Lithium secondary battery and method for manufacturing the same

Abstract

The present invention relates to a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises a first positive electrode active material and a second positive electrode active material having different average particle sizes, and the average particle size of the first positive electrode active material is (D 50 ) is the average particle size (D) of the second positive electrode active material. 50 The present invention relates to a lithium secondary battery wherein the IRF (Interfacial Resistance Factor) value, defined by the following formula 1, is greater than , the first positive electrode active material and the second positive electrode active material contain single-particle form particles, the negative electrode contains a silicon-based negative electrode active material, and the lithium secondary battery has an IRF (Interfacial Resistance Factor) value of 1 to 1.4. [Formula 1] IRF = R p / R n (In formula 1 above, each variable is as defined herein.)

Description

[Technical Field]

[0001] This application claims priority rights based on Korean Patent Application No. 10-2023-0188944 filed on 21 December 2023 and Korean Patent Application No. 10-2024-0151590 filed on 30 October 2024, and all content disclosed in the documents of the said Korean patent applications is incorporated herein by reference.

[0002] The present invention relates to a lithium secondary battery and a method for manufacturing the same, and more particularly to a lithium secondary battery and a method for manufacturing the same in which capacity, resistance characteristics, and life characteristics, such as high-temperature life characteristics, have been improved. [Background technology]

[0003] In recent years, with the rapid proliferation of electronic devices that use batteries, such as mobile phones, laptop computers, and electric vehicles, the demand for small, lightweight, and relatively high-capacity rechargeable batteries has been rapidly increasing. In particular, rechargeable batteries are attracting attention as power sources for portable devices because they are lightweight and have high energy density. Therefore, research and development and efforts to improve the performance of lithium-ion rechargeable batteries are being actively pursued. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The present invention aims to provide a lithium secondary battery with excellent capacity characteristics and excellent life characteristics, such as high-temperature life characteristics, and a method for manufacturing the same, by introducing a low-efficiency cathode material that can compensate for the problems caused by silicon-based anode active materials that have high irreversible capacity loss during initial charging and discharging. [Means for solving the problem]

[0005] [1] The present invention relates to a lithium secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. The positive electrode includes a first positive electrode active material and a second positive electrode active material having different average particle diameters. The average particle diameter (D 50 ) of the first positive electrode active material is larger than the average particle diameter (D 50 ) of the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are single-particle-shaped particles. The negative electrode includes a silicon-based negative electrode active material. The lithium secondary battery provides an IRF (Interfacial Resistance Factor) value defined by the following formula 1 of 1 to 1.4.

[0006] [Formula 1] IRF = R p / R n

[0007] In Formula 1, R n (Ω) means the interfacial resistance of the negative electrode measured after performing charge and discharge 100 cycles on the lithium secondary battery manufactured using the negative electrode, and R p (Ω) means the interfacial resistance of the positive electrode measured after performing charge and discharge 100 cycles on the lithium secondary battery manufactured using the positive electrode.

[0008] [2] The present invention provides the lithium secondary battery according to [1], wherein the first positive electrode active material includes a first lithium transition metal oxide represented by the following Chemical Formula 1.

[0009] [Chemical Formula 1] Li 1+a1 Ni x1 Co y1 Mn z1 Al w1 M 1 v1 O2

[0010] In Chemical Formula 1, 0 ≦ a1 ≦ 0.3, 0.82 ≦ x1 < 1.0, 0 < y1 ≦ 0.2, 0 < z1 ≦ 0.2, 0 < w1 ≦ 0.2, 0 ≦ v1 ≦ 0.1, and M 1This is one or more doped elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0011] [3] The present invention provides a lithium secondary battery according to [1] or [2], wherein the second positive electrode active material comprises a second lithium transition metal oxide represented by the following chemical formula 2.

[0012] [Chemical formula 2] Li 1+a2 Ni x2 Co y2 Mn z2 Al w2 M 2 v2 O2

[0013] In the above chemical formula 2, 0 ≤ a² ≤ 0.3, 0.82 ≤ x² < 1.0, 0 <y2≦0.2、0<z2≦0.2、0<w2≦0.2、0≦v2≦0.1であり、M 2 This is one or more doped elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0014] [4] The present invention relates to the R n The present invention provides a lithium secondary battery according to any one of [1] to [3] above, wherein the impedance is 0.6Ω or less.

[0015] [5] The present invention relates to the average particle size (D) of the first positive electrode active material. 50 The present invention provides a lithium secondary battery according to any one of the above [1] to [4], wherein the diameter is 6 μm to 12 μm.

[0016] [6] The present invention relates to the average particle size (D) of the second positive electrode active material. 50 The present invention provides a lithium secondary battery according to any one of the above [1] to [5], wherein the diameter of the sievert is 1.5 μm to 5 μm.

[0017] [7] The present invention provides a lithium secondary battery according to any one of [1] to [6] above, wherein the first positive electrode active material comprises a first lithium transition metal oxide and a first coating layer located on the surface of the first lithium transition metal oxide particles and containing 1.5 mol% to 5 mol% cobalt (Co).

[0018] [8] The present invention provides a lithium secondary battery according to any one of [1] to [7] above, wherein the second positive electrode active material comprises a second lithium transition metal oxide and a second coating layer located on the surface of the second lithium transition metal oxide particles and containing cobalt (Co) in an amount of 0.2 mol% to 2.5 mol%.

[0019] [9] The present invention provides a lithium secondary battery according to any one of [1] to [8] above, wherein the first positive electrode active material comprises a first lithium transition metal oxide and includes a first coating layer containing cobalt (Co) on the surface of the first lithium transition metal oxide particles, and the second positive electrode active material comprises a second lithium transition metal oxide and includes a second coating layer containing cobalt (Co) on the surface of the second lithium transition metal oxide particles, wherein the first coating layer contains a larger amount of cobalt than the second coating layer.

[0020]

[10] The present invention provides a lithium secondary battery according to any one of [1] to [9] above, wherein the first positive electrode active material and the second positive electrode active material are contained in a weight ratio of 80:20 to 40:60.

[0021]

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

[10] above, wherein the negative electrode comprises a carbon-based negative electrode active material, and the silicon-based negative electrode active material and the carbon-based negative electrode active material are present in a weight ratio of 1:99 to 30:70.

[0022]

[12] The present invention includes the steps of: mixing a first positive electrode active material in distilled water for a first wash and drying (S1); mixing a second positive electrode active material in distilled water for a second wash and drying (S2); applying a positive electrode slurry containing the first and second positive electrode active materials onto a positive electrode current collector to manufacture a positive electrode (S3); manufacturing a negative electrode containing a silicon-based negative electrode active material (S4); and manufacturing a lithium secondary battery containing the positive electrode, the negative electrode, and an electrolyte (S5), wherein the first wash is performed at a higher temperature than the second wash, and the average particle size (D 50 The present invention provides a method for manufacturing a lithium secondary battery, wherein the particle size (D50) of the second positive electrode active material is larger than the average particle size (D50) of the second positive electrode active material, the first positive electrode active material and the second positive electrode active material contain single-particle type particles, and the lithium secondary battery has an IRF (Interfacial Resistance Factor) value defined by the following formula 1 of 1 to 1.4.

[0023] [Formula 1] IRF=R p / R n

[0024] In formula 1, the R n (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode, and R p (Ω) represents the interface resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned positive electrode.

[0025]

[13] The present invention provides a method for manufacturing a lithium secondary battery as described in

[12] , wherein the first washing is performed at 20°C to 40°C.

[0026]

[14] The present invention provides a method for manufacturing a lithium secondary battery according to

[12] or

[13] , wherein the second washing is performed at 3°C ​​to 18°C.

[0027]

[15] The present invention provides a method for manufacturing a lithium secondary battery according to any one of

[12] to

[14] , wherein the first washing is performed by mixing the first positive electrode active material with distilled water in an amount of 50% to 70% by weight based on the total weight of the water.

[0028]

[16] The present invention provides a method for manufacturing a lithium secondary battery according to any one of

[12] to

[15] , wherein the second washing is performed by mixing the second positive electrode active material with distilled water in an amount of 65% to 85% by weight based on the total weight of the water. [Effects of the Invention]

[0029] According to the present invention, by using a positive electrode active material that is a single-particle type while containing a silicon-based negative electrode active material and having excellent capacity characteristics, the efficiency of the positive electrode can be reduced, thereby preventing or suppressing the loss of reversible capacity of the positive electrode due to the irreversible capacity of the silicon-based negative electrode active material. Furthermore, by adjusting the ratio of the interfacial resistance of the positive electrode to the interfacial resistance of the negative electrode to an appropriate range, the resistance of the positive and negative electrodes can be balanced at the discharge end, resulting in improved battery life characteristics and excellent high-temperature life characteristics. In addition, the lithium secondary battery according to the present invention can achieve high energy density and further improve capacity characteristics by containing a positive electrode active material having a bimodal particle size distribution. The following drawings attached to this specification are for illustrating preferred embodiments of the present invention and, together with the above-described content of the invention, serve to provide a better understanding of the technical concept of the present invention. Therefore, the present invention should not be construed as being limited solely to what is shown in these drawings. [Brief explanation of the drawing]

[0030] [Figure 1] This is a flowchart illustrating a method for manufacturing a lithium secondary battery according to one embodiment of the present invention. [Modes for carrying out the invention]

[0031] The present invention will be described in more detail below.

[0032] The terms and words used herein and in the claims shall not be interpreted in a manner limited to their ordinary or dictionary meanings, but in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention, and shall be interpreted in a manner consistent with the technical idea of ​​the present invention.

[0033] The terms used herein are for illustrative purposes only and are not intended to limit the invention. Unless the context clearly indicates otherwise, singular expressions include plural expressions.

[0034] In this specification, terms such as “includes,” “equip,” or “have” are intended to specify the presence of implemented features, figures, steps, components, or combinations thereof, and are understood not to preemptively exclude the presence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0035] In this invention, "single-particle type particle" refers to a particle formed by the aggregation of 30 or fewer sub-particles. The sub-particle unit that constitutes a single-particle type particle is called a nodule. Single-particle type particles include single particles consisting of one nodule, and pseudo-single particles which are composites of 2 to 30 nodules.

[0036] The aforementioned "nodule" is a lower particle unit that constitutes a single particle or a pseudo-single particle, and may be a single crystal without crystalline grain boundaries, or a polycrystal in which grain boundaries appear to be absent when observed with a scanning electron microscope at a field of view of 5,000 to 20,000 times.

[0037] 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 single-particle-type particles, the sub-particles that constitute secondary particles are called "primary particles."

[0038] In the present invention, "particle" is a concept that includes any one or all of the following: a single particle, a pseudo-single particle, a primary particle, a nodule, and a secondary particle.

[0039] In this invention, "average particle size D 50 This refers to the particle size at the 50% reference point of the volume-cumulative particle size distribution of the positive electrode active material powder, and can be measured by the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, it can be measured by introducing it into a commercially available laser diffraction particle size analyzer (e.g., Microtrac MT 3000), irradiating it with ultrasound at approximately 28 kHz with an output of 60 W, obtaining a volume-cumulative particle size distribution graph, and determining the particle size corresponding to 50% of the volume-cumulative amount.

[0040] In this invention, "the interfacial resistance of the positive electrode (R p The lithium secondary battery comprising the positive electrode, negative electrode, and electrolyte according to the present invention is manufactured, and then the lithium secondary battery is charged at 25°C under the conditions of CC (constant current) / CV (constant voltage), 0.1C, 4.2V, and 0.05C cutoff, and discharged under the conditions of CC, 0.1C, and 3.0V. One cycle is performed, and after 100 cycles, each lithium secondary battery is charged to a SOC (state of charge) of 50% or 10%, and the SOC of each lithium secondary battery that has been charged to 50% or 10% can be measured using a Biologic VMP3 instrument (100kHz~10mHz, 25°C). In this case, the electrolyte can be manufactured by dissolving 1.0M LiPF6 in an organic solvent which is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0041] In this invention, "the interfacial resistance of the negative electrode ( Rn The state of charge (SOC) can be measured using a Biologic VMP3 instrument (100kHz~10mHz, 25℃) after manufacturing a lithium secondary battery containing the negative electrode, positive electrode, and electrolyte according to the present invention. This can be done by charging the lithium secondary battery at 25℃ under conditions of CC / CV, 0.1C, 0.05V, and 0.05C cutoff, and discharging under conditions of CC, 0.1C, and 1.5V, which constitutes one cycle. After 100 cycles, each lithium secondary battery is charged to 50% or 10% SOC, and the SOC can be measured using a Biologic VMP3 instrument (100kHz~10mHz, 25℃). In this case, the electrolyte can be prepared by dissolving 1.0M LiPF6 in an organic solvent which is a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7.

[0042] While carbon-based materials such as graphite are primarily used as negative electrode materials for lithium-ion batteries, they have the disadvantage of low capacity per unit mass, making it difficult to increase the capacity of lithium-ion batteries. Therefore, non-carbon negative electrode materials that exhibit higher capacity compared to carbon-based materials, such as silicon, tin, and their oxides, which form intermetallic compounds with lithium, have been developed and are in use. However, these negative electrode materials have the problem of significant irreversible capacity loss during initial charging and discharging.

[0043] Considering this, methods have been studied and proposed to overcome the irreversible capacity loss of the negative electrode by using a material that can provide a lithium ion source or storage as the positive electrode material and exhibits electrochemical activity after the first cycle without degrading the performance of the battery itself. For example, one method involves using a lithium nickel oxide such as Li2NiO2 as the positive electrode material or over-discharge inhibitor.

[0044] However, considering that most of the aforementioned lithium nickel oxides are expensive and have the problem of generating a large amount of lithium byproducts and thus a large amount of gas, the present invention provides a lithium secondary battery and a method for manufacturing the same that have excellent capacity characteristics and life characteristics, such as high-temperature life characteristics, by using, for example, a positive electrode active material that is in the form of single particles.

[0045] The present invention will be described in detail below.

[0046] The lithium secondary battery and the method for manufacturing the lithium secondary battery according to the present invention include at least one of the configurations disclosed below, and may include any combination of technically feasible configurations from the configurations disclosed below.

[0047] To develop high-capacity cells, silicon-based negative electrode active materials with high capacity can be used. However, silicon-based negative electrode active materials have the disadvantages of low charge-discharge efficiency and a high lithium-ion loss rate due to irreversible reactions. Therefore, the more charge-discharge cycles are repeated, the greater the loss of lithium in the positive electrode active material, which can cause a rapid decrease in battery capacity during charging and discharging, and potentially lead to the collapse of the positive electrode active material structure.

[0048] In this case, when using a positive electrode active material that is a single-particle type, the efficiency of the positive electrode can be lowered during initial charging and discharging, thereby suppressing the loss of the reversible capacity of the positive electrode due to the irreversible capacity of the silicon-based negative electrode active material.

[0049] However, compared to using lithium nickel oxide in a secondary particle form with a positive electrode active material that is a single particle, the lithium diffusion path becomes longer, lithium ion mobility decreases, and initial resistance increases. This can reduce the positive electrode resistance, but in this case, the resistance of the positive and negative electrodes becomes unbalanced, which may degrade the battery's cycle characteristics.

[0050] Therefore, the present invention provides a lithium secondary battery with excellent capacity characteristics and life characteristics, by preventing or suppressing the loss of lithium ions from the positive electrode active material due to irreversible reactions of the silicon-based negative electrode active material. Specifically, the present invention provides a lithium secondary battery that achieves high energy density, excellent capacity characteristics, and excellent life characteristics, such as high-temperature life characteristics, by using a silicon-based negative electrode active material together with a positive electrode active material that is a single-particle type having a bimodal particle size distribution, and by appropriately adjusting the ratio of the interfacial resistance of the positive electrode to the interfacial resistance of the negative electrode to adjust the interfacial resistance of the positive electrode to a specific range.

[0051] The present invention will be described in more detail below.

[0052] Lithium-ion rechargeable battery The lithium secondary battery according to the present invention is a lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises a first positive electrode active material and a second positive electrode active material having different average particle sizes, and the average particle size of the first positive electrode active material is (D 50 ) is the average particle size (D) of the second positive electrode active material. 50 The IRF (Interfacial Resistance Factor) value of the lithium secondary battery is 1 to 1.4, defined by the following formula 1.

[0053] [Formula 1] IRF=R p / R n

[0054] In formula 1, the R n (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode, and R p (Ω) represents the interface resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned positive electrode.

[0055] The IRF value is between 1 and 1.4. Specifically, the IRF value may be 1 or greater, 1.02 or greater, 1.04 or greater, 1.06 or greater, 1.08 or greater, 1.1 or greater, 1.12 or greater, 1.14 or greater, 1.16 or greater, 1.18 or greater, and may be 1.4 or less, 1.38 or less, 1.36 or less, 1.34 or less, 1.3 or less, 1.28 or less, 1.26 or less, 1.24 or less, 1.22 or less, or 1.2 or less. For example, the IRF value may be between 1 and 1.4, 1.08 and 1.3, or 1.12 and 1.24.

[0056] When using a positive electrode active material that consists of single particles, the efficiency of the positive electrode can be reduced during initial charging and discharging. However, using a positive electrode active material that consists of single particles may reduce lithium mobility. Therefore, by forming the interfacial resistance of the positive electrode low, the reduction in lithium mobility can be suppressed. However, this creates a resistance difference between the positive and negative electrodes, and degradation is concentrated on the negative electrode, which has relatively higher resistance.

[0057] Therefore, the lithium secondary battery according to the present invention can reduce the resistance difference between the positive and negative electrodes by adjusting the ratio of the interfacial resistance of the positive electrode to the interfacial resistance of the negative electrode to an appropriate range using Formula 1, thereby suppressing the deterioration of the negative electrode during charge-discharge cycles and improving the battery's lifespan characteristics.

[0058] The lithium secondary battery includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte. More specifically, it may include an electrode assembly comprising the positive electrode, the negative electrode, and the separator, an electrolyte, and a battery case.

[0059] The following describes in detail each component of the lithium secondary battery according to the present invention.

[0060] (1) Electrode assembly The electrode assembly according to the present invention includes a positive electrode and a negative electrode, and more specifically, may further include a separator interposed between the positive electrode and the negative electrode.

[0061] Specifically, the electrode assembly can be formed by stacking a positive electrode, a separator, and a negative electrode in that order, and the positive electrode and the negative electrode can be insulated from each other by the separator.

[0062] On the other hand, the electrode assembly may be any of the various forms of electrode assemblies known in the art, such as a jelly roll type, a stack type, a stack-and-laminate type, or a stack-and-folding type electrode assembly, and its form is not particularly limited.

[0063] A jelly roll-type electrode assembly can be manufactured by interposing a sheet-shaped separator between a sheet-shaped positive electrode and a sheet-shaped negative electrode, and then winding the assembly in one direction.

[0064] A stacked electrode assembly can be manufactured by cutting the positive electrode, separator, and negative electrode into the desired shapes, and then stacking the cut positive electrode / separator / negative electrode in sequence.

[0065] A stack-and-laminate electrode assembly can be manufactured by stacking a positive electrode, a separator, and a negative electrode to produce multiple unit cells, stacking the multiple unit cells with a separator in between, and then laminating them by methods such as heating.

[0066] A stack-and-fold electrode assembly can be manufactured by stacking a positive electrode, a separator, and a negative electrode to produce multiple unit cells, arranging the multiple unit cells on one or both sides of a long folding separator, and then winding up the folding separator.

[0067] The following describes in detail each component of the electrode assembly according to the present invention.

[0068] 1) Positive electrode The positive electrode may include a positive electrode active material layer, and in one embodiment, the positive electrode may include a positive electrode current collector and a positive electrode active material layer located on the positive electrode current collector.

[0069] Various positive electrode current collectors used in the art can 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 with a surface treatment of carbon, nickel, titanium, silver, etc. The positive electrode current collector may usually have a thickness of 3 to 500 μm, and the adhesion strength of the positive electrode active material may be increased by forming fine irregularities on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric, etc.

[0070] The positive electrode active material layer is 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.

[0071] The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material.

[0072] The first positive electrode active material and the second positive electrode active material have an average particle size (D 50 ) differs, specifically the average particle size (D) of the first positive electrode active material. 50 ) is the average particle size (D) of the second positive electrode active material. 50 This is larger than ). As a result, when the electrode is rolled, the small-grained second positive electrode active material fills the voids in the large-grained first positive electrode active material, increasing the electrode density and enabling high energy density, thus allowing for high capacity characteristics.

[0073] The first positive electrode active material includes single-particle particles. When the first positive electrode active material includes single-particle particles, the large size of the single-particle particles results in a longer lithium diffusion distance and increased diffusion resistance, leading to low efficiency of the positive electrode. This balances the efficiency with that of the negative electrode when a silicon-based negative electrode active material is applied. This makes it possible to suppress lithium ion loss due to irreversible capacity when a silicon-based negative electrode active material is applied, and to prevent or suppress the lithium deposition phenomenon on the surface of the negative electrode, thereby improving the life characteristics of a lithium secondary battery using the positive electrode according to the present invention. Furthermore, when a first positive electrode active material consisting of single-particle particles is applied, unlike when a sacrificial positive electrode material is used as in the past, it is possible to prevent or suppress the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging, resulting in excellent high-temperature storage characteristics and high-temperature life characteristics.

[0074] The first positive electrode active material may include a first lithium transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). Unlike ternary lithium transition metal oxides containing nickel, cobalt, and manganese, the first positive electrode active material according to the present invention is structurally stable by further containing aluminum, which has a strong bonding force with oxygen atoms. This suppresses cation mixing during charging and discharging, and is electrochemically stable at high potential, thus further improving thermal stability and capacitance characteristics.

[0075] Furthermore, the first positive electrode active material may contain a first lithium transition metal oxide containing 82 mol% or more nickel among all metals excluding lithium. In this case, high capacity characteristics of the lithium secondary battery can be achieved.

[0076] Specifically, the first positive electrode active material may contain a first lithium transition metal oxide represented by the following chemical formula 1.

[0077] [Chemical formula 1] Li 1+a1 Ni x1 Co y1 Mn z1Al w1 M 1 v1 O2

[0078] In Chemical Formula 1 above, M 1 may be one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, 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.

[0079] 1 + a1 means the molar ratio of lithium (Li) in the first lithium transition metal oxide, and may be 0 ≦ a1 ≦ 0.3, 0 ≦ a1 ≦ 0.2, 0 ≦ a1 ≦ 0.15, or 0 ≦ a1 ≦ 0.1. When the above range is satisfied, a remarkable capacity characteristic improvement effect of the first positive electrode active material by controlling the Li content and a balance between the sinterability during the production of the first positive electrode active material can be achieved.

[0080] x1 means the molar ratio of nickel among all metals excluding lithium in the first lithium transition metal oxide, and may be 0.82 ≦ x1 < 1, 0.85 ≦ x1 < 1, 0.90 ≦ x1 < 1, or 0.92 ≦ x1 < 1. When the above range is satisfied, a nickel content sufficient to contribute sufficiently to charge and discharge in the lithium transition metal oxide is ensured, and high capacity can be achieved.

[0081] y1 means the molar ratio of cobalt among all metals excluding lithium in the first lithium transition metal oxide, and may be 0 < y1 ≦ 0.2, 0 < y1 ≦ 0.18, 0.01 ≦ y1 ≦ 0.15, 0.03 ≦ y1 ≦ 0.12, or 0.05 ≦ y1 ≦ 0.10. When the above range is satisfied, by including a small content of cobalt, good resistance characteristics and output characteristics can be realized while having a cost advantage.

[0082] In the first lithium transition metal oxide, z1 represents the molar ratio of manganese among all the metals excluding lithium, and it may be 0 < z1 ≦ 0.2, 0 < z1 ≦ 0.18, 0.01 ≦ z1 ≦ 0.15, or 0.03 ≦ z1 ≦ 0.10. When the above range is satisfied, the structural stability of the first lithium transition metal oxide can be improved.

[0083] In the first lithium transition metal oxide, w1 represents the molar ratio of aluminum among all the metals excluding lithium, and it may be 0 < w1 ≦ 0.2, 0 < w1 ≦ 0.18, 0.01 ≦ w1 ≦ 0.15, or 0.03 ≦ w1 ≦ 0.10. When the above range is satisfied, due to the high binding force with oxygen, the thermal stability of the lithium transition metal oxide can be improved.

[0084] In the first lithium transition metal oxide, v1 represents the molar ratio of M 1 among all the metals excluding lithium, and it may be 0 ≦ v1 ≦ 0.1, 0 ≦ v1 ≦ 0.08, or 0 ≦ v1 ≦ 0.05.

[0085] The first positive electrode active material may include a first lithium transition metal oxide and a first coating layer located on the surface of the first lithium transition metal oxide particles, and the first coating layer may contain cobalt (Co). The first coating layer can block the contact between the lithium transition metal oxide and the electrolyte, suppress the occurrence of electrolyte side reactions, and thereby suppress the deterioration of the surface structure of the lithium transition metal oxide that may occur during the charge and discharge process. As a result, an increase in resistance can be suppressed, and the high-temperature life characteristics can be improved.

[0086] The first coating layer may contain cobalt (Co) in amounts of 1.5 mol% to 5 mol%, 2 mol% to 4.5 mol%, 2.3 mol% to 4 mol%, 2.5 mol% to 3.5 mol%, or 2.7 mol% to 3.3 mol%. When the first coating layer contains cobalt within the above ranges, it contains a larger amount of cobalt than the second coating layer contained in the second positive electrode active material described later. This makes it possible to lower the resistance of the positive electrode interface when the lithium secondary battery containing the positive electrode according to the present invention is at a state of charge of 50%, and it is possible to suppress the increase in initial resistance during charging and discharging due to a decrease in ion mobility when a positive electrode active material in the form of single particles is used. As a result, the battery's lifespan and high-temperature lifespan characteristics can be improved.

[0087] The first coating layer may be formed on the entire surface of the first lithium transition metal oxide particles, or on a partial surface. Specifically, when the first coating layer is partially formed on the surface of the first lithium transition metal oxide particles, it may be formed on an area of ​​5% or more but less than 100%, or 20% or more but less than 100%, of the total surface area of ​​the first lithium transition metal oxide surface.

[0088] The average particle size (D) of the first positive electrode active material. 50The diameter may be between 6 μm and 12 μm. Specifically, the average particle size of the first positive electrode active material may be 6 μm or more, 6.2 μm or more, 6.4 μm or more, 6.6 μm or more, 6.8 μm or more, 7 μm or more, 7.2 μm or more, 7.4 μm or more, 7.6 μm or more, 7.8 μm or more, 8 μm or more, 8.2 μm or more, or 8.4 μm or more, and may be 12 μm or less, 11.8 μm or less, 11.6 μm or less, 11.4 μm or less, 11.2 μm or less, 11 μm or less, 10.8 μm or less, 10.6 μm or less, 10.4 μm or less, 10.2 μm or less, 10 μm or less, 9.8 μm or less, 9.6 μm or less, 9.4 μm or less, 9.2 μm or less, 9 μm or less, 8.8 μm or less, or 8.6 μm or less. For example, the average particle size of the first positive electrode active material may be 6 μm to 12 μm, 7.4 μm to 11 μm, 8 μm to 9.6 μm, or 8.2 μm to 9 μm. If the above range is met, the rolling density of the positive electrode material can be increased, thereby improving the electrode density during electrode manufacturing and achieving excellent energy density.

[0089] The first positive electrode active material may be present in an amount of 20% to 80% by weight, 30% to 70% by weight, or 40% to 60% by weight, based on the total weight of the positive electrode active material layer. When the above ranges are met, the rolling density can be improved and a high energy density can be achieved.

[0090] On the other hand, the second positive electrode active material contains single-particle particles. When the second positive electrode active material contains single-particle particles, the large size of the single-particle particles results in a longer diffusion distance for lithium and increased diffusion resistance, leading to low efficiency of the positive electrode. When a silicon-based negative electrode active material is applied, the efficiency of the positive electrode is balanced with that of the negative electrode. This makes it possible to suppress the loss of lithium ions due to irreversible capacity when a silicon-based negative electrode active material is applied, and to prevent or suppress the occurrence of lithium deposition on the surface of the negative electrode, thereby improving the life characteristics of a lithium secondary battery using the positive electrode according to the present invention. Furthermore, when a second positive electrode active material consisting of single-particle particles is applied, unlike when a sacrificial positive electrode material is used as in the past, it is possible to prevent or suppress the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging, resulting in excellent high-temperature storage characteristics and high-temperature life characteristics.

[0091] The second positive electrode active material may include a second lithium transition metal oxide containing nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). Unlike ternary lithium transition metal oxides containing nickel, cobalt, and manganese, the second lithium transition metal oxide according to the present invention is structurally stable by further containing aluminum, which has a strong bonding force with oxygen atoms. This suppresses cation mixing during charging and discharging, and makes the device electrochemically stable at high potentials, thereby further improving thermal stability and capacitance characteristics.

[0092] Furthermore, the second positive electrode active material may contain a lithium transition metal oxide containing approximately 82 mol% or more nickel among all metals excluding lithium. In this case, high capacity characteristics of the lithium secondary battery can be achieved.

[0093] The second positive electrode active material may contain a second lithium transition metal oxide represented by the following chemical formula 2.

[0094] [Chemical formula 2] Li 1+a2 Ni x2 Co y2 Mnz2 Al w2 M 2 v2 O2

[0095] In Chemical Formula 2 above, M 2 may be one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, 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.

[0096] 1 + a2 represents the molar ratio of lithium (Li) in the second lithium transition metal oxide, and may be 0 ≦ a2 ≦ 0.3, 0 ≦ a2 ≦ 0.2, 0 ≦ a2 ≦ 0.15, or 0 ≦ a2 ≦ 0.1. When the above range is satisfied, it is possible to achieve a remarkable effect of improving the capacity characteristics of the second positive electrode active material by controlling the content of Li, and to achieve a balance between the sinterability during the production of the second positive electrode active material.

[0097] x2 represents the molar ratio of nickel among all the metals excluding lithium in the second lithium transition metal oxide, and may be 0.82 ≦ x2 < 1, 0.85 ≦ x2 < 1, 0.90 ≦ x2 < 1, or 0.92 ≦ x2 < 1. When the above range is satisfied, a nickel content sufficient to contribute sufficiently to charge and discharge in the lithium transition metal oxide is ensured, and high capacity can be achieved.

[0098] <00:00518>y^{2} represents the molar ratio of cobalt among all the metals excluding lithium in the second lithium transition metal oxide, and may be 0 < y^{2} ≦ 0.2, 0 < y^{2} ≦ 0.18, 0.01 ≦ y^{2} ≦ 0.15, 0.03 ≦ y^{2} ≦ 0.12, or 0.05 ≦ y^{2} ≦ 0.10. When the above range is satisfied, by including a small content of cobalt, it is possible to achieve good resistance characteristics and output characteristics while having a cost advantage.

[0099] In the second lithium transition metal oxide, z2 represents the molar ratio of manganese among all the metals excluding lithium, and may be 0 < z2 ≤ 0.2, 0 < z2 ≤ 0.18, 0.01 ≤ z2 ≤ 0.15, or 0.03 ≤ z2 ≤ 0.10. When the above range is satisfied, the structural stability of the lithium transition metal oxide can be improved.

[0100] In the second lithium transition metal oxide, w2 represents the molar ratio of aluminum among all the metals excluding lithium, and may be 0 < w2 ≤ 0.2, 0 < w2 ≤ 0.18, 0.01 ≤ w2 ≤ 0.15, or 0.03 ≤ w2 ≤ 0.10. When the above range is satisfied, the thermal stability of the lithium transition metal oxide can be ensured due to the high binding force with oxygen.

[0101] In the second lithium transition metal oxide, v2 represents the molar ratio of M 2 among all the metals excluding lithium, and may be 0 ≤ v2 ≤ 0.1, 0 ≤ v2 ≤ 0.08, or 0 ≤ v2 ≤ 0.05.

[0102] The second positive electrode active material may include a second lithium transition metal oxide and a second coating layer located on the surface of the second lithium transition metal oxide particles, and the second coating layer may contain cobalt (Co). The second coating layer can block the contact between the lithium transition metal oxide and the electrolyte, suppress the occurrence of electrolyte side reactions, and thereby suppress the deterioration of the surface structure of the lithium transition metal oxide that may occur during the charge-discharge process. As a result, an increase in resistance can be suppressed, and the high-temperature life characteristics can be improved.

[0103] The first coating layer may contain a larger amount of cobalt than the second coating layer. In this case, when the SOC of the lithium secondary battery including the positive electrode according to the present invention is 50%, the resistance of the positive electrode interface can be lowered, and when a positive electrode active material in the form of single-particle particles is used, an increase in the initial resistance during charge and discharge due to a decrease in ion mobility can be suppressed. Therefore, the life characteristics and high-temperature life characteristics of the battery can be improved.

[0104] The second coating layer may contain cobalt (Co) in amounts of 0.2 mol% to 2.5 mol%, 0.3 mol% to 2 mol%, 0.5 mol% to 1.5 mol%, or 0.7 mol% to 1.3 mol%. When the second coating layer contains cobalt within the above ranges, by containing less cobalt than the first coating layer contained in the first positive electrode active material described above, the resistance of the positive electrode interface when the lithium secondary battery containing the positive electrode according to the present invention is at SOC 50% can be lowered. This suppresses the increase in initial resistance during charging and discharging due to a decrease in ion mobility when using a positive electrode active material that is a single-particle particle, thereby improving the battery's lifespan and high-temperature lifespan characteristics, and improving energy density.

[0105] The second coating layer may be formed on the entire surface of the second lithium transition metal oxide particles or on a partial surface. Specifically, when the second coating layer is partially formed on the surface of the second lithium transition metal oxide particles, it may be formed on an area of ​​5% or more but less than 100%, preferably 20% or more but less than 100%, of the total surface area of ​​the second lithium transition metal oxide surface.

[0106] The average particle size (D) of the aforementioned second positive electrode active material 50 The particle size of the second positive electrode active material may be 1.5 μm to 5 μm. Specifically, the average particle size of the second positive electrode active material may be 1.5 μm or more, 1.7 μm or more, 1.9 μm or more, 2 μm or more, 2.2 μm or more, 2.4 μm or more, 2.6 μm or more, 2.8 μm or more, 3 μm or more, and 5 μm or less, 4.8 μm or less, 4.6 μm or less, 4.4 μm or less, 4.2 μm or less, 4 μm or less, 3.8 μm or less, 3.6 μm or less, 3.4 μm or less, or 3.2 μm or less. For example, the average particle size of the second positive electrode active material may be 1.5 μm to 5 μm, 2 μm to 4.5 μm, 2.6 μm to 4.2 μm, 3 μm to 4 μm, or 3 μm to 3.4 μm. If the above range is met, the rolling density of the positive electrode material can be increased, which improves the electrode density during electrode manufacturing and enables the achievement of superior energy density.

[0107] The second positive electrode active material may be included in an amount of 20% to 80% by weight, 30% to 70% by weight, or 40% to 60% by weight, based on the total weight of the positive electrode active material layer. When the above ranges are met, the rolling density can be improved and a high energy density can be achieved.

[0108] The first positive electrode active material and the second positive electrode active material may be present in weight ratios of 80:20 to 40:60, 75:25 to 45:55, 70:30 to 50:50, or 65:45 to 55:45. When these weight ratios are met, the energy density can be improved, and the effect of improving high-temperature lifetime characteristics and resistance characteristics can be maximized.

[0109] On the other hand, the positive electrode active material layer may selectively further include at least one of a positive electrode conductive material and a positive electrode binder.

[0110] The positive electrode conductive material is used to impart conductivity to the electrode and is not particularly limited as long as it does not cause chemical changes and has electronic conductivity in the battery it is used in. In one embodiment, the positive electrode conductive material may be 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, or carbon nanotube; metal powder or metal fiber such as copper, nickel, aluminum, or silver; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; or conductive polymers such as polyphenylene derivatives. One of these may be used alone, or a mixture of two or more. The positive electrode conductive material may usually be included in an amount of 1% to 30% by weight, preferably 1% to 20% by weight, and more preferably 1% to 10% by weight, based on the total weight of the positive electrode active material layer.

[0111] 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. Examples of the positive electrode binder 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 can be used alone, or a mixture of two or more can be used. The positive electrode binder may be present in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight relative to the total weight of the positive electrode active material layer.

[0112] The positive electrode can be manufactured by applying a positive electrode slurry to one or both sides of a long, sheet-like positive electrode current collector, removing the solvent from the slurry through a drying process, and then rolling it. Alternatively, a positive electrode including a plain area 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.

[0113] Furthermore, the positive electrode slurry can be produced by dispersing the first positive electrode active material and the second positive electrode active material according to the present invention in a solvent such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water.

[0114] On the other hand, in the positive electrode, R p It is 0.85Ω or less. Specifically, the R p R may be 0.85Ω or less, 0.82Ω or less, 0.8Ω or less, 0.78Ω or less, 0.76Ω or less, 0.74Ω or less, 0.72Ω or less, 0.7Ω or less, 0.68Ω or less, 0.66Ω or less, 0.64Ω or less, 0.62Ω or less, 0.6Ω or less, and may be 0.3Ω or more, 0.32Ω or more, 0.34Ω or more, 0.36Ω or more, 0.38Ω or more, 0.4Ω or more, 0.42Ω or more, 0.44Ω or more, 0.46Ω or more, 0.48Ω or more, 0.5Ω or more, 0.52Ω or more, 0.54Ω or more, 0.56Ω or more, or 0.58Ω or more. For example, the R p The interface resistance may be 0.85Ω or less, 0.3Ω to 0.8Ω, 0.4Ω to 0.7Ω, 0.5Ω to 0.64Ω, or 0.54Ω to 0.6Ω. When the above range is met, the difference between the interface resistance of the positive electrode and the interface resistance of the negative electrode can be adjusted to an appropriate level, and degradation of both the positive and negative electrodes can be prevented.

[0115] In this case, the R p This can be adjusted by the composition of the first and second positive electrode active materials, the cobalt content of the first coating layer contained in the first positive electrode active material and the second coating layer contained in the second positive electrode active material, and the water washing conditions during the manufacturing of the first and second positive electrode active materials.

[0116] 2) Negative electrode The negative electrode includes a silicon-based negative electrode active material. Specifically, the negative electrode may include a negative electrode current collector and a negative electrode active material layer, and the negative electrode active material layer may include a silicon-based negative electrode active material.

[0117] The negative electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and has high conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., and aluminum-cadmium alloy may be used. The negative electrode current collector may also typically have a thickness of 3 to 500 μm.

[0118] 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 can be used in various forms such as film, sheet, foil, mesh, porous material, foam, and nonwoven fabric.

[0119] The negative electrode active material layer is 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.

[0120] The silicon-based negative electrode active material may be particles containing silicon (Si).

[0121] The silicon-based negative electrode active material is SiO x (0≦x≦2), Si / C composite, or a combination thereof. The SiO x (0≦x≦2) may be a form containing Si and SiO2. That is, x is the SiO x This corresponds to the ratio of the number of O atoms to Si atoms contained in (0≦x≦2). Alternatively, the silicon-based negative electrode active material is SiO x (0 ≤ x ≤ 2), or SiO₂.

[0122] When a silicon-based negative electrode active material is included in the negative electrode, it has the advantage of having a much higher charge / discharge capacity compared to conventional carbon-based negative electrode active materials. However, because the silicon-based negative electrode active material has a large irreversible capacity, there is a risk that the battery life characteristics will be reduced. However, the lithium secondary battery according to the present invention includes a positive electrode active material in the positive electrode form, which is a single-particle type, and by adjusting the interfacial resistance of the positive electrode to a specific range, the reduction in the battery life characteristics can be suppressed.

[0123] The silicon-based anode active material may be included in the anode active material layer in amounts of 1% to 30% by weight, 1% to 25% by weight, or 2% to 20% by weight. When these ranges are met, sufficient capacitance characteristics can be achieved.

[0124] On the other hand, the negative electrode active material layer may further contain a carbon-based negative electrode active material as the negative electrode active material.

[0125] The carbon-based anode active material may be one or more selected from the group consisting of graphite such as natural graphite or artificial graphite, and carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, carbon fiber, and carbon nanotubes. When the carbon-based anode active material is included, the deterioration of the lifetime characteristics due to volume changes of the silicon-based anode active material during charging and discharging can be suppressed.

[0126] If a carbon-based anode active material is further included, the silicon-based anode active material and the carbon-based anode active material may be included in a weight ratio of 1:99 to 30:70, 1.5:98.5 to 20:80, 2:98 to 15:85, or 2.5:97.5 to 10:90. When the above ranges are met, excellent capacity characteristics and excellent life characteristics can be achieved.

[0127] The carbon-based negative electrode active material may be included in the negative electrode active material layer in an amount of 70% to 99% by weight, preferably 75% to 99% by weight, and more preferably 80% to 98% by weight. When the above range is met, sufficient capacity characteristics can be achieved and the battery life characteristics can be improved.

[0128] 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.

[0129] The negative electrode conductive material is used to impart conductivity to the electrode and is not particularly limited as long as it does not cause chemical changes in the battery it is used in. Examples of the negative electrode conductive material 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 can be used alone, or a mixture of two or more. The negative electrode conductive material may typically be included in an amount of 1% to 30% by weight, 1% to 20% by weight, or 1% to 10% by weight relative to the total weight of the negative electrode active material layer.

[0130] The negative electrode binder plays a role in improving the adhesion between negative electrode active material particles and the adhesion between the negative electrode active material and the negative electrode current collector. Examples of the negative electrode binder 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 can be used alone or a mixture of two or more. The negative electrode binder may be present in an amount of 1 to 30% by weight, preferably 1 to 20% by weight, and more preferably 1 to 10% by weight, based on the total weight of the negative electrode active material layer.

[0131] On the other hand, in the negative electrode, R n It may be 0.6Ω or less. Specifically, the Rn R may be 0.6Ω or less, 0.58Ω or less, 0.56Ω or less, 0.54Ω or less, 0.52Ω or less, 0.5Ω or less, and may be 0.2Ω or more, 0.22Ω or more, 0.24Ω or more, 0.26Ω or more, 0.28Ω or more, 0.3Ω or more, 0.32Ω or more, 0.34Ω or more, 0.36Ω or more, 0.38Ω or more, 0.4Ω or more, 0.42Ω or more, 0.44Ω or more, 0.46Ω or more, or 0.48Ω or more. For example, the R n The resistance can be 0.6Ω or less, 0.2Ω to 0.58Ω, 0.3Ω to 0.54Ω, or 0.44Ω to 0.5Ω. If the above range is met, the imbalance in resistance between the positive and negative electrodes can be suppressed.

[0132] 3) Separator Next, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move, and can be used without particular limitations as long as it is a separator that is commonly used in lithium secondary batteries. In this case, the separator can be interposed between the positive electrode and the negative electrode.

[0133] As the separator, porous polymer films, such as porous polymer films made from polyolefin polymers like ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer, or laminated structures of two or more layers thereof can be used. Alternatively, ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, may be used. Furthermore, coated separators containing ceramic components or polymeric substances may be used to ensure heat resistance or mechanical strength.

[0134] (2) Electrolyte The electrolyte according to the present invention comprises a lithium salt and an organic solvent.

[0135] The lithium salt can be any compound capable of providing lithium ions for use in lithium secondary batteries, and is not particularly limited. Examples of lithium salts that may be used include LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2. The concentration of the lithium salt may be in the range of 0.1M to 5.0M, or 0.1M to 3.0M. When the concentration of the lithium salt falls within the above range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0136] The organic solvent may include at least one of the following: a cyclic carbonate organic solvent, a linear carbonate organic solvent, a linear ester organic solvent, and a cyclic ester organic solvent.

[0137] The cyclic carbonate-based organic solvent is a highly viscous organic solvent and may typically include at least one organic solvent selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

[0138] Furthermore, the linear carbonate-based organic solvent is an organic solvent having low viscosity and low dielectric constant, and as a typical example, at least one organic solvent 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 may be used, and specifically, it may include ethyl methyl carbonate (EMC).

[0139] Specific examples of the linear ester-based organic solvent include at least one organic solvent selected from the group consisting of methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate.

[0140] The cyclic ester organic solvents include at least one organic solvent selected from the group consisting of γ-butyrolactone, γ-valerolactone, γ-caprolactone, σ-valerolactone, and ε-caprolactone.

[0141] Preferably, the electrolyte according to the present invention may contain ethylene carbonate and dimethyl carbonate as organic solvents.

[0142] On the other hand, the electrolyte may also contain other 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.

[0143] Such other additives may include, as representative examples, at least one other additive selected from the group consisting of 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.

[0144] Specifically, the aforementioned other 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. sulfate (MTMS), tetraphenylborate, lithium oxalyl difluoroborate, succinonitrile, adiponitrile, acetonitrile, propionitrile, butyronitrile, valeronitrile, caprylonitrile, heptanenitrile, cyclopentanecarbonate, cyclohexanecarbonate, 2-fluorobenzonitrile, 4-fluorobenzonitrile, difluorobenzonitrile, trifluorobenzonitrile, phenylacetonitrile, 2-fluorophenylacetonitrile, 4-fluorophenylacetonitrile, fluorobenzenetriethanolamine, ethylenediamine, tetravinylsilane, LiN(SO2F)2(Lithium bis(fluorosulfonyl)imide, LIFSI), LiN(SO2CF3)2(lithium bis(trifluoromethane Examples include one or more compounds selected from the group consisting of sulfonyl)imide, LiTFSI, LiPO2F2, LiODFB (lithium difluorooxalate borate), LiBOB (lithium bisoxalate borate (LiB(C2O4)2), and LiBF4).

[0145] The aforementioned other additives may be present in an amount of 0.01 to 20% by weight, preferably 0.05 to 5.0% by weight, based on the total weight of the electrolyte. If the content of the aforementioned other additives is less than 0.01% by weight, the effect of improving the low-temperature output of the battery, as well as the high-temperature storage characteristics and high-temperature life characteristics, will be minimal. If the content of the aforementioned other additives exceeds 20% by weight, excessive side reactions may occur in the electrolyte during charging and discharging of the battery. In particular, if an excessive amount of the SEI film-forming additive is added, it may not decompose sufficiently at high temperatures and may remain unreacted or precipitated in the electrolyte at room temperature. Therefore, there is a risk of side reactions occurring that reduce the life or resistance characteristics of the secondary battery.

[0146] (3) Battery case The battery case is for housing the electrode assembly and electrolyte, and various battery cases known in the art, such as cylindrical battery cases, rectangular battery cases, pouch-type battery cases, etc., may be used.

[0147] The lithium secondary battery according to the present invention can be usefully used in portable devices such as mobile phones, notebook computers, and digital cameras, as well as in the field of electric vehicles such as hybrid electric vehicles (HEVs).

[0148] 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); and power storage systems.

[0149] 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 suitably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0150] Examples of the aforementioned medium- and large-sized devices include, but are not limited to, electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, and power storage systems.

[0151] Manufacturing method of lithium secondary batteries Next, a method for manufacturing a lithium secondary battery according to the present invention will be described.

[0152] Referring to Figure 1, the method for manufacturing a lithium secondary battery according to the present invention includes the steps of: mixing a first positive electrode active material in distilled water for a first wash and drying (S1); mixing a second positive electrode active material in distilled water for a second wash and drying (S2); applying a positive electrode slurry containing the first and second positive electrode active materials onto a positive electrode current collector to manufacture a positive electrode (S3); manufacturing a negative electrode containing a silicon-based negative electrode active material (S4); and manufacturing a lithium secondary battery containing the positive electrode, the negative electrode, and an electrolyte (S5), wherein the first wash is performed at a higher temperature than the second wash, and the average particle size (D 50 The particle size (D50) of the second positive electrode active material is larger than the average particle size (D50) of the second positive electrode active material, the first positive electrode active material and the second positive electrode active material contain single-particle type particles, and the lithium secondary battery has an IRF (Interfacial Resistance Factor) value of 1 to 1.4 as defined by the following formula 1.

[0153] [Formula 1] IRF=R p / R n

[0154] In formula 1, the R n (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode, and Rp (Ω) represents the interface resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned positive electrode.

[0155] The following describes in detail each step of the method for manufacturing a lithium secondary battery according to the present invention.

[0156] (1) S1 step: First positive electrode active material washing step First, the first positive electrode active material is mixed with distilled water, washed once, and dried (step S1).

[0157] The first positive electrode active material includes single-particle particles. When the first positive electrode active material is single-particle particles, the large size of the single-particle particles results in a long diffusion distance of lithium and increased diffusion resistance, leading to low efficiency of the positive electrode. When a silicon-based negative electrode active material is applied, the efficiency of the positive electrode is balanced with that of the negative electrode. This makes it possible to suppress lithium ion loss due to irreversible capacity when using conventional silicon-based negative electrode active materials, and to prevent or suppress lithium deposition on the surface of the negative electrode, thereby improving the life characteristics of a lithium secondary battery using the positive electrode according to the present invention. Furthermore, when a first positive electrode active material that is single-particle particles is applied, unlike when a sacrificial positive electrode material is used as in the past, it is possible to prevent or suppress the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging, resulting in excellent high-temperature storage characteristics and high-temperature life characteristics.

[0158] Since the first positive electrode active material is as described above, a detailed explanation will be omitted.

[0159] The S1 step adjusts the interfacial resistance of the positive electrode to a specific range by performing a water washing intensity of the first positive electrode active material higher than the water washing intensity of the second positive electrode active material in the S2 step described later.

[0160] Specifically, the first rinse is performed at a higher temperature than the second rinse.

[0161] The first rinse is performed at 20°C to 40°C, 25°C to 35°C, or 27°C to 38°C. When the first rinse is performed at these temperatures, the interfacial resistance of the positive electrode can be adjusted to the desired range.

[0162] Furthermore, the first washing may be carried out by mixing the first positive electrode active material with distilled water in an amount of 50% to 70% by weight, 55% to 65% by weight, or 57% to 63% by weight based on the total weight of the distilled water. In this case, the amount of residual lithium on the surface of the positive electrode active material can be reduced, and deterioration of high-temperature durability can be prevented.

[0163] The drying may be carried out at 60°C to 200°C, 70°C to 180°C, or 80°C to 160°C.

[0164] (2) S2 step: Second positive electrode active material washing step Next, the second positive electrode active material is mixed with distilled water for a second wash and then dried (step S2).

[0165] The second positive electrode active material includes single-particle particles. When the second positive electrode active material is single-particle particles, the large size of the single-particle particles results in a longer diffusion distance for lithium and increased diffusion resistance, leading to low efficiency of the positive electrode. However, when a silicon-based negative electrode active material is applied, the efficiency of the positive electrode is balanced with that of the negative electrode. This makes it possible to suppress lithium ion loss due to irreversible capacity when a silicon-based negative electrode active material is applied, and to prevent or suppress the occurrence of lithium deposition on the surface of the negative electrode, thereby improving the life characteristics of a lithium secondary battery using the positive electrode according to the present invention. Furthermore, when a second positive electrode active material that is single-particle particles is applied, unlike when a sacrificial positive electrode material is used as in the past, it is possible to prevent or suppress the generation of lithium byproducts from the sacrificial positive electrode material during charging and discharging, resulting in excellent high-temperature storage characteristics and high-temperature life characteristics.

[0166] The average particle size (D) of the first positive electrode active material. 50 ) is the average particle size (D) of the second positive electrode active material. 50 It is larger than ).

[0167] Since the second positive electrode active material is as described above, a detailed explanation will be omitted.

[0168] The S2 step prevents deterioration of the high-temperature durability of the second positive electrode active material and adjusts the interfacial resistance of the positive electrode to a specific range by applying a lower water washing intensity to the second positive electrode active material, which has a smaller particle size and a larger specific surface area than the first positive electrode active material, than to the first positive electrode active material.

[0169] The second washing may be performed on the second positive electrode active material at a temperature of 3°C to 18°C, 5°C to 15°C, or 7°C to 13°C. When the second washing is performed within these ranges, the interfacial resistance of the positive electrode can be adjusted to the desired range, and deterioration of high-temperature durability can be prevented or reduced.

[0170] Furthermore, the second washing may be carried out by mixing the second positive electrode active material with distilled water in an amount of 65% to 85% by weight, 70% to 80% by weight, or 72% to 78% by weight, based on the total weight of the distilled water. In this case, the residual lithium on the surface of the positive electrode active material can be reduced, and deterioration of high-temperature durability can be prevented.

[0171] The drying may be carried out at 60°C to 200°C, 70°C to 180°C, or 80°C to 160°C.

[0172] (3) S3 step: Cathode manufacturing step Next, a step (S3) is performed in which a positive electrode slurry containing the first positive electrode active material and the second positive electrode active material is applied to a positive electrode current collector to manufacture a positive electrode.

[0173] First, the first positive electrode active material, the second positive electrode active material, and the solvent can be mixed to produce a positive electrode slurry.

[0174] In this case, since the first positive electrode active material and the second positive electrode active material are as described above, a detailed explanation will be omitted.

[0175] The positive electrode slurry may further selectively contain a positive electrode binder and / or a positive electrode conductive material.

[0176] Since the positive electrode binder and positive electrode conductive material are as described above, a detailed explanation will be omitted.

[0177] On the other hand, the solvent used in the positive electrode slurry may be an aqueous solvent, an organic solvent, or a combination thereof.

[0178] The aqueous solvent may, for example, include water, and the organic solvent may contain one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dihydrolevoglucosenone (Cyrene), γ-valerolactone, dimethyl isosorbide (DMI), and methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate, and preferably contains N-methylpyrrolidone.

[0179] Next, the positive electrode slurry can be applied to the positive electrode current collector to form a positive electrode active material layer. Specifically, the positive electrode can be manufactured by applying the positive electrode slurry to one or both sides of the positive electrode current collector, followed by drying and rolling to form a positive electrode active material layer.

[0180] As the positive electrode current collector is as described above, a detailed explanation will be omitted.

[0181] On the other hand, the coating may be carried out continuously or discontinuously using various coating methods known in the art, such as slot die coating, slide coating, curtain coating, etc.

[0182] The drying may be carried out at 40°C to 180°C, 60°C to 160°C, or 70°C to 150°C.

[0183] The rolling may be performed by a roll press method in which the thickness of the positive electrode is adjusted by adjusting the vertical spacing of the rolls, but is not limited to this method.

[0184] (4) S4 step: Anode manufacturing step Next, a step (S4 step) is performed to manufacture a negative electrode containing a silicon-based negative electrode active material.

[0185] First, the silicon-based negative electrode active material and the solvent can be mixed to produce a negative electrode slurry.

[0186] In this case, since the silicon-based negative electrode active material is as described above, a detailed explanation will be omitted.

[0187] The anode slurry may further contain a carbon-based anode active material.

[0188] As the carbon-based anode active material is as described above, a detailed explanation will be omitted.

[0189] The negative electrode slurry may further selectively contain a negative electrode binder and / or a negative electrode conductive material.

[0190] Since the negative electrode binder and negative electrode conductive material are as described above, a detailed explanation will be omitted.

[0191] On the other hand, the solvent used in the negative electrode slurry may be an aqueous solvent, an organic solvent, or a combination thereof.

[0192] The aqueous solvent may, for example, include water, and the organic solvent may contain one or more selected from the group consisting of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), dihydrolevoglucosenone (Cyrene), γ-valerolactone, dimethyl isosorbide (DMI), and methyl-5-(dimethylamino)-2-methyl-5-oxopentanoate, and preferably contains N-methylpyrrolidone.

[0193] Next, the negative electrode slurry can be applied to the negative electrode current collector to form a negative electrode active material layer. Specifically, the negative electrode can be manufactured by applying the negative electrode slurry to one or both sides of the negative electrode current collector, followed by drying and rolling to form the negative electrode active material layer.

[0194] As the negative electrode current collector is as described above, a detailed explanation will be omitted.

[0195] On the other hand, the coating may be carried out continuously or discontinuously using various coating methods known in the art, such as slot die coating, slide coating, curtain coating, etc.

[0196] The drying may be carried out at 40°C to 180°C, 60°C to 160°C, or 70°C to 150°C.

[0197] The rolling may be carried out by a roll press method in which the thickness of the negative electrode is adjusted by adjusting the vertical spacing of the rolls, but is not limited to this method.

[0198] (5) Step S5: Lithium secondary battery manufacturing step Next, a step (S5 step) is performed to manufacture a lithium secondary battery including the positive electrode, the negative electrode, and the electrolyte.

[0199] First, an electrode assembly including the positive electrode and the negative electrode can be formed. Specifically, the electrode assembly can be formed by stacking the positive electrode, separator, and negative electrode in order.

[0200] Examples of electrode assemblies include stack type, jelly roll type, and stack-and-fold type, but are not limited to these.

[0201] Subsequently, the electrode assembly is placed inside the battery case, the electrolyte is injected, and then the battery case is sealed to manufacture a lithium secondary battery.

[0202] The sealing may be performed by heat welding or heat fusion of the opened portion of the battery case.

[0203] The aforementioned IRF value, R n , and R p As explained above, a detailed explanation will be omitted.

[0204] Since the separator, electrode assembly, electrolyte, and battery case are as described above, a detailed explanation will be omitted.

[0205] Hereinafter, embodiments of the present invention will be described in detail so that those with ordinary skill in the art to which the present invention pertains can easily implement it. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0206] Example 1 <Manufacturing of the first positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0207] Next, after deionized water was added to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and the inside of the reactor was made into a non-oxidizing atmosphere. Then, while adding NaOH, the coprecipitation reaction was allowed to proceed, with an average particle size (D 50 ) of 8.6 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was produced.

[0208] The precursor and LiOH were mixed at a ratio of 1:1.05, and Al was mixed as a doping element. By firing at 910 °C for 16 hours, Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 O2, a first lithium transition metal oxide, was produced.

[0209] Then, the first lithium transition metal oxide was mixed in distilled water at 30 °C so that the solid content was 60% by weight, washed with water, dried, and then Co(OH)2 was mixed. Then, heat treatment was performed at 750 °C for 5 hours to produce a first positive electrode active material coated with Co. The first positive electrode active material contains 3 mol% of Co, and the average particle size (D 50 ) was 8.6 μm, and it was confirmed to be single-particle-shaped particles.

[0210] <Production of the second positive electrode active material> NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10 to prepare an aqueous transition metal solution.

[0211] Next, after deionized water was added to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and the inside of the reactor was made into a non-oxidizing atmosphere. Then, while adding NaOH, the coprecipitation reaction was allowed to proceed, with an average particle size (D 50 [[ID=�8]]) of 3.1 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was produced.

[0212] The precursor and LiOH are mixed at a ratio of 1:1.05, Al is mixed as a doping element, and the mixture is calcined at 910 °C for 16 hours to produce a second lithium transition metal oxide represented by Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 O2.

[0213] Thereafter, the second lithium transition metal oxide is mixed with distilled water at 10 °C so that the solid content is 75% by weight, washed with water, dried, and then mixed with Co(OH)2. Thereafter, heat treatment is performed at 750 °C for 5 hours to produce a second positive electrode active material coated with Co. The second positive electrode active material contains 1 mol% of Co, and the average particle size (D 50 ) is 3.1 μm, and it was confirmed that the particles are single-particle-shaped particles.

[0214] <Manufacture of Positive Electrode> The first positive electrode active material and the second positive electrode active material manufactured above are mixed at a weight ratio of 60:40 to manufacture a positive electrode material. The positive electrode material, carbon black as a conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed at a weight ratio of 96:2:2 in an N-methylpyrrolidone solvent to manufacture a positive electrode slurry. The positive electrode slurry is applied to one side of an aluminum current collector with a thickness of 20 μm, dried at 130 °C, and then rolled to manufacture a positive electrode with a thickness of 70 μm.

[0215] <Manufacture of Lithium Secondary Battery> As a negative electrode active material, a negative electrode active material in which SiO and artificial graphite are mixed at a weight ratio of 5:95, carbon black as a conductive material, SBR as a binder, and CMC as a thickener are mixed in distilled water at a weight ratio of 95.6:1.0:2.3:1.1 to manufacture a negative electrode slurry. The negative electrode slurry is applied to one side of a copper current collector with a thickness of 12 μm, dried at 130 °C, and then rolled to manufacture a negative electrode (solid content of the slurry: 50% by weight based on the total weight of the negative electrode slurry).

[0216] After manufacturing an electrode assembly by interposing a porous polyethylene separator between each of the positive and negative electrodes manufactured above, it was placed inside a battery case, and a lithium secondary battery was manufactured by injecting an electrolyte. At this time, as the electrolyte, an electrolytic solution in which 1.0 M of LiPF6 was dissolved in an organic solvent obtained by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7 was used.

[0217] Example 2 <Manufacture of the First Positive Electrode Active Material> NiSO4, CoSO4, and MnSO4 were mixed in distilled water in an amount such that the molar ratio of nickel, cobalt, and manganese became 83:7:10, and an aqueous transition metal solution was prepared.

[0218] Next, after putting deionized water into a reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and after making the inside of the reactor a non-oxidizing atmosphere, a coprecipitation reaction was allowed to proceed while adding NaOH, and the average particle size (D 50 ) was 8.4 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was manufactured.

[0219] The precursor and LiOH were mixed at a ratio of 1:1.05, Al was mixed as a doping element, and by firing at 910 °C for 16 hours, Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 O2, the first lithium transition metal oxide was manufactured.

[0220] Thereafter, the first lithium transition metal oxide was mixed in distilled water at 25 °C so that the solid content was 60% by weight, washed with water, dried, and then Co(OH)2 was mixed. Thereafter, heat treatment was performed at 750 °C for 5 hours to manufacture a first positive electrode active material coated with Co. The first positive electrode active material was confirmed to contain 3 mol% of Co, have an average particle size (D 50 ) of 8.4 μm, and be single-particle-shaped particles.

[0221] <Manufacture of the Second Positive Electrode Active Material> NiSO4, CoSO4, and MnSO4 were mixed in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10 to prepare an aqueous transition metal solution.

[0222] Next, after deionized water was put into the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and after making the inside of the reactor a non-oxidizing atmosphere, a coprecipitation reaction was allowed to proceed while adding NaOH, and the average particle size (D 50 ) was 3.3 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was manufactured.

[0223] The precursor and LiOH were mixed at a ratio of 1:1.05, Al was mixed as a doping element, and by firing at 910 °C for 16 hours, Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 O2, a second lithium transition metal oxide, was manufactured.

[0224] Thereafter, the second lithium transition metal oxide was mixed in distilled water at 15 °C so that the solid content was 75% by weight, washed with water, dried, and then Co(OH)2 was mixed. Thereafter, heat treatment was performed at 750 °C for 5 hours to manufacture a second positive electrode active material coated with Co. The second positive electrode active material contains 1 mol% of Co, and the average particle size (D 50 ) is 3.3 μm, and it was confirmed that it is single-particle-shaped particles.

[0225] <Manufacture of the Positive Electrode> A positive electrode was manufactured by the same method except that the first positive electrode active material and the second positive electrode active material manufactured above were used.

[0226] <Manufacture of the Lithium Secondary Battery> A lithium secondary battery was manufactured by the same method as in Example 1 except that the positive electrode manufactured above was used.

[0227] Example 3 <Manufacturing of the first positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0228] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 8.1 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0229] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 We produced a lithium first transition metal oxide represented by ]O2.

[0230] Subsequently, the first lithium transition metal oxide was mixed in distilled water at 30°C to a solid content of 60% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a first positive electrode active material coated with Co. The first positive electrode active material contained 2.5 mol% Co and had an average particle size (D 50 The particle size was 8.1 μm, confirming that it was a single-particle type particle.

[0231] <Manufacturing of the second positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0232] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 3.5 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0233] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 A lithium-2 transition metal oxide represented by ]O2 was produced.

[0234] Subsequently, the second lithium transition metal oxide was mixed in distilled water at 10°C to a solid content of 75% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a second positive electrode active material coated with Co. The second positive electrode active material contained 1.5 mol% Co and had an average particle size (D 50 The particle size was 3.5 μm, confirming that it was a single-particle type particle.

[0235] <Manufacturing of positive electrodes> The positive electrode was manufactured using the same method as described above, except that the first and second positive electrode active materials were used.

[0236] <Manufacturing of lithium-ion secondary batteries> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0237] Comparative Example 1 <Manufacturing of the first positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0238] Next, after deionized water was added to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and the inside of the reactor was made into a non-oxidizing atmosphere. Then, while adding NaOH, the coprecipitation reaction was allowed to proceed, and the average particle size (D 50 ) was 7.2 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was produced.

[0239] The precursor and LiOH were mixed at a ratio of 1:1.05, and Al was mixed as a doping element. By firing at 910 °C for 16 hours, Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 O2, a first lithium transition metal oxide, was produced.

[0240] Thereafter, the first lithium transition metal oxide was mixed in distilled water at 10 °C so that the solid content was 75% by weight, washed with water, dried, and then Co(OH)2 was mixed. Then, heat treatment was performed at 750 °C for 5 hours to produce a first positive electrode active material coated with Co. The first positive electrode active material contains 3 mol% of Co, and the average particle size (D 50 ) was 7.2 μm, and it was confirmed that it was single-particle-shaped particles.

[0241] <Production of the second positive electrode active material> NiSO4, CoSO4, and MnSO4 were mixed in distilled water in an amount such that the molar ratio of nickel, cobalt, and manganese was 83:7:10 to prepare a transition metal aqueous solution.

[0242] Next, after deionized water was added to the reactor, nitrogen gas was purged into the reactor to remove dissolved oxygen in the water, and the inside of the reactor was made into a non-oxidizing atmosphere. Then, while adding NaOH, the coprecipitation reaction was allowed to proceed, and the average particle size (D 50 ) was 2.5 μm, and a precursor represented by Ni 0.83 Co 0.07 Mn 0.1 (OH)2 was produced.

[0243] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 A lithium-2 transition metal oxide represented by ]O2 was produced.

[0244] Subsequently, the second lithium transition metal oxide was mixed in distilled water at 10°C to a solid content of 75% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a second positive electrode active material coated with Co. The second positive electrode active material contained 1 mol% Co and had an average particle size (D 50 The particle size was 2.5 μm, confirming that it was a single-particle type particle.

[0245] <Manufacturing of positive electrodes> The positive electrode was manufactured using the same method as described above, except that the first and second positive electrode active materials were used.

[0246] <Manufacturing of lithium-ion secondary batteries> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0247] Comparative Example 2 <Manufacturing of the first positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0248] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 7.7 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0249] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 We produced a lithium first transition metal oxide represented by ]O2.

[0250] Subsequently, the first lithium transition metal oxide was mixed in distilled water at 30°C to a solid content of 60% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a first positive electrode active material coated with Co. The first positive electrode active material contained 1 mol% Co and had an average particle size (D 50 The particle size was 7.7 μm, confirming that it was a single-particle type particle.

[0251] <Manufacturing of the second positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0252] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 2.9 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0253] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 A lithium-2 transition metal oxide represented by ]O2 was produced.

[0254] Subsequently, the second lithium transition metal oxide was mixed in distilled water at 10°C to a solid content of 70% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a second positive electrode active material coated with Co. The second positive electrode active material contained 1 mol% Co and had an average particle size (D 50 The particle size was 2.9 μm, confirming that it was a single-particle type particle.

[0255] <Manufacturing of positive electrodes> The positive electrode was manufactured using the same method as described above, except that the first and second positive electrode active materials were used.

[0256] <Manufacturing of lithium-ion secondary batteries> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0257] Comparative Example 3 <Manufacturing of the first positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0258] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 8.5 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0259] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 We produced a lithium first transition metal oxide represented by ]O2.

[0260] Subsequently, the first lithium transition metal oxide was mixed in distilled water at 10°C to a solid content of 75% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a first positive electrode active material coated with Co. The first positive electrode active material contained 3 mol% Co and had an average particle size (D 50 The particle size was 8.5 μm, confirming that it was a single-particle type particle.

[0261] <Manufacturing of the second positive electrode active material> Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel, cobalt, and manganese was 83:7:10.

[0262] Next, after adding deionized water to the reactor, nitrogen gas is purged into the reactor to remove dissolved oxygen from the water, creating a non-oxidizing atmosphere inside the reactor. Then, the coprecipitation reaction proceeds while adding NaOH, and the average particle size (D 50 ) is 3.0 μm, Ni 0.83 Co 0.07 Mn 0.1 A precursor represented by (OH)2 was prepared.

[0263] The aforementioned precursor and LiOH are mixed in a ratio of 1:1.05, Al is added as a doping element, and the mixture is calcined at 910°C for 16 hours to obtain Li[Ni 0.81 Co 0.07 Mn 0.10 Al 0.02 A lithium-2 transition metal oxide represented by ]O2 was produced.

[0264] Subsequently, the second lithium transition metal oxide was mixed in distilled water at 10°C to a solid content of 70% by weight, washed with water, dried, and then mixed with Co(OH)2. Afterward, it was heat-treated at 750°C for 5 hours to produce a second positive electrode active material coated with Co. The second positive electrode active material contained 1 mol% Co and had an average particle size (D 50 The particle size was 3.0 μm, confirming that it was a single-particle type particle.

[0265] <Manufacturing of positive electrodes> The positive electrode was manufactured using the same method as described above, except that the first and second positive electrode active materials were used.

[0266] <Manufacturing of lithium-ion secondary batteries> A lithium secondary battery was manufactured in the same manner as in Example 1, except that the positive electrode manufactured as described above was used.

[0267] Experimental Example 1 - Measurement of IRF Values The IRF value, defined by the following formula 1, was measured for each of the lithium secondary batteries manufactured in Examples 1 to 3 and Comparative Examples 1 to 3. The results are shown in Table 1 below.

[0268] [Formula 1] IRF=R p / R n

[0269] In formula 1, the R n (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode, and R p (Ω) represents the interface resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned positive electrode.

[0270] (1) Interfacial resistance of the positive electrode (R p ) measurement Each of the lithium secondary batteries manufactured in Examples 1-3 and Comparative Examples 1-3 was charged at 25°C under CC / CV, 0.1C, 4.2V, and 0.05C cutoff conditions, and discharged under CC, 0.1C, and 3.0V conditions. This cycle was performed 100 times, after which each lithium secondary battery was charged to SOC 50% or SOC 10%, and the positive electrode interface resistance at SOC 50% and SOC 10% was measured using a Biologic VMP3 device (100kHz-10mHz range, 25°C conditions).

[0271] (2) Negative electrode interfacial resistance (R n ) measurement Each lithium secondary battery manufactured in Examples 1-3 and Comparative Examples 1-3 was charged at 25°C under CC / CV, 0.1C, 0.05V, and 0.05C cutoff conditions, and discharged under CC, 0.1C, and 1.5V conditions. This constituted one cycle, and after 100 cycles, each lithium secondary battery was charged to SOC 50% or SOC 10%, and the negative electrode interface resistance at SOC 50% and SOC 10% was measured using a Biologic VMP3 instrument (100kHz-10mHz range, 25°C conditions).

[0272] [Table 1]

[0273] Referring to Table 1 above, it can be seen that the lithium secondary batteries manufactured in Examples 1 to 3 satisfy the IRF value of 1 to 1.4, but the lithium secondary batteries manufactured in Comparative Examples 1 to 3 either have an IRF value less than 1 or greater than 1.4, thus failing to satisfy the 1 to 1.4 requirement.

[0274] Experimental Example 2 - Evaluation of High-Temperature Lifetime Characteristics The lithium secondary batteries manufactured in Examples 1-3 and Comparative Examples 1-3 were charged to 4.2V at 45°C under CC / CV and 0.5C conditions with a 0.05C cutoff condition, and then discharged to 3.0V under CC and 1.0C conditions. This process was defined as one cycle, and 100 charge-discharge cycles were performed.

[0275] (1) Capacity maintenance rate The capacity retention rate was calculated using the following formula, and the results are shown in Table 2 below.

[0276] Capacity retention rate (%) = {(Discharge capacity after 100 cycles / Discharge capacity after 1 cycle)} × 100

[0277] (2) Resistance increase rate After one charge-discharge cycle, the discharge capacity after one cycle was measured using an electrochemical charger. After adjusting the SOC to 50%, a 2.5C pulse was applied for 10 seconds, and the initial resistance was calculated from the difference between the voltage before and after pulse application.

[0278] After 100 charge-discharge cycles, the resistance after 100 cycles was calculated using the same method as described above, and the resistance increase rate was calculated using the following formula. The results are shown in Table 2 below.

[0279] Resistance increase rate (%) = (Resistance after 100 cycles - Initial resistance) / Initial resistance × 100

[0280] [Table 2]

[0281] Referring to Table 2 above, it can be confirmed that the lithium secondary batteries manufactured in Examples 1 to 3 have a higher capacity retention rate at 45°C and a lower resistance increase rate at 45°C compared to the lithium secondary batteries manufactured in Comparative Examples 1 to 3. From this, it can be seen that the lithium secondary batteries manufactured in Examples 1 to 3 using the positive electrode active material of the present invention have superior high-temperature life characteristics compared to lithium secondary batteries that do not use the positive electrode active material of the present invention.

[0282] Although preferred embodiments of the present invention have been described above with reference to the present invention, it will be understood that those skilled in the art, or those with ordinary knowledge in the art, can modify and change the present invention in various ways without departing from the spirit and technical scope of the invention as set forth in the appended claims. Therefore, the technical scope of the present invention is not limited to what is described in the detailed description of the specification, but is determined solely by the claims.

Claims

1. A lithium secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an electrolyte, The positive electrode comprises a first positive electrode active material and a second positive electrode active material having different average particle sizes. The average particle size (D) of the first positive electrode active material ５０ ) is the average particle size (D) of the second positive electrode active material. ５０ Larger than ) The first positive electrode active material and the second positive electrode active material contain single-particle particles. The aforementioned negative electrode contains a silicon-based negative electrode active material. The lithium secondary battery has an IRF (Interface Resistance Factor) value of 1 to 1.4, as defined by the following formula 1. [Formula 1] IRF=R ｐ / R ｎ In the above formula 1, The aforementioned R ｎ (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode. The aforementioned R ｐ (Ω) represents the interface resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned positive electrode.

2. The first positive electrode active material includes a first lithium transition metal oxide represented by the following chemical formula 1, [Chemical formula 1] Li １＋ａ１ Ni ｘ１ Co ｙ１ Mn ｚ１ Al ｗ１ M １ ｖ１ O ２ In the aforementioned chemical formula 1, 0 ≤ a1 ≤ 0.3, 0.82 ≤ x1 < 1.0, 0 < y1 ≤ 0.2, 0 < z1 ≤ 0.2, 0 < w1 ≤ 0.2, 0 ≤ v1 ≤ 0.1, M １ The lithium secondary battery according to claim 1, wherein is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

3. The second positive electrode active material comprises a second lithium transition metal oxide represented by the following chemical formula 2, [Chemical formula 2] Li １＋ａ２ Ni ｘ２ Co ｙ２ Mn ｚ２ Al ｗ２ M ２ ｖ２ O ２ In the aforementioned chemical formula 2, 0 ≤ a² ≤ 0.3, 0.82 ≤ x² < 1.0, 0 < y² ≤ 0.2, 0 < z² ≤ 0.2, 0 < w² ≤ 0.2, 0 ≤ v² ≤ 0.1, M ２ The lithium secondary battery according to claim 1, wherein is one or more doping elements selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, In, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

4. The aforementioned R ｎ A lithium secondary battery according to claim 1, wherein the impedance is 0.6 Ω or less.

5. The average particle size (D) of the first positive electrode active material ５０ The lithium secondary battery according to claim 1, wherein the diameter is 6 μm to 12 μm.

6. The average particle size (D) of the second positive electrode active material ５０ The lithium secondary battery according to claim 1, wherein the diameter is 1.5 μm to 5 μm.

7. The lithium secondary battery according to claim 1, wherein the first positive electrode active material comprises a first lithium transition metal oxide and a first coating layer located on the surface of the particles of the first lithium transition metal oxide and containing 1.5 mol% to 5 mol% cobalt (Co).

8. The lithium secondary battery according to claim 1, wherein the second positive electrode active material comprises a second lithium transition metal oxide and a second coating layer located on the surface of the particles of the second lithium transition metal oxide and containing 0.2 mol% to 2.5 mol% cobalt (Co).

9. The first positive electrode active material comprises a first lithium transition metal oxide and includes a first coating layer containing cobalt (Co) on the surface of the particles of the first lithium transition metal oxide. The second positive electrode active material comprises a second lithium transition metal oxide and includes a second coating layer containing cobalt (Co) on the surface of the particles of the second lithium transition metal oxide. The lithium secondary battery according to claim 1, wherein the first coating layer contains a larger amount of cobalt than the second coating layer.

10. The lithium secondary battery according to claim 1, wherein the first positive electrode active material and the second positive electrode active material are contained in a weight ratio of 80:20 to 40:

60.

11. The aforementioned negative electrode contains a carbon-based negative electrode active material. The lithium secondary battery according to claim 1, wherein the silicon-based anode active material and the carbon-based anode active material are contained in a weight ratio of 1:99 to 30:

70.

12. Step (S1) involves mixing the first positive electrode active material in distilled water, performing a first wash, and drying it. Step (S2) involves mixing the second positive electrode active material in distilled water, performing a second water wash, and drying it. Step (S3) of manufacturing a positive electrode by applying a positive electrode slurry containing the first positive electrode active material and the second positive electrode active material onto a positive electrode current collector, Step (S4) of manufacturing a negative electrode containing a silicon-based negative electrode active material, The process includes (S5) the step of manufacturing a lithium secondary battery comprising the positive electrode, the negative electrode, and the electrolyte, The first rinse is performed at a higher temperature than the second rinse. The average particle size (D) of the first positive electrode active material ５０ ) is larger than the average particle size (D50) of the second positive electrode active material, The first positive electrode active material and the second positive electrode active material contain single-particle particles. The lithium secondary battery has an IRF (Interface Resistance Factor) value of 1 to 1.4, as defined by the following formula 1. [Formula 1] IRF=R ｐ / R ｎ In the above formula 1, The aforementioned R ｎ (Ω) represents the interface resistance of the negative electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the aforementioned negative electrode. The aforementioned R ｐ A method for manufacturing a lithium secondary battery, wherein (Ω) represents the interfacial resistance of the positive electrode measured after 100 charge-discharge cycles of a lithium secondary battery manufactured using the positive electrode.

13. The method for manufacturing a lithium secondary battery according to claim 12, wherein the first washing is performed at 20°C to 40°C.

14. The method for manufacturing a lithium secondary battery according to claim 12, wherein the second washing is performed at a temperature of 3°C to 18°C.

15. The method for manufacturing a lithium secondary battery according to claim 12, wherein the first washing is carried out by mixing the first positive electrode active material with distilled water in an amount of 50% to 70% by weight based on the total weight of the distilled water.

16. The method for manufacturing a lithium secondary battery according to claim 12, wherein the second washing is carried out by mixing the second positive electrode active material with distilled water in an amount of 65% to 85% by weight based on the total weight of the distilled water.

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