Lithium secondary battery

Abstract

The present invention relates to a lithium secondary battery comprising: an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery case including an internal space for accommodating the electrode assembly and the electrolyte, in which the positive electrode includes a positive electrode active material including a lithium nickel-based oxide containing 50 mol% to 70 mol% of nickel in all metals other than lithium, and an electrolyte fill factor (EFF) index (unit: g / Ah) defined by the following Equation 1 is 1.82 to 2.06. [Equation 1] In Equation 1, RE [unit: g] represents the weight of the remaining electrolyte contained in the lithium secondary battery after activation, SU represents the ratio (SA / SE) of the volume (SA) of the electrode assembly to the volume (SE) of the lithium secondary battery, and NC [unit: Ah] represents the capacity of the lithium secondary battery when discharged from 4.4 V to 2.5 V at 0.33 C at 25 DEG C.

Description

[0001] Cross-reference to related applications

[0002] This application claims the benefit of Korean Patent Application No. 10-2024-0016255, filed on February 1, 2024, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to a lithium secondary battery, and more specifically, to a lithium secondary battery having high energy density and excellent high-temperature life characteristics. Background Technology

[0004] In recent years, as the application of lithium secondary batteries has rapidly expanded to power large equipment such as automobiles and energy storage systems, as well as electronic equipment such as electrical, electronic, communication, and computer equipment, the demand for high-capacity, high-output, and high-stability secondary batteries has been increasing.

[0005] Lithium-ion rechargeable batteries typically include a positive electrode containing a positive active material, a negative electrode containing a negative active material, an electrolyte serving as a medium for transporting lithium ions, and a separator. In this case, carbon-based active materials, silicon-based active materials, etc., can be used as the negative active material, and lithium transition metal oxides, such as lithium cobalt oxide, lithium nickel oxide, and lithium nickel-cobalt-manganese composite oxide, can be used as the positive active material.

[0006] Meanwhile, to improve the energy density of the cathode, recent research has focused on lithium-nickel-cobalt-manganese composite transition metal oxides with a nickel content of at least 80 mol% in metals other than lithium as cathode active materials. However, as the nickel content in the lithium-nickel-cobalt-manganese composite transition metal oxide increases, the cathode active material undergoes rapid structural stability collapse at high temperatures, leading to significant performance degradation and reduced thermal stability.

[0007] To prevent such problems, when reducing the nickel content in lithium nickel-cobalt-manganese composite transition metal oxides, the driving voltage needs to be increased to achieve the required energy density. However, when driven at such a high voltage, electrolyte side reactions at the positive electrode are aggravated and gas generation inside the battery increases.

[0008] Therefore, there is a need to develop a lithium secondary battery that exhibits excellent energy density and thermal stability, and allows for reduced electrolyte side reactions under high-voltage driving conditions. Summary of the Invention

[0009] [Technical Issues]

[0010] The present invention aims to overcome the above-mentioned limitations. Therefore, one aspect of the present invention provides a lithium secondary battery that achieves high energy density while exhibiting excellent high-temperature lifetime characteristics due to the reduction of electrolyte side reactions under high voltage, and the positive electrode active material exhibits excellent thermal stability.

[0011] [Technical Solution]

[0012] [1] According to one aspect of the present invention, a lithium secondary battery is provided, comprising: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery casing housing the electrode assembly and the electrolyte, wherein the positive electrode includes a positive electrode active material, the positive electrode active material including a lithium nickel-based oxide, the lithium nickel-based oxide containing 50 mol% to 70 mol% nickel in all metals except lithium, and the electrolyte fill factor (EFF) index (in g / Ah) defined by Equation 1 is 1.82 to 2.06.

[0013] [Equation 1]

[0014] In equation 1 above, R E [Unit: g] indicates the weight of the remaining electrolyte contained in the activated lithium secondary battery, in s. U The volume (S) of the electrode assembly A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), N C [Unit: Ah] indicates the capacity of a lithium secondary battery when discharged from 4.4 V to 2.5 V at 0.33C at 25°C.

[0015] [2] The present invention provides the lithium secondary battery described in [1] above, wherein R E It is 265–295 g.

[0016] [3] The present invention provides the lithium secondary battery described in [1] or [2] above, wherein S U The value ranges from 0.70 to 0.95.

[0017] [4] The present invention provides a lithium secondary battery according to at least one of [1] to [3] above, wherein N C It ranges from 90 to 150 Ah.

[0018] [5] The present invention provides a lithium secondary battery according to at least one of [1] to [4] above, wherein the ratio (R) E / N C The value of [unit: g / Ah] ranges from 2.00 to 3.30.

[0019] [6] The present invention provides a lithium secondary battery according to at least one of [1] to [5] above, wherein the volume (S A ) of the electrode assembly is 0.3 L to 1.35 L.

[0020] [7] The present invention provides a lithium secondary battery according to at least one of [1] to [6] above, wherein the volume (S E ) of the lithium secondary battery is 0.4 L to 1.5 L.

[0021] [8] The present invention provides a lithium secondary battery according to at least one of [1] to [7] above, wherein the lithium nickel-based oxide contains 15 mol% or less of cobalt (Co) among all metals other than lithium.

[0022] [9] The present invention provides a lithium secondary battery according to at least one of [1] to [8] above, wherein the lithium nickel-based oxide is represented by the following formula 1.

[0023] [Formula 1]

[0024] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 O2

[0025] In the above formula 1, 0 ≤ a1 ≤ 0.5, 0.5 ≤ x1 ≤ 0.7, 0 < y1 ≤ 0.15, 0 < z1 ≤ 0.4 and 0 ≤ w1 ≤ 0.2 are satisfied, and M 1 is at least one doping element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0026]

[10] The present invention provides a lithium secondary battery according to at least one of [1] to [9] above, wherein the lithium nickel-based oxide is a single-particle type particle.

[0027]

[11] The present invention provides a lithium secondary battery according to at least one of [1] to

[10] above, wherein the charging cut-off voltage of the lithium secondary battery is 4.3 V or more.

[0028]

[12] The present invention provides a lithium secondary battery according to at least one of [1] to

[11] above, wherein the nominal voltage of the lithium secondary battery is 3.68 V or more.

[0029]

[13] The present invention provides a lithium secondary battery according to at least one of [1] to

[12] above, wherein the negative electrode comprises graphite as a negative electrode active material.

[0030]

[14] The present invention provides a lithium secondary battery according to at least one of [1] to

[13] above, wherein the battery casing is a prismatic battery casing.

[0031]

[15] The present invention provides a lithium secondary battery according to at least one of [1] to

[14] above, wherein the electrode assembly is formed such that the positive electrode, the separator and the negative electrode are stacked in sequence and wound in one direction.

[0032] [Beneficial Effects]

[0033] According to the present invention, when the nickel content in all metals other than lithium is 50 mol% to 70 mol%, the positive electrode active material exhibits improved structural stability at high temperatures, thereby possessing excellent thermal stability. Furthermore, by appropriately adjusting the weight of the remaining electrolyte after activation according to the structure and capacity of the lithium secondary battery, it is possible to simultaneously reduce the generation of internal gas during high-voltage operation and achieve appropriate electrolyte impregnation. Therefore, the lithium secondary battery manufactured thereby can possess high energy density, high capacity characteristics, excellent lifetime characteristics, and high-temperature lifetime characteristics. Detailed Implementation

[0034] The present invention will now be described in detail.

[0035] It should be understood that the words or terms used herein and in the claims of this invention should not be construed as having the meanings defined in commonly used dictionaries. It should be further understood that, based on the principle that the inventors can appropriately define the meanings of words or terms to best interpret the invention, these words or terms should be interpreted as having meanings consistent with their context in the relevant field and in the technical concept of the invention.

[0036] The terminology used herein is for the purpose of describing particular exemplary embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular expressions “an,” “a,” and “the” are also intended to include the plural forms.

[0037] It should be further understood that the terms “comprising,” “including,” or “having” as used herein specify the presence of the stated features, numbers, steps, elements, or combinations thereof, but do not exclude the presence or addition of one or more other features, numbers, steps, elements, or combinations thereof.

[0038] As used herein, the term "monoparticle-type particle" refers to a particle composed of 30 or fewer subparticles. The subparticle unit constituting a monoparticle-type particle is defined as a nodule. Monoparticle-type particles include monoparticles formed from a single nodule or quasi-monoparticles as a complex of 30 or fewer nodules.

[0039] The term "granular unit" refers to the sub-granular unit that constitutes a single grain and a quasi-single grain, and a grain may be a single crystal without any grain boundaries, or a polycrystalline material without grain boundaries when observed with a scanning electron microscope (SEM) in a field of view of 5000× to 20000×.

[0040] As used herein, the term "secondary particle" refers to a particle formed by the aggregation of more than 30 subparticles. To distinguish this term from subparticles that form single-particle-type particles, each subparticle unit that forms a secondary particle is referred to as a "primary particle".

[0041] As used in this article, the term "particle" may encompass any or all of the following: single particle, quasi-single particle, primary particle, segment, and secondary particle.

[0042] As used in this article, the term "average particle size D" 50 "50% volumetric size" indicates the particle size at the 50% volumetric size distribution of the test powder and can be measured using laser diffraction. For example, the average particle size D50 can be measured as follows: the target powder to be measured is dispersed in a dispersion medium, the dispersion medium is introduced into a commercial laser diffraction particle size analyzer (e.g., Microtrac MT 3000), and the powder is irradiated with ultrasonic waves at a frequency of approximately 28 kHz and an output of 60 W to obtain a volumetric size distribution map, and the particle size at the 50% volumetric size is calculated.

[0043] The inventors conducted repeated research to develop a lithium secondary battery that exhibits excellent lifespan and storage performance at high temperatures and high voltages, while also achieving high capacity characteristics. They discovered that when nickel accounts for 50 to 70 mol% of all metals except lithium, and the structure, discharge capacity, and remaining electrolyte weight after activation of the lithium secondary battery are adjusted to satisfy a specific equation, the lithium secondary battery possesses excellent capacity characteristics, high voltage and high-temperature lifespan and storage characteristics, as well as improved electrolyte impregnation, thus completing this invention.

[0044] The present invention will now be described in detail.

[0045] The lithium secondary battery of the present invention may contain at least one of the following components, and may contain any technically feasible combination of the following components.

[0046] Lithium secondary batteries

[0047] The lithium secondary battery of the present invention includes: an electrode assembly comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery casing comprising an internal space accommodating the electrode assembly and the electrolyte, wherein the positive electrode comprises a positive electrode active material comprising a lithium nickel-based oxide, the lithium nickel-based oxide containing 50 mol% to 70 mol% nickel in all metals except lithium, and an electrolyte fill factor (EFF) index (in g / Ah) defined by Equation 1 is 1.82 to 2.06.

[0048] [Equation 1]

[0049] In equation 1 above, R E [Unit: g] indicates the weight of the remaining electrolyte contained in the activated lithium secondary battery, in s. U The volume (S) of the electrode assembly A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), N C [Unit: Ah] indicates the capacity of a lithium secondary battery when discharged from 4.4 V to 2.5 V at 0.33C at 25°C.

[0050] The EFF index (unit: g / Ah) of the lithium secondary battery of the present invention, as defined by Equation 1, can be from 1.82 to 2.06, specifically 1.82 or higher, 1.83 or higher, 1.84 or higher, 1.85 or higher, 1.86 or higher, 1.87 or higher, 1.88 or higher, 1.89 or higher, 1.90 or higher, and 1.91 or higher, and can be less than 2.06, less than 2.05, less than 2.04, less than 2.03, less than 2.02, less than 2.01, less than 2.00, less than 1.99, less than 1.98, less than 1.97, less than 1.96, less than 1.95, less than 1.94, less than 1.93, less than 1.92, and less than 1.91. For example, the EFF index can be from 1.82 to 2.06, 1.88 to 2.00, 1.89 to 1.96, and 1.90 to 1.94.

[0051] Recently, efforts have been made to increase the energy density of the cathode by using lithium nickel-based oxides containing nickel, cobalt, and manganese, with a higher nickel content, as the positive electrode active material, in order to achieve the high capacity characteristics of lithium secondary batteries. However, as the nickel content of lithium nickel-based oxides increases, due to the Ni... 2+ The ions are transformed into Ni 4+The presence of ions reduces the structural and chemical stability of the positive electrode active material, thus accelerating side reactions with the electrolyte and reducing its lifetime characteristics. This phenomenon is further accelerated when exposed to high temperatures, leading to a significant decrease in thermal stability.

[0052] While reducing the nickel content of lithium nickel-based oxides can improve their thermal stability at high temperatures, achieving the same energy density as high-nickel-content lithium nickel-based oxides requires driving them at high voltages (e.g., above 4.35 V). However, driving at such high voltages leads to oxygen desorption due to changes in the oxidation states of nickel and cobalt, exacerbating electrolyte side reactions and increasing gas generation, resulting in deterioration of lifetime and storage performance.

[0053] Therefore, it is necessary to reduce the amount of electrolyte injected to reduce gas generation. However, when the amount of electrolyte injected is reduced too much, the electrolyte impregnation of the electrode deteriorates, leading to an increase in lithium ion mobility and battery resistance. As a result, the battery may have reduced capacity and lifespan characteristics. Therefore, it is necessary to adjust the amount of electrolyte injected appropriately according to the characteristics of the battery.

[0054] Therefore, the lithium secondary battery of the present invention prevents the above-mentioned problems by adjusting the weight of the remaining electrolyte after activation to specific conditions based on the characteristics of the lithium secondary battery, according to the ratio of the volume of the lithium secondary battery excluding the battery casing to the volume of the lithium secondary battery and the discharge capacity of the lithium secondary battery.

[0055] Specifically, the lithium secondary battery of the present invention can achieve high energy density and high capacity characteristics by adjusting the EFF index defined in Equation 1 to 1.82 to 2.06, and can also exhibit excellent thermal stability, reduced gas generation and appropriate electrolyte impregnation, thereby having excellent high-temperature life characteristics and high-temperature storage characteristics.

[0056] R E This indicates the weight of the remaining electrolyte in the activated lithium secondary battery. The residual electrolyte included in a lithium secondary battery refers to the sum of the electrolyte impregnated in the internal pores of the electrode assembly and the electrolyte located outside the electrode assembly in the internal space of the battery casing.

[0057] The weight of the remaining electrolyte contained in the activated lithium secondary battery may differ from the weight of the electrolyte initially injected into the battery casing during the lithium secondary battery manufacturing process prior to activation.

[0058] Activation refers to the following process: charging and / or discharging a manufactured but uncharged or undischarged lithium secondary battery to provide electrical characteristics and forming a solid electrolyte interface (SEI) film on the electrodes to stabilize the battery, thereby making the battery practically usable.

[0059] Regarding R E Activation can be achieved by charging the lithium secondary battery to a voltage of 4.0 V or higher at 55°C at least once.

[0060] Specifically, regarding R E Activation can be achieved by performing the following operations: (1) charging the lithium secondary battery to 4.0V or 3% SOC at a constant current of 0.2C at 55°C, (2) charging the lithium secondary battery to 4.35V or 17% SOC at a constant current of 1.0C at 55°C, and (3) charging the lithium secondary battery to 4.35V or 60% SOC at a constant current of 1.0C at 55°C.

[0061] For example, the weight (R) of the remaining electrolyte contained in the activated lithium secondary battery. E The following methods can be used to measure: (1) the weight of the activated lithium secondary battery (M). L The lithium secondary battery includes an electrode assembly, an electrolyte, and a battery casing, wherein the battery casing is sealed; (2) the lithium secondary battery is disassembled to remove the electrolyte present in the battery casing; (3) the battery casing and electrode assembly are immersed in dimethyl carbonate solvent to remove the electrolyte present on the surface of the battery casing, the surface of the electrode assembly, and the internal pores, and then the battery casing and the electrode assembly are dried; and (4) the weight (M) of the dried battery casing is measured. C ) and the weight of the dried electrode assembly (M) A Then measure M L M C and M A Substitute into equation A below.

[0062] [Equation A]

[0063] R E =M L -M C -M A

[0064] R E The g value can be from 265 g to 295 g, 267 g to 290 g, more preferably from 270 g to 282 g or 272 g to 278 g. When the above ranges are met, electrolyte side reactions are reduced, resulting in reduced gas generation and sufficient electrolyte impregnation, thus ensuring sufficient lithium-ion mobility and achieving excellent lifetime, output, and high-temperature storage characteristics.

[0065] S U The volume (S) of the electrode assembly A ) and the volume (S) of lithium secondary batteries EThe ratio of (S) A / S E Volume of lithium secondary batteries (S) E This is the volume calculated for the external shape of a lithium-ion battery, specifically representing the volume of the space occupied by that external shape. In this case, when the battery casing is sealed, the external shape of the lithium-ion battery can be the same as the external shape of the battery casing. The volume of a lithium-ion battery can be determined based on its external dimensions, without considering the volume occupied by components such as electrolyte and electrode assemblies, or the volume of pores housed inside the battery casing.

[0066] When the battery casing is a prismatic shape, the volume (S) of the lithium secondary battery... E The volume (S) of the lithium secondary battery can be obtained according to Equation B below. Assuming the lithium secondary battery, including the prismatic battery casing, has a cuboid shape, the volume of the lithium secondary battery (S) can be obtained according to Equation B below. E ).

[0067] [Equation B]

[0068] S E = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0069] In equation B above, the thickness of the lithium secondary battery can be represented as the distance measured along the thickness direction of the lithium secondary battery relative to its external shape.

[0070] In equation B above, the length of the lithium secondary battery can be represented as the distance measured along the length direction of the lithium secondary battery relative to its external shape.

[0071] In equation B above, the width of the lithium secondary battery can be represented as the distance measured along the width direction of the lithium secondary battery relative to its external shape.

[0072] The shape of a lithium secondary battery is not limited to the shapes described above, and a lithium secondary battery can have any suitable shape. The volume of a lithium secondary battery can be determined based on its shape using appropriate measurement methods.

[0073] Volume of electrode assembly (S) A The volume represents the sum of the volumes occupied by the positive electrode, negative electrode, and separator. The volume of the electrode assembly can be adjusted by controlling the porosity and loading of the positive and negative electrodes and the N / P ratio (the ratio of negative electrode capacity to positive electrode capacity), or by changing the type of conductive material contained in the positive and negative electrodes. The volume of the electrode assembly can be measured relative to the shape of the positive electrode, negative electrode, or separator, and does not exclude the volume of pores included in the positive electrode, negative electrode, or separator.

[0074] Volume of electrode assembly (S) A It can be obtained through the following equation C.

[0075] [Equation C]

[0076] S A =(Volume of positive electrode) + (Volume of negative electrode) + (Volume of membrane)

[0077] In Equation C above, the volume of the positive electrode, the volume of the negative electrode, and the volume of the separator can be measured individually for the shape of the positive electrode, negative electrode, or separator, without considering the volume of the pores contained in the positive electrode, negative electrode, or separator.

[0078] S U It can be 0.70 to 0.95, 0.73 to 0.90, 0.75 to 0.85, or 0.77 to 0.82. When the above ranges are met, the relative space utilization can be increased within the same capacity, thereby achieving high energy density, and the gases generated due to electrolyte side reactions can be appropriately accommodated.

[0079] Volume of lithium secondary battery (S) E The electrolyte can be 0.4 L to 1.5 L, 0.5 L to 1.3 L, or 0.6 L to 1.1 L. When these ranges are met, the electrode assembly and electrolyte can be adequately accommodated, and S U The value can satisfy the appropriate range.

[0080] Volume of electrode assembly (S) A The energy density can be 0.3 L to 1.35 L, 0.4 L to 1.2 L, or 0.5 L to 1 L. When these ranges are met, excellent energy density can be achieved, and S U The value can satisfy the appropriate range.

[0081] N C This indicates the capacity of a lithium secondary battery when discharged from 4.4 V to 2.5 V at 0.33C at 25°C.

[0082] Specifically, N C This can refer to the capacity of a lithium secondary battery when it is activated, charged at 25°C, and discharged from 4.4 V to 2.5 V at 0.33 C. Specifically, it represents the discharge capacity during the first charge / discharge cycle after activation. For N... C The first charge / discharge after activation can be performed by charging the lithium secondary battery from 2.5 V to 4.35 V at a C rate of 0.33C at 25°C.

[0083] For N CThe activation can be carried out by charging the manufactured but not yet charged or discharged lithium secondary battery to 4.35 V (with a cutoff of 0.05C) at a constant current / constant voltage of 0.33C at 25°C, and discharging the lithium secondary battery to 2.0 V at a constant current of 0.33C.

[0084] N C It can be 90 to 150 Ah, 100 to 140 Ah, 105 to 130 Ah, or 110 to 120 Ah. When the above ranges are met, high capacity characteristics can be achieved.

[0085] When a lithium secondary battery is discharged from 4.4 V to 2.5 V at 0.33C at 25°C, the weight (R) of the remaining electrolyte contained in the activated lithium secondary battery is... E ) and capacity (N C The ratio of (R) E / N C The value of R [unit: g / Ah] can range from 2.00 to 3.30. Specifically, R E / N C [Unit: g / Ah] can be 2.05 or higher, 2.07 or higher, 2.10 or higher, 2.13 or higher, 2.15 or higher, 2.17 or higher, 2.20 or higher, 2.23 or higher, 2.25 or higher, 2.27 or higher, or 2.30 or higher; and can be below 3.30, below 3.10, below 3.00, below 2.90, below 2.80, below 2.70, below 2.60, below 2.55, below 2.50, below 2.45, or below 2.40. For example, R E / N C [Unit: g / Ah] can be 2.00 to 3.30, 2.15 to 2.90, 2.23 to 2.55, or 2.30 to 2.40. When the above ranges are met, the effects of reducing gas generation and improving electrolyte impregnation can be maximized, depending on the battery design.

[0086] The components of the lithium secondary battery of the present invention will be described in detail below.

[0087] The lithium secondary battery of the present invention comprises: an electrode assembly including a positive electrode, a negative electrode and a separator disposed between the positive electrode and the negative electrode; an electrolyte; and a battery casing housing the electrode assembly and the electrolyte.

[0088] (1) Electrode assembly

[0089] The electrode assembly of the present invention includes a positive electrode, a negative electrode, and a diaphragm disposed between the positive electrode and the negative electrode.

[0090] Specifically, an electrode assembly can be formed by sequentially stacking a positive electrode, a separator, and a negative electrode, and the positive and negative electrodes can be insulated from each other by the separator.

[0091] Electrode assemblies may include, but are not limited to, stacked, wound, and stacked folded types.

[0092] Preferably, the electrode assembly can be of the core type, and the electrode assembly can be formed in which the positive electrode, the separator and the negative electrode are stacked in sequence and wound in one direction. Specifically, multiple positive electrodes, separators and negative electrodes can be stacked alternately and wound in one direction.

[0093] Each component of the electrode assembly of the present invention will be described in detail below.

[0094] 1) Positive electrode

[0095] The positive electrode contains a positive electrode active material. Specifically, the positive electrode may contain a positive electrode current collector and a layer of positive electrode active material disposed on the positive electrode current collector, and the positive electrode active material layer may contain positive electrode active material.

[0096] As the positive electrode current collector, various positive electrode current collectors known in the art can be used. For example, stainless steel, aluminum, nickel, titanium, sintered carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, silver, etc., can be used as the positive electrode current collector. The positive electrode current collector can typically have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the positive electrode current collector to enhance the adhesion of the positive electrode active material. For example, the positive electrode current collector can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0097] The positive electrode active material layer can be disposed on the positive electrode current collector, and specifically, it can be disposed on one or both surfaces of the positive electrode current collector. The positive electrode active material layer can have a single-layer structure or a multi-layer structure with two or more layers.

[0098] The positive electrode active material comprises a lithium nickel-based oxide, wherein the nickel content of the lithium nickel-based oxide is 50 mol% to 70 mol%, 52 mol% to 68 mol%, 55 mol% to 65 mol%, or 57 mol% to 63 mol% relative to all metals except lithium. In this case, the positive electrode active material exhibits superior structural and chemical stability at high temperatures compared to positive electrode active materials containing lithium nickel-based oxides with high nickel content, thus possessing excellent thermal stability. Furthermore, it can mitigate gas generation and expansion caused by residual lithium byproducts (LiOH, Li2CO3, etc.) present on the surface of the positive electrode active material, thereby exhibiting excellent lifetime characteristics.

[0099] Compared to all metals except lithium, lithium nickel-based oxides may contain less than 15 mol%, 5 mol% to 15 mol%, 7 mol% to 13 mol%, or 8 mol% to 12 mol% of cobalt (Co). When cobalt is included in the above ranges, cost savings and improved resistance and output characteristics can be achieved through the lower Co content.

[0100] Specifically, lithium nickel-based oxides can be represented by the following formula 1.

[0101] [Formula 1]

[0102] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 O2

[0103] In Equation 1 above, M 1 This corresponds to doping elements that may or may not be included in lithium nickel-based oxides. M 1 The doping element may be selected from at least one of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo, or it may be selected from at least one of W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. When a doping element is included, it can promote particle growth during the sintering of the positive electrode active material or improve the stability of the crystal structure.

[0104] In Equation 1 above, 1+a1 can represent the molar ratio of lithium (Li) in the lithium nickel-based oxide, and can satisfy 0≤a1≤0.5, 0≤a1≤0.2, or 0≤a1≤0.1. When the above ranges are satisfied, the positive electrode active material can form a stable layered crystal structure.

[0105] In Equation 1 above, x1 can represent the molar ratio of nickel to all metals other than lithium in the lithium nickel-based oxide particles, and can satisfy 0.5≤x1≤0.7, 0.52≤x1≤0.68, 0.55≤x1≤0.65, or 0.57≤x1≤0.63. When the above ranges are met, the resulting lithium secondary battery exhibits excellent high-temperature storage characteristics, high-temperature lifespan characteristics, and thermal stability.

[0106] In Equation 1 above, y1 can represent the molar ratio of cobalt to all metals other than lithium in the lithium nickel-based oxide particles, and can satisfy 0 < y1 ≤ 0.15 or 0 < y1 ≤ 0.10 or 0 < y1 ≤ 0.07. When the above ranges are satisfied, cost savings, good resistance characteristics, and output characteristics can be achieved as the Co content decreases, and as the Mn ratio relatively increases, the positive electrode active material can have improved structural stability.

[0107] In Equation 1 above, z1 can represent the molar ratio of manganese to all metals other than lithium in the lithium nickel-based oxide particles, and can satisfy 0 < z1 ≤ 0.4, 0.1 ≤ z1 ≤ 0.4, 0.15 ≤ z1 ≤ 0.4 or 0.2 ≤ z1 ≤ 0.4. When the above ranges are satisfied, the positive electrode active material can have improved structural stability.

[0108] The above w1 represents M in the lithium nickel-based oxide 1 The molar ratio to all metals other than lithium, and can satisfy 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15 or 0 ≤ w1 ≤ 0.1. When the above ranges are satisfied, particle growth during the firing of the positive electrode active material can be promoted or the crystal structure stability can be improved.

[0109] In addition, the lithium nickel-based oxide can be single-particle type particles. <(

[0110] Specifically, when the lithium nickel-based oxide is secondary particles, particle breakage increases during electrode manufacturing, and internal cracks are caused by the volume expansion / contraction of the primary particles during charging / discharging, which may reduce the effect of improving the high-temperature life characteristics and high-temperature storage characteristics.

[0111] Therefore, when using lithium nickel oxide in the form of single-particle type particles as described above, since this lithium nickel oxide has higher particle strength than the common lithium nickel-based oxide in the form of secondary particles that aggregate more than 30 primary particles, fewer particles break during roll pressing. In addition, since the lithium nickel oxide of the present invention (which is single-particle type particles) has a small number of primary particles constituting the particles, the change caused by the volume expansion / contraction of the primary particles during charging and discharging is small, and thus, the generation of internal cracks in the particles is significantly reduced.

[0112] Therefore, the lithium secondary battery of the present invention uses a lithium nickel-based oxide as single-particle type particles, and thus can have excellent thermal stability due to reduced particle breakage and internal particle cracking during charge and discharge, thereby improving the high-temperature life characteristics and high-temperature storage characteristics.

[0113] Meanwhile, the average particle size (D of the positive electrode active material 50The micrometer diameter (μm) can be 1 μm to 8 μm, 2 μm to 7 μm, 2.5 μm to 6 μm, 3 μm to 5 μm, or 3.5 μm to 4.5 μm. When these ranges are met, side reactions with the electrolyte can be minimized while preventing increased resistance and deterioration of output characteristics, thus resulting in excellent high-temperature lifetime and high-temperature storage characteristics.

[0114] The positive electrode active material layer may comprise 90 wt% to 99 wt%, 92 wt% to 99 wt%, or 94 wt% to 98 wt% of positive electrode active material. When these ranges are met, the lithium secondary battery can exhibit improved energy density and capacity characteristics.

[0115] Additionally, the positive electrode active material layer may optionally include at least one of a positive electrode conductive material or a positive electrode binder.

[0116] The positive electrode conductive material is used to impart conductivity to the electrode, and any positive electrode conductive material can be used without particular limitation, as long as it is electronically conductive and does not cause chemical changes in the battery to be constructed. Specific examples can include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more of them can be used. The content of the positive electrode conductive material relative to the total weight of the positive electrode active material layer can typically be 0.1 wt% to 30 wt%, 0.3 wt% to 20 wt%, 0.5 wt% to 10 wt%, 0.7 wt% to 5 wt%, or 1 wt% to 3 wt%.

[0117] The positive electrode binder is used to improve the bonding between positive electrode material particles and the adhesion between the positive electrode material and the positive electrode current collector. Specific examples of positive electrode binders can be: fluoropolymer binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyol binders, including polyvinyl alcohol; polyolefin binders, including polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders, and any one or a mixture of two or more of them can be used. The content of the positive electrode binder relative to the total weight of the positive electrode active material layer can be 0.1% to 30% by weight, 0.3% to 20% by weight, 0.5% to 10% by weight, 0.7% to 5% by weight, or 1% to 3% by weight.

[0118] Meanwhile, the positive electrode can be prepared as follows: applying a positive electrode slurry to one or both sides of an elongated positive electrode current collector, removing the solvent from the positive electrode slurry through a drying process, and then rolling. Alternatively, when applying the positive electrode slurry, a positive electrode including an uncoated portion can be prepared by not applying the positive electrode slurry to a portion of the positive electrode current collector (e.g., one end of the positive electrode current collector).

[0119] Alternatively, the positive electrode slurry can be prepared by dispersing the positive electrode active material in solvents such as dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), acetone, or water.

[0120] 2) Negative electrode

[0121] The negative electrode may contain a negative electrode active material. Specifically, the negative electrode may contain a negative electrode current collector and a layer of negative electrode active material disposed on the negative electrode current collector, and the negative electrode active material layer may contain a negative electrode active material.

[0122] There are no particular restrictions on the negative electrode current collector, as long as it has high conductivity and does not cause chemical changes in the battery. For example, copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel with a surface treatment of carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloys can be used. The negative electrode current collector can typically have a thickness from 3 μm to 500 μm.

[0123] In addition, similar to positive electrode current collectors, negative electrode current collectors can have fine irregularities formed on their surface to improve the adhesion strength of the negative electrode active material. For example, current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, and nonwoven fabrics.

[0124] The negative electrode active material layer can be disposed on the negative electrode current collector, and specifically, it can be disposed on one or both surfaces of the negative electrode current collector. The negative electrode active material layer can have a single-layer structure or a multi-layer structure with two or more layers.

[0125] The negative electrode can contain graphite as the negative electrode active material. In this case, the volume change of the negative electrode active material during charging and discharging is smaller than that of silicon-based active materials, thus exhibiting excellent lifetime characteristics.

[0126] Specifically, the graphite may be at least one selected from the group consisting of artificial graphite and natural graphite, and preferably may be a combination of artificial graphite and natural graphite.

[0127] When the negative electrode contains both synthetic and natural graphite, the weight ratio of synthetic and natural graphite can be 6.5:3.5 to 9.5:0.5, 7:3 to 9:1, or 7.5:2.5 to 8.5:1.5. When these ranges are met, capacity characteristics can be improved, while output and lifetime characteristics can be excellent.

[0128] The content of the negative electrode active material relative to the total weight of the negative electrode active material layer can be 80% to 99% by weight, 85% to 98% by weight, or 90% to 97% by weight. When the above ranges are met, sufficient capacity characteristics can be achieved.

[0129] In addition to the negative electrode active material, the negative electrode active material layer may optionally include a negative electrode conductive material and a negative electrode binder.

[0130] The negative electrode conductive material is used to impart conductivity to the electrode, and any negative electrode conductive material can be used without particular limitation, as long as it is electronically conductive without causing chemical changes in the battery to be constructed. Specific examples can include: graphite, such as natural or artificial graphite; carbon-based materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermally cracked carbon black, carbon fibers, and carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers such as polyphenylene derivatives, and any one or a mixture of two or more of them can be used. The content of the negative electrode conductive material relative to the total weight of the negative electrode active material layer can typically be 0.1 wt% to 20 wt%, 0.2 wt% to 10 wt%, 0.3 wt% to 5 wt%, or 0.4 wt% to 2 wt%.

[0131] A negative electrode binder is used to improve the bonding between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Specific examples may include polyvinylidene fluoride (PVDF), polyvinylidene 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, or various copolymers thereof, and any one or a mixture of two or more thereof may be used. The content of the negative electrode binder relative to the total weight of the negative electrode active material layer may be 0.1% to 30% by weight, 0.3% to 20% by weight, 0.5% to 10% by weight, 0.7% to 5% by weight, or 1% to 3% by weight.

[0132] The negative electrode active material layer may optionally further comprise a thickener. Any thickener commonly used in lithium-ion secondary batteries can be used as the thickener, and an example is carboxymethyl cellulose (CMC). The thickener content relative to the total weight of the negative electrode active material layer can be from 0.1 wt% to 10 wt%, 0.3 wt% to 8 wt%, 0.5 wt% to 5 wt%, 0.7 wt% to 3 wt%, or 1 wt% to 2 wt%.

[0133] Anodes can be prepared using common anode manufacturing methods. For example, anode active material, anode conductive material, and / or anode conductive material can be mixed in anode solvent to prepare anode slurry, and the anode slurry can be coated onto anode current collector, then dried and rolled to prepare the anode.

[0134] In order to promote the dispersion of the components of the negative electrode slurry, the negative electrode solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol and isopropanol, preferably distilled water.

[0135] The solid content of the negative electrode slurry can be from 30% to 80% by weight, specifically from 40% to 70% by weight.

[0136] Alternatively, the negative electrode can be prepared by casting a separate support with a negative electrode slurry and then laminating the negative electrode current collector with a membrane separated from the support.

[0137] 3) Diaphragm

[0138] The diaphragm can be placed between the positive and negative electrodes.

[0139] A separator is positioned between the positive and negative electrodes, thereby separating the two electrodes and providing a migration channel for lithium ions. Any separator commonly used in lithium-ion secondary batteries can be used without particular limitation. Specifically, as the separator, porous polymer membranes can be used, such as porous polymer membranes formed from polyolefin polymers (e.g., ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers), or membranes having a stacked structure with two or more layers. Furthermore, typical porous nonwoven fabrics can be used, such as nonwoven fabrics formed from high-melting-point glass fibers or polyethylene terephthalate fibers. Additionally, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0140] (2) Electrolytes

[0141] The electrolyte of the present invention may contain lithium salt and organic solvent.

[0142] Any compound can be used as a lithium salt without particular limitation, as long as it is a compound capable of providing lithium ions used in lithium secondary batteries. Specifically, the lithium salt may include 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, with LiPF6 being preferred.

[0143] The lithium salt can be present at a concentration of 0.1 M to 3.0 M, preferably 0.1 M to 2.0 M, and more preferably 0.5 M to 1.5 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, and therefore can exhibit excellent performance, and lithium ions can move efficiently.

[0144] Organic solvents are commonly used non-aqueous solvents in lithium secondary batteries, and there are no particular restrictions, as long as their decomposition caused by oxidation reactions during the charging / discharging process of the secondary battery can be minimized.

[0145] Specifically, the organic solvent may include at least one selected from cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0146] Specifically, organic solvents may include cyclic carbonate organic solvents, linear carbonate organic solvents, or mixtures thereof.

[0147] Cyclic carbonate organic solvents are high-viscosity organic solvents that can effectively dissociate lithium salts in electrolytes due to their high dielectric constant. Specifically, they can be non-fluorinated saturated cyclic carbonate organic solvents. Cyclic carbonate organic solvents can include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentene carbonate, 2,3-pentene carbonate, and vinylene carbonate, and can more specifically include at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC), and can even more specifically include ethylene carbonate (EC).

[0148] Furthermore, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant, and specifically can be non-fluorinated linear carbonates. Linear carbonate organic solvents can include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl propyl carbonate, and ethyl propyl carbonate, and can more specifically include at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and can more specifically include ethyl methyl carbonate (EMC).

[0149] The organic solvent can be a mixture of cyclic carbonate organic solvents and linear carbonate organic solvents. In this case, the cyclic carbonate organic solvents and linear carbonate organic solvents can be mixed in volume ratios of 5:95 to 40:60, 10:90 to 38:62, or 25:75 to 35:65. When the mixing ratio of the cyclic carbonate organic solvents and linear carbonate organic solvents meets the above ranges, both high dielectric constant and low viscosity are achieved, and excellent ionic conductivity can be realized.

[0150] In addition, in order to prepare an electrolyte with high ionic conductivity, in addition to at least one carbonate organic solvent selected from the group consisting of cyclic carbonate organic solvents and linear carbonate organic solvents, the organic solvent may further include at least one ester organic solvent selected from the group consisting of linear ester organic solvents and cyclic ester organic solvents.

[0151] Straight-chain ester organic solvents may specifically include at least one selected from methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0152] In addition, cyclic ester solvents may specifically include at least one selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0153] Furthermore, when needed, organic solvents can be used by adding organic solvents commonly used in non-aqueous electrolytes, without limitation. For example, at least one organic solvent selected from ether organic solvents, glycol diether solvents, and nitrile organic solvents may be further included.

[0154] As an ether solvent, any one or a mixture of two or more of the group consisting of dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, methyl propyl ether, ethyl propyl ether, 1,3-dioxolane (DOL) and 2,2-bis(trifluoromethyl)-1,3-dioxolane (TFDOL) can be used, but the embodiments are not limited thereto.

[0155] Glycol diether solvents are solvents that have a higher dielectric constant and lower surface tension than linear carbonate organic solvents and are less reactive with metals. They may include, but are not limited to, at least one selected from dimethoxyethane (glycol dimethyl ether, DME), diethoxyethane, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether (TEGDME).

[0156] Nitrile solvents may include, but are not limited to, at least one selected from acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanoic acid, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, etc.

[0157] In addition to the electrolyte components, the electrolyte may further contain additives to improve battery life characteristics, prevent battery capacity reduction, and increase battery discharge capacity.

[0158] The additive may include at least one additive selected from the group consisting of nonfluorinated unsaturated cyclic carbonates, halogenated carbonates, sulfonyl lactones, sulfates / salts, borates / salts, nitriles, benzenes, amines, silanes, and lithium salts that are different from the lithium salts contained in the electrolyte.

[0159] Specifically, the additives may be selected from vinylene carbonate (VC), vinyl ethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propane sulpholactone (PS), 1,4-butane sulpholactone, vinyl sulpholactone, 1,3-propene sulpholactone (PRS), 1,4-butene sulpholactone, 1-methyl-1,3-propene sulpholactone, ethylene sulfate (Esa), trimethylene sulfate (TMS), methyl trimethylene sulfate (MTMS), tetraphenylborate, lithium oxaloyl difluoroborate, succinate, adiponitrile, acetonitrile, propionitrile, butyronitrile, valerate, octanoic acid, heptanonitrile, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 One or more of the following compounds: lithium bis(fluorosulfonyl)imide (LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), LiPO2F2, LiODFB, LiB(C2O4)2 (lithium bis(oxalatoborate) (LiBOB), and LiBF4.

[0160] The additive content relative to the total weight of the electrolyte can be from 0.01% to 20% by weight or from 0.05% to 5.0% by weight. When the above ranges are met, the low-temperature output, high-temperature storage characteristics and high-temperature life characteristics of the battery can be improved, side reactions in the electrolyte can be reduced, and the presence of the additive as an unreacted material can be suppressed.

[0161] (3) Battery casing

[0162] The battery casing can be used to house the electrode assembly and electrolyte.

[0163] Specifically, the battery casing is designed to house the electrode assembly, inject electrolyte, and then seal the component. It is made of a material with predetermined flexibility to form the housing and can preferably be cylindrical, coin-shaped, prismatic, or pouch-shaped, but is not limited thereto. The upper and lower casings constituting the battery casing can be separate components or substantially integral components connected at one end. The external shape of the battery casing can be manufactured using various methods, and is not limited in this invention.

[0164] For example, the battery casing can be a prismatic battery casing. Prismatic battery casings, shaped like metal cans, allow for high-density stacking and have a narrow width relative to their length.

[0165] The prismatic battery casing has an opening formed at the top and can be made of a conductive metal material such as aluminum or steel. The prismatic battery casing can accommodate electrode components and electrolyte in the internal space through the top opening of the battery can, and the top cover can be welded to the top opening to seal the battery casing.

[0166] Meanwhile, the charging cutoff voltage of the lithium secondary battery of the present invention can be 4.3 V or higher, specifically 4.35 V or higher, and more specifically 4.4 V or higher. In this case, excellent energy density equivalent to that of high-nickel content cathode active materials can be achieved, as well as improved high-temperature life performance and high-temperature storage performance.

[0167] Meanwhile, the nominal voltage of the lithium secondary battery can be 3.68 V or higher, preferably 3.68 V to 3.80 V, and more preferably 3.69 V to 3.75 V. In this case, the nominal voltage represents the average voltage value of the lithium secondary battery during discharge. Since the energy density of the lithium secondary battery is calculated by multiplying the average voltage and average current during discharge, the energy density increases when the nominal voltage is high. The nominal voltage of a typical lithium nickel cobalt manganese-based oxide as the positive electrode active material is 3.6 V, but in this invention, the charging cutoff voltage is increased to set the nominal voltage to 3.68 V or higher, thereby achieving a high energy density.

[0168] The lithium secondary battery of the present invention can be used in portable devices such as mobile phones, laptops and digital cameras, as well as electric vehicles such as hybrid electric vehicles (HEVs).

[0169] In addition, battery modules or battery packs containing the aforementioned lithium secondary batteries as unit cells can be used as power sources for one or more medium to large-sized devices, such as power tools; electric vehicles, such as electric vehicles (EVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0170] The lithium secondary battery of the present invention can be used as a single cell for powering small devices, and can also preferably be used as a unit cell in medium and large battery modules comprising multiple single cells.

[0171] Examples of medium to large-sized installations include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and energy storage systems (ESS).

[0172] Examples and Comparative Examples

[0173] Example 1

[0174] <Preparation of Electrode Components>

[0175] A positive electrode slurry was prepared by mixing the positive electrode active material, binder, and conductive material in an N-methylpyrrolidone solvent at a weight ratio of 97:1.8:1.2. The positive electrode slurry was then coated onto one surface of an aluminum current collector with a thickness of 12 μm, dried, and rolled to prepare the positive electrode. In this case, the positive electrode active material was Li[Ni] 0.6 Co0.1 Mn 0.3 O2, PVDF is the binder, and carbon nanotubes are the conductive material.

[0176] A negative electrode slurry was prepared by mixing the negative electrode active material, binder, conductive material, and thickener in distilled water at a weight ratio of 96.15:2.3:0.5:1.05. The negative electrode slurry was then coated onto a surface of a copper current collector with a thickness of 7.8 μm, dried, and rolled to a porosity of 30%, thereby preparing the negative electrode. In this case, the negative electrode active material was artificial graphite and natural graphite, the binder was styrene-butadiene rubber (SBR), the conductive material was Super C65, and the thickener was carboxymethyl cellulose (CMC).

[0177] A porous polyethylene diaphragm is placed between the negative and positive electrodes prepared above to prepare an electrode assembly.

[0178] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0179] <Preparation of Electrolytes>

[0180] As additives, 0.5% by weight of vinylene carbonate (VC), 0.5% by weight of propane sulpholol (PS), 1% by weight of ethylene sulfate (ESa), 1% by weight of lithium difluorophosphate and 0.2% by weight of LiBF4 were added to a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7, and then 1.0 M of LiPF6 was added to prepare the electrolyte.

[0181] <Manufacturing of Lithium Secondary Batteries>

[0182] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 303.19 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.813.

[0183] Example 2

[0184] <Preparation of Electrode Components>

[0185] The electrode assembly was prepared in the same manner as in Example 1.

[0186] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0187] <Preparation of Electrolytes>

[0188] The electrolyte was prepared in the same manner as in Example 1.

[0189] <Manufacturing of Lithium Secondary Batteries>

[0190] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 297.87 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.813.

[0191] Example 3

[0192] <Preparation of Electrode Components>

[0193] The electrode assembly was prepared in the same manner as in Example 1.

[0194] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0195] <Preparation of Electrolytes>

[0196] The electrolyte was prepared in the same manner as in Example 1.

[0197] <Manufacturing of Lithium Secondary Batteries>

[0198] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 292.55 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteriesE The ratio of (S) A / S E ), that is, S U It is 0.813.

[0199] Example 4

[0200] <Preparation of Electrode Components>

[0201] The electrode assembly was prepared in the same manner as in Example 1, except that it used Li[Ni] 0.62 Co 0.06 Mn 0.32 Positive electrode active material composed of O2.

[0202] In this case, the porosity of the positive electrode is 21.7%, and the loading is 4.33 mAh / cm³. 2 The porosity of the negative electrode is 26.1%. In this case, the N / P ratio of the positive and negative electrodes is 107.1, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0203] <Preparation of Electrolytes>

[0204] The electrolyte was prepared in the same manner as in Example 1.

[0205] <Manufacturing of Lithium Secondary Batteries>

[0206] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 319.15 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.830.

[0207] Example 5

[0208] <Preparation of Electrode Components>

[0209] The electrode assembly was prepared in the same manner as in Example 1.

[0210] In this case, the porosity of the positive electrode is 19.1%, and the loading is 4.28 mAh / cm³. 2 The porosity of the negative electrode is 24.7%. In this case, the N / P ratio of the positive and negative electrodes is 105.9, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0211] <Preparation of Electrolytes>

[0212] The electrolyte was prepared in the same manner as in Example 1.

[0213] <Manufacturing of Lithium Secondary Batteries>

[0214] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 319.15 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.820.

[0215] Example 6

[0216] The lithium secondary battery was manufactured in the same manner as in Example 1, except that an electrolyte prepared as follows was used instead of the electrolyte used in Example 1: 1.2 M LiPF6 was dissolved in an organic solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 2:7:1. Then, as additives, 0.3 wt% vinyl ethylene carbonate (VEC), 0.5 wt% vinylene carbonate, 0.5 wt% propane sulpholactone (PS), 1.0 wt% ethylene sulfate (ESa), 0.8 wt% lithium difluorophosphate (LiDFP, product name: SLO7), 0.5 wt% lithium oxaloyl difluoroborate (LiODFB), 0.1 wt% 1H imidazole-1-carboxypropargyl ether (HS02, CAS 83395-38-4), 0.5 wt% lithium bis(fluorosulfonyl)imide (LiFSI, product name: SL06), and 0.5 wt% lithium bis(fluorosulfonyl)imide (LiFSI, product name: SL06) were added. WNDFID% of fluoroethylene carbonate (FEC) and 0.5% by weight of trimethylsilyl phosphate (TMSPa).

[0217] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0218] Comparative Example 1

[0219] <Preparation of Electrode Components>

[0220] The electrode assembly was prepared in the same manner as in Example 1.

[0221] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0222] <Preparation of Electrolytes>

[0223] The electrolyte was prepared in the same manner as in Example 1.

[0224] <Manufacturing of Lithium Secondary Batteries>

[0225] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 319.15 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.813.

[0226] Comparative Example 2

[0227] <Preparation of Electrode Components>

[0228] The electrode assembly was prepared in the same manner as in Example 1.

[0229] In this case, the porosity of the positive electrode is 21.35%, and the loading is 4.03 mAh / cm³. 2 The porosity of the negative electrode is 28.01%. In this case, the N / P ratio of the positive and negative electrodes is 107.26, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0230] <Preparation of Electrolytes>

[0231] The electrolyte was prepared in the same manner as in Example 1.

[0232] <Manufacturing of Lithium Secondary Batteries>

[0233] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 276.60 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, SU It is 0.813.

[0234] Comparative Example 3

[0235] <Preparation of Electrode Components>

[0236] The electrode assembly was prepared in the same manner as in Example 1, except that it used Li[Ni] 0.65 Co 0.15 Mn 0.2 Positive electrode active material composed of O2.

[0237] In this case, the porosity of the positive electrode is 24.6%, and the loading is 4.02 mAh / cm³. 2 The porosity of the negative electrode is 26.9%. In this case, the N / P ratio of the positive and negative electrodes is 108.6, and the electrode assembly has a core-type structure in which the positive electrode, the separator, and the negative electrode are stacked and wound in sequence.

[0238] <Preparation of Electrolytes>

[0239] The electrolyte was prepared in the same manner as in Example 1.

[0240] <Manufacturing of Lithium Secondary Batteries>

[0241] The electrode assembly prepared as described above was placed inside a prismatic battery casing, and then 303.19 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a lithium secondary battery. In this case, the volume (S) of the electrode assembly in the manufactured lithium secondary battery is... A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / S E ), that is, S U It is 0.830.

[0242] Experimental Example 1—Evaluation of the EFF Index

[0243] The EFF index, defined by Equation 1 below, was measured for the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0244] [Equation 1]

[0245] In equation 1 above, R E [Unit: g] indicates the weight of the remaining electrolyte contained in the activated lithium secondary battery, in s. U The volume (S) of the electrode assembly A ) and the volume (S) of lithium secondary batteries E The ratio of (S) A / SE ), N C [Unit: Ah] indicates the capacity of a lithium secondary battery when discharged from 4.4 V to 2.5 V at 0.33C at 25°C.

[0246] (1) R E Measurement

[0247] The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were each activated by: (1) charging the lithium secondary battery to 3% SOC at a constant current of 0.2C at 55°C, (2) charging the lithium secondary battery to 17% SOC at a constant current of 1.0C at 55°C, and (3) charging the lithium secondary battery to 60% SOC at a constant current of 1.0C at 55°C.

[0248] Then, after activation, each lithium secondary battery was disassembled and the weight of the remaining electrolyte (R) was measured. E Specifically, the weight (R) of the remaining electrolyte contained in the activated lithium secondary battery is measured in the following manner. E (1) Measure the weight (M) of the activated lithium secondary battery before disassembling it. L (2) Disassemble the activated lithium secondary battery to remove the electrolyte present in the battery casing; (3) Immerse the battery casing and electrode assembly in dimethyl carbonate solvent to remove the electrolyte present in the surface of the battery casing, the surface of the electrode assembly and the internal pores, then dry the battery casing and electrode assembly; and (4) Measure the weight (M) of the dried battery casing. C ) and the weight of the dried electrode assembly (M) A Then measure M L M C and M A Substitute into equation A below.

[0249] [Equation A]

[0250] R E =M L -M C -M A

[0251] The results are shown in Table 1 below.

[0252] (2) N C Measurement

[0253] The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 and 3 were charged to 4.35V at 0.33C constant current / constant voltage (with a cutoff at 0.05C) at 25°C, and then discharged to 2.0V at a constant current of 0.33C for activation.

[0254] Subsequently, the lithium secondary battery was charged from 2.5 V to 4.35 V at 0.33C at 25°C, and then the capacity (Nk) of the lithium secondary battery was measured when it was discharged from 4.4 V to 2.5 V at 0.33C at 25°C. C The results are shown in Table 1 below.

[0255] (3) S U Measurement

[0256] For each lithium secondary battery manufactured in Examples 1 to 6 and Comparative Examples 1 to 3, the volume S of the electrode assembly was measured. A The volume S of the lithium secondary battery E And calculate S A With S E The ratio (S) A / S E ), thereby measuring S U S A and S E Each measurement was performed using the following methods. The results are shown in Table 1 below.

[0257] Volume of lithium secondary battery (S) E The volume of the lithium secondary battery (S) is obtained through equation B below. Equation B gives the volume of the lithium secondary battery (S). E This is obtained by assuming that the lithium secondary battery, including the prismatic battery casing, has a cuboid shape.

[0258] [Equation B]

[0259] S E = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0260] In Equation B above, the thickness of the lithium secondary battery represents the distance measured along the thickness direction of the lithium secondary battery relative to its external shape, the length of the lithium secondary battery represents the distance measured along the length direction of the lithium secondary battery relative to its external shape, and the width of the lithium secondary battery represents the distance measured along the direction perpendicular to the length direction of the lithium secondary battery relative to its external shape.

[0261] Volume of electrode assembly (S) A It is obtained through the following equation C.

[0262] [Equation C]

[0263] S A =(Volume of positive electrode) + (Volume of negative electrode) + (Volume of membrane)

[0264] In Equation C, the volume of the positive electrode, the volume of the negative electrode, and the volume of the separator are measured with respect to the external shape of the positive electrode, the negative electrode, or the separator, without excluding the volume of the pores contained in the positive electrode, the negative electrode, or the separator.

[0265] [Table 1]

[0266] Experimental Example 2: High-Temperature Storage Characteristics

[0267] The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were charged to 100% SOC at 0.33C under CC / CV conditions at 25°C, and then stored at 60°C for 12 weeks to measure the capacity retention and resistance increase rate of each lithium secondary battery. The specific measurement methods are described below.

[0268] (1) Capacity retention rate

[0269] Before storing at 60°C for 12 weeks, the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were charged to 4.25 V (0.05C cutoff) at 25°C with CC / CV and 0.33C, and discharged to 2.0 V with CC and 0.33C, for three cycles. The discharge capacity of the third cycle was then measured and used as the initial discharge capacity.

[0270] After being stored at 60°C for 12 weeks, the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were charged to 4.25 V (0.05C cutoff) at 25°C with CC / CV and 0.33C, and discharged to 2.0 V with CC and 0.33C for three cycles. The discharge capacity of the third cycle was then measured and taken as the discharge capacity after being stored at 60°C for 12 weeks.

[0271] The initial discharge capacity measured above was compared with the discharge capacity after 12 weeks of storage at 60°C, and the capacity retention rate was evaluated according to the following equation. The results are shown in Table 2 below.

[0272] Capacity retention (%) = (Discharge capacity after 12 weeks of storage at 60°C / Initial discharge capacity) × 100

[0273] (2) Rate of increase in resistance

[0274] The lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3 were charged to 4.25V (0.05C cutoff) at 25°C using CC / CV and 0.33C, and discharged to 2.0V using CC and 0.33C, for three cycles. Then, the discharge capacity of the third cycle was set to 50% SOC at CC / CV and 0.33C, and the battery was discharged at a current of 2.5C for 30 seconds. The resistance was measured based on the voltage drop under these conditions and used as the initial resistance. Subsequently, the batteries were stored at 60°C for 12 weeks, and the resistance was measured using the same method and used as the final resistance. The rate of increase in resistance was calculated using the following equation. The results are shown in Table 2 below.

[0275] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) × 100

[0276] [Table 2]

[0277] Referring to Table 2 above, it was found that the lithium secondary batteries manufactured in Examples 1 to 6 exhibited better capacity retention and resistance increase rates after 12 weeks of storage at 60°C than the lithium secondary batteries manufactured in Comparative Examples 1 to 3. Furthermore, despite using a different electrolyte than in Example 1, Example 6 showed superior capacity retention and resistance increase rates after 12 weeks of storage at 60°C compared to the lithium secondary batteries manufactured in Comparative Examples 1 to 3. Therefore, it can be understood that even with different electrolytes, excellent high-temperature storage characteristics can be achieved if the EFF value defined by Equation 1 above satisfies 1.82 to 2.06.

Claims

1. A lithium secondary battery, comprising: An electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; An electrolyte; And A battery case including an inner space for accommodating the electrode assembly and the electrolyte, Wherein the positive electrode includes a positive electrode active material including a lithium nickel-based oxide, the lithium nickel-based oxide contains 50 mol% to 70 mol% of nickel among all metals except lithium, and The electrolyte filling factor (EFF) index in g / Ah defined by the following Equation 1 is 1.82 to 2.06, [Equation 1] Wherein, in Equation 1, R E This indicates the weight of the remaining electrolyte contained in the activated lithium secondary battery, in grams. S U The volume (S) of the electrode assembly is indicated. A ) and the volume (S) of the lithium secondary battery E The ratio of (S) A / S E ), N C The capacity of the lithium secondary battery is expressed in Ah when it is discharged from 4.4 V to 2.5 V at 0.33C at 25°C.

2. The lithium secondary battery as described in claim 1, wherein, R E It ranges from 265 g to 295 g.

3. The lithium secondary battery as described in claim 1, wherein, S U The value ranges from 0.70 to 0.

95.

4. The lithium secondary battery as described in claim 1, wherein, N C It ranges from 90 Ah to 150 Ah.

5. The lithium secondary battery as described in claim 1, wherein, R E With N C The ratio (R) E / N C The value ranges from 2.00 to 3.30, with units of g / Ah.

6. The lithium secondary battery as described in claim 1, wherein, The volume (S) of the electrode assembly A The range is 0.3 L to 1.35 L.

7. The lithium secondary battery as described in claim 1, wherein, The volume (S) of the lithium secondary battery E The range is 0.4 L to 1.5 L.

8. The lithium secondary battery as described in claim 1, wherein, Among all metals except lithium, the lithium nickel-based oxide contains 15 mol% or less of cobalt (Co).

9. The lithium secondary battery as described in claim 1, wherein, The lithium nickel-based oxide is represented by the following Formula 1: [Formula 1] Li 1+a1 [Ni x1 Co y1 Mr z1 M 1 w1 ]O2 Wherein, in the above Formula 1, 0≤a1≤0.5, 0.5≤x1≤0.7, 0<y1≤0.15, 0<z1≤0.4, and 0≤w1≤0.2 are satisfied, and M 1 It is at least one doping element selected from W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

10. The lithium secondary battery as described in claim 1, wherein, The lithium nickel-based oxide is a single-particle type particle.

11. The lithium secondary battery as described in claim 1, wherein, The charging cut-off voltage of the lithium secondary battery is 4.3 V or more.

12. The lithium secondary battery as described in claim 1, wherein, The nominal voltage of the lithium secondary battery is 3.68 V or more.

13. The lithium secondary battery as described in claim 1, wherein, The negative electrode includes graphite as a negative electrode active material.

14. The lithium secondary battery as described in claim 1, wherein, The battery case is a prismatic battery case.

15. The lithium secondary battery as described in claim 1, wherein, The electrode assembly is formed such that the positive electrode, the separator, and the negative electrode are stacked in sequence and wound in one direction.

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