Improved safety of lithium secondary batteries

Abstract

The present invention relates to a lithium secondary battery, and the lithium secondary battery contains a ternary compound containing nickel (Ni), cobalt (Co), manganese (Mn) and the like as a positive electrode active material, and at the same time, a small amount of an iron phosphate compound and a silicon-based oxide are contained in the outermost shell of a composite layer adjacent to a separator in each of the positive electrode and the negative electrode, respectively. This not only provides excellent battery energy density, but also has the advantage of improving safety against internal short circuits in the secondary battery by reducing the amount of short circuit current due to the relatively low electrical conductivity of the positive electrode surface and the negative electrode surface.

Description

[Technical Field]

[0001] The present invention relates to a lithium secondary battery with improved safety against internal short circuits.

[0002] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0050712, filed on April 25, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference. [Background technology]

[0003] BACKGROUND ART In recent years, secondary batteries have been widely used not only in small devices such as portable electronic devices but also in medium- to large-sized devices such as battery packs for hybrid and electric vehicles, and power storage devices.

[0004] To apply such secondary batteries to medium- to large-scale devices, high energy density is required. Therefore, ternary compounds containing nickel (Ni), cobalt (Co), manganese (Mn), etc., specifically LiNi, which has a nickel (Ni) content of 60% or more, are being developed. a Co b Mn c O2 (0.6≦a≦0.9, a+b+c=1), a layered structure of lithium nickel metal oxide is used as the positive electrode active material to achieve high capacity. However, although the capacity of lithium nickel metal oxide increases as the nickel (Ni) content increases, it exhibits low chemical and structural stability, making it prone to exothermic reactions. In particular, lithium nickel metal oxide has a low onset point of heat generation, and once the exothermic reaction begins, it rapidly increases the temperature inside the battery, potentially leading to fire or explosion, resulting in low safety.

[0005] An exothermic reaction of the positive electrode active material can be induced when a short-circuit current flows inside the battery, i.e., when an internal short circuit occurs. More specifically, short-circuit current mainly occurs when a short circuit occurs inside the secondary battery due to penetration by a needle-like object or when a short circuit occurs in an electronic device connected to the secondary battery. When a short circuit occurs in a lithium secondary battery, a rapid electrochemical reaction occurs at the positive and negative electrodes, generating heat. This generated heat is conducted to surrounding materials, causing a rapid rise in the temperature of the secondary battery cells, ultimately leading to fire. In particular, in a battery pack containing multiple lithium secondary battery cells, heat generated in one cell can propagate to surrounding cells, affecting other cells and ultimately causing the battery pack to fire.

[0006] Therefore, there is a need to develop a battery that contains a lithium nickel metal oxide with a high content of nickel (Ni) and exhibits high energy density while improving safety issues due to internal short circuits. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Korean Patent Publication No. 10-2020-0024980 [Patent Document 2] Korean Patent Publication No. 10-2017-0004253 Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, an object of the present invention is to provide a lithium secondary battery and a secondary battery module including the same, which contain a ternary compound containing nickel (Ni) in the positive electrode, have a high energy density, and are improved in terms of safety issues caused by internal short circuits. [Means for solving the problem]

[0009] To solve the above-mentioned problems, there is provided a lithium secondary battery including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode has first to n-th negative electrode composite layers (where n≧2) disposed on a negative electrode current collector, the first to n-th negative electrode composite layers including a first negative electrode active material containing a carbon-based material and a second negative electrode active material containing a silicon-based material, and the content or content ratio of the second negative electrode active material increases as the position of the individual negative electrode composite layers changes from the first negative electrode composite layer to the n-th negative electrode composite layer.

[0010] In this case, the carbon-based material may include at least one selected from the group consisting of soft carbon, hard carbon, natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotubes, fullerene, activated carbon, graphene, and carbon fiber.

[0011] The silicon-based materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO q , where 0.8≦q≦2.5).

[0012] The second negative electrode active material may be contained in an amount of 1 to 20 wt % based on the total weight of the negative electrode active material.

[0013] Furthermore, the second negative electrode active material may have a sphericity of 0.5 to 1.0, and the sphericity may decrease as the position of the individual negative electrode mixture layer changes from the first negative electrode mixture layer to the nth negative electrode mixture layer.

[0014] The total thickness of the negative electrode mixture layer may be 50 μm to 300 μm.

[0015] The thickness of the first negative electrode mixture layer may be 10% to 60% of the total thickness of the negative electrode mixture layers.

[0016] The positive electrode may have first to m-th positive electrode composite layers (where m≧2) disposed on a positive electrode current collector, and the first to m-th positive electrode composite layers may contain a first positive electrode active material including a lithium composite metal oxide represented by Chemical Formula 1, and a second positive electrode active material including an iron phosphate compound represented by Chemical Formula 2 below.

[0017] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0018] [Chemical formula 2] Life a M 2 1-a XO4

[0019] In the above chemical formula 1 and chemical formula 2, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, and y+z+w+v=1; M 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, CO, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; X is one or more elements selected from the group consisting of P, Si, S, As, and Sb; and a is 0≦a≦0.5.

[0020] Here, the content or content ratio of the second positive electrode active material in each positive electrode mixture layer may increase as the position of the individual positive electrode mixture layer changes from the first positive electrode mixture layer to the mth positive electrode mixture layer.

[0021] The second positive electrode active material may be contained in an amount of less than 10 wt % based on the total weight of the positive electrode mixture layer.

[0022] The total thickness of the positive electrode mixture layer may be 50 μm to 300 μm.

[0023] Furthermore, in one embodiment, the present invention provides a secondary battery module including the lithium secondary battery according to the present invention described above. [Effects of the Invention]

[0024] The lithium secondary battery according to the present invention contains a ternary compound containing nickel (Ni), cobalt (Co), manganese (Mn), etc. as a positive electrode active material, and also contains small amounts of an iron phosphate compound and a silicon-based oxide in the outermost shell of a composite layer adjacent to a separator in each of the positive electrode and the negative electrode. This not only provides excellent battery energy density, but also has the advantage of improving safety in the event of an internal short circuit by reducing the electrical conductivity of the positive electrode surface and the negative electrode surface, thereby reducing the short circuit current in the event of an internal short circuit in the secondary battery. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a cross-sectional view showing the structure of a lithium secondary battery according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] Because the present invention is susceptible to various modifications and can have various embodiments, specific embodiments are described in detail in the detailed description.

[0027] However, this is not intended to limit the invention to any particular embodiment, but should be understood to include all modifications, equivalents, or alternatives falling within the spirit and scope of the invention.

[0028] In the present invention, the terms "comprise" and "have" are intended to specify the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the presence or possibility of addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0029] Furthermore, in the present invention, when a layer, film, region, plate, or other portion is described as being "on" another portion, this includes not only the case where it is "directly on" the other portion, but also the case where there is another portion therebetween. Conversely, when a layer, film, region, plate, or other portion is described as being "under" the other portion, this includes not only the case where it is "directly under" the other portion, but also the case where there is another portion therebetween. Furthermore, in this application, being "located on" can include not only the case where it is located at the top, but also the case where it is located at the bottom.

[0030] The present invention will now be described in more detail.

[0031] <Lithium secondary battery> In one embodiment, the present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode has first to n-th negative electrode composite layers (n≧2) disposed on a negative electrode current collector, the first to n-th negative electrode composite layers including a first negative electrode active material containing a carbon-based material and a second negative electrode active material containing a silicon-based material, and the content or content ratio of the second negative electrode active material increases as the position of the individual negative electrode composite layers changes from the first negative electrode composite layer to the n-th negative electrode composite layer.

[0032] The lithium secondary battery according to the present invention includes an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The electrode assembly is inserted into a battery case, into which an electrolyte composition is injected and the battery case is sealed.

[0033] The negative electrode includes a negative electrode composite layer prepared by applying a slurry containing a negative electrode active material onto a negative electrode current collector, drying the slurry, and pressing the slurry. The slurry may further include a conductive material, a binder, and other additives as needed.

[0034] Here, the negative electrode includes a negative electrode current collector and a negative electrode composite material layer having a multilayer structure in which two or more individual composite material layers are laminated on the negative electrode current collector.

[0035] 1, the negative electrode composite material layer has a structure in which n (n≧2) individual negative electrode composite material layers 121 are stacked on the negative electrode current collector 11. In this case, the negative electrode composite material layer stacked on the surface in contact with the negative electrode current collector 11 is a first negative electrode composite material layer 121a, and second to nth negative electrode composite material layers 121n are stacked sequentially on the first negative electrode composite material layer 121a, so that n individual negative electrode composite material layers 121 are located on the negative electrode current collector 11.

[0036] The number of layers of the negative electrode composite layer is not particularly limited as long as it has a structure of two or more layers (n≧2), and specifically may be 2 to 10 layers, 2 to 8 layers, 2 to 6 layers, or 2 to 4 layers. By adjusting the number of stacked negative electrode composite layers within the above range, the present invention can easily adjust the internal composition of the negative electrode composite layer depending on the position, for example, the composition of the negative electrode composite layer relatively adjacent to the positive electrode, while preventing a decrease in the production efficiency of the negative electrode.

[0037] In addition, the negative electrode composite layer may use a negative electrode active material commonly used in the art, but preferably may include both a first negative electrode active material including a carbon-based material and a second negative electrode active material including a silicon-based material.

[0038] Specifically, the first negative electrode active material may include one or more carbon-based materials such as graphite having a complete layered crystalline structure like natural graphite, soft carbon having a low-crystalline layered crystalline structure (graphene structure; a structure in which hexagonal honeycomb-shaped carbon planes are arranged in layers), hard carbon having such a structure mixed with an amorphous portion, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotubes, fullerene, activated carbon, graphene, and carbon fiber.

[0039] The second negative electrode active material may include a silicon-based material containing at least one of silicon (Si), silicon carbide (SiC), silicon monoxide (SiO), and silicon dioxide (SiO2). Here, when silicon monoxide (SiO2) and silicon dioxide (SiO2) are uniformly mixed or compounded and contained in the negative electrode composite layer, the silicon-based material is referred to as silicon oxide (SiO2). q , where 0.8≦q≦2.5).

[0040] The total negative electrode active material including both the first and second negative electrode active materials may be contained in an amount of 90 to 99 parts by weight, specifically 92 to 98 parts by weight, or 95 to 99 parts by weight, based on the total weight of the negative electrode composite layer.

[0041] The second negative electrode active material may be included in an amount of 1 to 20 wt % based on the total weight of the negative electrode active materials, specifically 1 to 9 parts by weight, 3 to 7 parts by weight, 5 to 15 parts by weight, 11 to 19 parts by weight, or 13 to 17 parts by weight based on the total weight of the negative electrode active materials. By adjusting the content of the second negative electrode active material within the above range, the present invention can minimize the volume change rate of the battery due to charge and discharge, and simultaneously reduce lithium consumption and irreversible capacity loss during initial charge and discharge of the battery, while improving the charge capacity per unit mass.

[0042] In addition, the first and second negative electrode active materials may both be included in the n-layer negative electrode active material, and the content or content ratio of the second negative electrode active material may increase as the position of the individual negative electrode composite layer changes from the first negative electrode composite layer adjacent to the negative electrode current collector to the n-th negative electrode composite layer farthest from the negative electrode current collector.

[0043] As one example, the second negative electrode active material may be contained in the first negative electrode composite layer at 1 to 45 wt % of the total weight of the second negative electrode active material, and may be contained in the second negative electrode composite layer at 55 to 99 wt % of the total weight of the second negative electrode active material.

[0044] As another example, the second negative electrode active material may be contained in the first negative electrode composite layer at 1 to 10 wt % of the total weight of the second negative electrode active material, in the second negative electrode composite layer at 10 to 40 wt % of the total weight, and in the third negative electrode composite layer at 40 to 89 wt % of the total weight.

[0045] As another example, the second negative electrode active material may be contained in the first negative electrode composite layer at 1 to 5 wt % of the total weight of the second negative electrode active material, in the second negative electrode composite layer at 5 to 15 wt % of the total weight, in the third negative electrode composite layer at 15 to 30 wt % of the total weight, and in the fourth negative electrode composite layer at 30 to 79 wt % of the total weight.

[0046] The first negative electrode active material contains a carbon-based material and exhibits excellent electrical properties, such as electrical conductivity. However, when a short circuit current flows inside the secondary battery, for example, if a short circuit occurs inside the secondary battery due to penetration by a needle-shaped object, the amount of short circuit current between the positive and negative electrodes increases due to the carbon-based material's high electrical conductivity, which can significantly generate short circuit heat and accelerate the heat-generating reaction of the battery.

[0047] However, in the present invention, the content or content ratio of the second negative electrode active material including a silicon-based material having a relatively lower electrical conductivity than a carbon-based material is increased from the innermost to the outermost negative electrode composite layers, i.e., from the first negative electrode composite layer to the nth negative electrode composite layer, thereby reducing the amount of short-circuit current in the event of an internal short circuit in the secondary battery, and thereby reducing and / or delaying heat generation in the secondary battery.

[0048] Furthermore, the second negative electrode active material may exhibit a tendency for the sphericity of the active material to decrease from the first negative electrode composite layer to the nth negative electrode composite layer. Here, "sphericity" refers to the ratio of the shortest diameter (minor axis) to the longest diameter (major axis) among any diameters passing through the center of a particle, and a sphericity of 1 indicates that the particle is spherical. The sphericity may be measured using a particle shape analyzer.

[0049] Specifically, the second negative electrode active material may have a sphericity of 0.5 to 1.0, and the sphericity may decrease from the first negative electrode composite layer to the nth negative electrode composite layer, thereby forming a constant sphericity gradient.

[0050] As one example, the second negative electrode active material contained in the first negative electrode composite layer may have a sphericity of 0.8 to 1.0, and the second negative electrode active material contained in the second negative electrode composite layer may have a sphericity of 0.5 to 0.7.

[0051] As another example, the second negative electrode active material contained in the first negative electrode composite layer may have a sphericity of 0.9 to 1.0, the second negative electrode active material contained in the second negative electrode composite layer may have a sphericity of 0.7 to 0.8, and the second negative electrode active material contained in the third negative electrode composite layer may have a sphericity of 0.5 to 0.6.

[0052] The present invention controls the sphericity of the second negative electrode active material to have a constant gradient depending on the position in the negative electrode composite layer containing the second negative electrode active material, thereby reducing the electrical conductivity at the surface of the negative electrode composite layer that contacts the separator without reducing the energy density of the negative electrode composite layer.

[0053] Furthermore, the total thickness of the negative electrode composite layer is not particularly limited, but may specifically be 50 μm to 300 μm, more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0054] Furthermore, among the individual negative electrode composite layers constituting the negative electrode composite layer, the first negative electrode composite layer in contact with the negative electrode current collector may have a thickness adjusted to a certain range. Specifically, the thickness of the first negative electrode composite layer may be 10% to 60% of the total thickness of the negative electrode composite layer, more specifically, 10% to 40%, 30% to 50%, 10% to 20%, or 40% to 60% of the total thickness of the negative electrode composite layer.

[0055] By adjusting the total thickness and individual thicknesses of the negative electrode composite layers to fall within the above ranges, the present invention can prevent a reduction in the energy density of the electrode and also achieve high adhesive strength between the negative electrode current collector and the negative electrode composite layer.

[0056] Meanwhile, the negative electrode mixture layer may contain a binder to bond the negative electrode active material, conductive material, and other additives while providing adhesion to the negative electrode current collector. Examples of such binders include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These binders may be used alone or in combination. The binder may be present in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of the negative electrode mixture layer.

[0057] The negative electrode may also include a negative electrode current collector that has high conductivity and does not induce chemical changes in the battery. For example, the negative electrode current collector may be made of copper, stainless steel, nickel, titanium, calcined carbon, or the like. In the case of copper or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, or the like. The negative electrode current collector may also have a finely textured surface to strengthen its binding strength with the negative electrode active material, and may be in various forms, such as a film, sheet, foil, net, porous material, foam, or nonwoven fabric. The average thickness of the negative electrode current collector may be preferably 3 to 500 μm, taking into account the conductivity and total thickness of the negative electrode to be manufactured.

[0058] Furthermore, the positive electrode may have m (where m≧2) positive electrode composite layers disposed on a positive electrode current collector, and the first to m-th positive electrode composite layers may each contain a first positive electrode active material including a lithium composite metal oxide represented by Chemical Formula 1, and a second positive electrode active material including an iron phosphate compound represented by Chemical Formula 2 below.

[0059] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0060] [Chemical formula 2] Life a M 2 1-a XO4

[0061] In the above chemical formula 1 and chemical formula 2, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, and y+z+w+v=1; M 2is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, CO, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; X is one or more elements selected from the group consisting of P, Si, S, As, and Sb; and a is 0≦a≦0.5.

[0062] In this case, the positive electrode includes a positive electrode current collector and a positive electrode composite material layer having a multilayer structure in which two or more (m≧2) individual composite material layers are laminated on the positive electrode current collector.

[0063] Specifically, the positive electrode composite layer has a structure in which m (where m≧2) individual positive electrode composite layers are stacked on a positive electrode current collector, as shown in Fig. 1. In this case, the positive electrode composite layer stacked on the surface in contact with the positive electrode current collector is a first positive electrode composite layer, and second to mth positive electrode composite layers are stacked sequentially on the first positive electrode composite layer, so that m individual positive electrode composite layers are located on the positive electrode current collector.

[0064] The number of layers in the positive electrode composite layer is not particularly limited as long as it has a structure of two or more layers (provided that m≧2), and specifically may be 2 to 10 layers, 2 to 8 layers, 2 to 6 layers, or 2 to 4 layers. By adjusting the number of stacked positive electrode composite layers within the above range, the present invention can improve the energy density of the electrode while preventing a decrease in the manufacturing efficiency of the positive electrode, and at the same time, can effectively release heat generated during charging and discharging of the battery to the outside.

[0065] The positive electrode composite layer is manufactured by applying, drying, and pressing a slurry containing a positive electrode active material that is capable of reversibly intercalating and deintercalating lithium ions during charging and discharging of the battery, and different types of the positive electrode active material may be contained in each layer.

[0066] Specifically, the positive electrode according to the present invention has a configuration in which a positive electrode composite layer includes a first positive electrode active material including a lithium composite metal oxide represented by the following Chemical Formula 1, and positive electrode composite layers separated from the positive electrode current collector, i.e., second to m-th positive electrode composite layers disposed on the first positive electrode composite layer, further include a second positive electrode active material including an iron phosphate compound represented by Chemical Formula 2:

[0067] [Chemical formula 1] Li x [Ni y Co z Mn w M 1 v ]O2

[0068] [Chemical formula 2] Life a M 2 1-a XO4

[0069] In the above chemical formula 1 and chemical formula 2, M 1 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, and x, y, z, w, and v are 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, 0≦v≦0.1, respectively, and y+z+w+v=1; M 2 is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, CO, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; X is one or more elements selected from the group consisting of P, Si, S, As, and Sb; and a is 0≦a≦0.5.

[0070] The lithium composite metal oxide represented by Chemical Formula 1 is a ternary lithium oxide composed primarily of nickel (Ni), cobalt (Co), and manganese (Mn), and has the advantage of being suitable for use in medium- to large-sized secondary batteries for power storage in the transportation sector, such as electric vehicles (EVs), and energy storage systems (ESSs), due to its high energy density and performance, such as high output. However, although the capacity of the lithium composite metal oxide increases as the nickel (Ni) content increases, it has the problem of being prone to exothermic reactions and therefore ignition due to its low chemical and structural stability.

[0071] The exothermic reaction may be induced when a short-circuit current flows inside the battery, i.e., when an internal short circuit occurs. Generally, the short-circuit current in a battery may occur inside the secondary battery due to penetration by a needle-like object, or may occur in an electronic device connected to the secondary battery.

[0072] Therefore, in the present invention, the entire multilayered cathode composite layer contains a lithium composite metal oxide represented by Chemical Formula 1 as a first cathode active material, and the second to m-th cathode composite layers, which are separated from the cathode current collector, further contain an iron phosphate compound represented by Chemical Formula 2 as a second cathode active material.This allows the first cathode active material, which generates heat during battery charge and discharge, to be located adjacent to the cathode current collector, where heat can be easily transferred to the outside, thereby improving the heat resistance of the cathode.In addition, when the second cathode active material is subjected to an overcharge voltage of about 4.5 V or more, lithium inside the second cathode active material is released and the volume shrinks, which rapidly interrupts the internal conductive path, thereby achieving an insulating effect. Furthermore, the electrical conductivity is relatively low compared to the first positive electrode active material, and an increase in the amount of short-circuit current on the surface of the positive electrode composite layer during an internal short circuit can be prevented, thereby suppressing the generation of short-circuit heat. Furthermore, the second positive electrode active material can increase the rigidity of the positive electrode surface, thereby reducing the risk of an internal short circuit due to external force or penetration by a needle-like object.

[0073] In this case, the first positive electrode active material including the lithium composite metal oxide represented by Chemical Formula 1 is a metal oxide including nickel (Ni), cobalt (Co) and manganese (Mn) together with lithium, and may optionally contain other transition metals (M 1 ) may be doped. In a specific example, more specifically, the lithium composite metal oxide may have a doped form of Li(Ni 0.6 Co 0.2 Mn 0.2 )O2, Li(Ni 0.7 Co 0.15 Mn 0.15 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 )O2, Li(Ni 0.9 Co 0.05 Mn 0.05 )O2, Li(Ni 0.6 Co 0.2 Mn 0.1 Zr 0.1 )O2, Li(Ni 0.6 Co 0.2 Mn 0.15 Zr 0.05 )O2 and Li(Ni 0.7 Co 0.1 Mn 0.1 Zr 0.1 )O2.

[0074] The particle size of the first positive electrode active material is not particularly limited, but may specifically have an average particle size of 0.5 to 5 μm, more specifically 0.8 to 1.5 μm, 1.0 to 3.0 μm, 1.2 to 1.8 μm, or 1.5 to 2.5 μm.

[0075] In addition, the iron phosphate compound represented by the above chemical formula 2 is a lithium phosphate oxide containing iron, and in some cases, other transition metals (M 2 For example, the iron phosphate compound may have a doped form of LiFePO4, LiFeMn 0.2 PO4, LiFe 0.5 Mn 0.5 It may contain PO4 etc.

[0076] The second positive electrode active material containing the iron phosphate compound may have an average particle size of 0.5 to 5 μm, specifically 0.5 to 1.0 μm, 0.8 to 1.2 μm, 1.0 to 2.0 μm, 1.5 to 3.0 μm, 2.0 to 3.0 μm, or 2.5 to 4.0 μm.

[0077] In addition, the second positive electrode active material may exhibit a tendency that the average particle size of the second positive electrode active material included in each positive electrode composite layer increases as the position of the individual positive electrode composite layer changes from the second positive electrode composite layer to the mth positive electrode composite layer.

[0078] Specifically, the second positive electrode active material contained in the second positive electrode composite layer may have an average particle size of 0.5 to 1.2 μm, and the second positive electrode active material contained in the mth positive electrode composite layer (where m≧2) may have an average particle size of 1.3 to 3.0 μm.

[0079] As one example, the second positive electrode active material contained in the second positive electrode mixture layer may have an average particle size of 0.8 to 1.0 μm, and the second positive electrode active material contained in the third positive electrode mixture layer may have an average particle size of 1.2 to 1.5 μm.

[0080] As another example, the second positive electrode active material contained in the second positive electrode composite layer may have an average particle size of 0.6 to 0.8 μm, the second positive electrode active material contained in the third positive electrode composite layer may have an average particle size of 1.5 to 1.8 μm, and the second positive electrode active material contained in the fourth positive electrode composite layer may have an average particle size of 2.0 to 2.2 μm.

[0081] In the positive electrode of the present invention, the average particle size of the second positive electrode active material increases as the position of the individual positive electrode composite layer changes from the second positive electrode composite layer to the mth positive electrode composite layer, thereby making it possible to further increase the rigidity of the positive electrode surface.

[0082] The second positive electrode active material may be included in an amount of less than 10 wt % relative to the weight of the entire positive electrode composite layer, specifically, 0.1 to 9.9 wt %, 0.5 to 8.0 wt %, 0.5 to 6.0 wt %, 0.1 to 5.0 wt %, 0.1 to 3.0 wt %, 1.0 to 3.0 wt %, 2.5 to 5.0 wt %, 4.0 to 8.0 wt %, or 6.0 to 9.9 wt % relative to the weight of the entire positive electrode composite layer.

[0083] The second positive electrode active material containing the iron phosphate compound represented by Chemical Formula 2 may be contained in an individual positive electrode composite layer in an amount of 0.5 to 20 wt % relative to the weight of each positive electrode composite layer, and more specifically, may be contained in an amount of 1 to 18 wt %, 1 to 15 wt %, 1 to 12 wt %, 1 to 10 wt %, 1 to 8 wt %, 1 to 5 wt %, 0.5 to 1 wt %, 0.5 to 5 wt %, 2 to 6 wt %, 0.5 to 0.9 wt %, 5 to 16 wt %, 7 to 15 wt %, or 8 to 12 wt % relative to the weight of each positive electrode composite layer.

[0084] By controlling the content of the second positive electrode active material within the above range relative to the weight of the entire positive electrode composite layer and the individual positive electrode composite layer, the present invention can prevent a situation in which a small content of the second positive electrode active material results in insufficient rigidity on the positive electrode surface, while preventing a deterioration in the electrical performance of the battery due to an increase in electrode resistance on the positive electrode surface caused by an excessive amount of the second positive electrode active material.

[0085] Furthermore, the second positive electrode active material is included in the second to mth positive electrode composite layers, and the content or content ratio of the second positive electrode active material tends to increase with position from the second positive electrode composite layer that is in contact with the first positive electrode composite layer to the mth positive electrode composite layer that is furthest from the first positive electrode composite layer. When the battery overheats or a short circuit occurs, the redox reaction of the second positive electrode active material proceeds relatively more slowly than that of the first positive electrode active material, so by increasing the concentration closer to the outermost surface of the positive electrode composite layer, there is an advantage in that the possibility of fire or explosion in the event of an internal short circuit in the battery is reduced.

[0086] Meanwhile, the positive electrode for a lithium secondary battery according to the present invention may further contain a conductive material, a binder, other additives, and the like in the positive electrode mixture layer, if necessary.

[0087] In this case, the first positive electrode active material and the second positive electrode active material contained in each positive electrode composite layer may be contained in an amount of 85 parts by weight or more, specifically 90 parts by weight or more, 93 parts by weight or more, or 95 parts by weight or more, based on the weight of each positive electrode composite layer.

[0088] The conductive material is used to improve the electrical performance of the positive electrode and may be any conductive material commonly used in the art. Specifically, the conductive material may include at least one selected from the group consisting of natural graphite, artificial graphite, carbon black, acetylene black, denka black, ketjen black, super-P, channel black, furnace black, lamp black, summer black, graphene, and carbon nanotubes.

[0089] The conductive material may be contained in an amount of 0.1 to 5 parts by weight, specifically 0.1 to 4 parts by weight, 2 to 4 parts by weight, 1.5 to 5 parts by weight, 1 to 3 parts by weight, 0.1 to 2 parts by weight, or 0.1 to 1 part by weight, based on the weight of each positive electrode composite layer.

[0090] The binder functions to bind the positive electrode active material, the positive electrode additive, and the conductive material together, and any material having this function may be used without particular limitation. Specifically, the binder may include one or more resins selected from the group consisting of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride (PVDF), polyacrylonitrile, polymethylmethacrylate, and copolymers thereof. For example, the binder may include polyvinylidene fluoride.

[0091] The binder may be contained in an amount of 1 to 10 parts by weight, specifically 2 to 8 parts by weight, or 1 to 5 parts by weight, based on the weight of each positive electrode mixture layer.

[0092] Furthermore, the total thickness of the positive electrode composite layer is not particularly limited, but may specifically be 50 μm to 300 μm, more specifically 100 μm to 200 μm, 80 μm to 150 μm, 120 μm to 170 μm, 150 μm to 300 μm, 200 μm to 300 μm, or 150 μm to 190 μm.

[0093] Furthermore, among the individual positive electrode composite layers constituting the positive electrode composite layer, the first positive electrode composite layer in contact with the positive electrode current collector may have a thickness adjusted to a certain range. Specifically, the thickness of the first positive electrode composite layer may be 10% to 60% of the total thickness of the positive electrode composite layer, more specifically, 10% to 40%, 30% to 50%, 10% to 20%, or 40% to 60% of the total thickness of the positive electrode composite layer.

[0094] By adjusting the total thickness and individual thicknesses of the positive electrode composite layers within the above ranges, the present invention can not only prevent a reduction in the energy density of the electrode, but also achieve high adhesive strength between the positive electrode current collector and the positive electrode composite layer.

[0095] Furthermore, the positive electrode current collector provided in the positive electrode may be made of a material that has high conductivity without inducing chemical changes in the battery, such as stainless steel, aluminum, nickel, titanium, or calcined carbon. In the case of aluminum or stainless steel, it may be surface-treated with carbon, nickel, titanium, silver, or the like.

[0096] The average thickness of the current collector is preferably 5 to 500 μm, taking into consideration the conductivity and total thickness of the positive electrode to be produced.

[0097] The separator is a thin insulating membrane interposed between the positive and negative electrodes, exhibiting high ion permeability and mechanical strength. The separator may be any commonly used material in the art, including sheets or nonwoven fabrics made of chemically resistant and hydrophobic materials such as polypropylene, glass fiber, or polyethylene. In some cases, composite separators may be used, in which inorganic particles or organic particles are coated on a porous polymer substrate such as a sheet or nonwoven fabric with an organic binder polymer. When a solid electrolyte such as a polymer is used as the electrolyte, the solid electrolyte may also function as the separator. The separator may have an average pore diameter of 0.01 to 10 μm and an average thickness of 5 to 300 μm.

[0098] In addition, examples of the electrolyte composition that can be used in producing a lithium secondary battery include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes, but are not limited to these.

[0099] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0100] The organic solvent may be any solvent capable of serving as a medium through which ions involved in the electrochemical reaction of the battery can move. For example, examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone, ether solvents such as dibutyl ether and tetrahydrofuran, ketone solvents such as cyclohexanone, aromatic hydrocarbon solvents such as benzene and fluorobenzene, dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of suitable solvents include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based solvents such as ethyl alcohol and isopropyl alcohol, nitriles such as R-CN (where R is a C2-C20 linear, branched, or cyclic hydrocarbon group that may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and mixtures of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can enhance the charge / discharge performance of batteries, and low-viscosity linear carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) are more preferred. In this case, the cyclic carbonate and the chain carbonate are mixed in a volume ratio of approximately 1:1 to 9 to achieve excellent electrolyte performance.

[0101] The lithium salt may be any compound capable of providing lithium ions used in lithium secondary batteries, without particular limitation. Specifically, the lithium salt may be LiPF, LiClO, LiAsF, LiBF, LiSbF, LiAlO, LiAlCl, LiCFSO, LiC4F9SO, LiN(C2F5SO3), LiN(C2F5SO2), LiN(CF3SO2), LiCl, LiI, or LiB(C2O4)2.

[0102] The lithium salt can be used at a concentration in the range of 0.1 M to 2.0 M. When the lithium salt concentration is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0103] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds such as difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additives may be contained in an amount of 0.1 wt % to 5 wt % based on the total weight of the electrolyte.

[0104] As described above, the lithium secondary battery according to the present invention stably exhibits excellent discharge capacity, output characteristics, and capacity retention rate, and is therefore useful in the fields of portable devices such as mobile phones, notebook computers, and digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs).

[0105] Furthermore, the lithium secondary battery according to the present invention is not limited in shape depending on the intended use of the battery, and may be shaped according to cases commonly used in the art. For example, the lithium secondary battery may be a battery including a cylindrical or prismatic battery case using a can, or a pouch or coin-shaped battery case.

[0106] As one example, the lithium secondary battery may be a prismatic secondary battery including a prismatic can as a battery case.

[0107] <Secondary battery module> Furthermore, in one embodiment, the present invention provides a secondary battery module including the above-described lithium secondary battery according to the present invention.

[0108] The secondary battery module according to the present invention includes the above-described lithium secondary battery of the present invention as a unit battery, and has excellent electrical performance and safety against internal short circuits, and therefore can be used as a power source for medium to large devices that require high-temperature stability, long cycle characteristics, high rate characteristics, etc.

[0109] Specific examples of such medium- to large-sized devices include power tools powered by battery-powered motors, electric vehicles including electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), electric bicycles (E-bikes), electric two-wheeled vehicles including electric scooters (E-scooters), electric golf carts, and power storage systems, and more specific examples include, but are not limited to, hybrid electric vehicles (HEVs).

[0110] The present invention will be described in more detail below with reference to examples and experimental examples.

[0111] However, the following examples and experimental examples are merely illustrative of the present invention, and the content of the present invention is not limited to the following examples and experimental examples.

[0112] <Examples 1 to 10 and Comparative Examples 1 to 4. Production of Lithium Secondary Batteries> a) Manufacturing of negative electrodes Water was poured into a homomixer, and a carbonaceous material in which natural graphite and artificial graphite were mixed in a weight ratio of 1:1 as the first negative electrode active material, and SiO as the second negative electrode active material were mixed. q (where 0.9≦q≦2.2), and styrene butadiene rubber (SBR) were then added. The mixture was then mixed at 2500 rpm for 80 minutes to prepare a first negative electrode composite layer forming slurry, a second negative electrode composite layer forming slurry, and a third negative electrode composite layer forming slurry.

[0113] The slurry prepared for forming each negative electrode composite layer contained 98.5 wt % of the negative electrode active material and 1.5 wt % of the binder based on the solid content. q ) the sphericity and (2) the content ratio (unit: parts by weight) of the first negative electrode active material and the second negative electrode active material contained in each slurry relative to 150 parts by weight of the total negative electrode active material were adjusted as shown in Table 1.

[0114] A copper sheet (average thickness: 12 μm) was prepared as a negative electrode current collector, and the previously prepared first to third negative electrode composite layer slurries were sequentially cast onto the prepared copper sheet. The copper sheet onto which the slurries were cast was dried in a vacuum oven at 130°C and then rolled to produce a negative electrode. The total thickness of the rolled negative electrode composite layers was 140 μm, and the thickness of each individual negative electrode composite layer was adjusted to be the same.

[0115] [Table 1]

[0116] b) Manufacturing of positive electrodes N-methylpyrrolidone solvent was poured into a homomixer, and LiNi was added as the first positive electrode active material. 0.8 Co 0.1 Mn 0.1 The first positive electrode active material was LiFePO4 (hereinafter referred to as "LFP"), with an average particle size of approximately 2 μm, and the second positive electrode active material was LiFePO4 (hereinafter referred to as "LFP"), with a conductive material of carbon black, and the binder of polyvinylidene fluoride (PVDF). The mixture was then mixed at 3,000 rpm for 60 minutes to prepare a first positive electrode composite layer slurry, a second positive electrode composite layer slurry, and a third positive electrode composite layer slurry.

[0117] The slurries prepared for forming each positive electrode composite layer contained 97 wt % of the positive electrode active material, 2 wt % of the conductive material, and 1 wt % of the binder based on the solid content. Additionally, (1) the average particle size (unit: μm) of the second positive electrode active material and (2) the content ratio (unit: parts by weight) of the first positive electrode active material and the second positive electrode active material contained in each slurry relative to 150 parts by weight of the total positive electrode active material were adjusted as shown in Table 1.

[0118] An aluminum thin plate (average thickness: 14 μm) was prepared as a positive electrode current collector, and the previously prepared slurries for forming the first to third positive electrode composite layers were sequentially cast onto the prepared aluminum thin plate, dried in a vacuum oven at 130°C, and rolled to prepare a positive electrode. The total thickness of the rolled positive electrode composite layers was 150 μm, and the thickness of each individual positive electrode composite layer was adjusted to be the same.

[0119] [Table 2]

[0120] c) Assembly of secondary batteries As shown in Table 3 below, electrode assemblies were fabricated by arranging the previously prepared positive and negative electrodes facing each other and placing an 18 μm polypropylene separator between them. Each electrode assembly was inserted into a prismatic battery case, and an electrolyte composition was injected into the battery case. The case was then sealed to fabricate a prismatic lithium secondary battery. The electrolyte composition used was a solution prepared by mixing lithium hexafluorophosphate (LiPF6, 1.0 M) and vinyl carbonate (VC, 2 wt %) in a 1:1:1 (volume ratio) mixture of ethylene carbonate (EC): dimethyl carbonate (DMC): diethyl carbonate (DEC).

[0121] [Table 3]

[0122] <Experimental Example> In order to evaluate the performance and safety of the lithium secondary battery according to the present invention, the following experiments were carried out.

[0123] a) Output evaluation of secondary batteries The lithium secondary batteries prepared in each of the examples and comparative examples were fully charged at 0.1 C-rate at room temperature (22°C). The fully charged lithium secondary batteries were then discharged at 0.1 C-rate to measure their initial discharge capacities. The lithium secondary batteries were then fully charged at 0.1 C-rate and discharged at 1.0 C, 2.0 C, 5.0 C, and 9.0 C-rates, respectively, to measure the relative discharge capacities based on the initial discharge capacities for each discharge rate. The results are shown in Table 4 below.

[0124] b) Evaluation of nail penetration test The lithium secondary batteries manufactured in each of the examples and comparative examples were subjected to two charge-discharge cycles at a current value of 0.5 C in a voltage range of 4.2 to 2.0 V in an environment of 25° C. After that, each lithium secondary battery was charged to 4.2 V, and then a metal object with a diameter of 3 mm was lowered at a speed of 80 mm / sec to penetrate the cell, in the same manner as the PV8450 certification conditions, and the presence or absence of ignition was evaluated. The results are shown in Table 5.

[0125] C) Evaluation of impact test The lithium secondary batteries manufactured in each of the examples and comparative examples were fully charged at room temperature (22°C) at a 0.1 C-rate. The fully charged lithium secondary batteries were then subjected to a secondary battery impact test in accordance with the UN1642DL impact certification standard. A 9 kg weight was used, and the test was conducted by dropping it onto a 16 mm diameter round bar placed on the secondary battery cell. The results are shown in Table 5 below.

[0126] [Table 4]

[0127] [Table 5]

[0128] As shown in Tables 4 and 5, it can be seen that the secondary battery according to the present invention not only has a high energy density but also has an excellent effect of improving the safety of the battery.

[0129] Specifically, the secondary battery according to the present invention maintained a discharge capacity ratio of 89% or more even during high-rate discharge at 5.0 C-rate or higher, which indicates that the lithium secondary battery manufactured in the example has excellent output.

[0130] Furthermore, it was confirmed that the secondary batteries of the examples did not ignite during nail penetration tests and impact tests, which indicates that the secondary batteries according to the present invention are highly safe.

[0131] These results show that the lithium secondary battery according to the present invention contains a ternary compound containing nickel (Ni), cobalt (Co), manganese (Mn), etc., and also contains small amounts of an iron phosphate compound and a silicon-based oxide in the outermost shell of the composite layer adjacent to the separator in the positive and negative electrodes, respectively, thereby not only providing excellent battery energy density but also relatively low electrical conductivity on the positive and negative electrode surfaces, thereby improving safety in the event of an internal short circuit in the secondary battery.

[0132] Although the present invention has been described above with reference to preferred embodiments, it will be understood by those skilled in the art or those with ordinary knowledge in the art that various modifications and changes can be made to the present invention without departing from the spirit and technical scope of the present invention as set forth in the claims below.

[0133] Therefore, the technical scope of the present invention should not be limited to the content described in the Summary of the Invention of the specification, but should be defined by the claims. [Explanation of symbols]

[0134] 1: Lithium secondary battery 10:Negative electrode 11: Negative electrode current collector 12: Multilayered negative electrode composite layer 121: Individual negative electrode composite layer 121a: First negative electrode composite layer 121n: nth negative electrode composite layer 20: Positive electrode 21: Positive electrode current collector 22: Multilayered positive electrode composite layer 221: Individual positive electrode composite layer 221a: First positive electrode composite layer 221m: mth positive electrode composite layer

Claims

1. The battery includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; the positive electrode comprises a ternary compound containing nickel, cobalt, and manganese; the negative electrode is disposed by sequentially stacking a first negative electrode composite layer to an n-th negative electrode composite layer (where n≧2) on a negative electrode current collector, the first negative electrode composite layer being stacked on a surface in contact with the negative electrode current collector; The first to n-th negative electrode composite layers are a first negative electrode active material including a carbon-based material and a second negative electrode active material including a silicon-based material; As the position of the individual negative electrode composite layer changes from the first negative electrode composite layer to the nth negative electrode composite layer, the content or the proportion of the content of the second negative electrode active material increases, the sphericity of the second negative electrode active material decreases as the position of the individual negative electrode mixture layer changes from the first negative electrode mixture layer to the nth negative electrode mixture layer, the second negative electrode active material contained in the first negative electrode composite layer has a sphericity of 0.9 to 1.0, and the second negative electrode active material contained in the second negative electrode composite layer has a sphericity of 0.7 to 0.

8.

2. 2. The lithium secondary battery according to claim 1, wherein the carbon-based material comprises at least one selected from the group consisting of soft carbon, hard carbon, natural graphite, artificial graphite, expanded graphite, non-graphitizable carbon, carbon black, acetylene black, ketjen black, carbon nanotubes, fullerene, activated carbon, graphene, and carbon fiber.

3. Silicon-based materials include silicon (Si), silicon carbide (SiC), and silicon oxide (SiO ｑ 2. The lithium secondary battery according to claim 1, wherein q is selected from the group consisting of 0.8≦q≦2.

5.

4. The lithium secondary battery according to claim 1 , wherein the second negative electrode active material is contained in an amount of 1% by weight to 20% by weight based on the total weight of the negative electrode active material.

5. 2. The lithium secondary battery according to claim 1, wherein the second negative electrode active material has a sphericity of 0.5 to 1.

0.

6. 2. The lithium secondary battery according to claim 1, wherein the total thickness of the negative electrode mixture layer is 50 μm to 300 μm.

7. 2. The lithium secondary battery according to claim 1, wherein the thickness of the first negative electrode mixture layer is 10% to 60% of the total thickness of the negative electrode mixture layers.

8. the positive electrode is disposed by sequentially stacking a first positive electrode composite layer to an mth positive electrode composite layer (where m≧2) on a positive electrode current collector, and the first positive electrode composite layer is stacked on a surface that is in contact with the positive electrode current collector; The first to mth positive electrode composite layers each include a first positive electrode active material including a lithium composite metal oxide represented by Chemical Formula 1, and a second positive electrode active material including an iron phosphate compound represented by the following Chemical Formula 2: [Chemical formula 1] Li ｘ [Ni ｙ Co ｚ Mn ｗ M １ ｖ ]O ２ [Chemical formula 2] LiFe ａ M ２ １－ａ XO ４ In the above Chemical Formula 1 and Chemical Formula 2, M １ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; x, y, z, w, and v are each in the ranges of 1.0≦x≦1.30, 0.1≦y<1, 0≦z≦1, 0≦w≦1, and 0≦v≦0.1, and y+z+w+v=1; M ２ is one or more elements selected from the group consisting of W, Cu, Fe, V, Cr, Co, Ni, Mn, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo; X is P, 2. The lithium secondary battery according to claim 1, wherein a is in the range of 0<a≦0.

5.

9. 9. The lithium secondary battery according to claim 8, wherein the content or the proportion of the content of the second positive electrode active material in each positive electrode mixture layer increases as the position of the individual positive electrode mixture layer changes from the 1st positive electrode mixture layer to the mth positive electrode mixture layer.

10. The lithium secondary battery according to claim 8 , wherein the second positive electrode active material is contained in an amount of less than 10 wt % based on the weight of the entire positive electrode mixture layer.

11. The lithium secondary battery according to claim 8, wherein the total thickness of the positive electrode mixture layer is 50 μm to 300 μm.

12. A secondary battery module comprising the lithium secondary battery according to any one of claims 1 to 11.

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