Battery diaphragm as well as preparation method and application thereof

Abstract

The invention provides a battery diaphragm as well as a preparation method and application thereof, and relates to the technical field of batteries. The lyophilic performance of the surface layer of the battery diaphragm is modified, and the diaphragm surface layer is communicated with micropores, so that an electrolyte diffusion path is shortened; the amphiphilic modified layer (methoxypolyethylene glycol-maleic anhydride copolymer layer) improves the lyophilic property, so that the electrolyte infiltration time is remarkably shortened compared with that of a traditional diaphragm; the liquid storage space is increased by the honeycomb mesopores in the inner layer and the three-dimensional fiber skeleton; the liquid retention capacity is enhanced through the hydrogen-bond interaction of SiO2-OH, and compared with a traditional diaphragm, the liquid retention capacity is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a battery separator and a preparation method and application thereof. BACKGROUND

[0002] The separator is one of the core components of the lithium ion battery, mainly playing a role in separating the positive and negative electrodes and preventing short circuit while allowing lithium ions to pass through. Currently, the commercialized separator is mainly based on polyolefin (PP), polyethylene (PE) or their composite films. However, such polyolefin separators have inherent defects: poor wettability, which leads to slow electrolyte infiltration speed, affects the adhesion between the separator and the electrode sheet, and thus affects the assembly efficiency; insufficient liquid retention capacity, which causes the electrolyte to dry out easily during high-rate cycling, resulting in rapid capacity decay; and large ion transmission resistance, which limits the high-rate performance of the battery.

[0003] To improve the wettability, the existing technology mainly adopts two types of solutions: one is to coat a ceramic (Al2O3, AlOOH) or a polymer coating (such as PVDF, PMMA) on the surface of the separator, but a single coating can only improve the surface affinity and cannot solve the problem of internal pore channel infiltration efficiency, and the coating is easy to fall off, affecting the stability; the other is to optimize the pore channel structure by stretching or solvent poration, but most of them are single-scale pores, which are difficult to balance the dual needs of "fast diffusion" and "long-term liquid storage". In addition, some solutions introduce functional additives, but lack of synergistic design with pore structure and surface modification, and the ion transmission enhancement effect is limited.

[0004] Therefore, the development of a separator that can realize the synergistic effect of "surface layer rapid conduction-internal layer efficient liquid storage-pore ion acceleration" can effectively improve the key shortcoming of the current polyolefin separator wettability and electrochemical performance.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The first object of the present application is to provide a battery separator to solve the above technical problems.

[0007] The second object of the present application is to provide a preparation method of the above battery separator.

[0008] The third object of the present application is to provide the application of the above battery separator in the preparation of lithium ion batteries.

[0009] In order to achieve the above objects, the following technical solutions are adopted: In a first aspect, the present application provides a battery separator, comprising a base skeleton layer; The base skeleton layer is mainly composed of PP resin, PE resin and polyimide nanofiber; the mass of the polyimide nanofiber accounts for 1%-2% of the total mass of the PP resin and the PE resin; The base skeleton layer has a multi-stage pore structure, and a surface layer thereof is distributed with connected micropores with a diameter of 0.1-0.5 μm, and a thickness of the surface layer is 5-8 μm; and an inner layer thereof is distributed with honeycomb-like mesopores with a diameter of 1-3 μm, and a thickness of the inner layer is 15-20 μm; The pore surface and the outer surface of the base skeleton layer are sequentially provided with a polyethylene glycol monomethyl ether-maleic anhydride copolymer (PEGMA-MAH) layer grafted to the pore surface and the outer surface of the base skeleton layer, and a hydroxylated silicon dioxide (SiO2-OH) nanoparticle layer. The base skeleton layer is loaded with a lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex (a complex compound obtained by reacting lithium trifluoromethanesulfonate and ethylenediaminetetraacetic acid) in the pores thereof.

[0010] As a further technical solution, the mass ratio of the PP resin to the PE resin is 4-7:3-6. The specific surface area of the base skeleton layer is 80-100 m 2 / g.

[0011] As a further technical solution, the preparation method of the base skeleton layer comprises the following steps: The PP resin, the PE resin, the polyimide nanofiber and the paraffin oil are mixed, and a cast sheet is obtained after melt co-extrusion, then the cast sheet is immersed in a solvent to dissolve the paraffin oil to form pores, and then the cast sheet is subjected to transverse and longitudinal stretching to form a base skeleton layer with a multi-stage pore structure.

[0012] As a further technical solution, in the cast sheet, the mass ratio of the paraffin oil is 60%-90%. The solvent comprises a mixed solution of butane and isopentane. The longitudinal stretching is performed at a stretching ratio of 3-5 times, and the transverse stretching is performed at a stretching ratio of 4-6 times.

[0013] As a further technical solution, the grafting rate of the polyethylene glycol monomethyl ether-maleic anhydride copolymer is 2%-5%.

[0014] As a further technical solution, the particle size of the hydroxylated silicon dioxide nanoparticles is 20-50 nm. In the battery separator, the mass ratio of the hydroxylated silicon dioxide nanoparticles is 1%-3%.

[0015] As a further technical solution, in the battery separator, the mass ratio of the lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex is 0.5%-1%.

[0016] In a second aspect, the application provides a preparation method of the battery separator, comprising the following steps: The substrate skeleton layer is immersed in a solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer, and after ultraviolet light irradiation treatment, the substrate skeleton layer grafted with polyethylene glycol monomethyl ether-maleic anhydride copolymer is obtained, then the substrate skeleton layer is immersed in a solution of tetraethyl orthosilicate, and a hydroxylated silicon dioxide nanoparticle layer is formed on the surface of the pore channel and the outer surface of the substrate skeleton layer by a sol-gel method, and then the substrate skeleton layer is immersed in a solution of lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex, and after drying, a battery separator is prepared.

[0017] As a further technical solution, the solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer is an ethanol solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer, and the concentration of polyethylene glycol monomethyl ether-maleic anhydride copolymer is 5%-10%; The solution of tetraethyl orthosilicate is an ethanol aqueous solution of tetraethyl orthosilicate, the concentration of tetraethyl orthosilicate is 3%-5%, and the volume ratio of ethanol to water is 2-4:0.8-1.2; The solution of lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex is an acetone solution of lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex, and the mass concentration of lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex is 1%-2%.

[0018] In a third aspect, the present application provides the use of the battery separator in the preparation of a lithium ion battery.

[0019] Compared with the prior art, the present application has the following beneficial effects: The present application modifies the liquid affinity of the surface layer of the battery separator, shortens the diffusion path of the electrolyte through the connected micro-pores (i.e. the three-dimensional network channel structure formed by the mutual penetration of numerous small pores in the separator), improves the liquid affinity through the double-philic modified layer (polyethylene glycol monomethyl ether-maleic anhydride copolymer layer), significantly shortens the electrolyte wetting time compared with the traditional separator, increases the liquid storage space through the inner layer of the honeycomb mesoporous and the three-dimensional fiber skeleton, and effectively improves the liquid retention capacity through the hydrogen bonding of SiO2-OH compared with the traditional separator. DETAILED DESCRIPTION

[0020] The embodiments of the present application will be described in detail below with reference to the embodiments and examples, but those skilled in the art will understand that the following embodiments and examples are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of the present application. If the specific conditions are not specified, the conventional conditions or the conditions recommended by the manufacturer are used. If the manufacturer of the reagent or instrument is not specified, it is a conventional product that can be purchased on the market.

[0021] In a first aspect, the present application provides a battery separator comprising a substrate skeleton layer; The base skeleton layer is mainly composed of PP resin, PE resin and polyimide nanofiber; the mass of the polyimide nanofiber accounts for 1%-2% of the total mass of the PP resin and the PE resin, for example, but not limited to 1%, 1.5% or 2%; The base skeleton layer has a multi-level pore structure, the surface layer is distributed with connected micropores with a diameter of 0.1-0.5 μm, and the thickness of the surface layer is 5-8 μm; the inner layer is distributed with honeycomb-like mesopores with a diameter of 1-3 μm, and the thickness of the inner layer is 15-20 μm; The pore surface and the outer surface (i.e. the outer surface of the base skeleton layer) of the base skeleton layer are sequentially provided with a polyethylene glycol monomethyl ether-maleic anhydride copolymer (PEGMA-MAH) layer grafted on the pore surface and the outer surface of the base skeleton layer, and a hydroxylated silicon dioxide (SiO2-OH) nanoparticle layer; The base skeleton layer is loaded with lithium triflate-ethylenediaminetetraacetic acid complex in the pores.

[0022] The present application modifies the liquid affinity of the surface layer of the battery separator, shortens the electrolyte diffusion path of the connected micropores of the surface layer of the separator, improves the liquid affinity by the amphiphilic modification layer (polyethylene glycol monomethyl ether-maleic anhydride copolymer layer), significantly shortens the electrolyte wetting time compared with the traditional separator, increases the liquid storage space by the inner layer honeycomb-like mesopores and the three-dimensional fiber skeleton, and effectively improves the liquid retention capacity by the hydrogen bonding of SiO2-OH compared with the traditional separator.

[0023] In some optional embodiments, the mass ratio of the PP resin and the PE resin may be, for example, but not limited to 4:6, 1:1 or 7:34-7:3-6; The specific surface area of the base skeleton layer is 80-100 m 2 / g.

[0024] In some optional embodiments, the melt index of the PP resin is 1.5-2.5 g / 10 min; The melt index of the PE resin is 0.8-1.2 g / 10 min.

[0025] In some optional embodiments, the preparation method of the base skeleton layer comprises the following steps: The PP resin, the PE resin, the polyimide nanofiber and the paraffin oil are mixed, and a cast sheet is obtained after melt co-extrusion, then the cast sheet is immersed in a solvent to dissolve the paraffin oil to form pores, and then the cast sheet is stretched in the transverse and longitudinal directions to form a base skeleton layer with a multi-level pore structure.

[0026] In some optional embodiments, the thickness of the cast sheet is 50-60 μm.

[0027] In some optional embodiments, the mass percentage of paraffin oil in the cast sheet may, for example, be, but is not limited to, 60%, 80%, or 90%. The solvent includes a mixed solution of butane and isopentane, and the volume ratio of the two may, for example, be 1:1. The longitudinal stretching is performed at a stretching ratio of 3-5 times (may, for example, be, but is not limited to, 3 times, 4 times, or 5 times), and the transverse stretching is performed at a stretching ratio of 4-6 times (may, for example, be, but is not limited to, 4 times, 5 times, or 6 times).

[0028] The substrate skeleton layer with a multi-level pore structure is obtained by stretching.

[0029] In some optional embodiments, the grafting rate of the polyethylene glycol monomethyl ether-maleic anhydride copolymer may, for example, be, but is not limited to, 2%, 3%, 4%, or 5%.

[0030] In some optional embodiments, the particle size of the hydroxylated silicon dioxide nanoparticles may, for example, be, but is not limited to, 20 nm, 30 nm, or 50 nm. In the battery separator, the mass percentage of hydroxylated silicon dioxide nanoparticles may, for example, be, but is not limited to, 1%, 2%, or 3%.

[0031] In some optional embodiments, in the battery separator, the mass percentage of lithium triflate-ethylenediaminetetraacetic acid complex may, for example, be, but is not limited to, 0.5%, 0.8%, or 1%.

[0032] In a second aspect, the present application provides a preparation method of the battery separator, comprising the following steps: The substrate skeleton layer is immersed in a solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer, and after ultraviolet light irradiation treatment, the substrate skeleton layer grafted with polyethylene glycol monomethyl ether-maleic anhydride copolymer is obtained, then the substrate skeleton layer is immersed in a solution of tetraethyl orthosilicate, and a layer of hydroxylated silicon dioxide nanoparticles is formed on the pore surface and the outer surface of the substrate skeleton layer by sol-gel method, then the substrate skeleton layer is immersed in a solution of lithium triflate-ethylenediaminetetraacetic acid complex, and after drying, the battery separator is prepared.

[0033] The preparation method is simple and convenient.

[0034] In some optional embodiments, the solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer is an ethanol solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer, and the concentration of polyethylene glycol monomethyl ether-maleic anhydride copolymer may, for example, be, but is not limited to, 5%, 8%, or 10%. The solution of tetraethyl orthosilicate is an aqueous ethanol solution of tetraethyl orthosilicate, and the concentration of tetraethyl orthosilicate can be, but is not limited to, 3%, 4% or 5%, and the volume ratio of ethanol and water can be, but is not limited to, 2:1.2, 3:1 or 4:0.82-4:0.8-1.2; The solution of lithium triflate-ethylenediamine tetraacetic acid complex is an acetone solution of lithium triflate-ethylenediamine tetraacetic acid complex, and the mass concentration of lithium triflate-ethylenediamine tetraacetic acid complex can be, but is not limited to, 1%, 1.5% or 2%.

[0035] In some optional embodiments, the pH of the sol-gel method reaction is 3-4, the temperature of the reaction is 50-60℃, and the reaction time is 20-30 min.

[0036] In a third aspect, the application provides the use of the battery separator in the preparation of a lithium ion battery.

[0037] The battery separator provided by the application can be used in the preparation of a lithium ion battery to improve the battery performance of the lithium ion battery.

[0038] The application will be further described below through specific examples, but it should be understood that these examples are only used for more detailed description and should not be understood as limiting the application in any form.

[0039] Example 1 A battery separator is prepared by the following method: Step 1: raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 7:3, 1.5% of polyimide nanofiber is added to the mixed resin, and 80% of paraffin oil is added, and the mixture is stirred uniformly to obtain a base material; Step 2: co-extrusion of a sheet. The base material is added to a double-screw extruder, and co-extrusion is carried out at 180-200℃, and the sheet is extruded through a T-shaped die to a thickness of 50-60 μm; Step 3: micro-phase separation and pore formation. The sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) at 40-50℃ for 30-40 min to induce phase separation of the resin and form preliminary pores; Step 4: two-way stretching. The sheet after micro-phase separation is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a multi-level pore base skeleton layer. Step 5: Parent modification. The substrate skeleton layer is immersed in an ethanol solution containing 8% PEGMA-MAH and irradiated under ultraviolet light (wavelength 254 nm, power 300 W) for 15-20 min to achieve in-situ grafting; then immersed in an ethanol-water mixture (volume ratio 4:1) containing 4% tetraethyl orthosilicate, and hydrochloric acid is added to adjust the pH to 3-4, and reacted at 50-60°C for 20-30 min to form a SiO2-OH filling phase in the pores by sol-gel method, and dried to obtain a modified substrate; Step 6: Additive loading. The modified substrate is immersed in an acetone solution containing 1.5% lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex, soaked for 10-15 min, vacuum dried at 60-70°C, and wound to obtain the target separator.

[0040] The pore surface and outer surface of the substrate skeleton layer of the battery separator are sequentially provided with: a polyethylene glycol monomethyl ether-maleic anhydride copolymer layer grafted on the pore surface and outer surface of the substrate skeleton layer, a hydroxylated silicon dioxide nanoparticle layer; and lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex loaded in the pores of the substrate skeleton layer.

[0041] Through testing, the substrate skeleton layer of the battery separator has a hierarchical pore structure, and the specific surface area is in the range of 80-100 m 2 / g, the surface layer has connected micropores with a diameter of 0.1-0.5 μm, and the surface layer thickness is 5-8 μm; the inner layer has a honeycomb-like mesopore with a diameter of 1-3 μm, and the inner layer thickness is 15-20 μm.

[0042] Example 2 A battery separator is prepared by the following method: Step 1: Raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 4:6, 1% polyimide nanofiber and 60% paraffin oil are added, and the mixture is stirred uniformly to obtain a base material; Step 2: Co-extrusion casting. The base material is added to a double-screw extruder, melted and co-extruded at 180-200°C, and extruded into a casting sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: Microphase separation pore formation. The casting sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) at 40-50°C for 30-40 min to induce resin phase separation and form preliminary pores; Step 4: Two-way stretching. The casting sheet after microphase separation is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a hierarchical pore substrate skeleton layer; Step 5: Parent modification. The substrate skeleton layer is immersed in an ethanol solution containing 5% PEGMA-MAH and irradiated under ultraviolet light (wavelength 254 nm, power 300 W) for 15-20 min to achieve in-situ grafting; then immersed in an ethanol-water mixture (volume ratio 2:1.2) containing 3% tetraethyl orthosilicate, and hydrochloric acid is added to adjust the pH to 3-4, and reacted at 50-60°C for 20-30 min to form a SiO2-OH filling phase in the pores by sol-gel method, and dried to obtain a modified substrate; Step 6: Additive loading. The modified substrate is immersed in an acetone solution containing 1% lithium triflate-ethylenediaminetetraacetic acid complex, soaked for 10-15 min, vacuum dried at 60-70°C, and wound to obtain the target separator.

[0043] The pore surface and outer surface of the substrate skeleton layer of the battery separator are sequentially provided with: a polyethylene glycol monomethyl ether-maleic anhydride copolymer layer grafted on the pore surface and outer surface of the substrate skeleton layer, a hydroxylated silicon dioxide nanoparticle layer; and a lithium triflate-ethylenediaminetetraacetic acid complex loaded in the pores of the substrate skeleton layer.

[0044] Tests show that the substrate skeleton layer of the battery separator has a hierarchical pore structure, and the specific surface area is in the range of 80-100 m 2 / g, the surface layer has connected micropores with a diameter of 0.1-0.5 μm, and the surface layer has a thickness of 5-8 μm; the inner layer has a honeycomb-like mesopore with a diameter of 1-3 μm, and the inner layer has a thickness of 15-20 μm.

[0045] Example 3 A battery separator is prepared by the following method: Step 1: Raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 1:1, 1-2% polyimide nanofibers are added to the mixed resin, and 90% paraffin oil is added, and stirred uniformly to obtain a base material; Step 2: Co-extrusion casting. The base material is added to a double-screw extruder, melted and co-extruded at 180-200°C, and extruded into a casting sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: Microphase separation pore formation. The casting sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) at 40-50°C for 30-40 min to induce resin phase separation and form preliminary pores; Step 4: Two-way stretching. The casting sheet after microphase separation is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a hierarchical pore substrate skeleton layer; Step 5: Biparent modification. The substrate skeleton layer is immersed in an ethanol solution containing 10% PEGMA-MAH and irradiated under ultraviolet light (wavelength 254 nm, power 300 W) for 15-20 min to achieve in-situ grafting; then immersed in an ethanol-water mixture (volume ratio 4:0.8) containing 5% tetraethyl orthosilicate, and hydrochloric acid is added to adjust the pH to 3-4, and reacted at 50-60°C for 20-30 min to form a SiO2-OH filling phase in the pores by sol-gel method, and dried to obtain a modified substrate; Step 6: Additive loading. The modified substrate is immersed in an acetone solution containing 2% lithium triflate-ethylenediaminetetraacetic acid complex, soaked for 10-15 min, vacuum dried at 60-70°C, and wound to obtain the target separator.

[0046] The pore surface and outer surface of the substrate skeleton layer of the battery separator are sequentially provided with: a polyethylene glycol monomethyl ether-maleic anhydride copolymer layer grafted on the pore surface and outer surface of the substrate skeleton layer, a hydroxylated silicon dioxide nanoparticle layer; and lithium triflate-ethylenediaminetetraacetic acid complex loaded in the pores of the substrate skeleton layer.

[0047] Tests show that the substrate skeleton layer of the battery separator has a hierarchical pore structure, and the specific surface area is in the range of 80-100 m 2 / g, the surface layer has connected micropores with a diameter of 0.1-0.5 μm, and the surface layer has a thickness of 5-8 μm; the inner layer has a honeycomb-like mesopore with a diameter of 1-3 μm, and the inner layer has a thickness of 15-20 μm.

[0048] Comparative Example 1 The difference between this comparative example and Example 1 is that it does not have a hierarchical pore structure, and the preparation steps are as follows: Step 1: Raw material preparation. Mix PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) at a mass ratio of 7:3, add 80% paraffin oil, and stir evenly to obtain a base material; Step 2: Co-extrusion casting. Add the base material to a double-screw extruder, melt co-extrude at 180-200°C, and extrude into a casting sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: Microphase separation pore formation. Immerse the casting sheet in a butane / isopentane mixed solvent (volume ratio 1:1) at 40-50°C for 30-40 min to induce resin phase separation and form preliminary pores; Step 4: Two-way stretching. Stretch the microphase-separated casting sheet in the longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretch it in the transverse stretching machine at a stretching ratio of 4-6 times to form a connected pore substrate skeleton layer; The base skeleton layer of the battery separator tested has a communicating pore structure with communicating micropores of 0.1-0.5 μm in diameter and a thickness of 20-28 μm.

[0049] Comparative Example 2 The difference from Example 1 is that the PEGMA-MAH layer is not included, and the preparation steps are as follows: Step 1: raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 7:3, 1.5% of polyimide nanofibers and 80% of paraffin oil are added, and the mixture is stirred uniformly to obtain a base material; Step 2: co-extrusion casting. The base material is added to a double-screw extruder, melted and co-extruded at 180-200°C, and extruded into a casting sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: micropore formation by microphase separation. The casting sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) and soaked at 40-50°C for 30-40 min to induce resin phase separation and form initial pores; Step 4: two-way stretching. The casting sheet after microphase separation is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a multi-level pore base skeleton layer; Step 5: single parent modification. The modified base material is immersed in an ethanol-water mixture (volume ratio 4:1) containing 4% tetraethyl orthosilicate, and hydrochloric acid is added to adjust the pH to 3-4. The reaction is carried out at 50-60°C for 20-30 min to form a SiO2-OH filling phase in the pores by sol-gel method, and the modified base is dried to obtain a modified base; Step 6: additive loading. The modified base is immersed in a 1.5% lithium trifluoromethyl sulfonate-ethylenediamine tetraacetic acid complex solution in acetone for 10-15 min, vacuum dried at 60-70°C, and wound to obtain the target separator.

[0050] The base skeleton layer of the battery separator tested has a multi-level pore structure with communicating micropores of 0.1-0.5 μm in diameter distributed on the surface layer, and a surface layer thickness of 5-8 μm; and honeycomb-like mesopores of 1-3 μm in diameter distributed in the inner layer, and an inner layer thickness of 15-20 μm.

[0051] Comparative Example 3 The difference from Example 1 is that the SiO2-OH layer is not included, and the preparation steps are as follows: Step 1: raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 7:3, 1.5% of polyimide nanofibers and 80% of paraffin oil are added, and the mixture is stirred uniformly to obtain a base material; Step 2: Co-extrusion cast sheet. The base material is added to a twin-screw extruder, melt co-extruded at 180-200°C, and extruded into a cast sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: Micro-phase separation pore formation. The cast sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) and soaked at 40-50°C for 30-40 min to induce resin phase separation and form initial pores; Step 4: Two-way stretching. The micro-phase separated cast sheet is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a multi-level pore base skeleton layer; Step 5: Single parent modification. The base skeleton layer is immersed in an ethanol solution containing 8% PEGMA-MAH and irradiated under ultraviolet light (wavelength 254 nm, power 300 W) for 15-20 min to achieve in-situ grafting; Step 6: Additive loading. The modified base is immersed in an acetone solution containing 1.5% lithium trifluoromethyl sulfonate-ethylene diamine tetraacetic acid complex, soaked for 10-15 min, dried at 60-70°C under vacuum, and wound to obtain the target separator.

[0052] The battery separator tested has a multi-level pore structure in the base skeleton layer, with connected micropores of 0.1-0.5 μm in diameter distributed in the surface layer, and a surface layer thickness of 5-8 μm; and honeycomb-like mesopores of 1-3 μm in diameter distributed in the inner layer, with an inner layer thickness of 15-20 μm.

[0053] Comparative Example 4 The difference from Example 1 is that lithium trifluoromethyl sulfonate-ethylene diamine tetraacetic acid complex is not loaded.

[0054] Step 1: Raw material preparation. PP resin (melt index 1.5-2.5 g / 10 min) and PE resin (melt index 0.8-1.2 g / 10 min) are mixed in a mass ratio of 7:3, 1.5% polyimide nanofibers are added to the mixed resin, and 80% paraffin oil is added, and the mixture is stirred uniformly to obtain the base material; Step 2: Co-extrusion cast sheet. The base material is added to a twin-screw extruder, melt co-extruded at 180-200°C, and extruded into a cast sheet with a thickness of 50-60 μm through a T-shaped die; Step 3: Micro-phase separation pore formation. The cast sheet is immersed in a butane / isopentane mixed solvent (volume ratio 1:1) and soaked at 40-50°C for 30-40 min to induce resin phase separation and form initial pores; Step 4: Two-way stretching. The micro-phase separated cast sheet is stretched in a longitudinal stretching machine at a stretching ratio of 3-5 times, and then stretched in a transverse stretching machine at a stretching ratio of 4-6 times to form a multi-level pore base skeleton layer; Step 5: Parent modification. The substrate skeleton layer is immersed in an ethanol solution containing 8% PEGMA-MAH and irradiated under ultraviolet light (wavelength 254 nm, power 300 W) for 15-20 min to achieve in-situ grafting; then immersed in an ethanol-water mixture (volume ratio 4:1) containing 4% tetraethyl orthosilicate, and hydrochloric acid is added to adjust the pH to 3-4, and reacted at 50-60°C for 20-30 min to form a SiO2-OH filling phase in the pores by sol-gel method, and dried to obtain a modified substrate. The substrate skeleton layer of the battery separator tested has a hierarchical pore structure, with connected micropores with a diameter of 0.1-0.5 μm distributed on the surface layer, and the surface layer has a thickness of 5-8 μm; the inner layer is distributed with honeycomb-like mesopores with a diameter of 1-3 μm, and the inner layer has a thickness of 15-20 μm.

[0055] Test Example 1 The above battery separator is tested as follows: 1. Contact angle test Liquid drop method is used for testing.

[0056] Sample preparation: The separator is baked at 85°C for 30 min, and then cut into 5*5 cm.

[0057] Test: The separator is placed flat on the sample stage and pressed tightly with a clamp, 5 μl of electrolyte is added to the surface of the separator by a syringe, and the contact angles on the left and right sides of the drop are read after the drop is stable, and the average value is taken, and the test is repeated 3 times to ensure the data is true and reliable.

[0058] 2. Electrolyte retention rate The weight method is used for testing.

[0059] Sample preparation: The separator is baked at 85°C for 30 min, and then cut into 5*5 cm.

[0060] Test: The dry separator mass is m1, then the separator is soaked in electrolyte for 5 min, the separator is taken out and wiped with non-woven fabric, and the wet separator mass is m2 when there is no obvious electrolyte drop on the surface of the separator, and the test is repeated 5 times to take the average value.

[0061] Electrolyte retention rate = (m2-m1) / m1*100%.

[0062] 3. Ionic conductivity Sample preparation: Take 32*37 mm size stainless steel electrode, 20*30 mm stainless steel electrode and 34*40 mm separator piece and place them in 85°C oven for 30 min.

[0063] Battery assembly: The separator was clamped between two stainless steel electrodes and fixed with brown tape. The fixed battery was placed in an aluminum-plastic film shell of type 503450, and then liquid injection and heat sealing were performed.

[0064] Test: The resistance of the assembled battery was tested using Chenhua chi660e, and each separator was tested 5 times, with a battery resistance range requirement of <0.02Ω.

[0065] The ion conductivity of the separator = d / (Rs*A*10).

[0066] d is the thickness of the separator, in units of μm, measured by a thickness gauge.

[0067] Rs is the resistance of the separator, in units of Ω.

[0068] A is the effective area of the separator in a symmetric battery, with a value of 6 cm 2 .

[0069] The results are shown in Table 1: Table 1

[0070] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A battery separator, characterized in that, Including the basal skeleton layer; The substrate framework layer is mainly composed of PP resin, PE resin and polyimide nanofibers; the mass of the polyimide nanofibers accounts for 1%-2% of the total mass of PP resin and PE resin; The substrate framework layer has a multi-level pore structure, with interconnected micropores of 0.1-0.5 μm in diameter distributed on its surface and a thickness of 5-8 μm; and honeycomb-like mesopores of 1-3 μm in diameter distributed on its inner layer and a thickness of 15-20 μm. The pore surface and outer surface of the substrate framework layer are sequentially provided with: a polyethylene glycol monomethyl ether-maleic anhydride copolymer layer grafted onto the pore surface and outer surface of the substrate framework layer, and a hydroxylated silica nanoparticle layer. The pores of the substrate framework layer are loaded with lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex.

2. The battery separator according to claim 1, characterized in that, The mass ratio of PP resin to PE resin is 4-7:3-6; The specific surface area of ​​the base skeleton layer is 80-100 m². 2 / g.

3. The battery separator according to claim 1, characterized in that, The method for preparing the substrate framework layer includes the following steps: PP resin, PE resin, polyimide nanofibers and paraffin oil are mixed and melt-co-extruded to obtain a cast sheet. The cast sheet is then immersed in a solvent to dissolve the paraffin oil and form channels. The cast sheet is then stretched in both the transverse and longitudinal directions to form a base skeleton layer with a multi-level channel structure.

4. The battery separator according to claim 3, characterized in that, In the cast sheet, the mass percentage of paraffin oil is 60%-90%; The solvent includes a mixed solution of butane and isopentane; Longitudinal stretching is performed at a stretch ratio of 3-5 times, and transverse stretching is performed at a stretch ratio of 4-6 times.

5. The battery separator according to claim 1, characterized in that, The grafting rate of the polyethylene glycol monomethyl ether-maleic anhydride copolymer is 2%-5%.

6. The battery separator according to claim 1, characterized in that, The hydroxylated silica nanoparticles have a particle size of 20-50 nm. In the battery separator, the mass percentage of hydroxylated silica nanoparticles is 1%-3%.

7. The battery separator according to claim 1, characterized in that, In the battery separator, the mass percentage of the lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex is 0.5%-1%.

8. A method for preparing the battery separator according to any one of claims 1-7, characterized in that, Includes the following steps: The substrate framework layer was immersed in a solution of polyethylene glycol monomethyl ether-maleic anhydride copolymer and treated with ultraviolet light to obtain a substrate framework layer grafted with polyethylene glycol monomethyl ether-maleic anhydride copolymer. Then, it was immersed in a solution of tetraethyl orthosilicate and a hydroxylated silica nanoparticle layer was formed on the pore surface and outer surface of the substrate framework layer by sol-gel method. After that, it was immersed in a solution of lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex and dried to prepare the battery separator.

9. The preparation method according to claim 8, characterized in that, The solution of the polyethylene glycol monomethyl ether-maleic anhydride copolymer is an ethanol solution of the polyethylene glycol monomethyl ether-maleic anhydride copolymer, and the concentration of the polyethylene glycol monomethyl ether-maleic anhydride copolymer is 5%-10%. The tetraethyl orthosilicate solution is an aqueous solution of tetraethyl orthosilicate in ethanol, with a concentration of 3%-5% for tetraethyl orthosilicate and a volume ratio of ethanol to water of 2-4:0.8-1.

2. The solution of the lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex is an acetone solution of the lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex, and the mass concentration of the lithium trifluoromethanesulfonate-ethylenediaminetetraacetic acid complex is 1%-2%.

10. The battery separator according to any one of claims 1-7, and its use in the preparation of lithium-ion batteries.

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