KR102053098B1 - Separator Adhesion Layer Having a Low Resistance and Manufacturing Method thereof - Google Patents

Abstract

The present invention is a separator having an adhesive layer on one or both sides, wherein the adhesive layer has a porosity of 50% to 99%, and at least one of hexafluoroethylene and hexafluoroprophylene and vinyl Comprising a copolymer of a monomer mixture comprising a vinylidene fluoride (vinylidene fluoride), the hexafluoroethylene or hexafluoropropylene provides a separator containing 0.1% to 18% of the total weight of the copolymer.

Description

Separator Adhesion Layer Having a Low Resistance and Manufacturing Method

The present invention relates to a separation membrane, and more particularly, having an adhesive layer on one side or both sides, the adhesive layer has a porosity of 50% to 99%, and 0.01% to hexafluoroethylene or hexafluoropropylene It is about a separator containing 18%.

As technology development and demand for mobile devices increase, the demand for batteries as energy sources is rapidly increasing, and accordingly, many studies on batteries that can meet various demands have been conducted.

In particular, there is a high demand for square secondary batteries and pouch secondary batteries that can be applied to products such as mobile phones with a thin thickness in terms of shape of the battery, and high energy density, discharge voltage, and output stability in terms of materials. Demand for lithium secondary batteries such as lithium ion batteries and lithium ion polymer batteries is high.

Such a lithium secondary battery uses a metal oxide such as LiCoO ₂ as a cathode active material and a carbon material, lithium metal, etc. as a cathode active material, inserts a separator between the anode and the cathode, and uses a non-aqueous electrolyte containing lithium salt such as LiPF ₆ . It is manufactured by putting.

Among them, the separator is one of the important factors that determine the life of the secondary battery, and serves to electrically insulate the positive electrode and the negative electrode.In order to be used as a separator, the membrane has high ion permeability, excellent mechanical strength, and excellent electrolyte strength. It is also desirable to have stability against.

However, the conventionally used separation membrane is not sufficient adhesive strength with the electrode due to its material properties, there is a problem such as partial lifting or wrinkles at the interface depending on the manufacturing process.

In order to solve this problem, a technique of forming an adhesive layer by coating a mixture of a binder polymer on a porous substrate has been developed, but in this case, although the problem can be solved, the thickness of the adhesive layer is formed to a predetermined value or more in order to exhibit sufficient adhesive force. As a result, it was difficult to pass the electrolyte through the adhesive layer, which itself acted as a resistance, resulting in deterioration of battery output and cycle characteristics.

In addition, the binder polymer used in the adhesive layer is expanded during the charging and discharging process, the resistance is a problem as the cycle progresses, and thus, the technology that can solve the problem by minimizing the resistance characteristics while sufficiently improving the adhesion to the electrode There is a high need.

The present invention aims to solve the problems of the prior art as described above and the technical problems that have been requested from the past.

Specifically, an object of the present invention comprises a copolymer of a monomer mixture having a porosity of 50% to 90%, at least one of hexafluoroethylene and hexafluoropropylene and vinylidene fluoride, wherein hexa Since fluoroethylene or hexafluoroflopropylene is included in an amount of 0.01 to 18% based on the total weight of the copolymer, it is possible to provide a separator that minimizes swelling and resistance while improving adhesion between the separator and the electrode.

Still another object of the present invention is to provide an electrode assembly and a secondary battery having excellent output and cycle characteristics, including the separator.

Separation membrane according to the present invention for achieving this object is a separator having an adhesive layer on one side or both sides,

The adhesive layer,

Has a porosity of 50% to 99%,

A copolymer of at least one of hexafluoroethylene and hexafluoroprophylene and a monomer mixture comprising vinylylidene fluoride,

The hexafluoroethylene or hexafluoropropylene is characterized in that it is contained in 0.01% to 18% of the total weight of the copolymer.

Therefore, the separator according to the present invention includes an adhesive layer that exhibits excellent ion permeability, and has a low resistance characteristic and an excellent adhesion effect, and thus prevents twisting of the electrode within a range in which output and cycle characteristics are not degraded, thereby providing excellent safety. Exert.

In general, the adhesive layer for adhering the electrode and the separator has a low porosity, and thus is an obstacle to ion permeation, and is a material having low conductivity, which itself acts as a resistance.

Thus, the adhesive layer in the present invention, including a copolymer containing at least one of hexafluoroethylene (HFE) or hexafluoropropylene (HFP) (hereinafter referred to as "HFP") in a predetermined ratio, Minimize the resistance.

Specifically, the copolymer is a copolymer of vinylidene fluoride (hereinafter referred to as "VDF") and HFP, and the adhesive strength, the degree of expansion, and the resistance characteristics vary depending on the ratio of HFP.

Therefore, in the present invention, the HFP is included in 0.1% to 18% of the total weight of the copolymer, and in detail, the hexafluoroethylene or hexafluoropropylene is 1% to 18 relative to the total weight of the copolymer It may be included in%, more specifically may be included in 1% to 15%.

Outside the above range, when the content of HFP and the like contained in the copolymer exceeds 18%, the swelling degree with respect to the electrolyte solution is high, the resistance characteristic is high, thereafter becomes a problem in cycle characteristics and output characteristics, too much content of HFP, etc. In the case of the VDF homopolymer which is less than 0.1% or does not contain HFP, it is not preferable because it is difficult to secure a desired adhesive force, and rather, the thickness of the adhesive layer becomes thick and can act as a resistance.

The molecular weight of such a copolymer may be 300,000 to 1,500,000 based on the weight average molecular weight (Mw).

The adhesive layer included in the separator according to the present invention has a porosity of 50 to 99% as well as the content of HFP contained in the copolymer, and thus exhibits low resistance and high ion permeability. The porosity may be 55% to 80% in detail.

In the case of a general binder polymer, it is difficult to achieve the porosity as described above, unless it is manufactured in a slurry form, but the adhesive layer of the separator according to the present invention is prepared by electrospinning or electrospray, and thus the porosity. Can be achieved.

Electrospinning method is a method of preparing a spinning solution by mixing a polymer in a solvent, spinning the spinning solution in the form of a fiber on a charged metal plate, and then drying or solidifying a polymer fiber having a nonwoven structure. There is an advantage that the shape control of the finished fiber can be relatively easy.

At this time, the thickness of the filament constituting the polymer fiber is characterized by the characteristics of the polymer such as molecular weight, degree of polymerization, glass transition temperature, and solubility, and the properties of solvent such as viscosity, elasticity, concentration, surface tension, and conductivity, temperature, humidity, spinning It can be controlled by electrospinning conditions such as distance of the sphere and the metal plate, spinning speed, and spinning time.

On the other hand, the electrospray method is a method of preparing a variety of fine particles by applying a voltage after injecting a solution having a certain viscosity and electrical conductivity into the capillary tube, unlike the electrospinning method, the coating layer in the form of fine particles, not in the form of fibers To form.

The separator adhesive layer according to the present invention may be prepared by such an electrospinning method or an electrospray method, and in this case, a copolymer obtained by dissolving or dispersing a copolymer obtained by polymerizing the HFP and the VDF monomer mixture in a solvent.

The solvent is not particularly limited as long as it can easily dissolve the copolymer, but water, NMP, formic acid, dimethyl formamide, tetrahydrofuran, dichloromethane, chloroform, dichloroform, toluene, methyl ethyl ketone, acetone, and the like are not particularly limited. It may be one or a mixture of two or more selected from the group consisting of.

The fiber coating layer formed by the electrospinning method or the electrospray method has a relatively higher porosity than the coating layer formed by the slurry, and thus, the adhesive layer included in the separator according to the present invention may have a porosity of 50 to 99%. .

On the other hand, the adhesive layer may include at least one of modified polyvinyl alcohol and modified polyvinyl butyral to control the adhesion in addition to the copolymer including VDF and HFP.

Specifically, the modified polyvinyl alcohol may have a cyanoethyl group or an acetoacetyl group introduced into the polyvinyl alcohol.

In this case, the modified polyvinyl alcohol or polyvinyl butyral may be included in an amount of 0.5 to 30 parts by weight based on 100 parts by weight of the homopolymer or copolymer.

That is, the modified polyvinyl alcohol and polyvinyl butyral may or may not be included in the adhesive layer, but when included, 0.5 to 30 parts by weight based on 100 parts by weight of the homopolymer or copolymer constituting the adhesive layer may be included. It is preferable.

Outside of the above range, when the content of polyvinyl alcohol or polyvinyl butyral is too large, physical properties are lowered or resistance properties are increased, which is not preferable.

For the same reason, the modified polyvinyl alcohol or polyvinyl butyral may be included in an amount of 1 part by weight to 10 parts by weight, and more specifically 2 parts by weight to 7 parts by weight, based on 100 parts by weight of the copolymer.

The thickness of the adhesive layer may be 0.5 ㎛ to 2.0 ㎛, the coating amount of the adhesive layer may be 0.1 g / m ² to 1.5 g / m ² .

If the thickness of the adhesive layer is too thick outside the above range, the resistance increases in the thickness range, the amount of the active material in the battery is relatively reduced, the capacity can be reduced, if too thin, it is difficult to secure a predetermined adhesive strength, Not desirable

The present invention also provides an electrode assembly comprising the separator.

The electrode assembly includes the separator interposed between the positive electrode and the negative electrode, the positive electrode and the negative electrode.

The type of the electrode assembly is not particularly limited, and for example, a jelly-roll (wound) electrode assembly having a structure in which long sheets of positive and negative electrodes are wound with a separator interposed therebetween, and cut into units of a predetermined size. The stacked electrode assembly having a structure in which a plurality of positive and negative electrodes are sequentially stacked with a separator interposed therebetween, and the unit cells stacked with a predetermined unit of positive and negative electrodes interposed with a separator on the separation film It may be a stack / foldable electrode assembly having a structure sequentially wound in a positioned state.

In one specific example, the electrode assembly is one or more electrodes and one or more separators are alternately stacked,

An adhesive layer may be formed between the electrode and the separator.

In another specific example, the electrode assembly is sequentially wound in a state in which one or more electrodes and unit cells in which unit separators are stacked are placed on a separation film,

An adhesive layer may be formed between the electrode and the unit separator and / or between the unit cells and the separator film.

That is, the electrode assembly has a stack type and a stack / fold type structure, and an adhesive layer is formed on a separator or a separator film, thereby achieving structural stability, but is not necessarily limited thereto.

The present invention also provides a lithium secondary battery including the electrode assembly and a device including at least one lithium secondary battery.

The device may be any one selected from the group consisting of a mobile phone, a tablet computer, a notebook computer, a power tool, a wearable electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage device.

As described above, the separator according to the present invention, the adhesive layer is provided on one side or both sides, the adhesive layer has a porosity of 50% to 99%, and includes a copolymer of a monomer mixture including HFP and VDF Since the HFP is included in an amount of 0.1% to 18% based on the total weight of the copolymer, while sufficiently improving the adhesion between the electrode and the separator, there is an effect of minimizing the resistance characteristic to improve the output characteristics and cycle characteristics of the battery. .

In the following, with reference to the embodiments of the present invention, this is for easier understanding of the present invention, the scope of the present invention is not limited thereto.

In addition, in the following examples, the material constituting the adhesive layer is indicated by a trade name of a specific manufacturer, and information such as specific materials related thereto may be obtained from each product.

Separator manufacturing

<Example 1>

After leaving the polyethylene porous thin film (Senior SD216E) as a separator substrate on the collector, the spinning solution containing PVdF-HFP (Arkema LBG, HFP content 5%) was electrospun with a loading amount of 0.7g / m ² to the adhesive layer To form a separator.

<Example 2>

A separator was prepared in the same manner as in Example 1, except that an adhesive layer was formed using a spinning solution containing PVdF-HFP (Arkema Kynar 2751, HFP content 13%).

<Example 3>

PVdF-HFP (Arkema LBG, HFP content 5%) and Cyanoethyl PVA (Shin-Etsu, CR-V) were mixed at a ratio of 93: 7, and dispersed in a solvent to form an adhesive layer using a spinning solution prepared. Except that, a separator was prepared in the same manner as in Example 1.

<Example 4>

PVdF-HFP (Arkema LBG, HFP content 5%) and PVB (Sekisui, BL-5) were mixed in a ratio of 93: 7, and dispersed in a solvent to form an adhesive layer using a spinning solution prepared. Except that, a separator was prepared in the same manner as in Example 1.

Comparative Example 1

A separator was prepared in the same manner as in Example 1, except that the adhesive layer was formed using a spinning solution containing PVdF-HFP (Arkema Kynar 2500, HFP content 20%).

Comparative Example 2

A separator was prepared in the same manner as in Example 1, except that the adhesive layer was formed using a spinning solution containing Zeon AFL (PX-LP17).

Comparative Example 3

A separator was manufactured in the same manner as in Example 1, except that an adhesive layer was formed by using a slurry coating method instead of an electrospinning method.

Experimental Example 1

Porosity measurement

The porosity of an adhesive layer cut | disconnects a measurement object to a fixed dimension (for example, circular shape of diameter 6cm), calculate | requires the volume and weight, and substitutes in following Formula.

Porosity (%) = 100 Hz (V-(W / D)) / V

V: Volume (cm ³ )

W: weight (g)

D: average density of the components (g / cm ³ )

An average hole diameter can be calculated | required by observing the cross section of the separator 4 with a scanning electron microscope. Specifically, the pore diameter is obtained by performing image processing on each of the pores existing within the range of 60 µm in the field of view and from the surface to a predetermined depth (for example, 1/5 to 1/100 of the thickness of the adhesive layer). These average values can be calculated | required as average hole diameter.

The porosity calculated through the above process is shown in Table 1 below.

Porosity (%) Example 1 63 Example 2 63 Example 3 62 Example 4 61 Comparative Example 1 59 Comparative Example 2 63 Comparative Example 3 32

As shown in Table 1, the porosities of the separators of Examples 1 to 4 and Comparative Examples 1 and 2 are similar, but the porosity of Comparative Example 3, which is not manufactured by the electrospinning method, is remarkably low.

Experimental Example 2

Adhesion test

After laminating the separators of Examples and Comparative Examples on a Shanshan artificial graphite trade name LN1-based negative electrode, and pressing them at 85 ° C. at 5 kg / cm ² for 5 minutes by heating / pressing process, the adhesive force between the negative electrode and the separator was measured. The experiment was performed.

The adhesive force is shown in Table 1 below the results of measuring the peel strength of 180 ㅀ peeling off the separator from the negative electrode. Evaluation was made into the average value by measuring five or more peeling strengths.

Adhesive force (gf / cm) Example 1 31 Example 2 36 Example 3 40 Example 4 38 Comparative Example 1 39 Comparative Example 2 21

* n / a means not measurable

As shown in Table 1, the adhesive force between the electrode and the separator using the separator of Examples 1 to 4 according to the present invention has a similar level of adhesive strength to that of the separator of Comparative Example 1 and Comparative Example 2, preventing distortion of the electrode You can see the effect.

However, it can be seen that the adhesive material included in the separator of Comparative Example 2 is low in adhesion and low in preventing distortion.

Experimental Example 2

Membrane Resistance Rating

The separator was cut and loaded into a Hoshen 2032 coin cell, and the electrolyte was filled. Then, the membrane resistance was measured by EIS, and the measurement results are shown in Table 3.

Fabric resistance (ohm) Membrane Resistance (ohm) Example 1 0.50 0.61 Example 2 0.50 0.66 Example 3 0.50 0.63 Example 4 0.50 0.62 Comparative Example 1 0.50 0.76

As shown in Table 2, when the separator of Examples 1 to 4 according to the present invention does not significantly increase the resistance compared to the fabric, when using the separator of Comparative Example 1, the resistance is significantly increased. Can be.

In addition, it can be seen that the thickness of the comparative example expanded relatively much compared to the example, contributing to the increase in the resistance characteristics.

Therefore, when the cycle is performed using the battery using the separator according to Comparative Example 1, the output and cycle characteristics may decrease as the cycle progresses, the battery using the separator according to the present invention, the adhesion between the electrode and the separator By securing, while preventing the distortion of the electrode, there is an effect of minimizing the action of the adhesive layer as a resistance.

Those skilled in the art to which the present invention pertains will be able to perform various applications and modifications within the scope of the present invention based on the above contents.

Claims (17)

As a polyolefin separator having an adhesive layer on one side or both sides,
The adhesive layer,
Has a porosity of 50% to 99%,
A copolymer of a monomer mixture comprising at least one of hexafluoroethylene and hexafluoroprophylene and vinylidene fluoride,
Separator, characterized in that the hexafluoroethylene or hexafluoropropylene is contained in 0.1% to 18% of the total weight of the copolymer. The separation membrane of claim 1, wherein the hexafluoroethylene or hexafluoropropylene is contained in an amount of 1% to 18% based on the total weight of the copolymer. The separation membrane of claim 1, wherein the hexafluoroethylene or hexafluoropropylene is contained in an amount of 1% to 15% based on the total weight of the copolymer. The separator according to claim 1, wherein the copolymer has a molecular weight of 300,000 to 1,500,000 based on a weight average molecular weight (Mw). The separator according to claim 1, wherein the porosity of the adhesive layer is 55% to 80%. The separator as claimed in claim 1, wherein the adhesive layer is prepared by electrospinning or electrospraying. The separation membrane of claim 1, wherein the adhesive layer comprises at least one of modified polyvinyl alcohol and polyvinyl butyral. The separator according to claim 7, wherein the modified polyvinyl alcohol or polyvinyl butyral is contained in an amount of 0.5 to 30 parts by weight based on 100 parts by weight of the copolymer. The separator according to claim 7, wherein the modified polyvinyl alcohol or polyvinyl butyral is included in an amount of 1 to 10 parts by weight based on 100 parts by weight of the copolymer. The separation membrane of claim 1, wherein the adhesive layer has a thickness of 0.5 μm to 2.0 μm. The separation membrane of claim 1, wherein the coating amount of the adhesive layer is 0.1 g / m ² to 1.5 g / m ² . An electrode assembly comprising a separator according to any one of claims 1 to 11 interposed between an anode and a cathode, the anode and the cathode. The method of claim 12, wherein the electrode assembly is one or more electrodes and one or more separators are alternately stacked,
The electrode assembly, characterized in that the adhesive layer is formed between the electrode and the separator. The method of claim 12, wherein the electrode assembly is sequentially wound in a state in which the unit cells in which at least one electrode and the unit separator are stacked on the separation film,
The electrode assembly, characterized in that the adhesive layer is formed between the electrode and the unit separator and / or between the unit cells and the separation film. A lithium secondary battery comprising the electrode assembly according to claim 12. A device comprising at least one lithium secondary battery according to claim 15. The device of claim 16, wherein the device is any one selected from the group consisting of a mobile phone, a tablet computer, a notebook computer, a power tool, a wearable electronic device, an electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, and a power storage device. Device characterized in that.