Ceramic composite separator for fast charging and low temperature lithium ion battery

Abstract

The application discloses a kind of ceramic composite diaphragm for fast charging, low temperature lithium ion battery, it is related to lithium ion battery diaphragm technical field, the formulation of water-based ceramic slurry for ceramic composite diaphragm preparation is improved in the application, can be without adding dispersing agent and binder under the condition, only with the resin coated ceramic particles prepared in the application as the component of water-based ceramic slurry, realize the uniform and stable dispersion of ceramic particles in water, and realize the uniform and firm stable adhesion of ceramic particles on polyolefin diaphragm, improve the heat resistance of polyolefin diaphragm using ceramic particles, to improve the safety of battery.

Description

Technical fields:

[0001] This invention relates to the field of lithium-ion battery separator technology, specifically to a ceramic composite separator for fast-charging, low-temperature lithium-ion batteries. Background technology:

[0002] In the structure of a lithium-ion battery, the separator is one of the key internal components. The performance of the separator determines the battery's interface structure, internal resistance, and other factors, directly affecting the battery's capacity, cycle life, and safety performance. The main function of the separator is to separate the positive and negative electrodes, preventing short circuits caused by contact between the electrodes. It also allows electrolyte ions to pass through. For lithium-ion batteries, since the electrolyte is an organic solvent system, separator materials resistant to organic solvents are required, typically high-strength, thin-film polyolefin porous membranes.

[0003] However, polyolefin separators have poor heat resistance. When the battery temperature rises due to internal or external reasons, the separator will shrink or even melt, lose its separating function, and cause a short circuit between the positive and negative electrodes, resulting in damage to the lithium-ion battery. In addition, polyolefin separators have poor hydrophilicity, which results in poor wettability of the separator to the electrolyte, directly affecting the cycle performance of the lithium-ion battery.

[0004] Ceramic composite separators are made by coating a polyolefin separator with a layer of inorganic ceramic particles. While maintaining the original basic properties of the polyolefin separator, this improves the separator's heat resistance, reduces thermal shrinkage, and more effectively reduces internal short circuits in the battery, preventing thermal runaway caused by internal short circuits and thus improving battery safety. The ceramic slurry used in the preparation of ceramic composite separators typically consists of inorganic ceramic particles, binders, dispersants, and solvents. To reduce solvent costs and improve the environmental friendliness of the process, water-based ceramic slurries are increasingly widely used. Although inorganic ceramic particles have good hydrophilicity, they cannot be uniformly and stably dispersed in water, easily agglomerating and settling. Dispersants are needed to improve the dispersibility of inorganic ceramic particles in water. Furthermore, inorganic ceramic particles themselves do not possess adhesiveness, requiring binders to achieve adhesion to the separator. Binders are generally polymeric compounds, and when water is used as a solvent, the binder must have excellent hydrophilicity; otherwise, its adhesive properties cannot be used to achieve uniform and stable adhesion of inorganic ceramic particles to the separator. Summary of the Invention:

[0005] The technical problem to be solved by the present invention is to provide a ceramic composite separator, which improves the thermal stability of the polyolefin separator by coating it with a ceramic coating, and at the same time gives the polyolefin separator good low temperature resistance, making it suitable for fast charging and low temperature lithium-ion batteries.

[0006] The technical problem to be solved by this invention is achieved by the following technical solution:

[0007] The first objective of this invention is to provide a ceramic composite membrane comprising a base membrane and a ceramic coating, wherein the ceramic coating is formed by curing an aqueous ceramic slurry uniformly coated on the base membrane, and the aqueous ceramic slurry is formed by mixing resin-coated ceramic particles with water.

[0008] Furthermore, the method for preparing the resin-coated ceramic particles is to first obtain modified polyacrylamide by copolymerization of acrylamide and allyl (tert-butyl)dimethylsilane, then heat and melt the modified polyacrylamide and mix it with ceramic particles, and finally pulverize it after cooling to obtain resin-coated ceramic particles.

[0009] Preferably, the molar ratio of acrylamide to allyl (tert-butyl)dimethylsilane is (4-5):1. This invention uses acrylamide and allyl (tert-butyl)dimethylsilane as monomers to introduce organosilicon molecular chains into polyacrylamide through a copolymerization reaction.

[0010] Preferably, the number-average molecular weight of the modified polyacrylamide is 3 × 10⁻⁶. 4 ~3.5×10 4 Only by selecting modified polyacrylamide with this molecular weight can uniform coating of ceramic particles be achieved and the adhesion of ceramic particles to the membrane be guaranteed.

[0011] Preferably, the mass ratio of the modified polyacrylamide to the ceramic particles is 100:(50-60). The modified polyacrylamide achieves uniform and rapid coating of the ceramic particles in the molten state.

[0012] This invention, through the preparation of resin-coated ceramic particles and their application in the formulation of water-based ceramic slurries, can greatly simplify the composition of water-based ceramic slurries. When formulating water-based ceramic slurries, there is no need to add dispersants and binders separately. By coating ceramic particles with modified polyacrylamide, uniform and stable dispersion of ceramic particles in water can be achieved, and uniform and firm adhesion of ceramic particles to the base film can be ensured.

[0013] Furthermore, the base membrane is one of PP membrane, PE membrane, or PP / PE composite membrane. PP membrane or PE membrane can be selected as the base membrane, or a PP / PE composite membrane can be selected as the base membrane.

[0014] Furthermore, the ceramic particles are at least one of alumina, boehmite, silicon dioxide, and titanium dioxide. Appropriate amounts of transition metal oxides or rare earth metal oxides such as cerium dioxide and zirconium dioxide may also be added.

[0015] Furthermore, the D50 particle size of the ceramic particles is 0.5–2 μm. It is necessary to control the particle size of the ceramic particles so that they adhere to the diaphragm without clogging the diaphragm pores.

[0016] Furthermore, the curing is either room temperature curing or heat curing. Water-based ceramic slurry can be air-dried and cured at room temperature or cured by heating, thus shortening the curing time.

[0017] Furthermore, the heating and curing temperature is 80–120°C. Curing can also be carried out at temperatures below 80°C, but the curing time will be longer.

[0018] Furthermore, the thickness of the ceramic coating is 2–4 μm. The ceramic coating can be prepared by coating only one side of the diaphragm, or by coating both sides of the diaphragm.

[0019] A second objective of this invention is to provide the application of the ceramic composite separator in fast-charging and low-temperature lithium-ion batteries. The ceramic composite separator of this invention possesses good thermal stability and low-temperature resistance, and can be used in the preparation of fast-charging and low-temperature lithium-ion batteries.

[0020] The beneficial effects of this invention are as follows: By improving the formulation of waterborne ceramic slurry for preparing ceramic composite separators, this invention enables uniform and stable dispersion of ceramic particles in water using only the resin-coated ceramic particles prepared in this invention as a component of the waterborne ceramic slurry without adding additional dispersants and binders. It also enables uniform and firm adhesion of ceramic particles to the polyolefin separator, thereby improving the heat resistance of the polyolefin separator and enhancing battery safety. Detailed implementation method:

[0021] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below with reference to specific embodiments.

[0022] The raw materials used in the embodiments and comparative examples of this invention are described below:

[0023] The PP membrane has a thickness of 25μm, an air permeability of 350sec / 100mL, and a porosity of 39%.

[0024] The PE membrane has a thickness of 20μm, an air permeability of 200sec / 100mL, and a porosity of 40%.

[0025] The D50 particle size of alumina is 0.5–1.0 μm, and the specific surface area is 4–8 m². 2 / g;

[0026] Boehmite has a D50 particle size of 0.5–1.4 μm and a specific surface area of ​​4–9 m². 2 / g.

[0027] Example 1

[0028] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 5:1 were copolymerized to obtain a number-average molecular weight of 3.2 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with alumina at a mass ratio of 100:60. After cooling, the mixture was crushed, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0029] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 45%.

[0030] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PP membrane and cured at 100℃ to form a ceramic coating with a thickness of 3μm, thus obtaining the ceramic composite membrane.

[0031] Example 2

[0032] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 4:1 were copolymerized to obtain a number-average molecular weight of 3.5 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with boehmite at a mass ratio of 100:55. After cooling, the mixture was pulverized, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0033] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 55%.

[0034] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PE membrane and cured at 120℃ to form a ceramic coating with a thickness of 3μm, thus obtaining the ceramic composite membrane.

[0035] Example 3

[0036] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 4:1 were copolymerized to obtain a number-average molecular weight of 3.1 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with alumina at a mass ratio of 100:50. After cooling, the mixture was crushed, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0037] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 50%.

[0038] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PP membrane and cured at 110℃ to form a ceramic coating with a thickness of 3μm, thus obtaining the ceramic composite membrane.

[0039] Example 4

[0040] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 5:1 were copolymerized to obtain a number-average molecular weight of 3.4 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with alumina at a mass ratio of 100:60. After cooling, the mixture was crushed, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0041] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 60%.

[0042] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PE membrane and heated and cured at 80°C to form a ceramic coating with a thickness of 4μm, thus obtaining the ceramic composite membrane.

[0043] Example 5

[0044] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 5:1 were copolymerized to obtain a number-average molecular weight of 3 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with boehmite at a mass ratio of 100:50. After cooling, the mixture was pulverized, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0045] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 55%.

[0046] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PP membrane and cured at 90°C to form a ceramic coating with a thickness of 4μm, thus obtaining the ceramic composite membrane.

[0047] Example 6

[0048] 1. Preparation of resin-coated ceramic particles: Acrylamide and allyl (tert-butyl)dimethylsilyl chloride in a molar ratio of 4:1 were copolymerized to obtain a number-average molecular weight of 3.2 × 10⁻⁶. 4 Modified polyacrylamide was heated and melted, then mixed with alumina at a mass ratio of 100:55. After cooling, the mixture was pulverized, ground, and passed through a 5000-mesh sieve to obtain resin-coated ceramic particles.

[0049] 2. Preparation of water-based ceramic slurry: Add the resin-coated ceramic particles prepared in step 1 to water and disperse at high speed to obtain a uniform water-based ceramic slurry with a solid content of 50%.

[0050] 3. Preparation of ceramic composite membrane: The aqueous ceramic slurry prepared in step 2 is uniformly coated on one side of the PE membrane and heated and cured at 110℃ to form a ceramic coating with a thickness of 4μm, thus obtaining the ceramic composite membrane.

[0051] Comparative Example 1

[0052] The method for preparing the ceramic composite diaphragm in Comparative Example 1 is the same as in Example 6, except that the comonomer allyl (tert-butyl)dimethylsilane is replaced with methyl acrylate when synthesizing the modified polyacrylamide.

[0053] Comparative Example 2

[0054] The method for preparing the ceramic composite membrane in Comparative Example 2 is the same as that in Example 6, except that the comonomer allyl (tert-butyl)dimethylsilane is not added when synthesizing the modified polyacrylamide, that is, only acrylamide is used as the monomer.

[0055] The transverse and longitudinal thermal shrinkage rates of the ceramic composite membranes prepared in Examples 1-6 and Comparative Examples 1-2 at 160℃ / 1h were tested, and the results are shown in Table 1.

[0056] Table 1 Thermal stability of ceramic composite membranes

[0057]

[0058] As can be seen from the data in Table 1, the modified polyacrylamide synthesized in this invention is beneficial to improving the thermal stability of ceramic composite membranes.

[0059] The puncture strength of the ceramic composite diaphragms prepared in Examples 1-6 and Comparative Examples 1-2 at -30℃ was tested using a universal testing machine. The results are shown in Table 2.

[0060] Table 2. Puncture strength of ceramic composite diaphragms at -30℃

[0061]

[0062]

[0063] As can be seen from the data in Table 2, the modified polyacrylamide synthesized in this invention is beneficial to improving the low-temperature resistance of ceramic composite membranes.

[0064] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A ceramic composite diaphragm, characterized in that: The ceramic composite diaphragm includes a base membrane and a ceramic coating. The ceramic coating is formed by curing an aqueous ceramic slurry uniformly coated on the base membrane. The aqueous ceramic slurry is formed by mixing resin-coated ceramic particles with water. The resin-coated ceramic particles are prepared by first copolymerizing acrylamide and allyl (tert-butyl)dimethylsilane to obtain modified polyacrylamide, then heating and melting the modified polyacrylamide and mixing it with ceramic particles, followed by cooling and pulverizing to obtain the resin-coated ceramic particles; the molar ratio of acrylamide to allyl (tert-butyl)dimethylsilane is (4-5):1; the number average molecular weight of the modified polyacrylamide is 3×10⁻⁶. 4 ~3.5×10 4 .

2. The ceramic composite diaphragm according to claim 1, characterized in that: The mass ratio of the modified polyacrylamide to the ceramic particles is 100:(50~60).

3. The ceramic composite diaphragm according to claim 1, characterized in that: The base membrane is one of PP membrane, PE membrane, or PP / PE composite membrane.

4. The ceramic composite diaphragm according to claim 1, characterized in that: The ceramic particles are at least one of alumina, boehmite, silicon dioxide, and titanium dioxide.

5. The ceramic composite diaphragm according to claim 1, characterized in that: The ceramic particles have a D50 particle size of 0.5~2μm.

6. The ceramic composite diaphragm according to claim 1, characterized in that: The curing process is either room temperature curing or heat curing.

7. The ceramic composite diaphragm according to claim 1, characterized in that: The thickness of the ceramic coating is 2~4μm.

8. The application of the ceramic composite separator according to any one of claims 1 to 7 in fast-charging, low-temperature lithium-ion batteries.

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