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

Abstract

To provide a positive electrode active material for a nonaqueous electrolyte secondary battery, capable of constituting a nonaqueous electrolyte secondary battery having a high initial efficiency and durability.SOLUTION: A positive electrode active material for a nonaqueous electrolyte secondary battery includes a lithium-transition metal composite oxide that contains lithium, nickel, cobalt, and manganese and that has a layered structure. The lithium-transition metal composite oxide has a ratio D50 / DSEM of 1 or more and 4 or less, in which D50 is a 50% particle diameter in a cumulative particle size distribution on a volumetric basis and DSEM is an average particle diameter of primary particles based on electron microscope observation, and also has such a composition that a ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is 0.03 or more and less than 0.2, and a ratio of the number of moles of manganese to the total number of moles of the metals other than lithium is 0.01 or more and less than 0.2. The disorder of elemental nickel is 1.8% or less, and the lithium-transition metal composite oxide may have a deposit containing boron on its surface.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Electrode active materials for nonaqueous electrolyte secondary batteries containing lithium nickel-cobalt aluminum oxide with a high nickel content are used in large power equipment such as electric vehicles, and these electrode active materials are required to have improved output characteristics. A positive electrode active material having a structure of secondary particles (hereinafter also referred to as agglomerated particles) formed by the aggregation of many primary particles is considered effective for achieving high output characteristics. However, with positive electrode active materials containing agglomerated particles, cracks may occur in the agglomerated particles due to pressure treatment during electrode formation and expansion and contraction of the electrode active material during charge and discharge, resulting in failure to achieve the desired output characteristics. In relation to this, a method for producing a positive electrode active material containing lithium transition metal oxide particles (hereinafter collectively referred to as single particles) that reduce the number of primary particles constituting a single particle or one secondary particle has been proposed (see, for example, Patent Document 1).

[0003] Meanwhile, a technique has been proposed for producing a lithium transition metal composite oxide containing nickel, in which the lithium site occupancy rate of the 3a site calculated by Rietveld analysis is 96.0% or more, by using a crystallization promoter containing an alkali metal other than lithium, and it is said that this technique improves cycle characteristics while maintaining charge / discharge capacity (see, for example, Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-188444 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-115658 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of one aspect of the present disclosure is to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can be used to form a non-aqueous electrolyte secondary battery having high initial efficiency and durability, and a method for producing the same. [Means for solving the problem]

[0006] A first aspect of the present disclosure is a positive electrode active material for a non-aqueous electrolyte secondary battery, which comprises a lithium transition metal composite oxide having a layered structure and containing lithium, nickel, cobalt, and manganese. The lithium transition metal composite oxide has an average particle size D SEM 50% particle size D of cumulative particle size distribution based on volume 50 Ratio of D 50 / D SEM is 1 or more and 4 or less, the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is greater than 0.8 and less than 1, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is less than 0.2, the ratio of the number of moles of manganese to the total number of moles of metals other than lithium is less than 0.2, and the ratio of the number of moles of manganese to the sum of the number of moles of cobalt and the number of moles of manganese is less than 0.58.

[0007] A second aspect of the present disclosure is a method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery, the method comprising: preparing a composite containing nickel, cobalt, and manganese as metal components, wherein the ratio of the number of moles of nickel to the total number of moles of the metal components is greater than 0.8 but less than 1; the ratio of the number of moles of cobalt to the total number of moles of the metal components is less than 0.2; the ratio of the number of moles of manganese to the total number of moles of the metal components is less than 0.2; and the ratio of the number of moles of manganese to the sum of the number of moles of cobalt and manganese is less than 0.58; mixing the composite with a lithium compound and an alkali metal compound having a melting point of 400°C or less and containing an alkali metal other than lithium to obtain a lithium mixture; heat-treating the lithium mixture at a temperature of 650°C to 800°C to obtain a heat-treated product; dry-dispersing the heat-treated product to obtain a first dispersion; contacting the first dispersion with a liquid medium and then removing at least a portion of the liquid medium to obtain a lithium transition metal composite oxide. The lithium transition metal composite oxide has an average particle size D SEM 50% particle size D of cumulative particle size distribution based on volume 50 Ratio of D 50 / D SEM is between 1 and 4. [Effects of the Invention]

[0008] According to the present disclosure, it is possible to provide a positive electrode active material for a non-aqueous electrolyte secondary battery that can constitute a non-aqueous electrolyte secondary battery having high initial efficiency and durability, and a method for producing the same. [Brief explanation of the drawings]

[0009] [Figure 1] 2 is an example of a scanning electron microscope (SEM) image of the positive electrode active material according to Example 1. [Figure 2] 1 is an example of an SEM image of a positive electrode active material according to Example 2. [Figure 3] 10 is an example of an SEM image of a positive electrode active material according to Example 3. [Figure 4] 10 is an example of an SEM image of the positive electrode active material according to Example 4. [Figure 5]10 is an example of an SEM image of the positive electrode active material according to Example 5. [Figure 6] 1 is an example of an SEM image of a positive electrode active material according to Comparative Example 1. [Figure 7] 10 is an example of an SEM image of a positive electrode active material according to Comparative Example 2. [Figure 8] 10 is an example of an SEM image of a positive electrode active material according to Comparative Example 3. [Figure 9] 10 is an example of an SEM image of a positive electrode active material according to Comparative Example 4. [Figure 10] 10 is an example of an SEM image of a positive electrode active material according to Comparative Example 5. [Figure 11] 10 is an example of an SEM image of a positive electrode active material according to Comparative Example 6. DETAILED DESCRIPTION OF THE INVENTION

[0010] In this specification, the term "process" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. Furthermore, the content of each component in a composition refers to the total amount of the multiple substances present in the composition, unless otherwise specified, when multiple substances corresponding to each component are present in the composition. Hereinafter, embodiments of the present invention will be described in detail. However, the embodiments described below are intended to exemplify a positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same, in order to embody the technical concept of the present invention. The present invention is not limited to the positive electrode active material for a non-aqueous electrolyte secondary battery and a method for producing the same described below.

[0011] Cathode active material for non-aqueous electrolyte secondary batteries The positive electrode active material for a non-aqueous electrolyte secondary battery (hereinafter simply referred to as the positive electrode active material) has an average particle diameter D SEM 50% particle size D of cumulative particle size distribution based on volume 50 Ratio of D 50 / D SEMThe lithium transition metal composite oxide particles (hereinafter simply referred to as composite oxide particles) have a layered structure and contain lithium, nickel, cobalt, and manganese as a composition, and have a molar ratio of 1 to 4. The lithium transition metal composite oxide (hereinafter simply referred to as composite oxide) constituting the composite oxide particles may have a composition in which the ratio of the number of moles of nickel to the total number of moles of metals other than lithium is greater than 0.8 and less than 1, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is less than 0.2, the ratio of the number of moles of manganese to the total number of moles of metals other than lithium is less than 0.2, and the ratio of the number of moles of manganese to the sum of the number of moles of cobalt and the number of moles of manganese is less than 0.58.

[0012] The mole ratio of nickel in the composition is equal to or greater than a predetermined value, and the mole ratio of manganese to cobalt and manganese is less than a predetermined value, and the ratio D 50 / D SEM A positive electrode active material comprising single-particle lithium transition metal composite oxide particles having a molar ratio of manganese to cobalt and manganese of a predetermined range can achieve both excellent initial efficiency and high durability in a nonaqueous electrolyte secondary battery comprising the positive electrode active material. This is thought to be because, for example, the crystal structure is more stable than that of single-particle lithium transition metal composite oxide particles that do not contain manganese in their composition, resulting in improved initial efficiency and durability. Furthermore, compared to single-particle lithium transition metal composite oxide particles having a molar ratio of manganese to cobalt and manganese equal to or greater than a predetermined value, the initial efficiency and durability are thought to be improved because manganese is less likely to act as a resistor.

[0013] The composite oxide particles constituting the positive electrode active material have a ratio of D 50 / D SEM The ratio D may be 1 or more and 4 or less. 50 / D SEM When the ratio D is 1, it indicates that the particles are single particles, and the closer it is to 1, the fewer the number of primary particles that make up the composite oxide particles. 50 / D SEM From the viewpoint of durability, the ratio D is preferably less than 4. 50 / D SEMThe lower limit of the number of primary particles constituting the composite oxide particles may be, for example, 1.1 or more. The number of primary particles constituting the composite oxide particles may be, for example, 30 or less, preferably 14 or less, and more preferably 7 or less. The lower limit of the number of primary particles constituting the composite oxide particles is 1 or more.

[0014] For composite oxide particles, the average particle size D SEM However, from the viewpoint of durability, the thickness may be, for example, 1 μm or more and 7 μm or less. SEM From the viewpoint of power density and electrode plate packing property, D is preferably 1.1 μm or more, more preferably 1.2 μm or more, and even more preferably 1.3 μm or more. SEM is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, particularly preferably 2 μm or less, and most preferably 1.6 μm or less.

[0015] Average particle size D based on electron microscope observation SEM is obtained by observing using a scanning electron microscope (SEM) at magnifications ranging from 1,000x to 10,000x depending on the particle size, selecting 100 primary particles whose particle outlines can be confirmed, calculating the equivalent spherical diameter of the selected particles using image processing software, and then taking the arithmetic mean of the resulting equivalent spherical diameters. Here, being able to confirm the particle outline means that the outline of the primary particle can be traced on the SEM image.

[0016] The 50% particle size D 50 For example, D may be 1 μm or more and 15 μm or less. 50 From the viewpoint of power density, the 50% particle size D is preferably 1.5 μm or more, more preferably 2.5 μm or more, even more preferably 3 μm or more, particularly preferably 3.2 μm or more, and most preferably 4 μm or more. 50 is preferably 8 μm or less, more preferably 6 μm or less, even more preferably 5.6 μm or less, and particularly preferably 5.4 μm or less.

[0017] 50% particle size D 50is determined as the particle size corresponding to 50% of the cumulative volume from the small diameter side in the cumulative particle size distribution on a volume basis measured under wet conditions using a laser diffraction particle size distribution analyzer. Similarly, the 90% particle size D 90 and 10% particle size D 10 are calculated as the particle diameters corresponding to 90% and 10% cumulative volumes from the small diameter side, respectively.

[0018] The composite oxide particles have a 90% particle size D 90 10% particle size D 10 The ratio D indicates, for example, the spread of the particle size distribution, and the smaller the ratio value, the more uniform the particle size of the particles. 90 / D 10 The ratio D may be, for example, 4.5 or less. 90 / D 10 From the viewpoint of power density, the ratio D is preferably 4 or less, and more preferably 3.9 or less. 90 / D 10 The lower limit can be set to, for example, 1.2 or more.

[0019] The lithium transition metal composite oxide (hereinafter also referred to as composite oxide) constituting the composite oxide particles contains lithium (Li), nickel (Ni), cobalt (Co), and manganese (Mn) in its composition and has a layered structure. The composition of the composite oxide may have a ratio of the number of moles of nickel to the total number of moles of metals other than lithium of, for example, greater than 0.8 and less than 1. The ratio of the number of moles of nickel to the total number of moles of metals other than lithium is preferably 0.82 or more, more preferably 0.85 or more, and particularly preferably 0.87 or more. The ratio of the number of moles of nickel to the total number of moles of metals other than lithium is preferably 0.92 or less, more preferably 0.9 or less. The composition of the composite oxide may have a ratio of the number of moles of cobalt to the total number of moles of metals other than lithium of, for example, less than 0.2. The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is preferably less than 0.19, more preferably less than 0.18, even more preferably 0.16 or less, even more preferably 0.13 or less, and particularly preferably 0.09 or less. The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is preferably 0.03 or more, more preferably 0.05 or more. In the composition of the composite oxide, the ratio of the number of moles of manganese to the total number of moles of metals other than lithium may be, for example, less than 0.2. The ratio of the number of moles of manganese to the total number of moles of metals other than lithium is preferably less than 0.19, more preferably less than 0.18, even more preferably 0.16 or less, even more preferably 0.1 or less, and particularly preferably 0.05 or less. The ratio of the number of moles of manganese to the total number of moles of metals other than lithium is preferably 0.01 or more, more preferably 0.03 or more. In the composition of the composite oxide, the molar ratio of lithium to the total number of moles of metals other than lithium may be, for example, 1 or more and 1.15 or less. The molar ratio of lithium to the total number of moles of metals other than lithium is preferably 1.01 or more, more preferably 1.03 or more. The molar ratio of lithium to the total number of moles of metals other than lithium is preferably 1.1 or less, more preferably 1.06 or less.

[0020] In terms of discharge capacity, the composition of the composite oxide may have a ratio of the number of moles of manganese to the total number of moles of cobalt and manganese of less than 0.58, for example. The ratio of the number of moles of manganese to the total number of moles of cobalt and manganese of is preferably 0.05 or more, more preferably 0.1 or more. The ratio of the number of moles of manganese to the total number of moles of cobalt and manganese of is preferably 0.5 or less, more preferably 0.4 or less, particularly preferably 0.3 or less, and most preferably 0.25 or less.

[0021] The molar ratio of nickel, cobalt, and manganese in the composite oxide may be, for example, nickel:cobalt:manganese=(0.8 to 0.98):(0.01 to 0.18):(0.01 to 0.18), and preferably (0.85 to 0.95):(0.03 to 0.15):(0.01 to 0.06).

[0022] The composite oxide is made of metals other than lithium, nickel, cobalt and manganese. 1 The metal M may further comprise 1 Examples of the element include aluminum (Al), boron (B), sodium (Na), magnesium (Mg), silicon (Si), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), zinc (Zn), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), barium (Ba), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), and gadolinium (Gd), and may be at least one element selected from the group consisting of these elements.

[0023] The composite oxide is metal M 1 When lithium is included, the metal M relative to the total number of moles of metals other than lithium 1 The ratio of the number of moles of metal M to the total number of moles of metals other than lithium may be, for example, 0.1 or less. 1is preferably 0.05 or less, more preferably 0.04 or less, and is preferably 0.005 or more, more preferably 0.01 or more.

[0024] The composite oxide may have a composition represented by the following formula (1), for example. Li p Ni x Co y Mn z M 1 w O2(1) In formula (1), 1≦p≦1.15, 0.8 <x<1、0<y<0.2、0<z<0.2、0≦w≦0.1、x+y+z+w≦1、0<z / (y+z)<0.58である。M 1 is at least one selected from the group consisting of Al, 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, and Gd. Preferably, 1.01≦p≦1.1, 0.82≦x≦0.92, 0.03≦y<0.18, 0.01≦z<0.18, 0≦w≦0.1, x+y+z+w≦1, 0.05≦z / (y+z)≦0.5, and more preferably, 1.01≦p≦1.1, 0.82≦x≦0.92, 0.03≦y<0.18, 0.01≦z<0.18, 0.005≦w≦0.05, x+y+z+w≦1, 0.05≦z / (y+z)≦0.5.

[0025] From the viewpoint of initial efficiency in nonaqueous electrolyte secondary batteries, the composite oxide may have a nickel disorder of, for example, 3% or less as determined by X-ray diffraction. The nickel disorder is preferably 2% or less, more preferably 1.8% or less, even more preferably 1.2% or less, particularly preferably 0.8% or less, and most preferably 0.4% or less. The lower limit of the nickel disorder can be, for example, 0.05% or more. Here, the nickel disorder refers to the chemical disorder of transition metal ions (nickel ions) that should occupy their original sites. In composite oxides with a layered structure, this is typically the interchange of lithium ions that should occupy the site represented by 3b in the Wyckoff notation (3b site, hereinafter the same) with transition metal ions that should occupy the 3a site. The smaller the nickel disorder, the more likely the initial efficiency is to improve.

[0026] The disorder of nickel element in the composite oxide can be determined as follows. The composite oxide is measured for X-ray diffraction spectrum using CuKα radiation. 1-d Ni d MeO2 (Me is the transition metal other than nickel in the composite oxide) is used, and structural optimization is performed using 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 disorder value of the nickel element.

[0027] The lithium transition metal composite oxide constituting the positive electrode active material may have a boron-containing deposit on at least a portion of its surface. The boron-containing deposit may further contain oxygen, lithium, or the like in addition to boron. Specific examples of the boron-containing deposit include lithium metaborate (LiBO2) and boric acid (H3BO3). The boron-containing deposit may be physically attached to the lithium transition metal composite oxide, or at least a portion of the boron-containing deposit may chemically form a complex with the lithium transition metal composite oxide. The content of the boron-containing deposit in the positive electrode active material may be, for example, 0.1 mol% or more and 3 mol% or less, expressed as a ratio of the number of moles of boron to the total number of moles of metals other than lithium in the lithium transition metal composite oxide. Furthermore, the content of the boron-containing deposit in the positive electrode active material is preferably 0.2 mol% or more, more preferably 0.3 mol% or more, and particularly preferably 0.5 mol% or more, expressed as a ratio of the number of moles of boron to the total number of moles of metals other than lithium in the lithium transition metal composite oxide. The content of the boron-containing deposits in the positive electrode active material is preferably 1.5 mol% or less, more preferably 1 mol% or less, and particularly preferably 0.6 mol% or less. The content of the boron-containing deposits in the positive electrode active material can be measured, for example, by an inductively coupled plasma optical emission spectrometer.

[0028] Method for producing positive electrode active material for non-aqueous electrolyte secondary battery A method for producing a positive electrode active material for a non-aqueous electrolyte secondary battery includes the following steps: preparing a composite containing nickel, cobalt, and manganese as metal components, wherein the ratio of the number of moles of nickel to the total number of moles of the metal components is greater than 0.8 and less than 1, the ratio of the number of moles of cobalt to the total number of moles of the metal components is less than 0.2, the ratio of the number of moles of manganese to the total number of moles of the metal components is less than 0.2, and the ratio of the number of moles of manganese to the sum of the number of moles of cobalt and manganese is less than 0.58; mixing the prepared composite with a lithium compound and an alkali metal compound having a melting point of 400°C or less and containing an alkali metal other than lithium to obtain a lithium mixture; synthesizing the lithium mixture by heat-treating it at a temperature of 650°C to 800°C to obtain a heat-treated product; dispersing the heat-treated product by dry dispersion to obtain a first dispersion; and contacting the first dispersion with a liquid medium and then removing at least a portion of the liquid medium. The lithium transition metal composite oxide obtained after the washing step has an average particle size D based on electron microscopy observation. SEM 50% particle size D of cumulative particle size distribution based on volume 50 Ratio of D 50 / D SEM may be 1 or more and 4 or less.

[0029] The alkali metal compound containing an alkali metal other than lithium having a melting point of 400°C or less promotes sintering, and thus, at a relatively low heat treatment temperature, the ratio of the number of moles of nickel in the composition is a predetermined value or more, the ratio of the number of moles of manganese to cobalt and manganese is less than a predetermined value, and the ratio D 50 / D SEM The lithium transition metal composite oxide particles obtained by this production method have a single particle form, and the specific surface area of ​​the lithium transition metal composite oxide particles is within a predetermined range. As a result, the lithium transition metal composite oxide particles obtained by this production method are prevented from generating impurity phases that become resistance components during charge and discharge due to thermal reduction during heat treatment. Therefore, it is believed that nonaqueous electrolyte secondary batteries containing these lithium transition metal composite oxide particles can achieve excellent initial efficiency and durability.

[0030] Preparation process In the preparation step, a composite having a desired composition is prepared. The composite may contain metal components including at least nickel, cobalt, and manganese, and oxygen atoms. The composite may contain oxides, hydroxides, carbonates, acetates, etc. of the metal components, and may contain at least oxides.

[0031] In the composition of the composite, the ratio of the number of moles of nickel to the total number of moles of the metal components may be, for example, greater than 0.8 and less than 1. The ratio of the number of moles of nickel to the total number of moles of the metal components is preferably 0.82 or more, more preferably 0.85 or more, and even more preferably 0.87 or more. The ratio of the number of moles of nickel to the total number of moles of the metal components is preferably 0.92 or less, and more preferably 0.90 or less. In the composition of the composite, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium may be, for example, less than 0.2. The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is preferably less than 0.19, more preferably 0.16 or less, even more preferably 0.13 or less, and particularly preferably 0.09 or less. The ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is preferably 0.03 or more, more preferably 0.05 or more. In the composition of the composite, the ratio of the number of moles of manganese to the total number of moles of metals other than lithium may be, for example, less than 0.2. The ratio of the number of moles of manganese to the total number of moles of metals other than lithium is preferably less than 0.19, more preferably 0.16 or less, even more preferably 0.1 or less, and particularly preferably 0.05 or less. The ratio of the number of moles of manganese to the total number of moles of metals other than lithium is preferably 0.01 or more, more preferably 0.03 or more.

[0032] In terms of discharge capacity, the composition of the composite may have a ratio of the number of moles of manganese to the total number of moles of cobalt and manganese of less than 0.58, for example. The ratio of the number of moles of manganese to the total number of moles of cobalt and manganese is preferably 0.05 or more, more preferably 0.1 or more. The ratio of the number of moles of manganese to the total number of moles of cobalt and manganese is preferably 0.5 or less, more preferably 0.4 or less, even more preferably 0.3 or less, and particularly preferably 0.25 or less.

[0033] The molar ratio of nickel, cobalt, and manganese in the composite may be, for example, nickel:cobalt:manganese=(0.8 to 0.98):(0.01 to 0.18):(0.01 to 0.18), preferably (0.85 to 0.95):(0.03 to 0.15):(0.01 to 0.06).

[0034] The compound contains metals other than lithium, nickel, cobalt and manganese. 1 The metal M may further comprise 1 Examples of the element include aluminum (Al), boron (B), sodium (Na), magnesium (Mg), silicon (Si), phosphorus (P), sulfur (S), potassium (K), calcium (Ca), titanium (Ti), vanadium (V), chromium (Cr), zinc (Zn), strontium (Sr), yttrium (Y), zirconium (Zr), niobium (Nb), molybdenum (Mo), indium (In), tin (Sn), barium (Ba), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), and gadolinium (Gd), and may be at least one element selected from the group consisting of these elements.

[0035] The compound is metal M 1 When lithium is included, the metal M relative to the total number of moles of metals other than lithium 1 The ratio of the number of moles of metal M to the total number of moles of metals other than lithium may be, for example, 0.1 or less. 1is preferably 0.05 or less, more preferably 0.04 or less, and is preferably 0.005 or more, more preferably 0.01 or more.

[0036] The composite may be prepared by appropriately selecting from commercially available products, or by preparing a composite having the desired composition by a conventional method. Examples of methods for obtaining a composite having the desired composition include a method in which raw material compounds (hydroxides, carbonates, etc.) are mixed according to the target composition and decomposed into a composite by heat treatment, and a coprecipitation method in which a solvent-soluble raw material compound is dissolved in a solvent, and a precursor precipitate having the target composition is obtained by adjusting the temperature, pH, adding a complexing agent, etc., and the obtained precursor precipitate is then heat-treated to obtain the composite. An example of a method for producing a composite is described below.

[0037] A method for obtaining a composite by coprecipitation may include a seed generation step of adjusting the pH of a mixed solution containing metal ions in a desired composition ratio to obtain seed crystals, a crystallization step of growing the generated seed crystals to obtain a precursor precipitate having desired properties, and a step of heat-treating the obtained precursor precipitate to obtain a composite. For details of the method for obtaining such a composite, see, for example, JP 2003-292322 A and JP 2011-116580 A (U.S. Patent Publication No. 2012-270107 A).

[0038] In the seed generation step, a liquid medium containing seed crystals is prepared by adjusting the pH of a mixed solution containing nickel ions, cobalt ions, and manganese ions in a desired composition ratio to, for example, 11 to 13. The seed crystals may contain, for example, a composite hydroxide containing nickel, cobalt, and manganese in a desired ratio. The mixed solution can be prepared by dissolving nickel salt, cobalt salt, and manganese salt in water in a desired ratio. Examples of nickel salt, cobalt salt, and manganese salt include sulfate, nitrate, and hydrochloride. In addition to nickel salt, cobalt salt, and manganese salt, the mixed solution may contain other metal salts (e.g., metal M) as needed. 1The temperature in the seed generation step may be, for example, 40°C to 80°C. The atmosphere in the seed generation step may be a low-oxidizing atmosphere, and the oxygen concentration may be maintained at, for example, 10% by volume or less.

[0039] In the crystallization step, the generated seed crystals are grown to obtain a precursor precipitate containing nickel, cobalt, and manganese with desired properties. The precursor precipitate may, for example, comprise a composite hydroxide containing nickel, cobalt, and manganese in the desired ratio. Seed crystal growth can be achieved, for example, by adding a mixed solution containing nickel ions, cobalt ions, and manganese ions, and optionally other metal ions, to a liquid medium containing the 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 may be, for example, 1 hour to 24 hours, preferably 3 hours to 18 hours. The temperature in the crystallization step may be, for example, 40°C to 80°C. The atmosphere in the crystallization step is the same as that in the seed generation step. The pH in the seed generation step and crystallization step can be adjusted using an acidic aqueous solution such as an aqueous sulfuric acid solution or an aqueous nitric acid solution, or an alkaline aqueous solution such as an aqueous sodium hydroxide solution or aqueous ammonia.

[0040] In the step of obtaining a composite, the precursor precipitate obtained in the crystallization step is heat-treated to obtain the composite. The heat treatment may be carried out by heating the precursor precipitate at a temperature of, for example, 500°C or less, preferably 350°C or less. The heat treatment temperature may be, for example, 100°C or more, preferably 200°C or more. The heat treatment time may be, for example, 0.5 to 48 hours, preferably 5 to 24 hours. The heat treatment atmosphere may be air or an oxygen-containing atmosphere. The heat treatment may be carried out using, for example, a box furnace, a rotary kiln furnace, a pusher furnace, a roller hearth kiln furnace, or the like.

[0041] The average particle size of the composite may be, for example, 2 μm or more and 30 μm or less. The average particle size of the composite is preferably 3 μm or more and 25 μm or less. The average particle size of the composite is a volume average particle size, and 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 is 50%.

[0042] Mixing process In the mixing step, the composite, a lithium compound, and an alkali metal compound having a melting point of 400°C or less and containing an alkali metal other than lithium are mixed to obtain a lithium mixture. Examples of lithium compounds include lithium hydroxide, lithium carbonate, and lithium oxide. The lithium compound used in the mixing may be either a solid or a solution. The particle size of the solid lithium compound may be, for example, 0.1 μm to 100 μm, preferably 2 μm to 20 μm, in terms of volume average particle size. The mixing ratio of the composite and the lithium compound may be such that the ratio of the number of moles of lithium contained in the lithium compound to the total number of moles of metal elements contained in the composite is, for example, 0.95 to 1.2, preferably 1 to 1.1.

[0043] Examples of alkali metals other than lithium contained in the alkali metal compound include sodium, potassium, rubidium, cesium, etc., and may be at least one selected from the group consisting of these, and may contain at least one of sodium and potassium. The alkali metal compound may be, for example, a hydroxide, oxide, carbonate, acetate, etc., and may be at least one selected from the group consisting of these. The melting point of the alkali metal compound may be, for example, 400°C or less or 365°C or less, or 200°C or more or 280°C or more. Specific examples of alkali metal compounds include potassium hydroxide (melting point 360°C), sodium hydroxide (melting point 318°C), potassium acetate (melting point 292°C), etc.

[0044] The alkali metal compound used for mixing may be either a solid or a solution. The particle size of the solid alkali metal compound may be, for example, 0.1 μm to 100 μm, preferably 2 μm to 20 μm, in terms of volume average particle size. The concentration of the alkali metal compound in the solution may be, for example, 10% by mass to 60% by mass, preferably 40% by mass to 55% by mass. The mixing ratio of the composite and the alkali metal compound may be such that the ratio of the number of moles of alkali metal contained in the alkali metal compound to the total number of moles of metal elements contained in the composite is, for example, 0.03 to 0.15. The mixing ratio of the composite and the alkali metal compound is such that the ratio of the number of moles of alkali metal to the total number of moles of metal elements in the composite is preferably 0.055 to 0.1.

[0045] In the mixing step, the composite, the lithium compound, and the alkali metal compound may be mixed simultaneously, or the composite and the lithium compound may be mixed and then the alkali metal compound may be mixed, or the composite and the alkali metal compound may be mixed and then the lithium compound may be mixed. The mixing may be performed using, for example, a high-speed shear mixer.

[0046] The lithium mixture may contain other metals other than nickel, cobalt, manganese, lithium, and alkali metals (e.g., metal M 1 The lithium mixture may further contain other metals (metals excluding alkali metals). Examples of the other metals include preferably Al, Zr, Ti, Mg, Ta, Nb, Mo, and W, and more preferably at least one selected from the group consisting of these. When the lithium mixture contains other metals, the lithium mixture can be obtained by mixing the other metals as simple substances or metal compounds with the composite, lithium compound, and alkali metal compound. Examples of metal compounds containing other metals include oxides, hydroxides, chlorides, nitrides, carbonates, sulfates, nitrates, acetates, and oxalates.

[0047] When the lithium mixture contains other metals, the ratio of the total number of moles of the other metals to the total number of moles of the metal components constituting the composite may be, for example, 0.005 or more and 0.1 or less, and preferably 0.01 or more and 0.05 or less.

[0048] Synthesis process In the synthesis step, the lithium mixture is heat-treated at a temperature of 650°C to 800°C to obtain a heat-treated product. The heat-treated product may contain, for example, a lithium transition metal composite oxide. The heat treatment may be performed at a single temperature or at multiple temperatures. When performing heat treatment at multiple temperatures, for example, the temperature may be raised to a first temperature, held at the first temperature for a predetermined time, and then further raised to a second temperature and held at the second temperature for a predetermined time. The first temperature may be, for example, 200°C to 600°C, preferably 400°C to 500°C. The second temperature may be, for example, 650°C to 800°C, preferably 700°C to 780°C. The heat treatment time may be, for example, 0.5 to 48 hours. When performing heat treatment at multiple temperatures, each may be 0.2 to less than 48 hours.

[0049] The heat treatment may be carried out in air or in an oxygen-containing atmosphere using, for example, a box furnace, a rotary kiln, a pusher furnace, a roller hearth kiln, or the like.

[0050] Dispersion process In the dispersion step, the heat-treated material is subjected to a dry dispersion treatment to obtain a first dispersion. By performing a dry dispersion treatment instead of a pulverization treatment that involves strong shearing force, impact, etc., the desired ratio D 50 / D SEM A first dispersion containing a lithium transition metal composite oxide having a particle size distribution, etc. can be obtained. In the method for producing a positive electrode active material, the heat-treated product may be subjected to a crushing treatment prior to the dispersion treatment, or may be subjected to a classification treatment after the dispersion treatment. The dry dispersion treatment can be carried out using, for example, a ball mill, a jet mill, etc., using, for example, air as a dispersion medium.

[0051] For example, when dispersion treatment is carried out using a ball mill, resin media can be used. Examples of the material for the resin media include urethane resin and nylon resin. By using resin media, the sintered primary particles are dissociated without being pulverized. The size of the resin media may be, for example, φ5 mm or more and 30 mm or less. For the body (shell), for example, urethane resin or nylon resin can be used. The time for dispersion treatment may be, for example, 3 minutes or more and 60 minutes or less, and preferably 10 minutes or more and 30 minutes or less. The conditions for dispersion treatment using a ball mill include the desired ratio D 50 / D SEM The ratio D of the raw compound 90 / D 10 The amount of media, rotation or vibration speed, dispersion time, media specific gravity, etc. may be adjusted depending on the above.

[0052] For example, when dispersion is performed using a jet mill, the primary particles are not pulverized and the desired ratio D 50 / D SEM The ratio D of the raw material composites is 90 / D 10 The supply pressure, pulverization pressure, supply speed, etc. may be adjusted depending on the above. The supply pressure may be, for example, 0.1 MPa or more and 0.5 MPa or less. The pulverization pressure may be, for example, 0.1 MPa or more and 0.6 MPa or less.

[0053] Cleaning process In the washing step, the first dispersion containing lithium transition metal composite oxide particles is contacted with a liquid medium, and then at least a portion of the liquid medium is removed to obtain a second dispersion. The second dispersion may be subjected to a dewatering treatment, a drying treatment, or the like, as necessary. The washing step may be, for example, a step of removing at least a portion of the unreacted raw material alkaline component (e.g., lithium compound) present in the first dispersion.

[0054] The liquid medium used in the washing step only needs to contain water, and may contain liquid components other than water, metal salts, etc., as necessary. Examples of liquid components other than water include water-soluble organic solvents such as alcohol. Examples of metal salts include alkali metal salts such as lithium and sodium. By including a metal salt in the liquid medium, the alkali components of the unreacted raw materials can be removed more efficiently. Examples of metal salts include sulfates and hydroxides. When the liquid medium includes a metal salt, the content of the metal salt may be, for example, 0.01 mol / L or more and 2.0 mol / L or less, in terms of the molar concentration of the metal ions. The content of the metal salt is preferably 0.015 mol / L or more and 1.0 mol / L or less, more preferably 0.015 mol / L or more and 0.2 mol / L or less, and even more preferably 0.015 mol / L or more and 0.15 mol / L or less.

[0055] The contact temperature between the first dispersion and the liquid medium may be, for example, 5°C to 60°C, and preferably 10°C to 40°C. The contact time may be, for example, 1 minute to 2 hours, and preferably 5 minutes to 30 minutes. The amount of liquid medium used for contact may be, for example, 0.5 to 10 times, and preferably 1 to 4 times the mass of the first dispersion.

[0056] The contact of the first dispersion with the liquid medium may be carried out by adding the first dispersion to the liquid medium to prepare a slurry. When the contact is carried out as a slurry, the solids concentration of the first dispersion in the slurry may be, for example, 10% by mass or more and 70% by mass or less, and preferably 20% by mass or more and 50% by mass or less. When the first dispersion is contacted with the liquid medium, the mixture of the first dispersion and the liquid medium may be stirred as needed. Stirring may be carried out using, for example, a high-speed stirring mixer, a double cone mixer, a kneader, or the like. Alternatively, the contact of the first dispersion with the liquid medium may be carried out by passing the liquid medium through the first dispersion held on a filter.

[0057] The second dispersion obtained in the washing step may be dried. The drying process may be performed by heat drying, air drying, vacuum drying, or the like, as long as it can remove at least a portion of the liquid medium attached to the second dispersion. The drying temperature for heat drying may be any temperature that sufficiently removes the liquid medium contained in the second dispersion. The drying temperature may be, for example, 80°C or higher and 300°C or lower, and preferably 150°C or higher and 280°C or lower. A drying temperature within the above range can sufficiently suppress the elution of lithium into the attached liquid medium. Furthermore, the collapse of the crystalline structure on the particle surface can be suppressed, and a decrease in charge / discharge capacity can be sufficiently suppressed. The drying time may be appropriately selected depending on the amount of water contained in the second dispersion. The drying time is, for example, 1 hour or higher and 12 hours or lower. The amount of water contained in the second dispersion after the drying process may be, for example, 0.2% by mass or lower, and preferably 0.1% by mass or lower.

[0058] The lithium transition metal composite oxide contained in the second dispersion obtained by the above-mentioned production method has a ratio D 50 / D SEM may be 1 or more and 4 or less. The composition may contain lithium, nickel, cobalt, and manganese, and the ratio of the number of moles of nickel to the total number of moles of metal components other than lithium may be greater than 0.8 and less than 1, the ratio of the number of moles of cobalt may be less than 0.2, the ratio of the number of moles of manganese to the total number of moles of cobalt and manganese may be less than 0.58. The lithium transition metal composite oxide may have a composition represented by the above formula (1), for example.

[0059] The method for producing a positive electrode active material may optionally include an attachment step of disposing a boron-containing deposit on the surface of the lithium transition metal composite oxide obtained in the washing step. By constructing a battery using a positive electrode active material containing a lithium transition metal composite oxide having a boron-containing deposit on its surface, the discharge capacity of the battery can be further improved. The attachment step may include, for example, a boron mixing step of mixing the lithium transition metal composite oxide with a boron source compound serving as a raw material for the boron-containing deposit to obtain a boron mixture, and a boron heat treatment step of heat-treating the boron mixture.

[0060] In the boron mixing step, a lithium transition metal composite oxide and a boron source compound are mixed to obtain a boron mixture. The lithium transition metal composite oxide and the boron source compound may be mixed in a dry system or a wet system. The mixing may be performed using, for example, a super mixer.

[0061] The boron source compound may be at least one selected from the group consisting of boron oxide, boron oxoacids, and boron oxoacid salts. More specific examples of the boron source compound include lithium tetraborate (Li2B4O7), ammonium pentaborate (NH4B5O8), orthoboric acid (H3BO3; so-called ordinary boric acid), lithium metaborate (LiBO2), boron oxide (BO3), etc. At least one selected from the group consisting of these may be used, and orthoboric acid may be used from the viewpoint of cost.

[0062] The boron source compound may be mixed with the lithium transition metal composite oxide in a solid state, or may be mixed with the lithium transition metal composite oxide as a solution of the boron source compound. When a solid boron source compound is used, the volume average particle size of the boron source compound may be, for example, 1 μm or more and 60 μm or less, and preferably 10 μm or more and 30 μm or less.

[0063] The content of the boron source compound in the boron mixture may be 0.1 mol% or more and 3 mol% or less, preferably 0.2 mol% or more, more preferably 0.3 mol% or more, particularly preferably 0.5 mol% or more, preferably 1.5 mol% or less, more preferably 1 mol% or less, and particularly preferably 0.6 mol% or less, as a ratio of the number of moles of elemental boron to the total number of moles of metals other than lithium in the lithium transition metal composite oxide.

[0064] The boron mixture may further contain a lithium compound as needed, such as at least one selected from the group consisting of lithium hydroxide, lithium oxide, lithium carbonate, and lithium nitrate.

[0065] The lithium compound may be mixed with the lithium transition metal composite oxide and the boron source compound in a solid state, or may be mixed with the lithium transition metal composite oxide and the boron source compound in the form of a solution of the lithium compound. When a solid lithium compound is used, the volume average particle size of the lithium compound may be, for example, 1 μm or more and 60 μm or less, and preferably 10 μm or more and 30 μm or less.

[0066] The content of the lithium compound in the boron mixture may be, for example, 0.05 mol% or more and 1 mol% or less, preferably 0.05 mol% or more and 0.5 mol% or less, and more preferably 0.1 mol% or more and 0.3 mol% or less, as a ratio of the number of moles of lithium to the total number of moles of metals other than lithium in the lithium transition metal composite oxide.

[0067] In the boron heat treatment step, the boron mixture is heat-treated to obtain a cathode active material containing a lithium transition metal composite oxide having a boron-containing deposit on its surface. The heat treatment temperature may be, for example, 100°C to 450°C, preferably 150°C to 400°C, more preferably 200°C to 400°C, more preferably 220°C to 350°C, and even more preferably 250°C to 350°C. The heat treatment may be performed in an oxygen-containing atmosphere or in air. The heat treatment time may be, for example, 1 hour to 20 hours, preferably 5 hours to 15 hours. The heat-treated product obtained in the boron heat treatment step may be subjected to crushing, classification, or other processes as needed.

[0068] Electrodes for non-aqueous electrolyte secondary batteries The electrode for a non-aqueous electrolyte secondary battery includes a current collector and a positive electrode active material layer disposed on the current collector and containing the positive electrode active material for a non-aqueous electrolyte secondary battery produced by the above-described production method. A non-aqueous electrolyte secondary battery including such an electrode can achieve high initial efficiency and high durability.

[0069] 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, a conductive material, a binder, and the like with a solvent onto the current collector, followed by drying and pressure treatments. Examples of conductive materials include natural graphite, artificial graphite, and acetylene black. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, and polyamide acrylic resin.

[0070] Nonaqueous electrolyte secondary battery The nonaqueous electrolyte secondary battery includes the above-described electrodes for a nonaqueous electrolyte secondary battery. The nonaqueous electrolyte secondary battery is configured to include, in addition to the electrodes for a nonaqueous electrolyte secondary battery, a negative electrode for a nonaqueous electrolyte secondary battery, a nonaqueous electrolyte, a separator, etc. For the negative electrode, nonaqueous electrolyte, separator, etc. of the nonaqueous electrolyte secondary battery, those for nonaqueous electrolyte secondary batteries described in, for example, JP 2002-075367 A, JP 2011-146390 A, JP 2006-12433 A (the disclosures of which are incorporated herein by reference in their entirety) can be used as appropriate. [Example]

[0071] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0072] Example 1 Seed generation process 10 kg of water was placed in a reaction vessel, and while stirring, an aqueous ammonia solution was added to adjust the ammonium ion concentration to 1.8% by mass. The temperature inside the vessel was set to 25°C, and nitrogen gas was circulated to maintain the oxygen concentration in the reaction vessel space at 10% or less. A 25% by mass aqueous sodium hydroxide solution was added to the water in the reaction vessel to adjust the pH value of the solution in the vessel to 13.5 or higher. Next, a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution were mixed in a molar ratio of 88:9:3 to prepare a mixed solution (1.7 mol / L). The mixed solution was added to the vessel until the solute amount reached 4 mol, and seed generation was carried out while controlling the pH value of the reaction solution to 12.0 or higher with sodium hydroxide solution.

[0073] Crystallization process After the seed generation step, the temperature inside the tank was maintained at 25°C or higher until the end of the crystallization step. A mixed solution of 1200 moles of solute was also prepared, and was simultaneously added to the reaction tank over a period of 5 hours or more, together with an aqueous ammonia solution, while maintaining the ammonium ion concentration in the solution at 2000 ppm or higher, to prevent new seed generation. During the reaction, the pH value of the reaction solution was controlled to be maintained between 10.5 and 12.0 using a sodium hydroxide solution. Sampling was carried out sequentially during the reaction, and the D of the composite hydroxide particles was measured. 50 The addition was stopped when the particle size reached about 4.4 μm. The product was then washed with water, filtered, and dried to obtain composite hydroxide particles as a precursor precipitate.

[0074] The obtained composite hydroxide particles were subjected to heat treatment at 300°C for 20 hours in an air atmosphere to obtain a composite hydroxide having a molar ratio of Ni / Co / Mn=0.88 / 0.09 / 0.03, D 10 = 3.4 μm, D 50 = 4.3 μm, D 90 = 5.5 μm, D 90 / D 10 The transition metal oxides were obtained as composites with a .DELTA.=1.6.

[0075] Synthesis process The resulting composite was mixed with a potassium hydroxide solution (50% concentration) to a molar ratio of K / (Ni+Co+Mn) = 0.05, followed by the addition and mixing of lithium hydroxide monohydrate to a molar ratio of Li / (Ni+Co+Mn) = 1.08 and aluminum hydroxide to a molar ratio of Al / (Ni+Co+Mn) = 0.01 to obtain a lithium mixture. The resulting lithium mixture was heat-treated in air at 450°C for 3 hours, followed by another heat treatment at 750°C for 8 hours to obtain a heat-treated product. The heat-treated product was then crushed and dispersed in a resin ball mill for 15 minutes to obtain a powder.

[0076] The obtained powder was added to pure water to prepare a slurry with a solids concentration of 30% by mass. The solids concentration was calculated by dividing the powder mass by the (powder mass + washing solution mass). After stirring for 30 minutes, the slurry was dehydrated in a funnel and separated as a cake. The separated cake was dried at 250°C for 10 hours to obtain a dried product. The dried product was crushed and sieved to obtain a cathode active material containing a lithium transition metal composite oxide. SEM images of the obtained cathode active material were obtained using a scanning electron microscope (SEM; accelerating voltage 20 kV). Figure 1 shows an SEM image of the obtained cathode active material, and Table 1 shows its physical properties.

[0077] Example 2 A lithium transition metal oxide was obtained in the same manner as in Example 1, except that in the seed generation step, a mixed solution was prepared by mixing a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution in a molar ratio of 90:9:1.

[0078] Adhesion process The resulting lithium transition metal oxide was mixed with orthoboric acid in an amount equivalent to 0.3 mol% boron and lithium hydroxide monohydrate in an amount equivalent to 0.15 mol% lithium, based on the total moles of metals other than lithium in the lithium transition metal composite oxide, and stirred to obtain a mixture containing boron and lithium. The resulting mixture was heat-treated in air at 300°C for 10 hours to obtain a cathode active material containing a lithium transition metal composite oxide bearing a boron-containing deposit on its surface. An SEM image of the resulting cathode active material is shown in Figure 2, and its physical properties are shown in Table 1.

[0079] Example 3 A positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface was obtained in the same manner as in Example 2, except that in the seed generation step, a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution were mixed in a molar ratio of 88:9:3. An SEM image of the obtained positive electrode active material is shown in FIG. 3, and its physical properties are shown in Table 1.

[0080] Example 4 A positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface was obtained in the same manner as in Example 3, except that a sodium hydroxide aqueous solution (concentration: 50%) was used instead of the potassium hydroxide aqueous solution in the synthesis step, and Na / (Ni+Co+Mn) = 0.08. An SEM image of the obtained positive electrode active material is shown in Figure 4, and its physical properties are shown in Table 1.

[0081] Example 5 A positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface was obtained in the same manner as in Example 4, except that in the seed generation step, a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution were mixed in a molar ratio of 92:5:3 to prepare a mixed solution, and in the synthesis step, aluminum hydroxide was added so that Al / (Ni+Co+Mn)=0.02. An SEM image of the obtained positive electrode active material is shown in FIG. 5, and its physical properties are shown in Table 1.

[0082] (Comparative Example 1) A positive electrode active material containing a lithium transition metal oxide was obtained in the same manner as in Example 1, except that in the seed generation step, a mixed solution was prepared by mixing a nickel sulfate solution and a cobalt sulfate solution at a molar ratio of 95:5 without using a manganese sulfate solution, that in the synthesis step, aluminum hydroxide was added so that Al / (Ni+Co+Mn)=0.02, and that the heat treatment temperature was changed from 750°C to 725°C. An SEM image of the obtained positive electrode active material is shown in FIG. 6, and its physical properties are shown in Table 1.

[0083] (Comparative Example 2) The lithium transition metal oxide obtained in Comparative Example 1 was subjected to the deposition process in the same manner as in Example 2 to obtain a positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface. An SEM image of the obtained positive electrode active material is shown in FIG. 7, and its physical properties are shown in Table 1.

[0084] (Comparative Example 3) A positive electrode active material containing a lithium transition metal oxide was obtained in the same manner as in Example 4, except that in the seed generation step, a nickel sulfate solution, a cobalt sulfate solution, and a manganese sulfate solution were mixed at a molar ratio of 88:5:7 to prepare a mixed solution, in the synthesis step, aluminum hydroxide was added so that Al / (Ni+Co+Mn)=0.01, and the heat treatment temperature was changed from 750°C to 810°C. An SEM image of the obtained positive electrode active material is shown in FIG. 8, and its physical properties are shown in Table 1.

[0085] Comparative Example 4 A positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface was obtained in the same manner as in Example 3, except that the potassium hydroxide aqueous solution (concentration: 50%) was not used in the synthesis step. An SEM image of the obtained positive electrode active material is shown in FIG. 9, and its physical properties are shown in Table 1.

[0086] (Comparative Example 5) A positive electrode active material containing a lithium transition metal oxide having a boron-containing deposit on its surface was obtained in the same manner as in Comparative Example 2, except that the potassium hydroxide aqueous solution (concentration: 50%) was not used in the synthesis step and the heat treatment temperature was changed from 725° C. to 710° C. An SEM image of the obtained positive electrode active material is shown in FIG. 10, and its physical properties are shown in Table 1.

[0087] (Comparative Example 6) Except for not using the potassium hydroxide aqueous solution (concentration 50%) in the synthesis step, a positive electrode active material containing a lithium transition metal oxide was obtained in the same manner as in Example 1. An SEM image of the obtained positive electrode active material is shown in FIG. 11, and the physical properties thereof are shown in Table 1.

[0088] Particle size evaluation The physical properties of the positive electrode active material obtained above were measured as follows. 50 The cumulative particle size distribution on a volume basis was measured using a laser diffraction particle size distribution analyzer (SALD-3100 manufactured by Shimadzu Corporation), and the particle size was calculated as the particle size corresponding to the cumulative 50% from the smallest diameter side. The average particle size D SEM Regarding the particle diameter, 100 particles whose particle outlines could be confirmed were selected from images observed at 1000 to 10,000 magnifications using a scanning electron microscope (SEM), and the spherical equivalent diameter of the selected particles was calculated using image processing software (ImageJ), and the arithmetic mean value of the obtained spherical equivalent diameters was obtained.

[0089] Nickel element disorder (Ni disorder) The positive electrode active material obtained above was subjected to X-ray diffraction spectroscopy (tube current 200 mA, tube voltage 45 kV) using CuKα radiation. Based on the obtained X-ray diffraction spectrum, a composition model was established (Li 1-d Ni d )(Ni x Co y Mn z Al w)O2(x+y+z+w=1), and the structure of the lithium transition metal composite oxide was optimized by Rietveld analysis using Rietan2000 software. The percentage of d calculated as a result of the structure optimization was taken as the Ni disorder.

[0090] [Table 1]

[0091] Preparation of evaluation battery Using the positive electrode active material obtained above, a battery for evaluation was fabricated in the following manner.

[0092] Preparation of the positive electrode A positive electrode mixture was prepared by dispersing 92 parts by weight of the positive electrode active material, 3 parts by weight of acetylene black, and 5 parts by weight of polyvinylidene fluoride (PVDF) in N-methyl-2-pyrrolidone (NMP). The resulting positive electrode mixture was applied to an aluminum foil current collector, dried, compressed using a roll press, and then cut to a predetermined size to fabricate a positive electrode.

[0093] Preparation of the negative electrode A negative electrode slurry was prepared by dissolving 97.5 parts by weight of artificial graphite, 1.5 parts by weight of carboxymethyl cellulose (CMC), and 1.0 part by weight of SBR (styrene butadiene rubber) in pure water. The resulting negative electrode slurry was applied to a copper foil current collector, dried, and then compression-molded using a roll press. The negative electrode was then cut to a specified size.

[0094] Preparation of evaluation battery After attaching lead electrodes to the positive and negative current collectors, a separator was placed between the positive and negative electrodes, and the assembly was then housed in a bag-shaped laminate pack. This was then vacuum dried at 65°C to remove moisture adsorbed to each component. An electrolyte solution was then poured into the laminate pack under an argon atmosphere and sealed to prepare a test battery. The electrolyte solution was a mixture of ethylene carbonate (EC) and methyl ethyl carbonate (MEC) in a volume ratio of 3:7, with lithium hexafluorophosphate (LiPF6) dissolved to a concentration of 1 mol / L. The test battery thus obtained was placed in a thermostatic chamber at 25°C and aged with a weak current. The following evaluations were then performed. The results are shown in Table 2.

[0095] Initial efficiency measurement The resulting evaluation battery was subjected to constant-voltage / constant-current charging at a charging voltage of 4.25 V and a charging current of 0.1 C to measure the charge capacity, and then discharged at a constant current of 2.5 V and a discharging current of 0.1 C to measure the discharge capacity.

[0096] Capacity retention rate measurement The obtained evaluation battery was aged by performing a single charge-discharge cycle consisting of a constant-voltage / constant-current charge at a charge voltage of 4.25 V (counter electrode Li) and a charge current of 0.2 C (1 C ≡ a current at which discharge is completed in 1 hour), and a constant-current discharge at a discharge voltage of 2.75 V (counter electrode Li) and a discharge current of 0.2 C.

[0097] After aging, one cycle consisted of a constant-voltage / constant-current charge at a charge voltage of 4.25 V (counter electrode Li) and a charge current of 0.3 C, followed by a constant-current discharge at a discharge voltage of 2.75 V (counter electrode Li) and a discharge current of 0.3 C. The discharge capacity after each cycle was measured at a constant temperature of 45°C. The ratio of the discharge capacity Ed(n) after the nth cycle to the discharge capacity Ed(1) after the first cycle (≡Ed(n) / Ed(1)) was defined as the capacity retention rate Rs(n) after the nth cycle. Note that the number of cycles n was 30.

[0098] [Table 2]

[0099] As shown in Table 2, the ratio D 50 / D SEM It was confirmed that a battery constructed including a positive electrode active material in which the ratio of the number of moles of manganese to the total number of moles of cobalt and manganese was less than 0.58 had a higher initial efficiency and capacity retention rate (durability) than those of Comparative Examples 1 to 3. It was also confirmed that in Examples 2 to 5, the discharge capacity was higher than that of Example 1 due to the presence of a deposit containing boron on the surface.

[0100] The discharge capacity of Comparative Example 4 (agglomerated particles), which contains manganese, is lower than that of Comparative Example 5 (agglomerated particles). On the other hand, the discharge capacity of Example 3 (single particle), which contains manganese, is improved compared to Comparative Example 2 (single particle). From these results, it can be seen that the effect of including manganese in the composition is 50 / D SEM It was confirmed that this is an effect specific to single-particle lithium transition metal oxides, in which the ρ is 1 or more and 4 or less.

[0101] [Table 3]

[0102] [Table 4]

[0103] [Table 5]

[0104] Tables 3 to 5 show the improvement in discharge capacity of the lithium transition metal composite oxide having a boron-containing deposit compared to the lithium transition metal composite oxide not having a boron-containing deposit. It was confirmed that the effect of the boron-containing deposit in the examples in Table 3 was greatest compared to the effect of the boron-containing deposit in the agglomerated particles in Table 5 and the effect of the boron-containing deposit in the single particles in Table 4 whose composition does not include manganese.

[0105] The disclosure of Japanese Patent Application No. 2019-217181 (filing date: November 29, 2019) 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 was specifically and individually indicated to be incorporated by reference.

Claims

1. a lithium transition metal composite oxide containing lithium, nickel, cobalt, and manganese and having a layered structure; The lithium transition metal composite oxide has an average primary particle diameter D ＳＥＭ 50% particle size D of cumulative particle size distribution based on volume ５０ Ratio D ５０ / D ＳＥＭ is between 1 and 4, the ratio of the number of moles of cobalt to the total number of moles of metals other than lithium is 0.03 or more and less than 0.2; a composition in which the ratio of the number of moles of manganese to the total number of moles of metals other than lithium is 0.01 or more and less than 0.2; The nickel element disorder is 1.8% or less, The lithium transition metal composite oxide has a boron-containing deposit on its surface, and is a positive electrode active material for a non-aqueous electrolyte secondary battery.

2. 2. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a nickel disorder of 1.2% or less.

3. 3. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a composition in which the ratio of the number of moles of manganese to the total number of moles of cobalt and manganese is less than 0.

58.

4. 4. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the content of the deposits is 0.1 mol % or more and 3 mol % or less, in terms of a boron content relative to the total number of moles of metals other than lithium in the lithium transition metal composite oxide.

5. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1 , wherein the deposit further contains lithium.

6. The lithium transition metal composite oxide has an average particle size D ＳＥＭ 6. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the average particle size is 1 μm or more and 7 μm or less.

7. The lithium transition metal composite oxide has a 90% particle size D ９０ 10% particle size D １０ Ratio D to ９０ / D １０ 7. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the σ is 4.5 or less.

8. 8. The positive electrode active material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the lithium transition metal composite oxide has a composition represented by the following formula: Li ｐ Ni ｘ Co ｙ Mn ｚ M １ ｗ O ２ (1≦p≦1.15, 0.8<x<1, 0.03≦y<0.2, 0.01≦<z<0.2, 0≦w≦0.1, x+y+z+w≦1, M １ is at least one selected from the group consisting of Al, 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, and Gd.

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