Modified diaphragm as well as preparation method and application thereof

Abstract

The invention discloses a modified diaphragm and a preparation method and application thereof, the modified diaphragm comprises a base layer and a coating, the coating is arranged on at least partial area of at least one surface of the base layer, and the material of the coating comprises a lithium compound and a conductive agent. According to the modified diaphragm disclosed by the invention, the coating containing the lithium compound and the conductive agent is arranged on the surface of the base layer, so that the wettability and the thermal stability of the modified diaphragm to an electrolyte can be effectively improved, and the high-temperature safety of the lithium ion battery is further ensured; meanwhile, the coating can participate in the electrochemical reaction of the lithium ion battery, so that the lithium separation window of the lithium ion battery is increased, the rate capability of the lithium ion battery is improved, the cycle life of the battery is prolonged, and the energy density of the lithium ion battery is not lost.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a modified diaphragm and a preparation method and application thereof. Background Art

[0002] Currently, commercial lithium-ion batteries primarily utilize microporous polyolefin separator materials, such as single- or multilayer films of polyethylene (PE) and polypropylene (PP). While polyolefin separators offer low cost and sufficient mechanical strength and chemical stability at room temperature due to the inherent characteristics of the polymer, they also exhibit certain drawbacks, such as a low melting point and high impedance. At high temperatures, they can exhibit significant thermal shrinkage or even melting, potentially leading to short circuits between the positive and negative electrodes and potentially causing safety issues.

[0003] To improve the thermal shrinkage of the separator and thus address battery safety issues, researchers have proposed various methods to modify the surface or structure of polyolefin separators. For example, these methods employ ceramic materials such as silica and alumina to modify the surface structure, thereby improving the thermal stability and mechanical strength of polyolefin separators. However, these modified materials are inert and do not participate in the battery's electrochemical reactions. This can increase impedance, reduce battery performance, and increase the weight and cost of the separator.

[0004] Therefore, there is an urgent need for a modified separator that has at least good lithium ion conductivity, mechanical strength, and thermal stability, and can participate in electrochemical reactions to improve battery performance. Summary of the Invention

[0005] The present application aims to solve one of the technical problems in the related art at least to a certain extent.

[0006] In view of this, one object of the present application is to provide a modified diaphragm, in which a coating containing a lithium compound and a conductive agent is arranged on the surface of a base layer, which can effectively improve the wettability, thermal stability and conductivity of the modified diaphragm to the electrolyte, thereby ensuring the high-temperature safety of the lithium-ion battery and improving the dynamic performance of the lithium-ion battery; at the same time, the coating can participate in the electrochemical reaction of the lithium-ion battery, increase the lithium plating window of the lithium-ion battery, improve the rate performance of the lithium-ion battery, and extend the battery cycle life without causing any loss in the energy density of the lithium-ion battery.

[0007] Another object of the present application is to provide a method for preparing a modified diaphragm.

[0008] Yet another object of the present application is to provide an electrochemical device.

[0009] Yet another object of the present application is to provide a vehicle.

[0010] To this end, the first aspect of the present application proposes a modified diaphragm, comprising:

[0011] Grassroots,

[0012] A coating layer is provided on at least a portion of at least one surface of the base layer, wherein the material of the coating layer comprises a lithium compound and a conductive agent.

[0013] In some embodiments, when the coating is provided on one surface of the base layer, the coating area is m% of the area of ​​the surface, 90≤m<100.

[0014] In some embodiments, the lithium compound includes at least one of lithium titanate, lithium iron phosphate, and lithium manganese iron phosphate.

[0015] In some embodiments, the conductive agent includes at least one of carbon black, carbon nanotubes, and conductive graphite.

[0016] In some embodiments, the base layer is a polyolefin film.

[0017] Preferably, the polyolefin film includes but is not limited to at least one of a polyethylene film, a polypropylene film and the like.

[0018] In some embodiments, the mass content of the lithium compound in the coating material is 76-88%.

[0019] In some embodiments, the conductive agent has a mass content of 6-12% in the coating material.

[0020] In some embodiments, the coating material further comprises a binder, and the binder comprises at least one of polyvinylidene fluoride, styrene acrylic emulsion, and styrene butadiene.

[0021] In some embodiments, the binder has a mass content of 6-12% in the coating material.

[0022] In some embodiments, the coating has a thickness of 0.5-5 μm.

[0023] In some embodiments, the lithium compound has a median particle size of 0.1-3 μm.

[0024] In some embodiments, the coating has a porosity of 40-60%.

[0025] In some embodiments, the lithium compound is lithium titanate, and the thermal yield of the modified separator at 130-140° C. is 1.3-2.5%.

[0026] The second aspect of the present application provides a method for preparing a modified diaphragm, comprising:

[0027] mixing the coating material with an organic solvent to obtain a slurry;

[0028] The slurry is coated on at least a portion of at least one surface of the base layer, and then dried to obtain the modified separator.

[0029] In a third aspect of the present application, an electrochemical device is proposed, comprising a negative electrode sheet, a positive electrode sheet, and the modified separator described in the present application, wherein the modified separator is disposed between the negative electrode sheet and the positive electrode sheet.

[0030] In some embodiments, the coating is provided on a surface of the base layer facing the negative electrode plate.

[0031] In a fourth aspect of the present application, a vehicle is proposed, comprising the electrochemical device described in the present application.

[0032] The modified diaphragm of the present application can at least bring the following beneficial effects:

[0033] 1. A coating containing a lithium compound and a conductive agent is provided on the surface of the substrate. On the one hand, the surface of the lithium compound has polar and partially charged properties, which can promote the adsorption of polar solvent molecules (such as carbonates) in the electrolyte, thereby increasing the affinity between the electrolyte and the separator and enhancing the wettability of the modified separator. On the other hand, the lithium compound is a material with a high melting point and good thermal stability. When the modified separator is heated, the coating containing the lithium compound can act as a thermal barrier to prevent the modified separator from melting prematurely, thereby enhancing the thermal stability and safety of the lithium-ion battery. At the same time, the lithium compound has a porous structure, which helps lithium ions pass through the pore structure of the substrate more smoothly and evenly during battery use. The lithium compound and the conductive agent work together to improve the ionic conductivity and kinetic performance of the lithium-ion battery. In addition, the coating can participate in the electrochemical reaction of the lithium-ion battery, increase the lithium plating window of the lithium-ion battery, improve the rate performance of the lithium-ion battery, and extend the battery cycle life without causing any loss in the energy density of the lithium-ion battery.

[0034] 2. This application provides a new strategy for designing a dual-functional separator, offering new possibilities for the next generation of lithium-ion batteries with higher performance and safety.

[0035] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings.

[0037] in:

[0038] Figure 1This is a structural diagram of a modified diaphragm shown as an exemplary embodiment of the present application.

[0039] Figure 2 This is a structural diagram of a three-electrode lithium-ion battery involved in some specific embodiments of this application.

[0040] Reference numerals:

[0041] 1-diaphragm; 11-base layer; 12-coating layer; 2-reference electrode; 3-positive electrode; 4-negative electrode. DETAILED DESCRIPTION

[0042] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present application, but should not be understood as limiting the present application.

[0043] Throughout this application, the disclosure of numerical ranges includes disclosure of all values ​​within the entire range and further subdivided ranges, including the endpoints and subranges given within those ranges.

[0044] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be produced through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0045] The inventors discovered that by coating the surface of a separator with lithium compounds such as lithium titanate (LTO), the lithium-philic LTO particles can increase the wettability of traditional PE separators to electrolytes. The large number of pores on the LTO-containing coating can effectively increase the separator's absorption rate of electrolytes, further improving the separator's lithium ion conductivity and mechanical strength. At the same time, traditional separators are prone to thermal shrinkage reactions at high temperatures, causing battery short circuits and even fire and explosion risks. Taking LTO as an example, the thermal shrinkage of LTO-coated separators at 130-140°C is only 1.3-2.5%, while bare PE separators begin to shrink significantly above 90°C, with a thermal shrinkage of up to 5.5% at 130°C and almost completely melting at 140°C. Therefore, the excellent thermal stability of separators coated with lithium compounds such as LTO can effectively ensure the high-temperature safety of batteries. In addition, lithium compounds such as LTO can participate in electrochemical reactions. Lithium compound materials such as LTO have a high platform potential (for example, the platform potential of LTO is 1.56V), which increases the negative electrode OCV, thereby increasing the lithium deposition window of the lithium-ion battery, avoiding the occurrence of lithium deposition reactions during fast charging, and effectively improving the battery's rate performance and cycle life. In addition, adding conductive agents to lithium compounds such as lithium titanate (LTO) can reduce impedance, increase conductivity, and thus improve the kinetic performance of lithium-ion batteries.

[0046] A modified membrane, a method for preparing the modified membrane, and an electrochemical device according to embodiments of the present application will be described below with reference to the accompanying drawings.

[0047] Figure 1 This is a schematic structural diagram of a modified diaphragm shown as an exemplary embodiment of the present application.

[0048] like Figure 1 As shown, the modified diaphragm of the embodiment of the present application includes a base layer 11 and a coating layer 12. The coating layer 12 is provided on at least a portion of at least one surface of the base layer 11, and the material of the coating layer 12 includes a lithium compound and a conductive agent.

[0049] It is understood that in the embodiments of the present application, the coating layer may be provided on one surface of the base layer, or may be provided on multiple (two or more) surfaces of the coating layer. Furthermore, when the coating layer is provided on one or more of the surfaces, it may cover the entire surface or surfaces, or may only cover a portion of the surface or surfaces. Alternatively, when the coating layer is provided on multiple surfaces, it may cover the entire surface of some of the surfaces, while the remaining surfaces may only cover a portion of the surface on which they are located.

[0050] As a preferred example, the coating layer 12 is provided on one surface of the base layer and covers the entire area or a part of the area of ​​the surface.

[0051] As another optional example, the coating layer 12 is provided on two opposite surfaces of the base layer.

[0052] As another optional example, when the coating layer 12 is provided on one surface of the base layer 11, the area of ​​the coating layer 12 is m% of the area of ​​the surface, and 90≤m<100. As a non-limiting example, m includes but is not limited to 90, 91, 92, 93, 94, 95, 96, 97, 98, or 99.

[0053] In some embodiments, the lithium compound includes but is not limited to at least one of lithium titanate, lithium iron phosphate, lithium iron manganese phosphate, and the like.

[0054] As a preferred example, the lithium compound is lithium titanate.

[0055] It should be noted that in the embodiments of the present application, lithium compounds are active negative electrode materials. In the embodiments of the present application, lithium titanate (LTO) is preferred. LTO has the characteristics of high thermal stability, high platform potential, long cycle life, low cost and environmental friendliness. By coating LTO nanoparticles on the surface of traditional polyolefin diaphragms such as PE / PP, a modified diaphragm material of the embodiment of the present application is formed, which has a dual function - not only can it improve the safety and stability of lithium-ion batteries, but it can also participate in electrochemical reactions during the charge and discharge process to increase the lithium plating window of the negative electrode, enhance the fast charging capability of the battery, and avoid the occurrence of lithium plating reaction.

[0056] In the embodiments of the present application, the conductive agent may be any conductive agent known in the art that can be applied to secondary batteries such as lithium-ion batteries.

[0057] As a non-limiting example, the conductive agent includes but is not limited to at least one of carbon black, carbon nanotubes, conductive graphite, and the like.

[0058] In some embodiments, the base layer is a polyolefin film.

[0059] In the embodiments of the present application, the polyolefin film may be any polyolefin film well known in the art that can be applied to secondary batteries such as lithium-ion batteries.

[0060] As a non-limiting example, the polyolefin film includes, but is not limited to, at least one of a polyethylene film (PE), a polypropylene (PP) film, and the like.

[0061] In some embodiments, the coating material has a lithium compound content of 76-88% by mass, including but not limited to 76%, 75%, 78%, 80%, 83%, 85%, or 88%. When the lithium compound content of the coating material is within the above range, it can effectively improve the safety and stability of the separator while benefiting the fast-charging performance of the lithium-ion battery. If it is less than 76%, there will be less active material embedded in and out of the lithium-ion battery, which is not conducive to the fast-charging performance of the battery. If it is greater than 88%, the binder content is too low, the coating adhesion is poor, and the coating is prone to peeling, resulting in poor safety.

[0062] In some embodiments, the conductive agent has a mass content of 6-12% in the coating material, including but not limited to 6%, 9%, 10%, 11% or 12%.

[0063] In some embodiments, the coating material further includes a binder.

[0064] In the embodiments of the present application, the binder may be any binder known in the art that can be applied to secondary batteries such as lithium-ion batteries.

[0065] As a non-limiting example, the binder includes but is not limited to at least one of polyvinylidene fluoride (PVDF), styrene acrylic emulsion (styrene / acrylate polymer), styrene-butadiene, and the like.

[0066] In some embodiments, the binder content in the coating material is 6-12% by mass, including but not limited to 6%, 9%, 10%, 11% or 12%.

[0067] As an optional example, the material of the coating layer consists of a lithium compound, a conductive agent and a binder, and the mass ratio of the lithium compound, the conductive agent and the binder is 8:1:1.

[0068] In some embodiments, the coating has a thickness of 0.5-5 μm, including but not limited to 0.5 μm, 1.0 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. A coating thickness within this range can effectively improve the safety and stability of the separator. A coating thickness less than 0.5 μm may have a poor effect on improving the thermal shrinkage of the separator. A coating thickness greater than 5 μm may increase the mass of the separator, resulting in a decrease in the energy density of the lithium-ion battery.

[0069] As a preferred example, the thickness of the coating layer is 1-2 μm.

[0070] In some embodiments, the lithium compound has a median particle size (D50) of 0.1-3 μm, including but not limited to 0.1 μm, 0.5 μm, 1.0 μm, 1.5 μm, 2.0 μm, 2.5 μm, or 3 μm.

[0071] As a preferred example, the median particle size of the coating material is 0.1-0.5 μm.

[0072] In some embodiments, the coating has a porosity of 40-60%, including but not limited to 40%, 45%, 50%, 55% or 60%, etc.

[0073] In some embodiments, when the lithium compound is lithium titanate, the thermal yield of the modified diaphragm at 130-140°C is 1.3-2.5%, including but not limited to 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.1%, 2.2%, 2.3%, 2.4% or 2.5%, etc.

[0074] The modified diaphragm of the embodiment of the present application can at least bring the following beneficial effects:

[0075] 1. A coating containing a lithium compound and a conductive agent is provided on the surface of the substrate. On the one hand, the surface of the lithium compound has polar and partially charged properties, which can promote the adsorption of polar solvent molecules (such as carbonates) in the electrolyte, thereby increasing the affinity between the electrolyte and the separator and enhancing the wettability of the modified separator. On the other hand, the lithium compound is a material with a high melting point and good thermal stability. When the modified separator is heated, the coating containing the lithium compound can act as a thermal barrier to prevent the modified separator from melting prematurely, thereby enhancing the thermal stability and safety of the lithium-ion battery. At the same time, the lithium compound has a porous structure, which helps lithium ions pass through the pore structure of the substrate more smoothly and evenly during battery use. The lithium compound and the conductive agent work together to improve the ionic conductivity and kinetic performance of the lithium-ion battery. In addition, the coating can participate in the electrochemical reaction of the lithium-ion battery, increase the lithium plating window of the lithium-ion battery, improve the rate performance of the lithium-ion battery, and extend the battery cycle life without causing any loss in the energy density of the lithium-ion battery.

[0076] 2. Compared with traditional polyethylene (PE) membranes, when the lithium compound is lithium titanate and the base layer is polyethylene film, the thermal yield of the modified membrane of the present application at 130-140°C is only 1.3-2.5%, which is much lower than the 5.5% of traditional PE membranes; the lithium precipitation window at a 4C rate is increased by 20mV, and the cycle life is increased by 20%.

[0077] 3. This application provides a new strategy for designing dual-functional separators, offering new possibilities for the next generation of lithium-ion batteries with higher performance and safety.

[0078] The method for preparing the modified diaphragm of the embodiment of the present application comprises the following steps:

[0079] S101, mixing the coating material with an organic solvent to obtain a slurry.

[0080] In some embodiments, the material of the coating layer includes the aforementioned lithium compound and the aforementioned conductive agent.

[0081] In other embodiments, the material of the coating layer includes the above-mentioned lithium compound, the above-mentioned conductive agent and the above-mentioned binder.

[0082] In the embodiments of the present application, the organic solvent may be any organic solvent well known in the art that can be applied to secondary batteries such as lithium-ion batteries.

[0083] As a non-limiting example, the organic solvent includes, but is not limited to, at least one of N-methylpyrrolidone (NMP) and the like.

[0084] In some embodiments, in order to mix the coating materials uniformly, the coating materials are mixed with an organic solvent, which can be performed under conditions such as stirring, ball milling, and ultrasonic dispersion.

[0085] In some embodiments, the coating material is mixed with the organic solvent by first mixing the components of the coating material and then adding the organic solvent for mixing; alternatively, the components of the coating material and the organic solvent are mixed at once.

[0086] S102, coating the slurry on at least a portion of at least one surface of the base layer, and then drying to obtain a modified separator.

[0087] In some embodiments, the coating method includes but is not limited to at least one of spray coating, slit coating, blade coating, spin coating, etc.

[0088] In some embodiments, the drying method includes but is not limited to at least one of drying, spray drying, vacuum drying, etc.

[0089] In the embodiments of the present application, the drying temperature and time are not limited, as long as the slurry coated on the base layer can be dried to form a coating.

[0090] The method for preparing the modified diaphragm of the embodiment of the present application has the following beneficial effects in addition to the beneficial effects of the modified diaphragm of the embodiment of the present application:

[0091] The modified diaphragm can be prepared through a simple coating process. The preparation method is simple and is very conducive to large-scale production.

[0092] The electrochemical device of the embodiment of the present application includes a negative electrode plate and a separator, and the separator is the modified separator of the embodiment of the present application.

[0093] In some embodiments, one of the surfaces of the separator provided with the coating faces the negative electrode sheet.

[0094] As a preferred example, when a surface of the base layer of the separator is provided with a coating, the coating side of the separator faces the negative electrode sheet.

[0095] In some embodiments, the electrochemical device further includes a positive electrode sheet, and the separator is disposed between the positive electrode sheet and the negative electrode sheet.

[0096] In some embodiments, the electrochemical device includes but is not limited to a secondary battery such as a lithium-ion battery, a capacitor, etc. The secondary battery is not limited to a button battery, a soft pack battery, etc.

[0097] As an optional example, the electrochemical device is a lithium-ion battery. This application does not limit the positive electrode and negative electrode of the lithium-ion battery, and the positive electrode and negative electrode can be any positive electrode and negative electrode known in the art.

[0098] The vehicle of the embodiment of the present application can be any vehicle containing the modified diaphragm of the embodiment of the present application or the electrochemical device of the embodiment of the present application, including but not limited to automobiles, motorcycles, power-assisted bicycles, bicycles, power tools, etc.

[0099] The electrochemical device and vehicle according to the embodiments of the present application both have at least the beneficial effects of the modified diaphragm according to the embodiments of the present application.

[0100] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0101] 1. Examples and Comparative Examples

[0102] Example 1

[0103] (Modified diaphragm)

[0104] like Figure 1 As shown, the modified diaphragm of this embodiment is a lithium-ion battery diaphragm, comprising a base layer 11 and a coating layer 12.

[0105] The base layer 11 is a PE film, and a coating layer 12 is provided on one surface of the base layer 11 .

[0106] The coating 12 is composed of the following components in the following mass percentages: 80% lithium titanate (LTO) particles, 10% conductive carbon black (SP), and 10% polyvinylidene fluoride (PVDF). The D50 of the LTO particles is 0.5 μm, and the thickness of the coating 12 is 1.5 μm.

[0107] (Method for preparing modified diaphragm)

[0108] The modified diaphragm of this embodiment is prepared by mixing LTO, SP, and PVDF in an NMP solution according to the formula to prepare a slurry with a solid content of 40 wt%; then, the slurry is coated on the entire surface of one side of a base PE film, and dried at 60°C for 1 hour to obtain the modified diaphragm of this embodiment.

[0109] Example 2

[0110] This embodiment is basically the same as embodiment 1, except that:

[0111] The D50 of the LTO particles is 0.1 μm.

[0112] Example 3

[0113] This embodiment is basically the same as embodiment 1, except that:

[0114] The D50 of the LTO particles is 2.7 μm.

[0115] Example 4

[0116] This embodiment is basically the same as embodiment 1, except that:

[0117] The thickness of the coating layer 12 is 0.5 μm.

[0118] Example 5

[0119] This embodiment is basically the same as embodiment 1, except that:

[0120] The thickness of the coating layer 12 is 3 μm.

[0121] Example 6 (Lower limit of lithium titanate content in coating material)

[0122] This embodiment is basically the same as embodiment 1, except that:

[0123] The material of the coating layer 12 is composed of the following components in the following mass percentages: 76% lithium titanate (LTO) particles, 12% conductive carbon black (SP), and 12% polyvinylidene fluoride (PVDF).

[0124] Example 7 (Upper limit of lithium titanate content in coating material)

[0125] This embodiment is basically the same as embodiment 1, except that:

[0126] The material of the coating layer 12 is composed of the following components in the following mass percentages: 88% lithium titanate (LTO) particles, 6% conductive carbon black (SP), and 6% polyvinylidene fluoride (PVDF).

[0127] Comparative Example 1

[0128] This comparative example is basically the same as Example 1, except that:

[0129] The modified separator does not include the coating layer 12 but only comprises a base layer 11 PE film.

[0130] Comparative Example 2

[0131] This comparative example is basically the same as Example 1, except that:

[0132] The LTO particles were replaced with boehmite with a D50 of 0.5 μm.

[0133] 2. Performance Testing

[0134] The separators of the above embodiments and comparative examples are used in lithium ion batteries (such as Figure 2The preparation method of the lithium-ion battery is as follows: the separators of each embodiment and comparative example are respectively combined with a positive electrode ternary 811 material and a negative electrode 5wt% SiO + graphite material to form a 5Ah soft-pack three-electrode battery. A copper wire plated with lithium is used as a reference electrode. When the separator of the lithium-ion battery contains a coating, the coated side of the separator faces the negative electrode. The electrolyte of the soft-pack three-electrode battery is 1 mol / L LiPF6. The solvent in the electrolyte is a mixed solvent of ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. The additive in the electrolyte is fluoroethylene carbonate (FEC), and the mass content of FEC in the electrolyte is 5%.

[0135] The thermal shrinkage test was performed on the separators of each embodiment and comparative example, and the rate performance test and cycle capacity retention test were performed on the lithium-ion batteries made from the separators of each embodiment and comparative example. The test methods are as follows:

[0136] (1) Thermal shrinkage test

[0137] The diaphragm was cut into a square with a side length of 50 mm, baked in an oven at 130°C for 1 hour and then naturally cooled. After cooling to room temperature (25°C), the diaphragm size was measured using a CCD (optical impact meter) to calculate the thermal shrinkage of the diaphragm.

[0138] (2) Rate performance test

[0139] At 25°C, the lithium-ion battery was discharged at 0.33C to a voltage of 2.5V, and then charged at a constant current of 4C to a voltage of 4.25V, and the negative electrode potential was recorded.

[0140] (3) Cyclic capacity retention test

[0141] At 25°C, the lithium-ion battery is charged at a constant current of 1C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, left to stand for 10 minutes, and then discharged at a constant current of 1C to 2.5V. This is a charge and discharge cycle process. The lithium-ion battery is subjected to 1000 cycle charge and discharge tests according to the above method. The capacity retention rate = discharge capacity of the 1000th cycle / discharge capacity of the first cycle × 100%.

[0142] The test results of the thermal shrinkage of the separators of the embodiments and comparative examples, and the rate performance and cycle capacity retention of the lithium-ion batteries prepared using the separators of the embodiments and comparative examples are shown in Table 1.

[0143] Table 1 Test results of thermal shrinkage, rate performance, and cycle capacity retention

[0144] project 130℃ baking thermal shrinkage / % 4C charging negative electrode potential / mV 1000 cycle capacity retention rate / % Example 1 1.3 15 90 Example 2 2.5 10 88 Example 3 3.4 12 89 Example 4 2.9 5 82 Example 5 3.7 13 85 Example 6 2.0 6 85 Example 7 3.0 8 88 Comparative Example 1 5.5 -5 75 Comparative Example 2 2.0 -3 78

[0145] As can be seen in Table 1, the modified separators of the present invention utilize a functional coating of LTO material applied to one side of the separator substrate. LTO's high thermal stability, high plateau potential, and long cycle life significantly improve the electrical properties of the interface between the separator and the negative electrode of lithium-ion batteries, enhancing the safety, rate capability, and cycling performance of lithium-ion batteries. The thermal shrinkage after baking at 130°C is 1.3-3.7%, the negative electrode potential after 4C charging is 5-15mV, and the capacity retention rate after 1000 cycles is 85%-90%.

[0146] More specifically:

[0147] Comparing Example 1 with Examples 2-3, it can be seen that the D50 of the modified separator coating LTO in Example 1 is 0.5 μm, which is within the preferred particle size range. It also has the lowest thermal shrinkage after baking at 130°C, the highest negative electrode potential after 4C charging, and the highest capacity retention after 1000 cycles. This shows that the D50 of the modified separator coating LTO in the examples of the present application within the preferred range is beneficial for improving the thermal stability of lithium-ion battery separators, and improving the safety, rate performance, and cycle performance of lithium-ion batteries.

[0148] Comparing Example 1 with Examples 4-5, it can be seen that the thickness of the modified separator coating LTO in Example 1 is 1.5 μm. Within the preferred range of coating thickness, the 130°C baking shrinkage is the lowest, the 4C charging negative electrode potential is the highest, and the 1000 cycle capacity retention rate is the highest. This shows that the thickness of the modified separator coating LTO in the examples of the present application within the preferred range is conducive to improving the thermal stability of the lithium-ion battery separator, and improving the safety performance, rate performance, and cycle performance of the lithium-ion battery.

[0149] By comparing Example 1 with Examples 6-7, it can be seen that the lithium titanate content gradually increases, the 130°C baking shrinkage first decreases and then increases, and the 4C charging negative electrode potential and 1000 cycle capacity retention rate first increase and then decrease. This may be because too much lithium titanate content will increase the impedance and affect the cycle performance, while too little lithium titanate will have poor safety and severe thermal shrinkage of the diaphragm.

[0150] Comparing Example 1 and Comparative Examples 1-2, it can be seen that the modified diaphragm in Example 1 includes a coating containing LTO, Comparative Example 1 only has a diaphragm base layer, and Comparative Example 2 includes a functional coating of boehmite. Compared with the three, the diaphragm coating LTO in Example 1 has the lowest thermal shrinkage rate after 130°C baking, the highest negative electrode potential after 4C charging, and the highest capacity retention rate after 1000 cycles. This shows that the modified diaphragm coated with LTO in the examples of the present application is beneficial to improving the thermal stability of lithium-ion battery diaphragms, while also improving the safety performance, rate performance, and cycle performance of lithium-ion batteries.

[0151] In summary, the modified diaphragm of the embodiment of the present application increases the lithium plating window of the lithium-ion battery by coating a coating containing LTO, etc. on the diaphragm base layer, thereby improving the safety performance, rate performance and cycle performance of the lithium-ion battery without causing any loss in the energy density of the lithium-ion battery.

[0152] In this application, the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and the features of different embodiments or examples without contradiction.

[0153] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A modified diaphragm, characterized in that: include: Grassroots, A coating layer is provided on at least a portion of at least one surface of the base layer, wherein the material of the coating layer comprises a lithium compound and a conductive agent.

2. The modified diaphragm according to claim 1, characterized in that The lithium compound includes at least one of lithium titanate, lithium iron phosphate, and lithium manganese iron phosphate.

3. The modified diaphragm according to claim 1, characterized in that When the coating is provided on one surface of the base layer, the coating area is m% of the area of ​​the surface, 90≤m<100.

4. The modified diaphragm according to claim 1, characterized in that The mass content of the lithium compound in the coating material is 76-88%; And / or, in the material of the coating, the mass content of the conductive agent is 6-12%.

5. The modified diaphragm according to claim 1, characterized in that The coating material further includes a binder, and the binder includes at least one of polyvinylidene fluoride, styrene acrylic emulsion, and styrene butadiene.

6. The modified diaphragm according to claim 5, characterized in that The binder has a mass content of 6-12% in the coating material.

7. The modified diaphragm according to any one of claims 1 to 6, characterized in that: The thickness of the coating is 0.5-5 μm; and / or, the lithium compound has a median particle size of 0.1-3 μm; and / or, the coating has a porosity of 40-60%; And / or, the lithium compound is lithium titanate, and the thermal yield of the modified diaphragm at 130-140° C. is 1.3-2.5%.

8. A method for preparing the modified diaphragm according to any one of claims 1 to 7, characterized in that: include: mixing the coating material with an organic solvent to obtain a slurry; The slurry is coated on at least a portion of at least one surface of the base layer, and then dried to obtain the modified separator.

9. An electrochemical device, characterized in that The device comprises a negative electrode sheet, a positive electrode sheet and a modified separator according to any one of claims 1 to 7, wherein the modified separator is arranged between the negative electrode sheet and the positive electrode sheet.

10. The electrochemical device according to claim 9, characterized in that The coating is provided on the surface of the base layer facing the negative electrode plate.

11. A vehicle, characterized in that: Comprising the electrochemical device according to claim 9 or 10.

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