Separator and lithium secondary battery comprising the same

Abstract

The present disclosure relates to a separator comprising: a porous polymer substrate; a porous coating layer formed on at least one surface of the porous polymer substrate and including a plurality of inorganic particles and a first binder polymer provided on surfaces of the inorganic particles in whole or in part such that the inorganic particles are interconnectable and fixable; and a conductive coating layer formed on one surface of the porous coating layer and including single-walled carbon nanotubes (SWCNTs) and a second binder polymer.

Description

Technical Field

[0001] This application claims priority to Korean Patent Application No. 10-2020-0135562, filed in Korea on October 19, 2020. This disclosure relates to a separator and a lithium secondary battery including the separator. Background Technology

[0002] Due to the rapid growth of the electric vehicle market, the demand for lithium-ion rechargeable batteries, including high-energy cells, has been increasing. Therefore, technologies using high-load electrodes (5mAh / cm²) have been developed. 2 Or larger (based on electrode area) batteries.

[0003] This type of lithium secondary battery includes a separator inserted between the positive and negative electrodes to prevent physical contact and electrical short circuits between the positive and negative electrodes. Such separators frequently use polyolefin-based porous polymer substrates, and separators with a porous coating comprising inorganic particles and binder polymers on at least one surface of the porous polymer substrate have been frequently used to prevent thermal shrinkage of the porous polymer substrate and enhance adhesion to the electrodes.

[0004] However, when commercially available separators are applied to batteries using high-load electrodes, it is difficult to ensure high-rate discharge characteristics and output / lifetime characteristics. Summary of the Invention

[0005] Technical issues

[0006] This disclosure is designed to address problems in the related art, and therefore relates to improving lithium-ion and electron transport rates by coating a porous surface with a conductive material. In this way, high-rate discharge characteristics and output characteristics can be improved.

[0007] Technical solution

[0008] In one aspect of this disclosure, a separator for a lithium secondary battery is provided according to any of the following embodiments.

[0009] According to a first embodiment, a separator for a lithium secondary battery is provided, comprising:

[0010] Porous polymer substrate;

[0011] A porous coating, wherein the porous coating is formed only on a first surface of the porous polymer substrate or on both the first and second surfaces of the porous polymer substrate, and comprises a plurality of inorganic particles and a first adhesive polymer disposed wholly or partially on the surface of the inorganic particles so that the inorganic particles can be interconnected and fixed; and

[0012] A conductive coating formed on the first surface of the porous coating and comprising a conductive material and a second adhesive polymer.

[0013] The conductive material loading in the conductive coating is 0.01 g / m. 2 Up to 0.5g / m 2 ,and

[0014] The conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 90% or greater of 100% by weight.

[0015] According to the second embodiment, a separator for a lithium secondary battery as defined in the first embodiment is provided.

[0016] The conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 99% or greater of 100% by weight.

[0017] According to the third embodiment, a separator for a lithium secondary battery as defined in the first or second embodiment is provided.

[0018] The conductive coating is a thin film with a thickness of 2 μm or less.

[0019] According to the fourth embodiment, a separator for a lithium secondary battery as defined in any of the first to third embodiments is provided.

[0020] The single-walled carbon nanotubes described therein have a diameter of 0.1 nm to 10 nm.

[0021] According to the fifth embodiment, a separator for a lithium secondary battery as defined in any of the first to fourth embodiments is provided.

[0022] The first adhesive and the second adhesive are each independently selected from polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, and cellulose acetate propionate. Any one of the group consisting of propionate, cyanoethyl pullullan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullullan, and carboxyl methyl cellulose, or a mixture of two or more of them.

[0023] According to the sixth embodiment, a separator for a lithium secondary battery as defined in any of the first to fifth embodiments is provided.

[0024] The conductive coating further comprises a particulate binder polymer.

[0025] According to the seventh embodiment, a separator for a lithium secondary battery as defined in the sixth embodiment is provided.

[0026] The particulate adhesive polymer has a glass transition temperature of 80°C or lower.

[0027] According to the eighth embodiment, a separator for a lithium secondary battery as defined in the sixth embodiment is provided.

[0028] The particulate adhesive polymer has an average diameter (D50) of 100 nm to 500 nm.

[0029] According to the ninth embodiment, a separator for a lithium secondary battery as defined in the sixth embodiment is provided.

[0030] The particulate adhesive polymer described herein includes any one of the following groups selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic copolymer, polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, polyvinyl alcohol, styrene, and polycyanoacrylate, or a mixture of two or more thereof.

[0031] According to the tenth embodiment, a separator for a lithium secondary battery as defined in any of the first to ninth embodiments is provided.

[0032] The weight ratio of the conductive material to the second adhesive polymer is 40:60 to 99:1.

[0033] According to the eleventh embodiment, a separator for a lithium secondary battery as defined in any of the first to tenth embodiments is provided.

[0034] The porous coating has a thickness of 1 μm to 10 μm.

[0035] In another aspect of this disclosure, a lithium secondary battery according to any of the following embodiments is provided.

[0036] According to the twelfth embodiment, a lithium secondary battery is provided, including a positive electrode, a negative electrode, and a separator inserted between the positive electrode and the negative electrode, wherein the separator is the same as that defined in any of the first to eleventh embodiments, and a conductive coating in the separator faces the positive electrode.

[0037] According to the thirteenth embodiment, a lithium secondary battery as defined in the twelfth embodiment is provided.

[0038] The positive electrode described herein has a capacity of 5 mAh / cm². 2 Or a high-load cathode with a larger positive electrode active material loading.

[0039] Beneficial effects

[0040] Since the separator for lithium secondary batteries according to embodiments of the present disclosure includes a conductive coating, the conductivity can be improved and the ionic conductivity of the separator can be ensured.

[0041] In addition, because the conductive coating includes an adhesive polymer, it improves the adhesion between the separator and the electrode. Attached Figure Description

[0042] The accompanying drawings illustrate preferred embodiments of the present disclosure and, together with the following disclosure, are used to provide a further understanding of the technical features of the present disclosure. Therefore, the present disclosure should not be construed as limited to the drawings. Furthermore, the shape, size, scale, or proportion of some components in the drawings may be exaggerated for the purpose of clearer description.

[0043] Figure 1 This is a scanning electron microscope (SEM) image illustrating a slurry dispersion used to form a conductive coating of single-walled carbon nanotubes prepared according to embodiments of the present disclosure.

[0044] Figure 2 This is a schematic SEM image of the slurry dispersion used to form the conductive coating of multi-walled carbon nanotubes prepared according to the comparative example.

[0045] Figure 3 It is a graph illustrating the change in electrical conductivity of each separator as a function of the amount of carbon nanotube coating according to the embodiments and comparative examples of this disclosure.

[0046] Figure 4 This is an illustration of an SEM image of the surface of a separator with a conductive coating according to Example 6.

[0047] Figure 5 This is a diagram of the SEM image of the surface of the separator with a conductive coating according to Comparative Example 6.

[0048] Figure 6 This is a schematic cross-sectional view illustrating a partition according to an embodiment of the present disclosure. Detailed Implementation

[0049] In the following description, preferred embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Before the description, it should be understood that the terminology used in the specification and appended claims should not be construed as limited to its common or dictionary meaning, but rather should be interpreted based on its meaning and concept in relation to the technical aspects of the present disclosure, on the principle that the inventors are allowed to appropriately define the terminology for the best interpretation. Therefore, the descriptions presented herein are merely preferred examples for illustrative purposes and are not intended to limit the scope of the present disclosure; thus, it should be understood that other equivalents and modifications may be made thereto without departing from the scope of the present disclosure.

[0050] Throughout the specification, the statement "a portion includes an element" does not exclude the presence of any other elements, but rather implies that the portion may further include other elements.

[0051] As used herein, the terms “approximately,” “substantially,” or similar, when implying an acceptable degree of preparation and material error unique to the claimed meaning, are used to mean from or to the claimed value and to prevent unintentional infringers from improperly using the claimed disclosure, including accurate or absolute values ​​provided to aid in understanding this disclosure.

[0052] As used in this article, the expression "A and / or B" means "A, B, or both of them".

[0053] The specific terms used in the following description are for illustrative purposes and are not intended to be limiting. Terms such as “right,” “left,” “top surface,” and “bottom surface” indicate directions in the accompanying drawings in which they are mentioned. Terms such as “inward” and “outward” indicate directions toward and away from the geometric center of the respective device, system, and its components, respectively. “Front,” “back,” “top,” and “bottom,” as well as related words and expressions, indicate positions and points in the accompanying drawings in which they are mentioned and should not be limiting. These terms include the words listed above, their derivatives, and words with similar meanings.

[0054] In electrochemical devices such as lithium-ion batteries, separators typically use porous polymer substrates, which undesirably exhibit thermal shrinkage behavior. Therefore, porous coatings have been introduced to reduce the thermal shrinkage rate of the separators.

[0055] However, when the separators currently in use are applied to batteries with high-load electrodes, it is difficult to ensure high-rate discharge characteristics and output / lifetime characteristics.

[0056] To address the aforementioned problems, this disclosure relates to improving lithium-ion and electron transport rates by coating a porous surface with a conductive material. In this way, high-rate discharge characteristics and output characteristics can be improved.

[0057] In one aspect of this disclosure, a separator for a lithium secondary battery is provided, comprising:

[0058] Porous polymer substrate;

[0059] A porous coating, wherein the porous coating is formed only on a first surface of the porous polymer substrate or on both the first and second surfaces of the porous polymer substrate, and comprises a plurality of inorganic particles and a first adhesive polymer disposed wholly or partially on the surface of the inorganic particles so that the inorganic particles can be interconnected and fixed; and

[0060] A conductive coating formed on the first surface of the porous coating and comprising a conductive material and a second adhesive polymer.

[0061] The conductive material loading in the conductive coating is 0.01 g / m. 2 Up to 0.5g / m 2 ,and

[0062] The conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 90% or greater of 100% by weight.

[0063] In addition, the loading of conductive material in the conductive coating is 0.01 g / m. 2 Up to 0.5g / m 2 The conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 90% or more of 100% by weight of the conductive material. Preferably, the SWCNT content is 99% or more of 100% by weight of the conductive material.

[0064] According to embodiments of the present disclosure, the separator includes a porous polymer substrate and a conductive coating, wherein the conductive coating is disposed on the outermost surface of either of the two surfaces of the separator, and the porous coating is disposed between the conductive coating and the porous polymer substrate. Alternatively, according to embodiments of the present disclosure, the separator may include a porous coating disposed on a surface of the porous polymer substrate that does not have the conductive coating disposed thereon. Figure 6 This is a schematic cross-sectional view illustrating a partition according to an embodiment of the present disclosure. (Refer to...) Figure 6A first porous coating 21 and a conductive coating 30 are successively disposed on the first surface 10a of the porous substrate 10, and a second porous coating 22 is disposed on the second surface 10b of the porous substrate, and no conductive coating is formed on the surface of the second porous coating.

[0065] As described below, when a separator according to this disclosure is applied to a battery, the conductive coating may be disposed in a manner in which it is oriented toward the positive electrode.

[0066] Carbon nanotubes (CNTs) are tubular, advanced materials containing carbon, and are tiny carbon compounds with diameters on the nanometer (nm) scale. Depending on their size, carbon nanotubes can be classified as conductors or semiconductors.

[0067] These carbon nanotubes have either a single-walled or multi-walled structure. Here, a multi-walled carbon nanotube (MWCNT) is a carbon structure that, as observed from the outside, has multiple tubes forming concentric circles, unlike a single-walled carbon nanotube, which, as observed from the cross-sectional shape at any point, comprises a multi-walled structure formed by multiple overlapping carbon layers. In contrast, a single-walled carbon nanotube has a structure consisting of a single tube forming concentric circles.

[0068] The inventors of this disclosure have conducted in-depth research to address the aforementioned problems by coating the surface of a porous coating with single-walled carbon nanotubes.

[0069] As from Figure 2 As can be seen, the problem with multi-walled carbon nanotubes is that most of them are cut during slurry preparation. On the other hand, as seen from... Figure 1 As can be seen, single-walled carbon nanotubes maintain a large fiber length without being cut. Therefore, when single-walled carbon nanotubes are applied to porous coatings and then dried, the connections between fibers are well maintained, thus improving cell performance.

[0070] It is believed that the reason why single-walled carbon nanotubes with one wall maintain a larger fiber length compared to multi-walled carbon nanotubes is that single-walled nanotubes have greater flexibility.

[0071] In addition, it is believed that single-walled carbon nanotubes have a significantly small diameter of several nanometers, but have a higher degree of graphitization and no structural defects compared to multi-walled carbon nanotubes. As a result, they can be grown in bundles and can undergo debulking during the preparation of dispersion slurries, while maintaining large fiber lengths without cutting the fibers.

[0072] According to embodiments of this disclosure, the preferred loading of single-walled carbon nanotubes is 0.01 g / m³.2 Up to 0.5g / m 2 The content of single-walled carbon nanotubes is based on the area (m²) of the conductive coating. 2 When the conductive coating is like Figure 6 When the area is the same as that of the separator, the content of single-walled carbon nanotubes can be expressed as the content per unit area of ​​separator. As the content of single-walled carbon nanotubes increases, the electrical conductivity increases. However, when an excessively high content of single-walled carbon nanotubes is used, the pores on the porous coating surface can become clogged, undesirably leading to an increase in air permeability to thousands of seconds per 100 cc and a decrease in ionic conductivity. Therefore, the content of single-walled carbon nanotubes is preferably controlled within the range defined above.

[0073] According to embodiments of this disclosure, single-walled carbon nanotubes may have a diameter of 0.1 nm or larger, 0.2 nm or larger, or 0.5 nm or larger, and 10 nm or smaller, 9 nm or smaller, 8 nm or smaller, or 7 nm or smaller.

[0074] The conductive coating includes a second adhesive polymer.

[0075] The second binder polymer can be of the type conventionally used in the art to form porous coatings. In particular, a glass transition temperature (Tg) of -200°C to 200°C can be used. g The polymer is used because it improves the mechanical properties of the resulting porous coating, such as flexibility and elasticity. This binder polymer acts as a binder that interconnects and stably holds the inorganic particles together, thus helping to prevent a decline in the mechanical properties of the separator with the porous coating.

[0076] In addition, the binder generally does not need to be ionicly conductive. However, the performance of the electrochemical device can be further improved when using polymers with ionic conductivity. Therefore, binder polymers with the highest possible dielectric constant can be used. In fact, since the degree of dissociation of salt in an electrolyte depends on the dielectric constant of the solvent used for the electrolyte, binder polymers with higher dielectric constants can improve the degree of salt dissociation in the electrolyte. Binder polymers can have dielectric constants (measured at a frequency of 1 kHz) ranging from 1.0 to 100, particularly 10 or higher.

[0077] In addition to the functions mentioned above, the adhesive polymer is also characterized by its gelation upon impregnation with a liquid electrolyte, thus exhibiting a high degree of swelling. Therefore, the adhesive polymer has a strength of 15 MPa. 1 / 2 up to 45MPa 1 / 2 or 15MPa1 / 2 Up to 25MPa 1 / 2 and 30MPa 1 / 2 up to 45MPa 1 / 2 The solubility parameter (Hildebrand solubility parameter) is used. Therefore, hydrophilic polymers with multiple polar groups can be used more frequently compared to hydrophobic polymers such as polyolefins. When the solubility parameter is less than 15 MPa... 1 / 2 or greater than 45MPa 1 / 2 At that time, the adhesive polymer was difficult to swell using conventional liquid electrolytes for batteries.

[0078] Non-limiting examples of adhesive polymers include, but are not limited to: polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetatebutyrate, and cellulose acetate propionate. Propionate, cyanoethyl pullullan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, cyanoethyl sucrose, pullullan, carboxyl methyl cellulose, or similar.

[0079] According to embodiments of this disclosure, when using an aqueous solvent, polyvinylpyrrolidone can be used as a second binder polymer to increase the dispersibility of inorganic particles.

[0080] According to embodiments of this disclosure, when using non-aqueous solvents, fluoropolymer binders can be used as a second binder polymer to increase the dispersibility of inorganic particles.

[0081] Here, the weight ratio of single-walled carbon nanotubes to the second binder polymer can be from 40:60 to 99:1, particularly from 70:30 to 95:5. When the weight ratio of single-walled carbon nanotubes to the second binder polymer meets the above-defined range, the problem of reduced pore size and porosity of the resulting conductive coating due to increased binder polymer content can be prevented. The problem of reduced peel resistance of the resulting coating due to reduced binder polymer content can also be solved, and the problem of reduced coatability due to reduced dispersibility of single-walled carbon nanotubes can be reduced.

[0082] The conductive coating is a thin film, and may have a thickness of, for example, 2 μm or less, or 1 μm or less. When the thickness of the conductive coating is greater than 2 μm, the loading of the paste used to form the conductive coating is too high, resulting in an increase in resistance.

[0083] Here, the conductive coating may further include a particulate adhesive polymer.

[0084] According to embodiments of this disclosure, the particulate adhesive polymer may have a glass transition temperature of 80°C or lower.

[0085] According to embodiments of this disclosure, the particulate adhesive polymer may have an average diameter (D50) of 100 nm to 500 nm.

[0086] Within the above-defined range, in conductive coatings, particulate binder polymers can be better dispersed between single-walled carbon nanotubes. Therefore, conductivity increases and adhesion to the electrodes can be further improved.

[0087] Specific examples of particulate adhesive polymers may include any one of the following groups selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic copolymer, polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, polyvinyl alcohol, styrene, and polycyanoacrylate, or mixtures of two or more of these.

[0088] When the conductive coating further includes a particulate binder polymer, it can have a structure comprising a particulate binder polymer dispersed between single-walled carbon nanotubes. Therefore, the conductivity increases and the adhesion to the electrode can be further improved.

[0089] According to embodiments of this disclosure, the porous coating comprises inorganic particles and a first binder polymer.

[0090] According to this disclosure, there are no particular limitations on the inorganic particles, as long as they are electrochemically stable. That is, there are no particular limitations on the inorganic particles, as long as they are within the operating voltage range of the applicable electrochemical device (e.g., based on Li / Li). + It should not cause oxidation and / or reduction in the 0-5V range. In particular, when using inorganic particles with high dielectric constants, they help increase the degree of dissociation of electrolyte salts, especially lithium salts, in liquid electrolytes, and thus they can improve the ionic conductivity of the electrolyte.

[0091] For these reasons, inorganic particles may include inorganic particles with a dielectric constant of 5 or greater, inorganic particles capable of transporting lithium ions, and mixtures thereof.

[0092] Inorganic particles with a dielectric constant of 5 or greater can be selected from Al2O3, SiO2, ZrO2, AlO(OH), TiO2, BaTiO3, Pb(Zr) x Ti 1-x O3(PZT, where 0 < x < 1), Pb 1-x La x Zr 1-y Ti yO3(PLZT, where 0 < x < 1, 0 < y < 1), (1-x)Pb(Mg) 1 / 3 Nb 2 / 3 The group consisting of at least one of the following: O3-xPbTiO3 (PMN-PT, where 0 < x < 1), hafnium oxide (HfO2), SrTiO3, SnO2, CeO2, MgO, NiO, CaO, ZnO, and SiC, or a mixture of two or more of these.

[0093] Inorganic particles capable of transporting lithium ions can be selected from lithium phosphate (Li3PO4), lithium titanium phosphate (Li... x Ti y (PO4)3, 0 < x < 2, 0 < y < 3), lithium aluminum titanium phosphate (Li x Al y Ti z (PO4)3, 0<x<2, 0<y<1, 0<z<3), (LiAlTiP) x O y -Based glass (1 < x < 4, 0 < y < 13), lithium lanthanum titanate (Li x La y TiO3, 0 < x < 2, 0 < y < 3), lithium germanium thiophosphate (Li x Ge y P z S w 0 < x < 4, 0 < y < 1, 0 < z < 1, 0 < w < 5), lithium nitride (Li x N y , 0 < x < 4, 0 < y < 2), SiS2-based glass (Li x Si y S z (where 0 < x < 3, 0 < y < 2, 0 < z < 4), and P2S5-based glass (Li x P y S z The group consisting of at least one of the groups (0 < x < 3, 0 < y < 3, 0 < z < 7), or a mixture of two or more of them.

[0094] Although there is no particular limitation on the average particle diameter of inorganic particles, the inorganic particles preferably have an average particle diameter of 0.001 μm to 10 μm, more preferably 100 nm to 2 μm, and most preferably 150 nm to 1 μm, in order to form a porous coating with uniform thickness and provide suitable porosity.

[0095] Inorganic particles can be added after they have been pre-crushed to a predetermined average particle diameter. Alternatively, the inorganic particles can be added to the binder polymer solution, then crushed and dispersed, while controlling them to have a predetermined average particle diameter using a ball milling process or the like.

[0096] The weight ratio of inorganic particles to the first binder polymer can be from 90:10 to 50:50. When the weight ratio of inorganic particles to the first binder polymer meets the above-defined range, the problem of reduced pore size and porosity of the resulting conductive coating due to increased first binder polymer content can be prevented. It also solves the problem of reduced peel resistance of the resulting coating due to decreased first binder polymer content.

[0097] According to embodiments of this disclosure, reference will be made to the above description of the second adhesive polymer in relation to the first adhesive polymer.

[0098] Here, the first adhesive polymer may be the same as or different from the second adhesive polymer.

[0099] According to embodiments of this disclosure, the porous coating may have a thickness of 1 μm to 10 μm.

[0100] According to this disclosure, the porous polymer substrate is a porous membrane that provides channels for lithium-ion transport while electrically insulating the negative and positive electrodes from each other to prevent short circuits. Any material can be used without particular limitation, as long as it is a material conventionally used as a separator in electrochemical devices.

[0101] In particular, the porous polymer substrate can be a porous polymer film substrate or a porous polymer nonwoven mesh substrate.

[0102] The porous polymer membrane substrate can be a porous polymer membrane comprising a polyolefin such as polyethylene or polypropylene. This polyolefin porous polymer membrane substrate achieves a shut-off function at temperatures ranging from 80°C to 150°C.

[0103] In this document, polyolefin-based porous polymer membranes may be formed from polymers, either alone or in combination of two or more of them, including polyolefin polymers such as polyethylene, polypropylene, polybutene, or polypentene, which contain high-density polyethylene, linear low-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene.

[0104] In addition, porous polymer membrane substrates can be obtained by molding various polymers other than polyolefins, such as polyesters, into a membrane shape. Furthermore, porous polymer membrane substrates can have a stacked structure of two or more membrane layers, wherein each membrane layer can be formed by a polymer, including the polymers mentioned above such as polyolefins or polyesters, alone or in combination of two or more of them.

[0105] In addition to the polyolefins mentioned above, porous polymer membrane substrates and porous polymer nonwoven substrates can also be formed from polyethylene terephthalate, polybutylene terephthalate, polyester, polyacetal, polyamide, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene oxide, polyphenylene sulfide, or polyethylene naphthalene, either alone or in combination.

[0106] While there are no particular limitations on the thickness of the porous polymer substrate, it can have a thickness of 1 μm to 100 μm, particularly 5 μm to 50 μm. Since batteries have recently offered high output / high capacity, it is advantageous to use thin films as porous polymer substrates. The pores present in the porous polymer substrate can have diameters of 10 nm to 100 nm, 10 nm to 70 nm, 10 nm to 50 nm, or 10 nm to 35 nm, and porosity of 5% to 90%, preferably 20% to 80%. However, according to this disclosure, these numerical ranges can be easily changed depending on the specific embodiment or as necessary.

[0107] The pores in a porous polymer substrate can include various types of pore structures. A substrate falls within the scope of this disclosure when either the average pore size measured using a porosimeter or the average pore size observed using a field emission scanning electron microscope (FE-SEM) meets the ranges defined above.

[0108] In this paper, in the case of dry separators with a commonly known uniaxial orientation, the median pore size, measured by FE-SEM in the transverse (TD) direction rather than the longitudinal (MD) direction, is taken as the standard pore size. In the case of other porous polymer substrates with a network structure (e.g., wet polyethylene (PE) separators), the pore size measured by a porosimeter is taken as the standard pore size.

[0109] The separator for lithium secondary batteries according to embodiments of this disclosure can be obtained using conventional methods known to those skilled in the art. According to embodiments of this disclosure, the separator can be obtained by applying a slurry comprising inorganic particles dispersed in a polymer solution containing a first binder polymer dissolved in a solvent to a porous substrate, followed by drying to form a porous coating. The porous coating may be formed on only one surface of the separator substrate or on both surfaces of the separator substrate. The solvent used herein preferably has a solubility parameter similar to the solubility of the first binder polymer and a low boiling point. This is because such a solvent allows for homogeneous mixing and can subsequently be easily removed. Non-limiting examples of solvents include any one of the group consisting of water, acetone, tetrahydrofuran, dichloromethane, chloroform, dimethylformamide, N-methyl-2-pyrrolidone (NMP), and cyclohexane, or mixtures of two or more of these.

[0110] Inorganic particles can be dispersed using methods commonly known to those skilled in the art. For example, a ball mill, bead mill, disperser, mixer, or similar method can be used. In particular, ball milling or bead milling is preferred. Here, the dispersion time can vary with the particle volume, but can suitably be from 1 hour to 20 hours. Furthermore, the particle size of the pulverized inorganic particles can be controlled by the size of the beads used in the ball milling or bead milling and the milling (bead milling) time.

[0111] While there are no particular limitations on the process of applying a slurry for forming a porous coating onto a porous polymer substrate, slot coating or dip coating processes are preferred. Slot coating involves applying a slurry supplied via a slot die to the entire surface of the substrate, and the coating thickness can be controlled depending on the flow rate supplied from a metering pump. Dip coating, on the other hand, involves immersing the substrate in a tank containing the composition to perform the coating, and the coating thickness can be controlled depending on the concentration of the composition and the rate at which the substrate is removed from the tank. Furthermore, for more precise control of the coating thickness, post-metering can be performed after immersion using a Mayer bar or similar method.

[0112] The porous polymer substrate coated with a slurry for forming a porous coating can then be dried in a dryer such as an oven to form a porous coating on at least one surface of the porous polymer substrate.

[0113] Drying can be carried out in a drying chamber, where the conditions are not particularly limited due to the use of non-solvents.

[0114] The drying step can be carried out at a relative humidity of 30% or greater, 35% or greater, or 40% or greater, and 80% or less, 75% or less, or 70% or less. For example, the drying step can be carried out at a relative humidity of 40% to 80%. Alternatively, the drying step can be carried out at a temperature of 20°C to 70°C for 0.1 to 2 minutes.

[0115] In the porous coating, inorganic particles are bonded together by a first binder polymer, while they stack up and come into contact with each other, thereby forming an interstitial volume between the inorganic particles, and the interstitial volume between the inorganic particles becomes an empty space to form pores.

[0116] In other words, the first adhesive polymer attaches the inorganic particles to each other so that they can maintain their bonded state, and for example, the first adhesive polymer connects and fixes the inorganic particles to each other. Furthermore, the pores in the porous coating are those formed by interstitial volumes between the inorganic particles, which become vacant spaces. These spaces can be defined by inorganic particles that are substantially facing each other in a closely packed or densely packed structure.

[0117] In addition to inorganic particles and a first binder polymer, the separator according to embodiments of this disclosure may further include other additives.

[0118] However, the conductive coating can be formed on the surface of the porous coating. As mentioned above, the conductive coating can be formed on only one or both surfaces of the separator. That is, when the porous coating is formed on both surfaces of the separator substrate, the conductive coating is formed only on the surface of one of the two porous coatings. Similarly, when the porous coating is formed only on one of the two surfaces of the separator, the conductive coating is formed on the corresponding surface.

[0119] For example, a conductive coating can be formed by applying a slurry comprising single-walled carbon nanotubes as conductive materials dissolved or dispersed in a solvent and a second binder polymer, followed by drying. While there are no particular limitations on the method of forming the conductive coating, slit-die coating is preferred because the conductive coating is formed on only one surface.

[0120] In another aspect of this disclosure, a lithium-ion secondary battery is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the separator described above according to the embodiment of this disclosure.

[0121] Meanwhile, the conductive coating of the separator can face the positive electrode.

[0122] Electrochemical devices include any device that performs an electrochemical reaction, and specific examples include all types of primary cells, secondary cells, fuel cells, solar cells, or capacitors such as supercapacitors. In particular, lithium secondary cells, including lithium metal secondary cells, lithium-ion secondary cells, lithium polymer secondary cells, or lithium-ion polymer batteries, are preferred among secondary cells.

[0123] There are no particular limitations on the electrodes used in conjunction with the separators according to this disclosure, and they can be obtained by incorporating electrode active materials into the electrode current collector using methods generally known in the art. Non-limiting examples of positive electrode active materials include conventional positive electrode active materials that can be used as positive electrodes in conventional electrochemical devices. In particular, lithium manganese oxide, lithium cobalt oxide, lithium nickel oxide, lithium iron oxide, or lithium composite oxides comprising combinations thereof are preferred.

[0124] In particular, the positive electrode active material may include, but is not limited to, LiCoO2, LiNiO2, LiMn2O4, LiCoPO4, LiFePO4, and LiNi 1-x-y-z Co x M1 y M2 z O2 (where M1 and M2 each independently represent any one selected from the group consisting of Al, Ni, Co, Fe, Mn, V, Cr, Ti, W, Ta, Mg, and Mo, x, y, and z each independently represent the atomic fraction of the element forming the oxide, and 0 ≤ x < 0.5, 0 ≤ y < 0.5, 0 ≤ z < 0.5, and 0 < x + y + z ≤ 1) or a mixture of two or more of these active materials. According to embodiments of this disclosure, the positive electrode active material may include lithium cobalt oxide and / or lithium nickel cobalt manganese oxide.

[0125] Meanwhile, according to the embodiments of this disclosure, the positive electrode can have a capacity of 5mAh / cm³. 2 Or a higher loading of positive electrode active material. The content of positive electrode active material is based on the area of ​​the positive electrode (cm²). 2 (1) Preferably, the area of ​​the positive electrode active material layer.

[0126] Non-limiting examples of negative electrode active materials include conventional negative electrode active materials that can be used as negative electrodes in conventional electrochemical devices. Specific examples of negative electrode active materials include lithium-intercalated materials such as lithium metal or lithium alloys, carbon, petroleum coke, activated carbon, graphite, or other carbonaceous materials. Non-limiting examples of positive electrode current collectors include foils made of aluminum, nickel, or combinations thereof. Non-limiting examples of negative electrode current collectors include foils made of copper, gold, nickel, copper alloys, or combinations thereof.

[0127] The electrolyte that can be used in the electrochemical device according to this disclosure is having A + B - Salts of structure, in which A + Including, for example, Li + Na + K + alkali metal cations such as B, or combinations thereof, - Including PF6, etc. - BF4 - Cl - ,Br - I - ClO4 - AsF6 - CH3CO2 - CF3SO3 - N(CF3SO2)2 - C(CF2SO2)3 - Anions such as propylene carbonate (PC), ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), dimethyl sulfoxide, acetonitrile, dimethoxyethane, diethoxyethane, tetrahydrofuran, N-methyl-2-pyrrolidone (NMP), ethyl methyl carbonate (EMC), gamma-butyrolactone (γ-butyrolactone), or combinations thereof, are present in organic solvents, including but not limited to these.

[0128] Depending on the manufacturing process of the final product and the desired properties of the final product, electrolyte injection can be performed at an appropriate step during the process used to manufacture the battery. That is, electrolyte injection can be performed before battery assembly or as a final step in battery assembly.

[0129] The embodiments will then be described in more detail so that this disclosure can be readily understood. However, the following embodiments may be embodied in many different forms and should not be construed as limited to the exemplary implementations set forth herein. Rather, these exemplary implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of this disclosure to those skilled in the art.

[0130] Test Example 1

[0131] Comparative Example 1

[0132] First, polyvinylidene fluoride-co-hexafluoropropylene (PVDF-HFP), serving as the first binder polymer, was introduced into acetone as a solvent and dissolved therein at 50°C for approximately 4 hours to prepare a binder polymer solution. Next, aluminum hydroxide (Al(OH)3) (particle size: 900 nm), serving as inorganic particles, was introduced into the binder polymer solution. Then, a cyano resin (weight average molecular weight: 400,000) and a liquid fatty acid (Fatty acid, available from BYTCo. P104) were introduced as dispersants. Here, the weight ratio of inorganic particles:first binder polymer:cyano resin:fatty acid was controlled at 73:25:1:1 to prepare a slurry for forming a porous coating. Here, the slurry has a solids content of 16 parts by weight per 100 parts by weight (solvent-free slurry).

[0133] A slurry for forming a porous coating was applied to both surfaces of a polyethylene porous membrane (porosity: 45%) using a dip-coating process and dried at 23°C and 45% relative humidity to obtain a separator with a porous coating of 3 μm thickness on each surface. The test results for the separator are shown in Tables 1 and 2 below.

[0134] Example 1

[0135] A conductive coating is formed on the porous coating of the separator obtained from Comparative Example 1.

[0136] Specifically, the conductive coating is prepared as follows.

[0137] Single-walled carbon nanotubes, polyvinylpyrrolidone as a second binder polymer, and tannic acid (TA) as a dispersant are introduced into water as a solvent at a controlled weight ratio of 45:45:10 to prepare a slurry for forming a conductive coating. Here, the slurry has a solids content of 2 parts by weight per 100 parts by weight (solvent-free slurry).

[0138] At room temperature, a slurry for forming a conductive coating was applied to either of the two porous coatings formed as described above using a slit-die coating process, followed by drying, to obtain a separator with a conductive coating formed thereon. Here, the actual loading of single-walled carbon nanotubes coated in the conductive coating was 0.22 g / m². 2 The test results for the partitions are shown in Tables 1, 2, and 3. Figure 3 middle.

[0139] Examples 2 to 4

[0140] The separators were obtained in the same manner as in Example 1, except that the loading of single-walled carbon nanotubes actually coated in the conductive coating was controlled as shown in Table 1. Test results for each separator are shown in Table 1 and... Figure 3 middle.

[0141] Comparative Examples 2 to 5

[0142] The separators were obtained in the same manner as in Example 1, except that multi-walled carbon nanotubes (MWCNTs) were used instead of single-walled carbon nanotubes, the solid content was controlled at 4% by weight, and the loading of MWCNTs was controlled as shown in Table 1. Here, the slurry used to form the conductive coating was controlled to have a weight ratio of MWCNTs:second binder polymer:dispersant of 80:10:10. Test results for each separator are shown in Table 1 and... Figure 3 middle.

[0143] [Table 1]

[0144]

[0145]

[0146] Methods for measuring conductivity

[0147] The conductivity of the separators was determined using a surface resistance analyzer (automated 4-point probe system, model number: CMT-SR2000N, available from AiT Co.). Specifically, each separator according to Examples 1 to 4 and Comparative Examples 1 to 5 was sampled in a 5cm × 5cm size, and the thickness of the sample was measured. The sample was then inserted into the surface resistance analyzer, and the measured thickness was input into the system to determine the surface resistance. Here, conductivity is expressed in Ω × cm, and the measured value was converted to its reciprocal to determine the conductivity.

[0148] Methods for calculating the increase / decrease rate of cell resistance

[0149] Using the cell resistance of Comparative Example 1 as a standard, the increase / decrease rate of cell resistance for each separator was calculated according to Formula 1 below.

[0150] [Formula 1]

[0151] (Resistance of the partition to be tested - Resistance of Comparative Example 1) / (Resistance of Comparative Example 1) × 100

[0152] In Table 1, when the absolute value of the rate of increase / decrease in the cell resistance of the separator, represented by a negative number, increases, the separator shows a lower resistance. In other words, the separator shows a greater effect in reducing resistance.

[0153] Method for calculating the increase / decrease rate of 2C rate discharge capacity

[0154] Comparative Example 1 uses the discharge capacity at a 2C rate as a standard, and calculates the increase / decrease rate of the 2C rate discharge capacity of each separator according to Formula 2 below.

[0155] [Equation 2]

[0156] (Discharge capacity of the cell under test at 2C rate - Discharge capacity of the cell according to Comparative Example 1 at 2C rate) / (Discharge capacity of the cell according to Comparative Example 1 at 2C rate) × 100

[0157] In Table 1, the cell shows a greater effect on increasing discharge capacity as the absolute value of the rate of increase / decrease in discharge capacity, represented by a positive number, increases.

[0158] As can be seen from Table 1, Examples 1 and 2, which have conductive coatings, show significant reductions in cell resistance of -17.7% and -13.4%, respectively, as measured by the rate of increase / decrease in cell resistance, based on Comparative Example 1. Furthermore, Examples 1 and 2 show significant increases in discharge capacity of 31.7% and 29.9%, respectively, as measured by the rate of increase / decrease in discharge capacity at a 2C rate, based on Comparative Example 1. In particular, when comparing Example 4 with Comparative Example 5, despite the same conductivity of 0.01 S / cm, there are significantly large differences in the rate of increase / decrease in cell resistance and the rate of increase / decrease in discharge capacity.

[0159] As a result, it can be seen that the separator using single-walled carbon nanotubes according to the embodiments of this disclosure ensures improved high-rate discharge characteristics and output / lifetime characteristics compared to the separator using multi-walled carbon nanotubes.

[0160] Test Example 2

[0161] Example 5

[0162] A conductive coating is formed on the separator obtained according to Comparative Example 1.

[0163] Specifically, the conductive coating is prepared as follows.

[0164] A slurry for forming a conductive coating is prepared by introducing single-walled carbon nanotubes, polyvinylpyrrolidone as a second binder polymer, tannic acid (TA) as a dispersant, and styrene-butadiene rubber (SBR) as a particulate binder polymer into water as a solvent at a controlled weight ratio of 10.8:10.7:2.5:76. Here, the slurry has a solids content of 1.5 parts by weight per 100 parts by weight (solvent-free slurry).

[0165] At room temperature, a slurry for forming a conductive coating was applied to either of the two porous coatings formed as described above using a slit-die coating process, followed by drying, to obtain a separator with a conductive coating formed thereon. Here, the actual loading of single-walled carbon nanotubes coated in the conductive coating was 0.2 g / m². 2 The test results for the partition are shown in Table 2 below.

[0166] [Table 2]

[0167]

[0168] As can be seen from Example 1 in Table 2, the conductivity increases when single-walled carbon nanotubes are used in the conductive coating. Furthermore, it can be seen that when a particulate binder polymer is further incorporated, both the conductivity and adhesion to the electrode are improved in Example 5. In contrast, in Comparative Example 1, the conductivity itself is not measurable when no conductive coating is present.

[0169] Test Example 3

[0170] Example 6

[0171] A conductive coating is formed on the separator obtained according to Comparative Example 1.

[0172] Specifically, the conductive coating is prepared as follows.

[0173] Single-walled carbon nanotubes, polyvinylpyrrolidone as a second binder polymer, and tannic acid (TA) as a dispersant are introduced into water as a solvent at a controlled weight ratio of 45:45:10 to prepare a slurry for forming a conductive coating. Here, the slurry has a solids content of 2 parts by weight per 100 parts by weight (solvent-free slurry).

[0174] At room temperature, a slurry for forming a conductive coating was applied to either of the two porous coatings formed as described above using a slit-die coating process, followed by drying, to obtain a separator with a conductive coating formed thereon. Here, the actual loading of single-walled carbon nanotubes coated in the conductive coating was 0.46 g / m². 2The test results for the partition are shown in Table 3 below.

[0175] Comparative Example 6

[0176] A conductive coating is formed on the separator obtained according to Comparative Example 1.

[0177] Specifically, the conductive coating is prepared as follows.

[0178] Single-walled carbon nanotubes, polyvinylpyrrolidone as a second binder polymer, and tannic acid (TA) as a dispersant are introduced into water as a solvent at a controlled weight ratio of 45:45:10 to prepare a slurry for forming a conductive coating. Here, the slurry has a solids content of 2 parts by weight per 100 parts by weight (solvent-free slurry).

[0179] At room temperature, a slurry for forming a conductive coating was applied to either of the two porous coatings formed as described above using a slit-die coating process, followed by drying, to obtain a separator with a conductive coating formed thereon. Here, the actual loading of single-walled carbon nanotubes coated in the conductive coating was 0.55 g / m². 2 The test results for the partition are shown in Table 3 below.

[0180] [Table 3]

[0181]

[0182] As can be seen from Table 3, when the molecular weight of SWCNT is greater than 0.5 g / m 2 At this time, the air permeation time increases rapidly, and the dielectric breakdown voltage decreases. Simultaneously, Figure 4 This is an illustration of an SEM image of the surface of a separator with a conductive coating according to Example 6. Figure 5 These are SEM images illustrating the surface of the separator with a conductive coating according to Comparative Example 6. These images show that in Comparative Example 6, where a higher load of SWCNTs is used, the pores become clogged because the SWCNTs are coated across the entire surface of the separator.

[0183] Test methods

[0184] 1) Methods for measuring thickness

[0185] The thickness of each partition was measured using a thickness gauge (VL-50S-B, available from Mitutoyo).

[0186] 2) Method for determining the adhesion (Lami strength) between the electrode and the separator.

[0187] To determine the adhesion (Lami strength) between the electrode and the separator, the negative electrode was prepared as follows.

[0188] First, artificial graphite, carbon black, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed with water in a weight ratio of 96:1:2:2 to prepare a negative electrode slurry. This negative electrode slurry was then used at a concentration of 3.5 mAh / cm³. 2 The capacity is applied to copper (Cu) foil and dried at 130°C for 3 hours or longer, followed by pressing to obtain the negative electrode.

[0189] The resulting negative electrode was cut into 25mm × 100mm dimensions. Additionally, each separator obtained according to the examples and comparative examples was cut into 15mm × 100mm dimensions. The separators were stacked with the negative electrode, and this stack was inserted between 100μm thick PET films and adhered using a flatbed press. Here, the flatbed press was heated and pressurized at 60°C for 1 second at a pressure of 6.5MPa. The adhered separators and negative electrodes were attached to a glass slide using double-sided tape. The ends of the separators (10mm or less from the end of the adhered surface) were peeled off and attached to the 25mm × 100mm PET film using single-sided tape, allowing them to be joined longitudinally. The glass slide was then mounted to the lower fixture of the UTM instrument (LLOYD Instrument LFPlus), and the PET film adhered to the separators was mounted to the upper fixture of the UTM instrument. Force was then applied at 180° and a rate of 300mm / min. The force required to separate the negative electrode from the porous coating facing the negative electrode is measured.

[0190] 3) Air permeability

[0191] The air permeability of each partition was measured according to JIS P-8117 using a Gurley type air permeability tester. Here, air permeability was measured as 100cc of air passing through 645mm. 2 The time required to cover the area and 28.6 mm in diameter. The air permeation time was recorded as the average of values ​​measured at three points, including one point each on the left, middle, and right sides of the sample.

[0192] 4) Dielectric breakdown voltage

[0193] The dielectric breakdown voltage was measured using an AC / DC / IR withstand voltage tester (model 19052, Chroma). A pressing fixture made of aluminum was used, with an upper clamp measuring 30 mmR and a lower clamp measuring 55 × 10⁵ mm.2 Each fixture is surface-treated with Teflon material.

[0194] The first aluminum foil, the separator, and the second aluminum foil are stacked on the lower clamp, and the upper clamp is placed on top of it to measure the dielectric breakdown voltage. The first and second aluminum foils each have a thickness of 15 μm, and the first aluminum foil has a diameter of 65 × 115 mm. 2 The second aluminum foil has dimensions of 40×40mm. 2 The size.

[0195] Then, the voltage is increased from DC 0V at a rate of 100V / s, and while holding the current at 0.5mA or greater for 3 seconds, it is determined whether each sample is unqualified, and the voltage value is checked in the case of unqualified samples.

[0196] 5) Determination of battery short circuit

[0197] After battery manufacturing, while discharging the batteries at a 1C rate, non-operating batteries or those showing a 20% or greater reduction in discharge capacity based on their theoretical capacity are inspected. For example, a battery achieving a capacity of 70mAh when the theoretical capacity is 100mAh is identified as a short-circuited battery.

Claims

1. A separator for a lithium secondary battery, comprising: Porous polymer substrate; A porous coating, wherein the porous coating is formed only on a first surface of the porous polymer substrate or on both the first and second surfaces of the porous polymer substrate, and comprises a plurality of inorganic particles and a first adhesive polymer disposed wholly or partially on the surface of the inorganic particles, thereby interconnecting and fixing the inorganic particles; and A conductive coating formed on the first surface of the porous coating and comprising a conductive material and a second adhesive polymer. The conductive material loading in the conductive coating is 0.01 g / m. 2 Up to 0.5g / m 2 ,and The conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 90% or greater of 100% by weight.

2. The separator for a lithium secondary battery according to claim 1, wherein the conductive material comprises single-walled carbon nanotubes (SWCNTs) in an amount of 99% by weight or greater based on 100% by weight of the conductive material.

3. The separator for a lithium secondary battery according to claim 1, wherein the conductive coating is a thin film and has a thickness of 2 μm or less.

4. The separator for a lithium secondary battery according to claim 1, wherein the single-walled carbon nanotubes have a diameter of 0.1 nm to 10 nm.

5. The separator for a lithium secondary battery according to claim 1, wherein the first adhesive and the second adhesive are each independently selected from polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polymethyl methacrylate, polyethylhexyl acrylate, polybutyl acrylate, polyacrylonitrile, polyvinylpyrrolidone, polyvinyl acetate, polyethylene-co-vinyl acetate, polyethylene oxide, polyarylate, cellulose acetate, cellulose acetate butyrate, and cellulose acetate propionate. The group consisting of acetatepropionate, cyanoethylpullulan, cyanoethylpolyvinylalcohol, cyanoethylcellulose, cyanoethylsucrose, pullulan, and carboxylmethylcellulose, or a mixture of two or more thereof.

6. The separator for a lithium secondary battery according to claim 1, wherein the conductive coating further comprises a particulate binder polymer.

7. The separator for a lithium secondary battery according to claim 6, wherein the particulate binder polymer has a glass transition temperature of 80°C or lower.

8. The separator for a lithium secondary battery according to claim 6, wherein the particulate binder polymer has an average diameter (D50) of 100 nm to 500 nm.

9. The separator for a lithium secondary battery according to claim 6, wherein the particulate adhesive polymer comprises any one of, or a mixture of two or more thereof, selected from the group consisting of styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, acrylic copolymer, polyacrylonitrile, polyvinyl chloride, polyvinylidene fluoride, polyvinyl alcohol, styrene, and polycyanoacrylate.

10. The separator for a lithium secondary battery according to claim 1, wherein the weight ratio of the conductive material to the second adhesive polymer is 40:60 to 99:

1.

11. The separator for a lithium secondary battery according to claim 1, wherein the porous coating has a thickness of 1 μm to 10 μm.

12. A lithium secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the separator is the same as that defined in any one of claims 1 to 11, and a conductive coating in the separator faces the positive electrode.

13. The lithium secondary battery according to claim 12, wherein the positive electrode has a capacity of 5 mAh / cm³. 2 Or a high-load cathode with a larger positive electrode active material loading.

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