CN112952284A - Lithium ion battery diaphragm, preparation method thereof and lithium ion battery - Google Patents

Lithium ion battery diaphragm, preparation method thereof and lithium ion battery Download PDF

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Publication number
CN112952284A
CN112952284A CN201911269549.XA CN201911269549A CN112952284A CN 112952284 A CN112952284 A CN 112952284A CN 201911269549 A CN201911269549 A CN 201911269549A CN 112952284 A CN112952284 A CN 112952284A
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base film
organic polymer
separator
treatment
stretching
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CN112952284B (en
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李乐星
孙健
许娇
罗明俊
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Huizhou BYD Battery Co Ltd
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Huizhou BYD Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The present disclosure relates to a lithium ion battery diaphragm and a preparation method thereof, and a lithium ion battery, wherein the diaphragm comprises a base film and a coating, the base film comprises a first surface and a second surface which are opposite in the thickness direction, the base film is provided with a through hole, and the aperture of the through hole is gradually expanded from the first surface to the second surface; a coating layer overlies the base film and at least a portion of the coating layer is embedded in the through-holes, the coating layer comprising a first organic polymer. The lithium ion battery diaphragm disclosed by the invention has good liquid retention and infiltration performance, and the adhesion with a pole piece is better.

Description

Lithium ion battery diaphragm, preparation method thereof and lithium ion battery
Technical Field
The disclosure relates to the field of lithium ion batteries, in particular to a lithium ion battery diaphragm, a preparation method thereof and a lithium ion battery.
Background
The diaphragm is one of the important structures in the lithium ion battery, and is continuously developed along with the update of the lithium ion battery. After the material of the separator undergoes the change from polypropylene (PP) to halogenated Polyethylene (PE), the lithium ion power battery commonly uses Al2O3A coated halogenated polyethylene film. PVDF is expected to replace Al2O3The organic coating diaphragm obtained by the coating method has a relatively obvious adhesive layer, and the obvious layer structure is easy to fall off powder or even fall off in the processes of winding, slitting and the like of the battery, which may cause short circuit of the battery.
Disclosure of Invention
The invention aims to solve the problems of poor adhesion between a diaphragm and a pole piece and poor wettability of the diaphragm in the prior art, and provides a lithium ion battery diaphragm, a preparation method of the lithium ion battery diaphragm and a lithium ion battery.
In order to achieve the above object, a first aspect of the present disclosure provides a lithium ion battery separator including a base film including first and second surfaces opposite in a thickness direction, the base film having a through-hole whose pore diameter is gradually expanded from the first surface to the second surface; the coating layer overlies the base film and at least a portion of the coating layer is embedded in the through-holes, the coating layer comprising a first organic polymer.
Optionally, the aperture of the first surface opening is 20-80nm, and the aperture of the second surface opening is 200-800 nm.
Optionally, the peel force between the base film and the coating is 2-8N.
Optionally, the coating is applied to the second surface.
Optionally, the base film has a thickness of 7-16 μm; the coating layer coated on the base film has a thickness of 0.1 to 5 μm.
Optionally, the porosity of the separator is 40-70%; the tensile strength in the first direction is 1000-2The tensile strength in the second direction is 100-400kg/cm2The shrinkage rate in the first direction is less than 10%, the shrinkage rate in the second direction is less than 12%, and the first direction is perpendicular to the second direction.
Optionally, the first organic polymer comprises one or more of polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene polyvinylidene fluoride, polyimide, polyamide, polytetrafluoroethylene, polyethylene terephthalate, meta-aramid, polyoxadiazole terephthalate and aramid nanofibers;
preferably, the first organic polymer comprises polyethylene oxide and/or polyvinylidene fluoride-hexafluoropropylene.
Optionally, the coating further comprises inorganic particles comprising one or more of alumina, silica, boehmite, and magnesium hydroxide.
Optionally, the base film contains a second organic polymer, and the second organic polymer comprises one or more of halogenated polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyamide, polytetrafluoroethylene, polyethylene terephthalate, meta-aramid, polyoxadiazole terephthalate and aramid nanofiber;
preferably, the second organic polymer comprises one or more of halogenated polyethylene, polyimide, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene and polyimide.
A second aspect of the present disclosure provides a method of preparing a separator provided by the first aspect of the present disclosure, the method comprising:
(1) carrying out first cooling treatment on the first surface of the second organic polymer film with the micro through holes, and carrying out second cooling treatment on the second surface of the second organic polymer film with the micro holes to obtain the base film; wherein the temperature of the first cooling process is higher than the temperature of the second cooling process;
(2) and coating the slurry containing the first organic polymer particles on the base film, and carrying out hot-pressing treatment on the obtained composite film.
And (3) coating the slurry on the base film by rotary spraying and mirror roller reverse transfer in the step (2).
Optionally, the method further comprises: stretching the sheet obtained after the hot pressing treatment; the stretching treatment comprises a first direction stretching treatment and a second direction stretching treatment, wherein the first direction stretching treatment is perpendicular to the second direction stretching treatment; the conditions of the stretching treatment include: the stretching ratio is 3-6, the stretching speed is 20-40m/min, and the stretching temperature is 100-140 ℃.
Optionally, the temperature of the first cooling treatment is 10-20 ℃ higher than the temperature of the second cooling treatment.
Optionally, the temperature of the first cooling treatment is 20-25 ℃, and the time is 1-3 min; the temperature of the second cooling treatment is 5-10 ℃, and the time is 1-3 min.
Optionally, the temperature of the hot pressing treatment is 120-150 ℃, and the pressure is 0.4-0.5 MPa.
Optionally, the first organic polymer particles in the slurry have a particle size range of 0 to 0.5 μm.
A third aspect of the present disclosure provides a lithium ion battery including the separator provided in the first aspect of the present disclosure.
Through the technical scheme, the battery diaphragm and the pole piece have good cohesiveness, and the diaphragm has good wetting performance and liquid retention performance.
Additional features and advantages of the disclosure will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure without limiting the disclosure. In the drawings:
fig. 1 is an SEM electron micrograph of a second surface of a base film prepared according to example 1 of the present disclosure;
fig. 2 is an SEM electron micrograph of a first surface of a base film prepared according to example 1 of the present disclosure.
Detailed Description
The following detailed description of specific embodiments of the present disclosure is provided in connection with the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.
The first aspect of the present disclosure provides a lithium ion battery separator including a base film and a coating layer, the base film including a first surface and a second surface opposite in a thickness direction, the base film having a through hole, a pore diameter of the through hole gradually expanding from the first surface to the second surface; the coating layer is coated on the base film, at least part of the coating layer is embedded in the through hole, and the coating layer contains a first organic polymer.
Embedding the coating in the via, according to the present disclosure, means that the via is partially or completely filled with the coating. The lithium ion battery diaphragm disclosed by the invention comprises the base films with different apertures on two sides and the coating at least partially embedded into the base film holes, so that the bonding property of the diaphragm and a pole piece can be effectively improved, and the wetting property and the liquid retention property of the diaphragm and electrolyte can be improved.
According to the present disclosure, the pore size of the first surface openings and the second openings may vary within a wide range, preferably the pore size of the first surface openings is 20-80nm and the pore size of the second surface openings is 200-800 nm. More preferably, the pore diameter of the first surface opening is 20-50nm, and the pore diameter of the second surface opening can be 300-400 nm. The pore diameter of the first surface opening and the pore diameter of the second surface opening are within the range, so that the diaphragm has good lithium conductivity, and the performance of the diaphragm is improved.
According to the present disclosure, the peeling force between the base film and the coating layer of the separator is large, and the peeling force between the base film and the coating layer may be 2 to 8N, preferably 3 to 5N. The base film and the coating in the diaphragm of the present disclosure are combined more tightly, and have higher strength.
In a preferred embodiment, the coating layer can cover the second surface with larger pore diameter and be embedded in the pores of the base film, so that the structure ensures that the diaphragm has good liquid absorption property, good air permeability and is not easy to fall off.
The thickness of the base film may vary within a wide range according to the present disclosure, preferably from 7 to 16 μm, more preferably from 9 to 12 μm. The coating layer on the base film may be a continuous coating layer or a discontinuous coating layer, and is not limited herein. The thickness of the coating can also vary within wide limits and can be, for example, from 0.1 to 5 μm, preferably from 0.5 to 5 μm, more preferably from 0.5 to 1 μm. An excessively thick separator may result in a decrease in energy density of the battery, and an excessively thin separator may result in a decrease in safety performance of the battery. When the thickness of the base film and the coating of the diaphragm is within the range, the performance of the diaphragm for soaking the electrolyte can be further improved, and the liquid retention amount and the adhesion between the base film and the pole piece are improved. In one embodiment, the coating may further comprise a binder to further improve the adhesion between the base film and the coating. Binders are well known to those skilled in the art and will not be described in detail herein.
According to the present disclosure, the porosity of the separator may be 40-70%, preferably 50-60%; the tensile strength in the first direction may be 1000-2Preferably 1000-2000kg/cm2More preferably 1400-2000kg/cm2The tensile strength in the second direction is 100-400kg/cm2Preferably 150-300kg/cm2. The shrinkage in the first direction is less than 10%, preferably 7-9%, and the shrinkage in the second direction is less than 12%, preferably 9-11%, the first direction being perpendicular to the second direction.
The first organic polymer contained in the coating layer according to the present disclosure may be conventionally employed by those skilled in the art, for example, the first organic polymer may include one or more of polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), Polyimide (PI), Polyamide (PA), Polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), meta-aramid (PMIA), polyoxadiazole terephthalate (PBO), and Aramid Nanofibers (ANF).
In one embodiment, the first organic polymer may include polyethylene oxide (PEO) and/or polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP). The first organic polymer of the above kind can further improve the adhesion property between the separator and the electrode sheet and the liquid retention of the separator.
The coating may also contain inorganic particles, which may be conventionally employed by those skilled in the art, including, for example, one or more of alumina, silica, boehmite, and magnesium hydroxide, in accordance with the present disclosure. The particle size of the inorganic particles is not particularly limited, and for example, the particle size of the inorganic particles may be very poor in the range of 0 to 0.5 μm, and the particle size of the inorganic particles within the above range has good uniformity, which is advantageous for reducing the air permeability of the separator to a more suitable range and further improving the liquid retention of the separator. The inorganic particles can be sprayed on the diaphragm by adopting an ion sputtering mode.
The second organic polymer contained in the base film according to the present disclosure may be conventionally employed by those skilled in the art, and is preferably an olefin polymer having a high molecular weight, for example, the second organic polymer includes one or more of halogenated Polyethylene (PE), polypropylene (PP), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), Polyimide (PI), Polyamide (PA), Polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), meta-aramid (PMIA), polyoxadiazole terephthalate (PBO), and Aramid Nanofiber (ANF).
In one embodiment, the second organic polymer may include one or more of halogenated Polyethylene (PE), polypropylene (PP), polyethylene oxide (PEO), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), and Polyimide (PI). The base film containing the polymer has higher stiffness, excellent appearance and better tensile property, and can improve the production line speed of film products.
A second aspect of the present disclosure provides a method of preparing a separator provided by the first aspect of the present disclosure, the method comprising:
(1) carrying out first cooling treatment on the first surface of the second organic polymer film with the micro through holes, and carrying out second cooling treatment on the second surface of the second organic polymer film with the micro holes to obtain a base film; wherein the temperature of the first cooling treatment is higher than the temperature of the second cooling treatment;
(2) and coating the slurry containing the first organic polymer particles on a base film, and carrying out hot-pressing treatment on the obtained composite film.
The disclosed method can make the pore size of both sides of the base film different through the first cooling treatment and the second cooling treatment, and then the coating is embedded into the pores of the base film through the subsequent hot pressing treatment. The method disclosed can prepare the diaphragm with good liquid retention, cohesiveness and small heat shrinkage.
The method for preparing the second organic polymer film having micropores is not limited, and for example, the second organic polymer film having micropores can be obtained by mixing the pore-forming agent with the second organic polymer, extruding the mixture to prepare the organic polymer film, and removing the pore-forming agent. The pore former may be, for example, white oil or kerosene. The method of removing the pore-forming agent is also not limited: when the pore former is white oil, the membrane may be washed with an organic solvent after the autoclave process of step (2) to remove the white oil, the organic solvent being well known to those skilled in the art, such as heptane; when the pore former is kerosene, it may be removed by volatilization by subjecting it to a heating treatment after extrusion to prepare an organic polymer film.
According to the present disclosure, the slurry may be coated on the base film by spin coating and mirror roller reverse transfer in step (2). Spin coating and mirror roller reversal are well known to those skilled in the art and will not be described in detail herein. In a preferred embodiment, the slurry containing the second organic polymer particles is coated on the chill roll by spin coating and then is reversely transferred to the base film by the mirror roll, thereby further improving the uniformity of the coating in the subsequent preparation process.
According to the present disclosure, the method may further comprise: stretching the sheet obtained after the hot pressing treatment; the stretching process includes a first direction stretching process and a second direction stretching process, the first direction stretching process being perpendicular to the second direction stretching process. The first stretching treatment and the second stretching treatment may be performed simultaneously or may not be performed simultaneously. The conditions of the stretching treatment may include: the stretching ratio is 3-6, the stretching speed is 20-40m/min, and the stretching temperature is 100-140 ℃. Preferably, the stretching ratio is 4-5, the stretching rate is 25-35m/min, and the stretching temperature is 100-110 ℃. Stretching processes are well known to those skilled in the art and may be performed, for example, by placing the membrane on a stretching roller. When the first stretching process is performed using the stretching roller, the running direction of the separator on the stretching roller is the first direction, and the axial direction of the stretching roller is the second direction. The operating parameters of the first stretching process and the operating parameters of the second stretching process may be the same or different. In one embodiment, the first stretching treatment has a stretching ratio of 5 to 6, a stretching rate of 20 to 40m/min, and a stretching temperature of 100 ℃ and 110 ℃. The stretching ratio of the second stretching treatment is 4-5, the stretching speed is 20-40m/min, and the stretching temperature is 100-. Can further carry out reaming to the diaphragm through tensile processing for the coating that inlays in the through-hole can distribute uniformly and fill in the internal surface of through-hole, is favorable to making the diaphragm have better gas permeability and liquid retention.
According to the present disclosure, the temperature of the first cooling process may be 10 to 20 ℃ higher than that of the second cooling process, and preferably, the temperature of the first cooling process may be 15 to 20 ℃ higher than that of the second cooling process. The two sides of the base film are treated at different cooling treatment temperatures, so that the pore sizes of the holes on the two sides are different, and the liquid absorption rate of the diaphragm is improved.
In a preferred embodiment, the temperature and time of the first cooling treatment and the second cooling treatment may vary within a wide range, preferably, the temperature of the first cooling treatment is 20 to 25 ℃, the temperature of the second cooling treatment is 5 to 10 ℃, more preferably, the temperature of the first cooling treatment is 23 to 25 ℃, and the temperature of the second cooling treatment is 5 to 7 ℃. The time of the first cooling treatment can be 1-3min, the time of the second cooling treatment can be 1-3min, and preferably, the time of the first cooling treatment is 1.5-2.5min, and the time of the second cooling treatment is 1.5-2.5 min. The cooling method is not particularly limited, for example, the first cooling process is water bath cooling, and the second cooling process is extreme speed cooling, and the extreme speed cooling may be refrigeration by a refrigerant, and the refrigerant may be one or more of liquid nitrogen, freon-12, R134a, and R404 a.
According to the disclosure, the hot pressing treatment can adopt a compression roller hot pressing mode, and the temperature of the hot pressing treatment can be changed in a large range, preferably 120-150 ℃, and more preferably 130-140 ℃; the pressure may be from 0.4 to 0.5MPa, preferably from 0.45 to 0.5 MPa. The autoclave process may embed at least a portion of the coating into the through-hole to improve the retention and wetting of the membrane.
According to the present disclosure, the particle size range of the first organic polymer particles in the slurry may be 0 to 0.5 μm, preferably 0 to 0.25 μm. When the particle size range of the first organic polymer particles in the slurry is within the range, the uniformity is better, and the first organic polymer particles are favorably and uniformly filled in the pores of the diaphragm, so that the lithium ion battery diaphragm with better liquid retention and wettability is prepared. In one embodiment, the first organic polymer may be selected by ball milling to have a particle size range within a specific range. And mixing the screened first organic polymer with a dispersant and a binder to obtain slurry.
A third aspect of the present disclosure provides a lithium ion battery including the separator provided in the second aspect of the present disclosure.
In one specific embodiment, the lithium ion battery is prepared by sequentially overlapping and winding the positive electrode, the diaphragm and the negative electrode into a coil, and then performing casing, liquid injection, sealing and formation.
The present disclosure is further illustrated by the following examples, but is not to be construed as being limited thereby.
In the examples and comparative examples halogenated polyethylene was purchased from Celanese, polyvinylidene fluoride was purchased from Suwei, PEO was purchased from King of flowers.
Example 1
The second organic polymer film having micro-through holes was prepared by mixing white oil with polyethylene (weight average molecular weight 250000, molecular weight dispersion index of 12) and extruding through a twin-screw extruder.
And placing the second organic polymer film with the micro-through holes on the surface of a chilling roller, drawing the second organic polymer film by the second organic polymer film, carrying out water cooling treatment on the first surface of the second organic polymer film at 25 ℃ for 2min, and carrying out chilling treatment on the second surface at 5 ℃ for 2 min. Coating slurry containing polyvinylidene fluoride particles (with the particle size range of 0.2 mu m), ethanol (dispersing agent) and Styrene Butadiene Rubber (SBR) on the second surface of the second organic polymer film in a rotary spraying and mirror surface reverse transfer mode, and then spraying aluminum oxide on the surface of the second organic polymer film coated with the slurry in an ion sputtering mode to obtain the base film.
And carrying out hot pressing treatment on the base film by using a hot pressing device at the temperature of 130 ℃ and the pressure of 0.5MPa to obtain the sheet with the coating partially embedded in the holes of the base film. The sheet is subjected to a first direction stretching process and a second direction stretching process, the first direction being perpendicular to the second direction. Wherein the stretching magnification of the first-direction stretching treatment is 5, the stretching speed is 20m/min, and the stretching temperature is 120 ℃; the stretching ratio of the second direction stretching treatment was 5, the stretching rate was 20m/min, and the stretching temperature was 120 ℃. And (3) removing white oil in the membrane by passing the membrane after the stretching treatment through an extraction pool filled with heptane, and finally preparing a finished membrane A.
The thickness of the base film of the separator was 16 μm and the thickness of the coating layer was 1 μm. SEM electron micrographs of the first and second surfaces of the base film are shown in fig. 1 and 2, respectively.
Example 2
A separator B was manufactured in the same manner as in example 1, except that the first surface of the second organic polymer film was subjected to a water-cooling treatment at 20 ℃ for 2min, and the second surface was chilled at 15 ℃ for 2 min.
The thickness of the base film of the separator B was 16 μm, and the thickness of the coating layer was 1 μm.
Example 3
A separator C was prepared in the same manner as in example 1, except that alumina was first ion-sputtered onto the second surface of the second organic polymer film coated with the slurry, and then the slurry containing polyvinyl chloride particles (particle size range 0.2 μm), ethanol (dispersant) and styrene butadiene rubber (binder) was coated onto the first surface of the second organic polymer film by spin coating and mirror-reverse transfer to obtain a base film.
The thickness of the base film of the separator C was 16 μm, and the thickness of the coating layer was 1 μm.
Example 4
A separator D was produced in the same manner as in example 1, except that the base film was subjected to a hot press treatment using a hot press apparatus at a temperature of 100 ℃ and a pressure of 0.3MPa to obtain a separator in which the coating layer was partially embedded in the pores of the base film.
The thickness of the base film of separator D was 16 μm, and the thickness of the coating layer was 1 μm.
Comparative example 1
The separator a was prepared by gravure roll coating. The thickness of the base film of the separator a was 16 μm and the thickness of the coating layer was 1 μm.
Comparative example 2
The separator b was prepared in the same manner as in example 1, except that both the first surface and the second surface of the second organic polymer film were subjected to water cooling treatment at 10 ℃ for 2 min.
The thickness of the base film of the separator b was 16 μm and the thickness of the coating layer was 1 μm.
Comparative example 3
A separator c was produced in the same manner as in example 1, except that the base film was not subjected to the hot press treatment.
The thickness of the base film of the separator c was 18 μm and the thickness of the coating layer was 2 μm.
Preparation examples
The separators prepared in the examples and the comparative examples were respectively stacked on the positive electrode and the negative electrode and wound into a roll, and then subjected to casing, injection, sealing and formation to prepare a lithium ion battery. The positive electrode active material is NCM811, the negative electrode is a graphite negative electrode, and the electrolyte is lithium hexafluorophosphate.
Test example
(1) Membrane peel force test
And testing the stripping force of the diaphragm by using a GB/T2792-81 pressure-sensitive adhesive tape 180-degree stripping strength test method. Specifically, the Peel strength test tape: a single-sided adhesive tape having a tackiness of 0.4. + -. 0.05N/mm and a width of 19. + -. 0.5mm was tested at a speed of 50. + -. 5mm/min and a peel length of 100. + -. 10mm, and the average of 3 patterns was taken as the peel strength of the sample.
(2) Testing of battery capacity
The battery capacity is tested in a Wuhan blue battery test system (LAND-CT2001B), the test temperature is 0-0.5 ℃, and the battery is cycled for 10 times.
(3) Adhesion test of diaphragm and pole piece
A tensile machine: sensor range < 200N; the resolution of the sensor is 0.01N, and the precision is +/-0.5%.
Testing the adhesive tape: the single-sided adhesive tape has the viscosity of 0.4 +/-0.05N/mm and the width of 19 +/-0.5 mm.
TABLE 1
Figure BDA0002313784840000111
The base film containing the second organic polymer in the separator of the present disclosure has hydrophobicity itself, and the polar solvent contained in the electrolyte is weak in wettability and liquid retention. The first organic polymer embedded in the base film is a polar molecule, and has better wettability and liquid retention to electrolyte, so that the diaphragm disclosed by the invention has better liquid retention capacity. The diaphragm and the pole piece also have good adhesion.
The preferred embodiments of the present disclosure are described in detail with reference to the accompanying drawings, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.
It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.
In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.

Claims (17)

1. A lithium ion battery separator comprising a base film and a coating layer, the base film comprising a first surface and a second surface opposed to each other in a thickness direction, the base film having a through-hole whose pore diameter is gradually expanded from the first surface to the second surface; the coating layer overlies the base film and at least a portion of the coating layer is embedded in the through-holes, the coating layer comprising a first organic polymer.
2. The membrane according to claim 1, wherein the first surface openings have a pore size of 20-80nm and the second surface openings have a pore size of 200-800 nm.
3. The separator according to claim 1, wherein a peeling force between the base film and the coating layer is 2 to 8N.
4. The separator of claim 1, wherein the coating overlies the second surface.
5. The separator according to claim 1, wherein the base film has a thickness of 7 to 16 μm; the coating layer coated on the base film has a thickness of 0.1 to 5 μm.
6. The separator according to claim 1, wherein the porosity of the separator is 40-70%; the tensile strength in the first direction is 1000-2The tensile strength in the second direction is 100-400kg/cm2The shrinkage rate in the first direction is less than 10%, the shrinkage rate in the second direction is less than 12%, and the first direction is perpendicular to the second direction.
7. The separator of claim 1, wherein the first organic polymer comprises one or more of polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene polyvinylidene fluoride, polyimide, polyamide, polytetrafluoroethylene, polyethylene terephthalate, meta-aramid, polyoxadiazole terephthalate, and aramid nanofibers;
preferably, the first organic polymer comprises polyethylene oxide and/or polyvinylidene fluoride-hexafluoropropylene.
8. The separator of claim 1, wherein the coating further comprises inorganic particles comprising one or more of alumina, silica, boehmite, and magnesium hydroxide.
9. The separator of claim 1, wherein the base film comprises a second organic polymer, the second organic polymer comprising one or more of halogenated polyethylene, polypropylene, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyamide, polytetrafluoroethylene, polyethylene terephthalate, meta-aramid, polyoxadiazole, and aramid nanofibers;
preferably, the second organic polymer comprises one or more of halogenated polyethylene, polyimide, polyethylene oxide, polyvinylidene fluoride-hexafluoropropylene and polyimide.
10. A method of making the separator of any one of claims 1-9, comprising:
(1) carrying out first cooling treatment on the first surface of the second organic polymer film with the micro through holes, and carrying out second cooling treatment on the second surface of the second organic polymer film with the micro holes to obtain the base film; wherein the temperature of the first cooling process is higher than the temperature of the second cooling process;
(2) and coating the slurry containing the first organic polymer particles on the base film, and carrying out hot-pressing treatment on the obtained composite film.
11. The method of claim 10, wherein the slurry is coated on the base film by spin coating and mirror roll reverse transfer in step (2).
12. The method of claim 10, further comprising: stretching the sheet obtained after the hot pressing treatment; the stretching treatment comprises a first direction stretching treatment and a second direction stretching treatment, wherein the first direction stretching treatment is perpendicular to the second direction stretching treatment; the conditions of the stretching treatment include: the stretching ratio is 3-6, the stretching speed is 20-40m/min, and the stretching temperature is 100-140 ℃.
13. The method according to claim 10, wherein the temperature of the first cooling process is 10-20 ℃ higher than the temperature of the second cooling process.
14. The method according to any one of claims 10 to 13, wherein the first cooling treatment is carried out at a temperature of 20 to 25 ℃ for 1 to 3 min; the temperature of the second cooling treatment is 5-10 ℃, and the time is 1-3 min.
15. The method as claimed in claim 10, wherein the temperature of the hot pressing treatment is 120-150 ℃ and the pressure is 0.4-0.5 MPa.
16. The method of claim 10, wherein the first organic polymer particles in the slurry have a particle size range of 0 to 0.5 μm.
17. A lithium ion battery, characterized in that it comprises a separator according to any one of claims 1 to 9.
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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5514461A (en) * 1993-10-05 1996-05-07 Kureha Chemical Industry Co., Ltd. Vinylidene fluoride porous membrane and method of preparing the same
CN101212035A (en) * 2006-12-29 2008-07-02 比亚迪股份有限公司 Battery isolating film and method for producing the same
CN101752539A (en) * 2008-12-01 2010-06-23 比亚迪股份有限公司 Polyimide diaphragm for lithium ion secondary battery and lithium ion battery
CN106898721A (en) * 2017-02-28 2017-06-27 沧州明珠隔膜科技有限公司 A kind of lithium ion battery separator for being suitable to hot dry-pressing and preparation method thereof

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5514461A (en) * 1993-10-05 1996-05-07 Kureha Chemical Industry Co., Ltd. Vinylidene fluoride porous membrane and method of preparing the same
CN101212035A (en) * 2006-12-29 2008-07-02 比亚迪股份有限公司 Battery isolating film and method for producing the same
CN101752539A (en) * 2008-12-01 2010-06-23 比亚迪股份有限公司 Polyimide diaphragm for lithium ion secondary battery and lithium ion battery
CN106898721A (en) * 2017-02-28 2017-06-27 沧州明珠隔膜科技有限公司 A kind of lithium ion battery separator for being suitable to hot dry-pressing and preparation method thereof

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