KR102658662B1 - A separator for an electrochemical device and a method of manufacturing the separator - Google Patents

Abstract

The present invention is a method of manufacturing a separator for an electrochemical device containing a silicon-based cathode, comprising the step of simultaneously electrospinning a first spinning solution containing inorganic particles and a second spinning solution containing a binder polymer to form a freestanding porous separator. It includes, and the flow rate of the first spinning solution is greater than the flow rate of the second spinning solution.

Description

Separator for electrochemical devices and method of manufacturing the separator {A SEPARATOR FOR AN ELECTROCHEMICAL DEVICE AND A METHOD OF MANUFACTURING THE SEPARATOR}

The present invention relates to a method of manufacturing a separator for an electrochemical device including a silicon-based cathode, and a separator for an electrochemical device manufactured thereby.

Electrochemical devices convert chemical energy into electrical energy using an electrochemical reaction. Recently, lithium secondary batteries, which have high energy density and voltage, long cycle life, and can be used in various fields, have been widely used.

A lithium secondary battery may include an electrode assembly made of a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, and the electrode assembly may be manufactured by being stored in a case together with an electrolyte solution. The positive electrode can provide lithium ions, and the lithium ions can pass through a separator made of a porous material and move to the negative electrode. The cathode preferably has an electrochemical reaction potential close to that of lithium metal and allows insertion and desorption of lithium ions. A negative electrode containing a carbon-based active material such as graphite has the advantage of being stable and having an excellent cycle life due to little change in crystal structure due to insertion and desorption of lithium ions.

Recently, as demand for lithium secondary batteries with larger capacity and higher energy density, such as those used in electric vehicles and energy storage devices, has increased, the development of non-carbon-based active materials using silicon, etc., which has higher capacity than carbon-based active materials, has been increasing. It is being done. However, since the volume of a lithium secondary battery containing a silicon-based negative electrode rapidly expands during the charging process, the separator may be deformed as charging and discharging are repeated, and deformation or damage to the separator may result in poor insulation or deterioration of the lifespan of the lithium secondary battery. It can lead to

Therefore, in electrochemical devices using silicon-based cathodes, research is being conducted on separators with compression resistance that do not cause deformation even when the cathode expands.

Korean Patent Publication No. 2021-0046405 Korean Patent Publication No. 2021-0033327

The present invention aims to provide, in an electrochemical device including a silicon-based cathode, a separator with a structure that is not deformed or damaged even when compressed by the cathode expanding during charging, a method of manufacturing the separator, and an electrochemical device including the separator. Do this.

One aspect of the present invention is a separator for an electrochemical device including a silicon-based cathode, wherein the separator is a freestanding porous separator that does not contain a polyolefin substrate, and includes a binder polymer and inorganic particles, with the inorganic particles being more concentrated than the binder polymer. A separator for an electrochemical device comprising an excess amount of is provided.

In the separator for an electrochemical device, the separator may include 60 to 95% by weight of the inorganic particles based on the total weight of the separator.

In the separator for electrochemical devices, the separator satisfies a thickness of 15 to 45㎛, and the value defined by the following equation 1 may be 1 to 18% or less.

[Equation 1]

(T1 - T2) / T1 × 100

In equation 1 above,

T1 is the initial thickness of the separator,

The T2 refers to the thickness of the separator after pressing it at 5.2 MPa and 70°C for 10 seconds in a cotton rolling mill.

Another aspect of the present invention provides an electrochemical device including an anode, a silicon-based cathode, a separator for an electrochemical device according to the above-described aspect, positioned between the anode and the silicon-based cathode, and an electrolyte.

Another aspect of the present invention is a method of manufacturing a separator for an electrochemical device including a silicon-based cathode, wherein a first spinning solution containing inorganic particles and a second spinning solution containing a binder polymer are simultaneously electrospun to produce freestanding (freestanding) material. ) It includes the step of forming a porous separator, wherein the flow rate of the first spinning solution is greater than the flow rate of the second spinning solution.

In the method of manufacturing a separator for an electrochemical device, the silicon-based anode may include one or more silicon-based active materials selected from the group consisting of Si, SiOx (0<x<2), SiC, and Si alloy.

In the method for manufacturing a separator for an electrochemical device, the inorganic particles are SiO ₂ , Al ₂ O ₃ , AlOOH, TiO ₂ , ZrO ₂ , BaSO ₄ , BaTiO ₃ , ZnO, MgO, Mg(OH) ₂ , Al(OH) ) ₃ , Pb(Zr,Ti)O ₃ , Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, It may be one or more selected from the group consisting of CaO, Y ₂ O ₃ , SiC, ZnSn(OH) ₆ , Zn ₂ SnO ₄ , ZnSnO ₃ , Sb ₂ O ₃ , Sb ₂ O ₄ and Sb ₂ O ₅ .

In the method for manufacturing a separator for an electrochemical device, the binder polymer is polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, polyetherimide, polysulfone, polyvinylidene fluoride, polyacrylonitrile, and polyethylene. , polypropylene, polyisoprene, polyethylene oxide, polypropylene oxide, polyvinylpyrrolidone, polyvinyl alcohol, polystyrene, polyacrylic acid, polymethyl methacrylate, polyacrylamide and derivatives thereof. there is.

In the method of manufacturing a separator for an electrochemical device, the step of forming the freestanding porous separator may be electrospinning the first spinning solution at a flow rate of 80 to 100 μl/min and 1 to 10 μl/min, respectively. .

The method of manufacturing a separator for an electrochemical device may further include pressurizing the separator formed in the step of forming the freestanding porous separator at 25 to 60°C.

In the method of manufacturing a separator for an electrochemical device, the resistance increase rate of the separator for an electrochemical device before and after the pressurizing step may be 50% or less.

The separator for electrochemical devices according to the present invention satisfies a thickness of 15 to 45 ㎛, the value defined by Equation 1 above is 1 to 18% or less, and the resistance increase rate after compression is 50% or less, and contains a silicon-based active material. Even when the separator is compressed as the cathode expands, the separator is not deformed or damaged.

Therefore, the electrochemical device including the separator can provide improved capacity and energy density and stable cycle characteristics by using a silicon-based anode.

Figure 1 is a graph showing the charge/discharge efficiency (Coulombic efficiency) according to the charge/discharge cycle of the pouch cell according to Example 1 and Comparative Example 3 in Experimental Example 2 of the present invention.
Figure 2 is a graph showing the areal capacity according to the charge/discharge cycle of the pouch cell according to Example 1 and Comparative Example 3 in Experimental Example 2 of the present invention.
Figure 3 is a graph showing the thickness of the separator according to Preparation Example 1 and Comparative Example 3 before and after compression in Experimental Example 3 of the present invention.
Figure 4 is a graph showing (a) the ionic conductivity of the separator according to Preparation Example 1 and (b) the ionic conductivity of the separator according to Comparative Example 3 in Experimental Example 3 of the present invention.
Figure 5 shows (a) an SEM image of the separator according to Preparation Example 1 before pressurization, (b) an SEM image of the separator according to Preparation Example 1 after pressurization, and (c) the separator according to Comparative Example 3 in Experimental Example 3 of the present invention. (d) SEM image before pressurization, (d) SEM image after pressurization of the separator according to Comparative Example 3.

Hereinafter, each configuration of the present invention will be described in more detail so that those skilled in the art can easily implement it. However, this is only an example, and the scope of rights of the present invention is determined by the following contents. Not limited.

As used herein, the term “comprising” is used to list materials, compositions, devices, and methods useful in the present invention and is not limited to the listed examples.

As used herein, “about” and “substantially” are used to mean a range or approximation of a number or degree, taking into account inherent manufacturing and material tolerances, and are provided as precise or absolute values to aid understanding of the present invention. is used to prevent infringers from unfairly using the mentioned disclosure.

As used herein, “electrochemical device” may mean a primary battery, secondary battery, super capacitor, etc.

As used herein, “particle size” means D50, which is the particle size corresponding to 50% of the cumulative distribution of particle numbers according to particle size, unless otherwise specified.

As used herein, “molecular weight” refers to the weight average molecular weight (Mw), unless otherwise specified, and the weight average molecular weight is polystyrene measured by gel permeation chromatography (GPC) using monodisperse polystyrene polymer as a standard material. Corresponds to the converted molecular weight.

One embodiment of the present invention is a method of manufacturing a separator for an electrochemical device containing a silicon-based cathode, wherein a free-standing porous separator is produced by simultaneously electrospinning a first spinning solution containing inorganic particles and a second spinning solution containing a binder polymer. A method including forming steps is provided.

A conventional porous separator forms a coating layer containing inorganic particles and a binder polymer on at least one side of a porous substrate, and the porous substrate uses a polyolefin substrate or nonwoven fabric manufactured through a dry or wet process. The freestanding porous separator refers to a separator in which a pore structure is formed using inorganic particles and a binder polymer without a porous substrate as described above. A separator that does not contain a porous substrate may be vulnerable to external forces and have low compression resistance as its outer shape is formed only with inorganic particles and binder polymers.

One embodiment of the present invention provides a free-standing porous separator having excellent compression resistance by composing a high content of inorganic particles compared to the binder without using a polyolefin substrate. Specifically, in one embodiment of the present invention, the flow rate of the first spinning solution is greater than the flow rate of the second spinning solution in the step of forming the freestanding porous separator.

Compression resistance can be expressed by the resistance increase rate or thickness ratio before and after pressurizing the separator under certain conditions. Excellent compression resistance means that even when the separator is pressed due to low compression resistance, the original pore structure is maintained and lithium ions can move smoothly. In addition, excellent compression resistance means excellent durability against external forces, so that deformation or damage to the separator is minimized or does not occur.

In one embodiment of the present invention, a freestanding porous separator is manufactured by electrospinning, so that a relatively small amount of binder polymer can be used compared to other manufacturing methods such as die coating, bar coating, dip coating, and roll coating. Through this, the content of the binder polymer can be reduced and a separator with a relatively high inorganic particle content can be manufactured. At the same time, electrospinning can achieve uniform distribution of inorganic particles compared to other manufacturing methods, and is therefore suitable for manufacturing a separator with properties suitable for use in electrochemical devices containing a silicon-based cathode.

The silicon-based negative electrode may include one or more silicon-based active materials selected from the group consisting of Si, SiOx (0<x<2), SiC, and Si alloy. For example, the Si alloy may include LiSi alloy, CoSi alloy, or TiSi alloy. Preferably, the silicon-based active material may contain 50% by weight or more of pure Si relative to the total weight. More preferably, the silicon-based active material may be composed only of pure Si.

Electrospinning can be performed by applying voltage between a nozzle through which a polymer solution is discharged and a current collector through which the polymer solution discharged from the nozzle is collected. The nozzle is connected to a container such as a syringe that stores the polymer solution, so that the polymer solution can be supplied at a predetermined flow rate. The nozzle may be charged with a positive or negative charge, and the current collector plate may be charged with an opposite charge to the nozzle or may be grounded. For example, the current collector plate may be a metal plate that collects the polymer solution radiated in the form of fibers, but its shape or size is not limited.

First, polymer droplets maintained by surface tension may form at the tip of the nozzle. At this time, when a high voltage of about 10 to 30 kV is applied to the nozzle, Coulomb's force due to an external electric field may be greater than the surface tension of the polymer droplet, and the polymer droplet may exhibit a cone shape (Taylor cone). You can. Preferably, by applying a high voltage of about 12 to 18 kV to the nozzle, a jet of polymer fibers can be spun and stretched from the cone-shaped polymer droplets, and the polymer fibers move in the direction of the current collector and are collected. It may coagulate afterward.

The step of forming the freestanding porous separator includes preparing a first spinning solution containing inorganic particles. The first spinning solution may be a dispersion of inorganic particles mixed with a dispersion medium.

The inorganic particles may be inorganic nanoparticles having an average particle diameter (D50) of 10 to 1,000 nm, preferably 10 to 500 nm, and more preferably 200 to 300 nm. The inorganic particles may be connected to and fixed to adjacent inorganic particles by a binder polymer, which will be described later, and the interstitial volume between the inorganic particles may be formed as pores of the separator. When the average particle diameter of the inorganic particles is within the above range, uniform pores can be formed in the separator. A separator with more uniform pores facilitates the movement of lithium ions and increases the impregnation rate of the electrolyte solution, which can contribute to improving battery performance.

The inorganic particles are SiO ₂ , Al ₂ O ₃ , AlOOH, TiO ₂ , ZrO ₂ , BaSO ₄ , BaTiO ₃ , ZnO, MgO, Mg(OH) ₂ , Al(OH) ₃ , Pb(Zr,Ti)O ₃ , Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, Y ₂ O ₃ , SiC, ZnSn( OH) ₆ , Zn ₂ SnO ₄ , ZnSnO ₃ , Sb ₂ O ₃ , Sb ₂ O ₄ and Sb ₂ O ₅ It may include one or more selected from the group consisting of. The inorganic material may be electrochemically stable so that no chemical reaction occurs within the operating voltage range of the electrochemical device. Preferably, the inorganic material may be one or more selected from the group consisting of SiO ₂ , Al ₂ O ₃ , AlOOH, TiO ₂ , ZrO ₂ and Al(OH) ₃ .

The dispersion may be a colloidal solution formed by mixing the inorganic particles and the dispersion medium. The dispersion medium may be water or alcohol that does not substantially dissolve the inorganic particles, but is not limited thereto. The dispersion medium may evaporate after forming the free-standing porous separator and not remain in the separator.

The first spinning solution may contain about 5 to 15% by weight of the inorganic particles based on the total weight. Preferably, the content of the inorganic particles may be about 8 to 12% by weight. The inorganic particles exhibit uniform dispersibility in the dispersion medium within the above content range, and uniform distribution of the inorganic material in the separation membrane can be achieved.

The first spinning solution may further contain polymers in addition to the inorganic particles and may have viscosity. The polymer may be one or more of the polymers that can be used as a binder polymer in the present invention, but may be different from the binder polymer used in the second spinning solution.

The step of forming the freestanding porous separator includes preparing a second spinning solution containing a binder polymer. The second spinning solution may be a binder polymer solution in which the binder polymer is dissolved in a solvent.

The binder polymer may have a molecular weight of 100,000 to 200,000, preferably 120,000 to 180,000, and more preferably 140,000 to 160,000. If the molecular weight of the binder polymer is lower than the above range, electrospinning cannot be performed while maintaining the shape of the fiber. If the molecular weight of the binder polymer is higher than the above range, the viscosity of the second spinning solution increases, preventing smooth electrospinning.

The binder polymer is polyethylene terephthalate (PET), polybutylene terephthalate, polyamide, polyimide, polyetherimide, polysulfone, poly polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP), polyisoprene, polyethylene oxide (PEO) , polypropylene oxide, polyvinyl pyrrolidone (PVP), polyvinyl alcohol (PVA), polystyrene, polyacrylic acid, polymethyl methacrylate It may be one or more selected from the group consisting of methacrylate (PMMA), polyacrylamide, and derivatives thereof. Preferably, the binder polymer may be a polymer that has excellent heat resistance at 150 to 200°C, and the manufactured separator has excellent thermal stability and can prevent internal short circuit of the electrochemical device. More preferably, the binder polymer may be at least one selected from the group consisting of polyethylene terephthalate, polyacrylonitrile, and polyphenylene oxide.

The solvent may be one or more organic solvents such as alcohol, acetone, dimethylacetamide (DMAc), dimethylformamide (DMF), and methylene chloride, but is not limited thereto. The solvent may evaporate after forming the free-standing porous separator and not remain in the separator.

The second spinning solution may contain about 5 to 20% by weight of the binder polymer based on the total weight. Preferably, the content of the binder polymer may be about 5 to 12% by weight. More preferably, the content of the binder polymer may be about 8 to 10% by weight. If the content of the binder polymer is lower than the above range, the viscosity of the second spinning solution is lowered and the fiber shape cannot be maintained during electrospinning. If the content of the binder polymer is higher than the above range, the viscosity of the second spinning solution increases, preventing smooth electrospinning.

Preparation of the first spinning solution and preparation of the second spinning solution may be performed simultaneously or in any order.

The step of forming a free-standing porous separator is to form a free-standing porous separator by simultaneously electrospinning the first spinning solution and the second spinning solution.

The first spinning liquid and the second spinning liquid may each be stored in a container equipped with a nozzle and then electrospun on one current collector plate. For example, the container may be a syringe, and the injection flow rate of the syringe in which the first radiation solution is stored may be higher than the injection flow rate in which the second radiation solution is stored. The electrospinning method of the first spinning solution and the second spinning solution is not limited as long as it can ensure uniform distribution of inorganic particles and binder polymer in the manufactured separator. Preferably, the first spinning liquid and the second spinning liquid may be well mixed with each other on the current collector plate and spun to form a flat plate shape.

The first spinning solution may be electrospun at a flow rate of 80 μl/min or more. Preferably, the first spinning solution may be electrospun at a flow rate of 80 to 100 μl/min. The content of inorganic particles contained in the separation membrane may be determined by the electrospinning flow rate of the first spinning solution. If the electrospinning flow rate of the first spinning solution is lower than the above range, the performance of the electrochemical device deteriorates due to an increase in the content of the binder polymer that acts as a resistor in the separator. If the electrospinning flow rate of the first spinning solution is lower than the above range, the compression resistance of the separator decreases due to an increase in the binder polymer content, making it impossible to apply to an electrochemical device including a silicon-based cathode.

The second spinning solution may be electrospun at a flow rate of 1 μl/min or more. Preferably, the second spinning solution may be electrospun at a flow rate of 1 to 10 μl/min. If the electrospinning flow rate of the second spinning solution is higher than the above range, the produced separator cannot secure sufficient compression resistance and cannot be applied to an electrochemical device using a silicon-based cathode.

The first spinning solution and the second spinning solution may be spun in the form of fibers and collected on the current collector plate. The method of manufacturing the separator includes leaving the freestanding porous separator at room temperature or drying it in an oven at room temperature to 60° C. to evaporate and remove the remaining solvent and dispersion that did not evaporate during the electrospinning process. It may further include.

The method of manufacturing a separator for an electrochemical device may further include pressurizing the separator formed in the step of forming the free-standing porous separator at 25 to 60°C.

The step of pressurizing the separator may include rolling the formed separator at a rolling rate of 10 to 50% and then rolling it with a rolling mill so that the thickness of the separator is 15 to 45 ㎛. If the rolling temperature, pressure, and rolling rate are outside the range, the inorganic particles contained in the separator may be destroyed. The rolling mill may be a roll rolling mill that injects and rolls a separator while the upper and lower rolls rotate. Preferably, the step of pressurizing the separator may include rolling the separator to 25 to 40% in a rolling mill so that the thickness of the separator after rolling is 20 to 40 ㎛.

The separator for electrochemical devices manufactured according to the method described above is a free-standing porous separator that does not form a coating layer containing inorganic particles and binder polymer on a porous substrate, and has a high content of inorganic particles compared to the binder polymer, and the inorganic particles are contained in the separator. distributed evenly throughout the body. The separator is not deformed or damaged even when the negative electrode containing the silicon-based active material expands, and has excellent compression resistance, so the resistance increase rate can be maintained below 50% even when the electrochemical device is repeatedly charged and discharged.

Another embodiment of the present invention provides a separator for an electrochemical device including a silicon-based cathode. The separator is a free-standing porous separator that does not contain a polyolefin substrate, and includes a binder polymer and inorganic particles, with the inorganic particles in excess of the binder polymer. The separator may be manufactured according to the separator manufacturing method according to the above and previous embodiments, and the same description as in the previous embodiment is replaced with the description of the above embodiment.

The separator is manufactured by simultaneously electrospinning a first spinning solution containing inorganic particles and a second spinning solution containing a binder polymer. During electrospinning, the flow rates of the first spinning solution and the second spinning solution can be adjusted to control the content of inorganic particles and binder polymer contained in the separator. When manufacturing a separator, the electrospinning flow rate of the first spinning solution may be greater than the electrospinning flow rate of the second spinning solution, so that the inorganic particles may be included in excess compared to the binder polymer. Specifically, the separator may contain 60 to 95% by weight of the inorganic material relative to the total weight of the separator. Preferably, the separator may contain 85 to 95% by weight of the inorganic material relative to the total weight. When the inorganic content is within the above range, the separator can provide compression resistance that can be used in an electrochemical device using a silicon-based anode.

The thickness of the separator may be 15 to 45 ㎛. Preferably, the thickness of the separator may be 20 to 40 ㎛. When the thickness of the separator is within the above range, deformation or damage to the separator due to expansion of the negative electrode containing the silicon-based active material can be minimized. If the thickness of the separator is lower than the above range, the separator may be damaged due to expansion of the separator. If the thickness of the separator is higher than the above range, it becomes difficult to move lithium ions through the separator.

The separator may have a resistance increase rate of 50% or less before and after compression. For example, when the separator is compressed for 10 seconds at 70°C and 5.2 MPa using a cotton rolling mill (Rhotec, pressing machine, V-30), the change in resistance before and after compression is within 0.01 to 1 Ohm. It can be.

The separation membrane may have a thickness change rate of 18% or less before and after compression, as defined by Equation 1 below. Preferably, the separation membrane may have a thickness change rate of 1 to 18% before and after compression. More preferably, the thickness change rate before and after compression may be 1 to 15%.

[Equation 1]

(T1 - T2) / T1

In equation 1 above,

T1 is the initial thickness of the separator,

The T2 refers to the thickness of the separator after pressing it in a cotton rolling mill (Rhotec pressing machine V-30) at 5.2 MPa, 70°C, and 10 seconds.

A separator that satisfies the resistance increase rate or the thickness change rate range maintains its pore structure before and after pressurization, enabling smooth movement of lithium ions, and even if the negative electrode containing the silicon-based active material expands, deformation or damage to the separator may be minimized or not occur. .

The separator may not substantially change in dimensions at a high temperature of 150°C or higher, and the volume change rate may be 1.5% or less.

The separator may have pores with an average size of 500 to 1,000 nm and a porosity of 50 to 60%. The separator may have a porosity of 100 sec/100cc or less in air permeability.

Another embodiment of the present invention provides an electrochemical device including an anode, a silicon-based cathode, a separator as described above, and an electrolyte solution. For example, the electrochemical device may be a lithium secondary battery including a positive electrode that provides lithium ions.

An electrochemical device can be manufactured by inserting the anode, cathode, separator, and electrolyte into a case or pouch and sealing it. The shape of the case or pouch is not limited. For example, the electrochemical device may be a cylindrical, prismatic, coin-shaped, or pouch-shaped lithium secondary battery.

The lithium secondary battery can be packed or modularized as a unit cell and used in electric vehicles (BEV), hybrid electric vehicles (HEV), plug-in hybrid vehicles (PHEV), electric motor bicycles, power storage devices, etc.

Below, the present invention will be described in more detail through specific examples and experimental examples. The following examples and experimental examples are intended to illustrate the present invention, and the present invention is not limited by the following examples and experimental examples.

Manufacturing Example 1

Manufacture of separation membrane

As a binder, 1.8 g of polyacrylonitrile (PAN) with a weight average molecular weight of 150,000 was added to 18.2 g of dimethylformamide (DMF) and stirred at 70°C at 250 rpm to prepare the first spinning solution, which is a solution of the binder. . The first spinning solution was injected into the first 10 mL syringe to which the nozzle was connected.

2.0 g of alumina (Al ₂ O ₃ ), an inorganic material with an average particle diameter (D50) of 450 nm, was added to 5.4 g of butanol (n-butanol) and 12.6 g of acetone, and then bead milled for 1 hour at room temperature. ) to prepare a second spinning solution, which is a dispersion of the inorganic material. The second spinning solution was injected into a 10 mL second syringe connected to a nozzle.

A current collector plate measuring 10 cm × 10 cm was placed under the nozzles of the first and second syringes, and the current collector plate was grounded. A voltage of 18 kV was applied to the nozzle and current collector of each syringe, and the first syringe was simultaneously injected at 80 μl/min and the second syringe at 4.5 μl/min for about 180 minutes to prepare a separator. Afterwards, it was dried at 60°C under vacuum conditions for 12 hours to remove the remaining solvent and dispersion medium.

The separator was injected into a roll mill (Rhotec) and compressed to obtain a separator with a thickness of about 30 ㎛.

Production example 2

A separator was prepared in the same manner as in Example 1, except that the first syringe was simultaneously injected at 90 μl/min and the second syringe was injected at 4.5 μl/min.

Production example 3

A separator was prepared in the same manner as in Example 1, except that the first syringe was simultaneously injected at 55 μl/min and the second syringe was injected at 4.5 μl/min.

Production example 4

A separator was prepared in the same manner as in Example 1, except that the first syringe was simultaneously injected at 70 μl/min and the second syringe was injected at 4.5 μl/min.

Example 1

Manufacturing of anode

A positive electrode slurry containing lithium manganese complex oxide (NCMA), a positive electrode active material, was applied to an aluminum thin film, dried, and compressed in a roll mill to prepare a positive electrode with a porosity of 26% and a capacity per unit area of 4.5 mAh/cm ² .

Preparation of cathode

A negative electrode slurry containing a carbon-based negative electrode active material was applied to a copper thin film, dried, and compressed in a roll mill to prepare a negative electrode with a porosity of 40% and a capacity per unit area of 8.5 mAh/cm ² .

Preparation of electrolyte solution

As an organic solvent, fluoroethylene carbonate (FEC) and ethylmethyl carbonate (EMC) were mixed at a volume ratio of 3:7, and LiPF ₆ was added to prepare an electrolyte solution with a LiPF ₆ concentration of 1.0M.

Manufacturing of electrochemical devices

A pouch-shaped monocell was manufactured as an electrochemical device using the anode, cathode, and electrolyte prepared as above, and the separator prepared according to Preparation Example 1.

The anode was cut to a size of 4 × 4 cm ² , and then the 0.5 × 1 cm ² at the top was welded with an aluminum tab having a width of 1 cm. The cathode was cut to a size of 4.5 × 4.5 cm ² , and then the 0.5 × 1 cm ² at the top was welded with a nickel tab having a width of 1 cm. The separator was cut to a size of ⁵ Cells were prepared.

Example 2

A pouch cell was manufactured in the same manner as in Example 1, except that the separator prepared according to Preparation Example 2 was used when manufacturing the electrochemical device.

Comparative Example 1

A pouch cell was manufactured according to the same method as Example 1, except that the separator prepared according to Preparation Example 3 was used when manufacturing the electrochemical device.

Comparative Example 2

A pouch cell was manufactured according to the same method as Example 1, except that the separator prepared according to Preparation Example 4 was used when manufacturing the electrochemical device.

Comparative Example 3

Manufacture of separation membrane

Alumina, boehmite, and dispersant (polyvinylpyrrolidone) are dispersed in acetone as inorganic particles, and polyvinylidene fluoride-hexafluoropropylene and chlorotrifluoroethylene are further added as polymer binders to form a porous coating layer. A slurry was prepared. Alumina, boehmite, polyvinylidene fluoride-hexafluoropropylene, chlorotrifluoroethylene, and dispersant were used in a weight ratio of 66.3:11.7:15.5:4.5:2.

A polyethylene porous substrate with a thickness of 15㎛ was coated on both sides using a dip coating method using a slurry for forming a porous coating layer. The porous coating layer was formed to a thickness of 4㎛ on each side, thereby producing a separator with a total thickness of 23㎛.

Manufacturing of electrochemical devices

A pouch cell was manufactured in the same manner as in Example 1, except that the separator prepared according to Comparative Example 1 was used when manufacturing the electrochemical device.

Experimental Example 1. Confirmation of separator properties and cell operation according to inorganic material injection speed

When the separators according to Preparation Examples 1 to 4 were manufactured to the same thickness, the required rolling rate and air permeability were confirmed as physical properties of the separator, and the results are shown in Table 1 below.

Measuring the thickness of the separator

The thickness of the separator was measured using a thickness gauge (Mitutoyo, VL-50S-B).

Breathability measurement

Breathability was measured using a Gurley densometer (Gurley, 4110N) to measure the time it takes for 100 cc of air to penetrate a separator with a diameter of 28.6 mm and an area of 645 mm ² .

Check whether the cell is running

When the pouch cell including the separator was manufactured (Examples 1 and 2, Comparative Examples 1 and 2), whether the pouch cell was operated according to the difference in the electrospinning flow rate of the first spinning solution was checked. The results are shown in Table 1 below. indicated.

division of the first spinning solution
electrospinning flow rate
(㎛/min) Separator thickness
(㎛) rolling rate
(%) ventilation
(sec/100cc) cell drive
Whether Comparative Example 1
(Production Example 3) 55 30 63 25 × Comparative Example 2
(Production Example 4) 70 30 50 39 × Example 1
(Production Example 1) 80 30 40 63 ○ Example 2
(Production Example 2) 90 30 25 67.4 ○

Referring to Table 1, it was confirmed that the separator used in Examples 1 and 2 contained an excessive amount of inorganic material compared to the binder, resulting in a low rolling rate and normal cell operation. On the other hand, the separator used in Comparative Examples 1 and 2 showed a high rolling rate and low air permeability, and it was confirmed that cell operation was not possible. These results indirectly indicate that the inorganic particles were destroyed during the process of pressing at a high rolling rate, resulting in the pores of the separator being clogged or the uniformity being reduced.

Experimental Example 2. Checking charge/discharge efficiency and capacity according to cycle

The charge/discharge efficiency (coulombic efficiency) and area capacity (areal capacity) according to the charge/discharge cycle of the pouch cells according to Example 1 and Comparative Example 3 were confirmed and shown in Figures 1 and 2, respectively.

Referring to Figure 1, the pouch cell of Example 1 including the separator according to Preparation Example 1 manufactured by electrospinning did not show a decrease in charge and discharge efficiency during 500 charge and discharge cycles, but the pouch cell of Comparative Example 3 It started to decrease from episode 200 and decreased by more than 5% at episode 500.

Referring to FIG. 2, the pouch cell of Example 1 including the separator according to Preparation Example 1 manufactured by electrospinning showed a capacity reduction rate of less than 8% during 200 charge and discharge cycles, whereas the pouch cell of Comparative Example 3 showed a capacity reduction rate of less than 8% during 200 charge and discharge cycles. Cells were found to have decreased by more than 70%.

This result is due to the fact that as the cathode containing pure-Si expands, the separator is deformed and the lifespan of the pouch cell deteriorates.

Experimental Example 3. Confirmation of physical properties of the separator after compression

Compression resistance evaluation

Two sheets of PET film (35 ㎛) with an area of 5 × 5 cm ² were placed on two sheets of A4 paper, and a separator with an area of 5 × 5 cm ² was placed on the PET film. One PET film (35 ㎛) with an area of 5 × 5 cm ² was placed on the separator, and two sheets of A4 paper were placed on the PET film. Pressure was applied to the A4 paper arranged up and down for 10 seconds at 70°C and 5.2 MPa using a cotton rolling mill (Rhotec, pressing machine, V-30).

Ionic conductivity measurement

A SUS spacer was used as a working electrode and a counter electrode, and the separator before and after the compression resistance evaluation was cut into a circle with a diameter of 19 mm and inserted between these electrodes to form a coin-shaped cell (blocking cell). ) was prepared, and then the ion conductivity was measured by measuring the impedance.

Compression resistance evaluation and ionic conductivity were measured for the separator of Preparation Example 1 and the separator of Comparative Example 3, and the results are shown in Figures 3 and 4, respectively. SEM images (×20K, 10kV) before and after compression resistance evaluation of the separator of Preparation Example 1 and Comparative Example 3 are shown in Figure 5.

Referring to FIG. 3, the separator of Preparation Example 1 showed a thickness reduction of about 15% after compression, while the thickness of the separator of Comparative Example 3 decreased by about 17% after compression.

Referring to (a) of Figure 4, the separator of Preparation Example 1 showed a resistance increase rate of 23.6% before and after compression, and referring to (b) of Figure 4, the separator of Comparative Example 3 showed a resistance increase rate of 68.5% before and after compression. .

The above results indicate that the separator according to Preparation Example 1 had excellent compression resistance and showed a low resistance increase rate before and after compression, which is consistent with the SEM image observation results in FIG. 5. Specifically, in Figure 5 (a) the separator according to Preparation Example 1 before pressurization and (b) the separator according to Preparation Example 1 after pressurization, the pore structure was well maintained before and after pressurization. However, when comparing the separator according to Comparative Example 3 before pressurization in (c) of FIG. 5 and the separator according to Comparative Example 3 after pressurization in (d) of FIG. 5, Comparative Example 3 shows pores such as part of the pores being blocked after pressurization. It was confirmed that the structure had collapsed.

Experimental Example 4. Confirmation of heat resistance of the separator

The separator according to Preparation Example 1 was left at 150°C for 30 minutes to confirm dimensional and volume changes.

The volume change rate of the separator according to Preparation Example 1 was found to be 0%.

Claims (11)

As a separator for an electrochemical device containing a silicon-based cathode,
The separator is,
It is a free-standing porous separator that does not contain a polyolefin base,
Contains a binder polymer and inorganic particles, and contains an excess amount of the inorganic particles compared to the binder polymer,
The weight average molecular weight of the binder polymer is 100,000 to 200,000,
The average particle diameter (D50) of the inorganic particles is 10 to 500 nm,
The separator has pores with an average size of 500 to 1,000 nm, a porosity of 50 to 60%, and an air permeability of 63 to 67.4 sec/100cc. According to paragraph 1,
The separator is,
A separator for an electrochemical device, comprising 60 to 95% by weight of the inorganic particles relative to the total weight of the separator. According to paragraph 1,
The separator is,
A separator for an electrochemical device that satisfies a thickness of 15 to 45 ㎛ and has a value of 1 to 18% defined by the following equation 1:
[Equation 1]
(T1 - T2) / T1 × 100
In equation 1 above,
T1 is the initial thickness of the separator,
The T2 refers to the thickness of the separator after pressing it at 5.2 MPa and 70°C for 10 seconds in a cotton rolling mill. anode;
Silicon-based cathode;
A separator for an electrochemical device according to any one of claims 1 to 3, located between the anode and the silicon-based cathode; and
An electrochemical device containing an electrolyte. A method of manufacturing a separator for an electrochemical device containing a silicon-based cathode,
It includes forming a freestanding porous separator by simultaneously electrospinning a first spinning solution containing inorganic particles and a second spinning solution containing a binder polymer,
A method of manufacturing a separator for an electrochemical device, wherein the flow rate of the first spinning solution is greater than the flow rate of the second spinning solution,
The weight average molecular weight of the binder polymer is 100,000 to 200,000,
The average particle diameter (D50) of the inorganic particles is 10 to 500 nm,
The separator has pores with an average size of 500 to 1,000 nm, a porosity of 50 to 60%, and an air permeability of 63 to 67.4 sec/100cc. According to clause 5,
The silicon-based cathode is,
A method of manufacturing a separator for an electrochemical device, comprising at least one silicon-based active material selected from the group consisting of Si, SiOx (0<x<2), SiC, and Si alloy. According to clause 5,
The inorganic particles are,
SiO ₂ , Al ₂ O ₃ , AlOOH, TiO ₂ , ZrO ₂ , BaSO ₄ , BaTiO ₃ , ZnO, MgO, Mg(OH) ₂ , Al(OH) ₃ , Pb(Zr,Ti)O ₃ , Pb(Mg _1/3 Nb _2/3 )O ₃ -PbTiO ₃ (PMN-PT), HfO ₂ , SrTiO ₃ , SnO ₂ , CeO ₂ , MgO, NiO, CaO, Y ₂ O ₃ , SiC, ZnSn(OH) ₆ , Zn ₂ SnO ₄ , ZnSnO ₃ , Sb ₂ O ₃ , Sb ₂ O ₄ and Sb ₂ O ₅ A method of producing a separator for an electrochemical device, at least one selected from the group consisting of. According to clause 5,
The binder polymer is,
Polyethylene terephthalate, polybutylene terephthalate, polyamide, polyimide, polyetherimide, polysulfone, polyvinylidene fluoride, polyacrylonitrile, polyethylene, polypropylene, polyisoprene, polyethylene oxide, polypropylene oxide, poly A method of producing a separator for an electrochemical device, which is at least one selected from the group consisting of vinylpyrrolidone, polyvinyl alcohol, polystyrene, polyacrylic acid, polymethyl methacrylate, polyacrylamide, and derivatives thereof. According to clause 5,
The step of forming the freestanding porous separator is,
A method for producing a separator for an electrochemical device, wherein the first spinning solution and the second spinning solution are electrospun at a flow rate of 80 to 100 μl/min and 1 to 10 μl/min, respectively. According to clause 5,
The method for manufacturing the separator for the electrochemical device is,
A method of manufacturing a separator for an electrochemical device further comprising pressurizing the separator formed in the step of forming the freestanding porous separator at 25 to 60°C. According to clause 5,
A method of manufacturing a separator for an electrochemical device, wherein the resistance increase rate of the separator for an electrochemical device is 50% or less after being pressed at 5.2 MPa and 70° C. for 10 seconds in a cotton rolling mill.

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