Secondary battery and preparation method thereof, energy storage system and electrical equipment

Abstract

The present application relates to the technical field of secondary batteries, and provides a secondary battery and its preparation method, energy storage system and electrical equipment, which are at least conducive to improving the stability of secondary batteries. The method includes: preparing a diaphragm, and the preparation steps include: preparing a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fiber network structure; preparing a self-repairing layer, the self-repairing layer is located on one side of the base layer, the material of the self-repairing layer includes polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the base layer is grafted with ‑SO3Li groups; providing a positive electrode and a negative electrode, and winding or stacking the positive electrode, diaphragm and negative electrode into a shell, wherein the self-repairing layer faces the negative electrode and the base layer faces the positive electrode, and an electrolyte is injected into the shell to obtain a secondary battery.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a secondary battery and a preparation method thereof, an energy storage system, and electrical equipment. Background Art

[0002] The primary function of the separator in a secondary battery is to be placed between the positive and negative electrodes, allowing rapid transport of ionic charge carriers while preventing direct contact between the electrodes. Although the separator is an inactive component of the battery, its properties can impact the battery's ion transport, cycle life, performance, and safety.

[0003] As an important component material that can affect battery performance, the diaphragm should also have high performance requirements, that is, further improve temperature resistance, enhance ion conduction, accelerate ion migration, and improve safety performance.

[0004] At present, the diaphragm has problems such as poor wettability with the electrolyte, severe shrinkage at high temperature, and lithium dendrite piercing, resulting in poor stability of secondary batteries. Summary of the Invention

[0005] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage system, and an electrical device, which are at least beneficial to improving the stability of the secondary battery in use.

[0006] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a method for preparing a secondary battery, including: preparing a diaphragm, the preparation steps including: preparing a base layer, the material of the base layer including polyimide and niobium pentoxide, and the base layer having a fiber network structure; preparing a self-repairing layer, the self-repairing layer being located on one side surface of the base layer, the material of the self-repairing layer including polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the base layer being grafted with -SO3Li groups; providing a positive electrode sheet and a negative electrode sheet, and winding or stacking the positive electrode sheet, the diaphragm and the negative electrode sheet and placing them in a shell, wherein the self-repairing layer faces the negative electrode sheet and the base layer faces the positive electrode sheet, and injecting an electrolyte into the shell to obtain a secondary battery.

[0007] In some embodiments, the steps of preparing the base layer include: preparing a polyimide base, adding polyamic acid to a solvent for ultrasonic dispersion to obtain a spinning solution, wherein the concentration of the polyamic acid is 0.15 g / mL to 0.25 g / mL; electrospinning the spinning solution to obtain an initial polyimide film; calcining the initial polyimide film in an inert gas to obtain a polyimide base having a fiber network structure; preparing a niobium pentoxide coating, dispersing niobium pentoxide in a solvent, adding a dispersant and stirring to mix, applying the mixture to one side of the polyimide base through a coating machine, and then drying to obtain a niobium pentoxide coating, wherein the niobium pentoxide in the niobium pentoxide coating is 100%. The mass ratio of niobium to polyimide in the polyimide substrate is (0.2-0.3):1, and the polyimide substrate and the niobium pentoxide coating constitute a base layer. The steps of preparing the self-healing layer include: dissolving a polyurethane prepolymer containing dynamic disulfide bonds in a solvent, wherein the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is (0.4-0.8):1; coating the mixed solution on the surface of the niobium pentoxide coating away from the polyimide substrate by a casting method and then curing it to form a self-healing layer; and performing plasma surface modification treatment on the self-healing layer so that the surface of the self-healing layer is grafted with -SO3Li groups.

[0008] In some embodiments, in the step of preparing a polyimide substrate, the process parameters of electrospinning include: voltage of 15kV~25kV, rotation speed of the spinning roller of 100r / min~300r / min, and propulsion speed of the spinning needle tube of 0.2mL / h~0.5mL / h; the process parameters of calcination include: temperature of 250℃~350℃, and time of 1.5h~2.5h.

[0009] In some embodiments, in the step of preparing the niobium pentoxide coating, the coating speed of the coating machine is 2 m / min to 5 m / min; the drying temperature is 50° C. to 80° C., and the drying time is 10 h to 12 h.

[0010] In some embodiments, the preparation steps of the polyurethane prepolymer containing dynamic disulfide bonds include: vacuum dehydrating polytetramethylene ether glycol, reacting the polytetramethylene ether glycol with hexamethylene diisocyanate at 60° C. to 80° C. using dibutyltin dilaurate as a catalyst for 2 h to 4 h, cooling to 45° C. to 55° C., adding a chain extender containing dynamic disulfide bonds, cystamine dissolved in tetrahydrofuran, and continuing the reaction for 2 h to 4 h to obtain a polyurethane prepolymer containing dynamic disulfide bonds.

[0011] In some embodiments, the steps of preparing the base layer and the self-healing layer include: adding polyamic acid and niobium pentoxide to a solvent to obtain a first spinning solution, the concentration of polyamic acid is 0.15g / mL~0.25g / mL, and the concentration of niobium pentoxide is 0.015g / mL~0.05g / mL, and the first spinning solution is electrospinning to obtain an initial base membrane; adding polyamic acid and polyurethane containing dynamic disulfide bonds to a solvent to obtain a second spinning solution, the concentration of polyamic acid is 0.1g / mL~0.25g / mL, and the concentration of polyurethane is 0.04g / mL~0.16g / mL, and the second spinning solution is electrospinning to form an initial self-healing layer on the surface of the initial base membrane; placing the initial base membrane and the initial self-healing layer in an inert gas and calcining them to convert the initial base membrane into a base layer, and converting the initial self-healing layer into a self-healing layer; performing plasma surface modification treatment on the self-healing layer so that the surface of the self-healing layer is grafted with -SO3Li groups.

[0012] In some embodiments, the step of performing plasma surface modification treatment on the self-repairing layer includes: ultrasonically cleaning the self-repairing layer with ethanol and deionized water in sequence; plasma bombarding the surface of the self-repairing layer, with the gas source being a mixture of argon and oxygen with a volume ratio of 4:1, so that hydroxyl groups and / or carboxyl groups are generated on the surface of the self-repairing layer; dissolving lithium benzenesulfonate in deionized water, and adding hydrochloric acid to adjust the pH value to 2~3; immersing the plasma-activated diaphragm in the lithium benzenesulfonate solution, performing ultrasonic treatment, and reacting at 55°C~65°C for 2h~4h to graft the -SO3Li group to the surface of the self-repairing layer; placing the diaphragm in deionized water for ultrasonic cleaning to remove unreacted lithium benzenesulfonate on the surface of the self-repairing layer.

[0013] According to some embodiments of the present application, on the other hand, the embodiments of the present application further provide a secondary battery, including: a positive electrode sheet, a negative electrode sheet and a diaphragm, the diaphragm is located between the positive electrode sheet and the negative electrode sheet, and the diaphragm includes: a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fiber network structure; a self-repairing layer, the self-repairing layer is located on one side surface of the base layer, the material of the self-repairing layer includes polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the base layer is grafted with -SO3Li groups; wherein the self-repairing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet.

[0014] In some embodiments, the base layer includes a polyimide substrate and a niobium pentoxide coating, the niobium pentoxide coating is located on one surface of the polyimide substrate, and the self-healing layer is located on a surface of the niobium pentoxide coating away from the polyimide substrate.

[0015] In some embodiments, the thickness of the polyimide substrate is 8 μm to 11 μm; the thickness of the niobium pentoxide coating is 1 μm to 3 μm; and the thickness of the self-healing layer is 1 μm to 3 μm.

[0016] In some embodiments, the mass ratio of the polyimide in the polyimide substrate, the niobium pentoxide in the niobium pentoxide coating, and the polyurethane containing dynamic disulfide bonds is 1:(0.2-0.3):(0.4-0.8).

[0017] In some embodiments, the average particle size of niobium pentoxide in the niobium pentoxide coating is 20 nm to 40 nm.

[0018] In some embodiments, the fiber network structure in the base layer is composed of polyimide, and niobium pentoxide is dispersed in the fiber network structure; the self-repairing layer has a fiber network structure, and the fiber network structure of the self-repairing layer is composed of polyimide and polyurethane containing dynamic disulfide bonds.

[0019] According to some embodiments of the present application, another aspect of the embodiments of the present application further provides an energy storage system, comprising a plurality of secondary batteries manufactured using the preparation method of the secondary batteries in the above embodiments, or the secondary batteries in the above embodiments.

[0020] According to some embodiments of the present application, on the other hand, embodiments of the present application further provide an electrical device, which includes a secondary battery manufactured by the secondary battery preparation method in the above embodiment; or includes a secondary battery in the above embodiment; or includes an energy storage system in the above embodiment.

[0021] The technical solution provided by the embodiments of the present application has at least the following advantages:

[0022] The preparation method of the secondary battery provided in the embodiment of the present application, in the step of preparing the diaphragm, first prepare a base layer including polyimide and niobium pentoxide, and the base layer has a fiber network structure, and then prepare a self-repairing layer including a polyurethane containing dynamic disulfide bonds on the surface of one side of the base layer, and the surface of the self-repairing layer away from the base layer is grafted with -SO3Li groups; in the step of preparing the secondary battery, the self-repairing layer is directed toward the negative electrode sheet, and the base layer is directed toward the positive electrode sheet. The fiber network structure of the base layer is conducive to the base layer having good mechanical strength and porosity, which is conducive to increasing the diaphragm's resistance to lithium dendrite penetration, and can promote the infiltration of the electrolyte and reduce the interface impedance. The niobium pentoxide in the base layer has a high dielectric constant and metal ion adsorption capacity, which can optimize the metal ion flux distribution and inhibit the growth of lithium dendrites. At the same time, the thermal stability of niobium pentoxide is high, which is conducive to improving the high temperature resistance of the diaphragm and reducing the risk of thermal runaway. The polyurethane containing dynamic disulfide bonds in the self-healing layer can achieve self-repair through the rupture and recombination of SS bonds, effectively addressing microcracks or lithium dendrite penetration caused by volume expansion during the secondary battery cycle. The -SO3Li groups grafted onto the surface of the self-healing layer away from the substrate layer provide uniform metal ion transmission channels and facilitate the formation of a negative charge repulsion layer, guiding the uniform deposition of metal ions through electrostatic effects. Self-healing is oriented toward the negative electrode, prioritizing the repair of damage to the negative electrode to match the volume change of the negative electrode. The substrate layer faces the positive electrode, utilizing the antioxidant properties of polyimide to protect the separator from corrosion by high-valent metal ions in the positive electrode, thereby extending the cycle life of the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplified descriptions do not constitute a limitation on the embodiments. Unless otherwise stated, the pictures in the drawings do not constitute a scale limitation. In order to more clearly illustrate the embodiments of the present application or the technical solutions in the traditional technology, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 A flowchart corresponding to a method for preparing a secondary battery provided in one embodiment of the present application;

[0025] Figure 2 A flowchart corresponding to a method for preparing a first diaphragm provided in one embodiment of the present application;

[0026] Figure 3 A flowchart corresponding to the second method for preparing a diaphragm provided in one embodiment of the present application;

[0027] Figure 4 for Figure 2 Schematic diagram of the structure of the diaphragm prepared by the preparation method shown;

[0028] Figure 5 for Figure 3 A schematic structural diagram of the diaphragm obtained by the preparation method.

[0029] Description of reference numerals:

[0030] The first example: 101, base layer; 102, self-healing layer; 111, polyimide substrate; 121, niobium pentoxide coating.

[0031] Second example: 201, base layer; 202, self-repairing layer. DETAILED DESCRIPTION

[0032] As can be seen from the background technology, the separator has problems such as poor wettability with the electrolyte, severe shrinkage at high temperature, and lithium dendrite piercing, resulting in poor stability in the use of secondary batteries.

[0033] The preparation processes of diaphragms mainly include dry and wet methods. In the dry method, the polymer is melted and extruded into a film, and micropores are formed through directional or biaxial stretching. However, the porosity of the prepared diaphragm is low, and the liquid absorption rate and ionic conductivity are poor. In the wet method, the concrete is mixed with liquid hydrocarbons (such as paraffin oil) and melted, and then extruded and cast to form a polymer / solvent bicontinuous structure. After stretching, the solvent is extracted to leave a porous structure. The prepared diaphragm has a high porosity, but the solvent residue may affect the performance of the secondary battery.

[0034] Common ways to modify diaphragms include coating, radiation grafting, and blending, among which coating modification is one of the simplest and most effective methods. Inorganic coating uses ceramic particles such as alumina and boehmite to modify polymer diaphragms to improve the wettability and dimensional stability of the diaphragm. However, the adhesion between the ceramic particles and the base membrane is poor, and they are easy to fall off, resulting in a decrease in cycle life; in addition, ceramic particles will significantly increase the mass of the diaphragm, resulting in a decrease in energy density. Organic coatings mostly use polymers such as aramid and polyvinylidene fluoride. These materials have strong adhesion and can enhance the cycle life of the battery, but they do not significantly improve the battery capacity and cycle stability, and it is difficult to have the ability to enhance dimensional stability and mechanical properties.

[0035] The embodiments of the present application provide a secondary battery and a preparation method thereof, an energy storage system, and an electrical device, which are at least beneficial to improving the stability of the secondary battery in use.

[0036] In the description of the embodiments of the present application, “multiple” means more than two, unless otherwise clearly and specifically defined.

[0037] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] In the description of the embodiments of this application, the term "and / or" is simply a description of the association relationship between associated objects, indicating that three relationships can exist. For example, A and / or B can represent the following three situations: A exists, A and B exist at the same time, and B exists. In addition, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0039] In the description of the embodiments of the present application, when a component “includes” another component, unless otherwise stated, other components are not excluded, and other components may be further included.

[0040] The terms used in the description of the various embodiments described herein are for describing specific embodiments only and are not intended to be limiting. As used in the description of the various embodiments described and the appended claims, "components" are also intended to include plural forms unless the context clearly indicates otherwise.

[0041] The following detailed description of the various embodiments of the present application is provided in conjunction with the accompanying drawings. However, those skilled in the art will appreciate that many technical details are provided in the various embodiments of the present application to facilitate a better understanding of the present application. However, even without these technical details and the various variations and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0042] Figure 1 This is a flow chart corresponding to a method for preparing a secondary battery provided in one embodiment of the present application.

[0043] refer to Figure 1 In one embodiment of the present application, there is provided a method for preparing a secondary battery, comprising:

[0044] A diaphragm is prepared, and the preparation steps include: preparing a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fiber network structure; preparing a self-repairing layer, the self-repairing layer is located on one side of the base layer, the material of the self-repairing layer includes polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the base layer is grafted with -SO3Li groups.

[0045] A positive electrode sheet and a negative electrode sheet are provided, and the positive electrode sheet, the separator and the negative electrode sheet are wound or stacked and then placed in a shell, wherein the self-repairing layer faces the negative electrode sheet and the base layer faces the positive electrode sheet, and an electrolyte is injected into the shell to obtain a secondary battery.

[0046] The preparation method of the secondary battery provided in the embodiment of the present application, in the step of preparing the diaphragm, first prepare a base layer including polyimide and niobium pentoxide, and the base layer has a fiber network structure, and then prepare a self-repairing layer including a polyurethane containing dynamic disulfide bonds on the surface of one side of the base layer, and the surface of the self-repairing layer away from the base layer is grafted with -SO3Li groups; in the step of preparing the secondary battery, the self-repairing layer is directed toward the negative electrode sheet, and the base layer is directed toward the positive electrode sheet. The fiber network structure of the base layer is conducive to the base layer having good mechanical strength and porosity, which is conducive to increasing the diaphragm's resistance to lithium dendrite penetration, and can promote the infiltration of the electrolyte and reduce the interface impedance. The niobium pentoxide in the base layer has a high dielectric constant and metal ion adsorption capacity, which can optimize the metal ion flux distribution and inhibit the growth of lithium dendrites. At the same time, the thermal stability of niobium pentoxide is high, which is conducive to improving the high temperature resistance of the diaphragm and reducing the risk of thermal runaway. The polyurethane containing dynamic disulfide bonds in the self-healing layer can achieve self-repair through the rupture and recombination of SS bonds, effectively addressing microcracks or lithium dendrite penetration caused by volume expansion during the secondary battery cycle. The -SO3Li groups grafted onto the surface of the self-healing layer away from the substrate layer provide uniform metal ion transmission channels and facilitate the formation of a negative charge repulsion layer, guiding the uniform deposition of metal ions through electrostatic effects. Self-healing is oriented toward the negative electrode, prioritizing the repair of damage to the negative electrode to match the volume change of the negative electrode. The substrate layer faces the positive electrode, utilizing the antioxidant properties of polyimide to protect the separator from corrosion by high-valent metal ions in the positive electrode, thereby extending the cycle life of the secondary battery.

[0047] The secondary battery can be a lithium battery, a lead-acid battery, a sodium battery, or a nickel-metal hydride battery. The present application embodiment will take the preparation method of a lithium-ion battery as an example. Those skilled in the art can replace the lithium ions in the positive electrode sheet, the negative electrode sheet, and the electrolyte with corresponding metal ions according to actual needs. For example, in a sodium battery, the lithium transition metal oxide of the subsequent positive electrode active material is replaced with any of the corresponding layered metal oxides (such as NaFeO2), polyanion compounds (NaFePO4), and Prussian blue compound systems (such as NaMnFe(CN)6-zH2O). The electrolyte can be replaced with any of an organic liquid electrolyte, a solid composite electrolyte, or a solid electrolyte.

[0048] The positive electrode sheet can be made by mixing a positive electrode active material, a binder, and an additive to form a paste, which is evenly applied to both sides of the aluminum foil, dried, and rolled. The positive electrode active material includes lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, or a ternary material.

[0049] The negative electrode sheet can be made by mixing a negative electrode active material, a binder, and additives to form a paste, which is evenly applied to both sides of the copper foil, dried, and rolled. Negative electrode active materials include carbon negative electrode materials, tin-based negative electrode materials, lithium-containing transition metal nitride negative electrode materials, alloy negative electrode materials, or nano-scale negative electrode materials.

[0050] Figure 2 and Figure 3 Flowchart corresponding to the preparation method of the two diaphragms provided in the embodiments of the present application, Figure 4 and Figure 5 This is a schematic diagram of the structures of two diaphragms provided in the embodiments of the present application, wherein: Figure 4 The diaphragm shown is made of Figure 2 The preparation method shown is obtained. Figure 5 The diaphragm shown is made of Figure 3 The following will describe in detail the various embodiments of the present application in conjunction with the accompanying drawings.

[0051] In the first example, refer to Figure 2 and Figure 4 The steps of preparing the base layer 101 include: preparing a polyimide base 111 and forming a niobium pentoxide coating 121 on the polyimide base 111, wherein the polyimide base 111 and the niobium pentoxide coating 121 together constitute the base layer 101; and the prepared self-healing layer 102 is located on a surface of the niobium pentoxide coating 121 away from the polyimide base 111.

[0052] The steps of preparing the polyimide substrate 111 include: adding polyamic acid to a solvent (such as dimethylacetamide) and ultrasonically dispersing it to obtain a spinning solution, wherein the concentration of the polyamic acid is 0.15 g / mL~0.25 g / mL, for example, it can be 0.15 g / mL, 0.18 g / mL, 0.2 g / mL, 0.23 g / mL or 0.25 g / mL; electrospinning the spinning solution to obtain an initial polyimide film; and calcining the initial polyimide film in an inert gas (such as nitrogen) to obtain a polyimide substrate 111 having a fiber network structure.

[0053] Among them, the process parameters of electrospinning include: voltage of 15kV~25kV, rotation speed of the spinning roller of 100r / min~300r / min, and propulsion speed of the spinning needle tube of 0.2mL / h~0.5mL / h. The process parameters of calcination include: temperature of 250℃~350℃, and time of 1.5h~2.5h. The process parameters of electrospinning within the above range are conducive to the uniform and continuous thickness of the fiber network structure of the polyimide substrate, which is conducive to the formation of a polyimide substrate with stable mechanical strength and uniform porosity. The key to calcination after electrospinning is to control the calcination temperature and time. The calcination temperature and time within the above range are conducive to ensuring the integrity of the fiber network structure while removing organic components.

[0054] The average molecular weight of the polyimide can be 50,000 g / mol to 100,000 g / mol, for example, 50,000 g / mol, 56,000 g / mol, 60,000 g / mol, 64,000 g / mol, 70,000 g / mol, 75,000 g / mol, 80,000 g / mol, 83,000 g / mol, 90,000 g / mol, 97,000 g / mol or 100,000 g / mol.

[0055] The steps of preparing the niobium pentoxide coating 121 include: dispersing niobium pentoxide in a solvent (e.g., ethanol), adding a dispersant (e.g., 3-aminopropyltriethoxysilane), stirring and mixing, applying the mixture to one surface of the polyimide substrate 111 using a coater, and then drying to obtain the niobium pentoxide coating 121. The mass ratio of niobium pentoxide in the niobium pentoxide coating 121 to the mass ratio of polyimide in the polyimide substrate 111 is (0.2-0.3):1.

[0056] The coating speed of the coating machine is 2m / min~5m / min, the drying temperature is 50℃~80℃, and the drying time is 10h~12h.

[0057] The steps of preparing the self-healing layer 102 include: dissolving a polyurethane prepolymer containing dynamic disulfide bonds in a solvent (e.g., tetrahydrofuran), wherein the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate 111 is (0.4-0.8):1; applying the mixed solution to the surface of the niobium pentoxide coating 121 away from the polyimide substrate 111 by a casting method and then curing it to form the self-healing layer 102; and performing a plasma surface modification treatment on the self-healing layer 102 so that the surface of the self-healing layer 102 is grafted with -SO3Li groups.

[0058] The preparation steps of the polyurethane prepolymer containing dynamic disulfide bonds include: vacuum dehydrating polytetramethylene ether glycol, reacting the polytetramethylene ether glycol with hexamethylene diisocyanate at 60°C to 80°C using dibutyltin dilaurate as a catalyst for 2h to 4h, cooling to 45°C to 55°C, adding a chain extender containing dynamic disulfide bonds dissolved in tetrahydrofuran, and continuing the reaction for 2h to 4h to obtain a polyurethane prepolymer containing dynamic disulfide bonds.

[0059] Polytetramethylene ether glycol serves as the soft segment of the polyurethane prepolymer, and hexamethylene diisocyanate serves as the hard segment. The soft segment accounts for 30% to 50% of the polyurethane prepolymer by weight, while the hard segment accounts for 50% to 70% of the polyurethane prepolymer by weight. For example, the weight of polytetramethylene ether glycol is 30% and the weight of hexamethylene diisocyanate is 70%; alternatively, the weight of polytetramethylene ether glycol is 40% and the weight of hexamethylene diisocyanate is 60%; or alternatively, the weight of polytetramethylene ether glycol is 50% and the weight of hexamethylene diisocyanate is 50%. The hard segment increases the hardness and strength of the polyurethane, while the soft segment increases its flexibility and elasticity. A hard-to-soft segment ratio within this range can help the polyurethane achieve both good mechanical strength and flexibility.

[0060] In the first method for preparing a diaphragm provided in an embodiment of the present application, after a polyimide substrate 111 is prepared by an electrospinning process, a niobium pentoxide coating 121 is formed by a coating method. The polyimide substrate 111 and the niobium pentoxide coating 121 together constitute a base layer 101. The composite base layer 101 can not only utilize the fiber network structure of the polyimide substrate 111 to provide good mechanical strength and electrolyte absorption rate, but also utilize the niobium pentoxide coating 121 to enhance ion conductivity and high voltage resistance; then, a self-healing layer 102 is formed on the surface of the niobium pentoxide coating 121 away from the polyimide substrate 111 by a casting method. The self-healing layer 102 is composed of a polyurethane containing dynamic disulfide bonds. The polyurethane containing dynamic disulfide bonds can achieve damage self-repair by breaking / recombining SS bonds; plasma grafting -SO3Li groups constructs ion channels, reduces interfacial impedance, and at the same time improves the electrolyte affinity of the surface of the self-healing layer 102, which is conducive to improving wettability.

[0061] In the second example, refer to Figure 3 and Figure 5 The base layer 201 and the self-repairing layer 202 are both made by electrospinning process.

[0062] Specifically, the steps of preparing the base layer 201 and the self-repairing layer 202 include: adding polyamic acid and niobium pentoxide to a solvent (e.g., dimethylacetamide) to obtain a first spinning solution, wherein the concentration of the polyamic acid is 0.15 g / mL to 0.25 g / mL (e.g., 0.15 g / mL, 0.18 g / mL, 0.2 g / mL, 0.23 g / mL, or 0.25 g / mL), and the concentration of the niobium pentoxide is 0.015 g / mL to 0. 0.05 g / mL (for example, specifically 0.015 g / mL, 0.018 g / mL, 0.02 g / mL, 0.022 g / mL, 0.025 g / mL, 0.03 g / mL, 0.035 g / mL, 0.04 g / mL, 0.045 g / mL or 0.05 g / mL), electrospinning the first spinning solution to obtain an initial basement membrane; adding polyamic acid and polyurethane containing dynamic disulfide bonds to a solvent (for example, dimethyl a second spinning solution is obtained from polyamide (polyamic acid), wherein the concentration of the polyamic acid is 0.1 g / mL to 0.25 g / mL (for example, specifically 0.1 g / mL, 0.13 g / mL, 0.15 g / mL, 0.18 g / mL, 0.2 g / mL or 0.25 g / mL), and the concentration of the polyurethane containing dynamic disulfide bonds is 0.04 g / mL to 0.16 g / mL (for example, specifically 0.04 g / mL, 0.08 g / mL, 0.1 g / mL, 0.13 g / mL or 0.16 g / mL); the second spinning solution is electrospun to form an initial self-healing layer on the surface of the initial base membrane; the initial base membrane and the initial self-healing layer are calcined in an inert gas to convert the initial base membrane into the base layer 201, and the initial self-healing layer is converted into the self-healing layer 202; the self-healing layer 202 is subjected to plasma surface modification treatment to graft -SO3Li groups on the surface of the self-healing layer 202.

[0063] In the base layer 201 or the self-healing layer 202, the average molecular weight of the polyimide can be 50,000 g / mol to 100,000 g / mol, for example, 50,000 g / mol, 56,000 g / mol, 60,000 g / mol, 64,000 g / mol, 70,000 g / mol, 75,000 g / mol, 80,000 g / mol, 83,000 g / mol, 90,000 g / mol, 97,000 g / mol or 100,000 g / mol.

[0064] Among them, the process parameters for electrospinning the first spinning solution include: voltage of 15kV~25kV, spinning roller speed of 100r / min~300r / min, and spinning needle propulsion speed of 3mL / h~8mL / h. The process parameters for electrospinning the second spinning solution include: voltage of 15kV~25kV, spinning roller speed of 100r / min~300r / min, and spinning needle propulsion speed of 5mL / h~10mL / h. The needle propulsion rate when the first spinning solution is electrospun to prepare the initial base membrane is less than the needle propulsion rate when the second spinning solution is electrospun to prepare the initial self-repairing layer, which is beneficial to make the porosity of the base layer higher than the porosity of the self-repairing layer. The self-repairing layer has a lower porosity and a relatively high density, which is beneficial for it to effectively deal with problems such as microcracks caused by volume expansion or piercing of lithium dendrites during the cycle of the secondary battery.

[0065] After preparing the base layer 201 and the self-healing layer 202, the process may further include forming a niobium pentoxide coating (not shown) on the surface of the base layer 201 away from the self-healing layer 202 and on the surface of the self-healing layer 202 away from the base layer 201. The step of forming the niobium pentoxide coating includes dispersing niobium pentoxide in a solvent (e.g., ethanol), adding a dispersant (e.g., 3-aminopropyltriethoxysilane), stirring and mixing, applying the mixture to the surface of the base layer 201 away from the self-healing layer 202 and on the surface of the self-healing layer 202 away from the base layer 201 using a coating machine, and then drying.

[0066] The coating speed of the coating machine is 2m / min~5m / min, the drying temperature is 50℃~80℃, and the drying time is 10h~12h.

[0067] In the preparation method of the second diaphragm provided in the embodiment of the present application, polyamic acid and niobium pentoxide are configured into a first spinning solution and then electrospun to obtain an initial base membrane, and polyamic acid and polyurethane containing dynamic disulfide bonds are configured into a second spinning solution and then electrospun to obtain an initial self-repairing layer. The initial base membrane and the initial self-repairing layer are then placed in an inert gas and calcined to obtain a base layer 201 and a self-repairing layer 202. The self-repairing layer 202 is then surface-modified to graft -SO3Li groups. In this way, both the base layer 201 and the self-repairing layer 202 have a fiber network structure, which is beneficial to improving the overall mechanical strength and porosity of the diaphragm, promoting the infiltration of the electrolyte, and reducing the interfacial impedance. The niobium pentoxide coating 121 in the base layer 201 enhances ion conductivity and high-voltage resistance. The polyurethane containing dynamic disulfide bonds in the self-healing layer 102 achieves self-repair through the breakage and recombination of SS bonds. Plasma-grafted -SO3Li groups create ion channels, reducing interfacial impedance and improving the electrolyte affinity of the self-healing layer 102 surface, thereby enhancing wettability. Furthermore, both the base layer 201 and the self-healing layer 202 are produced using an electrospinning process, which improves the efficiency of membrane preparation.

[0068] refer to Figure 2 and Figure 3 In the preparation methods of the above two membranes, the step of plasma surface modification treatment of the self-repairing layer includes: ultrasonically cleaning the self-repairing layer with ethanol and deionized water in sequence; plasma bombarding the surface of the self-repairing layer, with the gas source being a mixture of argon and oxygen with a volume ratio of 4:1, so that hydroxyl groups and / or carboxyl groups are generated on the surface of the self-repairing layer; dissolving lithium benzenesulfonate in deionized water, and adding hydrochloric acid to adjust the pH value to 2~3; immersing the plasma-activated membrane in the lithium benzenesulfonate solution, ultrasonically treating it, and reacting it at 55℃~65℃ for 2h~4h to graft the -SO3Li group to the surface of the self-repairing layer; placing the membrane in deionized water and ultrasonically cleaning it to remove unreacted lithium benzenesulfonate on the surface of the self-repairing layer.

[0069] Accordingly, another embodiment of the present application further provides a secondary battery, which can be manufactured using the manufacturing method of the secondary battery provided in the above embodiment. The secondary battery provided in another embodiment of the present application will be described in detail below with reference to the accompanying drawings. For parts that are identical or corresponding to the previous embodiment, please refer to the corresponding description of the previous embodiment and will not be described in detail below.

[0070] The secondary battery provided in an embodiment of the present application includes: a positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive and negative electrodes. The separator includes: a base layer, the base layer material comprising polyimide and niobium pentoxide, and having a fiber network structure; a self-repairing layer, located on one surface of the base layer, the self-repairing layer material comprising polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the base layer having -SO3Li groups grafted thereon; wherein the self-repairing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet.

[0071] In the secondary battery provided in the embodiment of the present application, the diaphragm includes a base layer and a self-healing layer. The base layer includes polyimide and niobium pentoxide, and the base layer has a fiber network structure. Niobium pentoxide has a high dielectric constant and metal ion adsorption capacity, which can optimize the metal ion flux distribution and inhibit the growth of lithium dendrites. At the same time, niobium pentoxide has high thermal stability, which is beneficial to improving the high temperature resistance of the diaphragm and reducing the risk of thermal runaway; the fiber network structure is beneficial to the base layer having good mechanical strength and porosity, which is beneficial to increasing the diaphragm's resistance to lithium dendrite penetration, and can promote the infiltration of the electrolyte and reduce the interface impedance. The polyurethane containing dynamic disulfide bonds in the self-healing layer can achieve damage self-repair through the rupture / recombination of SS bonds, so as to effectively deal with microcracks or lithium dendrite penetration caused by volume expansion during the cycle of the secondary battery; the -SO3Li group grafted on the surface of the self-healing layer away from the base layer can provide a uniform metal ion transmission channel, and is also beneficial to the formation of a negative charge repulsion layer, guiding the uniform deposition of metal ions through electrostatic action. The self-repairing direction is toward the negative electrode sheet, and the damage of the negative electrode sheet is repaired first, which is conducive to matching the volume change of the negative electrode sheet; the base layer is toward the positive electrode sheet, and the antioxidant properties of polyimide are used to protect the diaphragm from the corrosion of high-valent metal ions in the positive electrode sheet, thereby extending the cycle life of the secondary battery.

[0072] In one example, refer to Figure 3 The base layer 101 includes a polyimide base 111 and a niobium pentoxide coating 121 . The niobium pentoxide coating 121 is located on one side of the polyimide base 111 . The self-repairing layer 102 is located on the surface of the niobium pentoxide coating 121 away from the polyimide base 111 .

[0073] refer to Figure 3 The thickness of the polyimide substrate 111 is 8 μm to 11 μm, for example, 8 μm, 9 μm, 10 μm, or 11 μm. The thickness of the niobium pentoxide coating 121 is 1 μm to 3 μm, for example, 1 μm, 2 μm, or 3 μm. The thickness of the self-healing layer 102 is 1 μm to 3 μm, for example, 1 μm, 2 μm, or 3 μm.

[0074] refer to Figure 3The mass ratio of the polyimide in the polyimide substrate 111 , the niobium pentoxide in the niobium pentoxide coating 121 , and the polyurethane containing dynamic disulfide bonds is 1:(0.2-0.3):(0.4-0.8).

[0075] refer to Figure 3 The average particle size of niobium pentoxide in the niobium pentoxide coating 121 is 20 nm to 40 nm, for example, 20 nm, 25 nm, 30 nm, 35 nm or 40 nm.

[0076] In another example, refer to Figure 5 The fiber network structure in the base layer 201 is composed of polyimide, and niobium pentoxide is dispersed in the fiber network structure; the self-repairing layer 202 has a fiber network structure, and the fiber network structure of the self-repairing layer 202 is composed of polyimide and polyurethane containing dynamic disulfide bonds.

[0077] refer to Figure 5 In the base layer 201, the mass ratio of polyimide to niobium pentoxide is 1:(0.1-0.2). In the self-healing layer 202, the mass ratio of polyimide to polyurethane containing dynamic disulfide bonds is 1:(0.4-0.5).

[0078] refer to Figure 5 The thickness of the base layer 201 is 5 μm to 7 μm, for example, 5 μm, 5.5 μm, 6 μm, 6.5 μm or 7 μm. The thickness of the self-repairing layer 202 is 3 μm to 5 μm, for example, 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0079] refer to Figure 5 The average particle size of niobium pentoxide in the base layer 201 is 18 nm to 35 nm, for example, 18 nm, 20 nm, 23 nm, 25 nm, 28 nm, 30 nm, 33 nm or 35 nm.

[0080] Correspondingly, another aspect of the embodiments of the present application further provides an energy storage system, comprising a plurality of secondary batteries manufactured using the manufacturing method of the secondary batteries in the above embodiments, or the secondary batteries in the above embodiments.

[0081] Correspondingly, another aspect of the embodiments of the present application further provides an electrical device, which includes a secondary battery manufactured by the secondary battery preparation method in the above embodiment; or includes a secondary battery in the above embodiment; or includes an energy storage system in the above embodiment.

[0082] The following are specific examples of this application.

[0083] Example 1

[0084] S11. Prepare a diaphragm. The preparation steps are as follows.

[0085] S111. Preparation of polyimide substrate: 20 g of polyamic acid was added to dimethylacetamide for ultrasonic dispersion to obtain a spinning solution, the concentration of polyamic acid was 0.2 g / mL; the spinning solution was electrospun to obtain an initial polyimide membrane, and the process parameters of electrospinning were as follows: voltage of 20 kV, spinning roller speed of 200 r / min, and propulsion speed of the spinning tube of 0.3 mL / h; the initial polyimide membrane was placed in nitrogen and calcined to obtain a polyimide substrate (thickness of 10 μm) having a fiber network structure, and the calcination process parameters were as follows: temperature of 300°C and time of 2 h.

[0086] S112. Prepare a niobium pentoxide coating. Disperse niobium pentoxide (average particle size of 30 nm) in ethanol, add 3-aminopropyltriethoxysilane and stir to mix. Apply the mixture on one surface of a polyimide substrate using a coater and then dry to obtain a niobium pentoxide coating (thickness of 2 μm). The ratio of the mass of niobium pentoxide in the niobium pentoxide coating to the mass of polyimide in the polyimide substrate is 0.25:1. The polyimide substrate and the niobium pentoxide coating constitute a base layer. The coating speed is 3 m / min, the drying temperature is 80°C, and the drying time is 12 h.

[0087] S113. Preparation of a self-healing layer: dissolving a polyurethane prepolymer containing dynamic disulfide bonds in tetrahydrofuran, wherein the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is 0.6:1; applying the mixed solution to the surface of the niobium pentoxide coating away from the polyimide substrate by a casting method, and then curing the mixture at room temperature for 24 hours to form a self-healing layer; performing plasma surface modification treatment on the self-healing layer so that the surface of the self-healing layer is grafted with -SO3Li groups.

[0088] S12. Provide a positive electrode sheet and a negative electrode sheet, wind the positive electrode sheet, the separator and the negative electrode sheet and place them in a shell, wherein the self-repairing layer faces the negative electrode sheet and the base layer faces the positive electrode sheet, and inject electrolyte into the shell to obtain a secondary battery.

[0089] Example 2

[0090] The preparation steps of Example 2 are substantially the same as those of Example 1, except that in step S111 , the concentration of polyimide is 0.15 g / mL.

[0091] Example 3

[0092] The preparation steps of Example 3 are substantially the same as those of Example 1, except that in step S111 , the concentration of polyimide is 0.25 g / mL.

[0093] Example 4

[0094] The preparation steps of Example 4 are substantially the same as those of Example 1, except that in step S111 , the thickness of the polyimide substrate is 8 μm.

[0095] Example 5

[0096] The preparation steps of Example 5 are substantially the same as those of Example 1, except that in step S111 , the thickness of the polyimide substrate is 11 μm.

[0097] Example 6

[0098] The preparation steps of Example 6 are substantially the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 20 nm.

[0099] Example 7

[0100] The preparation steps of Example 7 are substantially the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 40 nm.

[0101] Example 8

[0102] The preparation steps of Example 8 are basically the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 1 μm.

[0103] Example 9

[0104] The preparation steps of Example 9 are basically the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 3 μm.

[0105] Example 10

[0106] The preparation steps of Example 10 are substantially the same as those of Example 1, except that in step S112, the mass ratio of niobium pentoxide in the niobium pentoxide coating to polyimide in the polyimide substrate is 0.2:1.

[0107] Example 11

[0108] The preparation steps of Example 11 are substantially the same as those of Example 1, except that in step S112, the mass ratio of niobium pentoxide in the niobium pentoxide coating to the mass ratio of polyimide in the polyimide substrate is 0.3:1.

[0109] Example 12

[0110] The preparation steps of Example 12 are substantially the same as those of Example 1, except that in step S113, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is 0.4:1.

[0111] Example 13

[0112] The preparation steps of Example 13 are substantially the same as those of Example 1, except that in step S113, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is 0.8:1.

[0113] Example 14

[0114] The difference between Example 14 and Example 1 is that the steps for preparing the diaphragm in step S11 are different. The steps for preparing the diaphragm in Example 14 are as follows: polyamic acid and niobium pentoxide are added to dimethylacetamide to obtain a first spinning solution, the concentration of polyamic acid is 0.2 g / mL, the concentration of niobium pentoxide is 0.03 g / mL, and the average particle size of niobium pentoxide is 30 nm. The first spinning solution is electrospun to obtain an initial base membrane, the voltage of electrospinning is 20 kV, the speed of the spinning roller is 200 r / min, and the propulsion speed of the spinning needle is 5 mL / h; polyamic acid and a polyurethane containing dynamic disulfide bonds are added to dimethylacetamide to obtain a second spinning solution, the concentration of polyamic acid is 0.15 g / mL, and the spinning speed is 200 r / min. mL, the concentration of the polyurethane containing dynamic disulfide bonds is 0.1 g / mL; the second spinning solution is electrospun to form an initial self-healing layer on the surface of the initial base membrane, the electrospinning voltage is 20 kV, the spinning roller speed is 200 r / min, and the spinning needle propulsion speed is 8 mL / h; the initial base membrane and the initial self-healing layer are calcined in an inert gas to convert the initial base membrane into a base layer (with a thickness of 6 μm), and the initial self-healing layer is converted into a self-healing layer (with a thickness of 4 μm); the self-healing layer is subjected to plasma surface modification treatment to graft -SO3Li groups on the surface of the self-healing layer.

[0115] Example 15

[0116] The preparation steps of Example 15 are basically the same as those of Example 14, except that the concentration of niobium pentoxide in the first spinning solution of Example 15 is 0.02 g / mL.

[0117] Example 16

[0118] The preparation steps of Example 16 are basically the same as those of Example 14, except that the concentration of niobium pentoxide in the first spinning solution of Example 16 is 0.04 g / mL.

[0119] Example 17

[0120] The preparation steps of Example 17 are basically the same as those of Example 14, except that in the second spinning solution of Example 17, the concentration of the polyurethane containing dynamic disulfide bonds is 0.04 g / mL.

[0121] Example 18

[0122] The preparation steps of Example 18 are basically the same as those of Example 14, except that in the second spinning solution of Example 18, the concentration of the polyurethane containing dynamic disulfide bonds is 0.16 g / mL.

[0123] Example 19

[0124] The preparation steps of Example 19 are basically the same as those of Example 14, except that the thickness of the base layer in Example 19 is 5 μm.

[0125] Example 20

[0126] The preparation steps of Example 20 are basically the same as those of Example 14, except that the thickness of the base layer in Example 20 is 7 μm.

[0127] Example 21

[0128] The preparation steps of Example 21 are basically the same as those of Example 14, except that the thickness of the self-repairing layer in Example 21 is 3 μm.

[0129] Example 22

[0130] The preparation steps of Example 22 are basically the same as those of Example 14, except that the thickness of the self-repairing layer in Example 22 is 5 μm.

[0131] Example 23

[0132] The preparation steps of Example 23 are basically the same as those of Example 14, except that the average particle size of niobium pentoxide in Example 23 is 18 nm.

[0133] Example 24

[0134] The preparation steps of Example 24 are basically the same as those of Example 14, except that the average particle size of niobium pentoxide in Example 24 is 35 nm.

[0135] Comparative Example 1

[0136] The preparation steps of Comparative Example 1 are substantially the same as those of Example 1, except that in step S11, steps S112 and S113 are removed, and the diaphragm is formed of a polyimide substrate.

[0137] Comparative Example 2

[0138] The preparation steps of Comparative Example 2 are substantially the same as those of Example 1, except that in step S11, step S113 is removed, and the diaphragm is composed of a polyimide substrate and a niobium pentoxide coating.

[0139] Comparative Example 3

[0140] The preparation steps of Comparative Example 3 are basically the same as those of Example 1, except that in S113, no surface modification treatment is performed after the self-repairing layer is prepared, the diaphragm is composed of a polyimide substrate, a niobium pentoxide coating and a self-repairing layer, and the surface of the self-repairing layer is not grafted with -SO3Li groups.

[0141] Comparative Example 4

[0142] The preparation steps of Comparative Example 4 are substantially the same as those of Example 1, except that in step S111, the concentration of polyamic acid is 0.05 g / mL.

[0143] Comparative Example 5

[0144] The preparation steps of Comparative Example 5 are substantially the same as those of Example 1, except that in step S111, the concentration of polyamic acid is 0.5 g / mL.

[0145] Comparative Example 6

[0146] The preparation steps of Comparative Example 6 are substantially the same as those of Example 1, except that in step S111 , the thickness of the polyimide substrate is 5 μm.

[0147] Comparative Example 7

[0148] The preparation steps of Comparative Example 7 are substantially the same as those of Example 1, except that in step S111 , the thickness of the polyimide substrate is 15 μm.

[0149] Comparative Example 8

[0150] The preparation steps of Comparative Example 8 are substantially the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 10 nm.

[0151] Comparative Example 9

[0152] The preparation steps of Comparative Example 9 are substantially the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 80 nm.

[0153] Comparative Example 10

[0154] The preparation steps of Comparative Example 10 are substantially the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 0.5 μm.

[0155] Comparative Example 11

[0156] The preparation steps of Comparative Example 11 are substantially the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 6 μm.

[0157] Comparative Example 12

[0158] The preparation steps of Comparative Example 12 are substantially the same as those of Example 1, except that in step S112, the mass ratio of niobium pentoxide in the niobium pentoxide coating to the mass ratio of polyimide in the polyimide substrate is 0.05:1.

[0159] Comparative Example 13

[0160] The preparation steps of Comparative Example 13 are substantially the same as those of Example 1, except that in step S112, the mass ratio of niobium pentoxide in the niobium pentoxide coating to the mass ratio of polyimide in the polyimide substrate is 0.5:1.

[0161] Comparative Example 14

[0162] The preparation steps of Comparative Example 14 are substantially the same as those of Example 1, except that in step S113 , the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is 0.1:1.

[0163] Comparative Example 15

[0164] The preparation steps of Comparative Example 15 are substantially the same as those of Example 1, except that in step S113 , the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is 2:1.

[0165] Comparative Example 16

[0166] The preparation steps of Comparative Example 16 are basically the same as those of Example 14, except that in the step of preparing the diaphragm, the self-repairing layer is not prepared, and the diaphragm is a base layer composed of polyimide and niobium pentoxide.

[0167] Comparative Example 17

[0168] The preparation steps of Comparative Example 17 are basically the same as those of Example 14, except that in the step of preparing the diaphragm, the base layer is not prepared, the diaphragm is a self-repairing layer composed of polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer is not grafted with -SO3Li groups.

[0169] Comparative Example 18

[0170] The preparation steps of Comparative Example 18 are basically the same as those of Example 14, except that the concentration of niobium pentoxide in the first spinning solution of Comparative Example 18 is 0.01 g / mL.

[0171] Comparative Example 19

[0172] The preparation steps of Comparative Example 19 are basically the same as those of Example 14, except that the concentration of niobium pentoxide in the first spinning solution of Comparative Example 19 is 0.1 g / mL.

[0173] Comparative Example 20

[0174] The preparation steps of Comparative Example 20 are basically the same as those of Example 14, except that in the second spinning solution of Comparative Example 20, the concentration of the polyurethane containing dynamic disulfide bonds is 0.01 g / mL.

[0175] Comparative Example 21

[0176] The preparation steps of Comparative Example 21 are basically the same as those of Example 14, except that in the second spinning solution of Comparative Example 21, the concentration of the polyurethane containing dynamic disulfide bonds is 0.3 g / mL.

[0177] Comparative Example 22

[0178] The preparation steps of Comparative Example 22 are basically the same as those of Example 14, except that the thickness of the base layer in Comparative Example 22 is 2 μm.

[0179] Comparative Example 23

[0180] The preparation steps of Comparative Example 23 are basically the same as those of Example 14, except that the thickness of the base layer in Comparative Example 23 is 10 μm.

[0181] Comparative Example 24

[0182] The preparation steps of Comparative Example 24 are basically the same as those of Example 14, except that the thickness of the self-repairing layer in Comparative Example 24 is 1 μm.

[0183] Comparative Example 25

[0184] The preparation steps of Comparative Example 25 are basically the same as those of Example 14, except that the thickness of the self-repairing layer in Comparative Example 25 is 10 μm.

[0185] Comparative Example 26

[0186] The preparation steps of Comparative Example 26 are basically the same as those of Example 14, except that the average particle size of niobium pentoxide in Comparative Example 26 is 15 nm.

[0187] Comparative Example 27

[0188] The preparation steps of Comparative Example 27 are substantially the same as those of Example 14, except that the average particle size of niobium pentoxide in Comparative Example 27 is 40 nm.

[0189] Comparative Example 28

[0190] The preparation steps of Comparative Example 28 are basically the same as those of Example 14, except that in the process of electrospinning the second spinning solution in Comparative Example 28, the propulsion speed of the spinning needle tube is 2 mL / h.

[0191] The gram capacity, initial coulombic efficiency, energy retention, and energy recovery of the secondary batteries of Examples 1 to 24, as well as the thermal stability and contact angle of the separators of Examples 1 to 28, were obtained. The energy retention was measured after 500 cycles at a rate of 0.3C; the energy recovery was measured after 48 hours of storage at 60°C in a fully charged state; and the thermal stability was measured after 1 hour of storage at 200°C. The test results are shown in Tables 1 to 3 below.

[0192] Table 1

[0193]

[0194] Table 2

[0195]

[0196] Table 3

[0197]

[0198] By comparing Examples 1 to 13 and Comparative Examples 1 to 3, or Comparative Examples 14 to 18 and Comparative Examples 16 to 17, it is found that in the secondary battery provided in the embodiments of the present application, the diaphragm is composed of a polyimide substrate, a niobium pentoxide coating and a self-healing layer, and the surface of the self-healing layer is grafted with -SO3Li groups. The niobium pentoxide coating is utilized to improve the overall thermal stability of the diaphragm, and the higher dielectric constant and metal ion adsorption capacity of niobium pentoxide can optimize the metal ion flux distribution, inhibit the growth of lithium dendrites, and improve the first coulombic efficiency of the secondary battery. The self-healing layer reduces the volume expansion and lithium dendrite piercing risk during the cycle of the secondary battery, thereby improving the energy retention rate and energy recovery rate of the secondary battery. The surface-grafted -SO3Li groups reduce the contact angle of the diaphragm and improve the wettability of the diaphragm.

[0199] By comparing Examples 1 to 13 and Comparative Examples 4 to 15, it was found that when the concentration of polyimide, the thickness of the polyimide substrate, the average particle size of niobium pentoxide, the thickness of the niobium pentoxide coating, the mass proportion of niobium pentoxide in the niobium pentoxide coating, and the mass proportion of the polyurethane containing dynamic disulfide bonds are all within appropriate ranges, it is more conducive to the overall performance of the secondary battery.

[0200] By comparing Examples 14 to 18 and Comparative Examples 18 to 20, it was found that the relationship between the concentration of niobium pentoxide in the first spinning solution and the mass proportion of niobium pentoxide in the base layer, the relationship between the concentration of polyurethane containing dynamic disulfide bonds in the second spinning solution and the mass proportion of polyurethane containing dynamic disulfide bonds in the self-healing layer, and that when the mass proportions of niobium pentoxide and polyurethane containing dynamic disulfide bonds are within an appropriate range, it is more conducive to the comprehensive performance of the secondary battery.

[0201] By comparing Examples 19 to 24 and Comparative Examples 21 to 27, it is found that when the thickness of the base layer, the thickness of the self-repairing layer and the average particle size of niobium pentoxide are all within an appropriate range, it is more conducive to the comprehensive performance of the secondary battery.

[0202] Comparing Examples 14 to 18 and Comparative Example 28, it was found that the needle tube advancement rate when the first spinning solution was electrospun to prepare the initial base membrane was lower than the needle tube advancement rate when the second spinning solution was electrospun to prepare the initial self-repairing layer, which is beneficial for making the porosity of the base layer higher than the porosity of the self-repairing layer. The self-repairing layer has a lower porosity and a relatively high density, which is beneficial for it to effectively deal with problems such as microcracks caused by volume expansion or puncture of lithium dendrites during the cycle of the secondary battery, thereby improving the performance of the secondary battery.

[0203] Those skilled in the art will appreciate that the above-described embodiments are specific examples for implementing the present application, and that in actual applications, various changes in form and detail may be made thereto without departing from the spirit and scope of the present application. Any person skilled in the art may make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined in the claims.

Claims

1. A method for preparing a secondary battery, characterized in that: include: Prepare the diaphragm, the preparation steps comprising: A base layer is prepared, wherein the base layer comprises polyimide and niobium pentoxide, and the base layer has a fiber network structure. The steps of preparing the base layer include: preparing a polyimide base, adding polyamic acid to a solvent and ultrasonically dispersing it to obtain a spinning solution, and electrospinning the spinning solution to obtain an initial polyimide film; calcining the initial polyimide film in an inert gas to obtain the polyimide base having a fiber network structure; and preparing a niobium pentoxide coating, dispersing niobium pentoxide in a solvent, adding a dispersant and stirring to mix, applying the mixture to one side of the polyimide base via a coater, and drying to obtain the niobium pentoxide coating. The polyimide base and the niobium pentoxide coating constitute the base layer. A self-repairing layer is prepared, wherein the self-repairing layer is located on one side surface of the base layer, the material of the self-repairing layer includes a polyurethane containing a dynamic disulfide bond, and the surface of the self-repairing layer away from the base layer is grafted with a -SO3Li group; the steps of preparing the self-repairing layer include: dissolving a polyurethane prepolymer containing a dynamic disulfide bond in a solvent; applying the mixed solution to the surface of the niobium pentoxide coating away from the polyimide substrate by a casting method and then curing to form the self-repairing layer; performing plasma surface modification treatment on the self-repairing layer to make the surface of the self-repairing layer The self-repairing layer is grafted with -SO3Li groups; the step of performing plasma surface modification treatment on the self-repairing layer includes: plasma bombarding the surface of the self-repairing layer to generate hydroxyl groups and / or carboxyl groups on the surface of the self-repairing layer; dissolving lithium benzenesulfonate in deionized water, adding hydrochloric acid to adjust the pH value to 2-3; immersing the plasma-activated diaphragm in the lithium benzenesulfonate solution, and performing ultrasonic treatment to graft -SO3Li groups on the surface of the self-repairing layer; placing the diaphragm in deionized water and performing ultrasonic cleaning to remove unreacted lithium benzenesulfonate on the surface of the self-repairing layer; A positive electrode sheet and a negative electrode sheet are provided, and the positive electrode sheet, the separator and the negative electrode sheet are wound or stacked and then placed in a shell, wherein the self-repairing layer faces the negative electrode sheet and the base layer faces the positive electrode sheet, and an electrolyte is injected into the shell to obtain a secondary battery.

2. The method for preparing a secondary battery according to claim 1, wherein: In the step of preparing the base layer, the concentration of polyamic acid is 0.15 g / mL to 0.25 g / mL; In the step of preparing the niobium pentoxide coating, the mass ratio of niobium pentoxide in the niobium pentoxide coating to the mass ratio of polyimide in the polyimide substrate is (0.2-0.3):1; In the step of preparing the self-repairing layer, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the polyimide in the polyimide substrate is (0.4-0.8):

1.

3. The method for preparing a secondary battery according to claim 1, wherein: In the step of preparing the polyimide substrate, the process parameters of electrospinning include: voltage of 15kV~25kV, rotation speed of the spinning roller of 100r / min~300r / min, and propulsion speed of the spinning needle tube of 0.2mL / h~0.5mL / h; the process parameters of calcination include: temperature of 250℃~350℃, and time of 1.5h~2.5h.

4. The method for preparing a secondary battery according to claim 1, wherein: In the step of preparing the niobium pentoxide coating, the coating speed of the coating machine is 2m / min~5m / min; the drying temperature is 50℃~80℃, and the drying time is 10h~12h.

5. The method for preparing a secondary battery according to claim 1, wherein: The preparation steps of the polyurethane prepolymer containing dynamic disulfide bonds include: The polytetramethylene ether diol is vacuum dehydrated, and the polytetramethylene ether diol is reacted with hexamethylene diisocyanate at 60°C to 80°C using dibutyltin dilaurate as a catalyst for 2h to 4h. After cooling to 45°C to 55°C, cystamine, a chain extender containing a dynamic disulfide bond dissolved in tetrahydrofuran, is added and the reaction is continued for 2h to 4h to obtain a polyurethane prepolymer containing a dynamic disulfide bond.

6. The method for preparing a secondary battery according to claim 1, wherein: In the step of plasma bombarding the surface of the self-repairing layer, the gas source is a mixture of argon and oxygen with a volume ratio of 4:1; The plasma-activated membrane is immersed in a lithium benzenesulfonate solution and subjected to an ultrasonic treatment step, and reacted at 55° C. to 65° C. for 2 h to 4 h.

7. A secondary battery, characterized in that: include: A positive electrode sheet, a negative electrode sheet, and a separator, wherein the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator comprises: A base layer, wherein the base layer comprises polyimide and niobium pentoxide, the base layer has a fiber network structure, and comprises a polyimide base and a niobium pentoxide coating, wherein the niobium pentoxide coating is located on one side surface of the polyimide base; A self-repairing layer, the self-repairing layer being located on a surface of the niobium pentoxide coating away from the polyimide substrate, the material of the self-repairing layer comprising a polyurethane containing dynamic disulfide bonds, and the surface of the self-repairing layer away from the substrate layer being grafted with -SO3Li groups; The self-repairing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet.

8. The secondary battery according to claim 7, wherein: The thickness of the polyimide substrate is 8 μm to 11 μm; the thickness of the niobium pentoxide coating is 1 μm to 3 μm; and the thickness of the self-repairing layer is 1 μm to 3 μm.

9. The secondary battery according to claim 7, wherein The mass ratio of the polyimide in the polyimide substrate, the niobium pentoxide in the niobium pentoxide coating, and the polyurethane containing dynamic disulfide bonds is 1:(0.2-0.3):(0.4-0.8).

10. The secondary battery according to claim 7, wherein The average particle size of niobium pentoxide in the niobium pentoxide coating is 20 nm to 40 nm.

11. An energy storage system, characterized in that: The invention comprises a plurality of secondary batteries manufactured by the method for manufacturing a secondary battery according to any one of claims 1 to 6, or a secondary battery according to any one of claims 7 to 10.

12. An electrical device, characterized in that: The electrical equipment includes a secondary battery manufactured by the method for preparing a secondary battery according to any one of claims 1 to 6; or includes a secondary battery according to any one of claims 7 to 10; or includes the energy storage system according to claim 11.

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