Precursor of positive electrode active material

Abstract

A precursor for a positive electrode active material is provided, which yields a positive electrode active material with excellent cycle characteristics. The precursor comprises secondary particles formed by the aggregation of multiple primary particles, wherein the primary particles comprise a nickel complex hydroxide. In the pore distribution (pore volume per unit weight relative to pore diameter) of the precursor determined by mercury intrusion porosimetry, the number of peaks having a peak area of ​​2% or more within a range where the pore diameter is less than or equal to twice the average particle size D50 of the precursor, and the total pore volume of the range is set to 100%, is 1, and the average pore diameter is 0.90 μm or more.

Description

Technical Field

[0001] This disclosure relates to precursors of positive electrode active materials. Background Technology

[0002] Various technologies have been proposed regarding the positive electrode active materials disclosed in Japanese Patent Application Publication No. 2024-83946 and Japanese Patent Application Publication No. 2021-24764. Summary of the Invention

[0003] In the past, various positive electrode active materials have been proposed in order to obtain positive electrodes with high battery characteristics such as high cycle performance and high output performance.

[0004] For example, Japanese Patent Application Publication No. 2024-83946 discloses a precursor for a positive electrode active material for lithium-ion secondary batteries, which is composed of a lithium metal composite hydroxide containing secondary particles formed by the aggregation of primary particles. Japanese Patent Application Publication No. 2024-83946 discloses the following: By forming a shell with excellent particle strength from a core having a high porosity, hollow, and porous particle structure, a positive electrode active material for lithium-ion secondary batteries that maintains good battery characteristics and has excellent particle strength can be obtained.

[0005] The positive electrode active material obtained by sintering the precursor described in Japanese Patent Application Publication No. 2024-83946 sometimes develops cracks when repeatedly charged and discharged. These cracks in the positive electrode active material cause a decrease in the capacity of the secondary battery; therefore, a positive electrode active material with excellent cycle characteristics is required.

[0006] This disclosure was made in view of the above-mentioned circumstances, and its main purpose is to provide a precursor of a positive electrode active material that can yield a positive electrode active material with excellent cycle characteristics.

[0007] That is, this disclosure includes the following methods.

[0008] <1>

[0009] A precursor for a positive electrode active material, said precursor comprising secondary particles formed by the aggregation of multiple primary particles.

[0010] The primary particles contain nickel complex hydroxide.

[0011] In the pore distribution (pore volume per unit weight relative to pore diameter) of the precursor determined by mercury intrusion porosimetry, there is one peak with a peak area of ​​2% or more when the total pore volume of the range within which the pore diameter is less than twice the average particle size D50 of the precursor is set to 100%, and the average pore diameter is 0.90 μm or more.

[0012] <2>

[0013] According to the precursor described in <1>, the average pore size is less than 4.20 μm.

[0014] <3>

[0015] According to the precursor described in <1> or <2>, the nickel complex hydroxide is a nickel-cobalt-manganese complex hydroxide.

[0016] According to this disclosure, a precursor for a positive electrode active material can be provided, which can yield a positive electrode active material with excellent cycle characteristics. Attached Figure Description

[0017] Hereinafter, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described with reference to the accompanying drawings, wherein the same reference numerals denote the same elements.

[0018] Figure 1A This is a schematic diagram illustrating a structural example of the precursor of this disclosure.

[0019] Figure 1B This is a schematic diagram illustrating a structural example of the precursor of this disclosure.

[0020] Figure 2 This is a schematic diagram of the reaction vessel used in the precursor synthesis of the embodiment.

[0021] Figure 3 This is a schematic diagram illustrating a precursor structure example where there are two peaks in the pore distribution. Detailed Implementation

[0022] The following describes embodiments of this disclosure. Furthermore, matters necessary for the implementation of this disclosure other than those specifically mentioned in this specification (e.g., the general composition and manufacturing process of positive electrode active materials and their precursors that are not features of this disclosure) can be grasped by those skilled in the art based on existing technology. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the art.

[0023] In addition, the dimensional relationships (length, width, thickness, etc.) in the diagram do not reflect the actual dimensional relationships.

[0024] In this disclosure, a precursor of a positive electrode active material is provided, the precursor comprising secondary particles formed by the aggregation of a plurality of primary particles, the primary particles comprising nickel complex hydroxide, wherein, in the pore distribution (pore volume per unit weight relative to pore diameter) of the precursor determined by mercury intrusion porosimetry, when the total pore volume of the range in which the pore diameter is less than twice the average particle diameter D50 of the precursor is set to 100%, the number of peaks having a peak area of ​​2% or more is 1, and the average pore diameter is 0.90 μm or more.

[0025] Here, the method for counting the number of peaks in the pore distribution described above in this disclosure will be explained.

[0026] First, in this disclosure, data for the precursor are used within the range of less than twice the average particle size D50 of the precursor, as determined by mercury porosimetry (pore volume per unit weight relative to pore diameter). Specifically, the vertical axis represents the pore volume per unit weight, and the horizontal axis represents the pore diameter, extending up to less than twice the average particle size D50 of the precursor. Peaks exceeding twice the average particle size D50 of the precursor are not considered.

[0027] Furthermore, the average particle size D50 of the precursor refers to the particle size at which the cumulative value of the particle size distribution on a volume basis reaches 50%, i.e., the median particle size, which can be determined by dynamic light scattering. Alternatively, the average particle size D50 can also be calculated using laser diffraction scattering, electrical detection banding, cross-sectional image analysis based on SEM (Scanning Electron Microscope), and cross-sectional image analysis based on TEM (Transmission Electron Microscope).

[0028] Next, in the micropore distribution within the aforementioned range, the point where the slope of the distribution changes from negative to positive is identified as a peak.

[0029] Then, the peak area of ​​each identified peak is calculated, which is the sum of the Y coordinate values ​​of each identified peak.

[0030] Then, when the total pore volume of the above range is set to 100%, in other words, when the total Y-coordinate values ​​of the above range are set to 100%, peaks with a calculated peak area of ​​2% or more are counted as one peak. Peaks with an area of ​​less than 2% are not counted as peaks. The percentage of each peak's area can be calculated using the following formula.

[0031] Peak area percentage (%) = Sum of Y-coordinate values ​​of all peaks ÷ Sum of total Y-coordinate values ​​× 100

[0032] Furthermore, the method for determining the pore size distribution based on mercury porosimetry can be any known method, such as using a mercury porosimetry instrument. Additionally, the method for calculating the average pore size based on the pore size distribution measured by mercury porosimetry can also be a known method.

[0033] The active material obtained by sintering the precursor of this disclosure, which has the microporous characteristics described above, has a dense structure and is therefore not prone to cracking even with repeated charge and discharge, exhibiting excellent cycle resistance. Therefore, according to this disclosure, it is possible to realize a secondary battery with excellent cycle characteristics that does not easily experience capacity degradation during charge and discharge.

[0034] Figure 1A , Figure 1B This is a schematic diagram illustrating a structural example of the precursor of this disclosure. Figure 1A It is an image of the precursor of micropore C1 with a relatively large pore size. Figure 1B This is an image of the precursor C2 with relatively small pore diameters. (Example:) Figure 1A , Figure 1B As shown, the precursor of this disclosure comprises secondary particles B formed by the condensation of multiple primary particles A. In addition to secondary particles, the precursor of this disclosure may also contain single, non-condensed primary particles.

[0035] Furthermore, the precursor of this disclosure, as determined by mercury porosimetry, exhibits only one peak in the aforementioned pore distribution; therefore, as Figure 1A , Figure 1B As shown, it is assumed that there are fine pores between secondary particles B. Conversely, it is assumed that when the number of peaks in the aforementioned fine pore distribution is two or more, such as... Figure 3 As shown, not only are there pores C3 between secondary particles B, but there are also pores C4 within secondary particles B (between primary particles A). Figure 3 This is a schematic diagram illustrating a precursor structure example where the number of peaks in the pore distribution is 2.

[0036] The precursor of this disclosure is characterized in that, apart from having only one peak in the aforementioned pore distribution, the average pore diameter calculated from the pore distribution measured using mercury porosimetry is 0.90 μm or more. It has been confirmed that if the average pore diameter is less than 0.90 μm, even if there is only one peak, the effect of improving circulation characteristics is not obtained. In the precursor of this disclosure, an average pore diameter of 0.90 μm or more is acceptable, but for example, it can also be 4.20 μm or less.

[0037] In this disclosure, the primary particles comprise nickel complex hydroxides. Nickel complex hydroxides are hydroxides comprising nickel (Ni) and other metals besides nickel. The other metals besides nickel can be one or more. Examples of other metals besides nickel include manganese (Mn), cobalt (Co), and aluminum (Al). Specific examples of nickel complex hydroxides include nickel-cobalt complex hydroxides comprising nickel and cobalt, nickel-cobalt-manganese complex hydroxides comprising nickel, cobalt, and manganese, and nickel-cobalt-aluminum complex hydroxides comprising nickel, cobalt, and aluminum. Nickel complex hydroxides can also be nickel-cobalt-manganese complex hydroxides.

[0038] In these nickel-cobalt composite hydroxides, the molar ratio (ratio) of nickel to each other metal relative to the total amount of nickel and other metals is not particularly limited. For nickel-cobalt composite hydroxides, the molar ratio can be as follows: Ni / NiCo can be 0.5 or more and 1.0 or less, and Co / NiCo can be 0 or more and 0.5 or less. For nickel-cobalt-manganese composite hydroxides, the molar ratio can be as follows: Ni / NiCoMn can be 0.5 or more and 1.0 or less, Co / NiCoMn can be 0 or more and 0.3 or less, and Mn / NiCoMn can be 0 or more and 0.3 or less. For nickel-cobalt-aluminum composite hydroxides, the molar ratio can be as follows: Ni / NiCoAl can be 0.5 or more and 1.0 or less, Co / NiCoAl can be 0 or more and 0.3 or less, and Al / NiCoAl can be 0 or more and 0.3 or less.

[0039] Furthermore, in this disclosure, the nickel complex hydroxide may also contain other metals besides nickel, cobalt, aluminum, and manganese. These other metals may be, for example, at least one selected from Zr, Mo, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, and Ag.

[0040] There is no particular limitation on the size of primary particles. For example, in the case of flat shapes such as plates or needles, the average value of the length (thickness) in the short side direction can be 10 nm to 200 nm. The size of a primary particle can be determined, for example, by measuring the thickness of the cross-section of multiple primary particles in TEM or SEM images and calculating their average value.

[0041] As described above, there is no particular limitation on the size of secondary particles formed by the aggregation of multiple primary particles. For example, the average particle size of secondary particles can be 4 μm to 15 μm, or 4 μm to 10 μm. The average particle size of secondary particles, like that of primary particles, can be determined by measuring the particle size of multiple secondary particles using TEM or SEM and calculating their average value.

[0042] The method for manufacturing the precursor of the positive electrode active material disclosed herein is not particularly limited, but the following methods can be listed as examples.

[0043] First, a water-soluble nickel source (nickel compound) and other water-soluble metal sources (cobalt compound, manganese compound, aluminum compound, etc.) that will become the raw materials for nickel hydroxide are dissolved in ion-exchanged water to prepare an aqueous metal raw material solution. In this solution, the stoichiometric ratio (mol%) of nickel and other metals relative to the total stoichiometric ratio (mol%) of nickel and other metals is typically equal to the stoichiometric ratio (mol%) of nickel and other metals constituting the nickel hydroxide. The water-soluble metal compounds are not particularly limited; for example, sulfates can be included. The concentration of the aqueous metal raw material solution is not particularly limited; for example, it can be set to a total concentration of the metals (the ratio of all raw materials to the aqueous metal raw material solution) of 1.5 mol / L.

[0044] Next, a certain amount of NH3 aqueous solution (ammonium ion donor) is added to the reaction vessel, and nitrogen replacement is carried out while stirring with a stirrer to form a non-oxidizing atmosphere.

[0045] Next, an aqueous sodium hydroxide solution is added to the reaction vessel, and while maintaining the pH value at an alkaline level (e.g., pH 11), the aforementioned aqueous solutions of the metal raw materials and NH3 are added dropwise into the reaction vessel. Here, if a certain amount of NH3 aqueous solution is added to the reaction vessel beforehand as the initial NH3 aqueous solution, the ratio of the initial NH3 aqueous solution volume (A) to the total volume of each aqueous solution used in the reaction [the total volume of the initial NH3 aqueous solution (A), NaOH aqueous solution (B), metal raw material aqueous solution (C), and added NH3 aqueous solution (D)] (calculated by the following formula) is not particularly limited, for example, it can be set to 1 / 20.

[0046] The initial proportion of NH3 aqueous solution (A) = (A) / [(A) + (B) + (C) + (D)]

[0047] There is no particular limitation on the reaction temperature. The reaction time can be, for example, 8 to 12 hours.

[0048] After the reaction is complete, a drying process is performed. For example, the drying process can be carried out at 110°C for 10 hours under an inert gas atmosphere.

[0049] The precursor of the positive electrode active material disclosed herein can be used as a positive electrode active material in lithium-ion batteries, for example, by being converted into lithium-nickel composite oxide.

[0050] The lithium-nickel composite oxide can be manufactured from the precursor of this disclosure, for example, by mixing a nickel composite hydroxide, which is the precursor of this disclosure, and a lithium compound, which is the lithium source, and then calcining the resulting mixture.

[0051] Examples of lithium compounds include at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, and lithium chloride.

[0052] Regarding the ratio of lithium compounds and precursors in the mixture, the molar percentage (mol%) of lithium and other metals relative to the total stoichiometric ratio (mol%) of lithium and metals contained in the precursors in the target cathode active material is typically equal to the molar percentage (mol%) of lithium and other metals in the mixture. There are no particular limitations on the mixing method; known methods may be used.

[0053] The resulting mixture can be used to obtain lithium-nickel composite oxides, for example, by calcining at 700–950 °C for 8–15 hours in an oxygen atmosphere. Calcination can be performed using a known calcining furnace such as a muffle furnace.

[0054] It is believed that the positive electrode active material obtained by burning the publicly disclosed precursor is usually composed of single crystal particles.

[0055] Here, a single crystal particle refers to a single particle that does not constitute a secondary particle; it is a particle that is essentially composed of a single crystal. Single crystal particles can be identified by the fact that grain boundaries cannot be observed in SEM images.

[0056] The precursors of the positive electrode active material provided by this disclosure can be used, for example, as precursors of the positive electrode active material constituting the positive electrode of a battery (such as a lithium-ion battery). That is, in this disclosure, a battery in which a positive electrode, an electrolyte layer, and a negative electrode are stacked in sequence can be provided, wherein the positive electrode contains a positive electrode active material obtained from the precursors of this disclosure.

[0057] The following is an explanation of the battery.

[0058] The positive electrode has a positive electrode layer and, if necessary, a positive electrode current collector.

[0059] The positive electrode layer is a layer containing at least a positive electrode active material. The positive electrode active material may contain only the positive electrode active material obtained from the precursor described above, or it may further contain other active materials. The content of the positive electrode active material in the positive electrode layer is not particularly limited, and may, for example, be 20-80% by mass.

[0060] The positive electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, as needed.

[0061] Examples of electrolytes include solid electrolytes. Solid electrolytes can be inorganic solid electrolytes such as sulfide solid electrolytes, halide solid electrolytes, oxide solid electrolytes, and complexed hydride solid electrolytes, or organic solid electrolytes such as gel electrolytes. The proportion of solid electrolyte in the positive electrode layer can be, for example, 10 to 60% by mass.

[0062] Examples of conductive materials include carbon materials, metal particles, and conductive polymers. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and Ketjen black (KB), fibrous carbon materials such as vapor-phase carbon fiber (VGCF), carbon nanotubes (CNTs), and carbon nanofibers (CNFs). The proportion of conductive material in the positive electrode layer can be, for example, 0.1 to 5% by mass.

[0063] Examples of adhesives include styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), butadiene rubber (BR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-isoprene-styrene block copolymer (SIS), and ethylene-propylene-diene copolymer (EPDM). The proportion of the adhesive in the positive electrode layer can be, for example, 0.5 to 5% by mass.

[0064] Materials used as positive current collectors include, for example, SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive current collector can be foil-like or plate-like. The top view shape of the positive current collector is not particularly limited; for example, circular, elliptical, rectangular, and arbitrary polygonal shapes can be used. The positive current collector can be a structure with a buffer layer, elastic layer, or PTC (Positive Temperature Coefficient) thermistor layer disposed on its surface.

[0065] The negative electrode has a negative electrode layer and, if necessary, a negative electrode current collector.

[0066] The negative electrode layer is a layer containing at least a negative electrode active material. Additionally, the negative electrode layer may contain at least one of an electrolyte, a conductive material, and a binder, depending on requirements. Examples of negative electrode active materials for lithium-ion batteries include carbon materials such as natural graphite, elemental Li, and Li alloys.

[0067] Regarding the electrolyte, conductive material, and binder used in the negative electrode layer, the same substances as those described in the positive electrode layer can be listed.

[0068] Materials used as negative current collectors include, for example, SUS, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the negative current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the negative current collector can be foil-like or plate-like. The top view shape of the negative current collector is not particularly limited; for example, circular, elliptical, rectangular, and arbitrary polygonal shapes can be used. The negative current collector can have a structure with a buffer layer, elastic layer, or PTC thermistor layer disposed on its surface.

[0069] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and it contains at least an electrolyte. Examples of electrolytes, besides the solid electrolytes described in the positive electrode layer above, include liquid electrolytes.

[0070] Electrolytes can be aqueous or non-aqueous. They can be used alone or in combination of two or more.

[0071] Aqueous electrolytes contain water as a main solvent component. That is, based on the total amount of solvent (liquid component) constituting the electrolyte (100 mol%), water can account for 50 mol% or more, particularly 70 mol% or more, and further 90 mol% or more. On the other hand, there is no particular upper limit to the proportion of water in the solvent.

[0072] The solvent may contain water as the main component, or it may contain solvents other than water. Examples of solvents other than water include one or more selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. The solvents other than water, based on the total amount (100 mol%) of the solvents (liquid components) constituting the electrolyte, may be 50 mol% or less, particularly 30 mol% or less, and further, 10 mol% or less.

[0073] Aqueous electrolytes contain electrolytes. Electrolytes used in aqueous electrolytes can be conventionally known electrolytes. Examples of electrolytes include lithium salts, nitrates, acetates, and sulfates of imide compounds. Specific examples of electrolytes include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium bis(nonafluorobutanesulfonyl)imide, lithium nonafluoro-N-[(trifluoromethanesulfonyl)butanesulfonamide], lithium N,N-hexafluoro-1,3-disulfonylimide, CH3COOLi, LiPF6, LiBF4, Li2SO4, and LiNO3.

[0074] The concentration of the electrolyte in an aqueous electrolyte solution can be appropriately set according to the required battery characteristics, within a range that does not exceed the saturation concentration of the electrolyte relative to the solvent. This is because if solid electrolyte residue remains in the aqueous electrolyte solution, the solid may hinder the battery reaction.

[0075] For example, when using LiTFSI as the electrolyte, the aqueous electrolyte may contain more than 1 mol of LiTFSI per 1 kg of the aforementioned water, particularly more than 5 mol, and further more than 7.5 mol. There is no particular upper limit, for example, it may be less than 25 mol.

[0076] As a non-aqueous electrolyte, an electrolyte containing lithium salt and non-aqueous solvent is usually used.

[0077] Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2 (Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3.

[0078] As non-aqueous solvents, examples include ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring high dielectric constant and low viscosity, it can be a mixture of cyclic carbonate compounds such as EC, PC, and BC with high dielectric constant and high viscosity, and chain carbonate compounds such as DMC, DEC, and EMC with low dielectric constant and low viscosity, or a mixture of EC and DEC.

[0079] The concentration of lithium salt in non-aqueous electrolytes can be, for example, 0.3~5M.

[0080] Non-aqueous electrolytes may contain ionic liquids. Ionic liquids may include, for example, sulfonium salts, ammonium salts, and pyridine. Salt, piperidine Salt, pyrrolidine Salt, Morpholine Salt, Salt, imidazole At least one of salts and their derivatives.

[0081] The electrolyte layer can be a membrane impregnated with the above-mentioned electrolyte and used to prevent the positive and negative electrode layers from contacting each other.

[0082] The material used for the membrane is not particularly limited as long as it is a porous membrane. Examples include resins such as polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide, among which polyethylene and polypropylene are possible. Furthermore, the membrane can be a single-layer or multi-layer structure. Examples of multi-layer membranes include two-layer PE / PP membranes, or three-layer PP / PE / PP or PE / PP / PE membranes.

[0083] The diaphragm can also be made of nonwoven fabrics such as resin nonwoven fabric and glass fiber nonwoven fabric.

[0084] The battery may also have a constraint clamp that applies constraint pressure to the positive electrode layer, electrolyte layer, and negative electrode layer along the thickness direction. The constraint pressure can be, for example, 0.1 MPa to 100 MPa.

[0085] There are no particular limitations on the type of battery; generally, they are batteries in which metal ions conduct electricity between the positive and negative electrode layers. Lithium-ion batteries are an example of such batteries. Furthermore, batteries can be primary or secondary batteries, and can also be secondary batteries. Because they can be repeatedly charged and discharged, they are useful, for example, as batteries for vehicles.

[0086] There are no particular limitations on the shape of the battery; for example, it can be coin-shaped, cylindrical, square, sheet-shaped, button-shaped, flat, or stacked.

[0087] Batteries are used in various applications, including as power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline cars, and diesel cars. In particular, they can be used as power sources for driving hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). Furthermore, batteries can be used as power sources for mobile bodies other than vehicles (such as railways, ships, and aircraft), and also for electrical appliances such as information processing devices.

[0088] Examples 1-3 and Comparative Examples 1-3

[0089] Synthesis of precursors for positive electrode active materials

[0090] NiSO4, CoSO4, and MnSO4 were dissolved in ion-exchanged water to prepare an aqueous solution of the metal raw materials. The Ni / Co / Mn ratio in the aqueous solution of the metal raw materials was 80 / 10 / 10 in mole percent.

[0091] Figure 2 This is a schematic diagram of the reaction vessel used in the precursor synthesis of the example. (Example:) Figure 2 As shown, a certain amount of NH3 aqueous solution (initial NH3 aqueous solution) was added to the reaction vessel, and nitrogen was purged while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel, and the above-mentioned metal raw material aqueous solution and NH3 aqueous solution were added dropwise while maintaining the pH value at alkaline. The pH value of the reaction solution and the reaction time are shown in Table 1. Furthermore, the proportion of the initial NH3 aqueous solution used in the reaction (A) to the total amount of each aqueous solution [the total amount of initial NH3 aqueous solution (A), NaOH aqueous solution (B), metal raw material aqueous solution (C), and added NH3 aqueous solution (D)] was calculated using the following formula. This is shown in Table 1.

[0092] The initial proportion of NH3 aqueous solution (A) = (A) / [(A) + (B) + (C) + (D)]

[0093] As shown in Table 1, the pH values ​​in Comparative Examples 1 and 2 were controlled such that the pH values ​​at the end of the addition of the aqueous metal raw material and the aqueous NH3 solution were lower than those at the beginning of the addition. After the reaction was completed, the mixture was dried at 110°C for 10 hours under an inert gas atmosphere.

[0094] (Table 1)

[0095]

[0096] For the precursors obtained in Examples 1-3 and Comparative Examples 1-3, the pore size distribution based on mercury porosimetry was measured using a mercury porosimetry apparatus. The number of peaks and average pore size for each precursor are shown in Table 2. As shown in Tables 1-3 and Comparative Example 3, it can be seen that in the synthesis of the precursor of the positive electrode active material, by maintaining the pH value at 11.0 from the start of the addition of the aqueous metal raw material and the aqueous NH3 solution until the end of the addition, the number of peaks in the pore size distribution based on mercury porosimetry can be controlled to 1. As shown in Tables 1-2, Comparative Examples 1-2, it can be seen that in the synthesis of the precursor of the positive electrode active material, by controlling the pH value so that the pH value at the end of the addition of the aqueous metal raw material and the aqueous NH3 solution is lower than the pH value at the start of the addition, the number of peaks in the pore size distribution based on mercury porosimetry can be controlled to 2 or more. In addition, it is speculated that the average pore size can be increased by extending the reaction time.

[0097] Synthesis of positive electrode active material

[0098] The precursors of Examples 1-3 and Comparative Examples 1-3 synthesized above were each mixed with a lithium compound (LiOH) as a lithium source in a mortar. The resulting mixtures were calcined in a calcining furnace at 750°C for 10 hours under an oxygen atmosphere, thereby synthesizing the positive electrode active materials (LiNi) of Examples 1-3 and Comparative Examples 1-3. 0.8 Co 0.1 Mn 0.1 O2).

[0099] Cell creation

[0100] Using the positive electrode active materials of Examples 1-3 and Comparative Examples 1-3, small laminated units of Examples 1-3 and Comparative Examples 1-3 were fabricated.

[0101] Specifically, firstly, a positive electrode paste containing a positive electrode active material and acetylene black as a conductive material is applied to the surface of a metal foil serving as the positive electrode current collector using a film applicator (manufactured by ALLGOOD Co., Ltd.) with a film thickness adjustment function. Then, it is dried at 80°C for 5 minutes using a dryer to create a positive electrode with a positive electrode layer on the positive electrode current collector.

[0102] On the other hand, a negative electrode paste containing natural graphite as the negative electrode active material is applied to the surface of a metal foil serving as the negative electrode current collector using a film applicator (manufactured by ALLGOOD Co., Ltd.) with a film thickness adjustment function. Subsequently, it is dried at 80°C for 5 minutes using a dryer to create a negative electrode with a negative electrode layer on the negative electrode current collector.

[0103] Prepare LiPF6 as the electrolyte and a 1M LiPF6 solution containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of EC / DMC / EMC = 3 / 4 / 3 as the solvent.

[0104] The above-mentioned positive electrode, separator and negative electrode are stacked, and the above-mentioned electrolyte is impregnated in the separator to produce small laminated units of Examples 1 to 3 and Comparative Examples 1 to 3.

[0105] Unit evaluation

[0106] For each small laminated cell fabricated, the discharge capacity was measured before and after a cyclic test. The cyclic test was conducted for 200 cycles under the following conditions.

[0107] <Discharge Capacity Measurement Conditions>

[0108] • C ratio: 0.1C

[0109] • Measurement mode: CCCV discharge

[0110] Temperature: 25℃

[0111] <Loop Condition>

[0112] • C ratio: 0.3C

[0113] • Mode: CC charge / discharge

[0114] Temperature: 50℃

[0115] Based on the discharge capacity measurements before and after the cycle test, the capacity retention rate after the cycle test was calculated using the following formula. The results are shown in Table 2.

[0116] Capacity retention (%) = (Capacity after cycle testing) / (Capacity before cycle testing) × 100

[0117] (Table 2)

[0118]

[0119] As shown in Table 2, in the micropore distribution based on mercury intrusion porosimetry, the capacity retention rates of Comparative Example 1, which has 2 or more peaks and an average micropore diameter of less than 0.90 μm, Comparative Example 2, which has an average micropore diameter of more than 0.90 μm but has 2 or more peaks, and Comparative Example 3, which has 1 peak but an average micropore diameter of less than 0.90 μm, are all as low as 65-68%.

[0120] In contrast, Examples 1-3, which have only one peak in the micropore distribution based on mercury intrusion porosimetry and an average micropore diameter of 0.90 μm or more, have a capacity retention rate of 79-83%, and all of them have improved cycle characteristics compared to Comparative Examples 1-3.

Claims

1. A precursor for a positive electrode active material, said precursor comprising secondary particles formed by the aggregation of multiple primary particles. The primary particles contain nickel complex hydroxide. In the pore distribution of the precursor determined by mercury intrusion porosimetry, when the total pore volume of the range in which the pore diameter is less than twice the average particle size D50 of the precursor is set to 100%, the number of peaks with a peak area of ​​2% or more is 1, and the average pore diameter is 0.90 μm or more. The pore distribution is represented by the distribution of pore volume per unit weight relative to pore diameter.

2. The precursor of the positive electrode active material according to claim 1, The average pore size is below 4.20 μm.

3. The precursor of the positive electrode active material according to claim 1, The nickel composite hydroxide is a nickel-cobalt-manganese composite hydroxide.

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