KR102414898B1 - Porous composite separator and electrochemical device including the same - Google Patents

Abstract

The present invention relates to a porous composite separator and an electrochemical device including the same, and more specifically, to a porous composite separator showing an elongation behavior without being immediately broken when a tensile stress is applied at a temperature higher than the melting temperature and using the same It relates to an electrochemical device characterized in that.
In the lithium secondary battery in which the porous composite separator according to the present invention is interposed between the positive electrode and the negative electrode plate, penetration safety can be secured by suppressing the internal short circuit due to penetration during the penetration test.

Description

A porous composite separator and an electrochemical device comprising the same

The present invention relates to a porous composite separator and an electrochemical device including the same. More specifically, it relates to a porous composite separator that does not immediately break even when a tensile stress is applied at a temperature higher than the melting temperature and exhibits an elongation behavior, and an electrochemical device that is safe from the risk of explosion by including the same.

Recently, interest in energy storage technology is rapidly increasing, and research on electrochemical devices used in mobile phones, laptops, and electric vehicles is rapidly increasing. There are studies on lithium secondary batteries.

A typical lithium secondary battery includes a positive electrode including lithium composite oxide, a negative electrode including a material capable of occluding and releasing lithium ions, and a separator and a non-aqueous electrolyte interposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode are laminated with a separator interposed therebetween, or are wound after lamination to form a columnar wound electrode.

The separator has a role of electrically insulating between the anode and the cathode and a role of supporting the non-aqueous electrolyte. As a separator of such a lithium secondary battery, it is common to use a polyolefin microporous membrane. The polyolefin microporous membrane exhibits excellent electrical insulation and ion permeability, and is widely used as a separator for lithium secondary batteries and capacitors. Such a battery part is similar to the shape of winding jelly (Jelly), so it is generally called a jelly roll (Jelly Roll).

Recently, in accordance with the trend of high capacity and high output of secondary batteries, the stability of batteries is more required, and improvement thereof is being conducted as one of the main research tasks. For example, in a lithium secondary battery, when an electrolyte decomposition reaction and thermal runaway occur due to heat generation due to an internal short circuit, overcharge, overdischarge, etc., the pressure inside the battery rapidly rises, which may cause ignition and explosion of the battery. In particular, an internal short circuit of a lithium secondary battery may be caused by a direct impact of a sharp object penetrating the outer case of the battery and penetrating the inner electrode plate.

At this time, since the high electrical energy stored in each electrode plate is instantaneously conducted due to a short circuit between the electrodes, there is a high risk of explosion unlike other safety accidents such as overcharging or overdischarging. Since an explosion can inflict fatal damage to users in addition to simply damaging the secondary battery, the secondary battery designer needs to develop secondary battery design technology in various aspects to secure stability from the explosion caused by an internal short circuit.

Accordingly, the secondary battery to which the new design technology is applied is subjected to a stability evaluation test to determine whether the design to prevent explosion due to an internal short circuit is well made. A typical example is a penetration test that checks whether safety is guaranteed after a secondary battery is penetrated with a sharp object such as a nail to cause an internal short circuit. The penetration test is to penetrate the nail from the outside of the battery cell, and is performed to prepare for a case where a serious internal short circuit occurs due to an external force.

When an internal short circuit occurs due to nail penetration, energy is instantaneously concentrated on the specific area where the short circuit occurred. At this time, the short circuit between the electrodes intensifies as the separator contracts and breaks due to instantaneous heat generation due to the short circuit, which increases the risk of explosion of the battery due to thermal runaway.

In the case of a conventional lithium secondary battery, battery design technology has been developed in various aspects to secure penetration safety. For example, Korean Patent Laid-Open Publication No. 2000-0066879 discloses a method of securing penetration stability by forming a coating layer by applying a slurry prepared by stirring a predetermined amount of a polymer material in an organic solvent on at least one surface of an electrode plate. Korean Patent Laid-Open No. 2008-0105853 discloses a lithium ion secondary battery including a positive electrode or a negative electrode coated with a ceramic layer on at least one of the electrode plate surfaces of the positive electrode or the negative electrode. In addition, Korean Patent Laid-Open Publication No. 2016-0089153 discloses a lithium secondary battery that secures penetration safety by including a bag accommodating an insulating material inside a case constituting the external appearance of the secondary battery. However, the above methods have problems in battery performance and fairness due to the change of the conventional electrode process and the introduction of separate auxiliary materials.

In recent years, attempts have been made to secure penetration stability through the application of a high heat-resistant separator with improved heat resistance of the separator. For this purpose, a method of improving the safety of a battery by forming a coating layer including an inorganic material on a conventional polyolefin-based film is used to improve the thermal stability of the separator. As an example of this method, Korean Patent Registration No. 0775310 discloses a separator in which an active layer coated with an inorganic particle and a binder polymer mixture is formed on a polyolefin microporous membrane.

In addition, research is being conducted to form pores using a polymer resin that has better heat resistance than polyolefin and to apply it as a separator. For example, in US Patent Publication No. 2006-0019154 A1, a polyolefin-based separator is impregnated in a polyamide, polyimide, or polyamideimide solution having a melting temperature of 180° C. or higher, and then immersed in a coagulating solution to extract the solvent to form a thin layer of porous heat-resistant resin. It presents a heat-resistant polyolefin-based separator that has been adhered, and claims to have low heat shrinkage and excellent heat resistance and cycle performance. The porous aramid nonwoven fabric using aramid fibers did not shrink even at 300°C, so research was conducted as a high heat-resistant separator.

However, in the case of the separator, the degree of safety may be insufficient to be used to secure penetration safety of batteries that have recently been increasing in capacity.

Republic of Korea Patent Publication No. 2000-0066879 Republic of Korea Patent Publication No. 2008-0105853 Republic of Korea Patent Publication No. 2016-0089153 Korean Patent Registration No. 0775310 US Patent Publication 2006-0019154 A1

The present invention aims to improve the safety of an electrochemical device, more specifically, a lithium secondary battery, and in particular, to prevent an electrical short circuit that may occur due to an external penetrating nail during nail safety evaluation, and ignition and explosion resulting therefrom. .

Another object of the present invention is not to cause deterioration in battery performance in achieving the above object.

An object of the present invention is to provide a porous composite separator having improved characteristics in order to secure the safety of a lithium secondary battery and an electrochemical device using the same.

One aspect of the present invention is a thermomechanical analyzer (TMA) when the temperature is raised to 5 ℃ / min in the state of applying a load of 0.015N to 0.2N in the longitudinal direction to a specimen having a width of 6mm × 10mm in length, Equations 1 and 2 It relates to a porous composite separator that satisfies

[Equation 1]

Melting temperature (T _m ) ≥ 250 °C at which the longitudinal length of the specimen exceeds the initial length

[Equation 2]

Melt fracture temperature at which the specimen fracture occurs (T _f ) ≥ T _m + 50 ℃

Another aspect of the present invention relates to an electrochemical device comprising an anode, a cathode, and a separator interposed between the anode and the cathode, wherein the separator includes the porous composite separator.

In the conventional battery cell structure, the intervening separator is assembled with a certain stress applied, and as a result, when the temperature rises to the melting temperature due to heat generated by a short circuit occurring during penetration, abrupt contraction or breakage of the penetration part occurs. This causes a serious short circuit between the electrodes, which exposes the battery to the risk of explosion.

By applying the separator according to the present invention, even if the temperature rises to the melting temperature of the separator due to heat generated by an internal short during penetration, the separator does not contract or break, but rather stretches the separator and wraps the electrode exposed at the penetrating portion, thereby suppressing short circuit. This can ensure penetration safety.

1 shows an aspect of a TMA graph for measuring the melt fracture temperature.

Hereinafter, the present invention will be described in more detail through embodiments or examples including the accompanying drawings. However, the following specific examples or examples are only a reference for describing the present invention in detail, and the present invention is not limited thereto, and may be implemented in various forms.

Also, unless defined otherwise, all technical and scientific terms have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description herein is for the purpose of effectively describing particular embodiments only and is not intended to limit the invention.

Also, the singular forms used in the specification and appended claims may also be intended to include the plural forms unless the context specifically dictates otherwise.

One aspect of the present invention is a thermomechanical analyzer (TMA) when the temperature is raised to 5 ℃ / min in the state of applying a load of 0.015N to 0.2N in the longitudinal direction to a specimen having a width of 6mm × 10mm in length, Equations 1 and 2 It is a porous composite membrane that satisfies

[Equation 1]

Melting temperature (T _m ) ≥ 250 °C at which the longitudinal length of the specimen exceeds the initial length

[Equation 2]

Melt fracture temperature at which the specimen fracture occurs (T _f ) ≥ T _m + 50 ℃

In one aspect of the present invention, the separation membrane may have a strain rate of 10% or more according to Equation 3 below.

[Equation 3]

Strain = [(longitudinal length of specimen deformed to melt rupture temperature - longitudinal length of initial specimen) / longitudinal length of initial specimen] × 100

In one aspect of the present invention, the thickness of the separator may be 5 to 40 ㎛.

In one aspect of the present invention, the separator may include a porous support made of fibers and a porous polymer matrix partially or completely impregnated in the porous support or coated on the surface.

In one aspect of the present invention, the porous support may be a nonwoven fabric having a melting temperature of 250 °C or higher, and the porous polymer matrix may be made of a thermoplastic resin having a melting temperature of 250 °C or higher.

In one aspect of the present invention, at least one of the porous support and the porous polymer matrix may satisfy Equations 1 and 2 above.

In one aspect of the present invention, the material of the fiber constituting the porous support is any one or two selected from the group consisting of polyester, polyimide, polyamide, polysulfone, polyvinylidene fluoride, polyacrylonitrile and polyolefin. It may be one selected from blends of two or more and copolymers of two or more.

In one aspect of the present invention, the porous polymer matrix may be made of any one or two or more high heat resistant polymers selected from polyimide, polyamide, aramid, polyamideimide, and polyparaphenylbenzobisoxazole.

In one aspect of the present invention, the porous polymer matrix may have pores formed by phase separation.

In one aspect of the present invention, the separation membrane may have a porosity of 10 to 90%.

Another aspect of the present invention is an electrochemical device comprising an anode, a cathode, and a separator interposed between the anode and the cathode, wherein the separator includes the porous composite separator.

In one aspect of the present invention, the electrochemical device may be a lithium secondary battery.

In one aspect of the present invention, the electrochemical device may not ignite or explode when penetrating a nail having a diameter of 8 mm at a speed of 40 mm/sec in a state where the filling rate is 70% or more.

Hereinafter, each configuration of the present invention will be described in more detail.

The porous composite separator according to an aspect of the present invention has a characteristic that the separator does not contract or break even at a temperature higher than the melting temperature in a state where a certain tensile stress is applied, and exhibits an elongation behavior, which is applied to an electrochemical device. In this case, penetration stability can be secured.

As a result of research conducted by the inventors of the present invention to solve the problem of ignition or explosion of the battery, the melt rupture temperature (T _f ) at which the separator breaks under a certain tensile stress is 50 ° C. or higher than the melting temperature (T _m ), specifically When the state of charge (SOC) of the battery employing it is higher than 100 ℃, more specifically 150 ℃ or higher, 70% or more, more specifically 70 ~ 100%, a nail with a diameter of 8mm is 40mm It has been found that penetration at a rate of /sec may not cause ignition or explosion. In the present invention, the "melting temperature (T _m )" is the initial length of the longitudinal length of the specimen when the temperature is raised to 5° C./min in a state where a load of 0.015 N to 0.2 N is applied to a specimen of width 6 mm × length 10 mm in the longitudinal direction. _means a _{temperature exceeding} means that it is measured as

In addition, if the temperature from the melting temperature (T _m ) to the melt rupture temperature (T _f ) is 50° C. or higher and the physical property of the strain rate according to Equation 3 is 10% or more, the charging rate of the battery employing this is simultaneously satisfied It was found that, in a state of charge (SOC) of 70% or more, more specifically, 70 to 100%, ignition or explosion did not occur even when a nail having a diameter of 8 mm was penetrated at a speed of 40 mm/sec. .

In other words, the separator does not contract or break even at a temperature higher than the melting temperature, rather, it is maintained at least 10% elongated under a constant tensile stress even at a temperature higher than the melting temperature (T _m ). It was found that it was possible to prevent ignition or explosion by securing penetration safety.

In one aspect of the present invention, the porous composite separator may include a porous support made of fibers and a porous polymer matrix partially or completely impregnated in the porous support or coated on the surface.

More specifically, it may be composed of a porous support made of fibers, and a porous high heat-resistant polymer matrix in which a polymer matrix is partially or completely impregnated in the space between the fibers constituting the porous support to fill the space between the fibers.

In one aspect of the present invention, the porous composite separator is a) a porous composite separator comprising a porous support made of fibers exhibiting melt stretching behavior in a situation where a constant tensile stress is applied, b) melts in a situation where a constant tensile stress is applied It may be a porous composite separator including a polymer matrix exhibiting stretching behavior or c) a porous composite separator including a polymer matrix and a porous support made of fibers exhibiting melt stretching behavior in a situation where a constant tensile stress is applied. That is, both the porous support and the polymer matrix may satisfy the above formulas 1 and 2 under tensile stress, but when either one of the porous support and the polymer matrix simultaneously satisfies the above formulas 1 and 2, they are combined, That is, when manufactured as a porous composite separator, the porous composite separator may satisfy Equations 1 and 2 above.

More specifically, the porous support may be a nonwoven fabric having a melting temperature of 250 ° C. or higher, and the porous polymer matrix may be a thermoplastic resin having a melting temperature of 250 ° C. or higher, and the melting temperature (T _m ) of the porous composite separator is the porous support and It may be a higher temperature than the melting temperature of the porous polymer matrix, specifically 250 °C or higher, more specifically 300 to 400 °C.

More specifically, the porous support made of the fiber means a woven fabric, a nonwoven fabric, and a nanofiber web. More preferably, it may be made of a nonwoven fabric in terms of easy raw material supply and low mechanical strength and low manufacturing cost, but is not limited thereto.

In one aspect of the present invention, the nonwoven fabric is not limited as long as it is manufactured by a conventional manufacturing method, but after dispersing the cut fibers using a dispersion solvent, removing the dispersion solvent to prepare a nonwoven fabric (wet laid) may be manufactured with In addition, the mechanical strength may be further improved by further comprising the step of heating and pressing after being manufactured by a conventional wet method so that the area where fibers constituting the nonwoven fabric intersect is physically bonded by fusion.

In one aspect of the present invention, the material of the polymer fiber constituting the porous support is any one selected from the group consisting of polyester, polyimide, polyamide, polysulfone, polyvinylidene fluoride, polyacrylonitrile and polyolefin, Polyester, more Specifically, polyethylene terephthalate may be used, but is not limited thereto.

In one aspect of the present invention, the material of the polymer fiber constituting the porous support is any one selected from the group consisting of polyester, polyimide, polyamide, polysulfone, polyvinylidene fluoride, polyacrylonitrile and polyolefin, Polyester, more Specifically, polyethylene terephthalate may be used, but is not limited thereto.

In addition, it is preferable that the average void between the fibers is 5 μm or less, more specifically 1 to 5 μm, because it is advantageous in applying the matrix composition to form a heat-resistant polymer matrix while having excellent battery stability, but is not limited thereto.

In one aspect of the present invention, the thickness of the porous support is not limited, but preferably 22 μm or less, preferably 17 μm or less, and more preferably 12 μm or less, but is not limited thereto. A thin film separator is required to increase battery capacity, and it is preferable to provide a thin film separator required in the above range, but is not limited thereto. More specifically, it may be 1 ~ 22 μm, but is not limited thereto.

In one aspect of the present invention, the porous high heat-resistant polymer matrix is impregnated in the pores of the porous support to fill the micro-sized pores of the porous support, and refers to a polymer matrix in which nano-sized pores are formed. That is, it has a plurality of nano-sized micropores inside the polymer matrix, has a structure in which these micropores are connected, and has permeability to gas or liquid.

In one embodiment of the present invention, the porous high heat resistant polymer matrix is prepared by using a phase separation agent that is incompatible with the high heat resistant polymer and a solvent capable of dissolving both the high heat resistant polymer and the phase separation agent, and then the porous After the support is immersed in the matrix composition or the porous support is impregnated by applying the matrix composition, the solvent is removed to induce phase separation of the high heat-resistant polymer and the phase separation agent, and after phase separation, the phase separation agent is removed to remove the phase separation agent. It is possible to form a porous high heat-resistant polymer matrix in which pores are formed.

In another aspect of the present invention, the porous high heat resistant polymer matrix is prepared by using a phase separation agent that is incompatible with the high heat resistant polymer and a solvent capable of dissolving both the high heat resistant polymer and the phase separation agent after preparing a matrix composition, After the porous support is immersed in the matrix composition or impregnated by applying the matrix composition to the porous support, it is immersed in a solvent having compatibility with the phase separation agent and the solvent to remove the solvent and the phase separation agent. It is possible to form a porous high heat-resistant polymer matrix in which pores are formed. In this case, when the phase separation agent and the solvent are immersed in a solvent having compatibility with them, the solvent with high affinity is first removed due to the difference in solvent affinity to induce phase separation to form pores, and then pores are formed by removing the phase separation agent. it may be

In one aspect of the present invention, the porous high heat resistant polymer matrix is a polymer commonly known as a high heat resistant polymer, and any thermoplastic polymer having a melting temperature of 200° C. or higher, more preferably 250° C. or higher, may be used without limitation. More preferably, it is preferable to use a resin excellent in stability to the electrolyte solution, excellent in heat resistance, and excellent in interfacial adhesion with the porous support. Specifically, for example, polyimide, polyamide, aramid, polyamideimide, and polyparaphenylbenzobisoxazole may be used from the above point of view, and may be used alone or in combination of two or more, but is not limited thereto.

More preferably, polyimide and polyamideimide may be used in the present invention in order to facilitate the control of pores, but the present invention is not limited thereto. The polyimide is a resin that is cured by heat from a polyamic acid precursor and polymerized, and pores are formed by inducing phase separation by removing a solvent during a heat treatment process using a phase separation agent incompatible with the polyamic acid precursor. In this case, the size and porosity of the pores can be controlled according to the content of the phase separation agent and the phase separation conditions.

In one aspect of the present invention, when the high heat resistant polymer is polyimide, polyamide, and polyamideimide, the phase separation agent means a material that is incompatible with the high heat resistant polymer, that is, does not mix with each other. In addition, it is preferable to use a material having a different boiling point from the solvent while being soluble in a solvent for dissolving the high heat-resistant polymer, and more preferably, a material having a higher boiling point than the solvent may be used, and the following formula 4 is satisfied may be doing

[Equation 4]

Melting temperature of high heat-resistant polymer > Boiling point of phase separation agent > Boiling point of solvent

More specifically, by using a material having a boiling point difference of 5 ° C or more, more preferably 20 ° C or more, as the phase separation agent between the phase separation agent and the solvent, the phase separation agent is not dried together during drying by heating the solvent, and phase separation is induced with the high heat-resistant polymer. can do.

In addition, from the viewpoint of easily removing the phase separation agent from the high heat resistant polymer after the phase separation is completed, it is dried and removed at a temperature below the melting temperature or pyrolysis temperature of the high heat resistant polymer, or by water or a solvent incompatible with the high heat resistant polymer. It is recommended to use a material that can be removed.

In this case, the degree of phase separation can be controlled by controlling the drying time of the solvent and the temperature increase conditions, and the size and porosity of the pores can be adjusted. For example, when the solvent is N-methyl-2-pyrrolidone, phase separation is induced by removing the solvent at 100 to 150 ° C. Then, the phase separation agent is removed or only the phase separation agent is dissolved while gradually raising the temperature to 300 ° C. It may be removed using a solvent. That is, by removing the phase separation agent by heating or washing, it is possible to form a porous high heat-resistant polymer matrix in which pores are formed in the portion where the phase separation agent was present. The phase separation agent may be removed from the polyimide by thermal decomposition or evaporation by heating. The washing may be immersed in a water washing tank containing a solution that dissolves and removes only the phase separation agent, and water or solvent is used alone, or alcohols such as methanol, ethanol, isopropyl alcohol, etc. having good compatibility with water are mixed with water. It may be mixed with and used.

In one aspect of the present invention, examples of the phase separation agent include polyethylene glycol, tetraethylene glycol dimethyl ether, polyvinylpyrrolidone, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, diethylene glycol, triethylene glycol, etc. It may be to use an ether-based solvent, and may be used alone or in mixture of two or more, but is not limited thereto.

In one embodiment of the present invention, the solvent capable of dissolving both the high heat resistance polymer and the phase separation agent may be a nitrogen-containing polar solvent. Although not limited, it may be, for example, N-methyl-2-pyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, tetramethylurea, dimethylethylene urea, and the like. Or two or more may be mixed and used.

In one aspect of the present invention, when the high heat resistant polymer is polyparaphenylbenzobisoxazole, the phase separation agent is incompatible with the high heat resistant polymer and is soluble in a solvent that dissolves the high heat resistant polymer, and also has solubility with the solvent It may be a material with a difference. Accordingly, the porous support is impregnated with a matrix composition in which a high heat-resistant polymer, a phase separation agent and a solvent are mixed, and then immersed in an exchange solution having compatibility with the phase separation agent and the solvent to sequentially remove the solvent and the phase separation agent. . That is, the solvent having higher affinity for the exchange solution is removed first to perform phase separation, and the phase separation agent is removed to form pores.

In one aspect of the present invention, when the high heat-resistant polymer is polyparaphenylbenzobisoxazole, the phase separation agent may be a fluoro-containing carboxylic acid such as trifluoroacetic acid, and may be used alone or in mixture of two or more. It is not limited thereto. In addition, the solvent may be a strong protic acid such as polyphosphoric acid, methanesulfonic acid, sulfuric acid, etc., and may be used alone or in combination of two or more, but is not limited thereto.

In one aspect of the present invention, when the high heat-resistant polymer is polyparaphenylene benzobisoxazole, the mixing ratio of the solvent and the phase separation agent may be preferably 1 to 1 volume ratio or more, more preferably 1 to 3 volume ratio or more. .

In one aspect of the present invention, when the high heat-resistant polymer is polyparaphenylenebenzobisoxazole, a solution of polyparaphenylenebenzobisoxazole, a solvent, and a phase separation agent is prepared, and then impregnated in the porous support, The impregnated material may be immersed in any one or a mixture of two or more selected from water, acetone, isopropyl alcohol, and the like to remove the solvent and the phase separation agent.

In one aspect of the present invention, the average diameter of the pores in the porous high heat-resistant polymer matrix is not limited, but is 1 μm or less, more specifically 0.01 to 1000 nm, preferably 0.1 to 500 nm, more preferably 0.1 to 50 nm. The pore size and porosity can be controlled according to the content of the phase separation agent and the phase separation process, and although not limited to the above range, the ionic conductivity in the range where the average diameter of the pores in the porous high heat-resistant polymer matrix is 1 μm or less can be controlled, and the possibility of an internal short circuit of the battery due to contact between the positive electrode and the negative electrode can be blocked, so it is preferable, but not limited thereto.

In one aspect of the present invention, the porosity of the porous composite separator is determined by the porous high heat-resistant polymer matrix and the porous support, and the porosity may be 10 to 90%. More preferably, it may be 20 to 90%. In the above range, the ion conductivity is excellent and the mechanical strength is excellent, but the present invention is not limited thereto.

In one aspect of the present invention, the porous composite separator may have an overall thickness of 40 μm or less, preferably 20 μm or less, and more preferably 15 μm or less. More specifically, it may be 5 to 40 μm, and a thickness suitable for use as a separator for an electrochemical device in the above range is not limited thereto. In addition, the thickness of the porous support in the porous composite separator may be 22 μm or less, preferably 17 μm or less, and more preferably 12 μm or less, but is not limited thereto.

[Physical properties of porous composite separator]

In one aspect of the present invention, the porous composite separator is a thermomechanical analyzer (TMA) using a thermomechanical analyzer (TMA) to apply a load of 0.015N to 0.2N in the longitudinal direction to a specimen having a width of 6mm × length 10mm when the temperature is raised to 5°C/min. It may satisfy Formula 1 and Formula 2 below.

[Equation 1]

Melting temperature (T _m ) ≥ 250 °C at which the longitudinal length of the specimen exceeds the initial length

[Equation 2]

Melt fracture temperature at which the specimen fracture occurs (T _f ) ≥ T _m + 50 ℃

Under the condition that Equation 1 and Equation 2 are simultaneously satisfied, the state of charge (SOC) of the battery employing the same is 70% or more, more specifically, 70 to 100%, and a nail having a diameter of 8mm is applied to 40mm/ Even if it penetrates at the speed of sec, ignition or explosion may not occur.

Specifically, the melting temperature (T _m ) of the porous composite separator may be 250 °C or higher, more specifically 300 °C or higher, and 500 °C or lower, more specifically 400 °C or lower. In the above range, the heat resistance is excellent, so that it can be safe against overheating of the battery, so it is preferable, but is not limited thereto. At this time, the melting temperature of each of the porous support and the porous polymer matrix constituting the porous composite separator may also be 250 ° C. or higher, and the melting temperature of the porous composite separator may be higher than that of each melting temperature by combining them. have. More specifically, when the melting temperature of each of the porous support and the porous polymer matrix is 250° C., the melting temperature (T _m ) of the porous composite separator in which they are combined may be 300° C. or higher.

In addition, the melt rupture temperature (T _f ) of the porous composite separator may be higher than the melting temperature (T _m ) of the porous composite separator by 50 ° C. or higher, specifically 100 ° C. or higher, and more specifically 150 ° C. or higher. The upper limit is not limited, but may be, for example, 450° C. or less. Specifically, the melt fracture temperature (T _f ) of the porous composite separator may be 300 to 700 °C, and more specifically 500 to 650 °C. As described above in the above range, it is more preferable to be safe against ignition or explosion due to penetration, but is not limited thereto.

In one aspect of the present invention, the porous composite separator may satisfy Equation 1 and Equation 2 and at the same time satisfy the strain rate according to Equation 3 below 10% or more, specifically 30% or more, more specifically 50% or more. have. As described above in the above range, it is more preferable to be safe against ignition or explosion due to penetration, but is not limited thereto.

[Equation 3]

Strain = [(longitudinal length of specimen deformed to melt rupture temperature - longitudinal length of initial specimen) / longitudinal length of initial specimen] × 100

[Method for manufacturing porous composite separator]

When explaining the method of manufacturing the porous composite separator of the present invention, first, a porous support made of fibers is prepared. Specifically, for example, it may be a nonwoven fabric, and a nonwoven fabric manufactured by a method prepared in the related field may be used, but more preferably a nonwoven fabric manufactured by a wet method may be used. Specifically, it may be prepared by dispersing the cut fibers using a dispersion solvent and then removing the dispersion solvent. In addition, if necessary, the nonwoven fabric manufactured by the wet method may be heat-pressed so that the fibers are fused and bonded.

Next, a matrix composition in which a high heat resistant polymer, a phase separation agent incompatible with the high heat resistant polymer, and a solvent compatible with both the phase separation agent and the high heat resistant polymer is mixed on the prepared porous support is coated and impregnated.

The method of applying the matrix composition may use methods such as dip coating, knife coating, roller coating, air knife coating, spray coating, brush coating, calendaring coating and slot die coating, but is not limited thereto.

In this case, as described above, the phase separation agent is incompatible with the high heat-resistant polymer, that is, a material that is not mixed with each other and is dissolved in a solvent at the same time, but has a different boiling point, more preferably a material having a higher boiling point than the solvent.

Next, it is a step of inducing phase separation between the phase separation agent and the high heat resistant polymer by removing the solvent by heating, wherein the heating is performed at a temperature below the melting temperature of the high heat resistant polymer and higher than the boiling point of the solvent. can More specifically, for example, it may be 100 ~ 150 ℃, but is not limited thereto.

Next, the phase separation agent is removed to form a porous high heat-resistant polymer matrix. The method of removing the phase separation agent may be removal by thermal decomposition or evaporation by heating, wherein the heating temperature is below the melting temperature of the high heat-resistant polymer and higher than the boiling point of the phase separation agent. More specifically, it may be 160 ~ 300 ℃, but is not limited thereto. Alternatively, it may be removed by washing, and in this case, it may be removed by immersion or washing in a solution that is incompatible with the high heat-resistant polymer and can be removed by dissolving only the phase separation agent. Alternatively, the solvent may be removed after the phase separation agent is removed by immersion in an exchange solution having compatibility with the phase separation agent and the solvent.

[Electrochemical device]

In one aspect of the present invention, the electrochemical device includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, and the separator may be the porous composite separator described above.

The electrochemical device includes all devices that perform an electrochemical reaction, and specific examples include all kinds of primary cells, secondary cells, fuel cells, solar cells, or capacitors such as super capacitor devices. In particular, a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery among the secondary batteries is preferable.

The electrochemical device may be manufactured according to a conventional method known in the art, for example, by inserting an electrolyte solution after assembling the porous composite separator according to the present invention between the positive electrode and the negative electrode.

The positive electrode, the negative electrode, and the electrolyte are not limited as long as they are commonly used in the art.

The electrochemical device according to an aspect of the present invention may be a lithium secondary battery, and when a nail having a diameter of 8 mm is penetrated at a speed of 40 mm/sec in a state of a charging rate of 70% or more, more specifically 70 to 100%, It may not ignite or explode.

Hereinafter, the present invention will be described in more detail based on Examples and Comparative Examples. However, the following examples and comparative examples are merely examples for explaining the present invention in more detail, and the present invention is not limited by the following examples and comparative examples.

[Example 1]

(Manufacture of anode)

94 wt% of LiCoO ₂ as a cathode active material, 2.5 wt% of polyvinylidene fluoride as an adhesive, 3.5 wt% of carbon-black as a conductive material, and NMP (N-methyl-2) as a solvent -pyrrolidone) and stirred to prepare a uniform positive electrode slurry. The slurry was coated, dried, and compressed on an aluminum foil having a thickness of 30 μm to prepare a positive electrode plate having a thickness of 150 μm.

(Production of cathode)

95% by weight of artificial graphite as an anode active material, 3% by weight of acrylic latex having a T _g of -52℃ as an adhesive, and 2% by weight of CMC (Carboxymethyl cellulose) as a thickener, added to water as a solvent and stirred to prepare a uniform negative electrode slurry. The slurry was coated, dried, and compressed on a 20 μm thick copper foil to prepare a 150 μm thick negative electrode plate.

(Preparation of separation membrane)

An aromatic polyester nonwoven fabric having a thickness of 10 μm and a Gurley transmittance of 1 sec/100cc air was prepared. Aromatic polyester nonwoven fabric has a pore size > 1㎛ or more, a porosity of 50% or more, and was manufactured through melt spinning and calendaring processes.

1.5 g of tetra-ethylene glycol dimethylether (TEGDME) was mixed with 52 g of N-methyl-2-pyrrolidone (NMP), and the melting temperature was 270 ° C. and the melt fracture temperature was 272 ° C. A coating solution having a solid content of 12 wt% was prepared by dissolving polyamideimide (PAI).

An aromatic polyester nonwoven fabric was placed on a glass support, a coating solution was applied to the prepared nonwoven fabric using a bar coater, and the coated nonwoven fabric was peeled off the support. Thereafter, it is fixed in a pin tenter and dried at 130 ° C. for 10 minutes to remove NMP, a solvent with a low boiling point, and phase separation is made between the remaining TEGDME and PAI. A composite separator impregnated with porous PAI in the pores of the nonwoven fabric was prepared.

Table 3 shows the TMA measurement results of the aromatic polyester nonwoven fabric used in Example 1 and the prepared composite separator.

(Manufacture of battery)

A pouch-type battery was assembled in a stacking method using a positive electrode, a negative electrode, and a separator, and 1M lithium hexafluorophosphate (LiPF ₆ ) was dissolved in each assembled battery. Ethylene carbonate (EC) / ethylmethyl carbonate ( EMC)/dimethyl carbonate (DMC)=3:5:2 (volume ratio) of an electrolyte solution was injected to prepare a high-capacity lithium secondary battery. The design capacity of all batteries was fixed at 30 Ah.

[Example 2]

(Preparation of separation membrane)

A polyester-based liquid-crystalline polymer (LCP) nonwoven fabric having a thickness of 10.5 μm and a Gurley transmittance of 1 sec/100cc air was prepared. The LCP nonwoven fabric has a pore size > 1㎛ or more, a porosity of 50% or more, and was manufactured through melt spinning and calendaring processes.

1.5 g of TEGDME was mixed with 52 g of NMP, and the same PAI as in Example 1 was dissolved therein to prepare a coating solution having a solid content of 12 wt%.

The LCP nonwoven was placed on a glass support. After applying the coating solution to the prepared non-woven fabric using a bar coater, the coated non-woven fabric is peeled off the glass support, fixed in a pin tenter and dried at 130 ° C. for 10 minutes to remove the low boiling point solvent NMP and remaining TEGMDE and PAI After allowing phase separation between them, the temperature was raised to 140° C. and dried for an additional 10 minutes to finally remove TEGDME, thereby preparing a composite separation membrane impregnated with porous PAI in the pores of the LCP nonwoven fabric.

The TMA measurement results of the LCP nonwoven fabric and the composite separator used in Example 1 are shown in Table 3.

[Example 3]

(Preparation of separation membrane)

An aromatic polyester nonwoven fabric having a thickness of 10 μm and a Gurley transmittance of 3 sec/100cc air was prepared. The aromatic polyester nonwoven fabric has a pore size > 1 μm or more, a porosity of 50% or more, and was manufactured through melt spinning and calendaring processes.

4.3 g of TEGDME was mixed with 6.7 g of dimethylacetamide (DMAc), and polyamic acid (PAA) having a melting temperature of 360 ° C and a melt fracture temperature of 360 ° C was dissolved to increase the solid content. A coating solution of 14 wt% was prepared.

Aromatic polyester non-woven fabric was placed on a glass support. After the coating solution was applied to the prepared nonwoven fabric using a bar coater, the coated nonwoven fabric was peeled off from the support and fixed in a pin tenter. After drying at 140 ° C. for 10 minutes to form a film, removing DMAc, a solvent with a low boiling point, and allowing phase separation between the remaining TEGDME and PAA, the temperature is raised to 250 ° C. A composite separator in which porous polyimide (PI) was impregnated in the pores was prepared.

The TMA measurement results of the PI-only film used in Example 3 and the prepared composite separator are shown in Table 3.

[Example 4]

(Preparation of separation membrane)

A polyethylene terephthalate (PET) nonwoven fabric having a thickness of 12 μm and a Gurley transmittance of 1 sec/100cc air was prepared.

NMP 51g was mixed with 1.5 g of polyethylene glycol (PET molecular weight: 6000) and 1.7 g of silica particles having a specific surface area of 100 m 2 /g, the melting temperature of which was 260 ° C, and the melting temperature of 563 A coating solution having a solid content of 9.7 wt% was prepared by dissolving PAI at °C.

A PET nonwoven was placed on a glass support. After applying the coating solution to the PET nonwoven fabric prepared using a bar coater, the coated nonwoven fabric was peeled off the support and fixed in a pintenter, dried at 120 ° C. .

After PEG was extracted from the phase-separation structure prepared using distilled water, it was again fixed in a pintenter and dried at 200° C. for 30 minutes to prepare a 23 μm-thick porous composite separation membrane.

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Example 5]

(Preparation of separation membrane)

A polyethylene terephthalate (PET) nonwoven fabric having a thickness of 15 μm and a Gurley transmittance of 3 sec/100cc air was prepared.

In 52 g of NMP, 2.0 g of TEGDME and 2.0 g of alumina particles having a specific surface area of 200 m 2 /g were mixed and mixed, and PAI having a melting temperature of 270 ° C and a melt fracture temperature of 325 ° C was dissolved to obtain a solid content of 10.2 wt. % of the coating solution was prepared.

A PET nonwoven was placed on a glass support. After applying the coating solution to the PET nonwoven fabric prepared using a bar coater, the coated nonwoven fabric was peeled off the support and fixed in a pintenter, dried at 120 ° C. .

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Comparative Example 1]

(Preparation of separation membrane)

As inorganic particles, 94 wt% of alumina particles with an average particle diameter of 0.5 μm, 2 wt% of polyvinyl alcohol having a melting temperature of 220°C and a saponification degree of 99%, and a T _g of -52°C acrylic latex (Acrylic latex) ) was added to water as a solvent at 4% by weight and stirred to prepare a uniform heat-resistant layer slurry. A 9㎛-thick polyolefin microporous membrane product (ENPASS, SK Innovation) was used as the substrate for coating, and the heat-resistant layer slurry was coated on both sides of the substrate using a slot coating die. The separation membrane was wound up in a roll form after evaporating water as a solvent through a dryer. The thickness of the heat-resistant layer on both sides measured after winding was 10.5 µm, respectively.

Other than that, the preparation of the positive electrode, the negative electrode and the battery is the same as in Example 1.

[Comparative Example 2]

(Preparation of separation membrane)

1.5 g of TEGDME was mixed with 52 g of NMP, and PAI used in Example 1 was dissolved therein to prepare a solid content of 12 wt%. After casting this coating solution on a PET support without a nonwoven fabric, it was dried at 120 ° C. for 30 minutes to evaporate NMP, a solvent with a low boiling point, to make a micro phase separation structure, and then peeled off the support to prepare a separation membrane.

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Comparative Example 3]

(Preparation of separation membrane)

A nonwoven fabric having a thickness of 22 μm was prepared using fibers of the same material as the aromatic polyester nonwoven fabric used in Example 1. A nonwoven fabric having a Gurley transmittance of 3 sec/100 cc and a porosity of 50% or more was used as a battery separator without polymer impregnation.

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Comparative Example 4]

(Preparation of separation membrane)

A PET nonwoven fabric having a thickness of 12 μm and a Gurley permeability of 1 sec/100cc air was prepared. In the same manner as in Example 1, 1.5 g of TEGDME was mixed with 52 g of NMP, and PAI was dissolved therein to prepare a coating solution having a solid content of 12 wt%.

A PET nonwoven was placed on a glass support. After applying the coating solution to the prepared nonwoven fabric using a bar coater, remove the support and dry at 130°C for 10 minutes to remove NMP, a solvent with a low boiling point, and allow phase separation between the remaining TEGDME and PAI, and then increase the temperature to 140°C And by drying for an additional 10 minutes to finally remove TEGDME, a composite separator impregnated with porous PAI in the pores of the PET nonwoven fabric was prepared.

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Comparative Example 5]

(Preparation of separation membrane)

A cellulose nonwoven fabric having a thickness of 15 μm and a Gurley permeability of 5 sec/100cc air was prepared.

65 g of N-methyl-2-pyrrolidone was mixed with 2.5 g of tetraethylene glycol dimethyl ether, and PAI used in Example 1 was dissolved therein to prepare a coating solution having a solid content of 8.1 wt%.

Cellulose nonwoven fabric was placed on a glass support. After applying the coating solution to the prepared nonwoven fabric using a bar coater, remove the support and dry at 130 ° C. for 10 minutes to remove NMP, a solvent with a low boiling point, and phase separation between the remaining TEGDME and PAI. Then, the temperature was raised to 140 ° C. and dried for an additional 10 minutes to finally remove TEGDME, thereby preparing a composite separator impregnated with porous PAI in the pores of the PET nonwoven fabric.

Table 3 shows the TMA measurement results of the cellulose nonwoven fabric used in Comparative Example 3 and the prepared composite separator.

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

[Comparative Example 6]

(Preparation of separation membrane)

A nonwoven fabric made of aramid fibers having a thickness of 21 μm and a Gurley transmittance of 45 sec/100cc air was prepared. Aramid fibers are manufactured using a spinning method, and the thickness of the fibers is 3 to 10 μm. The fabricated fibers were briefly chopped and then made into a nonwoven fabric using a wet-laid method.

The above aramid nonwoven fabric was used as a separator, and the preparation of the positive electrode, the negative electrode and the battery was the same as in Example 1.

[Comparative Example 7]

(Preparation of separation membrane)

A polyethylene terephthalate (PET) nonwoven fabric having a thickness of 15 μm and a Gurley transmittance of 3 sec/100cc air was prepared.

Mix 2.0 g of TEGDME and 2.0 g of alumina particles with a specific surface area of 200 m 2 /g in 52 g of NMP, and dissolve a polyamide-based polymer having a melting temperature of 255 ° C and a melt fracture temperature of 300 ° C. A coating solution of 9.3 wt% was prepared.

A PET nonwoven was placed on a glass support. After applying the coating solution to the PET nonwoven fabric prepared using a bar coater, the coated nonwoven fabric was peeled off the support and fixed in a pintenter, dried at 120 ° C. .

The other positive electrode, negative electrode and battery were prepared the same as in Example 1.

A heat shrinkage test was performed using the separation membranes prepared in Examples and Comparative Examples.

Hereinafter, the physical properties were measured as follows.

1) thickness

TESA-μHITE product was used as a contact-type thickness measuring device with a thickness precision of 0.1 μm.

2) gas permeability

Gas permeability was measured by Gurley permeability. It was measured according to the JIS P8117 standard using a Densometer from Toyoseiki. The time taken for 100 cc of air to pass through an area of 1 square inch of the separator was recorded in seconds and compared.

3) Tensile strength

The method of measuring the tensile strength of the separator follows the ASTM D882 standard, and after measuring the tensile strength of the separator in the longitudinal direction (MD, Machine Direction) and the width direction (TD, Transverse Direction), respectively, more The lower value is defined as the tensile strength of the separator. Each sample is cut into a rectangular shape with a width of 15 mm and a height of 120 mm, pulled through a stretching machine at a speed of 500 mm/min. Record and compare.

4) 250℃ shrinkage

In the method of measuring the thermal contraction rate of 250°C of the separator, the sample is prepared by cutting the separator into a square shape with one side of 10 cm, and then the area of the sample before the experiment is measured and recorded using a camera. Place 5 sheets of A4 paper at the top and bottom of the sample so that the sample is located in the center, and fix the four sides of the paper with clips. The paper-wrapped sample was left in a hot air drying oven at 250° C. for 1 hour. After leaving, the sample was taken out, the area of the separator was measured with a camera, and the shrinkage rate of the following equation was calculated.

[Equation]

Shrinkage (%) = (area before heating - area after heating) × 100 / area before heating

5) Qigongdo

The porosity was calculated by cutting the separator into 10 cm wide and 10 cm long, measuring the weight and thickness, calculating the density of the separator, and using the density of the material to calculate the following equation.

Density of the separator = (weight of the separator) / (volume of the separator) = (weight of the separator) / (10 cm × 10 cm × (thickness of the separator))

Porosity = (density of material - density of membrane)/(density of material) × 100

[Heat shrinkage test]

The shape retention rate of the separation membranes prepared in Examples and Comparative Examples was observed using a hot air oven. After standing for 1 hour at a temperature of 250° C. in a hot air oven, the shrinkage rate was calculated. The test results according to this are shown in Table 2.

As can be seen from Table 1, with the exception of Comparative Example 1, it can be seen that the separation membranes of Examples and Comparative Examples had excellent shape retention at high temperature.

Item
(unit)
Example
One
Example
2
Example
3
Example
4
Example
5
comparative example
One
comparative example
2
comparative example
3
comparative example
4
comparative example
5
comparative example
6
comparative example
7
rescue
μm
21
20
22
22
23
21
23
22
24
21
20
22
gas
permeability
sec/
100cc
17
15
20
96
42
195
25
3
18
23
24
24
Seal
burglar
kgf/cm
780
820
690
495
437
980
571
523
385
219
493
421
250℃ Shrinkage
%
0
0
0
2
One
>20
0.5
One
One
0
0
2
Qigongdo
%
51
42
46
41
39
38
42
40
51
50
48
43

[Method for measuring melt rupture temperature]

Using METTLER TOLEDO's TMA (Thermo-mechanical analysis) equipment, a 6mm × 10mm specimen was loaded so that a load of 0.015N to 0.2N was applied, and then the length of the specimen was measured while the temperature was raised at a rate of 5℃/min. In this case, the ratio of the strain length of the sample to the initial sample length during the temperature increase process is called the 'strain rate'. At this time, the size of the specimen refers to the size used for actual analysis after loading into a thermomechanical analyzer (TMA).

Strain = [(longitudinal length of specimen deformed to melt rupture temperature - longitudinal length of initial specimen) / longitudinal length of initial specimen] × 100

In general, in the case of a specimen manufactured through a high elongation process like a polyolefin separator, shrinkage occurs at a certain temperature, and near the melting temperature of the polymer, the specimen suddenly stretches due to the weight of the weight. In the case of TMA maximum shrinkage, it is defined as a value expressed as a percentage of the shrinkage strain length compared to the initial measured length at the maximum shrinkage point that occurs at a constant temperature. Afterwards, it starts to stretch by the weight of the weight. At this time, the temperature exceeding the initial length (zero point) of the specimen is defined as the 'melting temperature (T _m )'. As the sample is rapidly stretched beyond this temperature, fracture of the sample occurs, and the temperature at this time is called the 'melt fracture temperature (T _f )'. In the TMA graph of FIG. 1, an amplification of the items defined above is shown.

The melt elongation properties measured according to the above test are shown in Table 2 below (measured at a stress of 0.015N).

In the example of Table 2, in the case of a composite separator made of a material exhibiting a melt stretching behavior among nonwoven fabrics or impregnated polymers, fracture occurs at a temperature higher than the melting temperature of each of the nonwoven fabrics or impregnated polymers, and it is confirmed that 50% or more is increased in the process. can

In Table 2 below, the impregnated polymer means a porous polymer matrix, and the properties of the impregnated polymer were measured in a state in which a thin film was prepared in the same manner as in each Example without impregnating the nonwoven fabric.

　
melting temperature
(℃)
Maximum shrinkage (%)
Melt fracture temperature (℃)
strain rate
(%)
Example 1
Non-woven
330
0
530
83
impregnated polymer
270
0
272
One
Composite Membrane
360
0
650
62
Example 2
Non-woven
310
0
490
75
impregnated polymer
270
0
272
One
Composite Membrane
330
0
610
59
Example 3
Non-woven
330
0
530
83
impregnated polymer
360
0
360
0
Composite Membrane
385
0
552
35
Example 4
Non-woven
250
3
253
One
impregnated polymer
260
0
563
49
Composite Membrane
310
0
623
54
Example 5
Non-woven
250
3
253
One
impregnated polymer
270
0
325
31
Composite Membrane
275
0
330
33
Comparative Example 1
coating separator
170
28
175
3
Comparative Example 2
separator
270
0
272
8
Comparative Example 3
separator
252
3
254
6
Comparative Example 4
Non-woven
250
3
253
5
impregnated polymer
270
0
272
8
Composite Membrane
270
0
272
9
Comparative Example 5
Non-woven
265
0
266
5
impregnated polymer
270
0
272
6
Composite Membrane
270
0
272
7
Comparative Example 6
separator
560*
　
NA
-16**
Comparative Example 7
Non-woven
250
0
253
One
impregnated polymer
255
0
300
8
Composite Membrane
255
0
302
9

In Table 2, Comparative Example 6 is a decomposition temperature, not a melting temperature. Comparative Example 6 was not stretched and contracted as the temperature increased, but it was confirmed that it continued to contract without breaking even at a measurable temperature of 900°C.

[Electrochemical properties]

The batteries manufactured according to the above Examples and Comparative Examples were charged to a constant current-constant voltage (CC-CV) of 4.2V using a charge/discharge cycle device and then discharged to 2.7V (rate 1C1C). Table 3 below shows the chemical conversion charge capacity, the shipment discharge capacity, and the initial efficiency.

As shown in Table 3, it can be seen that in Examples and Comparative Examples, with the exception of Comparative Example 3, performance similar to that of a conventional commercially available ceramic-coated separator (Comparative Example 1) in terms of battery capacity and efficiency. In the case of Comparative Example 3, the separator using only the non-woven fabric had non-uniform pore sizes and a high risk of short-circuiting.

　
Mars charging capacity
(Ah)
Shipping discharge capacity
(Ah)
efficiency (%)
Example 1
34,066
30,927
90.78
Example 2
33,840
30,420
89.89
Example 3
33,826
30,321
89.64
Example 4
33,985
30,893
90.99
Comparative Example 1
33,950
30,800
90.72
Comparative Example 2
34,135
30,651
89.79
Comparative Example 3
Unable to evaluate due to short circuit
Comparative Example 4
33,540
30,556
91.1
Comparative Example 5
34,024
30,844
90.65
Comparative Example 6
34,600
30,690
88.69

[Penetration safety test]

A penetration test was performed on batteries manufactured using the separators of Examples and Comparative Examples. In the penetration test, after charging for each state of charge (SOC), a nail having a diameter of 8 mm was penetrated at a speed of 40 mm/sec, and then ignition or explosion was checked.

Table 4 shows the surface temperatures of the batteries measured according to the above test.

SOC 100%
SOC 90%
SOC 70%
SOC 60%
SOC 50%
Example 1
L3
L3
L3
L3
L3
Example 2
L3
L3
L3
L3
L3
Example 3
L3
L3
L3
L3
L3
Example 4
L3
L3
L3
L3
L3
Example 5
L3
L3
L3
L3
L3
Comparative Example 1
L5
L3
L3
L3
L3
Comparative Example 2
L5
L4
L3
L3
L3
Comparative Example 3
Unable to evaluate due to short circuit
Comparative Example 4
L5
L5
L3
L3
L3
Comparative Example 5
L5
L5
L4
L3
L3
Comparative Example 6
L5
L5
L3
L3
L3
Comparative Example 7
L4
L3
L3
L3
L3

In Table 4 above, L3: PASS, L4: ignition (FAIL), L5 explosion (FAIL).

As shown in Table 4, it can be seen that penetration stability up to SOC 100% is secured in the case of a composite separator using a material having a stretching behavior above the melting temperature.

On the other hand, the comparative examples do not sufficiently satisfy penetration safety, which causes internal short circuit as the sheet shrinks or breaks due to heat around the nail during nail penetration. seems to have become impossible.

Claims (13)

a porous support made of fibers and having a melting temperature of 250 °C or higher; and
Part or all of the porous support is impregnated or coated on the surface, and contains a porous polymer matrix having a melting temperature of 250 ° C. or higher,
A porous composite separator that satisfies Equations 1 and 2 below when the temperature is raised at 5°C/min while a load of 0.015N to 0.2N is applied in the longitudinal direction to a 6mm wide × 10mm long specimen using a thermomechanical analyzer (TMA). .
[Equation 1]
Melting temperature (T _m ) ≥ 250 °C at which the longitudinal length of the specimen exceeds the initial length
[Equation 2]
Melt fracture temperature at which the specimen fracture occurs (T _f ) ≥ T _m + 50 ℃ The method of claim 1,
The separator is a porous composite separator having a strain rate of 10% or more according to Equation 3 below.
[Equation 3]
Strain = [(longitudinal length of specimen deformed to melt rupture temperature - longitudinal length of initial specimen) / longitudinal length of initial specimen] × 100 The method of claim 1,
A porous composite separator having a thickness of 5 to 40 μm of the separator. delete delete The method of claim 1,
At least one of the porous support and the porous polymer matrix satisfies Formulas 1 and 2 above. The method of claim 1,
The material of the fiber constituting the porous support is any one selected from the group consisting of polyester, polyimide, polyamide, polysulfone, polyvinylidene fluoride, polyacrylonitrile and polyolefin, a blend of two or more, and two or more air A porous composite membrane selected from coalescence. The method of claim 1,
The porous polymer matrix is a porous composite separator made of any one or two or more high heat-resistant polymers selected from polyimide, polyamide, aramid, polyamideimide, and polyparaphenylbenzobisoxazole. The method of claim 1,
The porous polymer matrix is a porous composite separator in which pores are formed by phase separation. The method of claim 1,
The separator is a porous composite separator having a porosity of 10 to 90%. An electrochemical device comprising an anode, a cathode, and a separator interposed between the anode and the cathode,
The electrochemical device comprising the porous composite separator of any one of claims 1 to 3 and claim 6 to 10, wherein the separator is selected from the group consisting of: 12. The method of claim 11,
The electrochemical device is an electrochemical device that is a lithium secondary battery. 12. The method of claim 11,
The electrochemical device is an electrochemical device that does not ignite or explode when a nail having a diameter of 8mm is penetrated at a speed of 40mm/sec in a state where the charging rate is 70% or more.

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