CN110911620A

CN110911620A - Spotted coating diaphragm slurry, composite diaphragm and preparation method thereof

Info

Publication number: CN110911620A
Application number: CN201910996534.7A
Authority: CN
Inventors: 李义涛; 肖文武; 云晧; 程宗盛; 吴慧娟; 张魁; 杨华军; 徐胜
Original assignee: Dongguan HEC Tech R&D Co Ltd
Current assignee: Dongguan HEC Tech R&D Co Ltd
Priority date: 2019-10-19
Filing date: 2019-10-19
Publication date: 2020-03-24
Anticipated expiration: 2039-10-19
Also published as: CN110911620B

Abstract

The invention discloses a dot-coated diaphragm slurry, a composite diaphragm and a preparation method thereof. The slurry comprises: PVDF emulsion with solid content of 15-30%; a binder accounting for 1-10% of the mass of water in the emulsion; a surface tension regulator accounting for 10-30% of the mass of water in the emulsion; a wetting agent accounting for 0.2-2.0% of the mass of water in the emulsion; thickener accounting for 0.05-1% of the mass of water in the emulsion; an additive accounting for 2-5% of the mass of water in the emulsion; wherein the surface tension modifier is ethylene glycol and the additive is non-spherical alumina having an irregular shape. The composite diaphragm provided by the invention comprises a ceramic base film and a PVDF convex dot-shaped coating coated on one side or two sides of the ceramic base film. The composite diaphragm has good air permeability and strong bonding force with a battery pole piece, improves the cycle performance of the lithium battery, and prolongs the service life of the lithium battery.

Description

Spotted coating diaphragm slurry, composite diaphragm and preparation method thereof

Technical Field

The invention relates to the technical field of preparation of lithium ion battery diaphragms, in particular to diaphragm slurry suitable for point coating, a composite diaphragm prepared from the slurry and a lithium ion battery comprising the composite diaphragm.

Background

The lithium ion battery has the characteristics of high specific energy, long cycle life and no memory effect, and has the advantages of safety, reliability, quick charge and discharge and the like, and becomes a research hotspot of a novel power supply technology in recent years. The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the diaphragm is used as a barrier between the positive electrode and the negative electrode, plays an important role in the performance of the lithium ion battery, the performance of the diaphragm directly influences the capacity and the cycle of the battery, particularly important factors influencing the safety performance of the battery, and the coating of ceramic or polymer (such as polyvinylidene fluoride (PVDF)) on the surface of the diaphragm is an effective method for improving the safety of the diaphragm.

With the increasing national requirements for energy density of lithium ion batteries, the selection of ternary high-nickel positive electrode materials is a necessary trend, and the adoption of high-energy positive electrode materials must match with corresponding high-energy negative electrode materials, so that the battery cell is easy to deform in the charging and discharging process, and meanwhile, the rebound of the negative electrode piece is large, and the tendency of gradual increase is realized along with the continuous accumulation of cycle times, so that firm bonding force between the diaphragm and the positive and negative electrode pieces is required. However, the existing dot-coated PVDF separator has a low coverage rate (about 15% to 25%) while achieving air permeability, and the dot morphology is mostly "crater-shaped", so that the adhesion with the pole piece is insufficient (generally about 5N/m), and further improvement is required.

Disclosure of Invention

Aiming at the defects in the prior art, the invention provides diaphragm slurry suitable for point-like coating, wherein the slurry takes non-spherical alumina ceramic with irregular shape as a filler, takes an alcohol solvent as an additive, controls the dosage proportion of the alumina ceramic and the alcohol solvent, and can obtain a uniform composite diaphragm with a convex lattice by electrostatic spraying or atomizer spraying, the composite diaphragm and a pole piece have better bonding force, and the test result shows that the bonding force can reach more than 8N/m, so that the hardness of a battery cell is enhanced, and the electrochemical performance of a lithium battery is improved.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

firstly, the invention provides a composite diaphragm which comprises a ceramic base film, wherein one side or two sides of the ceramic base film are provided with PVDF convex point-shaped coatings.

Preferably, the raised dot-shaped coating of PVDF has a raised height of 4-10 μm.

In one aspect, the present invention provides a dot-coated separator paste, including:

PVDF emulsion with solid content of 15-30%; a binder accounting for 1-10% of the mass of water in the emulsion; a surface tension regulator accounting for 10-30% of the mass of water in the emulsion; a wetting agent accounting for 0.2-2.0% of the mass of water in the emulsion; thickener accounting for 0.05-1% of the mass of water in the emulsion; an additive accounting for 2-5% of the mass of water in the emulsion; wherein the surface tension modifier is ethylene glycol and the additive is non-spherical alumina having an irregular shape.

Specifically, the PVDF emulsion is obtained by copolymerizing vinylidene fluoride monomer (VDF) and hexafluoropropylene monomer (HFP) in an emulsion polymerization method, wherein the molar ratio of VDF to HFP is 97: 3.

Preferably, the non-spherical alumina having an irregular shape is fibrous alumina, rod-shaped alumina, or flake-shaped alumina.

Preferably, the binder is at least one of styrene-butadiene rubber emulsion, polyvinyl alcohol, ethylene-ethyl acetate and polyvinylpyrrolidone.

Specifically, the thickener is at least one of polyacrylic acid thickener, cellulose thickener, amide thickener, ether thickener and natural polymer thickener, and is preferably polyacrylic acid thickener.

Preferably, the polyacrylic acid thickener is at least one of sodium polyacrylate, polyacrylate and polyacrylic anhydride.

The cellulose thickener is at least one of sodium carboxymethylcellulose, methylcellulose, hydroxyethyl cellulose, hydroxyethyl methylcellulose and hydroxypropyl methylcellulose.

The amide thickener is polyacrylamide.

The ether thickener is polyoxyethylene.

The natural polymer thickener is at least one of bentonite, xanthan gum, sodium alginate, gelatin, xanthan gum and agar.

On the other hand, the invention provides a composite diaphragm which comprises a ceramic base film and PVDF convex point-shaped coatings respectively coated on one side or two sides of the ceramic base film, wherein the PVDF convex point-shaped coatings are prepared from the point-shaped coating diaphragm slurry.

The ceramic-based membrane is a commercial ceramic separator, such as: the two sides of the PE film are respectively coated with a diaphragm with a 2-micron ceramic coating.

On the other hand, the invention also provides a preparation method of the composite diaphragm, which comprises the following steps:

s1: providing point-coating diaphragm slurry;

the slurry comprises: PVDF emulsion with solid content of 15-30%; a binder accounting for 1-10% of the mass of water in the emulsion; a surface tension regulator accounting for 10-30% of the mass of water in the emulsion; a wetting agent accounting for 0.2-2.0% of the mass of water in the emulsion; thickener accounting for 0.05-1% of the mass of water in the emulsion; an additive accounting for 2-5% of the mass of water in the emulsion; wherein the surface tension modifier is ethylene glycol and the additive is non-spherical alumina having an irregular shape;

s2: and spraying the dot-shaped coating diaphragm slurry on one side or two sides of the ceramic base film, and drying to obtain the composite diaphragm with the PVDF convex dot-shaped coating.

Preferably, the height of the spray head from the base film is 5-20mm when electrohydrodynamic spray coating is performed.

Specifically, the spraying is electrostatic spraying or atomizer spraying.

The invention also provides a lithium ion battery which comprises the composite diaphragm.

The invention has the beneficial effects that:

(1) the invention adopts irregular non-spherical alumina as additive and alcohol solvent as surface tension regulator, and can obtain diaphragm with convex point coating by controlling the dosage of the two.

(2) The PVDF emulsion is adopted to replace the conventional PVDF aqueous dispersion liquid, and the preparation method has the advantages of low production cost, simple and convenient process (without steps of sanding, dispersing and the like), time saving and the like.

Drawings

Fig. 1 shows a photograph of a composite separator prepared in comparative example 1;

fig. 2 shows a photograph of the composite separator in example 1 of the present invention.

Detailed Description

The invention mainly aims at the problem that the adhesive property and the air permeability of the existing polymer dot coating diaphragm cannot be considered at the same time, and provides diaphragm slurry capable of obtaining a convex dot coating and a composite diaphragm obtained by the slurry.

The components of the slurry and the method of preparing the separator are described in detail below.

(1) Dot-coated separator slurry

According to some embodiments provided herein, the slurry comprises:

PVDF emulsion with solid content of 15-30%; a binder accounting for 1-10% of the mass of water in the emulsion; a surface tension regulator accounting for 10-30% of the mass of water in the emulsion; a wetting agent accounting for 0.2-2.0% of the mass of water in the emulsion; thickener accounting for 0.05-1% of the mass of water in the emulsion; non-spherical alumina with irregular shape accounting for 2-5% of the water in the emulsion.

According to the invention, the non-spherical alumina with the irregular shape is selected as the additive, and the irregular shape can increase the resistance of the slurry during diffusion, so that the slurry after spraying is not easy to diffuse in the drying process, the middle accumulation is large, the edge accumulation is small, and a convex structure is favorably formed. Specifically, the droplets just sprayed are ellipsoidal, the middle part is high and the edge is low, so that the edge part is dried first in the drying process, and the middle part is high and diffuses to the edge, so that if the droplets are spherical alumina, an annular point is easily formed, and the coffee ring effect is also called. However, the non-spherical alumina having an irregular shape has a large resistance in diffusion and a short drying time, and thus has no time for diffusion, thereby forming a point having a high center and a low edge, i.e., a convex structure.

Specifically, the non-spherical alumina having an irregular shape may be exemplified by: fibrous alumina, rod-shaped alumina or flake alumina, and aluminas of different shapes can be used singly or in combination. In addition to the above-listed non-spherical alumina having an irregular shape, other irregularly shaped aluminas capable of achieving similar effects may be used in the present invention.

In some embodiments, the non-spherical alumina having an irregular shape is a rod-shaped alumina having an aspect ratio of 4:1 and a diameter of 200-500 nm.

The amount of said non-spherical alumina having an irregular shape is not excessively large, preferably 2 to 5%, for example 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% of the water content in the PVDF emulsion.

If the amount of alumina used is too large, the adhesion to the electrode sheet is lowered.

In some embodiments of the present invention, the PVDF emulsion is copolymerized with vinylidene fluoride monomer (VDF) and hexafluoropropylene monomer (HFP) by emulsion polymerization. Wherein the molar ratio of VDF to HFP is 97: 3.

Preferably, the PVDF emulsion has a solids content of 10-30%, e.g., 10%, 13%, 15%, 18%, 20%, 23%, 25%, 28%, 30%.

The PVDF emulsion has the solid content of 10-30 percent, namely the mass content of solid resin is 10-30 percent, and the balance is water.

Compared with the PVDF dispersion liquid obtained by dispersing the PVDF resin in water, the PVDF emulsion has the advantages of low production cost, simple and convenient process (without steps of sanding, dispersing and the like), time saving and the like.

The surface tension regulator can regulate the surface tension of the coating slurry and regulate the spreading degree of the coating slurry on the surface of the ceramic base film. It is used in combination with an appropriate amount of non-spherical alumina having an irregular shape, and the surface tension of the slurry is controlled to be in an appropriate range so that the irregular alumina is difficult to flow during drying, thereby obtaining a dot-shaped coating having protrusions. Ethylene glycol can tend to form bump points because ethylene glycol has a surface tension lower than water and a very high boiling point (197.3 c, well above water), which results in a much slower rate of volatilization than water. When the water droplets mixed with ethylene glycol are dried on the solid surface, the concentration of ethylene glycol at the edges of the droplets is higher than at the center of the droplets, and the surface tension is low, which causes the liquid to flow from the edges to the center, and the PVDF particles dispersed in the liquid naturally flow with the PVDF particles. This flow inhibits the accumulation of solid particles at the edges of the droplets, thereby forming a centrally raised dot-like topography. Thus, ethylene glycol is particularly preferred in the present invention.

The dosage of the surface tension regulator is 10-30%, preferably 10-25% of the mass of water in the PVDF emulsion.

In some embodiments, the surface tension modifier is present in an amount of 10 to 15%, for example: 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%.

In the invention, the surface tension regulator and the non-spherical alumina with irregular shape are used simultaneously, so that the dot-shaped coating with a convex structure can be obtained by using lower dosage, and the bonding force with the pole piece is better. If surface tension modifiers or non-spherical alumina with irregular shape are used alone, similar point-like structures can be obtained theoretically, but the larger dosage is needed, and the requirement that the adhesion force to the pole piece is more than 8N/m is not met. For example, when the surface tension regulator is used alone, the dosage of the surface tension regulator accounts for about 50 percent of the mass of water in the PVDF emulsion, and the larger dosage can cause incomplete drying and low efficiency; when the irregular-shaped non-spherical alumina is used alone, the dosage of the alumina accounts for about 40% of the water mass in the PVDF emulsion, and the excessive dosage of the alumina is not beneficial to improving the binding force of the diaphragm and the pole piece.

The wetting agent can improve the wetting property of the PVDF polymer in the coating slurry on the surface of the ceramic base film, and promote the PVDF polymer to spread on the surface of the ceramic base film.

The dosage of the wetting agent is 0.2-2.0% of the mass of water in the PVDF emulsion.

In some embodiments, the wetting agent is used in an amount of 0.2 to 0.6%, e.g., 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0% of the mass of water in the PVDF emulsion.

In some embodiments, the wetting agent is used in an amount of 0.6 to 1.2%, e.g., 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2% of the mass of water in the PVDF emulsion.

In some embodiments, the wetting agent is used in an amount of 1.2 to 2.0% of the mass of water in the PVDF emulsion, e.g., 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%.

According to some embodiments of the invention, the wetting agent is a combination of one or more of alkyl sulfate, nonionic surfactant or silicone based surfactant, in some embodiments of the invention, preferably at least one of BYKLP-X20990, alkyl sulfate, tween 80.

The thickener mainly functions to adjust the viscosity of the coating slurry, so that the viscosity of the coating slurry is more suitable for spraying and is not easy to block spraying equipment.

According to some embodiments of the invention, the thickener is used in an amount of 0.05 to 1.0% by mass of water in the PVDF emulsion.

In some embodiments, the thickener is used in an amount of 0.05 to 0.12%, e.g., 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.12% of the mass of water in the PVDF emulsion.

In some embodiments, the thickener is used in an amount of 0.12 to 0.5% of the mass of water in the PVDF emulsion, e.g., 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, 0.3%, 0.32%, 0.34%, 0.36%, 0.38%, 0.4%, 0.42%, 0.44%, 0.46%, 0.48%, 0.5%.

In some embodiments, the thickener is used in an amount of 0.5 to 1.0% of the mass of water in the PVDF emulsion, e.g., 0.5%, 0.52%, 0.54%, 0.56%, 0.58%, 0.6%, 0.62%, 0.64%, 0.66%, 0.68%, 0.7%, 0.72%, 0.74%, 0.76%, 0.78%, 0.8%, 0.82%, 0.84%, 0.86%, 0.88%, 0.9%, 0.92%, 0.94%, 0.96%, 0.98%, 1.0%.

According to some embodiments of the present invention, the thickener may be at least one of polyacrylic acids, celluloses, ethers, and natural high molecular weight substances.

In some embodiments, at least one of sodium carboxymethylcellulose, methylcellulose, hydroxyethylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, polyacrylamide, polyethylene oxide, bentonite, xanthan gum, sodium alginate is preferred.

The binder can improve the binding force between the coating slurry and the ceramic base film, thereby improving the stability of the diaphragm structure. In some embodiments of the present invention, the binder may use any suitable binder known in the art, such as one or a combination of more than one of styrene-butadiene rubber emulsion (SBR), polyvinyl alcohol, ethylene-ethyl acetate, sodium carboxymethylcellulose, polyvinyl pyrrolidone.

The dosage of the binder is 1-10% of the mass of water in the PVDF emulsion.

In some embodiments, the binder is present in an amount of 1-5% of the mass of water in the PVDF emulsion, e.g., 1%, 1.2%, 1.5%, 2.0%, 2.2%, 2.5%, 3.0%, 3.2%, 3.5%, 4.0%, 4.2%, 4.5%, 5%, and in some embodiments, the binder is present in an amount of 5-10% of the mass of water in the PVDF emulsion, e.g., 5%, 5.5%, 6.0%, 6.5%, 7.0%, 7.5%, 8.0%, 8.5%, 9.0%, 9.5%, 10%.

The dot-coated separator paste may be prepared by any method known in the art.

According to some embodiments of the present invention, the method for preparing the dot-coated separator slurry includes the steps of: and stirring and mixing the PVDF emulsion, the binder and the wetting agent, adding the surface tension regulator and the alumina additive after the binder and the wetting agent are completely dissolved, and continuously stirring to uniformly disperse the PVDF emulsion.

(2) Preparation method of composite diaphragm

According to some embodiments of the invention, the method of preparing the composite separator comprises the steps of:

s1: providing point-coating diaphragm slurry;

The composition and preparation method of the dot-coated diaphragm slurry are as described above, and are not described in detail herein.

The spraying is electrostatic spraying or atomizer spraying.

Further, the electrostatic spraying parameters are as follows: the voltage is 5-30kv, the flow rate of sample injection is 1-50mL/min, and the speed of film running is 1-20 m/min. The balance of three parameters of voltage, sample introduction flow rate and film moving speed is well regulated in the electrostatic spraying process, and the uniformity of the convex points is ensured.

In some embodiments, the electrostatic spraying is performed at a voltage of 5-30kv, a sample flow rate of 1-50mL/min, and a film running speed of 1-20 m/min. The voltage is preferably 10-20kv, the flow rate of sample injection is preferably 3-10mL/min, and the speed of film running is preferably 5-13 m/min.

And then drying the membrane by using any suitable drying equipment and drying conditions in the field, for example, drying the membrane in a vacuum drying oven at 50-90 ℃ for 0.5-2h to obtain the composite membrane.

The ceramic-based membrane is a commercial ceramic separator, such as: the PE film produced by Enjie New Material science and technology Limited is a diaphragm coated with 2 micron ceramic coatings on both sides.

The preparation method has the advantages of simple and easily-obtained spraying equipment, low cost and easy popularization, uses water as a solvent required by the preparation of the polymer slurry, and has environment-friendly production process, high safety and low production cost.

(3) Composite diaphragm

The composite diaphragm prepared by the invention comprises a ceramic base film and PVDF convex dot-shaped coatings respectively coated on two sides of the ceramic base film. Compared with the diaphragm without the convex point-shaped coating, in the manufacturing process of the lithium battery, the convex points in the diaphragm can be embedded into the pole piece during hot pressing, so that the diaphragm and the pole piece have better adhesive force.

The convex height of the PVDF convex point-shaped coating is preferably controlled to be 4-10 mu m, the rolling is difficult when the point is too high, the bonding force with a pole piece is not obviously improved when the point is less than 4 mu m, and because the convex height is not enough, PVDF particles are difficult to embed into the pole piece in the hot pressing process so as to obtain higher bonding force, and the difference between the PVDF particles and the 'crater' shaped point is not obvious. The height of the protrusions is determined mainly by the amount of ethylene glycol and the amount of non-spherical alumina having an irregular shape, and interaction between the two is required to obtain the points having higher protrusions.

The thickness of the PVDF convex dot-shaped coating layers on the two sides of the ceramic base film can be the same or different.

The composite diaphragm is not too thick, the too thick diaphragm easily causes the resistance too large, is not favorable for the quick charge and discharge of battery, and the coiling number of times that also can make the diaphragm simultaneously reduces, increases the volume of battery, causes the charge and discharge capacity to descend.

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be described in further detail below with reference to the accompanying drawings and specific embodiments.

Example 1:

1. preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 12.3g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 7.38g BYKLP-X20990 and 0.62g low viscosity thickener sodium acrylate (CMC) are added to ②, stirring is carried out for 4h at 1000r/min, 123g surface tension regulator ethylene glycol and 24.6g additive rod-shaped aluminum oxide are added to ③, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 10kv, the flow rate of sample introduction is 2mL/min, the speed of membrane running is 6m/min, the point uniformity can be ensured by adjusting the balance of three parameters in the spraying process, ② is dried for about 40s and then rolled to obtain the composite membrane with PVDF convex point-like coating, and the height of the convex is 5 μm.

The photograph of the resulting composite separator is shown in fig. 2, and a uniform convex dot-shaped coating layer is formed on the outer surface of the separator.

Example 2:

1. preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 184.5g of surface tension regulator ethylene glycol and 36.9g of additive rod-shaped alumina are added to ③, and after stirring and uniform dispersion, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 12kv, the flow rate of sample introduction is 3mL/min, the speed of membrane running is 7m/min, the point uniformity can be ensured by adjusting the balance of three parameters during spraying, ② is dried for about 40s and then rolled to obtain the composite membrane with PVDF convex point-like coating, and the height of the convex is 6 μm.

Example 3:

1. preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 61.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 18.45g BYKLP-X20990 and 6.15g of low viscosity thickener sodium acrylate (CMC) are added to ②, stirring is carried out for 4h at 1000r/min, 246g of surface tension regulator ethylene glycol and 49.2g of additive rod-shaped aluminum oxide are added to ③, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying with voltage of 14kv, flow rate of sample introduction of 4mL/min, speed of membrane running of 8m/min, and balance of three parameters adjusted during spraying to ensure uniformity of the membrane, drying ② for about 40s, and rolling to obtain the composite membrane with PVDF raised point-like coating, wherein the height of the raised point is 7 μm.

Example 4:

1. preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 98.4g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 23.4g BYKLP-X20990 and 9.84g of low viscosity thickener sodium acrylate (CMC) are added to ②, stirring is carried out for 4h at 1000r/min, 369g of surface tension regulator ethylene glycol and 61.5g of additive rod-shaped aluminum oxide are added to ③, and after stirring and uniform dispersion, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying with voltage of 14kv, flow rate of sample introduction of 4mL/min, speed of membrane running of 8m/min, and balance of three parameters adjusted during spraying to ensure uniformity of the membrane, drying ② for about 40s, and rolling to obtain the composite membrane with PVDF raised point-like coating, wherein the height of the raised point is 8 μm.

Comparative example 1

1. Preparing slurry:

① PVDF emulsion with solid content of 18% is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out at 600r/min for 10min, ② is added with 14.1g BYKLP-X2099 and 1.5g sodium acrylate (CMC) as low viscosity thickening agent, stirring is carried out at 1000r/min for 4h, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 10kv, the flow rate of sample introduction is 2mL/min, the speed of membrane running is 5m/min, the point uniformity can be ensured by adjusting the balance of three parameters in the spraying process, ② is rolled after drying for about 40s to obtain PVDF coated membrane with point distribution morphology, and the thickness of the point coating is 2 μm.

As shown in fig. 1, a photograph of the obtained composite separator formed a dot-like coating layer in the form of a crater on the outer surface of the separator.

Comparative example 2

1. Preparing slurry:

① PVDF emulsion with solid content of 18% is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 184.5g ethylene glycol as surface tension regulator is added to ③, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 12kv, the flow rate of sample injection is 4mL/min, the speed of membrane running is 6m/min, the point uniformity can be ensured by adjusting the balance of three parameters during spraying, ② is dried for about 40s and rolled to obtain the composite membrane with PVDF convex point-like coating, and the convex height is 3 μm.

Comparative example 3

1. Preparing slurry:

① PVDF emulsion with solid content of 18% is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 36.9g rod-shaped alumina is added to ③, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 13kv, the flow rate of sample injection is 5mL/min, the speed of membrane running is 8m/min, the point uniformity can be ensured by adjusting the balance of three parameters during spraying, ② is dried for about 40s and rolled to obtain the composite membrane with PVDF convex point-like coating, and the convex height is 3 μm.

Comparative example 4

1. Preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 184.5g of surface tension regulator ethylene glycol and 12.3g of additive rod-shaped alumina are added to ③, and after stirring and uniform dispersion, coating slurry is prepared.

2. Preparing a coating diaphragm:

Comparative example 5

1. Preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 184.5g of surface tension regulator ethylene glycol and 73.8g of additive rod-shaped alumina are added to ③, and after stirring and uniform dispersion, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 13kv, the flow rate of sample injection is 5mL/min, the speed of membrane running is 8m/min, the point uniformity can be ensured by adjusting the balance of three parameters during spraying, ② is dried for about 40s and rolled to obtain the composite membrane with PVDF convex point-like coating, and the convex height is 5 μm.

Comparative example 6

1. Preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 98.4g of surface tension regulator ethylene glycol and 36.9g of additive rod-shaped aluminum oxide are added to ③, and after stirring and dispersing are carried out uniformly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 11kv, the flow rate of sample injection is 4mL/min, the speed of membrane running is 7m/min, the point uniformity can be ensured by adjusting the balance of three parameters in the spraying process, ② drying for about 40s and rolling to obtain the composite membrane with PVDF convex point-like coating, wherein the convex height is 4 μm.

Comparative example 7

1. Preparing slurry:

① PVDF emulsion with 18% solid content is weighed, 1500g is mixed with 25.5g binder polyvinylpyrrolidone (PVP K60), stirring is carried out for 10min at 600r/min, 14.1g BYKLP-X20990 and 1.5g sodium acrylate (CMC) as low-viscosity thickening agent are added to ②, stirring is carried out for 4h at 1000r/min, 184.5g of surface tension regulator ethylene glycol and 36.9g of additive spherical alumina are added to ③, and after stirring and uniform dispersion, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 13kv, the flow rate of sample injection is 5mL/min, the speed of membrane running is 8m/min, the point uniformity can be ensured by adjusting the balance of three parameters during spraying, ② is dried for about 40s and rolled to obtain the composite membrane with PVDF convex point-like coating, and the convex height is 4 μm.

Comparative example 8

1. Preparing slurry:

① PVDF emulsion with 18% solid content is weighed to be 1500g and mixed with binder polyvinylpyrrolidone (PVP K60) to be 25.5g, the mixture is stirred for 10min at 600r/min, ② BYKLP-X2099 and sodium acrylate (CMC) with low viscosity to be 1.5g are added to be stirred for 4h at 1000r/min, ③ is added with surface tension regulator methanol to be 184.5g and additive spherical alumina to be 36.9g, and after the mixture is stirred and dispersed evenly, coating slurry is prepared.

2. Preparing a coating diaphragm:

① spraying the slurry onto commercial ceramic membrane by electrostatic spraying, wherein the voltage is 10kv, the flow rate of sample introduction is 2mL/min, the speed of membrane running is 5m/min, the point uniformity can be ensured by adjusting the balance of three parameters in the spraying process, ② is rolled after drying for about 40s to obtain PVDF coated membrane with point distribution morphology, and the thickness of the point coating is 3 μm.

Performance testing and evaluation

The composite separators obtained in examples 1 to 4 and comparative examples 1 to 7 were subjected to the test of air permeability, adhesive force, and cycle performance of lithium batteries, as follows, and the test results are shown in table 1.

a. Air permeability

The air permeability of the composite membrane was tested using a Gurley 4110 air permeability tester and the results are shown in table 1.

b. Adhesive force

A diaphragm with a complete film surface and no abnormal appearance is taken, a sample with the width of 25mm and the length of 100mm is punched, two punched diaphragm samples are taken and stacked together, hot pressing is carried out on a hot press at the temperature of 80 ℃ for 30min under the pressure of 3MPa, and the tensile force of the two diaphragms bonded together is tested by a tensile machine, the tensile speed is l m/min, and the bonding strength unit is N/m. The results are shown in Table 1.

c. Cycle performance of lithium battery

The composite membrane of the PVDF convex point-shaped coating prepared in the examples 1-3 and the PVDF membrane of the normal spraying lattice of the comparative example 1 are respectively prepared into the flexible package lithium ion battery, then the prepared flexible package lithium ion battery is charged and discharged at normal temperature by adopting the 1C multiplying power, the cycle is carried out for 600 times, and the battery capacity before and after the cycle is recorded. The capacity retention after N cycles (the battery capacity after N cycles/the battery capacity before cycles) × 100%, the results are shown in table 1.

Table 1: properties of composite membranes prepared according to different formulations

As can be seen from the data in table 1:

in the embodiments 1 to 4, the bonding performance between the diaphragm and the pole piece can be obviously improved by adjusting the amount of the ethylene glycol and the rod-shaped alumina to obtain the composite diaphragm of the convex point-shaped PVDF, so that the hardness of the lithium battery cell is improved, and the cycle charge and discharge performance of the lithium battery is enhanced.

Comparative example 1 no ethylene glycol and rod-like alumina were used to adjust the surface tension of the slurry, and the sample obtained by spraying was in the shape of a crater, and not only was the pole piece adhesion performance good, but also the battery cycle performance poor.

The surface tension of the slurry is adjusted by independently adding the ethylene glycol or the rod-shaped alumina in comparative example 2 and comparative example 3, although the convex PVDF can be formed, the protrusion is not obvious, the adhesion of the electrode plate is not obviously improved, and the requirement of the adhesion of more than 8N/m cannot be met.

Comparative examples 4 and 5, which use excess or insufficient amount of rod-shaped alumina in combination with ethylene glycol, also formed a certain degree of protrusion, but still did not satisfy the practical requirements, and had adhesion force to the pole piece of less than 8N/m. This is because when the content of alumina is too low, the protrusion is not obvious, and when the content is too high, the content of PVDF is relatively reduced, so that the adhesion force with the pole piece is also reduced.

Comparative example 6, which used an insufficient amount of ethylene glycol and alumina in combination, was able to form a degree of protrusion, but the adhesion force with the pole piece was less than 8N/m.

Comparative example 7 spherical alumina was used instead of rod-like alumina, no raised PVDF particles were formed, and the adhesion between the resulting product and the pole piece was low and could not meet the 8N/m requirement.

In the comparative example 8, methanol is used for replacing ethylene glycol, so that the effect of forming the convex PVDF particles cannot be achieved, the adhesion force with a pole piece is low, and the requirement of 8N/m cannot be met.

In a word, compared with the conventional dot spraying, the composite diaphragm of the convex dot PVDF obtained by adjusting the amount of the ethylene glycol and the rod-shaped alumina has little difference in the air permeability and the cycle performance of the battery, but the diaphragm of the invention is greatly improved in the bonding performance with the pole piece, which shows that the convex dot PVDF has a remarkable effect in improving the bonding force with the pole piece.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. The composite diaphragm is characterized by comprising a ceramic base film, wherein one side or two sides of the ceramic base film are provided with PVDF convex dot-shaped coatings.

2. The composite membrane according to claim 1, wherein the raised dot-shaped coating of PVDF has a height of 4-10 μ ι η.

3. A dot-coated separator paste, comprising:

4. The dot-coated separator paste according to claim 3, wherein the non-spherical alumina having an irregular shape is fibrous alumina, rod-shaped alumina, or flake-shaped alumina.

5. The dot-coated separator slurry according to claim 3, wherein the binder is at least one of styrene-butadiene rubber emulsion, polyvinyl alcohol, ethylene-ethyl acetate, and polyvinyl pyrrolidone; the thickener is at least one of polyacrylic acid thickener, cellulose thickener, amide thickener, ether thickener and natural polymer thickener.

6. A composite separator comprising a ceramic base film, PVDF raised dot coatings respectively coated on one or both sides of the ceramic base film, the PVDF raised dot coatings being prepared from the dot-coated separator slurry according to any one of claims 3 to 5.

7. The composite membrane according to claim 6, wherein the raised dot-shaped coating of PVDF has a height of 4-10 μm.

8. A method of making a composite separator, comprising:

s1: providing point-coating diaphragm slurry;

s2: and spraying the dot-coated diaphragm slurry to one side or two sides of the ceramic base film, and drying to obtain the composite diaphragm with the PVDF convex dot-coated layer.

9. The method for producing a composite separator according to claim 8, wherein the non-spherical alumina having an irregular shape is fibrous alumina, rod-like alumina, or flake alumina.

10. The method of manufacturing a composite separator according to claim 8, wherein the spray coating is electrostatic spray coating or atomizer spray coating.

11. A composite separator, prepared by the method of any one of claims 8 to 10.

12. A lithium ion battery comprising the composite separator of any of claims 1-2, 6-7, or 11.