Modified diaphragm, preparation method thereof and lithium ion battery

Abstract

The invention provides a modified diaphragm, a preparation method thereof and a lithium ion battery. The modified diaphragm comprises a base membrane and a functional layer positioned on at least one side surface of the base membrane, the functional layer comprises an olefin polymer material; the olefin polymer material contains a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group. According to the present invention, the olefin polymer having the pyrrolopyrimidine heterocyclic group, the aromatic ring group and the siloxy group is used in the functional layer of the diaphragm, such that the balance of the mechanical strength and the flexibility of the modified diaphragm is achieved on the basis of ensuring the rapid charging performance of the battery, and the thermal stability and the ion transmission efficiency of the modified diaphragm are improved; and the wettability of the electrolyte is also enhanced.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion batteries, and relates to a modified diaphragm, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] In recent years, lithium ion batteries are widely used in electric vehicles, consumer electronics and energy storage fields due to their high energy density, long cycle life and other advantages. However, with the increasing demand for fast charging in the market, the performance and safety of the battery under high-rate charging and discharging conditions are facing severe challenges. As one of the key components of the battery, the performance of the diaphragm directly affects the fast charging capacity, thermal stability and cycle life of the lithium ion battery.

[0003] At present, although the commercial diaphragm (such as PE, PP, etc.) has good chemical stability and low cost, it still has the following technical bottlenecks in the fast charging process: 1) insufficient flexibility: during high-rate charging and discharging, uneven current distribution and lithium dendrite growth are easily generated inside the lithium ion battery, resulting in local stress concentration of the diaphragm. The traditional polyolefin diaphragm has poor flexibility, and it is difficult to effectively adapt to the volume change of the electrode, and micro-cracks may occur after long-term cycling, increasing the risk of internal short circuit. 2) limited thermal stability: the heat generation of the battery is intensified during fast charging, and the melting point of the polyolefin diaphragm is relatively low (PE about 130℃, PP about 160℃), which is easy to shrink or even melt at high temperature, causing thermal runaway. Although the ceramic coated diaphragm can partially improve the heat resistance, the interface bonding strength between the coating and the base film is insufficient, which may lead to the peeling of the coating and reduce the long-term reliability. 3) contradiction between mechanical strength and porosity: in order to improve the fast charging performance, the diaphragm needs to have high ionic conductivity (high porosity) and puncture resistance. However, the traditional diaphragm often sacrifices the mechanical strength while improving the porosity, and it is difficult to balance the lithium ion transmission efficiency and dendrite puncture protection requirements.

[0004] Therefore, it is of great significance to develop a diaphragm with excellent flexibility, high thermal stability and high mechanical strength for realizing safe and fast charging of lithium ion batteries. SUMMARY

[0005] In view of the deficiencies in the prior art, the purpose of the present application is to provide a modified diaphragm, a preparation method thereof and a lithium ion battery. The olefin polymer with pyrrolopyrimidine heterocyclic group, aromatic ring group and siloxyl group is used in the functional layer of the diaphragm, which balances the mechanical strength and flexibility of the modified diaphragm on the basis of ensuring the fast charging performance of the battery, improves the thermal stability and ion transmission efficiency of the modified diaphragm, and also enhances the electrolyte wettability.

[0006] In order to achieve the purpose of the present application, the following technical solutions are adopted:

[0007] In a first aspect, the present application provides a modified separator, which comprises a base film and a functional layer on at least one side surface of the base film; the functional layer comprises an olefin polymer material.

[0008] The olefin polymer material comprises a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group.

[0009] The following is a preferred technical solution of the present application, but not as a limitation of the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0010] Preferably, the functional layer further comprises an inorganic oxide material.

[0011] Preferably, the mass ratio of the olefin polymer material to the inorganic oxide material is (20-35):(5-18).

[0012] Preferably, the inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material, and the median particle size D50 of the first inorganic oxide material is smaller than the median particle size D50 of the second inorganic oxide material.

[0013] Preferably, the median particle size D50 of the first inorganic oxide material is 8-20 nm.

[0014] Preferably, the median particle size D50 of the second inorganic oxide material is 30-60 nm.

[0015] Preferably, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(2-3), and the first inorganic oxide material is filled in the interstitial gap of the second inorganic oxide material.

[0016] Preferably, the second inorganic oxide material comprises a mesoporous inorganic oxide material, and the pore volume of the mesoporous inorganic oxide material is 1 cm 3 / g-1.3 cm 3 / g.

[0017] Preferably, the first inorganic oxide material comprises ZrO2, and the second inorganic oxide material comprises mesoporous TiO2.

[0018] Preferably, the weight average molecular weight of the olefin polymer material is 60,000-2,000,000.

[0019] Preferably, the olefin polymer material further comprises an amine group.

[0020] Preferably, in the olefin polymer material, the molar ratio of pyrrolopyrimidine heterocyclic groups, aromatic ring groups and siloxy groups is 1:1:(0.8~1.2), more preferably 1:1:1.

[0021] Preferably, the olefin polymer material includes poly7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidine-4-amine.

[0022] Preferably, the thickness of the functional layer is 1μm to 4μm.

[0023] Preferably, the total thickness of the modified diaphragm is 7μm to 16μm.

[0024] Preferably, the functional layer further includes an adhesive.

[0025] Secondly, this application provides a method for preparing the modified diaphragm as described in the second aspect, the method comprising the following steps:

[0026] The modified diaphragm is obtained by coating a functional layer slurry onto at least one side of the base membrane.

[0027] The functional layer slurry comprises an olefin polymer material and a solvent; the olefin polymer material contains pyrrolopyrimidine heterocyclic groups, aromatic ring groups, and siloxy groups.

[0028] Preferably, the coating method includes any one or a combination of at least two of the following: blade coating, extrusion coating, spray coating, spin coating, roll coating, or microgravure printing coating, with microgravure printing coating being the most preferred.

[0029] Preferably, the monomer of the olefin polymer material includes 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidine-4-amine.

[0030] Preferably, the functional layer slurry further includes any one or a combination of at least two of the following: wetting agent, dispersant, inorganic oxide material, and binder.

[0031] Preferably, in the functional layer slurry, the mass ratio of olefin polymer material, inorganic oxide material, solvent, wetting agent, dispersant and binder is (20~35):(0~18):(42~72):(0~0.08):(0~0.3):(0~6), and more preferably (20~35):(5~18):(42~72):(0.02~0.08):0.1~0.3):(2~6).

[0032] Preferably, after the coating, a drying process is performed.

[0033] In a third aspect, the present application further provides a lithium ion battery, comprising a positive electrode, a modified separator as described in the first aspect or prepared by the method as described in the second aspect, a negative electrode and an electrolyte.

[0034] Preferably, the positive electrode active material in the positive electrode comprises a high-nickel positive electrode material, and the negative electrode active material in the negative electrode comprises a silicon-based negative electrode material.

[0035] Preferably, the electrolyte comprises an organic solvent and a main lithium salt.

[0036] Preferably, the electrolyte further comprises an electrolyte additive and / or an auxiliary lithium salt.

[0037] Compared with the prior art, the present application has the following beneficial effects:

[0038] In the present application, the olefin-based polymer material of the pyrrolopyrimidine heterocyclic group, the aromatic ring group and the siloxyl group is used in the functional layer of the base film surface, and the olefin-based polymer material can also provide adhesion to achieve good compounding of the base film and the functional layer, and a separator with excellent flexibility, high thermal stability and high mechanical strength is obtained, and the electrolyte has good wettability and high ion transport performance, and the fast charging performance of the battery is also fully played; in the molecular structure, the pyrrolopyrimidine heterocyclic ring and the aromatic ring provide a rigid skeleton, which can improve the thermal stability and mechanical strength of the coating, and the siloxyl group as a flexible segment improves the flexibility of the film and forms a weak interaction with the electrolyte through the siloxyl bond, enhances the wettability, and also coordinates lithium ions and promotes ion conduction, thereby improving the initial efficiency, fast charging performance and cycle performance of the battery. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only used to help understand the present application, and should not be regarded as specific limitations on the present application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the present application; the terms "comprise" and "have" and any variations thereof in the present application are intended to cover non-exclusive inclusion.

[0041] In the description of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is two or more, unless otherwise explicitly specified.

[0042] The prior art attempts to improve the performance of the separator by composite modification (such as the introduction of aramid, PI and other high-heat-resistant materials) or structural design (such as a three-dimensional porous skeleton), but there are still problems such as complex process, high cost or decreased electrolyte wettability.

[0043] To solve the above problems, the present application proposes the following solutions:

[0044] In one embodiment, the first aspect of the present application provides a modified separator, which comprises a base film and a functional layer located on at least one side surface of the base film; the functional layer comprises an olefin-based polymer material;

[0045] The olefin-based polymer material has a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group.

[0046] In the present application, the olefin-based polymer material with a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group is used in the functional layer on the surface of the base film, and the olefin-based polymer material can also provide a bonding effect, achieving good compounding of the base film and the functional layer, obtaining a separator with excellent flexibility, high thermal stability and high mechanical strength, good electrolyte wettability, high ion transport performance, and also ensuring that the fast charging performance of the battery is fully played; in its molecular structure, the pyrrolopyrimidine heterocyclic group and the aromatic ring provide a rigid skeleton, which can improve the thermal stability and mechanical strength of the coating, while the siloxy group as a flexible segment improves the flexibility of the film and forms a weak interaction with the electrolyte through the siloxy bond, enhances the wettability, and also coordinates lithium ions and promotes ion conduction, thereby improving the initial efficiency, fast charging performance and cycle performance of the battery.

[0047] In the olefin polymer material of the present application, the various groups cooperate and act together to achieve simultaneous improvement in performance.

[0048] The following is a preferred technical solution of the present application, but is not a limitation on the technical solutions provided by the present application. Through the following preferred technical solution, the technical purpose and beneficial effects of the present application can be better achieved and realized.

[0049] In some embodiments, the functional layer further comprises an inorganic oxide material.

[0050] The functional layer is formed on the basis of the olefin polymer material in the application by additionally adding inorganic oxide material, wherein the inorganic oxide material is dispersed in the olefin polymer material to form an organic-inorganic functional layer network structure, and the inorganic oxide material further provides rigidity and thermal barrier of the functional layer, and the olefin polymer material plays a bonding effect and provides stress buffering between particles, thereby achieving good improvement of high-temperature thermal shrinkage resistance of the modified separator and stress buffering during negative electrode expansion.

[0051] In some embodiments, the mass ratio of the olefin polymer material to the inorganic oxide material is (20-35):(5-18), for example, 20:5, 20:10, 20:18, 25:5, 25:10, 25:18, 35:5, 35:10 or 35:18, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0052] In the application, by adjusting the mass ratio of the olefin polymer material to the inorganic oxide material to be (20-35):(5-18), it is more conducive to completely wrapping the inorganic particles with the polymer, avoiding agglomeration of the inorganic particles, and at the same time, the coating has strong adhesion, the puncture strength and rigid support of the separator are also excellent, and the pores are not blocked, ensuring the liquid absorption effect of the separator, and also balancing the thermal stability and ion transmission.

[0053] In some embodiments, the inorganic oxide material includes a first inorganic oxide material and a second inorganic oxide material, and the median particle size D50 of the first inorganic oxide material is smaller than the median particle size D50 of the second inorganic oxide material.

[0054] In some embodiments, the median particle size D50 of the first inorganic oxide material is 8-20 nm, for example, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm or 20 nm, etc.

[0055] In some embodiments, the median particle size D50 of the second inorganic oxide material is 30-60 nm, for example, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm or 60 nm, etc.

[0056] In some embodiments, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(2-3), for example, 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5, 1:2.6, 1:2.7, 1:2.8, 1:2.9 or 1:3, etc., and the first inorganic oxide material is filled in the interstitial gap of the second inorganic oxide material.

[0057] It is worth noting that the present application adopts the form of a double inorganic oxide material in the functional layer, and by the first inorganic oxide material having a median particle size D50 that is less than the median particle size D50 of the second inorganic oxide material, and further by the mass ratio of the first inorganic oxide material to the second inorganic oxide material being 1:(2~3), the relatively small particle size of the first inorganic oxide material fills the gaps in the relatively large particle size of the second inorganic oxide material, thereby further optimizing the porosity of the modified separator, shortening the lithium ion transmission particle size, and improving the battery performance; further, preferably the first inorganic oxide material has a median particle size D50 of 8nm~20nm and / or the second inorganic oxide material has a median particle size D50 of 30nm~60nm, which ensures the gradation of the size of the particle size, and also helps the inorganic oxide material to be uniformly dispersed in the olefin-based polymer material, better playing the synergistic effect of the two.

[0058] In some embodiments, the second inorganic oxide material comprises a mesoporous inorganic oxide material, and the mesoporous inorganic oxide material has a pore volume of 1cm 3 / g~1.3cm 3 / g, such as 1cm 3 / g, 1.05cm 3 / g, 1.1cm 3 / g, 1.15cm 3 / g, 1.2cm 3 / g, 1.25cm 3 / g, or 1.3cm 3 / g, etc.

[0059] It can be understood that the mesoporous inorganic oxide material with a high pore volume of 1cm 3 / g~1.3cm 3 / g is selected as the second inorganic oxide material in the present application, which also has the effect of adsorbing electrolyte and improving the liquid absorption rate of the separator.

[0060] In some embodiments, the first inorganic oxide material comprises ZrO2, and the second inorganic oxide material comprises mesoporous TiO2.

[0061] For the technical solution of the present application, through the excellent synergistic effect of the olefin-based polymer material, ZrO2, and mesoporous TiO2, the performance improvement effect is more excellent compared to other inorganic oxide materials.

[0062] In some embodiments, the weight average molecular weight of the olefin-based polymer material is 600,000 to 2,000,000, such as 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,100,000, 1,200,000, 1,300,000, 1,400,000, 1,500,000, 1,600,000, 1,700,000, 1,800,000, 1,900,000, or 2,000,000, etc.

[0063] In the present application, the olefin-based polymer material has a weight average molecular weight of 600,000 to 2,000,000, which is beneficial to the film formation of the functional layer, improves the adhesion between the functional layer and the base film, and also ensures that the mechanical strength does not become brittle due to the increase of the number average molecular weight, and at the same time, the functional layer has sufficient flexibility, achieving a good balance of viscosity, mechanical strength and flexibility.

[0064] In some embodiments, the olefin-based polymer material further comprises an amine group.

[0065] In some preferred embodiments, the olefin-based polymer material in the present application further has an amine group, which can coordinate lithium ions as a polar site and promote ion conduction.

[0066] In some embodiments, the molar ratio of the pyrrolopyrimidine heterocyclic group, the aromatic ring group and the siloxy group in the olefin-based polymer material is 1:1:(0.8-1.2), such as 1:1:0.8, 1:1:1, 1:1:1.2, and preferably 1:1:1.

[0067] In the olefin-based polymer material of the present application, the pyrrolopyrimidine heterocyclic group, the aromatic ring group and the siloxy group complement each other and work together, and when the molar ratio is 1:1:(0.8-1.2), the performance balance of the rigidity and thermal stability of the functional layer is ensured.

[0068] In some embodiments, the olefin-based polymer material comprises poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine.

[0069] It should be noted that the present application does not specially limit the specific source and specific preparation process of the olefin-based polymer material, and any conventional polymerization process that meets the olefin-based polymer material in the present application is applicable to the present application without deviating from the inventive concept of the present application.

[0070] It can be understood that the monomer material of poly 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine in the present application is 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine; wherein the alkenyl group is located at the ortho position of the pyrrolopyrimidine heterocyclic group, forming an orthogonal arrangement with the p-tolyl group (i.e. aromatic ring) at position 5, avoiding excessive steric hindrance, and facilitating the improvement of crosslinking efficiency during polymerization.

[0071] To this end, the present application exemplarily provides a polymerization process of poly 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine:

[0072] Mix 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine (CAS: 821794-86-9), initiator and first solvent, and perform free radical polymerization process under the action of photo initiation, i.e. the polymerization process of carbon-carbon double bond breakage in ethoxyvinyl, to obtain the desired olefin polymer material with a certain weight average molecular weight.

[0073] Optionally, the initiator includes AIBN (azobisisobutyronitrile), the first solvent includes toluene, and the photo initiation includes ultraviolet light irradiation initiation; the polymerization temperature is 60°C~80°C.

[0074] Optionally, the results of polymerization are confirmed by NMR (checking the disappearance of vinyl group), GPC (molecular weight distribution), and FT-IR (functional group change).

[0075] Optionally, after the polymerization is completed, a post-treatment process such as purification can be performed.

[0076] In some embodiments, the thickness of the functional layer is 1 μm~4 μm, for example, 1 μm, 2 μm, 3 μm or 4 μm, etc., but is not limited to the listed values, and other unlisted values within this range are also applicable.

[0077] It is found through research that a suitable thickness of the functional layer can better play its role, and regulating to 1 μm-4 μm can avoid the problems of incomplete coating of the coating on the base film, insufficient buffering / protection of the expansion of the negative electrode, limited improvement of thermal stability, and insignificant improvement of Li+ transmission, while also preventing the problems of increasing the total thickness of the separator and the internal resistance, reducing the energy density and power density of the battery, causing the gas permeability (Gurley value) to be too high to affect the electrolyte infiltration and ion transmission, and increasing the cost.

[0078] In some embodiments, the total thickness of the modified separator is 7 μm-16 μm, for example, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, or 16 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0079] In some embodiments, the thickness of the base film is 6 μm-12 μm, for example, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, or 12 μm, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0080] In some embodiments, the total porosity of the modified separator is 45%-60%, for example, 45%, 50%, 55%, or 60%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0081] In this application, the total thickness of the modified separator is further regulated to 7 μm-16 μm and / or the thickness of the base film is 6 μm-12 μm and / or the total porosity of the modified separator is 45%-60%, which realizes the good performance of the modified separator with moderate thickness, porosity, high mechanical strength, excellent thermal stability, and high liquid absorption rate.

[0082] For the modified separator of the present application, the specific type of the base film is not additionally limited in the present application, and all types of base films suitable for the battery separator system are applicable in principle without deviating from the inventive concept of the present application; for example, the base film can be a single-layer olefin base film such as a polyethylene (PE) base film or a polypropylene (PP base film), or a multi-layer composite olefin base film such as a PP / PE / PP laminated combination layer structure.

[0083] In some embodiments, the functional layer further comprises a binder.

[0084] It can be understood that, in the functional layer of the present application, a binder can be additionally added, on the one hand to increase the bonding strength, and on the other hand to play a thickening role, the amine group (-NH-) of the polymer forms a hydrogen bond, which cooperatively improves the peeling strength of the coating and the base film (from 2 N / m to >4 N / m); at the same time, the thickening effect makes the viscosity of the slurry stable at 2000-3000 mPa⁺s, avoiding coating sagging.

[0085] In one embodiment, the present application provides a preparation method of the modified separator as described in the second aspect, comprising the following steps:

[0086] coating a functional layer slurry on at least one side of the surface of the base film to obtain the modified separator;

[0087] The functional layer slurry comprises an olefin-based polymer material and a solvent; the olefin-based polymer material has a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group.

[0088] In the preparation method of the present application, there is no need for a complex processing process, and an excellent modified separator structure can be obtained by simple coating, and the base film and the functional layer are tightly combined.

[0089] In some embodiments, the coating method comprises any one or a combination of at least two of blade coating, extrusion coating, spraying, spin coating, roller coating or micro-gravure printing coating, preferably micro-gravure printing coating.

[0090] In the present application, the method of micro-gravure printing coating is preferably used for coating the functional layer slurry, which can further improve the thickness uniformity and also better improve the cycle performance of the battery.

[0091] Notably, the method of micro-gravure printing coating in the present application comprises adjusting its preparation parameters to adapt to the coating effect of the functional layer slurry.

[0092] Optionally, in the micro-gravure printing method, the line number of the anilox roller is 150 lines / cm to 200 lines / cm, such as 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm or 200 lines / cm, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0093] Optionally, in the micro-gravure printing method, the coating speed is 10 m / min to 29 m / min, such as 12 m / min, 15 m / min, 18 m / min, 20 m / min, 23 m / min, 25 m / min, 28 m / min or 29 m / min, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0094] Optionally, in the microgravure printing method, the printing gap is 0.1 mm to 0.3 mm, such as 0.1 mm, 0.2 mm, or 0.3 mm, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0095] Optionally, in the microgravure printing method, the doctor blade angle is 45° to 65°, such as 45°, 50°, 55°, 60°, or 65°, but is not limited to the listed values, and other values not listed in the range are also applicable.

[0096] In some embodiments, the monomer of the olefinic polymeric material comprises 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine.

[0097] In some embodiments, the functional layer slurry further comprises any one or a combination of at least two of a wetting agent, a dispersant, an inorganic oxide material, and a binder.

[0098] It can be understood that the specific types of the binder, the wetting agent, the dispersant, and the solvent in the functional layer slurry of the present application are selected according to conventional techniques, and any substance suitable for the functional layer slurry of the separator that can be known by a person skilled in the art within a reasonable range without departing from the inventive concept of the present application is applicable.

[0099] For example, the binder includes, but is not limited to, at least one of carboxymethyl cellulose (CMC) / hydroxypropyl methyl cellulose (HPMC) or polyvinyl alcohol (PVA).

[0100] For example, the wetting agent includes, but is not limited to, at least one of sodium hexametaphosphate, sodium tripolyphosphate, or sodium pyrophosphate, and the main function of the wetting agent is to reduce the surface tension and enhance the flowability of the slurry.

[0101] For example, the dispersant includes, but is not limited to, at least one of a silicate dispersant, sodium polyacrylate, or sodium citrate.

[0102] For example, the solvent includes water and isopropyl alcohol.

[0103] In some embodiments, the mass ratio of the olefin polymer material, the inorganic oxide material, the solvent, the wetting agent, the dispersant and the binder in the functional layer slurry is (20-35):(0-18):(42-72):(0-0.08):(0-0.3):(0-6), preferably (20-35):(5-18):(42-72):(0.02-0.08):0.1-0.3):(2-6), such as 20:18:42:0.02:0.1:2, 35:18:71:0.08:0.3:6, 20:18:71:0.08:0.3:6, 35:18:42:0.02:0.1:2, 25:15:60:0.04:0.2:4, and the like, but not limited to the listed values, other values not listed in the range are also applicable.

[0104] It should be noted that the preparation process of the functional slurry is not unique, and a slurry system suitable for coating can be obtained.

[0105] Exemplarily, the present application provides a preparation process of a functional slurry:

[0106] The dispersant and water are first mixed, and then the inorganic oxide material is added for second mixing to obtain a second mixed solution; the remaining raw materials such as the polymer material, the binder and the additive are added again for third mixing in the second mixed solution to obtain a functional layer slurry.

[0107] Optionally, all the mixing processes can be simultaneously subjected to ultrasonic treatment.

[0108] In addition, the parameters in the mixing process can be adaptively selected and adjusted by those skilled in the art according to actual needs.

[0109] For example, the rotation speed in the mixing process can be independently 2000r / min-3100r / min, such as 2000r / min, 2300r / min, 2500r / min, 2800r / min, 3000r / min or 3100r / min, and the revolution speed can be independently 20r / min-40r / min, such as 20r / min, 25r / min, 30r / min, 35r / min or 40r / min, but not limited to the listed values, other values not listed in the range are also applicable.

[0110] In some embodiments, after the coating, a drying process is performed.

[0111] After the slurry coating is completed, a drying process is inevitably required, and the air speed and the drying temperature in the drying process are controlled to facilitate the rapid evaporation of the solvent on the coating surface and the absence of flow marks.

[0112] For example, the wind speed can be 15 m / s to 25 m / s, such as 12 m / s, 15 m / s, 18 m / s, 20 m / s, 23 m / s, or 25 m / s, etc., and the drying temperature can be 40℃ to 80℃, such as 40℃, 50℃, 60℃, 70℃, or 80℃, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0113] Meanwhile, when winding after drying, the winding tension can be controlled to be 10 N / m to 15 N / m, such as 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, or 15 N / m, etc., but not limited to the listed values, and other values not listed in the value range are also applicable.

[0114] In one embodiment, the third aspect of the present application also provides a lithium ion battery, which comprises a positive electrode, a modified separator as described in the first aspect or a modified separator prepared by the preparation method as described in the second aspect, a negative electrode, and an electrolyte.

[0115] In some embodiments, the positive active material in the positive electrode comprises a high-nickel positive material, and the negative active material in the negative electrode comprises a silicon-based negative material.

[0116] In the high-nickel-silicon-based battery system, although the fast-charging performance is excellent, the requirements for the separator are also higher due to the expansion problem of silicon; and the modified separator structure in the present application can well solve the volume expansion problem of the silicon-based negative active material and improve the interfacial compatibility between the modified separator and the negative electrode.

[0117] It can be understood that the silicon-based negative material described in the present application is a conventional silicon system negative material, such as pure silicon material, silicon-carbon negative material, and silicon-oxygen negative material, etc., and the source of the silicon-based negative material can be prepared by a conventional technical solution, or directly purchased by a commercial means.

[0118] The high-nickel positive material comprises a doped or coated nickel-cobalt-manganese positive material, a nickel-cobalt-aluminum positive material, or a cobalt-free nickel-manganese positive material, etc., and the molar proportion of nickel in the main elements is ≥80%, such as in the nickel-cobalt-manganese positive material, the main elements are nickel + cobalt + manganese.

[0119] In some embodiments, the electrolyte comprises an organic solvent and a main lithium salt.

[0120] In some embodiments, the organic solvent can include at least one of a carbonate compound, a carboxylate compound, an ether compound, a sulfone compound. As an example, the solvent can include, but is not limited to, at least one of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone, sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), diethyl sulfone (ESE), methylsulfolane, dimethyl sulfoxide, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, dimethyl ether, diethyl ether, nitromethane, N,N-dimethylformamide. The above-mentioned solvents can be used alone, or two or more of them can be used simultaneously.

[0121] In some embodiments, the main lithium includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6). The above-mentioned electrolyte salts can be used alone, or two or more of them can be used simultaneously.

[0122] In some embodiments, the electrolyte further includes an electrolyte additive and / or an auxiliary lithium salt.

[0123] In some embodiments, the auxiliary lithium salt includes a lithium lithium salt of sulfonimide, and the mass percentage of the auxiliary lithium salt in the electrolyte is 1% to 3%, for example, 1%, 2% or 3%, etc., but is not limited to the listed values, and other values not listed in this range are also applicable.

[0124] The addition of a lithium lithium salt of sulfonimide, such as lithium bis(fluorosulfonyl)imide LiFSI or lithium bis(trifluoromethanesulfonyl)imide LiTFSI, etc., further reduces the interface impedance of the battery, and plays a synergistic role with the modified separator.

[0125] In some embodiments, the electrolyte additive includes a phosphate ester additive and / or a low impedance additive, and the mass percentage of the electrolyte additive in the electrolyte is 0.1% to 1.5%, for example, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, or 1.5%, etc., but not limited to the listed values, and other values not listed in the range are also applicable.

[0126] In the presence of the base electrolyte, the electrolyte additive, the phosphate ester additive and / or the low impedance additive can also be added, and the modified separator can also work together to further improve the rate performance of the battery.

[0127] Specifically, the phosphate ester additive includes but is not limited to tris(4-nitrophenyl) phosphate, and the low impedance additive includes but is not limited to lithium bis(oxalato)borate (LiBOB).

[0128] In some embodiments, the positive electrode can include a positive electrode current collector and a positive electrode active material layer disposed on at least one side of the positive electrode current collector; and the negative electrode can include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0129] In some embodiments, the shape of the positive electrode current collector and the negative electrode current collector can be plate-shaped or foil-shaped, and the embodiments of the present application are not limited thereto.

[0130] In some embodiments, the material of the positive electrode current collector and the negative electrode current collector is not particularly limited, and a material having electronic conductivity can be selected. For example, a simple substance or an alloy containing at least one element selected from C, Ti, Cr, Mo, Ru, Rh, Ta, W, Os, Ir, Pt, Au, and Al (e.g., stainless steel, etc.) can be used.

[0131] From the viewpoint of high conductivity, high stability in electrolyte, and good oxidation resistance, the C layer, Al foil, stainless steel foil, etc. in the positive electrode current collector are optional. The C layer, Cu foil, etc. in the negative electrode current collector are optional. From the viewpoint of further reducing production costs, the Al foil in the positive electrode current collector is more preferred, and the Cu foil in the negative electrode current collector is more preferred; further, those skilled in the art can make adaptive adjustment and selection according to the actual situation.

[0132] Example 1

[0133] This embodiment provides a modified separator, which includes a PE base film (thickness of 8 μm) and a functional layer (thickness of 4 μm) located on both sides of the base film, and the total thickness of the modified separator is 16 μm, and the porosity is 55%.

[0134] The functional layer comprises an olefin polymer material poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine with a weight average molecular weight of 100,000, a first inorganic oxide material ZrO2 (D50 of 15 nm), and a second inorganic oxide material mesoporous TiO2 (D50 of 45 nm and pore volume of 1.3 cm 3 / g);

[0135] The mass ratio of the poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine to all inorganic oxide materials is 30:15;

[0136] The mass ratio of the first inorganic oxide material ZrO2 to the second inorganic oxide material mesoporous TiO2 is 1:2.

[0137] The preparation method of the modified separator comprises:

[0138] S1: first blend the dispersant sodium polyacrylate and the solvent pure water at a stirring speed of 2500 r / min, then blend the first inorganic oxide material and the second inorganic oxide material at a stirring speed of 2500 r / min to obtain a mixed solution, and perform ultrasonic treatment during the second blending, and then blend the solvent isopropyl alcohol, CMC, the olefin polymer material, and the wetting agent sodium hexametaphosphate in the mixed solution and perform vacuum oscillation stirring to prepare a functional layer slurry;

[0139] The mass ratio of the olefin polymer material, all inorganic oxide materials, pure water, wetting agent, dispersant, isopropyl alcohol, and CMC is 30:15:45:0.05:0.2:5:4;

[0140] S2: use a double-sided micro-gravure printing process to perform functional layer wet film coating on the double-sided surfaces of the base film, and during the coating process, the line number of the anilox roller is 180 lines / cm, the coating speed is 25 m / min, the printing gap is 0.2 mm, and the doctor blade angle is 55°, to obtain the functional layer wet film on the double-sided surfaces of the base film.

[0141] S3: dry the functional layer wet film obtained in step S3 at 60°C, and during the drying process, the air speed is 15 m / s, and the winding tension after drying is 10 N / m, to obtain the modified separator.

[0142] Example 2

[0143] The embodiment provides a modified diaphragm, which comprises a PE base film (6 μm in thickness) and functional layers (1 μm in thickness) located on two sides of the base film, the total thickness of the modified diaphragm is 8 μm, and the porosity is 45%;

[0144] The functional layer comprises an olefin polymer material poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine with a weight average molecular weight of 60,000, a first inorganic oxide material ZrO2 (D50 is 20 nm), and a second inorganic oxide material mesoporous TiO2 (D50 is 60 nm, and pore volume is 1.1 cm 3 / g);

[0145] The mass ratio of the poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine and all inorganic oxide materials is 20:18;

[0146] The mass ratio of the first inorganic oxide material ZrO2 and the second inorganic oxide material mesoporous TiO2 is 1:3.

[0147] The preparation method of the modified diaphragm comprises the following steps:

[0148] S1: first, the dispersant sodium polyacrylate and the solvent pure water are stirred and blended at a rotating speed of 2500 r / min once, then the first inorganic oxide material and the second inorganic oxide material are stirred and blended at a rotating speed of 2500 r / min twice to obtain a mixed solution, and ultrasonic is performed simultaneously in the process of the second stirring and blending, after the second stirring, the solvent isopropyl alcohol, CMC, the olefin polymer material and the wetting agent sodium hexametaphosphate are added into the mixed solution and stirred and blended by vacuum oscillation to prepare a functional layer slurry;

[0149] The mass ratio of the olefin polymer material, all inorganic oxide materials, pure water, wetting agent, dispersant, isopropyl alcohol and CMC is 20:18:40:0.08:0.1:2:2;

[0150] S2: the functional layer slurry in step S1 is used to perform functional layer wet film coating on the two sides of the base film by adopting a double-sided micro-gravure printing process, in the coating process, the line number of the anilox roll is 150 lines / cm, the coating speed is 10 m / min, the printing gap is 0.3 mm, and the doctor blade angle is 65°, so that the functional layer wet film on the two sides of the base film is obtained.

[0151] S3: drying the functional layer wet film obtained in step S3 at 40℃, the wind speed during the drying process is 25m / s, and the winding tension after drying is 15N / m, to obtain the modified separator.

[0152] Example 3

[0153] The modified separator provided in this example includes a PE base film (thickness of 7μm) and a functional layer (thickness of 2μm) on both sides of the base film, the total thickness of the modified separator is 11μm, and the porosity is 60%;

[0154] The functional layer includes an olefin polymer material poly7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine with a weight average molecular weight of 200,000, a first inorganic oxide material ZrO2 (D50 of 8nm), and a second inorganic oxide material mesoporous TiO2 (D50 of 60nm and pore volume of 1.2cm 3 / g);

[0155] The mass ratio of the poly7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine to all inorganic oxide materials is 35:5;

[0156] The mass ratio of the first inorganic oxide material ZrO2 to the second inorganic oxide material mesoporous TiO2 is 1:1.5.

[0157] The preparation method of the modified separator includes:

[0158] S1: first blend the dispersant sodium polyacrylate and the solvent pure water at a rotation speed of 2500r / min, then blend the first inorganic oxide material and the second inorganic oxide material at a rotation speed of 2500r / min to obtain a mixed solution, and perform ultrasonic treatment during the second blending process, then blend the solvent isopropyl alcohol, CMC, the olefin polymer material, and the wetting agent sodium hexametaphosphate in the mixed solution after the second blending, and perform vacuum oscillation blending to prepare a functional layer slurry;

[0159] The mass ratio of the olefin polymer material, all inorganic oxide materials, pure water, wetting agent, dispersant, isopropyl alcohol, and CMC is 35:5:66:0.08:0.3:3:6;

[0160] S2: the functional layer slurry of step S1 is used to perform functional layer wet film coating on both sides of the base film by double-sided micro-concave printing process, during the coating process, the number of lines of the screen roller is 200 lines / cm, the coating speed is 29 m / min, the printing gap is 0.1 mm, and the doctor blade angle is 455°, to obtain the functional layer wet film on both sides of the base film;

[0161] S3: the functional layer wet film obtained in step S3 is dried at 60°C, the wind speed during the drying process is 15 m / s, and the winding tension after drying is 10 N / m, to obtain the modified separator.

[0162] Example 4

[0163] The difference between this example and Example 1 is that the weight average molecular weight of the olefin-based polymer material in this example is 60,000.

[0164] The remaining conditions are consistent with Example 1.

[0165] Example 5

[0166] The difference between this example and Example 1 is that the weight average molecular weight of the olefin-based polymer material in this example is 200,000.

[0167] The remaining conditions are consistent with Example 1.

[0168] Example 6

[0169] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material ZrO2 and the second inorganic oxide material mesoporous TiO2 in this example is 1:1.

[0170] The remaining conditions are consistent with Example 1.

[0171] Example 7

[0172] The difference between this example and Example 1 is that the pore volume of the second inorganic oxide material mesoporous TiO2 in this example is 1 cm 3 / g.

[0173] The remaining conditions are consistent with Example 1.

[0174] Example 8

[0175] The difference between this example and Example 1 is that the weight average molecular weight of the olefin-based polymer material in this example is 50,000.

[0176] The remaining conditions are consistent with Example 1.

[0177] Example 9

[0178] The difference between this example and Example 1 is that the weight average molecular weight of the olefinic polymer material in this example is 210,000.

[0179] The remaining conditions are the same as Example 1.

[0180] Example 10

[0181] The difference between this example and Example 1 is that the mass ratio of the total mass of the olefinic polymer material to all inorganic oxide materials in this example is 20:20.

[0182] The remaining conditions are the same as Example 1.

[0183] Example 11

[0184] The difference between this example and Example 1 is that the mass ratio of the total mass of the olefinic polymer material to all inorganic oxide materials in this example is 35:1.

[0185] The remaining conditions are the same as Example 1.

[0186] Example 12

[0187] The difference between this example and Example 1 is that the first inorganic oxide material in this example is MgO and the second inorganic oxide material is mesoporous ZnO.

[0188] The remaining conditions are the same as Example 1.

[0189] Example 13

[0190] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material ZrO2 to the second inorganic oxide material mesoporous TiO2 in this example is 1:0.5.

[0191] The remaining conditions are the same as Example 1.

[0192] Example 14

[0193] The difference between this example and Example 1 is that the mass ratio of the first inorganic oxide material ZrO2 to the second inorganic oxide material mesoporous TiO2 in this example is 1:2.5.

[0194] The remaining conditions are the same as Example 1.

[0195] Example 15

[0196] The difference between this example and Example 1 is that the inorganic oxide material in this example only contains the first inorganic oxide material ZrO2.

[0197] The remaining conditions are the same as Example 1.

[0198] Example 16

[0199] The difference between this example and Example 1 is that the inorganic oxide material in this example contains only the second inorganic oxide material mesoporous Ti02.

[0200] The remaining conditions are the same as Example 1.

[0201] Example 17

[0202] The difference between this example and Example 1 is that the functional layer in this example does not contain an inorganic oxide material, including the first inorganic oxide material and the second inorganic oxide material.

[0203] The remaining conditions are the same as Example 1.

[0204] Example 18

[0205] The difference between this example and Example 1 is that the mesoporous Ti02in this example has a pore volume of 0.8 cm3 / g. 3

[0206] The remaining conditions are the same as Example 1.

[0207] Example 19

[0208] The difference between this example and Example 1 is that the mesoporous Ti02in this example has a pore volume of 1.5 cm3 / g. 3

[0209] The remaining conditions are the same as Example 1.

[0210] Comparative Example 1

[0211] The difference between this comparative example and Example 1 is that the functional layer in this comparative example does not contain an olefin-based polymer material.

[0212] The remaining conditions are the same as Example 1.

[0213] Comparative Example 2

[0214] The difference between this comparative example and Example 1 is that the olefin-based polymer in the functional layer in this comparative example is polystyrene (CAS: 9003-53-6).

[0215] The remaining conditions are the same as Example 1.

[0216] Comparative Example 3

[0217] ​​The difference between the present comparative example and Example 1 is that the olefin-based polymer in the functional layer of the present comparative example is polyvinyltrimethoxysilane, and the monomer is vinyltrimethoxysilane (CAS: 2768-02-7), which is free radical polymerization of a carbon-carbon double bond therein.

[0218] The remaining conditions are consistent with Example 1.

[0219] Comparative Example 4

[0220] The difference between the present comparative example and Example 1 is that the modified separator in the present comparative example is a PE-based film.

[0221] Application Example 1

[0222] The present application example provides a lithium ion battery, and a preparation method of the lithium ion battery is as follows:

[0223] (1) Preparation of the positive electrode sheet:

[0224] The ternary material NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2) positive active material, the binder PVDF (polyvinylidene fluoride), the conductive agent SP (conductive carbon black Super-P), and the SWCNT (single-walled carbon nanotube) are mixed and stirred uniformly at a mass ratio of 96:2:1.9:0.1 to obtain a positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil through a coating process, and the positive electrode sheet is obtained after a drying and cold pressing process.

[0225] (2) Preparation of the negative electrode sheet

[0226] The silicon-carbon negative electrode material, the conductive agent SP (conductive carbon black Super-P), the SWCNT (single-walled carbon nanotube), the binder PAA (polyacrylic acid), and the SBR are mixed and stirred uniformly at a mass ratio of 90:2:0.5:5:2.5 to obtain a negative electrode slurry, and the solid content is controlled to be 30%, and then the negative electrode slurry is coated on a copper foil current collector through a coating process, and the negative electrode sheet is obtained after a vacuum drying and cold pressing process.

[0227] (3) Selection of the electrolyte

[0228] The organic solvents ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, and fluoroethylene carbonate are mixed at a mass ratio of 15:20:25:30:10, and then LiPF6 is added to make the concentration thereof be 1 mol / L, and the electrolyte is obtained.

[0229] (4) Selection of the separator

[0230] The modified separator provided in Example 1 is used as the separator.

[0231] (5) Preparation of lithium ion battery

[0232] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode sheet and the negative electrode sheet to play a separating role, and then wound to obtain a bare battery cell; the bare battery cell is placed in an outer packaging shell, electrolyte is injected after drying, and a lithium ion battery is obtained through processes such as vacuum packaging, standing, formation, and shaping.

[0233] Application Example 2-19 and Comparative Application Example 1-4

[0234] The difference between Application Example 2-19 and Comparative Application Example 1-4 and Application Example 1 is that the modified separator provided by Example 2-19 and Comparative Example 1-4 is used as the separator, respectively.

[0235] The remaining conditions are consistent with those of Application Example 1.

[0236] Performance test

[0237] ①The modified separator structure provided by the examples and comparative examples is tested for thermal shrinkage, and the standard test method (GB / T36363) is used. Under a specified temperature (such as 150℃) and time (30min), the size change of the separator sample in a free state is measured, and the thermal shrinkage in the transverse direction (TD) and the longitudinal direction (MD) is calculated. The test conditions are as follows:

[0238] 1) The modified separator sample is placed in an environment of 23±2℃ and humidity of 50±5%RH for 24 hours. After placement, the modified separator is cut 10mm away from the edge to obtain a 100mm×100mm modified separator to be tested;

[0239] 2) The initial size of the modified separator is measured using an optical projector, and a cross line is drawn on the surface of the sample. The initial length L0 in the transverse direction (TD) and the longitudinal direction (MD) is recorded (accurate to 0.1mm);

[0240] 3) Then the modified separator to be tested after the initial size test in step 2) is fixed with a stainless steel frame clamp and placed in the center of a preheated high-temperature furnace at 150℃, ensuring that the sample does not touch the furnace wall; after constant temperature for 30min, the clamp is quickly removed and cooled at room temperature for 10min;

[0241] 4) The cross line length L1 of the sample after cooling is measured (TD and MD directions are measured respectively), 3 parallel samples are tested for each sample, and the average value is taken. The thermal shrinkage in the transverse and longitudinal directions is calculated based on the initial size and the sample after cooling. The calculation formula is: thermal shrinkage (%) = (L0-L1) / L0×100%, and the data results are recorded in Table 1.

[0242] Puncture strength test was performed on the modified separator structure provided by the examples and comparative examples, and the test conditions were as follows:

[0243] 1) Prepare the puncture fixture and blade before measurement;

[0244] 2) Cut the modified separator to be tested with the blade respectively, and the sample is a circular sample with a diameter of 100 mm. Notes: The modified separator must be flawless and free of any defects;

[0245] 3) After checking the cleanliness of the high-iron tension machine, install the puncture fixture, and place the first base film and the second base film in the center of the fixture, and cover the upper cover. Note: The sample must be placed flat without any wrinkles; the sample size must be larger than the puncture fixture, i.e. the sample is tightly pressed by the fixture all around;

[0246] 3) On the computer operation panel of the high-iron tension machine, set the test speed to 50 mm / min;

[0247] 4) Click "Start" to perform the puncture test in sequence, stop puncturing when the base film sample is pierced, and save the force-displacement curve; each group is tested in triplicate, and if the three force-displacement curves have good repeatability, the next sample is tested. Note: The unit of force F is N. Puncture resistance = force F / 9.8x103, unit: gf, the puncture resistance of the modified separator is obtained, and the data results are recorded in Table 1.

[0248] Table 1

[0249] 150°C / 30 min heat shrinkage - TD 150°C / 30 min heat shrinkage - MD Puncture resistance (gf) Example 1 0.5 0.6 2300 Example 2 0.6 0.7 2200 Example 3 0.4 0.5 2400 Example 4 0.7 0.8 2100 Example 5 0.5 0.7 2250 Example 6 0.6 0.8 2150 Example 7 0.5 0.6 2350 Example 8 1.1 1.3 1850 Example 9 1.0 1.2 1900 Example 10 1.3 1.6 1750 Example 11 1.2 1.5 1800 Example 12 1.5 1.8 1700 Example 13 1.0 1.2 1900 Example 14 0.9 1.1 2000 Example 15 1.3 1.6 1750 Example 16 1.1 1.4 1850 Example 17 0.8 1.0 1950 Example 18 1.4 1.7 1650 Example 19 1.3 1.6 1700 Comparative Example 1 3.5 4.2 1200 Comparative Example 2 4.8 5.5 1100 Comparative Example 3 5.2 6 1000 Comparative Example 4 11.9 13.2 900

[0250] ②Test on the LAND battery test system of Wuhan Jinuo Electronics Co., Ltd. at room temperature (25°C), and the specific test conditions are as follows:

[0251] a) First coulomb efficiency

[0252] At 25°C, charge the lithium ion battery to 4.2V at 0.33C rate, stand for 10 min, then discharge the lithium ion battery to 2.5V at 0.33C rate, stand for 10 min, and calculate the first coulomb efficiency of the lithium ion battery.

[0253] First coulomb efficiency (%) = lithium ion battery 0.33C first discharge total capacity / lithium ion battery 0.33C first charge total capacity x 100%.

[0254] b) 1C / 2C cycle capacity retention rate at room temperature for 1000 cycles

[0255] The lithium ion battery was charged at 1C rate to 4.2V at 25°C, and the cutoff current was 0.05C, and was rested for 10 min, then discharged at 2C rate to 2.5V, and was rested for 10 min, which was one charge-discharge cycle. The lithium ion battery was charged and discharged according to the above method for 1000 cycles, and the capacity retention rate of the lithium ion battery after 1000 cycles of 1C / 2C charge-discharge was calculated.

[0256] The capacity retention rate (%) of the lithium ion battery after N cycles = (discharge capacity of the Nth cycle / first discharge capacity) x 100%, and N was the cycle number of the lithium ion battery.

[0257] c) Normal temperature 6C rate performance - constant current charge-in ratio

[0258] The lithium ion battery was discharged at 1C rate to 2.5V at 25°C, and was rested for 10 min, then charged at 6C rate to 4.2V, and the cutoff current was 0.05C, and was rested for 10 min, and the constant current charge capacity Q1 and the total constant voltage charge capacity Q2 of the lithium ion battery were recorded, and the 6C rate charge constant current charge-in ratio was calculated according to the following formula: 6C rate charge constant current charge-in ratio = constant current charge capacity Q1 / total constant voltage charge capacity Q2 x 100%.

[0259] d) Normal temperature 1C / 8C discharge capacity retention rate

[0260] The lithium ion battery was charged at 1C rate to 4.2V at 25°C, and the cutoff current was 0.05C, and was rested for 10 min, then discharged at 2C rate to 2.5V, and was rested for 10 min, which was one charge-discharge cycle. The lithium ion battery was charged and discharged according to the above method for 1000 cycles, and the capacity retention rate of the lithium ion battery after 1000 cycles of 1C / 2C charge-discharge was calculated.

[0261] e) Cell thermal runaway ARC test: start ARC adiabatic thermal runaway test (test sample in the cavity from room temperature to 45±2℃, after 90min, detect the change of battery temperature rise rate, if the temperature rise is more than 0.2℃ (i.e. SHR>0.02℃ / min) within 10min, it is considered that the self-heat reaction occurs inside the battery, and the adiabatic environment is maintained until the battery thermal runaway occurs; if the temperature rise is not more than 0.2℃ (i.e. SHR≤0.02℃ / min) within 10min, continue to the next step temperature rise test; each temperature step is 5℃, repeat the steps at each step, the ARC test temperature range is 45℃~300℃, the self-heat starting temperature is T1 (the temperature rise rate SHR>0.02℃ / min), and the thermal runaway starting temperature is T2 (the temperature rise rate SHR>1℃ / min).

[0262] The battery performance test results are shown in Table 2.

[0263] Table 2

[0264] 0.33C first efficiency (%) Ambient 1C / 2C cycle 1000 cycles capacity retention rate (%) Ambient 6C constant current charge ratio (%) Ambient 1C / 8C discharge capacity retention rate (5) Self-heat starting temperature T1 (°C) thermal runaway starting temperature T2 (°C) Application Example 1 85.2 86.3 81.8 83.5 109.2 169.4 Application Example 2 84.5 85.0 80.5 82.2 108.8 168.5 Application Example 3 85.5 87.0 82.5 84.0 109.5 170.2 Application Example 4 84.0 84.5 79.8 81.5 108.5 167.8 Application Example 5 84.8 85.8 81.2 83.0 109.0 169.0 Application Example 6 84.2 85.2 80.0 82.0 108.7 168.2 Application Example 7 85.0 86.0 81.5 83.2 109.3 169.8 Application Example 8 82.0 80.5 76.5 78.0 107.5 165.0 Application Example 9 82.5 81.0 77.0 78.5 107.8 166.0 Application Example 10 81.5 79.8 75.8 77.2 107.0 164.5 Application Example 11 81.0 79.0 75.0 76.5 106.8 164.0 Application Example 12 80.5 78.5 74.5 76.0 106.5 163.5 Application Example 13 81.8 80.2 76.2 77.8 107.2 165.5 Application Example 14 81.2 79.5 75.5 77.0 107.0 165.0 Application Example 15 80.8 78.8 74.8 76.3 106.7 163.8 Application Example 16 80.2 78.0 74.0 75.5 106.2 163.0 Application Example 17 82.2 81.2 77.2 78.8 107.6 166.5 Application Example 18 80.0 77.5 73.8 75.2 106.0 162.5 Application Example 19 79.8 77.2 73.5 75.0 105.8 162.0 Comparative Application Example 1 76.5 65.0 68.0 69.5 105.0 145.0 Comparative Application Example 2 75.0 62.0 66.0 67.0 104.5 143.0 Comparative Application Example 3 74.5 60.5 65.0 66.0 104.0 142.0 Comparative Application Example 4 77.8 63.9 69.9 71.0 105.9 140.2

[0265] From Tables 1-2, it can be seen that:

[0266] In Example 1, Example 4, Example 5, Example 8 and Example 9, the weight average molecular weight of the polymer is in a suitable numerical range, the film forming effect of the functional layer is better, and a good balance of viscosity, mechanical strength and flexibility is achieved, while the relatively low or high weight average molecular weight will affect the synergistic effect of each group, resulting in the influence of the thermal shrinkage rate and the puncture resistance of the modified separator, thereby reducing the electrochemical performance of the battery.

[0267] In Example 1, Example 10 and Example 11, the mass ratio of the polymer material to the total mass of all inorganic oxide materials is adjusted to a suitable numerical range, which is beneficial to greatly exert the synergistic effect of the two, improve the thermal shrinkage rate and the puncture resistance of the modified separator, and at the same time, has better liquid retention effect, thereby realizing the improvement of the electrochemical performance of the battery.

[0268] In Example 1, Example 12, Example 15 and Example 16, the form of double inorganic oxide materials is used in the functional layer, and the combination of ZrO2 and mesoporous TiO2 inorganic oxide materials is passed, which further improves the thermal shrinkage rate and the puncture resistance of the modified separator, so that the battery has excellent electrochemical performance.

[0269] In Example 1, Example 6, Example 13 and Example 14, the mass ratio of the two inorganic oxide materials in the functional layer is adjusted, the effective gradation of the large and small particles is realized, the porosity of the modified separator is improved, and the battery performance is improved.

[0270] In the functional layer of the modified separator of the present application, the inorganic oxide material further provides rigidity and thermal barrier of the functional layer, the olefin-based polymer material plays a bonding effect and provides stress buffering between the particles, thereby achieving good improvement of the high-temperature heat shrinkage resistance of the modified separator and stress buffering during negative electrode expansion, thereby improving the performance of the modified separator and the electrochemical performance of the battery.

[0271] In the mesoporous inorganic oxide material of the modified separator of the present application, the pore volume is located in a suitable numerical range, which not only ensures that the modified separator has excellent heat shrinkage and puncture resistance, but also has the effect of adsorbing electrolyte and improving the liquid absorption rate of the separator, thereby better improving the electrochemical performance of the battery.

[0272] In the modified separator of the present application, the addition of the functional layer and the polymer material with specific groups in the functional layer can achieve a substantial improvement in the heat shrinkage and puncture resistance of the modified separator, thereby achieving excellent performance of the electrochemical performance of the battery.

[0273] The applicant states that the above is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto. It should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. A modified separator, characterized by, The modified separator comprises a base film and a functional layer on at least one side of the base film; the functional layer comprises an olefin polymer material; The olefin polymer material comprises a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group.

2. The modified separator according to claim 1, wherein The functional layer further comprises an inorganic oxide material; Preferably, the mass ratio of the olefin polymer material to the inorganic oxide material is (20-35):(5-18); Preferably, the inorganic oxide material comprises a first inorganic oxide material and a second inorganic oxide material, and the median particle size D50 of the first inorganic oxide material is smaller than the median particle size D50 of the second inorganic oxide material.

3. The modified separator of claim 2, wherein, The median particle size D50 of the first inorganic oxide material is 8-20 nm; Preferably, the median particle size D50 of the second inorganic oxide material is 30-60 nm; Preferably, the mass ratio of the first inorganic oxide material to the second inorganic oxide material is 1:(2-3), and the first inorganic oxide material is filled in the interstitial gaps of the second inorganic oxide material; Preferably, the second inorganic oxide material comprises a mesoporous inorganic oxide material having a pore volume of 1 cm 3 / g ~ 1.3 cm 3 / g; Preferably, the first inorganic oxide material comprises ZrO2, and the second inorganic oxide material comprises mesoporous TiO2.

4. The modified separator of claim 1, wherein The weight average molecular weight of the olefin polymer material is 60,000-200,000; Preferably, the olefin polymer material further comprises an amine group; Preferably, in the olefin polymer material, the molar ratio of the pyrrolopyrimidine heterocyclic group, the aromatic ring group and the siloxy group is 1:1:(0.8-1.2), preferably 1:1:1; Preferably, the olefin polymer material comprises poly-7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine.

5. The modified separator according to claim 1 or 2, wherein The thickness of the functional layer is 1-4 μm; Preferably, the total thickness of the modified separator is 7-16 μm; Preferably, the functional layer further comprises a binder.

6. A method for producing a modified separator according to any one of claims 1 to 5, characterized by, The preparation method comprises the following steps: coating a functional layer slurry on at least one side of the base film to obtain the modified separator; The functional layer slurry comprises an olefin polymer material and a solvent, and the olefin polymer material comprises a pyrrolopyrimidine heterocyclic group, an aromatic ring group and a siloxy group.

7. The production method according to claim 6, characterized by, The coating method comprises any one or a combination of at least two of blade coating, extrusion coating, spraying, spin coating, roller coating or microgravure printing coating, preferably microgravure printing coating; Preferably, the monomer of the olefin polymer material comprises 7-(3-((tert-butyldimethylsilyl)oxy)propyl)-6-(1-ethoxyvinyl)-5-(p-tolyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine; Preferably, the functional layer slurry further comprises any one or a combination of at least two of a wetting agent, a dispersant, an inorganic oxide material and a binder. Preferably, the mass ratio of the olefin polymer material, the inorganic oxide material, the solvent, the wetting agent, the dispersant and the binder in the functional layer slurry is (20-35):(0-18):(42-72):(0-0.08):(0-0.3):(0-6), preferably (20-35):(5-18):(42-72):(0.02-0.08):(0.1-0.3):(2-6); Preferably, after the coating, a drying process is performed.

8. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode, a modified separator as claimed in any one of claims 1-5 or prepared by the preparation method as claimed in claim 6 or 7, a negative electrode and an electrolyte.

9. The lithium-ion battery of claim 8, wherein, The positive electrode active material in the positive electrode comprises a high-nickel positive electrode material, and the negative electrode active material in the negative electrode comprises a silicon-based negative electrode material.

10. The lithium-ion battery of claim 8 or 9, wherein, The electrolyte comprises an organic solvent and a main lithium salt. Preferably, the electrolyte further comprises an electrolyte additive and / or an auxiliary lithium salt.