Aramid diaphragm for lithium battery and preparation method thereof

Abstract

The present application relates to the field of lithium battery separators, and specifically discloses an aramid separator for lithium batteries and a preparation method thereof; an aramid separator for lithium batteries, comprising an aramid slurry and a base film, wherein the aramid slurry is coated on both sides of the base film to form an aramid coating, the aramid slurry comprising the following raw materials in parts by weight: 20-40 parts of aramid polymer solution, 5-10 parts of Tencel fibrillated slurry, 1-3 parts of lithium titanium aluminum phosphate nanoparticles, 3-5 parts of nano-ceramic particles, and 8-15 parts of solvent; the aramid polymer solution comprising the following raw materials in parts by weight: 1-3 parts of p-phenylenediamine, 60-80 parts of polar solvent, 5-10 parts of terephthaloyl chloride, 1-3 parts of 3,4'-diaminodiphenyl ether, 1-3 parts of o-chloro-p-phenylenediamine, and 0.5-1 parts of a polyether surfactant; the present invention combines the aramid polymer solution with the nano-ceramic particles and the Tencel fibrillated slurry components to form an interconnected porous three-dimensional network structure, thereby improving the air permeability, thermal stability and porosity of the aramid separator.

Description

Technical Field

[0001] The present application relates to the field of lithium battery separators, and in particular to an aramid separator for lithium batteries and a preparation method thereof. Background Art

[0002] As a core component of energy storage, lithium-ion batteries are widely used in a variety of fields, including consumer electronics, electric vehicles, and grid energy storage. The separator, a thin film with a microporous structure, is a key internal component with technical barriers in the lithium-ion battery industry chain. Its primary function is to separate the positive and negative electrodes of the battery, preventing contact and short circuits. Furthermore, the micropores in the separator allow lithium ions to pass through, forming a charge and discharge circuit.

[0003] Traditional diaphragm materials are mainly polyolefin porous membranes. However, due to the low melting point of polyolefin materials, when the battery temperature rises due to internal or external factors, the diaphragm will shrink or melt and then rupture, causing the positive and negative poles of the battery to contact, resulting in a battery short circuit, causing battery combustion and explosion and other accidents, seriously affecting the safety and stability of the battery. Summary of the Invention

[0004] In order to improve the heat resistance and strength of traditional diaphragm materials, the present application provides an aramid diaphragm for lithium batteries and a preparation method thereof.

[0005] In a first aspect, the present application provides an aramid separator for a lithium battery, which adopts the following technical solution:

[0006] An aramid diaphragm for a lithium battery comprises an aramid slurry and a base film. The aramid slurry is coated on both sides of the base film to form an aramid coating. The aramid slurry comprises the following raw materials in parts by weight: 20-40 parts of aramid polymer solution, 5-10 parts of Tencel fibrillated slurry, 1-3 parts of lithium titanium aluminum phosphate nanoparticles, 3-5 parts of nano-ceramic particles, and 8-15 parts of solvent; the aramid polymer solution comprises the following raw materials in parts by weight: 1-3 parts of p-phenylenediamine, 60-80 parts of a polar solvent, 5-10 parts of terephthaloyl chloride, 1-3 parts of 3,4'-diaminodiphenyl ether, 1-3 parts of o-chloro-p-phenylenediamine, and 0.5-1 part of a polyether surfactant.

[0007] By adopting the above technical solution, para-phenylenediamine, terephthaloyl chloride, 3,4'-diaminodiphenyl ether, and o-chloro-p-phenylenediamine are polycondensed to form poly(p-phenylene terephthalamide), forming a para-aramid polymer solution. This solution has good solubility and can be directly used for coating lithium battery separators. This improves the heat resistance of the resulting aramid separator and reduces thermal shrinkage. An appropriate amount of polyether surfactant is added to the aramid polymer solution. The polyether surfactant binds to the poly(p-phenylene terephthalamide) and dissolves in the solvent. This allows the polyether surfactant to adsorb at the interface between the aramid polymer solution and the solvent, reducing interfacial tension and improving the fluidity and stability of the aramid slurry. This facilitates subsequent coating and film formation, facilitating the formation of a uniform aramid coating. Furthermore, the polyether surfactant enhances the wettability of the aramid polymer solution and the aramid slurry, ensuring a strong bond between the aramid slurry and the base film, thereby improving the structural stability and mechanical strength of the separator.

[0008] Tencel fibers are refined and fibrillated to form a Tencel fibrillated slurry. This slurry, combined with the aramid polymer solution, forms a porous, three-dimensional network within the aramid slurry. This creates a porous structure within the aramid separator, providing ample channels for lithium ion migration and improving the electrochemical performance of lithium-ion batteries. The Tencel fibrillated slurry also enhances the flexibility and air permeability of the aramid coating, thereby improving the electrochemical stability of lithium-ion batteries.

[0009] Lithium aluminum titanium phosphate nanoparticles and nano-ceramic particles can improve the strength and thermal stability of the separator. Lithium aluminum titanium phosphate nanoparticles can enhance the lithium ion transport capacity and cycling stability, improving the electrochemical stability of lithium batteries. Nano-ceramic particles have a high melting point, reducing the risk of short circuits between the electrode and the separator due to thermal contraction, thereby improving battery safety.

[0010] Preferably, the polyether surfactant is one of polyethylene glycol, polypropylene oxide, and polytetramethylene ether glycol.

[0011] Preferably, the solvent is a complex of a dispersant solvent and a cosolvent, the dispersant solvent is at least one of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, and acetone, and the cosolvent is at least one of calcium chloride, lithium chloride, and potassium hydroxide.

[0012] Preferably, the Tencel fibrillated pulp is prepared by subjecting Tencel fibers as raw materials to a refining and fibrillation treatment, and the beating degree of the Tencel fibrillated pulp is 75-85°SR.

[0013] By adopting the above technical solution, the beating degree of Tencel fibrillated pulp is controlled within the range of 75-85°SR, which increases the specific surface area of ​​the fiber and the contact area between Tencel fiber and aramid polymer liquid. At the same time, it can ensure that the Tencel fiber is evenly dispersed in the aramid pulp and maintains a good fiber structure, thereby improving the mechanical strength, structural stability and air permeability of the diaphragm.

[0014] Preferably, the nano-ceramic particles are silanized using a silane coupling agent, and the modification method comprises the following specific steps: mixing the nano-ceramic particles with the silane coupling agent and toluene, heating to 70-80° C. and stirring evenly, washing and drying to obtain silanized modified nano-ceramic particles.

[0015] By adopting the above technical solution and modifying the nano-ceramic particles with a silane coupling agent, the nano-ceramic particles can be evenly dispersed in the aramid slurry, reducing ceramic particle precipitation and uniformly improving the strength of the aramid membrane. Furthermore, the addition of the silane coupling agent can further enhance the bonding between the aramid slurry and the base membrane, extending the strength and structural stability of the aramid membrane.

[0016] Preferably, the nano-ceramic particles are at least one of nano-silicon dioxide, nano-titanium dioxide, and nano-aluminum oxide.

[0017] Preferably, the thickness of the aramid coating is 3-8 μm, and the thickness of the base film is 5-20 μm.

[0018] In a second aspect, the present application provides a method for preparing an aramid diaphragm for a lithium battery, which adopts the following technical solution: A method for preparing an aramid diaphragm for a lithium battery, comprising the following specific steps:

[0019] P-phenylenediamine, 3,4'-diaminodiphenyl and o-chloro-p-phenylenediamine are uniformly mixed, a polar solvent is added, and the mixture is stirred and dissolved at 10-30°C under the protection of nitrogen. The mixture is then cooled to -5-0°C, terephthaloyl chloride and a polyether surfactant are added, and the mixture is stirred and reacted to obtain a reaction mixture. The pH of the reaction mixture is adjusted to obtain an aramid polymer solution.

[0020] Aramid polymer liquid, Tencel fibrillated pulp, lithium titanium aluminum phosphate nanoparticles, nano-ceramic particles and solvent are mixed, heated, stirred and dissolved to obtain aramid slurry, and then the aramid slurry is coated on both sides of the base film and dried to form an aramid coating to obtain an aramid separator for lithium batteries.

[0021] By adopting the above technical solution, the prepared aramid membrane can have good thermal stability and strength, while maintaining good porosity and permeability, thereby improving the electrochemical performance of the lithium battery.

[0022] In summary, this application has the following beneficial effects:

[0023] 1. Since the present application adds a polyether surfactant to the para-aramid slurry raw material, it can improve the wettability of the aramid slurry, enhance the bonding strength between the aramid slurry and the base film, and form a uniform, heat-resistant aramid coating. By combining Tencel fibrillated slurry with aramid polymer, a three-dimensional interconnected porous network structure is formed in the aramid slurry system, thereby improving the pore structure of the aramid diaphragm and thus improving the electrochemical stability of the lithium battery. Lithium titanium aluminum phosphate nanoparticles and nano-ceramic particles are used to improve the strength and thermal stability of the aramid diaphragm, reduce the risk of short circuits between the electrode and the diaphragm due to thermal contraction, and improve the safety of the battery.

[0024] 2. In this application, Tencel fibers are subjected to a refining and fibrillation treatment to form a Tencel fibrillated slurry. This increases the specific surface area of ​​the fibers and the contact area between the Tencel fibers and the aramid polymer solution, while maintaining high fiber strength. This, in turn, improves the mechanical strength, structural stability, and air permeability of the aramid membrane. Nano-ceramic particles are silanized using a silane coupling agent to promote their uniform dispersion in the aramid slurry, reduce ceramic particle precipitation, and improve the uniformity of the aramid membrane's strength. DETAILED DESCRIPTION

[0025] The present application is further described in detail below with reference to the embodiments.

[0026] All raw materials in the examples are commercially available.

[0027] Preparation example of aramid polymer solution

[0028] Preparation Example 1

[0029] The aramid polymerization liquid comprises the following raw materials in parts by weight: 2 kg of p-phenylenediamine, 70 kg of a polar solvent, 8 kg of terephthaloyl chloride, 2 kg of 3,4'-diaminodiphenyl ether, 2 kg of o-chloro-p-phenylenediamine, and 0.8 kg of a polyether surfactant, wherein the polar solvent is N-methylpyrrolidone and the polyether surfactant is polyethylene glycol 400.

[0030] The preparation method of aramid polymer solution comprises the following specific steps:

[0031] P-phenylenediamine, 3,4'-diaminodiphenyl, and o-chloro-p-phenylenediamine are uniformly mixed, a polar solvent is added, and the mixture is stirred and dissolved at 20°C under the protection of nitrogen. The mixture is then cooled to -3°C, terephthaloyl chloride and a polyether surfactant are added, and the mixture is stirred for reaction to obtain a reaction mixture. The pH of the reaction mixture is adjusted to neutral using a 15wt% sodium hydroxide aqueous solution, and the mixture is continuously filtered and degassed to obtain an aramid polymer solution.

[0032] Preparation Example 2

[0033] The difference between Preparation Example 2 and Preparation Example 1 is that the amount of p-phenylenediamine used in the aramid polymer liquid raw material is 1 kg, the amount of polar solvent used is 60 kg, the amount of terephthaloyl chloride used is 5 kg, the amount of 3,4'-diaminodiphenyl ether used is 3 kg, the amount of o-chloro-p-phenylenediamine used is 3 kg, and the amount of polyether surfactant used is 0.5 kg.

[0034] Preparation Example 3

[0035] The difference between Preparation Example 3 and Preparation Example 1 is that the amount of p-phenylenediamine used in the aramid polymer liquid raw material is 3 kg, the amount of polar solvent used is 80 kg, the amount of terephthaloyl chloride used is 10 kg, the amount of 3,4'-diaminodiphenyl ether used is 1 kg, the amount of o-chloro-p-phenylenediamine used is 1 kg, and the amount of polyether surfactant used is 1 kg.

[0036] Preparation Example 4

[0037] The difference between Preparation Example 4 and Preparation Example 1 is that the polyether surfactant in the aramid polymer liquid raw material is polypropylene oxide, and the molecular weight of the polypropylene oxide is 5000.

[0038] Preparation Example 5

[0039] The difference between Preparation Example 5 and Preparation Example 1 is that no polyether surfactant is used in the aramid polymer liquid raw material.

[0040] The preparation method of aramid polymer solution comprises the following specific steps:

[0041] P-phenylenediamine, 3,4'-diaminodiphenyl and o-chloro-p-phenylenediamine are uniformly mixed, a polar solvent is added, and the mixture is stirred and dissolved at 20°C under the protection of nitrogen. The mixture is then cooled to -3°C, terephthaloyl chloride is added, and the mixture is stirred for reaction to obtain a reaction mixture. The pH of the reaction mixture is adjusted to neutral using a 15wt% sodium hydroxide aqueous solution, and the mixture is continuously filtered and degassed to obtain an aramid polymer solution.

[0042] Example

[0043] Example 1

[0044] This embodiment provides an aramid separator for lithium batteries, including an aramid slurry and a base film. The aramid slurry is coated on both sides of the base film to form an aramid coating. The aramid slurry includes the following raw materials in parts by weight: 30 kg of aramid polymer solution, 8 kg of Tencel fibrillated slurry, 2 kg of lithium titanium aluminum phosphate nanoparticles, 4 kg of nano-ceramic particles, and 11 kg of solvent. The aramid polymer solution is derived from Preparation Example 1, the Tencel fibrillated slurry is made by refining and fibrillating Tencel fibers, the beating degree of the Tencel fibrillated slurry is 80°SR, and the lithium titanium aluminum phosphate nanoparticles are Li 1.3 Al 0.3 Ti1.7 P3O 12 The average particle size of lithium aluminum titanium phosphate nanoparticles is 80-100 nm, the nano-ceramic particles are nano-silicon dioxide, the average particle size of the nano-ceramic particles is 50-80 nm, the solvent is a complex of dimethylformamide and potassium chloride, and the mass ratio of dimethylformamide to potassium chloride is 1:0.5.

[0045] The preparation method of the aramid diaphragm for lithium battery comprises the following specific steps:

[0046] Aramid polymer liquid, Tencel fibrillated slurry, lithium titanium aluminum phosphate nanoparticles, nano-ceramic particles and solvent are mixed and stirred to dissolve to obtain aramid slurry, and then the aramid slurry is coated on both sides of the base membrane. The base membrane is a polypropylene diaphragm with a thickness of 15 μm and a porosity of 80%. The coating rate is 8 m / min, and the immersion is carried out for 10 s. A three-stage oven is used for drying. The oven temperatures of each stage are 50°C, 60°C and 65°C, respectively. The aramid coating with a thickness of 5 μm is formed by drying to obtain an aramid diaphragm for lithium batteries.

[0047] Example 2

[0048] The difference between Example 2 and Example 1 is that the amount of aramid polymer liquid used in the aramid slurry raw material is 20 kg, the amount of Tencel fibrillated slurry used is 10 kg, the amount of lithium titanium aluminum phosphate nanoparticles used is 1 kg, the amount of nano-ceramic particles used is 3 kg, and the amount of solvent used is 8 kg.

[0049] Example 3

[0050] The difference between Example 3 and Example 1 is that the amount of aramid polymer liquid used in the aramid slurry raw material is 40 kg, the amount of Tencel fibrillated slurry used is 5 kg, the amount of lithium titanium aluminum phosphate nanoparticles used is 3 kg, the amount of nano-ceramic particles used is 5 kg, and the amount of solvent used is 15 kg.

[0051] Example 4

[0052] The difference between Example 4 and Example 1 is that the aramid polymer solution in the aramid slurry raw material comes from Preparation Example 2.

[0053] Example 5

[0054] The difference between Example 5 and Example 1 is that the aramid polymer solution in the aramid slurry raw material comes from Preparation Example 3.

[0055] Example 6

[0056] The difference between Example 6 and Example 1 is that the aramid polymer solution in the aramid slurry raw material comes from Preparation Example 4.

[0057] Example 7

[0058] The difference between Example 7 and Example 1 is that the solvent in the aramid slurry raw material is a complex of dimethylacetamide and lithium chloride, and the mass ratio of dimethylacetamide to lithium chloride is 1:0.5.

[0059] Example 8

[0060] The difference between Example 8 and Example 1 is that the nano-ceramic particles in the aramid slurry raw material are silanized using a silane coupling agent.

[0061] The preparation method of the aramid diaphragm for lithium battery comprises the following specific steps:

[0062] S1: Mix nano-ceramic particles with silane coupling agent KH-570 and toluene in a mass ratio of 1:0.5:1, heat to 75°C and stir for 2 hours, wash with ethanol and then dry to obtain silanized modified nano-ceramic particles.

[0063] S2: Mix aramid polymer liquid, Tencel fibrillated slurry, lithium titanium aluminum phosphate nanoparticles, silanized modified nano-ceramic particles and solvent, stir and dissolve to obtain aramid slurry, and then apply the aramid slurry on both sides of the base membrane. The base membrane is a polypropylene diaphragm with a thickness of 15μm and a porosity of 80%. The coating rate is 8m / min, immersed in water for 10s, and dried in a three-stage oven. The oven temperatures of each stage are 50℃, 60℃, and 65℃ respectively. Dry to form an aramid coating with a thickness of 5μm, thus obtaining an aramid diaphragm for lithium batteries.

[0064] Comparative Example

[0065] Comparative Example 1

[0066] The difference between Comparative Example 1 and Example 1 is that the aramid polymer solution in the aramid slurry raw material comes from Preparation Example 5.

[0067] Comparative Example 2

[0068] The difference between Comparative Example 2 and Example 1 is that Tencel fibrillated slurry is not used in the aramid slurry raw material.

[0069] Comparative Example 3

[0070] The difference between Comparative Example 3 and Example 1 is that lithium titanium aluminum phosphate nanoparticles are not used in the aramid slurry raw material.

[0071] Performance testing

[0072] The following performance tests were performed on the aramid diaphragms for lithium batteries provided in Examples 1-8 and Comparative Examples 1-3 of the present application. The specific test results are shown in Table 1.

[0073] Detection method

[0074] 1. Heat shrinkage performance

[0075] Thermal shrinkage test: Expel the air between the membranes of the aramid diaphragm sample for lithium batteries prepared in this application, cut it into a size of 300*100, measure the length A1 and width B1 of the cut sample, place the sample in an oven at 140°C and keep it warm for 2 hours, take out the diaphragm and cool it for 10 minutes, then measure the length A2 and width B2 of the sample; the thermal shrinkage performance of the diaphragm is characterized by the longitudinal thermal shrinkage rate and transverse thermal shrinkage rate of the diaphragm, the longitudinal thermal shrinkage rate of the diaphragm = ((A1-A2) / A1)x100%; the transverse thermal shrinkage rate of the diaphragm = ((B1-B2) / B1)x100%.

[0076] 2. Air permeability

[0077] The air permeability of the aramid diaphragm for lithium batteries prepared in this application was tested using an air permeability tester.

[0078] 3. Porosity

[0079] The n-butanol absorption method was used to test: a circular aramid diaphragm with a diameter of 18 mm prepared in this application was immersed in n-butanol solution for 4 h, and the mass after immersion was weighed. The porosity was calculated using the formula = [(M1-M0) / ρV]×100, where M0 and M1 are the masses of the diaphragm before and after immersion in n-butanol, respectively, in g; ρ is the density of n-butanol, 0.81 g / cm 3 ; V is the volume of the aramid diaphragm, unit: cm 3 .

[0080] Table 1: Performance test results data table

[0081]

[0082]

[0083] The performance test results show that the aramid diaphragm for lithium batteries prepared in this application has good thermal stability, reduces the phenomenon of thermal shrinkage of the diaphragm at high temperatures, and can also maintain good porosity and permeability, thereby improving the electrochemical stability of the lithium battery. By comparing Example 8 with Example 1, it can be seen that by silanizing the nano-ceramic particles using a silane coupling agent, the performance test results show that the air permeability and thermal stability of the prepared aramid diaphragm are significantly improved. This further illustrates that the modification of the nano-ceramic particles by the silane coupling agent reduces the precipitation of the nano-ceramic particles, while enhancing the bonding strength between the aramid slurry and the base film, thereby improving the thermal stability and strength of the aramid diaphragm.

[0084] By comparing Comparative Examples 1-3 with Example 1, it can be seen that the aramid polymer liquid in Comparative Example 1 does not use polyether surfactant, the aramid slurry raw material in Comparative Example 2 does not use Tencel fibrillated slurry, and the aramid slurry raw material in Comparative Example 3 does not use lithium titanium aluminum phosphate nanoparticles. It can be seen from the performance test results that the porosity and thermal stability of the prepared aramid membrane are reduced, which in turn affects the electrochemical performance of the lithium battery.

[0085] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. An aramid separator for lithium batteries, characterized in that: The invention comprises an aramid slurry and a base film. The aramid slurry is coated on both sides of the base film to form an aramid coating. The aramid slurry comprises the following raw materials in parts by weight: 20-40 parts of aramid polymer solution, 5-10 parts of Tencel fibrillated slurry, 1-3 parts of lithium titanium aluminum phosphate nanoparticles, 3-5 parts of nano-ceramic particles, and 8-15 parts of solvent. The aramid polymer solution is generated by polymerization reaction of the following raw materials in parts by weight: 1-3 parts of p-phenylenediamine, 60-80 parts of a polar solvent, 5-10 parts of terephthaloyl chloride, 1-3 parts of 3,4'-diaminodiphenyl ether, 1-3 parts of o-chloro-p-phenylenediamine, and 0.5-1 part of a polyether surfactant. The Tencel fibrillated pulp is made by refining and fibrillating Tencel fibers as raw materials, and the beating degree of the Tencel fibrillated pulp is 75-85°SR; The nano-ceramic particles are silanized and modified using a silane coupling agent. The modification method comprises the following specific steps: mixing the nano-ceramic particles with the silane coupling agent and toluene, heating to 70-80° C. and stirring evenly, washing and drying to obtain silanized modified nano-ceramic particles.

2. The aramid separator for lithium battery according to claim 1, characterized in that The polyether surfactant is one of polyethylene glycol, polypropylene oxide and polytetramethylene ether glycol.

3. The aramid separator for lithium battery according to claim 1, characterized in that The solvent is a complex of a dispersant solvent and a cosolvent, the dispersant solvent is at least one of dimethylacetamide, dimethylformamide, dimethyl sulfoxide, and acetone, and the cosolvent is at least one of calcium chloride, lithium chloride, and potassium hydroxide.

4. The aramid separator for lithium battery according to claim 1, characterized in that The nano ceramic particles are at least one of nano silicon dioxide, nano titanium dioxide and nano aluminum oxide.

5. The aramid separator for lithium battery according to claim 1, characterized in that The thickness of the aramid coating is 3-8 μm, and the thickness of the base film is 5-20 μm.

6. A method for preparing an aramid separator for a lithium battery according to any one of claims 1 to 5, characterized in that: The specific steps include: P-phenylenediamine, 3,4'-diaminodiphenyl and o-chloro-p-phenylenediamine are uniformly mixed, a polar solvent is added, and the mixture is stirred and dissolved at 10-30°C under the protection of nitrogen. The mixture is then cooled to -5-0°C, terephthaloyl chloride and a polyether surfactant are added, and the mixture is stirred and reacted to obtain a reaction mixture. The pH of the reaction mixture is adjusted to obtain an aramid polymer solution. Aramid polymer liquid, Tencel fibrillated pulp, lithium titanium aluminum phosphate nanoparticles, nano-ceramic particles and solvent are mixed, stirred and dissolved to obtain aramid slurry, and then the aramid slurry is coated on both sides of the base film and dried to form an aramid coating to obtain an aramid separator for lithium batteries.

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