Positive electrode, method for producing the same, and lithium secondary battery

Abstract

To provide a positive electrode capable of reducing resistance and improving adhesiveness and rollability by improving dispersibility of a conductive material, and a lithium secondary battery excellent in life characteristics.SOLUTION: And a positive electrode active material layer disposed on the positive electrode current collector and including a positive electrode active material, a binder, and a conductive material, wherein the binder includes a first binder and a second binder, the first binder includes a hydrogenated nitrile butadiene rubber, the second binder includes an imide-based binder, and the positive electrode active material layer includes 300 parts by weight to 1300 parts by weight of the second binder with respect to 100 parts by weight of the first binder.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a positive electrode, a method for producing the same, and a lithium secondary battery including the same. [Background technology]

[0002] Lithium secondary batteries, which have high energy density and are easy to carry, are widely used as power sources for mobile information terminals such as mobile phones, laptops, and smartphones. In particular, active research is being conducted into using high-energy-density lithium secondary batteries as power sources for hybrid and electric vehicles or as power storage sources.

[0003] A lithium secondary battery is a battery that contains a cathode and an anode, which contain active materials that allow lithium ions to be inserted and removed, and an electrolyte. Electrical energy is produced through oxidation and reduction reactions that occur when lithium ions are inserted and removed from the cathode and anode.

[0004] As the positive electrode active material of a lithium secondary battery, a transition metal compound such as lithium cobalt oxide, lithium nickel oxide, or lithium manganese oxide is mainly used, and as the negative electrode active material, a crystalline carbon material such as natural graphite or artificial graphite, or an amorphous carbon material is used. Summary of the Invention [Problem to be solved by the invention]

[0005] One embodiment provides a positive electrode that can reduce resistance and improve adhesion and rollability by improving the dispersibility of a conductive material, and a lithium secondary battery that has excellent life characteristics. [Means for solving the problem]

[0006] In one embodiment, a positive electrode is provided, comprising: a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector and including a positive electrode active material, a binder, and a conductive material; the binders include a first binder and a second binder, the first binder includes hydrogenated nitrile butadiene rubber, and the second binder includes an imide-based binder, and the positive electrode active material layer includes 300 parts by weight to 1300 parts by weight of the second binder relative to 100 parts by weight of the first binder.

[0007] In yet another embodiment, there is provided a method for producing a positive electrode, the method including: preparing a positive electrode slurry including a positive electrode active material, a binder, and a conductive material; and applying the positive electrode slurry onto a positive electrode current collector to form a positive electrode, the binders including a first binder and a second binder, the first binder including hydrogenated nitrile butadiene rubber, and the second binder including an imide-based binder, and the positive electrode slurry including 300 parts by weight to 1300 parts by weight of the second binder relative to 100 parts by weight of the first binder.

[0008] In yet another embodiment, a lithium secondary battery is provided, comprising: the aforementioned positive electrode; the negative electrode; and an electrolyte. [Effects of the Invention]

[0009] The positive electrode according to one embodiment may have reduced resistance and improved adhesion and rollability due to improved dispersion of the conductive material, and a lithium secondary battery including the positive electrode may achieve excellent life characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 2] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 3] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 4] 1 is a cross-sectional view schematically illustrating a lithium secondary battery according to an embodiment. [Figure 5] 1 shows the results of IR analysis of the binder produced in Production Example 1. [Figure 6] 1 shows the results of IR analysis of the binder produced in Production Example 3. [Figure 7] 1 shows the results of measuring the composite resistance of the positive electrode plates produced in Examples 1 and 2 and Comparative Example 1. [Figure 8] 1 shows the results of measuring the interface resistance of the lithium secondary batteries produced in Examples 1 and 2 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0011] Although specific embodiments are described below in detail so that those skilled in the art can easily implement the present invention, the present invention may be embodied in various different forms and is not limited to the embodiments described herein.

[0012] The terms used herein are merely used to describe exemplary embodiments and are not intended to limit the present invention. The singular forms include plural forms unless the context clearly indicates otherwise.

[0013] As used herein, "combinations thereof" refers to mixtures, laminates, composites, copolymers, alloys, blends, reaction products, and the like of compositions.

[0014] It should be understood that the terms "comprise," "comprise," or "have" are intended to specify the presence of embodied features, numbers, layers, components, or combinations thereof, but do not preclude the possible presence or addition of one or more other features, numbers, layers, components, or combinations thereof.

[0015] In order to clearly show multiple layers and regions in the drawings, thicknesses have been exaggerated, and similar parts have been given the same reference numerals throughout the specification. When a part such as a layer, film, region, or plate is "on" or "above" another part, this includes not only when it is "directly on" the other part, but also when there is another part in between. Conversely, when a part is said to be "directly on" another part, it means that there is no other part in between.

[0016] Furthermore, the term "layer" as used herein includes not only shapes formed on the entire surface when observed in a plan view, but also shapes formed on a portion of the surface.

[0017] The average particle size can be measured by methods well known to those skilled in the art, for example, by using a particle size analyzer or by using a transmission electron microscope image or a scanning electron microscope image. Alternatively, the average particle size can be calculated by measuring using a dynamic light scattering method, analyzing the data, and counting the number of particles in each particle size range. Unless otherwise defined, the average particle size is the diameter (D ) of particles with a cumulative volume of 50% in the particle size distribution. 50 ) Unless otherwise specified, the average particle size may be determined by measuring the size (diameter or length of the major axis) of 20 particles randomly selected from a scanning electron microscope image to obtain a particle size distribution, or by determining the diameter (D) of the particles whose cumulative volume is 50% by volume from the particle size distribution. 50 ) may be taken as the average particle size.

[0018] Here, "or" does not have an exclusive meaning; for example, "A or B" is interpreted as including A, B, A+B, etc.

[0019] The term "metal" is understood to include general metals, transition metals, and semimetals (metalloids).

[0020] "Substituted" means that at least one hydrogen atom is replaced with deuterium, halogen (F, Cl, Br, I), a hydroxy group or a salt thereof, a C1 to C20 alkoxy group, a nitro group, a cyano group, an amine group, an imino group, an azide group, an amidino group, a hydrazino group, a hydrazono group, a carbonyl group, a carbamyl group, a thiol group or a salt thereof, a thioether group, an ester group, an ether group, a carboxyl group or a salt thereof, a sulfonic acid group or a salt thereof, a phosphoric acid group or a salt thereof, a C1 to C2 "C1-C20 alkyl group, C2-C20 alkenyl group, C2-C20 alkynyl group, C6-C20 aryl group, C3-C20 cycloalkyl group, C3-C20 cycloalkenyl group, C3-C20 cycloalkynyl group, C2-C20 heterocycloalkyl group, C2-C20 heterocycloalkenyl group, C2-C20 heterocycloalkynyl group, C3-C20 heteroaryl group, or a combination thereof. As an example, "substituted" can mean that at least one hydrogen atom is substituted with deuterium, halogen, C1-C20 alkyl group, C6-C20 aryl group, C3-C20 heteroaryl group, or a combination thereof.

[0021] Here, the alkyl group may be a C1 to C20 alkyl group, a C1 to C10 alkyl group, or a C1 to C5 alkyl group, and the aryl group may be a C6 to C20 aryl group or a C6 to C10 aryl group.

[0022] positive electrode In one embodiment, a positive electrode is provided, comprising: a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector and including a positive electrode active material, a binder, and a conductive material; the binders include a first binder and a second binder, the first binder includes hydrogenated nitrile butadiene rubber, and the second binder includes an imide-based binder, and the positive electrode active material layer includes 300 parts by weight to 1300 parts by weight of the second binder relative to 100 parts by weight of the first binder.

[0023] The positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode current collector may be made of, but is not limited to, aluminum, stainless steel, or a combination thereof.

[0024] The positive electrode active material layer includes a positive electrode active material, a binder, and a conductive material. The binder used in the positive electrode active material layer serves to firmly adhere the positive electrode active material particles to each other and to firmly adhere the positive electrode active material to the current collector. Fluorine-based binders such as polyvinylidene fluoride (PVDF) are commonly used as such binders. However, due to recent environmental concerns, there is a need to replace fluorine-based binders such as PVDF with more environmentally friendly materials.

[0025] As part of the need for environmentally friendly research, fluorine-free binders are needed, but most fluorine-free binders lack adhesion and are not at the same level as PVDF. Furthermore, fluorine-based binders like PVDF have strong oxidation resistance, making it difficult to develop a cathode binder that can replace them. In particular, achieving high density is difficult with cathode active materials with small particle sizes, such as lithium iron phosphate (LFP) and lithium iron manganese phosphate (LMFP). Therefore, to achieve high density, it is necessary to develop a binder with excellent rolling properties that can be easily pressed during rolling.

[0026] Therefore, even if a binder that does not contain fluorine atoms partially improves the properties such as adhesiveness and rollability, there are problems such as insufficient dispersibility or oxidation resistance of the conductive material, or changes in physical properties in response to the electrolyte.

[0027] In one embodiment, a binder that does not contain fluorine atoms, has excellent adhesiveness and rollability, and has excellent dispersibility of conductive materials and a low expansion coefficient in response to an electrolyte solution is introduced into the positive electrode, thereby providing a positive electrode that can improve battery performance.

[0028] To achieve this, two types of binders, including a first binder and a second binder, are used, and in this case, the first binder and the second binder may be fluorine-free.

[0029] The first binder used in the positive electrode includes hydrogenated nitrile butadiene rubber (H-NBR), which can improve the dispersibility of the conductive material.

[0030] In one embodiment, the hydrogenated nitrile butadiene rubber may have a weight average molecular weight (Mw) of 100,000 g / mol to 2,000,000 g / mol, for example, 100,000 g / mol to 1,800,000 g / mol, 100,000 g / mol to 1,500,000 g / mol, or 900,000 g / mol to 1,500,000 g / mol. When this is satisfied, the effect of improving the dispersibility of the conductive material can be maximized.

[0031] For example, the hydrogenated nitrile butadiene rubber may contain 20% to 40% by weight of acrylonitrile or methacrylonitrile, for example, 21% to 37% by weight, or 22% to 35% by weight, which can further improve oxidation resistance or dispersibility of conductive materials.

[0032] In the positive electrode, the second binder includes an imide-based binder. The use of an imide-based binder as the second binder in combination with the first binder provides flexibility to the positive electrode plate, thereby enabling effective surface adhesion between components and improving adhesion. Furthermore, the high flexibility of the second binder allows for high-density rolling, ensuring excellent rollability while also achieving high density.

[0033] Meanwhile, the imide-based binder refers to a polymer containing an imide group in the repeating unit structure. For example, the imide-based binder may further include an additional functional group, such as an amide group, a urethane group, a urea group, or a combination thereof, in addition to the imide group. For example, the imide-based binder may further include the aforementioned additional functional group in addition to the imide group in the repeating unit structure.

[0034] For example, the second binder may include polyimide, poly(imide-amide), poly(imide-urethane), poly(imide-urea), or a combination thereof. Here, the polyimide may refer to a polymer containing an imide group but not an amide group, urethane group, or urea group, as described below, in the repeating unit structure. The poly(imide-amide) may refer to a polymer containing an imide group and an amide group in the repeating unit structure. The poly(imide-urethane) may refer to a polymer containing an imide group and a urethane group in the repeating unit structure, and the poly(imide-urea) may refer to a polymer containing an imide group and a urea group in the repeating unit structure. The second binder described above has excellent flexibility, and when used, it is possible to achieve a balance between the effects of improving adhesion and rollability, reducing the expansion rate in response to an electrolyte, and improving the elongation rate.

[0035] In one embodiment, the second binder may include at least one of a structure represented by the following Formula 1A and a structure represented by the following Formula 1B, or the imide group may be represented by the following Formula 1A or Formula 1B. When this is satisfied, it is advantageous for reducing swelling due to the electrolyte solution.

[0036] [ka]

[0037] In Chemical Formula 1A, R1 represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group, x1 represents an integer of 0 to 3, and * represents a linking site.

[0038] [ka]

[0039] In Chemical Formula 1B, R2 represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group, x2 represents an integer of 0 to 2, and * represents a linking site.

[0040] For example, the second binder may include at least one of a structure represented by the following Formula 2A and a structure represented by the following Formula 2B:

[0041] [ka]

[0042] In the chemical formula 2A, R 11 ~R 15 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x11 represents an integer of 0 to 3; y12 and z13 each independently represents an integer of 0 to 4; and * represents a linking site.

[0043] [ka]

[0044] In the above chemical formula 2B, R 21 ~R 25 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x21 represents an integer of 0 to 2; y22 and z23 each independently represents an integer of 0 to 4; and * represents a linking site.

[0045] For example, the second binder may include at least one of a structure represented by the following Formula 3A and a structure represented by the following Formula 3B:

[0046] [ka]

[0047] In the above Chemical Formula 3A, R 31 ~R 35 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x31 represents an integer of 0 to 3; y32 and z33 each independently represents an integer of 0 to 4; and * represents a linking site.

[0048] [ka]

[0049] In the chemical formula 3B, R 41 ~R 45 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x41 represents an integer of 0 to 2; y42 and z43 each independently represents an integer of 0 to 4; and * represents a linking site.

[0050] For example, the second binder may include one or more of the structures represented by the following Chemical Formulas 4A to 4C.

[0051] [ka]

[0052] In the above Chemical Formula 4A, m1, n1, p1, q1, and r1 may each independently be an integer of 0-50.

[0053] [ka]

[0054] In the above Chemical Formula 4B, m2, n2, p2, q2, and r2 may each independently be an integer of 0-50.

[0055] [ka]

[0056] In the above Chemical Formula 4C, m3, n3, p3, q3, and r3 may each independently be an integer of 0 to 50.

[0057] For example, in Chemical Formula 4A, m1, n1, p1, and q1 may each independently be an integer of 1 to 50, or r1 may be an integer of 1 to 50, an integer of 2 to 50, or an integer of 3 to 50.

[0058] For example, in Chemical Formula 4B, m2, n2, p2, and q2 may each independently be an integer of 1 to 50, or r2 may be an integer of 1 to 50, an integer of 2 to 50, or an integer of 3 to 50.

[0059] For example, in Chemical Formula 4C, m3, n3, p3, and q3 may each independently be an integer of 1 to 50, or r3 may be an integer of 1 to 50, an integer of 2 to 50, or an integer of 3 to 50.

[0060] In one embodiment, the weight average molecular weight (Mw) of the second binder may be 50,000 g / mol to 1,000,000 g / mol, which can maximize the effects of improving adhesiveness and rollability.

[0061] For example, the second binder may have a swelling rate of 10 wt% to 50 wt%, e.g., 10 wt% to 40 wt%, 10 wt%, 38 wt%, 15 wt% to 35 wt%, 25 wt% to 35 wt%, or 28 wt% to 33 wt%. Here, the swelling rate of the second binder with respect to the electrolyte may be a value P calculated by the following Equation 1 for a film manufactured using the second binder: [Formula 1] P = (P2 - P1) / P1 x 100

[0062] In the above formula 1, P1 represents the film weight before expansion, and P2 represents the film weight after expansion.

[0063] In one embodiment, the second binder may have an elastic elongation rate of 10% to 200% after immersion in the electrolyte solution for 24 hours, for example, 10% to 180%, 10% to 150%, or 40% to 160%, etc. Here, the elastic elongation rate after immersion in the electrolyte solution for 24 hours may be a value C calculated by the following equation 2 when a film made using the second binder is immersed in the electrolyte solution for 24 hours and then stretched. [Formula 2] E = (E2 - E1) / E1 x 100

[0064] In the above formula 2, E2 represents the length of the film after stretching, and E1 represents the length of the film before stretching.

[0065] The positive electrode active material layer is a binder, and by using the first binder and the second binder in combination, it is possible to reduce resistance by improving the dispersibility of the conductive material, improve adhesion and rollability, and also reduce expansion when immersed in an electrolyte for a long period of time, thereby ensuring excellent elastic elongation.

[0066] The positive electrode active material layer may contain 300 to 1300 parts by weight of the second binder, for example, 500 to 1200 parts by weight, or 800 to 1000 parts by weight, per 100 parts by weight of the first binder. Within this range, the effects of improving the dispersibility of the conductive material and reducing the resistance due to the addition of the first binder and the effects of ensuring adhesion and rollability due to the addition of the second binder can be balanced.

[0067] For example, the positive electrode active material layer may contain 3 wt% to 20 wt%, for example, 7 wt% to 18 wt%, or 10 wt% to 15 wt%, of the first binder, relative to 100 wt% of the total of the first binder and the second binder. Within this range, the first binder can improve the dispersibility of the conductive material, thereby maximizing the effects of reducing resistance and improving the battery life.

[0068] For example, the positive electrode active material layer may contain 80 to 97 wt % of the second binder, for example, 82 to 93 wt %, or 85 to 90 wt %, based on 100 wt % of the total of the first binder and the second binder. This range may maximize the effects of improving adhesion and rollability due to the second binder.

[0069] As an example, the positive electrode may have a loading level of 30 mg / cm 2 ~60mg / cm 2 Alternatively, the three-point bending strength may be 1.1 N or less, or the rolled density may be 2.4 g / cc or more.

[0070] For example, the positive electrode active material layer may further include an additional binder in addition to the first and second binders. Such additional binders may be any binder commonly used in the art. Representative examples of the additional binder include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, 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, and nylon.

[0071] In one embodiment, the content of the binder may be 0.5 wt % to 5 wt %, for example, 0.8 wt % to 4 wt %, or 1 wt % to 3 wt %, relative to 100 wt % of the positive electrode active material layer, and the content of the binder may be the total content of the binder in the positive electrode active material layer.

[0072] The positive electrode active material layer contains a positive electrode active material and a conductive material in addition to the binder component.

[0073] positive electrode active material The positive electrode active material may be a compound capable of reversibly inserting and extracting lithium (lithiate intercalation compound). Specifically, one or more composite oxides of lithium and a metal selected from cobalt, manganese, nickel, or a combination thereof may be used.

[0074] In one embodiment, the positive electrode active material may be a lithium transition metal composite oxide, such as a lithium nickel-based oxide, a lithium cobalt-based oxide, a lithium manganese-based oxide, a lithium composite phosphate, a lithium nickel-manganese-based oxide, a lithium-manganese-leach oxide, or a combination thereof.

[0075] More specifically, a compound represented by any of the following chemical formulas can be used: 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 eO2(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 O(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≦2);Li a FePO4(0.90≦a≦1.8)

[0076] In the above formula, A is Ni, Co, Mn, or a combination thereof; X is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, a rare earth element, 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; Q is Ti, Mo, Mn, or a combination thereof; Z is Cr, V, Fe, Sc, Y, or a combination thereof; L 1 is Mn, Al or a combination thereof.

[0077] For example, the positive electrode active material may include a lithium composite phosphate, which may include one or more of the compounds represented by the following chemical formulas 11 to 15. The positive electrode active material containing the lithium composite phosphate has small particles of about 2 μm or less, making it difficult to achieve high density. However, when mixed with a binder according to an embodiment, it is possible to maximize the energy density of the positive electrode while simultaneously ensuring the adhesive strength and flexibility of the electrode plate.

[0078] [Chemical formula 11] Li a1 Fe (1-s1) M 1 s1 PO4 In Chemical Formula 11, 0.90≦a1≦1.5, 0≦s1≦0.4, and M 1 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≦a1≦1.5 may be satisfied, for example, 0.90≦a1≦1.2 or 0.95≦a1≦1.1. Also, 0≦s1≦0.4, 0≦s1≦0.3, 0≦s1≦0.2, 0≦s1≦0.1, or 0≦s1≦0.05 may be satisfied.

[0079] [Chemical formula 12] Li a2 Mn s2 Fe (1-s2-t2) M 2 t2 PO4 In chemical formula 12, 0.90≦a2≦1.5, 0.1≦s2≦0.9, 0≦t2≦0.9, M 2 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≦a2≦1.5 may be satisfied, for example, 0.90≦a2≦1.2 or 0.95≦a2≦1.1. Also, 0.1≦s2≦0.9, 0.3≦s2≦0.9, or 0.4≦s2≦0.8 may be satisfied, and 0≦t2≦0.9, 0≦t2≦0.4, 0≦t2≦0.3, 0≦t2≦0.2, 0≦t2≦0.1, or 0≦t2≦0.05.

[0080] [Chemical formula 13] Li a3 Mn (1-s3) M 3 s3 PO4 In chemical formula 13, 0.90≦a3≦1.5, 0≦s3≦0.4, and M 3may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. Here, 0.90≦a3≦1.5 may be satisfied, for example, 0.90≦a3≦1.2 or 0.95≦a3≦1.1. Also, 0≦s3≦0.4, 0≦s3≦0.3, 0≦s3≦0.2, 0≦s3≦0.1, or 0≦s3≦0.05 may be satisfied.

[0081] [Chemical formula 14] Li a4 Ti (2-s4) M 4 s4 (PO4)3 In chemical formula 14, 0.90≦a4≦1.5, 0≦s4≦0.4, and M 4 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, where 0.90≦a4≦1.5 may be satisfied, for example, 0.90≦a4≦1.2 or 0.95≦a4≦1.1.

[0082] Alternatively, 0≦s4≦0.4, 0≦s4≦0.3, 0≦s4≦0.2, 0≦s4≦0.1, or 0≦s4≦0.05 may be satisfied.

[0083] [Chemical formula 15] Li a5 Ti (1-s5) M 5 s5 PO5 In chemical formula 15, 0.90≦a5≦1.5, 0≦s5≦0.4, and M 5 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof, where 0.90≦a5≦1.5 may be satisfied, for example, 0.90≦a5≦1.2 or 0.95≦a5≦1.1.

[0084] Alternatively, 0≦s5≦0.4, 0≦s5≦0.3, 0≦s5≦0.2, 0≦s5≦0.1, or 0≦s5≦0.05 may be satisfied.

[0085] More specifically, the lithium composite phosphate oxide is LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4, LiMnPO4, LiTiPO5, LiTi2(PO4)3, or combinations thereof.

[0086] For example, the positive electrode active material may include lithium iron phosphate, lithium iron manganese phosphate, or a combination thereof, such as a compound represented by Chemical Formula 11, a compound represented by Chemical Formula 12, or a combination thereof. Such a positive electrode active material can ensure cost reduction and safety effects, and can achieve high output characteristics. When combined with a binder according to an embodiment, it can increase the energy density of the positive electrode while improving the adhesion and flexibility of the electrode plate.

[0087] The lithium composite phosphate is in the form of particles, and the average particle size (D 50 ) may be 0.01 μm to 2 μm, for example, 0.1 μm to 1 μm, or 0.5 μm to 1 μm.

[0088] In one embodiment, the lithium composite phosphate may be in the form of first particles, second particles, or a mixture of first particles and second particles.

[0089] The first particles may be secondary particles or assemblies formed by agglomeration of a plurality of nano-sized primary particles. The first particles may have a spherical or oval spherical shape due to the primary particles closely agglomerating to each other. The average particle size of the first particles may be, for example, 2 μm to 15 μm, 3 μm to 12 μm, or 3 μm to 10 μm. The average particle size of the first particles may be larger than the average particle size of the second particles described below. The average particle size of the primary particles of the first particles may be, for example, 10 nm to 400 nm, 20 nm to 300 nm, or 50 nm to 200 nm. For example, the average particle size of the first particles may be determined by randomly selecting about 30 first particles from an electron microscope image of the lithium composite phosphate, measuring the particle sizes, and determining the diameter (D) of the particles with a cumulative volume of 50% by volume from the particle size distribution. 50 The average particle size of the primary particles of the first particles may be determined by measuring the size of about 30 primary particles from an electron microscope image of the surface or cross section of the first particles, and determining the diameter (D 50 ) may be used as the average particle size.

[0090] The porosity of the first particle may be about 20% to about 50%. For example, the porosity may be determined by measuring the area ratio of the voids in the particle from a scanning electron microscope image of a cross section of the first particle using an image analysis program such as Image J.

[0091] The second particles may have the shape of a single particle. The average particle size of the second particles may be, for example, 10 nm to 900 nm, 50 nm to 500 nm, or 100 nm to 300 nm. The average particle size of the second particles may be smaller than the average particle size of the first particles, or may be the same as or larger than the average particle size of the primary particles of the first particles. For example, the average particle size of the second particles may be determined by randomly selecting about 30 second particles from an electron microscope photograph of the lithium composite phosphate, measuring the particle sizes, and determining the diameter (D) of the particles with a cumulative volume of 50% by volume from the particle size distribution. 50 ) can be used as the average particle size.

[0092] The lithium composite phosphate may further include a carbon coating layer located on the particle surface. The carbon coating layer can improve the electrical conductivity of the lithium composite phosphate and reduce the resistance of the positive electrode. The carbon coating layer can be formed using at least one raw material selected from the group consisting of glucose, sucrose, lactose, starch, oligosaccharides, polyoligosaccharides, fructose, cellulose, furpril alcohol polymers, ethylene-ethylene oxide block copolymers, vinyl-based resins, cellulose-based resins, phenol-based resins, pitch-based resins, and tar-based resins. Specifically, the carbon coating layer can be formed by disposing the raw material on the surface of the lithium composite phosphate particles and then calcining the resulting material.

[0093] As another example, the positive electrode active material may include a cobalt-based positive electrode active material in which the cobalt content relative to 100 mol% of metals excluding lithium in the lithium transition metal composite oxide is 30 mol% or more, 50 mol% or more, or 80 mol% or more.

[0094] As another example, the positive electrode active material may include a high-nickel positive electrode active material in which the nickel content is 80 mol% or more relative to 100 mol% of the metals excluding lithium in the lithium transition metal composite oxide. The nickel content in the high-nickel positive electrode active material may be 85 mol% or more, 90 mol% or more, 91 mol% or more, or 94 mol% or more, relative to 100 mol% of the metals excluding lithium, or may be 99 mol% or less. The high-nickel positive electrode active material can achieve high capacity and can be used in high-capacity, high-density lithium secondary batteries.

[0095] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that does not undergo chemical change and is electronically conductive can be used in the battery. Examples of the conductive material include carbon-based materials such as natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials containing copper, nickel, aluminum, silver, etc. in the form of metal powder or metal fiber; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0096] For example, the conductive material may include particulate nanocarbon including carbon black, acetylene black, ketjen black, or a combination thereof, or may include fibrous nanocarbon including carbon nanofiber, carbon nanotube, or a combination thereof, for example, it may include both particulate nanocarbon and fibrous nanocarbon.

[0097] In one embodiment, the content of the conductive material may be 0.5 wt % to 5 wt %, or 1 wt % to 3 wt %, relative to 100 wt % of the positive electrode active material layer.

[0098] Positive electrode manufacturing method In one embodiment, there is provided a method for producing a positive electrode, the method including: preparing a positive electrode slurry including a positive electrode active material, a binder, and a conductive material; and applying the positive electrode slurry onto a positive electrode current collector to form a positive electrode, the binders including a first binder and a second binder, the first binder including hydrogenated nitrile butadiene rubber, and the second binder including an imide-based binder, and the positive electrode slurry including 300 parts by weight to 1300 parts by weight of the second binder relative to 100 parts by weight of the first binder.

[0099] First, a positive electrode slurry containing a positive electrode active material, a binder, and a conductive material is prepared. Here, the above-described descriptions can be similarly applied to the positive electrode active material, the binder, and the conductive material.

[0100] The binder includes a first binder and a second binder, the first binder includes hydrogenated nitrile butadiene rubber, and the second binder includes an imide-based binder. In this case, the above-mentioned description can be applied to the first binder and the second binder.

[0101] The positive electrode slurry may include 300 to 1300 parts by weight, for example, 500 to 1200 parts by weight, or 800 to 1000 parts by weight of the second binder relative to 100 parts by weight of the first binder.

[0102] In one embodiment, the positive electrode slurry preparation may include preparing a conductive material dispersion by mixing a first binder, a conductive material, and a solvent, adding a second binder to the conductive material dispersion to prepare a mixture, and then adding a positive electrode active material to the mixture and mixing. By incorporating a process of first adding the first binder and the conductive material to a solvent and mixing them before mixing the second binder with the positive electrode slurry components, such as the positive electrode active material and the conductive material, the use of a highly flexible second binder can prevent degradation of the conductive material dispersion and improve the dispersibility of the conductive material. This can improve the adhesion and rollability of the positive electrode plate while reducing interfacial resistance and composite resistance, effectively producing a secondary battery with long life characteristics.

[0103] The positive electrode slurry may then be applied to a positive electrode current collector to form a positive electrode, and the process of forming the positive electrode may further include drying and rolling the positive electrode slurry after application.

[0104] Lithium secondary battery In one embodiment, a lithium secondary battery is provided that includes the above-described positive electrode, negative electrode, and electrolyte. For example, the lithium secondary battery may include a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte.

[0105] Lithium secondary batteries can be classified into cylindrical, prismatic, pouch, and coin types depending on their shape. FIGS. 1 to 4 are schematic diagrams showing lithium secondary batteries according to an embodiment, with FIG. 1 illustrating a cylindrical type, FIG. 2 illustrating a prismatic type, and FIGS. 3 and 4 illustrating pouch-type battery configurations. Referring to FIGS. 1 to 4, a lithium secondary battery 100 may include an electrode assembly 40 having a positive electrode 10 and a negative electrode 20 with a separator 30 interposed therebetween, and a case 50 housing the electrode assembly 40. The positive electrode 10, the negative electrode 20, and the 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 FIG. 1. Also, in FIG. 2, the lithium secondary battery 100 may include a positive electrode lead tab 11, a positive electrode terminal 12, a negative electrode lead tab 21, and a negative electrode terminal 22. As shown in FIGS. 3 and 4, the lithium secondary battery 100 may include electrode tabs 70, i.e., a positive electrode tab 71 and a negative electrode tab 72, which serve as electrical paths for conducting the current generated in the electrode assembly 40 to the outside.

[0106] negative electrode The negative electrode may include 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, a conductive material, or a combination thereof.

[0107] negative electrode active material The negative electrode active material includes a material capable of reversibly inserting / extracting lithium ions, lithium metal, a lithium metal alloy, a material capable of being doped with and dedoped from lithium, or a transition metal oxide.

[0108] Examples of substances that can reversibly insert / desorb lithium ions include carbon-based negative electrode active materials, which can include, for example, crystalline carbon, amorphous carbon, or combinations thereof. Examples of the crystalline carbon include graphite such as amorphous, plate-like, flaky, spherical, or fibrous natural graphite or artificial graphite. Examples of the amorphous carbon include soft carbon or hard carbon, mesophase pitch carbide, calcined coke, and the like.

[0109] As the alloy of the lithium metal, an alloy of lithium and a metal 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.

[0110] As the substance that can be doped and undoped with lithium, a Si-based negative electrode active material or a Sn-based negative electrode active material can be used. The Si-based negative electrode active material can be silicon, a silicon-carbon composite, SiOx (0 < x ≤ 2), a Si-Q alloy (where Q is an element 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, for example, Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof), or combinations thereof. The Sn-based negative electrode active material can be Sn, SnO2, a Sn alloy, or combinations thereof.

[0111] The silicon-carbon composite may be a composite of silicon and amorphous carbon. The average particle size (D) of the silicon-carbon composite particles 50) may be, for example, 0.5 μm to 20 μm. According to one embodiment, the silicon-carbon composite may be in the form of silicon particles and the surfaces of the silicon particles coated with amorphous carbon. For example, it may include secondary particles (cores) formed by assembling silicon primary particles, and an amorphous carbon coating layer (shell) located on the surfaces of the secondary particles. The amorphous carbon may also be located between the silicon primary particles; for example, the silicon primary particles may be coated with amorphous carbon. The secondary particles may be dispersed in an amorphous carbon matrix.

[0112] The silicon-carbon composite may further include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer disposed on the core surface. The crystalline carbon may be artificial graphite, natural graphite, or a combination thereof. Examples of the amorphous carbon include soft carbon, hard carbon, mesophase pitch carbide, and calcined coke.

[0113] When the silicon-carbon composite contains silicon and amorphous carbon, the silicon content may be 10 to 50% by weight and the amorphous carbon content may be 50 to 90% by weight, based on 100% by weight of the silicon-carbon composite.Alternatively, when the composite contains silicon, amorphous carbon, and crystalline carbon, the silicon content may be 10 to 50% by weight, the crystalline carbon content may be 10 to 70% by weight, and the amorphous carbon content may be 20 to 40% by weight, based on 100% by weight of the silicon-carbon composite.

[0114] The thickness of the amorphous carbon coating layer may be 5 nm to 100 nm. 50) may be 10 nm to 1 μm, or 10 nm to 200 nm. The silicon particles can exist alone as silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented by SiO x (0 < x ≦ 2). At this time, the atomic content ratio of Si:O indicating the degree of oxidation may be 99:1 to 33:67. In this specification, unless otherwise defined, the average particle size (D 50 ) means the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution.

[0115] The Si-based negative electrode active material or the Sn-based negative electrode active material can be used by mixing with a carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material are mixed and used, the mixing ratio may be 1:99 to 90:10 by weight ratio.

[0116] binder The binder serves to make the negative electrode active material particles adhere well to each other and also make the negative electrode active material adhere well to the current collector. As the binder, a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof can be used.

[0117] Examples of the non-aqueous binder include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0118] The water-based binder may 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.

[0119] When an aqueous binder is used as the negative electrode binder, a cellulose-based compound that can impart viscosity may be further included. The cellulose-based compound may be a mixture of one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or alkali metal salts thereof. The alkali metal may be sodium, potassium, or lithium.

[0120] The dry binder is a polymeric material that can be fiberized, and may be, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0121] Conductive material The conductive material is used to impart conductivity to the electrodes, and any material that does not undergo chemical change and is electronically conductive 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, ketjen black, carbon fiber, carbon nanofiber, and carbon nanotube; metal-based materials in the form of metal powder or metal fiber, including copper, nickel, aluminum, and silver; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0122] The content of the negative electrode active material may be 95% to 99.5% by weight relative to 100% by weight of the negative electrode active material layer, and the content of the binder may be 0.5% to 5% by weight relative to 100% by weight of the negative electrode active material layer. For example, the negative electrode active material layer may contain 90% to 99% by weight of the negative electrode active material, 0.5% to 5% by weight of the binder, and 0.5% to 5% by weight of the conductive material.

[0123] current collector The negative electrode current collector may contain, for example, indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), or an alloy thereof, and may be in the form of a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, 1 μm to 20 μm, 5 μm to 15 μm, or 7 μm to 10 μm.

[0124] electrolyte An example of an electrolyte for a lithium secondary battery is an electrolytic solution, which can include a non-aqueous organic solvent and a lithium salt.

[0125] The non-aqueous organic solvent serves as a medium through which ions involved in the electrochemical reaction of the battery can migrate, and may be a carbonate-based, ester-based, ether-based, ketone-based, or alcohol-based solvent, an aprotic solvent, or a combination thereof.

[0126] Examples of carbonate 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). Examples of ester solvents include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, and valerolactone. Examples of caprolactone include ether solvents such as dibutyl ether, tetraglyme, diglyme, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, and tetrahydrofuran. In addition, cyclohexanone can be used as a ketone solvent. Ethyl alcohol, isopropyl alcohol, etc. can be used as an alcohol solvent. Aprotic solvents include nitriles such as R-CN (R is a hydrocarbon group having 2 to 20 carbon atoms and having a linear, branched, or cyclic structure, and may contain a double bond, an aromatic group, or an ether group), amides such as dimethylformamide, oxolanes such as 1,3-dioxolane and 1,4-dioxolane, and sulfolanes.

[0127] The non-aqueous organic solvents can be used alone or in combination of two or more kinds. When two or more kinds are used in combination, the mixing ratio can be appropriately adjusted depending on the desired battery performance, which is widely understood by those working in the field.

[0128] When a carbonate-based solvent is used, a cyclic carbonate and a chain carbonate can be mixed and used, and the cyclic carbonate and the chain carbonate can be mixed in a volume ratio of 1:1 to 1:9.

[0129] The non-aqueous organic solvent may further include an aromatic hydrocarbon organic solvent. For example, a carbonate solvent and an aromatic hydrocarbon organic solvent may be mixed in a volume ratio of 1:1 to 30:1.

[0130] The electrolyte may further contain vinyl ethyl carbonate, vinylene carbonate or ethylene carbonate based compounds to improve the battery life.

[0131] Representative examples of the ethylene carbonate compounds include fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0132] Lithium salts are substances that dissolve in organic solvents and act as a source of lithium ions within the battery, enabling basic lithium secondary battery operation and facilitating the movement of lithium ions between the positive and negative electrodes. Representative 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)(CyF 2y+1 SO2) (x and y are integers of 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalato)phosphate (LiDFOB), and lithium bis(oxalato)borate (LiBOB).

[0133] The lithium salt concentration is preferably within the range of 0.1 M to 2.0 M. When the lithium salt concentration is within this range, the electrolyte has appropriate ionic conductivity and viscosity, thereby exhibiting excellent performance and allowing lithium ions to migrate effectively.

[0134] Separator Depending on the type of lithium secondary battery, a separator may be present between the positive electrode and the negative electrode. Such a separator may be made of polyethylene, polypropylene, polyvinylidene fluoride, or a multilayer film of two or more of these materials. Of course, mixed multilayer films such as a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, or a polypropylene / polyethylene / polypropylene three-layer separator may also be used.

[0135] The separator may include a porous substrate and a coating layer containing an organic material, an inorganic material, or a combination thereof located on one or both sides of the porous substrate.

[0136] The porous substrate may be a polymer membrane formed of any one polymer selected from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyacetal, polyamide, polyimide, polycarbonate, polyether ketone, polyaryl ether ketone, polyetherimide, polyamide imide, polybenzimidazole, polyethersulfone, polyphenylene oxide, cyclic olefin copolymer, polyphenylene sulfide, polyethylene naphthalate, glass fiber, Teflon (registered trademark), and polytetrafluoroethylene, or a copolymer or mixture of two or more of these polymers.

[0137] The porous substrate can have a thickness of about 1 μm to 40 μm, for example, 1 μm to 30 μm, 1 μm to 20 μm, 5 μm to 15 μm, or 10 μm to 15 μm.

[0138] The organic material may include a (meth)acrylic copolymer including a first structural unit derived from (meth)acrylamide and a second structural unit including at least one of a structural unit derived from (meth)acrylic acid or a (meth)acrylate and a structural unit derived from (meth)acrylamidosulfonic acid or a salt thereof.

[0139] The inorganic material may include, but is not limited to, inorganic particles selected from Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. 50 ) may be 1 nm to 2000 nm, for example, 100 nm to 1000 nm, or 100 nm to 700 nm.

[0140] The organic material and the inorganic material may be mixed in one coating layer, or may be stacked in a form in which a coating layer containing an organic material and a coating layer containing an inorganic material are stacked.

[0141] The thickness of each of the coating layers may be 0.5 μm to 20 μm, for example, 1 μm to 10 μm, or 1 μm to 5 μm.

[0142] Examples of the present invention and comparative examples are described below. The following examples are illustrative of the present invention, and the present invention is not limited to the following examples.

[0143] Second binder manufacturing example 1 NMP was placed in a 100 mL two-neck round-bottom flask purged with nitrogen gas, and 0.002 mol of trimellitic anhydride chloride and 0.003 mol of 4,4-oxydiphthalic anhydride were added. A reflux apparatus was installed and the mixture was heated to dissolve. NMP was placed in another 100 mL one-neck round-bottom flask, and 0.004 mol of methylenediphenyl 4,4'-diisocyanate and 0.001 mol of 1,6-diaminohexane were added. The mixture was then heated to dissolve. In the presence of a reflux device such as a Dean-Stark apparatus, a solution of methylenephenyl 4,4'-diisocyanate and 1,6-diaminohexane was placed in a round-bottom flask containing a solution of 4,4-oxydiphthalic anhydride in NMP. The two solutions were mixed, and 0.001 mol of triethylamine was added. The mixture was then heated to 120°C for 24 hours to produce a poly(imide-amide) binder (Mw: 100,000 g / mol) having the structure represented by the following formula 4A.

[0144] [ka]

[0145] In Chemical Formula 4A, m1, n1, p1, q1, and r1 are defined as above.

[0146] Second binder manufacturing example 2 A 100 mL two-neck round-bottom flask was filled with distilled water and 0.005 mol of 4,4'-oxydiphthalic anhydride was added. A reflux apparatus was attached and the mixture was heated to dissolve. Another 100 mL one-neck round-bottom flask was filled with NMP, and 0.004 mol of methylenediphenyl 4,4'-diisocyanate and 0.001 mol of 1,6-dihexanol were added. The mixture was heated to dissolve. A solution of methylenephenyl 4,4'-diisocyanate and 1,6-dihexanol was added to a round-bottom flask containing a solution of 4,4-oxydiphthalic anhydride in NMP. The two solutions were mixed and heated at 120°C for 24 hours to produce a powder. This produced a poly(imide-urethane) binder (Mw: 150,000 g / mol) having the structure represented by Formula 4B below.

[0147] [ka]

[0148] In Chemical Formula 4B, m2, n2, p2, q2, and r2 are defined as above.

[0149] Second binder manufacturing example 3 A 100 mL two-neck round-bottom flask was filled with distilled water and 0.005 mol of 4,4'-oxydiphthalic anhydride was added. A reflux apparatus was attached and the mixture was heated to dissolve. Another 100 mL one-neck round-bottom flask was filled with NMP, and 0.004 mol of methylenediphenyl 4,4'-diisocyanate and 0.001 mol of 1,6-diaminohexane were added. The mixture was then heated to dissolve. A solution of methylenephenyl 4,4'-diisocyanate and 1,6-diaminohexane was added to a round-bottom flask containing a solution of 4,4-oxydiphthalic anhydride in NMP. The two solutions were mixed and heated at 120°C for 24 hours to produce a powder. This produced a poly(imide-urea) binder (Mw: 200,000 g / mol) having the structure represented by Formula 4C below.

[0150] [ka]

[0151] In Chemical Formula 4C, m3, n3, p3, q3, and r3 are defined as above.

[0152] Second binder comparative manufacturing example 1 Poly(urethane-urea) binder (Mw: 220,000 g / mol) represented by the following formula 4D was produced by condensation polymerization reaction between aromatic diisocyanate, glycol, and diamine to induce the formation of urethane and urea bonds.

[0153] [ka]

[0154] In the above chemical formula 4D, m and n each independently represent an integer of 1 to 100.

[0155] Example 1 H-NBR binder (AN (Acrylonitrile) ratio: 34-35 wt%, HBD (Hydrogenated butadiene) ratio: 65-66%, Mw: 1,000,000 g / mol) [product name: BM-451B, manufacturer: Zeon] and carbon black were added to an NMP solvent and dispersed using a PD mixer to produce a conductive material dispersion.

[0156] A PI (Polyimide) binder (product name: P84, manufacturer: Evonik) was added to the conductive material dispersion and further dispersed using a PD mixer to prepare a mixed solution.

[0157] Next, LiFePO4 (D 50 = 1 μm) were added and mixed to prepare a positive electrode slurry. At this time, the amount of each component added was adjusted so that the positive electrode slurry contained 94.0 wt% LiFePO4, 0.3 wt% H-NBR, 2.7 wt% PI binder, and 3.0 wt% carbon black.

[0158] The positive electrode slurry was then coated on an aluminum foil, dried, and rolled to prepare a positive electrode. At this time, the loading level of the positive electrode was 50 mg / cm. 2 It was.

[0159] Anode slurry was prepared by mixing 97.5 wt% graphite anode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene-butadiene rubber in an aqueous solvent. The anode slurry was coated on copper foil, dried, and rolled to prepare an anode.

[0160] A lithium secondary battery was fabricated in a conventional manner using a polytetrafluoroethylene separator and an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent containing a mixture of ethylene carbonate and dimethyl carbonate in a volume ratio of 3:7.

[0161] Example 2 A positive electrode and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that the poly(imide-amide) binder prepared in Preparation Example 1 was used instead of the PI binder.

[0162] Example 3 A positive electrode and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that the poly(imide-urethane) binder prepared in Preparation Example 2 was used instead of the PI binder.

[0163] Example 4 A positive electrode and a lithium secondary battery were prepared in substantially the same manner as in Example 1, except that the poly(imide-urea) binder prepared in Preparation Example 3 was used instead of the PI binder.

[0164] Comparative Example 1 A positive electrode and a lithium secondary battery were fabricated in substantially the same manner as in Example 1, except that the positive electrode was fabricated using a positive electrode slurry prepared by mixing 4.0 wt % LiFePO4, 3.0 wt % PVDF binder, and 3.0 wt % carbon black in an NMP solvent, without using H-NBR or PI binder.

[0165] Comparative Example 2 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the positive electrode was manufactured using a positive electrode slurry prepared by mixing 94.0 wt% of LiFePO4, 3.0 wt% of PI binder, and 3.0 wt% of carbon black in an NMP solvent, without using H-NBR as the binder.

[0166] Comparative Example 3 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the amounts of H-NBR and PI binder added to the positive electrode slurry were changed to 2.0 wt % and 1.0 wt %, respectively.

[0167] Comparative Example 4 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the amounts of H-NBR and PI binder added to the positive electrode slurry were changed to 2.5 wt % and 0.5 wt %, respectively.

[0168] Comparative Example 5 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the amounts of H-NBR and PI binder added to the positive electrode slurry were changed to 0.1 wt % and 2.9 wt %, respectively.

[0169] Comparative Example 6 A positive electrode and a lithium secondary battery were manufactured in substantially the same manner as in Example 1, except that the amounts of H-NBR and PI binder added to the positive electrode slurry were changed to 0.2 wt % and 2.8 wt %, respectively.

[0170] Evaluation example 1: IR evaluation Infrared spectroscopy (IR) was used to confirm the structure of each of the second binders prepared in Preparation Examples 1 and 3. The IR analysis results for the binder prepared in Preparation Example 1 are shown in FIG. 5, and the IR analysis results for the binder prepared in Preparation Example 3 are shown in FIG. 6.

[0171] Referring to Figure 5, 1770 cm -1 The characteristic peak of the C=O functional group of the imide group can be confirmed at 1710cm -1 A characteristic peak of the C=O functional group of the amide group can be confirmed in Fig. 1. Therefore, it can be seen that the binder produced in Production Example 1 is a poly(imide-amide) binder containing imide groups and amide groups in its structure.

[0172] Referring to Figure 6, 1770 cm -1 The characteristic peak of the C=O functional group in the imide can be confirmed at 1730 cm -1 A characteristic peak of the C=O functional group in urea can be confirmed. Therefore, it is clear that the binder produced in Production Example 3 is a poly(imide-urea) binder.

[0173] Evaluation example 2: Adhesion and rollability evaluation To evaluate the adhesiveness of the positive electrode plates, for each of the positive electrodes produced in Examples 1 and 2 and Comparative Examples 1 to 6, double-sided tape was attached to the positive electrode active material layer formed on the positive electrode current collector, and then peeled at a 180° peel angle and a rate of 25 mm / min. The adhesive strength was measured using a universal tester, and the results are shown in Table 1. In addition, the maximum rolling density of the electrode plates was measured by rolling them using a simple rolling machine and measuring the weight and thickness of the electrode plates, and the results are shown in Table 1.

[0174] [Table 1]

[0175] Referring to Table 1, it can be seen that the positive electrodes prepared in Examples 1 and 2 have high adhesive strength and high rolling density, and thus are excellent in both adhesiveness and rolling property.

[0176] On the other hand, in the case of the positive electrodes produced in Comparative Examples 1 to 6, it can be confirmed that the adhesive strength of the electrode plate is lower than in Examples 1 and 2, or the rolling density is lower.

[0177] Evaluation example 3: Resistance evaluation The positive electrode plates manufactured in Examples 1 and 2 and Comparative Example 1 were measured for the composite resistance and interface resistance at room temperature using an Electrode Resistance Measurement System RM2610. The results are shown in FIGS. 7 and 8, respectively.

[0178] 7 and 8, it can be seen that in Comparative Example 1, in which only PVDF was used as a binder when preparing the positive electrode slurry, the composite resistance and interface resistance of the electrode plate were very high.

[0179] In contrast, in Examples 1 and 2, in which a second binder such as polyimide (PI) or poly(imide-amide) was used in addition to H-NBR as the binder during the preparation of the positive electrode slurry, the electrode plate composite resistance and interfacial resistance were significantly lower. This is presumably due to the introduction of a conductive material dispersion process in which the first binder, H-NBR, is first mixed with the conductive material to produce a conductive material dispersion during the positive electrode slurry preparation process, which further improved the dispersibility of the conductive material. In particular, compared to Example 1, in which H-NBR and polyimide were used as binders, Example 2, in which H-NBR and poly(imide-amide) were used as binders, showed lower electrode plate composite resistance and interfacial resistance.

[0180] Evaluation example 4: Expansion rate and elastic elongation rate evaluation for electrolyte To evaluate the expansion ratio in response to the electrolyte, the PI binder used in Example 1 and each of the binders prepared in Preparation Examples 1 to 3 were dried at 130°C and then fabricated into films. The fabricated films were immersed in an electrolyte solution prepared by dissolving 1M LiPF6 in a solvent consisting of a 3:7 volume ratio of ethylene carbonate and dimethyl carbonate, and then stored at 70°C for 72 hours. After swelling occurred, the weights were measured. The expansion ratio (P) in response to the electrolyte was calculated using the following equation.

[0181] [Formula 1] P = (P2 - P1) / P1 x 100 In the above formula 1, P1 represents the film weight before expansion, and P2 represents the film weight after expansion.

[0182] To evaluate the elastic elongation in the electrolyte, the PI binder used in Example 1 and each of the binders produced in Production Examples 1 to 3 were dried at 130°C and formed into a film, which was then immersed in the electrolyte and then at 60°C for 24 hours. The film was then removed and pulled using a UTM (Universal Testing Machine) at a grip separation speed of 5 mm / min, the pulled length was measured, and the elastic elongation E was calculated using the following equation 1.

[0183] [Formula 2] E = (E2 - E1) / E1 x 100 In the above formula 2, E2 represents the length of the film after stretching, and E1 represents the length of the film before stretching.

[0184] The evaluation results of the expansion rate and elastic elongation rate for the above-mentioned electrolyte solution are shown in Table 2 below.

[0185] [Table 2]

[0186] Referring to Table 2, it can be seen that when the PI binder used in Example 1 and the binders prepared in Preparation Examples 1 to 3 were used, the expansion coefficient in the electrolyte was low and the elastic elongation ratio was excellent.

[0187] On the other hand, when the binder prepared in Comparative Preparation Example 1 was used, the film became brittle when it was removed after immersion in the electrolyte for 24 hours, and the elastic elongation rate in the electrolyte could not be measured.

[0188] Evaluation example 5: Bending strength evaluation The bending strength of each of the lithium secondary batteries produced in Examples 1 to 4 and Comparative Examples 1 to 4 was measured using a three-point bending analyzer, and the results are shown in Table 3 below.

[0189] [Table 3]

[0190] Referring to Table 3, it can be seen that the lithium secondary batteries manufactured in Examples 1 to 4 have bending strengths at the same level or lower than those of Comparative Examples 1 to 4, and that in terms of flexibility, Examples 1 to 4 are superior to Comparative Examples 1 to 4. Therefore, it can be seen that the lithium secondary batteries manufactured in Examples 1 to 4 have excellent flexibility and can be rolled at high density, thereby ensuring excellent rollability.

[0191] Evaluation example 6: Life characteristics evaluation Each of the lithium secondary batteries manufactured in Examples 1 to 4 and Comparative Examples 1 to 4 was charged at a constant current of 0.2 C at 25° C. until the voltage reached 4.20 V (vs. Li), and then discharged at a constant current of 0.2 C until the voltage reached 2.8 V (vs. Li) during discharge.

[0192] The lithium battery after the chemical formation step was charged at a constant current of 1.0 C at 25°C until the voltage reached 4.20 V (vs. Li). It was then discharged at a constant current of 0.5 C until the voltage reached 2.8 V (vs. Li) (first cycle). This charge / discharge cycle was repeated 300 times. Each charge / discharge cycle included a 10-minute rest period.

[0193] The results of the above-mentioned charge / discharge experiment are shown in Table 4 below, and the capacity retention rate after 300 cycles is defined by the following formula 2. [Formula 2] Capacity retention rate (%) = (discharge capacity after 300 cycles / discharge capacity after 1 cycle) x 100

[0194] [Table 4]

[0195] Referring to Table 4, it can be seen that the lithium secondary batteries prepared in Examples 1 to 4 have higher capacity retention rates, generally lower DCIR, and more excellent cycle life characteristics compared to Comparative Examples 1 to 4. [Explanation of symbols]

[0196] 100 Lithium secondary battery 10 positive electrode 11 Positive lead tap 12 Positive terminal 20 negative electrode 21 Negative lead tap 22 Negative terminal 30 Separator 40 Electrode assembly 50 cases 60 Sealing member 70 Electrode Taps 71 Positive tap 72 Negative tap

Claims

1. a positive electrode current collector; and a positive electrode active material layer located on the positive electrode current collector and including a positive electrode active material, a binder, and a conductive material; the binder comprises a first binder and a second binder; the first binder comprises hydrogenated nitrile butadiene rubber; the second binder includes an imide-based binder, The positive electrode active material layer contains 300 to 1,300 parts by weight of a second binder relative to 100 parts by weight of a first binder.

2. 2. The positive electrode according to claim 1, wherein the first binder has a weight average molecular weight (Mw) of 100,000 g / mol to 2,000,000 g / mol.

3. 2. The positive electrode according to claim 1, wherein the hydrogenated nitrile butadiene rubber contains 20% by weight to 40% by weight of acrylonitrile or methacrylonitrile.

4. 10. The positive electrode of claim 1, wherein the second binder comprises a polyimide, a poly(imide-amide), a poly(imide-urethane), a poly(imide-urea), or a combination thereof.

5. 2. The positive electrode of claim 1, wherein the second binder comprises at least one of a structure represented by the following Formula 1A and a structure represented by the following Formula 1B: 【Chemistry 1】 In the above formula 1A, R 1 represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group, x1 is an integer of 0 to 3, and * represents a linking site. 【Chemistry 2】 In the above formula 1B, R 2 represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group, x2 is an integer of 0 to 2, and * represents a linking site.

6. 2. The positive electrode of claim 1, wherein the second binder comprises at least one of a structure represented by the following Chemical Formula 2A and a structure represented by the following Chemical Formula 2B: 【Transformation 3】 In the chemical formula 2A, R 11 ~R 15 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x11 is an integer of 0 to 3; y12 and z13 are each independently an integer of 0 to 4; and * represents a linking site. 【Chemistry 4】 In the above chemical formula 2B, R 21 ~R 25 each independently represents hydrogen, deuterium, or a substituted or unsubstituted alkyl group; x21 is an integer of 0 to 2; y22 and z23 are each independently an integer of 0 to 4; and * represents a linking site.

7. 2. The positive electrode according to claim 1, wherein the second binder has an expansion coefficient P of 10% by weight to 50% by weight with respect to the electrolyte.

8. 2. The positive electrode according to claim 1, wherein the second binder has an elastic elongation rate of 10% to 200% after immersion in the electrolyte for 24 hours.

9. 2. The positive electrode according to claim 1, wherein the positive electrode active material layer contains 3% by weight to 20% by weight of the first binder relative to 100% by weight of the total of the first binder and the second binder.

10. 2. The positive electrode according to claim 1, wherein the positive electrode active material layer contains 80% by weight to 97% by weight of the second binder, relative to 100% by weight of the total of the first binder and the second binder.

11. The positive electrode according to claim 1 , wherein the positive electrode active material comprises a lithium transition metal composite oxide.

12. the positive electrode active material contains a lithium composite phosphate, The positive electrode according to claim 1, wherein the lithium composite phosphate includes one or more compounds represented by the following chemical formulas 11 to 15: [Chemical formula 11] Li a1 Fe (1-s1) M 1 s1 PO 4 In Chemical Formula 11, 0.90≦a1≦1.5, 0≦s1≦0.4, and M 1 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. [Chemical formula 12] Li a2 Mn s2 Fe (1-s2-t2) M 2 t2 PO 4 In chemical formula 12, 0.90≦a2≦1.5, 0.1≦s2≦0.9, 0≦t2≦0.9, M 2 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. [Chemical formula 13] Li a3 Mn (1-s3) M 3 s3 PO 4 In Chemical Formula 13, 0.90≦a3≦1.5, 0≦s3≦0.4, and M 3 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, or a combination thereof. [Chemical formula 14] Li a4 Today (2-s4) M 4 s4 (PO 4 ) 3 In Chemical Formula 14, 0.90≦a4≦1.5, 0≦s4≦0.4, and M 4 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof. [Chemical formula 15] Li a5 Today (1-s5) M 5 s5 PO 5 In Chemical Formula 15, 0.90≦a5≦1.5, 0≦s5≦0.4, and M 5 may be Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, V, W, Y, Zn, Zr, or a combination thereof.

13. 2. The positive electrode according to claim 1, wherein the first binder and the second binder do not contain fluorine.

14. preparing a positive electrode slurry containing a positive electrode active material, a binder, and a conductive material; and applying the positive electrode slurry onto a positive electrode current collector to form a positive electrode. the binder comprises a first binder and a second binder; the first binder comprises hydrogenated nitrile butadiene rubber; the second binder includes an imide-based binder, The positive electrode slurry contains 100 parts by weight of the first binder and 300 to 1,300 parts by weight of the second binder.

15. The positive electrode slurry is produced by: preparing a conductive material dispersion by mixing a first binder, a conductive material, and a solvent; Adding a second binder to the conductive material dispersion to prepare a mixture; The method for producing a positive electrode according to claim 14 , further comprising adding a positive electrode active material to the mixed solution and mixing the mixed solution.

16. The positive electrode according to any one of claims 1 to 13; a negative electrode; and an electrolyte;

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