Precursor of positive electrode active material

Abstract

This invention provides a precursor for a cathode active material that can be used to obtain a cathode active material with excellent capacity retention. [Solution] A precursor for a positive electrode active material, wherein the precursor is a particle of nickel-cobalt-manganese composite hydroxide, and the precursor has two peaks, peak A and peak B, in which the (100) plane peak, which is assigned to space group R3-m, is split into two in XRD analysis.

Description

Technical Field

[0001] The present disclosure relates to a precursor of a positive electrode active material.

Background Art

[0002] Various techniques have been proposed regarding positive electrode active materials as disclosed in Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, various positive electrode active materials have been proposed in order to obtain a positive electrode having high battery characteristics such as high cycle characteristics and high output characteristics. For example, in Patent Document 1, in the measurement of pore distribution by the nitrogen adsorption method, the average diameter of pores is 50 angstroms or more and 60 angstroms or less, and in powder X-ray diffraction using CuKα rays, the diffraction peak appearing in the range of 2θ = 51.9 ± 1.0° / the diffraction peak appearing in the range of 2θ = 19.1 ± 1.0° An integrated intensity ratio of 0.40 or more and 0.50 or less of nickel composite hydroxide is disclosed. As the composition of the nickel composite hydroxide of Patent Document 1, the molar ratio of Ni:Co:Mn:M is 1-x-y-z:x:y:z (0 < x ≤ 0.15, 0 < y ≤ 0.15, 0 ≤ z ≤ 0.05, M means one or more additive elements selected from the group consisting of Al, Fe, Ti, and Zr) is described. The nickel composite hydroxide described in Patent Document 1 is a precursor of a positive electrode active material, and can be made into a positive electrode active material by firing with a lithium compound. However, there is room for improvement in the capacity retention rate of the positive electrode active material obtained from the nickel composite hydroxide of Patent Document 1. This is because, when charge and discharge are repeated, cation mixing occurs in which lithium ions and other metal ions are exchanged within the positive electrode active material, causing a decrease in capacity.

[0005] The present disclosure has been made in view of the above circumstances, and the main object thereof is to provide a precursor of a positive electrode active material capable of obtaining a positive electrode active material excellent in capacity retention rate.

Means for Solving the Problems

[0006] That is, the present disclosure includes the following aspects. <1> A precursor of a positive electrode active material, The precursor is particles of a nickel cobalt manganese composite hydroxide, The precursor has peak A and peak B in which the peak of the (100) plane attributed to the space group R3-m is split into two peaks in XRD analysis.

[0007] <2> The angular difference C between the diffraction angles at the peak tops of the peak A and the peak B is 0.31° or more and 0.68° or less, The integrated intensity I of the peak A obtained by performing fitting of the peak A and the peak B with a Gaussian function and a Lorentz function A and the integrated intensity I of the peak B B The ratio D (the following formula) of the integrated intensity I of the peak B to the total of B is more than 0 and 0.63 or less. The precursor according to <1>. Ratio D = I B / (I A + I B )

Effects of the Invention

[0008] According to this disclosure, it is possible to provide a precursor for a cathode active material that can be obtained with excellent capacity retention. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows an example of an XRD diffraction pattern obtained by XRD analysis of the precursor of this disclosure (precursor of Example 4). [Figure 2] Figure 2 is a magnified view of the area enclosed by the dashed rectangle in Figure 1. [Figure 3] Figure 3 is a graph showing the XRD diffraction pattern from Figure 2 fitted with Gaussian and Lorentz functions. [Modes for carrying out the invention]

[0010] Embodiments of this disclosure will be described below. Matters other than those specifically mentioned herein but necessary for the implementation of this disclosure (for example, the general composition and manufacturing process of cathode active materials and their precursors that do not characterize this disclosure) can be understood as design matters for those skilled in the art based on the prior art. This disclosure can be implemented based on the contents disclosed herein and common technical knowledge in the art.

[0011] This disclosure provides a precursor for a positive electrode active material, wherein the precursor is a particle of nickel-cobalt-manganese composite hydroxide, and the precursor has two peaks, Peak A and Peak B, in which the (100) plane peak, which is assigned to space group R3-m, is split into two in XRD analysis.

[0012] An example of the XRD diffraction pattern obtained by XRD (X-ray diffraction) analysis of the precursor of the present disclosure (precursor of Example 4) is shown in FIG. 1. FIG. 2 is an enlarged view of the range surrounded by the dashed square in FIG. 1. In the range surrounded by the dashed squares in FIGS. 1 and 2, there are peaks of the (100) plane belonging to the space group R3-m. As can be seen from FIGS. 1 and 2, peak splitting is observed in the range surrounded by the dashed square in the precursor of the present disclosure. That is, the precursor of the present disclosure has peak A and peak B in which the peak of the (100) plane belonging to the space group R3-m is split into two. Of the two peaks, peak A with a relatively small diffraction angle (2θ) is a peak derived from a region (Mn-poor region) where the composition ratio of nickel (Ni) is relatively high and the composition ratio of manganese (Mn) is relatively low. On the other hand, peak B with a relatively large diffraction angle (2θ) is a peak derived from a region (Mn-rich region) where the composition ratio of manganese is relatively high and the composition ratio of nickel is relatively low. That is, the precursor of the positive electrode active material of the present disclosure is nickel cobalt manganese composite hydroxide particles having the above-described Mn-poor region and Mn-rich region. Further, since the precursor of the present disclosure has a peak belonging to the space group R3-m, it has a structure (layered rock salt structure) belonging to R3-m.

[0013] It is known that a positive electrode active material (lithium nickel cobalt manganese composite oxide) obtained by firing a nickel cobalt manganese composite hydroxide and a lithium compound causes cation mixing in which lithium ions and metal ions such as nickel are exchanged in the positive electrode active material during repeated charge and discharge, resulting in a decrease in capacity. In a lithium nickel cobalt manganese composite oxide having a layered structure belonging to the space group R3-m, when nickel exists in a divalent state (Ni 2+ ), the ionic radius is close to that of lithium, so the ratio of nickel entering the lithium site increases. Divalent nickel (Ni 2+ ) occurs not alone but in the coexistence of tetravalent manganese (Mn 4+ ).

[0014] As described above, the precursor of the positive electrode active material of this disclosure is a nickel-cobalt-manganese composite hydroxide particle, having a Mn-poor region in which the proportion of nickel (Ni) is relatively high and the proportion of manganese (Mn) is relatively low, and a Mn-rich region in which the proportion of manganese is relatively high and the proportion of nickel is relatively low. In the precursor of this disclosure, in the Mn-poor region, nickel (Ni) exists in a trivalent state. 3+ The proportion of nickel (Ni) in the divalent state increases, and nickel (Ni) exists in the divalent state. 2+ Because the proportion of nickel (Ni) decreases, nickel cation mixing is suppressed. Also, even in the Mn-rich region, the proportion of nickel in contact with manganese decreases relatively, and nickel (Ni) that exists in the divalent state... 2+ Because the proportion of ) decreases, nickel cation mixing is suppressed. As described above, by using the precursor of this disclosure, it is possible to obtain a cathode active material in which the generation of cation mixing is suppressed. In other words, according to this disclosure, it is possible to provide a cathode active material with excellent capacity retention.

[0015] The precursor of this disclosure is a particle of nickel-cobalt-manganese composite hydroxide. In this disclosure, particles may be primary particles or secondary particles formed by the aggregation of multiple primary particles. The particle shape is not particularly limited and examples include approximately spherical or approximately elliptical shapes. The particle size is not particularly limited. The particle size can be determined, for example, by measuring the cross-sectional size of multiple particles in a TEM (Transmission Electron Microscope) image or an SEM (Scanning Electron Microscope) image and calculating the average value. Furthermore, in this disclosure, nickel-cobalt-manganese composite hydroxide is a composite hydroxide containing nickel (Ni), cobalt (Co), and manganese (Mn) as essential metal species, and may also contain other metal species besides nickel, cobalt, and manganese. The other metal species may be, for example, at least one selected from the group consisting of Zr, Mo, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, and Ag. In nickel-cobalt-manganese composite hydroxide, the proportions (molar ratios) of nickel, cobalt, and manganese are not particularly limited. The molar ratios of nickel-cobalt-manganese composite hydroxide may be as follows: Ni / NiCoMn may be 0.5 or more and less than 1.0, Co / NiCoMn may be greater than 0 and 0.3 or less, and Mn / NiCoMn may be greater than 0 and 0.3 or less.

[0016] XRD analysis can be performed, for example, by powder XRD measurement using a known XRD analyzer such as the Rigaku Smart Lab II. Specific analytical conditions include, for example, the following: [XRD analysis conditions] • Analysis method: Wide-angle method • Measurement angle: 10~120° ·Tube:Cu ·Optical system: Kα Voltage: 45kV ·Current: 200mA • Measurement method: Continuous method Step width: 0.02° • Scan speed: 2° / min • IS: 1 / 2 • RS: 20mm • Detection mode: 1D

[0017] In the XRD analysis of the precursors of this disclosure, the splitting pattern of peak A and peak B is not particularly limited. For example, the angular difference C between the diffraction angles of the peak tops of peak A and peak B, which are formed when a peak on the (100) plane belonging to the space group R3-m is split into two, may be between 0.31° and 0.68°.

[0018] The peaks of the (100) plane assigned to the space group R3-m may also be peaks that appear in the range of 33.30 ± 2.00° with a diffraction angle (2θ). Here, the diffraction angle (2θ) of the peak top of peak A is A ) and the diffraction angle of the peak top B of peak B (2θ B The XRD pattern obtained from XRD analysis is approximated by polynomial approximation, processed in the background, and the point where the one-dimensional data intersects with 0 by differentiating is defined as the peak top (peak top of peak A and peak top of peak B), and the diffraction angle at that point is the diffraction angle of each peak (2θ). A , 2θ B ) That is, the diffraction angle (2θ) of the peak top of peak A. A ) and the diffraction angle (2θ) of the peak top of peak B B The angular difference C (°, degrees) is calculated using the following formula. C=2θ B -2θ A

[0019] Furthermore, the integral intensity I of peak A is obtained by fitting peak A and peak B with Gaussian and Lorentz functions, respectively. A and the integrated intensity I of peak B B The integral intensity I of peak B relative to the sum B The ratio D (formula below) may be greater than 0 and less than or equal to 0.63, or it may be between 0.06 and 0.63. Ratio D=I B / ( I A +I B )

[0020] The integral intensity I of peak A obtained by fitting with Gaussian and Lorentz functions A and the integrated intensity I of peak B B (Hereafter, each will simply be referred to as "Integrated intensity of peak A I A "Integrated intensity of peak B I B The following can be calculated: First, the XRD diffraction pattern obtained from the XRD analysis is processed using polynomial approximation to remove background noise, and the points where the one-dimensional data intersects with 0 by differentiating are defined as the peak tops (peak tops of peak A and peak tops of peak B). Next, a composite function of the Gaussian and Lorentz functions expressed by the following equation is used as one peak, and this is fitted to the two peaks, peak A and peak B, to obtain the integral intensity (I) of each peak. A , I B In other words, calculate the integrated intensity area. Composite function = (Gaussian function) * α + (Lorentzian function) * (1 - α) In the above formula, α represents the mixing ratio of the functions and can be set as appropriate.

[0021] Figure 3 shows the graph obtained by fitting the XRD diffraction pattern from Figure 2 with Gaussian and Lorentz functions. In Figure 3, based on the curve displayed as "Overall Fitting", the integral intensity (I) is calculated from the area formed by the curve. A , I B It is possible to calculate ).

[0022] The integrated intensity I of peak A calculated as described above A and the integrated intensity I of peak B B Using this, the integral intensity I A and integrated intensity I B The integral intensity I for the sum B The ratio D can be calculated.

[0023] In this disclosure, the angular difference C of the diffraction angles of the peak tops of peak A and peak B is 0.31° or more and 0.68° or less, and the integral intensity I of peak A obtained by fitting peak A and peak B with Gaussian and Lorentz functions is... A and the integrated intensity I of peak B B The integral intensity I of peak B relative to the sum B The ratio D may be greater than 0 and less than or equal to 0.63.

[0024] The method for producing the precursor of the positive electrode active material of this disclosure is not particularly limited, and examples include the following methods. First, an aqueous NiCo solution is prepared by dissolving a water-soluble nickel source (nickel compound) and a water-soluble cobalt source (cobalt compound) in deionized water, and an aqueous Mn solution is prepared by dissolving a water-soluble manganese source (manganese compound) in deionized water. At this time, the amounts of nickel and cobalt contained in the NiCo solution and the amounts of manganese contained in the Mn solution are set so that when these NiCo and Mn solutions are mixed, the ratio (mol%) of nickel, cobalt, and manganese to the total amount of nickel, cobalt, and manganese is typically equal to the ratio (mol%) of nickel, cobalt, and manganese that constitute the nickel-cobalt-manganese composite hydroxide. The water-soluble metal compounds are not particularly limited, but examples include sulfates. The concentrations of the NiCo and Mn solutions can be set as appropriate. Next, a fixed amount of NH3 aqueous solution (ammonium ion supply) is added to the reaction vessel, and while stirring with a stirrer or the like, nitrogen is purged to create a non-oxidizing atmosphere. Next, sodium hydroxide solution is added to the reaction vessel, and while maintaining an alkaline pH (for example, pH 12), the NiCo solution, Mn solution, and NH3 solution are added dropwise to the reaction vessel. The dropping rate of each solution can be set as appropriate. The reaction temperature is not particularly limited and can be, for example, 60°C. After the reaction is complete, a drying treatment is performed. The drying treatment can be carried out, for example, at 120°C for 1 hour under an inert gas atmosphere.

[0025] The precursor of the positive electrode active material of this disclosure can be used as a positive electrode active material for batteries such as lithium-ion batteries by, for example, converting it into a lithium nickel cobalt manganese composite oxide. Lithium nickel cobalt manganese composite oxide can be produced from the precursor of the present disclosure by, for example, the following method: mixing the nickel cobalt manganese composite hydroxide, which is the precursor of the present disclosure, with a lithium compound that serves as a lithium source, and then calcining the resulting mixture.

[0026] Examples of lithium compounds include at least one selected from lithium carbonate, lithium nitrate, lithium acetate, lithium hydroxide, lithium oxide, lithium chloride, and the like. The ratio of lithium compound to precursor in the mixture is such that the ratio (mol%) of lithium and each of the other metal species relative to the total amount of lithium in the target cathode active material and the metal species contained in the precursor is typically equal to the ratio (mol%) of lithium and each of the other metal species in the mixture. The mixing method is not particularly limited, and known methods can be employed.

[0027] The resulting mixture can be calcined, for example, at 700-950°C for 8-10 hours to obtain a lithium nickel cobalt manganese composite oxide. A known calcination furnace, such as a muffle furnace, can be used for calcination. The positive electrode active material obtained by calcining the precursor of this disclosure is generally considered to consist of single crystal particles. Here, a single-crystal particle refers to a single particle that does not constitute a secondary particle, essentially meaning a particle consisting of a single crystal. The fact that it is a single-crystal particle can be confirmed by the absence of grain boundaries in the SEM image.

[0028] The positive electrode active material precursor provided in this disclosure can be used, for example, as a precursor for the positive electrode active material that constitutes the positive electrode of a battery (such as a lithium-ion battery). That is, this disclosure provides a battery in which a positive electrode, an electrolyte layer, and a negative electrode are stacked in this order, and the positive electrode contains a positive electrode active material obtained from the precursor of this disclosure. The following explains batteries.

[0029] The positive electrode has a positive electrode layer and, if necessary, further includes a positive electrode current collector. 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 be, for example, 20 to 80% by mass. The positive electrode layer may optionally contain at least one of an electrolyte, a conductive material, and a binder. Examples of electrolytes include solid electrolytes. The solid electrolyte may be an inorganic solid electrolyte such as a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, or a complex hydride solid electrolyte, or it may be an organic solid electrolyte such as a gel electrolyte. The proportion of the solid electrolyte in the positive electrode layer may be, for example, 10 to 60% by mass. 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 Ketjenblack (KB), and fibrous carbon materials such as vapor-processed carbon fiber (VGCF), carbon nanotubes (CNT), and carbon nanofibers (CNF). The proportion of conductive material in the positive electrode layer may be, for example, 0.1 to 5% by mass. Examples of binders 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 binder in the positive electrode layer may be, for example, 0.5 to 5% by mass. Examples of materials for the positive electrode current collector include SUS, Cr, Au, Pt, Zn, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the positive electrode current collector may be foil-like or plate-like. The planar shape of the positive electrode current collector is not particularly limited, but examples include circular, elliptical, rectangular, and any polygonal shape. The positive electrode current collector may have a buffer layer, an elastic layer, or a PTC (Positive Temperature Coefficient) thermistor layer on its surface.

[0030] The negative electrode has a negative electrode layer and, if necessary, further has a negative electrode current collector. The negative electrode layer is a layer containing at least a negative electrode active material. The negative electrode layer may also optionally contain at least one of an electrolyte, a conductive material, and a binder. Examples of negative electrode active materials for lithium-ion batteries include carbon materials such as natural graphite, elemental Li, and Li alloys. The electrolyte, conductive material, and binder used in the negative electrode layer are the same as those described for the positive electrode layer above. Examples of materials for the negative electrode current collector include SUS, aluminum, copper, nickel, iron, titanium, and carbon. The thickness of the negative electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The shape of the negative electrode current collector may be foil-like or plate-like. The planar shape of the negative electrode current collector is not particularly limited, but examples include circular, elliptical, rectangular, and any polygonal shape. The negative electrode current collector may have a buffer layer, an elastic layer, or a PTC thermistor layer arranged on its surface.

[0031] The electrolyte layer is a layer formed between the positive electrode layer and the negative electrode layer, and contains at least an electrolyte. Examples of electrolytes include the solid electrolyte described for the positive electrode layer, as well as an electrolyte solution. Aqueous electrolytes and non-aqueous electrolytes can be used as the electrolyte. These may be used individually or in combination of two or more types.

[0032] The solvent in an aqueous electrolyte contains water as its main component. That is, water may account for 50 mol% or more, particularly 70 mol% or more, and even 90 mol% or more, of the total amount of solvent (liquid component) constituting the electrolyte, based on a standard (100 mol%). On the other hand, there is no particular upper limit to the proportion of water in the solvent. The solvent mainly consists of water, but may also 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 amount of solvent other than water may be 50 mol% or less, particularly 30 mol% or less, and even 10 mol% or less, based on the total amount of solvent (liquid component) constituting the electrolyte.

[0033] Aqueous electrolytes contain an electrolyte. Conventionally known electrolytes can be used for aqueous electrolytes. Examples of electrolytes include lithium salts, nitrates, acetates, and sulfates of imidic acid 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-[(trifluoromethane)sulfonyl]butanesulfonylamide, lithium N,N-hexafluoro-1,3-disulfonylimide, CH3COOLi, LiPF6, LiBF4, Li2SO4, and LiNO3.

[0034] The electrolyte concentration in an aqueous electrolyte can be appropriately set according to the desired battery characteristics, as long as it does not exceed the saturation concentration of the electrolyte relative to the solvent. This is because if solid electrolyte remains in the aqueous electrolyte, that solid may inhibit the battery reaction. For example, when LiTFSI is used as the electrolyte, the aqueous electrolyte may contain 1 mole or more of LiTFSI per 1 kg of water, and may contain 5 moles or more, and may contain 7.5 moles or more. The upper limit is not particularly limited and may be, for example, 25 moles or less.

[0035] As a non-aqueous electrolyte, one containing a lithium salt and a non-aqueous solvent is typically used. 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. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl 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, a mixture of cyclic carbonate compounds such as EC, PC, and BC having high dielectric constant and high viscosity, and chain-like carbonate compounds such as DMC, DEC, and EMC having low dielectric constant and low viscosity may be used, or a mixture of EC and DEC may be used. The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, 0.3 to 5 M.

[0036] The non-aqueous electrolyte may contain an ionic liquid. The ionic liquid may contain, for example, at least one selected from the group consisting of sulfonium salts, ammonium salts, pyridinium salts, piperidinium salts, pyrrolidinium salts, morpholinium salts, phosphonium salts, imidazolium salts, and derivatives thereof.

[0037] The electrolyte layer may be impregnated with the aforementioned electrolyte solution, and a separator may be used to prevent contact between the positive electrode layer and the negative electrode layer. The material for the separator is not particularly limited as long as it is a porous membrane. Examples include polyethylene (PE), polypropylene (PP), polyester, polyvinyl alcohol, cellulose, and polyamide resins, with polyethylene and polypropylene being particularly preferred. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a PE / PP two-layer separator, or a PP / PE / PP or PE / PP / PE three-layer separator. The separator may be made of nonwoven fabrics such as resin nonwoven fabric and glass fiber nonwoven fabric.

[0038] The battery may further include a restraining jig that applies restraining pressure to the positive electrode layer, electrolyte layer, and negative electrode layer along the thickness direction. The restraining pressure may be, for example, 0.1 MPa to 100 MPa.

[0039] The type of battery is not particularly limited, but it is usually a battery in which metal ions conduct between the positive and negative electrode layers. Lithium-ion batteries are an example of such batteries. The battery may be a primary battery or a secondary battery, but a secondary battery is preferable because it can be repeatedly charged and discharged and is useful, for example, as a battery for vehicles. The shape of the battery is not particularly limited and may be, for example, coin-type, cylindrical, prismatic, sheet-type, button-type, flat-type, or stacked-type.

[0040] Examples of battery applications include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), battery electric vehicles (BEVs), gasoline vehicles, and diesel vehicles. In particular, it may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or battery electric vehicles (BEVs). The battery may also be used as a power source for mobile bodies other than vehicles (e.g., railways, ships, aircraft), and may be used as a power source for electrical products such as information processing devices.

Examples

[0041] [Examples 1 to 4] (Synthesis of the precursor of the positive electrode active material) An NiCo aqueous solution in which NiSO4 and CoSO4 were dissolved in ion-exchanged water and an Mn aqueous solution in which MnSO4 was dissolved in ion-exchanged water were prepared. The Ni / Co / Mn ratio was adjusted so that the Ni / Co / Mn ratio became 80 / 10 / 10 in mol% when the NiCo aqueous solution and the Mn aqueous solution were mixed. A certain amount of NH3 aqueous solution was placed in a reaction vessel, and while stirring with a stirrer, the inside of the reaction vessel was purged with nitrogen. An NaOH aqueous solution was added to the reaction vessel, and while maintaining the pH at an alkaline level (pH = 12), the above-mentioned NiCo aqueous solution, Mn aqueous solution, and NH3 aqueous solution were each dropped. The reaction temperature was 60°C. After the reaction was completed, a drying treatment was performed at 120°C for 1 hour under an inert gas atmosphere. In Examples 1 to 4, each precursor was synthesized by changing the concentration and dropping rate of the Mn aqueous solution.

[0042] (XRD analysis of the precursor of the positive electrode active material) For the precursors obtained in Examples 1 to 4, powder XRD analysis was performed by the wide-angle method using an XRD analyzer (Rigaku Smart Lab II). The analysis conditions are as follows. Figs. 1 to 3 show the results of the XRD analysis of the precursor of Example 4.

[0043] <XRD analysis conditions> ·Measurement angle: 10 to 120° ·X-ray tube: Cu ·Optical system: Kα Voltage: 45kV ·Current: 200mA • Measurement method: Continuous method Step width: 0.02° • Scan speed: 2° / min • IS: 1 / 2 • RS: 20mm • Detection mode: 1D

[0044] XRD analysis confirmed that all of the precursors in Examples 1-4 have two peaks, Peak A and Peak B, which are split peaks in the (100) plane that belong to the space group R3-m. Furthermore, the diffraction angle (2θ) of the peak tops of Peak A and Peak B obtained by XRD analysis was also found. A , 2θ B ), the angular difference C of these diffraction angles, and the integrated intensity I of peak A. A and the integrated intensity I of peak B B The integral intensity I of peak B relative to the sum B The ratio D is shown in Table 1.

[0045] [Comparative Example 1] (Synthesis of precursors for positive electrode active material) Metal raw material aqueous solutions were prepared by dissolving NiSO4, CoSO4, and MnSO4 in deionized water. The Ni / Co / Mn ratio in the metal raw material aqueous solutions was 80 / 10 / 10 in mol%. The concentration of the metal raw material aqueous solutions (the ratio of all raw materials to the metal raw material aqueous solution) was 1.5 mol%. A fixed amount of NH3 aqueous solution was added to the reaction vessel, and the vessel was purged with nitrogen while stirring with a stirrer. NaOH aqueous solution was added to the reaction vessel, and while maintaining the pH at an alkaline level (pH=12), the above metal raw material aqueous solution and NH3 aqueous solution were added dropwise. The reaction temperature was 60°C and the reaction time was 10 hours. After the reaction was complete, the mixture was dried at 120°C for 1 hour under an inert gas atmosphere.

[0046] (XRD analysis of the precursor of the positive electrode active material) When XRD analysis was performed in the same manner as in the above example, a peak on the (100) plane, which is assigned to the space group R3-m, was observed, but no splitting of this peak was observed. The diffraction angle of the peak top of this peak was 33.30°. In addition, in Table 1, no splitting of the above peak was observed for Comparative Example 1, hence the diffraction angle 2θ. A and diffraction angle 2θ B We treated this as 33.30°, and set the angle difference C and integrated intensity ratio D to zero.

[0047] [Synthesis of positive electrode active material] The precursors of Examples 1-4 and Comparative Example 1, synthesized as described above, were mixed with a lithium compound (LiOH), which is a lithium source, in a mortar. The resulting mixtures were fired in a firing furnace at 950°C for 10 hours to produce the positive electrode active materials (LiNi) of Examples 1-4 and Comparative Example 1. 0.8 Co 0.1 Mn 0.1 O2) was synthesized.

[0048] [Cell creation] Using the respective positive electrode active materials from Examples 1-4 and Comparative Example 1, small laminate cells of Examples 1-4 and Comparative Example 1 were fabricated. Specifically, first, a positive electrode composite paste containing a positive electrode active material, acetylene black (a conductive material), and PVDF (4% by mass) (a binder) was coated onto the surface of the metal foil, which served as the positive electrode current collector, using a film applicator with a film thickness adjustment function (manufactured by AllGrid Co., Ltd.). Then, it was dried in a dryer at 80°C for 5 minutes to produce a positive electrode with a positive electrode layer on the positive electrode current collector. On the other hand, a negative electrode composite paste containing natural graphite, which is the negative electrode active material, was coated onto the surface of the metal foil, which is the negative electrode current collector, using a film applicator with a film thickness adjustment function (manufactured by AllGrid Co., Ltd.). Then, it was dried in a dryer at 80°C for 5 minutes to produce a negative electrode having a negative electrode layer on the negative electrode current collector. A 1M LiPF6 solution was prepared as the electrolyte, containing LiPF6 as the electrolyte and ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) as solvents in the ratio EC / DMC / EMC = 3 / 4 / 3 vol%. The positive electrode, separator, and negative electrode were laminated together, and the separator was impregnated with the electrolyte to produce the small laminate cells of Examples 1-4 and Comparative Example 1.

[0049] [Cell evaluation] The discharge capacity of each fabricated small laminate cell was measured before and after the cycle test. The cycle test was performed for 100 cycles under the following conditions. <Discharge capacity measurement conditions> • C-rating: 0.1C • Measurement mode: CCCV discharge ·Temperature: 25℃ <Cycle Conditions> • C rating: 0.3C • Mode: CC charge / discharge ·Temperature 50℃

[0050] Using the measured discharge capacity before and after the cycle test, the capacity retention rate after the cycle test was calculated using the following formula. Capacity retention rate (%) = (Discharge capacity after cycle test) / (Discharge capacity before cycle test) × 100 The volume retention rates of Examples 1 to 4 were normalized using the following formula, based on the volume retention rate of Comparative Example 1. Normalized capacity retention rate = (Capacity retention rate of each example) / (Capacity retention rate of Comparative Example 1) The results are shown in Table 1.

[0051] [Table 1]

[0052] As shown in Table 1, Examples 1-4, which used precursors in which the peak of the (100) plane assigned to space group R3-m was split into two, showed improved volume retention compared to Comparative Example 1, which used precursors in which the peak of the (100) plane assigned to space group R3-m was not split. The precursors of Examples 1-4 had an angular difference C of the diffraction angles of the peak tops of peak A and peak B of 0.31° to 0.68°, and the integrated intensity I of peak A A and the integrated intensity I of peak B B The integral intensity I of peak B relative to the sum B The ratio D was greater than 0 and less than or equal to 0.63. Furthermore, in Comparative Example 1, where aqueous solutions of metal raw materials, in which NiSO4, CoSO4, and MnSO4 were dissolved in deionized water, were added dropwise to the reaction vessel during precursor synthesis, the peak of the (100) plane, which is attributed to space group R3-m, did not split into two. On the other hand, in Examples 1 to 4, where aqueous solutions of NiCo (NiSO4 and CoSO4 dissolved in deionized water) and aqueous solutions of Mn (MnSO4 dissolved in deionized water) were added dropwise to the reaction vessel, respectively, the peak of the (100) plane, which is attributed to space group R3-m, split into two. This indicates that in nickel-cobalt-manganese composite hydroxide, the above-mentioned peak splits when aqueous solutions of NiCo and Mn are added dropwise to the reaction vessel, respectively.

Claims

1. A precursor of the positive electrode active material, The precursor is a particle of nickel-cobalt-manganese composite hydroxide, The precursor is a precursor having two peaks, peak A and peak B, in which the peak of the (100) plane, which is assigned to the space group R3-m, is split into two in XRD analysis.

2. The angular difference C between the diffraction angles of the peak tops of peak A and peak B is 0.31° or more and 0.68° or less. The integral intensity I of peak A is obtained by fitting peak A and peak B with Gaussian and Lorentz functions, respectively. Ａ and the integrated intensity I of peak B Ｂ The integrated intensity I of peak B relative to the sum Ｂ The precursor according to claim 1, wherein the ratio D (formula below) is greater than 0 and less than or equal to 0.

63. Ratio D=I Ｂ / (I Ａ +I Ｂ )

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