Lithium-ion rechargeable battery

Abstract

The present invention relates to a lithium secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case including an internal space that accommodates 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 containing 50 mol% to 70 mol% of nickel relative to all metals excluding lithium, and an EFF (Electrolyte Filling Factor) index (unit: g / Ah) defined by the following Formula 1 is 1.82 to 2.06. [Formula 1] JPEG2026529672000008.jpg19170 In Formula 1 above, R E [unit: g] represents the weight of residual electrolyte contained in the lithium secondary battery after activation, and S U is the volume of the electrode assembly (S A ) and the ratio of the volume of the lithium secondary battery (S E ) (S A / S E ), and N C [unit: Ah] represents the capacity when the lithium secondary battery is discharged from 4.4 V to 2.5 V at 25°C and 0.33 C.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2024-0016255 dated February 1, 2024, and all content disclosed in the said Korean Patent Application is incorporated herein by reference. The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery having high energy density and excellent high-temperature life characteristics. [Background technology]

[0002] In recent years, as the application areas of lithium-ion batteries have rapidly expanded from power supply for electronic devices such as electrical, electronic, telecommunications, and computers to power storage and supply for large-area devices such as automobiles and energy storage devices, the demand for high-capacity, high-power, and highly stable secondary batteries has increased.

[0003] Generally, the lithium secondary battery consists of a positive electrode containing a positive electrode active material, a negative electrode containing a negative electrode active material, an electrolyte that serves as a medium for transferring lithium ions, and a separator. In this case, carbon-based active materials and silicon-based active materials can be used as the negative electrode active material, and lithium transition metal oxides such as lithium cobalt oxide, lithium nickel oxide, and lithium nickel-cobalt-manganese composite transition metal oxide can be used as the positive electrode active material.

[0004] On the other hand, in recent years, lithium nickel-cobalt-manganese composite transition metal oxides, which contain 80 mol% or more nickel among the metals excluding lithium, have been mainly studied as cathode active materials in order to increase the energy density of the cathode. However, when the nickel content of lithium nickel-cobalt-manganese composite transition metal oxides is increased, the structural stability of the cathode active material rapidly collapses at high temperatures, leading to a significant deterioration in performance and a decrease in thermal stability.

[0005] To prevent such problems, reducing the nickel content of lithium nickel-cobalt-manganese composite transition metal oxide requires increasing the drive voltage to achieve the desired energy density. However, such high-voltage driving leads to more vigorous side reactions in the electrolyte at the positive electrode, resulting in increased gas generation inside the battery. Therefore, there is a need to develop lithium secondary batteries that offer excellent energy density and thermal stability, and that can reduce electrolyte side reactions during high-voltage operation. [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to solve the above-mentioned problems and to provide a lithium secondary battery that achieves high energy density, has excellent thermal stability of the positive electrode active material, reduces side reactions of the electrolyte at high voltage, and has excellent high-temperature life characteristics. [Means for solving the problem]

[0007] [1] The present invention provides a lithium secondary battery comprising an electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case housing the electrode assembly and the electrolyte, wherein the positive electrode comprises a positive electrode active material, and the positive electrode active material comprises a lithium nickel oxide containing 50 mol% to 70 mol% nickel among all metals excluding lithium, and the EFF (Electrolyte Filing Factor) index (unit: g / Ah) defined by the following formula 1 (unit: g / Ah) is 1.82 to 2.06.

[0008] [Formula 1]

number

[0009] In the above formula 1, R E [Unit: g] represents the weight of residual electrolyte contained in the activated lithium secondary battery, S Urepresents the volume of the electrode assembly (S A ) and the volume of the lithium secondary battery (S E ) ratio (S A / S E ), and N C [unit: Ah] means the capacity when the lithium secondary battery is discharged from 4.4 V to 2.5 V at 25°C and 0.33 C.

[0010] [2] Provided is the lithium secondary battery according to [1] above, wherein in the present invention, R E is 265 g to 295 g.

[0011] [3] Provided is the lithium secondary battery according to [1] or [2] above, wherein in the present invention, S U is 0.70 to 0.95.

[0012] [4] Provided is the lithium secondary battery according to any one of [1] to [3] above, wherein in the present invention, N C is 90 Ah to 150 Ah.

[0013] [5] Provided is the lithium secondary battery according to any one of [1] to [4] above, wherein in the present invention, the ratio of R C to N E (R E / N C ) [unit: g / Ah] is 2.00 to 3.30.

[0014] [6] Provided is the lithium secondary battery according to any one of [1] to [5] above, wherein in the present invention, the volume of the electrode assembly (S A ) is 0.3 L to 1.35 L.

[0015] [7] Provided is the lithium secondary battery according to any one of [1] to [6] above, wherein in the present invention, the volume of the lithium secondary battery (S E ) is 0.4 L to 1.5 L.

[0016] [8] The present invention provides a lithium secondary battery according to any one of the above [1] to [7], wherein the lithium nickel oxide contains 15 mol% or less of cobalt (Co) among all metals excluding lithium.

[0017] [9] In the present invention, the lithium nickel oxide is represented by the following chemical formula 1, and provides a lithium secondary battery according to any one of the above [1] to [8].

[0018] [Chemical formula 1] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 ]O2

[0019] In the above chemical formula 1, 0 ≤ a1 ≤ 0.5, 0.5 ≤ x1 ≤ 0.7, 0 <y1≦0.15、0<z1≦0.4、0≦w1≦0.2であり、M 1 is one or more doping elements 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.

[0020]

[10] The present invention provides a lithium secondary battery according to any one of the above [1] to [9], wherein the lithium nickel oxide is a single particulate particle.

[0021]

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

[10] , wherein the charge cut-off voltage of the lithium secondary battery is 4.3V or higher.

[0022]

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

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

[0023]

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

[12] , wherein the negative electrode contains graphite as the negative electrode active material.

[0024]

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

[13] , wherein the battery case is a rectangular battery case.

[0025]

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

[14] , wherein the electrode assembly is formed by sequentially stacking a positive electrode, a separator, and a negative electrode and winding them in one direction. [Effects of the Invention]

[0026] According to the present invention, by including 50 mol% to 70 mol% nickel among all metals excluding 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 electrolyte remaining 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 is reduced, and suitable electrolyte impregnation can be ensured. As a result, the manufactured lithium secondary battery can achieve high energy density and high capacity characteristics, and can exhibit excellent life characteristics and high-temperature life characteristics. [Modes for carrying out the invention]

[0027] The present invention will be described in more detail below. The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their general or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0028] The terms used herein are for illustrative purposes only and do not limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise.

[0029] In this specification, terms such as “include,” “provide,” or “have” indicate the presence of implemented features, figures, steps, components, or combinations thereof, and should be understood not to preemptively exclude the possibility of the presence or addition of one or more other features, figures, steps, components, or combinations thereof.

[0030] In the present invention, "single-particle-like particles" means particles consisting of 30 or fewer sub-particles. The sub-particle units that constitute the single-particle-like particles are called "nodules." The single-particle-like particles include single particles consisting of one single nodule, and analogous single particles which are composites of 30 or fewer nodules.

[0031] The term "nodule" refers to a sub-particle unit body that constitutes a single particle or an analogous single particle. The nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which no grain boundaries are visible when observed with a scanning electron microscope (SEM) at a field of view of 5,000 to 20,000 times magnification.

[0032] In this invention, "secondary particle" refers to a particle formed by the aggregation of more than 30 sub-particles. To distinguish it from the sub-particles that constitute the single-particle particles, each sub-particle unit that constitutes the secondary particle is referred to as a "primary particle."

[0033] The term "particle" as used in this invention may include one or all of the following: single particles, analogous single particles, primary particles, nodules, and secondary particles.

[0034] In this invention, "average particle size D 50 "50% of the volume of the cumulative particle size distribution of the powder being measured" refers to the size of the particle that corresponds to 50% of the cumulative volume, and can be measured using the laser diffraction method. For example, after dispersing the powder to be measured in a dispersion medium, it can be introduced into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiated with ultrasound at approximately 28 kHz at an output of 60 W, and after obtaining a graph of the cumulative volume particle size distribution, the size of the particle that corresponds to 50% of the cumulative volume can be determined to measure it.

[0035] The inventors of the present invention conducted extensive research to develop a lithium secondary battery that achieves high capacity characteristics and has excellent lifespan and storage performance at high temperatures and high voltages. As a result, they discovered that by including 50 mol% to 70 mol% nickel among the metals other than lithium, and by adjusting the structure, discharge capacity, and weight of the electrolyte remaining after activation to satisfy a specific formula, it is possible to improve the capacity characteristics of the lithium secondary battery, its high-voltage and high-temperature lifespan and storage characteristics, and its electrolyte impregnation properties, thus completing the present invention.

[0036] The present invention will be described in more detail below. The lithium secondary battery according to the present invention includes at least one of the following disclosed configurations, and may include any combination of technically feasible configurations from the following configurations.

[0037] Lithium-ion rechargeable battery The lithium secondary battery according to the present invention includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case comprising an internal space for housing the electrode assembly and the electrolyte. The positive electrode comprises a positive electrode active material, which comprises a lithium nickel oxide containing 50 mol% to 70 mol% nickel among all metals excluding lithium, and has an EFF (Electrolyte Filing Factor) index (unit: g / Ah) defined by the following formula 1 (unit: g / Ah) of 1.82 to 2.06.

[0038] [Formula 1]

number

[0039] In the above formula 1, R E [Unit: g] represents the weight of residual electrolyte contained in the activated lithium secondary battery, S U The volume of the electrode assembly (S A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E ) means N C [Unit: Ah] represents the capacity of the lithium secondary battery when it is discharged from 4.4V to 2.5V at 25°C and 0.33C.

[0040] The lithium secondary battery according to the present invention has an EFF index (unit: g / Ah) defined by formula 1 above, which is 1.82 to 2.06. Specifically, it may be 1.82 or more, 1.83 or more, 1.84 or more, 1.85 or more, 1.86 or more, 1.87 or more, 1.88 or more, 1.89 or more, 1.90 or more, or 1.91 or more, and may also be 2.06 or less, 2.05 or less, 2.04 or less, 2.03 or less, 2.02 or less, 2.01 or less, 2.00 or less, 1.99 or less, 1.98 or less, 1.97 or less, 1.96 or less, 1.95 or less, 1.94 or less, 1.93 or less, 1.92 or less, or 1.91 or less. For example, the EFF index may be 1.82 to 2.06, 1.88 to 2.00, 1.89 to 1.96, or 1.90 to 1.94.

[0041] In recent years, in order to achieve high capacity characteristics in lithium secondary batteries, there have been attempts to increase the energy density of the positive electrode by using lithium nickel oxide, which contains nickel, cobalt, and manganese and has an increased nickel content, as the positive electrode active material. However, when increasing the nickel content of lithium nickel oxide, Ni 2+ Ions are Ni 4+ The transformation into ions reduces the structural and chemical stability of the positive electrode active material, which in turn accelerates side reactions with the electrolyte and degrades its lifespan. This phenomenon is further accelerated when exposed to high temperatures, leading to a significant decrease in thermal stability.

[0042] Reducing the nickel content of lithium nickel oxides can improve thermal stability at high temperatures. However, to achieve an energy density equivalent to that of lithium nickel oxides containing high nickel content, high voltage (e.g., 4.35V or higher) is required. However, such high-voltage operation presents a problem: changes in the oxidation states of nickel and cobalt lead to oxygen desorption, intensifying electrolyte side reactions, increasing gas generation, and reducing lifespan and storage performance.

[0043] Therefore, it is necessary to reduce the amount of electrolyte injected in order to reduce gas generation. However, if the amount of electrolyte injected is reduced excessively, the electrolyte impregnation of the electrodes will decrease, increasing lithium ion mobility and cell resistance, which may actually decrease the battery's capacity and lifespan characteristics. For this reason, the amount of electrolyte injected must be appropriately adjusted according to the characteristics of the battery.

[0044] Therefore, the lithium secondary battery according to the present invention solves the above problem by adjusting the weight of the electrolyte remaining after activation to specific conditions, according to the characteristics of the lithium secondary battery, such as the ratio of the volume of the lithium secondary battery excluding the battery case to the volume of the lithium secondary battery itself, and the discharge capacity of the lithium secondary battery.

[0045] Specifically, the lithium secondary battery according to the present invention can achieve high energy density and high capacity characteristics, as well as excellent thermal stability, reduced gas generation, suitable electrolyte impregnation, and excellent high-temperature life characteristics and high-temperature storage characteristics, by adjusting the EFF index defined by formula 1 to 1.82 to 2.06.

[0046] The aforementioned R E This refers to the weight of residual electrolyte contained in the activated lithium secondary battery. The residual electrolyte contained in the lithium secondary battery refers to the sum of the electrolyte impregnated into the internal voids of the electrode assembly and the electrolyte located outside the electrode assembly in the internal space of the battery case.

[0047] The weight of the residual electrolyte contained in the activated lithium secondary battery may differ from the weight of the electrolyte initially injected into the battery case during the manufacturing process of the lithium secondary battery before activation.

[0048] The aforementioned activation refers to the process of making a lithium secondary battery, which has been manufactured but has not undergone charging or discharging, usable by charging and / or discharging it to impart electrical properties, and stabilizing the battery by forming an SEI (Solid Electrolyte Interphase) film on the electrodes.

[0049] The aforementioned R E In connection with this, the activation can be performed by carrying out one or more steps of charging the lithium secondary battery to a voltage of 4.0V or higher at 55°C.

[0050] Specifically, the aforementioned R E In connection with this, the activation can be performed by (1) charging the lithium secondary battery to 4.0V or SOC 3% under constant current conditions of 0.2C at 55°C, (2) charging to 4.35V or SOC 17% under constant current conditions of 1.0C at 55°C, and (3) charging to 4.35V or SOC 60% under constant current conditions of 1.0C at 55°C.

[0051] The weight of the residual electrolyte contained in the activated lithium secondary battery (R E ) is (1) the weight (M) of the activated lithium secondary battery, which includes the electrode assembly, electrolyte, and battery case, with the battery case sealed. L (1) the step of measuring the weight (M) of the dried battery case; (2) the step of disassembling the lithium secondary battery and removing the electrolyte present in the battery case; (3) the step of immersing the battery case and electrode assembly in a solvent such as dimethyl carbonate to remove the electrolyte present on the surface of the battery case, the surface of the electrode assembly and in the internal voids, and then drying the battery case and electrode assembly; and (4) the step of measuring the weight (M) of the dried battery case. C ) and the weight (M) of the dried electrode assembly A After going through the step of measuring ), the measured M L M C M A This can be measured by substituting it into the following equation A.

[0052] [Formula A] R E =M L -M C -M A

[0053] The aforementioned R E The amount may be 265g to 295g, 267g to 290g, 270g to 282g, or 272g to 278g. When the above range is met, the side reactions of the electrolyte are reduced, the amount of gas generated is decreased, and sufficient electrolyte impregnation can be achieved, so that lithium ion mobility can be sufficiently ensured, and excellent life characteristics, output characteristics, and high-temperature storage characteristics can be achieved.

[0054] S U The volume of the electrode assembly (S A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E ) means the volume (S) of the lithium secondary battery. EThe volume of the lithium secondary battery is calculated based on the external shape of the lithium secondary battery, and specifically refers to the volume of the space occupied by the external shape of the lithium secondary battery. In this case, the external shape of the lithium secondary battery may be the same as the external shape of the battery case when the battery case is sealed. The volume of the lithium secondary battery can be determined based on the external dimensions of the lithium secondary battery without considering the volume occupied by the electrolyte and electrode assembly components housed inside the battery case, or the volume of voids.

[0055] If the battery case is a rectangular battery case, the volume of the lithium secondary battery (S E The volume (S) of the lithium secondary battery according to the following formula B can be obtained by the following formula B. E This was obtained by assuming that the shape of the lithium secondary battery, including the rectangular battery case, is a rectangular parallelepiped.

[0056] [Formula B] S E = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0057] In formula B, the thickness of the lithium secondary battery means the distance measured along the thickness direction of the lithium secondary battery with respect to the external shape of the lithium secondary battery.

[0058] In formula B, the length of the lithium secondary battery means the distance measured along the length direction of the lithium secondary battery with respect to the external shape of the lithium secondary battery.

[0059] In formula B, the width of the lithium secondary battery means the distance measured along a direction perpendicular to the length direction of the lithium secondary battery, with reference to the external shape of the lithium secondary battery.

[0060] The shape of the lithium secondary battery is not limited to the shape described above, but may have any suitable shape. The volume of the lithium secondary battery can be determined by an appropriate measurement method depending on the shape of the lithium secondary battery.

[0061] The volume (S) of the electrode assembly A ) refers to the total volume occupied by the positive electrode, negative electrode, and separator. The volume of the electrode assembly may be adjusted by adjusting the porosity and loading amount of the positive and negative electrodes, the N / P ratio (the ratio of the negative electrode capacity to the positive electrode capacity), or by changing the type of conductive material contained in the positive and negative electrodes. The volume of the electrode assembly may also be measured based on the external shape of the positive electrode, negative electrode, and / or separator, without excluding the volume of voids contained in the positive electrode, negative electrode, and / or separator. The volume (S) of the electrode assembly A ) can be obtained by the following formula C.

[0062] [Formula C] S A = (Volume of positive electrode) + (Volume of negative electrode) + (Volume of separator)

[0063] In formula C, the volume of the positive electrode, the volume of the negative electrode, and the volume of the separator may be measured based on the external shape of the positive electrode, the negative electrode, or the separator, without considering the volume of air gaps contained in the positive electrode, the negative electrode, or the separator, respectively.

[0064] The aforementioned S U The range may be 0.70-0.95, 0.73-0.90, 0.75-0.85, or 0.77-0.82. When the above range is satisfied, the relative space utilization rate within the same volume can be increased, thereby achieving a high energy density and allowing for proper containment of gases generated by side reactions of the electrolyte.

[0065] The volume of the aforementioned lithium secondary battery (S E ) may be 0.4L to 1.5L, 0.5L to 1.3L, or 0.6L to 1.1L. When the above range is met, the electrode assembly and electrolyte can be sufficiently accommodated, S U The value can satisfy a suitable range.

[0066] The volume (S) of the electrode assembly A ) may be 0.3L to 1.35L, 0.4L to 1.2L, or 0.5L to 1L. When the above range is met, the energy density is excellent, S U The value can satisfy a suitable range.

[0067] The aforementioned N C This refers to the capacity of the lithium secondary battery when it is discharged from 4.4V to 2.5V at 25°C and 0.33C. Specifically, the aforementioned N C This is the capacity obtained when the lithium secondary battery is activated, charged at 25°C, and discharged from 4.4V to 2.5V at 0.33C, and specifically, it may represent the discharge capacity when the first charge and discharge is performed after activation. C In relation to this, the charging during the first charge / discharge after activation may be performed by charging the lithium secondary battery from 2.5V to 4.35V at 25°C with a C-rate of 0.33C.

[0068] The aforementioned N C In this case, the activation may involve charging a lithium secondary battery that has not been charged or discharged since manufacturing to 4.35V with a 0.05C cut-off under constant current / voltage conditions of 0.33C at 25°C, and then discharging it to 2.0V under constant current conditions of 0.33C.

[0069] The aforementioned N C The capacity may be 90Ah to 150Ah, 100Ah to 140Ah, 105Ah to 130Ah, or 110Ah to 120Ah. When the above range is met, high capacity characteristics can be achieved.

[0070] The capacity (N) of the lithium secondary battery when discharged from 4.4V to 2.5V at 25°C and 0.33C is... C The weight of the residual electrolyte contained in the activated lithium secondary battery relative to (R E ) ratio (R E / N C)[unit: g / Ah] may be 2.00 to 3.30. Specifically, the above R E / N C [Unit: g / Ah] may 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, 2.30 or higher, and may be 3.30 or lower, 3.10 or lower, 3.00 or lower, 2.90 or lower, 2.80 or lower, 2.70 or lower, 2.60 or lower, 2.55 or lower, 2.50 or lower, 2.45 or lower, 2.40 or lower. For example, the above R E / N C [Unit: g / Ah] may be 2.00~3.30, 2.15~2.90, 2.23~2.55, or 2.30~2.40. When the above range is met, the effect of reducing gas generation and improving electrolyte impregnation can be maximized depending on the battery design.

[0071] Next, we will describe in more detail each component of the lithium secondary battery according to the present invention. The lithium secondary battery according to the present invention includes an electrode assembly comprising a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode; an electrolyte; and a battery case housing the electrode assembly and the electrolyte.

[0072] (1) Electrode assembly The electrode assembly according to the present invention includes a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0073] Specifically, the electrode assembly may be formed by sequentially stacking a positive electrode, a separator, and a negative electrode, and the positive electrode and the negative electrode may be insulated from each other by the separator.

[0074] Examples of electrode assembly types include stack type, jelly roll type, and stack & folding type, but are not limited to these. Preferably, the electrode assembly may be of the jelly roll type, and the electrode assembly may be formed by sequentially stacking the positive electrode, separator, and negative electrode and winding it in one direction. Specifically, it may be formed by alternately stacking multiple positive electrodes, separators, and negative electrodes and winding them in one direction. The following describes in detail each component of the electrode assembly according to the present invention.

[0075] 1) Positive electrode The positive electrode includes a positive electrode active material. Specifically, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector, and the positive electrode active material layer may include a positive electrode active material.

[0076] Various positive electrode current collectors used in the art may be used as the positive electrode current collector. For example, the positive electrode current collector may be stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel whose surfaces have been surface-treated with carbon, nickel, titanium, silver, etc. The positive electrode current collector may typically have a thickness of 3 to 500 μm, and fine irregularities may be formed on the surface of the positive electrode current collector to increase the adhesion strength of the positive electrode active material. The positive electrode current collector may be used in various forms such as film, sheet, foil, mesh, porous body, foam, nonwoven fabric, etc.

[0077] The positive electrode active material layer may be located on the positive electrode current collector, specifically on one or both sides of the positive electrode current collector. The positive electrode active material layer may be a single layer or a multilayer structure of two or more layers.

[0078] The positive electrode active material contains a lithium nickel oxide in which nickel is present in an amount of 50 mol% to 70 mol%, 52 mol% to 68 mol%, 55 mol% to 65 mol%, or 57 mol% to 63 mol% of the total metals excluding lithium. In this case, compared to positive electrode active materials containing lithium nickel oxide with a high nickel content, the structural and chemical stability of the positive electrode active material at high temperatures is superior, resulting in superior thermal stability. Furthermore, gas generation and swelling phenomena due to residual lithium by-products (LiOH, Li2CO3, etc.) present on the surface of the positive electrode active material can be improved, resulting in superior lifetime characteristics.

[0079] The lithium nickel oxide may contain cobalt (Co) in amounts of 15 mol% or less, 5 mol% to 15 mol%, 7 mol% to 13 mol%, or 8 mol% to 12 mol% of the total metals excluding lithium. When cobalt is included within the above ranges, a cost advantage is obtained by including cobalt in a low amount, and the resistance characteristics and output characteristics can be improved. Specifically, the lithium nickel oxide may be represented by the following chemical formula 1.

[0080] [Chemical formula 1] Li 1+a1 [Ni x1 Co y1 Mn z1 M 1 w1 ]O2

[0081] In the above chemical formula 1, the above M 1 This corresponds to a doping element that may or may not be selectively included in the lithium nickel oxide. 1may be one or more doping elements 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, or may be one or more doping elements selected from the group consisting of W, Y, Ba, Ca, Ti, Mg, Ta, and Nb. When the doping element is contained, it can promote particle growth during firing of the positive electrode active material, or improve the stability of the crystal structure.

[0082] In Chemical Formula 1, 1+a1 represents the molar ratio of lithium (Li) in the lithium nickel-based oxide, and may satisfy 0≤a1≤0.5, 0≤a1≤0.2, or 0≤a1≤0.1. When the above range is satisfied, the positive electrode active material can form a stable layered crystal structure.

[0083] In Chemical Formula 1, x1 represents the molar ratio of nickel among all metals except lithium in the lithium nickel-based oxide particles, and may 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 range is satisfied, the manufactured lithium secondary battery can be excellent in high-temperature storage characteristics, high-temperature lifespan characteristics, and thermal stability.

[0084] In Chemical Formula 1, y1 represents the molar ratio of cobalt among all metals except lithium in the lithium nickel-based oxide particles, and may satisfy 0<y1≤0.15, 0<y1≤0.10, or 0<y1≤0.07. When the above range is satisfied, reducing the content of Co provides a cost advantage, enables realization of good resistance characteristics and output characteristics, and increasing the relative proportion of Mn can improve the structural stability of the positive electrode active material.

[0085] In Chemical Formula 1, z1 represents the molar ratio of manganese to all metals excluding lithium in the lithium nickel-based oxide particles, and may satisfy 0 < z1 ≤ 0.4, 0.1 ≤ z1 ≤ 0.4, 0.15 ≤ z1 ≤ 0.4, or 0.2 ≤ z1 ≤ 0.4. When the above range is satisfied, the structural stability of the positive electrode active material can be improved.

[0086] w1 is M among all metals excluding lithium in the lithium nickel-based oxide 1 which represents the molar ratio of the element, and may satisfy 0 ≤ w1 ≤ 0.2, 0 ≤ w1 ≤ 0.15, or 0 ≤ w1 ≤ 0.1. When the above range is satisfied, it can promote particle growth during calcination of the positive electrode active material, or function to improve the stability of the crystal structure.

[0087] In addition, the lithium nickel-based oxide may be single-particle particles. Specifically, when the lithium nickel-based oxide is secondary particles, particle cracking increases during electrode manufacturing, and the occurrence of internal cracks caused by expansion / contraction of the volume of primary particles during charge and discharge increases, so the effect of improving high-temperature lifespan characteristics and high-temperature storage characteristics may be reduced.

[0088] Therefore, when using the lithium nickel-based oxide that is single-particle particles as described above, the particle strength is higher than that of conventional secondary-particle lithium nickel-based oxide in which more than 30 primary particles are agglomerated, so there is less particle cracking during rolling. In addition, in the case of the single-particle lithium nickel-based oxide according to the present invention, since the number of primary particles constituting the particle is small, changes caused by expansion and contraction of the volume of primary particles during charge and discharge are small, thereby significantly reducing the occurrence of cracks inside the particle.

[0089] Therefore, the lithium secondary battery according to the present invention uses lithium nickel-based oxide that is single-particle particles, which reduces particle cracking and the occurrence of internal cracks inside the particles during charge and discharge, so that it can have excellent thermal stability, thereby improving high-temperature lifespan characteristics and high-temperature storage characteristics.

[0090] On the other hand, the average particle size (D) of the positive electrode active material 50 The thickness of the ) may 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 the above range is met, it is possible to prevent resistance increase and decrease in output characteristics, and to minimize side reactions with the electrolyte, thereby enabling excellent high-temperature lifetime characteristics and high-temperature storage characteristics.

[0091] The positive electrode active material layer may contain 90% to 99% by weight, 92% to 99% by weight, or 94% to 98% by weight of the positive electrode active material. When these ranges are met, the energy density and capacity characteristics of the lithium secondary battery can be improved.

[0092] On the other hand, the positive electrode active material layer may further selectively include at least one of a positive electrode conductive material and a positive electrode binder. The positive electrode conductive material is used to impart conductivity to the electrode and can be used in any battery without particular limitations as long as it has electronic conductivity without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The positive electrode conductive material may typically be included in amounts of 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 relative to the total weight of the positive electrode active material layer.

[0093] The positive electrode binder plays a role in improving the adhesion between positive electrode material particles and the adhesion between the positive electrode material and the positive electrode current collector. Specific examples include fluororesin binders containing polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE); rubber binders containing styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber, and styrene-isoprene rubber; cellulose binders containing carboxyl methyl cellulose (CMC), starch, hydroxypropyl cellulose, and regenerated cellulose; polyalcohol binders containing polyvinyl alcohol; polyolefin binders containing polyethylene and polypropylene; polyimide binders; polyester binders; and silane binders. One of these may be used alone or in mixtures of two or more. The positive electrode binder may be present in amounts of 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 relative to the total weight of the positive electrode active material layer.

[0094] On the other hand, the positive electrode can be manufactured by applying a positive electrode slurry to one or both sides of a long sheet-shaped positive electrode current collector, removing the solvent from the positive electrode slurry through a drying process, and then rolling it. Alternatively, a positive electrode including a plain portion can be manufactured by not applying the positive electrode slurry to a part of the positive electrode current collector, for example, one end of the positive electrode current collector.

[0095] Furthermore, the positive electrode slurry can be manufactured by dispersing the positive electrode active material in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water.

[0096] 2) Negative electrode The negative electrode may include a negative electrode active material. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector, and the negative electrode active material layer may include a negative electrode active material.

[0097] The negative electrode current collector is not particularly limited as long as it does not cause a chemical change in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may typically have a thickness of 3 μm to 500 μm.

[0098] Furthermore, similar to the positive electrode current collector, the negative electrode current collector may have fine irregularities formed on its surface to strengthen the bonding force of the negative electrode active material. For example, it may be used in various forms such as film, sheet, foil, mesh, porous material, foam, or nonwoven fabric.

[0099] The negative electrode active material layer may be located on the negative electrode current collector, specifically on one or both sides of the negative electrode current collector. The negative electrode active material layer may be a single layer or a multilayer structure of two or more layers.

[0100] The aforementioned negative electrode may 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 less than that of silicon-based active materials, resulting in superior lifespan characteristics.

[0101] Specifically, the graphite may be one or more selected from the group consisting of artificial graphite and natural graphite, and preferably a combination of artificial graphite and natural graphite.

[0102] If the negative electrode contains artificial graphite and natural graphite, the artificial graphite and natural graphite may be included in a weight ratio of 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 the above range is satisfied, the capacity characteristics can be improved, and the output characteristics and life characteristics can be excellent.

[0103] The negative electrode active material may be present in an amount of 80% to 99% by weight, 85% to 98% by weight, or 90% to 97% by weight, based on the total weight of the negative electrode active material layer. When these ranges are met, sufficient capacity characteristics can be achieved.

[0104] On the other hand, the negative electrode active material layer may selectively further contain a negative electrode conductive material and a negative electrode binder in addition to the negative electrode active material. The aforementioned negative electrode conductive material is used to impart conductivity to the electrode and can be used in any battery without particular limitations as long as it has electronic conductivity without causing a chemical change. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes; metal powders or metal fibers such as copper, nickel, aluminum, and silver; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone or in mixtures of two or more. The aforementioned negative electrode conductive material may typically be included in amounts of 0.1% to 20% by weight, 0.2% to 10% by weight, 0.3% to 5% by weight, or 0.4% to 2% by weight relative to the total weight of the negative electrode active material layer.

[0105] The negative electrode binder plays a role in improving adhesion between negative electrode active material particles and adhesion between the negative electrode active material and the negative electrode current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, 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 one of these alone or a mixture of two or more may be used. The anode binder may be present in amounts of 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 relative to the total weight of the anode active material layer.

[0106] The negative electrode active material layer may further selectively contain a thickening agent. Any thickening agent used in conventional lithium secondary batteries may be used as the thickening agent, one example being carboxymethylcellulose (CMC). The thickening agent may be included in amounts of 0.1% to 10% by weight, 0.3% to 8% by weight, 0.5% to 5% by weight, 0.7% to 3% by weight, or 1% to 2% by weight relative to the total weight of the negative electrode active material layer.

[0107] The negative electrode can be manufactured by a conventional negative electrode manufacturing method. For example, the negative electrode can be manufactured by mixing a negative electrode active material, a negative electrode conductive material, and / or a negative electrode binder in a negative electrode solvent to produce a negative electrode slurry, applying the negative electrode slurry onto a negative electrode current collector, drying, and rolling.

[0108] The negative electrode solvent may include at least one selected from the group consisting of distilled water, ethanol, methanol, and isopropyl alcohol, preferably distilled water, in order to facilitate the dispersion of the components of the negative electrode slurry. The solid content of the negative electrode slurry may be 30% to 80% by weight, specifically 40% to 70% by weight.

[0109] Alternatively, the negative electrode can be manufactured by casting the negative electrode slurry onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0110] 3) Separator The separator is interposed between the positive electrode and the negative electrode. The separator is interposed between the positive electrode and the negative electrode, separating them and providing a passage for lithium ions to move. It can be used without particular limitations as long as it is a separator commonly used in lithium secondary batteries. Specifically, the separator may be a porous polymer film, for example, a porous polymer film made from polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or a laminated structure of two or more layers thereof. Alternatively, a conventional porous nonwoven fabric, for example, a nonwoven fabric made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, a coated separator containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength.

[0111] (2) Electrolyte The electrolyte according to the present invention may also contain a lithium salt and an organic solvent. The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. Specifically, the lithium salt may include one or more 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, preferably LiPF6.

[0112] The concentration of the lithium salt may be 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 falls within the above range, the electrolyte has suitable conductivity and viscosity, thus exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0113] The aforementioned organic solvent is a non-aqueous solvent commonly used in lithium secondary batteries, and is not particularly limited as long as it can minimize decomposition due to oxidation reactions during the charging and discharging process of the secondary battery.

[0114] Specifically, the organic solvent may include at least one selected from the group consisting of cyclic carbonate organic solvents, linear carbonate organic solvents, linear ester organic solvents, and cyclic ester organic solvents.

[0115] Specifically, the organic solvent may include a cyclic carbonate organic solvent, a linear carbonate organic solvent, or a mixture thereof. The cyclic carbonate organic solvent is a highly viscous organic solvent that has a high dielectric constant and can readily dissociate lithium salts in the electrolyte. Specifically, it may be a non-fluorinated saturated cyclic carbonate organic solvent. The cyclic carbonate organic solvent 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-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate. More specifically, it may include at least one selected from the group consisting of ethylene carbonate (EC) and fluoroethylene carbonate (FEC). Even more specifically, it may include ethylene carbonate (EC).

[0116] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and may specifically be a non-fluorinated linear carbonate. The linear carbonate-based solvent may include at least one selected from the group consisting of dimethyl carbonate (dimethyl carbonate, DMC), diethyl carbonate (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).

[0117] The organic solvent may be a mixture of a cyclic carbonate organic solvent and a linear carbonate organic solvent. In this case, the cyclic carbonate organic solvent and the linear carbonate organic solvent may be mixed in a volume ratio 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 solvent and the linear carbonate organic solvent satisfies the above range, high dielectric constant and low viscosity properties can be simultaneously satisfied, and excellent ionic conductivity properties can be achieved.

[0118] Furthermore, in order to produce an electrolyte having high ionic conductivity, the organic solvent may further contain at least one ester-based organic solvent selected from the group consisting of linear ester-based organic solvents and cyclic ester-based organic solvents, in addition to at least one carbonate-based organic solvent selected from the group consisting of cyclic carbonate-based organic solvents and linear carbonate-based organic solvents.

[0119] The linear ester organic solvent may specifically include at least one selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0120] Furthermore, the cyclic ester organic solvent may specifically include at least one selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0121] On the other hand, the organic solvent may be used with any additional organic solvents commonly used for non-aqueous electrolytes, as needed. For example, it may further contain at least one or more organic solvents selected from ether-based organic solvents, grim-based solvents, and nitrile-based organic solvents.

[0122] The ether solvent may be any one selected from 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), or a mixture of two or more of these, but is not limited to these.

[0123] The aforementioned glycemic solvent has a higher dielectric constant and lower surface tension compared to linear carbonate-based organic solvents, and is a solvent with low reactivity with metals. It may include, but is not limited to, at least one selected from the group consisting of dimethoxyethane (glycemic, DME), diethoxyethane, diglyme, triglycemic, and tetraglycemic (TEGDME).

[0124] The nitrile solvent may be one or more selected from the group consisting of acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, and 4-fluorophenylacetonitrile, but is not limited thereto.

[0125] On the other hand, the electrolyte may also contain additives in addition to the components of the electrolyte, for purposes such as improving the battery's lifespan, suppressing the decrease in battery capacity, and improving the battery's discharge capacity.

[0126] The additive may include, for example, at least one additive selected from the group consisting of nonfluorinated unsaturated cyclic carbonate compounds, halogen-substituted carbonate compounds, sultone compounds, sulfate compounds, borate compounds, nitrile compounds, benzene compounds, amine compounds, silane compounds, and lithium salt compounds different from the lithium salt contained in the electrolyte.

[0127] Specifically, the additives include vinylene carbonate (VC), vinylethylene carbonate, fluoroethylene carbonate (FEC), 1,3-propanesultone (PS), 1,4-butanesultone, ethensultone, 1,3-propensultone (PRS), 1,4-butensultone, 1-methyl-1,3-propensultone, ethylene sulfate (Esa), trimethylene sulfate (TMS), and methyl trimethylene sulfate. Examples include one or more compounds selected from the group consisting of sulfate (MTMS), tetraphenyl borate, lithium oxalyl difluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonile, cyclohexanecarbonile, 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, LiBOB (lithium bisoxalate borate (LiB(C2O4)2)), and LiBF4.

[0128] The additive may be present in an amount of 0.01% to 20% by weight, or 0.05% to 5.0% by weight, based on the total weight of the electrolyte. When this range is 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 unreacted material can be suppressed.

[0129] (3) Battery case The battery case can serve to house the electrode assembly and the electrolyte.

[0130] Specifically, the battery case is for housing the electrode assembly and sealing it after the electrolyte is injected. It is manufactured from a material with a certain degree of flexibility that can form a housing, and its shape is not limited, but is preferably cylindrical, coin-shaped, rectangular, or pouch-shaped. The upper and lower cases constituting such a battery case may be independent members or may be substantially one member connected at one end. The external shape of the battery case may be manufactured in various ways, and is not limited in this invention.

[0131] For example, the battery case may be a rectangular battery case. The rectangular battery case has the advantage of being in the form of a rectangular metal can, being able to be stacked with a high degree of integration, and having a small width relative to its length.

[0132] The rectangular battery case may have an opening at its upper end and may be made of a conductive metal material such as aluminum or steel. The rectangular battery case may house an electrode assembly and an electrolyte in its internal space through the upper opening of the battery can, and the battery case may be sealed by welding a top cap to the upper opening.

[0133] On the other hand, the charge cut-off voltage of the lithium secondary battery of the present invention may be 4.3V or higher, specifically 4.35V or higher, and more specifically 4.4V or higher. In this case, it is possible to achieve excellent energy density at a level equivalent to that of a positive electrode active material containing a high nickel content, as well as improved high-temperature life performance and high-temperature storage performance.

[0134] On the other hand, the nominal voltage of the lithium secondary battery may be 3.68V or higher, preferably 3.68V to 3.80V, and more preferably 3.69V to 3.75V. In this case, the nominal voltage refers to the average voltage value during discharge of the lithium secondary battery. Since the energy density of a lithium secondary battery is calculated as the product of the average voltage and average current during discharge, the energy density increases when the nominal voltage is high. Conventional lithium secondary batteries using lithium nickel cobalt manganese oxide as the positive electrode active material had a nominal voltage of around 3.6V, but the present invention makes it possible to achieve high energy density by increasing the charge cut-off voltage and making the nominal voltage 3.68V or higher.

[0135] The lithium secondary battery according to the present invention is useful in portable devices such as mobile phones, laptop computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0136] Furthermore, a battery module or battery pack containing the lithium secondary battery as a unit cell can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0137] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing multiple battery cells.

[0138] Examples of the medium and large devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0139] Examples and Comparative Examples Example 1 <Manufacturing of Electrode Assembly> A positive electrode active material, a binder, and a conductive agent were mixed in an N-methylpyrrolidone solvent at a weight ratio of 97:1.8:1.2 to prepare a positive electrode slurry. Thereafter, the positive electrode slurry was applied onto one surface of an aluminum current collector having a thickness of 12 μm, dried, and then rolled to prepare a positive electrode. In this process, as the positive electrode active material, Li[Ni 0.6 Co 0.1 Mn 0.3 O2, PVDF as the binder, and carbon nanotubes as the conductive agent were used.

[0140] A negative electrode active material, a binder, a conductive agent, and a thickener were mixed in distilled water at a weight ratio of 96.15:2.3:0.5:1.05 to prepare a negative electrode slurry. Thereafter, the negative electrode slurry was applied onto one surface of a copper current collector having a thickness of 7.8 μm, dried, and then rolled such that the porosity became 30% to prepare a negative electrode. In this process, artificial graphite and natural graphite were used as the negative electrode active material, styrene-butadiene rubber (SBR) as the binder, Super C65 as the conductive agent, and carboxymethyl cellulose (CMC) as the thickener.

[0141] A porous polyethylene separator was interposed between the negative electrode and the positive electrode manufactured as described above, and the assembly was wound to manufacture an electrode assembly. In this process, the porosity of the positive electrode was 21.35%, and the loading amount was 4.03 mAh / cm 2 , and the porosity of the negative electrode was 28.01%. In this process, the N / P ratio of the positive electrode and the negative electrode was 107.26, and the electrode assembly has a jelly-roll form with a structure in which the positive electrode, the separator, and the negative electrode are sequentially stacked and wound.

[0142] <Preparation of Electrolyte> An electrolyte was prepared by adding 0.5 wt% of vinylene carbonate (VC), 0.5 wt% of propane sultone (PS), 1 wt% of ethylene sulfate (ESa), 1 wt% of lithium difluorophosphate and 0.2 wt% of LiBF4 as additives to an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7, and then adding 1.0 M of LiPF6.

[0143] <Preparation of Lithium Secondary Battery> After placing the electrode assembly prepared above inside a prismatic battery case, 303.19 g of the electrolyte prepared above was injected into the case and the case was sealed to prepare a lithium secondary battery. At this time, in the prepared lithium secondary battery, the volume of the electrode assembly (S A ) and the volume of the lithium secondary battery (S E ) the ratio (S A / S E ) which is S u was 0.813.

[0144] Example 2 <Preparation of Electrode Assembly> An electrode assembly was produced in the same manner as in Example 1 above. At this time, the porosity of the positive electrode was 21.35%, and the loading amount was 4.03 mAh / cm 2 , and the porosity of the negative electrode was 28.01%. At this time, the N / P ratio of the positive electrode and the negative electrode was 107.26, and the electrode assembly has a jelly-roll form with a structure obtained by sequentially stacking the positive electrode, a separator, and the negative electrode and winding the stacked structure.

[0145] <Preparation of Electrolyte> An electrolyte was prepared in the same manner as in Example 1 above.

[0146] <Preparation of Lithium Secondary Battery> After positioning the electrode assembly manufactured above inside a rectangular battery case, 297.87 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.813.

[0147] Example 3 <Manufacturing of electrode assemblies> An electrode assembly was manufactured using the same method as in Example 1. In this case, the porosity of the positive electrode is 21.35%, and the loading amount is 4.03 mAh / cm². 2 The void ratio of the negative electrode was 28.01%. In this case, the N / P ratio of the positive electrode to the negative electrode was 107.26, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0148] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0149] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 292.55 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.813.

[0150] Example 4 <Manufacturing of electrode assemblies> Li[Ni 0.62 Co 0.06 Mn 0.32An electrode assembly was manufactured in the same manner as in Example 1, except that a positive electrode active material having the composition of ]O2 was used.

[0151] In this case, the porosity of the positive electrode is 21.7%, and the loading amount is 4.33 mAh / cm². 2 The void ratio of the negative electrode was 26.1%. In this case, the N / P ratio of the positive electrode to the negative electrode was 107.1, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0152] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0153] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 319.15 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.830.

[0154] Example 5 <Manufacturing of electrode assemblies> An electrode assembly was manufactured using the same method as in Example 1. In this case, the porosity of the positive electrode is 19.1%, and the loading amount is 4.28 mAh / cm². 2 The void ratio of the negative electrode was 24.7%. In this case, the N / P ratio of the positive electrode to the negative electrode was 105.9, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0155] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0156] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 319.15 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.820.

[0157] Example 6 Instead of the electrolyte used in Example 1, 1.2 M LiPF6 was dissolved in an organic solvent prepared by mixing ethylene carbonate (EC): ethyl methyl carbonate (EMC): diethyl carbonate (DEC) in a volume ratio of 2:7:1. The following additives were then added: 0.3 wt% vinylethylene carbonate (VEC), 0.5 wt% vinylene carbonate, 0.5 wt% propanesultone (PS), 1.0 wt% ethylene sulfate (ESa), 0.8 wt% lithium difluorophosphate (LiDFP, product name: SLO 7), 0.5 wt% lithium oxalyl difluoroborate (LiODFB), and propargyl 1H-imidazole-1-carboxylate (HS02, CAS A lithium secondary battery was manufactured in the same manner as in Example 1, except that an electrolyte prepared by adding 0.1 wt% of (83395-38-4), 0.5 wt% of lithium bis(fluorosulfonyl)imide (LiFSI, product name: SL06), 0.5 wt% of fluoroethylene carbonate (FEC), and 0.5 wt% of trimethylsilyl phosphate (TMSPa) was used.

[0158] In this case, the porosity of the positive electrode is 21.35%, and the loading amount is 4.03 mAh / cm². 2The void ratio of the negative electrode was 28.01%. In this case, the N / P ratio of the positive electrode to the negative electrode was 107.26, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0159] Comparative Example 1 <Manufacturing of electrode assemblies> An electrode assembly was manufactured using the same method as in Example 1. In this case, the porosity of the positive electrode is 21.35%, and the loading amount is 4.03 mAh / cm². 2 The void ratio of the negative electrode was 28.01%. In this case, the N / P ratio of the positive electrode to the negative electrode was 107.26, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0160] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0161] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 319.15 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.813.

[0162] Comparative Example 2 <Manufacturing of electrode assemblies> An electrode assembly was manufactured using the same method as in Example 1. In this case, the porosity of the positive electrode is 21.35%, and the loading amount is 4.03 mAh / cm². 2The void ratio of the negative electrode was 28.01%. In this case, the N / P ratio of the positive electrode to the negative electrode was 107.26, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0163] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0164] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 276.60 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.813.

[0165] Comparative Example 3 <Manufacturing of electrode assemblies> Li[Ni 0.65 Co 0.15 Mn 0.2 An electrode assembly was manufactured in the same manner as in Example 1, except that a positive electrode active material having the composition of ]O2 was used.

[0166] In this case, the porosity of the positive electrode is 24.6%, and the loading amount is 4.02 mAh / cm². 2 The void ratio of the negative electrode was 26.9%. In this case, the N / P ratio of the positive electrode to the negative electrode was 108.6, and the electrode assembly had a jelly roll form in which the positive electrode, separator, and negative electrode were sequentially stacked and wound up.

[0167] <Electrolyte Manufacturing> The electrolyte was produced in the same manner as in Example 1.

[0168] <Manufacturing of lithium-ion secondary batteries> After positioning the electrode assembly manufactured above inside a rectangular battery case, 303.19 g of the electrolyte manufactured above was injected into the case and sealed to manufacture a lithium secondary battery. In this case, the volume of the electrode assembly (S) in the manufactured lithium secondary battery was A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E S is ) u The value was 0.830.

[0169] Experimental Example 1 - EFF Index Evaluation The EFF index, defined by the following formula 1, 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.

[0170] [Formula 1]

number

[0171] In the above formula 1, R E [Unit: g] represents the weight of residual electrolyte contained in the activated lithium secondary battery, S U The volume of the electrode assembly (S A ) and the volume (S) of the lithium secondary battery E ) ratio (S A / S E ) means N C [Unit: Ah] represents the capacity of the lithium secondary battery when it is discharged from 4.4V to 2.5V at 25°C and 0.33C.

[0172] (1)R E Measurement Each of the lithium secondary batteries produced in Examples 1 to 6 and Comparative Examples 1 to 3 was activated by performing the following steps: (1) charging the lithium secondary battery to a state of charge (SOC) of 3% at 55°C under a constant current of 0.2C; (2) charging the battery to a state of charge (SOC) of 17% at 55°C under a constant current of 1.0C; and (3) charging the battery to a state of charge (SOC) of 60% at 55°C under a constant current of 1.0C.

[0173] Afterward, each lithium secondary battery that had finished activating was disassembled, and the weight of the residual electrolyte (R E ) was measured. Specifically, the weight (R) of the residual electrolyte contained in the activated lithium secondary battery was measured. E ) (1) Before disassembling the activated lithium secondary battery, the weight (M) of the activated lithium secondary battery L (1) the step of measuring the weight (M) of the dried battery case; (2) the step of disassembling the activated lithium secondary battery and removing the electrolyte present in the battery case; (3) the step of immersing the battery case and electrode assembly in dimethyl carbonate, which is a solvent, to remove the electrolyte present on the surface of the battery case, the surface of the electrode assembly and in the internal voids, and then drying the battery case and electrode assembly; and (4) the step of measuring the weight (M) of the dried battery case. C ) and the weight (M) of the dried electrode assembly A After going through the step of measuring ), the measured M L M C M A The values ​​were substituted into equation A below and measured.

[0174] [Formula A] R E =M L -M C -M A The results are shown in Table 1 below.

[0175] (2)N C Measurement The lithium secondary batteries produced in Examples 1-6 and Comparative Examples 1-3 were each charged to 4.35V with a 0.05C cut-off under constant current / voltage conditions of 0.33C at 25°C, and then discharged to 2.0V under constant current conditions of 0.33C to activate them.

[0176] Next, the capacity (N) obtained when the lithium secondary battery is charged from 2.5V to 4.35V at 0.33C at 25°C and then discharged from 4.4V to 2.5V at 25°C and 0.33C is calculated. C The following measurements were taken, and the results are shown in Table 1 below.

[0177] (3)S U Measurement For each of the lithium secondary batteries manufactured in Examples 1 to 6 and Comparative Examples 1 to 3, S U The volume of the electrode assembly (S A ) and the volume (S) of the lithium secondary battery E ) are measured and the S A and S E The ratio (S A / S E The S was calculated and measured. A and S E Each was measured using the following method. The results are shown in Table 1 below.

[0178] The volume of the aforementioned lithium secondary battery (S E The volume (S) of the lithium secondary battery according to equation B below. E This was obtained by assuming that the shape of the lithium secondary battery, including the rectangular battery case, is a rectangular parallelepiped.

[0179] [Formula B] S E = (Thickness of lithium secondary battery) × (Length of lithium secondary battery) × (Width of lithium secondary battery)

[0180] In formula B, the thickness of the lithium secondary battery means the distance measured along the thickness direction of the lithium secondary battery with respect to the external shape of the lithium secondary battery, the length of the lithium secondary battery means the distance measured along the length direction of the lithium secondary battery with respect to the external shape of the lithium secondary battery, and the width of the lithium secondary battery means the distance measured along a direction perpendicular to the length direction of the lithium secondary battery with respect to the external shape of the lithium secondary battery. The volume (S) of the electrode assembly A ) was obtained by the following formula C.

[0181] [Formula C] S A = (Volume of positive electrode) + (Volume of negative electrode) + (Volume of separator)

[0182] In formula C, the volume of the positive electrode, the volume of the negative electrode, and the volume of the separator were measured based on the external shape of the positive electrode, the negative electrode, or the separator, without excluding the volume of voids contained in the positive electrode, the negative electrode, or the separator.

[0183] [Table 1]

[0184] Experimental Example 2: Evaluation of High-Temperature Storage Characteristics The lithium secondary batteries manufactured in Examples 1-6 and Comparative Examples 1-3 were charged to 100% SOC at 25°C under CC / CV and 0.33C conditions, and then stored at 60°C for 12 weeks. The capacity retention rate and resistance increase rate of each lithium secondary battery were then measured. The specific measurement method is as follows.

[0185] (1) Capacity maintenance rate Before storing them at 60°C for 12 weeks, the lithium secondary batteries manufactured in Examples 1-6 and Comparative Examples 1-3 were charged to 4.25V with a 0.05C cut-off at 25°C under CC / CV and 0.33C conditions, and then discharged to 2.0V under CC and 0.33C. This cycle was repeated three times, and the discharge capacity in the third cycle was measured and defined as the initial discharge capacity.

[0186] After being stored at 60°C for 12 weeks, the lithium secondary batteries produced in Examples 1-6 and Comparative Examples 1-3 were charged to 4.25V with a 0.05C cut-off under CC / CV and 0.33C conditions at 25°C, and then discharged to 2.0V under CC and 0.33C. This cycle was repeated three times, and the discharge capacity in the third cycle was measured and taken as the discharge capacity after being stored at 60°C for 12 weeks.

[0187] The initial discharge capacity measured above was compared with the discharge capacity after storage at 60°C for 12 weeks, and the capacity retention rate was evaluated using the following formula. The results are shown in Table 2 below. Capacity retention rate (%) = (Discharge capacity after 12 weeks of storage at 60°C / Initial discharge capacity) × 100

[0188] (2) Resistance increase rate The lithium secondary batteries manufactured in Examples 1-6 and Comparative Examples 1-3 were charged to 4.25V with a 0.05C cut-off at 25°C under CC / CV and 0.33C conditions, and discharged to 2.0V under CC and 0.33C conditions. This cycle was repeated three times. The discharge capacity from the third cycle was used as the reference, and the State of Charge (SOC) was set to 50% under CC / CV and 0.33C conditions. The batteries were discharged for 30 seconds at a current of 2.5C, and the resistance was measured from the voltage drop difference to determine the initial resistance. After storage at 60°C for 12 weeks, the resistance was measured again in the same manner to determine the final resistance, and the resistance increase rate was calculated using the following formula. The results are shown in Table 2 below. Resistance increase rate (%) = (Final resistance - Initial resistance) / (Initial resistance) × 100

[0189] [Table 2]

[0190] Referring to Table 2, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 to 6 exhibit 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. Furthermore, although Example 6 used a different electrolyte than Example 1, its capacity retention and resistance increase rates after 12 weeks of storage at 60°C were superior to those of the lithium secondary batteries manufactured in Comparative Examples 1 to 3. This suggests that even with a different electrolyte, superior high-temperature storage characteristics are achieved when the EFF value defined by Formula 1 satisfies 1.82 to 2.06.

Claims

1. An electrode assembly including a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode, Electrolytes, A battery case including an internal space for housing the electrode assembly and the electrolyte, Includes, The positive electrode includes a positive electrode active material. The positive electrode active material contains a lithium nickel oxide, which includes 50 mol% to 70 mol% nickel among all metals excluding lithium. A lithium secondary battery having an EFF (Electrolyte Filling Factor) index (unit: g / Ah) of 1.82 to 2.06, as defined by the following formula 1. [Formula 1] [Math 1] In the above formula 1, R Ｅ [Unit: g] refers to the weight of residual electrolyte contained in the activated lithium secondary battery. S Ｕ The volume (S) of the electrode assembly is Ａ ) and the volume (S) of the lithium secondary battery Ｅ ) ratio (S Ａ / S Ｅ ) means, N Ｃ [Unit: Ah] represents the capacity of the lithium secondary battery when it is discharged from 4.4V to 2.5V at 25°C and 0.33C.

2. The aforementioned R Ｅ The lithium secondary battery according to claim 1, wherein the weight is 265g to 295g.

3. The aforementioned S Ｕ is 0.70 to 0.95, the lithium secondary battery according to claim 1.

4. The aforementioned N Ｃ The lithium secondary battery according to claim 1, wherein the capacity is 90Ah to 150Ah.

5. The aforementioned N Ｃ R Ｅ Ratio (R Ｅ / N Ｃ The lithium secondary battery according to claim 1, wherein the [unit: g / Ah] is 2.00 to 3.

30.

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

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

8. The lithium nickel oxide contains 15 mol% or less of cobalt (Co) among all metals excluding lithium, as described in claim 1.

9. The lithium nickel oxide is represented by the following chemical formula 1, as described in claim 1, for the lithium secondary battery. [Chemical formula 1] Li １＋ａ１ [Ni ｘ１ Co ｙ１ Mn ｚ１ M １ ｗ１ ]O ２ In the aforementioned chemical formula 1, 0 ≤ a1 ≤ 0.5, 0.5 ≤ x1 ≤ 0.7, 0 < y1 ≤ 0.15, 0 < z1 ≤ 0.4, 0 ≤ w1 ≤ 0.2, M １ is one or more doping elements 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-ion secondary battery according to claim 1, wherein the lithium nickel oxide is in the form of single-particulate particles.

11. The lithium secondary battery according to claim 1, wherein the charge cutoff voltage of the lithium secondary battery is 4.3V or higher.

12. The lithium secondary battery according to claim 1, wherein the nominal voltage of the lithium secondary battery is 3.68V or higher.

13. The lithium secondary battery according to claim 1, wherein the negative electrode contains graphite as the negative electrode active material.

14. The lithium secondary battery according to claim 1, wherein the battery case is a rectangular battery case.

15. The lithium secondary battery according to claim 1, wherein the electrode assembly is formed by sequentially stacking a positive electrode, a separator, and a negative electrode and winding them in one direction.

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