Lithium secondary battery, battery pack, and electric vehicle

Abstract

The present invention relates to a lithium secondary battery, comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; an electrolyte; and a battery case including an internal space for accommodating the electrode assembly and the electrolyte, wherein the positive electrode includes a positive electrode active material, the positive electrode active material includes a lithium nickel-based oxide, the lithium nickel-based oxide contains 50 mol% to 70 mol% of nickel among all metals except lithium, and an electrolyte filling factor (EFF) index (unit: g / Ah) defined by Equation 1 is 1.52 to 1.88. In Equation 1, R E [unit: g] is the weight of the remaining electrolyte contained in the lithium secondary battery after activation, S U is the ratio (S E / S C ) of the volume (S E ) of the electrode assembly to the volume (S C ) of the lithium secondary battery, N C [unit: Ah] is the capacity of the lithium secondary battery when discharged from 4.4 V to 3.0 V at 0.33 C at 25°C.[Equation 1]

Description

[0001] Cross-references to related applications

[0002] This application claims priority to Korean Patent Application No. 10-2023-0190416, filed on December 22, 2023, and Korean Patent Application No. 10-2024-0190568, filed on December 18, 2024, 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, the application of lithium-ion rechargeable 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. This has led to a continuous increase in demand for high-capacity, high-output, and high-stability rechargeable batteries. Rechargeable batteries have gained attention as an energy source that improves environmental friendliness and energy efficiency. Using rechargeable batteries as an energy source significantly reduces the use of fossil fuels and produces no byproducts during the consumption of energy from such batteries.

[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, research is mainly 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, reducing the nickel content in lithium nickel-cobalt-manganese composite transition metal oxides requires increasing the driving voltage to achieve the desired energy density. Under such high voltage driving, electrolyte side reactions at the positive electrode and gas generation inside the battery increase.

[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] 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 reduced electrolyte side reactions at 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 located between the positive electrode and the negative electrode; an electrolyte; and a battery housing including an internal space configured to accommodate the electrode assembly and the electrolyte, wherein the positive electrode includes a positive electrode active material, wherein the positive electrode active material includes a lithium nickel-based oxide containing 50 mol% to 70 mol% nickel in all metals except lithium, and having an electrolyte fill factor (EFF) index (in g / Ah) of 1.52 to 1.88 as defined by Equation 1.

[0013] [Equation 1]

[0014] In equation 1, R E [Unit: g] is the weight of the electrolyte contained in the lithium secondary battery after activation, in s. U The volume (S) of the electrode assembly E ) and the volume (S) of the lithium secondary battery C The ratio of (S) E / S C ), N C [Unit: Ah] is the capacity of the lithium secondary battery when discharged from 4.4 V to 3.0 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 ranges from 70 g to 90 g.

[0016] [3] The present invention provides the lithium secondary battery described in [1] or [2] above, wherein S U It ranges from 0.75 to 0.95.

[0017] [4] The present invention provides a lithium secondary battery as described in any one of [1] to [3] above, wherein N C It ranges from 35 Ah to 50 Ah.

[0018] [5] The present invention provides the lithium secondary battery according to any one of [1] to [4] above, wherein, among all metals other than lithium, the lithium nickel-based compound contains 15 mol% or less of cobalt (Co).

[0019] [6] The present invention provides the lithium secondary battery according to any one of [1] to [5] above, wherein the lithium nickel-based oxide is represented by Formula 1: [Formula 1] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 O2 Wherein, in Formula 1, 0 ≤ a1 ≤ 0.5, 0.5 ≤ x1 ≤ 0.7, 0 < y1 ≤ 0.15, 0 < z1 ≤ 0.4 and 0 ≤ w1 ≤ 0.2, and M 1 is at least one doping element selected from the group consisting 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.

[0020] [7] The present invention provides the lithium secondary battery according to any one of [1] to [6] above, wherein the lithium nickel-based oxide is a single-particle type particle.

[0021] [8] The present invention provides the lithium secondary battery according to any one of [1] to [7] above, wherein the charge cut-off voltage of the lithium secondary battery is 4.3 V or more.

[0022] [9] The present invention provides the lithium secondary battery according to any one of [1] to [8] above, wherein the negative electrode contains graphite as a negative electrode active material.

[0023]

[10] The present invention provides the lithium secondary battery according to any one of [1] to [9] above, wherein the battery case is a pouch-type battery case.

[0024]

[11] The present invention provides the lithium secondary battery according to any one of [1] to

[10] above, wherein the ratio of R E to N C (R E / N C ) [unit: g / Ah] is 1.5 to 3.

[0025]

[12] The present invention provides the lithium secondary battery according to any one of [1] to

[11] above, wherein the volume (S E ) of the electrode assembly is 0.17 L to 1.1 L.

[0026]

[13] The present invention provides a lithium secondary battery as described in any one of [1] to

[12] above, wherein the volume (S) of the lithium secondary battery is... C The range is 0.23 L to 1.2 L.

[0027]

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

[13] above, wherein the electrolyte comprises an organic solvent and a lithium salt, and the concentration of the lithium salt is from 0.1 M to 3.0 M.

[0028]

[15] The present invention provides a lithium secondary battery as described in any one of [1] to

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

[0029]

[16] The present invention provides a battery pack comprising any one of the lithium secondary batteries described in any one of [1] to

[15] above.

[0030]

[17] The present invention provides an electric vehicle that includes the battery pack described above

[16] as a power source.

[0031] [Beneficial Effects]

[0032] According to the present invention, by including 50 mol% to 70 mol% nickel in all metals except lithium, the structural stability of the positive electrode active material at high temperatures is improved, resulting in 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, the amount of gas generated inside the battery during high-voltage operation can be reduced, and appropriate electrolyte impregnation can be ensured. Therefore, the manufactured lithium secondary batteries, battery packs, and electric vehicles can ensure high energy density and high capacity characteristics, and can also exhibit excellent lifetime and high-temperature lifetime characteristics. Attached Figure Description

[0033] Figure 1 This is an exploded view of a lithium secondary battery, one aspect of the present invention. Detailed Implementation

[0034] The various aspects of the present invention will be described in detail below.

[0035] It should be understood that the words or terms used in this disclosure and claims 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 conception of the invention.

[0036] The terminology used herein is for the purpose of describing specific aspects of the invention only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular form is intended to include the plural form as well.

[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 complexes composed of 30 or fewer nodules.

[0039] As used herein, the term “granular node” refers to a well-defined, but not separate, subgranular unit cell that constitutes a single grain or quasi-single grain, and a granular node can 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 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. As a result, the inventors discovered that by making the nickel content account for 50 to 70 mol% of all metals except lithium, and by adjusting the structure, discharge capacity, and weight of the remaining electrolyte after activation of the lithium secondary battery to satisfy specific equations, the lithium secondary battery exhibits excellent capacity characteristics, high voltage and high-temperature lifespan characteristics, and storage characteristics, and can also improve electrolyte impregnation, thus completing the present invention.

[0044] The various aspects of the present invention will be described in detail below.

[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 located between the positive electrode and the negative electrode. The lithium secondary battery further includes an electrolyte and a battery casing, the battery casing including an internal space for accommodating the electrode assembly and the electrolyte. 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. The electrolyte fill factor (EFF) index (in g / Ah) defined by Equation 1 below is 1.52 to 1.88. [Equation 1]

[0048] In equation 1 above, R E [Unit: g] is the weight of the electrolyte contained in the lithium secondary battery after activation, in s. U The volume (S) of the electrode assembly E ) and the volume (S) of the lithium secondary battery C The ratio of (S) E / S C ), N C [Unit: Ah] is the capacity of the lithium secondary battery when discharged from 4.4 V to 3.0 V at 0.33C at 25°C.

[0049] The EFF index (unit: g / Ah) of the lithium secondary battery of the present invention, as defined by Equation 1, can be from 1.52 to 1.88, specifically, 1.52 or more, 1.54 or more, 1.56 or more, 1.58 or more, 1.60 or more, 1.62 or more, and 1.64 or more. Furthermore, the EFF index (unit: g / Ah) defined by Equation 1 can be less than 1.88, less than 1.86, less than 1.84, less than 1.82, less than 1.80, less than 1.78, less than 1.76, less than 1.74, less than 1.72, less than 1.70, less than 1.68, and less than 1.66. For example, the EFF index can be from 1.52 to 1.88, preferably from 1.52 to 1.78, more preferably from 1.56 to 1.70, and even more preferably from 1.60 to 1.68.

[0050] 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. This accelerates side reactions with the electrolyte, leading to a decrease in lifetime characteristics. This phenomenon is further accelerated when exposed to high temperatures, resulting in a significant reduction in thermal stability.

[0051] Reducing the nickel content of lithium nickel-based oxides can improve their thermal stability at high temperatures. To achieve the same energy density as high-nickel-content lithium nickel-based oxides, it is necessary to drive 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, which can potentially degrade lifetime and storage performance.

[0052] 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 a decrease in lithium ion mobility and an increase in battery resistance. As a result, the battery may have reduced capacity and lifespan characteristics. Therefore, the amount of electrolyte injected needs to be adjusted appropriately according to the characteristics of the battery.

[0053] 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.

[0054] 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 1.52 to 1.88. This lithium secondary battery also exhibits excellent thermal stability, reduced gas generation, and appropriate electrolyte impregnation, thereby possessing excellent high-temperature life characteristics and high-temperature storage characteristics.

[0055] In equation 1, R E This indicates the weight of the remaining electrolyte in the lithium secondary battery after activation.

[0056] The residual electrolyte in a lithium secondary battery is 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] Residual electrolyte refers to the electrolyte remaining in the battery casing after the lithium secondary battery has been activated. The weight of the residual electrolyte may differ from the weight of the electrolyte initially injected into the battery casing during the manufacturing process of the lithium secondary battery before activation.

[0058] Activation is the process of charging and / or discharging a manufactured but uncharged or undischarged lithium secondary battery to provide electrical properties and forming a solid electrolyte interface (SEI) film on the electrodes to stabilize the battery, thereby making the battery ready for practical use.

[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, activation can be achieved by performing the following operations: (1) charging to 4.0V or 3% SOC at 55°C under a constant current of 0.2C; (2) charging to 4.35V or 20% SOC at 55°C under a constant current of 1.0C; and (3) charging to 4.35V or 60% SOC at 55°C under a constant current of 1.0C.

[0061] In addition, 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, and is in a sealed state; (2) the lithium secondary battery is disassembled and the electrolyte present in the internal space of the battery casing is removed; (3) the battery casing and electrode assembly are immersed in a solvent such as dimethyl carbonate to remove the electrolyte present on the surface of the battery casing, the surface of the electrode assembly, and the internal pores of the electrode assembly, 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 values ​​can be 70 g to 90 g, 72 g to 88 g, 75 g to 85 g, or 77 g to 83 g. When these ranges are met, electrolyte side reactions are reduced, leading to reduced gas generation and sufficient electrolyte impregnation. This ensures adequate lithium-ion mobility and allows for sufficient SEI film-forming additives to form a stable film. Therefore, excellent lifetime, output characteristics, and high-temperature storage characteristics can be achieved in the medium to long term.

[0065] In equation 1, S U The volume of the electrode assembly (S) E ) and the volume (S) of lithium secondary batteries C The ratio of (S) E / S C ).

[0066] The volume of an electrode assembly is 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, as well as 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.

[0067] When the battery casing is a pouch-type battery casing, the volume S of the electrode assembly E The volume S of the electrode assembly described in Equation B below can be obtained. E The following assumptions are made: the electrode assembly housed in the pouch-type battery casing has a cuboid shape formed by stacking a positive electrode, a negative electrode, and a separator, and the length and width of the electrode assembly are equal to the length and width of the negative electrode, respectively.

[0068] [Equation B]

[0069] S E =(Thickness of electrode assembly) × (Length of negative electrode) × (Width of negative electrode)

[0070] In Equation B above, the thickness of the electrode assembly is the total thickness of the structure with the positive electrode, negative electrode, and separator stacked, or it can be defined as the total distance measured in a direction perpendicular to the surface of each layer when the positive electrode, negative electrode, and separator are stacked. The thickness of the electrode assembly can be adjusted by controlling the porosity and loading of the positive and negative electrodes, as well as the N / P ratio, or by changing the type of conductive material contained in the positive and negative electrodes. The length of the negative electrode is a straight-line distance measured along the longest axis direction (length direction) of the negative electrode, and can be defined as a straight-line distance along the longest axis direction in a plane perpendicular to the thickness direction of the negative electrode. The width of the negative electrode is a straight-line distance measured along a direction perpendicular to the length direction of the negative electrode, and can be defined as a straight-line distance along a direction perpendicular to the length direction of the negative electrode in a plane perpendicular to the thickness direction of the negative electrode.

[0071] It should be understood that, as mentioned above, the shape of the electrode assembly is not limited to a cuboid shape. The electrode assembly can have any suitable shape, and the volume of the electrode assembly can be determined by any suitable measurement method.

[0072] The volume S of a lithium secondary battery C This is the volume calculated based on the external shape of the lithium-ion battery, specifically representing the volume of space occupied by the battery's external shape. In some cases, the external shape of a lithium-ion battery can be the same as that of the battery casing when sealed. The volume of a lithium-ion battery can be adjusted by controlling the porosity and loading of the positive and negative electrodes, as well as the N / P ratio, or by changing the type of conductive material contained in the positive and negative electrodes.

[0073] When the battery casing is a pouch-type battery casing, the volume S of the lithium secondary battery is... C The volume S of the lithium secondary battery described in Equation C below can be obtained. C This was obtained by assuming that the lithium secondary battery, including the pouch-shaped battery casing, has a cuboid shape.

[0074] [Equation C]

[0075] S C = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0076] In equation C above, the thickness of the lithium-ion battery can be a distance measured along the thickness direction of the battery relative to its external shape. The thickness of the lithium-ion battery can be adjusted by controlling the porosity and loading of the positive and negative electrodes, as well as the N / P ratio, or by changing the type of conductive material contained in the positive and negative electrodes. The length of the lithium-ion battery is a distance measured along its length direction relative to its external shape. The width of the lithium-ion battery is a distance measured along its width direction relative to its external shape.

[0077] It should be understood that, as mentioned above, the shape of a lithium secondary battery is not limited to a cuboid shape. A lithium secondary battery can have any suitable shape, and its volume can be determined by any suitable measurement method.

[0078] S U The value can be from 0.75 to 0.95, preferably from 0.78 to 0.92, and more preferably from 0.83 to 0.91. When the above range is met, the relative space utilization can be improved within the same capacity, thereby achieving high energy density, and the gas generation caused by electrolyte side reactions can be appropriately accommodated.

[0079] S E It can be 0.17 to 1.1 L, 0.25 to 1.0 L, or 0.4 to 0.8 L.

[0080] S C The amount can be from 0.23 to 1.2 L, preferably from 0.3 to 1.1 L, and more preferably from 0.5 to 1.0 L.

[0081] N C This indicates the capacity of a lithium secondary battery when discharged from 4.4 V to 3.0 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 3.0 V at 0.33 C. It indicates the discharge capacity during the first charge / discharge cycle after activation. For N... C The activation can be performed by charging a manufactured but uncharged 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 then discharging the lithium secondary battery to 2.0 V at a constant current of 0.33C. For N... C The first charge / discharge after activation can be performed by charging the lithium secondary battery from 3.0 V to 4.35 V at a C rate of 0.33C at 25°C.

[0083] In equation 1, N C The capacity can be 35 to 50 Ah, preferably 38 to 45 Ah, more preferably 41 to 44 Ah, and even more preferably 42 to 43 Ah. When the above ranges are met, high capacity characteristics can be achieved.

[0084] When a lithium secondary battery is discharged from 4.4 V to 3.0 V at 0.33C at 25°C, the weight R of the remaining electrolyte contained in the activated lithium secondary battery is... E With capacity N C The ratio (R) E / N C [Unit: g / Ah] can be 1.5 to 3. Specifically, R E / N C [Unit: g / Ah] can be 1.5 or higher, 1.53 or higher, 1.55 or higher, 1.57 or higher, 1.6 or higher, 1.63 or higher, 1.65 or higher, 1.67 or higher, 1.7 or higher, 1.73 or higher, 1.75 or higher, 1.77 or higher, 1.8 or higher, 1.83 or higher, 1.85 or higher, 1.87 or higher, 1.9 or higher, 1.93 or higher, 1.95 or higher, 1.97 or higher, 2.0 or higher; and can be below 3, below 2.97, below 2.95, below 2.93, below 2.9, below 2.87, below 2.85, below 2.83, below 2.8, 2.77 Below, 2.75, below 2.73, below 2.7, below 2.67, below 2.65, below 2.63, below 2.63, below 2.6, below 2.6, below 2.57, below 2.55, below 2.53, below 2.5, below 2.47, below 2.45, below 2.43, below 2.4, below 2.37, below 2.35, below 2.33, below 2.3, below 2.27, below 2.25, below 2.23, below 2.2, below 2.17, below 2.15, below 2.13, below 2.1, below 2.07, below 2.05, below 2.03, below 2.0. For example, R E / N C (Unit: g / Ah) can be 1.5 to 3, preferably 1.7 to 2.5, and more preferably 1.85 to 2.15.

[0085] The components of the lithium secondary battery of the present invention will be described in more detail below.

[0086] 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.

[0087] (1) Electrode assembly

[0088] 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.

[0089] 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.

[0090] Electrode assemblies may include, but are not limited to, stacked, wound, and stacked folded types.

[0091] Each component of the electrode assembly of the present invention will be described in detail below.

[0092] 1) Positive electrode

[0093] The positive electrode comprises a positive electrode active material. Specifically, the positive electrode may comprise a positive electrode current collector and a layer of positive electrode active material disposed on the positive electrode current collector. The positive electrode active material layer may comprise a positive electrode active material.

[0094] 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 positive electrode current collectors. Positive electrode current collectors can typically have a thickness from 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, positive electrode current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0095] The positive electrode active material layer can be disposed on the positive electrode current collector, and 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.

[0096] The positive electrode active material comprises a lithium nickel-based oxide. The nickel content of the lithium nickel-based oxide can be 50 mol% to 70 mol%, preferably 52 mol% to 68 mol%, more preferably 55 mol% to 65 mol%, and even more preferably 57 mol% to 63 mol%, relative to all metals except lithium. This positive electrode active material exhibits superior structural and chemical stability at high temperatures compared to positive electrode active materials containing high-nickel-content lithium nickel-based oxides, 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.

[0097] The lithium nickel-based oxide may contain cobalt (Co) in an amount of 15 mol% or less, preferably 5 mol% to 15 mol%, more preferably 7 mol% to 13 mol%, and still more preferably 8 mol% to 12 mol%, relative to all metals other than lithium. When cobalt is included within the above range, cost savings and improved resistance and output characteristics can be achieved with a lower Co content.

[0098] According to one or more aspects of the present invention, the lithium nickel-based oxide may be represented by the following Formula 1.

[0099] [Formula 1]

[0100] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 O2

[0101] In Formula 1 above, M 1 may be 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. Preferably, M 1 may be at least one doping element selected from W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. In Formula 1 above, 1 + a1 is the molar ratio of lithium (Li) in the lithium nickel-based oxide and may satisfy 0 ≤ a1 ≤ 0.5, specifically 0 ≤ a1 ≤ 0.2, more specifically 0 ≤ a1 ≤ 0.1. When the above range is satisfied, the positive electrode active material can form a stable layered crystal structure.

[0102] In Formula 1 above, x1 is the molar ratio of nickel to all metals other than lithium in the lithium nickel-based oxide particles and may satisfy 0.5 ≤ x1 ≤ 0.7, specifically 0.52 ≤ x1 ≤ 0.68, more specifically 0.55 ≤ x1 ≤ 0.65, and still more specifically 0.57 ≤ x1 ≤ 0.63. When the above range is satisfied, the resulting lithium secondary battery can be excellent in high-temperature storage characteristics, high-temperature life characteristics, and thermal stability.

[0103] In Formula 1 above, y1 is the molar ratio of cobalt to all metals other than lithium in the lithium nickel-based oxide particles and may satisfy 0 < y1 ≤ 0.15, specifically 0 < y1 ≤ 0.10, more specifically 0 < y1 ≤ 0.07. When the above range is 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.

[0104] In Equation 1 above, z1 is 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, specifically 0.1 ≤ z1 ≤ 0.4, more specifically 0.15 ≤ z1 ≤ 0.4, and more specifically 0.2 ≤ z1 ≤ 0.4. When the above range is satisfied, the positive electrode active material can have improved structural stability.

[0105] 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, specifically 0 ≤ w1 ≤ 0.15, and more specifically 0 ≤ w1 ≤ 0.1. When the above range is satisfied, particle growth during firing of the positive electrode active material can be promoted or crystal structure stability can be improved.

[0106] In addition, the lithium nickel-based oxide can be single-particle type particles.

[0107] Specifically, when the lithium nickel-based oxide is secondary particles, particle breakage increases during electrode manufacturing, and internal cracks are caused by volume expansion / contraction of primary particles during charge / discharge, which may reduce the effect of improving high-temperature life characteristics and high-temperature storage characteristics.

[0108] 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 common lithium nickel-based oxides in the form of secondary particles that aggregate dozens to hundreds of 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, the change caused by volume expansion / contraction of primary particles during charge and discharge is small, and thus, the generation of internal cracks in the particles is significantly reduced.

[0109] 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 high-temperature life characteristics and high-temperature storage characteristics.

[0110] Meanwhile, the average particle diameter (D 50 ) of the positive electrode active material can be 1 μm to 8 μm. Preferably, the average particle diameter (D 50 ) of the positive electrode active material can be 2 μm to 7 μm, more preferably 2.5 μm to 6 μm, more preferably 3 μm to 5 μm, and more preferably 3.5 μm to 4.5 μm. When the above range is satisfied, side reactions with the electrolyte can be minimized while preventing an increase in resistance and deterioration of output characteristics, and thus high-temperature life characteristics and high-temperature storage characteristics can be excellent.

[0111] The positive electrode active material layer may comprise 90% to 99% by weight, preferably 92% to 98% by weight, and more preferably 94% to 98% by weight of positive electrode active material. When the above ranges are met, the lithium secondary battery can have improved energy density and capacity characteristics.

[0112] Additionally, the positive electrode active material layer may optionally include at least one of a positive electrode conductive material or a positive electrode binder.

[0113] 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 may 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 fiber, or carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or 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 may be used. The content of the positive electrode conductive material relative to the total weight of the positive electrode active material layer is typically from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0114] 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 the positive electrode binder can be: fluoropolymer binders, including polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders, including styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, or styrene-isoprene rubber; cellulose binders, including carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, or regenerated cellulose; polyol binders, including polyvinyl alcohol; polyolefin binders, including polyethylene or polypropylene; polyimide binders; polyester binders; or 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 from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0115] 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).

[0116] 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.

[0117] 2) Negative electrode

[0118] 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.

[0119] 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.

[0120] 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, negative electrode current collectors can be used in various forms, such as membranes, sheets, foils, meshes, porous bodies, foams, or nonwoven fabrics.

[0121] 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.

[0122] 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.

[0123] Specifically, graphite can be at least one selected from the group consisting of artificial graphite and natural graphite. In some aspects, graphite can be a combination of artificial graphite and natural graphite.

[0124] When graphite comprises synthetic graphite and natural graphite, the synthetic graphite and natural graphite may be contained in a weight ratio of 6.5:3.5 to 9.5:0.5, preferably 7:3 to 9:1, and more preferably 7.5:2.5 to 8.5:1.5. When the above ranges are met, the capacity characteristics can be improved, while the output characteristics and lifetime characteristics can be excellent.

[0125] 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, preferably 85% to 99% by weight, and more preferably 90% to 98% by weight. When the above range is met, sufficient capacity characteristics can be achieved.

[0126] 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.

[0127] 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 has electronic conductivity without causing chemical changes in the battery to be constructed. Specific examples may 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 fiber, or carbon nanotubes; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or 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 may be used. The content of the negative electrode conductive material relative to the total weight of the negative electrode active material layer is typically from 1% to 30% by weight, preferably from 1% to 20% by weight, and preferably from 1% to 10% by weight.

[0128] Negative electrode binders are 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 The following materials may be used: polyvinyl alcohol (PFA), polyacrylonitrile (PA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone (PVP), polytetrafluoroethylene (PTFE), polyethylene, polypropylene, ethylene-propylene-diene monomer rubber (EPDM rubber), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, or various copolymers thereof, and any mixture of one 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 from 1% to 30% by weight, preferably from 1% to 20% by weight, and more preferably from 1% to 10% by weight.

[0129] The negative electrode can be prepared according to common negative electrode manufacturing methods. For example, the negative electrode active material, negative electrode conductive material and / or negative electrode binder can be mixed in the negative electrode solvent to prepare a negative electrode slurry, and the negative electrode slurry can be coated onto the negative electrode current collector, then dried and rolled to prepare the negative electrode.

[0130] The negative electrode solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropanol. In some aspects, the negative electrode solvent may include distilled water in order to promote the dispersion of the components of the negative electrode slurry.

[0131] The solid content of the negative electrode slurry can be from 30% to 80% by weight, specifically from 40% to 70% by weight.

[0132] 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.

[0133] 3) Diaphragm

[0134] The diaphragm can be placed between the positive and negative electrodes.

[0135] A separator is disposed between the positive and negative electrodes, thereby separating the negative and positive electrodes and providing a migration channel for lithium ions. Any separator commonly used in lithium-ion secondary batteries can be used without particular limitation. The separator can include a porous polymer membrane. For example, a porous polymer membrane formed from polyolefin polymers (e.g., ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer), or having a stacked structure with two or more layers, can be used as a separator. Furthermore, the separator can include a typical porous nonwoven fabric. For example, a nonwoven fabric formed from high-melting-point glass fibers or polyethylene terephthalate fibers can be used as a separator. Additionally, coated separators including ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength.

[0136] (2) Electrolytes

[0137] The electrolyte of the present invention may contain lithium salt and organic solvent.

[0138] Any compound can be used as a lithium salt without particular limitation, as long as it is a compound capable of providing lithium ions for use in lithium secondary batteries. Specifically, the lithium salt may include at least one selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. For example, the lithium salt may be LiPF6. The lithium salt may be present at a concentration of 0.1 M to 3.0 M, preferably 0.1 M to 2.0 M, 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.

[0139] 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.

[0140] Specifically, the organic solvent may include at least one selected from cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, or cyclic ester organic solvents.

[0141] Specifically, organic solvents may include cyclic carbonate organic solvents, linear carbonate organic solvents, or mixtures thereof.

[0142] Cyclic carbonate organic solvents are high-viscosity organic solvents that can dissociate lithium salts in electrolytes due to their high dielectric constant. Specifically, cyclic carbonate organic solvents may 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. More specifically, cyclic carbonate organic solvents may include at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). More specifically, cyclic carbonate organic solvents may include ethylene carbonate (EC).

[0143] Furthermore, linear carbonate organic solvents are organic solvents with low viscosity and low dielectric constant. Specifically, linear carbonate organic solvents may 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, more specifically, at least one selected from the group consisting of ethyl methyl carbonate (EMC) and diethyl carbonate (DEC), and even more specifically, ethyl methyl carbonate (EMC).

[0144] 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 a volume ratio of 5:95 to 40:60, specifically 10:90 to 25:75. When the mixing ratio of the cyclic carbonate organic solvents and linear carbonate organic solvents meets the above range, both high dielectric constant and low viscosity are achieved, and excellent ionic conductivity can be obtained.

[0145] 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.

[0146] 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.

[0147] In addition, cyclic ester solvents may specifically include at least one selected from γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0148] 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.

[0149] 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 ether solvent is not limited to this group.

[0150] Glycol diether solvents can be solvents with a higher dielectric constant and lower surface tension than straight-chain carbonate organic solvents, and lower reactivity with metals. Glycol diether solvents 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).

[0151] 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, and 4-fluorophenylacetonitrile.

[0152] In addition to the electrolyte components, the electrolyte may further contain other additives to improve battery life characteristics, prevent battery capacity reduction, and increase battery discharge capacity.

[0153] Common examples of other additives may include at least one selected from the group consisting of 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.

[0154] Specifically, other 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), and methyltrimethylamine sulfate (MTMS). One or more compounds selected from the following: tetraphenylborate, lithium oxaloyl difluoroborate, succinic acid, adiponitrile, acetonitrile, propionitrile, butyric acid, valerate, octanoic acid, heptanoic acid, cyclopentaneformitrile, cyclohexaneformitrile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzene, triethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2 (lithium bis(fluorosulfonyl)imide, LiFSI), LiN(SO2CF3)2 (lithium bis(trifluoromethanesulfonyl)imide, LiTFSI), LiPO2F2, LiODFB, LiB(C2O4)2 (lithium bis(oxaloylborate, LiBOB), and LiBF4.

[0155] The content of other additives relative to the total weight of the electrolyte can be from 0.01 wt% to 20 wt%, preferably from 0.03 wt% to 10 wt%, and more preferably from 0.05 wt% to 5.0 wt%. When the amount of other additives is less than 0.01 wt%, the effect of improving the low-temperature output, high-temperature storage characteristics, and high-temperature life characteristics of the battery is not significant. When the amount of other additives is greater than 20 wt%, excessive side reactions may occur in the electrolyte during battery charging and discharging. In particular, when the additives for SEI layer formation are added in excess, the additives may not decompose sufficiently at high temperatures, and therefore may remain in the electrolyte as unreacted substances or precipitates at room temperature. Therefore, side reactions that reduce the life or resistivity characteristics of the secondary battery may occur.

[0156] (3) Battery casing

[0157] The battery casing can be used to house the electrode assembly and electrolyte.

[0158] Specifically, the battery casing is designed to house the electrode assembly, the injected electrolyte, and then seal it. The battery casing 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 any aspect of the invention.

[0159] For example, the battery casing can be a pouch-type battery casing. A pouch-type battery casing can be manufactured by molding a pouch-film laminate. The pouch-type battery casing can house the electrode assembly within an outer material manufactured by molding a pouch-film laminate.

[0160] In the bag film laminate, the base layer, the gas barrier layer and the sealant layer are stacked in sequence, but the present invention is not limited thereto.

[0161] Specifically, a base layer is formed on the outermost layer of the bag membrane laminate to protect the secondary battery from external friction and impact. The base layer is made of polymer, thus providing electrical insulation between the electrode assembly and the external environment.

[0162] The base layer can be formed from at least one material selected from the group consisting of polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, nylon, polyester, poly(p-phenylenebenzodioxazole), polyarylate, and Teflon. In particular, the base layer is preferably made of polyethylene terephthalate (PET), nylon, or combinations thereof, which have abrasion resistance and heat resistance.

[0163] A gas barrier layer is stacked between the base layer and the sealant layer to ensure the mechanical strength of the bag, prevent the entry or exit of external gases or moisture into the secondary battery, and prevent electrolyte leakage from the inside of the pouch battery casing. The gas barrier layer can be formed of metal. For example, the gas barrier layer can be a thin film containing at least one metal selected from aluminum (Al), copper (Cu), stainless steel (SUS), nickel (Ni), titanium (Ti), and INVAR, but is not limited thereto.

[0164] When the pouch-type battery housing containing the electrode assembly 270 is sealed to completely seal the interior of the pouch-type battery housing, the sealant layer is thermally bonded together at the sealing portion. For this purpose, the sealant layer can be formed of a material with excellent heat-sealing strength.

[0165] The sealant layer can be formed of a material that is insulating, corrosion-resistant, and sealing. Specifically, the sealant layer is in direct contact with the electrode assembly 270 and / or electrolyte (not shown) inside the pouch cell housing, and therefore can be formed of a material that is insulating and corrosion-resistant. Additionally, the sealant layer should completely seal the interior of the pouch cell housing and prevent material migration between the interior and exterior, and therefore can be formed of a material with high sealing properties (e.g., excellent heat-sealing strength). To ensure such insulation, corrosion resistance, and sealing, the sealant layer can be formed of a polymer material.

[0166] Specifically, the sealant layer may be formed of at least one material selected from polyethylene, polypropylene, polycarbonate, polyethylene terephthalate, polyvinyl chloride, acrylic polymers, polyacrylonitrile, polyimide, polyamide, cellulose, nylon, polyester, poly(p-phenylenebenzodioxazole), polyarylate, and Teflon, and may preferably be formed of polyolefin resins such as polypropylene (PP) and / or polyethylene (PE). In this case, polypropylene may include cast polypropylene (CPP), acid-modified polypropylene (PPa), polypropylene-ethylene copolymer, and / or polypropylene-butene-ethylene terpolymer.

[0167] Figure 1 This is an exploded assembly diagram of the lithium secondary battery of the present invention.

[0168] Pouch-type battery casings can be manufactured by stretching, molding, or elongating the pouch membrane laminate using a punch or similar tool. Therefore, refer to... Figure 1 The pouch-type battery casing may include a cup portion 232 and a receiving portion 234. The receiving portion 234 is where the electrode assembly 270 is received, and may refer to a pouch-shaped storage space formed within the cup portion 232 during the formation of the cup portion 232. The receiving portion may correspond to the internal space of the battery casing that receives the electrode assembly and the electrolyte.

[0169] Meanwhile, the pouch-type battery casing may include a first casing 230 and a second casing 240. The first casing 230 may include a receiving portion 234 capable of accommodating the electrode assembly 270, and the second casing 240 may cover the receiving portion 234 from above to prevent the electrode assembly 270 from being separated from the outside of the battery casing. The first casing 230 and the second casing 240 may be manufactured such that one side of the first casing 230 and the other side of the second casing 240 are connected to each other, but the invention is not limited thereto, and the first casing 230 and the second casing 240 may be manufactured in various ways, such as being manufactured separately from each other.

[0170] According to another aspect of the invention, when cup portions 242 or 232 are formed in a pouch film laminate, two symmetrical cup portions 232 and 242 adjacent to each other can be stretched and molded in one pouch film laminate. In this case, cup portions 232 and 242 can be formed in a first housing 230 and a second housing 240, respectively. After the electrode assembly 270 is accommodated in the receiving portion 234 provided in the cup portion 232 of the first housing 230, the bridging portion 250 formed between the two cup portions 232 and 242 can be folded so that the two cup portions 242 face each other. In this case, the cup portion 242 of the second housing 240 can accommodate the electrode assembly 270 from above. Therefore, since two cup portions 232 and 242 accommodate one electrode assembly 270, a thicker electrode assembly 270 can be accommodated than when only one cup portion is present. In addition, by folding the pouch-type battery housing to form one edge of the secondary battery, the number of edges to be sealed can be reduced when a sealing process is performed later. Therefore, the processing speed of the pouch-type secondary battery 200 can be increased, and the number of sealing processes can be reduced.

[0171] The pouch-type battery housing can be sealed while accommodating the electrode assembly 270, leaving a portion (i.e., the terminal portion) of the electrode lead 10 exposed. Specifically, when the electrode lead 10 is connected to the electrode tab 280 of the electrode assembly 270 and the lead film 290 is attached to a portion of the electrode lead 10, the electrode assembly 270 can be accommodated in a receiving portion 234 provided in the cup portion 232 of the first housing 230, and the second housing 240 can cover the receiving portion 234 from above. Electrolyte (not shown) can then be injected into the receiving portion 234, and the sealing portions 260 formed on the edges of the first housing 230 and the second housing 240 can be sealed.

[0172] The sealing portion 260 can be used to seal the receiving portion 234. Specifically, the sealing portion 260 can be formed along the edge of the receiving portion 234, and thus can seal the receiving portion 234. The sealing temperature of the sealing portion 260 can be from 180°C to 250°C, specifically from 200°C to 250°C, and more specifically from 210°C to 240°C. When the sealing temperature meets the above numerical range, the pouch-type battery casing can obtain sufficient sealing strength through heat sealing.

[0173] In this case, in order to ensure the energy density of the lithium secondary battery, the sealing portion 260 can be formed by folding towards the receiving portion 234.

[0174] The lithium secondary battery of the present invention can have a charging cut-off voltage of 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 comparable to high-nickel-content cathode active materials can be achieved, along with improved high-temperature lifetime performance and high-temperature storage performance. The capacity of the cathode active material is affected by both the composition of the active material used and the driving voltage range. For example, even in lithium nickel cobalt manganese-based oxides with the same transition metal composition, as the charging cut-off voltage increases, side reactions with the electrolyte increase during charge and discharge, and the cathode active material undergoes rapid structural collapse, leading to rapid degradation of lifetime characteristics. This problem is more pronounced in high-nickel lithium nickel cobalt manganese-based oxides with high nickel content. Therefore, lithium nickel cobalt manganese-based oxides typically operate in a voltage range of 2.0 V to 4.3 V when used as cathode active materials. However, in the present invention, since the Ni content of the cathode active material is less than 70 mol% and the EFF index meets a specific range, the cathode active material can maintain excellent lifetime characteristics even when driven at high voltages above 4.3 V.

[0175] 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 cut-off voltage is increased to set the nominal voltage to 3.68 V or higher, thereby achieving a high energy density. Specifically, the energy density of the lithium secondary battery of this invention can be 500 Wh / L or higher, 550 Wh / L or higher, or 500 Wh / L to 800 Wh / L.

[0176] 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).

[0177] 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.

[0178] 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.

[0179] 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).

[0180] Examples and Comparative Examples

[0181] Example 1

[0182] <Preparation of Electrode Components>

[0183] 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 97:1.8:2.2. 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 Co 0.1 Mn 0.3 O2, the binder is polyvinylidene fluoride (PVDF), and the conductive material is carbon nanotubes.

[0184] A negative electrode slurry was prepared by mixing the negative electrode active material, binder, conductive material, and additives 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 7.8 μm thick copper current collector, dried, and rolled to prepare the negative electrode. In this case, the negative electrode active material was a mixture of artificial and natural graphite, the binder was styrene-butadiene rubber (SBR), the conductive material was Super C65, and the additive was carboxymethyl cellulose (CMC).

[0185] A porous polyethylene diaphragm is placed between the negative and positive electrodes prepared above to prepare an electrode assembly.

[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 structure of 23 dual cells (the smallest unit in which the positive electrode, separator and negative electrode are stacked in sequence) stacked together.

[0187] <Preparation of Electrolytes>

[0188] 1.0 M LiPF6 was dissolved in a mixed solvent containing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. Then, 0.5 wt% ethylene carbonate (VC), 0.5 wt% propane sulpholol (PS), 1 wt% ethylene sulfate (ESa), 1 wt% lithium difluorophosphate, and 0.2 wt% LiBF4 were added as additives to prepare an electrolyte.

[0189] <Manufacturing of Lithium Secondary Batteries>

[0190] The electrode assembly prepared as described above was placed inside a pouch battery casing, and then 90.42 g of the electrolyte prepared as described above was injected into the casing and sealed to manufacture a pouch lithium secondary battery.

[0191] Example 2

[0192] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 85.11 g of the prepared electrolyte was injected into the pouch-type battery casing.

[0193] Example 3

[0194] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 79.79 g of the prepared electrolyte was injected into the pouch-type battery casing.

[0195] Example 4

[0196] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that an electrode assembly was prepared by rolling the positive electrode to a porosity of 20% and the negative electrode to a porosity of 27%, and 85.11 g of the prepared electrolyte was injected into the pouch-type battery casing.

[0197] Example 5

[0198] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that a mixture of carbon nanotubes and Li₂SO₄ in a weight ratio of 2:1 was used as the positive electrode conductive material. The positive electrode had a porosity of 21% and a loading of 4.05 mAh / cm². 2 The porosity of the negative electrode is 27%, and the N / P ratio of the positive and negative electrodes is 106. 85.11 g of the electrolyte prepared was injected into the pouch cell casing.

[0199] Example 6

[0200] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that Li[Ni] was used. 0.62 Co 0.06 Mn 0.32O2 was used as the positive electrode active material, and a mixture of carbon nanotubes and Li2SO4 in a weight ratio of 2:1 was used as the positive electrode conductive material. The porosity of the positive electrode was 19.1%, and the loading was 4.12 mAh / cm³. 2 The porosity of the negative electrode is 26.8%, and the N / P ratio of the positive and negative electrodes is 106. 95.74 g of the electrolyte prepared was injected into the pouch cell casing.

[0201] Example 7

[0202] A pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that the porosity of the positive electrode was 23.5% and the loading was 3.87 mAh / cm³. 2 The porosity of the negative electrode is 29%, and the N / P ratio of the positive and negative electrodes is 109. 74.47 g of the prepared electrolyte is injected into the pouch battery casing.

[0203] Example 8

[0204] A pouch-type 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, and then 0.5 wt% vinyl ethylene carbonate (VEC), 0.5 wt% vinylene carbonate, 0.5 wt% propane sulpholol (PS), 1.0 wt% ethylene sulfate (ESa), 1.0 wt% lithium difluorophosphate (LiDFP, product name: SLO7), 0.2 wt% LiBF4, and 0.1 wt% 1H imidazole-1-carboxypropargyl ether (HS02, CAS 83395-38-4) were added as additives; the porosity of the positive electrode was 19.64%, and the loading was 3.98 mAh / cm³. 2 The porosity of the negative electrode is 26.55%, the N / P ratio of the positive and negative electrodes is 109.1, and 85.11 g of the prepared electrolyte is injected into the pouch cell casing.

[0205] Comparative Example 1

[0206] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 95.74 g of the prepared electrolyte was injected into the pouch-type battery casing.

[0207] Comparative Example 2

[0208] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that 74.47 g of the prepared electrolyte was injected into the pouch-type battery casing.

[0209] Comparative Example 3

[0210] The pouch-type lithium secondary battery was manufactured in the same manner as in Example 1, except that Li[Ni] was used. 0.62 Co 0.06 Mn 0.32 O2 was used as the positive electrode active material, and the positive electrode loading was adjusted to 3.9 mAh / cm³. 2 22 dual cells were stacked to prepare the electrode assembly, and 85.11 g of the prepared electrolyte was injected into the pouch cell housing.

[0211] Example 1 - Evaluation of the EFF Index

[0212] The EFF index, defined by Equation 1 below, was measured for the lithium secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0213] [Equation 1]

[0214] In equation 1 above, R E [Unit: g] refers to the weight of the electrolyte contained in the activated lithium secondary battery, in s. U The volume (S) of the electrode assembly E ) and the volume (S) of the lithium secondary battery C The ratio of (S) E / S C ), N C [Unit: Ah] is the capacity of the lithium secondary battery when discharged from 4.4 V to 3.0 V at 0.33C at 25°C.

[0215] (1) R E Measurement

[0216] The lithium secondary batteries manufactured in Examples 1 to 8 and Comparative Examples 1 to 3 were each activated by: (1) charging to 3% SOC at a constant current of 0.2C at 55°C, (2) charging to 20% SOC at a constant current of 1.0C at 55°C, and (3) charging to 60% SOC at a constant current of 1.0C at 55°C.

[0217] Then, after activation, each lithium secondary battery was disassembled and the weight R of the remaining electrolyte was measured. E For each lithium secondary battery, the weight of the remaining electrolyte was measured in the following manner: (1) The weight of the activated lithium secondary battery (M) was measured before disassembly. L(2) Disassemble the lithium secondary battery and remove the electrolyte present in the internal space of the battery casing; (3) Immerse the battery casing and electrode assembly in dimethyl carbonate as a solvent to remove the electrolyte present on the surface of the battery casing, the surface of the electrode assembly, and the internal pores of the electrode assembly, and then dry the battery casing and the 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.

[0218] [Equation A]

[0219] R E =M L -M C -M A

[0220] The results are shown in Table 1 below.

[0221] (2) N C Measurement

[0222] The lithium secondary batteries manufactured in Examples 1 to 5 and Comparative Examples 1 to 3 were charged to 4.35V at 25°C under constant current / constant voltage conditions of 0.33C (with a cutoff at 0.05C), and then discharged to 2.0V under constant current conditions of 0.33C to activate them.

[0223] Subsequently, the lithium secondary battery was charged from 3.0 V to 4.35 V at 0.33C (C rate) at 25°C. Then, the capacity N of the lithium secondary battery was measured when it was discharged from 4.4 V to 3.0 V at 0.33C at 25°C. C The results are shown in Table 1 below.

[0224] (3) S U Measurement

[0225] For each lithium secondary battery manufactured in Examples 1 to 8 and Comparative Examples 1 to 3, the volume (S) of the electrode assembly was measured. E ) and the volume (S) of lithium secondary batteries C And calculate S E With S C The ratio. S E and S C The measurements were taken using the following methods. The results are shown in Table 1 below.

[0226] Volume S of the electrode assembly E The volume S of the electrode assembly described in Equation B below is obtained.E The following assumptions are made: the electrode assembly housed in the pouch-type battery casing has a cuboid shape formed by stacking a positive electrode, a negative electrode, and a separator, and the length and width of the electrode assembly are equal to the length and width of the negative electrode, respectively.

[0227] [Equation B]

[0228] S E =(Thickness of electrode assembly) × (Length of negative electrode) × (Width of negative electrode)

[0229] The volume S of a lithium secondary battery C The volume S of the lithium secondary battery described in Equation C is obtained from the following equation. C This was obtained by assuming that the lithium secondary battery, including the pouch-shaped battery casing, has a cuboid shape.

[0230] [Equation C]

[0231] S C = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0232] In equation C above, the thickness of the lithium secondary battery is the distance measured along the thickness direction of the lithium secondary battery relative to its external shape. The length of the lithium secondary battery is the distance measured along the length direction of the lithium secondary battery relative to its external shape. The width of the lithium secondary battery is the distance measured along the width direction of the lithium secondary battery relative to its external shape.

[0233] The results are shown in Table 1 below.

[0234] [Table 1]

[0235] Experimental Example 2: Evaluation of Lifetime at High Temperatures

[0236] The lithium secondary batteries of Examples 1 to 8 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 28 weeks to measure the capacity retention and resistance increase rate of each lithium secondary battery. The specific measurement methods are described below.

[0237] (1) Capacity retention rate

[0238] Each lithium secondary battery was stored at 60°C for 28 weeks, then charged to 4.35 V at 0.33C CC / CV conditions at 25°C, cut off at 0.05C, and discharged to 2.0 V at 0.33C CC conditions to measure the capacity during discharge.

[0239] The capacity retention rate was evaluated according to the following equation, and the results are shown in Table 2 below.

[0240] Capacity retention (%) = (Discharge capacity after 28 weeks of storage at 60°C / Initial discharge capacity) × 100

[0241] (2) Rate of increase in resistance

[0242] Before storing the lithium-ion battery at 60°C, it was charged to 100% SOC at 0.33C CC / CV at 25°C. The capacity at room temperature was then determined. The battery was then charged to 50% SOC relative to its discharge capacity and discharged at 2.5C for 30 seconds. The resistance was measured using the voltage drop at this point as the initial resistance. After storing the battery at 25°C for 28 weeks, the resistance was measured in the same manner as the final resistance. The rate of increase in resistance was calculated using the following equation. The results are shown in Table 2 below.

[0243] Resistance increase rate (%) = (final resistance - initial resistance) / (initial resistance) × 100

[0244] [Table 2]

[0245] Referring to Table 2 above, it was found that the lithium secondary batteries manufactured in Examples 1 to 8 had better capacity retention and resistance increase rates after being stored at 60°C for 28 weeks than the lithium secondary batteries manufactured in Comparative Examples 1 to 3.

[0246] (Marker explanation)

[0247] 10: Electrode leads

[0248] 20: Positive lead

[0249] 30: Negative lead

[0250] 230: First shell

[0251] 232: Cup section

[0252] 234: Reception Department

[0253] 240: Part Two

[0254] 242: Cup section

[0255] 250: Bridging section

[0256] 260: Sealing part

[0257] 270: Electrode assembly

[0258] 280: Electrode tabs

[0259] 282: Positive electrode tab

[0260] 284: Negative electrode tab

[0261] 290: Lead film

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 internal space configured to accommodate the electrode assembly and the electrolyte, Wherein, the positive electrode includes a positive electrode active material, Wherein, the positive electrode active material includes a lithium nickel-based oxide, and the lithium nickel-based oxide contains 50 mol% to 70 mol% of nickel among all metals other than lithium, and Wherein, the electrolyte filling factor (EFF) index defined by Equation 1 is 1.52 to 1.88, [Equation 1] Wherein, in Equation 1, R E This refers to the weight of the remaining electrolyte in the lithium secondary battery after activation, expressed in grams. S U The volume (S) of the electrode assembly E ) and the volume (S) of the lithium secondary battery C The ratio of (S) E / S C ), N C It is the capacity of the lithium secondary battery when discharged from 4.4 V to 3.0 V at 0.33C at 25°C, in Ah.

2. The lithium secondary battery as described in claim 1, wherein, R E It ranges from 70 g to 90 g.

3. The lithium secondary battery as described in claim 1, wherein, S U It ranges from 0.75 to 0.

95.

4. The lithium secondary battery as described in claim 1, wherein, N C It ranges from 35 Ah to 50 Ah.

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

6. The lithium secondary battery as described in claim 1, wherein, The lithium nickel-based oxide is represented by Formula 1: [Formula 1] Li 1+a1 [Ni x1 Co y1 Mr z1 M 1 w1 ]O2 Wherein, in Formula 1, 0≤a1≤0.5, 0.5≤x1≤0.7, 0<y1≤0.15, 0<z1≤0.4, and 0≤w1≤0.2, and M 1 It is at least one doping element selected from the group consisting 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.

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

8. 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.

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

10. The lithium secondary battery as described in claim 1, wherein, The battery case is a pouch-type battery case.

11. 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 1.5 to 3, with units of g / Ah.

12. The lithium secondary battery as described in claim 1, wherein, The volume (S) of the electrode assembly E The range is 0.17 L to 1.1 L.

13. The lithium secondary battery as described in claim 1, wherein, The volume (S) of the lithium secondary battery C The range is 0.23 L to 1.2 L.

14. The lithium secondary battery as described in claim 1, wherein, The electrolyte includes an organic solvent and a lithium salt, and the concentration of the lithium salt is 0.1 M to 3.0 M.

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

16. A battery pack, comprising the lithium secondary battery according to any one of claims 1 to 15.

17. An electric vehicle, comprising the battery pack according to claim 16 as a power source.

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