Battery separator and secondary battery

Abstract

The application provides a battery diaphragm and a secondary battery, comprising a porous base film, a high-temperature-resistant coating layer coated on one side or both sides of the surface of the porous base film, and an organic adhesive layer covering the surface of the high-temperature-resistant coating layer; the high-temperature-resistant coating layer is prepared from the following raw materials by weight: 1-5 parts of modified acrylic modified polyurethane composite emulsion, 35-50 parts of inorganic nano ceramic particles, 5-10 parts of an adhesive, 0.1-1 parts of an additive, and 40-60 parts of deionized water; the battery diaphragm is designed in a three-layer composite structure of 'porous base film + high-temperature-resistant coating layer + organic adhesive layer', and the optimization of the raw material ratio and the preparation process is combined to realize the synergistic improvement of the high-temperature-resistant performance and the adhesive performance, accurately solve the pain points of poor high-temperature resistance and poor adhesion of the existing diaphragm, effectively prevent the high-temperature shrinkage and damage of the diaphragm, avoid the thermal runaway of the battery at high temperature, significantly improve the use safety of the battery, and reduce the risk of thermal runaway, fire or explosion.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, and more particularly to a battery separator and a secondary battery. Background Technology

[0002] With the rapid development of new energy vehicles, energy storage systems, and consumer electronics, the market has placed higher demands on the energy density, safety performance, and cycle life of lithium-ion batteries. Pouch lithium-ion batteries, due to their high energy density, light weight, and flexible design, occupy an important position in the market.

[0003] In the manufacturing process of pouch cells, the alignment of the electrode and the separator is one of the core indicators determining the cell quality. According to the electrochemical principles of lithium-ion batteries, the negative electrode must completely cover the positive electrode to ensure that, during charging, all lithium ions extracted from the positive electrode can be inserted into the active material region of the negative electrode. If the negative electrode fails to completely cover the positive electrode (i.e., electrode misalignment), lithium ions will deposit disorderly on the surface of the negative electrode current collector (copper foil) in the misaligned area, forming lithium dendrites. Lithium dendrites not only lead to rapid capacity decay and shortened cycle life, but more seriously, they may puncture the separator, causing a direct short circuit between the positive and negative electrodes, ultimately leading to serious safety accidents such as battery thermal runaway, fire, or even explosion.

[0004] Existing conventional polyolefin separators typically exhibit a thermal shrinkage rate exceeding 10% at 150℃ / 1h, with a rupture temperature generally below 160℃. When the battery is subjected to abnormally high-temperature conditions, the separator undergoes drastic shrinkage due to heat, leading to direct contact between the positive and negative electrodes, potentially causing an internal short circuit or even thermal runaway.

[0005] Therefore, it is necessary to develop a battery separator to solve the above problems. Summary of the Invention

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A battery separator includes a porous base membrane, a high-temperature resistant coating coated on one or both surfaces of the porous base membrane, and an organic adhesive layer covering the surface of the high-temperature resistant coating; the high-temperature resistant coating is prepared from the following raw materials in parts by weight: 1-5 parts of modified acrylic-modified polyurethane composite emulsion, 35-50 parts of inorganic nano-ceramic particles, 5-10 parts of adhesive, 0.1-1 parts of additives, and 40-60 parts of deionized water; The preparation method of the modified acrylic-modified polyurethane composite emulsion includes the following steps: S1: Mix polyether polyol N210, 1,5-naphthalene diisocyanate and dibutyltin dilaurate, and react at 90-95°C for 1-3 hours; S2: When the isocyanate group content is 6-15% remaining, cool down to 70-80℃, add dimethylolpropionic acid, and heat up to 90-95℃ to continue the reaction; S3: When the isocyanate group content is 3-5% remaining, cool to 40-50℃ and add hydroxyethyl methacrylate, adamantyl methacrylate and butyl acrylate to continue the reaction until there is no isocyanate group residue. Add 90% of the total amount of triethylamine for neutralization reaction for 1 hour to obtain isocyanate prepolymer. S4: Isocyanate prepolymer, deionized water, and initiator are placed in a reactor, heated to 85°C, and reacted for 4 hours. Then, 10% of the total amount of triethylamine is added for neutralization reaction for 1 hour to obtain modified acrylic acid modified polyurethane composite emulsion.

[0007] This battery separator employs a three-layer composite structure design consisting of a porous base membrane, a high-temperature resistant coating, and an organic adhesive layer. Combined with optimized raw material ratios and manufacturing processes, this achieves a synergistic improvement in both high-temperature resistance and adhesion, precisely addressing the shortcomings of existing separators such as poor high-temperature resistance and weak adhesion. In the high-temperature resistant coating, a modified acrylic-modified polyurethane composite emulsion forms a stable network structure with inorganic nano-ceramic particles. Utilizing the high heat resistance of the inorganic nano-ceramic particles, the thermal shrinkage rate of the separator is significantly reduced at 150℃ or even 180℃, and the membrane breakage temperature is significantly increased to over 200℃. This effectively prevents high-temperature shrinkage and breakage of the separator, avoiding thermal runaway at high battery temperatures and significantly improving battery safety. This reduces the risk of thermal runaway, fire, or explosion, and leverages the flexibility and adhesion of the modified acrylic-modified polyurethane composite emulsion to solve the problem of inorganic particles easily detaching. Simultaneously, this composite emulsion, prepared through a specific process, combines the chemical resistance of polyurethane with the weather resistance of acrylic, further enhancing the stability of the coating. The combination of additives and binders optimizes the film-forming and dispersing properties of the coating, ensuring uniform coverage. Deionized water, used as the dispersion medium, is environmentally friendly and ensures thorough dispersion of all raw materials. Ultimately, the separator possesses excellent high-temperature resistance, mechanical properties, and interfacial compatibility, meeting the high safety and long-cycle requirements of secondary batteries, laying the foundation for subsequent optimization of adhesion and improvement of overall battery performance.

[0008] More preferably, the organic adhesive layer is selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyolefin, and polyacrylic acid.

[0009] The organic adhesive layer uses materials such as polyvinylidene fluoride and polymethyl methacrylate. These materials have excellent adhesion and electrochemical inertness. On the one hand, they can enhance the interfacial bonding force between the separator and the positive and negative electrodes, solving the problem of poor adhesion between the separator and the electrodes and effectively preventing misalignment of the positive and negative electrodes. On the other hand, they will not react with the battery electrolyte, ensuring battery safety. At the same time, single materials or multiple materials can be flexibly selected according to the specific performance requirements of the battery, broadening the adaptability of the separator and providing material support for achieving stable adhesion between the separator and the electrodes and improving the quality of the battery cell.

[0010] More preferably, the areal density of the organic coating is 0.05–0.5 g / m³. 2 .

[0011] By controlling the areal density of the organic adhesive layer to 0.05–0.5 g / m², sufficient adhesive strength can be ensured to guarantee a tight fit between the separator and the electrode, further enhancing the adhesive effect and preventing electrode misalignment. At the same time, it avoids the problems of decreased separator permeability and increased battery internal resistance caused by excessively high areal density, thus achieving a balance between adhesive performance and permeability. This also reduces material usage, controls separator production costs, and takes into account both performance and industrial mass production requirements. More preferably, the density of the organic bonding layer is controlled at 0.15-0.45 g / m², and even more preferably at 0.2-0.4 g / m², which can further optimize the balance between bonding performance and electrolyte wetting effect. When the density of the organic bonding layer is too high, the electrode sheet will be tightly attached to the surface of the separator after hot pressing. During the electrolyte wetting process, the electrode sheet is difficult to be fully wetted, which leads to deformation of the cell due to uneven expansion of the electrode sheet during capacity testing. At the same time, there will be areas inside the cell that cannot be wetted, resulting in increased interfacial impedance, affecting the lithium ion transport efficiency between interfaces, and ultimately causing problems such as lithium plating at the cell interface, decreased battery capacity, deterioration of cycle performance, and degradation of rate performance. The above-mentioned preferred areal density range can effectively avoid such problems and further improve the overall performance of the battery.

[0012] More preferably, the porosity of the porous base membrane is 30-70%; the porous base membrane is any one of polyethylene, polypropylene, nonwoven fabric, polymethylpentene, polyimide, and polyvinylidene fluoride.

[0013] The porosity of the porous base membrane is controlled between 30% and 70%, which ensures sufficient electrolyte wetting, provides channels for the rapid migration of lithium ions, improves the battery's charge and discharge efficiency, and takes into account the battery's electrochemical performance. Various materials such as polyethylene and polypropylene are selected as porous base membranes, allowing for flexible selection based on the battery's high-temperature resistance and mechanical performance requirements. For example, polyimide base membranes can further enhance the separator's high-temperature resistance limit, while non-woven fabric base membranes can enhance the separator's electrolyte absorption capacity, significantly reduce battery internal resistance, improve charge and discharge performance, broaden the separator's application scenarios, and adapt to different types of secondary batteries such as new energy power batteries and consumer electronics batteries, providing a fundamental guarantee for optimizing the separator's high-temperature resistance and mechanical properties.

[0014] More preferably, the inorganic nano-ceramic particles are one or more of nano-alumina, nano-silicon oxide, nano-zirconium oxide, nano-magnesium oxide, nano-boehmite, nano-magnesium hydroxide, nano-aluminum hydroxide, nano-silicon nitride, and nano-hexagonal boron nitride.

[0015] Inorganic nano-ceramic particles are made from materials such as nano-alumina and boehmite. These nanoparticles have high specific surface area, high heat resistance, and excellent insulation properties, which can effectively improve the thermal stability and insulation of high-temperature coatings, further reduce the high-temperature shrinkage rate of the separator, increase the membrane rupture temperature, prevent battery short circuits, and enhance battery safety. At the same time, the small particle size of the nanoparticles allows them to be uniformly dispersed in the coating, avoiding the formation of pore defects and ensuring the mechanical properties and air permeability of the separator. In addition, multiple nanoparticles can be used in combination to achieve synergistic optimization of heat resistance and insulation, helping to solve the technical pain point of poor high-temperature resistance of existing separators.

[0016] More preferably, the adhesive is one or more of vinylpyrrolidone, polyvinylidene fluoride, polymethyl methacrylate, polybutyl acrylate, polyvinyl alcohol, polyacrylonitrile, and vinyl acetate copolymer.

[0017] The binder is made of vinylpyrrolidone polymers, polyvinylidene fluoride, and other materials. These binders have good adhesion and dispersion properties, which can firmly bond inorganic nano-ceramic particles and composite emulsions to the porous base membrane surface, prevent coating peeling, ensure the stability of the high-temperature resistant coating, and further enhance the high-temperature resistance and structural integrity of the separator. At the same time, these binders have good compatibility with the electrolyte, do not affect the migration of lithium ions, take into account the electrochemical performance of the battery, and have excellent electrochemical stability. They can withstand the electrochemical reactions during the battery charge and discharge process for a long time, extend the service life of the separator, and provide support for improving the long-term cycle performance of the battery.

[0018] More preferably, the additive is one or more of sodium polyacrylate, polyacrylate, polyether-modified siloxane, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylamide, and alkylbenzene sulfonate.

[0019] The additives selected include sodium polyacrylate and polyether-modified siloxanes, which can specifically optimize the performance of the high-temperature resistant coating. For example, sodium polyacrylate and carboxymethyl cellulose additives can improve the dispersibility of the coating, prevent the agglomeration of inorganic nanoparticles, ensure the uniformity of the coating, and guarantee the stability of the high-temperature resistance of the separator. Polyether-modified siloxanes can improve the film-forming properties and surface smoothness of the coating, reduce the friction between the separator and the electrode, and further prevent electrode misalignment. Alkylbenzene sulfonates can improve the wettability of the coating, facilitate electrolyte wetting, and ensure the charging and discharging efficiency of the battery. The synergistic effect of various additives further optimizes the overall performance of the separator, ensures the stability of the coating quality, and helps to realize the industrial mass production of the separator.

[0020] More preferably, in steps S1-S4, the weight ratio of polyether polyol N210, 1,5-naphthalene diisocyanate, dimethylolpropionic acid, hydroxyethyl methacrylate, adamantyl methacrylate, butyl acrylate, dibutyltin dilaurate, triethylamine, initiator, and deionized water is 9-12:3-5:0.5-1:1-3:3-5:1-3:0.001-0.01:0.1-1:0.01-0.1:74-80.

[0021] By limiting the weight ratio of each raw material in the preparation of modified acrylic-modified polyurethane composite emulsion, the structure and performance of the composite emulsion can be precisely controlled, ensuring that the emulsion has suitable viscosity, adhesion and heat resistance. This avoids problems such as poor emulsion stability and poor coating performance caused by imbalance of raw material ratios, and ensures the heat resistance and adhesion of the high-temperature resistant coating, further solving the pain points of poor high-temperature resistance and easy detachment of existing diaphragms. The specific ratio of polyether polyol N210 and 1,5-naphthalene diisocyanate can ensure the uniform molecular weight of the prepolymer. The addition of dimethylolpropionic acid can improve the hydrophilicity and film-forming properties of the emulsion. The controlled ratio of monomers such as hydroxyethyl methacrylate can optimize the flexibility and weather resistance of the emulsion. Ultimately, the composite emulsion and other raw materials of the high-temperature resistant coating form a good synergistic effect, ensuring the performance stability of the diaphragm and taking into account both performance and industrial mass production requirements.

[0022] A secondary battery includes a pouch cell formed by sequentially stacking a positive electrode, a separator, and a negative electrode, wherein the separator is any of the battery separators described above; the hot-pressing pressure of the pouch cell is 0.5–0.8 MPa, the hot-pressing temperature is 50–100°C, and the hot-pressing time is 10–120 s.

[0023] This invention specifies the hot-pressing parameters for pouch cells, wherein the hot-pressing pressure is 0.5–0.8 MPa, preferably 0.55–0.75 MPa, and more preferably 0.6–0.7 MPa; the hot-pressing temperature is 50–100°C, preferably 75–85°C; and the hot-pressing time is 10–120 s, preferably 25–60 s. These preferred parameters further optimize the hot-pressing effect and improve cell quality. The temperature, pressure, and time during hot-pressing must be controlled within appropriate ranges because: too low a temperature or too short a time will result in the binder not being softened; too low a pressure or too short a time will result in the binder not fully penetrating the pores on the electrode and separator, thus causing insufficient adhesion between the separator and the electrode, making it impossible to fix the positive and negative electrodes; too high a temperature, too high a pressure, or too long a time will result in excessive adhesion, affecting electrolyte wetting and causing defects such as black spots and lithium plating on the formed electrode. By precisely defining the range and preferred values ​​of hot-pressing parameters, this invention can effectively avoid the above-mentioned problems, ensure that the separator is tightly attached to the positive and negative electrode plates, reduce the interface gap, reduce the contact resistance, further prevent electrode misalignment, improve the cell hardness and flatness, and improve the cell appearance.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention significantly reduces the thermal shrinkage rate of the separator at 150°C or even 180°C by constructing a high heat-resistant coating on the surface of the base membrane, and greatly increases the membrane rupture temperature to over 200°C. This effectively prevents the separator from shrinking and breaking at high temperatures, significantly improves battery safety, and reduces the risk of thermal runaway, fire, or explosion. At the same time, through reasonable design, sufficient adhesion is achieved between the positive and negative electrode sheets of the lithium-ion battery and the separator, which can effectively prevent misalignment of the positive and negative electrode sheets, improve the hardness and flatness of the cell, and thus improve the appearance of the cell as well as the safety and long-term cycle performance of the battery.

[0025] This invention achieves core advantages such as improving the high-temperature resistance and safety reliability of the separator, optimizing the bonding effect between the separator and the electrode, taking into account the electrochemical performance of the battery, and facilitating industrial mass production. Its battery separator and secondary battery have broad application prospects in the fields of new energy power batteries and consumer electronics batteries, and can promote the secondary battery industry to develop in a safer, more stable and more efficient direction. Attached Figure Description

[0026] Figure 1 Test data on the heat shrinkage of the diaphragm in the examples and comparative examples; Figure 2 The test data for the cycle life of the cells in the examples and comparative examples are as follows. Detailed Implementation

[0027] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Example 1

[0028] A soft-pack stacked lithium-ion battery with a rated capacity of 20Ah adopts a single-ended tab structure and is mainly composed of a positive electrode, a negative electrode, an electrolyte, a separator, and an aluminum-plastic film. (I) Preparation of positive electrode The positive electrode uses lithium iron phosphate as the active material, and is mixed with conductive agent (acetylene black) and binder (polyvinylidene fluoride) in a mass ratio of 94:3:3. N-methylpyrrolidone (NMP) solvent is added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is uniformly coated on the surface of aluminum foil current collector with a coating density of 150 g / m². After drying at 80°C for 12 h and rolling (rolling pressure 12 MPa), it is cut into the size suitable for a 20Ah battery to obtain the positive electrode sheet.

[0029] (II) Anode Preparation The negative electrode uses graphite as the active material, and is mixed with a conductive agent (acetylene black) and a binder (sodium carboxymethyl cellulose + styrene-butadiene rubber) at a mass ratio of 95:2:3. Deionized water is added and the mixture is stirred evenly to form a negative electrode slurry. The negative electrode slurry is uniformly coated on the surface of a copper foil current collector with a coating density of 75 g / m². After drying at 80°C for 12 hours and rolling (rolling pressure 8 MPa), it is cut into the size suitable for a 20Ah battery to obtain the negative electrode sheet.

[0030] (III) Electrolyte preparation The main component of the electrolyte is lithium hexafluorophosphate (LiPF6). The solvent is a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1:1:1, with a lithium hexafluorophosphate concentration of 1.0 mol / L. 0.5 wt% of vinylene carbonate (VC) is added to the electrolyte as a film-forming additive. After stirring evenly, the electrolyte is sealed and stored under argon protection for later use.

[0031] (iv) Preparation of diaphragm The diaphragm is a polyethylene-based membrane with a high-temperature resistant ceramic layer coated on both sides and an organic adhesive layer (PVDF) sprayed on both sides. The specific parameters and manufacturing process are as follows: 1. Porous base membrane: A 7μm thick polyethylene (PE) porous base membrane with a porosity of 38% and uniform pore size distribution is selected to ensure electrolyte wettability and lithium-ion transport efficiency.

[0032] 2. High-temperature resistant ceramic layer: (1) Raw material ratio (weight fraction): 3 parts modified acrylic acid modified polyurethane composite emulsion, 42 parts inorganic nano-ceramic particles, 6 parts binder, 0.7 parts additives, and 48.3 parts deionized water; among which, the inorganic nano-ceramic particles are nano-alumina and nano-boehmite compounded in a mass ratio of 1:1, the binder is polyvinylidene fluoride, and the additives are polyether modified siloxane.

[0033] (2) Coating process: The high-temperature resistant ceramic slurry is uniformly coated on both sides of the porous base film using a micro-gravure coating method. The coating temperature is controlled at 40℃, the coating thickness on one side is 1.5μm, and the total coating thickness on both sides is 3.0μm. After coating, the film is dried at 48℃ for 1min to ensure that the coating is cured and formed without peeling or wrinkling.

[0034] 3. Organic adhesive layer: (1) Raw material ratio (weight fraction): 10.8 parts of polyvinylidene fluoride (PVDF), 8.1 parts of binder (polybutyl acrylate), 0.2 parts of additives (sodium polyacrylate), and 80.9 parts of deionized water; (2) Coating process: The adhesive layer slurry is evenly coated on both sides of the high-temperature resistant ceramic layer by spraying. The coating temperature is controlled at 40℃ and the coating surface density is 0.25g / ㎡. After coating, it is dried at 48℃ for 1 minute to ensure that the adhesive layer is evenly covered and the adhesion meets the standard, and finally the soft package adhesive diaphragm product is obtained.

[0035] (V) Preparation of modified acrylic acid-modified polyurethane composite emulsion This composite emulsion was prepared using the following synthesis process: S1: Take polyether polyol N210, 1,5-naphthalene diisocyanate and dibutyltin dilaurate in a weight ratio of 10.5:4.1:0.006, add them to the reaction vessel and mix evenly. Control the reaction temperature to 95℃ and react at a constant temperature for 3 hours. S2: The content of isocyanate (NCO) groups in the reaction system was determined by di-n-butylamine titration. When the content of NCO groups was 8%, the reaction system was cooled to 85°C, and dimethylolpropionic acid with a weight ratio of 0.9 was added. After stirring evenly, the temperature was raised to 95°C to continue the reaction. S3: Continue to monitor the NCO group content. When the NCO group content is 3%, cool the reaction system to 50°C, add 1.5 parts hydroxyethyl methacrylate, 4.8 parts adamantyl methacrylate, and 1.544 parts butyl acrylate by weight, stir evenly, and continue the reaction until no NCO group residue can be detected. Then add 90% of the total amount of triethylamine (the total weight ratio of triethylamine is 0.6), and carry out a neutralization reaction for 1 hour to obtain the isocyanate prepolymer. S4: Add the above isocyanate prepolymer, deionized water at a weight ratio of 76, and initiator (ammonium persulfate) at a weight ratio of 0.05 to the reactor. After stirring evenly, heat to 85°C and react at a constant temperature for 4 hours. After the reaction is completed, add the remaining 10% triethylamine and continue the neutralization reaction for 1 hour. Cool to room temperature, filter to remove impurities, and obtain the modified acrylic-modified polyurethane composite emulsion for later use.

[0036] III. Lithium-ion battery assembly and hot pressing process This lithium-ion battery is assembled using the following steps: (1) Stacking and assembly: The positive electrode, soft-pack adhesive diaphragm and negative electrode prepared above are stacked in the order of "negative electrode → diaphragm → positive electrode → ... → negative electrode", and the single-head electrode tab is used to ensure that the electrode tabs are aligned and there is no misalignment, and the soft-pack bare cell is assembled; wherein, the organic adhesive layer of the diaphragm faces the positive and negative electrode to ensure that the diaphragm and the electrode are tightly attached.

[0037] (2) Hot pressing of bare battery cells: The assembled soft-pack bare battery cells are placed in a hot press and hot-pressed according to the following parameters: hot pressing temperature 85℃, hot pressing pressure 0.6MPa, hot pressing time 20s; during the hot pressing process, the pressure of the hot press is controlled to be uniform to avoid wrinkles and damage to the battery cells.

[0038] (3) Encapsulation, liquid injection, formation and capacity separation (this is a conventional technique in this field and will not be elaborated on here). Example 2

[0039] The method in Example 2 is basically the same as that in Example 1, except that the differences are as follows: High-temperature resistant ceramic layer raw material ratio (weight fraction): 4 parts modified acrylic modified polyurethane composite emulsion, 42 parts inorganic nano-ceramic particles, 5 parts binder, 0.7 parts additives, and 48.3 parts deionized water; The thickness of the high-temperature resistant ceramic slurry coating on one side is 1.0 μm, and the total coating thickness on both sides is 2.0 μm. (3) The surface density of the organic adhesive layer is 0.2 g / m².

[0040] Comparative Example 1 The method of Comparative Example 1 is basically the same as that of Example 1, except that the difference between Comparative Example 1 and Example 1 is as follows: (1) Raw material ratio of high temperature resistant ceramic layer (weight fraction): 42 parts of inorganic nano-ceramic particles, 9 parts of binder, 0.7 parts of additives, and 48.3 parts of deionized water (no modified acrylic polyurethane composite emulsion was added).

[0041] Comparative Example 2 The method of Comparative Example 2 is basically the same as that of Example 1, except that the differences between them are as follows: The hot pressing parameters for the bare battery cell are: hot pressing temperature 100℃, hot pressing pressure 1.5MPa, and hot pressing time 120s.

[0042] The diaphragms produced in the examples and comparative examples were subjected to heat shrinkage tests. Test data are shown below. Figure 1 ;from Figure 1 The test data shows that, compared with Comparative Example 1, Examples 1-2 have better heat shrinkage performance and are more effective at high temperatures.

[0043] The pouch cells produced in the examples and comparative examples were subjected to cyclic testing at room temperature (25°C), voltage (2.5–4.2V), and current density (1C / 1C). The test data are shown below. Figure 2 ;from Figure 2 The test data shows that the lithium-ion batteries of Examples 1-2 have no significant difference in capacity retention rate after 1400 cycles compared with Comparative Example 1, but Comparative Example 2 shows a significant rapid capacity decay.

[0044] This invention effectively solves the technical pain points of existing technologies, such as poor high-temperature resistance of battery separators, weak adhesion between separators and electrodes, cell defects caused by unreasonable hot-pressing processes, and insufficient battery safety, by optimizing the structural design, raw material ratio, and preparation process of the battery separator, as well as precisely controlling the hot-pressing process of bare cells. Specifically, this invention constructs a high-heat-resistant coating on the surface of the base film, which significantly reduces the thermal shrinkage rate of the separator at 150°C or even 180°C, and greatly increases the membrane breakage temperature to over 200°C. This effectively prevents the separator from shrinking and breaking at high temperatures, significantly improves battery safety, and reduces the risk of thermal runaway, fire, or explosion. At the same time, through reasonable design, sufficient adhesion is achieved between the positive and negative electrodes of the lithium-ion battery and the separator, which can effectively prevent misalignment of the positive and negative electrodes, improve cell hardness and flatness, and thus improve cell appearance, battery safety, and long-term cycle performance. In summary, this invention ultimately achieves the core advantages of improving the high-temperature resistance and safety reliability of the separator, optimizing the bonding effect between the separator and the electrode, taking into account the electrochemical performance of the battery, and facilitating industrial mass production. Its battery separator and secondary battery have broad application prospects in the fields of new energy power batteries and consumer electronics batteries, and can promote the secondary battery industry to develop in a safer, more stable and more efficient direction.

Claims

1. A battery separator, characterized in that, It includes a porous base membrane, a high-temperature resistant coating coated on one or both surfaces of the porous base membrane, and an organic adhesive layer covering the surface of the high-temperature resistant coating. The high-temperature resistant coating is prepared from the following raw materials in parts by weight: 1-5 parts of modified acrylic-modified polyurethane composite emulsion, 35-50 parts of inorganic nano-ceramic particles, 5-10 parts of adhesive, 0.1-1 parts of additives, and 40-60 parts of deionized water. The preparation method of the modified acrylic-modified polyurethane composite emulsion includes the following steps: S1: Mix polyether polyol N210, 1,5-naphthalene diisocyanate and dibutyltin dilaurate, and react at 90-95°C for 1-3 hours; S2: When the isocyanate group content is 6-15% remaining, cool down to 70-80℃, add dimethylolpropionic acid, and heat up to 90-95℃ to continue the reaction; S3: When the isocyanate group content is 3-5% remaining, cool to 40-50℃ and add hydroxyethyl methacrylate, adamantyl methacrylate and butyl acrylate to continue the reaction until there is no isocyanate group residue. Add 90% of the total amount of triethylamine for neutralization reaction for 1 hour to obtain isocyanate prepolymer. S4: Isocyanate prepolymer, deionized water, and initiator are placed in a reactor, heated to 85°C, and reacted for 4 hours. Then, 10% of the total amount of triethylamine is added for neutralization reaction for 1 hour to obtain modified acrylic acid modified polyurethane composite emulsion.

2. The battery separator according to claim 1, characterized in that, The organic adhesive layer is selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polyolefin, and polyacrylic acid.

3. A battery separator according to claim 2, characterized in that, The areal density of the organic coating is 0.05–0.5 g / m³. 2 .

4. A battery separator according to claim 3, characterized in that, The porosity of the porous base membrane is 30-70%; the porous base membrane is any one of polyethylene, polypropylene, nonwoven fabric, polymethylpentene, polyimide, and polyvinylidene fluoride.

5. A battery separator according to claim 1, characterized in that, The inorganic nano-ceramic particles are one or more of the following: nano-alumina, nano-silicon oxide, nano-zirconia, nano-magnesium oxide, nano-boehmite, nano-magnesium hydroxide, nano-aluminum hydroxide, nano-silicon nitride, and nano-hexagonal boron nitride.

6. A battery separator according to claim 1, characterized in that, The adhesive is one or more of vinylpyrrolidone, polyvinylidene fluoride, polymethyl methacrylate, polybutyl acrylate, polyvinyl alcohol, polyacrylonitrile, and vinyl acetate copolymer.

7. A battery separator according to claim 1, characterized in that, The additive is one or more of sodium polyacrylate, polyacrylate, polyether-modified siloxane, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyacrylamide, and alkylbenzene sulfonate.

8. A battery separator according to claim 1, characterized in that, In steps S1-S4, the weight ratio of polyether polyol N210, 1,5-naphthalene diisocyanate, dimethylolpropionic acid, hydroxyethyl methacrylate, adamantyl methacrylate, butyl acrylate, dibutyltin dilaurate, triethylamine, initiator, and deionized water is 9-12:3-5:0.5-1:1-3:3-5:1-3:0.001-0.01:0.1-1:0.01-0.1:74-80.

9. A secondary battery, characterized in that, The invention comprises a pouch cell formed by sequentially stacking a positive electrode, a separator, and a negative electrode, characterized in that: the separator is the battery separator as described in any one of claims 1 to 8; the hot-pressing pressure of the pouch cell is 0.5 to 0.8 MPa, the hot-pressing temperature is 50 to 100°C, and the hot-pressing time is 10 to 120 s.

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