Composite separator and battery using the same

Abstract

The application provides a composite diaphragm and a battery using the same, and the composite diaphragm comprises a base film framework, a first functional layer, the base film framework comprises a base film layer and a nanofiber layer in sequence, at least one side of the base film layer is provided with the nanofiber layer in the thickness direction of the composite diaphragm, at least one surface of the composite diaphragm is provided with the first functional layer, the first functional layer is a glue layer, in the thickness direction of the composite diaphragm, the area of one side of the base film layer is S1, the projection area of the nanofiber layer on the base film layer is S2, S2 / S1=90-100%, the air permeability value of the composite diaphragm is 10000-20000 s / 100mL after 1h, and T1 is greater than or equal to 200 DEG C. The composite diaphragm can effectively improve the mechanical property, porosity and thermal stability of the composite diaphragm by setting a special layer combination and controlling specific parameters of the composite diaphragm, so that the cycle performance, safety performance and the like of the lithium battery can be effectively considered, and the application provides basic support for the further development of the high-performance lithium battery.

Description

Technical Field

[0001] This invention belongs to the field of separator and lithium battery technology, specifically relating to a composite separator and a battery using the same. Background Technology

[0002] Lithium batteries possess many excellent properties such as high energy density, high coulombic efficiency, low self-discharge, and long lifespan. These superior properties make them ideal for portable devices and they are widely used in aerospace, defense, new energy vehicles, and 3C electronic products.

[0003] The positive electrode, negative electrode, electrolyte, and separator are essential components for the normal operation of a lithium-ion battery. During battery operation, the separator, as an important functional part of the lithium-ion battery, mainly functions to prevent contact between the positive and negative electrodes and to effectively transport lithium ions. It acts like a strong barrier, separating the positive and negative electrodes and preventing short circuits.

[0004] Traditional separators are primarily made of a single material, such as polyolefin (e.g., polyethylene, polypropylene) separators, meaning they are mainly composed of a single-layer polymer film. While these separators possess good chemical stability and mechanical strength, they are prone to shrinkage at high temperatures, potentially leading to internal short circuits and posing safety hazards. Furthermore, single-material separators have limited ion conductivity, making them unsuitable for the demands of high-performance electrochemical devices.

[0005] To address these issues, composite membrane technology has emerged in recent years. Composite membranes typically consist of two or more layers, most commonly a layer of ceramic particles or a polymer coating coated onto a polyolefin substrate, to improve the membrane's thermal stability and ion conductivity. However, existing composite membranes still have some shortcomings. For example, ceramic particle coatings may reduce the membrane's flexibility, while the thermal stability of polymer coatings may be insufficient for use in high-temperature environments. Summary of the Invention

[0006] To address the problems and shortcomings of existing technologies, this invention provides a composite separator and a battery using the same. By setting a special layer combination and controlling specific parameters of the composite separator, the mechanical properties, porosity, and thermal stability of the composite separator can be effectively improved. Therefore, it can effectively balance the cycle performance and safety performance of lithium batteries, and can provide fundamental support for the further development of high-performance lithium batteries.

[0007] According to a first aspect of the present invention, a composite membrane is provided, comprising a base membrane skeleton and a first functional layer, wherein the base membrane skeleton comprises a base membrane layer and a nanofiber layer in sequence; in the thickness direction of the composite membrane, at least one side of the base membrane layer is provided with a nanofiber layer; at least one surface of the composite membrane is provided with the first functional layer; the first functional layer is an adhesive layer; in the thickness direction of the composite membrane, the area of ​​one side of the base membrane layer is S1, and the projected area of ​​the nanofiber layer on the base membrane layer is S2, wherein S2 / S1 = 90~100%; the air permeability of the composite membrane at T1 for 1 hour is 10000~20000s / 100mL, and T1 ≥ 200℃.

[0008] The polymer film layer primarily provides insulation, while the nanofiber layer mainly provides the framework function, optimizing the strength of the separator. Therefore, the base membrane framework containing both polymer and nanofiber layers can balance the insulation and mechanical strength of the separator. Furthermore, at least one surface of the composite separator is provided with a first functional layer, which is an adhesive layer with bonding properties. This enhances the adhesion and electrolyte retention of the composite separator, thus promoting tight adhesion between the positive and negative electrodes and the separator, and improving the wetting performance of the electrolyte, thereby optimizing the cycle performance of the lithium battery. With this unique multilayer structure, the resulting composite separator exhibits excellent bonding between its layers, significantly improving the overall mechanical properties of the composite separator and its performance in the battery. Therefore, the special structural design of the composite separator in this invention is beneficial for improving the overall performance of the separator, thereby enhancing battery performance.

[0009] Furthermore, controlling the ratio of the projected area S2 of the nanofiber layer on the polymer film to the area S1 of one side of the polymer film within a specific range can help to have a nanofiber layer of sufficient size as a skeleton to enhance the mechanical strength of the separator, while effectively improving the overall porosity of the separator, which is beneficial to provide a certain channel for lithium-ion transport and optimize the overall cycle performance of the lithium battery.

[0010] Furthermore, controlling the air permeability of the composite separator within the aforementioned range—that is, having a relatively high air permeability at high temperatures—can promote thermal pore closure of the composite separator at high temperatures (the high porosity of the nanofiber layer can cause the base film or adhesive layer to melt and block the pores of the nanofibers), thereby hindering the normal transport of lithium ions and preventing direct contact between the positive and negative electrodes of the battery at high temperatures, effectively improving the safety performance of the lithium battery. It should be noted that, taking "10000s / 100mL" as an example, this means that it takes 10000s for the composite separator to pass through 100mL of gas. The longer the time required to pass through 100mL of gas, the worse the air permeability of the separator. In other words, the higher the air permeability value mentioned in this invention, the worse the air permeability of the composite separator, which is more conducive to hindering the normal transport of lithium ions.

[0011] Preferably, the first functional layer is the adhesive layer, which includes an adhesive compound; or the first functional layer is a mixed layer, which contains an adhesive compound and ceramic particles mixed together.

[0012] In one optional embodiment, the nanofiber layer comprises a plurality of regions, which are spaced apart on at least one side of the base film layer. Even if the nanofiber layer is disposed on the surface of the base film layer with a plurality of regions spaced apart, as long as S2 / S1 = 90~100%, the skeletal properties of the nanofiber layer and the function of effectively improving the porosity of the membrane can still be achieved. Preferably, the plurality of regions have the same size, or the plurality of regions have different sizes.

[0013] In one optional embodiment, the composite membrane sequentially comprises an adhesive layer, a base membrane layer, and a nanofiber layer. The base membrane layer and the nanofiber layer sequentially form the base membrane framework.

[0014] In one optional embodiment, the composite membrane sequentially comprises a mixing layer, a base membrane layer, and a nanofiber layer. The base membrane layer and the nanofiber layer sequentially form the base membrane framework.

[0015] In one optional embodiment, the composite membrane sequentially comprises an adhesive layer, a base membrane layer, a nanofiber layer, and a hybrid layer. The base membrane layer and the nanofiber layer sequentially form the base membrane framework.

[0016] Preferably, in the thickness direction of the composite diaphragm, at least one first functional layer is provided on both sides of the base membrane skeleton. The presence of functional layers on both sides of the base membrane skeleton effectively balances the internal stress of the composite diaphragm under high temperature or external force, thereby further improving the overall mechanical properties and thermal stability of the diaphragm.

[0017] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a base film layer, a nanofiber layer, and a second adhesive layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the first adhesive layer and the second adhesive layer have the same composition and / or thickness.

[0018] In one optional embodiment, the composite membrane sequentially comprises a first mixing layer, a base film layer, a nanofiber layer, and a second mixing layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are the same.

[0019] Preferably, the composite separator further includes a second functional layer, which comprises a ceramic layer formed of ceramic particles. Furthermore, the addition of the ceramic layer can further enhance the thermal stability and mechanical properties of the composite separator, effectively suppressing thermal shrinkage of the separator, and to a certain extent assisting the separator's pore-closing function. When the temperature rises to the separator's pore-closing temperature, the ceramic layer can help maintain the stability of the pore-closing structure, preventing the separator from reopening after pore closure, ensuring that the lithium-ion transport channels are effectively blocked, thereby improving battery safety.

[0020] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a ceramic layer, a base film layer, a nanofiber layer, and a second adhesive layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the first adhesive layer and the second adhesive layer have the same composition and / or thickness.

[0021] In one optional embodiment, the composite membrane sequentially comprises an adhesive layer, a ceramic layer, a base membrane layer, a nanofiber layer, and a hybrid layer. The base membrane layer and the nanofiber layer sequentially form the base membrane framework.

[0022] In one optional embodiment, the composite membrane sequentially comprises a first mixing layer, a ceramic layer, a base film layer, a nanofiber layer, and a second mixing layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are the same.

[0023] Preferably, in the thickness direction of the composite membrane, both sides of the base membrane skeleton are provided with at least one first functional layer and at least one second functional layer.

[0024] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a first ceramic layer, a base film layer, a nanofiber layer, a second ceramic layer, and a second adhesive layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the first adhesive layer and the second adhesive layer have the same composition and / or thickness. Preferably, the first ceramic layer and the second ceramic layer have the same composition and / or thickness.

[0025] In one optional embodiment, the composite separator sequentially comprises a first mixing layer, a first ceramic layer, a base film layer, a nanofiber layer, a second ceramic layer, and a second mixing layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are the same. Preferably, the composition and / or thickness of the first ceramic layer and the second ceramic layer are the same.

[0026] Preferably, in the base film skeleton, the thickness of the base film layer is H1, and the thickness of the nanofiber layer is H2, where H1 = 3~20μm and H2 = 2~25μm.

[0027] Preferably, the thickness of the first functional layer is H3', where H3' = 1~5 μm. Preferably, when the first functional layer includes an adhesive layer, the thickness of the adhesive layer is H3, where H3 = 1~2 μm; when the first functional layer includes a hybrid layer, the thickness of the hybrid layer is H4, where H4 = 1~5 μm.

[0028] Preferably, the thickness of the second functional layer is H5, where H5 = 1~5 μm.

[0029] The thicknesses of the aforementioned base film layer, nanofiber layer, first functional layer (adhesive layer or hybrid layer), and second functional layer are each limited to specific ranges. This ensures that the performance of the base film layer, nanofiber layer, and each functional layer is fully utilized without restricting each other's effects, thus facilitating the acquisition of a composite membrane with excellent thermal stability and safety performance. Simultaneously, this prevents the total thickness of the final composite membrane from being...

[0030] Preferably, in the thickness direction of the composite membrane, at least one nanofiber layer is provided on both sides of the base membrane skeleton. That is, the base membrane skeleton sequentially includes a first nanofiber layer, a base membrane layer, and a second nanofiber layer. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are the same.

[0031] In one optional embodiment, the composite separator sequentially comprises an adhesive layer, a first nanofiber layer, a base film layer, and a second nanofiber layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the first nanofiber layer and the second nanofiber layer have the same composition and / or thickness.

[0032] In one optional embodiment, the composite membrane sequentially comprises a mixing layer, a first nanofiber layer, a base film layer, and a second nanofiber layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are identical.

[0033] In one optional embodiment, the composite separator sequentially comprises an adhesive layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a hybrid layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are identical.

[0034] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a second adhesive layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are the same. Preferably, the composition and / or thickness of the first adhesive layer and the second adhesive layer are the same.

[0035] In one optional embodiment, the composite membrane sequentially comprises a first mixing layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a second mixing layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are the same. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are the same.

[0036] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a second adhesive layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are the same. Preferably, the composition and / or thickness of the first adhesive layer and the second adhesive layer are the same.

[0037] In one optional embodiment, the composite separator sequentially comprises an adhesive layer, a ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a hybrid layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are identical.

[0038] In one optional embodiment, the composite separator sequentially comprises a first mixing layer, a ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, and a second mixing layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are identical. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are identical.

[0039] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, and a second adhesive layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the first nanofiber layer and the second nanofiber layer have the same composition and / or thickness. Preferably, the first adhesive layer and the second adhesive layer have the same composition and / or thickness. Preferably, the first ceramic layer and the second ceramic layer have the same composition and / or thickness.

[0040] In one optional embodiment, the composite separator sequentially comprises a first mixing layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, and a second mixing layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are identical. Preferably, the composition and / or thickness of the first mixing layer and the second mixed adhesive layer are identical. Preferably, the composition and / or thickness of the first ceramic layer and the second ceramic layer are identical.

[0041] Preferably, in the nanofiber layer, the nanofiber material includes at least one selected from wood fiber (cellulose), PAN (polyacrylonitrile), polyimide (PI), para-aramid (PPTA), polyethylene terephthalate (PET), poly(p-phenylenebenzodioxazole), and polyarylether sulfone ketone (PAESK). Preferably, in the adhesive layer, the adhesive compound includes at least one selected from polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA).

[0042] Preferably, in the mixed layer, the adhesive compound includes at least one of polyvinylidene fluoride (PVDF) and polymethyl methacrylate (PMMA); the ceramic particles include alumina. At least one of boehmite, zirconium oxide, and titanium oxide.

[0043] Preferably, when the mixed layer comprises an adhesive compound and ceramic particles, the mass ratio of the adhesive compound to the ceramic particles is W1:W2, where W1:W2 = 1:8~15.

[0044] Preferably, the ceramic particles in the ceramic layer include alumina. At least one of boehmite, zirconium oxide, and titanium oxide.

[0045] Preferably, the base film material in the base film layer includes at least one of polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polyimide (PI).

[0046] Preferably, the composite membrane includes a base membrane skeleton, a first functional layer, a second functional layer, and a third functional layer; the first functional layer includes a mixed layer formed by mixing an adhesive compound and ceramic particles, or the first functional layer includes an adhesive layer formed by an adhesive compound; the second functional layer includes a ceramic layer formed by ceramic particles; the third functional layer includes a thermosensitive layer formed by a thermosensitive material, wherein the thermosensitive material includes at least one homopolymer or copolymer of non-fluorinated alkenyl monomers, olefin monomers, unsaturated nitrile monomers, olefinic monomers, and ester monomers.

[0047] Preferably, the thickness of the third functional layer is H6, where H6 = 1~5 μm.

[0048] Preferably, the third functional layer is configured in the same way as the second functional layer, that is, a third functional layer is added to the base membrane skeleton, the first functional layer, and the second functional layer. Here, the base membrane skeleton sequentially includes a base membrane layer and a nanofiber layer, or sequentially includes a first nanofiber layer, a base membrane layer, and a second nanofiber layer. Furthermore, the first, second, and third functional layers are disposed on one or both sides of the base membrane skeleton, with the base membrane skeleton as the intermediate layer. The first, second, and third functional layers are either asymmetrically or symmetrically disposed on both sides of the base membrane skeleton.

[0049] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a first thermosensitive layer, a first ceramic layer, a base film layer, a nanofiber layer, a second ceramic layer, a second thermosensitive layer, and a second adhesive layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the first adhesive layer and the second adhesive layer have the same composition and / or thickness. Preferably, the first ceramic layer and the second ceramic layer have the same composition and / or thickness. Preferably, the first thermosensitive layer and the second thermosensitive layer have the same composition and / or thickness.

[0050] In one optional embodiment, the composite separator sequentially comprises a first mixing layer, a first thermosensitive layer, a first ceramic layer, a base film layer, a nanofiber layer, a second ceramic layer, a second thermosensitive layer, and a second mixing layer. The base film layer and the nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first mixing layer and the second mixing layer are the same. Preferably, the composition and / or thickness of the first ceramic layer and the second ceramic layer are the same. Preferably, the composition and / or thickness of the first thermosensitive layer and the second thermosensitive layer are the same.

[0051] In one optional embodiment, the composite separator sequentially comprises a first adhesive layer, a first thermosensitive layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, a second thermosensitive layer, and a second adhesive layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the composition and / or thickness of the first nanofiber layer and the second nanofiber layer are the same. Preferably, the composition and / or thickness of the first adhesive layer and the second adhesive layer are the same. Preferably, the composition and / or thickness of the first ceramic layer and the second ceramic layer are the same. Preferably, the composition and / or thickness of the first thermosensitive layer and the second thermosensitive layer are the same.

[0052] In one optional embodiment, the composite separator sequentially comprises a first mixing layer, a first thermosensitive layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, a second thermosensitive layer, and a second mixing layer. The first nanofiber layer, the base film layer, and the second nanofiber layer sequentially form the base film framework. Preferably, the first nanofiber layer and the second nanofiber layer have the same composition and / or thickness. Preferably, the first mixing layer and the second mixing layer have the same composition and / or thickness. Preferably, the first ceramic layer and the second ceramic layer have the same composition and / or thickness. Preferably, the first thermosensitive layer and the second thermosensitive layer have the same composition and / or thickness.

[0053] In addition, the composite membrane can also be provided with a fourth functional layer, a fifth functional layer, a sixth functional layer, etc. Different functional layers can be set according to actual performance requirements. These functional layers are set symmetrically or asymmetrically on both sides of the base membrane skeleton.

[0054] Preferably, a method for preparing a composite separator comprising a mixing layer, a base film layer, and a nanofiber layer is provided, specifically as follows: a mixing layer is coated on one side of the base film layer, and then thermally bonded to the nanofiber layer on the other side of the base film to obtain the above-mentioned composite separator.

[0055] Preferably, a method for preparing a composite membrane comprising a first mixing layer, a base film layer, a nanofiber layer, and a second mixing layer is provided, specifically as follows: a mixing layer is first coated on one side of the base film layer, denoted as composite membrane A; then a mixing layer is coated on the surface of the nanofiber layer, denoted as composite membrane B; finally, composite membrane A and composite membrane B (composite between the unmixed layers) are thermally bonded to obtain the above-mentioned composite membrane.

[0056] Preferably, a method for preparing a composite separator comprising a first adhesive layer, a ceramic layer, a base film layer, a nanofiber layer, and a second adhesive layer is provided, specifically as follows: a ceramic layer and an adhesive layer are coated sequentially on the same side of the base film surface, denoted as composite film A; then an adhesive layer is coated on the surface of the nanofiber layer, denoted as composite film B; finally, composite film A and composite film B (composite between the non-adhesive layers) are thermally bonded to obtain the above-mentioned composite separator.

[0057] Preferably, a method for preparing a composite separator comprising a first adhesive layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, and a second adhesive layer is provided, specifically as follows: a ceramic layer and an adhesive layer are successively coated on the same side of the nanofiber layer, denoted as composite film A; then, a nanofiber layer is taken, and a ceramic layer and an adhesive layer are successively coated on the same side of its surface, denoted as composite film B; then, thermal bonding is performed in the order of composite film A, base film layer, and composite film B (the base film is located in the middle, and the two sides of the base film are bonded to the layers without ceramic and adhesive layers) to obtain the above-mentioned composite separator.

[0058] Preferably, a method for preparing a composite separator comprising, in sequence, a first adhesive layer, a first thermosensitive layer, a first ceramic layer, a first nanofiber layer, a base film layer, a second nanofiber layer, a second ceramic layer, a second thermosensitive layer, and a second adhesive layer is provided, specifically as follows: A ceramic layer, a thermosensitive layer, and an adhesive layer are sequentially coated on the same side of the nanofiber layer, denoted as composite film A; then, a nanofiber layer is taken, and a ceramic layer, a thermosensitive layer, and an adhesive layer are sequentially coated on the same side of its surface, denoted as composite film B; then, thermal bonding is performed in the order of composite film A, base film layer, and composite film B (the base film is located in the middle, and the two sides of the base film are bonded to the layers without ceramic, thermosensitive, and adhesive layers) to obtain the aforementioned composite separator.

[0059] Preferably, the thickness of the composite separator is H, where H = 8~62 μm. Controlling the total thickness of the composite separator within this specific range can effectively improve various aspects of the lithium battery's performance, including lithium-ion transport, mechanical properties, safety performance, and energy density. For example, if the total thickness of the composite separator is too large, it will lengthen the lithium-ion transport path, increasing lithium-ion transport resistance and reducing charge-discharge efficiency. Simultaneously, an excessively thick composite separator will occupy more space inside the battery, resulting in a relatively smaller loading of positive and negative electrode active materials for a given battery volume, thus reducing the battery's energy density. If the total thickness of the composite separator is too small, it will cause insufficient mechanical properties, reducing thermal stability and safety. Furthermore, it cannot effectively block potential metal impurities or other particulate matter inside the battery. When these impurities pass through the separator and reach the opposite electrode, they may cause micro-short circuits, affecting battery performance and lifespan.

[0060] Preferably, the composite diaphragm has a thermal shrinkage rate of ≤3% at T2, and T2 ≥ 200℃.

[0061] Preferably, the liquid absorption rate of the composite diaphragm is ≥30mm / 10min.

[0062] According to another aspect of the present invention, a battery is provided comprising the above-described composite separator.

[0063] In summary, the composite separator provided by this invention possesses excellent mechanical properties and thermal stability, thus effectively improving the safety performance of lithium batteries. Simultaneously, the nanofiber layer in the composite separator increases the overall porosity of the separator, facilitating the smooth transport of lithium ions and further optimizing the cycle performance of the lithium battery under normal operating conditions. Attached Figure Description

[0064] Figure 1 This is a schematic diagram of the composite membrane structure in Embodiment 1 of the present invention.

[0065] Figure 2 This is a schematic diagram of the composite membrane structure in Embodiment 2 of the present invention.

[0066] Figure 3 This is a schematic diagram of the composite membrane structure in Embodiment 3 of the present invention.

[0067] Figure 4 This is a schematic diagram of the composite membrane structure in Embodiment 4 of the present invention.

[0068] Figure 5 This is a schematic diagram of the composite diaphragm structure in Embodiment 5 of the present invention.

[0069] Explanation of icon numbers

[0070] 1-Composite separator; 10-Base film layer; 11-Nanofiber layer; 111-First nanofiber layer; 112-Second nanofiber layer; 12-Mixed layer; 121-First mixed layer; 122-Second mixed layer; 131-First adhesive layer; 132-Second adhesive layer; 14-Ceramic layer; 141-First ceramic layer; 142-Second ceramic layer; 151-First thermosensitive layer; 152-Second thermosensitive layer. Detailed Implementation

[0071] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments.

[0072] Example 1

[0073] The composite membrane 1 provided in this embodiment includes a mixing layer 12, a base membrane layer 10, and a nanofiber layer 11 in sequence. That is, the base membrane skeleton is composed of the base membrane layer 10 and the nanofiber layer 11, and the mixing layer is the first functional layer.

[0074] The preparation method is as follows: On one side of the base film layer 10, a mixture of adhesive compound and ceramic particles is coated to form a mixed layer 12. Then, on the other side of the base film 10, it is thermally composited with the nanofiber layer 11 to obtain the above-mentioned composite membrane.

[0075] In the mixed layer 12, the mass ratio of adhesive compound to ceramic particles is 1:12, the adhesive compound is polyvinylidene fluoride (PVDF), and the ceramic particles are alumina.

[0076] The nanofiber layer 11 is made of polyacrylonitrile (PAN) nanofibers. The nanofiber layer 11 can be prepared using electrospinning, as detailed below:

[0077] (1) Dissolve PAN nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PAN nanofiber solution.

[0078] (2) Inject the above uniform PAN nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0079] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the desired nanofiber layer.

[0080] The base film layer 10 is made of polyethylene (PE).

[0081] In the composite membrane 1 of this embodiment, the thicknesses of the mixing layer 12, the base film layer 10, and the nanofiber layer 11 are 2 μm, 7 μm, and 9 μm, respectively. In the thickness direction of the composite membrane 1, the area of ​​one side of the base film layer 10 is defined as S1, and the projected area of ​​the nanofiber layer 11 on the base film layer 10 is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, the composite membrane 1 prepared in this embodiment has an air permeability value of 11500 s / 100 mL at 200°C for 1 hour. The air permeability value in the composite membrane 1 in this embodiment is controlled by adjusting the diameter and / or thickness of the nanofiber layer 11 and / or the thickness of each layer of the composite membrane 1. In this embodiment, the thickness of the nanofiber layer 11 is 9 μm, the diameter of the nanofibers in the nanofiber layer 11 is 50~800 nm with an average diameter of 400 nm, and the length is 200~2000 μm with an average length of 1200 μm.

[0082] The test method for the air permeability value of composite diaphragm 1 at 200℃ for 1 hour is as follows: Air permeability is evaluated based on the time required for gas to pass through a specific area of ​​material (volume method). Using a diaphragm air permeability tester, a certain pressure difference is established across the sample at 200℃ (constant pressure difference set at 0.1~1MPa). The time required for a certain amount of gas (e.g., 100 ml) to pass through the sample of known area and thickness is recorded, thereby calculating the material's air permeability parameter. The formula for calculating the air permeability value is: Air permeability value = Gas volume / (Time × Area × Pressure difference). At least three measurements are performed on the same sample, and the average value is taken as the final result.

[0083] In this embodiment, each layer can be prepared by conventional methods, and is not limited to the methods listed above.

[0084] Example 2

[0085] The composite membrane 1 provided in this embodiment includes a first mixing layer 121, a base membrane layer 10, a nanofiber layer 11, and a second mixing layer 122 in sequence. That is, the base membrane skeleton is composed of the base membrane layer 10 and the nanofiber layer 11, and the first mixing layer 121 and the second mixing layer 122 are both first functional layers.

[0086] The preparation method is as follows: On one side of the base film layer 10, a mixture of adhesive compound and ceramic particles is coated to form a first mixed layer 121, denoted as composite film A; then, a mixture of adhesive compound and ceramic particles is coated on the surface of the nanofiber layer 11 to form a second mixed layer 122, denoted as composite film B; finally, composite film A and composite film B (composite between unmixed layers) are thermally composited to obtain the composite diaphragm 1 of this embodiment.

[0087] In the first mixed layer 121 and the second mixed layer 122, the mass ratio of adhesive compound to ceramic particles is 1:12, the adhesive compound is polyvinylidene fluoride (PVDF), and the ceramic particles are alumina.

[0088] The nanofiber layer 11 is made of polyethylene terephthalate (PET) nanofibers. The nanofiber layer 11 can be prepared using electrospinning, as detailed below:

[0089] (1) Dissolve PET nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PET nanofiber solution;

[0090] (2) Inject the above uniform PET nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0091] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the required nanofiber layer 11.

[0092] The base film layer 10 is made of polyethylene (PE).

[0093] In this embodiment of the composite membrane, the thicknesses of the first mixing layer, the base film layer 10, the nanofiber layer 11, and the second mixing layer are 2 μm, 7 μm, 9 μm, and 2 μm, respectively. In the thickness direction of the composite membrane 1, the area of ​​one side of the base film layer 10 is defined as S1, and the projected area of ​​the nanofiber layer 11 on the base film layer 10 is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, the composite membrane 1 prepared in this embodiment has an air permeability value of 13200 s / 100 mL at 200°C for 1 hour. The air permeability value of the composite membrane 1 in this embodiment is controlled by adjusting the diameter and / or thickness of the nanofiber layer and / or the thickness of each layer of the composite membrane. In this embodiment, the thickness of the nanofiber layer 11 is 9 μm, the diameter of the nanofibers in the nanofiber layer is 50~800 nm, the average diameter is 400 nm, the length is 200~2000 μm, and the average length is 1200 μm.

[0094] Furthermore, the test method for the air permeability value of composite membrane 1 at 200°C for 1 hour is as described in Example 1.

[0095] In this embodiment, each layer can be prepared by conventional methods, and is not limited to the methods listed above.

[0096] Example 3

[0097] The composite membrane provided in this embodiment includes, in sequence, a first adhesive layer 131, a ceramic layer 14, a base membrane layer 10, a nanofiber layer 11, and a second adhesive layer 132. That is, the base membrane skeleton is composed of the base membrane layer 10 and the nanofiber layer 11. The first adhesive layer 131 and the second adhesive layer 132 are both first functional layers, and the ceramic layer 14 is the second functional layer.

[0098] The preparation method is as follows: ceramic particles and adhesive compound are sequentially coated on one side of the base film layer 10 to form a ceramic layer 10 and a first adhesive layer 131, denoted as composite film A; then adhesive compound is coated on the surface of the nanofiber layer 10 to form a second adhesive layer 132, denoted as composite film B; finally, composite film A and composite film B (composite between layers without adhesive) are thermally composited to obtain the composite diaphragm 1 of this embodiment.

[0099] In the first adhesive layer 131 and the second adhesive layer 132, the adhesive compound is polymethyl methacrylate (PMMA).

[0100] In ceramic layer 14, the ceramic particles are boehmite.

[0101] The nanofiber layer 11 is made of polyimide (PI) nanofibers. The nanofiber layer 11 can be prepared using electrospinning, as detailed below:

[0102] (1) Dissolve PI nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PI nanofiber solution.

[0103] (2) Inject the above uniform PI nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0104] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the required nanofiber layer 11.

[0105] The base film layer 10 is made of polyethylene (PE).

[0106] In the composite diaphragm 1 of this embodiment, the thicknesses of the first adhesive layer 131, the ceramic layer 14, the base film layer 10, the nanofiber layer 11, and the second adhesive layer 132 are 2μm, 2μm, 7μm, 9μm, and 2μm, respectively. In the thickness direction of the composite diaphragm 1, the area of ​​one side of the base film layer 10 is defined as S1, and the projected area of ​​the nanofiber layer 11 on the base film layer 10 is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, in the composite membrane 1 prepared in this embodiment, the air permeability value at 200℃ for 1 hour is 14700s / 100mL. In this embodiment, the air permeability value of the composite membrane 1 is controlled by adjusting the diameter and thickness of the nanofiber layer 10 or the thickness of each layer of the composite membrane 1. In this embodiment, the thickness of the nanofiber layer 11 is 9μm, the diameter of the nanofibers in the nanofiber layer 11 is 50~800nm, the average diameter is 400nm, the length is 200~2000μm, and the average length is 1200μm.

[0107] Furthermore, the test method for the air permeability value of composite membrane 1 at 200°C for 1 hour is as described in Example 1.

[0108] In this embodiment, each layer can be prepared by conventional methods, and is not limited to the methods listed above.

[0109] Example 4

[0110] The composite membrane 1 provided in this embodiment includes, in sequence, a first adhesive layer 131, a first ceramic layer 141, a first nanofiber layer 111, a base film layer 10, a second nanofiber layer 112, a second ceramic layer 142, and a second adhesive layer 132. That is, the base film skeleton is composed of the first nanofiber layer 111, the base film layer 10, and the second nanofiber layer 112. The first adhesive layer 131 and the second adhesive layer 132 are both first functional layers, and the first ceramic layer 141 and the second ceramic layer 142 are both second functional layers.

[0111] The preparation method is as follows: ceramic particles and adhesive compounds are successively coated on the same side of the surface of the first nanofiber layer 111 to form the first ceramic layer 141 and the first adhesive layer 131, denoted as composite membrane A; ceramic particles and adhesive compounds are successively coated on the same side of the surface of the second nanofiber layer 112 to form the second ceramic layer 142 and the second adhesive layer 132, denoted as composite membrane B; then, thermal bonding is performed in the order of composite membrane A, base membrane layer, and composite membrane B (base membrane 10 is located in the middle, and the two sides of the base membrane 10 are bonded to the layers without ceramic and adhesive layers) to obtain the composite membrane 1 of this embodiment.

[0112] In the first adhesive layer 131 and the second adhesive layer 132, the adhesive compound is polyvinylidene fluoride (PVDF).

[0113] In the first ceramic layer 141 and the second ceramic layer 142, the ceramic particles are alumina.

[0114] The nanofiber layer 11 is made of polyacrylonitrile (PAN) nanofibers. The nanofiber layer 11 can be prepared using electrospinning, as detailed below:

[0115] (1) Dissolve PAN nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PAN nanofiber solution.

[0116] (2) Inject the above uniform PAN nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0117] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the required nanofiber layer 11.

[0118] The base film layer 10 is made of polyethylene (PE).

[0119] In the composite membrane 1 of this embodiment, the thicknesses of the first adhesive layer 131, the first ceramic layer 141, the first nanofiber layer 111, the base film layer 10, the second nanofiber layer 112, the second ceramic layer 142, and the second adhesive layer 132 are 2μm, 2μm, 7μm, 9μm, 2μm, 2μm, and 2μm, respectively. In the thickness direction of the composite membrane 1, the area of ​​one side of the base film layer 10 is defined as S1, and the projected area of ​​the nanofiber layer 11 on the base film layer 10 is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, in the composite membrane 1 prepared in this embodiment, the air permeability value at 200℃ for 1 hour is 17500s / 100mL. In this embodiment, the air permeability value of the composite membrane 1 is controlled by adjusting the diameter and thickness of the nanofiber layer 11 or the thickness of each layer of the composite membrane 1. In this embodiment, the thickness of the nanofiber layer 11 is 9μm, the diameter of the nanofibers in the nanofiber layer 11 is 50~800nm, the average diameter is 400nm, the length is 200~2000μm, and the average length is 1200μm.

[0120] Furthermore, the test method for the air permeability value of composite membrane 1 at 200°C for 1 hour is as described in Example 1.

[0121] In this embodiment, each layer can be prepared by conventional methods, and is not limited to the methods listed above.

[0122] Example 5

[0123] The composite membrane 1 provided in this embodiment includes, in sequence, a first adhesive layer 131, a first thermosensitive layer 151, a first ceramic layer 141, a first nanofiber layer 111, a base film layer 10, a second nanofiber layer 112, a second ceramic layer 142, a second thermosensitive layer 152, and a second adhesive layer 132. That is, the base film skeleton is composed of the first nanofiber layer 111, the base film layer 10, and the second nanofiber layer 121. The first adhesive layer 131 and the second adhesive layer 132 are both first functional layers, the first ceramic layer 141 and the second ceramic layer 142 are both second functional layers, and the first thermosensitive layer 151 and the second thermosensitive layer 152 are both third functional layers.

[0124] The preparation method is as follows: On the same side of the surface of the first nanofiber layer 111, ceramic particles, a thermosensitive material, and an adhesive compound are successively coated to form a first ceramic layer 141, a first thermosensitive layer 151, and a first adhesive layer 131, denoted as composite membrane A; On the same side of the surface of the second nanofiber layer 112, ceramic particles, a thermosensitive material, and an adhesive compound are successively coated to form a second ceramic layer 142, a second thermosensitive material 152, and a second adhesive layer 132, denoted as composite membrane B; Then, thermal bonding is performed in the order of composite membrane A, base membrane layer, and composite membrane B (the base membrane is located in the middle, and the two sides of the base membrane are bonded to the layers without ceramic layers and adhesive layers) to obtain the composite separator of this embodiment.

[0125] In the first adhesive layer 131 and the second adhesive layer 132, the adhesive compound is polyvinylidene fluoride (PVDF).

[0126] In the first ceramic layer 141 and the second ceramic layer 142, the ceramic particles are alumina.

[0127] The first thermosensitive layer 151 and the second thermosensitive layer 152 are made of olefin-based monomers.

[0128] The nanofiber layer 11 is made of polyacrylonitrile (PAN) nanofibers. The nanofiber layer 11 can be prepared using electrospinning, as detailed below:

[0129] (1) Dissolve PAN nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PAN nanofiber solution.

[0130] (2) Inject the above uniform PAN nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0131] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the required nanofiber layer 11.

[0132] The base film layer 10 is made of polyethylene (PE).

[0133] In the composite membrane 1 of this embodiment, the thicknesses of the first adhesive layer 131, the first ceramic layer 141, the first nanofiber layer 111, the base film layer 10, the second nanofiber layer 112, the second ceramic layer 142, and the second adhesive layer 132 are 2μm, 2μm, 9μm, 7μm, 9μm, 2μm, 2μm, 2μm, and 2μm, respectively. In the thickness direction of the composite membrane 1, the area of ​​one side of the base film layer 10 is defined as S1, and the projected area of ​​the nanofiber layer 11 on the base film layer 10 is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, in the composite membrane 1 prepared in this embodiment, the air permeability value at 200℃ for 1 hour is 18800s / 100mL. In this embodiment, the air permeability value of the composite membrane 1 is controlled by adjusting the diameter and thickness of the nanofiber layer 11 or the thickness of each layer of the composite membrane 1. In this embodiment, the thickness of the nanofiber layer 11 is 9μm, the diameter of the nanofibers in the nanofiber layer 11 is 50~800nm, the average diameter is 400nm, the length is 200~2000μm, and the average length is 1200μm.

[0134] Furthermore, the test method for the air permeability value of composite membrane 1 at 200°C for 1 hour is as described in Example 1.

[0135] In this embodiment, each layer can be prepared by conventional methods, and is not limited to the methods listed above.

[0136] Example 6

[0137] The difference between this embodiment and embodiment 4 is that, in the thickness direction of the composite membrane 1, the area of ​​one side of the base membrane layer 10 is taken as S1, and the projected area of ​​the nanofiber layer 11 on the base membrane layer 10 is taken as S2. In this embodiment, S2 / S1 = 90%. The remaining operations are the same as in embodiment 4.

[0138] Furthermore, due to the change in S2 / S1, the air permeability value (1h at 200℃) of 1 in the composite membrane in this embodiment is 17600s / 100mL.

[0139] Example 7

[0140] The difference between this embodiment and Embodiment 1 is that the diameter and length of the nanofibers in the nanofiber layer 11 are adjusted to regulate the air permeability of the composite membrane 1. Specifically, after adjustment, the diameter of the nanofibers is 100~1000nm, the average diameter is 600nm, the length is 200~2000μm, and the average length is 1600μm. The remaining operations are the same as in Embodiment 1.

[0141] Therefore, the final air permeability value of the composite membrane 1 was 10000s / 100mL (1h at 200℃).

[0142] Example 8

[0143] The difference between this embodiment and Embodiment 4 lies in adjusting the diameter and length of the nanofibers in the nanofiber layer 11 to regulate the air permeability of the composite membrane 1. Specifically, after adjustment, the diameter of the nanofibers is 20~200nm, with an average diameter of 140nm, and the length is 200~1500μm, with an average length of 1000μm. The remaining operations are the same as in Embodiment 4. Therefore, the final air permeability value (at 200℃ for 1h) obtained by the composite membrane 1 is 20000s / 100mL.

[0144] Example 9

[0145] The difference between this embodiment and Embodiment 4 is that the thicknesses of the first adhesive layer 131, the first ceramic layer 141, the first nanofiber layer 111, the base film layer 10, the second nanofiber layer 112, the second ceramic layer 142, and the second adhesive layer 132 are adjusted to 9 μm, 9 μm, 10 μm, 14 μm, 10 μm, 9 μm, and 9 μm respectively, resulting in a total thickness of 70 μm for the composite membrane 1. The remaining operations are the same as in Embodiment 4.

[0146] Furthermore, due to the change in the total thickness of the composite membrane 1, the air permeability value (1h at 200℃) of the composite membrane 1 in this embodiment is 30000s / 100mL.

[0147] Comparative Example 1

[0148] The difference between this comparative example and Example 1 is that, in the thickness direction of the composite membrane, the area of ​​one side of the base film layer is defined as S1, and the projected area of ​​the nanofiber layer on the base film layer is defined as S2. In this example, S2 / S1 = 80%. The remaining operations are the same as in Example 1.

[0149] Furthermore, due to the change in S2 / S1, the air permeability value (1h at 200°C) of the composite membrane in this embodiment is 4000s / 100mL.

[0150] Comparative Example 2

[0151] The difference between this comparative example and Example 1 is that the diameter and length of the nanofibers in the nanofiber layer were adjusted to control the air permeability of the composite membrane. Specifically, after adjustment, the diameter of the nanofibers was 800~2000nm, with an average diameter of 1600nm, and the length was 2000~3000μm, with an average length of 2600μm. The remaining operations were the same as in Example 1. Therefore, the final air permeability value (at 200℃ for 1h) of the composite membrane was 3000s / 100mL.

[0152] Comparative Example 3

[0153] The difference between this comparative example and Example 1 is that the composite separator in this example comprises a mixing layer and a base film layer, i.e., it does not contain a nanofiber layer. The composite separator in this comparative example is obtained by directly coating the base film with a mixture composed of an adhesive compound and ceramic particles. The rest is the same as in Example 1.

[0154] Because the composite membrane does not have a nanofiber layer, it breaks down directly at high temperatures (1 hour at 200°C), making it impossible to test the air permeability value.

[0155] Comparative Example 4

[0156] The difference between this comparative example and Example 1 is that the composite separator in this example consists of a base film layer and a nanofiber layer, respectively, without a mixing layer. The composite separator in this comparative example is obtained by directly thermally bonding the base film and the nanofiber layer. The rest is the same as in Example 1.

[0157] The final air permeability value of the composite membrane (1h at 200℃) was 5000s / 100mL.

[0158] Comparative Example 5

[0159] The composite membrane provided in this comparative example comprises a ceramic layer, an adhesive layer, a base membrane layer, and a nanofiber layer, in that the base membrane skeleton is composed of the base membrane layer and the nanofiber layer.

[0160] The preparation method is as follows: ceramic particles and adhesive compound are sequentially coated on one side of the base membrane to form a ceramic layer and an adhesive layer, denoted as composite membrane A; then the nanofiber layer is thermally bonded to the other side of the base membrane to obtain the composite membrane of this comparative example.

[0161] In the first adhesive layer and the second adhesive layer, the adhesive compound is polyvinylidene fluoride (PVDF).

[0162] In the ceramic layer, the ceramic particles are alumina.

[0163] The nanofiber layer is made of polyacrylonitrile (PAN). The nanofiber layer can be prepared using electrospinning, as detailed below:

[0164] (1) Dissolve PAN nanofibers in a solvent (dimethylformamide (DMF)) at a certain ratio (8%~15%) to obtain a uniformly dispersed PAN nanofiber solution.

[0165] (2) Inject the above uniform PAN nanofiber solution into the electrospinning machine, adjust the parameters of the electrospinning machine (such as the distance between the needle and the receiving plate), and start electrospinning.

[0166] (3) Collect the above fiber membrane, dry and roll it at 60~80℃, and after curing, obtain the desired nanofiber layer.

[0167] The base film layer is made of polyethylene (PE).

[0168] In this comparative example, the thicknesses of the ceramic layer, adhesive layer, base film layer, and nanofiber layer are 2 μm, 2 μm, 7 μm, and 3 μm, respectively. In the thickness direction of the composite separator, the area of ​​one side of the base film layer is defined as S1, and the projected area of ​​the nanofiber layer on the base film layer is defined as S2. In this embodiment, S2 / S1 = 100%. Furthermore, the composite separator prepared in this embodiment has a permeability of 6400 s / 100 mL at 200°C for 1 hour. The permeability of the composite separator in this comparative example is controlled by adjusting the diameter and thickness of the nanofiber layer or the thickness of each layer of the composite separator. In this comparative example, the thickness of the nanofiber layer is 9 μm, the diameter of the nanofibers in the nanofiber layer is 50–800 nm with an average diameter of 400 nm, and the length is 200–2000 μm with an average length of 1200 μm.

[0169] The test method for the air permeability value of the composite membrane at 200°C for 1 hour is as described in Example 1.

[0170] In this comparative example, each layer can be prepared using conventional methods, and is not limited to the methods listed above.

[0171] Test case

[0172] 1. Experimental Construction Method

[0173] The composite membranes prepared in Examples 1-9 and Comparative Examples 1-5 were tested for heat shrinkage rate, liquid absorption rate, and safety performance. The specific test methods are as follows:

[0174] (1) Thermal shrinkage rate

[0175] Cut a piece of diaphragm, approximately 150mm x 150mm, and draw lines along its length and width. Mark 100mm intervals with a ruler and conduct a shrinkage test at 200℃ for 1 hour. After the test, measure the marked distance with a ruler. The ratio of the reduced distance to the original distance is the shrinkage rate.

[0176] (2) Liquid absorption rate

[0177] Sample preparation: Cut the diaphragm into strips of 25mm (width) * 300mm (length);

[0178] Prepare the electrolyte: Prepare a standard electrolyte, ensuring that the composition and concentration of the electrolyte meet the test requirements;

[0179] Sample immersion: One end of the diaphragm is suspended on an iron stand; the other end is completely immersed in the electrolyte; record the height h1.

[0180] After 10 minutes, record the electrolyte wetting height h2;

[0181] Calculate the liquid aspiration rate: i.e. the diaphragm climbing speed: v=(h2-h1) / 10min.

[0182] (3) Safety performance

[0183] Batteries were prepared using the composite separators obtained in Examples 1-9 and Comparative Examples 1-5. The battery preparation process is as follows:

[0184] (1) The positive electrode is made by dispersing lithium iron phosphate (LFP), SP, CNT and PVDF in NMP solvent in a certain ratio (mass ratio of (95~98): (0.5~1.0): (0~1.0): (1.0~2.0)), stirring to form a uniform slurry, coating it on aluminum foil, drying, rolling and cutting it to prepare the positive electrode sheet of the required size;

[0185] (2) The negative electrode is made by dispersing graphite Gr, SP, CMC and SBR in a certain proportion (mass ratio of (95~98): (0.5~1.0): (0.5~1.5): (1.0~2.0)) in deionized water, stirring to form a uniform slurry, coating it on copper foil, drying, rolling and cutting it to prepare a negative electrode sheet of the required size;

[0186] (3) The electrolyte used is 1M LiPF6 electrolyte with a lithium salt concentration;

[0187] (4) Assemble the positive electrode, composite separator and negative electrode in sequence, put them into the shell, inject electrolyte, form and adjust the volume to obtain the battery.

[0188] A. Needle puncture [10mm steel needle, (80±5) mm / s puncture], refer to YDT2344.2-2015 (stricter). Procedure: Use a 10mm steel needle (the needle surface is smooth, free of rust, oxide layer and oil) to puncture the battery cell at a speed of 80mm / s, perpendicular to the fully charged battery cell plates; record the battery cell condition. The standard for judging whether the safety standard is met after conventional needle puncture is: no fire, no explosion.

[0189] B. Thermal Runaway: Refer to GB / T 36276-2023 (Tightened). Procedure: Charge a fully charged cell at a constant current of 1C, start heating, and continuously heat the test object at its maximum power (800W) (double-sided heating, larger surface). When thermal runaway occurs, record the thermal runaway temperature. The conventional criteria for judging thermal runaway are: fire or explosion, or rupture at a location other than the explosion-proof valve or pressure relief valve.

[0190] 2. Experimental Results

[0191] The test results of thermal shrinkage rate, liquid absorption rate and safety performance of the composite membranes prepared in Examples 1-9 and Comparative Examples 1-5 are shown in Table 1.

[0192] Table 1 Test results of composite diaphragm thermal shrinkage rate, liquid absorption rate, and safety performance

[0193]

[0194] As shown in Table 1, the composite separator provided by this invention, due to its specific structure and high high-temperature permeability, exhibits a low thermal shrinkage rate, thus effectively improving the battery's puncture resistance and thermal runaway resistance, and optimizing battery safety performance. Simultaneously, the composite separator provided by this invention has a high liquid absorption rate, which can further improve the battery's cycle performance. See Examples 1-9 for details.

[0195] In Comparative Example 1, S2 / S1 = 80%, indicating a low proportion of nanofiber layer. This results in insufficient fiber layer when heated, leading to increased membrane shrinkage and a permeability value of 4000s / 100mL at 200℃ for 1 hour, which in turn affects the battery's safety performance.

[0196] In Comparative Example 2, the air permeability value was 3000s / 100mL, which is relatively low. Its high air permeability leads to a decrease in battery safety performance. As can be seen from the table, due to the low air permeability value of the separator, the battery cannot completely block the transmission of lithium ions, resulting in a higher thermal runaway temperature than normal batteries.

[0197] In Comparative Example 3, which did not contain a nanofiber layer, the membrane ruptured when heated to 200°C; this indicates that the nanofiber layer can effectively improve the heat resistance of the composite membrane.

[0198] In Comparative Example 4, the absence of a mixing layer (or adhesive layer) prevents the base film or adhesive layer from melting at high temperatures to block the pores of the nanofibers and form closed pores in the separator. This fails to completely hinder lithium-ion transport, thus affecting battery safety performance.

[0199] In Comparative Example 5, the adhesive layer is not on the outermost layer, which prevents the positive and negative electrode sheets from fully adhering, thus affecting the overall structural stability of the battery and consequently its safety performance.

[0200] Observing Examples 1 to 5, it can be found that the composite separator provided by the present invention can have a multi-layer functional layer structure, and the multi-layer functional layer structure is more conducive to improving the performance of the composite separator in all aspects, especially the battery safety performance and cycle performance can be effectively improved.

[0201] Comparing Example 4 and Example 6, in Example 6, S2 / S1=90%, that is, the proportion of the nanofiber layer has decreased, which has resulted in a decrease in the air permeability of the separator in Example 6, that is, an increase in air permeability, which has led to a decrease in the safety performance of the battery, that is, an increase in the thermal runaway temperature.

[0202] In Examples 7 and 8, the air permeability values ​​are at the critical point. Therefore, in Example 7, compared to Example 1, the fiber membrane has a larger diameter and a lower air permeability value, resulting in a slight decrease in safety performance. In Example 8, compared to Example 4, the fiber membrane has a smaller diameter and length, resulting in a higher air permeability value and improved safety performance. However, the higher air permeability value leads to a decrease in the battery's rate performance, affecting its high-rate performance.

[0203] Compared to Example 4, Example 9 has a thicker composite separator, which improves battery safety performance. However, the higher permeability will lead to a decrease in the battery's rate performance and affect its high-rate performance.

[0204] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application, but such modifications or substitutions are all within the scope of protection of this application.

Claims

1. A composite diaphragm, characterized in that: It includes a base membrane framework and a first functional layer, wherein the base membrane framework sequentially includes a base membrane layer and a nanofiber layer; In the thickness direction of the composite membrane, the nanofiber layer is provided on at least one side of the base membrane layer; In the thickness direction of the composite membrane, at least one surface of the composite membrane is provided with the first functional layer; the first functional layer is an adhesive layer. In the thickness direction of the composite membrane, the area of ​​one side of the base film layer is S1, and the projected area of ​​the nanofiber layer on the base film layer is S2, where S2 / S1 = 90~100%; The air permeability of the composite diaphragm is 10000~20000s / 100mL at T1 for 1 hour, and T1≥200℃.

2. The composite diaphragm as described in claim 1, characterized in that: The first functional layer is the adhesive layer, which includes an adhesive compound; or the first functional layer is a mixed layer, which contains the adhesive compound and ceramic particles mixed together.

3. The composite diaphragm as described in claim 1, characterized in that: In the thickness direction of the composite membrane, at least one layer of the first functional layer is provided on both sides of the base membrane skeleton.

4. The composite diaphragm as described in claim 1, characterized in that: The composite membrane further includes a second functional layer, which comprises a ceramic layer formed of ceramic particles.

5. The composite diaphragm as described in claim 4, characterized in that: In the thickness direction of the composite membrane, at least one first functional layer and at least one second functional layer are provided on both sides of the base membrane skeleton.

6. The composite diaphragm as described in claim 1, characterized in that: In the base membrane framework, the thickness of the base membrane layer is H1, and the thickness of the nanofiber layer is H2, where H1 = 3~20μm and H2 = 2~25μm.

7. The composite diaphragm as described in claim 1, characterized in that: The thickness of the first functional layer is H3', where H3' = 1~5μm.

8. The composite diaphragm as described in claim 5, characterized in that: The thickness of the second functional layer is H5, where H5 = 1~5μm.

9. The composite separator according to any one of claims 1 to 8, characterized in that: In the thickness direction of the composite membrane, at least one layer of nanofiber is provided on both sides of the base membrane skeleton.

10. A battery, characterized in that: Includes the composite membrane as described in any one of claims 9.

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