MOFs-doped lithium-sulfur battery diaphragm as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of battery diaphragms, and particularly relates to an MOFs (Metal-Organic Frameworks) doped lithium-sulfur battery diaphragm as well as a preparation method and application thereof. The MOFs-doped lithium-sulfur battery diaphragm provided by the invention comprises a Ketjen black conductive layer, a middle substrate layer and a ZIF-8 functional layer, the middle substrate layer and the ZIF-8 functional layer are fused at an interface to form a transition layer; the Ketjen black conductive layer is provided with dot matrix hole channels which are vertically arranged; and the middle substrate layer comprises a PAN nanofiber membrane. According to the invention, by adopting a picosecond laser surface processing technology, an electrostatic spinning flame-retardant diaphragm material with high ion passing rate, high area attachment sites and high stability is integrally constructed on the surface of the diaphragm, and the double problems of the existing diaphragm in structure and preparation process are solved. The diaphragm has excellent flame retardance and structural stability at the same time, the specific capacity, safety and cycle life of the battery are synergistically improved from the aspects of material design and preparation process, and the commercialization process of the high-performance diaphragm is powerfully promoted.

Description

A MOF-doped lithium-sulfur battery separator, its preparation method and application Technical Field

[0001] This invention belongs to the field of battery separator technology, and more specifically relates to a MOFs-doped lithium-sulfur battery separator, its preparation method, and its application. Background Technology

[0002] In the current popularization of new energy vehicles, battery efficiency and driving range remain core pain points restricting user experience. Issues with battery efficiency and driving range persist, while the rate of increase in the energy density of lithium-ion batteries has slowed significantly and is gradually approaching its theoretical limit. Among various electrochemical energy storage systems, lithium-sulfur batteries have unique advantages in high-energy-density battery design. Their positive electrode active material is based on a multi-electron reaction mechanism, achieving a theoretical energy density as high as 2600 Wh / kg. -1 This is about an order of magnitude higher than commercial lithium-ion batteries. However, the practical application of lithium-sulfur metal batteries (LSBs) is affected by problems such as uncontrolled lithium dendrite growth and the polysulfide "shuttle effect" during cycling, resulting in the actual energy density of lithium-sulfur batteries being lower than 2600 Wh / kg. -1 The theoretical energy density is still far from being achieved, making large-scale application and commercialization impossible.

[0003] Currently, the most popular processes for preparing PP (polypropylene) separators for lithium-sulfur batteries are dry and wet processes, with post-processing often used to optimize the performance of the finished product. The dry process primarily involves unidirectional or bidirectional stretching. High-purity PP particles are first melted to form a base film. Controlled cooling creates a crystalline and amorphous region separation structure. After stretching, the amorphous region forms micropores, which are then reheated for shaping. The bidirectional stretching process adds a β-crystal nucleating agent to improve pore uniformity. This process is environmentally friendly and low-cost. The wet process mostly involves bidirectional stretching. Plasticizers are mixed into the PP melt for molding. Extraction removes the plasticizers, forming uniform honeycomb micropores, followed by drying and shaping, suitable for high-end battery requirements. To effectively address the "shuttle effect" of polysulfides in lithium-sulfur batteries, it is necessary to selectively design composite layers on both sides of the separator. However, PP separators prepared by traditional processes have low porosity, which cannot accurately match the ion transport requirements of high-load electrodes. They only serve to physically isolate the positive and negative electrodes, without ion screening, catalytic conversion, or other functions. Furthermore, they have poor thermal stability and are prone to thermal shrinkage or even melting and cracking at high temperatures, leading to direct contact between the positive and negative electrodes and posing risks of short circuits and thermal runaway, which makes it difficult to meet the safety requirements of power batteries.

[0004] Some researchers have used electrospinning to design lithium-sulfur battery separators to improve the electrochemical performance of lithium-sulfur batteries. As a functional separator with an asymmetric structure, the two sides of the separator have distinctly different performance orientations, respectively adapting to the needs of the positive and negative electrodes. One side faces the positive electrode, possessing strong affinity and high conductivity, effectively restricting the migration of the positive electrode active material and its intermediates while promoting the rapid progress of related electrochemical reactions. The other side faces the negative electrode, focusing on selective ion transport and interface regulation, guiding uniform ion distribution, suppressing undesirable growth phenomena on the negative electrode surface, and achieving simultaneous optimization of the performance of both positive and negative electrodes. However, when using vacuum filtration deposition or coating methods to prepare separators, the target material on the surface becomes too dense after drying, has poor adhesion, and is easily detached, contaminating the electrolyte. This leads to slow polysulfide conversion kinetics and low battery specific capacity. Therefore, using only a simple separator cannot improve the overall capacity of the battery. Therefore, developing a separator with regular selectable pores, ultra-high adhesion area, excellent flame retardant properties, and stable cycle performance is of great significance and is a necessary condition for the commercialization of lithium-sulfur batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a MOF-doped lithium-sulfur battery separator, its preparation method, and its application, in order to solve the problems existing in the prior art.

[0006] To achieve the above objectives, the present invention provides the following solution: One of the technical solutions of the present invention is to provide a MOFs-doped lithium-sulfur battery separator, comprising: a Ketjen black (KB) conductive layer, an intermediate substrate layer, and a ZIF-8 functional layer; the intermediate substrate layer and the ZIF-8 functional layer are fused at the interface to form a transition layer; the Ketjen black (KB) conductive layer has vertically arranged lattice channels; the intermediate substrate layer comprises a PAN nanofiber membrane with a thickness of 100-150 μm.

[0007] The second technical solution of the present invention provides a method for preparing the above-mentioned MOFs-doped lithium-sulfur battery separator, comprising the following steps: mixing Ketjen Black (KB) and sodium carboxymethyl cellulose (CMC) with water to prepare slurry A; mixing ZIF-8 and sodium carboxymethyl cellulose (CMC) with water to prepare slurry B; coating the positive electrode side of the intermediate substrate with slurry A and the negative electrode side with slurry B, drying each side after coating in a vacuum oven, and then coating the other side to obtain a composite separator; and performing picosecond laser etching on the positive electrode side of the composite separator to obtain the MOFs-doped lithium-sulfur battery separator.

[0008] Furthermore, the mass ratio of Ketjen Black (KB), sodium carboxymethyl cellulose (CMC), and water in the slurry A is 1:1:20.

[0009] Furthermore, the mass ratio of ZIF-8, sodium carboxymethyl cellulose (CMC), and water in the slurry B is 9:1:50.

[0010] Furthermore, the coating thickness of the slurry A applied to the positive electrode side is 250µm.

[0011] Furthermore, the coating thickness of the slurry B applied to the negative electrode side is 250µm.

[0012] Furthermore, the drying temperature in the vacuum oven is 55°C, and the drying time is 8 hours.

[0013] Furthermore, the parameters of the picosecond laser etching process include: a processing spacing of 50µm, a laser scanning speed of 1000-2000mm / s, a power of 35-45W, a frequency of 20-40kHz, and the completion of a single dot matrix within 0.2-0.5ms.

[0014] The power of picosecond laser processing must be above 35W, otherwise the depth of the through-hole will not be sufficient; the maximum power should not exceed 45W, otherwise the material will be burned through by the laser.

[0015] Furthermore, the preparation steps of the PAN nanofiber membrane include: mixing polyacrylonitrile (PAN, molecular weight 15000) with N,N-dimethylformamide (DMF, 99.5%) to prepare a spinning solution with a polyacrylonitrile mass fraction of 12.5%, followed by electrospinning to obtain the PAN nanofiber membrane; the electrospinning parameters are: spinning voltage 15kV, roller speed 200rpm, reciprocating platform moving speed 500mm / min, liquid discharge rate 0.85mL / h, temperature 35-40℃, and humidity 35-40%RH.

[0016] The third technical solution of the present invention provides an application of the above-mentioned MOFs-doped lithium-sulfur battery separator in lithium-sulfur batteries.

[0017] The fourth technical solution of the present invention provides a lithium-sulfur battery, wherein the separator of the lithium-sulfur battery is the above-mentioned MOFs-doped lithium-sulfur battery separator.

[0018] This invention discloses the following technical effects: By employing picosecond laser surface processing technology, this invention integrates an electrospun flame-retardant separator material with high ion throughput, large area of ​​attachment sites, and high stability onto the separator surface. This comprehensively solves the dual challenges faced by existing separators in terms of structure and manufacturing process. On the one hand, it addresses the inherent defects of the material itself, such as low effective porosity, limited attachment sites for active materials, slow polysulfide conversion kinetics, high ion transport resistance, and low utilization rate of active materials due to multi-layer stacking and complex, tortuous pore structures. On the other hand, it overcomes the problems caused by traditional double-sided modification processes, such as easy damage to the modified surface, poor performance uniformity, porosity or cracks at the bonding interface, reduced mechanical strength and service stability, as well as poor adhesion of the target coating, easy detachment and electrolyte contamination, leading to battery capacity decay, poor cycle performance, and increased short-circuit risk. The separator prepared by this invention simultaneously possesses excellent flame retardancy and structural stability, synergistically improving the specific capacity, safety, and cycle life of the battery from the perspectives of material design and manufacturing process, thus powerfully promoting the commercialization of high-performance separators. Attached Figure Description

[0019] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 is a schematic flowchart of the preparation of MOF-doped lithium-sulfur battery separators and their use in lithium-sulfur batteries according to the present invention.

[0020] Figure 2 shows the morphology of the ZIF-8 surface of KB / PAN / ZIF-8 in Example 1, where (a) is a SEM image and (b)-(f) are EDS element surface distribution analysis diagrams of the dashed box area in (a).

[0021] Figure 3 shows the morphology of the ZIF-8 surface of Laser-KB / PAN@ZIF-8 in Example 1, where (a) is a SEM image and (b)-(f) are EDS element surface distribution analysis diagrams of the dashed box area in (a).

[0022] Figure 4 shows cross-sectional SEM images of KB / PAN / ZIF-8 and Laser-KB / PAN@ZIF-8 in Example 1, where (a) is a cross-sectional SEM image of KB / PAN / ZIF-8, (b) is a magnified SEM image of the intermediate basal layer of KB / PAN / ZIF-8, (c) is a cross-sectional SEM image of Laser-KB / PAN@ZIF-8, and (d) is a magnified SEM image of the intermediate basal layer of Laser-KB / PAN@ZIF-8.

[0023] Figure 5 shows the cross-sectional SEM image and elemental distribution map of KB / PAN / ZIF-8 in Example 1, where (a) is the SEM image and (b)-(d) are the elemental distribution maps.

[0024] Figure 6 shows the cross-sectional SEM image and elemental distribution map of Laser-KB / PAN@ZIF-8 in Example 1, where (a) is the SEM image and (b)-(d) are the elemental distribution maps.

[0025] Figure 7 is an SEM image of the PAN nanofiber membrane obtained in step S2 of Example 1, where (a) is an SEM image and (b) is a magnified view of a part.

[0026] Figure 8 shows the Laser-KB / PAN@ZIF-8 image obtained after selecting an appropriate area on the composite membrane for picosecond laser etching in step S6 of Example 1. In this image, (a) is a physical image, (b) and (c) are SEM images of the area not etched by picosecond laser, and (d) and (e) are SEM images of the area etched by picosecond laser.

[0027] Figure 9 shows the flame retardancy test results of commercial PP diaphragm and Laser-KB / PAN@ZIF-8 diaphragm. In the figure, ac represents the combustion test process, and d and e are comparison figures before and after the combustion test.

[0028] Figure 10 shows a visual penetration test of Laser-KB / PAN@ZIF-8 in Example 1.

[0029] Figure 11 shows a comparison of the first charge-discharge cycles of coin cells assembled with different separators. (a) shows the comparison of the first charge-discharge cycles of coin cells assembled with PAN, PP, and Laser-KB / PAN@ZIF-8 separators; (b) shows the comparison of the first charge-discharge cycles of coin cells assembled with Laser-KB / PAN@ZIF-8 and KB / PAN / ZIF-8 separators; (c) shows the comparison of the first charge-discharge cycles of coin cells assembled with PP, Laser-KB / PAN@ZIF-8, and Laser-KB / PP@ZIF-8 separators; and (d) shows the comparison of the first charge-discharge cycles of coin cells assembled with Laser-KB / PAN@ZIF-8 separators prepared under 35W, 40W, and 45W conditions.

[0030] Figure 12 shows a comparison of the 10th charge-discharge cycle of coin cells assembled with different separators. Among them, (a) is a comparison of the 10th charge-discharge cycle of coin cells assembled with PAN, PP and Laser-KB / PAN@ZIF-8 separators, (b) is a comparison of the 10th charge-discharge cycle of coin cells assembled with Laser-KB / PAN@ZIF-8 and KB / PAN / ZIF-8 separators, (c) is a comparison of the 10th charge-discharge cycle of coin cells assembled with PP, Laser-KB / PAN@ZIF-8 and Laser-KB / PP@ZIF-8 separators, and (d) is a comparison of the 10th charge-discharge cycle of coin cells assembled with Laser-KB / PAN@ZIF-8 separators prepared under 35W, 40W and 45W conditions.

[0031] Figure 13 shows the shape of the composite membranes in Comparative Example 1 (50W and 80W), Example 3 (45W) and Example 1 (40W) after being subjected to lasers of different powers.

[0032] Figure 14 shows images of slurry A and slurry B after coating and drying in Comparative Example 2. (a) is the diaphragm after coating with slurry A, (b) is the diaphragm after drying with slurry A, (c) is the diaphragm after coating with slurry B, and (d) is the diaphragm after drying with slurry B. Detailed Implementation

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0036] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0037] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0038] Unless otherwise specified, all raw materials and reagents involved in the specific embodiments of this invention are commercially available products.

[0039] In the specific embodiments of this invention, sodium carboxymethyl cellulose (CMC, 99% purity) was purchased from Kelude Company; N,N-dimethylformamide (DMF, 99.5%) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; polyacrylonitrile (PAN, molecular weight 15000) was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.; zeolite imidazole ester skeleton-8 (ZIF-8, particle size 100-200nm) was purchased from Guangdong Carbon Language New Materials Co., Ltd.; and Ketjen Black (KB, particle size 34nm) was produced by Lion Corporation of Japan.

[0040] Unless otherwise specified, room temperature and normal temperature in the specific embodiments of this invention refer to 20-30℃.

[0041] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0042] This invention involves coating both sides of a PAN separator substrate prepared by electrospinning with ZIF-8 and KB slurry respectively to form a composite separator (KB / PAN / ZIF-8). Then, the KB surface of the composite separator is processed using an ultrashort pulse picosecond laser to obtain a composite separator with vertical surface pores (Laser-KB / PAN@ZIF-8).

[0043] Picosecond lasers, characterized by ultrashort pulse widths and tunable frequencies, are laser beams with extremely high pulse energy density. Their short beam duration (10^6 seconds) is a significant advantage. -12With the characteristics of low thermal impact on the KB surface, low average energy, and short action time (on the order of s), a low-torsional pore structure is constructed on the surface of the high-torsional composite diaphragm, giving the positive electrode side of the composite diaphragm a porous and low-torsional functional characteristic. Combined with the ZIF-8 metal frame on the negative electrode side of the diaphragm, the "secondary sulfur collection" effect is achieved. When ZIF-8 is mixed with DMF (N,N-dimethylformamide), a suspension is formed. The spinning process typically takes more than 10 hours. During the spinning process, the suspension is prone to precipitation, making it impossible to effectively and uniformly spin ZIF-8 into the PAN separator. Therefore, this invention uses an environmentally friendly aqueous coating method to prepare ZIF-8 slurry, which is then uniformly coated on the negative electrode side of the separator. The energy of a picosecond laser is then transferred to the negative electrode side of the separator to generate thermal vibration energy. This causes a thermal physical change in the ZIF-8 on the back side of the irradiated area, resulting in a certain degree of fusion with the PAN separator substrate. This creates a certain cross-linking structure (transition layer) inside the composite separator, which can further improve the barrier against polysulfides, suppress the "shuttle effect," and improve the utilization rate of active materials.

[0044] The MOFs-doped lithium-sulfur battery separator provided in the specific embodiments of the present invention uses PAN material as the separator substrate. PAN-based spinning separators have the advantages of readily available raw materials and simple preparation process. In particular, they have strong structural controllability, can accurately control fiber diameter and porous network, have good high-temperature shape stability, and can prepare continuous, high-performance functional fibers through composite and calcination. Moreover, the spinning solution is not easy to gel, has higher spinnability than PVA, and has stronger adaptability.

[0045] PVA, a highly hydrophilic polymer, is soluble in water. The numerous hydroxyl groups on its molecular chains readily form hydrogen bonds with water, causing it to swell and even dissolve in water. This characteristic makes PVA difficult to use directly in aqueous coating systems, as the coating is prone to structural changes in a humid environment, significantly reducing its barrier properties. In contrast, PAN is soluble in organic solvents such as DMF, classifying it as an oil-based material. Furthermore, oil-based coating systems are more widely used in current industrial applications, with PAN being one of the representative materials in this field.

[0046] In conventional oil-based coating processes for diaphragms, N-methylpyrrolidone (NMP) is commonly used as a solvent or binder carrier. It's important to note that NMP may exhibit corrosiveness or compatibility issues with certain polymer materials. Therefore, although PVA itself possesses advantages such as good film-forming properties and low toxicity, its water sensitivity limits its direct application in current mainstream oil-based coating systems. Considering both solubility and process compatibility, PVA is indeed not an ideal choice for oil-based coating modification of diaphragms and should not be used as a comparative object under such conditions.

[0047] ZIF-8 material possesses a precisely controlled microporous structure (such as the ion sieving effect of specific pore sizes) and a high specific surface area. Through a combination of physical trapping and chemical adsorption, it effectively captures polysulfide intermediates in the electrolyte, preventing their diffusion to the lithium metal anode. This fundamentally suppresses the "shuttle effect," reducing irreversible loss of positive electrode active material and significantly improving battery cycle stability and capacity retention. The composite structure of ZIF-8 and PAN optimizes the interfacial contact between the separator and the positive and negative electrodes, reducing interfacial impedance. The high conductivity and dispersion characteristics of ZIF-8 material also help improve the electron transport efficiency of sulfur in the positive electrode, promoting the redox reaction kinetics of polysulfides, increasing sulfur utilization, and thus improving the battery's energy density and charge / discharge efficiency. From a thermal perspective, ZIF-8 exhibits high thermal stability, with a melting point exceeding 400 °C; while PAN has no obvious melting point, possessing only a low glass transition temperature (T) of 90 °C. When the temperature reaches this glass transition temperature, the surface physical properties of the electrospun PAN film undergo significant changes, exhibiting a certain degree of flexibility and fluidity. Under the in-situ texturing effect of picosecond laser, PAN fibers undergo a phase transition process of "glassy fiber → molten high-viscosity liquid → rapid cooling to restore glassy state", achieving efficient composite with ZIF-8 particles.

[0048] In the MOF-doped lithium-sulfur battery separator provided in the specific embodiments of this invention, the ZIF-8 material can intercept polysulfides in the electrolyte and suppress a certain shuttle effect. This invention innovatively employs picosecond laser surface processing technology for etching. Notably, the picosecond laser precision processing system is characterized by "cold processing," resulting in a minimal heat-affected zone during processing. This effectively prevents structural damage to high-melting-point ZIF-8 particles due to high temperatures. Simultaneously, it can precisely control the melting range and phase transition degree of PAN fibers, providing an ideal processing method for the precise construction of the PAN@ZIF-8 dual polymer network layer (transition layer). This fully matches the differences in the thermal properties of the two materials, ensuring the structural integrity and functional stability of the composite network layer.

[0049] The method for preparing MOF-doped lithium-sulfur battery separators provided by this invention differs significantly from conventional laser modification processes. Common methods rely on the thermal effect of lasers to melt or modify the surface of metal composite materials. However, the picosecond laser used in this invention has low power, making it difficult to directly melt the material surface, and therefore unsuitable for metal composite systems that rely on thermal effects. However, for the KB / PAN / ZIF-8 inorganic amorphous composite system, this invention, by precisely controlling the processing parameters of the picosecond laser, can controllably construct a uniquely oriented array of channels on the separator surface. This structure not only effectively suppresses the dissolution and shuttle of lithium polysulfides but also enhances the interfacial stability of the cathode material, thereby improving the overall electrochemical performance of the battery.

[0050] Example 1: Preparation steps of MOF-doped lithium-sulfur battery separator: S1, 2.5g of PAN and 17.5g of DMF were stirred on a magnetic stirrer for 8 hours, then allowed to stand for 30 minutes to prepare a spinning solution with a PAN mass fraction of 12.5%; S2, the spinning solution obtained in step S1 was drawn into a 5mL sterile syringe and spun with a No. 22 needle. After spinning, the voltage was turned off, the roller was kept rotating, and the temperature inside the chamber was raised to 40℃. After drying for 2 hours, the spun separator was removed, bagged, and dried in a 55℃ oven for 8 hours to obtain a PAN nanofiber membrane with a thickness of 120μm. The electrospinning parameters were: spinning voltage 15kV, roller speed 200rpm, reciprocating platform moving speed 500mm / min, liquid discharge rate 0.85mL / h, temperature between 35-40℃, and humidity between 35-40%RH; S3, 0.5g of KB and 0.5g of DMF were stirred on a magnetic stirrer for 8 hours, then allowed to stand for 30 minutes to prepare a spinning solution with a PAN mass fraction of 12.5%; S4, 0.5g of PAN and 0.5g of DMF were stirred on a magnetic stirrer for 8 hours, then allowed to stand for 30 minutes to prepare a spinning solution with a PAN mass fraction of 12.5%; S5, the spinning solution obtained in step S1 was drawn into a 5mL sterile syringe and 0.5g of DMF. Mix CMC, add 10g of water, and mix thoroughly using a vacuum mixer to obtain slurry A; S4, mix 1.8g of ZIF-8 and 0.2g of... CMC is mixed with 10g of water and mixed evenly using a vacuum mixer to obtain slurry B; S5, slurry A from step S3 is coated on one side of the PAN nanofiber membrane obtained in step S2, with a coating thickness of 250µm, and slurry B from step S4 is coated on the other side. After each side is coated, it is placed in a vacuum oven at 55℃ and dried for 8h. Then the other side is coated, with a coating thickness of 250µm, to obtain a composite separator, denoted as KB / PAN / ZIF-8; S6, an appropriate area is selected on the composite separator obtained in step S5 and etched using a picosecond laser. The surface dot matrix is ​​processed using a picosecond laser to obtain a MOFs-doped lithium-sulfur battery separator, denoted as Laser-KB / PAN@ZIF-8; the parameters for processing the surface dot matrix using a picosecond laser are: processing spacing of 50µm, laser scanning speed of 1000mm / s, power of 40W, frequency of 20kHz, and the construction of a single dot matrix is ​​completed within 0.2ms.

[0051] The only difference between Example 2 and Example 1 is that the power in step S6 is 35W.

[0052] The only difference between Example 3 and Example 1 is that the power in step S6 is 45W.

[0053] The only difference between Comparative Example 1 and Example 1 is that the power in step S6 is 50W or 80W.

[0054] Figure 13 shows the shapes of the composite membranes in Comparative Example 1 (50W and 80W), Example 3 (45W), and Example 1 (40W) after being treated with lasers of different powers. The figure shows that, after laser processing with various powers, the laser gradually burns through the membrane when the power reaches 45W or higher.

[0055] Compared with Example 1, Comparative Example 2 differs only in that the preparation step of slurry A in step S3 is adjusted to: mix 0.6g KB and 0.4g CMC, add 10g water, and mix evenly using a vacuum mixer to obtain slurry A; or, the preparation step of slurry B in step S4 is adjusted to: mix 1.9g ZIF-8 and 0.1g CMC, add 10g water, and mix evenly using a vacuum mixer to obtain slurry B.

[0056] Figure 14 shows images of slurry A and slurry B after coating and drying in Comparative Example 2. (a) shows the diaphragm after coating with slurry A, (b) shows the diaphragm after drying with slurry A, (c) shows the diaphragm after coating with slurry B, and (d) shows the diaphragm after drying with slurry B. As can be seen from the figures, when using either slurry A or slurry B from Comparative Example 2 for coating, the surface coating cracks after drying.

[0057] Compared with Example 1, Comparative Example 3 differs only in that the preparation step of slurry A in step S3 is adjusted to: mix 0.4g KB and 0.6g CMC, add 10g water, and mix evenly using a vacuum mixer to obtain slurry A; or, the preparation step of slurry B in step S4 is adjusted to: mix 1.6g ZIF-8 and 0.4g CMC, add 10g water, and mix evenly using a vacuum mixer to obtain slurry B.

[0058] The slurry obtained in this comparative example is too dry to be coated. In addition, if water is added to adjust the concentration, surface cracking will also occur after coating and drying.

[0059] Comparative Example 4 differs from Example 1 only in that the PAN nanofiber membrane is replaced with a PP membrane, and the resulting product is denoted as Laser-KB / PP@ZIF-8.

[0060] Figure 1 is a schematic diagram of the process for preparing MOFs-doped lithium-sulfur battery separators and their application in lithium-sulfur batteries according to the present invention.

[0061] Figure 2 shows the morphology of the ZIF-8 surface of KB / PAN / ZIF-8 in Example 1, where (a) is a SEM image and (b)-(f) are EDS element surface distribution analysis diagrams of the dashed box area in (a).

[0062] Figure 3 shows the morphology of the ZIF-8 surface of Laser-KB / PAN@ZIF-8 in Example 1, where (a) is a SEM image and (b)-(f) are EDS element surface distribution analysis diagrams of the dashed box area in (a).

[0063] As shown in Figures 2 and 3, Figure 2(b) shows the morphology of the ZIF-8 slurry surface before laser treatment, while Figure 3(b) shows the morphology of the ZIF-8 slurry surface after 40W laser treatment. It is clear that before laser treatment, the ZIF-8 particle surface was relatively smooth. After 40W laser treatment, molten polyacrylonitrile (PAN) formed in the interparticle gaps, effectively coating and bridging most of the ZIF-8 particles. The molten PAN fibers further constructed a PAN@ZIF-8 dual polymer network layer from the surface ZIF-8 particles. This in-situ laser-processed dual polymer interface provides sufficient structural margin to suppress the polysulfide shuttle effect and mitigate the volume expansion of the sulfur cathode, significantly optimizing electrode interface stability, enhancing the adhesion between the coating and the base film, preventing detachment during cycling, and ensuring the durability of the permeation barrier.

[0064] Figure 4 shows cross-sectional SEM images of KB / PAN / ZIF-8 and Laser-KB / PAN@ZIF-8 in Example 1. (a) is a cross-sectional SEM image of KB / PAN / ZIF-8, (b) is a magnified SEM image of the intermediate substrate layer of KB / PAN / ZIF-8, (c) is a cross-sectional SEM image of Laser-KB / PAN@ZIF-8, and (d) is a magnified SEM image of the intermediate substrate layer of Laser-KB / PAN@ZIF-8. As can be seen from the figures, no ZIF-8 particles appear in the PAN nanofiber membrane of KB / PAN / ZIF-8. In Laser-KB / PAN@ZIF-8, the PAN nanofiber membrane partially transforms into a molten state, and the molten PAN encapsulates a large number of ZIF-8 particles, forming a dense composite layer.

[0065] Figure 5 shows the cross-sectional SEM image and elemental distribution diagram of KB / PAN / ZIF-8 in Example 1, where (a) is the SEM image and (b)-(d) are the elemental distribution diagrams. It can be seen from the figures that Zn element is not present in the PAN nanofiber membrane and the Ketjen Black conductive layer.

[0066] Figure 6 shows the cross-sectional SEM image and elemental distribution diagram of Laser-KB / PAN@ZIF-8 in Example 1, where (a) is the SEM image and (b)-(d) are the elemental distribution diagrams. As can be seen from the figure, Zn element exhibits a large distribution in both the PAN nanofiber membrane and the Ketjen Black conductive layer.

[0067] Figure 7 shows the SEM image of the PAN nanofiber membrane obtained in step S2 of Example 1, where (a) is the SEM image and (b) is a magnified view. As can be seen from the figure, the PAN spun membrane forms nanoscale pores, providing channels for ion transport and improving electrochemical activity.

[0068] Figure 8 shows images of Laser-KB / PAN@ZIF-8 obtained after picosecond laser etching of an appropriate area on the composite diaphragm in step S6 of Example 1. (a) is a physical image, (b) and (c) are SEM images of the area without picosecond laser etching, and (d) and (e) are SEM images of the area etched by picosecond laser etching. As can be seen from the figure, after laser construction, a lattice channel structure of a certain depth is formed on the surface. The rough surface and gradient channels generated by laser etching optimize electrolyte wetting and Li... + The transport path is improved, the interfacial impedance is reduced, and the surface adsorption area and the absorption rate of polysulfides are increased.

[0069] Diaphragm performance test: 1. Flame retardant test: The commercial PP diaphragm and the Laser-KB / PAN@ZIF-8 diaphragm of Example 1 were sandwiched on a glass rod, with the distance between them being approximately the distance between the heads of a double-headed alcohol lamp. The alcohol lamp was lit, and the entire process was simultaneously filmed using an infrared camera and a regular camera, as shown in Figure 9.

[0070] Figure 9 shows the flame retardancy test results of the commercial PP diaphragm and the Laser-KB / PAN@ZIF-8 diaphragm. Figure ac shows the combustion test process, and figures d and e show comparisons before and after the combustion test. As can be observed in the figures, the commercial PP diaphragm (supplied by Celgard) burned completely, while the Laser-KB / PAN@ZIF-8 diaphragm only curled slightly and did not exhibit flame combustion.

[0071] 2. Visual Permeation Test: In the H-type glass cell test, the left glass bottle contained Li2S6 and DME:DOL=1:1 Vol% solvent (a mixed solvent composed of 1,2-dimethoxyethane and 1,3-dioxolane in a volume ratio of 1:1), with the concentration of Li2S6 being 0.005 mol / L. The right glass bottle contained only DME:DOL=1:1 Vol% solvent, and the test time was 24 hours.

[0072] Figure 10 shows a visualization of the permeation experiment of Laser-KB / PAN@ZIF-8 in Example 1. As can be seen from the figure, in the H-type glass cell test, after 24 hours, lithium polysulfides are basically not permeated through the Laser-KB / PAN@ZIF-8 membrane, and the Laser-KB / PAN@ZIF-8 membrane has a significant absorption effect on the colored lithium polysulfide material on the left.

[0073] 3. Electrochemical performance testing: Battery assembly: Lithium foil was used as the negative electrode, and sulfur-carbon material with a sulfur content of 68% and a carbon content of 32% was used as the positive electrode, employing a 1 mol / L... -1A 1,3-dioxolane (DOL)-ethylene glycol dimethyl ether (DME)-based lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte, denoted as LiTFSI / DOL-DME (DOL to DME volume ratio 1:1), was prepared, with 0.1 mol / L added. -1 The LiNO3 was used to assemble the prepared separator into a coin cell.

[0074] The membranes were the Laser-KB / PAN@ZIF-8 membrane, PP membrane (Celgard), and PAN nanofiber membrane (prepared in step S2 of Example 1, PAN membrane) prepared in Example 1.

[0075] Test conditions: The test was conducted using the Blue Battery Test System in a dry, well-ventilated, and light-protected environment at room temperature of 25±2℃. The battery was first activated at 0.05 C for 3 cycles, and then at 0.2 C for the conventional long-cycle test. The charge and discharge capacity and coulombic efficiency were recorded for each cycle.

[0076] Figure 11 shows a comparison of the first charge-discharge cycles of coin cells assembled with different separators. (a) shows the comparison of the first charge-discharge cycles of coin cells assembled with PAN, PP, and Laser-KB / PAN@ZIF-8 separators; (b) shows the comparison of the first charge-discharge cycles of coin cells assembled with Laser-KB / PAN@ZIF-8 and KB / PAN / ZIF-8 separators; (c) shows the comparison of the first charge-discharge cycles of coin cells assembled with PP, Laser-KB / PAN@ZIF-8, and Laser-KB / PP@ZIF-8 separators; and (d) shows the comparison of the first charge-discharge cycles of coin cells assembled with Laser-KB / PAN@ZIF-8 separators prepared under 35W, 40W, and 45W conditions.

[0077] Figure 12 shows a comparison of the 10th charge-discharge cycle of coin cells assembled with different separators. Among them, (a) is a comparison of the 10th charge-discharge cycle of coin cells assembled with PAN, PP and Laser-KB / PAN@ZIF-8 separators, (b) is a comparison of the 10th charge-discharge cycle of coin cells assembled with Laser-KB / PAN@ZIF-8 and KB / PAN / ZIF-8 separators, (c) is a comparison of the 10th charge-discharge cycle of coin cells assembled with PP, Laser-KB / PAN@ZIF-8 and Laser-KB / PP@ZIF-8 separators, and (d) is a comparison of the 10th charge-discharge cycle of coin cells assembled with Laser-KB / PAN@ZIF-8 separators prepared under 35W, 40W and 45W conditions.

[0078] Figures 11-12 show the following discharge capacities at 0.2C rate in Figures 11 and 12(a): Laser-KB / PAN@ZIF-8 separator: 1405.3 μAh, PP separator: 364.8 μAh, PAN separator: 1017.8 μAh; discharge capacities at 10th cycle: Laser-KB / PAN@ZIF-8 separator: 1215.1 μAh, PP separator: 361.4 μAh, PAN separator: 974.6 μAh; first charge capacity: Laser-KB / PAN@ZIF-8 separator: The membrane capacity is 1388.5 μAh, the PP membrane capacity is 358.4 μAh, and the PAN membrane capacity is 995.8 μAh; the 10th charge cycle capacity is: Laser-KB / PAN@ZIF-8 membrane capacity is 1272.8 μAh, PP membrane capacity is 364.4 μAh, and PAN membrane capacity is 978.4 μAh; as can be seen from the above data, at a 0.2C rate, whether in the first or 10th charge-discharge cycle, the battery capacity using the Laser-KB / PAN@ZIF-8 membrane is far greater than that of the battery assembled using the PP or PAN membrane.

[0079] In Figures 11 and 12(b), the first discharge capacity of the KB / PAN@ZIF-8 separator at a 0.2C rate is 898.1 μAh, and the first charge capacity is 870.1 μAh; the discharge capacity of the 10th cycle is 770.5 μAh, and the charge capacity of the 10th cycle is 765.4 μAh.

[0080] In Figures 11 and 12(c), the first discharge capacity of the Laser-KB / PP@ZIF-8 separator at 0.2C rate is 516.9 μAh, and the first charge capacity is 593 μAh; the discharge capacity of the 10th cycle is 456.9 μAh, and the charge capacity of the 10th cycle is 430.3 μAh.

[0081] In Figures 11 and 12(d), at a 0.2C rate, the first-cycle discharge capacity of the 35W Laser-KB / PAN@ZIF-8 separator is 749.4 μAh, and the first-cycle charge capacity is 726 μAh; the discharge capacity on the 10th cycle is 612.6 μAh, and the charge capacity on the 10th cycle is 609.4 μAh. At a 0.2C rate, the first-cycle discharge capacity of the 45W Laser-KB / PAN@ZIF-8 separator is 714.9 μAh, and the first-cycle charge capacity is 704.1 μAh; the discharge capacity on the 10th cycle is 588.7 μAh, and the charge capacity on the 10th cycle is 610.7 μAh.

[0082] Battery charge-discharge cycle tests show that KB and ZIF-8 synergistically catalyze LiPSs conversion, reducing the formation of "dead sulfur," maintaining the reversibility of active materials, and preventing rapid capacity decay. Furthermore, the three-dimensional conductive network constructed by KB shortens the electron transport path, while ZIF-8's Zn... 2+The site reduces the redox activation energy of LiPSs, promotes the rapid conversion of S8→Li2S4→Li2S, reduces polarization, improves the first-cycle utilization rate, and results in a more stable discharge platform and a capacity closer to the theoretical value.

[0083] In summary, this invention designs a MOFs-doped lithium-sulfur battery separator based on electrospinning and laser fabrication processes. It has good flame retardant and heat resistance properties, the ability to prevent the "shuttle effect", and the assembled lithium-sulfur battery has high capacity and low decay rate, making it suitable for commercialization.

[0084] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0085] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A MOF-doped lithium-sulfur battery separator, characterized in that, include: The structure comprises a Ketjen black conductive layer, an intermediate substrate layer, and a ZIF-8 functional layer; the intermediate substrate layer and the ZIF-8 functional layer are fused at the interface to form a transition layer. The Ketjen black conductive layer has vertically arranged lattice channels; the intermediate substrate layer includes a PAN nanofiber membrane with a thickness of 100-150 μm.

2. A method for preparing a MOFs-doped lithium-sulfur battery separator according to claim 1, characterized in that the step... include: Slurry A was prepared by mixing Ketjen Black and sodium carboxymethyl cellulose with water; slurry B was prepared by mixing ZIF-8 and sodium carboxymethyl cellulose with water; slurry A was coated on the positive electrode side of the intermediate substrate and slurry B was coated on the negative electrode side. After each side was coated, it was dried in a vacuum oven before coating the other side to obtain a composite separator; the positive electrode side of the composite separator was subjected to picosecond laser etching to obtain a MOFs-doped lithium-sulfur battery separator.

3. The preparation method according to claim 2, characterized in that, The mass ratio of Ketjen Black, sodium carboxymethyl cellulose, and water in slurry A is 1:1:20; and / or, the mass ratio of ZIF-8, sodium carboxymethyl cellulose, and water in slurry B is 9:1:

50.

4. The preparation method according to claim 2, characterized in that, The coating thickness of the slurry A applied to the positive electrode side is 250µm.

5. The preparation method according to claim 2, characterized in that, The coating thickness of the slurry B applied to the negative electrode side is 250µm.

6. The preparation method according to claim 2, characterized in that, The drying temperature in the vacuum oven is 55°C, and the drying time is 8 hours.

7. The preparation method according to claim 2, characterized in that, The parameters of the picosecond laser etching process include: a processing spacing of 50µm, a laser scanning speed of 1000-2000mm / s, a power of 35-45W, a frequency of 20-40kHz, and the completion of a single dot matrix within 0.2-0.5ms.

8. The preparation method according to claim 2, characterized in that, The preparation steps of the PAN nanofiber membrane include: mixing polyacrylonitrile with N,N-dimethylformamide to prepare a spinning solution with a polyacrylonitrile mass fraction of 12.5%, followed by electrospinning to obtain the PAN nanofiber membrane; the electrospinning parameters are: spinning voltage 15kV, roller speed 200rpm, reciprocating platform moving speed 500mm / min, liquid discharge rate 0.85mL / h, temperature 35-40℃, and humidity 35-40%RH.

9. The application of the MOFs-doped lithium-sulfur battery separator as described in claim 1 in a lithium-sulfur battery.

10. A lithium-sulfur battery, characterized in that, The separator of the lithium-sulfur battery is the MOFs-doped lithium-sulfur battery separator as described in claim 1.

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