Polyvinyl lithium battery separator and method of making
A gradient porous polyethylene-based lithium battery separator was prepared by asymmetric cooling, multi-stage stretching, plasma treatment, enhanced slurry coating, vacuum-assisted infiltration, and vapor deposition processes. This solved the problems of poor mechanical strength, poor thermal stability, and poor compatibility, and achieved high safety and excellent battery performance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ANHUI JINKUN TECHNOLOGY CO LTD
- Filing Date
- 2025-09-25
- Publication Date
- 2026-07-31
AI Technical Summary
Polyethylene-based lithium battery separators suffer from poor mechanical strength, poor thermal stability, and poor compatibility with organic electrolytes, leading to safety hazards and decreased battery performance.
A gradient porous structure is formed by asymmetric cooling and multi-stage stretching. Combined with plasma treatment, enhanced slurry coating, vacuum-assisted infiltration and vapor deposition processes, a polyethylene-based lithium battery separator is prepared to enhance mechanical strength and thermal stability. A lithiophilic boron nitride film is also prepared on the small pore side to regulate lithium ion flow.
It significantly improves the puncture resistance, heat shrinkage resistance and ionic conductivity of the separator, inhibits lithium dendrite growth, and enhances the safety and electrochemical performance of lithium batteries.
Smart Images
Figure CN121332098B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of lithium battery separator technology, specifically relating to a polyethylene-based lithium battery separator and its preparation method. Background Technology
[0002] In lithium-ion batteries, the separator is a crucial component. Although it does not directly participate in electrochemical reactions, its performance profoundly affects the battery's power density, cycle life, and safety. Among numerous materials, polyolefins, represented by polyethylene (PE), have become the dominant material for commercial lithium-ion battery separators due to their comprehensive advantages.
[0003] The primary function of the separator is to act as a physical barrier, mechanically isolating the positive and negative electrodes to prevent internal electronic short circuits caused by direct contact between them. Simultaneously, it must possess a carefully designed microporous structure, allowing lithium ions to freely migrate during charging and discharging, forming complete ion pathways. Its porous structure can effectively absorb and lock in a large amount of liquid electrolyte, which is crucial for maintaining high ionic conductivity throughout the battery's lifespan. Polyethylene (PE) materials exhibit excellent stability in the highly reactive environment inside the battery, effectively resisting the erosion of organic solvents and maintaining structural integrity under strong oxidizing and reducing conditions. A critical characteristic of PE separators is their inherent thermal shutdown safety feature. PE has a relatively low melting point of approximately 130°C to 135°C. When the battery experiences an abnormal temperature rise and approaches this temperature, the polymer matrix of the separator begins to melt, causing the microporous structure to collapse and close. This process rapidly blocks the migration path of lithium ions, halting the internal electrochemical reaction, thus providing valuable time to prevent the battery from entering a more dangerous thermal runaway state.
[0004] Although polyethylene (PE) separators offer numerous advantages, their application in lithium-ion battery separators still faces several pressing technical challenges: PE's inherent thermal instability and thermal shrinkage can lead to severe, irreversible thermal shrinkage, resulting in electrode exposure and direct contact, posing significant safety hazards; the mechanical strength of PE films makes them prone to puncture by lithium dendrites; and the poor compatibility of PE materials with organic electrolytes results in high interfacial impedance, impacting battery performance.
[0005] To address the issues of poor mechanical strength and thermal stability in existing polyethylene-based lithium battery separators, a polyethylene-based lithium battery separator and its preparation method are proposed. Summary of the Invention
[0006] The purpose of this invention is to provide a polyethylene-based lithium battery separator and its preparation method. This invention involves melt-blending polyethylene raw materials and liquid paraffin to obtain a polymer matrix; further asymmetric cooling to obtain a polyethylene-based membrane; multi-stage stretching to obtain a porous membrane; extraction and heat setting of the porous membrane to obtain a pre-formed membrane; plasma treatment and reinforcement filler coating on the large-pore side; vacuum-assisted infiltration; hot pressing; and vapor deposition on the small-pore side to obtain the polyethylene-based lithium battery separator.
[0007] To achieve the above objectives, the present invention provides the following technical solution:
[0008] A method for preparing a polyethylene-based lithium battery separator includes the following steps:
[0009] Unless otherwise specified, the parts in this invention refer to parts by mass.
[0010] Polyethylene raw material and liquid paraffin were melt-blended to obtain a polymer matrix; the mass ratio of polyethylene raw material to liquid paraffin was 1:3, and the melt-blending temperature was 200℃.
[0011] The polyethylene raw material is ultra-high molecular weight polyethylene, with an average molecular weight of 2.5 × 10⁻⁶. 7 g / mol; the grade of liquid paraffin is 32#.
[0012] After extruding the polymer matrix, asymmetric cooling is performed to obtain a polyethylene-based film;
[0013] A porous membrane is obtained by stretching a polyethylene-based membrane in multiple stages.
[0014] Multi-stage stretching includes densification stretching and pore-opening stretching.
[0015] The porous base membrane is extracted and heat-set to obtain a pre-made base membrane.
[0016] Plasma treatment is performed on the large-pore side of the pre-fabricated base film.
[0017] Boehmite, alumina, sodium carboxymethyl cellulose and styrene-butadiene emulsion are dispersed and mixed to obtain a reinforced slurry.
[0018] The dispersion and mixing process is as follows: 1 part of sodium carboxymethyl cellulose is dissolved in deionized water, 85 parts of boehmite and 12 parts of alumina are added in sequence, and after stirring for 2 hours, 5 parts of styrene-butadiene emulsion are added. After stirring for another 30 minutes, the solid content is adjusted to 45%, and the viscosity is controlled at 3000-3500 mPa·s.
[0019] Among them, the boehmite has a D50 particle size of 1.5 μm and a flake diameter-to-thickness ratio of >10:1; the alumina is α-phase alumina with a D50 particle size of 400 nm; the sodium carboxymethyl cellulose has a viscosity of 2500-2800 mPa·s; and the styrene-butadiene emulsion has a solid content of 50%.
[0020] The reinforcing slurry is coated on the large-pore side of the pre-made base membrane and dried to obtain the reinforced diaphragm.
[0021] Aramid nanofiber dispersion was impregnated on the large-pore side of the reinforced diaphragm, and vacuum-assisted infiltration was performed followed by hot pressing.
[0022] The preparation method of the aramid nanofiber dispersion is as follows: 0.1 parts of aramid nanofiber and 100 parts of dimethyl sulfoxide are mixed and dispersed under ultrasonic treatment at 500W for 1 hour; the average length of the aramid nanofiber used is 0.5-1μm and the average diameter is 50nm.
[0023] The reinforced separator, after hot pressing, is subjected to vapor phase deposition to obtain a polyethylene-based lithium battery separator.
[0024] Preferably, the asymmetric cooling process is as follows: the polymer matrix is cooled by blowing air at 25°C above it, the surface temperature of the cooling roller in contact below is maintained at 50°C, and the thickness of the polymer matrix is 0.5-1cm.
[0025] Preferably, the specific process of multi-stage stretching is as follows: densification stretching, which aims to form a small-pore surface, specifically involves heating the polyethylene film to 115°C and then stretching it longitudinally by 1.5 times; and opening stretching, which aims to form a large-pore surface, specifically involves heating the film to 125°C-130°C and then stretching it transversely by 5 times.
[0026] Preferably, the specific process of extraction and heat setting is as follows: the porous base membrane after multi-stage stretching is immersed in dichloromethane, extracted at 40°C for 5 min, and then taken out and heat-set at 120°C for 3-5 min to obtain the pre-made base membrane.
[0027] Preferably, the plasma treatment process is as follows: on the large-pore side of the pre-fabricated base film, plasma treatment is performed with a mixture of oxygen and argon, wherein the volume ratio of oxygen to argon is 1:4, the radio frequency power is 300W, and the treatment time is 30-50s.
[0028] Preferably, the vacuum-assisted permeation process is as follows: the aramid nanofiber dispersion is immersed in the large pore side of the reinforced membrane, and a negative pressure of -0.08 MPa is applied to the small pore side for a permeation time of 10-20 min; after permeation, the dimethyl sulfoxide is removed by rinsing with acetone; the hot pressing process is as follows: the reinforced membrane with the dimethyl sulfoxide removed is hot pressed for 3 min at an operating temperature of 120°C and an operating pressure of 5 MPa.
[0029] Preferably, the specific process of vapor deposition is as follows: under an operating pressure of 5-10 Pa, the surface temperature of the small-pore side of the reinforcing membrane is controlled at 100°C, argon gas is introduced at a flow rate of 50 sccm, and borazine (CAS: 6569-51-3) is introduced at a flow rate of 2 sccm. Deposition is controlled at 50 W power under a radio frequency of 13.56 MHz for 90 s, with a target film thickness of 15 nm.
[0030] A polyethylene-based lithium battery separator includes: a polyethylene-based membrane, a boron nitride reinforcing layer, a framework layer, and aramid nanofibers; wherein the framework layer is obtained by coating and drying a reinforcing slurry, and the boron nitride reinforcing layer is obtained by vapor deposition.
[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0032] 1. Through asymmetric cooling and multi-stage stretching processes, the microporous structure of the polyethylene-based membrane is transformed from a traditional uniform porous structure to an asymmetric porous structure with gradient variations. One side has larger pore sizes, providing excellent sites for the penetration of subsequent functional materials, while the other side has smaller, denser pores to maintain the membrane's puncture resistance and good heat shrinkage resistance. Furthermore, plasma treatment of the large-pore side introduces polar groups into the polyethylene matrix, providing excellent chemical bonding sites for subsequent coatings and laying the foundation for the excellent basic performance of lithium-ion battery separator products.
[0033] 2. A reinforcing slurry, prepared by blending boehmite and alumina, is coated onto the large-pore side of the base membrane, thereby improving the thermal stability of the base membrane and providing it with a certain mechanical strength. After the reinforcing slurry, composed of a specific ratio of lamellar boehmite and spherical alumina particles, is coated onto the base membrane, its gradient pore size design allows it to partially penetrate into the larger pore areas, forming a strong physical bond and thus inhibiting dimensional shrinkage of the base membrane at melting temperatures. Simultaneously, alumina ensures the density and uniformity of the coating, and its polar groups enhance the wettability of the membrane to the electrolyte. After drying and curing, the skeletal layer formed by the reinforcing slurry organically bonds with the base membrane, maintaining the patency of ion channels while significantly improving the heat shrinkage resistance of the base membrane.
[0034] 3. The reinforced diaphragm is immersed in an aramid nanofiber dispersion for vacuum-assisted infiltration, allowing the aramid nanofibers to be uniformly deposited in the large-pore area. Subsequently, it undergoes hot pressing to enhance the bonding force between the aramid nanofibers and the framework layer and base membrane. The high intrinsic strength of the aramid nanofibers penetrates and fills the gaps in the framework layer, absorbing and dispersing stress at the microscopic level. Together with the framework layer, they improve the puncture resistance and tensile strength of the diaphragm and reduce the brittleness introduced by the framework layer.
[0035] 4. On the small-pore side of the separator facing the negative electrode, a lithiophilic boron nitride film is prepared using a vapor deposition process. Its surface exhibits strong adsorption and guiding effects on lithium ions, effectively regulating the electric field distribution at the separator / negative electrode interface, homogenizing the lithium ion flow, and guiding lithium metal to deposit uniformly on the negative electrode surface, thereby fundamentally inhibiting the nucleation and growth of lithium dendrites. This layer, together with the internal aramid reinforcement network, constitutes a composite reinforcement system: the internal physical barrier ensures that the separator will not be punctured by small-scale lithium dendrites, while the external interface layer aims to eliminate the dendrite formation environment, actively preventing the separator from being punctured and greatly improving safety. Attached Figure Description
[0036] Figure 1 This is a flowchart of the preparation method of the polyethylene-based lithium battery separator in this invention. Detailed Implementation
[0037] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.
[0038] Reference Figure 1 The process flow diagram shown illustrates that this invention provides a polyethylene-based lithium battery separator and its preparation method. The technical solution is as follows:
[0039] Example 1
[0040] Polyethylene raw material and liquid paraffin were melt-blended to obtain a polymer matrix; the mass ratio of polyethylene raw material to liquid paraffin was 1:3, and the melt-blending temperature was 200℃.
[0041] The polymer matrix is cooled by blowing air at 25°C above it, while the surface temperature of the cooling rollers below is maintained at 50°C. The thickness of the polymer matrix is 0.5cm.
[0042] Densification stretching aims to create a small-pore surface, specifically by heating the polyethylene film to 115°C and then stretching it longitudinally by 1.5 times. Open-pore stretching aims to create a large-pore surface, specifically by heating to 125°C and then stretching it transversely by 5 times. After stretching, a porous base film is obtained.
[0043] The multi-stage stretched porous base membrane was immersed in dichloromethane and extracted at 40°C for 5 minutes. After extraction, it was removed and heat-set at 120°C for 3 minutes to obtain the pre-formed base membrane. This step aims to remove liquid paraffin, retain the polyethylene matrix, dissolve the micropores, and then heat-set the membrane.
[0044] On the large-pore side of the pre-fabricated base film, plasma treatment is performed using a mixture of oxygen and argon, with a volume ratio of oxygen to argon of 1:4, a radio frequency power of 300W, and a treatment time of 30s.
[0045] The reinforcing slurry is coated on the large-pore side of the pre-made base membrane and dried to obtain the reinforced diaphragm.
[0046] The preparation method of the reinforced slurry is as follows: Dissolve 1 part of sodium carboxymethyl cellulose in deionized water, add 85 parts of boehmite and 12 parts of alumina in sequence, stir for 2 hours, add 5 parts of styrene-butadiene emulsion, continue stirring for 30 minutes, adjust the solid content to 45%, and control the viscosity at 3000-3500 mPa·s.
[0047] The aramid nanofiber dispersion was impregnated on the large pore side of the reinforced membrane, and a negative pressure of -0.08 MPa was applied on the small pore side for 10 min. After permeation, the membrane was rinsed with acetone to remove dimethyl sulfoxide. The reinforced membrane with dimethyl sulfoxide removed was then hot-pressed at an operating temperature of 120°C and an operating pressure of 5 MPa for 3 min.
[0048] The preparation method of the aramid nanofiber dispersion is as follows: 0.1 parts of aramid nanofiber and 100 parts of dimethyl sulfoxide are mixed and dispersed under ultrasonic treatment at 500W for 1 hour; the average length of the aramid nanofiber used is 0.5-1μm and the average diameter is 50nm.
[0049] Under an operating pressure of 5 Pa, the surface temperature of the small-pore side of the reinforced separator was controlled at 100 °C. Argon gas was introduced at a flow rate of 50 sccm, and borazine was introduced at a flow rate of 2 sccm. Deposition was controlled at 50 W power for 90 s under 13.56 MHz radio frequency, with a target film thickness of 15 nm. After completion, a polyethylene-based lithium battery separator was obtained.
[0050] Examples 2-16 differ from Example 1 in operating parameters, but the other process steps and the range of raw material selection are the same.
[0051] The specific changes in operating parameters are summarized in Table 1.
[0052] Table 1. Changes in operating parameters in Examples 1-16
[0053]
[0054] Comparative Example 1
[0055] Unlike Example 1, the stretching ratios for both densification stretching and opening stretching were adjusted to 2.5 times, while other process parameters remained the same.
[0056] Comparative Example 2
[0057] Unlike Example 1, the plasma treatment step is omitted, while all other process parameters remain the same.
[0058] Comparative Example 3
[0059] Unlike Example 5, no reinforcing slurry coating was performed, but all other process parameters remained the same.
[0060] Comparative Example 4
[0061] Unlike Example 5, boehmite was not used in the reinforcing slurry, but all other process parameters remained the same.
[0062] Comparative Example 5
[0063] Unlike Example 5, alumina is not used in the reinforcing slurry, but all other process parameters are the same.
[0064] Comparative Example 6
[0065] Unlike Example 9, vacuum-assisted permeation was not performed, but all other process parameters remained the same.
[0066] Comparative Example 7
[0067] Unlike Example 9, in the vacuum-assisted permeation process, the reinforced diaphragm was immersed on both sides in an aramid nanofiber dispersion without applying negative pressure, while all other process parameters remained the same.
[0068] Comparative Example 8
[0069] Unlike Example 13, no vapor deposition process was performed, but all other process parameters remained the same.
[0070] Comparative Example 9
[0071] Unlike Example 13, in this case, the vapor deposition process was performed on the side of the enhanced diaphragm with large pores, while all other process parameters remained the same.
[0072] Experimental Example 1
[0073] The puncture resistance and tensile strength of the polyethylene-based lithium battery separator products prepared in Examples 1-4 and Comparative Examples 1-2 were tested, and the relevant results are summarized in Table 2.
[0074] The test methods for puncture resistance and tensile strength refer to the relevant test methods in GB / T 36363-2018 standard.
[0075] Table 2 shows the puncture resistance and tensile strength of the diaphragm products prepared in Examples 1-4 and Comparative Examples 1-2.
[0076]
[0077]
[0078] As shown in Table 2, the diaphragms prepared in Examples 1-4 exhibited excellent overall performance in terms of puncture resistance and tensile strength, significantly outperforming Comparative Example 1 and Comparative Example 2.
[0079] Comparative Example 1, by changing the asymmetric multi-stage stretching process to symmetric stretching, resulted in a significant decrease in the longitudinal tensile strength of the diaphragm. This indicates that the asymmetric stretching process is crucial for forming a dense, small-pore surface and providing sufficient basic mechanical strength for the diaphragm. Comparative Example 2, by eliminating the plasma treatment step, showed a significant deterioration in both the puncture resistance and tensile strength of its diaphragm. This confirms that plasma treatment on the large-pore side, introducing polar groups into the base membrane, is essential for establishing the foundation for excellent mechanical properties of the diaphragm product.
[0080] In summary, this invention constructs an asymmetric porous structure with gradient changes through asymmetric cooling and multi-stage stretching processes. The densely packed small-pore side maintains the puncture resistance and good mechanical strength of the separator substrate. Furthermore, plasma treatment of the large-pore side introduces polar groups into the polyethylene matrix, providing excellent chemical bonding sites for subsequent coatings. These two process designs produce a significant synergistic effect, jointly laying a solid foundation for the excellent overall performance of the lithium battery separator product.
[0081] Experiment Example 2
[0082] The ionic conductivity and heat shrinkage resistance of the polyethylene-based lithium battery separator products prepared in Examples 5-8 and Comparative Examples 3-5 were tested, and the relevant results are summarized in Table 3.
[0083] The test methods for ionic conductivity and heat shrinkage resistance refer to the relevant test methods in GB / T 36363-2018 standard.
[0084] Table 3 shows the ionic conductivity and heat shrinkage resistance of the membrane products prepared in Examples 5-8 and Comparative Examples 3-5.
[0085]
[0086] As shown in Table 3, the membranes prepared in Examples 5-8 exhibited excellent performance in terms of ionic conductivity and heat shrinkage resistance, showing significant advantages compared to Comparative Examples 3, 4, and 5. This indicates that the coating of the reinforcing slurry on the base membrane played a decisive role in improving thermal stability.
[0087] In Comparative Example 3, without the application of reinforcing slurry, the diaphragm experienced severe dimensional shrinkage and even curling failure at high temperatures. This directly demonstrates that the skeleton layer formed by the reinforcing slurry is crucial for suppressing the dimensional shrinkage of the base membrane at melting temperatures. In Comparative Example 4, without the use of boehmite in the slurry, the heat shrinkage resistance of the diaphragm significantly decreased, indicating that the lamellar boehmite can form a strong physical bond with the large-pore area of the base membrane, playing a major supporting role in suppressing heat shrinkage. In Comparative Example 5, without the use of alumina in the slurry, the ionic conductivity of the diaphragm decreased and the heat shrinkage rate was higher, indicating that alumina plays an important role in ensuring the density and uniformity of the coating, improving electrolyte wettability, and maintaining ion channel patency.
[0088] In summary, this invention utilizes the gradient pore size design of the base membrane to allow the reinforcing slurry obtained by blending boehmite and alumina to partially penetrate into the base membrane, forming strong physical anchors. Specifically, the lamellar boehmite and spherical alumina particles produce a significant synergistic effect: the boehmite framework effectively inhibits the dimensional shrinkage of the base membrane, while the alumina ensures the uniformity of the coating and good wettability to the electrolyte. Together, they significantly improve the heat shrinkage resistance of the base membrane while maintaining the patency of ion channels, achieving a balance between the membrane's thermal stability and electrochemical performance.
[0089] Experimental Example 3
[0090] The puncture resistance and tensile strength of the polyethylene-based lithium battery separator products prepared in Examples 9-12 and Comparative Examples 6-7 were tested. The relevant results are summarized in Table 4.
[0091] The relevant test methods are referenced in the GB / T 36363-2018 standard.
[0092] Table 4 shows the puncture resistance and tensile strength of the battery separator products prepared in Examples 9-12 and Comparative Examples 6-7.
[0093]
[0094] As shown in Table 4, the diaphragm products prepared in Examples 9-12 exhibited excellent puncture resistance while maintaining high tensile strength, and their overall mechanical properties were significantly better than those of Comparative Examples 6 and 7.
[0095] Comparative Example 6, without vacuum-assisted infiltration, showed a significant decrease in puncture resistance, indicating that applying negative pressure is a crucial step for the effective entry and filling of aramid nanofibers into the interlayer gaps. Comparative Example 7, using double-sided wetting without applying negative pressure, exhibited significantly deteriorated puncture resistance and tensile strength. This underscores the importance of unidirectional vacuum-assisted infiltration on the large-pore side for constructing an effective reinforcing network, ensuring uniform deposition of aramid nanofibers within the designated area.
[0096] In summary, this invention utilizes a vacuum-assisted infiltration process to impregnate a reinforced membrane in an aramid nanofiber dispersion, enabling the aramid nanofibers to be uniformly deposited in large-pore regions. Subsequent hot pressing allows the high intrinsic strength of the aramid nanofibers to penetrate and fill the gaps in the framework layer, absorbing and dispersing stress at the microscopic level. The aramid nanofibers and the framework layer exhibit a significant synergistic effect, jointly improving the puncture resistance and tear resistance of the membrane while reducing the brittleness introduced by the framework layer.
[0097] Experiment Example 4
[0098] The ionic conductivity and capacity retention of the polyethylene-based lithium battery separator products prepared in Examples 13-16 and Comparative Examples 8-9 were tested, and the relevant results are summarized in Table 5.
[0099] The test method for ionic conductivity refers to the relevant test method in GB / T 36363-2018 standard.
[0100] The capacity retention test method was as follows: An NCM811 positive electrode was used; a lithium metal negative electrode was used; the electrolyte was a 1.0 M LiPF6 solution, with a mixed solvent of EC / DEC / DMC in a volume ratio of 1:1:1, and 2% fluoroethylene carbonate was added; the separator used was the separator product prepared in the various embodiments and comparative examples of this application. A lithium-ion battery was assembled using the above materials. Formation was performed at 25°C and a 0.1C rate for two charge-discharge cycles, followed by a charge-discharge cycle at 1.8 mA / cm². 2 The current density was subjected to long-cycle charge-discharge tests within a voltage range of 2.8V to 4.3V, and the capacity retention rate (%) of the assembled battery was calculated after 300 cycles.
[0101] Table 5 shows the ionic conductivity and capacity retention of the battery separator products prepared in Examples 13-16 and Comparative Examples 8-9.
[0102]
[0103] As shown in Table 5, the membrane products prepared in Examples 13-16 exhibited significantly higher capacity retention than Comparative Examples 8 and 9 after long-cycle testing, while maintaining good ionic conductivity. This indicates that the vapor deposition process plays a decisive role in improving the cycle stability of the battery.
[0104] Comparative Example 8, without vapor deposition, showed a significant decrease in battery capacity retention. This directly confirms that the lithiophilic boron nitride film plays a fundamental role in regulating the separator-anode interface, guiding uniform lithium metal deposition, and thus suppressing lithium dendrite nucleation and growth. Comparative Example 9, with the vapor deposition location changed to the larger pore side, also exhibited poor battery capacity retention. This demonstrates that precisely depositing the lithiophilic layer on the smaller pore side facing the anode is crucial for effectively homogenizing lithium-ion flow and stabilizing the electrode interface.
[0105] In summary, this invention fabricates a lithium-affinity boron nitride film on the small-pore side of the separator facing the negative electrode using a vapor deposition process. Its surface exhibits strong adsorption and guiding effects on lithium ions, effectively regulating the electric field distribution at the separator-negative electrode interface and fundamentally suppressing lithium dendrite growth. This external interface layer, together with the internal aramid reinforcement network, constitutes a composite reinforcement system: the internal physical barrier ensures that the separator will not be punctured by small-scale lithium dendrites, while the external interface layer aims to eliminate the dendrite formation environment, actively preventing separator puncture. The synergistic effect of both significantly improves battery safety and long-cycle performance.
[0106] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method of making a polyvinyl lithium battery separator, characterized by: The preparation method is as follows: Polyethylene raw material and liquid paraffin are melt-blended to obtain a polymer matrix; The polymer matrix is extruded and then subjected to asymmetric cooling to obtain a polyethylene film, which is then stretched in multiple stages to obtain a porous film. The porous base membrane is extracted and heat-set to obtain a pre-formed base membrane; wherein, the two sides of the pre-formed base membrane are a large pore diameter side and a small pore diameter side, respectively; Plasma treatment is performed on the large-pore side of the pre-formed base membrane; then, a reinforcing slurry is coated on the large-pore side of the pre-formed base membrane, and after drying, a reinforced diaphragm is obtained. The aramid nanofiber dispersion is impregnated on the large pore side of the reinforced separator, vacuum-assisted infiltration is performed, and after hot pressing, vapor deposition is performed on the small pore side to obtain the polyethylene-based lithium battery separator. The specific process of vacuum-assisted permeation is as follows: the aramid nanofiber dispersion is immersed in the large pore side of the reinforced diaphragm, and a negative pressure is applied to the small pore side; after permeation, dimethyl sulfoxide is removed by rinsing with acetone; the specific process of hot pressing is as follows: the reinforced diaphragm with dimethyl sulfoxide removed is hot pressed for 3 minutes at an operating temperature of 120°C and an operating pressure of 5 MPa.
2. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The preparation method of the reinforced slurry is as follows: Sodium carboxymethyl cellulose is dissolved in deionized water, boehmite and alumina are added in sequence, and after stirring, styrene-butadiene emulsion is added. Stirring is continued and the solid content is adjusted to 45%, and the viscosity is controlled at 3000-3500 mPa·s.
3. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The preparation method of the aramid nanofiber dispersion is as follows: aramid nanofibers and dimethyl sulfoxide are mixed and dispersed under ultrasonic treatment at 500W for 1 hour.
4. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The specific process of the asymmetric cooling is as follows: a 25°C airflow is used to blow and cool the polymer matrix above it, the surface temperature of the cooling roller in contact below is maintained at 50°C, and the thickness of the polymer matrix is 0.5-1cm.
5. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The multi-stage stretching includes densification stretching and opening stretching; the densification stretching process is as follows: after heating the polyethylene film to 115°C, it is stretched longitudinally by 1.5 times; the opening stretching process is as follows: after the polyethylene film has undergone densification stretching, it is heated to 125°C-130°C and stretched laterally by 5 times.
6. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The specific processes of extraction and heat setting are as follows: the porous base membrane is immersed in dichloromethane, extracted at 40°C for 5 minutes, and then taken out and heat-set at 120°C for 3-5 minutes.
7. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The specific process of plasma treatment is as follows: on the large-pore side of the pre-fabricated base film, plasma treatment is performed with a mixture of oxygen and argon, wherein the volume ratio of oxygen to argon is 1:4, the radio frequency power is 300W, and the treatment time is 30-50s.
8. The method for preparing a polyethylene-based lithium battery separator according to claim 1, characterized in that: The specific process of vapor deposition is as follows: under an operating pressure of 5-10 Pa, the surface temperature of the small pore side of the enhanced diaphragm is controlled at 100°C, argon gas is introduced at a flow rate of 50 sccm, and borazine is introduced at a flow rate of 2 sccm. Deposition is controlled at 50 W power under a radio frequency of 13.56 MHz for 90 s, with a target film thickness of 15 nm.
9. A polyethylene-based lithium battery separator, comprising: The membrane comprises a polyethylene-based film, a boron nitride reinforcing layer, a framework layer, and aramid nanofibers; characterized in that: the framework layer is obtained by coating and drying a reinforcing slurry, and the boron nitride reinforcing layer is obtained by vapor deposition; the polyethylene-based lithium battery separator is prepared by the preparation method according to any one of claims 1-8.