Metal composite compound, method for producing a metal composite compound, and method for producing a lithium metal composite oxide

Abstract

This metal complex compound contains at least Ni. The metal complex compound includes primary particles and secondary particles which are an aggregate of the primary particles. The standard deviation of the short diameter in the primary particles forming the secondary particles is 0.1-100 Å. The secondary particles include secondary particles X each having a high-density part where the primary particles are highly densely aggregated, and a low-density part where the primary particles are sparsely aggregated. From a scanning electron microscope image of a cross section of the secondary particles X, when a binary image is obtained by binarizing the high-density part and the low-density part, the standard deviation of the area proportion of the low-density part in the secondary particles X calculated from the binary image is 0.5-20%, and the aspect ratio of the primary particles forming the secondary particles X is at least 7.

Description

[Technical Field]

[0001] The present invention relates to metal composite compounds, methods for producing metal composite compounds, and methods for producing lithium metal composite oxides. This application claims priority based on Japanese Patent Application No. 2022-114299, filed in Japan on July 15, 2022, and the contents of that application are incorporated herein by reference. [Background technology]

[0002] One method for manufacturing positive electrode active materials for lithium secondary batteries is to mix a lithium compound with a metal composite compound containing metal elements other than Li and then calcine the mixture.

[0003] To achieve battery characteristics of lithium secondary batteries, such as improved cycle performance, reduced resistance, or increased output, studies are being conducted to control the average particle size, particle size distribution, or particle shape of the positive electrode active material within an appropriate range. One possible approach is to control the particle shape of the precursor metal composite compound within an appropriate range.

[0004] For example, Patent Document 1 discloses a method for producing nickel-containing hydroxide that suppresses the formation of a ring-like structure consisting of layers of different densities, which is observed in the cross-section of nickel composite hydroxide particles and adversely affects the characteristics of lithium secondary batteries. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] WO2017 / 217367A1 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] Further investigation is needed regarding the internal structure of precursor metal composite compound particles in order to further improve the performance of lithium secondary batteries.

[0007] The present invention has been made in view of the above circumstances, and aims to provide a lithium secondary battery with high initial efficiency, a metal composite compound that can be used as a raw material for a positive electrode active material, a method for producing the metal composite compound, and a method for producing a lithium metal composite oxide using the same. [Means for solving the problem]

[0008] The present invention encompasses the following aspects. [1] A metal composite compound comprising at least Ni, wherein the metal composite compound comprises primary particles and secondary particles which are aggregates of the primary particles, wherein the primary particles constituting the secondary particles have a standard deviation of their short axis of 0.1 Å or more and 100 Å or less, and the secondary particles have a secondary particle X having a high-density portion where the primary particles are aggregated at a high density and a low-density portion where the primary particles are aggregated at a low density, wherein when a binarized image is obtained by binarizing the high-density portion and the low-density portion of a scanning electron microscope image of the cross-section of the secondary particle X, the standard deviation of the ratio of the area of ​​the low-density portion obtained from the binarized image is 0.5% or more and 20% or less, and the aspect ratio of the primary particles constituting the secondary particle X is 7 or more. [2] The metal composite compound D 50 The metal composite compound described in [1] satisfies the following formula (1). 5μm≦D 50 ≤20μm ···(1) (D 50 This refers to the particle size (μm) at which, when the cumulative particle size distribution curve obtained by measuring the metal composite compound using a laser diffraction particle size distribution analyzer is set to 100%, the cumulative volume from the smallest particles accounts for 50%. [3] A metal composite compound represented by the following compositional formula (A), as described in [1] or [2]. Ni (1-x) M x O z (OH) 2-t ...(A) (In the compositional formula (A), 0 < x ≤ 0.5, 0 ≤ z ≤ 3, -0.5 ≤ t ≤ 2, and t - z < 2, and M is one or more elements selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P) [4] The metal composite compound according to any one of [1] to [3], wherein when the number of the secondary particles X is A and the total number of the secondary particles contained in the metal composite compound is B, A / B is 0.20 or more. [5] The metal composite compound according to any one of [1] to [4], wherein in the cross-section of the secondary particle X, the low-density portion is present substantially continuously in the circumferential direction of the secondary particle X. [6] A reaction step of continuously supplying a metal-containing aqueous solution containing Ni and an alkaline aqueous solution to a reaction tank, continuously growing crystals, and continuously taking out a metal composite compound, wherein in the reaction step, the flow rate of the alkaline aqueous solution is increased or decreased and continuously supplied to the reaction tank, the number of fluctuations per hour of the increase or decrease is 30 or more and 100 or less, and the change rate of the flow rate of the alkaline aqueous solution is 3% or more and 20% or less. A method for producing a metal composite compound. [7] A method for producing a lithium metal composite oxide, comprising a step of mixing the metal composite compound according to any one of [1] to [5] and a lithium compound and firing the obtained mixture. [Advantages of the Invention]

[0009] According to the present invention, a lithium secondary battery having a high initial efficiency can be obtained, and a metal composite compound as a raw material of a positive electrode active material, a method for producing a metal composite compound, and a method for producing a lithium metal composite oxide using the same can be provided. [Brief Description of the Drawings]

[0010] [Figure 1] It is a schematic configuration diagram showing an example of a lithium secondary battery. [Figure 2] It is a schematic diagram showing the overall configuration of an all-solid-state lithium secondary battery. [Figure 3] It is a conceptual diagram of the cross-section of a secondary particle. [Figure 4]This is a conceptual diagram of a cross-section of a secondary particle. [Figure 5] This is a conceptual diagram of a cross-section of a secondary particle. [Figure 6] This is a schematic diagram illustrating the measurement method for ASD. [Figure 7] This is an SEM image of a cross-section of a single secondary particle contained in the metal composite compound manufactured in Example 1. [Figure 8] This is a binarized image of the cross-section shown in Figure 7, obtained using SEM. [Figure 9] Figure 8 shows the binarized image with the diameter (major axis length) indicated. [Figure 10] This image shows the binarized image shown in Figure 8 with a grid overlaid on it. [Figure 11] This figure shows the grid superimposed on the binarized image shown in Figure 10, indicating the number of cells that overlap with the binarized image. [Figure 12] This figure shows an example of the change in the flow rate of the alkaline aqueous solution during the reaction step of the method for producing the metal composite compound of this embodiment. [Modes for carrying out the invention]

[0011] In this specification, "high initial efficiency" means that the initial efficiency value measured by the following method is 80% or higher. In this specification, metal composite compounds are hereinafter referred to as "MCCs," and lithium metal composite oxides are hereinafter referred to as "LiMOs." Cathode Active Material for lithium secondary batteries will be referred to as "CAM" below. The notation "Ni" indicates the element Ni, not the metallic Ni, unless otherwise specified. The same applies to the notations of other elements such as Co and Mn.

[0012] If a numerical range is described as, for example, "1-10μm," it means the range from 1μm to 10μm, including the lower limit of 1μm and the upper limit of 10μm.

[0013] [Calculation of initial efficiency of lithium secondary batteries] The initial efficiency of a lithium-ion secondary battery is calculated by manufacturing the lithium-ion secondary battery using the following method.

[0014] (CAM fabrication) MCC and lithium hydroxide monohydrate powder are weighed and mixed in a molar ratio of Li / (Ni+Co+M)=1.02 to obtain a mixture. The obtained mixture is calcined at 740°C for 5 hours in an oxygen-containing atmosphere to obtain LiMO.

[0015] (Fabrication of positive electrodes for lithium secondary batteries) A paste-like cathode mixture is prepared by adding CAM (LiMO) produced by the above method, a conductive material (acetylene black), and a binder (PVdF) in a composition of CAM:conductive material:binder = 92:5:3 (mass ratio) and kneading them together. N-methyl-2-pyrrolidone is used as the organic solvent when preparing the cathode mixture.

[0016] The resulting positive electrode mixture is applied to a 40 μm thick aluminum foil, which will serve as the current collector, and vacuum-dried at 150°C for 8 hours to obtain a positive electrode for a lithium secondary battery. The electrode area of ​​this lithium secondary battery positive electrode is 1.65 cm². 2 Let's assume that.

[0017] (Manufacturing of lithium secondary batteries) Perform the following operations inside a glove box under an argon atmosphere. (Fabrication of positive electrode for lithium secondary battery) The positive electrode for the lithium secondary battery, fabricated in the above step, is placed with the aluminum foil side facing down on the bottom cover of a coin-type battery R2032 part (for example, manufactured by Hosen Co., Ltd.), and a separator (porous polyethylene film) is placed on top of it. 300 μl of electrolyte is then injected. The electrolyte is a mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate in a volume ratio of 30:35:35, to which LiPF6 is dissolved at a ratio of 1.0 mol / l.

[0018] Next, using metallic lithium as the negative electrode, the negative electrode is placed on top of the laminated film separator, the top cover is closed with a gasket, and the lithium secondary battery (coin-type half-cell R2032) is manufactured by crimping with a crimping machine. As the laminated film separator, a 16 μm thick film is used, in which a heat-resistant porous layer is laminated on top of a porous polyethylene film.

[0019] (Charge / Discharge Test) Using the lithium secondary battery manufactured by the method described above, an initial efficiency test is conducted using the following method, and the initial efficiency of the lithium secondary battery is calculated.

[0020] (Measurement method) First, the lithium secondary battery prepared by the aforementioned method is left to stand at room temperature for 12 hours to allow the separator and positive electrode mixture layer to be sufficiently impregnated with the electrolyte. Next, at a test temperature of 25°C, both charging and discharging are performed with a current setting of 0.2CA, and constant current constant voltage charging and constant current constant voltage discharging are performed, respectively. The maximum charging voltage is 4.3V, and the minimum discharging voltage is 2.5V. The charging capacity is measured, and the obtained value is defined as the "initial charging capacity" (mAh / g). Furthermore, the discharging capacity is measured, and the obtained value is defined as the "initial discharging capacity" (mAh / g).

[0021] Then, using the initial discharge capacity value and the initial charge capacity value, the initial efficiency is calculated using the following formula. Initial efficiency (%) = Initial discharge capacity (mAh / g) / Initial charge capacity (mAh / g) × 100

[0022] <mcc> The MCC in this embodiment contains at least Ni. Preferably, the MCC contains Ni and element M. Examples of element M include one or more elements selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P. More preferably, the MCC contains one or more elements selected from the group consisting of Co, Mn, and Al, and even more preferably two or more elements selected from the group consisting of Co, Mn, and Al. LiMO can be produced by mixing MCC with a lithium compound and firing the mixture.

[0023] MCC comprises primary particles and secondary particles, which are aggregates of primary particles. The secondary particles include secondary particle X. Secondary particle X is a secondary particle having a high-density region where primary particles are aggregated at a high density and a low-density region where primary particles are aggregated at a low density. MCC may also contain secondary particles that do not fall under secondary particle X. In other words, MCC may contain secondary particle X and secondary particles different from secondary particle X. MCC is preferably in powder form. A "primary particle" refers to a particle that, when observed at a magnification of 5,000 to 30,000 using a scanning electron microscope or similar device, does not exhibit visible grain boundaries. A "secondary particle" is a particle formed by the aggregation of primary particles. In other words, a secondary particle is an aggregate of primary particles.

[0024] Examples of MCCs include metal composite oxides or metal composite hydroxides containing Ni, and metal composite oxides or metal composite hydroxides containing Ni and element M.

[0025] [Method for obtaining SEM images of secondary particle cross-sections] Scanning electron microscope images (SEM images) of cross-sections of secondary particles in MCCs can be obtained by the following method. First, the secondary particles are processed to obtain a cross-section. As a method for obtaining a cross-section, for example, a method of processing with a Cross section Polisher (hereinafter sometimes referred to as CP) to obtain a cross-section of the secondary particles can be mentioned.

[0026] Here, the sample of the secondary particles to be cross-sectioned is randomly selected.

[0027] Next, using the CP, the secondary particles selected above are processed under the following processing conditions to obtain a cross-section.

[0028] <Processing conditions> CP: Manufactured by JEOL Ltd., "SM-09010" Gas used: Argon Acceleration voltage: 5 kV

[0029] Among the cross-sections of the secondary particles obtained under the above processing conditions, select the cross-sections of the secondary particles with a major axis length of D 50 (μm) ± 5%, and observe with the secondary electron image of a scanning electron microscope. Note that the cross-sections of the secondary particles with a major axis length of D 50 (μm) ± 5% can be regarded as the cross-sections of the secondary particles cut so as to pass through the vicinity of the center (center of gravity) of the secondary particles before processing.

[0030] Specific observation conditions are as follows. Scanning electron microscope: Manufactured by JEOL Ltd., FE-SEM "JSM-IT500HR" Acceleration voltage: 15.0 kV Irradiation current: 50.0 pA Focal length: 10.0 ± 1.5 mm

[0031] As the resolution of the SEM image of the cross-section of the secondary particles, the number of pixels based on the specifications of the scanning electron microscope used can be appropriately selected. With such a number of pixels, the values of ASD and MSD can be calculated without depending on the number of pixels. For example, the FE-SEM "JSM-IT500HR" from JEOL Ltd. allows users to select image acquisition resolutions of 640 x 480 (300,000 pixels), 1280 x 960 (1 million pixels), 2560 x 1920 (5 million pixels), or 5120 x 3840 (20 million pixels). In this embodiment, a resolution in the range of 1 million pixels to 5 million pixels is preferred.

[0032] The primary particles constituting the secondary particles have a plate-like, rectangular, or needle-like shape with discernible short and long axes. The standard deviation of the short axis of the primary particles constituting the secondary particles is 0.1–100 Å. Furthermore, the primary particles constituting secondary particle X have an aspect ratio of 7 or greater. Hereafter, the standard deviation of the minor diameter may be referred to as "MSD (Minor diameter Standard Deviation)".

[0033] [Method for measuring MSD] The minor axis of the primary particles constituting the secondary particles is measured using the SEM image of the cross-section of the secondary particles obtained by the method described above [Method for obtaining SEM images of the cross-section of secondary particles]. Specifically, for the SEM image of the cross-section of the acquired secondary particle, the minor axis of 30 or more primary particles constituting the same secondary particle is measured within a field of view at a magnification of 20,000x or higher. The shorter of the two orthogonal lines within the contour of the primary particle is defined as the minor axis. At this time, the primary particle to be measured is arbitrarily selected from those visible at the foreground of the field of view, where at least three sides of the contour do not overlap with other primary particles. The minor axis of the primary particles constituting the secondary particle is measured, and the MSD is calculated.

[0034] The MSD of the primary particles constituting the secondary particles is preferably 0.1 Å or more, more preferably 3 Å or more, and even more preferably 6 Å or more. The MSD is preferably 80 Å or less, and even more preferably 60 Å or less. The MSD is preferably 0.1-80 Å, more preferably 3-80 Å, and even more preferably 6-60 Å.

[0035] In the SEM image of the cross-section of a secondary particle obtained by the method described above [Method for obtaining an SEM image of a cross-section of a secondary particle], a secondary particle having a high-density region where primary particles are densely aggregated and a low-density region where primary particles are densely aggregated is a secondary particle X. When a binarized image is obtained by binarizing the SEM image of the cross-section of secondary particle X, the standard deviation of the ratio of the area of ​​the low-density region obtained from the binarized image is 0.5-20%. In this specification, the standard deviation of the ratio of the area of ​​the low-density region obtained from the binarized image may be referred to as "ASD (Area Standard Deviation)".

[0036] "High-density area" refers to the region that turns white in the binarized image obtained by binarizing the 256-level grayscale image of the secondary particle cross-section SEM image acquired by the above [Method for acquiring SEM images of secondary particle cross-sections] with a threshold of 90.

[0037] "Low-density areas" refer to regions that turn black in a binarized image obtained by binarizing a 256-level grayscale image of a secondary particle cross-section obtained by the above [Method for obtaining SEM images of secondary particle cross-sections] with a threshold of 90.

[0038] The SEM image of the cross-section of a secondary particle used to obtain a binarized image is set to a magnification level where the entire cross-section of a single secondary particle is included in one field of view. Such a magnification level is, for example, 2000-20000x. When calculating the ASD, if the magnification level is such that the entire cross-section of a single secondary particle is included in one field of view, the ASD value can be calculated independently of the magnification level.

[0039] [How to obtain a binarized image] The image analysis software "Image J" is used for the binarization process. First, the SEM images of secondary particle cross-sections obtained using the method described above [Method for obtaining SEM images of secondary particle cross-sections] are converted to 256-level grayscale images using the image analysis software "Image J".

[0040] Next, we set the threshold for converting to two tones, white and black, to 90. If the threshold is 90 or higher, it will be converted to white; if it is less than 90, it will be converted to black. The upper limit of the threshold is set to the maximum value (255).

[0041] This method allows for the calculation of ASD regardless of the version or settings of the image analysis software.

[0042] Figure 8 shows a binarized image obtained by importing an SEM image of a cross-section of a secondary particle contained in the MCC obtained in Example 1 (described later) into ImageJ, obtaining a 256-level image, and setting the threshold to 90. In the binarized image shown in Figure 8, the areas that have turned white represent high-density regions, while the areas that have turned black, observed in the cross-section of secondary particles, represent low-density regions.

[0043] In a binarized image, it is preferable that the low-density areas exist substantially continuously in the circumferential direction of the secondary particles. For example, in the cross-section of a secondary particle, a high-density region is observed in the center, a low-density region is observed outside the center and on the outer periphery of the center, and a high-density region is observed in the outermost layer of the secondary particle, outside the low-density region.

[0044] Figures 3 to 5 show conceptual diagrams of a cross-section of a single secondary particle X. The secondary particle 40 shown in Figure 3 has a first high-density portion 43 in the center, a low-density portion 42 outside the center, and a second high-density portion 41 outside the low-density portion 42.

[0045] The low-density portion can be any ASD within the range of this embodiment. For example, as shown in Figure 4, the secondary particle 50 may have a first high-density portion 53 in the center, a low-density portion 52 outside the center, and a second high-density portion 51 outside the low-density portion 52, with the low-density portion 52 being formed near the center.

[0046] The low-density portion may exist in a manner that is observed in a ring-like pattern in the cross-section of the secondary particle X. For example, the secondary particle 60 shown in Figure 5 may have a first high-density portion 65 in the center, a low-density portion 64 outside the center, a second high-density portion 63 outside the low-density portion 64, a second low-density portion 62 outside the high-density portion 63, and a third high-density portion 61 outside the low-density portion 62.

[0047] [Methods for measuring ASD] For the binarized image obtained using the method described above [Method for obtaining a binarized image], measure the diameter (long axis length) of one arbitrarily selected secondary particle. Next, we consider a grid (mesh) where the length of each side is one-tenth the length of the major axis of the secondary particle. For example, if the diameter of a secondary particle is 10 μm, then one cell is defined as a square with a side length of 1 μm. This grid is overlaid on a binarized image, and for all 30 or more overlapping cells where one cell completely overlaps with the binarized image, the percentage of black area within each cell is measured. The percentage of black area within each cell can be determined using ImageJ tools.

[0048] Using the schematic diagram shown by reference numeral 70 in Figure 6, the ratio of the black area within each cell is measured for all 30 or more overlapping cells (cells 1 to 52) that completely overlap with the binarized image 71.

[0049] Let ASD be the standard deviation of the proportion of black areas. ASD is preferably 1.0% or more, and more preferably 2.0% or more. ASD is preferably 18% or less, and more preferably 16% or less. ASD is preferably 1.0-18%, and more preferably 2.0-16%.

[0050] [Method for measuring aspect ratio] The minor and major axes of the primary particles constituting the secondary particle X are measured using the SEM image of the cross-section of the secondary particle X obtained by the method described above [Method for obtaining SEM image of secondary particle cross-section]. Specifically, for the SEM image of the cross-section of the acquired secondary particle X, the major and minor axes of 30 or more primary particles constituting the same secondary particle X are measured within a field of view at a magnification of 20,000x or higher. Of the orthogonal lines within the contour of the primary particle, the longer one is defined as the major axis and the shorter one as the minor axis. At this time, the primary particles to be measured are arbitrarily selected from those visible at the foreground of the field of view, where at least three sides of the contour do not overlap with other primary particles, and their major and minor axes are measured. The aspect ratio is defined as the ratio of the major axis to the minor axis, i.e., major axis / minor axis.

[0051] The aspect ratio of the primary particles constituting the secondary particle X is preferably 7.0 or higher, more preferably 7.1 or higher, and even more preferably 7.2 or higher. The above aspect ratio is preferably 10.0 or lower, more preferably 9.9 or lower, and even more preferably 9.8 or lower. The above aspect ratio is preferably between 7.0 and 10.0, more preferably 7.1 and 9.9, and even more preferably 7.2 and 9.8.

[0052] When MCC containing secondary particles composed of primary particles within the aforementioned MSD range is mixed with a lithium compound and calcined, it tends to calcine uniformly. Furthermore, when MCC containing secondary particles X, whose primary particle aspect ratio and ASD are within the above-mentioned range, is mixed with a lithium compound and fired, Li easily penetrates through the low-density regions, and the firing process is more uniform.

[0053] CAM obtained using such MCC as a raw material is less prone to reaction unevenness and tends to produce uniform particles. Lithium secondary batteries equipped with such CAM tend to have higher initial efficiency because lithium ions can move smoothly within the battery.

[0054] MCC's D 50 It is preferable that the following equation (1) is satisfied. 5μm≦D 50 ≤20μm ···(1) (D 50 This refers to the particle diameter (μm) at which the cumulative volume from the smallest particles accounts for 50% of the total volume in the cumulative particle size distribution curve obtained by measuring MCC using a laser diffraction particle size distribution analyzer, with the total volume being set to 100%.

[0055] MCC's D 50 When the particle size is 5 μm or larger, low-density regions are more likely to form, and lithium penetration pathways are more easily created. As a result, the initial efficiency of lithium secondary batteries tends to be higher. MCC's D 50 When the particle size is 20 μm or less, coarse particles are less likely to be generated, and uneven reaction with the Li compound is less likely to occur. As a result, the initial efficiency of lithium secondary batteries tends to be higher.

[0056] [How to obtain the cumulative particle size distribution curve] "Cumulative volume particle size distribution" is a value measured by laser diffraction scattering. MCC powder is added to 0.25 ml of a 10% by mass sodium hexametaphosphate aqueous solution at a ratio that results in a transmittance of 80±5% in a particle size distribution analyzer, and a dispersion of the MCC powder is obtained.

[0057] Next, the particle size distribution of the obtained dispersion is measured using a laser diffraction scattering particle size distribution analyzer (for example, Microtrac MT3300EXII, manufactured by Microtrac-Bell Corporation) to obtain a volume-based cumulative particle size distribution curve. From the obtained cumulative particle size distribution curve, D 50 Find the (μm) unit.

[0058] MCC's D 50 The particle size is preferably 6 μm or larger, and more preferably 7 μm or larger. 50 The particle size is preferably 18 μm or less, and more preferably 16 μm or less. 50 The particle size is preferably 6-18 μm, and more preferably 7-16 μm.

[0059] [How to calculate A / B] In multiple fields of view of the SEM image of the cross-section of the secondary particles obtained by the above [method for obtaining SEM image of cross-section of secondary particles], when the number of secondary particles X is A and the total number of all secondary particles contained in the MCC is B, it is preferable that A / B is 0.20 or more, more preferably 0.22 or more, and even more preferably 0.24 or more. Also, A / B is preferably 0.50 or less, more preferably 0.48 or less, and even more preferably 0.46 or less. The above upper limit value and lower limit value of A / B can be arbitrarily combined. A / B is preferably 0.20 - 0.50, more preferably 0.22 - 0.48, and even more preferably 0.24 - 0.46. When using MCC where A / B is within the above range, the initial efficiency of the lithium battery tends to be high.

[0060] MCC is preferably represented by the following compositional formula (A). Ni (1-x) M x O z (OH) 2-t ···(A) (In the compositional formula (A), 0 < x ≤ 0.5, 0 ≤ z ≤ 3, -0.5 ≤ t ≤ 2, and M is one or more elements selected from the group consisting of Co, Mn, Fe, Cu, Ti, Mg, Al, W, Mo, Nb, Zn, Sn, Zr, Ga, V, B, Si, S, and P)

[0061] MCC is preferably a hydroxide represented by the following compositional formula (A)-1. Ni (1-x1-y) Co x1 M1 y (OH) 2-t ··· formula (A)-1 (In the compositional formula (A)-1, 0 ≤ x1 ≤ 0.5, 0 ≤ y ≤ 0.5, 0 < x1 + y ≤ 0.5, and -0.5 ≤ t < 2, and M1 is one or more elements selected from the group consisting of Mn, Fe, Cu, Ti, Mg, Al, Zn, Sn, Zr, Nb, Ga, W, Mo, B, Si, S, and P.)

[0062] In compositional formula (A), M is preferably one or more elements selected from the group consisting of Co, Mn, Al, W, B, Nb, and Zr. Furthermore, M preferably contains one or more elements selected from the group consisting of Co, Mn, and Al, and more preferably contains two or more elements selected from the group consisting of Co, Mn, and Al. In compositional formula (A)-1, M1 is preferably one or more elements selected from the group consisting of Mn and Al.

[0063] (x) From the viewpoint of increasing initial efficiency, x is preferably 0.01 or higher, more preferably 0.02 or higher, and even more preferably 0.03 or higher. Furthermore, x is preferably 0.44 or less, more preferably 0.42 or less, and even more preferably 0.40 or less.

[0064] The above upper and lower limits for x can be combined in any way. The above compositional formula (A) preferably satisfies 0.01 ≤ x ≤ 0.44, more preferably 0.02 ≤ x ≤ 0.42, and even more preferably 0.03 ≤ x ≤ 0.40.

[0065] (x1) From the viewpoint of increasing the initial efficiency, x1 is preferably 0.01 or higher, more preferably 0.02 or higher, and even more preferably 0.03 or higher. Furthermore, x1 is preferably 0.44 or less, more preferably 0.42 or less, and even more preferably 0.40 or less.

[0066] The above upper and lower limits for x1 can be combined in any way. The above compositional formula (A)-1 preferably satisfies 0.01 ≤ x1 ≤ 0.44, more preferably 0.02 ≤ x1 ≤ 0.42, and even more preferably 0.03 ≤ x1 ≤ 0.40.

[0067] (y) From the viewpoint of increasing the initial efficiency, y is preferably 0.01 or higher, more preferably 0.02 or higher, and particularly preferably 0.03 or higher. Furthermore, y is preferably 0.44 or less, more preferably 0.42 or less, and particularly preferably 0.40 or less.

[0068] The above upper and lower limits for y can be combined in any way. The above compositional formula (A)-1 preferably satisfies 0.01 ≤ y ≤ 0.44, more preferably 0.02 ≤ y ≤ 0.42, and even more preferably 0.03 ≤ y ≤ 0.40.

[0069] (x1+y) From the viewpoint of increasing the initial efficiency, x1+y is preferably 0.01 or higher, more preferably 0.02 or higher, and even more preferably 0.03 or higher. Furthermore, x1+y is preferably 0.44 or less, more preferably 0.42 or less, and even more preferably 0.40 or less.

[0070] The above upper and lower limits for x1+y can be combined in any way. The above compositional formula (A)-1 preferably satisfies 0.01 ≤ x1 + y ≤ 0.44, more preferably 0.02 ≤ x1 + y ≤ 0.42, and even more preferably 0.03 ≤ x1 + y ≤ 0.40.

[0071] (z) z is preferably 0.02 or higher, more preferably 0.03 or higher, and even more preferably 0.05 or higher. z is preferably 2.8 or less, more preferably 2.6 or less, and even more preferably 2.4 or less.

[0072] The above upper and lower limits for z can be combined in any way. The above compositional formula (A) preferably satisfies 0 ≤ z ≤ 2.8, more preferably 0.02 ≤ z ≤ 2.8, even more preferably 0.03 ≤ z ≤ 2.6, and particularly preferably 0.05 ≤ z ≤ 2.4.

[0073] (t) t is preferably -0.45 or more, more preferably -0.40 or more, and still more preferably -0.35 or more. t is preferably 1.8 or less, more preferably 1.6 or less, and still more preferably 1.4 or less. The above upper and lower limit values of t can be arbitrarily combined.

[0074] The above compositional formula (A) or the above compositional formula (A)-1 preferably satisfies -0.45 ≤ t ≤ 1.8, more preferably satisfies -0.40 ≤ t ≤ 1.6, and still more preferably satisfies -0.35 ≤ t ≤ 1.4.

[0075] The above compositional formula (A) preferably satisfies 0.01 ≤ x ≤ 0.44, 0 ≤ z ≤ 2.8, and -0.45 ≤ t ≤ 1.8. The above compositional formula (A)-1 preferably satisfies 0.01 ≤ x1 ≤ 0.44, 0.01 ≤ y ≤ 0.44, 0.01 ≤ x1 + y ≤ 0.44, and -0.45 ≤ t ≤ 1.8.

[0076] [Composition analysis of MCC] The composition analysis of MCC can be measured using an ICP emission spectrometer after dissolving the obtained MCC powder in hydrochloric acid. As the ICP emission spectrometer, for example, Optima8300 manufactured by PerkinElmer Co., Ltd. can be used.

[0077] [Manufacturing method of MCC] The above manufacturing method of MCC is a method including a reaction step of continuously supplying a metal-containing aqueous solution containing Ni and an alkaline aqueous solution to a reaction tank, continuously growing crystals, and continuously taking out MCC.

[0078] Examples of the metal element other than Ni that the metal-containing aqueous solution may contain include the aforementioned element M.

[0079] Examples of the metal-containing aqueous solution containing Ni include a metal-containing aqueous solution containing Ni, Co, and Mn or a metal-containing aqueous solution containing Ni, Co, and Al. Metal-containing aqueous solutions containing Ni, Co, and Mn are mixtures of nickel salt solutions, cobalt salt solutions, and manganese salt solutions. Metal-containing aqueous solutions containing Ni, Co, and Al are mixtures of nickel salt solutions, cobalt salt solutions, and aluminum salt solutions.

[0080] As the nickel salt solute in the above nickel salt solution, one or more of the following can be used: nickel sulfate, nickel nitrate, nickel chloride, and nickel acetate.

[0081] As the cobalt salt solute in the above cobalt salt solution, one or more of the following can be used: cobalt sulfate, cobalt nitrate, cobalt chloride, and cobalt acetate.

[0082] As the solute of the above manganese salt solution, one or more of the following can be used: manganese sulfate, manganese nitrate, manganese chloride, and manganese acetate.

[0083] As the aluminum salt that serves as the solute in the above-mentioned aluminum salt solution, for example, aluminum sulfate can be used.

[0084] Each metal salt is used in such a ratio that the atomic ratio of each metal element corresponds to the compositional ratio of the above compositional formula (A), i.e., (1-x):x.

[0085] Furthermore, the solvent for nickel salt solutions, cobalt salt solutions, manganese salt solutions, and aluminum salt solutions is water. In other words, nickel salt solutions, cobalt salt solutions, manganese salt solutions, and aluminum salt solutions are aqueous solutions.

[0086] A metal-containing aqueous solution containing Ni and an alkaline aqueous solution are reacted using the continuous coprecipitation method described in JP-A-2002-201028 to produce a metal-compound hydroxide.

[0087] Alkaline aqueous solutions include, for example, sodium hydroxide or potassium hydroxide. To adjust the pH of the metal-containing aqueous solution that includes Ni, an alkaline aqueous solution is added. In this specification, the pH value is defined as the value measured when the temperature of the mixture is 40°C. The pH of the mixture is measured when the temperature of the mixture sampled from the reaction vessel reaches 40°C.

[0088] In the reaction process, the flow rate of the alkaline aqueous solution is increased or decreased and continuously supplied to the reaction vessel. It is preferable to increase or decrease the flow rate of the alkaline aqueous solution multiple times in a continuous manner. This allows the ASD and MSD to be adjusted to the aforementioned ranges.

[0089] "Increasing the flow rate of an alkaline aqueous solution" means increasing the current flow rate of the alkaline aqueous solution (e.g., S1) to a set flow rate (e.g., S2) that is greater than the current flow rate.

[0090] "Reducing the flow rate of the alkaline aqueous solution" means decreasing the current flow rate of the alkaline aqueous solution (e.g., S2) to a set flow rate smaller than the current flow rate (e.g., S3). Here, since the alkaline aqueous solution is continuously supplied to the reaction vessel, all flow rates will be greater than 0.

[0091] "Continuously increasing or decreasing the flow rate of the alkaline aqueous solution multiple times" means increasing or decreasing the flow rate of the alkaline aqueous solution multiple times until the end of the reaction process. In Figure 12, this means continuously changing the flow rate of the alkaline aqueous solution in the order of S3, S2, S3, S2.

[0092] The flow rate of the alkaline aqueous solution supplied to the reaction vessel during the reaction process will be explained using Figure 12. Figure 12 shows an example of the change in the flow rate (unit: L / h) of the alkaline aqueous solution during the reaction process. In Figure 12, the horizontal axis represents time, and the vertical axis represents the flow rate of the alkaline aqueous solution.

[0093] In Figure 12, S1 is the initial flow rate of the alkaline aqueous solution. S1 is the initial setting value when supplying the alkaline aqueous solution to the reaction vessel, and S1 is a value greater than 0. S2 refers to the flow rate set to increase the flow rate of the alkaline aqueous solution from S1, and S3 refers to the flow rate set to decrease the flow rate of the alkaline aqueous solution from S2.

[0094] In Figure 12, an example is shown in which the flow rate of the alkaline aqueous solution repeatedly increases and decreases between S2 and S3. However, after reaching S3, a new flow rate S4 may be set, or after reaching S2, a new flow rate S5 may be set. For example, the flow rate may increase and decrease sequentially from S1 to S2 to S3, and then increase from S3 to S4, or the flow rate may increase and decrease sequentially from S1 to S2 to S3, and then decrease from S2 to S5. Also, S2 or S3 may be the same value as S1. For example, if S3 is the same value as S1, the flow rate may increase from S1 to S2, then decrease from S2 to S1 (=S3), and then increase again from S1 to S2.

[0095] The number of fluctuations is calculated by counting the flow rate from the current flow rate, increasing it, and then decreasing it until it reaches the reduced flow rate as one cycle. For example, in Figure 12, if the flow rate is increased from S1 to S2, and then decreased from S2 to S3, the time from S1 to S3 is considered one fluctuation. In other words, S1→S2→S3 is the "first" fluctuation. Subsequently, the flow rate is increased from S3 to S2, and then decreased from S2 to S3 again. This cycle is counted as one variation. In other words, the initial S3→S2→S3 cycle is the "second" variation.

[0096] When the flow rate of an alkaline aqueous solution is increased or decreased and continuously supplied to the reaction vessel, the pH near the inlet of the alkaline aqueous solution fluctuates instantaneously. In this case, the pH around the growing metal composite hydroxide that remains in the reaction vessel fluctuates instantaneously. When the pH around the metal composite hydroxide increases, high-density areas are formed, and when it decreases, low-density areas are formed. Furthermore, since the growth rate and direction of the primary particles of the metal composite hydroxide differ depending on the surrounding pH, it is possible to control the short diameter of the primary particles, i.e., the medium-scaled particle size (MSD), by changing the pH around the growing metal composite hydroxide. As a result, the initial efficiency can be improved.

[0097] The number of fluctuations per hour in the flow rate of the alkaline aqueous solution, whether increasing or decreasing, is 30-100 times. Preferably, the number of fluctuations is 40 or more, more preferably 50 or more. Preferably, the number of fluctuations is 90 or less, more preferably 80 or less. Preferably, the number of fluctuations is 40-90, more preferably 50-80 times.

[0098] If the number of fluctuations mentioned above is greater than or equal to the lower limit, the time during which the area around the metal composite hydroxide during the growth process is maintained within the same pH range is less likely to be prolonged. In this case, the time during which primary particles are maintained in a pH range that is unfavorable for growth and the time during which they are maintained in a pH range that is favorable for growth are both less likely to be prolonged. As a result, there is less variation in the degree of primary particle growth, and the MSD is less likely to be excessive. Therefore, the initial efficiency can be improved.

[0099] If the number of fluctuations is below the upper limit, the surrounding pH fluctuates appropriately during the growth of primary particles, making it easier for low-density and high-density regions to form. Furthermore, the growth cycle of primary particles in the low-density region does not become too short, nor does the layer thickness of the low-density region become too thin. In addition, because the pH inside the reaction vessel is less prone to fluctuation, there is less variation in primary particle nucleation. As a result, ASD is less likely to be underestimated. Therefore, the initial efficiency can be improved.

[0100] During the reaction process, the rate of change in the flow rate of the alkaline aqueous solution is 3-20%. The rate of change of flow rate of an alkaline aqueous solution refers to the average of the absolute values ​​of the rate of change for each flow rate change from the initial flow rate to one hour later. For example, in Figure 12, the absolute value of the rate of change of flow rate from S1 to S2 is calculated as "|S2-S1| / S1×100". The absolute value of the rate of change of flow rate from S2 to S3 is calculated as "|S2-S3| / S1×100". The same calculation is performed for subsequent flow rate changes to obtain the absolute value of the rate of change for each flow rate, and the average of these values ​​is taken as the "rate of change of flow rate of the alkaline aqueous solution".

[0101] The above rate of change is preferably 5% or more, more preferably 7% or more. The above rate of change is preferably 18% or less, more preferably 16% or less. The above rate of change is preferably 5-18%, more preferably 7-16%.

[0102] If the above rate of change is above the above lower limit, i.e., the range of fluctuation is not too small, a moderate pH difference will occur around the metal composite hydroxide during the growth process, making it easier for low-density and high-density regions to form. In addition, the growth cycles of the low-density and high-density regions will not become too short, and the layer thickness of the low-density region will not become too thin, so ASD is less likely to be underestimated. Therefore, the initial efficiency can be improved. If the above rate of change is below the above upper limit, that is, if the range of fluctuation is not too large, then variations in the growth rate of primary particles are less likely to occur, and the MSD is less likely to become excessive. Therefore, the initial efficiency can be improved.

[0103] It is preferable to supply a complexing agent in addition to a metal-containing aqueous solution containing Ni and an alkaline aqueous solution. When the complexing agent is continuously supplied to the reaction vessel, for example, Ni, Co and Mn react, and Ni (1-x1-y) Co x1 Mn y (OH)2 is produced. Also, Ni, Co and Al react, and Ni (1-x1-y) Co x1 Al y (OH)2 is produced.

[0104] Complexing agents are compounds capable of forming complexes with nickel ions, cobalt ions, aluminum ions, and manganese ions in aqueous solution. Examples of complexing agents include ammonium ion suppliers (ammonium salts such as ammonium hydroxide, ammonium sulfate, ammonium chloride, ammonium carbonate, and ammonium fluoride), hydrazine, ethylenediaminetetraacetic acid, nitrilotriacetic acid, uracildiacetic acid, and glycine.

[0105] The amount of complexing agent in a mixed solution containing a metal-containing aqueous solution including Ni is such that, for example, its molar ratio to the total number of moles of metal salts is greater than 0 and 2.0 or less. The amount of complexing agent in a mixed solution containing a nickel salt solution, a cobalt salt solution, a manganese salt solution, and a complexing agent is such that, for example, its molar ratio to the total number of moles of metal salts is greater than 0 and 1.0 or less.

[0106] During the reaction, the temperature of the reaction vessel is controlled to be within a range of, for example, 20-80°C, preferably 30-70°C.

[0107] Furthermore, during the reaction, the pH value in the reaction vessel is controlled to be within a range of, for example, 9-14, preferably 10-13.

[0108] The flow rates of the metal-containing aqueous solution containing Ni, the alkaline aqueous solution, and the complexing agent are controlled so that the pH value in the reaction vessel is within the above range.

[0109] When controlling the pH in the reaction vessel, the alkaline aqueous solution is added while varying its flow rate 30-100 times, and the rate of change in flow rate within the range of 3-20%.

[0110] The substances in the reaction vessel should be stirred and mixed as needed. In the continuous coprecipitation method, a reaction vessel of the type that allows for overflow of the formed reaction precipitate for separation can be used.

[0111] In addition to controlling the above conditions, various gases, such as inert gases like nitrogen, argon, and carbon dioxide, oxidizing gases like air and oxygen, or mixtures thereof, may be supplied to the reaction vessel to control the oxidation state of the resulting reaction product.

[0112] More specifically, the reaction vessel may be kept in an inert atmosphere. An inert atmosphere in the reaction vessel suppresses the aggregation of metal elements in the mixture that are more easily oxidized than Ni, preventing them from accumulating before Ni. Therefore, a uniform MCC can be obtained.

[0113] After the above reaction, the resulting reaction product is washed with water and then dried to obtain a metal composite hydroxide (MCC).

[0114] If the MCC is a metal composite oxide, the metal composite hydroxide is oxidized to produce the metal composite oxide. The heating time for oxidation is preferably 1 to 30 hours in total, from the start of heating until the temperature is reached and the temperature is maintained. The heating temperature for oxidation is preferably 400 to 700°C. By oxidizing within the above heating time and temperature range, the particle shape of the metal composite hydroxide (MSD, ASD, aspect ratio, D) is obtained. 50 Metal composite oxides can be obtained while maintaining (etc.).

[0115] <Method for manufacturing lithium metal composite oxides> The method for producing LiMO includes a step of mixing MCC and a lithium compound, and then calcining the resulting mixture (calcination step).

[0116] As the lithium compound, one or more selected from the group consisting of lithium carbonate, lithium hydroxide, and lithium hydroxide monohydrate can be used.

[0117] The lithium compound and MCC are mixed, taking into consideration the composition ratio of the final product, to obtain a mixture of the lithium compound and MCC.

[0118] [Firing process] The resulting mixture is fired, for example, in an oxygen-containing atmosphere at a firing temperature of 500-1000°C. By firing the mixture, LiMO crystals grow.

[0119] In this specification, firing temperature refers to the temperature of the atmosphere inside the firing furnace, and means the maximum temperature at which the firing temperature is maintained (maximum holding temperature). If the firing process involves multiple firing stages, the firing temperature refers to the temperature at the stage where the firing was performed at the highest holding temperature among all stages.

[0120] Specifically, the firing temperature is preferably 550-980°C, and more preferably 600-960°C.

[0121] Furthermore, the holding time at the firing temperature can range from 0.1 to 20 hours, with 0.5 to 10 hours being preferred.

[0122] Furthermore, it is preferable to calcine the mixture under an oxygen-containing atmosphere. Specifically, it is preferable to introduce oxygen gas to create an oxygen-containing atmosphere inside the calcination furnace.

[0123] For firing, tunnel kilns, roller hearth kilns, rotary kilns, etc., can be used.

[0124] After the calcination process, the calcined material obtained is crushed and sieved as appropriate to obtain LiMO.

[0125] <Lithium-ion secondary battery> This section describes a suitable positive electrode for lithium secondary batteries when the above-mentioned LiMO is used as the CAM. Hereafter, the positive electrode for lithium secondary batteries may be referred to simply as the positive electrode. Furthermore, we will describe lithium secondary batteries that are suitable for use as a positive electrode.

[0126] A suitable example of a lithium secondary battery when the above-mentioned LiMO is used as the CAM includes a positive electrode and a negative electrode, a separator sandwiched between the positive and negative electrodes, and an electrolyte placed between the positive and negative electrodes.

[0127] Figure 1 is a schematic diagram showing an example of a lithium secondary battery. For example, a cylindrical lithium secondary battery 10 is manufactured as follows.

[0128] First, as shown in the partially enlarged view of Figure 1, a pair of strip-shaped separators 1, a strip-shaped positive electrode 2 having a positive electrode lead 21 at one end, and a strip-shaped negative electrode 3 having a negative electrode lead 31 at one end are stacked in the order of separator 1, positive electrode 2, separator 1, negative electrode 3, and then wound to form an electrode group 4.

[0129] The positive electrode 2, as an example, has a positive electrode active material layer 2a containing CAM and a positive electrode current collector 2b on which the positive electrode active material layer 2a is formed on one surface. Such a positive electrode 2 can be manufactured by first preparing a positive electrode mixture containing CAM, a conductive material, and a binder, and then supporting the positive electrode mixture on one surface of the positive electrode current collector 2b to form the positive electrode active material layer 2a.

[0130] The negative electrode 3 can be, as an example, an electrode in which a negative electrode mixture containing a negative electrode active material (not shown) is supported on a negative electrode current collector, or an electrode consisting of the negative electrode active material alone, and can be manufactured in the same manner as the positive electrode 2.

[0131] Next, the electrode group 4 and an insulator (not shown) are placed in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with electrolyte 6, and the electrolyte is placed between the positive electrode 2 and the negative electrode 3. Furthermore, the top of the battery can 5 is sealed with a top insulator 7 and a sealing body 8 to manufacture the lithium secondary battery 10.

[0132] As for the shape of the electrode group 4, for example, a columnar shape can be given such that the cross-sectional shape when the electrode group 4 is cut perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0133] Furthermore, the shape of the lithium secondary battery having such electrode group 4 can be one of those specified in IEC60086 or JIS C 8500, which are battery standards established by the International Electrotechnical Commission (IEC). For example, cylindrical or prismatic shapes can be used.

[0134] Furthermore, lithium secondary batteries are not limited to the wound configuration described above; they may also have a stacked configuration in which a stacked structure of positive electrode, separator, negative electrode, separator is repeatedly stacked. Examples of stacked lithium secondary batteries include so-called coin-type batteries, button-type batteries, or paper-type (or sheet-type) batteries.

[0135] For the positive electrode, separator, negative electrode, and electrolyte that constitute the lithium secondary battery, for example, the configuration, materials, and manufacturing methods described in sections

[0113] to

[0140] of WO2022 / 113904A1 can be used.

[0136] <All-solid-state lithium secondary battery> The above LiMO can be used as a CAM for all-solid-state lithium secondary batteries.

[0137] Figure 2 is a schematic diagram showing an example of an all-solid-state lithium secondary battery. The all-solid-state lithium secondary battery 1000 shown in Figure 2 has a laminate 100 having a positive electrode 110, a negative electrode 120, and a solid electrolyte layer 130, and an outer casing 200 that houses the laminate 100. The all-solid-state lithium secondary battery 1000 may also have a bipolar structure in which the CAM and the negative electrode active material are arranged on both sides of the current collector. A specific example of a bipolar structure is the structure described in JP-A-2004-95400.

[0138] The positive electrode 110 comprises a positive electrode active material layer 111 and a positive electrode current collector 112. The positive electrode active material layer 111 contains the aforementioned CAM and solid electrolyte. The positive electrode active material layer 111 may also contain a conductive material and a binder.

[0139] The negative electrode 120 comprises a negative electrode active material layer 121 and a negative electrode current collector 122. The negative electrode active material layer 121 contains a negative electrode active material. The negative electrode active material layer 121 may also contain a solid electrolyte and a conductive material.

[0140] The laminated body 100 may have an external terminal 113 connected to the positive electrode current collector 112 and an external terminal 123 connected to the negative electrode current collector 122. In addition, the all-solid-state lithium secondary battery 1000 may have a separator between the positive electrode 110 and the negative electrode 120.

[0141] The all-solid-state lithium secondary battery 1000 further includes an insulator (not shown) that insulates the laminate 100 from the outer casing 200 and a seal (not shown) that seals the opening 200a of the outer casing 200.

[0142] The outer casing 200 can be a container formed from a highly corrosion-resistant metal material such as aluminum, stainless steel, or nickel-plated steel. Alternatively, the outer casing 200 can be a container made by processing a laminate film with corrosion-resistant treatment applied to at least one side into a bag shape.

[0143] Examples of shapes for the all-solid-state lithium secondary battery 1000 include coin-shaped, button-shaped, paper-shaped (or sheet-shaped), cylindrical, rectangular, or laminated (pouch-shaped).

[0144] Although the all-solid-state lithium secondary battery 1000 is shown in one example configuration having a single stacked body 100, this embodiment is not limited to this configuration. The all-solid-state lithium secondary battery 1000 may also have a configuration in which the stacked body 100 is used as a unit cell, and multiple unit cells (stacked bodies 100) are sealed inside the outer casing 200.

[0145] For all-solid-state lithium secondary batteries, for example, the configuration, materials, and manufacturing methods described in sections

[0151] to

[0181] of WO2022 / 113904A1 can be used.

[0146] In a lithium secondary battery with the above configuration, since CAM uses the aforementioned MCC as a raw material, the initial efficiency of the lithium secondary battery using this CAM can be improved.

[0147] The present invention has the following aspects.

[10] An MCC comprising at least Ni, wherein the MCC comprises primary particles and secondary particles which are aggregates of the primary particles, wherein the primary particles constituting the secondary particles have an MSD of 0.1-80 Å, the secondary particles have the secondary particle X, the secondary particle X has an ASD of 2.0-16%, and the aspect ratio of the primary particles constituting the secondary particle X is 7.2-9.8.

[11] D of the MCC 50 The MCC described in

[10] satisfies the following equation (1'). 7μm≦D 50 ≤16μm ···(1')

[12] The MCC represented by the composition formula (A)-1 as described in

[10] or

[11] .

[13] The MCC described in

[12] , wherein the composition formula (A)-1 satisfies 0.01≦x1≦0.44, 0.01≦y≦0.44, 0.01≦x1+y≦0.44, and -0.45≦t≦1.8.

[14] The MCC described in any one of

[10] to

[13] , wherein the A / B ratio is 0.24-0.46.

[15] In the cross-section of the secondary particle X, the low-density portion is substantially continuous in the circumferential direction of the secondary particle X, as described in any one of

[10] to

[14] .

[16] MCC described in any one of

[10] to

[15] , wherein the MSD is 6-60 Å.

[17] A method for producing MCC, comprising a reaction step of continuously supplying a metal-containing aqueous solution containing Ni and an alkaline aqueous solution to a reaction vessel, continuously growing crystals, and continuously extracting MCC, wherein in the reaction step, the flow rate of the alkaline aqueous solution is increased or decreased and continuously supplied to the reaction vessel, the number of times the increase or decrease is varied per hour is 50-80 times, and the rate of change of the flow rate of the alkaline aqueous solution is 7-16%. A method for producing LiMO, comprising a step of mixing an MCC according to any one of

[18] to

[16] with a lithium compound and firing the resulting mixture.

Example

[0148] Next, the present invention will be described in more detail with reference to examples.

[0149] <Calculation of the initial efficiency of a lithium secondary battery> The initial efficiency of the lithium secondary battery was calculated by the method described in the above <Calculation of the initial efficiency of a lithium secondary battery>.

[0150] <Method for measuring the aspect ratio> The aspect ratio was measured as described in the above <Method for measuring the aspect ratio>.

[0151] <Method for measuring MSD> MSD was measured as described in the above <Method for measuring MSD>.

[0152] <Method for obtaining a binary image> The binary image was obtained as described in the above <Method for obtaining a binary image>.

[0153] <Method for measuring ASD> ASD was measured by the method described in the above <Method for measuring ASD>.

[0154] <Method for obtaining a SEM image of a secondary particle cross-section> The SEM image of the secondary particle cross-section was obtained as described in the above <Method for obtaining a SEM image of a secondary particle cross-section>.

[0155] <D 50 Measurement> The D of MCC 50 was measured as described in [Method for obtaining a cumulative particle size distribution curve].

[0156] <Composition analysis of MCC> The composition analysis of MCC was carried out by the method described in the above <Composition analysis of MCC>.

[0157] <Example 1> First, water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied to maintain the liquid temperature (temperature of the reaction vessel) at 70°C.

[0158] A metal-containing aqueous solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of manganese sulfate.

[0159] Next, a metal-containing aqueous solution and an ammonium sulfate aqueous solution as a complexing agent were continuously added to the reaction vessel under stirring, in a ratio such that the atomic ratio of Ni, Co, and Mn in the reaction vessel was 83:12:5. In addition, the flow rate of the sodium hydroxide aqueous solution was continuously supplied to the reaction vessel, increasing or decreasing. Specifically, an initial flow rate S1 of the sodium hydroxide aqueous solution was set, the flow rate was increased from the initial flow rate S1 to the set flow rate S2, and the flow rate was decreased from S2 to the set flow rate S3. Next, the flow rate of the sodium hydroxide solution was increased again to S2, and then decreased from S2 to S3. Thereafter, the process of increasing the flow rate of the sodium hydroxide solution to S2 and then decreasing it to S3 was repeated.

[0160] At this time, the flow rate of the sodium hydroxide solution was controlled so that the number of fluctuations in the flow rate of the sodium hydroxide solution per hour was 31, and the rate of change in the flow rate of the sodium hydroxide solution was 6.3%.

[0161] This yielded the reaction product.

[0162] After washing the reaction product, it was dehydrated using a centrifuge, isolated, and dried at 105°C to obtain MCC1, a nickel-cobalt-manganese metal composite hydroxide.

[0163] MCC1 contained secondary particles, which are aggregates of primary particles. In the empirical formula (A), MCC1 had x=0.166, z=0, and t=0. In the empirical formula (A)-1, MCC1 had x1 = 0.119, y = 0.047, and t = 0.

[0164] Figure 7 shows an SEM image of a cross-section of a single secondary particle contained in MCC1. Figure 7 is a 1280 x 960 pixel SEM image at a magnification of 10,000x.

[0165] The SEM image in Figure 7 was imported into ImageJ to obtain a 256-level image. The threshold was set to 90 to obtain a binarized image. The resulting binarized image is shown in Figure 8. In Figure 8, the white areas represent high-density areas, and the black areas represent low-density areas.

[0166] The diameter (major axis length) of one secondary particle obtained from the binarized image was measured to be 11.4 μm. This major axis length is shown by a dashed line in Figure 9.

[0167] Next, as shown in Figure 10, a grid was superimposed on the binarized image. The length of one side of this grid was set to 1.14 μm, which is one-tenth of the major axis length of 11.4 μm. Furthermore, for all 30 or more overlapping cells where one cell completely overlaps with the binarized image, the percentage of black area within each cell was measured. As shown in Figure 11, there were 56 cells that completely overlapped with the extracted binarized image. The percentage of black area within each cell was determined using ImageJ tools.

[0168] Based on the percentage of black area within each cell in all obtained cells, the ASD score was calculated to be 8.31%.

[0169] The secondary particles shown in Figure 7 are confirmed to be secondary particles X having high-density and low-density regions, as seen from the binarized image in Figure 8, and it was confirmed that MCC1 contains secondary particles X. Furthermore, in the cross-section of secondary particle X, the low-density region existed in the manner shown in Figure 3, substantially continuous in the circumferential direction of the secondary particle.

[0170] For MCC1, the total number of secondary particles B contained in MCC1 was calculated from multiple fields of view of the SEM images of the secondary particle cross-section obtained using the method described above [Method for obtaining SEM images of secondary particle cross-sections], and it was found to be 83. In addition, the aspect ratio of the ASD and primary particle was calculated for each secondary particle using the method described above. The number of particles A whose aspect ratio of the ASD and primary particle falls within the range corresponding to secondary particle X was calculated to be 28. The result of calculating A / B from the obtained values ​​was 0.33.

[0171] For MCC1, the MSD of the secondary particle, the ASD of secondary particle X, the aspect ratio of the primary particle contained in secondary particle X, and the A / B and D ratios of MCC1. 50 The results of the initial efficiency of the lithium secondary battery are shown in Table 1 (the same applies to subsequent examples and comparative examples).

[0172] <Example 2> First, water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied to maintain the liquid temperature at 70°C.

[0173] A metal-containing aqueous solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of cobalt sulfate, and an aqueous solution of aluminum sulfate.

[0174] Next, a metal-containing aqueous solution and an ammonium sulfate aqueous solution as a complexing agent were continuously added to the reaction vessel under stirring, in a ratio such that the atomic ratio of Ni, Co, and Al in the reaction vessel was 88:9:3. The flow rate of the sodium hydroxide aqueous solution was also continuously supplied to the reaction vessel, increasing or decreasing it as needed. The flow rate of the sodium hydroxide aqueous solution was controlled in the same manner as in Example 1, except that the number of increases or decreases in the flow rate of the sodium hydroxide aqueous solution per hour was 50, and the rate of change in the flow rate of the sodium hydroxide aqueous solution was 14.4%. This resulted in the acquisition of the reaction product.

[0175] After washing the reaction product, it was dehydrated using a centrifuge, isolated, and dried at 105°C to obtain MCC2, a nickel-cobalt-aluminum metal composite hydroxide.

[0176] MCC2 contained secondary particles, which are aggregates of primary particles. In the empirical formula (A), MCC2 had x=0.095, z=0, and t=0. In the empirical formula (A)-1, MCC2 had x1 = 0.043, y = 0.052, and t = 0.

[0177] From the binarized image, MCC2 had high-density and low-density regions, and in the cross-section of the secondary particle, the low-density region was substantially continuous in the circumferential direction of the secondary particle and existed in the manner shown in Figure 3.

[0178] <Example 3> First, water was placed in a reaction vessel equipped with a stirrer and an overflow pipe, and then an aqueous sodium hydroxide solution was supplied to maintain the liquid temperature at 70°C.

[0179] A metal-containing aqueous solution was prepared by mixing an aqueous solution of nickel sulfate, an aqueous solution of manganese sulfate, and an aqueous solution of aluminum sulfate.

[0180] Next, a metal-containing aqueous solution and an ammonium sulfate aqueous solution as a complexing agent were continuously added to the reaction vessel under stirring, in a ratio such that the atomic ratio of Ni, Mn, and Al in the reaction vessel was 93:3.5:3.5. The flow rate of the sodium hydroxide aqueous solution was also continuously supplied to the reaction vessel, increasing or decreasing it as needed. The flow rate of the sodium hydroxide aqueous solution was controlled in the same manner as in Example 1, except that the number of increases or decreases in the flow rate of the sodium hydroxide aqueous solution per hour was 88, and the rate of change in the flow rate of the sodium hydroxide aqueous solution was 4.0%. This yielded the reaction product.

[0181] After washing the reaction product, it was dehydrated using a centrifuge, isolated, and dried at 105°C to obtain MCC3, a nickel-manganese-aluminum metal composite hydroxide.

[0182] MCC3 contained secondary particles, which are aggregates of primary particles. In the empirical formula (A), MCC3 had x=0.073, z=0, and t=0. In the empirical formula (A)-1, MCC3 had x1 = 0.036, y = 0.037, and t = 0.

[0183] From the binarized image, MCC3 had high-density and low-density regions, and in the cross-section of the secondary particle, the low-density region was substantially continuous in the circumferential direction of the secondary particle and existed in the manner shown in Figure 3.

[0184] <Comparative Example 1> MCC11, a nickel-cobalt-manganese metal composite hydroxide, was obtained by the same method as in Example 1, except that the number of fluctuations per hour in increasing or decreasing the flow rate of the sodium hydroxide aqueous solution was 29, and the rate of change in the flow rate of the sodium hydroxide aqueous solution was 1.4%.

[0185] MCC11 contained secondary particles, which are aggregates of primary particles. In the empirical formula (A), MCC11 had x=0.17, z=0, and t=0. In the empirical formula (A)-1, MCC11 had x1 = 0.121, y = 0.049, and t = 0.

[0186] MCC11 did not have low-density areas in the binarized image.

[0187] [Table 1]

[0188] As shown in the results above, it was confirmed that a lithium secondary battery with high initial efficiency can be obtained by using CAM made from MCC containing secondary particles X having high-density and low-density regions. On the other hand, in a comparative example using MCC, which is a secondary particle without low-density regions, the initial efficiency was lower than in the examples. This can be presumed to be because, lacking low-density regions where lithium ions can easily penetrate, the MCC and lithium compound were not uniformly calcined during the calcination process. [Explanation of symbols]

[0189] 1: Separator, 2: Positive electrode, 2a: Positive electrode active material layer, 2b: Positive electrode current collector, 3: Negative electrode, 4: Electrode group, 5: Battery can, 6: Electrolyte, 7: Top insulator, 8: Sealing body, 10: Lithium secondary battery, 21: Positive electrode lead, 31: Negative electrode lead, 100: Laminate, 110: Positive electrode, 111: Positive electrode active material layer, 112: Positive electrode current collector, 113: External terminal, 120: Negative electrode, 121: Negative electrode active material layer, 122: Negative electrode current collector, 123: External terminal, 130: Solid electrolyte layer, 200: Outer casing, 200a: Opening, 1000: All-solid-state lithium secondary battery< / mcc>

Claims

1. A raw material for a positive electrode active material for lithium secondary batteries, which is a metal composite compound containing at least Ni, The metal composite compound comprises primary particles and secondary particles which are aggregates of the primary particles. The primary particles constituting the secondary particles have a standard deviation of their short axis of 0.1 Å or more and 100 Å or less. The secondary particle X has a high-density portion in which primary particles are aggregated at a high density and a low-density portion in which primary particles are aggregated at a low density. The secondary particle X is such that, when a binarized image is obtained by binarizing the high-density portion and the low-density portion of a scanning electron microscope image of the cross-section of the secondary particle X, the standard deviation of the ratio of the area of ​​the low-density portion obtained from the binarized image is 0.5% or more and 20% or less, and the aspect ratio of the primary particles constituting the secondary particle X is 7 or more. The high-density region is a region that turns white in a binarized image obtained by binarizing a 256-level image of a scanning electron microscope image of the cross-section of the secondary particle X with a threshold of 90. The low-density region is a region that turns black in a binarized image obtained by binarizing a 256-level image of a scanning electron microscope image of the cross-section of the secondary particle X with a threshold of 90. The high-density region is a region that turns white in a binarized image obtained by binarizing a 256-level image of a scanning electron microscope image of the cross-section of the secondary particle X with a threshold of 90. The low-density region is a region that turns black in a binarized image obtained by binarizing a 256-level image of a scanning electron microscope image of the cross-section of the secondary particle X with a threshold of 90. A metal composite compound represented by composition formula (A), which is a raw material for positive electrode active material in lithium secondary batteries. Here, the standard deviation is obtained by the following method. For the 256-level image of the cross-section of the secondary particle X, a threshold of 90 is set, and a binarized image is obtained by converting values ​​of 90 or higher to white and values ​​of less than 90 to black. For the aforementioned binarized image, the diameter (long axis length) of one arbitrarily selected secondary particle is measured. Next, we consider a grid (mesh) where the length of each side is one-tenth the length of the major axis of the secondary particle. This grid is superimposed onto the binarized image, and for all 30 or more overlapping cells where one cell completely overlaps with the binarized image, the proportion of black area within each cell is measured. Calculate the standard deviation of the percentage of black area obtained. Ni (1-x) M x O z (OH) 2-t...(A) (In compositional formula (A), 0 < x ≤ 0.5, 0 ≤ z ≤ 3, -0.5 ≤ t ≤ 1.8, and t - z < 2, and M is one or more elements selected from the group consisting of Co, Mn, and Al.)

2. The metal composite compound D ５０ The positive electrode active material raw material for a lithium secondary battery according to claim 1, wherein the following formula (1) is satisfied. 5μm≦D ５０ ≦20μm ・・・(1) (D ５０ This refers to the particle diameter (μm) at which, when the cumulative particle size distribution curve obtained by measuring the metal composite compound using a laser diffraction particle size distribution analyzer is set to 100%, the cumulative volume from the smallest particles accounts for 50%.

3. The positive electrode active material raw material for lithium secondary batteries according to claim 1 or 2, wherein when the number of secondary particles X is A and the total number of secondary particles contained in the metal composite compound is B, A / B is 0.20 or more.

4. The positive electrode active material raw material for lithium secondary batteries according to claim 1 or 2, wherein in the cross-section of the secondary particle X, the high-density portion is in the center, the low-density portion is outside the center and on the outer circumference of the center, and the high-density portion is outside the low-density portion and on the outermost layer of the secondary particle.

5. A method for producing a positive electrode active material raw material for lithium secondary batteries, which is a metal composite compound according to claim 1, comprising a reaction step of continuously supplying a metal-containing aqueous solution containing Ni and an alkaline aqueous solution to a reaction vessel, continuously growing crystals, and continuously extracting a metal composite compound, wherein in the reaction step, the flow rate of the alkaline aqueous solution is increased or decreased and continuously supplied to the reaction vessel, the number of times the increase or decrease is varied per hour is 30 or more and 100 or less, and the rate of change of the flow rate of the alkaline aqueous solution is 3% or more and 20% or less.

6. A method for producing a lithium metal composite oxide, comprising the steps of mixing a lithium compound, which is a positive electrode active material raw material for a lithium secondary battery, which is a metal composite compound according to claim 1 or 2, with a lithium compound, and firing the resulting mixture.

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