CN113904059A

CN113904059A - High-pore-uniformity microporous membrane, preparation method thereof and battery

Info

Publication number: CN113904059A
Application number: CN202111127876.9A
Authority: CN
Inventors: 庄志; 宫晓明; 彭锟; 李堃; 虞少波; 程跃
Original assignee: Shanghai Energy New Materials Technology Co Ltd
Current assignee: Shanghai Energy New Materials Technology Co Ltd
Priority date: 2021-09-26
Filing date: 2021-09-26
Publication date: 2022-01-07
Also published as: WO2023045312A1

Abstract

The invention relates to the technical field of lithium battery diaphragms, and particularly discloses a preparation method of a microporous membrane with high pore uniformity, which comprises the following steps: (1) mixing and heating polyolefin and pore-forming agent to be molten; (2) cooling to form a sheet through a die head; (3) sucking out the pore-forming agent in the thin slice through an oil removing roller; (4) heating and stretching along at least one axial direction; (5) stretching and shaping along at least one axial direction again; (6) rolling to obtain a microporous membrane with high pore uniformity; wherein, in the step (3), the surface of the oil removing roller is provided with a micropore flow passage, and the center of the oil removing roller is provided with a hollow pipeline and a heating coil; the hollow pipeline is connected with the micropore flow channel on the surface of the roller, and the outside of the hollow pipeline is connected with the vacuumizing machine; the heating coil is connected with an external heat exchange station. The diaphragm prepared by the method has the characteristics of low porosity, extremely high pore uniformity, low surface resistivity and extremely high D value (D is the needling strength/thickness).

Description

High-pore-uniformity microporous membrane, preparation method thereof and battery

Technical Field

The invention relates to the technical field of lithium battery diaphragms, in particular to a high-pore-uniformity microporous membrane and a preparation method thereof.

Background

At present, lithium ion batteries are widely applied in the field of power, and as a core component diaphragm of lithium battery safety guarantee, the application modes of a polyethylene microporous membrane are mainly two, wherein one is directly loaded between a positive pole piece and a negative pole piece as the diaphragm; the other one is used as a diaphragm, is coated with ceramic, boehmite, PVDF, aramid fiber and the like for the second time to enhance the heat resistance of the diaphragm, and is loaded between the positive and negative pole pieces.

In either case, the ion channel between the positive and negative electrodes is provided by a microporous polyethylene membrane. In recent years, the requirement of high energy density of the battery has been that the separator is continuously thinned, and the polyethylene microporous membrane itself is required to have high needle punching strength, high tensile strength, low closed pore temperature, and the like, so as to ensure the safety of the lithium battery in case of abnormal deformation and high temperature. The pores of the microporous polyethylene membrane are required to have high uniformity, so that the following effects are ensured: 1. after charging and discharging for many times, lithium ions cannot be separated out at the negative electrode corresponding to the position with more and larger holes, lithium dendrite growth after negative electrode full load inlaying is accumulated, and therefore the polyethylene microporous membrane is pierced to form short circuit; 2. when a high-rate charge/discharge is used in a portion having a high surface resistivity of the separator, excessive heat generation occurs, and thermal runaway occurs.

In summary, it is the uniformity of the pores of the microporous polyethylene membrane itself that is important.

At present, a wet asynchronous stretching process is often used for the polyethylene microporous membrane applied to the lithium ion battery. The preparation process comprises the following steps: by heating the polyolefin and pore forming solvent to melt on an extruder. After passing through the T-shaped die head, a plurality of groups of cooling rollers through which chilled water/cooling water passes are cooled to form a thin sheet. Then, the film is stretched in the MD (in-line direction) at an elevated temperature. Then stretching along TD (vertical production line), removing pore-forming agent, and stretching along at least one axial direction again to obtain the microporous polyethylene membrane. Both MD roll extrusion stretching and TD double side nip stretching are high speed stretching. At this moment, the polyethylene microporous membrane, the internal pore structure is complicated and intricate, soft texture and vulnerable damage under high temperature state, the extrusion of stress action this moment, pore-forming agent can't get rid of outside the polyethylene microporous membrane in the very first time, pore-forming agent liquid drop in the hole is four scurries, link up, merges, arouses on the diaphragm microstructure, take place the layering, show that diaphragm macropore proportion rises, whole through-hole quantity is less, the homogeneity is relatively poor, when maintaining certain ventilative & face resistivity, often there is higher porosity, lower D value (D ═ needling strength/thickness).

Disclosure of Invention

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

the invention aims to provide a preparation method of a microporous membrane with high pore uniformity, which comprises the following steps:

(1) mixing and heating polyolefin and pore-forming agent to be molten;

(2) cooling to form a sheet through a die head;

(3) sucking out the pore-forming agent in the thin slice through an oil removing roller;

(4) heating and stretching along at least one axial direction;

(5) stretching and shaping along at least one axial direction again;

(6) rolling to obtain a microporous membrane with high pore uniformity;

in the step (3), the surface of the oil removing roller is provided with a micropore flow passage, and the center of the oil removing roller is provided with a hollow pipeline and a heating coil; the hollow pipeline is connected with the micropore flow channel on the surface of the roller, and the outside of the hollow pipeline is connected with the vacuumizing machine; the heating coil is connected with an external heat exchange station.

Furthermore, the diameter of the pore of the micropore runner is less than or equal to 1.0 mm.

Furthermore, the diameter of the pore of the micropore flow passage is less than or equal to 0.01 mm.

Furthermore, the area of the micropore flow channel on the surface of the oil removing roller accounts for more than or equal to 50% of the total area of the roller surface of the oil removing roller.

Furthermore, the area of the micropore flow channel on the surface of the oil removing roller accounts for more than or equal to 80 percent of the total area of the roller surface of the oil removing roller.

Further, the vacuum degree in the oil removing roller is more than or equal to 0.05 Mpa.

Furthermore, the vacuum degree in the oil removing roller is more than or equal to 0.08 MPa.

Furthermore, the wrap angle between the surface of the oil removing roller and the thin sheet is more than or equal to 60 degrees.

Furthermore, the wrap angle between the surface of the oil removing roller and the thin sheet is more than or equal to 180 degrees.

Furthermore, the heating temperature of the oil removing roller is more than or equal to 60 ℃ and less than or equal to 100 ℃.

Furthermore, the heating temperature of the oil removing roller is more than or equal to 80 ℃ and less than or equal to 100 ℃.

Furthermore, the number of the oil removing rollers is more than or equal to 4.

Furthermore, the number of the oil removing rollers is more than or equal to 8.

Further, after the step (3) is finished, the residual oil rate of the thin slice is less than or equal to 20 percent.

Further, after the step (3) is finished, the residual oil rate of the thin slice is less than or equal to 2 percent.

Further, an extraction process is also included, wherein the extraction process is positioned before or after the step (4).

The invention aims to further provide a microporous membrane with high pore uniformity, wherein the microporous membrane is a polyolefin diaphragm, the pore diameter is measured by a bubble point method, and the ratio of the maximum pore diameter to the median pore diameter is less than or equal to 1.3.

Further, the median pore diameter of the polyolefin diaphragm is 25-30 nm.

Further, the maximum pore diameter of the polyolefin diaphragm ranges from 26 nm to 39 nm.

Further, the ratio of the maximum pore diameter to the median pore diameter is less than or equal to 1.05 when the pore diameter is tested by a bubble point method.

Further, the porosity of the polyolefin separator is less than or equal to 30%.

Still further, the polyolefin membrane has a gas permeability value and a thickness satisfying the following relationship: e is less than or equal to 10s/165 ml/mum, and E is air permeability value/thickness.

Further, the surface resistivity of the polyolefin diaphragm is less than or equal to 0.05 omega cm²。

Further, the polyolefin diaphragm needle punching strength and the thickness satisfy the following relations: d is not less than 150 gf/mum, and D is the needling strength/thickness.

Still further, the polyolefin separator has a needle punching strength and a thickness satisfying the following relationship: d is more than or equal to 200 gf/mum, and D is the needling strength/thickness.

Further, the polyolefin separator is a single component polyethylene separator.

The present invention also provides a battery comprising any one of the above-described microporous membranes having high pore uniformity as an element for separating positive and negative electrodes.

Compared with the prior art, the invention has the following beneficial effects:

the invention provides a preparation method of a microporous membrane with high pore uniformity, when the method is adopted, a large amount of pore-forming agent which is pre-extracted in the process can be directly added into a pore-forming agent finished product tank for reuse after simple filtration, the use amount of the extracting agent in the later extraction process can be greatly reduced, the energy consumption for separating the extracting agent from the pore-forming agent is also reduced, the condition that the pore-forming agent cannot be reused after the quality is reduced due to secondary thermal processing (MD + TD or SBS) of the pore-forming agent is avoided, and the production cost and the raw material cost are greatly reduced. In addition, the microporous membrane with high pore uniformity provided by the invention has no layering on the microstructure, has the characteristics of low porosity, extremely high pore uniformity, low resistivity, extremely high D value (D is the needling strength/thickness) and low E value (E is the ventilation value/thickness), has good electrochemical properties such as high-rate charge and discharge and excellent safety when being applied to a battery, and can be well used in the market of power batteries with higher specific energy requirements.

Drawings

FIG. 1 is a schematic cross-sectional view of a sucker rod of the present invention;

FIG. 2 is a side view of a pump roll construction according to the present invention;

FIG. 3 is a flow chart of the pumping section of the present invention;

FIG. 4 is a flow diagram of a normal process for preparing a prior art separator;

FIG. 5 is a flow chart of a process for preparing a separator according to one embodiment of the present invention;

description of the element reference numerals

1. Oil removing roller

2. Microporous flow passage

3. Hollow pipeline

4. Heating coil

S1, extrusion

S2, cooling into pieces

S3 extraction of pore-forming agent

S4, at least one-way stretching

S5, extraction

S6, at least one-time stretching and shaping

S7, rolling

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

Referring to fig. 1 to 3, an embodiment of the present invention provides a method for preparing a microporous membrane with high pore uniformity, including the following steps:

(1) mixing and heating polyolefin and pore-forming agent to be molten;

(2) extruding the mixture through a die head to form S1, and cooling to form a sheet S2;

(3) sucking out the pore-forming agent inside the sheet through the oil removing roller 1S 3;

(4) increasing the temperature to stretch in at least one axial direction S4;

(5) stretch-setting again in at least one axial direction S6;

(6) rolling S7 to obtain a microporous membrane with high pore uniformity;

in the step (3), the surface of the oil removing roller 1 is provided with a micropore flow passage 2, and the center of the oil removing roller is provided with a hollow pipeline 3 and a heating coil pipe 4; the hollow pipeline 3 is connected with the micropore flow passage 2 on the surface of the roller 1, and the outside of the hollow pipeline is connected with a vacuum-pumping machine; the heating coil 4 is connected to an external heat exchange station.

Here, the hollow pipe 3 is connected with the micropore flow channel 2 extending to the surface of the oil removing roller 1, the pipe is in a negative pressure state by a vacuum pumping machine, and the oil removing roller 1 is internally provided with a heating coil 4 which is connected with an external heat exchange station to heat the roller 1. The pore-forming agent in the contact thin slice can be preheated and softened, and after the viscosity is reduced, the pore-forming agent is forcibly sucked out.

Further, the pore-forming agent is selected from one or more of liquid paraffin, mineral oil, soybean oil and white oil.

Furthermore, the diameter of the micropore flow channel 2 is less than or equal to 1.0 mm. Preferably, the diameter of the pore of the micropore flow channel 2 is less than or equal to 0.01 mm.

Here, smaller diameter holes are preferred to allow the sheet to be more structurally supported by the roller surface, avoiding too high a single hole suction, more uniform suction, thus ensuring less probability of forced deformation of the sheet and more uniform pore former aspiration.

Further, the area of the micropore flow channel 2 on the surface of the oil removing roller 1 accounts for more than or equal to 50% of the total area of the roller surface of the oil removing roller 1. Preferably, the area of the micropore flow channel 2 on the surface of the oil removing roller 1 accounts for more than or equal to 80 percent of the total area of the roller surface of the oil removing roller 1.

Here, the surface of the degreasing roller 1 is provided with a plurality of groups of micropore flow passages 2, and preferably, the occupied area of the micropore flow passages 2 is larger so as to have larger suction area, thereby ensuring that the pore-forming agent is sucked out more quickly.

Further, the vacuum degree in the oil removing roller 1 is more than or equal to 0.05 Mpa. Preferably, the vacuum degree in the oil removing roller 1 is more than or equal to 0.08 Mpa.

Here, a greater vacuum is preferred to ensure that the sheet is sufficiently sucked and thus that the pore former is sucked out more sufficiently.

Furthermore, the wrap angle between the surface of the oil removing roller 1 and the thin sheet is more than or equal to 60 degrees. Preferably, the wrap angle between the roll surface of the oil removing roll 1 and the thin sheet is more than or equal to 180 degrees.

Here, a larger wrap angle is preferred, a larger contact area is expanded, and the time for extracting the pore-forming agent is increased at the same rotational speed.

Further, the heating temperature of the oil removing roller 1 is more than or equal to 60 ℃ and less than or equal to 100 ℃. The heating temperature of the oil removing roller 1 is preferably more than or equal to 80 ℃ and less than or equal to 100 ℃.

Here, the use of higher temperatures for porogen preheating reduces the porogen kinematic viscosity and allows for more complete removal of the porogen under fixed suction.

Furthermore, the number of the oil removing rollers is more than or equal to 4. Preferably, the number of the oil removing rollers is more than or equal to 8.

Here, more number of the degreasing rollers 1 is preferable, so that the pumping time of the pore-forming agent can be increased.

Further, after the step (3) is finished, the residual oil rate of the thin slice is less than or equal to 20 percent. Preferably, after the step (3) is finished, the residual oil rate of the thin slice is less than or equal to 2 percent.

Further, an extraction process S5 is included, wherein the extraction process S5 is located before or after the step (4).

Further, as shown in fig. 5, step (4) is asynchronous biaxial stretching (MD + TD) or Synchronous Biaxial Stretching (SBS).

Further, the microporous membrane is a polyolefin separator.

Further, the ratio of the maximum pore diameter to the median pore diameter of the polyolefin diaphragm is less than or equal to 1.30 by a bubble point method. Preferably, the ratio of the maximum pore size to the median pore size is ≦ 1.05.

Furthermore, the median pore diameter of the polyolefin separator ranges from 25 nm to 30 nm. Preferably, the maximum pore diameter of the polyolefin diaphragm is 26-39 nm.

Further, the polyolefin separator has a porosity of 30% or less.

Further, the polyolefin separator has a surface resistivity of 0.05 Ω cm or less²。

Still further, the polyolefin separator has a needle punching strength and a thickness satisfying the following relationship: d is 150gf/μm or more, D is a needling strength/thickness, and D is 200gf/μm or more is preferable.

Still further, the polyolefin membrane has the following needle punching strength, thickness, porosity and air permeability values: e is equal to or less than 10s/165 ml/mum, E is the air permeability value/thickness, and E is preferably equal to or less than 7s/165 ml/mum on the basis of the porosity of 30% or less.

Further, the polyolefin separator has a needle punching strength of 1000 to 1500 gf.

Further, the polyolefin separator has a biaxial tensile strength of 4100 to 4350kgf/cm²In the meantime.

Further, the polyolefin separator has an elongation percentage of 40 to 70% in the MD direction and 50 to 65% in the TD direction.

Furthermore, the thermal shrinkage rate of the polyolefin diaphragm is less than or equal to 2.7 percent in the MD direction and less than or equal to 1.0 percent in the TD direction at 110 ℃ under the condition of 1 hour.

Still further, the polyolefin separator is a single component polyethylene separator.

The present invention will be described in detail below by way of examples.

In the following examples and comparative examples, the relevant data were determined as follows:

(1) film thickness

And measuring by using a Mark thickness gauge.

(2) Air permeability value

The steady value after 5 seconds was measured stably at room temperature using a joker's permeameter to set a 165cc gas transit time through the septum.

(3) Porosity of the material

Intercepting a 100mm multiplied by 100mm sample wafer, weighing using an electronic balance and according to the formula: (1-weight/area of sample)/weight X0.957X 100% conversion.

(4) Pore size testing

The apparatus used was a Capillary Flow Porometer (CFP 1500AE) from PMI, and the surface tension of the immersion fluid was 15.9 Dynes/cm. The median pore diameter (φ mean) is obtained from the semi-dry curve of the "dry-wet method". Both the maximum and minimum apertures can be obtained from the aperture profile obtained from the test. The maximum aperture (phi max) is the last value in the aperture distribution map data, namely the aperture corresponding to the bubble point.

(5) Tensile strength & elongation at break

Using an electronic universal material testing machine XJ830, cutting the specification: the measurement was carried out at a traveling speed of 200mm/min of 15 mm. times.20 cm.

(6) Strength of needling

The measurement was carried out using an electronic universal material tester XJ830, 50mm/min traveling speed.

(7) Thermal shrinkage rate

The 100mm x 100mm microporous membrane was placed at 110 ℃ for 1H using a high temperature test chamber Espec SEG-021H and measured by an image measuring instrument XTY-5040, with the TD and MD direction lengths using the formula: (before heat treatment-after heat treatment)/before heat treatment X100% conversion.

(8) Kinematic viscosity

And (3) using a kinematic viscosity determinator DSY-004, setting the measurement temperature to be 60 ℃, and carrying out kinematic viscosity measurement after stabilizing for 1 h.

(9) Residual oil rate

A10 mm × 10mm diaphragm sample piece is cut, weighed by using an electronic balance, pure water is placed in an Ultrasonic Cleaner 1740T, 300ml of pure dichloromethane in a 500ml beaker is placed, the sample piece is placed, Ultrasonic time is set to be 60s, then the sample piece is placed in an oven at 105 ℃ for drying for 5min, and the sample piece is weighed by using the electronic balance, and the residual oil rate is converted.

(10) Surface resistivity

Standard ambient temperature of experiment: (23. + -. 2). degree.C. GB/T36363-2018 stipulates that the number of the test samples in each test sample is 4, and in order to further improve the accuracy, stipulates that the number of the test samples in each test group is not less than 4, and is generally 5. Cutting 5 pieces of the diaphragm matched with a resistance testing mold (slightly larger than the size of the mold), putting the diaphragm into electrolyte with the concentration of 1.0mol/L lithium hexafluorophosphate (LiPF6), Ethylene Carbonate (EC) and methyl ethyl carbonate (EMC) dimethyl carbonate (DMC) in the volume of 1:1:1, keeping sealing, and soaking for 2 h. And slightly clamping the diaphragms soaked in the electrolyte by using plastic tweezers, sequentially putting the diaphragms into a test fixture, testing the alternating current impedance of 1 layer of diaphragm, putting 1 layer of diaphragm, testing the alternating current impedance resistance of the double layers until 5 layers of diaphragm are put, and respectively measuring five alternating current impedance resistances R1, R2, R3, R4 and R5. And (3) taking the number of the diaphragm layers as an abscissa and the diaphragm resistance as an ordinate to make a curve, calculating the slope and the linear fitting degree of the curve, when the linear fitting degree is more than 0.99, calculating the ionic conductivity of the diaphragm according to the formula (1) and the formula (2), and when the linear fitting degree is less than 0.99, retesting.

R＝k×1…………………………(1)

In the formula:

r is the resistance value of 1 layer of diaphragm, and the unit is ohm (omega);

k-the slope of the curve with a fitness greater than 0.99;

IR＝(R×S)…………………………(2)

in the formula:

IR-Ionic surface resistivity of a diaphragm in ohms per square centimeter (Ω cm)²)；

R is the resistance value of 1 layer of diaphragm, and the unit is ohm (omega);

s-area of diaphragm cut at test in square centimeters (cm 2).

Example 1

Mw is 1.0X 10⁶Polyethylene and white oil as raw materials. Polyethylene with the raw material mass percentage of 20 percent and white oil with the raw material mass percentage of 80 percent are put into a double-screw extruder, extruded by a T-shaped die head under the condition of 150 ℃, and are contacted and cooled by a cold roll with the temperature of 5 ℃ to form a sheet. The oil removing roller 1 which passes through the micropore flow channel 2 with the diameter of 1.0mm on the surface, the area of the micropore flow channel 2 on the surface accounts for 50 percent of the total area of the roller surface of the oil removing roller 1, the wrap angle between the roller surface and the sheet is 60 degrees, the vacuum degree in the roller is 0.05Mpa, the temperature is 60 ℃, and the number of the rollers is 4, and the process S3 is carried out. Then, the film was subjected to MD stretching and 10-fold stretching at 110 ℃. The obtained product is subjected to TD1 stretching and 10 times of stretching at 110 ℃. After extraction of S5, the product is subjected to TD2 stretching S6 and 2-fold stretching and setting at 120 ℃.

Example 2

The experimental conditions were the same as those of example 1 except that the oil roll 1 passed through the micropore flow paths 2 having a pore diameter of 0.08mm on the surface, the surface micropore flow paths 2 occupied 60% of the total area of the roll surface except for the oil roll 1, the wrap angle between the roll surface and the sheet was 80 °, the degree of vacuum in the roll was 0.06Mpa, the temperature was 70 ℃, and the number of rolls was 5, and the step S3 was performed.

Example 3

The experimental conditions were the same as those of example 1 except that the oil roll 1 and the step S3 were used, except that the oil roll 1 was passed through the micropore flow paths 2 having a surface with a pore diameter of 0.06mm, the surface micropore flow paths 2 occupied 70% of the total roll surface area of the oil roll 1, the wrap angle between the roll surface and the sheet was 120 °, the degree of vacuum in the roll was 0.07Mpa, the temperature was 80 ℃.

Example 4

The experimental conditions were the same as those of example 1 except that the oil roll 1 and the step S3 were used, except that the oil roll 1 was passed through the micropore flow paths 2 having a surface with a pore diameter of 0.04mm, the surface micropore flow paths 2 occupied 80% of the total roll surface area of the oil roll 1, the wrap angle between the roll surface and the sheet was 140 °, the degree of vacuum in the roll was 0.08Mpa, the temperature was 90 ℃.

Example 5

The experimental conditions were the same as those of example 1 except that the oil roll 1 passed through the micropore flow paths 2 having a pore diameter of 0.02mm on the surface, the surface micropore flow paths 2 occupied 85% of the total area of the roll surface except for the oil roll 1, the wrap angle between the roll surface and the sheet was 160 °, the degree of vacuum in the roll was 0.09Mpa, the temperature was 95 ℃, and the number of rolls was 8, and the step S3 was performed.

Example 6

The experimental conditions were the same as those of example 1 except that the oil feed roll passed through the micropore flow paths 2 having a pore diameter of 0.01mm on the surface, the surface micropore flow paths 2 occupied 90% of the total area of the roll surface of the oil feed roll 1, the wrap angle between the roll surface and the sheet was 180 °, the degree of vacuum in the roll was 0.09Mpa, the temperature was 100 ℃, and the number of rolls was 9, and the step S3.

Comparative example 1

Mw is 1.0X 10⁶Polyethylene and white oil as raw materials. Polyethylene with the raw material mass percentage of 20 percent and white oil with the raw material mass percentage of 80 percent are put into a double-screw extruder, extruded by a T-shaped die head under the condition of 150 ℃, and are contacted and cooled by a cold roll with the temperature of 5 ℃ to form a sheet. The resulting film was subjected to MD stretching and 10-fold stretching at 110 ℃. The obtained product is subjected to TD1 stretching and 10 times of stretching at 110 ℃. After extraction of S5, the product is subjected to TD2 stretching S6 and 2-fold stretching and setting at 120 ℃.

TABLE 1 summary of relevant parameters and test data for examples and comparative examples

The above matters related to the common general knowledge are not described in detail and can be understood by those skilled in the art.

The present invention is not intended to be limited to the particular embodiments shown and described, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The technical scope of the present invention is not limited to the content of the specification, and must be determined according to the scope of the claims.

Claims

1. The preparation method of the microporous membrane with high pore uniformity is characterized by comprising the following steps:

(1) mixing and heating polyolefin and pore-forming agent to be molten;

(2) cooling to form a sheet through a die head;

(4) heating and stretching along at least one axial direction;

(5) stretching and shaping along at least one axial direction again;

(6) rolling to obtain a microporous membrane with high pore uniformity;

2. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the diameter of the micropore runner is less than or equal to 1.0 mm.

3. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the area of the micropore flow channel on the surface of the oil removing roller accounts for more than or equal to 50% of the total area of the surface of the oil removing roller.

4. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the vacuum degree in the oil removing roller is more than or equal to 0.05 Mpa.

5. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the wrap angle between the surface of the oil removing roller and the thin sheet is more than or equal to 60 degrees.

6. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the heating temperature of the oil removing roller is more than or equal to 60 ℃ and less than or equal to 100 ℃.

7. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: the number of the oil removing rollers is more than or equal to 4.

8. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: and (4) after the step (3) is finished, the residual oil rate of the thin slice is less than or equal to 20%.

9. The method for preparing a microporous membrane with high pore uniformity according to claim 1, wherein: and (3) an extraction process, wherein the extraction process is positioned before or after the step (4).

10. The method for preparing a microporous membrane with high pore uniformity according to claim 2, wherein: the diameter of the micropore runner is less than or equal to 0.01 mm.

11. The method for preparing a microporous membrane with high pore uniformity according to claim 3, wherein: the area of the micropore flow channel on the surface of the oil removing roller accounts for more than or equal to 80 percent of the total area of the surface of the oil removing roller.

12. The method for preparing a microporous membrane with high pore uniformity according to claim 4, wherein: the vacuum degree in the oil removing roller is more than or equal to 0.08 Mpa.

13. The method for preparing a microporous membrane with high pore uniformity according to claim 5, wherein: the wrap angle between the surface of the oil removing roller and the thin sheet is more than or equal to 180 degrees.

14. The method for preparing a microporous membrane with high pore uniformity according to claim 6, wherein: the heating temperature of the oil removing roller is more than or equal to 80 ℃ and less than or equal to 100 ℃.

15. The method for preparing a microporous membrane with high pore uniformity according to claim 7, wherein: the number of the oil removing rollers is more than or equal to 8.

16. The method for preparing a microporous membrane with high pore uniformity according to claim 8, wherein: and (4) after the step (3) is finished, the residual oil rate of the slice is less than or equal to 2%.

17. A microporous membrane having high pore uniformity, characterized by: the microporous membrane is a polyolefin diaphragm, the pore diameter is tested by a bubble point method, and the ratio of the maximum pore diameter to the median pore diameter is less than or equal to 1.3.

18. The microporous membrane with high pore uniformity of claim 17, wherein: the median pore diameter range of the polyolefin diaphragm is 25-30 nm.

19. The microporous membrane with high pore uniformity of claim 17, wherein: the maximum aperture range of the polyolefin diaphragm is 26-39 nm.

20. The microporous membrane with high pore uniformity of claim 17, wherein: the bubble point method is used for testing the pore diameter, and the ratio of the maximum pore diameter to the median pore diameter is less than or equal to 1.05.

21. The microporous membrane with high pore uniformity of claim 17, wherein: the porosity of the polyolefin diaphragm is less than or equal to 30 percent.

22. The microporous membrane with high pore uniformity of claim 17, wherein: the surface resistivity of the polyolefin diaphragm is less than or equal to 0.05 omega cm²。

23. The microporous membrane with high pore uniformity of claim 17, wherein: the needling strength and the thickness of the polyolefin diaphragm meet the following relations: d is not less than 150 gf/mum, and D is the needling strength/thickness.

24. The microporous membrane with high pore uniformity of claim 17, wherein: the polyolefin diaphragm is a single-component polyethylene diaphragm.

25. The microporous membrane with high pore uniformity of claim 21, wherein: the polyolefin membrane has the following air permeability value and thickness: e is less than or equal to 10s/165 ml/mum, and E is air permeability value/thickness.

26. The microporous membrane with high pore uniformity of claim 23, wherein: the needling strength and the thickness of the polyolefin diaphragm meet the following relations: d is more than or equal to 200 gf/mum, and D is the needling strength/thickness.

27. A battery, characterized by: a microporous membrane with high pore uniformity according to any one of claims 17 to 26, comprising the microporous membrane as a member for separating a positive electrode from a negative electrode.