Title of the invention: Separator for electrochemical device and electrochemical device including the same
Technical field
[One]
The present invention relates to a separator that can be used in an electrochemical device such as a lithium secondary battery and an electrochemical device including the same.
[2]
This application is an application for claiming priority for Korean Patent Application No. 10-2018-0134654 filed on November 5, 2018, and all contents disclosed in the specification and drawings of the application are incorporated herein by reference.
Background
[3]
Recently, interest in energy storage technology is increasing. As the field of application to mobile phones, camcorders, notebook PCs, and even electric vehicles is expanded, efforts for research and development of electrochemical devices are increasingly being materialized. Electrochemical devices are the field that is receiving the most attention in this respect, and among them, the development of secondary batteries capable of charging and discharging has become the focus of interest. It is proceeding with research and development on the design of the battery and battery.
[4]
Among the currently applied secondary batteries, the lithium secondary battery developed in the early 1990s has the advantage of having a higher operating voltage and significantly higher energy density than conventional batteries such as Ni-MH, Ni-Cd, and sulfuric acid-lead batteries using aqueous electrolyte solutions. Is in the limelight.
[5]
Electrochemical devices such as lithium secondary batteries are produced by many companies, but their safety characteristics show different aspects. It is very important to evaluate the safety of these electrochemical devices and ensure safety. The most important consideration is that if an electrochemical device malfunctions, it should not injure the user, and for this purpose, the safety standards strictly regulate ignition and smoke in the electrochemical device. In terms of the safety characteristics of an electrochemical device, there is a high concern that an explosion may occur when the electrochemical device is overheated to cause thermal runaway or a separator is penetrated. In particular, the polyolefin-based porous polymer substrate commonly used as a separator of an electrochemical device exhibits extreme heat shrinkage behavior at a temperature of 100° C. or higher due to material properties and manufacturing process characteristics including stretching. Caused a short circuit.
[6]
In order to solve the safety problem of such an electrochemical device, a separator in which a porous coating layer is formed by coating a mixture of an excess of inorganic particles and a binder polymer on at least one surface of a porous polymer substrate having a plurality of pores has been proposed.
[7]
These separators are being developed to be thinner by thinning the separator in order to increase the energy density of the battery. However, as the thickness of the separator decreases, the dielectric breakdown voltage of the battery decreases, resulting in a decrease in battery safety and a high defect rate in the Hi-pot test.
[8]
On the other hand, when assembling a battery via a separator, heat and pressure are applied according to a lamination process, and accordingly, there is a problem that the dielectric breakdown voltage decreases, resulting in deformation of the separator.
Detailed description of the invention
Technical challenge
[9]
The problem to be solved by the present invention is to provide a separator for an electrochemical device with high dielectric breakdown voltage, high safety, and low deformation when heat or pressure is applied, thereby increasing mechanical strength.
[10]
Another problem to be solved by the present invention is to provide an electrochemical device including the separator.
Means of solving the task
[11]
An aspect of the present invention provides a separator for an electrochemical device according to the following embodiments.
[12]
The first embodiment,
[13]
A porous polymer substrate having a plurality of pores;
[14]
A first binder polymer formed on at least one surface of the porous polymer substrate and positioned on a part or all of the surface of the first inorganic particles and the first inorganic particles to connect and fix the inorganic particles. Porous coating layer; And
[15]
A second porosity formed on the surface of the first porous coating layer and comprising a second inorganic material particle and a second binder polymer positioned on a part or all of the surface of the second inorganic material particle to connect and fix the inorganic material particle Includes; a coating layer,
[16]
The Mohs hardness of the first inorganic particles is 4.5 or less, and the Mohs hardness of the second inorganic particles is 7 or more, relates to a separator for an electrochemical device.
[17]
In the second embodiment, in the first embodiment,
[18]
The difference between the Mohs hardness of the first inorganic particles and the Mohs hardness of the second inorganic particles is 2.5 or more, relates to a separator for an electrochemical device.
[19]
In the third embodiment, in the first or second embodiment,
[20]
The first inorganic particles relate to a separator for an electrochemical device comprising boehmite, zinc oxide, magnesium oxide, magnesium hydroxide, aluminum hydroxide, or a mixture of at least two or more thereof.
[21]
In the fourth embodiment, in any one of the first to third embodiments,
[22]
The second inorganic particles relate to a separator for an electrochemical device comprising alumina, aluminum nitride, or a mixture of two or more thereof.
[23]
In the fifth embodiment, in any one of the first to fourth embodiments,
[24]
The average particle diameter of the first inorganic particles is 50 nm to 3000 nm, relates to a separator for an electrochemical device.
[25]
In the sixth embodiment, in any one of the first to fifth embodiments,
[26]
The average particle diameter of the second inorganic particles is 50 nm to 3000 nm, relates to a separator for an electrochemical device.
[27]
In the seventh embodiment, in any one of the first to sixth embodiments,
[28]
The weight ratio of the first inorganic particles: the first binder polymer is 20:80 to 95:5, and relates to a separator for an electrochemical device.
[29]
In the eighth embodiment, in any one of the first to seventh embodiments,
[30]
The weight ratio of the second inorganic particles: the second binder polymer is 20:80 to 95:5, and relates to a separator for an electrochemical device.
[31]
In the ninth embodiment, in any one of the first to eighth embodiments,
[32]
The thickness of the first porous coating layer is 1 ㎛ to 20 ㎛, the thickness of the second porous coating layer is 1 ㎛ to 20 ㎛, relates to a separator for an electrochemical device.
[33]
In the tenth embodiment, in any one of the first to ninth embodiments,
[34]
The first binder polymer or the second binder polymer are each independently polyvinylidene fluoride- hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene ), polymethylmethacrylate, polyetylexyl acrylate, polybutylacrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate ( polyvinylacetate), a copolymer of ethylhexyl acrylate and methyl methacrylate, an ethylene vinyl acetate copolymer (polyethylene-co-vinyl acetate), polyethylene oxide, polyarylate ), cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylpolyvinylalcohol, cyanoethylpolyvinylalcohol Noethylcellulose, cyanoethylsucrose, flulan,It relates to a separator for an electrochemical device comprising carboxyl methyl cellulose or a mixture of two or more of them.
[35]
In the eleventh embodiment, in any one of the first to tenth embodiments,
[36]
The second porous coating layer is the outermost layer of the separator, relates to a separator for an electrochemical device.
[37]
In the twelfth embodiment, in any one of the first to tenth embodiments,
[38]
It relates to a separator for an electrochemical device, which further comprises an adhesive layer including adhesive resin particles on the second porous coating layer.
[39]
In the thirteenth embodiment, in the twelfth embodiment,
[40]
The adhesive resin particles are styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, ethylhexyl acryl. Copolymer of ethylhexyl acrylate and methyl methacrylate, copolymer of butyl acrylate and methyl methacrylate, polyacrylonitrile, polyvinylchloride, polyvinylidene pullluo An electrochemical device comprising any one selected from the group consisting of polyvinylidene fluoride, polyvinylalcohol, styrene, and polycyanoacrylate, or a mixture of two or more of them It is about a dragon separator.
[41]
Another aspect of the present invention provides an electrochemical device according to the following embodiments.
[42]
The fourteenth embodiment,
[43]
In an electrochemical device comprising a cathode, an anode, and a separator interposed between the cathode and the anode, the separator is a separator according to any one of the first to thirteenth embodiments.It relates to an electrochemical device.
[44]
In the fifteenth embodiment, in the 14th embodiment,
[45]
The electrochemical device relates to an electrochemical device, which is a lithium secondary battery.
Effects of the Invention
[46]
According to an embodiment of the present invention, two or more porous coating layers including inorganic particles having different hardness are provided. At this time, the outermost layer has a high hardness of inorganic particles and has high resistance to external foreign substances such as metal. Accordingly, the breakdown voltage increases, thereby improving the safety of the battery.
[47]
Meanwhile, the porous coating layer directly facing the porous polymer substrate may reduce deformation of the separator due to heat and/or pressure by using inorganic particles having low hardness.
Brief description of the drawing
[48]
1 is a schematic diagram schematically showing a separator according to an embodiment of the present invention.
[49]
2 is a schematic diagram schematically showing a separator according to a comparative example of the present invention.
[50]
3 is a schematic diagram schematically showing a dielectric breakdown voltage measuring device.
Mode for carrying out the invention
[51]
Hereinafter, the present invention will be described in detail. The terms or words used in the specification and claims should not be construed as being limited to their usual or dictionary meanings, and the inventor may appropriately define the concept of terms in order to describe his own invention in the best way. It should be interpreted as a meaning and concept consistent with the technical idea of ​​the present invention based on the principle that there is.
[52]
[53]
In the entire specification of the present application, when a certain part is said to be ``connected'' with another part, this includes not only the ``directly connected'' but also the ``indirectly connected'' with another member interposed therebetween. . In addition, the connection implies an electrochemical connection as well as a physical connection.
[54]
[55]
In the entire specification of the present application, when a certain part "includes" a certain constituent element, it means that other constituent elements may be further included rather than excluding other constituent elements unless otherwise stated.
[56]
In addition, when used in this specification, ``comprise'' and/or ``comprising'' refers to the mentioned shapes, numbers, steps, actions, members, elements, and/or the presence of these groups. And does not exclude the presence or addition of one or more other shapes, numbers, actions, members, elements and/or groups.
[57]
[58]
The terms "about", "substantially" and the like used throughout the specification of the present application are used as a meaning at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and are accurate to aid the understanding of the present application. Or absolute figures are used to prevent unfair use of the stated disclosure by unconscionable infringers.
[59]
[60]
In the entire specification of the present application, the term "combination(s) thereof" included on the surface of the Makushi-type refers to one or more mixtures or combinations selected from the group consisting of components described in the expression of the Makushi-type, It means to include at least one selected from the group consisting of the above components.
[61]
[62]
In the entire specification of the present application, description of "A and/or B" means "A or B or both".
[63]
[64]
A separator used in an electrochemical device such as a lithium secondary battery is located between the anode and the cathode, physically separating the anode and the cathode, and electrically insulates it.
[65]
These separators typically use polyolefin-based porous polymer substrates, and exhibit extreme heat shrinkage behavior at temperatures above 100 ℃ due to the characteristics of the manufacturing process including material properties and stretching, which may cause a short circuit between the cathode and the anode. I did.
[66]
In order to solve the safety problem of such an electrochemical device, a separator in which a porous coating layer is formed by coating a mixture of an excess of inorganic particles and a binder polymer on at least one surface of a porous polymer substrate having a plurality of pores has been proposed.
[67]
Such separators are being developed in the direction of thinning the separator to increase the energy density of the battery. However, as the thickness of the separator decreases, the dielectric breakdown voltage of the battery decreases, resulting in a decrease in battery safety and a high defect rate in the Hi-pot test.
[68]
On the other hand, when assembling a battery via a separator, heat and pressure are applied according to a lamination process, and accordingly, there is a problem that the dielectric breakdown voltage decreases, resulting in deformation of the separator.
[69]
[70]
In order to solve the above problems, the separator for an electrochemical device according to an aspect of the present invention,
[71]
A porous polymer substrate having a plurality of pores;
[72]
A first binder polymer formed on at least one surface of the porous polymer substrate and positioned on a part or all of the surface of the first inorganic particles and the first inorganic particles to connect and fix the inorganic particles. Porous coating layer; And
[73]
A second porosity formed on the surface of the first porous coating layer and comprising a second inorganic material particle and a second binder polymer positioned on a part or all of the surface of the second inorganic material particle to connect and fix the inorganic material particle Includes; a coating layer,
[74]
The Mohs hardness of the first inorganic particles is 4.5 or less, and the Mohs hardness of the second inorganic particles is 7 or more.
[75]
[76]
1 is a schematic diagram schematically showing a separator according to an embodiment of the present invention.
[77]
As shown in Figure 1, the separator 100 according to the present invention is a porous polymer substrate 10; It is formed on at least one surface of the porous polymer substrate 10 and is located on a part or all of the surface of the first inorganic particles 21 and the first inorganic particles 21 to connect and fix the inorganic particles. A first porous coating layer 20 comprising a first binder polymer (not shown); And
[78]
It is formed on the surface of the first porous coating layer 20 and is located on a part or all of the surface of the second inorganic particles 31 and the second inorganic particles 31 to connect the inorganic particles 31 and A second porous coating layer 30 comprising a second binder polymer (not shown) to be fixed; and the Mohs hardness of the first inorganic particles is 4.5 or less, and the Mohs hardness of the second inorganic particles is 7 or more. will be.
[79]
[80]
The separator for an electrochemical device according to an aspect of the present invention includes a first porous coating layer and a second porous coating layer, and the Mohs hardness of the first inorganic particles included in the first porous coating layer is 4.5 or less, and the second porous coating layer The Mohs hardness of the second inorganic material particles contained in the inside is 7 or more.
[81]
In the case of a separator 200 including a single porous coating layer 40 using only inorganic particles 41 having the same hardness as in FIG. 2, the separator is deformed or crushed by heat or pressure when manufacturing an electrode assembly. There was. In addition, as the separator becomes thinner, the dielectric breakdown performance of the battery decreases and the high-pot test defect rate increases.
[82]
In order to solve this problem, the separator according to an aspect of the present invention uses inorganic particles having low Mohs hardness in the first porous coating layer directly facing the porous polymer substrate, and inorganic particles having high Mohs hardness in the second porous coating layer Use particles.
[83]
[84]
The term'Mohs hardness' in the present invention refers to 10 kinds of minerals (Mohs hardness 1: talc, Mohs hardness 2: gypsum, Mohs hardness 3: calcite, Mohs hardness 4: fluorspar, Mohs hardness 5: apatite, Mohs hardness 6: jeongteol, Mohs hardness 7: Quartz, Mohs hardness 8: Topaz, Mohs hardness 9: Corundum, Mohs hardness 10: Diamond) as a standard material, which is a value obtained by evaluating the hardness compared with these. The standard substance and the sample are rubbed, and the side where the scratch occurs is judged as having a lower hardness. In addition, if it is difficult to directly measure the Mohs hardness, the composition can be determined from the composition analysis and judged from the material Mohs hardness of the same composition.
[85]
[86]
Meanwhile, the separator according to an aspect of the present invention has a Mohs hardness of 4.5 or less of the first inorganic particles included in the first porous coating layer.
[87]
When the Mohs hardness of the first inorganic particles exceeds 4.5, there is a problem in that the inorganic particles having a high Mohs hardness contained in the porous coating layer damage the porous polymer substrate, thereby reducing insulation performance.
[88]
Since the first porous coating layer includes first inorganic particles having low Mohs hardness, deformation of the separator due to heat or pressure may be prevented.
[89]
[90]
In a specific embodiment of the present invention, the first inorganic particles are boehmite (AlO(OH)) (Mohs hardness: 3.5 to 4), zinc oxide (ZnO) (Mohs hardness: 4.5), magnesium oxide (MgO) (Mohs hardness: 4), magnesium hydroxide (Mg(OH) 2 ) (Mohs hardness: 2.5), aluminum hydroxide (Al(OH) 3 ) (Mohs hardness: 2.5 to 3.5), or a mixture of at least two or more thereof can do.
[91]
[92]
In a specific embodiment of the present invention, the first inorganic particles, especially in the case of aluminum hydroxide, have a low Mohs hardness, so that damage to the porous polymer substrate can be minimized, thereby minimizing battery performance reduction, and assembly processability. It is preferable in terms of being able to improve. In addition, it is possible to minimize a reduction in porosity due to the first inorganic particles during a lamination process with an electrode, and a decrease in insulation voltage can be minimized. In addition, aluminum hydroxide and boehmite are preferred over magnesium oxide in terms of dispersibility.
[93]
[94]
In a specific embodiment of the present invention, the average particle diameter of the first inorganic particles may be 50 to 3000 nm, or 100 to 2000 nm, or 200 to 1000 nm. It is preferable from the viewpoint of simultaneously realizing heat resistance and dispersibility as the average particle diameter of the first inorganic particles satisfies the above numerical range.
[95]
[96]
Meanwhile, the separator according to an aspect of the present invention has a Mohs hardness of 7 or more of the second inorganic particles included in the second porous coating layer.
[97]
When the second inorganic particles have a Mohs hardness of less than 7, there is a problem that they are vulnerable to external foreign substances in the assembling process. For example, in the case of iron (Mohs hardness: 5), resistance to external foreign matter is not large, and damage to the separator may occur.
[98]
[99]
On the other hand, when the second inorganic particles are used as a material having a Mohs hardness of 7 or higher as in the present invention, resistance to external foreign substances such as metal may be increased.
[100]
In a specific embodiment of the present invention, the second inorganic particles include alumina (Al 2 O 3 ) (Mohs hardness: 9), aluminum nitride (AlN) (Mohs hardness: 7), or a mixture of two or more thereof can do.
[101]
In a specific embodiment of the present invention, the second inorganic particles are particularly preferred in terms of battery performance and assembly processability, since the hardness of alumina is particularly high when alumina is used. For example, damage to the separator due to friction with the device/device during the assembly process can be reduced. In particular, it is possible to minimize damage to the separator due to foreign substances when applying lamination of the electrode and the separator.
[102]
In a specific embodiment of the present invention, the difference between the Mohs hardness of the first inorganic particle and the second inorganic particle may be 2.5 or more, or 3 or more, or 5 or more. In particular, as the difference in Mohs' hardness increases, resistance to external foreign matter increases, damage to the porous polymer substrate may decrease, and it is preferable in terms of battery assembly processability.
[103]
[104]
In a specific embodiment of the present invention, the average particle diameter of the second inorganic particles may be 50 to 3000 nm, or 100 to 2000 nm, or 200 to 1000 nm. As the average particle diameter of the second inorganic particles satisfies the above numerical range, it is preferable from the viewpoint of simultaneously realizing heat resistance and dispersibility.
[105]
[106]
The term'average particle diameter' of the present invention refers to the average particle diameter (D50) of inorganic particles, and may be defined as a particle diameter based on 50% of the particle diameter distribution. In an embodiment of the present invention, the particle diameter may be measured using a laser diffreaction method. In general, the laser diffraction method can measure a particle diameter of about several nm in a submicron region, and results of high reproducibility and high resolution can be obtained.
[107]
[108]
In the separator according to an aspect of the present invention, as the binder polymer used for forming the porous coating layer, a polymer commonly used in forming the porous coating layer in the art may be used. In particular, a polymer having a glass transition temperature (Tg) of -200 to 200°C may be used, because mechanical properties such as flexibility and elasticity of the finally formed porous coating layer can be improved. Such a binder polymer faithfully performs the role of a binder that connects and stably fixes the inorganic particles, thereby contributing to the prevention of deterioration of mechanical properties of the separator into which the porous coating layer is introduced.
[109]
In addition, the binder polymer does not necessarily have ion conduction capability, but when a polymer having ion conduction capability is used, the performance of the electrochemical device may be further improved. Therefore, the binder polymer may be used having a high dielectric constant as possible. In fact, since the degree of dissociation of the salt in the electrolyte depends on the dielectric constant of the solvent of the electrolyte, the higher the dielectric constant of the binder polymer, the higher the degree of dissociation of the salt in the electrolyte. The dielectric constant of the binder polymer may be in the range of 1.0 to 100 (measurement frequency = 1 kHz), and in particular, may be 10 or more.
[110]
In addition to the above-described functions, the binder polymer may have a characteristic capable of exhibiting a high degree of swelling by gelling when impregnated with a liquid electrolyte. Thus, the solubility parameter, i.e. hildeo brand solubility parameter (Hildebrand solubility parameter) of 15 to 45 MPa in the binder polymer 1 /2 or 15 to 25 MPa 1 /2 , and 30 to 45 MPa 1 /2 range. Therefore, hydrophilic polymers having a large number of polar groups can be used more than hydrophobic polymers such as polyolefins. The solubility parameter is 15 MPa 1 /2 less than 45 MPa and 1 /2 if it exceeds, because it can be difficult to swell (swelling) by conventional liquid electrolyte batteries.
[111]
In a specific embodiment of the present invention, the first binder polymer or the second binder polymer may each independently include a polyvinylidene fluoride binder polymer or an acrylic binder polymer.
[112]
In a specific embodiment of the present invention, the polyvinylidene fluoride-based binder polymer is fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, polyvinylidene Fluoride-co-tetrafluoroethylene (polyvinylidene fluoride-co-trichloroethylene), polyvinylidene fluoride-trifluoroethylene (polyvinylidene fluoride-trifluoroethylene), polyvinylidene fluoride-trifluorochloroethylene ( polyvinylidene trifluorochloroethylene), polyvinylidene fluoride-ethylene, or a mixture of two or more thereof.
[113]
In a specific embodiment of the present invention, the acrylic binder polymer is a copolymer of ethylhexyl acrylate and methyl methacrylate, polymethylmethacrylate, and polyethylhexyl acrylate. (polyetylexyl acrylate), polybutylacrylate, polyacrylonitrile, a copolymer of butyl acrylate and methyl methacrylate, or a mixture of two or more of them may be included.
[114]
In addition, as a non-limiting example of the binder polymer, the first binder polymer or the second binder polymer are each independently polyvinylpyrrolidone, polyvinylacetate, ethylene vinyl acetate copolymer co-vinyl acetate), polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyano Ethyl flulan (cyanoethylpullulan), cyanoethylpolyvinylalcohol (cyanoethylpolyvinylalcohol), cyanoethylcellulose (cyanoethylcellulose), cyanoethylsucrose (cyanoethylsucrose), flulan (pullulan) and carboxyl methyl cellulose (carboxyl methyl cellulose) May be mentioned, but is not limited thereto.
[115]
The weight ratio of the inorganic particles and the binder polymer is, for example, 20:80 to 95:5, and in detail, 70:30 to 95:5. When the content ratio of the inorganic particles to the binder polymer satisfies the above range, the problem of reducing the pore size and porosity of the porous coating layer formed due to an increase in the content of the binder polymer can be prevented, and since the binder polymer content is small The problem of weakening the peeling resistance of the formed porous coating layer may also be solved.
[116]
The electrode assembly according to an aspect of the present invention may further include other additives in addition to the aforementioned inorganic particles and polymers as a component of the porous coating layer.
[117]
In a specific embodiment of the present invention, the thickness of the first porous coating layer may be 1 µm to 20 µm, and the thickness of the second porous coating layer may be 1 µm to 20 µm. For example, in the case of the first porous coating layer, it is sufficient if the thickness of the coating layer is larger than the diameter of the first inorganic particles, and in the case of the second porous coating layer, the thicker the thickness, the higher the resistance from external foreign matters, which is advantageous. However, when the thickness of the second porous coating layer exceeds 20 μm, there is a problem that resistance increases and volume increases.
[118]
In a specific embodiment of the present invention, a porous coating layer may be formed on one or both surfaces of the porous polymer substrate.
[119]
In a specific embodiment of the present invention, an adhesive layer including adhesive resin particles may be further included on the second porous coating layer.
[120]
In a specific embodiment of the present invention, the adhesive resin particles are styrene butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene rubber (acrylonitrile). -butadiene-styrene rubber), copolymer of ethylhexyl acrylate and methyl methacrylate, copolymer of butyl acrylate and methyl methacrylate, polyacrylonitrile, polyvinyl Any one selected from the group consisting of chloride (polyvinylchloride), polyvinylidene fluoride, polyvinylalcohol, styrene, and polycyanoacrylate, or two or more of them It may contain mixtures.
[121]
Such an adhesive layer is formed to increase the adhesion between the separator and the electrode, and is particularly preferable when the second porous coating layer is an aqueous slurry using water as a solvent.
[122]
On the other hand, in a specific embodiment of the present invention, the second porous coating layer may be an outermost layer, and in this case, the second porous coating layer is particularly preferable when coating with a slurry using an organic solvent. This is because, when an organic solvent is used, the binder polymer distributed on the surface of the second porous coating layer according to phase separation is larger than that of the binder polymer distributed inside the porous coating layer, thereby increasing the adhesion between the separator and the electrode.
[123]
In the present invention, the porous polymer substrate is a porous membrane that can provide a path for lithium ions to move while preventing short circuits by electrically insulating the anode and the cathode, and is generally used as a separator material for an electrochemical device without special limitation. This is possible.
[124]
The porous polymer substrate may be specifically a porous polymer film substrate or a porous polymer nonwoven fabric substrate.
[125]
The porous polymer film substrate may be a porous polymer film made of a polyolefin such as polyethylene, polypropylene, polybutene, and polypentene, and such a polyolefin porous polymer film substrate has a shutdown function at a temperature of, for example, 80°C to 130°C. Manifest.
[126]
At this time, the polyolefin porous polymer film substrate is a polyolefin-based polymer such as high-density polyethylene, linear low-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene, polypropylene, polybutylene, and polypentene, respectively, or a mixture of two or more thereof. It can be formed from a polymer.
[127]
In addition, the porous polymer film substrate may be manufactured by molding into a film shape using various polymers such as polyester in addition to polyolefin. In addition, the porous polymer film substrate may be formed in a structure in which two or more film layers are stacked, and each film layer may be formed of a polymer such as polyolefin or polyester described above alone or a mixture of two or more of them. have.
[128]
In addition, the porous polymer film substrate and the porous nonwoven fabric substrate include polyethylene terephthalate, polybutyleneterephthalate, polyester, polyacetal, and polyamide in addition to the polyolefin-based materials described above. ), polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenyleneoxide, polyphenylenesulfide, polyethylenenaphthalene And the like may be formed of a polymer alone or a mixture thereof.
[129]
The thickness of the porous polymer substrate is not particularly limited, but in detail it is 1 to 100 μm, more specifically 5 to 50 μm, and it is advantageous to use a thin film for the porous polymer substrate as the high power/capacity of the battery has progressed recently. . The pore diameter present in the porous polymer substrate is 10 nm to 100 nm, or 10 nm to 70 nm, or 10 nm to 50 nm, or 10 nm to 35 nm, and the porosity is 5% to 90%, preferably 20% to 80%. Can be formed as However, in the present invention, these numerical ranges can be easily modified according to specific embodiments or needs.
[130]
The pores of the porous polymer substrate have various types of pore structures, and if any one of the average sizes of pores measured using a porosimeter or observed on the FE-SEM satisfies the above conditions Included in the present invention.
[131]
Here, in the case of a generally known uniaxially stretched dry separator, the pore size in the center of the pore size in the TD direction is not the pore size in the MD direction on the FE-SEM, and a porous polymer substrate having a net structure. (For example, a wet PE separator) may be based on the size of pores measured with a porosimeter.
[132]
A method of manufacturing a separator according to an aspect of the present invention can be formed by a conventional method in the art. In a specific embodiment of the present invention, a slurry for forming a first porous coating layer in which the first inorganic particles are dispersed in a binder polymer solution in which the first binder polymer is dissolved or dispersed in a solvent, and the second binder polymer are dissolved in a solvent or A slurry for forming a second porous coating layer in which second inorganic particles are dispersed in the dispersed binder polymer solution is prepared.
[133]
Thereafter, the first porous coating layer may be formed by applying and drying the slurry for forming the first porous coating layer on the porous polymer substrate.
[134]
Next, a second porous coating layer may be formed by drying and applying the slurry for forming the second porous coating layer on the surface of the first porous coating layer.
[135]
Thereafter, an adhesive layer may be further formed on the second porous coating layer.
[136]
The method of applying the slurry for forming the first and second porous coating layers to the porous polymer substrate is not particularly limited, but a slot coating or dip coating method is preferably used. In the slot coating, the composition supplied through the slot die is applied to the entire surface of the substrate, and the thickness of the coating layer can be adjusted according to the flow rate supplied from the metering pump. In addition, dip coating is a method of coating by immersing a substrate in a tank containing the composition, and the thickness of the coating layer can be adjusted according to the concentration of the composition and the speed of removing the substrate from the composition tank. It can be subsequently weighed through.
[137]
The porous polymer substrate coated with the slurry for forming the first and second porous coating layers is dried using a dryer such as an oven to form a porous coating layer formed on at least one surface of the porous polymer substrate.
[138]
In the first and second porous coating layers, inorganic particles are filled and bound to each other by the binder polymer in a state in which they are in contact with each other, thereby forming an interstitial volume between the inorganic particles. The interstitial volume between the inorganic particles becomes an empty space and can form pores.
[139]
That is, the binder polymer may be attached to each other so that the inorganic particle binder polymers remain bound to each other. For example, the binder polymer may connect and fix the inorganic particles. In addition, the pores of the porous coating layer are pores formed by the interstitial volume between inorganic particles becoming an empty space, which is an inorganic material that is substantially interviewed in a closed packed or densely packed structure by inorganic particles. It may be a space defined by particles.
[140]
[141]
An electrochemical device according to an aspect of the present invention includes a cathode, an anode, and a separator interposed between the cathode and the anode, and the separator is a separator according to an embodiment of the present invention described above.
[142]
Such an electrochemical device includes all devices that undergo an electrochemical reaction, and specific examples include all types of primary and secondary batteries, fuel cells, solar cells, or capacitors such as supercapacitor devices. Particularly, among the secondary batteries, lithium secondary batteries including lithium metal secondary batteries, lithium ion secondary batteries, lithium polymer secondary batteries or lithium ion polymer secondary batteries are preferred.
[143]
The positive electrode of the cathode and the anode to be applied together with the separator of the present invention is not particularly limited, and an electrode active material may be manufactured in a form bound to an electrode current collector according to a conventional method known in the art. As a non-limiting example of the cathode active material among the electrode active materials, a conventional cathode active material that can be used for the cathode of a conventional electrochemical device can be used, and in particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or a combination thereof It is preferable to use one lithium composite oxide. Non-limiting examples of the anode active material may be a conventional anode active material that can be used for the anode of a conventional electrochemical device, and in particular, lithium metal or lithium alloy, carbon, petroleum coke, activated carbon, Lithium adsorption materials such as graphite or other carbons are preferred. Non-limiting examples of the cathode current collector include aluminum, nickel, or a foil manufactured by a combination thereof, and non-limiting examples of the anode current collector include copper, gold, nickel, or a copper alloy or a combination thereof. Such as foil.
[144]
The electrolyte that can be used in the electrochemical device of the present invention is a salt having a structure such as A + B - , where A + contains an ion consisting of an alkali metal cation such as Li + , Na + , K + or a combination thereof - is PF 6 - , BF 4 - , Cl - , Br - , I - , ClO 4 - , AsF 6 - , CH 3 CO 2 - , CF 3 SO 3 -, N (CF 3 SO 2 ) 2 - , C (CF 2 SO 2 ) 3 - anion, or a salt containing an ion composed of a combination of propylene carbonate (PC) such as, ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl Some dissolved or dissociated in an organic solvent consisting of methyl carbonate (EMC), gamma butyrolactone (γ-butyrolactone), or a mixture thereof, but are not limited thereto.
[145]
The electrolyte injection may be performed at an appropriate step in the battery manufacturing process according to the manufacturing process and required physical properties of the final product. That is, it can be applied before battery assembly or at the final stage of battery assembly.
[146]
[147]
Hereinafter, examples will be described in detail to illustrate the present invention in detail. However, the embodiments according to the present invention may be modified in various forms, and the scope of the present invention should not be construed as being limited to the embodiments described below. The embodiments of the present invention are provided to more completely describe the present invention to those of ordinary skill in the art.
[148]
[149]
Example 1
[150]
1) anode manufacturing
[151]
Artificial graphite, carbon black, carboxy methyl cellulose (CMC, Carboxy Methyl Cellulose), and styrene butadiene rubber (SBR, Styrene-Butadiene Rubber) were added to water at a weight ratio of 96:1:2:2 and mixed to prepare an anode slurry. . The anode slurry was coated on a 50 µm thick copper foil (Cu-foil) as an anode current collector at a capacity of 3.55 mAh/g to form a thin electrode plate, dried at 135° C. for 3 hours or more, and then rolled. Thus, an anode was prepared.
[152]
[153]
2) cathode manufacturing
[154]
LiNi 0 . 6 Co 0 . 2 Mn 0 . 2 O 2 Cathode active material, carbon black, polyvinylidene fluoride (PVDF, Polyvinylidene Fluoride) was added to N-methyl-2-pyrrolidone (NMP) at a weight ratio of 96: 2: 2 and mixed to prepare a cathode slurry. I did. The cathode slurry was coated on an aluminum foil having a thickness of 20 μm as a cathode current collector at a capacity of 3.28 mAh/g to prepare a cathode.
[155]
[156]
3) manufacture of separator
[157]
3-1) Formation of the first porous coating layer
[158]
After dissolving 105 g of Carboxyl Methyl Cellulose (CMC) in water as a solvent at room temperature, 4500 g of the first inorganic particles (Al(OH) 3 , 700 nm, Mohs hardness: 2.5) were added for 3 hours. During the preparation, the first inorganic particles were crushed and pulverized by a ball mill. Thereafter, 700 g of an acrylic binder (a copolymer of ethylhexyl acrylate and methyl methacrylate, Tg -5 °C, average particle diameter: 300 nm), which is a first binder polymer, was added to the prepared result. Then, the mixture was stirred for 1 hour to prepare a slurry for forming a first porous coating layer. At this time, the weight ratio of the first inorganic particles and the first binder polymer was controlled to 86.5:13.5.
[159]
The slurry for forming the first porous coating layer was applied to both sides of a 9 μm-thick polyethylene porous film (porosity: 45%) by dip coating, dried at 80° C., and each having a thickness of 2 μm on both sides of the polyethylene porous film. 1 A porous coating layer was formed.
[160]
[161]
3-2) Formation of the second porous coating layer
[162]
After dissolving 105 g of Carboxyl Methyl Cellulose (CMC) in water as a solvent at room temperature, 4500 g of second inorganic particles (Al 2 O 3 , 500 nm, Mohs hardness: 9) were added for 3 hours. It was prepared by crushing and pulverizing the second inorganic particles by a ball mill method. Then, 700 g of an acrylic binder (a copolymer of ethylhexyl acrylate and methyl methacrylate, Tg -5°C, average particle diameter: 300 nm), which is a second binder polymer, was added to the prepared result for 1 hour. While stirring to prepare a slurry for forming a second porous coating layer. At this time, the weight ratio of the second inorganic particles and the second binder polymer was controlled to 86.5:13.5.
[163]
The second porous coating layer-forming slurry was coated with a dip coating method and dried at 80° C. so that the thickness of each side of the first porous coating layer formed on both sides prepared in 3-1) was 2 μm. A coating layer was formed.
[164]
[165]
3-3) Formation of adhesive layer
[166]
Slurry for forming an adhesive layer by dispersing an acrylic binder (a copolymer of ethylhexyl acrylate and methyl methacrylate, Tg -5 ℃, average particle diameter: 300nm solid content 30%) at room temperature in water as a solvent Was prepared. The prepared adhesive layer forming slurry was coated on each side of the second porous coating layer formed on both sides by a dip coating method, and dried at 80° C. to form an adhesive layer so that the thickness was each 1 μm.
[167]
[168]
4) Separator and electrode adhesion
[169]
Next, the separator and the electrode were stacked so that the adhesive layer and the cathode active material layer of the electrode of 1) face each other, and then rolled at 70° C. and 600 kgf for 1 second (sec) to prepare an electrode assembly in which the cathode and the separator are stacked.
[170]
[171]
Example 2
[172]
Zinc oxide (Mohs hardness: 4.5, average particle diameter: 500 nm) is used as the first inorganic particles used in the first porous coating layer, and aluminum nitride (Mohs hardness: 7) is used as the second inorganic particles used in the second porous coating layer. , An electrode assembly was manufactured in the same manner as in Example 1, except that the average particle diameter: 800 nm) was used.
[173]
[174]
Comparative Example 1
[175]
An electrode assembly was manufactured in the same manner as in Example 1, except that a single-layer porous coating layer was formed as follows.
[176]
1) Formation of porous coating layer
[177]
Specifically, after dissolving 105 g of Carboxyl Methyl Cellulose (CMC) in water as a solvent at room temperature, 4500 g of inorganic particles (Al 2 O 3 , 500 nm, Mohs hardness: 9) were added for 3 hours. During the preparation, inorganic particles were crushed and pulverized by a ball mill. 700 g of an acrylic binder (a copolymer of ethylhexyl acrylate and methyl methacrylate, Tg -5 °C, average particle diameter: 300 nm), which is a binder polymer, was added to the prepared result and stirred for 1 hour Thus, a slurry for forming a porous coating layer was prepared. At this time, the weight ratio of inorganic particles: binder polymer was controlled to 86.5:13.5.
[178]
The slurry for forming the porous coating layer was applied to both sides of a 9 μm-thick polyethylene porous film (porosity: 45%) by dip coating, and dried at 80° C. to form a porous coating layer having a thickness of 4 μm on both sides of the polyethylene porous film. Formed.
[179]
2) Formation of adhesive layer
[180]
An adhesive layer was formed on both sides of the porous coating layer in the same manner as in 3-3) described in Example 1.
[181]
[182]
Comparative Example 2
[183]
An electrode assembly was manufactured in the same manner as in Example 1, except that a single-layer porous coating layer was formed as follows.
[184]
1) Formation of porous coating layer
[185]
Specifically, after dissolving 105 g of Carboxyl Methyl Cellulose (CMC) in water as a solvent at room temperature, 4500 g of inorganic particles (Al(OH) 3 , 700 nm, Mohs hardness: 2.5) were added and 3 It was prepared by crushing and pulverizing inorganic particles by a ball mill for a period of time. 700 g of an acrylic binder (a copolymer of ethylhexyl acrylate and methyl methacrylate, Tg -5 °C, average particle diameter: 300 nm), which is a binder polymer, was added to the prepared result and stirred for 1 hour. Thus, a slurry for forming a porous coating layer was prepared. At this time, the weight ratio of inorganic particles: binder polymer was controlled to 86.5:13.5.
[186]
The slurry for forming the porous coating layer was applied to both sides of a 9 μm-thick polyethylene porous film (porosity: 45%) by dip coating, and dried at 80° C. to form a porous coating layer having a thickness of 4 μm on both sides of the polyethylene porous film. Formed.
[187]
2) Formation of adhesive layer
[188]
An adhesive layer was formed on both sides of the porous coating layer in the same manner as in 3-3) described in Example 1.
[189]
[190]
Comparative Examples 3 to 6
[191]
An electrode assembly was manufactured in the same manner as in Example 1, except that the first inorganic particles used for the first porous coating layer and the second inorganic particles used for the second porous coating layer were respectively controlled as shown in Table 1.
[192]
[193]
Evaluation results
[194]
For the above-described Examples 1 to 2 and Comparative Examples 1 to 6, the thickness, particle diameter, dielectric breakdown voltage, and hardness were respectively evaluated and shown in Table 1.
[195]
[196]
These specific evaluation methods are as follows.
[197]
[198]
1) Method of measuring particle diameter
[199]
The particle diameter of the inorganic particles was measured using a laser diffraction method (Microtrac MT 3000).
[200]
[201]
2) Insulation breakdown voltage measurement method (pressed O)
[202]
After laminating the separators and cathodes prepared in Examples 1 to 2 and Comparative Examples 1 to 6, the resultant was thermocompressed at a temperature of 70° C., a pressure of 4 MPa, and a time of 1 sec using a flat plate press equipped with a heater.
[203]
Next, the thermocompressed separator was mounted between a pair of jigs facing each other. When the jig was mounted, a pressure of 10 KPa was applied to the thermo-compressed separator as a measurement object. Specifically, a separator 113 was interposed between the aluminum foil 112 and the bonded aluminum jig 111 as shown in FIG. 3.
[204]
Thereafter, the DC voltage 120 applied from the voltage applying unit directly connected to the pair of jigs facing each other was gradually increased at a rate of 100 V/sec so that it became from 0 V to 5,000 V over time. At this time, the voltage value when the measured current measured by the current measuring unit directly connected to the pair of jigs was maintained at 0.5 mA or more for 3 seconds was determined as the dielectric breakdown voltage.
[205]
[206]
3) Insulation breakdown voltage measurement method (pressurized X)
[207]
After laminating the separator and the cathode prepared in Examples 1 to 2 and Comparative Examples 1 to 6, the resultant of the laminated separator and the cathode was mounted between a pair of jigs facing each other.
[208]
Thereafter, the DC voltage applied from the voltage applying unit directly connected to the pair of jigs facing each other was gradually increased at a rate of 100 V/sec so that it became from 0 V to 5,000 V over time. At this time, the voltage value when the measured current measured by the current measuring unit directly connected to the pair of jigs was maintained at 0.5 mA or more for 3 seconds was determined as the dielectric breakdown voltage.
[209]
[210]
4) Method of measuring the hardness of the porous coating layer
[211]
The hardness was measured according to ASTM D3363 standard.
[212]
Specifically, 50 mm X 50 mm coated with a porous coating layer was fixed on a PET film with a sample thickness of 100 μm with double-sided tape. Thereafter, the surface of the fixed porous coating layer was scratched to a level (6B~3B <2B