Preparation method of high-wettability lithium ion battery diaphragm

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a preparation method of a high-wettability lithium ion battery diaphragm. The preparation method comprises the following steps: preparing an AlOOH dispersion liquid, coating at least one side of a basement membrane with the AlOOH dispersion liquid in the step S1 to obtain a primary modified basement membrane, preparing a dopamine (DA) buffer solution, contacting the primary modified basement membrane with a DA buffer solution to obtain a secondary modified basement membrane, and optionally washing with water and drying to obtain the lithium ion battery diaphragm. The polyolefin diaphragm prepared by the method has good wettability, high liquid absorption rate, good hot working performance and high ion transference number, and can effectively inhibit the growth of lithium dendrites. The prepared lithium ion battery positive electrode material has excellent safety performance, wettability and electrochemical performance when applied to a lithium ion battery, the attenuation of battery capacity is inhibited, the rate capability of the battery is improved, and the service life of the battery is prolonged.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a method for preparing a highly wettable lithium-ion battery separator and the highly wettable lithium-ion battery separator itself. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices due to their high energy density and good cycle life. Furthermore, lithium-ion batteries are considered the most competitive power source for large-scale batteries such as electric vehicles (EVs) and energy storage systems, provided their safety is significantly improved and costs are reduced. Traditional polyolefin films exhibit high thermal shrinkage at high temperatures, which can lead to internal short circuits under thermal runaway conditions, potentially causing fires or even explosions. Power lithium-ion batteries offer advantages such as high energy density and long cycle life. Improving the wettability and electrolyte retention of polyolefin separators can effectively improve battery cycle performance, especially high-rate discharge performance. Enhancing the thermal shrinkage strength of polyolefin separators can improve the safety and cycle performance of lithium-ion batteries.

[0003] Modifying the surface of industrial polyolefin membranes is the simplest and most feasible method to improve their performance. Coating the surface of polyolefin membranes with inorganic ceramics such as Al2O3 and SiO2 has been shown to effectively improve the mechanical strength of the membrane. However, the ceramic layer is prone to peeling off, resulting in poor film-forming properties. Therefore, in industry, organic / inorganic hybrid coatings are often introduced to improve the thermal and mechanical stability of the membrane.

[0004] Dopamine (DA) is a commercially available chemical that can self-polymerize and form polydopamine (PDA) coatings on various materials. Considering its strong adhesion, combining inorganic materials with PDA overcomes the tendency of inorganic materials to detach. Furthermore, PDA exhibits excellent electrolyte wettability, effectively improving electrolyte absorption. Developing lithium-ion battery separators with superior wettability and stable mechanical properties is crucial for achieving high-performance lithium-ion batteries. Summary of the Invention

[0005] The inventors of this invention have discovered that by sequentially forming an AlOOH layer and a dopamine (DA) layer on a base film using a specific method according to this invention, the resulting lithium-ion battery separator not only possesses excellent mechanical strength and thermal stability, suppressing lithium dendrite puncture of the separator, but also exhibits excellent wettability and good electrolyte retention, which is highly beneficial for improving battery cycle performance, especially high-rate discharge performance. Furthermore, in this invention, the use of a specific binder to form a composition with AlOOH demonstrates excellent effects, and the interaction between AlOOH and dopamine (DA) further promotes the adhesion of AlOOH to the base film, ensuring the structural stability of the battery separator during charge-discharge cycles and maintaining battery cycle stability.

[0006] Specifically, the present invention provides a method for preparing a lithium-ion battery separator, characterized by comprising the following steps:

[0007] S1, Prepare AlOOH dispersion;

[0008] S3, the AlOOH dispersion in S1 is coated on at least one side of the basement membrane and dried to obtain a primary modified basement membrane;

[0009] S4, prepare a slow solution of dopamine (DA);

[0010] S5, the basement membrane modified in S3 is brought into contact with the dopamine (DA) slow solution in S4 to obtain the basement membrane modified in S2;

[0011] S6. The substrate membrane modified in S5 is optionally washed with water and then dried to obtain a lithium-ion battery separator.

[0012] Furthermore, the present invention provides a lithium-ion secondary battery separator, which is obtained by the preparation method of the present invention.

[0013] Technical effect

[0014] The lithium-ion secondary battery separator obtained by the preparation method of this invention exhibits excellent mechanical strength and thermal stability, even when thin, which is beneficial for suppressing lithium dendrites from piercing the separator and maintaining its thermomechanical stability. Furthermore, the separator of this invention exhibits excellent wettability and good electrolyte retention, which is highly beneficial for improving battery cycle performance, especially high-rate discharge performance. Moreover, in this invention, by using AlOOH and dopamine in a sequential combination, the adhesion of AlOOH to the substrate film is further enhanced.

[0015] The high wettability lithium-ion battery separator of the present invention exhibits a high electrolyte absorption rate even with a thin coating thickness, which promotes the rapid migration of lithium ions between the positive and negative electrodes. Therefore, lithium-ion batteries using lithium iron phosphate as the positive electrode achieve excellent cycle and rate performance as well as high energy density.

[0016] Furthermore, the preparation method of the present invention is simple, highly automated, efficient, and easy to scale up for production. Attached Figure Description

[0017] Figure 1 The contact angles obtained in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention;

[0018] Figure 2 These are actual photographs of the diaphragm heat shrinkage rates obtained in Embodiment 1, Comparative Example 1, and Comparative Example 2 of the present invention.

[0019] Figure 3 The following are DSC curves obtained from Example 1, Comparative Example 1, and Comparative Example 2;

[0020] Figure 4 The decomposed voltage diagrams obtained in Example 1, Comparative Example 1, and Comparative Example 2 are shown.

[0021] Figure 5 These are ion transport number diagrams obtained from Example 1, Comparative Example 1, and Comparative Example 2.

[0022] Figure 6 The 1C charge-discharge curve of the lithium iron phosphate / lithium battery assembled with the highly wettable lithium-ion battery separator obtained in Example 1 is shown at room temperature.

[0023] Figure 7 The image shows the 1C cycle performance curve of a lithium iron phosphate / lithium battery assembled with the high wettability lithium-ion battery separator obtained in Example 1 at room temperature. Detailed Implementation

[0024] The following describes specific embodiments of the present invention in detail. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the claims in the appendix.

[0025] In the context of this specification, except where expressly stated, any matters or issues not mentioned herein shall apply directly to those known in the art without any modification. Furthermore, any implementation described herein may be freely combined with one or more other implementations described herein, and any resulting technical solutions or concepts shall be considered part of the original disclosure or original record of this invention, and should not be regarded as new content not disclosed or anticipated herein, unless those skilled in the art consider such combination to be clearly unreasonable.

[0026] Unless otherwise specified, all percentages, parts, ratios, etc. mentioned in this specification are based on weight, unless being based on weight would not be in accordance with the common understanding of those skilled in the art.

[0027] The specific embodiments of the present invention will be described in detail below. However, it should be noted that the scope of protection of the present invention is not limited to these specific embodiments, but is determined by the appended claims.

[0028] In the context of this invention, unless otherwise specified, the physical properties of substances (such as boiling point) are measured at room temperature (25°C) and normal pressure (101325 Pa).

[0029] This invention provides a method for preparing a lithium-ion battery separator, characterized by comprising the following steps:

[0030] S1, Prepare AlOOH dispersion;

[0031] S3, the AlOOH dispersion in S1 is coated on at least one side of the basement membrane and dried to obtain a primary modified basement membrane;

[0032] S4, prepare a slow solution of dopamine (DA);

[0033] S5, the basement membrane modified in S3 is brought into contact with the DA slow solution in S4 to obtain the basement membrane modified in S2;

[0034] S6. The substrate membrane modified in S5 is optionally washed with water and then dried to obtain a lithium-ion battery separator.

[0035] In this invention, AlOOH refers to pseudoboehmite (γ-AlOOH), also known as pseudo-boehmite, which is a type of aluminum hydroxide with fine particles, incomplete crystallization, and thin, wrinkled lamellar layers. In this invention, AlOOH can be conventionally available AlOOH, which can be obtained commercially or prepared using conventional methods in the art (e.g., gas-phase method, sol-gel method, microemulsion method, precipitation-hydrolysis method, etc.).

[0036] In this invention, step S1 involves preparing an AlOOH dispersion. In one embodiment of this invention, the solvent for the AlOOH dispersion can be one or more selected from amide solvents (e.g., dimethylformamide (DMF), dimethylacetamide, etc.), sulfoxide solvents (e.g., dimethyl sulfoxide, etc.), ketone solvents (e.g., acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), aromatic solvents (e.g., toluene, xylene, etc.), ether solvents (e.g., dioxane, tetrahydrofuran, etc.), ester solvents (e.g., ethyl acetate, butyl acetate, etc.), and alcohol solvents (e.g., ethanol, etc.), preferably amide solvents, and more preferably dimethylformamide (DMF).

[0037] In one embodiment of the present invention, in step S1, the size of AlOOH is 200-500 nm.

[0038] In one embodiment of the present invention, the AlOOH dispersion in step S1 preferably further comprises a binder. The binder at this time is preferably at least one selected from polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR); more preferably, it is selected from two of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR). In one embodiment of the present invention, when the binder is a mixture of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR), the mass ratio is preferably 1:0.2 to 10, more preferably 1:0.5 to 2, and even more preferably 1:0.8 to 1.5.

[0039] In one embodiment of the present invention, when the adhesive is used in step S1, the preferred mass ratio of the adhesive to AlOOH is 1:4 to 15, more preferably 1:5 to 12.

[0040] In one embodiment of the present invention, in step S1, the mass concentration of AlOOH in the AlOOH dispersion is 5% to 50% by mass, preferably 10% to 40% by mass.

[0041] In step S3 of the present invention, the AlOOH dispersion in S1 is coated on at least one side of the base membrane and dried to obtain a primary modified base membrane.

[0042] In this invention, the base membrane can be any conventional membrane used in the art to form lithium-ion battery separators, preferably a polyolefin membrane, more preferably a polyethylene membrane (PE membrane) or a polypropylene membrane (PP membrane).

[0043] In one embodiment of the present invention, the basement membrane may be a lithium salt modified basement membrane obtained by modifying the basement membrane with lithium salt. In the present invention, regardless of whether the basement membrane is lithium salt modified, it is collectively referred to as a basement membrane. The lithium salt used here is the conventional lithium salt used in the preparation of lithium-ion batteries, and it can be at least one selected from lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate-borate) (LiBOB), lithium difluoroborate oxalate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), bis(malonyl)boronic acid (LiBMB), lithium malonic acid oxalate borate (LiMOB), lithium hexafluoroantimonyate (LiSbF6), lithium difluorophosphate (LiPF2O2), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO2CF3)2), LiN(SO2C2F5)2, LiC(SO2CF3)3, and LiN(SO2F)2. Lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethyl)sulfonyl)imide (LiTFSI) are preferred.

[0044] In this invention, the method for modifying the basement membrane using lithium salt is a conventional method known in the art. In one embodiment of this invention, the basement membrane is immersed in a lithium salt solution. The solvent used to prepare the lithium salt solution can be a conventional solvent known in the art, and can be at least one selected from alcohol-based solvents, ether-based solvents, and water, preferably an alcohol-based solvent, and more preferably ethanol.

[0045] In one embodiment of the present invention, the concentration of lithium salt in the lithium salt solution is 1% to 10% by weight, preferably 2% to 5% by weight. In another embodiment of the present invention, the immersion time of the base membrane in the lithium salt solution is not particularly limited, and can be 10 minutes to 2 hours, or 20 minutes to 1 hour. In another embodiment of the present invention, the lithium salt-modified base membrane after immersion is dried. The drying conditions are not particularly limited, for example, drying at 20 to 80°C for 10 minutes to 2 hours, preferably at 20 to 60°C for 10 minutes to 1 hour. A vacuum oven can be used at this time.

[0046] In step S3 of the present invention, coating can be performed using methods conventional in the art, such as at least one selected from forward roll coating, reverse roll coating, microgravure coating, direct metering coating, and cast coating, but not limited to these methods. The coating method can be, for example, cast coating followed by scraping.

[0047] In step S3 of the present invention, the AlOOH dispersion is coated on one or both sides of the basement membrane.

[0048] In step S3 of the present invention, the AlOOH dispersion is coated on one or both sides of the base film to form a coating thickness of 2 μm to 50 μm, preferably 5 μm to 40 μm.

[0049] In step S3 of this invention, the coated base film is dried. There are no particular limitations on the drying conditions at this stage; for example, drying at 20–80°C for 10 minutes to 10 hours, preferably at 20–60°C for 30 minutes to 8 hours. A vacuum oven can be used at this stage.

[0050] In one embodiment of the present invention, when drying the coated base film, the drying can be carried out in steps. Preferably, the first step of drying is to dry at 20-80°C for 10 minutes to 2 hours, or more preferably at 20-60°C for 30 minutes to 1 hour. The second step of drying is to dry at 20-80°C for 30 minutes to 10 hours, or more preferably at 20-60°C for 1 minute to 8 hours.

[0051] In one embodiment of the present invention, when coating both sides of the base film, drying can be performed after coating both sides, or drying can be performed separately after each coating. Preferably, drying can be performed separately after each coating. The drying conditions for the two drying operations can be the same or different.

[0052] In step S4 of the present invention, a dopamine (DA) slow solution is prepared.

[0053] In one embodiment of the present invention, the DA buffer solution in step S4 can be prepared by various methods known in the art, such as using dopamine as a solute and pH buffer as a solvent, and stirring under light-proof and aerobic conditions to prepare a dopamine buffer solution.

[0054] In one embodiment of the present invention, the DA buffer solution in step S4 uses tris(hydroxymethyl)aminomethane as a buffer. At this time, other solvents can be added as needed, such as alcohol solvents, water, and preferably ethanol.

[0055] In one embodiment of the present invention, in step S4, the amount of buffer solvent is adjusted so that the pH of the DA buffer solution is 7.5 to 9.0.

[0056] In one embodiment of the present invention, in step S4, the mass ratio of DA to AlOOH in step S1 is 1:0.5 to 3, preferably 1:1 to 2.

[0057] In step S5 of the present invention, the basement membrane modified in S3 is brought into contact with the DA slow solution in S4 to obtain a basement membrane modified in S2.

[0058] In one embodiment of the present invention, the contact method in step S5 is not particularly limited; the basement membrane modified in step S3 can be immersed in the DA slow solution in step S4. The immersion time is not particularly limited and can be 8–24 hours.

[0059] In step S6 of the present invention, the substrate membrane modified in step S5 is optionally washed with water and then dried to obtain a lithium-ion battery separator.

[0060] In one embodiment of the present invention, in step S6, the base membrane modified in step S5 is washed with distilled water, preferably three or more times.

[0061] In one embodiment of the present invention, in step S6, the washed base membrane is dried. The drying conditions are not particularly limited and can be conventional drying conditions in the art, such as drying at 20–80°C for 10 minutes to 10 hours, preferably at 20–60°C for 30 minutes to 8 hours. A vacuum oven can be used in this process.

[0062] In one embodiment of the present invention, step S2 may be performed between step S1 and step S3, in which the basement membrane is cleaned to obtain a clean basement membrane.

[0063] The cleaning method in step S2 is not particularly limited; the basement membrane can be washed with a solvent and then dried. The washing solvent can be selected arbitrarily according to the type of basement membrane, as long as it does not damage or dissolve the basement membrane. In one embodiment of the present invention, the washing solvent can be one or more selected from amide solvents (e.g., dimethylformamide (DMF), dimethylacetamide, etc.), sulfoxide solvents (e.g., dimethyl sulfoxide, etc.), ether solvents (e.g., dioxane, tetrahydrofuran, etc.), ester solvents (e.g., ethyl acetate, butyl acetate, etc.), and alcohol solvents (e.g., ethanol, isopropanol, etc.), preferably alcohol solvents, and more preferably one or more selected from ethanol and isopropanol.

[0064] In one embodiment of the present invention, in step S2, there is no particular limitation on the washing time, which can be from 10 minutes to 1 hour.

[0065] In one embodiment of the present invention, in step S2, the drying conditions for drying the washed base membrane are not particularly limited. It can be dried at 20–80°C for 10 minutes to 10 hours, preferably at 20–60°C for 30 minutes to 8 hours. In this case, a vacuum oven can be used.

[0066] This invention provides a lithium-ion secondary battery separator, which is obtained by the preparation method of this invention.

[0067] The highly wettable lithium-ion battery separator prepared by the method of this invention can be applied to all-solid-state lithium batteries. Specifically, the highly wettable lithium-ion battery separator can be cut and applied to lithium-ion batteries. The specific size of the cut depends on the requirements, generally cut into a circle with a diameter of 15-25 mm.

[0068] Example

[0069] The present invention will be further described below with reference to specific embodiments. The illustrative embodiments and descriptions herein are used to explain the present invention, but are not intended to limit the present invention.

[0070] Example 1

[0071] A method for preparing a highly wettable lithium-ion battery separator includes the following steps:

[0072] 1) Mix 0.1g CMC and 0.1g SBR and stir for 1 hour to obtain 0.2g composite binder;

[0073] 2) Add 1.8g AlOOH and 5ml DMF to the mixed binder in 1) and stir for 4 hours to obtain a uniform AlOOH coating slurry;

[0074] 3) Wipe the surface of the polyethylene diaphragm with isopropanol, and dry it in a vacuum drying oven at 60°C for 6 hours;

[0075] 4) On a casting coating machine, the AlOOH coating slurry in 2) is coated onto the polyethylene diaphragm in 3) to obtain a one-sided modified film. The coating thickness is adjusted to 20μm.

[0076] 5) The obtained one-sided modified film was dried once at room temperature for 1 hour;

[0077] 6) Transfer the single-sided modified film from step 5) into a vacuum drying oven for secondary drying. Set the temperature to 60℃ and the drying time to 8 hours.

[0078] 7) On a casting coating machine, the AlOOH coating slurry in 2) is scraped onto the other side of the single-sided modified film in 6) to obtain a double-sided modified film. The coating thickness is adjusted to 20μm.

[0079] 8) After the double-sided modified diaphragm from step 7) is dried once under the drying conditions in step 5), it is dried a second time under the drying conditions in step 6). A single-sided modified polyethylene diaphragm is obtained.

[0080] 9) Weigh 1.53g of DA into a beaker, and slowly add DA to it using ethanol and tris(hydroxymethyl)aminomethane in a volume ratio of 1:1 as a co-solvent;

[0081] 10) As solvent is added, the pH value of the DA solution in the beaker is continuously tested until pH = 8.5 to obtain the DA buffer solution;

[0082] 11) The primary modified polyethylene membrane in 8) is immersed in the DA buffer solution in 10) for 12 hours to obtain the secondary modified polyethylene membrane.

[0083] 12) After washing the modified polyethylene diaphragm from 11) three times with distilled water, dry it in a vacuum drying oven at 60°C for 6 hours to obtain the modified polyethylene diaphragm.

[0084] In this embodiment, the positive electrode material of the lithium-ion battery is lithium iron phosphate. Specifically, a slurry with a mass ratio of lithium iron phosphate: conductive carbon black: binder of 8:1:1 is coated onto an aluminum foil current collector with a diameter of 12 mm and vacuum dried at 60°C for 12 hours. The negative electrode material of the lithium-ion battery is a commercially available lithium sheet with a diameter of 16 mm. The double-sided modified film is cut into 19 mm diameter discs and assembled into a lithium-ion battery.

[0085] Performance tests were conducted on the highly wettable lithium-ion battery separator and the battery assembled with it. The results are as follows: the contact angle of the highly wettable lithium-ion battery separator is 8.4° at room temperature; the decomposition voltage is 5.20V at 25℃; the melting point measured by DSC is 144.0℃; the ion transport number is 0.65; and the initial discharge capacity at 25℃ and 1C is 173.3 mAh·g. -1 The discharge capacity after 1000 cycles is 148.9 mAh·g. -1 .

[0086] like Figure 1 The figure shows the contact angle obtained in Example 1 of the present invention. Figure 1 This demonstrates intuitively that the highly wettable lithium-ion battery separator prepared in this embodiment has good electrolyte wettability.

[0087] like Figure 2 The image shown is a thermal shrinkage diagram of the highly wettable lithium-ion battery separator obtained in Example 1 of the present invention. Figure 2 This clearly demonstrates that the highly wettable lithium-ion battery separator prepared in this embodiment has excellent thermal processing performance.

[0088] like Figure 3 The image shown is a thermal shrinkage diagram of the highly wettable lithium-ion battery separator obtained in Example 1 of the present invention. Figure 3 This demonstrates intuitively that the highly wettable lithium-ion battery separator prepared in this embodiment has a high melting point.

[0089] Example 2

[0090] A method for preparing a highly wettable lithium-ion battery separator includes the following steps:

[0091] 1) Mix 0.1g CMC and 0.1g SBR and stir for 1 hour to obtain 0.2g composite binder;

[0092] 2) Add 2.2g AlOOH and 5ml DMF to the mixed binder in 1) and stir for 4 hours to obtain a uniform AlOOH coating slurry;

[0093] 3) Wipe the surface of the polyethylene diaphragm with isopropanol, and dry it in a vacuum drying oven at 60°C for 6 hours;

[0094] 4) On a casting coating machine, the AlOOH coating slurry in 2) is coated onto the polyethylene diaphragm in 3) to obtain a one-sided modified film. The coating thickness is adjusted to 30μm.

[0095] 5) The obtained one-sided modified film was dried once at room temperature for 1 hour;

[0096] 6) Transfer the single-sided modified film from step 5) into a vacuum drying oven for secondary drying. Set the temperature to 60℃ and the drying time to 8 hours.

[0097] 7) On a casting coating machine, the AlOOH coating slurry in 2) is scraped onto the other side of the single-sided modified film in 6) to obtain a double-sided modified film. The coating thickness is adjusted to 30μm.

[0098] 8) After the double-sided modified diaphragm from step 7) is dried once under the drying conditions in step 5), it is dried a second time under the drying conditions in step 6). A single-sided modified polyethylene diaphragm is obtained.

[0099] 9) Weigh 1.66g of DA into a beaker, and slowly add DA to it using ethanol and tris(hydroxymethyl)aminomethane in a volume ratio of 1:1 as a co-solvent;

[0100] 10) As solvent is added, the pH value of the DA solution in the beaker is continuously tested until pH = 8.5 to obtain the DA buffer solution;

[0101] 11) The primary modified polyethylene membrane in 8) is immersed in the DA buffer solution in 10) for 15 hours to obtain the secondary modified polyethylene membrane.

[0102] 12) After washing the modified polyethylene diaphragm from 11) three times with distilled water, dry it in a vacuum drying oven at 60°C for 6 hours to obtain the modified polyethylene diaphragm.

[0103] The modified polyethylene diaphragm of Example 2 was used for performance testing. The results were as follows: the contact angle of the modified polyethylene diaphragm was 9.8°; the decomposition voltage at 25°C was 5.16V; the melting point measured by DSC was 144.3°C; and the ion transference number was 0.63.

[0104] Example 3

[0105] A method for preparing a highly wettable lithium-ion battery separator includes the following steps:

[0106] 1) Mix 0.1g CMC and 0.1g SBR and stir for 1 hour to obtain 0.2g composite binder;

[0107] 2) Add 1.08g AlOOH and 3ml DMF to the mixed binder in 1) and stir for 4 hours to obtain a uniform AlOOH coating slurry;

[0108] 3) Wipe the surface of the polyethylene diaphragm with isopropanol, and dry it in a vacuum drying oven at 60°C for 6 hours;

[0109] 4) On a casting coating machine, the AlOOH coating slurry in 2) is scraped onto the polyethylene diaphragm in 3) to obtain a one-sided modified film. The coating thickness is adjusted to 10μm.

[0110] 5) The obtained one-sided modified film was dried once at room temperature for 1 hour;

[0111] 6) Transfer the single-sided modified film from step 5) into a vacuum drying oven for secondary drying. Set the temperature to 60℃ and the drying time to 8 hours.

[0112] 7) On a casting coating machine, the AlOOH coating slurry in 2) is scraped onto the other side of the single-sided modified film in 6) to obtain a double-sided modified film. The coating thickness is adjusted to 10μm.

[0113] 8) After the double-sided modified diaphragm from step 7) is dried once under the drying conditions in step 5), it is dried a second time under the drying conditions in step 6). A single-sided modified polyethylene diaphragm is obtained.

[0114] 9) Weigh 0.77g of DA into a beaker, and slowly add DA to it using ethanol and tris(hydroxymethyl)aminomethane in a volume ratio of 1:1 as a co-solvent;

[0115] 10) As solvent is added, the pH value of the DA solution in the beaker is continuously tested until pH = 8.5 to obtain the DA buffer solution;

[0116] 11) The primary modified polyethylene membrane in 8) is immersed in the DA buffer solution in 10) for 12 hours to obtain the secondary modified polyethylene membrane.

[0117] 12) After washing the modified polyethylene diaphragm from 11) three times with distilled water, dry it in a vacuum drying oven at 60°C for 6 hours to obtain the modified polyethylene diaphragm.

[0118] The modified polyethylene diaphragm of Example 3 was used for performance testing. The results were as follows: the contact angle of the modified polyethylene diaphragm was 10.2°; the decomposition voltage at 25°C was 5.14V; the melting point measured by DSC was 144.2°C; and the ion transference number was 0.63.

[0119] Comparative Example 1

[0120] A method for preparing a pure inorganic coated modified polyethylene separator includes the following steps:

[0121] 1) Mix 0.1g CMC and 0.1g SBR and stir for 1 hour to obtain 0.2g composite binder;

[0122] 2) Add 1.8g AlOOH and 5ml DMF to the mixed binder in 1) and stir for 4 hours to obtain a uniform AlOOH coating slurry;

[0123] 3) Wipe the surface of the polyethylene diaphragm with isopropanol, and dry it in a vacuum drying oven at 60°C for 6 hours;

[0124] 4) On a casting coating machine, the AlOOH coating slurry in 2) is coated onto the polyethylene diaphragm in 3) to obtain a one-sided modified film. The coating thickness is adjusted to 20μm.

[0125] 5) The obtained one-sided modified film was dried once at room temperature for 1 hour;

[0126] 6) Transfer the single-sided modified film from step 5) into a vacuum drying oven for secondary drying. Set the temperature to 60℃ and the drying time to 8 hours.

[0127] 7) On a casting coating machine, the AlOOH coating slurry in 2) is scraped onto the other side of the single-sided modified film in 6) to obtain a double-sided modified film. The coating thickness is adjusted to 20μm.

[0128] 8) After the double-sided modified diaphragm in 7) is dried once under the drying conditions in 5), it is dried a second time under the drying conditions in 6) to obtain the modified polyethylene diaphragm;

[0129] The performance of the pure inorganic coating modified polyethylene diaphragm was tested, and the results were as follows: the contact angle of the pure inorganic coating modified polyethylene diaphragm was 32.8°; the decomposition voltage at 25℃ was 5.06V; the melting point measured by DSC was 145.1℃; and the ion transference number was 0.52.

[0130] Comparative Example 2

[0131] A method for preparing a polymer-coated modified polyethylene separator includes the following steps:

[0132] 1) Weigh 1.53g of DA into a beaker, and slowly add DA to it using ethanol and tris(hydroxymethyl)aminomethane in a volume ratio of 1:1 as a co-solvent;

[0133] 2) As solvent is added, the pH value of the DA solution in the beaker is continuously tested until pH = 8.5 to obtain the DA buffer solution;

[0134] 3) Wipe the surface of the polyethylene diaphragm with isopropanol, and dry it in a vacuum drying oven at 60°C for 6 hours to obtain a clean polyethylene diaphragm.

[0135] 4) The clean polyethylene diaphragm from 3) is immersed in the DA buffer solution from 2) using a solution immersion process for 12 hours;

[0136] 5) After washing the modified polyethylene diaphragm from 4) three times with distilled water, dry it in a vacuum drying oven at 60°C for 6 hours to obtain the modified polyethylene diaphragm.

[0137] The performance of the organic-coated modified polyethylene diaphragm was tested, and the results were as follows: the contact angle of the pure organic-coated modified polyethylene diaphragm was 13.0°; the decomposition voltage at 25°C was 5.12V; the melting point measured by DSC was 143.9°C; and the ion transference number was 0.46.

[0138] Comparative Example 3

[0139] A method for preparing a highly wettable lithium-ion battery separator includes the following steps:

[0140] 1) Mix 0.05g CMC and 0.05g SBR and stir for 1 hour to obtain 0.1g composite adhesive;

[0141] The remaining steps are the same as in Example 1.

[0142] The modified polyethylene diaphragm of Comparative Example 3 was used for performance testing. The results were as follows: the contact angle of the modified polyethylene diaphragm was 15.6°; the decomposition voltage at 25°C was 5.11V; the melting point measured by DSC was 144.1°C; and the ion transport number was 0.48.

[0143] Comparative Example 4

[0144] A method for preparing a highly wettable lithium-ion battery separator includes the following steps:

[0145] 1) Mix 0.4g CMC and 0.4g SBR and stir for 1 hour to obtain 0.8g composite binder;

[0146] The remaining steps are the same as in Example 1.

[0147] The modified polyethylene diaphragm of Comparative Example 4 was used for performance testing. The results were as follows: the contact angle of the modified polyethylene diaphragm was 16.2°; the decomposition voltage at 25°C was 5.09V; the melting point measured by DSC was 144.1°C; and the ion transference number was 0.47.

[0148] like Figure 1 The figures show the contact angles obtained in Example 1, Comparative Example 1, and Comparative Example 2. Compared with the pure inorganic coating modified polyethylene separator and the pure organic coating modified polyethylene separator, the high wettability lithium-ion battery separator obtained in Example 1 has a good electrolyte absorption rate due to its good electrolyte wettability.

[0149] like Figure 2 The images shown are actual photographs of the heat shrinkage rates obtained in Example 1, Comparative Example 1, and Comparative Example 2; Figure 3 The figures shown are DSC curves obtained in Example 1, Comparative Example 1, and Comparative Example 2. Compared with pure inorganic coating modified polyethylene separators and pure organic coating modified polyethylene separators, the high wettability lithium-ion battery separator obtained in Example 1 has good thermal processing performance, high melting point, and high heat resistance due to its good mechanical properties and good electrolyte wettability.

[0150] like Figure 4 The diagrams shown are the decomposition voltage diagrams obtained in Example 1, Comparative Example 1, and Comparative Example 2. Compared with the pure inorganic coating modified polyethylene separator and the pure organic coating modified polyethylene separator, the high wettability lithium-ion battery separator obtained in Example 1 has good electrochemical stability due to its higher decomposition voltage.

[0151] like Figure 5 The diagram shows the ion transference number obtained in Example 1, Comparative Example 1, and Comparative Example 2. Compared with the pure inorganic coating modified polyethylene separator and the pure organic coating modified polyethylene separator, the high wettability lithium-ion battery separator obtained in Example 1 has a good lithium-ion diffusion rate due to its higher ion transference number, which is beneficial to the stable cycling of lithium-ion batteries.

[0152] like Figure 6 The figure shows the 1C charge-discharge curves of a lithium iron phosphate / lithium battery assembled with the high wettability lithium-ion battery separator obtained in Example 1 at room temperature; Figure 7 The figure shows the 1C cycle performance curve of a lithium iron phosphate / lithium battery assembled with the high wettability lithium-ion battery separator obtained in Example 1 at room temperature; it proves that the high wettability lithium-ion battery separator obtained in Example 1 of the present invention has excellent room temperature ionic conductivity, thermal stability and mechanical strength, which makes it exhibit excellent cycle performance in lithium-ion battery applications.

[0153] On the other hand, as shown in Comparative Examples 3-4 of the present invention, when the binder content is too high or too low, the wettability of the obtained modified polyethylene diaphragm deteriorates, and its ion migration number is low, resulting in poor electrochemical performance.

[0154] Industrial practicality

[0155] In this invention, the lithium-ion secondary battery separator prepared using the specific method of this invention exhibits excellent mechanical strength and thermal stability, even when thin. This is beneficial for suppressing lithium dendrite punctures into the separator and maintaining its thermomechanical stability. Furthermore, the separator of this invention exhibits excellent wettability and good electrolyte retention, which is highly beneficial for improving battery cycle performance, especially high-rate discharge performance. Therefore, the lithium-ion secondary battery separator of this invention is very suitable for use in lithium-ion secondary batteries.

Claims

1. A method for preparing a lithium-ion battery separator, characterized in that, Includes the following steps: S1, Prepare AlOOH dispersion; S3, the AlOOH dispersion from step S1 is coated on at least one side of the basement membrane and dried to obtain a primary modified basement membrane; S4, prepare dopamine slow solution; S5, the basement membrane modified in step S3 is brought into contact with the dopamine slow solution in step S4 to obtain the basement membrane modified in step S4. S6. The substrate membrane modified in step S5 is optionally washed with water and then dried to obtain a lithium-ion battery separator.

2. The preparation method according to claim 1, wherein, The solvent used in the AlOOH dispersion is selected from one or more of amide solvents, sulfoxide solvents, ketone solvents, aromatic solvents, ether solvents, ester solvents, and alcohol solvents, preferably an amide solvent, and more preferably dimethylformamide (DMF).

3. The preparation method according to claim 1 or 2, wherein, The AlOOH dispersion further comprises a binder, said binder being at least one selected from polyvinyl alcohol, carboxymethyl cellulose, and styrene-butadiene rubber; more preferably, it is selected from two of carboxymethyl cellulose and styrene-butadiene rubber, and preferably the mass ratio of carboxymethyl cellulose to styrene-butadiene rubber is 1:0.2 to 10, more preferably 1:0.5 to 2. Preferably, the mass ratio of the binder to AlOOH is 1:4 to 15, more preferably 1:5 to 12.

4. The preparation method according to any one of claims 1-3, wherein, In the AlOOH dispersion, the mass concentration of AlOOH is 5% to 50% by mass, preferably 10% to 40% by mass.

5. The preparation method according to any one of claims 1-4, wherein, The base membrane is a polyolefin membrane, preferably a polyethylene membrane or a polypropylene membrane; and / or, The base membrane is a lithium salt modified base membrane obtained by modifying the base membrane with lithium salts. The lithium salts are selected from lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalate-borate) (LiBOB), lithium difluoroborate (LiDFOB), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), and bis(malonyl)boronic acid (LiBM). B) At least one of lithium oxalate borate (LiMOB), lithium hexafluoroantimony oxide (LiSbF6), lithium difluorophosphate (LiPF2O2), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2), LiN(SO2C2F5)2, LiC(SO2CF3)3 and LiN(SO2F)2, preferably lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

6. The preparation method according to any one of claims 1-5, wherein, In step S3, the coating method is selected from at least one of forward roll coating, reverse roll coating, microgravure coating, direct metering coating, and cast coating, and / or In step S3, the AlOOH dispersion is coated on one or both sides of the base film to form a coating thickness of 2 μm to 50 μm, preferably 5 μm to 40 μm.

7. The preparation method according to any one of claims 1-6, wherein, In step S3, the drying is carried out in steps. The preferred drying conditions for the first step are drying at 20-80°C for 10 minutes to 2 hours, and preferably drying at 20-60°C for 30 minutes to 1 hour. The preferred drying conditions for the second step are drying at 20-80°C for 30 minutes to 10 hours, and preferably drying at 20-60°C for 1 minute to 8 hours.

8. The preparation method according to any one of claims 1-7, wherein, In step S4, the dopamine slow solution uses tris(hydroxymethyl)aminomethane as a buffer, and optionally the dopamine slow solution further contains an alcohol solvent or water, preferably ethanol.

9. The preparation method according to any one of claims 1-8, wherein, In step S4, the pH of the dopamine slow solution is in the range of 7.5-9.0; the mass ratio of dopamine to AlOOH is 1:0.5-3, preferably 1:1-2.

10. The preparation method according to any one of claims 1-9, wherein, In step S5, the modified basement membrane obtained in step S3 is immersed in the dopamine slow solution in step S4 for contact; preferably, the contact time is 8 to 24 hours.

11. The preparation method according to any one of claims 1-10, wherein, In step S6, the secondary modified basement membrane obtained in step S5 is washed with water, preferably three or more times.

12. The preparation method according to any one of claims 1-11, wherein, In step S6, the drying conditions are drying at 20-80°C for 10 minutes to 10 hours, preferably drying at 20-60°C for 30 minutes to 8 hours.

13. The preparation method according to any one of claims 1-12, wherein, Step S2 is performed between steps S1 and S3, in which the basement membrane is cleaned to obtain a clean basement membrane.

14. The preparation method according to claim 13, wherein, The cleaning method is as follows: the base membrane is washed with a solvent and then dried; the solvent used for washing is selected from one or more of amide solvents, sulfoxide solvents, ether solvents, ester solvents, and alcohol solvents, preferably an alcohol solvent, and more preferably one or more of ethanol and isopropanol.

15. A lithium-ion secondary battery separator, obtained by any one of claims 1-14.

Images