Lithium ion battery diaphragm as well as preparation method and application thereof

Abstract

The invention provides a lithium ion battery diaphragm as well as a preparation method and application thereof, and relates to the technical field of lithium ion batteries. Specifically, the lithium ion battery diaphragm comprises a polyimide nanofiber substrate layer, a dynamic cross-linked polyurethane self-repairing layer and a ceramic coating which are connected in sequence, and the lithium ion battery diaphragm also comprises poly (N-isopropylacrylamide) microspheres embedded into the layers. The technical problems that a traditional lithium battery diaphragm is prone to failure at a high temperature, the lithium dendrite penetration risk is high, and the electrolyte wettability is poor can be solved at the same time, through collaborative innovation of materials, structures and functions, comprehensive improvement of safety and electrochemical performance of a lithium ion battery is achieved through the diaphragm layer, and the lithium ion battery diaphragm has good application prospects.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery separator and a preparation method and application thereof. Background Art

[0002] The rapid development of high-energy-density lithium-ion battery systems places stringent demands on the performance of core materials. However, separator technology faces multiple technical barriers and industrialization difficulties, urgently requiring systematic breakthroughs. First, separators suffer from significant thermal stability deficiencies. Mainstream polyolefin separators (PE / PP) generally have low melting points, making them susceptible to melting and shrinking in the event of battery overcharge, short circuit, or high temperatures, leading to direct contact between the positive and negative electrodes and thermal runaway. While ceramic coatings (such as Al2O3 and SiO2) can improve temperature resistance (above 200°C), the coating process increases separator thickness (typically >25μm), which conflicts with the demand for thinner and lighter batteries (target <10μm). Furthermore, the ceramic particles lack interfacial adhesion to the base film, making them susceptible to detachment after long-term cycling, exacerbating internal resistance.

[0003] Furthermore, current separators face the mechanical-transport balance challenge of lithium dendrite isolation. Conventional separators have limited mechanical strength (puncture strength <300gf), making it difficult to prevent the vertical growth of lithium dendrites in high-energy-density batteries. Existing modification schemes, such as multilayer composite structures (PP / PE / PP), improve mechanical strength, but the linear fiber arrangement causes dendrites to spread laterally along the pores, increasing the risk of short circuits. Another example is the introduction of inorganic coatings to enhance hardness, but this sacrifices ionic conductivity (<0.5mS / cm) due to pore blockage, worsening the battery's rate performance.

[0004] In summary, existing technologies have significant shortcomings in multi-objective collaborative optimization, and there is an urgent need to develop a new membrane system with high safety and efficient ion transport through material innovation and structural design.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The first purpose of the present invention is to provide a lithium-ion battery separator; the present invention mainly addresses the three core problems of traditional lithium battery separators, namely, easy failure at high temperatures, high risk of lithium dendrite penetration, and poor electrolyte wettability. Through the collaborative innovation of materials, structures and functions, the present invention achieves a comprehensive improvement in safety and performance.

[0007] The second object of the present invention is to provide a method for preparing the lithium-ion battery separator.

[0008] A third object of the present invention is to provide a lithium ion battery.

[0009] A fourth object of the present invention is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A lithium-ion battery separator comprising layers connected in the following order: a polyimide nanofiber base layer, a dynamically cross-linked polyurethane self-healing layer, and a ceramic coating; The lithium-ion battery separator further includes poly(N-isopropylacrylamide) microspheres embedded in the layers.

[0011] Preferably, in the polyimide nanofiber base layer, the molecular weight of polyimide is 10,000-50,000, the fiber diameter is 180 nm-240 nm, and the fibers form a three-dimensional cross-linked network structure.

[0012] Preferably, the dynamic cross-linked polyurethane self-repairing layer comprises a polyurethane prepolymer containing a dynamic disulfide bond, and the polyurethane prepolymer is obtained by polymerization of polytetrahydrofuran, isophorone diisocyanate, and a chain extender containing a dynamic disulfide bond; More preferably, the chain extender comprises at least one of dithiodipropionic acid, a dithiol chain extender or a thioether chain extender; More preferably, the molar ratio of the polytetrahydrofuran, the isophorone diisocyanate, and the chain extender is (1.5-2.5): (2.5-3.5):1.

[0013] Preferably, the ceramic coating comprises nano-alumina, graphene and a binder, and the mass ratio of the three is (7-9): (0.5-1.5): (0.5-1.5); More preferably, the particle size of the nano-aluminum oxide is 40 nm to 80 nm, and the graphene is a double-layer graphene formed by combining two single-layer graphene layers in a stacked manner.

[0014] Preferably, the particle size of the poly(N-isopropylacrylamide) microspheres is 150 nm to 250 nm; Preferably, the mass ratio of the poly(N-isopropylacrylamide) microspheres to the dynamic cross-linked polyurethane self-healing layer is 4% to 8%.

[0015] A method for preparing a lithium-ion battery separator comprises the following steps: S1, preparing a polyimide nanofiber substrate layer by electrospinning; S2. preparing a solution containing a polyurethane prepolymer, and immersing the polyimide nanofiber base layer in the solution to obtain a dynamically cross-linked polyurethane self-healing layer; S3, preparing a ceramic slurry, and then spraying it onto the surface of the dynamically cross-linked polyurethane self-repairing layer, and heat-treating it to obtain a ceramic coating; S4. Prepare a dispersion containing poly (N-isopropylacrylamide) microspheres, spray it onto the surface of the ceramic coating, and perform hot pressing to obtain the lithium-ion battery separator.

[0016] Preferably, in the electrospinning method: the voltage is 20 kV to 30 kV, the receiving distance is 10 cm to 20 cm, the injection rate is 0.8 mL / h to 1.5 mL / h, the humidity is 20% to 40%, and the temperature is 20° C. to 30° C.

[0017] Preferably, the impregnation treatment includes: immersing the polyimide nanofiber base layer in the solution for 3 minutes to 10 minutes, then pulling the film layer at a speed of 5 mm / s to 20 mm / s, and then thermally curing to obtain the dynamic cross-linked polyurethane self-healing layer.

[0018] Preferably, the preparation of the ceramic slurry comprises: mixing nano-alumina, graphene, a binder and a solvent and ball-milling the mixture; the rotation speed of the ball mill is 250 rpm to 350 rpm, and the ball milling time is 10 h to 15 h.

[0019] Preferably, for the spraying in step S4, the spray gun pressure is 0.1 MPa to 0.3 MPa, the number of spraying is 2 to 3 times, and the interval between each spraying is 8 s to 15 s.

[0020] A lithium-ion battery comprises the lithium-ion battery separator.

[0021] An electrical device comprises the lithium-ion battery.

[0022] Compared with the prior art, the present invention has the following beneficial effects: (1) Traditional polyolefin separators, such as PE or PP, will rapidly melt and shrink at temperatures exceeding 130°C, leading to internal short circuits in the battery and even fire and explosion, which is a major safety hazard for electric vehicles and energy storage systems. The present invention uses polyimide nanofibers as the base material. This material is high-temperature resistant and can withstand temperatures above 500°C. Even if the battery is abnormally heated, the separator will not melt or deform, fundamentally blocking the risk of high-temperature short circuits.

[0023] (2) The present invention also incorporates intelligent temperature-sensitive protection, namely, temperature-sensitive microspheres embedded in the diaphragm. When the temperature exceeds 130°C, the microspheres rapidly expand and block the pores, actively cutting off the lithium ion transmission path, effectively preventing the spread of thermal runaway. This improves the safety of lithium-ion batteries at extreme high temperatures by more than 80%, passing the 150°C hot box test, while traditional diaphragms typically fail at 130°C. Therefore, the composite layered diaphragm of the present invention is suitable for high-energy-density batteries such as high-nickel ternary batteries, and can remain stable even under fast charging or overcharging conditions, significantly reducing the risk of fire in electric vehicles.

[0024] (3) During the cycling process of lithium batteries, needle-shaped lithium dendrites grow on the negative electrode surface, piercing the separator and causing a short circuit. This is the core reason for the short battery life and rapid capacity decay. The present invention adds a dynamic cross-linked polyurethane layer in the middle of the separator, in which the dynamic chemical disulfide bonds can automatically reorganize at 60°C; when lithium dendrites pierce the separator, the damaged area can "self-heal" by simply heating. Furthermore, through the structural design of the PU layer, the surface layer adopts dense small pores (0.05μm) to prevent dendrite penetration, and the interior is designed with large pores (0.2μm) to ensure the efficient passage of lithium ions. This achieves an extension of the cycle life of the lithium-ion battery by more than 50%, and the capacity retention rate still exceeds 85% after 1000 charge and discharge cycles.

[0025] (4) To address the defects of the traditional diaphragm surface being incompatible with the electrolyte, resulting in uneven electrolyte distribution, high battery internal resistance, and poor fast charging performance, the present invention coats the diaphragm surface with a composite ceramic coating of nano-alumina and graphene. This coating strongly adsorbs the electrolyte, and the contact angle is reduced from 50° of the traditional diaphragm to nearly 0°, ensuring uniform distribution of the electrolyte; thereby reducing the battery internal resistance by 30%, supporting fast charging of more than 4C, and significantly reducing heat generation. At the same time, the amount of electrolyte used is reduced by 15%, further reducing battery costs. DETAILED DESCRIPTION

[0026] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments, but those skilled in the art will understand that the embodiments described below are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially. In addition, the terms "first", "second" and "third" are only used for descriptive purposes and are not to be understood as indicating or implying relative importance.

[0027] The first aspect of the present invention is to provide a lithium-ion battery separator, which mainly includes layers connected in the following order: a polyimide nanofiber base layer, a dynamically cross-linked polyurethane self-healing layer and a ceramic coating; in addition, it also includes poly(N-isopropylacrylamide) microspheres embedded in the layers.

[0028] Among them, the poly (N-isopropylacrylamide) microspheres are temperature-sensitive microspheres; combined with the preparation process provided by the present invention, the poly (N-isopropylacrylamide) microspheres are mainly embedded in the surface pores of the dynamically cross-linked polyurethane self-healing layer, but it is not ruled out that a small portion of them are embedded in the polyimide nanofiber base layer and the ceramic coating.

[0029] It can be understood that the lithium-ion battery separator of the present invention can be a structure of "polyimide nanofiber base layer-dynamic cross-linked polyurethane self-repairing layer-ceramic coating" or a structure of "ceramic coating-dynamic cross-linked polyurethane self-repairing layer-polyimide nanofiber base layer-dynamic cross-linked polyurethane self-repairing layer-ceramic coating", and the poly (N-isopropylacrylamide) microspheres are contained in any of the dynamic cross-linked polyurethane self-repairing layers.

[0030] As a preferred embodiment, the polyimide nanofiber base layer can be an existing polyimide membrane obtained through commercial channels, and the polyimide satisfies the nanoscale fibrous arrangement; at the same time, the polyimide nanofiber base layer can also be prepared by electrospinning a polyimide solution.

[0031] As can be seen from the naming of the "polyimide nanofiber base layer" in the present invention, the base layer is mainly composed of nano-scale fibrous polyimide; high-temperature resistant polyimide (PI) is an aromatic polymer containing rigid benzene rings and imide rings in the molecular chain, and has extremely high chemical bond energy (CN bond energy of about 305kJ / mol, CC bond energy of about 347kJ / mol), which makes its thermal decomposition temperature >500°C, much higher than the traditional PE with a melting point of about 130°C.

[0032] As a preferred embodiment, in the polyimide nanofiber base layer, the molecular weight of the polyimide is 10,000-50,000 (g / mol), more preferably 30,000 g / mol.

[0033] As a preferred embodiment, the fiber diameter of the polyimide nanofiber base layer is 180 nm to 240 nm, and the fibers form a three-dimensional cross-linked network structure.

[0034] The above-mentioned structural features ensure that the base layer will not melt at high temperatures and will only experience slight thermal expansion. In some more preferred embodiments, the thermal expansion coefficient of the polyimide nanofiber base layer is <20ppm / °C, and the thermal shrinkage rate at 150°C is <1%. In comparison, the thermal shrinkage rate of conventional PE diaphragms at 150°C is >15%, which is far inferior to the heat resistance performance of the polyimide nanofiber base layer of the present invention.

[0035] As a preferred embodiment, the dynamic cross-linked polyurethane self-healing layer includes a polyurethane (PU) prepolymer containing dynamic disulfide bonds, and the polyurethane prepolymer is obtained by polymerization of polytetramethylene glycol (PTMG), isophorone diisocyanate (IPDI), and a chain extender containing dynamic disulfide bonds.

[0036] In the present invention, by adopting the polyurethane prepolymer containing dynamic disulfide bonds, lithium dendrite penetration can be effectively inhibited, mainly due to the reversible breakage and recombination of dynamic disulfide bonds (SS) at 60°C; when lithium dendrites pierce the diaphragm, local heating (such as internal hot spots of the battery or external triggering) activates the recombination of the disulfide bonds and repairs the pore damage.

[0037] Furthermore, the elastic modulus of the polyurethane prepolymer of the present invention is about 50 MPa, which is higher than the hardness of lithium dendrites (~10 MPa), and its cross-linked network can absorb dendrite penetration energy and inhibit crack propagation.

[0038] As a preferred embodiment, the dynamically cross-linked polyurethane self-healing layer has a gradient pore structure; the pore size on its surface is 0.05μm±0.02μm, approximately 1 / 10 the diameter of lithium dendrites, inhibiting dendrite penetration through physical blocking; the pore size inside is 0.2μm±0.08μm, with a porosity of 60%-70%, forming a low-tortuosity ion channel (tortuosity <1.5), which can ensure uniform lithium ion deposition and reduce local dendrite nucleation. This gradient pore size, on the one hand, physically blocks dendrites, and on the other hand, chemically self-heals the damage. The combination of the two reduces the risk of dendrite penetration by over 90%.

[0039] As a preferred embodiment, the ceramic coating includes nano-alumina, graphene and a binder, and the binder includes but is not limited to polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC) and the like.

[0040] As a more preferred embodiment, the mass ratio of the nano-alumina, the graphene and the binder is (7-9): (0.5-1.5): (0.5-1.5), and more preferably 8:1:1.

[0041] As a more preferred embodiment, the particle size of the nano-aluminum oxide is 40 nm to 80 nm, and the graphene is a double-layer graphene formed by combining two single-layer graphene layers in a stacked manner.

[0042] In the present invention, the outermost ceramic coating can effectively enhance the electrolyte wettability of the diaphragm. The surface of the nano-alumina is rich in hydroxyl groups (-OH), which form hydrogen bonds with polar solvents (such as EC, DEC, etc.) in the electrolyte, making the contact angle less than 10°. In comparison, the contact angle of conventional PE film is usually greater than 50°. In addition, the π-π conjugated structure of the graphene can adsorb lithium ions in the electrolyte, forming a local high-concentration ion region and reducing the interfacial impedance.

[0043] As a more preferred embodiment, the in-plane thermal conductivity of the graphene is ≥5300 W / m·K. After compounding with alumina (30 W / m·K), the overall thermal conductivity of the ceramic coating is >5 W / m·K, which can accelerate heat diffusion and avoid local boiling of the electrolyte.

[0044] The poly(N-isopropylacrylamide) (PNIPAM) microspheres introduced in the present invention have temperature-responsive properties, with a lower critical solution temperature of 32°C. When the operating temperature of the diaphragm exceeds 130°C, the hydrogen bonds within the PNIPAM microspheres break, the hydrophobic effect is enhanced, and the volume expansion rate is >300%. The present invention embeds the PNIPAM microspheres into the PU layer, which expands at high temperature to block the diaphragm pores (reducing the pore size of the PU layer from 0.2μm to <0.01μm), thereby blocking the lithium ion transmission path. This blocking process only takes 5 seconds. In comparison, traditional PE diaphragms require more than 30 seconds to melt and close the pores. Therefore, the present invention can quickly cut off the thermal runaway reaction chain.

[0045] The present invention provides passive high-temperature resistant support through the PI substrate, while the temperature-sensitive PNIPAM microspheres realize active closed-cell protection. The dual mechanism ensures the safety performance of the diaphragm in the full temperature range from 130°C to 500°C.

[0046] As a preferred embodiment, the particle size of the poly(N-isopropylacrylamide) microspheres is 150 nm to 250 nm, more preferably 200 nm.

[0047] As a preferred embodiment, the mass ratio of the poly(N-isopropylacrylamide) microspheres to the dynamic cross-linked polyurethane self-healing layer is 4% to 8%, more preferably 5%.

[0048] The second aspect of the present invention is to provide a method for preparing a lithium-ion battery separator as described in the first aspect, which mainly includes the following steps: S1, preparing a polyimide nanofiber base layer by an electrospinning method; S2, preparing a solution containing a polyurethane prepolymer, and immersing the polyimide nanofiber base layer in the solution to obtain a dynamic cross-linked polyurethane self-healing layer; S3, preparing a ceramic slurry, and then spraying it onto the surface of the dynamic cross-linked polyurethane self-healing layer, heat treating it to obtain a ceramic coating; S4, preparing a dispersion containing poly (N-isopropylacrylamide) microspheres, and then spraying it onto the surface of the ceramic coating, performing hot pressing treatment, and obtaining the lithium-ion battery separator of the present invention.

[0049] As a preferred embodiment, the spinning solution of the electrospinning method includes polyimide and a solvent, and the mass ratio of the polyimide is 8% to 15%, more preferably 10% to 12%.

[0050] As a more preferred embodiment, the solvent includes N,N-dimethylacetamide (DMAC) and acetone, and the volume ratio of the two is (6-8): (2-4), and more preferably 7:3.

[0051] As a preferred embodiment, the spinning solution of the electrospinning method is obtained by fully mixing the raw material components, and can be assisted by oscillation, stirring, shaking, centrifugation, ultrasound, heating, etc., which helps to accelerate dispersion and obtain a relatively uniform dispersion system; as an optional embodiment, the sufficient mixing is carried out by stirring, the stirring speed is 300rpm~800rpm, the stirring time is 12h~48h, and the stirring is carried out at room temperature.

[0052] As a preferred embodiment, for the electrospinning method: the voltage is 20kV~30kV, more preferably 25kV; the receiving distance is 10cm~20cm, more preferably 15cm; the injection rate is 0.8mL / h~1.5mL / h, more preferably 1.2mL / h; the humidity range is 20%~40%, more preferably <30%; the temperature range is 20℃~30℃, more preferably 25℃.

[0053] As a preferred embodiment, the polyurethane prepolymer is prepared by the following steps: mixing polytetrahydrofuran and isophorone diisocyanate under a protective atmosphere at 50°C to 70°C for 2.5 hours to 4 hours to obtain an isocyanate-terminated precursor; adding a chain extender containing a dynamic disulfide bond, maintaining the reaction conditions and continuing the reaction for 2 hours to 5 hours to obtain the polyurethane prepolymer.

[0054] As a more preferred embodiment, the protective atmosphere includes but is not limited to at least one of nitrogen, helium, neon, argon, etc.

[0055] As a more preferred embodiment, the chain extender includes at least one of dithiodipropionic acid, a bisthiol chain extender, or a thioether chain extender, wherein the bisthiol chain extender includes but is not limited to 1,2-ethanedithiol, bis(2-mercaptoethyl) sulfide, and 4,4'-dimercaptodiphenyl sulfide, and the thioether chain extender includes but is not limited to bis(2-hydroxyethyl) sulfide and 1,4-phenylenedisulfide derivatives. In a further preferred embodiment, the use of the thioether chain extender results in a repair efficiency of >90% for the dynamically cross-linked polyurethane self-healing layer.

[0056] As a more preferred embodiment, the molar ratio of the polytetrahydrofuran, the isophorone diisocyanate, and the chain extender is (1.5-2.5):(2.5-3.5):1, and more preferably 2:3:1.

[0057] As a more preferred embodiment, the molecular weight of the polytetrahydrofuran is 1600~2500.

[0058] As a preferred embodiment, for the solution containing the polyurethane prepolymer, the solvent includes N,N-dimethylformamide (DMF), and the concentration of the polyurethane prepolymer is 8 wt.% to 12 wt.%, more preferably 10 wt.%.

[0059] As a preferred embodiment, the impregnation treatment includes: immersing the polyimide nanofiber base layer in the solution for 3 minutes to 10 minutes, then pulling the film layer at a speed of 5 mm / s to 20 mm / s, and then thermally curing to obtain the dynamic cross-linked polyurethane self-healing layer.

[0060] As a more preferred embodiment, the heat curing time is 70° C. to 90° C., and the heat curing time is 40 min to 120 min.

[0061] As a preferred embodiment, the ceramic slurry includes nano-alumina, graphene, a binder and a solvent, and the solid content of the ceramic slurry is 15% to 25%, and the solvent is more preferably NMP.

[0062] As a preferred embodiment, the ceramic slurry is prepared by ball-milling nano-alumina, graphene, a binder, and a solvent; wherein the ball milling speed is 250-350 rpm and the ball milling time is 10-15 hours. More preferably, the ball milling speed is 300 rpm and the ball milling time is 12 hours. In some more preferred embodiments, the ball milling is performed using zirconia grinding balls with a ball-to-material ratio of (4-8):1. Ball milling not only helps to uniformly mix the reaction raw materials, but also refines the raw material particle size. These ball milling parameters effectively balance dispersion efficiency and the risk of particle breakage.

[0063] As a preferred embodiment, the heat treatment includes: pre-baking at 70°C to 90°C for 20 minutes to 50 minutes, and then vacuum drying at 110°C to 140°C for 3 hours to 5 hours.

[0064] As a preferred embodiment, the preparation of the dispersion includes: mixing the poly(N-isopropylacrylamide) microspheres with ethanol, and performing ultrasonic treatment to ensure that there is no agglomeration.

[0065] As a more preferred embodiment, for the dispersion, the concentration of the poly(N-isopropylacrylamide) microspheres is 3 wt.% to 7 wt.%, more preferably 5 wt.%.

[0066] As a more preferred embodiment, the power of the ultrasonic treatment is 150W~250W, and the time of the ultrasonic treatment is 20min~40min, more preferably 200W, 30min.

[0067] As a preferred embodiment, for the spraying in step S4, the spray gun pressure is 0.1 MPa~0.3 MPa to avoid microsphere agglomeration or excessive atomization; at the same time, the number of sprays is 2~3 times, and the interval between each spraying is 8s~15s to avoid droplet accumulation and achieve uniform loading of the microspheres.

[0068] A third object of the present invention is to provide a lithium-ion battery comprising the lithium-ion battery separator. It is understood that, in addition to the lithium-ion battery separator, the lithium-ion battery should include positive and negative electrodes, an electrolyte, and other necessary or non-essential functional elements or packaging components, etc., which can be arbitrarily selected and combined by those skilled in the art. When the lithium-ion battery comprises the lithium-ion battery separator of the present invention, whether or not other separator functional components are also used in the lithium-ion battery, it can be regarded as an embodiment of the present invention.

[0069] A fourth object of the present invention is to provide an electrical device comprising the lithium-ion battery. The electrical device may be any device or apparatus that relies on electrical energy for operation or function, including but not limited to new energy vehicles, building electrical equipment, industrial appliances, and household and agricultural appliances. When the lithium-ion battery is included, any electrical device equipped with the lithium-ion battery may be an embodiment of the present invention.

[0070] Example 1 (1) 70 mL of N,N-dimethylacetamide and 30 mL of acetone were mixed as solvent, 12 g of polyimide powder (molecular weight 30,000) was added, and magnetic stirring was carried out at 500 rpm for 24 h until it was completely dissolved to form a 12 wt.% spinning solution.

[0071] Using an electrospinning machine, a 5μm thick PI nanofiber membrane was obtained by electrospinning under the conditions of voltage 25kV, receiving distance 15cm, injection rate 1.2mL / h, and humidity <30%. After vacuum drying at 80℃ for 6 hours and heat treatment at 250℃ for 2 hours, a high-temperature resistant substrate (heat shrinkage rate <1%) was obtained.

[0072] (2) Take 200g of polytetrahydrofuran (molecular weight of 2000), 33.34g of isophorone diisocyanate, and 7.715g of dithiodipropionic acid (the molar ratio of the three is 2:3:1), and react them at 60℃ under nitrogen protection for 6 hours to synthesize PU prepolymer.

[0073] The prepolymer was dissolved in DMF to prepare a 10 wt.% solution with a total mass of 2000 g. The PI film of step (1) was immersed in the solution for 5 minutes and then pulled out at 10 mm / s. It was then cured at 80 ° C for 1 hour to form a 3 μm thick self-healing PU layer (elastic modulus 50 MPa, repair efficiency > 90%).

[0074] (3) 8 g of nano-alumina (50 nm), 1 g of double-layer graphene, and 1 g of PVDF were mixed, and 40 g of NMP solvent was added to obtain a dispersion with a solid content of 20%. The dispersion was ball-milled at a frequency of 300 rpm for 12 h to obtain a slurry.

[0075] The slurry was evenly sprayed onto the surface of the PU layer using a high-pressure spray gun at a pressure of 0.3 MPa and a spraying distance of 20 cm. After pre-baking at 80°C for 30 minutes and vacuum heat treatment at 120°C for 4 hours, a super-hydrophilic coating (contact angle <10°, thermal conductivity 5 W / m·K) was formed.

[0076] (4) 0.5 g of PNIPAM thermosensitive microspheres (200 nm in diameter) were mixed with 9.5 g of ethanol, ultrasonically dispersed at 200 W for 30 min, and sprayed onto the superhydrophilic coating in three batches (0.33 g each). The composite membrane of this embodiment was then obtained by hot pressing at 10 MPa and 100°C for 30 s to integrate the various layers.

[0077] Example 2 It is basically the same as Example 1, except that: (3) 7 g of nano-alumina (50 nm), 1 g of double-layer graphene, and 2 g of PVDF were mixed, and 40 g of NMP solvent was added to obtain a dispersion with a solid content of 20%. The dispersion was ball-milled at a frequency of 350 rpm for 10 h to obtain a slurry.

[0078] The slurry was evenly sprayed onto the surface of the PU layer using a high-pressure spray gun at a pressure of 0.25 MPa and a spraying distance of 20 cm, with a wet film thickness of 12 μm. After pre-baking at 80°C for 30 minutes and vacuum heat treatment at 120°C for 4 hours, a super-hydrophilic ceramic coating was formed (contact angle <15°. Compared with Example 1, the adhesion of this ceramic coating was improved from 4B to 5B level. The ionic conductivity was 1.0 mS / cm, a slight decrease of 0.2 mS / cm but meeting high adhesion requirements).

[0079] Example 3 It is basically the same as Example 1, except that: (1) Electrospinning conditions: voltage 30 kV, receiving distance 10 cm, injection rate 2.0 mL / h, humidity <25%; (3) The same as step (3) of Example 2.

[0080] Example 4 It is basically the same as Example 1, except that: (1) 60 mL of N,N-dimethylacetamide and 40 mL of acetone were mixed as solvent, 25 g of polyimide powder (molecular weight 30,000) was added, and magnetic stirring was carried out at 500 rpm for 36 h until it was completely dissolved to form a 15 wt.% spinning solution.

[0081] A 5 μm thick PI nanofiber membrane was electrospun using an electrospinning machine at a voltage of 28 kV, a receiving distance of 12 cm, an injection rate of 0.8 mL / h, and a humidity of <25%. This membrane was then vacuum-dried at 80°C for 6 hours and heat-treated at 250°C for 3 hours to obtain a high-temperature resistant substrate (heat shrinkage <1%). (3) The same as step (3) of Example 2.

[0082] Comparative Example 1 The method is basically the same as Example 1, except that step (2) is omitted.

[0083] Comparative Example 2 The method is basically the same as Example 1, except that step (3) is eliminated.

[0084] Comparative Example 3 The method is basically the same as Example 1, except that step (4) is eliminated.

[0085] In each embodiment, a diaphragm with a thickness of 9 μm was obtained, and its porosity was distributed in the range of 65%±1%; after testing, the puncture strength of the composite diaphragm corresponding to each embodiment was distributed in the range of 600±20 gf, and the ionic conductivity was distributed in the range of 1.2±0.3 mS / cm; in contrast, the performance of the comparative example in porosity, puncture strength and ionic conductivity was far inferior to that of the embodiment.

[0086] Although the present invention has been illustrated and described using specific embodiments, it should be appreciated that the above embodiments are merely intended to illustrate the technical solutions of the present invention rather than to limit them. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents, without departing from the spirit and scope of the present invention. However, these modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A lithium ion battery separator, characterized in that The lithium-ion battery separator comprises layers connected in the following order: a polyimide nanofiber base layer, a dynamically cross-linked polyurethane self-healing layer, and a ceramic coating; The lithium-ion battery separator further includes poly(N-isopropylacrylamide) microspheres embedded in the layers.

2. The lithium-ion battery separator according to claim 1, characterized in that In the polyimide nanofiber base layer, the molecular weight of polyimide is 10,000-50,000, the fiber diameter is 180nm-240nm, and the fibers form a three-dimensional cross-linked network structure.

3. The lithium-ion battery separator according to claim 1, characterized in that The dynamic cross-linked polyurethane self-repairing layer includes a polyurethane prepolymer containing a dynamic disulfide bond, and the polyurethane prepolymer is obtained by polymerizing polytetrahydrofuran, isophorone diisocyanate, and a chain extender containing a dynamic disulfide bond; Preferably, the chain extender includes at least one of dithiodipropionic acid, a bisthiol chain extender or a thioether chain extender.

4. The lithium-ion battery separator according to claim 3, characterized in that The molar ratio of the polytetrahydrofuran, the isophorone diisocyanate, and the chain extender is (1.5-2.5): (2.5-3.5):

1.

5. The lithium-ion battery separator according to claim 1, characterized in that The ceramic coating comprises nano-aluminum oxide, graphene and a binder, and the mass ratio of the three is (7-9): (0.5-1.5): (0.5-1.5); Preferably, the particle size of the nano-aluminum oxide is 40 nm to 80 nm, and the graphene is a double-layer graphene formed by combining two single-layer graphene layers in a stacked manner.

6. The lithium-ion battery separator according to claim 1, characterized in that The particle size of the poly(N-isopropylacrylamide) microspheres is 150 nm to 250 nm; And / or, the mass ratio of the poly(N-isopropylacrylamide) microspheres to the dynamic cross-linked polyurethane self-healing layer is 4% to 8%.

7. The method for preparing a lithium ion battery separator according to any one of claims 1 to 6, wherein: The steps include: S1, preparing a polyimide nanofiber substrate layer by electrospinning; S2. preparing a solution containing a polyurethane prepolymer, and immersing the polyimide nanofiber base layer in the solution to obtain a dynamically cross-linked polyurethane self-healing layer; S3, preparing a ceramic slurry, and then spraying it onto the surface of the dynamically cross-linked polyurethane self-repairing layer, and heat-treating it to obtain a ceramic coating; S4. Prepare a dispersion containing poly (N-isopropylacrylamide) microspheres, spray it onto the surface of the ceramic coating, and perform hot pressing to obtain the lithium-ion battery separator.

8. The preparation method according to claim 7, characterized in that Satisfy at least one of the following characteristics (a) to (d): (a) For the electrospinning method: voltage 20 kV to 30 kV, receiving distance 10 cm to 20 cm, injection rate 0.8 mL / h to 1.5 mL / h, humidity 20% to 40%, and temperature 20°C to 30°C; (b) the immersion treatment comprises: immersing the polyimide nanofiber base layer in the solution for 3 minutes to 10 minutes, then pulling the film layer at a speed of 5 mm / s to 20 mm / s, and then thermally curing to obtain the dynamically cross-linked polyurethane self-healing layer; (c) preparing the ceramic slurry comprising: mixing nano-alumina, graphene, a binder, and a solvent and ball milling the mixture; the ball milling speed is 250 rpm to 350 rpm, and the ball milling time is 10 h to 15 h; (d) For the spraying in step S4 , the spray gun pressure is 0.1 MPa to 0.3 MPa, the number of spraying is 2 to 3 times, and the interval between each spraying is 8 seconds to 15 seconds.

9. A lithium-ion battery, characterized in that: The invention comprises the lithium-ion battery separator according to any one of claims 1 to 6.

10. An electrical device, characterized in that: Comprising the lithium-ion battery as claimed in claim 9.