Multifunctional lithium ion diaphragm coating

Abstract

The utility model belongs to the technical field of battery diaphragm coatings, and particularly relates to a multifunctional lithium ion diaphragm coating. Comprising a base film and a layer of nanocellulose microcrystal coating which directly covers the base film and is tightly combined with the base film, a mixed coating formed by mixing hollow spherical binding material particles and nano ceramics is directly coated on the nano cellulose microcrystal coating; or, the surface of the nano cellulose microcrystal coating is sequentially coated with a nano ceramic layer and a hollow spherical binding material particle coating from bottom to top. According to the diaphragm coating provided by the utility model, through a special multi-layer composite structure design, the thermal stability, the mechanical strength and the electrochemical performance of the lithium ion battery are greatly improved while good physical and chemical properties are maintained, so that the diaphragm coating is suitable for wider application scenes and harsh operation conditions.

Description

Technical Field

[0001] This utility model belongs to the field of battery separator coating technology, specifically relating to a multifunctional lithium-ion separator coating. Background Technology

[0002] As a crucial internal component of a battery, the battery separator plays a vital role in preventing short circuits between the positive and negative electrodes, providing a transport channel for lithium ions, and automatically shutting off at high temperatures to prevent short circuits. Currently, polymer materials such as PP and PE are widely used in the market. Their excellent mechanical properties prevent lithium dendrites from piercing the separator and causing short circuits, but their heat resistance is poor; at high temperatures, the separator shrinks, causing a short circuit between the positive and negative electrodes. Separator coatings mainly consist of inorganic materials such as alumina, boehmite, silicon dioxide, and magnesium hydroxide, or ceramics combined with organic materials such as aramid, PVDF, PMMA, and nanocellulose microcrystals. These coatings improve the separator's high-temperature resistance and adhesion to the electrodes, ensuring normal operation of the battery even at high temperatures. They also enhance the separator's liquid absorption and retention capacity, improving the battery's electrochemical performance.

[0003] Current lithium-ion battery separators mostly employ two structures: 1. PE / PP with inorganic coatings such as alumina and boehmite (single-sided or double-sided); 2. PE / PP with inorganic coatings (alumina, boehmite) and high-heat-resistant materials plus organic binder coatings (such as PVDF, PMMA, acrylic resin, etc.). These two structures improve the separator's heat resistance, wettability, and adhesion to the battery electrodes. However, as the base film and ceramic coating become thinner, the separator's thermal shrinkage performance and liquid retention capacity correspondingly deteriorate. Utility Model Content

[0004] (a) Technical problems to be solved

[0005] This invention addresses the above-mentioned problems by proposing a multifunctional lithium-ion membrane coating, which aims to solve the technical issues of membrane thermal shrinkage and liquid retention capacity.

[0006] (II) Technical Solution

[0007] To achieve the above objectives, this utility model provides a multifunctional lithium-ion membrane coating, comprising:

[0008] Base film;

[0009] A layer of nano-cellulose microcrystalline coating directly covering and tightly bonded to the base film;

[0010] A hybrid coating consisting of hollow spherical binder particles and nano-ceramics is directly applied over the nanocellulose microcrystalline coating; or, a nano-ceramic layer and a hollow spherical binder particle coating are sequentially applied from bottom to top on the surface of the nanocellulose microcrystalline coating.

[0011] Furthermore, the base film comprises polypropylene, polyethylene, or nonwoven fabric, and the base film has a thickness of 1-20 μm and a porosity of 25-70%.

[0012] Furthermore, the nanocellulose microcrystalline material includes: cellulose nanocrystals, cellulose nanofibers, electrospun fibers, and one or more of bacterial cellulose, methylcellulose, hydroxyethyl methylcellulose, carboxymethyl cellulose, ethylcellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose, and phenyl cellulose, with a coating thickness of 0.1-1 μm.

[0013] Furthermore, the mixed coating comprises inorganic powders of alumina, boehmite, magnesium hydroxide, and silicon dioxide, wherein the inorganic powders have a particle size of 0.01-5 μm.

[0014] Furthermore, the hollow adhesive material of the hybrid coating comprises one or more of the following: acrylic resin, polymethacrylic acid, methacrylic acid, polymethyl methacrylate, polyvinylidene fluoride, vinylidene fluoride, and polyvinylidene fluoride, and is a spherical hollow adhesive material with a diameter of 0.1-10 μm and a wall thickness of 2-1000 nm.

[0015] Furthermore, the hollow spherical adhesive material particles of the hybrid coating have a coverage rate of 1-50% on the coating surface.

[0016] (III) Beneficial Effects

[0017] Compared with the prior art, the multifunctional lithium-ion membrane coating provided by this utility model achieves the following effects by setting an ultrathin nano-cellulose microcrystalline coating and a hybrid coating of hollow spherical binder particles and nano-ceramics on the base membrane (Solution 1), or by setting an additional nano-ceramic layer and a hollow spherical binder particle coating (Solution 2):

[0018] 1. Improved thermal stability: The ultra-thin nano-cellulose microcrystalline coating possesses high heat resistance, effectively reducing membrane shrinkage at high temperatures and preventing short circuits between the positive and negative electrodes caused by high temperatures. Simultaneously, the addition of the nano-ceramic layer and hollow spherical binder particles further enhances the coating's heat resistance, enabling the battery to maintain stable performance even in extreme environments.

[0019] 2. Enhanced Mechanical Strength: The use of nano-ceramic materials and hollow spherical binder particles not only increases the hardness of the separator coating but also improves its resistance to lithium dendrite penetration. This helps prevent internal short circuits in lithium-ion batteries during long-term use, thereby extending battery life.

[0020] 3. Optimized Electrochemical Performance: Due to its micro- and nano-sized pores and high specific surface area, the nano-cellulose single-crystal layer provides more active sites, promoting lithium-ion transport. Furthermore, this layer can enhance the electrolyte's adsorption capacity and improve the migration rate of lithium ions within the battery, thereby improving the overall electrochemical performance of the battery.

[0021] 4. Enhanced electrolyte retention: Due to their high liquid absorption, the nano-cellulose single crystals in the coating layer can effectively retain the electrolyte during battery operation, reduce the risk of drying out, and ensure that the ion conduction channels inside the battery are always moist. This is crucial for maintaining the battery's performance during continuous discharge and charge cycles.

[0022] 5. Reduced thermal shrinkage rate: The multi-layer structure design significantly reduces the thermal shrinkage of the separator when exposed to high temperatures through the combined use of high-temperature resistant materials, ensuring that the battery maintains the stability of its physical dimensions in high-temperature environments and avoiding impact on battery structure and performance.

[0023] 6. Improved breakdown voltage: The combined use of various materials, especially the addition of nano-ceramic layers and hollow spherical binder particles, helps to improve the insulation performance of the separator, thereby giving the separator a higher safe breakdown voltage and providing better safety protection for the battery. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the structure of a multifunctional lithium-ion membrane coating scheme 1 disclosed in this application.

[0025] Figure 2 This is a schematic diagram of the structure of a multifunctional lithium-ion membrane coating scheme 2 disclosed in this application.

[0026] The reference numerals in the figure are as follows: 1. Base film; 2. Nanocellulose microcrystalline coating; 3. Hybrid coating; 3-1. Hollow spherical binder particles; 4. Nanoceramic layer; 5. Hollow spherical binder particle coating. Detailed Implementation

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

[0028] It should be noted that when a component is described as "fixed to" another component, it can be directly on the other component or may have a component in between. When a component is considered "connected to" another component, it can be directly connected to the other component or may have a component in between. When a component is considered "set on" another component, it can be directly set on the other component or may have a component in between. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0029] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0030] Currently, the main types of separators on the market include those with a base membrane (PP, PE, non-woven fabric) plus a coating, and those with a conventional base membrane plus a ceramic coating. However, as the energy density of battery cells increases, the thickness of the base membrane is correspondingly reduced. This leads to problems such as poor liquid retention and inability to withstand ultra-high temperature thermal shrinkage. Therefore, it is necessary to introduce some new coatings to improve these issues.

[0031] This scheme involves first coating an ultrathin nano-cellulose microcrystalline coating 2 onto the base membrane 1, and then coating a mixed coating 3 of ceramic and hollow spherical binder particles or a nano-ceramic layer 4 plus a hollow spherical binder particle coating 5 onto the nano-cellulose microcrystalline coating 2, making the entire diaphragm resemble a sandwich structure. This structure can improve the diaphragm's liquid retention capacity, reduce the diaphragm's thermal shrinkage rate, and increase the diaphragm's breakdown voltage, among other properties.

[0032] Please refer to the detailed plan. Figure 1 , Figure 2 The diagram shown is a schematic representation of a multifunctional lithium-ion membrane coating structure provided in a preferred embodiment of this application. Figure 1 , Figure 2 In the illustrated embodiment, the coating structure includes:

[0033] A base film 1, which is made of polypropylene (PP), polyethylene (PE) or non-woven fabric, with a thickness of 1-20 μm and a porosity of 25-70%;

[0034] An ultrathin nanofiber cellulose microcrystalline coating 2 is directly covered and tightly bonded to the base film 1. This coating has high heat resistance and good liquid absorption, and has a thickness of 0.1-1 μm.

[0035] At least one additional coating is disposed above the nanocellulose microcrystalline coating 2 to improve the overall thermal stability, mechanical strength, and electrochemical performance of the membrane; the additional coating can be either Scheme 1 or Scheme 2, as detailed below:

[0036] like Figure 1 Scheme 1 includes: a mixed coating 3 consisting of hollow spherical binder particles 3-1 directly coated on top of nanocellulose microcrystalline coating 2 and nano-ceramics. The mixed coating 3 includes inorganic material powders such as alumina and boehmite with a particle size of 0.01-5 μm, and is mixed with spherical hollow binder materials with a diameter of 0.1-10 μm and a wall thickness of 2-1000 nm.

[0037] like Figure 2 Scheme 2 includes: a nano-ceramic layer 4 directly coated on the nano-cellulose microcrystalline coating 2, wherein the inorganic material used in the nano-ceramic layer 4 is alumina, boehmite, silicon dioxide, magnesium hydroxide, attapulgite, mullite, etc., with a particle size of 0.01um-5um and a specific surface area of ​​5-100g / m². 2 A hollow spherical adhesive material particle coating 5 is applied over the nano-ceramic layer 4. The organic adhesive material of the hollow spherical adhesive material particle coating 5 is a spherical hollow adhesive material such as polymethyl methacrylate, polyvinylidene fluoride, polyacrylic acid resin, PMMA, and PVDF. The material diameter is 0.1-10 μm, the spherical wall thickness is 2-1000 nm, and the coverage of the organic adhesive material on the coating surface is 5-100%.

[0038] In Scheme 1, the hollow spherical binder particles 3-1 of the hybrid coating 3 have a coverage of 1-50% on the coating surface and form a composite structure with the ceramic material powder to enhance the physical and chemical stability of the diaphragm.

[0039] In Scheme 2, the hollow spherical adhesive material particle coating 5 serves as the outermost layer to provide additional adhesion and ensure good contact between the nano-ceramic layer 4 and the battery electrode.

[0040] The base film 1, nanocellulose microcrystalline coating 2, nanoceramic layer 4, and hollow spherical binder particle coating 5 together exhibit excellent heat resistance, mechanical strength, and electrochemical performance, enabling the battery to maintain stable operation in high-temperature environments while reducing thermal shrinkage and preventing excessive electrolyte loss.

[0041] In this embodiment, the nanocellulose microcrystalline coating 2 is applied to the surface of the base film 1 by adding an acrylic resin binder to a nanocellulose single crystal solution, stirring until homogeneous, and then using a microgravure coating device, followed by drying to a fixed thickness (approximately 0.2-2 μm). Specifically, the heat-resistant and highly absorbent material (nanocellulose microcrystalline coating 2) is selected from cellulose nanocrystals, cellulose nanofibers, electrospun fibers, and materials such as bacterial cellulose, methylcellulose, hydroxyethyl methylcellulose, carboxymethyl cellulose, ethylcellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methylcellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose, and phenyl cellulose, with a diameter of 0.01-0.5 μm, a material length of 0.05-10 μm, and a specific surface area of ​​8-100 g / m². 2 .

[0042] The hybrid coating 3 is made by mixing alumina or boehmite heat-resistant material, water, and dispersant, adding sodium carboxymethyl cellulose thickener, and finally adding acrylic resin adhesive, polyether wetting agent, hollow spherical adhesive and other materials, stirring evenly to obtain a slurry, which is then coated onto the surface of nanocellulose microcrystalline coating 2 and cured to a certain thickness.

[0043] In this embodiment, a multifunctional lithium-ion separator has a total thickness of 2-10 μm and a porosity of 25-80%.

[0044] Table 1 provides a set of comparative examples and three sets of embodiments for this application, wherein Embodiment 1 and Embodiment 2 are Scheme 1 in the above scheme, and Embodiment 3 is Scheme 2 in the above scheme.

[0045] Table 1

[0046]

[0047] Therefore, the embodiments should be considered exemplary and non-limiting in all respects. The scope of this application is defined by the appended claims rather than the foregoing description, and all variations falling within the meaning and scope of equivalents of the claims are intended to be embraced within this application. No reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it is clear that the word "comprising" does not exclude other units or steps, and the singular does not exclude the plural. Multiple units or devices recited in the apparatus claims may also be implemented by the same unit or device in software or hardware. The terms "first," "second," etc., are used to indicate names and do not indicate any particular order.

[0048] The above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the spirit and scope of the technical solutions of this application.

Claims

1. A multifunctional lithium-ion membrane coating, characterized in that, include: Base film; A layer of nano-cellulose microcrystalline coating directly covering and tightly bonded to the base film; It also includes a layer of nano-ceramic layer and a layer of hollow spherical binder particles coated sequentially from bottom to top on the surface of the nano-cellulose microcrystalline coating.

2. The multifunctional lithium-ion membrane coating according to claim 1, characterized in that, The base film comprises polypropylene, polyethylene or nonwoven fabric, and the base film has a thickness of 1-20 μm and a porosity of 25-70%.

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