Positive electrode active material for non-aqueous electrolyte secondary batteries and method for producing the same

Abstract

A non-aqueous electrolyte secondary battery capable of constructing a non-aqueous electrolyte secondary battery with excellent output characteristics. This invention provides a method for producing a positive electrode active material. [Solution] Average particle size D based on electron microscope observation SEM 50% particle size D of the cumulative particle size distribution based on volume 50 Ratio D 50 / D SEM The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery comprises: preparing a lithium transition metal composite oxide having a layered structure, a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of 0.3 or more and less than 1, and a ratio of the number of moles of cobalt to the total number of moles of metals other than lithium of 0 or more and less than 0.5; contacting the lithium transition metal composite oxide with a cobalt compound in a liquid medium to obtain a deposit with the cobalt compound attached; and heat-treating the deposit at a temperature of 800°C or more and 1000°C or less to obtain a heat-treated product.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material for non-aqueous electrolyte secondary batteries and a method for producing the same. [Background technology]

[0002] High power output characteristics are required for electrode active materials in non-aqueous electrolyte secondary batteries used in large power equipment such as electric vehicles. To obtain high power output characteristics, positive electrode active materials having a structure of secondary particles formed by the aggregation of many primary particles are considered effective. However, in such positive electrode active materials, cracks may occur in the secondary particles due to pressurization during electrode formation and expansion and contraction during charging and discharging. In connection with this, a method for manufacturing positive electrode active materials containing lithium transition metal composite oxide particles that reduce the number of primary particles constituting a single particle or a single secondary particle has been proposed (see, for example, Patent Document 1).

[0003] On the other hand, a technique has been proposed in which a lithium transition metal composite oxide containing nickel is used as a core material and coated with a lithium transition metal composite oxide containing cobalt, which is said to improve stability while maintaining capacitance characteristics (see, for example, Patent Document 2). [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2017-188443 [Patent Document 2] Japanese Patent Publication No. 2006-199229 [Overview of the project] [Problems that the invention aims to solve]

[0005] One aspect of the present invention aims to provide a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, which can constitute a non-aqueous electrolyte secondary battery having excellent output characteristics. [Means for solving the problem]

[0006] A first aspect of the present invention is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery. This production method is based on the average particle size D observed by electron microscopy. SEM 50% particle size D of the cumulative particle size distribution based on volume 50 Ratio D 50 / D SEM The method includes: preparing a lithium transition metal composite oxide in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 1 or more and 4 or less, having a layered structure, having a ratio of moles of nickel to the total number of moles of metals other than lithium of 0.3 or more and less than 1, and having a ratio of moles of cobalt to the total number of moles of metals other than lithium of 0 or more and less than 0.5; contacting the lithium transition metal composite oxide with a cobalt compound to obtain a deposit; and heat-treating the deposit at a temperature greater than 700°C and less than 1100°C to obtain a heat-treated product.

[0007] A second aspect of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery. This positive electrode active material has an average particle size D based on electron microscope observation. SEM 50% particle size D of the cumulative particle size distribution based on volume 50 Ratio D 50 / D SEM The lithium transition metal composite oxide has a composition in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1, and the ratio of moles of cobalt to the total number of moles of metals other than lithium is 0.01 or more and less than 0.5. The lithium transition metal composite oxide constituting the positive electrode active material has a ratio of moles of nickel to the total number of moles of metals other than lithium that is 0.2 or more in the first region at a depth of 500 nm from the particle surface, and 0.06 or more in the second region at a depth of 10 nm or less from the particle surface, and the ratio of moles of cobalt to the total number of moles of metals other than lithium is greater in the second region than in the first region. [Effects of the Invention]

[0008] According to one aspect of the present invention, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery capable of constituting a non-aqueous electrolyte secondary battery having excellent output characteristics and a method for producing the same.

Brief Description of the Drawings

[0009] [Figure 1] It is an example of a scanning electron microscope (SEM) image of the positive electrode active material according to Example 1. [Figure 2] It is an example of an SEM image of the positive electrode active material according to Comparative Example 5.

Modes for Carrying Out the Invention

[0010] In this specification, the term "step" includes not only an independent step but also a step included in this term if the intended purpose of the step is achieved even when it cannot be clearly distinguished from other steps. Also, the content of each component in the composition means the total amount of the plurality of substances corresponding to each component in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments shown below are examples of a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same for embodying the technical idea of the present invention, and the present invention is not limited to the positive electrode active material for a non-aqueous electrolyte secondary battery and the method for producing the same shown below.

[0011] Method for Producing Positive Electrode Active Material for Non-Aqueous Electrolyte Secondary Battery The method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter, also simply referred to as a positive electrode active material) is based on the average particle size D by electron microscope observation SEM The ratio of the 50% particle size D of the cumulative particle size distribution based on volume to the average particle size D 50 of D 50 / D SEMThe method includes a preparation step of preparing a lithium transition metal composite oxide in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1, and the ratio of moles of cobalt is 0 or more and less than 0.5; an adhesion step of contacting the prepared lithium transition metal composite oxide with a cobalt compound to obtain a deposit with the cobalt compound attached; and a heat treatment step of heat treating the obtained deposit at a temperature greater than 700°C and less than 1100°C to obtain a heat-treated product.

[0012] D 50 / D SEM A positive electrode active material capable of achieving excellent output characteristics in a non-aqueous electrolyte secondary battery can be manufactured by attaching a cobalt compound to a single lithium transition metal composite oxide particle (hereinafter collectively also simply referred to as "single particle") which has a small number of primary particles constituting one secondary particle, such that the ratio is between 1 and 4, and then heat-treating it at a specific temperature. This can be attributed, for example, to the presence of a high concentration of cobalt near the surface of the lithium transition metal composite oxide particle, originating from the cobalt compound attached to the surface.

[0013] Preparation process In the preparation process, D 50 / D SEM A lithium transition metal composite oxide is prepared having a layered structure in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1, and the ratio of moles of cobalt is 0 or more and less than 0.5. The lithium transition metal composite oxide contains at least lithium, nickel and cobalt, and may further contain at least one metal element selected from the group consisting of manganese, aluminum, etc. The lithium transition metal composite oxide may be appropriately selected from commercially available products, or it may be prepared by manufacturing a lithium transition metal composite oxide having a desired composition and structure.

[0014] In the lithium transition metal composite oxide prepared in the preparation step, the ratio of moles of nickel to the total number of moles of metals other than lithium is, for example, 0.3 or more and less than 1. The lower limit of the ratio of moles of nickel to the total number of moles of metals other than lithium is preferably 0.31 or more, more preferably 0.32 or more. The upper limit of the ratio of moles of nickel to the total number of moles of metals other than lithium is preferably 0.98 or less, more preferably 0.8 or less, and particularly preferably 0.6 or less. When the molar ratio of nickel is within the above range, it is possible to achieve both high-voltage charge / discharge capacity and cycle characteristics in a non-aqueous electrolyte secondary battery.

[0015] In the lithium transition metal composite oxide prepared in the preparation step, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is, for example, 0 or more and less than 0.5, preferably 0.15 or more and 0.45 or less, and more preferably 0.3 or more and 0.4 or less, from the viewpoint of charge and discharge capacity.

[0016] The lithium transition metal composite oxide prepared in the preparation step contains at least one metal element M selected from the group consisting of manganese and aluminum. 1 It may further contain a lithium transition metal composite oxide containing the metal element M. 1 If it includes, M for the total number of moles of metals other than lithium. 1 The ratio of moles is, for example, 0 or more and less than 0.5, preferably 0.15 or more and 0.45 or less from the viewpoint of safety, and more preferably 0.3 or more and 0.4 or less.

[0017] The lithium transition metal composite oxide prepared in the preparation step contains at least one metallic element M selected from the group consisting of boron, sodium, magnesium, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, zinc, strontium, yttrium, zirconium, niobium, molybdenum, indium, tin, barium, lanthanum, cerium, neodymium, samarium, europium, gadolium, tantalum, tungsten, bismuth, etc. 2It may further contain a lithium transition metal composite oxide containing the metal element M. 2 If it includes, M for the total number of moles of metals other than lithium. 2 The ratio of the number of moles is, for example, 0 or more and 0.1 or less, preferably 0.001 or more and 0.05 or less.

[0018] In the lithium transition metal composite oxide prepared in the preparation step, the ratio of moles of lithium to the total number of moles of metals other than lithium is, for example, 0.95 or more and 1.5 or less, preferably 1 or more and 1.3 or less.

[0019] When the lithium transition metal composite oxide prepared in the preparation step contains manganese in addition to nickel and cobalt, the molar ratio of nickel, cobalt, and manganese is, for example, nickel:cobalt:manganese = (0.3 to 0.95):(0 to 0.5):(0 to 0.5), preferably (0.3 to 0.6):(0.15 to 0.45):(0.15 to 0.45), and more preferably (0.3 to 0.4):(0.3 to 0.4):(0.3 to 0.4).

[0020] The composition of the lithium transition metal composite oxide prepared in the preparation step may be, for example, the composition represented by formula (1) below. Note that the composition of the lithium transition metal composite oxide referred to here means the composition of the lithium transition metal composite oxide as a whole. Li p Ni x Co y M 1 z M 2 w O2(1) 0.95≦p≦1.5, 0.3≦x<1, 0≦y<0.5, 0≦z<0.5, 0≦w≦0.1, x+y+z+w≦1, M 1 is at least one selected from the group consisting of Al and Mn, and M 2is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi. 0.9 ≤ x + y + z + w.

[0021] The lithium transition metal composite oxide prepared in the preparation step may be in the form of a so-called single particle, consisting of, for example, four or fewer primary particles. The lithium transition metal composite oxide has a 50% particle size D in the cumulative particle size distribution based on volume. 50 Based on electron microscope (SEM) observations, the average particle size D SEM Ratio D 50 / D SEM It may be between 1 and 4.

[0022] In the lithium transition metal composite oxide prepared in the preparation step, D 50 / D SEM A value of 1 indicates a single particle, and the closer it is to 1, the fewer primary particles it contains. 50 / D SEM From the viewpoint of durability, a value of 1 to 4 is preferred, and from the viewpoint of power density, a value of 3.5 or less is preferred, a value of 3 or less is more preferred, a value of 2.5 or less is even more preferred, and a value of 2 or less is particularly preferred.

[0023] In the lithium transition metal composite oxide prepared in the preparation process, the average particle size D is determined by electron microscopy observation. SEM From the viewpoint of durability, the thickness is, for example, 0.1 μm or more and 20 μm or less. From the viewpoint of power density and electrode plate packing, it is preferably 0.3 μm or more, more preferably 0.5 μm or more, preferably 15 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 5 μm or less.

[0024] Average particle size D based on electron microscope observation SEM D is the average value of the spherical equivalent diameter of primary particles measured from scanning electron microscope (SEM) images. SEMSpecifically, it is determined as follows: Using a scanning electron microscope, observation is performed at magnifications ranging from 1,000x to 10,000x depending on the particle size. 100 primary particles whose contours can be confirmed are selected. Using image processing software, the contour length of the selected primary particles is determined by tracing their contours. The spherical equivalent diameter is calculated from the contour length, and the average particle size D is taken as the arithmetic mean of the obtained spherical equivalent diameters. SEM This is required.

[0025] Furthermore, the 50% particle size D of the lithium transition metal composite oxide prepared in the preparation process 50 For example, the particle size is 1 μm or more and 30 μm or less, preferably 1.5 μm or more, more preferably 3 μm or more, and from the viewpoint of power density, preferably 10 μm or less, and more preferably 5.5 μm or less.

[0026] 50% particle size D 50 This is determined using a laser diffraction particle size distribution analyzer, as the particle size corresponding to the cumulative 50% from the smallest diameter side in the volume-based cumulative particle size distribution measured under wet conditions. Similarly, the 90% particle size D described later is determined. 90 and 10% particle size D 10 These are determined as particle sizes corresponding to 90% and 10% cumulatively from the smaller diameter side, respectively.

[0027] In the preparation process, the 90% particle size D in the cumulative particle size distribution based on volume of the lithium transition metal composite oxide prepared. 90 10% particle size D 10 The ratio to indicates the extent of the particle size distribution; a smaller value indicates that the particle size is more uniform. 90 / D 10 For example, it may be 4 or less, and from the viewpoint of power density, it is preferably 3 or less, and more preferably 2.5 or less. 90 / D 10 The lower limit may be, for example, 1.2 or higher.

[0028] D is prepared in the preparation process 50 / D SEMFor lithium transition metal composite oxides where is between 1 and 4, for example, refer to Japanese Patent Publication No. 2017-188443 (US Published Patent No. 2017-0288221), Japanese Patent Publication No. 2017-188444 (US Published Patent No. 2017-0288222), Japanese Patent Publication No. 2017-188445 (US Published Patent No. 2017-0288223), etc.

[0029] The lithium transition metal composite oxide prepared in the preparation step contains nickel in its composition. From the viewpoint of initial efficiency in non-aqueous electrolyte secondary batteries, the nickel element disorder of the lithium transition metal composite oxide, as determined by X-ray diffraction, is preferably 4.0% or less, more preferably 2.0% or less, and even more preferably 1.5% or less. Here, nickel element disorder refers to the chemical disorder of the transition metal ions (nickel ions) that should occupy their original sites. In layered lithium transition metal composite oxides, a typical example is the swapping of alkali metal ions that should occupy the site represented by 3b in Wyckoff notation (3b site, hereinafter the same) and transition metal ions that should occupy the 3a site. A smaller nickel element disorder is preferable because it improves initial efficiency.

[0030] The nickel disorder in lithium transition metal composite oxides can be determined by X-ray diffraction. X-ray diffraction spectra are measured for lithium transition metal composite oxides using CuKα radiation. The compositional model is (Li 1-d Ni d )(Ni x Co y Mn z The system is defined as O2(x+y+z=1), and structural optimization is performed by Rietveld analysis based on the obtained X-ray diffraction spectrum. The percentage of d calculated as a result of structural optimization is taken as the value of the nickel element disorder.

[0031] The lithium transition metal composite oxide prepared in the preparation step can be specifically prepared as follows. The method for preparing the lithium transition metal composite oxide may include, for example, a precursor preparation step for preparing a precursor and a synthesis step for synthesizing the lithium transition metal composite oxide from the precursor and a lithium compound.

[0032] In the precursor preparation step, a precursor containing a composite oxide (hereinafter also simply referred to as a composite oxide) containing nickel and cobalt is prepared. The precursor may be appropriately selected from commercially available products, or a composite oxide having the desired composition may be prepared by conventional methods. Methods for obtaining a composite oxide having the desired composition include mixing raw material compounds (hydroxides, carbonate compounds, etc.) according to the desired composition and decomposing them into a composite oxide by heat treatment, and coprecipitation methods in which raw material compounds soluble in a solvent are dissolved in a solvent, and precipitates having the desired composition are obtained by temperature adjustment, pH adjustment, addition of complexing agents, etc., and the composite oxide is obtained by heat treatment of these precipitates. An example of a method for producing a composite oxide is described below.

[0033] A method for obtaining a composite oxide by coprecipitation may include a seed generation step of adjusting the pH of a mixed solution containing metal ions in a desired ratio to obtain seed crystals, a crystallization step of growing the generated seed crystals to obtain a composite hydroxide having desired properties, and a step of heat-treating the obtained composite hydroxide to obtain the composite oxide. For details on such a method for obtaining a composite oxide, see, for example, Japanese Patent Publication No. 2003-292322 and Japanese Patent Publication No. 2011-116580 (US Patent Publication No. 2012-270107).

[0034] In the seed generation process, a liquid medium containing seed crystals is prepared by adjusting the pH of a mixed solution containing nickel ions and cobalt ions in a desired ratio to, for example, 11 to 13. The seed crystals can include, for example, hydroxides containing nickel and cobalt in a desired ratio. The mixed solution can be prepared by dissolving nickel salts and cobalt salts in water in a desired ratio. Examples of nickel salts and cobalt salts include sulfates, nitrates, hydrochlorides, etc. In addition to nickel salts and cobalt salts, the mixed solution may optionally contain other metal salts in a desired ratio. The temperature in the seed generation process can be, for example, 40°C to 80°C. The atmosphere in the seed generation process can be a low-oxidizing atmosphere, for example, by maintaining an oxygen concentration of 10% by volume or less.

[0035] In the crystallization step, the generated seed crystals are grown to obtain a precipitate containing nickel and cobalt with desired properties. Seed crystal growth can be carried out, for example, by adding a mixed solution containing nickel ions, cobalt ions, and other metal ions as needed to a liquid medium containing seed crystals, while maintaining the pH at, for example, 7 to 12.5, preferably 7.5 to 12. The addition time of the mixed solution is, for example, 1 to 24 hours, preferably 3 to 18 hours. The temperature in the crystallization step can be, for example, 40°C to 80°C. The atmosphere in the crystallization step is the same as in the seed generation step. pH adjustment in the seed generation step and crystallization step can be carried out using acidic aqueous solutions such as sulfuric acid aqueous solution and nitric acid aqueous solution, or alkaline aqueous solutions such as sodium hydroxide aqueous solution and ammonia aqueous solution.

[0036] In the step of obtaining the composite oxide, the precipitate containing the composite hydroxide obtained in the crystallization step is heat-treated to obtain the composite oxide. The heat treatment in the step of obtaining the composite oxide can be carried out by heating the composite hydroxide at a temperature of, for example, 500°C or lower, preferably 350°C or lower. The heat treatment temperature is, for example, 100°C or higher, preferably 200°C or higher, and the heat treatment time can be, for example, 0.5 hours to 48 hours, preferably 5 hours to 24 hours. The atmosphere for the heat treatment may be air or an atmosphere containing oxygen. The heat treatment can be carried out using, for example, a box furnace, rotary kiln furnace, pusher furnace, roller hearth kiln furnace, etc.

[0037] The resulting composite oxide contains nickel and cobalt, in addition to other metallic elements M. 1 It may also contain other metal elements M. 1 Examples of suitable metals include Mn and Al, and it is preferable to select at least one from the group consisting of these, and more preferably to include at least Mn. If the composite oxide contains other metals, the other metal ions can be added in the desired configuration to the mixed aqueous solution containing the precipitate. This allows the precipitate to contain nickel, cobalt, and other metals, and a composite oxide with the desired composition can be obtained by heat-treating the precipitate.

[0038] The average particle size of the composite oxide is, for example, 2 μm to 30 μm, preferably 3 μm to 25 μm. The average particle size of the composite oxide is the volume-average particle size, which is the value at which the volume integrated value from the small particle size side in the volume-based particle size distribution obtained by laser scattering method becomes 50%.

[0039] In the synthesis process, a mixture containing lithium, obtained by mixing a composite oxide and a lithium compound, is heat-treated to obtain a heat-treated product. The resulting heat-treated product has a layered structure and contains a lithium transition metal composite oxide containing nickel and cobalt.

[0040] Examples of lithium compounds to be mixed with the composite oxide include lithium hydroxide, lithium carbonate, and lithium oxide. The particle size of the lithium compound used in the mixture is preferably 2 μm to 20 μm, with a 50% average particle size of 0.1 μm to 100 μm, based on the cumulative particle size distribution by volume.

[0041] The ratio of the total number of moles of lithium to the total number of moles of metal elements constituting the composite oxide in the mixture is, for example, between 0.95 and 1.5. The mixing of the composite oxide and the lithium compound can be carried out, for example, using a high-speed shear mixer.

[0042] The mixture contains lithium, nickel, and cobalt, as well as other metallic elements M. 2 It may further contain other metallic elements M. 2 Examples of suitable metals include B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, Bi, etc., and at least one selected from the group consisting of these is preferred. If the mixture contains other metals, the mixture can be obtained by mixing the other metal in elemental form or as a metal compound together with the composite oxide and the lithium compound. Examples of metal compounds containing other metals include oxides, hydroxides, chlorides, nitrides, carbonates, sulfates, nitrates, acetates, oxalates, etc.

[0043] If the mixture contains other metals, the ratio of the total number of moles of the metal elements constituting the composite oxide to the total number of moles of the other metals is, for example, 1:0.015 to 1:0.1, and preferably 1:0.025 to 1:0.05.

[0044] The heat treatment temperature of the mixture is, for example, 550°C to 1100°C, but preferably 600°C to 1080°C, and more preferably 700°C to 1080°C. The heat treatment of the mixture may be carried out at a single temperature, but it is preferable to carry out the treatment at multiple temperatures from the viewpoint of discharge capacity at high voltage. When heat treatment is carried out at multiple temperatures, for example, it is desirable to hold the first temperature for a predetermined time, then raise the temperature further, and hold the second temperature for a predetermined time. The first temperature is, for example, 850°C to 950°C, preferably 900°C to 940°C. The second temperature is, for example, 980°C to 1100°C, preferably 1000°C to 1080°C. The difference between the first and second temperatures is, for example, 30°C or more, preferably 100°C or more, and also, for example, 250°C or less, preferably 180°C or less.

[0045] When heat treatment is performed at a single temperature, the heat treatment time is, for example, 1 hour or more and 20 hours or less, preferably 5 hours or more and 10 hours or less. When heat treatment is performed at multiple temperatures, the heat treatment time at the first temperature is, for example, 1 hour or more and 20 hours or less, preferably 5 hours or more and 10 hours or less. The heat treatment time at the second temperature is, for example, 1 hour or more and 20 hours or less, preferably 2 hours or more and 10 hours or less. The heat treatment time at the first temperature and the heat treatment time at the second temperature may be the same or different. When the heat treatment time at the first temperature and the heat treatment time at the second temperature are different, for example, the heat treatment time at the first temperature can be made longer than the heat treatment time at the second temperature. Specifically, for example, the heat treatment time at the second temperature can be 1.05 to 2 times the heat treatment time at the first temperature, preferably 1.1 to 1.5 times. Here, the first and second heat treatments may be performed consecutively or independently. When the first and second heat treatments are performed consecutively, the heating rate from the first temperature to the second temperature can be, for example, 5°C / min.

[0046] The heat treatment atmosphere may be in the open air or an oxygen-containing atmosphere. The heat treatment can be carried out using, for example, a box furnace, rotary kiln, pusher furnace, roller hearth kiln, etc.

[0047] Dispersion treatment is performed on the heat-treated material as needed. Rather than pulverization treatment involving strong shear force or impact, dispersion treatment dissociates the sintered primary particles, resulting in lithium transition metal composite oxide particles with a narrow particle size distribution and uniform particle size. Dispersion treatment may be performed dry or wet, but dry treatment is preferred. Dispersion treatment can be performed using, for example, a ball mill or jet mill. The conditions for dispersion treatment are, for example, the D of the lithium transition metal composite oxide particles after dispersion treatment. 50 / D SEM This can be set to a desired range, for example, between 1 and 4.

[0048] For example, when performing dispersion processing with a ball mill, resin media can be used. Examples of resin media materials include urethane resin and nylon resin. Generally, alumina and zirconia are used as media materials in ball mills, and particles are pulverized by these media. In contrast, using resin media allows for the dissociation of sintered primary particles without pulverization. The size of the resin media can be, for example, φ5mm to 30mm. For the shell, for example, urethane resin or nylon resin can be used. The dispersion processing time is, for example, 3 to 60 minutes, with 10 to 30 minutes being preferable. The conditions for dispersion processing using a ball mill are as follows: 50 / D SEM To achieve this, the amount of media, rotation or amplitude speed, dispersion time, media specific gravity, etc., should be adjusted.

[0049] For example, when dispersion processing is performed with a jet mill, the primary particles are not pulverized, and the desired D 50 / D SEM To achieve this, the supply pressure, grinding pressure, etc., should be adjusted. The supply pressure can be, for example, 0.1 to 0.5 MPa, and the grinding pressure can be, for example, 0.1 to 0.6 MPa. By the above preparation method, single-particle lithium transition metal composite oxides can be efficiently produced.

[0050] Adhesion process In the deposition process, the prepared lithium transition metal composite oxide and the cobalt compound are brought into contact to obtain a deposit in which the cobalt compound adheres to the surface of the lithium transition metal composite oxide particles. The contact between the lithium transition metal composite oxide and the cobalt compound may be carried out dry or wet. When carried out dry, the lithium transition metal composite oxide and the cobalt compound can be mixed using, for example, a high-speed shear mixer, and then the contact can be performed. Examples of cobalt compounds include cobalt hydroxide, cobalt oxide, and cobalt carbonate.

[0051] In a wet process, contact between the lithium transition metal composite oxide and the cobalt compound can be achieved by bringing the lithium transition metal composite oxide into contact with a liquid medium containing a cobalt compound. The liquid medium may be stirred as needed. The liquid medium containing the cobalt compound may be a solution of the cobalt compound or a dispersion of the cobalt compound. Alternatively, the lithium transition metal composite oxide may be suspended in a solution of the cobalt compound, and the cobalt compound may be precipitated into the solution by adjusting the pH, temperature, etc., thereby adhering the cobalt compound to the surface of the lithium transition metal composite oxide particles.

[0052] Examples of cobalt compounds in the solution include cobalt sulfate, cobalt nitrate, and cobalt chloride. Examples of cobalt compounds in the dispersion include cobalt hydroxide, cobalt oxide, and cobalt carbonate. The liquid medium may contain water, for example, or it may contain a water-soluble organic solvent such as alcohol in addition to water. The concentration of the cobalt compound in the liquid medium can be, for example, 1% by mass or more and 8.5% by mass or less.

[0053] The total amount of cobalt compound brought into contact with the lithium transition metal composite oxide is, for example, 1 mol% to 20 mol%, preferably 3 mol% to 15 mol%, relative to the lithium transition metal composite oxide, based on cobalt.

[0054] The contact temperature between the lithium transition metal composite oxide and the cobalt compound is, for example, 40°C to 80°C, preferably 40°C to 60°C. Alternatively, the contact temperature may be, for example, 20°C to 80°C. The contact time is, for example, 30 minutes to 180 minutes, preferably 30 minutes to 60 minutes.

[0055] After contact with a liquid medium containing a cobalt compound, the lithium transition metal composite oxide to which the cobalt compound has adhered may be subjected to treatments such as filtration, washing with water, and drying, if necessary. Alternatively, preliminary heat treatment may be performed depending on the type of cobalt compound adhering to it. If preliminary heat treatment is performed, the temperature is, for example, 100°C to 350°C, preferably 120°C to 320°C. The treatment time is, for example, 5 hours to 20 hours, preferably 8 hours to 15 hours. The atmosphere for the preliminary heat treatment may be, for example, an oxygen-containing atmosphere, or an air atmosphere.

[0056] Heat treatment process In the heat treatment process, the deposits obtained in the deposition process are heat-treated at a predetermined temperature between 700°C and 1100°C to obtain a heat-treated product. The resulting heat-treated product is a positive electrode active material containing a lithium transition metal composite oxide with a high cobalt concentration near the particle surface, and excellent output characteristics can be achieved in a non-aqueous electrolyte secondary battery constructed using this material.

[0057] The deposit subjected to heat treatment may be a mixture with a lithium compound. That is, the manufacturing method may include a mixing step before the heat treatment step in which the deposit and the lithium compound are mixed to obtain a mixture. By heat-treating the deposit together with the lithium compound at a predetermined temperature, the output characteristics of the non-aqueous electrolyte secondary battery can be further improved.

[0058] Examples of lithium compounds to be mixed with the deposited material include lithium hydroxide, lithium carbonate, and lithium chloride. The amount of lithium compound added is such that the molar ratio of lithium to cobalt (Li:Co) relative to the amount of cobalt deposited in the deposition process is, for example, 0.95 to 1.50:1, preferably 1.00 to 1.30:1. Mixing can be carried out, for example, using a high-speed shear mixer.

[0059] The heat treatment temperature for the deposits is, for example, above 700°C and below 1100°C. The lower limit of the heat treatment temperature is preferably 750°C or higher, more preferably 800°C or higher, and particularly preferably 860°C or higher. The upper limit of the heat treatment temperature is preferably 1080°C or lower, more preferably 1060°C or lower, even more preferably 1020°C or lower, and particularly preferably 1000°C or lower. The heat treatment time is, for example, 1 hour or more and 20 hours or less, preferably 3 hours or more and 10 hours or less. The heat treatment atmosphere is, for example, an oxygen-containing atmosphere, and may be an air atmosphere.

[0060] The heat-treated material may be subjected to further processing such as crushing, grinding, classification, and sizing, as needed.

[0061] The heat-treated material obtained as described above contains single-particle lithium transition metal composite oxide particles, with a higher cobalt concentration near the particle surface. Specifically, in the lithium transition metal composite oxide particles, the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.2 or more in the first region, where the depth from the particle surface is around 500 nm, and 0.06 or more in the second region, where the depth from the particle surface is around 10 nm. Furthermore, the ratio of moles of cobalt to the total number of moles of metals other than lithium is greater in the second region than in the first region. The depth from the particle surface in the first region can be, for example, 450 nm to 550 nm, and the depth from the particle surface in the second region can be, for example, 5 nm to 15 nm.

[0062] Cathode active material for non-aqueous electrolyte secondary batteries The positive electrode active material for non-aqueous electrolyte secondary batteries (hereinafter also simply referred to as positive electrode active material) has an average particle size D based on electron microscope observation. SEM 50% particle size D of the cumulative particle size distribution based on volume 50 Ratio D 50 / D SEM The lithium transition metal composite oxide includes a lithium transition metal composite oxide in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1, and the ratio of moles of cobalt to the total number of moles of metals other than lithium is 0.01 or more and less than 0.5. In the lithium transition metal composite oxide, the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.2 or more in the first region at a depth of 500 nm from the particle surface, and 0.06 or more in the second region at a depth of 10 nm or less from the particle surface. Furthermore, in the lithium transition metal composite oxide, the ratio of moles of cobalt to the total number of moles of metals other than lithium is larger in the second region than in the first region.

[0063] In lithium transition metal composite oxide particles that constitute the positive electrode active material, cobalt is unevenly distributed and its concentration is high near the surface of the particles. This improves the output characteristics when a battery is constructed using such a positive electrode active material. The exact form of cobalt near the particle surface is not clear, but possible forms include solid solution of cobalt near the surface of the lithium transition metal composite oxide particles, or a cobalt-containing compound coating the surface of the lithium transition metal composite oxide particles that serve as the base material.

[0064] The effect of improving output characteristics due to the uneven distribution of cobalt near the surface of the particles is due to the fact that a large number of primary particles are aggregated and D 50 / D SEM Compared to the case of so-called aggregated particles where D is greater than 4, 50 / D SEMThis effect is more effective in the case of single particles where the ratio is 4 or less. This can be thought of as follows: In aggregated particles, a three-dimensional grain boundary network is formed, and it is thought that the output characteristics are improved by grain boundary conduction. On the other hand, in single particles, it is difficult to fully utilize grain boundary conduction, and it can be thought that the improvement in lithium conductivity due to cobalt unevenly distributed near the surface of the particle is more effectively utilized, thus improving the output characteristics.

[0065] D 50 / D SEM However, for example, it is between 1 and 4, and from the viewpoint of power density, 3.5 or less is preferred, 3 or less is more preferred, 2.5 or less is even more preferred, and 2 or less is particularly preferred. Average particle size D based on electron microscope observation. SEM and 50% particle size D 50 The measurement method is as previously described.

[0066] In lithium transition metal composite oxide particles, the average particle size D is determined by electron microscopy observation. SEM From a durability standpoint, the particle size is, for example, between 0.1 μm and 20 μm. Average particle size D based on electron microscope observation. SEM The lower limit is preferably 0.3 μm or more, more preferably 0.5 μm or more, from the viewpoint of power density and electrode plate packing, and the upper limit is preferably 15 μm or less, more preferably 10 μm or less, even more preferably 8 μm or less, and particularly preferably 5 μm or less.

[0067] 50% particle size D of lithium transition metal composite oxide particles 50 For example, the particle size is 1 μm or more and 30 μm or less, preferably 1.5 μm or more, more preferably 3 μm or more, and from the viewpoint of power density, preferably 10 μm or less, and more preferably 5.5 μm or less.

[0068] D of lithium transition metal composite oxide particles 90 / D 10 For example, it may be 4 or less, and from the viewpoint of power density, it is preferably 3 or less, and more preferably 2.5 or less. 90 / D 10The lower limit is, for example, 1.2 or higher.

[0069] In lithium transition metal composite oxide particles, the ratio of moles of nickel to the total number of moles of metals other than lithium in the first region, which is approximately 500 nm deep from the particle surface (hereinafter also simply referred to as the "nickel ratio"), is, for example, 0.2 or more, preferably 0.25 or more. The nickel ratio in the first region is, for example, 1 or less, preferably 0.5 or less. Furthermore, the nickel ratio in the second region, which is approximately 10 nm deep from the particle surface, is, for example, 0.06 or more, preferably 0.1 or more. The nickel ratio in the second region is, for example, 0.9 or less, preferably 0.5 or less. Moreover, the value obtained by dividing the nickel ratio in the second region by the nickel ratio in the first region is, for example, less than 1, preferably 0.9 or less or 0.8 or less. Furthermore, the value obtained by dividing the nickel ratio in the second region by the nickel ratio in the first region is, for example, 0.02 or more, preferably 0.03 or more or 0.07 or more. Here, the depth from the particle surface of the second region is, for example, 10 nm or less, but may be approximately 10 nm.

[0070] Furthermore, in lithium transition metal composite oxide particles, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium (hereinafter also simply referred to as the "cobalt ratio") is greater in the second region than in the first region. The cobalt ratio in the first region is, for example, 0 or more, and preferably 0.2 or more. The cobalt ratio in the first region is, for example, 0.5 or less, and preferably 0.4 or less. The cobalt ratio in the second region is, for example, 0.3 or more, and preferably 0.5 or more. The cobalt ratio in the second region is, for example, 0.9 or less, and preferably 0.8 or less. The value obtained by dividing the cobalt ratio in the second region by the sum of the cobalt ratios in the first and second regions is, for example, greater than 0.5 and less than 1, and preferably 0.55 or more and 0.72 or less.

[0071] The nickel ratio and cobalt ratio in the first and second regions can be calculated by measuring SEM-EDX in the cross-section of lithium transition metal composite oxide particles.

[0072] In the lithium transition metal composite oxide particles, the cobalt ratio may continuously or discontinuously decrease from the particle surface to the particle interior. The cobalt concentration gradient, which is the absolute value of the difference in the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium in the first region and the second region divided by the difference in the depth from the surfaces of the first region and the second region, is, for example, greater than 0.00004 (nm -1 ) and less than 0.00122 (nm -1 ) and preferably is 0.00005 (nm -1 ) or more and 0.0011 (nm -1 ) or less, or 0.00006 (nm -1 ) or more and 0.00009 (nm -1 ) or less. Specifically, the cobalt concentration gradient is obtained by dividing the value obtained by subtracting the cobalt ratio in the first region from the cobalt ratio in the second region by the value obtained by subtracting the depth from the surface of the second region from the depth from the surface of the first region.

[0073] The composition of the lithium transition metal composite oxide contained in the positive electrode active material can be considered as the composition considering the cobalt compound attached to the composition of the lithium transition metal composite oxide before the cobalt compound is attached in the above-described production method.

[0074] The ratio of the number of moles of nickel to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the positive electrode active material is, for example, 0.3 or more and less than 1. The lower limit of the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is preferably 0.31 or more, more preferably 0.32 or more. The upper limit of the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is preferably 0.98 or less, more preferably 0.8 or less, and particularly preferably 0.6 or less. When the nickel molar ratio is within the above-described range, in a non-aqueous electrolyte secondary battery, it is possible to achieve both the charge-discharge capacity at high voltage and the cycle characteristics.

[0075] The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the positive electrode active material may be, for example, more than 0 and less than 0.5 or 0.01 or more and less than 0.5, and from the viewpoint of charge-discharge capacity, it is preferably 0.15 or more and 0.45 or less, and more preferably 0.3 or more and 0.4 or less.

[0076] The composition of the lithium transition metal composite oxide contained in the positive electrode active material contains at least one metal element M selected from the group consisting of manganese and aluminum. 1 It may further contain. When the lithium transition metal composite oxide contains the metal element M 1 The ratio of the number of moles of M to the total number of moles of metals other than lithium is, for example, 0 or more and less than 0.5, and from the viewpoint of safety, it is preferably 0.15 or more and 0.45 or less, and more preferably 0.3 or more and 0.4 or less.

[0077] The composition of the lithium transition metal composite oxide contained in the positive electrode active material contains at least one metal element M selected from the group consisting of boron, sodium, magnesium, silicon, phosphorus, sulfur, potassium, calcium, titanium, vanadium, chromium, zinc, strontium, yttrium, zirconium, niobium, molybdenum, indium, tin, barium, lanthanum, cerium, neodymium, samarium, europium, gadolinium, tantalum, tungsten, bismuth, etc. 2 It may further contain. When the lithium transition metal composite oxide contains the metal element M 2 The ratio of the number of moles of M to the total number of moles of metals other than lithium is, for example, 0 or more and 0.1 or less, and preferably 0.001 or more and 0.05 or less.

[0078] The ratio of the number of moles of lithium to the total number of moles of metals other than lithium in the composition of the lithium transition metal composite oxide contained in the positive electrode active material is, for example, 0.95 or more and 1.5 or less, and preferably 1 or more and 1.3 or less.

[0079] ​​​​When the lithium transition metal composite oxide contained in the positive electrode active material contains manganese in addition to nickel and cobalt, the molar ratio of nickel, cobalt, and manganese is, for example, nickel:cobalt:manganese = (0.3 to 0.95):(0.01 to 0.5):(0 to 0.5), preferably (0.3 to 0.6):(0.15 to 0.45):(0.15 to 0.45), and more preferably (0.3 to 0.4):(0.3 to 0.4):(0.3 to 0.4).

[0080] When expressing the composition of the lithium transition metal composite oxide contained in the positive electrode active material, a lithium transition metal composite oxide having a composition represented by the following formula is preferred. Li q Ni r Co s M 1 t M 2 u O2 0.95≦q≦1.5, 0.3≦r<1, 0.01≦s<0.5, 0≦t<0.5, 0≦u≦0.1, r+s+t+u≦1, M 1 is at least one selected from the group consisting of Al and Mn, and M 2 is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi. 0.9 ≤ r + s + t + u is also acceptable.

[0081] From the viewpoint of initial efficiency in non-aqueous electrolyte secondary batteries, the lithium transition metal composite oxide contained in the positive electrode active material preferably has a nickel element disorder of 4.0% or less, more preferably 2.0% or less, and even more preferably 1.5% or less, as determined by X-ray diffraction. The nickel element disorder is as previously described.

[0082] [Nonaqueous electrolyte secondary battery electrode] The electrode for a non-aqueous electrolyte secondary battery comprises a current collector and a positive electrode active material layer disposed on the current collector and containing a positive electrode active material for a non-aqueous electrolyte secondary battery manufactured by the aforementioned manufacturing method. A non-aqueous electrolyte secondary battery equipped with such an electrode can achieve high output characteristics.

[0083] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying a positive electrode mixture, obtained by mixing the above-mentioned positive electrode active material, conductive material, binder, etc., with a solvent, onto the current collector, and then performing drying, pressurizing, etc. Examples of conductive materials include natural graphite, artificial graphite, and acetylene black. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

[0084] [Nonaqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery comprises electrodes for a non-aqueous electrolyte secondary battery. In addition to the electrodes for a non-aqueous electrolyte secondary battery, the non-aqueous electrolyte secondary battery is configured to include a negative electrode for a non-aqueous secondary battery, a non-aqueous electrolyte, a separator, etc. For the negative electrode, non-aqueous electrolyte, separator, etc. in a non-aqueous electrolyte secondary battery, for example, those described in Japanese Patent Publication No. 2002-075367, Japanese Patent Publication No. 2011-146390, Japanese Patent Publication No. 2006-12433 (the entire disclosures of these are incorporated herein by reference), etc., can be used as appropriate. [Examples]

[0085] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples.

[0086] (Example 1) Seed generation process 30 kg of water was added to the reaction vessel and stirred while nitrogen gas was circulated, setting the vessel temperature to 40°C. After maintaining the oxygen concentration in the reaction vessel space at 10% by volume or less, 197 g of 25% by mass sodium hydroxide aqueous solution was added to adjust the pH of the solution in the reaction vessel to 11 or higher. Next, nickel sulfate solution, manganese sulfate solution, and cobalt sulfate solution were mixed to prepare a mixed aqueous solution containing nickel ions, manganese ions, and cobalt ions in a molar ratio of 1:1:1, with a total ion concentration of nickel ions, manganese ions, and cobalt ions of 1.7 mol / L. While stirring the solution in the reaction vessel, 4.76 L of the prepared mixed aqueous solution was added to prepare a liquid medium containing seed crystals.

[0087] Crystallization process After the seed generation step, while maintaining a temperature of 40°C, 452 moles of 25% by mass sodium hydroxide and 201 moles of the mixed aqueous solution were added to the reaction vessel at a constant flow rate over a period of 18 hours or more. The pH was maintained between 11.0 and 12.0 during this time. The 50% particle size D50 of the obtained hydroxide containing nickel, manganese, and cobalt was 10.1 μm. Next, the resulting precipitate was washed with water and filtered to obtain a composite hydroxide. The obtained composite hydroxide was heat-treated at 320°C for 12 hours under an atmospheric environment to obtain a composite oxide with a composition ratio of Ni / Co / Mn = 0.33 / 0.33 / 0.33.

[0088] Synthesis process The obtained composite oxide and lithium carbonate were mixed in a ratio of Li:(Ni+Co+Mn)=1.15:1 to obtain a raw material mixture. The obtained raw material mixture was heat-treated in air at 925°C for 7.5 hours, and then heat-treated again at 1060°C for 4 hours to obtain a heat-treated product. The obtained heat-treated product was dispersed to obtain a 50% particle size D 50 It is 10.5 μm, and the composition formula is Li 1.14 Ni 0.33 Co 0.33 Mn 0.33 A lithium transition metal composite oxide having a composition represented by O2 was obtained.

[0089] Adhesion process and heat treatment process Five kilograms of the obtained lithium transition metal composite oxide were suspended in 50 kilograms of water in a reaction vessel, and the vessel temperature was set to 40°C. Two and a half kilograms of cobalt sulfate with a concentration of 8.1% by mass were used as the cobalt source, and the pH was adjusted to 9.5 with 25% sodium hydroxide while blowing in carbon dioxide at a rate of 0.56 L / min to obtain a cobalt deposit precursor. The amount of cobalt sulfate used was 6 mol% in terms of cobalt relative to the lithium transition metal composite oxide. Next, the generated cobalt deposit precursor was washed with water and filtered to obtain the composite hydroxide. The obtained composite hydroxide was heat-treated at 300°C for 12 hours under an atmospheric atmosphere to obtain a cobalt deposit in which the cobalt compound was attached to the lithium transition metal composite oxide. Subsequently, lithium hydroxide was mixed in such a way that the molar ratio of added cobalt to lithium was Li:Co = 1.15:1 to obtain a mixture. The obtained mixture was heat-treated at 1000°C for 3 hours under an atmospheric environment. The resulting heat-treated material is subjected to a dry sieve, and then treated with Co and Li 1.14 Ni 0.313 Co 0.374 Mn 0.313 A positive electrode active material containing a lithium transition metal composite oxide having a composition represented by O2 was obtained. The physical properties of the obtained positive electrode active material are shown in Table 1.

[0090] (Example 2) The positive electrode active material for Example 2 was manufactured in the same manner as in Example 1, except that the heat treatment temperature of the mixture was changed to 900°C, as shown in Table 1.

[0091] (Example 3) The positive electrode active material of Example 3 was manufactured in the same manner as in Example 1, except that the heat treatment temperature of the mixture was changed to 850°C, as shown in Table 1.

[0092] (Comparative Example 1) The lithium transition metal composite oxide obtained in the synthesis process of Example 1 was used as the positive electrode active material for Comparative Example 1.

[0093] (Comparative Example 2) The positive electrode active material for Comparative Example 2 was manufactured in the same manner as in Example 1, except that the heat treatment temperature of the mixture was changed to 1100°C as shown in Table 1.

[0094] (Comparative Example 3) The positive electrode active material of Comparative Example 3 was manufactured in the same manner as in Example 1, except that the heat treatment temperature of the mixture was changed to 700°C as shown in Table 1.

[0095] (Comparative Example 4) The composite oxide obtained in the crystallization step of Example 1 and lithium carbonate were mixed in a ratio of Li:(Ni+Co+Mn)=1.15:1 to obtain a raw material mixture. The obtained raw material mixture was heat-treated in air at 930°C for 12 hours to obtain a heat-treated product. The obtained heat-treated product was dispersed to obtain a 50% particle size D 50 It is 9.6 μm, and the composition formula is Li 1.14 Ni 0.33 Co 0.33 Mn 0.33 A positive electrode active material containing a lithium transition metal composite oxide having a composition represented by O2 was obtained.

[0096] (Comparative Example 5) Five kilograms of the lithium transition metal composite oxide obtained in Comparative Example 4 were suspended in 50 kg of water in a reaction vessel, and the vessel temperature was set to 40°C. Two and a half kilograms of cobalt sulfate with a concentration of 8.1% by mass were used as the cobalt source, and the pH was adjusted to 9.5 with 25% sodium hydroxide while blowing in carbon dioxide at a rate of 0.56 L / min to obtain a cobalt deposit precursor. Next, the generated cobalt deposit precursor was washed with water and filtered to obtain a composite hydroxide. The obtained composite hydroxide was heat-treated at 300°C for 12 hours under an atmospheric atmosphere to obtain a cobalt deposit. Subsequently, lithium hydroxide was added with a ratio of Li:Co = 1.15:1 to obtain a mixture. The obtained mixture was heat-treated at 900°C for 3 hours under an atmospheric environment. The obtained heat-treated product was sieved using a dry sieve to obtain the Co-treated Li 1.14 Ni 0.313 Co 0.374 Mn 0.313 A positive electrode active material containing a lithium transition metal composite oxide having a composition represented by O2 was obtained.

[0097] Particle size evaluation The positive electrode active material obtained above was measured for its physical properties as follows: D50 For this, the cumulative particle size distribution based on volume was measured using a laser diffraction particle size distribution analyzer (SALD-3100, manufactured by Shimadzu Corporation), and the particle size corresponding to 50% of the cumulative distribution from the smallest diameter side was determined. In addition, the average particle size D was determined based on electron microscope observation. SEM The following method was used to calculate the particle size D based on electron microscopy observations. Using a scanning electron microscope (SEM), 100 primary particles were selected from images observed at magnifications ranging from 1000x to 10000x, in which the contours of primary particles could be confirmed. The contour length of the selected primary particles was determined by tracing their contours using image processing software (ImageJ). The spherical equivalent diameter was calculated from the contour length, and the average particle size D based on electron microscopy observations was calculated as the arithmetic mean of the obtained spherical equivalent diameters. SEM They sought it.

[0098] Evaluation of cobalt and nickel distribution The cobalt and nickel distributions within the particles of the positive electrode active material obtained above were evaluated. Specifically, the nickel and cobalt content in the first and second regions were evaluated as follows.

[0099] Composition analysis The positive electrode active materials obtained in Examples 1 to 3 and Comparative Examples 1 to 5 were dispersed in epoxy resin and solidified. Then, a cross-section polisher (manufactured by JEOL) was used to create cross-sections of the secondary particles of the positive electrode active material to prepare measurement samples. At one point each in the first and second regions of the measurement sample, the intensity ratios of each metal component other than lithium were determined using a scanning electron microscope (SEM) / energy-dispersive X-ray spectrometer (EDX) (manufactured by Hitachi High-Technologies Corporation; acceleration voltage 3kV). The cobalt ratio was defined as the intensity ratio of cobalt to the sum of the intensity ratios of the metal components other than lithium, and the nickel ratio was defined as the intensity ratio of nickel to the sum of the intensity ratios of the metal components other than lithium.

[0100] Scanning electron microscope observation Scanning electron microscope (SEM; accelerating voltage 1.5kV) images were obtained for the positive electrode active materials obtained in Example 1 and Comparative Example 5. Figure 1 shows the SEM image of the positive electrode active material of Example 1, and Figure 2 shows the SEM image of the positive electrode active material of Comparative Example 5.

[0101] Fabrication of evaluation batteries Using the positive electrode active material obtained above, an evaluation battery was fabricated according to the following procedure.

[0102] Fabrication of the positive electrode A positive electrode mixture was prepared by dispersing 90 parts by mass of positive electrode active material, 5 parts by mass of acetylene black, and 5 parts by mass of polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP). The obtained positive electrode mixture was applied to aluminum foil to be used as a current collector, dried, compressed and molded using a roll press, and then cut to a predetermined size to produce a positive electrode.

[0103] (Fabrication of the negative electrode) A negative electrode slurry was prepared by dispersing and dissolving 97.5 parts by weight of artificial graphite, 1.5 parts by weight of carboxymethylcellulose (CMC), and 1.0 part by weight of SBR (styrene-butadiene rubber) in pure water. The obtained negative electrode slurry was applied to a current collector made of copper foil, dried, compressed and molded using a roll press, and then cut to a predetermined size to produce a negative electrode.

[0104] (Preparation of evaluation batteries) After attaching lead electrodes to the positive and negative electrode current collectors, a separator was placed between the positive and negative electrodes, and these were then placed in a laminated pouch. Next, this was vacuum-dried at 65°C to remove moisture adsorbed on each component. After that, an electrolyte solution was injected into the laminated pouch under an argon atmosphere and sealed to fabricate an evaluation battery. The electrolyte solution used was a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 3:7, with lithium hexafluoride phosphate (LiPF6) dissolved in it to a concentration of 1 mol / L. The resulting evaluation battery was placed in a constant temperature bath at 25°C and aged with a weak current, after which the following evaluation was performed.

[0105] (DC internal resistance measurement) The evaluation batteries, after aging, were placed in an environment of -25°C, and their DC internal resistance was measured. After constant current charging to a depth of charge of 50% at a full charge voltage of 4.75V, pulse discharge with a specific current i was performed for 10 seconds, and the voltage V at 10 seconds was measured. The intersection points were plotted with current i on the x-axis and voltage V on the y-axis, and the slope of the line connecting the intersection points was defined as the DC internal resistance (DC-IR). The currents i were set to 0.03A, 0.05A, 0.08A, 0.105A, and 0.13A. A low DC-IR indicates good output characteristics.

[0106] [Table 1]

[0107] Like the positive electrode active materials in Examples 1 to 3, D 50 / D SEM A battery comprising a positive electrode active material in which the ratio is 1 or more and 4 or less, the nickel ratio in the first region is 0.2 or more, the nickel ratio in the second region is 0.06 or more, and the cobalt ratio in the second region is greater than the cobalt ratio in the first region, exhibits improved output characteristics compared to Comparative Examples 1 to 3.

[0108] [Table 2]

[0109] [Table 3]

[0110] Tables 2 and 3 show the improvement rate of the output characteristics of lithium transition metal composite oxides obtained by a manufacturing method that includes a cobalt deposition process and a heat treatment process, compared to lithium transition metal composite oxides obtained by a manufacturing method that does not include a cobalt deposition process and a heat treatment process. Compared to the effect of the manufacturing method with a cobalt deposition process and a heat treatment process using aggregated particles in Table 3, it was confirmed that the effect of the manufacturing method with a cobalt deposition process and a heat treatment process in the examples in Table 2 was greater.

[0111] The disclosure of Japanese Patent Application No. 2020-010848 (filing date: January 27, 2020) is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard had been specifically and individually noted to be incorporated by reference.

Claims

1. Average particle size D based on electron microscope observation ＳＥＭ 50% particle size D of the cumulative particle size distribution based on volume ５０ Ratio D ５０ / D ＳＥＭ To prepare a lithium transition metal composite oxide in which the ratio of moles of nickel to the total number of moles of metals other than lithium is 1 or more and 4 or less, has a layered structure, the ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1, and the ratio of moles of cobalt to the total number of moles of metals other than lithium is 0 or more and less than 0.5, The lithium transition metal composite oxide and a cobalt compound are brought into contact in a liquid medium to obtain a deposit on which the cobalt compound is attached. A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, comprising heat-treating the aforementioned deposit at a temperature of 800°C to 1000°C to obtain a heat-treated product.

2. The heat-treated material has a first region with a depth of 500 nm from the particle surface and a second region with a depth of 10 nm or less from the particle surface. The absolute value of the difference in the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium, divided by the difference in the depth from the surface of the first and second regions, is 0.00041 (nm). －１ ) or more 0.00079 (nm －１ The manufacturing method according to claim 1, which is as follows:

3. The manufacturing method according to claim 1 or 2, wherein the temperature of the heat treatment is 860°C or higher and 1000°C or lower.

4. The manufacturing method according to any one of claims 1 to 3, wherein the total amount of the cobalt compound to be brought into contact is 1 mol% or more and 20 mol% or less based on cobalt relative to the lithium transition metal composite oxide.

5. The manufacturing method according to any one of claims 1 to 4, wherein the heat treatment of the deposit comprises mixing a lithium compound with the deposit to obtain a mixture, and heat treating the mixture.

6. The manufacturing method according to any one of claims 1 to 5, wherein the lithium transition metal composite oxide prepared has a composition represented by the following formula. Li ｐ Ni ｘ Co ｙ M １ ｚ M ２ ｗ O ２ (0.95≦p≦1.5, 0.3≦x<1, 0≦y<0.5, 0≦z<0.5, 0≦w≦0.1, x+y+z+w≦1, M １ is at least one selected from the group consisting of Al and Mn, and M ２ (This is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi.)

7. The manufacturing method according to any one of claims 1 to 6, further comprising performing a preliminary heat treatment at 100°C to 350°C before heat-treating the deposit to obtain a heat-treated product.

8. Average particle size D based on electron microscope observation ＳＥＭ 50% of the cumulative particle size distribution based on volume % particle size D ５０ Ratio D ５０ / D ＳＥＭ If it is between 1 and 4, It has a layered structure, The ratio of moles of nickel to the total number of moles of metals other than lithium is 0.3 or more and less than 1. Yes, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is 0.01 or greater. It contains a lithium transition metal composite oxide having a composition of less than 5, The lithium transition metal composite oxide has a ratio of nickel to the total number of moles of metals other than lithium. The ratio of moles of ru is 0.2 or greater in the first region where the depth from the particle surface is 500 nm. The second region, where the depth from the particle surface is 10 nm or less, is 0.06 or greater. The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is greater than the first region. The second region is larger, and the metals other than lithium in the first and second regions The difference in the ratio of the number of moles of cobalt to the total number of moles is determined from the surface of the first and second regions. The absolute value of the value divided by the difference in depth is 0.00041 (nm). －１ ) or more 0.00079 (nm －１ ) The following are positive electrode active materials for non-aqueous electrolyte secondary batteries.

9. The lithium transition metal composite oxide has a composition represented by the following formula, as described in claim 8, for a positive electrode active material for a non-aqueous electrolyte secondary battery. Li ｑ Ni ｒ CosM １ ｔ M ２ ｕ O ２ (0.95≦p≦1.5, 0.3≦r<1, 0.01≦s<0.5, 0≦t<0.5, 0≦u≦0.1, r+s+t+u≦1, M １ is at least one selected from the group consisting of Al and Mn, and M ２ (This is at least one selected from the group consisting of B, Na, Mg, Si, P, S, K, Ca, Ti, V, Cr, Zn, Sr, Y, Zr, Nb, Mo, In, Sn, Ba, La, Ce, Nd, Sm, Eu, Gd, Ta, W, and Bi.)

10. The absolute value of the difference in the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium in the first region and the second region, divided by the difference in depth from the surface of the first region and the second region, is 0.00041 (nm). －１ ) or more 0.00071 (nm －１ ) The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 8 or 9, which is as follows:

11. The aforementioned D ５０ / D ＳＥＭ A positive electrode active material for a non-aqueous electrolyte secondary battery according to any one of claims 8 to 10, wherein the ratio is 1 or more and 2.5 or less.

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