High heat-resistant self-repairing diaphragm and its preparation method and application

Abstract

The present application relates to the technical field of battery separators, and more specifically to a highly heat-resistant self-repairing separator, and its preparation method and application, wherein the separator comprises coaxial electrospun nanofibers of a core-shell structure; the nanofibers form a porous network structure; the nanofibers comprise a first nanofiber and a second nanofiber, the first nanofiber comprising a first shell layer and a first core layer, the first shell layer being coated on the outside of the first core layer; the second nanofiber comprising a second shell layer and a second core layer, the second shell layer being coated on the outside of the second core layer. Since the separator is a porous network structure formed by two coaxial electrospun nanofibers, the separator has advantages such as high porosity, unique pore structure, and large specific surface area, which can significantly improve the electrolyte absorption rate and retention rate of the separator, and can improve the ionic conductivity and electrochemical performance of the separator to meet the use requirements of energy storage cells.

Description

Technical Field

[0001] The present application relates to the technical field of battery separators, and more specifically to a highly heat-resistant self-repairing separator and a preparation method and application thereof. Background Art

[0002] Energy storage and power have experienced rapid growth in recent years. Large-capacity battery cells, driven by economies of scale, can reduce unit costs, making them economically attractive. However, large-capacity cells exhibit high energy density and generate significant heat, which can easily lead to thermal runaway. Traditional separators, due to limitations in production technology and raw materials, lack the heat resistance, membrane rupture temperature, and mechanical strength required for energy storage cells.

[0003] Therefore, how to improve the performance of the diaphragm is a technical problem that needs to be solved urgently in this field. Summary of the Invention

[0004] The present application provides a highly heat-resistant self-repairing diaphragm and its preparation method and application to solve the problem of poor heat resistance and mechanical strength of the diaphragm and meet the use requirements of energy storage batteries.

[0005] The present application provides a highly heat-resistant self-healing membrane, which includes coaxial electrospun nanofibers with a core-shell structure; the nanofibers form a porous network structure; the nanofibers include a first nanofiber and a second nanofiber, the first nanofiber includes a first shell layer and a first core layer, and the first shell layer is coated on the outside of the first core layer; the second nanofiber includes a second shell layer and a second core layer, and the second shell layer is coated on the outside of the second core layer.

[0006] In an optional embodiment, the first core layer includes free radical polymerization monomers; the second core layer includes a cross-linking agent, and the cross-linking agent can induce cross-linking of the free radical polymerization monomers.

[0007] In an optional embodiment, the free radical polymerization monomer includes at least one of dicyclopentadiene, isoprene, methyl methacrylate, polydiethoxysiloxane, terminal hydroxylated polydimethylsiloxane and N,N-methylenebisacrylamide.

[0008] In an optional embodiment, the cross-linking agent includes at least one of Grubbs' catalyst, di-n-butyltin dilaurate, tungsten hexachloride phenylacetylene mixture, and azide.

[0009] In an optional embodiment, the first shell layer and / or the second shell layer includes a high-temperature resistant polymer material, and the high-temperature resistant polymer material includes at least one of polyimide, polyarylethersulfoneketone, polyetherimide, polyphenylsulfone, polyisophthalamide, etc.

[0010] In an optional embodiment, the diaphragm satisfies at least one of the conditions (1)-(6):

[0011] (1) The diameter of the first nanofiber and / or the second nanofiber is 0.2 μm to 2.0 μm;

[0012] (2) The mass ratio of the first nanofiber to the second nanofiber is 1:1;

[0013] (3) In the first nanofiber, the mass ratio of the first core layer to the first shell layer is 1:0.4-1:2.0;

[0014] (4) In the second nanofiber, the mass ratio of the second core layer to the second shell layer is 1:0.4-1:2.0;

[0015] (5) The thickness d of the diaphragm is in the range of 3 μm ≤ d ≤ 100 μm;

[0016] (6) The porosity of the diaphragm is 30%-60%.

[0017] The present application provides a method for preparing a high-heat-resistant self-repairing diaphragm, which is used to prepare the diaphragm as described above, comprising the following steps:

[0018] Dissolving the materials for preparing the first shell layer and the second shell layer in a solvent according to a preset ratio, stirring and mixing them uniformly to obtain a shell spinning solution;

[0019] Dissolving the materials for preparing the first core layer in a solvent according to a preset ratio, and stirring and mixing to obtain a first core layer spinning solution;

[0020] Dissolving the material for preparing the second core layer in a solvent according to a preset ratio, stirring and mixing to obtain a second core layer spinning solution;

[0021] The shell layer spinning solution, the first core layer spinning solution and the second core layer spinning solution are used as electrospinning solutions, and a high heat-resistant self-repairing nanofiber membrane with a porous network structure including first nanofibers and second nanofibers is obtained on a receiver by a coaxial electrospinning method;

[0022] After the high heat-resistant self-repairing nanofiber membrane is vacuum-dried, hot pressing is performed under preset conditions to obtain the high heat-resistant self-repairing nanofiber membrane.

[0023] In an optional embodiment, the diaphragm satisfies at least one of the conditions (1)-(3):

[0024] (1) The first core layer includes a free radical polymerizable monomer;

[0025] Optionally, the free radical polymerization monomer includes at least one of dicyclopentadiene, isoprene, methyl methacrylate, polydiethoxysiloxane, terminal hydroxylated polydimethylsiloxane and N,N-methylenebisacrylamide;

[0026] (2) the second core layer includes a crosslinking agent, and the crosslinking agent is capable of initiating crosslinking of the free radical polymerization monomer;

[0027] Optionally, the cross-linking agent includes at least one of Grubbs' catalyst, di-n-butyltin dilaurate, tungsten hexachloride phenylacetylene mixture and azide;

[0028] (3) Both the first shell layer and the second shell layer are made of a high-temperature resistant polymer material;

[0029] Optionally, the high-temperature resistant polymer material includes at least one of polyimide, polyarylethersulfoneketone, polyetherimide, polyphenylsulfone, polyisophthalamide, and the like.

[0030] In an optional embodiment, the diaphragm satisfies at least one of the conditions (1)-(8):

[0031] (1) In the shell layer spinning solution, the mass percentage of the material for preparing the first shell layer and the second shell layer is 5wt.%-30wt.%;

[0032] (2) In the first core layer spinning solution, the mass percentage of the material for preparing the first core layer is 5wt.%-30wt.%;

[0033] (3) In the second core layer spinning solution, the mass percentage of the material for preparing the second core layer is 5wt.%-30wt.%;

[0034] (4) The coaxial electrospinning method includes preparing the diaphragm by using a transmitter and a receiver in combination under the action of an electric field, the voltage of the electric field is 10kV-20kV, the distance between the transmitter and the receiver is 10cm-20cm, the injection rate of the shell layer spinning solution is 0.5mL / h-1.0mL / h, and the injection rate of the first core layer spinning solution and / or the second core layer spinning solution is 0.05mL / h-1.0mL / h;

[0035] (5) The thickness d of the diaphragm is in the range of 3 μm ≤ d ≤ 100 μm;

[0036] (6) The mass ratio of the first nanofiber to the second nanofiber is 1:1;

[0037] (7) The diameters of the first nanofiber and the second nanofiber are both 0.2 μm to 2.0 μm;

[0038] (8) The preset conditions during hot pressing include hot pressing temperature and hot pressing pressure. The hot pressing temperature ranges from 40°C to 100°C, and the hot pressing pressure ranges from 5MPa to 20MPa.

[0039] The present application provides a secondary battery, comprising the separator as described above or the separator prepared by the preparation method as described above.

[0040] According to the high heat-resistant self-repairing membrane in the above embodiment, the membrane includes coaxial electrospun nanofibers with a core-shell structure, and the nanofibers form a porous network structure. The nanofibers include a first nanofiber and a second nanofiber. The first nanofiber includes a first shell layer and a first core layer, and the first shell layer is coated on the outside of the first core layer; the second nanofiber includes a second shell layer and a second core layer, and the second shell layer is coated on the outside of the second core layer. Since the membrane is a porous network structure mainly formed by two coaxial electrospun nanofibers, the membrane has the advantages of high porosity, unique pore structure and large specific surface area, which can significantly improve the electrolyte absorption rate and retention rate of the membrane, thereby allowing the battery to accommodate more electrolytes so that more ions can be freely transferred and transmitted, thereby improving the ionic conductivity of the membrane and ultimately stably improving the electrochemical performance of the battery. Since the coaxial electrospun nanofibers have a large aspect ratio, the resulting membrane has high integrity, heat resistance and high mechanical strength. Since the diaphragm is formed by a plurality of nanofibers, there is a "loose" molecular force between the "microscopic" nanofibers, which gives the diaphragm a certain flexibility on a "macro" level. Therefore, it can easily pass mechanical performance tests such as bending, twisting, and folding, overcoming the safety problems caused by the diaphragm being easily wrinkled during the assembly, storage, and transportation of the battery. This makes the diaphragm promising as a new generation of battery diaphragm that can meet the use requirements of energy storage cells and improve the safety and electrochemical properties of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 A schematic structural diagram of a diaphragm in one embodiment;

[0042] Figure 2 Schematic diagram of the structure of nanofibers in one embodiment.

[0043] Wherein: 100, first nanofiber; 110, first shell layer; 120, first core layer; 200, second nanofiber; 210, second shell layer; 220, second core layer. DETAILED DESCRIPTION

[0044] The present application is further described in detail below by means of specific embodiments in conjunction with the accompanying drawings. Similar elements in different embodiments are numbered with associated similar elements. In the following embodiments, many detailed descriptions are provided to enable the present application to be better understood. However, those skilled in the art will readily appreciate that some of the features may be omitted in different circumstances, or may be replaced by other elements, materials, or methods. In some cases, some operations related to the present application are not shown or described in the specification. This is to avoid the core portion of the present application being overwhelmed by excessive descriptions. For those skilled in the art, it is not necessary to describe these related operations in detail. They can fully understand the related operations based on the description in the specification and the general technical knowledge in the art.

[0045] In addition, the features, operations, or characteristics described in the specification may be combined in any appropriate manner to form various implementations, and the operational steps involved in each embodiment may be interchanged or adjusted in a manner that is obvious to those skilled in the art. Therefore, the specification and drawings are only for the purpose of clearly describing a particular embodiment and do not imply a required composition and / or sequence.

[0046] The serial numbers assigned to components herein, such as "first," "second," etc., are used solely to distinguish the objects being described and do not convey any sequential or technical meaning. References to "connection" and "coupling" herein, unless otherwise specified, include both direct and indirect connections (couplings).

[0047] In this application, the term "secondary battery" refers to a battery that can be used to activate the active material by recharging after the battery is discharged. This type of battery usually utilizes the reversibility of chemical reactions, that is, after a chemical reaction is converted into electrical energy, the electrical energy can be used to repair the chemical system, and then the chemical reaction can be converted into electrical energy again. Among them, the more common secondary batteries include but are not limited to nickel-metal hydride batteries, nickel-cadmium batteries, lead-acid (or lead storage) batteries, lithium-ion batteries, polymer lithium-ion batteries, sodium-ion batteries, etc.

[0048] In this application, the term "diaphragm" refers to a crucial component of a secondary battery cell. During electrolysis, the diaphragm separates the positive and negative electrodes, preventing energy loss from the direct reaction. The performance of the diaphragm determines the battery's interface structure and internal resistance, directly impacting its capacity, cycle life, and safety. High-performance composite battery diaphragms are crucial for improving the battery's overall performance.

[0049] The mechanical properties of battery separators can largely determine the durability and safety of batteries during cycling. The mechanical strength of separators is characterized by testing the strength in both the MD and TD directions, where MD (machine direction) and TD (perpendicular to MD) are the two directions.

[0050] See also Figure 1 and Figure 2 The present application provides a high heat-resistant self-healing membrane, which includes coaxial electrospun nanofibers with a core-shell structure, and the nanofibers form a porous network structure. The nanofibers include a first nanofiber 100 and a second nanofiber 200. The first nanofiber 100 includes a first shell layer 110 and a first core layer 120, and the first shell layer 110 is coated on the outside of the first core layer 120; the second nanofiber 200 includes a second shell layer 210 and a second core layer 220, and the second shell layer 210 is coated on the outside of the second core layer 220. The first nanofiber 100 and the second nanofiber 200 are both prepared by a coaxial electrospinning method, and then the first nanofiber 100 and the second nanofiber 200 are alternately arranged to form a membrane.

[0051] Different from the existing diaphragms prepared by forming various functional coatings on the base membrane, the present application pioneered the use of nanofibers to directly prepare the diaphragm, which simplifies the diaphragm preparation process and can reduce the cost of the diaphragm; when the first nanofiber 100 and the second nanofiber 200 are arranged, multiple pores are naturally formed between them, and the pores can serve as ion channels, which are equivalent to the pores on the base membrane. The pores of the base membrane are formed by dry stretching or wet stretching, while those in the present application are formed during the preparation of the diaphragm. The pores are easy to shape and control, and the pores are more uniform, which is more conducive to regulating the ionic conductivity and air permeability of the diaphragm.

[0052] Because the separator is a porous network structure primarily formed by two coaxially electrospun nanofibers, it has advantages such as high porosity, unique pore structure, and large specific surface area. This can significantly improve the separator's electrolyte absorption and retention rate, allowing the battery to accommodate more electrolyte, allowing more ions to transfer and transmit freely, thereby improving the separator's ionic conductivity and ultimately steadily improving the battery's electrochemical performance. Due to the large aspect ratio of the coaxial electrospun nanofibers, the resulting separator has high integrity, heat resistance, and high mechanical strength. Because the separator is formed by a plurality of nanofibers, the "loose" molecular forces between the "microscopic" nanofibers give the separator a certain degree of "macroscopic" flexibility, allowing it to easily pass mechanical performance tests such as bending, twisting, and folding. This overcomes the safety issues caused by the separator's easy wrinkling during battery assembly, storage, and transportation. This makes the separator promising as a new generation of battery separators that can meet the new national standard for energy storage cells and improve battery safety and electrochemical performance.

[0053] In some embodiments, the first core layer 120 includes free radical polymerization monomers, and the second core layer 220 includes a crosslinking agent that can initiate crosslinking of the free radical polymerization monomers. When the battery is damaged, the first nanofibers 100 and the second nanofibers 200 can release free radical polymerization monomers and crosslinking agent. These free radical polymerization monomers and crosslinking agent flow toward the damaged interface of the battery separator, causing the free radical polymerization monomers to undergo a crosslinking reaction at the damaged interface. This allows the battery separator to self-repair, improve puncture resistance, prevent short circuits, and improve the cycle life and safety of the secondary battery.

[0054] In some embodiments, the free radical polymerization monomer can be at least one of dicyclopentadiene, isoprene, methyl methacrylate, polydiethoxysiloxane, hydroxylated polydimethylsiloxane, and N,N-methylenebisacrylamide. The crosslinking agent can be at least one of Grubbs' catalyst, di-n-butyltin dilaurate, a tungsten hexachloride-phenylacetylene mixture, and an azide.

[0055] It should be understood that the first shell layer 110 and the second shell layer 210 may be the same or different, and this application does not make any specific restrictions on this. Exemplary, for example, the first shell layer 110 and / or the second shell layer 210 are made of a high-temperature resistant polymer material, and the first shell layer 110 and the second shell layer 210 may be independently selected from at least one of polyimide, polyarylethersulfoneketone, polyetherimide, polyphenylsulfone, polyisophthalamide, etc. The selection of a high-temperature resistant polymer material can enhance the mechanical stability and heat resistance of the nanofiber, and give the diaphragm high heat resistance and high film breaking performance. At the same time, the high-temperature resistant polymer material has high heat resistance and flame retardancy, so that the nanofiber has good thermal stability and self-extinguishing properties, and the diaphragm has excellent thermal stability and non-flammability, which can improve the safety performance of the secondary battery.

[0056] In some embodiments, the diameters of the first nanofiber 100 and the second nanofiber 200 may be the same or different, which is not specifically limited herein. The diameters of the first nanofiber 100 and / or the second nanofiber 200 are both 0.2 μm to 2.0 μm. For example, the diameters of the first nanofiber 100 and / or the second nanofiber 200 may be 0.2 μm, 0.5 μm, 1.0 μm, 1.5 μm, or 2.0 μm.

[0057] In some embodiments, the mass ratio of the first nanofiber 100 to the second nanofiber 200 is 1:1, so that the free radical polymer can be fully cross-linked.

[0058] In some embodiments, in the first nanofiber 100, the mass ratio of the first core layer 120 to the first shell layer 110 is 1:0.4-1:2.0; in the second nanofiber 200, the mass ratio of the second core layer 220 to the second shell layer 210 is 1:0.4-1:2.0; the mass ratio of the core layer and the shell layer of the nanofiber is within the above range, which is conducive to the balance of heat resistance, high membrane rupture temperature, integrity, mechanical strength, and self-healing performance.

[0059] In some embodiments, the thickness d of the separator is in the range of 3 μm ≤ d ≤ 100 μm. For example, the thickness d of the separator is 3 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, or 100 μm. A separator thickness d within the above range is beneficial for improving the mechanical strength, heat resistance, and ionic conductivity of the separator, and is beneficial for improving the safety, cycle life, power, and energy density of the secondary battery.

[0060] In some embodiments, the porosity of the separator is 30%-60%. For example, the porosity of the separator can be 30%, 35%, 40%, 45%, 50%, 55%, or 60%. The porous mesh structure formed by the first nanofibers 100 and the second nanofibers 200 can well meet this condition. By adjusting the size and gaps between the first nanofibers 100 and the second nanofibers 200, the purpose of adjusting the separator porosity can be achieved.

[0061] It should be noted that porosity refers to the percentage of the pore volume in the diaphragm material to the total volume of the material in its natural state.

[0062] The present application provides a method for preparing a highly heat-resistant self-repairing diaphragm, comprising the following steps:

[0063] Dissolving the materials for preparing the first shell layer 110 and the second shell layer 210 in a solvent according to a preset ratio, and stirring and mixing them uniformly to obtain a shell spinning solution;

[0064] Dissolving the materials for preparing the first core layer 120 in a solvent according to a preset ratio, stirring and mixing to obtain a spinning solution for the first core layer 120;

[0065] Dissolve the materials for preparing the second core layer 220 in a solvent according to a preset ratio, and stir and mix them evenly to obtain a spinning solution for the second core layer 220;

[0066] The shell layer spinning solution, the first core layer 120 spinning solution, and the second core layer 220 spinning solution are used as electrospinning solutions, and a high heat-resistant self-repairing nanofiber membrane having a porous network structure including the first nanofiber 100 and the second nanofiber 200 is obtained on a receiver by a coaxial electrospinning method;

[0067] After the high heat-resistant self-repairing nanofiber membrane is vacuum-dried, it is hot-pressed under preset conditions to obtain a high heat-resistant self-repairing nanofiber membrane.

[0068] In some embodiments, the solvent is a highly volatile solvent, including dimethylacetamide. During the process of preparing the diaphragm, the solvent can evaporate, thereby preparing a diaphragm that is resistant to high temperatures and has good mechanical strength.

[0069] In some embodiments, in the shell layer spinning solution, the mass percentage of the material for preparing the first shell layer 110 and the second shell layer 210 is 5wt.%-30wt.%; in the first core layer 120 spinning solution, the mass percentage of the material for preparing the first core layer 120 is 5wt.%-30wt.%; in the second core layer 220 spinning solution, the mass percentage of the material for preparing the second core layer 220 is 5wt.%-30wt.%. The selection of the above mass ratio is conducive to forming a uniform spinning solution, thereby facilitating the improvement of the spinning rate and the uniformity of the nanofibers, and facilitating the improvement of the uniformity of the diaphragm performance. For example, the mass percentages in the shell layer spinning solution, the first core layer 120 spinning solution, and the second core layer 220 spinning solution can be 5wt.%, 10wt.%, 15wt.%, 20wt.%, 25wt.%, or 30wt.%.

[0070] It should be further explained that the coaxial electrospinning method is a special electrospinning technology that allows solutions of different properties to be injected into two coaxial capillaries respectively, thereby preparing nanofibers with specific structures. The basic principle of this technology is that under the action of an electric field, the solutions in two coaxial capillaries with different inner diameters (one is a core layer solution and the other is a shell layer solution) converge at the end of the nozzle and solidify into composite nanofibers. When preparing a film with a core-shell structure, two capillaries are used as transmitters and a rotating cylinder is set as a receiver. The nanofibers are fully and evenly laid (laid out) by rotating the rotating cylinder, and then hot-pressed and dried to prepare a diaphragm. Therefore, the distance between the receiver and the transmitter, the electric field voltage and the injection rate of the spinning solution can all affect the properties of the prepared nanofibers, and then affect the properties of the diaphragm.

[0071] In some embodiments, the coaxial electrospinning method includes using a transmitter and a receiver to form a diaphragm under the action of an electric field, and the voltage of the electric field is 10kV-20kV. For example, the voltage of the electric field can be 10kV, 12kV, 15kV, 17kV and 20kV.

[0072] In some embodiments, the distance between the transmitter and the receiver is 10 cm-20 cm. For example, the distance between the transmitter and the receiver can be 10 cm, 12 cm, 15 cm, 17 cm and 20 cm.

[0073] In some embodiments, the injection rate of the shell spinning solution is 0.5 mL / h-1.0 mL / h. For example, the injection rate of the shell spinning solution is 0.5 mL / h, 0.6 mL / h, 0.7 mL / h, 0.8 mL / h, 0.9 mL / h and 1.0 mL / h. The injection rate of the first core layer 120 spinning solution and / or the second core layer 220 spinning solution is 0.05 mL / h-1.0 mL / h. For example, the injection rate of the first core layer 120 spinning solution and / or the second core layer 220 spinning solution can be 0.05 mL / h, 0.1 mL / h, 0.5 mL / h, 0.6 mL / h, 0.7 mL / h, 0.8 mL / h, 0.9 mL / h and 1.0 mL / h. The injection rates of the first core layer 120 spinning solution and the second core layer 220 spinning solution can be the same or different. Preferably, the injection rates of the first core layer 120 spinning solution and the second core layer 220 spinning solution are the same. Controlling the injection rates of the core layer spinning solution and the shell layer spinning solution can effectively ensure the morphology and diameter of the prepared nanofibers, so that the fiber aspect ratio is appropriate and the morphology is smooth, which is conducive to filamentation and nanofiber bonding, can ensure production efficiency and enhance fiber strength, and effectively improve the mechanical properties of the diaphragm.

[0074] It should be understood that the injection rates of the first core layer 120 spinning solution, the second core layer 220 spinning solution and the shell layer spinning solution mentioned herein refer to the rates at which the syringe injects the liquid into the coaxial spinning needle.

[0075] In some embodiments, the preset conditions during hot pressing include hot pressing temperature and hot pressing pressure. The hot pressing temperature ranges from 40°C to 100°C. For example, the hot pressing temperature is 40°C, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C. The hot pressing pressure ranges from 5MPa to 20MPa. For example, the hot pressing pressure is 5MPa, 6MPa, 7MPa, 8MPa, 9MPa, 10MPa, 15MPa or 20MPa. Hot pressing can improve the mechanical strength of the diaphragm. Since the nanofibers produced by coaxial electrospinning are often fluffy and the bonding force between the fibers is weak, resulting in insufficient mechanical strength, after hot pressing treatment, the originally fluffy fibers can be in close contact to form bonding points, thereby effectively reducing the phenomenon of slippage between fibers under force, and can significantly improve the tensile strength and elongation at break of the diaphragm, effectively improving the mechanical properties of the diaphragm. At the same time, hot pressing can also remove solvents and moisture in the fibers, thereby enhancing the bonding between fibers, adjusting the porosity and structure of the diaphragm, and improving the flatness and density of the diaphragm.

[0076] In addition, the present application also provides a secondary battery, comprising the above-mentioned diaphragm or the diaphragm prepared by the above-mentioned preparation method.

[0077] In order to facilitate the description of the beneficial effects of the present application, the present application also provides the following several more specific embodiments.

[0078] Example 1

[0079] The present embodiment provides a highly heat-resistant self-healing diaphragm, comprising a first nanofiber 100 and a second nanofiber 200. The first nanofiber 100 and the second nanofiber 200 are both core-shell structures, each including a core layer and a shell layer coated on the outside of the core layer. The core layers of the first nanofiber 100 and the second nanofiber 200 are free radical polymerization monomers and cross-linking agents, respectively. After the first nanofiber 100 and the second nanofiber 200 are broken, the free radical polymerization monomers and the cross-linking agent can be released. After the free radical polymerization monomers and the cross-linking agent meet, a cross-linking reaction can occur and solidify to form a repair material to repair the damaged area.

[0080] Calculated by mass ratio, the mass ratio of the core layer:shell layer in the first nanofiber 100 and the second nanofiber 200 is 1:0.4; wherein, the core layer components of the first nanofiber 100 and the core layer components of the second nanofiber 200 are dicyclopentadiene monomer and a crosslinking agent, respectively; and the shell layers of the first nanofiber 100 and the second nanofiber 200 are polyimide.

[0081] The above-mentioned high heat-resistant self-repairing nanofiber membrane is prepared by a coaxial electrospinning method, which specifically includes the following steps:

[0082] (1) Add polyimide to DMA (dimethylacetamide) and stir magnetically until completely dissolved to obtain a shell spinning solution;

[0083] (2) adding dicyclopentadiene to DMA (dimethylacetamide) to prepare a first core layer 120 spinning solution, and adding tri(ethylene glycol) diazide formate to DMA (dimethylacetamide) to prepare a second core layer 220 spinning solution;

[0084] (3) A coaxial electrospinning device was used to prepare core-shell structured coaxial electrospinning nanofibers. The shell layer spinning solution was loaded into the outer layer solution needle. The first core layer 120 spinning solution and the second core layer 220 spinning solution were then loaded into the inner layer solution needle for electrospinning. The voltage across the coaxial electrospinning device was set to 13.5 kV, the injection speed of the inner layer solution needle was 0.04 mL / h, and the injection speed of the outer layer solution needle was 0.8 mL / h. The vertical distance between the needle outlet and the receiver was 14 cm. Finally, a high heat-resistant self-healing nanofiber membrane was obtained on the receiver. The self-healing fibers were continuous, with a relatively uniform diameter distribution, a small amount of beads, and no leakage of the core layer material. The obtained high heat-resistant self-healing membrane was peeled off from the receiver, vacuum-dried, and hot-pressed at 80°C and 8 MPa. The final high heat-resistant self-healing membrane had a thickness of 5 μm.

[0085] Examples 2 to 11, and Comparative Examples 1 to 7

[0086] Referring to the method provided in Example 1, Examples 2 to 10 were prepared, and the parameter settings of each example or comparative example are shown in Table 1 below.

[0087] Table 1

[0088]

[0089] The puncture resistance of the above embodiments and control examples was tested. The test method is as follows:

[0090] Before puncturing the battery separator, the initial permeability of the battery separator is measured. The sample battery separator and Teflon sheet are then placed on a puncture fixture, maintaining a flat, wrinkle-free surface. A needle with a 0.5mm cross-sectional area is used to press the separator with a force of 2N for 5 seconds. After the puncture, the permeability of the battery separator is measured again. If the permeability of the battery separator increases before and after puncture, it indicates that the sample has good self-healing properties.

[0091] Air permeability test: The air permeability value of the diaphragm is tested with reference to the air permeability test method described in GB / T 458-2008. During the test, three samples are taken and tested using an air permeability meter, and the average value of the measurements is taken as the air permeability value.

[0092] Heat shrinkage test: Heat shrinkage: The test method refers to GB / T 12027-2004. Take 3 samples greater than or equal to 100mm×100mm and measure the dimensions before heating. The samples are sandwiched between A4 papers and placed in the oven. After the set time is reached, take out and measure the dimensions after heating. The heat shrinkage is calculated according to the formula.

[0093] Film rupture temperature test: Cut samples into 80mm x 4mm dimensions and test them using a static thermomechanical analyzer under a nitrogen atmosphere, using a tensile force of 0.03N, a heating rate of 5°C / min, and an end temperature of 400°C. Select the measured TMA curve, with temperature as the abscissa and deformation as the ordinate. The film rupture temperature is the temperature on the abscissa where the directional deformation on the ordinate is maximum.

[0094] The specific test results are shown in Table 2.

[0095] Table 2

[0096]

[0097] It can be seen from the above table that the high heat-resistant self-repairing membrane provided in the above embodiment has an initial permeability value related to the core-shell ratio, the electrospinning voltage, the distance from the transmitter to the receiver, and the hot pressing pressure. When the core layer ratio is high, the membrane's permeability, mechanical strength, and heat resistance deteriorate; when the spinning voltage is too low, due to insufficient electric field strength, it is difficult to overcome the surface tension of the spinning solution itself, resulting in insufficient stretching and splitting of the spinning solution in the electric field. Therefore, the prepared nanofibers have a larger diameter, and may have uneven fiber diameters, rough surfaces, and even the formation of beaded fibers. When the spinning voltage is too high, the electric field strength is too large, which increases the jet flow of the spinning solution and accelerates the injection speed, which may cause the jet to be excessively stretched in the electric field, causing the fiber diameter to increase and the uniformity to deteriorate. Due to the increase in fiber diameter and the decrease in uniformity, the mechanical properties of the formed membrane are reduced. When the distance between the receiver and the transmitter is too short, the flight time of the spinning jet in the electric field is reduced, and the solvent is not fully evaporated. This may cause the fibers to still contain a large amount of solvent when they are deposited, forming beaded fibers or structurally collapsed, sticky fiber bundles. Excessively long distances may also cause the jet to experience more air resistance and disturbances during flight, making the distribution of fibers on the receiving device uneven, and even causing fiber breakage or inability to collect fibers. Uneven fiber distribution will result in poor air permeability, porosity, and mechanical properties of the resulting spinning membrane. Excessively low hot pressing pressure is not conducive to forming a dense and flat diaphragm. Too low pressure can cause excessive fiber adhesion and pore clogging, and can also cause coaxial nanofiber rupture and reduce the diaphragm porosity.

[0098] The above specific examples are used to illustrate the present application, which is only used to help understand the present application and is not intended to limit the present application. For those skilled in the art of the present application, based on the concept of the present application, they can also make some simple deductions, modifications or substitutions.

Claims

1. A high heat-resistant self-repairing diaphragm, characterized in that: The diaphragm comprises coaxial electrospun nanofibers with a core-shell structure; the nanofibers form a porous network structure; the nanofibers comprise a first nanofiber and a second nanofiber, the first nanofiber comprising a first shell layer and a first core layer, the first shell layer being coated on the outside of the first core layer; the second nanofiber comprising a second shell layer and a second core layer, the second shell layer being coated on the outside of the second core layer; The first core layer includes free radical polymerization monomers; the second core layer includes a cross-linking agent, and the cross-linking agent can induce cross-linking of the free radical polymerization monomers; The first shell layer and / or the second shell layer comprises a high-temperature resistant polymer material, and the high-temperature resistant polymer material comprises at least one of polyimide, polyarylethersulfoneketone, polyetherimide, polyphenylsulfone, poly(m-phenylene isophthalamide), and the like.

2. The high heat-resistant self-repairing membrane according to claim 1, characterized in that: The free radical polymerization monomer includes at least one of dicyclopentadiene, isoprene, methyl methacrylate, polydiethoxysiloxane, terminal hydroxylated polydimethylsiloxane and N,N-methylenebisacrylamide.

3. The high heat-resistant self-repairing membrane according to claim 1, characterized in that: The cross-linking agent includes at least one of Grubbs catalyst, di-n-butyltin dilaurate, tungsten hexachloride phenylacetylene mixture and azide.

4. The high heat-resistant self-repairing membrane according to claim 1, characterized in that: The diaphragm satisfies at least one of the conditions (1) to (6): (1) The diameter of the first nanofiber and / or the second nanofiber is 0.2 μm to 2.0 μm; (2) The mass ratio of the first nanofiber to the second nanofiber is 1:1; (3) In the first nanofiber, the mass ratio of the first core layer to the first shell layer is 1:0.4-1:2.0; (4) In the second nanofiber, the mass ratio of the second core layer to the second shell layer is 1:0.4-1:2.0; (5) The thickness d of the diaphragm is in the range of 3 μm ≤ d ≤ 100 μm; (6) The porosity of the diaphragm is 30%-60%.

5. A method for preparing a high heat-resistant self-repairing diaphragm, for preparing the diaphragm according to any one of claims 1 to 4, characterized in that: The following steps are involved: Dissolving the materials for preparing the first shell layer and the second shell layer in a solvent according to a preset ratio, stirring and mixing them uniformly to obtain a shell spinning solution; Dissolving the materials for preparing the first core layer in a solvent according to a preset ratio, and stirring and mixing to obtain a first core layer spinning solution; Dissolving the material for preparing the second core layer in a solvent according to a preset ratio, stirring and mixing to obtain a second core layer spinning solution; The shell layer spinning solution, the first core layer spinning solution and the second core layer spinning solution are used as electrospinning solutions, and a high heat-resistant self-repairing nanofiber membrane with a porous network structure including first nanofibers and second nanofibers is obtained on a receiver by a coaxial electrospinning method; After the high heat-resistant self-repairing nanofiber membrane is vacuum-dried, hot pressing is performed under preset conditions to obtain the high heat-resistant self-repairing nanofiber membrane.

6. The method for preparing a high heat-resistant self-repairing membrane according to claim 5, characterized in that: The diaphragm satisfies at least one of the conditions (1) to (3): (1) The first core layer includes a free radical polymerizable monomer; The free radical polymerization monomer includes at least one of dicyclopentadiene, isoprene, methyl methacrylate, polydiethoxysiloxane, terminal hydroxylated polydimethylsiloxane and N,N-methylenebisacrylamide; (2) the second core layer includes a crosslinking agent, wherein the crosslinking agent is capable of initiating crosslinking of the free radical polymerization monomer; The cross-linking agent includes at least one of Grubbs catalyst, di-n-butyltin dilaurate, tungsten hexachloride phenylacetylene mixture and azide; (3) Both the first shell layer and the second shell layer are made of a high-temperature resistant polymer material; The high temperature resistant polymer material includes at least one of polyimide, polyarylethersulfoneketone, polyetherimide, polyphenylsulfone, polyisophthalamide and the like.

7. The method for preparing a high heat-resistant self-repairing membrane according to claim 5 or 6, characterized in that: The diaphragm satisfies at least one of the conditions (1) to (8): (1) In the shell layer spinning solution, the mass percentage of the material for preparing the first shell layer and the second shell layer is 5wt.%-30wt.%; (2) In the first core layer spinning solution, the mass percentage of the material for preparing the first core layer is 5wt.%-30wt.%; (3) In the second core layer spinning solution, the mass percentage of the material for preparing the second core layer is 5wt.%-30wt.%; (4) The coaxial electrospinning method includes producing the diaphragm by using a transmitter and a receiver in combination under the action of an electric field, wherein the voltage of the electric field is 10 kV-20 kV, the distance between the transmitter and the receiver is 10 cm-20 cm, the injection rate of the shell layer spinning solution is 0.5 mL / h-1.0 mL / h, and the injection rate of the first core layer spinning solution and / or the second core layer spinning solution is 0.05 mL / h-1.0 mL / h; (5) The thickness d of the diaphragm is in the range of 3 μm ≤ d ≤ 100 μm; (6) The mass ratio of the first nanofiber to the second nanofiber is 1:1; (7) The diameters of the first nanofiber and the second nanofiber are both 0.2 μm to 2.0 μm; (8) The preset conditions during hot pressing include hot pressing temperature and hot pressing pressure. The hot pressing temperature ranges from 40°C to 100°C, and the hot pressing pressure ranges from 5MPa to 20MPa.

8. A secondary battery, characterized in that: The invention comprises the diaphragm according to any one of claims 1 to 4 or the diaphragm prepared by the preparation method according to any one of claims 5 to 7.

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