CN110993863A

CN110993863A - High-cohesiveness water-based PVDF slurry, preparation method and application thereof

Info

Publication number: CN110993863A
Application number: CN201911094925.6A
Authority: CN
Inventors: 王成豪; 李正林; 贡晶晶; 张立斌; 尚文滨
Original assignee: Jiangsu Housheng New Energy Technology Co Ltd
Current assignee: Jiangsu Housheng New Energy Technology Co Ltd
Priority date: 2019-11-11
Filing date: 2019-11-11
Publication date: 2020-04-10
Anticipated expiration: 2039-11-11
Also published as: CN110993863B; KR102421795B1; WO2021093572A1; KR20210154845A

Abstract

The invention belongs to the technical field of lithium ion battery diaphragm production, and particularly relates to high-cohesiveness water-based PVDF slurry, a preparation method and application thereof, wherein the high-cohesiveness water-based PVDF slurry specifically comprises the following raw materials in percentage by weight: 3-7% of a dispersing agent, 1-5% of a wetting agent, 5-10% of a co-binder, 0.5-3% of a defoaming agent, 0.1-3% of an anti-settling agent, 15-25% of PVDF (polyvinylidene fluoride), 0.05-2.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 10 to 300. By uniformly dispersing SiC in the PVDF long chain, a large number of micro-capacitor structures are formed, and external heat can be quickly transferred into the PVDF slurry by virtue of the high heat conduction capacity and the bridging action of SiC, so that the bonding of the PVDF slurry is accelerated, the bonding performance of the aqueous PVDF slurry is further improved, and the aqueous PVDF slurry with a thin coating and good bonding force is obtained.

Description

High-cohesiveness water-based PVDF slurry, preparation method and application thereof

Technical Field

The invention relates to the technical field of lithium ion battery diaphragm production, in particular to high-cohesiveness water-based PVDF slurry, a preparation method and application thereof.

Background

The diaphragm is an indispensable key material of the electrode, although the diaphragm does not participate in the electrochemical reaction in the battery, the key performances of the battery, such as capacity, cycle performance, charge-discharge current density and the like, have a direct relation with the diaphragm, and the improvement of the diaphragm performance plays an important role in improving the comprehensive performance of the lithium battery. The separator mainly plays a role in connecting an electrode active material, a conductive agent and an electrode current collector, and maintains the structural integrity of an electrode. The diaphragm also has high temperature self-closing properties to block current conduction from explosion during overcharge or elevated temperatures.

Currently, the most common binder used in the lithium ion battery industry is polyvinylidene fluoride (PVDF), which has the advantages of strong oxidation and reduction resistance, good thermal stability, easy dispersion, and the like. However, the adhesive capacity of the glued membrane to the electrode current collector has a great relationship with the coating amount of the PVDF, the higher the coating amount is, the better the adhesive performance is, but with the increase of the coating amount of the PVDF, the increment of the air permeability value of the membrane is larger, the risk of pore blocking of the membrane is increased, the internal resistance of the lithium battery is increased, the multiplying power is reduced, and the cycle performance is reduced, so that the PVDF slurry with a thinner coating and better adhesive force is needed.

Chinese patent No. CN201811140887.9 discloses a preparation method of a ceramic coating diaphragm for a lithium ion battery, wherein the ceramic coating diaphragm comprises a polymer porous base film, polymer glue solution coated on one side or two sides of the surface of the base film, a ceramic coating coated on the surface of the polymer glue solution, and PVDF and copolymer glue solution coated on the surface of the ceramic coating and the other side of the surface of the base film. The adhesion of the ceramic coating to the polymer porous base membrane is increased by a multilayer design. In addition, Chinese patent No. CN201810623817.2 discloses a diaphragm and a preparation method thereof and a lithium-sulfur battery, wherein the diaphragm comprises a base material diaphragm, and water system glue layers are formed on the two side surfaces of the base material diaphragm; an aqueous heat conductive material layer is formed on the aqueous adhesive layer on the surface of the base separator. The negative electrode of the lithium-sulfur battery is opposite to the water-based heat conduction material layer, and the positive electrode is opposite to the water-based glue layer. The slurry is water-based slurry, which is beneficial to generating cohesive force between the anode and the diaphragm, better forming the battery cell and relieving the dissolution and diffusion of polysulfide ions. However, in the process of coating the multilayer structure, the thickness of the diaphragm coating is increased virtually, and the porosity of the coating is inconsistent, so that the aperture tortuosity of the composite diaphragm is increased, the internal resistance of the lithium battery is increased, the electrochemical performance is reduced, the bonding performance between the composite diaphragm and the positive plate and the negative plate of the battery is poor, and the battery performance cannot achieve the ideal effect.

Disclosure of Invention

In view of the above-mentioned disadvantages of the prior art, the present invention aims to provide a highly adhesive aqueous PVDF slurry, a preparation method and applications thereof.

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 3-7% of a dispersing agent, 1-5% of a wetting agent, 5-10% of a co-binder, 0.5-3% of a defoaming agent, 0.1-3% of an anti-settling agent, 15-25% of PVDF (polyvinylidene fluoride), 0.05-2.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 10 to 300.

Adopt above-mentioned technical scheme: the silicon carbide (SiC) ceramic has stable chemical property, high heat conductivity coefficient up to 490W/mK, small thermal expansion coefficient and high dielectric constant. SiC is dispersed in the aqueous PVDF slurry, a large number of heat conduction paths are generated inside PVDF, and a large number of micro-capacitor structures are formed, so that in the hot-pressing polymerization bonding process of the diaphragm coated with the aqueous PVDF slurry, due to the high heat conduction capacity of SiC, external heat can be quickly transferred into the PVDF slurry, the bonding of the PVDF slurry is accelerated, the bonding performance of the aqueous PVDF slurry is improved, and abnormal phenomena such as powder falling, stripping and falling of the aqueous PVDF slurry are reduced. Secondly, chlorine atoms in PVDF are strong electron-withdrawing groups, and on the surface of SiC, the surface of silicon atoms hybridized by sp3 has a large amount of positive charges, and the chlorine atoms can adsorb the silicon atoms through electrostatic action, so that SiC ceramic particles are uniformly dispersed in a PVDF long chain structure to form more micro capacitive structures.

Further, the adding amount of the silicon carbide and the adding amount of the PVDF are 1: 20 to 100. The proper addition amount can ensure good bonding performance and electrochemical performance; if the addition amount of the silicon carbide is too low, an effective number of micro-capacitor structures cannot be formed, and the improvement effect on the bonding performance is limited; however, if the amount of silicon carbide added is too high, part of the silicon carbide ceramic particles can be uniformly dispersed in PVDF, but the bonding between the silicon carbide ceramic particles and PVDF is poor, part of the silicon carbide ceramic particles are almost completely exposed to PVDF, and the number of agglomerated particles increases, so that many pores exist in the separator, and electrochemical performance is reduced.

Further, the material comprises the following raw materials in percentage by weight: 5% of dispersing agent, 3% of wetting agent, 7% of binder aid, 1.5% of defoaming agent, 1% of anti-settling agent, 20% of PVDF (polyvinylidene fluoride), 0.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 40.

further, the dispersant is alkali metal phosphate.

Further, the alkali metal phosphate is one or more of sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate. The SiC ceramic particles are directly added into the aqueous PVDF slurry, and because the specific surface area of the SiC ceramic particles is large and the incompatibility of multiple phases is easy to cause the SiC ceramic particles to agglomerate and introduce air holes into the slurry, the loss of the diaphragm is increased, and the compressive strength is reduced; alkali metal phosphates are dissociated in water to generate ions with positive charges, and the ions are dispersed around silicon carbide, so that the surface of the SiC ceramic particles is provided with strong positive charges, and strong charge repulsion is generated among the ions to limit agglomeration and promote dispersion, therefore, the SiC ceramic particles can be stably dispersed in the aqueous PVDF slurry to form a more compact network in a limited volume, and the enhancement of the positive charges is also beneficial to the uniform dispersion of the SiC ceramic particles in a PVDF long-chain structure, so that the overlapping among the sheet layers is more obvious, more heat conduction paths beneficial to heat transfer are formed, and the hot-pressing bonding performance is enhanced.

Further, the wetting agent is a mixture of one or more of an anionic surfactant and a nonionic surfactant. The anionic surfactant is sodium alkylaryl sulfonate, sodium butylnaphthalene sulfonate, sodium hydroxyethyl sulfonate or sodium dodecyl sulfonate; the nonionic surfactant is long-chain fatty alcohol-polyoxyethylene ether, alkylphenol polyoxyethylene, polyoxyethylene alkylolamide or fatty alcohol-polyoxyethylene ether. The wetting agent is added, so that the interfacial tension of SiC ceramic particles can be increased, the hydrophilicity of the aqueous PVDF slurry and the wettability between the aqueous PVDF slurry and a PVDF diaphragm are improved, the aqueous PVDF slurry is more easily coated on the diaphragm, and the thickness uniformity of a coating layer is improved.

Further, the auxiliary binder is an acrylic type binder.

Further, the defoaming agent is one of a higher alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane.

Adopt above-mentioned technical scheme: the defoaming agent is added to reduce the quantity of foams in the slurry and improve the coating quality of the coated diaphragm, the defoaming agent is utilized to reduce the wetting effect of the wetting agent, so that the water-based PVDF slurry in partial areas cannot be wetted with the surface of the diaphragm, and a non-full-coverage coating is formed after drying, so that the air permeability of the diaphragm is improved, and the battery performance is improved.

Further, the anti-settling agent is one of urea modified polyamide and polyamide wax. The addition of the anti-settling agent can prevent the SiC ceramic particles from settling too quickly when the SiC ceramic particles are kept stand and stored.

The preparation method of the aqueous PVDF slurry comprises the following steps:

s1, adding silicon carbide and a dispersing agent into water, and performing ultrasonic dispersion to obtain a suspension A;

s2, adding PVDF, an anti-settling agent and a defoaming agent into the suspension A, and stirring at normal temperature at the stirring speed of 100-200r/min for 30-40min to obtain a mixed solution B;

and S3, adding the auxiliary binder and the wetting agent into the mixed solution B, and stirring at normal temperature to obtain the high-cohesiveness water-based PVDF slurry.

The application of the aqueous PVDF slurry in the preparation of the lithium battery diaphragm comprises the PVDF diaphragm and the aqueous PVDF slurry coated on one side or two sides of the PVDF diaphragm.

Further, the aqueous PVDF slurry is coated on the lithium battery diaphragm in a rolling, spraying or spot coating mode.

Further, drying the diaphragm coating at 50-80 ℃.

By adopting the technical scheme provided by the invention, the method has the following beneficial effects:

1. by uniformly dispersing SiC in the PVDF long chain, a large number of micro-capacitor structures are formed, and external heat can be quickly transferred into the PVDF slurry by virtue of the high heat conduction capacity and the bridging action of SiC, so that the bonding of the PVDF slurry is accelerated, the bonding performance of the aqueous PVDF slurry is further improved, and the aqueous PVDF slurry with a thin coating and good bonding force is obtained.

2. The SiC ceramic particles are provided with strong positive charges through the dissociation of alkali metal phosphates, so that strong charge repulsion is generated among the SiC ceramic particles, the stable dispersion of the SiC ceramic particles in the water-based PVDF slurry is promoted, a more compact network is formed in a limited volume, the enhancement of the positive charges is also beneficial to the uniform dispersion of the SiC ceramic particles in a PVDF long chain structure, the overlapping among the sheet layers is more obvious, more heat conduction paths which are beneficial to heat transfer are formed, and the hot-pressing bonding performance is enhanced.

3. The defoaming agent is utilized to reduce the wetting effect of the wetting agent, so that the water-based PVDF slurry in a partial area cannot be wetted with the surface of the diaphragm, and a non-full-coverage coating is formed after drying, thereby improving the air permeability of the diaphragm and improving the battery performance.

4. According to the invention, through the interaction among the dispersing agent, the wetting agent, the binder aid, the defoaming agent, the anti-settling agent and the silicon carbide, N-methylpyrrolidone (NMP) is not required to be used as a solvent, so that the liquid absorption rate of the battery diaphragm is reduced, and the battery performance is improved.

Detailed Description

The technical solutions of the present invention are described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The alkali metal phosphate is one or more of sodium tripolyphosphate, sodium hexametaphosphate and sodium pyrophosphate; the wetting agent is one or a mixture of anionic surfactant and nonionic surfactant. The anionic surfactant is sodium alkylaryl sulfonate, sodium butylnaphthalene sulfonate, sodium hydroxyethyl sulfonate or sodium dodecyl sulfonate; the nonionic surfactant is long-chain fatty alcohol-polyoxyethylene ether, alkylphenol ethoxylate, polyoxyethylene alkylolamide or fatty alcohol-polyoxyethylene ether; the auxiliary binder is an acrylic acid type binder; the defoaming agent is one of a high-alcohol fatty acid ester compound, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane; the anti-settling agent is one of urea modified polyamide and polyamide wax. The inventors have conducted extensive studies to find that the kind of the wetting agent, the defoaming agent and the anti-settling agent does not greatly affect the binding properties of the aqueous PVDF slurry when one or more kinds thereof are selected within the scope of the claims of the present invention.

s1, adding silicon carbide and a dispersing agent into water, and performing ultrasonic dispersion to obtain a suspension A; s2, adding PVDF, an anti-settling agent and a defoaming agent into the suspension A, and stirring at normal temperature at the stirring speed of 100-200r/min for 30-40min to obtain a mixed solution B; and S3, adding the auxiliary binder and the wetting agent into the mixed solution B, and stirring at normal temperature to obtain the high-cohesiveness water-based PVDF slurry. The following examples and comparative examples were prepared using this method to obtain aqueous PVDF slurries.

Example 1

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 7% of sodium tripolyphosphate, 5% of sodium alkylaryl sulfonate, 5% of an acrylic acid type binder, 3% of a higher alcohol fatty acid ester composite, 0.1% of polyamide wax, 15% of PVDF and 0.05% of silicon carbide, and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 300.

example 2

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 6% of sodium hexametaphosphate, 4% of sodium butylnaphthalene sulfonate, 6% of an acrylic acid type binder, 2% of polyoxyethylene polyoxypropylene pentaerythritol ether, 0.5% of polyamide wax, 20% of PDVF and 0.2% of silicon carbide, and the balance being water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 100.

example 3

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 5% of sodium tripolyphosphate, 3% of long-chain fatty alcohol-polyoxyethylene ether, 7% of an acrylic binder, 1.5% of polyoxypropylene glycerol ether, 1% of urea modified polyamide, 20% of VDF (P-vinyl fluoride), 0.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of PVDF (polyvinylidene fluoride) are 1: 40.

example 4

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 4% of sodium pyrophosphate, 2% of alkylphenol polyoxyethylene, 10% of acrylic binder, 1% of polyoxypropylene polyoxyethylene glycerol ether, 2% of urea modified polyamide, 20% of PVDF and 1% of silicon carbide, and the balance being water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are in a mass ratio of 1: 20.

example 5

The high-cohesiveness aqueous PVDF slurry comprises the following raw materials in percentage by weight: 3% of sodium pyrophosphate, 1% of polyoxyethylene alkylolamide, 10% of an acrylic acid type binder, 0.5% of polydimethylsiloxane, 3% of urea modified polyamide, 25% of PVD F and 2.5% of silicon carbide, and the balance being water, wherein the addition amount of the silicon carbide and the addition amount of PVDF are 1: 10.

comparative example 1

Comparative example 1 is essentially the same as example 3, except that: the raw materials of the aqueous PVDF slurry do not comprise silicon carbide, namely the aqueous PVDF slurry comprises the following raw materials in percentage by weight: 5% of sodium tripolyphosphate, 3% of long-chain fatty alcohol-polyoxyethylene ether, 7% of an acrylic binder, 1.5% of polyoxypropylene glycerol ether, 1% of urea modified polyamide, 20% of PVDF and the balance of water.

Comparative example 2

Comparative example 2 is essentially the same as example 3, except that: the water-based PVDF slurry comprises 5% of sodium tripolyphosphate, 3% of long-chain fatty alcohol-polyoxyethylene ether, 7% of an acrylic binder, 1.5% of polyoxypropylene glycerol ether, 1% of urea modified polyamide, 20% of PVDF and 0.05% of silicon carbide, and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 400.

comparative example 3

Comparative example 3 is substantially the same as example 3 except that: the water-based PVDF slurry comprises 5% of sodium tripolyphosphate, 3% of long-chain fatty alcohol-polyoxyethylene ether, 7% of an acrylic binder, 1.5% of polyoxypropylene glycerol ether, 1% of urea modified polyamide, 20% of PVDF and 4% of silicon carbide, and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 5.

comparative example 4

Comparative example 4 is essentially the same as example 3, except that: replacing the raw material silicon carbide of the aqueous PVDF slurry with equal mass of silicon dioxide, namely, the addition amount of the silicon dioxide and the addition amount of the PVDF are 1: 40.

application example Performance detection

Coating the aqueous PVDF slurry obtained in the examples 1-5 and the comparative examples 1-4 on a PVDF diaphragm of a lithium battery in a roller coating, spraying or spot coating mode, and then drying the diaphragm at the temperature of 50-80 ℃, wherein the thickness of the dried diaphragm is about 3 mu m; then, the adhesive force of the diaphragm is measured by an adhesive force tester, and the measuring method refers to a GB/T2792-1998 pressure-sensitive adhesive tape 180o peeling strength test method; the specific method comprises the following steps: the pole pieces were cut into 12mm wide and 20mm long sample strips and mounted on an aluminum plate. The 3M scotch tape was adhered to the sample strip, the tape was pulled down using a universal tensile machine 180 ° and the peel strength was recorded. The peeling speed was 5 mm/min. The specific measurement results are shown in Table 1.

TABLE 1 Performance data for aqueous PVDF slurries

As can be seen from Table 1, after the SiC ceramic particles are added (examples 1-5), the cohesive force of the diaphragm is greatly improved and is obviously stronger than that of a common PVDF diaphragm without silicon carbide. With the increase of the adding proportion of the silicon carbide, the bonding performance is gradually improved, because the SiC ceramic particles have good thermal conductivity, the hot-pressing bonding of the PVDF membrane can be promoted, so that the peeling force required for destroying a bonding system is greatly increased, the bonding strength of the PVDF membrane is obviously improved, but the dispersity of the PVDF membrane is gradually reduced as the content of the SiC ceramic particles is further improved, the electrochemical performance is reduced in spite of higher bonding strength, especially when the content of the SiC ceramic particles is too high, if the content is increased to the content of comparative example 3, part of the silicon carbide ceramic particles are almost completely exposed out of the PVDF, a conglomerate structure is formed, more air holes exist in the membrane, and the electrochemical performance is obviously reduced. Comparative example 4 in comparison with example 3, SiC was replaced by SiO with similar properties₂Due to SiO₂The thermal conductivity coefficient is extremely low, only 7.6W/mK, a micro-capacitor structure cannot be formed in PVDF, and the bonding performance is not basically improved. Therefore, only the good proportion of the silicon carbide and the PVDF can ensure the bonding performance and the electrochemical performance of the lithium battery.

Claims

1. The high-cohesiveness aqueous PVDF slurry is characterized by comprising the following raw materials in percentage by weight: 3-7% of a dispersing agent, 1-5% of a wetting agent, 5-10% of a co-binder, 0.5-3% of a defoaming agent, 0.1-3% of an anti-settling agent, 15-25% of PVDF (polyvinylidene fluoride), 0.05-2.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 10 to 300.

2. The highly-binding aqueous PVDF slurry according to claim 1, wherein the ratio of the addition amount of silicon carbide to the addition amount of PVDF is 1: 20 to 100.

3. The high-cohesiveness aqueous PVDF paste as described in claim 1, comprising the following raw materials in weight percent: 5% of dispersing agent, 3% of wetting agent, 7% of binder aid, 1.5% of defoaming agent, 1% of anti-settling agent, 20% of PVDF (polyvinylidene fluoride), 0.5% of silicon carbide and the balance of water, wherein the addition amount of the silicon carbide and the addition amount of the PVDF are 1: 40.

4. the highly cementitious aqueous PVDF slurry of claim 1, where the dispersant is an alkali metal phosphate.

5. The highly cementitious aqueous PVDF slurry of claim 4, wherein the alkali metal phosphate is one or more of sodium tripolyphosphate, sodium hexametaphosphate, and sodium pyrophosphate.

6. The highly cohesive aqueous PVDF slurry of claim 1, wherein the wetting agent is a mixture of one or more of anionic and non-ionic surfactants.

7. The high-adhesion aqueous PVDF slurry of claim 1, wherein the co-binder is an acrylic-type binder.

8. The highly adherent aqueous PVDF slurry according to claim 1, wherein the defoaming agent is one of a higher alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glycerol ether, polyoxypropylene polyoxyethylene glycerol ether and polydimethylsiloxane.

9. The method for preparing the aqueous PVDF slurry as claimed in any one of claims 1 to 8, comprising the steps of:

10. Use of the aqueous PVDF slurry of any one of claims 1 to 8 in the preparation of a lithium battery separator, wherein the lithium battery separator comprises a PVDF separator and the aqueous PVDF slurry coated on one or both sides of the PVDF separator.