Lithium ion battery, composite separator and method for preparing the same

Abstract

The application discloses a lithium ion battery, a composite diaphragm and a preparation method thereof, and the composite diaphragm comprises a base film and a coating layer; the coating layer comprises an SBR@LATP composite material. The technical scheme prepares the SBR-coated titanium aluminum phosphate composite material, and when the LATP is used as the coating material and applied to the lithium battery diaphragm, the amount of electrolyte can be reduced, the safety performance and the energy density of the battery can be improved; the SBR has high bonding strength and good mechanical stability and operability; the composite diaphragm modified by the SBR@LATP composite material benefits from the modification of the SBR to the LATP, so that the coating film improves the pole piece bonding performance of the coating film while taking into account the excellent performance of the LATP, improves the energy density of the battery, and in general, the binder used for the battery negative electrode is SBR; when the SBR@LATP composite material modified composite diaphragm and the SBR in the battery negative electrode are applied to the battery, the SBR in the SBR@LATP composite material modified composite diaphragm and the SBR in the battery negative electrode can improve the bonding performance of the diaphragm to the negative electrode through the similar solubility principle between SBR-SBR.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a lithium-ion battery, a composite separator, and a method for preparing the same. Background Technology

[0002] With the rapid development of portable electronic devices, electric vehicles, and other fields, the performance requirements for lithium batteries are increasing. As a key component of lithium batteries, the performance of the lithium battery separator significantly impacts the overall performance of the battery. However, there are still some unresolved issues regarding the bonding performance between the lithium battery separator and the negative electrode.

[0003] Currently, polyolefin separators such as polyethylene and polypropylene, which are widely used in the technology, possess good chemical stability and mechanical strength. However, their crystal structure and molecular chain arrangement determine their low porosity and relatively high density. For example, the high crystallinity of polyethylene separators results in a relatively small effective space for lithium-ion transport within them. During the charging and discharging process of lithium batteries, lithium ions need to shuttle back and forth between the positive and negative electrodes. The low porosity of the separator limits the migration rate of lithium ions, thus affecting the charging and discharging efficiency and energy density of the battery. Furthermore, polyolefin separators have fewer functional groups on their surface, resulting in weaker interactions with the active materials on the surface of the negative electrode. During battery assembly and use, it is difficult for the separator and the negative electrode to form a tight chemical bond or strong physical adsorption, leading to poor adhesion between them. The low surface energy of the separator also makes it incompatible with components such as binders in the negative electrode slurry, thus failing to effectively bond the negative electrode sheet and the separator together. As lithium ions are inserted and extracted during battery charging and discharging, the negative electrode sheet and the separator are prone to separation, affecting the battery's performance and lifespan.

[0004] Therefore, there is an urgent need to study a lithium-ion battery separator that can maintain the high energy density of lithium-ion batteries and have strong adhesion to the electrodes, thereby improving the shortcomings of the existing composite materials and thus improving the safety of lithium-ion batteries. Summary of the Invention

[0005] The main objective of this invention is to provide a lithium-ion battery, a composite separator, and a method for preparing the same, aiming to solve the technical problem that the adhesion between the separator and the electrode in existing lithium batteries is low, which affects the charging and discharging efficiency and energy density improvement of the battery.

[0006] To achieve the above objectives, the first aspect of the present invention provides a lithium-ion battery separator, comprising a base film and a coating layer; the coating layer comprises an SBR@LATP composite material.

[0007] Furthermore, the coating layer also includes a dispersant, a thickener, a binder, and a wetting agent.

[0008] Furthermore, the coating layer is applied to one or both sides of the base film.

[0009] Furthermore, the dispersant, thickener, and binder are all polymer-based reagents.

[0010] Furthermore, the wetting agent is a silanol reagent.

[0011] Furthermore, the base film is a porous thin film.

[0012] A second aspect of this invention provides a method for preparing a composite separator, comprising the following steps:

[0013] The dispersant, SBR@LATP composite material, thickener, binder, wetting agent and first solvent are mixed evenly and reacted fully to obtain SBR@LATP composite material coating slurry;

[0014] The SBR@LATP composite material coating slurry is coated onto one or both sides of the base membrane, and after drying, the composite membrane is obtained.

[0015] Furthermore, the components of the SBR@LATP composite material coating slurry, by weight fraction, are: dispersant 0.5%-1.5%, SBR@LATP composite material 25%-35%, thickener 0.2%-0.9%, binder 5%-15%, wetting agent 0.1%-0.7%, and the remainder is the first solvent.

[0016] Furthermore, prior to the step of uniformly mixing and fully reacting the dispersant, SBR@LATP composite material, thickener, binder, wetting agent, and first solvent to obtain the SBR@LATP composite material coating slurry, the following step is also included:

[0017] The LATP and the first solvent were thoroughly mixed to obtain an LATP solution;

[0018] SBR and the second solvent are thoroughly mixed to obtain an SBR solution;

[0019] SBR solution was added to LATP solution and allowed to react fully to obtain SBR@LATP composite material.

[0020] A third aspect of the present invention provides a lithium-ion battery comprising a composite separator prepared by any of the methods described above or any of the composite separators described above, a positive electrode material, a negative electrode material, and an electrolyte.

[0021] Furthermore, the binder used in the negative electrode material is one or more of SBR styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0022] Beneficial effects:

[0023] This invention discloses a composite separator comprising a base membrane and a coating layer; the coating layer comprises an SBR@LATP composite material. This technical solution prepares an SBR-coated titanium aluminum phosphate composite material, wherein LATP possesses excellent low flammability and high temperature resistance, as well as advantages such as high structural stability, high thermal stability, and low explosion hazard, which can significantly improve the safety performance of lithium-ion batteries. Furthermore, ceramic materials have low conductivity, requiring the addition of a large amount of electrolyte when ceramic separators are used in lithium-ion batteries. LATP, however, has high lithium-ion conductivity, improving lithium-ion transport efficiency. Using LATP as a coating material in lithium battery separators can significantly reduce the amount of electrolyte used, thereby substantially improving battery safety and energy density. SBR has high... The SBR@LATP composite material modified composite separator, with its excellent bonding strength, good mechanical stability, and operability, benefits from the modification of LATP by SBR. This allows the coating film to maintain the excellent performance of LATP while significantly improving the electrode bonding performance, thereby significantly increasing the energy density of the battery. Meanwhile, since the binder used in the negative electrode of a battery is usually SBR, when the SBR@LATP composite material modified composite separator provided by this invention is used in the battery, the SBR in it and the SBR in the negative electrode will improve the bonding performance of the separator to the negative electrode through the principle of similar solubility between SBR and SBR.

[0024] Compared with the prior art, a lithium-ion battery according to an embodiment of this application includes the composite separator described in any of the above claims. It is understood that the lithium-ion battery of this application may include all the technical features and effects of the aforementioned composite separator, which will not be repeated here. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the composite diaphragm in Embodiment 1 of the present invention;

[0026] Figure 2 This is a schematic diagram of the composite diaphragm in another embodiment of the present invention;

[0027] Figure 3 This is a schematic diagram of the process steps for preparing the composite membrane in Embodiment 1 of the present invention.

[0028] in,

[0029] 1. Base membrane;

[0030] 2. Coating layer.

[0031] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0032] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0033] In this application, some industry terms are explained as follows:

[0034] SBR: Styrene Butadiene Rubber; LATP: Lithium Aluminum Titanium Phosphate; Coating areal density: the ratio of the mass of the coating material applied to the surface of a specific material to the area covered by the coating, expressed in grams per square meter (g / m²). 2 Units are: ); Cathode-thermal stripping: Under specific temperature conditions, the battery separator attached to the electrode is heated and then peeled off from the electrode; Ultrapure water: Refers to water with a resistivity of 18 MΩ·cm (25℃) or close to the limit of 18.3 MΩ·cm (25℃), produced by applying distillation, deionization, reverse osmosis technology or other appropriate supercritical fine technology, which can effectively remove various impurities in the water, thereby achieving the ultrapure standard; In SBR@LATP composite material, "@" is used to indicate the composite method or structural relationship between SBR and LATP materials, such as core-shell structure. In this application, "@" can be understood as "coating", "attaching", "composite on", or "embedded in", used to describe the bonding state between SBR and LATP.

[0035] Please refer to Figure 1 One embodiment of the present invention provides a lithium-ion battery separator, comprising a base film 1 and a coating layer 2; the coating layer 2 comprises an SBR@LATP composite material.

[0036] In the above embodiments, when LATP is used as a coating material in the battery separator, its relatively stable chemical properties and good compatibility with the electrolyte allow it to reduce adverse reactions between the electrolyte and the positive and negative electrode materials during battery operation. This reduces electrolyte decomposition and consumption, eliminating the need for excessive electrolyte addition during initial filling to compensate for subsequent consumption. Consequently, the amount of electrolyte used is reduced, improving battery safety and energy density. Furthermore, the LATP coating can suppress side reactions that may lead to electrolyte loss. For example, during battery charging and discharging, reactions detrimental to electrolyte stability may occur on the electrode surface. LATP can, to some extent, prevent these side reactions, reducing electrolyte loss and thus decreasing electrolyte requirements. SBR, with its high bonding strength, good mechanical stability, and operability, is commonly used as a binder in negative electrode materials. It effectively bonds the active material particles in the battery negative electrode together and ensures a tight bond between the active material layer and the current collector. To ensure the stability of the electrode structure during battery use, the active material will not easily detach from the current collector, guaranteeing the normal charge and discharge function of the battery. SBR is used to modify LATP, resulting in the SBR@LATP composite material. SBR is a high molecular polymer with flexibility and viscosity, while LATP has surface energy. SBR forms hydrogen bonds with the polar sites on the LATP surface through polar groups, making SBR and LATP form a stable composite material. At the same time, the unsaturated double bonds provided by the butadiene unit in the SBR molecule react chemically with the active groups on the LATP surface to form covalent bonds, further enhancing the bonding force between SBR and LATP and improving the stability and mechanical strength of the composite material. Thanks to the modification of LATP by SBR, the coating film retains the excellent performance of LATP. At the same time, the addition of SBR brings higher electrode adhesion performance to the composite separator. The adhesion effect of SBR can enhance the bonding force between the separator and the electrode, reduce the interfacial resistance, and improve the charge and discharge efficiency and cycle performance of the battery. Moreover, the binder used in the negative electrode of the battery is usually SBR. In the composite separator modified by SBR@LATP composite material, the SBR in it and the SBR in the negative electrode of the battery will improve the adhesion performance of the separator to the negative electrode through the principle of similar solubility between SBR-SBR.

[0037] In the above embodiments, since the composite separator modified with SBR@LATP composite material retains the properties of LATP material while being compatible with the bonding properties of SBR, it has better overall performance. It can more effectively promote ion transport and electrode reaction inside the battery, reduce energy loss, and at the same time, it is lightweight and structurally stable, so it will not put too much burden on the volume and weight of the battery. Therefore, it can improve the energy density and bonding performance of the battery.

[0038] Please refer to Figure 1 , Figure 2 In one embodiment, the coating layer 2 further includes a dispersant, a thickener, a binder, and a wetting agent. The dispersant, thickener, and binder are all polymeric reagents. The wetting agent is a silanol reagent.

[0039] In this embodiment, during the preparation of coating layer 2, the dispersant adjusts the rheological properties of the slurry, for example, by reducing the viscosity of the slurry, to stabilize the entire slurry system. Under magnetic stirring, the material can be mixed with ultrapure water and maintain a stable dispersion state during the mixing process, preventing precipitation or stratification. Furthermore, during the preparation of the composite membrane, the SBR@LATP composite material needs to be prepared as a slurry. Due to its surface properties and other factors, SBR@LATP may agglomerate. The dispersant can adsorb onto the surface of the SBR@LATP composite material particles, reducing the attraction between particles, thereby ensuring uniform dispersion of the composite material in the slurry. This avoids uneven composite material content at various locations in coating layer 2 when the slurry is coated onto the base membrane 1, which would affect the membrane performance. During the preparation of coating layer 2, a thickener is used to increase the viscosity of the slurry. Understandably, after adding the SBR@LATP composite material and dispersant and stirring, the viscosity of the slurry will decrease. Adding a thickener prevents the SBR@LATP composite material from settling in the slurry, ensuring the uniform distribution of various components and increasing the viscosity to guarantee the consistent performance of the coating slurry. During the preparation of coating layer 2, a binder can bond the SBR@LATP composite material particles together. Adding a binder further enhances this bonding effect. It can form bonding bridges on the surface of the composite material particles, creating a more stable connection between the particles and preventing them from loosening or falling off during subsequent processing or use. The binder can fill the gaps between the SBR@LATP composite material particles, making coating layer 2 denser and more uniform. This helps improve the mechanical properties of coating layer 2; simultaneously, when the coating slurry is used as a substrate material such as a battery separator, the binder can improve the adhesion between coating layer 2 and the substrate. This helps ensure that coating layer 2 adheres firmly to the substrate and will not peel off during battery use (such as during charge-discharge cycles under internal stress or vibration). Good adhesion maintains the integrity of coating layer 2, ensuring its continued effectiveness in improving membrane performance, such as maintaining the stability of ion transport channels. The wetting agent, a surfactant, consists of hydrophilic and lipophilic groups. When in contact with the surface of SBR@LATP composite particles, the lipophilic groups adhere to the solid particle surface, while the hydrophilic groups extend outwards into the liquid (water), making it easier for the aqueous phase to spread on the solid surface, thus wetting the solid material.This effect allows the SBR@LATP composite material, which is normally difficult to wet, to be fully wetted by water and maintain good dispersion in the aqueous system. The wetting agent reduces the surface or interfacial tension of the solvent, making it easier for the solvent to spread and penetrate the surface of the SBR@LATP composite particles. This improves the contact and mixing of the components in the slurry system, ensuring that all solid particles are fully wetted by the solvent, forming a uniform slurry. Good wetting properties also help the SBR@LATP composite particles disperse uniformly in water, preventing particle agglomeration or sedimentation. During stirring, the wetting agent can form a thin water film on the particle surface, reducing the attractive forces between particles and increasing the repulsive forces, thereby improving the dispersion stability of the particles.

[0040] In the above embodiments, the dispersant is a hydrolyzed polymaleic anhydride polymer. This type of polymer is a polyelectrolyte that can ionize into charged ions in water, causing the particle surface to carry the same charge. Due to the mutual repulsion between like charges, the particles are less likely to agglomerate, thus effectively dispersing the SBR@LATP composite particles in the aqueous system and maintaining the uniformity and stability of the slurry. Meanwhile, various other components, such as binders and thickeners, are usually added to the coating slurry system. The hydrolyzed polymaleic anhydride dispersant is well compatible with these components, working synergistically without affecting the performance of the coating slurry due to incompatibility. The thickener is sodium carboxymethyl cellulose, a polymer that significantly increases the viscosity of the system. Within a certain temperature and pH range, the viscosity maintains stable coatability and adhesion of the SBR@LATP composite material. Sodium carboxymethyl cellulose also has good compatibility with organic solvents and surfactants, producing a synergistic effect with the thickener. The binder is a polyacrylic acid polymer with a linear structure, providing a higher degree of particle anchoring. This allows for tighter bonding of the components in the slurry, enhancing the cohesion of the electrode. It contains numerous polar groups such as carboxyl groups, which can form strong hydrogen bonds with the hydroxyl groups on the surface of the SBR@LATP composite material, promoting uniform coating on the electrode surface and thus improving adhesion. As a water-based binder, it has good solubility in water, facilitating uniform mixing with other components during slurry preparation. The silanol reagent is a silanol nonionic surfactant. In the SBR@LATP slurry, this nonionic surfactant reduces the surface tension between water and the SBR@LATP composite particles. The silanol groups and hydrophobic groups in its molecular structure interact with the particle surface, making it easier for water molecules to spread and ensuring thorough wetting of the particles. This process helps improve the dispersibility of SBR@LATP composites in slurries, prevents particle agglomeration, and makes the slurry more uniform and stable. It also helps maintain the stability of the slurry and prevents separation between different phases. Furthermore, in SBR@LATP slurries, silanol nonionic surfactants exhibit good compatibility with other components such as binders (e.g., polyacrylic acid polymers) and thickeners (e.g., sodium carboxymethyl cellulose). It can synergistically work with binders to improve the adhesion of the binder to the SBR@LATP composites and enhance the bonding force between the slurry and the substrate. Simultaneously, it works in conjunction with thickeners to optimize the rheological properties and stability of the slurry, allowing all components to work together to improve the overall performance of the slurry.

[0041] In one embodiment, the coating layer 2 is coated on one or both sides of the base film 1.

[0042] In the above embodiments, single-sided coating is a coating operation performed only on one side of the base film 1; while double-sided coating is coating the base film 1 with the coating layer 2 on both sides. This application does not impose a specific limitation on the number of coating surfaces. Since the performance of the two sides of the separator is more uniform and consistent after coating on both sides, the performance difference between the two sides of the separator caused by single-sided coating is avoided. During battery assembly and use, the performance stability and consistency of the battery can be better guaranteed. This application preferably adopts double-sided coating.

[0043] In one embodiment, the base film 1 is a porous thin film.

[0044] In the above embodiments, the porous structure of the base membrane 1 is beneficial for improving lithium-ion conductivity, reducing internal resistance, and enhancing electrical performance. Specifically, the base membrane 1 of this application is at least one of polyolefin membrane, ceramic membrane, cellulose membrane, polyimide membrane, polyarylamide-based membrane 1, polyphenylene sulfide-based membrane 1, and polytetrafluoroethylene membrane 1. These base membranes 1 are high-temperature resistant and high-mechanical-strength engineering plastics, enabling the composite membrane to have high strength and good high-temperature resistance.

[0045] Please refer to Figure 3 Another embodiment of the present invention provides a method for preparing a composite separator, which is used to prepare the composite separator described in any of the above claims, comprising the following steps:

[0046] The dispersant, SBR@LATP composite material, thickener, binder, wetting agent and first solvent are mixed evenly and reacted fully to obtain SBR@LATP composite material coating slurry;

[0047] The SBR@LATP composite material coating slurry is coated on one or both sides of the base membrane 1, and after drying, a composite membrane modified with SBR@LATP composite material is obtained.

[0048] In one embodiment, the components of the SBR@LATP composite material coating slurry, by weight fraction, are: dispersant 0.5%-1.5%, SBR@LATP composite material 25%-35%, thickener 0.2%-0.9%, binder 5%-15%, wetting agent 0.1%-0.7%, and the remainder is the first solvent.

[0049] In one embodiment, before the step of mixing and fully reacting the dispersant, SBR@LATP composite material, thickener, binder, wetting agent, and first solvent to obtain the SBR@LATP composite material coating slurry, the following step is further included:

[0050] The LATP and the first solvent were thoroughly mixed to obtain an LATP solution;

[0051] SBR and the second solvent are thoroughly mixed to obtain an SBR solution;

[0052] SBR solution was added to LATP solution and allowed to react fully to obtain SBR@LATP composite material.

[0053] In the above embodiments, the first solvent is a solvent that is insoluble in LATP. For example, the first solvent in this application can be ultrapure water. When preparing the LATP solution, ultrapure water is used to uniformly disperse the LATP powder in water to avoid particle agglomeration. At the same time, it can make LATP more uniformly distributed in the system when mixed with other components (such as binders, dispersants, etc.) in the future, which helps to form a composite material or coating slurry with uniform performance. The second solvent is a solvent that can dissolve SBR. For example, it can be an aromatic solvent, a halogenated hydrocarbon solvent, a ketone solvent, etc. Among them, the aromatic solvent can be toluene, xylene (including ortho, meta, and para isomers), the halogenated hydrocarbon solvent can be chlorobenzene, and the ketone can be methyl ethyl ketone. This application does not make specific restrictions on the above-mentioned second solvent. Since chlorobenzene is toxic and ketones are expensive, toluene is preferred as the second solvent in this application.

[0054] Another embodiment of the present invention provides a lithium-ion battery, comprising a composite separator prepared by the method described in any one of the preceding claims, a positive electrode material, a negative electrode material, and an electrolyte. The binder used in the negative electrode material is one or more of styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.

[0055] In this embodiment, the SBR in the SBR@LATP composite separator of this application is similarly miscible with the binder used in the negative electrode material, further improving the bonding performance of the composite separator. Specifically, sodium carboxymethyl cellulose and styrene-butadiene rubber are both water-based binders with good solubility and dispersibility in water. This allows them to be uniformly dispersed in the system when mixed with the negative electrode material to form a slurry, without easily agglomerating or separating. Furthermore, both sodium carboxymethyl cellulose and styrene-butadiene rubber contain functional groups that can interact with the surface of the negative electrode material, such as the carboxymethyl functional groups on the sodium carboxymethyl cellulose molecular chain and the active groups on the styrene-butadiene rubber molecular chain. These can form hydrogen bonds and other interactions with hydroxyl groups and other groups on the surface of the negative electrode material particles, thereby binding the negative electrode active material together and enhancing the structural stability of the electrode. Polyacrylic acid is also a water-soluble polymer with similar solubility to styrene-butadiene rubber, allowing for uniform dispersion in water and facilitating mixing and processing with the negative electrode material. Meanwhile, polyacrylic acid molecules contain carboxyl functional groups, which share certain chemical similarities with some groups on styrene-butadiene rubber (SBR) molecules. Both can interact with the surfaces of the negative electrode material and the current collector, such as forming hydrogen bonds, thus producing an adhesive effect. Furthermore, when polyacrylic acid and SBR are mixed, there may be some entanglement between the molecular chains, further enhancing the adhesive performance. In the preparation of negative electrodes for lithium-ion batteries, sodium carboxymethyl cellulose (CMC) is often used in combination with SBR. CMC acts as a thickener and stabilizer, improving the viscosity and stability of the slurry and preventing the precipitation of active materials. SBR, on the other hand, mainly provides adhesive force, allowing the active materials to adhere better to the current collector. The synergistic effect of the two improves the performance of the electrode and the cycle life of the battery. When polyacrylic acid and SBR are used together, the anchoring effect of polyacrylic acid on particles and the adhesive properties of SBR make the adhesion of the negative electrode material stronger, improving the stability of the electrode during charge and discharge, inhibiting the shedding and expansion of active materials, thereby improving the battery's capacity retention and cycle performance.

[0056] The preparation process and performance of the present invention will be illustrated below with some specific examples.

[0057] Example 1:

[0058] Membrane preparation:

[0059] S1: Preparation of SBR@LATP composite material:

[0060] S11: Add 3.557g of LATP powder and 250mL of ultrapure water to a 500ml three-necked flask, stir magnetically at 650rpm for 6 hours, and then sonicate at 45KHZ and 450w ultrasonic power for 8 hours to obtain LATP dispersion.

[0061] S12: Slowly add 1.15g of SBR powder to 9.5g of toluene, seal the mixture, and magnetically stir at 600rpm for 5 hours to obtain an SBR solution.

[0062] S13: Under the conditions of magnetic stirring at 1000 rpm and ultrasonic power at 40 kHz and 400 W, the SBR solution prepared in step S12 was slowly added to the LATP dispersion prepared in S11 through the side opening of a three-necked flask at a flow rate of 0.55 ml / min to ensure complete reaction of the SBR solution; magnetic stirring was continued at 450 rpm for 5 h, followed by ultrasonic treatment at 45 kHz and 400 W for 5 h; then the resulting mixture was transferred to a centrifuge and centrifuged at 9500 rpm for 20 min. The precipitate obtained by centrifugation was thoroughly washed with deionized water and vacuum dried at 0.08 MPa and 60 °C for 48 h to obtain the SBR@LATP composite material.

[0063] S2: Preparation of SBR@LATP composite coating slurry:

[0064] S21: Add 0.9% of the dispersant and 25% of the SBR@LATP composite material to ultrapure water by mass ratio, and mix for 70 min under magnetic stirring at 1100 rpm.

[0065] S22: Add 0.85% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0066] S23: Add 12% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0067] S24: Add 0.6% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the SBR@LATP composite material coating slurry is obtained.

[0068] S3: Preparation of composite membrane modified with SBR@LATP composite material:

[0069] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is uniformly roller coated onto the substrate by a coating machine. After baking in a 75℃ oven, it is rolled up for later use, thus obtaining the composite separator modified with SBR@LATP composite material for lithium-ion batteries.

[0070] Example 2:

[0071] The only difference between this embodiment and Embodiment 1 is that, in step S21 of step S2, the mass ratio of SBR@LATP composite material added is 30%.

[0072] Example 3:

[0073] The only difference between this embodiment and Embodiment 1 is that, in step S21 of step S2, the mass ratio of SBR@LATP composite material added is 35%.

[0074] Example 4:

[0075] Membrane preparation:

[0076] S1: Preparation of SBR@LATP composite material:

[0077] S11: Add 3.557g of LATP powder and 250mL of ultrapure water to a 500ml three-necked flask, stir magnetically at 650rpm for 6 hours, and then sonicate at 45KHZ and 450w ultrasonic power for 8 hours to obtain LATP dispersion.

[0078] S12: Slowly add 1.15g of SBR powder to 9.5g of toluene, seal the mixture, and magnetically stir at 600rpm for 5 hours to obtain an SBR solution.

[0079] S13: Under the conditions of magnetic stirring at 1000 rpm and ultrasonic power at 40 kHz and 400 W, the SBR solution prepared in step S12 was slowly added to the LATP dispersion prepared in S11 through the side opening of a three-necked flask at a flow rate of 0.55 ml / min to ensure complete reaction of the SBR solution; magnetic stirring was continued at 450 rpm for 5 h, followed by ultrasonic treatment at 45 kHz and 400 W for 5 h; then the resulting mixture was transferred to a centrifuge and centrifuged at 9500 rpm for 20 min. The precipitate obtained by centrifugation was thoroughly washed with deionized water and vacuum dried at 0.08 MPa and 60 °C for 48 h to obtain the SBR@LATP composite material.

[0080] S2: Preparation of SBR@LATP composite coating slurry:

[0081] S21: Add 0.5% of the dispersant and 35% of the SBR@LATP composite material to ultrapure water by mass ratio, and mix for 70 min under magnetic stirring at 1100 rpm.

[0082] S22: Add 0.2% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0083] S23: Add 5% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0084] S24: Add 0.1% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the SBR@LATP composite material coating slurry is obtained.

[0085] S3: Preparation of composite membrane modified with SBR@LATP composite material:

[0086] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is uniformly roller coated onto the substrate by a coating machine. After baking in a 75℃ oven, it is rolled up for later use, thus obtaining the composite separator modified with SBR@LATP composite material for lithium-ion batteries.

[0087] Example 5:

[0088] Membrane preparation:

[0089] S1: Preparation of SBR@LATP composite material:

[0090] S11: Add 3.557g of LATP powder and 250mL of ultrapure water to a 500ml three-necked flask, stir magnetically at 650rpm for 6 hours, and then sonicate at 45KHZ and 450w ultrasonic power for 8 hours to obtain LATP dispersion.

[0091] S12: Slowly add 1.15g of SBR powder to 9.5g of toluene, seal the mixture, and magnetically stir at 600rpm for 5 hours to obtain an SBR solution.

[0092] S13: Under the conditions of magnetic stirring at 1000 rpm and ultrasonic power at 40 kHz and 400 W, the SBR solution prepared in step S12 was slowly added to the LATP dispersion prepared in S11 through the side opening of a three-necked flask at a flow rate of 0.55 ml / min to ensure complete reaction of the SBR solution; magnetic stirring was continued at 450 rpm for 5 h, followed by ultrasonic treatment at 45 kHz and 400 W for 5 h; then the resulting mixture was transferred to a centrifuge and centrifuged at 9500 rpm for 20 min. The precipitate obtained by centrifugation was thoroughly washed with deionized water and vacuum dried at 0.08 MPa and 60 °C for 48 h to obtain the SBR@LATP composite material.

[0093] S2: Preparation of SBR@LATP composite coating slurry:

[0094] S21: Add 1.5% of the dispersant and 35% of the SBR@LATP composite material to ultrapure water by mass ratio, and mix for 70 min under magnetic stirring at 1100 rpm.

[0095] S22: Add 0.9% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0096] S23: Add 15% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0097] S24: Add 0.7% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the SBR@LATP composite material coating slurry is obtained.

[0098] S3: Preparation of composite membrane modified with SBR@LATP composite material:

[0099] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is uniformly roller coated onto the substrate by a coating machine. After baking in a 75℃ oven, it is rolled up for later use, thus obtaining the composite separator modified with SBR@LATP composite material for lithium-ion batteries.

[0100] Example 6:

[0101] Membrane preparation:

[0102] S1: Preparation of SBR@LATP composite material:

[0103] S11: Add 3.557g of LATP powder and 250mL of ultrapure water to a 500ml three-necked flask, stir magnetically at 650rpm for 6 hours, and then sonicate at 45KHZ and 450w ultrasonic power for 8 hours to obtain LATP dispersion.

[0104] S12: Slowly add 1.15g of SBR powder to 9.5g of toluene, seal the mixture, and magnetically stir at 600rpm for 5 hours to obtain an SBR solution.

[0105] S13: Under the conditions of magnetic stirring at 1000 rpm and ultrasonic power at 40 kHz and 400 W, the SBR solution prepared in step S12 was slowly added to the LATP dispersion prepared in S11 through the side opening of a three-necked flask at a flow rate of 0.55 ml / min to ensure complete reaction of the SBR solution; magnetic stirring was continued at 450 rpm for 5 h, followed by ultrasonic treatment at 45 kHz and 400 W for 5 h; then the resulting mixture was transferred to a centrifuge and centrifuged at 9500 rpm for 20 min. The precipitate obtained by centrifugation was thoroughly washed with deionized water and vacuum dried at 0.08 MPa and 60 °C for 48 h to obtain the SBR@LATP composite material.

[0106] S2: Preparation of SBR@LATP composite coating slurry:

[0107] S21: Add 1% of the dispersant and 35% of the SBR@LATP composite material to ultrapure water by mass ratio, and mix for 70 min under magnetic stirring at 1100 rpm.

[0108] S22: Add 0.55% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0109] S23: Add 10% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0110] S24: Add 0.4% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the SBR@LATP composite material coating slurry is obtained.

[0111] S3: Preparation of composite membrane modified with SBR@LATP composite material:

[0112] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is uniformly roller coated onto the substrate by a coating machine. After baking in a 75℃ oven, it is rolled up for later use, thus obtaining the composite separator modified with SBR@LATP composite material for lithium-ion batteries.

[0113] Comparative Example 1: No SBR@LATP composite material was prepared or added; otherwise, it was the same as in Example 1.

[0114] Add 0.9% of the dispersant to ultrapure water by mass ratio and mix for 70 min with magnetic stirring at 1100 rpm.

[0115] Add 0.85% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0116] Add 12% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0117] Add 0.6% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the coating slurry is obtained.

[0118] The coating slurry prepared above is uniformly coated onto the substrate using a micro-gravure roller coating process. After baking in a 75°C oven, it is rolled up for later use, thus obtaining the composite separator for lithium-ion batteries to be prepared.

[0119] Comparative Example 2:

[0120] S1: Preparation of LATP material coating slurry

[0121] S11: Add 0.9% dispersant and 35% LATP material to ultrapure water by mass ratio, and mix for 70 min under magnetic stirring at 1100 rpm.

[0122] S12: Add 0.85% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0123] S13: Add 12% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0124] S14: Add 0.6% wetting agent, and continue stirring for 40 minutes under magnetic stirring at 350 rpm. After filtering to remove iron, the LATP material coating slurry is obtained.

[0125] S2: Preparation of LATP-modified diaphragms:

[0126] S21: Using a micro-gravure roller coating process, the LATP material coating slurry prepared in S1 is uniformly roller coated onto the polyolefin separator using a coating machine. After baking in a 75°C oven, it is rolled up for later use, thus obtaining the composite separator modified with LATP material for lithium-ion batteries.

[0127] Comparative Example 3:

[0128] S1: Preparation of SBR material coating slurry

[0129] S11: Add 0.9% dispersant and 35% SBR material to ultrapure water by mass ratio, and mix for 70 min with magnetic stirring at 1100 rpm.

[0130] S12: Add 0.85% thickener and continue stirring for 60 minutes with magnetic stirring at 700 rpm;

[0131] S13: Add 12% binder and continue stirring for 120 minutes with magnetic stirring at 950 rpm;

[0132] S14: Add 0.6% wetting agent, stir for 40 minutes under magnetic stirring at 350 rpm, filter to remove iron, and obtain SBR material coating slurry.

[0133] S2: Preparation of SBR material-modified diaphragm:

[0134] S21: Using a micro-gravure roller coating process, the SBR material coating slurry prepared in S1 is uniformly roller coated onto the polyolefin separator using a coating machine. After baking in a 75°C oven, it is rolled up for later use, thus obtaining the composite separator modified with SBR material for lithium-ion batteries.

[0135] Comparative Example 4:

[0136] The only difference between this comparative example and Example 3 is that this comparative example only has a base film 1, and compared with the polyolefin separator mentioned above, it does not have a coating layer 2.

[0137] Testing: The membranes prepared in the above examples and comparative examples were subjected to performance tests according to the testing standard GB / T36363-2018. The peel strength was tested using a universal testing machine, and the air permeability was tested using a Gurley air permeability meter. The data obtained are shown in the table below:

[0138] Table 1. Results of diaphragm air permeability, peel strength, and heat shrinkage tests.

[0139]

[0140] As can be seen from Table 1:

[0141] In the air permeability performance test, the air permeability value of Comparative Example 2 was 213.6 s / 100 mL, and that of Comparative Example 3 was 225.5 s / 100 mL, both higher than those of Examples 1 to 6. This is because when LATP or SBR materials are used alone for coating, their physicochemical properties significantly affect the pore structure of the membrane, resulting in higher air permeability. For example, LATP particles have irregular growth characteristics, making it easy for pores to appear on the electrode surface. When pores exist on the electrode surface: on the one hand, pores interrupt the originally continuous ion transport channels. Ions need to move orderly in a dense structure during conduction, but the presence of pores forces ions to change paths and bypass the pore areas, increasing the distance and difficulty of ion transport; on the other hand, the presence of pores may lead to confusion in the direction of ion transport. In the ideal case without pores, ions can be conducted along a relatively clear direction, but pores disperse the direction of ion transport, reducing the overall transport efficiency and leading to a decrease in the conductivity of LATP ions. In the examples, the SBR@LATP composite material, through the synergistic effect of the two components, optimized the pore structure to a certain extent, resulting in a relatively low air permeability. In Examples 1 to 3, the air permeability gradually increased with the increase of SBR content in the SBR@LATP composite material. The air permeability of Example 1 was 146.6 s / 100 mL, Example 2 was 159.3, and Example 3 was 200.1 s / 100 mL. This is because the SBR@LATP composite material is coated on the membrane, and the increase of SBR content changes the pore structure of the membrane, causing a change in the resistance to gas passage through the membrane. The increase of SBR content makes the pore channels more complex, and the gas passage path becomes longer, thus increasing the air permeability. The air permeability of Comparative Example 4 is 90 s / 100 mL, which is significantly lower than that of the examples with coating and the comparative examples. This is because the base membrane is not modified by the coating layer, its pore structure is relatively simple, the resistance to gas passage is small, and therefore the air permeability is low. When the mass ratio of SBR@LATP composite material in the slurry gradually increases from 25% to 30%, the air permeability of the corresponding composite membrane deteriorates. When the mass ratio of SBR@LATP composite material further increases to 35%, the air permeability value is significantly higher than that of Comparative Example 1 and Comparative Example 4, and the air permeability becomes even worse. Therefore, in order to balance the performance of the composite membrane, the amount of SBR@LATP composite material added needs to be adjusted according to the actual design requirements of the battery, and more is not necessarily better.

[0142] In the anodic-hot-press peel strength test, the peel strength of Comparative Example 2 was 1.4 N / m, and that of Comparative Example 3 was 6.9 N / m, both significantly lower than those of the Example Group. This is because LATP material alone has weak adhesion to the anode. While SBR material alone has some adhesion, it is not as strong as the adhesion when the SBR content in the SBR@LATP composite material increases. Therefore, the interaction between SBR and LATP in the composite material improves the adhesion performance. In Examples 1 to 3, the anodic-hot-press peel strength gradually increases with the increase of SBR content in the SBR@LATP composite material. The peel strength of Example 1 was 11.1 N / m, Example 2 was 15.3 N / m, and Example 3 was 17.6 N / m. This is because SBR has good adhesion properties, and the increase of SBR content enhances the adhesion between the diaphragm and the anode. The peel strength of Comparative Example 4 (base film only) was 0.8 N / m, significantly lower than that of the Examples and Comparative Examples with coatings. This is because the base film lacks the adhesive effect of the coating layer, resulting in weaker adhesion between it and the anode, thus leading to lower peel strength. Comparative Example 1 shows a peel strength of 5.6 N / m. This is because although the coating layer does not contain SBR@LATP composite material, adhesives and thickeners still enhance adhesion. However, compared to electrodes with added SBR@LATP composite material, the adhesion between the composite membrane and the anode is significantly weaker.

[0143] In the heat shrinkage performance test, the heat shrinkage rates of Comparative Example 2 were 3.3% and 2.1%, and those of Comparative Example 3 were 1.5% and 1.0%, which were higher than those of Examples 1 to 6. When using LATP or SBR materials alone, their heat resistance was not as good as that of the SBR@LATP composite material. This is because the two components in the composite material work synergistically, with SBR improving the thermal stability of the membrane. As the SBR content in the SBR@LATP composite material in the examples increased, the heat shrinkage rate gradually decreased. The longitudinal MD heat shrinkage rates of Example 1 were 0.9% and 0.7%, Example 2 were 0.8% and 0.5%, and Example 3 were 0.6% and 0.4%. This is because SBR has certain heat resistance properties, while LATP plays a role in stabilizing the structure at high temperatures. With the increase of SBR content, the heat resistance of the composite material further improved, thus reducing the heat shrinkage rate. The heat shrinkage rate of Comparative Example 4 (base film only) was 5.0% and 2.5%, which was higher than that of the examples and comparative examples with coatings. This is because the thermal stability of the base film is relatively poor, and without the protection and reinforcement of the coating, the heat shrinkage rate is higher.

[0144] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention's specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A composite diaphragm, characterized in that, It includes a base film and a coating layer, wherein the coating layer comprises an SBR@LATP composite material; in the SBR@LATP composite material, SBR is coated with LATP; The coating layer improves the adhesion performance of the separator to the negative electrode by utilizing the principle of similar compatibility between SBR and SBR used in the negative electrode material. The SBR@LATP composite material is obtained by adding an SBR solution to an LATP solution and mixing thoroughly. The coating layer also includes dispersants, thickeners, binders, and wetting agents; The coating layer is applied to one or both sides of the base film; The dispersant, thickener, and binder are all polymer-based reagents; The wetting agent is a silanol reagent; The base film is a porous film; the components of the SBR@LATP composite coating slurry, by weight fraction, are: dispersant 0.5%-1.5%, SBR@LATP composite material 25%-35%, thickener 0.2%-0.9%, binder 5%-15%, wetting agent 0.1%-0.7%, and the remainder is the first solvent.

2. A method for preparing a composite diaphragm, characterized in that, The preparation of the composite separator as described in claim 1 includes the following steps: The dispersant, SBR@LATP composite material, thickener, binder, wetting agent and first solvent are mixed evenly and reacted fully to obtain SBR@LATP composite material coating slurry; The SBR@LATP composite material coating slurry was coated onto the base film and dried to obtain the composite membrane.

3. The method for preparing the composite diaphragm according to claim 2, characterized in that, The components of the SBR@LATP composite coating slurry, by weight fraction, are: dispersant 0.5%-1.5%, SBR@LATP composite material 25%-35%, thickener 0.2%-0.9%, binder 5%-15%, wetting agent 0.1%-0.7%, and the remainder is the first solvent.

4. The method for preparing the composite diaphragm according to claim 2, characterized in that, Before the step of mixing and fully reacting the dispersant, SBR@LATP composite material, thickener, binder, wetting agent, and first solvent to obtain the SBR@LATP composite material coating slurry, the following steps are also included: The LATP and the first solvent were thoroughly mixed to obtain an LATP solution; SBR and the second solvent are thoroughly mixed to obtain an SBR solution; The SBR solution was added to the LATP solution and mixed thoroughly to obtain the SBR@LATP composite material.

5. A lithium-ion battery, characterized in that, It includes the composite separator, positive electrode material, negative electrode material, and electrolyte as described in claim 1.

6. The lithium-ion battery according to claim 5, characterized in that, The binder used in the negative electrode material is one or more of styrene-butadiene rubber, sodium hydroxymethyl cellulose, and polyacrylic acid.

Images