Positive electrode and rechargeable lithium battery including same

Abstract

A disclosed example includes a positive electrode including: a current collector; a positive electrode active material layer on the current collector and including a positive electrode active material and a conductive material; and a conductive layer located inside the positive electrode active material layer as a separate layer and including carbon nanotubes, in which an amount of a conductive material is about 0.01 wt% to about 0.5 wt% based on 100 wt% of the positive electrode active material layer. Examples also include a positive electrode that can maintain a high energy density while maintaining a low total resistance of the electrode plate by reducing the content of the conductive material, and a rechargeable lithium battery including the positive electrode.

Description

Technical Field

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

[0002] Portable information devices (such as, for example, cellular phones, laptop computers, smart phones, etc.) or electric vehicles generally use rechargeable lithium batteries having a high energy density and being easy to carry as a driving power source. Recently, research has been actively conducted to use rechargeable lithium batteries having a high energy density as a driving power source or a power storage source for, for example, hybrid vehicles or electric vehicles.

[0003] In such a rechargeable lithium battery, it is advantageous to reduce the resistance of the electrode plate included in the rechargeable lithium battery. However, in order to reduce the resistance of the electrode plate, the conductivity of the electrode plate should be increased by adding a conductive material, and when the content of the conductive material increases, a reduction in energy density may occur. Therefore, it is advantageous to maintain a low resistance of the electrode plate while reducing the content of the conductive material. Summary of the Invention

[0004] Some example embodiments provide a positive electrode and a rechargeable lithium battery including the positive electrode, the positive electrode maintaining a high energy density while reducing the content of the conductive material and maintaining a low total resistance of the electrode plate.

[0005] In some example embodiments, the positive electrode includes: a current collector; a positive electrode active material layer located on the current collector and including a positive electrode active material and a conductive material; and a conductive layer located inside the positive electrode active material layer as a separate layer and including carbon nanotubes; wherein, based on 100 wt% of the total positive electrode active material layer, the content of the conductive material is about 0.01 wt% to about 0.5 wt%.

[0006] In some example embodiments, the rechargeable lithium battery includes the positive electrode; a negative electrode; and an electrolyte.

[0007] The positive electrode and the rechargeable lithium battery including the positive electrode according to some example embodiments can maintain a high energy density while reducing the content of the conductive material and maintaining a low total resistance of the electrode plate. Brief Description of the Drawings

[0008] Figures 1 to 4 is a cross-sectional view schematically showing a rechargeable lithium battery according to some example embodiments. Detailed Description

[0009] In the following, exemplary embodiments will be described in detail so that those of ordinary skill in the art can easily implement them. However, the present disclosure can be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0010] The terms used herein are for the purpose of describing only the exemplary embodiments and are not intended to limit the present disclosure. Unless the context clearly dictates otherwise, singular expressions include plural expressions.

[0011] As used herein, "a combination thereof" refers to a mixture of components, a laminate, a composite, a copolymer, an alloy, a blend, a reaction product, and the like.

[0012] Here, it should be understood that terms such as "including", "comprising", or "having" are intended to indicate the presence of the embodied features, quantities, steps, elements, or combinations thereof, but do not preclude the presence or addition of one or more other features, quantities, steps, elements, or combinations thereof.

[0013] In the drawings, for clarity, the thicknesses of layers, films, panels, regions, etc. are exaggerated, and like reference numerals throughout the specification denote like elements. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element, or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" another element, no intervening elements are present.

[0014] In addition, a "layer" here includes not only a shape formed on the entire surface when viewed in plan view, but also a shape formed on a partial surface.

[0015] The average particle diameter can be measured by methods well known to those skilled in the art (e.g., by a particle size analyzer, or by a transmission electron microscope image or a scanning electron microscope image). Alternatively, the average particle diameter value can be obtained by the following steps: measuring using dynamic light scattering; performing data analysis; counting the number of particles for each particle size range; and calculating therefrom. Unless otherwise defined, the average particle diameter can mean the diameter (D 50 ) of the particles having a cumulative volume of 50 volume% in the particle size distribution. As used herein, when no other definition is provided, the average particle diameter refers to the diameter (D 50 ) of the particles having a cumulative volume of 50 volume% in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in a scanning electron microscope image.

[0016] Here, "or" is not to be construed in an exclusive sense. For example, "A or B" is construed to include A, B, A + B, etc.

[0017] "Metal" is interpreted to include the concepts of common metals, transition metals, and metalloids (semi-metals).

[0018] Soft carbon refers to carbon materials that can be graphitized and are materials that can be easily graphitized by heat treatment at a high temperature (e.g., about 2800 °C). Hard carbon is a carbon material that cannot be graphitized or is slightly graphitized by heat treatment.

[0019] When the terms "about" or "substantially" are used in conjunction with a numerical value in this specification, it means that the relevant numerical value includes a tolerance of ±10% around the stated numerical value. When a range is specified, the range includes all values therebetween, such as increments of 0.1%.

[0020] Positive electrode In some example embodiments, the positive electrode includes a current collector, a positive electrode active material layer located on the current collector and including a positive electrode active material and a conductive material, and a conductive layer located inside the positive electrode active material layer as a separate layer and including carbon nanotubes, wherein, based on 100 wt% of the total positive electrode active material layer, the content of the conductive material is about 0.01 wt% to about 0.5 wt%. Such a positive electrode can achieve a high energy density by reducing the content of the conductive material while maintaining a low resistance by increasing the electron conductivity.

[0021] Current collector The current collector according to some example embodiments is not particularly limited as long as the current collector is conductive and does not cause a chemical change in the rechargeable lithium battery, but examples may include aluminum (Al), stainless steel (SUS), indium (In), magnesium (Mg), titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), germanium (Ge), lithium (Li), or a combination thereof, and may include, for example, aluminum (Al). Herein, the shape of the current collector may be plate-like or sheet-like.

[0022] The thickness of the current collector according to some example embodiments may be about 1 μm to about 50 μm, for example, about 2 μm to about 40 μm, about 5 μm to about 30 μm, or about 10 μm to about 20 μm, to ensure current collection in the depth direction of the electrode. Additionally, the tensile strength of the current collector may be about 200 N / mm 2 to about 1000 N / mm 2 for example, about 200 N / mm 2 to about 800 N / mm 2 about 200 N / mm 2 to about 600 N / mm 2 or about 200 N / mm 2 to about 300 N / mm 2When a current collector including a thickness and a tensile strength within the above ranges is included, the strength of the current collector can be improved, such that a positive electrode having a high density can be manufactured, which increases the capacity of the positive electrode.

[0023] Positive electrode active material layer The positive electrode active material layer according to some example embodiments includes a positive electrode active material.

[0024] The positive electrode active material according to some example embodiments may be or include a compound capable of intercalating and deintercalating lithium (lithiated intercalation compound). For example, one or more types of composite oxides of a metal including at least one of cobalt, manganese, nickel, and combinations thereof with lithium may be used.

[0025] The composite oxide may be or include a lithium transition metal composite oxide, and examples thereof may include at least one of lithium nickel-based oxides, lithium cobalt-based oxides, lithium manganese-based oxides, lithium iron phosphate-based compounds, cobalt-free lithium nickel manganese-based oxides, lithium-rich manganese composite oxides, and combinations thereof.

[0026] As an example, a compound represented by any one or more of the following chemical formulas may be used. Li a A 1- b X b O 2-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Mn 2-b X b O 4-c D c (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.05); Li a Ni 1-b-c Co b X c O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni 1-b-c Mn b X c O 2-α D α (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.5, 0 ≤ c ≤ 0.5, 0 < α < 2); Li a Ni b Co c L 1 d G eO2 (0.90 ≤ a ≤ 1.8, 0 ≤ b ≤ 0.9, 0 ≤ c ≤ 0.5, 0 ≤ d ≤ 0.5, 0 ≤ e ≤ 0.1); Li a NiG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a CoG b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-b G b O2 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn2G b O4 (0.90 ≤ a ≤ 1.8, 0.001 ≤ b ≤ 0.1); Li a Mn 1-g G g PO4 (0.90 ≤ a ≤ 1.8, 0 ≤ g ≤ 0.5); Li (3-f) Fe2(PO4)3 (0 ≤ f ≤ 2); and Li a FePO4 (0.90 ≤ a ≤ 1.8).

[0027] In the above chemical formulas, A is or includes Ni, Co, Mn, or a combination thereof; X is or includes Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, rare earth elements, or a combination thereof; D is or includes O, F, S, P, or a combination thereof; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, V, or a combination thereof; and L 1 is or includes Mn, Al, or a combination thereof.

[0028] The positive electrode active material may include, for example, at least one of a lithium nickel-based oxide represented by Chemical Formula 1, a lithium cobalt-based oxide represented by Chemical Formula 2, a lithium iron phosphate-based compound represented by Chemical Formula 3, a cobalt-free lithium nickel manganese-based oxide represented by Chemical Formula 4, and combinations thereof.

[0029] [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 In Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, M 1 and M 2Each independently is one or more elements including Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements including F, P, and S.

[0030] In Chemical Formula 1, 0.6 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.4 and 0 ≤ z1 ≤ 0.4, or 0.8 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.2 and 0 ≤ z1 ≤ 0.2.

[0031] [Chemical Formula 2] Li a2 Co x2 M 3 y2 O 2-b2 X b2 In Chemical Formula 2, 0.9 ≤ a2 ≤ 1.8, 0.7 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.3, 0.9 ≤ x2 + y2 ≤ 1.1 and 0 ≤ b2 ≤ 0.1, M 3 is one or more elements including Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements including F, P, and S.

[0032] [Chemical Formula 3] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 In Chemical Formula 3, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.4 and 0 ≤ b3 ≤ 0.1, M 4 is one or more elements including Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements including F, P, and S.

[0033] [Chemical Formula 4] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 In Chemical Formula 4, 0.9 ≤ a4 ≤ 1.8, 0.8 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1 and 0 ≤ b4 ≤ 0.1, M 5 is one or more elements including Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements including F, P, and S.

[0034] As an example, the positive electrode active material may be or include a high-nickel type positive electrode active material. Based on 100 mol% of the metals other than lithium in the lithium transition metal composite oxide, the nickel content of the high-nickel type positive electrode active material is greater than or equal to about 80 mol%, greater than or equal to about 85 mol%, greater than or equal to about 90 mol%, greater than or equal to about 91 mol%, greater than or equal to about 94 mol%, or greater than or equal to 99 mol%. Such a high-nickel type positive electrode active material can achieve high capacity and can be applied to high-capacity, high-density rechargeable lithium batteries.

[0035] The positive electrode active material may be formed of particles or include particles, and the average particle diameter (D 50 ) may be, for example, about 1 μm to about 30 μm. As an example, the positive electrode active material may be or include large particles with an average particle diameter (D 50 ) of about 9 μm to about 25 μm, or may be or include small particles with an average particle diameter (D 50 ) of about 0.5 μm to about 8 μm, and the large particles and small particles are appropriately mixed. The average particle diameter (D 50 ) of the large particles may be, for example, about 10 μm to about 20 μm, or about 12 μm to about 18 μm, and the average particle diameter (D 50 ) of the small particles may be, for example, about 1 μm to about 6 μm, or about 2 μm to about 5 μm. When the positive electrode active material includes a mixture of large particles and small particles, based on 100 wt% of the total large particles and small particles, the content of the large particles may be about 60 wt% to about 95 wt%, or about 70 wt% to about 90 wt%, and the content of the small particles may be about 5 wt% to about 40 wt%, or about 10 wt% to about 30 wt%. When the large particles and small particles are mixed within the above content ranges, the cycle life characteristics can be improved while improving the capacity and energy density. The average particle diameter (D 50 ) refers to the diameter of the particle with a cumulative volume of 50% by volume in the particle size distribution obtained by randomly measuring the sizes (diameter or major axis length) of about 20 particles in the scanning electron microscope image of the positive electrode active material.

[0036] Based on the total weight of the positive electrode active material layer, the content of the positive electrode active material can be about 90 wt% to about 99.8 wt%, or about 95 wt% to about 99 wt%.

[0037] The positive electrode active material layer according to some exemplary embodiments may include a conductive material and may also include a binder.

[0038] A conductive material is included to provide electrode conductivity, and any conductive material can be used as the conductive material unless the conductive material causes a chemical change in the positive electrode. Examples of the conductive material may include at least one of the following: carbonaceous materials such as graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including metal powders or metal fibers such as copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives; and mixtures thereof.

[0039] Based on the total weight of the positive electrode active material layer, the content of the conductive material can be about 0.01 wt% to about 0.5 wt%, for example, about 0.01 wt% to about 0.4 wt%, about 0.01 wt% to about 0.3 wt%, about 0.01 wt% to about 0.2 wt%, or about 0.01 wt% to about 0.1 wt%. Compared with a common positive electrode, a positive electrode including the conductive material in any range of the above content ranges can achieve a high energy density by reducing the content of the conductive material, while maintaining a low resistance by increasing the electron conductivity through the conductive layer described below.

[0040] The binder improves the binding properties between the positive electrode active material particles and between the positive electrode active material particles and the current collector. Examples of the binder may include at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, (meth)acrylated styrene-butadiene rubber, epoxy resin, (meth)acrylic resin, polyester resin, and nylon, but are not limited thereto.

[0041] Based on the total weight of the positive electrode active material layer, the content of the binder can be about 0.1 wt% to about 5 wt%, for example, about 0.1 wt% to about 4.5 wt%, about 0.1 wt% to about 4 wt%, about 0.1 wt% to about 3.5 wt%, about 0.1 wt% to about 3 wt%, or about 0.5 wt% to about 2.5 wt%.

[0042] The positive electrode according to some example embodiments can achieve a high energy density, and the density of the positive electrode active material layer can be from about 3.5 g / cc to about 4.2 g / cc, for example, from about 3.5 g / cc to about 4.1 g / cc, from about 3.5 g / cc to about 4.0 g / cc, from about 3.5 g / cc to about 3.9 g / cc, or from about 3.5 to about 3.8 g / cc. When the density of the positive electrode active material layer is within any of the above ranges, a positive electrode with a desired, improved, or favorable discharge capacity can be achieved. The positive electrode has a high energy density and a high capacity, and reduces or prevents challenges such as insufficient electrolyte impregnation, deterioration of high-rate performance, crushing of active material particles, or rupture of the current collector that becomes difficult to withstand during the process.

[0043] The thickness of the positive electrode active material layer according to some example embodiments can be from about 20 μm to about 400 μm, for example, from about 30 μm to about 300 μm, from about 50 μm to about 200 μm, or from about 80 μm to about 100 μm. Accordingly, the ratio of the thickness of the current collector to the thickness of the positive electrode active material layer can be from about 1:5 to about 1:30, for example, from about 1:6 to about 1:25, from about 1:7 to about 1:20, from about 1:8 to about 1:15, or from about 1:9 to about 1:12. When the thickness range of the positive electrode active material layer and the thickness ratio between the current collector and the positive electrode active material layer are within any of the above ranges, a positive electrode with a high density can be manufactured, which has the advantages of increasing the capacity of the positive electrode and other advantages.

[0044] Conductive layer The conductive layer included in the positive electrode according to some example embodiments can be located inside the positive electrode active material layer as a separate layer and can include carbon nanotubes.

[0045] The positive electrode can have a structure including, for example, a current collector, a lower positive electrode active material layer located on the current collector and including a positive electrode active material and a first conductive material, a conductive layer located on the lower positive electrode active material layer and including carbon nanotubes, and an upper positive electrode active material layer located on the conductive layer and including a positive electrode active material and a second conductive material. In an example, the positive electrode can have a structure in which the current collector, the lower positive electrode active material layer, the conductive layer, and the upper positive electrode active material layer are stacked (e.g., sequentially stacked). In another example, the positive electrode can have a structure in which the conductive layer is interposed between the positive electrode active material layers. The conductive layer and the positive electrode active material layer can be further stacked (e.g., sequentially further stacked) on the upper positive electrode active material layer to introduce multiple conductive layers.

[0046] Generally, a conductive layer is disposed between the current collector and the positive electrode active material layer or on the surface of the positive electrode active material layer, or carbon nanotubes are dispersed inside the positive electrode active material layer. However, these methods have difficulties in ensuring the adhesion of the conductive layer, so the conductive layer separates in the battery. In addition, when these methods are applied to a positive electrode active material layer with high conductivity or a high-power battery, a high-density battery, or a high-capacity battery, thermal stability cannot generally be fully ensured.

[0047] In contrast to the above, the positive electrode according to some exemplary embodiments provides advantages including ensuring the adhesion and thermal stability of the conductive layer by introducing the conductive layer inside the positive electrode active material layer, maintaining a low resistance by improving electron conductivity, and achieving a high energy density by reducing the content of the conductive material.

[0048] The lower positive electrode active material layer according to the disclosed exemplary embodiments may have a thickness of about 50 μm to about 100 μm, for example, a thickness of about 55 μm to about 100 μm, about 60 μm to about 100 μm, about 65 μm to about 95 μm, or about 70 μm to about 90 μm. In addition, the upper positive electrode active material layer may have a thickness of about 50 μm to about 100 μm, for example, a thickness of about 55 μm to about 100 μm, about 60 μm to about 100 μm, about 65 μm to about 95 μm, or about 70 μm to about 90 μm. When the lower positive electrode active material layer and the upper positive electrode active material layer satisfy any of the above thickness ranges, not only can a high capacity be achieved, but also the problem of deterioration of the positive electrode active material particles due to repeated charging and discharging can be reduced or effectively prevented, thereby improving the cycle life characteristics of the battery.

[0049] The conductive layer may be substantially parallel to the current collector inside the positive electrode active material layer and may be composed of one or more layers or include one or more layers, such as, for example, from about 1 layer to about 10 layers, from about 1 layer to about 5 layers, or from about 1 layer to 3 layers. Since the conductive layer is composed of about 1 layer to about 3 layers, the content of the conductive material can be reduced to improve electron conductivity, thereby maintaining a low resistance and achieving a high energy density, while having the advantage of being easily set in terms of the process.

[0050] The conductive layer may be composed of or include a plurality of layers, wherein each conductive layer may have a thickness of about 0.1 μm to about 3.0 μm, for example, a thickness of about 0.2 μm to about 3.0 μm, about 0.3 μm to about 2.5 μm, about 0.4 μm to about 2.0 μm, or about 0.5 μm to about 1.5 μm. When the conductive layer satisfies any of the above thickness ranges, electrons or ions have a sufficiently short moving distance in the conductive layer, exhibiting uniform battery performance and improving output characteristics.

[0051] The thickness ratio of the conductive layer to the positive electrode active material layer can be from about 0.0003 to about 0.15, for example, from about 0.0005 to about 0.1, from about 0.001 to about 0.05, or from about 0.005 to about 0.02. When the thickness ratio of the conductive layer to the positive electrode active material layer satisfies the above range, not only can the energy density of the positive electrode be increased, but also the resistance can be effectively reduced.

[0052] When a plurality of conductive layers are formed inside the positive electrode active material layer, the distance between the conductive layers can be from about 5 μm to about 100 μm, for example, from about 10 μm to about 80 μm, or from about 30 μm to about 50 μm. When the distance between the conductive layers satisfies the above range, such a distance is advantageous in terms of processability, and can improve the energy density while reducing the resistance of the positive electrode.

[0053] Carbon nanotubes refer to carbon allotropes in which one carbon atom is bonded to another carbon atom in a hexagonal or other polyhedral honeycomb pattern to form sheets, and form tubes with nanoscale diameters. Carbon nanotubes can be more easily dispersed in water than other conductive materials (such as carbon black, etc.) to form a thin coating layer with a uniformly coated surface, so as to ensure the desired, improved or favorable conductivity with a small amount of carbon nanotubes.

[0054] Carbon nanotubes can include single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, or two or more of them. Carbon nanotubes can have a length of about 50 nm to about 500 nm, for example, a length of about 50 nm to about 400 nm, a length of about 50 nm to about 300 nm, or a length of about 100 nm to about 250 nm. In addition, carbon nanotubes can have a diameter of about 0.1 nm to about 50 nm, for example, a diameter of about 0.2 nm to about 40 nm, a diameter of about 0.5 nm to about 30 nm, or a diameter of about 1 nm to about 20 nm. For example, when the carbon nanotubes are single-walled carbon nanotubes, the carbon nanotubes can have a diameter of about 0.4 nm to about 2 nm, and when the carbon nanotubes are multi-walled carbon nanotubes, the carbon nanotubes can have a diameter of about 10 nm to about 20 nm.

[0055] Based on the total 100 wt% of the conductive layer, the content of carbon nanotubes can be greater than or equal to about 90 wt%, for example, it can be, for example, from about 90 wt% to about 99.9 wt%, for example, from about 95 wt% to about 99 wt%, or from about 96 wt% to about 98 wt%. When including carbon nanotubes in any range of the above content range in the conductive layer, the carbon nanotubes can be substantially dispersed and can improve the battery performance.

[0056] The conductive layer may further include a conductive material. For example, the conductive material included in the conductive layer, the first conductive material included in the lower positive electrode active material layer, and the second conductive material included in the upper positive electrode active material layer may be the same as or different from each other. In an example, they may be the same as each other. Each or one or more of the first conductive material, the second conductive material, and the conductive material in the conductive layer may include a carbon material, a metal material, a metal carbide, a metal nitride, a metal silicide, or a combination thereof. The carbon material may be or include carbon black, graphite, carbon fiber, or a combination thereof. Carbon black may include, for example, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or a combination thereof, and graphite may include natural graphite, artificial graphite, or a combination thereof. The metal material may be or include at least one of metal particles (such as nickel) and metal fibers. The metal carbide may include, for example, WC, B4C, ZrC, NbC, MoC, TiC, TaC, or a combination thereof. The metal nitride may include TiN, ZrN, TaN, or a combination thereof, and the metal silicide may include, for example, WSi2, MoSi2, or a combination thereof.

[0057] Based on the total weight of the conductive layer, the content of the conductive material may be from about 0.1 wt% to about 10 wt%, for example, from about 0.5 wt% to about 8 wt%, from about 1.0 wt% to about 6 wt%, from about 1.5 wt% to about 5 wt%, or from about 2 wt% to about 4 wt%. When the conductive material is included in the conductive layer within any of the above content ranges, the conductive layer may exhibit desired, improved, or favorable conductivity.

[0058] The conductive layer may further include a binder.

[0059] The binder may serve to adhere the substances in the conductive layer to each other and to adhere the conductive layer between the active material layers. The binder may be a non-water-soluble binder, a water-soluble binder, or a combination thereof.

[0060] The non-water-soluble binder may include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, a polymer containing ethylene oxide, an ethylene propylene copolymer, polystyrene, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0061] Examples of the water-soluble binder may include rubber-based binders or polymer resin binders. The water-soluble binder may be or include an acrylic binder. The rubber-based binder may be or include styrene-butadiene rubber (SBR), acrylated styrene-butadiene rubber, acrylonitrile-butadiene rubber (ABR), acrylic rubber, butyl rubber, fluororubber, and combinations thereof. The polymer resin binder may be or include polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin polymer, polyphosphazene, polyacrylamide, poly(N-vinylformamide), polyacrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, and combinations thereof.

[0062] When using a water-soluble binder as the binder, a cellulose-based compound capable of imparting adhesiveness may also be included. As the 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.

[0063] Based on the total weight of the conductive layer, the content of the binder may be from about 0.1 wt% to about 10 wt%, for example, from about 0.5 wt% to about 8 wt%, from about 1.0 wt% to about 6 wt%, from about 1.5 wt% to about 5 wt%, or from about 2 wt% to about 4 wt%. When the binder is included in any of the above content ranges in the conductive layer, the conductive layer may exhibit desired, improved, or favorable adhesiveness while maintaining desired, improved, or favorable properties.

[0064] The positive electrode according to some example embodiments may have a positive electrode resistance of less than or equal to about 8.50 Ω cm, or the interfacial resistance between the positive electrode active material layer and the current collector may be less than or equal to about 0.045 Ω cm 2 。

[0065] Rechargeable lithium battery In some example embodiments, the rechargeable lithium battery includes a positive electrode, a negative electrode, and an electrolyte. Here, the electrolyte may be or include a liquid electrolyte or a solid electrolyte.

[0066] For example, in some example embodiments, the rechargeable lithium battery may include the aforementioned positive electrode, negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte solution. As another example, the all-solid-state rechargeable battery may include the aforementioned positive electrode, negative electrode, and a solid electrolyte layer between the positive electrode and the negative electrode.

[0067] In the following, a rechargeable lithium battery using an electrolyte solution will be described as an example.

[0068] Rechargeable lithium batteries can be classified according to their shape as cylindrical, prismatic, pouch-shaped, coin-type, etc. Figures 1 to 4 is a schematic diagram showing a rechargeable lithium battery according to some example embodiments, where Figure 1 is a cylindrical battery, Figure 2 is a prismatic battery, Figure 3 and Figure 4 is a pouch-shaped battery. Referring to 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 disposed between a positive electrode 10 and a negative electrode 20, and the electrode assembly 40 is accommodated in the housing 50. The positive electrode 10, the negative electrode 20, and the separator 30 may be impregnated with an electrolyte solution (not shown). As Figure 1 shown in Figure 2 , the rechargeable lithium battery 100 may include a sealing member 60 that seals the housing 50. Additionally, in Figure 3 and Figure 4 shown in

[0069] , the rechargeable lithium battery 100 includes electrode tabs 70 (i.e., a positive electrode tab 71 and a negative electrode tab 72) that serve as a circuit path for leading out the current formed in the electrode assembly 40 to the outside.

[0069] Rechargeable lithium batteries according to some example embodiments can be recharged at high voltages or can be suitable for driving at high voltages. For example, the charging voltage of the rechargeable lithium battery can be greater than or equal to about 4.45 V, and can be about 4.45 V to about 4.7 V, about 4.45 V to about 4.6 V, or about 4.45 V to about 4.55 V. A rechargeable lithium battery applying a positive electrode according to some example embodiments can maintain a low resistance and a high energy density of the entire electrode plate, thereby achieving a high capacity and improved cycle life characteristics.

[0070] Negative electrode The negative electrode may include a current collector and a negative electrode active material layer on the current collector. The negative electrode active material layer may include a negative electrode active material and may also include a binder, a conductive material, or a combination thereof.

[0071] Negative electrode active material The negative electrode active material may include at least one of a material that reversibly intercalates / deintercalates lithium ions, lithium metal, a lithium metal alloy, a material capable of doping / dedoping lithium, and a transition metal oxide.

[0072] Materials that can reversibly embed / desorb lithium ions can include, for example, at least one of crystalline carbon, amorphous carbon, and combinations thereof as carbonaceous negative electrode active materials. The crystalline carbon can be natural graphite or artificial graphite that is amorphous or in the form of flakes, platelets, spheres, or fibers. The amorphous carbon can be or include at least one of soft carbon, hard carbon, mesophase pitch carbonization products, calcined coke, etc.

[0073] Lithium metal alloys include alloys of lithium with metals including at least one of Na, K, Rb, Cs, Fr, Be, Mg, Ca, Sr, Si, Sb, Pb, In, Zn, Ba, Ra, Ge, Al, and Sn.

[0074] Materials capable of doping / dedoping lithium can be or include Si-based negative electrode active materials or Sn-based negative electrode active materials. The Si-based negative electrode active materials can include silicon, silicon-carbon composites, SiO x (0 < x ≤ 2), Si-Q alloys (where Q is an element including at least one of alkali metals, alkaline earth metals, group 13 elements, group 14 elements (excluding Si), group 15 elements, group 16 elements, transition metals, rare earth elements, and combinations thereof, such as 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, Oy, 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, or combinations thereof). The Sn-based negative electrode active materials can be or include Sn, SnO2, Sn alloys, or combinations thereof.

[0075] 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, from about 0.5 μm to about 20 μm. According to some example embodiments, the silicon-carbon composite can be formed of silicon particles and amorphous carbon coated on the surface of the silicon particles or include 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 silicon primary particles are aggregated and an amorphous carbon coating layer (shell) on the surface of the secondary particles. The amorphous carbon can also be present between the silicon primary particles. For example, the silicon primary particles can be coated with amorphous carbon. The secondary particles can be dispersed in the amorphous carbon matrix.

[0076] The silicon-carbon composite may also include crystalline carbon. For example, the silicon-carbon composite may include a core containing crystalline carbon and silicon particles, and an amorphous carbon coating layer on the surface of the core. The crystalline carbon may be or include artificial graphite, natural graphite, or a combination thereof. The amorphous carbon may include at least one of soft carbon, hard carbon, mesophase pitch carbonization products, and calcined coke.

[0077] When the silicon-carbon composite includes silicon and amorphous carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt%, and the content of amorphous carbon may be about 50 wt% to about 90 wt%. In addition, when the composite includes silicon, amorphous carbon, and crystalline carbon, based on 100 wt% of the silicon-carbon composite, the content of silicon may be about 10 wt% to about 50 wt%, the content of crystalline carbon may be about 10 wt% to about 70 wt%, and the content of amorphous carbon may be about 20 wt% to about 40 wt%.

[0078] In addition, the thickness of the amorphous carbon coating layer may be about 5 nm to about 100 nm. The average particle diameter (D 50 ) of the silicon particles (silicon primary particles) may be about 10 nm to about 1 μm, or about 10 nm to about 200 nm. The silicon particles may exist as individual silicon, in the form of a silicon alloy, or in an oxidized form. The oxidized form of silicon may be represented by SiO x (0 < x ≤ 2). At this time, the atomic content ratio of Si:O representing the degree of oxidation may be about 99:1 to about 33:67. 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% by volume in the particle distribution.

[0079] The Si-based negative electrode active material or the Sn-based negative electrode active material may be mixed with the carbon-based negative electrode active material. When the Si-based negative electrode active material or the Sn-based negative electrode active material is mixed and used with the carbon-based negative electrode active material, the mixing ratio may be a weight ratio of about 1:99 to about 90:10.

[0080] Binder The binder is used to sufficiently adhere the negative electrode active material particles to each other and is also used to adhere the negative electrode active material to the current collector. The binder may be or include a non-aqueous binder, an aqueous binder, a dry binder, or a combination thereof.

[0081] The non-aqueous binder may at least include polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene-propylene copolymer, polystyrene, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamideimide, polyimide, or a combination thereof.

[0082] The aqueous binder may include at least styrene-butadiene rubber, (meth)acrylic acid esterified styrene-butadiene rubber, (meth)acrylonitrile-butadiene rubber, (meth)acrylic rubber, butyl rubber, fluororubber, polyethylene oxide, polyvinylpyrrolidone, epichlorohydrin polymer, polyphosphazene, poly(meth)acrylonitrile, ethylene propylene diene copolymer, polyvinylpyridine, chlorosulfonated polyethylene, latex, polyester resin, (meth)acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, or a combination thereof.

[0083] When using the aqueous binder as the negative electrode binder, it may further include a cellulose compound capable of imparting viscosity. As the cellulose 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 Na, K, or Li.

[0084] The dry binder may be a polymer material capable of becoming fibers, and may be or include, for example, polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyethylene oxide, or a combination thereof.

[0085] Conductive material A conductive material is included to provide electrode conductivity, and any conductive material may be used as the conductive material unless the conductive material causes a chemical change. Examples of the conductive material include at least one of the following: carbonaceous materials such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanofiber, carbon nanotube, etc.; metallic materials including metal powder or metal fiber of at least one of copper, nickel, aluminum, silver, etc.; conductive polymers including at least polyphenylene derivatives; and mixtures thereof.

[0086] Based on 100 wt% of the negative electrode active material layer, the content of the negative electrode active material may be about 95 wt% to about 99.5 wt%, and based on 100 wt% of the negative electrode active material layer, the content of the binder may be about 0.5 wt% to about 5 wt%. For example, the negative electrode active material layer may include about 90 wt% to about 99 wt% of the negative electrode active material, about 0.5 wt% to about 5 wt% of the binder, and about 0.5 wt% to about 5 wt% of the conductive material.

[0087] Current collector The negative electrode current collector may include, for example, at least one of indium (In), copper (Cu), magnesium (Mg), stainless steel, titanium (Ti), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), aluminum (Al), germanium (Ge), lithium (Li), and their alloys, and may be in the form of at least a foil, sheet, or foam. The thickness of the negative electrode current collector may be, for example, about 1 μm to about 20 μm, about 5 μm to about 15 μm, or about 7 μm to about 10 μm.

[0088] Electrolyte For example, the electrolyte for a rechargeable lithium battery may be or include an electrolytic solution that may contain a non-aqueous organic solvent and a lithium salt.

[0089] The non-aqueous organic solvent serves as a medium for transporting ions participating in the battery electrochemical reaction. The non-aqueous organic solvent may be or include a carbonate solvent, an ester solvent, an ether solvent, a ketone solvent, or an alcohol solvent, an aprotic solvent, or a combination thereof.

[0090] The carbonate solvent 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), butylene carbonate (BC), etc. The ester solvent may include at least one of methyl acetate, ethyl acetate, n-propyl acetate, dimethyl acetate, methyl propionate, ethyl propionate, decanolide, mevalonolactone, valerolactone, caprolactone, etc. The ether solvent 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, the ketone solvent may at least include cyclohexanone, etc. The alcohol solvent may include at least one of ethanol, isopropanol, etc., and the aprotic solvent may include: nitriles such as R-CN (where R is a C2 to C20 straight-chain, branched-chain, or cyclic hydrocarbon group and may include double bonds, aromatic rings, or ether groups, etc.); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane, 1,4-dioxolane, etc.; sulfolane; etc.

[0091] The non-aqueous organic solvent may be used alone or as a mixture of two or more types, and when using a mixture of two or more types, the mixing ratio may be appropriately adjusted according to the desired battery performance.

[0092] When using a carbonate solvent, a cyclic carbonate and a chain carbonate may be mixed and used, and the cyclic carbonate and the chain carbonate may be mixed in a volume ratio of about 1:1 to about 1:9.

[0093] The non-aqueous organic solvent may also include aromatic hydrocarbon organic solvents. For example, the carbonate solvent and the aromatic hydrocarbon organic solvent may be mixed and used in a volume ratio of about 1:1 to about 30:1.

[0094] The electrolyte may also include at least one of vinylene carbonate, vinylene carbonate and ethylene carbonate compounds, for example, to improve the battery cycle life.

[0095] Examples of the ethylene carbonate compound may include at least one of fluoroethylene carbonate, difluoroethylene carbonate, chloroethylene carbonate, dichloroethylene carbonate, bromoethylene carbonate, dibromoethylene carbonate, nitroethylene carbonate and cyanoethylene carbonate.

[0096] The lithium salt dissolved in the organic solvent supplies lithium ions in the battery, enabling the rechargeable lithium battery to operate basically and improving the transport of lithium ions between the positive electrode and the negative electrode. Examples of the lithium salt 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 SO2) (where x and y are integers from 1 to 20), lithium trifluoromethanesulfonate, lithium tetrafluoroethanesulfonate, lithium difluoro bis(oxalate) phosphate (LiDFBOP), lithium difluoro bis(oxalate) borate (LiDFBOB) and lithium bis(oxalate) borate (LiBOB), etc.

[0097] The concentration of the lithium salt may be in the range of about 0.1 M to about 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has appropriate ionic conductivity and viscosity, so that desired, improved or favorable performance can be achieved and lithium ions can move effectively.

[0098] Separator According to the type of the rechargeable lithium battery, a separator may be present between the positive electrode and the negative electrode. The separator may include at least one of polyethylene, polypropylene, polyvinylidene fluoride and their multi-layer films of two or more layers, such as a mixed multi-layer film including at least one of a polyethylene / polypropylene two-layer separator, a polyethylene / polypropylene / polyethylene three-layer separator, a polypropylene / polyethylene / polypropylene three-layer separator, etc.

[0099] The separator may include a porous substrate and a coating layer on one or both surfaces of the porous substrate, the coating layer including an organic material, an inorganic material, or a combination thereof.

[0100] The porous substrate may be a polymer film formed of any one polymer, the polymer including at least one of polyolefins (such as polyethylene and polypropylene), polyesters (such as polyethylene terephthalate and polybutylene terephthalate), polyacetals, polyamides, polyimides, polycarbonates, polyether ketones, polyarylether ketones, polyether ketones, polyetherimides, polyamideimides, polybenzimidazoles, polyethersulfones, polyphenylene ethers, cycloolefin copolymers, polyphenylene sulfides, polyethylene naphthalate, glass fibers, Teflon, and polytetrafluoroethylene, or a copolymer or mixture of two or more of them.

[0101] The porous substrate may have a thickness of about 1 μm to about 40 μm, for example, a thickness of 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.

[0102] The organic material may include a (meth)acrylic copolymer containing a first structural unit and a second structural unit, the first structural unit being derived from (meth)acrylamide, and the second structural unit including at least one of a structural unit derived from (meth)acrylic acid or (meth)acrylate and a structural unit derived from (meth)acrylamidesulfonic acid or a salt thereof.

[0103] The inorganic material may include inorganic particles, the inorganic particles including 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, but not limited thereto. The average particle size (D 50 ) of the inorganic particles may be about 1 nm to about 2000 nm, for example, about 100 nm to about 1000 nm, or about 100 nm to about 700 nm.

[0104] The organic material and the inorganic material may be mixed in one coating layer, or a coating layer including the organic material and a coating layer including the inorganic material may be stacked.

[0105] The thickness of the coating layer may be about 0.5 μm to about 20 μm, for example, about 1 μm to about 10 μm, or about 1 μm to about 5 μm.

[0106] Examples and comparative examples of the present disclosure are described below. However, the following examples are only examples of the present disclosure, and the present disclosure is not limited to the following examples.

[0107] Example 1 (1) Fabrication of the positive electrode 98.1 wt% of LiNi 0.8 Mn 0.2 O2, 1.5 wt% of polyvinylidene fluoride as a binder, and 0.4 wt% of carbon black as a conductive material were mixed in a solvent of N-methylpyrrolidone to prepare a positive electrode active material slurry.

[0108] A conductive layer slurry was prepared by mixing 90 wt% of carbon nanotubes with a length of 150 nm and a diameter of 10 nm, 5 wt% of carbon black, and 5 wt% of an acrylic binder.

[0109] The prepared positive electrode active material slurry was coated on an aluminum current collector and dried at 120 °C for 10 minutes. Subsequently, the conductive layer slurry was coated on the positive electrode active material layer by using micro gravure and dried. Then, the positive electrode active material slurry was coated on the conductive layer again and dried, such that the conductive layer was sandwiched between two positive electrode active material layers. The dried electrode plate was pressed to fabricate a positive electrode plate. In the cross-section of the pressed positive electrode, the lower positive electrode active material layer had a thickness of about 80 μm, the upper positive electrode active material layer had a thickness of about 80 μm, and the conductive layer had a thickness of about 1 μm.

[0110] Example 2 The positive electrode was fabricated in substantially the same manner as in Example 1, except that the conductive layer consisted of two layers by repeating the coating and drying of the conductive layer slurry twice on the positive electrode active material layer, wherein the content of the conductive material in the positive electrode active material slurry was changed to 0.2 wt%, and the content of the positive electrode active material was changed to 98.3 wt%. In other words, the positive electrode of Example 2 was formed by sequentially stacking a current collector, a positive electrode active material layer, a conductive layer, a positive electrode active material layer, a conductive layer, and a positive electrode active material layer. In the cross-section of the finally pressed positive electrode, the positive electrode active material layer had a total thickness of about 160 μm, and the conductive layer had a thickness of about 1 μm.

[0111] Example 3 The positive electrode is manufactured in substantially the same manner as in Example 1, except that the conductive layer is composed of three layers by repeating the coating and drying of the conductive layer paste three times on the positive electrode active material layer. Herein, the content of the conductive material in the positive electrode active material paste is changed to 0.15 wt%, and the content of the positive electrode active material is changed to 98.35 wt%. In other words, the positive electrode of Example 3 is formed by sequentially stacking a current collector, a positive electrode active material layer, a conductive layer, a positive electrode active material layer, a conductive layer, a positive electrode active material layer, a conductive layer, and a positive electrode active material layer. In the cross-section of the finally pressed positive electrode, the positive electrode active material layer has a total thickness of about 160 μm, and the conductive layer has a thickness of about 1 μm.

[0112] Comparative Example 1 The positive electrode is manufactured in substantially the same manner as in Example 1, except that the step of coating the conductive layer paste on the positive electrode active material layer and then drying is not performed, and the content of the conductive material in the positive electrode active material paste is changed to 1.2 wt%, and the content of the positive electrode active material is changed to 97.3 wt%. In the cross-section of the finally pressed positive electrode, the positive electrode active material layer has a thickness of about 160 μm.

[0113] Evaluation Example 1: Resistance evaluation The contents of the conductive materials in the positive electrode active material layers according to Examples 1 to 3 and Comparative Example 1 are shown in Table 1, and the active material resistances and interface resistances of the positive electrodes according to Examples 1 to 3 and Comparative Example 1 are measured by using an electrode resistance meter (in-plane, HIOKI E.E. CORPORATION), and the results are shown in Table 2. Herein, the active material refers to the active material layer, the active material resistance refers to the volume resistance, and the interface resistance refers to the contact resistance between the positive electrode active material layer and the current collector.

[0114] Table 1

[0115] (Table 2)

[0116] Referring to Table 1 and Table 2, compared with Comparative Example 1 in which the conductive layer is not included inside the positive electrode active material layer, Examples 1 to 3 in which the conductive layer is included inside the positive electrode active material layer exhibit low active material resistances and interface resistances even when the content of the conductive material in the positive electrode active material layer is reduced. In addition, compared with Examples 1 and 2, Example 3 in which three conductive layers are included inside the positive electrode active material layer exhibits low active material resistances and interface resistances.

[0117] This low interfacial resistance is understood to facilitate the insertion and extraction of lithium ions during charging and discharging, and significantly maintain the charge / discharge efficiency (Coulombic efficiency), thereby significantly increasing the battery capacity. In other words, Examples 1 to 3 (particularly Example 3 in which three conductive layers are included in the positive electrode active material layer) that include a conductive layer inside the positive electrode active material layer reduce the content of the conductive material in the positive electrode plate, thereby maintaining the energy density and at the same time maintaining the overall low resistance of the electrode plate.

[0118] Evaluation Example 2: Energy density evaluation After inserting a polytetrafluoroethylene separator between each of the positive electrodes according to Examples 1 to 3 and Comparative Example 1 and the graphite negative electrode, an electrolyte solution prepared by dissolving 1M LiPF6 in a mixed solvent of ethylene carbonate and dimethyl carbonate with a volume ratio of 3:7 was injected therein to fabricate a battery. The battery was charged and discharged at a rate of 0.2C / 0.2C in a voltage range of 3.0V to 4.45V at 25°C to calculate the energy density. The energy density was obtained according to the calculation formula of {(average driving voltage (V) × capacity (Ah)) / battery volume (m 3 ), where the capacity was calculated as the product of the positive electrode volume (cc) and the discharge capacity (mAh / cc).

[0119] (Table 3)

[0120] Referring to Table 3, Examples 1 to 3 achieved an energy density equivalent to or equal to that of Comparative Example 1. Therefore, the batteries of Examples 1 to 3 improved the energy density by reducing the content of the conductive material in the positive electrode active material layer, and at the same time effectively reduced the resistance of the electrode plate by introducing such a conductive layer.

[0121] Although the present invention has been described in connection with what are presently considered to be practical example embodiments, it will be understood that the invention is not limited to the disclosed example embodiments. On the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

[0122] <Description of Symbols> 100: Rechargeable lithium battery 10: Positive electrode 11: Positive electrode lead tab 12: Positive electrode terminal 20: Negative electrode 21: Negative electrode lead tab 22: Negative electrode terminal 30: Separator 40: Electrode assembly 50: Housing 60: Sealing member 70: Electrode terminal 71: Positive electrode terminal 72: Negative electrode terminal.

Claims

1. A positive electrode, the positive electrode comprising: A current collector; A positive electrode active material layer located on the current collector and comprising a positive electrode active material and a conductive material; And A conductive layer located inside the positive electrode active material layer and comprising carbon nanotubes; Wherein, based on 100 wt% of the positive electrode active material layer, the content of the conductive material is 0.01 wt% to 0.5 wt%.

2. The positive electrode according to claim 1, wherein The positive electrode comprises two or more positive electrode active material layers, and The conductive layer is sandwiched between two positive electrode active material layers.

3. The positive electrode according to claim 1, wherein The positive electrode comprises a single conductive layer or multiple conductive layers.

4. The positive electrode according to claim 1, wherein The positive electrode comprises 1 to 10 conductive layers.

5. The positive electrode according to claim 3, wherein The positive electrode comprises 1 to 3 conductive layers.

6. The positive electrode according to claim 1, wherein The conductive layer has a thickness of 0.1 μm to 3.0 μm.

7. The positive electrode according to claim 1, wherein The positive electrode active material layer has a thickness of 20 μm to 400 μm.

8. The positive electrode according to claim 1, wherein The ratio of the thickness of the conductive layer to the thickness of the positive electrode active material layer is 0.0003 to 0.

15.

9. The positive electrode according to claim 1, wherein The conductive layer comprises multiple conductive layers within the positive electrode active material layer, at least one of the multiple conductive layers has a thickness of 0.1 μm to 3.0 μm, and the gap between adjacent conductive layers is 5 μm to 100 μm.

10. The positive electrode according to claim 1, wherein Based on 100 wt% of the total conductive layer, the content of the carbon nanotubes is 90 wt% to 99.9 wt%.

11. The positive electrode according to claim 1, wherein The length of the carbon nanotubes is 50 nm to 500 nm, and The diameter of the carbon nanotubes is 0.1 nm to 50 nm.

12. The positive electrode according to claim 1, wherein The conductive material comprises one of carbon-based materials, metal-based materials, conductive polymers, and combinations thereof.

13. The positive electrode according to claim 12, wherein The conductive material comprises one of graphite, carbon black, acetylene black, Ketjen black, and combinations thereof.

14. The positive electrode according to claim 1, wherein The positive electrode active material comprises a lithium transition metal composite oxide, and the lithium transition metal composite oxide is represented by one of Chemical Formula 1, Chemical Formula 2, Chemical Formula 3, and Chemical Formula 4: [Chemical Formula 1] Li a1 Ni x1 M 1 y1 M 2 z1 O 2-b1 X b1 Among them, in Chemical Formula 1, 0.9 ≤ a1 ≤ 1.8, 0.3 ≤ x1 ≤ 1, 0 ≤ y1 ≤ 0.7, 0 ≤ z1 ≤ 0.7, 0.9 ≤ x1 + y1 + z1 ≤ 1.1 and 0 ≤ b1 ≤ 0.1, M 1 and M 2 each independently represents one or more elements including Al, B, Ba, Ca, Ce, Co, Cr, Cu, Fe, Mg, Mn, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X represents one or more elements including F, P, and S; [Chemical Formula 2] Li a2 Co x2 M 3 y2 O 2-b2 X b2 Among them, in Chemical Formula 2, 0.9 ≤ a2 ≤ 1.8, 0.7 ≤ x2 ≤ 1, 0 ≤ y2 ≤ 0.3, 0.9 ≤ x2 + y2 ≤ 1.1 and 0 ≤ b2 ≤ 0.1, M 3 is one or more elements including Al, B, Ba, Ca, Ce, Cr, Cu, Fe, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn and Zr, and X is one or more elements including F, P and S; [Chemical Formula 3] Li a3 Fe x3 M 4 y3 PO 4-b3 X b3 Among them, in Chemical Formula 3, 0.9 ≤ a3 ≤ 1.8, 0.6 ≤ x3 ≤ 1, 0 ≤ y3 ≤ 0.4, and 0 ≤ b3 ≤ 0.1, M 4 is one or more elements including Al, B, Ba, Ca, Ce, Co, Cr, Cu, Mg, Mn, Mo, Ni, Se, Si, Sn, Sr, Ti, V, W, Y, Zn, and Zr, and X is one or more elements including F, P, and S; and [Chemical Formula 4] Li a4 Ni x4 Mn y4 M 5 z4 O 2-b4 X b4 Among them, in Chemical Formula 4, 0.9 ≤ a4 ≤ 1.8, 0.8 ≤ x4 < 1, 0 < y4 ≤ 0.2, 0 ≤ z4 ≤ 0.2, 0.9 ≤ x4 + y4 + z4 ≤ 1.1 and 0 ≤ b4 ≤ 0.1, M 5 is one or more elements including Al, B, Ba, Ca, Ce, Cr, Fe, Mg, Mo, Nb, Si, Sn, Sr, Ti, V, W, and Zr, and X is one or more elements including F, P, and S.

15. The positive electrode according to claim 1, wherein, The positive electrode active material layer comprises: A lower positive electrode active material layer located on the current collector and comprising the positive electrode active material and a first conductive material, wherein the conductive layer is located on the lower positive electrode active material layer; and The upper positive electrode active material layer is located on the conductive layer and includes the positive electrode active material and a second conductive material.

16. The positive electrode according to claim 15, wherein the first conductive material and the second conductive material are the same material.

17. The positive electrode according to claim 15, wherein the thickness of the lower positive electrode active material layer is 50 μm to 100 μm, the thickness of the upper positive electrode active material layer is 50 μm to 100 μm, and the thickness of the conductive layer is 0.1 μm to 3.0 μm.

18. The positive electrode according to claim 1, wherein the positive electrode active material layer has a density of 3.5 g / cc to 4.2 g / cc.

19. The positive electrode according to claim 1, wherein the positive electrode resistance of the positive electrode is less than or equal to 8.50 Ω·cm, and The interfacial resistance between the positive electrode active material layer and the current collector is less than or equal to 0.045 Ω·cm 2 .

20. A rechargeable lithium battery, the rechargeable lithium battery comprising: the positive electrode according to claim 1; a negative electrode; and an electrolyte.

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