Precursor and intermediate for positive electrode active material for lithium ion secondary battery

Abstract

Provided are a precursor and an intermediate for obtaining a positive electrode active material for a lithium ion secondary battery, the positive electrode active material having excellent particle strength while maintaining good battery characteristics. A precursor for a positive electrode active material for a lithium ion secondary battery, the precursor comprising a lithium metal composite oxide, the lithium metal composite oxide comprising secondary particles obtained by aggregating primary particles, or comprising both the primary particles and the secondary particles, the present invention is characterized in that: the precursor is a metal composite hydroxide comprising secondary particles obtained by aggregating primary particles, or a metal composite hydroxide comprising both the primary particles and the secondary particles; the secondary particles comprise a core part occupying the inside of the secondary particles and a shell part surrounding the core part and covering the outside, the core part has a porous structure, the shell part has a solid structure, the metal composite hydroxide contains nickel, manganese and cobalt, and the metal composite hydroxide has a pore volume of 0.2-0.5 mL / g and an average pore diameter of 11.5-15.0 nm.

Description

Technical Field

[0001] The present invention relates to a precursor and an intermediate of a positive electrode active material for a lithium ion secondary battery. Background Art

[0002] Recently, from the viewpoint of global environmental protection, clean energy vehicles friendly to the global environment such as hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and electric vehicles (EV) with low carbon dioxide emissions are becoming popular. Among the batteries used for these clean energy vehicles, the development of lithium ion secondary batteries has been ongoing due to their excellent output characteristics and charge-discharge cycle characteristics.

[0003] In addition, in the case where it is difficult to newly build a thermal power station that burns fossil fuels, in order to cope with the increase in power demand, as one of the effective methods of power utilization, excess night power is stored in a lithium ion secondary battery installed in ordinary households and used during the day when power consumption is high, and load balancing for load equalization is performed.

[0004] Furthermore, measures to use a household storage battery composed of a lithium ion secondary battery together with a solar power generation system are gradually expanding. The stored clean power can be used not only during the day but also at night. In addition, it is highly expected as a backup power source in the event of a power outage caused by disasters such as earthquakes and typhoons.

[0005] As the positive electrode active material of such a lithium ion secondary battery, a lithium ion secondary battery using a lithium metal composite oxide having a layered or spinel-type crystal structure can obtain a voltage of up to 4V level. Therefore, as a secondary battery showing a high energy density, it is being put into practical use.

[0006] As such a lithium metal composite oxide, starting with lithium cobalt composite oxide (LiCoO2) which is relatively easy to manufacture, lithium nickel composite oxide (LiNiO2) using nickel which is cheaper than cobalt, lithium manganese composite oxide (LiMn2O4), lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O2), lithium nickel manganese cobalt composite oxide (for example, LiNi 1 / 3Mn 1 / 3 Co 1 / 3 O2), lithium nickel cobalt aluminum composite oxide (for example, LiNi 0.75 Co 0.15 Al 0.10 O2), etc. have been proposed.

[0007] Among these lithium metal composite oxides, a positive electrode active material composed of a lithium nickel cobalt aluminum composite oxide (NCA) containing nickel, cobalt, and aluminum at a specific ratio, and a positive electrode active material composed of a lithium nickel manganese cobalt composite oxide (NMC) containing nickel, manganese, and cobalt at a specific ratio, are particularly attracting attention as materials with excellent thermal stability, high capacity, good cycle characteristics, low resistance, and high output.

[0008] In addition, in the case of being used for a lithium ion secondary battery, for the purpose of obtaining a positive electrode active material with high performance, several techniques focusing on the particle structure of the above-mentioned lithium metal composite oxides have been disclosed.

[0009] In Patent Document 1, a positive electrode active material for a non-aqueous electrolyte secondary battery capable of reducing the positive electrode resistance is disclosed. The positive electrode active material is characterized in that the positive electrode active material is composed of a lithium nickel manganese composite oxide, and the lithium nickel manganese composite oxide is represented by the general formula Li 1+u Ni x Mn y Co z M t O2 (-0.05 ≤ u ≤ 0.50, x + y + z + t = 1, 0.3 ≤ x ≤ 0.7, 0.1 ≤ y ≤ 0.55, 0 ≤ z ≤ 0.4, 0 ≤ t ≤ 0.1, M is an additive element and is one or more elements selected from Mg, Ca, Al, Ti, V, Cr, Zr, Nb, Mo, W), and is composed of a hexagonal lithium-containing composite oxide having a layered structure. The average particle size of the positive electrode active material is 2 to 8 μm, [(d90 - d10) / average particle size], which is an index representing the width of the particle size distribution, is 0.60 or less, the specific surface area is 1 to 2 m 2 / g, and has a hollow structure composed of a hollow part inside the particle and a shell part outside it, and the thickness of the shell part is 0.5 to 2.5 μm.

[0010] In Patent Document 2, a positive electrode active material for a non-aqueous electrolyte secondary battery with excellent Coulomb efficiency and reaction resistance is disclosed. The positive electrode active material is characterized in that it is composed of a lithium nickel manganese composite oxide, and the lithium nickel manganese composite oxide is represented by the general formula Li a Ni x Mn y Co z M tO2 (where 0.95 ≤ a ≤ 1.20, 0.2 ≤ x ≤ 0.8, 0 ≤ y < 0.3, 0.07 < z ≤ 0.8, 0 ≤ t ≤ 0.1, x + y + z + t = 1, and M is at least one element selected from Mg, Ca, Ba, Sr, Al, Ti, V, Cr, Zr, Mo, Hf, Ta, and W) is represented and has a hollow or porous structure. The sulfate content of the positive electrode active material is 0.4 mass% or less, and the sodium content is 0.035 mass% or less.

[0011] In Patent Document 3, a positive electrode active material for a lithium battery is disclosed. It is a particle having a porous structure in which pores are distributed in the entire internal region of secondary particles formed by agglomerates of primary particles. The pores are radially distributed from the center of the secondary particles, thereby having a large specific surface area. As a result, the electrolyte easily flows into the interior of the pores, the migration resistance of lithium ions decreases, and a secondary battery with high output characteristics can be manufactured.

[0012] In Patent Document 4, a positive electrode active material for a lithium secondary battery is disclosed. As a positive electrode active material for a lithium secondary battery with excellent rate characteristics, it includes secondary particles formed by agglomeration of plural primary particles of a lithium composite metal oxide. The secondary particles have pores formed inside and through holes connecting the pores to the surface of the secondary particles, and all of the following (i) to (iii) are satisfied.

[0013] (i) In the cross-section of the secondary particles, the ratio (B / A) of the minor axis length B of the figure surrounded by the outer edge of the cross-section to the major axis length A of the figure is 0.75 or more and 1.0 or less.

[0014] (ii) The ratio of the total area of the pores exposed in the cross-section to the area of the figure is 2.0% or more and 40% or less.

[0015] (iii) The ratio of the area of the pores existing in the central portion of the secondary particles among the pores exposed in the cross-section to the total area of the pores exposed in the cross-section is 60% or more and 99% or less. (Here, the major axis length is the longest diameter among the diameters of the figure passing through the centroid position of the figure in the figure.) The central portion is the portion surrounded by a circle when assuming that the area of the figure is S and the radius r is calculated by the formula "r = (S / π) 0.5 / 2".

[0016] Prior Art Documents

[0017] Patent Documents

[0018] Patent Document 1: Japanese Patent Application Laid-Open No. 2012-254889.

[0019] Patent Document 2: International Publication No. WO2015 / 146598.

[0020] Patent Document 3: Japanese Patent Application Laid-Open No. 2017-533571.

[0021] Patent Document 4: Japanese Patent Application Laid-Open No. 2019-096406. Summary of the Invention

[0022] Problems to be Solved by the Invention

[0023] However, in the technologies of Patent Documents 1 to 4 described above, in order to improve battery characteristics, the lithium metal composite oxide has a particle structure such as high porosity, hollow, porous, or multilayer. As a result, there is a problem that the strength of the particles themselves decreases and sufficient durability cannot be obtained. Nevertheless, a solution to this problem has not been clearly known so far.

[0024] Therefore, the present inventors conducted intensive studies and found that the above problems can be solved by forming a shell portion having excellent particle strength with respect to a core portion having a particle structure such as high porosity, hollow, porous, or multilayer.

[0025] The present invention has been completed in view of the above problems, and an object thereof is to provide a precursor and an intermediate for a positive electrode active material for a lithium ion secondary battery that maintain good battery characteristics and have excellent particle strength.

[0026] Means for Solving the Problems

[0027] That is, according to one aspect of the present invention for solving the above problems, a first aspect of the present invention is a precursor for a positive electrode active material for a lithium ion secondary battery, which is a precursor for a positive electrode active material for a lithium ion secondary battery composed of a lithium metal composite oxide, the lithium metal composite oxide being composed of secondary particles aggregated from primary particles or composed of both the primary particles and the secondary particles, characterized in that the precursor is a metal composite hydroxide composed of secondary particles aggregated from primary particles or a metal composite hydroxide composed of both the primary particles and the secondary particles, the secondary particles being composed of a core portion occupying the inside of the secondary particles and a shell portion surrounding the core portion and covering the outside, the core portion having a porous structure, the shell portion having a solid structure, the metal composite hydroxide containing nickel, manganese, and cobalt, the pore volume of the metal composite hydroxide being 0.2 to 0.5 mL / g, and the average pore diameter being 11.5 to 15.0 nm.

[0028] The second aspect of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery. In the invention of the first aspect, in the particle structure observed by photographing the cross section of the secondary particles of the metal composite hydroxide, the porous structure is a cross-sectional state showing two or more pores in the particle cross section, and the solid structure is a cross-sectional state showing a filled state in the particle cross section.

[0029] The third aspect of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery. In the invention of the first or second aspect, the metal composite hydroxide has an average particle size of 3 to 8 μm.

[0030] The fourth aspect of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery. In the invention of the first or second aspect, the metal composite hydroxide has a specific surface area of 35 to 55 m 2 / g, the tap density of the metal composite hydroxide is 0.5 to 1 g / cm 3 , and the oil absorption amount of the metal composite hydroxide is 40 to 70 mL / 100 g.

[0031] The fifth aspect of the present invention is a precursor of a positive electrode active material for a lithium ion secondary battery. In the invention of the first or second aspect, the metal composite hydroxide is represented by the general formula A, namely Ni 1-x-y-z Mn x Co y M z (OH) 2+α (where 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, and M includes one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S).

[0032] The sixth aspect of the present invention is an intermediate of a positive electrode active material for a lithium ion secondary battery. The intermediate of the positive electrode active material for a lithium ion secondary battery is composed of a lithium metal composite oxide. The lithium metal composite oxide is composed of secondary particles aggregated from primary particles or composed of both the primary particles and the secondary particles. The intermediate is a metal composite oxide composed of secondary particles aggregated from primary particles or a metal composite oxide composed of both the primary particles and the secondary particles. The secondary particles are composed of a core part occupying the inside of the secondary particles and a shell part surrounding the core part and covering the outside. The core part has a porous structure, the shell part has a solid structure, and the metal composite oxide is represented by the general formula B, namely Ni 1-x-y-z Mn xCo y M z O 1+α (Satisfying 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, M contains one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S) is represented.

[0033] Effects of the Invention

[0034] It is possible to provide a precursor and an intermediate for a positive electrode active material for a lithium ion secondary battery that can obtain a lithium ion secondary battery having good battery characteristics and excellent particle strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic cross-sectional view of the metal composite hydroxide (precursor) of the present invention.

[0036] Figure 2 It is a schematic cross-sectional view of the lithium metal composite oxide of the present invention.

[0037] Figure 3 It is a schematic cross-sectional view of a coin-type battery used in the evaluation of the battery characteristics of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0038] Hereinafter, the precursor and the intermediate of the positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described in detail.

[0039] It should be noted that the present invention is not limited to the content described below, and various modification examples and substitution examples can be included without departing from the gist of the present invention.

[0040] <Positive Electrode Active Material Precursor for Lithium Ion Secondary Battery>

[0041] In the present invention, there is provided a precursor of a positive electrode active material for a lithium ion secondary battery, which is a precursor of a positive electrode active material for a lithium ion secondary battery composed of a lithium metal composite oxide. The lithium metal composite oxide is composed of secondary particles aggregated from primary particles, or composed of both the primary particles and the secondary particles. It is characterized in that the precursor is a metal composite hydroxide composed of secondary particles aggregated from primary particles, or a metal composite hydroxide composed of both the primary particles and the secondary particles. The secondary particles are composed of a core part occupying the inside of the secondary particles and a shell part surrounding the core part and covering the outside. The core part has a porous structure, and the shell part has a solid structure. The metal composite hydroxide contains nickel, manganese, and cobalt, and the pore volume of the metal composite hydroxide is 0.2 to 0.5 mL / g, and the average pore diameter is 11.5 to 15.0 nm.

[0042] (1) Composition

[0043] The metal composite hydroxide as a precursor of the positive electrode active material according to an embodiment of the present invention contains nickel, manganese, and cobalt. Specifically, it is represented by the general formula A, that is, Ni 1-x-y-z Mn x Co y M z (OH) 2+α (where 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, and M contains one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S). In addition, its critical significance is as follows.

[0044] "1 - x - y - z" representing the molar ratio of nickel (Ni) is preferably in the range of 0.2 to 0.98, more preferably in the range of 0.25 to 0.95, and particularly preferably in the range of 0.3 to 0.93. If within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, high potential / high capacity of the lithium ion secondary battery can be achieved. In contrast, when "1 - x - y - z" is less than 0.2, high potential / high capacity cannot be fully achieved, and if it is greater than 0.98, the molar ratio of other elements decreases, and its effects cannot be fully obtained.

[0045] "x", which represents the molar ratio of manganese (Mn), is preferably in the range of 0.01 to 0.5, more preferably in the range of 0.05 to 0.45, and particularly preferably in the range of 0.1 to 0.4. If within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, the thermal stability of the lithium ion secondary battery can be improved. In contrast, when "x" is less than 0.01, the thermal stability cannot be sufficiently improved. If it is greater than 0.5, manganese dissolves out from the positive electrode active material during high-temperature operation, and the cycle characteristics may deteriorate.

[0046] "y", which represents the molar ratio of cobalt (Co), is preferably in the range of 0.01 to 0.5, more preferably in the range of 0.05 to 0.45, and particularly preferably in the range of 0.1 to 0.4. If within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, the cycle characteristics of the lithium ion secondary battery can be improved. In contrast, when "y" is less than 0.01, the effect of reducing the expansion and contraction behavior of the lattice is insufficient, and the cycle characteristics cannot be sufficiently improved. If it is greater than 0.5, the amount of cobalt added is excessive, and the initial discharge capacity decreases significantly.

[0047] M is an element that contributes to the output characteristics, durability, stability, etc. of the lithium ion secondary battery and can be added arbitrarily. The value of "z", which represents the molar ratio of M, can be 0, but in order to fully obtain the above effects, it is preferably set to be greater than 0 and 0.1 or less, more preferably set to be greater than 0 and 0.05 or less, and particularly preferably set to be greater than 0 and 0.01 or less. When the value of "z" is 0, the output characteristics, durability, stability, etc. of the lithium ion secondary battery cannot be improved. On the other hand, if the value of "z" is greater than 0.1, the molar ratio of other elements decreases, and its effect cannot be fully obtained.

[0048] As such an M, one or more selected from tungsten (W), molybdenum (Mo), vanadium (V), calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), titanium (Ti), chromium (Cr), zirconium (Zr), aluminum (Al), niobium (Nb), tantalum (Ta), silicon (Si), phosphorus (P), boron (B), and sulfur (S) can be used.

[0049] (2) Pore volume

[0050] The pore volume of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably in the range of 0.2 to 0.5 mL / g, more preferably in the range of 0.2 to 0.48 mL / g, and particularly preferably in the range of 0.2 to 0.46 mL / g.

[0051] If it is within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, sintering between primary particles can be suppressed, the strength of secondary particles can be made appropriate, an increase in resistance / capacity decline and particle breakage accompanying a decrease in specific surface area can be suppressed, and the cycle characteristics can be further improved. When the pore volume is less than 0.2 mL / g, the filling property as the positive electrode active material becomes insufficient, and if it is greater than 0.5 mL / g, the strength of secondary particles becomes insufficient.

[0052] (3) Average pore diameter

[0053] The average pore diameter of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably in the range of 11.5 to 15.0 nm, more preferably in the range of 11.8 to 14.8 nm, and particularly preferably in the range of 12.0 to 14.5 nm.

[0054] If it is within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, sintering between primary particles can be suppressed, the strength of secondary particles can be made appropriate, an increase in resistance / capacity decline and particle breakage accompanying a decrease in specific surface area can be suppressed, and the cycle characteristics can be further improved. When the average pore diameter is less than 11.5 nm, the filling property as the positive electrode active material becomes insufficient, and if it is greater than 15.0 nm, the strength of secondary particles becomes insufficient.

[0055] (4) Particle morphology / Internal particle structure

[0056] The metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention almost entirely has the morphology of secondary particles formed by aggregation of a plurality of primary particles, but may also partially contain primary particles in a state not aggregated into secondary particles.

[0057] There is no particular limitation on the shape of the primary particles constituting the above secondary particles and the primary particles existing alone, and various shapes such as spherical, plate-like, needle-like, cuboid, elliptical, and rhombohedral can be adopted. In addition, there is no particular limitation on the aggregation morphology of a plurality of primary particles. In addition to the morphology of aggregation in a random direction, various morphologies such as a morphology in which secondary particles are formed by aggregating approximately evenly and radially from the central part and forming a substantially spherical shape or an elliptical shape can also be adopted.

[0058] For the particles of the precursor of the lithium metal composite oxide having the morphology of the above secondary particles, the core part occupying the inside of the particles has a porous structure, and the shell part surrounding the core part and covering the outside has a solid structure.

[0059] Here, the porous structure refers to a cross-sectional state in which, when observing the cross-sectional particle structure of the lithium metal composite oxide by photographing the cross-section of the secondary particles, there are two or more pores in the particle cross-section, that is, a structure in which a large number of pores are dispersed inside the entire secondary particle. On the other hand, the solid structure refers to a cross-sectional structure in which the particle cross-section shows a filled state.

[0060] If the above secondary particles are used, a positive electrode active material for a lithium ion secondary battery that can finally maintain good battery characteristics and has excellent particle strength can be obtained.

[0061] (5) Average particle size (MV)

[0062] The average particle size (MV) of the secondary particles of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably in the range of 3 to 8 μm, more preferably in the range of 3.5 to 7.5 μm, and particularly preferably in the range of 4 to 7 μm. If it is within the above range, in a secondary battery in which the lithium metal composite oxide obtained from the precursor is assembled as a positive electrode active material into the positive electrode, the battery capacity per unit volume can be increased, and the safety is improved and the cycle characteristics are good. In contrast, when the average particle size is less than 3 μm, the packing density of the particles becomes low when manufacturing the positive electrode, and the battery capacity per unit volume of the positive electrode deteriorates. If it is greater than 8 μm, the specific surface area of the positive electrode active material becomes low, and the interface with the electrolyte of the secondary battery decreases. As a result, the resistance of the positive electrode increases and the output characteristics of the battery deteriorate.

[0063] (6) Specific surface area

[0064] The specific surface area of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably 35 to 55 m 2 / g, more preferably 36 to 54 m 2 / g, and particularly preferably 37 to 53 m 2 / g. If it is within the above range, when using the lithium metal composite oxide obtained from the precursor as the positive electrode active material, the particle contact surface that can contact the electrolyte can be sufficiently ensured. When the specific surface area is less than 35 m 2 / g, the particle contact surface becomes too small, and the charge-discharge capacity of the particles with a porous structure cannot be obtained. If it is greater than 55 m 2 / g, the particle contact surface becomes too large, and the surface activity may become too high.

[0065] (7) Tap density

[0066] The tap density of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably 0.5 to 1 g / cm 3, more preferably 0.6 to 1 g / cm 3 , particularly preferably 0.7 to 1 g / cm 3 within the range. If within the above range, when using the lithium metal composite oxide obtained from this precursor as the positive electrode active material, the battery capacity per unit volume and the cycle characteristics of the secondary battery can be improved simultaneously. When the tapped density is less than 0.5 g / cm 3 , the filling property as the positive electrode active material is low, and thus the charge-discharge capacity cannot be sufficiently improved. If it is greater than 1 g / cm 3 , the specific surface area of the positive electrode active material decreases, and thus the reaction area with the electrolyte decreases, and the output characteristics cannot be sufficiently improved.

[0067] (8) Oil absorption amount

[0068] The oil absorption amount of the metal composite hydroxide as the precursor of the positive electrode active material in the embodiment of the present invention is preferably in the range of 40 to 70 mL / 100 g, more preferably 41 to 69 mL / 100 g, and particularly preferably 42 to 68 mL / 100 g. If within the above range, when used as the positive electrode active material, the particle contact surface that can contact the electrolyte can be sufficiently ensured. If the oil absorption amount is less than 40 mL / 100 g, the particle contact surface becomes too small, and the charge-discharge capacity of the particles with a porous structure cannot be obtained. If it is greater than 70 mL / 100 g, the particle contact surface becomes too large, and the surface activity may become too high.

[0069] <Intermediate of Positive Electrode Active Material for Lithium Ion Secondary Battery>

[0070] In the present invention, there is provided an intermediate of a positive electrode active material for a lithium ion secondary battery, which is a metal composite oxide as an intermediate of a lithium metal composite oxide. The lithium metal composite oxide is composed of secondary particles aggregated from primary particles or composed of both the primary particles and the secondary particles. It is characterized in that the secondary particles are composed of a core part and a shell part. The core part has a porous structure, the shell part has a solid structure, and the metal composite oxide is represented by the general formula B, i.e., Ni 1-x-y-z Mn x Co y M z O 1+α (satisfying 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, and M contains one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, S).

[0071] It should be noted that in the firing for obtaining the lithium metal composite oxide, a precursor, an intermediate, or a mixture thereof can be used.

[0072] (1) Composition

[0073] Preferably, the composition of the metal composite hydroxide as the intermediate of the positive electrode active material in the embodiment of the present invention is represented by the above general formula B. When the intermediate of this composition is used as the positive electrode active material and further used in a lithium ion secondary battery, a lithium ion secondary battery with excellent battery characteristics such as battery capacity (charge-discharge capacity) can be obtained. Moreover, the molar ratio (content) of nickel, manganese, cobalt, and M that can be optionally added and the critical significance are the same as those described in the above precursor.

[0074] (2) Particle morphology / Internal particle structure

[0075] Regarding the particle morphology / Internal particle structure, the core part of the secondary particles of the metal composite hydroxide as the intermediate of the positive electrode active material in the embodiment of the present invention has a porous structure, and the shell part has a solid structure, almost completely retaining the characteristics of the above precursor.

[0076] Examples

[0077] Hereinafter, the present invention will be specifically described using examples and comparative examples. In addition, in the following examples and comparative examples, unless otherwise specified, reagents manufactured by Fujifilm Wako Pure Chemical Corporation are used. Furthermore, the present invention is not limited by any of the following examples and comparative examples.

[0078] It should be noted that the various evaluation methods and battery evaluation methods used in the examples and comparative examples are as follows.

[0079] (Various evaluation methods)

[0080] (1) Composition

[0081] Regarding the composition, the sample is heated and decomposed with an inorganic acid to become an analysis sample solution, and this analysis sample solution is measured using ICPE-9000 (manufactured by Shimadzu Corporation), a multi-functional inductively coupled plasma (ICP) optical emission spectrometer, to obtain the result.

[0082] (2) Pore volume

[0083] Regarding the pore volume, it is obtained by analyzing the sample using the nitrogen adsorption / desorption method based on the Barrett-Joyner-Halenda method (BJH method), and the measurement is performed using QUADRASORB-SI (manufactured by Quantachrome Instruments), an independent four-station specific surface area / pore distribution measuring device.

[0084] (3) Average pore diameter

[0085] For the average pore diameter, it was determined by analyzing the sample using the nitrogen adsorption / desorption method with the Barrett-Joyner-Halenda method (BJH method), and the measurement was carried out using QUADRASORB-SI (manufactured by Quantachrome Instruments, USA), an independent four-station specific surface area / pore size distribution measuring device.

[0086] (4) Particle structure

[0087] For the particle structure, the sample particles were cut using a cross-section polishing machine IB-19530CP (manufactured by JEOL Ltd., Japan) as a cross-section preparation device. In addition, the cross-section was observed using a JSM-7001F (manufactured by JEOL Ltd., Japan) as a Schottky field emission scanning electron microscope (SEM-EDS).

[0088] (5) Average particle size

[0089] The sample was measured using the laser diffraction / scattering method, and the average particle size (MV) was determined based on the volume-based distribution. It should be noted that for the measuring device, Microtrac MT3300EX-II (manufactured by Microtrac Bellcompany), a particle size distribution measuring device that uses the laser diffraction / scattering method and has an ultrasonic generator built-in, was used.

[0090] (6) Specific surface area

[0091] The specific surface area was determined by analyzing the sample using the nitrogen adsorption / desorption method based on the BET (Brunauer-Emmett-Teller) single-point method, and the measurement was carried out using the Macsorb1200 series (manufactured by MOUNTECH Co., Ltd.), a specific surface area measuring device with a gas flow method.

[0092] (7) Tap density

[0093] For the tap density, 12 g of the sample was collected and placed in a 20 mL graduated cylinder. After installing this graduated cylinder on a KRS-409 (manufactured by Kuramochi Scientific Instruments Co., Ltd.) as a vibration densitometer, the operation of freely dropping it from a height of 2 cm was repeated 500 times to determine it.

[0094] (8) Oil absorption

[0095] For the oil absorption, DBP (dibutyl phthalate, di-n-butyl phthalate) is used as the reagent liquid, and the measurement is carried out using an absorption amount measuring device based on "JIS_K_6217-4:2008 (Carbon black for rubber - Basic characteristics - Part 4: Method for determination of oil absorption (including compressed specimens))", and the result is obtained as the DBP absorption amount. This measurement result is calculated as the absorption amount per 100 g of the specimen, so the unit is expressed as "mL / 100 g". In addition, S-500 (manufactured by ASAHISOUKEN CORPORATION) is used for the measurement.

[0096] (Battery evaluation method)

[0097] (1) Method for manufacturing the evaluation battery (coin-type battery CBA)

[0098] For Figure 3 the method for manufacturing the evaluation battery (coin-type battery CBA) shown, first, 52.5 mg of the above-mentioned positive electrode active material, 15 mg of acetylene black, and 7.5 mg of polytetrafluoroethylene are weighed and mixed respectively, and are press-molded at a pressure of 100 MPa into a shape with a diameter of 11 mm and a thickness of 100 μm to manufacture the positive electrode PE (evaluation electrode). Then, the manufactured positive electrode PE is dried in a vacuum dryer at 120 °C for 12 hours, and using this positive electrode PE, a 2032-type coin-type battery CBA is manufactured in a glove box with an argon gas environment where the dew point is managed at -80 °C.

[0099] In addition, for the negative electrode NE, metallic lithium with a diameter of 17 mm and a thickness of 1 mm is used, for the electrolyte, an equal-volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (manufactured by Toyama Chemical Co., Ltd.) with 1 mole of LiClO4 as the supporting electrolyte is used, and for the separator SE, a polyethylene porous membrane with a film thickness of 25 μm is used. It should be noted that the coin-type battery CBA is assembled into a coin-type battery by arranging a gasket GA and a corrugated washer WW between the positive electrode can PC and the negative electrode can NC.

[0100] (2) Initial discharge capacity

[0101] For the initial discharge capacity, after manufacturing Figure 3 the evaluation battery (coin-type battery CBA) shown and leaving it for about 24 hours, after the open-circuit voltage OCV (open_circuit_voltage) is stabilized, the current density of the positive electrode is set to 0.1 mA / cm 2, the initial charge capacity was obtained by charging to a cut-off voltage of 4.3V, and after a 1-hour interruption, it was obtained as the capacity when discharging to a cut-off voltage of 3.0V. In addition, measurement was performed using the R6741A (manufactured by ADVANTEST CORPORATION), a multi-channel voltage / current generator.

[0102] (3) Positive electrode resistance

[0103] For the positive electrode resistance, an evaluation battery (coin-type battery CBA) as shown in Figure 3 was fabricated. The evaluation battery was charged at a charging potential of 4.1V, and measurement was performed using a frequency response analyzer and a potentiostat by the AC impedance method to obtain a Nyquist plot. And this Nyquist plot is represented as the sum of characteristic curves showing solution resistance, negative electrode resistance and its capacitance, and positive electrode resistance and its capacitance. Based on the Nyquist plot, fitting calculation was performed using an equivalent circuit to calculate the positive electrode resistance.

[0104] Example 1

[0105] (1) Manufacture of metal composite hydroxide (precursor)

[0106] First, 15L of water was placed in a 60L reaction tank, and while stirring, the temperature inside the tank was set to 40°C. Under stirring, a mixed gas with an air-to-argon ratio of 1:6 was continuously introduced into the tank. In this way, by using a mixed gas of air and argon and / or helium, secondary particles with excellent strength can be obtained.

[0107] Then, an appropriate amount of an alkali solution (25 mass% sodium hydroxide aqueous solution) and an ammonium ion donor (25 mass% ammonia water) were added to the water in the tank to prepare a reaction solution such that the pH (based on a liquid temperature of 25°C, the same below) became 12.8 and the ammonium ion concentration became 10 g / L.

[0108] On the other hand, nickel sulfate hexahydrate, manganese sulfate monohydrate, and cobalt sulfate heptahydrate were weighed so that the composition ratio of nickel, manganese, and cobalt was Ni:Mn:Co = 50:30:20, and they were dissolved in water so that the total concentration of nickel, manganese, and cobalt was 2 mol / L to prepare a raw material solution.

[0109] Then, the raw material solution was added to the reaction solution in the tank at a rate of 100 mL / min. At the same time, the alkali solution and the ammonium ion donor were also added to the reaction solution at a specified rate. Nucleation was carried out by performing crystallization for 1 minute while maintaining the pH of the reaction solution at 12.8 (nucleation process pH) and the ammonium ion concentration at 10 g / L.

[0110] After temporarily stopping the supply of the raw material solution, the alkali solution, and the ammonium ion donor, sulfuric acid is added until the pH of the reaction solution becomes 11.6 (particle growth process pH). After reaching 11.6, the supply of the raw material solution, the alkali solution, and the ammonium ion donor is started again. Crystallization is carried out for 4.5 hours while maintaining the pH at 11.6 and the ammonium ion concentration at 10 g / L, thereby growing the particles.

[0111] Through the above crystallization process, a nickel-manganese-cobalt composite hydroxide (Ni 0.5 Mn 0.3 Co 0.2 (OH)2) slurry containing a metal composite hydroxide with a porous structure in the core part and a solid structure in the shell part (precursor) is obtained.

[0112] The slurry containing the obtained metal composite hydroxide is put into a filter press, and the metal composite hydroxide cake is recovered by pressure filtration. The metal composite hydroxide cake is returned to the reaction tank, the tank is filled with an alkali washing solution (5 mass% sodium hydroxide aqueous solution), stirred for 30 minutes for alkali washing, and then pressure filtration using the filter press is carried out again to recover the alkali washing cake. The alkali washing cake is returned to the reaction tank, the tank is filled with water, stirred for 30 minutes for fine washing, and then pressure filtration using the filter press is carried out again to recover the washing cake.

[0113] The recovered washing cake is dried at 150 °C for 5 hours using an electric heating dryer to obtain a metal composite hydroxide.

[0114] It should be noted that the evaluation results of each of the obtained metal composite oxides are shown in Table 1.

[0115] (2) Manufacture of metal composite oxide (intermediate)

[0116] The obtained metal composite hydroxide (precursor) is pre-calcined by heating in an air (oxygen concentration: 21 vol%) stream at 450 °C for 2 hours, and then oxidized and roasted by heating in an air (oxygen concentration: 21 vol%) stream at 600 °C for 5 hours to obtain a nickel-manganese-cobalt composite oxide (intermediate) with a porous structure in the core part and a solid structure in the shell part (Ni 0.5 Mn 0.3 Co 0.2 O).

[0117] (3) Manufacture of lithium metal composite oxide (positive electrode active material)

[0118] Weigh the metal composite oxide (intermediate) obtained by oxidative roasting and lithium hydroxide as a lithium compound in such a way that the ratio of the number of lithium atoms (Li) to the number of metal atoms other than lithium (Me), i.e., "ratio (Li / Me)", becomes 1.03, and mix them well to obtain a lithium mixture. After pre-calcining the lithium mixture by heating it at 450 °C for 10 hours in a stream of oxygen (oxygen concentration: 100% by volume), sinter it by heating at 860 °C for 5 hours in a stream of oxygen (oxygen concentration: 100% by volume) to obtain a lithium sintered product.

[0119] By pulverizing the aggregates contained in the lithium sintered product, finally obtain lithium nickel manganese cobalt composite oxide (Li 1.03 Ni 0.5 Mn 0.3 Co 0.2 O2), which is a positive electrode active material with a porous structure in the core part and a solid structure in the shell part.

[0120] It should be noted that the evaluation results of each of the obtained lithium metal composite oxides are shown in Table 1.

[0121] Example 2

[0122] Except for the following conditions, the same steps as in Example 1 were carried out.

[0123] [Manufacture of metal composite hydroxide (precursor)]

[0124] In the crystallization step, while stirring, continuously introduce a mixed gas with a ratio of air to argon of 1:4 into the reaction tank and carry out crystallization for 4.5 hours.

[0125] [Manufacture of metal composite oxide (intermediate)]

[0126] Do not carry out the manufacture of the metal composite oxide (intermediate), and use the metal composite hydroxide (precursor) as the raw material for sintering.

[0127] It should be noted that the evaluation results of each of the obtained metal composite hydroxide and lithium metal composite oxide are shown in Table 1.

[0128] Example 3

[0129] Except for the following conditions, the same steps as in Example 1 were carried out.

[0130] [Manufacture of metal composite hydroxide (precursor)]

[0131] In the crystallization step, while stirring, continuously introduce a mixed gas with a ratio of air to argon of 1:2 into the reaction tank and carry out crystallization for 4.5 hours.

[0132] [Manufacture of Metal Composite Oxide (Intermediate)]

[0133] Instead of manufacturing the metal composite oxide (intermediate), firing was carried out using the metal composite hydroxide (precursor) as the raw material.

[0134] It should be noted that the respective evaluation results of the obtained metal composite hydroxide and lithium metal composite oxide are shown in Table 1.

[0135] (Comparative Example 1)

[0136] Except for the following conditions, the same steps as in Example 1 were carried out.

[0137] [Manufacture of Metal Composite Hydroxide (Precursor)]

[0138] In the crystallization step, while stirring, a mixed gas obtained by mixing air in nitrogen so that the oxygen concentration becomes 7% by volume was continuously introduced into the reaction tank, and crystallization was carried out for 4.5 hours.

[0139] [Manufacture of Metal Composite Oxide (Intermediate)]

[0140] Instead of manufacturing the metal composite oxide (intermediate), firing was carried out using the metal composite hydroxide (precursor) as the raw material.

[0141] It should be noted that the respective evaluation results of the obtained metal composite hydroxide and lithium metal composite oxide are shown in Table 1.

[0142] (Comparative Example 2)

[0143] Except for the following conditions, the same steps as in Example 1 were carried out.

[0144] [Manufacture of Metal Composite Hydroxide (Precursor)]

[0145] In the crystallization step, first, the inside of the reaction tank was controlled to a non-oxidizing environment with an oxygen concentration of 0.1% by volume while stirring. After nucleation was carried out while entraining the gas phase part gas into the liquid phase part, crystallization was continued for 0.9 hours in the non-oxidizing environment to carry out particle growth.

[0146] Then, the supply of the raw material solution, the alkali solution, and the ammonium ion donor was stopped, and the inside of the reaction tank was switched to an oxidizing environment (air environment) while stirring. The supply of the raw material solution, the alkali solution, and the ammonium ion donor was started again, and crystallization was carried out for 0.9 hours in the oxidizing environment.

[0147] Then, the switching between the crystallization in the non-oxidizing environment and the crystallization in the oxidizing environment as described above was carried out 3 times (a total of 4 times, that is, non-oxidation → oxidation → non-oxidation → oxidation → non-oxidation).

[0148] [Manufacture of Metal Composite Oxide (Intermediate)]

[0149] Instead of manufacturing the metal composite oxide (intermediate), firing was carried out using a metal composite hydroxide (precursor) as a raw material.

[0150] It should be noted that the evaluation results of the obtained metal composite hydroxide and lithium metal composite oxide are shown in Table 1.

[0151] Table 1

[0152]

[0153] [Comprehensive Evaluation]

[0154] It was confirmed that compared with the lithium metal composite oxides of Comparative Examples 1 and 2 using the precursors and intermediates of the positive electrode active materials for lithium ion secondary batteries that are outside the scope of the present invention, the lithium metal composite oxides (positive electrode active materials) of Examples 1 to 3 using the precursors and intermediates of the positive electrode active materials for lithium ion secondary batteries within the scope of the present invention have excellent particle strength in any case.

[0155] In addition, it was also confirmed that when the lithium metal composite oxides of Examples 1 to 3 are used in lithium ion secondary batteries, compared with the lithium metal composite oxides of Comparative Examples 1 and 2, if the overall porosity is considered, the initial discharge capacity is equal to or higher and the positive electrode resistance is small. It should be noted that in Comparative Example 1, although similarly to Examples 1 to 3, the core part of the secondary particles of the lithium metal composite oxide has a porous structure and the shell part has a solid structure, the particle strength has not been improved. As a reason, it can be considered that there are relatively large problems in the environmental control (composition of the mixed gas, etc.) in the reaction tank during the crystallization process.

[0156] In addition, the technical scope of the present invention is not limited to the modes described in the above-mentioned one embodiment or the like. One or more of the requirements described in the above-mentioned one embodiment or the like can be omitted. It should be noted that the requirements described in the above-mentioned one embodiment or the like can be appropriately combined. In addition, within the maximum scope permitted by law, the contents of all documents cited in this specification are incorporated herein by reference as part of the description.

[0157] Explanation of Reference Numerals

[0158] CBA: Coin-type battery (for evaluation).

[0159] PE: Positive electrode (evaluation electrode).

[0160] NE: Negative electrode.

[0161] SE: Spacer.

[0162] GA: Gasket.

[0163] WW: Wave washer.

[0164] PC: Positive can.

[0165] NC: Negative can.

Claims

1. A precursor of a positive electrode active material for a lithium ion secondary battery, which is a precursor of a positive electrode active material for a lithium ion secondary battery composed of a lithium metal composite oxide, the lithium metal composite oxide being composed of secondary particles aggregated from primary particles, or composed of both the primary particles and the secondary particles, characterized in that, the precursor is a metal composite hydroxide composed of secondary particles aggregated from primary particles, or a metal composite hydroxide composed of both the primary particles and the secondary particles, the secondary particles are composed of a core part occupying the inside of the secondary particles and a shell part surrounding the core part and covering the outside, the core part has a porous structure and the shell part has a solid structure, the metal composite hydroxide contains nickel, manganese and cobalt, the pore volume of the metal composite hydroxide is 0.2 to 0.5 mL / g and the average pore diameter is 11.5 to 15.0 nm.

2. The precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1, characterized in that, in the particle structure observed by photographing the cross section of the secondary particles of the metal composite hydroxide, the porous structure is a structure showing a cross-sectional state having two or more pores in the particle cross section, the solid structure is a structure showing a cross-sectional state in which the particle cross section is in a filled state.

3. The precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that, the metal composite hydroxide has an average particle diameter of 3 to 8 μm.

4. The precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that, The metal composite hydroxide has a specific surface area of 35 to 55 m 2 / g, the tapped density of the metal composite hydroxide is 0.5 to 1 g / cm 3 , and the oil absorption amount of the metal composite hydroxide is 40 to 70 mL / 100 g.

5. The precursor of a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, characterized in that, The metal composite hydroxide is represented by General Formula A, i.e., Ni 1-x-y-z Mn x Co y M z (OH) 2+α wherein General Formula A satisfies 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, and M includes one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S.

6. An intermediate of a positive electrode active material for a lithium ion secondary battery, which is an intermediate of a positive electrode active material for a lithium ion secondary battery composed of a lithium metal composite oxide, the lithium metal composite oxide being composed of secondary particles aggregated from primary particles, or composed of both the primary particles and the secondary particles, characterized in that, the intermediate is a metal composite oxide composed of secondary particles aggregated from primary particles, or a metal composite oxide composed of both the primary particles and the secondary particles, the secondary particles are composed of a core part occupying the inside of the secondary particles and a shell part surrounding the core part and covering the outside, the core part has a porous structure and the shell part has a solid structure, The metal composite oxide is represented by General Formula B, i.e., Ni 1-x-y-z Mn x Co y M z O 1+α where General Formula B satisfies 0.01 ≤ x ≤ 0.5, 0.01 ≤ y ≤ 0.5, 0 ≤ z ≤ 0.1, and -0.1 ≤ α ≤ 0.2, and M contains one or more elements selected from W, Mo, V, Ca, Mg, Sr, Ba, Ti, Cr, Zr, Al, Nb, Ta, Si, P, B, and S.

Images