Separator, and preparation method therefor and use thereof

Abstract

The present disclosure belongs to the technical field of battery materials, and discloses a separator, and a preparation method therefor and the use thereof. The separator comprises a base membrane and a coating applied to at least one side surface of the base membrane. The coating comprises an inorganic adhesive and inorganic particles. The coating contains crystals formed by the inorganic adhesive, wherein the crystals comprise at least acicular whiskers, some of the crystals jointly form whisker clusters, and the remaining crystals are located between the inorganic particles. The separator exhibits good stability and durability at high temperatures, and also has high peel strength, wettability, ionic conductivity, puncture strength and air permeability, ensuring that a battery can still operate safely and efficiently under high-temperature conditions. The preparation method for the separator is simple, and is easy for industrial scale production, offering good prospects for industrialization.

Description

A diaphragm, its preparation method and application

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese Patent Application No. 2024117099234, filed on November 27, 2024, entitled "A diaphragm and its preparation method and application", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This disclosure relates to the field of battery materials technology, and more specifically, to a separator, its preparation method, and its application. Background Technology

[0004] Lithium-ion batteries possess advantages such as high operating voltage, high energy density, long cycle life, small size, light weight, fast charging, and environmental friendliness, leading to their rapid development in recent years and widespread application in portable electronic products, new energy vehicles, and other fields. However, while the lithium battery industry is developing rapidly, the safety performance of lithium-ion batteries must also be considered.

[0005] Lithium-ion batteries mainly consist of four parts: a positive electrode, a negative electrode, an electrolyte, and a separator. The separator primarily separates the positive and negative electrodes, preventing direct contact and providing a transport path for lithium ions while blocking electrons to prevent short circuits. The performance of the separator significantly affects the interface structure and internal resistance of the lithium-ion battery, directly influencing its electrochemical performance and safety. When the battery short-circuits or overcharges, it releases a large amount of heat, leading to heat accumulation and temperature rise. Therefore, when the temperature rises, a separator with high thermal stability can maintain good dimensional integrity to effectively prevent direct contact between the positive and negative electrodes.

[0006] Currently, battery separators are typically made of polyethylene (PE) or polypropylene (PP). These separators lack sufficient heat resistance, softening and deforming above 130°C. Under conditions of overcharging, over-discharging, rapid charging and discharging, abuse, or high temperatures, the separator is prone to melting and rupture, leading to internal short circuits and thermal runaway, potentially causing battery fires or even explosions. This makes it difficult to meet the stringent safety requirements of high-capacity, high-energy-density lithium-ion batteries. Furthermore, polyethylene and polypropylene have low surface energy and poor wettability with the electrolyte, resulting in incomplete filling of the electrolyte pores in the separator, which also affects battery performance.

[0007] To improve the wettability and heat resistance of the separator, surface coating modification can be applied. For example, inorganic particles, adhesives, solvents, and other additives can be formulated into a slurry and coated onto the surface of the base membrane. However, current separator coatings suffer from problems such as easy powdering and peeling, especially in high-temperature environments. The inorganic particle layer of inorganic-coated separators is prone to pulverization and breakage, causing the separator to collapse and failing to effectively suppress thermal runaway. Consequently, it is difficult to ensure that the battery can still operate safely and efficiently under high-temperature conditions.

[0008] In view of this, this disclosure is hereby made. Summary of the Invention

[0009] The purpose of this disclosure is to provide a diaphragm, its preparation method, and its application, which can solve or improve the above-mentioned technical problems.

[0010] This disclosure can be implemented as follows:

[0011] In a first aspect, this disclosure provides a diaphragm comprising a base membrane and a coating applied to at least one surface of the base membrane; the coating comprises an inorganic adhesive and inorganic particles;

[0012] The coating contains crystals formed by an inorganic adhesive; the crystals include at least needle-like whiskers, some of which together form whisker clusters, and the remaining crystals are located between the inorganic particles.

[0013] In a second aspect, this disclosure provides a diaphragm comprising a base membrane and a coating applied to at least one surface of the base membrane; the coating comprises an inorganic adhesive and inorganic particles;

[0014] The coating contains crystals formed by an inorganic adhesive; the crystals include at least needle-like whiskers, some of which together form whisker clusters, and the remaining crystals are located between the inorganic particles;

[0015] Inorganic adhesives include components with the chemical formula M2O·nSiO2, wherein M includes at least one of Na, K and Li, and 1≤n≤4;

[0016] The mass of the component with the chemical formula M2O·nSiO2 is 1% to 35% of the mass of inorganic particles in the coating.

[0017] In an optional embodiment, the crystals in the diaphragm in any of the above aspects have at least one of the following characteristics:

[0018] Feature 1: The crystal also includes at least one of plate-like crystals and spherical crystals;

[0019] Feature 2: The diameter of the whiskers ranges from 40 nm to 900 nm;

[0020] Feature 3: The longest length of the whisker group is 1μm to 20μm.

[0021] In an optional embodiment, the diameter of the whisker is 50 nm to 600 nm.

[0022] In an optional embodiment, the longest length of the whisker group is 5 μm to 11 μm.

[0023] In an optional embodiment, the longest distance between any two points on the surface of the plate-like crystal is 1 μm to 3 μm.

[0024] In an optional embodiment, the longest distance between any two points on the surface of the spherical crystal is 1 μm to 3 μm.

[0025] In an optional embodiment, the mass of the component with the chemical formula M2O·nSiO2 is 1% to 20% of the mass of the inorganic particles in the coating, and more preferably 1% to 12%.

[0026] In an optional embodiment, the average particle size of the inorganic particles is 10 nm to 5 μm, and more preferably 11 nm to 4.9 μm.

[0027] In optional embodiments, the inorganic particles include at least one selected from Al2O3, SiO2, BaSO4, BaO, titanium dioxide, MgO, LiF, MgF2, BaF2, CuO, Mg(OH)2, LiAlO2, ZrO2, carbon nanotubes, SiC, Si3N4, Fe2O3, BaTiO3, MoS2, α-V2O5, PbTiO3, TiB2, CaSiO3, molecular sieves, clay, boehmite, and kaolin, and may further include at least one selected from Al2O3, boehmite, SiO2, and BaTiO3.

[0028] In optional embodiments, the thickness of the diaphragm is 2.3 μm to 48 μm, further preferably 3 to 45 μm, and even more preferably 12 μm to 35 μm.

[0029] In optional embodiments, the thickness of the base film is 2 μm to 40 μm, further preferably 3 μm to 39 μm, and even more preferably 12 μm to 28 μm.

[0030] In an optional embodiment, the coating thickness is 0.3 μm to 9 μm, further preferably 0.4 μm to 8 μm, and even more preferably 1.2 μm to 5 μm.

[0031] In an optional embodiment, the base film includes at least one of a polymer base film and a ceramic base film.

[0032] In optional embodiments, the polymer-based film includes at least one of polyamide-based film, polyimide-based film, polyolefin-based film, polyacrylonitrile-based film, cellulose-based film, polyester-based film, nanofiber nonwoven film, and aramid-based film.

[0033] Secondly, this disclosure provides a method for preparing a diaphragm as described in any of the foregoing embodiments, comprising the following steps: coating at least one side surface of a base membrane with a coating slurry containing an inorganic adhesive and inorganic particles, and drying.

[0034] In optional embodiments, the solid content of the coating slurry is 2% to 50%, more preferably 6% to 48%, and even more preferably 20% to 43%.

[0035] In optional embodiments, the viscosity of the coating slurry is 10cp to 1000cp, further preferably 20cp to 350cp, and even more preferably 20cp to 100cp.

[0036] In an optional embodiment, the drying temperature is 50°C to 70°C.

[0037] In an optional embodiment, the drying time is 2 min to 5 min.

[0038] Thirdly, this disclosure provides a lithium-ion battery, which includes the separator of any of the foregoing embodiments.

[0039] The beneficial effects of this disclosure include:

[0040] This disclosure involves providing a coating comprising an inorganic adhesive and inorganic particles on at least one side surface of a base film, the coating containing crystals formed by the inorganic adhesive, the crystals including at least needle-like whiskers; some of the crystals together form a whisker cluster, and the remaining crystals are located between the inorganic particles.

[0041] The whisker clusters in the above coating are "rooted" in the coating and "pin" the moving shrinkage interface at high temperatures, playing a "pinning effect" in the diaphragm, which can effectively inhibit the shrinkage of the diaphragm. In addition, the crystals located between the inorganic particles can form a network, giving the coating a continuous self-supporting characteristic. This allows the coating to maintain good integrity at high temperatures and when the base film melts, without breaking or pulverizing, and exhibiting excellent geothermal protection effect.

[0042] The separator with the above characteristics has good stability and durability at high temperatures, and it also has high peel strength, wettability, ionic conductivity, puncture strength and air permeability, which can ensure that the battery can still operate safely and efficiently under high temperature conditions.

[0043] The diaphragm preparation method disclosed herein is simple, easy to scale up for industrial production, and has good industrialization prospects. Attached Figure Description

[0044] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the accompanying drawings used in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of this disclosure and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 is a SEM image of a certain region of the surface of the diaphragm (denoted as 2NSO5-22) prepared in Example 3;

[0046] Figure 2 is a magnified view of the SEM results in the first box in Figure 1 (in order from top to bottom);

[0047] Figure 3 is a magnified view of the SEM results in the second box in Figure 1 (in order from top to bottom);

[0048] Figure 4 is a SEM image of another region of the surface of the membrane (denoted as 2NSO5-22) prepared in Example 3;

[0049] Figure 5 is a SEM image of a certain region of the surface of the diaphragm (denoted as 2NSO5-30) prepared in Example 5;

[0050] Figure 6 is a magnified view of the SEM results at the boxed area in Figure 5;

[0051] Figure 7 is a magnified view of the SEM results at the boxed area in Figure 6;

[0052] Figure 8 is a SEM image of a certain region of the surface of the diaphragm (denoted as 2NSO10-22) prepared in Example 6;

[0053] Figure 9 is a SEM image of a certain region of the surface of the diaphragm (denoted as 2NSO20-22) prepared in Example 7;

[0054] Figure 10 is a SEM image of another region of the surface of the diaphragm prepared in Example 7;

[0055] Figure 11 is a SEM image of a certain region of the surface of the diaphragm (denoted as NSO5-22) prepared in Example 11;

[0056] Figure 12 is a magnified view of the SEM results at the box in Figure 11;

[0057] Figure 13 is a SEM image of another region of the surface of the diaphragm prepared in Example 11;

[0058] Figure 14 is a magnified view of the SEM results at the box in Figure 13;

[0059] Figure 15 is a cross-sectional SEM image of the diaphragm prepared in Example 4 after being kept at 130°C for 1 hour.

[0060] Figure 16 is a cross-sectional SEM image of the diaphragm prepared in Example 3 after being kept at 200°C for 1 hour. Detailed Implementation

[0061] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions in the embodiments of this disclosure will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0062] The following provides a detailed description of the diaphragm, its preparation method, and its applications provided in this disclosure.

[0063] This disclosure provides a diaphragm comprising a base membrane and a coating applied to at least one surface of the base membrane; the coating comprising an inorganic adhesive and inorganic particles.

[0064] In some alternative embodiments, the coating may be applied to either side of the base film; in other alternative embodiments, the coating may be applied to both sides of the base film.

[0065] The inorganic particles in the coating have a high specific surface area (e.g., 10 m²). 2 / g~88m 2 The inorganic particles possess excellent hydrophilicity and good wettability to organic electrolytes, especially to carbonate solvents with high dielectric constants that are difficult to wet by polyolefin membranes. Furthermore, the inorganic particles exhibit excellent temperature resistance, non-flammability, and refractory properties, which are beneficial for giving the diaphragm good temperature resistance and mechanical properties. However, current coatings containing inorganic particles suffer from problems such as easy powdering, peeling, and pulverization. A major reason for these defects is that the adhesives used in current inorganic particle coatings are usually organic adhesives. Organic adhesives exhibit significant swelling problems in electrolytes; once absorbed, they easily lead to a decline in cell performance. In addition, organic adhesives are unstable at high temperatures, easily melting or decomposing, causing their bonding with inorganic ceramic particles to fail. Therefore, this disclosure eliminates the traditionally used organic adhesive in the coating and uses an inorganic adhesive instead. Inorganic adhesives are less prone to swelling in electrolytes, are low in cost, easy to operate, have better bonding effects, and are environmentally friendly. Furthermore, inorganic adhesives can overcome the instability of organic adhesives at high temperatures, exhibiting superior high-temperature resistance.

[0066] However, not all inorganic adhesives are suitable for this disclosure. The coating of this disclosure contains crystals formed by inorganic adhesives; some of the crystals together form a whisker group, the crystals including at least needle-shaped whiskers, and the remaining crystals are located between the inorganic particles.

[0067] The diameter of the whiskers ranges from 40 nm to 900 nm. The longest length of the whisker group ranges from 1 μm to 20 μm.

[0068] It should be noted that the diameter of a whisker and the longest length of a whisker cluster can both be measured using a scanning electron microscope. Whiskers are a special crystal form, fibrous crystals grown from high-purity raw materials. The diameter of a whisker can be understood as its width relative to its length. The diameter of other crystal shapes can be understood as the maximum value obtained by comparing the shortest distances between any two points on the crystal surface.

[0069] In some alternative embodiments, the crystal further includes at least one of plate-like crystals and spherical crystals. This can be understood as follows: in some embodiments, the crystal may contain only needle-like whiskers; in other embodiments, the crystal may contain both needle-like whiskers and plate-like crystals; in still other embodiments, the crystal may contain needle-like whiskers, spherical crystals, and plate-like crystals.

[0070] In some alternative embodiments, the diameter of the whisker can be 50nm to 600nm, such as 50nm, 70nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, 500nm, 550nm or 600nm, or any value or range within the range of 50nm to 600nm.

[0071] In some alternative embodiments, the longest length of the whisker group can be 5μm to 11μm, such as 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm or 11μm, or any value or range within the range of 5μm to 11μm.

[0072] In some alternative implementations, the whisker clusters can appear as "grass clumps".

[0073] In some alternative implementations, the longest distance between any two points on the surface of the plate-like crystal is 1 μm to 3 μm.

[0074] In some alternative implementations, the longest distance between any two points on the surface of the spherical crystal is 1 μm to 3 μm.

[0075] In the present disclosure, during the diaphragm drying and dehydration process, the inorganic adhesive in the coating crystallizes. The crystallization stage is the hardening process of the inorganic adhesive. At this time, the gel transforms into crystals. In some areas, the crystals gradually grow, interpenetrate between coating layers, and overlap and cross-attach, transforming the gel into a three-dimensionally firmly bonded, dense "grass-like" whisker cluster. In other areas, the whiskers are located (e.g., uniformly dispersed) between inorganic particles, interlacing to form a network support. The whiskers in the coating are tightly bonded to the inorganic particles, forming a "reinforced concrete" structure.

[0076] The heat resistance of the diaphragm in this disclosure is related to the whiskers grown in the coating. The "grass-like" whisker clusters are "rooted" in the coating and "pin" the moving shrinkage interface at high temperatures, playing a "pinning effect" in the diaphragm, which can effectively inhibit the shrinkage of the diaphragm. In addition, the dispersed high-temperature resistant inorganic whiskers form a network, giving the coating a continuous self-supporting characteristic. This allows the coating to maintain good integrity even at high temperatures and when the base film melts, without breaking or pulverizing, thus exhibiting excellent geothermal protection effect.

[0077] In an optional embodiment, the inorganic adhesive includes a component with the chemical formula M2O·nSiO2, wherein M includes at least one of Na, K and Li, and 1≤n≤4.

[0078] The aforementioned chemical formula M2O·nSiO2 is an inorganic compound composed of metal cations and polymer silicate anions. Here, n represents the number of SiO2 units in the polymer anion, called the modulus, and n = SiO2 / M2O (molar ratio). In this disclosure, the value of n can be 1, 1.5, 2, 2.5, 3, 3.5, or 4.

[0079] The inorganic adhesive used in this disclosure has a silicon atom outer electron configuration of 3s. 2 3p 2 It exhibits the property of heating and dehydrating polymerization. As the temperature rises, the water in the liquid inorganic adhesive evaporates, silicate anions aggregate to form a film, producing more silanol groups. The condensation between adjacent silanol groups forms Si-O-Si bonds. The remaining water molecules continue to catalyze the dehydration and condensation of silanol groups, and the viscosity of the adhesive continuously increases, eventually forming a three-dimensional network structure connected by Si-O-Si bonds. This structure has strong adhesive properties.

[0080] The modulus n in inorganic adhesives affects their bonding performance. A higher modulus results in stronger adhesion, easier curing into a film, and increased heat resistance of the diaphragm and peel strength of the coating. However, an excessively high modulus n not only increases the viscosity and reduces workability of the inorganic adhesive but also lowers the cationic proportion, leading to decreased ionic conductivity. Therefore, this disclosure specifically uses inorganic adhesives with n values ​​between 1 and 4.

[0081] In this disclosure, the cations in the inorganic adhesive are selected from at least one of Na, Li, and K, which are relatively lightweight and have small ionic radii. This is beneficial for improving the energy density and ion mobility of the material, and avoids the harm to the battery or the environment caused by using magnetic elements such as Fe, Cr, or Ni, or other heavy metal elements. In some typical embodiments, M can be at least one of Na and Li.

[0082] In some optional embodiments, the mass of the component with the chemical formula M2O·nSiO2 can be 1% to 35% of the mass of the inorganic particles in the coating, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, or 35%, or other values ​​within the range of 1% to 35%. In some typical embodiments, the mass of the component with the chemical formula M2O·nSiO2 can be 1% to 20% of the mass of the inorganic particles in the coating; in some more typical embodiments, the mass of the component with the chemical formula M2O·nSiO2 can be 1% to 12% of the mass of the inorganic particles in the coating.

[0083] The higher the content of inorganic adhesive in the coating, the larger the whiskers contained in the coating. Furthermore, the modulus of the inorganic adhesive also affects the size of the whiskers; the higher the modulus, the larger the diameter of both the "grass-like" whisker clusters and the dispersed whiskers, resulting in better heat resistance of the corresponding membrane. In addition, setting the mass of the component with the chemical formula M2O·nSiO2 within the above-mentioned range can not only avoid the problem of insufficient addition leading to low bonding strength, but also avoid the problem of excessive addition causing rapid agglomeration of slurry particles, resulting in phenomena such as incomplete coating, uneven coating thickness, shrinkage, and edge curling.

[0084] By combining inorganic adhesives with the above-mentioned characteristics with inorganic particles, the inorganic particles can act as curing agents for the inorganic adhesives. The inorganic particles and inorganic adhesives can form a network structure through hydrogen bonds, van der Waals forces, and their own bonding, achieving good adhesion. Even under high temperature conditions, they will not melt or decompose, maintaining their size and structure well, which is beneficial to improving the performance of the battery.

[0085] In some optional embodiments, when the component with the chemical formula M2O·nSiO2 accounts for 5% of the mass of inorganic particles in the coating, the diameter of the whiskers can be 50nm to 415nm, such as 50nm, 70nm, 80nm, 90nm, 100nm, 120nm, 140nm, 160nm, 180nm, 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, or 415nm, or any value or range within the range of 50nm to 415nm.

[0086] In some optional embodiments, when the component with the chemical formula M2O·nSiO2 accounts for 20% of the mass of inorganic particles in the coating, the diameter of the whiskers can be 300nm to 600nm, such as 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, 420nm, 440nm, 460nm, 480nm, 500nm, 520nm, 540nm, 560nm, 580nm or 600nm, or any value or range within the range of 300nm to 600nm.

[0087] In some optional embodiments, the average particle size of the inorganic particles can be from 10 nm to 5 μm, such as 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, 200 nm, 500 nm, 800 nm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, or 5 μm, or any value or range within the range of 10 nm to 5 μm. In some more typical embodiments, the average particle size of the inorganic particles can be from 11 nm to 4.9 μm.

[0088] In some alternative embodiments, the inorganic particles may, by way of example but not limitation, include at least one of Al2O3 (including α-type, β-type and / or γ-type, etc.), SiO2, BaSO4, BaO, titanium dioxide (including TiO2, rutile and / or anatase, etc.), MgO, LiF, MgF2, BaF2, CuO, Mg(OH)2, LiAlO2, ZrO2, carbon nanotubes (CNTs), SiC, Si3N4, Fe2O3, BaTiO3, MoS2, α-V2O5, PbTiO3, TiB2, CaSiO3, molecular sieves (such as ZSM-5, etc.), clay, boehmite, and kaolin. In some more typical embodiments, the inorganic particles may include at least one of Al2O3, boehmite, SiO2, and BaTiO3.

[0089] In some optional embodiments, the thickness of the diaphragm can be from 2.3 μm to 48 μm, such as 2.3 μm, 2.5 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, 40 μm, 42 μm, 45 μm, or 48 μm, or any value or range within the range of 2.3 μm to 48 μm. In some more typical embodiments, the thickness of the diaphragm can be from 3 μm to 45 μm; in some even more typical embodiments, the thickness of the diaphragm can be from 12 μm to 35 μm.

[0090] In some optional embodiments, the thickness of the base film can be from 2 μm to 40 μm, such as 2 μm, 2.3 μm, 2.5 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 25 μm, 28 μm, 30 μm, 32 μm, 35 μm, 38 μm, or 40 μm, or any value or range within the range of 2 μm to 40 μm. In some more typical embodiments, the thickness of the base film can be from 3 μm to 39 μm; in some even more typical embodiments, the thickness of the base film can be from 12 μm to 28 μm.

[0091] In some alternative embodiments, the thickness of the coating can be 0.3 μm to 9 μm, such as 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5 μm, 5.2 μm, 5.5 μm, 5.8 μm, 6 μm, 6.2 μm, 6.5 μm, 6.8 μm, 7 μm, 7.2 μm, 7.5 μm, 7.8 μm, 8 μm, 8.2 μm, 8.5 μm, 8.8 μm, or 9 μm, or any value or range within the range of 0.3 μm to 9 μm. In some typical embodiments, the coating thickness can be 0.4 μm to 8 μm; in some more typical embodiments, the coating thickness can be 1.2 μm to 5 μm.

[0092] If the coating thickness is less than 0.3 μm, it can easily lead to a decrease in the thermal dimensional stability, liquid retention rate, and capacity retention rate of the separator. If the coating thickness is greater than 9 μm, it will increase the difficulty of coating, and at the same time, the liquid retention rate of the electrolyte and the mass of the separator will increase, resulting in a decrease in the energy density of the battery.

[0093] With increasing M2O·nSiO2 content and coating thickness, the heat resistance of the separator improves and the peel strength of the coating increases. This is because: increased M2O·nSiO2 content intensifies the interaction between the adhesive and inorganic particles, resulting in a tighter bond; increased thickness effectively increases the amount of adhesive and inorganic particles per unit area, which improves the bonding strength between the inorganic particles and the base membrane, inhibits separator shrinkage at high temperatures, and enhances the separator's heat resistance. Furthermore, with increasing M2O·nSiO2 content and thickness in the coating, the ionic conductivity of the separator increases. This may be attributed to the base membrane's difficulty in wetting, leading to poor electrolyte retention and absorption rates. The porous structure of the coating and the good hydrophilicity of the inorganic particles increase the wettability of the separator. Good wettability not only effectively shortens the electrolyte filling time during battery assembly but also improves electrolyte retention, facilitating effective ion transport during battery operation. Furthermore, thicker coatings allow for greater electrolyte retention and absorption, and higher inorganic binder content increases the conductive ion content, all of which improve the ionic conductivity of the membrane. However, excessive coating thickness can increase ion transport distance, thus reducing ionic conductivity. Therefore, coating thickness needs to be carefully controlled according to requirements. In addition, excessive inorganic binder content not only makes the slurry difficult to coat but also causes rapid agglomeration of the coating slurry, significantly increasing particle size, deteriorating slurry stability, and leading to incomplete coating application.

[0094] In some optional embodiments, the base film includes at least one of a polymer base film and a ceramic base film. The polymer base film may, by way of example but not limitation, include at least one of a polyamide base film, a polyimide base film, a polyolefin base film (wherein the polyolefin may include, for example, polyethylene, polypropylene, polyvinylidene fluoride and / or polytetrafluoroethylene, etc.), a polyacrylonitrile base film, a cellulose base film, a polyester base film (wherein the polyester may include, for example, polyethylene terephthalate, etc.), and an aramid base film. Furthermore, other lithium-ion battery base films may be used as needed.

[0095] In some alternative implementations, the base film can be single-layer, double-layer, or multi-layer. When the base film has two or more layers, the material of each layer can be the same or different; similarly, the thickness of each layer can be equal or unequal. When the base film has two or more layers, the layers can be bonded together by co-extrusion and / or lamination.

[0096] As mentioned above, the separator provided in this disclosure has good stability and durability at high temperatures, and the separator also has high peel strength, wettability, ionic conductivity, puncture strength and air permeability, which can ensure that the battery can still operate safely and efficiently under high temperature conditions.

[0097] Accordingly, this disclosure also provides a method for preparing the above-mentioned diaphragm, comprising the following steps: coating at least one side surface of the base membrane with a coating slurry containing inorganic adhesive and inorganic particles, and drying.

[0098] The coating can be performed by, but is not limited to, electrostatic spraying, scraping, extrusion coating, transfer coating, dip coating, gravure or microgravure coating, as long as the coating slurry can be applied to the surface of the base film.

[0099] In some optional embodiments, the solid content of the coating slurry can be 2% to 50%, such as 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, or 50%, or any value or range within the 2% to 50% range. In some more typical embodiments, the solid content of the coating slurry can be 6% to 48%; in some even more typical embodiments, the solid content of the coating slurry can be 20% to 43%.

[0100] In some optional embodiments, the viscosity of the coating slurry can be from 10 cp to 1000 cp, such as 10 cp, 20 cp, 50 cp, 80 cp, 100 cp, 200 cp, 500 cp, 800 cp, or 1000 cp, or any value or range within the range of 10 cp to 1000 cp. In some more typical embodiments, the viscosity of the coating slurry can be from 20 cp to 350 cp; in some even more typical embodiments, the viscosity of the coating slurry can be from 20 cp to 100 cp.

[0101] The above-mentioned coating slurry is obtained by mixing the raw materials for coating preparation with a solvent, and the solvent can be water, for example.

[0102] The raw materials for preparing the coating include inorganic adhesives and inorganic particles, and may further include at least one of thickeners, dispersants, flame retardants and wetting agents.

[0103] The thickener may be 0.5% to 5% of the mass of the inorganic particles, such as 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value or range within the range of 0.5% to 5%. Carboxymethyl cellulose (CMC) may be included, by example but not exclusively, as a thickener.

[0104] The mass of the dispersant can be 0.2% to 5% of the mass of the inorganic particles, such as 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value or range within the range of 0.2% to 5%. The dispersant may, by way of example but not by way of limitation, include at least one of polyacrylamide, sodium hexametaphosphate, and methylpentanol.

[0105] The flame retardant may be 1% to 5% of the mass of the inorganic particles, such as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value or range within the range of 1% to 5%. Exemplary but not limited, flame retardants may include at least one of brominated flame retardants, ammonium phosphate, ammonium hydroxide, alumina trihydrate, and phosphate esters.

[0106] The wetting agent can be 0.05% to 5% of the inorganic particle mass, such as 0.05%, 0.1%, 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, or any value or range within the range of 0.05% to 5%. Exemplary but not limiting wetting agents may include at least one of ethanol, propylene glycol, glycerin, polyoxyethylene alkylphenol ether, polyoxyethylene fatty alcohol ether, fatty acid ester sulfate, and vinyltriethoxysilane.

[0107] In some alternative embodiments, the drying temperature can be 50°C to 70°C, such as 50°C, 55°C, 60°C, 65°C or 70°C, or any value or range within the range of 50°C to 70°C.

[0108] The drying time can be 2 min to 5 min, such as 2 min, 2.5 min, 3 min, 3.5 min, 4 min, 4.5 min or 5 min, or any value or range within the range of 2 min to 5 min.

[0109] Drying conditions affect crystal formation. At the start of drying, water in the adhesive evaporates, anions aggregate to form a film, generating numerous silanol groups. Water molecules in the adhesive rearrange, catalyzing the condensation between adjacent silanol groups to form Si-O-Si bonds. As temperature increases or drying time extends, remaining water molecules continue to catalyze the dehydration and condensation of silanol groups. Subsequently, localized reactions occur on the surface of the dispersed anhydrous compound particles, forming a gel with a significant exothermic effect. The crystallization stage is the hardening process of the inorganic adhesive. At this point, the gel transforms into crystals. The crystals gradually grow and overlap, cross-attaching and transforming the gel into a firmly bonded, dense three-dimensional solid, accompanied by a small amount of heat release.

[0110] If the drying temperature is set too low, it will not only cause slow crystal growth, but also require extending the drying cycle to ensure the membrane reaches the predetermined moisture standard, reducing production efficiency. Conversely, if the drying temperature is too high, the whiskers may not grow densely enough, resulting in a loose crystal structure and weakening its mechanical properties. Furthermore, high-temperature drying will increase the energy consumption of the drying equipment, negatively impacting cost control. Regarding the control of drying time, excessively long drying times will lead to abnormally large whisker sizes, also accompanied by increased energy consumption, which is detrimental to both cost control and production efficiency. Conversely, excessively short drying times will make it difficult to ensure the moisture content of the membrane meets production standards.

[0111] In addition, this disclosure also provides a lithium-ion battery including the above-described separator.

[0112] Specifically, the lithium-ion battery includes a positive electrode, a negative electrode, and a separator, with the separator separating the positive and negative electrodes. Lithium-ion batteries with this separator offer good safety in use.

[0113] The features and performance of this disclosure will be further described in detail below with reference to embodiments.

[0114] Example 1

[0115] This embodiment provides a diaphragm, which includes a base membrane and coatings applied to both sides of the base membrane.

[0116] The base membrane is made of 9μm thick porous polyethylene (PE), and the coatings on both sides of the base membrane are 2μm thick. The total thickness of the diaphragm is 13μm.

[0117] The coating slurry used to prepare the coating is obtained by dissolving the raw materials in water. The solid content of the coating slurry is 26.3%, and the viscosity is about 20 cp.

[0118] The raw materials, by mass, include 100 parts inorganic particles (alumina powder with an average particle size of 500 nm), 5 parts inorganic adhesive (Na2O·3SiO2), 1.5 parts thickener (CMC), 0.5 parts dispersant (polyacrylamide), and 0.1 parts wetting agent (vinyltriethoxysilane).

[0119] The preparation method of the diaphragm includes:

[0120] S1: According to the above-mentioned raw material dosage, add 100 parts of inorganic particles, 0.5 parts of dispersant, and 1.5 parts of thickener to 300 parts of deionized water, and mechanically stir at 2000 rpm for 4 hours to obtain the first slurry; fully disperse the first slurry in a ball mill jar by ball milling at a speed of 60 rpm for 24 hours to obtain the second slurry.

[0121] S2: Filter the second slurry, add 5 parts of inorganic adhesive and 0.1 parts of wetting agent to the filtered second slurry, and mechanically stir for 1 hour at a stirring speed of 500 rpm to obtain the coating slurry.

[0122] S3: The above coating slurry is evenly coated on both sides of the base film on a coating machine and vacuum dried at 60°C for 5 minutes to obtain a diaphragm with a coating on both sides of the base film.

[0123] Example 2

[0124] The difference between this embodiment and Embodiment 1 is that the amount of inorganic adhesive used is 2 parts, and the inorganic adhesive is Na2O·2SiO2.

[0125] Example 3

[0126] The difference between this embodiment and Embodiment 2 is that the amount of inorganic adhesive used is 5 parts;

[0127] This can also be understood as follows: the difference between this embodiment and Embodiment 1 is that the inorganic adhesive is Na2O·2SiO2.

[0128] Example 4

[0129] The difference between this embodiment and Embodiment 3 is that a 2μm coating is only applied to one side of the base film.

[0130] Example 5

[0131] The difference between this embodiment and Embodiment 4 is that the coating thickness is 3μm;

[0132] This can also be understood as follows: the difference between this embodiment and Embodiment 1 is that a 3μm coating is only provided on one side of the base film.

[0133] Example 6

[0134] The difference between this embodiment and Embodiment 2 is that the amount of inorganic adhesive used is 10 parts;

[0135] It can also be understood that the difference between this embodiment and embodiment 1 is that the inorganic adhesive is Na2O·2SiO2 and the amount of inorganic adhesive used is 10 parts.

[0136] Example 7

[0137] The difference between this embodiment and Embodiment 2 is that the amount of inorganic adhesive used is 20 parts;

[0138] It can also be understood that the difference between this embodiment and embodiment 1 is that the inorganic adhesive is Na2O·2SiO2 and the amount of inorganic adhesive used is 20 parts.

[0139] Example 8

[0140] The difference between this embodiment and Embodiment 3 is that the inorganic adhesive is Na2O·1.5SiO2;

[0141] This can also be understood as follows: the difference between this embodiment and Embodiment 1 is that the inorganic adhesive is Na2O·1.5SiO2.

[0142] Example 9

[0143] The difference between this embodiment and embodiment 8 is that a 2μm coating is only applied to one side of the base film.

[0144] Example 10

[0145] The difference between this embodiment and embodiment 9 is that a 3μm coating is only applied to one side of the base film.

[0146] Example 11

[0147] The difference between this embodiment and Embodiment 3 is that the inorganic adhesive is Na2O·SiO2;

[0148] This can also be understood as follows: the difference between this embodiment and Embodiment 1 is that the inorganic adhesive is Na2O·SiO2.

[0149] Example 12

[0150] The difference between this embodiment and Embodiment 11 is that the amount of inorganic adhesive used is 10 parts.

[0151] Example 13

[0152] The difference between this embodiment and Embodiment 1 is that the inorganic adhesive is Na2O·4SiO2.

[0153] Example 14

[0154] The difference between this embodiment and Embodiment 1 is that the inorganic adhesive is K2O·3SiO2.

[0155] Example 15

[0156] The difference between this embodiment and Embodiment 1 is that the inorganic adhesive is Li2O·3SiO2.

[0157] Example 16

[0158] The difference between this embodiment and Embodiment 1 is as follows: the inorganic particles are SiO2; the mass of Na2O·3SiO2 is 1% of the mass of the inorganic particles in the coating; the mass of the thickener is 0.5% of the mass of the inorganic particles; the mass of the dispersant is 0.2% of the mass of the inorganic particles; the mass of the flame retardant (ammonium phosphate) is 1% of the mass of the inorganic particles; the mass of the wetting agent is 0.1% of the mass of the inorganic particles; the thickness of the base film is 2 μm, and the coating thickness on each side of the base film is 0.3 μm. The solid content of the coating slurry is 2%, the viscosity of the coating slurry is 10 cp; the drying temperature is 50℃, and the drying time is 5 min.

[0159] Example 17

[0160] The difference between this embodiment and Example 1 is as follows: the inorganic particles are BaTiO3; the mass of Na2O·3SiO2 is 35% of the mass of the inorganic particles in the coating; the mass of the thickener is 5% of the mass of the inorganic particles; the mass of the dispersant is 5% of the mass of the inorganic particles; the mass of the flame retardant (alumina trihydrate) is 5% of the mass of the inorganic particles; the mass of the wetting agent is 5% of the mass of the inorganic particles; the thickness of the base film is 40 μm, and the coating thickness on each side of the base film is 9 μm. The solid content of the coating slurry is 50%, the viscosity of the coating slurry is 1000 cp; the drying temperature is 70℃, and the drying time is 2 min.

[0161] Example 18

[0162] The difference between this embodiment and Embodiment 1 is that the mass of Na2O·3SiO2 is 12% of the mass of the inorganic particles in the coating. The inorganic particles are boehmite.

[0163] Example 19

[0164] The difference between this comparative example and Example 1 is that the inorganic adhesive is Na2O·5SiO2.

[0165] Example 20

[0166] The difference between this comparative example and Example 1 is that the mass of the inorganic adhesive is 40% of the mass of the inorganic particles in the coating.

[0167] Example 21

[0168] The difference between this comparative example and Example 1 is that the coating thickness is 12 μm.

[0169] Comparative Example 1

[0170] The difference between this comparative example and Example 1 is that no coating is applied to the surface of the base film.

[0171] Comparative Example 2

[0172] The difference between this comparative example and Example 1 is that the inorganic adhesive is replaced with polymethyl methacrylate adhesive.

[0173] Comparative Example 3

[0174] The difference between this comparative example and Example 1 is that the inorganic adhesive is replaced with a polyacrylamide adhesive.

[0175] Comparative Example 4

[0176] The difference between this comparative example and Example 1 is that the inorganic adhesive is aluminum sol.

[0177] Test case

[0178] (1) The membranes obtained in Examples 1 to 21 and Comparative Examples 1 to 4 were subjected to performance tests. The performance results are shown in Table 1 and Table 2.

[0179] Performance testing methods are as follows:

[0180] ① Shrinkage Rate: The diaphragm was cut into multiple 120mm × 100mm (length × width) pieces along the longitudinal (MD) and transverse (TD) directions. An A4 sheet of paper was placed over the diaphragm surface, and the pieces were placed in an oven at 130℃, 150℃, and 200℃ for 1 hour each. The shrinkage in each direction was measured, and the shrinkage percentage was calculated. The shrinkage rates in Table 1 are based on the average values ​​obtained from three measurements in the MD and TD directions.

[0181] ② Peel Strength: The peel strength between the coating and the base film was tested using a universal tensile testing machine. The coated diaphragm was cut into 150mm × 30mm (length × width) sample strips using a sampler. These strips were adhered to double-sided adhesive tape on the test plate. A 200mm × 20mm (length × width) transparent tape was then adhered above the sample strips. A cylindrical pressure roller was then used to press the diaphragm naturally in the same direction. When the diaphragm was coated on one side, the corresponding base film side faced down and the coated side faced up. One end of the transparent tape was peeled off the coated diaphragm surface until the adhesive length between the transparent tape and the coated diaphragm surface was 80mm. The free end of the transparent tape was folded in half, and the free end of the transparent tape and the test plate were clamped onto upper and lower clamps respectively. In the same environment, a tensile testing machine was used to continuously peel the diaphragm at a tensile speed of 100mm / min until the coating and base film were completely separated. The peel strength of the diaphragm coating was directly read and recorded.

[0182] ③ Air permeability and puncture strength: refer to the standard GBT36363-2018; thickness is measured using a Mal film thickness gauge.

[0183] ④ Water contact angle: The contact angle was measured using a contact angle measuring instrument in accordance with the GB / T 30693-2014 standard.

[0184] ⑤ Electrolyte wettability: The wettability of the diaphragm is characterized by measuring the size change of the droplets formed after 5 seconds and 5 minutes by adding electrolyte droplets to the diaphragm surface. Specifically, the droplet size is represented by the sum of the longest distances in the MD and TD directions divided by 2. The wettability is represented by the difference between the droplet sizes at 5 seconds and 5 minutes, divided by 2.

[0185] ⑥ Ionic conductivity: Cut 5 diaphragms that match the resistance test mold. Immerse the diaphragms in a 1 mol / L lithium hexafluorophosphate (LiPF6) electrolyte. The solvent in this electrolyte is ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of 1:1:1. Keep the diaphragms sealed and soak for 2 hours. Use an electrochemical workstation at 25℃, 0.01Hz~1×10⁻⁶ Hz. 6 Electrochemical impedance spectroscopy was tested and recorded within a frequency range of Hz. The slope and linearity of the curve were calculated by plotting the number of membrane layers on the x-axis and the membrane resistance on the y-axis. When the linearity was greater than 0.99, the slope (k) was taken as the membrane impedance value. The membrane ionic conductivity was calculated using the formula σ = d / (kS), where σ is the membrane ionic conductivity, d is the membrane thickness, k is the membrane impedance value, and S is the area of ​​the membrane used during testing.

[0186] ⑦ Slurry particle size: The prepared coating slurry was tested for particle size using a Malvern MS3000 laser particle size analyzer.

[0187] ⑧. Slurry stabilization time: Particle size D measured by Malvern MS3000 laser particle size analyzer 50 Time greater than 2μm.

[0188] Table 1 Performance Test Results

[0189] Table 2 Performance Test Results (Continued)

[0190] Referring to Tables 1 and 2, the embodiments of this disclosure use inorganic adhesives instead of traditional organic adhesives, while controlling the amount and modulus of the inorganic adhesive. This results in a diaphragm with high ionic conductivity, good wettability, and good high-temperature resistance. In some preferred embodiments, with a coating thickness of 4 μm and a diaphragm thickness not exceeding 13 μm, the shrinkage rate after heat treatment at 200°C for 1 hour is less than 3% without powdering, indicating that the adhesive has not failed and the safety of the diaphragm is significantly improved, meeting the application requirements.

[0191] Comparing Examples 2-7 and Examples 9-10, it can be seen that as the amount of inorganic adhesive and the coating thickness increase, the heat resistance of the diaphragm improves and the peel strength of the coating increases. This is because the increased amount of inorganic adhesive intensifies the interaction between the inorganic adhesive and the inorganic particles, resulting in a tighter bond between them. The increased coating thickness is equivalent to increasing the content of inorganic adhesive and inorganic particles per unit area, thereby increasing the bonding strength between the inorganic particles and the base membrane, inhibiting diaphragm shrinkage at high temperatures, and improving heat resistance.

[0192] Furthermore, compared to the base membrane of Comparative Example 1, the ionic conductivity of the separator provided in the above embodiments is significantly increased, and this increase is accompanied by an increase in the amount of inorganic adhesive and the coating thickness. This can be attributed to the fact that the base membrane (PE) is difficult to wet, resulting in poor electrolyte retention and absorption rates. The highly developed porous structure of the inorganic coating and the excellent hydrophilic properties of the inorganic particles significantly increase the wettability of the separator (contact angle decreases from 114° to below 14°). Good wettability of the separator can not only effectively shorten the electrolyte filling time during battery assembly but also improve the electrolyte retention capacity, which is more conducive to the effective transport of ions during battery operation. Moreover, a thicker coating results in greater electrolyte retention and absorption, and a higher content of inorganic adhesive increases the content of conductive ions, all of which improve the ionic conductivity of the separator. However, excessively high coating thickness can increase the ion transport distance, thereby reducing the ionic conductivity. In addition, when the content of inorganic adhesive is too high, not only is the coating slurry difficult to apply, but it also causes the coating slurry to agglomerate rapidly, the particle size to increase significantly, the stability of the coating slurry to deteriorate, and the coating to be missed.

[0193] The results from Examples 3, 8, 11, and 12 show that, for the same thickness and inorganic adhesive content, the heat resistance of the diaphragm and the peel strength of the coating increase with the increase of the inorganic adhesive modulus. However, since the increase in modulus reduces the proportion of cations, the ionic conductivity decreases slightly. Furthermore, Example 3, containing 5 parts Na₂O·2SiO₂, exhibits a lower shrinkage rate than Example 12, containing 10 parts Na₂O·SiO₂ at the same temperature, indicating that the modulus of the inorganic adhesive has a significant impact on the heat resistance of the diaphragm.

[0194] As can be seen from Examples 1 and 19-21, the modulus, dosage, and coating thickness of the inorganic adhesive all affect the performance of the separator. Improper conditions can reduce the performance of the separator. An excessively high modulus (as in Example 19) can actually reduce heat resistance, ionic conductivity, and slurry stability. Higher adhesive content results in larger slurry particle sizes and shorter stabilization times; exceeding a certain amount (as in Example 20) can cause incomplete coating, leading to a sharp deterioration in performance. While increasing the thickness improves heat resistance, it also increases air permeability, reduces ionic conductivity, and decreases the volumetric energy density of the battery (as in Example 21).

[0195] Compared with Comparative Examples 2 and 3, the membranes obtained by all examples using inorganic adhesives with the same amount of organic adhesive and coating thickness as those two comparative examples showed higher heat resistance, peel strength and ionic conductivity.

[0196] Compared with Comparative Example 4, the diaphragm obtained in Example 1 has better performance, indicating that even if inorganic adhesives are used, it is not always possible to obtain a diaphragm with excellent performance.

[0197] (2) Scanning electron microscopy (SEM) observation of the diaphragms obtained in the embodiments of this disclosure revealed that the coatings of the diaphragms prepared in the embodiments of this disclosure all contain crystals. Some crystals collectively form whisker clusters resembling "grass clumps," while the remaining crystals are located between inorganic particles. The shapes of the crystals include needle-like, plate-like, and spherical; the diameters of the whiskers are all in the range of 40 nm to 900 nm, and the longest length of the whisker clusters is in the range of 1 μm to 20 μm. The longest distance between any two points on the surface of the plate-like crystals and the longest distance between any two points on the surface of the spherical crystals are 1 μm to 3 μm.

[0198] The scanning electron microscope images of the membranes prepared in Examples 3, 5-7 and 11 are used as examples. Please refer to Figures 1 to 14 for details.

[0199] As shown in Figures 1 to 14, the coating of the diaphragm contains crystals, which include needle-like, plate-like, and spherical shapes. Referring to Figures 1 to 7, in some areas of the coating, crystals are interspersed between layers, overlapping and crisscrossing to form a dense, three-dimensionally bonded "grass-like" whisker cluster; in other areas, crystals are uniformly dispersed among inorganic particles, interlacing to form a network support. The whiskers between the coating layers are tightly bonded to the inorganic particles, forming a "reinforced concrete" structure.

[0200] Furthermore, as the amount of inorganic adhesive increases, the whiskers formed in the coating become larger. In Example 3, with an inorganic adhesive content of 5 parts, the diameter of the whiskers formed in the coating is approximately 78 nm to 415 nm. In Example 7, with an inorganic adhesive content of 20 parts, the diameter of the whiskers formed in the coating is approximately 300 nm to 586 nm, and the morphology has also changed compared to Example 3. The whiskers in Example 7 are plate-like or spherical, and the main body size of the whisker group (i.e., the longest length of the whisker) is mostly in the range of 5 μm to 11 μm.

[0201] As can be seen from the SEM images corresponding to Examples 3 and 11, the modulus of the inorganic adhesive affects the size of the whiskers. The higher the modulus, the larger the "grass-like" whisker clusters and the larger the whisker diameter, and the better the heat resistance of the corresponding diaphragm. This further illustrates the influence of whisker size on the heat resistance of the diaphragm.

[0202] It should be noted that when the ceramic separator is heated, the friction and adhesion between the ceramic layer and the base membrane layer, the gravity of the ceramic layer, or the pressure during battery assembly will all hinder the shrinkage and movement of the base membrane, thus maintaining its structural integrity and increasing its stability.

[0203] Figure 15 is a SEM cross-sectional view of the diaphragm of Example 4 after being kept at 130°C for 1 hour. As can be seen from the figure, the pores of the base membrane and the ceramic particle layer structure remain intact at this temperature. At higher temperatures, the base membrane melts and the pores close, but the ceramic particles embed into the base membrane to form an interlocking structure, ensuring the integrity of the diaphragm structure, preventing direct contact between the positive and negative electrodes, and inhibiting further temperature increases, thereby improving the thermal safety of the diaphragm.

[0204] Figure 16 is a SEM cross-sectional view of the diaphragm of Example 3 after being kept at 200°C for 1 hour. As can be seen from the figure, the molten base film is embedded in the voids of the alumina particles, forming an interlocking interface structure. The formation of this structure can significantly increase the contact area between the alumina particles and the base film, making the diaphragm structure intact and thus improving the thermal safety of the diaphragm.

[0205] (3) Taking Examples 1, 3, 6-8, 12 and Comparative Examples 1-3 as examples, the separators and positive and negative electrode sheets prepared in the above examples and comparative examples were used to prepare battery cells by a stacking process, and insulation breakdown short-circuit tests were performed. The number of cells that passed the 250V voltage test was counted. The results are shown in Table 3.

[0206] Table 3 Results of Insulation Breakdown Short Circuit Test

[0207] As can be seen from the test results in Table 3, compared with organic adhesive composite separators based on PE and PE separators without inorganic coating, the separator provided in this disclosure has better insulation resistance, with a 250V breakdown short-circuit test pass rate of over 95%, while the pass rate of the PE separator without inorganic coating is 79%, and the pass rate of the organic adhesive composite separator based on PE is less than 90%. Therefore, the separator provided in this disclosure has high insulation performance, which is beneficial to improving the yield of batteries.

[0208] (4) Taking Examples 1, 3, 6-8, 12 and Comparative Examples 1-3 as examples, the separators and positive and negative electrode sheets prepared in the above examples and comparative examples were used to prepare cells by stacking process. Then, conventional lithium battery processes such as liquid injection, encapsulation and formation were carried out. The completed batteries were tested for safety performance, and the results are shown in Table 4.

[0209] 150℃ thermal shock pass rate: Tested according to the national standard GB / T18287-2013, the judgment criteria are no leakage, no fire and no explosion.

[0210] Short circuit pass rate: Tested according to the national standard GB / T18287-2013. The judgment criteria are no fire, no explosion, and external surface temperature below 150℃.

[0211] 10V / 3C overcharge pass rate: Tested according to the national standard GB / T18287-2013, the judgment standard is no fire and no explosion.

[0212] Table 4 Safety Performance Test Results

[0213] As shown in Table 4, the battery prepared using the separator disclosed herein exhibits superior safety performance compared to organic adhesive composite separators based on PE and PE separators without inorganic coating. The separator provided herein has a low thermal shrinkage rate at high temperatures, contributing to the battery's excellent safety performance. In the event of thermal runaway or accidents caused by improper use, it can more effectively prevent battery fires and explosions.

[0214] In summary, the separator provided in this disclosure exhibits excellent stability and durability at high temperatures, simultaneously possessing high peel strength, wettability, ionic conductivity, puncture strength, and permeability, ensuring the safe and efficient operation of the battery under high-temperature conditions. The separator's preparation method is simple and easy to scale up for industrial production, demonstrating promising industrialization prospects.

[0215] The above description is merely a preferred embodiment of this disclosure and is not intended to limit this disclosure. Various modifications and variations can be made to this disclosure by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the scope of protection of this disclosure. Industrial applicability

[0216] The separator disclosed herein exhibits excellent stability and durability at high temperatures, and also possesses high peel strength, wettability, ionic conductivity, puncture strength, and air permeability, ensuring safe and efficient battery operation even under high-temperature conditions. The separator is simple to prepare and easily scalable for industrial application, demonstrating promising prospects for industrialization.

Claims

1. A diaphragm, characterized in that, The diaphragm includes a base membrane and a coating applied to at least one surface of the base membrane; the coating includes an inorganic adhesive and inorganic particles; The coating contains crystals formed by the inorganic adhesive; the crystals include at least needle-like whiskers, some of the crystals together form whisker clusters, and the remaining crystals are located between the inorganic particles.

2. A diaphragm, characterized in that, The diaphragm includes a base membrane and a coating applied to at least one surface of the base membrane; the coating includes an inorganic adhesive and inorganic particles; The coating contains crystals formed by the inorganic adhesive; the crystals include at least needle-like whiskers, some of the crystals together form whisker clusters, and the remaining crystals are located between the inorganic particles; The inorganic adhesive includes components with the chemical formula M2O·nSiO2, wherein M includes at least one of Na, K and Li, and 1≤n≤4; The mass of the component with the chemical formula M2O·nSiO2 is 1% to 35% of the mass of the inorganic particles in the coating.

3. The diaphragm according to claim 1 or 2, characterized in that, The crystal has at least one of the following characteristics: Feature 1: The crystal further includes at least one of plate-like crystals and spherical crystals; Feature 2: The diameter of the whiskers is 40nm to 900nm; Feature 3: The longest length of the whisker group is 1μm to 20μm.

4. The diaphragm according to claim 3, characterized in that, The diameter of the whiskers is 50 nm to 600 nm.

5. The diaphragm according to claim 3, characterized in that, The longest length of the whisker group is 5 μm to 11 μm.

6. The diaphragm according to any one of claims 2 to 5, characterized in that, The mass of the component with the chemical formula M2O·nSiO2 is 1% to 20% of the mass of the inorganic particles in the coating.

7. The diaphragm according to claim 6, characterized in that, The mass of the component with the chemical formula M2O·nSiO2 is 1% to 12% of the mass of the inorganic particles in the coating.

8. The diaphragm according to any one of claims 1 to 7, characterized in that, The average particle size of the inorganic particles is 10 nm to 5 μm.

9. The diaphragm according to any one of claims 1 to 8, characterized in that, The inorganic particles include at least one of Al2O3, SiO2, BaSO4, BaO, titanium dioxide, MgO, LiF, MgF2, BaF2, CuO, Mg(OH)2, LiAlO2, ZrO2, carbon nanotubes, SiC, Si3N4, Fe2O3, BaTiO3, MoS2, α-V2O5, PbTiO3, TiB2, CaSiO3, molecular sieves, clay, boehmite, and kaolin.

10. The diaphragm according to any one of claims 1 to 9, characterized in that, The inorganic particles include at least one of Al2O3, boehmite, SiO2, and BaTiO3.

11. The diaphragm according to any one of claims 1 to 10, characterized in that, The thickness of the diaphragm is 2.3 μm to 48 μm.

12. The diaphragm according to any one of claims 1 to 11, characterized in that, The thickness of the base film is 2μm to 40μm.

13. The diaphragm according to any one of claims 1 to 12, characterized in that, The thickness of the coating is 0.3 μm to 9 μm.

14. The diaphragm according to any one of claims 1 to 13, characterized in that, The base film includes at least one of a polymer base film and a ceramic base film.

15. A method for preparing a diaphragm as described in any one of claims 1 to 14, characterized in that, Includes the following steps: A coating slurry containing the inorganic adhesive and the inorganic particles is coated onto at least one side of the base film and then dried.

16. The preparation method according to claim 15, characterized in that, The solid content of the coating slurry is 2% to 50%.

17. The preparation method according to claim 15 or 16, characterized in that, The viscosity of the coating slurry is 10cp to 1000cp.

18. The preparation method according to any one of claims 15 to 17, characterized in that, The drying temperature is 50℃~70℃.

19. The preparation method according to any one of claims 15 to 18, characterized in that, The drying time is 2 to 5 minutes.

20. A lithium-ion battery, characterized in that, The lithium-ion battery includes the separator as described in any one of claims 1 to 14.

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