Composite diaphragm, preparation method thereof, battery, battery pack and electric device

Abstract

The application provides a composite diaphragm, a preparation method thereof, a battery, a battery pack and an electric device, and the composite diaphragm comprises a base film and a composite material layer existing on at least one side surface of the base film, the composite material layer comprises a first ceramic material and a second ceramic material, the first ceramic material is a high-entropy porous ceramic material containing at least five metal elements, and the second ceramic material is a ceramic material containing less than five metal elements. The composite material layer in the composite diaphragm provided by the application comprises the first ceramic material and the second ceramic material, which can not only exert the advantages of the second ceramic material, such as compactness and high compressive strength, but also exert the characteristics of the first ceramic material, such as low thermal conductivity, low density and high porosity, so that the mechanical strength and the thermal stability of the composite diaphragm are relatively high, and when the composite diaphragm is applied to a battery, the safety of the battery can be improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a composite diaphragm, a preparation method thereof, a battery, a battery pack and an electrical equipment. BACKGROUND

[0002] With the rapid development of new energy vehicles, the energy density requirement of power batteries is becoming more and more urgent. With the continuous improvement of the energy density of power batteries, longer endurance is brought, and at the same time, the safety of power batteries is more challenged, especially in the process of battery thermal abuse, mechanical abuse and electrical abuse, lithium ion batteries are prone to positive and negative short circuit and thermal runaway problems. Among them, the mechanical properties and thermal stability of the diaphragm material are directly related to the safety of the battery, therefore, it is an urgent technical problem in the field to provide a diaphragm with high mechanical strength and high thermal stability. SUMMARY

[0003] The main purpose of the application is to provide a composite diaphragm with high mechanical strength and high thermal stability.

[0004] The application also provides a preparation method of a composite diaphragm, which can prepare the above-mentioned composite diaphragm, and the process is simple and the cost is low.

[0005] The application also provides a battery comprising the above-mentioned composite diaphragm, therefore, the battery has high safety.

[0006] The application also provides a battery pack comprising the above-mentioned battery, therefore, the battery pack has high safety.

[0007] The application also provides an electrical equipment comprising the above-mentioned battery or battery pack, therefore, the electrical equipment has high safety.

[0008] In the first aspect, the application provides a composite diaphragm, comprising a base film and a composite material layer existing on at least one side surface of the base film, the composite material layer comprising a first ceramic material and a second ceramic material, the first ceramic material being a high-entropy porous ceramic material containing at least 5 metal elements, and the second ceramic material being a ceramic material containing less than 5 metal elements.

[0009] The composite diaphragm as described above, the first ceramic material comprises at least one of high-entropy porous oxide ceramic material, high-entropy porous carbide ceramic material, high-entropy porous nitride ceramic material, high-entropy porous boride ceramic material, high-entropy porous sulfide ceramic material, and preferably high-entropy porous carbide ceramic material.

[0010] The composite diaphragm as described above, the first ceramic material comprises (Zr 0.2 Hf 0.2 Ti0.2 Nb 0.2 Ta 0.2 )C, (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )N, (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )O 、 (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )B, preferably (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C.

[0011] The composite separator as described above, the second ceramic material comprises at least one of boehmite, alumina, silica, titanium oxide, barium oxide, magnesium oxide, barium titanate, zirconium oxide, magnesium hydroxide.

[0012] The composite separator as described above, the mass fraction of the first ceramic material in the sum of the mass of the first ceramic material and the second ceramic material is 5%-50%, preferably 15%-40%.

[0013] The composite separator as described above, the thickness of the composite material layer is 1 μm-3 μm, preferably 1.5 μm-3 μm.

[0014] The composite separator as described above, the D50 of the first ceramic material is 0.8 μm-2 μm, preferably 1.0 μm-1.6 μm;

[0015] And / or, the D50 of the second ceramic material is 0.2 μm-0.8 μm, preferably 0.3 μm-0.6 μm.

[0016] In a second aspect, the present application provides a battery comprising the composite separator as described above.

[0017] In a third aspect, the present application provides a battery pack comprising the battery as described above.

[0018] In a fourth aspect, the present application provides an electrical equipment comprising the battery as described above or the battery pack as described above.

[0019] The composite material layer in the composite diaphragm comprises the first ceramic material and the second ceramic material, and the advantages of the second ceramic material, such as high compression strength and high density, can be exerted, and the characteristics of the first ceramic material, such as low thermal conductivity, low density and high porosity, can be exerted, so that the mechanical strength and the thermal stability of the composite diaphragm are high, and the safety of the battery can be improved when the composite diaphragm is applied to the battery. DETAILED DESCRIPTION

[0020] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0021] The battery diaphragm plays a crucial role in lithium ion batteries, fuel cells and other energy storage devices. Its main function is to separate the positive and negative electrodes of the battery to prevent internal short circuit, while allowing ions to pass through to complete the electrochemical reaction. Therefore, the mechanical properties and thermal stability of the diaphragm material are directly related to the safety of the battery.

[0022] The thermal runaway process of the battery is sorted from low temperature to high temperature, and the lithium ion power battery will experience the following processes in turn: high temperature capacity attenuation, SEI film decomposition, negative electrode-electrolyte reaction, diaphragm melting process, positive electrode decomposition reaction, electrolyte solution decomposition reaction, negative electrode and adhesive reaction, electrolyte combustion, etc. The battery thermal runaway heat release usually starts from the decomposition of the negative electrode SEI film and the negative electrode-electrolyte reaction. As the temperature continues to rise, heat is transferred to the diaphragm, the diaphragm begins to melt and disintegrate, and then a short circuit occurs in the battery, releasing a large amount of heat, so that the battery temperature rapidly increases from 170℃ to 200℃ or even higher, reaching the thermal runaway trigger point of the positive electrode active material.

[0023] Conventional PE, PP separators are prone to shrinkage or puncture rupture under heat due to low melting temperature and poor mechanical strength, resulting in direct contact between positive and negative electrodes and short circuit, causing thermal runaway. In order to improve the safety performance of the separator, a conventional ceramic material mainly composed of Al2O3 and boehmite is usually coated on both sides of the conventional separator to improve the mechanical strength and thermal stability of the separator. This solution has been widely used in various lithium ion batteries, including power batteries and 3C batteries. However, the current conventional ceramic material has a large specific surface area and poor adhesion to the separator, which is easy to fall off from the separator, resulting in dust and foreign matter during battery assembly, and the mechanical strength decreases. The high thermal conductivity of the conventional ceramic material causes the heat to easily transfer, and once there is a local thermal runaway point inside the battery, the thermal runaway is easy to transfer, and the safety performance of the battery decreases. Therefore, improving the mechanical strength and thermal stability of the separator and prolonging the thermal runaway time of the battery are crucial to improve the safety of the battery.

[0024] Therefore, in a first aspect, the present application provides a composite separator, comprising a base film and a composite material layer existing on at least one side surface of the base film, the composite material layer comprising a first ceramic material and a second ceramic material, the first ceramic material being a high-entropy porous ceramic material containing at least 5 kinds of metal elements, and the second ceramic material being a ceramic material containing less than 5 kinds of metal elements.

[0025] The composite material layer in the composite separator of the present application comprises a first ceramic material and a second ceramic material, so that the mechanical strength and thermal stability of the composite separator are higher, and the safety of the battery can be improved when applied to the battery.

[0026] The multiple elements in the first ceramic material, i.e. the high-entropy porous ceramic material, can form a highly mixed solid solution structure, which can effectively enhance the tear resistance and puncture resistance of the composite separator. The porous structure can provide good mechanical support and can disperse stress to prevent local stress concentration. The second ceramic material has high strength and high hardness, which can improve the mechanical strength and wear resistance of the composite separator. The micron-sized high-entropy porous ceramic material and the nanometer-sized second ceramic material are interpenetrated and coated on the base film, which can significantly improve the adhesion and mechanical strength between the composite material layer and the base film, avoiding the peeling of the coating layer caused by the use of nanometer-sized second ceramic material alone, and the poor mechanical strength of the coating layer caused by the use of micron-sized high-entropy porous ceramic material alone due to the large number of micropores. The composite separator can effectively avoid the risk of negative pre-lithiation cell short circuit detection (hi-pot) failure, and improve the process yield and safety of the cell.

[0027] In addition, the first ceramic material generally has a low thermal conductivity, can maintain the stability of its structure and performance in a high-temperature environment, and prevent the composite separator from shrinking, melting or decomposing at high temperatures. Its porous structure can provide a certain thermal insulation effect, slow down the conduction of heat in the composite separator, thereby improving the stability of the composite separator in a high-temperature environment. The second ceramic material generally has a high thermal conductivity, can quickly transfer heat, and can maintain dimensional stability when the temperature changes, preventing the separator from deforming at high temperatures. In the thermal runaway process of the battery, the low thermal conductivity of the first ceramic material can effectively isolate the further expansion of the thermal runaway site, and in the middle and later stages of the thermal runaway diffusion, the high thermal conductivity of the second ceramic material can quickly transfer heat, and through this two-step protection, the safety performance of the battery can be improved.

[0028] In addition, due to the existence of a large number of micropores in the first ceramic material, the air permeability of the composite separator can be significantly improved, and more electrolyte can be stored, thereby avoiding the problem of reduced rate performance caused by the excessive densification of the second ceramic material. The nanoscale second ceramic material is effectively filled between the micrometer-scale first ceramic material gaps, and the particles are more densely packed, which can avoid the problem of insufficient lightweight of the separator caused by the high weight ratio of the coating of the second ceramic material alone; at the same time, the problem of low bulk density of the separator caused by the non-dense filling of the first ceramic material alone can be avoided. While achieving lightweight of the separator, the high thermal stability of the first ceramic material is utilized to further improve the thermal stability of the composite material layer, thereby effectively preventing the composite separator from shrinking or melting under thermal runaway conditions.

[0029] It can be understood that high-entropy ceramic material generally refers to a ceramic material with a simple crystal structure composed of five or more metal elements and one non-metal element. The high-entropy porous ceramic material, i.e., the first ceramic material, is a porous high-entropy ceramic material prepared by in-situ reaction through gas release based on high-entropy ceramic material. Compared with the ceramic material with less than 5 metal elements, i.e., the second ceramic material, the high-entropy porous ceramic material has excellent properties such as low thermal conductivity, low density and high porosity, and the particle size thereof is relatively large, generally micrometer-scale, and has good compressibility. The second ceramic material is generally nanoscale.

[0030] The present application does not limit the specific type of base film, and conventional separators used in the art can be used, such as PP film, PE film, PVDF film, etc.

[0031] The composite material layer in the composite separator provided by the present application comprises the first ceramic material and the second ceramic material, which can not only take advantage of the high density and high compressive strength of the second ceramic material, but also take advantage of the low thermal conductivity, low density and high porosity of the first ceramic material, thereby making the mechanical strength and thermal stability of the composite separator higher, and improving the safety of the battery when applied to the battery.

[0032] The preparation method of the composite separator of the present application can comprise the following steps:

[0033] The first ceramic material and the second ceramic material are coated on the base film by using a micro gravure roll coating process to obtain the composite separator.

[0034] The preparation method of the composite separator of the present application adopts a micro gravure roll coating process, and can specifically comprise the following steps:

[0035] 1) The first ceramic material, the second ceramic material, the binder and the dispersant are sequentially added into water, and each component is uniformly dispersed in water by stirring to obtain a stable composite material slurry.

[0036] 2) The composite material slurry prepared in step 1) is uniformly coated on the polymer base film (which can be coated on one side surface or both side surfaces of the base film) by using a micro gravure roll to obtain a composite separator precursor. According to the viscosity and solid content of the composite material slurry, the operating parameters of the micro gravure roll are adjusted to meet the requirements of the coating thickness and the area density of the composite material layer.

[0037] 3) The composite separator precursor is subjected to drying treatment to obtain the composite separator.

[0038] It can be understood that the so-called micro in the micro gravure roll refers to the diameter of the anilox roll being smaller than that of a traditional anilox roll. The diameter of the traditional anilox roll which is widely used at present is usually 125 mm-250 mm. The diameter of the micro gravure roll is usually only 20 mm-50 mm. The size of the diameter of the roll is largely referred to the coating width. In the case of wider coating, the strength and straightness of the roll need to be ensured, and a roll with a larger diameter needs to be selected. For example, a 20 mm diameter roll can be selected for coating 300 mm wide, and a 50 mm roll can be selected for coating 1.6 m wide. The smaller the diameter of the roll, the smaller the contact line between the substrate and the roll, and the smaller the possibility of coating defects when the contact line is smaller.

[0039] The preparation method of the composite separator of the present application adopts a micro gravure roll coating process, and the composite separator of the present application can be prepared. The preparation method is simple and easy to implement, and has low cost. The composite separator has high mechanical strength and high thermal stability, and can improve the safety of the battery when applied to the battery.

[0040] In some embodiments of the present application, the line number of the micro gravure roll in the micro gravure roll coating process is 100 lines / cm-200 lines / cm, the line depth is 20 μm-90 μm, the coating speed is 20 m / min-60 m / min, and the speed ratio is 90%-120%.

[0041] Exemplarily, the line number of the micro gravure roll in the micro gravure roll coating process can be in a range of 100 lines / cm, 110 lines / cm, 120 lines / cm, 130 lines / cm, 140 lines / cm, 150 lines / cm, 160 lines / cm, 170 lines / cm, 180 lines / cm, 190 lines / cm, 200 lines / cm, or any two thereof. The line depth can be in a range of 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or any two thereof. The coating speed can be in a range of 20 m / min, 30 m / min, 40 m / min, 50 m / min, 60 m / min, or any two thereof. The speed ratio can be in a range of 90%, 95%, 100%, 105%, 110%, 115%, 120%, or any two thereof.

[0042] It can be understood that the speed ratio refers to the ratio of the running speed of the micro gravure roll and the running speed of the base film.

[0043] In the micro gravure roll coating process, the line number of the micro gravure roll is in the above range, which can provide higher resolution, make the coating more uniform and smooth, and ensure the coating quality while providing higher coating efficiency.

[0044] In the micro gravure roll coating process, the line depth of the micro gravure roll is in the above range, which can ensure that the first ceramic material and the second ceramic material are uniformly distributed on the surface of the base film, avoiding the occurrence of stripes, spots or other uneven phenomena.

[0045] In the micro gravure roll coating process, the coating speed of the micro gravure roll is in the above range, which can improve the production efficiency.

[0046] In the micro gravure roll coating process, the speed ratio is in the above range, which can ensure the speed matching between the coating roll and the base film, optimize the coating thickness and uniformity, and the coating process is relatively stable, avoiding the occurrence of uneven coating or coating layer falling off, thereby improving the consistency and reliability of the coating.

[0047] In some embodiments, the first ceramic material includes at least one of high-entropy porous oxide ceramic material, high-entropy porous carbide ceramic material, high-entropy porous nitride ceramic material, high-entropy porous boride ceramic material, high-entropy porous sulfide ceramic material, and preferably high-entropy porous carbide ceramic material. Specifically, the first ceramic material includes (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C, (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2Ta 0.2 )N, (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )O 、 (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )B, preferably (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C.

[0048] The first ceramic material has low thermal conductivity, can maintain stable physical and chemical properties at high temperature, and can further improve the thermal stability of the composite separator; and the high porosity of the ceramic material can improve the air permeability of the composite separator, store more electrolyte, and also make the composite separator lightweight.

[0049] In some embodiments of the present application, the second ceramic material includes at least one of boehmite, alumina, silicon oxide, titanium oxide, barium oxide, magnesium oxide, barium titanate, zirconium oxide, and magnesium hydroxide.

[0050] The second ceramic material has high density and high mechanical strength, which can further improve the mechanical strength of the composite separator; in addition, the high thermal conductivity can quickly transfer heat, thereby improving the safety of the battery.

[0051] In some embodiments of the present application, the mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material is 5%-50%, preferably 15%-40%.

[0052] For example, the mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material can be 5%, 10%, 15%, 20%, 30%, 40%, 50%, or a range formed by any two of them.

[0053] The mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material is in the above range, which helps to disperse stress and prevent local stress concentration, thereby further improving the overall mechanical strength of the composite separator. And keep the structure stable at high temperature, prevent the composite separator from shrinking, melting or decomposing at high temperature. If the mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material is too low, the characteristics of low thermal conductivity, low density and high porosity of the first ceramic material cannot be fully utilized, and the advantages of liquid absorption, light weight and effective prevention of heat diffusion cannot be achieved. If the mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material is too high, the density of the composite material layer will decrease, and the mechanical strength will decrease, so that the heat diffusion will have poor heat transfer capacity.

[0054] The present application does not limit the test method of the mass fraction of the first ceramic material in the total mass of the first ceramic material and the second ceramic material, for example, the element and component composition can be detected by SEM-EDS surface scanning or XRD scanning.

[0055] In some embodiments of the present application, the thickness of the composite material layer is 1 μm-3 μm, preferably 1.5 μm-3 μm.

[0056] Exemplarily, the thickness of the composite material layer can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or a range formed by any two of them.

[0057] It can be understood that the thickness of the composite material layer in the present application refers to the single-sided thickness of the composite material layer. When the base film is coated with a composite material layer on both surfaces, the thickness of the composite material layer on each surface is in the range of 1 μm-3 μm. The thickness of the composite material layer can be adjusted by changing the thread number, thread depth, coating speed and speed ratio of the micro-gravure roll in the micro-gravure roll coating process.

[0058] The thickness of the composite material layer in the above range can provide sufficient mechanical support and significantly improve the tear resistance and puncture resistance of the composite separator; it can also effectively disperse stress and prevent local stress concentration, thereby improving the overall mechanical strength and durability of the composite separator. In addition, the thickness of the composite material layer in the above range can provide good thermal insulation effect, slow down the conduction of heat in the composite separator, thereby improving the stability of the composite separator in high temperature environment, preventing the composite separator from shrinking, melting or decomposing at high temperature. If the composite material layer is too thin, the safety performance is insufficient; if the composite material layer is too thick, it will hinder the transmission of lithium ions and reduce the energy density of the battery. More preferably, the coating thickness is 1.5-2.5 um.

[0059] The present application does not limit the test method of the thickness of the composite material layer, for example, it can be measured by SEM cross-section scanning.

[0060] In some embodiments of the present application, the D50 of the first ceramic material is 0.8 μm-2 μm, preferably 1.0 μm-1.6 μm.

[0061] In some embodiments, the D50 of the second ceramic material is 0.2 μm-0.8 μm, preferably 0.3 μm-0.6 μm.

[0062] For example, the D50 of the first ceramic material can be 0.8 μm, 0.9 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 2 μm, or a range consisting of any two of them. The D50 of the second ceramic material can be 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, or a range consisting of any two of them.

[0063] The D50 of the first ceramic material and the D50 of the second ceramic material in the present application are in the above ranges, wherein the first ceramic material can provide good mechanical reinforcement effect, and the second ceramic material helps to improve the mechanical strength and toughness of the composite layer. The smaller D50 of the second ceramic material can fill the micropores of the first ceramic material, further enhancing the mechanical strength and toughness, and the uniform distribution of the smaller D50 of the second ceramic material in the micropores of the first ceramic material can prevent stress concentration and improve the overall mechanical properties of the composite separator.

[0064] The present application does not limit the testing method of the D50 of the first ceramic material and the D50 of the second ceramic material, which can be tested by a laser particle size analyzer, for example.

[0065] In a third aspect, the present application provides a battery comprising the composite separator as described above, which has advantages corresponding to the composite separator described above, and will not be repeated here.

[0066] The battery of the present application further comprises a positive electrode sheet, a negative electrode sheet, an electrolyte, and a shell in addition to the composite separator. The composite separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0067] The positive electrode sheet comprises a positive electrode active material, a conductive agent, and a binder. The positive electrode active material is selected from at least one of ternary layered materials such as LiNi x Co y M (1-x-y) (M is Mn and / or Al), lithium-rich manganese-based material Li2MnO3·LiMO2 (M includes at least one of Ni, Co, Mn), lithium cobaltate LiCoO2, preferably lithium nickel cobalt manganese oxide.

[0068] The negative electrode sheet comprises a negative electrode active material, a conductive agent and a binder, the negative electrode active material is selected from at least one of silicon, tin, silicon oxide, tin oxide, a silicon-carbon composite material, a tin-carbon composite material, a halide of silicon, a halide of tin, a silicon alloy and a tin alloy, and is preferably a graphite silicon-doped composite material. A pre-lithiation layer comprising a lithium foil or lithium powder can be arranged on the surface of the negative electrode sheet, and the pre-lithiation layer and the negative electrode sheet are combined into a pre-lithiation negative electrode sheet through rolling.

[0069] The present application does not particularly limit the specific types of conductive agents and binders, and the components such as conductive agents and binders can be selected from conventional materials in the art. For example, the conductive agent can be selected from one or more of conductive carbon black, carbon nanotubes, conductive graphite and graphene, and the binder can be selected from one or more of polyvinylidene fluoride (PVDF), acrylic modified PVDF, polyacrylate polymer, polyimide, butadiene-styrene rubber and styrene-butadiene rubber.

[0070] In a fourth aspect, the present application provides a battery pack comprising the battery as described above, which has the advantages corresponding to the composite separator described above, and will not be repeated here.

[0071] In a fifth aspect, the present application provides a power-consuming device comprising the battery as described above or the battery pack as described above, which has the advantages corresponding to the composite separator described above, and will not be repeated here.

[0072] The power-consuming device of the present application can be a conventional power-consuming device in the art, such as a power device (e.g., an electric vehicle), an electronic device (e.g., a computer, a mobile phone, a digital camera, a printer, a fax machine, etc.), a wearable device (e.g., a watch, a bracelet, VR glasses, etc.), a household appliance (e.g., an air conditioner, a refrigerator, a washing machine, a microwave oven, etc.), etc., and is not particularly limited.

[0073] The technical solutions of the present application will be further described below in combination with specific embodiments.

[0074] Embodiment 1

[0075] The preparation method of the battery cell of the present embodiment comprises the following steps:

[0076] Preparation of the composite separator:

[0077] 1) 15 parts by mass of the first ceramic material (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2)C (D50 = 1.2 pm), 85 parts by mass of a second ceramic material, alumina powder (D50 = 0.5 pm), 270 parts by mass of pure water, and 0.8 parts by mass of a dispersant (PVP-K30 type) were stirred and dispersed, after which 15 parts by mass of a binder (CM-1020 type) and 0.5 parts by mass of a wetting agent (Capstone FS-31 type) were sequentially added, and stirred and dispersed uniformly to obtain a stable composite material slurry.

[0078] 2) The above composite material slurry was coated on both surfaces of a PE microporous base film with a thickness of 9 pm using a microgravure roll coating process, and the thickness of the composite material layer on each surface was 1.5 pm, to obtain a composite separator precursor, wherein the thread count of the microgravure roll was 150 threads / cm, the thread depth was 40 pm, the coating speed was 40 m / min, and the speed ratio was 110%; the composite separator precursor was dried to obtain a composite separator.

[0079] Positive electrode sheet preparation:

[0080] The ternary positive electrode active material NCM811, conductive carbon black Spuer_Li, and binder PVDF_5130 were mixed in a mass ratio of 100:2:2.2 in N-methylpyrrolidone (NMP) to obtain a uniform slurry, which was then coated on an aluminum current collector, dried, rolled, and die-cut to obtain a positive electrode sheet with an area density of 440 g / m 2 .

[0081] Negative electrode sheet preparation:

[0082] Graphite, silicon-carbon material, CNT, and binder PAA were mixed uniformly in a mass ratio of 87:13:1.2:5 in deionized water to obtain a negative electrode slurry, which was then coated on a copper foil, and the density of the double-sided negative electrode active material layer was 198 g / m 2 . After rolling, a lithium supplement negative electrode sheet was obtained.

[0083] Pre-lithiation of the negative electrode sheet: Lithium powder was added to both sides of the lithium supplement negative electrode sheet, and the surface density of the lithium supplement was 1.5 g / m 2 and the double-sided surface density was 3.0 g / m 2 . A pre-lithiated negative electrode sheet was obtained.

[0084] Battery cell preparation:

[0085] The above-prepared positive electrode sheet, composite separator, and pre-lithiated negative electrode sheet were stacked in order to obtain a 7+8 layer soft-pack battery, and the rated capacity of the battery was 2450 mAh.

[0086] Example 2

[0087] Example 2 and Example 1 were prepared by the same method, except that 40 parts by mass of a first ceramic material (Zr0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C (D50 = 1.2 μm), 60 parts by mass of the second ceramic material alumina powder (D50 = 0.5 μm).

[0088] Example 3

[0089] The preparation method of the battery cell in Example 3 is basically the same as that in Example 1. The difference is that the line count of the microgravure roller is changed to 100 lines / cm and the line depth is 60μm, resulting in a composite material layer thickness of 2.5μm.

[0090] Example 4

[0091] The preparation method of the battery cell in Example 4 is basically the same as that in Example 2. The difference is that the line count of the microgravure roller is changed to 100 lines / cm and the line depth is 60μm, resulting in a composite material layer thickness of 2.5μm.

[0092] Example 5

[0093] The preparation method of the battery cell in Example 5 is basically the same as that in Example 1, except that the first ceramic material is (Zr) 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The first ceramic material is N (D50 = 2.0 μm), and the second ceramic material is boehmite with a D50 of 0.8 μm.

[0094] Example 6

[0095] The preparation method of the battery cell in Example 6 is basically the same as that in Example 1, except that the first ceramic material is (Zr) 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 The first ceramic material is boehmite (D50 = 0.8 μm), and the second ceramic material is boehmite with a D50 of 0.2 μm.

[0096] Example 7

[0097] The preparation method of the battery cell in Example 7 is basically the same as that in Example 1, except that 5 parts by mass of the first ceramic material (Zr) are added. 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 B (D50 = 1.2 μm), 95 parts by mass of the second ceramic material alumina powder (D50 = 0.5 μm).

[0098] Example 8

[0099] The preparation method of the battery cell of Example 8 is basically the same as that of Example 1, except that 50 parts by mass of the first ceramic material (Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )C(D50 = 1.2 pm), 50 parts by mass of the second ceramic material alumina powder (D50 = 0.5 pm) are added.

[0100] Example 9

[0101] The preparation method of the battery cell of Example 9 is basically the same as that of Example 1, except that the line number of the micro gravure roller is changed to 180 lines / cm, the line depth is 20 pm, and the thickness of the composite material layer is 1.0 pm.

[0102] Example 10

[0103] The preparation method of the battery cell of Example 10 is basically the same as that of Example 1, except that the line number of the micro gravure roller is changed to 80 lines / cm, the line depth is 70 pm, and the thickness of the composite material layer is 3.0 pm.

[0104] Comparative Example 1

[0105] The preparation method of the battery cell of Comparative Example 1 is basically the same as that of Example 1, except that the first ceramic material is not added during the preparation of the composite material slurry, and 100 parts by mass of the second ceramic material alumina powder is added.

[0106] Comparative Example 2

[0107] The preparation method of the battery cell of Comparative Example 2 is basically the same as that of Example 1, except that the second ceramic material alumina powder is not added during the preparation of the composite material slurry, and 100 parts by mass of the first ceramic material is added.

[0108] Test Example:

[0109] 1. D50: Take a 5 mm x 5 mm composite separator for SEM-EDS surface observation, and use software to count the particle size distribution and size of the first ceramic material and the second ceramic material.

[0110] 2. Thickness of the composite material layer: After ion cutting of a 5 mm x 5 mm composite separator, perform SEM cross-section test to measure the thickness of the composite material layer.

[0111] 3. Air permeability test: cut 100mm x 100mm composite separator, use American GURLEY-4110N tester, pressure (water column height) 12.39cm, measure the time (s / 100ml) required for 100ml gas (air) to pass through the composite separator. The smaller the value, the better the air permeability.

[0112] 4. Heat shrinkage test: cut the composite separator into 120mm / 100mm according to the mechanical direction / transverse direction (MD / TD), cover an A4 paper on the surface of the composite separator, and stand at 180℃ for 1 hour. Measure the shrinkage size in each direction and calculate the shrinkage ratio.

[0113] 5. Peel strength: cut 40mm x 100mm composite separator, use adhesive tape to fix the composite separator on the fixed clamp and the movable clamp respectively, and stretch reversely at 180℃ to make the composite material layer and the base film peel off. The greater the required tension, the higher the peel strength of the composite separator.

[0114] 6. Hi-pot test: after stacking the core, use 1.25Mpa pressure and 90℃ hot pressing for 60s in the hot press, then perform hi-pot test, hi-pot test voltage U=300V, voltage ramp time t1=1s, voltage holding time t2=5s, leakage current I=25uA. Continuously measure 100pcs cores and count the hi-pot failure rate.

[0115] 7. Capacity test: first, perform liquid injection, aging and formation on the core. Formation steps: 0.05C charging for 2h, standing for 10min, 0.2C charging for 3h, standing for 10min. 0.33C constant current and constant voltage charging to 4.3V, 0.05C cutoff, standing for 10min; 0.33C constant current discharging to 2V, standing for 10min, cycle three times, and take the third discharge capacity as the core capacity, and stand for 10min.

[0116] 8. Thermal runaway test: use 0.33C CC-CV to charge to 4.3V, 0.05C to full charge, stand for 30min, then put the battery in the temperature box, and the temperature box is raised from room temperature to the temperature at which the battery voltage sharply decreases and the battery produces gas and expands at a rate of 5℃ / min. Record the temperature and time experienced at this time.

[0117] Table 1

[0118]

[0119] As can be seen from Table 1, compared with the comparative examples, the composite material layer in the composite separator provided by the application comprises the first ceramic material and the second ceramic material, which can not only play the advantages of the second ceramic material of being dense and high in compressive strength, but also play the characteristics of the first ceramic material of being low in thermal conductivity, low in density and high in porosity, so that the mechanical strength and the thermal stability of the composite separator are relatively high, and the safety of the battery can be improved when the composite separator is applied to the battery.

[0120] As can be seen from the comparison between Example 1 and Comparative Example 1-2, the composite separator provided by the application has a low thermal shrinkage ratio, a high thermal runaway temperature, a long duration of heating to thermal runaway, a low Hi-pot failure rate and a high peeling strength.

[0121] Finally, it should be noted that: the above examples are only used to illustrate the technical solutions of the application, but not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacement for part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the application.

Claims

1. A composite diaphragm, characterized in that, The material includes a base film and a composite material layer present on at least one side of the base film. The composite material layer includes a first ceramic material and a second ceramic material. The first ceramic material is a high-entropy porous ceramic material containing at least five metal elements, and the second ceramic material is a ceramic material containing fewer than five metal elements. The D50 of the first ceramic material is 0.8μm-2μm; And / or, the D50 of the second ceramic material is 0.2μm-0.8μm.

2. The composite diaphragm according to claim 1, characterized in that, The first ceramic material includes at least one of high-entropy porous oxide ceramic material, high-entropy porous carbide ceramic material, high-entropy porous nitride ceramic material, high-entropy porous boride ceramic material, and high-entropy porous sulfide ceramic material.

3. The composite diaphragm according to claim 2, characterized in that, The first ceramic material includes (Zr) 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 C、(Zr) 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 )N、(Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 O、(Zr 0.2 Hf 0.2 Ti 0.2 Nb 0.2 Ta 0.2 At least one of B.

4. The composite diaphragm according to any one of claims 1-3, characterized in that, The second ceramic material includes at least one of boehmite, alumina, silicon dioxide, titanium dioxide, barium oxide, magnesium oxide, barium titanate, zirconium oxide, and magnesium hydroxide.

5. The composite diaphragm according to claim 1, characterized in that, The first ceramic material accounts for 5%-50% of the total mass of the first ceramic material and the second ceramic material.

6. The composite diaphragm according to claim 5, characterized in that, The first ceramic material accounts for 15%-40% of the total mass of the first ceramic material and the second ceramic material.

7. The composite diaphragm according to claim 1, characterized in that, The thickness of the composite material layer is 1μm-3μm.

8. The composite diaphragm according to claim 7, characterized in that, The thickness of the composite material layer is 1.5μm-3μm.

9. The composite diaphragm according to claim 1, characterized in that, The D50 of the first ceramic material is 1.0μm-1.6μm; And / or, the D50 of the second ceramic material is 0.3μm-0.6μm.

10. A battery, characterized in that, Includes the composite diaphragm according to any one of claims 1-9.

11. A battery pack, characterized in that, Includes the battery as described in claim 10.

12. An electrical appliance, characterized in that, Includes the battery of claim 10 or the battery pack of claim 11.

Images