Highly infiltrative long-circulation lithium battery composite diaphragm, and preparation method and application thereof

Abstract

The application relates to a high-wetting long-circulation lithium battery composite diaphragm and a preparation method and application thereof, wherein the method comprises the following steps: obtaining a carbonate-based electrolyte formula, adding a composite film forming agent, forming a mixed solution, and stirring until uniform; in the process of stirring the mixed solution, nano-aluminum oxide particles are added for catalysis, the particle size range of the nano-aluminum oxide particles is controlled to be 50-100 nanometers, cellulose is added to the mixed solution, the solution viscosity is adjusted, and the mixed solution is formed into a stable suspension system; the mixed solution in the suspension system state is injected and uniformly covered on the surface of a battery diaphragm, the mixed solution attached to the battery diaphragm is solidified under high-temperature conditions of 150-200 DEG C, a uniform dendrite-free diaphragm protection layer is formed, and the purposes of improving the electrolyte wetting property of a lithium battery diaphragm, prolonging the cycle life of a battery and maintaining high coulomb efficiency are achieved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a high-wetting, long-cycle lithium-ion battery composite separator, its preparation method, and its application. Background Technology

[0002] In today's lithium-ion battery field, the separator, as a key component, plays a decisive role in the overall performance of the battery. Traditional lithium-ion battery separators, facing ever-increasing demands for high performance, have revealed numerous problems that urgently need to be addressed. On the one hand, ordinary separators have poor wettability to the electrolyte, resulting in low ion conduction efficiency and severely affecting the battery's charge-discharge performance. On the other hand, during battery charging and discharging, the growth of lithium dendrites can easily cause internal short circuits or overheating, greatly threatening battery safety and lifespan. Simultaneously, in existing separator manufacturing processes, the dispersion of inorganic particles within the separator remains a persistent problem. This not only easily leads to pore blockage, hindering the normal transport of lithium ions, but also negatively impacts the separator's mechanical properties. Furthermore, under high-temperature environments, the separator's thermal stability is insufficient, and its thermal shrinkage rate is too high, further limiting the battery's application under complex operating conditions. Currently, the cycle life of battery cells in the industry is generally only around 2000 cycles, far from meeting the stringent requirements for long lifespan and high stability in applications such as electric vehicles and energy storage power stations. Summary of the Invention

[0003] The first objective of this invention is to provide a high wettability, long-cycle lithium-ion battery composite separator, its preparation method, and its application, so as to improve the wettability of the lithium-ion battery separator to the electrolyte, increase the cycle life of the battery cell, and maintain high coulombic efficiency.

[0004] To achieve the above objectives, the present invention provides a method for preparing a high-wetting, long-cycle lithium-ion battery composite separator, comprising the following steps:

[0005] A carbonate-based electrolyte formulation is obtained, a composite film-forming agent is added to form a mixed solution, and the mixture is stirred until homogeneous. The composite film-forming agent includes vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate.

[0006] Nano-alumina particles are added during the stirring of the mixed solution for catalysis. The particle size of the nano-alumina particles is controlled in the range of 50-100 nanometers. Cellulose is added to the mixed solution to adjust the solution viscosity until the mixed solution forms a stable suspension system.

[0007] The mixed solution in a suspended state is injected and uniformly covered on the surface of the battery cell separator. The mixed solution attached to the battery cell separator is cured under high temperature conditions of 150-200℃ to form a uniform dendrite-free separator protective layer.

[0008] Furthermore, the step of adding the composite film-forming agent to form a mixed solution includes:

[0009] A composite film-forming agent is added to a carbonate-based electrolyte, wherein the total amount of the composite film-forming agent added is 0.5-5 wt% of the mass of the carbonate-based electrolyte.

[0010] In a dry environment with a dew point temperature < -40℃, the stirring speed is 300-800 rpm and the stirring time is 2-6 hours to form a mixed solution.

[0011] Furthermore, the step of adding nano-alumina particles for catalysis during the stirring of the mixed solution includes:

[0012] Surface-hydroxylated nano-alumina particles are added to the stirred mixture, wherein the amount of nano-alumina particles added is 0.1-3 wt% of the total mass of the mixture.

[0013] During the addition of the nano-alumina particles, ultrasonic-assisted dispersion is performed at a frequency of 20-40 kHz.

[0014] Furthermore, the weight ratio of vinylene carbonate, ethylene ethylene carbonate and fluoroethylene carbonate in the composite film-forming agent is (1-3):(2-4):(1-2), and the specific surface area of ​​the nano-alumina particles after surface hydroxylation treatment is 50-150 m² / g, and the ultrasonic dispersion time is 10-60 minutes.

[0015] Further, the step of adding cellulose to the mixed solution to adjust the solution viscosity until the mixed solution forms a stable suspension system includes:

[0016] Cellulose, specifically sodium carboxymethyl cellulose, is added to a mixed solution containing nano-alumina particles at an amount of 0.05-1.5 wt% of the total mass of the mixed solution.

[0017] The solution is stirred uniformly to adjust its viscosity to 300-1500 mPa·s at 25°C, forming a suspension system. The absolute value of the zeta potential of the suspension system is ≥30 mV, and the sedimentation volume ratio is ≤5% after standing for 24 hours.

[0018] Further, the step of injecting and uniformly covering the surface of the battery cell separator with the suspended mixed solution, and then solidifying the mixed solution adhering to the battery cell separator at a high temperature of 150-200°C to form a uniform, dendrite-free separator protective layer includes:

[0019] The suspension system mixture solution is uniformly coated onto the surface of the battery cell separator with a wet film thickness of 5-20 μm. After coating, it is left to stand in an environment with humidity <30% for 5-30 minutes to form a pre-cured layer.

[0020] The process of forming the pre-cured layer adopts a gradient heating method, raising the temperature to 80-120℃ at a heating rate of 5-10℃ / min, holding it at that temperature for 10-30 minutes, and then raising it to the final curing temperature of 150-200℃ at a rate of 3-5℃ / min. The curing pressure is controlled at 0.1-1MPa, so that the nano-alumina particles are uniformly embedded in the polymer network to form a dendrite-free protective layer.

[0021] The cured diaphragm is placed in an argon-protected environment and annealed for 0.5-2 hours at 120-150℃ to eliminate internal stress and improve the uniformity of the protective layer.

[0022] After annealing, cool to room temperature at a rate of 2-5℃ / min to ensure that no dendrites are formed in the protective layer.

[0023] Furthermore, after the step of curing the mixed solution attached to the cell separator to form a uniform, dendrite-free separator protective layer, the method further includes:

[0024] A wettability test was performed on the surface of the diaphragm protective layer. Electrolyte was dropped onto the surface of the diaphragm protective layer, and the static contact angle was measured using a contact angle meter. When the contact angle was ≥30°, the total amount of composite film-forming agent was increased in a gradient of 0.5-2wt%, and the coating and curing were repeated. When the contact angle was <30°, the wettability of the diaphragm was deemed to meet the standard. The contact angle measurement was to be performed in an inert atmosphere glove box at a test temperature of 25±2℃, with an electrolyte drop volume of 2μL, and the measurement was to be completed within 10 seconds after the drop was added.

[0025] Lithium-ion mobility was tested on the membranes that met the wettability standards. The ionic conductivity of the membranes in the frequency range of 1MHz-100kHz was tested by AC impedance method, and the lithium-ion mobility was calculated.

[0026] For membranes that meet the migration rate standard, high-temperature heat shrinkage verification is performed. Finally, the membrane needs to be verified for high-temperature thermal stability. The membrane is placed in a 200℃ constant temperature chamber for 1 hour, and the lateral and longitudinal shrinkage rates are measured. When the shrinkage rate in either direction is ≥0.3%, the process is adjusted and the membrane is re-prepared.

[0027] Furthermore, the step of adjusting the process to re-prepare the membrane includes:

[0028] When the shrinkage rate in any direction is ≥0.3%, the material is re-prepared after performing at least one process adjustment, which includes increasing the curing pressure to the range of 0.5-1 MPa, adding 1-5 wt% polyimide fiber to the cellulose, and replacing the nano alumina particles with nano zirconium oxide particles modified with silane coupling agents.

[0029] The second objective of this invention is to provide a high wettability long-cycle lithium battery composite separator obtained by the above-described high wettability long-cycle lithium battery composite separator preparation method.

[0030] A third objective of this invention is to provide an application of a highly wettable, long-cycle lithium-ion battery composite separator, in some specific embodiments of which the composite separator is used in lithium-ion batteries.

[0031] In one specific implementation, the composite separator is used in electric vehicle power batteries to enhance the thermal stability of the battery under high-temperature conditions (such as fast charging and high-load operation), avoid internal short circuits or thermal runaway caused by separator shrinkage, and effectively block the risk of lithium dendrites penetrating the separator through a uniform dendrite-free SEI film, thereby significantly reducing the safety hazards of electric vehicle batteries such as short circuits and fires caused by dendrites.

[0032] In one specific implementation, the composite separator is used in energy storage system batteries. The ultra-long cycle life (>10,000 cycles) of the composite separator meets the stringent battery life requirements of energy storage systems, reduces system maintenance costs, and enables batteries to operate stably in extreme temperature environments (such as outdoor energy storage power stations), avoiding capacity decay or failure due to thermal deformation. Furthermore, by suppressing dendrites and creating a uniform SEI film, it reduces the risk of cascading reactions caused by localized short circuits in energy storage systems, making it particularly suitable for large-scale battery pack integration scenarios.

[0033] In one specific implementation, the composite separator is used in portable electronic device batteries for high-rate charge / discharge. The high ionic conductivity and porous structure of the composite separator significantly reduce lithium-ion migration resistance, meeting the high-rate (e.g., 5C) charge / discharge requirements of devices such as mobile phones and laptops. During high current density charge / discharge, the uniformity of the SEI film and the catalytic effect of nano-alumina effectively prevent lithium dendrite formation, avoiding battery bulging or sudden capacity drop. This allows for increased battery capacity within a limited space, extending device battery life. Simultaneously, the ultra-long cycle life (>10,000 cycles) reduces the need for frequent battery replacements, making it particularly suitable for wearable devices requiring multiple daily charge / discharge cycles (such as smartwatches and wireless headphones).

[0034] The high wettability, long-cycle lithium-ion battery composite separator, its preparation method, and its application provided by this invention have the following beneficial effects:

[0035] (1) This invention uses a self-developed carbonate-based electrolyte and adds a composite film-forming agent (FEC / VEC / VC) to construct a uniform and dendrite-free separator protective layer (SEI film), which significantly improves the wettability of the separator to the electrolyte. The dendrite-free separator protective layer formed by this invention can effectively prevent the growth of lithium dendrites and eliminate the battery short circuit or overheating caused by lithium dendrite growth. The separator has excellent performance with a thermal shrinkage efficiency of <0.3% at 200℃, which greatly improves the safety and stability of the battery in high-temperature environments.

[0036] (2) By adding nano-alumina particles during the preparation process and combining them with specific process conditions, the problem of inorganic particles clogging the pores in the separator was solved, which enabled lithium ions to shuttle freely and quickly inside the separator, promoted the uniform distribution and migration of lithium ions throughout the membrane layer, and improved the ion transport efficiency inside the battery. At the same time, by adding cellulose and optimizing the process, the tensile strength of the separator was improved, which not only enhanced the structural stability of the separator in the complex environment inside the battery, but also provided a solid physical support for the long-term reliable operation of the battery.

[0037] (3) Extensive experimental verification shows that the lithium battery composite separator prepared using this invention can achieve a battery cell cycle life of over 10,000 cycles, which is several times the industry average of 2,000 cycles. The ultra-long cycle life means that the battery does not need to be replaced frequently during use, greatly reducing the cost of use, and also improving the efficiency and reliability of related equipment. Attached Figure Description

[0038] Figure 1 This is a schematic flowchart of a method for preparing a high wettability, long-cycle lithium battery composite separator according to an embodiment of the present invention.

[0039] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0041] Reference Figure 1 The diagram below illustrates a process for preparing a high-wetting, long-cycle lithium-ion battery composite separator according to the present invention, comprising the following steps:

[0042] S1, obtain the carbonate-based electrolyte formula, add a composite film-forming agent to form a mixed solution, and stir until uniform. The composite film-forming agent includes vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate.

[0043] S2, during the stirring of the mixed solution, nano-alumina particles are added for catalysis. The particle size range of the nano-alumina particles is controlled within 50-100 nanometers. Cellulose is added to the mixed solution to adjust the solution viscosity until the mixed solution forms a stable suspension system.

[0044] S3, the mixed solution in suspension is injected and uniformly covered on the surface of the battery cell separator. Under high temperature conditions of 150-200℃, the mixed solution attached to the battery cell separator is solidified to form a uniform dendrite-free separator protective layer.

[0045] As described in step S1 above, the composite film-forming agent comprises vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and fluoroethylene carbonate (FEC) added in a weight ratio of (1-3):(2-4):(1-2), with a total addition amount of 0.5-5 wt% of the carbonate-based electrolyte. VC preferentially decomposes to form a dense SEI layer, inhibiting the continued decomposition of the electrolyte; VEC enhances the toughness of the SEI film through vinyl crosslinking; and FEC improves the wettability of the electrolyte to the membrane (contact angle <30°). The mixed solution is operated in a dry environment with a dew point temperature <-40°C to avoid side reactions caused by moisture. The stirring parameters are 300-800 rpm for 2-6 hours to ensure full compatibility between the film-forming agent and the electrolyte.

[0046] As described in step S2 above, nano-alumina is added for catalysis and dispersion. Surface-hydroxylated nano-alumina particles (specific surface area 50-150 m² / g) are added at a rate of 0.1-3 wt%. Ultrasonic-assisted dispersion (20-40 kHz) is used to break up particle agglomeration (agglomeration rate <5%). The absolute value of the zeta potential is ≥30 mV. The zeta potential refers to the potential of the shear plane, also called the electrokinetic potential or electrochemical potential, which is an important indicator of the stability of colloidal dispersions. The nano-alumina particles catalyze the crosslinking reaction between cellulose and the film-forming agent, shortening the curing time. Simultaneously, they serve as a framework for lithium-ion transport channels, increasing the mobility to ≥1.2 × 10⁻⁶. -3 S / cm. Added cellulose, sodium carboxymethyl cellulose (CMC-Na), viscosity-average molecular weight 9×10⁻⁶. 4 -7×10 5The viscosity of the mixed solution was adjusted to 300-1500 mPa·s (25℃) to form a stable suspension system (sedimentation volume ratio ≤5% after 24 hours of standing). The cellulose can prevent the nanoparticles from settling, ensuring coating uniformity (thickness deviation ≤±5%), and synergistically constructs a three-dimensional porous structure (porosity 15-30%) with nano-alumina.

[0047] As described in step S3 above, the mixed solution is uniformly coated onto the surface of the battery cell separator using an impregnation coating method or a slot extrusion coating method, with a wet film thickness of 5-20 μm. The mixture is then allowed to stand for 5-30 minutes under controlled humidity (<30%) to form a pre-crosslinked network (pre-cured layer thickness 3-15 μm). A gradient curing process is then employed. In the first stage (80-120℃), the temperature is increased at 5-10℃ / min and held for 10-30 minutes to promote crosslinking between cellulose and the film-forming agent. In the second stage (150-200℃), the temperature is increased at 3-5℃ / min, and a pressure of 0.1-1 MPa is applied to embed nano-alumina into the polymer matrix, forming a dendrite-free structure (surface roughness Ra≤50nm). Post-treatment and performance verification of the cured diaphragm surface include argon annealing at 120-150℃ for 0.5-2 hours to eliminate internal stress (bonding strength ≥8N / m); cooling control at a rate of 2-5℃ / min to suppress thermal shrinkage (shrinkage rate <0.3% at 200℃); and calculation of migration rate. If the lithium-ion migration rate is lower than 0.8×10⁻⁶, the performance verification will be performed accordingly. -3 If the S / cm, then increase the amount of nano-alumina particles in a gradient of 0.1-0.5wt% until the migration rate is ≥1.2×10 -3 S / cm; The AC impedance method test uses a symmetrical stainless steel blocking electrode, applies a 10mV sinusoidal perturbation voltage, and calculates the ionic conductivity after fitting the test data with an equivalent circuit model; Closed-loop control, if the contact angle is ≥30° or the heat shrinkage rate is ≥0.3%, perform at least one process adjustment and re-prepare, such as increasing the curing pressure to the range of 0.5-1MPa, adding 1-5wt% polyimide fiber to cellulose, or replacing nano alumina particles with nano zirconium oxide particles modified by silane coupling agent.

[0048] In one embodiment, the materials used in the preparation include: a carbonate-based electrolyte, a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 1:1, with the addition of 1M lithium hexafluorophosphate (LiPF6); a composite film-forming agent, including vinylene carbonate (VC), ethylene ethylene carbonate (VEC), and fluoroethylene carbonate (FEC), with a purity ≥99.9%; nano-alumina particles, surface-hydroxylated, with a particle size of 60-80 nm and a specific surface area of ​​80-120 m² / g; and cellulose, sodium carboxymethyl cellulose (CMC-Na, viscosity-average molecular weight 3×10⁻⁶). 5); Base membrane, polyethylene / polypropylene (PE / PP) composite membrane, 20μm thick, 45% porosity.

[0049] In a dry glove box with a dew point temperature of -50°C, a composite film-forming agent (VC:VEC:FEC = 2:3:1, total addition 3wt%) was added to 100g of carbonate-based electrolyte; the mixture was stirred at 500 rpm for 4 hours to form a homogeneous solution. 1.5wt% nano-alumina particles were added to the stirred solution, and the mixture was treated with an ultrasonic disperser (frequency 30kHz) for 30 minutes; 0.8wt% CMC-Na was added, and stirring continued for 2 hours to adjust the solution viscosity to 800 mPa·s (25°C); the zeta potential of the suspension was measured to be -35mV, and the sedimentation volume ratio was 3% after standing for 24 hours. The suspension was uniformly coated onto the surface of the PE / PP base film with a wet film thickness of 15 μm using a slot coater. After coating, the membrane was left to stand for 20 minutes in an environment with 25% humidity to form a pre-cured layer. The temperature was increased to 100℃ at 8℃ / min and held for 20 minutes. The temperature was increased to 180℃ at 4℃ / min and a pressure of 0.5MPa was applied for curing for 40 minutes. After curing, the membrane was transferred to an argon annealing furnace (argon purity 99.999%) and annealed at 135℃ for 1 hour, followed by cooling to room temperature at 3℃ / min.

[0050] Test 1: Wetting verification. 2 μL of electrolyte was added to the glove box, and the contact angle was measured to be 28° (meets the standard, no adjustment required). Test 2: Lithium-ion mobility test. The ionic conductivity was measured to be 1.3 × 10⁻⁶ using AC impedance spectroscopy. -3 S / cm (meets standards). Test 3: High-temperature thermal shrinkage rate. After being kept at 200℃ for 1 hour, the transverse shrinkage rate was 0.22%, and the longitudinal shrinkage rate was 0.25% (meets standards). Test 4: Dendrite suppression effect. Constant current charge-discharge test (1C rate, 4.5V cutoff). After 10,000 cycles, the capacity retention rate was 86.5%, the coulombic efficiency was 99.6%, and SEM observation showed no dendrite protrusions on the surface of the protective layer.

[0051] A comparative experiment was added (process parameters were adjusted) to simulate the situation where the heat shrinkage rate exceeded the standard (0.35%). The adjustment involved increasing the curing pressure to 0.8 MPa and adding 3 wt% polyimide fiber. After reprocessing, the test results showed that the heat shrinkage rate decreased to 0.18%; the ion mobility remained at 1.25 × 10⁻⁶. -3 S / cm; contact angle is 26°.

[0052] In this embodiment, a specific ratio (2:3:1) of the composite film-forming agents VC / VEC / FEC forms a gradient SEI film during curing. The fluorine-rich layer from the decomposition of FEC on the surface reduces interfacial resistance; the cross-linking of VEC in the middle layer enhances mechanical strength; and the VC in the bottom layer reacts with cellulose to form interconnected channels. Hydroxylation treatment combined with ultrasonic dispersion allows the nano-alumina particles to be uniformly embedded in the polymer network, increasing the ion channel density to 1.5 × 10⁻⁶. 4 Channels / μm². Through real-time monitoring and parameter adjustments (such as pressure increase and fiber addition), the yield rate has been increased from 80% to 98% using traditional processes.

[0053] In summary, this invention obtains a carbonate-based electrolyte formula, adds a composite film-forming agent to form a mixed solution, and stirs it to a homogeneous state. During the stirring of the mixed solution, nano-alumina particles are added for catalysis, with the particle size range of the nano-alumina particles controlled within 50-100 nanometers. Cellulose is added to the mixed solution to adjust the solution viscosity until a stable suspension system is formed. The suspended mixed solution is injected and uniformly covers the surface of the battery cell separator. Under high temperature conditions of 150-200℃, the mixed solution attached to the battery cell separator is solidified to form a uniform, dendrite-free separator protective layer, thereby achieving the purpose of improving the wettability of the lithium battery separator to the electrolyte, increasing the cycle life of the battery cell, and maintaining high coulombic efficiency.

[0054] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, apparatus, article, or method that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, apparatus, article, or method. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, apparatus, article, or method that includes that element.

[0055] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a highly wettable, long-cycle lithium-ion battery composite separator, characterized in that, Includes the following steps: Obtain a carbonate-based electrolyte formulation, add a composite film-forming agent to form a mixed solution, and stir until homogeneous. The composite film-forming agent includes vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate, and the weight ratio of vinylene carbonate, ethylene ethylene carbonate, and fluoroethylene carbonate is (1-3):(2-4):(1-2). During the stirring of the mixed solution, nano-alumina particles are added for catalysis. The particle size of the nano-alumina particles is controlled in the range of 50-100 nanometers. The nano-alumina particles are surface-hydroxylated nano-alumina particles with a specific surface area of ​​50-150 m² / g. The addition amount is 0.1-3 wt% of the total mass of the mixed solution. The addition process is carried out with ultrasonic-assisted dispersion at 20-40 kHz. Cellulose is added to the mixed solution to adjust the solution viscosity until a stable suspension system is formed. The cellulose is sodium carboxymethyl cellulose. The addition amount is 0.05-1.5 wt% of the total mass of the mixed solution. The solution viscosity is adjusted to 300-1500 mPa·s at 25℃. The absolute value of the Zeta potential of the resulting suspension system is ≥30 mV, and the sedimentation volume ratio is ≤5% after standing for 24 hours. A mixed solution in a suspended state is injected and uniformly covered on the surface of the cell separator. The mixed solution in a suspended state is uniformly coated on the surface of the cell separator with a wet film thickness of 5-20 μm. The mixed solution attached to the cell separator is cured to form a uniform dendrite-free separator protective layer. The curing process employs a gradient temperature increase, comprising: after coating, the membrane is placed in an environment with humidity <30% for 5-30 minutes to form a pre-cured layer; the temperature is increased to 80-120℃ at a heating rate of 5-10℃ / min, held for 10-30 minutes, and then increased to the final curing temperature of 150-200℃ at a rate of 3-5℃ / min, with the curing pressure controlled at 0.1-1MPa; after curing, the membrane is placed in an argon-protected environment and annealed a second time at 120-150℃ for 0.5-2 hours, and then cooled to room temperature at a rate of 2-5℃ / min.

2. The method for preparing the high wettability long-cycle lithium battery composite separator according to claim 1, characterized in that, The step of adding the composite film-forming agent to form a mixed solution includes: A composite film-forming agent is added to a carbonate-based electrolyte, wherein the total amount of the composite film-forming agent added is 0.5-5 wt% of the mass of the carbonate-based electrolyte. In a dry environment with a dew point temperature < -40℃, the stirring speed is 300-800 rpm and the stirring time is 2-6 hours to form a mixed solution.

3. The method for preparing the high wettability long-cycle lithium battery composite separator according to claim 1, characterized in that, The ultrasonic dispersion time of the nano-alumina particles is 10-60 minutes.

4. The method for preparing the high wettability long-cycle lithium battery composite separator according to claim 1, characterized in that, After the step of curing the mixed solution attached to the battery cell separator to form a uniform, dendrite-free separator protective layer, the method further includes: A wettability test was performed on the surface of the diaphragm protective layer. Electrolyte was dropped onto the surface of the diaphragm protective layer, and the static contact angle was measured using a contact angle meter. When the contact angle was ≥30°, the total amount of composite film-forming agent was increased in a gradient of 0.5-2wt%, and the coating and curing were repeated. When the contact angle was <30°, the wettability of the diaphragm was deemed to meet the standard. The contact angle measurement was to be performed in an inert atmosphere glove box at a test temperature of 25±2℃, with an electrolyte drop volume of 2μL, and the measurement was to be completed within 10 seconds after the drop was added. Lithium-ion mobility was tested on the membranes that met the wettability standards. The ionic conductivity of the membranes in the frequency range of 1MHz-100kHz was tested by AC impedance method, and the lithium-ion mobility was calculated. For membranes that meet the migration rate standard, high-temperature heat shrinkage verification is performed. Finally, the membrane needs to be verified for high-temperature thermal stability. The membrane is placed in a 200℃ constant temperature chamber for 1 hour, and the lateral and longitudinal shrinkage rates are measured. When the shrinkage rate in either direction is ≥0.3%, the process is adjusted and the membrane is re-prepared.

5. The method for preparing the high wettability long-cycle lithium battery composite separator according to claim 4, characterized in that, The step of adjusting the process to re-prepare the membrane includes: When the shrinkage rate in any direction is ≥0.3%, the material is re-prepared after performing at least one process adjustment, which includes increasing the curing pressure to the range of 0.5-1 MPa, adding 1-5 wt% polyimide fiber to the cellulose, and replacing the nano alumina particles with nano zirconium oxide particles modified with silane coupling agents.

6. A highly wettable, long-cycle lithium-ion battery composite separator, characterized in that, It is prepared by the method of any one of claims 1-5 for high wettability long-cycle lithium battery composite separator.

7. The application of the high wettability long-cycle lithium battery composite separator according to claim 6, characterized in that, The composite separator is used in lithium-ion batteries.

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