Composite diaphragm doped with modified mica and preparation method thereof

Abstract

The invention provides a composite diaphragm doped with modified mica and a preparation method thereof. According to the composite diaphragm doped with the modified mica and the preparation method of the composite diaphragm, technical innovation is achieved through a two-step modification process of CTAB intercalation and KH550 surface grafting, firstly, the CTAB is used for expanding the interlayer spacing of the mica and breaking agglomeration, then a stable interface of the mica and ANF is constructed through the KH550, and then the uniform composite diaphragm can be efficiently prepared through the steps of ultrasonic dispersion, gradient drying, phase inversion and the like; the raw materials are wide in source, special high-end equipment is not needed, and the industrial mass production potential is achieved; according to the performance of the composite diaphragm, the synergistic effect of KH550 and CTAB enables the diaphragm to have high thermal stability, excellent electrochemical performance and reliable safety, and the problems that a common diaphragm is easy to shrink at a high temperature, the cycle life of a battery is short, and the risk of thermal runaway is high are effectively solved; according to the composite diaphragm and the preparation method thereof, the high-performance requirement of the lithium ion battery on the diaphragm is met, the cost and the mass production feasibility are also considered, and the composite diaphragm has wide application prospects and market value.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically, to a composite separator with doped and modified mica and its preparation method. Background Technology

[0002] Lithium-ion batteries are widely used in electric vehicles, portable electronic devices, and other fields due to their high energy density and lack of memory effect. However, thermal runaway and lithium dendrite growth remain core issues restricting their safety performance. The separator, as the heart barrier of a lithium-ion battery, must simultaneously achieve four major functions: physical isolation of the positive and negative electrodes, promotion of Li⁺ transport, suppression of lithium dendrites, and high-temperature resistance. Existing commercially available polyolefin separators have poor thermal stability (melting point 135-165℃) and are prone to shrinkage under thermal stress, leading to short circuits. Furthermore, the inherent porosity in the separator structure may promote unexpected chemical interactions between electrodes, thereby exacerbating the spread of thermal runaway. Aramid nanofibers (ANFs) are a new type of polymer nanofiber synthesized through a "top-down" deprotonation process of poly(p-phenylene terephthalamide) (PPTA). These materials have attracted widespread scientific attention due to their excellent mechanical properties and extremely high thermal stability. Advanced preparation techniques such as sol / gel layer-by-layer self-assembly (LBL) and vacuum-assisted filtration (VAF) papermaking have enabled the successful development of ANF membranes with excellent thermal stability, electrochemical stability, and mechanical properties. Furthermore, the lithiophilic polar functional groups (CO, NH) in ANF membranes provide numerous active sites for lithium-ion interactions, promoting their uniform distribution and migration. Researchers have already fabricated composite membranes with a pore size of 20 μm, exhibiting thermal stability up to 400°C and a modulus of 5 GPa. However, the low porosity of these membranes significantly limits their ionic conductivity and long-term electrochemical performance. Mica, as a natural layered silicate mineral, possesses high thermal stability (temperature resistance ≥800°C) and mechanical strength (tensile strength ≥50 MPa), and its layered structure can naturally construct Li⁺ transport channels. Therefore, theoretically, mica can be used as an ANF composite filler to enhance the ion conduction efficiency of ANF membranes.

[0003] However, existing mica has the following problems when used as a composite filler: In existing technologies, when mica is used as a composite filler, the thick layers of native mica (50-100 nm) tend to agglomerate in the ANF matrix, leading to uneven membrane porosity. Furthermore, mica has weak hydrophilicity and lacks lithium-philic functional groups, resulting in poor compatibility with electrolytes and low ionic conductivity. The interfacial bonding between unmodified mica and ANF is weak, making the composite membrane prone to interlayer delamination during charge and discharge, thus affecting the battery's cycle stability.

[0004] This invention addresses the problems of ordinary separators, such as easy shrinkage at high temperatures, short battery cycle time, and high risk of thermal runaway, by combining CTAB intercalation with KH550 grafted modified mica and ANF. It significantly improves the thermal stability, electrochemical performance, and safety of the separator, meeting the requirements of lithium batteries. It is also easy to mass-produce and provides support for upgrading the safety performance of new energy batteries. Summary of the Invention

[0006] The present invention aims to solve the technical problems mentioned in the background art and provide a composite membrane of doped modified mica and its preparation method.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a composite membrane of doped and modified mica, comprising the following steps: S1. Take 10g of natural mica powder, add 500mL of deionized water, and disperse by ultrasonication to obtain a mica suspension; S2. Add 2g of cetyltrimethylammonium bromide to the mica suspension and stir at 50℃ for 4h to complete the intercalation reaction. S3. Add 1.5g of γ-aminopropyltriethoxysilane, heat to 80℃ and continue stirring for 6h to graft the silane coupling agent onto the mica surface. S4. The mica is centrifuged, washed three times with deionized water, and freeze-dried to obtain modified mica powder. S5. Take 5g of Kevlar fiber, cut it into small pieces, add 100mL of DMSO, and stir until completely soaked; slowly add 2g of KOH powder, stir at 25℃ for 24h to carry out the deprotonation reaction, and obtain an ANF dispersion with a concentration of 50mg / mL; S6. Ultrasonic treatment to remove unpeeled fiber aggregates, ready for use.

[0008] S7. According to the mass ratio of ANF dispersion: modified mica powder (m-Mica) = 50:50, add modified mica powder to ANF dispersion and disperse with ultrasonic assistance to obtain a uniform composite slurry. S8. Apply the composite slurry to a clean glass plate using a scraper, with a wet film thickness of 100μm, and then use a gradient drying process to avoid diaphragm cracking. S9. Immerse the dried membrane in a 0.1 mol / L acetic acid solution for 1 hour for phase inversion, wash with deionized water until neutral, and freeze-dry again to obtain the ANF composite membrane.

[0009] A further preferred embodiment: In step S1, mica powder is mixed with deionized water and then ultrasonically dispersed for 30 minutes to obtain a mica suspension.

[0010] A further preferred embodiment: In step S4, the centrifugation speed is 8000 rpm and the time is 15 min, and the freeze drying is carried out at -50℃ for 24 h.

[0011] A further preferred option: In step S6, the ultrasonic treatment power is 500W and the time is 1h.

[0012] A further preferred option: In step S7, the ultrasonic-assisted dispersion power is 400W and the time is 2h.

[0013] A further preferred option: In step S8, the gradient drying process involves first drying at 40°C for 2 hours to remove surface solvent, and then drying at 80°C for 4 hours for deep dehydration.

[0014] A further preferred embodiment: In step S9, freeze drying is carried out at -50°C for 12 hours.

[0015] A composite membrane doped with modified mica, the composite membrane comprising the composite membrane obtained by any one of the preparation methods described above. Beneficial effects

[0016] 1. By adding hexadecyltrimethylammonium bromide (CTAB), mica interlayer modification is achieved. The long-chain alkyl groups of CTAB can be inserted into the interlayer of natural mica, increasing the interlayer spacing, breaking the aggregation of mica sheets, and creating sites for subsequent silane coupling agent grafting. At the same time, it improves the dispersibility of mica in ANF dispersion, avoids uneven composite slurry caused by mica aggregation, and ensures the uniformity of the membrane structure. The CTAB-modified mica and ANF work synergistically, resulting in a membrane shrinkage rate of 0 at 120℃ and 150℃, and only 15.6% at 180℃, which is far better than the 19.8% shrinkage at 120℃ of the control group without CTAB modification. Because CTAB modification enhances the interfacial bonding between mica and ANF, a stable support structure is formed at high temperatures, inhibiting membrane shrinkage. CTAB modification makes it easier for mica to combine with ANF, constructing continuous ion conduction channels, resulting in a 1C cycle capacity retention rate of 96.5% for the battery, compared to only 47.3% for the control group. It effectively inhibits dendrite growth, reduces side reactions, and ensures the long-term cycle stability of the battery. 2. By adding γ-aminopropyltriethoxysilane, the interfacial bonding between mica and ANF is strengthened. The ethoxy group at one end of the KH550 molecule can react with the hydroxyl groups on the surface of CTAB-modified mica to form a covalent bond, while the amino group at the other end can form a hydrogen bond with the carboxyl group of ANF, thus constructing a stable mica-ANF interface. This avoids delamination due to weak interfacial bonding during the coating and drying of the composite slurry, ensuring the integrity of the separator structure. The mica grafted with KH550 forms a tighter composite system with ANF, which can more effectively block heat transfer at high temperatures. The shrinkage rate of the separator at 180℃ is only 15.6%, and the ignition time of the soft-pack battery is delayed to 207s, with the peak surface temperature reduced to 472℃. Compared with the case without KH550 modification, this significantly reduces the risk of thermal runaway. The organic functional groups of KH550 can regulate the internal microstructure of the separator, helping to construct a more regular lithium-ion conduction channel. Combined with the increased interlayer spacing of mica due to CTAB modification, the battery's 1C cycle capacity retention rate reaches 96.5%, contributing to improved electrochemical performance stability. 3. In summary, this type of doped and modified mica composite membrane and its preparation method achieve technological innovation through a two-step modification process of CTAB intercalation and KH550 surface grafting. It exhibits significant advantages in both membrane performance and practicality. From the preparation method perspective, CTAB is first used to expand the interlayer spacing of mica and break up agglomeration, and then KH550 is used to construct a stable interface between mica and ANF. Subsequent steps such as ultrasonic dispersion, gradient drying, and phase transformation can efficiently prepare a uniform composite membrane. Furthermore, the raw materials are widely available and do not require specialized high-end equipment, possessing potential for industrial-scale mass production. From the perspective of composite membrane performance, KH550 and C… The synergistic effect of TAB gives the separator high thermal stability, a shrinkage rate of only 15.6% at 180℃, excellent electrochemical performance, a 1C cycle capacity retention rate of 96.5%, and reliable safety. The ignition time of the soft-pack battery is delayed to 207s and the peak surface temperature is reduced to 472℃, effectively solving the pain points of ordinary separators such as easy shrinkage at high temperatures, short battery cycle life, and high risk of thermal runaway. This composite separator and its preparation method not only meet the high performance requirements of lithium-ion batteries for separators, but also take into account cost and mass production feasibility, providing important technical support for battery safety and performance upgrades in the new energy field, and has broad application prospects and market value. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention.

[0018] In this embodiment of the invention, a method for preparing a composite membrane of doped and modified mica includes the following steps: S1. Take 10g of natural mica powder, add 500mL of deionized water, and disperse by ultrasonication to obtain a mica suspension; S2. Add 2g of cetyltrimethylammonium bromide to the mica suspension and stir at 50℃ for 4h to complete the intercalation reaction. S3. Add 1.5g of γ-aminopropyltriethoxysilane, heat to 80℃ and continue stirring for 6h to graft the silane coupling agent onto the mica surface. S4. The mica is centrifuged, washed three times with deionized water, and freeze-dried to obtain modified mica powder. S5. Take 5g of Kevlar fiber, cut it into small pieces, add 100mL of DMSO, and stir until completely soaked; slowly add 2g of KOH powder, stir at 25℃ for 24h to carry out the deprotonation reaction, and obtain an ANF dispersion with a concentration of 50mg / mL; S6. Ultrasonic treatment to remove unpeeled fiber aggregates, ready for use.

[0019] S7. According to the mass ratio of ANF dispersion: modified mica powder (m-Mica) = 50:50, add modified mica powder to ANF dispersion and disperse with ultrasonic assistance to obtain a uniform composite slurry. S8. Apply the composite slurry to a clean glass plate using a scraper, with a wet film thickness of 100μm, and then use a gradient drying process to avoid diaphragm cracking. S9. Immerse the dried membrane in a 0.1 mol / L acetic acid solution for 1 hour for phase inversion, wash with deionized water until neutral, and freeze-dry again to obtain the ANF composite membrane.

[0020] In step S1, mica powder is mixed with deionized water and ultrasonically dispersed for 30 minutes to obtain a mica suspension; in step S4, centrifugation is performed at 8000 rpm for 15 minutes, and freeze-drying is carried out at -50℃ for 24 hours; in step S6, ultrasonic treatment is performed at 500W for 1 hour; in step S7, ultrasonic-assisted dispersion is performed at 400W for 2 hours; in step S8, the gradient drying process involves first drying at 40℃ for 2 hours to remove surface solvent, and then drying at 80℃ for 4 hours for deep dehydration; in step S9, freeze-drying is carried out at -50℃ for 12 hours.

[0021] A composite membrane doped with modified mica, wherein the composite membrane is obtained by any of the preparation methods described above; The preparation is carried out through the above steps: The present invention will be described in detail below through embodiments.

[0022] First, 10g of mica powder was added to 500mL of deionized water and sonicated at 300W for 30min. Then, 2g of cetyltrimethylammonium bromide (CTAB) was added, and the mixture was magnetically stirred at 50℃ for 4h at 500rpm. Next, 1.5g of γ-aminopropyltriethoxysilane (KH550) was added, the temperature was raised to 80℃, and the mixture was stirred at 800rpm for 6h. After centrifugation at 8000rpm for 15min, the mixture was washed three times with 100mL of deionized water each time, and then freeze-dried at -50℃ for 24h to obtain modified mica powder (m-Mica powder). X-ray diffraction (XRD) showed d001=2.35nm. 5g of Kevlar fiber was then added... After chopping, add 100 mL of DMSO and stir for 2 hours until wetted. Add 2 g of KOH, stir at 25°C for 24 hours, and sonicate at 500 W for 1 hour to obtain an ANF dispersion. Add m-Mica powder to the ANF dispersion at a mass ratio of ANF:m-Mica = 50:50, sonicate at 400 W for 2 hours, stir magnetically for 1 hour at 600 rpm, and finally use a scraper to coat the composite slurry onto a scraper plate to achieve a wet film thickness of 100 μm. Dry at 40°C for 2 hours, dry at 80°C for 4 hours, immerse in 0.1 mol / L acetic acid solution for 1 hour, wash with deionized water until pH = 7, and freeze-dry at -50°C for 12 hours to obtain a composite membrane. The specific steps for comparison are as follows: In the comparative example, no modified mica was added; only pure ANF membrane was used. 5g of Kevlar fiber was chopped and added to 100mL of DMSO. The mixture was stirred for 2 hours until it was soaked. Then, 2g of KOH was added, and the mixture was stirred at 25℃ for 24 hours and sonicated at 500W for 1 hour to obtain an ANF dispersion. The ANF dispersion was then coated onto a coating plate using a doctor blade to achieve a wet film thickness of 100μm. The film was dried at 40℃ for 2 hours and at 80℃ for 4 hours. It was then immersed in 0.1mol / L acetic acid solution for 1 hour, washed with deionized water until pH=7, and freeze-dried at -50℃ for 12 hours to obtain a pure ANF membrane. Both types of diaphragms underwent thermal stability testing, electrochemical performance testing, and safety performance testing. In the thermal stability test, the diaphragm was heated in a muffle furnace at 120℃, 150℃, and 180℃ for 30 minutes. After cooling, the dimensions were measured and the shrinkage rate was calculated. The specific data are shown in Table 1. 120℃ 150℃ 180℃ Example of shrinkage rate 0 0 15.6% proportional shrinkage rate 19.8% 52.1% 87.4% In the electrochemical performance test, an LFP / / Li half-cell was assembled using the experimentally prepared membrane, with LFP as the positive electrode, metallic Li as the negative electrode, and 1 mol / L LiPF6-EC / DEC / FEC electrolyte. After formation, a 1C long-cycle test was performed, and the specific data are shown in Table 2. capacity before loop Capacity after loop Capacity retention Example 149.2mAh / g 144.3mAh / g 96.5% Comparative Example In the safety performance test, a soft-pack battery (LFP / / AG system) was prepared using the experimentally prepared separator. Continuous external heating was applied to it, and the combustion behavior of the battery was analyzed using thermocouples and a cone calorimeter. Specific data are shown in Table 3. Time of fire Peak heat release rate Battery surface peak temperature Example 207s <![CDATA[199.6KW / m 2 ]]> 472℃ Comparative Example 139s <![CDATA[108.9KW / m 2 ]]> 643.7℃ As shown in Table 1, the shrinkage rate of the separator in the example was 0 after heating at 120°C and 150°C, indicating that it has excellent dimensional stability within this temperature range. Even at a high temperature of 180°C, the shrinkage rate was only 15.6%, and it could still maintain basic structural integrity. In contrast, the shrinkage rate of the separator in the comparative example reached 19.8% at 120°C and soared to 87.4% at 180°C. It was very easy for the positive and negative electrodes inside the battery to be short-circuited due to the drastic shrinkage. This fully demonstrates that the present invention significantly improves the thermal stability and high-temperature shrinkage resistance of the separator by introducing modified mica. As shown in Table 2, the initial capacities of the half-cells assembled with the separators of the examples and the comparative examples are similar, at 149.2 mAh / g and 148.75 mAh / g, respectively. However, after long-term cycling, the capacity retention rate of the examples is as high as 96.5%, which is far superior to the 47.3% of the comparative examples. This result indicates that the composite separator prepared in this invention can not only ensure the initial electrochemical activity of the battery, but also suppress dendrite growth during lithium-ion deposition through the synergistic effect of modified mica and ANF, reduce internal side reactions of the battery, significantly improve the cycle life and long-term stability of the battery, and indirectly prove that the separator has better lithium-ion conduction efficiency. Based on the safety test data in Table 3, the ignition time of the soft-pack battery in the embodiment (207s) was delayed by 68s compared to the 139s in the comparative example, allowing more time for safety warnings and emergency handling after battery thermal runaway. Furthermore, the peak surface temperature of the battery in the embodiment (472℃) was 171.7℃ lower than that in the comparative example (643.7℃), effectively mitigating the risk of a sudden temperature rise during battery thermal runaway. In addition, the peak heat release rate of the embodiment (199.6KW / m²) was higher than that of the comparative example, indicating that it could release heat more smoothly during combustion, avoiding serious safety accidents such as explosions and fires caused by concentrated heat, further verifying the safety protection performance advantages of the composite separator. This invention utilizes a two-step functionalized composite modification process involving CTAB intercalation modification and surface grafting of a silane coupling agent (KH550) to synthesize a membrane by combining modified mica with ANF. Compared to ordinary membranes, this process offers the following core advantages: High thermal stability: The layered structure of the modified mica forms a supporting framework at high temperatures, effectively inhibiting membrane shrinkage and addressing the issue of easy deformation at high temperatures in ordinary membranes; Excellent electrochemical performance: The synergistic effect of the nanofiber network of ANF and the ion conduction channels of the modified mica enhances lithium-ion conductivity and inhibits dendrite growth, ensuring a long cycle life for the battery; Reliable safety performance: The composite system slows down the battery's thermal runaway process and reduces the peak surface temperature, providing more comprehensive safety protection for battery use; Low cost: The raw materials used, such as natural mica and Kevlar fiber, are widely available, and the preparation process does not require specialized high-end equipment, making it easy to mass-produce industrially and offering good economic benefits and application prospects.

[0023] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. In addition, it should be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. Furthermore, various different embodiments of the present invention can also be arbitrarily combined, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A method for preparing a composite membrane doped with modified mica, characterized in that: Includes the following steps: S1. Take 10g of natural mica powder, add 500mL of deionized water, and disperse by ultrasonication to obtain a mica suspension; S2. Add 2g of cetyltrimethylammonium bromide to the mica suspension and stir at 50℃ for 4h to complete the intercalation reaction. S3. Add 1.5g of γ-aminopropyltriethoxysilane, heat to 80℃ and continue stirring for 6h to graft the silane coupling agent onto the mica surface. S4. The mica is centrifuged, washed three times with deionized water, and freeze-dried to obtain modified mica powder. S5. Take 5g of Kevlar fiber, cut it into small pieces, add 100mL of DMSO, and stir until completely soaked; slowly add 2g of KOH powder, stir at 25℃ for 24h to carry out the deprotonation reaction, and obtain an ANF dispersion with a concentration of 50mg / mL; S6. Ultrasonic treatment to remove unpeeled fiber aggregates, ready for use. 2.S7. According to the mass ratio of ANF dispersion: modified mica powder (m-Mica) = 50:50, add the modified mica powder to the ANF dispersion and disperse with ultrasonic assistance to obtain a uniform composite slurry. S8. Apply the composite slurry to a clean glass plate using a scraper, with a wet film thickness of 100μm, and then use a gradient drying process to avoid diaphragm cracking. S9. Immerse the dried membrane in a 0.1 mol / L acetic acid solution for 1 hour for phase inversion, wash with deionized water until neutral, and freeze-dry again to obtain the ANF composite membrane.

3. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S1, mica powder is mixed with deionized water and then ultrasonically dispersed for 30 minutes to obtain a mica suspension.

4. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S4, the centrifugation speed is 8000 rpm and the time is 15 min, and the freeze drying is carried out at -50℃ for 24 h.

5. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S6, the ultrasonic treatment power is 500W and the time is 1 hour.

6. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S7, the ultrasonic-assisted dispersion power is 400W, and the time is 2h.

7. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S8, the gradient drying process involves first drying at 40°C for 2 hours to remove surface solvent, and then drying at 80°C for 4 hours for deep dehydration.

8. The method for preparing a composite membrane of doped and modified mica according to claim 1, characterized in that: In step S9, freeze drying is carried out at -50°C for 12 hours.

9. A composite membrane doped with modified mica, characterized in that: The composite membrane includes the composite membrane obtained by the preparation method according to any one of claims 1-7.