Positive electrode active material and positive electrode containing the same

Abstract

This invention relates to a positive electrode active material and a positive electrode containing the same, which can realize a battery with improved initial resistance characteristics and lifespan characteristics. [Solution] A positive electrode comprising a positive electrode active material in single-particle form, wherein the positive electrode active material is present in a positive electrode active material layer containing 80% by weight or more of the positive electrode active material relative to the total weight of the positive electrode active material layer, and the density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 This invention relates to a positive electrode active material and a positive electrode containing the same, wherein, after being rolled to the above extent, the positive electrode active material layer is analyzed by XRD, and the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10°~90° interval is 30% or more.

Description

[Technical Field]

[0001] This application claims priority under Korean Patent Application No. 10-2022-0062288 dated May 20, 2022, and all content disclosed in the said Korean Patent Application is incorporated herein by reference.

[0002] The present invention relates to a positive electrode active material in single-particle form and a positive electrode containing the same. [Background technology]

[0003] Recently, with the technological development and increasing demand for mobile devices and electric vehicles, the demand for rechargeable batteries as an energy source has been rapidly increasing.

[0004] A lithium secondary battery generally consists of a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and negative electrode contain an active material that allows for the insertion and deintercalation of lithium ions.

[0005] On the other hand, the positive electrode active material used in lithium secondary batteries generally has the form of spherical secondary particles, which are formed by the aggregation of hundreds of submicron-sized primary particles. However, positive electrode active materials in the form of secondary particles have the problem that the secondary particles break down as the aggregated primary particles separate during repeated charging and discharging, resulting in a decrease in battery performance.

[0006] To address these issues, active development is underway regarding single-particle positive electrode active materials. However, when manufacturing electrodes using single-particle positive electrode active materials, there are difficulties in aligning the c-axis direction, which is the main expansion direction of the single-particle positive electrode active material, as desired, or in quantifying the degree of such alignment. On the other hand, if the c-axis direction, which is the main expansion direction of the single-particle positive electrode active material, is not aligned and exists randomly, problems such as a decrease in battery life characteristics, a decrease in capacity, and a decrease in output occur. Therefore, technology to resolve these issues is needed. [Overview of the project] [Problems that the invention aims to solve]

[0007] The object of the present invention is to provide a positive electrode active material and a positive electrode containing the same that can realize a battery with improved initial resistance characteristics and life characteristics. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a positive electrode active material and a positive electrode containing the same.

[0009] (1) The present invention relates to a positive electrode active material in single-particle form, wherein the positive electrode includes a positive electrode active material layer in which the positive electrode active material is present in an amount of 80% by weight or more relative to the total weight of the positive electrode active material layer, and the density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 The present invention provides a positive electrode active material that, after being rolled to the above extent, satisfies the requirement that when the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 30% or more.

[0010] (2) The present invention provides a positive electrode active material that satisfies the difference in the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10° to 90° section when the positive electrode active material layer is analyzed by XRD before and after rolling the positive electrode, in the present invention.

[0011] (3) The present invention provides a positive electrode active material in the form of a single particle, wherein the ratio of the length in the a-axis direction to the length in the c-axis direction of the crystal is greater than 1.

[0012] (4) In any one of (1) to (3) above, the present invention provides a positive electrode active material in single-particle form consisting of 1 to 50 single crystal particles.

[0013] (5) In the present invention, in (4) above, the single crystal particles have an average particle size (D EBSDProvide a positive electrode active material in which () is 0.1 μm to 10 μm.

[0014] (6) In any one of the above (1) to (5), the present invention provides a positive electrode active material in which the single-particle form positive electrode active material is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0015] (7) In the above (6), the present invention provides a positive electrode active material in which the lithium composite transition metal oxide contains 60 mol% or more of nickel (Ni) among all metals other than lithium.

[0016] (8) In the above (6) or (7), the present invention provides a positive electrode active material in which the lithium composite transition metal oxide has a composition represented by the following Chemical Formula 1. [Chemical Formula 1] Li a Ni b Co c Mn d M 1 e O2 In the above Chemical Formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S, 0.90 ≦ a ≦ 1.1, 0.60 ≦ b < 1.0, 0 < c < 0.40, 0 < d < 0.40, 0 ≦ e ≦ 0.10, and b + c + d + e = 1.

[0017] (9) The present invention provides a positive electrode including a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer contains a positive electrode active material according to any one of the above (1) to (8).

[0018] (10) In the above (9), when the positive electrode active material layer before and after rolling the positive electrode is analyzed by XRD, the present invention provides a positive electrode in which the ratio difference of the area of the (003) peak to the area of all peaks confirmed in the 2θ 10° to 90° range is 10% or more.

[0019] (11) In the present invention, when the angle between the lithium migration path of the single-particle positive electrode active material and the axis parallel to the upper surface of the current collector is θ, (cosθ) 2 Provide a positive electrode with a value of 0.6 or greater.

[0020] (12) The present invention provides a positive electrode in any one of (9) to (11) above, wherein the positive electrode active material in single-particle form is aligned such that the c-axis direction of the crystal is perpendicular to the upper surface of the current collector.

[0021] (13) The present invention provides a positive electrode in any one of (9) to (12) above, wherein the positive electrode active material in single-particle form has a ratio of the length in the a-axis direction to the length in the c-axis direction of the crystal greater than 1.

[0022] (14) In any one of (9) to (13) above, the present invention provides a positive electrode in which the positive electrode active material in single particle form consists of 1 to 50 single crystal particles.

[0023] (15) In the present invention, in (14) above, the single crystal grains are the average particle size (D EBSD The positive electrode is provided with a diameter of 0.1 μm to 10 μm.

[0024] (16) The present invention provides a cathode in any one of (9) to (15) above, wherein the positive electrode active material in single particle form is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn).

[0025] (17) The present invention provides a positive electrode in which, in (16) above, the lithium composite transition metal oxide contains 60 mol% or more of nickel (Ni) among the total metals other than lithium.

[0026] (18) The present invention provides a positive electrode in which, in (16) or (17) above, the lithium composite transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2 In the aforementioned chemical formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S. 0.90≦a≦1.1, 0.60≦b<1.0, 0 <c<0.40、0<d<0.40、0≦e≦0.10、b+c+d+e=1である。 [Effects of the Invention]

[0027] The positive electrode active material according to the present invention comprises a positive electrode containing a positive electrode active material layer in which the positive electrode active material is present in an amount of 80% by weight or more relative to the total weight of the positive electrode active material layer, wherein the density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 After rolling to the above specifications, when the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10°~90° interval is 30% or more. This suppresses the expansion of the positive electrode active material when applied to the positive electrode, thereby improving the initial resistance characteristics and life characteristics of batteries containing this material.

[0028] In the positive electrode according to the present invention, when the positive electrode active material layer is analyzed by XRD after rolling the positive electrode, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10°~90° interval is 30% or more. The c-axis direction of the crystal structure, which is the contraction / expansion direction of the positive electrode active material crystals contained in the positive electrode active material layer, is aligned perpendicular to the upper surface of the current collector, and the expansion of the positive electrode active material can be suppressed. As a result, the initial resistance characteristics and life characteristics of batteries containing this can be improved. [Brief explanation of the drawing]

[0029] [Figure 1] This is an SEM image of the positive electrode active material of Example 1. [Figure 2] This is an SEM image of the positive electrode active material of Comparative Example 1. [Figure 3] This is an SEM image of the positive electrode active material of Comparative Example 3. [Figure 4] These are XRD data of the positive electrode active material layer before and after rolling of the positive electrode containing the positive electrode active material of Examples 1 and 2 and Comparative Examples 3 and 4. [Figure 5] This is an EBSD Band Contrast (BC) image of the cross-section of the positive electrode containing the positive electrode active material of Example 1. [Figure 6] This figure shows the angle between the c-axis vector of the crystal grain (Euler angle) and the direction vector perpendicular to the electrode (= angle between the lithium migration path (Li path) and the direction vector parallel to the electrode). [Modes for carrying out the invention]

[0030] The terms and words used herein and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may appropriately define the concepts of terms in order to best describe their invention.

[0031] In this specification, terms such as “includes,” “equip,” or “have” specify the presence of implemented features, figures, steps, components, or combinations thereof, but should be understood not to preclude the existence or possibility of adding one or more other features, figures, steps, components, or combinations thereof.

[0032] In this specification, the term “on top of” means not only when one configuration is formed directly on top of another, but also when a third configuration is interposed between these configurations.

[0033] In this specification, "single-particle positive electrode active material" is a concept contrasted with spherical secondary particle positive electrode active material formed by the aggregation of several hundred primary particles manufactured by conventional methods, and refers to a positive electrode active material consisting of 50 or fewer single crystal particles. Specifically, in the present invention, the single-particle positive electrode active material may be a single single crystal particle, or it may be in the form of aggregated single crystal particles of 2 to 50, 2 to 40, 2 to 30, 2 to 20, 2 to 15, 2 to 10, or 2 to 5 particles. Here, "single crystal particle" refers to the smallest unit of particle that can be recognized when the positive electrode active material is observed through a scanning electron microscope.

[0034] In this specification, the average particle size (D 50 ) refers to the particle size at the 50% reference level of the volume cumulative particle size distribution of the positive electrode active material precursor, positive electrode active material, or lithium transition metal oxide powder. The average particle size (D 50 The particle size can be measured using the laser diffraction method. For example, after dispersing the positive electrode active material powder in a dispersion medium, the particle size 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 then determining the particle size corresponding to 50% of the volume-cumulative amount.

[0035] In this specification, the average particle size (D) of single crystal particles EBSD ) refers to the particle size at the 50% reference level of the volume cumulative particle size distribution of single crystal particles obtained by EBSD analysis using SEM. The EBSD analysis can be performed by acquiring images with SEM-EBSD equipment (e.g., FEI, Quanta200-EDAX, Velocity super OIM 8) and analyzing them with image analysis software (EDAX OIM Analysis).

[0036] The present invention will be described in detail below.

[0037] positive electrode active material The present invention relates to a positive electrode active material in single-particle form, wherein the positive electrode includes a positive electrode active material layer containing the positive electrode active material in an amount of 80% by weight or more relative to the total weight of the positive electrode active material layer, and the density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 The present invention provides a positive electrode active material that, after being rolled to the above extent, satisfies the requirement that when the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 30% or more.

[0038] In this invention, rolling is performed so that the electrode density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 Specifically, the above is 2.7 g / cm³. 3 ~3.0g / cm 3 The rolling process may be carried out using a roll persing method. Specifically, the rolling process may be carried out so that the electrode density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 It may be possible to roll-press it to achieve this result.

[0039] The positive electrode active material according to the present invention comprises a positive electrode containing a positive electrode active material layer in which the positive electrode active material accounts for 80% by weight or more of the total weight of the positive electrode active material layer, and the density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 After rolling to the above specifications, when the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10°~90° interval can satisfy the condition of being 30% or more, specifically 50%, 60% or more, 85%, or 95% or less.

[0040] The (003) plane is the direction in which lithium moves, and the normal direction of the (003) plane is the c-axis direction of the crystal structure, which is the contraction / expansion direction of the positive electrode active material crystal (hereinafter, the c-axis direction). Therefore, when the above conditions are met, when the positive electrode active material according to the present invention is applied to the positive electrode, the c-axis direction of the positive electrode active material crystal contained in the positive electrode active material layer is aligned perpendicular to the upper surface (or electrode surface) of the current collector. As a result, when a positive electrode containing the positive electrode active material according to the present invention is applied to a battery, the expansion of the positive electrode active material crystal in the c-axis direction is suppressed by the external case, etc., which has the effect of improving the battery's lifespan. On the other hand, during XRD measurement, the sample is positioned so that X-rays are incident in the direction of the positive electrode active material layer, not in the direction of the current collector.

[0041] According to the present invention, when the positive electrode active material of the present invention, which includes a positive electrode active material layer containing 80% by weight or more of the positive electrode active material relative to the total weight of the positive electrode active material layer, is analyzed by XRD before and after rolling the positive electrode, the difference in the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval can satisfy the requirements of 10%, 20%, 30% or more, and 75% or less. In other words, the difference between the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval when the positive electrode active material layer of the positive electrode before rolling is analyzed by XRD and the difference between the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval when the positive electrode active material layer of the positive electrode after rolling is analyzed by XRD can be 10%, 20%, 30% or more, and 75% or less. In this case, the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, is aligned perpendicular to the upper surface (or electrode surface) of the current collector, which has the effect of improving the battery's lifespan.

[0042] When the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval can be 10%, 20% or more, 40%, or 49% or less.

[0043] The positive electrode active material in single-particle form has an average particle size (D 50The average particle size (D) of the positive electrode active material in single particle form can be 0.1 μm to 10 μm. Specifically, the average particle size (D) of the positive electrode active material in single particle form can be 0.1 μm to 10 μm. 50 The particle size can be 0.1 μm, 1.0 μm, 2.0 μm or more, 5.0 μm, 6.0 μm, 7.0 μm, 8.0 μm, 9.0 μm, or 10.0 μm or less. In this case, the rolling ratio of the battery containing the single-particle positive electrode active material can be increased, and the performance of the battery can be further improved.

[0044] According to the present invention, the single-particle positive electrode active material can consist of 1 to 50 single crystal particles for alignment of the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, and the lithium migration path. Specifically, the single-particle positive electrode active material can consist of 1 to 5, 10, 20, 30, 40, or 50 or fewer single crystal particles.

[0045] According to the present invention, the single crystal particles have an average particle size (D EBSD The particle size can be 0.1 μm to 10 μm, specifically 0.1 μm, 0.2 μm or more, 5 μm, 8 μm, or 10 μm or less. In this case, it is possible to prevent the slurry (composition for forming the positive electrode active material layer) from agglomerating or gelling during electrode manufacturing, and to reduce the occurrence of cracks within the particles during repeated charging and discharging.

[0046] According to the present invention, the positive electrode active material in single-particle form can be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). Here, the lithium composite transition metal oxide may contain 60 mol%, 65 mol%, or more of nickel (Ni) among the total metals other than lithium.

[0047] According to the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1.

[0048] [Chemical formula 1] Li a Ni b Co c Mn dM 1 e O2

[0049] In the aforementioned chemical formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S. 0.90≦a≦1.1, 0.60≦b<1.0, 0 <c<0.40、0<d<0.40、0≦e≦0.10、b+c+d+e=1である。

[0050] The above b refers to the atomic fraction of nickel among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.60, 0.65, 0.8, 0.85 or more, 0.95 or 0.98 or less.

[0051] The aforementioned c represents the atomic fraction of cobalt among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.01 or more, 0.10, 0.20, 0.30, or 0.40 or less.

[0052] The above d represents the atomic fraction of manganese among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.01 or more, 0.10, 0.20, 0.30, or 0.40 or less.

[0053] The aforementioned e is M, which is one of the metal elements other than lithium in the lithium composite transition metal oxide. 1 This refers to the elemental fraction of an element, and can be between 0 and 0.02, 0.05, or 0.10.

[0054] Here, the positive electrode active material can be included in an amount of 80% to 99% by weight, more specifically, 85% to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above-mentioned content range, excellent capacity characteristics can be observed.

[0055] positive electrode The present invention provides a positive electrode comprising a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer comprises the positive electrode active material according to the present invention described above. That is, the present invention provides a positive electrode comprising a current collector and a positive electrode active material layer located on the current collector, wherein the positive electrode active material layer contains 80% by weight or more of single-particle positive electrode active material relative to the total weight of the positive electrode active material layer, and after rolling the positive electrode, when the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° section is 30% or more.

[0056] In this invention, rolling is performed so that the electrode density of the positive electrode active material layer after rolling is 2.7 g / cm³. 3 Specifically, the above is 2.7 g / cm³. 3 ~3.0g / cm 3 The rolling process may be carried out using a roll persing method to achieve a positive electrode active material layer density of 2.7 g / cm³ after rolling. 3 It may be possible to roll-press it to achieve this result.

[0057] Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer located on at least one surface of the positive electrode current collector, which contains positive electrode active material in single-particle form. Furthermore, when the positive electrode active material layer is analyzed by XRD after the positive electrode has been rolled, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 30% or more. Specifically, when the positive electrode active material layer is analyzed by XRD after the positive electrode has been rolled, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval can be 50%, 60% or more, 85%, or 95% or less.

[0058] The (003) plane is the direction in which lithium moves, and the normal direction of the (003) plane is the c-axis direction of the crystal structure, which is the contraction / expansion direction of the positive electrode active material crystal (hereinafter, the c-axis direction). Therefore, when the above conditions are met, the c-axis direction of the positive electrode active material crystal contained in the positive electrode active material layer is aligned perpendicular to the upper surface (or electrode surface) of the current collector, and as a result, when the positive electrode according to the present invention is applied to a battery, the expansion of the positive electrode active material crystal in the c-axis direction is suppressed by the external case, etc., which has the effect of improving the battery's lifespan performance. On the other hand, during XRD measurement, the sample is positioned so that X-rays are incident in the direction of the positive electrode active material layer, not in the direction of the current collector.

[0059] According to the present invention, when the positive electrode active material layer of the positive electrode is analyzed by XRD before and after rolling, the difference in the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval can be 10%, 20%, 30% or more, or 75% or less. That is, the difference between the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval when the positive electrode active material layer of the positive electrode before rolling is analyzed by XRD and the ratio of the area of ​​the (003) peak to the area of ​​all peaks confirmed in the 2θ 10°~90° interval when the positive electrode active material layer of the positive electrode after rolling is analyzed by XRD can be 10%, 20%, 30% or more, or 75% or less. In this case, the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, is aligned perpendicular to the upper surface (or electrode surface) of the current collector, which has the effect of improving the battery's lifespan.

[0060] When the positive electrode active material layer is analyzed by XRD, the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval can be 10%, 20% or more, 40%, or 49% or less.

[0061] Furthermore, in the positive electrode, when the angle between the lithium migration path of the single-particle positive electrode active material and the axis parallel to the upper surface of the current collector is θ, then (cosθ) 2 The value is 0.6 or greater. (cosθ) 2The value can be 0.6 or higher, 0.7, 0.8, 0.9, or 1 or lower. In this case, the battery life performance can be further improved.

[0062] The positive electrode current collector is not particularly limited as long as it does not cause chemical changes in the battery and is conductive. For example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel with surface treatment using carbon, nickel, titanium, silver, etc., can be used. The positive electrode current collector can usually have a thickness of 3 μm to 500 μm, and fine irregularities can be formed on the surface of the current collector to enhance the adhesion of the positive electrode active material. For example, it can be used in various forms such as film, sheet, foil, mesh, porous material, foam, nonwoven fabric.

[0063] The positive electrode active material layer may include a conductive material and a binder, along with the positive electrode active material in single-particle form.

[0064] According to the present invention, the single-particle positive electrode active material can be aligned so that the c-axis direction of the crystal is perpendicular to the upper surface of the current collector. In this case, the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, is aligned perpendicular to the upper surface (or electrode surface) of the current collector. When the positive electrode is applied to a battery, the expansion of the positive electrode active material crystal in the c-axis direction is suppressed by the external case, etc., thereby improving the lifespan performance.

[0065] According to the present invention, the positive electrode active material in single-particle form may have a ratio of the length in the a-axis direction to the length in the c-axis direction of the crystal greater than 1, so that the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, is aligned perpendicular to the upper surface (or electrode surface) of the current collector. That is, the positive electrode active material in single-particle form may have a shape in which the length of the particle in one direction, specifically in the c-axis direction, is short.

[0066] According to the present invention, the single-particle positive electrode active material can consist of 1 to 50 single crystal particles for alignment of the c-axis direction, which is the contraction / expansion direction of the positive electrode active material crystal, and the lithium migration path. Specifically, the single-particle positive electrode active material can consist of 1 to 5, 10, 20, 30, 40, or 50 single crystal particles.

[0067] According to the present invention, the single crystal particles have an average particle size (D EBSD The particle size can be 0.1 μm to 10 μm, specifically 0.1 μm, 0.2 μm or more, 5 μm, 8 μm, or 10 μm or less. In this case, it is possible to prevent the slurry (composition for forming the positive electrode active material layer) from agglomerating or gelling during electrode manufacturing, and to reduce the occurrence of cracks within the particles during repeated charging and discharging.

[0068] According to the present invention, the positive electrode active material in single-particle form can be a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn). Here, the lithium composite transition metal oxide may contain 60 mol%, 65 mol%, or more of nickel (Ni) among the total metals other than lithium.

[0069] According to the present invention, the lithium composite transition metal oxide may have a composition represented by the following chemical formula 1.

[0070] [Chemical formula 1] Li a Ni b Co c Mn d M 1 e O2

[0071] In the aforementioned chemical formula 1, M 1 is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S. 0.90≦a≦1.1, 0.60≦b<1.0, 0 <c<0.40、0<d<0.40、0≦e≦0.10、b+c+d+e=1である。

[0072] The above b refers to the atomic fraction of nickel among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.60, 0.65, 0.8, 0.85 or more, 0.95 or 0.98 or less.

[0073] The aforementioned c represents the atomic fraction of cobalt among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.01 or more, 0.10, 0.20, 0.30, or 0.40 or less.

[0074] The above d represents the atomic fraction of manganese among the metal elements other than lithium in the lithium composite transition metal oxide, and can be 0.01 or more, 0.10, 0.20, 0.30, or 0.40 or less.

[0075] The aforementioned e is M, which is one of the metal elements other than lithium in the lithium composite transition metal oxide. 1 This refers to the elemental fraction of an element, and can be between 0 and 0.02, 0.05, or 0.10.

[0076] Here, the positive electrode active material can be included in an amount of 80% to 99% by weight, more specifically, 85% to 98% by weight, relative to the total weight of the positive electrode active material layer. When included within the above-mentioned content range, excellent capacity characteristics can be observed.

[0077] The conductive material is used to impart conductivity to the electrodes and can be used without particular limitations in the battery it is configured in, as long as it does not cause chemical changes and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; 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 alone or a mixture of two or more can be used. The conductive material can be included in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer.

[0078] Here, the conductive material is used to impart conductivity to the electrodes and can be used without particular limitations as long as it does not cause chemical changes in the battery and has electronic conductivity. Specific examples include graphite such as natural graphite or artificial graphite; carbon-based materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, and carbon fiber; 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. Of these, one or more can be used. The conductive material may be included in an amount of 1% to 30% by weight relative to the total weight of the positive electrode active material layer.

[0079] The positive electrode can be manufactured by a conventional method for manufacturing a positive electrode, except for using the positive electrode active material described above. Specifically, it can be manufactured by applying a composition (slurry) for forming a positive electrode active material layer, prepared by dissolving or dispersing the positive electrode active material and selectively a binder and a conductive material in a solvent, onto a positive electrode current collector, followed by drying and rolling. Here, the types and contents of the positive electrode active material, binder, and conductive material are as described above. Alternatively, the positive electrode can also be manufactured by casting the composition for forming a positive electrode active material layer onto another support, peeling it off this support, and laminating the resulting film onto a positive electrode current collector.

[0080] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or water, and one or more of these can be used individually or in mixtures of two or more. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, and binder, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode, taking into consideration the coating thickness of the slurry and the manufacturing yield.

[0081] Lithium-ion battery Furthermore, the present invention can be used to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element can be a battery, a capacitor, and more specifically, a lithium secondary battery.

[0082] The lithium secondary battery specifically includes a positive electrode, a negative electrode positioned opposite the positive electrode, and a separator and electrolyte interposed between the positive and negative electrodes. As the positive electrode is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0083] Furthermore, the lithium secondary battery may selectively further include a battery container for housing the electrode assembly comprising the positive electrode, negative electrode, and separator, and a sealing member for sealing the battery container.

[0084] In the lithium secondary battery described above, the negative electrode includes a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0085] 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 can be used. The negative electrode current collector can usually have a thickness of 3 μm to 500 μm, and, similar to the positive electrode current collector, fine irregularities can be formed on the surface of the current collector 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.

[0086] The negative electrode active material layer selectively includes a binder and a conductive material together with the negative electrode active material.

[0087] As the negative electrode active material, compounds capable of reversible intercalation and deintercalation of lithium can be used. Specific examples include carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metallic compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloys, Sn alloys, or Al alloys; and SiO2. βExamples include metallic oxides that can be doped and dedoped with lithium, such as (0<β<2), SnO2, vanadium oxide, and lithium vanadium oxide; or composites containing the metallic compound and carbonaceous material, such as Si-C composites or Sn-C composites, and any one or more mixtures thereof can be used. A metallic lithium thin film can also be used as the negative electrode active material. Furthermore, both low-crystallinity carbon and high-crystallinity carbon can be used as the carbon material. Typical examples of low-crystalline carbon include soft carbon and hard carbon, while typical examples of high-crystalline carbon include amorphous, plate-like, flaky, spherical, or fibrous natural or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, meso-carbon microbeads, mesophase pitches, and high-temperature calcined carbon such as petroleum or coal tar pitch-derived cokes.

[0088] The anode active material can be present in an amount of 80% to 99% by weight relative to the total weight of the anode active material layer.

[0089] The binder is a component that facilitates bonding between the conductive material, active material, and current collector, and can usually be added in an amount of 0.1% to 10% by weight relative to the total weight of the negative electrode active material layer. Examples of such binders include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0090] The conductive material is a component for further improving the conductivity of the negative electrode active material and can be added in an amount of 10% by weight or less, preferably 5% by weight or less, relative to the total weight of the negative electrode active material layer. Such a conductive material is not particularly limited as long as it does not cause a chemical change in the battery and is conductive, and for example, graphite such as natural graphite or artificial graphite; carbon black such as acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metal fibers; metal powders such as carbon fluoride, aluminum, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and conductive materials such as polyphenylene derivatives can be used.

[0091] The negative electrode active material layer can be manufactured by coating a negative electrode active material layer-forming composition, which is prepared by dissolving or dispersing a negative electrode active material and a binder and conductive material selectively in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode active material layer-forming composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0092] On the other hand, in the lithium secondary battery, the separator separates the negative electrode and the positive electrode and provides a passage for lithium ions to move. Generally, any separator used in lithium secondary batteries can be used without particular limitations, but those with low resistance to ion movement of the electrolyte and excellent electrolyte moisture absorption capacity are particularly preferred. Specifically, porous polymer films, such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures of two or more layers thereof can be used. Ordinary porous nonwoven fabrics, such as nonwoven fabrics made of high-melting-point glass fibers or polyethylene terephthalate fibers, can also be used. Furthermore, coated separators containing ceramic components or polymeric substances can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0093] Furthermore, the electrolytes used in the present invention include, but are not limited to, organic liquid electrolytes, inorganic liquid electrolytes, solid polymer electrolytes, gel-type polymer electrolytes, solid inorganic electrolytes, and molten inorganic electrolytes that can be used in the manufacture of lithium secondary batteries.

[0094] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0095] The organic solvent can be used without particular limitations as long as it serves as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the organic solvents include ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone, and ε-caprolactone; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcohol solvents such as ethyl alcohol and isopropyl alcohol; nitriles such as R-CN (where R is a linear, branched, or cyclic hydrocarbon group having 2 to 20 carbon atoms, and can include a double-bonded aromatic ring or ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes can be used. Among these, carbonate solvents are preferred, and a mixture of a cyclic carbonate (e.g., ethylene carbonate or propylene carbonate) having high ionic conductivity and high dielectric constant that can improve the charge and discharge performance of the battery, and a low-viscosity linear carbonate compound (e.g., ethyl methyl carbonate, dimethyl carbonate, or diethyl carbonate) is more preferred. In this case, mixing the cyclic carbonate and linear carbonate in a volume ratio of about 1:1 to about 1:9 allows the electrolyte to exhibit excellent performance.

[0096] The lithium salt can be used without particular limitations as long as it is a compound that can provide lithium ions for use in lithium secondary batteries. Specifically, the lithium salt can be 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 lithium salt is preferably used within a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt falls within this range, the electrolyte has appropriate conductivity and viscosity, exhibiting excellent electrolyte performance and allowing lithium ions to move effectively.

[0097] In addition to the components of the electrolyte, the electrolyte may also contain one or more additives, such as haloalkylene carbonate compounds like difluoroethylene carbonate, pyridine, triethyl phosphite, triethanolamine, cyclic ethers, ethylenediamine, n-glyme, hexaphosphate triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxyethanol, or aluminum trichloride, for purposes such as improving battery life characteristics, suppressing battery capacity reduction, and improving battery discharge capacity. In this case, the additive may be present in an amount of 0.1% to 5% by weight relative to the total weight of the electrolyte.

[0098] As described above, lithium secondary batteries containing the positive electrode active material according to the present invention exhibit excellent discharge capacity, output characteristics, and life characteristics in a stable manner, making them useful 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).

[0099] Therefore, according to another embodiment of the present invention, a battery module including the lithium secondary battery as a unit cell and a battery pack including the same are provided.

[0100] The aforementioned battery module or battery pack can be used as a power source for one or more medium-to-large devices, including power tools; electric vehicles (EVs), hybrid electric vehicles, and plug-in hybrid electric vehicles (PHEVs); or power storage systems.

[0101] The external shape of the lithium secondary battery of the present invention is not particularly limited, but it can be cylindrical, rectangular, pouch-type, or coin-type, using a can.

[0102] The lithium secondary battery according to the present invention can be used not only as a battery cell used as a power source for small devices, but also preferably as a unit battery in medium- and large-sized battery modules containing a large number of battery cells.

[0103] Hereinafter, embodiments of the present invention will be described in detail so that they can be easily implemented by a person with ordinary skill in the art to which the present invention pertains. However, the present invention can be realized in various different forms and is not limited to the embodiments described herein.

[0104] Examples and Comparative Examples Example 1 Ni 0.95 Co 0.03 Mn 0.02 It has a composition represented by (OH)2 and an average particle size (D 50 A positive electrode active material precursor with a diameter of 3.5 μm is mixed with LiOH in a molar ratio of 1:1.05, and a calcined product is produced by primary calcination at a temperature of 870°C for 9 hours under an oxygen atmosphere. After pulverizing the calcined product, it is secondary calcined at a temperature of 750°C for 9 hours under an oxygen atmosphere to produce LiNi 0.95 Co 0.03 Mn0.02 A lithium composite transition metal oxide in single-particle form having a composition represented by O2 was fabricated.

[0105] A mixture was prepared by mixing the manufactured single-particle lithium composite transition metal oxide with powdered Co(OH)2 (manufactured by HUAYOU COBALT) in a molar ratio of 1:0.02. The mixture was heat-treated at 700°C for 5 hours under an oxygen atmosphere to produce a single-particle cathode active material.

[0106] Example 2 Ni 0.88 Co 0.03 Mn 0.09 It has a composition represented by (OH)2 and an average particle size (D 50 A positive electrode active material precursor with a diameter of 3.5 μm is mixed with LiOH in a molar ratio of 1:1.05, and a calcined product is produced by primary calcination at a temperature of 900°C for 9 hours under an oxygen atmosphere. After pulverizing the calcined product, it is secondary calcined at a temperature of 780°C for 9 hours under an oxygen atmosphere to produce LiNi 0.88 Co 0.03 Mn 0.09 A lithium composite transition metal oxide in single-particle form having a composition represented by O2 was fabricated.

[0107] A mixture was prepared by mixing the manufactured single-particle lithium composite transition metal oxide with powdered Co(OH)2 (manufactured by HUAYOU COBALT) in a molar ratio of 1:0.02. The mixture was heat-treated at 700°C for 5 hours under an oxygen atmosphere to produce a single-particle cathode active material.

[0108] Comparative Example 1 Ni 0.95 Co 0.03 Mn 0.02 It has a composition represented by (OH)2 and an average particle size (D 50 A positive electrode active material precursor with a diameter of 3.5 μm is mixed with LiOH in a molar ratio of 1:1.05, and a calcined product is produced by primary calcination at a temperature of 800°C for 9 hours under an oxygen atmosphere. After pulverizing the calcined product, it is secondary calcined at a temperature of 750°C for 9 hours under an oxygen atmosphere to produce LiNi 0.95 Co 0.03 Mn 0.02A lithium composite transition metal oxide, which is an intermediate form between a single-particle form and a secondary-particle form and has a composition represented by O2, was produced.

[0109] Powdery Co(OH)2 (manufactured by HUAYOU COBALT) was mixed with the produced lithium composite transition metal oxide in a single-particle form at a molar ratio of 1:0.02 to prepare a mixture. The mixture was heat-treated at a temperature of 700 °C for 5 hours in an oxygen atmosphere to produce a cathode active material, which is an intermediate form between a single-particle form and a secondary-particle form.

[0110] Comparative Example 2 Ni 0.88 Co 0.03 Mn 0.09 A cathode active material precursor having a composition represented by (OH)2 and an average particle diameter (D 50 ) of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.05 and primary fired at a temperature of 820 °C for 9 hours in an oxygen atmosphere to produce a calcined product. After the calcined product was pulverized, it was secondary fired at a temperature of 780 °C for 9 hours in an oxygen atmosphere to produce a lithium composite transition metal oxide, which is an intermediate form between a single-particle form and a secondary-particle form and has a composition represented by LiNi 0.88 Co 0.03 Mn 0.09 O2.

[0111] Powdery Co(OH)2 (manufactured by HUAYOU COBALT) was mixed with the produced lithium composite transition metal oxide in a single-particle form at a molar ratio of 1:0.02 to prepare a mixture. The mixture was heat-treated at a temperature of 700 °C for 5 hours in an oxygen atmosphere to produce a cathode active material, which is an intermediate form between a single-particle form and a secondary-particle form.

[0112] Comparative Example 3 Ni 0.95 Co 0.03 Mn 0.02 A cathode active material precursor having a composition represented by (OH)2 and an average particle diameter (D 50 ) of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.05 and fired at a temperature of 750 °C for 9 hours in an oxygen atmosphere to produce LiNi 0.95 Co 0.03 Mn 0.02A lithium composite transition metal oxide having a composition represented by O2 was produced.

[0113] Powdery Co(OH)2 (manufactured by HUAYOU COBALT) was mixed with the produced lithium composite transition metal oxide in a single particle form at a molar ratio of 1:0.02 to prepare a mixture. The mixture was heat-treated at a temperature of 700 °C for 5 hours in an oxygen atmosphere to produce a cathode active material in a secondary particle form.

[0114] Comparative Example 4 Ni 0.88 Co 0.03 Mn 0.09 (OH)2 having a composition represented by, and an average particle diameter (D 50 ) of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.05 and fired at a temperature of 800 °C for 9 hours in an oxygen atmosphere to produce a lithium composite transition metal oxide having a composition represented by LiNi 0.88 Co 0.03 Mn 0.09 O2.

[0115] Powdery Co(OH)2 (manufactured by HUAYOU COBALT) was mixed with the produced lithium composite transition metal oxide in a single particle form at a molar ratio of 1:0.02 to prepare a mixture. The mixture was heat-treated at a temperature of 700 °C for 5 hours in an oxygen atmosphere to produce a cathode active material in a secondary particle form.

[0116] Comparative Example 5 Ni 0.88 Co 0.03 Mn 0.09 (OH)2 having a composition represented by, and an average particle diameter (D 50 ) of 3.5 μm was mixed with LiOH at a molar ratio of 1:1.05 and fired at a temperature of 840 °C for 9 hours in an oxygen atmosphere to produce a lithium composite transition metal oxide having a composition represented by LiNi 0.88 Co 0.03 Mn 0.09 O2.

[0117] A mixture was prepared by mixing the manufactured lithium composite transition metal oxide with powdered Co(OH)2 (manufactured by HUAYOU COBALT) in a molar ratio of 1:0.02. The mixture was heat-treated at 700°C for 5 hours under an oxygen atmosphere to produce a cathode active material in the form of secondary particles.

[0118] Experimental example Experimental Example 1: SEM Image Analysis The positive electrode active materials of Example 1, Comparative Example 1, and Comparative Example 3 were measured using a scanning electron microscope (SEM) (JEOL Corporation, JSM-7900F; acceleration voltage 20kV), and SEM images were acquired for each, which are shown in Figures 1, 2, and 3, respectively.

[0119] Figure 1 is an SEM image of the positive electrode active material of Example 1, Figure 2 is an SEM image of the positive electrode active material of Comparative Example 1, and Figure 3 is an SEM image of the positive electrode active material of Comparative Example 3.

[0120] Referring to Figures 1 to 3, the positive electrode active material of Example 1 consists of one to a few particles in single-particle form (average particle size (D) EBSD While the particle size of Comparative Example 1 is 1.5 μm, the positive electrode active material of Comparative Example 3 is in the form of secondary particles, and it can be confirmed that the positive electrode active material of Comparative Example 1 is in an intermediate form between the single particle form and the secondary particle form as defined in the present invention.

[0121] Experiment Example 2: XRD Data Analysis (Preparation of electrode samples for analysis) The cathode active materials, carbon black (DenkaBlack, manufactured by Denka Corporation), and PVdF (KF1300, manufactured by Kureha Corporation) binders prepared in a weight ratio of 95:3:2 were added to N-methylpyrrolidone (NMP) (manufactured by Oi Chemical Co., Ltd.) to prepare a cathode active material layer forming composition.

[0122] The positive electrode active material layer forming composition was applied to one surface of a 20 μm thick aluminum foil current collector and dried at 135°C for 3 hours to form a positive electrode active material layer. Subsequently, the electrode density of the positive electrode active material layer after rolling was 2.7 g / cm³.3 The positive electrode was manufactured by rolling it using a roll persing method to achieve the desired result.

[0123] For reference, electrode density is the value obtained by dividing the mass of positive electrode active material per unit area of ​​the electrode (excluding the weight of conductive material, binder, and current collector) by the unit volume of the electrode (thickness excluding the current collector × unit area).

[0124] (XRD measurement and analysis) Using an Empyrean XRD system manufactured by Panalytical (Cu-target, voltage: 45kV, current: 40mA, 2θ: 10°~90°), XRD data of the positive electrode active material layers before and after rolling of the positive electrode containing the positive electrode active materials of Examples 1 and 2 and Comparative Examples 1 to 4 were obtained and are shown in Figure 4. The ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10~90° range is shown in Table 1 below.

[0125] [Table 1]

[0126] Referring to Figure 4, it can be seen that in Examples 1 and 2, the ratio of the area of ​​the (003) peak is higher both before and after rolling compared to Comparative Examples 3 and 4. In particular, it can be seen that the particles are rearranged during the rolling process, resulting in a very large difference between before and after rolling, and the post-rolling values ​​also show a large difference compared to Comparative Examples 3 and 4.

[0127] Experiment Example 3: EBSD Data Analysis The electrode sample for analysis was prepared using the same method as in Experimental Example 2. An argon (Ar) ion beam was irradiated onto the positive electrode using a Hitachi IM5000 (acceleration voltage: 6kV), and the cross-section of the positive electrode was obtained by cutting it using an ion milling method. The cross-section of the positive electrode was then measured and analyzed using a JEOL JSM-7900F (acceleration voltage: 20kV). AztecCrystal from Oxford Instruments was used as the image processing-EBSD quantification analysis software.

[0128] Figure 5 is an EBSD Band Contrast (BC) image of the cross-section of the positive electrode containing the positive electrode active material of Example 1. In Figure 5(A), the long axis of the particles is indicated by a red arrow, and in Figure 5(B), the crystal grain model according to the crystal orientation is shown in a hexagonal prismatic shape (the longer direction of the crystal structure model represents the c-axis). In the EBSD BC image, the vertical direction (Y1) is perpendicular to the electrode, and the horizontal direction (X1) is parallel to the electrode.

[0129] For reference, the image in Figure 5 is a cross-section, and in reality, in three-dimensional particles, the length of the particle in any one axis direction is longer than that of the other two axes.

[0130] Let θ be the angle between the c-axis vector (Euler angle) of all crystal grains (approximately 50 to 100) in the image obtained by EBSD analysis and the direction vector perpendicular to the electrode (= angle between the lithium migration path (Li path) and the direction vector parallel to the electrode). Then, for each crystal grain, (cosθ) 2 Calculate the value of (cosθ) for all crystal grains. 2 The average values ​​are shown in Table 2 below, and the degree to which the lithium migration path of the positive electrode active material and the electrodes were aligned was confirmed.

[0131] Figure 6 shows the angle between the c-axis vector of the crystal grain (Euler angle) and the direction vector perpendicular to the electrode (= angle between the lithium migration path (Li path) and the direction vector parallel to the electrode), and (cosθ) 2The closer the value is to 1, the more likely it is that the lithium migration path and the electrode surface direction are parallel.

[0132] [Table 2]

[0133] Experimental Example 4: Evaluation of Battery Characteristics (Half-cell manufacturing) The cathode active materials, carbon black (DenkaBlack, manufactured by Denka Corporation), and PVdF (KF1300, manufactured by Kureha Corporation) binders prepared in a weight ratio of 95:3:2 were added to N-methylpyrrolidone (NMP) (manufactured by Oi Chemical Co., Ltd.) to prepare a cathode active material layer forming composition.

[0134] A positive electrode active material layer-forming composition was applied to one surface of a 20 μm thick aluminum foil current collector and dried at 135°C for 3 hours to form a positive electrode active material layer. Next, the positive electrode was manufactured by rolling using a roll persing method so that the porosity of the positive electrode active material layer after rolling was 20 volume%.

[0135] A half-cell was manufactured using lithium metal as the negative electrode along with the aforementioned positive electrode.

[0136] (1) Initial resistance (DCIR) evaluation Each of the half-cells manufactured as described above was charged at 25°C with a constant current (CC) of 0.2C until it reached 4.25V. Then, it was charged with a constant voltage (CV) of 4.25V until the charging current reached 0.05mAh (cut-off current). After that, the initial resistance was calculated by dividing the voltage difference between the fully charged state and the state 10 seconds after the start of discharge by the current while discharging with a constant current of 0.2C for 10 seconds. The results are shown in Table 3 below.

[0137] (2) Evaluation of capacity retention rate and resistance increase rate Each of the half-cells manufactured as described above was charged at 25°C with a constant current (CC) of 0.2C until it reached 4.25V. Then, it was charged with a constant voltage (CV) of 4.25V until the charging current reached 0.05mAh (cut-off current). After being left for 20 minutes, it was discharged with a constant current of 0.2C until it reached 2.5V.

[0138] Subsequently, the cell was moved to a 45°C chamber and charged with a constant current of 0.33C until it reached 4.25V. Then, it was charged with a constant voltage (CV) of 4.25V until the charging current reached 0.05mAh (cut-off current). Finally, it was discharged with a constant current of 0.33C until it reached 2.5V. This constituted one cycle, and 30 charge-discharge cycles were performed. Here, the capacity retention rate is defined as the percentage of the discharge capacity of the 30th cycle relative to the discharge capacity of the first cycle, and is shown in Table 3 below. Also, the resistance increase rate is defined as the percentage of the DCIR value of the 30th cycle relative to the DCIR value of the first cycle, and is also shown in Table 3 below. For reference, the DCIR value of the nth cycle is calculated by dividing the voltage difference between the fully charged state and the voltage 10 seconds after the start of discharge by the current, obtained while discharging with a constant current of 0.33C until it reached 2.5V in the nth cycle.

[0139] [Table 3]

[0140] Referring to Tables 1-3, when the positive electrode active material layer of the positive electrode was analyzed by XRD after rolling the positive electrode, the positive electrodes containing single-particle positive electrode active material of Examples 1 and 2, in which the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10-90° interval is 30% or more, can be seen to have superior initial resistance characteristics and lifetime characteristics compared to the positive electrodes containing secondary-particle positive electrode active material of Comparative Examples 3 and 4, and the positive electrodes containing intermediate-form positive electrode active material between single-particle and secondary-particle forms of Comparative Examples 1 and 2. Furthermore, the positive electrodes containing single-particle positive electrode active material of Examples 1 and 2 can be seen to have significantly superior lifetime characteristics compared to the positive electrode active material of Comparative Example 5, in which a mixture of secondary-particle form (agglomerated hundreds of primary particles) and single-particle form exists.

Claims

1. A positive electrode active material in single-particle form, A positive electrode containing a positive electrode active material layer in which the positive electrode active material is present at a concentration of 80% by weight or more relative to the total weight of the positive electrode active material layer, wherein the density of the positive electrode active material layer after rolling is 2.7 g / cm³. ３ A positive electrode active material in which, after being rolled to the above extent, the positive electrode active material layer is analyzed by XRD and the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 30% or more.

2. The positive electrode active material according to claim 1, wherein when the positive electrode active material layer is analyzed by XRD before and after rolling the positive electrode, the difference in the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 10% or more.

3. The positive electrode active material according to claim 1, wherein the positive electrode active material in single-particle form has a ratio of the length in the a-axis direction to the length in the c-axis direction of the crystal greater than 1.

4. The positive electrode active material according to claim 1, wherein the positive electrode active material in single-particle form consists of 1 to 50 single crystal particles.

5. The single crystal grains have an average particle size (D ＥＢＳＤ The positive electrode active material according to claim 4, wherein the diameter is 0.1 μm to 10 μm.

6. The positive electrode active material according to claim 1, wherein the positive electrode active material in single-particle form is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn).

7. The positive electrode active material according to claim 6, wherein the lithium composite transition metal oxide contains 60 mol% or more of nickel (Ni) among the total metals other than lithium.

8. The positive electrode active material according to claim 6, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the aforementioned chemical formula 1, M １ is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S. 0.90 ≤ a ≤ 1.1, 0.60 ≤ b < 1.0, 0 < c < 0.40, 0 < d < 0.40, 0 ≤ e ≤ 0.10, and b + c + d + e = 1.

9. Current collector and, A positive electrode comprising a positive electrode active material layer located on the current collector, The positive electrode comprises the positive electrode active material layer described in claim 1.

10. The positive electrode according to claim 9, wherein when the positive electrode active material layer is analyzed by XRD before and after rolling the positive electrode, the difference in the ratio of the area of ​​the (003) peak to the area of ​​all peaks observed in the 2θ 10° to 90° interval is 10% or more.

11. When θ is the angle between the lithium migration path of the single-particle positive electrode active material and the axis parallel to the upper surface of the current collector, (cosθ) ２ The positive electrode according to claim 9, wherein the value is 0.6 or greater.

12. The positive electrode according to claim 9, wherein the positive electrode active material in single-particle form has its crystal c-axis aligned perpendicular to the upper surface of the current collector.

13. The positive electrode according to claim 9, wherein the positive electrode active material in single-particle form has a ratio of the length in the a-axis direction to the length in the c-axis direction of the crystal greater than 1.

14. The positive electrode according to claim 9, wherein the positive electrode active material in single-particle form consists of 1 to 50 single crystal particles.

15. The single crystal grains have an average particle size (D ＥＢＳＤ The positive electrode according to claim 14, wherein the diameter is 0.1 μm to 10 μm.

16. The positive electrode according to claim 9, wherein the positive electrode active material in single-particle form is a lithium composite transition metal oxide containing nickel (Ni), cobalt (Co), and manganese (Mn).

17. The positive electrode according to claim 16, wherein the lithium composite transition metal oxide contains 60 mol% or more of nickel (Ni) among the total metals other than lithium.

18. The positive electrode according to claim 16, wherein the lithium composite transition metal oxide has a composition represented by the following chemical formula 1. [Chemical formula 1] Li ａ Ni ｂ Co ｃ Mn ｄ M １ ｅ O ２ In the aforementioned chemical formula 1, M １ is one or more selected from Al, Zr, B, W, Mo, Cr, Nb, Mg, Hf, Ta, La, Ti, Sr, Ba, Ce, Sn, Y, Zn, F, P, and S. 0.90 ≤ a ≤ 1.1, 0.60 ≤ b < 1.0, 0 < c < 0.40, 0 < d < 0.40, 0 ≤ e ≤ 0.10, and b + c + d + e = 1.

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