Sodium secondary battery cell and electrical device

Abstract

Provided in the present application are a sodium secondary battery cell and an electrical device. The sodium secondary battery cell comprises a separator, wherein the separator comprises a porous base film and a heat-resistant coating provided on at least one side of the porous base film, the heat-resistant coating comprises a fibrous material and a filler, and the coating weight of the heat-resistant coating on one side is 1.3 g / m2-2.0 g / m2.

Description

Sodium secondary battery cells and electrical devices Cross-references to related applications This application claims priority to Chinese patent application 202510122831.4, filed on January 26, 2025, entitled “Sodium secondary battery cell and power supply device”, the entire contents of which are incorporated herein by reference. Technical Field

[0001] This application relates to the field of battery technology, and in particular to a sodium secondary battery cell and an electrical device. Background Technology

[0002] Sodium metal is considered the most likely electrode material to replace lithium metal due to its high theoretical capacity, abundant reserves, and low cost. However, because sodium ions have a lower surface energy than lithium ions, they are more likely to reach the electrode surface for reduction reactions. Therefore, the faster reduction reaction rate makes it easier for dendrites to form, increasing the risk of dendrites piercing the separator and consequently increasing the risk of battery short circuits. Summary of the Invention

[0003] This application provides a sodium secondary battery cell and an electrical device to control the risk of sodium dendrites puncturing the separator and improve the cycle performance of the battery cell.

[0004] The first aspect of this application provides a sodium secondary battery cell, including a separator membrane. The separator membrane comprises a porous base membrane and a heat-resistant coating disposed on at least one side of the porous base membrane. The heat-resistant coating comprises a fibrous material and fillers, and the coating weight of the heat-resistant coating on one side is 1.3 g / m³. 2 -2.0g / m 2 .

[0005] The heat-resistant coating of the separator in this application includes fibrous materials and fillers, and the coating weight is greater than that of conventional heat-resistant coatings. Therefore, it is beneficial to reduce the pore size of the pores in the coating, increase the pore density, and increase the tortuosity of the pores in the coating, thereby reducing the risk of battery short circuit.

[0006] In some embodiments, the coating weight of the heat-resistant coating on one side is 1.52 g / m². 2 -1.85g / m 2 .

[0007] In some embodiments, the tortuosity of the separator is 1.6-3.4, optionally 1.8-3.3. This improves the control over sodium dendrite growth without significantly increasing the sodium ion transport path, thereby better improving the capacity retention of the battery cells.

[0008] In some embodiments, the thickness of the heat-resistant coating on one side is 1.0 μm-3.0 μm, optionally 1.4 μm-2.2 μm. This allows for better utilization of the additive effect of the coating weight on pore tortuosity and control of the influence of tortuosity on ion conductivity.

[0009] In some embodiments, the average pore size of the separator is between 15 nm and 80 nm, and optionally between 20 nm and 60 nm. This is beneficial for improving the conductivity of sodium ions.

[0010] In some embodiments, the morphology of the fibrous material includes one or more of the following: fibrous, rod-shaped, tubular, bar-shaped, and filamentous.

[0011] In some embodiments, the average diameter of the fibrous material is ≤80nm, optionally 10nm-80nm. Dendritic fibers with the above-mentioned average diameter have greater strength to support the fibers and form a skeletal framework, and can also create more pores between the fibers. These pores are beneficial for improving ionic conductivity and for accommodating fillers, thereby synergistically enhancing the strength of the coating with the fillers.

[0012] In some embodiments, the average length of the fibrous material is 100 nm to 800 nm, and more preferably 200 nm to 600 nm. The fibrous materials with the above-mentioned lengths form a relatively stable entanglement, thereby providing better strength support for the coating.

[0013] In some embodiments, the aspect ratio of the fibrous material is 5-60, and more preferably 10-30. By controlling the aspect ratio of the fibrous material, the entanglement and mutual support between the fibrous materials form a better match, 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 a supporting effect on 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, and gives the diaphragm better heat resistance and voltage breakdown resistance.

[0014] In some embodiments, the fibrous material includes at least one of organic and inorganic materials.

[0015] In some embodiments, the organic material includes at least one of cellulose nanofibers, polytetrafluoroethylene nanofibers, and polyamide nanofibers. Optionally, the cellulose nanofibers include at least one of cellulose nanofibers, cellulose nanowhiskers, and bacterial cellulose nanofibers.

[0016] In some embodiments, the inorganic material includes at least one of halloysite nanotubes, nanorod alumina, nanorod boehmite, nanorod silica, and glass fiber.

[0017] In some embodiments, the fibrous material in the coating has a weight content of 5%-40%, optionally 6%-20%.

[0018] In some embodiments, the filler includes a first filler, the particle size of which is 12nm-80nm, optionally 15nm-50nm.

[0019] In some embodiments, the first filler includes at least one of primary particles and secondary particles.

[0020] In some embodiments, the particle size of the first filler with a primary particle morphology is 10nm-80nm, and optionally 15nm-75nm.

[0021] In some embodiments, the particle size of the first filler with secondary particle morphology is 100nm-500nm, and can be selected as 120nm-400nm.

[0022] The first filler with nano-sized particles can be better dispersed in the pores formed by fibrous materials, and has a better supporting effect on fibrous materials.

[0023] In some embodiments, the first filler comprises one or more of inorganic particles and organic particles.

[0024] 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.

[0025] 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.

[0026] In some embodiments, the first filler comprises inorganic particles, and the crystal form of the inorganic particles includes at least one of the θ crystal form, δ crystal form, γ crystal form, and η crystal form.

[0027] In some embodiments, the crystal forms of inorganic particles include δ crystal form and θ crystal form.

[0028] In some embodiments, based on the total weight of the inorganic particles in the first filler, the content of δ-crystalline inorganic particles is 50wt%-60wt%, and the content of θ-crystalline inorganic particles is 40wt%-50wt%.

[0029] In some embodiments, the BET specific surface area of ​​the first packing is ≥15m². 2 / g, optional 18m 2 / g-65m 2 / g.

[0030] In some embodiments, the content of the first filler is ≥15wt% based on the total weight of the coating, optionally 20wt%-75wt%.

[0031] In some embodiments, the filler further includes a second filler with a particle size larger than that of the first filler. The larger particle size of the second filler allows it to better perform its supporting role in the coating, reducing the shrinkage of the first filler, decreasing the amount of adhesive required, and thus improving the heat resistance of the separator. The larger particle size of the second filler also helps to create a coating with more pores and less water content with a smaller amount used, further improving the ion conductivity and electrolyte wetting and retention properties of the separator.

[0032] In some embodiments, the particle size of the second filler is 100nm-450nm, which may be 150nm-350nm.

[0033] When the average particle size of the second filler is within the above range, the coating can have a more suitable pore size result, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charging and discharging, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0034] In some embodiments, the second packing satisfies one or more of the following conditions (1) to (6):

[0035] (1) The second filler has a primary particle morphology;

[0036] (2) The BET specific surface area of ​​the second packing is ≤15m². 2 / g, optional 7m 2 / g-15m 2 / g;

[0037] (3) Based on the total weight of the coating, the content of the second filler is ≤40wt%, and can be selected as 2wt%-35wt%;

[0038] (4) The second filler includes at least one of inorganic particles and organic particles;

[0039] (5) The second filler includes inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with a primary particle morphology includes at least one of α crystal form and γ crystal form, optionally including α crystal form;

[0040] (6) The second filler includes inorganic particles with primary particle morphology, and the crystal form of the inorganic particles with primary particle morphology includes α crystal form. Based on the total weight of the inorganic particles with primary particle morphology in the second filler, the content of α crystal form inorganic particles is ≥80wt%, and can be selected as 90wt%-100wt%.

[0041] In some embodiments, the heat-resistant coating further includes a non-particulate adhesive.

[0042] In some embodiments, non-particulate adhesives include aqueous adhesives.

[0043] In some embodiments, the content of non-particulate adhesive in the heat-resistant coating is ≤3 wt% based on the total weight of the heat-resistant coating.

[0044] In some embodiments, the heat-resistant coating does not include fluorinated adhesives.

[0045] In some embodiments, the thickness of the porous base film is ≤16μm, and can be selected as 4μm-14μm.

[0046] In some embodiments, the separator further includes an adhesive layer disposed on at least a portion of the surface of the heat-resistant coating away from the porous base membrane, the adhesive layer comprising an adhesive.

[0047] In some embodiments, the adhesive layer comprises a granular adhesive.

[0048] In some embodiments, the particulate adhesive comprises non-fluorinated adhesive particles.

[0049] In some embodiments, the adhesive layer does not include fluorinated adhesives.

[0050] In some embodiments, the non-fluorinated adhesive 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.

[0051] In some embodiments, the non-fluorinated adhesive particles comprise 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.

[0052] In some embodiments, the non-fluorinated adhesive 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, and acrylate-acrylonitrile-acrylamide-styrene copolymers.

[0053] In some embodiments, the separator membrane satisfies one or more of the following conditions (1) to (9):

[0054] (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%;

[0055] (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%;

[0056] (3) The ion conductivity of the separator is 0.3 ms / cm 2 -1.6ms / cm 2 The speed can be set to 0.35 ms / cm. 2 -1.2ms / cm 2 ;

[0057] (4) The resistance of the separator is 0.5Ω-3.0Ω, and can be selected as 0.8Ω-2.5Ω;

[0058] (5) The longitudinal tensile strength of the separator is 1500 kg / cm². 2 -5500kg / cm 2 2000kg / cm² is available. 2 -4500kg / cm 2 ;

[0059] (6) The transverse tensile strength of the separator is ≥1800 kg / cm². 2 2500kg / cm² is available. 2 -5500kg / cm 2 ;

[0060] (7) The wetting length of the separator in 120 seconds is 40mm-90mm, and can be selected as 45mm-80mm;

[0061] (8) The wetting speed of the separator is 0.2 mm / s-0.8 mm / s, and can be selected as 0.3 mm / s-0.7 mm / s;

[0062] (9) The air permeability of the isolation membrane is 150s / 100mL-380s / 100mL, and can be selected as 180s / 100mL-350s / 100mL.

[0063] 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.

[0064] A second aspect of this application provides an electrical device including a battery cell, which includes any of the battery cells provided in the first aspect described above. Attached Figure Description

[0065] 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.

[0066] Figure 1 is a schematic diagram of a secondary battery cell according to an embodiment of this application.

[0067] Figure 2 is an exploded view of a secondary battery cell according to an embodiment of this application shown in Figure 1.

[0068] Figure 3 is a schematic diagram of a battery module according to one embodiment of this application.

[0069] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0070] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0071] 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.

[0072] The accompanying drawings are not drawn to scale.

[0073] Explanation of reference numerals in the attached figures:

[0074] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 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 following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the sodium-ion battery cell, separator, and power supply device of this application. 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 unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling 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] [Battery cell]

[0084] In this embodiment of the application, the battery cell is a secondary battery, which refers to a battery cell that can be recharged after being discharged to activate the active materials and continue to be used.

[0085] The sodium secondary battery cell in this application can be a sodium-ion secondary battery cell or a sodium metal secondary battery cell.

[0086] As analyzed in the background section, sodium ions in a sodium-ion battery cell have a lower surface energy than lithium ions, making it easier for them to reach the electrode surface for reduction reactions. This faster reduction reaction rate leads to the formation of dendrites, increasing the risk of dendrites piercing the separator and consequently increasing the risk of a short circuit. To address this issue, the inventors of this application discovered that after sodium deposition, dendrite growth easily changes direction when encountering obstacles. Based on this discovery, the first embodiment of this application provides a sodium-ion battery cell including a separator. The separator comprises a porous base film and a heat-resistant coating disposed on at least one side of the porous base film. The heat-resistant coating comprises fibrous material and filler, and the coating weight of the heat-resistant coating on one side is 1.3 g / m³. 2 -2.0g / m 2 .

[0087] The coating weight of a single-sided heat-resistant coating can be within a range of any two values ​​listed below as endpoints: 1.3, 1.33, 1.35, 1.38, 1.4, 1.45, 1.48, 1.5, 1.52, 1.55, 1.57, 1.6, 1.63, 1.65, 1.68, 1.7, 1.72, 1.75, 1.78, 1.8, 1.82, 1.85, 1.88, 1.90, 1.95, 2.0. For example, the coating weight of a single-sided heat-resistant coating can be 1.35 g / m². 2 -2.0g / m 2 1.35g / m 2 -1.95g / m 2 1.4g / m 2 -2.0g / m 2 1.4g / m 2 -1.85g / m 2 1.5g / m 2 -2.0g / m 2 1.52g / m 2 -1.85g / m 2 1.55g / m 2 -1.75g / m 2 .

[0088] The heat-resistant coating of the separator in this application includes fibrous materials and fillers, and its coating weight is greater than that of conventional heat-resistant coatings. Therefore, it is beneficial to reduce the pore size of the pores in the coating, increase the pore density, and increase the tortuosity of the pores in the coating, thereby reducing the risk of battery short circuit. Specifically:

[0089] 1. The reduced pore size and increased density of the heat-resistant coating facilitate more uniform sodium ion flow through the isolation membrane, effectively controlling local sodium ion accumulation caused by uneven pore size and uneven position distribution, thereby reducing sodium dendrite formation.

[0090] 2. Once sodium dendrites grow into the pores of the coating, the increased tortuosity of the pores increases the obstacles to sodium dendrite growth, causing the trend of sodium dendrites to change from growing along the coating thickness direction to growing along the coating transverse direction. This effectively controls dendrite puncture and facilitates the uniform deposition and growth of sodium metal on the surface of the negative electrode current collector, improving the utilization effect of active sodium and thus extending the cycle life of sodium secondary battery cells.

[0091] 3. Due to the increased weight of the heat-resistant coating, not only is the growth of sodium dendrites effectively suppressed, but the increased heat-resistant coating also significantly improves the wetting / liquid retention capacity. Even after the electrolyte is consumed in the later stages, the electrolyte held in the coating still has good wetting ability for the positive and negative electrodes, effectively avoiding the drying of ion channels and causing a series of further side reactions, thus improving the later cycle performance of sodium secondary battery cells.

[0092] It should be noted that when the separator is sampled from the battery, the coating weight can be tested using the following method:

[0093] Cut the separator into separator samples with an area of ​​S (e.g., 100mm*100mm), weigh them and record the weight as m1;

[0094] The isolation membrane sample was soaked in dimethyl carbonate (DMC) and ultrasonically removed. The weight of the porous base membrane was recorded as m2.

[0095] The coating weight is (m1-m2) / S.

[0096] [Negative electrode plate]

[0097] A sodium secondary battery cell includes a negative electrode.

[0098] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0099] 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. As an example, the negative current collector has two surfaces opposite each other in its own thickness direction, and the negative active material is disposed on either or both of the two opposite surfaces of the negative current collector.

[0100] 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.

[0101] 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).

[0102] 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.

[0103] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0104] 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.

[0105] 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 electrodeless sodium metal secondary battery (AFSMB) cell.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] [Isolation membrane]

[0111] In some embodiments of this application, the tortuosity of the separator is 1.6-3.4, optionally 1.8-3.3, such as 1.8, 2.3, 2.6, 2.8, 3.0 or 3.3, and further optionally 2.3-3.0.

[0112] This improves the control of sodium dendrite growth without significantly increasing the sodium ion transport path, thereby improving the capacity retention of individual battery cells.

[0113] The test method for the tortuosity mentioned above is as follows:

[0114] 1. Testing the porosity ε of the isolation membrane (gas displacement method): The isolation membrane with a known apparent volume V1 is crumpled into a ball and stuffed into a sample cup. The sample cup containing the sample is placed in a true density tester, the test system is sealed, and helium gas is introduced according to the procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, the true volume V2 is calculated according to Bohr's law (PV=nRT). ε=(V1-V2) / V1*100%, where V1 is the apparent volume of the sample and V2 is the true volume of the sample.

[0115] 2. Calculate the NM MacMullin number, NM = σ0 / σeff, where σ0 represents the conductivity of the pure liquid electrolyte and σeff represents the conductivity when the separator is combined with the pure liquid electrolyte. The solvent of the pure liquid electrolyte is a mixed solution of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2, and LiPF6 is used as the lithium salt with a concentration of 1 mol / L.

[0116] 3. Calculate tortuosity: Tortuosity (τ) = (NM × ε) 1 / 2 .

[0117] Because the coating weight is increased in this application, in order to better utilize the additive effect of the coating weight on the pore tortuosity and control the influence of tortuosity on ion conductivity, in some embodiments, the thickness of the heat-resistant coating on one side is 1.0 μm-3.0 μm, such as 1.2 μm, 1.4 μm, 1.9 μm, 2.2 μm, 2.6 μm or 2.8 μm, and optionally 1.4 μm-2.2 μm.

[0118] The thickness test method for the above heat-resistant coating is as follows:

[0119] First, use cryo-ion cutting to cut the isolation membrane and take a cross-section for SEM testing; mark the coating thickness at 12 locations and take the average value.

[0120] Because this application utilizes coating weight to increase the tortuosity of the coating pores, thereby increasing the blocking effect on sodium dendrites, the pore size in the heat-resistant coating can be appropriately increased in some embodiments. In some embodiments of this application, the average pore size of the separator is between 15nm and 80nm, such as 15nm, 21nm, 23nm, 25nm, 29nm, 32nm, or 36nm, optionally between 20nm and 60nm, and further optionally between 25nm and 32nm. This is beneficial for improving the conductivity of sodium ions.

[0121] In some embodiments of this application, the median pore size of the separator is 10 nm-40 nm, optionally 15 nm-38 nm. The median pore size refers to the median of the pore size distribution of the separator, i.e., the pore diameter located in the middle of the pore size distribution curve. It is evident that the pore size in the separator is relatively small and the small pore size distribution is relatively concentrated, thus improving the uniformity of sodium ion transport, more significantly controlling the accumulation of local sodium ion flow, and controlling the formation and growth of sodium dendrites.

[0122] The average and median pore size of the separator membrane can be tested using a capillary porosity analyzer (bubble point method). An exemplary testing method is as follows: Take a circular sample with a diameter of 25 mm, and drop 3-5 drops of wetting solution onto it. After the sample is completely wetted, place it in a mold. Then, use an inert gas to compress the wetting solution in the pores of the sample. The compression pressure and flow rate are inversely proportional to the pore size. The average pore size of the sample is obtained through software sampling and pressure-pore size conversion analysis. The median pore size is determined by the value at the middle of the obtained pore size distribution curve. The testing instrument can be a PMI CFP 1500 pore size analyzer, with a testing pressure ranging from 100 psi to 350 psi.

[0123] Fibrous materials and fillers can form a stable spatial network structure, thereby further improving the heat resistance and ion conductivity of the separator. In this application, "fibrous material" refers to a material with an aspect ratio of 5 or greater. The fibrous material used in this application can be a commonly used fibrous material in nanofiber coatings, and exemplary morphologies of fibrous materials include one or more of the following: fibrous, rod-shaped, tubular, bar-shaped, and filamentous.

[0124] In some embodiments, the average diameter of the fibrous material is ≤80nm, and can be selected from 10nm to 80nm, such as 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, or 80nm. Dendritic fibers with the above-mentioned average diameter have greater strength to support the fibers and form a skeletal framework, and can also form more pores between the fibers. These pores are beneficial for improving ionic conductivity and for accommodating fillers, thereby synergistically enhancing the strength of the coating with the fillers.

[0125] 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 may further be 200nm-600nm; the fibrous materials with the above lengths form a relatively stable entanglement, thereby providing better strength support for the coating.

[0126] In some embodiments, the aspect ratio of the fibrous material is 5-60, such as 5, 7, 10, 12, 15, 18, 20, 25, 30, 33, 35, 37, 40, 45, 50, 55, or 60, and more preferably 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 diaphragm better heat resistance and voltage breakdown resistance.

[0127] 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.

[0128] The average particle size of the first and second fillers can be determined by referring to the test method for the average diameter or length of the fibrous materials above. The longest diameter of each particle is taken as the test particle size, and then the average value is taken.

[0129] The fibrous material used in this application can be selected from nanofibers conventionally used for fiber coatings, as long as it meets 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, and 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.

[0130] 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 the separator. Furthermore, compared to traditional inorganic ceramic particles, nanocellulose has a lower density, which can reduce the weight of the secondary battery and increase its gravimetric energy density.

[0131] In some embodiments, the weight content of the fibrous material in the coating is 5%-40%, such as 5%, 6%, 10%, 15%, 17%, 20%, 25%, 30%, 35%, or 40%, optionally from 6% to 20%. This fully utilizes the fibrous material to form pores and improve the heat resistance of the separator.

[0132] In some embodiments, the filler includes a first filler with a particle size of 12nm-80nm, optionally 15nm-50nm. The smaller average particle size of the first filler allows it to disperse more smoothly in the pores formed by the overlapping of the fibrous material, providing support to the fibrous material and giving the coating a more stable spatial network structure. This increases the ion conductivity of the separator, improves its heat resistance and electrolyte wetting and retention properties, and allows sodium-ion battery cells using the separator of this application to achieve high thermal safety performance, long service life, and good cycle and kinetic performance.

[0133] In some embodiments, the first filler includes at least one of primary particles and secondary particles. The primary particles have a more stable structure, which is more conducive to improving the structural stability and heat resistance of the coating; the secondary particles are generally larger in size than the primary particles, thus contributing to the stability of the coating porosity.

[0134] In some embodiments, the particle size of the first filler with a primary particle morphology is from 10 nm to 80 nm, such as 12 nm, 15 nm, 20 nm, 23 nm, 30 nm, 32 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm or 80 nm, and can be selected from 15 nm to 75 nm.

[0135] In some embodiments, the particle size of the first filler with secondary particle morphology is 100nm to 500nm, such as 100nm, 120nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm or 500nm, and can be selected as 120nm to 400nm.

[0136] The first filler with nano-sized particles can be better dispersed in the pores formed by fibrous materials, and has a better supporting effect on fibrous materials.

[0137] In some embodiments, the first filler includes 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 have hydroxyl groups, which facilitate the formation of a stable spatial network structure with the fibrous material. Organic particles are characterized by good thermal stability and resistance to decomposition. Furthermore, when the internal temperature of a battery cell reaches the melting point of the organic particles due to overcharging, overheating, or other 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 agent, thereby improving the safety performance of the battery cell.

[0138] 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.

[0139] 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.

[0140] In some embodiments, the first filler comprises inorganic particles, and the crystal form of the inorganic particles includes at least one of the θ crystal form, δ crystal form, γ crystal form, and η crystal form; optionally, the crystal form of the inorganic particles includes δ crystal form and θ crystal form; optionally, based on the total weight of the inorganic particles in the first filler, the content of δ crystal form inorganic particles is 50wt%-60wt%, and the content of θ crystal form inorganic particles is 40wt%-50wt%.

[0141] The δ-crystal form belongs to the tetragonal crystal system and has a high specific surface area. It not only has good heat resistance but also a large number of active centers distributed on its surface, exhibiting strong adsorption capacity for electrolytes, thus possessing high wetting and electrolyte retention properties. Theta-crystal inorganic particles have moderate specific surface area and hardness, thereby better improving both the heat resistance and ion conductivity of the separator. γ-crystal and η-crystal inorganic particles have the advantage of large specific surface areas. Selecting different crystal forms as the first filler helps to improve at least one of the following: heat resistance, ion conductivity, and electrolyte wetting and retention properties of the separator.

[0142] The δ-crystalline inorganic particles exhibit diffraction peaks at 2θ values ​​of 66.95°±0.2°, 45.62°±0.2°, 46.48°±0.2°, and 32.76°±0.2° in their X-ray diffraction patterns. The θ-crystalline inorganic particles exhibit diffraction peaks at 2θ values ​​of 67.28°±0.2°, 31.35°±0.2°, 32.89°±0.2°, 36.95°±0.2°, and 40.05°±0.2° in their X-ray diffraction patterns. The γ-crystalline inorganic particles exhibit diffraction peaks at 2θ values ​​of 66.95°±0.2° and 45.91°±0.2° in their X-ray diffraction patterns. The η-type inorganic particles exhibit diffraction peaks at 2θ of 31.89°±0.2° and 19.37°±0.2° in the X-ray diffraction pattern determined by X-ray diffractometer.

[0143] In some embodiments, the BET specific surface area of ​​the first packing is ≥15m². 2 / g, optional 18m 2 / g-65m 2 / g, for example, 18m 2 / g、20m 2 / g、25m 2 / g、30m 2 / g、35m 2 / g、40m 2 / g、45m 2 / g, 50m 2 / g、55m 2 / g、60m 2 / g or 65m 2 / g.

[0144] In some embodiments, the content of the first filler is ≥15wt% based on the total weight of the coating, optionally 20wt%-75wt%, such as 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, or 75wt%.

[0145] In some embodiments, the packing material further includes a second packing material with a particle size larger than that of the first packing material.

[0146] The larger particle size of the second filler allows it to better support the coating, reduce the shrinkage of the first filler, and decrease the amount of adhesive required, thereby improving the heat resistance of the separator. The larger particle size of the second filler also helps to create a coating with more pores and less water content when used in smaller quantities, which further improves the ion conductivity of the separator and its wetting and retention properties with electrolyte.

[0147] In some embodiments, the particle size of the second filler is 100nm-450nm, such as 100nm, 120nm, 150nm, 200nm, 250nm, 300nm, 310nm, 350nm, 400nm or 450nm, or optionally 150nm-350nm.

[0148] When the average particle size of the second filler is within the above range, the coating can have a more suitable pore size result, and the heat resistance and ion conductivity of the separator can be further improved. In addition, the supporting role of the second filler can be better utilized, the moisture content of the coating can be reduced, and the coating can maintain a stable pore structure during long-term charging and discharging, which is conducive to ion transport and can also improve the heat resistance of the separator.

[0149] The particle size of the fillers can be determined by the following method: A 3.6mm × 3.6mm 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 3kV and a magnification of 30,000x to obtain the SEM image. Based on the obtained SEM image, multiple (e.g., more than 5 or 10) test regions are selected for particle size analysis. Each test region has a size of 150nm × 2000nm. The average particle size obtained from each test region is then taken as the particle size constituting the corresponding filler.

[0150] In some embodiments, the second packing material satisfies one or more of the following conditions (1) to (6):

[0151] (1) The second filler has a primary particle morphology;

[0152] (2) The BET specific surface area of ​​the second packing is ≤15m². 2 / g, optional 7m 2 / g-15m 2 / g;

[0153] (3) Based on the total weight of the coating, the content of the second filler is ≤40wt%, such as 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%, and can be selected as 2wt%-35wt%;

[0154] (4) The second filler includes at least one of inorganic particles and organic particles;

[0155] (5) The second filler includes inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with a primary particle morphology includes at least one of α crystal form and γ crystal form, optionally including α crystal form;

[0156] (6) The second filler includes inorganic particles with primary particle morphology, and the crystal form of the inorganic particles with primary particle morphology includes α crystal form. Based on the total weight of the inorganic particles with primary particle morphology in the second filler, the content of α crystal form inorganic particles is ≥80wt%, and can be selected as 90wt%-100wt%.

[0157] The α-crystalline second filler has advantages such as high hardness, good heat resistance, low dielectric constant, high safety, and high true density, which can further improve the heat resistance of the coating. The α-crystalline inorganic particles exhibit diffraction peaks at 2θ of 57.48°±0.2° and 43.34°±0.2° in the X-ray diffraction pattern determined using an X-ray diffractometer.

[0158] The inorganic and organic particles of the second packing can be selected from the inorganic and organic particles of the first packing, and will not be elaborated further here.

[0159] In some embodiments, the heat-resistant coating further includes a non-particulate adhesive. This application does not impose particular limitations on the type of non-particulate adhesive; any known material with good adhesion can be selected. Optionally, the non-particulate adhesive includes an aqueous solution adhesive, which has the advantages of good thermodynamic stability and environmental friendliness, thereby facilitating the preparation and application of the coating slurry. As an example, the aqueous solution adhesive may include at least one of aqueous solution acrylic resins (e.g., homopolymers of acrylic acid, methacrylic acid, sodium acrylate monomers, or copolymers with other comonomers), polyvinyl alcohol (PVA), isobutylene-maleic anhydride copolymers, and polyacrylamide.

[0160] In some embodiments, the content of non-particulate adhesive in the heat-resistant coating is ≤3 wt% based on the total weight of the heat-resistant coating. The fibrous materials and fillers in the heat-resistant coating can form a stable spatial network structure, thereby enabling the release membrane to maintain high adhesion while reducing the amount of adhesive used.

[0161] In some implementations, the heat-resistant coating does not include fluorinated adhesives.

[0162] In some embodiments, the thickness of the porous base film is ≤16μm, and can be selected as 4μm-14μm.

[0163] In some embodiments, the separator further includes an adhesive layer disposed on at least a portion of the surface of the coating away from the porous base membrane, the adhesive layer comprising an adhesive. The adhesive layer not only prevents the coating from detaching, improving the safety performance of the battery cell, but also improves the interface between the separator and the electrode, enhancing the cycle performance of the battery cell.

[0164] In some embodiments, the adhesive layer may optionally comprise a particulate adhesive; alternatively, the particulate adhesive may comprise non-fluorinated adhesive particles.

[0165] In some implementations, the adhesive layer does not include fluorinated adhesives.

[0166] In some embodiments, the non-fluorinated adhesive 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.

[0167] In some embodiments, the non-fluorinated adhesive particles comprise 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.

[0168] In some embodiments, the non-fluorinated adhesive 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.

[0169] From the perspective of manufacturing process, the primary particle size of non-fluorinated binder particles is easier to adjust, thus better adapting to the requirements of electrode components with different structures and sizes. Moreover, its glass transition temperature can be flexibly adjusted according to the composition and ratio of its monomers, better meeting the different adhesion requirements of sodium secondary battery cells.

[0170] In some embodiments, the separator membrane satisfies one or more of the following conditions (1) to (9):

[0171] (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%;

[0172] (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%;

[0173] (3) The ion conductivity of the separator is 0.3 ms / cm 2 -1.6ms / cm 2 The speed can be set to 0.35 ms / cm. 2 -1.2ms / cm 2 ;

[0174] (4) The resistance of the separator is 0.5Ω-3.0Ω, and can be selected as 0.8Ω-2.5Ω;

[0175] (5) The longitudinal tensile strength of the separator is ≥1500 kg / cm². 2 -5500kg / cm 2 2000kg / cm² is available. 2 -4500kg / cm 2 ;

[0176] (6) The transverse tensile strength of the separator is ≥1800 kg / cm². 22500kg / cm² is available. 2 -5500kg / cm 2 ;

[0177] (7) The wetting length of the separator is 40mm-90mm, such as 40mm, 45mm, 50mm, 55mm, 60mm, 63mm, 65mm, 68mm, 70mm, 80mm, 85mm or 90mm, and can be selected as 45mm-80mm;

[0178] (8) The wetting speed of the separator is 0.2 mm / s-0.8 mm / s, and can be selected as 0.3 mm / s-0.7 mm / s;

[0179] (9) The air permeability of the isolation membrane is 150s / 100mL-380s / 100mL, and can be selected as 180s / 100mL-350s / 100mL.

[0180] In this application, the specific surface area of ​​materials (e.g., the first packing material, the second packing material) has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be tested using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer-Emmett-Teller) method. Optionally, the nitrogen adsorption specific surface area analysis can be performed using a Tri-Star 3020 specific surface area and pore size analyzer from Micromeritics, Inc., USA.

[0181] In this application, the heat shrinkage rate, tensile strength, and air permeability of the separator have meanings known in the art and can be measured using methods known in the art. For example, they can all be tested with reference to the standard GB / T 36363-2018.

[0182] In this application, the wetting length and wetting speed of the separator have meanings known in the art and can be measured using methods known in the art. An exemplary test method is as follows: The separator is cut into samples with a width of 5 mm and a length of 100 mm. The two ends of the sample are fixed and placed horizontally. 0.5 mg of electrolyte is dropped into the center of the sample. After a specified time (120 s in this application), a photograph is taken and the length of electrolyte diffusion is measured, thereby obtaining the wetting length and wetting speed of the separator. To ensure the accuracy of the test results, multiple samples (e.g., 5 to 10) can be tested, and the test results are obtained by calculating the average value. The electrolyte can be prepared as follows: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed in a mass ratio of 30:50:20 to obtain an organic solvent. Thoroughly dried LiPF6 is dissolved in the above organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0183] The ion conductivity and resistance of the separator can be obtained through AC impedance spectroscopy. Specifically, the separator is cut into circular pieces of a certain area, dried, and placed between two stainless steel electrodes. After absorbing a sufficient amount of electrolyte, it is sealed to form a coin cell, and then AC impedance spectroscopy is performed.

[0184] [Positive electrode plate]

[0185] 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.

[0186] 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.

[0187] 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.).

[0188] In some embodiments, the positive electrode active material may be a positive electrode active material known in the art for use in batteries.

[0189] As an example, the positive electrode active material of a sodium secondary battery cell may include at least one of the following materials: 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.

[0190] 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.

[0191] 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.

[0192] 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.

[0193] 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.

[0194] 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).

[0195] 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.

[0196] 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.

[0197] 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.

[0198] 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.

[0199] [Electrolytes]

[0200] 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.

[0201] In some embodiments, the electrolyte is liquid and includes an electrolyte salt and a solvent.

[0202] 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.

[0203] 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.

[0204] 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.

[0205] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0206] In some implementations, the secondary battery includes a single secondary battery cell, or a battery module and a battery pack.

[0207] 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.

[0208] 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.

[0209] This application does not impose any particular limitation on the shape of the secondary battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0210] 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 sheet, a negative electrode sheet, and a separator can 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 a single battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0211] In some implementations, individual 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 based on the application and capacity of the battery module.

[0212] Figure 3 shows a battery module 4 as an example. Referring to Figure 3, in the battery module 4, multiple 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, these multiple battery cells 5 can be fixed in place using fasteners.

[0213] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0214] 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.

[0215] 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.

[0216] In addition, this application also provides an electrical device, which includes a sodium-ion battery cell provided in this application. The sodium-ion battery cell 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.

[0217] As the electrical device, sodium-ion battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0218] 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 sodium-ion battery cells in this device, battery packs or battery modules can be used.

[0219] [Example]

[0220] 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.

[0221] Example 1 of membrane preparation

[0222] We offer porous PE substrates with a thickness of 5μm and a porosity of 30%.

[0223] Preparation of coating slurry 1: Nanocellulose (average diameter 25nm, average length 310nm, aspect ratio 12.4), primary filler alumina (average particle size of primary particles 23nm, average particle size of secondary particles 120nm, BET specific surface area 44m²) 2 / g), the second filler is alumina (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 evenly in an appropriate amount of deionized water at a mass ratio of 17:65:15:3, and then stirred at a shear rate of 18 m / s to obtain a coating slurry with a solid content of 20 wt%. The δ-crystal and θ-crystal contents in the first filler, alumina, were 57.4 wt% and 42.6 wt%, respectively, while the α-crystal content of the second filler was 100%.

[0224] Preparation of coating slurry 2: Commercially available vinylidene fluoride-hexafluoropropylene copolymer particles, adhesive polyacrylate, dispersant sodium carboxymethyl cellulose, and ether-based surfactants are mixed evenly in deionized water at a solid content mass ratio of 90:7.5:2:0.5 to obtain adhesive coating slurry 2;

[0225] Coating: Coating slurry 1 is roller-coated onto both surfaces of the PE porous base membrane to form a heat-resistant coating. Coating slurry 2 is sprayed onto both surfaces of the heat-resistant coating to form an adhesive coating. Through drying, slitting, and other processes, the release membrane 1 is obtained. The coating weight of the heat-resistant coating on one side is 1.35 g / m². 2 .

[0226] The preparation processes of isolation membrane preparation examples 2-6 and isolation membrane comparative preparation examples 1-2 are similar to those of isolation membrane preparation example 1, except that the coating weight of the heat-resistant coating is adjusted, as detailed in Table 1.

[0227] The preparation process of the separator membrane in Example 7 is similar to that in Example 1, except that non-fluorinated adhesive particles are used instead of commercially available vinylidene fluoride-hexafluoropropylene copolymer particles in the coating slurry 2. The non-fluorinated adhesive particles are secondary particles with a 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. 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. The mass ratio of the first polymer to the second polymer is 1:1.5.

[0228] Test section

[0229] The thickness of the heat-resistant coating of the separator, the average pore size, tortuosity and wetting length of the separator were tested using the test methods described above.

[0230] Example 1

[0231] The manufacturing process of a single battery cell is as follows:

[0232] Production of positive electrode sheets:

[0233] Sodium iron pyrophosphate (the positive electrode active material), carbon nanotubes (the conductive agent), and metahexafluorophosphate (the binder) were thoroughly mixed in N-methylpyrrolidone (NMP) at a mass ratio of 95:2:3 to form a uniform positive electrode slurry. This slurry was then coated onto the surface of an aluminum foil current collector. After drying, cold pressing, and die-cutting, a positive electrode sheet with a thickness of 200 μm was obtained. The coating weight of the positive electrode film on the positive electrode sheet was 350 mg / 1540.15 mm. 2 .

[0234] Preparation of negative electrode sheet:

[0235] 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.

[0236] Electrolyte preparation:

[0237] 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.

[0238] Assembly of individual battery cells:

[0239] The positive electrode, separator, and negative electrode obtained in the above steps are stacked in sequence, so that the separator is between the positive and negative electrode and can isolate the positive and 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 a negative electrode is obtained.

[0240] Performance testing:

[0241] Cyclic performance test: Each battery cell was charged to 3.65V at a 1C rate at room temperature, 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.

[0242] Table 1

[0243] A comparison of the data from each embodiment and Comparative Examples 1 and 2 shows that when the coating weight of the single-sided heat-resistant coating is 1.3 g / m², 2 -2.0g / m 2 When the coating weight is increased, the heat-resistant coating thickness increases, resulting in a decrease in the average pore size and an increase in tortuosity of the separator. Simultaneously, with increasing coating weight, the wetting length of the separator first increases and then decreases, and the corresponding cycle capacity retention of the battery cells also first increases and then decreases. This indicates that the heat-resistant coating's wetting and electrolyte retention capabilities are enhanced with increasing coating weight. However, when the coating weight exceeds a certain amount, the increased thickness and reduced pore size lead to an excessively large transport path for sodium ions within the heat-resistant coating, thus affecting the battery cell capacity retention.

[0244] 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, the separator comprising a porous base membrane and a heat-resistant coating disposed on at least one side of the porous base membrane, the heat-resistant coating comprising a fibrous material and fillers, wherein the coating weight of the heat-resistant coating on one side is 1.3 g / m³. 2 -2.0g / m 2 .

2. The sodium secondary battery cell according to claim 1, wherein, The coating weight of the heat-resistant coating on one side is 1.52 g / m². 2 -1.85g / m 2 .

3. The sodium secondary battery cell according to claim 1 or 2, wherein, The tortuosity of the isolation membrane is 1.6-3.4, and can be selected as 1.8-3.

3.

4. The sodium secondary battery cell according to any one of claims 1 to 3, wherein, The thickness of the heat-resistant coating on one side is 1.0μm-3.0μm, and can be selected as 1.4μm-2.2μm.

5. The sodium secondary battery cell according to any one of claims 1 to 4, wherein, The average pore size of the isolation membrane is between 15nm and 80nm, and optionally between 20nm and 60nm.

6. The sodium secondary battery cell according to any one of claims 1 to 5, wherein, The morphology of the fibrous material includes one or more of the following: fibrous, rod-shaped, tubular, rod-shaped, and filamentous.

7. The sodium secondary battery cell according to any one of claims 1 to 6, wherein, The average diameter of the fibrous material is ≤80nm, and can be selected as 10nm-80nm; Optionally, the average length of the fibrous material is 100nm-800nm, and more preferably 200nm-600nm; Optionally, the aspect ratio of the fibrous material is 5-60, and more preferably 10-30.

8. The sodium secondary battery cell according to any one of claims 1 to 7, wherein, 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, and 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 alumina, nanorod boehmite, nanorod silica, and glass fiber.

9. The sodium secondary battery cell according to any one of claims 1 to 8, wherein, The fibrous material in the coating has a weight content of 5%-40%, and optionally 6%-20%.

10. The sodium secondary battery cell according to any one of claims 1 to 9, wherein, The filler includes a first filler, the particle size of which is 12nm-80nm, and optionally 15nm-50nm.

11. The sodium secondary battery cell according to claim 10, wherein, The first filler includes at least one of primary particles and secondary particles; Optionally, the particle size of the first filler with the primary particle morphology is 10nm-80nm, and optionally 15nm-75nm; Optionally, the particle size of the first filler with the secondary particle morphology is 100nm-500nm, and can be selected as 120nm-400nm.

12. The sodium secondary battery cell according to claim 10 or 11, wherein, The first filler includes 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, 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. Optionally, 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.

13. The sodium secondary battery cell according to any one of claims 10 to 12, wherein, The first filler comprises inorganic particles, and the crystal form of the inorganic particles includes at least one of the following: θ crystal form, δ crystal form, γ crystal form, and η crystal form; Optionally, the inorganic particles may have δ-type and θ-type crystal forms. Optionally, based on the total weight of the inorganic particles in the first filler, the content of the δ-crystal inorganic particles is 50wt%-60wt%, and the content of the θ-crystal inorganic particles is 40wt%-50wt%.

14. The sodium secondary battery cell according to any one of claims 10 to 13, wherein, The BET specific surface area of ​​the first packing is ≥15m². 2 / g, optional 18m 2 / g-65m 2 / g; and / or, Based on the total weight of the coating, the content of the first filler is ≥15wt%, optionally 20wt%-75wt%.

15. The sodium secondary battery cell according to any one of claims 10 to 14, wherein, The filler also includes a second filler, the particle size of which is larger than that of the first filler; Optionally, the particle size of the second filler is 100nm-450nm, or 150nm-350nm.

16. The sodium secondary battery cell according to claim 15, wherein, The second packing material satisfies one or more of the following conditions (1) to (6): (1) The second filler has a primary particle morphology; (2) The BET specific surface area of ​​the second packing is ≤15m². 2 / g, optional 7m 2 / g-15m 2 / g; (3) Based on the total weight of the coating, the content of the second filler is ≤40wt%, and can be selected as 2wt%-35wt%; (4) The second filler includes at least one of inorganic particles and organic particles; (5) The second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with the primary particle morphology includes at least one of α crystal form and γ crystal form, optionally including α crystal form; (6) The second filler comprises inorganic particles with a primary particle morphology, and the crystal form of the inorganic particles with the primary particle morphology includes α crystal form. Based on the total weight of the inorganic particles with the primary particle morphology in the second filler, the content of α crystal form inorganic particles is ≥80wt%, and can be selected as 90wt%-100wt%.

17. The sodium secondary battery cell according to any one of claims 1 to 16, wherein, The heat-resistant coating also includes a non-particulate adhesive; Optionally, the non-particulate adhesive includes an aqueous solution adhesive; Optionally, based on the total weight of the heat-resistant coating, the content of the non-particulate adhesive in the heat-resistant coating is ≤3wt%.

18. The sodium secondary battery cell according to any one of claims 1 to 17, wherein, The thickness of the porous base film is ≤16μm, and can be selected as 4μm-14μm.

19. The sodium secondary battery cell according to any one of claims 1 to 18, wherein, The isolation membrane further includes an adhesive layer disposed on at least a portion of the surface of the heat-resistant coating away from the porous base membrane, the adhesive layer comprising an adhesive; Optionally, the adhesive layer comprises a granular adhesive; Optionally, the granular adhesive includes non-fluorinated adhesive particles; Optionally, the heat-resistant coating and / or the adhesive layer do not include fluorinated adhesives; Optionally, the non-fluorinated adhesive 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. Optionally, the non-fluorinated adhesive particles comprise 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 modified compounds of the above copolymers. Further optionally, the non-fluorinated adhesive 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.

20. The sodium secondary battery cell according to any one of claims 1 to 19, wherein, The isolation membrane satisfies one or more of the following conditions (1) to (9): (1) The longitudinal thermal shrinkage rate of the isolation membrane at 140℃ for 1h is 0.5%-12%, and can be selected as 2%-10%; (2) The transverse thermal shrinkage rate of the isolation membrane at 140℃ for 1h is 0.3%-10%, and can be selected as 1%-8%; (3) The ion conductivity of the isolation membrane is 0.3 ms / cm 2 -1.6ms / cm 2 The speed can be set to 0.35 ms / cm. 2 -1.2ms / cm 2 ; (4) The resistance of the isolation membrane is 0.5Ω-3.0Ω, and can be selected as 0.8Ω-2.5Ω; (5) The longitudinal tensile strength of the separator is 1500 kg / cm². 2 -5500kg / cm 2 2000kg / cm² is available. 2 -4500kg / cm 2 ; (6) The transverse tensile strength of the separator is ≥1800 kg / cm². 2 2500kg / cm² is available. 2 -5500kg / cm 2 ; (7) The wetting length of the isolation membrane in 120s is 40mm-90mm, and can be selected as 45mm-80mm; (8) The wetting speed of the isolation membrane is 0.2 mm / s-0.8 mm / s, and can be selected as 0.3 mm / s-0.7 mm / s; (9) The air permeability of the isolation membrane is 150s / 100mL-380s / 100mL, and can be selected as 180s / 100mL-350s / 100mL.

21. The sodium secondary battery cell according to any one of claims 1 to 20, 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 sodium metal secondary battery cell without a negative electrode.

22. An electrical device comprising a single battery cell, wherein, The battery cell includes any one of claims 1 to 21.

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