Method for preparing positive electrode active material

Abstract

Provided is a method for producing a highly purified positive electrode active material. Also provided is a method for producing a positive electrode active material that is not susceptible to a collapse in the crystal structure thereof even when charging and discharging repeatedly. This method for producing a positive electrode active material having lithium and a transition metal comprises: a first step in which a hydroxide having a transition metal is produced using an aqueous solution having a transition metal and a basic aqueous solution; a second step in which a lithium compound is prepared; a third step in which the lithium compound is mixed with the hydroxide and a mixture is formed; and a fourth step in which the mixture is heated and a composite oxide having the lithium and the transition metal is formed. In the second step, a material having 99.99% purity or greater is prepared as the lithium compound, and in the fourth step, heating is performed in an oxygen-containing atmosphere with a dew point of -50°C or less.

Description

[Technical Field]

[0001] This relates to a method for producing a positive electrode active material, or a method for producing a secondary battery, or a portable information terminal, vehicle, etc., that has a secondary battery.

[0002] One aspect of the present invention relates to a product, a method, or a method of manufacture. Alternatively, the present invention relates to a process, a machine, a manufacture, or a composition of matter. One aspect of the present invention relates to a semiconductor device, a display device, a light-emitting device, a power storage device, a lighting device, an electronic device, or a method for manufacturing the same. One aspect of the present invention particularly relates to a method for producing a positive electrode active material, or to a positive electrode active material. Alternatively, one aspect of the present invention particularly relates to a method for producing a secondary battery, or to a secondary battery.

[0003] In this specification, the term "semiconductor device" refers to all devices that can function by utilizing semiconductor properties, and electro-optical devices, semiconductor circuits, and electronic devices are all considered semiconductor devices.

[0004] In this specification, "electronic equipment" refers to all devices having a positive electrode active material, a secondary battery, or an energy storage device, and electro-optical devices having a positive electrode active material, a secondary battery, or an energy storage device, as well as information terminal devices having an energy storage device, are all considered electronic equipment.

[0005] In this specification, the term "energy storage device" refers to all elements and devices that have an energy storage function. For example, this includes energy storage devices such as lithium-ion secondary batteries (also called secondary batteries), lithium-ion capacitors, and electric double-layer capacitors. [Background technology]

[0006] In recent years, various energy storage devices such as lithium-ion secondary batteries, lithium-ion capacitors, and air batteries have been actively developed. In particular, lithium-ion secondary batteries with high output and high energy density are essential in modern information-based societies as a source of rechargeable energy, and their demand has rapidly increased in line with the development of the semiconductor industry, for applications such as portable information terminals like mobile phones, smartphones, or notebook computers, portable music players, digital cameras, medical devices, or next-generation clean energy vehicles such as hybrid vehicles (HV), electric vehicles (EV), or plug-in hybrid vehicles (PHV).

[0007] Therefore, in order to improve the cycle characteristics and increase the capacity of lithium-ion secondary batteries, the improvement of cathode active materials has been studied (Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] Since the cathode active material is a high-cost material in lithium-ion secondary batteries, there are high demands for high performance (for example, increased capacity, improved cycle characteristics, and improved reliability or safety). In particular, as one aspect of high performance, there is a problem that it is desired to increase the purity of the cathode active material in order to achieve increased capacity.

[0010] Therefore, an aspect of the present invention aims to provide a method for producing a highly purified positive electrode active material. Alternatively, an aspect of the present invention aims to provide a method for producing a positive electrode active material whose crystal structure is difficult to collapse even when charge and discharge are repeated. Alternatively, an aspect of the present invention aims to provide a method for producing a positive electrode active material with excellent charge-discharge cycle characteristics. Alternatively, an aspect of the present invention aims to provide a method for producing a positive electrode active material with a large charge-discharge capacity. Alternatively, an aspect of the present invention aims to provide a secondary battery with high reliability or safety.

[0011] Further, an aspect of the present invention aims to provide a novel substance, active material particles, secondary battery, power storage device, or a method for producing them. Further, an aspect of the present invention aims to provide a method for producing a secondary battery having any one or more characteristics selected from high purity, high performance, and high reliability, or a secondary battery.

[0012] Note that the description of these problems does not prevent the existence of other problems. Note that an aspect of the present invention does not need to solve all of these problems. Note that it is possible to extract other problems from the description of the specification, drawings, and claims.

Means for Solving the Problems

[0013] An aspect of the present invention is a method for producing a positive electrode active material having lithium and a transition metal, comprising: a first step of producing a hydroxide having a transition metal by using at least an aqueous solution having a transition metal and a basic aqueous solution; a second step of preparing a lithium compound; a third step of mixing the lithium compound and the hydroxide to form a mixture; and a fourth step of heating the mixture to form a composite oxide having lithium and a transition metal. In the second step, as the lithium compound, a material with a purity of 99.99% or more is prepared, and the heating in the fourth step is performed in an oxygen-containing atmosphere with a dew point of -50°C or lower.

[0014] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material having lithium, nickel, cobalt, and manganese, comprising: a first step of producing a hydroxide having nickel, cobalt, and manganese using at least an aqueous solution of nickel, an aqueous solution of cobalt, and an aqueous solution of manganese, and a basic aqueous solution; a second step of preparing a lithium compound; a third step of mixing the lithium compound and the hydroxide to form a mixture; and a fourth step of heating the mixture to form a composite oxide having lithium, nickel, cobalt, and manganese, wherein in the second step, a material with a purity of 99.99% or higher is prepared as the lithium compound, and the heating in the fourth step is carried out in an oxygen-containing atmosphere with a dew point of -50°C or lower.

[0015] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material having lithium, nickel, cobalt, manganese, and aluminum, comprising: a first step of producing a hydroxide having nickel, cobalt, manganese, and aluminum using at least an aqueous solution of nickel, an aqueous solution of cobalt, an aqueous solution of manganese, and an aqueous solution of aluminum, and an aqueous solution of basic water; a second step of preparing a lithium compound; a third step of mixing the lithium compound and the hydroxide to form a mixture; and a fourth step of heating the mixture to form a composite oxide having lithium, nickel, cobalt, manganese, and aluminum, wherein in the second step, a material with a purity of 99.99% or higher is prepared as the lithium compound, and the heating in the fourth step is carried out in an oxygen-containing atmosphere with a dew point of -50°C or lower.

[0016] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material having lithium, nickel, cobalt, manganese, and aluminum, comprising: a first step of producing a hydroxide having nickel, cobalt, and manganese using at least an aqueous solution of nickel, an aqueous solution of cobalt, and an aqueous solution of manganese, and a basic aqueous solution; a second step of preparing a lithium compound and an aluminum source; a third step of mixing the lithium compound, the aluminum source, and the hydroxide to form a mixture; and a fourth step of heating the mixture to form a composite oxide having lithium, nickel, cobalt, manganese, and aluminum, wherein in the second step, a material with a purity of 99.99% or higher is prepared as the lithium compound, and a material with a purity of 99.9% or higher is prepared as the aluminum source, and the heating in the fourth step is carried out in an oxygen-containing atmosphere with a dew point of -50°C or lower.

[0017] Alternatively, one aspect of the present invention is a method for producing a positive electrode active material having lithium, nickel, cobalt, manganese, aluminum, magnesium, and fluorine, comprising: a first step of producing a hydroxide having nickel, cobalt, and manganese using at least an aqueous solution of nickel, an aqueous solution of cobalt, and an aqueous solution of manganese, and a basic aqueous solution; a second step of preparing a lithium compound and an aluminum source; a third step of mixing the lithium compound, the aluminum source, and the hydroxide to form a first mixture; a fourth step of heating the first mixture to form a first composite oxide having lithium, nickel, cobalt, manganese, and aluminum; and preparing a magnesium source and a fluorine source. The method for producing a positive electrode active material comprises a fifth step of mixing a first composite oxide, a magnesium source, and a fluorine source to form a second mixture, and a seventh step of heating the second mixture to form a second composite oxide having lithium, nickel, cobalt, manganese, aluminum, magnesium, and fluorine, wherein in the second step, a material with a purity of 99.99% or higher is prepared as the lithium compound, and a material with a purity of 99.9% or higher is prepared as the aluminum source, and in the fifth step, a material with a purity of 99% or higher is prepared as the magnesium source, and a material with a purity of 99% or higher is prepared as the fluorine source, and the heating in the fourth and seventh steps is carried out in an oxygen-containing atmosphere with a dew point of -50°C or lower. [Effects of the Invention]

[0018] According to one aspect of the present invention, a method for producing a highly purified positive electrode active material can be provided. Alternatively, a method for producing a positive electrode active material whose crystal structure is resistant to collapse even after repeated charging and discharging can be provided. Alternatively, a method for producing a positive electrode active material with excellent charge-discharge cycle characteristics can be provided. Alternatively, a method for producing a positive electrode active material with a large charge-discharge capacity can be provided. Alternatively, a highly reliable or safe secondary battery can be provided.

[0019] Furthermore, according to one aspect of the present invention, it is possible to provide novel materials, active material particles, secondary batteries, energy storage devices, or methods for producing the same. Also, according to one aspect of the present invention, it is possible to provide a method for producing a secondary battery having one or more characteristics selected from high purity, high performance, and high reliability, or a secondary battery.

[0020] Furthermore, the description of these effects does not preclude the existence of other effects. Moreover, one aspect of the present invention does not necessarily have to possess all of these effects. Other effects will naturally become apparent from the description in the specification, drawings, and claims, and it is possible to extract other effects from the description in the specification, drawings, and claims. [Brief explanation of the drawing]

[0021] Figure 1 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figure 2 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figures 3A to 3E illustrate an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 4 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figure 5 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 6 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 7 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 8 illustrates an example of a method for producing a positive electrode active material according to one embodiment of the present invention. Figure 9 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figure 10 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figure 11 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figure 12 illustrates an example of a method for producing a positive electrode active material according to one aspect of the present invention. Figures 13A and 13B are cross-sectional views of the positive electrode active material. Figures 14A, 14B, and 14C illustrate the concentration distribution within the positive electrode active material. Figure 15 is a cross-sectional view illustrating an example of the positive electrode of a secondary battery. Figure 16A is an exploded perspective view of a coin-type rechargeable battery, Figure 16B is a perspective view of a coin-type rechargeable battery, and Figure 16C is a cross-sectional perspective view thereof. Figure 17A shows an example of a cylindrical secondary battery, Figure 17B shows an example of a cylindrical secondary battery, Figure 17C shows an example of multiple cylindrical secondary batteries, and Figure 17D shows an example of an energy storage system having multiple cylindrical secondary batteries. Figures 18A and 18B illustrate examples of secondary batteries, while Figure 18C shows the inside of a secondary battery. Figures 19A to 19C illustrate examples of secondary batteries. Figures 20A and 20B show the external appearance of a secondary battery. Figures 21A to 21C illustrate the method for manufacturing a secondary battery. Figures 22A to 22C show examples of battery pack configurations. Figures 23A and 23B illustrate an example of a secondary battery. Figures 24A to 24C illustrate an example of a secondary battery. Figures 25A and 25B illustrate examples of secondary batteries. Figure 26A is a perspective view of a battery pack showing one embodiment of the present invention, Figure 26B is a block diagram of the battery pack, and Figure 26C is a block diagram of a vehicle having a motor. Figures 27A to 27D illustrate an example of a transport vehicle. Figures 28A and 28B illustrate an energy storage device according to one embodiment of the present invention. Figure 29A shows an electric bicycle, Figure 29B shows the secondary battery of an electric bicycle, and Figure 29C illustrates an electric motorcycle. Figures 30A to 30D illustrate an example of an electronic device. Figure 31A shows an example of a wearable device, Figure 31B shows a perspective view of a wristwatch-type device, Figure 31C shows a side view of a wristwatch-type device, and Figure 31D shows an example of wireless earphones. [Modes for carrying out the invention]

[0022] Embodiments of the present invention will be described in detail below with reference to the drawings. However, it will be readily apparent to those skilled in the art that the present invention is not limited to the following description, and its form and details can be modified in various ways. Furthermore, the present invention is not to be interpreted as being limited to the embodiments described below.

[0023] A secondary battery has, for example, a positive electrode and a negative electrode. The positive electrode is composed of a positive electrode active material. The positive electrode active material is, for example, a substance that performs a reaction that contributes to the charge and discharge capacity. However, the positive electrode active material may also contain a portion of substances that do not contribute to the charge and discharge capacity.

[0024] In this specification, the positive electrode active material of one aspect of the present invention may be expressed as a positive electrode material, a positive electrode material for secondary batteries, a composite oxide, etc. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a compound. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composition. In this specification, it is preferable that the positive electrode active material of one aspect of the present invention has a composite.

[0025] In this specification, segregation refers to the phenomenon in which a certain element (e.g., B) is spatially non-uniformly distributed in a solid composed of multiple elements (e.g., A, B, C).

[0026] Furthermore, in this specification, the term "crack" is defined not only as one that occurs during the manufacturing process of the positive electrode active material, but also as one that occurs due to subsequent pressurization and charging / discharging. Surfaces formed by cracks (which may also be called fissures) may also be considered surfaces.

[0027] In this specification, the surface layer of particles such as active material refers to, for example, the region extending from the surface inward within 50 nm, more preferably within 35 nm, even more preferably within 20 nm, and most preferably within 10 nm. This region is sometimes referred to as the vicinity of the surface. The region deeper than the surface layer is referred to as the interior.

[0028] Furthermore, in this specification, when the term "defect" is used simply, it refers to a crystal defect or a lattice defect. Defects include point defects, dislocations, stacking faults (two-dimensional defects), and voids (three-dimensional defects).

[0029] Furthermore, in this specification, the term "particle" is not limited to spherical shapes (circular cross-sections), but may include elliptical, rectangular, trapezoidal, conical, rounded-cornered quadrilateral, asymmetrical shapes, and individual particles may have irregular shapes.

[0030] Furthermore, Miller indices are used to indicate crystal planes and directions in this specification. Individual planes are indicated by parentheses ( ). In crystallography, crystal planes, directions, and space groups are indicated by superscripts above the numbers, but in this specification, due to limitations in patent application notation, a minus sign (-) may be placed before the number instead of a superscript above it.

[0031] Furthermore, in this specification, the layered rock salt type crystal structure of a composite oxide containing lithium and a transition metal refers to a crystal structure having a rock salt type ionic arrangement in which cations and anions are arranged alternately, and in which the transition metal and lithium are regularly arranged to form a two-dimensional plane, thereby enabling two-dimensional diffusion of lithium. It should be noted that the layered rock salt type crystal structure may have defects such as vacancies in cations or anions. Also, strictly speaking, the layered rock salt type crystal structure may have a distorted lattice structure of the rock salt type crystal.

[0032] Furthermore, in this specification, a rock salt-type crystal structure refers to a structure in which cations and anions are arranged alternately. Note that rock salt-type crystal structures may have vacancies in either cations or anions.

[0033] Furthermore, in this specification, the theoretical capacity of the positive electrode active material refers to the amount of electricity when all of the insertable and detachable lithium present in the positive electrode active material has been detached. For example, the theoretical capacity of LiCoO2 is 274 mAh / g, the theoretical capacity of LiNiO2 is 274 mAh / g, and the theoretical capacity of LiMn2O4 is 148 mAh / g.

[0034] Furthermore, in this specification, the charge depth when all the insertable and detachable lithium in the positive electrode active material is inserted is defined as 0, and the charge depth when all the insertable and detachable lithium in the positive electrode active material has been detached is defined as 1.

[0035] Furthermore, while this specification and other documents may show an example of a secondary battery using a positive electrode and positive electrode active material according to one aspect of the present invention in which lithium metal is used as the counter electrode, the secondary battery according to one aspect of the present invention is not limited to this. Other materials, such as graphite or lithium titanate, may be used for the negative electrode. The properties of the positive electrode and positive electrode active material according to one aspect of the present invention, such as resistance to crystal structure breakdown even after repeated charging and discharging and obtaining good cycle characteristics, are not affected by the material of the negative electrode. Also, regarding the secondary battery according to one aspect of the present invention, while an example of a secondary battery using lithium metal as the counter electrode and charging and discharging at a relatively high voltage such as 4.6V may be shown, charging and discharging may be performed at a lower voltage. When charging and discharging at a lower voltage, it is expected that the cycle characteristics will be even better than those shown in this specification and other documents.

[0036] Furthermore, in this specification, the term "adhesion" refers to the process by which particles come together and solidify after heating. While it is presumed that these particle bonds are due to ionic bonds or van der Waals forces, the term "adhesion" is used simply to describe the process by which particles come together and solidify, regardless of the heating temperature, crystal state, elemental distribution, etc.

[0037] Furthermore, in this specification, "kiln" refers to a device for heating a material to be processed. For example, instead of "kiln," you may use terms such as furnace, oven, or heating device.

[0038] Furthermore, in this specification, a secondary battery having high-purity properties refers to a battery in which at least one or more materials selected from the positive electrode, negative electrode, separator, and electrolyte have high purity. Furthermore, a highly purified positive electrode active material refers to a positive electrode active material in which the materials contained therein have high purity. For example, the purity of the materials that can be used in the positive electrode active material of one embodiment of the present invention is 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher, for Li2CO3 and Co3O4, respectively.

[0039] Furthermore, the purity of the materials that can be used as elements (additive element X) that can be added to the positive electrode active material according to one embodiment of the present invention is such that LiF and MgF2 are each 2N (99%) or higher, preferably 3N (99.9%) or higher, and more preferably 4N (99.99%) or higher. Also, Ni(OH)2 and Al(OH)3 are each 3N (99.9%) or higher, preferably 4N (99.99%) or higher, more preferably 4N5 (99.995%) or higher, and even more preferably 5N (99.999%) or higher. Details of the addable elements (additive element X) will be described later.

[0040] The positive electrode active material may be expressed as a composite oxide (LiMO2) containing lithium, a transition metal M, and oxygen. Preferably, the transition metal M is a metal that can form a layered rock salt-type composite oxide belonging to the space group R-3m together with lithium. Details of the transition metal M will be described later.

[0041] Lithium composite oxide (NCM: nickel-cobalt-manganate lithium) containing Ni, Co, and Mn is a layered rock salt type composite oxide belonging to the space group R-3m along with lithium, and at a charging depth of 0 (discharge state), it has regions with a crystalline structure of space group R-3m. When the charging depth is greater than 0 and less than or equal to 1, it may have a layered structure belonging to the space group C2 / m, and the R-3m phase and the C2 / m phase may be phase-separated. In this embodiment, the term "crystal" refers to the crystalline structure immediately after the crystal formation process, and therefore basically refers to the R-3m phase, but even if it contains some or part of the C2 / m phase or other crystalline phases, it is referred to as an R-3m phase crystal in this specification.

[0042] (Embodiment 1)

[0043] In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 1.

[0044] As step S21 in Figure 1, a transition metal M source 801 is prepared.

[0045] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0046] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0047] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0048] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0049] Next, in step S31, the above transition metal M source 801 is mixed to obtain the mixture 811 of step S32.

[0050] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0051] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0052] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0053] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0054] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0055] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0056] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0057] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0058] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0059] Next, in step S37, the hydroxide containing the transition metal M after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0060] Crystallinity can be evaluated using, for example, TEM (transmission electron microscope) images, STEM (scanning transmission electron microscope) images, HAADF-STEM (high-angle scattering annular dark-field scanning transmission electron microscope) images, and ABF-STEM (annular bright-field scanning transmission electron microscope) images. X-ray diffraction (XRD), electron diffraction, and neutron diffraction can also be used as criteria for evaluating crystallinity.

[0061] Next, in step S42, lithium compound 822 is prepared, and in step S51, the mixture 821 from step S41 and lithium compound 822 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary, to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0062] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0063] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0064] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0065] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0066] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0067] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0068] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0069] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. The mortar itself should also be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0070] Next, in step S55, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S56. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0071] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. More of the crystal planes for lithium entry and exit can be exposed to the electrolyte, improving battery characteristics. Furthermore, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is robust and does not degrade easily even after repeated charging and discharging.

[0072] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, when three types of transition metals M are used, such as cobalt, manganese, and nickel, the positive electrode active material 100 becomes a composite oxide (NCM: nickel-cobalt-manganate lithium) having Ni, Co, and Mn. In NCM, the ratio of Ni:Co:Mn can be Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. NCM has a layered rock salt structure, and is preferable because it exhibits small expansion and contraction associated with the inflow and outflow of lithium during charging and discharging.

[0073] As described above, in one embodiment of the present invention, high-purity materials are used as raw materials during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. The positive electrode active material obtained by such a method is a material with a low impurity concentration, in other words, a highly purified material. Furthermore, the positive electrode active material obtained by such a method is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method of producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0074] (Embodiment 2)

[0075] In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figures 2 and 3A to 3E.

[0076] As step S21 in Figure 2, a transition metal M source 801 is prepared.

[0077] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0078] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0079] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0080] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0081] Next, in step S31, the above transition metal M source 801 is mixed to obtain the mixture 811 of step S32.

[0082] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0083] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0084] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0085] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0086] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0087] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0088] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0089] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0090] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0091] Next, in step S37, the hydroxide having the transition metal M after washing is dried, recovered, and crushed or sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0092] Next, in step S42, lithium compound 822 is prepared, and in step S51, the mixture 821 from step S41 and lithium compound 822 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary, to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer such as the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0093] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0094] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0095] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0096] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0097] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0098] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0099] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0100] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. The mortar itself should also be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher. Note that the same conditions as in step S54 can be applied to the heating processes described later, other than step S54.

[0101] Next, in step S62, the additive element X source 833 is prepared.

[0102] The additive element X in the additive element X source 833 can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0103] The source of element X 833 in step S62 of Figure 2 can be any one or more of the following: an aqueous solution containing element X, an alkoxide containing element X, or a solid compound containing element X. For example, as the source of element X 833 in step S62 of Figure 2, a solid compound containing one or more elements X may be prepared, crushed, and mixed (mixture 833a or mixture 833b), as shown as S62a or S62b in Figures 3A and 3B, and used as the source of element X 833 in step S62. When using a solid compound containing one or more elements X, it may be mixed after crushing, crushed after mixing, or used as the source of element X 833 in step S62 without crushing.

[0104] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0105] When the mixing and crushing steps are carried out wet, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used.

[0106] Next, in step S71 of Figure 2, the mixture 832 from step S61 and the additive element X source 833 from step S62 are mixed. After mixing, the mixture is recovered in step S72, crushed and sieved as necessary to obtain the mixture 841 from step S73. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, ball mill, and bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0107] Next, in step S74, the mixture 841 from step S73 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 841. This prevents unnecessary evaporation of the raw materials. The heating temperature in step S74 is preferably 500°C to 1100°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0108] Furthermore, heating in step S74 may be performed using a roller hearth kiln. When heat-treating with a roller hearth kiln, the mixture 841 may be processed using a heat-resistant container with a lid.

[0109] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0110] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S74 is not essential.

[0111] Next, in step S75, the calcined material is recovered, crushed and sieved as necessary, to obtain the mixture 842 in step S81. The mixture 842 obtained in step S81 can be used as the positive electrode active material 100. Alternatively, the mixture 842 obtained in step S81 can be used in the processes from step S81 onward shown in Figure 3C.

[0112] Next, the steps from step S81 onwards, as shown in Figure 3C, will be explained. In step S82, the additive element X source 843 is prepared.

[0113] The additive element X added in step S82 can be selected from the additive elements X described above. The additive element X source 843 in step S82 can be any one or more of the following: an aqueous solution containing additive element X, an alkoxide containing additive element X, or a solid compound containing additive element X. For example, as the additive element X source 843 in step S82 in Figure 3C, a solid compound containing one or more additive elements X may be prepared, as shown as S82a or S82b in Figures 3D and 3E, then crushed and mixed (mixture 843a or mixture 843b), and used as the additive element X source 843 in step S82. When using a solid compound containing one or more additive elements X, it may be mixed after crushing, crushed after mixing, or used as the additive element X source 843 in step S82 without crushing.

[0114] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0115] Next, in step S91 of Figure 3C, the mixture 842 from step S81 and the additive element X source 843 from step S82 are mixed. After mixing, the mixture is recovered in step S92, crushed and sieved as necessary to obtain the mixture 851 from step S93. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, ball mill, and bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0116] In this embodiment, the mixing is performed dry using a ball mill with zirconia balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixing is carried out in a dry room with a dew point of -100°C to -10°C.

[0117] Next, in step S94, the mixture 851 from step S93 is heated. The heating temperature in step S94 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0118] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0119] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to cool the material from the specified temperature to room temperature for 10 hours or more and 50 hours or less.

[0120] However, cooling to room temperature in step S94 is not mandatory. If there are no problems with the subsequent processes, cooling may be extended to a temperature higher than room temperature.

[0121] Next, in step S95, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S101. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0122] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0123] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (called NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0124] As shown in Figures 2 and 3A to 3E, by separating the process of introducing the transition metal M from the process of introducing the additive element X, it is sometimes possible to change the depth profile of the concentration of each element. For example, the concentration of the additive element X can be increased in the surface layer compared to the interior of the particle. Also, the ratio of the number of atoms of the additive element X to the number of atoms of the transition metal M can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0125] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, a positive electrode active material can be obtained in which regions with low impurity concentrations and regions with introduced additive elements are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0126] (Embodiment 3)

[0127] In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figures 4 and 5.

[0128] In steps S21a, S21b, and 21c of Figure 4, a transition metal M source is prepared. In this embodiment, we will describe the case in which three types of transition metal M sources are used: nickel source 803, cobalt source 804, and manganese source 805.

[0129] For nickel source 803, an aqueous solution containing nickel can be a nickel sulfate solution or an aqueous solution containing nickel nitrate, etc. For cobalt source 804, an aqueous solution containing cobalt can be a cobalt sulfate solution or an aqueous solution containing cobalt nitrate, etc. For manganese source 805, an aqueous solution containing manganese can be a manganese sulfate solution or an aqueous manganese nitrate solution, etc.

[0130] Furthermore, it is preferable to use high-purity materials as the nickel source 803, cobalt source 804, and manganese source 805 used in the synthesis. Specifically, when using aqueous solutions containing nickel source 803, cobalt source 804, and manganese source 805, the purity of the solute material when preparing the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0131] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0132] Next, in step S31, the nickel source 803, cobalt source 804, and manganese source 805 are mixed to obtain the mixture 811 of step S32.

[0133] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0134] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0135] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0136] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0137] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0138] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0139] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0140] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0141] Next, the solution containing a hydroxide having nickel, cobalt, and manganese, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having nickel, cobalt, and manganese can be removed. This makes it possible to obtain a high-purity hydroxide having nickel, cobalt, and manganese as a precursor for the positive electrode active material 100.

[0142] Next, in step S37, the hydroxide containing nickel, cobalt, and manganese after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0143] Next, in step S42, lithium compound 822 is prepared, and in step S51, the mixture 821 from step S41 and lithium compound 822 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary, to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer such as the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0144] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0145] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0146] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0147] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0148] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0149] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0150] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0151] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. The mortar itself should also be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher. Note that the same conditions as in step S54 can be applied to the heating processes described later, other than step S54.

[0152] Next, in step S55, the calcined material is recovered, crushed and sieved as necessary, to obtain the mixture 832 of step S61.

[0153] Next, in steps S63 and S64, a magnesium source 834 and a fluorine source 835 are prepared as the source of additive element X. Subsequently, in step S65, the magnesium source 834 and the fluorine source 835 are crushed and mixed to obtain the mixture 836 in step S66.

[0154] For example, magnesium fluoride, magnesium oxide, magnesium hydroxide, magnesium carbonate, etc., can be used as the magnesium source 834.

[0155] As the fluorine source 835, for example, lithium fluoride (LiF), magnesium fluoride (MgF2), aluminum fluoride (AlF3), titanium fluoride (TiF4), cobalt fluoride (CoF2, CoF3), nickel fluoride (NiF2), zirconium fluoride (ZrF4), vanadium fluoride (VF5), manganese fluoride, iron fluoride, chromium fluoride, niobium fluoride, zinc fluoride (ZnF2), calcium fluoride (CaF2), sodium fluoride (NaF), potassium fluoride (KF), barium fluoride (BaF2), cerium fluoride (CeF2), lanthanum fluoride (LaF3), sodium aluminum hexafluoride (Na3AlF6), etc. can be used. Furthermore, the fluorine source is not limited to a solid; for example, fluorine (F2), carbon fluoride, sulfur fluoride, oxygen fluoride (OF2, O2F2, O3F2, O4F2, O2F), etc., may be used and mixed in the atmosphere during the heating process described later. Multiple fluorine sources may also be used in combination. Among these, lithium fluoride is preferred because it has a relatively low melting point of 848°C and is easily melted during the annealing process described later.

[0156] In this embodiment, lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The effect of lowering the melting point is greatest when lithium fluoride (LiF) and magnesium fluoride (MgF2) are mixed in a molar ratio of approximately LiF:MgF2 = 65:35. On the other hand, if the amount of lithium fluoride is too high, there is a concern that the lithium will be in excess and the cycle characteristics will deteriorate. Therefore, the molar ratio of lithium fluoride (LiF) and magnesium fluoride (MgF2) is preferably LiF:MgF2 = x:1 (0 ≤ x ≤ 1.9), more preferably LiF:MgF2 = x:1 (0.1 ≤ x ≤ 0.5), and even more preferably LiF:MgF2 = x:1 (x = around 0.33). In this specification, "around" means a value greater than 0.9 times and less than 1.1 times the value.

[0157] Furthermore, if the crushing and mixing process in step S65 is carried out wet, a solvent is prepared. Suitable solvents include ketones such as acetone, alcohols such as ethanol and isopropanol, ethers, dioxane, acetonitrile, and N-methyl-2-pyrrolidone (NMP). It is more preferable to use an aprotic solvent that does not react easily with lithium. In this embodiment, dehydrated acetone with a purity of 99.5% or higher is used.

[0158] Furthermore, it is preferable to use high-purity materials as the magnesium and fluorine sources during synthesis. Specifically, the purity of these materials should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0159] Next, in step S71, the mixture 832 from step S61 and the mixture 836 from step S66 are mixed. After mixing, the mixture is collected in step S72, crushed and sieved as necessary to obtain the mixture 841 from step S73. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is good to carry out the process with a peripheral speed of 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0160] Next, in step S74, the mixture 841 from step S73 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 841. This prevents unnecessary evaporation of the raw material gas. The heating temperature in step S74 is preferably 500°C to 1100°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0161] Furthermore, heating in step S74 may be performed using a roller hearth kiln. When heat-treating with a roller hearth kiln, the mixture 841 may be processed using a heat-resistant container with a lid.

[0162] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0163] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S74 is not essential.

[0164] Next, in step S75, the calcined material is recovered, crushed and sieved as necessary, to obtain the mixture 842 of step S81. Lithium fluoride (LiF) is prepared as the fluorine source, and magnesium fluoride (MgF2) is prepared as both the fluorine source and the magnesium source. The container (crucible) is covered, and an appropriate amount of fluorine is introduced into the mixture 842. The fluorine from LiF and MgF2 may migrate to the surface layer of the mixture 842. The fluorine-containing region on the surface layer of the mixture 842 functions as a barrier film. This fluorine makes the surface of the mixture 842 smooth and less uneven. Heating after mixing in fluorine promotes the single crystallization of the mixture 842.

[0165] The mixture 842 obtained in step S81 can be used as the positive electrode active material 100. Alternatively, the mixture 842 obtained in step S81 can be used in the steps after step S81 shown in Figure 5.

[0166] Next, the steps from step S81 onwards, as shown in Figure 5, will be explained. In steps S83 and S84, nickel source 845 and aluminum source 846 are prepared as the source of additive element X. In steps S85 and S86, nickel source 845 and aluminum source 846 are crushed, respectively, and then mixed in step S87 to obtain the mixture 847 in step S88.

[0167] Nickel sources such as nickel oxide and nickel hydroxide can be used.

[0168] Aluminum oxide, aluminum hydroxide, and the like can be used as aluminum sources.

[0169] Furthermore, it is preferable to use high-purity materials as the nickel and aluminum sources during synthesis. Specifically, the purity of these materials should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0170] Next, in step S91, the mixture 842 from step S81 and the mixture 847 from step S88 are mixed. After mixing, the mixture is collected in step S92, crushed and sieved as necessary to obtain the mixture 851 from step S93. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is good to carry out the process with a peripheral speed of 838 mm / s (rotation speed 400 rpm, ball mill diameter 40 mm).

[0171] In this embodiment, the mixing is performed dry using a ball mill with zirconia balls with a diameter of 1 mm at 150 rpm for 1 hour. The mixing is carried out in a dry room with a dew point of -100°C to -10°C.

[0172] Next, in step S94, the mixture 851 from step S93 is heated. The heating temperature in step S94 is preferably 500°C to 1130°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0173] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0174] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S94 is not essential.

[0175] Next, in step S95, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S101. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0176] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0177] Since the positive electrode active material 100 contains fluorine, it is preferable that its surface is smooth and has few irregularities. When the particle surface roughness information is quantified from the measurement data in a cross-section of the positive electrode active material 100 cut toward the center, it is preferable that at least a portion of the particles have a surface roughness of less than 3 nm, preferably less than 1 nm. Nickel and aluminum may migrate to the surface layer of the positive electrode active material 100. The nickel-containing region or aluminum-containing region on the surface layer of the positive electrode active material 100 functions as a barrier film.

[0178] The positive electrode active material 100 is a lithium composite oxide containing at least nickel, cobalt, and manganese, and further containing aluminum and nickel. In this lithium composite oxide, the ratio of Ni:Co:Mn can be any of the following: Ni:Co:Mn = 1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. In this lithium composite oxide, aluminum and nickel are added in small amounts, and for example, when Ni:Mn:Co = 8:1:1 or nearby, it is preferable that the concentration of aluminum is 0.1 at% or more and 2 at% or less.

[0179] As shown in Figures 4 and 5, by separating the process of introducing the transition metal M from the process of introducing the additive element X, it is sometimes possible to change the depth profile of the concentration of each element. For example, the concentration of the additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of the additive element X to this reference can be made higher in the surface layer than in the interior. In the above lithium composite oxide, the region in which the aluminum concentration is between 0.1 at% and 2 at% may be either the surface layer or the interior of the particle.

[0180] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0181] (Embodiment 4) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 6.

[0182] In step S21 of Figure 6, a transition metal M source 801 is prepared, and in step S22, an additive element X source 802 is prepared.

[0183] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0184] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0185] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0186] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, bromine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. As the additive element X source 802, any one or more can be selected from an aqueous solution containing the additive element X, an alkoxide containing the additive element X, or a solid compound containing the additive element X. It is preferable that the additive element X source 802 in step S22 be prepared as an aqueous solution containing the additive element X.

[0187] Furthermore, it is preferable to use a high-purity material as the additive element X source 802 used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0188] Next, in step S31, the above-mentioned transition metal M source 801 and additive element X source 802 are mixed to obtain the mixture 811 of step S32.

[0189] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0190] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0191] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0192] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0193] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0194] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0195] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0196] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH of the solution in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0197] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0198] Next, in step S36, the hydroxide having the washed transition metal M and additive element X is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0199] Next, in step S42, lithium compound 822 is prepared, and in step S51, the mixture 821 from step S41 and lithium compound 822 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary, to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer such as the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0200] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0201] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0202] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C. When heating, it is advisable to cover the container (crucible) containing the mixture 831. This prevents unnecessary evaporation of the raw material gas.

[0203] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0204] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0205] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0206] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0207] Next, in step S55, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S56. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0208] This embodiment is preferable because it has a low heating step, making it highly producible. The positive electrode active material 100 is preferably highly crystalline, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. More of the crystal planes for lithium entry and exit can be exposed to the electrolyte, improving battery characteristics. Furthermore, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is more durable and provides an active material that does not easily degrade even after repeated charging and discharging.

[0209] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0210] As shown in Figure 6, by separating the processes for introducing the transition metal M and the additive element X, it is sometimes possible to change the depth-direction profile of the concentration of each element. For example, the concentration of additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of additive element X to this reference can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0211] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0212] (Embodiment 5) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 7.

[0213] As step S21 in Figure 7, a transition metal M source 801 is prepared.

[0214] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source is prepared as an aqueous solution containing the transition metal M.

[0215] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0216] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0217] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0218] Next, in step S31, the above transition metal M source 801 is mixed to obtain the mixture 811 of step S32.

[0219] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0220] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0221] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0222] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0223] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0224] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0225] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0226] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0227] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0228] Next, in step S36, the hydroxide containing the transition metal M after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0229] Next, a lithium compound 822 is prepared in step S42, and an additive element X source 823 is prepared in step S43. In step S51, the mixture 821 from step S41, the lithium compound 822, and the additive element X source 823 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer, for example, the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0230] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0231] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0232] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0233] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0234] The source of the additive element X in step S43, 823, can be any one or more of the following: an aqueous solution containing the additive element X, an alkoxide containing the additive element X, or a solid compound containing the additive element X.

[0235] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0236] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0237] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0238] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0239] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0240] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0241] Next, in step S55, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S56. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0242] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0243] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0244] As shown in Figure 7, by separating the processes for introducing the transition metal M and the additive element X, it is sometimes possible to change the depth-direction profile of the concentration of each element. For example, the concentration of additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of additive element X to this reference can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0245] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0246] (Embodiment 6) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 8.

[0247] As step S21 in Figure 8, a transition metal M source 801 is prepared.

[0248] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0249] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0250] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0251] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0252] Next, in step S31, the above transition metal M source 801 is mixed to obtain the mixture 811 of step S32.

[0253] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0254] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0255] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0256] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0257] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0258] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0259] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0260] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0261] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0262] Next, in step S36, the hydroxide containing the transition metal M after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0263] Next, in step S42, lithium compound 822 is prepared, and in step S51, the mixture 821 from step S41 and lithium compound 822 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary, to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer such as the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0264] By sufficiently mixing in step S51, it is preferable that the mixture 821 and the lithium compound 822 can be homogeneously mixed.

[0265] As the lithium compound 822, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium fluoride, etc. can be used. The lithium compound 822 is sometimes referred to as a lithium source.

[0266] In addition, as the lithium compound 822 used in the synthesis, it is preferable to use a high-purity material. Specifically, the purity of the material is preferably 4N (99.99%) or more, more preferably 4N5UP (99.995%) or more, and even more preferably 5N (99.999%) or more. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be enhanced.

[0267] Next, as step S54, the mixture 831 in step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably carried out at 700°C or more and less than 1100°C, more preferably at 800°C or more and 1000°C or less, and even more preferably at 800°C or more and 950°C or less.

[0268] The heating time can be, for example, 1 hour or more and 100 hours or less, and preferably 2 hours or more and 20 hours or less. The heating is preferably carried out in an oxygen-containing atmosphere with little water such as oxygen or dry air (for example, the dew point is -50°C or less, more preferably the dew point is -80°C or less). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Also, heating is preferably carried out in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, because impurities that can be mixed into the material can be suppressed.

[0269] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0270] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0271] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0272] Next, in step S55, the calcined material is recovered and crushed to obtain the mixture 832 from step S61.

[0273] Next, in step S62, the additive element X source 833 is prepared.

[0274] The additive element X in the additive element X source 833 can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0275] The source of element X 833 in step S62 of Figure 8 can be any one or more of the following: an aqueous solution containing element X, an alkoxide containing element X, or a solid compound containing element X. For example, as the source of element X 833 in step S62 of Figure 8, a solid compound containing one or more elements X may be prepared, as shown as S62a or S62b in Figures 3A and 3B, then crushed and mixed (mixture 843a or mixture 843b), and used as the source of element X 833 in step S62. When using a solid compound containing one or more elements X, it may be mixed after crushing, crushed after mixing, or used as the source of element X 833 in step S62 without crushing.

[0276] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0277] Next, in step S71, the mixture 832 from step S61 and the additive element X source 833 from step S62 are mixed. After mixing, the mixture is recovered in step S72, crushed and sieved as necessary to obtain the mixture 841 from step S73. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0278] Next, in step S74, the mixture 841 from step S73 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 841. This prevents unnecessary evaporation of the raw material gas. The heating temperature in step S74 is preferably 500°C to 1100°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0279] Furthermore, heating in step S74 may be performed using a roller hearth kiln. When heat-treating with a roller hearth kiln, the mixture 841 may be processed using a heat-resistant container with a lid.

[0280] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0281] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S74 is not essential.

[0282] Next, in step S75, the calcined material is recovered and crushed to obtain the positive electrode active material 100 in step S76. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0283] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0284] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0285] As shown in FIG. 8, by separating the steps of introducing the transition metal M and the additive element X, it may be possible to change the profiles of the respective element concentrations in the depth direction. For example, the concentration of the additive element X can be increased in the surface layer portion compared to the inside of the particles. Further, based on the number of atoms of the transition metal M, the ratio of the number of atoms of the additive element X to the reference can be made higher in the surface layer portion than in the inside. In NCMA, the region where the aluminum concentration is 0.1 at% or more and 2 at% or less may be either the surface layer portion or the inside of the particles.

[0286] Further, in one aspect of the present invention, a high-purity material is used for the transition metal M source used in the synthesis, and the positive electrode active material is produced in a process with less impurity incorporation during the synthesis. Further, by using a production method that thoroughly eliminates the incorporation of impurities during the synthesis with the transition metal M source and controls the desired additive element X to introduce it into the positive electrode active material, a positive electrode active material in which a region with a low impurity concentration and a region into which the additive element X is introduced are controlled can be obtained. Further, the positive electrode active material shown in the present embodiment is a material having high crystallinity. Further, the positive electrode active material obtained by the production method of one aspect of the present invention can increase the capacity of the secondary battery and / or improve the reliability of the secondary battery.

[0287] (Embodiment 7) In the present embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using FIG. 9.

[0288] As step S21 in FIG. 9, a transition metal M source 801 is prepared, and as step S22, an additive element X source 802 is prepared.

[0289] As the transition metal M, for example, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, there are cases where only cobalt is used, only nickel is used, two kinds of cobalt and manganese are used, two kinds of cobalt and nickel are used, or three kinds of cobalt, manganese, and nickel are used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0290] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0291] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0292] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive elements. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X mentioned above.

[0293] As the source of additive element X 802, any one or more of the following can be used: an aqueous solution containing additive element X, an alkoxide containing additive element X, or a solid compound containing additive element X. It is preferable that the source of additive element X 802 in step S22 be prepared as an aqueous solution containing additive element X.

[0294] Furthermore, it is preferable to use a high-purity material as the additive element X source 802 used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0295] Next, in step S31, the above-mentioned transition metal M source 801 and additive element X source 802 are mixed to obtain the mixture 811 of step S32.

[0296] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0297] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0298] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0299] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0300] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0301] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0302] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0303] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0304] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0305] Next, in step S36, the hydroxide having the washed transition metal M and additive element X is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0306] Next, a lithium compound 822 is prepared in step S42, and an additive element X source 823 is prepared in step S43. In step S51, the mixture 821 from step S41, the lithium compound 822, and the additive element X source 823 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer, for example, the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0307] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0308] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0309] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0310] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0311] The source of the additive element X in step S43, 823, can be any one or more of the following: an aqueous solution containing the additive element X, an alkoxide containing the additive element X, or a solid compound containing the additive element X.

[0312] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0313] Next, in step S54, the mixture 831 from step S53 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 831. This prevents unnecessary evaporation of the raw material gas. Heating is preferably carried out at 700°C or higher and less than 1100°C, more preferably at 800°C or higher and 1000°C or lower, and even more preferably at 800°C or higher and 950°C or lower.

[0314] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0315] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0316] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0317] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0318] Next, in step S55, the material that has been calcined above is recovered and crushed to obtain the positive electrode active material 100 in step S56. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0319] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0320] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0321] As shown in Figure 9, by separating the process of introducing the transition metal M from the process of introducing the additive element X, it is sometimes possible to change the depth profile of the concentration of each element. For example, the concentration of additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of additive element X to this reference can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0322] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0323] (Embodiment 8) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 10.

[0324] As step S21 in Figure 10, a transition metal M source 801 is prepared.

[0325] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0326] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0327] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0328] Furthermore, when using multiple transition metal M sources 801, for example, a cobalt source, a manganese source, and a nickel source, it is preferable to use a mixing ratio within a range that allows for a layered rock salt type crystal structure.

[0329] Next, in step S31, the above transition metal M source is mixed to obtain the mixture 811 in step S32.

[0330] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0331] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0332] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0333] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0334] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0335] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0336] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0337] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0338] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0339] Next, in step S36, the hydroxide containing the transition metal M after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0340] Next, a lithium compound 822 is prepared in step S42, and an additive element X source 823 is prepared in step S43. In step S51, the mixture 821 from step S41, the lithium compound 822, and the additive element X source 823 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer, for example, the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0341] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0342] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0343] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0344] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0345] The source of the additive element X in step S43, 823, can be any one or more of the following: an aqueous solution containing the additive element X, an alkoxide containing the additive element X, or a solid compound containing the additive element X.

[0346] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0347] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0348] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0349] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0350] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0351] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0352] Next, in step S55, the calcined material is recovered and crushed to obtain the mixture 832 from step S61. If necessary, sieving may be performed after crushing.

[0353] Next, in step S62, the additive element X source 833 is prepared.

[0354] The additive element X in the additive element X source 833 can be one or more selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0355] The source of element X 833 in step S62 of Figure 10 can be any one or more of the following: an aqueous solution containing element X, an alkoxide containing element X, or a solid compound containing element X. For example, as the source of element X 833 in step S62 of Figure 10, a solid compound containing one or more elements X may be prepared, as shown as S62a or S62b in Figures 3A and 3B, then crushed and mixed (mixture 843a or mixture 843b), and used as the source of element X 833 in step S62. When using a solid compound containing one or more elements X, it may be mixed after crushing, crushed after mixing, or used as the source of element X 833 in step S62 without crushing.

[0356] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0357] Next, in step S71, the mixture 832 from step S61 and the additive element X source 833 from step S62 are mixed. After mixing, the mixture is recovered in step S72, crushed and sieved as necessary to obtain the mixture 841 from step S73. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0358] Next, in step S74, the mixture 841 from step S73 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 841. This prevents unnecessary evaporation of the raw material gas. The heating temperature in step S74 is preferably 500°C to 1100°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0359] Furthermore, heating in step S74 may be performed using a roller hearth kiln. When heat-treating with a roller hearth kiln, the mixture 841 may be processed using a heat-resistant container with a lid.

[0360] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0361] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S74 is not essential.

[0362] Next, in step S75, the calcined material is recovered and crushed to obtain the positive electrode active material 100 in step S76. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0363] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0364] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0365] As shown in Figure 10, by separating the process of introducing the transition metal M from the process of introducing the additive element X, it is sometimes possible to change the depth profile of the concentration of each element. For example, the concentration of additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of additive element X to this reference can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0366] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0367] (Embodiment 9) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 11.

[0368] As step S21 in Figure 11, a transition metal M source 801 is prepared, and as step S22, an additive element X source 802 is prepared.

[0369] As the transition metal M, at least one of manganese, cobalt, and nickel can be used. For example, as the transition metal M, only cobalt may be used, only nickel may be used, two types of cobalt and manganese may be used, two types of cobalt and nickel may be used, or three types of cobalt, manganese, and nickel may be used. The transition metal M source 801 is prepared as an aqueous solution containing the transition metal M.

[0370] As the transition metal M source 801, an aqueous solution containing cobalt can be an aqueous solution of cobalt sulfate or an aqueous solution of cobalt nitrate, an aqueous solution containing nickel can be an aqueous solution of nickel sulfate or an aqueous solution of nickel nitrate, and an aqueous solution containing manganese can be an aqueous solution of manganese sulfate or an aqueous solution of manganese nitrate.

[0371] Furthermore, it is preferable to use a high-purity material as the transition metal M source 801 used in the synthesis. Specifically, when using an aqueous solution containing the transition metal M, the purity of the solute material used to prepare the aqueous solution should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. The water should preferably be pure water with a resistivity of 1 MΩ·cm or higher, more preferably 10 MΩ·cm or higher, and even more preferably 15 MΩ·cm or higher, with few impurities. By using high-purity materials, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0372] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0373] As the source of additive element X 802, any one or more of the following can be used: an aqueous solution containing additive element X, an alkoxide containing additive element X, or a solid compound containing additive element X. It is preferable that the source of additive element X 802 in step S22 be prepared as an aqueous solution containing additive element X.

[0374] Furthermore, it is preferable to use a high-purity material as the additive element X source 802 used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0375] Next, in step S31, the above-mentioned transition metal M source 801 and additive element X source 802 are mixed to obtain the mixture 811 of step S32.

[0376] Next, aqueous solution A812 is prepared as step S33, and aqueous solution B813 as step S34.

[0377] As aqueous solution A812, one or more aqueous solutions containing at least one chelating agent such as glycine, oxine, 1-nitroso-2-naphthol, or 2-mercaptobenzothiazole, or aqueous ammonia can be used.

[0378] As aqueous solution B813, one or more of the following can be used: aqueous solution of sodium hydroxide, aqueous solution of potassium hydroxide, or aqueous solution of lithium hydroxide.

[0379] Next, in step S35, the mixture 811 from step S32, aqueous solution A 812, and aqueous solution B 813 are mixed.

[0380] As a mixing method for step S35, a method can be used in which the mixture 811 from step S32 and the aqueous solution B813 from step S32 are added dropwise to the aqueous solution A812 placed in the reaction vessel. It is desirable to add the mixture 811 from step S32 dropwise at a constant rate, and to add the aqueous solution B813 dropwise as needed to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing of step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, the aqueous solution A812, and the aqueous solution B813 by N2 bubbling. In the mixing of step S35, the pH in the reaction vessel should preferably be 9 to 11, more preferably 10.0 to 10.5. In the mixing of step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0381] Alternatively, as a mixing method in step S35, aqueous solutions A812 and B813 can be added dropwise to the mixture 811 from step S32 placed in the reaction vessel. It is preferable to adjust the dropping rate of aqueous solutions A812 and B813 in order to maintain the solute ion concentration and hydroxyl group concentration of aqueous solution A812 in the reaction vessel within a predetermined range. In the mixing of step S35, it is preferable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is preferable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing of step S35, the temperature of the solution in the reaction vessel is preferably 40°C to 80°C, more preferably 50°C to 70°C.

[0382] Alternatively, a method of mixing in step S35 in which aqueous solution A812 is not used will be described. A fixed amount of aqueous solution B813 is added dropwise to the mixture 811 from step S32 placed in the reaction vessel. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C to 80°C, more preferably 50°C to 70°C.

[0383] Alternatively, as a method of mixing in step S35, a case in which pure water is used in addition to the mixture 811, aqueous solution A812, and aqueous solution B813 from step S32 will be described. The mixture 811 and aqueous solution A812 from step S32 are added dropwise to the pure water in the reaction vessel at a constant rate, and aqueous solution B813 can be added dropwise as appropriate to maintain the pH of the mixed solution in the reaction vessel within a predetermined range. In the mixing in step S35, it is desirable to stir the solution in the reaction vessel with a stirring blade or stirrer, and it is desirable to remove dissolved oxygen from the solution in the reaction vessel, the mixture 811 from step S32, aqueous solution A812, and aqueous solution B813 by N2 bubbling. In the mixing in step S35, the pH in the reaction vessel should preferably be 9 or more and 11 or less, more preferably 10.0 or more and 10.5 or less. In the mixing in step S35, the temperature of the solution in the reaction vessel should preferably be 40°C or more and 80°C or less, more preferably 50°C or more and 70°C or less.

[0384] Next, the solution containing the hydroxide having the transition metal M, formed by the mixing in step S35, is filtered and then washed with water in step S36. The water used for washing is preferably pure water with a resistivity of 1 MΩ·cm or more, more preferably 10 MΩ·cm or more, and even more preferably 15 MΩ·cm or more, and low in impurities. By using pure water with low impurities for washing, impurities contained in the hydroxide having the transition metal M can be removed. This makes it possible to obtain a hydroxide having high purity of the transition metal M as a precursor for the positive electrode active material 100.

[0385] Next, in step S36, the hydroxide containing the transition metal M after washing is dried, recovered, crushed and sieved as necessary to obtain the mixture 821 of step S41. The mixture 821 is also called the precursor of the positive electrode active material 100. The precursor is preferably highly crystalline, and more preferably has single crystal grains. That is, the precursor is preferably a single crystal.

[0386] Next, a lithium compound 822 is prepared in step S42, and an additive element X source 823 is prepared in step S43. In step S51, the mixture 821 from step S41, the lithium compound 822, and the additive element X source 823 are mixed. After mixing, the mixture is recovered in step S52, crushed and sieved as necessary to obtain the mixture 831 from step S53. Mixing can be done dry or wet. For mixing, mixers such as a rotary-orbit mixer, ball mills, and bead mills can be used. When using a rotary-orbit mixer, for example, the Awatori Rentaro rotary-orbit mixer manufactured by Shinky Co., Ltd., it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0387] It is preferable that the mixture 821 and the lithium compound 822 are homogeneously mixed by thoroughly mixing them in step S51.

[0388] Examples of lithium compound 822 include lithium hydroxide, lithium carbonate, lithium nitrate, and lithium fluoride. Lithium compound 822 is sometimes referred to as a lithium source.

[0389] Furthermore, it is preferable to use a high-purity material for the lithium compound 822 used in the synthesis. Specifically, the purity of the material should be 4N (99.99%) or higher, preferably 4N5UP (99.995%) or higher, and even more preferably 5N (99.999%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0390] As the additive element X, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as additive element X. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X described above.

[0391] The source of the additive element X in step S43, 823, can be any one or more of the following: an aqueous solution containing the additive element X, an alkoxide containing the additive element X, or a solid compound containing the additive element X.

[0392] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0393] Next, in step S54, the mixture 831 from step S53 is heated. The heating temperature is preferably near the melting point of the mixture 821 and the lithium compound 822, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C. When heating, it is advisable to cover the container (crucible) containing the mixture 831. This prevents unnecessary evaporation of the raw material gas.

[0394] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0395] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S54 is not essential.

[0396] Furthermore, the crucible used during heating in step S54 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0397] Furthermore, when collecting the material after heating in step S54, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. It is also preferable that the mortar itself be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0398] Next, in step S55, the calcined material is recovered, crushed and sieved as necessary, to obtain the mixture 832 of step S61.

[0399] Next, in step S62, the additive element X source 833 is prepared.

[0400] As the additive element X source 833, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as the additive element X source. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X sources described above.

[0401] The source of element X 833 in step S62 of Figure 11 can be any one or more of the following: an aqueous solution containing element X, an alkoxide containing element X, or a solid compound containing element X. For example, as the source of element X 833 in step S62 of Figure 11, a solid compound containing one or more elements X may be prepared, as shown as S62a or S62b in Figures 3A and 3B, and then crushed and mixed (mixture 843a or mixture 843b) which can be used as the source of element X 833 in step S62. When using a solid compound containing one or more elements X, it may be mixed after crushing, crushed after mixing, or used as the source of element X 833 in step S62 without crushing.

[0402] Furthermore, it is preferable to use a high-purity material as the source of additive element X used in the synthesis. Specifically, the purity of the material should be 2N (99%) or higher, preferably 3N (99.9%) or higher, and even more preferably 4N (99.99%) or higher. By using a high-purity material, the capacity of the secondary battery can be increased and / or the reliability of the secondary battery can be improved.

[0403] Next, in step S71, the mixture 832 from step S61 and the additive element X source 833 from step S62 are mixed. After mixing, the mixture is recovered in step S72, crushed and sieved as necessary to obtain the mixture 841 from step S73. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using the rotary-orbit mixer Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is good to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media. Also, when using a ball mill or a bead mill, it is preferable to set the peripheral speed to 100 mm / s or more and 2000 mm / s or less in order to suppress contamination from the media or material. For example, it is recommended to perform the process at a peripheral speed of 838 mm / s (rotational speed of 400 rpm, ball mill diameter of 40 mm).

[0404] Next, in step S74, the mixture 841 from step S73 is heated. When heating, it is advisable to cover the container (crucible) containing the mixture 841. This prevents unnecessary evaporation of the raw material gas. The heating temperature in step S74 is preferably 500°C to 1100°C, more preferably 500°C to 1000°C, even more preferably 500°C to 950°C, and even more preferably 500°C to 900°C.

[0405] Furthermore, heating in step S74 may be performed using a roller hearth kiln. When heat-treating with a roller hearth kiln, the mixture 841 may be processed using a heat-resistant container with a lid.

[0406] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0407] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S74 is not essential.

[0408] Next, in step S75, the calcined material is recovered and crushed to obtain the positive electrode active material 100 in step S76. If necessary, sieving may be performed after crushing. By the above steps, a positive electrode active material 100 according to one embodiment of the present invention can be produced.

[0409] The positive electrode active material 100 preferably has high crystallinity, and if the mixture 821 in step S41 has high crystallinity, the crystallinity of the positive electrode active material 100 will also be high. If the positive electrode active material 100 has high crystallinity and also contains single crystal grains, the crystal planes for lithium entry and exit can be aligned. If more of the crystal planes for lithium entry and exit can be exposed to the electrolyte, the battery characteristics will be improved. In addition, if the positive electrode active material 100 has high crystallinity and also contains single crystal grains, it is possible to provide an active material that is durable and does not degrade easily even after repeated charging and discharging.

[0410] The positive electrode active material 100 may be expressed as a composite oxide (LiMO2) having lithium, a transition metal M, and oxygen. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented as LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2. For example, if three types of transition metals M are used—cobalt, manganese, and nickel—and aluminum is used as the additive element X, the positive electrode active material 100 becomes a composite oxide (NCMA) having Ni, Co, Mn, and Al. As an NCMA, Al can be added to any NCM with a Ni:Co:Mn ratio of Ni:Co:Mn=1:1:1 or nearby, 9:0.5:0.5 or nearby, 8:1:1 or nearby, 6:2:2 or nearby, or 5:2:3 or nearby. For example, when Ni:Co:Mn = 8:1:1 or near that ratio, it is preferable that the aluminum concentration is between 0.1 at% and 2 at%.

[0411] As shown in Figure 11, by separating the process of introducing the transition metal M from the process of introducing the additive element X, it is sometimes possible to change the depth profile of the concentration of each element. For example, the concentration of additive element X can be increased in the surface layer compared to the interior of the particle. Also, using the number of atoms of the transition metal M as a reference, the ratio of the number of atoms of additive element X to this reference can be made higher in the surface layer than in the interior. In NCMA, the region where the aluminum concentration is between 0.1 at% and 2 at% can be either the surface layer or the interior of the particle.

[0412] Furthermore, in one embodiment of the present invention, a high-purity material is used as the transition metal M source during synthesis, and the positive electrode active material is produced in a process that minimizes the inclusion of impurities during synthesis. In addition, by thoroughly eliminating the inclusion of impurities during synthesis and controlling the introduction of a desired additive element X into the positive electrode active material using a transition metal M source, it is possible to obtain a positive electrode active material in which regions with low impurity concentrations and regions in which additive element X is introduced are controlled. Furthermore, the positive electrode active material shown in this embodiment is a material with high crystallinity. Moreover, the positive electrode active material obtained by the method for producing a positive electrode active material according to one embodiment of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0413] (Embodiment 10) In this embodiment, an example of a method for producing a positive electrode active material according to one aspect of the present invention will be described using Figure 12.

[0414] Figure 12 shows an example of a manufacturing method in which step S150, a lithium desorption step, is performed on the positive electrode active material 100 obtained through the steps shown in any one of Embodiments 1 to 9, to reduce or remove lithium. Step S150 is not particularly limited as long as it is a method of desorbing and reducing lithium from the positive electrode active material 100, and lithium can be desorbed by performing a charging reaction or a chemical reaction using a solution. Step S150 can also be described as a step of creating a locally degraded portion in the obtained positive electrode active material 100 by reducing the amount of lithium by approximately half. In this embodiment, a configuration in which the amount of lithium from the positive electrode active material 100 is reduced by approximately half is illustrated, but it is not limited to this. The amount of lithium to be desorbed from the positive electrode active material 100 is 5% to 95%, preferably 30% to 70%, and more preferably 40% to 60%.

[0415] As step S120 in Figure 12, a source of additive element X1 is prepared. As the additive element X1 source, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as the additive element X1 source. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X1 source described above.

[0416] As the additive element X1, one or more of magnesium, fluorine, and calcium can be suitably used. Since the amount of lithium is reduced by approximately half in step S150, it is preferable to use a compound with lithium, such as lithium fluoride or magnesium fluoride, as the source of the additive element X1 to replenish the lithium.

[0417] Step S131 involves mixing the lithium-desorbed positive electrode active material with the X1 source. After mixing, the mixture is recovered in step S132, crushed and sieved as necessary, to obtain the mixture 907 in step S133. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using a rotary-orbit mixer manufactured by Thinky Co., Ltd., for example, it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media.

[0418] Next, in step S134, the mixture 907 recovered in step S132 is heated. The heating temperature is preferably near the melting point of the positive electrode active material from which lithium has been desorbed and the X1 source, preferably between 700°C and 1100°C, more preferably between 800°C and 1000°C, and even more preferably between 800°C and 950°C.

[0419] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0420] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S134 is not essential.

[0421] Furthermore, the crucible used during heating in step S134 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0422] Furthermore, when collecting the material after heating in step S134, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. The mortar itself should also be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0423] Next, in step S135, the calcined material is recovered, crushed and sieved as necessary, to obtain the mixture 908 in step S136.

[0424] Then, in step S140, a source of additive elements X2 is prepared. As the additive element X2 source, one or more can be selected from nickel, cobalt, magnesium, calcium, chlorine, fluorine, aluminum, manganese, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic. In addition to the above elements, bromine and beryllium may also be used as the additive element X2 source. However, since bromine and beryllium are toxic to living organisms, it is preferable to use the additive element X2 source described above.

[0425] As the additive element X2, one or more selected from nickel, titanium, boron, zirconium, and aluminum can be suitably used.

[0426] Step S151 involves mixing mixture 908 with source X2. After mixing, the mixture is collected in step S152, crushed and sieved as necessary to obtain mixture 909 in step S153. Mixing can be done dry or wet. Mixers such as a rotary-orbit mixer, a ball mill, and a bead mill can be used for mixing. When using a rotary-orbit mixer such as the Awatori Rentaro manufactured by Shinky Co., Ltd., for example, it is preferable to set the rotation speed to 2000 rpm and repeat the process for 1.5 minutes three times. When using a ball mill, it is preferable to use zirconia balls as the media.

[0427] Next, in step S154, the mixture 909 is heated. The heating temperature is preferably 700°C or higher and less than 1100°C, more preferably 800°C or higher and 1000°C or lower, and even more preferably 800°C or higher and 950°C or lower.

[0428] The heating time can be, for example, 1 hour to 100 hours, and preferably 2 hours to 20 hours. Heating is preferably carried out in an oxygen-containing atmosphere with low water content, such as oxygen or dry air (for example, with a dew point of -50°C or lower, more preferably -80°C or lower). In this embodiment, heating is carried out in an atmosphere with a dew point of -93°C. Furthermore, heating is preferable in an atmosphere where the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb (parts per billion) or less, as this suppresses the incorporation of impurities into the material.

[0429] Furthermore, for example, when heating at 850°C for 10 hours, it is preferable to raise the temperature at 200°C / h and the flow rate of the dry atmosphere at 10 L / min. After that, the heated material can be cooled to room temperature. For example, it is preferable to set the cooling time from the specified temperature to room temperature to 10 hours or more and 50 hours or less. However, cooling to room temperature in step S154 is not essential.

[0430] Furthermore, the crucible used during heating in step S154 is preferably made of a material that does not allow impurities to enter. In this embodiment, a crucible made of alumina with a purity of 99.9% is used.

[0431] Furthermore, when collecting the material after heating in step S154, it is preferable to transfer it from the crucible to a mortar before collection to prevent impurities from contaminating the material. The mortar itself should also be made of a material that does not allow impurities to enter. Specifically, it is preferable to use a mortar made of alumina with a purity of 90 wt% or higher, preferably 99 wt% or higher.

[0432] Next, in step S155, the calcined material is recovered and crushed to obtain the positive electrode active material 106 in step S176. If necessary, sieving may be performed after crushing.

[0433] As step S176, a positive electrode active material 106 can be prepared by repeatedly adding a metal oxide, specifically aluminum or nickel, to the positive electrode active material 100. In addition, since step S150 involves adding a source of additive element X1 and a source of additive element X2 after approximately halving the amount of lithium from the positive electrode active material 100, lithium is extracted from the positive electrode active material 100, and additive element X1 or additive element X2 can be selectively introduced into the locally degraded portion. Additive element X1 or additive element X2 can be easily introduced into the interior of the particles.

[0434] A positive electrode active material obtained by a method for producing a positive electrode active material according to one aspect of the present invention can increase the capacity of a secondary battery and / or improve the reliability of a secondary battery.

[0435] (Embodiment 11) In this embodiment, a positive electrode active material according to one aspect of the present invention will be described using Figures 13A to 14C.

[0436] Figure 13A shows a cross-sectional view of the positive electrode active material 100. The positive electrode active material 100 has a plurality of primary particles 101. At least some of the plurality of primary particles 101 adhere to form secondary particles 102. There are also primary particles 101 that do not become secondary particles. An enlarged view of the secondary particles 102 is shown in Figure 13B. The positive electrode active material 100 may have voids 105. Note that the shapes of the primary particles 101 and secondary particles 102 shown in Figures 13A and 13B are examples and are not limited thereto.

[0437] In this specification, a primary particle is the smallest solid unit that is recognized as having a clear boundary in a microscopic image such as an SEM image, TEM image, or STEM image. A secondary particle is a particle formed by the sintering, bonding, or aggregation of multiple primary particles. The bonding force acting between the multiple primary particles is irrelevant. It may be a covalent bond, an ionic bond, a hydrophobic interaction, a van der Waals force, or any other intermolecular interaction, and multiple bonding forces may be at work. Furthermore, the term "particle" includes both primary and secondary particles.

[0438] <Contained elements> The positive electrode active material 100 comprises lithium, a transition metal M, oxygen, and an additive element X.

[0439] The positive electrode active material 100 can be described as a composite oxide represented by LiMO2 to which multiple additive elements X have been added. However, the positive electrode active material in one embodiment of the present invention only needs to have the crystal structure of a lithium composite oxide represented by LiMO2, and its composition is not strictly limited to Li:M:O=1:1:2.

[0440] The transition metal M in the positive electrode active material 100 is preferably a metal that can form a layered rock salt type composite oxide belonging to space group R-3m together with lithium. For example, at least one of manganese, cobalt, and nickel can be used. In other words, the transition metal in the positive electrode active material 100 may be cobalt only, nickel only, two types of cobalt and manganese, two types of cobalt and nickel, or three types of cobalt, manganese, and nickel. In other words, the positive electrode active material 100 can have composite oxides containing lithium and a transition metal M, such as lithium cobalt oxide, lithium nickel oxide, lithium cobalt oxide in which part of the cobalt is substituted with manganese, lithium cobalt oxide in which part of the cobalt is substituted with nickel, and nickel-manganese-lithium cobalt oxide.

[0441] In particular, using cobalt as the transition metal M in the positive electrode active material 100 in an amount of 75 atomic% or more, preferably 90 atomic% or more, and more preferably 95 atomic% or more, offers many advantages, such as being relatively easy to synthesize, easy to handle, and having excellent cycle properties.

[0442] On the other hand, if nickel is used as the transition metal M in the positive electrode active material 100 in an amount of 33 atomic percent or more, preferably 60 atomic percent or more, and more preferably 80 atomic percent or more, the raw materials may be cheaper compared to the case where cobalt is abundant, and the charge / discharge capacity per unit weight may increase, which is preferable.

[0443] Furthermore, if the transition metal M contains some nickel along with cobalt, it may suppress the displacement of the layered structure consisting of octahedra of cobalt and oxygen. Therefore, the crystal structure may become more stable, especially in the charged state at high temperatures, which is preferable. This is because nickel can easily diffuse into the interior of lithium cobalt oxide, and while it is present at the cobalt sites during discharge, it can be located at the lithium sites through cation mixing during charging. Nickel present at the lithium sites during charging is thought to function as pillars supporting the layered structure consisting of octahedra of cobalt and oxygen, contributing to the stabilization of the crystal structure.

[0444] Furthermore, the transition metal M does not necessarily have to include manganese, nickel, or cobalt.

[0445] It is preferable to use at least one of the following as the additive element X: magnesium, fluorine, aluminum, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, and arsenic.

[0446] In particular, the positive electrode active material 100 can be made more durable by adding phosphorus, which is preferable as it allows for a safer secondary battery.

[0447] Furthermore, since manganese, titanium, vanadium, and chromium are materials that readily and stably form the tetravalent state, using them as the transition metal M in the positive electrode active material 100 can sometimes enhance their contribution to structural stability.

[0448] These additive elements X may further stabilize the crystal structure of the positive electrode active material 100, as described later. In other words, the positive electrode active material 100 can include lithium cobalt oxide with magnesium and fluorine, lithium nickel cobalt oxide with magnesium and fluorine, lithium cobalt-aluminate with magnesium and fluorine, lithium nickel cobalt-aluminate, lithium nickel cobalt-aluminate with magnesium and fluorine, lithium nickel manganese-cobalt oxide with magnesium and fluorine, etc. In lithium cobalt oxide, the magnesium concentration is preferably 0.1 at% or more and 2 at% or less. In this specification, the additive elements X may be referred to as a mixture, part of the raw materials, impurities, etc.

[0449] Furthermore, it is preferable that the additive element X in the positive electrode active material 100 is added at a concentration that does not significantly alter the crystallinity of the composite oxide represented by LiMO2. For example, it is preferable that the amount is such that it does not exhibit the Jahn-Teller effect.

[0450] Furthermore, the additive element X does not necessarily have to include magnesium, fluorine, aluminum, titanium, zirconium, yttrium, vanadium, iron, chromium, niobium, lanthanum, hafnium, zinc, silicon, sulfur, phosphorus, boron, or arsenic.

[0451] <Elemental distribution> It is preferable that at least one of the additive elements X in the positive electrode active material 100 has a concentration gradient.

[0452] For example, it is preferable that the primary particle 101 has a surface layer 11a and an interior layer 11b, with a higher concentration of the added element X in the surface layer 11a than in the interior layer 11b. Figures 13A and 13B show the concentration of the added element X in the primary particle 101 as a gradient. A darker gradient, i.e., closer to black, means a higher concentration of the added element X, while a lighter gradient, i.e., closer to white, means a lower concentration of the added element X.

[0453] Furthermore, it is preferable that the concentration of the added element X at and near the interface 103 between primary particles is higher than the concentration inside 11b of the primary particle 101. In this specification, the vicinity of the interface 103 refers to the region from the interface 103 to about 10 nm.

[0454] Figure 14A shows an example of the concentration distribution of additive element X between the dashed-dotted line A and B in the positive electrode active material 100 shown in Figure 13B. In Figure 14A, the horizontal axis represents the distance between the dashed-dotted line A and B in Figure 13B, and the vertical axis represents the concentration of additive element X.

[0455] Compared to the primary particles 101, the interface 103 and its vicinity have regions with higher concentrations of the added element X. Note that the shape of the concentration distribution of the added element X is not limited to the shape shown in Figure 14A.

[0456] Furthermore, if there are multiple additive elements X, it is preferable that the peak positions of the concentrations differ depending on the additive element X.

[0457] For example, as shown in Figure 14B, examples of preferred additive elements X that have a concentration gradient increasing from the interior 11b toward the surface include magnesium, fluorine, and titanium.

[0458] Furthermore, for some other additive elements X, it is preferable that the concentration peak in the positive electrode active material 100 is in a region closer to the interior 11b than the region where the additive elements X are distributed as shown in Figure 14B, as shown in Figure 14C. Aluminum is an example of an additive element X for which such a distribution is preferable. The concentration peak may be located in the surface layer or deeper than the surface layer. For example, it is preferable to have the concentration peak in a region between 5 nm and 30 nm from the surface.

[0459] Furthermore, it is preferable that a portion of the added element X, such as magnesium, has a concentration gradient that increases from the interior 11b towards the surface, as shown in Figure 14B, but it is also preferable that it is thinly distributed throughout the primary particle 101. For example, it is preferable that the magnesium concentration in the surface layer 11a, as measured by XPS or the like, is higher than the average magnesium concentration of the entire particle, as measured by ICP-MS or the like.

[0460] Furthermore, in one embodiment of the present invention, when the positive electrode active material 100 contains one or more metals other than cobalt, such as nickel, aluminum, manganese, iron, and chromium, it is preferable that the concentration of the metal in the surface layer of the primary particles 101 is higher than the average concentration of the entire particle. For example, it is preferable that the concentration of elements other than cobalt in the surface layer 11a, as measured by XPS or the like, is higher than the average concentration of the element in the entire particle, as measured by ICP-MS or the like.

[0461] Unlike the interior of the crystal, the surface layer of the particle has broken bonds, and during charging, lithium is released from the surface, making it a region where the lithium concentration tends to be lower than in the interior 11b. Therefore, it is a region that is prone to instability and the crystal structure is easily disrupted. If the concentration of additive element X in the surface layer 11a is high, changes in the crystal structure can be suppressed more effectively. Furthermore, a high concentration of additive element X in the surface layer 11a can also be expected to improve corrosion resistance to hydrofluoric acid produced by the decomposition of the electrolyte.

[0462] Thus, it is preferable that the surface layer 11a of the positive electrode active material 100 in one aspect of the present invention has a different composition from the interior 11b, with a higher concentration of the added element X than the interior 11b. Furthermore, it is preferable that the composition adopts a crystalline structure that is stable at room temperature (25°C). For this reason, the surface layer 11a may have a different crystalline structure from the interior 11b. For example, at least a part of the surface layer 11a of the positive electrode active material 100 in one aspect of the present invention may have a rock salt type crystalline structure. Also, if the surface layer 11a and the interior 11b have different crystalline structures, it is preferable that the orientation of the crystals in the surface layer 11a and the interior 11b is approximately the same.

[0463] However, if the surface layer 11a consists only of additive element X and oxygen, for example, only MgO, or only a solid solution of MgO and CoO(II), then lithium insertion and removal becomes difficult. Therefore, the surface layer 11a must contain at least a transition metal M, and in the discharge state, it must also contain lithium and have a pathway for lithium insertion and removal. Furthermore, it is preferable that the concentration of the transition metal M is higher than that of each additive element X.

[0464] The positive electrode active material 100 in one embodiment of the present invention is not limited to this. It may also contain additive elements X that do not have a concentration gradient.

[0465] Furthermore, it is preferable that the transition metal M, particularly cobalt and nickel, is uniformly dissolved in the entire positive electrode active material 100.

[0466] Furthermore, the positive electrode active material 100 may have a concentration gradient in which a portion of the transition metal M, such as manganese, becomes more concentrated from the interior 11b towards the surface.

[0467] The distribution of additive element X as described above reduces the degradation of the positive electrode active material 100 even after charging and discharging. In other words, it suppresses the degradation of the secondary battery. Furthermore, it makes for a highly safe secondary battery.

[0468] Generally, as a secondary battery undergoes repeated charging and discharging, side reactions can occur in the positive electrode active material, such as the leaching of transition metals M (e.g., cobalt and manganese) into the electrolyte, the desorption of oxygen, and the instability of the crystal structure, which can lead to degradation of the positive electrode active material. This degradation can result in a decrease in the capacity of the secondary battery. In this specification, the chemical and structural changes in the positive electrode active material, such as the leaching of transition metals M into the electrolyte, the desorption of oxygen, and the instability of the crystal structure, may be referred to as degradation of the positive electrode active material. In this specification, the decrease in the capacity of the secondary battery may be referred to as degradation of the secondary battery.

[0469] Metals leached from the positive electrode active material can be reduced and deposited at the negative electrode, potentially interfering with the electrode reaction at the negative electrode. This metal deposition at the negative electrode can lead to degradation, such as a decrease in capacity.

[0470] Due to the insertion and removal of lithium during charging and discharging, the crystal lattice of the positive electrode active material may expand and contract, causing volume changes and distortion of the crystal lattice. Volume changes and distortion of the crystal lattice can cause the positive electrode active material to crack, leading to degradation such as a decrease in capacity. Furthermore, cracking of the positive electrode active material may originate at the interface 103 between primary particles.

[0471] When the inside of a secondary battery becomes hot, oxygen may be released from the positive electrode active material, potentially compromising the safety of the battery. Furthermore, oxygen release can alter the crystal structure of the positive electrode active material, leading to degradation such as a decrease in capacity. Oxygen can also be released from the positive electrode active material due to the insertion and removal of lithium during charging and discharging.

[0472] Therefore, the positive electrode active material 100 has an additive element X or compound (for example, an oxide of additive element X) on its surface layer 11a or interface 103, which is more chemically and structurally stable than the lithium composite oxide represented by LiMO2. This makes the positive electrode active material 100 chemically and structurally stable, and suppresses structural changes, volume changes, and distortion due to charging and discharging. In other words, the crystal structure of the positive electrode active material 100 becomes more stable, and transformation of the crystal structure can be suppressed even after repeated charging and discharging. Furthermore, cracking of the positive electrode active material 100 can be suppressed. In other words, degradation such as capacity reduction can be suppressed, which is preferable. When the charging voltage is high and the amount of lithium present in the positive electrode during charging becomes smaller, the crystal structure becomes unstable and more susceptible to degradation. By using the positive electrode active material 100 according to one aspect of the present invention, the crystal structure can be made more stable, so degradation such as capacity reduction can be suppressed, which is particularly preferable.

[0473] In one aspect of the present invention, the positive electrode active material 100 has a stable crystal structure, which suppresses the elution of the transition metal M from the positive electrode active material. In other words, it can suppress degradation such as a decrease in capacity, which is preferable.

[0474] Furthermore, in one embodiment of the present invention, when the positive electrode active material 100 cracks along the interface 103 between primary particles 101, the surface of the cracked primary particles 101 has a compound of the additive element X. In other words, side reactions can be suppressed even in the cracked positive electrode active material 100, and the degradation of the positive electrode active material 100 can be reduced. In other words, the degradation of the secondary battery can be suppressed.

[0475] <Analysis method> ≪Particle size≫ In one embodiment of the present invention, if the particle size of the positive electrode active material 100 is too large, problems arise such as difficulty in lithium diffusion and excessive roughness of the surface of the active material layer when coated onto the current collector. On the other hand, if the particle size is too small, problems arise such as difficulty in supporting the active material layer when coating onto the current collector and excessive reaction with the electrolyte.

[0476] Therefore, the positive electrode active material 100 having primary particles 101 and secondary particles 102 preferably has an average particle diameter (D50: also called median diameter) measured by a laser diffraction / scattering particle size analyzer of 1 μm to 100 μm, more preferably 2 μm to 40 μm, and even more preferably 5 μm to 30 μm. Or preferably 1 μm to 40 μm. Or preferably 1 μm to 30 μm. Or preferably 2 μm to 100 μm. Or preferably 2 μm to 30 μm. Or preferably 5 μm to 100 μm. Or preferably 5 μm to 40 μm.

[0477] Furthermore, a mixture of positive electrode active materials 100 having two or more different particle sizes may be used. In other words, a positive electrode active material 100 that produces multiple peaks when the particle size distribution is measured by laser diffraction / scattering may be used. In this case, it is preferable to use a mixing ratio that increases the powder packing density, as this can improve the capacity per unit volume of the secondary battery.

[0478] The size of the primary particles 101 in the positive electrode active material 100 can be determined, for example, from the full width at half maximum of the XRD pattern of the positive electrode active material 100. The primary particles 101 are preferably between 50 nm and 200 nm in size.

[0479] ≪XPS≫ X-ray photoelectron spectroscopy (XPS) allows for analysis of regions from the surface to a depth of 2 nm to 8 nm (usually around 5 nm), enabling quantitative analysis of the concentration of each element in approximately half of the surface layer 11a. Furthermore, narrow-scan analysis allows for analysis of the bonding state of elements. The quantitative accuracy of XPS is generally around ±1 atomic percent, and the detection limit is approximately 1 atomic percent, although this varies depending on the element.

[0480] When XPS analysis is performed on the positive electrode active material 100 according to one embodiment of the present invention, the number of atoms of the additive element X is preferably 1.6 to 6.0 times the number of atoms of the transition metal M, and more preferably 1.8 to less than 4.0 times. When the additive element X is magnesium and the transition metal M is cobalt, the number of atoms of magnesium is preferably 1.6 to 6.0 times the number of atoms of cobalt, and more preferably 1.8 to less than 4.0 times. Furthermore, the number of atoms of halogens such as fluorine is preferably 0.2 to 6.0 times the number of atoms of the transition metal M, and more preferably 1.2 to 4.0 times.

[0481] For XPS analysis, monochromatic aluminum can be used as the X-ray source, for example. The output can be set to, for example, 1486.6 eV. The extraction angle can be set to, for example, 45°. Under these measurement conditions, as mentioned above, it is possible to analyze a region from the surface to a depth of 2 nm to 8 nm (usually around 5 nm).

[0482] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between fluorine and other elements is preferably 682 eV or more and less than 685 eV, and more preferably around 684.3 eV. This value is different from both the bond energy of lithium fluoride, which is 685 eV, and the bond energy of magnesium fluoride, which is 686 eV. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains fluorine, it is preferable that the bond is with something other than lithium fluoride and magnesium fluoride.

[0483] Furthermore, when the positive electrode active material 100 according to one embodiment of the present invention is subjected to XPS analysis, the peak indicating the bond energy between magnesium and other elements is preferably 1302 eV or more and less than 1304 eV, and more preferably around 1303 eV. This value is different from the bond energy of magnesium fluoride, which is 1305 eV, and is close to the bond energy of magnesium oxide. In other words, when the positive electrode active material 100 according to one embodiment of the present invention contains magnesium, it is preferable that the bond is with an element other than magnesium fluoride.

[0484] It is preferable that the concentration of additive element X, such as magnesium, aluminum, and titanium, which is preferably abundant in the surface layer 11a, is higher when measured by XPS or the like than when measured by ICP-MS (inductively coupled plasma mass spectrometry) or GD-MS (glow discharge mass spectrometry).

[0485] When magnesium, aluminum, titanium, etc., have their cross-sections exposed by processing and the cross-sections are analyzed using TEM-EDX, it is preferable that the concentration in the surface layer 11a is higher than the concentration in the interior 11b. For example, in TEM-EDX analysis, it is preferable that the magnesium concentration is attenuated to 60% or less of the peak at a depth of 1 nm from the peak top. It is also preferable that it is attenuated to 30% or less of the peak at a depth of 2 nm from the peak top. Processing can be carried out, for example, using a FIB (Focused Ion Beam) apparatus.

[0486] In XPS (X-ray photoelectron spectroscopy) analysis, the number of magnesium atoms is preferably 0.4 to 1.5 times the number of cobalt atoms. On the other hand, the ratio of magnesium atoms (Mg / Co) determined by ICP-MS analysis is preferably 0.001 to 0.06.

[0487] On the other hand, it is preferable that the nickel contained in the transition metal M is not concentrated in the surface layer 11a, but is distributed throughout the entire positive electrode active material 100.

[0488] ≪EPMA≫ EPMA (Electron Probe Microanalysis) allows for the quantitative determination of elements. Surface analysis allows for the analysis of the distribution of each element.

[0489] EPMA analyzes the region from the surface to a depth of approximately 1 μm. Therefore, the concentrations of each element may differ from those measured using other analytical methods. For example, when surface analysis is performed on cathode active material 100, the concentration of additive element X present in the surface layer may be lower than that obtained with XPS. Conversely, the concentration of additive element X present in the surface layer may be higher than that obtained with ICP-MS or the value of the raw material composition during the production of the cathode active material.

[0490] When an EPMA surface analysis is performed on a cross-section of the positive electrode active material 100 according to one embodiment of the present invention, it is preferable that the concentration of the added element X has a concentration gradient that increases from the interior to the surface. More specifically, as shown in Figure 14B, it is preferable that magnesium, fluorine, and titanium have a concentration gradient that increases from the interior to the surface. Also, as shown in Figure 14C, it is preferable that aluminum has a concentration peak in a region deeper than the concentration peaks of the above elements. The aluminum concentration peak may be located in the surface layer or deeper than the surface layer.

[0491] It should be noted that the surface of the positive electrode active material in one aspect of the present invention does not contain carbon dioxide, hydroxyl groups, etc., that have been chemically adsorbed after the positive electrode active material has been manufactured. Furthermore, it does not contain electrolyte, binder, conductive agent, or compounds derived therefrom that have adhered to the surface of the positive electrode active material. Therefore, when quantifying the elements contained in the positive electrode active material, corrections may be made to exclude carbon, hydrogen, excess oxygen, excess fluorine, etc., which can be detected by surface analysis such as XPS and EPMA. For example, with XPS, it is possible to separate the types of bonds through analysis, and corrections may be made to exclude CF bonds derived from the binder.

[0492] Furthermore, before subjecting the sample to various analyses, the positive electrode active material and positive electrode active material layer may be washed to remove electrolyte, binder, conductive agent, or compounds derived therefrom that adhere to the surface of the positive electrode active material. In this case, lithium may dissolve into the solvent used for washing, but even in that case, the transition metal M and additive element X are unlikely to dissolve, so it will not affect the atomic ratio of the transition metal M and additive element X.

[0493] ≪Surface roughness and specific surface area≫ In one embodiment of the present invention, the primary particles 101 of the positive electrode active material 100 preferably have a smooth surface with few irregularities. A smooth surface with few irregularities is one factor indicating that the distribution of the added element X in the surface layer 11a is good.

[0494] The smooth surface of the primary particle 101 with few irregularities can be determined, for example, from a cross-sectional SEM image or cross-sectional TEM image of the positive electrode active material 100.

[0495] For example, the surface smoothness of the positive electrode active material 100 can be quantified from a cross-sectional SEM image, as shown below.

[0496] First, the positive electrode active material 100 is processed using FIB or the like to expose its cross-section. At this time, it is preferable to cover the positive electrode active material 100 with a protective film, protective agent, etc. Next, an SEM image of the interface between the protective film, etc. and the positive electrode active material 100 is taken. Noise processing is performed on the SEM image using image processing software. For example, Gaussian blurring (σ=2) is performed, followed by binarization. Interface extraction is then performed using image processing software. Furthermore, the interface line between the protective film, etc. and the positive electrode active material 100 is selected using an automatic selection tool, etc., and the data is extracted into spreadsheet software, etc. Using the functions of the spreadsheet software, correction is performed from the regression curve (quadratic regression), and parameters for roughness calculation are obtained from the slope-corrected data, and the root mean square surface roughness (RMS) is calculated by calculating the standard deviation. In addition, this surface roughness is the surface roughness of the positive electrode active material at least at 400 nm from the outer circumference of the particle.

[0497] In this embodiment, the surface roughness (RMS) of the primary particles 101 of the positive electrode active material 100 is preferably less than 3 nm, more preferably less than 1 nm, and more preferably less than 0.5 nm.

[0498] The image processing software used for noise reduction, interface extraction, etc., is not particularly limited.

[0499] The contents described in this embodiment can be used in combination with the contents described in other embodiments.

[0500] (Embodiment 12) This embodiment describes a lithium-ion secondary battery containing a positive electrode active material according to one aspect of the present invention. The secondary battery comprises at least an outer casing, a current collector, an active material (positive electrode active material or negative electrode active material), a conductive agent, and a binder. It also has an electrolyte in which a lithium salt or the like is dissolved. In the case of a secondary battery using an electrolyte, a positive electrode, a negative electrode, and a separator between the positive and negative electrodes are provided.

[0501] [Positive electrode] The positive electrode comprises a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer preferably contains the positive electrode active material shown in Embodiments 1 to 11, and may further contain a binder, a conductive agent, etc.

[0502] Figure 15 shows an example of a schematic diagram of a cross-section of the positive electrode.

[0503] The current collector 550 is a metal foil, and the positive electrode is formed by applying a slurry to the metal foil and drying it. After drying, pressing may be applied further. The positive electrode is formed by creating an active material layer on the current collector 550.

[0504] A slurry is a liquid material used to form an active material layer on a current collector 550, and it contains at least an active material, a binder, and a solvent, preferably further mixed with a conductive agent. The slurry is sometimes called an electrode slurry or an active material slurry, and when forming a positive electrode active material layer, a positive electrode slurry is used, and when forming a negative electrode active material layer, it is sometimes called a negative electrode slurry.

[0505] Conductive agents, also called conductivity imparters or conductivity enhancers, are typically made of carbon. By attaching a conductive agent between multiple active materials, the materials become electrically connected to each other, increasing conductivity. Note that "attachment" does not only refer to physical contact between the active materials and the conductive agent, but also includes cases where covalent bonds are formed, bonds are formed by van der Waals forces, the conductive agent covers a portion of the surface of the active materials, the conductive agent fits into surface irregularities of the active materials, or where electrical connections are formed even without physical contact.

[0506] A typical example of a carbon material used as a conductive agent is carbon black (furnace black, acetylene black, graphite, etc.).

[0507] Figure 15 shows acetylene black 553, graphene and graphene compounds 554, and carbon nanotubes 555 as conductive materials. Note that the positive electrode active material 100 shown in Embodiments 1 to 10 corresponds to the active material 561 in Figure 15.

[0508] For the positive electrode of a secondary battery, a binder (resin) is mixed with the active material to fix the current collector 550, such as metal foil, to it. The binder is also called a binding agent. The binder is a polymer material, and if too much binder is included, the proportion of active material in the positive electrode decreases, reducing the discharge capacity of the secondary battery. Therefore, the amount of binder mixed in is kept to a minimum.

[0509] Graphene is a carbon material that possesses remarkable electrical, mechanical, and chemical properties, making it promising for applications in various fields, including field-effect transistors and solar cells.

[0510] In this specification, the term "graphene compound" includes multilayer graphene, multigraphene, graphene oxide, multilayer graphene oxide, multigraphene oxide, reduced graphene oxide, reduced multilayer graphene oxide, reduced multigraphene oxide, etc. A graphene compound is defined as a material having carbon atoms, having a plate-like or sheet-like shape, and possessing a two-dimensional structure formed by six-membered carbon rings. It is also preferable that it has a bent shape. It may also be called a carbon sheet. It is also preferable that it has functional groups. Furthermore, the graphene compound may be rolled up to resemble carbon nanofibers.

[0511] Graphene and graphene compounds may possess excellent electrical properties, such as high conductivity, and excellent physical properties, such as high flexibility and high mechanical strength. Furthermore, graphene and graphene compounds may have a sheet-like shape. Graphene and graphene compounds may have curved surfaces, enabling surface contact with low contact resistance. They may also exhibit very high conductivity even when thin, allowing for efficient formation of conductive paths within the active material layer with a small amount. Therefore, using graphene and graphene compounds as conductive agents can increase the contact area between the active material and the conductive agent. It is preferable that the graphene and graphene compounds overlap at least a portion of the secondary particles 102 in the positive electrode active material 100. Alternatively, it is preferable that the shape of the graphene and graphene compounds matches at least a portion of the shape of the secondary particles 102. The shape of the secondary particles 102 refers, for example, to the irregularities of a single secondary particle 102, or the irregularities formed by multiple secondary particles 102. It is also preferable that the graphene compound surrounds at least a portion of the secondary particles 102. Furthermore, the graphene compound may have holes.

[0512] In Figure 15, the areas not filled with the active material 561, graphene and graphene compounds 554, acetylene black 553, and carbon nanotubes 555 represent voids or binders. While voids are necessary for electrolyte permeation, too many voids reduce electrode density, too few voids prevent electrolyte permeation, and if voids remain after the secondary battery is formed, the energy density decreases.

[0513] Furthermore, the conductive agent does not necessarily have to contain all of acetylene black 553, graphene and graphene compounds 554, and carbon nanotubes 555. It is sufficient to have at least one conductive agent.

[0514] By using the positive electrode active material 100 shown in Embodiments 1 to 11 as the positive electrode, a secondary battery with high energy density and good output characteristics can be obtained.

[0515] A secondary battery can be manufactured by using the positive electrode shown in Figure 15, placing a separator on top of the positive electrode, and a negative electrode on top of the separator, then placing the resulting laminate in a container (such as an outer casing or metal can), and filling the container with electrolyte.

[0516] Furthermore, the above configuration is an example of a secondary battery using an electrolyte, but it is not particularly limited.

[0517] For example, a semi-solid-state battery or a fully solid-state battery can be manufactured using the positive electrode active material 100 shown in Embodiments 1 to 11.

[0518] In this specification, a semi-solid battery refers to a battery having a semi-solid material in at least one of its components: the electrolyte layer, the positive electrode, or the negative electrode. Here, "semi-solid" does not mean that the solid material makes up 50% of the battery. A semi-solid material possesses solid properties, such as small volume change, while also having some liquid-like properties, such as flexibility. As long as these properties are met, the battery may consist of a single material or multiple materials. For example, a liquid material may be impregnated into a porous solid material.

[0519] In the present specification and the like, a polymer electrolyte secondary battery refers to a secondary battery having a polymer in the electrolyte layer between the positive electrode and the negative electrode. The polymer electrolyte secondary battery includes a dry (or solid) polymer electrolyte battery and a polymer gel electrolyte battery. The polymer electrolyte secondary battery may also be referred to as a semi-solid battery.

[0520] When a semi-solid battery is fabricated using the positive electrode active material hundred as shown in Embodiments 1 to 11, the semi-solid battery becomes a secondary battery with a large charge-discharge capacity. Also, a semi-solid battery with a high charge-discharge voltage can be obtained. Alternatively, a semi-solid battery with high safety or reliability can be realized.

[0521] Also, the positive electrode active material described in any one of Embodiments 1 to 11 may be mixed with another positive electrode active material and used.

[0522] Examples of other positive electrode active materials include composite oxides having an olivine-type crystal structure, a layered rock salt-type crystal structure, or a spinel-type crystal structure. For example, compounds such as LiFePO4, LiFeO2, LiNiO2, LiMn2O4, V2O5, Cr2O5, and MnO2 can be mentioned.

[0523] Also, as another positive electrode active material, a lithium-containing material having a spinel-type crystal structure containing manganese such as LiMn2O4 is preferably mixed with lithium nickelate (LiNiO2 or LiNi ,

[0523] ,

[0524] , , , , c , d , a , b , 1-x , x M x O2 (0 < x < 1) (M = Co, Al, etc.)). By adopting such a configuration, the characteristics of the secondary battery can be improved.

[0524] Also, as another positive electrode active material, a composition formula Li a Mn b M c O dA lithium manganese composite oxide can be used, which can be represented as follows: Here, element M is preferably a metallic element selected from lithium and manganese, or silicon or phosphorus, and more preferably nickel. When measuring the entire particle of lithium manganese composite oxide, <a / (b+c)<2、かつc>it is preferable that the discharge is 0 0 and 0.26 ≤ (b+c) / d < 0.5. The composition of metals, silicon, phosphorus, etc., of the entire particle of lithium manganese composite oxide can be measured, for example, using ICP-MS (inductively coupled plasma mass spectrometer). The oxygen composition of the entire particle of lithium manganese composite oxide can be measured, for example, using EDX (energy dispersive X-ray spectrometry). It can also be determined by using valence evaluation of molten gas analysis and XAFS (X-ray absorption fine structure) analysis in combination with ICPMS analysis. Lithium manganese composite oxide refers to an oxide containing at least lithium and manganese, and may also contain at least one element selected from the group consisting of chromium, cobalt, aluminum, nickel, iron, magnesium, molybdenum, zinc, indium, gallium, copper, titanium, niobium, silicon, and phosphorus.

[0525] <Binder> As a binder, it is preferable to use rubber materials such as styrene-butadiene rubber (SBR), styrene-isoprene-styrene rubber, acrylonitrile-butadiene rubber, butadiene rubber, or ethylene-propylene-diene copolymer. Fluororubber can also be used as a binder.

[0526] Furthermore, it is preferable to use a water-soluble polymer as the binder. Examples of water-soluble polymers include polysaccharides. Examples of polysaccharides include cellulose derivatives such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, diacetylcellulose, and regenerated cellulose, as well as starch. It is even more preferable to use these water-soluble polymers in combination with the aforementioned rubber material. ​

[0527] Alternatively, it is preferable to use materials such as polystyrene, methyl polyacrylate, polymethyl methacrylate (PMMA), sodium polyacrylate, polyvinyl alcohol (PVA), polyethylene oxide (PEO), polypropylene oxide, polyimide, polyvinyl chloride, polytetrafluoroethylene, polyethylene, polypropylene, polyisobutylene, polyethylene terephthalate, nylon, polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), ethylene propylene diene polymer, polyvinyl acetate, or nitrocellulose as the binder.

[0528] You may use a combination of several of the binders mentioned above.

[0529] For example, a material with particularly excellent viscosity-modifying properties may be used in combination with other materials. For instance, rubber materials have excellent adhesive and elastic properties, but their viscosity can be difficult to adjust when mixed with a solvent. In such cases, it is preferable to mix them with a material with particularly excellent viscosity-modifying properties. As a material with particularly excellent viscosity-modifying properties, a water-soluble polymer may be used. As a water-soluble polymer with particularly excellent viscosity-modifying properties, the aforementioned polysaccharides, such as carboxymethylcellulose (CMC), methylcellulose, ethylcellulose, hydroxypropylcellulose, and diacetylcellulose, cellulose derivatives such as regenerated cellulose, or starch can be used.

[0530] Furthermore, cellulose derivatives such as carboxymethylcellulose can be made more effective as viscosity modifiers by increasing their solubility, for example, by using salts such as sodium or ammonium salts of carboxymethylcellulose. Increased solubility also improves the dispersibility of the active material and other components when preparing electrode slurries. In this specification, cellulose and cellulose derivatives used as electrode binders include their salts.

[0531] Water-soluble polymers stabilize viscosity by dissolving in water and can stably disperse other materials, such as styrene-butadiene rubber, which are combined as active materials or binders, in aqueous solutions. Furthermore, because they possess functional groups, they are expected to be easily and stably adsorbed onto the surface of the active material. In addition, cellulose derivatives such as carboxymethylcellulose often contain functional groups such as hydroxyl groups or carboxyl groups, and because they have functional groups, the polymers interact with each other and are expected to broadly cover the surface of the active material.

[0532] When a binder covers or is in contact with the surface of the active material, it is expected to act as a passivation film, suppressing the decomposition of the electrolyte. Here, a passivation film is a film that does not conduct electricity, or has extremely low electrical conductivity. For example, when a passivation film is formed on the surface of the active material, the decomposition of the electrolyte can be suppressed at the battery reaction potential. Furthermore, it is even more desirable for the passivation film to suppress electrical conductivity while still allowing lithium ions to conduct.

[0533] <Positive electrode current collector> As the current collector, highly conductive materials such as stainless steel, gold, platinum, aluminum, titanium, and alloys thereof can be used. Furthermore, it is preferable that the material used for the positive electrode current collector does not dissolve at the positive electrode potential. Aluminum alloys with added elements that improve heat resistance, such as silicon, titanium, neodymium, scandium, and molybdenum, can also be used. Alternatively, it may be formed from a metallic element that reacts with silicon to form a silicide. Examples of metallic elements that react with silicon to form a silicide include zirconium, titanium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, and nickel. The current collector can be in various shapes, such as foil, plate, sheet, mesh, perforated metal, or expanded metal. The current collector should preferably have a thickness of 5 μm to 30 μm.

[0534] [Negative electrode] The negative electrode comprises a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer may also contain a negative electrode active material, a conductive agent, and a binder.

[0535] <Negative electrode active material> As the negative electrode active material, for example, alloy-based materials, carbon-based materials, and mixtures thereof can be used.

[0536] As the negative electrode active material, elements capable of undergoing charge-discharge reactions through alloying and dealloying reactions with lithium can be used. For example, materials containing at least one of silicon, tin, gallium, aluminum, germanium, lead, antimony, bismuth, silver, zinc, cadmium, indium, etc., can be used. Such elements have a larger capacity than carbon, and silicon in particular has a high theoretical capacity of 4200 mAh / g. For this reason, it is preferable to use silicon as the negative electrode active material. Compounds containing these elements may also be used. Examples include SiO, Mg2Si, Mg2Ge, SnO, SnO2, Mg2Sn, SnS2, V2Sn3, FeSn2, CoSn2, Ni3Sn2, Cu6Sn5, Ag3Sn, Ag3Sb, Ni2MnSb, CeSb3, LaSn3, La3Co2Sn7, CoSb3, InSb, SbSn, etc. In this context, elements capable of undergoing charge-discharge reactions through alloying and de-alloying reactions with lithium, and compounds containing such elements, are sometimes referred to as alloying materials.

[0537] In this specification, SiO refers to silicon monoxide, for example. Alternatively, SiO refers to SiO x It can also be expressed as follows. Here, x is preferably 1 or a value in its immediate vicinity. For example, x is preferably between 0.2 and 1.5, and preferably between 0.3 and 1.2.

[0538] Suitable carbon-based materials include graphite, easily graphitizable carbon (soft carbon), difficult-to-graphitize carbon (hard carbon), carbon nanotubes, graphene, and carbon black.

[0539] Examples of graphite include artificial graphite and natural graphite. Examples of artificial graphite include mesocarbon microbeads (MCMB), coke-based artificial graphite, pitch-based artificial graphite, etc. Here, spherical graphite having a spherical shape can be used as the artificial graphite. For example, MCMB may have a spherical shape, which is preferable. Also, MCMB can relatively easily reduce its surface area, which may be preferable. Examples of natural graphite include flake graphite, spheroidized natural graphite, etc.

[0540] Graphite exhibits a potential as low as that of lithium metal (0.05 V or more and 0.3 V or less vs.Li / Li) when lithium ions are inserted into graphite (when a lithium-graphite intercalation compound is formed). + ) As a result, a lithium-ion secondary battery using graphite can exhibit a high operating voltage. Furthermore, graphite has advantages such as a relatively high capacity per unit volume, relatively small volume expansion, low cost, and high safety compared to lithium metal, and thus is preferable.

[0541] Also, as the negative electrode active material, oxides such as titanium dioxide (TiO2), lithium titanate (Li4Ti5O 12 ), lithium-graphite intercalation compound (Li x C6), niobium pentoxide (Nb2O5), tungsten oxide (WO2), molybdenum oxide (MoO2), etc. can be used.

[0542] Also, as the negative electrode active material, Li 3-x [[ID=2,0]]M x N (M = Co, Ni, Cu) having a Li3N-type structure, which is a complex nitride of lithium and a transition metal, can be used. For example, Li 2.6 Co 0.4 N3 exhibits a large charge-discharge capacity (900 mAh / g, 1890 mAh / cm 3 ) and is preferable.

[0543] Using a lithium-transition metal complex nitride is preferable because it contains lithium ions in the negative electrode active material, allowing it to be combined with lithium-ion-free materials such as V2O5 and Cr3O8 as the positive electrode active material. Even when using a lithium-ion-containing material as the positive electrode active material, the lithium-transition metal complex nitride can be used as the negative electrode active material by pre-desorbing the lithium ions contained in the positive electrode active material.

[0544] Furthermore, materials that undergo a conversion reaction can also be used as the negative electrode active material. For example, transition metal oxides that do not form alloys with lithium, such as cobalt oxide (CoO), nickel oxide (NiO), and iron oxide (FeO), may be used as the negative electrode active material. Other materials that undergo a conversion reaction include oxides such as Fe2O3, CuO, Cu2O, RuO2, Cr2O3, and CoS 0.89 This can also occur with sulfides such as NiS and CuS, nitrides such as Zn3N2, Cu3N, and Ge3N4, phosphides such as NiP2, FeP2, and CoP3, and fluorides such as FeF3 and BiF3.

[0545] The conductive agent and binder that the negative electrode active material layer can have can be the same materials as the conductive agent and binder that the positive electrode active material layer can have.

[0546] <Negative electrode current collector> In addition to the same materials as the positive electrode current collector, copper and other materials can also be used for the negative electrode current collector. It is preferable to use a material for the negative electrode current collector that does not alloy with carrier ions such as lithium.

[0547] [Separator] A separator is placed between the positive and negative electrodes. The separator can be made from materials such as cellulose fibers including paper, nonwoven fabrics, glass fibers, ceramics, or synthetic fibers using nylon (polyamide), vinylon (polyvinyl alcohol-based fiber), polyester, acrylic, polyolefin, or polyurethane. It is preferable that the separator be processed into a bag shape and positioned to enclose either the positive or negative electrode.

[0548] The separator may have a multilayer structure. For example, an organic material film such as polypropylene or polyethylene can be coated with a ceramic material, a fluorine material, a polyamide material, or a mixture thereof. Examples of ceramic materials include aluminum oxide particles and silicon oxide particles. Examples of fluorine materials include PVDF and polytetrafluoroethylene. Examples of polyamide materials include nylon and aramid (meta-aramid, para-aramid).

[0549] Coating with ceramic materials improves oxidation resistance, suppressing separator degradation during high-voltage charging and discharging, and thus improving the reliability of secondary batteries. Coating with fluorine-based materials improves adhesion between the separator and electrodes, thereby improving output characteristics. Coating with polyamide materials, particularly aramid, improves heat resistance, thus enhancing the safety of secondary batteries.

[0550] For example, a polypropylene film may be coated on both sides with a mixture of aluminum oxide and aramid. Alternatively, the side of the polypropylene film in contact with the positive electrode may be coated with a mixture of aluminum oxide and aramid, and the side in contact with the negative electrode may be coated with a fluorine-based material.

[0551] By using a multi-layered separator, the safety of the secondary battery can be maintained even if the overall thickness of the separator is thin, thus increasing the capacity per unit volume of the secondary battery.

[0552] [Electrolyte] The electrolyte contains a solvent and an electrolyte. The solvent for the electrolyte is preferably an aprotic organic solvent, such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, chloroethylene carbonate, vinylene carbonate, γ-butyrolactone, γ-valerolactone, dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl formate, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, 1,3-dioxane, 1,4-dioxane, dimethoxyethane (DME), dimethyl sulfoxide, diethyl ether, methyl diglyme, acetonitrile, benzonitrile, tetrahydrofuran, sulfolane, sultone, etc., or two or more of these can be used in any combination and ratio.

[0553] Furthermore, by using one or more flame-retardant and non-volatile ionic liquids (room-temperature molten salts) as the solvent for the electrolyte, it is possible to prevent the energy storage device from rupturing or catching fire even if the internal temperature rises due to an internal short circuit or overcharging. Ionic liquids consist of cations and anions, and include organic cations and anions. Examples of organic cations used in the electrolyte include aliphatic onium cations such as quaternary ammonium cations, tertiary sulfonium cations, and quaternary phosphonium cations, as well as aromatic cations such as imidazolium cations and pyridinium cations. Examples of anions used in the electrolyte include monovalent amide anions, monovalent methide anions, fluorosulfonic acid anions, perfluoroalkyl sulfonate anions, tetrafluoroborate anions, perfluoroalkyl borate anions, hexafluorophosphate anions, or perfluoroalkyl phosphate anions.

[0554] Furthermore, examples of electrolytes to be dissolved in the above solvent include LiPF6, LiClO4, LiAsF6, LiBF4, LiAlCl4, LiSCN, LiBr, LiI, Li2SO4, and Li2B. 10 Cl 10 Li2B12 Cl 12 Lithium salts such as LiCF3SO3, LiC4F9SO3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiN(CF3SO2)2, LiN(C4F9SO2)(CF3SO2), LiN(C2F5SO2)2, and lithium bis(oxalate) borate (Li(C2O4)2, LiBOB) can be used individually or in any combination and ratio of two or more of these salts.

[0555] It is preferable to use a highly purified electrolyte in which particulate matter or elements other than the constituent elements of the electrolyte (hereinafter simply referred to as "impurities") are present in small amounts. Specifically, it is preferable that the weight ratio of impurities to the electrolyte be 1% or less, preferably 0.1% or less, and more preferably 0.01% or less.

[0556] Furthermore, additives such as vinylene carbonate, propanesultone (PS), tert-butylbenzene (TBB), fluoroethylene carbonate (FEC), lithium bis(oxalate)borate (LiBOB), and dinitrile compounds such as succinonitrile and adiponitrile may be added to the electrolyte. The concentration of the additive should be, for example, 0.1 wt% to 5 wt% relative to the total solvent.

[0557] Alternatively, a polymer gel electrolyte, obtained by swelling a polymer with an electrolyte solution, may be used.

[0558] Using polymer gel electrolytes enhances safety against leakage and other issues. Furthermore, it enables the secondary battery to be made thinner and lighter.

[0559] As the polymer to be gelled, silicone gels, acrylic gels, acrylonitrile gels, polyethylene oxide gels, polypropylene oxide gels, fluorine-based polymer gels, etc., can be used. For example, polymers having a polyalkylene oxide structure such as polyethylene oxide (PEO), PVDF, polyacrylonitrile, and copolymers containing them can be used. For example, PVDF-HFP, a copolymer of PVDF and hexafluoropropylene (HFP), can be used. Furthermore, the formed polymer may have a porous structure.

[0560] Furthermore, instead of an electrolyte, a solid electrolyte containing inorganic materials such as sulfides or oxides, or a solid electrolyte containing polymeric materials such as PEO (polyethylene oxide), can be used. When a solid electrolyte is used, the installation of separators or spacers becomes unnecessary. In addition, since the entire battery can be solidified, the risk of leakage is eliminated, dramatically improving safety.

[0561] Therefore, the positive electrode active material 100 obtained in Embodiments 1 to 11 can also be applied to all-solid-state batteries. By applying the positive electrode slurry or electrode to an all-solid-state battery, an all-solid-state battery with high safety and good characteristics can be obtained.

[0562] [Exterior] The outer casing of a secondary battery can be made of a metal material such as aluminum or a resin material. Alternatively, a film-like outer casing can be used. As a film, for example, a three-layer film can be used, in which a highly flexible metal thin film such as aluminum, stainless steel, copper, or nickel is provided on a film made of a material such as polyethylene, polypropylene, polycarbonate, ionomer, or polyamide, and an insulating synthetic resin film such as a polyamide resin or polyester resin is provided on the metal thin film as the outer surface of the outer casing.

[0563] The contents described in this embodiment can be combined with the contents described in other embodiments.

[0564] (Embodiment 13) This embodiment describes examples of multiple shapes of secondary batteries having a positive or negative electrode, manufactured by the manufacturing method described in the previous embodiment.

[0565] [Coin-type rechargeable battery] An example of a coin-type rechargeable battery is described below. Figure 16A is an exploded perspective view of a coin-type (single-layer flat type) rechargeable battery, Figure 16B is an external view, and Figure 16C is a cross-sectional view thereof. Coin-type rechargeable batteries are mainly used in small electronic devices. In this specification, the term "coin-type battery" includes button-type batteries.

[0566] Figure 16A is a schematic diagram to show the overlapping (upper and lower relationships and positional relationships) of the components for clarity. Therefore, Figures 16A and 16B are not perfectly identical corresponding diagrams.

[0567] In Figure 16A, the positive electrode 304, separator 310, negative electrode 307, spacer 322, and washer 312 are stacked. These are sealed with the negative electrode can 302 and the positive electrode can 301. Note that the gasket for sealing is not shown in Figure 16A. The spacer 322 and washer 312 are used to protect the inside or fix their position within the can when the positive electrode can 301 and the negative electrode can 302 are crimped together. The spacer 322 and washer 312 are made of stainless steel or insulating material.

[0568] The positive electrode 304 is a laminated structure in which a positive electrode active material layer 306 is formed on a positive electrode current collector 305.

[0569] To prevent a short circuit between the positive and negative electrodes, a separator 310 and a ring-shaped insulator 313 are arranged to cover the sides and top surfaces of the positive electrode 304, respectively. The separator 310 has a larger planar area than the positive electrode 304.

[0570] Figure 16B is a perspective view of the completed coin-type rechargeable battery.

[0571] The coin-type secondary battery 300 has a positive electrode casing 301, which also serves as the positive electrode terminal, and a negative electrode casing 302, which also serves as the negative electrode terminal, insulated and sealed by a gasket 303 made of polypropylene or the like. The positive electrode 304 is formed by a positive electrode current collector 305 and a positive electrode active material layer 306 provided in contact with it. The negative electrode 307 is formed by a negative electrode current collector 308 and a negative electrode active material layer 309 provided in contact with it. Furthermore, the negative electrode 307 is not limited to a laminated structure, and lithium metal foil or a lithium-aluminum alloy foil may be used.

[0572] Furthermore, for the positive electrode 304 and negative electrode 307 used in the coin-type secondary battery 300, the active material layer only needs to be formed on one side.

[0573] The positive electrode can 301 and the negative electrode can 302 can be made of metals such as nickel, aluminum, or titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat them with nickel and aluminum, etc., to prevent corrosion by the electrolyte. The positive electrode can 301 is electrically connected to the positive electrode 304, and the negative electrode can 302 is electrically connected to the negative electrode 307.

[0574] The negative electrode 307, positive electrode 304, and separator 310 are immersed in an electrolyte solution, and as shown in Figure 16C, the positive electrode 304, separator 310, negative electrode 307, and negative electrode 302 are stacked in this order with the positive electrode 301 at the bottom, and the positive electrode 301 and negative electrode 302 are crimped together via a gasket 303 to manufacture a coin-type secondary battery 300.

[0575] By using a rechargeable battery, a coin-type rechargeable battery 300 can be made with high capacity, high charge / discharge capacity, and excellent cycle characteristics. Furthermore, if a rechargeable battery is used between the negative electrode 307 and the positive electrode 304, the separator 310 can be omitted.

[0576] [Cylindrical rechargeable battery] An example of a cylindrical secondary battery will be explained with reference to Figure 17A. As shown in Figure 17A, the cylindrical secondary battery 616 has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap 601 and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0577] Figure 17B is a schematic diagram showing a cross-section of a cylindrical secondary battery. The cylindrical secondary battery shown in Figure 17B has a positive electrode cap (battery cover) 601 on the top surface and a battery casing (outer casing) 602 on the sides and bottom. The positive electrode cap and the battery casing (outer casing) 602 are insulated from each other by a gasket (insulating packing) 610.

[0578] Inside the hollow cylindrical battery casing 602, a battery element is provided, in which a strip-shaped positive electrode 604 and a negative electrode 606 are wound with a separator 605 in between. Although not shown, the battery element is wound around a central axis. The battery casing 602 is closed at one end and open at the other. The battery casing 602 can be made of metals such as nickel, aluminum, and titanium, or alloys thereof, or alloys of these with other metals (e.g., stainless steel), which are corrosion-resistant to the electrolyte. Furthermore, it is preferable to coat the battery casing 602 with nickel and aluminum to prevent corrosion by the electrolyte. Inside the battery casing 602, the battery element, in which the positive electrode, negative electrode, and separator are wound, is sandwiched between a pair of opposing insulating plates 608 and 609. In addition, a non-aqueous electrolyte (not shown) is injected into the inside of the battery casing 602 in which the battery element is provided. The non-aqueous electrolyte can be the same as that used in coin-type secondary batteries.

[0579] Since the positive and negative electrodes used in cylindrical storage batteries are wound, it is preferable to form the active material on both sides of the current collector. Figures 17A to 17D illustrate a secondary battery 616 in which the height of the cylinder is greater than the diameter of the cylinder, but the battery is not limited to this configuration. A secondary battery in which the diameter of the cylinder is greater than the height of the cylinder is also possible. Such a configuration allows for, for example, miniaturization of the secondary battery.

[0580] By using the positive electrode active material 100 obtained in Embodiments 1 to 11 as the positive electrode 604, a cylindrical secondary battery 616 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0581] A positive electrode terminal (positive electrode current collector lead) 603 is connected to the positive electrode 604, and a negative electrode terminal (negative electrode current collector lead) 607 is connected to the negative electrode 606. Both the positive electrode terminal 603 and the negative electrode terminal 607 can be made of metal materials such as aluminum. The positive electrode terminal 603 is resistance-welded to the safety valve mechanism 613, and the negative electrode terminal 607 is resistance-welded to the bottom of the battery can 602. The safety valve mechanism 613 is electrically connected to the positive electrode cap 601 via a PTC element (Positive Temperature Coefficient) 611. The safety valve mechanism 613 disconnects the electrical connection between the positive electrode cap 601 and the positive electrode 604 when the internal pressure of the battery rises above a predetermined threshold. The PTC element 611 is a thermal resistance element whose resistance increases when the temperature rises, and it prevents abnormal heat generation by limiting the amount of current through the increase in resistance. Barium titanate (BaTiO3) based semiconductor ceramics can be used for the PTC element.

[0582] Figure 17C shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616. The positive electrode of each secondary battery is in contact with a conductor 624 separated by an insulator 625 and is electrically connected. The conductor 624 is electrically connected to a control circuit 620 via wiring 623. The negative electrode of each secondary battery is also electrically connected to the control circuit 620 via wiring 626. The control circuit 620 can be a protective circuit to prevent overcharging or over-discharging, etc.

[0583] Figure 17D shows an example of an energy storage system 615. The energy storage system 615 has multiple secondary batteries 616, which are sandwiched between conductive plates 628 and 614. The multiple secondary batteries 616 are electrically connected to conductive plates 628 and 614 by wiring 627. The multiple secondary batteries 616 may be connected in parallel, in series, or connected in parallel and then in series. By configuring an energy storage system 615 with multiple secondary batteries 616, a large amount of power can be extracted.

[0584] Multiple secondary batteries 616 may be connected in parallel and then further connected in series.

[0585] A temperature control device may be provided between the multiple secondary batteries 616. When a secondary battery 616 overheats, it can be cooled by the temperature control device, and when a secondary battery 616 becomes too cold, it can be heated by the temperature control device. This makes the performance of the energy storage system 615 less susceptible to the influence of ambient temperature.

[0586] Furthermore, in Figure 17D, the energy storage system 615 is electrically connected to the control circuit 620 via wiring 621 and wiring 622. Wiring 621 is electrically connected to the positive terminals of the multiple secondary batteries 616 via conductive plate 628, and wiring 622 is electrically connected to the negative terminals of the multiple secondary batteries 616 via conductive plate 614.

[0587] [Other structural examples of secondary batteries] Examples of secondary battery structures will be explained using Figures 18 and 19.

[0588] The secondary battery 913 shown in Figure 18A has a wound body 950 with terminals 951 and 952 inside a housing 930. The wound body 950 is immersed in an electrolyte inside the housing 930. Terminal 952 is in contact with the housing 930, while terminal 951 is not in contact with the housing 930 due to the use of an insulating material or the like. In Figure 18A, the housing 930 is shown separated for convenience, but in reality, the wound body 950 is covered by the housing 930, and terminals 951 and 952 extend outside the housing 930. The housing 930 can be made of a metal material (e.g., aluminum) or a resin material.

[0589] Furthermore, as shown in Figure 18B, the housing 930 shown in Figure 18A may be formed from multiple materials. For example, in the secondary battery 913 shown in Figure 18B, housing 930a and housing 930b are bonded together, and the winding body 950 is provided in the area surrounded by housing 930a and housing 930b.

[0590] For the housing 930a, an insulating material such as organic resin can be used. In particular, by using a material such as organic resin on the surface where the antenna is formed, shielding of the electric field by the secondary battery 913 can be suppressed. If the shielding of the electric field by housing 930a is small, the antenna may be placed inside housing 930a. For housing 930b, for example, a metal material can be used.

[0591] Furthermore, the structure of the wound body 950 is shown in Figure 18C. The wound body 950 has a negative electrode 931, a positive electrode 932, and a separator 933. The wound body 950 is a wound body in which the negative electrode 931 and the positive electrode 932 are stacked on top of each other with the separator 933 in between, and the stacked sheets are wound up. Note that multiple stacks of the negative electrode 931, positive electrode 932, and separator 933 may be stacked.

[0592] Alternatively, the secondary battery 913 may have a wound body 950a as shown in Figures 19A to 19C. The wound body 950a shown in Figure 19A has a negative electrode 931, a positive electrode 932, and a separator 933. The negative electrode 931 has a negative electrode active material layer 931a. The positive electrode 932 has a positive electrode active material layer 932a.

[0593] By using the positive electrode active material 100 obtained in Embodiments 1 to 11 as the positive electrode 932, a secondary battery 913 with high capacity, high charge / discharge capacity, and excellent cycle characteristics can be obtained.

[0594] The separator 933 has a wider width than the negative electrode active material layer 931a and the positive electrode active material layer 932a, and is wound so as to overlap with the negative electrode active material layer 931a and the positive electrode active material layer 932a. Furthermore, it is preferable from a safety standpoint that the negative electrode active material layer 931a is wider than the positive electrode active material layer 932a. A wound body 950a of this shape is also preferable due to its good safety and productivity.

[0595] As shown in Figure 19B, the negative terminal 931 is electrically connected to terminal 951. Terminal 951 is electrically connected to terminal 911a. The positive terminal 932 is electrically connected to terminal 952. Terminal 952 is electrically connected to terminal 911b.

[0596] As shown in Figure 19C, the coiled body 950a and electrolyte are covered by the housing 930, forming a secondary battery 913. It is preferable to provide a safety valve, an overcurrent protection element, etc., in the housing 930. The safety valve is a valve that opens the inside of the housing 930 at a predetermined internal pressure to prevent the battery from rupturing.

[0597] As shown in Figure 19B, the secondary battery 913 may have multiple windings 950a. By using multiple windings 950a, a secondary battery 913 with a larger charge and discharge capacity can be made. Other elements of the secondary battery 913 shown in Figures 19A and 19B can be referenced from the description of the secondary battery 913 shown in Figures 18A to 18C.

[0598] <Laminated rechargeable battery> Next, an example of a laminate-type secondary battery is shown in Figures 20A and 20B, which show an example of its external appearance. Figures 20A and 20B show a positive electrode 503, a negative electrode 506, a separator 507, an outer casing 509, a positive electrode lead electrode 510, and a negative electrode lead electrode 511.

[0599] Figure 21A shows the external views of the positive electrode 503 and the negative electrode 506. The positive electrode 503 has a positive electrode current collector 501, and the positive electrode active material layer 502 is formed on the surface of the positive electrode current collector 501. The positive electrode 503 also has a region where the positive electrode current collector 501 is partially exposed (hereinafter referred to as the tab region). The negative electrode 506 has a negative electrode current collector 504, and the negative electrode active material layer 505 is formed on the surface of the negative electrode current collector 504. The negative electrode 506 also has a region where the negative electrode current collector 504 is partially exposed, i.e., the tab region. The area and shape of the tab regions of the positive and negative electrodes are not limited to the example shown in Figure 21A.

[0600] <Method for manufacturing laminated rechargeable batteries> Here, an example of a method for manufacturing a laminate-type secondary battery, whose external view is shown in Figure 20A, will be explained using Figures 21B and 21C.

[0601] First, the negative electrode 506, separator 507, and positive electrode 503 are stacked. Figure 21B shows the stacked negative electrode 506, separator 507, and positive electrode 503. Here, an example using 5 sets of negative electrodes and 4 sets of positive electrodes is shown. This can also be called a laminate consisting of negative electrodes, separators, and positive electrodes. Next, the tab regions of the positive electrode 503 are joined together, and the positive electrode lead electrode 510 is joined to the tab region of the outermost positive electrode. For joining, ultrasonic welding, for example, can be used. Similarly, the tab regions of the negative electrode 506 are joined together, and the negative electrode lead electrode 511 is joined to the tab region of the outermost negative electrode.

[0602] Next, the negative electrode 506, separator 507, and positive electrode 503 are placed on the outer casing 509.

[0603] Next, as shown in Figure 21C, the outer casing 509 is bent at the portion indicated by the dashed line. Then, the outer periphery of the outer casing 509 is joined. For joining, for example, heat compression bonding may be used. At this time, a region that is not joined (hereinafter referred to as the inlet) is provided on a part (or one side) of the outer casing 509 so that the electrolyte can be added later.

[0604] Next, an electrolyte (not shown) is introduced into the inside of the outer casing 509 through an inlet provided in the outer casing 509. It is preferable to introduce the electrolyte under a reduced pressure atmosphere or an inert atmosphere. Finally, the inlet is sealed. In this way, a laminate-type secondary battery 500 can be manufactured.

[0605] By using the positive electrode active material 100 shown in any one of Embodiments 1 to 11 as the positive electrode 503, a secondary battery 500 can be made that has high capacity, high charge / discharge capacity, and excellent cycle characteristics.

[0606] [Example of a battery pack] An example of a secondary battery pack according to one embodiment of the present invention, which is capable of wireless charging using an antenna, will be explained with reference to Figures 22A to 22C.

[0607] Figure 21A shows the external appearance of the secondary battery pack 531, which has a thin rectangular parallelepiped shape (it can also be called a thick flat plate shape). Figure 22B is a diagram illustrating the configuration of the secondary battery pack 531. The secondary battery pack 531 has a circuit board 540 and a secondary battery 513. A label 529 is attached to the secondary battery 513. The circuit board 540 is fixed by a seal 515. The secondary battery pack 531 also has an antenna 517.

[0608] The internal structure of the secondary battery 513 may have a wound structure or a laminated structure.

[0609] In the secondary battery pack 531, for example, as shown in Figure 22B, a control circuit 590 is located on the circuit board 540. The circuit board 540 is electrically connected to terminal 514. The circuit board 540 is also electrically connected to the antenna 517, one of the positive and negative leads 551 of the secondary battery 513, and the other of the positive and negative leads 552.

[0610] Alternatively, as shown in Figure 22C, the system may have a circuit system 590a provided on the circuit board 540 and a circuit system 590b electrically connected to the circuit board 540 via terminals 514.

[0611] The antenna 517 is not limited to a coil shape; for example, it may be linear or plate-shaped. Alternatively, antennas such as planar antennas, aperture antennas, traveling wave antennas, EH antennas, magnetic field antennas, and dielectric antennas may be used. Alternatively, the antenna 517 may be a flat conductor. This flat conductor can function as one of the conductors for electric field coupling. In other words, the antenna 517 may function as one of the two conductors of the capacitor. This allows for power exchange not only through electromagnetic and magnetic fields, but also through electric fields.

[0612] The secondary battery pack 531 has a layer 519 between the antenna 517 and the secondary battery 513. The layer 519 has the function of shielding, for example, the electromagnetic field from the secondary battery 513. For the layer 519, a magnetic material can be used, for example.

[0613] The contents of this embodiment can be freely combined with the contents of other embodiments.

[0614] (Embodiment 14) This embodiment shows an example of fabricating an all-solid-state battery using the positive electrode active material 100 shown in Embodiments 1 to 11.

[0615] As shown in Figure 23A, a secondary battery 400 according to one embodiment of the present invention has a positive electrode 410, a solid electrolyte layer 420, and a negative electrode 430.

[0616] The positive electrode 410 has a positive electrode current collector 413 and a positive electrode active material layer 414. The positive electrode active material layer 414 has a positive electrode active material 411 and a solid electrolyte 421. The positive electrode active material 411 is the positive electrode active material 100 shown in Embodiments 1 to 11. The positive electrode active material layer 414 may also have a conductive agent and a binder.

[0617] The solid electrolyte layer 420 has a solid electrolyte 421. The solid electrolyte layer 420 is located between the positive electrode 410 and the negative electrode 430 and is a region that does not contain either the positive electrode active material 411 or the negative electrode active material 431.

[0618] The negative electrode 430 has a negative electrode current collector 433 and a negative electrode active material layer 434. The negative electrode active material layer 434 has a negative electrode active material 431 and a solid electrolyte 421. The negative electrode active material layer 434 may also have a conductive agent and a binder. When metallic lithium is used as the negative electrode active material 431, it is not necessary to form it into particles, so the negative electrode 430 can be made without the solid electrolyte 421, as shown in Figure 23B. Using metallic lithium in the negative electrode 430 is preferable because it can improve the energy density of the secondary battery 400.

[0619] As the solid electrolyte 421 in the solid electrolyte layer 420, for example, a sulfide-based solid electrolyte, an oxide-based solid electrolyte, a halogen-based solid electrolyte, etc., can be used.

[0620] Sulfide-based solid electrolytes include thiolysicone-based (Li 10 GeP2S 12 Li 3.25 Ge 0.25 P 0.75 S4, etc.), sulfide glass (70Li2S·30P2S5, 30Li2S·26B2S3·44LiI, 63Li2S·36SiS2·1Li3PO4, 57Li2S·38SiS2·5Li4SiO4, 50Li2S·50GeS2, etc.), sulfide crystallized gla...

Claims

[Claim 1] A method for producing a positive electrode active material having lithium, nickel, cobalt, manganese, aluminum, magnesium, and fluorine, A first step of preparing a hydroxide containing nickel, cobalt, and manganese using at least a mixed solution of an aqueous solution containing nickel, an aqueous solution containing cobalt, and an aqueous solution containing manganese, as well as a basic aqueous solution. The second step is to prepare a lithium compound and an aluminum source, A third step involves mixing the lithium compound, the aluminum source, and the hydroxide to form a first mixture. A fourth step involves heating the first mixture to form a first composite oxide having lithium, nickel, cobalt, manganese, and aluminum. The fifth step is to prepare the magnesium source and the fluorine source, A sixth step is to mix the first composite oxide, the magnesium source, and the fluorine source to form a second mixture. The seventh step is to heat the second mixture to form a second composite oxide having lithium, nickel, cobalt, manganese, aluminum, magnesium, and fluorine, In the second step described above, a material with a purity of 99.99% or higher is prepared as the lithium compound, and a material with a purity of 99.9% or higher is prepared as the aluminum source. In the fifth step described above, a material with a purity of 99% or higher is prepared as the magnesium source, and a material with a purity of 99% or higher is prepared as the fluorine source. The heating in the fourth and seventh steps is carried out in an oxygen-containing atmosphere in which the impurity concentrations of CH4, CO, CO2, and H2 are each 5 ppb or less and the dew point is -50°C or less. A method for producing a positive electrode active material, wherein the positive electrode active material produced using the above method has single crystal grains.

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