Cathode material, a cathode containing the same, and a lithium secondary battery

Abstract

The present invention relates to a cathode material comprising: a first cathode active material in the form of secondary particles formed by aggregation of multiple grains, at least a portion of which has an oriented structure in which the long axes of the grains are aligned from the center toward the surface of the secondary particles, and in which the cobalt concentration at the grain boundaries, which are the interfaces between the grains, is higher than the cobalt concentration within the grains; a central portion having the form of at least one of a single particle consisting of a single nodule and a quasi-single particle, which is a composite of 30 or fewer nodules; and a second cathode active material formed on the central portion and including a coating layer containing cobalt.

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0183385 filed on December 13, 2022, and all the contents disclosed in the literature of the Korean Patent Application are incorporated herein by reference as part of this specification.

[0002] The present invention relates to a positive electrode active material, a positive electrode including the same, and a lithium secondary battery. More specifically, the present invention relates to a positive electrode active material having few particle cracks during rolling, little gas generation at high temperatures, excellent life characteristics, and low initial resistance, a positive electrode including the positive electrode active material, and a lithium secondary battery.

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] As the positive electrode active material of a lithium secondary battery, lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (such as LiMnO2 or LiMnO4), lithium iron phosphate compound (LiFePO4), etc. have been used. Among these, lithium cobalt oxide has the advantages of a high operating voltage and excellent capacity characteristics, but the price of cobalt as a raw material is high, the supply is unstable, and it is difficult to apply commercially to large-capacity batteries. Lithium nickel oxide has poor structural stability and it is difficult to achieve sufficient life characteristics. On the other hand, lithium manganese oxide has excellent stability but has a problem of inferior capacity characteristics. Therefore, in order to complement the problems of lithium transition metal oxides containing Ni, Co, or Mn alone, lithium composite transition metal oxides containing two or more transition metals have been developed. Among them, lithium nickel cobalt manganese oxide containing Ni, Co, and Mn is widely used in the battery field of electric vehicles.

[0005] Conventional lithium nickel cobalt manganese oxide typically exists in the form of spherical secondary particles, which are aggregates of tens to hundreds of primary particles. However, in the case of lithium nickel cobalt manganese oxide in this form of secondary particles, there is a problem that during the manufacturing of the positive electrode, cracks are likely to occur as primary particles detach during the rolling process, and cracks are likely to occur inside the particles during the charge and discharge process. When cracks or fractures occur in the particles of the positive electrode active material, the contact area with the electrolyte increases, leading to increased gas generation due to side reactions with the electrolyte and increased degradation of the active material, thus reducing the lifespan characteristics.

[0006] To solve the above problems, single-particle cathode active materials consisting of a single particle have been developed. Single-particle cathode active materials have the advantage of high particle strength, less particle cracking during rolling, and excellent lifetime characteristics, but the lithium diffusion resistance within the particle is large, and the resistance and power characteristics deteriorate when the particle size is increased. Therefore, currently, in the case of single particles, D 50 This material is utilized in the form of small particles at the 4 μm level. However, when such small particle cathode active materials are used alone, the electrode processability is poor, so a technique has been proposed to use a mixture of secondary particles and single particles. However, when secondary particles and single particles are mixed, the difference in particle strength between the single particles and secondary particles causes the secondary particles to crack even more severely during electrode rolling, resulting in little effect in suppressing gas generation and improving lifespan, and thus it has not been commercialized. [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to solve the above-mentioned problems and provides a cathode material that uses a mixture of secondary particles and single-particle cathode active material, specifically by using a mixture of secondary particles having a particular orientation structure and composition and a single-particle cathode active material having a cobalt coating layer formed on its surface. This provides a cathode material that exhibits less particle cracking during rolling, less gas generation at high temperatures, and achieves excellent lifespan characteristics and low initial resistance.

[0008] Furthermore, the present invention provides a positive electrode and a lithium secondary battery containing the positive electrode material described above. [Means for solving the problem]

[0009] According to one embodiment, the present invention provides a cathode material comprising: a first cathode active material having the form of secondary particles in which a plurality of grains are aggregated, and including an oriented structure in which the long axes of the grains are aligned from the center of the secondary particle toward the surface in at least a portion thereof, wherein the concentration of cobalt at the grain boundaries, which are the interfaces between the grains, is higher than the concentration of cobalt inside the grains; a central part having the form of at least one of a single particle consisting of one nodule and a pseudo-single particle which is a composite of 30 or fewer nodules; and a second cathode active material formed on the central part and including a coating layer containing cobalt.

[0010] According to another embodiment, the present invention provides a positive electrode including the positive electrode material according to the present invention, and a lithium secondary battery including the positive electrode. [Effects of the Invention]

[0011] The cathode material according to the present invention comprises a first cathode active material in the form of secondary particles having a specific orientation structure and composition, and a second cathode active material in the form of single particles with a cobalt coating layer formed on its surface. Compared to conventional cathode materials mixed with secondary and single particles, it exhibits less particle cracking during rolling, less gas generation at high temperatures, excellent lifetime characteristics, and low initial resistance.

[0012] The first positive electrode active material contained in the positive electrode material according to the present invention includes an oriented structure in which the long axes of the grains are arranged so that they radiate from the center of the secondary particles toward the surface. As a result, the lithium diffusion path within the particles is short, thereby achieving excellent lithium mobility and low resistance characteristics. However, as described above, positive electrode active materials with an oriented structure are more prone to cracking during electrode rolling compared to positive electrode active materials in the form of non-oriented secondary particles. In particular, when used in mixture with single particles of high particle strength, the cracking becomes even more severe. When cracking occurs in the particles of the positive electrode active material, side reactions with the electrolyte increase, reducing the lifetime characteristics and increasing gas generation. However, when a high concentration of cobalt is formed at the grain boundary of secondary particles having an oriented structure, as in the first positive electrode active material of the present invention, the strength of the particles increases due to the cobalt concentrated at the grain boundary. This reduces particle cracking even when used in mixture with single particles, minimizing degradation of the positive electrode active material and gas generation.

[0013] The second positive electrode active material contained in the positive electrode material according to the present invention has high particle strength, less particle cracking during rolling, and a cobalt coating layer formed on the surface minimizes the electrically inert rock salt phase, resulting in low surface resistance. [Brief explanation of the drawing]

[0014] [Figure 1] This is a cross-sectional SEM image of a lithium composite transition metal oxide produced by Production Example 1. [Figure 2] This is a cross-sectional SEM image of a lithium composite transition metal oxide produced by Manufacturing Example 3. [Figure 3] This is an SEM image of a lithium composite transition metal oxide produced by manufacturing example 4. [Modes for carrying out the invention]

[0015] The terms and words used in this specification and in the claims should not be interpreted in a manner limited to their ordinary or dictionary meanings, but rather should be interpreted in a manner consistent with the technical idea of ​​the present invention, in accordance with the principle that inventors may define the concepts of terms as appropriate to best describe their invention.

[0016] In the present invention, "grain" refers to the smallest particle unit that, when observed with a scanning electron microscope at a field of view of 5,000x to 20,000x, does not appear to have grain boundaries and can be distinguished as a single mass. It may consist of one crystallite or multiple crystallites. In the present invention, the average grain size can be measured by measuring the size of each particle distinguished by cross-sectional SEM data of the positive electrode active material particles and then calculating the arithmetic mean of these sizes.

[0017] In this invention, "secondary particle" means a secondary structure formed by the aggregation of multiple grains.

[0018] In the present invention, "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 powder. The average particle size D 50 This 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.

[0019] In the present invention, "oriented structure" means a structure in which the long axes of the grains are aligned from the center of the secondary particle toward the surface. Here, "the long axes of the grains are aligned from the center of the secondary particle toward the surface" means that the angle between the shortest line segment connecting the center and surface of the secondary particle while passing through the grains and the long axis of the grains is in the range of -15° to 15°.

[0020] In this invention, "grain aspect ratio" means the ratio of the major axis length to the minor axis length of the grain, and "average aspect ratio" means the arithmetic mean of the aspect ratios of the grains in that region.

[0021] In this invention, "single particle" refers to a particle consisting of one single nodule. In this invention, "pseudo-single particle" refers to a particle that is a composite formed of 30 or fewer nodules.

[0022] In this invention, "nodule" refers to a particle unit body that constitutes a single particle or a pseudo-single particle. The nodule may be a single crystal lacking crystalline grain boundaries, or a polycrystalline material in which no grain boundaries are visible when observed at a field of view of 5,000 to 20,000 times using a scanning electron microscope (SEM) or electron backscatter diffraction pattern analyzer (EBSD). The average grain size of the nodule refers to the arithmetic mean calculated after measuring the grain size of the nodule observed by SEM or EBSD.

[0023] As used in this invention, the term "particle" may include one or all of the following: single particles, pseudo-single particles, primary particles, nodules, and secondary particles.

[0024] The present invention will be described in detail below.

[0025] <Positive electrode material> The cathode material according to the present invention comprises a first cathode active material and a second cathode active material, wherein the first cathode active material is in the form of secondary particles formed by the aggregation of a plurality of grains, and at least a portion of the secondary particles includes an oriented structure in which the long axes of the grains are aligned from the center of the secondary particles toward the surface, the concentration of cobalt at the grain boundaries, which are the interfaces between the grains, is higher than the concentration of cobalt inside the grains, and the second cathode active material comprises a central part having at least one form of a single particle consisting of one nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and a coating layer formed on the central part and containing cobalt.

[0026] Preferably, the cathode material according to the present invention can have a bimodal particle size distribution in which the particle size of the first cathode active material is larger than that of the second cathode active material. When the cathode material according to the present invention has a bimodal particle size distribution, a high electrode density can be achieved, thereby improving the battery capacity characteristics. However, in the case of the second cathode active material, which is a single-particle cathode active material, if the particle size is large, the lithium diffusion path within the particle becomes longer, which can reduce resistance and power characteristics. Therefore, it is preferable to make the particle size of the first cathode active material, which is in the form of secondary particles, larger than that of the second cathode active material to minimize the reduction in resistance and power characteristics and to achieve a high electrode density.

[0027] Specifically, the D of the aforementioned first positive electrode active material 50 The diameter of the second positive electrode active material can be 8 μm to 20 μm, preferably 8 μm to 18 μm, and more preferably 8 μm to 15 μm. 50 The diameter of the first positive electrode active material and the second positive electrode active material can 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 satisfied, the capacitance characteristics, resistance characteristics, and output characteristics are further improved.

[0028] On the one hand, the first positive electrode active material and the second positive electrode active material can have the same or different compositions. For example, the first positive electrode active material and the second positive electrode active material can each independently contain a nickel-based lithium composite transition metal oxide represented by the following [Chemical Formula 1].

[0029] [Chemical Formula 1] Li X [Ni a Co b M 1 c M 2 d O 2-y A y

[0030] In the above [Chemical Formula 1], the M 1 can be one or more elements selected from the group consisting of Mn and Al, and for example, can be Mn or a combination of Mn and Al.

[0031] The M 2 can be one or more elements 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.

[0032] Also, the A can be one or more elements selected from the group consisting of F, Cl, Br, I, At, and S.

[0033] The x represents the ratio of the number of moles of Li to the total number of moles of transition metals, and can be 0.98 ≦ x ≦ 1.20, preferably 0.99 ≦ x ≦ 1.10, more preferably 1.0 ≦ x ≦ 1.10.

[0034] The a represents the ratio of the number of moles of Ni to the total number of moles of the remaining metals other than lithium, and can be 0 < a < 1, preferably 0.3 ≦ a < 1, more preferably 0.6 ≦ a < 1, even more preferably 0.8 ≦ a < 1, and even more preferably 0.85 ≦ a < 1.

[0035] 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 0 < b < 1, preferably 0 < b < 0.7, more preferably 0 < b < 0.4, still more preferably 0 < b < 0.2, even more preferably 0 < b ≤ 0.1.

[0036] c represents..., 1 the ratio of the number of moles of M to the total number of moles of the remaining metals other than lithium, where 0 < c < 1, preferably 0 < c < 0.7, more preferably 0 < c < 0.4, still more preferably 0 < c < 0.2, even more preferably 0 < c ≤ 0.1.

[0037] d represents..., 2 the ratio of the number of moles of M to the total number of moles of the remaining metals other than lithium, where 0 ≤ d ≤ 0.2, preferably 0 ≤ d ≤ 0.15, more preferably 0 ≤ d ≤ 0.10.

[0038] y represents the ratio of the number of moles of element A substituted at the oxygen site, where 0 ≤ y ≤ 0.2, preferably 0 ≤ y ≤ 0.15, more preferably 0 ≤ y ≤ 0.10.

[0039] On the other hand, the first positive electrode active material and the second positive electrode active material can be contained 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 positive electrode active material and the second positive electrode active material satisfies the above range, a high electrode density can be achieved.

[0040] When using both a first positive electrode active material having an oriented structure in which grains are arranged from the center to the surface direction of secondary particles and having a composition with a higher cobalt concentration at grain boundaries than inside the grains, and a single-particle-based second positive electrode active material with a cobalt coating layer formed on the surface, as in the positive electrode material of the present invention, during rolling, not only are there few cracks in the secondary particles, but even when cracks occur in the particles, the surfaces of the grains are coated with cobalt, resulting in few side reactions with the electrolytic solution, so there is little gas generation at high temperatures and the life characteristics are excellent.

[0041] Next, the first and second positive electrode active materials constituting the positive electrode material of the present invention will be described in more detail.

[0042] First positive electrode active material The first positive electrode active material is in the form of secondary particles formed by the aggregation of multiple grains, and at least a portion of the secondary particles includes an oriented structure in which the long axes of the grains are aligned from the center of the secondary particle toward the surface. Here, "the long axes of the grains are aligned from the center of the secondary particle toward the surface" means that the angle between the long axis of the grain and the shortest line segment connecting the center and surface of the secondary particle while passing through the grain is in the range of -15° to 15°. The grain long axis means the line segment having the longest length among the straight lines connecting two points on the surface of the grain while passing through the center of the grain. Within the secondary particles of the positive electrode active material, the interfaces between grains become diffusion pathways for lithium ions. When grains are aligned so as to be directed from the center of the secondary particle toward the surface, the diffusion pathway for lithium ions within the secondary particle is shortened, increasing lithium mobility, which in turn improves the power and / or resistance characteristics.

[0043] On the other hand, in grains where the long axes of the grains are aligned from the center of the secondary particles toward the surface, the angle between the long axis and the a-axis direction of the crystal structure can be within -15° to 15°, preferably within -10° to 10°. Since lithium ions move in the a-axis direction within the grain, when the angle between the long axis of the grain and the a-axis direction of the crystal structure is -15° to 15°, the insertion and removal of lithium ions becomes easier, thereby improving the output and / or resistance characteristics.

[0044] On the other hand, grains in which the long axis of the grain is aligned from the center of the secondary particle toward the surface can have an aspect ratio of 1.5 to 15, preferably 2 to 15, and more preferably 4 to 15. When the aspect ratio of the grain satisfies the above range, the contraction and expansion of the grain during charging and discharging mainly occurs in the direction of the short axis perpendicular to the orientation direction, and the occurrence of cracks due to non-uniform contraction and expansion of grain within the secondary particle can be effectively suppressed.

[0045] On the other hand, the first positive electrode active material may have a core-shell structure comprising a core portion in which grains are aggregated without any special orientation, and a shell portion in which the long axes of the grains are aligned from the center of the secondary particles toward the surface.

[0046] The core portion is a region in which grains aggregate disorderly without any particular orientation, and is formed in the center of the secondary particle. The core portion can be a portion formed as a seed during a coprecipitation reaction for the formation of a precursor for the positive electrode active material, and can be, for example, a region at a distance of 1 / 3R from the center of the secondary particle, or a region at a distance of 1 / 4R from the center of the secondary particle, where R is the radius of the secondary particle.

[0047] The grains within the core can be nearly spherical in shape, and their aspect ratio can be 0.7 to 1.3, preferably 0.8 to 1.2.

[0048] Next, the shell portion is a region formed on the outside of the core portion in which grains are arranged in an oriented structure. The shell portion can be a part formed as particles grow during a coprecipitation reaction for the formation of a precursor for the positive electrode active material, and can be, for example, a region from 1 / 3R to R of the secondary particle, or a region from 1 / 4R to R of the secondary particle, where R is the radius of the secondary particle from the center of the secondary particle.

[0049] The grain within the shell portion can be rod-shaped, and its aspect ratio can be 1.5 to 15, preferably 2 to 15, and more preferably 4 to 15.

[0050] On the other hand, in the first positive electrode active material of the present invention, the average grain size can 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 grain size is too large, a rock salt phase may be formed, which may reduce the resistance characteristics and lifetime characteristics. If the average grain size is too small, the contact area with the electrolyte may increase, which may lead to rapid degradation.

[0051] On the other hand, the first positive electrode active material may include a nickel-based lithium composite transition metal oxide, for example, a nickel-based lithium composite transition metal oxide represented by the following [Chemical Formula 1-1].

[0052] [Chemical formula 1-1] Li X1 [Ni a1 Co b1 M 1 c1 M 2 d1 ]O 2-y1 A y1

[0053] In the above [Chemical Formula 1-1], the above M 1 can be one or more elements selected from the group consisting of Mn and Al, for example, Mn or a combination of Mn and Al.

[0054] Said M 2 This can be one or more elements 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.

[0055] Furthermore, A can be one or more elements selected from the group consisting of F, Cl, Br, I, At, and S.

[0056] The aforementioned x1 represents the ratio of the number of moles of Li to the total number of moles of the transition metal, and can be 0.98 ≤ x1 ≤ 1.20, preferably 0.99 ≤ x1 ≤ 1.10, and more preferably 1.0 ≤ x1 ≤ 1.10.

[0057] The a1 above represents the ratio of the number of moles of Ni to the total number of moles of the remaining metals other than lithium, and can be 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.

[0058] The b1 above represents the ratio of the number of moles of Co to the total number of moles of the remaining metals other than lithium, and can be 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.

[0059] The aforementioned c1 is M relative to the total number of moles of the remaining metals other than lithium. 1 This represents the ratio of the number of moles, and can be 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.

[0060] The aforementioned d1 is M relative to the total number of moles of the remaining metals other than lithium. 2 This represents the ratio of the number of moles, and can be 0≦d1≦0.2, preferably 0≦d1≦0.15, and more preferably 0≦d1≦0.10.

[0061] The above y1 represents the ratio of the number of moles of element A substituted at the oxygen position, and can be 0 ≤ y1 ≤ 0.2, preferably 0 ≤ y1 ≤ 0.15, and more preferably 0 ≤ y1 ≤ 0.10.

[0062] On the other hand, the first positive electrode active material according to the present invention is characterized in that the concentration of cobalt at the grain boundary, which is the interface between grains, is higher than the concentration of cobalt inside the grains. Here, the cobalt concentration refers to the molar ratio of cobalt among the remaining metals other than lithium. In other words, the first positive electrode active material is enriched with cobalt at the grain boundaries. As described above, when cobalt is enriched at the grain boundaries, even though it contains an oriented structure, the cracking of the particles of the first positive electrode active material is reduced during rolling, and even if particle cracking occurs due to rolling, side reactions with the electrolyte are minimized. Therefore, when the first positive electrode active material is applied, superior high-temperature properties can be achieved compared to conventional positive electrode active materials having an oriented structure.

[0063] On the other hand, the first positive electrode active material described above is in the form of secondary particles in which a plurality of grains are aggregated, and at least a portion of the secondary particles have an oriented structure in which the long axes of the grains are aligned from the center of the secondary particles toward the surface. This lithium composite transition metal oxide can be produced by immersing such a material in a coating solution containing a cobalt element and then heat-treating it.

[0064] Here, the lithium composite transition metal oxide containing the oriented structure may be prepared by purchasing a commercially available product, or it may be manufactured using a lithium composite transition metal oxide manufacturing method that is well known in the industry. For example, a lithium composite transition metal oxide containing an oriented structure can be manufactured by mixing a cathode active material precursor with a lithium raw material and then calcining it.

[0065] As in the present invention, in order to produce a positive electrode active material having an oriented structure, a positive electrode active material precursor having an oriented structure in which primary particles are arranged from the center toward the surface of secondary particles must be used. The aggregation morphology of the primary particles of the positive electrode active material precursor is affected by the pH, stirring speed, and reaction temperature during the coprecipitation reaction. Therefore, by appropriately adjusting the pH, stirring speed, and reaction temperature during the production of the positive electrode active material precursor, a positive electrode active material precursor having an oriented structure can be formed, and a lithium composite transition metal oxide having an oriented structure can be produced using this precursor.

[0066] The lithium raw material and the positive electrode active material precursor can be mixed such that the molar ratio of Li to total transition metals 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 metals in the positive electrode active material precursor satisfies the above range, the crystal structure of the positive electrode active material develops well, and a positive electrode active material with excellent capacity characteristics and structural stability can be produced.

[0067] Examples of the lithium raw material include lithium-containing carbonates (e.g., lithium carbonate), hydrates (e.g., lithium hydroxide hydrate (LiOH·H2O)), hydroxides (e.g., lithium hydroxide), nitrates (e.g., lithium nitrate (LiNO3)), and chlorides (e.g., lithium chloride (LiCl)). One of these alone or a mixture of two or more can be used.

[0068] The firing can be carried out at an appropriate temperature, taking into account the composition of the lithium composite transition metal oxide, for example, 600°C to 1000°C, preferably 700°C to 900°C. The firing time can be, for example, 5 to 30 hours, preferably 8 to 15 hours, but is not limited thereto.

[0069] Next, the lithium composite transition metal oxide containing the oriented structure described above is subjected to post-heat treatment in a coating solution containing cobalt, thereby concentrating cobalt at the grain boundaries of the lithium composite transition metal oxide.

[0070] The aforementioned coating solution containing the cobalt element can be formed by dissolving one or more elements selected from the group consisting of Co(NO3)2, Co(NO3)2·6H2O, CoCl2, CoSO4, Co(OCOCH3)2·4H2O, and Co(OH)2 in a solvent such as water or ethanol.

[0071] As described above, when a wet coating process is performed by mixing a lithium composite transition metal oxide coating solution and then heat-treating it, the cobalt elements contained in the coating solution penetrate not only to the surface of the secondary particles of the lithium composite transition metal oxide but also to the interfaces (grain boundaries) between grains, making it possible to create a higher concentration of cobalt at the grain boundaries than inside the grains.

[0072] On the other hand, the heat treatment can be carried out at 300°C to 800°C, preferably 400°C to 700°C, and more preferably 500°C to 650°C. When the heat treatment temperature is within the above range, the cobalt elements contained in the coating solution concentrate at the grain boundaries, and a higher concentration of cobalt can be formed at the grain boundaries than inside the grains. If the first heat treatment temperature is too low, the coating will not be carried out smoothly, and if the first heat treatment temperature is too high, the cobalt will diffuse into the inside of the grains and will not concentrate at the grain boundaries.

[0073] Second positive electrode active material The second positive electrode active material comprises a central part in the form of a single particle and / or a pseudo-single particle, and a coating layer formed on the central part and containing cobalt.

[0074] The central part is a single particle consisting of one nodule and / or a pseudo-single particle which is a composite of 30 or fewer nodules, preferably 2 to 20, more preferably 2 to 10.

[0075] The second positive electrode active material, in which the core is in a single-particle and / or pseudo-single-particle form, has higher particle strength compared to existing positive electrode active materials in which tens to hundreds of primary particles are aggregated, resulting in less particle cracking during rolling. Furthermore, because the second positive electrode active material has fewer nodules constituting the positive electrode active material particles, there is less change due to the expansion and contraction of the nodules' volume during charging and discharging, which significantly reduces the occurrence of cracks inside the particles.

[0076] On the other hand, the central portion may contain a nickel-based lithium composite transition metal oxide represented by the following [Chemical Formula 1-2].

[0077] [Chemical formula 1-2] Li X2 [Ni a2 Co b2 M 1 C2 M 2 d2 ]O 2-y2 A y2

[0078] In the above chemical formula 1-2, the M 1 This can be one or more elements selected from the group consisting of Mn and Al, preferably Mn, Al, or a combination thereof, and more preferably Mn or Mn and Al.

[0079] Said M 2 is one or more elements 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 one or more elements selected from the group consisting of Zr, Y, Mg, and Ti, and more preferably Zr, Y, or a combination thereof. 2 While elements are not essential, when present in appropriate amounts, they can promote grain growth during firing or improve crystal structure stability.

[0080] The x2 represents the molar ratio of lithium in the lithium nickel-based oxide, and can be 0.8 ≦ a ≦ 1.2, 0.85 ≦ a ≦ 1.15, or 0.9 ≦ a ≦ 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.

[0081] The a2 represents the molar ratio of nickel among all the metals other than lithium, and can be 0.8 ≦ a2 < 1, 0.82 ≦ a2 < 1, or 0.83 ≦ a2 < 1. When the molar ratio of nickel satisfies the above range, it shows a high energy density and enables the realization of a high capacity.

[0082] The b2 represents the cobalt molar ratio among all the metals other than lithium, and can be 0 < b2 < 0.2, 0 < b2 < 0.18, or 0.01 ≦ b2 ≦ 0.17. When the cobalt molar ratio satisfies the above range, good resistance characteristics and output characteristics can be realized.

[0083] The c2 represents the molar ratio of the M 1 element among all the metals other than lithium, and can be 0.01 ≦ c2 < 0.2, 0.01 ≦ c2 < 0.18, or 0.01 ≦ d ≦ 0.17. When the molar ratio of the M 1 element satisfies the above range, the structure stability of the positive electrode active material is excellent.

[0084] The d2 represents the ratio of the molar number of M 2 to the total molar number of the remaining metals other than lithium, and can be 0 ≦ d2 ≦ 0.2, preferably 0 ≦ d2 ≦ 0.15, and more preferably 0 ≦ d2 ≦ 0.10.

[0085] The y2 represents the ratio of the molar number of the A element substituted at the oxygen site, and can be 0 ≦ y2 ≦ 0.2, preferably 0 ≦ y2 ≦ 0.15, and more preferably 0 ≦ y2 ≦ 0.10.

[0086] On the other hand, the second positive electrode active material according to the present invention includes a coating layer containing cobalt on the central portion including the single particles and / or pseudo-single particles.

[0087] Typically, single-particle and / or pseudo-single-particle positive electrode active materials are manufactured by firing at a higher temperature than secondary-particle positive electrode active materials. However, higher firing temperatures increase the amount of electrically inert rock salt phase on the particle surface, thereby increasing the resistance of the positive electrode active material. In contrast, as in the present invention, when a cobalt-containing coating layer is formed on the surface of single-particle and / or pseudo-single-particle materials, recrystallization occurs through reaction with cobalt during the formation of the coating layer, reducing the rock salt phase on the surface of the single-particle and / or pseudo-single-particle materials, thereby improving the resistance characteristics.

[0088] Specifically, the coating layer can be an oxide containing lithium and cobalt, and may have a composition represented by the following [Chemical Formula 2].

[0089] [Chemical formula 2] Li z Co 1-w M 3 w O2

[0090] In the above [Chemical Formula 2], the M 3 This can be one or more 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 can satisfy 0.8 ≤ z ≤ 1.2 and 0 ≤ w ≤ 0.2. Preferably, the M 3 z can be one or more elements selected from the group consisting of Ni, Mn, Al, Ti, Zr, and Mg, and can satisfy the conditions 0.8 ≤ z ≤ 1.1 and 0 ≤ w ≤ 0.1.

[0091] When the coating layer satisfies the above-mentioned composition, improvements in initial resistance characteristics and high-temperature lifetime characteristics can be obtained.

[0092] On the other hand, the shape and area of ​​the coating layer are not particularly limited. For example, the coating layer may be a continuous film that surrounds the entire surface of the single particles and / or pseudo-single particles constituting the central part, or it may be particulate that is discontinuously distributed on the surface of the single particles and / or pseudo-single particles. Furthermore, the area of ​​the coating layer can be 10% to 100%, 10% to 80%, or 20% to 70% of the total surface area of ​​the central part.

[0093] On the other hand, the second positive electrode active material according to the present invention may have an average particle size of nodules of 0.5 μm to 3 μm, preferably 0.8 μm to 2.5 μm, and more preferably 0.8 μm to 1.5 μm. When the average particle size of the nodules satisfies the above range, a positive electrode active material in the form of single particles and / or pseudo-single particles with excellent electrochemical properties can be formed. If the average particle size of the nodules is too small, the number of aggregated nodules forming the center increases, reducing the effect of suppressing the occurrence of particle cracking during rolling. If the average particle size of the nodules is too large, the lithium diffusion path inside the nodule becomes longer, increasing resistance and potentially degrading the output characteristics.

[0094] On the other hand, the second positive electrode active material has an average particle size D 50 The diameter can be 2 μm to 7 μm, preferably 2.5 μm to 7 μm, and more preferably 3 μm to 7 μm. The second positive electrode active material D 50 If the size is too small, slurry aggregation will occur, making electrode manufacturing difficult, and electrolyte impregnation will decrease, leading to a decline in electrochemical properties. 50 If the value is too large, the resistance increases, which leads to a problem of reduced output characteristics.

[0095] Furthermore, the second positive electrode active material can have an average crystallite size of 150 nm to 300 nm, 200 nm to 280 nm, or 200 nm to 250 nm. When the average crystallite size satisfies the above range, the formation of the rock salt phase is reduced during the production of lithium nickel oxide, making it possible to produce a single-particle and / or pseudo-single-particle positive electrode active material with excellent resistance characteristics. Generally, single-particle and / or pseudo-single-particle positive electrode active materials are produced by increasing the firing temperature to increase the size of the nodules. However, if only the size of the nodules is increased while the crystallite size is small, there is a problem that the rock salt phase is formed on the surface of the nodules, increasing the resistance. However, when both the average crystallite size and the average grain size of the nodules are increased, the formation of the rock salt phase is minimized, and the increase in resistance is suppressed.

[0096] On the other hand, the second positive electrode active material can be manufactured by mixing a positive electrode active material precursor and a lithium raw material, firing them to form single particles and / or pseudo-single particles, mixing the single particles and / or pseudo-single particles with a coating raw material containing Co, and then heat-treating the mixture.

[0097] Here, the positive electrode active material precursor can be purchased and used as a commercially available precursor such as nickel-cobalt-manganese hydroxide, or it can be manufactured by a precursor manufacturing method well known in the art, such as the coprecipitation method.

[0098] Preferably, the cathode active material precursor used in the present invention may be a transition metal hydroxide containing nickel and cobalt, with a Ni content of 80 mol% or more of the total transition metal, and more preferably, a nickel-cobalt-manganese hydroxide with 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.

[0099] As the lithium raw material, 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.

[0100] On the other hand, the lithium raw material and the positive electrode active material precursor can be mixed such that the molar ratio of Li to 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 develops well, and a positive electrode active material with excellent capacity characteristics and structural stability can be produced.

[0101] On the other hand, the firing is carried out at a temperature capable of forming single particles and / or pseudo-single particles. In order to form single particles and / or pseudo-single particles, firing must be carried out at a higher temperature than conventionally used when manufacturing positive electrode active materials in the form of secondary particles. For example, if the composition of the precursor is the same, firing must be carried out at a temperature approximately 30°C to 100°C higher than conventionally used when manufacturing positive electrode active materials in the form of secondary particles. The firing temperature for forming single particles and / or pseudo-single particles can vary depending on the composition of the metal in the precursor. For example, when forming single particles and / or pseudo-single particles of high-nickel (High-Ni) lithium nickel oxide with a nickel (Ni) content of 80 mol% or more, the primary firing temperature can be approximately 800°C to 1000°C, preferably 800°C to 950°C, and more preferably 800°C to 900°C. When the firing temperature satisfies the above range, single particles and / or pseudo-single particles with excellent electrochemical properties can be produced. If the firing temperature is below 800°C, a positive electrode active material in the form of secondary particles is produced, and if it exceeds 1000°C, the firing is excessive, preventing the proper formation of a layered crystalline structure, resulting in a decrease in electrochemical properties.

[0102] Furthermore, the calcination can be carried out in an oxygen atmosphere for 6 to 35 hours, preferably 6 to 20 hours, and more preferably 6 to 12 hours. When the calcination time falls within the above range, single particles and / or pseudo-single particles can be formed. If the calcination time is too short, particle growth will be insufficient, and lithium nickel oxide in the form of secondary particles will be formed. If it is too long, a rock salt phase may occur, and the electrochemical properties of the active material may deteriorate. In this specification, an oxygen atmosphere means an atmosphere containing an amount of oxygen sufficient for calcination, including an atmospheric atmosphere. In particular, it is preferable to carry out the calcination in an atmosphere in which the partial pressure of oxygen is even higher than that of an atmospheric atmosphere.

[0103] On the other hand, the coating raw material containing Co can be, but is not limited to, cobalt hydroxide, etc.

[0104] The method for mixing single particles and / or pseudo-single particles with the Co-containing coating material is not particularly limited, and various coating methods known in the art, such as dry coating and wet coating, can be applied.

[0105] On the other hand, the heat treatment can be carried out, for example, at 300°C to 800°C, preferably 600°C to 750°C, for 5 to 20 hours, preferably 10 to 12 hours.

[0106] <Positive electrode> Next, the positive electrode according to the present invention will be described.

[0107] The positive electrode includes the positive electrode material according to 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, and the positive electrode active material layer includes the positive electrode material according to the present invention.

[0108] As the positive electrode material is as described above, a detailed explanation will be omitted, and only the remaining components will be described in detail below.

[0109] The positive electrode current collector is not particularly limited as long as it contains a highly conductive metal, allows for easy adhesion of the positive electrode active material layer, and is unreactive within the battery voltage range. Examples of materials that can be used for the positive electrode current collector include stainless steel, aluminum, nickel, titanium, heat-treated carbon, or aluminum or stainless steel with surface treatments such as carbon, nickel, titanium, or silver. Furthermore, the positive electrode current collector can typically have a thickness of 3 to 500 μm, and fine irregularities can be formed on its surface to enhance the adhesion of the positive electrode active material. It can be used in various forms, such as films, sheets, foils, meshes, porous materials, foams, and nonwoven fabrics.

[0110] The positive electrode active material layer may, as necessary, selectively include a conductive material and a binder together with the positive electrode material.

[0111] Here, the positive electrode material can be included in an amount of 80 to 99% by weight, more specifically 85 to 98.5% by weight, relative to the total weight of the positive electrode active material layer, and when included within this range, it can exhibit excellent capacitance characteristics.

[0112] 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 tubes such as carbon nanotubes; 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 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0113] The binder plays a role in improving the adhesion between positive electrode active material particles and the adhesion between the positive electrode active material and the current collector. Specific examples include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, polymethyl methacrylate, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, polyacrylic acid, and polymers in which the hydrogen atoms of these materials are substituted with Li, Na, or Ca, or various copolymers thereof. One of these materials alone or a mixture of two or more materials can be used. The binder can be present in an amount of 0.1 to 15% by weight relative to the total weight of the positive electrode active material layer.

[0114] The positive electrode can be manufactured by conventional methods for manufacturing positive electrodes, except that the positive electrode material of the present invention is used. Specifically, it can be manufactured by applying a positive electrode slurry composition, prepared by dissolving or dispersing the positive electrode material and, if necessary, selectively, a binder, a conductive material, and a dispersant in a solvent, onto a positive electrode current collector, followed by drying and rolling.

[0115] The solvent can be any solvent commonly used in the art, such as dimethyl sulfoxide (DMSO), isopropyl alcohol, N-methylpyrrolidone (NMP), dimethylformamide (DMF), acetone, or water, and one of these alone or a mixture of two or more can be used. The amount of solvent used should be sufficient to dissolve or disperse the positive electrode active material, conductive material, binder, and dispersant, taking into consideration the coating thickness of the slurry and the manufacturing yield, and to have a viscosity that allows for excellent thickness uniformity when applied for the manufacture of the positive electrode.

[0116] Alternatively, the positive electrode can also be manufactured by casting the positive electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the positive electrode current collector.

[0117] <Electrochemical elements> The present invention makes it possible to manufacture an electrochemical element including the positive electrode. Specifically, the electrochemical element may be a battery, a capacitor, and more specifically, a lithium secondary battery.

[0118] The lithium secondary battery can specifically include 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.

[0119] 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.

[0120] In the lithium secondary battery, the negative electrode may include a negative electrode current collector and a negative electrode active material layer located on the negative electrode current collector.

[0121] 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.

[0122] The negative electrode active material layer may selectively include a binder and a conductive material together with the negative electrode active material.

[0123] 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.

[0124] 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.

[0125] The binder is a component that helps to bond the conductive material, active material, and current collector, and is usually 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, polytetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene polymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, nitrile-butadiene rubber, fluororubber, and various copolymers thereof.

[0126] 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; carbon fluoride; metal powders such as 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.

[0127] The negative electrode active material layer can be manufactured by coating a negative electrode slurry composition, which is prepared by dissolving or dispersing a negative electrode active material and, selectively, a binder and a conductive material in a solvent, onto a negative electrode current collector and then drying it, or by casting the negative electrode slurry composition onto another support, peeling it off the support, and then laminating the resulting film onto the negative electrode current collector.

[0128] 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 as single-layer or multi-layer structures.

[0129] 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.

[0130] Specifically, the electrolyte may include an organic solvent and a lithium salt.

[0131] The aforementioned organic solvent can be used without particular limitations, as long as it can act as a medium through which ions involved in the electrochemical reaction of the battery can move. Specifically, the aforementioned 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), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), and propylene carbonate (propylene Carbonate solvents such as carbonate (PC); alcoholic 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.

[0132] 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 anion of the lithium salt is 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 - The lithium salt can be selected from the group consisting of LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO2, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, or LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt falls within this range, the electrolyte can exhibit excellent electrolyte performance due to having appropriate conductivity and viscosity, and lithium ions can move effectively.

[0133] As described above, the lithium secondary battery containing the positive electrode active material according to the present invention exhibits excellent capacity characteristics and lifespan characteristics, and can be usefully used in various fields such as portable devices like mobile phones, notebook computers, and digital cameras, as well as electric vehicles.

[0134] The present invention will be described in detail below with reference to examples. However, the examples of the present invention can be modified into various other forms, and the scope of the present invention should not be construed as being limited to the examples detailed below. The examples of the present invention are provided to give a more complete explanation of the present invention to a person of average skill in the art.

[0135] [Manufacturing Example 1] Transition metal aqueous solutions were prepared by mixing NiSO4, CoSO4, and MnSO4 in distilled water in amounts such that the molar ratio of nickel:cobalt:manganese was 8:1:1.

[0136] Next, deionized water was added to the reactor, then nitrogen gas was purged into the reactor to remove dissolved oxygen from the water, and NaOH was added to maintain a pH of 11 inside the reactor.

[0137] Next, the transition metal aqueous solution, NaOH aqueous solution, and NH4OH aqueous solution were added to the reactor, and a coprecipitation reaction was carried out for 30 hours under the conditions of a reaction temperature of 50°C, pH 11, and stirring speed of 400 rpm, to obtain the average particle size (D 50 The precursor Ni for positive electrode active material has a diameter of 12 μm. 0.8 Co 0.1 Mn 0.1 (OH)2 was prepared. Here, the molar ratio of transition metal ions to NH4OH was 1:1.10.

[0138] The aforementioned cathode active material precursor and LiOH were mixed so that the molar ratio of Li to transition metal (Ni+Co+Mn) was 1.02:1. After firing at 730°C for 20 hours, the mixture was washed with water and dried to produce a lithium composite transition metal oxide.

[0139] Figure 1 shows a scanning electron microscope (SEM) image of a cross-section of the lithium composite transition metal oxide manufactured as described above. Referring to Figure 1, it can be confirmed that the lithium composite transition metal oxide manufactured by the above method has the form of secondary particles in which multiple grains are aggregated, and that the long axes of the grains are aligned in the direction from the center of the secondary particle toward the surface.

[0140] [Manufacturing Example 2] A Co-containing coating solution was prepared by dissolving Co(NO3)2·6H2O in deionized water (DI water).

[0141] The lithium composite transition metal oxide produced by Production Example 1 was added to the coating solution, stirred at 500 rpm for 3 hours, and then heat-treated at 600°C to produce the cathode active material.

[0142] [Manufacturing Example 3] Lithium composite transition metal oxide was produced in the same manner as in Production Example 1, except that, during the production of the cathode active material precursor, transition metal aqueous solution, NaOH aqueous solution, and NH4OH aqueous solution were added to achieve a transition metal to NH4OH molar ratio of 1:0.8, a coprecipitation reaction was carried out for 30 hours under conditions of a reaction temperature of 60°C, pH 11, and stirring speed of 300 rpm, and calcination was performed at 750°C.

[0143] Figure 2 shows a scanning electron microscope (SEM) image of a cross-section of the lithium composite transition metal oxide manufactured as described above. Referring to Figure 2, it can be seen that the lithium composite transition metal oxide manufactured by the above method is in the form of secondary particles in which multiple grains are aggregated, and the grains are arranged disorderly without any particular orientation.

[0144] A Co-containing coating solution was prepared by dissolving Co(NO3)2·6H2O in deionized water (DI water). 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 produce a positive electrode active material.

[0145] [Manufacturing Example 4] 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 the transition metal (Ni+Co+Mn):Li was 1:1.03. After firing at 900°C for 10 hours, the mixture was milled to produce a nickel-based lithium composite transition metal oxide.

[0146] Figure 3 shows a scanning electron microscope (SEM) image of a nickel-based lithium composite transition metal oxide produced by the method described above. Referring to Figure 3, it can be confirmed that the lithium composite transition metal oxide produced by the method described above is in single-particle and / or pseudo-single-particle form.

[0147] [Manufacturing Example 5] A nickel-based lithium composite transition metal oxide produced by the above-mentioned production example 4 was mixed with Co(OH)2 in a weight ratio of 100:0.2, and the mixture was heat-treated at 700°C for 10 hours to produce a positive electrode active material with a cobalt coating layer formed on top.

[0148] [Examples] A cathode material was manufactured by mixing the cathode active material produced by manufacturing example 2 and the cathode active material produced by manufacturing example 5 in a weight ratio of 6:4.

[0149] [Comparative Example 1] A cathode material was manufactured by mixing the cathode active material produced by manufacturing example 3 and the cathode active material produced by manufacturing example 5 in a weight ratio of 6:4.

[0150] [Comparative Example 2] A cathode material was manufactured by mixing the cathode active material produced by manufacturing example 2 and the cathode active material produced by manufacturing example 4 in a weight ratio of 6:4.

[0151] [Comparative Example 3] A cathode material was manufactured by mixing the cathode active material produced by manufacturing example 1 and the cathode active material produced by manufacturing example 5 in a weight ratio of 6:4.

[0152] <Manufacturing of lithium-ion secondary batteries> The positive electrode materials prepared in Examples and Comparative Examples 1-3 were mixed with a conductive material (Denka Black) and a binder (PVDF) in an N-methyl-2-pyrrolidone (NMP) solvent in a weight ratio of 96:2:2 to produce a positive electrode slurry. The positive electrode slurry was applied to one surface of an aluminum current collector, dried, and then rolled to produce a positive electrode.

[0153] Next, a negative electrode slurry was prepared by mixing a negative electrode active material (natural graphite), a conductive material (carbon black), and a binder (PVDF) in an N-methylpyrrolidone solvent in a weight ratio of 96:2:2. The negative electrode slurry composition was applied to a copper current collector, dried, and then rolled to produce a negative electrode.

[0154] After manufacturing an electrode assembly with a separator interposed between the positive and negative electrodes, the assembly was placed inside a battery case, and then an electrolyte was injected to manufacture a lithium secondary battery. The electrolyte used was a solution of 1.0 M LiPF6 dissolved in an organic solvent, which was a mixture of ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7.

[0155] [Experimental Example 1: High-Temperature Lifetime Characteristics] Each of the lithium secondary batteries manufactured as described above was charged to 4.2V at 45°C with a constant current of 1.0C, and then discharged to 2.5V with a constant current of 0.5C. This constituted one charge-discharge cycle, and after 50 cycles, the capacity retention rate was measured. The measurement results are shown in [Table 1] below.

[0156] [Experimental Example 2: Gas Generation During High-Temperature Storage] Each of the lithium secondary batteries manufactured as described above was charged to a State of Charge (SOC) of 100, stored at 60°C for 8 weeks, then perforated in a vacuum chamber to expel the gas from inside the battery and collect it inside the vacuum chamber. The amount of gas generated in the chamber was analyzed using a gas chromatography-flame ionization detector (GC-FID). The ratio of the gas generation amount of lithium secondary batteries using the cathode materials of Comparative Examples 1 to 3 is shown in [Table 1] below, when the gas generation amount of the lithium secondary battery using the cathode material of the example is set to 100%.

[0157] [Experiment Example 3: Resistance Evaluation] Each of the lithium secondary batteries manufactured as described above was charged and discharged for one cycle at 25°C under conditions of 0.2 / 0.2C. Then, in the next cycle, a current of 0.2C was applied to charge and discharge the batteries to achieve SOC 50 and SOC 10 based on discharge capacity. After that, a 1C pulse was applied for 10 seconds, and the DCIR resistance was measured. The measurement results are shown in [Table 1].

[0158] [Experimental Example 4: Evaluation of the fracture rate of secondary particles] Three g of each of the cathode material powders from Examples and Comparative Examples 1-3 were taken, and their volume-cumulative particle size distribution graphs were measured. Then, the collected cathode material powders were placed in a holder with a diameter of 1.3 cm, and a pressure of 6 tons was applied. After this, the volume-cumulative particle size distribution graph was measured again. In the volume-cumulative particle size distribution graph before pressurization, the range of particle sizes larger than the particle size at the point where dY / dX (where X is particle size and Y is volume) is minimized was defined as the secondary particle region. The value calculated using the following mathematical formula within this secondary particle region was evaluated as the secondary particle cracking rate.

[0159]

number

[0160] In the above mathematical formula, X0 and Y0 are the particle size and volume in the volume cumulative particle size distribution graph before pressurization, respectively. p and Yp This shows the particle size and volume in the volume cumulative particle size distribution graph after pressurizing with 6 tons of pressure.

[0161] [Table 1]

[0162] Referring to Table 1, it can be confirmed that the cathode material of the example shows less particle cracking after pressurization compared to the cathode materials of Comparative Examples 1 to 3. Furthermore, it can be confirmed that the lithium secondary battery using the cathode material of the example exhibits superior high-temperature life characteristics, less gas generation after high-temperature storage, and excellent high-temperature performance compared to the lithium secondary battery using the cathode materials of Comparative Examples 1 to 3.

Claims

1. A first positive electrode active material having a form of secondary particles in which multiple grains are aggregated, and at least a portion of the secondary particles includes an oriented structure in which the long axes of the grains are aligned from the center of the secondary particles toward the surface, and the concentration of cobalt at the grain boundaries, which are the interfaces between the grains, is higher than the concentration of cobalt inside the grains, A cathode material comprising a central part having at least one form of a single particle consisting of one nodule and a pseudo-single particle which is a composite of 30 or fewer nodules, and a second cathode active material formed on the central part and including a coating layer containing cobalt.

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

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

4. The cathode material according to claim 1, wherein the first cathode active material and the second cathode active material each independently contain a nickel-based lithium composite transition metal oxide represented by the following chemical formula 1. [Chemical formula 1] Li ｘ [Ni ａ Co ｂ M １ ｃ M ２ ｄ ]O ２－ｙ A ｙ In the above [Chemical Formula 1], Said M １ is one or more elements selected from the group consisting of Mn and Al, Said M ２ is one or more elements 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. A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S. 0.98 ≤ x ≤ 1.20, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d ≤ 0.2, 0 ≤ y ≤ 0.

2.

5. The cathode material according to claim 1, wherein the first cathode active material and the second cathode active material are contained in a weight ratio of 90:10 to 50:

50.

6. The cathode material according to claim 1, wherein the first cathode active material includes a nickel-based lithium composite transition metal oxide represented by the following chemical formula [Chemical Formula 1-1]. [Chemical formula 1-1] Li ｘ１ [Ni ａ１ Co ｂ１ M １ ｃ１ M ２ ｄ１ ]O ２－ｙ１ A ｙ１ In the above [Chemical Formula 1-1], Said M １ is one or more elements selected from the group consisting of Mn and Al, Said M ２ is one or more elements 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. A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S. 0.98 ≤ x1 ≤ 1.20, 0.6 ≤ a1 ≤ 0.9, 0.01 ≤ b1 < 0.4, 0.01 ≤ c1 < 0.4, 0 ≤ d1 ≤ 0.2, 0 ≤ y1 ≤ 0.

2.

7. The positive electrode material according to claim 1, wherein the grains in the first positive electrode active material, whose long axes are arranged from the center of the secondary particles toward the surface, have an angle between their long axis and the a-axis direction of the crystal structure of -15° to 15°.

8. The positive electrode material according to claim 1, wherein the grains in the first positive electrode active material, whose long axes are arranged from the center of the secondary particles toward the surface, have an aspect ratio of 1.5 or more and 15 or less.

9. The cathode material according to claim 1, wherein the first cathode active material includes a core portion in which grains are randomly aggregated and a shell portion formed outside the core portion in which grains are arranged in an oriented structure.

10. The positive electrode material according to claim 9, wherein the grain in the core portion has an aspect ratio of 0.8 or more and 1.2 or less.

11. The positive electrode material according to claim 9, wherein the grain within the shell portion has an aspect ratio of 1.5 or more and 15 or less.

12. The cathode material according to claim 1, wherein the average particle size of the grains of the first cathode active material is 0.05 μm or more and 4 μm or less.

13. The cathode material according to claim 1, wherein the central part of the second cathode active material contains a nickel-based lithium composite transition metal oxide represented by the following chemical formula [Chemical Formula 1-2]. [Chemical formula 1-2] Li ｘ２ [Ni ａ２ Co ｂ２ M １ ｃ２ M ２ ｄ２ ]O ２－ｙ２ A ｙ２ In the above [Chemical Formula 1-2], Said M １ is one or more elements selected from the group consisting of Mn and Al, Said M ２ is one or more elements 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. A is one or more elements selected from the group consisting of F, Cl, Br, I, At, and S. 0.8 ≤ x² ≤ 1.20, 0.8 ≤ a² < 1, 0 < b² < 0.2, 0.01 ≤ c² < 0.2, 0 ≤ d² ≤ 0.2, 0 ≤ y² ≤ 0.

2.

14. The cathode material according to claim 1, wherein the coating layer of the second cathode active material has a composition represented by the following [Chemical Formula 2]. [Chemical formula 2] Li ｚ Co １－ｗ M ３ ｗ O ２ In the above [Chemical Formula 2], the M ３ z is one or more elements 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 satisfies 0.8 ≤ z ≤ 1.2 and 0 ≤ w ≤ 0.

2.

15. The cathode material according to claim 1, wherein the average particle size of the nodules of the second cathode active material is 0.5 μm or more and 3.5 μm or less.

16. The positive electrode material according to claim 9, wherein the grains within the shell portion are rod-shaped.

17. A positive electrode comprising the positive electrode material described in any one of claims 1 to 16.

18. A lithium secondary battery comprising the positive electrode described in claim 17.

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