Membrane structure and its preparation method, battery cell, sodium-ion battery

Abstract

This application provides a separator structure and its fabrication method, a battery cell, and a sodium-ion battery. The separator structure includes a base membrane, a sodium-replenishing layer, and a ceramic adhesive layer / a ceramic-containing sodium-replenishing adhesive layer. The sodium-replenishing layer is disposed on a first side of the base membrane to replenish sodium ions, and the ceramic adhesive layer / a ceramic-containing sodium-replenishing adhesive layer is disposed on a second side of the base membrane. At least through the sodium-replenishing layer, sodium ions can be replenished during the operation of the sodium-ion battery, improving the initial charge-discharge efficiency and discharge capacity retention rate of the sodium-ion battery, and reducing the temperature rise in the later stages of cell cycling.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a separator structure and its preparation method, a battery cell, and a sodium-ion battery. Background Technology

[0002] With the intensification of global climate change and the increasing depletion of fossil fuels, the development and application of safe and environmentally friendly clean energy are receiving increasing attention. Electrochemical energy storage is an indispensable key technology in the collection and utilization of clean energy sources such as wind and solar power.

[0003] Electrochemical energy storage can be achieved using either lithium-ion or sodium-ion batteries. Compared to lithium-ion batteries, sodium-ion batteries have the following advantages: First, sodium resources are abundant and inexpensive, giving them a price advantage and helping to reduce the cost of sodium-ion batteries. Second, sodium ions do not readily react with aluminum casings to form aluminum-sodium alloys, which improves the safety and stability of sodium-ion batteries. Third, sodium-ion batteries have no over-discharge characteristics, allowing them to discharge to zero volts, thus extending their battery life. Due to their lower cost, sodium-ion batteries have broad application prospects in energy storage fields where high energy density is not a primary concern.

[0004] However, the continuous consumption of sodium ions in sodium-ion batteries during the first charge-discharge cycle and subsequent cycles leads to a decrease in the first charge-discharge efficiency (first efficiency) and discharge capacity. Summary of the Invention

[0005] The diaphragm structure and its preparation method, battery cell, and sodium-ion battery provided in this application are used to improve the first charge and discharge efficiency and discharge capacity.

[0006] In a first aspect, embodiments of this application provide a diaphragm structure, comprising:

[0007] Base film, the base film having opposing first and second sides;

[0008] A sodium replenishment layer is disposed on the first side of the base film to replenish sodium ions;

[0009] A ceramic adhesive layer or a ceramic sodium-containing adhesive layer is disposed on the second side of the base film.

[0010] In some possible implementations, the sodium-supplementing layer is made of a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant.

[0011] In some possible implementations, in the sodium-supplementing layer, the first sodium-containing compound accounts for a mass percentage greater than or equal to 10% and less than or equal to 25%, the first conductive agent accounts for a mass percentage greater than or equal to 67% and less than or equal to 75%, the first binder accounts for a mass percentage greater than or equal to 3% and less than or equal to 5%, and the first dispersant accounts for a mass percentage greater than or equal to 1% and less than or equal to 3%; and / or,

[0012] The first sodium-containing compound is one of Na₂CO₃, Na₂C₂O₄, Na₃C₆H₅O₇, Na₂C₆O₆, or a mixture of at least two of them; and / or,

[0013] The first conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon; and / or,

[0014] The first adhesive is one of polytetrafluoroethylene, styrene-butadiene rubber, and polyacrylic acid, or a mixture of at least two of them; and / or,

[0015] The first dispersant is one of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, polyvinyl butyral, or a mixture of at least two of them.

[0016] In some possible implementations, the ceramic adhesive layer is made of a first ceramic and a second adhesive;

[0017] The material of the ceramic-containing sodium-supplementing adhesive layer includes a second ceramic, a third adhesive, a second conductive agent, a second dispersant, and a second sodium-containing compound.

[0018] In some possible embodiments, the first ceramic and the second ceramic are one or a mixture of at least two of α-spherical alumina, granular burmesite, cerium dioxide, and zirconium dioxide; and / or,

[0019] The second conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon; and / or,

[0020] At least one of the second and third adhesives is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR; and / or,

[0021] The second dispersant is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral; and / or,

[0022] The second sodium-containing compound is one of Na2CO3, Na2C2O4, Na3C6H5O7, Na2C6O6, or a mixture of at least two of them.

[0023] In some possible implementations, in the ceramic adhesive layer, the first ceramic component accounts for more than or equal to 75% and less than or equal to 88% by mass, and the second adhesive component accounts for more than or equal to 12% and less than or equal to 25% by mass; and / or,

[0024] In the ceramic-containing sodium-supplemented adhesive layer, the mass percentage of the second ceramic is greater than or equal to 60% and less than or equal to 73%, the mass percentage of the third adhesive is greater than or equal to 10% and less than or equal to 20%, the mass percentage of the second conductive agent is greater than or equal to 30% and less than or equal to 35%, the mass percentage of the second dispersant is greater than or equal to 0.5% and less than or equal to 1%, and the mass percentage of the second sodium-containing compound is greater than or equal to 5% and less than or equal to 10%.

[0025] In some possible implementations, the thickness of the base film is greater than or equal to 6 μm and less than or equal to 10 μm; and / or,

[0026] The thickness of the sodium-supplementing layer is greater than or equal to 1 μm and less than or equal to 3 μm; and / or,

[0027] The thickness of the ceramic adhesive layer is greater than or equal to 3 μm and less than or equal to 6 μm; and / or,

[0028] The thickness of the ceramic sodium-containing adhesive layer is greater than or equal to 3 μm and less than or equal to 8 μm.

[0029] Secondly, embodiments of this application provide a battery cell, including: a positive electrode, a negative electrode, and a separator structure as described above disposed between the positive electrode and the negative electrode, wherein a sodium-supplementing layer of the separator structure is adjacent to the negative electrode.

[0030] In some possible implementations, along a first direction intersecting the thickness direction of the base film, the length of both ends of the separator structure extending beyond the corresponding ends of the negative electrode sheet is greater than or equal to 1 mm and less than or equal to 5 mm; and / or,

[0031] Along the first direction intersecting the thickness direction of the base film, the length of both ends of the negative electrode extending beyond the corresponding ends of the positive electrode is greater than or equal to 1 mm and less than or equal to 3 mm; and / or,

[0032] Along a second direction intersecting the thickness direction of the base film and the first direction, the length of both ends of the separator structure extending beyond the corresponding ends of the negative electrode sheet is greater than or equal to 1 mm and less than or equal to 2 mm; and / or,

[0033] Along the second direction intersecting the thickness direction of the base film and the first direction, the length of the two ends of the negative electrode extending beyond the corresponding ends of the positive electrode is greater than or equal to 1.5 mm and less than or equal to 2 mm.

[0034] Thirdly, embodiments of this application provide a sodium-ion battery, including at least one cell as described above.

[0035] Fourthly, embodiments of this application provide a method for preparing a diaphragm structure, comprising:

[0036] A first mixed material is provided, comprising a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant; wherein the first sodium-containing compound comprises a mass percentage greater than or equal to 10% and less than or equal to 25%, the first conductive agent comprises a mass percentage greater than or equal to 67% and less than or equal to 75%, the first binder comprises a mass percentage greater than or equal to 3% and less than or equal to 5%, and the first dispersant comprises a mass percentage greater than or equal to 1% and less than or equal to 3%.

[0037] The first mixed material is coated on the first side of the base film to form a sodium-supplementing layer;

[0038] A second mixture of a first ceramic and a second binder is provided, or a third mixture of a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound is provided;

[0039] The second mixed material is coated onto the second side of the base film to form a ceramic adhesive layer, and the base film, the sodium-supplementing layer, and the ceramic adhesive layer form the membrane structure; or, the third mixed material is coated onto the second side of the base film to form a ceramic-containing sodium-supplementing adhesive layer, and the base film, the sodium-supplementing layer, and the ceramic-containing sodium-supplementing adhesive layer form the membrane structure.

[0040] The separator structure, its preparation method, cell, and sodium-ion battery provided in this application improve the initial charge-discharge efficiency and discharge capacity retention, and reduce the temperature rise in the later stages of cell cycling, by setting a sodium-supplementing layer on the first side of the base film and a ceramic adhesive layer or a ceramic-containing sodium-supplementing adhesive layer on the second side of the base film, at least by supplementing sodium ions through the sodium-supplementing layer. Furthermore, it can reduce the number or size of the positive and / or negative electrode plates in the sodium-ion battery, thereby increasing the energy density per unit mass and providing higher energy. By pre-sodiumizing the separator structure, pre-sodiumizing the negative / positive electrode plates is unnecessary, avoiding the impact of sodium residues in the negative / positive electrode plates and gases released from some additives on the performance of the sodium-ion battery, thus ensuring long-term operation and extending the battery's lifespan. Attached Figure Description

[0041] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0042] Figure 1 This is a schematic diagram of a diaphragm structure in an embodiment of this application;

[0043] Figure 2 This is another schematic diagram of the diaphragm structure in the embodiments of this application;

[0044] Figure 3 This is a schematic diagram of a battery cell in an embodiment of this application;

[0045] Figure 4 This is another schematic diagram of the battery cell in the embodiments of this application;

[0046] Figure 5 The cycling curves of the sodium-supplemented membrane cell and the base sample membrane cell in the embodiments of this application are shown.

[0047] Figure 6 The above are charge-discharge curves of the sodium-supplemented membrane cell and the base sample membrane cell in the embodiments of this application.

[0048] Figure 7 This is a flowchart of the preparation method of the diaphragm structure in the embodiments of this application;

[0049] Figure 8 This is a comparative schematic diagram showing the highest temperature of the sodium-supplemented membrane cell and the base sample membrane cell when charged from 0% SOC to 100% SOC at a high rate of 5C in the embodiments of this application.

[0050] Figure 9 Temperature rise curves of the positive electrode side of the sodium-supplemented membrane cell and the base sample membrane cell under 1C discharge rate;

[0051] Figure 10 Temperature rise curves of the negative electrode side of the sodium-supplemented membrane cell and the base sample membrane cell under 1C discharge rate.

[0052] Explanation of reference numerals in the attached figures:

[0053] 10-Diaphragm structure;

[0054] 11-Base film;

[0055] 12-Sodium supplement layer;

[0056] 13-Ceramic adhesive layer;

[0057] 14- Contains ceramic-based sodium-replenishing adhesive layer;

[0058] 20-Negative electrode;

[0059] 30-Positive electrode plate.

[0060] The accompanying drawings illustrate specific embodiments of this application, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the concept in any way, but rather to illustrate the concept of this application to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0061] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0062] Sodium-ion batteries have low discharge capacity and low energy density per unit mass. The inventors have found that this is because a solid-electrolyte (SEI) film is formed during the first charge of a sodium-ion battery. During cycling, the decomposition and reconstruction of the SEI film consume sodium ions in the electrolyte and the positive electrode, which reduces the discharge capacity of the sodium-ion battery.

[0063] To maintain the discharge capacity and long-cycle performance of sodium-ion batteries, sodium ions need to be replenished. Pre-sodium treatment of the positive / negative electrode, i.e., replenishing sodium ions through the positive or negative electrode, results in residual sodium compounds in the electrode and gases released from some additives, affecting the entire sodium-ion battery. In particular, the released gases can easily affect the microstructure of the active materials in the positive electrode, making it difficult for the sodium-ion battery to operate long-term.

[0064] The separator structure provided in this application, by placing the sodium replenishment layer on the first side of the base membrane, replenishes sodium ions, thereby improving the initial efficiency and discharge capacity retention rate of the sodium-ion battery, and reducing the temperature rise in the later stages of cell cycling. By pre-sodium-izing the separator structure, pre-sodium-izing of the negative / positive electrode plates is unnecessary, avoiding the impact of sodium residues in the negative electrode plate and gases released from some additives on the performance of the sodium-ion battery. This ensures long-term operation of the sodium-ion battery, thus guaranteeing its lifespan.

[0065] The technical solution of this application and how the technical solution of this application solves the above-mentioned technical problems are described in detail below with specific embodiments. These specific embodiments can be combined with each other, and the same or similar concepts or processes may not be described again in some embodiments. The embodiments of this application will now be described with reference to the accompanying drawings.

[0066] See Figures 1 to 6 This application provides a diaphragm structure 10, which includes a base membrane 11, a sodium replenishing layer 12, and a ceramic adhesive layer 13 or a ceramic sodium replenishing adhesive layer 14. The base membrane 11 has a first side and a second side disposed opposite to each other. The sodium replenishing layer 12 is disposed on the first side of the base membrane 11 for replenishing sodium ions; the ceramic adhesive layer 13 or the ceramic sodium replenishing adhesive layer 14 is disposed on the second side of the base membrane 11.

[0067] The base membrane 11 is the core support layer of the separator structure, used to separate the positive electrode 30 and the negative electrode 20, blocking the passage of electrons during charging and discharging while allowing sodium ions in the electrolyte to pass through. The first side and the second side of the base membrane 11 are arranged opposite each other along the thickness direction of the base membrane 11. The thickness direction of the base membrane 11 can be consistent with the stacking direction of the ceramic adhesive layer 13 / ceramic sodium-supplemented adhesive layer 14, the base membrane 11, and the sodium-supplemented layer 12. The first side of the base membrane 11 ( Figure 1 and Figure 2 The upper side shown can be the side adjacent to the negative electrode 20, and the second side of the base film 11 (as shown above). Figure 1 and Figure 2 The lower side shown can be the side adjacent to the positive electrode 30.

[0068] The base film 11 can be made of polypropylene (PP), polyethylene (PE), or a mixture of the two. The thickness of the base film 11 is greater than or equal to 6 μm and less than or equal to 10 μm. For example, the thickness of the base film 11 can be any one of 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, or any combination of both. A thickness within the above range ensures mechanical strength and ion transport capability.

[0069] See Figure 1 and Figure 2 A sodium replenishment layer 12 is provided on the first side of the base film 11. For example, the sodium replenishment layer 12 is coated on the first side of the base film 11, that is, the sodium replenishment layer 12 is coated on the surface of the base film 11 facing the negative electrode 20. The sodium replenishment layer 12 contains sodium element, which dynamically releases sodium ions through chemical decomposition during the operation of the sodium-ion battery to replenish cycle losses, compensate for the sodium ion losses during the formation of the SEI film during the first charge and discharge and during the cycle process, improve the first charge and discharge efficiency and the discharge capacity of the sodium-ion battery, and can reduce the number or size of the positive electrode 30 and / or negative electrode 20 of the sodium-ion battery, thereby improving the energy density per unit mass of the sodium-ion battery and providing higher energy.

[0070] Furthermore, by placing the sodium-supplementing layer 12 on the first side of the base film 11, the separator structure 10 is pre-sodium-treated, eliminating the need for pre-sodium treatment of the negative electrode 20 / positive electrode 30. This avoids the impact of sodium residues in the negative electrode 20 / positive electrode 30 and the gas released from some additives on the performance of the sodium-ion battery, thereby ensuring the long-term operation and service life of the sodium-ion battery.

[0071] Continue reading Figure 1 and Figure 2 The thickness of the sodium-supplementing layer 12 is greater than or equal to 1 μm and less than or equal to 3 μm. For example, the thickness of the sodium-supplementing layer 12 is any one of 1 μm, 2 μm, and 3 μm, or any combination of two. With the thickness of the sodium-supplementing layer 12 within the above range, the amount of material used can be reduced and the sodium ion release efficiency can be improved, achieving a balance between lightweighting and performance enhancement of the membrane structure 10.

[0072] In some possible examples, the sodium-supplementing layer 12 is a mixture of a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant. Exemplarily, the sodium-supplementing layer 12 can be formed by uniformly mixing the first sodium-containing compound, the first conductive agent, the first binder, and the first dispersant, and then adhered to the corresponding surface of the base film 11 by spraying. The first sodium-containing compound releases sodium ions to compensate for sodium ion loss; the first conductive agent forms a conductive network to promote uniform distribution of sodium ions and avoid excessively high local concentrations; the first binder ensures the structural stability of the sodium-supplementing layer 12 through physical bonding; and the first dispersant ensures the uniformity of the material through chemical dispersion. The composite structure formed by the mixture of the first sodium-containing compound, the first conductive agent, the first binder, and the first dispersant improves the overall performance of the sodium-supplementing layer 12.

[0073] In the sodium-supplementing layer 12, the mass percentage of the first sodium-containing compound is greater than or equal to 10% and less than or equal to 25%, for example, any one or a combination of 10%, 15%, 20%, and 25%. The mass percentage of the first conductive agent is greater than or equal to 67% and less than or equal to 75%, for example, any one or a combination of 67%, 69%, 70%, 71%, 73%, and 75%. The mass percentage of the first binder is greater than or equal to 3% and less than or equal to 5%, for example, any one or a combination of 3%, 4%, and 5%. The mass percentage of the first dispersant is greater than or equal to 1% and less than or equal to 3%, for example, any one or a combination of 1%, 2%, and 3%.

[0074] The aforementioned mass percentages refer to the mass ratio of each component in the mixture. By controlling the mass percentages of each component, the performance of the sodium-supplementing layer 12 can be optimized. Specifically, the higher mass percentage of the first sodium-containing compound ensures sufficient sodium ion release to meet the requirements during the initial charge-discharge and cycling processes. The higher mass percentage of the first conductive agent enables the formation of an efficient conductive network, reducing ion migration resistance. The lower mass percentages of the first binder and the first dispersant reduce material costs while ensuring structural stability.

[0075] In some possible implementations, the first sodium-containing compound is one or a mixture of at least two of Na₂CO₃, Na₂C₂O₄, Na₃C₆H₅O₇, and Na₂C₆O₆. For example, the first sodium-containing compound is a mixture of Na₂CO₃ and Na₂C₂O₄. Another example is a mixture of Na₂CO₃, Na₂C₂O₄, and Na₃C₆H₅O₇. In this configuration, the carbon dioxide (CO₂) and carbon monoxide (CO) gases generated during the initial sodium replenishment process can be discharged under negative pressure, reducing their impact on the thickness of the sodium-ion battery.

[0076] In some possible implementations, the first conductive agent is one or a mixture of at least two of conductive carbon (SP), short multi-walled carbon nanotubes (s-MWCNTs), Ketjen black (KB), and ordered mesoporous carbon (CMK-3). For example, the first conductive agent is conductive carbon, or a mixture of conductive carbon and short multi-walled carbon nanotubes. Another example is a mixture of conductive carbon, short multi-walled carbon nanotubes, and Ketjen black. The first conductive agent can improve the conductivity of the sodium-supplement layer 12, thereby improving the conductivity of the membrane structure 10, and consequently improving the rate performance of the sodium-ion battery.

[0077] In some possible implementations, the first binder is one or a mixture of at least two of polytetrafluoroethylene (PVDF), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA). For example, the first binder is a mixture of PVDF, SBR, and polyacrylic acid. Preferably, the first binder is PVDF, which has a wide operating temperature range, excellent chemical stability, electrical insulation, self-lubrication, and aging resistance.

[0078] In some possible implementations, the first dispersant is one or a mixture of at least two of sodium polymethylcellulose (CMC), polyvinylpyrrolidone (PVP), N-methylpyrrolidone (NMP), and polyvinyl butyral (PVB). For example, the first dispersant is a mixture of sodium polymethylcellulose, polyvinylpyrrolidone, and polyvinyl butyral.

[0079] Continue reading Figures 1 to 4 A ceramic adhesive layer 13 or a ceramic sodium-supplemented adhesive layer 14 is disposed on the second side of the base film 11. For example, the ceramic adhesive layer 13 or the ceramic sodium-supplemented adhesive layer 14 is coated on the surface of the base film 11 facing the positive electrode 30.

[0080] In some possible examples, such as Figure 1 As shown, the ceramic adhesive layer 13 is disposed on the second side of the base membrane 11, that is, the ceramic adhesive layer 13, the base membrane 11, and the sodium supplement layer 12 are stacked in sequence. By providing the ceramic adhesive layer 13, the mechanical strength and thermal stability of the diaphragm structure 10 can be improved, preventing the diaphragm structure 10 from thermally shrinking or cracking under high temperature or overcharge conditions.

[0081] In other possible examples, such as Figure 2 As shown, the ceramic-containing sodium-supplementing adhesive layer 14 is disposed on the second side of the base film 11, that is, the ceramic-containing sodium-supplementing adhesive layer 14, the base film 11, and the sodium-supplementing layer 12 are stacked sequentially. By providing the ceramic-containing sodium-supplementing adhesive layer 14, the ceramic-containing sodium-supplementing adhesive layer 14 provides mechanical reinforcement while further supplementing sodium ions, thereby improving the initial efficiency, discharge capacity, and energy density per unit mass of the sodium-ion battery, and providing higher energy.

[0082] Meanwhile, by setting the ceramic sodium-containing adhesive layer 14 on the second side of the base film 11, the surface of the base film 11 is pre-sodium-treated, eliminating the need for pre-sodium treatment of the positive electrode 30 / negative electrode 20. This avoids the impact of sodium residues in the positive electrode 30 / negative electrode 20 and the gas released from some additives on the performance of the sodium-ion battery. In particular, it avoids the released gas affecting the microstructure of the active materials of the positive electrode 30 / negative electrode 20, thereby ensuring that the sodium-ion battery can operate for a long time, that is, ensuring the service life of the sodium-ion battery.

[0083] In some possible examples, the thickness of the ceramic adhesive layer 13 is greater than or equal to 3 μm and less than or equal to 6 μm, for example, any one or a combination of 3 μm, 4 μm, 5 μm, and 6 μm. The thickness of the ceramic adhesive layer 13 within the above range provides mechanical reinforcement and thermal stability while avoiding excessive increase in the weight of the diaphragm structure 10 and preventing thermal shrinkage due to increased thickness.

[0084] In some possible examples, the ceramic adhesive layer 13 is a mixture of a first ceramic and a second adhesive. Exemplarily, the first ceramic and the second adhesive are mixed uniformly and then coated onto the corresponding surface of the base film 11. The ceramic adhesive layer 13 provides mechanical strength and thermal stability through the mixture of the first ceramic and the second adhesive.

[0085] In the ceramic adhesive layer 13, the first ceramic component accounts for a mass percentage greater than or equal to 75% and less than or equal to 88%, for example, any one or a combination of 75%, 77%, 80%, 82%, 84%, 86%, and 88%. The second adhesive component accounts for a mass percentage greater than or equal to 12% and less than or equal to 25%, for example, any one or a combination of 12%, 15%, 20%, and 25%. By optimizing the ratio of the first ceramic component and the second adhesive, the overall performance of the ceramic adhesive layer 13 is improved.

[0086] In some possible implementations, the first ceramic is one or a mixture of at least two of α-spherical alumina, granular borax, cerium dioxide (CeO2), and zirconium dioxide (ZrO2). For example, the first ceramic is a mixture of cerium dioxide and zirconium dioxide. Preferably, the first ceramic is α-spherical alumina, which has properties such as porosity, high dispersibility, insulation, stable crystal phase, high hardness, and good dimensional stability. The first ceramic can increase the mechanical strength of the diaphragm structure 10 and improve the thermal shrinkage stability of the diaphragm structure 10.

[0087] In some possible implementations, the second adhesive is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR, to prevent cracking after drying, thereby ensuring the reliability of the bond between the ceramic adhesive layer 13 and the base film 11. It is understood that the second adhesive may be the same as or different from the first adhesive.

[0088] like Figure 2As shown, the thickness of the ceramic-containing sodium-supplemented adhesive layer 14 is greater than or equal to 3 μm and less than or equal to 6 μm, for example, any one of 3 μm, 4 μm, 5 μm, and 6 μm or any combination of two. The thickness of the ceramic-containing sodium-supplemented adhesive layer 14 is within the above range, which provides mechanical reinforcement and thermal stability while avoiding excessive increase in the weight of the diaphragm structure 10 and avoiding thermal shrinkage due to increased thickness.

[0089] In some possible examples, the material of the ceramic-containing sodium-replenishing adhesive layer 14 is a mixture of a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound. Exemplarily, the second ceramic, third binder, second conductive agent, second dispersant, and second sodium-containing compound are uniformly mixed and then coated onto the corresponding surface of the base film 11. The ceramic-containing sodium-replenishing adhesive layer 14, through the mixture of the second ceramic, third binder, second conductive agent, second dispersant, and second sodium-containing compound, further replenishes sodium ions while providing mechanical reinforcement.

[0090] The second ceramic component comprises 60% or more and 73% by mass, for example, any one or a combination of 60%, 65%, 70%, and 73%. The third binder comprises 10% or more and 20% by mass, for example, any one or a combination of 10%, 15%, and 20%. The second conductive agent comprises 30% or more and 35% by mass, for example, any one or a combination of 30%, 31%, 32%, 33%, 34%, and 35%. The second dispersant comprises 0.5% or more and 1% by mass, for example, any one or a combination of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%. The second sodium-containing compound comprises 5% or more and 10% by mass, for example, any one or a combination of 5%, 6%, 7%, 8%, 9%, and 10%.

[0091] In the ceramic-containing sodium-supplementing adhesive layer 14, the second ceramic component has a higher mass proportion, which can improve mechanical strength and thermal stability; the third binder and the second conductive agent work synergistically to enhance the material's bonding force and promote ion transport; the second dispersant improves the material's dispersibility; and the second sodium-containing compound has a lower mass proportion, providing additional sodium ion supplementation while avoiding excessive increases in material cost. Through the optimization of the above material ratios, a synergistic effect of mechanical strengthening and sodium supplementation is achieved.

[0092] In some possible implementations, the second ceramic is one or a mixture of at least two of α-spherical alumina, granular burmesh, cerium dioxide, and zirconium dioxide. For example, the second ceramic is granular burmesh. The second ceramic may be the same as or different from the first ceramic.

[0093] In some possible implementations, the second conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon. For example, the second conductive agent is a mixture of conductive carbon and ordered mesoporous carbon. The second conductive agent may be the same as or different from the first conductive agent.

[0094] In some possible implementations, the third adhesive is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR, to prevent cracking after drying, thereby ensuring the reliability of the connection between the ceramic-containing sodium-filled adhesive layer 14 and the base film 11. For example, the third adhesive is PTFE. The third adhesive, the second adhesive, and the first adhesive may be partially the same or all different. For example, the third adhesive may be the same as the second adhesive but different from the first adhesive.

[0095] In some possible implementations, the second dispersant is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral. For example, the second dispersant is polyvinyl butyral. The second dispersant may be the same as or different from the first dispersant.

[0096] In some possible examples, the second sodium-containing compound is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral. For example, the second sodium-containing compound is sodium polymethylcellulose. The second sodium-containing compound may be the same as or different from the first sodium-containing compound.

[0097] The separator structure 10 in this embodiment includes a base film 11, a sodium-supplementing layer 12, and a ceramic adhesive layer 13 / a ceramic-containing sodium-supplementing adhesive layer 14. The sodium-supplementing layer 12 is disposed on the first side of the base film 11, and the ceramic adhesive layer 13 / a ceramic-containing sodium-supplementing adhesive layer 14 is disposed on the second side of the base film 11. At least through the sodium-supplementing layer 12, sodium ions are replenished during the operation of the sodium-ion battery, improving the initial charge-discharge efficiency and discharge capacity retention rate, and reducing the temperature rise in the later stages of cell cycling. By disposing of the sodium-supplementing layer 12 on the first side of the base film 11, the separator structure 10 is pre-sodium-treated, eliminating the need for pre-sodium treatment of the negative electrode 20 / positive electrode 30. This avoids the impact of sodium residues in the negative electrode 20 / positive electrode 30 and the gas released from some additives on the performance of the sodium-ion battery, thereby ensuring long-term operation and extending its service life.

[0098] See Figure 3 and Figure 4 This application also provides a battery cell, which can be a cylindrical cell or a prismatic cell. The cell includes a positive electrode 30, a negative electrode 20, and a separator structure 10. The separator structure 10 is disposed between the positive electrode 30 and the negative electrode 20, and the sodium-supplementing layer 12 of the separator structure 10 is adjacent to the negative electrode 20. The proximity of the sodium-supplementing layer 12 to the negative electrode 20 can optimize the sodium ion transport path, reduce internal resistance, and improve rate performance. The specific structure of the separator structure 10 can be referred to the above embodiments and will not be repeated here.

[0099] Considering the extension and manufacturing deviations of the positive electrode 30 and the negative electrode 20, as well as their dimensions, along a first direction intersecting (e.g., perpendicular to) the thickness direction of the base film 11, the lengths of the two ends of the separator structure 10 extending beyond the corresponding ends of the negative electrode 20 are greater than or equal to 1 mm and less than or equal to 5 mm, for example, any one or any combination of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm. The longer separator structure 10 along the first direction can prevent internal short circuits during cycling and also consider the utilization rate of the internal space of the cell. The first direction can be the width direction of the cell.

[0100] like Figure 3 and Figure 4 As shown, the left end of the separator structure 10 extends beyond the left end of the negative electrode 20 by a length greater than or equal to 1 mm and less than or equal to 5 mm, and the right end of the separator structure 10 extends beyond the right end of the negative electrode 20 by a length greater than or equal to 1 mm and less than or equal to 5 mm. Along the first direction, the lengths by which the two ends of the separator structure 10 extend beyond the corresponding ends of the negative electrode 20 can be the same or different.

[0101] Along the first direction, the two ends of the negative electrode 20 extend beyond the corresponding ends of the positive electrode 30 by a length greater than or equal to 1 mm and less than or equal to 3 mm, for example, any one of 1 mm, 2 mm, and 3 mm, or any combination of two. The fact that the two ends of the negative electrode 20 extend beyond the corresponding ends of the positive electrode 30 along the first direction provides sufficient safety redundancy, avoids insufficient coverage by the negative electrode 20, fully utilizes the internal space of the cell, ensures the energy density of the cell, and reduces costs.

[0102] like Figure 3 and Figure 4 As shown, the left end of the negative electrode 20 extends beyond the left end of the positive electrode 30 by a length greater than or equal to 1 mm and less than or equal to 3 mm; the right end of the negative electrode 20 extends beyond the right end of the positive electrode 30 by a length greater than or equal to 1 mm and less than or equal to 3 mm. The lengths by which the two ends of the negative electrode 20 extend beyond the corresponding ends of the positive electrode 30 can be the same or different.

[0103] Along a second direction intersecting the thickness direction of the base membrane 11 and the first direction, the length of both ends of the separator structure 10 extending beyond the corresponding ends of the negative electrode 20 is greater than or equal to 1 mm and less than or equal to 2 mm, for example, any one or any combination of 1 mm, 1.5 mm, and 2 mm. The longer separator structure 10 is along the second direction, it can prevent internal short circuits during cycling and also consider the utilization rate of the internal space of the cell; the second direction can be the height direction of the cell.

[0104] like Figure 3 and Figure 4 As shown, the front end of the separator structure 10 extends beyond the front end of the negative electrode 20 by a length greater than or equal to 1 mm and less than or equal to 2 mm; the rear end of the separator structure 10 extends beyond the rear end of the negative electrode 20 by a length greater than or equal to 1 mm and less than or equal to 5 mm. Along the second direction, the lengths by which the two ends of the separator structure 10 extend beyond the corresponding ends of the negative electrode 20 can be the same or different.

[0105] The length of the separator structure 10 extending beyond the negative electrode 20 along the first direction is greater than its length extending beyond the negative electrode 20 along the second direction, which is adapted to the mechanical stress, deformation characteristics, and manufacturing tolerances of the battery cell in these two directions. Specifically, along the first direction, the battery cell is under weak stress and easily deformed, so the separator structure 10 extends outward more to ensure safety; along the second direction, the battery cell is supported and constrained, making it less prone to deformation, so the separator structure 10 extends outward less to improve energy density.

[0106] Furthermore, the outer peripheral surface of the diaphragm structure 10 protrudes beyond the outer peripheral surface of the negative electrode 20, preventing the negative electrode 20 and the positive electrode 30 from directly contacting each other and causing a short circuit, thus ensuring the safety of cell manufacturing and long-term reliability during use.

[0107] Along the second direction, the length of the two ends of the negative electrode 20 extending beyond the corresponding ends of the positive electrode 30 is greater than or equal to 1.5 mm and less than or equal to 2 mm, for example, any one or any combination of 1.5 mm, 1.7 mm, and 2 mm. Along the second direction, the two ends of the negative electrode 20 extend beyond the corresponding ends of the positive electrode 30 to provide sufficient safety redundancy, avoid insufficient coverage by the negative electrode 20, fully utilize the internal space of the cell, ensure the energy density of the cell, and reduce costs.

[0108] like Figure 3 and Figure 4As shown, the front end of the negative electrode 20 extends beyond the front end of the positive electrode 30 by a length greater than or equal to 1.5 mm and less than or equal to 2 mm; the rear end of the negative electrode 20 extends beyond the rear end of the positive electrode 30 by a length greater than or equal to 1.5 mm and less than or equal to 2 mm. Along the second direction, the lengths by which the two ends of the negative electrode 20 extend beyond the corresponding ends of the positive electrode 30 can be the same or different.

[0109] The negative electrode 20 extends beyond the positive electrode 30 in the first direction by a greater length than it extends beyond the positive electrode 30 in the second direction. This extension is compatible with the manufacturing tolerances and alignment tolerances of the battery cell in these two directions. Specifically, alignment is more difficult in the first direction, requiring the negative electrode 20 to extend further to ensure safety; alignment is less difficult in the second direction, requiring the negative electrode 20 to extend less further to improve energy density.

[0110] Furthermore, the outer peripheral surface of the negative electrode 20 protrudes beyond the outer peripheral surface of the positive electrode 30 to prevent short circuits caused by sodium deposition at the edge of the negative electrode 20 during cycling, thus ensuring the manufacturing safety of the battery cell and its long-term reliability during use.

[0111] See Figure 3 In some possible examples, the separator structure 10 includes a base membrane 11, a sodium-supplementing layer 12, and a ceramic adhesive layer 13, which are stacked sequentially. The sodium-supplementing layer 12 is adjacent to the negative electrode 20, that is, the surface of the base membrane 11 coated with the sodium-supplementing layer 12 faces the negative electrode 20, and the sodium-supplementing layer 12 can be bonded to the negative electrode 20. The ceramic adhesive layer 13 is adjacent to the positive electrode 30, that is, the surface of the base membrane 11 coated with the ceramic adhesive layer 13 faces the positive electrode 30, and the ceramic adhesive layer 13 can be bonded to the positive electrode 30. Figure 3 As shown, the negative electrode 20, sodium supplement layer 12, base film 11, ceramic adhesive layer 13 and positive electrode 30 are arranged sequentially from top to bottom.

[0112] See Figure 4 In some other possible examples, the separator structure 10 includes a base membrane 11, a sodium-supplementing layer 12, and a ceramic adhesive layer 13, which are sequentially stacked. The sodium-supplementing layer 11, the sodium-supplementing layer 12, and the ceramic sodium-supplementing adhesive layer 14 are adjacent to the negative electrode 20, meaning the surface of the base membrane 11 coated with the sodium-supplementing layer 12 faces the negative electrode 20, and the sodium-supplementing layer 12 can be bonded to the negative electrode 20. The ceramic sodium-supplementing adhesive layer 14 is adjacent to the positive electrode 30, meaning the surface of the base membrane 11 coated with the ceramic sodium-supplementing adhesive layer 14 faces the positive electrode 30, and the ceramic sodium-supplementing adhesive layer 14 can be bonded to the positive electrode 30. Figure 4 As shown, the negative electrode 20, sodium-supplementing layer 12, base film 11, ceramic-containing sodium-supplementing adhesive layer 14, and positive electrode 30 are arranged sequentially from top to bottom.

[0113] Through the synergistic design of the sodium replenishment layer 12 and the ceramic adhesive layer 13 / ceramic sodium replenishment adhesive layer 14, dynamic replenishment and mechanical strengthening of sodium ions are achieved. The sodium replenishment layer releases sodium ions during the first charge-discharge cycle and during cycling to compensate for the loss during SEI film formation and cycling. The ceramic adhesive layer 13 provides mechanical strength and thermal stability through the mixing of ceramic particles and binder. The ceramic sodium replenishment adhesive layer 14, through the composite of ceramic particles and sodium replenishment material, further replenishes sodium ions while providing mechanical strengthening.

[0114] The battery cell including the membrane structure 10 in the embodiments of this application and the base sample membrane battery cell were tested. The battery cell including the membrane structure 10 in the embodiments of this application is a sodium-supplemented membrane battery cell, while the base sample membrane battery cell is not sodium-supplemented, that is, the base sample membrane battery cell does not have a sodium-supplemented layer 12. The cycling curves of the sodium-supplemented membrane battery cell and the base sample membrane battery cell are as follows. Figure 5 As shown, the charge-discharge curves are as follows: Figure 6 As shown. The positive electrode 30 active material in these two cells is the same, and a small current of 0.1C is used, with a charging cut-off voltage of 4.35V.

[0115] See Figure 5 After 290 cycles, the capacity retention of the sodium-supplemented membrane cell remained stable, while the capacity retention of the membrane cell with insufficient sodium source began to decline during cycling. (See also...) Figure 6 During the initial charge and discharge cycle, the base sample membrane cell had a charging capacity of 159.52 Ah and a discharging capacity of 132.07 Ah, with an initial efficiency of 82.79%. The sodium-added membrane cell had a charging capacity of 167.08 Ah and a discharging capacity of 149.05 Ah, with an initial efficiency of 89.2%. The initial discharge capacity of the sodium-added membrane cell was 16.98 Ah higher than that of the base sample membrane cell, and its initial efficiency was 6.21% higher. The sodium-added membrane cell showed improvements in both charge / discharge capacity and initial efficiency, resulting in an increased energy density.

[0116] See Figure 8 , Figure 8 This diagram compares the maximum temperatures of a sodium-supplemented membrane cell and a base sample membrane cell when charged from 0% SOC to 100% SOC at a high rate of 5C. The maximum temperature of the sodium-supplemented membrane cell is 39.9℃, while the maximum temperature of the base sample membrane cell is 53.6℃. During cycling, the sodium-supplemented membrane cell exhibits lower sodium ion insertion / extraction polarization, lower impedance, and lower temperature rise due to the replenishment of sodium ions.

[0117] See Figure 9 and Figure 10 , Figure 9 Temperature rise curves of the positive electrode side of the sodium-supplemented membrane cell and the base sample membrane cell under 1C discharge rate; Figure 10The graphs show the temperature rise curves of the negative electrode side of the sodium-supplemented membrane battery cell and the base sample membrane battery cell under 1C discharge. At the end of discharge, the temperature of the sodium-supplemented membrane battery cell is significantly lower than that of the base sample membrane battery cell. Specifically, the highest temperatures on the positive electrode side of the sodium-supplemented membrane battery cell and the base sample membrane battery cell are 29.1℃ and 32.2℃, respectively, while the highest temperatures on the negative electrode side of the sodium-supplemented membrane battery cell and the base sample membrane battery cell are 28.9℃ and 31.8℃, respectively. The highest temperatures on both the positive and negative electrode sides of the sodium-supplemented membrane battery cell are approximately 3℃ lower than those of the base sample membrane battery cell.

[0118] In summary, the battery cell in this embodiment includes a positive electrode 30, a negative electrode 20, and a separator structure 10. The separator structure 10 is disposed between the positive electrode 30 and the negative electrode 20, and the sodium replenishment layer 12 of the separator structure 10 is adjacent to the negative electrode 20 for replenishing sodium ions. This battery cell includes the separator structure 10, and therefore has advantages such as high initial charge / discharge efficiency, high discharge capacity, and high energy density per unit mass. Specific effects are described above and will not be repeated here.

[0119] This application also provides a sodium-ion battery, including at least one of the above-described cells. For example, the sodium-ion battery includes multiple cells, which may be connected in series, parallel, or a combination thereof. By integrating multiple cells, the sodium-ion battery can improve energy density and system stability. The sodium-ion battery also includes a frame surrounding the multiple cells. Since the sodium-ion battery includes cells, it has advantages such as high initial charge / discharge efficiency, high discharge capacity, and high energy density per unit mass. Specific effects are described above and will not be repeated here.

[0120] This application also provides a method for preparing a diaphragm structure, see below. Figure 7 The method specifically includes the following steps:

[0121] Step S100: Provide a first mixed material comprising a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant; wherein the mass percentage of the first sodium-containing compound is greater than or equal to 10% and less than or equal to 25%, the mass percentage of the first conductive agent is greater than or equal to 67% and less than or equal to 75%, the mass percentage of the first binder is greater than or equal to 3% and less than or equal to 5%, and the mass percentage of the first dispersant is greater than or equal to 1% and less than or equal to 3%.

[0122] A first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant are uniformly mixed to form a first mixed material. The first sodium-containing compound is used to release sodium ions and compensate for sodium ion loss; the first conductive agent forms a conductive network to promote the uniform distribution of sodium ions and avoid excessively high local concentrations; the first binder ensures structural stability through physical bonding; and the first dispersant ensures the uniformity of the material through chemical dispersion.

[0123] The first sodium-containing compound comprises, by mass, 10% or more and 25% or less, for example, any one or a combination of 10%, 15%, 20%, and 25%. The first conductive agent comprises, by mass, 67% or more and 75% or less, for example, any one or a combination of 67%, 69%, 70%, 71%, 73%, and 75%. The first binder comprises, by mass, 3% or more and 5% or less, for example, any one or a combination of 3%, 4%, and 5%. The first dispersant comprises, by mass, 1% or more and 3% or less, for example, any one or a combination of 1%, 2%, and 3%.

[0124] The first sodium-containing compound is one or a mixture of at least two of Na₂CO₃, Na₂C₂O₄, Na₃C₆H₅O₇, and Na₂C₆O₆. For example, the first sodium-containing compound is a mixture of Na₂CO₃ and Na₂C₂O₄. Another example is a mixture of Na₂CO₃, Na₂C₂O₄, and Na₃C₆H₅O₇. In this case, the carbon dioxide (CO₂) and carbon monoxide (CO) gases generated during the initial sodium replenishment process can be discharged by forming a negative pressure, reducing the impact on the thickness of the sodium-ion battery.

[0125] The first conductive agent is one or a mixture of at least two of conductive carbon (SP), short multi-walled carbon nanotubes (s-MWCNTs), Ketjen black (KB), and ordered mesoporous carbon (CMK-3). For example, the first conductive agent is conductive carbon, or a mixture of conductive carbon and short multi-walled carbon nanotubes. Another example is a mixture of conductive carbon, short multi-walled carbon nanotubes, and Ketjen black. The first conductive agent can improve the conductivity of the sodium-supplement layer 12, thereby improving the conductivity of the membrane structure 10, and consequently improving the rate performance of the sodium-ion battery.

[0126] The first binder is one or a mixture of at least two of polytetrafluoroethylene (PVDF), styrene-butadiene rubber (SBR), and polyacrylic acid (PAA). For example, the first binder is a mixture of PVDF, SBR, and polyacrylic acid. Preferably, the first binder is PVDF, which has a wide operating temperature range, excellent chemical stability, electrical insulation, self-lubrication, and aging resistance.

[0127] The first dispersant is one or a mixture of at least two of sodium polymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), N-methylpyrrolidone (NMP), and polyvinyl butyral (PVB). For example, the first dispersant is a mixture of sodium polymethyl cellulose, polyvinylpyrrolidone, and polyvinyl butyral.

[0128] Step S200: The first mixed material is coated on the first side of the base film to form a sodium-supplementing layer.

[0129] See Figure 1 and Figure 2 The first mixed material is uniformly coated onto the first side of the base film 11, for example, using a slot extrusion coating process or a spraying process, to form a sodium-supplementing layer 12. The base film 11 can be made of polypropylene, polyethylene, or a mixture of the two. The thickness of the base film 11 is greater than or equal to 6 μm and less than or equal to 10 μm. For example, the thickness of the base film 11 can be any one of 6 μm, 7 μm, 8 μm, 9 μm, and 10 μm, or any combination of both.

[0130] The thickness of the sodium-supplementing layer 12 is greater than or equal to 1 μm and less than or equal to 3 μm. For example, the thickness of the sodium-supplementing layer 12 is any one of 1 μm, 2 μm, and 3 μm, or any combination of two. With the thickness of the sodium-supplementing layer 12 within the above range, the amount of material used can be reduced and the sodium ion release efficiency can be improved, achieving a balance between lightweighting and performance enhancement of the membrane structure 10.

[0131] Step S300: Provide a second mixture of a first ceramic and a second binder, or a third mixture of a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound.

[0132] The first ceramic and the second binder are uniformly mixed to form a second composite material. The mass percentage of the first ceramic is greater than or equal to 75% and less than or equal to 88%, for example, any one or any combination of 75%, 77%, 80%, 82%, 84%, 86%, and 88%. The mass percentage of the second binder is greater than or equal to 12% and less than or equal to 25%, for example, any one or any combination of 12%, 15%, 20%, and 25%.

[0133] The first ceramic is one or a mixture of at least two of the following: α-spherical alumina, granular borax, cerium dioxide (CeO2), and zirconium dioxide (ZrO2). For example, the first ceramic is a mixture of cerium dioxide and zirconium dioxide. Preferably, the first ceramic is α-spherical alumina, which has properties such as porosity, high dispersibility, insulation, stable crystal phase, high hardness, and good dimensional stability. The first ceramic can increase the mechanical strength of the diaphragm structure 10 and improve the thermal shrinkage stability of the diaphragm structure 10.

[0134] The second adhesive is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR, to prevent cracking after drying, thereby ensuring the reliability of the connection between the ceramic adhesive layer 13 and the base film 11. It is understood that the second adhesive can be the same as or different from the first adhesive.

[0135] A third composite material is formed by uniformly mixing a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound. The second ceramic comprises 60% or more and 73% by mass, for example, any one or a combination of 60%, 65%, 70%, and 73%. The third binder comprises 10% or more and 20% by mass, for example, any one or a combination of 10%, 15%, and 20%. The second conductive agent comprises 30% or more and 35% by mass, for example, any one or a combination of 30%, 31%, 32%, 33%, 34%, and 35%. The second dispersant comprises 0.5% or more and 1% by mass, for example, any one or a combination of 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, and 1%. The second sodium-containing compound comprises 5% or more and 10% by mass, for example, any one or a combination of 5%, 6%, 7%, 8%, 9%, and 10%.

[0136] The second ceramic is one or a mixture of at least two of the following: α-spherical alumina, granular burme, cerium dioxide, and zirconium dioxide. For example, the second ceramic is granular burme. The second ceramic may be the same as or different from the second ceramic.

[0137] The second conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon. For example, the second conductive agent is a mixture of conductive carbon and ordered mesoporous carbon. The second conductive agent may be the same as or different from the first conductive agent.

[0138] The third adhesive is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR, to prevent cracking after drying, thereby ensuring the reliability of the connection between the ceramic-containing sodium-filled adhesive layer 14 and the base film 11. For example, the third adhesive is PTFE. The third adhesive, the second adhesive, and the first adhesive may be partially the same or all different. For example, the third adhesive may be the same as the second adhesive but different from the first adhesive.

[0139] The second dispersant is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral. For example, the second dispersant is polyvinyl butyral. The second dispersant may be the same as or different from the first dispersant.

[0140] The second sodium-containing compound is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral. For example, the second sodium-containing compound is sodium polymethylcellulose. The second sodium-containing compound may be the same as or different from the first sodium-containing compound.

[0141] Step S400: The second mixed material is coated on the second side of the base film to form a ceramic adhesive layer, and the base film, the sodium supplement layer and the ceramic adhesive layer form a membrane structure; or, the third mixed material is coated on the second side of the base film to form a ceramic sodium supplement adhesive layer, and the base film, the sodium supplement layer and the ceramic sodium supplement adhesive layer form a membrane structure.

[0142] In some possible implementations, see [reference] Figure 1 The second mixed material is uniformly coated onto the second side of the base film 11, for example, using a slot extrusion coating process or a spraying process, to form a ceramic adhesive layer 13. The ceramic adhesive layer 13, the base film 11, and the sodium-supplementing layer 12 form the diaphragm structure 10. The thickness of the ceramic adhesive layer 13 is greater than or equal to 3 μm and less than or equal to 6 μm, for example, any one or any combination of 3 μm, 4 μm, 5 μm, and 6 μm. The thickness of the ceramic adhesive layer 13 is within the above range, which provides mechanical reinforcement and thermal stability while avoiding excessive increase in the weight of the diaphragm structure 10 and preventing thermal shrinkage due to increased thickness.

[0143] In other possible implementations, see [reference] Figure 2 The second mixed material is uniformly coated on the second side of the base film 11, for example by slit extrusion coating or spraying, to form a ceramic sodium-replenishing adhesive layer 14. The ceramic sodium-replenishing adhesive layer 14, the base film 11 and the sodium-replenishing layer 12 form a diaphragm structure 10 to further replenish sodium ions.

[0144] The thickness of the ceramic-containing sodium-supplemented adhesive layer 14 is greater than or equal to 3 μm and less than or equal to 6 μm, for example, any one or any combination of 3 μm, 4 μm, 5 μm, and 6 μm. The thickness of the ceramic-containing sodium-supplemented adhesive layer 14 is within the above range, which provides mechanical reinforcement and thermal stability while avoiding excessive increase in the weight of the diaphragm structure 10 and avoiding thermal shrinkage due to increased thickness.

[0145] In this embodiment, the diaphragm structure 10 forms a sodium replenishing layer 12 on the first side of the base membrane 11 and a ceramic adhesive layer 13 / ceramic sodium replenishing adhesive layer 14 on the second side of the base membrane 11. Sodium ions are dynamically released through the sodium replenishing layer 12 to replenish the losses during SEI membrane formation and cycling, thereby improving the first charge / discharge efficiency and discharge capacity.

[0146] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0147] Those skilled in the art should understand that, in the disclosure of this application, the terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the system or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limitations on this application.

[0148] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with an embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0149] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A diaphragm structure, characterized in that, include: Base film, the base film having opposing first and second sides; A sodium replenishment layer is disposed on the first side of the base film to replenish sodium ions; A ceramic adhesive layer or a ceramic sodium-containing adhesive layer is disposed on the second side of the base film.

2. The diaphragm structure according to claim 1, characterized in that, The sodium-supplementing layer is made of a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant.

3. The diaphragm structure according to claim 2, characterized in that, In the sodium-supplementing layer, the first sodium-containing compound accounts for a mass percentage greater than or equal to 10% and less than or equal to 25%, the first conductive agent accounts for a mass percentage greater than or equal to 67% and less than or equal to 75%, the first binder accounts for a mass percentage greater than or equal to 3% and less than or equal to 5%, and the first dispersant accounts for a mass percentage greater than or equal to 1% and less than or equal to 3%; and / or, The first sodium-containing compound is one of Na₂CO₃, Na₂C₂O₄, Na₃C₆H₅O₇, Na₂C₆O₆, or a mixture of at least two of them; and / or, The first conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon; and / or, The first adhesive is one of polytetrafluoroethylene, styrene-butadiene rubber, and polyacrylic acid, or a mixture of at least two of them; and / or, The first dispersant is one of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, polyvinyl butyral, or a mixture of at least two of them.

4. The diaphragm structure according to any one of claims 1-3, characterized in that, The ceramic adhesive layer is made of a first ceramic and a second adhesive. The material of the ceramic-containing sodium-supplemented adhesive layer includes a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound.

5. The diaphragm structure according to claim 4, characterized in that, The first ceramic and the second ceramic are one or a mixture of at least two of the following: α-spherical alumina, granular burmesite, cerium dioxide, and zirconium dioxide; and / or, The second conductive agent is one or a mixture of at least two of conductive carbon, short multi-walled carbon nanotubes, Ketjen black, and ordered mesoporous carbon; and / or, At least one of the second and third adhesives is polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), or a mixture of PTFE and SBR; and / or, The second dispersant is one or a mixture of at least two of sodium polymethylcellulose, polyvinylpyrrolidone, N-methylpyrrolidone, and polyvinyl butyral; and / or, The second sodium-containing compound is one of Na2CO3, Na2C2O4, Na3C6H5O7, Na2C6O6, or a mixture of at least two of them.

6. The diaphragm structure according to claim 4, characterized in that, In the ceramic adhesive layer, the first ceramic component accounts for more than or equal to 75% and less than or equal to 88% by mass, and the second adhesive component accounts for more than or equal to 12% and less than or equal to 25% by mass; and / or, In the ceramic-containing sodium-supplemented adhesive layer, the mass percentage of the second ceramic is greater than or equal to 60% and less than or equal to 73%, the mass percentage of the third adhesive is greater than or equal to 10% and less than or equal to 20%, the mass percentage of the second conductive agent is greater than or equal to 30% and less than or equal to 35%, the mass percentage of the second dispersant is greater than or equal to 0.5% and less than or equal to 1%, and the mass percentage of the second sodium-containing compound is greater than or equal to 5% and less than or equal to 10%.

7. The diaphragm structure according to any one of claims 1-3, characterized in that, The thickness of the base film is greater than or equal to 6 μm and less than or equal to 10 μm; and / or, The thickness of the sodium-supplementing layer is greater than or equal to 1 μm and less than or equal to 3 μm; and / or, The thickness of the ceramic adhesive layer is greater than or equal to 3 μm and less than or equal to 6 μm; and / or, The thickness of the ceramic sodium-containing adhesive layer is greater than or equal to 3 μm and less than or equal to 8 μm.

8. A battery cell, characterized in that, include: A positive electrode, a negative electrode, and a separator structure as described in any one of claims 1-7 disposed between the positive electrode and the negative electrode, wherein a sodium supplement layer of the separator structure is adjacent to the negative electrode.

9. The battery cell according to claim 8, characterized in that, Along a first direction intersecting the thickness direction of the base film, the length of both ends of the separator structure extending beyond the corresponding ends of the negative electrode sheet is greater than or equal to 1 mm and less than or equal to 5 mm; and / or, Along the first direction intersecting the thickness direction of the base film, the length of both ends of the negative electrode extending beyond the corresponding ends of the positive electrode is greater than or equal to 1 mm and less than or equal to 3 mm; and / or, Along a second direction intersecting the thickness direction of the base film and the first direction, the length of both ends of the separator structure extending beyond the corresponding ends of the negative electrode sheet is greater than or equal to 1 mm and less than or equal to 2 mm; and / or, Along the second direction intersecting the thickness direction of the base film and the first direction, the length of the two ends of the negative electrode extending beyond the corresponding ends of the positive electrode is greater than or equal to 1.5 mm and less than or equal to 2 mm.

10. A sodium-ion battery, characterized in that, It includes at least one battery cell as described in claim 9.

11. A method for preparing a diaphragm structure, characterized in that, include: A first mixed material is provided, comprising a first sodium-containing compound, a first conductive agent, a first binder, and a first dispersant; wherein the first sodium-containing compound comprises a mass percentage greater than or equal to 10% and less than or equal to 25%, the first conductive agent comprises a mass percentage greater than or equal to 67% and less than or equal to 75%, the first binder comprises a mass percentage greater than or equal to 3% and less than or equal to 5%, and the first dispersant comprises a mass percentage greater than or equal to 1% and less than or equal to 3%. The first mixed material is coated on the first side of the base film to form a sodium-supplementing layer; A second mixture of a first ceramic and a second binder is provided, or a third mixture of a second ceramic, a third binder, a second conductive agent, a second dispersant, and a second sodium-containing compound is provided; The second mixed material is coated onto the second side of the base film to form a ceramic adhesive layer, and the base film, the sodium-supplementing layer, and the ceramic adhesive layer form the membrane structure; or, the third mixed material is coated onto the second side of the base film to form a ceramic-containing sodium-supplementing adhesive layer, and the base film, the sodium-supplementing layer, and the ceramic-containing sodium-supplementing adhesive layer form the membrane structure.

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