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

Abstract

The invention relates to the field of energy storage, and provides a secondary battery and a preparation method thereof, an energy storage system and electric equipment, the secondary battery comprises a battery shell, the battery shell is internally provided with a cavity, and the cavity is internally provided with an electrolyte; the battery cell assembly is located in the cavity, and the battery cell assembly is soaked in the electrolyte; the battery cell assembly comprises a wound positive plate, a diaphragm and a negative plate, the diaphragm comprises a base material layer, and a through hole is formed in the base material layer; the functional layer is located on at least one surface of the base material layer, and the functional layer is formed by arranging a plurality of scale units in a hinge type connecting structure; the functional layer comprises a trigger material, the trigger material is connected to the surface of the scale unit, the trigger material is used for opening and closing the scale unit to form a through hole, and the through hole exposes at least one through hole. According to the secondary battery and the preparation method thereof, the energy storage system and the electric equipment provided by the invention, at least the thermal runaway problem of the secondary battery can be improved.

Description

Technical Field

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

[0002] Safety issues are the main obstacle to the large-scale application of lithium-ion batteries in the field of energy storage. As the energy density of lithium-ion batteries continues to increase, improving their safety is increasingly urgent for the development of the energy storage field. Thermal runaway is a key issue in battery safety research. Thermal runaway refers to the rapid rise in the temperature of a lithium-ion battery, either locally or as a whole. The heat cannot be dissipated in time, and a large amount of heat accumulates inside, inducing further side reactions, which may cause catastrophic accidents such as battery fire and explosion. Common triggering mechanisms of thermal runaway include internal short circuit, overcharge and over-discharge, high temperature environment and battery material characteristics.

[0003] Although some measures have been taken to solve the thermal runaway problem, the preparation difficulty and improvement effect are poor. Therefore, the thermal runaway problem of current secondary batteries still needs to be further improved. Summary of the invention

[0004] 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 thermal runaway problem of the secondary battery.

[0005] According to some embodiments of the present application, on the one hand, the embodiments of the present application provide a secondary battery, comprising: a battery shell, the battery shell having a cavity, the cavity having an electrolyte; a battery cell assembly, the battery cell assembly being located in the cavity and immersed in the electrolyte; the battery cell assembly comprising a wound positive electrode sheet, a separator and a negative electrode sheet, wherein the separator comprises: a substrate layer having a through hole; a functional layer, the functional layer being located on at least one surface of the substrate layer, the functional layer being composed of a plurality of scale units arranged in a hinged connection structure; the functional layer comprising a trigger material, the trigger material being connected to the surface of the scale unit, the trigger material being used to make the scale unit open and close to form a through hole, the through hole exposing at least one of the through holes.

[0006] In some embodiments, the trigger material is a temperature-sensitive material, and the temperature-sensitive material is used to change in volume as the temperature changes, so as to drive the scale unit to open and close.

[0007] In some embodiments, the thermosensitive material includes a thermosensitive polymer having an acrylic polymer grafted on the surface.

[0008] In some embodiments, the material of the thermosensitive polymer includes poly(N-isopropylacrylamide) or polyvinylpyrrolidone.

[0009] In some embodiments, the scale unit includes a structural layer and a connection layer. The connection layer is located between the substrate layer and the structural layer, at the edge of the structural layer, and the triggering material is connected to the surface of the structural layer.

[0010] In some embodiments, the scale unit further includes an isolation layer located on the side of the structural layer close to the substrate layer.

[0011] In some embodiments, the separator further includes a functional modification layer located on the surface of the functional layer close to the substrate layer, and the ionic conductivity of the material of the functional modification layer is 8×10 -5 S / cm~2×10 - ³S / cm.

[0012] In some embodiments, the material of the functional modification layer includes lithium titanium aluminum phosphate, lithium lanthanum titanium oxide / lithium lanthanum titanate, or lithium lanthanum zirconium oxide / lithium lanthanum zirconate.

[0013] According to some embodiments of the present application, on the other hand, an embodiment of the present application provides a method for manufacturing a secondary battery, including: forming a separator, the separator including: a substrate layer; through holes are formed in the substrate layer; a functional layer located on at least one surface of the substrate layer, the functional layer is composed of a plurality of scale units arranged in a hinge-like connection structure; the functional layer includes a triggering material connected to the surface of the scale unit, and the triggering material is used to open and close the scale unit to form a through hole, and the through hole exposes at least one of the through holes; providing a positive electrode sheet and a negative electrode sheet; stacking the negative electrode sheet, the separator, and the positive electrode sheet in sequence, and stacking the negative electrode sheet, the separator, and the positive electrode sheet in sequence, obtaining a battery cell assembly by winding or laminating, placing the battery cell assembly into a battery case, injecting electrolyte into the battery case, and then encapsulating to obtain a secondary battery.

[0014] In some embodiments, the scale unit is formed by using a microelectromechanical process or an ion etching process.

[0015] In some embodiments, the process steps for forming the scale unit include: forming a sacrificial layer on the surface of the substrate layer; patterning the sacrificial layer to form a first hole, the bottom surface of the first hole exposes the substrate layer; forming a connection layer located in the first hole; forming a first film layer on the surface of the sacrificial layer and the surface of the connection layer; patterning the first film layer to form a plurality of scale-like structural layers; removing the sacrificial layer.

[0016] In some embodiments, the scale unit is formed by using a laser etching process.

[0017] In some embodiments, the process steps for forming the separator further include: forming prepolymer capsules, the prepolymer capsules comprising a urea-formaldehyde resin shell and prepolymer particles, the prepolymer particles comprising a hydroxyl-containing silicone prepolymer and a platinum catalyst; dispersing the prepolymer capsules in an adhesive solution to form a mixed slurry; performing screen printing, screen printing the mixed slurry on the surface of the substrate layer, and performing curing treatment to form an adhesive layer on the surface of the functional layer.

[0018] According to some embodiments of the present application, on the other hand, the present application embodiments provide an energy storage system, comprising: a secondary battery prepared by the method for preparing a secondary battery according to any one of the above embodiments or a secondary battery as described in the above embodiments.

[0019] According to some embodiments of the present application, on yet another hand, the present application embodiments provide an electrical device, comprising: a secondary battery prepared by the method for preparing a secondary battery according to any one of the above embodiments, a secondary battery as described in the above embodiments, or an energy storage battery pack as described in the above embodiments.

[0020] The technical solution provided by the embodiments of the present application has at least the following advantages: The secondary battery provided by the embodiments of the present application, by providing a functional layer on the surface of the substrate layer, the functional layer is composed of an array of multiple scale units, the functional layer further includes a trigger material, the trigger material is connected to the surface of the scale unit, and the trigger material is used to open and close the scale unit to form through holes, the through holes expose at least one through hole, instantaneously opening a large number of additional, low-resistance ion channels on the separator, greatly reducing the ion transport resistance, making the current distribution more uniform, and effectively alleviating the violent lithium dendrite precipitation caused by the too-high local current density on the negative electrode surface at high temperature. After a large number of through holes are opened, the electrolyte can freely flow through the separator under the action of convection, which is beneficial to enhancing the heat transfer efficiency inside the battery. Heat can spread from the hot spot to the entire battery or the housing faster, effectively avoiding the situation where the local temperature soars sharply beyond the critical point or even thermal runaway. The formation of the through holes ensures that even at high temperature, the electrolyte can fully infiltrate the electrode sheet, maintaining a relatively normal interface, reducing local high impedance and violent heat generation side reactions caused by poor infiltration, and improving the yield of the secondary battery. Description of the Drawings

[0021] One or more embodiments are exemplarily illustrated by the figures in the corresponding drawings. These exemplary illustrations do not limit the embodiments. Unless otherwise stated, the figures in the drawings do not constitute a scale limitation. To more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings in the following description 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.

[0022] Figure 1 It is a cross-sectional view of a cell assembly in a secondary battery provided by an embodiment of the present application. Figure 2 It is a top view of a separator in a secondary battery provided by an embodiment of the present application. Figure 3 It is a cross-sectional view of a separator in a secondary battery provided by an embodiment of the present application. Figure 4 It is another cross-sectional view of a separator in a secondary battery provided by an embodiment of the present application. Figure 5 It is yet another cross-sectional view of a separator in a secondary battery provided by an embodiment of the present application. Figure 6 It is still another cross-sectional view of a separator in a secondary battery provided by an embodiment of the present application.

[0023] Explanation of reference numerals: 1, positive electrode sheet; 2, negative electrode sheet; 3, separator; 100, base material layer; 101, through hole; 110, scale unit; 11, functional layer; 111, trigger material; 112, structural layer; 113, connection layer; 114, functional modification layer; 12, through hole; 120, adhesive layer. Detailed implementation manners

[0024] As can be seen from the background art, current secondary batteries have potential safety hazards of thermal runaway.

[0025] Currently, the solutions to thermal runaway mainly include: 1. Coating and modifying the positive electrode material, improving the compatibility between the solid electrolyte and the electrode, and enhancing the heat conduction of the cell; 2. Selecting an electrolyte with high safety to achieve a flame retardant effect; 3. Selecting a safe and efficient thermal management system to inhibit the temperature rise of the lithium-ion battery; 4. Adding fins, embedding foam metal, coating phase change materials, etc.

[0026] However, although coating and modification of the positive electrode material can solve the thermal runaway problem, the preparation cost is relatively high; the high safety of the electrolyte has limited improvement on the performance of the secondary battery; the selection of the thermal management system and the increase of heat dissipation measures increase the preparation difficulty and reduce the preparation efficiency.

[0027] The embodiments of the present application provide a secondary battery and a preparation method thereof. By improving the separator, the separator not only has conventional through holes, but also has a functional layer, and it is set that the functional layer includes scale units and trigger materials to form through holes, and these through holes communicate with the through holes, so as to greatly improve the thermal runaway problem.

[0028] In the description of the embodiments of the present application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "a plurality of" is more than two, unless otherwise clearly and specifically defined.

[0029] Referring to "embodiments" herein means that specific features, structures or characteristics described in connection with the embodiments can be included in at least one embodiment of the present application. The phrase appearing in various positions in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment mutually exclusive with other embodiments. Those skilled in the art explicitly and implicitly understand that the embodiments described herein can be combined with other embodiments.

[0030] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: the existence of A, the simultaneous existence of A and B, and the existence of B. In addition, the character " / " in this article generally represents an "or" relationship between the associated objects before and after.

[0031] In the description of the embodiments of the present application, the term "a plurality of" refers to more than two (including two). Similarly, "a plurality of groups" refers to more than two groups (including two groups), and "a plurality of sheets" refers to more than two sheets (including two sheets).

[0032] In the description of the embodiments of the present application, technical terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the embodiments of the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the embodiments of the present application.

[0033] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installation", "connection", "connection", "fixation", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to specific situations.

[0034] In the corresponding drawings of the embodiments of the present application, for better understanding and convenience of description, the thickness and area of the layer are enlarged. When describing a component (such as a layer, film, region, or substrate) on or on the surface of another component, the component can be "directly" on the surface of the other component, or there can be a third component between the two components. On the contrary, when describing a component on the surface of another component or when another component is formed or provided on the surface of a component, it means that there is no third component between the two components. In addition, when describing a component "substantially" formed on another component, it means that the component is not formed on the entire surface (or front surface) of the other component, nor on a partial edge of the entire surface.

[0035] In the description of the embodiments of the present application, when a certain component "includes" another component, unless otherwise stated, other components are not excluded, and other components may further be included. In addition, when a component such as a layer, film, region, or plate is referred to as "on / at" another component, it can be "directly on" the other component (that is, on the surface of the other component and there is no other component between them), or there can be another component between them. In addition, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it means that there is no other component between them.

[0036] 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, "the part" is also intended to include the plural form unless the context clearly indicates otherwise. Among them, the components include components such as layers, films, regions, or plates.

[0037] The embodiments of the present application will be described in detail below with reference to 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.

[0038] Figure 1 A cross-sectional view of a cell assembly in a secondary battery provided by an embodiment of the present application; Figure 2 A top view of a separator in a secondary battery provided by an embodiment of the present application; Figure 3 A cross-sectional view of a separator in a secondary battery provided by an embodiment of the present application.

[0039] It should be noted that, to illustrate and distinguish the separator, the positive electrode sheet, and the negative electrode sheet, Figure 1 in the figure, the separator is schematically shown by a dashed line, the negative electrode sheet is schematically shown by a thinner solid line, and the positive electrode sheet is schematically shown by a thicker solid line. However, this does not represent the thickness relationship among the separator, the positive electrode sheet, and the negative electrode sheet. Secondly, Figure 1 there are gaps between the separator, the positive electrode sheet, and the negative electrode sheet pairwise. This is to clearly show the winding correspondence relationship among the separator, the positive electrode sheet, and the negative electrode sheet. However, it does not mean that there must be gaps between the separator and the positive electrode sheet or between the separator and the negative electrode sheet. That is to say, the separator and the positive electrode sheet can be in contact with each other, or the separator and the negative electrode sheet can be in contact with each other.

[0040] According to some embodiments of the present application, on the one hand, an embodiment of the present application provides a secondary battery, including: a battery case, having a cavity inside, and an electrolyte inside the cavity; a cell assembly, located inside the cavity, and the cell assembly is immersed in the electrolyte; the cell assembly includes a wound positive electrode sheet 1, a separator 3, and a negative electrode sheet 2, wherein the separator 3 includes: a base material layer 100, having a through hole 101 inside; a functional layer 11, located on at least one surface of the base material layer 100, and the functional layer 11 is composed of a plurality of scale units 110 arranged in a hinge connection structure; the functional layer 11 includes a trigger material 111, the trigger material 111 is connected to the surface of the scale unit 110, and the trigger material 111 is used to open and close the scale unit 110 to form a through hole 12, and the through hole 12 exposes at least one through hole 101.

[0041] In the secondary battery provided by the embodiment of the present application, by disposing a functional layer 11 on the surface of the substrate layer 100, the functional layer 11 is composed of an array arrangement of a plurality of scale units 110. The functional layer 11 further includes a trigger material 111, and the trigger material 111 is connected to the surface of the scale unit 110. The trigger material 111 is used to open and close the scale unit 110 to form a through hole 12, and the through hole 12 exposes at least one through hole 101, instantaneously opening a large number of additional and low-resistance ion channels on the separator 3, greatly reducing the ion transport resistance, making the current distribution more uniform, and effectively alleviating the violent lithium dendrite precipitation caused by the excessive local current density on the negative electrode surface at high temperature. After a large number of through holes 12 are opened, the electrolyte can freely flow through the separator 3 under the action of convection, which is beneficial to enhancing the heat transfer efficiency inside the battery. Heat can spread from the overheating point to the entire battery or the housing faster, effectively avoiding the situation where the local temperature soars sharply beyond the critical point or even thermal runaway. The formation of the through hole 12 ensures that even at high temperature, the electrolyte can fully infiltrate the electrode sheet, maintain a relatively normal interface, reduce the local high impedance and violent heat generation side reactions caused by poor infiltration, and improve the yield of the secondary battery.

[0042] Classified by appearance, the prepared secondary battery can be divided into square battery cells, round battery cells or soft-pack battery cells. Classified by capacity, the secondary battery can be divided into models such as 50Ah, 100Ah, 150Ah, 200Ah, 280Ah, 306Ah, 314Ah, 500+Ah, 800+Ah and 1000+Ah. Classified by the chemical composition and working principle of the battery cell components of the secondary battery, the secondary battery can be a lithium-ion battery, a lead-acid battery, a sodium-ion battery or a nickel-metal hydride battery. The embodiment of the present application takes 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 1, the negative electrode sheet 2 and the electrolyte with corresponding metal ions according to actual needs. For example, for a sodium-ion battery, replace the lithium transition metal oxide of the positive electrode active material in the following 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 replace the electrolyte with any one of organic liquid electrolytes, solid composite electrolytes or solid electrolytes.

[0043] Reference Figure 1 , the positive electrode sheet 1 serves as the cathode in the redox reaction. During discharge, the positive electrode material (lithium salt material) releases lithium ions and electrons through a chemical reaction; during charging, it reaccepts lithium ions.

[0044] The positive electrode sheet 1 includes a positive electrode current collector and a positive electrode active layer. The positive electrode current collector can be aluminum foil. The price of aluminum foil is lower than that of copper foil. A dense oxide film is formed on the surface of the aluminum foil, and the oxide film is very thin, which can improve the corrosion resistance of the aluminum foil, and electrons can achieve conductivity through the tunneling effect.

[0045] In some embodiments, the current collector of the positive electrode sheet 1 can also be a composite current collector. The composite current collector includes three stacked layers. The middle layer is an organic substance, and the upper and lower layers are copper-plated and aluminum-plated. The organic substance is PET (polyester), PP (polypropylene), PI (polyimide), etc.

[0046] The positive electrode active material in the positive electrode active layer is an energy storage material, usually composed of metal oxides, metal sulfides or polymers, etc. Its main function is to chemically react with the lithium ions in the negative electrode during battery charging, thereby storing lithium ions, increasing the lithium ion concentration, and thus causing the positive electrode of the battery to release charge current. At the same time, during battery discharge, the lithium ions stored in the positive electrode active material move to the negative electrode and react with the negative electrode material, forming a potential difference between the positive and negative electrodes of the battery, thereby generating current output.

[0047] The negative electrode sheet 2 serves as the anode in the oxidation-reduction reaction. During discharge, the negative electrode material (such as graphite, silicon-based material) accepts and stores lithium ions; during charging, lithium ions are released.

[0048] The negative electrode sheet 2 includes a negative electrode current collector and a negative electrode active layer, and the negative electrode active layer is located on the negative electrode current collector.

[0049] The negative electrode current collector can be copper foil. The copper foil has low conductivity, can have high electron transport ability, and has weak lithium intercalation ability, capturing fewer lithium ions, thereby effectively reducing the loss of lithium ions. In some other embodiments, the negative electrode current collector can also be a foam copper current collector, a copper mesh current collector, and a three-dimensional nano-copper array current collector.

[0050] In some embodiments, the negative electrode current collector can be a composite current collector, including a polymer material layer and metal coatings. The metal coatings are located on the upper and lower sides of the polymer material layer. The polymer material layer is PET (polyester), PP (polypropylene), PI (polyimide), etc., and the metal coating is a copper layer.

[0051] In some embodiments, the negative electrode current collector can also be a carbon-based current collector, that is, there is a conductive carbon layer on the copper foil. The conductive carbon layer can serve as a protective layer to effectively protect the current collector to prevent corrosion of the metal current collector, thereby improving the life of the current collector; secondly, the conductive carbon layer itself has a low resistivity, so that excessive electrical losses will not occur. Among them, the material of the conductive carbon layer can be flake graphite, spherical graphite, carbon nanotubes, graphene, etc.

[0052] In some embodiments, the negative electrode active material particles in the negative electrode active layer are the carriers for the oxidation reaction of the battery cell. The negative electrode active material can be divided into two categories: carbon materials and non-carbon materials. Carbon-based materials include graphite materials (natural graphite, artificial graphite, and mesophase carbon microspheres) and other carbon-based materials (hard carbon, soft carbon, and graphene). Non-carbon materials can be further divided into titanium-based materials, silicon-based materials, tin-based materials, nitrides, metallic lithium, etc.

[0053] In some embodiments, the negative electrode active layer may include a first negative electrode active layer and a second negative electrode active layer. The first negative electrode active layer is located between the negative electrode current collector and the second negative electrode active layer. By providing the first active layer and the second active layer on the negative electrode current collector, firstly, since the first negative electrode active layer is closer to the negative electrode current collector, the stability and conductivity of the lower surface where the negative electrode current collector is connected to the active coating are better, thereby improving the electrochemical performance and cycling performance of the negative electrode. Secondly, for the second negative electrode active layer far from the negative electrode current collector, which is in contact with the separator 3, lithium deposition is likely to occur on the corresponding surface on the negative electrode side. Therefore, the second negative electrode active layer in contact with the separator 3 can focus on stability and conductivity, which is conducive to the smooth insertion and extraction of lithium ions inside the positive and negative electrode materials.

[0054] The separator 3 is located between the positive electrode sheet 1 and the negative electrode sheet 2 to prevent short circuits caused by physical contact between the positive electrode sheet 1 and the negative electrode sheet 2. At the same time, it allows lithium ions to freely shuttle through the micropores and hinders electron transmission, so that ions and electrons form a circuit during the charge and discharge process of the battery. As the carrier of the electrolyte, it adsorbs the electrolyte to ensure the ion transport efficiency. It closes the pores at high temperatures to block ion flow and prevent thermal runaway.

[0055] The separator 3 can be any one of a microporous membrane, a modified microporous membrane, a non-woven separator 3, and a composite separator 3. The microporous membrane is a separator 3 with pore diameters in the micron range, mainly including polyolefin microporous membranes and other polymer microporous membranes. The modified microporous membrane is a separator 3 obtained by modifying the microporous membrane. Common modification methods include surface treatment, chemical grafting, surface coating, etc. The non-woven separator 3 has a small fiber diameter and usually exhibits a higher porosity than other types of separators 3. The composite separator 3 is prepared by coating or filling inorganic materials in the microporous membrane or the non-woven separator 3, and has higher thermal stability and electrolyte wettability compared to other types of separators 3.

[0056] The substrate layer 100 is the base of the separator 3, and the substrate layer 100 can be any one of a microporous membrane, a modified microporous membrane, a non-woven separator 3, and a composite separator 3.

[0057] The materials of the substrate layer 100 include polyimide (PI), polypropylene (PP), polyethylene (PE), and nano-silica wrapped with PVP.

[0058] The substrate layer 100 can be a 3D network structure woven from nanofibers, and the network structure has through-holes 101. In this way, by changing the spinning conditions, a separator 3 with controllable morphology and adjustable porosity can be obtained, thereby controlling the conductivity of the separator 3.

[0059] In some embodiments, the porosity of the substrate layer 100 is 60% - 70%. The porosity of the substrate layer 100 can be 60%, 62%, 64%, 66%, 68% or 70%. In this way, when the scale units 110 of the functional layer 11 are opened by heat, the high porosity of 60% - 70% of the substrate layer 100 means that its through-hole 101 network is extremely developed. After the through-holes 12 are formed, the electrolyte can flow at high speed under the convection action through these high-density and large-size through-holes 101, quickly transferring the heat of the hot spots inside the winding core to the whole electrolyte, significantly reducing the local temperature rise rate.

[0060] In some embodiments, the substrate layer 100 is a 3D network structure woven from PI nanofibers, with a porosity of 60% - 70%. The glass transition temperature (Tg) of PI usually exceeds 300°C, and the decomposition temperature reaches above 500°C. In the initial stage of thermal runaway, the PI substrate layer 100 can remain rigid and unchanged, ensuring the stability of the through-hole 101 structure and avoiding a decrease in porosity or contact between the positive and negative electrodes caused by softening and shrinkage. In the later stage of thermal runaway, PI can still maintain the skeleton structure, providing the final physical barrier to prevent direct large-area short circuit between the positive and negative electrodes. Secondly, PI has relatively high mechanical strength and can still maintain relatively high mechanical strength at high porosity, so it can resist the stress during the winding or thermal expansion of the battery cell and, when the scale units 110 open and close, withstand the dynamic stress of the hinge structure without breaking.

[0061] The functional layer 11 acts as a switch, which can form a notch during thermal runaway and allow the electrolyte to flow freely through the separator 3.

[0062] The functional layer 11 is composed of an array arrangement of multiple scale units 110.

[0063] The scale unit 110 can be as Figure 2 shown, presenting a regular hexagon. In this way, when closely packed, the regular hexagon can maximize the coverage area and reduce defects, such as edge dangling bonds; the regular hexagon is one of the polygons with the strongest isotropy, with uniform stress distribution when subjected to external forces and is not easily broken; compared with pentagons, quadrilaterals, and triangles, hexagons are less likely to generate local stress concentration when bent or stretched.

[0064] In some other embodiments, the scale unit 110 can be a pentagon, quadrilateral, triangle or irregular shape, as long as it is ensured that a part of the scale unit 110 is fixed on the substrate layer 100 and can open and close.

[0065] In some embodiments, the scale unit 110 is a regular hexagon with a side length of 20 μm to 25 μm. In this way, in the Micro-Electro-Mechanical Systems (MEMS) lithography process, a size of 20 μm to 25 μm can match the resolution of conventional ultraviolet lithography, thus eliminating the need for high-cost equipment such as electron beams and reducing the manufacturing cost. When the 20 μm to 25 μm scales bend on the substrate layer 100, the strain is moderate, avoiding breakage. The side length of the scale unit 110 can be 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, or 25 μm.

[0066] In some embodiments, the scale unit 110 includes a structural layer 112 and a connection layer 113. The connection layer 113 is located between the substrate layer 100 and the structural layer 112. The connection layer 113 is located at the edge of the structural layer 112, and the trigger material 111 is connected to the surface of the structural layer 112.

[0067] In some embodiments, the structural layer 112 is a regular hexagon with a side length of 20 μm to 25 μm.

[0068] In some embodiments, the material of the structural layer 112 can be polysilicon, silicon nitride, Su-8 photoresist, alumina, silicon oxide, hexagonal boron nitride (h-BN), MXenes.

[0069] In some embodiments, the thickness of the structural layer 112 is 1 μm to 10 μm. The thickness of the structural layer 112 can be 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, or 10 μm.

[0070] The connection layer 113 is used to connect the structural layer 112 and the substrate layer 100, so that the structural layer 112 can rotate freely along a fixed or movable axis.

[0071] The material of the connection layer 113 can be PI or a metal material, such as aluminum foil or copper foil. In this way, the connection layer 113 can have a high strength, so that the scale unit 110 still has a high mechanical strength after multiple openings and closings, improving the safety and stability of the secondary battery.

[0072] In some embodiments, the scale unit 110 further includes an isolation layer, and the isolation layer is located on the side of the structural layer 112 close to the substrate layer 100. The isolation layer is used to prevent adhesion between the structural layer 112 and the substrate layer 100, thereby affecting subsequent opening and closing.

[0073] The material of the isolation layer can be alumina.

[0074] Figure 4 Another cross-sectional view of the separator in a secondary battery provided by an embodiment of the present application.

[0075] In some embodiments, referring to Figure 4 , the triggering material 111 is a temperature-sensitive material, which is used to undergo volume deformation with the change of temperature to drive the opening and closing of the scale unit 110. The temperature-sensitive material is combined with the active functional groups on the surface of the structural layer 112 through chemical bonds or strong physical interactions. For example, the material of the structural layer 112 is MXenes (Ti3C2T x ), and the -O or -OH functional groups on its surface directly esterify with the terminal carboxyl groups of PNIPAM in the temperature-sensitive material to form covalent bonds (C-N or Si-O). The deformation path is that the temperature-sensitive material expands when heated, and then pushes the structural layer 112 to rotate around the hinge of the connecting layer 113, and the scale gap expands to form a through hole 12, ensuring that the through hole 101 can be exposed.

[0076] Among them, PNIPAM is poly(N-isopropylacrylamide), and its chemical formula is (C6H 11 NO) n , which is polymerized from the monomer N-isopropylacrylamide (NIPAM). In some embodiments, the temperature-sensitive material includes a temperature-sensitive polymer grafted with an acrylate polymer on its surface. Based on the grafted polymer, a nanoscale brush-like structure is formed on the matrix surface. When heated, each side chain expands synergistically, pushing the scale unit 110 to rotate directionally, providing high sensitivity. The acrylate polymer grafted layer can shield the direct contact between the temperature-sensitive groups and the electrolyte, avoiding swelling failure.

[0077] In some embodiments, the material of the temperature-sensitive polymer includes poly(N-isopropylacrylamide) (PNIPAM) or polyvinylpyrrolidone (PVP). By grafting a polymer with a lower critical solution temperature (LCST≈32°C) such as poly(N-isopropylacrylamide), the material undergoes a hydrophilic-hydrophobic mutation when reaching the set temperature, triggering a sharp volume expansion, and thus can quickly respond to temperature and seize the safety time window.

[0078] In some embodiments, the opening degree of the structural layer 112 is 0° to 100°. This range can enable the structural layer 112 to open, and while more through holes 101 are exposed, the deformation of the structural layer 112 itself will not exceed the mechanical strength of the structural layer 112, reducing the safety hazard of hidden cracks. The opening degree of the structural layer 112 is 10°, 20°, 30°, 40°, 50°, 60°, 70°, 80°, 90° or 100°.

[0079] In some embodiments, the molecular weight of the temperature-sensitive polymer of the acrylate polymer (abbreviated as AAc) is 20 kDa to 50 kDa, taking into account the response speed and film-forming property.

[0080] In some embodiments, the molar ratio of AAc is less than or equal to 20 mol%. Excessive AAc will destroy the thermosensitivity of PNIPAM, resulting in the blurring or even disappearance of the low critical solution temperature (LCST).

[0081] In some embodiments, the trigger material 111 is a shape memory alloy, such as NiTi.

[0082] Figure 5 This is another cross-sectional view of the separator in a secondary battery provided by an embodiment of the present application; Reference Figure 5 , in some embodiments, the separator 3 further includes: a functional modification layer 114, the functional modification layer 114 is located on the surface of the functional layer 11 close to the substrate layer 100, and the ionic conductivity of the material of the functional modification layer 114 is 8×10 -5 S / cm~2×10 - 3 S / cm. In this way, at a higher temperature, the functional modification layer 114 can provide good ion transport performance and alleviate thermal runaway.

[0083] In some embodiments, the material of the functional modification layer 114 includes lithium aluminum titanium phosphate (LATP), lithium lanthanum titanium oxide / lithium lanthanum titanate (LLTO), or lithium lanthanum zirconium oxide / lithium lanthanum zirconate (LLZO).

[0084] In some embodiments, the thickness of the functional modification layer 114 is 180 nm to 220 nm. The thickness of the functional modification layer 114 can be 180 nm, 190 nm, 200 nm, 210 nm, or 220 nm.

[0085] Figure 6 This is yet another cross-sectional view of the separator in a secondary battery provided by an embodiment of the present application.

[0086] Combined with reference Figure 1 and Figure 6 , in some embodiments, the separator 3 can be coated with a polyvinylidene fluoride (PVDF) material as the adhesive layer 120, so that the separator 3 has excellent adhesiveness and flexibility. Since the separator 3 has excellent adhesiveness, it can make the separator 3 have good contact performance with the positive electrode sheet 1 or the separator 3 with the negative electrode sheet 2, thereby reducing the assembly time of the energy storage cell, and further effectively reducing the overall production cost of the energy storage cell. Since the separator 3 has excellent flexibility, the strength of the separator 3 is improved, which is beneficial to effectively improving the impact resistance of the separator 3.

[0087] In some embodiments, the secondary battery further includes a positive electrode tab and a negative electrode tab. The positive electrode tab / negative electrode tab is a metal conductor that leads out the positive electrode sheet 1 / negative electrode sheet 2 of the energy storage cell from the cell core. The positive electrode tab / negative electrode tab is the contact point between the positive electrode sheet 1 / negative electrode sheet 2 and the external contact component during charge and discharge of the cell. The external contact component can be a terminal post.

[0088] The electrolyte is a carrier for conducting electrons between the positive and negative electrodes of the battery. In some embodiments, the electrolyte can be an electrolyte solution, which is composed of a solvent, a lithium salt, and an additive. The solvent is used to dissolve the lithium salt, and the solvent can include cyclic carbonates (PC, EC); chain carbonates (DEC, DMC, EMC); carboxylic acid esters (MF, MA, EA, MA, MP, etc.). The lithium salt can be LiPF6, LiClO4, LiBF4, LiAsF6, etc. The additive can be one or more of a film-forming additive, a conductive additive, a flame retardant additive, an overcharge protection additive, an additive for controlling the content of H2O and HF in the electrolyte solution, an additive for improving low-temperature performance, and a multifunctional additive.

[0089] In some embodiments, the secondary battery may further include a top cover, a connecting piece, and a terminal post. The top cover is engaged with the outer shell. The connecting piece is located in the chamber and is electrically connected to the tab. The terminal post passes through the top cover, and one end of the terminal post is electrically connected to the connecting piece.

[0090] Among them, the connecting piece at least includes a first connecting piece and a second connecting piece. The terminal post includes a positive electrode terminal post and a negative electrode connecting post. The first connecting piece is electrically connected to the positive electrode tab of the positive electrode sheet 1 and the positive electrode terminal post respectively, and the second connecting piece is electrically connected to the negative electrode tab of the negative electrode sheet 2 and the negative electrode connecting post respectively.

[0091] In the secondary battery provided by the embodiment of the present application, by providing a functional layer 11 on the surface of the substrate layer 100, the functional layer 11 is composed of a plurality of scale units 110 arranged in an array, and the functional layer 11 further includes a trigger material 111. The trigger material 111 is connected to the surface of the scale unit 110, and the trigger material 111 is used to open and close the scale unit 110 to form a through hole 12. The through hole 12 exposes at least one through hole 101, instantaneously opening a large number of additional and low-resistance ion channels on the separator 3, greatly reducing the ion transport resistance, making the current distribution more uniform, and effectively alleviating the severe lithium dendrite precipitation caused by the excessive local current density on the negative electrode surface at high temperatures. After a large number of through holes 12 are opened, the electrolyte can freely flow through the separator 3 under the action of convection, which is beneficial to enhancing the heat transfer efficiency inside the battery. Heat can spread from the hot spot to the entire battery or the housing faster, effectively avoiding the situation where the local temperature soars sharply beyond the critical point or even thermal runaway. The formation of the through hole 12 ensures that even at high temperatures, the electrolyte can fully infiltrate the electrode sheet, maintain a relatively normal interface, reduce local high impedance and severe heat generation side reactions caused by poor infiltration, and improve the yield of the secondary battery.

[0092] Correspondingly, according to some embodiments of the present application, on the other hand, the embodiment of the present application provides a method for manufacturing a secondary battery for manufacturing the secondary battery provided in the above embodiment. The same or corresponding technical features as those in the above embodiment will not be described in detail here.

[0093] The manufacturing method includes: forming a separator 3, the separator 3 includes: a substrate layer 100; the substrate layer 100 has a through hole 101 therein; a functional layer 11, the functional layer 11 is located on at least one surface of the substrate layer 100, and the functional layer 11 is composed of a plurality of scale units 110 arranged in a hinge-type connection structure; the functional layer 11 includes a trigger material 111, the trigger material 111 is connected to the surface of the scale unit 110, and the trigger material 111 is used to open and close the scale unit 110 to form a through hole 12, and the through hole 12 exposes at least one through hole 101.

[0094] The manufacturing method includes forming the substrate layer 100.

[0095] The substrate layer 100 is prepared by an electrospinning method. The process steps for forming the substrate layer 100 include: preparing a PI solution with a solid content of 13 wt% to 17 wt%, and forming a substrate layer 100 with a fiber diameter of 80 nm to 100 nm, a porosity of 65 ± 5%, and a thickness of 20 μm under the process parameters of a voltage of 25 KV, a receiving distance of 15 cm, and a flow rate of 1.2 mL / h.

[0096] The substrate layer 100 is prepared by the sol-gel method. The technological steps for forming the substrate layer 100 include: preparing a coating solution using polyvinylpyrrolidone, tetraethyl orthosilicate, and butanol. Mixing nanoscale silica into the coating solution. Forming a spin-coated film at a spin-coating speed of 3000 rpm and drying it at a drying temperature of 80 °C for 2 h to prepare a substrate layer 100 with a pore size of 50 nm to 200 nm and a thickness of 10 μm to 50 μm.

[0097] In some embodiments, the flake unit 110 is formed by using a microelectromechanical process or an ion etching process.

[0098] In some embodiments, the technological steps for forming the flake unit 110 include: forming a sacrificial layer on the surface of the substrate layer 100; patterning the sacrificial layer to form a first hole, with the bottom surface of the first hole exposing the substrate layer 100; forming a connection layer 113, where the connection layer 113 is located in the first hole; forming a first film layer, where the first film layer is located on the surface of the sacrificial layer and the surface of the connection layer 113; patterning the first film layer to form a plurality of scaly structural layers 112; removing the sacrificial layer.

[0099] The material of the sacrificial layer can be silicon oxide, borosilicate glass, or phosphosilicate glass. The etching solution for removing the sacrificial layer can be a 49% HF solution.

[0100] In some embodiments, the flake unit 110 is formed by using a laser etching process.

[0101] In some embodiments, a temperature-sensitive material is formed by using a surface photografting process, including: forming a temperature-sensitive polymer of acrylate polymer; mixing the temperature-sensitive polymer of acrylate polymer with an initiator, and at a temperature of 80 °C, a pressure of 10 Pa, and a deposition rate of 0.1 μm / min, the temperature-sensitive polymer is grafted onto the surface of the structural layer 112 through surface photografting. The initiator in the temperature-sensitive polymer of acrylate polymer and the temperature-sensitive polymer of acrylate polymer are grafted onto the surface of the structural layer 112 through ultraviolet irradiation to form short linear graft chains, which grow into branched chains through continuous ultraviolet irradiation, and finally form a coating composed of the temperature-sensitive material.

[0102] In some embodiments, a temperature-sensitive material is formed by using a spraying process, including: forming a prepolymer solution, where the dispersion liquid is ethanol, the solid content of the temperature-sensitive polymer of acrylate polymer is 8% to 12%, and the particle size distribution D50 of the temperature-sensitive polymer of acrylate polymer is 0.8 μm; forming a temperature-sensitive material with a thickness of 1 μm to 2 μm and a phase change temperature of 45 ± 3 °C under the parameters of a nozzle diameter of 100 μm, a pressure of 0.2 MPa, and a spacing of 5 cm.

[0103] The technological steps for forming the functional modification layer 114 include: providing the material of the functional modification layer as a target; at a vacuum pressure of 5×10 -4Under the process parameters of Pa and an Ar gas flow rate of 20 sccm, a sputtering power of 150 W, a substrate temperature of 200 °C, and a deposition rate of 0.3 nm / s, a functional modification layer 114 with a thickness of 200 ± 10 nm is sputtered.

[0104] In some embodiments, the process steps for forming the separator 3 further include: forming prepolymer capsules, the prepolymer capsules including urea-formaldehyde resin shells and prepolymer particles, the prepolymer particles including hydroxyl-containing siloxane prepolymers and platinum catalysts; dispersing the prepolymer capsules in an adhesive solution to form a mixed slurry; performing screen printing, screen printing the mixed slurry on the surface of the substrate layer 100, and curing to form an adhesive layer 120 on the surface of the functional layer 11.

[0105] In some embodiments, the urea-formaldehyde resin shell is obtained by in-situ polymerization with a molar ratio of urea:formaldehyde of 1:(1.2 - 1.8).

[0106] Provide a positive electrode sheet 1 and a negative electrode sheet 2; stack the negative electrode sheet 2, the separator 3, and the positive electrode sheet 1 in sequence, and stack the negative electrode sheet 2, the separator 3, and the positive electrode sheet 1 in sequence, obtain an electrode assembly through winding or laminating, place the electrode assembly in a battery case, inject an electrolyte into the battery case, and then encapsulate to obtain a secondary battery.

[0107] According to some embodiments of the present application, on the other hand, the present application provides an energy storage system, including: a secondary battery prepared by the method for preparing a secondary battery according to any one of the above embodiments or a secondary battery according to the above embodiments.

[0108] According to some embodiments of the present application, on yet another aspect, the present application provides an electrical device, including: a secondary battery prepared by the method for preparing a secondary battery according to any one of the above embodiments, a secondary battery according to the above embodiments, or an energy storage battery pack according to the above embodiments.

[0109] The beneficial effects of the embodiments of the present application will be further described below in combination with examples and comparative examples.

[0110] Example 1: (1) Prepare a separator, the separator including: a PI substrate layer with through holes therein; a functional layer located on at least one surface of the substrate layer, the functional layer being composed of a plurality of scale units arranged in a hinge-like connection structure; the functional layer including a trigger material connected to the surface of the scale units, the trigger material being used to cause the scale units to open and close to form through holes, and the through holes exposing at least one through hole.

[0111] (2) Assemble a secondary battery.

[0112] The examples were successively subjected to thermal performance tests, mechanical strength tests, sensitivity tests, and electrochemical performance tests, and the test results were summarized and recorded in Table 1.

[0113] Thermal performance test: The separator was cut into a square sample size of 100 mm according to the standard of GB / T 13542.2, and then the sample was suspended in an oven with natural circulating air and dried at a temperature of 180 °C for 1 h; then the sample was taken out of the oven and cooled to room temperature, and the dimensions in each direction were measured again; and the thermal shrinkage rate was calculated.

[0114] Needle puncture strength test: The puncture strength of the separator was tested according to the standard of GB / T 36363, and the thickness at 4 points around the pinhole was tested, and the average value was taken, and the puncture strength was calculated.

[0115] Table 1

[0116] It can be seen from the data in Table 1 that the secondary battery provided by the embodiments of the present application has high mechanical strength, moderate ionic conductivity, and low thermal shrinkage rate, and thus can maintain the free penetration of lithium ions and improve the thermal runaway situation.

[0117] Those of ordinary skill in the art can understand that the above embodiments are specific embodiments for implementing the present application, and 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 subject to the scope defined by the claims.

Claims

1. A secondary battery, characterized in that, Comprising: A battery case, within which there is a cavity, and within the cavity there is an electrolyte; A battery cell assembly, which is located within the cavity and is immersed in the electrolyte; the battery cell assembly includes a wound positive electrode sheet, a separator, and a negative electrode sheet. Among them, the separator includes: A substrate layer, within which there are through holes; A functional layer, which is located on at least one surface of the substrate layer, and the functional layer is composed of a plurality of scale units arranged in a hinge - type connection structure; the functional layer includes a trigger material, which is connected to the surface of the scale unit, and the trigger material is used to open and close the scale unit to form a through - hole, and the through - hole exposes at least one of the through holes.

2. The secondary battery according to claim 1, wherein The trigger material is a temperature - sensitive material, which is used to undergo volume deformation with the change of temperature to drive the opening and closing of the scale unit.

3. The secondary battery according to claim 2, characterized in that, The temperature - sensitive material includes a temperature - sensitive polymer grafted with acrylate polymers on the surface.

4. The secondary battery according to claim 3, wherein The material of the temperature - sensitive polymer includes poly(N - isopropylacrylamide) or polyvinylpyrrolidone.

5. The secondary battery according to claim 1, characterized in that, The scale unit includes a structural layer and a connection layer, the connection layer is located between the substrate layer and the structural layer, the connection layer is located at the edge of the structural layer, and the trigger material is connected to the surface of the structural layer.

6. The secondary battery according to claim 5, characterized in that, The scale unit further includes: an isolation layer, which is located on the side of the structural layer close to the substrate layer.

7. The secondary battery according to claim 1 or 2, characterized in that, The separator further includes: a functional modification layer, the functional modification layer is located on the surface of the functional layer close to the substrate layer, and the ionic conductivity of the material of the functional modification layer is 8×10 -5 S / cm~2×10 -3 S / cm.

8. The secondary battery according to claim 7, wherein, The material of the functional modification layer includes lithium titanium phosphate, lithium lanthanum titanium oxide / lithium titanate lanthanum, or lithium lanthanum zirconium oxide / zirconium titanate lanthanum.

9. A method for preparing a secondary battery, characterized in that, Comprising: Forming a separator, the separator includes: a substrate layer; a substrate layer, within which there are through holes; a functional layer, which is located on at least one surface of the substrate layer, and the functional layer is composed of a plurality of scale units arranged in a hinge - type connection structure; the functional layer includes a trigger material, which is connected to the surface of the scale unit, and the trigger material is used to open and close the scale unit to form a through - hole, and the through - hole exposes at least one of the through holes; Providing a positive electrode sheet and a negative electrode sheet; stacking the negative electrode sheet, the separator, and the positive electrode sheet in sequence, and obtaining a battery cell assembly by winding or laminating. After placing the battery cell assembly into the battery case and injecting the electrolyte into the battery case, a secondary battery is obtained by encapsulation.

10. The method for preparing a secondary battery according to claim 9, wherein Forming the scale unit by using a micro - electromechanical process or an ion etching process.

11. The method for preparing a secondary battery according to claim 10, wherein The process steps for forming the scale unit include: Forming a sacrificial layer on the surface of the substrate layer; Patterning the sacrificial layer to form a first hole, and the bottom surface of the first hole exposes the substrate layer; Forming a connection layer, which is located within the first hole; Forming a first film layer, which is located on the surface of the sacrificial layer and the surface of the connection layer; Patterning the first film layer to form a plurality of scale - shaped structural layers; Removing the sacrificial layer.

12. The method for preparing a secondary battery according to claim 9, wherein, Forming the scale unit by using a laser etching process.

13. The method for preparing a secondary battery according to claim 9, wherein The process steps for forming the separator further include: Forming a prepolymer capsule, the prepolymer capsule includes a urea - formaldehyde resin shell and prepolymer particles, and the prepolymer particles include a hydroxyl - containing silicone prepolymer and a platinum catalyst; Disperse the prepolymer capsules in an adhesive solution to form a mixed slurry; Perform screen printing on the surface of the substrate layer with the mixed slurry, and perform a curing treatment to form an adhesive layer on the surface of the substrate layer away from the functional layer.

14. An energy storage system, characterized in that, Comprising: A secondary battery according to any one of claims 1 to 8, or a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 9 to 13.

15. An electrical device, characterized in that, Comprising: A secondary battery according to any one of claims 1 to 8, a secondary battery prepared by the method for preparing a secondary battery according to any one of claims 9 to 13, or an energy storage system according to claim 14.

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