Lithium secondary battery

Abstract

The present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein an average resistance X1 of the positive electrode at room temperature and SOC 20 to 100% and an average resistance Y1 of the negative electrode at room temperature and SOC 20 to 100% satisfy the following formula (1), and an average resistance X2 of the positive electrode at room temperature and SOC 0 to 20% and an average resistance Y2 of the negative electrode at room temperature and SOC 0 to 20% satisfy the following formula (2). Formula (1): 0.6×Y1≦X1≦0.9×Y1 Formula (2): 2×Y2≦X2

Description

[Technical Field]

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0091706, filed on July 14, 2023, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery. [Background technology]

[0003] Demand for lithium secondary batteries as energy sources has increased dramatically with technological advances in electric vehicles, portable electronic devices, etc. In particular, with the recent development of electric vehicle technology, batteries with high energy density and high power output are required.

[0004] High-energy density lithium secondary batteries, for example, lithium secondary batteries for electric vehicles and power storage, are likely to be exposed to high-temperature external environments, and the temperature of the battery may rise due to instantaneous charging and discharging. In such high-temperature environments, the battery's lifespan may be shortened and the amount of stored energy may decrease.

[0005] Therefore, there is a demand for the development of a high-capacity battery system that can improve the life characteristics not only at room temperature but also at high temperatures.

[0006] The lifespan characteristics of lithium secondary batteries are influenced by various factors, among which a well-balanced design of the positive and negative electrodes is essential. Even if a secondary battery is manufactured by selecting positive and negative electrode materials with generally known good performance, if the thermodynamic or electrochemical balance between the positive and negative electrodes is not achieved, problems such as reduced lifespan characteristics may occur. Summary of the Invention [Problem to be solved by the invention]

[0007] The inventors of the present invention aim to prevent a rapid deterioration in the normal temperature and high temperature life characteristics of a lithium secondary battery containing the positive electrode and negative electrode by achieving a thermodynamic or electrochemical balance between the positive electrode and negative electrode. [Means for solving the problem]

[0008] [1] The present invention provides a lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein an average resistance X1 of the positive electrode at room temperature and an SOC of 20 to 100% and an average resistance Y1 of the negative electrode at room temperature and an SOC of 20 to 100% satisfy the following formula (1), and an average resistance X2 of the positive electrode at room temperature and an SOC of 0 to 20% and an average resistance Y2 of the negative electrode at room temperature and an SOC of 0 to 20% satisfy the following formula (2): Formula (1): 0.6×Y1≦X1≦0.9×Y1 Formula (2): 2×Y2≦X2

[0009] [2] The present invention provides the lithium secondary battery according to [1] above, wherein an average resistance X3 of the positive electrode at 40°C and SOC 20 to 100% and an average resistance Y3 of the negative electrode at 40°C and SOC 20 to 100% further satisfy the following formula (3): Formula (3): 0.75×Y3≦X3≦Y3

[0010] [3] The present invention provides the lithium secondary battery according to [1] or [2] above, wherein an average resistance X4 of the positive electrode at 40°C and an SOC of 0 to 20% and an average resistance Y4 of the negative electrode at 40°C and an SOC of 0 to 20% further satisfy the following formula (4): Formula (4): 1.5×Y4≦X4

[0011] [4] The present invention provides the lithium secondary battery according to any one of [1] to [3] above, wherein the positive electrode includes a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder, and the positive electrode active material is a lithium-nickel-based transition metal oxide in which the content of nickel among the transition metals excluding lithium is 85 atm% or more.

[0012] [5] The present invention provides the lithium secondary battery according to the above [4], wherein the positive electrode active material is a single particle or a quasi-single particle.

[0013] [6] The present invention provides the lithium secondary battery according to the above [4] or [5], wherein the conductive material is contained in an amount of 0.1 to 2.5% by weight based on the total weight of the positive electrode active material layer.

[0014] [7] The present invention can provide the lithium secondary battery according to any one of [4] to [6] above, wherein the powder resistance of the positive electrode active material is 100 to 500 Ω.

[0015] [8] The present invention can provide the lithium secondary battery according to any one of [1] to [7], wherein the negative electrode includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder, and the negative electrode active material includes a silicon-based negative electrode active material.

[0016] [9] The present invention can provide the lithium secondary battery according to the above [8], wherein the silicon-based negative electrode active material is selected from the group consisting of SiO, SiC, and Si.

[0017]

[10] The present invention can provide the lithium secondary battery according to the above [8] or [9], wherein the silicon-based negative electrode active material is contained in an amount of 3 wt % or more based on the total weight of the negative electrode active material layer.

[0018]

[11] The present invention can provide the lithium secondary battery according to any one of [8] to

[10] above, wherein the conductive material is contained in an amount of 0.05 to 2.50% by weight based on the total weight of the negative electrode active material layer. [Effects of the Invention]

[0019] The present inventors have found that when degradation of both the positive and negative electrodes occurs during operation of a lithium secondary battery, the lithium secondary battery can be operated stably by controlling the degree of degradation of the negative electrode relative to the positive electrode at a specific temperature and in a specific charging section.

[0020] While degradation occurs in both the positive and negative electrodes during operation of a lithium secondary battery, the degree of degradation of the positive and negative electrodes can be controlled depending on the charge / discharge region, allowing the lithium secondary battery to have excellent long-life characteristics. In particular, by controlling the resistance of the positive and negative electrodes at room and high temperatures, the use of the negative electrode can be reduced, and the degradation of the positive electrode can be relatively induced, resulting in excellent long-life characteristics. [Brief explanation of the drawings]

[0021] [Figure 1] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 1 at 24° C. according to SOC. [Figure 2] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 1 at 40° C. according to SOC. [Figure 3] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 2 at 24° C. according to SOC. [Figure 4] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 2 at 40° C. according to the SOC. [Figure 5] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 3 at 24° C. according to SOC. [Figure 6] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Example 3 at 40° C. according to SOC. [Figure 7] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 1 at 24° C. according to the SOC. [Figure 8] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 1 at 40° C. according to the SOC. [Figure 9] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 2 at 24° C. according to the SOC. [Figure 10]1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 2 at 40° C. according to the SOC. [Figure 11] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 3 at 24° C. according to SOC. [Figure 12] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 3 at 40° C. according to the SOC. [Figure 13] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 4 at 24° C. according to SOC. [Figure 14] 1 shows the results of measuring the resistance values ​​of the positive electrode and negative electrode of the lithium secondary battery of Comparative Example 4 at 40° C. according to the SOC. DETAILED DESCRIPTION OF THE INVENTION

[0022] The present invention will be described in more detail below.

[0023] The terms and words used in this specification and claims should not be interpreted in a limited way to their ordinary or dictionary meanings, but should be interpreted in a way that is consistent with the technical idea of ​​the present invention, based on the principle that the inventors can appropriately define the concepts of terms in order to best explain their inventions.

[0024] In the present invention, "primary particles" refers to particle units that do not appear to have grain boundaries when observed under a scanning electron microscope at a magnification of 5,000 to 20,000 times. "Average particle size of primary particles" refers to the arithmetic mean value calculated after measuring the particle sizes of primary particles observed in an image under a scanning electron microscope.

[0025] In the present invention, a "secondary particle" is a particle formed by aggregating a plurality of primary particles. In order to distinguish it from conventional secondary particles formed by aggregating tens to hundreds of primary particles, a secondary particle formed by aggregating 10 or less primary particles is referred to as a "quasi-single particle" in the present invention.

[0026] In the present invention, the "average particle size D 50 " refers to the particle size at 50% of the volume cumulative particle size distribution of the positive electrode active material powder, and can be measured by a laser diffraction method. For example, the positive electrode active material powder is dispersed in a dispersion medium, and then introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and ultrasonic waves of about 28 kHz are irradiated at an output of 60 W. A volume cumulative particle size distribution graph is then obtained, and the particle size corresponding to 50% of the volume cumulative amount can be measured.

[0027] The lithium secondary battery according to the present invention includes a positive electrode, a negative electrode, and an electrolyte, wherein an average resistance X1 of the positive electrode at room temperature and SOC 20 to 100% and an average resistance Y1 of the negative electrode at room temperature and SOC 20 to 100% satisfy the following formula (1), and an average resistance X2 of the positive electrode at room temperature and SOC 0 to 20% and an average resistance Y2 of the negative electrode at room temperature and SOC 20 to 100% satisfy the following formula (2). Formula (1): 0.6×Y1≦X1≦0.9×Y1 Formula (2): 2×Y2≦X2

[0028] The room temperature means a constant temperature without heating or cooling, and may be within the range of 15 to 25°C.

[0029] Lithium secondary batteries are charged and discharged as lithium ions move between the positive and negative electrodes. As charging and discharging progresses, degradation of the lithium secondary battery occurs due to side reactions between the electrolyte at the positive and negative electrodes and structural collapse. Ideally, the degradation of the positive and negative electrodes progresses to similar degrees. The positive electrode has the property of degrading more rapidly at high voltages, while the negative electrode, when containing a silicon-based active material, has the property of increasing the reaction of the silicon-based active material at the lower end of discharge (SOC 0-20%). The lithium secondary battery of the present invention can suppress degradation of the positive electrode by slightly lowering the resistance of the positive electrode compared to the negative electrode at SOC 20-100%, where high voltages are applied. Furthermore, the lithium secondary battery of the present invention can suppress degradation of the negative electrode active material by adjusting the resistance of the positive electrode higher at SOC 0-20%, which is the lower end of discharge, to prevent the negative electrode potential from increasing during discharge. This minimizes the difference in degradation level between the positive electrode and the negative electrode, thereby maximizing the life characteristics of the lithium secondary battery.

[0030] The average resistance of the positive electrode and the average resistance of the negative electrode can be measured using a first coin cell fabricated using the positive electrode and a lithium metal counter electrode, and a second coin cell fabricated using the negative electrode and a lithium metal counter electrode, respectively. Specifically, the first coin cell and the second coin cell can be fabricated by disassembling the positive electrode and the negative electrode from a fabricated lithium secondary battery, connecting a 200 μm thick lithium metal to the counter electrode, injecting an electrolyte containing LiPF6 lithium salt and an organic solvent (a mixed solvent of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate) into the counter electrode, and aging for 24 hours.

[0031] In the formula (1), X1 is the average resistance of the positive electrode at room temperature with an SOC of 20 to 100%, and is the average resistance value (Ω) of the first coin cell in the SOC range of 20 to 100% when discharged at room temperature at 1 C. Specifically, X1 is the average resistance value calculated in the SOC range of 20 to 100% after fully charging the first coin cell and discharging it at 1 C using an HPPC (Hybrid Pulse Power Characteristic) test at room temperature, and then measuring the resistance value according to the state of charge (SOC).

[0032] In the formula (1), Y1 is the average resistance of the negative electrode at room temperature with an SOC of 20 to 100%, and can be measured as the average resistance (Ω) of the second coin cell in the SOC range of 20 to 100% when discharging at room temperature at 1 C. Specifically, Y1 is the average resistance calculated in the SOC range of 20 to 100% after fully charging the second coin cell and discharging at 1 C using an HPPC (hybrid pulse power characteristic) test at room temperature, and then measuring the resistance according to the state of charge (SOC).

[0033] At SOCs of 20 to 100%, a high potential is applied, maximizing the structural collapse of the positive electrode and side reactions with the electrolyte. This rapidly accelerates degradation of the positive electrode, reducing the capacity retention rate of the lithium secondary battery. The lithium secondary battery of the present invention satisfies formula (1) at room temperature, thereby adjusting the positive electrode resistance and negative electrode resistance to similar levels in the SOC range of 20 to 100%, preventing significant overvoltage at the positive electrode during charging. Furthermore, preventing a large increase in the potential of the positive electrode during constant current (CC) charging reduces structural collapse of the positive electrode material and side reactions with the electrolyte.

[0034] In the formula (2), X2 is the average resistance of the positive electrode at room temperature and SOC 0-20%, and can be measured as the average resistance value (Ω) of the first coin cell in the SOC range of 0-20% when discharging at room temperature at 1 C. Specifically, X2 is the average resistance value calculated in the SOC range of 0-20% after fully charging the first coin cell and discharging at 1 C using an HPPC (Hybrid Pulse Power Characteristic) test at room temperature, and then measuring the resistance value according to the state of charge (SOC).

[0035] In the formula (2), Y2 is the average resistance of the negative electrode at room temperature with an SOC of 0 to 20%, and can be measured as the average resistance (Ω) of the second coin cell in the SOC range of 0 to 20% when discharging at room temperature at 1 C. Specifically, Y2 is the average resistance calculated in the SOC range of 0 to 20% after fully charging the second coin cell and discharging at 1 C using an HPPC (hybrid pulse power characteristic) test at room temperature, and then measuring the resistance according to the state of charge (SOC).

[0036] Silicon-based negative electrode active materials are highly activated at an SOC of 0 to 20%. When a lithium secondary battery discharges, the negative electrode potential rises significantly in the SOC range of 0 to 20%, resulting in increased use of the silicon-based negative electrode active material, maximizing pulverization and side reactions with the electrolyte, and causing degradation of the lithium secondary battery's performance. The lithium secondary battery of the present invention satisfies formula (2) at room temperature, setting the resistance of the positive electrode higher than that of the negative electrode. During discharge, the positive electrode potential drops before the negative electrode potential rises, allowing the lithium secondary battery to quickly terminate operation. As a result, the potential of the negative electrode is not high during discharge in the SOC range of 0 to 20%, reducing the use of the silicon-based negative electrode active material. This is thought to suppress degradation of the negative electrode and result in excellent battery life.

[0037] More preferably, the lithium secondary battery according to the present invention may satisfy the following formula (2-1): Formula (2-1): 2×Y2≦X2≦6.5×Y2

[0038] In the formula (2-1), X2 and Y2 are as defined in the formula (2).

[0039] Furthermore, the lithium secondary battery according to the present invention may satisfy the following formula (A): Formula (A): 0.9×Y1+Y2≦1.5×(X1+0.5×X2)

[0040] In the formula (A), X1, X2, Y1, and Y2 are as defined in the formulas (1) and (2).

[0041] In the lithium secondary battery according to the present invention, the average resistance X3 of the positive electrode at 40° C. and SOC 20 to 100% and the average resistance Y3 of the negative electrode at 40° C. and SOC 20 to 100% may satisfy the condition of the following formula (3). Formula (3): 0.75×Y3≦X3≦Y3

[0042] In the formula (3), X3 is the average resistance of the positive electrode at 40°C and SOC 20 to 100%, and can be measured as the average resistance value (Ω) of the first coin cell in the SOC 20 to 100% range when discharging at 1 C at 40°C. Specifically, X3 is the average resistance value calculated in the SOC 20 to 100% range after fully charging the first coin cell and discharging at 1 C using an HPPC (Hybrid Pulse Power Characteristic) test at 40°C, and measuring the resistance value according to the state of charge (SOC).

[0043] In the formula (3), Y3 is the average resistance of the negative electrode at 40°C and SOC 20 to 100%, and can be measured as the average resistance value (Ω) of the second coin cell in the SOC 20 to 100% range when discharging at 1 C at 40°C. Y3 is the average resistance value calculated in the SOC 20 to 100% range after fully charging the second coin cell and discharging at 1 C using an HPPC (hybrid pulse power characteristic) test at 40°C, and then measuring the resistance value according to the state of charge (SOC).

[0044] The lithium secondary battery of the present invention satisfies formula (3) at 40°C, and when the positive electrode resistance and the negative electrode resistance in the SOC range of 20 to 100% are adjusted to levels more similar than those at room temperature, the degradation levels of the positive electrode and the negative electrode can be adjusted to be similar.

[0045] In the lithium secondary battery according to the present invention, the average resistance X4 of the positive electrode at 40° C. and SOC 0 to 20% and the average resistance Y4 of the negative electrode at 40° C. and SOC 0 to 20% may satisfy the condition of the following formula (4). Formula (4): 1.5×Y4≦X4

[0046] In the formula (4), X4 is the average resistance of the positive electrode at 40°C and SOC 0-20%, and can be measured as the average resistance value (Ω) of the first coin cell in the SOC 0-20% range when discharging at 1 C at 40°C. Specifically, X4 is the average resistance value calculated in the SOC 0-20% range after fully charging the first coin cell and discharging at 1 C using an HPPC (Hybrid Pulse Power Characteristic) test at 40°C, and measuring the resistance value according to the state of charge (SOC).

[0047] In the formula (4), Y4 is the average resistance of the negative electrode at 40°C and SOC 0-20%, and can be measured as the average resistance value (Ω) of the second coin cell in the SOC 0-20% range when discharging at 1 C at 40°C. Specifically, Y4 is the average resistance value calculated in the SOC 0-20% range after fully charging the second coin cell and discharging at 1 C using an HPPC (hybrid pulse power characteristic) test at 40°C, measuring the resistance value according to the state of charge (SOC).

[0048] Silicon-based negative electrode active materials are highly activated at an SOC of 0-20%. When a lithium secondary battery discharges, the negative electrode potential rises significantly in the 0-20% SOC range. This increases the consumption of silicon-based negative electrode active materials, maximizing pulverization and side reactions with the electrolyte, leading to degradation of the lithium secondary battery's performance. By setting the resistance of the positive electrode higher than that of the negative electrode, the positive electrode potential drops before the negative electrode potential rises during discharge, allowing the lithium secondary battery to terminate operation quickly. This reduces the negative electrode potential during discharge in the 0-20% SOC range, reducing the consumption of silicon-based negative electrode active materials. This is thought to suppress negative electrode degradation and provide excellent life characteristics. Compared to the room temperature condition in Equation (2), the difference in resistance between the negative and positive electrodes is smaller at 40°C in Equation (4). This is thought to be due to the faster degradation of the positive electrode at high temperatures, so a slightly lower positive electrode resistance is acceptable.

[0049] More preferably, the lithium secondary battery according to the present invention may satisfy the following formula (4-1): Formula (4-1): 1.5×Y4≦X4≦6.5×Y4

[0050] In the formula (4-1), X4 and Y4 are as defined in the formula (4).

[0051] The lithium secondary battery according to the present invention may satisfy the following formula (B): Formula (B): Y3+1.5×Y4≦X3+X4

[0052] In the formula (B), X3, X4, Y3, and Y4 are as defined in the formulas (3) and (4).

[0053] The positive electrode of the present invention has a structure in which a positive electrode active material layer is formed on one or both sides of a positive electrode current collector, and the positive electrode active material layer may contain a positive electrode active material, a conductive material, and a binder.

[0054] The positive electrode current collector can be any of various positive electrode current collectors used in the art. For example, the positive electrode current collector can be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surface has been treated with carbon, nickel, titanium, silver, or the like. The positive electrode current collector typically has a thickness of 3 to 500 μm, and the adhesive strength of the positive electrode active material can be increased by forming fine irregularities on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0055] On the other hand, the positive electrode active material may be any positive electrode active material commonly used in the technical field.

[0056] Preferably, the positive electrode active material may include a lithium nickel-based oxide, specifically, a lithium nickel-based transition metal oxide having a nickel content of 85 atm% or more, or 90 atm% or more, among transition metals excluding lithium. Preferably, the lithium nickel-based oxide may contain Ni in an amount of 90 mol% or more and less than 100 mol%, 93 mol% or more and less than 100 mol%, or 95 mol% or more and less than 100 mol%. When a lithium nickel-based oxide having a high Ni content is used as described above, a high capacity can be achieved.

[0057] More specifically, the positive electrode active material may include a lithium nickel-based oxide represented by the following Chemical Formula 5:

[0058] [Chemical formula 5] Li a Ni b Co c M 1 d M 2 e O2

[0059] In the above Chemical Formula 5, M 1 may be Mn, Al, or a combination thereof, preferably Mn, or Mn and Al.

[0060] The above-mentioned M 2 is one or more selected from the group consisting of Zr, W, Y, Ba, Ca, Ti, Mg, Ta, and Nb, preferably one or more selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. M 2 The element is not necessarily included, but when included in an appropriate amount, it can play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0061] The above-mentioned a represents the molar ratio of lithium in the lithium nickel-based oxide, and may be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the lithium nickel-based oxide can be stably formed.

[0062] The above-mentioned b represents the molar ratio of nickel among all the metals excluding lithium in the lithium nickel-based oxide, and may be 0.85 ≦ b < 1, 0.9 ≦ b < 1, or 0.95 ≦ b < 0.98. When the molar ratio of nickel satisfies the above range, it shows a high energy density and high capacity can be realized.

[0063] The above-mentioned c represents the molar ratio of cobalt among all the metals excluding lithium in the lithium nickel-based oxide, and may be 0 < c < 0.15, 0 < c < 0.1, or 0.02 ≦ c ≦ 0.07. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0064] The above-mentioned d represents the molar ratio of the M 1 element among all the metals excluding lithium in the lithium nickel-based oxide, and may be 0 < d < 0.15, 0 < d < 0.1, or 0.01 ≦ d ≦ 0.05. M 1 When the molar ratio of the element satisfies the above range, it has excellent structural stability of the positive electrode active material.

[0065] The above-mentioned e is M among all metals except for lithium in the lithium nickel-based oxide. 2 It represents the molar ratio of the elements and may be 0≦e≦0.1, or 0≦e≦0.01.

[0066] Meanwhile, the positive electrode active material according to the present invention may further include, as necessary, a coating layer on the surface of the lithium nickel-based oxide particles, the coating layer containing one or more coating elements selected from the group consisting of Al, Ti, W, B, F, P, Mg, Ni, Co, Fe, Cr, V, Cu, Ca, Zn, Zr, Nb, Mo, Sr, Sb, Bi, Si, and S. Preferably, the coating element may be Al, B, Co, or a combination thereof, and most preferably, the coating element may be B.

[0067] When a coating layer is present on the surface of the lithium nickel-based oxide particles, the coating layer suppresses contact between the electrolyte and the lithium composite transition metal oxide, thereby reducing the elution of the transition metal and the generation of gas due to side reactions with the electrolyte.

[0068] On the other hand, the form of the positive electrode active material is not particularly limited, and may be in the form of secondary particles formed by agglomeration of multiple primary particles, in the form of a single particle formed by one primary particle, or in the form of a combination thereof.

[0069] Preferably, the positive electrode active material may include a positive electrode active material made of a single particle consisting of one primary particle and / or a pseudo-single particle which is an aggregate of 10 or less primary particles. By using a positive electrode active material made of a single particle consisting of one primary particle and / or a pseudo-single particle which is an aggregate of 10 or less primary particles as the positive electrode active material, a lithium secondary battery that achieves high capacity and is excellent in safety can be obtained.

[0070] Positive electrode active materials in the form of single particles consisting of one primary particle or pseudo-single particles formed by agglomeration of 10 or fewer primary particles have higher particle strength than conventional positive electrode active materials in the form of secondary particles formed by agglomeration of tens to hundreds of primary particles, and therefore hardly ever suffer particle cracking during rolling. Furthermore, positive electrode active materials in the form of single particles or pseudo-single particles have a small number of primary particles that make up the particle, and therefore experience little change due to volume expansion and contraction of the primary particles during charge and discharge, significantly reducing the occurrence of cracks within the particles.

[0071] Therefore, increasing the Ni content in the cathode material to achieve high energy can lead to increased structural instability of the cathode, but using the cathode active material in the form of single particles and / or quasi-single particles can significantly reduce the amount of gas generated due to particle cracking and internal cracking, thereby achieving excellent safety. However, using a cathode active material with a high nickel content in single particle form is limited by its high resistance, so the amount of lithium secondary battery and the resistance characteristics of the anode must be adjusted to satisfy the conditions of equations (1) and (2).

[0072] In particular, the powder resistance of the positive electrode active material may be 100 to 500 Ω, preferably 200 to 400 Ω, and more preferably 300 to 350 Ω. When the powder resistance is within the above range, it can be adjusted to have a similar level of degradation as the negative electrode.

[0073] On the other hand, the positive electrode active material in the form of single particles and / or pseudo-single particles according to the present invention has an average particle diameter D 50 The average particle size D of the positive electrode active material may be 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. 50 If satisfies the above range, the increase in resistance can be minimized.

[0074] Positive electrode active materials in the form of single particles and / or quasi-single particles have fewer interfaces between primary particles, which serve as diffusion paths for lithium ions within the particles, and therefore have inferior lithium mobility compared to positive electrode active materials in the form of secondary particles, resulting in a problem of increased resistance. This increase in resistance becomes more pronounced as the particle size increases, and the increased resistance adversely affects capacity and output characteristics. Therefore, in the present invention, the average particle size D 50 The company applied a single-particle or pseudo-single-particle positive electrode active material with a particle size of 5 μm or less, minimizing the diffusion distance of lithium ions inside the particle and suppressing an increase in resistance.

[0075] The positive electrode active material in the form of single particles and / or pseudo-single particles may have an average primary particle size of 5 μm or less, 4 μm or less, 3 μm or less, or 2 μm or less, for example, 0.5 μm to 5 μm, preferably 1 μm to 5 μm, and more preferably 2 μm to 5 μm. When the average primary particle size satisfies the above range, a positive electrode active material in the form of single particles and / or pseudo-single particles with excellent electrochemical properties can be formed. If the average primary particle size is too small, the number of agglomerates of the primary particles forming the positive electrode active material increases, reducing the effect of suppressing particle cracking during rolling. If the average primary particle size is too large, the lithium diffusion path within the primary particles may become longer, increasing resistance and potentially reducing output characteristics.

[0076] In the present invention, the positive electrode active material in the form of single particles and / or quasi-single particles preferably has a unimodal particle size distribution. Conventionally, to improve the electrode density of the positive electrode active material layer, bimodal positive electrode active materials have been used, in which a large-particle positive electrode active material with a large average particle size is mixed with a small-particle positive electrode active material with a small average particle size. However, with positive electrode active materials in the form of single particles or quasi-single particles, increasing particle size lengthens the lithium migration path, significantly increasing resistance. Therefore, when large-particle particles are mixed, problems may arise in terms of reduced capacity and output characteristics. Therefore, in the present invention, a positive electrode active material with a unimodal particle size distribution is used to minimize the increase in resistance.

[0077] The conductive material is used to impart conductivity to the electrodes and can be any material that does not cause chemical changes in the resulting battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbonaceous materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; 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; and conductive polymers such as polyphenylene derivatives. These materials can be used alone or in combination.

[0078] The conductive material may be contained in an amount of 0.1 to 2.5% by weight, preferably 0.5 to 2.0% by weight, and more preferably 1.0 to 1.8% by weight, relative to the total weight of the positive electrode active material layer.

[0079] The binder serves to improve adhesion between the positive electrode active material particles and between the positive electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0080] The binder may be contained in an amount of 1 to 30% by weight, preferably 1 to 10% by weight, and more preferably 1.5 to 5.0% by weight, based on the total weight of the positive electrode active material layer.

[0081] The negative electrode of the present invention has a structure in which a negative electrode active material layer is formed on one or both sides of a negative electrode current collector, and the negative electrode active material layer may contain a negative electrode active material, a conductive material, and a binder.

[0082] As the negative electrode current collector, a negative electrode current collector generally used in the art can be used. For example, copper, stainless steel, aluminum, nickel, titanium, fired carbon, or those obtained by surface treatment with carbon, nickel, titanium, silver, etc. on the surface of copper or stainless steel, aluminum-cadmium alloy, etc. may be used. The negative electrode current collector usually has a thickness of 3 μm to 500 μm. Similar to the positive electrode current collector, the binding force of the negative electrode active material may be strengthened by forming fine irregularities on the surface of the current collector. For example, it can be used in various forms such as films, sheets, foils, meshes, porous bodies, foams, non-woven fabrics, etc.

[0083] The negative electrode active material may include silicon-based negative electrode active materials such as Si, Si-Me alloy (where Me is one or more selected from the group consisting of Al, Sn, Mg, Cu, Fe, Pb, Zn, Mn, Cr, Ti, and Ni), SiOy (where 0 < y < 2), Si-C composite, etc. Most preferably, it may include silicon-based negative electrode active materials selected from the group consisting of SiO, SiC, and Si. A negative electrode containing a silicon-based negative electrode active material can achieve a high capacity. However, when a high-resistance positive electrode is used together with a negative electrode containing a silicon-based negative electrode active material, the usable capacity of the negative electrode containing the silicon-based negative electrode material increases at room temperature, and there is a limit where the negative electrode rapidly degrades and the performance of the lithium secondary battery rapidly degrades. Therefore, it is necessary to adjust the amount of the lithium secondary battery and the resistance characteristics of the negative electrode so as to satisfy the conditions of the above formulas (1) and (2).

[0084] As the negative electrode active material other than the silicon-based negative electrode active material, a compound capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; lithium metal thin film; and metallic materials capable of alloying with lithium, such as Sn and Al. Any one or a mixture of two or more of these may be used.

[0085] The silicon-based negative electrode active material may be contained in an amount of 3% by weight or more, preferably 3 to 10% by weight, and more preferably 3 to 6% by weight, based on the total weight of the negative electrode active material layer.

[0086] The conductive material is used to impart conductivity to the negative electrode and can be any material that does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite and artificial graphite; carbon-based materials such as carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; 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; and conductive polymers such as polyphenylene derivatives. These materials can be used alone or in combination.

[0087] The conductive material may be contained in an amount of usually 0.05 to 2.50% by weight, preferably 0.5 to 2.0% by weight, and more preferably 1.0 to 1.5% by weight, relative to the total weight of the negative electrode active material layer.

[0088] The binder serves to improve adhesion between negative electrode active material particles and between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, and various copolymers thereof. These may be used alone or in combination.

[0089] The binder may be contained in an amount of 1 to 10% by weight, preferably 1 to 5% by weight, and more preferably 1.5 to 3.0% by weight, based on the total weight of the negative electrode active material layer.

[0090] In addition to the positive electrode and negative electrode, a separator interposed between the positive electrode and negative electrode serves to separate the negative electrode from the positive electrode and provide a path for lithium ions to move. Any separator commonly used in lithium secondary batteries can be used without particular limitations. Specifically, the separator can be a porous polymer film, such as 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, or an ethylene / methacrylate copolymer, or a laminate structure of two or more layers thereof. Conventional porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. To ensure heat resistance or mechanical strength, a coated separator containing a ceramic component or a polymeric material can also be used.

[0091] Furthermore, examples of the electrolyte used in the present invention include organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the production of lithium secondary batteries, but are not limited to these.

[0092] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0093] The organic solvent may be any solvent capable of acting as a medium for the movement of ions involved in the electrochemical reaction of the battery. Specific examples of the organic solvent include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether and tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethylcarbonate (DMC), diethylcarbonate (DEC), ethylmethylcarbonate (EMC), ethylene carbonate (EC), and propylene carbonate. Examples of solvents that can be used include carbonate-based solvents such as ethylene carbonate (PC), alcohol-based 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, which may contain a double-bonded aromatic ring or an ether bond), amides such as dimethylformamide, dioxolanes such as 1,3-dioxolane, and sulfolanes. Among these, carbonate-based solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and a high dielectric constant, which can improve the charge / discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred.

[0094] The lithium salt can be any compound that can provide lithium ions used in lithium secondary batteries without any particular limitations. Specifically, the anion of the 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, LiAlO4, 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 in the range of 0.1 to 2.0 M. When the lithium salt concentration is within the above range, the electrolyte has appropriate conductivity and viscosity, thereby exhibiting excellent electrolyte performance and allowing lithium ions to migrate effectively.

[0095] In addition to the electrolyte components, the electrolyte may further contain one or more additives, such as haloalkylene carbonate compounds (e.g., difluoroethylene carbonate), pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphoric acid triamide, nitrobenzene derivatives, sulfur, quinoneimine dyes, N-substituted oxazolidinones, N,N-substituted imidazolidines, ethylene glycol dialkyl ethers, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for the purpose of improving battery life characteristics, suppressing battery capacity reduction, improving battery discharge capacity, etc. In this case, the additives may be contained in an amount of 0.1 to 10 wt % based on the total weight of the electrolyte.

[0096] The external shape of the lithium secondary battery of the present invention is not particularly limited, and may be a cylindrical shape using a can, a square shape, a pouch shape, a coin shape, or the like.

[0097] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also as a unit battery in a medium- to large-sized battery module containing a large number of battery cells.

[0098] Examples of the medium to large size devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0099] The present invention will be described in more detail below with reference to specific examples. However, the following examples are merely illustrative for understanding the present invention and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the present description and technical concept, and it goes without saying that such changes and modifications fall within the scope of the appended claims.

[0100] Example Example 1 D50 The positive electrode active material (LiNi 0.958 Co 0.015 Mn 0.027 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.6:1.8:2.6 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0101] Anode active materials (a mixture of natural graphite, artificial graphite, and SiO2 in a weight ratio of 47.75:47.75:4.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.95:1.05:1.70:1.30 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0102] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0103] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0104] The positive and negative electrodes were separated from the activated lithium secondary battery. The first coin cell was fabricated using the separated positive electrode and lithium metal counter electrode, and the second coin cell was fabricated using the separated negative electrode and lithium metal counter electrode. The resistance of the first and second coin cells was measured while discharging at 1 C at 24°C, and the results are shown in Figure 1.

[0105] In the graph of Figure 1, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0106] In the graph of Figure 1, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0107] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG. 2.

[0108] In the graph of Figure 2, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0109] From the graph in Figure 2, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0110] Example 2 D 50 The positive electrode active material (LiNi 0.891 Co 0.066 Mn 0.043 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.95:1.50:2.55 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0111] Anode active material (natural graphite), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.7:1.4:1.5:1.4 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0112] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0113] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0114] The positive and negative electrodes were separated from the activated lithium secondary battery. The separated positive electrode and lithium metal counter electrode were used to fabricate a first coin cell, and the separated negative electrode and lithium metal counter electrode were used to fabricate a second coin cell. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C, and the results are shown in Figure 3.

[0115] In the graph of Figure 3, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0116] From the graph in Figure 3, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0117] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0118] In the graph of FIG. 4, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0119] From the graph in Figure 4, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0120] Example 3 D 50 The positive electrode active material (LiNi 0.962 Co 0.029 Mn 0.009 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.69:1.30:3.01 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0121] Anode active materials (a mixture of natural graphite, artificial graphite, and SiO2 in a weight ratio of 46.75:46.75:6.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.625:1.075:1.900:1.400 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0122] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0123] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0124] The positive and negative electrodes were separated from the activated lithium secondary battery. The first coin cell was fabricated using the separated positive electrode and lithium metal counter electrode, and the second coin cell was fabricated using the separated negative electrode and lithium metal counter electrode. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C. The results are shown in Figure 5.

[0125] In the graph of FIG. 5, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0126] From the graph in Figure 5, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0127] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0128] In the graph of FIG. 6, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0129] In the graph of FIG. 6, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0130] Comparative Example 1 D 50 The positive electrode active material (LiNi 0.962 Co 0.029 Mn 0.009 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.19:1.80:3.01 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0131] Anode active materials (a mixture of natural graphite, artificial graphite, and SiO2 in a weight ratio of 46.75:46.75:6.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.625:1.0750:1.900:1.400 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0132] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0133] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0134] The positive and negative electrodes were separated from the activated lithium secondary battery. The separated positive electrode and lithium metal counter electrode were used to fabricate a first coin cell, and the separated negative electrode and lithium metal counter electrode were used to fabricate a second coin cell. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C, and the results are shown in Figure 7.

[0135] In the graph of FIG. 7, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0136] In the graph of FIG. 7, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0137] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0138] In the graph of FIG. 8, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0139] In the graph of FIG. 8, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0140] Comparative Example 2 D 50 The positive electrode active material (LiNi 0.962 Co 0.029 Mn 0.009 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.19:1.80:3.01 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0141] Anode active materials (a mixture of natural graphite, artificial graphite, and SiO2 in a weight ratio of 44.75:44.75:10.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.625:1.075:1.900:1.400 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0142] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0143] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0144] The positive and negative electrodes were separated from the activated lithium secondary battery. A first coin cell was fabricated using the separated positive electrode and lithium metal counter electrode, and a second coin cell was fabricated using the separated negative electrode and lithium metal counter electrode. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C, and the results are shown in Figure 9.

[0145] In the graph of FIG. 9, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0146] From the graph in FIG. 9, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0147] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0148] In the graph of FIG. 10, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0149] In the graph of FIG. 10, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0150] Comparative Example 3 D 50 The positive electrode active material (LiNi 0.962 Co 0.029 Mn 0.009 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.6:1.8:2.6 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0151] Anode active materials (a mixture of natural graphite, artificial graphite, and SiO2 in a weight ratio of 44.75:44.75:10.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.625:1.075:1.900:1.400 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0152] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0153] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0154] The positive and negative electrodes were separated from the activated lithium secondary battery. The separated positive electrode and lithium metal counter electrode were used to fabricate a first coin cell, and the separated negative electrode and lithium metal counter electrode were used to fabricate a second coin cell. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C, and the results are shown in Figure 11.

[0155] In the graph of FIG. 11, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0156] In the graph of FIG. 11, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0157] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0158] In the graph of FIG. 12, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0159] In the graph of FIG. 12, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0160] Comparative Example 4 D 50 The positive electrode active material (LiNi 0.962 Co 0.029 Mn 0.009 O2), carbon nanotubes, and PVDF binder were mixed in N-methylpyrrolidone in a weight ratio of 95.69:1.30:3.01 to prepare a cathode slurry. The cathode slurry was applied to both sides of an aluminum current collector sheet, dried at 120°C, and rolled to prepare a cathode.

[0161] Anode active material (a mixture of natural graphite and SiO2 in a weight ratio of 93.5:6.5), Super C, styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in water in a weight ratio of 95.625:1.075:1.900:1.400 to prepare anode slurry. The anode slurry was applied to both sides of a copper current collector sheet, dried at 150°C, and rolled to prepare anodes.

[0162] An electrolyte was produced by dissolving LiPF6 in an organic solvent (ethylene carbonate (EC): ethyl methyl carbonate (EMC): dimethyl carbonate (DMC) = 20:5:75 volume ratio) to a concentration of 1.3 M.

[0163] A separator was interposed between the positive and negative electrodes prepared as described above, and the stacked electrodes were then wound up to prepare a jelly-roll type electrode assembly. The electrode assembly prepared as described above was inserted into a cylindrical battery can. The electrolyte was injected into the battery can to prepare a 4680 cell, which was then activated to prepare a lithium secondary battery.

[0164] The positive and negative electrodes were separated from the activated lithium secondary battery. A first coin cell was fabricated using the separated positive electrode and lithium metal counter electrode, and a second coin cell was fabricated using the separated negative electrode and lithium metal counter electrode. The resistance of the first and second coin cells was measured while discharging at 1 C at 24 °C, and the results are shown in Figure 13.

[0165] In the graph of FIG. 13, the average resistance value (Ω) X1 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω) Y1 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0166] In the graph of FIG. 13, the average resistance value (Ω)X2 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y2 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0167] Furthermore, the resistance of the manufactured first coin cell and second coin cell was measured while discharging at 1 C at 40° C., and the results are shown in FIG.

[0168] In the graph of FIG. 14, the average resistance value (Ω)X3 of the first coin cell in the SOC range of 20 to 100% and the average resistance value (Ω)Y3 of the second coin cell in the SOC range of 20 to 100% were calculated and shown in Table 1 below.

[0169] In the graph of FIG. 14, the average resistance value (Ω)X4 of the first coin cell in the SOC range of 0 to 20% and the average resistance value (Ω)Y4 of the second coin cell in the SOC range of 0 to 20% were calculated and shown in Table 1 below.

[0170] [Table 1]

[0171] Experimental example 1 - Evaluation of life characteristics at room temperature The room temperature life characteristics of 4680 cells of Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated.

[0172] Specifically, each of the 4680 cells of Examples 1 to 3 and Comparative Examples 1 to 4 was charged at 24° C. at a constant current of 0.5 C to 4.2 V and discharged at a constant current of 0.5 C to 2.5 V, and then subjected to 70 charge-discharge cycles, after which the capacity retention rate relative to the initial capacity after 70 cycles was measured. The results are shown in Table 2 below.

[0173] [Table 2]

[0174] As shown in Table 2, it was confirmed that the lithium secondary batteries satisfying formulas (1) and (2) in Examples 1 to 3 have superior room-temperature life characteristics compared to the lithium secondary batteries in Comparative Examples 1 to 4 that do not satisfy at least one of formulas (1) and (2).

[0175] Experimental example 2: Evaluation of high temperature life characteristics The 4680 cells of Examples 1 to 3 and Comparative Examples 1 to 4 were evaluated for high-temperature life characteristics.

[0176] Specifically, each of the 4680 cells of Examples 1 to 3 and Comparative Examples 1 to 4 was charged at 40° C. at a constant current of 0.5 C to 4.2 V and discharged at a constant current of 0.5 C to 2.5 V, and then subjected to 70 charge-discharge cycles, after which the capacity retention rate relative to the initial capacity after 70 cycles was measured. The results are shown in Table 3 below.

[0177] [Table 3]

[0178] As shown in Table 3, it was confirmed that the lithium secondary batteries satisfying formulas (1) and (2) in Examples 1 to 3 have superior high-temperature life characteristics compared to the lithium secondary batteries in Comparative Examples 1 to 4 that do not satisfy at least one of formulas (1) and (2).

Claims

1. A lithium secondary battery including a positive electrode, a negative electrode, and an electrolyte, A lithium secondary battery in which an average resistance X1 of the positive electrode at room temperature and SOC 20 to 100% and an average resistance Y1 of the negative electrode at room temperature and SOC 20 to 100% satisfy the following formula (1), and an average resistance X2 of the positive electrode at room temperature and SOC 0 to 20% and an average resistance Y2 of the negative electrode at room temperature and SOC 0 to 20% satisfy the following formula (2): Formula (1): 0.6×Y1≦X1≦0.9×Y1 Formula (2): 2×Y2≦X2.

2. The lithium secondary battery according to claim 1, wherein an average resistance X3 of the positive electrode at 40 ° C. and SOC 20 to 100% and an average resistance Y3 of the negative electrode at 40 ° C. and SOC 20 to 100% further satisfy the following formula (3): Formula (3): 0.75×Y3≦X3≦Y3.

3. The lithium secondary battery according to claim 1, wherein an average resistance X4 of the positive electrode at 40 ° C. and SOC 0 to 20% and an average resistance Y4 of the negative electrode at 40 ° C. and SOC 0 to 20% further satisfy the following formula (4): Formula (4): 1.5×Y4≦X4.

4. the positive electrode includes a positive electrode active material layer and a positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, a conductive material, and a binder; 2. The lithium secondary battery according to claim 1, wherein the positive electrode active material is a lithium-nickel-based transition metal oxide in which the nickel content of transition metals other than lithium is 85 atomic % or more.

5. The lithium secondary battery according to claim 4 , wherein the positive electrode active material is in the form of a single particle or a pseudo-single particle.

6. 5. The lithium secondary battery according to claim 4, wherein the conductive material is contained in an amount of 0.1 to 2.5% by weight based on the total weight of the positive electrode active material layer.

7. 5. The lithium secondary battery according to claim 4, wherein the powder resistance of the positive electrode active material is 100 to 500 Ω.

8. the negative electrode includes a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer includes a negative electrode active material, a conductive material, and a binder, The lithium secondary battery according to claim 1 , wherein the negative electrode active material includes a silicon-based negative electrode active material.

9. 9. The lithium secondary battery according to claim 8, wherein the silicon-based negative electrode active material is selected from the group consisting of SiO, SiC, and Si.

10. 9. The lithium secondary battery according to claim 8, wherein the silicon-based negative electrode active material is contained in an amount of 3% by weight or more based on the total weight of the negative electrode active material layer.

11. 9. The lithium secondary battery according to claim 8, wherein the conductive material is contained in an amount of 0.05 to 2.50% by weight based on the total weight of the negative electrode active material layer.

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