A separator for lithium ion batteries

Abstract

The utility model relates to battery technology field especially relates to a kind of separator for lithium ion battery, including the base film, adhesive layer, ceramic coating layer and polymer coating layer that are sequentially stacked and set;Wherein the adhesive layer is porous adhesive layer.The separator for lithium ion battery provided by the utility model introduces the adhesive layer with porous structure between ceramic coating layer and base film, improves the adhesion and heat resistance between ceramic coating layer and base film, avoids ceramic particles to penetrate into base film aperture to cause hole blocking, reduces the air permeability increment of separator whole.

Description

Technical Field

[0001] This utility model relates to the field of battery technology, and in particular to a separator for lithium-ion batteries. Background Technology

[0002] As the "third electrode" of lithium-ion batteries, the separator is a key material that ensures the safety of the battery system and affects battery performance. It needs to have characteristics such as high strength, heat resistance, flame retardancy, high porosity, uniformity, and good wettability. Traditional separators are polyolefin microporous membranes with polypropylene (PP) and polyethylene (PE) as the matrix. Their low melting point makes the battery prone to thermal runaway due to separator shrinkage, which can cause short circuits.

[0003] Currently, composite separators are often made by coating the surface of a polyolefin separator with an inorganic ceramic layer to improve the high-temperature thermal shrinkage of the separator. At the same time, a polymer binder is added to the ceramic coating layer to bond with the electrode sheets, increasing the cell rigidity and ensuring the consistency of the cell winding thickness.

[0004] However, due to the weak adhesion between PP and PE and the ceramic coating, the ceramic coating is prone to delamination. Utility Model Content

[0005] To address the problem of weak adhesion between the ceramic coating layer and the base film in existing composite separators, this invention provides a separator for lithium-ion batteries. This separator, by setting a porous adhesive layer between the base film and the ceramic coating layer, not only ensures heat resistance and improves the adhesion between the ceramic coating layer and the base film, but also avoids pore blockage of the base film caused by the ceramic coating layer, ensuring air permeability, thus solving the problem of weak adhesion between the ceramic coating layer and the base film in existing composite separators.

[0006] The technical solution adopted by this utility model to solve its technical problem is:

[0007] A separator for lithium-ion batteries includes a base film, an adhesive layer, a ceramic coating layer, and a polymer coating layer stacked sequentially; wherein the adhesive layer is a porous adhesive layer.

[0008] Optionally, the adhesive layer is made of acrylic-modified polyurethane.

[0009] Optionally, the thickness of the adhesive layer is 2.0-5.0 μm.

[0010] Optionally, the ceramic coating layer is formed by coating with a mixed slurry; the mixed slurry is composed of inorganic particles and a binder mixed in a mass ratio of 95:4; the inorganic particles are alumina or boehmite.

[0011] Optionally, the adhesive is composed of an acrylic solution adhesive and an acrylic emulsion adhesive mixed in a mass ratio of 1:3.

[0012] Optionally, the thickness of the ceramic coating layer is 0.5-4.0 μm.

[0013] Optionally, the polymer coating layer is a PMMA coating layer.

[0014] Optionally, the polymer coating layer is composed of large-diameter polymer microspheres and small-diameter polymer microspheres in a mass ratio of 2:1; the large-diameter polymer microspheres have a particle size D50 of 5.0~7.0μm and a glass transition temperature of 10-30℃; the small-diameter polymer microspheres have a particle size D50 of 0.3~2.0μm and a glass transition temperature of 30-50℃.

[0015] Optionally, the polymer coating layer includes a first polymer coating layer and a second polymer coating layer stacked together; the first polymer coating layer is disposed between the ceramic coating layer and the second polymer coating layer; the particle size D50 of the polymer microspheres in the first polymer coating layer is 0.3~2.0μm, and the glass transition temperature is 30-50℃; the particle size D50 of the polymer microspheres in the second polymer coating layer is 5.0~7.0μm, and the glass transition temperature is 10-30℃.

[0016] Optionally, the thickness of the first polymer coating layer is 0.5~3.0 μm; the thickness of the second polymer coating layer is 5.0~10 μm.

[0017] The beneficial effects of this utility model are:

[0018] The lithium-ion battery separator provided by this utility model introduces an adhesive layer with a porous structure between the ceramic coating layer and the base film. This improves the adhesion between the ceramic coating layer and the base film and the overall high temperature resistance, while avoiding pore blockage between the base film and the ceramic layer and reducing the increase in gas permeability of the separator. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 This is a schematic diagram of the structure of the separator for lithium-ion batteries in this utility model. Figure 1 ;

[0021] Figure 2 This is a schematic diagram of the structure of the separator for lithium-ion batteries in this utility model. Figure 2 ;

[0022] Figure 3 This is a schematic diagram of the structure of the separator for lithium-ion batteries in this utility model. Figure 3 .

[0023] In the figure: 1-base film; 2-adhesive layer; 3-ceramic coating layer; 4-polymer coating layer; 41-first polymer coating layer; 42-second polymer coating layer. Detailed Implementation

[0024] The present invention will now be described in further detail. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0025] In the description of this utility model, it should be understood that the terms "first" and "second" are used only for simplification and should not be construed as indicating or implying relative importance, or implicitly specifying the number of indicated technical features. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, "a plurality of" means two or more, unless otherwise explicitly specified.

[0026] In this utility model, unless otherwise explicitly specified and limited, "above" or "below" the first feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "on top of," and "over" the first feature includes the first feature being directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the first feature includes the first feature being directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0027] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings.

[0028] Existing composite separators, made by coating an inorganic ceramic layer onto the surface of a polyolefin separator, are prone to ceramic coating delamination and pore blockage due to direct contact between the ceramic coating and the base membrane, thus affecting gas permeability. Therefore, this invention provides a separator for lithium-ion batteries. (See attached image) Figure 1 , Figure 2As shown, the separator for lithium-ion batteries includes a base film 1, an adhesive layer 2, a ceramic coating layer 3, and a polymer coating layer 4 stacked sequentially. The base film 1 is a polyolefin microporous plastic film of polyethylene or polypropylene, and preferably has a thickness of 5.0-20 μm, more preferably 5.0-9.0 μm. To improve the adhesion between the ceramic coating layer 3 and the base film 1, the adhesive layer 2 is preferably provided between them. Furthermore, by providing the adhesive layer 2, direct contact between the ceramic coating layer 3 and the base film 1 can be avoided, thus preventing pore blockage. To further enhance the heat resistance of the separator coating layer and reduce the shrinkage rate of the separator under high-temperature conditions while ensuring the adhesion between the ceramic coating layer 3 and the base film 1, the adhesive layer 2 is preferably a porous adhesive layer, reducing pore blockage, increasing porosity, and reducing gas permeability.

[0029] The lithium-ion battery separator provided by this utility model introduces an adhesive layer 2 with a porous structure between the ceramic coating layer 3 and the base film 1. This improves the adhesion between the ceramic coating layer 3 and the base film 1 while preventing pore blockage in the base film 1, thereby increasing the porosity and reducing the gas permeability increase of the separator.

[0030] The porous adhesive layer 2 of this invention can be prepared by dissolving existing polymer materials suitable for lithium-ion battery separators in a solvent (such as 1,4-dioxane), then adding a non-solvent (such as water, ethanol, etc.) that is partially miscible with the solvent, and then allowing the solvent to evaporate after coating, resulting in phase separation. Alternatively, a polymer material containing a foaming agent, such as polyurethane containing a foaming agent, can be selected, and the porous adhesive layer 2 can be obtained through thermal decomposition or a chemical reaction during the curing process. Or, electrospinning technology can be used to apply a high voltage of several thousand volts or more to the polymer solution (such as polyurethane solution), and the charged polymer droplets are accelerated at the apex of the Taylor cone of the capillary by the action of the electric field until they can overcome the surface tension, forming a jet stream onto the base film, and then drying to obtain the porous adhesive layer 2.

[0031] The preferred material for the adhesive layer 2 of this invention is acrylic-modified polyurethane, specifically SEAPUR50K09 from Guangdong Dongde New Materials. Specifically, the adhesive layer 2 can be prepared as follows: Acrylic-modified polyurethane is dissolved in a solvent 1,4-dioxane, and then non-solvent deionized water, partially miscible with the solvent, is added. The mass ratio of acrylic-modified polyurethane, 1,4-dioxane, and water is 2:7:1, resulting in a mixed solution. The mixed solution obtained by the above method is coated onto the substrate and dried to obtain a porous acrylic-modified polyurethane adhesive layer. This layer enhances the bonding strength between the ceramic substrate 3 and the base membrane 1. Its porous support structure reduces contact clogging between ceramic particles and the base membrane, while maintaining high porosity and reducing gas permeability. Furthermore, the acrylic-modified polyurethane exhibits better support and stability under high-temperature conditions, demonstrating excellent high-temperature resistance, which helps to further improve the high-temperature performance of the diaphragm.

[0032] To balance adhesion and breathability, the thickness of the adhesive layer 2 is preferably 2.0-5.0 μm, and its glass transition temperature is preferably ≥100℃.

[0033] To ensure the heat resistance of the ceramic coating layer 3, the present invention preferably uses a mixed slurry to coat the ceramic coating layer 3. The mixed slurry is composed of inorganic particles and binder mixed in a mass ratio of 95:4. The inorganic particles are alumina or boehmite, and preferably the D50 particle size range of the inorganic particles is 0.3~1.5μm.

[0034] Currently, the binders used in conventional separator ceramic slurries are mostly acrylic or acrylate emulsions with low glass transition temperatures (Tg), which are difficult to meet the increasing demand for heat-resistant batteries in the market.

[0035] The adhesive in this invention can be a conventional acrylic or acrylate emulsion; to further improve the heat resistance, the adhesive is preferably composed of an acrylic solution adhesive and an acrylate emulsion adhesive in a mass ratio of 1:3.

[0036] Among them, the acrylic solution adhesive has a higher glass transition temperature (Tg), while the acrylic emulsion adhesive has a lower Tg. The high-Tg acrylic solution adhesive has the advantage of not softening or melting under high temperature conditions, which helps to reduce the shrinkage of the coating film. The low-Tg acrylic emulsion alleviates the overall stress roll-up and thermal shrinkage of the diaphragm under high temperature conditions in the form of soft bonding. Thus, by combining the high-Tg acrylic solution adhesive with the low-Tg acrylic emulsion, the heat resistance of the ceramic coating layer 3 is further improved.

[0037] The ceramic coating layer 3 provided by this invention maintains the structural stability of the diaphragm coating layer under high temperature conditions, thereby improving the high temperature resistance of the diaphragm.

[0038] Specifically, the preferred acrylic solution adhesive of this invention is DS-985 from Suzhou Derby Electronic Materials Technology Co., Ltd., whose main component is an acrylamide-modified acrylic solution. It is a type of high-Tg solution adhesive that forms a hyperbranched structure through block polymerization. In the solution provided by this invention, it can coat the surface of ceramic particles. Under high temperature conditions, the molecular chain segments can still maintain ultra-high rigidity, supporting the overall membrane without deformation or shrinkage. The branched structure is anchored to the adhesive layer 2, improving the bonding support and enhancing the high-temperature resistance of the ceramic coating layer 3.

[0039] The preferred acrylic emulsion adhesive of this invention is DS-9260 from Suzhou Derby Electronic Materials Technology Co., Ltd.

[0040] The present invention further preferably has a ceramic coating layer 3 with a thickness of 0.5-4.0 μm, and more preferably 1.5-3.0 μm, so as to effectively reduce the phenomenon of thermal shrinkage of the diaphragm.

[0041] To improve the interface uniformity between the separator layer and the electrode layer, provide ion channels, reduce interface resistance, and thus improve the charge and discharge performance of the battery, the polymer coating layer 4 of this invention is preferably a polymethyl methacrylate coating layer, i.e., a PMMA coating layer.

[0042] Based on the good compatibility between PMMA and electrolyte, the PMMA coating layer in this invention is set on the top layer of the diaphragm, which helps to improve the wettability of the electrolyte.

[0043] The polymer coating layer 4 in this invention is composed of polymer microspheres, specifically PMMA microspheres. PMMA microspheres are a type of electrolyte-loving, non-fluorinated polymer binder that can effectively connect the separator layer and the electrode layer. They can improve the interface between the separator and the electrode layer, form stable and uniform ion channels, improve rate performance, and improve the electrolyte wetting and liquid retention capacity of the battery cell, ensuring the consistency of the battery cell during charging and discharging.

[0044] Polymer coating layer 4 can be prepared from PMMA microspheres with uniform particle size; to further improve the adhesion between ceramic coating layer 3 and the electrode, see [reference needed]. Figure 1 As shown, in one embodiment of this utility model, the polymer coating layer 4 is composed of large-diameter polymer microspheres and small-diameter polymer microspheres in a mass ratio of (1~3):(0.5~2). Specifically, preferably, the polymer coating layer 4 is composed of large-diameter PMMA microspheres and small-diameter PMMA microspheres in a mass ratio of 2:1. The large-diameter polymer microspheres have a particle size D50 of 5.0~7.0μm and a glass transition temperature of 10-30℃; the small-diameter polymer microspheres have a particle size D50 of 0.3~2.0μm and a glass transition temperature of 30-50℃.

[0045] The polymer coating layer 4 in this invention is composed of a mixture of large and small-sized PMMA microspheres. The small-sized PMMA microspheres have a high Tg, which is beneficial for stabilizing the morphology and structure under high temperature conditions. They can also prevent the large-sized microspheres from deforming and collapsing due to external forces or causing pore blockage due to film formation. The large-sized PMMA microspheres have a low Tg, which can provide adhesion between the separator and the electrode. They can fully contact the electrode layer surface at lower temperatures to achieve efficient adhesion, which reduces manufacturing energy consumption and improves the interface between the electrode layer and the separator layer under high temperature conditions, thereby improving battery consistency and yield. It is particularly noteworthy that the large-sized PMMA microspheres can achieve adhesion between the separator layer and the electrode layer under cold pressing conditions.

[0046] The preferred thickness of the polymer coating layer 4 with mixed particle sizes in this invention is 5.5~13μm.

[0047] The number of polymer coating layers 4 with mixed particle sizes can be only one, which is disposed on the outside of the ceramic coating layer 3; further, the number of polymer coating layers 4 can also be two, one disposed on the outside of the ceramic coating layer 3, and the other disposed on the side of the base film 1 away from the adhesive layer 2.

[0048] This invention also provides another implementation method, see [link to implementation details] Figure 2 As shown, the polymer coating layer 4 includes a first polymer coating layer 41 and a second polymer coating layer 42 stacked together; the first polymer coating layer 41 is disposed between the ceramic coating layer 3 and the second polymer coating layer 42; the particle size D50 of the polymer microspheres in the first polymer coating layer 41 is 0.3~2.0μm, and the glass transition temperature is 30-50℃; the particle size D50 of the polymer microspheres in the second polymer coating layer 42 is 5.0~7.0μm, and the glass transition temperature is 10-30℃.

[0049] Taking advantage of the high Tg of small-diameter PMMA microspheres, the first polymer coating layer 41 stabilizes the morphology and structure under high temperature conditions, while preventing the large-diameter microspheres from deforming and collapsing due to external forces or causing pore blockage due to film formation. Taking advantage of the low Tg of large-diameter PMMA microspheres, the second polymer coating layer 42 provides adhesion between the separator and the electrode, enabling full contact with the electrode layer surface at lower temperatures to achieve efficient adhesion. This reduces manufacturing energy consumption, improves the interface between the electrode layer and the separator layer, and enhances battery consistency and yield. It is particularly noteworthy that the PMMA coating layer can achieve adhesion between the separator layer and the electrode layer under cold pressing conditions.

[0050] Specifically, the large-particle-size PMMA microspheres in this invention are DS-553 from Suzhou Derby Electronic Materials Technology Co., Ltd., and the small-particle-size PMMA microspheres are DS-513 from Suzhou Derby Electronic Materials Technology Co., Ltd.

[0051] Furthermore, the thickness of the first polymer coating layer 41 is preferably 0.5~3.0μm, and the thickness of the second polymer coating layer 42 is preferably 5.0~10μm.

[0052] In this invention, the first polymer coating layer 41 and the second polymer coating layer 42 can be provided as a single set, such as... Figure 2 As shown, it is disposed on the outer side of the ceramic coating layer 3; further, see... Figure 3 As shown, the first polymer coating layer 41 and the second polymer coating layer 42 can also be configured as two sets, one set on the outside of the ceramic coating layer 3, and the other set on the side of the base film 1 away from the adhesive layer 2.

[0053] The lithium-ion battery separator provided by this utility model features high adhesion, high heat resistance, and low air permeability. The porous adhesive layer 2 is placed on a polyolefin base film 1 to improve the adhesion between the base film 1 and the ceramic coating layer 3, improve the contact interface between the ceramic coating layer 3 and the polyolefin base film 1, reduce the air permeability increase of the separator, increase the adhesion strength, improve the stability of the separator coating layer, and facilitate the formation of uniform ion channels. The PMMA coating consists of microspheres of varying sizes, which can improve the adhesion between the ceramic coating layer 3 and the electrode layer, prevent active material detachment, improve the interface, and enhance the integrity of the battery. The mixed PMMA coating layer can adapt to room temperature or low temperature cold pressing, reduce energy consumption, improve the electrolyte wetting ability of the battery, ensure the stability of the battery during charging and discharging, and increase cycle life.

[0054] In this invention, the ceramic coating layer 3 is located in the middle layer, which can improve the heat resistance and hardness of the separator, reduce the shrinkage of the separator under high temperature conditions, and reduce the hidden dangers caused by short circuits in the battery under extreme conditions. The porous adhesive layer 2 is located at the bottom layer, which has good affinity with the polyolefin base film 1 and the ceramic coating layer 3, enhances the bonding strength and heat resistance between the ceramic coating layer 3 and the polyolefin base film 1, improves the consistency of the separator, and the porous structure also helps to reduce the pore blockage of the ceramic coating layer 3 and the base film 1, and reduce the increase in air permeability.

[0055] Based on the above-described preferred embodiments of this utility model, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the technical concept of this utility model. The technical scope of this utility model is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A separator for lithium-ion batteries, characterized in that, It includes a base film (1), an adhesive layer (2), a ceramic coating layer (3), and a polymer coating layer (4) stacked in sequence; wherein the adhesive layer (2) is a porous adhesive layer.

2. The separator for lithium-ion batteries as described in claim 1, characterized in that, The adhesive layer (2) is made of acrylic-modified polyurethane.

3. The separator for lithium-ion batteries as described in claim 1, characterized in that, The thickness of the adhesive layer (2) is 2.0-5.0 μm.

4. The separator for lithium-ion batteries as described in any one of claims 1-3, characterized in that, The ceramic coating layer (3) is formed by coating with a mixed slurry; the mixed slurry is composed of inorganic particles and binder mixed in a mass ratio of 95:4; the inorganic particles are alumina or boehmite.

5. The separator for lithium-ion batteries as described in claim 4, characterized in that, The adhesive is composed of an acrylic solution adhesive and an acrylic emulsion adhesive in a mass ratio of 1:

3.

6. The separator for lithium-ion batteries as described in claim 5, characterized in that, The thickness of the ceramic coating layer (3) is 0.5-4.0 μm.

7. The separator for lithium-ion batteries as described in any one of claims 1-3, characterized in that, The polymer coating layer (4) is a PMMA coating layer.

8. The separator for lithium-ion batteries as described in claim 7, characterized in that, The polymer coating layer (4) is composed of large-diameter polymer microspheres and small-diameter polymer microspheres in a mass ratio of 2:1; the particle size D50 of the large-diameter polymer microspheres is 5.0~7.0 μm and the glass transition temperature is 10-30℃; the particle size D50 of the small-diameter polymer microspheres is 0.3~2.0 μm and the glass transition temperature is 30-50℃.

9. The separator for lithium-ion batteries as described in claim 7, characterized in that, The polymer coating layer (4) includes a first polymer coating layer (41) and a second polymer coating layer (42) stacked together; the first polymer coating layer (41) is disposed between the ceramic coating layer (3) and the second polymer coating layer (42); the particle size D50 of the polymer microspheres in the first polymer coating layer (41) is 0.3~2.0 μm and the glass transition temperature is 30-50℃; the particle size D50 of the polymer microspheres in the second polymer coating layer (42) is 5.0~7.0 μm and the glass transition temperature is 10-30℃.

10. The separator for lithium-ion batteries as described in claim 9, characterized in that, The thickness of the first polymer coating layer (41) is 0.5~3.0μm; the thickness of the second polymer coating layer (42) is 5.0~10μm.

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