Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: a cathode comprising a cathode active material layer including a single particle-type cathode active material, a cathode conductive material, a cathode binder and a cathode dispersant; an anode; and an electrolyte, wherein: the anode comprises a first anode active material layer and a second anode active material layer formed on the first anode active material layer, each of the first anode active material and the second anode active material independently including natural graphite, artificial graphite or a combination thereof; the ratio of the amount of a first anode binder to the amount of a second anode binder is 1.5-3.0; the difference in porosity between the cathode and the anode is 4.2-9.8%; and the FBR of the cathode, which is associated with the amounts and true density values of each of the binder and dispersant and the average particle diameter of the cathode active material, is 30-180.

Description

Lithium secondary battery Cross-citation with related applications This application claims the benefit of priority from Korean Patent Application No. 10-2023-0191346, filed December 26, 2023, the entire contents of which are incorporated herein by reference. Technical field The present invention relates to a lithium secondary battery. Due to the rapid increase in fossil fuel use, the demand for alternative or clean energy is increasing, and the field being most actively researched as part of this is power generation and storage using electrochemical reactions. Currently, a representative example of an electrochemical device that utilizes such electrochemical energy is a secondary battery, and its application area is expanding more and more. Recently, as the demand for portable devices such as portable computers, portable phones, and cameras increases and the technology development, the demand for secondary batteries as an energy source is rapidly increasing, and among such secondary batteries, lithium secondary batteries are in the spotlight due to their advantages of high operating voltage and superior energy density. Lithium secondary batteries are generally manufactured by forming an electrode assembly by interposing a separator between a positive electrode including a positive electrode active material made of a transition metal oxide containing lithium and an anode including an anode active material capable of storing lithium ions, inserting the electrode assembly into a battery case, injecting a non-aqueous electrolyte that serves as a medium for transferring lithium ions, and then sealing the electrode assembly. The non-aqueous electrolyte is generally composed of a lithium salt and an organic solvent capable of dissolving the lithium salt. Recently, as the demand for high energy density secondary batteries, such as batteries for electric vehicles, has increased, development of high voltage secondary batteries that operate at high voltage is actively underway. Meanwhile, demand for lithium secondary batteries with excellent rapid charging performance is increasing in order to shorten the charging time, which is the biggest obstacle to the commercialization of electric vehicles. However, the rapid charging batteries developed to date have not shown satisfactory performance in terms of life characteristics or energy density. Therefore, there is a need to develop a lithium secondary battery that improves the rapid charging performance of the battery while minimizing the degradation of life characteristics or energy density. The present invention is to solve the above problems, and includes a positive electrode in which the average particle diameter of a positive electrode active material, the contents of a positive electrode binder and a positive electrode dispersant, and the true density of the positive electrode binder and the positive electrode dispersant satisfy specific conditions, and a negative electrode in which the composition of a negative electrode active material and the distribution of a negative electrode binder are controlled, and by controlling the difference in porosity between the positive electrode and the negative electrode within a specific range, it is intended to provide a lithium secondary battery with improved rapid charging performance, life characteristics, and energy density characteristics. [1] The present invention comprises a cathode comprising a cathode active material layer including a single particle type cathode active material, a cathode conductive material, a cathode binder and a cathode dispersant; a cathode; And an electrolyte, wherein the negative electrode is formed on a negative current collector and includes a first negative electrode active material layer including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder, wherein the first negative electrode active material and the second negative electrode active material each independently include natural graphite, artificial graphite, or a combination thereof, and a ratio of the content of the first negative electrode binder to the content of the second negative electrode binder is 1.5 to 3.0, a difference in porosity between the positive electrode and the negative electrode is 4.2% to 9.8%, and the positive electrode has an FBR of 30 to 180 defined by the following Equation 1. [Formula 1] FBR = [(Rb × TDb) + (Rd × TDd)] × A 2 In the above equation 1, Rb is a dimensionless number of the weight % of the positive electrode binder with respect to the total weight of the positive electrode active material layer, Rd is a dimensionless number of the weight % of the positive electrode dispersant with respect to the total weight of the positive electrode active material layer, TDb is a dimensionless number of the true density (g / cc) of the positive electrode binder, TDd is a dimensionless number of the true density (g / cc) of the positive electrode dispersant, and A is the average particle diameter (D) of the single-particle positive electrode active material. 50 , ㎛) is a dimensionless number. [2] The present invention provides a lithium secondary battery, wherein, in the above [1], the single particle type positive electrode active material includes a lithium nickel-based oxide containing Ni at 70 mol% or less based on the total molar number of metals other than lithium. [3] The present invention provides a lithium secondary battery, wherein, in the above [1] or [2], the single particle type positive electrode active material includes a lithium nickel-based oxide represented by the following [chemical formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2 In the above [chemical formula 1], M 1 It contains at least one element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.7, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2 이다. [4] The present invention, in at least one of the above [1] to [3], the single particle type positive electrode active material has an average particle diameter (D 50 ) is 3.5 ㎛ to 7.8 ㎛, a lithium secondary battery is provided. [5] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [4], the single particle type positive electrode active material includes 1 to 30 nodules. [6] The present invention, in at least one of the above [1] to [5], the nodule has an average particle diameter (D mean ) is 0.8 ㎛ to 4.0 ㎛, a lithium secondary battery is provided. [7] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [6], the positive electrode active material layer contains 0.5 wt% to 2 wt% of the positive electrode binder. [8] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [7], the porosity of the positive electrode is 20% to 25%. [9] The present invention provides a lithium secondary battery, wherein in at least one of the above [1] to [8], the first negative electrode active material and the second negative electrode active material are each independently made of natural graphite, artificial graphite, or a combination thereof.

[0010] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to [9], the first negative electrode active material contains more than 50 wt% of the natural graphite, and the second negative electrode active material contains less than 50 wt% of the natural graphite.

[0011] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0010] , the ratio of the content of the first negative electrode binder to the content of the second negative electrode binder is 1.6 to 2.4.

[0012] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0011] , the first negative electrode active material layer contains 1.5 to 3.0 wt% of a first negative electrode binder.

[0013] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0012] , the negative electrode has a QBR value of 1.1 to 1.28 defined by the following equation 2. [Formula 2] QBR = Bs / Bf The above Bs is an average value of the binder content in the negative electrode active material layer surface area from the outermost surface of the second negative electrode active material layer to within 15% of the total thickness of the negative electrode active material layer, and the above Bf is an average value of the binder content in the negative electrode active material layer bottom area from the first negative electrode active material layer interface where it meets the negative electrode current collector to within 15% of the total thickness of the negative electrode active material layer.

[0014] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0013] , the porosity of the negative electrode is 25% to 32%.

[0015] The present invention provides a lithium secondary battery, wherein, in at least one of the above [1] to

[0014] , the difference in porosity between the positive electrode and the negative electrode is 6% to 8%. The present invention comprises a positive electrode having a positive electrode active material having an average particle diameter, a positive electrode binder and a positive electrode dispersant content, and a positive electrode binder and a positive electrode dispersant density satisfying specific conditions, and a negative electrode including a multilayer negative electrode active material layer comprising a first negative electrode active material layer (lower layer) and a second negative electrode active material layer (upper layer) formed on the first negative electrode active material layer, each of which has a different composition of negative electrode active material and a different distribution of negative electrode binder, wherein a difference in porosity between the positive electrode and the negative electrode satisfies a specific range. By including a positive electrode satisfying the above specific conditions, the initial capacity, initial resistance and life characteristics of a lithium secondary battery are improved, while the proportion of natural graphite included in an upper layer of a negative electrode active material layer is lowered and the proportion of artificial graphite is increased, thereby improving the initial resistance and rapid charge performance, and by increasing the proportion of natural graphite included in a lower layer of a negative electrode active material layer, controlling the negative electrode binder proportion, and appropriately controlling the difference in porosity between the positive and negative electrodes, a lithium secondary battery having excellent rapid charge performance and excellent electrochemical performance such as life characteristics can be implemented. Hereinafter, the present invention will be described in more detail. The terms or words used in this specification and claims should not be interpreted as limited to their usual or dictionary meanings, but should be interpreted as having meanings and concepts consistent with the technical idea of ​​the present invention, based on the principle that the inventor can appropriately define the concept of the term in order to explain his or her own invention in the best manner. The terminology used herein is for the purpose of describing embodiments only and is not intended to limit the invention. In this specification, the singular also includes the plural unless specifically stated otherwise in the phrase. When it is said in this specification that a part includes a certain component, this does not mean that other components are excluded, but rather that other components may be included, unless otherwise specifically stated. In the present invention, the “single-particle type positive electrode active material” means a positive electrode active material particle composed of 30 or fewer sub-particles. The sub-particle unit constituting the single-particle type positive electrode active material is referred to as a “nodule.” The single-particle type positive electrode active material includes a single particle composed of one single nodule and a pseudo-single particle which is a composite of 30 or fewer nodules. The above “nodule” refers to a sub-particle unit body constituting a single particle and a quasi-single particle, and the nodule may be a single crystal lacking a crystalline grain boundary, or a polycrystal in which no grain boundary exists in appearance when observed with a scanning electron microscope (SEM) at a magnification of 5,000 to 20,000 times. In the present invention, “secondary particle” means a particle formed by agglomeration of more than 30 sub-particles. In order to distinguish it from the sub-particles constituting the single-particle type positive electrode active material particles, each lower particle unit constituting the secondary particle is called a “primary particle.” The expression “particle” used in the present invention may include any one or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle. In this specification, the "average particle diameter (D) of nodules or primary particles mean )" means the arithmetic mean of the measured values ​​of the particle diameters of nodules or primary particles observed in SEM images obtained by analyzing with a scanning electron microscope. In this specification, "average particle diameter (D 50)" means the particle size corresponding to 50% of the volume accumulation amount of the volume accumulation particle size distribution of the target powder, and can be measured using the laser diffraction method. For example, the target powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W, and then a volume accumulation particle size distribution graph is obtained, and then the particle size corresponding to 50% of the volume accumulation amount is measured. In this specification, “porosity (%)” can be calculated as 1 - (electrode density / electrode true density). In this specification, "true density" can be measured using a Gas Pycnometer. A Gas Pycnometer is a device that can measure density by placing a measurement sample of known weight in a sample chamber, injecting helium or nitrogen gas, and finding out the volume occupied by the sample excluding pores. Specifically, the volume of the sample is measured from the pressure change between the sample chamber into which the sample is placed and a reference chamber of known volume, and then the density value of the sample can be calculated by applying the ideal gas state equation (PV=nRT). In this specification, “QBR” can be calculated from SEM images obtained by analysis with a scanning electron microscope. A lithium secondary battery according to the present invention comprises at least one of the configurations disclosed below, and may comprise any combination between technically possible configurations among the configurations below. The present inventors have conducted repeated studies to develop a lithium secondary battery having excellent rapid charging performance and minimal degradation of life characteristics, and as a result, the present inventors have developed a multilayered anode including an anode current collector; a first anode active material layer formed on the anode current collector; and a second anode active material layer formed on the first anode active material layer, wherein the anode has a content and density of a cathode binder and a cathode dispersant, and an average particle diameter (D) of a cathode active material. 50 ) The present invention has been completed by finding out that a lithium secondary battery including a positive electrode satisfying specific conditions and a porosity difference between the positive and negative electrodes satisfying a specific range can have excellent rapid charging performance while suppressing degradation of cell performance during long-term cycling. Hereinafter, the present invention will be described in detail. Lithium secondary battery A lithium secondary battery according to the present invention comprises: a cathode including a cathode active material layer including a single particle type cathode active material, a cathode conductive material, a cathode binder, and a cathode dispersant; an anode; And an electrolyte, wherein the negative electrode is formed on a negative current collector and includes a first negative electrode active material layer including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder, wherein the first negative electrode active material and the second negative electrode active material each independently include natural graphite, artificial graphite, or a combination thereof, and a ratio of the content of the first negative electrode binder to the content of the second negative electrode binder is 1.5 to 3.0, a difference in porosity between the positive electrode and the negative electrode is 4.2% to 9.8%, and the positive electrode satisfies an FBR defined by the following Equation 1 of 30 to 180. [Formula 1] FBR = [(Rb × TDb) + (Rd × TDd)] × A 2 In the above formula 1, Rb is the weight % of the positive electrode binder with respect to the total weight of the positive electrode active material layer, Rd is the weight % of the positive electrode dispersant with respect to the total weight of the positive electrode active material layer, TDb is the true density of the positive electrode binder (g / cc), TDd is the true density of the positive electrode dispersant (g / cc), and A is the average particle diameter (D) of the positive electrode active material. 50 , ㎛). According to the research of the present inventors, in the case of a lithium secondary battery including a multilayer structured negative electrode including a positive electrode having a FBR value satisfying a specific range, a first negative electrode active material layer formed on a negative electrode current collector, and a second negative electrode active material layer formed on the first negative electrode active material layer, it was found that the cell resistance and rapid charge performance were excellent, while the degradation of cell performance was suppressed during long-term cycling. Meanwhile, the difference in porosity between the anode and cathode is 4.2% to 9.8%. Specifically, the difference in porosity between the positive and negative electrodes may be 4.2% or more, 4.5% or more, 4.8% or more, 5% or more, 5.2% or more, 5.5% or more, 5.8% or more, 6% or more, 6.2% or more, 6.5% or more, 6.8% or more, 7% or more, 7.2% or more, 7.5% or more, 7.8% or more, 8% or more, 9.8% or less, 9.5% or less, 9.2% or less, 9% or less, 8.8% or less, 8.5% or less, 8.2% or less, 8% or less, 7.8% or less, 7.5% or less, 7.2% or less, 7% or less, 6.8% or less, 6.5% or less, 6.2% or less, or 6% or less. For example, the porosity difference between the positive and negative electrodes is 4.2% to 9.8%, 4.5% to 9.5%, 5% to 9%, 5.5% to 8.5%, or 6% to 8%. When the porosity difference between the positive and negative electrodes satisfies the above range, the battery volume according to the electrode thickness is optimized, so that the energy density can be improved, and when lithium ions move from the positive electrode to the negative electrode, the diffusion resistance of lithium ions in the positive electrode is reduced and the insertion of lithium ions in the negative electrode is facilitated, so that the rapid charging characteristics can be improved, and in addition, the resistance of the battery is lowered and the structural stability of the negative electrode and the positive electrode can be improved, so that the effects of improving the adhesion of the negative electrode and improving the life characteristics are more excellent. According to the present invention, when the FBR value defined by the above formula 1 satisfies a range of 30 to 180, the ratio of the content of the first negative electrode binder to the content of the second negative electrode binder is 1.5 to 3.0, and the porosity difference between the positive and negative electrodes simultaneously satisfies a range of 4.2 to 9.8%, the effects of shortening the rapid charging time, improving the capacity characteristics, reducing the initial resistance, and improving the life characteristics can be simultaneously implemented. Hereinafter, each component of the lithium secondary battery according to the present invention will be described in more detail. anode The lithium secondary battery according to the present invention may include a positive electrode including a positive electrode active material layer and a positive electrode current collector. Specifically, the positive electrode includes a positive electrode active material layer including a positive electrode active material including single-particle particles, a positive electrode conductive material, a positive electrode binder, and a positive electrode dispersant, and may have an FBR defined by the following Equation 1 of 30 to 180, preferably 35 to 180, and more preferably 40 to 175. [Formula 1] FBR = [(Rb × TDb) + (Rd × TDd)] × A 2 In the above formula 1, Rb is the weight % of the positive electrode binder with respect to the total weight of the positive electrode active material layer, Rd is the weight % of the positive electrode dispersant with respect to the total weight of the positive electrode active material layer, TDb is the true density of the positive electrode binder (g / cc), TDd is the true density of the positive electrode dispersant (g / cc), and A is the average particle diameter (D) of the positive electrode active material. 50 , ㎛). When the above FBR satisfies the scope of the present invention, the effects of improving the initial capacity, initial resistance, and life characteristics of the lithium secondary battery can be obtained. Specifically, when the FBR is less than 30, the energy density and cell stability may be reduced, and when the FBR exceeds 180, the cell resistance may increase, causing problems such as reduced output performance and reduced rapid charging performance. Meanwhile, the positive electrode current collector is not particularly limited as long as it is conductive and does not cause a chemical change in the battery, and for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. may be used. In addition, the positive electrode current collector can typically have a thickness of 3 ㎛ to 500 ㎛, and fine unevenness can be formed on the surface of the current collector to increase the adhesion of the positive electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, a non-woven fabric, etc. The positive electrode active material according to the present invention may include a lithium nickel-based oxide containing Ni in an amount of 70 mol% or less based on the total mole number of metals excluding lithium. Specifically, the positive electrode active material may contain Ni in an amount of 50 mol% to 70 mol%, preferably 55 mol% to 70 mol%, and more preferably 60 mol% to 70 mol%. As described above, when a positive electrode active material having a relatively low Ni content is used, since the contact area with the electrolyte is small, the battery can be stably operated even at a high voltage of 4.35 V or higher to realize a high energy density, and side reactions with the electrolyte are suppressed to reduce gas generation, and rapid charging performance can be improved by suppressing cell performance degradation due to conductive material agglomeration. More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by [chemical formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mn c M 1 d ]O2 In the above [chemical formula 1], M 1M may include at least one doping element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and preferably at least one doping element selected from the group consisting of Al, W, Y, Ba, Ca, Ti, Mg, and Nb. 1 The element may or may not be optionally included in the lithium nickel-based oxide, and when included, may play a role in promoting grain growth or improving structural stability during sintering of the positive electrode. Meanwhile, the above 1+x represents the molar ratio of lithium in the lithium nickel-based oxide, and may be -0.1≤x≤0.1, 0≤x≤0.1, or 0≤x≤0.07. When x satisfies the above range, a stable layered crystal structure can be formed. The above a represents the molar ratio of nickel among the total metals excluding lithium in the lithium nickel-based oxide, and may be 0.5≤a≤0.7, 0.55≤a≤0.7, or 0.55≤a≤0.65. When a satisfies the above range, structural stability can be secured during charge and discharge, thereby suppressing cathode degradation, and realizing high energy density. The above b is the molar ratio of cobalt among all metals excluding lithium in the lithium nickel oxide, 0. <b<0.5, 0.03≤b≤0.4, 0.05≤b≤0.3, 또는 0.08≤b≤0.15일 수 있다. b가 상기 범위를 만족할 경우, 양호한 저항 특성 및 출력 특성을 구현할 수 있고, 상대적으로 망간의 몰 비를 높일 수 있어 구조적 안정성을 개선할 수 있다. The above c is the molar ratio of manganese among all metals except lithium in lithium nickel oxide, 0 <c<0.5, 0.1≤c≤0.45, 0.15≤c≤0.4, 0.2≤c≤0.35, 또는 0.25≤c≤0.35일 수 있다. c가 상기 범위를 만족할 경우, 양극 활물질의 구조 안정성이 우수하게 나타날 수 있다. The above d is M among all metals except lithium in lithium nickel oxide. 1 The molar ratio of elements can be 0≤d≤0.2, 0≤d≤0.1, 0≤d≤0.05, or d=0. M 1 Although the element is not necessarily included as a doping element, if included in an appropriate amount, it can play a role in promoting particle growth during sintering or improving the stability of the crystal structure. Meanwhile, the single particle type positive electrode active material has an average particle diameter (D 50 ) may be 3.0 ㎛ to 7.9 ㎛, preferably 3.5 ㎛ to 7.8 ㎛, and more preferably 3.7 ㎛ to 7.6 ㎛. If the average particle diameter of the positive electrode active material is too small, the processability during electrode manufacturing may deteriorate, the electrolyte impregnation property may deteriorate, and the electrochemical properties may increase, and if the average particle diameter is too large, the resistance may increase and the output characteristics may deteriorate. Meanwhile, it is preferred that the single-particle type positive electrode active material contains 1 to 30 nodules, preferably 1 to 25 nodules, and more preferably 1 to 15 nodules per particle. When the number of nodules constituting the single-particle type positive electrode active material particle exceeds 30, particle breakage increases during electrode manufacturing, and internal cracks occur more due to volume expansion / contraction of the nodules during charge / discharge, which may deteriorate the life characteristics. Meanwhile, the above nodules have an average particle diameter (D mean ) may be 0.8 ㎛ to 4.0 ㎛, preferably 0.8 ㎛ to 3.0 ㎛, and more preferably 1.0 ㎛ to 3.0 ㎛. When the average particle diameter of the nodule satisfies the above range, particle breakage is minimized during electrode manufacture, and an increase in resistance can be suppressed more effectively. Meanwhile, the positive electrode active material layer may further include a positive electrode conductive material, a positive electrode binder, and a positive electrode dispersant in addition to a single particle type positive electrode active material. At this time, the positive electrode conductive material is used to provide conductivity to the electrode, and can be used without special restrictions as long as it does not cause a chemical change in the battery to be formed and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, summer black, carbon fiber, and carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and the like, and one of these may be used alone or a mixture of two or more may be used. The conductive material may be included in an amount of 0.4 wt% to 10 wt%, preferably 0.4 wt% to 7 wt%, and more preferably 0.4 wt% to 5 wt%, relative to the total weight of the positive electrode active material layer. When the content of the challenge material satisfies the above range, the conductivity and capacity of the anode can be excellently implemented. Meanwhile, the positive electrode binder serves to improve the adhesion between positive electrode active material particles and the adhesive strength between the positive electrode active material and the positive electrode current collector. Specific examples thereof include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated-EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and one of these may be used alone or a mixture of two or more thereof may be used. The above positive electrode binder may be included in an amount of 0.5 wt% to 2 wt%, preferably 1 wt% to 2 wt%, and more preferably 1.5 wt% to 2 wt%, based on the total weight of the positive electrode active material layer. When the positive electrode binder content satisfies the above range, the adhesive strength between the current collector and the positive electrode active material layer is high, so that excellent capacity characteristics and life characteristics can be realized even after long-term cycling. Meanwhile, the positive electrode dispersant is intended to improve the dispersibility of lithium nickel-based oxide, conductive material, etc., and examples thereof include, but are not limited to, hydrogenated nitrile-butadiene rubber (H-NBR). The dispersant may be included in an amount of 2 wt% or less, preferably 0.1 to 2 wt%, and more preferably 0.1 to 0.5 wt%, based on the total weight of the positive electrode active material layer. If the dispersant content is too small, the effect of improving dispersibility is minimal, and if it is excessive, it may have a negative effect on battery performance. Meanwhile, the positive electrode may have a porosity of 20% to 25%, 20.5% to 25%, 21% to 25%, or 21% to 23%. When the positive electrode porosity satisfies the above range, the positive electrode thickness can be reduced, thereby improving the energy density by reducing the battery volume when applied to a battery. Meanwhile, the positive electrode can be manufactured according to a conventional positive electrode manufacturing method. For example, the positive electrode can be manufactured by mixing a positive electrode active material, a positive electrode binder, and / or a positive electrode conductive material in a solvent to manufacture a positive electrode slurry, applying the positive electrode slurry onto a positive electrode current collector, and then drying and rolling, or by casting the positive electrode slurry onto a separate support, and then peeling the film from the support and laminating the obtained film onto a positive electrode current collector. At this time, solvents generally used in the relevant technical field can be used as the solvent of the positive electrode slurry, and for example, dimethylsulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, water, etc. can be used alone or in combination of two or more. The amount of the solvent used is sufficient to dissolve or disperse the positive electrode active material, positive electrode conductive material, and positive electrode binder, taking into account the coating thickness and manufacturing yield of the slurry, and to have a viscosity that can exhibit excellent thickness uniformity during subsequent coating for manufacturing the positive electrode. cathode A lithium secondary battery according to the present invention may include an anode including a negative electrode active material, a negative electrode conductive material, and a negative electrode binder. Specifically, the negative electrode is formed on a negative electrode current collector and includes a first negative electrode active material layer including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder, and the first negative electrode active material and the second negative electrode active material may each independently include natural graphite, artificial graphite, or a combination thereof. The above negative electrode current collector is not particularly limited as long as it has high conductivity without causing a chemical change in the battery, and for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., an aluminum-cadmium alloy, etc. can be used. In addition, the negative electrode current collector can typically have a thickness of 3 to 500 ㎛, and, like the positive electrode current collector, fine unevenness can be formed on the surface of the current collector to strengthen the bonding strength of the negative electrode active material. For example, it can be used in various forms such as a film, a sheet, a foil, a net, a porous body, a foam, and a non-woven fabric. The first negative electrode active material and the second negative electrode active material may each independently be made of natural graphite, artificial graphite, or a combination thereof. At this time, the first negative electrode active material may contain the natural graphite in an amount of more than 50 wt%, more than 50 wt% and 100 wt% or less, and preferably 55 wt% to 100 wt%, and the second negative electrode active material may contain the natural graphite in an amount of less than 50 wt%, 0 wt% to 50 wt%, and 0 wt% to 45 wt%. When the above ranges are satisfied, the ratio of natural graphite included in the first negative electrode active material layer is high, and the ratio of artificial graphite included in the second negative electrode active material layer is high, so that the cell resistance is lowered and the initial capacity development rate is increased, thereby improving the energy density. Meanwhile, the first cathode conductive material and the second cathode conductive material may be the same as those described above for the anode. In addition, the first negative electrode binder and the second negative electrode binder serve to improve the adhesion between negative electrode active material particles and the adhesive strength between the negative electrode active material and the negative electrode current collector, and a specific example may be the same as that described above for the positive electrode. Meanwhile, the ratio of the content of the first negative electrode binder to the content of the second negative electrode binder may be 1.5 to 3.0, preferably 1.5 to 2.8, and more preferably 1.6 to 2.4. At this time, the first negative electrode active material layer may contain 1.5 wt% to 3.0 wt% of the first negative electrode binder, preferably 1.5 wt% to 2.8 wt%, and more preferably 1.6 wt% to 2.4 wt%. When the above range is satisfied, the ratio of the first negative electrode binder included in the first negative electrode active material layer in contact with the negative electrode current collector increases, so that the adhesive strength between the negative electrode current collector and the first negative electrode active material layer can be improved, and the structural collapse of the negative electrode active material is suppressed by the binder, so that the life characteristics can be significantly improved. Meanwhile, the cathode according to the present invention may have a QBR (Quantified Binder Ratio) value defined by Equation 2 below of 1.1 to 1.28, preferably 1.1 to 1.26, and more preferably 1.1 to 1.24. [Formula 2] QBR = Bs / Bf The above Bs represents an average value of the binder content in the negative electrode active material layer surface area from the outermost surface of the second negative electrode active material layer to within 15% of the total thickness of the negative electrode active material layer, and Bf represents an average value of the binder content in the negative electrode active material layer bottom area from the interface of the first negative electrode active material layer where it meets the negative electrode current collector to within 15% of the total thickness of the negative electrode active material layer. At this time, the QBR value can be calculated as follows. The cross-section of the negative electrode is fabricated using argon ion milling. Afterwards, the energy dispersive X-ray spectroscopy (EDS) detector of a scanning electron microscope (SEM) is used to map the components within the negative electrode active material layer of the fabricated negative electrode cross-section. From the EDS mapping results, a line profile is extracted in the thickness direction of the negative electrode active material layer, and from the extracted line profile results, the average value (Bs) of the binder content in the surface area of ​​the negative electrode active material layer and the average value (Bf) of the binder content in the bottom area of ​​the negative electrode active material layer are extracted, and the QBR value is calculated using the above Equation 2. The above QBR value is a numerical value that represents the uniformity of distribution of the binder in the thickness direction within the entire negative electrode active material layer through the ratio of the content of the binder contained in the surface area to the content of the binder contained in the bottom area of ​​the entire negative electrode active material layer. When the QBR value satisfies the above range, when the same ratio of negative binder is injected, the negative binder within the negative electrode is appropriately distributed, so that even after long-term cycles, when evaluating the life characteristics, side reactions are suppressed due to uniform charge and discharge, thereby improving the life characteristics. Meanwhile, the negative electrode may have a porosity of 25% to 32%, 25% to 31%, 25.5% to 31%, 27% to 30.5%, or 28% to 30%. When the negative electrode porosity satisfies the above range, lithium movement is smooth, so that the cell resistance characteristics are excellent, and the swelling characteristics are improved by buffering the volume expansion due to continuous degradation of the negative electrode active material through the pores, so that the life characteristics can be improved. As described above, in the lithium secondary battery according to the present invention, the negative electrode active material layer may have a multilayer structure of two or more layers including a first negative electrode active material layer and a second negative electrode active material layer. In this case, when the negative electrode active material layer is a multilayer structure composed of two or more layers, each layer may have different types and / or contents of the negative electrode active material, binder, and / or conductive agent. For example, the weight ratio of natural graphite to the total weight of the negative electrode active material in the first negative electrode active material layer (lower layer) may be formed to be higher than the weight ratio of natural graphite to the total weight of the negative electrode active material in the second negative electrode active material layer (upper layer), and the weight ratio of artificial graphite to the total weight of the negative electrode active material in the second negative electrode active material layer may be formed to be higher than the weight ratio of artificial graphite to the total weight of the negative electrode active material in the first negative electrode active material layer. Alternatively, the weight ratio of the first negative electrode binder to the total weight of the first negative electrode active material layer (lower layer) may be formed to be higher than the weight ratio of the second negative electrode binder to the total weight of the second negative electrode active material layer (upper layer). By forming the negative active material layer in a multilayer structure in this way and varying the composition of each layer, the performance characteristics of the battery, such as rapid charging performance and life characteristics, can be further improved. The above negative electrode can be manufactured according to a conventional negative electrode manufacturing method. For example, the negative electrode can be manufactured by mixing a negative electrode active material, a negative electrode binder, and / or a negative electrode conductive material in a solvent to manufacture a negative electrode slurry, applying the negative electrode slurry onto a negative electrode current collector, and then drying and rolling, or by casting the negative electrode slurry onto a separate support, and then peeling the film from the support and laminating the obtained film onto a negative electrode current collector. Meanwhile, solvents generally used in the relevant technical field can be used as the solvent for the cathode slurry, and the specific details are the same as those for the solvent for the cathode slurry. Membrane The lithium secondary battery according to the present invention may further include a separator between the positive electrode and the negative electrode, if necessary. The separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Any separator commonly used in lithium secondary batteries may be used without particular limitation, and particularly, one having low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity is preferable. Specifically, a porous polymer film, for example, a porous polymer film made of a polyolefin polymer such as an ethylene homopolymer, a propylene homopolymer, an ethylene / butene copolymer, an ethylene / hexene copolymer, and an ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof may be used. In addition, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers, polyethylene terephthalate fibers, etc. may also be used. Additionally, a coated separator containing ceramic components or polymeric materials may be used to secure heat resistance or mechanical strength, and may optionally be used in a single-layer or multi-layer structure. Electrolyte In the lithium secondary battery according to the present invention, the electrolyte may include an organic solvent and a lithium salt. As the organic solvent, any solvent that can act as a medium through which ions involved in the electrochemical reaction of the battery can move may be used without particular limitation. Specifically, the organic solvent may include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; Examples of solvents that can be used include carbonate solvents such as dimethylcarbonate (DMC), diethylcarbonate (DEC), methylethylcarbonate (MEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms and may include a double-bonded aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; and sulfolanes. Among these, a carbonate solvent is preferable, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate, etc.) having high ionic conductivity and high dielectric constant capable of improving the charge / discharge performance of the battery and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate, etc.) is more preferable. The above lithium salt can be used without any special limitation as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the anion of the above lithium salt is F - , Cl - , Br - , I - , NO3 - , N(CN)2 - , BF4 - , CF3CF2SO3 - , (CF3SO2)2N - , (FSO2)2N - , CF3CF2(CF3)2CO - , (CF3SO2)2CH - , (SF5)3C - , (CF3SO2)3C - , CF3(CF2)7SO3 - , CF3CO2 - , CH3CO2 - , SCN - and (CF3CF2SO2)2N - The lithium salt may be at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAl04, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt is preferably used within the range of 0.1 M to 4.0 M, preferably 0.5 M to 3.0 M, and more preferably 1.0 M to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte can exhibit excellent electrolyte performance because it has appropriate conductivity and viscosity, and lithium ions can move effectively. In addition to the electrolyte components, the electrolyte may additionally contain additives for the purposes of improving the life characteristics of the battery, suppressing battery capacity reduction, and improving the discharge capacity of the battery. The above additives include various additives used in the relevant technical field, for example, fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinylethylene carbonate (VEC), ethylene sulfate (ESa), lithium difluorophosphate (LiPO2F2), lithium bisoxalato borate (LiBOB), lithium tetrafluoro borate (LiBF4), lithium difluorooxalato borate (LiDFOB), lithium difluoro bisoxalatophosphate (LiDFBP), lithium tetrafluorooxalato phosphate (LiTFOP), lithium methyl sulfate (LiMS), lithium ethyl sulfate (LiES), propane sultone (PS), propene sultone (PRS), succinonitrile (SN), adiponitrile (AND), 1,3,6-hexane tricarbonitrile (HTCN), 1,4-dicyano-2-butene (DCB), fluorobenzene (FB), Ethyldi(pro-2-yl-1-yl)phosphate (EDP), 5-methyl-5-propazyloxylcarbonyl-1,3-dioxane-2-one (MPOD), etc. can be used alone or in combination, but are not limited thereto. The above additives can be included in an amount of 0.1 to 10 wt%, preferably 0.1 to 5 wt%, based on the total weight of the electrolyte. The lithium secondary battery according to the present invention as described above can be usefully used in portable devices such as mobile phones, laptop computers, digital cameras, and electric vehicles such as hybrid electric vehicles (HEVs). Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are intended to illustrate the present invention and the scope of the present invention is not limited to these examples. Example 1 <Polar manufacturing> A cathode slurry containing cathode active material, cathode conductive agent, cathode binder, and cathode dispersant in a weight ratio of 97:1.2:1.44:0.36 was prepared. At this time, the cathode active material had an average particle diameter (D 50 ) is a single particle Li[Ni with a size of 3.7 ㎛ 0.60 Co 0.10 Mn 0.30 ]O2 was used, and carbon nanotubes (CNT) were used as the anode conductive material. In addition, polyvinylidene fluoride (PVdF) with a density of 1.77 g / cc was used as the anode binder, and hydrogenated nitrile-butadiene rubber (H-NBR) with a density of 1.3 g / cc was used as the anode dispersant. Meanwhile, the positive electrode conductive agent, positive electrode binder, and positive electrode dispersant were added to the positive electrode slurry solvent (N-methylpyrrolidone) in the form of a pre-dispersed solution dispersed in the dispersion solution. Then, the positive electrode slurry was applied on an aluminum current collector, dried, and then rolled to manufacture a positive electrode. The porosity of the positive electrode was 22%. <Cathode Manufacturing> First negative electrode slurry was prepared by mixing first negative electrode active material (natural graphite): first negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): first negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 96.9:0.5:1.0:1.6 in water. Second negative electrode slurry was prepared by mixing second negative electrode active material (artificial graphite): second negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): second negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 97.4:0.5:1.1:1.0 in water. The first negative electrode slurry and the second negative electrode slurry were simultaneously applied onto a negative electrode collector (copper metal thin film), such that the first negative electrode slurry was disposed on the negative electrode collector, and the second negative electrode slurry was disposed on the first negative electrode slurry. Thereafter, the negative electrode collector onto which the first negative electrode slurry and the second negative electrode slurry were applied was dried and then rolled to manufacture a negative electrode. The porosity of the negative electrode was 30%. <Lithium secondary battery manufacturing> As described above, a separator was interposed between the manufactured positive and negative electrodes to manufacture one bicell having the structure of separator / negative electrode / separator / positive electrode / separator / negative electrode / separator, and then the bicell was wound with a separator film to manufacture an electrode assembly, which was then placed in a battery case and an electrolyte solution prepared by dissolving 1 M LiPF6 in a solvent of ethylene carbonate: ethyl methyl carbonate: diethyl carbonate in a ratio of 1:1:1 was injected to manufacture a lithium secondary battery. Example 2 <Cathode Manufacturing> A first negative electrode slurry was prepared by mixing first negative electrode active material (artificial graphite: natural graphite = 25:75): first negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): first negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 96.1:0.5:1.0:2.4 in water. A second negative electrode slurry was prepared by mixing a second negative electrode active material (artificial graphite: natural graphite = 75:25): a second negative electrode conductive agent (super C): a thickener (carboxymethyl cellulose, CMC): and a second negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 97.4:0.5:1.1:1.0 in water. The first negative electrode slurry and the second negative electrode slurry were simultaneously applied onto a negative electrode collector (copper metal thin film), such that the first negative electrode slurry was disposed on the negative electrode collector, and the second negative electrode slurry was disposed on the first negative electrode slurry. Thereafter, the negative electrode collector onto which the first negative electrode slurry and the second negative electrode slurry were applied was dried and then rolled to manufacture a negative electrode. The porosity of the manufactured negative electrode was 29%. A positive electrode and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above negative electrode was used. Example 3 Average particle diameter (D) of the cathode active material 50 ) is a single particle Li[Ni with a diameter of 7.6 μm 0.60 Co 0.10 Mn 0.30 ]O2 was used, and a positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2. The porosity of the manufactured positive electrode was 22%. Example 4 <Polar manufacturing> A positive electrode was manufactured in the same manner as in Example 1, except that the positive electrode slurry was prepared so that the positive electrode active material: positive electrode conductive material: positive electrode binder: positive electrode dispersant were included in a weight ratio of 97.24:1.2:1.35:0.21. The porosity of the manufactured positive electrode was 22%. A negative electrode and a lithium secondary battery were manufactured in the same manner as in Example 2, except that the above positive electrode was used. Example 5 <Polar manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 22%. <Cathode Manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 28%. <Lithium secondary battery> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive and negative electrodes manufactured above were used. Comparative Example 1 <Cathode Manufacturing> A first negative electrode slurry was prepared by mixing first negative electrode active material (artificial graphite: natural graphite = 50:50): first negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): first negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 95.2:0.5:1.0:3.3 in water. A second negative electrode slurry was prepared by mixing a second negative electrode active material (artificial graphite: natural graphite = 50:50): a second negative electrode conductive agent (super C): a thickener (carboxymethyl cellulose, CMC): and a second negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 97.4:0.5:1.1:1.0 in water. The first negative electrode slurry and the second negative electrode slurry were simultaneously applied onto a negative electrode collector (copper metal thin film), such that the first negative electrode slurry was disposed on the negative electrode collector, and the second negative electrode slurry was disposed on the first negative electrode slurry. Thereafter, the negative electrode collector onto which the first negative electrode slurry and the second negative electrode slurry were applied was dried and then rolled to manufacture a negative electrode. The porosity of the manufactured negative electrode was 27%. A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 1, except that the above negative electrode was used. Comparative Example 2 Except that the first negative electrode slurry was prepared by mixing the first negative electrode active material (artificial graphite: natural graphite = 25:75): first negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): first negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 93.5:0.5:1.0:5.0 in water, a positive electrode, an negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2. The porosity of the manufactured negative electrode was 26%. Comparative Example 3 Except that the first negative electrode slurry was prepared by mixing the first negative electrode active material (artificial graphite: natural graphite = 25:75): first negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): first negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 97.5:0.5:1.0:1.0 in water, a positive electrode, an negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2. The porosity of the manufactured negative electrode was 29%. Comparative Example 4 Average particle diameter (D) of the cathode active material 50 ) is a single particle Li[Ni with a diameter of 8.0 μm 0.60 Co 0.10 Mn 0.30 ]O2 was used, and a positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2. The porosity of the manufactured positive electrode was 22%. Comparative Example 5 <Cathode Manufacturing> A negative electrode slurry was prepared by mixing negative electrode active material (artificial graphite: natural graphite = 50:50): negative electrode conductive agent (super C): thickener (carboxymethyl cellulose, CMC): negative electrode binder (styrene butadiene rubber, SBR) in a weight ratio of 96.8:0.5:1.0:1.7 in water. The above negative electrode slurry was applied onto a negative electrode current collector (copper metal thin film), dried, and then rolled to manufacture a negative electrode. The porosity of the manufactured negative electrode was 29%. A positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2, except that the above negative electrode was used. Comparative Example 6 Average particle diameter (D) of the cathode active material 50 ) is a single particle Li[Ni with a size of 2.2 μm 0.60 Co 0.10 Mn 0.30 ]O2 was used, and a positive electrode, a negative electrode, and a lithium secondary battery were manufactured in the same manner as in Example 2. The porosity of the manufactured positive electrode was 22%. Comparative Example 7 <Polar manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 22%. <Cathode Manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 32%. <Lithium secondary battery> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive and negative electrodes manufactured above were used. Comparative Example 8 <Polar manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 22%. <Cathode Manufacturing> An anode was manufactured in the same manner as in Example 1, except that the anode was manufactured so that the porosity was 26%. <Lithium secondary battery> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive and negative electrodes manufactured above were used. Experimental Example 1: Evaluation of FBR value, cathode binder and porosity (1) Measurement of FBR value For the lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 8, the FBR value defined by Equation 1 below was measured. The results are shown in Table 1 below. [Formula 1] FBR = [(Rb × TDb) + (Rd × TDd)] × A 2 The above Rb is a dimensionless number of the ratio (weight %) of the positive electrode binder, Rd is a dimensionless number of the ratio (weight %) of the positive electrode dispersant, TDb is a dimensionless number of the true density (g / cc) of the positive electrode binder, TDd is a dimensionless number of the true density (g / cc) of the positive electrode dispersant, and A is the average particle diameter (D) of the positive electrode active material. 50 , ㎛) is a dimensionless number. (2) Evaluation of negative binder and porosity The ratio of the first negative electrode binder content to the second negative electrode binder content of the negative electrodes of the lithium secondary batteries manufactured in the above Example 1 SOWL 5 and Comparative Examples 1 to 8, the total binder content in the negative electrode, and the difference in porosity between the positive electrode and the negative electrode are shown in Table 1 below. Anode Cathode D 50 (㎛)FBRFirst cathode binder / Second cathode binder ratioTotal binder content (weight %)Difference in porosity between positive and negative electrodesExample 13.741.31.61.38Example 23.741.32.41.77Example 37.6174.32.41.77Example 43.736.42.41.77Example 53.741.31.61.36Comparative Example 13.741.33.32.175Comparative Example 23.741.353.04Comparative Example 33.741.311.07Comparative Example 48.01932.41.77Comparative Example 53.741.3-1.77Comparative Example 62.214.62.41.77Comparative Example 73.741.31.61.310Comparative Example 83.741.31.61.34 Experimental Example 2. Evaluation of Binder Migration Degree For the cathodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 8, the QBR value defined by Equation 2 below was measured. The results are shown in Table 2 below. [Formula 2] QBR = Bs / Bf The above Bs represents an average value of the binder content in the negative electrode active material layer surface area from the outermost surface of the second negative electrode active material layer to within 15% of the total thickness of the negative electrode active material layer, and Bf represents an average value of the binder content in the negative electrode active material layer bottom area from the interface of the first negative electrode active material layer where it meets the negative electrode current collector to within 15% of the total thickness of the negative electrode active material layer. At this time, the binder content is obtained by manufacturing a cross-section of the negative electrode using argon ion milling. Thereafter, an energy dispersive X-ray analysis (EDS) detector of a scanning electron microscope (SEM) is used to perform EDS mapping of the components within the negative active material layer of the manufactured negative electrode cross-section. From the EDS mapping results, a line profile is extracted in the thickness direction of the negative active material layer, and from the extracted line profile results, an average value (Bs) of the binder content in the surface area of ​​the negative active material layer and an average value (Bf) of the binder content in the bottom area of ​​the negative active material layer are extracted. Experimental Example 3. Evaluation of Negative Electrode Adhesion The cathodes manufactured in Examples 1 to 5 and Comparative Examples 1 to 8 were stamped (width 20 mm, length 15 cm) and attached to a slide glass using double-sided tape, and then the cathodes were pressed with a constant pressure. Specifically, a 90˚ peel test was performed to confirm the cathode adhesive strength in units of gf / 20 mm. The results are shown in Table 2 below. QBR (B S / B F )Cathode adhesion (gf / 20mm)Example 11.2449.2Example 21.1150.3Example 31.2449.2Example 41.1150.3Example 51.2449.2Comparative Example 11.0166.0Comparative Example 20.8893.1Comparative Example 31.5027.0Comparative Example 41.1150.8Comparative Example 50.8860.0Comparative Example 61.1150.3Comparative Example 71.4530.5Comparative Example 81.4726.0 Referring to Table 2 above, the lithium secondary batteries manufactured in Examples 1 to 5 have QBR values ​​of 1.1 to 1.28 when compared to the lithium secondary batteries manufactured in Comparative Examples 1 to 8, confirming that the binder is uniformly distributed in the thickness direction within the entire negative electrode active material layer and that the negative electrode adhesive strength is excellent. Experimental Example 4. Rapid Charging Performance Evaluation The lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 8 were charged by the step charging method, and the time (unit: minutes) taken to charge up to SOC 8% to 80% was measured. At this time, the step charging is a method in which, after charging at a constant charge rate (C-rate), the charge rate is lowered when a constant voltage (4.35 V) is reached and charging is performed sequentially. In the present invention, charging was performed sequentially under the C-rate conditions of 0.25C → 0.5C → 0.75C → 1C → 1.25C → 1.5C → 1.75C → 2C → 2.25C → 2.5C → 2.75C → 3C → 3.25C. The measurement results are shown in Table 3 below. Experimental Example 5. Evaluation of Initial Capacity and Resistance Characteristics Each of the lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 8 was charged to 4.35 V at 0.1 C at 25°C, and then discharged to 2.5 V at 0.1 C to measure the initial capacity. At this time, the resistance was measured through the voltage change when a current of 2.5 C was applied for 10 seconds. The measurement results are shown in Table 3 below. Experimental Example 6. Evaluation of Life Characteristics Each of the lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 8 was charged to 4.35 V at 0.33 C at 25° C., then discharged to 2.5 V at 0.33 C, which was considered one cycle, and then 200 charge-discharge cycles were performed. The capacity retention was measured to evaluate the life characteristics. The measurement results are shown in Table 3 below. Rapid charge (min) Initial capacity (mAh) Initial resistance (ohm) Capacity retention rate (%) Example 129.947.11.5496.4 Example 235.356.91.63296.5 Example 329.947.01.6596.0 Example 435.347.51.596.0 Example 530.247.01.696.6 Comparative example 140.847.11.64296.6 Comparative example 245.346.51.70396.8 Comparative example 327.847.31.48995.8 Comparative example 435.445.01.78095.7 Comparative example 540.346.51.68095.7 Comparative example 635.346.51.6395.8Comparative Example 727.543.22.393.0Comparative Example 827.040.03.089.5 Referring to Table 3 above, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 to 5 have superior rapid charge characteristics, initial capacity, initial resistance, and capacity retention rate compared to the lithium secondary batteries manufactured in Comparative Examples 1 to 8.

Claims

1. A cathode including a cathode active material layer including a single particle type cathode active material, a cathode conductive material, a cathode binder and a cathode dispersant; a cathode; and an electrolyte. The above negative electrode comprises a first negative electrode active material layer formed on a negative electrode current collector and including a first negative electrode active material, a first negative electrode conductive material, and a first negative electrode binder, and a second negative electrode active material layer formed on the first negative electrode active material layer and including a second negative electrode active material, a second negative electrode conductive material, and a second negative electrode binder. The first negative electrode active material and the second negative electrode active material each independently include natural graphite, artificial graphite, or a combination thereof, The ratio of the content of the first cathode binder to the content of the second cathode binder is 1.5 to 3.0, The difference in porosity between the positive and negative electrodes is 4.2% to 9.8%, The above positive electrode is a lithium secondary battery having an FBR of 30 to 180, as defined by the following equation 1. [Formula 1] FBR = [(Rb × TDb) + (Rd × TDd)] × A 2 In the above equation 1, Rb is a dimensionless number of the weight % of the positive electrode binder with respect to the total weight of the positive electrode active material layer, Rd is a dimensionless number of the weight % of the positive electrode dispersant relative to the total weight of the positive electrode active material layer, TDb is a dimensionless number of the true density (g / cc) of the positive binder, TDd is a dimensionless number of the true density (g / cc) of the above anode dispersant, A is the average particle diameter (D) of the positive electrode active material 50 , ㎛) is a dimensionless number.

2. In claim 1, A lithium secondary battery, wherein the single particle type positive electrode active material comprises a lithium nickel-based oxide containing Ni in an amount of 70 mol% or less based on the total molar number of metals excluding lithium.

3. In claim 1, A lithium secondary battery, wherein the single particle type positive electrode active material comprises a lithium nickel-based oxide represented by the following [chemical formula 1]. [Chemical Formula 1] Li 1+x [Ni a Co b Mr c M 1 d ]O2 In the above [chemical formula 1], M 1 It contains at least one doping element selected from the group consisting of Ti, Mg, Al, Zr, Y, Ba, Ca, Sr, W, Ta, Nb, and Mo, and -0.1≤x≤0.1, 0.5≤a≤0.7, 0 <b<0.5, 0<c<0.5, 0≤d≤0.2 이다.

4. In claim 1, The above single particle type positive electrode active material has an average particle diameter (D 50 ) is 3.5 ㎛ to 7.8 ㎛.

5. In claim 1, A lithium secondary battery, wherein the single particle type positive electrode active material comprises 1 to 30 nodules.

6. In claim 5, The above nodules have an average particle diameter (D mean ) is 0.8 ㎛ to 4.0 ㎛.

7. In claim 1, A lithium secondary battery, wherein the positive electrode active material layer contains 0.5 to 2 wt% of the positive electrode binder.

8. In claim 1, A lithium secondary battery, wherein the porosity of the positive electrode is 20% to 25%.

9. In claim 1, A lithium secondary battery, wherein the first negative electrode active material and the second negative electrode active material are each independently made of natural graphite, artificial graphite, or a combination thereof.

10. In claim 1, The above first negative electrode active material contains more than 50 wt% of the natural graphite, A lithium secondary battery, wherein the second negative electrode active material contains less than 50 wt% of the natural graphite.

11. In claim 1, A lithium secondary battery, wherein the ratio of the content of the first negative electrode binder to the content of the second negative electrode binder is 1.6 to 2.

4.

12. In claim 1, A lithium secondary battery, wherein the first negative electrode active material layer contains 1.5 to 3.0 wt% of a first negative electrode binder.

13. In claim 1, A lithium secondary battery, wherein the negative electrode has a QBR value of 1.1 to 1.28, as defined by the following Equation 2. [Formula 2] QBR = Bs / Bf The above Bs is the average value of the binder content in the negative electrode active material layer surface area from the outermost surface of the second negative electrode active material layer to within 15% of the total thickness of the negative electrode active material layer, The above Bf is the average value of the binder content in the bottom region of the negative electrode active material layer from the interface of the first negative electrode active material layer meeting the negative electrode current collector to within 15% of the total thickness of the negative electrode active material layer.

14. In claim 1, A lithium secondary battery, wherein the porosity of the negative electrode is 25% to 32%.

15. In claim 1, A lithium secondary battery, wherein the difference in porosity between the positive electrode and the negative electrode is 6% to 8%.