Positive electrode for rechargeable lithium battery and rechargeable lithium battery comprising the same

Abstract

Disclosed is a cathode for a rechargeable lithium battery and a rechargeable lithium battery including the same, and the cathode for a rechargeable lithium battery includes a first cathode active material and a second cathode active material, wherein the first cathode active material includes at least one nickel-based lithium composite oxide, and the second cathode active material is represented by Chemical Formula 2 and has an average particle diameter of about 300 nm to about 600 nm.[Chemical Formula 2]Li a1 Fe 1‑x1 M1 x1 PO4in Chemical Formula 2, 0.90≤a1≤1.8, 0≤x1≤0.7, and M1 is Mg, Co, Ni, or a combination thereof.

Description

[0001] This application is a divisional application of the invention patent application filed on February 19, 2019, with application number 201910121827.0 and invention title "Positive electrode active material for rechargeable lithium battery, positive electrode including the same and rechargeable lithium battery including the positive electrode". Technical Field

[0002] This disclosure relates to a positive electrode active material for a rechargeable lithium battery, a positive electrode including the positive electrode active material, and a rechargeable lithium battery including the positive electrode. Background Technology

[0003] Portable information devices (such as mobile phones, laptops, smartphones, etc.) or electric vehicles have been using rechargeable lithium batteries with high energy density and easy portability as their power source.

[0004] Typically, rechargeable lithium batteries are manufactured by using materials capable of reversibly inserting and de-inserting lithium ions as positive and negative active materials, and filling an electrolyte between the positive and negative electrodes, which respectively include the positive and negative active materials.

[0005] Recently, with the increasing application areas of rechargeable lithium batteries, research has been conducted on improving the performance of positive electrode active materials and positive electrodes that include such active materials in their constituent elements, in order to develop rechargeable lithium batteries with improved battery characteristics even under high temperature and high voltage conditions. Summary of the Invention

[0006] This application provides a positive electrode active material for a rechargeable lithium battery, a positive electrode including the positive electrode active material, and a rechargeable lithium battery, wherein the positive electrode active material enables a rechargeable lithium battery with improved thermal stability and improved cycle life characteristics.

[0007] The positive electrode active material for a rechargeable lithium battery according to an embodiment includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material includes at least one nickel-based lithium composite oxide, and the second positive electrode active material is represented by chemical formula 2 and has an average particle size of about 300 nm to about 600 nm.

[0008] [Chemical Formula 2]

[0009] Li a1 Fe 1-x1 M1 x1 PO4

[0010] In chemical formula 2, 0.90≤a1≤1.8, 0≤x1≤0.7, and M1 is Mg, Co, Ni or a combination thereof.

[0011] The positive electrode for a rechargeable lithium battery according to an embodiment includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector, wherein the positive electrode active material layer includes the positive electrode active material for a rechargeable lithium battery according to an embodiment.

[0012] A rechargeable lithium battery according to an embodiment includes a positive electrode, a negative electrode, and an electrolyte solution for a rechargeable lithium battery according to an embodiment.

[0013] The embodiments of this application can provide a positive electrode active material for a rechargeable lithium battery, which has excellent capacity by significantly reducing sheet resistance and excellent thermal stability by incorporating a positive electrode active material with excellent heat resistance.

[0014] Therefore, by applying a positive electrode including a positive electrode active material according to the embodiments to a rechargeable lithium battery, a rechargeable lithium battery with excellent capacity, improved cycle life characteristics, and excellent thermal stability can be achieved. Attached Figure Description

[0015] Figure 1 a to Figure 1 c is a view schematically showing the shape of the plate particles.

[0016] Figure 2 The diagram illustrates the definition of the radial shape in the secondary particles of the second nickel-based lithium composite oxide.

[0017] Figure 3 The structure of the second nickel-based lithium composite oxide is schematically illustrated.

[0018] Figure 4 This is a schematic diagram of a rechargeable lithium battery according to an embodiment.

[0019] <Marker Description>

[0020] 100: Rechargeable lithium battery

[0021] 10: Positive electrode

[0022] 20: Negative electrode

[0023] 30: Partition Detailed Implementation

[0024] The present disclosure will be described more fully below with reference to the accompanying drawings, which illustrate exemplary embodiments of the invention. The described embodiments may be modified in various ways without departing from the spirit or scope of the invention.

[0025] The accompanying drawings and description are intended to be illustrative rather than restrictive. Throughout the description, the same reference numerals denote the same elements.

[0026] For ease of description, the dimensions and thicknesses of the components in the accompanying drawings are arbitrarily expressed; therefore, the present invention is not limited by the drawings.

[0027] Furthermore, unless explicitly stated otherwise, the words “including” and variations such as “contains” or “comprising” will be understood to imply inclusion of the stated element but not exclusion of any other element.

[0028] The positive electrode active material for a rechargeable lithium battery according to embodiments of this disclosure may include a first positive electrode active material and a second positive electrode active material.

[0029] Here, the first positive electrode active material may include at least one nickel-based lithium composite oxide. Specifically, the first positive electrode active material may include at least one of a first nickel-based lithium composite oxide and a second nickel-based lithium composite oxide. Optionally, the first positive electrode active material may include at least two nickel-based lithium composite oxides with different average particle sizes.

[0030] First, the embodiments of this disclosure include a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material includes a first nickel-based lithium composite oxide.

[0031] In this embodiment of the application, the first positive electrode active material may include a first nickel-based lithium composite oxide.

[0032] The first nickel-based lithium complex oxide can, without limitation, include any compound capable of intercalating and deintercalating lithium (lithiation intercalation compound). Specifically, one or more complex oxides of metals selected from cobalt, manganese, nickel, and combinations thereof, and lithium can be used. More specific examples may include compounds represented by one of the following chemical formulas: Li a A 1-b X b D2(0.90≤a≤1.8,0≤b≤0.5); Li a A 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05); Li a E 1-b X b O 2-c D c (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05); Li a E 2-b X b O4-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 D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.5,0<α≤2);Li a Ni 1-b- c Co b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Co b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c D α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α≤2);Li a Ni 1-b-c Mr b X c O 2-α T α (0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni 1-b-c Mr b X c O 2-α T2(0.90≤a≤1.8,0≤b≤0.5,0≤c≤0.05,0<α<2);Li a Ni b HAVE BEEN c G d O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0.001≤d≤0.1);Li a Ni b Co c Mr d G e O2(0.90≤a≤1.8,0≤b≤0.9,0≤c≤0.5,0≤d≤0.5,0.001≤e≤0.1);Li a NiGb O2(0.90≤a≤1.8,0.001≤b≤0.1); Li a CoG b O2(0.90≤a≤1.8,0.001≤b≤0.1); Li a Mn 1-b G b O2(0.90≤a≤1.8,0.001≤b≤0.1); Li a Mn2G b O4(0.90≤a≤1.8,0.001≤b≤0.1); Li a Mn 1-g G g PO4(0.90≤a≤1.8,0≤g≤0.5); LiNiVO4; Li (3-f) J2(PO4)3(0≤f≤2).

[0033] In the chemical formula, A is selected from Ni, Co, Mn and their combinations; X is selected from Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements and their combinations; D is selected from O, F, S, P and their combinations; E is selected from Co, Mn and their combinations; T is selected from F, S, P and their combinations; G is selected from Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V and their combinations; and J is selected from V, Cr, Mn, Co, Ni, Cu and their combinations.

[0034] The first nickel-based lithium composite oxide may have a coating on its surface, or it may be mixed with another nickel-based lithium composite oxide that has a coating.

[0035] The coating may include a compound selected from at least one coating element: an oxide of the coating element, a hydroxide of the coating element, a hydroxy oxide of the coating element, an oxycarbonate of the coating element, and a hydroxy carbonate of the coating element. The compound used for the coating may be amorphous or crystalline. Coating elements included in the coating may include Mg, Al, Co, K, Na, Ca, Si, Ti, V, Sn, Ge, Ga, B, As, Zr, or mixtures thereof. By using these elements in the compound, the coating can be formed in a manner that does not adversely affect the properties of the positive electrode active material. For example, this method may include any coating method (e.g., spraying, dipping, etc.), but because it is well known to those skilled in the art, it is not described in more detail here.

[0036] On the other hand, the first nickel-based lithium composite oxide may include a compound represented by chemical formula 1.

[0037] [Chemical Formula 1]

[0038] Li a2 (Ni 1-x2-y-z Co x2 Me y M2 z )O2

[0039] In Chemical Formula 1, M2 is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), 0.95 ≤ a2 ≤ 1.3, x2 < (1 - x2 - y - z), y < (1 - x2 - y - z), 0 < x2 < 1, 0 ≤ y < 1, 0 ≤ z < 1, and Me is at least one of Mn and Al. As described above, in the compound of Chemical Formula 1, the nickel content is higher than the cobalt content, and the nickel content is higher than the manganese content.

[0040] In Chemical Formula 1, a2 can be in the range of 0.95 ≤ a2 ≤ 1.3, and more specifically, 1.0 ≤ a2 ≤ 1.1. In addition, x2 can be in the range of 0 < x2 ≤ 0.33, and more specifically, 0.1 ≤ x2 ≤ 0.33. In addition, y can be in the range of 0 ≤ y ≤ 0.5, and more specifically, 0.05 ≤ y ≤ 0.3, and z can be in the range of 0 ≤ z ≤ 0.05. In Chemical Formula 1, x2, y, and z can satisfy, for example, the range of 0.33 ≤ (1 - x2 - y - z) ≤ 0.95. In addition, z, x2, and y can satisfy, for example, the range of 0 ≤ z ≤ 0.05, 0 < x2 ≤ 0.33, and 0 ≤ y ≤ 0.33.

[0041] According to a modified embodiment of the embodiment of the present application, z can be zero (0) in Chemical Formula 1.

[0042] In the nickel-based lithium composite oxide including the compound represented by Chemical Formula 1, based on the total amount of transition metals (Ni, Co, Mn), the nickel content range can be from about 0.33 mol% to about 0.95 mol%, and this nickel content can be higher than the manganese content and the cobalt content. In the nickel-based lithium composite oxide, based on a total of 1 mole of transition metals, the nickel content is higher than each of the other transition metals. By using a positive electrode active material including a nickel-based lithium composite oxide having a large amount of nickel, a rechargeable lithium battery including the positive electrode can provide high lithium diffusivity, excellent conductivity, and higher capacity at the same voltage.

[0043] More specifically, the first nickel-based lithium composite oxide can include a compound represented by at least one of the following: LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.1 Al 0.05 O2 and LiNi 0.95 Co 0.025 Al 0.025 O2.

[0044] Meanwhile, based on the total positive electrode active material according to the embodiments, the amount of the first positive electrode active material according to the embodiments of this application can be from about 70 wt% to about 99 wt%, more specifically, from about 85 wt% to about 99 wt%, from about 87 wt% to about 95 wt%, or from about 90 wt% to about 98 wt%. When the amount of the first positive electrode active material meets this range, safety can be improved without compromising capacity.

[0045] The first positive electrode active material can have an average particle size of about 1 μm to about 25 μm. Specifically, the average particle size of the first positive electrode active material can be about 1 μm to about 20 μm, or about 2 μm to about 16 μm. More specifically, it can be about 8 μm to about 15 μm, or about 1 μm to about 5 μm. When the average particle size of the first positive electrode active material meets this range, the active mass density can be significantly increased by applying a positive electrode active material mixed with a second positive electrode active material to the positive electrode, thus enabling the rechargeable lithium battery to have a high capacity.

[0046] Next, the second positive electrode active material will be described.

[0047] The second positive electrode active material can be represented by chemical formula 2.

[0048] [Chemical Formula 2]

[0049] Li a1 Fe 1-x1 M1 x1 PO4

[0050] In chemical formula 2, 0.90≤a1≤1.8, 0≤x1≤0.7, and M1 is Mg, Co, Ni or a combination thereof.

[0051] The second positive electrode active material can have an average particle size of, for example, from about 300 nm to about 600 nm. When the average particle size of the second positive electrode active material meets this range, the active mass density can be significantly increased by applying a positive electrode active material mixed with the first positive electrode active material to the positive electrode, thus enabling the rechargeable lithium battery to have a high capacity. In this specification, the average particle size of the second positive electrode active material means the average diameter of the second positive electrode active material when it is spherical, or the average length of its major axis when it is elliptical or amorphous. Particle size analysis can be performed using small-angle X-ray scattering (SAXS) according to international standards.

[0052] Based on the total amount of positive electrode active material used in the rechargeable lithium battery, the amount of the second positive electrode active material can be from about 1 wt% to about 15 wt%, more specifically, from about 2 wt% to about 15 wt%, from about 2 wt% to about 12 wt%, or from about 2 wt% to about 10 wt%. When the amount of the second positive electrode active material meets this range, safety can be improved without reducing capacity.

[0053] Next, as another embodiment of this disclosure, a case is illustrated including a first positive electrode active material and a second positive electrode active material containing a second nickel-based lithium composite oxide.

[0054] The embodiments of this application are substantially the same as the positive electrode active materials according to embodiments of the present invention, except that the first positive electrode active material includes a second nickel-based lithium composite oxide, which includes secondary particles having at least a partially radially arranged structure. Therefore, detailed descriptions of substantially the same constituent elements can be omitted; however, the following description will primarily focus on the first positive electrode active material including the second nickel-based lithium composite oxide, which includes secondary particles having at least a partially radially arranged structure.

[0055] Specifically, will refer to Figures 1 to 3 The first positive electrode active material includes a second nickel-based lithium composite oxide.

[0056] Figure 1 a to Figure 1 c schematically illustrates the shape of the plate particles, and Figure 2 The diagram illustrates the definition of the radial shape in the secondary particles of a nickel-based lithium composite oxide. Figure 3 The structure of the second nickel-based lithium composite oxide is schematically shown.

[0057] According to an embodiment of this application, the first positive electrode active material may include a second nickel-based lithium composite oxide, which includes secondary particles having at least a portion of radially arranged structures.

[0058] The second nickel-based lithium composite oxide may include secondary particles, in which multiple primary particles are aggregated. The secondary particles may include an outer portion having a radially shaped arrangement and an inner portion having an irregular porous structure. In this case, the pore size of the inner portion of the secondary particle may be larger than the pore size of the outer portion.

[0059] In this disclosure, the particle size of the primary particles used for secondary particles is kept sufficiently small to improve the properties of the nickel-based lithium composite oxide. For example, it can range from about 0.01 μm to about 1 μm, specifically, from about 0.05 μm to about 1 μm. More specifically, it can range from about 0.05 μm to about 0.5 μm.

[0060] The internal pore size can be, for example, from about 150 nm to about 1 μm, more specifically, from about 150 nm to about 550 nm or from about 200 nm to about 500 nm. Furthermore, the external pore size can be, for example, less than about 150 nm, more specifically, less than or equal to about 100 nm or from about 20 nm to about 90 nm. Because the internal pore size is larger than the external pore size, it has the advantage of shortening the lithium diffusion distance in secondary particles of the same size as described above, and this is advantageous because the volume change during charging and discharging is reduced, while the pores are not exposed to the electrolyte.

[0061] In this specification, "aperture" refers to the average diameter of an aperture when it is spherical or circular, or the length of its major axis when it is elliptical. Furthermore, the term "outer" refers to the region extending from approximately 30% to approximately 50% (e.g., approximately 40%) of the total distance from the center of the nickel-based lithium oxide secondary particle to the surface, or the region within approximately 2 μm of the outermost surface of the nickel-based lithium oxide secondary particle. The term "inner" refers to the region extending from approximately 50% to approximately 70% (e.g., approximately 60%) of the total distance from the center of the nickel-based lithium oxide secondary particle to the surface, or the region other than the region within approximately 2 μm of the outermost surface of the nickel-based lithium oxide secondary particle.

[0062] The secondary particles may have openings with a size of less than about 150 nm, more specifically, from about 25 nm to about 148 nm, in the central portion of the internal part. These openings are exposed pores through which electrolyte solutions can flow in and out. According to embodiments, the openings can be formed at a depth of approximately 150 nm, more specifically, from about 0.001 nm to about 100 nm, or from about 1 nm to about 50 nm, from the surface of the nickel-based lithium composite oxide secondary particles.

[0063] Meanwhile, the nickel-based lithium composite oxide comprises plate particles, and the long axis of the plate particles is arranged radially. In this case, the lithium inflow and outflow plane (the plane perpendicular to the (001) plane) is exposed to the surface of the secondary particles.

[0064] In this specification, "plate particle" means that the thickness of a plate particle is less than its major axis length (in the planar direction). Major axis length means the longest length based on the widest surface of the plate particle.

[0065] More specifically, when t refers to the length of a plate particle along one axial direction (which is the length along the thickness direction) and a refers to the length along another axial direction (which is the length of the major axis in the planar direction), a plate particle means a structure in which the length of t is less than the length of a.

[0066] refer to Figure 1 a to Figure 1 c. Plate particles can have polygonal nanosheet shapes, such as Figure 1 The hexagon shown in figure a Figure 1 The nanodisc shape shown in b, or Figure 1 The rectangular hexahedron shape shown in Figure c. Figure 1 a to Figure 1 In c, the thickness t of the plate particle is less than its lengths a and b in the planar direction. In the planar direction, a can be longer than b, or they can be the same length. In the plate particle, the direction defining thickness t refers to the thickness direction, and the direction containing lengths a and b is defined as the planar direction.

[0067] refer to Figure 2 In this specification, the term "radial" means that the thickness (t) direction of the plate ((001) direction) is arranged at a perpendicular angle to the direction (R) toward the center of the secondary particle or at an angle of ±5° to the direction toward the center.

[0068] The second nickel-based lithium composite oxide has irregularly porous pores in its internal portion. In this specification, an irregularly porous structure means a structure with pores, wherein the pore size and shape are neither regular nor uniform.

[0069] The internal portion, which has an irregular porous structure, includes plate-like particles, similar to those in the external portion. Unlike the external portion, the plate-like particles are arranged irregularly.

[0070] Next, the average length of the plate particles in the inner and outer portions of the secondary particles ranges from about 150 nm to about 500 nm, for example, from about 200 nm to about 380 nm, specifically from about 290 nm to about 360 nm. The average length means the average length of the average major axis and the average minor axis in the planar direction of the plate particle.

[0071] The average thickness of the plate particles in the inner and outer portions of the secondary particles ranges from about 100 nm to about 200 nm, for example, from about 120 nm to about 180 nm, specifically, from about 130 nm to about 150 nm. The ratio of average thickness to average length ranges from about 1:2 to about 1:5, for example, from about 1:2 to about 1:3. When the average length, average thickness, and the ratio of average thickness to average length meet this range, and when the primary particles are radially arranged in the outer portion while having small-sized plate particles, the rechargeable lithium battery according to this disclosure can provide high initial efficiency and capacity. This is because the paths for lithium to be transported to the crystalline surface of the outer portion and for lithium diffusion between grain boundaries are relatively more exposed on the surface of the second nickel-based lithium composite oxide having this structure, thereby improving lithium diffusion.

[0072] Furthermore, when the primary particles of the plate are arranged radially, the pores exposed on the surfaces between them also face the center, thereby accelerating lithium diffusion from the surface. As lithium is inserted and extracted by the radially arranged primary particles, it can shrink and expand uniformly, and the pores exist in the 001 direction (the direction of particle expansion during lithium extraction) to provide a buffering effect. Moreover, due to the small size of the primary particles, the likelihood of cracks forming during shrinkage and expansion is reduced, and as the internal pores further mitigate volume changes, cracks occurring between primary particles during charging and discharging are reduced. Therefore, the rechargeable lithium battery using a positive electrode comprising a positive electrode active material according to this disclosure improves cycle life characteristics and reduces resistance increase.

[0073] In the second nickel-based lithium composite oxide, the inner pore size ranges from about 150 nm to about 550 nm, and the outer pore size is less than about 150 nm.

[0074] Closed pores may exist in the internal portion of the second nickel-based lithium composite oxide, and closed pores and / or open pores may exist in the external portion. Closed pores may contain almost no electrolyte, while open pores may contain electrolyte. In this specification, a closed pore may be referred to as an independent pore, wherein all walls of the pore are closed and therefore not connected to other pores; and an open pore may be referred to as a continuous pore, wherein at least a portion of the pore walls are open and therefore connected to the external portion of the particle. The secondary particle has an open pore with a size less than about 150 nm toward the central portion of the internal portion.

[0075] Meanwhile, the total porosity of the first positive electrode active material comprising the second nickel-based lithium composite oxide according to embodiments of this application ranges from about 1% to about 8%, for example, from about 1.5% to about 7.5%. In the second nickel-based lithium composite oxide, the porosity of the outer portion is less than that of the inner portion. The pores exposed on the surface face the center direction of the inner portion, and when viewed from the surface, the pore size is less than about 150 nm, for example, from about 10 nm to about 100 nm. The porosity of the inner portion ranges from about 2% to about 20%, and the closed-cell porosity of the outer portion ranges from about 0.1% to about 2%. The term "closed-cell porosity" means the percentage of closed pores (pores that can not be permeated by electrolyte solution) relative to the total volume of pores. In this specification, porosity and pore percentage have the same meaning, which refers to the ratio of pore area to the total area. The internal porosity (pore percentage) of the second nickel-based lithium composite oxide is from about 3.3% to about 16.5%, and the external porosity (pore percentage) is from about 0.3% to about 0.7%.

[0076] In the following text, reference will be made to Figure 3 The specific description includes the structure of the first positive electrode active material of the second nickel-based lithium composite oxide according to embodiments of this application.

[0077] like Figure 3 As shown, the first positive electrode active material according to an embodiment of this application includes primary particles 13 and secondary particles 10, and contains an outer portion 14 having a structure in which the primary particles 13 are radially arranged, and an inner portion 12 having an irregular arrangement of plate-like particles. The internal portion 12 contains more voids between the plate-like particles than the external portion. The pore size and porosity in the internal portion are larger and more irregular than those in the external portion. Figure 3 In the middle, arrow 100 refers to the transfer of Li. + The orientation of the ions. In this case, the original particle 13 can have a plate shape. Figure 3 Only one example of the first positive electrode active material according to an embodiment of this application is shown, but the structure of the positive electrode active material according to the invention is not limited thereto. The first positive electrode active material according to an embodiment of this application facilitates lithium diffusion by including radial plate particles and suppresses stress due to volume changes during lithium charging and discharging to prevent cracking. This also reduces the thin resistive layer and exposes more of the direction of lithium diffusion to the surface, thereby increasing the effective surface area required for lithium diffusion.

[0078] The first positive electrode active material according to an embodiment of this application may be in the form of plate particles having a long radial shape along the long axis present in the outer portion, and short, flat plate particles, particularly nanodisc-shaped particles, having a length of about 150 nm to about 200 nm present in the inner portion.

[0079] Furthermore, the first positive electrode active material according to embodiments of this application may include radially shaped plate particles and non-radially shaped plate particles as primary particles. Based on the total weight of 100 parts by weight of radially shaped and non-radially shaped plate particles, the amount of non-radially shaped plate particles is less than or equal to about 20 wt%, more specifically, about 0.01 wt% to about 10 wt%, or about 0.1 wt% to about 5 wt%. When the non-radially shaped plate particles, in addition to the radially shaped plate particles, are included within the range of the second nickel-based lithium composite oxide, lithium readily diffuses to provide a rechargeable lithium battery with improved cycle life characteristics.

[0080] The second nickel-based lithium composite oxide can be represented by chemical formula 1, similar to the first nickel-based lithium composite oxide, and more specifically, the second nickel-based composite oxide can be represented, for example, by at least one of the following: LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.1 Al 0.05 O2 and LiNi 0.95 Co 0.025 Al 0.025 O2.

[0081] In the following, according to another exemplary embodiment of the present invention, it includes a first positive electrode active material and a second active material, the first positive electrode active material comprising at least two positive electrode active materials having different average diameters.

[0082] The positive electrode active material according to the embodiments of this application is substantially the same as the positive electrode active material according to the exemplary embodiments of the present invention, except that the first positive electrode active material includes at least two positive electrode active materials with different average particle sizes. Therefore, detailed descriptions of substantially the same constituent elements are omitted, and in the following, they will be described based on the first positive electrode active material including at least two positive electrode active materials with different average particle sizes.

[0083] The first positive electrode active material according to embodiments of this application may include positive electrode active materials having at least two positive electrode active materials with different average particle sizes, that is, it may include at least one large-size positive electrode active material and at least one small-size positive electrode active material. The average particle size of the large-size positive electrode active material may be from about 7 μm to about 15 μm, more specifically, from about 10 μm to about 13 μm. The average particle size of the small-size positive electrode active material may be from about 1 μm to about 5 μm, more specifically, from about 2 μm to about 4 μm. When the first positive electrode active material includes large-size and small-size positive electrode active materials having the above-mentioned average particle sizes, the capacity of the rechargeable lithium battery including the first positive electrode active material can be further improved.

[0084] Simultaneously, the first positive electrode active material may include a mixture in which large-size positive electrode active material and small-size positive electrode active material are mixed in a weight ratio of about 9:1 to about 6:4, for example, about 9:1 to about 7:3. When the weight ratio of large-size positive electrode active material to small-size positive electrode active material in the mixture is within this range, the rechargeable lithium battery can have excellent cycle life characteristics and excellent capacity. In this specification, the average particle size of the active material means the average diameter of the active material when the active material is spherical, or the average length of the major axis, which is the average major axis when the active material is elliptical or amorphous.

[0085] In the embodiments of this application, each of the large-size positive electrode active material and the small-size positive electrode active material can be at least one of the first nickel-based lithium composite oxide and the second nickel-based lithium composite oxide described in the above embodiments.

[0086] Next, the positive electrode for a rechargeable lithium battery according to an embodiment of the present disclosure includes a current collector and a positive electrode active material layer disposed on at least one surface of the current collector. In this case, the positive electrode active material layer may include the positive electrode active material for a rechargeable lithium battery according to the above embodiments.

[0087] The positive electrode can be obtained, for example, by coating a slurry of a positive electrode active material composition onto a current collector and drying and pressing the slurry to provide a positive electrode active material layer.

[0088] The average thickness of the positive electrode active material layer can be from about 50 μm to about 70 μm, and more specifically, from about 50 μm to about 60 μm or from about 60 μm to about 70 μm. When the thickness of the positive electrode active material layer is within this range, the energy density can increase with increasing thickness, and it also has the advantage of applying the positive electrode active material layer to various batteries depending on the aspects of the device to be used.

[0089] On the other hand, based on the total weight of the positive electrode active material layer, the positive electrode active material can be included in an amount of about 90 wt% to about 98 wt%.

[0090] In this embodiment, the positive electrode active material layer may include a binder and a conductive material. Here, based on the total amount of the positive electrode active material layer, the binder and the conductive material may each be included in an amount of about 1 wt% to about 5 wt%.

[0091] Adhesives improve the adhesion between positive electrode active material particles and to the current collector. Examples of adhesives may include, but are not limited to, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acryloyl-styrene-butadiene rubber, epoxy resin, nylon, etc.

[0092] Conductive materials are included to provide electrode conductivity. Any conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials can include carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials such as metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0093] A current collector, also known as a positive current collector, can be aluminum foil, nickel foil, or a combination thereof, but is not limited to these.

[0094] According to another exemplary embodiment of this disclosure, the positive electrode for a rechargeable lithium battery may include a current collector, a positive electrode active material layer disposed on at least one surface of the current collector, and a functional layer disposed on the positive electrode active material layer. The description of the current collector and positive electrode active material layer according to embodiments of this application is the same as above and will be omitted.

[0095] The functional layer may include a compound represented by the following chemical formula 3 and a binder. Since the functional layer includes a compound represented by chemical formula 3 in the embodiments of this application, the exothermic value generated by the compound in the positive electrode active material layer can be reduced, thereby further improving the stability of the rechargeable lithium battery employing this positive electrode active material layer.

[0096] [Chemical Formula 3]

[0097] Li a3 Fe 1-x3 M3 x3 PO4

[0098] In chemical formula 3, 0.90≤a3≤1.8, 0≤x3≤0.7, and M3 is Mg, Co, Ni or a combination thereof.

[0099] According to an embodiment of this application, a positive electrode active material layer is disposed between the current collector and the functional layer. When a functional layer is pre-formed on the current collector and then the positive electrode active material is disposed on the functional layer, the resistance and output characteristics are adversely deteriorated due to the low electronic conductivity of the compound represented by Formula 3. In this case, the positive electrode active material layer can have a dense structure, and the functional layer can have a porous structure.

[0100] In this case, the average particle size of the compound represented by Formula 3 can be less than or equal to about 2 μm, more specifically, about 0.2 μm to about 1 μm. When the average particle size of the compound represented by Formula 3 meets this range, it is possible to prevent a decrease in electronic conductivity and improve the utilization rate of the compound represented by Formula 3, and it is also possible to prevent an increase in battery resistance. Therefore, this can improve the cycle life characteristics of the rechargeable lithium battery employing the positive electrode according to the embodiments of this application.

[0101] In this specification, the average particle size of the compound represented by chemical formula 3 refers to the average diameter when the compound is spherical, while when the compound is elliptical or amorphous, it refers to the average of the major diameter, that is, the average major diameter.

[0102] The adhesive can be a strong oxidizing agent, for example, it can be a positive electrode potential less than or equal to about 4.45V (relative to Li). + Any adhesive that has antioxidant properties.

[0103] Such adhesives may include, for example, styrene-butadiene rubber, acrylate compounds, imide compounds, polyvinylidene fluoride compounds, polyvinylpyrrolidone compounds, nitrile compounds, acetate compounds, cellulose compounds, cyanide compounds, etc.

[0104] Specific examples of acrylate compounds may include polyacrylic acid (PAA), polymethyl methacrylate, polyisobutyl methacrylate, polyethyl acrylate, polybutyl acrylate, poly(2-ethylhexyl acrylate), or combinations thereof.

[0105] Specific examples of imide compounds may include polyimides, polyamide-imides, or combinations thereof. Furthermore, specific examples of polyvinylidene fluoride (PVDF) compounds may include polyvinylidene fluoride-co-hexafluoropropylene, polyvinylidene fluoride-co-trichloroethylene, polyvinylidene fluoride-co-tetrafluoroethylene, polyvinylidene fluoride-co-trifluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trichloroethylene, or combinations thereof, and specific examples of polyvinylpyrrolidone (PVP) compounds may include polyvinylpyrrolidone.

[0106] In addition, specific examples of nitrile compounds may include polyacrylonitrile, acrylonitrile-styrene-butadiene copolymer or combinations thereof; specific examples of acetate compounds may include polyvinyl acetate, ethylene-co-vinyl acetate, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate or combinations thereof; specific examples of cellulose compounds may include cyanoethyl cellulose, carboxymethyl cellulose or combinations thereof; and specific examples of cyanide compounds may include cyanoethyl sucrose.

[0107] The adhesive with excellent antioxidant properties can bond well with the compound represented by chemical formula 3 and the first and second positive electrode active materials included in the positive electrode active material layer, thus it can firmly maintain the bond between the functional layer and the positive electrode active material layer.

[0108] When using adhesives, water or alcohol can be used as solvents for the functional layers. When the solvent includes water or alcohol, it has the advantage of not damaging the electrodes.

[0109] According to another embodiment, the functional layer can have a thickness of about 1 μm to about 13 μm, or about 2 μm to about 4 μm. When the thickness of the functional layer is within this range, it can have the advantage of further enhancing security.

[0110] On the other hand, the average thickness of the positive electrode active material layer can be from about 50 μm to about 70 μm, and more specifically, from about 50 μm to about 60 μm or from about 60 μm to about 70 μm. When the thickness of the positive electrode active material layer is within this range, the energy density can be increased by increasing the thickness, and it also has the advantage of being able to apply various batteries depending on the aspect of the device to be used.

[0111] Furthermore, the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer can range from about 30:1 to about 10:1. When the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer is within this range, a coating that improves safety and minimizes energy density degradation can be provided. In particular, when the thicknesses of the functional layer and the positive electrode active material layer are within this range, and when the ratio of the thickness of the positive electrode active material layer to the thickness of the functional layer is within this range, it has the advantage of enhancing safety by providing a functional layer of appropriate thickness according to the thickness of the positive electrode active material layer.

[0112] The thickness of the positive electrode active material layer can be the thickness after the pressing process during the manufacturing of the positive electrode.

[0113] Next, the mixing ratio of the compound represented by Chemical Formula 3 to the adhesive can be, for example, a weight ratio of about 24:1 to about 50:1, or a weight ratio of about 43:1 to about 50:1. When the mixing ratio of the compound represented by Chemical Formula 3 to the adhesive is within this range, it can have the advantage of providing an appropriate proportion of energy density, adhesion, dispersibility, etc.

[0114] The functional layer may further include a thickener. Such a thickener may include, for example, at least one selected from carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or an alkali metal salt thereof. The alkali metal may be Na, K, or Li. When the functional layer further includes a thickener, the amount of thickener may be from about 0.6 parts by weight to about 2 parts by weight based on 100 parts by weight of the compound of Formula 3. When the amount of thickener is within this range, the increase in resistance can be minimized, and the thickening and dispersing properties can also be improved.

[0115] As described above, the functional layer comprises a compound represented by chemical formula 3 and a binder, selectively including a thickener, but excluding conductive materials. When the functional layer includes conductive materials, this is disadvantageous because safety deteriorates, for example, short circuits may occur.

[0116] In addition to the compound represented by chemical formula 3, the functional layer may further include polymer particles.

[0117] The polymer particles may include, for example, polyethylene wax, acrylic particles, or combinations thereof, with a glass transition temperature (Tg) less than or equal to about 100°C, such as about 50°C. Based on the total amount of the functional layer, the amount of polymer particles can range from about 20 wt% to about 70 wt%, specifically, from about 20 wt% to about 60 wt%, and more specifically, from about 30 wt% to about 50 wt%. When the amount of polymer particles meets this range, the shut-off function of the rechargeable lithium battery can be further enhanced without degrading battery performance.

[0118] The weight-average molecular weight of the polymer particles can be from about 300 to about 10,000.

[0119] In addition, the average particle size of the polymer particles can be from about 100 nm to about 5 μm.

[0120] The weight-average molecular weight of the polymer particles can be from about 300 to about 10,000, specifically from about 2,000 to about 6,000. Furthermore, the particle size of the polymer particles can be from about 100 nm to about 5 μm, specifically from about 200 nm to about 3 μm.

[0121] When the weight-average molecular weight and average particle size of the polymer particles meet this range, pores in the internal portion of the second positive electrode active material prevent lithium-ion transfer from being blocked, thereby minimizing resistance. Therefore, although a nickel-based lithium composite oxide is used as the first positive electrode active material, the stability of the rechargeable lithium battery using the positive electrode active material according to the embodiments of this application can be significantly improved.

[0122] As described above, when the functional layer further includes polymer particles having this characteristic, the shut-off function of the rechargeable lithium battery using the positive electrode according to the embodiments of this application can be further enhanced, thereby suppressing the heating of the rechargeable lithium battery as early as possible and further improving thermal stability.

[0123] A rechargeable lithium battery according to embodiments of the present disclosure may include a positive electrode, a negative electrode, and an electrolyte solution.

[0124] Figure 4 This is a schematic diagram of a rechargeable lithium battery according to an embodiment.

[0125] refer to Figure 4 According to an embodiment, the rechargeable lithium battery 100' includes an electrode assembly 40 manufactured by winding a separator 30 inserted between a positive electrode 10' and a negative electrode 20, and a housing 50 housing the electrode assembly 40. An electrolyte solution (not shown) may be impregnated in the positive electrode 10', the negative electrode 20, and the separator 30.

[0126] In this embodiment, the positive electrode for a rechargeable lithium battery according to the embodiment can be used as the positive electrode. In this embodiment, the description of the positive electrode is the same as above, and therefore will be omitted.

[0127] Next, the negative electrode 20 includes a negative electrode 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.

[0128] Negative electrode active materials may include materials that can reversibly insert / deintercalate lithium ions, lithium metal, lithium metal alloys, materials that can be doped / dedoped with lithium, or transition metal oxides.

[0129] Materials that can reversibly insert / deintercalate lithium ions include carbon materials. Carbon materials can be any carbon-based anode active material commonly used in rechargeable lithium batteries. Examples of carbon-based anode active materials can include crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon can be shapeless, or in the form of flakes, sheets, spheres, or fibers—natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbonization products, coke, etc.

[0130] The lithium metal alloy includes 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.

[0131] The material capable of doping / dedoping lithium can be a silicon-based material, for example, Si, SiO x (0 < x < 2), Si-Q alloy (where Q is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Si), Si-carbon composite, Sn, SnO2, Sn-R alloy (where R is an element selected from alkali metals, alkaline earth metals, Group 13 elements, Group 14 elements, Group 15 elements, Group 16 elements, transition metals, rare earth elements, and combinations thereof, but not Sn), Sn-carbon composite, etc. At least one of these materials can be mixed with SiO2. The elements Q and R can be selected from 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, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof.

[0132] The transition metal oxide includes lithium titanium oxide.

[0133] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, it can include a negative electrode active material in an amount of about 95 wt% to about 99 wt%.

[0134] The negative electrode active material layer includes a negative electrode active material and a binder, and optionally includes a conductive material.

[0135] In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the negative electrode active material can be about 95 wt% to about 99 wt%. In the negative electrode active material layer, based on the total weight of the negative electrode active material layer, the content of the binder can be about 1 wt% to about 5 wt%. When the negative electrode active material layer includes a conductive material, the negative electrode active material layer includes about 90 wt% to about 98 wt% of the negative electrode active material, about 1 wt% to about 5 wt% of the binder, and about 1 wt% to about 5 wt% of the conductive material.

[0136] The binder improves the adhesion properties between the negative electrode active material particles and with the current collector. The binder includes a water-insoluble binder, a water-soluble binder, or a combination thereof.

[0137] The non-water-soluble adhesive may be selected from polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyimide, or combinations thereof.

[0138] Water-soluble adhesives may be styrene-butadiene rubber, acrylamide styrene-butadiene rubber, polyvinyl alcohol, sodium polyacrylate, copolymers of propylene and C2 to C8 olefins, copolymers of (meth)acrylic acid and (meth)acrylate alkyl esters, or combinations thereof.

[0139] When a water-soluble binder is used as the negative electrode binder, a cellulose compound can be further used as a thickener to provide viscosity. Cellulose compounds include one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, or their alkali metal salts. The alkali metal can be Na, K, or Li. Based on 100 parts by weight of the negative electrode active material, the thickener content can be from about 0.1 parts by weight to about 3 parts by weight.

[0140] Conductive materials are included to provide electrode conductivity. Any conductive material can be used as a conductive material unless it causes a chemical change. Examples of conductive materials include carbon-based materials such as natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, Tenca black, carbon fibers, etc.; metal-based materials such as metal powders or metal fibers, including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives; or mixtures thereof.

[0141] The negative current collector may include one selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with conductive metal, and combinations thereof.

[0142] On the other hand, such as Figure 4 As shown, the electrode assembly can have a structure obtained by inserting a separator 30 between the strip-shaped positive electrode 10 and the negative electrode 20, spirally winding them together and flattening them. Furthermore, although not shown, multiple quadrilateral sheet-shaped positive and negative electrodes can be stacked alternately, with multiple separators between them.

[0143] Electrolyte solution can be impregnated in the positive electrode 10, the negative electrode 20 and the separator 30.

[0144] The separator 30 can be any separator commonly used in lithium batteries, separating the positive electrode 10 and the negative electrode 20 and providing a transport channel for lithium ions. In other words, it can have low ion transport resistance and excellent impregnation with the electrolyte solution. The separator 30 can be, for example, selected from glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or combinations thereof. It can be in the form of nonwoven or woven fabric. For example, in rechargeable lithium batteries, polyolefin polymer separators, such as polyethylene and polypropylene, are mainly used. To ensure heat resistance or mechanical strength, coated separators including ceramic components or polymer materials can be used. Optionally, it can have a single-layer or multi-layer structure.

[0145] Electrolyte solutions include non-aqueous organic solvents and lithium salts.

[0146] Non-aqueous organic solvents are used as media for transporting ions that participate in the electrochemical reactions of rechargeable lithium batteries.

[0147] Non-aqueous organic solvents can include carbonates, esters, ethers, ketones, alcohols, or aprotic solvents. Carbonate solvents can 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), butyl carbonate (BC), etc. Ester solvents can include methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, mevalonate lactone, caprolactone, etc. Ether solvents can include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, etc., and ketone solvents can include cyclohexanone, etc. Alcohol solvents can include ethanol, isopropanol, etc., and aprotic solvents can include nitriles, such as R-CN (R is a C2 to C20 linear, branched or cyclic hydrocarbon group, double bond, aromatic ring or ether bond), amides, such as dimethylformamide, dioxolane, such as 1,3-dioxolane, sulfolane, etc.

[0148] Non-aqueous organic solvents can be used alone or in mixtures. When organic solvents are used in mixtures, the mixing ratio can be controlled according to the desired battery performance.

[0149] Carbonate solvents can include mixtures of cyclic carbonates and linear (straight-chain) carbonates. When cyclic carbonates and linear carbonates are mixed together in a volume ratio of about 1:1 to about 1:9, electrolyte performance can be improved.

[0150] In addition to carbonate solvents, the non-aqueous organic solvents disclosed herein may further include aromatic organic solvents. Here, carbonate solvents and aromatic organic solvents may be mixed in a volume ratio of about 1:1 to about 30:1.

[0151] Aromatic organic solvents can be aromatic compounds of chemical formula 4.

[0152] [Chemical Formula 4]

[0153]

[0154] In chemical formula 4, R1 to R6 may be the same or different, and are selected from hydrogen, halogens, C1 to C6. 10 Alkyl groups, haloalkyl groups, and combinations thereof.

[0155] Specific examples of aromatic organic solvents may be selected from benzene, fluorobenzene, 1,2-difluorobenzene, 1,3-difluorobenzene, 1,4-difluorobenzene, 1,2,3-trifluorobenzene, 1,2,4-trifluorobenzene, chlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene, 1,2,3-trichlorobenzene, 1,2,4-trichlorobenzene, iodobenzene, 1,2-diiodobenzene, 1,3-diiodobenzene, 1,4-diiodobenzene, 1,2,3-triiodobenzene, 1,2,4-triiodobenzene, toluene, and fluoromethylbenzene. Benzene, 2,3-difluorotoluene, 2,4-difluorotoluene, 2,5-difluorotoluene, 2,3,4-trifluorotoluene, 2,3,5-trifluorotoluene, chlorotoluene, 2,3-dichlorotoluene, 2,4-dichlorotoluene, 2,5-dichlorotoluene, 2,3,4-trichlorotoluene, 2,3,5-trichlorotoluene, iodotoluene, 2,3-diiodotoluene, 2,4-diiodotoluene, 2,5-diiodotoluene, 2,3,4-triiodotoluene, 2,3,5-triiodotoluene, xylene and combinations thereof.

[0156] The non-aqueous electrolyte may further include ethylene carbonate or ethylene carbonate compounds of formula 5 in order to improve the cycle life of the battery.

[0157] [Chemical Formula 5]

[0158]

[0159] In Formula 5, R7 and R8 may be the same or different and are selected from hydrogen, halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, provided that at least one of R7 and R8 is selected from halogen, cyano (CN), nitro (NO2) and fluorinated C1 to C5 alkyl, and R7 and R8 are not both hydrogen.

[0160] Examples of ethylene carbonate compounds may include difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, cyanoethylene carbonate, or fluoroethylene carbonate. The amount of additives used to improve cycle life can be used within appropriate limits.

[0161] Lithium salts, dissolved in organic solvents, supply lithium ions to the battery, enabling the basic operation of rechargeable lithium batteries and improving lithium ion transport between the positive and negative electrodes. Examples of lithium salts include at least one supporting salt selected from the following: LiPF6, LiBF4, LiSbF6, LiAsF6, LiN(SO2C2F5)2, Li(CF3SO2)2N, LiN(SO3C2F5)2, LiC4F9SO3, LiClO4, LiAlO2, LiAlCl4, LiN(C x F 2x+1 SO2)(C y F 2y+1 SO2 (where x and y are natural numbers, for example, integers from 1 to 20), LiCl, LiI, and LiB(C2O4)2 (lithium dioxolane borate; LiBOB). The concentration range of lithium salts used can be from about 0.1 M to about 2.0 M. When the lithium salt content is within the above concentration range, the electrolyte can exhibit excellent performance and lithium-ion mobility due to optimal electrolyte conductivity and viscosity.

[0162] The separator 30 disposed between the positive electrode 10 and the negative electrode 20 can be a polymer membrane. The separator can include, for example, polyethylene, polypropylene, polyvinylidene fluoride, and multiple layers thereof, such as a polyethylene / polypropylene double-layer separator, a polyethylene / polypropylene / polypropylene triple-layer separator, and a polypropylene / polypropylene / polypropylene triple-layer separator.

[0163] Furthermore, the rechargeable lithium battery according to the embodiments can be included in the device. Such a device can be, for example, a mobile phone, tablet computer, laptop computer, power tool, wearable electronic device, electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, and energy storage device. In this way, devices using rechargeable lithium batteries are well known in the relevant art, and therefore will not be specifically shown in this specification.

[0164] The present disclosure will be specifically examined through examples below.

[0165] Example 1

[0166] (1) Manufacturing of the positive electrode

[0167] A mixture of 97.4 wt% of a mixture (in which a first positive electrode active material and a second positive electrode active material of a LiFePO4 composition with an average particle size of 500 nm are mixed at a weight ratio of 9:1), 1.3 wt% of Denca Black, and 1.3 wt% of polyvinylidene fluoride are mixed in an N-methylpyrrolidone solvent to provide a positive electrode active material slurry.

[0168] In this case, the first positive electrode active material is LiNi with an average particle size of 12 μm. 0.6 Co 0.2 Mn 0.2 The large-size positive electrode active material of the O2 composition and LiNi with an average particle size of 3μm 0.6 Co 0.2 Mn 0.2 The O2 composition is a mixture of small-sized positive electrode active materials mixed in a weight ratio of 7:3.

[0169] Next, the positive electrode active material slurry is coated onto an aluminum foil current collector and dried. Subsequently, the dried product is pressed to provide a positive electrode active material layer with a thickness of 60 μm (based on its cross-section excluding the current collector) to provide the positive electrode.

[0170] (2) Manufacturing of negative electrode and rechargeable lithium battery

[0171] 98 wt% graphite, 0.8 wt% carboxymethyl cellulose, and 1.2 wt% styrene-butadiene rubber were mixed in pure water to provide a negative electrode active material slurry. The negative electrode active material slurry was coated onto Cu foil and dried and pressed to provide a negative electrode.

[0172] A rechargeable lithium battery is manufactured using a positive electrode, a negative electrode, and an electrolyte, following commonly used methods. The electrolyte is prepared by dissolving 1.0 M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate (volume ratio 50:50).

[0173] Example 2

[0174] 96 wt% of LiFePO4 with an average particle size of 400 nm, 2 wt% of carboxymethyl cellulose thickener and 2 wt% of acrylic compound binder are mixed in an aqueous solvent to provide a slurry for the functional layer.

[0175] The functional layer slurry was coated onto the positive electrode active material layer obtained in Example 1 and dried to provide a functional layer with a thickness of 3.5 μm. Thus, a positive electrode having a structure in which the current collector, the positive electrode active material layer, and the functional layer are sequentially stacked was obtained.

[0176] Next, the negative electrode and rechargeable lithium battery cell are manufactured according to the same steps as in Example 1.

[0177] Example 3

[0178] The positive electrode was obtained according to the same steps as in Example 2, except that the functional layer slurry was prepared by mixing 48 wt% of LiFePO4 with an average particle size of 400 nm, 2 wt% of carboxymethyl cellulose thickener, 48 wt% of PE wax (Mitsui chemical, W401: weight average molecular weight 1000-5000) with a particle size of 1 μm and 2 wt% of acrylate compound binder in an aqueous solvent.

[0179] Comparative Example 1

[0180] 97.4 wt% of positive electrode active material, 1.3 wt% of Denca Black and 1.3 wt% of polyvinylidene fluoride were mixed in N-methylpyrrolidone solvent to provide a positive electrode active material slurry.

[0181] In this case, LiNi with an average particle size of 12 μm was mixed at a weight ratio of 7:3. 0.6 Co 0.2 Mn 0.2 The large-size positive electrode active material of the O2 composition and LiNi with an average particle size of 3μm 0.6 Co 0.2 Mn 0.2 Small-sized positive electrode active materials containing O2 are used to prepare positive electrode active materials.

[0182] Next, the positive electrode active material slurry is coated onto an aluminum foil current collector and dried. Subsequently, the dried product is pressed to provide a positive electrode active material layer with a thickness of 60 μm (based on its cross-section excluding the current collector) to provide the positive electrode.

[0183] Then, the negative electrode and rechargeable lithium battery cell are manufactured according to the same steps as in Example 1.

[0184] Comparative Example 2

[0185] The positive electrode, negative electrode, and rechargeable lithium battery cell were manufactured according to the same steps as in Example 1, except that a second positive electrode active material with an average particle size of 1 μm was used during the preparation of the positive electrode active material slurry.

[0186] Comparative Example 3

[0187] The positive electrode, negative electrode, and rechargeable lithium battery cell are manufactured according to the same steps as in Example 1, except that a second positive electrode active material with an average particle size of 1 μm is used, and the first positive electrode active material and the second positive electrode active material are mixed at a weight ratio of 89:11 to provide a positive electrode active material slurry.

[0188] Experimental Example 1: Evaluation of Specific Capacity

[0189] The rechargeable lithium battery cells obtained from Examples 1 and Comparative Examples 1 to 3 were cycled at a current of 0.2C at room temperature (25°C) to measure their specific capacity, and the results are shown in Table 1.

[0190] In this case, the upper limit voltage for charging at room temperature (25°C) is 2V, and the discharge cutoff voltage is 4.3V.

[0191] Referring to Table 1, the rechargeable lithium battery cell based on Comparative Example 1, which does not include the second positive electrode active material, shows a specific capacity of 184 mAh / g, confirming that the rechargeable lithium battery cell according to Example 1 rarely shows capacity degradation.

[0192] However, it was confirmed that the rechargeable lithium battery cells according to Comparative Examples 2 to 3 exhibited a capacity degradation of at least 3% or greater.

[0193] Experimental Example 2: Measurement of Thermal Stability

[0194] To verify thermal stability, a differential scanning calorimeter (DSC) evaluation was performed. The DSC evaluation was conducted using a Q2000 instrument manufactured by TA Instruments by monitoring changes in calorie content.

[0195] The rechargeable lithium-ion battery cells obtained from Examples 1 to 2 and Comparative Example 1 were charged at 0.1C to 100% until 4.3V, and then the battery cells were disassembled to separate the positive electrode. The separated electrode was washed with DMC (dimethyl carbonate) and then dried for 10 hours or longer. The positive electrode active material was then peeled off from the current collector, and an electrolyte solution was added to the peeled active material (mass ratio of positive electrode active material to electrolyte solution = 1:2) for DSC evaluation. The measurement scan rate was 5°C / min.

[0196] Table 1

[0197]

[0198] Referring to Table 1, it is confirmed that the rechargeable lithium battery cells according to Examples 1 and 2, which include a second cathode material having an average particle size within the range in the cathode active material layer, all exhibit excellent capacity and stability.

[0199] On the other hand, it was confirmed that the rechargeable lithium battery cell according to Comparative Example 1, which does not include a second positive electrode active material in the positive electrode active material layer, exhibited significantly worse stability.

[0200] Furthermore, it was confirmed that the capacity of the rechargeable lithium battery cells according to Comparative Examples 2 and 3, which included a second positive electrode active material with an average particle size outside the scope of the embodiments according to this application, was significantly worse.

[0201] As a result, summarizing the results of Experimental Example 1 and Experimental Example 2, it was understood that when the active material layer includes a second positive electrode active material that satisfies the conditions of the embodiments according to this application, the rechargeable lithium battery can have excellent stability and also excellent capacity.

[0202] Experimental Example 3: Accelerated Calorimetry (ARC) Analysis

[0203] The rechargeable lithium battery cells obtained from Examples 1 to 3 and Comparative Example 1 were subjected to accelerated calorimetry (ARC) analysis according to the following method, and the results are shown in Table 2.

[0204] Thermal stability was evaluated under the following ARC evaluation conditions: the rechargeable lithium battery cell was charged at 0.5C at 25°C, and the charging was paused for 12 hours. The temperature was then increased at a rate of 5°C / min until 400°C, and the battery temperature change was measured.

[0205] Table 2

[0206]

[0207] Referring to Table 2, it is confirmed that Examples 1 to 3 exhibit both higher exothermic initiation temperatures and higher thermal runaway initiation temperatures than Comparative Example 1.

[0208] Therefore, due to the high exothermic initiation temperature in Examples 1 to 3, the rechargeable lithium battery cells according to Examples 1 to 3 demonstrate superior safety compared to Comparative Example 1. Furthermore, since Examples 1 to 3 also exhibited high thermal runaway initiation temperatures, it confirms that the exothermic reaction occurs smoothly, sufficient to provide a rechargeable lithium battery with excellent stability.

[0209] Experimental Example 4 - Room Temperature Cyclic Life Characteristics

[0210] The rechargeable lithium-ion battery cells according to Examples 1 to 2 and Comparative Example 1 were subjected to 100 charge-discharge cycles under the following conditions: The rechargeable lithium-ion battery cells were charged at room temperature (25°C) with a constant current-constant voltage and cutoff conditions of 0.5C, 4.3V, and 0.05C; then allowed to stand for 10 minutes; and then discharged at a constant current of 0.5C and a cutoff condition of 2.8V; after a 10-minute standoff, the discharge capacity was measured. The capacity retention rate of the 100th cycle relative to the discharge capacity at the first cycle was obtained, and the results are shown in Table 3.

[0211] Table 3

[0212]

[0213]

[0214] Experimental Example 5 - High Temperature Cyclic Life Characteristics

[0215] The rechargeable lithium-ion battery cells obtained from Examples 1 to 2 and Comparative Example 1 were subjected to 100 charge-discharge cycles under the following conditions: The rechargeable lithium-ion battery cells were charged at a high temperature (45°C) with a constant current-constant voltage at cutoff conditions of 0.75C, 4.3V, and 0.05C, then allowed to rest for 10 minutes, and then discharged at a constant current of 0.5C and a cutoff condition of 2.8V, followed by a 10-minute rest period, during which the discharge capacity was measured. The capacity retention rate of the 100th cycle relative to the discharge capacity at the first cycle was obtained, and the results are shown in Table 4.

[0216] Table 4

[0217] 100 cycles (%) Example 1 (10% blend) 99.1 Example 2 (10% blend + LFP coating) 99.7 Comparative Example 1 (NCM622 alone) 95.4

[0218] Experimental Example 6 - Safety Evaluation

[0219] Ten rechargeable lithium battery cells were manufactured according to Examples 1 to 3 and Comparative Example 1, and a penetration test was performed.

[0220] The penetration test was performed as follows: the rechargeable lithium battery cell was charged at 0.5C for 3 hours until it reached 4.25V, and then after 10 minutes, a 3mm diameter needle was used to penetrate the center of the battery cell at a speed of 80mm / s. The results are shown in Table 5.

[0221] Table 5

[0222] Unignited smoke ignite Example 1 10 - - Example 2 10 - - Example 3 10 Comparative Example 1 - - 10

[0223] Referring to Table 5, none of the 10 rechargeable lithium battery cells obtained from Examples 1 to 3 caught fire during the penetration test, but all 10 rechargeable lithium battery cells obtained from Comparative Example 1 caught fire and exploded.

[0224] Therefore, it has been confirmed that the rechargeable lithium battery cell employing the positive electrode active material according to the embodiments of this application exhibits excellent safety.

[0225] While this disclosure has been described in conjunction with what are now considered to be practical exemplary embodiments, it will be understood that this disclosure is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Therefore, the foregoing embodiments should be understood as exemplary and not as limiting the invention in any way.

Claims

1. A positive electrode for a rechargeable lithium battery, comprising: a current collector; and a positive electrode active material layer provided on at least one surface of the current collector; and a functional layer provided on the positive electrode active material layer, wherein the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is composed of at least one nickel-based lithium composite oxide, the second positive electrode active material is represented by Chemical Formula 2, and has an average particle size of 300 nm to 600 nm, and the functional layer comprises a compound represented by the following Chemical Formula 3 and a binder: [Chemical Formula 2] Li a1 Fe 1-x1 M1 x1 PO4 where 0.90 ≤ a1 ≤ 1.8, 0 ≤ x1 ≤ 0.7, and M1 is Mg, Co, Ni, or a combination thereof, [Chemical Formula 3] Li a3 Fe 1-x3 M3 x3 PO4 where 0.90 ≤ a3 ≤ 1.8, 0 ≤ x3 ≤ 0.7, and M3 is Mg, Co, Ni, or a combination thereof.

2. The positive electrode according to claim 1, wherein the nickel-based lithium composite oxide comprises a compound represented by Chemical Formula 1: [Chemical Formula 1] Li a2 (Ni 1-x2-y-z Co x2 Along with y M2 z )O2 where M2 is an element selected from boron (B), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), titanium (Ti), vanadium (V), chromium (Cr), iron (Fe), copper (Cu), and zirconium (Zr), 0.95 ≤ a2 ≤ 1.3, x2 < (1 - x2 - y - z), y < (1 - x2 - y - z), 0 < x2 < 1, 0 ≤ y < 1, 0 ≤ z < 1, and Me is at least one of Mn and Al.

3. The positive electrode of claim 1, wherein the nickel-based lithium composite oxide is represented by at least one of the following: LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.1 Al 0.05 O2 and LiNi 0.95 Co 0.025 Al 0.025 O2.

4. The positive electrode according to claim 1, wherein the first positive electrode active material comprises at least two nickel-based lithium composite oxides having different average particle sizes.

5. The positive electrode according to claim 1, wherein based on the total amount of the positive electrode active material for the rechargeable lithium battery, the amount of the second positive electrode active material is 1 wt% to 15 wt%.

6. The positive electrode according to claim 1, wherein the average particle size range of the compound represented by Chemical Formula 3 is 0.2 μm to 1 μm.

7. The positive electrode according to claim 1, wherein the binder comprises at least one of the following: styrene-butadiene rubber, acrylate compounds, imide compounds, polyvinylidene fluoride compounds, polyvinylpyrrolidone compounds, nitrile compounds, acetate compounds, cellulose compounds, and cyanide compounds.

8. The positive electrode according to claim 1, wherein the thickness ratio of the positive electrode active material layer to the functional layer ranges from 30:1 to 10:

1.

9. The positive electrode according to claim 1, wherein the functional layer further comprises polymer particles, and based on the total amount of the functional layer, the amount of the polymer particles ranges from 20 wt% to 70 wt%.

10. The positive electrode according to claim 9, wherein the polymer particles are at least one selected from the following: polyethylene wax having a glass transition temperature Tg less than or equal to 100 °C, acrylic particles, and combinations thereof.

11. A rechargeable lithium battery, comprising: the positive electrode for a rechargeable lithium battery according to any one of claims 1 - 10; a negative electrode; and Electrolyte solution.

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