KR20220051982A - A polyphenylene sulfide/porogen composite, a porous separator for lithium secondary battery comprising the same, method for manufacturing the polyphenylene sulfide/porogen composite and method for manufacturing the porous separator for lithium secondary battery - Google Patents

Abstract

The present invention relates to a polyphenylene sulfide/porogen composite, a porous separator for lithium secondary battery containing the same, a method for preparing the polyphenylene sulfide/porogen composite, and a method for preparing a porous separator for lithium secondary battery. More specifically, the porogen may be uniformly dispersed in a polymer resin by improving interfacial affinity between polyphenylene sulfide polymer particle and the porogen by forming a composite in which the polymer particle is coated with the porogen through plasma treatment. In addition, the porous separator for lithium secondary batteries of the present invention can easily form uniform micropores on the surface and inside of the membrane, and remarkably improve porosity and ionic conductivity due to the ionic functional groups bonded to the inner walls of the pores through a simple process of removing porogen using polyphenylene sulfide/porogen complex while maintaining the excellent heat resistance, mechanical stability and chemical resistance of polyphenylene sulfide polymer.

Description

A polyphenylene sulfide / porogen composite, a porous separator for a lithium secondary battery comprising the same, a method for producing the polyphenylene sulfide / porogen composite, and a method for producing a porous separator for a lithium secondary battery {A polyphenylene sulfide / porogen composite, a porous separator for lithium secondary battery comprising the same, method for manufacturing the polyphenylene sulfide/porogen composite and method for manufacturing the porous separator for lithium secondary battery}

The present invention relates to a polyphenylene sulfide/porogen composite having excellent mechanical strength and chemical stability, a porous separator for a lithium secondary battery with improved ionic conductivity and porosity including the same, a method for preparing the polyphenylene sulfide/porogen composite, and the lithium It relates to a method for manufacturing a porous separator for a secondary battery.

A separator essential for the construction of a secondary battery system typified by a lithium ion battery is manufactured using a wet method, a compression method, or a dry method. In the wet method, a polymer solution prepared by dissolving a polymer, which is a membrane medium, in a suitable solvent is cast on a flat plate to form a film, and pores are formed in the process of drying and removing the solvent to prepare a separator. In addition, the compression method is a method of manufacturing a porous polymer film by applying heat and pressure in a non-woven state in which the fibrous polymer is disorderly. In addition, the dry method is a method of manufacturing a porous polymer film by repeatedly exposing a preformed polymer film to mechanical stress such as uniaxial or biaxial stretching and forming pores through a process of physical damage caused by an external force.

Lithium secondary batteries require a controlled pore size and a homogeneous pore distribution in terms of maintaining constant charge/discharge performance and improving charge/discharge-related properties. The disadvantage is still pointed out that it is very difficult to precisely control the

In particular, in the case of a commercially available separator, it is manufactured by applying a dry method to an olefinic thermoplastic polymer such as polyethylene or polypropylene. However, the olefinic thermoplastic polymer has poor heat resistance, so it cannot be used in a high temperature environment of 150 ° C. or higher, and while chemical stability is good, mechanical strength and durability are weak, so that it can be easily weakened when exposed to a harsh operating environment.

In order to overcome the above problems, various efforts are currently being made to replace olefinic thermoplastic polymers by using super engineering plastics with excellent heat resistance and mechanical properties, and in particular, polyphenylene sulfide, one of super engineering plastics, is being tried. Separation membrane research using (polyphenylene sulfide, PPS) is of major interest.

However, polyphenylene sulfide has high polymer chain bonding strength, so it has excellent mechanical durability against external impact even at high temperatures. there is. In addition, while chemical resistance is excellent due to low chemical reactivity, it is very difficult to secure solution conditions for wet film forming method, and diphenyl ether, N-methylpyrrolidone, N-cyclohexylpyrrolidone Limited dissolution occurs only in a high-temperature environment above 150 ℃ using some special solvents with high boiling point and high polarity, such as (N-cyclohexylpyrrolidone). In addition, polyphenylene sulfide, like other polymer materials, has very low ionic conductivity, so even if a pore-formed structure is obtained, additional treatment to improve ion conductivity is essential for functionality as an ion conductive separator, but chemical reactivity is low It requires a much harsher or more complex process.

In addition to the above-described wet solvent method and dry process based on physical damage caused by external force, the method for manufacturing a porous film based on general-purpose polymer resin as well as super engineering plastic includes porogen, a precursor material that promotes formation of pores, that is, foreign substances in the resin. (porogen) is injected to form a polymer-porogen complex, molded into a film, and then only the porogen component is selectively removed therefrom to promote pore formation. In this case, the polymer resin reacts Since it uses a solvent that can selectively elute only the porogen present in the polymer resin, it is known as an advantage that it can easily promote the formation of various and homogeneous pores according to the size and shape of the introduced porogen.

However, since the interfacial affinity between the metal oxide-based inorganic component and the polymer resin, which can be mainly used as a porogen, is generally poor, when the two components are mixed, the porogen component is seriously agglomerated in the polymer resin, and the porogen component Since the distribution in the resin is also very non-uniform, it is essential to significantly improve the interface affinity between the porogen and the polymer resin in order to achieve the desired pore composition and homogeneous pore distribution of a certain size. As described above, due to the low chemical reactivity, it requires a much more severe or complicated process for additional treatment to improve the interfacial affinity with porogen.

As such, in order to replace the olefinic thermoplastic polymer used as a separator for lithium ion batteries with polyphenylene sulfide, not only the physical properties of the resin itself expected in terms of heat and chemical resistance, but also homogeneous pores and excellent ion transfer ability are required. There are many difficulties in forming a separation membrane in the form of a porous film, and it is not easy to prepare countermeasures for this.

Korea Patent Publication No. 2016-0129538

In order to solve the above problems, the present invention improves the interface affinity between polyphenylene sulfide polymer particles and porogen, which is a precursor material for pore formation, by plasma treatment to improve the polyphenylene An object of the present invention is to provide a polyphenylene sulfide/porogen complex in which a high content of porogen particles are evenly dispersed in a sulfide polymer.

Another object of the present invention is to provide a porous separator for a lithium secondary battery with improved ion conductivity and porosity by uniformly forming pores on the surface and inside using a polyphenylene sulfide/porogen composite.

Another object of the present invention is to provide a lithium secondary battery with improved battery performance and lifespan characteristics including the porous separator.

Another object of the present invention is to provide a device including the lithium secondary battery.

Another object of the present invention is to provide a method for preparing a polyphenylene sulfide/porogen complex.

Another object of the present invention is to provide a method for manufacturing a porous separator for a lithium secondary battery.

The present invention provides a polyphenylene sulfide/porogen composite including a form in which a porogen is coated on the surface of a polyphenylene sulfide polymer particle, wherein the porogen is a spherical ceramic particle.

In addition, the present invention is a porous separator for a lithium secondary battery in which pores are uniformly formed inside and on the surface using the polyphenylene sulfide/porogen composite, wherein the pores are removed from the polyphenylene sulfide/porogen composite It provides a porous separator for a lithium secondary battery that is formed by being formed, and the inner wall of the pores includes an ionic functional group bonded to polyphenylene sulfide.

In addition, the present invention provides a lithium secondary battery including the porous separator.

In addition, the present invention provides a device including the lithium secondary battery, wherein the device is any one selected from a communication device, a transportation device, and an energy storage device.

In addition, the present invention comprises the steps of adding polyphenylene sulfide polymer particles and porogen to the chamber of the dry mixer; and generating a plasma inside the chamber to prepare a polyphenylene sulfide/porogen composite in which the polyphenylene sulfide polymer particles and porogen are mechanically and chemically bonded to the particle surface; Polyphenylene sulfide/ A method for preparing a porogen complex is provided.

In addition, the present invention comprises the steps of manufacturing a separation membrane by molding the polyphenylene sulfide / porogen complex; cooling the separator to lower the crystallinity of the separator; And immersing the cooled separator in an acid or base solution to remove the porogen present on the surface and inside of the separator to prepare a porous separator in which pores are uniformly formed; a method for producing a porous separator for a lithium secondary battery comprising a to provide.

The polyphenylene sulfide/porogen complex of the present invention activates the surfaces of polyphenylene sulfide and porogen by plasma treatment, thereby improving the interface affinity between polyphenylene sulfide polymer particles and porogen, During the extrusion process of the phenylene sulfide/porogen complex, the porogen can be uniformly dispersed in the polyphenylene sulfide medium without agglomeration of the porogen.

In addition, since the porous separator of the present invention uses a plasma-treated polyphenylene sulfide/porogen composite, excellent porosity can be obtained by forming pores having a uniform size and distribution on the surface and inside of the membrane when the porogen is removed.

In addition, the porous separator of the present invention can easily form micropores by a simple process while maintaining the excellent heat resistance, mechanical stability and chemical resistance of the polyphenylene sulfide polymer, and has excellent porosity, The ionic conductivity can be significantly improved due to the ionic functional groups remaining on the inner wall. Furthermore, when applied to a lithium secondary battery by using this, the performance and lifespan characteristics of the battery can be improved.

The effects of the present invention are not limited to the above-mentioned effects. It should be understood that the effects of the present invention include all effects that can be inferred from the following description.

1 is a photograph of the porous separator prepared in Example 2.
2 is an SEM photograph of the porous separator prepared in Example 2 in the vertical direction (cross-section).
3 is an enlarged SEM photograph of pores formed in the vertical direction (cross-section) of the porous separator prepared in Example 2;
4 shows the results of measuring the charging and discharging performance of the lithium secondary battery using the porous separator prepared in Example 2 above.

Hereinafter, the present invention will be described in more detail by way of one embodiment.

The present invention relates to a polyphenylene sulfide/porogen composite, a porous separator for a lithium secondary battery comprising the same, a method for preparing the polyphenylene sulfide/porogen composite, and a method for manufacturing the porous separator for a lithium secondary battery.

Existing polyphenylene sulfide polymers have low ionic conductivity, micropores are not easily formed in both wet and dry processes, and are limitedly dissolved by polar solvents at high temperatures above 150 ° C. There was a difficult and complex problem.

Therefore, in the present invention, the interfacial affinity between the polyphenylene sulfide polymer particles and the porogen is improved by plasma treatment of a mixture of polyphenylene sulfide polymer particles and porogen to uniformly disperse the porogen in the polymer even when melting. can

In addition, the porous separator using the same can improve porosity by removing the porogen from the polyphenylene sulfide/porogen complex to form uniform pores on the surface and inside of the membrane. In addition, the porous separator of the present invention can easily form micropores by a simple process while maintaining the excellent heat resistance, mechanical stability and chemical resistance of the polyphenylene sulfide polymer, and has excellent porosity, Due to the ionic functional group bound to the inner wall, the ionic conductivity can be significantly improved. Furthermore, when applied to a lithium secondary battery by using this, the performance and lifespan characteristics of the battery can be improved.

Specifically, as an embodiment of the present invention, polyphenylene sulfide polymer particles; and a porogen coated on the surface of the polymer particle in a form bonded to the outside of the polyphenylene sulfide polymer particle, wherein the porogen is a spherical ceramic particle.

The polyphenylene sulfide/porogen complex contains polyphenylene sulfide polymer particles and porogen in a weight ratio of 1:9 to 9:1, preferably 3:7 to 7:3, more preferably 4:6 to 6 It may consist of a :4 weight ratio, most preferably a 5:5 weight ratio. At this time, if the mixing ratio of the porogen is more than 9 weight ratio, the content of the polyphenylene sulfide is too small, the mechanical stability and chemical resistance physical properties may be reduced. , it may be difficult to apply to a separation membrane, and ionic conductivity may be remarkably reduced.

The polyphenylene sulfide polymer particles may have an average particle diameter of 10 to 1000 μm, preferably 60 to 650 μm, more preferably 100 to 500 μm, and most preferably 400 μm. At this time, if the average particle diameter of the polyphenylene sulfide polymer particles does not satisfy the above range and is too small or too large, the frictional force with the porogen is lowered, so it may be difficult to form a chemical bond between the polymer and the particles and the porogen .

The porogen is preferably spherical ceramic particles of uniform size to form micropores in the polyphenylene sulfide-based separator. In particular, when spherical ceramic particles of uniform size are used as porogen, pores are uniformly and regularly formed compared to conventional olefin-based membranes with irregularly sized pores, so that the ion flux is very uniform across the entire surface of the membrane. This can be achieved and the ionic conductivity can be significantly improved.

The spherical ceramic fine particles may have an average particle diameter of 100 to 1000 nm, preferably 140 to 300 nm, more preferably 185 to 210 nm, and most preferably 200 nm. At this time, if the average particle diameter of the spherical ceramic particles is less than 100 nm, the particle diameter is too small to interfere with ion movement and consequently ion conductivity may be lowered. there is.

The spherical ceramic particles may be at least one selected from the group consisting of metal nitride, metal sulfide, and metal oxide. The metal nitride-based is at least one selected from the group consisting of AIN, TiN, BN, and InN, the metal sulfide-based is at least one selected from the group consisting of MoS ₂ , ZnS and WS ₂ , and the metal oxide is Al ₂ O ₃ , SiO ₂ , ZnO, ZrO ₂ and TiO ₂ It may be at least one selected from the group consisting of. Preferably, the spherical ceramic fine particles may be metal oxide-based, more preferably Al ₂ O ₃ , SiO ₂ , or a mixture thereof, and most preferably SiO ₂ .

The polyphenylene sulfide / porogen complex may be one in which the polyphenylene sulfide polymer particles and the porogen are mixed and plasma-treated in a dry process that does not use a solvent to have a structure in which the particles are coated with the porogen. . The polyphenylene sulfide/porogen composite is a dry type plasma machine that induces chemical bonding by applying a low-energy plasma between the polymer and the porogen ceramic particles instead of the wet method, which is complicated and expensive due to solvent treatment By using a chemical process, the interfacial affinity between the polyphenylene sulfide polymer and the spherical ceramic particles can be easily increased without solvent treatment, and the distribution of the spherical ceramic particles in the medium can be controlled.

In addition, as another embodiment of the present invention, there is provided a porous separator for a lithium secondary battery in which pores are uniformly formed inside and on the surface using the polyphenylene sulfide/porogen composite, wherein the pores are formed from the polyphenylene sulfide/porogen composite. It is formed by removing the rosen, and the inner wall of the pores provides a porous separator for a lithium secondary battery that includes an ionic functional group bonded to polyphenylene sulfide.

The ionic functional group is a polar functional group derived from porogen, and as the porogen is removed from the complex, uniform pores are formed on the inside and surface of the membrane, and the porogen is combined with polyphenylene sulfide on the inner wall of the formed pores to form a coating. may contain. In particular, the ionic functional group is bound to the inner wall of the pore in the form of an ionic group, so it has a high affinity with lithium ions in the electrolyte, and increases the wetting property with most electrolytes having a functional group such as a carbonate group, thereby significantly improving the ionic conductivity of the membrane can do it

The ionic functional group is a polar functional group derived from porogen, and is selected from the group consisting of an aluminate group (Al-O-Al), a siloxane group (Si-O-Si), and a titanate group (Ti-O-Ti). It may be one or more, preferably an aluminate group, a siloxane group, or a mixture thereof, and most preferably a siloxane group.

The ionic functional group may be included in an amount of 0.1 to 10% by weight, preferably 1.0 to 8.0% by weight, more preferably 3.0 to 5.0% by weight based on 100% by weight of the porous separator. At this time, when the ionic functional group is bound to the inner wall of the pores in an amount of less than 0.1 wt%, the wettability with the electrolyte is reduced, resulting in a decrease in ionic conductivity. It may be difficult to manufacture in the form of a film.

The porous membrane may have a porosity of 0.1 to 95% by volume, preferably 30 to 81% by volume, more preferably 40 to 72% by volume, and most preferably 69% by volume. If the porous separator does not satisfy the porosity range, ion conductivity may be lowered, and when applied to a secondary battery, charge/discharge performance may deteriorate.

The porous separator may have a thickness of 10 to 1000 μm, preferably 15 to 450 μm, more preferably 20 to 150 μm, and most preferably 25 to 53 μm. At this time, if the thickness of the porous separator is less than 10 μm, physical properties such as mechanical rigidity and durability of the membrane may be rapidly reduced, and if it exceeds 1000 μm, ion conductivity may be decreased as the ion migration time is relatively long. there is.

In another embodiment of the present invention, there is provided a lithium secondary battery including the porous separator.

In another embodiment of the present invention, as a device including the lithium secondary battery, the device provides a device that is any one selected from a communication device, a transportation device, and an energy storage device.

In addition, in another embodiment of the present invention, the step of introducing polyphenylene sulfide polymer particles and porogen into the chamber of the dry mixer; and generating a plasma inside the chamber to prepare a polyphenylene sulfide/porogen complex having a structure in which porogen is chemically bonded to the surface of the polymer particle in a form that surrounds the outside of the polyphenylene sulfide polymer particle; It provides a method for producing a polyphenylene sulfide / porogen complex comprising.

In general, since the polyphenylene sulfide polymer particles and ceramic particles have very poor interface affinity, when the two components are mixed, the ceramic particles are largely agglomerated, forming a large dispersed phase, and the interface between them can form a very unstable state. Accordingly, when a separation membrane is formed using a polyphenylene sulfide/ceramic particle mixture mixed by a general mixing method, the inherent high mechanical strength and chemical resistance of the polyphenylene sulfide polymer is weak, and the ceramic particles are evenly dispersed. There is a problem in that it is difficult to form uniform pores. To solve this problem, in the present invention, a polyphenylene sulfide/porogen complex was formed by inducing chemical bonding by applying plasma to the polyphenylene sulfide polymer particles and ceramic fine particles. In the present invention, the ceramic fine particles may be used as a precursor porogen for pore formation.

Since the polyphenylene sulfide polymer particles do not have a functional group, a high level of frictional force is required to induce a mechanochemical reaction with the ceramic fine particles. Accordingly, in order to improve the frictional force and interface affinity between the two components and to evenly distribute the porogen, it is very important that the plasma generation time, the internal voltage, the pressure, and the rotational speed conditions are all satisfied as follows.

In the step of preparing the polyphenylene sulfide/porogen complex, a plasma may be generated for 1 to 30 minutes by applying a voltage of 0.1 to 4 kV inside the chamber under an oxygen, air, nitrogen or argon atmosphere. Preferably, the plasma may be generated for 10 to 20 minutes in an oxygen atmosphere and a voltage of 0.5 to 1 kV.

In addition, plasma treatment may be performed by rotating the chamber at a speed of 500 to 4000 rpm under the condition that the internal pressure of the chamber is 1.0 x 10 ² to 10 x 10 ² Pa. Preferably it can be carried out at a pressure of 2.0 x 10 ² to 8.0 x 10 ² Pa and a speed of 1300 to 3500 rpm, and more preferably at a pressure of 5.6 x 10 ² to 7.3 x 10 ² Pa and 2000 to 3000 rpm. speed, and most preferably at a pressure of 6.0 x 10 ² Pa and a speed of 2700 rpm.

At this time, if any one of the conditions of plasma generation time, internal voltage, pressure, and rotation speed is not satisfied, the polyphenylene sulfide polymer particles or ceramic particles are damaged or the friction force between the two components is lowered, so that the interface between the two materials A polyphenylenesulfide/porogen complex with improved affinity cannot be formed. In addition, the porogen may not be evenly dispersed on the surface of the polyphenylene sulfide polymer particles.

In particular, although not explicitly described in the following Examples or Comparative Examples, in the method for preparing a polyphenylene sulfide/porogen composite according to the present invention, a porous separator is formed using the composite prepared under different conditions Then, electrode adhesion and heat shrinkage were evaluated. Electrode adhesion was performed under heating and pressurization conditions at a temperature of 70° C. and a pressure of 600 kgf, and the thermal shrinkage was maintained in an oven heated to 150° C. for 30 minutes to measure the length of change in MD and TD directions. In addition, after manufacturing a lithium secondary battery using the separator, a charge/discharge test was performed 500 times by a conventional method.

As a result, unlike in other conditions and other numerical ranges, it was confirmed that when all of the following conditions were satisfied, the adhesion to the electrode was improved and thermal stability was improved due to the increase in the adhesion surface area due to the pores formed on the surface and inside of the separator fine and uniformly. . In addition, it was confirmed that the output and lifespan characteristics of the battery were maintained at a high level even after charging and discharging 500 times.

① the polyphenylene sulfide polymer particles have an average particle diameter of 100 to 500 μm, ② the porogen is spherical ceramic particles, ③ the spherical ceramic particles have an average particle diameter of 185 to 210 nm, ④ the spherical ceramic particles are Al ₂ O ₃ , SiO ₂ or a mixture thereof, ⑤ the step of preparing the polyphenylene sulfide / porogen complex is generated by applying a voltage of 0.5 to 1 kV inside the chamber under an oxygen atmosphere for 10 to 20 minutes, ⑥ The step of preparing the polyphenylene sulfide / porogen complex is performed by rotating the chamber at a speed of 2000 to 3000 rpm under the condition that the internal pressure of the chamber is 5.6 x 10 ² to 7.3 x 10 ² Pa, ⑦ the polyphenylene The sulfide/porogen complex may include polyphenylene sulfide polymer particles and porogen in a weight ratio of 4:6 to 6:4.

However, when any one of the above seven conditions was not satisfied, electrode adhesion was sharply decreased, and there was a problem in that thermal stability was deteriorated. In addition, as a result of charging and discharging, it was confirmed that the output and lifespan characteristics of the battery were remarkably deteriorated after 300 cycles.

In another embodiment of the present invention, manufacturing a separation membrane by molding the polyphenylene sulfide / porogen complex; cooling the separator to lower the crystallinity of the separator; And immersing the cooled separator in an acid or base solution to remove the porogen present on the surface and inside of the separator to prepare a porous separator in which pores are uniformly formed; a method for producing a porous separator for a lithium secondary battery comprising a to provide.

The manufacturing of the separation membrane may include: extruding the polyphenylene sulfide/porogen complex to prepare pellets; and compression molding the pellet to prepare a separation membrane.

In the step of preparing the pellet, extrusion may be performed at a die temperature of 250 to 275 °C and a screw speed of 80 to 200 rpm, preferably at a die temperature of 260 to 275 °C and a screw speed of 90 to 110 rpm. can do. In this case, if the die temperature and the screw speed do not satisfy all of the above ranges, it may not be possible to obtain pellets in which the porogen is homogeneously dispersed in the polyphenylene sulfide polymer particles. In particular, the polyphenylene sulfide polymer particles have a melting point of about 280 ° C. However, since it can be molded into a fiber form when a certain level of viscosity is secured, it is important to extrude by setting the maximum die temperature of 275 ° C, which is 5 ° C lower than the melting point. Do.

Compression molding in the step of manufacturing the separation membrane by compression molding the pellet may be performed at a temperature of 270 to 320 °C and a pressure of 3 to 6 MPa. Preferably it is carried out at a temperature of 290 to 310 °C and a pressure of 4 to 5.5 MPa, more preferably at a temperature of 300 °C and a pressure of 5 MPa. In this case, if neither of the above temperature and pressure ranges is satisfied, a separator having an even and uniform thickness may not be formed, and mechanical properties may be deteriorated. In addition, the polyphenylene sulfide polymer particles have a melting point of about 280 ° C., but in order to manufacture a separator of an appropriate thickness, the lower the viscosity when pressure is applied, the more advantageous. Contrary to the extrusion process, compression molding at a temperature higher than the melting point it's good

In the cooling of the separator, the separator may be rapidly cooled by immersing the separator in a dry ice/ethanol mixed solution in order to lower the polyphenylene sulfide crystallinity of the separator to 10% or less. In order to easily remove not only the porogens exposed on the surface of the separation membrane but also the porogens present therein, it is important to lower the polyphenylene sulfide crystallinity of the separation membrane. When the crystallinity of the polymer is lowered, the crystalline region decreases and the amorphous region increases. In the amorphous region, polymer chains form a random coil, thereby forming a free volume. Allow the acid or base solution to penetrate through the spaces to the porogens inside the separation membrane.

In the manufacturing of the porous membrane, porogen present on the surface and inside of the membrane may be removed by immersion in an acid or base solution for 20 to 30 hours. In this case, the acid or base solution may be KOH or HF that does not affect the polyphenylene sulfide polymer, and the KOH may be an alcohol/KOH saturated solution. Preferably, an HF solution can be used. The acid or base solution can easily dissolve the porogen to selectively remove only the porogen from the surface and the inside of the separation membrane.

The porous membrane may include an ionic functional group bonded to polyphenylene sulfide on the inner wall of the pores formed while the porogen is removed. The ionic functional group is an ionic functional group derived from porogen and is formed in a state of being coated on the inner wall of the pores of the separator, and the remaining 0.1 to 10.0 wt%, preferably 1.0 to 8.0 wt%, based on 100 wt% of the porous separator , more preferably 3.0 to 5.0% by weight.

The ionic functional group is a polar functional group derived from porogen, and is selected from the group consisting of an aluminate group (Al-O-Al), a siloxane group (Si-O-Si), and a titanate group (Ti-O-Ti). It may be one or more, preferably an aluminate group, a siloxane group, or a mixture thereof, and most preferably a siloxane group.

The ionic functional group can easily improve the ionic conductivity of the separation membrane without going through a synthetic reaction with a new component for improving the ionic conductivity. This is because the ionic functional group has a polar functional group, so it has a high affinity with ions in the electrolyte on the inner wall of the pores of the separator and increases the wetting property with most electrolytes having a functional group such as carbonate group, thereby improving the ionic conductivity of the membrane.

Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited by the following examples.

Example 1: Preparation of polyphenylene sulfide/porogen complex

Polyphenylene sulfide (PPS) polymer particles having an average particle diameter of 400 μm and porogen were used to prepare spherical silica particles having an average particle diameter of 200 nm. Then, a mixture of 50 g of PPS polymer particles and 50 g of porogen (spherical silica particles) was administered to the chamber of an elliptical rotor-type mixer coupled with plasma equipment. After forming a low vacuum state inside the chamber through a vacuum pump, oxygen was injected to adjust the pressure to have a pressure of 6.0 x 10 ² Pa. Mechanical and chemical kneading was performed by setting the rotation speed of the elliptical rotor in the chamber in the range of 2700 rpm. During the mechanochemical kneading, a voltage of 0.5 to 1 kV is applied inside the chamber and plasma is generated inside the chamber for 15 minutes so that the porogen (silica particles) forms a chemical bond on the surface of the PPS polymer particles. A polyphenylene sulfide/porogen (PPS/silica) composite having a structure coated with silica particles) was prepared.

Example 2: Preparation of a porous separator

The PPS/silica composite of Example 1 was put into an extruder and extruded. At this time, the die temperature was set to 260 ~ 275 ℃, the screw speed was set to 100 rpm, the extruded sample was processed into pellets of a certain size using a pelletizer (pelletizer). Next, the PPS/silica composite processed into pellets was compression-molded at 300° C. at about 5 MPa using a press machine to prepare a film-shaped separator. The compression molded separator was immersed in a dry ice/ethanol mixed solution and rapidly cooled to lower the crystallinity of the PPS medium to 10%.

The separation membrane was supported in 10% by weight of HF, an acid solution, for one day to remove the silica particle component present on the surface and inside of the separation membrane. At this time, pores were formed while the silica particles were removed, and it was confirmed that siloxane groups (Si-O-Si) derived from silica particles were bonded to the inner wall of the pores in an amount of 4.8 wt% based on 100 wt% of the separator. . In addition, as the silica particle component was removed from the space occupied by the silica particle, pores having a size of 200 ± 50 nm corresponding to the diameter of the silica particle were formed. The porous membrane with pores was immersed in distilled water several times to completely remove the HF solution present on the membrane surface and inside.

Comparative Example 1: Preparation of a porous separator

A porous separator using the PPS/silica composite was prepared in the same manner as in Examples 1 and 2, except that kneading was performed without generating plasma in the chamber during the preparation of the PPS/silica composite. At this time, as the silica component was removed from the space occupied by the silica particles, pores having a size of 2000 ± 600 nm were formed. The porous membrane with pores was immersed in distilled water several times to remove the HF solution present on the membrane surface and inside.

Experimental Example 1: Scanning electron microscope (SEM) analysis

A scanning electron microscope (SEM) analysis was performed on the porous separator prepared in Example 2 to confirm the thickness and pore size distribution of the separator. The results are shown in FIGS. 1 to 3 .

1 is a photograph of the porous separator prepared in Example 2.

2 is an SEM photograph of the porous separator prepared in Example 2 in the vertical direction (cross-section). 1 and 2, it was confirmed that the separation membrane was uniformly formed to a thickness of about 50.17 μm, and it was found that the pore sizes were evenly distributed. At this time, it was confirmed that the porosity of the porous separator was 69% by volume.

3 is an enlarged SEM photograph of pores formed in the vertical direction (cross-section) of the porous separator prepared in Example 2; Referring to FIG. 3 , it was confirmed that pores of uniform size were formed after the acid solution treatment on the inside as well as the surface of the separation membrane. In addition, it was confirmed that all silica particles were removed through the micropores in the separation membrane. It can be seen that this was achieved because the ratio of the amorphous region in the separator was increased by rapidly cooling the separator to lower the crystallinity. This is because the amorphous region of the polymer resin, unlike the crystalline region, has an irregular arrangement of polymer chains to form a fine free volume between the chains. It was found that pores were formed by dissolving and removing them.

Experimental Example 2: Charging/discharging performance evaluation

A half-cell of a lithium secondary battery was manufactured using the porous separator prepared in Example 2 and Comparative Example 1, an LFP (LiFePO ₄ ) positive electrode, and a lithium metal negative electrode. The half-cell thus prepared was charged and discharged, and the results are shown in FIG. 4 .

4 shows the results of measuring the charging and discharging performance of the lithium secondary battery using the porous separator prepared in Example 2 above. Referring to FIG. 4 , it was confirmed that the porous separator had stable charge/discharge performance by using the PPS/silica composite obtained through the mechanochemical reaction of plasma treatment.

In addition, although not explicitly disclosed in Experimental Example 2, it was confirmed that it can be expressed for a long time compared to a secondary battery using a conventional commercially available separator even under an environment requiring a high temperature of 200° C. or more and chemical stability.

On the other hand, in the case of Comparative Example 1, when a separator was prepared by dispersing silica particles in a PPS resin without a mechanochemical reaction process of plasma, the battery's inherent charge/discharge behavior was not measured. It can be seen that this is because the dispersibility of the silica particles is not good and the silica particles are largely agglomerated in some areas, so that the pores, which are passages for lithium ions between the electrodes, are not formed properly and are formed irregularly.

Through this, it was found that the aggregation of silica particles in the PPS resin was greatly suppressed by the mechanochemical reaction of the plasma treatment, so that the uniformity of the pore distribution could be controlled, and the pore size could also be easily adjusted according to the size of the silica particles. . In addition, as a result, it was found that the separation membrane had a uniform pore size and pore distribution, so that the amount of ion movement and ion permeability could be remarkably improved.

Claims (26)

polyphenylene sulfide polymer particles; and
Including; porogen coated on the surface of the polymer particle in a form surrounding the outside of the polyphenylene sulfide polymer particle;
The porogen is a polyphenylene sulfide / porogen composite that is a spherical ceramic fine particles.
According to claim 1,
The polyphenylene sulfide/porogen composite is a polyphenylene sulfide/porogen composite in which the polyphenylene sulfide polymer particles and the porogen are in a weight ratio of 1:9 to 9:1.
According to claim 1,
The polyphenylene sulfide polymer particles have an average particle diameter of 10 to 1000 ㎛ polyphenylene sulfide / porogen composite.
According to claim 1,
The spherical ceramic microparticles have an average particle diameter of 100 to 1000 nm.
According to claim 1,
The spherical ceramic fine particles is a polyphenylene sulfide / porogen composite that is at least one selected from the group consisting of metal nitride-based, metal sulfide-based and metal oxide-based.
6. The method of claim 5,
The metal nitride system is at least one selected from the group consisting of AIN, TiN, BN and InN,
The metal sulfide system is at least one selected from the group consisting of MoS ₂ , ZnS and WS ₂ ,
The metal oxide-based polyphenylene sulfide/porogen composite is at least one selected from the group consisting of Al ₂ O ₃ , SiO ₂ , ZnO, ZrO ₂ and TiO ₂ .
According to claim 1,
The polyphenylene sulfide / porogen composite is a polyphenylene sulfide polymer particle and a porogen mixed state, and plasma-treated in a dry process that does not use a solvent to form a structure in which the polymer particles are coated with porogen A phenylenesulfide/porogen complex.
A porous separator for a lithium secondary battery in which pores are uniformly formed inside and on the surface using the polyphenylene sulfide/porogen composite of any one of claims 1 to 7,
The pores are formed by removing the porogen from the polyphenylene sulfide/porogen complex,
The porous separator for a lithium secondary battery, wherein the inner wall of the pores includes an ionic functional group bonded to polyphenylene sulfide.
9. The method of claim 8,
The ionic functional group is at least one selected from the group consisting of an aluminate group (Al-O-Al), a siloxane group (Si-O-Si) and a titanate group (Ti-O-Ti). separator.
9. The method of claim 8,
The ionic functional group is a porous separator for a lithium secondary battery comprising 0.1 to 10% by weight based on 100% by weight of the porous separator.
9. The method of claim 8,
The porous separator has a porosity of 0.1 to 95% by volume of a porous separator for a lithium secondary battery.
9. The method of claim 8,
The porous separator is a porous separator for a lithium secondary battery that has a thickness of 10 to 1000 ㎛.
A lithium secondary battery comprising the porous separator of claim 8.
A device comprising the lithium secondary battery of claim 13,
The device will be any one selected from a communication device, a transportation device, and an energy storage device.
adding polyphenylene sulfide polymer particles and porogen to the chamber of the dry mixer; and
generating a plasma inside the chamber to prepare a polyphenylene sulfide/porogen complex having a coated structure by chemically bonding porogen to the surface of the polymer particle in a form surrounding the outside of the polyphenylene sulfide polymer particle;
A method for producing a polyphenylene sulfide / porogen complex comprising a.
16. The method of claim 15,
The step of preparing the polyphenylene sulfide / porogen complex is to generate plasma for 1 to 30 minutes by applying a voltage of 0.1 to 3 kV inside the chamber under an oxygen, air, nitrogen or argon atmosphere. A method for preparing a rosen complex.
16. The method of claim 15,
Polyphenylene sulfide which is performed by rotating the chamber at a speed of 1000 to 8000 rpm under the condition that the internal pressure of the chamber is 1.0 x 10 ² to 10 x 10 ² Pa in the step of preparing the polyphenylene sulfide / porogen complex / Method for producing the porogen complex.
16. The method of claim 15,
The polyphenylene sulfide polymer particles have an average particle diameter of 100 to 500 μm,
The porogen is a spherical ceramic particle,
The spherical ceramic particles have an average particle diameter of 185 to 210 nm,
The spherical ceramic fine particles are Al ₂ O ₃ , SiO ₂ or a mixture thereof,
In the step of preparing the polyphenylene sulfide / porogen complex, a voltage of 0.5 to 1 kV is applied to the inside of the chamber under an oxygen atmosphere to generate plasma for 10 to 20 minutes,
The step of preparing the polyphenylene sulfide / porogen complex is performed by rotating the chamber at a speed of 2000 to 5000 rpm under the condition that the internal pressure of the chamber is 5.6 x 10 ² to 7.3 x 10 ² Pa,
The polyphenylene sulfide / porogen complex is a method for producing a polyphenylene sulfide / porogen complex consisting of polyphenylene sulfide polymer particles and porogen in a weight ratio of 4:6 to 6:4.
A method for manufacturing a separation membrane comprising: forming a polyphenylene sulfide/porogen complex of any one of claims 1 to 7;
cooling the separator to lower the crystallinity of the separator; and
preparing a porous separator having uniform pores by immersing the cooled separator in an acid or base solution to remove porogen present on the surface and inside of the separator;
A method of manufacturing a porous separator for a lithium secondary battery comprising a.
20. The method of claim 19,
The step of preparing the separation membrane,
extruding the polyphenylene sulfide/porogen complex to prepare pellets; and
manufacturing a separation membrane by compression molding the pellet;
A method of manufacturing a porous separator for a lithium secondary battery comprising a.
21. The method of claim 20,
Extrusion in the step of preparing the pellet is a method for producing a porous separator for a lithium secondary battery that is performed at a die temperature of 250 to 275 ℃ and a screw speed of 80 to 200 rpm.
21. The method of claim 20,
Compression molding in the step of preparing the separator is a method of manufacturing a porous separator for a lithium secondary battery that is performed at a temperature of 270 to 320 ℃ and a pressure of 3 to 6 MPa.
20. The method of claim 19,
The method for producing a porous separator for a lithium secondary battery, wherein the acid or base solution is KOH or HF.
20. The method of claim 19,
The porous separator is a method of manufacturing a porous separator for a lithium secondary battery comprising an ionic functional group bonded to polyphenylene sulfide on the inner wall of the pores.
20. The method of claim 19,
The ionic functional group is at least one selected from the group consisting of an aluminate group (Al-O-Al), a siloxane group (Si-O-Si) and a titanate group (Ti-O-Ti). A method for manufacturing a separation membrane.
20. The method of claim 19,
The method for manufacturing a porous separator for a lithium secondary battery, wherein the ionic functional group comprises 0.1 to 10% by weight based on 100% by weight of the porous separator.

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