Aramid pulp and method of making, battery separator and method of making and use

Abstract

This application provides an aramid slurry and its preparation method, a battery separator and its preparation method, and its application. The aramid slurry comprises aramid fibers, a non-protic strongly polar solvent, and a co-solvent. The co-solvent has a pH value of 5–7.5 at 25°C and 101.325 kPa; the rotational viscosity of the aramid slurry is 500 mPa·s–5000 mPa·s. The aramid slurry of this application eliminates the need for strong alkaline co-solvents such as sodium hydroxide or potassium hydroxide to dissolve the aramid, avoiding the damage to aramid molecules caused by such co-solvents, extending the operating time window, and improving the stability of the slurry. The slurry can be stably stored for more than 168 hours, reducing the difficulty of production operations and the investment in personnel and equipment, thus facilitating large-scale production. Furthermore, the rotational viscosity of the aramid slurry formed in this application has a suitable range; within this range, the slurry not only exhibits good stability but also provides ideal separator performance.

Description

Technical Field

[0001] This application belongs to the field of battery separator technology, specifically relating to an aramid slurry and its preparation method, a battery separator and its preparation method, and its application. Background Technology

[0002] In recent years, lithium-ion batteries have been considered the most promising large-scale power and energy storage devices, and they are increasingly widely used in various fields such as power batteries, consumer 3C batteries, and large-scale energy storage systems. As one of the key components of a battery, the battery separator serves both to separate the positive and negative electrodes and to provide a rapid migration channel for electrolyte ions.

[0003] As a key material in batteries, the properties of the battery separator are closely related to the battery's electrochemical performance. Currently, commercially available battery separators are mainly polyolefin separators, which have poor thermal stability, poor wettability to electrolytes, and low ionic conductivity. Furthermore, battery separators are formed by coating with a separator slurry, and the properties of the slurry are also closely related to the performance of the separator. Summary of the Invention

[0004] This application provides an aramid slurry and its preparation method, a battery separator and its preparation method, and its application, which can at least solve one of the above-mentioned technical problems.

[0005] The first aspect of this application provides an aramid slurry, comprising aramid, a non-protic strongly polar solvent, and a co-solvent. The co-solvent has a pH value of 5 to 7.5 at 25°C and 101.325 kPa. The rotational viscosity of the aramid slurry is 500 mPa·s to 5000 mPa·s, and can be selected from 1000 mPa·s to 3500 mPa·s, for example, any value within the range of 1000, 1200, 1328, 1500, 1552, 1669, 1943, 2000, 2500, 2895, 3127, 3300, 3500, or 1000 mPa·s to 3500 mPa·s.

[0006] In a feasible embodiment of the first aspect of this application, the aramid slurry has a Δμ ≤ (500~2000) mPa·s, where Δμ=μ2-μ1, μ1 is the rotational viscosity of the aramid slurry after being sealed in a centrifuge tube at room temperature and placed for one day at a relative humidity of 50%~60%, and μ2 is the rotational viscosity of the aramid slurry after being sealed in a centrifuge tube at room temperature and placed for 7 days at a relative humidity of 50%~60%.

[0007] In a feasible embodiment of the first aspect of this application, μ2 = 1000 mPa·s to 5000 mPa·s, optionally 2000 mPa·s to 4000 mPa·s; and / or; μ1 = 500 mPa·s to 3000 mPa·s, optionally 1000 mPa·s to 2000 mPa·s.

[0008] In a feasible embodiment of the first aspect of this application, the solid content of the aramid slurry is 5.3% to 8%.

[0009] In a feasible embodiment of the first aspect of this application, the aprotic strong polar solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid and acetic acid, and may be selected as N-methylpyrrolidone.

[0010] In a feasible embodiment of the first aspect of this application, the co-solvent includes one or more of lithium chloride, sodium chloride, and calcium chloride, and may be selected as calcium chloride.

[0011] In a feasible embodiment of the first aspect of this application, the aramid slurry further includes a capping agent, which includes an amino group or an acyl chloride group.

[0012] In a feasible embodiment of the first aspect of this application, the capping agent includes one or more of 4-aminobenzidine, p-methylaniline, butylamine, aniline, and benzoyl chloride.

[0013] A second aspect of this application provides a method for preparing an aramid slurry, comprising:

[0014] p-phenylenediamine, a capping agent, and terephthaloyl chloride are reacted in solution to obtain an aramid sizing agent; the capping agent includes an amino group or an acyl chloride group.

[0015] In a feasible embodiment of the second aspect of this application, the mass ratio of the sum of the masses of p-phenylenediamine and terephthaloyl chloride to the mass of the capping agent is (99-1.2):1, optionally (15-25):1, and further optionally 19:1.

[0016] In a feasible embodiment of the second aspect of this application, the preparation of the aramid slurry includes:

[0017] Terephthaloyl chloride and a capping agent are mixed and stirred in a solution, and then reacted with p-phenylenediamine to obtain aramid sizing; or;

[0018] p-phenylenediamine and a capping agent are mixed and stirred in a solution, and then mixed with terephthaloyl chloride to react and obtain aramid slurry.

[0019] In a feasible embodiment of the second aspect of this application, p-phenylenediamine is mixed and stirred in solution under an inert gas environment for 1 min to 30 min, then a capping agent is added under ice bath conditions, and terephthaloyl chloride is added after mixing and stirring for 1 min to 20 min. The mixture is then reacted for 0.01 h to 2 h to obtain aramid slurry. The mixing and stirring time can be selected as 5 min to 20 min, and the reaction time can be selected as 0.1 h to 1 h.

[0020] In a feasible embodiment of the second aspect of this application, the solution includes an aprotic strong polar solvent and a co-solvent; optionally, the aprotic strong polar solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid and acetic acid; optionally, the co-solvent includes one or more of lithium chloride, sodium chloride and calcium chloride.

[0021] In a feasible embodiment of the second aspect of this application, the preparation of the solution includes adding dry calcium chloride to an N-methylpyrrolidone solution and stirring for 0.1 h to 3 h at a temperature of 10 °C to 120 °C to obtain a solution; the optional temperature is 25 °C to 55 °C and the stirring time is 0.5 h to 2 h.

[0022] A third aspect of this application provides a battery separator, comprising a base film and a coating applied to at least one side of the base film, the coating comprising aramid fiber; the battery separator exhibits a weight loss rate W at 500°C under thermogravimetric analysis testing mode. 500 satisfy:

[0023] W 500 =20%~70%,

[0024] Among them, W 500 =W2 / W1, where W2 is the mass of the battery separator at 500℃ and W1 is the initial mass of the battery separator.

[0025] In a feasible embodiment of the third aspect of this application, the mass change rate of the battery separator at 400°C to 600°C is <2%; and / or;

[0026] The mass change rate of the battery separator at 500℃~600℃ is <1%.

[0027] In a feasible embodiment of the third aspect of this application, the mass percentage of aramid in the coating is greater than or equal to 99%.

[0028] In a feasible embodiment of the third aspect of this application, the battery separator satisfies at least one of the following characteristics:

[0030] a. The coating thickness is 1μm to 50μm;

[0031] b. The liquid absorption rate of the battery separator is 100%–300%;

[0032] c. The liquid retention rate of the battery separator is 50%–200%;

[0033] d. The ionic conductivity of the battery separator is 1×10⁻⁴ S / cm~1×10⁻³ S / cm;

[0034] e. The lithium-ion transference number of the battery separator is 0.3–0.8;

[0035] f. The thermal shrinkage rate of the battery separator after heating at 180°C for 1 hour is 30%–70%;

[0036] h. The thermal shrinkage rate of the battery separator after heating at 130°C for 1 hour is 2% to 10%;

[0037] i. The elongation at break of the battery separator is 80%–150%;

[0038] j. The tensile strength of the battery separator is 100MPa~150MPa.

[0039] The fourth aspect of this application provides a method for preparing a battery separator, wherein the aramid slurry provided in the first aspect of this application is coated on at least one side of a base film and cured to obtain a battery separator.

[0040] In a feasible embodiment of the fourth aspect of this application, the curing includes at least one coagulation bath, at least one water wash, and at least one ethanol wash. The solution used in the coagulation bath is a mixture of NMP and water with a volume ratio of (0.6 to 9):1. The soaking time in the coagulation bath is 1 min to 50 min, and the number of soakings includes one or two. The water wash includes pure water or deionized water, and the number of water washes includes one, two, or three. The number of ethanol washes includes one or two.

[0041] In a feasible implementation of the fourth aspect of this application, when the soaking is performed twice, a new coagulation bath solution needs to be replaced.

[0042] The fifth aspect of this application provides an electrochemical battery, including the battery separator provided in the third aspect of this application.

[0043] The sixth aspect of this application provides an electrical device, including the electrochemical battery provided in the fifth aspect of this application. Attached Figure Description

[0044] Figure 1 This is the ionic conductivity diagram of the membrane in Experiment Examples 1-3;

[0045] Figure 2 This is a lithium-ion transport number graph of the membrane in Experiment Example 1;

[0046] Figure 3 This is a scanning electron microscope image of the diaphragm in Experiment Example 1;

[0047] Figure 4 This is a graph showing the thermal shrinkage rate of the diaphragm in Experiment Example 1;

[0048] Figure 5 These are thermogravimetric analysis (TGA) curves of the diaphragm and base membrane in Experimental Example 1 and Example 3. The upper part is the TGA curve, and the lower part is the DTG curve obtained by the first derivative of the upper TGA curve. Detailed Implementation

[0049] To make the inventive objectives, technical solutions, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely illustrative and not intended to limit the scope of this application.

[0050] For simplicity, this paper only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, just as any upper limit can be combined with any other upper limit to form an undefined range. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form an undefined range.

[0051] In the description herein, when a composition is described as containing, comprising, or including a specific component, or when a process is described as containing, comprising, or including a specific process step, it is anticipated that the composition of this application is also primarily composed of or consisting of the said component, and that the process of this application is also primarily composed of or consisting of the said process step.

[0052] Unless otherwise expressly stated, the use of the terms “including,” “contains,” “comprising,” “containing,” and “having” should generally be interpreted as open-ended and non-restrictive.

[0053] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0054] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0055] p-Phenyl terephthalamide (also known as para-aramid, abbreviated as PPTA) is a para-aramid polymer material formed by the condensation polymerization of p-phenylenediamine and terephthaloyl chloride. It has a glass transition temperature above 300℃ and exhibits high modulus and high tensile strength. Using PPTA to coat base films can improve the performance of membranes.

[0056] However, the inventors discovered that common PPTA-coated polyolefin separators are mostly produced using a "top-down" approach, which involves preparing nano- or micron-sized para-aramid short fibers (millimeter and centimeter scale) using various etching techniques before coating. However, this etching and dissolution process requires a large amount of strong alkali as a co-solvent. The alkali solution not only disrupts the hydrogen bonds between PPTA molecules, dissolving solid PPTA, but also breaks the amide bonds within PPTA molecules, causing a decrease in PPTA molecular weight and a deterioration in slurry stability. Therefore, this method not only has strict requirements on the amount of alkali used and a short operating time window, resulting in high production costs, complex processes, and low production efficiency, but also produces poor slurry stability. Consequently, the PPTA-coated base film process is difficult to mass-produce, and the resulting separators exhibit unstable performance, with unsatisfactory ionic conductivity and thermal stability.

[0057] The inventors analyzed that the reason is that the polymerization reaction of PPTA monomers is rapid and releases a lot of heat. It can usually be completed in about 12 minutes to form PPTA with a high degree of polymerization. It is difficult to dissolve in solvents, so it will quickly undergo phase separation, resulting in poor slurry stability, which in turn affects the production and performance of the diaphragm.

[0058] In view of this, after extensive experimental research and demonstration, the inventors have proposed an aramid slurry and its preparation method, a battery separator and its preparation method, and its application in this application.

[0059] The first aspect of this application provides an aramid slurry, comprising aramid, a non-protic strongly polar solvent, and a co-solvent. The co-solvent has a pH value of 5 to 7.5 at 25°C and 101.325 kPa. The rotational viscosity of the aramid slurry is 500 mPa·s to 5000 mPa·s, and can be selected from 1000 mPa·s to 3500 mPa·s, for example, any value within the range of 1000, 1200, 1328, 1500, 1552, 1669, 1943, 2000, 2500, 2895, 3127, 3300, 3500, or 1000 mPa·s to 3500 mPa·s.

[0060] This application's aramid slurry eliminates the need for strong alkaline solvents such as sodium hydroxide and potassium hydroxide to dissolve the aramid, avoiding the damage these solvents can cause to the aramid molecules. This extends the operating time window, improves slurry stability, and allows the slurry to be stored stably for over 168 hours. This reduces the difficulty of production operations and the investment in personnel and equipment, facilitating large-scale production. Furthermore, the rotational viscosity of the aramid slurry formed in this application has a suitable range; within this range, the slurry not only exhibits good stability but also provides ideal diaphragm performance.

[0061] When the viscosity of aramid slurry is low, it may be difficult to coat, or the thermal stability of the coated diaphragm may not differ much from that before coating, and the thermal shrinkage rate of the diaphragm may still be high, resulting in unsatisfactory safety performance. On the other hand, when the viscosity is too high, the aramid slurry is prone to curing, which not only makes it difficult to coat, but also results in an uneven diaphragm coating that is prone to cracking and powdering, thus reducing the performance of the diaphragm.

[0062] In this application, aramid refers to an oligomer composed of fewer repeating units of aromatic polyamide, and may also be called aramid oligomer.

[0063] As can be seen from the preparation method of the slurry provided in the second aspect of this application, in the preparation process of aramid slurry, due to the addition of a capping agent, a portion of the polymer can be capped, blocking the continuous polymerization of PPTA monomers. Therefore, the degree of polymerization of the aramid polymer is lower than that of the traditional aramid polymer without a capping agent. Therefore, it can be called an aramid oligomer.

[0064] In some embodiments, the aramid slurry has a Δμ ≤ (500~2000) mPa·s, for example, it can be any value within the range of 500, 800, 1200, 1000, 1500, 1800, 2000 or 500 mPa·s~2000 mPa·s. Wherein Δμ = μ2 - μ1, μ1 is the rotational viscosity of the aramid slurry after one day of storage in a centrifuge tube at room temperature and relative humidity of 50%~60%, and μ2 is the rotational viscosity of the aramid slurry after seven days of storage in a centrifuge tube at room temperature and relative humidity of 50%~60%.

[0065] In some implementations, μ2 = 1000 mPa·s to 5000 mPa·s, and can be selected from 2000 mPa·s to 4000 mPa·s, for example, it can be any value within the range of 2000, 2400, 2600, 2800, 2895, 3000, 3127, 3500, 3800, 4000 or 2000 mPa·s to 4000 mPa·s; and / or; μ1 = 500 mPa·s to 3000 mPa·s, and can be selected from 1000 mPa·s to 2000 mPa·s, for example, it can be any value within the range of 1200, 1000, 1669, 1500, 1800, 1943, 2000 or 1000 mPa·s to 2000 mPa·s.

[0066] The process of synthesizing aramid slurry in this application involves the reaction of p-phenylenediamine, a capping agent, and terephthaloyl chloride in solution, which is completely different from the "top-down" method. The viscosity of the slurry in this application does not decrease over time, whereas the viscosity of the slurry may increase over time. Experimental results demonstrate that the slurry in this application has good stability. When sealed in centrifuge tubes at room temperature and under a relative humidity of 50%–60%, the rotational viscosity remains within the range of 1000 mPa·s to 5000 mPa·s after 7 days.

[0067] The inventors also discovered that the solids content of the slurry affects the performance of the diaphragm. To reduce the curing time of the aramid slurry and extend the workable time window, the viscosity of the slurry cannot be too high, nor can the solids content be too low. A low solids content will cause sagging during coating, resulting in an uneven coating and less active material per unit area for the same coating thickness, leading to poor diaphragm performance.

[0068] The slurry used to form the coating in this application not only has a moderate viscosity but also a high solids content. In some embodiments, the solids content of the slurry forming the coating is 5.3% to 8%, for example, it can be any value within the range of 5.3%, 5.5%, 5.92%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, or 5.3% to 8%. When the solids content of the slurry forming the coating in this application is within the above range, the resulting coating not only has a suitable thickness but is also uniformly applied, which can enhance the needle penetration strength of the diaphragm and improve its thermal stability.

[0069] In some embodiments, the aprotic strongly polar solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid, and acetic acid, with N-methylpyrrolidone being an option.

[0070] In some embodiments, the co-solvent includes one or more of lithium chloride, sodium chloride, and calcium chloride, with calcium chloride being an option.

[0071] In this application, only a small amount of co-solvent is needed to dissolve the aramid fiber in the slurry to form a stable slurry.

[0072] In some embodiments, the mass percentage of the co-solvent (e.g., calcium chloride) in the aramid sizing is 1% to 3%.

[0073] In some embodiments, the aramid sizing also includes a capping agent, which comprises an amino group or an acyl chloride group.

[0074] In some embodiments, the capping agent includes one or more of 4-aminobenzidine, p-methylaniline, butylamine, aniline, and benzoyl chloride.

[0075] A second aspect of this application provides a method for preparing an aramid slurry, comprising:

[0076] p-phenylenediamine, a capping agent, and terephthaloyl chloride are reacted in solution to obtain an aramid sizing agent; the capping agent includes an amino group or an acyl chloride group.

[0077] This application uses an organic compound that can regulate the reaction rate of the first and second monomers of aramid and the degree of polymerization of aramid as a capping agent to reduce the polymerization rate of p-phenylenediamine and terephthaloyl chloride, and to shorten the molecular chain of the aramid polymer, forming aramid with a lower molecular weight and lower degree of polymerization. This solves the phase separation problem of PPTA slurry in the synthesis step, and avoids the problem of a short operating time window that requires the use of strong alkali to dissolve solid PPTA. This greatly enhances the stability of the slurry, which can be stably stored for more than 168 hours, extending the working time, reducing the difficulty of production operation and the investment in personnel and equipment, and facilitating large-scale production.

[0078] The polymerization of PPTA monomers is rapid and releases a large amount of heat, completing in approximately 12 minutes. The resulting product is insoluble in solvents and undergoes rapid phase separation, leading to poor slurry stability. Compared to directly using aramid fibers and then dissolving them to form a slurry, this application uses a capping agent to reduce the polymerization rate of p-phenylenediamine and terephthaloyl chloride. Furthermore, by capping part of the polymer, it blocks the continuous polymerization of PPTA monomers, forming a low-polymerization-degree aramid fiber with better solubility, thus overcoming the problems of poor solubility and phase separation.

[0079] In a feasible embodiment of the second aspect of this application, the mass ratio of the sum of the masses of p-phenylenediamine and terephthaloyl chloride to the mass of the capping agent is (99-1.2):1, which can be (15-25):1, and more preferably 19:1. For example, it can be any value within the range of 95:5, 96:4, 80:20, 75:25 or (15-25):1.

[0080] In particular, when the mass ratio of the sum of p-phenylenediamine and terephthaloyl chloride to the capping agent in this application is within the above-mentioned range, a slurry with a suitable rotational viscosity and good storage stability can be obtained. When the amount of capping agent added is too high, it excessively inhibits the polymerization effect, resulting in less aramid polymer in the slurry, lower viscosity, poor adhesion of the coating, poor thermal stability, low liquid absorption, and mediocre lithium-ion transport performance. When the amount of capping agent added is too low, the inhibition effect is poor, easily forming aramid polymers with high viscosity, which are easy to cure and have a short shelf life.

[0081] The inventors also discovered that the timing or sequence of adding the capping agent affects the properties of the slurry. In some embodiments, the step of reacting p-phenylenediamine, the capping agent, and terephthaloyl chloride in solution to obtain the aramid slurry includes:

[0082] The p-phenylenediamine and the capping agent are mixed and stirred in a solution, and then reacted with terephthaloyl chloride to obtain a slurry; or;

[0083] Terephthaloyl chloride and a capping agent are mixed and stirred in a solution, and then mixed and reacted with p-phenylenediamine to obtain a slurry.

[0084] By first mixing the capping agent with one of p-phenylenediamine and terephthaloyl chloride, and then adding the other substance, the rapid reaction between p-phenylenediamine and terephthaloyl chloride can be more effectively prevented, thus forming the desired aramid fiber.

[0085] For example, in some embodiments, p-phenylenediamine is mixed and stirred in solution under an inert gas environment for 1 min to 30 min, then a capping agent is added under ice bath conditions, and terephthaloyl chloride is added after mixing and stirring for 1 min to 20 min. The mixture is then reacted for 0.01 h to 2 h to obtain aramid slurry. The mixing and stirring time can be selected as 5 min to 20 min, and the reaction time can be selected as 0.1 h to 1 h.

[0086] By controlling the aforementioned time points, aramid slurry with better stability can be obtained.

[0087] In some embodiments, the solution includes an aprotic strongly polar solvent and a co-solvent. Optionally, the aprotic strongly polar solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid, and acetic acid; optionally, the co-solvent includes one or more of lithium chloride, sodium chloride, and calcium chloride.

[0088] In this application, aramid with a low degree of polymerization is formed directly by the reaction of p-phenylenediamine, end-capping agent, and terephthaloyl chloride in NMP solution. It has good solubility and does not require the use of strong alkaline co-solvents such as sodium hydroxide or potassium hydroxide. This avoids the damage of such co-solvents to aramid molecules and improves the stability of the slurry.

[0089] In some embodiments, the preparation of the solution includes adding dry calcium chloride to an N-methylpyrrolidone solution and stirring for 0.1 h to 3 h at a temperature of 10 °C to 120 °C to obtain a solution; optionally, the temperature is 25 °C to 55 °C and the stirring time is 0.5 h to 2 h.

[0090] In some embodiments, the aramid slurry may also include one or more of a dispersant, a defoamer, and a leveling agent.

[0091] A third aspect of this application provides a battery separator, comprising a base film and a coating covering at least one side of the base film, the coating comprising aramid fiber; the battery separator exhibits a weight loss rate W at 500°C under thermogravimetric analysis testing mode. 500 satisfy:

[0092] W 500 = 20% to 70% (optional 30% to 60%, for example, it can be any value within the range of 20%, 30%, 40%, 50%, 55%, 60%, 65%, 70%, or 20% to 70%),

[0093] Among them, W 500 =W2 / W1, where W2 is the mass of the battery separator at 500℃ and W1 is the initial mass of the battery separator.

[0094] The aramid fibers in the coating of the battery separator of this application have a relatively low degree of polymerization. This not only reduces the rate of phase separation during the coating process, resulting in good stability and an extended operating time window, but also, during the curing or drying process, as the solvent evaporates, the aramid molecules continuously rearrange, creating localized aramid-rich and solvent-rich phases, thus forming a porous membrane structure. This facilitates electrolyte penetration, shortens the lithium-ion transport path, and increases the lithium-ion transport rate, thereby improving the ionic conductivity of the separator. Furthermore, the aramid coating of this application can improve the thermal stability of the formed battery separator, with a weight loss rate W at 500℃. 500 With a conductivity of 20% to 70%, a battery separator with high ionic conductivity, good thermal stability, and a long operating time window can be obtained, which is conducive to large-scale production.

[0095] In some embodiments, the mass change rate of the battery separator at 400°C to 600°C is <2%, optionally <1.5%, for example, it can be any value within the range of 0.5%, 0.6%, 0.8%, 1.0%, 1.2%, 1.3%, 1.5%, 1.7%, 1.8%, 1.9%, or <2%.

[0096] The battery separator in this application exhibits good thermal stability at high temperatures. Figure 5As can be seen, in some embodiments, the mass change rate is small (<2%) between 400℃ and 600℃, while the mass change rate of the uncoated base film is close to 3% between 400℃ and 500℃. At 470℃ to 480℃, the base film undergoes a violent chemical reaction, resulting in rapid decomposition, a rapid decrease in thermal stability, and a large mass change rate. The separator composed of the aramid coating in this application consistently exhibits a mass change rate of less than 2% between 400℃ and 600℃, without any drastic mass change. This is partly due to the good stability of the aramid coating, which can absorb more heat, and partly due to the strong adhesion between the aramid coating and the base film in this application, which slows down the decomposition rate of the base film. This improves the overall thermal stability of the battery separator and prevents rapid heat accumulation at high temperatures, which could affect battery safety performance.

[0097] In some embodiments, the mass change rate of the battery separator at 500°C to 600°C is <1%, for example, it can be any value in the range of 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 0.9%, 0.95%, or <1%.

[0098] from Figure 5 It can also be seen that in some embodiments, the mass change rate of the battery separator of this application is <1% at 500℃ to 600℃. Among them, the main decomposition at 550℃ to 600℃ is the aramid coating. From the mass change rate of <1%, it can be inferred that even at higher temperatures, the aramid coating of this application decomposes slowly. This is because the degree of polymerization of aramid is relatively small, and the thermal motion of the molecular chains is relatively less intense. Therefore, there will be no drastic mass change, the mass change rate is small, and the high-temperature thermal stability is better.

[0099] In some embodiments, the aramid may be one or a combination of para-aramid and meta-aramid, with para-aramid being the preferred option.

[0100] In some embodiments, the main material of the coating is aramid, and the mass percentage of aramid in the coating is greater than or equal to 99%.

[0101] The membrane with an aramid content within the above range has good compatibility and strong adhesion with the organic base membrane, and will not peel off or shed powder, thus exhibiting good stability.

[0102] This application enables the separator to possess excellent physicochemical properties and electrochemical performance by coating the surface of the base membrane with a coating including aramid fibers. For example, in some embodiments, the separator satisfies at least one of the following characteristics:

[0103] a. The coating thickness is 1μm to 50μm, with 3μm to 8μm being optional;

[0104] b. The liquid absorption rate of the battery separator is 100%–300%, and 150%–200% can be selected;

[0105] c. The liquid retention rate of the battery separator is 50%–200%, with 100%–150% being optional;

[0106] d. The ionic conductivity of the battery separator is 1×10⁻⁶. -4 S / cm~1×10 -3 S / cm, 5×10 available -4 S / cm~1×10 -3 S / cm;

[0107] e. The lithium-ion transference number of the battery separator is 0.3 to 0.8, and can be selected as 0.5 to 0.8;

[0108] f. The heat shrinkage rate of the battery separator after heating at 180°C for 1 hour is 30%–70%, with 40%–65% being optional;

[0109] h. The heat shrinkage rate of the battery separator after heating at 130°C for 1 hour is 2% to 10%, and can be selected as 5% to 9.5%;

[0110] i. The elongation at break of the battery separator is 80%–150%, with 90%–110% being optional;

[0111] j. The tensile strength of the battery separator is 100MPa to 150MPa, and 110MPa to 130MPa is optional.

[0112] Alternatively, by controlling certain conditions, appropriate amounts of ceramic materials, PVDF, or PVDF-HFP can be added to the coating of this application to form a composite film.

[0113] In some embodiments, the coating further includes a ceramic material and one or a combination of PVDF, PVDF-HFP; optionally, the ceramic particles include one or more of alumina, boehmite, silicon dioxide, magnesium oxide, zirconium oxide, titanium dioxide, calcium oxide, aluminum nitride, boron nitride, barium sulfate, calcium fluoride, barium fluoride, and barium titanate.

[0114] The fourth aspect of this application provides a method for preparing a battery separator, wherein the aramid slurry provided in the first aspect of this application is coated on at least one side of a base film and cured to obtain a battery separator.

[0115] In a feasible embodiment of the fourth aspect of this application, the curing includes at least one coagulation bath, at least one water wash, and at least one ethanol wash. The solution used in the coagulation bath is a mixture of NMP and water with a volume ratio of (0.6 to 9):1. The soaking time in the coagulation bath is 1 min to 50 min, and the number of soakings includes one or two. The water wash includes pure water or deionized water, and the number of water washes includes one, two, or three. The number of ethanol washes includes one or two.

[0116] The coagulation bath solution used in this application is a neutral organic solution, not a strong alkaline solution, which is environmentally and equipment-friendly.

[0117] In a feasible implementation of the fourth aspect of this application, when the soaking is performed twice, a new coagulation bath solution needs to be replaced.

[0118] The fifth aspect of this application provides an electrochemical battery, including the battery separator provided in the third aspect of this application.

[0119] The sixth aspect of this application provides an electrical device, including the electrochemical battery provided in the fifth aspect of this application.

[0120] Example

[0121] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0122] Experimental Example 1

[0123] This experimental example provides a battery separator with high stability modified para-aramid end-capped by aniline, and its preparation process is as follows:

[0124] Preparation of aramid sizing agent: 2g of calcium chloride was added to 100mL of NMP and stirred for 30min at 50℃; an inert gas was passed into the solution at room temperature; 1.73g of p-phenylenediamine was added to the solution and stirred for 10min at room temperature; the solution was cooled to 0℃ in an ice bath, and 256μL of aniline (capping agent) was added, followed by 3.271g of terephthaloyl chloride after 5min; after 12min, a highly stable modified para-aramid sizing agent capped with the capping agent was obtained, with a solid content of 5.92%. The mass ratio of the sum of p-phenylenediamine and terephthaloyl chloride to the capping agent was 95:5. All stirring was carried out at 800rpm / min, and the density of aniline was 1.02g / cm³. 3 .

[0125] Coating: After the above slurry was left to stand for 1 day, it was rolled onto one side of the base film using a wire rod. After standing in the air for 3 minutes, it was immersed in a coagulation bath solution of NMP:water = 6:4 (volume ratio) for 10 minutes. After removal, it was washed twice with deionized water and once with ethanol, and then dried in an oven at 100°C for 10 minutes. The above steps were repeated to coat the other side of the base film with the slurry, resulting in a battery separator with aniline end-capped high stability modified para-aramid with a single-sided thickness of 4 μm (±1 μm).

[0126] The diaphragm obtained in Experiment 1 was tested, and some test results are as follows: Figures 1-5 As shown. From Figures 1-2 It is evident that the membrane in Experimental Example 1 exhibits high ionic conductivity and a relatively ideal lithium-ion transference number. From... Figure 3 Scanning electron microscopy revealed that the membrane in Experimental Example 1 had a porous structure, which facilitated electrolyte permeation and thus improved the ionic conductivity of the membrane. Figure 4 It is evident that the diaphragm in this experimental example exhibits a small thermal shrinkage rate at 180℃. From... Figure 5 As can be seen, the diaphragm in this experiment lost approximately 60% of its mass at 500℃, about 1.5% of its mass at 400℃ to 500℃, and about 0.2% of its mass at 500℃ to 600℃, demonstrating its good high-temperature thermal stability.

[0127] Experimental Example 2 differed from Experimental Example 1 in that the timing of the aniline capping agent's addition was changed during slurry preparation; it was added 5 minutes after the addition of terephthaloyl chloride instead of before. However, the resulting slurry solidified within 0.5 hours and could not be coated onto the base film.

[0128] In Experiment 3, the difference from Experiment 1 is that the capping agent is benzoyl chloride, the amount of which is 208.4 mg, the mass ratio of the sum of p-phenylenediamine and terephthaloyl chloride to the capping agent is 96:4, and the solid content is 6.05%.

[0129] Example 4 uses the slurry prepared in Example 1, but with the difference that the coating contains silica ceramic particles with a particle size of 30 nm, and the mass ratio of aramid to nano-silica particles is 98:2. The specific steps are as follows: Nano-silica is placed in a muffle furnace and heated from room temperature to 800°C at a heating rate of 5°C / min, and held for 2 hours. 102.1 mg of calcined nano-silica is added to 100 mL of the slurry obtained in Example 1 and sonicated for 30 minutes. This yields a modified para-aramid slurry containing ceramic particles. The coating procedure is the same as in Example 1. The coating thickness is 5 μm.

[0130] In Experiment 5, the difference from Experiment 1 is that the mass ratio of the sum of p-phenylenediamine and terephthaloyl chloride to the capping agent is 70:30, or 2.33:1. The resulting slurry has a viscosity <100 mPa·s and cannot be coated onto the base film (viscosity less than 100 cannot form a film on the base film surface).

[0131] Experimental Example 6 differs from Experimental Example 1 in that no sealing agent is used in the preparation of the slurry. The resulting slurry solidifies within 0.5 hours, resulting in a short operating time window, making it impossible to coat onto the base film (it solidifies within 30 minutes, making film formation impossible).

[0132] Test section

[0133] Method for testing the rotational viscosity of slurry:

[0134] The test was conducted using the Zhonghu Yixin SNB-1 automatic scanning rotational viscometer. The rotor was inserted into the adhesive, ensuring that the rotor's liquid level mark was level with the adhesive level. Automatic identification was selected, and a suitable rotor was replaced based on the automatic identification result. The automatic identification operation was then repeated, and the viscosity test was performed using the rotational speed recommended by the automatic identification result. After the viscosity reading on the control panel stabilized, the viscosity data was read.

[0135] Slurry solids content:

[0136] Weigh the beaker and record it as m0. Place the prepared slurry in the beaker and weigh it, record it as m1. Place the beaker in a vacuum drying oven and dry it at 200℃ for 24 hours to obtain the dried solid. Weigh it and record it as m2. The solid content of the slurry = (m2-m0) / (m1-m0).

[0137] Diaphragm performance testing

[0138] After the prepared slurry was left to stand for 1 day, it was then coated onto the base film to form a diaphragm, and the following tests were performed.

[0139] Test methods for liquid absorption rate and liquid retention rate:

[0140] Cut the sample into Ф19mm round pieces using a cutting machine. Place the weighing bottle on a 0.01% balance and zero it. Place the sample in the weighing bottle and record its mass as W1. Immerse the sample in a beaker containing electrolyte and soak for 60 minutes. After removing the sample, gently absorb the electrolyte from both sides of the sample using folded filter paper until there are no obvious small liquid droplets or whitening on the surface. Zero the weighing bottle on the balance and weigh the sample, recording its mass as W2. Place the weighed sample in a fume hood and let it stand for 60 minutes, then weigh it again and record its mass as W3. Calculate the sample's liquid absorption rate and liquid retention rate using the following formulas.

[0141]

[0142] Methods for testing ionic conductivity:

[0143] The sample was cut into Ф19mm round pieces and stacked in the following order: stainless steel sheet || electrolyte membrane || stainless steel sheet, to assemble a CR2032 button cell. After standing for 1 hour, electrochemical impedance spectroscopy (EIS) (Metrohm, PGSTAT204) was performed using an electrochemical workstation, with values ​​ranging from 0.1 to 10. 6 A frequency scan is performed at Hz, with a voltage amplitude of 10mV. The intersection of the graph and the horizontal axis represents the impedance R of the polymer membrane. The ionic conductivity σ can be calculated using the formula σ=d / RA, where d is the thickness of the electrolyte membrane, R is the impedance value, and A is the area of ​​the stainless steel sheet (diameter Ф16mm).

[0144] Methods for testing lithium-ion transference number:

[0145] The sample was cut into Ф19mm round pieces, and CR2032 button cells were assembled according to the lithium sheet||electrolyte membrane||lithium sheet configuration. After standing for 1 hour, EIS testing was performed using an electrochemical workstation (Metrohm, PGSTAT204) at a frequency of 0.1-10. 6 The frequency was set at Hz, amplitude 10mV, followed by CA testing with a bias voltage of 10mV for 2000s, and then EIS testing at a frequency of 0.1-10 Hz. 6 Hz, amplitude 10mV. According to the formula...

[0146]

[0147] Among them, I s I 0 , ΔV represents steady-state current, initial current, initial impedance, steady-state impedance, and bias voltage, respectively.

[0148] TGA temperature testing method:

[0149] The change in sample mass with temperature was measured using a Mettler Toledo TGA / DSC 3+ thermogravimetric analyzer. Test conditions were set as follows: temperature range: room temperature - 600℃, nitrogen atmosphere, heating rate: 10℃ / min. The DTG curve was obtained by first-order differentiation of the TGA curve.

[0150] Test method for heat shrinkage rate:

[0151] Cut the sample into Ф19mm round pieces, place them in a forced-air drying oven at 180℃ and let them stand for 1 hour. The heat shrinkage rate can be obtained by the following formula.

[0152] Heat shrinkage rate (%) = |(Area of ​​diaphragm before heating - Area of ​​diaphragm after heating) ÷ Area of ​​diaphragm before heating| × 100.

[0153] Tensile strength and elongation at break tests:

[0154] The diaphragm was cut into strips of 100mm × 10mm and subjected to uniaxial tensile testing using an MST C43.104Y universal testing machine with a gauge length of 50mm and a tensile speed of 10mm / min.

[0155] The above experimental examples were tested, and the test results are shown in Table 1.

[0156] Table 1. Test data of battery separator and battery slurry for each experimental example.

[0157]

[0158] Continued from Table 1:

[0159]

[0160] In Experiment 2, the slurry solidified within 0.5 hours due to its short setting time and short operating window, making it impossible to coat onto the base membrane; therefore, no membrane performance test results were available. In Experiment 5, the excessive amount of end-capping agent resulted in a very low slurry viscosity, hindering film formation; therefore, no membrane performance test results were also available. In Experiment 6, the absence of end-capping agent during slurry preparation resulted in a very high slurry viscosity, which solidified within 0.5 hours, making it impossible to coat onto the base membrane; therefore, no membrane performance test results were also available.

[0161] In some embodiments of this application, to meet the requirements of large-scale production, particular attention is paid to the stability of the slurry, such as the length of its operating time window. This is because in large-scale production, the slurry is often left to stand for a period of time after stirring before coating, such as 1 day, 2 days, 3 days, and even 7 days or longer at a certain scale. The battery separators in Experimental Examples 1 and 3 of this application not only have high ionic conductivity and good thermal stability, but also good slurry stability, with a stable storage time of ≥168 hours, resulting in a long operating time window, which is beneficial for battery separators in large-scale production.

[0162] The above embodiments of the present invention are merely examples for clearly illustrating the present invention and are not intended to limit the implementation of the present invention. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively describe all possible implementations here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. An aramid slurry, characterized in that, The aramid slurry comprises aramid, an aprotic strong polar solvent, and a co-solvent, wherein the co-solvent has a pH value of 5 to 7.5 at 25°C and 101.325 kPa. The rotational viscosity of the aramid slurry is 500 mPa·s to 5000 mPa·s.

2. The aramid slurry according to claim 1, characterized in that, The aramid slurry has a Δμ≤(500~2000)mPa·s, where Δμ=μ2-μ1, μ1 is the rotational viscosity of the aramid slurry after one day of storage in a centrifuge tube at room temperature with a relative humidity of 50%~60%, and μ2 is the rotational viscosity of the aramid slurry after seven days of storage in a centrifuge tube at room temperature with a relative humidity of 50%~60%. Optionally, μ2 = 1000 mPa·s to 5000 mPa·s, optionally 2000 mPa·s to 4000 mPa·s; and / or, μ1 = 500 mPa·s to 3000 mPa·s, optionally 1000 mPa·s to 2000 mPa·s.

3. The aramid slurry according to claim 1, characterized in that, The solid content of the aramid slurry is 5.3% to 8%.

4. The aramid slurry according to claim 1, characterized in that, The aprotic strong polar solvent includes one or more of dimethylformamide, dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, formic acid, and acetic acid; and / or, the co-solvent includes one or more of lithium chloride, sodium chloride, and calcium chloride.

5. The aramid slurry according to any one of claims 1 to 4, characterized in that, The aramid slurry further includes a capping agent, which comprises an amino group or an acyl chloride group; optionally, the capping agent comprises one or more of 4-aminobenzidine, p-methylaniline, butylamine, aniline and benzoyl chloride.

6. A method for preparing an aramid slurry, characterized in that, include: p-phenylenediamine, a capping agent, and terephthaloyl chloride are reacted in a solution to obtain an aramid sizing agent; The capping agent includes an amino group or an acyl chloride group.

7. The method for preparing aramid slurry according to claim 6, characterized in that, The mass ratio of the sum of the masses of p-phenylenediamine and terephthaloyl chloride to the capping agent is (99-1.2):1, which can be (15-25):1, and more preferably 19:

1.

8. The method for preparing aramid slurry according to claim 6, characterized in that, The preparation of the aramid slurry includes: Terephthaloyl chloride and a capping agent are mixed and stirred in a solution, and then reacted with p-phenylenediamine to obtain the aramid slurry; or; p-phenylenediamine and a capping agent are mixed and stirred in a solution, and then mixed and reacted with terephthaloyl chloride to obtain the aramid slurry; Optionally, p-phenylenediamine is mixed and stirred in solution under an inert gas environment for 1 min to 30 min, then a capping agent is added under ice bath conditions, and terephthaloyl chloride is added after mixing and stirring for 1 min to 20 min. The mixture is then reacted for 0.01 h to 2 h to obtain aramid slurry. Optionally, the mixing and stirring time is 5 min to 20 min, and the reaction time is 0.1 h to 1 h.

9. The method for preparing aramid slurry according to any one of claims 6 to 8, characterized in that, The solution comprises an aprotic strongly polar solvent and a co-solvent; optionally, the preparation of the solution comprises adding dry calcium chloride to an N-methylpyrrolidone solution and stirring for 0.1 h to 3 h at a temperature of 10 °C to 120 °C to obtain the solution; optionally, the temperature is 25 °C to 55 °C and the stirring time is 0.5 h to 2 h.

10. A battery separator, characterized in that, The battery separator comprises a base film and a coating applied to at least one side of the base film, the coating being obtained by coating with the aramid slurry according to any one of claims 1 to 5; the weight loss W of the battery separator at 500°C under thermogravimetric analysis test mode. 500 satisfy: W 500 ＝20％～70％， Among them, W 500 =W2 / W1, where W2 is the mass of the battery separator at 500°C and W1 is the initial mass of the battery separator.

11. The battery separator according to claim 10, characterized in that, The mass change rate of the battery separator at 400℃~600℃ is <2%; and / or; The mass change rate of the battery separator is <1% at 500℃~600℃.

12. The battery separator according to claim 11, characterized in that, The aramid fiber content in the coating is greater than or equal to 99% by mass.

13. The battery separator according to any one of claims 9 to 12, characterized in that, The battery separator must satisfy at least one of the following characteristics: a. The thickness of the coating is 1μm to 50μm; b. The liquid absorption rate of the battery separator is 100% to 300%; c. The liquid retention rate of the battery separator is 50% to 200%; d. The ionic conductivity of the battery separator is 1×10⁻⁶. -4 S / cm~1×10 -3 S / cm; e. The lithium-ion transference number of the battery separator is 0.3 to 0.8; f. The thermal shrinkage rate of the battery separator after heating at 180°C for 1 hour is 30% to 70%; h. The thermal shrinkage rate of the battery separator after heating at 130°C for 1 hour is 2% to 10%; i. The elongation at break of the battery separator is 80% to 150%; j. The tensile strength of the battery separator is 100MPa to 150MPa.

14. A method for preparing a battery separator, characterized in that, The aramid slurry according to any one of claims 1 to 5 is coated on at least one side of the base film and cured to obtain a battery separator.

15. The method for preparing the battery separator according to claim 14, characterized in that, The solidification process includes at least one coagulation bath, at least one water wash, and at least one ethanol wash. The coagulation bath solution is a mixture of NMP and water with a volume ratio of (0.6–9):

1. The soaking time in the coagulation bath is 1 min–50 min, and the number of soakings includes one or two. The water wash includes pure water or deionized water, and the number of water washes includes one, two, or three. The number of ethanol washes includes one or two.

16. An electrochemical battery comprising a component coated with an aramid slurry according to any one of claims 1 to 5 or a battery separator according to any one of claims 10 to 13.

17. An electrical device comprising the electrochemical battery of claim 16.

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