the mass fraction of the intrinsically microporous polymer and / or the modified intrinsically microporous polymer in the slurry to be 20% - 30%, the slurry has a suitable viscosity (100–1000 mPa·s) required for coating, and the slurry is successfully adhered to the other side of the porous polyolefin intermediate layer by coating.

[0057] Specifically, during the coating process of the slurry, in this embodiment, after the coating of the first skin layer is completed, a gradient heating drying method is used for drying. The gradient heating method includes: drying at 50 °C for 30 - 60 min, then heating to 80 °C and drying for 30 - 40 min, and continuing to heat to 100 °C and drying for 30 min. Similarly, after the coating of the second skin layer is completed, the gradient heating drying method is still used for drying to avoid the shrinkage or foaming of the coating caused by the rapid volatilization of the solvent. The gradient heating method includes: drying at 50 °C for 30 - 60 min, then heating to 80 °C and drying for 30 - 40 min, and continuing to heat to 100 °C and drying for 30 min.

[0058] The present invention also provides a lithium-ion battery including the above-mentioned coated separator.

[0059] To enable those skilled in the art to understand the present invention more clearly, the following examples are used to elaborate in detail a coated separator for a lithium-ion battery, a preparation method thereof, and a lithium-ion battery according to the present invention.

[0060] The synthesis process of the PIM-based materials used in the following examples is as follows: PIM-1 (number-average molecular weight is about 100,000, and the preparation process refers to Journal of Membrane Science 333(2009) 125–131): Add DMAc into a three-necked flask, protect it with nitrogen, add KOH as a catalyst, and stir and mix evenly. Then slowly add the above TTSBI monomer into the solvent. After it is completely dissolved, gradually add an equimolar amount of TFTPN. Heat the reaction mixture to about 160 - 165 °C and keep the reaction for 48 hours under stirring. After the reaction is completed, transfer it to 100 mL of neutral water for separation. Add the reaction mixture to methanol for precipitation to obtain the crude polymer PIM-1. Wash the precipitate with deionized water multiple times to remove solvent residues and unreacted small molecule monomers, and dry it in a suction filtration device. Place the obtained crude precipitate in a vacuum drying oven and dry it at 60 - 80 °C until a completely dry yellow powder or glassy polymer block is formed (the appearance of the C≡N (2200 cm⁻¹) and benzene ring characteristic peaks (1600 cm⁻¹) in the IR spectrum analysis can confirm the molecular skeleton; use nuclear magnetic resonance (NMR) to further confirm the phenyl, tetramethyl, and cyano structures on the main chain).

[0061] PIM-CA (number-average molecular weight is about 80,000, and the preparation process refers to: Adv Sustain Syst 2018;2(10):1800044.): Place PIM-1 in a 20% - 30% potassium hydroxide ethanol / water (volume ratio 1 - 1.5 / 1) solution, heat it to 100 - 120 °C, and react for 10 - 20 hours. After the reaction is completed, neutralize the alkalinity with excessive acetic acid, filter by suction and wash with methanol to obtain the preliminary hydrolysis product. Add the preliminary hydrolysis product into a sulfuric acid / water / acetic acid (volume ratio 2 - 2.5 / 2 / 1) solution, heat it to 100 - 120 °C, and react for 10 - 20 hours. After cooling to room temperature, pour the mixture into excessive water, filter by suction and wash it thoroughly with methanol to obtain a green powder. Place the powder in a vacuum drying oven and dry it at 60 - 80 °C to obtain the final product PIM-CA.

[0062] PIM-EA-TB (number-average molecular weight is about 80,000, preparation process reference: Polymer 236 (2021) 124295): Dissolve ethylenediamine (EA) and tröger's base (TB) monomers in chloroform in a certain ratio (1:1 molar ratio) to form a homogeneous solution. The mass fraction is 20%. Place the above mixed solution in a reactor and add 1% p-toluenesulfonic acid to promote the polymerization reaction. Under nitrogen protection, heat the reactor to 60 °C - 80 °C, and the reaction time is 24 hours. The monomers form PIM-EA-TB polymer through polycondensation reaction. After the reaction is completed, pour the reaction mixture into a large amount of cold ethanol to precipitate the polymer. Collect the precipitated polymer by suction filtration and wash it with ethanol multiple times to remove unreacted monomers and catalysts. Dry the washed polymer in a vacuum drying oven at 60 °C for 24 hours to obtain pure PIM-EA-TB polymer.

[0063] PIM-TOT (number-average molecular weight is about 100,000, reference: J. Mater. Chem. A, 2021, 9, 2840–2849): Add DMF to a three-necked flask, protect it with nitrogen, add KOH as a catalyst, and stir evenly. Then slowly add TTSBI monomer to the solvent. After it is completely dissolved, gradually add an equimolar amount of TOT. Heat the temperature of the reaction mixture to about 180 °C and keep the reaction for 40 hours with stirring. After the reaction is completed, transfer it to water for separation. Add the reaction mixture to ethanol for precipitation, wash the precipitate with deionized water multiple times to remove solvent residues and unreacted small molecule monomers, and dry it in a suction filtration device. Place the obtained crude precipitate in a vacuum drying oven and dry it at 80 °C to finally obtain PIM-TOT.

[0064] PIM-PI (number-average molecular weight is about 90,000, preparation process reference: ACS Appl. Polym. Mater. 2023,5, 1420−1429): Dissolve PMDA and SBF in DMAc in a 1:1 molar ratio. Under nitrogen protection, slowly stir the reaction mixture at 0 °C - 5 °C for 1 - 2 hours to ensure complete dissolution of the monomers. Then raise the temperature to room temperature and react for 48 hours. After the reaction is completed, transfer it to water for separation. Add the reaction mixture to ethanol for precipitation, wash the precipitate with deionized water multiple times to remove solvent residues and unreacted small molecule monomers, and dry it in a suction filtration device. Place the obtained crude precipitate in a vacuum drying oven and dry it at 80 °C to finally obtain PIM-PI.

[0065] PIM-EN (number-average molecular weight is about 70,000, preparation process reference: J Membr Sci 2021;629:119284.): Dissolve TTSBI, TFTPN, and EN (molar ratio of 1:1:1) in chloroform to form a homogeneous solution with a mass fraction of 30%. Under nitrogen protection, heat to 160 °C and react for 48 hours. The monomers form PIM-EN polymer through polycondensation reaction. After the reaction is completed, pour the reaction mixture into a large amount of cold ethanol to precipitate the polymer. Collect the precipitated polymer by suction filtration and wash it with ethanol multiple times to remove unreacted monomers. Dry the washed polymer in a vacuum drying oven at 80 °C for 24 hours to obtain pure PIM-EN polymer.

[0066] PIM-Trip-TB (number-average molecular weight is about 90,000, preparation process reference: J Membr Sci 2023;677:121614.): Dissolve tellurium oxychloride (TB) and triptycene diamine (Trip) (molar ratio of 1:1) in chloroform to form a homogeneous solution with a mass fraction of 20%. Under nitrogen protection, heat to 100 °C and react for 48 hours. The monomers form PIM-Trip-TB polymer through polycondensation reaction. After the reaction is completed, pour the reaction mixture into a large amount of cold ethanol to precipitate the polymer. Collect the precipitated polymer by suction filtration and wash it with ethanol multiple times to remove unreacted monomers. Dry the washed polymer in a vacuum drying oven at 100 °C for 24 hours to obtain pure PIM-Trip-TB polymer.

[0067] Example 1 Mix nanofibers (6.4%, mass fraction, the same below), nanoceramic particles (75.9%), dispersant (11.7%), and binder (6%) and stir evenly at high speed to obtain the first slurry; among them, the selected nanoceramic particles are alumina, and the particle sizes include the first particle size (100 - 300 nm) nanoceramic particle D 1 、the second particle size (500 - 700 nm) nanoceramic particle D 2 and the third particle size (900 - 1000 nm) nanoceramic particle D 3 , and their mass percentage composition is: D 1 is 5%, D 2 is 90%, D 3 is 5%, and the mass ratio relationship of the first particle size nanoceramic particle D 1 , the second particle size nanoceramic particle D 2 and the third particle size nanoceramic particle D 3 satisfies the following formula: (D 2 ) 0.5 ≤D 1 +D 3≤(D 2 ) 0.61 , and D 3 ≤D 1 ; The selected nanofibers are aramid nanofibers, with an average length L of 20 μm and a diameter D 0 of 50 nm. Thus, the mass fraction S of the nanofibers is confirmed to be 6.4% according to S = k*(L / D 0 ) 3 (k = 1), and the mass fraction R of the nanoceramic particles is confirmed to be 75.9% according to the relationship R = x*(S 1 / 2 )*2.5 (x = 1.2); The selected dispersant is sodium acrylate; The selected binder is a combination of methacrylamide and 2-hydroxyethyl acrylate, and the mass ratio of the two is 9; Dissolve PIM-1 in the organic solvent N,N-dimethylacetamide (DMAc) to form a second slurry with a mass fraction of PIM-1 of 30%; Select a polyethylene film with a thickness of 15 μm and a porosity of 50% as the porous polyolefin intermediate layer; And spray the first slurry on one side of the porous polyolefin intermediate layer. After coating, dry it at 50 °C for 30 min, then heat it up to 80 °C and dry for 40 min, and continue to heat it up to 100 °C and dry for 30 min; After drying, a first skin layer is formed; Continue to spray the second slurry on the other side of the porous polyolefin intermediate layer. After spraying, dry it at 50 °C for 30 min, then heat it up to 80 °C and dry for 40 min, and continue to heat it up to 100 °C and dry for 30 min; After drying, a second skin layer is formed, and a coated separator for a lithium-ion battery with a sandwich structure is obtained.

[0068] The overall thickness of the obtained polyolefin-coated separator is 17.5 μm, and the thickness T 2 of the first skin layer is 2 μm, and the thickness T 1 of the second skin layer is 0.5 μm; The thickness T 2 of the first skin layer, the thickness T 1 of the second skin layer, and the thickness T 3 of the porous polyolefin intermediate layer satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2. The physical diagram is as shown in Figure 3 .

[0069] Example 2 Mix nanofibers (3.8 wt%, the same below), nano-ceramic particles (86.6 %), dispersant (6.6 %) and binder (3 %) and stir them evenly at high speed to obtain the first slurry; among them, the selected nano-ceramic particles are magnesium oxide, and the particle sizes include nano-ceramic particles D1 with the first particle size (100 - 300 nm), nano-ceramic particles D2 with the second particle size (500 - 700 nm) and nano-ceramic particles D3 with the third particle size (900 - 1000 nm), and their mass percentage composition is: D1 is 10%, D2 is 88%, D3 is 2%, and the mass ratio relationship of the nano-ceramic particles D1 with the first particle size, D2 with the second particle size 1 and D3 with the third particle size 2 satisfies the following formula: (D 3 ) 2 ≤D 0.5 +D 1 ≤(D 3 ) 2 ), and D 0.61 ≤D 3 ; the selected nanofibers are nanocellulose, with an average length L of 10 μm and a diameter D 1 of 30 nm. Thus, the mass ratio S of the nanofibers is confirmed to be 3.8 % according to S = k*(L / D 0 ) 0 (k takes 1), and the mass ratio R of the nano-ceramic particles is confirmed to be 86.6 % according to the relationship R = x*(S 3 )*2.5 (x takes 1.8); the selected dispersant is ammonium polyacrylate; the selected binder is a combination of N,N-dimethylacrylamide and 3-hydroxypropyl acrylate, and the mass ratio of the two is 1.5; 1 / 2 Dissolve PIM-CA in the organic solvent N,N-dimethylacetamide (DMAc) to form a second slurry with a mass ratio of PIM-1 of 30 %; Select a polypropylene film with a thickness of 5 μm and a porosity of 40 % as the porous polyolefin intermediate layer; and spray the first slurry on one side of the porous polyolefin intermediate layer. After coating, dry it at 50 °C for 30 min, then heat it up to 80 °C and dry for 40 min, and continue to heat it up to 100 °C and dry for 30 min; after drying, form the first skin layer; Continue to spray the second slurry on the other side of the porous polyolefin intermediate layer. After spraying, dry it at 50 °C for 30 min, then heat it up to 80 °C and dry for 40 min, and continue to heat it up to 100 °C and dry for 30 min; after drying, form the second skin layer and obtain a coated separator for a lithium-ion battery with a sandwich structure.

[0070] ​The overall thickness of the obtained polyolefin-coated separator is 7.5 μm, the thickness of the first skin layer is 1 μm, and the thickness of the second skin layer is 1.5 μm; the thickness T of the first skin layer 2 and the thickness T of the second skin layer 1 and the thickness T of the porous polyolefin intermediate layer 3 satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0071] Example 3 Mix nanofibers (8.6%, mass fraction, the same below), nanoceramic particles (80.8%), a dispersant (8.6%), and a binder (2%) and stir evenly at high speed to obtain a first slurry; among them, the selected nanoceramic particles are silicon oxide, and the particle sizes include nanoceramic particles D1 with a first particle size (100 - 300 nm), nanoceramic particles D2 with a second particle size (500 - 700 nm), and nanoceramic particles D3 with a third particle size (900 - 1000 nm). Their mass percentage composition is: D1 is 10%, D2 is 85%, and D3 is 5%. The mass ratio relationship of the first particle size nanoceramic particles D 1 , the second particle size nanoceramic particles D 2 and the third particle size nanoceramic particles D 3 satisfies the following formula: (D 2 ) 0.5 ≤D 1 +D 3 ≤(D 2 ) 0.61 , and D 3 ≤D 1 ; the selected nanofibers are nanocellulose, with an average length L of 30 μm and a diameter D 0 of 50 nm; thus, the mass ratio S of the nanofibers is confirmed to be 8.6% according to S = k*(L / D 0 ) 3 (k takes 0.4), and the mass ratio R of the nanoceramic particles is confirmed to be 80.8% according to the relationship R = x*(S 1 / 2 )*2.5 (x takes 1.1); the selected dispersant is sodium acrylate; the selected binder is a combination of N-(2-hydroxyethyl) acrylamide and 3-hydroxypropyl methacrylate, and the mass ratio of the two is 2.3; Dissolve PIM-MP in the organic solvent N,N-dimethylacetamide (DMAc) to form a second slurry with a mass ratio of PIM-MP of 30%. Select a polyethylene film with a thickness of 10 μm and a porosity of 48% as the porous polyolefin intermediate layer; and spray the first slurry on one side of the porous polyolefin intermediate layer. After coating, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; after drying, form the first skin layer; Continue to spray the second slurry on the other side of the porous polyolefin intermediate layer. After spraying, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; after drying, form the second skin layer, and obtain a coated separator for a lithium-ion battery with a sandwich structure.

[0072] The overall thickness of the obtained polyolefin-coated separator is 12.3 μm, the thickness of the first skin layer is 1.5 μm, and the thickness of the second skin layer is 0.8 μm; the thickness T of the first skin layer 2 , the thickness T of the second skin layer 1 and the thickness T of the porous polyolefin intermediate layer 3 satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0073] Example 4 Mix nanofibers (4%, mass fraction, the same below), nano-ceramic particles (85%), dispersant (8%) and binder (3%), and stir evenly at high speed to obtain the first slurry; among them, the selected nano-ceramic particles are alumina, and the particle sizes include nano-ceramic particles D1 with the first particle size (100 - 300 nm), nano-ceramic particles D2 with the second particle size (500 - 700 nm) and nano-ceramic particles D3 with the third particle size (900 - 1000 nm), and their mass percentage composition is: D1 is 8%, D2 is 88%, D3 is 4%, and the mass ratio relationship of the first particle size nano-ceramic particles D 1 , the second particle size nano-ceramic particles D 2 and the third particle size nano-ceramic particles D 3 satisfies the following formula: (D 2 ) 0.5 ≤D 1 +D 3 ≤(D 2 ) 0.61 , and D 3 ≤D 1 ; the selected nanofibers are bacterial cellulose, with an average length L of 10 μm and a diameter D 0 of 50 nm. Thus, the mass ratio S of the nanofibers is calculated according to S = k*(L / D 0) 3 It is confirmed to be 4% (when k = 5), and the mass fraction R of the nano-ceramic particles is confirmed to be 85% (when x = 1.7) according to the relationship of R = x*(S 1 / 2 )*2.5; the dispersant selected is sodium acrylate; the binder selected is a combination of N-(2-hydroxyethyl) acrylamide and 3-hydroxypropyl methacrylate, and the mass ratio of the two is 4; Dissolve PIM-PI in the organic solvent N,N-dimethylacetamide (DMAc) to form a second slurry with a mass fraction of PIM-PI of 20%; Select a polypropylene membrane with a thickness of 8 μm and a porosity of 48% as the porous polyolefin intermediate layer; and spray the first slurry on one side of the porous polyolefin intermediate layer. After coating, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; after drying, form the first skin layer; Continue to spray the second slurry on the other side of the porous polyolefin intermediate layer. After spraying, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; after drying, form the second skin layer, and obtain a coated separator for a lithium-ion battery with a sandwich structure.

[0074] The overall thickness of the obtained polyolefin-coated separator is 9.5 μm, the thickness of the first skin layer is 1 μm, and the thickness of the second skin layer is 0.5 μm; the thickness T 2 of the first skin layer and the thickness T 1 of the second skin layer and the thickness T 3 of the porous polyolefin intermediate layer satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0075] Example 5 Mix nanofibers (10%, mass fraction, the same below), nano-ceramic particles (79.1%), dispersant (5.9%) and binder (5%) and stir evenly at high speed to obtain the first slurry; among them, the nano-ceramic particles selected are magnesium oxide, and the particle sizes include nano-ceramic particles D1 with the first particle size (100 - 300 nm), nano-ceramic particles D2 with the second particle size (500 - 700 nm) and nano-ceramic particles D3 with the third particle size (900 - 1000 nm), and their mass percentage compositions are: D1 is 9%, D2 is 89%, D3 is 2%, the nano-ceramic particles D with the first particle size 1 , the nano-ceramic particles D with the second particle size 2 and the nano-ceramic particles D with the third particle size3 The mass ratio relationship satisfies the following formula: (D 2 ) 0.5 ≤D 1 +D 3 ≤(D 2 ) 0.61 , and D 3 ≤D 1 ; The selected nanofibers are aramid nanofibers, with an average length L of 30 μm and a diameter D 0 of 30 nm. Thus, the mass ratio S of the nanofibers is confirmed to be 10% according to S = k*(L / D 0 ) 3 (k is taken as 0.1). The mass ratio R of the nanoceramic particles is confirmed to be 79.1% according to the relationship R = x*(S 1 / 2 )*2.5 (x is taken as 1); The selected dispersant is ammonium polyacrylate; The selected binder is a combination of N,N-dimethylacrylamide and 3-hydroxypropyl acrylate, and the mass ratio of the two is 5.7; Dissolve PIM-EN in an organic solvent of N,N-dimethylacetamide (DMAc) to form a second slurry with a mass ratio of PIM-EN of 30%; Select a polyethylene film with a thickness of 8 μm and a porosity of 48% as the porous polyolefin intermediate layer; And spray the first slurry on one side of the porous polyolefin intermediate layer. After coating, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; After drying, a first skin layer is formed; Continue to spray the second slurry on the other side of the porous polyolefin intermediate layer. After spraying, dry it at 50 °C for 30 min, then raise the temperature to 80 °C and dry for 40 min, and continue to raise the temperature to 100 °C and dry for 30 min; After drying, a second skin layer is formed, and a coated separator for a lithium-ion battery with a sandwich structure is obtained.

[0076] The overall thickness of the obtained polyolefin-coated separator is 9.5 μm, the thickness of the first skin layer is 1 μm, and the thickness of the second skin layer is 0.5 μm; The thickness T 2 of the first skin layer, the thickness T 1 of the second skin layer, and the thickness T 3 of the porous polyolefin intermediate layer satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0077] Example 6 Compared with Example 1, the difference is that the slurry provided in this example is formed by dissolving PIM-EN in an organic solvent of N,N-dimethylacetamide (DMAc) to form a second slurry with a mass ratio of PIM-EA-TB of 30%; the remaining processes are the same. The overall thickness of the obtained polyolefin-coated separator is 17.5 μm, the thickness of the first skin layer is 2 μm, and the thickness of the second skin layer is 0.5 μm.

[0078] Example 7 Compared with Example 1, the difference is that the slurry provided in this example is formed by dissolving PIM-Trip-TB in an organic solvent of DMAc to form a second slurry with a mass ratio of PIM-Trip-TB of 30%; the remaining processes are the same. The overall thickness of the obtained polyolefin-coated separator is 17.5 μm, the thickness of the first skin layer is 2 μm, and the thickness of the second skin layer is 0.5 μm.

[0079] Example 8 Compared with Example 1, the difference is that the slurry provided in this example is formed by dissolving PIM-TOT and PIM-1 together in an organic solvent of DMAc to form a slurry with a mass ratio of PIM-TOT and PIM-1 of 30%; among them, the mass ratio of PIM-TOT is 15%; the remaining processes are the same.

[0080] The overall thickness of the obtained polyolefin-coated separator is 17.5 μm, the thickness of the first skin layer is 2 μm, and the thickness of the second skin layer is 0.5 μm.

[0081] Example 9 Compared with Example 1, the difference is that the second slurry provided in this example is formed by dissolving PIM-Trip-TB and PIM-1 together in an organic solvent of DMAc to form a second slurry with a mass ratio of PIM-Trip-TB and PIM-1 of 30%; among them, the mass ratio of PIM-Trip-TB is 15%; the remaining processes are the same.

[0082] The overall thickness of the obtained coated separator is 17.5 μm, the thickness of the first skin layer is 2 μm, and the thickness of the second skin layer is 0.5 μm.

[0083] Comparative Example 1 Compared with Example 1, the difference is that in Comparative Example 1, the composition of the second slurry is the same as that of the first slurry (nanofibers (6.4%), nanoceramic particles (75.9%), dispersant (11.7%), and binder (6%)); the remaining steps are the same.

[0084] The overall thickness of the obtained coated separator is 17.5 μm, the thickness of the first skin layer is T 2is 2 μm, and the thickness T of the second skin layer 1 is 0.5 μm.

[0085] Comparative Example 2 Compared with Example 1, the difference lies in that the thickness T of the first skin layer of the obtained polyolefin-coated separator 2 is 0.1 μm; the remaining steps are the same; the thickness T of the first skin layer 2 , the thickness T of the second skin layer 1 and the thickness T of the porous polyolefin intermediate layer 3 do not satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0086] Comparative Example 3 Compared with Example 1, the difference lies in that the thickness T of the second skin layer of the obtained polyolefin-coated separator 1 is 0.05 μm; the rest are the same; the thickness T of the first skin layer 2 , the thickness T of the second skin layer 1 and the thickness T of the porous polyolefin intermediate layer 3 do not satisfy the formula (T 3 ) 0.25 ≤T 1 +T 2 ≤T 3 / 2.

[0087] Comparative Example 4 Commercial double-sided coated polyethylene lithium-ion battery separator, thickness 16 μm. Model SH716E22HL.

[0088] Performance Test Measure the thermal shrinkage, electrolyte wetting area, moisture content, and ion penetration rate of the coated separators obtained in the above Examples 1-9 and Comparative Examples 1-4: Thermal shrinkage rate: Cut the coated separator into the size of A4 paper sample, where the long direction is the MD direction and the short direction is the TD direction. Draw a frame of 100 mm × 100 mm in the middle. Clamp 11 sheets of A4 paper on both the upper and lower sides of the separator, put it into an oven at 150 °C for 60 min, take it out, measure the size of the drawn frame, and record it as L. The thermal shrinkage rate = (100 - L)%.

[0089] Electrolyte wetting area: Cut the coated separator into the size of 50 mm × 50 mm. Use a micro-syringe to take 2 μL of electrolyte and drop it vertically on the surface of the sample. Take a photo with an industrial camera and measure the size of the electrolyte diffusion area after 5 min. The obtained data is the area wetted by the electrolyte.

[0090] Moisture content test: In an environment where the dew point is less than -40 °C, take 1 - 1.5 g of the coated separator as a sample, bake at a temperature of 120 °C for 5 minutes, and use the Karl Fischer method to test the moisture content in the coated separator.

[0091] Both the areal density and the ion diffusion coefficient are tested according to the standard test methods. Areal density: GB / T 30428.1 - 2013; Ion diffusion coefficient: GB / T 30428.1 - 2013.

[0092] The test results are shown in Table 1 below.

[0093] Table 1 Test Results of Separator Performance

[0094] From the test results shown in Table 1, it can be seen that the thickness T3 of the porous polyolefin intermediate layer in Examples 1 - 9 is all within 5 μm - 15 μm, the thickness T1 of the second skin layer is 0.5 - 1.5 μm, and the thickness T2 of the first skin layer is 1 μm - 2 μm; and, among the thickness T2 of the first skin layer, the thickness T3 of the porous polyolefin intermediate layer, and the thickness T1 of the second skin layer, it satisfies (T3) 0.25 ≤T1 + T2≤T3 / 2; the moisture content of the obtained coated separator is 500 - 560 ppm; the electrolyte wetting area of the coated separator is 84.3 - 93.2; the areal density of the coated separator is 8.59 - 8.92 g / m 2 ; the diffusion coefficient of the coated separator for nickel ions is 3.21×10 -9 ~ 4.65×10 -9 cm 2 / s, and the diffusion coefficient for manganese ions is 5.75×10 -10 ~ 6.88×10 -10 cm 2 / s; and, the thermal shrinkage rate of the coated separator is 1.8% - 4.3% under the condition of being kept at 150 °C for 1 hour.

[0095] By comparing the test results of Examples 1 - 9 and Comparative Example 1, it can be seen that for Comparative Example 1, nanofiber / nanoceramic particle coating layers (the first skin layer) are sprayed on both sides of the porous intermediate layer, and the mechanical properties of the obtained coated separator are inferior to those of Examples 1 - 9, and the permeability of the coated separator in Comparative Example 1 to nickel and manganese ions is greater.

[0096] By comparing the test results of Example 1 and Comparative Examples 2 - 3, it can be seen that for Comparative Example 2, the thickness of the first skin layer (T2) does not satisfy the relationship of (T3) 0.25 ≤T1 + T2≤T3 / 2, and for Comparative Example 3, the thickness of the second skin layer (T1) does not satisfy the relationship of (T3) 0.25In the relation of ≤T1+T2≤T3 / 2, the permeability management of the coated separators obtained in Comparative Example 2 and Comparative Example 3 for nickel and manganese ions is inferior to that of Example 1.

[0097] Comparing the test results of Examples 1-9 and Comparative Example 4, it can be seen that the mechanical properties of the coated separator provided by Comparative Example 4 are inferior to those of Examples 1-9, and the diffusion coefficients of the coated separator of Comparative Example 4 for nickel and manganese ions are greater than those of Examples 1-9.

[0098] In the description of this specification, the description with reference to terms such as "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic descriptions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0099] For method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0100] The above has introduced in detail a coated separator for a lithium-ion battery, a preparation method, and a lithium-ion battery provided by the present invention. Specific examples are used herein to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A coated separator for a lithium ion battery, characterized in that: The coated diaphragm is composed of a porous polyolefin middle layer, and a first skin layer and a second skin layer located on both sides of the porous polyolefin middle layer; the first skin layer comprises nanofibers and nano-ceramic particles; The second skin layer comprises an intrinsic microporous polymer PIM or a modified intrinsic microporous polymer PIM.

2. The coated separator for lithium ion battery according to claim 1, characterized in that: The intrinsic microporous polymer PIM is selected from PIM-1 or PIM-2; the modified intrinsic microporous polymer PIM is selected from one or more of PIM-PI, PIM-CA, PIM-EN, PIM-EA-TB, PIM-Trip-TB and PIM-TOT, and the structural formula is as follows: 、 、 、 、 、 、 、 ； In the structural formula, the value of n satisfies the requirement that the molecular weight of the intrinsic microporous polymer PIM or the modified intrinsic microporous polymer PIM is between 50,000 and 100,000.

3. The coated separator for lithium ion battery according to claim 1, characterized in that: The nanofiber is selected from one or more of Kevlar aramid nanofiber, bacterial cellulose, nanocellulose and cotton nanofiber, and the nanoceramic particles are selected from one or more of alumina, boehmite, barium titanate, magnesium oxide, silicon oxide and magnesium hydroxide.

4. The coated separator for lithium ion battery according to claim 1, characterized in that: The thickness T2 of the first skin layer is 1 μm to 2 μm; The thickness T3 of the porous polyolefin intermediate layer is 5 to 15 μm; The thickness T1 of the second skin layer is 0.5-1.5 μm.

5. The coated separator for lithium ion battery according to claim 1, characterized in that: The thickness T2 of the first skin layer, the thickness T3 of the porous polyolefin intermediate layer and the thickness T1 of the second skin layer satisfy (T3) 0.25 ≤T1+T2≤T3 / 2.

6. The coated separator for lithium ion battery according to claim 1, characterized in that: The average length L of the nanofibers is 10 to 30 μm, and the diameter D0 is 30 to 50 nm.

7. The coated separator for lithium ion battery according to claim 1, characterized in that: The particle sizes of the nano-ceramic particles include first-size nano-ceramic particles D1, second-size nano-ceramic particles D2 and third-size nano-ceramic particles D3. The particle size of the first-size nano-ceramic particles D1 ranges from 100 to 300 nm, and the mass proportion is 5% to 10%. The particle size of the second-size nano-ceramic particles D2 is in the range of 500-700 nm, accounting for 85-90% by mass. The particle size of the third particle size nano-ceramic particles D3 is in the range of 900 to 1000 nm, and the mass percentage is 1% to 6%.

8. The coated separator for lithium ion battery according to claim 7, characterized in that: The mass proportion of the first particle size nano-ceramic particles D1, the second particle size nano-ceramic particles D2 and the third particle size nano-ceramic particles D3 satisfies the following formula: (D2) 0.5 ≤D1+D3≤(D2) 0.61 , and D3≤D1.

9. The coated separator for lithium ion battery according to claim 1, characterized in that: The porous polyolefin intermediate layer is composed of polyethylene and / or polypropylene, and has a porosity of 40% to 50%.

10. The coated separator for lithium ion battery according to claim 1, characterized in that: The moisture content of the coated diaphragm is 500-560 ppm; and / or The electrolyte infiltration area of ​​the coated diaphragm is 84.3 to 93.2 mm 2 ; and / or The surface density of the coated diaphragm is 8.59-8.92 g / m 2 .

11. The coated separator for lithium ion battery according to claim 1, characterized in that: The diffusion coefficient of the coated membrane for nickel ions is 3.21×10 -9 ~ 4.65×10 -9 cm 2 / s; and / or The diffusion coefficient of the coated membrane for manganese ions is 5.75×10 -10 ~ 6.88×10 -10 cm 2 / s.

12. A method for preparing a coated separator for a lithium ion battery according to any one of claims 1 to 11, characterized in that: The preparation method comprises: The nanofibers, nano-ceramic particles, dispersant and binder are mixed uniformly to form a first slurry; the intrinsic microporous polymer and / or modified intrinsic microporous polymer are dissolved in an organic solvent to form a second slurry; Applying the first slurry on one side of the porous polyolefin intermediate layer, and drying to form a first skin layer on one side of the porous polyolefin intermediate layer; The second slurry is then coated on the other side of the porous polyolefin intermediate layer, and after drying, a second skin layer is formed on the other side of the porous polyolefin intermediate layer, thereby completing the preparation of the coated diaphragm.

13. The method for preparing a coated separator for a lithium ion battery according to claim 12, characterized in that: In the first slurry, the mass proportion of the nanofibers is 3.8% to 10%; the mass proportion of the nano-ceramic particles is 75.9% to 86.6%; the mass proportion of the dispersant is 5.9% to 11.7%; and the mass proportion of the binder is 2% to 6%.

14. The method for preparing a coated separator for a lithium ion battery according to claim 12, characterized in that: The dispersant is selected from sodium acrylate and / or ammonium polyacrylate.

15. The method for preparing a coated separator for a lithium ion battery according to claim 12, characterized in that: The binder is selected from acrylamide monomers.

16. The method for preparing a coated separator for a lithium ion battery according to claim 15, characterized in that: The acrylamide monomer is selected from acrylamide, methacrylamide, N,N-dimethylacrylamide, N-hydroxymethylacrylamide, N,N-methylenebisacrylamide, N-(2-hydroxyethyl)acrylamide, N-(2-hydroxypropyl)acrylamide and an acrylate monomer: a combination of any two of 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 3-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate and 3-hydroxypropyl methacrylate, with a mass ratio of 1.5 to 9.

17. The method for preparing a coated separator for a lithium ion battery according to claim 12, characterized in that: In the second slurry, the mass proportion of the intrinsic microporous polymer PIM or the modified intrinsic microporous polymer PIM is 20% to 30%.

18. The method for preparing a coated separator for a lithium ion battery according to claim 12, characterized in that: In the second slurry, the organic solvent is selected from one or more of N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide and chloroform.

19. A lithium ion battery, characterized in that: The lithium-ion battery comprises the coated separator according to any one of claims 1 to 11.

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