Lightweight high-heat-resistance high-wettability lithium battery diaphragm and preparation method thereof

Abstract

The invention discloses a light-weight lithium battery diaphragm with high heat resistance and high wettability and a preparation method thereof.The light-weight lithium battery diaphragm with high heat resistance and high wettability comprises a base membrane and a coating on the base membrane, and the coating comprises porous aluminum oxide, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate; the porous aluminum oxide, the carboxymethylated nanocellulose, the acetylated nanocellulose, the polyurethane, the sodium hexametaphosphate and the ammonium polyacrylate cooperate to improve the liquid absorption rate, the liquid retention rate, the peel strength, the ionic conductivity, the heat resistance and the wettability of the diaphragm, and meanwhile, the water content of the diaphragm is reduced. The density of the porous aluminum oxide, the carboxymethylated nanocellulose and the acetylated nanocellulose is relatively low, so that the diaphragm is light in weight.

Description

A lightweight, heat-resistant, and highly wettable lithium battery separator and its preparation method Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically relating to a lightweight, heat-resistant, and highly wettable lithium battery separator and its preparation method. Background Technology

[0002] With increasingly severe environmental problems, more and more new energy projects are attracting social attention, among which electric vehicles are particularly favored. Lithium-ion batteries, as the core power source of electric vehicles, are widely used in the new energy field due to their advantages such as high energy density and long cycle life. The separator, as a key component of lithium-ion batteries, directly affects the safety and cycle stability of the battery. Existing separators are generally ceramic separators, often made by coating a base membrane surface with a slurry formed by combining ceramic particles (such as alumina and silicon dioxide) with a binder. This preparation method has the following shortcomings: First, the bonding force between ceramic particles and the base membrane is weak, as is the bonding force between ceramic particles, making the coating prone to detachment during lithium-ion battery charging and discharging, leading to increased internal resistance and affecting the battery's long-term cycle life and safety. Second, poor wettability limits the separator's electrolyte retention capacity and reduces ion conduction efficiency, affecting the battery's rate performance and cycle life. Third, the separator is prone to shrinkage under high-temperature environments, posing a short-circuit risk to the lithium-ion battery. Furthermore, the high areal density of traditional ceramic separators increases the non-active mass of the battery. Summary of the Invention

[0003] To address the shortcomings of existing technologies, the present invention aims to provide a lightweight, heat-resistant, and highly wettable lithium battery separator.

[0004] Another object of the present invention is to provide a method for preparing the above-mentioned lightweight, heat-resistant, and highly wettable lithium battery separator.

[0005] The objective of this invention is achieved through the following technical solution.

[0006] A lightweight, heat-resistant, and highly wettable lithium-ion battery separator includes: a base film and a coating on the base film. The coating comprises: porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate, and ammonium polyacrylate. By mass parts, the ratio of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate, and ammonium polyacrylate is (20~35):(0.02~0.2):(0.02~0.2):(1.5~4):(0.035~0.225):(0.025~0.175).

[0007] In the above technical solution, the preferred ratio of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate and ammonium polyacrylate by mass is (25~35):(0.03~0.16):(0.02~0.12):(1.5~4):(0.035~0.225):(0.025~0.175).

[0008] The above-mentioned method for preparing a lightweight, heat-resistant, and highly wettable lithium battery separator includes: coating a slurry onto at least one side of a base film, drying it, obtaining a coating on the base film, and obtaining a lightweight, heat-resistant, and highly wettable lithium battery separator.

[0009] In the above technical solution, the thickness of the single-sided coating is 1~2.5μm.

[0010] In the above technical solution, the coating speed is 30~50m / min.

[0011] In the above technical solution, the drying temperature is 80~120℃ and the drying time is 1~3min.

[0012] In the above technical solution, the particle size of the slurry is: D50 < 0.6 micrometers, D90 < 1.3 micrometers.

[0013] The method for preparing the above-mentioned slurry includes: mixing porous alumina, carboxymethylated nanocellulose (CM-NFC) dispersion, acetylated nanocellulose (Ac-NFC) dispersion, water, adhesive, first dispersant and second dispersant until uniform to obtain a slurry, wherein the adhesive is an aqueous polyurethane (PU) emulsion, the first dispersant is a sodium hexametaphosphate solution, and the second dispersant is an ammonium polyacrylate solution. By mass parts, the ratio of porous alumina, carboxymethylated nanocellulose (CM-NFC) dispersion, acetylated nanocellulose (Ac-NFC) dispersion, water, adhesive, first dispersant and second dispersant is (20~35):(2~5):(2~5):(47~71.2):(5~8):(0.1~0.5):(0.1~0.5).

[0014] In the above technical solution, the solid content of the carboxymethylated nanocellulose (CM-NFC) dispersion is 1~4wt%.

[0015] In the above technical solution, the solid content of the acetylated nanocellulose (Ac-NFC) dispersion is 1~4wt%.

[0016] In the above technical solution, the solid content of the waterborne polyurethane (PU) emulsion is 30~50wt%.

[0017] In the above technical solution, the solid content of the sodium hexametaphosphate solution is 35~45wt%.

[0018] In the above technical solution, the solid content of the ammonium polyacrylate solution is 25~35wt%.

[0019] In the above technical solution, the porous alumina has a D50 of 0.3~0.6μm, a D90 of 0.9~1.3μm, and a porosity of 40~60%; its specific surface area is 50~100m². 2 / g, pore size 30~80nm, density 1.2~2.1 g / cm³ 3 .

[0020] In the above technical solution, the preferred ratio of porous alumina, carboxymethylated nanocellulose (CM-NFC) dispersion, acetylated nanocellulose (Ac-NFC) dispersion, water, adhesive, first dispersant and second dispersant by mass parts is (25~35):(3~4):(2~3):(55~65):(5~8):(0.1~0.5):(0.1~0.5).

[0021] The method for preparing the above-mentioned slurry includes the following steps:

[0022] Step 1: Mix the first dispersant, water, and porous alumina until homogeneous to obtain the first solution;

[0023] In step 1, the first dispersant, water, and porous alumina are mixed and stirred at room temperature until homogeneous to obtain the first solution. The rotation speed of the stirrer is 1500~3100 r / min, the revolution speed is 20~50 r / min, and the stirring time is 10~25 min.

[0024] Step 2: Mix the first solution, carboxymethylated cellulose nanoparticles (CM-NFC) dispersion, acetylated cellulose nanoparticles (Ac-NFC) dispersion, and the second dispersant until homogeneous to obtain the second solution;

[0025] In step 2, the first solution, carboxymethylated cellulose nanoparticles (CM-NFC) dispersion, acetylated cellulose nanoparticles (Ac-NFC) dispersion, and the second dispersant are mixed and sonicated at room temperature until homogeneous to obtain the second solution. The sonication frequency is 10~50kHz, and the sonication time is 20~40min.

[0026] Step 3: Mix the second solution and adhesive until homogeneous to obtain a slurry.

[0027] In step 3, the second solution and adhesive are mixed and simultaneously ultrasonicated and stirred for 10-20 minutes at room temperature and under vacuum until homogeneous, resulting in a slurry. The vacuum level is 0.06-0.08 kPa. The ultrasonic frequency is 5-8 kHz, the rotation speed of the stirring is 1000-3800 r / min, and the revolution speed is 20-40 r / min.

[0028] Applications of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate, and ammonium polyacrylate to synergistically improve the liquid absorption rate, liquid retention rate, peel strength, and / or ionic conductivity of diaphragms.

[0029] Application of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate and ammonium polyacrylate to synergistically improve the heat resistance of membranes.

[0030] Application of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate and ammonium polyacrylate to synergistically improve membrane wettability.

[0031] The application of porous alumina, carboxymethylated nanocellulose (CM-NFC), acetylated nanocellulose (Ac-NFC), polyurethane (PU), sodium hexametaphosphate and ammonium polyacrylate in synergistic reduction of membrane water content.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] 1. Carboxymethylated cellulose nanofibers (CM-NFC) and acetylated cellulose nanofibers (Ac-NFC) possess high aspect ratios and abundant surface functional groups. CM-NFC and Ac-NFC are deeply entangled within porous alumina and fill its pores, while also becoming physically entangled with the molecular chains of the adhesive, forming a three-dimensional nanofiber network. This prevents the coating from detaching during charge-discharge cycles, and the three-dimensional nanofiber network maintains structural integrity at high temperatures, improving the membrane's heat resistance. Furthermore, the carboxyl and hydroxyl groups of CM-NFC form multiple hydrogen bonds with the hydroxyl groups on the alumina surface and the functional groups of the base membrane, enhancing interfacial adhesion and solving the problem of insufficient peel strength between the coating and the base membrane.

[0034] 2. Carboxymethylated cellulose nanoparticles (CM-NFC) are rich in negatively charged carboxymethyl anionic groups (-CH2COO) on their surface. -The acetylated cellulose nanofibers (Ac-NFC) form strong hydrogen bonds and ion-dipole interactions with polar molecules in the electrolyte, achieving instantaneous and complete wetting of the membrane and significantly reducing the contact angle between the electrolyte and the membrane. Simultaneously, the acetylated cellulose nanofibers (Ac-NFC) groups (acetyl groups (-OOCCH3)) possess a certain degree of hydrophobicity. The synergistic effect of Ac-NFC and carboxymethylated cellulose nanofibers (CM-NFC) can regulate the overall liquid absorption rate and liquid retention capacity of the membrane, preventing excessive swelling from affecting the membrane's mechanical strength, and also facilitating uniform lithium-ion transport at the interface. The porous structure of the porous alumina provides a large specific surface area and capillary force, which helps to adsorb and store more electrolyte.

[0035] 3. Porous alumina has the advantage of low density. Compared with solid alumina, porous alumina is lighter in weight while providing the same volume of support. Carboxymethylated nanocellulose (CM-NFC) and acetylated nanocellulose (Ac-NFC) also have relatively low density, which further makes the membrane lightweight. Attached Figure Description

[0036] Figure 1 shows the SEM image of the diaphragm prepared in Example 4. Detailed Implementation

[0037] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0038] The porous alumina has the following particle sizes: D50 = 0.523 μm, D90 = 1.128 μm, and a porosity of 50%; its specific surface area is 70 m². 2 / g, average pore size 70nm, density 1.5 g / cm³ 3 .

[0039] Solid alumina: D50 = 0.513 μm, D90 = 1.216 μm, specific surface area 8 m² 2 / g, density is 3.95g / cm³ 3 .

[0040] Carboxymethylated cellulose nanoparticles (CM-NFC) dispersion: solid content 2 wt%, carboxymethylated cellulose nanoparticles with diameter 5~50 nm, length 1~5 μm, degree of carboxymethyl substitution (DS) 0.5, Shenzhen Cellu CM-20 Technology Co., Ltd.

[0041] Acetylated cellulose nanoparticles (Ac-NFC) dispersion: solid content 2 wt%, acetylated cellulose nanoparticles with diameter 5~50 nm, length 1~5 μm, degree of acetyl substitution (DS) 0.5, Shenzhen CelluAc-NFC Technology Co., Ltd., product model: CelluAc-NFC-001.

[0042] Waterborne polyurethane (PU) emulsion: Yantai Daocheng Chemical Co., Ltd., model: DC-4500, solid content: 45%.

[0043] Sodium hexametaphosphate solution: Hubei Xingfa Chemical Group, model: XF-SHMP-L40, solid content 40wt%.

[0044] Ammonium polyacrylate solution: Shandong Xinjinghe Chemical Technology Co., Ltd., model PA30, solid content 30wt%.

[0045] Liquid absorption rate test: Cut a diaphragm sample (3cm × 3cm, avoiding edge defects), place it in an environment of 23~27℃ and 40~50%RH for 2 hours, and weigh it as m0 (accuracy 0.1mg). Completely immerse the sample in the electrolyte at room temperature and let it stand for 30 minutes (to ensure sufficient liquid absorption and no air bubbles remain). Gently absorb excess electrolyte from the surface of the sample with a dust-free filter paper (only absorb the surface, do not squeeze the inside of the diaphragm), and then weigh it immediately and record it as m1. Liquid absorption rate (%) = (m1-m0) / m0 × 100%. Perform 3 parallel tests and take the average value.

[0046] Liquid retention rate test (centrifugation method): Place the sample (mass m1) after the above liquid absorption rate test into a centrifuge tube (with filter paper at the bottom to prevent direct contact between the sample and the tube wall). Centrifuge at 23~27℃ and 3000 rpm for 5 minutes. After centrifugation, remove the sample and gently aspirate the surface electrolyte again. Weigh the sample and record the weight as m2. Liquid retention rate (%) = (m2 - m0) / (m1 - m0) × 100%. The liquid retention rate reflects the electrolyte retention capacity of the diaphragm.

[0047] Heat shrinkage rate test: Prepare a diaphragm with dimensions of 18cm × 6cm as a test piece. Suspend one end of the test piece (without tension) in an oven at T℃ for 60 minutes. Remove from the oven and calculate the heat shrinkage rate. T℃ = 150℃ or 180℃. Longitudinal (MD) heat shrinkage rate (%) = (Length of test piece before heat treatment - Length of test piece after heat treatment) / (Length of test piece before heat treatment) × 100%. Transverse (TD) heat shrinkage rate (%) = (Width of test piece before heat treatment - Width of test piece after heat treatment) / (Width of test piece before heat treatment) × 100%.

[0048] Peel strength test: Select a flat diaphragm and cut it into a size of 30mm wide and 200mm long. Apply 3M tape to the coated surface of the diaphragm and press the sample three times at a uniform speed using a standard roller. Tear off one end of the 3M transparent tape using a tensile tester to obtain the peel strength.

[0049] Ionic conductivity test: The ionic conductivity test is performed in accordance with the relevant methods for ionic conductivity test specified in GB / T 36363-2018. The test conditions in this invention are as follows: test temperature is 40℃ and relative humidity is 45~50%.

[0050] The formula for calculating the wetting rate is: v = h / t, where h is the wetting height (the height to which the electrolyte penetrates the membrane in the vertical direction), in mm, and t is the wetting time, in min.

[0051] Water content: The test standard is GB / T 6283-2008.

[0052] Dual planetary mixer: XFZH-30L.

[0053] In the following examples and comparative examples, the water is pure water.

[0054] In the following examples and comparative examples, the electrolyte is a mixture of electrolyte and solvent, the electrolyte is LiPF6, the concentration of the electrolyte in the electrolyte is 1 mol / L, and the solvent is a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC), with the ratio of EC to DMC being 1:1 by volume.

[0055] In this invention, the base film is a PE film with a thickness of 7 micrometers. It should be noted that other thicknesses of PE film can also be used in the technical solution of this invention.

[0056] Examples 1-3

[0057] A method for preparing a slurry includes the following steps:

[0058] Step 1: Mix the first dispersant, water and porous alumina in a double planetary mixer and stir at room temperature until homogeneous to obtain the first solution. The first dispersant is sodium hexametaphosphate solution. The rotation speed of the mixer is 2000 r / min, the revolution speed is 40 r / min, and the stirring time is 15 min.

[0059] Step 2: Mix the first solution, carboxymethylated cellulose nanoparticles (CM-NFC) dispersion, acetylated cellulose nanoparticles (Ac-NFC) dispersion, and the second dispersant, and sonicate at room temperature until homogeneous to obtain the second solution. The second dispersant is an ammonium polyacrylate solution. The sonication frequency is 20 kHz and the sonication time is 30 min.

[0060] Step 3: Mix the second solution and the adhesive, and simultaneously sonicate and stir for 15 min under room temperature and vacuum conditions until homogeneous to obtain a slurry. The adhesive is an aqueous polyurethane (PU) emulsion, the vacuum degree is 0.07 kPa, the sonication frequency is 5 kHz, the rotation speed of the stirrer is 1500 r / min, and the revolution speed is 30 r / min.

[0061] The ratio of porous alumina, carboxymethylated nanocellulose (CM-NFC) dispersion, acetylated nanocellulose (Ac-NFC) dispersion, water, adhesive, first dispersant, and second dispersant by mass parts is X. X is shown in Table 1.

[0062] Table 1

[0063]

[0064] The particle size of the slurry prepared in Example 1 was: D50 = 0.451 μm, D90 = 1.106 μm. The particle size of the slurry prepared in Example 2 was: D50 = 0.462 μm, D90 = 1.158 μm. The particle size of the slurry prepared in Example 3 was: D50 = 0.481 μm, D90 = 1.173 μm.

[0065] Comparative Example 1

[0066] A method for preparing a slurry is basically the same as that in Example 1, except that “porous alumina” is replaced with “solid alumina”.

[0067] Comparative Example 2

[0068] A method for preparing a slurry is basically the same as that in Example 1, except that acetylated nanocellulose (Ac-NFC) dispersion is not added.

[0069] Comparative Example 3

[0070] A method for preparing a slurry is basically the same as that in Example 1, except that carboxymethylated cellulose nanoparticles (CM-NFC) dispersion is not added.

[0071] Comparative Example 4

[0072] A method for preparing a slurry is basically the same as that in Example 1, except that no first dispersant is added.

[0073] Comparative Example 5

[0074] A method for preparing a slurry is basically the same as that in Example 1, except that a second dispersant is not added.

[0075] Examples 4-6 and Comparative Examples 6-10

[0076] A method for preparing a separator includes: coating a slurry onto a base film at a coating speed of 30 m / min on one side, drawing it into a drying device via a traction roller, drying it at 85°C for 3 min, and obtaining a coating with a single-sided thickness of 2 μm on the base film to obtain a separator (the separators prepared in Examples 4-6 are lightweight, high heat resistance, and high wettability lithium battery separators).

[0077] Table 2

[0078]

[0079] Figure 1 shows the SEM image of the diaphragm prepared in Example 4.

[0080] The thickness, areal density, and air permeability of the membranes prepared in Examples 4-6 and Comparative Examples 6-10 are shown in Table 3.

[0081] The liquid absorption rate, liquid retention rate, peel strength, heat shrinkage rate (150℃ / 1h(%)-MD, 150℃ / 1h(%)-TD, 180℃ / 1h(%)-MD, 180℃ / 1h(%)-TD), water content, electrolyte contact angle, wetting rate and ionic conductivity of the diaphragms prepared in Examples 4-6 and Comparative Examples 6-10 are shown in Table 4.

[0082] Table 3

[0083]

[0084] Table 4

[0085]

[0086] Acetylated cellulose nanoparticles (Ac-NFC) possess a certain degree of hydrophobicity, which can inhibit the hygroscopicity of carboxymethylated cellulose nanoparticles (CM-NFC), reducing the water content of the membrane. With the synergistic effect of sodium hexametaphosphate and ammonium polyacrylate, the membrane exhibits optimal overall performance. The membrane prepared in Example 4 demonstrates the best performance.

[0087] The present invention has been described above by way of example. It should be noted that any simple modifications, alterations or other equivalent substitutions that can be made by those skilled in the art without creative effort without departing from the core of the present invention fall within the protection scope of the present invention.

Claims

1. A lightweight, heat-resistant, and highly wettable lithium battery separator, characterized in that, include: The base film and the coating on the base film, the coating comprising: porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate, wherein the ratio of porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate by mass parts is (20~35):(0.02~0.2):(0.02~0.2):(1.5~4):(0.035~0.225):(0.025~0.175).

2. The lightweight, high-heat-resistant, and high-wetness lithium battery separator according to claim 1, characterized in that, Porous alumina has a D50 of 0.3–0.6 μm, a D90 of 0.9–1.3 μm, and a porosity of 40–60%; its specific surface area is 50–100 m² / g. 2 / g, pore size 30~80nm, density 1.2~2.1 g / cm³ 3 .

3. The method for preparing the lightweight, high-heat-resistant, and high-wetness lithium battery separator as described in claim 1, characterized in that, include: The slurry is coated on at least one side of the base film and dried to obtain a coating on the base film, resulting in a lightweight, heat-resistant, and highly wettable lithium battery separator.

4. The preparation method according to claim 3, characterized in that, The thickness of the single-sided coating is 1~2.5μm.

5. A method for preparing a slurry, characterized in that, include: Porous alumina, carboxymethylated nanocellulose dispersion, acetylated nanocellulose dispersion, water, adhesive, first dispersant and second dispersant are mixed until homogeneous to obtain a slurry. The adhesive is an aqueous polyurethane emulsion, the first dispersant is a sodium hexametaphosphate solution and the second dispersant is an ammonium polyacrylate solution. The ratio of porous alumina, carboxymethylated nanocellulose dispersion, acetylated nanocellulose dispersion, water, adhesive, first dispersant and second dispersant by mass is (20~35):(2~5):(2~5):(47~71.2):(5~8):(0.1~0.5):(0.1~0.5).

6. The method according to claim 5, characterized in that, The solid content of the carboxymethylated nanocellulose dispersion is 1-4 wt%; the solid content of the acetylated nanocellulose dispersion is 1-4 wt%; the solid content of the aqueous polyurethane emulsion is 30-50 wt%; the solid content of the sodium hexametaphosphate solution is 35-45 wt%; and the solid content of the ammonium polyacrylate solution is 25-35 wt%.

7. Application of porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate to synergistically improve the liquid absorption rate, liquid retention rate, peel strength and / or ionic conductivity of diaphragms.

8. Application of porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate to synergistically improve the heat resistance of diaphragms.

9. Application of porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate in synergistic improvement of membrane wettability.

10. The application of porous alumina, carboxymethylated nanocellulose, acetylated nanocellulose, polyurethane, sodium hexametaphosphate and ammonium polyacrylate in synergistic reduction of membrane water content.

Images