positive electrode active material

Abstract

Provided is a positive electrode active material capable of reducing an increase rate of resistance generated with charge and discharge of a battery. The positive electrode active material contains at least one element selected from the group consisting of a Ni element, a Co element, and a Mn element, has a shape in which two or more primary particles are stacked, the primary particles are single crystals having a crystal structure belonging to space group R-3m, and the positive electrode active material includes at least a first particle and a second particle connected in this order as the two or more primary particles, the first particle and the second particle are oriented and stacked in such a manner that a 003 plane of the first particle is parallel to a 003 plane of the second particle, and in a transmission electron microscope (TEM), a length of the first particle and a length of the second particle are different in a direction parallel to the 003 plane of each primary particle.

Description

Technical Field

[0001] This disclosure relates to positive electrode active materials. Background Technology

[0002] Various technologies have been proposed regarding the positive electrode active materials disclosed in Patent Documents 1 and 2.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2013-65397

[0006] Patent Document 2: International Publication No. 2012 / 046557 Summary of the Invention

[0007] The problem that the invention aims to solve

[0008] In the past, various positive electrode active materials have been proposed in order to obtain positive electrodes with high battery characteristics such as high cycle performance and high output performance.

[0009] In Patent Document 1, the positive electrode active material particles are in a state where lithium intercalation / deintercalation planes are dispersed within an aggregate of multiple 003-plane oriented particles. The short-axis crystal plane of the primary particles is the 003 plane, and these short-axis crystal planes combine to form secondary particles. It is believed that the structure of these secondary particles is prone to change with the charging and discharging of the battery, leading to an increase in battery resistance.

[0010] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide a positive electrode active material capable of reducing the rate of increase in resistance during the charging and discharging of the battery.

[0011] Methods for solving problems

[0012] That is, this disclosure includes the following methods.

[0013] <1>

[0014] A positive electrode active material,

[0015] The positive electrode active material contains at least one element selected from the group consisting of Ni, Co, and Mn.

[0016] The positive electrode active material has a shape of two or more primary particles stacked together.

[0017] The primary particle is a single crystal with a crystal structure belonging to space group R-3m.

[0018] The positive electrode active material has at least a first particle and a second particle connected in sequence as the two or more primary particles.

[0019] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 surface of each primary particle is exposed at its outer edge.

[0020] The first particle and the second particle are stacked with the 003 facet of the first particle parallel to the 003 facet of the second particle.

[0021] When the positive electrode active material is cross-sectionally observed using the transmission electron microscope, the length of the first particle is different from the length of the second particle in the direction parallel to the 003 plane of each primary particle.

[0022] <2>

[0023] According to the positive electrode active material described in <1>, wherein...

[0024] The positive electrode active material has a shape of three or more primary particles stacked together.

[0025] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 surface of each primary particle is exposed at its outer edge.

[0026] Each of the primary particles is stacked with its 003 facet parallel to that of the primary particle.

[0027] When the positive electrode active material is cross-sectionally observed using the transmission electron microscope, the lengths of adjacent primary particles are different in the direction parallel to the 003 plane of each primary particle.

[0028] <3>

[0029] According to the positive electrode active material described in <1> or <2>, wherein,

[0030] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, the outer edges, in a direction perpendicular to the 003 plane of each primary particle, show the surfaces other than the 003 plane of each primary particle.

[0031] The other faces of each primary particle besides the 003 face are the 012 face, 101 face, 104 face, or 110 face.

[0032] <4>

[0033] The positive electrode active material according to any one of <1> to <3>, wherein...

[0034] The positive electrode active material has a shape of two or more but less than 100 primary particles stacked together.

[0035] <5>

[0036] The positive electrode active material according to any one of <1> to <4>, wherein...

[0037] In a direction parallel to the 003 plane of each of the primary particles, the ratio of the length of the first particle to the length of the second particle is 1.1 to 2.0.

[0038] <6>

[0039] According to the positive electrode active material described in <1>, wherein...

[0040] In the volume-based particle size distribution, the (D90-D10) / D50 of two or more primary particles is greater than 1.30 and less than 1.70.

[0041] <7>

[0042] A positive electrode layer containing any one of <1> to <6> positive electrode active materials.

[0043] <8>

[0044] A battery comprising a positive electrode layer containing any one of the positive electrode active materials described in <1> to <6>.

[0045] <9>

[0046] A method for manufacturing a positive electrode active material, wherein the positive electrode active material is manufactured as described in any one of <1> to <6>.

[0047] include:

[0048] In the first stage of the firing process, a first mixture of large particles of transition metal hydroxide, small particles of the transition metal hydroxide having a smaller particle size than the large particles, and lithium compound is fired at 700℃~1100℃ to obtain the precursor of the positive electrode active material.

[0049] The magnetic field application process includes applying a magnetic field to a slurry obtained by dispersing the precursor of the positive electrode active material in a solvent.

[0050] The drying process includes drying the slurry to obtain a dried product; and

[0051] The second stage firing process involves firing the dried material at 800℃~1000℃ to obtain the positive electrode active material.

[0052] Invention Effects

[0053] According to this disclosure, a positive electrode active material can be provided that can reduce the rate of increase in resistance during battery charging and discharging. Attached Figure Description

[0054] Figure 1 This is a schematic diagram illustrating an example of the structure of the positive electrode active material of this disclosure. Detailed Implementation

[0055] The following describes embodiments of this disclosure. It should be noted that matters not specifically mentioned in this specification but necessary for implementing this disclosure (e.g., the general composition and manufacturing process of the positive electrode active material that does not constitute a feature of this disclosure) are design matters understood by those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field.

[0056] In addition, the dimensional relationships (length, width, thickness, etc.) in the attached drawings do not reflect the actual dimensional relationships.

[0057] Unless otherwise specified, elements described in the "singular form" may include plural forms. For example, a particle may also represent multiple particles (a swarm of particles).

[0058] In this disclosure, an example of a method for calculating the average particle size is shown below. First, for a single particle, the particle size is calculated by considering the particle as spherical in a transmission electron microscope (TEM) image or a scanning electron microscope (SEM) image at an appropriate magnification (e.g., 50,000 to 1,000,000 times). For 200 to 300 particles of the same type, the particle size is calculated based on the TEM or SEM observations described above, and the average value of these particles is taken as the average particle size.

[0059] 1. Positive electrode active material

[0060] In this disclosure, the positive electrode active material contains at least one element selected from the group consisting of Ni, Co, and Mn.

[0061] The positive electrode active material has a shape of two or more primary particles stacked together.

[0062] The primary particle is a single crystal with a crystal structure belonging to space group R-3m.

[0063] The positive electrode active material has at least a first particle and a second particle connected in sequence as the two or more primary particles.

[0064] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 surface of each primary particle is exposed at its outer edge.

[0065] The first particle and the second particle are stacked with the 003 facet of the first particle parallel to the 003 facet of the second particle.

[0066] When the positive electrode active material is cross-sectionally observed using the transmission electron microscope, the length of the first particle is different from the length of the second particle in the direction parallel to the 003 plane of each primary particle.

[0067] In this disclosure, stress relaxation is achieved by alternately exposing the 003 surface (serving as a stabilizing surface) with other surfaces such as the 104 surface (serving as a lithium entry / exit surface), thereby suppressing structural damage to particles in the positive electrode active material. Because the 003 surface is alternately exposed with other surfaces, the structure of particles in the positive electrode active material can be maintained during battery charging and discharging, suppressing an increase in battery resistance.

[0068] Figure 1 This is a schematic diagram illustrating an example of the structure of the positive electrode active material of this disclosure. For example... Figure 1 As shown, the positive electrode active material 100 of this disclosure has a first particle 10, a second particle 20, a third particle 30 and a fourth particle 40 connected in sequence.

[0069] When the positive electrode active material 100 is cross-sectionally observed, at least a portion of the 003 surface of each of the primary particles 10 to 40 is exposed at the outer edge.

[0070] Each of the primary particles 10 to 40 is stacked in an orientation parallel to the 003 plane of each of the primary particles 10 to 40. That is, the primary particles 10 to 40 are not stacked in the direction parallel to the 003 plane.

[0071] In the cross-sectional view of the positive electrode active material 100, in the direction parallel to the 003 plane of each primary particle 10 to 40, the length L1 of the first particle 10 is greater than the length L2 of the second particle 20, the length L2 of the second particle 20 is less than the length L3 of the third particle 30, and the length L3 of the third particle 30 is greater than the length L4 of the fourth particle 40.

[0072] When the positive electrode active material 100 is observed in cross-section, the 104 facet of each of the primary particles 10 to 40 is exposed in a direction perpendicular to the 003 facet of each of the primary particles 10 to 40. Therefore, when the positive electrode active material 100 is observed in cross-section, the 003 facet of the positive electrode active material 100 is alternately exposed with the 104 facet, which is another facet.

[0073] The positive electrode active material must contain at least one transition metal (TM) element selected from the group consisting of Ni, Co, and Mn. The positive electrode active material can be a lithium transition metal composite oxide containing Li, a transition metal, and O. The lithium transition metal composite oxide must contain at least Ni as a transition metal, but can also contain two, three, or more transition metals. Examples of transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Zr, and Nb.

[0074] Lithium transition metal composite oxides need to contain at least Ni as a transition metal, and may further contain, for example, Co and Mn.

[0075] Lithium transition metal composite oxides can also contain other metals M besides Li and transition metals, based on Li and transition metals. 1 (Including semi-metals). As other metals M 1 Examples include Al, Si, Ga, Ge, In, Sn, etc.

[0076] Lithium transition metal composite oxides may also contain Li, Ni, Co, Mn, and O.

[0077] For a lithium transition metal composite oxide to contain 1 mol of all metals except Li, the total proportion of Ni, Co, and Mn in the lithium transition metal composite oxide can be, for example, 0.80 mol or more, 0.90 mol or more, 0.95 mol or more, or 1 mol. It should be noted that "the total proportion of Ni, Co, and Mn" also includes cases where the proportion of one or two of Ni, Co, and Mn is 0.

[0078] Lithium transition metal composite oxides can have the general formula Li x Ni a Co b Mn c O y The composition represented by (0.1≦x≦1.5, 0.5≦a≦1.0, 0≦b≦0.3, 0≦c≦0.3, a+b+c=1.0, 1.5≦y≦2.1).

[0079] In the general formula, the Li component ratio "x" must satisfy the relationship "0.1 ≤ x ≤ 1.5". For example, the Li component ratio "x" can be 0.4 or higher, 0.6 or higher, 0.8 or higher, 1.0 or higher, or 1.1 or higher. For example, the Li component ratio "x" can be 1.4 or lower or 1.2 or lower.

[0080] In the above general formula, the ratio of component O "y" must satisfy the relationship "1.5 ≤ y ≤ 2.1". For example, the ratio of component O "y" can be 1.6 or higher, 1.7 or higher, 1.8 or higher, or 1.9 or higher. For example, the ratio of component O "y" can be 2.0 or lower.

[0081] The Ni component ratio "a", Co component ratio "b", and Mn component ratio "c" in the above general formula satisfy the relationship "a+b+c=1.0".

[0082] In the above general formula, the Ni component ratio "a" must satisfy the relationship of "0.5 ≤ a ≤ 1.0". For example, the Ni component ratio "a" can be 0.6 or higher, 0.7 or higher, 0.8 or higher, or 0.85 or higher. For example, the Ni component ratio "a" can be 0.9 or lower.

[0083] In the above general formula, the Co component ratio "b" must satisfy the relationship "0 ≤ b ≤ 0.3". For example, the Co component ratio "b" can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. For example, the Co component ratio "b" can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0084] In the above general formula, the Mn component ratio "c" must satisfy the relationship "0 ≤ c ≤ 0.3". For example, the Mn component ratio "c" can be 0.01 or higher, 0.02 or higher, 0.03 or higher, 0.04 or higher, 0.05 or higher, 0.06 or higher, 0.07 or higher, or 0.075 or higher. For example, the Mn component ratio "c" can be 0.25 or lower, 0.20 or lower, 0.15 or lower, 0.10 or lower, 0.09 or lower, or 0.08 or lower.

[0085] Any dopant can be added to the lithium transition metal composite oxide. The dopant represents an element other than Li, Ni, Co, Mn, and O. For example, the dopant may contain at least one element selected from the group consisting of Zr, Mo, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, and Ag. The dopant composition ratio d relative to a+b+c = 1.0 can be, for example, 0.005 or more, 0.01 or more, 0.02 or more, 0.03 or more, or 0.04 or more. The dopant composition ratio d relative to a+b+c = 1.0 can be, for example, 0.05 or less.

[0086] The positive electrode active material is used in the battery. Details about the battery will be described later.

[0087] The positive electrode active material can have a shape with two or more primary particle stacks, or it can have a shape with n primary particle stacks. Here, n is an integer greater than or equal to 2, with upper limits such as less than 100, less than 50, less than 10, less than 4, or less than 3.

[0088] The primary particles of the positive electrode active material are single crystals with a crystal structure belonging to space group R-3m. In SEM images, a single crystal appears as an independent, unaggregated single particle (primary particle). Single crystals do not exhibit grain boundaries in SEM images. The magnification of SEM images is, for example, 10,000x to 30,000x.

[0089] The crystal structure of primary particles of positive electrode active material can also be a layered rock salt structure.

[0090] The positive electrode active material can also be a polycrystalline structure composed of two or more primary particles. The positive electrode active material has more than one grain boundary in the SEM image, and the upper limit can be, for example, below 100, below 50, below 10, below 3, or below 2.

[0091] The positive electrode active material can be a particle. Positive electrode active material particles can also be secondary particles formed by stacking two or more primary particles.

[0092] The particle size of the primary particles in the positive electrode active material can be 0.5 μm or larger, 0.6 μm or larger, 0.8 μm or larger, or 1.0 μm or larger. If the particle size of the primary particles is too small, the particles cannot grow sufficiently, making it difficult to prepare single crystals. On the other hand, the particle size of the primary particles can be, for example, 10 μm or smaller, 5 μm or smaller, or 3 μm or smaller. The particle size of the primary particles can be obtained, for example, from the longest diameter in TEM or SEM images. Furthermore, if the positive electrode layer contains primary particles, the particle size of the primary particles can be obtained from the longest diameter of the primary particles in the SEM cross-sectional image of the positive electrode layer. The "particle size of the primary particles" mentioned here is not the average particle size. That is, when the positive electrode active material contains multiple primary particles, the "particle size of the primary particles" refers to the "particle size of each individual primary particle".

[0093] The average particle size of the positive electrode active material can be, for example, greater than 0.5 μm or greater than 1.0 μm. The average particle size of the positive electrode active material can be less than 100 μm or less than 30 μm.

[0094] The positive electrode active material has at least two or more primary particles, namely a first particle and a second particle connected in sequence, and may further have a third particle and a fourth particle. The positive electrode active material may also have two or more primary particles, namely, the first particle to the nth particle connected in sequence. Here, n can be an integer greater than or equal to 2, with upper limits such as less than 100, less than 50, less than 4, or less than 3.

[0095] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 facet of each primary particle is exposed at the outer edge.

[0096] The first and second particles are stacked with their 003 faces parallel to each other. If the positive electrode active material further includes a third particle, the first, second, and third particles can also be stacked with their 003 faces parallel to each other. That is, each primary particle can also be stacked with its 003 face parallel to its own.

[0097] In this disclosure, parallelism includes not only perfect parallelism, but also slightly inclined configurations within a range of ±5 degrees.

[0098] The primary particles constituting the positive electrode active material can also be arranged without stacking in the direction parallel to the 003 plane. By ensuring that the primary particles do not stack in the direction parallel to the 003 plane, the diffusion distance of lithium ions within the positive electrode active material in the direction parallel to the 003 plane can be shortened.

[0099] When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, the outer edge is not exposed in the direction perpendicular to the 003 plane of each primary particle, except for the other surfaces of each primary particle other than the 003 plane.

[0100] Other than the 003 facet of each primary particle, the other faces can be the 012 facet, the 101 facet, the 104 facet, or the 110 facet.

[0101] When the positive electrode active material contains a first particle and a second particle, and when the positive electrode active material is cross-sectionally observed using a transmission electron microscope, the length of the first particle is different from the length of the second particle in the direction parallel to the 003 plane of each primary particle. The length of the first particle can be greater than or less than the length of the second particle. When the positive electrode active material includes a third particle in addition to the first and second particles, when observed using a transmission electron microscope, the length of the first particle can be different from the length of the second particle in the direction parallel to the 003 plane of each primary particle, and the length of the second particle can be different from the length of the third particle. If the length of the first particle is different from the length of the second particle, then the length of the first particle can be the same as the length of the third particle. The lengths of the first and third particles can be greater than or less than the length of the second particle. That is, in the positive electrode active material, the lengths of adjacent primary particles are different in the direction parallel to the 003 plane of each primary particle. The length of the primary particle mentioned here can be the particle size of the primary particle, or it can be something other than the particle size of the primary particle. When the length of a primary particle is the longest diameter of a primary particle in TEM or SEM images, the length of a primary particle is its particle diameter. By making the lengths of adjacent primary particles different in a direction parallel to the 003 facet of the primary particle, the 003 facet of the positive electrode active material is alternately exposed with other faces when the outer edge is observed during cross-sectional viewing.

[0102] In the direction parallel to the 003 plane of each primary particle, the ratio of the length of the first particle to the length of the second particle can be 1.1 to 2.0. That is, the ratio of the length of the (n-1)th particle to the length of the nth particle can be 1.1 to 2.0. Here, n can be an integer greater than or equal to 2, with an upper limit of, for example, less than 100, less than 50, less than 4, or less than 3. Furthermore, the ratio of the length of the (m-1)th particle to the length of the mth particle can be 1.1 to 2.0. Here, m can be an even number greater than or equal to 2, with an upper limit of, for example, less than 100, less than 50, or less than 4.

[0103] Furthermore, in this disclosure, for ease of explanation, all particles having the same length as the first particle can be considered as the first particle, and all particles having the same length as the second particle can be considered as the second particle.

[0104] In the volumetric particle size distribution, the (D90-D10) / D50 of two or more primary particles can be greater than 1.30 and less than 1.70, or greater than 1.32 and less than 1.65. The volumetric particle size distribution can be obtained, for example, by randomly selecting 2 to 50 primary particles from positive electrode active materials from TEM or SEM images, calculating the radius of the longest diameter of each primary particle, and creating a histogram.

[0105] In a volume-based particle size distribution, the D50 of the first particle can be, for example, 3.1 μm to 4.2 μm.

[0106] In a volume-based particle size distribution, the D50 of the second particle can be, for example, 1.0 μm to 1.1 μm.

[0107] 2. Method for manufacturing positive electrode active material

[0108] In this disclosure, a method for manufacturing the aforementioned positive electrode active material includes:

[0109] In the first stage of the firing process, a first mixture of large particles of transition metal hydroxide, small particles of the transition metal hydroxide having a particle size smaller than that of the large particles, and lithium compound is fired at 700℃~1100℃ to obtain the precursor of the positive electrode active material.

[0110] The magnetic field application process involves applying a magnetic field to a slurry obtained by dispersing the precursor of the positive electrode active material in a solvent.

[0111] The drying process includes drying the slurry to obtain a dried product; and

[0112] The second stage firing process involves firing the dried material at 800℃~1000℃ to obtain the positive electrode active material.

[0113] The method for manufacturing the positive electrode active material disclosed herein includes (1) a first-stage firing process, (2) a magnetic field application process, (3) a drying process, and (4) a second-stage firing process.

[0114] In this disclosure, primary particles of transition metal hydroxides with different particle sizes are synthesized. These particles are then mixed and subjected to a first-stage calcination to obtain a precursor for the positive electrode active material. Subsequently, by applying a magnetic field to a slurry containing the precursor, the precursor is oriented along the direction of the magnetic field, thereby ensuring the crystal orientation of the primary particles in the precursor is consistent. The slurry is then dried, allowing the 003 faces of the primary particles to connect with each other through a second-stage calcination. In the first-stage calcination, by using primary particles of transition metal hydroxides with different particle sizes, the 003 facets of the positive electrode active material particles obtained through the second-stage calcination are alternately exposed with other faces.

[0115] (1) First stage firing process

[0116] In the first stage of the firing process, a first mixture of large particles of transition metal hydroxide, small particles of the transition metal hydroxide having a particle size smaller than that of the large particles, and lithium compounds is fired at 700°C to 1100°C to obtain the precursor of the positive electrode active material.

[0117] The method for manufacturing transition metal hydroxides disclosed herein is not particularly limited, and the following methods may be cited as examples. First, an aqueous solution of the transition metal hydroxide as a raw material is prepared. For example, a method of dissolving a water-soluble transition metal compound in water may be cited as a method of preparing the aqueous solution. For example, metal salts such as sulfates and nitrates may be cited as transition metal compounds. For example, NiSO4 and Ni(NO3)2 may be cited as Ni sources. For example, CoSO4, Co(NO3)2, and Co(NO3)3 may be cited as Co sources. For example, MnSO4 and Mn(NO3)2 may be cited as Mn sources. The composition of the aqueous solution may be appropriately adjusted according to the target positive electrode active material.

[0118] Next, a certain amount of NH3 aqueous solution is added to the reaction vessel, and nitrogen replacement is carried out under stirring with a stirrer or similar device to obtain a non-oxidizing atmosphere. The nitrogen flow rate for nitrogen replacement is not particularly limited, for example, it can be set to 2 to 6 L / min.

[0119] Next, an aqueous sodium hydroxide solution is added to the reaction vessel to maintain an alkaline pH (e.g., pH = 11.3–12.0), while simultaneously adding the above-mentioned raw material aqueous solution and NH3 aqueous solution dropwise into the reaction vessel for 1–7 hours. The reaction temperature is not particularly limited; for example, it can be set above 50°C and below 65°C. By varying the reaction time, primary particles of transition metal hydroxides with different particle sizes are obtained. For example, by setting the reaction time to 1–3 hours, small particles of transition metal hydroxides are obtained, and by setting the reaction time to 5–7 hours, large particles of transition metal hydroxides are obtained. The small particles have a smaller particle size than the large particles. The particle size referred to here, in the case of a single particle, can be the particle size of each particle; in the case of multiple particles, it can be the average particle size D50.

[0120] After the reaction is complete, pre-firing can be carried out. Pre-firing can be carried out for 4 to 10 hours at 120℃~220℃ and 0.2~1.0MPa, for example.

[0121] After the reaction or pre-calcination is complete, the mixture is washed with water and filtered to remove the transition metal hydroxide, which is then dried. The drying process can be carried out, for example, at 110°C for 10–12 hours.

[0122] In this disclosure, the transition metal hydroxide contains a transition metal. The transition metal hydroxide may be a nickel-cobalt-manganese composite hydroxide containing nickel (Ni), cobalt (Co), and manganese (Mn). In the nickel-cobalt-manganese composite hydroxide, the molar ratio of each metal relative to the total amount of nickel, cobalt, and manganese is the same as the component ratio expressed by the above general formula of the lithium transition metal composite oxide in the positive electrode active material.

[0123] The lithium compound (Li source) can be, for example, selected from at least one of lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride. The lithium compound can also be lithium hydroxide. The molar ratio of Li in the Li source to the TM contained in the transition metal hydroxide can be, for example, 0.4 or more, 0.6 or more, 0.8 or more, 1.0 or more, or 1.1 or more, or 1.4 or less or 1.2 or less.

[0124] The ratio of lithium compound and transition metal hydroxide in the first mixture is set such that the molar ratio of lithium and other metals relative to the total stoichiometric ratio of lithium and metals contained in the transition metal hydroxide in the target cathode active material is typically equal to the molar ratio of lithium and other metals in the first mixture. The mixing method is not particularly limited and known methods can be used.

[0125] The first mixture may also contain molten salt. By allowing the molten salt to function as a flux, sufficient grain growth of the primary particles can be achieved. The molten salt may contain Li. Examples of molten salts include lithium hydroxide. The molar ratio (Li / TM) of Li in the molten salt relative to the transition metal hydroxide may, for example, be 0.01 or more, 0.05 or more, 0.10 or more, or 0.15 or more. On the other hand, the Li / TM ratio may, for example, be 0.60 or less, 0.50 or less, 0.40 or less, or 0.30 or less.

[0126] The first mixture may also contain lithium hydroxide as a Li source and a molten salt. The molar ratio of Li in the Li source and the molten salt to the TM in the transition metal hydroxide (Li´ / TM) may, for example, be 1.01 or more, 1.05 or more, 1.10 or more, or 1.15 or more. On the other hand, Li´ / TM may, for example, be 1.60 or less, 1.50 or less, 1.40 or less, or 1.30 or less.

[0127] For example, lithium transition metal composite oxides can be obtained by calcining the first mixture at 700℃ to 1100℃ for 8 to 15 hours. Known calcining furnaces such as muffle furnaces can be used for this process.

[0128] The firing temperature in the first stage of the firing process is limited to a lower limit of 800℃, 850℃, 900℃, or 950℃, and an upper limit of 1000℃.

[0129] The firing time in the first stage of the firing process can be more than 9 hours or more than 10 hours.

[0130] The firing time in the first stage of the firing process can be less than 13 hours or less than 11 hours.

[0131] The precursor of the positive electrode active material obtained by calcining the transition metal hydroxide of this disclosure is usually a single-crystal active material composed of primary particles.

[0132] (2) Magnetic field application process

[0133] In the magnetic field application process, a magnetic field is applied to the slurry obtained by dispersing the precursor of the positive electrode active material in a solvent.

[0134] Solvents can be N-methylpyrrolidone (NMP), etc.

[0135] The applied magnetic field strength can be 0.8–2T or 1–1.5T.

[0136] The magnetic field can be applied for 1 minute to 1 hour, or for 5 minutes to 10 minutes.

[0137] (3) Drying process

[0138] In the drying process, the slurry is dried to obtain a dried product.

[0139] The drying temperature is, for example, 90℃~110℃, or 100℃.

[0140] The drying time can be, for example, 1 minute to 1 hour, or 5 minutes to 10 minutes.

[0141] (4) Second stage firing process

[0142] In the second stage of the firing process, the dried material is fired at 800℃~1000℃ to obtain the positive electrode active material.

[0143] The firing temperature in the second stage of the firing process can be above 850℃ or 900℃ at the lower limit and below 950℃ at the upper limit.

[0144] The firing time in the second stage firing process can be more than 1 hour, more than 9 hours, or more than 10 hours. On the other hand, the firing time in the second stage firing process can be less than 15 hours, less than 13 hours, or less than 11 hours.

[0145] 3. Battery

[0146] The positive electrode active material provided in this disclosure is, for example, a positive electrode active material that can be used as the positive electrode of a battery (such as a lithium-ion battery). That is, in this disclosure, a battery in which a positive electrode, an electrolyte layer, and a negative electrode are stacked in sequence is provided, i.e., a battery in which the positive electrode contains the positive electrode active material of this disclosure.

[0147] According to this disclosure, by using the above-mentioned positive electrode active material in a battery, the rate of increase in resistance during battery charging and discharging can be reduced.

[0148] The following is an explanation of the battery.

[0149] [positive electrode]

[0150] The positive electrode has a positive electrode layer and may be further equipped with a positive electrode current collector as needed.

[0151] The positive electrode layer is a layer that contains at least the positive electrode active material disclosed herein as the positive electrode active material.

[0152] The positive electrode layer can be disposed on one side or both sides of the positive electrode current collector. The positive electrode can be a multilayer structure consisting of two or more positive electrode layers formed on at least one side of the positive electrode current collector. In addition, when two or more positive electrode layers are formed, the types of positive electrode active materials contained in each positive electrode layer can be the same or different.

[0153] The positive electrode active material used in the positive electrode layer may contain only the positive electrode active material disclosed herein, or it may further contain other active materials. Additionally, the positive electrode layer may, as needed, contain at least one of an electrolyte, a conductive material, and a binder.

[0154] The mixing ratio (mass ratio) of the positive electrode active material and other active materials disclosed herein can be, for example, "positive electrode active material of this disclosure: other active materials = 9.5:0.5~0.5:9.5", "positive electrode active material of this disclosure: other active materials = 9:1~1:9", "positive electrode active material of this disclosure: other active materials = 8:2~2:8", "positive electrode active material of this disclosure: other active materials = 7:3~3:7", or "positive electrode active material of this disclosure: other active materials = 6:4~4:6". Other active materials can be polycrystalline active materials (polycrystalline particles) composed of secondary particles of the aforementioned lithium transition metal composite oxide. Other active materials include, for example, lithium iron phosphate (olivine structure), lithium manganese phosphate (olivine structure), lithium manganese iron phosphate (olivine structure), LiMnO2 (rock salt structure), Li(NiMn)2O4 (spinel structure), and LiCoO2 (layered structure).

[0155] The proportion of positive electrode active material in the positive electrode layer can be, for example, 20% by mass or more, or 30% by mass or more, or 40% by mass or more. If the proportion of positive electrode active material is too small, there is a possibility that sufficient energy density cannot be obtained. On the other hand, the proportion of positive electrode active material in the positive electrode layer can be, for example, 95% by mass or less, or 70% by mass or less, or 60% by mass or less. If the proportion of positive electrode active material is too large, there is a possibility that the ionic conductivity and electronic conductivity in the positive electrode layer will be relatively reduced.

[0156] As an electrolyte, examples include solid electrolytes. Solid electrolytes can be inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complexed hydride solid electrolytes, or organic solid electrolytes such as gel electrolytes.

[0157] Sulfide solid electrolytes are electrolytes containing sulfur (S). They typically contain at least lithium (Li) and sulfur. Sulfide solid electrolytes may also further contain nitrogen (M) (M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In). Additionally, sulfide solid electrolytes may also contain halogens such as sulfur (F), chlorine (Cl), br, and iodine (I).

[0158] Sulfide solid electrolytes can be glass-based (amorphous), glass-ceramic, or crystalline. They can also possess crystalline phases. Examples of such crystalline phases include the Thio-LISICON type, the argyrodite type, and the LGPS type.

[0159] The composition of sulfide solid electrolytes is not particularly limited; examples include xLi₂S・(1-x)P₂S₅ (0.5≦x<1) and yLiI・zLiBr・(100-yz)(xLi₂S・(1-x)P₂S₅) (0.5≦x<1, 0≦y≦30, 0≦z≦30). In the above compositions, x can satisfy 0.7≦x≦0.8. Other examples of sulfide solid electrolyte compositions include Li 7-x PS 6-x X x X is at least one of F, Cl, Br, and I, and x satisfies 0 ≤ x < 2. Other examples of sulfide solid electrolytes include Li. 4-x Me 1-x P x S4 (0 < x < 1). Me is at least one of Al, Zn, In, Ge, Si, Sn, Sb, Ga, and Bi. Examples of sulfide solid electrolytes include LiI-LiBr-Li2S-P2S5, LiI-Li2S-P2S5, LiI-Li2S-P2O5, and LiI-Li3PO4-P2S5.

[0160] Examples of oxide solid electrolytes include substances with a garnet-type crystal structure containing Li, La, A (where A is at least one of Zr, Nb, Ta, and Al), and O. Examples of oxide solid electrolytes include Li₂O-B₂O₃-P₂O₅, Li₂O-SiO₂, Li₂O-B₂O₃, and Li₂O-P₂O₃. 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 Li7La3Zr2O 12Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, and Li 3+x PO 4-x N x (1≦x≦3), etc.

[0161] As a halide solid electrolyte, it can be, for example, a solid electrolyte containing Li, D, and X (D represents at least one of Ti, Al, and Y, and X represents F, Cl, or Br).

[0162] Gel electrolytes may also contain an electrolyte and a polymeric material. The polymeric material can form a polymeric matrix. The polymeric material includes, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyvinylidene fluoride-polyacrylonitrile (PVdF-PAN), polyethylene oxide (PEO), polyethylene glycol (PEG), and derivatives of the above substances.

[0163] From an operational point of view, solid electrolytes can be in granular form.

[0164] In addition, the average particle size of the solid electrolyte is not particularly limited and can be from 1 nm to 100 μm.

[0165] The proportion of solid electrolyte in the positive electrode layer is, for example, 1% by mass or more. If the proportion of solid electrolyte is too small, there is a possibility that the ion conduction pathways in the positive electrode layer are insufficient. On the other hand, the proportion of solid electrolyte in the positive electrode layer is, for example, 60% by mass or less. If the proportion of solid electrolyte is too large, there is a possibility that the proportion of positive electrode active material will be relatively reduced, resulting in a decrease in energy density.

[0166] The positive electrode layer can also contain conductive materials. By adding conductive materials, the electronic conductivity of the positive electrode layer is improved. Examples of conductive materials include carbon-based conductive materials, metal particles, and conductive polymers. Examples of carbon-based conductive materials include granular materials such as acetylene black (AB) and Ketjen black (KB), fibrous materials such as vapor-grown carbon fibers (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs).

[0167] The proportion of conductive material in the positive electrode layer is, for example, 0.1% by mass or more. If the proportion of conductive material is too small, there is a possibility that the electron conduction pathways in the positive electrode layer are insufficient. On the other hand, the proportion of conductive material in the positive electrode layer is, for example, 5% by mass or less. If the proportion of conductive material is too large, there is a possibility that the proportion of positive electrode active material will be relatively reduced, resulting in a decrease in energy density.

[0168] The positive electrode layer may also contain a binder. Examples of binders include styrene-butadiene rubber (SBR), polyimide (PI), polyacrylic acid (PAA), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-diene terpolymer (EPDM).

[0169] The proportion of binder in the positive electrode layer can be, for example, 0.5% by mass or more. If the proportion of binder is too small, there is a possibility that the increase in resistance caused by charging and discharging may not be sufficiently reduced. On the other hand, the proportion of binder in the positive electrode layer can be, for example, 15% by mass or less. If the proportion of binder is too large, there is a possibility that the proportion of positive electrode active material will be relatively reduced, resulting in a decrease in energy density.

[0170] The thickness of the positive electrode layer can be, for example, 0.1 μm or more and 1000 μm or less, or 1 μm or more and 500 μm or less, or 30 μm or more and 100 μm or less.

[0171] The manufacturing method of the positive electrode layer is not particularly limited. For example, a method can be used to mix the above-mentioned positive electrode active material, the above-mentioned conductive material, and a solvent to obtain a positive electrode slurry, coat the positive electrode slurry onto a positive electrode current collector, and dry it to form a positive electrode layer. During the formation of the positive electrode layer, a compaction process can be performed to compact the positive electrode layer in the thickness direction. Examples of compaction processes include roller compaction and plate compaction.

[0172] Examples of solvents include N-methylpyrrolidone (NMP), tetrahydronaphthalene, diisobutyl ketone, butyl butyrate, mesitylene, heptane, dibutyl ether, decane, dodecane, isodecane, and toluene, and may contain two or more of these components.

[0173] Materials used as positive current collectors include, for example, SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be foil-like or plate-like. The top view shape of the positive current collector is not particularly limited; for example, it can be circular, elliptical, rectangular, or any polygonal shape. The positive current collector can be constructed with a buffer layer, an elastic layer, or a positive temperature coefficient (PTC) thermistor layer disposed on its surface.

[0174] [negative electrode]

[0175] The negative electrode has a negative electrode layer and may be further equipped with a negative electrode current collector as needed.

[0176] The negative electrode layer is a layer containing at least a negative electrode active material. Additionally, the negative electrode layer may, as needed, contain at least one of an electrolyte, a conductive material, and a binder. The negative electrode layer can have a larger area than the positive electrode layer.

[0177] The negative electrode active material can be in granular or flake form. The average particle size of the negative electrode active material can be, for example, 1 μm or more. Alternatively, the average particle size can be, for example, 30 μm or less.

[0178] The negative electrode active material may include at least one selected from the group consisting of carbon-based active materials, Li-based active materials, Si-based active materials, Si-C composite materials, and lithium titanate.

[0179] Carbon-based active materials may include at least one material selected from the group consisting of graphite, soft carbon, and hard carbon. "Graphite" is a general term for both natural and artificial graphite. Graphite can also be a mixture of natural and artificial graphite. The mixing ratio (mass ratio) of natural and artificial graphite can be, for example, "natural graphite:artificial graphite = 1:9 to 9:1" or "natural graphite:artificial graphite = 3:7 to 7:3".

[0180] Examples of Li-based active materials include Li, lithium silicate, and Li alloys.

[0181] Examples of Si-based active materials include Si, SiO, and Si alloys.

[0182] Si-C composite materials refer to composite materials of carbon-based active materials (such as graphite) and Si-based active materials (such as Si). For example, Si particles can be dispersed within carbon particles. For example, Si particles can also be dispersed within graphite particles. For example, lithium silicate particles can also be coated with carbon materials (such as amorphous carbon).

[0183] Regarding the electrolyte, conductive material, and binder used in the negative electrode layer, the same substances as those described in the positive electrode layer can be listed.

[0184] The negative electrode layer may also contain a thickener as needed. Examples of thickeners include carboxymethyl cellulose (CMC).

[0185] Materials used as negative electrode current collectors include, for example, SUS, aluminum, copper, nickel, iron, titanium, and carbon. Furthermore, the thickness of the negative electrode current collector varies depending on its shape, ranging from 1 μm to 50 μm. The shape of the negative electrode current collector can be foil-like or plate-like. The top-view shape of the negative electrode current collector is not particularly limited; examples include circular, elliptical, rectangular, and arbitrary polygonal shapes. The negative electrode current collector can be constructed with a buffer layer, an elastic layer, or a PTC thermistor layer disposed on its surface.

[0186] [Electrolyte layer]

[0187] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. The electrolyte can be a solid electrolyte or a liquid electrolyte (electrolyte).

[0188] The electrolyte layer may also contain solid electrolytes and electrolyte solutions.

[0189] Solid electrolytes can be listed as the same substances described in the above positive electrode layer.

[0190] Electrolytes can be aqueous or non-aqueous. They can be used alone or in combination.

[0191] Aqueous electrolytes contain water as a main solvent component. That is, based on the total amount of solvent (liquid component) constituting the electrolyte (100 mol%), water can account for more than 50 mol%, especially more than 70 mol%, and can also account for more than 90 mol%. On the other hand, there is no particular upper limit to the proportion of water in the solvent.

[0192] The solvent contains water as the main component, but may also contain solvents other than water. Examples of solvents other than water include one or more selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur-containing compounds, and hydrocarbons. Based on the total amount of solvent (liquid component) constituting the electrolyte (100 mol%), the solvents other than water may be 50 mol% or less, particularly 30 mol% or less, or even 10 mol% or less.

[0193] The aqueous electrolyte used in this disclosure contains an electrolyte. The electrolyte used in the aqueous electrolyte can be any electrolyte known in the past. Examples of electrolytes include lithium salts, nitrates, acetates, and sulfates of imide compounds. Specific examples of electrolytes include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(nonafluorobutylsulfonyl)imide, lithium nonafluoro-N-[(trifluoromethane)sulfonyl]butanesulfonamide, lithium N,N-hexafluoro-1,3-propanedisulfonylimide, CH3COOLi, LiPF6, LiBF4, Li2SO4, and LiNO3.

[0194] The concentration of the electrolyte in an aqueous electrolyte solution can be appropriately set according to the required battery characteristics, within a range that does not exceed the saturation concentration of the electrolyte relative to the solvent. This is because the presence of solid electrolyte residues in the aqueous electrolyte solution can hinder the battery reaction.

[0195] For example, when using LiTFSI as the electrolyte, the aqueous electrolyte may contain more than 1 mol of LiTFSI per kilogram of water, particularly more than 5 mol, and may also contain more than 7.5 mol. There is no specific upper limit; for example, it may be less than 25 mol.

[0196] As a non-aqueous electrolyte, a non-aqueous electrolyte containing lithium salt and non-aqueous solvent is usually used.

[0197] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6, and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2 (Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0198] Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butenyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring high dielectric constant and low viscosity, mixtures of cyclic carbonate compounds such as EC, PC, and BC with high dielectric constant and high viscosity and chain carbonate compounds such as DMC, DEC, and EMC with low dielectric constant and low viscosity can be used. Mixtures of EC and DEC can also be used.

[0199] The concentration of lithium salt in non-aqueous electrolytes can be, for example, 0.3–5 M.

[0200] Non-aqueous electrolytes may also contain ionic liquids. Ionic liquids may contain, for example, at least one of the following groups: sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidineium salts, morpholinium salts, phosphate salts, imidazolium salts, and their derivatives.

[0201] The electrolyte layer can be a membrane immersed in the electrolyte and preventing the positive electrode layer from contacting the negative electrode layer. The membrane material can be a porous membrane, and is not particularly limited; examples include resins such as polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide, with polyethylene and polypropylene being preferred. Furthermore, the membrane can be a single-layer structure or a multi-layer structure. Examples of multi-layer membranes include a PE / PP two-layer structure membrane, or a PP / PE / PP or PE / PP / PE three-layer structure membrane.

[0202] The diaphragm can also be made of resin nonwoven fabric or glass fiber nonwoven fabric, etc.

[0203] [Solid electrolyte layer]

[0204] The electrolyte layer can be a solid electrolyte layer composed of solids.

[0205] When the electrolyte layer is a solid electrolyte layer, the solid electrolyte layer contains solid electrolyte and may contain binders, etc., as needed.

[0206] Solid electrolytes can be listed as the same substances described in the above positive electrode layer.

[0207] Solid electrolytes can be used alone or in combination with one or more other solid electrolytes. Furthermore, when using two or more solid electrolytes, they can be mixed, or each solid electrolyte can be formed into two or more separate layers to create a multilayer structure.

[0208] The proportion of solid electrolyte in the solid electrolyte layer is not particularly limited. For example, it can be 50% or more by mass, or it can be in the range of 60% or more and less than 100% by mass, or it can be in the range of 70% or more and less than 100% by mass, or it can be 100% by mass. The solid electrolyte layer may also contain less than 1% by mass of electrolyte relative to the total amount of solid electrolyte layer.

[0209] Examples of binders that may be contained in the above-mentioned positive electrode layer can be cited as examples.

[0210] The content of binder in the solid electrolyte layer can be 0% to 10% by mass relative to the total amount of the solid electrolyte layer.

[0211] The thickness of the electrolyte layer can be, for example, 0.1 μm or more and 1000 μm or less, or 0.1 μm or more and 500 μm or less, or 0.1 μm or more and 100 μm or less.

[0212] The battery disclosed herein also includes a constraint clamp that applies constraint pressure to the positive electrode layer, the electrolyte layer, and the negative electrode layer along the thickness direction. In particular, when the electrolyte layer is a solid electrolyte layer, constraint pressure can be applied to form good ion conduction paths and electron conduction paths. The constraint pressure can be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. On the other hand, the constraint pressure can be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less.

[0213] [Battery]

[0214] The type of battery disclosed herein is not particularly limited, but a typical example is a lithium-ion battery. Furthermore, the battery disclosed herein can be a liquid battery with an electrolyte layer containing an electrolyte solution, or a solid battery with an electrolyte layer containing a solid electrolyte. A solid battery can be a semi-solid battery or a fully solid battery. In this disclosure, a semi-solid battery is a battery in which the electrolyte layer contains both solid components such as an inorganic solid electrolyte and liquid components (e.g., solvents and electrolyte solutions). In this disclosure, a fully solid battery is a battery in which the electrolyte layer contains only solid components such as an inorganic solid electrolyte as the electrolyte. Additionally, the battery disclosed herein can be a primary battery or a secondary battery, preferably a secondary battery. This is because secondary batteries can be repeatedly charged and discharged, making them useful, for example, as automotive batteries.

[0215] The shape of the battery is not particularly limited; for example, it can be button-shaped, cylindrical, square, sheet-shaped, push-button-shaped, flat, or stacked.

[0216] A battery stack consisting of multiple stacked batteries can be either unipolar or bipolar.

[0217] Batteries are used in various applications, including as power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. They are particularly preferred as drive power sources for HEVs, PHEVs, or BEVs. Furthermore, batteries can be used as power sources for mobile bodies other than vehicles (e.g., railways, ships, aircraft) and for electrical products such as information processing devices.

[0218] It should be noted that this disclosure is not limited to the embodiments described above. The embodiments described above are merely illustrative, and solutions having substantially the same structure and achieving the same effect as the technical concept described in the claims of this disclosure are also included within the technical scope of this disclosure.

[0219] [Example]

[0220] (Example 1)

[0221] Synthesis of transition metal hydroxides

[0222] NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to prepare a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was set as Ni:Co:Mn = 80:10:10. The concentration of the raw material aqueous solution (the proportion of all raw materials to the raw material aqueous solution) was 30% by mass.

[0223] <Hydrothermal Synthesis (Crystallization)>

[0224] A certain amount of NH3 aqueous solution was added to the reaction vessel, and nitrogen was replaced under stirring. NaOH aqueous solution was then added to maintain an alkaline pH (pH=12), and while maintaining a constant temperature, the above-mentioned raw material aqueous solution and NH3 aqueous solution were added dropwise to precipitate the transition metal hydroxide. The reaction temperature was set to 60℃. Small particles and large particles of transition metal hydroxide were obtained. The reaction time for obtaining small particles was 2 hours, and the reaction time for obtaining large particles was 6 hours.

[0225] <Filtering>

[0226] After hydrothermal synthesis, the transition metal hydroxides are dispersed using ion-exchanged water for washing. The washed transition metal hydroxides are then filtered and removed.

[0227] <Drying>

[0228] The transition metal hydroxides were dried at 120°C for 16 hours to evaporate the moisture. The dried transition metal hydroxides were then fractionated into small and large particles using molecular sieves.

[0229] Synthesis of positive electrode active materials

[0230]

[0231] Small particles of transition metal hydroxide were mixed with large particles of transition metal hydroxide at a mass ratio of 1:1. The mixed transition metal hydroxide was then mixed with LiOH, a lithium compound used as a Li source, using an agate mortar to obtain a mixture.

[0232] The lithium compound is mixed in such a way that the molar ratio (Li / NCM ratio) of the lithium compound relative to the total amount of Ni, Co, and Mn contained in the transition metal hydroxide (NCM) reaches 1.1.

[0233] <First Stage Firing>

[0234] The obtained mixture was calcined in a furnace at 1000℃ under an oxygen atmosphere for 10 hours to synthesize the positive electrode active material (Li). 1.1 Ni 0.8 Co 0.1 Mn 0.1 O2), to obtain the first stage of fired product.

[0235] <First Stage Crushing>

[0236] The first-stage fired material is pulverized using a jet mill to achieve the specified particle size.

[0237] <Magnetic Field Orientation>

[0238] Add 100ml of NMP and 50g of the first-stage calcination material to a beaker and stir to obtain a slurry. Let the slurry stand for 10 minutes in a space with 1T magnets positioned above and below.

[0239] <Slurry Drying>

[0240] After settling, the beaker is moved smoothly to the dryer and the slurry is dried at 150°C for 6 hours.

[0241] <Second Stage Firing>

[0242] The dried material was smoothly transferred to an alumina crucible and calcined in a furnace at 850°C under an oxygen atmosphere for 10 hours to obtain the positive electrode active material (Li). 1.1 Ni 0.8 Co 0.1 Mn 0.1 The second stage of firing (O2).

[0243] <Second Stage Crushing>

[0244] The second-stage calcined material is pulverized using a jet mill to pulverize the positive electrode active material, which is the second-stage calcined material, to a specified particle size, thereby obtaining positive electrode active material particles.

[0245] (Example 2)

[0246] Except for setting the firing temperature to 950°C in the above-mentioned "Second Stage Firing", the positive electrode active material was prepared in the same manner as in Example 1.

[0247] (Comparative Example 1)

[0248] In the above-mentioned <hydrothermal synthesis (crystallization)> section, the reaction time was set to 3 hours to obtain medium-sized particles of transition metal hydroxide. Then, in the [synthesis of positive electrode active material], <magnetic field orientation> to <second stage pulverization> were not performed. The particles of the first-stage calcined product obtained in the <first stage pulverization> of the [synthesis of positive electrode active material] were used as the positive electrode active material. Otherwise, the positive electrode active material was prepared in the same manner as in Example 1.

[0249] (Comparative Example 2)

[0250] Except that the firing temperature was set to 650°C in the above-mentioned "Second Stage Firing", the positive electrode active material was prepared in the same manner as in Example 1.

[0251] [SEM Analysis of Positive Electrode Active Material]

[0252] For the positive electrode active materials of Examples 1-2 and Comparative Example 2, 50 primary particles were randomly selected from the SEM images, and the radius of the longest diameter of each primary particle was calculated to create a histogram. The particle size distribution of large and small particles was determined based on the histogram, and the D50 of large and small particles under the volume-based particle size distribution was calculated. The results are shown in Table 1.

[0253] [TEM Analysis]

[0254] The positive electrode active materials of Examples 1-2 and Comparative Examples 1-2 were observed using TEM images.

[0255] It was observed that, at the outer edge as seen in the TEM cross-sectional image, the 003 facet of the positive electrode active material in Examples 1 and 2 was alternately exposed with other faces. It was also observed that, in the direction parallel to the 003 facet, the lengths of adjacent primary particles in the positive electrode active material of Examples 1 and 2 were different.

[0256] When the positive electrode active material was cross-sectionally observed by TEM, it was confirmed that the positive electrode active materials of Examples 1 and 2 were stacked in an orientation in which the 003 planes of each primary particle were parallel.

[0257] It was observed that, at the outer edge observed through TEM cross-sectional images, the 003 facet of the positive electrode active material in Comparative Examples 1 and 2 did not alternate with other faces. This is presumably because, in the positive electrode active material of Comparative Example 2, since the D50 values ​​of the large and small particles used were close, the 003 facet was not exposed at the grain boundary where the first and second particles were stacked. Furthermore, it was observed that, in the positive electrode active materials of Comparative Examples 1 and 2, adjacent primary particles had the same length in the direction parallel to the 003 facet.

[0258] [Fabrication of Battery Cells (Wound Cylindrical Battery Cells)]

[0259] Using the positive electrode active materials of Examples 1-2 and Comparative Examples 1-2, wound cylindrical battery cells of Examples 1-2 and Comparative Examples 1-2 were fabricated.

[0260] Specifically, firstly, using a coating machine (manufactured by Allgood Co., Ltd.) with film thickness adjustment function, a positive electrode composite slurry containing a positive electrode active material, acetylene black as a conductive material, and polyvinylidene fluoride as a binder is coated onto the surface of a metal foil serving as the positive electrode current collector. Then, it is dried at 80°C for 5 minutes using a dryer to create a positive electrode with a positive electrode layer on the positive electrode current collector. The composition of the positive electrode composite slurry is as follows: positive electrode active material: conductive material: binder = 88:10:2 by mass.

[0261] On the other hand, using a coating machine (manufactured by Allgood Co., Ltd.) with film thickness adjustment function, a negative electrode composite slurry containing natural graphite as the negative electrode active material, SBR as the binder, and CMC as the thickener is coated onto the surface of a metal foil serving as the negative electrode current collector. Then, it is dried at 80°C for 5 minutes using a dryer to create a negative electrode with a negative electrode layer on the negative electrode current collector.

[0262] Prepare a 1M LiPF6 solution as the electrolyte, which contains LiPF6 as the electrolyte, ethylene carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as solvents, and the volume ratio is EC:DMC:EMC = 3:4:3.

[0263] The above-mentioned positive electrode, separator and negative electrode are stacked, and the separator is immersed in the above-mentioned electrolyte to produce the wound cylindrical battery cells of Examples 1-2 and Comparative Examples 1-2.

[0264] [Evaluation of Battery Cells]

[0265] Each of the fabricated wound cylindrical battery cells was subjected to a 100-cycle cycle test, and the IV resistance was measured before and after the cycle test. The cycle test was conducted for 100 cycles under the following conditions.

[0266] <Loop Condition>

[0267] • Voltage range: 3.0V~4.3V

[0268] • C-ratio: 0.3C

[0269] • Mode: CC charge / discharge

[0270] • Temperature: 50℃

[0271] [IV Resistance Measurement]

[0272] Within a voltage range of 3.0V to 4.3V, the upper limit voltage of 4.3V is set to SOC 100%, and voltage adjustment is performed in a way that achieves SOC 50%.

[0273] The voltage drop (V) after 10 seconds of discharge was measured at 0°C under various C-rate conditions of 0.1C, 0.3C, 0.5C, 0.7C, and 1.0C.

[0274] Plot the voltage drop (V) relative to the current value, fit a linear function to the line, and use the slope of the resulting line as the IV resistance.

[0275] [Calculation of the increase rate of IV resistance after 100 cycles]

[0276] The above measurements were performed before and after 100 cycles of the cyclic test, and the change before and after the cyclic test was calculated as the resistance increase rate.

[0277] The increase in IV resistance after 100 cycles (%) = (IV resistance after cycle test) / (IV resistance before cycle test) × 100

[0278] [SEM Analysis of the Cathode Layer]

[0279] The positive electrode layers of the battery cells in Examples 1-2 and Comparative Example 2 were observed using SEM. Fifty primary particles of the positive electrode active material in the positive electrode layers were randomly selected from the SEM images, and the radius of the longest diameter of each primary particle was calculated to create a histogram. The (D90-D10) / D50 ratio of the primary particles in the positive electrode active material was calculated based on the histogram. The results are shown in Table 1.

[0280] [Table 1]

[0281]

[0282] Based on the results shown in Table 1, the following comparative analysis is conducted.

[0283] As shown in Table 1, it can be seen that the batteries using the positive electrode active materials of Examples 1-2 have a smaller resistance increase rate after 100 cycles compared to the batteries using the positive electrode active materials of Comparative Examples 1-2. Therefore, it can be seen that by using positive electrode active materials with alternating exposure of the outer edge, 003 surface and other surfaces as observed in the cross-sectional image of the TEM, the resistance increase rate during battery charging and discharging can be reduced.

[0284] Explanation of reference numerals in the attached figures

[0285] 10 …The First Particle

[0286] 20 …the second particle

[0287] 30 …The Third Particle

[0288] 40 …the fourth particle

[0289] 100 …positive electrode active material

Claims

1. A positive electrode active material, The positive electrode active material contains at least one element selected from the group consisting of Ni, Co, and Mn. The positive electrode active material has a shape of two or more primary particles stacked together. The primary particle is a single crystal with a crystal structure belonging to space group R-3m. The positive electrode active material includes at least a first particle and a second particle connected in sequence as two or more primary particles. When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 surface of each primary particle is exposed at its outer edge. The first particle and the second particle are stacked with the 003 facet of the first particle parallel to the 003 facet of the second particle. When the positive electrode active material is cross-sectionally observed using the transmission electron microscope, the length of the first particle is different from the length of the second particle in the direction parallel to the 003 plane of each primary particle.

2. The positive electrode active material according to claim 1, wherein, The positive electrode active material has a shape of three or more primary particles stacked together. When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, at least a portion of the 003 surface of each primary particle is exposed at its outer edge. Each of the primary particles is stacked with its 003 facet parallel to that of the primary particle. When the positive electrode active material is cross-sectionally observed using the transmission electron microscope, the lengths of adjacent primary particles are different in the direction parallel to the 003 plane of each primary particle.

3. The positive electrode active material according to claim 1, wherein, When the positive electrode active material is cross-sectionally observed using a transmission electron microscope, the outer edges, in a direction perpendicular to the 003 plane of each primary particle, show the surfaces other than the 003 plane of each primary particle. The other faces of each primary particle besides the 003 face are the 012 face, 101 face, 104 face, or 110 face.

4. The positive electrode active material according to claim 1, wherein, The positive electrode active material has a shape of two or more but less than 100 primary particles stacked together.

5. The positive electrode active material according to claim 1, wherein, In a direction parallel to the 003 plane of each of the primary particles, the ratio of the length of the first particle to the length of the second particle is 1.1 to 2.

0.

6. The positive electrode active material according to claim 1, wherein, In the volume-based particle size distribution, the (D90-D10) / D50 of two or more primary particles is greater than 1.30 and less than 1.

70.

7. A positive electrode layer comprising the positive electrode active material as described in claim 1.

8. A battery comprising a positive electrode layer containing the positive electrode active material as described in claim 1.

9. A method for manufacturing a positive electrode active material, comprising manufacturing the positive electrode active material according to claim 1. include: In the first stage of the firing process, a first mixture of large particles of transition metal hydroxide, small particles of the transition metal hydroxide having a particle size smaller than that of the large particles, and lithium compound is fired at 700℃~1100℃ to obtain the precursor of the positive electrode active material. The magnetic field application process includes applying a magnetic field to a slurry obtained by dispersing the precursor of the positive electrode active material in a solvent. The drying process includes drying the slurry to obtain a dried product; and The second stage firing process involves firing the dried material at 800℃~1000℃ to obtain the positive electrode active material.

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