Lithium battery separator with high coating peel strength and method of making same

Abstract

The application relates to the technical field of lithium battery diaphragm, and discloses a lithium battery diaphragm with high coating peeling strength and a preparation method thereof; the method comprises the following operation steps: S1: premixing a porous PVA@PVDF composite material with ultrapure water, adding a binder to uniformly mix, and then adding a wetting agent to uniformly mix, so as to obtain a porous PVA@PVDF composite material coating slurry; and S2: uniformly roller coating the porous PVA@PVDF composite material coating slurry on a polyolefin diaphragm, baking at 70-75 DEG C, and winding to obtain a lithium battery diaphragm.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery separator, in particular to a lithium battery separator with high coating peeling strength and a preparation method thereof. BACKGROUND

[0002] The lithium battery separator is an insulating material for isolating the positive and negative electrodes of the battery, so that lithium ions move between the positive and negative electrodes through the separator; therefore, the excellent properties of the separator directly affect the performance of the lithium battery, and even indirectly affect the safety of the lithium battery. The commercialized separators mainly include polyolefin separators (polyethylene PE, polypropylene PP, and composite film PP / PE / PP) and non-woven fabrics, etc. The polyolefin separators have good mechanical properties, low price, and non-toxicity, and are widely used in lithium batteries.

[0003] However, the commercial microporous membrane shrinks and closes near the melting temperature, causing short circuit of the battery, which makes the lithium battery have the risk of burning and exploding at high temperatures; and the polyolefin separator has poor adsorption of electrolyte, which is not conducive to the conduction of lithium ions during the charging and discharging process; research has found that inorganic nanoparticle coatings and polymer porous coatings have higher thermal stability and stronger electrolyte adsorption capacity, thereby improving the thermal stability and electrolyte adsorption capacity of the composite separator.

[0004] To solve the problem of poor adhesion and electrolyte wettability of the polyolefin separator, the current main solution is to coat a water-based PVDF adhesive layer on one side or both sides of the separator; such a coating layer can effectively improve the adhesion of the separator and has good wettability with the electrolyte; however, since PVDF itself is hydrophobic, it cannot be directly dispersed in water; therefore, in the prior art, a large amount of additives, or even multiple different additives, need to be added to prepare the PVDF slurry to ensure that it can be uniformly dispersed in water; however, the preparation process is complicated, time-consuming, and greatly reduces the production efficiency, increases the production cost, and further compresses the profit space of the separator; therefore, developing a water-based PVDF coating separator with high adhesion and easy preparation has become a common goal of the industry. SUMMARY

[0005] The present application relates to the technical field of lithium battery separator, in particular to a lithium battery separator with high coating peeling strength and a preparation method thereof.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A preparation method of a lithium battery separator with high coating peeling strength, comprising the following operation steps:

[0008] S1: premix the porous PVA@PVDF composite material with ultrapure water, add the binder and mix uniformly, then add the wetting agent and mix uniformly, to obtain a porous PVA@PVDF composite material coating slurry;

[0009] S2: uniformly roll coat the porous PVA@PVDF composite material coating slurry on the polyolefin separator, bake at 70~75℃, and wind up, to obtain a lithium battery separator.

[0010] More preferably, the raw materials of the porous PVA@PVDF composite material coating slurry include the following components: 5~15wt% porous PVA@PVDF composite material, 2~11wt% binder, 0.1~0.7wt% wetting agent, and the rest is ultrapure water.

[0011] More preferably, the coating area density of the porous PVA@PVDF composite material coating slurry on the lithium battery separator is 0.7±0.1g / m 2 .

[0012] In the scheme, the porous PVA@PVDF composite material coating slurry is coated on the polyolefin separator on both sides or one side.

[0013] More preferably, the binder is polyacrylonitrile, and the wetting agent is polyether organosilicon.

[0014] More preferably, the preparation method of the porous PVA@PVDF composite material is as follows: (1) uniformly mix the PVDF powder into ultrapure water to obtain a PVDF suspension; (2) seal the polyvinyl alcohol into formamide and mix at a temperature of 35~40℃ for 5~7 hours to obtain a polyvinyl alcohol solution; (3) slowly add the polyvinyl alcohol solution into the PVDF suspension at a flow rate of 0.7~0.85ml / min under the conditions of stirring and ultrasonic treatment; then reduce the rotation speed to 700~750rpm and mix for 2~3 hours and ultrasonic treat for 4~6 hours to obtain a mixed solution; centrifuge, wash, and vacuum dry the mixed solution to obtain the porous PVA@PVDF composite material.

[0015] More preferably, the raw materials of the porous PVA@PVDF composite material include the following components: 4~5 parts PVDF powder, 1.5~2.5 parts polyvinyl alcohol, 250~300 parts ultrapure water, and 8~10 parts formamide.

[0016] More preferably, the rotation speed of the stirring is 1000~12000rpm; and the power of the ultrasonic treatment is 350~450w and the frequency is 30~45KHz.

[0017] More preferably, the vacuum drying is performed at a vacuum degree of 0.05-0.08 MPa and a temperature of 60-65 DEG C for 40-48 hours.

[0018] Compared with the prior art, the present application has the following advantages:

[0019] The porous PVA@PVDF composite material modified composite diaphragm provided by the present application; PVA is a high polymer containing a large number of hydroxyl groups, and hydroxyl groups are strong hydrophilic groups. By modifying PVDF with porous PVA, the problem of difficult dispersion of PVDF in water can be significantly improved. The modified PVDF can be directly dispersed in water, and the slurry preparation process is very simple, thereby greatly improving the production efficiency and reducing the production cost, and further greatly improving the profit space of the diaphragm.

[0020] The introduction of PVDF can effectively improve the adhesion and wettability of the diaphragm. In addition, PVA has good adhesion, and the introduction of PVA further improves the adhesion of the diaphragm. The PVA@PVDF composite material in the scheme has a porous structure, which can improve the air permeability of the PVDF coated film. The polyether organosilicon wetting agent has good mechanical properties, heat resistance and wettability, thereby improving the hot pressing peeling performance of the diaphragm. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0022] The following specific embodiments are parts by mass, and in this embodiment, it should be noted that there is no special restriction on the purchase manufacturer of all raw materials involved in the present application, which exemplarily includes: PVDF powder model LBG-8200, purchased from Arkema; polyvinyl alcohol (PVA) model 2699, purchased from Shenzhen Boshun Chemical Co., Ltd.; polyolefin separator material is polyethylene, purchased from Shenzhen Liyou New Energy Technology Co., Ltd.; adhesive (polyacrylonitrile) model LA133, purchased from Hubei Maideluo Biological Technology Co., Ltd.; wetting agent (polyether organosilicon) model WE3220, purchased from Shanghai Zhenli Shihui Network Technology Co., Ltd.; thickening agent is sodium hydroxymethyl cellulose, item number S14014, purchased from Yuanye Bio; defoamer (polyether defoamer) item number XP1809C, purchased from Luoyang Xipeng Environmental Protection Technology Co., Ltd.; dispersant (aliphatic amide dispersant) is vinyl bis-stearamide, CAS number 110-30-5, purchased from Wuhan Jixingyibang Biological Technology Co., Ltd.; adhesive (polyacrylic acid) is polyacrylic acid, specification BR, molecular weight 3000, purchased from Shanghai Huzhen Industry Co., Ltd.; formamide CAS number 75-12-7; polydimethylsiloxanol (average Mn ~ 5600) CAS number 156327-07-0, purchased from Macklin.

[0023] Example 1: A lithium battery separator with high coating peeling strength and a preparation method thereof, comprising the following operation steps:

[0024] S1.1: (1) 4.25 parts of PVDF powder and 280 parts of ultrapure water were placed in a 500 ml three-necked flask, first stirred at 1200 rpm for 120 minutes, and then ultrasonically treated at 45 KHz and 450 w for 12 hours to obtain a PVDF suspension; (2) 1.85 parts of polyvinyl alcohol was added to 8 parts of formamide, sealed and treated, stirred at 400 rpm at 40°C for 5 hours to obtain a polyvinyl alcohol solution; (3) first, the polyvinyl alcohol solution was slowly added to the PVDF suspension at a flow rate of 0.85 ml / min under the conditions of stirring (rotation speed 1000 rpm) and ultrasonic treatment (frequency 40 KHz, power 400 w); then the rotation speed was reduced to 750 rpm and stirred for 3 hours, and then ultrasonically treated (frequency 35 KHz, power 450 w) for 5 hours to obtain a mixed solution; centrifuged at 8500 rpm for 20 minutes, washed, and vacuum dried at a vacuum degree of 0.08 MPa and a temperature of 60°C for 48 hours to obtain a porous PVA@PVDF composite material;

[0025] S1.2: The porous PVA@PVDF composite material is pre-mixed with ultrapure water at a speed of 700 rpm for 90 minutes, a binder is added, stirring at a speed of 1000 rpm for 40 minutes, the speed is reduced to 350 rpm, a wetting agent is added and stirred for 30 minutes, and a porous PVA@PVDF composite material coating slurry is obtained;

[0026] The raw materials of the porous PVA@PVDF composite material coating slurry include the following components: 5wt% porous PVA@PVDF composite material, 9wt% binder (polyacrylonitrile, LA133), 0.5wt% wetting agent (polyether silicone, WE3220), and the rest is ultrapure water;

[0027] S2: The porous PVA@PVDF composite material coating slurry is uniformly roller-coated on both sides of the polyolefin separator, and after passing through a 75℃ oven, it is wound up to obtain a lithium battery separator.

[0028] Example 2: A lithium battery separator with high coating peeling strength and a preparation method thereof, comprising the following operation steps:

[0029] S1.1: (1) 4.25 parts of PVDF powder and 280 parts of ultrapure water are placed in a 500ml three-necked flask, first stirred at a speed of 1200 rpm for 120 minutes, and then ultrasonically treated at a frequency of 45KHz and a power of 450w for 12 hours to obtain a PVDF suspension; (2) 1.85 parts of polyvinyl alcohol is added to 8 parts of formamide, sealed and treated, stirred at a speed of 400 rpm at a temperature of 40℃ for 5 hours to obtain a polyvinyl alcohol solution; (3) the polyvinyl alcohol solution is slowly added to the PVDF suspension at a flow rate of 0.85ml / min under the conditions of stirring (speed 1000rpm) and ultrasonic treatment (frequency 40KHz, power 400w); then the speed is reduced to 750rpm and stirred for 3 hours, and then ultrasonically treated (frequency 35KHz, power 450w) for 5 hours to obtain a mixed solution; centrifugation at 8500rpm for 20 minutes, washing, and vacuum drying at a vacuum degree of 0.08MPa and a temperature of 60℃ for 48 hours to obtain a porous PVA@PVDF composite material;

[0030] S1.2: The porous PVA@PVDF composite material is pre-mixed with ultrapure water at a speed of 700 rpm for 90 minutes; a binder is added, stirring at a speed of 1000 rpm for 40 minutes, the speed is reduced to 350 rpm; a wetting agent is added and stirred for 30 minutes to obtain a porous PVA@PVDF composite material coating slurry;

[0031] The raw materials of the porous PVA@PVDF composite coating slurry include the following components: 10wt% porous PVA@PVDF composite, 9wt% binder (polyacrylonitrile, LA133), 0.5wt% wetting agent (polyether silicone, WE3220), and the rest is ultrapure water;

[0032] S2: uniformly roll-coat the porous PVA@PVDF composite coating slurry on both sides of the polyolefin separator, and then roll it up after baking in a 75°C oven to obtain a lithium battery separator.

[0033] Example 3: A lithium battery separator with high coating peeling strength and a preparation method thereof, comprising the following operation steps:

[0034] S1.1: (1) Put 4.25 parts of PVDF powder and 280 parts of ultrapure water in a 500ml three-necked flask, first stir at a speed of 1200rpm for 120 minutes, and then ultrasonically treat under the conditions of 45KHz and 450w for 12 hours to obtain a PVDF suspension; (2) Put 1.85 parts of polyvinyl alcohol into 8 parts of formamide, seal, stir at a speed of 400rpm at a temperature of 40°C for 5 hours to obtain a polyvinyl alcohol solution; (3) first slowly add the polyvinyl alcohol solution to the PVDF suspension at a flow rate of 0.85ml / min under the conditions of stirring (speed 1000rpm) and ultrasonic treatment (frequency 40KHz, power 400w); then reduce the stirring speed to 750rpm for 3 hours, and then ultrasonically treat (frequency 35KHz, power 450w) for 5 hours to obtain a mixed solution; centrifuge at 8500rpm for 20 minutes, wash, and vacuum dry at a vacuum degree of 0.08MPa and a temperature of 60°C for 48 hours to obtain a porous PVA@PVDF composite material;

[0035] S1.2: Pre-mix the porous PVA@PVDF composite material with ultrapure water at a stirring speed of 700rpm for 90 minutes, add a binder, stir at a speed of 1000rpm for 40 minutes, reduce the stirring speed to 350rpm, and then add a wetting agent and stir for 30 minutes to obtain a porous PVA@PVDF composite coating slurry;

[0036] The raw materials of the porous PVA@PVDF composite coating slurry include the following components: 10wt% porous PVA@PVDF composite, 9wt% binder (polyacrylonitrile, LA133), 0.5wt% wetting agent (polyether silicone, WE3220), and the rest is ultrapure water;

[0037] S2: The polyolefin separator is uniformly roll-coated with the porous PVA@PVDF composite coating slurry on both sides, and after baking in a 75°C oven, it is wound up to obtain a lithium battery separator.

[0038] Example 4: The polyolefin separator is coated on one side;

[0039] S1.1: (1) 4.25 parts of PVDF powder and 280 parts of ultrapure water are placed in a 500 ml three-necked flask, first stirred at 1200 rpm for 120 minutes, and then ultrasonically treated at 45 KHz and 450 w for 12 hours to obtain a PVDF suspension; (2) 1.85 parts of polyvinyl alcohol is added to 8 parts of formamide, sealed and treated, stirred at 400 rpm at 40°C for 5 hours to obtain a polyvinyl alcohol solution; (3) the polyvinyl alcohol solution is slowly added to the PVDF suspension at a flow rate of 0.85 ml / min under the conditions of stirring (1000 rpm) and ultrasonic treatment (frequency 40 KHz, power 400 w); then the stirring speed is reduced to 750 rpm for 3 hours, and then ultrasonic treatment (frequency 35 KHz, power 450 w) is carried out for 5 hours to obtain a mixed solution; centrifugation is carried out at 8500 rpm for 20 minutes, washing is carried out, and vacuum drying is carried out at a vacuum degree of 0.08 MPa and a temperature of 60°C for 48 hours to obtain a porous PVA@PVDF composite material;

[0040] S1.2: The porous PVA@PVDF composite material is premixed with ultrapure water at a stirring speed of 700 rpm for 90 minutes, a binder is added, stirring is carried out at a stirring speed of 1000 rpm for 40 minutes, the stirring speed is reduced to 350 rpm, a wetting agent is added and stirred for 30 minutes to obtain a porous PVA@PVDF composite coating slurry;

[0041] The raw materials of the porous PVA@PVDF composite coating slurry include the following components: 15wt% of porous PVA@PVDF composite material, 9wt% of binder (polyacrylonitrile, LA133), 0.5wt% of wetting agent (polyether organosilicon, WE3220), and the rest is ultrapure water;

[0042] S2: The polyolefin separator is uniformly roll-coated with the porous PVA@PVDF composite coating slurry on both sides, and after baking in a 75°C oven, it is wound up to obtain a lithium battery separator.

[0043] Comparative Example 1: Preparation of a conventional PVDF modified polyolefin separator;

[0044] S1: (1) Add dispersant into ultrapure water, pre-mix for 50 minutes at a rotation speed of 600 rpm; (2) Add conventional PVDF powder, stir for 120 minutes at a rotation speed of 700 rpm; (3) Add thickening agent, stir for 90 minutes at a rotation speed of 800 rpm; (4) Add binder, stir for 60 minutes at a rotation speed of 1000 rpm; (5) Add wetting agent, stir for 40 minutes at a rotation speed of 350 rpm; (6) Add defoaming agent, stir for 30 minutes at a rotation speed of 450 rpm, to obtain conventional PVDF coating slurry;

[0045] The raw materials of the conventional PVDF coating slurry include the following components: 0.95wt% of dispersant, 5wt% of conventional PVDF powder, 8wt% of thickening agent (sodium hydroxymethyl cellulose), 15wt% of binder (polyacrylic acid with a molecular weight of 3000), 0.7wt% of wetting agent (polydimethylsiloxanol), 0.3wt% of defoaming agent (polyether type defoaming agent, XP1809C), and the rest is ultrapure water;

[0046] S2: Uniformly roll coat the conventional PVDF coating slurry on both sides of the polyolefin separator, and after passing through a 75°C oven, wind up to obtain a lithium battery separator.

[0047] Comparative Example 2: Uncoated slurry;

[0048] The polyolefin separator is not coated with a coating layer, and is directly used as a lithium battery separator.

[0049] Comparative Example 3: Based on Example 3, the wetting agent is replaced with polydimethylsiloxanol;

[0050] S1.1: (1) Put 4.25 parts of PVDF powder and 280 parts of ultrapure water into a 500 ml three-necked flask, first stir at a rotation speed of 1200 rpm for 120 minutes, and then ultrasonically treat under the conditions of 45 KHz and 450 w for 12 hours to obtain a PVDF suspension; (2) Put 1.85 parts of polyvinyl alcohol into 8 parts of formamide, seal, stir at a rotation speed of 400 rpm at a temperature of 40°C for 5 hours, to obtain a polyvinyl alcohol solution; (3) Slowly add the polyvinyl alcohol solution into the PVDF suspension at a flow rate of 0.85 ml / min under the conditions of stirring (rotation speed 1000 rpm) and ultrasonic treatment (frequency 40 KHz, power 400 w); then reduce the rotation speed to 750 rpm and stir for 3 hours, and then ultrasonically treat (frequency 35 KHz, power 450 w) for 5 hours to obtain a mixed solution; centrifuge at 8500 rpm for 20 minutes, wash, and vacuum dry at a vacuum degree of 0.08 MPa and a temperature of 60°C for 48 hours to obtain a porous PVA@PVDF composite material;

[0051] S1.2: The porous PVA@PVDF composite material is premixed with ultrapure water at a rotation speed of 700 rpm for 90 minutes, a binder is added, stirring at a rotation speed of 1000 rpm for 40 minutes, the rotation speed is reduced to 350 rpm, a wetting agent is added and stirred for 30 minutes, to obtain a porous PVA@PVDF composite material coating slurry;

[0052] The raw materials of the porous PVA@PVDF composite material coating slurry include the following components: 15wt% porous PVA@PVDF composite material, 9wt% binder (polyacrylonitrile, LA133), 0.5wt% wetting agent (polydimethylsiloxanol, Mn~5600), and the rest is ultrapure water;

[0053] S2: The porous PVA@PVDF composite material coating slurry is uniformly roll-coated on the polyolefin separator, and after passing through a 75℃ oven, it is wound up to obtain a lithium battery separator.

[0054] Detection test: compare the performances of the lithium battery separators prepared in Examples 1-4 and Comparative Examples 1-3, see Table 1;

[0055] Table 1

[0056]

[0057] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be regarded as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application. Any mark in the claims should not be regarded as limiting the involved claims.

Claims

1. A method of producing a lithium battery separator with high coating peel strength, characterized by: The method comprises the following steps: S1: mixing the porous PVA@PVDF composite material with ultrapure water, adding a binder and uniformly mixing, and then adding a wetting agent and uniformly mixing to obtain a porous PVA@PVDF composite material coating slurry; S2: uniformly roll coating the porous PVA@PVDF composite material coating slurry on a polyolefin separator, baking at 70-75°C, and winding to obtain a lithium battery separator; The preparation method of the porous PVA@PVDF composite material is as follows: (1) uniformly mixing PVDF powder in ultrapure water to obtain a PVDF suspension; (2) sealing polyvinyl alcohol in formamide and mixing at a temperature of 35-40°C for 5-7 hours to obtain a polyvinyl alcohol solution; (3) slowly adding the polyvinyl alcohol solution to the PVDF suspension at a flow rate of 0.7-0.85 ml / min under stirring and ultrasonic treatment; then reducing the rotation speed to 700-750 rpm for 2-3 hours of mixing and 4-6 hours of ultrasonic treatment to obtain a mixed solution; centrifuging, washing, and vacuum drying the mixed solution to obtain the porous PVA@PVDF composite material.

2. The method of claim 1, wherein the method is characterized by: The raw material of the porous PVA@PVDF composite material coating slurry comprises the following components: 5-15 wt% of the porous PVA@PVDF composite material, 2-11 wt% of a binder, 0.1-0.7 wt% of a wetting agent, and the rest being ultrapure water.

3. The method of claim 1, wherein the method is characterized by: The porous PVA@PVDF composite coating slurry has a coating area density of 0.7±0.1 g / m 2 .

4. The method of claim 2, wherein the method is characterized by: The binder is a polyacrylonitrile type, and the wetting agent is a polyether organic silicone type.

5. The method of claim 1, wherein the method is characterized by: The raw material of the porous PVA@PVDF composite material comprises the following components: 4-5 parts of PVDF powder, 1.5-2.5 parts of polyvinyl alcohol, 250-300 parts of ultrapure water, and 8-10 parts of formamide.

6. The method of claim 1, wherein the method further comprises: The rotation speed of the stirring is 1000-12000 rpm; the ultrasonic treatment has a power of 350-450 w and a frequency of 30-45 KHz.

7. The method of claim 1, wherein the method further comprises: The vacuum drying has a vacuum degree of 0.05-0.08 MPa, a temperature of 60-65°C, and a drying time of 40-48 hours.

8. A lithium battery separator prepared by the method of any one of claims 1-7.

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