Positive electrode for rechargeable lithium battery and rechargeable lithium battery including same

Abstract

Disclosed are a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the same. A positive electrode for a rechargeable lithium battery includes a positive electrode current collector, a first positive electrode active material layer on the positive electrode current collector and including a first positive electrode active material including a lithium iron phosphate-based compound, and a second positive electrode active material layer on the positive electrode current collector and including a second positive electrode active material including a lithium iron phosphate-based compound. The second positive electrode active material layer is on the first positive electrode active material layer and includes a second positive electrode active material including a lithium nickel-based composite oxide and a third positive electrode active material including a lithium manganese-based oxide.

Description

Technical Field

[0001] A positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the positive electrode are disclosed. Background Technology

[0002] Portable and high-energy-density rechargeable lithium batteries are widely used as power sources for mobile information terminals, such as smartphones and laptops. It is advantageous to have rechargeable lithium batteries with high safety and high capacity for use as power sources in hybrid and electric vehicles or for storing electricity.

[0003] Furthermore, because rechargeable lithium batteries typically require fast charging and high safety, low-cost lithium iron phosphate compounds can be used as the positive electrode active material. However, lithium iron phosphate compounds have limitations in exhibiting high energy density and high capacity.

[0004] Attempts have been made to form electrode plates by mixing lithium nickel composite oxides and lithium iron phosphate compounds to achieve high energy density, high stability, and high capacity, while also improving price competitiveness. However, when manufacturing electrode plates by mixing lithium nickel composite oxides and lithium iron phosphate compounds, voltage separation may occur, which reduces capacity and degrades the cycle life characteristics of the battery due to the degradation of the positive electrode active material. Summary of the Invention

[0005] Some example embodiments include a positive electrode for a rechargeable lithium battery and a rechargeable lithium battery including the positive electrode, wherein the positive electrode for the rechargeable lithium battery improves rate performance and cycle life characteristics by mixing three types of positive electrode active materials and employing a bilayer structure without separating the operating voltage.

[0006] In some example embodiments, the positive electrode for a rechargeable lithium battery includes a positive electrode current collector, a first positive electrode active material layer, and a second positive electrode active material layer. The first positive electrode active material layer is on the positive electrode current collector and includes a first positive electrode active material comprising a lithium iron phosphate compound. The second positive electrode active material layer is on the first positive electrode active material layer and includes a second positive electrode active material comprising a lithium nickel composite oxide and a third positive electrode active material comprising a lithium manganese oxide.

[0007] In some example embodiments, the rechargeable lithium battery includes the aforementioned positive electrode, negative electrode, and electrolyte.

[0008] The positive electrode for a rechargeable lithium battery according to some example embodiments includes a structurally stable, low-cost lithium iron phosphate positive electrode active material, a lithium nickel positive electrode active material with high capacity and energy density, and a low-cost lithium manganese positive electrode active material that exhibits capacity at a voltage of about 4V. The positive electrode employs a double-layer structure so that the operating voltage does not separate and can improve rate performance and cycle life characteristics. Attached Figure Description

[0009] Figures 1 to 4 This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments.

[0010] Figure 5 The graph shows the voltage distribution of the rechargeable lithium battery cell of Comparative Example 4 and Comparative Example 5 during the first charge and discharge, based on capacity.

[0011] Figure 6 This is a schematic diagram illustrating the positive electrode according to some example embodiments. Detailed Implementation

[0012] Hereinafter, exemplary embodiments are described in detail to enable those skilled in the art to readily implement them. However, this disclosure may be implemented in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0013] The terminology used herein is for describing exemplary embodiments only and is not intended to limit this disclosure. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0014] As used here, “combination of” refers to mixtures, laminates, complexes, copolymers, alloys, blends, reaction products, etc. of the components.

[0015] Here it should be understood that terms such as “comprising,” “including,” or “having” are intended to indicate the presence of the features, quantities, steps, elements, or combinations thereof embodied, but do not preclude the possibility of the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0016] In the accompanying drawings, for clarity, the thickness of layers, films, plates, regions, etc., may be exaggerated, and the same reference numerals indicate the same elements throughout the specification. It is understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element may be "directly on" said other element, or there may be an intervening element between them. Conversely, when an element is referred to as being "directly on" another element, there is no intervening element.

[0017] In addition, the term "layer" here includes not only shapes that form across the entire surface when viewed from a plan view, but also shapes that form on a portion of the surface.

[0018] The average particle size can be measured by methods known to those skilled in the art (e.g., by a particle size analyzer, or by transmission electron microscopy or scanning electron microscopy). Optionally, the average particle size value can be obtained by measuring using dynamic light scattering, performing data analysis, counting the number of particles in each particle size range, and thereby calculating. Unless otherwise defined, the average particle size (D) 50 The average particle size (D) can represent the diameter of particles that constitute 50% of the total volume in the particle size distribution. As used herein, unless otherwise defined, the average particle size (D) is... 50 () represents the diameter of particles that constitute 50% of the total volume in a particle size distribution obtained by randomly measuring the size (diameter or major axis length) of approximately 20 particles in a scanning electron microscope image.

[0019] Here, "or" should not be interpreted as having an exclusive meaning. For example, "A or B" is interpreted as including A, B, A+B, etc.

[0020] The term "metal" is interpreted as encompassing common metals, transition metals, and metalloids (semi-metals).

[0021] When the terms “about” or “substantially” are used in conjunction with numerical values ​​in this specification, it is intended that the relevant numerical values ​​include a tolerance of ±10% around the stated value. When a range is specified, the range includes all values ​​within that range (such as increments of 0.1%).

[0022] positive electrode In some example embodiments, the positive electrode for a rechargeable lithium battery includes: a positive electrode current collector; a first positive electrode active material layer on the positive electrode current collector and including a first positive electrode active material comprising a lithium iron phosphate compound; and a second positive electrode active material layer on the first positive electrode active material layer and including a second positive electrode active material comprising a lithium nickel composite oxide and a third positive electrode active material comprising a lithium manganese oxide.

[0023] Figure 5 This is a graph showing the voltage distribution in Comparative Example 4, described below, where the positive electrode is fabricated by mixing lithium iron phosphate compounds and lithium nickel composite oxides, and in Comparative Example 5, also described below, where the positive electrode is fabricated by mixing lithium iron phosphate compounds, lithium nickel composite oxides, and lithium manganese oxides. Figure 5In the case of the rechargeable lithium-ion battery cell in Comparative Example 4, which includes a positive electrode in which lithium iron phosphate compounds and lithium nickel composite oxides are mixed in a weight ratio of 80:20, a challenge may arise: the driving voltage of the lithium iron phosphate compound is 3.4V to 3.6V, while the driving voltage of the lithium nickel composite oxide is 3.5V to 4.25V, resulting in a separation of operating voltages. Due to this separation of driving voltages, high currents may flow through the lithium nickel composite oxide at 3.5V or higher during cycle life testing, which may have an adverse effect when evaluating the lithium nickel composite oxide at a C-rate higher than the actual C-rate. As a result, the lithium nickel composite oxide exhibits a lower capacity than the actual capacity, and degradation may occur with repeated charging and discharging, which may reduce the overall cycle life of the battery.

[0024] To address the aforementioned issues, one approach involves mixing lithium iron phosphate compounds and lithium nickel composite oxides, while simultaneously adding lithium manganese oxides, which exhibit capacity at voltages similar to those of the lithium nickel composite oxides. When a portion of the lithium iron phosphate compound is replaced with lithium manganese oxide, it can exhibit capacity alongside the lithium nickel composite oxide near 4V, thereby mitigating the high current flowing to the lithium nickel composite oxide. Figure 5 In Comparative Example 5, where lithium manganese oxides were added to and mixed with lithium iron phosphate compounds and lithium nickel composite oxides, performance was improved compared to the case where only lithium iron phosphate compounds and lithium nickel composite oxides were mixed. However, even when lithium manganese oxides were added to and mixed with lithium iron phosphate compounds and lithium nickel composite oxides, rate performance and cycle life characteristics were still low.

[0025] Therefore, in some example embodiments, a dual-layer structure is employed, comprising: a first positive electrode active material layer including a first positive electrode active material comprising a lithium iron phosphate compound; a second positive electrode active material layer including a second positive electrode active material comprising a lithium nickel composite oxide and a third positive electrode active material comprising a lithium manganese oxide. For example, the first positive electrode active material layer is located below the second positive electrode active material layer to improve rate performance and cycle life characteristics. High current flow primarily occurs at high voltages, and rate performance and cycle life characteristics can be improved by placing a material exhibiting capacity at high voltages at the top.

[0026] Figure 6This is a schematic diagram illustrating a positive electrode according to some example embodiments. According to some example embodiments, the positive electrode 4 has a structure in which a positive electrode current collector 1, a first positive electrode active material layer 2, and a second positive electrode active material layer 3 are stacked (e.g., stacked in this order). However, the positive electrode is not limited to this structure; positive electrode active material layers may be stacked on both surfaces of the positive electrode current collector, or other positive electrode active material layers or other functional layers may be added at any location.

[0027] Positive electrode current collector There are no particular restrictions on the positive electrode current collector, as long as it is conductive and does not cause adverse chemical changes in the rechargeable lithium battery, and it can be, for example, an aluminum (Al) film or a stainless steel (SUS) film.

[0028] First positive electrode active material layer The first positive electrode active material layer includes a first positive electrode active material, and the first positive electrode active material includes a lithium iron phosphate compound. The inclusion of a first positive electrode active material comprising a lithium iron phosphate compound in the first positive electrode active material layer ensures price competitiveness and improves energy density.

[0029] Lithium iron phosphate compounds can be represented by, for example, chemical formula 1 or chemical formula 2.

[0030] Chemical Formula 1: Li a1 Fe (1-x1) M 1 x1 PO4 In chemical formula 1, 0.9 ≤ a1 ≤ 1.5, 0 ≤ x1 ≤ 0.4, and M 1 It is or includes at least one of the following: Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, and combinations thereof. Here, 0.90 ≤ a1 ≤ 1.5 (e.g., 0.90 ≤ a1 ≤ 1.2 or 0.95 ≤ a1 ≤ 1.1). Additionally, 0 ≤ x1 ≤ 0.4, 0 ≤ x1 ≤ 0.3, 0 ≤ x1 ≤ 0.2, 0 ≤ x1 ≤ 0.1, or 0 ≤ x1 ≤ 0.05.

[0031] Chemical formula 2: Li a2 Mn x2 Fe (1-x2-y2) M 2 y2 PO4 In chemical formula 2, 0.9 ≤ a² ≤ 1.5, 0.1 ≤ x² ≤ 0.9, 0 ≤ y² < 0.9, and M 2It is or includes at least one of the following: Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, Zr, and combinations thereof. Here, 0.90 ≤ a² ≤ 1.5 (e.g., 0.90 ≤ a² ≤ 1.2 or 0.95 ≤ a² ≤ 1.1). Additionally, 0.1 ≤ x² ≤ 0.9, 0.3 ≤ x² ≤ 0.9 or 0.4 ≤ x² ≤ 0.8, 0 ≤ y² ≤ 0.4, 0 ≤ y² ≤ 0.3, 0 ≤ y² ≤ 0.2, 0 ≤ y² ≤ 0.1 or 0 ≤ y² ≤ 0.05.

[0032] For example, lithium iron phosphate compounds may include at least one of the following: LiFePO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.3 Fe 0.7 PO4 and its combinations.

[0033] For example, in chemical formula 1 and chemical formula 2, M 1 and M 2 It may include at least one of Al, Mg, Ti, V, and combinations thereof.

[0034] The first positive electrode active material is in the form of particles, and may be in the form of first particles, second particles, or a mixture thereof.

[0035] The first particle can be or includes secondary particles formed by the aggregation of multiple primary particles. Because the primary particles are closely aggregated, the secondary particles of the first particle can have a generally spherical or generally elliptical shape. The secondary particles can be represented as an assembly. The average particle size (D) of the secondary particles of the first particle... 50 The average particle size (D) of the secondary particles of the first particle can be, for example, in the range of about 5 μm to about 20 μm, about 6 μm to about 20 μm, or about 6 μm to about 15 μm. 50 The particle size (D) of a single particle can be larger than the average particle size of the second particle described later. 50 The average particle size (D) of the primary particles that form the secondary particles of the first particle. 50It can be in the range of about 0.1 μm to about 2 μm, about 0.1 μm to about 1.2 μm or about 0.5 μm to about 0.9 μm, and for example, it can be less than or equal to about 500 nm, and for example, it can be in the range of about 100 nm to about 400 nm, about 120 nm to about 400 nm or about 140 nm to about 400 nm.

[0036] The average particle size (D) of the secondary particles of the first particle 50 For example, the particle size can be measured by randomly or unsystematically selecting approximately 30 first particles from an electron micrograph of the first positive electrode active material, and the diameter of the particles whose cumulative volume is 50% of the particle size distribution can be taken as the average particle size (D). 50 The average particle size of the primary particles that form the secondary particles of the first particle can be determined by measuring the size of approximately 30 primary particles in an electron micrograph of the surface or cross-section of the first particle, and in the particle size distribution, the diameter of the particles that constitute 50% of the cumulative volume can be used as the average particle size (D). 50 ).

[0037] The secondary particles of the first particle may include pores, and the porosity may be in the range of about 20% to about 50%. The porosity can be obtained by measuring the ratio of the area occupied by the pores within the secondary particles to the cross-sectional area of ​​the secondary particles using an image analysis program such as ImageJ, for example, a scanning electron microscope image from a cross-section of the first particle.

[0038] The second particle can be in the form of a single particle. Here, a single particle exists alone without grain boundaries within the particle, consists of or includes a single particle, and can be or include a single particle, an integral structure, a monolithic structure, or a non-aggregated particle in which the particles do not aggregate with each other but exist as an independent phase in terms of morphology, and can be represented as a single particle (monolithic particle, single grain), for example, as a single crystal. A single particle can exist alone or can aggregate together. For example, about two to about ten single particles can aggregate together and contact each other. The average particle size (D) of the single particles of the second particle... 50 The average particle size (D) of the second particle can be less than or equal to about 5 μm, and can, for example, range from about 0.5 μm to about 5 μm, from about 0.6 μm to about 3 μm, from about 0.7 μm to about 2 μm, or from about 0.8 μm to about 1.5 μm. 50 The particle size of the secondary particles can be smaller than the average particle size (D) of the first particle. 50 ), and can be equal to or greater than the average particle size (D) of the primary particles that form the secondary particles of the first particle. 50For example, the particle size can be measured by randomly or unsystematically selecting about 30 second particles from an electron micrograph of the first positive electrode active material, and the diameter of particles whose cumulative volume is about 50% of the particle size distribution can be taken as the average particle size (D). 50 To obtain the average particle size (D) of the second particle. 50 ).

[0039] Based on 100 wt% of the first positive electrode active material, the amount of the first particle can range from about 20 wt% to about 100 wt%, and the amount of the second particle can range from about 0 wt% to about 80 wt%. For example, the amount of the first particle can range from about 20 wt% to about 90 wt%, and the amount of the second particle can range from about 10 wt% to about 80 wt%. As an example, based on 100 wt% of the first positive electrode active material, the amount of the first particle can range from about 40 wt% to about 80 wt%, and the amount of the second particle can range from about 20 wt% to about 60 wt%, or the amount of the first particle can range from about 40 wt% to about 60 wt%, and the amount of the second particle can range from about 40 wt% to about 60 wt%.

[0040] The first positive electrode active material may further include a carbon coating formed on the surface of secondary particles of the first particle, the surface of primary particles forming secondary particles of the first particle, and / or the surface of individual particles of the second particle. The carbon coating can improve the conductivity of the first positive electrode active material and reduce the resistance of the positive electrode. The carbon coating can be formed, for example, using at least one carbon raw material, such as or including at least one of glucose, sucrose, lactose, starch, oligosaccharides, polyoligosaccharides, fructose, cellulose, furfuryl alcohol polymers, ethylene and ethylene oxide block copolymers, vinyl resins, cellulose resins, phenolic resins, pitch resins, and tar resins. For example, the carbon coating can be formed by arranging the carbon raw material on the surface of the first positive electrode active material particles and then performing a firing process. For example, the carbon raw material and primary particles can be mixed and heat-treated to form a carbon coating on the surface of the primary particles, and then secondary particles in which the primary particles aggregate can be prepared by post-processing; or the carbon raw material and secondary particles can be mixed and heat-treated to form a carbon coating on the surface of the secondary particles.

[0041] The carbon coating may be included in an amount ranging from about 0.1 wt% to about 3.9 wt% based on 100 wt% of the first particles, and the carbon coating may be included in an amount ranging from about 0.1 wt% to about 3.9 wt% based on 100 wt% of the second particles.

[0042] Based on a 100wt% first positive electrode active material layer, the amount of the first positive electrode active material can be in the range of about 60wt% to about 99.9wt%, about 70wt% to about 99.8wt%, about 80wt% to about 99wt%, about 90wt% to about 99.8wt%, or about 90wt% to about 99wt%.

[0043] In addition to the first positive electrode active material mentioned above, the first positive electrode active material layer may optionally include a first binder, a first conductive material, or a combination thereof.

[0044] The first adhesive is configured to adhere the first positive electrode active material to each other and to the positive electrode current collector. Examples of the first adhesive may include, but are not limited to, at least one of 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, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylate resin, polyester resin, and nylon.

[0045] A first conductive material is included to provide conductivity to the positive electrode, and any electrically conductive material can be used as the conductive material unless it causes an adverse chemical change in the battery. Examples of the first conductive material may include carbon-based materials (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.), metallic materials including at least one of copper, nickel, aluminum, silver, etc., metal powders or metal fibers, conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0046] Based on a 100wt% first positive electrode active material layer, the amount of the first binder in the first positive electrode active material layer may be in the range of about 0.1wt% to about 5wt% or about 0.5wt% to about 3wt%, and based on the 100wt% first positive electrode active material layer, the amount of the first conductive material may be in the range of about 0.1wt% to about 5wt% or about 0.5wt% to about 3wt%.

[0047] The thickness of the first positive electrode active material layer can range from about 20 μm to about 200 μm (e.g., about 40 μm to about 150 μm or about 60 μm to about 100 μm). The thickness of the first positive electrode active material layer can be measured by taking a cross-section of the positive electrode using, for example, a scanning electron microscope. When the thickness of the first positive electrode active material layer is not constant, the average of the minimum and maximum thicknesses can be calculated, and in this case, the thickness can be the average thickness.

[0048] The loading level of the first positive electrode active material layer can be from about 5 mg / cm 2 to about 25 mg / cm 2 (e.g., from about 5 mg / cm 2 to about 20 mg / cm 2 , from about 5 mg / cm 2 to about 15 mg / cm 2 or from about 5 mg / cm 2 to about 10 mg / cm 2 ). The loading level can refer to the amount of the active material per unit area of the electrode.

[0049] Second positive electrode active material layer The second positive electrode active material layer includes a second positive electrode active material and a third positive electrode active material. Among them, the second positive electrode active material includes a lithium nickel-based composite oxide, and the third positive electrode active material includes a lithium manganese-based oxide. The second positive electrode active material layer can be or include a mixed form of a lithium nickel-based composite oxide and a lithium manganese-based oxide that exhibits capacity at a high voltage. According to some exemplary embodiments, the positive electrode can improve the rate performance and cycle life characteristics of the battery by adopting a double-layer structure, in which the first positive electrode active material is coated as the first positive electrode active material layer (lower layer), and the second positive electrode active material and the third positive electrode active material are coated as the second positive electrode active material layer (upper layer). Specifically, the second positive electrode active material layer (upper layer) where the electrochemical reaction at the positive electrode occurs most actively includes a lithium nickel-based composite oxide and a lithium manganese-based oxide that exhibit capacity at a high voltage, and the first positive electrode active material layer (lower layer) includes a lithium iron phosphate-based compound that exhibits capacity at a relatively low voltage.

[0050] For example, the lithium nickel-based composite oxide can be represented by Chemical Formula 3.

[0051] Chemical Formula 3: Li a3 Ni x3 M 3 y3 M 4 z3 O 2-b3 X b3 In Chemical Formula 3, 0.9 ≤ a3 ≤ 1.2, 0.3 ≤ x3 < 1, 0 < y3 ≤ 0.7, 0 ≤ z3 ≤ 0.7, 0.9 ≤ x3 + y3 + z3 ≤ 1.1 and 0 ≤ b3 ≤ 0.1, M 3 and M 4Each independently is or comprises one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, M 3 and M 4 are different elements, and X is or comprises one or more of F, P, and S.

[0052] In Chemical Formula 3, 0.3 ≤ x3 ≤ 0.8, 0.1 ≤ y3 ≤ 0.6 and 0.1 ≤ z3 ≤ 0.6, or 0.3 ≤ x3 ≤ 0.6, 0.2 ≤ y3 ≤ 0.5 and 0.2 ≤ z3 ≤ 0.5.

[0053] As an example, the lithium nickel-based composite oxide can be represented by Chemical Formula 4 or Chemical Formula 5.

[0054] Chemical Formula 4: Li a4 Ni x4 Co y4 M 5 z4 O 2-b4 X b4 In Chemical Formula 4, 0.9 ≤ a4 ≤ 1.2, 0.3 ≤ x4 < 1, 0 < y4 ≤ 0.7, 0 ≤ z4 ≤ 0.7, 0.9 ≤ x4 + y4 + z4 ≤ 1.1 and 0 ≤ b4 ≤ 0.1, M 5 is or comprises one or more of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is or comprises at least one of F, P, S, and combinations thereof.

[0055] In Chemical Formula 4, 0.3 ≤ x4 ≤ 0.8, 0.1 ≤ y4 ≤ 0.6 and 0.1 ≤ z4 ≤ 0.6, or 0.3 ≤ x4 ≤ 0.6, 0.2 ≤ y4 ≤ 0.5 and 0.2 ≤ z4 ≤ 0.5.

[0056] Chemical Formula 5: Li a5 Ni x5 Co y5 ... M 6 z5 M 7 w5 O 2-b5 X b5 In chemical formula 5, 0.9 ≤ a5 ≤ 1.2, 0.3 ≤ x5 ≤ 0.98, 0.01 ≤ y5 ≤ 0.69, 0.01 ≤ z5 ≤ 0.69, 0 ≤ w5 ≤ 0.68, 0.9 ≤ x5 + y5 + z5 + w5 ≤ 1.1 and 0 ≤ b5 ≤ 0.1, M 6 It is or includes at least one of Al, Mn and combinations thereof, M 7 X is or includes one or more of B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is or includes at least one of F, P, S, and combinations thereof.

[0057] In chemical formula 5, 0.3≤x5≤0.8, 0.1≤y5≤0.6, 0.1≤z5≤0.6 and 0≤w5≤0.5, or 0.3≤x5≤0.6, 0.2≤y5≤0.5, 0.2≤z5≤0.5 and 0≤w5≤0.3.

[0058] Lithium-nickel composite oxides can be or include high-nickel positive electrode active materials. For example, in lithium-nickel composite oxides, based on 100 mol% of total metals other than lithium, the nickel content can be greater than or equal to about 80 mol%, for example, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, or greater than or equal to about 94 mol% and less than or equal to about 99 mol%. High-nickel positive electrode active materials can achieve high capacity and high performance. High-nickel positive electrode active materials can improve capacity, efficiency, energy density, and cycle life characteristics by being coated as a top layer of a first positive electrode active material layer comprising a first positive electrode active material containing lithium iron phosphate compounds.

[0059] The second positive electrode active material can take the form of secondary particles in which multiple primary particles are aggregated, as a single particle, or as a mixture thereof.

[0060] The average particle size (D) of the active material of the second positive electrode 50 The particle size can range from about 1 μm to about 20 μm or from about 3 μm to about 18 μm. For example, the second positive electrode active material can include an average particle size (D... 50 Large particles in the range of approximately 9 μm to approximately 20 μm, approximately 10 μm to approximately 18 μm, or approximately 12 μm to approximately 15 μm, with an average particle size (D) 50Small particles or combinations thereof in the range of about 1 μm to about 8 μm, about 1.5 μm to about 7 μm, or about 2 μm to about 6 μm. Large particles may be in the form of secondary particles formed by aggregates of multiple primary particles, and small particles may be in the form of secondary particles formed by aggregates of multiple primary particles, single particles, or mixtures thereof. The average particle size (D) of the primary particles forming the secondary particles... 50 The average particle size (D) can be less than or equal to about 1 μm, and can, for example, range from about 0.1 μm to about 1 μm, from about 0.2 μm to about 0.9 μm, from about 0.2 μm to about 0.8 μm, or from about 0.3 μm to about 0.6 μm. 50 The particle size can range from about 1 μm to about 8 μm or from about 1 μm to about 5 μm. For example, the average particle size (D) can be determined by selecting about 20 random particles from a scanning electron microscope image, measuring their particle size (particle diameter, major axis, or major axis length), obtaining the particle size distribution, and taking the size of the particles that constitute 50% of the cumulative volume from the particle size distribution. 50 ).

[0061] The second positive electrode active material may include, for example, both large and small particles, and in this case, the large and small particles may be mixed in a weight ratio ranging from about 20:80 to about 95:5. When the second positive electrode active material includes both large and small particles, capacity, energy density, and cycle life characteristics can be improved.

[0062] Lithium manganese oxides may be or include, for example, lithium manganese oxides with a spinel structure having LiMn2O4 as their basic composition. In addition to manganese, lithium manganese oxides may also include at least one of aluminum, magnesium, yttrium, and combinations thereof, and may not include cobalt, or may include a considerable amount of cobalt.

[0063] Lithium manganese oxides can be represented, for example, by chemical formula 6.

[0064] Chemical Formula 6: Li a6 Mn x6 M 8 y6 O 4-b6 X b6 In chemical formula 6, 0.9 ≤ a6 ≤ 1.8, 1.7 ≤ x6 ≤ 2, 0 ≤ y6 ≤ 0.3, 1.9 ≤ x6 + y6 ≤ 2.1 and 0 ≤ b6 ≤ 0.1, M 8 X is or includes one or more of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is or includes one or more of F, P, and S.

[0065] In Chemical Formula 6, 1.8 ≤ x6 ≤ 2 and 0 ≤ y6 ≤ 0.2; 1.9 ≤ x6 ≤ 2 and 0 ≤ y6 ≤ 0.1; or 1.7 ≤ x6 < 2 and 0 < y6 ≤ 0.3.

[0066] For example, the lithium manganese-based oxide can be represented by Chemical Formula 7.

[0067] Chemical Formula 7: Li a7 Mn x7 Al y7 Mg z7 M 9 w7 O 4-b7 X b7 In Chemical Formula 7, 0.9 ≤ a7 ≤ 1.8, 1.7 ≤ x7 < 2.0, 0 < y7 ≤ 0.015, 0 < z7 ≤ 0.010, 0 ≤ w7 < 0.3, 1.9 ≤ x7 + y7 + z7 + w7 ≤ 2.1 and 0 ≤ b7 ≤ 0.1, M 9 is or includes one or more of B, Ba, Ca, Ce, Cr, Cu, Fe, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is or includes one or more of F, P and S.

[0068] The third positive electrode active material can be in the form of secondary particles formed by aggregation of a plurality of primary particles, in the form of single particles, or a mixed form thereof. Here, the definition of a single particle is as described in the first positive electrode active material.

[0069] The average particle size (D 50 ) of the third positive electrode active material can be in the range of about 1 μm to about 15 μm or about 3 μm to about 10 μm. For example, the average particle size (D 50 ) of the secondary particles can be in the range of about 5 μm to about 15 μm or about 5 μm to about 10 μm, and the average particle size (D 50 ) of the primary particles forming the secondary particles can be in the range of about 0.1 μm to about 5 μm, about 0.1 μm to about 4 μm or about 0.1 μm to about 3 μm. The average particle size (D 50 ) of the single particles can be less than or equal to about 10 μm, and can be, for example, in the range of about 0.1 μm to about 10 μm, about 0.5 μm to about 9.5 μm or about 0.7 μm to about 9 μm. For example, the average particle size (D 50 can be determined by selecting about 20 random particles from a scanning electron micrograph, measuring their particle sizes (particle diameter, long axis or long axis length), obtaining a particle size distribution, and taking the size of the particle with a cumulative volume of 50% by volume from the particle size distribution.When secondary particles and individual particles are mixed, the mixing ratio of secondary particles to individual particles can be in the range of about 1:9 to about 9:1, but this disclosure is not limited thereto.

[0070] Based on a 100 wt% second positive electrode active material layer, the amounts of the second and third positive electrode active materials can range from about 60 wt% to about 99.9 wt%, about 70 wt% to about 99.8 wt%, about 80 wt% to about 99 wt%, about 90 wt% to about 99.8 wt%, or about 94 wt% to about 99 wt%. The total content of the second and third positive electrode active materials refers to the total content of the second positive electrode active material included in the second positive electrode active material layer and the third positive electrode active material included in the second positive electrode active material layer.

[0071] The weight ratio of the second positive electrode active material, comprising a lithium nickel composite oxide, to the third positive electrode active material, comprising a lithium manganese oxide, in the second positive electrode active material layer can be in the range of about 10:90 to about 90:10 (e.g., about 10:90 to about 80:20, about 10:90 to about 70:30, about 10:90 to about 60:40, about 10:90 to about 50:50, or about 20:80 to about 40:60). When the weight ratio of the lithium nickel composite oxide and the lithium manganese oxide in the second positive electrode active material layer meets the above range, by reducing or minimizing the amount of expensive lithium nickel composite oxide, while incorporating relatively inexpensive lithium manganese oxide that exhibits capacity at high voltage, the rate performance and cycle life characteristics of the battery can be improved.

[0072] In the total amount of the first positive electrode active material layer and the second positive electrode active material layer, based on the total amount of 100 wt% of the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material, the first positive electrode active material may be included in an amount ranging from about 10 wt% to about 70 wt%, the second positive electrode active material may be included in an amount ranging from about 10 wt% to about 50 wt%, and the third positive electrode active material may be included in an amount ranging from about 20 wt% to about 80 wt%. As an example, based on the total amount of 100 wt% of the first, second, and third positive electrode active materials, the first positive electrode active material may be included in an amount ranging from about 30 wt% to about 50 wt%, the second positive electrode active material may be included in an amount ranging from about 10 wt% to about 30 wt%, and the third positive electrode active material may be included in an amount ranging from about 40 wt% to about 60 wt%. When the amounts of each of the first, second, and third positive electrode active materials meet the above ranges, manufacturing costs can be reduced to allow for the manufacture of low-cost positive electrode active materials, while achieving high capacity and high energy density and improving rate performance and cycle life characteristics.

[0073] For example, in both the first and second positive electrode active material layers, the manganese content can range from about 30 mol% to about 70 mol% (e.g., about 40 mol% to about 60 mol%) based on 100 mol% of total metals excluding lithium. In this case, the unit cost required to manufacture the positive electrode can be reduced, while safety, capacity characteristics, rate performance, and cycle life characteristics can be improved.

[0074] In addition to the second positive electrode active material and the third positive electrode active material, the second positive electrode active material layer may optionally include a second binder, a second conductive material, or a combination thereof.

[0075] The use of "first" or "second" for the adhesive and conductive material is solely for the purpose of distinguishing the second adhesive and the second conductive material from the first adhesive and the first conductive material included in the first positive electrode active material layer, and does not necessarily indicate that they are different.

[0076] The second binder and the second conductive material may include the types of binders and conductive materials typically included in the positive electrode active material layer, and since these types are described in the first binder and the first conductive material respectively, their descriptions are omitted below.

[0077] Based on a 100wt% second positive electrode active material layer, the amount of the second binder in the second positive electrode active material layer may be in the range of about 0.1wt% to about 5wt% or about 0.5wt% to about 3wt%, and based on the 100wt% second positive electrode active material layer, the amount of the second conductive material may be in the range of about 0.1wt% to about 5wt% or about 0.5wt% to about 3wt%.

[0078] The thickness of the second positive electrode active material layer can range from about 20 μm to about 200 μm (e.g., about 40 μm to about 150 μm or about 60 μm to about 100 μm). The thickness of the second positive electrode active material layer can be measured by taking a cross-section of the positive electrode using, for example, a scanning electron microscope. When the thickness of the second positive electrode active material layer is not constant, the average of the minimum and maximum thicknesses can be calculated, and in this case, the thickness can be the average thickness.

[0079] The loading level of the second positive electrode active material layer can be approximately 5 mg / cm³. 2 Approximately 25 mg / cm 2 (For example, approximately 7 mg / cm³) 2 Approximately 23 mg / cm 2 Approximately 9 mg / cm 2 Approximately 21 mg / cm 2 or about 10mg / cm 2 Approximately 20 mg / cm 2 Within the range of ).

[0080] The total mixture density of the first positive electrode active material layer and the second positive electrode active material layer can be in the range of about 2.0 g / cc to about 4.0 g / cc (e.g., about 2.2 g / cc to about 3.8 g / cc, about 2.4 g / cc to about 3.6 g / cc, or about 2.6 g / cc to about 3.4 g / cc).

[0081] In addition to the above-described structure, the first positive electrode active material layer and the second positive electrode active material layer may further include known components without impairing battery performance.

[0082] Rechargeable lithium batteries In some example embodiments, the rechargeable lithium battery includes the aforementioned positive electrode, negative electrode, and electrolyte.

[0083] A rechargeable lithium battery may include a positive electrode, a negative electrode, a separator between the positive and negative electrodes, and an electrolyte.

[0084] Based on their shape, rechargeable lithium batteries can be classified into cylindrical, prismatic, pouch-shaped, coin-shaped, and other shapes. Figures 1 to 4This is a schematic diagram illustrating a rechargeable lithium battery according to some example embodiments, wherein, Figure 1 It is a cylindrical battery. Figure 2 It is a prismatic battery, and Figure 3 and Figure 4 It's a pouch battery. (See reference) Figures 1 to 4 The rechargeable lithium battery 100 includes an electrode assembly 40 and a housing 50. The electrode assembly 40 has a separator 30 inserted between a positive electrode 10 and a negative electrode 20. The electrode assembly 40 is housed within the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte (not shown). Figure 1 As shown, the rechargeable lithium battery 100 may include a sealing member 60 of the sealed housing 50. Additionally, in Figure 2 In this context, the rechargeable lithium battery 100 may include a positive electrode lead connector 11, a positive electrode terminal 12 connected to the positive electrode lead connector 11, a negative electrode lead connector 21, and a negative electrode terminal 22 connected to the negative electrode lead connector 21. For example... Figure 3 and Figure 4 As shown, the rechargeable lithium battery 100 includes Figure 4 The electrode connector 70 shown in the figure, or Figure 3 The positive electrode terminal 71 and negative electrode terminal 72 shown in the figure form an electrical path for guiding the current formed in the electrode assembly 40 to the outside of the battery 100.

[0085] negative electrode The negative electrode for a rechargeable lithium battery includes a negative electrode current collector and a negative electrode active material layer on the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material and may optionally include at least one of a binder, a conductive material, and combinations thereof.

[0086] There are no particular restrictions on the negative electrode current collector, as long as it is conductive and does not cause chemical changes in the rechargeable lithium battery, and it can be or include copper foil with a thickness in the range of about 10 μm to about 15 μm.

[0087] The negative electrode active material includes at least one of the following: materials capable of reversibly inserting / deintercalating lithium ions, lithium metal, alloys of lithium metal, materials capable of doping and dedoping lithium, and transition metal oxides.

[0088] Materials capable of reversibly inserting / deintercalating lithium ions can be or include carbon-based negative electrode active materials, such as crystalline carbon, amorphous carbon, or combinations thereof. Crystalline carbon can be irregular, or in the form of flakes, sheets, spheres, or fibers, of natural or artificial graphite. Amorphous carbon can be or include at least one of soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0089] As a lithium metal alloy, an alloy of lithium and a metal can be used, and the metal is such as or includes at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0090] The material capable of doping / dedoping lithium can be or include a Si-based negative electrode active material or a Sn-based negative electrode active material. The Si-based negative electrode active material can be or include silicon, a silicon-carbon composite, SiO x (0 < x ≤ 2), a Si-Q alloy (where Q is or includes at least one of an alkali metal, an alkaline earth metal, a Group 13 element, a Group 14 element (excluding Si), a Group 15 element, a Group 16 element, a transition metal, a rare earth element, and combinations thereof, and for example includes at least one of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po, and combinations thereof) and combinations thereof. The Sn-based negative electrode active material can be or include at least one of Sn, SnO2, a Sn alloy, and combinations thereof.

[0091] The silicon-carbon composite can be or include a composite of silicon and amorphous carbon. The average particle size (D 50 ) can be, for example, in the range of about 0.5 μm to about 20 μm. According to some exemplary embodiments, the silicon-carbon composite can be in the form of silicon particles and amorphous carbon coated on the surface of the silicon particles. For example, the silicon-carbon composite can include secondary particles (cores) in which primary silicon particles are assembled and an amorphous carbon coating (shell) on the surface of the secondary particles. Amorphous carbon can also be present between the primary silicon particles. For example, the primary silicon particles can be coated with amorphous carbon. The secondary particles can be dispersed in an amorphous carbon matrix.

[0092] The silicon-carbon composite can also include crystalline carbon. For example, the silicon-carbon composite can include a core containing crystalline carbon and silicon particles and an amorphous carbon coating on the surface of the core. The crystalline carbon can be or include artificial graphite, natural graphite, or a combination thereof. The amorphous carbon can include at least one of soft carbon or hard carbon, mesophase pitch carbonized products, calcined coke, etc.

[0093] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the amount of silicon can be in the range of about 10 wt% to about 50 wt%, and the amount of amorphous carbon can be in the range of about 50 wt% to about 90 wt%. Additionally, when the composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the amount of silicon can be in the range of about 10 wt% to about 50 wt%, the amount of crystalline carbon can be about 10 wt% to about 70 wt%, and the amount of amorphous carbon can be about 20 wt% to about 40 wt%.

[0094] Additionally, the thickness of the amorphous carbon coating can be in the range of about 5 nm to about 100 nm. The average particle diameter (D 50 ) of the silicon particles (primary particles) can be in the range of about 10 nm to about 1 μm or about 10 nm to about 200 nm. The silicon particles can exist as elemental silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon can be represented as SiO x (0 < x ≤ 2). At this time, the atomic weight ratio of Si:O representing the degree of oxidation can be in the range of about 99:1 to about 33:67. In this specification, as used herein, when no other definition is provided, the average particle diameter (D 50 ) represents the diameter of the particles with a cumulative volume of about 50 volume% in the particle size distribution.

[0095] The Si-based negative electrode active material or the Sn-based negative electrode active material can be mixed with the carbon-based negative electrode active material. When using a mixture of the Si-based negative electrode active material or the Sn-based negative electrode active material and the carbon-based negative electrode active material, the mixing ratio can be in the range of about 1:99 to about 90:10 by weight.

[0096] Based on 100 wt% of the negative electrode active material layer, the negative electrode active material can be included in an amount in the range of about 90 wt% to about 99.8 wt% or about 94 wt% to about 99 wt%.

[0097] The binder is configured to adhere the negative electrode active material particles to each other and to adhere the negative electrode active material to the current collector. The binder can be or include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0098] The non-aqueous binder can include at least one of the following: polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0099] Waterborne adhesives may include at least one of the following: styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyepoxychloropropane, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or combinations thereof.

[0100] When using an aqueous binder as the negative electrode binder, it may further include a cellulose-based compound capable of imparting viscosity. As a cellulose-based compound, one or more of carboxymethyl cellulose, hydroxypropyl methyl cellulose, methyl cellulose, and their alkali metal salts may be mixed and used. The alkali metal may be or include at least one of Na, K, and Li.

[0101] The dry binder may be or include a polymeric material capable of being turned into fibers, and may be or include at least one of, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, and combinations thereof.

[0102] Conductive materials are included to provide electrode conductivity, and any electrically conductive material can be used as a conductive material unless it causes a chemical change in the battery. Examples of conductive materials include carbon-based materials (such as at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.), metallic materials including at least one of copper, nickel, aluminum, silver, etc., metal powders or metal fibers, conductive polymers (such as polyphenylene derivatives), or mixtures thereof.

[0103] Based on a 100wt% negative electrode active material layer, the amount of binder can be in the range of about 0.1wt% to about 5wt%, and based on a 100wt% negative electrode active material layer, the amount of conductive material can be in the range of about 0.1wt% to about 5wt%.

[0104] electrolytes For example, the electrolyte used in rechargeable lithium batteries can be an electrolyte solution that may include non-aqueous organic solvents and lithium salts.

[0105] Non-aqueous organic solvents are configured as media for transporting ions that participate in the electrochemical reactions of a battery. Non-aqueous organic solvents can be at least one of carbonate solvents, ester solvents, ether solvents, ketone solvents, alcohol solvents, aprotic solvents, and combinations thereof.

[0106] Carbonate solvents may include at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate (BC). Ester solvents may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolactone, mevalonolactone, valproic acid lactone, caprolactone, etc. Ether solvents may include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, dimethoxyethane, 2-methyltetrahydrofuran, 2,5-dimethyltetrahydrofuran, tetrahydrofuran, etc. Additionally, ketone solvents may include cyclohexanone, etc. Alcohol solvents may include ethanol, isopropanol, etc. Aprotic solvents may include at least one of the following: nitriles, such as R-CN (wherein R is a C2 to C20 straight-chain, branched or cyclic hydrocarbon group, and may include double bonds, aromatic rings or ether groups, etc.); amides, such as dimethylformamide; dioxolane, such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane, etc.

[0107] Non-aqueous organic solvents can be used alone or in combination of two or more solvents, and when two or more types of solvents are used in combination, the mixing ratio can be adjusted as needed according to the expected battery performance, which is widely understood by those in the relevant field.

[0108] When using carbonate solvents, cyclic carbonates and chain carbonates can be mixed, and the cyclic carbonates and chain carbonates can be mixed in a volume ratio ranging from about 1:1 to about 1:9.

[0109] Non-aqueous organic solvents may also include aromatic hydrocarbon organic solvents. For example, carbonate solvents and aromatic hydrocarbon organic solvents can be mixed and used in a volume ratio ranging from about 1:1 to about 30:1.

[0110] The electrolyte solution may also include at least one of vinyl ethyl carbonate, vinylene carbonate, and ethylene carbonate compounds to improve battery cycle life.

[0111] Examples of ethylene carbonate compounds may include at least one of fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate, and cyanoethylene carbonate.

[0112] Lithium salts dissolved in organic solvents are configured to supply lithium ions in batteries to enable rechargeable lithium batteries to operate and to improve lithium ion transport between the positive and negative electrodes. Examples of lithium salts may include LiPF6, LiBF4, LiSbF6, LiAsF6, LiClO4, LiAlO2, LiAlCl4, LiPO2F2, LiCl, LiI, LiN(SO3C2F5)2, Li(FSO2)2N (lithium bis(fluorosulfonyl)imide; LiFSI), LiC4F9SO3, LiN(C x F 2x+1 SO2)(C y F 2y+1 At least one of the following: (SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluorobis(oxalate)phosphate (LiDFBOP), and lithium bis(oxalate)borate (LiBOB).

[0113] The concentration of lithium salt can be in the range of about 0.1 M to about 2.0 M. When the concentration of lithium salt is within the above range, the electrolyte solution has the desired ionic conductivity and viscosity, thus achieving the desired or improved performance and allowing lithium ions to move efficiently.

[0114] diaphragm Depending on the type of rechargeable lithium battery, a separator may be present between the positive and negative electrodes. The separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride, and multilayer films of two or more layers (e.g., hybrid multilayer films such as polyethylene / polypropylene bilayer separators, polyethylene / polypropylene / polyethylene trilayer separators, polypropylene / polypropylene / polypropylene trilayer separators, etc.)).

[0115] The diaphragm may include a porous substrate and a coating on one or both surfaces of the porous substrate, comprising organic materials, inorganic materials, or combinations thereof.

[0116] The porous substrate can be formed from or comprise a polymer membrane of any polymer, such as polyolefins (e.g., polyethylene and polypropylene), polyesters (e.g., polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyetherketones, polyaryletherketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cyclic olefin copolymers, polyphenylene sulfide, polyethylene naphthalate, glass fibers, and polytetrafluoroethylene (e.g., TEFLON). ® ( ) at least one of them or copolymers or mixtures of two or more of them.

[0117] The porous substrate may have a thickness in the range of about 1 μm to about 40 μm (e.g., about 1 μm to about 30 μm, about 1 μm to about 20 μm, about 5 μm to about 15 μm or about 10 μm to about 15 μm).

[0118] Organic materials may include (meth)acrylic acid copolymers comprising a first structural unit and a second structural unit, wherein the first structural unit is derived from (meth)acrylamide and the second structural unit comprises at least one of structural units derived from (meth)acrylic acid or (meth)acrylate and structural units derived from (meth)acrylamide sulfonic acid or a salt thereof.

[0119] Inorganic materials may include, but are not limited to, inorganic particles containing at least one of Al2O3, SiO2, TiO2, SnO2, CeO2, MgO, NiO, CaO, GaO, ZnO, ZrO2, Y2O3, SrTiO3, BaTiO3, Mg(OH)2, boehmite, and combinations thereof. 50 It can be in the range of about 1nm to about 2000nm (e.g., about 100nm to about 1000nm or about 100nm to about 700nm).

[0120] Organic and inorganic materials can be mixed in a coating, or coatings containing organic materials and coatings containing inorganic materials can be stacked together.

[0121] The thickness of the coating can range from about 0.5 μm to about 20 μm (e.g., from about 1 μm to about 10 μm or from about 1 μm to about 5 μm).

[0122] Examples and comparative examples of this disclosure are described below. However, the examples below are merely examples of this disclosure, and this disclosure is not limited to the examples below.

[0123] Example 1 (1) Manufacturing of the positive electrode The average particle size (D) of the active material used as the first positive electrode 50 Secondary particles with a diameter of 8 μm (among which, aggregated particles with an average particle size of (D) 50 A first positive electrode active material layer composition was prepared by mixing a lithium iron phosphate compound (LiFePO4) in the form of multiple primary particles (200 nm in size), polyvinylidene fluoride as a first binder, and carbon black as a first conductive material in a weight ratio of 95:2.5:2.5 (first positive electrode active material: first binder: first conductive material). This composition was then dispersed in an N-methylpyrrolidone solvent to prepare a first positive electrode active material layer slurry.

[0124] The second positive electrode active material layer composition is prepared by the following method: the average particle size (D) of the aggregated primary particles is increased. 50 LiNi alloy composite oxides with large secondary particles of 14 μm (LiNi) 0.885 Mn 0.1 Al 0.015 O2) and average particle size (D) 50 LiNi alloy composite oxides with small secondary particles of 4 μm (LiNi) 0.885 Mn 0.1 Al 0.015 O2) was mixed at a weight ratio of 3:1 to prepare the second positive electrode active material; the second positive electrode active material was then mixed with an average particle size (D) 50 The third positive electrode active material, lithium manganese oxide (LiMn2O4) in the form of individual particles with a particle size of 7.5 μm, was mixed at a weight ratio of 31.75:68.25; then, this mixture was mixed with polyvinylidene fluoride as a second binder and carbon black as a second conductive material at a weight ratio of 98.5:1:0.5 (mixture: second binder: second binder). This composition was dispersed in N-methylpyrrolidone solvent to prepare a slurry for the second positive electrode active material layer.

[0125] A first positive electrode active material layer slurry is coated onto a 15 μm thick aluminum film and then dried to form the first positive electrode active material layer. A second positive electrode active material layer slurry is then coated onto the first positive electrode active material layer and dried to form the second positive electrode active material layer. Subsequently, the positive electrode is manufactured by sequentially rolling a stack of positive electrode current collector, first positive electrode active material layer, and second positive electrode active material layer.

[0126] Here, based on a total of 100 wt% of the first, second, and third positive electrode active materials, the weight percentage of the first positive electrode active material is 37 wt%, the weight percentage of the second positive electrode active material is 20 wt%, and the weight percentage of the third positive electrode active material is 43 wt%. The first positive electrode active material layer has a content of approximately 7.4 mg / cm³. 2 The loading level, and the second positive electrode active material layer has a loading level of 12.6 mg / cm². 2 The loading level. Additionally, the first and second positive electrode active material layers have a total mixture density of approximately 3 g / cc.

[0127] (2) Manufacturing of rechargeable lithium battery cells A negative electrode active material slurry was prepared by mixing 97.5 wt% graphite negative electrode active material, 1.5 wt% carboxymethyl cellulose, and 1 wt% styrene-butadiene rubber in an aqueous solvent. The negative electrode active material slurry was coated onto a 12 μm thick copper foil current collector, then dried and compressed to fabricate the negative electrode.

[0128] The prepared positive and negative electrodes were used to fabricate a coin half-cell. An electrolyte was prepared using a polypropylene membrane (Celgard 3510) as the separator by mixing ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate in a volume ratio of 2:6:2, and then dissolving 1.3 M LiPF6 in the mixed solvent.

[0129] Comparison Example 1 The positive electrode and rechargeable lithium battery cell were manufactured in essentially the same manner as in Example 1, except that a first positive electrode active material layer slurry was coated onto a 15 μm thick aluminum film, then dried and compressed to form the positive electrode active material layer. The positive electrode of Comparative Example 1 has a monolayer structure of positive electrode current collector-positive electrode active material layer. The positive electrode active material layer has a concentration of 20 mg / cm³. 2 The loading level and the mixture density of 2.4 g / cc.

[0130] Comparison Example 2 The positive electrode and rechargeable lithium battery cell were manufactured in essentially the same manner as in Example 1, except that a second positive electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed in a weight ratio of 95:2.5:2.5 (second positive electrode active material: binder: conductive material) to prepare a positive electrode active material composition. This composition was dispersed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The slurry was coated onto a 15 μm thick aluminum film, then dried and compressed to form a positive electrode active material layer. The positive electrode of Comparative Example 2 has a monolayer structure with a positive electrode current collector and a sequentially stacked positive electrode active material layer. The positive electrode active material layer has a concentration of 20 mg / cm³. 2 The loading level and the mixture density of 3.7 g / cc.

[0131] Comparison Example 3 The positive electrode and rechargeable lithium battery cell were manufactured in essentially the same manner as in Example 1, except that a third positive electrode active material, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed in a weight ratio of 95:2.5:2.5 (third positive electrode active material: binder: conductive material) to prepare a positive electrode active material composition. This composition was dispersed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated onto a 15 μm thick aluminum film, then dried and compressed to form a positive electrode active material layer. The positive electrode of Comparative Example 3 has a monolayer structure with a positive electrode current collector and a sequentially stacked positive electrode active material layer. The positive electrode active material layer has a concentration of 20 mg / cm³. 2 The loading level and the mixture density of 2.8 g / cc.

[0132] Compare Example 4 The positive electrode and rechargeable lithium battery cell were manufactured in essentially the same manner as in Example 1, except that a mixture of a first positive electrode active material and a second positive electrode active material in a weight ratio of 80:20, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed in a weight ratio of 95:2.5:2.5 (positive electrode active material: binder: conductive material) to prepare a positive electrode active material composition. This composition was dispersed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated onto a 15 μm thick aluminum foil film, then dried and compressed to form a positive electrode active material layer. The positive electrode of Comparative Example 4 has a monolayer structure with a positive electrode current collector and a positive electrode active material layer stacked sequentially. The positive electrode active material layer has a concentration of 20 mg / cm³. 2 The load level and the mixture density of 3 g / cc.

[0133] Compare Example 5 The positive electrode and rechargeable lithium battery cell were manufactured in essentially the same manner as in Example 1, except that a mixture of a first, second, and third positive electrode active material in a weight ratio of 37:20:43, polyvinylidene fluoride as a binder, and carbon black as a conductive material were mixed in a weight ratio of 95:2.5:2.5 (positive electrode active material: binder: conductive material) to prepare a positive electrode active material composition. This composition was dispersed in an N-methylpyrrolidone solvent to prepare a positive electrode active material slurry. The positive electrode active material slurry was coated onto a 15 μm thick aluminum film, then dried and compressed to form a positive electrode active material layer. The positive electrode of Comparative Example 5 has a monolayer structure with a positive electrode current collector and a positive electrode active material layer stacked sequentially. The positive electrode active material layer has a concentration of 20 mg / cm³. 2The load level and the mixture density of 3 g / cc.

[0134] Comparison Example 6 The positive electrode and rechargeable lithium battery cell are manufactured in essentially the same manner as in Example 1, except that the positive electrode is manufactured in the order of positive electrode current collector - second positive electrode active material layer - first positive electrode active material layer by changing the stacking order of the first and second positive electrode active material layers. The first positive electrode active material layer has a content of 12.6 mg / cm³. 2 The loading level of the second positive electrode active material layer is 7.4 mg / cm². 2 The loading level. Additionally, the total mixture density of the first positive electrode active material layer and the second positive electrode active material layer is 3 g / cc.

[0135] Evaluation Example: Single Cell Performance Evaluation In the following text, Table 1 below shows the evaluation voltages in the evaluation examples.

[0136] Table 1:

[0137] (1) Measurement of initial charge / discharge capacity and efficiency The rechargeable lithium battery cells of Example 1 and Comparative Examples 1 to 6 were charged at 25°C at a constant current rate of 0.2C to the upper limit voltage shown in Table 1, and discharged at a constant current rate of 0.2C to the cutoff voltage shown in Table 1 for initial charge / discharge to measure the initial charge / discharge capacity, which was used to calculate the initial charge and discharge efficiency according to Equation 1 below, and the results are shown in Table 2 below.

[0138] Equation 1: Initial charge and discharge efficiency [%] = [Discharge capacity in the first cycle / Charge capacity in the first cycle] × 100 (2) Average voltage measurement The average voltage of the rechargeable lithium battery cells of Example 1 and Comparative Examples 1 to 6 was measured when the SOC (state of charge) was 50% during the initial discharge, as shown in Table 2 below.

[0139] (3) Cycle life characteristics After initial charging and discharging, the rechargeable lithium battery cells of Example 1 and Comparative Examples 1 to 6 were charged and discharged at a rate of 1.0C for 50 cycles or more within the voltage range shown in Table 1. The ratio of the discharge capacity of the 50th cycle to the initial discharge capacity was then calculated according to Equation 2 below, and the cycle life is shown in Table 2 below.

[0140] Equation 2: Cycle life [%] = [Discharge capacity at 50th cycle / Discharge capacity at 1st cycle] × 100 (4) Ratio performance After initial charging and discharging at a rate of 0.2C, the rechargeable lithium-ion battery cells of Example 1 and Comparative Examples 1 to 6 were then charged and discharged at a rate of 1.0C. The ratio of the discharge capacity at 1.0C to the discharge capacity at 0.2C was calculated according to Equation 3 below, and this ratio is presented as the rate performance in Table 2 below.

[0141] Equation 3: Rate performance [%] = [Discharge capacity at 1.0C rate / Discharge capacity at 0.2C rate] × 100 Table 2:

[0142] in conclusion Referring to Table 2, in the case of a rechargeable lithium-ion battery cell including the positive electrode of Example 1, compared with a rechargeable lithium-ion battery cell including the positive electrode of Comparative Example 5, the initial charge and discharge efficiency, cycle life, and rate performance are improved. The positive electrode of Example 1 has a bilayer structure, in which a first positive electrode active material layer comprising a first positive electrode active material containing a lithium iron phosphate compound is stacked as the lower layer, and a second positive electrode active material layer comprising a second positive electrode active material containing a lithium nickel composite oxide and a third positive electrode active material containing a lithium manganese oxide is stacked as the upper layer. The positive electrode of Comparative Example 5 comprises a single positive electrode active material layer prepared by mixing the first, second, and third positive electrode active materials. Therefore, by employing a bilayer structure instead of simple mixing, battery performance is improved.

[0143] On the other hand, compared with the rechargeable lithium battery cell according to Example 1, which includes a double-layer structure of a positive electrode having a first positive electrode active material layer as the lower layer and a second positive electrode active material layer as the upper layer containing a second positive electrode active material and a third positive electrode active material, the rechargeable lithium battery according to Comparative Example 6, which includes a double-layer structure of a positive electrode having a first positive electrode active material layer as the upper layer and a second positive electrode active material layer as the lower layer, exhibits significantly degraded initial charge and discharge efficiency, cycle life, and rate performance, especially significantly degraded rate performance. Therefore, by employing a double-layer structure, particularly by placing lithium nickel composite oxides and lithium manganese oxides, which exhibit high capacity at high voltages, in the upper layer where the electrochemical reaction is most active, while placing lithium iron phosphate compounds, which exhibit capacity at relatively low voltages, in the lower layer, the rate performance and cycle life characteristics of the battery can be improved.

[0144] While this disclosure has been described in conjunction with what are now considered to be exemplary embodiments, it will be understood that the disclosure is not limited to the disclosed exemplary embodiments, but rather is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0145] Description of reference numerals in the attached figures: 1: Positive electrode current collector 2: First positive electrode active material layer 3: Second positive electrode active material layer 4: Positive electrode 100: Rechargeable lithium battery 10: Positive electrode 11: Positive electrode lead connector 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead connector 22: Negative electrode terminal 30: Diaphragm 40: Electrode assembly 50: Casing 60: Sealing component 70: Electrode connector 71: Positive electrode connector 72: Negative electrode connector.

Claims

1. A positive electrode for a rechargeable lithium battery, the positive electrode comprising: Positive electrode current collector; A first positive electrode active material layer is provided on the positive electrode current collector, and includes a first positive electrode active material comprising a lithium iron phosphate compound. as well as The second positive electrode active material layer is on the first positive electrode active material layer and includes a second positive electrode active material comprising a lithium nickel composite oxide and a third positive electrode active material comprising a lithium manganese oxide.

2. The positive electrode according to claim 1, wherein, The lithium iron phosphate compound is represented by one of chemical formulas 1 and 2: Chemical Formula 1: Li a1 Fe (1-x1) M 1 x1 PO4 In chemical formula 1, 0.9 ≤ a1 ≤ 1.5, 0 ≤ x1 ≤ 0.4, and M 1 Including at least one of Al, Ca, Ce, Cr, Cu, La, Mg, Mn, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, and Zr. Chemical formula 2: Li a2 Mn x2 Fe (1-x2-y2) M 2 y2 PO4 In chemical formula 2, 0.9 ≤ a² ≤ 1.5, 0.1 ≤ x² ≤ 0.9, 0 ≤ y² < 0.9, and M 2 It includes at least one of Al, Ca, Ce, Cr, Cu, La, Mg, Mo, Nb, Ni, Sn, Sr, Ti, V, W, Y, Zn, and Zr.

3. The positive electrode according to claim 1, wherein: The first positive electrode active material includes one of the first particles, the second particles, and a mixture thereof. The first particle includes secondary particles formed by the aggregation of multiple primary particles, and The second particle is in the form of a single particle.

4. The positive electrode according to claim 3, wherein: The average particle size D of the secondary particles of the first particle 50 Within the range of 5μm to 20μm, The average particle size D of the primary particles forming the secondary particles 50 Within the range of 0.1 μm to 2 μm, and The average particle size D of the individual particles of the second particle 50 Within the range of 0.5μm to 5μm.

5. The positive electrode according to claim 3, wherein, Based on 100 wt% of the first positive electrode active material, the amount of the first particles is in the range of 20 wt% to 100 wt%; and The amount of the second particle is in the range of 0 wt% to 80 wt%.

6. The positive electrode according to claim 3, wherein, The first positive electrode active material further includes at least one of the following: A carbon coating formed on the surface of the secondary particles of the first particle; A carbon coating formed on the surface of the primary particle that forms the secondary particle of the first particle; as well as A carbon coating is formed on the surface of the individual particles of the second particle.

7. The positive electrode according to claim 6, wherein: The carbon coating is included in an amount ranging from 0.1 wt% to 3.9 wt% based on 100 wt% of the first particles, and The carbon coating is included in an amount ranging from 0.1 wt% to 3.9 wt% based on 100 wt% of the second particles.

8. The positive electrode according to claim 1, wherein, The lithium-nickel composite oxide in the second positive electrode active material is represented by chemical formula 3: Chemical formula 3: Li a3 Ni x3 M 3 y3 M 4 z3 O 2-b3 X b3 Among them, in Chemical Formula 3, 0.9 ≤ a3 ≤ 1.2, 0.3 ≤ x3 < 1, 0 < y3 ≤ 0.7, 0 ≤ z3 ≤ 0.7, 0.9 ≤ x3 + y3 + z3 ≤ 1.1 and 0 ≤ b3 ≤ 0.1, M 3 and M 4 each independently includes one or more of Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X includes one or more of F, P and S.

9. The positive electrode according to claim 1, wherein, Based on 100 mol% of total metals excluding lithium, the lithium-nickel composite oxide in the second positive electrode active material includes nickel in an amount of greater than or equal to 80 mol%.

10. The positive electrode according to claim 1, wherein, The second positive electrode active material comprises materials having an average particle size D in the range of 9 μm to 20 μm. 50 Large particles and an average particle size D in the range of 1 μm to 8 μm. 50 At least one of the small particles.

11. The positive electrode according to claim 10, wherein: The second positive electrode active material includes both the large particles and the small particles, and The large particles and the small particles are mixed in a weight ratio ranging from 20:80 to 95:

5.

12. The positive electrode according to claim 1, wherein, The lithium manganese oxide is represented by chemical formula 6: Chemical formula 6: Li a6 Mn x6 M 8 y6 O 4-b6 X b6 In chemical formula 6, 0.9 ≤ a6 ≤ 1.8, 1.7 ≤ x6 ≤ 2, 0 ≤ y6 ≤ 0.3, 1.9 ≤ x6 + y6 ≤ 2.1 and 0 ≤ b6 ≤ 0.1, M 8 It includes one or more of Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X includes one or more of F, P, and S.

13. The positive electrode according to claim 1, wherein: The third positive electrode active material includes secondary particles formed by the aggregation of multiple primary particles, single particles, or mixtures thereof. The average particle size D of the secondary particles 50 Within the range of 5μm to 15μm, and The average particle size D of the individual particles 50 Within the range of 0.1 μm to 10 μm.

14. The positive electrode according to claim 1, wherein, The weight ratio of the second positive electrode active material to the third positive electrode active material in the second positive electrode active material layer is in the range of 10:90 to 90:

10.

15. The positive electrode according to claim 1, wherein: In the total amount of the first positive electrode active material layer and the second positive electrode active material layer, based on the total amount of the first positive electrode active material, the second positive electrode active material and the third positive electrode active material of 100wt%, the first positive electrode active material is included in an amount ranging from 10wt% to 70wt%, the second positive electrode active material is included in an amount ranging from 10wt% to 50wt%, and the third positive electrode active material is included in an amount ranging from 20wt% to 80wt%.

16. The positive electrode according to claim 1, wherein, Based on 100 mol% of total metals excluding lithium, the manganese content in the total amount of the first positive electrode active material layer and the second positive electrode active material layer is in the range of 30 mol% to 70 mol%.

17. The positive electrode according to claim 1, wherein: The first positive electrode active material layer further includes at least one of a first binder and a first conductive material, and The second positive electrode active material layer further includes at least one of a second binder and a second conductive material.

18. The positive electrode according to claim 1, wherein: The loading level of the first positive electrode active material layer is 5 mg / cm³. 2 Up to 25 mg / cm 2 Within the range, and The loading level of the second positive electrode active material layer is 5 mg / cm². 2 Up to 25 mg / cm 2 Within the range.

19. The positive electrode according to claim 1, wherein, The total mixture density of the first positive electrode active material layer and the second positive electrode active material layer is in the range of 2.0 g / cc to 4.0 g / cc.

20. A rechargeable lithium battery, said rechargeable lithium battery comprising: The positive electrode according to any one of claims 1 to 19, negative electrode, and Electrolytes.

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