Lithium ion battery cell diaphragm based on carbonic ester-based electrolyte as well as preparation method and application of lithium ion battery cell diaphragm

Abstract

The invention relates to a lithium ion battery cell diaphragm based on a carbonic ester-based electrolyte and a preparation method and application thereof, and the method comprises the following steps: obtaining the composition proportion of the carbonic ester-based electrolyte, and combining the type and concentration parameters of a composite film-forming agent to obtain an electrolyte basic composition; calculating the mixing ratio of the nanometer aluminum oxide to the cellulose in combination with preset particle size distribution of the nanometer aluminum oxide and the cellulose to obtain a nanometer particle mixture; stirring the electrolyte basic composition and the nano-particle mixture to obtain an electrolyte mixed system; obtaining the porosity of the battery cell diaphragm, and calculating the infiltration time of the electrolyte mixed system in the diaphragm through the infiltration kinetic model; and injecting the electrolyte mixed system into the battery cell diaphragm, and fully infiltrating the electrolyte mixed system into diaphragm pores according to the infiltration time to obtain the battery cell diaphragm, so as to realize the purpose of preparing the lithium ion battery cell diaphragm which is excellent in performance, high in stability and capable of self-adapting to the battery operation change so as to improve the comprehensive performance of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and particularly relates to a separator for a lithium-ion battery cell based on a carbonate-based electrolyte, a preparation method thereof, and an application thereof. Background Art

[0002] In the field of lithium-ion batteries, the separator of the battery cell is a key component and plays a crucial role in the performance, safety, and lifespan of the battery. There are many deficiencies in the traditional preparation methods of lithium-ion battery cell separators. On the one hand, the existing electrolyte systems show poor compatibility with the separators. Common electrolytes lack an effective compound film-forming agent formulation strategy and are difficult to form a stable and uniform protective film during the charge and discharge process of the battery cell, resulting in a shortened battery cycle life and a reduced Coulomb efficiency. For example, the use of a single film-forming agent cannot meet the requirements of a complex electrochemical environment, and after multiple charge and discharge cycles of the battery, problems such as lithium plating and dendrite growth are likely to occur on the electrode surface. On the other hand, in the wetting process of the separator and the electrolyte, traditional methods lack precise control means. The relationship between the porosity of the separator and the wetting time of the electrolyte has not been fully studied and optimized, resulting in uneven wetting of the electrolyte in the separator, affecting the uniformity of lithium-ion migration in the separator, and thus reducing the overall performance of the battery. These deficiencies seriously affect the safety and performance stability of the battery. Summary of the Invention

[0003] The first object of the present invention is to provide a separator for a lithium-ion battery cell based on a carbonate-based electrolyte, a preparation method thereof, and an application thereof, so as to achieve the purpose of preparing a lithium-ion battery cell separator with excellent performance, high stability, and the ability to adapt to the changes in battery operation, and improving the comprehensive performance of the battery.

[0004] To achieve the above object, the present invention provides a preparation method for a separator for a lithium-ion battery cell based on a carbonate-based electrolyte, comprising the following steps: Obtain the composition ratio of the carbonate-based electrolyte, and combine the types and concentration parameters of the compound film-forming agents to obtain a basic electrolyte composition, wherein the compound film-forming agents include at least two of FEC, VEC, and VC, and the total concentration is 0.5 - 5 wt%; Based on the viscosity and polarity parameters of the basic electrolyte composition, combine the preset particle size distributions of nano-aluminum oxide and cellulose to calculate the mixing ratio of nano-aluminum oxide and cellulose, and obtain a nano-particle mixture; Perform a staged stirring treatment on the basic electrolyte composition and the nano-particle mixture, and the staged stirring treatment includes variable-speed mixing and ultrasonic dispersion to obtain a uniform electrolyte mixing system; Obtain the porosity data of the battery cell separator, and calculate the wetting time of the electrolyte mixing system in the separator through a wetting kinetics model; Inject the electrolyte mixture system into the cell separator. Based on the calculated wetting time parameter, fully wet the electrolyte mixture system into the pores of the separator to obtain the cell separator.

[0005] Further, the step of obtaining the composition ratio of the carbonate-based electrolyte and combining the types and concentration parameters of the composite film-forming agent to obtain the basic electrolyte composition includes: Obtain the mixing ratio of the carbonate-based electrolyte, and mix ethylene carbonate and dimethyl carbonate according to a preset volume ratio; Add a composite film-forming agent, which is a combination of at least two of FEC, VEC, and VC, and the concentration of a single film-forming agent is 0.5-3 wt%, and the total concentration of the composite film-forming agent does not exceed 5 wt%; Optimize the concentration range of the lithium salt to 1.0-1.5 mol / L through an orthogonal experiment to obtain the basic electrolyte composition, and control the viscosity of the basic electrolyte composition within the range of 2.5-4.0 mPa·s.

[0006] Further, the step of calculating the mixing ratio of nano-aluminum oxide and cellulose based on the viscosity and polarity parameters of the basic electrolyte composition and combining the preset particle size distributions of nano-aluminum oxide and cellulose to obtain the nano-particle mixture includes: Determine the mass ratio of nano-aluminum oxide to cellulose according to the viscosity and polarity parameters of the basic electrolyte composition, where the D50 particle size of the nano-aluminum oxide is 20-50 nm, and the D50 particle size of the cellulose is 100-200 nm; Surface-modify the nano-aluminum oxide with a silane coupling agent, and the addition amount of the modifier is 0.5-1.2% of the total mass of the nano-aluminum oxide and cellulose; Detect the dispersion uniformity by dynamic light scattering method, control the absolute value of the Zeta potential ≥30 mV, and the sedimentation volume ratio ≤5% after standing for 24 hours to obtain the nano-particle mixture.

[0007] Further, the step of subjecting the basic electrolyte composition and the nano-particle mixture to staged stirring treatment to obtain a uniform electrolyte mixture system includes: Mix the basic electrolyte composition and the nano-particle mixture; Stir at a low speed of 200-400 rpm for 30-60 min, and then stir at a high speed of 800-1200 rpm for 15-30 min. Control the stirring temperature at 25±2 °C, and continuously introduce dry nitrogen during the stirring process; After the stirring is completed, perform ultrasonic-assisted dispersion with an ultrasonic power of 200-500 W and a frequency of 28-40 kHz to obtain the electrolyte mixture system.

[0008] Further, the step of obtaining the porosity data of the cell separator and calculating the wetting time of the electrolyte mixture system in the separator includes: Determine the pore size distribution of the cell separator by mercury intrusion porosimetry, and control the effective wetting path length ≤ 50 μm; Set the wetting end determination criterion as the mass change rate of the separator ≥ 98%; Calculate the wetting time of the electrolyte mixture system in the separator through a pre-constructed wetting kinetics model, and verify the wetting effect by the weighing method.

[0009] Further, the step of injecting the electrolyte mixture system into the cell separator, and based on the calculated wetting time parameter, fully wetting the electrolyte mixture system into the pores of the separator to obtain the cell separator includes: Based on the calculated wetting time parameter, adopt the vacuum pressure gradient injection method, control the vacuum degree at -90 kPa to -50 kPa, the injection pressure at 0.1 - 0.3 MPa, and perform stepwise pressurized wetting three times, with a pressure increment of 0.05 MPa each time and an interval time of 5 - 10 min, to wet the electrolyte mixture system into the pores of the cell separator; After wetting, perform hot pressing treatment, control the temperature at 60 - 80 °C, the pressure at 1 - 3 MPa, and the duration at 10 - 30 min to obtain the cell separator.

[0010] Further, the crystallinity change of the cell separator obtained after hot pressing treatment is ≤ 5%, and it is verified by differential scanning calorimetry.

[0011] Further, after the step of obtaining the cell separator, it further includes: During the charge and discharge process of the cell, monitor the distribution of lithium ions in the separator in real time, judge whether the lithium ion migration is uniform, and if the distribution is not uniform, adjust the mixing ratio of the electrolyte mixture; Perform charge and discharge tests on the cell through preset cycle test conditions to obtain the cycle life data and Coulomb efficiency value of the cell; According to the cycle test results, analyze the thermal shrinkage rate and tensile resistance performance of the cell. If the thermal shrinkage rate is higher than the preset threshold, optimize the proportion of the composite film-forming agent in the electrolyte formula; Combined with the lithium ion distribution data and cycle test results, judge the uniformity of the separator protective layer. If there is a dendrite growth phenomenon, adjust the mixing ratio of nano-aluminum oxide and cellulose.

[0012] The second object of the present invention is to provide a lithium ion cell separator obtained by the above lithium ion cell separator preparation method based on a carbonate-based electrolyte.

[0013] The third object of the present invention is to provide an application of a separator for a lithium-ion cell based on a carbonate-based electrolyte. In some specific embodiments, the composite separator is used in a lithium-ion battery.

[0014] The lithium-ion cell separator based on a carbonate-based electrolyte, its preparation method and application provided by the present invention have the following beneficial effects: By adjusting the electrolyte system and the composite film-forming agent, the reaction environment during the charge and discharge process of the cell is improved, resulting in a significant increase in the cycle life and Coulomb efficiency of the battery; In the separator preparation process, the present invention has developed precise control methods for key links such as nanoparticle addition and electrolyte infiltration, realizing refined operation in the preparation process, improving the product consistency and the yield rate; Through the optimized electrolyte system and preparation process, adverse phenomena such as lithium deposition and dendrite growth can be effectively inhibited, reducing the risk of battery thermal shrinkage and improving the tensile resistance of the separator, thereby significantly enhancing the safety performance of the battery and reducing potential safety hazards. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a process schematic diagram of a method for preparing a separator for a lithium-ion cell based on a carbonate-based electrolyte in an embodiment of the present invention; The realization of the object, functional characteristics and advantages of the present invention will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] In order to make the object, technical solution and advantages of the present invention clearer, the present 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 here are only used to explain the present invention and are not used to limit the present invention.

[0017] Referring to Figure 1 , which is a process schematic diagram of a method for preparing a separator for a lithium-ion cell based on a carbonate-based electrolyte proposed by the present invention, includes the following steps: S1. Obtain the composition ratio of the carbonate-based electrolyte, and combine the types and concentration parameters of the composite film-forming agent to obtain a basic electrolyte composition. The composite film-forming agent includes at least two of FEC, VEC, and VC, and the total concentration is 0.5-5 wt%. S2. Based on the viscosity and polarity parameters of the basic electrolyte composition, and in combination with the preset particle size distributions of nano-aluminum oxide and cellulose, calculate the mixing ratio of nano-aluminum oxide and cellulose to obtain a nanoparticle mixture. S3. Perform staged stirring treatment on the basic electrolyte composition and the nanoparticle mixture. The staged stirring treatment includes variable-speed mixing and ultrasonic dispersion to obtain a uniform electrolyte mixing system. S4. Obtain the porosity data of the cell separator, and calculate the wetting time of the electrolyte mixture system in the separator through the wetting kinetics model; S5. Inject the electrolyte mixture system into the cell separator, and based on the calculated wetting time parameter, fully wet the electrolyte mixture system into the pores of the separator to obtain the cell separator.

[0018] As described in step S1 above, in this step, a formulation system of the electrolyte base composition is constructed. A binary solvent system of ethylene carbonate (EC) and dimethyl carbonate (DMC) is used, and the balance between the electrolyte viscosity and the ionic conductivity is regulated by a volume ratio of 1:(0.8 - 1.2); A binary or ternary composite system of three film-forming agents, fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), and vinylene carbonate (VC), is introduced. The concentration gradients of each component are determined through orthogonal experiments (0.5 - 3 wt% for a single component, and the total amount ≤ 5 wt%). The synergistic effect of different film-forming agents is utilized to enhance the stability of the SEI film; Through the coupled design of lithium salt concentration optimization (1.0 - 1.5 mol / L) and viscosity control (2.5 - 4.0 mPa·s), the rheological properties of the electrolyte system in the subsequent nanoparticle dispersion stage are ensured.

[0019] As described in step S2 above, select the particle size grading of nano-aluminum oxide (Al2O3, D50 = 20 - 50 nm) and micro-scale cellulose (D50 = 100 - 200 nm) according to the electrolyte polarity parameter (dielectric constant ε = 20 - 30), and calculate and determine the mass ratio range through the Hansen solubility parameter (Al2O3:cellulose = 3:1 - 5:1); Use silane coupling agent KH-550 to conduct surface graft modification on Al2O3, with the dosage of the modifier being 0.5 - 1.2 wt%. Verify that the coating rate ≥ 85% through TGA thermogravimetric analysis; Establish an evaluation standard for dispersion stability: the absolute value of the Zeta potential ≥ 30 mV (tested by Malvern Zetasizer), and the sedimentation volume ratio ≤ 5% (monitored by a laser sedimentation instrument) to ensure the suspension stability of the nanoparticles in the electrolyte.

[0020] As described in step S3 above, mix and stir the electrolyte base composition of S1 and the nanoparticle mixture of S2, and adopt a variable-speed mixing strategy: in the low-speed stage (200 - 400 rpm × 30 - 60 min), conduct macroscopic dispersion, and in the high-speed stage (800 - 1200 rpm × 15 - 30 min), break the nanoaggregates; Introduce ultrasonic-assisted dispersion (200 - 500 W, 28 - 40 kHz), and generate microjets with a local pressure > 100 MPa through the cavitation effect to deagglomerate the nanoparticles; Control the process environment temperature at 25 ± 2 °C (to avoid solvent volatilization), and a nitrogen atmosphere (dew point ≤ -40 °C) to prevent the hydrolysis of the lithium salt (i.e., LiPF6).

[0021] As described in step S4 above, the mercury intrusion method is used to measure the pore structure parameters of the separator (median pore size 0.1 - 0.3 μm, porosity 40 - 60%), and the effective wetting path length ≤ 50 μm; through the pre-established wetting kinetics model t = (2ηL²) / (γrcosθ) × (1 + 3r / 4L), where η is the electrolyte viscosity, γ is the surface tension, θ is the contact angle, L is the wetting path length, and the mass change rate ≥ 98% is set as the determination standard for the wetting end point to calculate the wetting time. Among them, the wetting kinetics model is obtained by modifying the Washburn equation in combination with the interaction between the electrolyte and the separator. Through real-time monitoring by a high-precision balance (accuracy 0.1 mg), experimental verification shows that the deviation between the calculated value and the measured value ≤ 15%.

[0022] As described in step S5 above, the vacuum pressure gradient injection method is used to fully infiltrate the electrolyte mixture system obtained in S3 into the pores of the separator. In the initial stage, vacuum degassing is carried out at -90 kPa, and then stepwise pressurization is carried out three times (0.1 - 0.15 - 0.2 MPa), with a 5 - 10 min interval for each stage to allow capillary penetration of the electrolyte; optimize the hot pressing treatment parameters, control the temperature at 60 - 80 °C (below the melting point of the separator), and the pressure at 1 - 3 MPa (maintaining the structural integrity of the separator), and confirm through DSC testing that the change in the crystallinity of the separator after hot pressing ≤ 5%; finally, test the performance of the separator. The separator performance indicators include an electrolyte retention capacity ≥ 3.5 g / Ah, an ionic conductivity ≥ 1.2 mS / cm (tested at 25 °C), and a puncture strength ≥ 300 gf / μm.

[0023] In one embodiment, a lithium-ion battery cell separator is prepared based on a carbonate-based electrolyte. The materials include a solvent, ethylene carbonate (EC) and dimethyl carbonate (DMC), with a volume ratio of 4:6; a composite film-forming agent, fluoroethylene carbonate (FEC) and vinylene carbonate (VC), with concentrations of 1.5 wt% and 1.5 wt% respectively; a lithium salt (LiPF6), with a concentration of 1.2 mol / L; nanoparticles, alumina (Al2O3, D50 = 30 nm), cellulose (D50 = 150 nm), with a mass ratio of 1:0.5; a silane coupling agent, KH-550 (the dosage is 0.8% of the total mass of the nanoparticles); a separator substrate: a polyethylene (PE) porous film (porosity 55%, thickness 20 μm).

[0024] Mix EC and DMC in a volume ratio of 4:6 and stir magnetically for 30 min (25 °C); successively add FEC (1.5 wt%) and VC (1.5 wt%), and stir until completely dissolved; add LiPF6 powder in three portions, control the solution temperature ≤ 30 °C, and finally the LiPF6 concentration is 1.2 mol / L; measure the viscosity of the electrolyte as 3.2 mPa·s (25 °C) using a rotational viscometer. Mix Al2O3 and cellulose in a mass ratio of 1:0.5; add KH-550 (0.8 wt%) for surface modification: ultrasonically treat in an ethanol solvent for 1 h (40 kHz) and vacuum dry at 80 °C; dynamic light scattering test shows that the Zeta potential is -35 mV and the sedimentation volume ratio is 3% after standing for 24 h; confirm the compatibility with the electrolyte by Hansen parameter calculation (δd = 18.2, δp = 8.6, δh = 7.3). Add the nanoparticle mixture to the electrolyte base composition in three batches. Stir at low speed, 400 rpm × 40 min (under nitrogen protection, dew point -45 °C); stir at high speed, 1000 rpm × 20 min, and the solution temperature is 25 ± 1 °C; ultrasonically disperse at a power of 300 W, a frequency of 35 kHz, and treat for 30 min (amplitude 80%); finally, there is no visible agglomeration in the mixed system (observed by SEM, particle spacing ≥ 200 nm). Measure the pore size distribution of the separator by mercury intrusion porosimetry, the median pore size is 0.22 μm, and the porosity is 55%; calculate the wetting time as 12.8 minutes through the wetting kinetics model:

[0025] Measure the actual wetting time as 13.5 min (mass change rate 98.2%) by the gravimetric method, with a deviation ≤ 5%. Inject the electrolyte mixed system into the separator by the vacuum gradient injection method. In the first stage, degas under -80 kPa vacuum for 5 min, and the injection pressure is 0.1 MPa; in the second stage, maintain the pressure at 0.15 MPa for 8 min; in the third stage, maintain the pressure at 0.2 MPa for 5 min; then perform hot pressing treatment, 70 °C × 2 MPa × 20 min (DSC shows a crystallinity change of 4.3%); finally, the separator performance is an electrolyte retention of 3.8 g / Ah, an ionic conductivity of 1.35 mS / cm (25 °C), and a puncture strength of 325 gf / μm. Perform performance tests and optimization verification on the separator. Cycle test (0.5C charge and discharge, 2.5 - 4.2 V); measure the thermal shrinkage rate (bake at 85 °C for 1 h), the longitudinal shrinkage rate is 2.1%, and the transverse is 1.8%; measure the tensile strength: 125 MPa in the MD direction and 118 MPa in the TD direction (ASTM D882 standard).

[0026] In this embodiment, the impedance of the SEI film is reduced by 32% through the synergistic effect of the composite film-forming agent (FEC + VC) (EIS test), the thermal stability of the separator is improved by the nano-particle grading design (the initial decomposition temperature of TGA is increased by 28 °C), and the uniformity of the electrolyte distribution reaches 93.5% by the gradient injection process (X-ray CT scan analysis). Finally, the cycle life is increased by 35% (compared with the traditional EC / DMC electrolyte system); the capacity attenuation is ≤5% after storing at high temperature (60 °C) for 7 days; the discharge capacity retention rate at 5C rate is ≥85%.

[0027] In summary, the present invention obtains the composition ratio of the carbonate-based electrolyte, combines the types and concentration parameters of the composite film-forming agent to obtain the basic electrolyte composition; based on the viscosity and polarity parameters of the basic electrolyte composition, combines the preset particle size distributions of nano-aluminum oxide and cellulose to calculate the mixing ratio of nano-aluminum oxide and cellulose to obtain a nano-particle mixture; performs a staged stirring process on the basic electrolyte composition and the nano-particle mixture, and the staged stirring process includes variable-speed mixing and ultrasonic dispersion to obtain a uniform electrolyte mixing system; obtains the porosity data of the cell separator, and calculates the infiltration time of the electrolyte mixing system in the separator through an infiltration kinetics model; injects the electrolyte mixing system into the cell separator, and based on the calculated infiltration time parameter, fully infiltrates the electrolyte mixing system into the pores of the separator to obtain a cell separator, so as to achieve the preparation of a lithium-ion cell separator with excellent performance, high stability and the ability to adapt to battery operation changes, and to improve the comprehensive performance of the battery.

[0028] It should be noted that in this article, the terms "include", "comprise" or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, device, article or method including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, device, article or method. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of additional identical elements in the process, device, article or method including that element.

[0029] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte, characterized in that, It includes the following steps: Obtain the composition ratio of the carbonate-based electrolyte, and combine the types and concentration parameters of the composite film-forming agent to obtain the basic electrolyte composition. The composite film-forming agent includes at least two of FEC, VEC, and VC, and the total concentration is 0.5-5 wt%; Based on the viscosity and polarity parameters of the basic electrolyte composition, and in combination with the preset particle size distributions of nano-aluminum oxide and cellulose, calculate the mixing ratio of nano-aluminum oxide and cellulose to obtain a nano-particle mixture; Perform staged stirring treatment on the basic electrolyte composition and the nano-particle mixture. The staged stirring treatment includes variable-speed mixing and ultrasonic dispersion to obtain a uniform electrolyte mixing system; Obtain the porosity data of the cell separator, and calculate the infiltration time of the electrolyte mixing system in the separator through the infiltration kinetics model; Inject the electrolyte mixing system into the cell separator, and based on the calculated infiltration time parameter, fully infiltrate the electrolyte mixing system into the pores of the separator to obtain the cell separator.

2. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, characterized in that, The step of obtaining the composition ratio of the carbonate-based electrolyte, and combining the types and concentration parameters of the composite film-forming agent to obtain the basic electrolyte composition includes: Obtain the mixing ratio of the carbonate-based electrolyte, and mix ethylene carbonate and dimethyl carbonate according to a preset volume ratio; Add a composite film-forming agent, which is a combination of at least two of FEC, VEC, and VC, and the concentration of a single film-forming agent is 0.5-3 wt%, and the total concentration of the composite film-forming agent does not exceed 5 wt%; Optimize the concentration range of the lithium salt to 1.0-1.5 mol / L through orthogonal experiments to obtain the basic electrolyte composition, and control the viscosity of the basic electrolyte composition within the range of 2.5-4.0 mPa·s.

3. The method for preparing a separator of a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, characterized in that, The step of calculating the mixing ratio of nano-aluminum oxide and cellulose based on the viscosity and polarity parameters of the basic electrolyte composition, and in combination with the preset particle size distributions of nano-aluminum oxide and cellulose to obtain a nano-particle mixture includes: Determine the mass ratio of nano-aluminum oxide to cellulose according to the viscosity and polarity parameters of the basic electrolyte composition, where the D50 particle size of the nano-aluminum oxide is 20-50 nm, and the D50 particle size of the cellulose is 100-200 nm; Surface-modify the nano-aluminum oxide with a silane coupling agent, and the addition amount of the modifier is 0.5-1.2% of the total mass of nano-aluminum oxide and cellulose; Detect the dispersion uniformity by dynamic light scattering method, control the absolute value of Zeta potential ≥30 mV, and the sedimentation volume ratio ≤5% after standing for 24 hours to obtain a nano-particle mixture.

4. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, wherein The step of performing staged stirring treatment on the basic electrolyte composition and the nano-particle mixture to obtain a uniform electrolyte mixing system includes: Mix the basic electrolyte composition and the nano-particle mixture; Stir at a low speed of 200-400 rpm for 30-60 min, and then stir at a high speed of 800-1200 rpm for 15-30 min. The stirring temperature is controlled at 25±2 °C, and dry nitrogen is continuously introduced during the stirring process; After stirring is completed, ultrasonic wave with a power of 200 - 500 W and a frequency of 28 - 40 kHz is used for auxiliary dispersion to obtain an electrolyte mixing system.

5. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, characterized in that, The step of obtaining the porosity data of the cell separator and calculating the infiltration time of the electrolyte mixing system in the separator includes: Determining the pore size distribution of the cell separator by mercury intrusion porosimetry, and controlling the effective infiltration path length ≤ 50 μm; Setting the infiltration end determination criterion as the mass change rate of the separator ≥ 98%; Calculating the infiltration time of the electrolyte mixing system in the separator through a pre - constructed infiltration kinetic model, and verifying the infiltration effect by the weighing method.

6. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, characterized in that, The step of injecting the electrolyte mixing system into the cell separator and fully infiltrating the electrolyte mixing system into the separator pores based on the calculated infiltration time parameter to obtain the cell separator includes: Based on the calculated infiltration time parameter, adopting the vacuum pressure gradient injection method, controlling the vacuum degree at - 90 kPa to - 50 kPa, the injection pressure at 0.1 - 0.3 MPa, and performing step - by - step pressure - increasing infiltration three times, with a pressure increment of 0.05 MPa each time and an interval time of 5 - 10 min, to infiltrate the electrolyte mixing system into the pores of the cell separator; After infiltration is completed, hot - pressing treatment is carried out, controlling the temperature at 60 - 80 °C, the pressure at 1 - 3 MPa, and the duration at 10 - 30 min to obtain the cell separator.

7. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 6, characterized in that, After hot - pressing treatment, the crystallinity change of the obtained cell separator is ≤ 5%, and it is verified by differential scanning calorimetry.

8. The method for preparing a separator for a lithium-ion battery cell based on a carbonate-based electrolyte according to claim 1, wherein, After the step of obtaining the cell separator, it further includes: During the charge and discharge process of the cell, real - time monitoring the distribution of lithium ions in the separator, judging whether the migration of lithium ions is uniform, and if the distribution is not uniform, adjusting the mixing ratio of the electrolyte; Through the preset cycle test conditions, performing charge and discharge tests on the cell to obtain the cycle life data and Coulomb efficiency value of the cell; According to the cycle test results, analyzing the thermal shrinkage rate and tensile resistance performance of the cell. If the thermal shrinkage rate is higher than the preset threshold, optimizing the proportion of the composite film - forming agent in the electrolyte formula; Combining the lithium ion distribution data and the cycle test results, judging the uniformity of the separator protective layer. If there is a dendrite growth phenomenon, adjusting the mixing ratio of nano - alumina and cellulose.

9. A separator for a lithium-ion battery cell based on a carbonate-based electrolyte, characterized in that, Prepared by the method of the lithium - ion cell separator based on carbonate - based electrolyte according to any one of claims 1 - 8.

10. Application of a separator for a lithium-ion battery cell based on a carbonate-based electrolyte, characterized in that, The lithium - ion cell separator is used in a lithium - ion battery.

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