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

Abstract

The invention relates to the technical field of secondary batteries, provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, and at least facilitates the improvement of the use stability of the secondary battery. The method comprises the following steps: preparing a diaphragm: preparing a substrate layer which is made of polyimide and niobium pentoxide and has a fiber network structure; a self-repairing layer is prepared, the self-repairing layer is located on the surface of one side of the substrate layer, the material of the self-repairing layer comprises polyurethane containing dynamic disulfide bonds, and the surface, away from the substrate layer, of the self-repairing layer is grafted with-SO3Li groups; a positive plate and a negative plate are provided, the positive plate, the diaphragm and the negative plate are subjected to winding treatment or lamination treatment and then put into the shell, the self-repairing layer faces the negative plate, the substrate layer faces the positive plate, and electrolyte is injected into the shell to obtain the secondary battery.

Description

Technical Field

[0001] This application relates to the technical field of secondary batteries, and particularly to a secondary battery, a preparation method thereof, an energy storage system, and an electrical device. Background Art

[0002] The main function of the separator in a secondary battery is to be placed between the positive and negative electrodes, allowing the rapid transmission of ionic charge carriers and preventing direct contact between the electrodes. Although the separator is an inactive component of the battery, the characteristics of the separator will affect the ion transport, cycle life, performance, and safety of the battery.

[0003] As an important component material that can affect the battery performance, high-performance requirements should also be put forward for the separator, that is, further improving the temperature resistance performance, enhancing ion conduction, accelerating ion migration, and improving the safety performance, etc.

[0004] Currently, there are problems such as poor wettability with the electrolyte, severe shrinkage at high temperatures, and lithium dendrite piercing in the separator, resulting in poor use stability of the secondary battery. Summary of the Invention

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

[0006] According to some embodiments of this application, on the one hand, a preparation method of a secondary battery is provided, including: preparing a separator, 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 fibrous network structure; preparing a self-healing layer, the self-healing layer is located on one surface of the base layer, the material of the self-healing layer includes polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted on the surface of the self-healing layer away from the base layer; providing a positive electrode sheet and a negative electrode sheet, winding or laminating the positive electrode sheet, the separator, and the negative electrode sheet and then putting them into a housing, wherein the self-healing layer faces the negative electrode sheet, the base layer faces the positive electrode sheet, and injecting an electrolyte into the housing to obtain a secondary battery.

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

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

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

[0010] In some embodiments, the steps of preparing the polyurethane prepolymer containing dynamic disulfide bonds include: performing vacuum dehydration on polytetrahydrofuran ether glycol, reacting polytetrahydrofuran 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, and then adding cystamine, a chain extender containing dynamic disulfide bonds dissolved in tetrahydrofuran, and continuing to react for 2 h to 4 h to obtain the 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 into a solvent to obtain a first spinning solution, where the concentration of polyamic acid is 0.15 g / mL to 0.25 g / mL, and the concentration of niobium pentoxide is 0.015 g / mL to 0.05 g / mL, and subjecting the first spinning solution to electrospinning to obtain an initial base membrane; adding polyamic acid and polyurethane containing dynamic disulfide bonds into a solvent to obtain a second spinning solution, where the concentration of polyamic acid is 0.1 g / mL to 0.25 g / mL, and the concentration of polyurethane is 0.04 g / mL to 0.16 g / mL, and subjecting the second spinning solution to 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 for calcination to convert the initial base membrane into a base layer and convert the initial self-healing layer into a self-healing layer; performing plasma surface modification treatment on the self-healing layer to graft -SO3Li groups onto the surface of the self-healing layer.

[0012] In some embodiments, the steps of performing plasma surface modification treatment on the self-healing layer include: ultrasonically cleaning the self-healing layer successively with ethanol and deionized water; performing plasma bombardment on the surface of the self-healing layer, with the gas source being a mixed gas of argon and oxygen with a volume ratio of 4:1, to generate hydroxyl groups and / or carboxyl groups on the surface of the self-healing layer; dissolving lithium benzenesulfonate in deionized water, adding hydrochloric acid to adjust the pH value to 2 to 3; immersing the plasma-activated diaphragm in the lithium benzenesulfonate solution, performing ultrasonic treatment, and reacting at 55°C to 65°C for 2 h to 4 h to graft -SO3Li groups onto the surface of the self-healing layer; placing the diaphragm in deionized water for ultrasonic cleaning to remove the unreacted lithium benzenesulfonate on the surface of the self-healing layer.

[0013] According to some embodiments of the present application, on the other hand, the present application embodiments also provide a secondary battery, including: a positive electrode sheet, a negative electrode sheet, and a separator, where the separator is located between the positive electrode sheet and the negative electrode sheet, and the separator includes: a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fibrous network structure; a self-healing layer, the self-healing layer is located on one surface of the base layer, the material of the self-healing layer includes polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted onto the surface of the self-healing layer away from the base layer; wherein, the self-healing 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 the 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; the thickness of the self-healing layer is 1 μm to 3 μm.

[0016] In some embodiments, the mass ratio of polyimide in the polyimide substrate, niobium pentoxide in the niobium pentoxide coating, and 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 fibrous network structure in the base layer is composed of polyimide, and niobium pentoxide is dispersed in the fibrous network structure; the self-repair layer has a fibrous network structure, and the fibrous network structure of the self-repair layer is composed of polyimide and polyurethane containing dynamic disulfide bonds.

[0019] According to some embodiments of the present application, on the other hand, the present application embodiments further provide an energy storage system, including a plurality of secondary batteries manufactured by using the manufacturing method of the secondary battery in the above embodiments, or the secondary battery in the above embodiments.

[0020] According to some embodiments of the present application, on yet another aspect, the present application embodiments further provide an electrical device, which includes a secondary battery manufactured by using the manufacturing method of the secondary battery in the above embodiments; or includes the secondary battery in the above embodiments; or includes the energy storage system in the above embodiments.

[0021] The technical solution provided by the embodiments of the present application has at least the following advantages: The preparation method of the secondary battery provided by the embodiment of the present application, in the step of preparing the separator, first prepare a base layer including polyimide and niobium pentoxide, and the base layer has a fibrous network structure, and then prepare a self-healing layer including polyurethane containing dynamic disulfide bonds on one surface of the base layer, and a -SO3Li group is grafted on the surface of the self-healing layer away from the base layer; in the step of preparing the secondary battery, the self-healing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet. The fibrous network structure of the base layer is beneficial to the base layer having good mechanical strength and porosity, which is beneficial to increasing the lithium dendrite piercing resistance of the separator and promoting the infiltration of the electrolyte, and reducing the interfacial impedance. 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, niobium pentoxide has high thermal stability, which is beneficial to improving the high temperature resistance of the separator and reducing the risk of thermal runaway. The polyurethane containing dynamic disulfide bonds in the self-healing layer can achieve self-healing of damage through S-S bond cleavage / recombination to effectively deal with the microcracks caused by volume expansion or the piercing of lithium dendrites during the cycling process 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 transport channel, and at the same time is beneficial to the formation of a negative charge repulsion layer to guide the uniform deposition of metal ions through electrostatic interaction. The self-healing layer faces the negative electrode sheet, preferentially repairing the damage of the negative electrode sheet, which is beneficial to matching the volume change of the negative electrode sheet; the base layer faces the positive electrode sheet, and the antioxidant property of polyimide is used to protect the separator from the erosion of high-valent metal ions in the positive electrode sheet, and the cycle life of the secondary battery is extended. Description of the Drawings

[0022] One or more embodiments are exemplarily illustrated by the pictures in the corresponding drawings. These exemplary illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation; in order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required to be used in the embodiments. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0023] Figure 1 It is a flowchart corresponding to a preparation method of a secondary battery provided by an embodiment of the present application; Figure 2 It is a flowchart corresponding to the first preparation method of the separator provided by an embodiment of the present application; Figure 3 It is a flowchart corresponding to the second preparation method of the separator provided by an embodiment of the present application; Figure 4 is Figure 2 A schematic structural diagram of the separator prepared by the shown preparation method; Figure 5 For Figure 3 The structural schematic diagram of the separator prepared by the described preparation method.

[0024] Explanation of the reference numerals in the drawings: The first example: 101, base layer; 102, self-healing layer; 111, polyimide substrate; 121, niobium pentoxide coating.

[0025] The second example: 201, base layer; 202, self-healing layer. Detailed implementation manners

[0026] As can be seen from the background art, there are problems with the separator such as poor wettability with the electrolyte, severe shrinkage at high temperatures, and lithium dendrite piercing, resulting in poor use stability of secondary batteries.

[0027] The preparation process of the separator mainly includes dry method and wet method. In the dry method, the polymer is melted and extruded into a film, and micropores are formed by unidirectional or bidirectional stretching. However, the separator prepared by this method has a low porosity, poor liquid absorption rate and ionic conductivity. In the wet method, the polymer is mixed and melted with a liquid hydrocarbon (such as paraffin oil) and then extruded and cast to form a polymer / solvent bicontinuous structure. After stretching, the solvent is extracted to leave a porous structure. The separator prepared by this method has a high porosity, but the solvent residue may affect the performance of secondary batteries.

[0028] Generally, the methods for modifying the separator mainly include coating, radiation grafting, blending, etc. Among them, coating modification is one of the simplest and most effective methods. Inorganic coating uses ceramic particles such as alumina and boehmite to modify the polymer separator to improve the wettability and dimensional stability of the separator. However, the adhesion between the ceramic particles and the base film is poor and they are easy to fall off, resulting in a decrease in the cycle life. In addition, the ceramic particles will significantly increase the mass of the separator, resulting in a decrease in the energy density. Organic coating mostly uses polymers such as aramid and polyvinylidene fluoride. These materials have strong adhesion and can enhance the cycle life of the battery, but their improvement of the battery capacity and cycle stability is not significant, and it is also difficult to enhance the dimensional stability and mechanical properties.

[0029] The embodiments of the present application provide a secondary battery, its preparation method, an energy storage system, and an electrical device, which are at least beneficial to improving the use stability of the secondary battery.

[0030] In the description of the embodiments of the present application, the meaning of "a plurality" is more than two, unless otherwise specifically defined.

[0031] Reference to "embodiment" in this document means that the specific features, structures, or characteristics described in connection with the embodiment may be included in at least one embodiment of the present application. The phrase appears in various places in the specification and does not necessarily refer to the same embodiment each time, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0032] In the description of the embodiments of the present application, the term "and / or" is merely a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: there is A, there is both A and B at the same time, and there is B, these three situations. In addition, the character " / " in this document generally indicates that the associated objects before and after are in an "or" relationship.

[0033] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise specified, other components are not excluded, and other components may further be included.

[0034] The terms used in the description of the various embodiments herein are only for describing specific embodiments and are not intended to be limiting. As used in the description of the various embodiments and the appended claims, "component" is also intended to include the plural form unless the context clearly indicates otherwise.

[0035] The embodiments of the present application will be described in detail below in conjunction with the accompanying drawings. However, those of ordinary skill in the art can understand that in the embodiments of the present application, many technical details are provided to help readers better understand the present application. However, even without these technical details and various changes and modifications based on the following embodiments, the technical solutions claimed in the present application can still be implemented.

[0036] Figure 1 A flowchart corresponding to a method for preparing a secondary battery provided in an embodiment of the present application.

[0037] Reference Figure 1 , an embodiment of the present application provides a method for preparing a secondary battery, including: Prepare a separator, and the preparation steps include: prepare a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fibrous network structure; prepare a self-healing layer, the self-healing layer is located on one surface of the base layer, the material of the self-healing layer includes polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted on the surface of the self-healing layer away from the base layer.

[0038] A positive electrode sheet and a negative electrode sheet are provided. After the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated and then placed into a casing, 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 casing to obtain a secondary battery.

[0039] In the method for preparing a secondary battery provided by an embodiment of the present application, in the step of preparing the separator, a base layer including polyimide and niobium pentoxide is first prepared, and the base layer has a fibrous network structure. Then, a self-repairing layer including polyurethane containing dynamic disulfide bonds is prepared on one surface of the base layer, and -SO3Li groups are grafted on the surface of the self-repairing layer away from the base layer. In the step of preparing the secondary battery, the self-repairing layer faces the negative electrode sheet and the base layer faces the positive electrode sheet. The fibrous network structure of the base layer is beneficial for the base layer to have good mechanical strength and porosity, which is beneficial for increasing the ability of the separator to resist lithium dendrite piercing and can also promote the infiltration of the electrolyte and reduce the interfacial impedance. Niobium pentoxide in the base layer has a high dielectric constant and metal ion adsorption ability, 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 for improving the high-temperature resistance performance of the separator and reducing the risk of thermal runaway. The polyurethane containing dynamic disulfide bonds in the self-repairing layer can achieve self-repair of damage through S-S bond breakage / recombination to effectively cope with the microcracks caused by volume expansion or the piercing of lithium dendrites during the cycling process of the secondary battery. The -SO3Li groups grafted on the surface of the self-repairing layer away from the base layer can provide a uniform metal ion transport channel and are also beneficial for forming a negative charge repulsion layer to guide the uniform deposition of metal ions through electrostatic interaction. The self-repairing layer faces the negative electrode sheet to preferentially repair the damage of the negative electrode sheet, which is beneficial for matching the volume change of the negative electrode sheet; the base layer faces the positive electrode sheet, and the antioxidant property of polyimide is used to protect the separator from being eroded by the high-valent metal ions in the positive electrode sheet and extend the cycle life of the secondary battery.

[0040] The secondary battery can be a lithium battery, a lead-acid battery, a sodium battery, or a nickel-metal hydride battery. In the embodiment of the present application, the preparation method of a lithium-ion battery will be taken 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, for a sodium battery, the lithium transition metal oxide of the positive electrode active material in the following can be replaced with any one of the corresponding layered metal oxides (such as NaFeO2), polyanion compounds (NaFePO4), and Prussian blue compound systems (such as NaMnFe(CN)6-zH2O), and the electrolyte can be replaced with any one of an organic liquid electrolyte, a solid composite electrolyte, or a solid electrolyte.

[0041] The positive electrode sheet can be made by uniformly applying a paste adhesive, which is prepared by mixing a positive electrode active material, a binder, and an additive, on both sides of an aluminum foil, followed by drying and rolling. The positive electrode active material includes lithium cobaltate, lithium manganate, lithium iron phosphate, or ternary materials.

[0042] The negative electrode sheet can be made by uniformly applying a paste adhesive, which is prepared by mixing a negative electrode active material, a binder, and an additive, on both sides of a copper foil, followed by drying and rolling. The negative electrode active material includes carbon negative electrode materials, tin-based negative electrode materials, lithium-containing transition metal nitride negative electrode materials, alloy-based negative electrode materials, or nanoscale negative electrode materials.

[0043] Figure 2 and Figure 3 are flowcharts corresponding to the preparation methods of two kinds of separators provided by the embodiments of the present application. Figure 4 and Figure 5 are schematic structural diagrams of two kinds of separators provided by the embodiments of the present application. Among them, Figure 4 the separator shown is made by Figure 2 the preparation method shown, Figure 5 the separator shown is made by Figure 3 the preparation method shown. The following will elaborate on each embodiment of the present application in conjunction with the accompanying drawings.

[0044] In the first example, referring to Figure 2 and Figure 4 , the steps for preparing the base layer 101 include: preparing a polyimide substrate 111 and forming a niobium pentoxide coating 121 on the polyimide substrate 111. The polyimide substrate 111 and the niobium pentoxide coating 121 together constitute the base layer 101; the prepared self-repair layer 102 is located on the surface of the niobium pentoxide coating 121 away from the polyimide substrate 111.

[0045] The steps for preparing the polyimide substrate 111 include: adding polyamic acid to a solvent (such as dimethylacetamide) and performing ultrasonic dispersion to obtain a spinning solution. The concentration of the polyamic acid is 0.15 g / mL to 0.25 g / mL, for example, specifically it can be 0.15 g / mL, 0.18 g / mL, 0.2 g / mL, 0.23 g / mL, or 0.25 g / mL; performing electrospinning on the spinning solution to obtain an initial polyimide film; calcining the initial polyimide film in an inert gas (such as nitrogen) to obtain a polyimide substrate 111 with a fibrous network structure.

[0046] Among them, the process parameters of electrospinning include: the voltage is 15 kV to 25 kV, the rotation speed of the spinning roller is 100 r / min to 300 r / min, and the advancing speed of the spinning needle tube is 0.2 mL / h to 0.5 mL / h. The process parameters of calcination include: the temperature is 250 °C to 350 °C, and the time is 1.5 h to 2.5 h. The process parameters of electrospinning within the above ranges are beneficial to the uniform and continuous thickness of the fibrous network structure of the polyimide substrate, and thus are beneficial to forming a polyimide substrate with stable mechanical strength and uniform pores. The key to calcination after electrospinning lies in controlling the calcination temperature and time. The calcination temperature and time within the above ranges are beneficial to ensuring the integrity of the fibrous network structure while removing organic components.

[0047] The average molecular weight of the polyimide can be 50,000 g / mol to 100,000 g / mol. For example, specifically, it can be 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.

[0048] The steps for preparing the niobium pentoxide coating 121 include: dispersing niobium pentoxide in a solvent (such as ethanol), adding a dispersant (such as 3-aminopropyltriethoxysilane) and stirring and mixing. After coating the mixture on one side surface of the polyimide substrate 111 by a coater and drying, the niobium pentoxide coating 121 is obtained. The mass ratio of niobium pentoxide in the niobium pentoxide coating 121 to the mass of polyimide in the polyimide substrate 111 is (0.2 to 0.3):1.

[0049] Among them, the coating speed of the coater 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.

[0050] The steps for preparing the self-healing layer 102 include: dissolving a polyurethane prepolymer containing dynamic disulfide bonds in a solvent (such as tetrahydrofuran). The mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the mass of polyimide in the polyimide substrate 111 is (0.4 to 0.8):1; using the casting method to coat the mixed solution on the surface of the niobium pentoxide coating 121 away from the polyimide substrate 111 and then curing to form the self-healing layer 102; performing 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.

[0051] Among them, the preparation steps of the polyurethane prepolymer containing dynamic disulfide bonds include: vacuum dehydrating polytetrahydrofuran ether glycol, reacting polytetrahydrofuran ether glycol with hexamethylene diisocyanate at 60°C to 80°C for 2 h to 4 h using dibutyltin dilaurate as a catalyst, cooling to 45°C to 55°C, and then adding cystamine, a chain extender containing dynamic disulfide bonds dissolved in tetrahydrofuran, and continuing the reaction for 2 h to 4 h to obtain a polyurethane prepolymer containing dynamic disulfide bonds.

[0052] Polytetrahydrofuran ether glycol serves as the soft segment of the polyurethane prepolymer, and hexamethylene diisocyanate serves as the hard segment of the polyurethane prepolymer. The mass ratio of the soft segment in the polyurethane prepolymer is 30% to 50%, and the mass ratio of the hard segment in the polyurethane prepolymer is 50% to 70%. For example, the mass ratio of polytetrahydrofuran ether glycol in the polyurethane prepolymer is 30%, and the mass ratio of hexamethylene diisocyanate in the polyurethane prepolymer is 70%; or, the mass ratio of polytetrahydrofuran ether glycol in the polyurethane prepolymer is 40%, and the mass ratio of hexamethylene diisocyanate in the polyurethane prepolymer is 60%; or, the mass ratio of polytetrahydrofuran ether glycol in the polyurethane prepolymer is 50%, and the mass ratio of hexamethylene diisocyanate in the polyurethane prepolymer is 50%. The hard segment is used to increase the hardness and strength of the polyurethane, and the soft segment is used to increase the flexibility and elasticity of the polyurethane. The ratio of the hard segment to the soft segment within the above range can help the polyurethane have both good mechanical strength and flexibility.

[0053] In the preparation method of the first separator provided in the embodiments of the present application, after preparing the polyimide substrate 111 by the electrospinning process, a niobium pentoxide coating 121 is formed by the coating method. The polyimide substrate 111 and the niobium pentoxide coating 121 together constitute the base layer 101. The composite base layer 101 can utilize the fibrous network structure of the polyimide substrate 111 to provide good mechanical strength and electrolyte absorption rate, and can 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 the casting method. The self-healing layer 102 is composed of a polyurethane containing dynamic disulfide bonds. The polyurethane containing dynamic disulfide bonds can achieve self-healing of damage through the cleavage / recombination of S-S bonds; plasma grafting -SO3Li groups to construct an ion channel, reduce the interfacial impedance, and at the same time improve the electrolyte affinity on the surface of the self-healing layer 102, which is beneficial to improving the wettability.

[0054] In the second example, refer to Figure 3 and Figure 5 Both the base layer 201 and the self-healing layer 202 are prepared by the electrospinning process.

[0055] Specifically, the steps for preparing the base layer 201 and the self-healing layer 202 include: adding polyamic acid and niobium pentoxide into a solvent (such as dimethylacetamide) to obtain a first spinning solution. The concentration of polyamic acid is 0.15 g / mL to 0.25 g / mL (for example, specifically it can be 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 niobium pentoxide is 0.015 g / mL to 0.05 g / mL (for example, specifically it can be 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 base film; adding polyamic acid and a polyurethane containing dynamic disulfide bonds into a solvent (such as dimethylacetamide) to obtain a second spinning solution. The concentration of polyamic acid is 0.1 g / mL to 0.25 g / mL (for example, specifically it can be 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 it can be 0.04 g / mL, 0.08 g / mL, 0.1 g / mL, 0.13 g / mL or 0.16 g / mL); electrospinning the second spinning solution to form an initial self-healing layer on the surface of the initial base film; placing the initial base film and the initial self-healing layer in an inert gas for calcination to convert the initial base film into the base layer 201 and convert the initial self-healing layer into the self-healing layer 202; performing a plasma surface modification treatment on the self-healing layer 202 so that the surface of the self-healing layer 202 is grafted with -SO3Li groups.

[0056] 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, specifically it can be 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.

[0057] Among them, the process parameters for electrospinning the first spinning solution include: the voltage is 15 kV to 25 kV, the rotation speed of the spinning roller is 100 r / min to 300 r / min, and the advancing speed of the spinning needle tube is 3 mL / h to 8 mL / h. The process parameters for electrospinning the second spinning solution include: the voltage is 15 kV to 25 kV, the rotation speed of the spinning roller is 100 r / min to 300 r / min, and the advancing speed of the spinning needle tube is 5 mL / h to 10 mL / h. The needle tube advancing rate when electrospinning the first spinning solution to prepare the initial base film is less than the needle tube advancing rate when electrospinning the second spinning solution to prepare the initial self-healing layer, which is beneficial to making the porosity of the base layer higher than that of the self-healing layer. The porosity of the self-healing layer is relatively low and the density is relatively high, which is beneficial to effectively dealing with problems such as microcracks caused by volume expansion during the cycling of secondary batteries or the piercing of lithium dendrites.

[0058] After preparing the base layer 201 and the self-healing layer 202, it may further include: forming a niobium pentoxide coating (not shown in the figure) 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. Among them, the steps of forming the niobium pentoxide coating include: dispersing niobium pentoxide in a solvent (such as ethanol), adding a dispersant (such as 3-aminopropyltriethoxysilane) and stirring and mixing, and drying after coating the mixture 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 by a coater.

[0059] Among them, the coating speed of the coater 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.

[0060] In the preparation method of the second separator provided by the embodiments of the present application, a polyamic acid and niobium pentoxide are configured into a first spinning solution, and then electrospinning is carried out to obtain an initial base film. Also, the polyamic acid and a polyurethane containing dynamic disulfide bonds are configured into a second spinning solution, and then electrospinning is carried out to obtain an initial self-healing layer. Then, the initial base film and the initial self-healing layer are placed together in an inert gas for calcination to obtain a base layer 201 and a self-healing layer 202. Then, the surface of the self-healing layer 202 is modified to graft -SO3Li groups. In this way, both the base layer 201 and the self-healing layer 202 have a fibrous network structure, which is beneficial to improving the overall mechanical strength and porosity of the separator, promoting the infiltration of the electrolyte, and reducing the interfacial impedance. In the base layer 201, the niobium pentoxide coating 121 is used to enhance the ion conductivity and high-voltage resistance; in the self-healing layer 102, the polyurethane containing dynamic disulfide bonds can achieve self-healing of damage through the breakage / recombination of S-S bonds; plasma grafting of -SO3Li groups constructs ion channels, reduces the interfacial impedance, and at the same time improves the electrolyte affinity on the surface of the self-healing layer 102, which is beneficial to improving the wettability. In addition, both the base layer 201 and the self-healing layer 202 are prepared by the electrospinning process, which is beneficial to improving the preparation efficiency of the separator.

[0061] Reference Figure 2 and Figure 3 In the preparation methods of the above two separators, the steps of performing plasma surface modification treatment on the self-healing layer include: sequentially ultrasonically cleaning the self-healing layer with ethanol and deionized water; bombarding the surface of the self-healing layer with plasma, and the gas source is a mixed gas 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-healing layer; dissolving lithium benzenesulfonate in deionized water, and adding hydrochloric acid to adjust the pH value to 2-3; immersing the plasma-activated separator in the lithium benzenesulfonate solution, performing ultrasonic treatment, and reacting at 55°C - 65°C for 2h - 4h, so that -SO3Li groups are grafted onto the surface of the self-healing layer; placing the separator in deionized water for ultrasonic cleaning to remove the unreacted lithium benzenesulfonate on the surface of the self-healing layer.

[0062] Correspondingly, another embodiment of the present application further provides a secondary battery, which can be prepared by using the manufacturing method of the secondary battery provided by the above embodiments. The secondary battery provided by another embodiment of the present application will be described in detail below with reference to the accompanying drawings. For the same or corresponding parts as those in the previous embodiment, reference can be made to the corresponding description of the previous embodiment, and details will not be repeated below.

[0063] The secondary battery provided by the embodiment of the present application includes a positive electrode sheet, a negative electrode sheet, and a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet. The separator includes a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fibrous network structure; a self-healing layer, the self-healing layer is located on one surface of the base layer, the material of the self-healing layer includes polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted on the surface of the self-healing layer away from the base layer; wherein, the self-healing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet.

[0064] In the secondary battery provided by the embodiment of the present application, the separator includes a base layer and a self-healing layer. The base layer includes polyimide and niobium pentoxide, and the base layer has a fibrous 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 separator and reducing the risk of thermal runaway; the fibrous network structure is beneficial to the base layer having good mechanical strength and porosity, which is not only beneficial to increasing the anti-lithium dendrite piercing ability of the separator, but also can promote the infiltration of the electrolyte and reduce the interfacial impedance. The polyurethane containing dynamic disulfide bonds in the self-healing layer can achieve self-healing of damage through the cleavage / recombination of S-S bonds to effectively cope with the microcracks caused by volume expansion or the piercing of lithium dendrites during the cycling process of the secondary battery; the -SO3Li groups grafted on the surface of the self-healing layer away from the base layer can provide a uniform metal ion transport channel, and at the same time is beneficial to the formation of a negative charge repulsion layer to guide the uniform deposition of metal ions through electrostatic interaction. The self-healing layer faces the negative electrode sheet and preferentially repairs the damage of the negative electrode sheet, which is beneficial to matching the volume change of the negative electrode sheet; the base layer faces the positive electrode sheet, and the antioxidant property of polyimide is used to protect the separator from the erosion of high-valent metal ions in the positive electrode sheet and extend the cycle life of the secondary battery.

[0065] In one example, referring to Figure 3 , the base layer 101 includes a polyimide substrate 111 and a niobium pentoxide coating 121. The niobium pentoxide coating 121 is located on one surface of the polyimide substrate 111, and the self-healing layer 102 is located on the surface of the niobium pentoxide coating 121 away from the polyimide substrate 111.

[0066] Referring to Figure 3 , the thickness of the polyimide substrate 111 is 8 μm to 11 μm, for example, specifically it can be 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, specifically it can be 1 μm, 2 μm or 3 μm. The thickness of the self-healing layer 102 is 1 μm to 3 μm, for example, specifically it can be 1 μm, 2 μm or 3 μm.

[0067] Referring to Figure 3, the mass ratio of polyimide in the polyimide substrate 111, 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).

[0068] Reference Figure 3 , the average particle size of niobium pentoxide in the niobium pentoxide coating 121 is 20 nm - 40 nm, for example, specifically it can be 20 nm, 25 nm, 30 nm, 35 nm or 40 nm.

[0069] In another example, reference Figure 5 , the fibrous network structure in the base layer 201 is composed of polyimide, and niobium pentoxide is dispersed in the fibrous network structure; the self - repairing layer 202 has a fibrous network structure, and the fibrous network structure of the self - repairing layer 202 is composed of polyimide and polyurethane containing dynamic disulfide bonds.

[0070] Reference Figure 5 , in the base layer 201, the mass ratio of polyimide to niobium pentoxide is 1: (0.1 - 0.2). In the self - repairing layer 202, the mass ratio of polyimide to the polyurethane containing dynamic disulfide bonds is 1: (0.4 - 0.5).

[0071] Reference Figure 5 , the thickness of the base layer 201 is 5 μm - 7 μm, for example, specifically it can be 5 μm, 5.5 μm, 6 μm, 6.5 μm or 7 μm. The thickness of the self - repairing layer 202 is 3 μm - 5 μm, for example, specifically it can be 3 μm, 3.5 μm, 4 μm, 4.5 μm or 5 μm.

[0072] Reference Figure 5 , the average particle size of niobium pentoxide in the base layer 201 is 18 nm - 35 nm, for example, specifically it can be 18 nm, 20 nm, 23 nm, 25 nm, 28 nm, 30 nm, 33 nm or 35 nm.

[0073] Correspondingly, on the other hand, an embodiment of the present application further provides an energy storage system, including a plurality of secondary batteries manufactured by using the manufacturing method of the secondary battery in the above - mentioned embodiment, or the secondary battery in the above - mentioned embodiment.

[0074] Correspondingly, on yet another aspect, an embodiment of the present application further provides an electrical device, which includes a secondary battery manufactured by using the manufacturing method of the secondary battery in the above - mentioned embodiment; or includes the secondary battery in the above - mentioned embodiment; or includes the energy storage system in the above - mentioned embodiment.

[0075] The following are specific embodiments of the present application.

[0076] Example 1 S11. Prepare a separator, and the preparation steps are as follows.

[0077] S111. Prepare a polyimide substrate: Add 20 g of polyamic acid to dimethylacetamide and perform ultrasonic dispersion to obtain a spinning solution. The concentration of polyamic acid is 0.2 g / mL. Electrospin the spinning solution to obtain an initial polyimide film. The process parameters of electrospinning are: voltage is 20 kV, the rotation speed of the spinning roller is 200 r / min, and the advancing speed of the spinning tube is 0.3 mL / h. Place the initial polyimide film in nitrogen for calcination to obtain a polyimide substrate with a fibrous network structure (thickness is 10 μm). The process parameters of calcination are: temperature is 300 °C, and time is 2 h.

[0078] S112. Prepare a niobium pentoxide coating. Disperse niobium pentoxide (average particle size is 30 nm) in ethanol, add 3-aminopropyltriethoxysilane and stir to mix. Coating the mixture on one side surface of the polyimide substrate by a coater and then drying to obtain a niobium pentoxide coating (thickness is 2 μm). The mass ratio 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 form a base layer. The coating speed is 3 m / min, the drying temperature is 80 °C, and the drying time is 12 h.

[0079] S113. Prepare a self-healing layer: Dissolve a polyurethane prepolymer containing dynamic disulfide bonds in tetrahydrofuran. The mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the mass of polyimide in the polyimide substrate is 0.6:1. Use the casting method to coat the mixed solution on the surface of the niobium pentoxide coating away from the polyimide substrate and then cure at room temperature for 24 h to form a self-healing layer. Perform plasma surface modification treatment on the self-healing layer so that the surface of the self-healing layer is grafted with -SO3Li groups.

[0080] S12. Provide a positive electrode plate and a negative electrode plate. Wind the positive electrode plate, the separator, and the negative electrode plate and then place them in a housing. Among them, the self-healing layer faces the negative electrode plate, and the base layer faces the positive electrode plate. Inject electrolyte into the housing to obtain a secondary battery.

[0081] Example 2 The preparation steps of Example 2 are basically the same as those of Example 1, except that in step S111, the concentration of polyimide is 0.15 g / mL.

[0082] Example 3 The preparation steps of Example 3 are basically the same as those of Example 1, except that in step S111, the concentration of polyimide is 0.25 g / mL.

[0083] Example 4 The preparation steps of Example 4 are basically the same as those of Example 1, except that in step S111, the thickness of the polyimide substrate is 8 μm.

[0084] Example 5 The preparation steps of Example 5 are basically the same as those of Example 1, except that in step S111, the thickness of the polyimide substrate is 11 μm.

[0085] Example 6 The preparation steps of Example 6 are basically the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 20 nm.

[0086] Example 7 The preparation steps of Example 7 are basically the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 40 nm.

[0087] Example 8 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.

[0088] Example 9 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.

[0089] Example 10 The preparation steps of Example 10 are basically 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 of polyimide in the polyimide substrate is 0.2:1.

[0090] Example 11 The preparation steps of Example 11 are basically 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 of polyimide in the polyimide substrate is 0.3:1.

[0091] Example 12 The preparation steps of Example 12 are basically 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 mass of polyimide in the polyimide substrate is 0.4:1.

[0092] Example 13 The preparation steps of Example 13 are basically 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 mass of polyimide in the polyimide substrate is 0.8:1.

[0093] Example 14 Example 14 is different from Example 1 in that the steps for preparing the separator in step S11 are different. The steps for preparing the separator 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 substrate film. The voltage for electrospinning is 20 kV, the rotation speed of the spinning roller is 200 r / min, and the feeding speed of the spinning needle tube is 5 mL / h. Polyamic acid and 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 concentration of 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 substrate film. The voltage for electrospinning is 20 kV, the rotation speed of the spinning roller is 200 r / min, and the feeding speed of the spinning needle tube is 8 mL / h. The initial substrate film and the initial self-healing layer are calcined in an inert gas to convert the initial substrate film into a base layer (with a thickness of 6 μm) and the initial self-healing layer into a self-healing layer (with a thickness of 4 μm). The self-healing layer is subjected to plasma surface modification treatment so that -SO3Li groups are grafted onto the surface of the self-healing layer.

[0094] Example 15 The preparation steps of Example 15 are basically the same as those of Example 14, except that in the first spinning solution of Example 15, the concentration of niobium pentoxide is 0.02 g / mL.

[0095] Example 16 The preparation steps of Example 16 are basically the same as those of Example 14, except that in the first spinning solution of Example 16, the concentration of niobium pentoxide is 0.04 g / mL.

[0096] Example 17 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 polyurethane containing dynamic disulfide bonds is 0.04 g / mL.

[0097] Example 18 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 polyurethane containing dynamic disulfide bonds is 0.16 g / mL.

[0098] Example 19 The preparation steps of Example 19 are basically the same as those of Example 14, except that in Example 19, the thickness of the base layer is 5 μm.

[0099] Example 20 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.

[0100] Example 21 The preparation steps of Example 21 are basically the same as those of Example 14, except that the thickness of the self-healing layer in Example 21 is 3 μm.

[0101] Example 22 The preparation steps of Example 22 are basically the same as those of Example 14, except that the thickness of the self-healing layer in Example 22 is 5 μm.

[0102] Example 23 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.

[0103] Example 24 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.

[0104] Comparative Example 1 The preparation steps of Comparative Example 1 are basically the same as those of Example 1. The difference is that in step S11, steps S112 and S113 are removed, and the separator is composed of a polyimide substrate.

[0105] Comparative Example 2 The preparation steps of Comparative Example 2 are basically the same as those of Example 1. The difference is that in step S11, step S113 is removed, and the separator is composed of a polyimide substrate and a niobium pentoxide coating.

[0106] Comparative Example 3 The preparation steps of Comparative Example 3 are basically the same as those of Example 1. The difference is that in S113, after the self-healing layer is prepared, no surface modification treatment is carried out. The separator is composed of a polyimide substrate, a niobium pentoxide coating and a self-healing layer, and no -SO3Li group is grafted on the surface of the self-healing layer.

[0107] Comparative Example 4 The preparation steps of Comparative Example 4 are basically the same as those of Example 1. The difference is that in step S111, the concentration of polyamic acid is 0.05 g / mL.

[0108] Comparative Example 5 The preparation steps of Comparative Example 5 are basically the same as those of Example 1. The difference is that in step S111, the concentration of polyamic acid is 0.5 g / mL.

[0109] Comparative Example 6 The preparation steps of Comparative Example 6 are basically the same as those of Example 1, except that in step S111, the thickness of the polyimide substrate is 5 μm.

[0110] Comparative Example 7 The preparation steps of Comparative Example 7 are basically the same as those of Example 1, except that in step S111, the thickness of the polyimide substrate is 15 μm.

[0111] Comparative Example 8 The preparation steps of Comparative Example 8 are basically the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 10 nm.

[0112] Comparative Example 9 The preparation steps of Comparative Example 9 are basically the same as those of Example 1, except that in step S112, the average particle size of niobium pentoxide is 80 nm.

[0113] Comparative Example 10 The preparation steps of Comparative Example 10 are basically the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 0.5 μm.

[0114] Comparative Example 11 The preparation steps of Comparative Example 11 are basically the same as those of Example 1, except that in step S112, the thickness of the niobium pentoxide coating is 6 μm.

[0115] Comparative Example 12 The preparation steps of Comparative Example 12 are basically 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 0.05:1.

[0116] Comparative Example 13 The preparation steps of Comparative Example 13 are basically 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 0.5:1.

[0117] Comparative Example 14 The preparation steps of Comparative Example 14 are basically the same as those of Example 1, except that in step S113, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to polyimide in the polyimide substrate is 0.1:1.

[0118] Comparative Example 15 The preparation steps of Comparative Example 15 are basically the same as those of Example 1, except that in step S113, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to polyimide in the polyimide substrate is 2:1.

[0119] Comparative Example 16 The preparation steps of Comparative Example 16 are basically the same as those of Example 14, except that in the step of preparing the separator, the self-healing layer is not prepared, and the separator is a base layer composed of polyimide and niobium pentoxide.

[0120] Comparative Example 17 The preparation steps of Comparative Example 17 are basically the same as those of Example 14, except that in the step of preparing the separator, the base layer is not prepared, and the separator is a self-healing layer composed of polyurethane containing dynamic disulfide bonds, and the surface of the self-healing layer is not grafted with -SO3Li groups.

[0121] Comparative Example 18 The preparation steps of Comparative Example 18 are basically the same as those of Example 14, except that in the first spinning solution of Comparative Example 18, the concentration of niobium pentoxide is 0.01 g / mL.

[0122] Comparative Example 19 The preparation steps of Comparative Example 19 are basically the same as those of Example 14, except that in the first spinning solution of Comparative Example 19, the concentration of niobium pentoxide is 0.1 g / mL.

[0123] Comparative Example 20 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 polyurethane containing dynamic disulfide bonds is 0.01 g / mL.

[0124] Comparative Example 21 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 polyurethane containing dynamic disulfide bonds is 0.3 g / mL.

[0125] Comparative Example 22 The preparation steps of Comparative Example 22 are basically the same as those of Example 14, except that in Comparative Example 22, the thickness of the base layer is 2 μm.

[0126] Comparative Example 23 The preparation steps of Comparative Example 23 are basically the same as those of Example 14, except that in Comparative Example 23, the thickness of the base layer is 10 μm.

[0127] Comparative Example 24 The preparation steps of Comparative Example 24 are basically the same as those of Example 14, except that in Comparative Example 24, the thickness of the self-healing layer is 1 μm.

[0128] Comparative Example 25 The preparation steps of Comparative Example 25 are basically the same as those of Example 14, except that in Comparative Example 25, the thickness of the self-healing layer is 10 μm.

[0129] Comparative Example 26 The preparation steps of Comparative Example 26 were basically the same as those of Example 14, except that the average particle size of niobium pentoxide in Comparative Example 26 was 15 nm.

[0130] Comparative Example 27 The preparation steps of Comparative Example 27 were basically the same as those of Example 14, except that the average particle size of niobium pentoxide in Comparative Example 27 was 40 nm.

[0131] Comparative Example 28 The preparation steps of Comparative Example 28 were basically the same as those of Example 14, except that during the electrospinning of the second spinning solution in Comparative Example 28, the advancing speed of the spinning needle tube was 2 mL / h.

[0132] The specific capacity, first Coulombic efficiency, energy retention rate, energy recovery rate corresponding to the secondary batteries of Examples 1 to 24 were obtained, as well as the thermal stability and contact angle corresponding to the separators of Examples 1 to 28. The energy retention rate was the energy retention rate after 500 cycles at a rate of 0.3 C; the energy recovery rate was the energy recovery rate after storing at 60 °C for 48 h in a fully charged state; the thermal stability was the dimensional shrinkage rate after storing at 200 °C for 1 h. The test results are shown in Tables 1 to 3 below.

[0133] Table 1

[0134] Table 2

[0135] Table 3

[0136] By comparing Examples 1 to 13 and Comparative Examples 1 to 3, or by comparing Examples 14 to 18 and Comparative Examples 16 to 17, it was found that in the secondary batteries provided by the embodiments of the present application, the separator was composed of a polyimide substrate, a niobium pentoxide coating, and a self-healing layer. The surface of the self-healing layer was grafted with -SO3Li groups. The niobium pentoxide coating improved the overall thermal stability of the separator, and the relatively high dielectric constant and metal ion adsorption ability of niobium pentoxide could 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 reduced the volume expansion and the risk of lithium dendrite piercing during the cycling of the secondary battery, resulting in an improvement in the energy retention rate and energy recovery rate of the secondary battery. The grafted -SO3Li groups on the surface reduced the contact angle of the separator and improved the wettability of the separator.

[0137] It was found by comparing Examples 1 to 13 and Comparative Examples 4 to 15 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 ratio of niobium pentoxide in the niobium pentoxide coating, and the mass ratio of the polyurethane containing dynamic disulfide bonds are all within appropriate ranges, it is more conducive to the good performance of the secondary battery.

[0138] It was found by comparing Examples 14 to 18 and Comparative Examples 18 to 20 that the concentration of niobium pentoxide in the first spinning solution is related to the mass ratio of niobium pentoxide in the base layer, and the concentration of the polyurethane containing dynamic disulfide bonds in the second spinning solution is related to the mass ratio of the polyurethane containing dynamic disulfide bonds in the self-healing layer. When the mass ratios of niobium pentoxide and the polyurethane containing dynamic disulfide bonds are all within appropriate ranges, it is more conducive to the good performance of the secondary battery.

[0139] It was found by comparing Examples 19 to 24 and Comparative Examples 21 to 27 that when the thickness of the base layer, the thickness of the self-healing layer, and the average particle size of niobium pentoxide are all within appropriate ranges, it is more conducive to the good performance of the secondary battery.

[0140] It was found by comparing Examples 14 to 18 and Comparative Example 28 that when the syringe needle advancing rate during the electrospinning of the first spinning solution to prepare the initial base film is less than the syringe needle advancing rate during the electrospinning of the second spinning solution to prepare the initial self-healing layer, it is beneficial to make the porosity of the base layer higher than that of the self-healing layer. The lower porosity of the self-healing layer and the relatively higher density are beneficial to effectively deal with problems such as microcracks caused by volume expansion during the cycling of the secondary battery or the piercing of lithium dendrites, and thus are beneficial to the improvement of the performance of the secondary battery.

[0141] Those of ordinary skill in the art can understand that the above embodiments are specific examples for implementing the present application. In actual applications, various changes can be made in form and details without departing from the spirit and scope of the present application. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, the protection scope of the present application should be determined by the scope defined by the claims.

Claims

1. A method for preparing a secondary battery, characterized in that, Including: Preparing a separator, 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 fibrous network structure; Preparing a self-healing layer, the self-healing layer is located on one surface of the base layer, the material of the self-healing layer includes a polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted on the surface of the self-healing layer away from the base layer; Providing a positive electrode sheet and a negative electrode sheet, winding or laminating the positive electrode sheet, the separator and the negative electrode sheet and then putting them into a housing, wherein the self-healing layer faces the negative electrode sheet, the base layer faces the positive electrode sheet, and an electrolyte is injected into the housing to obtain a secondary battery.

2. The method for preparing a secondary battery according to claim 1, wherein: The steps for preparing the base layer include: Preparing a polyimide substrate, adding polyamic acid to a solvent and performing ultrasonic dispersion to obtain a spinning solution, the concentration of the polyamic acid is 0.15 g / mL to 0.25 g / mL; performing electrospinning on the spinning solution to obtain an initial polyimide film; calcining the initial polyimide film in an inert gas to obtain the polyimide substrate having a fibrous network structure; Preparing a niobium pentoxide coating, dispersing niobium pentoxide in a solvent, adding a dispersant and stirring and mixing, coating the mixture on one surface of the polyimide substrate by a coater and then drying to obtain the niobium pentoxide coating, the mass ratio of niobium pentoxide in the niobium pentoxide coating to the mass of polyimide in the polyimide substrate is (0.2 to 0.3):1, and the polyimide substrate and the niobium pentoxide coating constitute the base layer; The steps for preparing the self-healing layer include: Dissolving a polyurethane prepolymer containing dynamic disulfide bonds in a solvent, the mass ratio of the polyurethane prepolymer containing dynamic disulfide bonds to the mass of polyimide in the polyimide substrate is (0.4 to 0.8):1; coating the mixture on the surface of the niobium pentoxide coating away from the polyimide substrate by a casting method and then curing to form the self-healing layer; performing plasma surface modification treatment on the self-healing layer so that -SO3Li groups are grafted on the surface of the self-healing layer.

3. The manufacturing method of the secondary battery according to claim 2, wherein In the steps for preparing the polyimide substrate, the process parameters of electrospinning include: the voltage is 15 kV to 25 kV, the rotation speed of the spinning roller is 100 r / min to 300 r / min, and the advancing speed of the spinning needle tube is 0.2 mL / h to 0.5 mL / h; the process parameters of calcining include: the temperature is 250 °C to 350 °C, and the time is 1.5 h to 2.5 h.

4. The manufacturing method of the secondary battery according to claim 2, characterized in that, In the steps for preparing the niobium pentoxide coating, the coating speed of the coater is 2 m / min to 5 m / min; the drying temperature is 50 °C to 80 °C, and the time is 10 h to 12 h.

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

6. The method for preparing a secondary battery according to claim 1, wherein, The steps for preparing the base layer and the self-healing layer include: Polyamic acid and niobium pentoxide are added to a solvent to obtain a first spinning solution. The concentration of polyamic acid is 0.15 g / mL to 0.25 g / mL, and the concentration of niobium pentoxide is 0.015 g / mL to 0.05 g / mL. The first spinning solution is electrospun to obtain an initial base film; Polyamic acid and polyurethane containing dynamic disulfide bonds are added to a solvent to obtain a second spinning solution. The concentration of polyamic acid is 0.1 g / mL to 0.25 g / mL, and the concentration of polyurethane containing dynamic disulfide bonds is 0.04 g / mL to 0.16 g / mL. The second spinning solution is electrospun to form an initial self-healing layer on the surface of the initial base film; The initial base film and the initial self-healing layer are calcined in an inert gas so that the initial base film is converted into the base layer and the initial self-healing layer is converted into the self-healing layer; The self-healing layer is subjected to plasma surface modification treatment so that -SO3Li groups are grafted onto the surface of the self-healing layer.

7. The method for preparing a secondary battery according to claim 2 or 6, characterized in that, The steps for performing plasma surface modification treatment on the self-healing layer include: The self-healing layer is ultrasonically cleaned successively with ethanol and deionized water; The surface of the self-healing layer is bombarded with plasma, and the gas source is a mixed gas 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-healing layer; Lithium benzenesulfonate is dissolved in deionized water, and hydrochloric acid is added to adjust the pH value to 2 to 3; The plasma-activated diaphragm is immersed in the lithium benzenesulfonate solution, ultrasonically treated, and reacted at 55 °C to 65 °C for 2 h to 4 h so that -SO3Li groups are grafted onto the surface of the self-healing layer; The diaphragm is placed in deionized water for ultrasonic cleaning to remove unreacted lithium benzenesulfonate on the surface of the self-healing layer.

8. A secondary battery, characterized in that, including: a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet. The separator includes: a base layer, the material of the base layer includes polyimide and niobium pentoxide, and the base layer has a fibrous network structure; a self-healing layer, the self-healing layer is located on one surface of the base layer. The material of the self-healing layer includes polyurethane containing dynamic disulfide bonds, and -SO3Li groups are grafted onto the surface of the self-healing layer away from the base layer; wherein, the self-healing layer faces the negative electrode sheet, and the base layer faces the positive electrode sheet.

9. The secondary battery according to claim 8, wherein 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 the surface of the niobium pentoxide coating away from the polyimide substrate.

10. The secondary battery according to claim 9, characterized in that, 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; the thickness of the self-healing layer is 1 μm to 3 μm.

11. The secondary battery according to claim 9 or 10, characterized in that, 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 to 0.3):(0.4 to 0.8).

12. The secondary battery according to claim 9 or 10, characterized in that, The average particle size of the niobium pentoxide in the niobium pentoxide coating is 20 nm to 40 nm.

13. The secondary battery according to claim 8, wherein The fibrous network structure in the base layer is composed of polyimide, and the niobium pentoxide is dispersed in the fibrous network structure; the self-healing layer has a fibrous network structure, and the fibrous network structure of the self-healing layer is composed of polyimide and polyurethane containing dynamic disulfide bonds.

14. An energy storage system, characterized in that, Including a plurality of secondary batteries manufactured by using the manufacturing method of the secondary battery according to any one of claims 1 to 7, or the secondary battery according to any one of claims 8 to 13.

15. An electrical device, characterized in that, The electrical equipment includes a secondary battery manufactured by using the manufacturing method of the secondary battery according to any one of claims 1 to 7; or includes the secondary battery according to any one of claims 8 to 13; or includes the energy storage system according to claim 14.

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