KR101993277B1 - Separator with sandwiched configuration for secondary battery, method for fabricating the same, and secondary battery comprising the same - Google Patents

Abstract

The present invention provides a polymer electrolyte fuel cell comprising: a first polymer separator; A porous ceramic layer disposed on the first polymer separator; And a second polymer separator disposed on the porous ceramic layer. Accordingly, when the secondary battery separator according to the present invention is applied to a secondary battery, it is thermally and mechanically stable, has high electrolyte wettability, inhibits the formation of lithium dendrites, stabilizes the lithium / separator interface, The thickness and the weight can be maintained at similar levels, so that the electrochemical performance and stability can be improved.

Description

TECHNICAL FIELD The present invention relates to a separator for a sandwich type secondary battery, a method for manufacturing the separator, and a secondary battery including the separator for sandwich type secondary battery,

The present invention relates to a separation membrane for a secondary battery, a production method thereof, and a secondary battery comprising the same, and more particularly, to a separation membrane for a lithium ion battery or a lithium metal battery, To a separator for a secondary battery capable of improving the wettability of an electrolyte and improving the electrochemical characteristics by inhibiting the growth of lithium dendrites, a method for producing the same, and a secondary battery comprising the same.

The first concept of a Li-ion battery (LiB) was set up in 1962, and a LiB secondary battery was proposed by MS Whittingham of Exxon, leading to the invention of a Li-TiS ₂ battery. However, commercialization of a lithium-metal and TiS ₂ -based battery system failed, due to the weak safety of LiM and the high manufacturing cost of TiS ₂ , which is sensitive to air / water. LiB was commercialized by solving these problems by using graphite and anodic oxide (developed by JO Besenhard), which reversibly intercalate and deintercalate lithium, as cathodes and anodes, respectively. For the first time in 1991, LiB's commercial products were launched by Sony and Asahi Hwaseong, bringing innovative breakthroughs that have led to successful market proliferation of portable electronic devices. Since then, LiB has been used explosively and has met the electrical energy needs directly connected with the constant innovation of everyday electrical devices such as cell phones, music players, speakers, drones, automobiles and micro sensors. Many researchers and scientists have investigated and studied new and advanced energy materials, chemistry and physics for fixed and mobile energy storage systems that meet growing energy needs.

Since the development of commercial LiB technology has recently reached saturation, where only gradual improvement of the electrochemical performance of LiB has been reported, research and development of new energy materials with different forms and compositions must be made to meet energy demands. Do. Therefore, secondary batteries such as lithium-sulfur batteries and lithium-air batteries having a LiM cathode and a switching anode have high energy densities and are attracting attention as a next-generation battery. Sulfur and carbon-based air anode theoretically have energy densities of ~ 2,600 Wh / kg and ~ 11,400 Wh / kg respectively and almost 10 times the energy density of LiB (~ 360 Wh / kg, C / Co ₂ O ₄ ) It represents a high value to reach. LiM, one of the anode materials, has a very low redox potential (-3.04 V vs. SHE) and a density of 0.59 g / cm ³ with a high theoretical energy density of ~ 3,560 Wh / kg, whereas the graphite cathode material has ~ It has a theoretical energy density of 372 mAh / g and a slightly higher redox potential and density. Therefore, when the graphite cathode is replaced with a lithium cathode, the energy density per weight of the existing LiB may be greatly increased. If lithium-sulfur and lithium-air cells are to be commercialized in the future, such LiM cathodes and switchable cathodes will be a promising way to overcome future high energy density requirements.

Despite these advantages, commercialization of LiM cathode batteries requires some tough challenges. And the reversibility of the electrodeposition and dissolution of lithium ions is secured at the center thereof. High reactivity and non-uniform electrodeposition of lithium can cause problems such as thermal runaway, electrolyte decomposition, and lithium loss. Uneven electrodeposition of lithium ions during the charging process causes dendritic growth to penetrate the separator, which causes a lot of heat and sparks, resulting in a serious safety problem that causes ignition of the electrolyte, a flammable organics. Therefore, physical dendrite blocking for dendrite inhibition is required to enhance safety, which can be compensated by improving the membrane. The heat-resistant membrane minimizes the adhesive area of the electrode when the battery is short-circuited and minimizes the ignition. Further, the surfaces of the electrode contacting the separation membrane can be chemically modified to improve the electrochemical characteristics of the lithium surface and the performance of the battery.

Polyethylene separators are mainly used for lithium ion batteries, but they are not stable against heat. PP separator (mainly Celgard separator) is used for lithium metal battery and lithium-sulfur battery, which are one of the next generation batteries, and this separator has better thermal stability than polyethylene separator but exhibits low wettability to carbonate electrolyte. Electrolytic wetting properties of the separator have a great influence on the electrochemical performance of the battery because it affects the process of lithium ion dissolution from the electrode into the electrolyte and migration through the separator, that is, lithium ion conductivity.

In addition, active and smoother LiM during electrochemical cycles tends to form dendrites during the charging process due to local current density differences due to surface roughness. Once lithium is formed on the surface, it can penetrate through the separator and cause an internal short circuit, which generates a lot of heat, which can cause battery explosion. Especially, high density lithium metal battery has more than 10 times higher energy density than conventional lithium ion battery, so development of technology that minimizes the risk of battery explosion and increases safety is the key to the commercialization of lithium metal battery.

On the other hand, in addition to conventional lithium ion batteries used in future unmanned electric vehicles and power grid energy storage systems, lithium metal is used with various anodes such as transition metal oxides, sulfur, and air poles used in lithium metal batteries having high energy densities . In addition, the development of lithium ion batteries or lithium metal batteries will contribute to the field of unmanned aerospace such as the newly emerging drones. Especially, when dealing with materials with high density energy, recent safety studies are attracting attention as one of the core researches. The reason for this is the lowering of safety due to the implementation of high energy density in commercialization of products. Due to the recent social and technological ups and downs caused by smartphone firing, it is inevitable to secure battery safety with high energy density. In particular, it is very important to study the stability of the secondary battery because the energy density of the existing lithium ion battery is expected to be about 10 times higher than that of the next generation battery.

Therefore, the development of a separator having electrochemical characteristics and stability by keeping the thickness and weight at a similar level to that of the conventional separator while being thermally and mechanically stable, having high electrolyte wettability and suppressing the formation of lithium dendrite It is necessary.

Korean Patent Publication No. 10-2015-0071251 Korean Patent Registration No. 10-1711261

An object of the present invention is to solve the problems of the prior art and to provide a lithium secondary battery which is stable in terms of thermal and mechanical properties, has high electrolyte wettability, stabilizes the lithium / separator interface by inhibiting the formation of lithium dendrites, And the weight of the secondary battery is maintained at a similar level, thereby improving electrochemical performance and stability, and a method for manufacturing the secondary battery.

Another object of the present invention is to provide a secondary battery, particularly a lithium ion battery or a lithium metal battery, in which a separator having improved thermal and mechanical stability and electrolyte wettability is introduced into an energy storage device included in various electronic and electrical products And to secure competitiveness in the electrochemical capacitor industry.

According to an aspect of the present invention,

A first polymer separator; A porous ceramic layer disposed on the first polymer separator; And a second polymer separator disposed on the porous ceramic layer.

The first and second polymer separation membranes may be modified polymer separation membranes having a surface coated with a polydodamine layer.

The modified polymer membrane may have a thickness of 5 to 50 탆.

The first and second polymeric membranes may comprise polypropylene or polyethylene.

The first and second polymer membranes may be prepared according to a wet or dry process.

The porous ceramic layer may comprise a functionalized ceramic wherein the surface is lithium-terminal sulfonated.

The functionalized ceramics may be represented by the following structural formula (1).

[Structural formula 1]

In formula 1,

n is a repetition number, and is any integer selected from 1 to 10. [

Preferably, the functionalized ceramic may be represented by the following structural formula (2).

[Structural formula 2]

The porous ceramic layer may include pores having an average diameter of 50 to 200 nm.

The porous ceramic layer may have a thickness of 1 to 10 mu m.

The porous ceramic layer may include at least one selected from titania, alumina, silica, and zirconia.

The secondary battery separator may have a thickness of 12 to 40 탆.

The weight per unit area of the secondary battery separator may be 0.5 to 2.0 mg / cm ² .

According to another aspect of the present invention,

There is provided a method of manufacturing a separator for a secondary battery, which comprises forming a porous ceramic layer on a first polymer separator, and then laminating a second polymer separator on the porous ceramic layer to produce a separator for a secondary battery according to claim 1.

The first and second polymer membranes may be prepared according to a wet or dry process.

The method for preparing the separation membrane for a secondary battery includes the steps of: (a) preparing a functionalized ceramic particle by lithium-end-sulfonating a surface of the ceramic particle; (b) coating polydopamine on the surface of the polymer separator to prepare a modified polymer separator; (c) coating the functionalized ceramic particles prepared according to step (a) on the modified polymer membrane prepared according to step (b) to prepare a first polymer membrane having a porous ceramic layer; And (d) depositing a second polymeric membrane prepared according to the method of step (b) on the porous ceramic layer of the first polymeric membrane having the porous ceramic layer formed according to step (c) And manufacturing a battery separator.

The step (a) comprises the steps of: (a-1) dispersing the ceramic particles in a solvent to prepare a dispersion; (a-2) preparing a mixture comprising the sulfonated ceramic particles by mixing and reacting the dispersion with a sulfonating agent; And (a-3) adding lithium hydroxide to the mixture to form a lithium end group, thereby preparing a lithium-end-sulfonated functionalized ceramic particle.

The ceramic particles may include at least one selected from titania, alumina, silica, and zirconia.

The functionalized ceramic particles may be represented by the following structural formula (1).

[Structural formula 1]

In formula 1,

n is a repetition number, and is any integer selected from 1 to 10. [

The functionalized ceramic particles may be represented by the following structural formula (2).

[Structural formula 2]

The sulfonating agent may be 3-trihydroxysilyl-1-propanesulfonic acid.

The ceramic particles may have an average particle diameter of 30 to 50 nm.

After step (a-3)

The step of removing the remaining sulfonating agent by centrifugation can be further carried out.

Step (b)

(b-1) immersing the polymer separation membrane in an alcohol solvent; (b-2) preparing an aqueous base solution containing a dopamine salt; And (b-3) reacting the resultant aqueous polymer solution with an aqueous alcohol solution immersed in the polymer membrane and an aqueous base solution containing a resultant dopamine salt in step (b-2) To prepare a modified polymer separating membrane.

After the step (b-3), the step of washing and drying the modified polymer separating membrane may be further performed.

The coating of step (c) may be carried out by any one of Langmuir-Blodgett scoop coating, spray coating, slurry casting and ink jet printing.

Step (d) may be carried out according to a method of pressing or heat-sealing.

According to another aspect of the present invention,

And a separator for the secondary battery.

The secondary battery may be a lithium ion battery or a lithium metal battery.

According to another aspect of the present invention,

Any one of a portable electronic device including the secondary battery, a mobile unit, a power device, and an energy storage device is provided.

When the secondary battery separator of the present invention is applied to a secondary battery, it is thermally and mechanically stable, has high electrolyte wettability, stabilizes the lithium / separator interface by inhibiting the formation of lithium dendrites, Can be maintained at a similar level, the secondary battery including the secondary battery can have improved electrochemical performance and stability.

In addition, by applying such a secondary battery to an energy storage device included in various electronic and electric products, the competitiveness of the electrochemical capacitor industry can be secured.

1 is a schematic view of a separation membrane produced according to Example 1 of the present invention.
FIG. 2 shows the time-dependent changes of PP membrane (wet polypropylene membrane) and PP 'membrane (dry polypropylene membrane) having various thicknesses ranging from 5.3 μm to 25 μm at 80 ° C.
3 is a photograph of the separation membrane in the heat shrinkage test at 80 캜.
Fig. 4 shows the time-dependent changes of PP membrane (wet type) and PP 'membrane (dry type) at various temperatures ranging from 5.3 탆 to 25 탆 at 150 캜.
5 is a photograph of a separation membrane in a heat shrinkage test at 150 ° C.
FIG. 6 is a graph showing the results of measurement of the sandwich type separator of Comparative Examples 1, 2, and 3 prepared by changing the thickness of the LTST ceramic layer to 2 to 4 μm by the method provided by the embodiment using a 11 μm thick PP separator (wet) Lt; 0 > C.
7 shows a photograph of the separation membrane according to the experimental result of FIG.
FIG. 8 shows the results of the heat shrinkage test at 150.degree. C. for the membranes of Examples 1, 2, and 3 in which polydopamine was coated using a 11 μm thick PP membrane (wet).
9 is a photograph showing the appearance of the separator of Example 1 in the result of FIG.
10 is a scanning electron micrograph of a polypropylene separation membrane having a thickness of 11 탆.
11 is a scanning electron microscope (SEM) image of the separation membrane coated with polydodamine on the separation membrane of FIG.
12 is a scanning electron microscope (SEM) image of a 25 탆 thick commercial cell guard separator.
13 is a scanning electron microscope (SEM) image of the separation membrane of FIG. 12 coated with polydodamine.
14 is a scanning electron microscope (SEM) image of a surface of a 2 μm thick LTST layer coated on a 11 μm thick PP membrane coated with polydodamine.
FIG. 15 shows the voltage change for lithium stripping and plating in a symmetric lithium cell.
FIG. 16 shows results obtained by performing an experiment similar to the experiment shown in FIG. 15, with applied current and capacity being 5 mAcm ^-2 and 5 mAhcm ^-2, respectively.
Figure 17 shows a cell with copper as in Example 1, the Coulomb efficiency and the capacity obtained by the current applied to each of 1 mAcm ^-2 and 1 mAhcm ^-2 in cell used with the sandwich-type membrane consists of copper and the untreated membrane.
FIG. 18 shows the discharge capacity and coulomb efficiency using a NCM ternary anode, a capacity of 120 mAh / g up to 100 cycles and a coulombic efficiency of 90% or more.
19 is a photograph showing electrolyte impregnation characteristics before and after coating with polydodamine.

In the following, various aspects and various embodiments of the present invention will be described in more detail.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

However, the following description does not limit the present invention to specific embodiments. In the following description of the present invention, detailed description of related arts will be omitted if it is determined that the gist of the present invention may be blurred .

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises ",or" having ", and the like, specify that the presence of stated features, integers, steps, operations, elements, or combinations thereof, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, or combinations thereof.

Hereinafter, the secondary battery separator of the present invention will be described.

The separator for a secondary battery of the present invention comprises: a first polymer separator; A porous ceramic layer disposed on the first polymer separator; And a second polymer separator disposed on the porous ceramic layer.

Preferably, the first and second polymer separation membranes are modified polymer separation membranes having a surface coated with a polydodamine layer.

The modified polymeric membrane may have a thickness of 5 to 50 mu m, preferably 7 to 30 mu m, more preferably 10 to 25 mu m.

The first and second polymer separation membranes may include polypropylene or polyethylene, and preferably polypropylene.

The first and second polymer separation membranes may be those prepared according to a wet or dry preparation method, preferably those prepared by a wet preparation method.

The porous ceramic layer may comprise a functionalized ceramic wherein the surface is lithium-terminal sulfonated.

The porous ceramic layer may include at least one selected from titania, alumina, silica, and zirconia.

The functionalized ceramics may be represented by the following structural formula (1).

[Structural formula 1]

In formula 1,

n is a repetition number, and is any integer selected from 1 to 10. [

Preferably, the functionalized ceramic may be represented by the following structural formula (2).

[Structural formula 2]

The porous ceramic layer may include pores having an average diameter of 50 to 200 nm.

The porous ceramic layer may have a thickness of 1 to 10 mu m, preferably 1.5 to 5 mu m, more preferably 2 to 3 mu m.

The secondary battery separator may have a thickness of 12 to 40 mu m, preferably 15 to 30 mu m, more preferably 20 to 25 mu m.

The weight per unit area of the secondary battery separator is 0.5 to 2.0 mg / cm < ² > .

Hereinafter, a method for producing a separator for a secondary battery of the present invention will be described.

The separation membrane for a secondary battery of the present invention can be manufactured by forming a porous ceramic layer on a first polymer separation membrane and then laminating a second polymer separation membrane on the porous ceramic layer.

The polymer separator may be one prepared by a wet or dry preparation method, more preferably a polymer produced by a wet preparation method.

The method for producing the separation membrane for a secondary battery of the present invention will be described in more detail as follows.

First, the surface of the ceramic particle was treated with a lithium terminal Sulfonation  Functionalized ceramic particles are prepared (step a).

Specifically, the ceramic particles are dispersed in a solvent to prepare a dispersion (step a-1).

The ceramic particles may include at least one selected from titania, alumina, silica, and zirconia.

It is preferable that the ceramic particles have an average particle diameter of 30 to 50 nm.

Thereafter, the dispersion is mixed with a sulfonating agent and reacted to prepare a mixture containing the sulfonated ceramic particles (step a-2).

The sulfonating agent may be 3-trihydroxysilyl-1-propanesulfonic acid, but the scope of the present invention is not limited thereto, and various sulfonating agents may be used depending on the final sulfonated structure.

Next, lithium hydroxide is added to the mixture to form a lithium end group, whereby a functionalized ceramic particle having lithium-end sulfonated is prepared (step a-3).

The functionalized ceramic particles may be represented by the following structural formula (1).

[Structural formula 1]

In formula 1,

n is a repetition number, and is any integer selected from 1 to 10. [

Preferably, the functionalized ceramic particles can be represented by the following structural formula (2).

[Structural formula 2]

Thereafter, a step of removing the remaining sulfonating agent by centrifugation may be further carried out.

Next, on the surface of the polymer membrane, Polydopamine  Coated Reformed  A polymer membrane is prepared (step b).

First, the polymer separation membrane is immersed in an alcohol solvent (step b-1).

Thereafter, an aqueous base solution containing a dopamine salt is prepared (step b-2).

(b-1) is reacted with an aqueous base solution containing an alcohol solvent immersed in the resultant polymer membrane and a resultant dopamine salt in the step (b-2) to polydodamine on the surface of the polymer membrane to obtain a modified polymer membrane Can be prepared.

Thereafter, the modified polymer separation membrane may be washed and then dried.

The compound of formula (I) Reformed  The functionalized ceramic particles prepared according to step (a) are coated on the polymer membrane to prepare a first polymer membrane having a porous ceramic layer (step c).

The coating of step (c) may be performed by Langmuir-Blodgett scoop coating, spray coating, slurry casting, inkjet printing, etc., but the scope of the invention is not limited thereto.

Finally, a second polymer separator prepared according to the method of step (b) is formed on the porous ceramic layer of the first polymer separator having the porous ceramic layer formed according to step (c) Laminated  A separator for a sandwich type secondary battery is prepared (step d).

The lamination of the modified polymer separation membrane can be performed by compression bonding or thermal fusion bonding.

The present invention provides a secondary battery including the secondary battery separator.

The secondary battery may be a lithium ion battery or a lithium metal battery.

The secondary battery may include an ether-based electrolyte or a carbonate-based electrolyte.

Further, the present invention provides any one of the portable electronic device including the secondary battery, the mobile unit, the electric power device, and the energy storage device.

Hereinafter, embodiments of the present invention will be described in detail.

[Example]

Manufacturing example  1: lithium terminal Sulfonated Titania ( LTST ) Synthesis method

For functionalization, titania nanoparticles were dispersed in water and ultrasonicated for 30 minutes. Then, 3- (trihydroxysilyl) -1-propanesulfonic acid was dropped to pH 2. The mixture was allowed to react at room temperature overnight. High-concentration LiOH was added until the pH reached 7 for lithium-termination and centrifugation was performed 10 times or more by adding deionized water to remove excess lithium 3- (trihydroxysilyl) -1-propanesulfonic acid. In the last step, ethanol was used and then dried overnight in an oven at 80 ° C to obtain the final product.

Manufacturing example  2: Polydopamine  Coated polypropylene ( PP ) Membrane Manufacturing

First, the wet PP membrane was put into 120 ml of methanol and ultrasonicated for 5 minutes. 0.26 g trisma base, 0.14 g trisma hydrochloride, and 0.76 g dopamine salt were dissolved in 125 ml deionized water to prepare a dopamine solution. Then, methanol and dopamine solution containing the separation membrane were slowly mixed and reacted for one day. The reacted membranes were washed with deionized water at least five times, finally washed with ethanol, and then dried in an oven at 60 ° C.

Example  One: Sandwich type  Preparation of Membrane

(1-3 wt%) of lithium-terminal sulfonated titania (LTST) particles prepared according to Preparation Example 1 was mixed with ethanol and ultrasonically dispersed for 30 minutes to prepare a dispersion. According to Production Example 2 Lithium-terminated sulfonated ultra-thin films with a thickness of 2 탆 were formed by the Langmuir-Blodgett scooping coating method using the prepared polydopamine-coated PP separator as a substrate.

Thereafter, LTST was sandwiched with a polydodamine-coated separator by thermally laminating the ends of the separation membrane using another polypodamine-coated PP separation membrane prepared according to Production Example 2 on the sulfonated titania ultra-thin film The membrane was completed.

1 is a schematic view of a separation membrane produced according to Example 1 of the present invention. A PP layer (DPP) coated with polydodamine on both sides of a lithium-terminal sulfonated titania (LTST) layer is located, and one surface of the porous ceramic is lithium-terminal sulfonated. Titania having a high stiffness ratio can be functionalized as a lithium end-sulphone group to suppress the puncture of the lithium dendrite and improve the thermal characteristics of the SCS-structure separator. Polydopamine coated on the membrane improves thermal stability and wettability, and lithium metal and catechol interaction can inhibit the growth of lithium dendrite. Such a sandwich membrane has improved thermal stability and electrochemical stability and inhibits the growth of lithium dendrite to prevent separation of the separator, thereby enhancing the stability and safety of the lithium metal battery and the lithium ion battery.

Example  2

A sandwich type membrane was prepared in the same manner as in Example 1, except that the lithium-terminal sulfonated titania thin film was formed to a thickness of 3 탆 instead of 2 탆.

Example  3

A sandwich type membrane was prepared in the same manner as in Example 1, except that the lithium-terminal sulfonated titania thin film was formed to a thickness of 4 탆 instead of 2 탆.

Comparative Example  One: Not reformed  Use of non-polypropylene membrane

A sandwich type membrane was prepared in the same manner as in Example 1, except that a PP separation membrane in which polydodamine was not coated was used in place of the PP separation membrane coated with polydodamine.

Comparative Example  2: Not reformed  Use of non-polypropylene membrane

A sandwich membrane was prepared in the same manner as in Example 2, except that a PP separation membrane not coated with polypodamine was used in place of the PP separation membrane coated with polydodamine.

Comparative Example  3: Not reformed  Use of non-polypropylene membrane

A sandwich type membrane was prepared in the same manner as in Example 3, except that a PP separation membrane not coated with polypodamine was used in place of the PP separation membrane coated with polypodamine.

[Test Example]

Heat shrinkage test method

The modified or unmodified membranes were cut into disks of 1.8 cm diameter and then the tip of the next slide glass positioned between the two slide glasses was taped with capton tape and kept in the oven at the desired temperature and time.

Electrochemical analysis method of protective film coating lithium metal

In order to investigate the electrochemical properties of lithium metal through membrane deformation, a constant current strip / plating measurement was performed and the potential change was measured from the symmetric cell. Stripping and plating were carried out at various current densities (3-5 ㎃ / ㎠) and capacities (3-5 ㎃h / ㎠), and 1M LiPF ₆ 2 wt.% VC in EC: DMC) (1: 1, v: v ) electrolyte was used. In addition, the lithium metal battery was modified with a modified separator, 1M LiPF ₆ (1: 1, v: v ) electrolyte, NCM anode. Cu and Li symmetric cells were prepared to measure the Coulomb efficiency. The membrane before and after reforming and 1M LiPF ₆ (1 mA / cm2) and capacity (1 mAh / cm2) using an electrolyte (1: 1, v: v ) Unmodified membrane samples were made using two sheets (22 mu m) in a thickness similar to that of a modified SCS-structured membrane (24 mu m).

Test Example  1: Depends on the thickness of polypropylene membrane Heat shrinkage  observe

FIG. 2 shows the time-dependent changes of the PP separator (wet polypropylene separator) and PP 'separator (dry polypropylene separator) at various temperatures ranging from 5.3 μm to 25 μm at 80 ° C. As can be seen from FIGS. 10 and 12 (manufactured by Celgard), they have pore structures of different structures, which are caused by differences in the manufacturing process. The thermal stability of 5.3 ㎛ thick membranes was low and other membranes showed little heat shrinkage at 80 ℃. 3 is a photograph of the separation membrane in the heat shrinkage test at 80 캜. According to this, it can be confirmed that the diameter of the circular separation membrane having a thickness of 5.3 μm is apparently small, and it is not well recognized in other separation membranes.

Fig. 4 shows the time-dependent changes of PP membrane (wet type) and PP 'membrane (dry type) at various temperatures ranging from 5.3 탆 to 25 탆 at 150 캜. Except for the membrane with a thickness of 16 ㎛, both show a large heat shrinkage. 5 is a photograph of a separation membrane in a heat shrinkage test at 150 ° C. As a result, it can be seen that the original circular shape shrinks and a large change can be confirmed except for the circular separation membrane having the appearance of 16 탆 thickness, and it can be seen that the thinner the thickness is, the more severe it appears.

FIG. 6 is a graph showing the results of measurement of the sandwich type separator of Comparative Examples 1, 2, and 3 prepared by changing the thickness of the LTST ceramic layer to 2 to 4 μm by the method provided by the embodiment using a 11 μm thick PP separator (wet) Lt; 0 > C. According to this, the heat shrinkage was greatly improved at the LTST layer 2 μm, and the decrease in the heat shrinkage was not greatly improved as the LTST thickness increased. 7 shows a photograph of the separation membrane according to the experimental result of FIG. According to this, the shrinkage of LTST-coated other membranes hardly changed, except that the LTST-uncoated separator became transparent and changed its shape.

FIG. 8 shows the results of the heat shrinkage test at 150.degree. C. for the membranes of Examples 1, 2, and 3 in which polydopamine was coated using a 11 μm thick PP membrane (wet). The heat shrinkage phenomenon was remarkably improved by 20% or more by coating with polydodamine, and the separator of Example 1 having the thickness of the LTST ceramic layer of 2 탆 showed a further shrinkage of less than 5% due to a further reduction of heat shrinkage. 9 is a photograph showing the appearance of the separator of Example 1 in the result of FIG. According to the results, it can be seen that the sandwich type separator of the present invention coated with the polydodamine coating and the 2 탆 LTST has insufficient thermal deformation at 150 ° C and thus has excellent thermal stability.

Test Example  2: SEM  analysis

FIG. 10 is a scanning electron microscope photograph of a polypropylene separation membrane having a thickness of 11 μm, and it can be confirmed that it has a typical wet production separation membrane shape and pores of 50 nm or less.

FIG. 11 is a scanning electron microscope (SEM) image of the separation membrane coated with polypodamine on the separation membrane of FIG. 10, showing that the pore decreased to 40 nm or less by dopamine coating.

12 is a scanning electron microscope (SEM) image of a 25 탆 thick commercial cell guard separator showing a pore structure formed by tearing and tearing in one direction. The pore size was 64 nm or less.

FIG. 13 is a scanning electron micrograph of a separation membrane having a polypodamine coating on the separation membrane of FIG. 12, wherein the pore decreased to 55 nm or less by dopamine coating.

14 is a scanning electron microscope (SEM) image of a surface of a 2 μm-thick LTSTR layer on a 11 μm-thick PP separator coated with polydodamine, and has a pore size of 100 nm or less.

Test Example  3: Cycle characteristics

FIG. 15 shows the voltage change for lithium stripping and plating in a symmetric lithium cell. The results obtained in the cell using the untreated separation membrane and the cell using the sandwich type separation membrane produced according to Example 1 using the poly dopamine-coated 11 탆 separation membrane. At this time, the electrolyte is 1M LiPF ₆ 2wt% VC EC used: DMC (1: 1, v : v) , and applying a current, and capacity of each of 3 mAcm ^-2 and 3 mAhcm ^{- 2.} The lithium cell using the sandwich type separator of Example 1 was stable even for over 200 cycles, while the lithium cell using the general separator was gradually increased in voltage from ~ 60 cycles to ~ 135 cycles in the end.

FIG. 16 shows results of experiments similar to the experiment shown in FIG. 15, in which the applied current and the capacity are 5 mAcm ^-2 and 5 mAhcm ^-2 , respectively. In the case of the cell using the general separation membrane, The battery using the sandwich type separator of Example 1 showed a voltage increase after ~ 40 cycles, but maintained a stable voltage even after 80 cycles.

Test Example  4: coulomb  Efficiency and Charging and discharging  characteristic

Figure 17 shows a cell with copper as in Example 1, the Coulomb efficiency and the capacity obtained by the current applied to each of 1 mAcm ^-2 and 1 mAhcm ^-2 in cell used with the sandwich-type membrane consists of copper and the untreated membrane. As a result, the Cu + unmodified membrane cell exhibited a broad Coulomb efficiency change of 20 to 70% after a ~ 25 cycle, while the Cu + modified membrane cell showed a 90% Respectively.

FIG. 18 shows the discharge capacity and coulombic efficiency of the NCM ternary anode, showing a capacity of 120 mAh / g up to 100 cycles and a coulombic efficiency of 90% or more. The sandwich type membrane of Example 1 and a 1M LiPF ₆ 2 wt% VC EC: DMC (1: 1, v: v ) electrolyte were used. According to the results, it was confirmed that the coulomb efficiency and the discharge capacity were higher when the separation membrane of Example 1 was used.

19 is a photograph showing electrolyte impregnation characteristics before and after coating with polydodamine. It can be seen that the electrolytic solution wetting property of the polypodamine-coated separator is superior.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, many modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention as defined in the appended claims. The present invention can be variously modified and changed by those skilled in the art, and it is also within the scope of the present invention.

Claims (21)

A first polymer separator;
A porous ceramic layer disposed on the first polymer separator; And
And a second polymer separator disposed on the porous ceramic layer,
Wherein the first and second polymer separation membranes are modified polymer membranes having a surface coated with a polydodamine layer,
Wherein the porous ceramic layer comprises a functionalized ceramic whose surface is lithium-terminal sulfonated. delete The method according to claim 1,
Wherein the modified polymer separation membrane has a thickness of 5 to 50 占 퐉. The method according to claim 1,
Wherein the first and second polymer separation membranes comprise polypropylene or polyethylene. The method according to claim 1,
Wherein the first and second polymer separation membranes are manufactured according to a wet or dry production method. delete The method according to claim 1,
Wherein the functionalized ceramics are represented by the following structural formula (1).
[Structural formula 1]

In formula 1,
n is a repetition number, and is any integer selected from 1 to 10. [ The method according to claim 1,
Wherein the porous ceramic layer comprises pores having an average diameter of 50 to 200 nm. The method according to claim 1,
Wherein the porous ceramic layer has a thickness of 1 to 10 mu m. The method according to claim 1,
Wherein the porous ceramic layer comprises at least one selected from the group consisting of titania, alumina, silica, and zirconia. The method according to claim 1,
Wherein the separation membrane for a secondary battery has a thickness of 12 to 40 mu m. 11. The method of claim 10,
Wherein the weight per unit area of the secondary battery separator is 0.5 to 2.0 mg / cm ² . delete (a) preparing a functionalized ceramic particle by lithium-end-sulfonating the surface of the ceramic particle;
(b) coating polydopamine on the surface of the polymer separator to prepare a modified polymer separator;
(c) coating the functionalized ceramic particles prepared according to step (a) on the modified polymer membrane prepared according to step (b) to prepare a first polymer membrane having a porous ceramic layer; And
(d) depositing a second polymeric membrane prepared according to the method of step (b) on the porous ceramic layer of the first polymeric membrane having the porous ceramic layer prepared according to step (c) to form a sandwich- And a step of preparing a separation membrane for a secondary battery. 15. The method of claim 14,
Step (a)
(a-1) dispersing the ceramic particles in a solvent to prepare a dispersion;
(a-2) preparing a mixture comprising the sulfonated ceramic particles by mixing and reacting the dispersion with a sulfonating agent; And
(a-3) adding lithium hydroxide to the mixture to form a lithium end group, thereby producing a functionalized ceramic particle having lithium end sulfonation. 15. The method of claim 14,
Wherein the ceramic particles have an average particle diameter of 30 to 50 nm. 15. The method of claim 14,
Step (b)
(b-1) immersing the polymer separation membrane in an alcohol solvent;
(b-2) preparing an aqueous base solution containing a dopamine salt; And
(b-3) reacting the resultant aqueous polymer solution with an aqueous alcohol solution immersed in the polymer membrane and an aqueous base solution containing a resultant dopamine salt in step (b-2) to form a polymer membrane on the surface of the polymer membrane, And a step of preparing a modified polymer separating membrane by coating. 15. The method of claim 14,
Wherein the coating of step (c) is carried out by any one of Langmuir-Blodgett coating, Langmuir-Blodgett squop coating, spray coating, slurry casting and ink printing. Way. A secondary battery comprising a separator for a secondary battery according to any one of claims 1, 3, 4, 5, and 7 to 12. 20. The method of claim 19,
Wherein the secondary battery is a lithium ion battery or a lithium metal battery. A portable electronic device comprising the secondary battery of any one of claims 19 to 19, a mobile unit, a power device, and an energy storage device.

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