Lithium ion battery, composite diaphragm and preparation method thereof

Abstract

The invention discloses a lithium ion battery, a composite diaphragm and a preparation method of the composite diaphragm. The composite diaphragm comprises a base diaphragm and a coating layer, the coating layer includes an SBR (at) LATP composite material. According to the SBR-coated titanium aluminum phosphate composite material prepared by the technical scheme, when LATP is used as a coating material to be applied to a lithium battery diaphragm, the use amount of an electrolyte can be reduced, and the safety performance and the energy density of a battery are improved; according to the present invention, the SBR has high bonding strength and good mechanical stability and operability, the SBR-coated LATP composite material-modified composite membrane benefits from the modification of the SBR on the LATP, such that the excellent performance of the LATP is considered while the pole piece bonding performance of the coating film is improved so as to improve the energy density of the battery, and the bonding agent used by the battery negative electrode is the SBR under the normal condition so as to improve the energy density of the battery; when the SBR and the LATP composite material are applied to the battery, the SBR in the composite diaphragm modified by the SBR and the LATP composite material and the SBR in the negative electrode of the battery can improve the bonding performance of the diaphragm to the negative electrode through the principle that the SBR and the SBR are similar and dissoluble.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a lithium ion battery, a composite diaphragm and a preparation method thereof. Background Art

[0002] With the rapid development of portable electronic devices, electric vehicles and other fields, the performance requirements for lithium batteries are increasing. As one of the key components of lithium batteries, the performance of lithium battery separators has an important impact on the overall performance of lithium batteries. However, there are still some urgent problems to be solved in the bonding performance between lithium battery separators and negative electrode sheets.

[0003] In the prior art, the widely used polyolefin separators such as polyethylene and polypropylene have good chemical stability and mechanical strength, but their own crystal structure and molecular chain arrangement determine their low porosity and relatively high density. For example, the polyethylene separator has a high degree of crystallinity, which makes the effective space inside it available for lithium ion transmission relatively small. During the charging and discharging process of lithium batteries, lithium ions need to shuttle back and forth between the positive and negative electrodes, and the low porosity of the separator limits the migration rate of lithium ions, which in turn affects the battery's charging and discharging efficiency and energy density. In addition, there are fewer functional groups on the surface of the polyolefin separator, and the interaction force between it and the active material on the surface of the negative electrode is weak. During the assembly and use of the battery, it is difficult to form a tight chemical bond or a strong physical adsorption effect between the separator and the negative electrode, resulting in poor bonding performance between the two. The low surface energy of the diaphragm surface also makes it incompatible with the binder and other components in the negative electrode slurry, making it impossible to effectively bond the negative electrode sheet and the diaphragm together. As a result, during the battery charging and discharging process, as lithium ions are embedded and released, the negative electrode sheet and the diaphragm are easily separated, affecting the performance and life of the battery.

[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 has strong adhesion to the pole pieces, so as to improve the shortcomings of the above-mentioned existing composite materials and further improve the safety of lithium-ion batteries. Summary of the invention

[0005] The main purpose of the present invention is to provide a lithium-ion battery, a composite diaphragm and a preparation method thereof, aiming to solve the technical problem that the existing lithium battery diaphragm has low adhesion with the pole piece, thereby affecting the battery's charging and discharging efficiency and energy density improvement.

[0006] In order to achieve the above-mentioned object, 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 a 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 coated on one side or both sides of the base film.

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

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

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

[0012] A second aspect of the present invention provides a method for preparing a composite diaphragm, which is used to prepare any of the composite diaphragms described above, comprising the following steps:

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

[0014] The SBR@LATP composite material coating slurry is coated on one side or both sides of the base film and dried to obtain the composite diaphragm.

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

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

[0017] Fully mixing LATP and the first solvent to obtain a LATP solution;

[0018] Fully mixing SBR and a second solvent to obtain an SBR solution;

[0019] The SBR solution was added into the LATP solution and fully reacted to obtain the SBR@LATP composite material.

[0020] A third aspect of the present invention provides a lithium-ion battery, comprising a diaphragm as described in any one of the above or a composite diaphragm prepared by the method for preparing a composite diaphragm as described in any one of the above, a positive electrode material, a negative electrode material and an electrolyte.

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

[0022] Beneficial effects:

[0023] A composite diaphragm of the present invention comprises a base film and a coating layer; the coating layer comprises an SBR@LATP composite material. In this technical solution, an SBR-coated titanium aluminum phosphate composite material is prepared, wherein LATP has good low flammability and high temperature resistance, and has the advantages of high structural stability, high thermal stability, low explosion hazard, etc., which can greatly improve the safety performance of lithium-ion batteries; in addition, ceramic materials have low electrical conductivity, and ceramic diaphragms need to add a large amount of electrolyte when used in lithium-ion batteries, while LATP has high lithium ion conductivity, which can improve the transmission efficiency of lithium ions. When LATP is selected as a coating material for lithium battery diaphragms, the amount of electrolyte used can be greatly reduced, thereby greatly improving the safety performance and energy density of the battery; SBR has high The composite diaphragm modified with SBR@LATP composite material has excellent bonding strength, good mechanical stability and operability, thanks to the modification of LATP by SBR, so that the coating film has the excellent performance of LATP while greatly improving the electrode bonding performance of the coating film, thereby significantly improving the energy density of the battery; at the same time, the binder used in the negative electrode of the battery is usually SBR, so when the composite diaphragm modified with SBR@LATP composite material provided by the present invention is used in a battery at the same time, the SBR therein and the SBR in the negative electrode of the battery will improve the bonding performance of the diaphragm to the negative electrode through the principle of similar miscibility between SBR-SBR.

[0024] Compared with the prior art, a lithium-ion battery in an embodiment of the present application includes any of the composite diaphragms described above. It is understandable that the lithium-ion battery of the present application can include all the technical features and technical effects of the composite diaphragm described above, which will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 2 This is a schematic diagram of a composite diaphragm in another embodiment 1 of the present invention;

[0027] Figure 3 Schematic diagram of the process steps of the method for preparing the composite diaphragm in Example 1 of the present invention.

[0028] in,

[0029] 1. Basement membrane;

[0030] 2. Coating layer.

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

[0032] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

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

[0034] SBR: Styrene Butadiene Rubber; LATP: Lithium Aluminum Titanium Phosphate; Coating surface density: refers to the ratio of the mass of the coating material applied on the surface of a specific material to the area covered by the coating, expressed in grams per square meter (g / m 2 ) as a unit; cathode-thermal stripping: under specific temperature conditions, the battery diaphragm bonded to the electrode is heated and the battery diaphragm is stripped from the electrode; ultrapure water: refers to water with a resistivity of 18MΩ·cm (25°C) or close to the limit value of 18.3MΩ·cm (25°C). It is produced by applying distillation, deionization, reverse osmosis technology or other appropriate supercritical fine technology, which can effectively remove various impurities in the water, thereby reaching the ultrapure standard; in the SBR@LATP composite material, "@" is used to indicate the composite mode or structural relationship between the two materials SBR and LATP, such as the core-shell structure. In this application, "@" can be understood as "coated", "attached", "compounded on..." or "embedded in", which is used to describe the bonding state between SBR and LATP.

[0035] Please refer to Figure 1 An 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 a SBR@LATP composite material.

[0036] In the above embodiment, when LATP is used as a coating material in a battery separator, since LATP is relatively stable in chemical properties and has good compatibility with the electrolyte, during the operation of the battery, the LATP coating can reduce the adverse reactions between the electrolyte and the positive and negative electrode materials, thereby reducing the decomposition and consumption of the electrolyte. It is not necessary to add too much electrolyte during the initial injection to make up for the subsequent consumption, thereby reducing the amount of electrolyte used, improving the safety performance and energy density of the battery, and at the same time, the LATP coating can inhibit some side reactions that may cause the loss of the electrolyte. For example, during the battery charging and discharging process, some reactions that are not conducive to the stability of the electrolyte may occur on the electrode surface. LATP can block the occurrence of these side reactions to a certain extent, reduce the loss of the electrolyte due to side reactions, and thereby reduce the demand for the electrolyte. SBR has high bonding strength and good mechanical stability and operability. It is usually used as a binder in the negative electrode material, which can well bond the active material particles in the negative electrode of the battery, and can make the active material layer and the current collector tightly combined. Ensure that the electrode structure remains stable during the use of the battery, and the active material will not easily fall off the current collector, thereby ensuring the normal charging and discharging function of the battery; SBR is used to modify LATP. In the obtained SBR@LATP composite material, SBR is a high molecular polymer with flexibility and viscosity, and LATP has surface energy. SBR forms hydrogen bonds with polar sites on the surface of LATP through polar groups, so that 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 surface of LATP to form covalent bonds, further enhancing the binding 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 maintains the excellent performance of LATP. At the same time, the addition of SBR brings higher electrode bonding performance to the composite diaphragm. The bonding effect of SBR can enhance the bonding force between the diaphragm and the electrode, reduce the interface resistance, and improve the charging and discharging efficiency and cycle performance of the battery. The binder used in the negative electrode of the battery is usually SBR. The composite diaphragm modified with SBR@LATP composite material, the SBR therein and the SBR in the negative electrode of the battery will improve the bonding performance of the diaphragm to the negative electrode through the principle of similar solubility between SBR-SBR.

[0037] In the above embodiment, since the composite diaphragm modified by the SBR@LATP composite material retains the properties of the LATP material while being compatible with the bonding properties of SBR, it has better overall performance, can more effectively promote ion transport and electrode reaction inside the battery, and reduce energy loss. At the same time, its own weight is light and the structure is stable, which will not cause excessive burden on the volume and weight of the battery, thereby improving 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 comprises a dispersant, a thickener, a binder and a wetting agent. The dispersant, the thickener and the binder are all polymer reagents. The wetting agent is a silanol reagent.

[0039] In this embodiment, during the preparation of the 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 dispersed state during the mixing process, which can prevent precipitation or stratification. Further, during the preparation of the composite diaphragm, the SBR@LATP composite material needs to be prepared as a slurry. Due to its own surface properties and other factors, SBR@LATP will agglomerate. The dispersant can be adsorbed on the surface of the SBR@LATP composite material particles to reduce the attraction between the particles, thereby ensuring the uniform dispersion of the composite material in the slurry, avoiding uneven content of the composite material at various positions of the coating layer 2 when the slurry is applied to the base film 1, thereby affecting the performance of the diaphragm. During the preparation of coating layer 2, the thickener is used to increase the viscosity of the slurry. It is understood that after adding the SBR@LATP composite material and the dispersant and stirring, the viscosity of the slurry will decrease. After adding the thickener, the SBR@LATP composite material can be prevented from settling in the slurry, ensuring that the various components in the slurry are evenly distributed, and the viscosity of the slurry is increased to ensure the performance consistency of the coating slurry. During the preparation of coating layer 2, the binder can bond the particles of the SBR@LATP composite material together, and the addition of the binder can further enhance this bonding effect. It can form a bonding bridge on the surface of the composite material particles, so that the particles form a more stable connection, and prevent the particles from loosening or falling off during subsequent processing or use. The binder can be filled in the gaps between the SBR@LATP composite material particles to make the coating layer 2 more dense and uniform. This helps to improve the mechanical properties of the coating layer 2; at the same time, when the coating slurry is used for a substrate material such as a battery separator, the binder can improve the bonding between the coating layer 2 and the substrate. This helps to ensure that the coating layer 2 is firmly attached to the substrate, and the coating layer 2 will not peel off from the substrate during the use of the battery (such as when subjected to internal stress, vibration, etc. during the charge and discharge cycle). Good bonding can maintain the integrity of the coating layer 2, thereby ensuring that its improvement effect on the performance of the diaphragm can be continuously exerted, such as maintaining the stability of the ion transmission channel. The wetting agent is a surfactant, which is composed of a hydrophilic group and a lipophilic group. When it contacts the surface of the SBR@LATP composite material particles, the lipophilic group will adhere to the surface of the solid particles, while the hydrophilic group will extend outward into the liquid (water), making it easier for the water phase to spread on the solid surface, thereby wetting the solid material.This effect enables the SBR@LATP composite material, which is not easily wetted by water, to be fully wetted by water and maintain a good dispersion state in the water phase system. The wetting agent can reduce the surface tension or interfacial tension of the solvent, making it easier for the solvent to spread and penetrate on the surface of the SBR@LATP composite material particles, thereby improving the contact and mixing degree between the components in the slurry system, ensuring that all solid particles can be fully wetted by the solvent to form a uniform slurry, and good wettability helps the SBR@LATP composite material particles to be evenly dispersed in water and prevent particles from agglomerating or settling. During the stirring process, the wetting agent can form a thin layer of water film on the surface of the particles, reduce the mutual attraction between the particles, increase the repulsion between the particles, and thus improve the dispersion stability of the particles.

[0040] In the above embodiment, the dispersant is a hydrolyzed polymaleic acid dry polymer, which belongs to a polyelectrolyte and can ionize charged ions in water, so that the particle surface carries the same charge. Due to the mutual repulsion between the same charges, it is not easy for the particles to agglomerate, so that the SBR@LATP composite material particles can be effectively dispersed in the aqueous phase system to maintain the uniformity and stability of the slurry; at the same time, in the coating slurry system, a variety of other ingredients such as binders and thickeners are usually added. Hydrolyzed polymaleic anhydride dispersants can be well compatible with these ingredients and work together, and will not affect the performance of the coating slurry due to mutual incompatibility. The thickener is sodium hydroxymethyl cellulose, which can significantly increase the viscosity of the system, and within a certain range of temperature, pH value and other conditions, the viscosity keeps the SBR@LATP composite material with stable coating and adhesion. Sodium hydroxymethyl cellulose can also have good compatibility with organic solvents, surfactants, etc., and can produce a synergistic effect with the thickener. The binder is a polyacrylic acid polymer with a linear structure and a higher degree of anchoring to the particles. It can make the components in the slurry tightly combined and enhance the cohesion of the electrode. It has more polar groups such as carboxyl groups, which can form strong hydrogen bonds with groups such as hydroxyl groups contained on the surface of the SBR@LATP composite material, promote the formation of uniform coating on the electrode surface, thereby improving the bonding effect. At the same time, as a water-based binder, it has good solubility in water, which is convenient for mixing with other components during the slurry preparation process. The silanol reagent is a silanol nonionic surfactant. In the SBR@LATP slurry, the silanol nonionic surfactant can reduce the surface tension between water and the SBR@LATP composite material particles. The silanol group and hydrophobic group in its molecular structure can interact with the particle surface, making it easier for water molecules to spread on the particle surface, thereby ensuring that the particles are fully wetted by water. It helps to improve the dispersibility of SBR@LATP composite materials in the slurry, prevent particle agglomeration, make the slurry more uniform and stable, help maintain the stability of the slurry, and prevent separation between different phases. At the same time, in the SBR@LATP slurry, the silanol nonionic surfactant has good compatibility with other ingredients such as binders (such as polyacrylic acid polymers) and thickeners (such as sodium hydroxymethyl cellulose). It can work synergistically with the binder to improve the bonding effect of the binder on the SBR@LATP composite material and enhance the bonding force between the slurry and the substrate. At the same time, it cooperates with the thickener to optimize the rheological properties and stability of the slurry, so that each component can work together to improve the comprehensive performance of the slurry.

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

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

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

[0044] In the above embodiment, the porous structure of the base film 1 is conducive to improving the lithium ion conductivity, reducing the internal resistance, and improving the electrical performance. Specifically, the base film 1 of the present application is at least one of a polyolefin diaphragm, a ceramic diaphragm, a cellulose diaphragm, a polyimide diaphragm, a polyaryl diaphragm 1, a polyphenylene sulfide diaphragm 1, and a polytetrafluoroethylene-based film 1. These base films 1 are engineering plastics with high temperature resistance and high mechanical strength, which can make the composite diaphragm 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 membrane, which is used to prepare any of the composite membranes described above, comprising the following steps:

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

[0047] The SBR@LATP composite material coating slurry is coated on one side or both sides of the base film 1 and dried to obtain a composite diaphragm modified with the SBR@LATP composite material.

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

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

[0050] Fully mixing LATP and the first solvent to obtain a LATP solution;

[0051] Fully mixing SBR and a second solvent to obtain an SBR solution;

[0052] The SBR solution was added into the LATP solution and fully reacted to obtain the SBR@LATP composite material.

[0053] In the above embodiment, the first solvent is a solvent that is not compatible with LATP. For example, ultrapure water can be used as the first solvent in the present application. When preparing the LATP solution, ultrapure water is used to evenly disperse the LATP powder in the water to avoid particle agglomeration. At the same time, LATP can be more evenly distributed in the system when mixed with other components (such as binders, dispersants, etc.) in the future, which helps to finally form a composite material or coating slurry with uniform performance. The second solvent is a solvent that can dissolve SBR, for example, such as aromatic solvents, halogenated hydrocarbon solvents, ketone solvents, etc., wherein the aromatic solvent can be toluene, xylene (including three isomers of ortho, meta, and para), the halogenated hydrocarbon solvent can be chlorobenzene, and the ketone can be methyl ethyl ketone. The present application does not specifically limit the above second solvent. Due to the toxicity of chlorobenzene and the high cost of ketones, the preferred second solvent of the present application is toluene.

[0054] Another embodiment of the present invention provides a lithium-ion battery, comprising a diaphragm as described in any one of the above or a composite diaphragm prepared by the method for preparing a composite diaphragm as described in any one of the above, 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 hydroxymethyl cellulose and polyacrylic acid.

[0055] In this embodiment, the SBR in the SBR@LATP composite diaphragm of the present application can be similarly soluble with the binder used in the negative electrode material, further improving the bonding performance of the composite diaphragm. Specifically, sodium hydroxymethyl cellulose and styrene butadiene rubber are both water-based binders with good solubility and dispersibility in water, which enables them to be evenly dispersed in the system when mixed with the negative electrode material to form a slurry, and it is not easy to agglomerate or stratify each other. In addition, sodium hydroxymethyl cellulose and styrene butadiene rubber both contain some functional groups that can interact with the surface of the negative electrode material, such as the carboxymethyl functional groups on the molecular chain of sodium hydroxymethyl cellulose and the active groups on the molecular chain of styrene butadiene rubber, which can form hydrogen bonds and other interactions with the hydroxyl groups on the surface of the negative electrode material particles, thereby bonding the negative electrode active materials together and enhancing the structural stability of the electrode. Polyacrylic acid is also a water-soluble polymer, which is similar to styrene butadiene rubber in solubility, can be evenly dispersed in water, and is easy to mix and process with the negative electrode material. At the same time, polyacrylic acid contains carboxyl functional groups on its molecular chain, which have certain similarities in chemical properties with certain groups on the molecular chain of styrene-butadiene rubber. They can interact with the surface of the negative electrode material and the current collector, such as forming hydrogen bonds, thereby producing a bonding effect. After polyacrylic acid is mixed with styrene-butadiene rubber, there may be a certain entanglement between the molecular chains, which further enhances the bonding performance. In the preparation of negative electrodes for lithium-ion batteries, sodium hydroxymethyl cellulose is often used in combination with styrene-butadiene rubber. As a thickener and stabilizer, sodium hydroxymethyl cellulose can improve the viscosity and stability of the slurry and prevent the precipitation of active substances; while styrene-butadiene rubber mainly provides bonding force, so that the active substances are better attached 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 styrene-butadiene rubber are used together, the anchoring effect of polyacrylic acid on the particles and the bonding performance of styrene-butadiene rubber are used to make the bonding of the negative electrode material more firm, improve the stability of the electrode during the charge and discharge process, and inhibit the shedding and expansion of the active substances, thereby improving the capacity retention rate and cycle performance of the battery.

[0056] The preparation process and performance of the present invention are described below with reference to some specific embodiments.

[0057] Embodiment 1:

[0058] Diaphragm preparation:

[0059] S1: Preparation of SBR@LATP composites:

[0060] S11: 3.557 g of LATP powder and 250 mL of ultrapure water were added to a 500 ml three-necked flask, and magnetic stirring was performed at a speed of 650 rpm for 6 hours, and then ultrasonic treatment was performed at 45 kHz and 450 w ultrasonic power for 8 hours to obtain a LATP dispersion;

[0061] S12: 1.15 g of SBR powder was slowly added to 9.5 g of toluene, the mixture was sealed, and magnetically stirred at 600 rpm for 5 hours to obtain an SBR solution;

[0062] S13: The SBR solution obtained in step S12 is slowly added to the LATP dispersion obtained in step S11 through the side port of a three-necked flask at a flow rate of 0.55 ml / min under magnetic stirring at a speed of 1000 rpm and an ultrasonic device at 40 KHZ and 400 W ultrasonic power to ensure that the SBR solution is completely reacted; the magnetic stirring is continued at a speed of 450 rpm for 5 hours, and then ultrasonic treatment is performed at 45 KHZ and 400 W ultrasonic power for 5 hours; then the obtained mixed solution is transferred to a centrifuge, centrifuged in a centrifuge at a speed of 9500 rpm for 20 minutes, the precipitate obtained by centrifugation is fully washed with deionized water, and vacuum dried at a vacuum degree of 0.08 MPa and 60° C. for 48 hours to obtain an SBR@LATP composite material.

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

[0064] S21: 0.9% dispersant and 25% SBR@LATP composite material were added to ultrapure water according to the mass ratio and mixed under magnetic stirring at a speed of 1100 rpm for 70 min;

[0065] S22: adding 0.85% thickener, stirring for 60 min under magnetic stirring at a speed of 700 rpm;

[0066] S23: adding 12% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0067] S24: 0.6% of a wetting agent was added, and the mixture was stirred for 40 minutes under magnetic stirring at a rotation speed of 350 rpm. After filtering and removing iron, the SBR@LATP composite material coating slurry was obtained.

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

[0069] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is evenly rolled onto the substrate by a coater, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining a composite diaphragm modified with the SBR@LATP composite material for lithium-ion batteries to be prepared.

[0070] Embodiment 2:

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

[0072] Embodiment 3:

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

[0074] Embodiment 4:

[0075] Diaphragm preparation:

[0076] S1: Preparation of SBR@LATP composites:

[0077] S11: 3.557 g of LATP powder and 250 mL of ultrapure water were added to a 500 ml three-necked flask, and magnetic stirring was performed at a speed of 650 rpm for 6 hours, and then ultrasonic treatment was performed at 45 kHz and 450 w ultrasonic power for 8 hours to obtain a LATP dispersion;

[0078] S12: 1.15 g of SBR powder was slowly added to 9.5 g of toluene, the mixture was sealed, and magnetically stirred at 600 rpm for 5 hours to obtain an SBR solution;

[0079] S13: The SBR solution obtained in step S12 is slowly added to the LATP dispersion obtained in step S11 through the side port of a three-necked flask at a flow rate of 0.55 ml / min under magnetic stirring at a speed of 1000 rpm and an ultrasonic device at 40 KHZ and 400 W ultrasonic power to ensure that the SBR solution is completely reacted; the magnetic stirring is continued at a speed of 450 rpm for 5 hours, and then ultrasonic treatment is performed at 45 KHZ and 400 W ultrasonic power for 5 hours; then the obtained mixed solution is transferred to a centrifuge, centrifuged in a centrifuge at a speed of 9500 rpm for 20 minutes, the precipitate obtained by centrifugation is fully washed with deionized water, and vacuum dried at a vacuum degree of 0.08 MPa and 60° C. for 48 hours to obtain an SBR@LATP composite material.

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

[0081] S21: 0.5% dispersant and 35% SBR@LATP composite material were added to ultrapure water according to the mass ratio and mixed under magnetic stirring at a speed of 1100 rpm for 70 min;

[0082] S22: adding 0.2% thickener, stirring for 60 min under magnetic stirring at a speed of 700 rpm;

[0083] S23: adding 5% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0084] S24: 0.1% of a wetting agent was added, and the mixture was stirred for 40 minutes under magnetic stirring at a rotation speed of 350 rpm. After filtering and removing iron, the SBR@LATP composite material coating slurry was obtained.

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

[0086] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is evenly rolled onto the substrate by a coater, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining a composite diaphragm modified with the SBR@LATP composite material for lithium-ion batteries to be prepared.

[0087] Embodiment 5:

[0088] Diaphragm preparation:

[0089] S1: Preparation of SBR@LATP composites:

[0090] S11: 3.557 g of LATP powder and 250 mL of ultrapure water were added to a 500 ml three-necked flask, and magnetic stirring was performed at a speed of 650 rpm for 6 hours, and then ultrasonic treatment was performed at 45 kHz and 450 w ultrasonic power for 8 hours to obtain a LATP dispersion;

[0091] S12: 1.15 g of SBR powder was slowly added to 9.5 g of toluene, the mixture was sealed, and magnetically stirred at 600 rpm for 5 hours to obtain an SBR solution;

[0092] S13: The SBR solution obtained in step S12 is slowly added to the LATP dispersion obtained in step S11 through the side port of a three-necked flask at a flow rate of 0.55 ml / min under magnetic stirring at a speed of 1000 rpm and an ultrasonic device at 40 KHZ and 400 W ultrasonic power to ensure that the SBR solution is completely reacted; the magnetic stirring is continued at a speed of 450 rpm for 5 hours, and then ultrasonic treatment is performed at 45 KHZ and 400 W ultrasonic power for 5 hours; then the obtained mixed solution is transferred to a centrifuge, centrifuged in a centrifuge at a speed of 9500 rpm for 20 minutes, the precipitate obtained by centrifugation is fully washed with deionized water, and vacuum dried at a vacuum degree of 0.08 MPa and 60° C. for 48 hours to obtain an SBR@LATP composite material.

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

[0094] S21: 1.5% dispersant and 35% SBR@LATP composite material were added into ultrapure water according to the mass ratio and mixed under magnetic stirring at a speed of 1100 rpm for 70 min;

[0095] S22: adding 0.9% thickener, stirring for 60 min under magnetic stirring at a speed of 700 rpm;

[0096] S23: adding 15% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0097] S24: 0.7% of a wetting agent was added, and the mixture was stirred for 40 minutes under magnetic stirring at a rotation speed of 350 rpm. After filtering and removing iron, the SBR@LATP composite material coating slurry was obtained.

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

[0099] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is evenly rolled onto the substrate by a coater, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining a composite diaphragm modified with the SBR@LATP composite material for lithium-ion batteries to be prepared.

[0100] Embodiment 6:

[0101] Diaphragm preparation:

[0102] S1: Preparation of SBR@LATP composites:

[0103] S11: 3.557 g of LATP powder and 250 mL of ultrapure water were added to a 500 ml three-necked flask, and magnetic stirring was performed at a speed of 650 rpm for 6 hours, and then ultrasonic treatment was performed at 45 kHz and 450 w ultrasonic power for 8 hours to obtain a LATP dispersion;

[0104] S12: 1.15 g of SBR powder was slowly added to 9.5 g of toluene, the mixture was sealed, and magnetically stirred at 600 rpm for 5 hours to obtain an SBR solution;

[0105] S13: The SBR solution obtained in step S12 is slowly added to the LATP dispersion obtained in step S11 through the side port of a three-necked flask at a flow rate of 0.55 ml / min under magnetic stirring at a speed of 1000 rpm and an ultrasonic device at 40 KHZ and 400 W ultrasonic power to ensure that the SBR solution is completely reacted; the magnetic stirring is continued at a speed of 450 rpm for 5 hours, and then ultrasonic treatment is performed at 45 KHZ and 400 W ultrasonic power for 5 hours; then the obtained mixed solution is transferred to a centrifuge, centrifuged in a centrifuge at a speed of 9500 rpm for 20 minutes, the precipitate obtained by centrifugation is fully washed with deionized water, and vacuum dried at a vacuum degree of 0.08 MPa and 60° C. for 48 hours to obtain an SBR@LATP composite material.

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

[0107] S21: 1% dispersant and 35% SBR@LATP composite material were added into ultrapure water according to the mass ratio and mixed under magnetic stirring at a speed of 1100 rpm for 70 min;

[0108] S22: adding 0.55% thickener, stirring for 60 min under magnetic stirring at 700 rpm;

[0109] S23: adding 10% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0110] S24: 0.4% of a wetting agent was added, and the mixture was stirred for 40 minutes under magnetic stirring at a rotation speed of 350 rpm. After filtering and removing iron, the SBR@LATP composite material coating slurry was obtained.

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

[0112] S31: Using a micro-gravure roller coating process, the SBR@LATP composite material coating slurry prepared in S2 is evenly rolled onto the substrate by a coater, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining a composite diaphragm modified with the SBR@LATP composite material for lithium-ion batteries to be prepared.

[0113] Comparative Example 1: No SBR@LATP composite material was prepared or added, and the rest was the same as Example 1.

[0114] 0.9% of the dispersant was added to ultrapure water according to the mass ratio and mixed for 70 min under magnetic stirring at a speed of 1100 rpm;

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

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

[0117] 0.6% of a wetting agent was added, and the mixture was stirred for 40 minutes under magnetic stirring at a rotation speed of 350 rpm. The coating slurry was obtained after filtering to remove iron.

[0118] The micro-gravure roller coating process is adopted to evenly roll the coating slurry prepared above onto the substrate through a coater, and after being baked in an oven at 75° C., the composite separator for lithium-ion batteries to be prepared is obtained.

[0119] Comparative Example 2:

[0120] S1: Preparation of LATP material coating slurry

[0121] S11: 0.9% of dispersant and 35% of LATP material were added to ultrapure water according to the mass ratio, and mixed under magnetic stirring at a speed of 1100 rpm for 70 min;

[0122] S12: adding 0.85% thickener, and continuing stirring for 60 min under magnetic stirring at a speed of 700 rpm;

[0123] S13: adding 12% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0124] S14: Add 0.6% of a wetting agent, continue stirring for 40 minutes under magnetic stirring at a rotation speed of 350 rpm, and filter to remove iron to obtain a LATP material coating slurry.

[0125] S2: Preparation of LATP material modified membrane:

[0126] S21: Using a micro-gravure roller coating process, the LATP material coating slurry prepared in S1 is evenly rolled onto the polyolefin separator by a coater, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining a composite separator modified with the LATP material for lithium-ion batteries to be prepared.

[0127] Comparative Example 3:

[0128] S1: Preparation of SBR material coating slurry

[0129] S11: 0.9% dispersant and 35% SBR material were added into ultrapure water according to the mass ratio, and mixed for 70 min under magnetic stirring at a speed of 1100 rpm;

[0130] S12: adding 0.85% thickener, and continuing stirring for 60 min under magnetic stirring at a speed of 700 rpm;

[0131] S13: adding 12% of a binder, and continuing stirring for 120 min under magnetic stirring at a speed of 950 rpm;

[0132] S14: Add 0.6% of wetting agent, continue stirring for 40 minutes under magnetic stirring at a rotation speed of 350 rpm, and filter to remove iron to 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 evenly rolled onto the polyolefin separator by a coating machine, and after being baked in an oven at 75°C, it is rolled up for use, thereby obtaining the composite separator modified with the SBR material for lithium-ion batteries to be prepared.

[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 above-mentioned polyolefin separator, no coating layer 2 is provided.

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

[0138] Table 1 Diaphragm air permeability, peel strength and thermal shrinkage test results

[0139]

[0140] From Table 1 we can see that:

[0141] In the performance test of the air permeability value, the air permeability value of comparative example 2 is 213.6s / 100mL, and the air permeability value of comparative example 3 is 225.5s / 100mL, both of which are higher than those of Examples 1 to 6. This is because when LATP material or SBR material is used alone for coating, due to its own physical and chemical properties, it has a greater impact on the pore structure of the diaphragm, resulting in a higher air permeability value. For example, the growth of LATP particles has the characteristics of irregular growth, and pores are easily formed on the surface of the electrode. When there are pores on the electrode surface: on the one hand, the pores will interrupt the original continuous ion transmission channel, and the ions need to move orderly in the dense structure during the conduction process, and the appearance of pores forces the ions to change the path during transmission, bypassing the pore area, increasing the distance and difficulty of ion transmission; on the other hand, the presence of pores may cause confusion in the direction of ion transmission. In the ideal case without pores, ions can be conducted in a clearer direction, but the pores will disperse the transmission direction of the ions, reducing the overall transmission efficiency and causing the conductivity of the LATP ions to decrease. And the SBR@LATP composite material in the embodiment optimizes the pore structure to a certain extent through the synergistic effect of the two, such as, making the permeability value relatively low. In Example 1 to Example 3, with the increase of SBR content in the SBR@LATP composite material in the embodiment, the permeability value gradually increases. The permeability value of Example 1 is 146.6s / 100mL, Example 2 is 159.3, and Example 3 is 200.1s / 100mL. This is because the SBR@LATP composite material is coated on the diaphragm, and with the increase of SBR content, the pore structure of the diaphragm is changed, so that the resistance of gas passing through the diaphragm changes. The increase in SBR content causes the pore channel to become more complicated, and the path for gas to pass becomes longer, thereby increasing the permeability value. The numerical value of the permeability value of Comparative Example 4 is 90s / 100mL, which is significantly lower than the embodiment and comparative example with a coating layer. This is because the base film is not modified by the coating layer, its pore structure is relatively simple, and the resistance of gas passing through is small, so the permeability value is low. When the mass ratio of the 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 the 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 worse. Therefore, in order to balance the performance of various aspects of the composite membrane, the addition amount of the SBR@LATP composite material needs to be adjusted according to the actual design requirements of the battery, and the more the better.

[0142] In the performance test of anode-hot pressing stripping force, the stripping force of comparative example 2 is 1.4N / m, and the stripping force of comparative example 3 is 6.9N / m, both of which are much lower than the embodiment group. This is because when the LATP material is used alone, its bonding force with the anode is weak. When the SBR material is used alone, although there is a certain bonding force, it is not as strong as the bonding force when the SBR content in the SBR@LATP composite material increases. Therefore, under the interaction between SBR and LATP in the composite material, the bonding performance is improved. In Examples 1 to 3, as the SBR content in the SBR@LATP composite material increases, the anode-hot pressing stripping force gradually increases. The stripping force values ​​of Example 1 are 11.1, Example 2 is 15.3N / m, and Example 3 is 17.6N / m. This is because SBR has good bonding properties, and as the SBR content increases, the bonding force between the diaphragm and the anode is enhanced. The stripping force value of Comparative Example 4 (only base film) is 0.8N / m, which is much lower than the embodiments and comparative examples with coating layers. This is because the base film does not have the bonding effect of the coating layer, and the bonding force between the base film and the anode is weak, so the peeling force is low. The peeling force value of Comparative Example 1 is 5.6N / m. This is because although the coating layer does not add SBR@LATP composite material, the adhesive, thickener, etc. still have the effect of improving the bonding property. However, compared with the electrode with SBR@LATP composite material added, the bonding force between the composite diaphragm and the anode is significantly weaker.

[0143] In the performance test of thermal shrinkage, the thermal shrinkage of Comparative Example 2 was 3.3% and 2.1%, and the thermal shrinkage of Comparative Example 3 was 1.5% and 1.0%, which were higher than those of Examples 1 to 6. When LATP material or SBR material is used alone, its heat resistance is not as good as that of SBR@LATP composite material. This is because the two components in the composite material cooperate with each other, and the performance of SBR improves the thermal stability of the diaphragm. As the SBR content in the SBR@LATP composite material in the embodiment increases, the thermal shrinkage gradually decreases. The longitudinal MD thermal shrinkage of Example 1 is 0.9% and 0.7%, that of Example 2 is 0.8% and 0.5%, and that of Example 3 is 0.6% and 0.4%. This is because SBR has certain heat resistance, and LATP plays a role in stabilizing the structure at high temperatures. As the SBR content increases, the heat resistance of the composite material is further improved, thereby reducing the thermal shrinkage. The thermal shrinkage of Comparative Example 4 (only base film) is 5.0% and 2.5%, which is higher than that of the embodiment and comparative example with a coating layer. This is because the thermal stability of the base film is relatively poor, and there is no protection and reinforcement effect of the coating layer, so the thermal shrinkage is high.

[0144] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A composite diaphragm, characterized in that: The invention comprises a base film and a coating layer, wherein the coating layer comprises a SBR@LATP composite material.

2. The composite diaphragm according to claim 1, characterized in that: The coating layer also includes a dispersant, a thickener, a binder and a wetting agent.

3. The composite diaphragm according to claim 1, characterized in that: The coating layer is coated on one side or both sides of the base film.

4. The composite diaphragm according to claim 2, characterized in that: The dispersant, thickener and binder are all polymer reagents.

5. The composite diaphragm according to claim 2, characterized in that: The wetting agent is a silanol agent.

6. The composite diaphragm according to claim 1, characterized in that: The base film is a porous structure film.

7. A method for preparing a composite diaphragm, characterized in that: The method for preparing the composite diaphragm according to any one of claims 1 to 6 comprises the following steps: The dispersant, the SBR@LATP composite material, the thickener, the binder, the wetting agent and the first solvent are mixed evenly and reacted sufficiently to obtain a SBR@LATP composite material coating slurry; The SBR@LATP composite material coating slurry is coated on a base film and dried to obtain the composite diaphragm.

8. The method for preparing the composite diaphragm according to claim 7, characterized in that: The components of the SBR@LATP composite material coating slurry are calculated by weight: the dispersant is 0.5%-1.5%, the SBR@LATP composite material is 25%-35%, the thickener is 0.2%-0.9%, the binder is 5%-15%, the wetting agent is 0.1%-0.7%, and the rest is the first solvent.

9. The method for preparing a composite diaphragm according to claim 7, characterized in that: The step of uniformly mixing the dispersant, the SBR@LATP composite material, the thickener, the binder, the wetting agent and the first solvent and reacting them sufficiently to obtain the SBR@LATP composite material coating slurry also includes the following steps: Fully mixing LATP and the first solvent to obtain a LATP solution; Fully mixing SBR and a second solvent to obtain an SBR solution; The SBR solution was added into the LATP solution and mixed thoroughly to obtain the SBR@LATP composite material.

10. A lithium ion battery, characterized in that: The invention comprises the composite separator as claimed in any one of claims 1 to 6, a positive electrode material, a negative electrode material and an electrolyte.

11. The lithium ion battery according to claim 10, characterized in that: The binder used for the negative electrode material is one or more of styrene-butadiene rubber, sodium hydroxymethyl cellulose and polyacrylic acid.

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