Positive electrode active material for lithium-ion batteries and method for manufacturing the same

Abstract

The present invention provides a method for producing a positive electrode active material for lithium-ion batteries that can be used to construct lithium-ion batteries exhibiting good cycle characteristics and suppressing gas generation during storage. [Solution] A method for producing a positive electrode active material for a lithium-ion battery includes: contacting a heat-treated product of a nickel-containing metal compound and a lithium compound with a first liquid medium, then separating the solid and liquid to obtain a first treated product and a second liquid medium; contacting the second liquid medium with an alkaline earth metal compound, then separating the solid and liquid to obtain a third liquid medium; and contacting the first treated product with the third liquid medium, then separating the solid and liquid to obtain a second treated product and a fourth liquid medium. The heat-treated product includes a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

Description

[Technical Field]

[0001] This disclosure relates to a positive electrode active material for lithium-ion batteries and a method for producing the same. [Background technology]

[0002] From the viewpoint of energy density, lithium transition metal composite oxides with a high nickel content have attracted attention as positive electrode active materials for lithium-ion batteries. In lithium-ion batteries containing lithium transition metal composite oxides with a high nickel content as positive electrode active materials, cycle characteristics may deteriorate or gas may be generated during storage. For example, Patent Document 1 describes a method for producing lithium composite compound particle powder consisting of a step of removing impurities with an aqueous solvent and a step of heat treatment in air or oxygen with a carbon dioxide concentration of 100 ppm or less. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-200875 [Overview of the project] [Problems that the invention aims to solve]

[0004] One aspect of this disclosure aims to provide a positive electrode active material for a lithium-ion battery and a method for producing the same, which can constitute a lithium-ion battery that exhibits good cycle characteristics and suppresses gas generation during storage. [Means for solving the problem]

[0005] The first embodiment is a method for producing a positive electrode active material for a lithium-ion battery, comprising: contacting a heat-treated product of a nickel-containing metal compound and a lithium compound with a first liquid medium, then performing solid-liquid separation to obtain a first treated product and a second liquid medium; contacting the second liquid medium with an alkaline earth metal compound, then performing solid-liquid separation to obtain a third liquid medium; and contacting the first treated product with the third liquid medium, then performing solid-liquid separation to obtain a second treated product and a fourth liquid medium. The heat-treated product contains a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

[0006] The second embodiment is a positive electrode active material for a lithium-ion battery comprising a lithium transition metal composite oxide containing lithium and nickel in its composition, a calcium compound, a lithium compound, and a boron compound. The lithium compound contains lithium carbonate, with a lithium carbonate content of less than 0.4% by mass. The boron compound is disposed on at least a portion of the surface of the lithium transition metal composite oxide.

[0007] The third aspect is a method for producing a positive electrode active material for a lithium-ion battery, comprising a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1. The method for producing a positive electrode active material for a lithium-ion battery includes: a first step of contacting a heat-treated product of a metal compound containing nickel and a lithium compound with a liquid medium to clean the heat-treated product; a second step of solid-liquid separation of the cleaned heat-treated product and the liquid medium after cleaning; a third step of contacting the liquid medium separated in the second step with an alkaline earth metal compound to obtain a solid product containing alkaline earth metal; a fourth step of solid-liquid separation of the solid product obtained in the third step and the liquid medium; a fifth step of further cleaning the heat-treated product by contacting the cleaned heat-treated product obtained in the second step with the liquid medium obtained in the fourth step; and a sixth step of solid-liquid separation of the cleaned heat-treated product obtained in the fifth step and the liquid medium after cleaning.

[0008] The third embodiment of the method for producing a positive electrode active material for a lithium-ion battery may further include performing the same steps as those in steps 3 to 6 at least once using the washed heat-treated material obtained in step 6 and the liquid medium after washing. The method for producing a positive electrode active material for a lithium-ion battery may further include heat-treating a mixture of the washed heat-treated material and a boron compound at a temperature of 100°C to 450°C. [Effects of the Invention]

[0009] According to one aspect of this disclosure, it is possible to provide a positive electrode active material for a lithium-ion battery and a method for manufacturing the same, which can constitute a lithium-ion battery that exhibits good cycle characteristics and suppresses gas generation during storage. [Modes for carrying out the invention]

[0010] In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. Furthermore, the content of each component in a composition refers to the total amount of multiple substances present in the composition, unless otherwise specified, if multiple substances corresponding to each component exist in the composition. In addition, the upper and lower limits of the numerical ranges described herein can be arbitrarily selected and combined from the numerical values ​​exemplified as numerical ranges. Embodiments of the present invention will now be described based on the drawings. However, the embodiments shown below are illustrative examples of positive electrode active materials for lithium-ion batteries and methods for producing them, in order to embody the technical concept of the present invention, and the present invention is not limited to the positive electrode active materials for lithium-ion batteries and methods for producing them shown below.

[0011] Method for manufacturing positive electrode active material for lithium-ion batteries The method for manufacturing a positive electrode active material for a lithium-ion battery may include a first step of contacting a heat-treated product of a metal compound containing nickel and a lithium compound with a first liquid medium, followed by solid-liquid separation to obtain a first treated product and a second liquid medium; a second step of contacting the second liquid medium with an alkaline earth metal compound, followed by solid-liquid separation to obtain a third liquid medium; and a third step of contacting the first treated product with the third liquid medium, followed by solid-liquid separation to obtain a second treated product and a fourth liquid medium. The heat-treated product may contain a lithium transition metal composite oxide in which the molar ratio of nickel atoms to the total molar number of metal atoms other than lithium is 0.6 or more and less than 1.

[0012] The method for manufacturing a positive electrode active material for a lithium-ion battery may further include a fourth step of contacting the fourth liquid medium with an alkaline earth metal compound, followed by solid-liquid separation to obtain a fifth liquid medium; and a fifth step of contacting the second treated product with the fifth liquid medium, followed by solid-liquid separation to obtain a liquid medium-treated product and a post-treatment liquid medium. By further subjecting the second treated product to liquid medium treatment, impurities contained in the heat-treated product can be more effectively removed, and in a lithium-ion battery including the obtained positive electrode active material for a lithium-ion battery, better cycle characteristics and more effective suppression of gas generation during storage can be achieved.

[0013] Furthermore, the method for manufacturing a positive electrode active material for a lithium-ion battery may further include a sixth step of contacting the post-treatment liquid medium with an alkaline earth metal compound, followed by solid-liquid separation to obtain a treatment liquid medium; and a seventh step of contacting the liquid medium-treated product with the treatment liquid medium, followed by solid-liquid separation to obtain a liquid medium-treated product and a post-treatment liquid medium, and the sixth step and the seventh step may be included in two or more repetitions.

[0014] By subjecting the first processed material to a liquid medium treatment using a third liquid medium obtained by bringing the liquid medium used for the liquid medium treatment (e.g., washing treatment) of the heat-treated material containing the lithium transition metal composite oxide into contact with an alkaline earth metal compound, impurities (e.g., lithium carbonate) contained in the heat-treated material can be efficiently removed. As a result, a positive electrode active material for a lithium ion battery that exhibits good cycle characteristics and suppresses gas generation during storage can be efficiently produced. This can be considered, for example, as follows. By subjecting the first processed material to a liquid medium treatment using the third liquid medium obtained by removing at least a part of the impurities (e.g., lithium carbonate) contained in the liquid medium after contact with the heat-treated material as a solid content by contact with an alkaline earth metal compound, it is possible to efficiently remove the impurities while suppressing excessive removal of lithium from the first processed material.

[0015] In the first step, after bringing a heat-treated material of a metal compound containing nickel and a lithium compound (hereinafter also referred to as the first lithium compound) into contact with a first liquid medium, solid-liquid separation is performed to obtain a first processed material and a second liquid medium. The heat-treated material is a heat-treated material of a mixture containing a metal compound containing nickel and a lithium compound, and contains at least a lithium transition metal composite oxide in which the molar ratio of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1. In addition to the lithium transition metal composite oxide, the heat-treated material may contain, for example, a second lithium compound as an impurity. Examples of the second lithium compound contained in the heat-treated material include lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfate, etc., and may contain at least lithium carbonate. The content of lithium carbonate contained in the heat-treated material may be, for example, 0.1 mass% or more and 2.0 mass% or less. The heat-treated material may be a mixture independently containing a lithium transition metal composite oxide and a second lithium compound, or may contain a lithium transition metal composite oxide to which at least a part of the second lithium compound is attached to at least a part of the surface.

[0016] <00,00101>The lithium transition metal composite oxide contained in the heat-treated material may have a composition in which the ratio of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1. The composition of the lithium transition metal composite oxide may have a ratio of moles of nickel to the total number of moles of metals other than lithium that is, for example, 0.6 or more and less than 1, preferably 0.7 or more, 0.75 or more, 0.8 or more, 0.9 or more, 0.92 or more, or 0.94 or more, preferably 0.98 or less, 0.96 or less, 0.95 or less, or 0.94 or less. The higher the ratio of moles of nickel atoms, the higher the charge / discharge capacity, while the content of lithium-2 compounds as impurities tends to increase. However, within the above range, the effects of this disclosure are greater. The lithium transition metal composite oxide may contain cobalt in its composition. When the lithium transition metal composite oxide contains cobalt, the ratio of moles of cobalt to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less. Preferably, it may be 0.01 or more, 0.02 or more, 0.03 or more, or 0.05 or more, and may be 0.2 or less, 0.15 or less, 0.1 or less, 0.08 or less, or 0.05 or less. The lithium transition metal composite oxide may contain manganese in its composition. When the lithium transition metal composite oxide contains manganese, the ratio of moles of manganese to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.3 or less. Preferably, it may be 0.001 or more, 0.005 or more, 0.008 or more, or 0.01 or more, and may be 0.15 or less, 0.1 or less, 0.06 or less, 0.03 or less, or 0.01 or less. The lithium transition metal composite oxide may contain aluminum in its composition. When the lithium transition metal composite oxide contains aluminum, the ratio of moles of aluminum to the total number of moles of metals other than lithium may be, for example, greater than 0 and 0.1 or less. Preferably, it may be 0.01 or higher, and may be 0.6 or lower, 0.1 or lower, or 0.08 or lower.When the lithium transition metal composite oxide contains at least one of manganese and aluminum in its composition, the ratio of the total molar number of manganese and aluminum to the total molar number of metals other than lithium may be, for example, greater than 0 and not more than 0.3, preferably greater than 0 and not more than 0.25, or may be not less than 0.01 and not more than 0.15.

[0017] The lithium transition metal composite oxide may contain at least one element M selected from the group consisting of zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), and tungsten (W) in its composition. When the lithium transition metal composite oxide contains element M, the ratio of the molar number of element M to the total molar number of metals other than lithium may be, for example, greater than 0 and not more than 0.1. Preferably, it may be not less than 0.0001, not less than 0.0005, or not less than 0.001, and may be not more than 0.03 or not more than 0.01.

[0018] The lithium transition metal composite oxide may have, for example, a composition represented by the following formula (1). Li (1+p) Ni (1-x-y-z-w) Co x Mn y Al z M w O2(1)

[0019] In the formula, -0.05 ≤ p ≤ 0.2, 0 < x + y + z + w ≤ 0.4, 0 ≤ x ≤ 0.3, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.1, and 0 ≤ w ≤ 0.1 are satisfied. M contains at least one selected from the group consisting of Zr, Ti, Mg, Ta, Nb, Mo, and W.

[0020] The lithium transition metal composite oxide contained in the heat-treated product may contain secondary particles formed by aggregation of a plurality of primary particles, or may be composed of secondary particles. The primary particles may contain a lithium transition metal composite oxide containing lithium and a transition metal such as nickel, and may be a single crystal of the lithium transition metal composite oxide. The lithium transition metal composite oxide may have a layered structure. The average particle diameter of the primary particles is the average particle diameter D based on electron microscope observationSEM For example, it may be 1 μm or less, preferably 600 nm or less, or 300 nm or less, and may be, for example, 100 nm or more. Also, the volume average particle diameter D of the secondary particles 50 may be, for example, 2 μm or more and 6 μm or less, preferably more than 3 μm and less than 5 μm, or 3.5 μm or more and 4.5 μm or less.

[0021] The number of primary particles constituting the secondary particles of the lithium transition metal composite oxide may be, for example, 20 or more and 10,000 or less, preferably 200 or more and 1,000 or less. Also, the secondary particles of the lithium transition metal composite oxide have an average particle diameter D based on electron microscope observation SEM with respect to the volume average particle diameter D 50 The ratio (D 50 / D SEM ) may be, for example, 3 or more and 20 or less, preferably 5 or more and 10 or less. The volume average particle diameter is the value at which the volume integration value from the small particle diameter side in the volume-based particle size distribution obtained by the laser scattering method becomes 50%.

[0022] The average particle diameter D based on electron microscope observation SEM is the average value of the spherical equivalent diameters of the primary particles measured from the scanning electron microscope (SEM) image. The average particle diameter D SEM is specifically measured as follows. Observe using a scanning electron microscope in the range of 1,000 times to 10,000 times according to the particle diameter. Select 100 primary particles whose outlines can be confirmed, and for the selected particles, use image processing software to trace the outline of the primary particles to obtain the contour length. Calculate the spherical equivalent diameter from the contour length, and obtain the average particle diameter D SEM as the arithmetic mean value of the obtained spherical equivalent diameters.

[0023] The heat-treated product is obtained by heat-treating a mixture of a first lithium compound and a metal compound containing nickel. That is, a method for producing a positive electrode active material for a lithium ion battery may further include a preparation step of obtaining a heat-treated product from a first lithium compound and a metal compound containing nickel. Details of the preparation step will be described later.

[0024] The first liquid medium may be any liquid medium capable of removing at least some of the impurities, such as the second lithium compound, contained in the heat-treated product, and may be any liquid medium capable of dissolving at least the second lithium compound. The first liquid medium may contain at least water, and may consist of water. The water contained in the first liquid medium may be deionized water, pure water, etc.

[0025] Contact between the heat-treated material and the first liquid medium can be achieved by mixing the heat-treated material and the first liquid medium. The contact temperature between the heat-treated material and the first liquid medium may be, for example, 5°C to 60°C, preferably 10°C to 40°C. The contact time may be, for example, 1 minute to 2 hours, preferably 3 minutes to 30 minutes. The amount of the first liquid medium used for contact may be, for example, 0.25 to 10 times the mass of the heat-treated material, preferably 0.5 to 4 times.

[0026] Contact between the heat-treated material and the first liquid medium may be carried out by preparing a slurry by adding the heat-treated material to the first liquid medium. When contact is carried out as a slurry, the solid content concentration of the heat-treated material in the slurry may be, for example, 10% by mass or more and 80% by mass or less, and preferably 20% by mass or more and 60% by mass or less.

[0027] In the first step, the heat-treated material is brought into contact with the first liquid medium, and then solid-liquid separation is performed to obtain the first treated material and the second liquid medium. Solid-liquid separation may be performed, for example, using a filter or by centrifugal separation. Alternatively, the contact and solid-liquid separation of the heat-treated material and the first liquid medium in the first step may be performed by passing the first liquid medium through the heat-treated material held on a filter. The liquid may be passed through only once, or the process of passing the liquid medium through once or more times may be repeated. When the heat-treated material is brought into contact with the first liquid medium by passing it through, the second liquid medium is obtained as the liquid medium after passing through, and the first treated material is obtained as a solid on the filter.

[0028] In the second step, the second liquid medium is brought into contact with the alkaline earth metal compound, and then solid-liquid separation is performed to obtain the third liquid medium. It is believed that by bringing the second liquid medium into contact with the alkaline earth metal compound, for example, carbonate ions contained in the second liquid medium react with the alkaline earth metal compound, causing sparingly soluble alkaline earth metal carbonates to precipitate. The precipitated alkaline earth metal carbonates are removed from the liquid medium by solid-liquid separation. This makes it possible to remove at least a portion of the carbonate ions derived from lithium carbonate contained in the heat-treated product from the second liquid medium. Here, the sparingly soluble alkaline earth metal carbonate may have a solubility of 0.005 g or less, or 0.002 g or less, in 100 g of water at 25°C.

[0029] Examples of alkaline earth metals included in alkaline earth metal compounds include calcium (Ca), strontium (Sr), barium (Ba), beryllium (Be), and magnesium (Mg), and may contain at least calcium. The alkaline earth metal compound is not particularly limited as long as it is a water-soluble alkaline earth metal compound, but examples include hydroxides, nitrates, acetates, and oxides of alkaline earth metals, and may contain at least a hydroxide. Here, the water-soluble alkaline earth metal compound only needs to have a greater solubility in water than the precipitated sparingly soluble alkaline earth metal carbonate, and may have a solubility of, for example, 10 times or more, 50 times or more, or 100 times or more than that of the alkaline earth metal carbonate. Specifically, the water-soluble alkaline earth metal compound may have a solubility of, for example, 0.1 g or more in 100 g of water at 25°C. The alkaline earth metal compound may be used in contact as a solid (powder), or as a solution dissolved in a liquid medium or as a dispersed dispersion. Alkaline earth metal compounds may preferably be used in contact as solids (powder).

[0030] Contact between the second liquid medium and the alkaline earth metal compound in the second step can be carried out by mixing the second liquid medium and the alkaline earth metal compound. The contact temperature between the second liquid medium and the alkaline earth metal compound may be, for example, 5°C to 60°C, preferably 10°C to 40°C. The contact time may be, for example, 1 second to 5 minutes. The amount of alkaline earth metal compound used for contact may be, for example, 0.1 mol% to 10 mol%, preferably 0.5 mol% or 2 mol%, as the ratio of the number of moles of alkaline earth metal atoms to the total number of moles of metals other than lithium in the lithium transition metal composite oxide contained in the heat-treated product. The content of lithium transition metal composite oxide in the heat-treated product may be the content calculated from the amount charged in the synthesis step.

[0031] After contacting the second liquid medium with the alkaline earth metal compound, the solid components are removed by solid-liquid separation to obtain the third liquid medium. Solid-liquid separation may be performed, for example, using a filter or by centrifugation. Alternatively, the contact and solid-liquid separation of the second liquid medium and the alkaline earth metal compound in the second step may be performed by passing the second liquid medium through the alkaline earth metal compound held on a filter. The liquid may be passed through once, or the process of passing the liquid medium through once or more times may be repeated. In this case, the third liquid medium is obtained as the liquid medium after passing through.

[0032] In the third step, the first material to be treated is brought into contact with the third liquid medium, and then solid-liquid separation is performed to obtain the second material to be treated and the fourth liquid medium. The third liquid medium can also be described as a regenerated cleaning solution obtained by bringing the second liquid medium, obtained by solid-liquid separation from the first material, into contact with an alkaline earth metal compound, and then performing solid-liquid separation. By liquid-treatment (e.g., cleaning) the first material with the third liquid medium, impurities can be efficiently removed while suppressing damage to the lithium transition metal composite oxide contained in the first material.

[0033] Contact between the first processed material and the third liquid medium can be achieved by mixing the first processed material and the third liquid medium. The contact temperature between the first processed material and the third liquid medium may be, for example, 5°C to 60°C, preferably 10°C to 40°C. The contact time may be, for example, 1 minute to 2 hours, preferably 3 minutes to 30 minutes. The amount of the third liquid medium used for contact may be, for example, 0.25 to 10 times the mass of the first processed material, preferably 0.5 to or 4 times.

[0034] Contact between the first processed material and the third liquid medium may be carried out by preparing a slurry by adding the first processed material to the third liquid medium. When contact is carried out using a slurry, the solid content concentration of the first processed material in the slurry may be, for example, 10% by mass or more and 80% by mass or less, and preferably 20% by mass or more and 60% by mass or less.

[0035] In the third step, the first processed material and the third liquid medium are brought into contact, followed by solid-liquid separation to obtain the second processed material and the fourth liquid medium. Solid-liquid separation may be performed, for example, using a filter or by centrifugal separation. Alternatively, the contact and solid-liquid separation of the first processed material and the third liquid medium in the third step may be performed by passing the third liquid medium through the first processed material held on the filter. The liquid medium may be passed through only once, or the process of passing the liquid medium through once or more times may be repeated. When the first processed material is brought into contact with the third liquid medium by passing it through, the fourth liquid medium is obtained as the liquid medium after passing through, and the second processed material is obtained as the residue (solid content) on the filter.

[0036] In the method for producing a positive electrode active material for lithium-ion batteries, the second processed material may be a positive electrode active material containing a lithium transition metal composite oxide, or the processed material obtained by further liquid medium treatment (e.g., washing treatment), boron compound treatment, etc., of the second processed material may be used as the positive electrode active material.

[0037] A method for producing a positive electrode active material for lithium-ion batteries may further include a fourth step of contacting a fourth liquid medium with an alkaline earth metal compound and then performing solid-liquid separation to obtain a fifth liquid medium (processing liquid medium), and a fifth step of contacting a second processed product with the fifth liquid medium (processing liquid medium) and then performing solid-liquid separation to obtain a liquid medium processed product and a post-processed liquid medium. By liquid medium processing the second processed product, which has been liquid medium processed (e.g., washed), with a liquid medium for liquid medium processing (fifth liquid medium) obtained by removing at least a portion of the impurities, a liquid medium processed product with a further reduced content of impurities affecting battery characteristics can be obtained.

[0038] The contact between the fourth liquid medium and the alkaline earth metal compound in the fourth step can be carried out in the same manner as the contact between the second liquid medium and the alkaline earth metal compound in the second step. Furthermore, the contact between the second treated material and the fifth liquid medium and the subsequent solid-liquid separation in the fifth step can be carried out in the same manner as the contact between the first treated material and the third liquid medium and the subsequent solid-liquid separation in the third step.

[0039] The method for producing a positive electrode active material for lithium-ion batteries may further include performing the combination of the fourth and fifth steps one or more times. That is, the processing liquid medium may be prepared using the processed liquid medium obtained in the preceding fifth step as the fourth liquid medium in the fourth step, and the liquid medium processing of the fifth step may be performed using the processed liquid medium obtained in the preceding fifth step as the second processed product in the fifth step, and this process may be repeated. The method for producing a positive electrode active material for lithium-ion batteries may include the combination of the fourth and fifth steps one to five times, preferably two to three times.

[0040] A method for producing a positive electrode active material for lithium-ion batteries may further include drying the second processed material or its liquid medium processed material. The drying process only needs to remove at least a portion of the moisture adhering to the second processed material or its liquid medium processed material, and can be carried out by heating, air drying, vacuum drying, etc. The drying temperature in the case of heating should be a temperature at which the moisture contained in the second processed material or its liquid medium processed material is sufficiently removed. The drying temperature may be, for example, 80°C to 300°C, and preferably 150°C to 280°C. When the drying temperature is within the above range, the elution of lithium into the adhering water can be sufficiently suppressed. In addition, the collapse of the crystal structure on the particle surface can be suppressed, and the decrease in charge / discharge capacity can be sufficiently suppressed. The drying time can be appropriately selected according to the amount of moisture contained in the second particles. The drying time may be, for example, 1 hour to 10 hours. The amount of moisture contained in the second processed material or its liquid medium processed material after drying may be, for example, 0.2% by mass or less, and preferably 0.1% by mass or less.

[0041] A method for producing a positive electrode active material for lithium-ion batteries may further include a sixth step of heat-treating a mixture of the second processed material or its liquid medium processed material and a boron compound (boron mixture) at a temperature of 100°C to 450°C. By heat-treating the second processed material or its liquid medium processed material together with the boron compound at a predetermined temperature, a boron-containing compound adheres to at least a portion of the surface of the lithium transition metal composite oxide. This tends to reduce gas generation by preventing side reactions with the electrolyte when forming a lithium-ion battery. Furthermore, lithium deficiencies that may occur due to liquid medium processing (e.g., cleaning processing) are compensated, and inhibition of lithium ion desorption and insertion is suppressed, which tends to improve charge-discharge characteristics and cycle characteristics.

[0042] The liquid medium processed product of the second processed product constituting the boron mixture may be obtained by performing at least one combination of the fourth and fifth steps on the second processed product obtained in the third step, or by performing one or more or five or fewer combinations of the fourth and fifth steps.

[0043] The sixth step may include a mixing step of mixing the second treatment material or its liquid medium treatment material with a boron compound to obtain a boron mixture, and a heat treatment step of heat-treating the boron mixture at a predetermined temperature. The mixing of the second treatment material or its liquid medium treatment material with the boron compound may be carried out dry or wet. The mixing can be carried out using, for example, a super mixer. In addition to the boron compound, other metallic elements, alloys, or metallic compounds may be mixed in this mixing step. Examples of other metallic elements include aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), etc., and may further include at least one selected from the group consisting of these elements.

[0044] The boron compound can be selected from at least one selected from the group consisting of boron oxide, boron oxoacids, and boron oxoates. More specific examples of boron compounds include lithium tetraborate (Li2B4O7), ammonium pentaborate (NH4B5O8), orthoboric acid (H3BO3; so-called ordinary boric acid), lithium metaborate (LiBO2), boron oxide (B2O3), etc., and may contain at least one selected from the group consisting of these, and may contain at least orthoboric acid from a cost perspective.

[0045] The boron compound may be mixed with the second treated material or its liquid medium treated material in a solid state, or it may be mixed with the second treated material or its liquid medium treated material as a solution of the boron compound. When using the boron compound in a solid state, the volume-average particle size of the boron compound may be, for example, 1 μm or more and 60 μm or less, preferably 10 μm or more and 30 μm or less.

[0046] The content of the boron compound in the boron mixture may be, for example, 0.1 mol% or more and 2 mol% or less, preferably 0.5 mol% or more or 0.8 mol% or more, or 1.5 mol% or less or 1.2 mol% or less, as a ratio of the number of moles of boron element to the total number of moles of metals other than lithium in the lithium transition metal composite oxide contained in the second treated product or the liquid medium treated product.

[0047] In the heat treatment step, the boron mixture is heat-treated at a temperature of, for example, 100°C to 450°C to obtain the positive electrode active material. The heat treatment temperature may be 200°C to 400°C, preferably 220°C to 350°C, and more preferably 250°C to 350°C. In some cases, the charge and discharge capacity can be further improved by setting the heat treatment temperature higher than the drying temperature. The atmosphere for the heat treatment may be an oxygen-containing atmosphere or air. The heat treatment time is, for example, 1 hour to 20 hours, preferably 5 hours to 10 hours. The heat-treated material obtained in the heat treatment step may be subjected to crushing, classification, etc., as needed.

[0048] Lithium-deficient regions may form near the surface of the second treated material obtained by liquid medium treatment, and the desorption and insertion of lithium ions may be inhibited in these lithium-deficient regions. However, it is believed that by mixing a boron compound with the second treated material or the liquid treated material after liquid medium treatment and then heat-treating it, the lithium deficiency is compensated for, the inhibition of lithium ion desorption and insertion is suppressed, and the charge-discharge characteristics and cycle characteristics are improved.

[0049] The positive electrode active material obtained by the method for producing a positive electrode active material for lithium-ion batteries may contain a lithium transition metal composite oxide obtained by drying the second processed material or the liquid medium processed material, and may also contain a lithium transition metal composite oxide to which a boron compound has been attached in the sixth step.

[0050] A method for producing a positive electrode active material for lithium-ion batteries may further include a preparation step of obtaining a heat-treated product from a first lithium compound and a nickel-containing metal compound. The preparation step may include, for example, a precursor preparation step of preparing a nickel-containing metal compound to serve as a precursor, and a synthesis step of obtaining a heat-treated product containing a lithium transition metal composite oxide from a mixture of the precursor and the first lithium compound.

[0051] In the precursor preparation step, a nickel-containing metal compound is prepared. The nickel-containing metal compound may be prepared by acquisition or by preparing a nickel-containing metal compound with the desired composition by conventional methods. Examples of nickel-containing metal compounds include nickel-containing oxides, composite oxides containing nickel and metals other than nickel, nickel-containing hydroxides, and composite hydroxides containing nickel and metals other than nickel. Examples of metals other than nickel include cobalt (Co), manganese (Mn), aluminum (Al), titanium (Ti), and niobium (Nb).

[0052] Methods for obtaining nickel-containing metal compounds with a desired composition include mixing raw material compounds (hydroxides, carbonates, etc.) to the desired composition and decomposing them into nickel-containing composite oxides by heat treatment; preparing a solution in which the raw material compounds are dissolved and obtaining a precursor precipitate (e.g., nickel-containing composite hydroxide) with the desired composition by adjusting the temperature, pH, and adding a complexing agent; and obtaining a nickel-containing composite oxide by heat treatment of the precursor precipitate (coprecipitation method). Below, an example of a method for producing nickel-containing composite oxides (hereinafter also simply referred to as composite oxides) will be described.

[0053] A method for obtaining a composite hydroxide 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, and a crystallization step of growing the generated seed crystals to obtain a composite hydroxide having desired properties. Furthermore, the method for obtaining a composite oxide may be further modified to include a step of heat-treating the obtained composite hydroxide to obtain a composite oxide. For details on such a method for obtaining a composite hydroxide or composite oxide, see, for example, Japanese Patent Application Publication No. 2003-292322 and Japanese Patent Application Publication No. 2011-116580 (US Patent Application Publication No. 2012 / 270107).

[0054] In the seed generation process, a liquid medium containing seed crystals is prepared by adjusting the pH of a mixed solution containing nickel ions in a desired ratio to, for example, 11 to 13. The seed crystals can include, for example, hydroxides containing nickel in a desired ratio. The mixed solution can be prepared by dissolving nickel salts, etc., in water in a desired proportion. Examples of nickel salts include sulfates, nitrates, hydrochlorides, etc. In addition to nickel 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.

[0055] In the crystallization step, the generated seed crystals are grown to obtain a nickel-containing precursor precipitate having the desired properties. Seed crystal growth can be carried out, for example, by adding a mixed solution containing nickel ions and, if necessary, other metal ions to a liquid medium containing seed crystals, while maintaining the pH in the range of, 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. The precursor precipitate obtained in the crystallization step contains a complex hydroxide. The obtained precursor precipitate may be dried if necessary. The complex hydroxide can also be obtained by drying.

[0056] pH adjustment in the seed generation and crystallization processes can be performed 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.

[0057] In the crystallization process, it is desirable to control the particle size of the precursor precipitate. This can be achieved by adjusting the temperature, pH, and stirring speed of the reaction field. These conditions can be appropriately adjusted according to actual conditions such as the shape of the vessel housing the reaction field, the starting materials, and the rate at which the starting materials are introduced into the reaction field. Furthermore, the particle size of the precursor precipitate can be controlled by the maturation time and stirring speed after the start of precipitation. These conditions, too, can be appropriately adjusted according to actual conditions, as the particle growth rate and shape differ depending on the shape of the reaction vessel.

[0058] In the process of obtaining the composite oxide, the precursor precipitate containing the composite hydroxide obtained in the crystallization process is heat-treated to obtain the composite oxide. The heat treatment may be carried out by heating the composite hydroxide at a temperature of, for example, 500°C or lower, preferably at 350°C or lower. The heat treatment temperature may also be, for example, 100°C or higher, preferably 200°C or higher. The heat treatment time may be, for example, 0.5 hours to 48 hours, preferably 5 hours 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, rotary kiln furnace, pusher furnace, roller hearth kiln furnace, etc.

[0059] The resulting composite oxide or composite hydroxide may contain other metallic elements in addition to nickel. Examples of other metals include cobalt (Co), manganese (Mn), aluminum (Al), titanium (Ti), niobium (Nb), etc. Preferably, at least one selected from this group is included, and more preferably, at least one selected from the group consisting of cobalt (Co), manganese (Mn), and aluminum (Al). If the composite oxide contains other metals, the mixed aqueous solution used to obtain the precursor precipitate can be made to contain the other metal ions in the desired configuration. This allows the precursor precipitate to contain nickel and other metals. Furthermore, the precursor precipitate can be heat-treated to obtain a composite oxide with the desired composition.

[0060] The average particle size of the composite oxide or composite hydroxide may be, for example, 2 μm or more and 30 μm or less, preferably 3 μm or more and 25 μm or less. The average particle size of the composite oxide or composite hydroxide is the volume-average particle size, which is the value at which the integrated volume from the small particle size side in the volume distribution obtained by laser scattering method accounts for 50%.

[0061] In the synthesis step to obtain a heat-treated product containing a lithium transition metal composite oxide, a lithium mixture obtained by mixing a metal compound containing nickel as a precursor with a primary lithium compound is heat-treated at a temperature of, for example, 550°C to 1000°C to obtain the heat-treated product. The resulting heat-treated product has a layered structure and may contain a lithium transition metal composite oxide containing nickel.

[0062] Examples of the first lithium compound include lithium hydroxide, lithium carbonate, and lithium oxide. The particle size of the first lithium compound used in the mixture may be, for example, 0.1 μm to 100 μm as a volume average particle size, preferably 2 μm to 20 μm. The ratio of the total number of moles of lithium to the total number of moles of metal elements constituting the nickel-containing metal compound in the lithium mixture may be, for example, 0.95 to 1.2. The mixing of the nickel-containing metal compound and the first lithium compound can be carried out, for example, using a high-speed shear mixer.

[0063] The lithium mixture may further contain other metal elements besides the metal elements that constitute the metal compound containing lithium and nickel. Examples of other metal elements include aluminum (Al), silicon (Si), zirconium (Zr), titanium (Ti), magnesium (Mg), tantalum (Ta), niobium (Nb), molybdenum (Mo), tungsten (W), etc., and may contain at least one element M selected from the group consisting of these. For example, if the lithium mixture contains W, Nb, etc. as the other metal element M, the output characteristics are improved. For example, if the lithium mixture contains Al, Zr, etc., it is suitable for further improvement of cycle characteristics. For example, if the lithium mixture contains Ti, Si, etc., it is suitable for further improvement of cycle characteristics under high voltage. If the lithium mixture contains other metal elements M, the lithium mixture can be obtained by mixing the other metal element M in its elemental form or in a metal compound with a nickel-containing metal compound and the first lithium compound. Examples of metal compounds containing other metal elements M include oxides, hydroxides, chlorides, nitrides, carbonates, sulfates, nitrates, acetates, oxalates, and the like. When a lithium mixture contains other metal elements M, the ratio of the total number of moles of other metal elements M to the total number of moles of metal elements constituting the nickel-containing metal compound may be, for example, 0.0001 to 0.1, preferably 0.0005 to 0.03, or 0.001 to 0.01.

[0064] The heat treatment temperature of the lithium mixture may be, for example, 550°C to 1000°C, preferably 600°C or 700°C or higher, and may be 950°C or lower. The heat treatment of the lithium mixture may be carried out at a single temperature or at two or more temperatures. Heat treatment at multiple temperatures tends to increase the discharge capacity at high voltage. When heat treatment at multiple temperatures, for example, it is desirable to hold the first temperature for a predetermined time, then further increase the temperature, and hold the second temperature for a predetermined time. The first temperature is, for example, 200°C to 600°C, preferably 400°C to 500°C, and the second temperature is, for example, 600°C to 900°C, preferably 650°C to 750°C. The heat treatment time is, for example, 0.5 hours to 48 hours, and when heat treatment is carried out at multiple temperatures, each time can be 0.2 hours to 47 hours.

[0065] The heat treatment can be carried out using, for example, a box furnace, rotary kiln, pusher furnace, roller hearth kiln, etc. The atmosphere for the heat treatment may be air or an atmosphere containing oxygen. Preferably, the atmosphere may have an oxygen content of 20% by volume or more or 50% by volume or more, and may have an oxygen content of 100% by volume or less, 90% by volume or less, 80% by volume or less, or 70% by volume or less. An atmosphere with an oxygen content of 80% by volume or less reduces the burden on the equipment used for heat treatment. Furthermore, with the method for manufacturing positive electrode active material for lithium-ion batteries of this embodiment, even in an atmosphere with an oxygen content of 80% by volume or less, a positive electrode active material with excellent cycle characteristics in lithium-ion batteries and suppressed gas generation can be efficiently manufactured.

[0066] Cathode active material for lithium-ion batteries The positive electrode active material for lithium-ion batteries (hereinafter also simply referred to as "positive electrode active material") may contain a lithium transition metal composite oxide containing lithium and nickel, a calcium compound, a lithium compound (hereinafter also referred to as a third lithium compound), and a boron compound. The lithium compound contains at least lithium carbonate, and the lithium carbonate content may be less than 0.4% by mass. The boron compound may be disposed on at least a portion of the surface of the lithium transition metal composite oxide, and may be disposed on at least a portion of the surface of secondary particles consisting of primary particles containing the lithium transition metal composite oxide. The positive electrode active material for lithium-ion batteries can be manufactured by the method for manufacturing the positive electrode active material for lithium-ion batteries described above.

[0067] The positive electrode active material contains a third lithium compound and a boron compound, and the lithium carbonate content is within a predetermined range, thereby enabling the construction of a lithium-ion battery that exhibits good cycle characteristics and suppresses gas generation during storage.

[0068] Details of the lithium transition metal composite oxide constituting the positive electrode active material have been previously described. The positive electrode active material contains a calcium compound. The calcium compound may be present as a result of the manufacturing method of the positive electrode active material for lithium-ion batteries. The calcium compound may be attached to the surface of the lithium transition metal composite oxide, for example, or to at least a portion of the surface of the secondary particles. Examples of calcium compounds include calcium carbonate and calcium hydroxide, and the material may contain at least calcium carbonate.

[0069] The calcium compound content in the positive electrode active material may be 10 ppm or more and less than 300 ppm on a mass basis of calcium relative to the positive electrode active material, preferably 30 ppm or more or 50 ppm or more, and may be 200 ppm or less or 100 ppm or less. Including calcium compounds in addition to boron compounds in the positive electrode active material tends to suppress the rate of resistance increase in lithium-ion batteries. This can be thought to be because, for example, the presence of a predetermined amount of calcium element in the area where the boron compound is attached to the surface of the lithium transition metal composite oxide reduces its reactivity with the electrolyte.

[0070] The calcium compound content in the positive electrode active material can be measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES). Furthermore, the resistance increase rate (%) in lithium-ion batteries is the rate of increase in the battery's internal resistance due to repeated charging and discharging. Specifically, it is calculated as the ratio (%) of the cell resistance value after n cycles to the cell resistance value after one cycle, based on the cell resistance value measured from the IR drop, which is the difference between the voltage at the start of discharge and the voltage 10 seconds after the start of discharge.

[0071] The positive electrode active material contains a tertiary lithium compound. The tertiary lithium compound may be attached to the surface of, for example, a lithium transition metal composite oxide, or to at least a portion of the surface of secondary particles. Examples of tertiary lithium compounds include lithium carbonate, lithium hydroxide, lithium oxide, lithium sulfate, etc., and may contain at least lithium carbonate.

[0072] The lithium carbonate content in the positive electrode active material may be less than 0.4% by mass relative to the positive electrode active material, preferably 0.3% by mass or less, or 0.2% by mass or less. The lithium carbonate content may also be greater than 0% by mass relative to the positive electrode active material, and may be 0.01% by mass or more. The positive electrode active material may also contain lithium compounds other than lithium carbonate. If the positive electrode active material contains lithium compounds other than lithium carbonate, the content of these other lithium compounds relative to the positive electrode active material may be, for example, 0.1% by mass or more and 0.6% by mass or less, or 0.15% by mass or more, or 0.5% by mass or less. If the third lithium compound contains lithium carbonate and lithium compounds other than lithium carbonate, the content ratio of the lithium compounds other than lithium carbonate to lithium carbonate may be 0.5 to 3, or 2 or less. The content of the third lithium compound in the positive electrode active material can be measured from the titration value of acid-base titration based on the principle of the Warder method.

[0073] The positive electrode active material contains a boron compound. The boron compound may be attached to the surface of, for example, a lithium transition metal composite oxide, or to at least a portion of the surface of secondary particles. Alternatively, the boron compound may be attached to at least a portion of the surface of primary particles containing the lithium transition metal composite oxide, and the positive electrode active material may be composed of secondary particles formed by the aggregation of multiple primary particles to which the boron compound is attached. Examples of boron compounds include lithium metaborate (LiBO2), lithium tetraborate (Li2B4O7), and lithium borate (Li3BO3). The boron compound may also form a composite with the lithium transition metal composite oxide.

[0074] The boron compound content in the positive electrode active material may be, for example, 0.1 mol% to 2 mol%, preferably 0.5 mol% to 1.5 mol%, as the ratio of the number of moles of boron element to the total number of moles of metals other than lithium in the lithium transition metal composite oxide. The boron content in the positive electrode active material can be measured, for example, by an inductively coupled plasma emission spectrometer.

[0075] The positive electrode active material can be applied to the positive electrode of a non-aqueous electrolyte lithium-ion secondary battery (hereinafter also referred to as a non-aqueous electrolyte secondary battery) to constitute a non-aqueous electrolyte secondary battery that can achieve excellent cycle characteristics. The positive electrode active material can be contained in a positive electrode active material layer arranged on a current collector to constitute the positive electrode. That is, the present invention encompasses an electrode for a non-aqueous electrolyte secondary battery containing the positive electrode active material and a non-aqueous electrolyte secondary battery equipped with said electrode.

[0076] Non-aqueous 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, which contains the positive electrode active material described above or a positive electrode active material manufactured by the manufacturing method described above. A non-aqueous electrolyte secondary battery equipped with such an electrode can achieve excellent cycle characteristics.

[0077] The density of the positive electrode active material layer is, for example, 2.6 g / cm³. 3 More than 3.9g / cm 3 The following may be the case, preferably 2.8 g / cm³ 3 More than 3.8g / cm 3 More preferably, 3.1 g / cm³ 3 More than 3.7g / cm 3 More preferably, 3.2 g / cm³ 3 More than 3.6g / cm 3 The following may apply: The density of the active material layer is calculated by dividing the mass of the active material layer by the volume of the active material layer. Here, the density of the active material layer can be adjusted by applying pressure after the electrode composition described later is applied to the current collector.

[0078] Examples of materials for the current collector include aluminum, nickel, and stainless steel. The positive electrode active material layer can be formed by applying an electrode composition 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. Examples of solvents include N-methyl-2-pyrrolidone (NMP).

[0079] 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.

[0080] The invention relating to this disclosure may encompass, for example, the following embodiments: [1] After contacting a heat-treated product of a lithium compound and a metal compound containing nickel with a first liquid medium, solid-liquid separation is performed to obtain the first treated product and the second liquid medium, The second liquid medium is brought into contact with an alkaline earth metal compound, and then solid-liquid separation is performed to obtain a third liquid medium. This includes bringing the first processed material and the third liquid medium into contact, and then performing solid-liquid separation to obtain the second processed material and the fourth liquid medium. A method for producing a positive electrode active material for a lithium-ion battery, wherein the heat-treated product includes a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

[0081] [2] After contacting the fourth liquid medium with an alkaline earth metal compound, solid-liquid separation is performed to obtain the fifth liquid medium, The manufacturing method according to [1], further comprising bringing the second processed material and the fifth liquid medium into contact, and then performing solid-liquid separation to obtain a liquid medium processed material and a post-processed liquid medium.

[0082] [3] The manufacturing method according to [1] or [2], further comprising heat-treating a mixture of the second treated product or the liquid treated product with a boron compound at a temperature of 100°C to 450°C.

[0083] [4] A method for producing a positive electrode active material for a lithium-ion battery, comprising: a first step of cleaning a heat-treated product of a lithium compound and a metal compound containing nickel by contacting the heat-treated product with a liquid medium; a second step of solid-liquid separation of the cleaned heat-treated product and the liquid medium after cleaning; a third step of obtaining a solid containing alkaline earth metal by contacting the liquid medium separated in the second step with an alkaline earth metal compound; a fourth step of solid-liquid separation of the solid obtained in the third step and the liquid medium; a fifth step of further cleaning the heat-treated product by contacting the cleaned heat-treated product obtained in the second step with the liquid medium obtained in the fourth step; and a sixth step of solid-liquid separation of the cleaned heat-treated product obtained in the fifth step and the liquid medium after cleaning, wherein the heat-treated product contains a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

[0084] [5] The manufacturing method according to [4], further comprising heat-treating a mixture of the washed heat-treated material separated in the sixth step and a boron compound at a temperature of 100°C to 450°C.

[0085] [6] The manufacturing method according to [4], further comprising performing the same steps as in steps 3 to 6 at least once using the washed heat-treated product obtained in step 6 and the liquid medium after washing.

[0086] [7] The manufacturing method according to [6], further comprising performing the steps corresponding to the third to sixth steps at least once using the washed heat-treated product obtained in the sixth step and the liquid medium after washing, and then heat-treating a mixture of the washed heat-treated product separated into solid and liquid in the step corresponding to the sixth step and a boron compound at a temperature of 100°C to 450°C.

[0087] [8] The method for producing the alkaline earth metal compound according to any one of [1] to [7], wherein the alkaline earth metal compound comprises at least calcium.

[0088] [9] The method for producing the alkaline earth metal compound according to any one of [1] to [8], comprising at least calcium hydroxide.

[0089]

[10] A lithium transition metal composite oxide comprising lithium and nickel, a calcium compound, a lithium compound, and a boron compound, The lithium compound contains lithium carbonate, and the lithium carbonate content is less than 0.4% by mass. The boron compound is a positive electrode active material for a lithium-ion battery, which is disposed on at least a portion of the surface of the lithium transition metal composite oxide.

[0090]

[11] The positive electrode active material for lithium-ion batteries according to

[10] , wherein the content of the calcium compound is 10 ppm or more and less than 300 ppm on a mass basis of calcium.

[0091]

[12] The lithium transition metal composite oxide is a positive electrode active material for a lithium-ion battery according to

[10] or

[11] , wherein the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1. [Examples]

[0092] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. In the following examples and comparative examples, the volume-average particle size is the 50% particle size D, which is the value at which the integrated volume from the small particle size side in the volume distribution obtained by the laser scattering method becomes 50%. 50 Specifically, the volume-average particle size was measured using a laser diffraction particle size distribution analyzer (SALD-3100, Shimadzu Corporation). The lithium content was measured by adding the positive electrode active material to pure water and titrating the dissolved lithium with sulfuric acid. The composition of the metal compounds was measured using an inductively coupled plasma atomic emission spectrometer (ICP-AES, PerkinElmer). The calcium (Ca) and boron (B) content in the positive electrode active material was measured using an ICP-AES (Hitachi Corporation). The calcium content in the comparative example and reference example was below the detection limit of 10 ppm.

[0093] Example 1 Precursor preparation process By coprecipitation, the volume-average particle size of the secondary particles was 10 μm, and (Ni 0.94 Co 0.05 Mn 0.01 Composite hydroxide particles having a composition represented by )(OH)2 were obtained.

[0094] Synthesis process The obtained composite hydroxide particles, aluminum hydroxide, zirconium oxide, and lithium hydroxide were mixed in a molar ratio of Li:(Ni+Co+Mn):Al:Zr=1.09:1.00:0.0075:0.0015 to obtain a raw material mixture (lithium mixture). The obtained raw material mixture was heat-treated in an atmosphere with an oxygen concentration of approximately 60% by volume. The heat treatment was carried out in two stages: the first at 450°C for 3 hours, and the second at 710°C for 4 hours. After the heat treatment, the mixture was dispersed to obtain a heat-treated product containing a lithium transition metal composite oxide.

[0095] 1st step The resulting heat-treated product was added to a first liquid medium, which was pure water, to obtain a slurry with a solid content of 60% by mass. The solid content concentration was determined by dividing the mass of the heat-treated product by the sum of the mass of the heat-treated product and the mass of the first liquid medium. This slurry was stirred at 20°C for 5 minutes, then dewatered using a funnel to obtain the first treated product as the solid content and the second liquid medium as the filtrate.

[0096] 2nd process To the obtained second liquid medium, calcium hydroxide was added in an amount such that the ratio of the number of moles of calcium element to the total number of moles of metals other than lithium in the lithium transition metal composite oxide contained in the heat-treated product was 10 mol%, forming a slurry. This slurry was stirred at 20°C for 5 minutes, then dehydrated with a funnel to obtain a third liquid medium as a filtrate and a first calcium hydroxide cake containing calcium carbonate as a solid.

[0097] 3rd process The first treated material was added to the obtained third liquid medium to form a slurry with a solid content of approximately 60% by mass. The solid content was determined by dividing the mass of the first treated material by the sum of the mass of the first treated material and the mass of the third liquid medium. This slurry was stirred at 20°C for 5 minutes, then dewatered using a funnel to obtain the fourth liquid medium as a filtrate and the second treated material as solid content.

[0098] 4th step The first calcium hydroxide cake was added to the obtained fourth liquid medium to form a slurry. This slurry was stirred at 20°C for 5 minutes, then dehydrated using a funnel to obtain the fifth liquid medium as a filtrate and a second calcium hydroxide cake containing calcium carbonate as a solid.

[0099] 5th step The second treated material was added to the obtained fifth liquid medium to form a slurry with a solid content of approximately 60% by mass. The solid content was determined by dividing the mass of the second treated material by the sum of the mass of the second treated material and the mass of the fifth liquid medium. This slurry was stirred at 20°C for 5 minutes, then dewatered using a funnel to obtain the sixth liquid medium, which is the treated liquid medium, as the filtrate, and the third treated material, which is the liquid medium treated material, as the solid content.

[0100] 6th step The obtained sixth liquid medium was mixed with calcium hydroxide cake to form a slurry. This slurry was stirred at 20°C for 5 minutes, then dehydrated using a funnel to obtain the seventh liquid medium, which was the processing liquid medium, as the filtrate.

[0101] 7th step The obtained seventh liquid medium was mixed with the third treated material to form a slurry with a solid content of approximately 60% by mass. The solid content was determined by dividing the mass of the third treated material by the sum of the mass of the third treated material and the mass of the seventh liquid medium. This slurry was stirred at 20°C for 4.5 minutes, then dewatered using a funnel to obtain the fourth treated material as solid content.

[0102] Drying process The resulting fourth treatment product was dried at 250°C for 10 hours to obtain a dried treatment product containing a lithium transition metal composite oxide.

[0103] Boron treatment Orthoboric acid was added in an amount equal to 1 mol% of the total number of moles of boron element relative to the total number of moles of metals other than lithium in the lithium transition metal composite oxide contained in the dried product, and the mixture was mixed and stirred to obtain a boron mixture. The obtained boron mixture was heat-treated at 300°C in air for 10 hours to obtain the positive electrode active material of Example 1 containing the target lithium transition metal composite oxide.

[0104] Comparative Example 1 The positive electrode active material for Comparative Example 1 was obtained in the same manner as in Example 1, except that the stirring time of the slurry in the first step was changed to 18 minutes to obtain the comparative processed material, and that the comparative processed material was subjected to a drying step and then boron treatment without performing steps 2 through 7.

[0105] Reference example In the synthesis process, heat treatment was performed using an atmospheric furnace under an atmosphere of 100% by volume oxygen; the stirring time of the slurry in the first step was changed to 18 minutes to obtain a reference treated product; and steps 2 through 7 were omitted, and the reference treated product was subjected to a drying step followed by boron treatment. The reference cathode active material was obtained in the same manner as in Example 1.

[0106] 1. Battery characteristics evaluation The discharge capacity, storage gas characteristics, and cycle characteristics of the positive electrode active materials obtained in Example 1, Comparative Example 1, and Reference Example described above were evaluated as follows.

[0107] Fabrication of the negative electrode A negative electrode slurry was prepared by dispersing 97.5 parts by mass of artificial graphite, 1.5 parts by mass of CMC (carboxymethylcellulose), and 1.0 part by mass of SBR (styrene-butadiene rubber) in water. The obtained negative electrode slurry was coated onto copper foil, dried, and then compressed to obtain a negative electrode. The obtained negative electrode was used in all of the following battery characteristic evaluations.

[0108] Preparation of non-aqueous electrolytes Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed in a volume ratio of 3:7 to obtain a mixed solvent. Lithium hexafluoride phosphate (LiPF6) was dissolved in the resulting mixed solvent to a concentration of 1 mol / L to obtain a non-aqueous electrolyte. The obtained non-aqueous electrolyte was used in all of the following battery characteristic evaluations.

[0109] (1) Evaluation of discharge capacity For the positive electrode active materials of Example 1, Comparative Example 1, and Reference Example, evaluation batteries were prepared as follows, and their discharge capacity was evaluated.

[0110] Fabrication of the positive electrode A positive electrode slurry was prepared by dispersing and dissolving 92 parts by mass of positive electrode active material, 3 parts by mass of acetylene black, and 5 parts by mass of PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone). The obtained positive electrode slurry was applied to a current collector made of aluminum foil, dried, and then pressed using a roll press to obtain a positive electrode layer density of 3.3 g / cm³. 3 It is compressed and molded to a size of 15cm. 2 The positive electrode was obtained by cutting it in that manner.

[0111] Fabrication of evaluation batteries After attaching lead electrodes to the positive and negative electrode current collectors, the batteries were vacuum-dried at 120°C. Next, a separator was placed between the positive and negative electrodes, and the batteries were placed in a laminated pouch. This pouch was then vacuum-dried at 60°C to remove any moisture adsorbed on each component. Subsequently, a non-aqueous electrolyte was injected into the laminated pouch under an argon atmosphere, and the pouch was sealed to produce an evaluation battery.

[0112] Measurement of discharge capacity Constant current constant voltage charging (cutoff current 0.005C) was performed with a charging voltage of 4.2V and a charging current of 0.1C, followed by constant current discharge with a discharge termination voltage of 2.5V and a discharge current of 0.1C, and the discharge capacity was measured. Table 1 shows the discharge capacities of the evaluation batteries using the positive electrode active materials of Example 1, Comparative Example 1, and Reference Example.

[0113] (2) Evaluation of storage gas properties The storage gas characteristics of the positive electrode active materials in Example 1, Comparative Example 1, and Reference Example were evaluated as follows.

[0114] Fabrication of a positive electrode for gas generation evaluation A positive electrode slurry was prepared by dispersing and dissolving 90 parts by mass of positive electrode active material, 2.5 parts by mass of graphite carbon, 2.5 parts by mass of acetylene black, and 5 parts by mass of PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone). The obtained positive electrode slurry was applied to a current collector made of aluminum foil, with a size of 15 cm. 2 After cutting in this manner, the positive electrode layer density is increased to 3.2 g / cm³ using a roll press machine. 3 The positive electrode was obtained by compression molding and then drying.

[0115] Fabrication of a battery for gas generation evaluation After attaching lead electrodes to the positive and negative electrode current collectors, the batteries were vacuum-dried at 120°C. Next, a separator was placed between the positive and negative electrodes, and the batteries were placed in a laminated pouch. This pouch was then vacuum-dried at 60°C to remove any moisture adsorbed on each component. Subsequently, a non-aqueous electrolyte was injected into the laminated pouch under an argon atmosphere, and the pouch was sealed to produce an evaluation battery.

[0116] Measurement of gas generation After fully charging the evaluation battery, the fully charged positive electrode was removed from the laminate pack and dried. Next, the removed positive electrode and electrolyte were placed back into the laminate pack and sealed to obtain a cell. The amount of storage gas generated during storage was measured by the Archimedes method, by measuring the cell specific gravity immediately after sealing and after standing at 80°C for 24 hours. The results are shown in Table 1.

[0117] (3) Evaluation of cycle characteristics The cycle characteristics of the positive electrode active materials obtained in Example 1, Comparative Example 1, and Reference Example were evaluated as follows.

[0118] Fabrication of a positive electrode for cycle characteristic evaluation A positive electrode slurry was prepared by dispersing and dissolving 97.5 parts by mass of the above positive electrode active material, 1 part by mass of a conductive additive, and 1.5 parts by mass of PVDF (polyvinylidene fluoride) in NMP (N-methyl-2-pyrrolidone). The obtained positive electrode slurry was applied to a current collector made of aluminum foil, with a size of 15 cm. 2 After cutting in this manner, the positive electrode layer density is increased to 3.5 g / cm³ using a roll press machine. 3 The positive electrode was obtained by compression molding and then drying.

[0119] Fabrication of evaluation batteries After attaching lead electrodes to the positive and negative electrode current collectors, the batteries were vacuum-dried at 120°C. Next, a separator was placed between the positive and negative electrodes, and the batteries were placed in a laminated pouch. This pouch was then vacuum-dried at 60°C to remove any moisture adsorbed on each component. Subsequently, a non-aqueous electrolyte was injected into the laminated pouch under an argon atmosphere, and the pouch was sealed to produce an evaluation battery.

[0120] Measurement of capacitance retention rate and resistance increase rate A constant current constant voltage charge (cutoff current 0.05C) was performed with a charging voltage of 4.35V and a charging current of 2C, and a constant current discharge with a discharge termination voltage of 3.71V and a discharge current of 2C was performed as one cycle. The discharge capacity after each cycle was measured at a constant temperature of 45°C. The ratio of the discharge capacity Ed(n) after n cycles to the discharge capacity Ed(1) after one cycle (≡Ed(n) / Ed(1)) was defined as the capacity retention rate Cs(n) after n cycles, and the number of cycles was set to n=400. In addition, the cell resistance was measured from the IR drop of the voltage at the start of discharge and the voltage 10 seconds after the start of discharge. The ratio of the resistance value Rd(n) after n cycles to the resistance value Rd(1) after one cycle (≡Rd(n) / Rd(1)) was defined as the resistance increase rate Rs(n) after n cycles, and the number of cycles was set to n=400.

[0121] Regarding capacity retention, the evaluation battery using the positive electrode active material of Example 1 had a retention rate of 48.7%, while the evaluation battery using the positive electrode active material of Comparative Example 1 had a retention rate of 31.0%. Furthermore, regarding resistance increase rate, the evaluation battery using the positive electrode active material of Example 1 had a resistance increase rate of 114.5%, while the evaluation battery using the positive electrode active material of the Reference Example had a resistance increase rate of 119.7%.

[0122] Measurement of unreacted lithium content in positive electrode active material The unreacted lithium content of the positive electrode active materials obtained in Example 1, Comparative Example 1, and Reference Example was measured as follows. First, 10 g of each positive electrode active material was taken, placed in a lidded container, 50 mL of pure water was added, and the container was covered and stirred for 60 minutes. After standing, the supernatant was filtered. The filtrate was titrated with a 0.025 mol / L sulfuric acid standard solution. In the titration, the inflection point around pH 8 was defined as the first endpoint, and the inflection point around pH 4 was defined as the second endpoint. The amounts of lithium hydroxide (LiOH) and lithium carbonate (Li2CO3) were calculated from the titration values ​​at the first and second endpoints based on the principle of the Warder method. The results are shown in Table 1.

[0123] [Table 1]

[0124] As shown in Table 1, the evaluation battery constructed using the positive electrode active material of Example 1, obtained by washing a liquid medium from which carbonate ions were removed using calcium hydroxide as a washing solution, and then heat-treating it with a boron compound, exhibited excellent gas characteristics and capacity retention. This is thought to be because, for example, removing carbonate ions from the liquid with calcium hydroxide reduced the lithium carbonate (Li2CO3) content in the positive electrode active material. On the other hand, the evaluation battery constructed using the positive electrode active material of Comparative Example 1 had poor gas characteristics and capacity retention, resulting in inferior battery performance. The evaluation battery constructed using the positive electrode active material of Reference Example exhibited excellent gas characteristics and capacity retention, but had a poor resistance increase rate. This is thought to be because, for example, a specific amount of calcium (Ca) is contained on the surface of the boron coating of the positive electrode active material particles, which reduces the reactivity with the electrolyte without hindering the charging and discharging of the positive electrode active material.

Claims

1. The process involves contacting a heat-treated product of a nickel-containing metal compound and a lithium compound with a first liquid medium, followed by solid-liquid separation to obtain the first treated product and the second liquid medium. The second liquid medium is brought into contact with an alkaline earth metal compound, and then solid-liquid separation is performed to obtain a third liquid medium. This includes bringing the first processed material and the third liquid medium into contact, and then performing solid-liquid separation to obtain the second processed material and the fourth liquid medium. A method for producing a positive electrode active material for a lithium-ion battery, wherein the heat-treated product includes a lithium transition metal composite oxide in which the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

2. The fourth liquid medium is brought into contact with an alkaline earth metal compound, and then solid-liquid separation is performed to obtain the fifth liquid medium. The manufacturing method according to claim 1, further comprising bringing the second processed material and the fifth liquid medium into contact, and then performing solid-liquid separation to obtain a liquid medium processed material and a post-processed liquid medium.

3. The manufacturing method according to claim 1, further comprising heat-treating a mixture of the second processed product or the liquid medium processed product and a boron compound at a temperature of 100°C to 450°C.

4. The method for producing the alkaline earth metal compound according to claim 1, wherein the alkaline earth metal compound comprises at least calcium.

5. The method for producing the alkaline earth metal compound according to claim 1, comprising at least calcium hydroxide.

6. It comprises a lithium transition metal composite oxide containing lithium and nickel, a calcium compound, a lithium compound, and a boron compound. The lithium compound contains lithium carbonate, and the lithium carbonate content is less than 0.4% by mass. The boron compound is a positive electrode active material for a lithium-ion battery, which is disposed on at least a portion of the surface of the lithium transition metal composite oxide.

7. The positive electrode active material for lithium-ion batteries according to claim 6, wherein the content of the calcium compound is 10 ppm or more and less than 300 ppm on a mass basis of calcium.

8. The lithium transition metal composite oxide is a positive electrode active material for a lithium-ion battery according to claim 6, wherein the ratio of the number of moles of nickel atoms to the total number of moles of metal atoms other than lithium is 0.6 or more and less than 1.

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