Separator for secondary batteries and secondary batteries containing the same

Abstract

To provide a separator for secondary batteries that is free of porous substrates and offers excellent heat resistance, low film resistance, and high adhesive strength. [Solution] The present invention relates to a separator for lithium secondary batteries and a lithium secondary battery containing the same. The separator comprises one or more fiber layers, at least one of which comprises a fiber network of fibers containing a first copolymer, and at least one of which comprises a core-shell fiber containing a polyimide fiber or a polyimide resin. The first copolymer comprises a copolymer of monomer mixtures comprising a first structural unit containing a unit derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer with four or more carbon atoms in the main chain in the ester portion; and a third structural unit derived from a sulfonic acid group-containing monomer. The copolymer is composed of 5 to 80 mol% of the first structural unit, 10 to 60 mol% of the second structural unit, and 5 to 80 mol% of the third structural unit per 100 mol% of the copolymer.

Description

[Technical Field]

[0001] This invention relates to a separator for secondary batteries and a secondary battery containing the same. [Background technology]

[0002] (Reference to related applications) This application is based on the priority claim of Korean Patent Application No. 10-2024-0157090, filed with the Korean Intellectual Property Office on November 7, 2024, and incorporates its full disclosure by reference herein.

[0003] (Background technology) Recently, with the rapid proliferation of electronic devices using batteries, such as mobile phones, laptops, and electric vehicles, the demand for high-energy-density, high-capacity rechargeable batteries has been rapidly increasing. This has led to active research and development efforts to improve the performance of lithium-ion rechargeable batteries.

[0004] A lithium secondary battery is a battery that includes a positive electrode and a negative electrode containing an active material that allows for the insertion and deintercalation of lithium ions, and an electrolyte. It generates electrical energy through oxidation and reduction reactions that occur when lithium ions are inserted into and deintercalated from the positive and negative electrodes. [Overview of the project] [Means for solving the problem]

[0005] One example is a separator for secondary batteries that does not have a porous substrate and provides excellent heat resistance, low film resistance, and high adhesive strength.

[0006] Another example is the provision of a secondary battery including a separator for secondary batteries.

[0007] One example is a separator for secondary batteries.

[0008] The separator for secondary batteries includes one or more fiber layers, at least one of which includes a fiber network of fibers containing a first copolymer, and at least one of which includes a core-shell fiber containing a polyimide fiber or a polyimide resin. The first copolymer includes a copolymer of monomer mixtures containing a first structural unit having units derived from an aromatic vinyl monomer; a second structural unit having an alkyl group with 4 or more carbon atoms in the main chain in the ester moiety, derived from an alkyl group (meth)acrylic monomer; and a third structural unit having a sulfonic acid group. The first structural unit is present in an amount of 5-80 mol%, the second structural unit in an amount of 10-60 mol%, and the third structural unit in an amount of 5-80 mol% per 100 mol% of the copolymer.

[0009] Another example is the provision of a secondary battery.

[0010] A secondary battery includes a positive electrode, a negative electrode, and a separator for the secondary battery located between the positive and negative electrodes.

[0011] A separator for secondary batteries, according to one embodiment, does not have a porous substrate and does not shrink the separator overhang when the battery is exposed to heat, thus preventing short circuits and improving battery reliability. A separator for secondary batteries, according to one embodiment, can improve battery capacity, safety, and lifespan by providing excellent heat resistance, high adhesive strength, and low film resistance. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 2] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 3] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 4] This is a schematic cross-sectional view showing a lithium secondary battery as an example. [Figure 5] This is a schematic cross-sectional view showing a separator for a lithium secondary battery based on one example. [Figure 6] This is a schematic cross-sectional view showing a separator for a lithium secondary battery based on one example. [Figure 7] This is a schematic cross-sectional view showing a separator for a lithium secondary battery based on one example. [Figure 8] This is a schematic cross-sectional view showing a separator for a lithium secondary battery based on one example. [Figure 9] This is a schematic cross-sectional view showing a separator for a lithium secondary battery based on one example. [Modes for carrying out the invention]

[0013] The following describes in detail some examples of the present invention. However, these are presented as examples only and do not limit the present invention, which is defined solely by the appended claims.

[0014] Unless otherwise specified in this specification, when a layer, film, region, plate, or other part is described as being "on top of" another part, this includes not only cases where it is "directly on top" of the other part, but also cases where there are other parts in between.

[0015] Unless otherwise specified, singular nouns may also include plural nouns. Unless otherwise specified, "A or B" may mean "including A, including B, or including both A and B."

[0016] In this specification, “these combinations” may mean mixtures, laminates, composites, copolymers, alloys, blends, and reaction products of the constituents.

[0017] In this specification, "particle size D50" means the average particle size representing the diameter of particles with a cumulative volume of 50% in the particle size distribution. The particle size distribution can be measured by methods widely known to those skilled in the art. For example, the particle size distribution can be measured with a particle size analyzer, or it can also be measured from a transmission electron micrograph or a scanning electron micrograph. As another method, it can be measured using a measuring device employing the dynamic light scattering method. After performing data analysis to count the number of particles for each particle size range, the D50 value can then be calculated therefrom. Alternatively, it can be measured using the laser diffraction method. When measuring by the laser diffraction method, more specifically, after dispersing the particles to be measured in a dispersion medium, it is introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac, MT3000), irradiated with ultrasonic waves of about 28 kHz at an output of 60 W, and then the D50 at the 100% standard of the particle size distribution in the measuring device can be calculated.

[0018] In this specification, "(meth)acrylic" means acrylic and / or methacrylic.

[0019] Hereinafter, unless otherwise defined, "substitution" means that hydrogen in a compound is replaced with a C1-C 30 alkyl group, C2-C 30 alkenyl group, C2-C 30 alkynyl group, C6-C 30 aryl group, C7-C 30 alkylaryl group, C1-C 30 alkoxy group, C1-C 30 heteroalkyl group, C3-C 30 heteroalkylaryl group, C3-C 30 cycloalkyl group, C3-C 15 cycloalkenyl group, C6-C <� 30 cycloalkynyl group, C2-C 30 heterocycloalkyl group, halogen (F, Cl, Br or I), hydroxy group (-OH), nitro group (-NO2), cyano group (-CN), amino group (-NRR') (where R and R' are independently of each other hydrogen or a C1-C6 alkyl group), sulfobetaine group (-RR'N +(CH2) n SO3 - (where n is a natural number from 1 to 10), carboxybetaine group (-RR'N + (CH2) n COO - (where n is a natural number from 1 to 10) (where R and R' are independent of each other, C1 to C 20 C1-C6 alkyl group, C1-C6 alkyl group, C1-C6 alkoxy group, or C6-C6 alkyl group. 12 This means that the molecule is substituted with substituents selected from an aryl group, a carboxyl group (-COOH) or its salt (-C(=O)OM, where M is an organic or inorganic cation), a sulfonic acid group (-SO3H) or its salt (-SO3M, where M is an organic or inorganic cation), a phosphate group (-PO3H2) or its salt (-PO3MH or -PO3M2, where M is an organic or inorganic cation), and combinations thereof.

[0020] In the following, C1-C3 alkyl groups refer to methyl, ethyl, or propyl groups. 10 The alkylene group can be, for example, a C1-C6 alkylene group, a C1-C5 alkylene group, or a C1-C3 alkylene group, and can also be a methylene group, an ethylene group, or a propylene group. 20 Cycloalkylene groups are, for example, C3-C 10 Cycloalkylene group, or C5~C 10 It can be a cycloalkylene group, for example, a cyclohexylene group. C6~C 20 The arylene group is, for example, C6~C 10 It can be an allerene group, for example, a phenylene group. C3~C 20 A heterocyclic group is, for example, C3~C 10 It can be a heterocyclic group, for example, a pyridine group.

[0021] In the following, "hetero" means containing one or more heteroatoms selected from N, O, S, Si, and P.

[0022] Furthermore, in chemical formulas, the asterisk (*) indicates a portion that is linked to the same or different atoms, groups, or structural units. Unless otherwise specified, the chemical formulas described herein may also be considered to have hydrogen atoms bonded to them.

[0023] In the following, "alkali metals" refers to elements belonging to Group 1 of the periodic table, such as lithium, sodium, potassium, rubidium, cesium, or francium, and may exist in a cationic or neutral state.

[0024] In this specification, when describing a numerical range, "X~Y" means "X or greater and Y or less (X ≤ and ≤ Y)."

[0025] The present invention will be described in detail below. The following description will focus on a separator for lithium secondary batteries. However, the separator of the present invention can also be applied to secondary batteries other than lithium secondary batteries.

[0026] The separator for secondary batteries does not have a porous substrate, and there is no shrinkage of the separator's overhang when the battery is exposed to heat, thus preventing short circuits and improving the reliability of the battery.

[0027] Separators for secondary batteries can improve battery capacity, safety, and lifespan by providing excellent heat resistance, high adhesion, and low film resistance.

[0028] A lithium secondary battery separator according to one embodiment includes one or more fiber layers, at least one of which includes a fiber network of fibers containing a first copolymer, the first copolymer containing a copolymer of monomer mixtures including a first structural unit containing a unit derived from an aromatic vinyl monomer; a second structural unit containing an alkyl group with four or more carbon atoms in the main chain in the ester moiety; and a third structural unit derived from a sulfonic acid group containing monomer, the first structural unit is present in an amount of 5-80 mol%, the second structural unit in an amount of 10-60 mol%, and the third structural unit in an amount of 5-80 mol% per 100 mol% of the copolymer.

[0029] In this specification, “fiber layer” may mean a layer formed by a network of fibers resembling a mesh. Here, the fibers may include one or more types of nanofibers and microfibers. Although not particularly limited, the fibers may be produced by electrospinning. Electrospinning may be carried out by conventional methods known to those skilled in the art. Electrospinning methods are described in more detail below.

[0030] The fibers have an average diameter of 300 nm or less (for example, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm, 105 nm, 110 nm, 115 nm, 120 nm, 125 nm, 130 nm, 135 nm, 140 nm, 145 nm, 150 nm, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, (180nm, 185nm, 190nm, 195nm, 200nm, 205nm, 210nm, 215nm, 220nm, 225nm, 230nm, 235nm, 240nm, 245nm, 250nm, 255nm, 260nm, 265nm, 270nm, 275nm, 280nm, 285nm, 290nm, 295nm, 300nm), and possibly 200nm to 50nm.

[0031] Each fiber layer may have a thickness of 20 μm or less (e.g., 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm), or between 2 and 10 μm. Within this range, they can be used in batteries.

[0032] The separator may have a thickness of 20 μm or less (for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm), or 5 to 10 μm. Within this range, it can be used in batteries.

[0033] The separator does not necessarily have to contain conventionally known porous substrates, such as porous polyolefin substrates. Porous substrates are manufactured by stretching or other means, and at high temperatures, thermal shrinkage and melting occur, which can cause overhangs to shrink within the separator when the battery is exposed to heat, potentially leading to a short circuit. However, since the separator does not contain a porous substrate, the possibility of a short circuit is low, which can improve the reliability of the battery.

[0034] The separator can be used in batteries without a porous substrate by including a fiber network of fibers, in which at least one layer of the fiber layer contains the first copolymer. The separator can improve the capacity, safety, and lifespan of the battery by providing excellent heat resistance, high adhesion, and low film resistance.

[0035] <First copolymer> The first copolymer comprises a copolymer of monomer mixtures including a first structural unit containing units derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer with four or more carbon atoms in the main chain in the ester moiety; and a third structural unit derived from a sulfonic acid group-containing monomer. The first structural unit is present in an amount of 5-80 mol%, the second structural unit in an amount of 10-60 mol%, and the third structural unit in an amount of 5-80 mol% per 100 mol% of the copolymer.

[0036] The first copolymer can improve the capacity of lithium secondary batteries by reducing the film resistance of the separator and improve the safety and lifespan of lithium secondary batteries by providing high adhesion. Furthermore, the first copolymer provides resistance improvement effects by offering high electrolyte impregnation and improved flexibility, and can provide high capacity retention and low rate of change in DC internal resistance at both room temperature (e.g., 20-30°C) and high temperature (e.g., 40-50°C), respectively.

[0037] In one example, the first copolymer functions as an adhesive binder to ensure adhesion to the separator electrodes. Film resistance and adhesive strength are in a trade-off relationship. The first copolymer can increase the adhesive strength while reducing the film resistance of the separator.

[0038] If a glass transition temperature exists, the first copolymer may have a glass transition temperature of 60°C to 80°C, for example, 60°C to 70°C. Within this range, it may not only exhibit excellent adhesion to electrodes but also good ionic conductivity. The glass transition temperature of the first copolymer can be measured by conventional methods known to those skilled in the art using thermomechanical analysis (TMA). The glass transition temperature of a copolymer can be measured by conventional methods known to those skilled in the art using thermomechanical analysis (TMA). For example, the glass transition temperature can be measured as follows. 1. Prepare the sample by cutting the copolymer or binder to be analyzed into a 0.5 mm x 8 mm size, attach it to the holder, and place it on the sample probe of the TMA instrument. 2. Set the mechanical load to 0.0150 N and the heating rate to 5 °C / min, and measure the change in sample length due to temperature. 3. The temperature at which the slope of the graph obtained from the TMA instrument changes is defined as the glass transition temperature.

[0039] The sum of the first, second, and third structural units in the first copolymer may be 95 mol% or more, for example, 95 to 100 mol%, or for example, 100 mol%. Within this range, the aforementioned separator effect can be easily realized.

[0040] (First structural unit) The first structural unit includes units derived from aromatic vinyl monomers. The units derived from aromatic vinyl monomers can provide adhesive strength so that the separator adheres well to the electrode and can improve the permeability of the separator.

[0041] The units derived from aromatic vinyl monomers are represented by the following chemical formula 1, and the first copolymer may contain one or more of the units represented by the following chemical formula 1:

[0042] [ka]

[0043] (In chemical formula 1, R 1 and R 2 Each of these is independently hydrogen, or a substituted or unsubstituted C1-C5 alkyl group. Ar is a substituted or unsubstituted monocyclic or polycyclic C6-C6 molecule. 20 (It is an aryl group.)

[0044] In one specific example, in chemical formula 1, Ar is C6~C 20 It is a monocyclic or polycyclic aryl group, such as a phenyl group, naphthalenyl group, anthracenyl group, pyrenyl group, etc.

[0045] In one specific example, the aromatic vinyl monomer is represented by the following chemical formula 2, and the first copolymer may contain one or more units represented by the following chemical formula 2:

[0046] [ka]

[0047] (In chemical formula 2, R 3 and R 4Each of these is independently hydrogen, or a substituted or unsubstituted C1-C5 alkyl group. R is C1-C with substitution or non-substitution. 20 Alkyl, substituted or unsubstituted C3-C 20 Cycloalkyl groups, substituted or unsubstituted C1-C 20 Alkoxy groups, substituted or unsubstituted C3-C 20 Aryl groups, halogens, and substituted or unsubstituted C2-C 20 It is one of the types selected from the group consisting of alkenyl groups. m is an integer between 0 and 5.

[0048] In one specific example, in chemical formula 2, R is a substituted or unsubstituted C1-C 20 Alkyl groups or substituted or unsubstituted C1-C 20 It may be an alkoxy group. In one specific example, in chemical formula 2, m may be 0 or 1.

[0049] For example, the aromatic vinyl monomer may contain one or more of the following: styrene; alpha-methylstyrene; 4-butylstyrene including 4-n-butylstyrene, 4-i-butylstyrene, 4-t-butylstyrene, etc.; butoxystyrene including 4-n-butoxystyrene, 4-i-butoxystyrene, 4-t-butoxystyrene, etc.; halostyrene including chlorostyrene, bromostyrene, fluorostyrene, etc.; vinyltoluene including 4-vinyltoluene, 3-vinyltoluene, 2-vinyltoluene, etc.; and vinylnaphthalene including 1-vinylnaphthalene, 2-vinylnaphthalene, etc.

[0050] The first structural unit may further contain units in the ester portion derived from alkyl group-containing (meth)acrylic monomers with 1 to 3 carbon atoms in the main chain. The units derived from (meth)acrylic monomers can further provide an adhesive strength improvement effect.

[0051] The units derived from (meth)acrylic monomers are represented by the following chemical formula 3, and the first copolymer may contain one or more of the units represented by the following chemical formula 3:

[0052] [ka]

[0053] (In chemical formula 3, R 5 and R 6 These are, independently, hydrogen or a methyl group. L 1 (These are substituted or unsubstituted, linear or branched C1-C3 alkyl groups.)

[0054] In one specific example, the (meth)acrylic monomer may contain one or more of the following: methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, and i-propyl (meth)acrylate.

[0055] For example, the (meth)acrylic monomer may have a homopolymer glass transition temperature of 50°C or higher, for example, 50 to 150°C. Within this range, the glass transition temperature of the first copolymer described above can be easily reached. For example, such (meth)acrylic monomers may be methyl methacrylate, ethyl methacrylate, etc.

[0056] The first structural unit is present in an amount of 5 to 80 mol% relative to 100 mol% of the first copolymer. If the first structural unit is present in an amount of 5 mol% or more, electrolyte impregnation is improved, and the capacity retention rate at high temperatures may be high. If the first structural unit is present in an amount of 80 mol% or less, the film resistance does not increase, and the capacity retention rate at both room temperature and high temperatures may be high. For example, for 100 mol% of copolymer, the first structural units are 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, 44 mol% It may be contained in mol%, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, or in amounts of 10-70 mol%, 20-60 mol%, or 30-60 mol%. When included within this range, the separator can exhibit low film resistance, excellent adhesion to porous substrates and electrodes, as well as breathability and oxidation resistance.

[0057] For every 100 mol% of copolymer, the units derived from aromatic vinyl monomers are 5-80 mol%, for example, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, 4 It may be contained in amounts of 4 mol%, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, or 10-70 mol%, 10-60 mol%, 10-35 mol%, 15-30 mol%, and 5-35 mol%. Within this range, the effects of the separator described above may be easily realized.

[0058] For every 100 mol% of copolymer, the units derived from the (meth)acrylic monomer range from 0 to 80 mol%, for example, 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, and 44 mol%. It may be contained in the following amounts: %, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, or in amounts of 5-80 mol%, 10-70 mol%, 10-60 mol%, 10-35 mol%, 15-30 mol%, and 5-35 mol%. Within this range, the effects of the separator mentioned above can be easily realized.

[0059] According to one example, with respect to 100 mol% of the copolymer, units derived from aromatic vinyl monomers and units derived from (meth)acrylic monomers may be present in a molar ratio of 1:0.5 to 2 (e.g., 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1, 1:1.1, 1:1.2, 1:1.3, 1:1.4, 1:1.5, 1:1.6, 1:1.7, 1:1.8, 1:1.9, 1:2), 1:1 to 1:2, for example, 1:1. Within this range, the aforementioned separator effect can be easily realized.

[0060] (Second structural unit) The second structural unit is located in the ester portion and is derived from an alkyl group-containing (meth)acrylic monomer with four or more carbon atoms in the main chain. The second structural unit can improve the dispersibility of the coating layer slurry and improve the electrolyte impregnation rate and flexibility of the coating layer.

[0061] Units derived from (meth)acrylic monomers are represented by the following chemical formula 4, and copolymers may contain one or more structural units represented by the following chemical formula 4:

[0062] [ka]

[0063] (In chemical formula 4, R 7 and R 8 These are, independently, hydrogen or a methyl group. L 2 This refers to substituted or unsubstituted, linear or branched C4-C4 atoms. 30 (It is an alkyl group.)

[0064] Here, alkyl groups are defined as having a main chain of C4~C 20 Alkyl, C4~C 10 It may be an alkyl or C4-C8 alkyl group.

[0065] According to one example, the (meth)acrylic monomer may contain one or more of the following: 2-ethylhexyl (meth)acrylate, n-butyl (meth)acrylate, i-butyl (meth)acrylate, t-butyl (meth)acrylate, pentyl (meth)acrylate, hexyl (meth)acrylate, heptyl (meth)acrylate, n-octyl (meth)acrylate, nonyl (meth)acrylate, isononyl (meth)acrylate, decyl (meth)acrylate, and isodecyl (meth)acrylate.

[0066] The second structural unit is present in an amount of 10 to 60 mol% relative to 100 mol% of the copolymer. If the second structural unit is 10 mol% or more, the film resistance will be lower when impregnated with electrolyte, and the volume retention rate may be high at both room temperature and high temperature. If the second structural unit is 60 mol% or less, the permeability will be improved, and the volume retention rate may be high at both room temperature and high temperature. For example, relative to 100 mol% of the first copolymer, the second structural unit is present in amounts of 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol% It may contain 100%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, 44 mol%, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, or 15-35 mol%, for example, 20-60 mol%, 20-30 mol%. Within this range, it may be easier to increase the adhesion and flexibility of the separator to the electrode.

[0067] (Third structural unit) The third structural unit is derived from a sulfonic acid group-containing monomer. This unit, derived from the sulfonic acid group-containing monomer, can reduce the membrane resistance of the separator by increasing the mobility of lithium ions in the presence of the first and second structural units.

[0068] In one embodiment, the third structural unit, by containing a bulky functional group derived from (meth)acrylamide sulfonic acid or a salt thereof, increases the glass transition temperature of the copolymer and provides a structural safety effect. Additionally, when the third structural unit is a functional group derived from a salt of (meth)acrylamide sulfonic acid, the metal (M) can be moved through the third structural unit by the metal (M) substituted sulfonic acid functional group, resulting in a significantly lower film resistance of the separator.

[0069] The third structural unit may be represented by chemical formula 5, chemical formula 6, or chemical formula 7 below. The copolymer may contain one or more of the following chemical formulas: chemical formula 5, chemical formula 6, and chemical formula 7.

[0070] [ka]

[0071] (In chemical formulas 5 to 7, R 9 , R 10 , R 11 , R 12 , R 13 and R 14 Each of these is independently either hydrogen or a C1-C3 alkyl group. L 3 , L 5 and L 7 These are, independently, -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-, L 4 , L 6 and L 8 These are, independently, substituted or non-substituted C1-C 10 Alkylene group, substituted or unsubstituted C3-C 20 Cycloalkylene group, substituted or unsubstituted C6-C 20 Arylene group or substituted or unsubstituted C3-C 20 It is a heterocyclic group, a, b, c, d, e, and f are each independent integers between 0 and 2. In chemical formula 6, M is an alkali metal.

[0072] As an example, in chemical formulas 5 to 7, L 3 , L 5 and L 7 Each of these is independently -C(=O)NH-, L 4 , L 6 and L8 These are, independently, C1~C 10 It is an alkylene group, a, b, c, d, e, and f can be integers of 1.

[0073] A sulfonate group-containing structural unit may contain only one of the structural units represented by chemical formula 5, chemical formula 6, or chemical formula 7, or it may contain two or more of these. For example, a sulfonate group-containing structural unit may contain the structural unit represented by chemical formula 6, and in other examples, a sulfonate group-containing structural unit may contain the structural unit represented by chemical formula 6 and the structural unit represented by chemical formula 7.

[0074] Sulfonate group-containing structural units may be derived from, for example, vinyl sulfonic acid, allyl sulfonic acid, styrene sulfonic acid, anethole sulfonic acid, (meth)acrylamide alkane sulfonic acid, sulfoalkyl (meth)acrylate, or salts thereof.

[0075] Here, alkanes are C1~C 20 Alkane, C1~C 10 It can be an alkane or a C1-C6 alkane, and alkyl is C1-C 20 Alkyl, C1-C 10 It can be alkyl or C1-C6 alkyl. The term "salt" refers to a salt composed of the aforementioned sulfonic acid and a suitable ion. The ion can be, for example, an alkali metal ion, in which case the salt can be an alkali metal sulfonic acid salt.

[0076] (Meth)acrylamide alkanesulfonic acid may be, for example, 2-(meth)acrylamide-2-methylpropanesulfonic acid, and sulfoalkyl (meth)acrylate may be, for example, 2-sulfoethyl (meth)acrylate, 3-sulfopropyl (meth)acrylate, etc.

[0077] The third structural unit is present in an amount of 5 to 80 mol% of 100 mol% of the copolymer. If the third structural unit is present in an amount of 5 mol% or more, the film resistance of the separator may decrease, and the rate of change of DC internal resistance may decrease at both room temperature and high temperature. If the third structural unit is present in an amount of 80 mol% or less, the capacity retention rate of the battery may increase at both room temperature and high temperature, and the rate of change of DC internal resistance may decrease at both room temperature and high temperature.

[0078] For example, the third structural unit may be present in 10 to 60 mol% of 100 mol% of the first copolymer. For example, the third structural unit may be present in 5 mol%, 6 mol%, 7 mol%, 8 mol%, 9 mol%, 10 mol%, 11 mol%, 12 mol%, 13 mol%, 14 mol%, 15 mol%, 16 mol%, 17 mol%, 18 mol%, 19 mol%, 20 mol%, 21 mol%, 22 mol%, 23 mol%, 24 mol%, 25 mol%, 26 mol%, 27 mol%, 28 mol%, 29 mol%, 30 mol%, 31 mol%, 32 mol%, 33 mol%, 34 mol%, 35 mol%, 36 mol%, 37 mol%, 38 mol%, 39 mol%, 40 mol%, 41 mol%, 42 mol%, 43 mol%, and 44 mol% of 100 mol% of the copolymer. It may be contained in amounts of 100%, 45 mol%, 46 mol%, 47 mol%, 48 mol%, 49 mol%, 50 mol%, 51 mol%, 52 mol%, 53 mol%, 54 mol%, 55 mol%, 56 mol%, 57 mol%, 58 mol%, 59 mol%, 60 mol%, 61 mol%, 62 mol%, 63 mol%, 64 mol%, 65 mol%, 66 mol%, 67 mol%, 68 mol%, 69 mol%, 70 mol%, 71 mol%, 72 mol%, 73 mol%, 74 mol%, 75 mol%, 76 mol%, 77 mol%, 78 mol%, 79 mol%, 80 mol%, or 20-60 mol%, 30-60 mol%, and 30-40 mol%. If the third structural unit is included within this range, the separator may exhibit significantly lower film resistance, higher battery capacity retention at both room temperature and high temperature, and a lower rate of change in DC internal resistance at both room temperature and high temperature.

[0079] The copolymer of monomer mixtures may contain alkali metals. The alkali metals may exist in cationic form and may be, for example, lithium, sodium, potassium, rubidium, or cesium. For example, the alkali metals may be bonded to the copolymer binder of the monomer mixture and exist in the form of salts. Alkali metals can aid in the synthesis of the copolymer of monomer mixtures in aqueous solvents, improving the adhesion of the coating layer and enhancing the permeability and oxidation resistance of the separator.

[0080] Copolymers of monomer mixtures may have a glass transition temperature of 60°C to 80°C. Specifically, this could be 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 71°C, 72°C, 73°C, 74°C, 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, or 62°C to 78°C, for example, 64°C to 75°C. Excellent adhesive strength can be achieved within this range, and separators containing such copolymers can exhibit excellent breathability and oxidation resistance. The glass transition temperature of a copolymer can be measured by thermomechanical analysis (TMA) using conventional methods known to those skilled in the art. For example, the glass transition temperature can be measured as follows: 1. Prepare the sample by cutting the copolymer or binder to be analyzed into a 0.5 mm x 8 mm size, attach it to the holder, and place it on the sample probe of the TMA instrument. 2. Set the mechanical load to 0.0150 N and the heating rate to 5 °C / min, and measure the change in sample length due to temperature. 3. The temperature at which the slope of the graph obtained from the TMA instrument changes is defined as the glass transition temperature.

[0081] Alkali metals may be present in a binder containing a copolymer of alkali metals and monomer mixtures in an amount of 1 to 40% by weight, for example, 1 to 30% by weight, or 1 to 20% by weight, or 10 to 20% by weight. For example, the monomer mixture copolymer binder and alkali metals may be present in a weight ratio of 99:1 to 60:40, 99:1 to 70:30, for example, 99:1 to 80:20, for example, 90:10 to 80:20.

[0082] Alkali metals may be present in an amount of 0.1 to 1.0 mol% relative to the total content of the copolymer of alkali metals and monomer mixtures. When alkali metals are present within this range, the coating layer can have excellent adhesion, and the separator containing it can exhibit excellent breathability and oxidation resistance.

[0083] The first copolymer can take various forms, such as an alternating polymer in which structural units are distributed alternately, a random polymer in which they are distributed arbitrarily, or a graft polymer in which some structural units are grafted.

[0084] The weight-average molecular weight of the first copolymer may be 100,000 to 1,000,000 g / mol, 100,000 to 500,000 g / mol, 100,000 to 150,000 g / mol, 200,000 to 130,000 g / mol, or 300,000 to 900,000 g / mol. When the weight-average molecular weight of the first copolymer falls within this range, it can exhibit excellent adhesion and low resistance. The weight-average molecular weight may be the average molecular weight on a polystyrene basis, measured using gel permeation chromatography.

[0085] The first copolymer can be produced by a solution polymerization method.

[0086] The separator includes one or more fiber layers containing a fiber network of fibers comprising a first copolymer without a porous substrate. The fiber layers can facilitate the reduction of the separator's thermal shrinkage rate in the electrolyte and the reduction of its resistance.

[0087] The separator may include one or more fiber layers containing a fiber network comprising the first copolymer.

[0088] According to one example, the separator may include two or more fiber layers, each containing a fiber network comprising the first copolymer.

[0089] The first copolymer may be present in the fibers in an amount of 50% by weight or more, for example, 60-100% by weight.

[0090] The separator includes a fiber layer containing a fiber network containing the first copolymer, and may be a single-layer separator or a multilayer separator containing multiple fiber layers. Here, a multilayer separator means one in which multiple fiber layers are stacked on top of each other. A multilayer separator can easily incorporate multiple polymers with different electrospinning conditions into the separator, thereby increasing the strength of the separator.

[0091] The following section provides a detailed description of separators containing multiple fiber layers.

[0092] <Multilayer separator> The multilayer separator may include a fiber network of fibers containing the first copolymer.

[0093] According to one embodiment, the multilayer separator may include one or more or two or more fiber layers, each containing a fiber network of fibers comprising the first copolymer.

[0094] The multilayer separator may further include one or more fiber layers comprising a fiber network of fibers containing one or more second copolymers of a different type from the first copolymer.

[0095] In one specific example, the multilayer separator may be a three-layer separator in which a fiber layer containing a network of fibers containing a first copolymer; a fiber layer containing a network of fibers containing a second copolymer; and a fiber layer containing a network of fibers containing the first copolymer are sequentially laminated.

[0096] In another specific example, a multilayer separator may be a three-layer separator in which a fiber layer containing a network of fibers containing a second copolymer; a fiber layer containing a network of fibers containing a first copolymer; and a fiber layer containing a network of fibers containing a second copolymer are sequentially laminated.

[0097] In other embodiments, the multilayer separator may include one or more or two or more fiber layers comprising a network of core-shell type fibers containing the first copolymer. In this case, the first copolymer may be contained in the core or the shell of the core-shell type fiber.

[0098] The multilayer separator may further include one or more fiber layers comprising a network of fibers containing one or more second copolymers of a different type from the first copolymer.

[0099] The multilayer separator may further include one or more or two or more fiber layers, each containing a network of fibers comprising the first copolymer.

[0100] In one specific example, the multilayer separator may be a three-layer separator in which a fiber layer containing a network of fibers including one or more types of second copolymers; a fiber layer containing a network of core-shell type fibers; and a fiber layer containing a network of fibers including one or more types of second copolymers are sequentially laminated. The core-shell type fibers may be shell type fibers containing a core-second copolymer containing a first copolymer. Alternatively, the core-shell type fibers may be shell type fibers containing a core-first copolymer containing a second copolymer.

[0101] In other specific examples, a multilayer separator may be a three-layer separator in which a fiber layer containing a network of core-shell type fibers; a fiber layer containing a network of fibers containing one or more types of second copolymers; and a fiber layer containing a network of core-shell type fibers are sequentially laminated. The core-shell type fiber may be a shell-type fiber containing a core-second copolymer containing a first copolymer. Alternatively, the core-shell type fiber may be a shell-type fiber containing a core-first copolymer containing a second copolymer.

[0102] Furthermore, according to other embodiments, the multilayer separator may include one or more or two or more fiber layers comprising a network of fibers containing a mixture of the first copolymer and the second copolymer.

[0103] In the mixture, the first copolymer is present in 10-90% by weight (for example, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 4 7% by weight, 48% by weight, 49% by weight, 50% by weight, 51% by weight, 52% by weight, 53% by weight, 54% by weight, 55% by weight, 56% by weight, 57% by weight, 58% by weight, 59% by weight, 60% by weight, 61% by weight, 62% by weight, 63% by weight, 64% by weight, 65% by weight, 66% by weight, 67% by weight, 68% by weight, 69% by weight, 70% by weight, 71% by weight, 72% by weight, 73% by weight, 74% by weight, 75% by weight, 76% by weight, 77% by weight, 78% by weight, 79% by weight, 80% by weight, 81% by weight, 82% by weight, 83% by weight, 84% by weight, 85% by weight, 86% by weight, 87% by weight, 88% by weight 89% by weight, 90% by weight, 20-50% by weight, the second copolymer is 10-90% by weight (e.g., 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44 Weight%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 6 5% by weight, 66% by weight, 67% by weight, 68% by weight, 69% by weight, 70% by weight, 71% by weight, 72% by weight, 73% by weight, 74% by weight, 75% by weight, 76% by weight, 77% by weight, 78% by weight, 79% by weight, 80% by weight, 81% by weight, 82% by weight, 83% by weight, 84% by weight, 85% by weight,It may contain 86% by weight, 87% by weight, 88% by weight, 89% by weight, 90% by weight, or 50-80% by weight.

[0104] The multilayer separator may further include one or more or two or more fiber layers, each containing a network of fibers comprising the first copolymer.

[0105] The multilayer separator may contain one or more or two or more fiber layers, each containing a network of fibers including the second copolymer.

[0106] In one specific example, the multilayer separator may be a three-layer separator in which a fiber layer containing a network of fibers comprising a first copolymer and a second copolymer; a fiber layer containing a network of fibers comprising a second copolymer; and a fiber layer containing a network of fibers comprising a first copolymer and a second copolymer are sequentially laminated.

[0107] In other specific examples, the multilayer separator may be a three-layer separator in which a fiber layer containing a network of fibers including the second copolymer; a fiber layer containing a network of fibers including the first copolymer and the second copolymer; and a fiber layer containing a network of fibers including the second copolymer are sequentially laminated.

[0108] The second copolymer will be described in detail below.

[0109] <Second copolymer> The second copolymer is a different copolymer from the first copolymer.

[0110] According to one example, the second copolymer may contain units derived from different monomers compared to the first copolymer, or copolymers with different molar ratios of each monomer.

[0111] The second copolymer is not particularly limited, as long as it can be used to produce fibers by electrospinning and does not affect the separator's effect.

[0112] The second copolymer may contain one or more selected from the group consisting of polyacrylonitrile, polyaniline, polypyrrole, polyrhodanine, melamine, polyurea, polyvinyl chloride, polyvinyl alcohol, polyethylene oxide, polymethyl methacrylate, polyacrylic acid, polylactic acid, polyimide, polyamide-imide, polyaramid, polybenzylimidazole, polypropylene, resorcinol-formaldehyde resin, melamine-formaldehyde resin, pitch, sucrose, glucose, cellulose, and polyvinylidene fluoride.

[0113] In one specific example, the second copolymer may be polyimide or a mixture containing 50% by weight or more of polyimide. Such a second copolymer can improve the heat resistance of the separator and, when combined with a fiber layer containing a network of fibers including the first copolymer, may be advantageous in reducing battery resistance, increasing adhesion, lowering the shutdown temperature, and improving processability. The first copolymer is excellent at counteracting the resistance of the second copolymer containing polyimide or a mixture containing 50% by weight or more of polyimide.

[0114] In other specific examples, the second copolymer may be a mixture containing 50% by weight or more of polyvinylidene fluoride or polyvinylidene fluoride. Such a second copolymer can increase the flexibility of the separator and further enhance the adhesive strength of the separator.

[0115] In further specific examples, the second copolymer may be a mixture containing 50% by weight or more of a mixture of polyimide and polyvinylidene fluoride. Such a second copolymer can increase the flexibility of the separator, further enhance the adhesive strength of the separator, and counteract the brittleness of polyimide to improve the processability of the separator.

[0116] <Electrospinning> The fibrous layer can be produced by electrospinning solutions containing the first copolymer and the second copolymer, respectively.

[0117] The solution facilitates the dispersion and dissolution of the first and second copolymers, allowing for successful electrospinning. The solvent may include, but is not limited to, methylformamide, dimethylacetamide, dimethyl sulfoxide, methylpyrrolidone, etc. Further stirring and / or heat treatment may be performed to enhance the dispersion and dissolution of the copolymers.

[0118] Electrospinning is preferably carried out in a space with an internal temperature of 25°C or higher, for example, between 25°C and 60°C. Within this range, the degree to which the solvent in the electrospinning solution volatilizes is high, so there is no residual solvent, and the influence of the solvent on the battery can be reduced.

[0119] Electrospinning can be performed by positioning a nozzle pack, consisting of a tip with a needle size of 23G (gauge) to 30G, and a collector roller at a certain distance apart, adding an electrospinning solution to the tip, positioning the substrate on the collector roller, and then applying a voltage of 35kV to 90kV to the tip. The distance between the nozzle pack and the active material layer may be 10cm to 20cm. A needle size of 25G to 30G in the tip is preferable because it allows for the formation of a fiber layer of the desired shape.

[0120] In the electrospinning process, the electrospinning solution is spun and stretched into fiber form, thereby forming a layer containing nanofibers on a substrate. This occurs when the electrospinning solution is suspended in droplet form by surface tension at the tip, and when a voltage is applied, electric charge accumulates on the surface of the solution, generating a repulsive force between the charges. When a critical voltage is reached where the repulsive force between the charges exceeds the surface tension of the solution, a cone-shaped Taylor cone is formed, and a jet of the electrospinning solution is ejected from the apex of the cone's end. The jet is highly stretched, forming nanofibers, which are collected on the substrate, and a fiber layer is formed.

[0121] The air pressure at the nozzle can be 1 MPa or higher. Within this range, the degree of solvent evaporation is high, and the impact of residual solvent on the battery can be reduced.

[0122] It is preferable to appropriately adjust the tip air to minimize interference between tips and ensure uniform electrospinning. The tip air can be adjusted by flowing compressed air at a pressure of 0.1 MPa to 0.3 MPa.

[0123] The roll speed of the collector roller can be adjusted so that the fiber layer can be formed to an appropriate thickness, for example, a speed of 1 m / min to 3 m / min. Furthermore, the flow rate of the electrospinning solution discharged from the tip can be adjusted to a rate of 20 μl / min to 200 μl / min. In one specific example, a drying process can be carried out at 20°C to 30°C after the electrospinning process.

[0124] Core-shell fibers can be produced by simultaneously electrospinning a first copolymer and a second copolymer into nozzles for the core and shell, respectively. Methods for producing core-shell fibers are conventionally known to those skilled in the art.

[0125] <Separator Manufacturing> The separator can be manufactured by press-forming the fiber layers together after they have been produced.

[0126] According to one example, a separator can be manufactured by separately manufacturing multiple fiber layers, and then sequentially laminating and pressing the manufactured fiber layers together.

[0127] In other embodiments, the separator may be manufactured by sequentially injecting an electrospinning solution containing the copolymer into sequentially positioned nozzles, and then sequentially spinning and simultaneously crimping the copolymer.

[0128] The crimping method is not particularly limited, but it can be performed by crimping with rollers or the like.

[0129] The separator can exhibit excellent ventilation, for example, 250 seconds / 100 cm. 3 Less than, for example, 230 seconds / 100cm3 Below, or 200 seconds / 100cm 3 The following degree of air permeability can be achieved: namely, 40 seconds / 100 cm per unit thickness. 3 • Less than 1 μm, e.g., 30 seconds / 100 cm 3 • Less than 1 μm, or 25 seconds / 100 cm 3 • It can have an air permeability of 1 μm or less. Here, the air permeability is 100 cm 3 This refers to the time (in seconds) it takes for air to pass through a unit thickness of separator. Air permeability per unit thickness can be determined by measuring the air permeability relative to the total thickness of the separator and then dividing by the thickness. Air permeability is measured using an air permeability measuring device (Asahi Seiko Co., Ltd., EG01-55-1MR) at a rate of 100 cm². 3 It can be measured as the time (in seconds) it takes for air to pass through.

[0130] The separator's shrinkage rate within the electrolyte may be 0.1% or less, for example, 0-0.1% or even 0%. Within this range, the reliability of the battery can be improved. Figures 5 to 9 are schematic cross-sectional views showing a separator for a secondary battery according to one embodiment of the present invention. Referring to Figure 5, the separator may comprise a layer 210 containing a fiber network of fibers 211 containing the first copolymer, a layer 220 containing a fiber network of polyimide fibers 221, and a layer 230 containing a fiber network of fibers 211 containing the first copolymer. Referring to Figure 6, the separator may comprise a layer 210 containing a fiber network of fibers 211 containing the first copolymer and polyimide fibers 221, a layer 220 containing a fiber network of polyimide fibers 221, and a layer 230 containing a fiber network of fibers 211 containing the first copolymer and polyimide fibers 221. Refer to Figure 7. As shown in Figure 7, the separator may include a layer 210 containing a fiber network of core-shell fibers 212 containing the first copolymer, a layer 220 containing a fiber network of polyimide fibers 221, and a layer 230 containing a fiber network of core-shell fibers 212 containing the first copolymer. Referring to Figure 8, the separator may comprise a layer 210 containing a fiber network of polyimide fibers 221, a layer 220 containing a fiber network of core-shell fibers 212 containing a first copolymer, and a layer 230 containing a fiber network of polyimide fibers 221. Referring to Figure 9, the separator may comprise a layer 210 containing a fiber network of polyimide fibers 221, a layer 220 containing a fiber network of core-shell fibers 212 containing the first copolymer, and a layer 230 containing a fiber network of polyimide fibers 221. As shown in Figure 9, the separator may comprise a layer 210 containing a fiber network of fibers 213, a layer 220 containing a fiber network of fibers 211 containing the first copolymer and polyimide fibers 221, and a layer 230 containing a fiber network of fibers 213.

[0131] Lithium-ion battery Another embodiment provides a lithium secondary battery including a separator, a positive electrode, and a negative electrode according to one embodiment.

[0132] The lithium secondary battery separator is as described above. The lithium secondary battery separator may be located between the positive and negative electrodes.

[0133] positive electrode active material As the positive electrode active material, a compound capable of reversible intercalation and deintercalation of lithium (lithium-intercalated intercalation compound) can be used. Specifically, one or more composite oxides of lithium with metals selected from cobalt, manganese, nickel, and combinations thereof can be used.

[0134] The composite oxide may be a lithium transition metal composite oxide, and specific examples include lithium nickel oxides, lithium cobalt oxides, lithium manganese oxides, lithium iron phosphate compounds, cobalt-free nickel-manganese oxides, or combinations thereof.

[0135] As an example, a compound represented by any one of the following chemical formulas can be used. Li a A 1-b X b O 2-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.5, 0 ≦ c ≦ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G e O2(0.90 ≦ a ≦ 1.8, 0 ≦ b ≦ 0.9, 0 ≦ c ≦ 0.5, 0 ≦ d ≦ 0.5, 0 ≦ e ≦ 0.1); Li a NiG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a CoG b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn 1-b G b O2(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn2G b O4(0.90 ≦ a ≦ 1.8, 0.001 ≦ b ≦ 0.1); Li a Mn 1-g G g PO4(0.90 ≦ a ≦ 1.8, 0 ≦ g ≦ 0.5); Li (3-f) Fe2(PO4)3(0 ≦ f ≦a FePO4 (0.90 ≤ a ≤ 1.8). In the formula, A is Ni, Co, Mn or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements or a combination thereof; D is O, F, S, P or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V or a combination thereof; L 1 These are Mn, Al, or a combination of these.

[0136] As an example, the positive electrode active material may be a high-nickel positive electrode active material in which the nickel content relative to 100 mol% of the metal excluding lithium in the lithium transition metal composite oxide is 80 mol% or more, 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, and 99 mol% or less. High-nickel positive electrode active materials can achieve high capacity and can be applied to high-capacity, high-density lithium secondary batteries.

[0137] positive electrode The positive electrode for a lithium secondary battery may include a current collector and a positive electrode active material layer formed on the current collector. The positive electrode active material layer may include a positive electrode active material and further include a binder and / or a conductive material.

[0138] For example, the positive electrode may further contain additives that can act as a sacrificial positive electrode.

[0139] The content of the positive electrode active material is 90% to 99.5% by weight of 100% by weight of the positive electrode active material layer, and the content of the binder and conductive material may be 0.5% to 5% by weight, respectively, relative to 100% by weight of the positive electrode active material layer.

[0140] The binder plays a role in ensuring good adhesion between positive electrode active material particles and good adhesion of the positive electrode active material to the current collector. Typical examples of binders include, but are not limited to, polyvinyl alcohol, carboxymethylcellulose, hydroxypropylcellulose, diacetylcellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, nylon, etc.

[0141] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery that is constructed can be used. Examples of conductive materials include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0142] Al can be used as the current collector, but it is not limited to this.

[0143] negative electrode active material The negative electrode active material includes a substance capable of reversibly intercalating / deintercalating lithium ions, lithium metal, an alloy of lithium metal, a substance that can be doped and dedoped with lithium, or a transition metal oxide.

[0144] As substances capable of reversibly intercalating / deintercalating lithium ions, carbon-based negative electrode active materials may be included, for example, crystalline carbon, amorphous carbon, or a combination thereof. Examples of crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite, and examples of amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, etc.

[0145] As alloys of lithium metal, alloys of lithium and metals selected from Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn can be used.

[0146] As substances capable of doping and undoping lithium, Si-based negative electrode active materials or Sn-based negative electrode active materials can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiO x (0 < x < 2), an Si-Q alloy (Q is selected from alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof), or a combination thereof. The Sn-based negative electrode active material can be Sn, SnO2, an Sn-based alloy, or a combination thereof.

[0147] The silicon-carbon composite can be a composite of silicon and amorphous carbon. According to one embodiment, the silicon-carbon composite can be in a form where silicon particles and amorphous carbon are coated on the surface of the silicon particles. For example, it may include secondary particles (cores) formed by granulating primary silicon particles and an amorphous carbon coating layer (shell) located on the surface of the secondary particles. Amorphous carbon may also be located between the primary silicon particles, for example, the primary silicon particles may be coated with amorphous carbon. The secondary particles may be dispersed and present in an amorphous carbon matrix.

[0148] The silicon-carbon composite may further contain crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer located on the surface of the core.

[0149] Si-based or Sn-based anode active materials can be used in combination with carbon-based anode active materials.

[0150] negative electrode The negative electrode for a lithium secondary battery includes a current collector and a negative electrode active material layer located on the current collector. The negative electrode active material layer includes a negative electrode active material and may further include a binder and / or a conductive material.

[0151] For example, the negative electrode active material layer may contain 90% to 99% by weight of negative electrode active material, 0.5% to 5% by weight of binder, and 0% to 5% by weight of conductive material.

[0152] The binder plays a role in ensuring good adhesion between the negative electrode active material particles and good adhesion of the negative electrode active material to the current collector. Non-aqueous binders, aqueous binders, dry binders, or combinations thereof can be used as binders.

[0153] Examples of non-aqueous binders include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0154] The aqueous binder can be selected from styrene-butadiene rubber, (meth)acrylate styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepichlorohydrin, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0155] When using an aqueous binder as the negative electrode binder, it may further contain a cellulosic compound that can impart viscosity. This cellulosic compound can be a mixture of one or more carboxymethylcellulose, hydroxypropylmethylcellulose, methylcellulose, or alkali metal salts thereof. As the alkali metal, Na, K, or Li can be used.

[0156] The dry binder is a polymeric substance that can be formed into fibers, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0157] Conductive materials are used to impart conductivity to electrodes, and any electronically conductive material that does not cause chemical changes in the battery that is constructed can be used. Specific examples include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjenblack, carbon fibers, carbon nanofibers, and carbon nanotubes; metallic materials containing copper, nickel, aluminum, silver, etc., in the form of metal powders or metal fibers; conductive polymers such as polyphenylene derivatives; or mixtures thereof.

[0158] As the negative electrode current collector, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, and combinations thereof can be selected.

[0159] electrolyte The electrolyte for lithium secondary batteries contains a non-aqueous organic solvent and a lithium salt.

[0160] Non-aqueous organic solvents act as a medium through which ions involved in the electrochemical reactions of batteries can move.

[0161] Non-aqueous organic solvents may be carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvents, aprotic solvents, or combinations thereof.

[0162] Examples of carbonate-based solvents that can be used include dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0163] Suitable ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, and caprolactone.

[0164] As ether-based solvents, dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. can be used. As ketone-based solvents, cyclohexanone, etc. can be used. As alcohol-based solvents, ethyl alcohol, isopropyl alcohol, etc. can be used, and as aprotic solvents, nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and may include a double bond, aromatic ring, or ether group); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane and 1,4-dioxolane; sulfolanes, etc. can be used.

[0165] Non-aqueous organic solvents can be used alone or in combination of two or more.

[0166] Furthermore, when using carbonate-based solvents, cyclic carbonates and linear carbonates can be mixed and used together, and the cyclic carbonates and linear carbonates may be mixed in a volume ratio of 1:1 to 1:9.

[0167] Lithium salts dissolve in organic solvents and act as a source of lithium ions within batteries, enabling the operation of basic lithium secondary batteries and facilitating the movement of lithium ions between the positive and negative electrodes. Typical examples of lithium salts include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N(lithium bis(fluorosulfonyl)imide (LiFSI), LiC4F9SO3, and LiN(C x F 2x+1 SO2)(C y F 2y+1SO2) (where x and y are integers from 1 to 20), may contain one or more selected from lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFOB), and lithium bis(oxalate)borate (LiBOB).

[0168] In one specific example, the electrolyte may contain ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of EC:EMC:DEC = 2-4:4-6:1-2, for example 3:5:2, based on a total volume of 10, and may contain 1-1.5 M of LiPF6.

[0169] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch-type, coin-type, etc., depending on their form. Figures 1 to 4 are schematic diagrams showing a lithium secondary battery according to one embodiment. Figure 1 can be described as a cylindrical battery form, Figure 2 as a prismatic battery form, and Figures 3 and 4 as pouch-type batteries. Referring to Figures 1 to 4, the lithium secondary battery 100 may include an electrode assembly 40 with a separator 30 interposed between a positive electrode 10 and a negative electrode 20, and a case 50 in which the electrode assembly 40 is housed. The positive electrode 10, negative electrode 20, and separator 30 may be impregnated with an electrolyte (not shown). The lithium secondary battery 100 may include a sealing member 60 that seals the case 50, as shown in Figure 1. Also, in Figure 2, the lithium secondary battery 100 may include a positive electrode lead tap 11 and a positive electrode terminal 12, a negative electrode lead tap 21 and a negative electrode terminal 22. As shown in Figures 3 and 4, the lithium secondary battery 100 may include electrode taps 70, namely a positive electrode tap 71 and a negative electrode tap 72, which serve as electrical pathways for inducing the current formed in the electrode assembly 40 to the outside.

[0170] A lithium secondary battery according to one embodiment of the present invention may be applied to automobiles, mobile phones, and / or various forms of electrical devices, and the present invention is not limited thereto.

[0171] Examples and comparative examples of the present invention are described below. However, the following examples are merely one embodiment of the present invention, and the present invention is not limited to these examples.

[0172] 1. Verification of the first copolymer Manufacturing Example 1 In a 3L four-neck separable flask equipped with a stirrer, thermometer, and condenser, DMAc (850g), styrene (SM, 36.45g, 0.35mol), methyl methacrylate (MMA, 35.04g, 0.35mol), 2-ethylhexyl acrylate (EHA, 36.83g, 0.20mol), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, 20.73g, 0.10mol) were added, and 1.1mol of LiOH was added relative to AMPS. After adding the initiator AIBN (0.164g, 0.001mol), the internal pressure was reduced to 10mmHg using a diaphragm pump, and the internal pressure was returned to atmospheric pressure with nitrogen. This procedure was repeated three times.

[0173] The reaction was carried out for 12 hours while controlling the heating to maintain a stable temperature between 65°C and 70°C.

[0174] After cooling to room temperature, approximately 10 mL of the reaction solution was taken and the non-volatile components (NV) were measured, resulting in a copolymer with a NV content of 9.8% (theoretical value 10%). In the obtained copolymer, poly(styrene-co-methyl methacrylate-co-2-ethylhexyl acrylate-co-2-acrylamide-2-methylpropanesulfonic acid) lithium salt, the molar ratio of the first structural unit derived from styrene and methyl methacrylate, the second structural unit derived from 2-ethylhexyl acrylate, and the third structural unit derived from 2-acrylamide-2-methylpropanesulfonic acid was 70:20:10, and the glass transition temperature (Tg) of the copolymer was 65.1°C.

[0175] Manufacturing Examples 2-7 The first copolymer was produced in the same manner as in Production Example 1, except that the molar ratios of each monomer were changed as shown in Table 1 below, in a total of 100 mol% of styrene (SM), methyl methacrylate (MMA), 2-ethylhexyl acrylate (EHA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

[0176] Comparative Manufacturing Examples 1 to 5 The first copolymer was produced in the same manner as in Production Example 1, except that the molar ratios of each monomer were changed as shown in Table 1 below, in a total of 100 mol% of styrene (SM), methyl methacrylate (MMA), 2-ethylhexyl acrylate (EHA), and 2-acrylamido-2-methylpropanesulfonic acid (AMPS).

[0177] Table 1 below shows the molar ratios of each monomer in the binders produced in Production Examples 1 to 7 and Comparative Production Examples 1 to 5.

[0178] [Table 1]

[0179] Reference example 1 A composition for the adhesive layer was prepared by mixing 10 parts by weight of the binder from Production Example 1 with 90 parts by weight of distilled water.

[0180] A porous substrate, a polyethylene film (thickness: 5.5 μm, CZMZ Corporation, air permeability: 110 sec / 100 cc, puncture strength: 360 kgf), was coated on both sides with a manufactured adhesive layer composition using a die-coating method at a speed of 80 m / min, and then coated at 60°C at a density of 14 g / m². 3 A separator for lithium secondary batteries was manufactured by drying it in the presence of an absolute water vapor amount (average value) to form an adhesive layer with a total thickness of 1.4 μm.

[0181] Reference example 2~Reference example 12 A lithium secondary battery separator was manufactured using the same method as in Example 1, except that the type of binder was changed in Reference Example 1.

[0182] Battery manufacturing (Manufacturing of negative electrodes) A slurry of 97% by weight of graphite particles with an average particle size of 25 μm, 1.5% by weight of styrene-butadiene rubber (SBR) binder, and 1.5% by weight of carboxymethylcellulose (CMC) was mixed, then added to distilled water and stirred for 60 minutes using a mechanical stirrer to produce a negative electrode active material slurry. The slurry was applied to a 10 μm thick copper current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, then further dried under vacuum and at 120°C for 4 hours, and rolled to produce a negative electrode.

[0183] (Manufacturing of positive electrodes) A cathode active material slurry was prepared by mixing 97% by weight of LiCoO2, 1.5% by weight of carbon black powder as a conductive material, and 1.5% by weight of polyvinylidene fluoride (PVdF), adding the mixture to N-methyl-2-pyrrolidone solvent, and stirring with a mechanical stirrer for 30 minutes. The slurry was then applied to a 20 μm thick aluminum current collector using a doctor blade, dried in a hot air dryer at 100°C for 0.5 hours, further dried under vacuum and at 120°C for 4 hours, and then rolled to produce a cathode.

[0184] (Electrode assembly jelly roll) After interposing the separators obtained in the examples and comparative examples between the positive and negative electrodes manufactured above, the assembly was wound up to prepare an electrode assembly jelly roll. The jelly roll was inserted into a pouch, the electrolyte was injected, and the pouch was vacuum sealed. As the electrolyte, a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 3:5:2 was used, in which 1.3 M LiPF6 was dissolved. The jelly roll inserted into the pouch was subjected to a load of 11.7 kgf / cm². 2 Lithium-ion batteries were manufactured by applying pressure and pressing at a temperature of 80°C for 3 minutes.

[0185] Air permeability (unit: seconds / 100cm) 3 ) The air permeability of the manufactured separator was measured using a measuring device (EG01-55-1MR, Asahi Seiko) by determining the time (in seconds) it took for 100cc of air to pass through the separator. [Setting conditions for the air permeability measuring device] Measured pressure: 0.5 kg / cm² 2 Cylinder pressure: 2.5 kg / cm² 2 Set time: 10 seconds

[0186] Electrolyte impregnation rate (unit: weight %) The manufactured binder was dried in a 120°C oven for 12 hours to obtain a film (thickness: 20 μm, weight W1 measured before immersion). After placing the film in the manufactured pouch, it was immersed in the electrolyte solution and the pouch was vacuum-sealed. The sealed pouch was left in a 60°C oven for 72 hours, after which the film was immediately removed and its weight W2 was measured. The impregnation rate was measured using W2 / W1 x 100.

[0187] Positive electrode adhesive strength (unit: N) After attaching the separator to the positive electrode (manufactured in the same way as the battery), it is inserted into a pouch, and the electrolyte (1.3 M LiPF6 in a 3 / 5 / 2 (volume ratio) mixed solvent of ethylene carbonate (EC) / ethyl methyl carbonate (EMC) / diethyl carbonate (DEC)) is injected. After standing for 12 hours, the pressure is increased to 10-20 kgf / cm². 2 The material was pressed at a temperature of 70°C to 90°C for 5 to 20 seconds, and then disassembled. After removing the separator and positive electrode from the pouch, the positive electrode and separator were spread to 180°, and the force required to separate the positive electrode from the separator was measured using a tension measuring instrument (Tinius Olsen, HT400).

[0188] Film resistance (unit: Ω) The film resistance was evaluated using EIS (electrochemical impedance spectroscopy). Separators prepared in the examples and comparative examples were impregnated with an electrolyte solution in which 1.5 M LiPF6 was dissolved in a mixed solvent of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio (3 / 5 / 2)). These were then sandwiched between aluminum foil electrodes with lead taps and sealed in aluminum packs to prepare test cells. The resistance (Ω) of these test cells was measured at 20°C using the AC impedance method (measurement frequency 100 kHz).

[0189] 200-cycle capacity retention rate (unit: %) Batteries manufactured using the separators of the examples and comparative examples were charged with a constant current at a rate of 0.5C at 25°C and 45°C, respectively, until the voltage reached 4.2V, and then cut off in constant voltage mode at a rate of 0.025C. Subsequently, the batteries were discharged at a rate of 0.5C until the voltage reached 2.5V, and this cycle was repeated 200 times. The capacity retention rate, i.e., the life characteristics, was evaluated based on the number of cycles, and the results were obtained.

[0190] DC internal resistance (DC-IR (unit: mΩ)) Batteries with a cell capacity of 75mAh, manufactured using the separators of the examples and comparative examples, were charged at 25°C and 45°C, respectively, under constant current / constant voltage conditions of 0.2C, 4.25V, and 0.05C cut-off. After a 10-minute pause, they were discharged under constant current conditions of 0.33C and 2.80V cut-off, followed by a 10-minute pause. One charge-discharge cycle was performed, and the voltage drop (V) generated while applying a current of 1C for 10 seconds at SOC50 (a state where the battery is charged to 50% of its total charge capacity, meaning that it has been discharged to 50% from the perspective of the discharge state) was measured, and the DC-IR internal resistance was measured.

[0191] The DC internal resistance change rate is the ratio of the DC internal resistance after 200 cycles to the initial DC internal resistance, expressed as a percentage.

[0192] [Table 2]

[0193] [Table 3]

[0194] As is clear from Table 2, the first copolymer exhibits low film resistance and can improve the capacity, safety, and lifespan of the battery. Furthermore, the first copolymer has high adhesion to electrodes, such as the positive electrode, which can enhance reliability.

[0195] As shown in Table 3, polymers other than the first copolymer were unable to obtain the effects of the first copolymer described above.

[0196] 2. Separator Verification Example 1 (1) Preparation of Solution 1 and Solution 3 The copolymer from Production Example 1 and the solvent dimethylacetamide were mixed to prepare the first solution and the third solution, respectively.

[0197] (2) Preparation of the second solution A second solution was prepared by mixing polyimide (PI) and the solvent dimethylacetamide.

[0198] (3) Manufacture of electrospinning and separators An electrospinning apparatus was prepared, equipped with a first nozzle, a second nozzle, and a third nozzle positioned sequentially along the direction of movement of the substrate. The first solution, the second solution, and the third solution were injected into the first nozzle, the second nozzle, and the third nozzle, respectively.

[0199] While moving the substrate, the first, second, and third solutions were sequentially electrospun from the first, second, and third nozzles, respectively, and then compressed. After that, the substrate was removed to produce a separator.

[0200] The electrospinning process was carried out as follows: The internal space temperature for electrospinning was 22 °C. A single nozzle pack with a needle size of 25G was positioned at a distance of 16 cm from the collector roller. The electrospinning solution was added to the tip, a voltage of 40 - 75 kV was applied, and electrospinning was performed. The roll speed of the collector roller was set at 1 - 3 m / min. Also, electrospinning was carried out while flowing air at a pressure of 0.275 MPa. After completion of electrospinning, it was dried with hot air at 90 °C.

[0201] Example 2 (1) Preparation of the first solution and the third solution A mixture of 40 parts by weight of the copolymer of Production Example 1 and 60 parts by weight of polyimide was mixed with dimethylacetamide as a solvent to prepare the first solution and the third solution respectively. (2) Preparation of the second solution Polyimide and dimethylacetamide as a solvent were mixed to prepare the second solution. (3) Electrospinning and preparation of the separator A separator was prepared by referring to the method in Example 1.

[0202] Example 3 (1) Preparation of the first solution and the third solution The copolymer of Production Example 1 and dimethylacetamide as a solvent were mixed to prepare the core solution. Polyimide and dimethylacetamide as a solvent were mixed to prepare the shell solution. (2) Preparation of the second solution Polyimide and dimethylacetamide as a solvent were mixed to prepare the second solution. (3) Electrospinning and preparation of the separator A separator was prepared by referring to the method in Example 1.

[0203] Example 4 (1) Preparation of the first solution and the third solution Polyimide and dimethylacetamide as a solvent were mixed to prepare the first solution and the third solution respectively. (2) Preparation of the second solution The copolymer of Production Example 1 and dimethylacetamide as a solvent were mixed to produce a core solution. Polyimide and dimethylacetamide as a solvent were mixed to produce a shell solution. (3) Electrospinning and production of separator A separator was produced referring to the method in Example 1.

[0204] Example 5 (1) Production of the first solution and the third solution Polyvinylidene fluoride and dimethylacetamide as a solvent were mixed to produce the first solution and the third solution, respectively. (2) Production of the second solution The copolymer of Production Example 1 and polyimide were mixed with dimethylacetamide as a solvent to produce the second solution. (3) Electrospinning and production of separator A separator was produced referring to the method in Example 1.

[0205] Example 6 (1) Production of the first solution and the third solution Polyvinylidene fluoride and dimethylacetamide as a solvent were mixed to produce the first solution and the third solution, respectively. (2) Production of the second solution The copolymer of Production Example 1 and dimethylacetamide as a solvent were mixed to produce a core solution. Polyimide and dimethylacetamide as a solvent were mixed to produce a shell solution. (3) Electrospinning and production of separator A separator was produced referring to the method in Example 1.

[0206] Comparative Example 1 Polyimide and dimethylacetamide as a solvent were mixed to produce an electrospinning solution, and a separator consisting of a fiber layer alone containing a polyimide nanofiber network was produced referring to the method in Example 1.

[0207] Comparative Example 2 The separator was manufactured in the same manner as in Example 2, except that the copolymer of Comparative Production Example 1 was used instead of the copolymer of Production Example 1 in Example 2.

[0208] Comparative Example 3 In Example 3, the separator was manufactured in the same manner as in Example 1, except that the copolymer of Comparative Production Example 1 was used instead of the copolymer of Production Example 1.

[0209] Comparative Example 4 The separator was manufactured in the same manner as in Example 1, except that polyethylene was used instead of polyimide.

[0210] Comparative Example 5 The separator was manufactured in the same manner as in Example 5, except that polyimide was used instead of the copolymer and polyimide mixture in Production Example 1.

[0211] The following physical properties were evaluated for the separators produced in the examples and comparative examples.

[0212] Thermal shrinkage rate in electrolyte solution (unit: %) Prepare samples by cutting out lithium secondary battery separators from the examples and comparative examples to a size of 8cm x 8cm. Draw a 5cm x 5cm rectangle on the surface of the sample.

[0213] A cathode slurry was prepared by mixing 97% by weight of LiCoNiAl as the cathode active material, 1.5% by weight of carbon nanotubes as conductive materials, and 1.5% by weight of polyvinylidene fluoride, and then adding water. The prepared cathode slurry was applied to aluminum foil, dried, and rolled to produce a cathode.

[0214] A negative electrode active material slurry was prepared by mixing 97.4% by weight of negative electrode active material, 1.0% by weight of carboxymethylcellulose, 1.5% by weight of styrene-butadiene rubber, and 0.1% by weight of carbon nanotubes as a conductive material. A silicon-based negative electrode active material was used as the negative electrode active material. The prepared negative electrode slurry was coated onto copper foil, dried, and rolled to produce a negative electrode.

[0215] A sample was placed between the positive and negative electrodes, and three sets of positive-sample-negative electrode laminates were fabricated and placed in pouches. 2g of electrolyte (1.5M LiPF6 dissolved in ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (30:50:20 volume ratio)) was injected to completely impregnate the laminates with the electrolyte, and after sealing, the pouches were left at 25°C for 12 hours. Next, the pouches were left in an oven at 150°C for 1 hour, after which the samples were removed, the dimensions of the sides of the drawn rectangles were measured, and the shrinkage rates in the mechanical direction (MD) and perpendicular direction (width direction, TD) were calculated. The shrinkage rates are calculated using the following formula 1. Contraction rate = (L0 - L1) / L0 × 100 [Formula 1] (L0 is the initial length of the separator, and L1 is the length of the separator after being left at 150°C for 1 hour).

[0216] DC internal resistance (DC-IR (unit: mΩ)) Batteries with a cell capacity of 75mAh, manufactured using the separators of the examples and comparative examples, were charged at 25°C and 45°C respectively under constant current / constant voltage conditions of 0.2C, 4.25V, and 0.05C cut-off, then rested for 10 minutes, and discharged under constant current conditions of 0.33C and 2.80V cut-off, followed by a 10-minute rest. A single charge-discharge cycle was performed, and the voltage drop (V) generated while applying a current of 1C for 10 seconds at SOC50 (a state where the battery is charged to 50% of its total charge capacity, meaning that it has been discharged to 50% from the perspective of the discharge state) was measured, and the DC-IR internal resistance was measured.

[0217] [Table 4]

[0218]

Table 5

[0219] As is clear from Table 4 and Table 5, the separator of the embodiment can provide excellent heat resistance, low membrane resistance, and high adhesive force without a porous substrate.

[0220] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited thereto, and various modifications can be made within the scope of the claims, the detailed description of the invention, and the accompanying drawings, and this naturally belongs to the scope of the present invention.

Claims

1. A separator for lithium secondary batteries comprising one or more fiber layers, At least one of the fiber layers includes a fiber network of fibers containing the first copolymer, At least one of the fiber layers includes polyimide fibers or core-shell fibers containing polyimide resin, The first copolymer comprises a copolymer of monomer mixtures including a first structural unit containing a unit derived from an aromatic vinyl monomer; a second structural unit derived from an alkyl group-containing (meth)acrylic monomer with four or more carbon atoms in the main chain in the ester moiety; and a third structural unit derived from a sulfonic acid group-containing monomer. The copolymer is composed of 100 mol%, the first structural unit in an amount of 5 to 80 mol%, the second structural unit in an amount of 10 to 60 mol%, and the third structural unit in an amount of 5 to 80 mol%. Separator for lithium secondary batteries.

2. The separator for a lithium secondary battery according to claim 1, wherein the first copolymer is an adhesive binder.

3. The separator for lithium secondary batteries according to claim 1, wherein the first copolymer has a glass transition temperature of 60 to 80°C.

4. The separator for lithium secondary batteries according to claim 1, wherein the total amount of the first structural unit, the second structural unit, and the third structural unit in the copolymer is 95 mol% or more.

5. The unit derived from the aforementioned aromatic vinyl monomer is given by the following chemical formula 1: 【Chemistry 1】 (In the above chemical formula 1, R 1 and R 2 These are, independently, hydrogen or substituted or unsubstituted C 1 ~C 5 It is an alkyl group, Ar is a substituted or unsubstituted monocyclic or polycyclic C. 6 ~C 20 It is represented by the aryl group of, The second structural unit is given by the following chemical formula 4: 【Chemistry 2】 (In the above chemical formula 4, R 7 and R 8 These are, independently, hydrogen or a methyl group. L 2 is a substituted or unsubstituted, linear or branched C 4 -C 30 alkyl group), and is represented by The third structural unit is represented by the following chemical formulas 5, 6, and 7: 【Transformation 3】 (In the above chemical formulas 5 to 7, R 9 , R 10 , R 11 , R 12 , R 13 and R 14 Each of them is independently of hydrogen or C 1 ~C 3 It is an alkyl group, L 3 , L 5 and L 7 These are, independently, -C(=O)-, -C(=O)O-, -OC(=O)-, -O-, or -C(=O)NH-, L 4 , L 6 and L 8 These are, independently, substitutional or non-substitutional C. 1 ~C 10 Alkylene group, substituted or unsubstituted C 3 ~C 20 Cycloalkylene group, substituted or unsubstituted C 6 ~C 20 Arylene group or substituted or unsubstituted C 3 ~C 20 It is a heterocyclic group, a, b, c, d, e, and f are each independent integers between 0 and 2. In the aforementioned chemical formula 6, M is an alkali metal. A separator for a lithium secondary battery according to claim 1, which is represented by any one of the following.

6. The lithium secondary battery separator according to claim 1, wherein the first structural unit further comprises a unit in the ester portion derived from an alkyl group-containing (meth)acrylic monomer having 1 to 3 carbon atoms in the main chain.

7. The units derived from the (meth)acrylic monomers are given by the following chemical formula 3: 【Chemistry 4】 (In the above chemical formula 3, R 5 and R 6 These are, independently, hydrogen or a methyl group. L 1 This is a substituted or unsubstituted, linear or branched C 1 ~C 3 A separator for a lithium secondary battery according to claim 6, wherein the unit is represented by (an alkyl group).

8. The separator for a lithium secondary battery according to claim 1, wherein the separator is a multilayer separator including the fiber layer.

9. The lithium secondary battery separator according to claim 8, wherein the multilayer separator comprises one or more or two or more fiber layers, each comprising a fiber network of fibers containing the first copolymer.

10. The lithium secondary battery separator according to claim 8, wherein the multilayer separator further comprises one or more fiber layers including a fiber network of fibers containing one or more second copolymers.

11. The separator for a lithium secondary battery according to claim 8, wherein the multilayer separator comprises one or more or two or more fiber layers including a network of core-shell type fibers, and the first copolymer is contained in the core or shell of the core-shell type fibers.

12. The separator for lithium secondary batteries according to claim 11, wherein the core-shell type fiber further comprises a second copolymer.

13. The separator for a lithium secondary battery according to claim 11, wherein the multilayer separator further comprises one or more of the following: a fiber layer comprising a network of fibers comprising the first copolymer, and a fiber layer comprising a network of fibers comprising one or more types of the second copolymer.

14. The lithium secondary battery separator according to claim 8, wherein the multilayer separator comprises one or more or two or more fiber layers, each fiber layer comprising a network of fibers containing a mixture of the first copolymer and the second copolymer.

15. The lithium secondary battery separator according to claim 14, wherein the multilayer separator further comprises one or more of the following: a fiber layer comprising a network of fibers comprising the first copolymer, and a fiber layer comprising a network of fibers comprising one or more of the second copolymer.

16. The lithium secondary battery separator according to any one of claims 10, 12 to 15, wherein the second copolymer comprises one or more selected from the group consisting of polyacrylonitrile, polyaniline, polypyrrole, polyrhodanine, melamine, polyurea, polyvinyl chloride, polyvinyl alcohol, polyethylene oxide, polymethyl methacrylate, polyacrylic acid, polylactic acid, polyimide, polyamideimide, polyaramid, polybenzylimidazole, polypropylene, resorcinol-formaldehyde resin, melamine-formaldehyde resin, pitch, sucrose, glucose, cellulose, and polyvinylidene fluoride.

17. The separator is a separator for a lithium secondary battery according to claim 1, wherein the separator does not have a porous substrate.

18. The separator for a lithium secondary battery according to claim 1, wherein the separator has a thickness of 8 μm or less.

19. A lithium secondary battery comprising a positive electrode; a negative electrode; and a lithium secondary battery separator according to claim 1, positioned between the positive electrode and the negative electrode.

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