Diaphragm, preparation method thereof and battery

Abstract

The invention provides a diaphragm, a preparation method thereof and a battery, and belongs to the technical field of batteries. The separator includes: a base film; the first functional layer is arranged on at least one side of the base film; the second functional layer is arranged on one side, deviating from the base film, of the first functional layer; wherein each of the first functional layer and the second functional layer comprises whisker-shaped ceramic and sheet-shaped ceramic, the mass ratio of the whisker-shaped ceramic to the sheet-shaped ceramic in the first functional layer is M, the mass ratio of the whisker-shaped ceramic to the sheet-shaped ceramic in the second functional layer is N, and M is greater than N. The mechanical strength of the first functional layer is higher due to the whisker-shaped ceramic in a large proportion, the electrolyte storage capacity and the electrolyte infiltration capacity of the first functional layer are matched due to the sheet-shaped ceramic in a small proportion, and meanwhile a heat conduction network is rich; and the porosity of the second functional layer is relatively large due to the whisker-shaped ceramic with a low proportion, and meanwhile, the capacity of the electrolyte is relatively strong due to the sheet-shaped ceramic with a high proportion, so that the diaphragm with excellent structure and performance is finally formed.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a separator and its preparation method, and a battery. Background Technology

[0002] Lithium-ion batteries are characterized by high operating voltage, high energy density, and fast charging, and are widely used in the field of new energy vehicles. The separator is an important component of lithium-ion batteries. Polyolefin separators not only have a melting point below 180°C, making them prone to thermal shrinkage in high-temperature environments, which can lead to direct contact between the positive and negative electrodes and cause short circuits, but their puncture resistance is usually below 120 MPa, making it difficult to effectively prevent the growth and penetration of lithium dendrites, resulting in battery failure or even safety accidents.

[0003] Aluminum nitride (AlN) has high thermal conductivity, high temperature resistance, and high mechanical strength, while boehmite (AlOOH) has low-temperature heat absorption properties. In order to improve the performance of polyolefin membranes, related technologies have successively coated the surface of polyolefin membranes with aluminum nitride and boehmite coatings. Although this can improve the performance of polyolefin membranes, the inner aluminum nitride coating has limited wetting ability of electrolyte, the outer boehmite coating has poor mechanical properties, and the composition and material structure of the inner and outer layers are simple, resulting in relatively poor membrane performance. Summary of the Invention

[0004] This application provides a separator, its preparation method, and a battery, aiming to solve the problem that the performance of existing separators formed by multilayer ceramic coatings is relatively poor due to the composition of different layers and the simple structure of the materials used.

[0005] In a first aspect, embodiments of this application provide a diaphragm, comprising: Base film; A first functional layer is disposed on at least one side of the base film; and The second functional layer is disposed on the side of the first functional layer that is away from the base film; The first functional layer and the second functional layer both include whisker-shaped ceramics and sheet-shaped ceramics. The mass ratio of whisker-shaped ceramics to sheet-shaped ceramics in the first functional layer is M, and the mass ratio of whisker-shaped ceramics to sheet-shaped ceramics in the second functional layer is N, where M > N.

[0006] Both the first and second functional layers of this application comprise whisker-like ceramics, sheet-like ceramics, and a binder. Firstly, the high aspect ratio of the whisker-like ceramics allows different whiskers to intertwine and form a network framework. Simultaneously, the sheet-like ceramics fill the network framework formed by the whisker-like ceramics, improving the mechanical strength, puncture resistance, and stability of both the first and second functional layers. Furthermore, the first and second functional layers provide better binding to the base film, while the ceramic material possesses certain thermal conductivity and high-temperature resistance, reducing the thermal shrinkage rate of the separator. Secondly, the three-dimensional network framework formed by the whiskers can adsorb and store a large amount of electrolyte, and the sheet-like structure increases the contact area with the electrolyte, improving the wettability of the electrolyte. Thirdly, the mass ratio M of the whisker-like ceramics to the sheet-like ceramics in the first functional layer of this application is greater than that in the second functional layer. The mass ratio N of whisker-like ceramics to plate-like ceramics in the energy layer is as follows: In the first functional layer, the larger proportion of whisker-like ceramics makes the whiskers more densely intertwined, resulting in higher mechanical strength. The relatively dense network structure and the smaller proportion of plate-like ceramics make the first functional layer's ability to store and wet electrolytes well-matched. In the second functional layer, the proportion of whisker-like ceramics is relatively low, resulting in relatively high porosity. At the same time, the proportion of plate-like ceramics is relatively high, making the plate-like structure have a stronger ability to wet electrolytes. The high porosity and high proportion of plate-like ceramics in the second functional layer make its ability to store and wet electrolytes well-matched, ultimately achieving a gradient structure of electrolyte wetting ability and mechanical strength. Combined with a rich thermally conductive network, this results in excellent membrane performance.

[0007] Optionally, in the first functional layer, whisker-shaped ceramics account for 25% to 35% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, and sheet-shaped ceramics account for 65% to 75% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics; and / or, in the second functional layer, whisker-shaped ceramics account for 5% to 15% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, and sheet-shaped ceramics account for 85% to 95% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics.

[0008] The appropriate proportion of whisker-like ceramics in the first functional layer of this application makes the whisker-like ceramics more tightly intertwined, increasing the mechanical strength of the first functional layer; the relatively small proportion of whisker-like ceramics in the second functional layer makes the second functional layer more porous, improving the electrolyte storage capacity, while the larger proportion of plate-like ceramics improves the electrolyte wetting ability, making the overall electrolyte wetting ability of the second functional layer stronger, allowing lithium ions to pass through the separator better.

[0009] Optionally, the material of the whisker ceramic includes at least one of aluminum nitride, silicon carbide, silicon nitride and beryllium oxide; and / or, the material of the sheet ceramic includes at least one of boehmite and boron nitride; and / or, the base film includes at least one of polyethylene film, polypropylene film and polyethylene / polypropylene film.

[0010] The whisker-shaped ceramic material selected in this application has high mechanical strength, good heat resistance, and good thermal conductivity, resulting in high mechanical strength of the first and second functional layers. Simultaneously, it forms a thermally conductive network between the first and second functional layers, improving the heat resistance of the diaphragm and reducing its thermal shrinkage rate. The surface of the selected sheet-like ceramic material is rich in hydroxyl groups, which can bond with the solvent in the electrolyte through hydrogen bonds, thereby improving the wettability of the electrolyte. Polyolefins have good chemical stability and relatively low cost, which is beneficial for improving the stability of the diaphragm and reducing costs.

[0011] Optionally, the whisker-shaped ceramic is a polydopamine-coated modified whisker-shaped ceramic; and / or, the sheet-shaped ceramic is a silane coupling agent modified sheet-shaped ceramic.

[0012] This application modifies whisker-like ceramics. The molecular structure of polydopamine contains active groups such as hydroxyl and amino groups. The bonding force between polydopamine-coated and modified whisker-like ceramics and the base film is increased, and the bonding strength between different whisker-like ceramics is stronger, thereby improving the mechanical strength of the separator. The silane coupling agent can not only bond with the surface of the sheet ceramics, but also bond with the base film, thereby improving the bonding force between the sheet ceramics and the base film and effectively solving the problem of poor interfacial compatibility between sheet ceramics and the base film.

[0013] Optionally, in the first functional layer, the total mass ratio of whisker-shaped ceramics and flake-shaped ceramics to the binder is 0.75:0.25~0.85:0.15; and / or, in the second functional layer, the total mass ratio of whisker-shaped ceramics and flake-shaped ceramics to the binder is 0.45:0.55~0.55:0.45.

[0014] The relatively small proportion of binder and the relatively large proportion of whisker-like and plate-like ceramics in the first functional layer of this application allow the whisker-like and plate-like ceramics to be tightly stacked, thereby forming a more effective protective barrier and a richer thermal conductivity network, reducing the thermal shrinkage rate of the base film. The relatively large proportion of binder in the second functional layer not only firmly bonds the whisker-like and plate-like ceramics, but the smaller proportion of inorganic ceramics and the larger proportion of organic binder also make the second functional layer more porous and abundant, thereby improving the ability of the second functional layer to store and wet the electrolyte, improving the lithium-ion transport efficiency, and reducing the interfacial impedance.

[0015] Optionally, the porosity of the first functional layer is 60% to 70%; and / or, the porosity of the second functional layer is 70% to 80%; and / or, the porosity of the base film is 40% to 60%.

[0016] This application rationally sets the porosity of the first functional layer, the second functional layer, and the base membrane, ensuring that the electrolyte can smoothly wet the diaphragm while giving the diaphragm high mechanical strength and improving its puncture resistance.

[0017] Optionally, the thickness of the first functional layer is 1 μm to 2 μm; and / or, the thickness of the second functional layer is 0.5 μm to 1 μm; and / or, the thickness of the base film is 5 μm to 12 μm; and / or, the diameter of the whisker ceramic is 0.1 μm to 0.5 μm; and / or, the thickness of the sheet ceramic is 0.1 μm to 0.3 μm.

[0018] This application ensures good mechanical properties and electrolyte wetting properties by reasonably setting the thickness of the first functional layer, the second functional layer and the base film, while also making the lithium ion transport channel length suitable and the battery energy density relatively high; the control of the diameter of the whisker ceramic and the thickness of the sheet ceramic can better control the thickness of the first and second functions.

[0019] Secondly, this application provides a method for preparing the diaphragm provided in the first aspect of this application, comprising: Provide base film, Whisker-like ceramics, flake-like ceramics, dispersants, and binders are mixed to obtain a first slurry; Whisker-like ceramics, flake-like ceramics, dispersant and binder are mixed to obtain a second slurry. The mass ratio of whisker-like ceramics to flake-like ceramics in the first slurry is greater than that in the second slurry. The first slurry is coated onto at least one side of the base film and dried to form a first functional layer on the base film; The second slurry is coated onto the side of the first functional layer away from the base film and dried to form the second functional layer on the first functional layer.

[0020] This application first mixes whisker-like ceramics, flake-like ceramics, and a dispersant to obtain a first slurry and a second slurry with uniform composition. Then, a first functional layer and a second functional layer are formed on a base film by sequential coating and drying. The preparation process ensures that the mass ratio of whisker-like ceramics to flake-like ceramics in the first slurry is greater than that in the second slurry. Through the synergistic effect of the different structures and proportions of whisker-like ceramics and flake-like ceramics, the first functional layer and the second functional layer formed in the end form a gradient structure with electrolyte wetting ability and mechanical strength.

[0021] Optionally, before mixing the whisker-like ceramic, the flake-like ceramic, and the dispersant to obtain a first slurry; and before mixing the whisker-like ceramic, the flake-like ceramic, and the dispersant to obtain a second slurry, the method further includes: Whisker-like ceramics were modified by coating them with polydopamine to obtain modified whisker-like ceramics. Modified sheet ceramics are obtained by modifying sheet ceramics with silane coupling agents.

[0022] This application modifies both whisker-shaped ceramics and sheet-shaped ceramics, which not only strengthens the bonding between the whisker-shaped ceramics and sheet-shaped ceramics, but also makes the base film, the first functional layer and the second functional layer more firmly bonded, thus providing stability to the separator.

[0023] Thirdly, this application provides a battery comprising a positive electrode, a negative electrode, and a separator prepared by the method for preparing the separator provided in the first aspect of this application or the method for preparing the separator provided in the second aspect of this application.

[0024] In this application, a separator with a specific structure is applied to the battery, resulting in better rate performance, safety, and stability of the battery. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the preparation process of the diaphragm provided in the application embodiments. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] This application provides a separator, a method for preparing the same, and a battery. These are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms "first", "second", etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single digits within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0029] The technical solution of this application is as follows: In a first aspect, embodiments of this application provide a separator, including a base membrane, a first functional layer, and a second functional layer. The first functional layer is disposed on at least one side of the base membrane, and the second functional layer is disposed on the side of the first functional layer opposite to the base membrane. Both the first and second functional layers comprise whisker-like ceramics and sheet-like ceramics. The mass ratio of whisker-like ceramics to sheet-like ceramics in the first functional layer is M, and the mass ratio of whisker-like ceramics to sheet-like ceramics in the second functional layer is N, where M > N.

[0030] In this application, a first functional layer and a second functional layer are sequentially disposed on at least one side of the base membrane. Both the first and second functional layers include whisker-like ceramics, sheet-like ceramics, and a binder. First, the high aspect ratio of the whisker-like ceramics causes different whiskers to intertwine and form a mesh framework, improving the mechanical strength of the first and second functional layers, thereby increasing the puncture resistance of the membrane. Simultaneously, the sheet-like ceramics fill the mesh framework formed by the whisker-like ceramics, enhancing the mechanical interlocking of different whiskers, further improving the mechanical strength and stability of the first and second functional layers. Qualitatively, this allows the first and second functional layers to better bind the base film, reducing the thermal shrinkage rate of the separator. Secondly, the three-dimensional network framework formed by whiskers can adsorb and store a large amount of electrolyte, while the plate-like structure can increase the contact area with the electrolyte. That is, the synergy between whisker-like ceramics and plate-like ceramics can improve the wettability of the electrolyte. Furthermore, ceramic materials have a certain thermal conductivity compared to the base film, which can promptly dissipate the heat generated during battery operation, avoiding thermal damage to the base film. At the same time, ceramics have good heat resistance, which can reduce the risk of thermal runaway of the battery.

[0031] It is understood that the mass ratio M of whisker-like ceramics to plate-like ceramics in the first functional layer of this application is greater than the mass ratio N of whisker-like ceramics to plate-like ceramics in the second functional layer. That is, the proportion of whisker-like ceramics in the first functional layer is relatively high. This higher proportion of whisker-like ceramics results in more dense whisker entanglement, leading to higher mechanical strength in the first functional layer. The relatively dense network structure and the smaller proportion of plate-like ceramics ensure a good match between the electrolyte storage and wetting capabilities of the first functional layer. Conversely, the relatively lower proportion of whisker-like ceramics in the second functional layer results in relatively higher porosity, allowing it to store more electrolyte. Simultaneously, the relatively higher proportion of plate-like ceramics enhances the electrolyte wetting ability of the plate structure. The high porosity and high proportion of plate-like ceramics in the second functional layer further ensure a good match between its electrolyte storage and wetting capabilities. In other words, a gradient structure of electrolyte wetting capability and mechanical strength is formed from the second functional layer to the first functional layer.

[0032] This application achieves a high-performance separator through a two-phase composite structure of whisker-like ceramics and plate-like ceramics, simultaneously solving the problems of mechanical strength and thermal management of the separator, and raising the upper limit of the temperature at which the battery triggers a safety accident.

[0033] For example, the adhesive includes at least one of polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), and polyacrylates (such as polymethyl acrylate, polyethyl acrylate, etc.).

[0034] In some embodiments, in the first functional layer, whisker-shaped ceramics account for 25% to 35% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, for example, 25%, 30%, and 35%, etc., and sheet-shaped ceramics account for 65% to 75% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, for example, 65%, 70%, and 75%, etc.

[0035] In this application, whisker-like ceramics account for 25% to 35% of the total mass of whisker-like ceramics and sheet-like ceramics. This proportion range allows the whisker-like ceramics to be tightly intertwined, giving full play to their skeletal role, increasing the mechanical strength of the first functional layer, and preventing lithium dendrites from piercing through. At the same time, the appropriate proportion of sheet-like ceramics and the pore structure of the first functional layer make the first functional layer have certain electrolyte wetting properties.

[0036] In some embodiments, in the second functional layer, whisker-shaped ceramics account for 5% to 15% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, for example, 5%, 10%, and 15%, etc., and sheet-shaped ceramics account for 85% to 95% of the total mass of whisker-shaped ceramics and sheet-shaped ceramics, for example, 85%, 90%, and 95%, etc.

[0037] Understandably, whisker-shaped ceramics account for 5% to 15% of the total mass of whisker-shaped and sheet-shaped ceramics. The relatively small proportion of whisker-shaped ceramics results in a higher porosity in the second functional layer, improving the electrolyte storage capacity. At the same time, the larger proportion of sheet-shaped ceramics is evenly spread, improving the electrolyte wetting ability. This makes the overall electrolyte wetting ability of the second functional layer stronger, allowing lithium ions to pass through the separator better.

[0038] In some embodiments, the material of the whisker ceramic includes at least one of aluminum nitride, silicon carbide, silicon nitride, and beryllium oxide.

[0039] In this application, materials such as aluminum nitride, silicon carbide, silicon nitride, and beryllium oxide have high mechanical strength, which in turn results in high mechanical strength of the first and second functional layers, preventing lithium dendrite puncture. At the same time, these materials have good heat resistance and thermal conductivity, and the whisker structure can form a thermally conductive network in the first and second functional layers. That is, this application improves the mechanical strength, thermal conductivity, and thermal runaway trigger temperature of the first and second functional layers and reduces the thermal shrinkage rate of the separator through the synergistic effect of the whisker structure and ceramic type of the whisker ceramic.

[0040] In some embodiments, the material of the sheet ceramic includes at least one of boehmite and boron nitride.

[0041] It is understandable that boehmite and similar materials are rich in hydroxyl groups on their surface. These hydroxyl groups can bond with the solvent in the electrolyte through hydrogen bonds, thereby improving the wettability of the electrolyte. Furthermore, boehmite has a layered structure, which can further improve the wettability of the electrolyte. At the same time, the plate-like structure can also improve the wettability of the electrolyte to a certain extent. In other words, this application improves the electrolyte wettability of the first and second functional layers through the synergistic effect of the plate-like structure of the ceramic and the type of ceramic.

[0042] In some embodiments, the base film includes at least one of polyethylene (PE), polypropylene (PP), and polyethylene / polypropylene (PP / PE).

[0043] Understandably, materials such as polyethylene and polypropylene have good chemical stability, are resistant to electrolyte corrosion, and do not react with electrode materials, thereby improving the stability of the diaphragm, and are relatively inexpensive.

[0044] In some embodiments, the whisker ceramic is a polydopamine (PDA) coated and modified whisker ceramic.

[0045] In this application, by setting a polydopamine coating layer on the surface of whisker-shaped ceramics, the polydopamine molecular structure contains active groups such as hydroxyl and amino groups. Compared with simple inorganic ceramic materials, the bonding force between polydopamine-coated modified whisker-shaped ceramics and the base film is increased. At the same time, different whisker-shaped ceramics are bonded to each other through the polydopamine layer on the surface, which improves the bonding strength between different whiskers.

[0046] In some embodiments, the sheet ceramic is a silane coupling agent modified sheet ceramic.

[0047] Understandably, silane coupling agents can undergo hydrolysis-condensation reactions with active groups such as hydroxyl groups on the surface of sheet ceramics, thereby bonding the sheet ceramics to them. On the other hand, silane coupling agents can combine with the base film, thereby improving the bonding force between the sheet ceramics and the base film and effectively solving the problem of poor interfacial compatibility between the sheet ceramics and the base film.

[0048] Understandably, silane coupling agents modifying the surface of sheet ceramics allow for better contact with the electrolyte, thus improving the electrolyte wetting effect of the silane coupling agent-modified sheet ceramics. Furthermore, the hydrophobic properties of the coupling agent reduce the contact angle between the sheet ceramic surface and the electrolyte, further enhancing electrolyte wettability. Additionally, modifying whisker-like and sheet ceramics improves the stability of the first and second functional layers, resulting in a tighter bond between the base film, the first functional layer, and the second functional layer. This leads to a more stable thermal network structure and better thermal conductivity, resulting in better heat resistance and thermal conductivity of the diaphragm.

[0049] In some embodiments, both the first functional layer and the second functional layer further include an adhesive. In the first functional layer, the total mass ratio of whisker ceramics and sheet ceramics to the adhesive is 0.75:0.25 to 0.85:0.15, for example, it can be 0.75:0.25, 0.8:0.2, 0.85:0.15, etc.

[0050] In this application, by providing an adhesive, the whisker-like ceramic and the sheet-like ceramic can be bonded together, thereby improving the stability of the first functional layer and the second functional layer. At the same time, the presence of the adhesive can make the bonding force between the base film, the first functional layer and the second functional layer stronger, thereby improving the stability of the separator.

[0051] Understandably, the relatively small proportion of binder and the relatively large proportion of whisker-shaped and plate-shaped ceramics in the first functional layer result in the close stacking of whisker-shaped and plate-shaped ceramics, thereby forming a more effective protective barrier that effectively blocks the penetration of lithium dendrites. It also makes the thermal conductive network in the first functional layer richer, better dissipating the heat of the base film, forming an efficient thermal management path, and reducing the thermal shrinkage rate of the base film.

[0052] In some embodiments, in the second functional layer, the total mass ratio of whisker ceramics and sheet ceramics to the mass ratio of the binder is 0.45:0.55 to 0.55:0.45, for example, it can be 0.45:0.55, 0.5:0.5, 0.55:0.45, etc.

[0053] Understandably, the proportion of whisker-shaped ceramics in the second functional layer is relatively small, and their bonding force with the plate-shaped ceramics is relatively weak. The relatively large proportion of binder can, on the one hand, firmly bond the whisker-shaped ceramics and plate-shaped ceramics, improving the mechanical strength of the second functional layer. On the other hand, the smaller proportion of inorganic ceramics and the larger proportion of binder can make the second functional layer more porous and abundant (the binder is an organic material, and the larger proportion of binder results in a relatively larger organic film in the second functional layer. The density of organic films is worse than that of ceramic materials, thus making the second functional layer more porous and abundant). This improves the ability of the second functional layer to store and wet electrolyte, increases the lithium-ion transport efficiency, and reduces interfacial impedance.

[0054] In some embodiments, the porosity of the first functional layer is 60% to 70%, for example, it can be 60%, 65%, 70%, etc.

[0055] In this application, by reasonably setting the porosity of the first functional layer, the first functional layer is made to have high mechanical strength while ensuring that it has a certain electrolyte wettability, thereby improving its puncture resistance.

[0056] In some embodiments, the porosity of the second functional layer is 70% to 80%, for example, it can be 70%, 75%, 80%, etc., which improves the wetting effect of the electrolyte.

[0057] Understandably, the relatively large porosity of the second functional layer enables it to have excellent electrolyte wetting properties, ensuring that the electrolyte can smoothly penetrate the first functional layer and the base film, and providing favorable conditions for the smooth transport of lithium ions.

[0058] In some embodiments, the porosity of the base membrane is 40% to 60%, for example, it can be 40%, 50%, 60%, etc.

[0059] Understandably, a suitable porosity of the base film ensures that the electrolyte can wet the film, allowing lithium ions to pass through smoothly, while also maintaining mechanical strength. This application achieves this by gradient porosity between the first functional layer, the second functional layer, and the base film, enabling the electrolyte to gradually wet from the second functional layer to the base film. This facilitates smooth and uniform lithium ion transport during battery charging and discharging, reducing lithium ion accumulation and the formation of lithium dendrites.

[0060] In some embodiments, the thickness of the first functional layer is 1μm to 2μm, for example, it can be 1μm, 1.5μm, 2μm, etc.

[0061] In this application, by setting the thickness of the first functional layer to 1μm~2μm, the relatively large thickness can improve the mechanical properties of the first functional layer. The thickness of the first functional layer and the synergy between the whisker ceramics can play the role of the protective barrier of the first functional layer. At the same time, the thickness allows the first functional layer to store a certain amount of electrolyte and provide a channel of suitable length for the transport of lithium ions.

[0062] In some embodiments, the thickness of the second functional layer is 0.5 μm to 1 μm, for example, it can be 0.5 μm or 0.8 μm. 、 1μm, etc.

[0063] Understandably, setting the thickness of the second functional layer, which has relatively high porosity, to 0.5 μm to 1 μm ensures that it can store a certain amount of electrolyte while allowing lithium ions to pass through smoothly, and minimizes the decrease in battery energy density. This application, through the synergy of the first and second functional layers, improves the separator performance while reducing the weakening effect of the presence of both layers on battery energy density.

[0064] In some embodiments, the thickness of the base film is 5μm to 12μm, for example, it can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, etc.

[0065] It is understandable that setting the thickness of the base membrane to an appropriate range will give it better mechanical strength, thereby improving the stability and service life of the diaphragm.

[0066] In some embodiments, the diameter of the whisker-shaped ceramic is 0.1 μm to 0.5 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, etc.

[0067] Understandably, the relatively small diameter of whisker-shaped ceramics allows for better entanglement between different whiskers, while also providing better control over the thickness of the primary and secondary functions.

[0068] In some embodiments, the thickness of the sheet ceramic is 0.1 μm to 0.3 μm, for example, it can be 0.1 μm, 0.2 μm, 0.3 μm, etc.

[0069] It is understandable that sheet ceramics of appropriate thickness can better fill the network framework structure formed by whisker ceramics, and make the thickness of the first and second functions relatively small.

[0070] Secondly, please refer to Figure 1 The embodiments of this application provide a method for preparing the diaphragm provided in the first aspect of this application, comprising: Provide base film; Whisker-like ceramics, flake-like ceramics, dispersants, and binders are mixed to obtain a first slurry; Whisker-like ceramics, flake-like ceramics, dispersant and binder are mixed to obtain a second slurry. The mass ratio of whisker-like ceramics to flake-like ceramics in the first slurry is greater than that in the second slurry. The first slurry is coated onto at least one side of the base film and dried to form a first functional layer on the base film; The second slurry is coated onto the side of the first functional layer away from the base film and dried to form the second functional layer on the first functional layer.

[0071] In this application, whisker-like ceramics, plate-like ceramics, and a dispersant are first mixed to ensure uniform distribution of the whisker-like and plate-like ceramics in the first slurry. Then, the whisker-like and plate-like ceramics are mixed again to ensure uniform distribution of the whisker-like and plate-like ceramics in the second slurry. Next, a first functional layer and a second functional layer are formed on a base film through sequential coating and drying. The preparation process ensures that the mass ratio of whisker-like to plate-like ceramics in the first slurry is greater than that in the second slurry. Through the synergistic effect of the different structures and proportions of the whisker-like and plate-like ceramics, the final first and second functional layers form a gradient structure with varying electrolyte wetting ability and mechanical strength.

[0072] For example, mixing whisker-like ceramics, flake-like ceramics, and a dispersant to obtain a first slurry and / or mixing whisker-like ceramics, flake-like ceramics, and a dispersant to obtain a second slurry includes: mixing whisker-like ceramics and flake-like ceramics in a desired ratio, then adding an organic solvent and a dispersant, pre-dispersing using a high-speed shear emulsifier, then adding a binder in a desired ratio, and stirring to obtain the first slurry and / or the second slurry. The organic solvent includes at least one of N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), dimethylformamide (DMF), and dimethyl sulfoxide (DMSO); the dispersant includes at least one of ammonium polyacrylate and polyurethane, and the amount of dispersant added is 0.4% to 0.6% of the mass of the first slurry and / or the second slurry; the shearing speed of the shear emulsifier is 6000 rpm to 10000 rpm, and the shearing time is 20 min to 40 min.

[0073] For example, coating the first slurry and / or the second slurry includes at least one of roller coating, spray coating and dot coating, and the first slurry may be coated on one or both sides of the base film.

[0074] In some embodiments, please refer to Figure 1 Before mixing whisker-shaped ceramics, flake-shaped ceramics, and a dispersant to obtain a first slurry, and before mixing whisker-shaped ceramics, flake-shaped ceramics, and a dispersant to obtain a second slurry, the process further includes: Whisker-like ceramics were modified by coating them with polydopamine to obtain modified whisker-like ceramics. Modified sheet ceramics are obtained by modifying sheet ceramics with silane coupling agents.

[0075] In this application, the whisker-shaped ceramic and the sheet-shaped ceramic are modified respectively, which not only makes the bonding force between the whisker-shaped ceramic and the sheet-shaped ceramic stronger, but also makes the bonding between the base film, the first functional layer and the second functional layer more robust, thus providing the stability of the separator.

[0076] For example, modifying whisker-like ceramics by coating them with polydopamine to obtain modified whisker-like ceramics involves: dispersing the whisker-like ceramics in a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer (Tris-HCl buffer) at pH=8.5, adding dopamine hydrochloride, and stirring at room temperature for 20-30 hours. The amount of dopamine hydrochloride added is 1%-2% of the mass of the whisker-like ceramics.

[0077] For example, modifying sheet ceramics with a silane coupling agent to obtain modified sheet ceramics involves: adding a silane coupling agent and sheet ceramics to an ethanol / water mixed solvent, and refluxing at 75°C to 85°C for 1 to 3 hours. The volume ratio of ethanol to water is 85 to 95:5 to 15, and the amount of silane coupling agent added is 0.5% to 1.5% of the mass of the sheet ceramics.

[0078] Thirdly, embodiments of this application provide a battery comprising a positive electrode, a negative electrode, and a separator prepared by the method for preparing the separator provided in the first aspect of this application or the method for preparing the separator provided in the second aspect of this application.

[0079] In this application, a separator with a specific structure is applied to the battery, resulting in better rate performance, safety, and stability of the battery.

[0080] For example, a method for preparing a battery includes: (1) Weigh out the positive electrode active material, conductive agent, binder and dispersant in a mass ratio of 9.5~9.7:0.1~0.3:0.15~0.2:0.02~0.04, mix them and add them to an organic solvent, stir evenly to obtain a positive electrode slurry. Coat the obtained positive electrode slurry evenly on aluminum foil, and after drying, obtain a positive electrode sheet.

[0081] The positive electrode active material includes at least one of lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), and lithium nickel cobalt manganese oxide (DCM); the conductive agent includes at least one of graphite, conductive carbon black, carbon nanotubes, and graphene; the binder includes at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); the dispersant includes at least one of polypyrrolidone (PVP), phosphate esters, and modified acrylates; and the organic solvent includes at least one of N-methylpyrrolidone (NMP) and dimethylacetamide (DMAC).

[0082] (2) Weigh the negative electrode active material, conductive agent, binder and dispersant according to the mass ratio of 95~97:0.4~0.6:0.4~0.6:2~4, mix them and add them to deionized water, stir evenly to obtain a negative electrode slurry. Coat the obtained negative electrode slurry evenly on copper foil, and after drying, obtain a negative electrode sheet.

[0083] The negative electrode active material includes at least one of graphite and silicon carbide; the conductive agent includes at least one of graphite, conductive carbon black, carbon nanotubes and graphene; the binder includes at least one of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA); and the dispersant includes at least one of carboxymethyl cellulose (CMC) and polyvinyl alcohol (PVA).

[0084] (3) Cut the positive and negative electrode sheets to the required size, then stack the positive electrode sheets, separator and negative electrode sheets, insert them into the shell, vacuum bake, inject electrolyte, let stand, and perform capacity testing to obtain the battery. Among them, the electrolyte is a commercially available electrolyte, which is composed of lithium salt, solvent and additives.

[0085] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0086] Example 1 This embodiment provides a diaphragm, comprising: a base membrane, a first functional layer, and a second functional layer. The first functional layer is disposed on opposite sides of the base membrane, and the second functional layer is disposed on the side of the first functional layer opposite to the base membrane. Both the first and second functional layers comprise AlN whiskers, lamellar boehmite, and PVDF. The diameter of the AlN whiskers is 0.3 μm, and the thickness of the lamellar boehmite is 0.2 μm.

[0087] The base film is a PE film with a thickness of 8 μm and a porosity of 50%.

[0088] In the first functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.8:0.2. AlN whiskers account for 25% of the total mass of AlN whiskers and platy boehmite, and platy boehmite accounts for 75% of the total mass of AlN whiskers and platy boehmite. The thickness of the first functional layer is 1 μm, and the porosity is 65%.

[0089] In the second functional layer, the total mass ratio of AlN whiskers and lamellar boehmite to PVDF is 0.5:0.5. AlN whiskers account for 10% of the total mass of AlN whiskers and lamellar boehmite, and lamellar boehmite accounts for 90% of the total mass of AlN whiskers and lamellar ceramics. The thickness of the second functional layer is 1 μm, and the porosity is 75%.

[0090] The preparation method of the diaphragm includes: (1) Provide PE film; (2) AlN whiskers and lamellar boehmite were mixed in the required mass ratio and then added to NMP solvent; then ammonium polyacrylate was added to NMP and pre-dispersed using a high-speed shear emulsifier; then the required mass of PVDF was added and stirred evenly to obtain the first slurry. The shearing speed of the high-speed shear emulsifier was 8000 rpm and the shearing time was 30 min. The amount of ammonium polyacrylate added was 0.5% of the mass of the first slurry, and the solid content of the first slurry was 25%. (3) AlN whiskers and lamellar boehmite were mixed in the required mass ratio and then added to NMP solvent; then ammonium polyacrylate was added to NMP and pre-dispersed using a high-speed shear emulsifier; then the required mass of PVDF was added and stirred evenly to obtain the second slurry. The shearing speed of the high-speed shear emulsifier was 8000 rpm and the shearing time was 30 min. The amount of ammonium polyacrylate added was 0.5% of the mass of the second slurry, and the solid content of the second slurry was 18%. (4) The first slurry is coated on both sides of the PE film and dried to form a first functional layer on the PE film; (5) The second slurry is coated on the side of the first functional layer away from the base film and dried to form the second functional layer on the first functional layer; (6) Hot pressing and shaping to obtain a diaphragm, and the finished product is rolled up for use.

[0091] Example 2 This embodiment provides a diaphragm, which differs from Embodiment 1 only in that the AlN whiskers are PDA-coated and modified, and the lamellar boehmite is modified with a silane coupling agent. The AlN whisker modification method is as follows: AlN whiskers are dispersed in Tris-HCl buffer at pH=8.5, dopamine hydrochloride is added, and the mixture is stirred at room temperature for 24 hours. The amount of dopamine hydrochloride added is 1.5% of the mass of the AlN whiskers. The lamellar boehmite modification method is as follows: KH-550 and lamellar ceramic are added to an ethanol / water mixed solvent, and the mixture is refluxed at 80°C for 2 hours. The volume ratio of ethanol to water is 90:10, and the amount of KH-550 added is 1% of the mass of the lamellar ceramic. In the first functional layer, the PDA-coated AlN whiskers (abbreviated as PDA-coated AlN whiskers) are used. The total mass ratio of modified AlN whiskers and silane coupling agent-modified lamellar boehmite (hereinafter referred to as modified lamellar boehmite) to PVDF is 0.8:0.2. Modified AlN whiskers account for 25% of the total mass of modified AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounts for 75% of the total mass of modified AlN whiskers and modified lamellar boehmite. In the second functional layer, the total mass ratio of modified AlN whiskers and modified lamellar boehmite to PVDF is 0.5:0.5. Modified AlN whiskers account for 10% of the total mass of modified AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounts for 90% of the total mass of modified AlN whiskers and modified lamellar boehmite. Other aspects are consistent with Example 1 and will not be repeated here.

[0092] Example 3 This embodiment provides a diaphragm. Compared with Embodiment 2, the only difference is that in the first functional layer, the modified AlN whiskers account for 20% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 80% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 2, and will not be repeated here.

[0093] Example 4 This embodiment provides a diaphragm. Compared with Embodiment 2, the only difference is that in the first functional layer, the modified AlN whiskers account for 30% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 70% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 2, and will not be repeated here.

[0094] Example 5 This embodiment provides a diaphragm. Compared with Embodiment 2, the only difference is that in the first functional layer, modified AlN whiskers account for 35% of the total mass of modified AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounts for 65% of the total mass of modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 2, and will not be repeated here.

[0095] Example 6 This embodiment provides a diaphragm. Compared with Embodiment 2, the only difference is that in the first functional layer, modified AlN whiskers account for 40% of the total mass of modified AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounts for 60% of the total mass of modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 2, and will not be repeated here.

[0096] Example 7 This embodiment provides a diaphragm. Compared with Embodiment 4, the only difference is that in the second functional layer, the modified AlN whiskers account for 2% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 98% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 4, and will not be repeated here.

[0097] Example 8 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the modified AlN whiskers account for 5% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 95% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in embodiment 4, and will not be repeated here.

[0098] Example 9 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the modified AlN whiskers account for 15% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 85% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in embodiment 4, and will not be repeated here.

[0099] Example 10 This embodiment provides a diaphragm. Compared with Embodiment 4, the only difference is that in the second functional layer, the modified AlN whiskers account for 20% of the total mass of the modified AlN whiskers and modified lamellar boehmite, and the modified lamellar boehmite accounts for 80% of the total mass of the modified AlN whiskers and modified lamellar boehmite. The rest is the same as in Embodiment 4, and will not be repeated here.

[0100] Example 11 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the first functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.7:0.3. The rest is the same as in embodiment 4, and will not be repeated here.

[0101] Example 12 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the first functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.75:0.25. The rest is the same as in embodiment 4, and will not be repeated here.

[0102] Example 13 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the first functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.85:0.15. The rest is the same as in embodiment 4, and will not be repeated here.

[0103] Example 14 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the first functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.9:0.1. The rest is the same as in embodiment 4, and will not be repeated here.

[0104] Example 15 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.4:0.6. The rest is the same as in embodiment 4, and will not be repeated here.

[0105] Example 16 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.45:0.55. The rest is the same as in embodiment 4, and will not be repeated here.

[0106] Example 17 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.55:0.45. The rest is the same as in embodiment 4, and will not be repeated here.

[0107] Example 18 This embodiment provides a diaphragm. Compared with embodiment 4, the only difference is that in the second functional layer, the total mass ratio of AlN whiskers and platy boehmite to PVDF is 0.6:0.4. The rest is the same as in embodiment 4, and will not be repeated here.

[0108] Example 19 This embodiment provides a diaphragm. Compared with Embodiment 1, the only difference is that the AlN whiskers are modified with PDA coating, and the lamellar boehmite is not modified with silane coupling agent. In the first functional layer, the mass ratio of the total mass of modified AlN whiskers and lamellar boehmite to PVDF is 0.8:0.2, with modified AlN whiskers accounting for 25% of the total mass of modified AlN whiskers and lamellar boehmite, and lamellar boehmite accounting for 75% of the total mass of modified AlN whiskers and lamellar boehmite. In the second functional layer, the mass ratio of the total mass of modified AlN whiskers and lamellar boehmite to PVDF is 0.5:0.5, with modified AlN whiskers accounting for 10% of the total mass of modified AlN whiskers and lamellar boehmite, and lamellar boehmite accounting for 90% of the total mass of modified AlN whiskers and lamellar boehmite. Other aspects are consistent with Embodiment 1 and will not be repeated here.

[0109] Example 20 This embodiment provides a diaphragm. Compared with Embodiment 1, the only difference is that the AlN whiskers are not modified, while the lamellar boehmite is modified with a silane coupling agent. In the first functional layer, the mass ratio of the total mass of AlN whiskers and modified lamellar boehmite to PVDF is 0.8:0.2, with AlN whiskers accounting for 25% of the total mass of AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounting for 75% of the total mass of AlN whiskers and modified lamellar boehmite. In the second functional layer, the mass ratio of the total mass of AlN whiskers and modified lamellar boehmite to PVDF is 0.5:0.5, with AlN whiskers accounting for 10% of the total mass of AlN whiskers and modified lamellar boehmite, and modified lamellar boehmite accounting for 90% of the total mass of AlN whiskers and modified lamellar boehmite. Other aspects are consistent with Embodiment 1 and will not be repeated here.

[0110] Comparative Example 1 This comparative example provides a diaphragm that differs from Example 2 only in that the first functional layer consists only of modified AlN whiskers and PVDF, and the second functional layer consists only of modified lamellar boehmite and PVDF. The mass ratio of modified AlN whiskers to PVDF in the first functional layer is 0.8:0.2, and the mass ratio of modified lamellar boehmite to PVDF in the second functional layer is 0.5:0.5. All other aspects remain the same as in Example 2 and will not be repeated here.

[0111] Comparative Example 2 This comparative example provides a diaphragm that differs from Example 2 only in that the PDA-coated modified AlN whiskers are replaced with PDA-coated modified lamellar AlN. That is, both the modified lamellar AlN and the modified lamellar boehmite have a lamellar structure, and the thickness of the lamellar AlN is 0.2 μm. Everything else is the same as in Example 2 and will not be repeated here.

[0112] Comparative Example 3 This comparative example provides a diaphragm that differs from Example 2 only in that the silane coupling agent-modified lamellar boehmite is replaced with silane coupling agent-modified boehmite whiskers. That is, both the modified AlN whiskers and the modified boehmite whiskers are whisker-like structures, and the diameter of the whisker-like boehmite is 0.3 μm. Everything else is the same as in Example 2, and will not be repeated here.

[0113] The separators prepared in Examples 1-20 and Comparative Examples 1-3 were assembled into pouch cells according to the following steps: 1) LFP, Super P, PVDF, and PVP were weighed in a mass ratio of 9.6:0.2:0.17:0.03, mixed, and added to NMP. The mixture was stirred until homogeneous to obtain a positive electrode slurry. The obtained positive electrode slurry was uniformly coated onto a 12 μm thick aluminum foil and dried to obtain a positive electrode sheet. 2) Graphite, silicon carbide, Super P, CMC, and SBR were weighed in a mass ratio of 95:5:0.5:0.5:3, mixed, and added to deionized water. The mixture was stirred until homogeneous to obtain a negative electrode slurry. The obtained negative electrode slurry was uniformly coated onto a 5 μm thick copper foil and dried to obtain a negative electrode sheet. 3) Cut the positive and negative electrode sheets to the required size, then stack the positive electrode sheets, the separators prepared in Examples 1-20 and Comparative Examples 1-3, and the negative electrode sheets, insert them into the casing, vacuum bake, inject liquid, let stand, and perform capacity testing to obtain the battery.

[0114] The membranes prepared in Examples 1-20 and Comparative Examples 1-3 were tested for tensile strength, thermal shrinkage rate, thermal conductivity, needle penetration strength and electrolyte contact angle. The assembled pouch cells were tested for thermal runaway trigger temperature. The results are shown in Table 1.

[0115] Among them, the tensile strength was tested using an electronic universal testing machine, with the reference standard being GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries"; Heat shrinkage rate refers to the heat shrinkage rate at 200℃ / 1h. It is tested using a battery separator heat shrinkage (oil bath) tester, with the reference standard being GB / T 36363-2018 "Polyolefin separator for lithium-ion batteries". The thermal conductivity was measured using a laser thermal conductivity meter, with reference to the standard GB / T 22588 "Measuring Thermal Diffusion Coefficient or Thermal Conductivity by Flash Method"; The needle penetration strength was tested using an electronic universal testing machine with a special puncture clamp, in accordance with GB / T 36363-2018 "Polyolefin separators for lithium-ion batteries"; The contact angle of the electrolyte was measured using a contact angle measuring instrument. The thermal runaway trigger temperature was detected using a large battery adiabatic calorimeter, with reference to the standard GB 38031-2020 "Safety Requirements for Power Batteries for Electric Vehicles".

[0116] Table 1

[0117] As can be seen from the data in Examples 1-2 and Examples 19-20 in Table 1, when one of AlN whiskers and lamellar boehmite is modified, the performance of the resulting separator is improved compared to Example 1. When AlN whiskers and lamellar boehmite are modified simultaneously, the tensile strength, needle penetration strength, and thermal conductivity of the separator are significantly improved, the electrolyte contact angle is significantly reduced, and the thermal runaway trigger temperature of the battery is significantly increased. This indicates that the mechanical properties, thermal conductivity, heat resistance, and electrolyte wettability of the separator are significantly improved. This may be because when AlN whiskers and lamellar boehmite are modified simultaneously, not only is the bonding force between AlN whiskers, lamellar boehmite, and binder in the first and second functional layers stronger, but the bonding force between the base film, the first functional layer, and the second functional layer is also stronger, thereby improving the battery performance of the separator.

[0118] As shown by the data from Examples 2-6, with the gradual increase of the proportion of modified AlN whiskers in the first functional layer, the tensile strength, puncture resistance, and thermal conductivity of the separator first increase and then decrease, while the thermal shrinkage rate and electrolyte contact angle first decrease and then increase, and the thermal runaway trigger temperature of the battery first increases and then decreases. When the modified AlN whiskers account for 25% to 35% of the total mass of modified AlN whiskers and modified lamellar boehmite, the performance of the resulting separator and battery is significantly better. This is mainly because when the proportion of modified AlN whiskers is 25% to 35%, the composite structure formed by the modified AlN whiskers and modified lamellar boehmite is relatively dense. At the same time, the synergistic effect of the appropriate proportion of lamellar ceramics and the porosity of the first functional layer can better promote the wetting of the electrolyte, and the thermally conductive network in the first functional layer is more uniformly distributed, thus resulting in better separator performance. When the proportion of modified AlN whiskers is too small, the network skeleton cannot be formed well, resulting in low mechanical strength of the first functional layer and poor thermal conductivity of the thermal network, thus leading to poor performance of the separator and battery. When the proportion of modified AlN whiskers is too large, the whiskers are too tightly wound and tend to agglomerate, resulting in uneven distribution of modified AlN whiskers and modified lamellar boehmite in the first functional layer, which in turn affects the performance of the separator and battery.

[0119] As shown by the data from Examples 4 and 7-10, as the proportion of modified lamellar boehmite in the second functional layer gradually increases, the tensile strength, puncture resistance, and thermal conductivity of the separator first increase and then decrease, while the thermal shrinkage rate and electrolyte contact angle first decrease and then increase, and the thermal runaway trigger temperature of the battery first increases and then decreases. When the modified lamellar boehmite accounts for 85% to 95% of the total mass of modified AlN whiskers and modified lamellar boehmite, the performance of the resulting separator and battery is relatively good. This is mainly because when the proportion of modified lamellar boehmite is relatively high, the electrolyte wettability of the second functional layer is relatively good, and the relatively small proportion of AlN whiskers makes the porosity of the second functional layer more abundant, making it easier to store electrolyte and further improving the electrolyte wettability of the second functional layer. At the same time, a suitable ratio of modified AlN whiskers and modified lamellar boehmite can make the structure of the second functional layer more stable and the thermally conductive network more uniformly distributed, thereby making the mechanical properties and thermal conductivity of the separator better.

[0120] Data from Examples 4 and 11-14 show that when the total mass of modified AlN whiskers and modified lamellar boehmite in the first functional layer is large or small, the performance of both the separator and the battery is poor. This may be because when the total mass of modified AlN whiskers and modified lamellar boehmite is large, an excessive proportion of ceramics will agglomerate, affecting the uniform distribution of ceramics in the first functional layer. At the same time, it will result in less and less uniform porosity in the first functional layer, thus affecting the wetting of the electrolyte. In addition, fewer pores will affect heat transfer, thereby affecting the thermal management performance of the separator and the battery. When the total mass of modified AlN whiskers and modified lamellar boehmite is small, it affects the mechanical strength of the first functional layer and the formation of the thermal conductive network, and also affects its ability to store electrolyte, thus affecting the performance of the battery.

[0121] As can be seen from the data of Examples 4 and 15-18, the change in the total mass of modified AlN whiskers and modified lamellar boehmite in the second functional layer also affects the performance of the separator and the battery. This may be because the change in the total mass of modified AlN whiskers and modified lamellar boehmite affects the distribution of ceramic materials and pores in the second functional layer and its ability to store electrolyte, thereby affecting the electrolyte wettability of the separator. At the same time, it affects the mechanical strength of the second functional layer, thereby affecting the performance of the separator.

[0122] As can be seen from the data of Comparative Examples 1 to 3, when the first and second functional layers are made of only a single ceramic material, or when AlN and boehmite have the same shape, the performance of the resulting diaphragm decreases significantly. This is mainly because when AlN and boehmite have the same shape, the structure of the first and second functional layers is simple. When the first and second functional layers are made of only a single ceramic material, the synergistic effect between the first and second functional layers is poor, which leads to a significant decrease in the performance of the diaphragm. This indicates that the diaphragm of this application is the result of the combined action of ceramics of different shapes and ceramic materials of different compositions in the first and second functional layers.

[0123] In summary, this application incorporates AlN whiskers and lamellar boehmite in both the first and second functional layers, and controls the proportions of AlN whiskers, lamellar boehmite, and PVDF in the first and second functional layers to create a gradient structure in terms of mechanical strength and electrolyte wettability. Simultaneously, a thermally conductive network is formed in the first and second functional layers, resulting in better mechanical strength, heat resistance, and electrolyte wettability of the diaphragm.

[0124] The above provides a detailed description of a separator, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A diaphragm, characterized in that, include: Base film; A first functional layer is disposed on at least one side of the base film; and The second functional layer is disposed on the side of the first functional layer that is away from the base film; The first functional layer and the second functional layer both include whisker-shaped ceramics and sheet-shaped ceramics. The mass ratio of the whisker-shaped ceramics to the sheet-shaped ceramics in the first functional layer is M, and the mass ratio of the whisker-shaped ceramics to the sheet-shaped ceramics in the second functional layer is N, where M > N.

2. The diaphragm according to claim 1, characterized in that, In the first functional layer, the whisker-like ceramics account for 25% to 35% of the total mass of the whisker-like ceramics and the plate-like ceramics, and the plate-like ceramics account for 65% to 75% of the total mass of the whisker-like ceramics and the plate-like ceramics; and / or, In the second functional layer, the whisker-shaped ceramic accounts for 5% to 15% of the total mass of the whisker-shaped ceramic and the sheet-shaped ceramic, and the sheet-shaped ceramic accounts for 85% to 95% of the total mass of the whisker-shaped ceramic and the sheet-shaped ceramic.

3. The diaphragm according to claim 1 or 2, characterized in that, The whisker-like ceramic material includes at least one of aluminum nitride, silicon carbide, silicon nitride, and beryllium oxide; and / or, The material of the sheet-like ceramic includes at least one of boehmite and boron nitride; and / or, The base film includes at least one of polyethylene film, polypropylene film, and polyethylene / polypropylene film.

4. The diaphragm according to any one of claims 1 to 3, characterized in that, The whisker-like ceramic is a polydopamine-coated modified whisker-like ceramic; and / or, The sheet ceramic is a silane coupling agent modified sheet ceramic.

5. The diaphragm according to any one of claims 1 to 4, characterized in that, Both the first functional layer and the second functional layer further include a binder. In the first functional layer, the mass ratio of the total mass of the whisker-like ceramics and the plate-like ceramics to the mass of the binder is 0.75:0.25 to 0.85:0.15; and / or, In the second functional layer, the total mass ratio of the whisker ceramic and the sheet ceramic to the mass ratio of the binder is 0.45:0.55 to 0.55:0.

45.

6. The diaphragm according to any one of claims 1 to 5, characterized in that, The porosity of the first functional layer is 60%~70%; and / or, The porosity of the second functional layer is 70%~80%; and / or, The porosity of the base membrane is 40%~60%.

7. The diaphragm according to any one of claims 1 to 6, characterized in that, The thickness of the first functional layer is 1 μm to 2 μm; and / or, The thickness of the second functional layer is 0.5 μm to 1 μm; and / or, The thickness of the base film is 5 μm to 12 μm; and / or, The whisker-like ceramic has a diameter of 0.1 μm to 0.5 μm; and / or, The thickness of the sheet-like ceramic is 0.1μm~0.3μm.

8. A method for preparing a diaphragm according to any one of claims 1 to 7, characterized in that, include: Provide base film, Whisker-like ceramics, flake-like ceramics, dispersants, and binders are mixed to obtain a first slurry; The whisker-like ceramic, the flake-like ceramic, the dispersant, and the binder are mixed to obtain a second slurry, wherein the mass ratio of the whisker-like ceramic to the flake-like ceramic in the first slurry is greater than the mass ratio of the whisker-like ceramic to the flake-like ceramic in the second slurry; The first slurry is coated onto at least one side of the base film and dried to form a first functional layer on the base film; The second slurry is coated onto the side of the first functional layer away from the base film and dried to form a second functional layer on the first functional layer.

9. The method for preparing the diaphragm according to claim 8, characterized in that, Before mixing the whisker-like ceramic, the flake-like ceramic, and the dispersant to obtain a first slurry, and mixing the whisker-like ceramic, the flake-like ceramic, and the dispersant to obtain a second slurry, the method further includes: The whisker-like ceramic was modified by coating it with polydopamine to obtain modified whisker-like ceramic. The sheet-like ceramic was modified with a silane coupling agent to obtain modified sheet-like ceramic.

10. A battery, characterized in that, The membrane includes a positive electrode, a negative electrode, and a separator prepared by the method described in any one of claims 1 to 7 or any one of claims 8 to 9.

Images