Battery cells and their secondary batteries and energy storage devices

Abstract

This application discloses a battery cell and a secondary battery and energy storage device including the same, relating to the field of electrochemical energy storage technology. The battery cell proposed in this application has a thermal protection layer between the positive / negative electrode and the separator. This thermal protection layer includes an electrospun layer and a thermally conductive layer. When the internal temperature of the battery cell exceeds the melting point of the electrospun layer, the electrospun layer melts, covering the active particles on the electrode. This slows down the heat generation from the continued contact reaction between the active particles and the electrolyte, and slows down the continued crosstalk reaction of oxidizing or reducing gases on the electrode, thereby reducing the probability of battery thermal runaway. The thermally conductive layer improves the heat dissipation performance of the battery cell, especially the heat generated inside the wound or stacked battery cell, dissipating the heat generated inside the cell in a timely manner and reducing the probability of battery thermal runaway. The thermally conductive layer is gradient-set, with its thickness being the thickest inside the battery cell after winding or stacking, which can improve internal heat dissipation efficiency and increase battery energy density.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and in particular to a battery cell and a secondary battery and energy storage device including the same. Background Technology

[0002] In the field of rechargeable batteries, lithium-ion batteries are widely used in smartphones, electric vehicles, and other applications due to their high energy density and long cycle life. However, as requirements for lithium-ion battery performance (such as energy density, charging speed, and cycle life) become increasingly stringent, safety issues are becoming more prominent, and the probability of thermal runaway is increasing. Therefore, improving the thermal safety performance of lithium-ion batteries has become an urgent problem to be solved. In response to these problems, engineers have developed various thermal safety technologies. However, current thermal safety technologies are often fragmented, targeting only a specific stage of thermal runaway, such as the initial, development, or outbreak stages, lacking a multi-level, coordinated protection mechanism that can cover the entire thermal runaway path. Once heat accumulation exceeds the safety threshold of a certain stage, thermal runaway will rapidly develop along subsequent paths, ultimately leading to a fire or explosion.

[0003] Therefore, addressing the problem that most current thermal safety technologies are "fragmented," targeting only a specific stage of thermal runaway and lacking a multi-level collaborative protection mechanism that can cover the entire thermal runaway path, improving the heat dissipation performance of battery cells, reducing the probability of battery thermal runaway, and improving the lifespan and safety of energy storage batteries has significant practical application value. Summary of the Invention

[0004] This application aims to address at least one of the technical problems existing in the prior art. To this end, this application proposes a battery cell and a secondary battery and energy storage device including the same, aiming to solve the problem that most current thermal safety technologies only target a certain stage of thermal runaway and lack a multi-level collaborative protection mechanism that can cover the entire thermal runaway path, thereby improving the heat dissipation performance of the battery cell, reducing the probability of battery thermal runaway, and improving the lifespan and safety of the energy storage battery.

[0005] A first aspect of this application provides a battery cell comprising a positive electrode, a negative electrode, a separator, and a thermal protection layer, wherein the separator is disposed between the positive electrode and the negative electrode; the thermal protection layer is disposed between the positive electrode and the separator, and / or between the negative electrode and the separator; the thermal protection layer comprises an electrospinning layer and a thermally conductive layer; and the thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

[0006] In some embodiments, the thickness of the thermal conductive layer is uniformly distributed within each winding unit along the winding direction of the battery cell; the thickness of the thermal conductive layer decreases in a stepped manner between adjacent winding units, and the thickness difference is ≥0.05μm.

[0007] In some embodiments, along the winding direction of the battery cell, the thickness of the starting end of the thermal conductive layer is T1, and the thickness of the ending end of the thermal conductive layer is T2, satisfying T1-T2≥ 0.5 μm.

[0008] In some embodiments, the battery cell satisfies at least one of the following conditions: A1. The porosity of the coating of the thermal protection functional layer is 70%~95%; A2. The thickness of the thermal protection functional layer is 1μm~9μm; A3. The thickness of the electrospun layer is 0.5~4.5μm; A4. The thickness of the thermally conductive layer is 0.5~4.5μm; A5. The thermally conductive layer is disposed on the side close to the diaphragm.

[0009] In some embodiments, the electrospun layer comprises at least one of ethylene-propylene random polymer, ethylene-vinyl acetate copolymer, ethylene-propylene rubber, block copolymer polypropylene, polyisobutylene rubber, thermoplastic elastomer, amino-terminated liquid nitrile rubber, thermoplastic polyurethane, or polycaprolactone.

[0010] In some embodiments, the melting point Tm of the electrospun layer satisfies: 60℃ ≤ Tm ≤ 140℃, preferably 90℃ ≤ Tm ≤ 120℃.

[0011] In some embodiments, the thermally conductive layer comprises at least one of a ceramic material or a carbon material, wherein the ceramic material comprises at least one of boron nitride, aluminum nitride, or silicon carbide, and the carbon material comprises at least one of graphene, carbon nanotubes, or carbon fibers.

[0012] In some embodiments, the thermal conductivity of the thermally conductive layer is 10 W / (m·k) to 6000 W / (m·k), preferably 150 W / (m·k) to 6000 W / (m·k).

[0013] In some embodiments, the electrospun layer further includes a flame-retardant material.

[0014] In some embodiments, the battery cell satisfies at least one of the following conditions: B1. The flame retardant material includes at least one of inorganic hydroxides, intumescent flame retardants, boron-based flame retardants, nitrogen-based flame retardants, or phosphorus-based flame retardants; B2. The particle size Dv50 of the flame retardant material particles is 100nm~3μm; B3. The mass fraction of the flame-retardant material in the electrospun layer is 2% to 15%. B4. The decomposition temperature of the flame retardant material is ≥200℃.

[0015] A second aspect of this application also proposes a secondary battery comprising the aforementioned battery cell.

[0016] A third aspect of this application also proposes an energy storage device comprising the aforementioned secondary battery.

[0017] This application has at least the following beneficial effects: The battery cell proposed in this application has a thermal protection functional layer between the positive / negative electrode and the separator. The thermal protection functional layer includes an electrospinning layer and a thermally conductive layer. The function of the electrospinning layer is: when the internal temperature of the battery cell is higher than the melting point of the electrospinning layer, the electrospinning layer melts and then covers the active particles on the electrode, which can slow down the process of heat generation from the continued contact reaction between the active particles and the electrolyte, and can also slow down the process of heat generation from the crosstalk reaction of oxidizing or reducing gases on the electrode, thereby reducing the probability of battery thermal runaway. The electrospinning layer can also be doped with flame-retardant materials. When thermal runaway occurs in the battery cell, the flame-retardant materials can interrupt the exothermic chain reaction inside the battery and prevent the combustion of flammable materials, thereby reducing the open flame time and lowering the maximum temperature of the battery cell. The function of the thermally conductive layer is: to improve the heat dissipation performance of the battery cell, especially the heat generated inside the wound or stacked battery cell, and to dissipate the heat generated inside the battery cell in a timely manner, reducing the probability of battery thermal runaway. The thermally conductive layer is arranged in a stepped, decreasing thickness along the MD direction. This design ensures the thickest layer is inside the cell after winding, improving internal heat dissipation efficiency and reducing the thickness of the external thermally conductive layer to increase battery energy density. The electrospun layer and thermally conductive layer also have a chain-like effect: when heat initially accumulates in the cell, the thermally conductive layer dissipates heat promptly, preventing further thermal runaway. However, when heat accumulates to the reaction temperature between the electrode and electrolyte, the electrospun layer begins to melt, slowing down the more severe thermal runaway reaction. When the thermally conductive and electrospun layers alone are insufficient to control the continued thermal runaway, flame-retardant materials reduce the cell's open flame time and lower its maximum temperature. Ultimately, through the synergistic effect of the electrospun layer and thermally conductive layer, this cell improves heat dissipation performance, reduces the probability of thermal runaway, and enhances the lifespan and safety of energy storage batteries, making it highly valuable in the field of rechargeable batteries. Attached Figure Description

[0018] Figure 1 In the first embodiment of the battery cell in this application, a thermally conductive layer is coated on the surface of the separator, and an electrospinning layer is coated on the surface of the negative electrode sheet.

[0019] Figure 2 In the second embodiment of the battery cell in this application, a thermally conductive layer and an electrospinning layer are sequentially coated on the surface of the separator, with the thermally conductive layer on the side closer to the separator.

[0020] Figure 3 In the third embodiment of the battery cell in this application, the electrospinning layer and the thermal conductive layer are sequentially coated on the surface of the negative electrode sheet, with the thermal conductive layer on the side close to the separator.

[0021] Figure 4 In the fourth embodiment of the battery cell in this application, a thermally conductive layer is coated on the surface of the separator, and an electrospinning layer is coated on the surface of the negative electrode sheet. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features. As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate small variations. When used in conjunction with an event or situation, the terms may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the terms may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, if the difference between two values ​​is less than or equal to ±10% of the average of the values ​​(e.g., less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%), then the two values ​​can be considered "substantially" the same. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified. In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements. In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. In the following description, all figures disclosed in this application are approximate values, regardless of whether the terms "about" or "approximately" are used in conjunction. They may vary by 1%, 2%, 5%, or sometimes 10% to 20%. Whenever a range of values ​​with a lower limit (RL) and an upper limit (RU) is disclosed, any values ​​falling within that range are specifically disclosed. Specifically, the following values ​​within this range are specifically disclosed: R = RL + k * (RU - RL), where k is a variable ranging from 1% to 100% with a 1% increment, i.e., k is 1%, 2%, 3%, 4%, 5%, ..., 50%, 51%, 52%, ..., 95%, 96%, 97%, 98%, 99%, or 100%. Furthermore, any range of values ​​defined by the two R values ​​as defined above are also specifically disclosed. Throughout this specification, references to "implementation," "partial implementation," "one implementation," "another implementation," "specific method," or "partial method" mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment. In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated. Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

[0023] The term "polymer" refers to a polymeric compound prepared by polymerizing the same or different types of monomers. The general term "polymer" includes the terms "homopolymer," "copolymer," "trimer," and "interpolymer." The term "coating" refers to one or more layers applied to one or both sides of a porous substrate material. Functional coatings comprise a mixture of at least one organic binder and at least one inorganic filler. In addition to the organic binder and inorganic filler, the protective porous layer may also include one or more additives. Functional coatings can be single-layer, double-layer, or multi-layer structures. The term "binder" refers to a substance used to bond inorganic fillers to or to each other in a porous substrate material. Any organic binder that can bond inorganic fillers to or to each other in a porous substrate material may be used herein. Some non-limiting examples of organic binders include polyesters, polyamides, polyacrylic acid, polyethers, polyimides, polyolefins, rubbers, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, cellulose, cellulose derivatives, latexes, and combinations thereof.

[0024] The term "inorganic filler" refers to a non-conductive material. Some non-limiting examples of inorganic fillers include metal oxides, as well as non-oxide materials and non-metallic materials. Some non-limiting examples of metal oxides include alumina, zirconium oxide, barium titanate, lead zirconate titanate, ferrites, zinc oxide, and combinations thereof. Some non-limiting examples of non-oxide materials and non-metallic materials include silicon carbide, silicon nitride, aluminum nitride, boron nitride, titanium boride, molybdenum silicide, and combinations thereof. The term "water-soluble polymer" refers to a high molecular weight polymer that is soluble in water or uniformly dispersed in water. The term "oil-soluble polymer" refers to a high molecular weight polymer that is soluble in water or uniformly dispersed in an organic polar solvent, including but not limited to N-methylpyrrolidone (NMP) and dimethyl sulfoxide (DMSO).

[0025] Positive electrode active material: As used herein and in the claims, the term "positive electrode active material" (also known as cathode active material) is defined as a material that is electrochemically active in a positive electrode or cathode. Active material should be understood as a material capable of capturing and releasing Li and / or Na ions when subjected to voltage changes over a predetermined time period.

[0026] <Battery Cell> In a first aspect, this application proposes a battery cell comprising a positive electrode, a negative electrode, a separator, and a thermal protection layer, wherein the separator is disposed between the positive electrode and the negative electrode; the thermal protection layer is disposed between the positive electrode and the separator, and / or between the negative electrode and the separator; the thermal protection layer comprises an electrospinning layer and a thermally conductive layer; and the thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

[0027] The battery cell provided in this application includes a positive electrode, a negative electrode, and a separator. A thermal protection layer is disposed between the positive electrode and / or the negative electrode and the separator. The thermal protection layer includes an electrospun layer and a thermally conductive layer. The material used for the electrospun layer has a melting point generally below the battery's thermal runaway temperature and is not resistant to high temperatures. When the internal temperature of the battery cell exceeds the melting point of the electrospun layer, the electrospun layer melts, covering the active particles on the electrode. This slows down the process of the active particles continuing to react and generate heat with the electrolyte, and also slows down the process of oxidizing or reducing gases from the electrode continuing to crosstalk and generate heat. This reduces the probability of a chain reaction occurring inside the battery and thus reduces the probability of battery thermal runaway. The function of the thermally conductive layer is to improve the heat dissipation performance of the battery cell, especially the heat generated inside the wound or stacked cells. It dissipates the heat generated inside the cell in a timely manner, reducing the probability of thermal runaway. The thermally conductive layer is gradient-designed, with its thickness decreasing along the MD direction. This ensures that after winding, its thickness is greatest inside the cell, improving internal heat dissipation efficiency and reducing the thickness of the external thermally conductive layer to increase battery energy density. The electrospinning layer and the thermally conductive layer also have a chain-like effect. Specifically, when heat initially accumulates in the cell, the thermally conductive layer dissipates the heat promptly, preventing further thermal runaway chain reactions. However, when the heat has gradually accumulated to the reaction temperature between the electrodes and the electrolyte, the electrospinning layer begins to melt, slowing down the more severe thermal runaway reactions caused by the reaction heat generated by the electrodes and electrolyte. Ultimately, through the synergistic effect of the electrospinning layer and the thermally conductive layer, the aforementioned battery cell can improve its heat dissipation performance, reduce the probability of thermal runaway, and improve the lifespan and safety of energy storage batteries, making it highly valuable in the field of rechargeable batteries.

[0028] In some implementations, the thermally conductive layer is disposed on the side close to the diaphragm.

[0029] In some embodiments, the electrospun layer and the thermally conductive layer can be independently coated onto the surface of the electrode or the separator. The electrospun layer and the thermally conductive layer only need to be positioned between the separator and the electrode to function. In specific implementations, they can be coated onto the surface of the separator as a separator coating or onto the surface of the electrode as an electrode coating, as long as the thermally conductive layer is located on the side closest to the separator.

[0030] In some embodiments, the battery cell includes a positive electrode, a negative electrode, a separator, and a thermal protection layer. The separator is disposed between the positive and negative electrode, and the thermal protection layer is disposed between the negative electrode and the separator. The thermal protection layer includes an electrospinning layer and a thermally conductive layer. The electrospinning layer is disposed on the side closer to the negative electrode, and the thermally conductive layer is disposed on the side closer to the separator. The thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

[0031] Figure 1-3The figure shows some specific embodiments of the battery cell of this application. As shown in the figure, the electrospinning layer and the thermally conductive layer are located between the negative electrode sheet and the separator. The thermally conductive layer is disposed on the side close to the separator, and the electrospinning layer is disposed on the side close to the negative electrode sheet.

[0032] In some embodiments, a thermally conductive layer is coated on the surface of the separator, and an electrospun layer is coated on the surface of the negative electrode. For example... Figure 1 As shown.

[0033] In some embodiments, a thermally conductive layer and an electrospun layer are sequentially coated on the surface of the diaphragm, with the thermally conductive layer disposed on the side closest to the diaphragm. For example... Figure 2 As shown.

[0034] In some embodiments, an electrospun layer and a thermally conductive layer are sequentially coated on the surface of the negative electrode sheet, with the thermally conductive layer disposed on the side closest to the separator. For example... Figure 3 As shown.

[0035] In some embodiments, the battery cell includes a positive electrode, a negative electrode, a separator, and a thermal protection layer. The separator is disposed between the positive and negative electrode, and the thermal protection layer is disposed between the positive electrode and the separator. The thermal protection layer includes an electrospinning layer and a thermally conductive layer. The electrospinning layer is disposed on the side closer to the positive electrode, and the thermally conductive layer is disposed on the side closer to the separator. The thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

[0036] In some embodiments, a thermally conductive layer is coated on the surface of the diaphragm, and an electrospun layer is coated on the surface of the positive electrode.

[0037] In some embodiments, a thermally conductive layer and an electrospinning layer are sequentially coated on the surface of the diaphragm, with the thermally conductive layer disposed on the side closest to the diaphragm.

[0038] In some embodiments, an electrospinning layer and a thermally conductive layer are sequentially coated on the surface of the positive electrode sheet, with the thermally conductive layer disposed on the side close to the separator.

[0039] In some embodiments, the battery cell includes a positive electrode, a negative electrode, a separator, and a thermal protection layer. The separator is disposed between the positive and negative electrode, and the thermal protection layer is disposed between the positive electrode and the separator, and between the negative electrode and the separator. The thermal protection layer includes an electrospun layer and a thermally conductive layer. The thermally conductive layer is disposed between the positive electrode and the separator, and the electrospun layer is disposed between the negative electrode and the separator. The thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell. Figure 4 The figure shows another specific embodiment of the battery cell of this application. As shown in the figure, the thermally conductive layer is coated on the surface of the separator, and the electrospinning layer is coated on the surface of the negative electrode sheet.

[0040] In some embodiments, the battery cell includes a positive electrode, a negative electrode, a separator, and a thermal protection layer. The separator is disposed between the positive and negative electrode, and the thermal protection layer is disposed between the positive electrode and the separator, and between the negative electrode and the separator. The thermal protection layer includes an electrospinning layer and a thermally conductive layer. The thermally conductive layer is disposed between the negative electrode and the separator, and the electrospinning layer is disposed between the positive electrode and the separator. The thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

[0041] In this application, the electrospinning layer and the thermally conductive layer can function as long as they are located between the diaphragm and the electrode. In specific implementation, they can be coated on the diaphragm surface as a diaphragm coating or coated on the electrode surface as an electrode coating.

[0042] In some embodiments, the thickness of the thermal conductive layer is uniformly distributed within each winding unit along the winding direction of the battery cell; the thickness of the thermal conductive layer decreases in a stepped manner between adjacent winding units, and the thickness difference is ≥0.05μm.

[0043] In some specific implementations, the battery cell is a wound battery cell. Along the winding direction of the battery cell, the thickness of the heat-conducting layer is uniformly distributed in each winding unit. Between each adjacent winding unit, the thickness of the heat-conducting layer decreases in a stepwise manner, and the thickness difference is ≥0.05μm.

[0044] In this application, "winding unit" refers to an electrode complex (including positive electrode plate, negative electrode plate and separator) in a wound cell, which includes multiple straight segments and multiple curved segments arranged alternately. The curved segments connect adjacent straight segments. The electrode complex of n straight segments and n curved segments that are equidistant from the innermost side of the cell is collectively referred to as a winding unit, where n is 1 or 2, usually 2.

[0045] This application provides a segmented thickness distribution for the thermal conductive layer, wherein the thickness of the thermal conductive layer in each winding unit is equal and uniformly distributed; along the winding direction of the electrode, the thickness of the thermal conductive layer between adjacent winding units gradually decreases, and the difference in the thickness of the thermal conductive layer between adjacent winding units is ≥0.05μm.

[0046] In some implementations, the decreasing magnitude of the step-like decrease is the same, partially the same, or different from each other.

[0047] In some embodiments, the thickness difference of the thermally conductive layer between adjacent winding units is 0.05~0.1μm. Exemplarily, it can be 0.05μm, 0.06μm, 0.07μm, 0.08μm, 0.09μm, 0.1μm, or within any two of the above values. Preferably, the thickness difference of the thermally conductive layer between adjacent winding units is 0.05μm. For example, along the cell winding direction, if the thickness of the thermally conductive layer of the innermost winding unit is T1μm, then the thickness of the thermally conductive layer of the second winding unit is T1-0.5μm, the thickness of the thermally conductive layer of the third winding unit is T1-0.5-0.5μm, and so on.

[0048] The thermal conductive layer in this application is set with a gradient, and the thickness decreases along the winding direction. This way, after winding, the thickness is the thickest inside the cell, which can improve the internal heat dissipation efficiency and increase the battery energy density.

[0049] In some implementations, along the winding direction of the battery cell, the thickness of the starting end of the thermal conductive layer is T1, and the thickness of the ending end of the thermal conductive layer is T2, satisfying T1-T2≥ 0.5 μm.

[0050] In some specific implementations, the battery cell is a wound battery cell. Along the winding direction of the battery cell, the thickness of the starting end of the heat-conducting layer is T1, and the thickness of the ending end of the heat-conducting layer is T2, satisfying T1-T2≥ 0.5 μm.

[0051] In some implementations, the range of T1-T2 is 0.5~4 μm. For example, it can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, or within any two of the above values.

[0052] The thickness of the thermal conductive layer in this application decreases from the inside to the outside along the winding direction of the battery cell. The thickness of the innermost starting end is T1, and the thickness of the outermost ending end is T2. T1>T2, and T1-T2≥ 0.5 μm.

[0053] In some embodiments, the thickness of the thermal protection layer is 1 μm to 9 μm. For example, it can be 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or within any two of the above values.

[0054] In some embodiments, the thickness of the electrospun layer is 0.5 to 4.5 μm. Exemplarily, it can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, or within any two of the above values.

[0055] In some embodiments, the thickness of the thermally conductive layer is 0.5 to 4.5 μm. For example, it can be 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 4.5 μm, or within any two of the above values.

[0056] The thermally conductive layer thickness of this application is segmented and gradually decreases, while the electrospinning layer thickness is uniformly distributed.

[0057] In some embodiments, the porosity of the thermal protection functional layer coating is 70% to 95%. Exemplarily, it can be 70%, 75%, 80%, 85%, 90%, 95%, or within any two of the above values.

[0058] In some embodiments, the electrospun layer includes at least one of ethylene-propylene random polymer, ethylene-vinyl acetate copolymer, ethylene-propylene rubber, block copolymer polypropylene, polyisobutylene rubber, thermoplastic elastomer, amino-terminated liquid nitrile rubber, thermoplastic polyurethane, or polycaprolactone, but is not limited thereto.

[0059] In some embodiments, the melting point Tm of the electrospun layer satisfies: 60℃ ≤ Tm ≤ 140℃, preferably 90℃ ≤ Tm ≤ 120℃. Exemplarily, Tm can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, or within any two of the above values.

[0060] The materials used for the electrospun layer in this application are primarily polymers with melting points below the battery's thermal runaway temperature, such as ethylene-propylene random polymers, ethylene-vinyl acetate copolymers, ethylene-propylene rubber, block copolymer polypropylene, polyisobutylene rubber, thermoplastic elastomers, amino-terminated liquid nitrile rubber, thermoplastic polyurethane, polycaprolactone, etc. The melting point Tm of the electrospun layer material satisfies: 60℃ ≤ Tm ≤ 140℃, preferably 90℃ ≤ Tm ≤ 120℃. The electrospun layer material is not heat-resistant. When the internal temperature of the battery cell exceeds the melting point of the electrospun layer material, the electrospun layer melts, covering the active particles on the electrode. This slows down the continued contact and reaction between the active particles and the electrolyte, and also slows down the continued crosstalk and heat generation from the oxidizing or reducing gases on the electrode, thereby reducing the probability of a chain reaction and continued heat generation inside the battery, and thus reducing the probability of battery thermal runaway.

[0061] In some embodiments, the electrospun layer also includes a flame-retardant material.

[0062] In some embodiments, the flame retardant material includes at least one of inorganic hydroxides, intumescent flame retardants, boron-based flame retardants, nitrogen-based flame retardants, or phosphorus-based flame retardants, but is not limited thereto.

[0063] Specifically, inorganic hydroxides include, but are not limited to, at least one of aluminum hydroxide or magnesium hydroxide.

[0064] Specifically, intumescent flame retardants include at least one of pentaerythritol diphosphate melamine salt, expandable graphite, or classic ternary flame retardant systems, but are not limited to these. Specifically, classic ternary flame retardant systems are physically mixed acid, carbon, and gaseous flame retardant substances.

[0065] Specifically, boron-based flame retardants include, but are not limited to, at least one of zinc borate, inorganic borates (such as borax, i.e., sodium tetraborate), boric acid, barium metaborate, ammonium pentaborate, or organic boron-based flame retardants.

[0066] Specifically, nitrogen-based flame retardants include, but are not limited to, at least one of melamine and its derivatives (e.g., melamine), melamine cyanurate, melamine phosphate, dicyandiamide, or guanidine salts.

[0067] Specifically, phosphorus-based flame retardants include inorganic phosphorus-based (e.g., red phosphorus, ammonium polyphosphate, ammonium phosphate salts, etc.) and organic phosphorus-based (e.g., phosphate esters, phosphaphenanthrene (DOPO) and its derivatives, phosphazene compounds, organic phosphonates, etc.), but are not limited to these.

[0068] In some embodiments, the particle size Dv50 of the flame retardant material is 100nm to 3μm. For example, it can be 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1μm, 2μm, 3μm, or within any two of the above values.

[0069] In some embodiments, the mass fraction of the flame-retardant material in the electrospun layer is 2% to 15% (wt). For example, it can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or within any two of the above values.

[0070] In some implementations, the decomposition temperature of the flame-retardant material is ≥200°C.

[0071] In some embodiments, the decomposition temperature of the flame-retardant material is 200°C to 2000°C. Exemplarily, it can be 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, 1700°C, 1800°C, 1900°C, 2000°C, or within any two of the above values.

[0072] The electrospun layer may also include flame-retardant materials, which include at least one of inorganic hydroxides, intumescent flame retardants, boron-based flame retardants, nitrogen-based flame retardants, or phosphorus-based flame retardants; the particle size Dv50 of the flame-retardant material is 100 nm to 3 μm, and the decomposition temperature is ≥200℃. The purpose of incorporating flame-retardant materials into the electrospun layer in this application is that when thermal runaway occurs in the battery cell, the flame-retardant material is activated and can interrupt the exothermic chain reaction inside the battery and prevent the combustion of combustibles by capturing combustion free radicals, forming a heat-insulating carbon layer, or absorbing heat, thereby reducing the open flame time and lowering the maximum combustion temperature of the battery cell.

[0073] The electrospun layer and the thermally conductive layer have a chain-like effect. Specifically: the thermally conductive layer is responsible for dissipating heat when it first begins to accumulate in the cell, preventing heat buildup from triggering a chain reaction of thermal runaway. However, when the heat has gradually accumulated to the reaction temperature between the electrode and the electrolyte, the electrospun layer begins to melt, slowing down the more severe thermal runaway reaction caused by the heat generated during the reaction between the electrode and the electrolyte. When the thermally conductive layer and the electrospun layer alone are no longer sufficient to control the continued thermal runaway reaction, flame-retardant materials can reduce the open flame time of the cell and lower the maximum temperature of the cell. Ultimately, through the synergistic effect of the electrospun layer and the thermally conductive layer, the above-mentioned cell can improve the heat dissipation performance of the cell, reduce the probability of battery thermal runaway, and improve the life and safety of energy storage batteries, making it extremely valuable in the field of rechargeable batteries.

[0074] In some embodiments, the thermally conductive layer includes at least one of ceramic or carbon materials, but is not limited thereto.

[0075] In some embodiments, the ceramic material includes at least one of boron nitride, aluminum nitride, or silicon carbide, but is not limited thereto.

[0076] In some embodiments, the carbon material includes at least one of graphene, carbon nanotubes, or carbon fibers, but is not limited thereto.

[0077] In some embodiments, the thermal conductivity of the heat-conducting layer is 10 W / (m·k) to 6000 W / (m·k), preferably 150 W / (m·k) to 6000 W / (m·k). Exemplarily, it can be 10 W / (m·k), 50 W / (m·k), 100 W / (m·k), 150 W / (m·k), 500 W / (m·k), 1000 W / (m·k), 2000 W / (m·k), 3000 W / (m·k), 4000 W / (m·k), 5000 W / (m·k), 6000 W / (m·k), or within any two of the above values.

[0078] The thermal conductive layer of this application is made of ceramic materials (such as boron nitride, aluminum nitride, silicon carbide, etc.) or carbon materials (such as graphene, carbon nanotubes, carbon fibers, etc.); the thermal conductivity of the thermal conductive layer material is from 10 W / (m·k) to 6000 W / (m·k), preferably from 150 W / (m·k) to 6000 W / (m·k). The function of the thermal conductive layer is to improve the heat dissipation performance of the battery cell, especially the heat generated inside the wound or stacked battery cell, so as to dissipate the heat generated inside the battery cell in a timely manner and reduce the probability of battery thermal runaway; and the thermal conductive layer is thickest inside the battery cell, which can improve the internal heat dissipation efficiency and increase the battery energy density.

[0079] In some embodiments, the positive electrode includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer including a positive active material.

[0080] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, LiNixMnyO2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0081] In some embodiments, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, LiFeO2, LiFePO4 and combinations thereof, wherein each x is independently 0.4 to 0.6; each y is independently 0.2 to 0.4; and each z is independently 0 to 0.1.

[0082] In some embodiments, the positive electrode active material is Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2; where -0.2≤x≤0.2, 0≤a<1, 0≤b<1, 0≤c<1 and a+b+c≤1.

[0083] In some embodiments, the positive electrode active material has the general formula Li 1+x Ni a Mn b Co c Al (1-a-b-c) O2, where 0.33≤a≤0.92, 0.33≤a≤0.9, 0.33≤a≤0.8, 0.5≤a≤0.92, 0.5≤a≤0.9, 0.5≤a≤0.8, 0.6≤a≤0.92 or 0.6≤a≤0.9; 0≤b≤0.5, 0≤b≤0.3, 0.1≤b≤0.5, 0.1≤b≤0.4, 0.1≤b≤0.3, 0.1≤b≤0.2 or 0.2≤b≤0.5; 0≤c≤0.5, 0≤c≤0.3, 0.1≤c≤0.5, 0.1≤c≤0.4, 0.1≤c≤0.3, 0.1≤c≤0.2 or 0.2≤c≤0.5.

[0084] In some embodiments, the positive electrode active material is doped with a dopant selected from the group consisting of Fe, Ni, Mn, Al, Mg, Zn, Ti, La, Ce, Sn, Zr, Ru, Si, Ge, and combinations thereof. In some embodiments, the dopant is not Fe, Ni, Mn, Mg, Zn, Ti, La, Ce, Ru, Si, or Ge. In some embodiments, the dopant is not Al, Sn, or Zr.

[0085] In some embodiments, the positive electrode active material may include LiNi. 0.33 Mn 0.33 Co 0.33 O2, LiNiO2, LiNi 0.4 Mn 0.4 Co 0.2 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.7 Mn 0.15 Co 0.15 O2, LiNi 0.8 Mn0.1 Co 0.1 O2, LiNi 0.92 Mn 0.04 Co 0.04 O2, LiNi 0.8 Co 0.15 Al 0.05 At least one of O2.

[0086] In some embodiments, the positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0087] In some embodiments, the mass percentage of each component, taking the positive electrode active material, conductive agent, and binder as a whole, is as follows: positive electrode active material 80-98%, conductive agent 1-10%, and binder 1-10%.

[0088] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders. In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0089] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is aluminum foil. The composite current collector may include a metal foil substrate and a safety coating disposed on at least one side of the metal foil substrate.

[0090] The positive current collector can be pure aluminum foil or a current collector containing a safety coating.

[0091] In some implementations, the thickness of the positive current collector is 3~20 μm.

[0092] In some embodiments, the preparation method of the positive electrode sheet includes the following steps: thoroughly mixing the positive electrode material, conductive agent, binder, and solvent according to a mass ratio, coating the mixture onto the positive electrode current collector, and then drying, cold pressing, and slitting to obtain the positive electrode sheet. The preparation method of the positive electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0093] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one side of the negative current collector, the negative active material layer including a negative active material.

[0094] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0095] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent.

[0096] In some embodiments, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders. In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0097] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0098] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0099] In some implementations, the thickness of the negative electrode current collector is 3~20 μm.

[0100] In some embodiments, a method for preparing the above-mentioned negative electrode sheet is also provided, including the steps of: thoroughly mixing the negative electrode active material, conductive agent, and binder according to a mass ratio, coating the mixture onto the negative electrode current collector, and then drying, cold pressing, and slitting to obtain the negative electrode sheet. The preparation method of the negative electrode sheet can adopt conventional methods in the industry, and this application does not limit it.

[0101] In some embodiments, the secondary battery also includes a separator located between the positive and negative electrode plates.

[0102] The separator separates the negative and positive electrodes and provides a pathway for lithium-ion migration. The use of the separator is not particularly limited, as long as it is a separator commonly used in lithium-ion secondary batteries. In particular, separators with low resistance to electrolyte ion movement and excellent electrolyte permeability are preferred. Specifically, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin-based polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, ethylene / methacrylate copolymers, etc.) or laminated structures with two or more layers. Alternatively, nonwoven fabrics formed from conventional porous nonwoven fabrics (e.g., glass fibers with high melting points, polyethylene terephthalate fibers, etc.) can be used. Furthermore, coated separators containing ceramic components or polymer materials to ensure heat resistance or mechanical strength can be used, and can optionally be used as single-layer or multi-layer structures. Generally, a diaphragm includes a substrate and a coating applied to the surface of the substrate.

[0103] In some embodiments, the porous substrate is, but is not limited to, at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0104] In some embodiments, the coating is disposed on one side of the substrate. In some embodiments, the coating is disposed on both sides of the substrate.

[0105] In some embodiments, the coating includes inorganic fillers and adhesives.

[0106] In some embodiments, the inorganic filler comprises Al2O3, SiO2, TiO2, ZrO2, Mg(OH)2, MgO, SnO2, CaCO3, BaSO4, TiN, AlN, Na2O·mTiO2, K2O·nTiO2, BaO x MTiO3 and combinations thereof, wherein m is 3 or 6, n is 1, 2, 4, 6 or 8, x is 1 or 2, and M is Ba, Sr or Ca. Inorganic fillers may be spherical, plate-like, disc-like, needle-like, cylindrical, irregular or other known particle shapes.

[0107] In some embodiments, the inorganic filler includes one or more of alumina, hydrated alumina, boehmite, magnesium hydroxide, magnesium oxide, titanium dioxide, zirconium oxide, and barium sulfate.

[0108] In some implementations, the binder is a water-soluble polymer.

[0109] In some implementations, the water-soluble polymer is a homopolymer or copolymer.

[0110] In some embodiments, the water-soluble binder includes at least one of polyamide, polycarboxylate, polycarboxylic acid, polyacrylic acid, polyacrylate, polymethacrylic acid, polymethacrylate, polyvinyl alcohol, polyvinyl acetate, polyacrylamide, cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, carboxymethyl cellulose, cyanoethyl cellulose, nitrile rubber (NBR), styrene-butadiene rubber (SBR), and latex.

[0111] In some implementations, the binder is an oil-soluble polymer.

[0112] In some embodiments, non-limiting examples of oil-soluble polymers include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyester, polyether, polyvinyl compounds, polyolefins, rubber, polyvinylpyrrolidone, polystyrene, nitrile rubber (NBR), styrene-butadiene rubber (SBR), latex, acrylonitrile-styrene-butadiene copolymer, halogenated polymers, fluorinated polymers, chlorinated polymers, unsaturated polymers, conjugated diene polymers, and combinations thereof.

[0113] Secondary batteries A second aspect of this application also proposes a secondary battery comprising the aforementioned battery cell.

[0114] In some embodiments, the secondary battery includes a lithium-ion battery. The lithium-ion battery of this application, which uses the above-mentioned cell, can improve the heat dissipation performance of the cell, reduce the probability of battery thermal runaway, and improve the lifespan and safety of the energy storage battery.

[0115] In some implementations, the secondary battery also contains an electrolyte.

[0116] In some embodiments, the electrolyte may include at least one of a gel electrolyte, a solid electrolyte, and a liquid electrolyte. In some embodiments, the liquid electrolyte may include a non-aqueous solvent and a lithium salt.

[0117] In some embodiments, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB, and lithium difluoroborate. In some embodiments, the non-aqueous solvent may be at least one of carbonate compounds, carboxylic acid ester compounds, and ether compounds. In some embodiments, the carbonate compound may include at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorocarbonate compounds. In some embodiments, the chain carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. In some embodiments, the cyclic carbonate compound may include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. In some embodiments, the fluorocarbonate compound may include at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. In some embodiments, the carboxylic acid ester compound may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonate lactone, caprolactone, and methyl formate. In some embodiments, the ether compound may include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof. In some embodiments, the non-aqueous solvent may also include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters.

[0118] <Energy Storage Devices> A third aspect of this application also proposes an energy storage device comprising the aforementioned secondary battery.

[0119] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. The purpose of the electronic device described in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, the electronic device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, android robots, etc.

[0120] Unless otherwise specified in the following examples, the techniques or conditions described in the literature in this field or in accordance with the product instructions shall apply. All reagents or instruments without a specified manufacturer are commercially available conventional products.

[0121] Example 1 This embodiment provides a secondary battery, such as Figure 1 As shown, the battery includes a battery cell, which includes a negative electrode, a separator, and a positive electrode. The separator is disposed between the negative electrode and the positive electrode. The negative electrode includes a negative current collector, a negative active material layer, and an electrospun layer arranged in sequence. The positive electrode includes a positive current collector and a positive active material layer arranged in sequence. A thermally conductive layer is coated on the surface of the separator, and the electrospun layer is adjacent to and in contact with the thermally conductive layer.

[0122] The thickness of the positive electrode active material layer is 70 μm, and the thickness of the negative electrode active material layer is 50 μm.

[0123] The preparation method of secondary batteries is as follows: 1. Preparation of the diaphragm: (1) Select a coated membrane with a porosity of 38% and a thickness of 9μm, of which the base membrane is 6μm thick, a ceramic layer of 2μm is coated on one side, and an adhesive layer of 0.5μm is coated on both sides. (2) Graphene material and binder PAA are mixed at a mass ratio of 95:5 and added to deionized water to prepare a graphene slurry with a solid content of 30%. The graphene slurry is coated on the uncoated ceramic layer side of the separator and dried to obtain the thermally conductive layer. The thermally conductive layer adopts a segmented thickness distribution, which can be controlled by the segmented thickness when coating the separator with a gravure printing plate, including controlling parameters such as the solid content and viscosity of the slurry, the mesh size of the gravure roller, and the number of coatings. The thermally conductive layer adopts a gradient thickness. The thickness of the thermally conductive layer at the innermost starting end of the cell is 2μm, and the difference in thickness between the innermost starting end and the outermost ending end is 0.5μm (i.e., the thickness at the outermost ending end is 1.5μm).

[0124] 2. Preparation of the negative electrode sheet: (1) Silicon carbide (SiC), conductive carbon nanotubes (CNT), binder polyacrylic acid (PAA), and sodium carboxymethyl cellulose (CMC) are mixed thoroughly in deionized water solvent at a mass ratio of SiC:CNT:PAA:CMC=97:1:1.2:0.8 to obtain a negative electrode slurry with a solid content of 70%. The negative electrode slurry is coated on the current collector copper foil, dried at 85°C, and then cold-pressed to form a negative electrode active material layer. Then the edges are cut and strips are slit. (2) Dissolve polyisobutylene rubber in a mixed solution of N,N-dimethylformamide and acetone (50%wt:50%wt), with a solid content of 15%, and electrospin the above solution on the surface of the negative electrode to form an electrospun layer with a thickness of 2μm. (3) Dry the negative electrode sheet under vacuum at 85℃ for 12 hours; then weld the tabs to obtain the negative electrode sheet.

[0125] 3. Preparation of the positive electrode sheet: The positive electrode active material LiCoO2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in N-methylpyrrolidone solvent (NMP) at a mass ratio of 97:2:1 to obtain a positive electrode slurry with a solid content of 70%. The positive electrode slurry was coated on a current collector aluminum foil, dried at 85°C, and then cold-pressed. After trimming and slitting, it was dried under vacuum at 85°C for 6 hours and then the tabs were welded to obtain the positive electrode sheet.

[0126] 4. Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent of dimethyl carbonate (DMC), ethylene carbonate (EC), and ethyl methyl carbonate (EMC) (mass ratio of DMC, EC, and EMC was 3:5:2) to obtain the electrolyte.

[0127] 5. Preparation of secondary batteries: The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets, and then wound to obtain the battery cell. The battery cell is then sealed in an aluminum-plastic film outer packaging and baked in an 85°C vacuum oven for 48 hours. Electrolyte is injected into the dried battery, followed by sealing, settling, formation, shaping, and capacity testing, and then a second sealing to obtain a secondary battery.

[0128] Example 2 The difference from Example 1 is that the thickness of the electrospun layer is different; the thickness of this example is 0.5 μm.

[0129] The rest is the same as in Example 1, and will not be repeated here.

[0130] Example 3 The difference from Example 1 is that the thickness of the electrospun layer is different; the thickness of this example is 4.5 μm.

[0131] The rest is the same as in Example 1, and will not be repeated here.

[0132] Example 4 The difference from Example 1 is that the electrospinning layer material is different. In this example, the electrospinning layer material is ethylene-vinyl acetate copolymer with a melting point of 90°C.

[0133] The rest is the same as in Example 1, and will not be repeated here.

[0134] Example 5 The difference from Example 1 is that the electrospinning layer material is different. In this example, the electrospinning layer material is ethylene propylene rubber with a melting point of 120°C.

[0135] The rest is the same as in Example 1, and will not be repeated here.

[0136] Example 6 The difference from Example 1 is that in this example, 5 wt% of the flame retardant melamine cyanurate was added to the electrospun layer.

[0137] The rest is the same as in Example 1, and will not be repeated here.

[0138] Example 7 The difference from Example 1 is that the thermally conductive material is different. In this example, the thermally conductive layer material is silicon carbide with a thermal conductivity of 500 W / (m·K).

[0139] The rest is the same as in Example 1, and will not be repeated here.

[0140] Example 8 The difference from Example 1 is that the thermally conductive material is different. In this example, the thermally conductive layer material is boron nitride with a thermal conductivity of 300 W / (m·K).

[0141] The rest is the same as in Example 1, and will not be repeated here.

[0142] Example 9 The difference from Example 1 is that the thickness of the thermal conductive layer is different. In this example, the thickness of the thermal conductive layer at the innermost starting end of the cell is 1 μm, and the difference between the thickness of the thermal conductive layer at the outermost ending end is 0.5 μm (that is, the thickness of the outermost ending end is 0.5 μm).

[0143] The rest is the same as in Example 1, and will not be repeated here.

[0144] Example 10 The difference from Example 1 is that the thickness of the thermal conductive layer is different. In this example, the thickness of the thermal conductive layer in the innermost region of the battery cell is 4.5 μm, and the difference between the thickness of the thermal conductive layer in the outermost region and the thickness of the thermal conductive layer is 0.5 μm.

[0145] The rest is the same as in Example 1, and will not be repeated here.

[0146] Example 11 The difference from Example 1 is that the thickness of the thermal conductive layer at the innermost starting end of the battery cell in this example is 1 μm.

[0147] The rest is the same as in Example 1, and will not be repeated here.

[0148] Comparative Example 1 The difference from Example 1 is that no thermally conductive layer and electrospinning layer (i.e. no thermal protection layer) are provided in this comparative example.

[0149] The rest is the same as in Example 1, and will not be repeated here.

[0150] Comparative Example 2 The difference from Example 1 is that no heat-conducting layer is provided in this comparative example.

[0151] The rest is the same as in Example 1, and will not be repeated here.

[0152] Comparative Example 3 The difference from Example 1 is that no electrospinning layer was provided in this comparative example.

[0153] The rest is the same as in Example 1, and will not be repeated here.

[0154] Comparative Example 4 The difference from Example 1 is that the thermal conductive layer in this comparative example has a uniform thickness, and the thickness of the thermal conductive layer at the innermost starting end and the outermost ending end of the battery cell is 2μm.

[0155] The rest is the same as in Example 1, and will not be repeated here.

[0156] The parameter settings for the embodiments and comparative examples are shown in Table 1: Table 1 Electrospinning layer material Melting point of electrospun layer (°C) Electrospun layer thickness (μm) Does it contain flame retardant? Thermal conductive layer material Thermal conductivity of the heat-conducting layer (W / (m·K)) Thermal conductive layer thickness (μm) 130℃ hot box pass rate 135℃ hot box pass rate Example 1 Polyisobutylene rubber 105 2 none graphene 5300 2~1.5 20 / 20 16 / 20 Example 2 Polyisobutylene rubber 105 0.5 none graphene 5300 2~1.5 20 / 20 14 / 20 Example 3 Polyisobutylene rubber 105 4.5 none graphene 5300 2~1.5 20 / 20 17 / 20 Example 4 Ethylene-vinyl acetate copolymer 90 2 none graphene 5300 2~1.5 20 / 20 17 / 20 Example 5 EPDM rubber 120 2 none graphene 5300 2~1.5 20 / 20 14 / 20 Example 6 Polyisobutylene rubber 105 2 have graphene 5300 2~1.5 20 / 20 17 / 20 Example 7 Polyisobutylene rubber 105 2 none silicon carbide 500 2~1.5 17 / 20 11 / 20 Example 8 Polyisobutylene rubber 105 2 none Boron nitride 300 2~1.5 15 / 20 8 / 20 Example 9 Polyisobutylene rubber 105 2 none graphene 5300 1~0.5 19 / 20 14 / 20 Example 10 Polyisobutylene rubber 105 2 none graphene 5300 4.5~4 20 / 20 17 / 20 Example 11 Polyisobutylene rubber 105 2 none graphene 5300 2~1 20 / 20 16 / 20 Comparative Example 1 / / / / / / / 3 / 20 0 / 20 Comparative Example 2 Polyisobutylene rubber 105 2 none / / / 8 / 20 0 / 20 Comparative Example 3 / / / / graphene 5300 2~1.5 11 / 20 2 / 20 Comparative Example 4 Polyisobutylene rubber 105 2 none graphene 5300 2 14 / 20 6 / 20 Performance testing High-temperature abuse test: 1) Place the battery in a heated box after fully charging it; 2) Heat the hot chamber at a rate of 5±0.5℃ / min to raise the temperature of the hot chamber from room temperature to the test temperature, for example: the test temperature is 130℃ or 135℃; 3) The hot box is left to stand at the test temperature for 60 minutes. Observe whether the battery catches fire. If it does not catch fire, it passes. Calculate the ratio of the number of batteries that do not catch fire to the total number of batteries to obtain the pass rate of the batteries under the test temperature conditions.

[0157] The test data for the examples and comparative examples are shown in Table 1.

[0158] Examples 1-3 (with varying electrospun layer thicknesses) illustrate that as the electrospun layer thickness increases, its ability to melt and prevent the electrolyte from reacting with the active material on the electrode increases after the cell temperature rises. This makes it more likely to prevent further heat generation from the electrolyte and active material, thus improving battery safety. However, increasing the electrospun layer thickness reduces the cell's energy density. Therefore, this application sets its thickness in the range of 0.5-4.5 μm.

[0159] Examples 1 and 4-5 (with different melting points of the electrospun layers) illustrate that electrospun layers with different melting points need to be matched in different systems. In the examples, the battery cells are all lithium cobalt oxide systems, which usually undergo an initial reaction between the electrolyte and the active material at 90-130°C. When the melting point of the electrospun layer is lower, it will prevent the reaction between the electrolyte and the active material from generating heat earlier, thereby improving the safety performance of the battery.

[0160] Example 6 (with added electrospinning layer flame retardant) illustrates that the addition of flame retardant improves the safety performance of the battery cell, mainly by reducing the open flame time and the maximum combustion temperature of the battery cell after thermal runaway.

[0161] Examples 1 and 7-8 (with different thermal conductivity of the thermally conductive materials) illustrate that the higher the thermal conductivity, the faster the heat generated inside the battery cell can be dissipated, avoiding thermal runaway caused by the accumulation of heat inside the battery cell.

[0162] Examples 1 and 9-10 (with different thermal conductive layer thicknesses) illustrate that a thicker thermal conductive layer results in better heat dissipation and higher cell safety performance, but also lower cell energy density. Therefore, this application sets the thickness in the range of 0.5-4.5 μm.

[0163] Examples 1, 11 and Comparative Example 4 (with or without segmented thickness distribution of the thermal conductive layer) illustrate that when the thermal conductive layer adopts segmented thickness distribution, the heat inside the cell can dissipate to the outside more quickly.

[0164] As can be seen from Examples 1-10 and Comparative Examples 1-3, this application, by setting a thermal protection functional layer between the electrode and the separator, and by adjusting parameters, achieves higher 130°C and 135°C hot box pass rates for the lithium-ion battery, indicating that the lithium-ion battery of this application has good thermal safety performance. In contrast, the lithium-ion batteries of the comparative examples, which either lack a thermal protection functional layer or have only one layer, have lower 130°C and 135°C hot box pass rates, indicating poor thermal safety performance.

[0165] The embodiments described above are merely examples of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these modifications and improvements all fall within the protection scope of this application.

Claims

1. A battery cell, characterized in that, The battery includes a positive electrode, a negative electrode, a separator, and a thermal protection layer. The separator is disposed between the positive electrode and the negative electrode. The thermal protection layer is disposed between the positive electrode and the separator, and / or between the negative electrode and the separator. The thermal protection layer includes an electrospinning layer and a thermally conductive layer. The thickness of the thermally conductive layer decreases in a stepped manner along the winding direction of the battery cell.

2. The battery cell according to claim 1, characterized in that, Along the winding direction of the battery cell, the thickness of the thermal conductive layer is uniformly distributed within each winding unit; between adjacent winding units, the thickness of the thermal conductive layer decreases in a stepped manner, and the thickness difference is ≥0.05μm.

3. The battery cell according to claim 1, characterized in that, Along the winding direction of the battery cell, the thickness of the starting end of the thermal conductive layer is T1, and the thickness of the ending end of the thermal conductive layer is T2, satisfying T1-T2≥ 0.5 μm.

4. The battery cell according to any one of claims 1-3, characterized in that, At least one of the following conditions must be met: A1. The porosity of the coating of the thermal protection functional layer is 70%~95%; A2. The thickness of the thermal protection functional layer is 1μm~9μm; A3. The thickness of the electrospun layer is 0.5~4.5μm; A4. The thickness of the thermally conductive layer is 0.5~4.5μm; A5. The thermally conductive layer is disposed on the side close to the diaphragm.

5. The battery cell according to claim 1, characterized in that, The electrospun layer comprises at least one of the following: ethylene-propylene random polymer, ethylene-vinyl acetate copolymer, ethylene-propylene rubber, block copolymer polypropylene, polyisobutylene rubber, thermoplastic elastomer, amino-terminated liquid nitrile rubber, thermoplastic polyurethane, or polycaprolactone. And / or, the melting point Tm of the electrospun layer satisfies: 60℃ ≤ Tm ≤ 140℃, preferably, 90℃ ≤ Tm ≤ 120℃.

6. The battery cell according to claim 1, characterized in that, The thermally conductive layer comprises at least one of ceramic materials or carbon materials, wherein the ceramic material comprises at least one of boron nitride, aluminum nitride or silicon carbide, and the carbon material comprises at least one of graphene, carbon nanotubes or carbon fibers. And / or, the thermal conductivity of the thermal conductive layer is 10 W / (m·k) to 6000 W / (m·k), preferably 150 W / (m·k) to 6000 W / (m·k).

7. The battery cell according to claim 1, characterized in that, The electrospun layer also includes flame-retardant materials.

8. The battery cell according to claim 7, characterized in that, At least one of the following conditions must be met: B1. The flame retardant material includes at least one of inorganic hydroxides, intumescent flame retardants, boron-based flame retardants, nitrogen-based flame retardants, or phosphorus-based flame retardants; B2. The particle size Dv50 of the flame retardant material particles is 100nm~3μm; B3. The mass fraction of the flame-retardant material in the electrospun layer is 2% to 15%. B4. The decomposition temperature of the flame retardant material is ≥200℃.

9. A secondary battery, characterized in that, It includes the battery cell as described in any one of claims 1 to 8.

10. An energy storage device, characterized in that, It includes the secondary battery as described in claim 9.

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