Positive electrode material, positive electrode comprising same, and lithium secondary battery

Abstract

The present invention relates to a positive electrode material comprising: a first positive electrode active material in the form of a secondary particle in which a plurality of crystal grains are aggregated, the first positive electrode active material comprising an orientation structure in which the long axes of the crystal grains are aligned from the center toward the surface of the secondary particle in at least a part of the secondary particle, and the cobalt concentration at a grain boundary, which is an interface between the grains, is higher than the cobalt concentration inside the grains; and a second positive electrode active material including a central portion having at least one form of a single particle composed of one nodule and a quasi-single particle composed of a composite of at most 30 nodules, and a coating layer formed on the central portion and containing cobalt.

Description

Technical Field

[0001] This application claims the benefit of Korean Patent Application No. 10-2022-0183385, filed on December 13, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0002] The present invention relates to a positive electrode material, a positive electrode and a lithium secondary battery containing the same, and more specifically, to a positive electrode material having a small amount of gas generated at high temperature due to less particle breakage during rolling, excellent life characteristics, and low initial resistance, as well as a positive electrode and a lithium secondary battery containing the positive electrode material. Background Art

[0003] A lithium secondary battery generally includes a positive electrode, a negative electrode, a separator, and an electrolyte, and the positive electrode and the negative electrode include an active material capable of intercalating and deintercalating lithium ions.

[0004] Lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2 or LiMnO4, etc.) or lithium iron phosphate compounds (LiFePO4) have been used as positive electrode active materials for lithium secondary batteries. Among these materials, lithium cobalt oxide has the advantages of high operating voltage and excellent capacity characteristics, but due to the high price and unstable supply of cobalt as a raw material, it is difficult to commercialize lithium cobalt oxide for large-capacity batteries. Lithium nickel oxide has poor structural stability, so it is difficult to achieve sufficient life characteristics. At the same time, lithium manganese oxide has excellent stability, but has the limitation of poor capacity characteristics. Therefore, lithium composite transition metal oxides containing two or more transition metals have been developed to compensate for the limitations of lithium transition metal oxides containing Ni, Co or Mn alone. Among these oxides, lithium nickel cobalt manganese oxide containing Ni, Co and Mn is widely used in electric vehicle batteries.

[0005] Conventional lithium metal oxides are generally in the form of spherical secondary particles in which tens to hundreds of primary particles are aggregated. However, for lithium metal oxides in the form of secondary particles in which many primary particles are aggregated as described above, there is a limitation in that particle crushing of primary particles falling off during rolling during the preparation of the positive electrode is likely to occur, and cracking will occur in the particles during charging and discharging. When particle crushing or cracking of the positive electrode active material occurs, since the contact area with the electrolyte increases, gas generation and degradation of the active material due to side reactions with the electrolyte increase, and as a result, there is a limitation in the degradation of life characteristics.

[0006] In order to solve the above limitations, single-particle cathode active materials composed of single particles have been developed. Single-particle cathode active materials have the advantages of high particle strength and less particle breakage during rolling, thereby achieving excellent life characteristics, but due to the high lithium diffusion resistance inside the particles, the resistance and output characteristics are poor when the particle size increases. Therefore, single particles are currently used in the form of D 50 The small particles of the positive electrode active material are used in the form of small particles of 4 μm. However, when such small particles of the positive electrode active material are used alone, the electrode processability is deteriorated, so a technology of mixing secondary particles and single particles has been proposed. However, when the secondary particles and the single particles are mixed, the secondary particles are severely broken during electrode rolling due to the difference in particle strength between the single particles and the secondary particles, so the effect of suppressing gas generation and improving life is not significant, and thus it is not commercially available. Summary of the invention

[0007] Technical issues

[0008] In order to solve the above-mentioned limitations, one aspect of the present invention provides a positive electrode material, which is obtained by using a mixture of secondary particles and single-particle positive electrode active materials, wherein secondary particles having a specific orientation structure and composition are mixed with single-particle positive electrode active materials having a cobalt coating formed on the surface, thereby achieving excellent life characteristics and lower initial resistance due to less particle breakage during rolling, and reducing the amount of gas generated at high temperatures.

[0009] In addition, another aspect of the present invention provides a positive electrode and a lithium secondary battery including the positive electrode material.

[0010] Technical Solution

[0011] According to one aspect of the present invention, a positive electrode material is provided, which includes: a first positive electrode active material, which is in the form of secondary particles in which a plurality of crystal grains are aggregated, and includes an oriented structure in which the long axes of the crystal grains in at least a portion of the secondary particles are arranged from the center toward the surface of the secondary particles, and the cobalt concentration at the grain boundaries which are interfaces between the crystal grains is higher than the cobalt concentration inside the crystal grains; and a second positive electrode active material, which includes a central portion and a coating, the central portion having at least one of the forms of a single particle consisting of one nodule and a quasi-single particle consisting of a composite of up to 30 nodules, the coating being formed on the central portion and containing cobalt.

[0012] According to another aspect of the present invention, a positive electrode including the positive electrode material of the present invention and a lithium secondary battery including the positive electrode are provided.

[0013] Beneficial Effects

[0014] The positive electrode material of the present invention includes a first positive electrode active material in the form of secondary particles with a specific orientation structure and composition; and a single particle-type second positive electrode active material with a cobalt coating formed on the surface, so that compared with conventional positive electrode materials in which secondary particles and single particles are mixed, the particles are less broken during rolling, the amount of gas generated at high temperature is less, and it has excellent life characteristics and lower initial resistance.

[0015] Since the first positive electrode active material included in the positive electrode material of the present invention includes an oriented structure in which the long axis of the crystal grains is arranged from the center of the secondary particles toward the surface, the lithium diffusion path inside the particles is short, thereby achieving excellent lithium mobility and low resistance characteristics. However, the positive electrode active material with an oriented structure as described above is more serious in particle crushing when the electrode is rolled, compared with the positive electrode active material in the form of non-oriented secondary particles, and in particular, when mixed with a single particle with high particle strength, the particle crushing is further aggravated. When particle crushing of the positive electrode active material occurs, the side reaction with the electrolyte increases, resulting in reduced life characteristics and increased gas generation. However, when a higher cobalt concentration is formed at the grain boundaries of the secondary particles with an oriented structure as in the first positive electrode active material of the present invention, due to the cobalt enriched at the grain boundaries, the particle strength increases, so that even when mixed with a single particle, the particle crushing is less, and the degradation and gas generation of the positive electrode active material can be minimized.

[0016] The second positive electrode active material included in the positive electrode material of the present invention has high particle strength, resulting in less particle breakage during rolling, and has low surface resistance due to the cobalt coating formed on its surface minimizing the electrically inert rock salt phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a scanning electron microscope (SEM) image of a cross section of the lithium composite transition metal oxide prepared in Preparation Example 1.

[0018] Figure 2 is a SEM image of a cross section of the lithium composite transition metal oxide prepared in Preparation Example 3.

[0019] Figure 3 is a SEM image of the lithium composite transition metal oxide prepared in Preparation Example 4. DETAILED DESCRIPTION

[0020] The terms or words used in the present specification and claims should not be construed as limited to the conventional or dictionary meanings, but should be construed as meanings and concepts consistent with the technical spirit based on the principle that the inventor can appropriately define the concepts of the terms in order to interpret the invention in the best manner.

[0021] As used herein, the term "grain" refers to the smallest particle unit that is distinguished as a block without an apparent grain boundary when observed in a field of view at a magnification of 5,000 to 20,000 times using a scanning electron microscope, and may be formed of one crystallite or a plurality of crystallites. In the present invention, the average particle size of the crystal grains can be determined by measuring each particle size distinguished in the cross-sectional SEM data of the positive electrode active material particles, and then calculating the arithmetic mean thereof.

[0022] As used herein, the term "secondary particle" refers to a secondary structure formed by aggregation of a plurality of crystallites.

[0023] As used herein, the term "D 50 ” refers to the particle size at which 50% of the volume cumulative particle size distribution of the measured powder is found. 50 The measurement can be performed using a laser diffraction method. For example, the powder of the positive electrode active material can be dispersed in a dispersion medium and then introduced into a commercially available laser diffraction particle size measuring device (e.g., Microtrac MT 3000) and irradiated with an ultrasonic wave of about 28 kHz at an output of 60 W. Then, a volume cumulative particle size distribution graph can be obtained, and then the particle size corresponding to 50% of the volume cumulative amount can be determined to measure the average particle size D 50 .

[0024] As used herein, the term "oriented structure" refers to a structure in which the major axis of the grains is arranged from the center toward the surface of the secondary particle. In this case, the expression "the major axis of the grains is arranged from the center toward the surface of the secondary particle" means that the angle formed by the shortest line segment connecting the center and the surface of the secondary particle when passing through the corresponding grain and the major axis of the grain is in the range of -15° to 15°.

[0025] As used herein, the term “aspect ratio of a grain” refers to a ratio of a major axis length to a minor axis length of a grain, and the term “average aspect ratio” refers to an arithmetic mean of aspect ratios of grains in a corresponding region.

[0026] As used herein, the term "single particle" refers to a particle consisting of a single nodule. As used herein, the term "quasi-single particle" refers to a particle that is a composite formed of up to 30 nodules.

[0027] As used herein, the term "nodule" refers to a particle unit body constituting a single particle and a quasi-single particle, and the nodule may be a single crystal without a crystal grain boundary, or may be a polycrystal without a grain boundary in appearance when observed in a field of view at a magnification of 5,000 to 20,000 times using a scanning electron microscope (SEM) or electron backscatter diffraction (EBSD). The average particle size of the nodule refers to the arithmetic mean value calculated after measuring the particle sizes of the nodules observed by SEM or EBSD.

[0028] The expression "particle" used herein may include any or all of a single particle, a quasi-single particle, a primary particle, a nodule, and a secondary particle.

[0029] Hereinafter, the present invention will be described in detail.

[0030] <Cathode Materials>

[0031] The positive electrode material of the present invention includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material is in the form of secondary particles in which multiple grains are aggregated, and contains an oriented structure in which the long axes of the grains in at least a portion of the secondary particles are arranged from the center toward the surface of the secondary particles, and the cobalt concentration at the grain boundaries which are the interfaces between the grains is higher than the cobalt concentration inside the grains, and the second positive electrode active material includes a central part and a coating, the central part has at least one of the forms of a single particle composed of one nodule and a quasi-single particle composed of a composite of up to 30 nodules, and the coating is formed on the central part and contains cobalt.

[0032] Preferably, the positive electrode material of the present invention may have a bimodal particle size distribution, wherein the particle size of the first positive electrode active material is larger than the particle size of the second positive electrode active material. When the positive electrode material of the present invention has a bimodal particle size distribution, a high electrode density can be achieved, and thus the battery capacity characteristics can be improved. However, in the case of a second positive electrode active material as a single particle type positive electrode active material, when the particle size increases, the lithium diffusion path in the particle is extended, and thus the resistance and output characteristics may deteriorate, and therefore it is preferred to achieve a high electrode density by making the particle size of the first positive electrode active material in the form of secondary particles larger than the particle size of the second positive electrode active material, while minimizing the degradation of the resistance and output characteristics.

[0033] Specifically, the D of the first positive electrode active material 50 The D of the second positive electrode active material may be 8 μm to 20 μm, preferably 8 μm to 18 μm, and more preferably 8 μm to 15 μm. 50 The D of the first positive electrode active material and the second positive electrode active material may be 2 μm to 7 μm, preferably 2.5 μm to 7 μm, and more preferably 3 μm to 7 μm. 50 When the above range is met, the capacity characteristics, resistance characteristics and output characteristics are better.

[0034] Meanwhile, the first positive electrode active material and the second positive electrode active material may have the same or different compositions. For example, the first positive electrode active material and the second positive electrode active material may each independently comprise a nickel-based lithium composite transition metal oxide represented by the following formula 1:

[0035] [Formula 1]

[0036] Li x [Nia Co b M 1 c M 2 d O 2-y A y

[0037] In the above formula (1), the above M 1 may be at least one element selected from the group consisting of Mn and Al, and may be, for example, Mn or a combination of Mn and Al.

[0038] The above M 2 may be at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B, and Mo.

[0039] In addition, the above A may be at least one element selected from the group consisting of F, Cl, Br, I, At, and S.

[0040] The above x represents the ratio of the number of moles of Li to the total number of moles of transition metals, where x may satisfy 0.98 ≤ x ≤ 1.20, preferably 0.99 ≤ x ≤ 1.10, and more preferably 1.0 ≤ x ≤ 1.10.

[0041] The above a represents the ratio of the number of moles of Ni to the total number of moles of the remaining metals other than lithium, where a may satisfy 0 < a < 1, preferably 0.3 ≤ a < 1, more preferably 0.6 ≤ a < 1, even more preferably 0.8 ≤ a < 1, and still even more preferably 0.85 ≤ a < 1.

[0042] The above b represents the ratio of the number of moles of Co to the total number of moles of the remaining metals other than lithium, where b may satisfy 0 < b < 1, preferably 0 < b < 0.7, more preferably 0 < b < 0.4, even more preferably 0 < b < 0.2, and still even more preferably 0 < b ≤ 0.1.

[0043] The above c represents the ratio of the number of moles of M 1 to the total number of moles of the remaining metals other than lithium, where c may satisfy 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, even more preferably 0 < c < 0.2, and still even more preferably 0 < c ≤ 0.1.

[0044] The above d represents the ratio of the number of moles of M 2 to the total number of moles of the remaining metals other than lithium, where d may satisfy 0 ≤ d ≤ 0.2, preferably 0 ≤ d ≤ 0.15, and more preferably 0 ≤ d ≤ 0.10.

[0045] The above y represents the ratio of the number of moles of the element A substituted at the oxygen position, wherein y may satisfy 0≤y≤0.2, preferably 0≤y≤0.15, and more preferably 0≤y≤0.10.

[0046] Meanwhile, the first cathode active material and the second cathode active material may be included in a weight ratio of 90:10 to 50:50, preferably 80:20 to 50:50, more preferably 70:30 to 50:50. When the mixing ratio of the first cathode active material and the second cathode active material satisfies the above range, high electrode density can be achieved.

[0047] As in the positive electrode material of the present invention, when a first positive electrode active material having an oriented structure in which grains are arranged from the center toward the surface of the secondary particles and having a cobalt concentration at the grain boundaries higher than the cobalt concentration inside the grains and a single-particle second positive electrode active material having a cobalt coating formed on the surface are used together, not only are the secondary particles less likely to break during rolling, but even if particle breakage occurs, the grain surface is coated with cobalt and there are fewer side reactions with the electrolyte, so that the amount of gas generated at high temperatures is less and the life characteristics are excellent.

[0048] Next, the first positive electrode active material and the second positive electrode active material constituting the positive electrode material of the present invention will be described in more detail.

[0049] First positive electrode active material

[0050] The first positive electrode active material is in the form of a secondary particle in which a plurality of crystal grains are aggregated, and contains an orientation structure in which the long axis of the crystal grains is arranged from the center toward the surface of the secondary particle in at least a portion of the secondary particle. In this case, the expression "the long axis of the crystal grain is arranged from the center toward the surface of the secondary particle" means that the angle formed by the shortest line segment connecting the center and the surface of the secondary particle when passing through the corresponding crystal grain and the long axis of the crystal grain is in the range of -15° to 15°. The long axis of the crystal grain refers to the longest line segment in the straight line connecting two points on the surface of the crystal grain when passing through the center of the crystal grain. In the secondary particles of the positive electrode active material, the interface between the crystal grains becomes a diffusion channel for lithium ions. When the crystal grains are arranged from the center to the surface of the secondary particle, the diffusion path of the lithium ions inside the secondary particle is shortened, so the lithium mobility is increased, and thus the output and / or resistance characteristics can be improved.

[0051] At the same time, the angle formed by the long axis of the grain arranged from the center toward the surface of the secondary particle and the a-axis direction of the crystal structure can be within -15° to 15°, preferably within -10° to 10°. Since lithium ions move along the a-axis direction in the grain, when the long axis of the grain forms an angle of -15° to 15° with the a-axis direction of the crystal structure, the insertion and extraction of lithium ions can be promoted, thereby improving the output and / or resistance characteristics.

[0052] At the same time, the aspect ratio of the grains whose long axes are arranged from the center toward the surface of the secondary particles can be 1.5 to 15, preferably 2 to 15, and more preferably 4 to 15. When the aspect ratio of the grains satisfies the above range, the contraction and expansion of the grains during charging and discharging mainly occur in the short axis direction perpendicular to the orientation, thereby effectively suppressing the occurrence of cracking due to uneven contraction and expansion of the grains in the secondary particles.

[0053] Meanwhile, the first positive active material is not limited thereto but may have a core-shell structure including a core portion where crystal grains are aggregated without a particular orientation and a shell portion where major axes of the crystal grains are arranged from the center toward the surface of the secondary particle.

[0054] The core portion is a region where crystal grains are randomly aggregated without a particular orientation, and is formed at the center of the secondary particle. The core portion may be a portion formed as a seed during a coprecipitation reaction for forming a precursor for a positive electrode active material, for example, when the radius of the secondary particle from the center of the secondary particle is referred to as R, the core portion may be a region located at a distance of 1 / 3R from the center of the secondary particle, or a region located at a distance of 1 / 4R from the center of the secondary particle.

[0055] The grains in the core portion may have a nearly spherical shape, and may have an aspect ratio of 0.7 to 1.3, preferably 0.8 to 1.2.

[0056] Next, the shell portion is a region formed outside the core portion and in which the crystal grains are arranged in an oriented structure. The shell portion may be a portion formed when the particles grow during the coprecipitation reaction for forming a precursor for a positive electrode active material, for example, when the radius of the secondary particle from the center of the secondary particle is referred to as R, the shell portion may be a region from 1 / 3R to R of the secondary particle or a region from 1 / 4R to R of the secondary particle.

[0057] The crystal grains in the shell portion may have a rod shape, and may have an aspect ratio of 1.5 to 15, preferably 2 to 15, and more preferably 4 to 15.

[0058] Meanwhile, in the first positive electrode active material of the present invention, the average particle size of the crystal grains may be 0.05 μm to 4 μm, preferably 0.1 μm to 3 μm, and more preferably 0.1 μm to 2 μm. If the average particle size of the crystal grains is too large, a rock salt phase may be formed, deteriorating the resistance characteristics and life characteristics, and if the average particle size of the crystal grains is too small, the contact area with the electrolyte may increase, so that degradation may occur rapidly.

[0059] Meanwhile, the first positive electrode active material may include a nickel-based lithium composite transition metal oxide, for example, may include a nickel-based lithium composite transition metal oxide represented by the following Formula 1-1:

[0060] [Formula 1-1]

[0061] Li x1 [Ni a1 Co b1 M 1 c1 M 2 d1 ]O 2-y1 A y1

[0062] In the above formula 1-1, the above M 1 It may be at least one element selected from the group consisting of Mn and Al, and may be, for example, Mn or a combination of Mn and Al.

[0063] The above M 2 It can be at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo.

[0064] In addition, the above-mentioned A may be at least one element selected from the group consisting of F, Cl, Br, I, At and S.

[0065] The above x1 represents the ratio of the molar number of Li to the total molar number of transition metals, and may satisfy 0.98≤x1≤1.20, preferably 0.99≤x1≤1.10, and more preferably 1.0≤x1≤1.10.

[0066] The above a1 represents the ratio of the molar number of Ni to the total molar number of the remaining metals except lithium, and may satisfy 0.6≤a1≤0.9, preferably 0.7≤a1≤0.9, more preferably 0.8≤a1≤0.9, and even more preferably 0.8≤a1≤0.86.

[0067] The above b1 represents the ratio of the molar number of Co to the total molar number of the remaining metals except lithium, and may satisfy 0.01≤b1<0.4, preferably 0.01≤b1<0.3, more preferably 0.01≤b1<0.2, and even more preferably 0.01≤b1≤0.1.

[0068] The above c1 represents M 1 The ratio of the molar number of to the total molar number of the remaining metals except lithium, and may satisfy 0.01≤c1<0.4, preferably 0.01≤c1<0.3, more preferably 0.01≤c1<0.2, and even more preferably 0.01≤c1≤0.1.

[0069] The above d1 represents M 2The ratio of the molar number of to the total molar number of the remaining metals except lithium, and may satisfy 0≤d1≤0.2, preferably 0≤d1≤0.15, and more preferably 0≤d1≤0.10.

[0070] The above y1 represents the ratio of the number of moles of the A element substituted at the oxygen position, and may satisfy 0≤y1≤0.2, preferably 0≤y1≤0.15, and more preferably 0≤y1≤0.10.

[0071] At the same time, the first positive active material of the present invention is characterized in that the cobalt concentration at the grain boundary, which is the interface between the grains, is higher than the cobalt concentration inside the grains. In this case, the cobalt concentration refers to the molar ratio of cobalt in the remaining metals other than lithium. That is, in the first positive active material, cobalt is enriched on the grain boundaries. When cobalt is enriched on the grain boundaries as described above, although an oriented structure is included, the particle crushing of the first positive active material is reduced during rolling, and even if particle crushing occurs due to rolling, the side reaction with the electrolyte is minimized. Therefore, compared with conventional positive active materials having an oriented structure, when the first positive active material is applied, excellent high temperature characteristics can be achieved.

[0072] At the same time, the first positive electrode active material as described above can be prepared by injecting a lithium composite transition metal oxide into a coating solution containing a cobalt element and then performing a heat treatment, wherein the lithium composite transition metal oxide is in the form of secondary particles in which multiple grains are aggregated, and contains an oriented structure in which the long axis of the grains in at least a portion of the secondary particles is arranged from the center toward the surface of the secondary particles.

[0073] In this case, the lithium composite transition metal oxide containing an oriented structure can be prepared by purchasing a commercially available product, or can be prepared by using a method for preparing a lithium composite transition metal oxide known in the art. For example, the lithium composite transition metal oxide containing an oriented structure can be prepared by mixing a precursor for a positive electrode active material and a lithium raw material and then sintering the mixture.

[0074] In order to prepare a positive electrode active material having an oriented structure such as the present invention, a positive electrode active material precursor having an oriented structure in which primary particles are arranged from the center toward the surface of the secondary particles should be used. The aggregation form of the primary particles of the positive electrode active material precursor is affected by the pH, stirring speed, reaction temperature, etc. during the coprecipitation reaction. Therefore, when preparing a positive electrode active material precursor, the pH, stirring speed, reaction temperature, etc. can be appropriately adjusted to form a positive electrode active material precursor having an oriented structure, and by using the precursor, a lithium composite transition metal oxide having an oriented structure can be prepared.

[0075] The lithium raw material and the positive electrode active material precursor may be mixed so that the molar ratio of Li to the total transition metal in the precursor is 1: 1 to 1.2: 1, preferably 1: 1 to 1.1: 1. When the mixing ratio of the lithium raw material and the transition metal in the positive electrode active material precursor satisfies the above range, the crystal structure of the positive electrode active material is well developed, and thus a positive electrode active material having excellent capacity characteristics and structural stability can be prepared.

[0076] Examples of lithium raw materials may include lithium-containing carbonates (e.g., lithium carbonate, etc.), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O), etc.), hydroxides (e.g., lithium hydroxide, etc.), nitrates (e.g., lithium nitrate (LiNO3)), etc.), chlorides (e.g., lithium chloride (LiCl)), etc., and any one of them alone or a mixture of two or more thereof may be used.

[0077] The calcination may be performed at an appropriate temperature in consideration of the composition of the lithium composite transition metal oxide, for example, at 600 to 1,000° C., preferably 700 to 900° C. The calcination time may be, for example, 5 to 30 hours, preferably 8 to 15 hours, but is not limited thereto.

[0078] Next, the lithium composite transition metal oxide including the above-mentioned oriented structure is added to a coating solution containing a cobalt element, and then heat-treated, so that cobalt is enriched on the grain boundaries of the lithium composite transition metal oxide.

[0079] The coating solution containing the cobalt element can be formed by dissolving at least one selected from the group consisting of CoNO3, Co(NO3)2.6H2O, CoCl2, CoSO4, Co(OCOCH3)2.4H2O and Co(OH)2 in a solvent such as water or ethanol.

[0080] As described above, when wet coating is performed by mixing a coating solution and a lithium composite transition metal oxide and then heat treating the mixture, the cobalt element contained in the coating solution can penetrate not only the surface of the secondary particles of the lithium composite transition metal oxide, but also the interface (grain boundary) between the grains, so that the cobalt concentration at the grain boundary can be higher than the cobalt concentration inside the grain.

[0081] Meanwhile, the heat treatment may be performed in the range of 300°C to 800°C, preferably 400°C to 700°C, and more preferably 500°C to 650°C. When the heat treatment temperature satisfies the above range, the cobalt element contained in the coating solution may be enriched at the grain boundaries, and a higher cobalt concentration is formed at the grain boundaries than inside the grains. If the first heat treatment temperature is too low, coating cannot be performed smoothly, and if the first heat treatment temperature is too high, cobalt diffuses into the grains without being enriched at the grain boundaries.

[0082] Second positive electrode active material

[0083] The second positive electrode active material includes a core portion in the form of a single particle and / or a quasi-single particle, and a coating layer formed on the core portion and containing cobalt.

[0084] The central part is a single particle consisting of a single nodule and / or a quasi-single particle which is a composite of up to 30 nodules, preferably 2 to 20 nodules, more preferably 2 to 10 nodules.

[0085] The second positive electrode active material having a central portion in the form of a single particle and / or a quasi-single particle has a higher particle strength than the existing positive electrode active material in the form of secondary particles aggregated by tens to hundreds of primary particles, so the particles are less broken during rolling. In addition, since the number of nodules constituting the positive electrode active material particles in the second positive electrode active material is small, the change caused by the volume expansion and contraction of the nodules during charging and discharging is small, so the occurrence of cracks in the particles is significantly reduced.

[0086] Meanwhile, the central portion may include a nickel-based lithium composite transition metal oxide represented by the following Formula 1-2:

[0087] [Formula 1-2]

[0088] Li x2 [Ni a2 Co b2 M 1 c2 M 2 d2 ]O 2-y2 A y2

[0089] In the above formula 1-2, the above M 1 It may be at least one element selected from the group consisting of Mn and Al, preferably Mn, Al or a combination thereof, more preferably Mn or Mn and Al.

[0090] The above M 2 It may be at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, preferably, it may be at least one element selected from the group consisting of Zr, Y, Mg and Ti, more preferably, it may be Zr, Y or a combination thereof. It does not necessarily contain M 2 elements, but when included in appropriate amounts, M 2 The elements may play a role in promoting grain growth during firing or improving the stability of the crystal structure.

[0091] The above x2 represents the molar ratio of lithium in the lithium nickel-based oxide and can satisfy 0.8 ≤ x2 ≤ 1.2, 0.85 ≤ x2 ≤ 1.15 or 0.9 ≤ x2 ≤ 1.2. When the molar ratio of lithium satisfies the above range, the crystal structure of the positive electrode active material can be stably formed.

[0092] The above a2 represents the molar ratio of nickel among all metals other than lithium and can satisfy 0.8 ≤ a2 < 1, 0.82 ≤ a2 ≤ 1 or 0.83 ≤ a2 ≤ 1. When the molar ratio of nickel satisfies the above range, high energy density can be exhibited and high capacity can be achieved.

[0093] The above b2 represents the molar ratio of cobalt among all metals other than lithium and can satisfy 0 < b2 < 0.2, 0 < b2 < 0.18 or 0.01 ≤ b2 ≤ 0.17. When the molar ratio of cobalt satisfies the above range, good resistance characteristics and output characteristics can be achieved.

[0094] The above c2 represents the molar ratio of element M among all metals other than lithium 1 and can satisfy 0.01 ≤ c2 ≤ 0.2, 0.01 ≤ c2 ≤ 0.18 or 0.01 ≤ c2 ≤ 0.17. When the molar ratio of element M 1 satisfies the above range, the positive electrode active material exhibits excellent structural stability.

[0095] The above d2 represents the ratio of the number of moles of M 2 to the total number of moles of the remaining metals other than lithium and can satisfy 0 ≤ d2 ≤ 0.2, preferably 0 ≤ d2 ≤ 0.15, more preferably 0 ≤ d2 ≤ 0.10.

[0096] The above y2 represents the ratio of the number of moles of element A substituted at the oxygen position and can satisfy 0 ≤ y2 ≤ 0.2, preferably 0 ≤ y2 ≤ 0.15, more preferably 0 ≤ y2 ≤ 0.10.

[0097] Meanwhile, the second positive electrode active material of the present invention includes a cobalt-containing coating on the central portion including single particles and / or quasi-single particles.

[0098] Generally, the positive electrode active material in the form of single particles and / or quasi-single particles is prepared by firing at a higher temperature than when preparing the positive electrode active material in the form of secondary particles. When the firing temperature is high, the electro-inactive rock salt phase on the particle surface increases, thereby increasing the resistance of the positive electrode active material. However, when a cobalt-containing coating is formed on the surface of single particles and / or quasi-single particles as in the present invention, recrystallization occurs through reaction with cobalt during the coating formation process, thereby reducing the rock salt phase on the surface of single particles and / or quasi-single particles, and thus improving the resistance characteristics.

[0099] Specifically, the coating layer may be an oxide containing lithium and cobalt, and may have a composition represented by, for example, the following Formula 2:

[0100] [Formula 2]

[0101] Li z Co 1-w M 3 w O2

[0102] In the above formula 2, the above M 3 It may be at least one selected from the group consisting of Ni, Mn, Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, and may satisfy 0.8≤z≤1.2 and 0≤w≤0.2. Preferably, the M 3 It may be at least one selected from the group consisting of Ni, Mn, Al, Ti, Zr, and Mg, and may satisfy 0.8≤z≤1.1 and 0≤w≤0.1.

[0103] When the coating layer satisfies the above composition, the effects of improving initial resistance characteristics and high temperature life can be obtained.

[0104] Meanwhile, the shape or area of ​​the coating is not particularly limited. For example, the coating may be in the form of a continuous film surrounding the entire surface of the single particle and / or quasi-single particle constituting the central portion, or may be in the form of particles discontinuously distributed on the single particle and / or quasi-single particle. In addition, the area of ​​the coating may be 10% to 100%, 10% to 80%, or 20% to 70% based on the total surface area of ​​the central portion.

[0105] At the same time, the average particle size of the nodules of the second positive electrode active material of the present invention can be 0.5-3 μm, preferably 0.8-2.5 μm, and more preferably 0.8-1.5 μm. When the average particle size of the nodules meets the above range, a single particle and / or quasi-single particle positive electrode active material with excellent electrochemical properties can be formed. If the average particle size of the nodules is too small, the number of aggregates of the nodules forming the central part increases, thereby reducing the effect of suppressing the occurrence of particle crushing during rolling, and if the average particle size of the nodules is too large, the lithium diffusion path inside the nodules is extended, thereby increasing resistance and reducing output characteristics.

[0106] Meanwhile, the average particle size D of the second positive electrode active material 50 The D of the second positive electrode active material may be 2 μm to 7 μm, preferably 2.5 μm to 7 μm, and more preferably 3 μm to 7 μm. 50 If the D is too small, the slurry will aggregate, making it difficult to prepare the electrode, the electrolyte impregnation will deteriorate, and the electrochemical properties will deteriorate.50 When it is too large, the resistance increases and the output characteristics deteriorate.

[0107] In addition, the average crystallite size of the second positive electrode active material can be 150nm to 300nm, 200nm to 280nm, or 200nm to 250nm. When the average crystallite size meets the above range, the generation of rock salt phase can be reduced when preparing lithium nickel oxide, so that single particle and / or quasi-single particle positive electrode active materials with excellent resistance characteristics can be prepared. Generally, single particle and / or quasi-single particle positive electrode active materials are prepared by increasing the size of nodules by increasing the sintering temperature, and there is the following limitation: when only the nodule size is increased when the crystal size is small, a rock salt phase is formed on the surface of the nodule, thereby increasing the resistance. However, when the average crystallite size and the average particle size of the nodules increase together, the formation of the rock salt phase is minimized, thereby obtaining the effect of suppressing the increase in resistance.

[0108] Meanwhile, the second positive electrode active material can be prepared by mixing a positive electrode active material precursor and a lithium raw material and sintering the mixture to form single particles and / or quasi-single particles, mixing the single particles and / or quasi-single particles with a coating raw material containing Co, and then heat treating the mixture.

[0109] In this case, the positive electrode active material precursor may be prepared by purchasing a commercially available precursor such as nickel-cobalt-manganese hydroxide or by a precursor preparation method known in the art such as a coprecipitation method.

[0110] Preferably, the positive electrode active material precursor used herein may be a transition metal hydroxide containing nickel and cobalt and having a Ni content of 80 mol % or more in all transition metals, more preferably, a nickel cobalt manganese hydroxide having a Ni content of 80 mol % or more. When the nickel content in the transition metal precursor satisfies the above range, high capacity characteristics can be achieved.

[0111] As lithium raw materials, lithium-containing sulfates, nitrates, acetates, carbonates, oxalates, citrates, halides, hydroxides or oxyhydroxides can be used. For example, Li2CO3, LiNO3, LiNO2, LiOH, LiOH·H2O, LiH, LiF, LiCl, LiBr, LiI, CH3COOLi, Li2O, Li2SO4, CH3COOLi, Li3C6H5O7 or mixtures thereof can be used.

[0112] Meanwhile, the lithium raw material and the positive electrode active material precursor may be mixed so that the molar ratio of Li to the total metal in the precursor is 1: 1 to 1.1: 1, preferably 1.02: 1 to 1.05: 1. When the mixing ratio of the lithium raw material and the metal in the positive electrode active material precursor satisfies the above range, the layered crystal structure of the positive electrode active material is well developed, and thus a positive electrode active material having excellent capacity characteristics and structural stability can be prepared.

[0113] At the same time, the calcination is carried out at a temperature at which single particles and / or quasi-single particles can be formed. In order to form single particles and / or quasi-single particles, the calcination should be carried out at a higher temperature than when preparing conventional positive electrode active materials in the form of secondary particles. For example, in the case of the same precursor composition, the calcination should be carried out at a temperature 30°C to 100°C higher than when preparing conventional positive electrode active materials in the form of secondary particles. The calcination temperature for forming single particles and / or quasi-single particles can vary depending on the metal composition in the precursor. For example, when a high-Ni lithium nickel oxide having a nickel (Ni) content of 80 mol% or more is to be formed into single particles and / or quasi-single particles, the primary calcination temperature can be about 800°C to about 1,000°C, preferably about 800°C to about 950°C, and more preferably about 800°C to about 900°C. When the calcination temperature satisfies the above range, single particles and / or quasi-single particles with excellent electrochemical properties can be prepared. When the firing temperature is less than 800° C., the positive electrode active material is prepared in the form of secondary particles, and when the temperature is greater than 1,000° C., the firing is excessively performed, and thus a layered crystal structure cannot be properly formed, resulting in deterioration of electrochemical characteristics.

[0114] In addition, calcination can be carried out in an oxygen atmosphere for 6 hours to 35 hours, preferably 6 hours to 20 hours, and more preferably 6 hours to 12 hours. When the calcination time meets the above range, single particles and / or quasi-single particles can be formed. When the calcination time is too short, the particle growth is insufficient, so that lithium nickel oxides in the form of secondary particles are formed. When the time is too long, a rock salt phase may appear, resulting in degradation of the electrochemical properties of the active material. In this specification, an oxygen atmosphere refers to an atmosphere containing an amount of oxygen sufficient for calcination, and the atmosphere includes an air atmosphere. In particular, it is preferred to calcination in an atmosphere where the oxygen partial pressure is higher than that of the air atmosphere.

[0115] Meanwhile, as the coating raw material containing Co, cobalt hydroxide or the like may be used, but the present invention is not limited thereto.

[0116] The method of mixing the single particles and / or quasi-single particles with the Co-containing coating raw material is not particularly limited, and various coating methods known in the art, such as dry coating and wet coating, can be applied.

[0117] Meanwhile, the heat treatment may be performed at, for example, 300° C. to 800° C., preferably 600° C. to 750° C., for 5 hours to 20 hours, preferably 10 hours to 12 hours.

[0118] <Positive electrode>

[0119] Next, the positive electrode of the present invention will be described.

[0120] The positive electrode includes the positive electrode material of the present invention. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the positive electrode current collector, wherein the positive electrode active material layer includes the positive electrode material of the present invention.

[0121] Since the positive electrode material is the same as described above, a detailed description thereof will be omitted, and only the remaining configuration will be described in detail below.

[0122] The positive electrode current collector may include a metal with high conductivity, without particular limitation, as long as the positive electrode active material layer is easily adhered thereto and is not reactive within the voltage range of the battery. As the positive electrode current collector, for example, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum or stainless steel surface-treated with one of carbon, nickel, titanium, or silver, etc., may be used. Moreover, the thickness of the positive electrode current collector may generally be 3 μm to 500 μm, and fine concavoconvexities may be formed on the surface of the current collector to improve the adhesion of the positive electrode active material. For example, the positive electrode current collector may be used in various forms, such as films, sheets, foils, nets, porous bodies, foams, and non-woven fabrics.

[0123] The positive electrode active material layer may optionally further contain a conductive agent, a binder, and the like together with the positive electrode material, if necessary.

[0124] In this case, the content of the positive electrode material may be 80 wt % to 99 wt %, more specifically 85 wt % to 98.5 wt % relative to the total weight of the positive electrode active material layer. When the content of the positive electrode active material is within the above range, excellent capacity characteristics may be obtained.

[0125] The conductive agent is used to provide conductivity to the electrode, wherein any conductive agent can be used without particular limitation, as long as it has suitable electronic conductivity without causing adverse chemical changes in the battery. Specific examples of the conductive agent can be: graphite, such as natural graphite or artificial graphite; carbon materials, such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; powders or fibers of metals such as copper, nickel, aluminum and silver; conductive tubes, such as carbon nanotubes; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive polymers, such as polyphenylene derivatives, and any one of them or a mixture of two or more thereof can be used. The content of the conductive agent can be 0.1 wt % to 15 wt % based on the total weight of the positive electrode active material layer.

[0126] The binder improves the adhesion between the positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples of the binder can be: polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid and hydrogen are replaced by Li, Na or Ca polymers or various copolymers thereof, and any one or a mixture of two or more thereof can be used. Based on the total weight of the positive electrode active material layer, the content of the binder can be 0.1 wt % to 15 wt %.

[0127] In addition to using the above-mentioned positive electrode material of the present invention, the positive electrode can be prepared according to a typical method for preparing a positive electrode. Specifically, a positive electrode slurry composition is coated on a positive electrode collector, and then the positive electrode collector is dried and rolled to manufacture a positive electrode, and the positive electrode slurry composition is prepared by dissolving or dispersing a binder, a conductive agent and a dispersant as necessary and a positive electrode material in a solvent.

[0128] The solvent may be a commonly used solvent in the art. The solvent may include dimethyl sulfoxide (DMSO), isopropanol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone or water, and any one thereof or a mixture of two or more thereof may be used. If the solvent can dissolve or disperse the positive electrode active material, the conductive agent, the binder and the dispersant in consideration of the coating thickness and manufacturing yield of the slurry, and can achieve a viscosity that can provide excellent thickness uniformity during the subsequent coating of the positive electrode, the amount of the solvent may be sufficient.

[0129] In addition, as another method, the positive electrode may be prepared by casting the positive electrode slurry composition on a separate support and then laminating a film separated from the support on a positive electrode current collector.

[0130] <Electrochemical Device>

[0131] In the present invention, an electrochemical device including a positive electrode can be manufactured. The electrochemical device can be specifically a battery or a capacitor, and more specifically, a lithium secondary battery.

[0132] The lithium secondary battery may include a positive electrode, a negative electrode disposed opposite to the positive electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte. Since the positive electrode is the same as above, its detailed description will be omitted, and only the remaining components will be described in detail below.

[0133] In addition, the lithium secondary battery may further optionally include a battery container accommodating an electrode assembly of a positive electrode, a negative electrode, and a separator, and a sealing member for sealing the battery container.

[0134] In a lithium secondary battery, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0135] The negative electrode current collector is not particularly limited as long as it has high conductivity without causing adverse chemical changes in the battery, for example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, copper or stainless steel surface-treated with one of carbon, nickel, titanium or silver, and aluminum-cadmium alloy can be used. Moreover, the thickness of the negative electrode current collector can generally be 3 μm to 500 μm, and as in the case of the positive electrode current collector, fine concavoconvexities can be formed on the surface of the negative electrode current collector to enhance the adhesion of the negative electrode active material. For example, the negative electrode current collector can be used in various shapes, such as a film, a sheet, a foil, a net, a porous body, a foam body, and a non-woven fabric body.

[0136] The negative electrode active material layer may optionally contain a binder and a conductive agent in addition to the negative electrode active material.

[0137] As the negative electrode active material, a compound capable of reversibly intercalating and deintercalating lithium can be used. Specific examples of the negative electrode active material may be: carbonaceous materials such as artificial graphite, natural graphite, graphitized carbon fiber, and amorphous carbon; metal compounds capable of alloying with lithium, such as Si, Al, Sn, Pb, Zn, Bi, In, Mg, Ga, Cd, Si alloy, Sn alloy, or Al alloy; metal oxides that can be doped and dedoped with lithium, such as SiO β (0<β<2), SnO2, vanadium oxide and lithium vanadium oxide; or a composite comprising a metal compound and a carbonaceous material, such as a Si-C composite or a Sn-C composite, and any one of them or a mixture of two or more thereof can be used. In addition, a metallic lithium film can be used as a negative electrode active material. In addition, both low-crystalline carbon and high-crystalline carbon can be used as carbon materials. Typical examples of low-crystalline carbon can be soft carbon and hard carbon, and typical examples of high-crystalline carbon can be irregular, planar, flaky, spherical or fibrous natural graphite or artificial graphite, Kish graphite, pyrolytic carbon, mesophase pitch-based carbon fibers, mesophase carbon microbeads, mesophase pitch and high-temperature calcined carbon, such as coke derived from petroleum or coal tar pitch.

[0138] The negative electrode active material may be contained in an amount of 80 wt % to 99 wt % based on the total weight of the negative electrode active material layer.

[0139] The binder is a component that helps to bind the conductive agent, the active material and the current collector, wherein the binder is generally added in an amount of 0.1 wt % to 10 wt % based on the total weight of the negative electrode active material layer. Examples of binders may include polyvinylidene fluoride (PVDF), polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene propylene diene monomer rubber (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile rubber, fluororubber and various copolymers thereof.

[0140] The conductive agent is a component for further improving the conductivity of the negative electrode active material, wherein the added amount of the conductive agent can be 10% by weight or less, for example, 5% by weight or less, based on the total weight of the negative electrode active material layer. The conductive agent is not particularly limited as long as it has conductivity and does not cause adverse chemical changes in the battery. 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 or metal fibers; fluorocarbons; metal powders, such as aluminum powder or nickel powder; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium oxide; or conductive materials such as polyphenylene derivatives, etc. can be used.

[0141] The negative electrode active material layer may be prepared, for example, by coating a negative electrode slurry composition prepared by dissolving or dispersing an optional binder and a conductive agent and a negative electrode active material in a solvent on a negative electrode collector and drying the coated negative electrode collector, or may be prepared by casting the negative electrode slurry composition on a separate support and then laminating a film separated from the support on the negative electrode collector.

[0142] In lithium secondary batteries, the diaphragm separates the negative electrode from the positive electrode and provides a path for the movement of lithium ions, wherein any diaphragm can be used as a diaphragm without particular limitation, as long as it is commonly used in lithium secondary batteries, in particular, a diaphragm having high moisture retention capacity for electrolytes and low resistance to the transmission of electrolyte ions can be used. Specifically, a porous polymer film can be used, such as a porous polymer film prepared by a polyolefin polymer (such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylate copolymer), or a laminated structure having more than two layers thereof. Moreover, a typical porous nonwoven fabric can be used, for example, a nonwoven fabric formed by high melting point glass fiber or polyethylene terephthalate fiber. In addition, in order to ensure heat resistance or mechanical strength, a coated diaphragm including a ceramic component or a polymer material can be used, and a diaphragm with a single layer or multilayer structure can be optionally used.

[0143] In addition, the electrolyte used in the present invention may include an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel-type polymer electrolyte, a solid inorganic electrolyte, or a molten inorganic electrolyte that can be used to manufacture a lithium secondary battery, but is not limited thereto.

[0144] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0145] Any organic solvent can be used as the organic solvent without particular limitation, as long as it can act as a medium through which ions participating in the electrochemical reaction of the battery can move. Specifically, as the organic solvent, ester solvents such as methyl acetate, ethyl acetate, γ-butyrolactone and ε-caprolactone can be used; ether solvents such as dibutyl ether or tetrahydrofuran; ketone solvents such as cyclohexanone; aromatic hydrocarbon solvents such as benzene and fluorobenzene; or carbonate solvents such as dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC) and propylene carbonate (PC); alcohol solvents such as ethanol and isopropanol; nitriles such as R-CN (wherein R is a linear, branched or cyclic C2-C20 hydrocarbon group, and may include a double bond aromatic ring or an ether bond); amides such as dimethylformamide; dioxolanes such as 1,3-dioxolane; or sulfolanes. Among these solvents, carbonate solvents can be used. For example, a mixture of cyclic carbonates (e.g., ethylene carbonate or propylene carbonate) with high ionic conductivity and high dielectric constant and low viscosity straight-chain carbonate compounds (e.g., ethyl methyl carbonate, dimethyl carbonate or diethyl carbonate) that can improve the charge and discharge performance of the battery can be used.

[0146] The lithium salt can be used without particular limitation as long as it is a compound capable of providing lithium ions used in a lithium secondary battery. Specifically, the anion of the lithium salt can be selected from F - , Cl - Br - ,I - 、NO3 - 、N(CN)2 - 、BF4 - CF3CF2SO3 - 、(CF3SO2)2N - 、(FSO2)2N - CF3CF2(CF3)2CO - 、(CF3SO2)2CH - 、(SF5)3C - 、(CF3SO2)3C - CF3(CF2)7SO3 - CF3CO2 -、CH3CO2 - 、SCN - and (CF3CF2SO2)2N - At least one of the group consisting of, and as the lithium salt, LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI or LiB(C2O4)2, etc. can be used. It is preferred to use a lithium salt with a concentration range of 0.1M to 2.0M. When the concentration of the lithium salt is within the above range, the electrolyte can have suitable conductivity and viscosity, thereby showing excellent performance, and lithium ions can be effectively moved.

[0147] As described above, the lithium secondary battery including the cathode active material of the present invention exhibits excellent capacity characteristics and life characteristics, and can be used in various fields such as portable devices (eg, mobile phones, notebook computers, and digital cameras) or electric vehicles.

[0148] Example

[0149] Hereinafter, the present invention will be described in detail according to specific examples. However, the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments set forth herein. On the contrary, these example embodiments are provided so that this description will be sufficient and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0150] Preparation Example 1

[0151] NiSO 4 , CoSO 4 , and MnSO 4 were mixed in distilled water in such amounts that the molar ratio of nickel:cobalt:manganese was 8:1:1 to prepare an aqueous transition metal solution.

[0152] Then, after deionized water was put into the reactor, dissolved oxygen in the water was removed by purging the reactor with nitrogen, and NaOH was added to maintain the pH in the reactor at 11.

[0153] Then, while adding the transition metal aqueous solution, the NaOH aqueous solution and the NH4OH aqueous solution to the reactor, a coprecipitation reaction was carried out at a reaction temperature of 50°C, a pH of 11 and a stirring speed of 400 rpm for 30 hours to prepare a granular material with an average particle size (D 50 ) is 12 μm for the positive electrode active material precursor Ni 0.8 Co 0.1 Mn 0.1 (OH)2. In this case, the molar ratio of transition metal ions to NH4OH is 1:1.10.

[0154] The positive electrode active material precursor and LiOH were mixed so that the molar ratio of Li:transition metal (Ni+Co+Mn) was 1.02:1, calcined at 730° C. for 20 hours, and then washed and dried to prepare a lithium composite transition metal oxide.

[0155] Figure 1 A scanning electron microscope (SEM) image obtained by measuring a cross section of the lithium composite transition metal oxide prepared as described above is shown. Figure 1 It can be confirmed that the lithium composite transition metal oxide prepared by this method is in the form of secondary particles in which a plurality of crystal grains are aggregated, and the major axis of the crystal grains is arranged from the center toward the surface of the secondary particle.

[0156] Preparation Example 2

[0157] Co(NO3)2·6H2O was dissolved in deionized water (DI water) to prepare a Co-containing coating solution.

[0158] The lithium composite transition metal oxide prepared in Preparation Example 1 was added to the coating solution, stirred at 500 rpm for 3 hours, and then heat-treated at 600° C. to prepare a positive electrode active material.

[0159] Preparation Example 3

[0160] A lithium composite transition metal oxide was prepared in the same manner as in Preparation Example 1, except that an aqueous transition metal solution, an aqueous NaOH solution and an aqueous NH4OH solution were added during the preparation of the precursor for the positive electrode active material so that the molar ratio of the transition metal to the NH4OH was 1:0.8, and a coprecipitation reaction was carried out at a reaction temperature of 60°C, a pH of 11, and a stirring speed of 300 rpm for 30 hours, and calcined at 750°C.

[0161] Figure 2 A scanning electron microscope (SEM) image obtained by measuring a cross section of the lithium composite transition metal oxide prepared as described above is shown. Figure 2 , it can be confirmed that the lithium composite transition metal oxide prepared by the above method is in the form of secondary particles in which a plurality of crystal grains are aggregated, and the crystal grains are arranged in a disordered manner without a particular directionality.

[0162] Co(NO3)2·6H2O was dissolved in deionized water (DI water) to prepare a Co-containing coating solution, the lithium composite transition metal oxide prepared above was added to the coating solution, stirred at 500 rpm for 3 hours, and then heat-treated at 600°C to prepare a positive electrode active material.

[0163] Preparation Example 4

[0164] The transition metal precursor Ni 0.83 Co 0.11 Mn 0.06 (OH)2 and LiOH·H2O were mixed so that the weight ratio of transition metal (Ni+Co+Mn) to Li was 1:1.03, and the mixture was sintered at 900°C for 10 hours and then ground to prepare nickel-based lithium composite transition metal oxide.

[0165] Figure 3 The SEM image of the nickel-based lithium composite transition metal oxide prepared by the above method is shown. Figure 3 It can be confirmed that the lithium composite transition metal oxide prepared by the above method is in the form of single particles and / or quasi-single particles.

[0166] Preparation Example 5

[0167] The nickel-based lithium composite transition metal oxide prepared in Preparation Example 4 and Co(OH) 2 were mixed in a weight ratio of 100:0.2 and heat-treated at 700° C. for 10 hours to prepare a positive electrode active material having a cobalt coating formed thereon.

[0168] Example

[0169] The positive electrode active material prepared in Preparation Example 2 and the positive electrode active material prepared in Preparation Example 5 were mixed at a weight ratio of 6:4, thereby preparing a positive electrode material.

[0170] Comparative Example 1

[0171] The positive electrode active material prepared in Preparation Example 3 and the positive electrode active material prepared in Preparation Example 5 were mixed at a weight ratio of 6:4, thereby preparing a positive electrode material.

[0172] Comparative Example 2

[0173] The positive electrode active material prepared in Preparation Example 2 and the positive electrode active material prepared in Preparation Example 4 were mixed at a weight ratio of 6:4, thereby preparing a positive electrode material.

[0174] Comparative Example 3

[0175] The positive electrode active material prepared in Preparation Example 1 and the positive electrode active material prepared in Preparation Example 5 were mixed at a weight ratio of 6:4, thereby preparing a positive electrode material.

[0176] <Manufacturing of lithium secondary batteries>

[0177] The positive electrode material, conductive agent (Denka black) and binder (PVDF) prepared in each of Examples and Comparative Examples 1 to 3 were mixed in an N-methyl-2-pyrrolidone (NMP) solvent at a weight ratio of 96:2:2 to prepare a positive electrode slurry. One surface of an aluminum current collector was coated with the positive electrode slurry, dried, and then rolled to prepare a positive electrode.

[0178] Next, the negative electrode active material (natural graphite), the conductive agent (carbon black) and the binder (PVDF) were mixed in an N-methylpyrrolidone solvent at a weight ratio of 96:2:2 to prepare a negative electrode slurry. The copper current collector was coated with the negative electrode slurry composition, dried, and then rolled to prepare a negative electrode.

[0179] Each lithium secondary battery is prepared by providing an electrode assembly by providing a separator between the positive electrode and the negative electrode, providing the electrode assembly in a battery case, and then injecting an electrolyte. In this case, as the electrolyte, an electrolyte in which 1.0M LiPF6 is dissolved in an organic solvent in which ethylene carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7 is used.

[0180] Experimental Example 1: High temperature life characteristics

[0181] Each of the lithium secondary batteries prepared above was charged to 4.2V at a constant current of 1.0C at 45°C, and then discharged to 2.5V at a constant current of 0.5C, which was set as one cycle. After 50 cycles of charge and discharge, the capacity retention rate was measured. The measurement results are shown in Table 1 below.

[0182] Experimental Example 2: Gas Generation During High-Temperature Storage

[0183] Each lithium secondary battery prepared above was charged to SOC 100, stored at 60°C for 8 weeks, then perforated in a chamber of vacuum atmosphere to exhaust the gas inside the battery and collect the gas inside the vacuum chamber, and the gas generation was analyzed using a gas chromatography-flame ionization detector (GC-FID). When the gas generation of the lithium secondary battery using the positive electrode material of the embodiment is set to 100%, the ratio of the gas generation of the lithium secondary battery using each positive electrode material of Comparative Examples 1 to 3 is shown in Table 1 below.

[0184] Experimental Example 3: Evaluation of resistance

[0185] Each of the lithium secondary batteries prepared above was subjected to one charge and discharge cycle at 25°C under the condition of 0.2 / 0.2C, and in the next cycle, a 0.2C current was applied to charge and discharge to SOC 50 and SOC 10 based on the discharge capacity, and then a 1C pulse was applied for 10 seconds to measure the DCIR resistance. The measurement results are shown in Table 1.

[0186] Experimental Example 4: Evaluation of the crushing rate of secondary particles

[0187] Collect 3g of each positive electrode material powder of Examples and Comparative Examples 1 to 3, and draw a volume cumulative particle size distribution diagram. Then, the collected positive electrode material powder is placed in a retainer with a diameter of 1.3cm, a pressure of 6 tons is applied to it, and the volume cumulative particle size distribution diagram is drawn again. In the volume cumulative particle size distribution diagram before pressurization, the particle size range larger than the particle size at the point where dY / dX (where X is the particle size and Y is the volume) is minimized is defined as the secondary particle region, and the value calculated by the following mathematical formula in the secondary particle region is evaluated as the crushing rate of the secondary particles.

[0188] (Mathematical formula)

[0189] Secondary particle crushing rate = ∑(X0Y0-X P Y P )

[0190] In the above mathematical formula, X0 and Y0 are the particle size and volume in the volume cumulative particle size distribution diagram before pressurization, respectively. p and Y p They are the particle size and volume in the volume cumulative particle size distribution diagram after applying 6 tons of pressure.

[0191] [Table 1]

[0192]

[0193] With reference to Table 1, it can be confirmed that, compared with the positive electrode materials of Comparative Examples 1 to 3, the positive electrode materials of the embodiment have less particle breakage after pressurization, and it can be confirmed that, compared with the lithium secondary batteries using the positive electrode materials of Comparative Examples 1 to 3, the lithium secondary batteries using the positive electrode materials of the embodiment have excellent high temperature life characteristics, and exhibit excellent high temperature characteristics due to less gas generation after high temperature storage.

Claims

1. A positive electrode material, comprising: A first positive electrode active material in the form of secondary particles aggregated from a plurality of crystal grains, including an orientation structure in which the long axes of the crystal grains in at least a part of the secondary particles are arranged from the center of the secondary particles toward the surface, and the cobalt concentration at the grain boundaries, which are the interfaces between the crystal grains, is higher than the cobalt concentration inside the crystal grains; and A second positive electrode active material, including a central portion and a coating, the central portion having at least one of the forms of a single particle composed of one nodule and a quasi-single particle composed of a composite of at most 30 nodules, and the coating being formed on the central portion and containing cobalt.

2. The positive electrode material according to claim 1, wherein The positive electrode material has a bimodal particle size distribution, and the particle size of the first positive electrode active material is larger than the particle size of the second positive electrode active material.

3. The positive electrode material according to claim 1, wherein The D of the first positive electrode active material 50 is 8 μm to 20 μm, and the D of the second positive electrode active material 50 2μm to 7μm.

4. The positive electrode material according to claim 1, wherein The first positive electrode active material and the second positive electrode active material each independently contain a nickel-based lithium composite transition metal oxide represented by the following Formula 1: [Formula 1] Li x [Ni a Co b M 1 c M 2 d ]O 2-y A y Wherein, in the above Formula 1, M 1 is at least one element selected from the group consisting of Mn and Al, M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, A is at least one element selected from the group consisting of F, Cl, Br, I, At, and S, and 0.98 ≤ x ≤ 1.20, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d ≤ 0.2, and 0 ≤ y ≤ 0.

2.

5. The positive electrode material according to claim 1, wherein The weight ratio of the included first positive electrode active material and the second positive electrode active material is 90:10 to 50:

50.

6. The positive electrode material according to claim 1, wherein The first positive electrode active material contains a nickel-based lithium composite transition metal oxide represented by the following Formula 1-1: [Formula 1-1] Li x1 [Ni a1 Co b1 M 1 c1 M 2 d1 ]O 2-y1 A y1 Wherein, in the above Formula 1-1, M 1 is at least one element selected from the group consisting of Mn and Al, M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, A is at least one element selected from the group consisting of F, Cl, Br, I, At, and S, and 0.98 ≤ x1 ≤ 1.20, 0.6 ≤ a1 ≤ 0.9, 0.01 ≤ b1 < 0.4, 0.01 ≤ c1 < 0.4, 0 ≤ d1 ≤ 0.2, and 0 ≤ y1 ≤ 0.

2.

7. The positive electrode material according to claim 1, wherein In the first positive electrode active material, the angle formed by the long axis of the crystal grains whose long axes are arranged from the center of the secondary particles toward the surface and the a-axis direction of the crystal structure is within -15° to 15°.

8. The positive electrode material according to claim 1, wherein In the first positive electrode active material, the aspect ratio of the crystal grains whose long axes are arranged from the center of the secondary particles toward the surface is 1.5 to 15.

9. The positive electrode material according to claim 1, wherein The first positive electrode active material includes a core portion where the crystal grains are aggregated in a disordered manner, and a shell portion formed outside the core portion where the crystal grains are arranged in an orientation structure.

10. The positive electrode material according to claim 9, wherein The aspect ratio of the crystal grains in the core portion is 0.8 to 1.

2.

11. The positive electrode material according to claim 9, wherein The aspect ratio of the crystal grains in the shell portion is 1.5 to 15.

12. The positive electrode material according to claim 1, wherein The average particle size of the crystal grains of the first positive electrode active material is 0.05 μm to 4 μm.

13. The positive electrode material according to claim 1, wherein The central portion of the second positive electrode active material contains a nickel-based lithium composite transition metal oxide represented by the following Formula 1-2: [Formula 1-2] Li x2 [Ni a2 Co b2 M 1 c2 M 2 d2 ]O 2-y2 A y2 Wherein, in the above Formula 1-2, M 1 is at least one element selected from the group consisting of Mn and Al, M 2 is at least one element selected from the group consisting of W, Cu, Fe, V, Cr, Ti, Zr, Zn, Al, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, A is at least one element selected from the group consisting of F, Cl, Br, I, At, and S, and 0.98 ≤ x2 ≤ 1.20, 0.8 ≤ a2 < 1, 0 < b2 < 0.2, 0.01 ≤ c2 < 0.2, 0 ≤ d2 ≤ 0.2, and 0 ≤ y2 ≤ 0.

2.

14. The positive electrode material according to claim 1, wherein The coating of the second positive electrode active material has a composition represented by the following Formula 2: [Formula 2] Li z Yes 1-w M 3 w O2 Among them, in the above formula 2, M 3 It is at least one selected from the group consisting of Ni, Mn, Al, W, Cu, Fe, V, Cr, Ti, Zr, Zn, Ta, Y, In, La, Sr, Ga, Sc, Gd, Sm, Ca, Ce, Nb, Mg, B and Mo, 0.8≤z≤1.2 and 0≤w≤0.

2.

15. The positive electrode material according to claim 1, wherein The average particle size of nodules of the second positive electrode active material is 0.5 μm to 3.5 μm. 16 . A positive electrode comprising the positive electrode material according to claim 1 . 17 . A lithium secondary battery comprising the positive electrode according to claim 16 .

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