Sodium secondary battery cell and electric device

Abstract

A sodium secondary battery cell and an electric device. The sodium secondary battery cell comprises a separator, the separator comprises a porous substrate and a porous coating, the porous coating is provided on at least one surface of the porous substrate, the porous coating comprises heat-resistant particles and bonding particles, and the bonding particles comprise fluorine-free organic particles.

Description

Sodium secondary battery cells and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese patent application 202510123061.5, filed on January 26, 2025, entitled “Sodium Secondary Battery Cell and Power Consumption Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a sodium secondary battery cell and an electrical device. Background Technology

[0004] In the field of new energy, sodium batteries have advantages such as abundant sodium resources, low cost, high energy density and environmental friendliness, and have gradually become a research hotspot in the field of new energy. Sodium batteries can effectively alleviate the problem of lithium resource shortage and reduce the dependence of new energy development on lithium resources. Summary of the Invention

[0005] This application provides a sodium secondary battery cell and an electrical device to improve the initial coulombic efficiency and cycle performance of the sodium secondary battery cell.

[0006] The first aspect of this application provides a sodium secondary battery cell including a separator membrane. The separator membrane includes a porous substrate and a porous coating. The porous coating is disposed on at least one surface of the porous substrate membrane. The porous coating includes heat-resistant particles and adhesive particles, and the adhesive particles include fluorine-free organic particles.

[0007] The adhesive particles of the separator of the sodium secondary battery cell of this application include fluorine-free organic particles, thus avoiding the reduction and defluorination of sodium elements with fluorine-containing organic particles and the consumption of sodium ions, thereby avoiding the reduction of sodium ion quantity, improving the initial coulombic efficiency of the battery cell and maintaining the cycle stability of the sodium secondary battery cell.

[0008] In some embodiments, the porous coating does not include fluorinated adhesive particles.

[0009] In some embodiments, the number-average particle size of the fluorine-free organic particles is 7 μm-25 μm, optionally 7 μm-15 μm.

[0010] In some embodiments, the morphology of the fluorine-free organic particles includes aggregates of primary particles.

[0011] In some embodiments, the porous coating includes a heat-resistant layer and an adhesive layer, the heat-resistant layer being disposed between the porous substrate and the adhesive layer, and fluorine-free organic particles being disposed in the adhesive layer.

[0012] In some embodiments, the mass percentage of fluorine-free organic particles is 80%-95% based on the total mass of the adhesive layer.

[0013] In some embodiments, fluorine-free organic particles are embedded in heat-resistant particles and form protrusions on the surface of the porous coating.

[0014] In some embodiments, the fluorine-free organic particles include a first glass transition temperature Tg1 and a second glass transition temperature Tg2, wherein Tg1 < Tg2.

[0015] In some embodiments, 2℃≤Tg1≤30℃; alternatively, 2.5℃≤Tg1≤26℃.

[0016] In some embodiments, 26℃≤Tg2≤55℃; alternatively, 35℃≤Tg2≤51℃.

[0017] In some embodiments, the fluorine-free organic particles include at least two types of monomer units selected from acrylate monomer units, acrylic monomer units, vinyl monomer units, unsaturated nitrile monomer units, and amide monomer units.

[0018] Optionally, the fluorine-free organic particles include at least three types of monomer units selected from acrylate monomer units, acrylic monomer units, vinyl monomer units, unsaturated nitrile monomer units, and amide monomer units.

[0019] In some embodiments, the fluorine-free organic particles include one or more of the following: copolymers containing acrylate monomer units and styrene monomer units; copolymers containing acrylate monomer units and styrene monomer units; copolymers containing acrylate monomer units, acrylate monomer units, and styrene monomer units; copolymers containing styrene monomer units, aliphatic olefin monomer units, and unsaturated nitrile monomer units; and copolymers containing styrene monomer units, aliphatic olefin monomer units, and unsaturated nitrile monomer units; and modified compounds of the above copolymers.

[0020] In some embodiments, the fluorine-free organic particles include at least one of the following: acrylate-styrene-acrylamide copolymers, acrylate-styrene-acrylonitrile copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylic acid-acrylamide copolymers, acrylate-acrylic acid-acrylonitrile copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide-styrene copolymers, acrylate-styrene-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, and acrylate-acrylonitrile-acrylamide-styrene copolymers.

[0021] In some embodiments, the fluorine-free organic particles comprise a first polymer and a second polymer, wherein the first polymer and / or the second polymer comprises one or more of copolymers of acrylate monomer units, copolymers of acrylate monomer units, and copolymers containing vinyl monomer units.

[0022] Optionally, the first polymer and / or the second polymer include at least one of carboxyl, amide, and cyano groups.

[0023] In some embodiments, the first polymer and / or the second polymer comprises acrylate monomer units;

[0024] Optionally, the structural formula of the acrylate monomer forming the acrylate monomer unit is as follows:

[0025] Wherein, R1 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, and R2 includes a substituted or unsubstituted C1-C15 alkyl group, a substituted or unsubstituted 3-6 membered cycloalkyl group or isobornyl group. In the case of substitution, the substituent includes a halogen, a hydroxyl group or a C1-C6 alkyl group.

[0026] Optionally, the acrylate monomers include one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, trifluoroethyl methacrylate, glycidyl methacrylate, and trimethylolpropane triacrylate; further optionally, the acrylate monomers include one or more of methyl methacrylate, lauryl acrylate, lauryl methacrylate, and trimethylolpropane triacrylate.

[0027] In some embodiments, the first polymer and / or the second polymer comprises acrylic monomer units;

[0028] Optionally, the structural formula of the acrylic monomer forming the acrylic monomer unit is:

[0029] R3 includes hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups;

[0030] Optionally, the acrylic monomer includes one or more of acrylic acid, methacrylic acid, butenoic acid, and heptenoic acid.

[0031] In some embodiments, the first polymer and / or the second polymer comprises unsaturated nitrile monomer units;

[0032] Optionally, the structural formula of the unsaturated nitrile monomer forming the unsaturated nitrile monomer unit is as follows:

[0033] R4 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group;

[0034] Optionally, the unsaturated nitrile monomer includes at least one of acrylonitrile, methacrylonitrile, and ethyl acrylonitrile.

[0035] In some embodiments, the first polymer and / or the second polymer comprises unsaturated amide monomer units;

[0036] Optionally, the structural formula of the unsaturated amide monomer forming the unsaturated amide monomer unit is as follows:

[0037] Wherein, R5 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, and R6 includes a hydrogen atom, a hydroxyl-substituted C1-C6 alkyl group or a C1-C6 alkoxy group;

[0038] Optionally, the unsaturated amide monomers include one or more of acrylamide, N-hydroxymethylacrylamide, and N-butoxymethylacrylamide.

[0039] In some embodiments, the first polymer and / or the second polymer comprises vinyl monomer units;

[0040] Optionally, the structural formula for forming a vinyl monomer containing vinyl monomer units is as follows:

[0041] Among them, R7, R8, R9, R 10 Each independently includes a hydrogen atom, a substituted or unsubstituted phenyl group, a substituted or unsubstituted 3-6 membered cycloalkyl group, a straight-chain C1-C6 alkyl group, or a branched C3-C6 alkyl group;

[0042] Optionally, the vinyl monomer includes one or more of the following: ethylene monomer units, styrene monomer units, butadiene monomer units, and isoprene monomer units.

[0043] In some embodiments, the porous coating further includes a fibrous material;

[0044] Optionally, the morphology of the fibrous material includes one or more of the following: fibrous, rod-shaped, tubular, bar-shaped, and filamentous.

[0045] In some embodiments, the average diameter of the fibrous material is ≤80nm, and can be selected as 10nm-80nm.

[0046] In some embodiments, the average length of the fibrous material is 100nm-800nm, and more preferably 200nm-600nm.

[0047] In some embodiments, the aspect ratio of the fibrous material is 5-60, and more preferably 10-30.

[0048] In some embodiments, the fibrous material includes at least one of organic and inorganic materials.

[0049] In some embodiments, the organic material includes at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, or polyamide nanofibers; optionally, the cellulose nanofibers include at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial cellulose nanofibers; optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fiber.

[0050] In some embodiments, the heat-resistant particles include first heat-resistant particles, which include primary particles or aggregates of primary particles.

[0051] In some embodiments, the particle size of the first heat-resistant particle in the primary particle is 10 nm-80 nm.

[0052] In some embodiments, the particle size of the first heat-resistant particle in the aggregate of primary particles is 50 nm to 180 nm.

[0053] In some embodiments, the heat-resistant particles further include second heat-resistant particles, the particle size of which is larger than that of the first heat-resistant particles.

[0054] In some embodiments, the particle size of the second heat-resistant particle is greater than or equal to 150 nm, and can be selected as 200 nm-400 nm.

[0055] In some embodiments, the heat-resistant particles include one or more of inorganic particles and organic particles.

[0056] In some embodiments, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride. More preferably, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, silicon oxide, titanium oxide, zinc oxide, cerium oxide, and barium titanate.

[0057] In some embodiments, the organic particles include at least one of polystyrene particles, polyacrylic wax particles, melamine-formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamide-imide particles, polyarylamide particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

[0058] In some embodiments, the separator membrane satisfies one or more of the following conditions (1) to (5):

[0059] (1) The longitudinal thermal shrinkage rate of the isolation film at 140℃ for 1h is 0.5%-12%, and can be selected as 2%-10%;

[0060] (2) The transverse thermal shrinkage rate of the isolation film at 140℃ for 1h is 0.3%-10%, and can be selected as 1%-8%;

[0061] (3) The longitudinal tensile strength of the separator is 1500 kg / cm². 2 -5500kg / cm 2 2000kg / cm² is available. 2 -4500kg / cm 2 ;

[0062] (4) The transverse tensile strength of the separator is ≥1800 kg / cm².2 2500kg / cm² is available. 2 -5500kg / cm 2 ;

[0063] (5) The air permeability of the isolation membrane is 150s / 100mL-380s / 100mL, and can be selected as 180s / 100mL-350s / 100mL.

[0064] In some embodiments, the sodium secondary battery cell is a sodium metal secondary battery cell or a sodium-ion secondary battery cell; optionally, the sodium metal secondary battery cell is a sodium metal secondary battery cell without a negative electrode.

[0065] A second aspect of this application provides an electrical device including a secondary battery cell, the secondary battery cell including the sodium secondary battery cell provided in any of the above embodiments. Attached Figure Description

[0066] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0067] Figure 1 is a schematic diagram of a sodium secondary battery cell according to an embodiment of this application.

[0068] Figure 2 is an exploded view of a sodium secondary battery cell according to an embodiment of this application shown in Figure 1.

[0069] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0070] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0071] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0072] Figure 6 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0073] The accompanying drawings are not drawn to scale.

[0074] Explanation of reference numerals in the attached diagram: 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Sodium secondary battery cell; 51 Housing; 52 Electrode assembly; 53 Top cover assembly. Detailed Implementation

[0075] The embodiments of this application will be described in further detail below with reference to the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of this application by way of example, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0076] The embodiments of the sodium secondary battery cell and the power supply device of this application are hereby specifically disclosed in detail with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically 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. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0077] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0078] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0079] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0080] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0081] Unless otherwise specified, the terms "comprising" and "including" as used in this application are open-ended. For example, "comprising" and "including" may mean that other components not listed may also be included or contained.

[0082] Unless otherwise specified, the term "or" is inclusive in this application. For example, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0083] [Sodium secondary battery cell]

[0084] Secondary batteries, also known as rechargeable batteries or storage batteries, are batteries that can be recharged after being discharged to activate the active materials and continue to be used.

[0085] Typically, a secondary battery consists of a positive electrode, a negative electrode, a separator, and an electrolyte. During charging and discharging, sodium active ions repeatedly insert and extract between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing active ions to pass through. The electrolyte, also located between the positive and negative electrodes, mainly conducts the active ions.

[0086] Sodium in sodium-ion batteries exhibits strong reducing properties, leading to reduction and defluorination with fluorine-containing substances. This process consumes sodium ions to form sodium fluoride, resulting in a decrease in the number of mobile sodium ions. Consequently, this causes technical problems such as low initial efficiency and poor electrical performance in later stages of cycling. To address this issue, one embodiment of this application provides a sodium-ion secondary battery cell, including a separator. The separator comprises a porous substrate and a porous coating. The porous coating is disposed on at least one surface of the porous substrate and includes heat-resistant particles and adhesive particles, wherein the adhesive particles comprise fluorine-free organic particles.

[0087] The adhesive particles of the separator of the sodium secondary battery cell of this application include fluorine-free organic particles, thus avoiding the reduction and defluorination of sodium elements with fluorine-containing organic particles and the consumption of sodium ions, thereby avoiding the reduction of sodium ion quantity, improving the first efficiency of the battery cell and maintaining the stability of the sodium secondary battery cell during the cycle.

[0088] In some embodiments, the porous coating does not include fluorinated binder particles. The absence of fluorinated materials in the porous coating more effectively avoids sodium consumption and side reaction problems caused by the reduction of fluorinated substances by sodium.

[0089] [Isolation membrane]

[0090] In some embodiments, the number average particle size of the fluorine-free organic particles is 7μm-25μm, such as 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 12μm, 15μm, 17μm, 20μm, 22μm, 24μm or 25μm, optionally 7μm-15μm.

[0091] The aforementioned fluorine-free organic particles have a larger particle size, which is beneficial for forming a larger gap (GAP) between the separator and the electrode, and is conducive to electrolyte wetting, thereby reducing the risk of lithium plating in sodium secondary battery cells.

[0092] The number-average particle size of the aforementioned fluorine-free organic particles can be tested using equipment and methods known in the art. For example, a scanning electron microscope (SEM) can be used (e.g., ZEISS Sigma 300), referring to JY / T010-1996, to obtain an image of the separator. As an example, the test can be performed as follows: Randomly select a test sample of length × width = 50 mm × 100 mm on the separator. Randomly select multiple test areas (e.g., 5 areas) within the test sample, and at a certain magnification (e.g., 500x or 1000x), read the particle size of each intact organic particle in each test area (i.e., take the distance between the two farthest points on the intact organic particle as the particle size). Count the number and particle size of intact organic particles in each test area, and take the arithmetic mean of the particle sizes of intact organic particles in each test area, which is the number-average particle size of the organic particles in the test sample. To ensure the accuracy of the test results, multiple test samples (e.g., 10) can be taken and the above test can be repeated. The average value of each test sample can be taken as the final test result.

[0093] In some embodiments, the morphology of the aforementioned fluorine-free organic particles includes aggregates of primary particles. The morphology of the fluorine-free organic particles can be observed from ion-polished cross-sectional (CP) images of the separator.

[0094] In some embodiments, the porous coating includes a heat-resistant layer and an adhesive layer. The heat-resistant layer is disposed between the porous substrate and the adhesive layer, and the fluorine-free organic particles are disposed within the adhesive layer. Separating the heat-resistant layer and the adhesive layer allows for flexible configuration of the composition and structure of each layer. In sodium secondary battery cells, the adhesive layer bonds to the electrode; placing the fluorine-free organic particles within the adhesive layer fully utilizes the adhesive properties and stability of the fluorine-free organic particles.

[0095] Of course, the porous coating can be configured in ways other than those described above. The heat-resistant layer and the adhesive layer can also be combined into one layer to form a heat-resistant adhesive layer.

[0096] In some embodiments, the mass percentage of fluorine-free organic particles is 80%-95% based on the total mass of the adhesive layer, for example, 80%, 82%, 85%, 87%, 90%, 92%, or 95%. This mass percentage of fluorine-free organic particles provides sufficient adhesive force to the adhesive layer and maintains good dispersibility of the fluorine-free organic particles, thus fully utilizing their adhesive and supporting effects.

[0097] In addition to fluorine-free organic particles, the adhesive layer may also include liquid adhesives commonly used in adhesive layers, as well as optional dispersants, surfactants, etc. The liquid adhesive can be commonly used acrylic copolymers, acrylate copolymers, and other common adhesives, which will not be listed individually in this application.

[0098] In some embodiments, fluorine-free organic particles are embedded in heat-resistant particles and form protrusions on the surface of the porous coating. A portion of the fluorine-free organic particles are embedded in the heat-resistant particles, thereby forming a strong bond with the heat-resistant layer, while the protrusions formed on the surface of the porous coating create a gap between the separator and the electrode.

[0099] The glass transition temperature (Tg) is the temperature at which a polymer transitions from a rubbery state to a glassy state. It refers to the transition temperature of an amorphous polymer (including the non-crystalline portion of a crystalline polymer) from a glassy state to a rubbery state, or vice versa. It is the lowest temperature at which the macromolecular chains of an amorphous polymer can move freely, and is usually represented by Tg. The glass transition temperature is an important process indicator for polymers. Above the glass transition temperature, the polymer exhibits elasticity; below the glass transition temperature, the polymer exhibits brittleness. In some embodiments, the fluorine-free organic particles include a first glass transition temperature Tg1 and a second glass transition temperature Tg2, where Tg1 < Tg2.

[0100] The fluorine-free organic particles have two distinct glass transition temperatures. The structure of the fluorine-free organic particles with the second glass transition temperature is in a glassy state, preventing the separator from sticking together during coating, winding, and storage. Simultaneously, under significant stress at 18℃-30℃, the structure with the first glass transition temperature places the fluorine-free organic particles in a rubbery state, ensuring proper adhesion between the separator and the electrode while exhibiting pressure sensitivity. Furthermore, with increasing temperature, some polymers in the fluorine-free organic particles transition to a highly elastic state, especially after reaching 100℃. For example, at thermal runaway temperatures, the adhesion between the first organic particles in the rubbery state and the positive and negative electrode sheets is even stronger. Therefore, during overcharge thermal runaway, the separator does not easily shrink due to the binding force of the adhesion.

[0101] The glass transition temperature can be measured by methods commonly used in the art, such as by differential scanning calorimetry as described in GB / T19466.2.

[0102] In some embodiments of this application, 2℃≤Tg1≤30℃; optionally, 2.5℃≤Tg1≤26℃. The partial structure of the fluorine-free organic particles having the aforementioned first glass transition temperature Tg1 can exert sufficient adhesion in conventional cold pressing processes, which is beneficial for improving the adhesion between the separator and the electrode after cold pressing, and improving the structural stability of the battery cell.

[0103] In some embodiments of this application, 26℃≤Tg2≤55℃; optionally, 35℃≤Tg2≤51℃. The partial structure of the fluorine-free organic particles having the aforementioned second glass transition temperature Tg2 is in a glassy state at a certain temperature, thus facilitating their use as a skeletal structure for bonding particles at that temperature, providing a stable gap between the separator and the electrode; simultaneously, it transforms into a rubbery state at thermal runaway temperature, better achieving adhesion between the separator and the electrode, thereby effectively suppressing the shrinkage and deformation of the separator.

[0104] In some embodiments, the fluorine-free organic particles include at least two types of monomer units selected from acrylate monomer units, acrylic monomer units, vinyl monomer units, unsaturated nitrile monomer units, and amide monomer units; optionally, the fluorine-free organic particles include at least three types of monomer units selected from acrylate monomer units, acrylic monomer units, vinyl monomer units, unsaturated nitrile monomer units, and amide monomer units.

[0105] In some embodiments, the fluorine-free organic particles include one or more of the following: copolymers containing acrylate monomer units and styrene monomer units; copolymers containing acrylate monomer units and styrene monomer units; copolymers containing acrylate monomer units, acrylate monomer units, and styrene monomer units; copolymers containing styrene monomer units, aliphatic olefin monomer units, and unsaturated nitrile monomer units; and copolymers containing styrene monomer units, aliphatic olefin monomer units, and unsaturated nitrile monomer units; and modified compounds of the above copolymers.

[0106] In some embodiments, the fluorine-free organic particles include at least one of the following: acrylate-styrene-acrylamide copolymers, acrylate-styrene-acrylonitrile copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylic acid-acrylamide copolymers, acrylate-acrylic acid-acrylonitrile copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers, acrylate-acrylonitrile-acrylamide copolymers.

[0107] To more flexibly control the glass transition temperature of the fluorine-free organic particles, in some embodiments, the fluorine-free organic particles include a first polymer and a second polymer. The first polymer and / or the second polymer include one or more of copolymers of acrylate monomer units, copolymers of acrylic monomer units, and copolymers containing vinyl monomer units. These copolymers exhibit minimal swelling in the electrolyte and enhanced adhesion to the electrode at increasing temperatures. Therefore, they maintain the wetting effect of the separator on the electrolyte under normal operating conditions and provide better adhesion between the separator and the electrode during thermal runaway, thus better controlling the risk of thermal runaway.

[0108] In some embodiments, the first polymer and / or the second polymer optionally includes at least one of carboxyl, amide, and cyano groups. Carboxyl groups can form bonding forces with functional groups on the electrode and separator materials, improving adhesion. Amide groups are beneficial for improving polymer tackiness. Nitrile groups help improve ionic conductivity while also enhancing polymer adhesion.

[0109] The carboxyl, amide, and nitrile groups in the above polymer structure were tested according to the general rules of infrared spectroscopy analysis method in national standard GB / T 6040-2002. The sample was pressed into a KBr pellet using the transmission method, and the KBr background blank was subtracted by transmission method to obtain the sample test spectrum (resolution: 4 cm⁻¹).-1 Wavenumber range: 400cm -1 -4000cm - 1 ).

[0110] In some embodiments, the first polymer and / or the second polymer comprises acrylate monomer units; optionally, the acrylate monomers forming the acrylate monomer units have the following structural formula:

[0111] Wherein, R1 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, and R2 includes a substituted or unsubstituted C1-C15 alkyl group, a substituted or unsubstituted 3-6 membered cycloalkyl group or isobornyl group. In the case of substitution, the substituent includes a halogen, a hydroxyl group or a C1-C6 alkyl group.

[0112] Acrylic monomers contain unsaturated ester groups, which are beneficial for monomer polymerization and can improve the polymer's resistance to swelling. Furthermore, as flexible monomer segments in the molecular chain, they can regulate the glass transition temperature of organic polymers, helping to adjust the glass transition temperature of polymers within a suitable range.

[0113] In some embodiments, the acrylate monomers include one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, tert-butyl acrylate, cyclohexyl acrylate, isooctyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, trifluoroethyl methacrylate, glycidyl methacrylate, and trimethylolpropane triacrylate; further optionally, the acrylate monomers include one or more of methyl methacrylate, lauryl acrylate, lauryl methacrylate, and trimethylolpropane triacrylate.

[0114] In some embodiments, the first polymer and / or the second polymer comprises acrylic monomer units; optionally, the acrylic monomer forming the acrylic monomer unit has the following structural formula:

[0115] R3 includes hydrogen atoms, substituted or unsubstituted C1-C6 alkyl groups.

[0116] Acrylic monomers contain unsaturated carboxyl groups, which are beneficial to monomer polymerization. The presence of carboxyl-containing acrylic monomer units in fluorine-free organic particles allows the carboxyl groups to form bonding forces with the functional groups on the electrode and separator materials during the cold pressing process, thereby improving the adhesion effect.

[0117] In some embodiments, the acrylic monomer includes one or more of acrylic acid, methacrylic acid, butenoic acid, and heptenoic acid.

[0118] In some embodiments, the first polymer and / or the second polymer comprises unsaturated nitrile monomer units; optionally, the unsaturated nitrile monomer forming the unsaturated nitrile monomer unit has the following structural formula:

[0119] R4 includes hydrogen atoms or substituted or unsubstituted C1-C6 alkyl groups.

[0120] Unsaturated nitrile monomers contain unsaturated cyano groups, which are beneficial for monomer polymerization, help improve ionic conductivity, and enhance polymer adhesion.

[0121] In some embodiments, the unsaturated nitrile monomer includes at least one of acrylonitrile, methacrylonitrile, and ethyl acrylonitrile.

[0122] In some embodiments, the first polymer and / or the second polymer comprises unsaturated amide monomer units; optionally, the unsaturated amide monomer forming the unsaturated amide monomer unit has the following structural formula:

[0123] R5 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, and R6 includes a hydrogen atom, a hydroxyl-substituted C1-C6 alkyl group, or a C1-C6 alkoxy group.

[0124] Unsaturated amide monomers contain unsaturated amide groups, which are beneficial to the polymerization of monomers. These monomers also play a role in regulating molecular weight and giving the polymer good adhesion.

[0125] In some embodiments, the unsaturated amide monomers include one or more of acrylamide, N-hydroxymethylacrylamide, and N-butoxymethylacrylamide.

[0126] In some embodiments, the first polymer and / or the second polymer comprises vinyl monomer units; optionally, the vinyl monomer forming the vinyl monomer units has the following structural formula:

[0127] Among them, R7, R8, R9, R 10Each of these components independently includes a hydrogen atom, a substituted or unsubstituted phenyl group, a substituted or unsubstituted 3-6 membered cycloalkyl group, a straight-chain C1-C6 alkyl group, or a branched C3-C6 alkyl group.

[0128] The glass transition temperature of the fluorine-free organic particles can be further adjusted using the aforementioned vinyl monomers, and their swelling properties in the electrolyte can be improved.

[0129] In some embodiments, the vinyl monomer includes one or more of ethylene monomer units, styrene monomer units, butadiene monomer units, and isoprene monomer units.

[0130] In some embodiments, the porous coating also includes fibrous materials; the overlapping of the fibrous materials can form a porous structure with rich and stable pores in the porous coating, which is beneficial to improving the conduction of sodium ions and thus improving the cycle performance of the battery cell.

[0131] In this application, "fibrous material" refers to a material with an aspect ratio of 5 or greater. The fibrous material used in this application may be a fibrous material commonly used in nanofiber coatings, and exemplary morphologies of fibrous materials include one or more of the following: fibrous, rod-shaped, tubular, bar-shaped, and filamentous.

[0132] In some embodiments, the average diameter of the fibrous material is ≤80nm, optionally between 10nm and 80nm. Examples include 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, or 80nm. Fibers with the aforementioned average diameter possess greater strength to support the fiber structure and form a skeletal framework. Furthermore, they can create numerous pores between the fibers. These pores not only improve ionic conductivity but also facilitate the inclusion of fillers, thereby synergistically enhancing the strength of the porous coating.

[0133] In some embodiments, the average length of the fibrous material is 100nm-800nm, such as 100nm, 150nm, 200nm, 250nm, 300nm, 310nm, 350nm, 400nm, 450nm, 500nm, 550nm, 600nm, 650nm, 700nm, 750nm, or 800nm, and further optionally 200nm-600nm. The fibrous materials with the above-mentioned lengths form a relatively stable entanglement, thereby providing better strength support for the porous coating.

[0134] In some embodiments, the aspect ratio of the fibrous material is 5-60, such as 5, 7, 10, 12, 12.4, 15, 18, 20, 25, 30, 33, 35, 37, 40, 45, 50, 55, or 60, and further optionally 10-30. By controlling the aspect ratio of the fibrous material, the entanglement and mutual support between the fibrous materials are better matched, which is beneficial for constructing pores with appropriate porosity and pore size. This allows the filler to be dispersed in the pores built by the fibrous material, and the dispersion of the filler in the pores also provides support for the skeleton formed by the fibrous material. This is beneficial for improving the stability of the pores in the coating and the strength of the coating, giving the separator better heat resistance and voltage breakdown resistance.

[0135] The average length and average diameter of the fibrous material can be determined by the following method: A 3.6 mm × 3.6 mm sample is cut from any region of the separator. The microstructure of the coating in the sample is mapped using a scanning electron microscope (e.g., ZEISS Sigma 300). A high vacuum mode is selected, with a working voltage of 3 kV and a magnification of 30,000x to obtain a SEM image. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for length statistics. Each test region has a size of 150 nm × 2000 nm. The average length of each test region is then taken as the average length of the fibrous material. Based on the obtained SEM image, multiple (e.g., more than 5) test regions are selected for diameter statistics using Nano Measurer particle size distribution statistical software. Each test region has a size of 150 nm × 2000 nm. The average diameter of each test region is then taken as the average diameter of the fibrous material.

[0136] The average particle size of the first and second heat-resistant particles can be determined by referring to the test method for the average diameter or length of the fibrous materials mentioned above. The longest diameter of each particle is taken as the test particle size, and then the average value is calculated.

[0137] The fibrous material used in this application can be selected from nanofibers conventionally used for porous coatings of separators, as long as they meet the requirements of electrochemical stability, electrical insulation, and electrolyte stability required by the separator. In some embodiments, the fibrous material includes at least one of organic and inorganic materials; optionally, the organic material includes at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, or polyamide nanofibers; optionally, the cellulose nanofibers include at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial cellulose nanofibers; optionally, the inorganic material includes at least one of halloysite nanotubes, nanorod-shaped alumina, nanorod-shaped boehmite, nanorod-shaped silica, and glass fibers.

[0138] Nanocellulose refers to cellulose with any dimension within the nanometer range (e.g., within 100 nm). It possesses both the characteristics of cellulose and those of nanoparticles. Nanocellulose also exhibits excellent high-temperature resistance and minimal volume change upon heating, thereby improving the heat resistance of separators. Furthermore, compared to traditional inorganic ceramic particles, nanocellulose has a lower density, which can reduce the weight of sodium secondary battery cells and increase their gravimetric energy density.

[0139] In some embodiments, the weight content of the fibrous material in the above-mentioned heat-resistant coating is 5%-40%, such as 5%, 6%, 10%, 15%, 17%, 20%, 25%, 30%, 35% or 40%, optionally 6% to 20%. This fully utilizes the fibrous material to form pores and improve the heat resistance of the insulating membrane.

[0140] In some embodiments, the heat-resistant particles include first heat-resistant particles, which comprise primary particles or aggregates of primary particles. The primary particles have a more stable structure, thus improving the structural stability and heat resistance of the porous coating; the aggregates of primary particles typically have a larger particle size than the primary particles, thus contributing to the stability of the porosity of the porous coating.

[0141] In some embodiments, optionally, the particle size of the first heat-resistant particle of the primary particles is 10nm-80nm; for example, 12nm, 15nm, 20nm, 23nm, 30nm, 32nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm or 80nm. Optionally, the particle size of the first heat-resistant particle of the aggregate of primary particles is 50nm to 180nm.

[0142] In some embodiments, the heat-resistant particles further include a second heat-resistant particle, the particle size of which is larger than that of the first heat-resistant particle; optionally, the particle size of the second heat-resistant particle is greater than or equal to 150 nm, such as 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm, or optionally 200 nm-400 nm.

[0143] The first heat-resistant particles with a nanoscale diameter can be better dispersed in the pores formed by fibrous materials, resulting in better support for the fibrous materials.

[0144] In some embodiments, the heat-resistant particles include one or more of inorganic and organic particles. Inorganic particles are characterized by high hardness, high thermal stability, and resistance to decomposition, and their surfaces typically contain hydroxyl groups, which facilitate the formation of a stable spatial network structure with the fibrous materials. Organic particles are characterized by good thermal stability and resistance to decomposition. Furthermore, when the internal temperature of a sodium secondary battery cell reaches the melting point of the organic particles due to overcharging, abuse, or thermal abuse, the organic particles can melt and be drawn into the micropores of the porous substrate through capillary action, acting as a pore-closing and circuit-breaking mechanism, thereby improving the safety performance of the sodium secondary battery cell.

[0145] In some embodiments, the inorganic particles may optionally include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride. More preferably, the inorganic particles may include at least one of boehmite, alumina, barium sulfate, magnesium oxide, silicon oxide, titanium oxide, zinc oxide, cerium oxide, and barium titanate.

[0146] In some embodiments, the organic particles may optionally include at least one of polystyrene particles, polyacrylic wax particles, melamine-formaldehyde resin particles, phenolic resin particles, polyester particles, polyimide particles, polyamide-imide particles, polyarylamide particles, polyphenylene sulfide particles, polysulfone particles, polyethersulfone particles, polyetheretherketone particles, and polyaryletherketone particles.

[0147] In some embodiments, the separator membrane satisfies one or more of the following conditions (1) to (5):

[0148] (1) The longitudinal thermal shrinkage rate of the isolation film at 140℃ for 1h is 0.5%-12%, and can be selected as 2%-10%;

[0149] (2) The transverse thermal shrinkage rate of the isolation film at 140℃ for 1h is 0.3%-10%, and can be selected as 1%-8%;

[0150] (3) The longitudinal tensile strength of the separator is 1500 kg / cm². 2 -5500kg / cm 2 2000kg / cm² is available. 2 -4500kg / cm 2 ;

[0151] (4) The transverse tensile strength of the separator is ≥1800 kg / cm². 2 2500kg / cm² is available. 2 -5500kg / cm 2 ;

[0152] (5) The air permeability of the isolation membrane is 150s / 100mL-380s / 100mL, and can be selected as 180s / 100mL-350s / 100mL.

[0153] [Positive electrode plate]

[0154] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0155] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0156] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0157] In some embodiments, the positive electrode active material may be a known positive electrode active material for batteries. As an example, the positive electrode active material for a sodium-ion secondary battery may include at least one of the following: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds. However, this application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries may also be used.

[0158] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0159] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n-The price state.

[0160] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0161] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0162] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO4) y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0163] Prussian blue compounds can be a class of compounds containing sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Examples of Prussian blue compounds include Na. a Me b Me' c (CN)6, wherein Me and Me' are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0164] In some embodiments, the positive electrode film layer may optionally include an adhesive. As an example, the adhesive may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0165] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0166] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0167] [Negative electrode plate]

[0168] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0169] As an example, the negative electrode current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material substrate and a metal layer. The composite current collector can be formed by forming a metal material (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0170] When the sodium secondary battery cell is a sodium-ion secondary battery cell, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0171] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode active material is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0172] As an example, the negative electrode active material may be a negative electrode active material known in the art for use in battery cells. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for battery cells may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0173] In some embodiments, the negative electrode current collector may be made of copper foil. In some embodiments, the negative electrode film layer may also optionally include an adhesive. As an example, the adhesive may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0174] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0175] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0176] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0177] When the sodium secondary battery cell is a sodium metal secondary battery cell, the negative electrode includes a negative electrode current collector and a sodium metal layer. The sodium metal layer can be prepared using methods known in the art. When the sodium metal layer is formed by the deposition of sodium ions on the negative electrode current collector during the charging and discharging process of the battery, it is also called a negative electrode-free sodium metal battery (AFSMB) cell.

[0178] In some embodiments, the negative electrode sheet is a negative electrode current collector or a negative electrode current collector with a conductive layer on its surface. That is, the sodium secondary battery cell of this application is a negative electrode-free sodium metal secondary battery cell. During the manufacturing process, a sodium metal layer (also called "sodium foil") is not formed on the negative electrode side through coating or deposition processes. Instead, during the first charge, in the negative electrode-free sodium metal battery cell, sodium ions gain electrons on the negative electrode side, undergo reduction, and are deposited on the current collector surface in the form of metallic sodium. During discharge, the metallic sodium can be converted back into sodium ions and return to the positive electrode, achieving cyclic charging and discharging. The negative electrode-free sodium metal battery cell does not require metallic sodium or other negative electrode materials, significantly reducing the overall weight and volume of the battery and giving it a higher energy density. Furthermore, the negative electrode-free design eliminates the need to process and produce metallic sodium foil, saving costs while improving the safety performance of the battery cell.

[0179] In some embodiments, the negative electrode sheet is a negative current collector or a negative current collector with a conductive layer on its surface, the conductive layer comprising a conductive agent. By providing a conductive layer on the surface of the negative current collector, when the separator between the positive and negative electrodes is damaged, the negative current collector is short-circuited to the positive electrode through the conductive layer, thereby preventing short circuits within the electrode assembly that could lead to thermal runaway. Furthermore, the short-circuit connection between the negative current collector and the positive electrode via the conductive layer allows energy within the electrode assembly to be rapidly dissipated, thus preventing thermal runaway of the battery electrode assembly. Moreover, the conductive layer reduces the contact resistance between sodium metal and the negative current collector, increases the interaction force between them, and effectively controls the peeling off of the sodium metal layer. Simultaneously, the conductive layer also helps reduce the overpotential required for sodium deposition during charging, reduces the probability of dendrite formation, and improves the uniformity of active ion deposition after the first charge and discharge.

[0180] In some embodiments, the conductive agent is selected from one or more of metals, conductive polymers, conductive ceramic materials, carbon black (such as superconducting carbon, acetylene black, and Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The amount of the conductive agent used is very small, resulting in a thin conductive layer that cannot function as a negative electrode active material.

[0181] In some embodiments, the thickness of the conductive coating is 1μm-10μm. Specifically, the thickness of the conductive coating can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, etc., and there is no limitation here. If the thickness of the conductive coating is greater than 10μm, it will cause a certain loss of energy density. If the thickness of the conductive coating is less than 1μm, the coating distribution will be uneven and it will not play the corresponding role.

[0182] [Electrolytes]

[0183] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0184] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0185] In some embodiments, the electrolyte salt is a sodium salt, which includes one or more of sodium nitrate, sodium perchlorate, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium tetrafluorobutanoate, sodium hexafluorobenzene, sodium acetate, sodium trifluoroacetate, sodium bis(fluorosulfonyl)imide, sodium difluorooxalate-borate, sodium tetraphenylborate, sodium trifluoromethanesulfonate, sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethanesulfonyl)imide, and sodium (perfluorobutylsulfonyl)imide.

[0186] In some embodiments, the solvent in the electrolyte includes ether solvents or fluoroether solvents. Emittingly, ether solvents include one or more of ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, methyltetrahydrofuran, diphenyl ether, and crown ethers. Emittingly, fluoroether solvents include 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 2-(2-ethoxyethoxy)-1,1,1-trifluoroethane, 1,2-bis(2,2-difluoroethoxy)ethane, 2-(2-(2,2-difluoroethoxy)ethoxy)-1,1,1-trifluoroethane, 1,1, 1,3,3,3-Hexafluoroisopropylmethyl ether, 2,2,2-trifluoroethyl-1,1,2,3,3,3-hexafluoropropyl ether, 2,2-bis(trifluoromethyl)-1,3-dioxolane, 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane, 2-ethoxy-4-(trifluoromethyl)-1,3-dioxolane, octafluorotetrahydrofuran, and at least one fluorine atom. One or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether substituted with at least one fluorine atom, triethylene glycol dimethyl ether substituted with at least one fluorine atom, tetraethylene glycol dimethyl ether substituted with at least one fluorine atom, diethylene glycol diethyl ether substituted with at least one fluorine atom, diisopropyl ether substituted with at least one fluorine atom, dibutyl ether substituted with at least one fluorine atom, diethylene glycol dibutyl ether substituted with at least one fluorine atom, 1,4-diethoxybutane substituted with at least one fluorine atom, 15-crown ether-5 substituted with at least one fluorine atom, 12-crown ether-4 substituted with at least one fluorine atom, and 18-crown ether-6 substituted with at least one fluorine atom; optionally, at least one of 2,2,3,3-tetrafluoro-1,4-dimethoxybutane and 2,2-dimethoxy-4-(trifluoromethyl)-1,3-dioxolane.

[0187] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0188] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0189] In some implementations, the secondary battery includes a single secondary battery cell, or a battery module and a battery pack.

[0190] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0191] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0192] This application does not impose any particular limitation on the shape of the sodium secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square sodium secondary battery cell 5 as an example.

[0193] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a top cover assembly 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the top cover assembly 53 can cover the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the sodium secondary battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0194] In some implementations, the secondary battery cells can be assembled into a battery module. The number of secondary battery cells contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0195] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple sodium secondary battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple sodium secondary battery cells 5 can be fixed in place using fasteners.

[0196] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple sodium secondary battery cells 5 are received.

[0197] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0198] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0199] In addition, this application also provides an electrical device, which includes the secondary battery provided in this application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0200] As the electrical device, a single secondary battery cell, a battery module, or a battery pack can be selected according to its usage requirements.

[0201] Figure 6 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0202] [Example]

[0203] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0204] Example of membrane preparation

[0205] Preparation Example 1

[0206] (1) Provide a PE substrate with a thickness of 12μm and a porosity of 40%;

[0207] (2) Preparation of slurry 1: Inorganic alumina particles, organic polymer binder polymethyl methacrylate, dispersant sodium carboxymethyl cellulose and surfactant organosilicon modified polyether are mixed evenly in deionized water at a mass ratio of 93:6:0.5:0.5 to obtain slurry 1, which is used to form a heat-resistant layer.

[0208] (3) Preparation of slurry 2: Fluorine-free organic particles and aqueous solution of organic polymer adhesive polyacrylic acid are mixed evenly in deionized water at a mass ratio (dry weight ratio) of 8:2 to obtain slurry 2, which is used to form the adhesive layer. The fluorine-free organic particles are secondary particles with a number average particle size of 7.5 μm formed by mixing two polymers. The first polymer is copolymerized from methyl acrylate, isooctyl acrylate, acrylic acid, acrylamide, acrylonitrile and styrene in a mass ratio of 1:0.05:0.1:0.03:0.05:0.05, and its glass transition temperature is 20.1℃. The second polymer is copolymerized from methyl acrylate, isooctyl acrylate, 2-hydroxyethyl acrylate, acrylic acid, acrylamide, acrylonitrile and styrene in a mass ratio of 1:0.05:0.05:0.15:0.1:0.18:0.2, and its glass transition temperature is 43.8℃. The mass ratio of the first polymer and the second polymer is 1:1.5.

[0209] (4) Coating: First, slurry 1 is coated onto both sides of the substrate using a roller coating method. After drying, slurry 2 is coated onto both sides of the substrate using a spray coating method. The release film 1 is obtained through processes such as oven drying, slitting, and winding. The coating weight (dry matter basis) of slurry 1 on one side is 1.2 g / m. 2 The coating weight (dry matter basis) of slurry 2 on one side is 0.6 g / m. 2 .

[0210] Preparation Example 2

[0211] The preparation steps are the same as in Preparation Example 1, except for step (2):

[0212] Preparation of slurry 1: Nanocellulose (average diameter 25nm, average length 310nm, aspect ratio 12.4), first heat-resistant alumina particles (average particle size of primary particles 23nm, average particle size of secondary particles 120nm, BET specific surface area 44m²) 2 / g), second heat-resistant alumina particles (the average particle size of the primary particles is 310nm, and the BET specific surface area is 15m²). 2 The adhesive aqueous solution of polyacrylic acid was mixed in an appropriate amount of deionized water at a mass ratio of 15:63:20:2, and then stirred evenly to obtain a slurry 1 with a solid content of 23wt%. The δ-crystal and θ-crystal contents of the first filler, alumina, were 57.4wt% and 42.6wt%, respectively, and the α-crystal content of the second filler was 100%. The resulting separator was separator 2.

[0213] Comparative Preparation Example 1

[0214] The difference from Preparation Example 1 is that the fluorine-free organic particles in the above slurry 2 are replaced with PVDF particles with a Dv50 particle size of approximately 7.5 μm. The resulting separator is separator 3.

[0215] The battery manufacturing process is as follows:

[0216] Example 1

[0217] Production of positive electrode sheets:

[0218] The positive electrode active material sodium iron pyrophosphate, the conductive agent carbon nanotubes, and the binder metahexafluorophosphate are thoroughly mixed in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 to form a uniform positive electrode slurry. The positive electrode slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, cold pressing, and die cutting, the positive electrode sheet is obtained.

[0219] Preparation of negative electrode sheet:

[0220] Conductive agent carbon nanotubes and binder sodium carboxymethyl cellulose are dispersed in an aqueous solution at a mass ratio of 1:1, wherein the mass ratio of conductive agent to water is 1:200, to prepare a conductive slurry. The conductive slurry is coated on a copper foil current collector to form a conductive layer. After drying, a negative electrode sheet is obtained, wherein the thickness of the conductive layer is 2 μm.

[0221] Electrolyte preparation:

[0222] In an argon-filled glove box with a water content of <1ppm, diethylene glycol dimethyl ether and tetrahydrofuran were mixed at a mass ratio of 1:3, and sodium hexafluorophosphate (NaPF6) with a concentration of 1.0mol / L was added. After stirring evenly, an electrolyte was obtained.

[0223] Battery assembly:

[0224] The positive electrode, separator 1, and negative electrode obtained by the above steps are stacked in sequence, so that the separator is between the positive electrode and the negative electrode and can isolate the positive electrode and the negative electrode. Then, the stacked components are wound to obtain the electrode assembly. The electrode assembly is placed in the outer packaging, dried, and then injected with electrolyte. After formation, settling and other processes, a sodium metal battery without negative electrode is obtained.

[0225] Performance testing:

[0226] Methods for testing initial coulomb efficiency:

[0227] At 55℃, the formed battery cells were charged at a constant current rate of 0.33C (CC) to the charging cutoff voltage of 3.65V, and then charged at a constant voltage rate of 3.65V (CV) to the current of 0.05C. After standing for 10 minutes, the charging capacity was recorded. Then, the cells were discharged at a constant current rate of 0.33C (DC) to the discharge cutoff voltage of 1.5V, and the discharge capacity was recorded. The initial coulombic efficiency = discharge capacity / charging capacity × 100%.

[0228] Cyclic performance test: The battery cell was charged to 3.65V at a 1C rate at room temperature (25℃), and then discharged to 1.5V at a 1C rate. The reversible capacity was measured as C0. The charge and discharge cycle was repeated continuously, and the discharge capacity C2 was recorded after 700 cycles. The capacity retention rate after 700 cycles was calculated as (C2 / C1) × 100%. The test results are detailed in Table 1.

[0229] Table 1

[0230] The comparison of Examples 1, 2, and Comparative Example 1 shows that the initial efficiency and capacity retention rates of Examples 1 and 2 are significantly better than those of Comparative Example 1, demonstrating that using fluorine-free organic particles in the separator helps reduce sodium consumption and improve the initial efficiency and cycle performance of the battery cells. Furthermore, the comparison between Examples 1 and 2 reveals that adding fibrous materials to the heat-resistant coating can further improve the initial efficiency and cycle performance of the battery cells.

[0231] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A sodium secondary battery cell comprising a separator film, the separator film comprising a porous substrate and a porous coating layer, the porous coating layer being disposed on at least one surface of the porous substrate, the porous coating layer comprising heat-resistant particles and binder particles, and the binder particles comprising fluorine-free organic particles.

2. The sodium secondary battery cell according to claim 1, wherein, The porous coating layer does not comprise fluorine-containing binder particles.

3. The sodium secondary battery cell of claim 1, wherein, The fluorine-free organic particles have a number average particle size of 7 μm to 25 μm, optionally 7 μm to 15 μm.

4. The sodium secondary battery cell according to any one of claims 1 to 3, wherein, The fluorine-free organic particles have a morphology comprising aggregates of primary particles.

5. The sodium secondary battery cell according to any one of claims 1 to 4, wherein, The porous coating layer comprises a heat-resistant layer and a binder layer, the heat-resistant layer being disposed between the porous substrate and the binder layer, and the fluorine-free organic particles being disposed in the binder layer.

6. The sodium secondary battery cell of claim 5, wherein, The fluorine-free organic particles have a mass fraction of 80% to 95%, based on the total mass of the binder layer.

7. The sodium secondary battery cell according to claims 1 to 6, wherein, The fluorine-free organic particles are embedded in the heat-resistant particles and form protrusions on the surface of the porous coating layer.

8. The sodium secondary battery cell according to any one of claims 1 to 7, wherein, The fluorine-free organic particles comprise a first glass transition temperature Tg1 and a second glass transition temperature Tg2, and Tg1 < Tg2.

9. The sodium secondary battery cell of claim 8, wherein, 2℃ ≤ Tg1 ≤ 30℃; optionally, 2.5℃ ≤ Tg1 ≤ 26℃.

10. The sodium secondary battery cell according to claim 8 or 9, wherein, 26℃ ≤ Tg2 ≤ 55℃; optionally, 35℃ ≤ Tg2 ≤ 51℃.

11. The sodium secondary battery cell according to any one of claims 1 to 10, wherein, The fluorine-free organic particles comprise at least two types of monomer units selected from the group consisting of acrylate monomer units, acrylic monomer units, vinyl-containing monomer units, unsaturated nitrile monomer units, and amide monomer units. Optionally, the fluorine-free organic particles comprise at least three types of monomer units selected from the group consisting of acrylate monomer units, acrylic acid monomer units, vinyl-containing monomer units, unsaturated nitrile monomer units, amide monomer units.

12. The sodium secondary battery cell according to any one of claims 1 to 11, wherein, The fluorine-free organic particles comprise one or more of a copolymer comprising acrylate-styrene monomer units, a copolymer comprising acrylic acid-styrene monomer units, a copolymer comprising acrylic acid-acrylate-styrene monomer units, a copolymer comprising styrene-unsaturated nitrile monomer units, a copolymer comprising styrene-aliphatic olefin-unsaturated nitrile monomer units, and a modified compound of the above copolymers.

13. The sodium secondary battery cell according to any one of claims 1 to 12, wherein, The fluorine-free organic particles comprise at least one of an acrylate-styrene-acrylamide copolymer, an acrylate-styrene-acrylonitrile copolymer, an acrylate-acrylonitrile-acrylamide copolymer, an acrylate-acrylic acid-acrylamide copolymer, an acrylate-acrylic acid-acrylonitrile copolymer, an acrylate-acrylonitrile-acrylic acid copolymer, an acrylate-acrylonitrile-acrylamide-styrene copolymer, an acrylic acid-styrene-acrylamide copolymer, an acrylic acid-styrene-acrylonitrile copolymer, an acrylic acid-acrylonitrile-acrylamide copolymer, an acrylic acid-acrylonitrile-acrylamide-styrene copolymer.

14. The sodium secondary battery cell of any one of claims 1 to 13, wherein, The fluorine-free organic particles include one or more of a copolymer of acrylic ester monomer units, a copolymer of acrylic monomer units, and a copolymer containing vinyl monomer units; Optionally, the first polymer and / or the second polymer includes at least one of a carboxyl group, an amide group, and a cyano group.

15. The sodium secondary battery cell of claim 14, wherein, The first polymer and / or the second polymer includes acrylic ester monomer units; Optionally, the acrylic monomer forming the acrylic monomer unit has a structural formula of: wherein R1 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, and R2 includes a substituted or unsubstituted C1-C15 alkyl group, a substituted or unsubstituted 3-6 membered cycloalkyl group, or an isobornyl group, and in the case of substitution, the substituent includes a halogen, a hydroxyl group, or a C1-C6 alkyl group. Optionally, the acrylic ester monomer includes one or more of methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, isobutyl acrylate, sec-butyl acrylate, t-butyl acrylate, cyclohexyl acrylate, iso-octyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, 2-ethylhexyl methacrylate, isobornyl methacrylate, lauryl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, trifluoroethyl methacrylate, glycidyl methacrylate, and trimethylolpropane triacrylate; further optionally, the acrylic ester monomer includes one or more of methyl methacrylate, lauryl acrylate, lauryl methacrylate, and trimethylolpropane triacrylate.

16. The sodium secondary battery cell according to claim 14 or 15, wherein, The first polymer and / or the second polymer includes acrylic monomer units; Optionally, the acrylic monomer forming the acrylic monomer unit has a structural formula of: R3 includes a hydrogen atom, a substituted or unsubstituted C1-C6 alkyl group; Optionally, the acrylic monomer includes one or more of acrylic acid, methacrylic acid, butenoic acid, and heptenoic acid.

17. The sodium secondary battery cell of any one of claims 14 to 16, wherein, The first polymer and / or the second polymer includes unsaturated nitrile monomer units; Optionally, the unsaturated nitrile monomer forming the unsaturated nitrile monomer unit has a structure of: wherein R4 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group; Optionally, the unsaturated nitrile monomer includes at least one of acrylonitrile, methacrylonitrile, and ethyl acrylonitrile.

18. The sodium secondary battery cell of any one of claims 14 to 17, wherein, The first polymer and / or the second polymer includes unsaturated amide monomer units; Optionally, the unsaturated amide monomer forming the unsaturated amide monomer unit has the following structural formula: wherein R5 includes a hydrogen atom or a substituted or unsubstituted C1-C6 alkyl group, R6 includes a hydrogen atom, a hydroxyl-substituted C1-C6 alkyl group, or a C1-C6 alkoxy group; Optionally, the unsaturated amide monomer includes one or more of acrylamide, N-hydroxymethyl acrylamide, and N-butoxymethyl acrylamide.

19. The sodium secondary battery cell of any one of claims 14 to 18, wherein, The first polymer and / or the second polymer includes vinyl-containing monomer units; Optionally, the vinyl-based monomer forming the vinyl-based monomer units has a structure of: wherein R7, R8, R9, R 10 each independently comprises a hydrogen atom, a substituted or unsubstituted phenyl group, a substituted or unsubstituted 3-6-membered cycloalkyl group, a straight-chain C1-C6 alkyl group, or a branched C3-C6 alkyl group; Optionally, the vinyl-containing monomer includes one or more of ethylene monomer units, styrene monomer units, butadiene monomer units, and isoprene monomer units.

20. The sodium secondary battery cell of any one of claims 1 to 19, wherein, The porous coating further includes a fibrous material; Optionally, the morphology of the fibrous material includes one or more of fibrous, rod-like, tubular, rod-shaped, and filamentous.

21. The sodium secondary battery cell of claim 20, wherein, The average diameter of the fibrous material is ≤ 80 nm, optionally 10 nm to 80 nm; and / or, The average length of the fibrous material is 100 nm to 800 nm, further optionally 200 nm to 600 nm; and / or, The aspect ratio of the fibrous material is 5 to 60, further optionally 10 to 30.

22. The sodium secondary battery cell of claim 20 or 21, wherein, The fibrous material includes at least one of an organic material and an inorganic material; Optionally, the organic material includes at least one of nanocellulose, polytetrafluoroethylene nanofiber, or polyamide nanofiber; optionally, the nanocellulose includes at least one of cellulose nanofiber, cellulose nanowhisker, and bacterial nanocellulose; Optionally, the inorganic material includes at least one of halloysite nanotube, nanorod-like alumina, nanorod-like boehmite, nanorod-like silica, and glass fiber.

23. The sodium secondary battery cell of any one of claims 1 to 22, wherein, The heat-resistant particles include first heat-resistant particles, the first heat-resistant particles including primary particles or aggregates of primary particles; Optionally, the particle size of the first heat-resistant particles of the primary particles is 10 nm to 80 nm; Optionally, the particle size of the first heat-resistant particles of the aggregates of primary particles is 50 nm to 180 nm.

24. The sodium secondary battery cell of claim 23, wherein, The heat-resistant particles further include second heat-resistant particles, the particle size of the second heat-resistant particles being greater than the particle size of the first heat-resistant particles; Optionally, the particle size of the second heat-resistant particles is greater than or equal to 150 nm, optionally 200 nm to 400 nm.

25. The sodium secondary battery cell of claims 1-24, wherein, The heat-resistant particles include one or more of inorganic particles and organic particles; Optionally, the inorganic particles include at least one of boehmite, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, silicon oxide compound, tin dioxide, titanium oxide, calcium oxide, zinc oxide, zirconium oxide, yttrium oxide, nickel oxide, hafnium dioxide, cerium oxide, zirconium titanate, barium titanate, and magnesium fluoride, more optionally, the inorganic particles include at least one of boehmite, alumina, barium sulphate, magnesium oxide, silicon oxide compound, titanium oxide, zinc oxide, cerium oxide, and barium titanate; Optionally, the organic particles include at least one of polystyrene particles, polyacrylic wax particles, melamine formaldehyde resin particles, phenol formaldehyde resin particles, polyester particles, polyimide particles, polyamide-imide particles, polyaramid particles, polyphenylene sulfide particles, polysulfone particles, polyether sulfone particles, polyether ether ketone particles, and polyaryletherketone particles.

26. The sodium secondary battery cell of any one of claims 1 to 25, wherein, The release film satisfies one or more of the following conditions (1) to (5): (1) The release film has a longitudinal heat shrinkage of 0.5% to 12%, optionally 2% to 10%, at 140°C for 1 h; (2) The release film has a transverse heat shrinkage of 0.3% to 10%, optionally 1% to 8%, at 140°C for 1 h; (3) the longitudinal tensile strength of the separator film is 1500 kg / cm 2 - 5500 kg / cm 2 , optionally 2000 kg / cm 2 - 4500 kg / cm 2 ; (4) the transverse tensile strength of the separator film is ≥ 1800 kg / cm 2 , optionally 2500 kg / cm 2 - 5500 kg / cm 2 ; (5) The release film has an air permeability of 150 s / 100 mL to 380 s / 100 mL, optionally 180 s / 100 mL to 350 s / 100 mL.

27. The sodium secondary battery cell of any one of claims 1 to 26, wherein, The sodium secondary battery cell is a sodium metal secondary battery cell or a sodium ion secondary battery cell; optionally, the sodium metal secondary battery cell is a negative electrode-free sodium metal secondary battery cell.

28. An electrically powered device comprising a secondary battery cell, wherein The secondary battery cell comprises the sodium secondary battery cell of any one of claims 1 to 27.

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