Separator and manufacturing method therefor, and secondary battery

Abstract

A separator and a manufacturing method therefor, and a secondary battery. The separator comprises a porous substrate and a coating which is provided on at least one surface of the porous substrate, wherein the coating comprises nanofibers and ceramic particles. A heat-resistance skeleton is formed in a coating by means of nanofibers, and ceramic particles have relatively good thermal stability and electrical conductivity and act synergistically with the nanofibers, so as to endow the nanofibers with good thermal stability and electrical conductivity, such that a separator has both relatively high safety at high temperatures and relatively good rate performance when being used in secondary batteries, thereby having wide application prospects in the field of secondary batteries, and particularly in the field of large-capacity and large-rate secondary batteries.

Description

Separator, preparation method thereof, and secondary battery Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and more specifically to a diaphragm and a preparation method thereof, and a secondary battery. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density and power density, high operating voltage, light weight, small size, long cycle life, high operating voltage, high energy density, good safety, and green environmental protection. They have broad application prospects in portable appliances, digital products, power tools, large-scale energy storage, electric transportation power supply, electric vehicles, etc.

[0003] The four key materials in lithium-ion batteries are the positive electrode material, the negative electrode material, the electrolyte, and the separator. The separator's primary function is to separate the positive and negative electrodes and prevent electrons from passing through them, while allowing ions to pass through. This allows for the rapid transfer of lithium ions between the positive and negative electrodes during charging and discharging, preventing contact and short circuits between the positive and negative electrodes.

[0004] However, conventional PP separator substrates have a melting point of 164-170°C, soften at around 155°C, and easily deform and shrink when heated, resulting in suboptimal high-temperature heat resistance. Ceramic coatings are often applied to the substrate surface to improve heat resistance, but conventional heat-resistant coated separators often struggle to balance high-temperature safety and rate performance in secondary batteries.

[0005] Therefore, how to solve the problem of balancing heat resistance and rate performance when using PP separators in secondary batteries is a technical problem that urgently needs to be solved in this field.

[0006] Summary of the Invention

[0007] The present application provides a diaphragm, a preparation method thereof, and a secondary battery, wherein the diaphragm can effectively solve the problem of difficulty in achieving both high-temperature safety and good rate performance.

[0008] According to a first aspect, the present application provides a membrane comprising a porous substrate and a coating provided on at least one surface of the porous substrate;

[0009] The coating includes nanofibers and ceramic particles.

[0010] In an optional embodiment, the MD thermal shrinkage / coating air permeability increment of the diaphragm baked at 180° C. for 1 hour is ≤0.3%·s -1 100 mL

[0011] The MD thermal shrinkage of the membrane baked at 180°C for 1 hour / coating surface density is ≤0.75%·g -1 ·m 2;

[0012] And, the coating air permeability value-added is 10s / 100mL-100s / 100mL.

[0013] In an optional embodiment, the diaphragm satisfies at least one of the conditions (1) to (4):

[0014] (1) The MD thermal shrinkage of the diaphragm after baking at 180°C for 1 hour is ≤3%;

[0015] (2) The surface density of the coating is ≤4g / m 2 ;

[0016] (3) The thickness of the coating on one side is 0.2 μm to 3 μm;

[0017] (4) The total thickness of the coating is 0.2 μm-6 μm.

[0018] In an optional embodiment, the diaphragm satisfies at least one of the conditions (1) to (3):

[0019] (1) In the coating, the mass percentage of the nanofibers is 3%-20%;

[0020] (2) In the coating, the mass percentage of the ceramic particles is 65%-90%;

[0021] (3) In the coating, the mass ratio of the nanofibers to the ceramic particles is (0.15-0.3):1.

[0022] In an optional embodiment, the nanofibers include at least one of inorganic nanofibers and organic nanofibers; the nanofibers satisfy at least one of the conditions (1) to (4):

[0023] (1) The inorganic nanofiber includes at least one of silicon carbide fiber, titanium carbide fiber, zirconium carbide fiber, tungsten carbide fiber, boron carbide fiber, boron nitride fiber, silicon nitride fiber, and carbon nanotube;

[0024] (2) The organic nanofiber includes at least one of nanocellulose, aramid fiber, and polyimide fiber;

[0025] (3) The nanofibers include nanocellulose, and the diameter of the nanocellulose is 4 nm to 10 nm;

[0026] (4) The nanofibers include nanocellulose, and the length of the nanocellulose is 100 nm to 500 nm.

[0027] In an optional embodiment, the ceramic particles include at least one of oxide ceramics, nitride ceramics and carbide ceramics; and the ceramic particles meet at least one of the conditions (1) to (4):

[0028] (1) The oxide ceramic comprises at least one of silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, and zinc oxide;

[0029] (2) The nitride ceramic includes at least one of boron nitride and silicon nitride;

[0030] (3) The carbide ceramic includes at least one of silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, and boron carbide;

[0031] (4) The particle size D50 of the ceramic particles is 50nm-1000nm.

[0032] In an optional embodiment, the coating further comprises a binder, and the binder satisfies at least one of the conditions (1) to (2):

[0033] (1) In the coating, the mass percentage of the binder is 0.1%-15%;

[0034] (2) The adhesive includes at least one of polyacrylate, polyacrylonitrile, styrene-butadiene rubber, and polyurethane.

[0035] In an optional embodiment, the coating further comprises a dispersant; the dispersant satisfies at least one of the conditions (1) to (2):

[0036] (1) In the coating, the mass percentage of the dispersant is 0.1%-5%;

[0037] (2) The dispersant includes at least one of sodium carboxymethyl cellulose, sodium polyacrylate, ammonium polyacrylate, n-butanol, and cyclohexanol.

[0038] According to a second aspect, the present application provides a method for preparing a diaphragm, the steps of which include:

[0039] Dispersing the nanofibers and ceramic particles in a solvent to prepare a coating slurry;

[0040] The coating slurry is applied on at least one surface of a porous substrate and dried to form a coating layer, thereby finally obtaining the separator.

[0041] In an optional embodiment, the coating slurry has a solid content of 20%-80%.

[0042] According to a third aspect, the present application provides a secondary battery, comprising the separator as described above, or a separator prepared by the method as described above.

[0043] The beneficial effects of the present application are as follows: the diaphragm prepared by the present application forms a heat-resistant skeleton in the coating through nanofibers, and the ceramic particles have good thermal stability and conductivity, which synergize with the nanofibers to give them good thermal stability and conductivity, so that the diaphragm has both good high-temperature safety and good rate performance when used in secondary batteries. It has broad application prospects in the field of secondary batteries, especially in the field of large-capacity and high-rate secondary batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] FIG1 is a schematic structural diagram of a diaphragm in one embodiment;

[0045] FIG2 is a schematic structural diagram of a diaphragm in another embodiment. DETAILED DESCRIPTION

[0046] The present application is further described in detail below by means of specific embodiments in conjunction with the accompanying drawings. Similar elements in different embodiments are numbered with associated similar elements. In the following embodiments, many detailed descriptions are provided to enable the present application to be better understood. However, those skilled in the art will readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid the core portion of the present application being overwhelmed by excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0047] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various implementations, and the operational steps involved in each embodiment may be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the specification and drawings are only for the purpose of clearly describing a particular embodiment and do not imply a required composition and / or sequence.

[0048] The serial numbers assigned to components herein, such as "first," "second," etc., are used solely to distinguish the objects being described and do not convey any sequential or technical meaning. References to "connection" and "coupling" herein, unless otherwise specified, include both direct and indirect connections (couplings).

[0049] The diaphragm is a crucial component of lithium-ion batteries, isolating the positive and negative electrodes to prevent short circuits. It also provides ion conduction, allowing electrochemical reactions to proceed smoothly. The diaphragm significantly impacts the battery's cycling performance, rate capability, and safety. Generally, due to the impact of its operating environment, the diaphragm requires high heat resistance, meaning good thermal shrinkage. However, while commonly used methods can improve heat resistance, they can also affect the rate performance of the diaphragm in batteries.

[0050] To this end, the present application provides a separator, comprising a porous substrate 100 and a coating 200 disposed on at least one surface of the porous substrate 100 , wherein the coating 200 comprises nanofibers and ceramic particles.

[0051] 1 and 2 , the at least one surface mentioned above includes a coating 200 optionally provided on one surface of the porous substrate 100 , as shown in FIG. 1 , or a coating 200 provided on both surfaces of the porous substrate 100 , as shown in FIG. 2 .

[0052] The aforementioned nanofibers form a heat-resistant skeleton within coating 200. The ceramic particles, which possess excellent thermal stability, are incorporated into the nanofiber skeleton and, acting synergistically with the nanofibers, form a heat-resistant coating 200 on the surface of porous substrate 100, thereby enhancing the heat resistance of the separator in battery applications. Furthermore, the ceramic particles themselves possess excellent electrical conductivity, ensuring good rate performance for the battery. This separator is particularly suitable for high-capacity, high-rate secondary batteries.

[0053] In an optional embodiment, the MD thermal shrinkage of the membrane baked at 180° C. for 1 hour / the increase in air permeability of the coating is ≤0.3%·s -1 100mL, and the MD thermal shrinkage of the separator baked at 180℃ for 1h / coating surface density ≤ 0.75%·g -1 ·m 2 , the coating permeability value-added is 10s / 100mL-100s / 100mL. For example, the MD heat shrinkage rate / coating permeability value-added of the diaphragm baked at 180°C for 1 hour can be selected as 0.01%·s -1 100mL, 0.02%·s -1 100mL, 0.05%·s -1 100mL, 0.1% s -1 100mL, 0.2%·s -1 100mL, 0.03%·s -1 ·Any value within the range of 100mL or above. The MD thermal shrinkage / coating surface density of the separator baked at 180°C for 1 hour can be selected as 0.1%·g -1 ·m2 , 0.2%·g -1 ·m 2 , 0.3%·g -1 ·m 2 , 0.4%·g -1 ·m 2 , 0.5% g -1 ·m 2 , 0.6%·g -1 ·m 2 , 0.7%·g -1 ·m 2 , 0.75%·g -1 ·m 2 The added value of coating air permeability is 10s / 100mL, 20s / 100mL, 30s / 100mL, 40s / 100mL, 50s / 100mL, 60s / 100mL, 70s / 100mL, 80s / 100mL, 90s / 100mL and 100s / 100mL.

[0054] MD, or Machine Direction, refers to the longitudinal direction of the membrane. MD thermal shrinkage refers to the rate of change in the membrane's dimensions in the MD direction when heated.

[0055] The coating permeability value-added refers to the difference between the permeability value of the membrane with coating and the permeability value of the membrane without coating (i.e., pure porous substrate), which is used to illustrate the effect of coating on the permeability of the membrane.

[0056] The coating surface density refers to the coating mass per unit area of ​​the diaphragm.

[0057] By controlling the thermal shrinkage rate of the diaphragm baked at 180°C for 1 hour, the coating air permeability value-added and the coating surface density to meet the above relationship, the above diaphragm can be used in secondary batteries with both good high-temperature safety and good rate performance, and is particularly suitable for large-capacity, high-rate secondary batteries.

[0058] Optionally, the MD thermal shrinkage of the membrane baked at 180°C for 1 hour / the increase in air permeability of the coating is 0.02%·s -1 100mL-0.3%·s -1 ·100mL. The MD thermal shrinkage of the separator baked at 180℃ for 1h / coating surface density is 0.35%·g -1 .m 2 -0.75%·g -1 ·m 2 .

[0059] In an optional embodiment, the MD thermal shrinkage of the separator after baking at 180°C for 1 hour is ≤3%. By controlling the MD thermal shrinkage within the above range, the separator has better heat resistance. Optionally, the MD shrinkage of the separator after baking at 180°C for 1 hour is ≤2%, ≤1%, or ≤0.5%.

[0060] In an optional embodiment, the surface density of the coating 200 is ≤ 4 g / m 2 By controlling the appropriate coating surface density, the separator can ensure better heat resistance while avoiding excessive increase in separator weight and affecting battery energy density. Optionally, the surface density of the coating 200 is 0.5g / m 2 -4g / m 2 For example, you can choose 0.5g / m 2 , 0.54g / m 2 , 2g / m 2 , 3g / m 2 , 3.8g / m 2 , 4g / m 2 Or any value within the range of the above values. In some embodiments, the coating surface density is 1.5g / m 2 -4g / m 2 .

[0061] In an optional embodiment, the single-side thickness of the coating 200 is 0.2 μm-3 μm. Optionally, the single-side thickness of the coating 200 is 0.2 μm-2 μm, for example, the single-side thickness of the coating 200 can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, etc.

[0062] In an optional embodiment, the total thickness of the coating 200 is 0.2 μm-6 μm. Alternatively, the total thickness of the coating 200 may be 0.2 μm, 0.4 μm, 1 μm, 2 μm, 3 μm, 4.1 μm, 4.5 μm, 6 μm, or any range thereof.

[0063] In an optional embodiment, the nanofibers include at least one of inorganic nanofibers and organic nanofibers. Optionally, the inorganic nanofibers include at least one of silicon carbide fibers, titanium carbide fibers, zirconium carbide fibers, tungsten carbide fibers, boron carbide fibers, boron nitride fibers, silicon nitride fibers, and carbon nanotubes. The organic nanofibers include at least one of nanocellulose, aramid fibers, and polyimide fibers.

[0064] In an optional embodiment, the nanofiber comprises nanocellulose. The diameter of the nanocellulose is 4 nm to 10 nm. For example, the diameter of the nanocellulose can be optionally set to 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, or any range consisting of the above values.

[0065] In an alternative embodiment, the nanofibers have a length of 100 nm to 500 nm. For example, the length of the nanofibers can be set to 100 nm, 120 nm, 130 nm, 140 nm, 150 nm, 160 nm, 170 nm, 180 nm, 190 nm, 200 nm, 300 nm, 400 nm, 500 nm, or any range thereof. Alternatively, the length of the nanocellulose is 100 nm to 200 nm.

[0066] In an optional embodiment, the ceramic particles include at least one of oxide ceramics, nitride ceramics, and carbide ceramics. Oxide ceramics include, but are not limited to, silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, and zinc oxide. Nitride ceramics include, but are not limited to, boron nitride and silicon nitride. Carbide ceramics include, but are not limited to, silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, and boron carbide.

[0067] In an optional embodiment, the particle size D50 of the ceramic particles is 50 nm to 1000 nm. For example, the particle size D50 of the ceramic particles can be set to 50 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or any range thereof. Alternatively, the particle size D50 of the ceramic particles is 100 nm to 600 nm or 200 nm to 500 nm.

[0068] In an optional embodiment, the mass percentage of nanofibers in the coating is 3%-20%. For example, the mass percentage of nanofibers can be 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or any range thereof.

[0069] In an optional embodiment, the mass percentage of ceramic particles in the coating is 65%-90%. For example, the mass percentage of ceramic particles can be 65%, 70%, 75%, 80%, 85%, 90%, or any range thereof. Optionally, the mass percentage of ceramic particles is 70%-85%.

[0070] In an optional embodiment, the ratio of nanofibers to ceramic particles in the coating is (0.15-0.3) : 1 by weight. For example, the ratio of nanofibers to ceramic particles can be 0.15:1, 0.2:1, 0.25:1, 0.3:1, or any range thereof.

[0071] In an optional embodiment, in order to improve the bonding force and make the final film have a certain strength, the coating 200 further includes a binder. Optionally, the binder includes polyacrylate, polyacrylonitrile, styrene-butadiene rubber, and polyurethane.

[0072] In an optional embodiment, the mass percentage of the binder is 0.1%-15%. For example, the mass percentage of the binder can be 0.1%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or any range thereof. Optionally, the mass percentage of the binder is 1%-10%.

[0073] In an optional embodiment, in order to improve the uniformity of the coating 200 and make the various components dispersed and mixed evenly, the coating 200 also includes a dispersant, and the dispersant includes one of sodium carboxymethyl cellulose, sodium polyacrylate, ammonium polyacrylate, n-butanol, and cyclohexanol. The mass percentage of the dispersant is 0.1%-5%. For example, the mass percentage of the dispersant can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 2%, 3%, 4%, 5% or any value above.

[0074] In an optional embodiment, the porous substrate 100 can be selected from a single-layer polyolefin substrate, a double-layer polyolefin substrate, and a multi-layer polyolefin substrate. Specifically, in a double-layer polyolefin substrate or a multi-layer polyolefin substrate, the polyolefin type used in each layer can be the same or different. Optionally, the porous substrate 100 can be prepared by a dry stretching process. Specifically, the porous substrate 100 is prepared by a dry uniaxial stretching process.

[0075] In an optional embodiment, the porosity of the porous substrate 100 is 10%-70%. For example, the porosity of the porous substrate 100 can be 10%, 20%, 30%, 40%, 50%, 60%, 70%, or any range thereof.

[0076] In an optional embodiment, the average pore size of the porous substrate 100 is 10 nm to 120 nm. For example, the average pore size of the porous substrate 100 can be 10 nm, 20 nm, 40 nm, 50 nm, 60 nm, 80 nm, 100 nm, 120 nm, or any range thereof.

[0077] In an optional embodiment, the thickness of the porous substrate 100 is 2 μm-25 μm. For example, the thickness of the porous substrate 100 can be 2 μm, 4 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, or any range thereof.

[0078] Furthermore, the present application also provides a method for preparing a diaphragm, the steps of which include:

[0079] S1: Provide nanofibers, ceramic particles, dispersants and binders that meet the ratio requirements.

[0080] The mass percentage of the nanofibers is 3%-20%, the mass percentage of the ceramic particles is 65%-90%, the mass percentage of the dispersant is 0.1%-5%, and the mass percentage of the binder is 0.1%-15%.

[0081] S2: The nanofibers and ceramic particles are dispersed in a solvent by means of a dispersant and a binder, and the coating slurry is prepared after being fully mixed. During the mixing, a mixer or other equipment can be used for fully and evenly mixing.

[0082] S3: coating the coating slurry on at least one surface of the porous substrate, and drying to form a coating layer 200, thereby finally obtaining a separator.

[0083] Optionally, the coating slurry can be applied to the surface of the porous substrate by dip coating, air knife coating, curtain coating, roll coating, wire rod coating, gravure coating, or die coating. The drying method can be low-temperature drying, such as drying at 30-50 degrees.

[0084] In an optional embodiment, the coating slurry has a solid content of 20%-80%. For example, the coating slurry may have a solid content of 20%, 30%, 40%, 50%, 60%, 70%, 80%, or any range thereof. Alternatively, the coating slurry has a solid content of 40%-60%.

[0085] Furthermore, the present application also provides a secondary battery, comprising a positive electrode sheet, a negative electrode sheet, and a separator separated between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator provided in any of the above embodiments.

[0086] In an optional embodiment, the secondary battery includes a lithium ion battery, a lithium metal battery, a sodium ion battery, a solid electrolyte battery, etc.

[0087] In alternative embodiments, the secondary battery may be used in vehicles, cell phones, portable devices, laptop computers, ships, spacecraft, electric toys, electric tools, and the like.

[0088] In order to illustrate the effects of this application, this application also provides the following more specific embodiments.

[0089] Example 1

[0090] Nanofibers, ceramic particles, dispersants and binders that meet the ratio requirements are provided, and raw materials are provided according to the mass ratio of nanocellulose, Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a ratio of 15:75:9.8:0.2. The nanofibers and ceramic particles are dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after fully stirring, a coating slurry with a solid content of 50% is prepared.

[0091] The diameter of the nanocellulose is 10 nm and the length is 200 nm, and the particle size D50 of the ceramic particles is 200 nm.

[0092] A PP microporous membrane with a thickness of 12 μm was selected as the porous substrate 100 , and the coating slurry was coated on two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating layer 200 was formed, and finally a diaphragm was prepared.

[0093] The total thickness of the membrane coating finally prepared above is 4.5 μm, and the coating surface density is 3.8 g / m 2 .

[0094] Example 2

[0095] The diaphragm was prepared according to the method of Example 1.

[0096] The difference is that the proportion of each component in this embodiment is deionized water, nanocellulose, Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a mass ratio of 20:70:9.8:0.2. The diameter of nanocellulose is 10nm and the length is 200nm. The particle size D50 of the above-mentioned ceramic particles is 200nm. The nanofibers and ceramic particles are dispersed in deionized water by sodium carboxymethyl cellulose and polyacrylate, and after being fully stirred, a coating slurry with a solid content of 20% is prepared. A PP microporous membrane with a thickness of 12μm is selected as the porous substrate 100, and the above-mentioned coating slurry is coated on the two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating 200 is formed, and finally a diaphragm is prepared. The total thickness of the diaphragm coating finally prepared is 2μm, and the coating surface density is 3.1g / m 2 The above-mentioned separator is then used to prepare a battery.

[0097] Example 3

[0098] The diaphragm was prepared according to the method of Example 1.

[0099] The difference is that the proportion of each component in this embodiment is nanocellulose, Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a mass ratio of 3:81:15:1. The diameter of nanocellulose is 10nm and the length is 200nm. The particle size D50 of the above-mentioned ceramic particles is 200nm. The nanofibers and ceramic particles are dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after being fully stirred, a coating slurry with a solid content of 80% is prepared. A PP microporous membrane with a thickness of 12μm is selected as the porous substrate 100, and the above-mentioned coating slurry is coated on the two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating 200 is formed, and finally a diaphragm is prepared. The total thickness of the diaphragm coating finally prepared is 4.2μm, and the coating surface density is 4g / m 2 The above-mentioned separator is then used to prepare a battery.

[0100] Example 4

[0101] The diaphragm was prepared according to the method of Example 1.

[0102] The difference is that the proportion of each component in this embodiment is nanocellulose, Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a mass ratio of 15:75:9.8:0.2. The diameter of nanocellulose is 10nm and the length is 200nm. The particle size D50 of the above-mentioned ceramic particles is 200nm. The nanofibers and ceramic particles are dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after being fully stirred, a coating slurry with a solid content of 20% is prepared. A PP microporous membrane with a thickness of 12μm is selected as the porous substrate 100, and the above-mentioned coating slurry is coated on the two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating 200 is formed, and finally a diaphragm is prepared. The total thickness of the diaphragm coating finally prepared is 1.5μm, and the coating surface density is 1.5g / m 2 The above-mentioned separator is then used to prepare a battery.

[0103] Example 5

[0104] The diaphragm was prepared according to the method of Example 1.

[0105] The difference is that the proportion of each component in this embodiment is nanocellulose, Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a mass ratio of 15:75:9.8:0.2. The diameter of nanocellulose is 10nm and the length is 200nm. The particle size D50 of the above-mentioned ceramic particles is 200nm. The nanofibers and ceramic particles are dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after being fully stirred, a coating slurry with a solid content of 80% is prepared. A PP microporous membrane with a thickness of 12μm is selected as the porous substrate 100, and the above-mentioned coating slurry is coated on the two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating 200 is formed, and finally a diaphragm is prepared. The total thickness of the diaphragm coating finally prepared is 6.5μm, and the coating surface density is 4.5g / m 2 The above-mentioned separator is then used to prepare a battery.

[0106] Example 6

[0107] A high heat-resistant and high breathability diaphragm was prepared by referring to the method of Example 1.

[0108] The difference is that the proportion of each component in this embodiment is nanocellulose, Al2O3, adhesive polyacrylate, and dispersant sodium carboxymethyl cellulose in a mass ratio of 20:70:9.8:0.2. The diameter of the nanocellulose is 10nm and the length is 200nm. The particle size D50 of the above-mentioned ceramic particles is 200nm. The nanofibers and ceramic particles are dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after being fully stirred, a coating slurry with a solid content of 60% is prepared. A PP microporous membrane with a thickness of 12μm is selected as the porous substrate 100, and the above-mentioned coating slurry is coated on the two opposite surfaces of the porous substrate 100 by double-sided roller coating. After drying, a coating 200 is formed, and finally a diaphragm is prepared. The total thickness of the diaphragm coating finally prepared is 5.1μm, and the coating surface density is 4.1g / m 2 The above-mentioned separator is then used to prepare a battery.

[0109] Example 7

[0110] A PP microporous membrane with a thickness of 12 μm was directly selected as the separator.

[0111] Example 8

[0112] The diaphragm was prepared according to the method of Example 1.

[0113] In this embodiment, the proportion of each component is Al2O3, adhesive polyacrylate and dispersant sodium carboxymethyl cellulose in a mass ratio of 84:15:1. Al2O3 is dispersed in deionized water through sodium carboxymethyl cellulose and polyacrylate, and after thorough stirring, a coating slurry with a solid content of 80% is prepared. A PP microporous membrane with a thickness of 12 mm is selected as the porous substrate 100. The above coating slurry is applied to the two opposite surfaces of the porous substrate 100 by double-sided roller coating to form a coating 200. After drying, the coating 200 is prepared, and finally a diaphragm is obtained. The total thickness of the diaphragm coating finally prepared is 4 μm, and the coating surface density is 3.7 g / m 2 The above-mentioned separator is then used to prepare a battery.

[0114] Example 9

[0115] The membranes prepared in Examples 1 to 8 were tested for total coating thickness, coating surface density, MD shrinkage after baking at 180° C. for 1 h, coating air permeability value, voltage resistance, and ionic conductivity.

[0116] Among them, the total coating thickness test can refer to the standard GB / T6672-2001 "Plastic film and sheeting - Mechanical measurement method" and use a non-contact method to measure the total thickness of the coating on the diaphragm. During the measurement, at least 5 measurement points are selected along the length of the diaphragm, and the final result is the average value of the 5 measurement points.

[0117] The coating areal density refers to the mass of the coating per unit area of ​​the separator. This parameter is directly related to the performance and lifespan of the battery. The coating areal density test method includes the following steps: Take three 100mm samples, weigh the samples before and after coating using an analytical balance, and calculate the coating areal density based on the mass and area of ​​the separator.

[0118] The test method for the thermal shrinkage rate of MD after baking at 180°C for 1 hour is carried out in accordance with the requirements of GB / T12027-2004. The test includes the following steps:

[0119] Cut a diaphragm of 15*15cm in size, mark the longitudinal and transverse lengths of the sample on the surface of the diaphragm with a ruler, and measure the longitudinal and transverse lengths of the sample respectively with a ruler; place the sample flat in a fixture, and then place it in an oven at 180℃ for 1h; after heating, take out the sample, and after returning to room temperature, measure the longitudinal marked length again, calculate the shrinkage rate according to the following formula, and finally take the average value of several samples as the thermal shrinkage rate.

[0120] ΔL: thermal shrinkage of the sample in the longitudinal direction, expressed in %; L0: length of the sample in the longitudinal direction before heating, in millimeters (mm); L: length of the sample in the longitudinal direction after heating, in millimeters (mm).

[0121] The test method for the value-added air permeability of the coating includes the following steps:

[0122] A 100mm x 100mm membrane sample was tested using a Gurley 4110N air permeability tester (USA) using 100mL of test gas. The time required for the test gas to completely pass through the membrane sample was recorded as the air permeability value. The coating air permeability value was calculated by subtracting the air permeability value of the uncoated membrane (i.e., the pure porous substrate) from the air permeability value of the coated membrane.

[0123] The withstand voltage test method includes the following steps: selecting a 100 mm x 100 mm membrane sample, applying a certain voltage on both sides of the membrane, and testing its breakdown value, which is the withstand voltage of the membrane sample.

[0124] Among them, the testing method of ionic conductivity is to use three electrodes as working electrode, reference electrode and calculation electrode respectively, and calculate the ionic conductivity by measuring the potential difference between the electrodes. The steps are to place the diaphragm prepared in this application in the electrolyte solution and place it between the two electrodes, then apply current and voltage, measure the potential difference and record it, and calculate the ionic conductivity based on the measurement results and the calibrated curve.

[0125] The specific test results are shown in Tables 1 and 2 below.

[0126] Table 1

[0127] Table 2

[0128] It can be seen from the above table that compared with Example 1 and Example 4, the coating thickness and surface density of Example 4 are smaller, the heat shrinkage rate is higher, and it is difficult to meet the heat resistance requirements. In addition, the coating thickness and surface density are reduced, and the ion conductivity is not significantly improved.

[0129] It can be seen from the above table that, compared with Example 1, Example 7 and Example 8, Examples 7 and 8 have poor thermal shrinkage. It can also be seen that the addition of nanocellulose can significantly improve the heat resistance.

[0130] It can be seen from the above table that, compared with Example 2, Example 6 has better heat resistance, but the air permeability value is too high, which affects ion conduction.

[0131] In summary, the heat resistance, withstand voltage, and ionic conductivity of Examples 1 to 5 are significantly better than those of Examples 6 to 8. This illustrates a membrane made of a porous substrate 100 and a coating made of nanofibers and ceramic particles on at least one surface thereof, and by controlling its surface density, thickness, and solid content, the membrane satisfies the MD shrinkage / coating air permeability increase requirement of ≤0.3%·s after baking at 180°C for 1 hour. -1 ·100mL, and the MD shrinkage of the separator baked at 180℃ for 1h / coating surface density ≤0.75%·g -1 ·m 2 The coating permeability value-added is 10s / 100mL-100s / 100mL. The diaphragm has good heat resistance, good pressure resistance and ionic conductivity. The diaphragm prepared by it can perfectly solve the problem that traditional ceramic coating diaphragms cannot have both good heat resistance and rate performance.

[0132] The secondary battery separator provided in this application is endowed with good thermal stability and conductivity through nanofibers and ceramic particles, so that the separator has both good high-temperature safety and good rate performance when used in secondary batteries. It has broad application prospects in the field of secondary batteries, especially in the field of large-capacity and high-rate secondary batteries.

[0133] The above specific examples are used to illustrate the present application, which is only used to help understand the present application and is not intended to limit the present application. For those skilled in the art of the present application, based on the concept of the present application, they can also make some simple deductions, modifications or substitutions.

Claims

1. A diaphragm, characterized in that: It comprises a porous substrate and a coating disposed on at least one surface of the porous substrate; The coating comprises nanofibers and ceramic particles, and the MD thermal shrinkage rate / coating air permeability increment of the diaphragm baked at 180° C. for 1 hour is ≤0.3%·s -1 ·100mL, and the MD thermal shrinkage of the membrane baked at 180°C for 1h / coating surface density ≤0.75%·g -1 ·m 2 , and the coating has an added value of air permeability of 10s / 100mL-100s / 100mL.

2. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the conditions (1) to (4): (1) The MD thermal shrinkage of the diaphragm baked at 180° C. for 1 hour is ≤3%; (2) The surface density of the coating is ≤4 g / m 2 ; (3) The single-side thickness of the coating is 0.2 μm-3 μm; (4) The total thickness of the coating is 0.2 μm-6 μm.

3. The diaphragm according to claim 1, characterized in that The diaphragm satisfies at least one of the conditions (1) to (3): (1) In the coating, the mass percentage of the nanofibers is 3%-20%; (2) In the coating, the mass percentage of the ceramic particles is 65%-90%; (3) In the coating, the mass ratio of the nanofibers to the ceramic particles is (0.15-0.3):

1.

4. The diaphragm according to claim 1, characterized in that The nanofibers include at least one of inorganic nanofibers and organic nanofibers; the nanofibers satisfy at least one of the conditions (1) to (4): (1) The inorganic nanofibers include at least one of silicon carbide fibers, titanium carbide fibers, zirconium carbide fibers, tungsten carbide fibers, boron carbide fibers, boron nitride fibers, silicon nitride fibers, and carbon nanotubes; (2) The organic nanofibers include at least one of nanocellulose, aramid fibers, and polyimide fibers; (3) The nanofibers include nanocellulose, and the diameter of the nanocellulose is 4 nm-10 nm; (4) The nanofibers include nanocellulose, and the length of the nanocellulose is 100nm-500nm.

5. The diaphragm according to claim 1, characterized in that The ceramic particles include at least one of oxide ceramics, nitride ceramics and carbide ceramics; the ceramic particles meet at least one of the conditions (1) to (4): (1) The oxide ceramic comprises at least one of silicon dioxide, aluminum oxide, zirconium oxide, titanium oxide, and zinc oxide; (2) The nitride ceramic includes at least one of boron nitride and silicon nitride; (3) The carbide ceramic includes at least one of silicon carbide, titanium carbide, zirconium carbide, tungsten carbide, and boron carbide; (4) The particle size D50 of the ceramic particles is 50nm-1000nm.

6. The diaphragm according to any one of claims 1 to 5, characterized in that The coating further comprises a binder, and the binder satisfies at least one of the conditions (1) to (2): (1) In the coating, the mass percentage of the binder is 0.1%-15%; (2) The binder includes at least one of polyacrylate, polyacrylonitrile, styrene-butadiene rubber, and polyurethane.

7. The diaphragm according to any one of claims 1 to 5, characterized in that The coating further comprises a dispersant; the dispersant satisfies at least one of the conditions (1) to (2): (1) In the coating, the mass percentage of the dispersant is 0.1%-5%; (2) The dispersant includes at least one of sodium carboxymethyl cellulose, sodium polyacrylate, ammonium polyacrylate, n-butanol, and cyclohexanol.

8. A method for preparing a diaphragm, wherein the diaphragm is the diaphragm according to any one of claims 1 to 7, characterized in that: The steps include: Dispersing the nanofibers and ceramic particles in a solvent to prepare a coating slurry; The coating slurry is applied on at least one surface of a porous substrate and dried to form a coating layer, thereby finally obtaining the separator.

9. The method for preparing a diaphragm according to claim 8, characterized in that: The solid content of the coating slurry is 20%-80%.

10. A secondary battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 7, or comprises the diaphragm prepared by the method according to any one of claims 8 to 9.

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