Method for manufacturing positive electrode active material for lithium-ion secondary batteries

Abstract

To provide a manufacturing method for a positive electrode active material for a lithium ion secondary battery, in which gas generation can be suppressed in the use for a lithium ion secondary battery.SOLUTION: A manufacturing method for a positive electrode active material for a lithium ion secondary battery includes a mixing step of mixing a nickel containing object containing at least nickel and a lithium compound, thereby preparing a raw material mixture, a burning step of burning the raw material mixture in an oxidative atmosphere, thereby obtaining a burned object, a water-washing step of water-washing the burned object obtained in the burning step, thereby obtaining water-washed powder, and a boron adding step of spraying the water-washed powder obtained in the water-washing step with a boron containing solution containing a boron containing object corresponding to at least one kind selected from a boron simple substance and a boron containing compound.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a method for producing a positive electrode active material for lithium-ion secondary batteries. [Background technology]

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of small, lightweight rechargeable batteries with high energy density and durability. Furthermore, there is a strong demand for high-output rechargeable batteries for use in power tools and electric vehicles, including hybrid cars. In addition to the above-mentioned required characteristics, there is also a growing need for rechargeable batteries with high durability that do not degrade easily even after repeated use.

[0003] Lithium-ion batteries are a type of secondary battery that meets these requirements. A lithium-ion battery consists of a negative electrode, a positive electrode, and an electrolyte, and the active materials of the negative and positive electrodes are materials that can detach and insert lithium. As mentioned above, lithium-ion batteries have high energy density, power output characteristics, and durability.

[0004] While research and development are currently thriving on lithium-ion secondary batteries, lithium-ion secondary batteries using layered or spinel-type lithium metal composite oxides as the cathode material are particularly gaining practical application as batteries with high energy density, as they can achieve high voltages of around 4V.

[0005] As cathode materials for lithium-ion secondary batteries, lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel that is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 Lithium manganese composite oxide (LiMn2O4) and lithium nickel manganese composite oxide (LiNi) using manganese (O2). 0.5 Mn 0.5Lithium metal composite oxides such as O2 have been proposed.

[0006] In recent years, there has been a demand for further improvements in the battery characteristics of lithium-ion secondary batteries, and research is underway on improving cycle characteristics (e.g., Patent Document 1) and increasing power output. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2016-189320 [Overview of the project] [Problems that the invention aims to solve]

[0008] In recent years, there has been a growing demand for positive electrode active materials for lithium-ion secondary batteries that can suppress gas generation when used in lithium-ion secondary batteries.

[0009] Therefore, in view of the problems of the above-mentioned conventional technology, one aspect of the present invention aims to provide a method for producing a positive electrode active material for lithium-ion secondary batteries that can suppress gas generation when used in lithium-ion secondary batteries. [Means for solving the problem]

[0010] To solve the above problems, according to one aspect of the present invention, A method for producing a positive electrode active material for a lithium-ion secondary battery, which contains a lithium nickel composite oxide having a hexagonal layered structure and containing secondary particles formed by the aggregation of multiple primary particles, A mixing step of preparing a raw material mixture by mixing a nickel-containing material containing at least nickel with a lithium compound, A firing step in which the raw material mixture is fired in an oxidizing atmosphere to obtain a fired product, A washing step is performed to wash the fired product obtained in the firing step with water to obtain a water-washed powder, A boron addition step of spraying a boron-containing solution containing at least one boron-containing substance selected from elemental boron and boron-containing compounds onto the washed powder obtained in the washing step; The lithium nickel composite oxide contains lithium (Li), nickel (Ni), boron (B), and element M (M) in a molar ratio of Li:Ni:B:M = a:b:c:d (where 0.95 ≦ a ≦ 1.10, 0.50 ≦ b < 1.00, 0.00 < c ≦ 0.03, 0.00 ≦ d ≦ 0.47, b + c + d = 1, and the element M is at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Ti, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al). death, In a titration curve obtained by stirring 10 g of the lithium-ion secondary battery positive electrode active material in 50 mL of pure water for 5 minutes and then neutralizing the filtered filtrate with 1.0 M HCl, the volume ratio of the amount of HCl added in the pH region greater than 11.0 to the amount of HCl added in the pH region between 8.0 and 11.0 is 2.0 or less. Provided is a method for producing a positive electrode active material for a lithium-ion secondary battery.

Advantages of the Invention

[0011] According to one aspect of the present invention, there is provided a method for producing a positive electrode active material for a lithium-ion secondary battery that can suppress gas generation when used in a lithium-ion secondary battery.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is an explanatory diagram of a laminated battery fabricated in Examples and Comparative Examples. [Figure 2] FIG. 2 is a flow chart of a method for producing a positive electrode active material for a lithium-ion secondary battery according to one aspect of the present disclosure.

Embodiments for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention. [Method for Producing Positive Electrode Active Material for Lithium-Ion Secondary Battery] Hereinafter, a method for manufacturing a positive electrode active material for a lithium ion secondary battery of the present embodiment (hereinafter, also simply referred to as "positive electrode active material") will be described.

[0014] First, after explaining the positive electrode active material obtained by the method for manufacturing a positive electrode active material for a lithium ion secondary battery of the present embodiment, details of the method for manufacturing the positive electrode active material of the present embodiment will be described. (1) Regarding the positive electrode active material (1-1) Regarding the lithium nickel composite oxide The positive electrode active material of the present embodiment contains a lithium nickel composite oxide. The positive electrode active material of the present embodiment may be composed only of the lithium nickel composite oxide, but even in this case, it does not exclude containing inevitable impurities mixed in during the manufacturing process and the like. (1-1-1) Regarding the composition The above lithium nickel composite oxide can contain lithium (Li), nickel (Ni), and boron (B).

[0015] The lithium nickel composite oxide can also contain elements other than lithium, nickel, and boron, and for example, can also contain element M described below.

[0016] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), boron (B), and element M (M) in a ratio of Li:Ni:B:M = a:b:c:d in terms of the molar ratio.

[0017] It is preferable that the above a, b, c, and d satisfy 0.95 ≦ a ≦ 1.10, 0.50 ≦ b < 1.00, 0.00 < c ≦ 0.03, 0.00 ≦ d ≦ 0.47, and b + c + d = 1. Also, element M is preferably at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Ti, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al.

[0018] The lithium nickel composite oxide has, for example, the general formula: Li a Nib B c M d O 2+α It can be represented as. Since a, b, c, d, and the element M in the above general formula have been described above, the description is omitted here. α preferably satisfies, for example, -0.2 ≤ α ≤ 0.2. (Nickel (Ni)) In the lithium nickel composite oxide, the higher the nickel content ratio, the higher the capacity can be achieved when used as the positive electrode material of a lithium ion secondary battery.

[0019] Also, in the lithium nickel composite oxide, the higher the nickel content ratio, the more likely gas generation due to reaction with the electrolyte occurs when used in a lithium ion secondary battery. However, according to the positive electrode active material for a lithium ion secondary battery of the present embodiment, since the gas generation can be suppressed, a particularly high effect can be exhibited.

[0020] Therefore, as described above, b indicating the nickel content ratio is preferably 0.50 or more, more preferably 0.60 or more, further preferably 0.70 or more, and particularly preferably 0.80 or more.

[0021] The upper limit value of b indicating the nickel content ratio is preferably less than 1.00, more preferably 0.97 or less, as described above. (Boron (B)) As described above, the lithium nickel composite oxide of the present embodiment can contain boron. According to the study by the inventors of the present invention, when the lithium nickel composite oxide contains boron, gas generation can be suppressed when used in a lithium ion secondary battery.

[0022] Although the exact mechanism by which gas generation can be suppressed is not clear, it is thought that the presence of boron in the lithium nickel composite oxide causes the boron to form a compound that does not readily react with the electrolyte, with the lithium component adhering to the particle surface of the lithium nickel composite oxide. Therefore, it is presumed that the proportion of components that react with the electrolyte and cause gas generation, such as lithium hydroxide and lithium carbonate, can be suppressed on the particle surface of the lithium nickel composite oxide. Furthermore, it is thought that this compound further suppresses gas generation due to the decomposition of the electrolyte.

[0023] As described above, c, which indicates the boron content, is preferably greater than 0.00, more preferably 0.001 or greater, even more preferably 0.002 or greater, and particularly preferably 0.003 or greater.

[0024] While there is no particular upper limit to c, which indicates the boron content, it is preferable that the effect saturates even if added excessively, so it is preferable that it be 0.03 or less, more preferably 0.025 or less, and particularly preferable 0.02 or less. (Element M) As described above, the lithium nickel composite oxide of this embodiment may also contain element M as an optional component. The group of elements that can be suitably used for element M has already been described, so its description will be omitted here. In particular, from the viewpoint of improving the thermal stability of the lithium nickel composite oxide and suppressing, for example, the thermal decomposition of the lithium nickel composite oxide, it is preferable to include at least one selected from at least cobalt (Co), manganese (Mn), and titanium (Ti) as element M.

[0025] Since element M is an optional component, the value d, which indicates the content of element M, is preferably 0.00 or higher, more preferably 0.05 or higher, and even more preferably 0.10 or higher, as described above.

[0026] As mentioned above, the upper limit of d, which indicates the content of element M, is preferably 0.47 or less, more preferably 0.25 or less, and even more preferably 0.20 or less.

[0027] Furthermore, if the lithium nickel composite oxide contains multiple types of element M, it is preferable that the sum of the content ratios of these multiple types of element M satisfies the above range. (1-1-2) About the crystal structure Lithium nickel composite oxides preferably have a hexagonal layered structure. The inclusion of a hexagonal layered structure in the lithium nickel composite oxide allows for easy insertion and removal of lithium between layers, particularly improving output characteristics and cycle performance when applied to lithium-ion secondary batteries.

[0028] The crystal structure of lithium nickel composite oxide can be confirmed by Rietveld analysis. (1-1-3) Regarding the morphology of particles Lithium nickel composite oxide particles can contain secondary particles formed by the aggregation of multiple primary particles.

[0029] Furthermore, lithium nickel composite oxide may contain primary particles that have not aggregated, in addition to secondary particles. In other words, lithium nickel composite oxide can contain both primary and secondary particles. (1-2) Regarding titration curves In this embodiment, the positive electrode active material is preferably such that, in the titration curve obtained by neutralizing the filtrate obtained by filtering after mixing with pure water, the volume ratio of the amount of HCl added in the pH region greater than 11.0 to the amount of HCl added in the pH region of 8.0 to 11.0 is 2.0 or less.

[0030] The filtrate used to prepare the titration curve described above can be obtained by adding 10 g of the positive electrode active material of this embodiment to 50 mL of pure water, stirring in the pure water for 5 minutes, filtering, and separating the solid and liquid. The pure water is preferably water from which components that affect the neutralization titration have been removed as much as possible, and distilled water or the like can be suitably used. Furthermore, when preparing the titration curve described above, the hydrochloric acid (HCl) used to neutralize the filtered filtrate should be 1.0 M, i.e., 1.0 mol / dm³. 3 (1.0 mol / L) hydrochloric acid can be used.

[0031] According to the inventors' investigations, the amount of HCl added in the region where the pH in the titration curve is greater than 11.0 mainly represents the HCl consumed in the reaction with the lithium hydroxide contained in the positive electrode active material.

[0032] Furthermore, when the filtrate of the positive electrode active material of this embodiment is subjected to neutralization titration, a region appears in the titration curve where the pH fluctuation is suppressed and the curve becomes nearly flat compared to other pH regions, specifically in the pH range of 8.0 to 11.0.

[0033] As previously described, it is believed that the lithium nickel composite oxide contains a small amount of boron, and that this boron forms a lithium-boron-containing compound with the lithium component attached to the particle surface of the lithium nickel composite oxide, which does not readily react with the electrolyte. Furthermore, it is thought that this lithium-boron-containing compound further suppresses gas generation due to the decomposition of the electrolyte.

[0034] Furthermore, in the titration curve described above, the amount of HCl added in the pH range of 8.0 to 11.0 is presumed to represent the HCl consumed mainly in the reaction with the lithium-boron-containing compound.

[0035] Therefore, by keeping the volume ratio (VR1) of HCl added in the pH range greater than 11.0 to the amount added in the pH range of 8.0 to 11.0 2.0 or less, it is considered that the lithium hydroxide content is suppressed, and the lithium-boron-containing compound is sufficiently produced. Consequently, when this positive electrode active material is applied to a lithium-ion secondary battery, it is considered that the reaction with the electrolyte is suppressed and gas generation is suppressed.

[0036] The volume ratio VR1 of the amount of HCl dropped in the pH range greater than 11.0 to the amount of HCl dropped in the pH range between 8.0 and 11.0 can be calculated using the following formula (1).

[0037] In the following equation (1), the amount of HCl added in the pH range of 8.0 to 11.0 is denoted as "V(8.0~11.0)", and the amount of HCl added in the pH range greater than 11.0 is denoted as "V(11.0~)".

[0038] VR1=V(11.0~)÷V(8.0~11.0) ···(1) As described above, VR1 is preferably 2.0 or less, more preferably 1.5 or less, even more preferably 1.0 or less, and particularly preferably 0.75 or less.

[0039] The lower limit of VR1 is not particularly limited, but since it is difficult to completely remove lithium hydroxide, it is preferably 0.05 or higher, and more preferably 0.1 or higher.

[0040] Furthermore, in the titration curve described above, it is preferable that the volume ratio of the amount of HCl added in the pH range of 5.0 to less than 8.0 to the amount of HCl added in the pH range of 8.0 to 11.0 is 0.3 or less.

[0041] According to the inventors of the present invention, the amount of HCl added in the region where the pH in the above titration curve is 5.0 or higher and less than 8.0 mainly represents the HCl consumed in the reaction with the lithium carbonate contained in the positive electrode active material.

[0042] Therefore, by setting the volume ratio of HCl added in the pH range of 5.0 to less than 8.0 to the amount added in the pH range of 8.0 to 11.0 to 0.3 or less, it is considered that the lithium carbonate content is suppressed, and the lithium-boron-containing compound is sufficiently produced. Consequently, when this positive electrode active material is applied to a lithium-ion secondary battery, it is considered that the reaction with the electrolyte is particularly suppressed, and gas generation can be further suppressed.

[0043] The volume ratio VR2 of the amount of HCl dropped in the pH range between 5.0 and 8.0 to the amount of HCl dropped in the pH range between 8.0 and 11.0 can be calculated using the following formula (2).

[0044] In the following equation (2), the amount of HCl dropped in the pH range of 8.0 to 11.0 is denoted as "V(8.0~11.0)", and the amount of HCl dropped in the pH range of 5.0 to less than 8.0 is denoted as "V(5.0~8.0)".

[0045] VR2=V(5.0~8.0)÷V(8.0~11.0) ···(2) As described above, the VR2 is preferably 0.3 or less, more preferably 0.25 or less, and even more preferably 0.2 or less.

[0046] The lower limit of VR2 is not particularly limited, but since it is difficult to completely remove lithium carbonate, it is preferably 0.01 or higher, and more preferably 0.05 or higher. (1-3) Particle size variation index and volume-average particle size In this embodiment, the positive electrode active material preferably has a particle size variation index [(D90-D10) / volume average particle size Mv] of 0.70 or more and 1.20 or less, and more preferably 0.80 or more and 1.00 or less.

[0047] In this specification, D10 represents the 10% cumulative particle diameter, meaning the particle size at 10% of the volume-based diameter in the particle size distribution determined by laser diffraction-scattering, i.e., the particle size at 10% of the integrated volume. D90 represents the 90% cumulative particle diameter, meaning the particle size at 90% of the volume-based diameter in the particle size distribution determined by laser diffraction-scattering, i.e., the particle size at 90% of the integrated volume. In other parts of this specification, D10 and D90 have the same meanings.

[0048] The volume-average particle size Mv is the average particle size weighted by particle volume. In a particle aggregate, it is calculated by summing the products of the diameters of individual particles multiplied by their volumes, and then dividing the sum by the total volume of the particles. The volume-average particle size can also be measured and calculated using the laser diffraction and scattering method with a laser diffraction particle size analyzer.

[0049] By setting the particle size variation index of the positive electrode active material to 0.70 or higher, for example, when manufacturing the positive electrode, relatively small particle sizes will be arranged between relatively large particle sizes, thereby increasing the packing density of the positive electrode active material.

[0050] By setting the particle size variation index of the positive electrode active material to 1.20 or less, the inclusion of excessively coarse or fine particles can be suppressed, and when such a positive electrode active material is used in a lithium-ion secondary battery, the output characteristics can be particularly improved.

[0051] The volume-average particle size Mv of the positive electrode active material in this embodiment is not particularly limited, but is preferably 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 18 μm or less.

[0052] By setting the volume-average particle size Mv of the positive electrode active material in this embodiment within the above range, when the positive electrode active material of this embodiment is used as the positive electrode of a lithium-ion secondary battery, it is possible to particularly enhance the output characteristics and battery capacity while simultaneously achieving high packing efficiency into the positive electrode. Specifically, by setting the volume-average particle size Mv of the positive electrode active material of this embodiment to 8 μm or more, packing efficiency into the positive electrode can be improved. Furthermore, by setting the volume-average particle size Mv of the positive electrode active material of this embodiment to 20 μm or less, the output characteristics and battery capacity can be particularly enhanced. (2) Method for producing positive electrode active material for lithium-ion secondary batteries The method for producing the positive electrode active material for lithium-ion secondary batteries according to this embodiment will now be described. According to the method for producing the positive electrode active material for lithium-ion secondary batteries according to this embodiment, the positive electrode active material described above can be produced. Therefore, some of the previously explained matters will be omitted.

[0053] The method for producing the positive electrode active material of this embodiment may include the following steps, as shown in the flow chart 20 in Figure 2: mixing step (S1), calcination step (S2), washing step (S3), and boron addition step (S4).

[0054] In the mixing process, a lithium compound can be mixed with a nickel-containing material that includes elements other than lithium (Li), boron (B), and oxygen (O) from the elements contained in the lithium nickel composite oxide, such as nickel (Ni), and optionally element M (M), to prepare a raw material mixture.

[0055] In the firing process, the above raw material mixture is fired in an oxidizing atmosphere to obtain a fired product.

[0056] In the washing process, the fired product obtained in the firing process above can be washed with water to obtain a water-washed powder.

[0057] In the boron addition step, a boron-containing solution containing at least one boron-containing substance selected from elemental boron and boron-containing compounds can be sprayed onto the water-washed powder.

[0058] The following describes each step. (2-1) Mixing process

[0059] In the mixing process, a nickel-containing material containing at least nickel, as described above, can be mixed with a lithium compound to prepare a raw material mixture. The raw materials used are described below. (2-1-1) Nickel-containing materials The nickel-containing material used in the mixing process may contain nickel, which is an element other than lithium, boron, and oxygen among the elements contained in the target lithium-nickel composite oxide as described above, and element M as needed. However, since element M is an optional additive in the above-mentioned nickel-containing material, it does not need to be included.

[0060] The nickel-containing material only needs to contain elements corresponding to the desired composition of the lithium nickel composite oxide, and its composition is not particularly limited. For example, the nickel-containing material can suitably contain nickel composite hydroxide or nickel composite compounds, which are roasted products of nickel composite hydroxide. The nickel-containing material can also be composed of the above-mentioned nickel composite compounds. Examples of roasted products of nickel composite hydroxide include nickel composite oxide and mixtures of nickel composite oxide and nickel composite hydroxide.

[0061] Furthermore, the nickel-containing material may be nickel oxide, a material having a coating layer containing element M on the surface of nickel hydroxide, or a mixture of nickel oxide, nickel hydroxide, etc., and a compound of element M.

[0062] When a lithium nickel composite oxide contains multiple elements M, a mixture of a nickel composite compound containing some of the elements M and a compound of the remaining elements M can also be used to make a nickel-containing material. In this case, the nickel composite compound is preferably one or more selected from nickel composite oxides or nickel composite hydroxides.

[0063] Furthermore, if the nickel-containing material contains a compound of element M, the form of the compound of element M is not particularly limited, and one or more compounds selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc., can be used.

[0064] The nickel-containing material preferably contains nickel (Ni) and element M (M) in a molar ratio of Ni:M=b:d. The b, d, and element M in the above formula can be the same preferred range and materials as described in "(1-1-1) Composition" of "(1-1) Lithium Nickel Composite Oxide" for the positive electrode active material, so their explanation is omitted here.

[0065] If the nickel-containing material is a nickel composite oxide, the nickel-containing material is, for example, a material with the general formula: Ni b´ M d´ O 1+β It can be expressed as follows.

[0066] If the nickel-containing material is a nickel-compound hydroxide, the nickel-containing material is, for example, a nickel-containing material with the general formula: Ni b´ M d´ (OH) 2+γ It can be expressed as follows.

[0067] Furthermore, b' and d' are related to b':d'=b:d with the previously described b and d, and satisfy b'+d'=1. Since b, d, and element M have already been explained, their explanation will be omitted here. Preferably, β and γ are -0.2≦β≦0.2 and -0.2≦γ≦0.2, respectively.

[0068] When a nickel-containing material contains nickel composite hydroxide, the method for producing the nickel composite hydroxide is not particularly limited, and nickel composite hydroxide obtained by crystallization methods such as coprecipitation or homogeneous precipitation can be used.

[0069] In the mixing process, the above-mentioned nickel composite hydroxide can be used as is, either as part or all of the nickel-containing material, or it may be used after being oxidized and roasted to form a roasted product.

[0070] The conditions for oxidative roasting of nickel composite hydroxides are not particularly limited, but it is preferable to oxidative roast the aforementioned nickel composite hydroxides in an oxidizing atmosphere at a temperature of 500°C to 800°C.

[0071] When a roasted nickel complex hydroxide is used as the nickel complex compound, the composition ratio of Li to Ni and element M in the lithium nickel complex oxide can be particularly stabilized when the raw material mixture, which is mixed with a lithium compound, is calcined to obtain a lithium nickel complex oxide.

[0072] The atmosphere used for oxidative roasting is not particularly restricted, but as mentioned above, it is preferable to carry it out in an oxidizing atmosphere, and it is even more preferable to carry it out in an air atmosphere (air atmosphere) or in an airflow, as these can be easily implemented. (2-1-2) Lithium compounds The lithium compound is not particularly limited, but preferably one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride, and lithium oxide can be used. More preferably, one or more selected from lithium hydroxide and lithium carbonate can be used as the lithium compound. Since lithium hydroxide has high reactivity with nickel composite compounds and a low reaction temperature, it is even more preferable to use lithium hydroxide as the lithium compound.

[0073] Furthermore, in the method for producing the positive electrode active material of this embodiment, a raw material mixture can be prepared by mixing a nickel-containing material and a lithium compound as described above.

[0074] The mixing ratio of nickel-containing material and lithium compound is not particularly limited, but the composition of lithium, nickel, and element M in the calcined product obtained after calcination is approximately the same as the composition in the raw material mixture obtained by mixing nickel-containing material and lithium compound.

[0075] However, since lithium may decrease slightly when the washing process described later is carried out, it is preferable to adjust the amount of lithium (Li) in the lithium compound to be 1.005 or more and 1.100 or less in terms of the amount of substance ratio (Li / Me) with respect to the total amount of nickel and element M (Me) in the nickel-containing material.

[0076] By setting the above Li / Me ratio to 1.005 or higher, the crystallinity of the resulting lithium nickel composite oxide can be increased, and the content ratio of lithium in the resulting lithium nickel composite oxide relative to elements other than oxygen can be set to the desired composition.

[0077] Furthermore, by setting the Li / Me ratio to 1.100 or less, it is possible to suppress excessive firing, which can lead to processes such as sintering of secondary particles within the resulting lithium nickel composite oxide.

[0078] The apparatus or method for mixing nickel-containing materials and lithium compounds is not particularly limited, as long as it can uniformly mix the two. For example, a dry mixer such as a V-blender or a mixing and granulation apparatus can be used. (2-2) Firing process In the calcination process, the raw material mixture is calcined in an oxidizing atmosphere to obtain a calcined product. When the raw material mixture is calcined in the calcination process, a calcined product is obtained in which lithium from the lithium compound diffuses and reacts with the nickel-containing material.

[0079] In the firing process, the firing temperature for firing the raw material mixture is not particularly limited, but it is preferably 600°C to 1000°C, more preferably 650°C to 950°C, and even more preferably 680°C to 900°C.

[0080] By setting the firing temperature to 600°C or higher, the diffusion of lithium into the nickel-containing material can be sufficiently promoted.

[0081] Furthermore, by setting the firing temperature to 1000°C or lower, it is possible to suppress the progression of sintering between the particles of the resulting fired product. In addition, it is possible to suppress the occurrence of abnormal grain growth and prevent the particles of the resulting fired product from becoming coarser.

[0082] During the process of raising the temperature to the firing temperature, the lithium compound used can be kept in a temperature range from near its melting point to the firing temperature, for example, between 400°C and 550°C, for about 1 to 5 hours. Keeping it in this temperature range allows the reaction to proceed particularly uniformly.

[0083] It is preferable to use an oxidizing atmosphere during firing. The oxidizing atmosphere is not particularly limited, but an oxygen-containing gas atmosphere can be used, and it is more preferable to have an atmosphere with an oxygen concentration of 18% to 100% by volume.

[0084] This is because maintaining an oxygen concentration of 18% by volume or higher in the atmosphere during firing promotes the reaction between the lithium compound and the nickel-containing material, thereby increasing the crystallinity of the lithium-nickel composite oxide.

[0085] When an oxygen-containing gas atmosphere is used, the gas constituting the atmosphere can be, for example, air, oxygen, or a mixture of oxygen and an inert gas.

[0086] Furthermore, when using a mixed gas of oxygen and an inert gas as the gas constituting the oxygen-containing gas atmosphere, for example, as described above, it is preferable that the oxygen concentration in the mixed gas satisfies the above-mentioned range.

[0087] In particular, the firing process is preferably carried out in an oxygen-containing gas stream, and more preferably in air or an oxygen stream. Considering the battery characteristics, the firing process is even more preferably carried out in an oxygen stream.

[0088] The furnace used for firing is not particularly limited; any furnace capable of firing the raw material mixture in a predetermined atmosphere is acceptable. However, from the viewpoint of maintaining a uniform atmosphere inside the furnace, an electric furnace that does not generate gas is preferred, and either a batch-type or continuous-type furnace can be used.

[0089] In the method for producing a positive electrode active material of this embodiment, if agglomeration occurs in the particles of the calcined material during the calcination process, a crushing step (first crushing step) for crushing the calcined material may be included.

[0090] Here, "disintegration" refers to the process of applying mechanical energy to an aggregate of multiple secondary particles formed during firing due to sintering necking between secondary particles, thereby separating the secondary particles without destroying them and loosening the aggregate. For example, a pin mill, hammer mill, or pulperizer can be used to disintegrate the secondary particles to the extent that they are not destroyed.

[0091] The method for producing the calcined product prepared in the calcination process is not limited to the method described above. For example, it can also be prepared by spray pyrolysis of a solution containing all the desired metal elements, or by grinding and mixing all the compounds of the desired elements using a ball mill or other mechanical grinding method, and then calcining them. (2-3)Water washing process In the washing process, the fired product obtained in the firing process is washed with water to obtain a water-washed powder.

[0092] The washing process may include, for example, a slurrying process, a solid-liquid separation process, and a drying process, as described below.

[0093] Specifically, in the washing process, the calcined product obtained in the calcination process is mixed with water to form a slurry for washing (slurrying process). The slurry concentration when washing the calcined product is not particularly limited, but is preferably 200 g / L or more and 5000 g / L or less, and more preferably 500 g / L or more and 2000 g / L or less. By setting the slurry concentration to 5000 g / L or less, stirring of the slurry can be facilitated and the dissolution rate of adhering substances can be improved.

[0094] On the other hand, by setting the slurry concentration to 200 g / L or higher, the desorption of lithium from the crystal lattice of the calcined product can be prevented, and the collapse of the crystals can be suppressed. Furthermore, by setting the slurry concentration to 5000 g / L or lower, the reprecipitation of lithium carbonate due to the absorption of carbon dioxide from the atmosphere by the high pH aqueous solution can be prevented.

[0095] Furthermore, it is preferable to carry out the washing with water while controlling the slurry temperature to be in the range of 10°C to 40°C and the electrical conductivity of the liquid portion of the slurry to be between 30 mS / cm and 90 mS / cm.

[0096] By setting the electrical conductivity of the slurry prepared in the water washing process to the above range, excess components adhering to the surface of the fired product particles, such as excess lithium, can be selectively and sufficiently reduced.

[0097] The water used in the washing process is not particularly limited, but for example, water with an electrical conductivity of less than 10 μS / cm, preferably 1 μS / cm or less, can be used.

[0098] While there are no particular limitations on the washing time, it can be set to, for example, 3 minutes to 2 hours, in order to sufficiently remove excess components adhering to the surface of the fired material particles while also increasing productivity. It is preferable to stir the prepared slurry during the washing process.

[0099] In the washing process, after slurry formation, the slurry can be separated into solid and liquid components, i.e., filtered and dewatered, to recover the washed powder (solid-liquid separation process). The filtration and dewatering are not particularly limited, and for example, a filter press type solid-liquid separation apparatus can be used.

[0100] In the washing step, it is preferable to dry the water-washed powder containing water obtained after solid-liquid separation before subjecting it to the boron addition step. This allows the water-washed powder to be dried (drying step). The drying conditions are not particularly limited.

[0101] Drying is preferably carried out at a temperature of 100°C to 250°C in an oxidizing atmosphere or a vacuum atmosphere. A drying temperature of 100°C or higher allows for sufficient evaporation of moisture from the washed powder. Furthermore, a drying temperature of 250°C or lower reduces the energy required for drying, thereby lowering costs.

[0102] The atmosphere during drying should preferably be one in which water vapor and carbon dioxide are suppressed or absent, in order to avoid the reaction between moisture and carbon dioxide in the atmosphere and the water-washed powder. Specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. Furthermore, from the viewpoint of quickly discharging the water vapor generated during drying, it is preferable to add an exhaust mechanism to the drying apparatus.

[0103] The drying time is not particularly limited, but it is preferably between 0.5 hours and 48 hours. By setting the drying time, that is, the holding time at the highest temperature reached during drying, to 0.5 hours or more, the moisture in the water-washed powder can be sufficiently reduced and removed. Furthermore, productivity can be increased by setting the drying time to 48 hours or less. (2-4) Boron addition process In the boron addition step, a boron-containing solution containing boron-containing material is sprayed onto the water-washed powder obtained in the water-washing step to obtain treated powder.

[0104] The boron-containing substance to be added is not particularly limited, but may be, for example, elemental boron or a boron-containing compound. In other words, it is preferable that the boron-containing substance be at least one selected from elemental boron and boron-containing compounds. Suitable boron-containing compounds include, for example, orthoboric acid (H3BO3), boron oxide (B2O3), and boron nitride (BN).

[0105] The solvent for the boron-containing solution is not particularly limited. Any solvent capable of dissolving or dispersing the boron-containing substance can be suitably used. Examples of such solvents include one or more selected from water, ethanol, methanol, etc. A mixture of two or more solvents can also be used. Water is particularly preferable as the solvent because it is easy to handle and suppresses carbon contamination.

[0106] Furthermore, since the boron-containing solution may be a solution in which the boron-containing material is not dissolved but dispersed, the above solvent may also be referred to as a dispersion medium.

[0107] The amount of boron contained in the boron-containing solution sprayed onto the water-washed powder is not particularly limited and can be selected according to the desired composition of the resulting lithium nickel composite oxide. Therefore, the spray amount (addition amount) can be selected by conducting tests in advance so that the lithium nickel composite oxide obtained after the boron addition step or the heat treatment step described later has the desired composition.

[0108] It is preferable to stir the water-washed powder during the boron addition process so that the boron-containing solution can be uniformly sprayed onto the water-washed powder.

[0109] In the boron addition process, a boron-containing solution can be sprayed onto the water-washed powder to place the boron-containing compound on the surface of the powder particles. It is believed that at this time, the boron reacts with the lithium component adhering to the surface of the water-washed powder to produce a lithium-boron compound.

[0110] In the method for producing the positive electrode active material of this embodiment, the processed powder obtained in the boron addition step can also be used as the positive electrode active material. However, in the method for producing the positive electrode active material of this embodiment, the processed powder may be further subjected to the following heat treatment step as needed. (2-5) Heat treatment process The method for producing the positive electrode active material in this embodiment may also include a heat treatment step if necessary after the boron addition step. In the heat treatment step, the treated powder, which is the water-washed powder to which the boron-containing solution has been sprayed after the boron addition step, can be heat-treated.

[0111] The heat treatment process promotes the reaction between the boron contained in the treated powder and the lithium components adhering to the surface of the fired particles. Furthermore, the heat treatment process removes the solvent present in the boron-containing solution added during the boron addition process.

[0112] In the heat treatment process, the heat treatment temperature for the processed powder is not particularly limited and can be selected according to the added boron-containing substances, etc. In the heat treatment process, it is preferable to heat treat at a temperature of 100°C to 500°C, and more preferably at a temperature of 200°C to 400°C.

[0113] By setting the heat treatment temperature to 100°C or higher, the reaction between the boron and lithium component can be sufficiently carried out.

[0114] Furthermore, by setting the heat treatment temperature to 500°C or lower, it is possible to prevent boron from scattering into the atmosphere before it reacts with the lithium component.

[0115] The atmosphere during the heat treatment process is not particularly limited and can be carried out, for example, under an oxidizing atmosphere or an inert gas atmosphere.

[0116] The oxidizing atmosphere is not particularly limited, but an oxygen-containing gas atmosphere can be used, and it is preferable to use an atmosphere with an oxygen concentration of 18% to 100% by volume.

[0117] When an oxygen-containing gas atmosphere is used, the gas constituting the atmosphere can be, for example, air, oxygen, or a mixture of oxygen and an inert gas.

[0118] The furnace used for heat treatment is not particularly limited; any furnace capable of heat-treating the powder in a predetermined atmosphere is acceptable. However, from the viewpoint of maintaining a uniform atmosphere inside the furnace, an electric furnace that does not generate gas is preferred, and either a batch-type or continuous-type furnace can be used.

[0119] The method for producing the positive electrode active material of this embodiment may also include a crushing step (second crushing step) to crush the lithium nickel composite oxide if aggregation occurs in the lithium nickel composite oxide particles after the boron addition step or heat treatment step. Since the crushing can be carried out in the same manner as in the first crushing step described above, a detailed explanation is omitted. [Lithium-ion rechargeable battery] The lithium-ion secondary battery of this embodiment (hereinafter also referred to as "secondary battery") comprises at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode may include the positive electrode active material for lithium-ion secondary batteries described above.

[0120] The following describes an example configuration of the secondary battery of this embodiment, with each component explained separately. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of components similar to those of a general lithium-ion secondary battery. The embodiments described below are merely illustrative, and the lithium-ion secondary battery of this embodiment can be implemented in various modified and improved forms based on the knowledge of those skilled in the art, including the embodiments described below. Furthermore, the secondary battery does not particularly limit its applications. (positive electrode) The positive electrode of the secondary battery of this embodiment may include the positive electrode active material described above.

[0121] An example of a method for manufacturing a positive electrode is described below. First, the positive electrode active material (in powder form), conductive material, and binder are mixed to form a positive electrode mixture. Then, activated carbon and solvents for purposes such as viscosity adjustment are added as needed, and this mixture is kneaded to produce a positive electrode mixture paste.

[0122] The mixing ratio of each material in the positive electrode composite is a factor that determines the performance of the lithium-ion secondary battery, and therefore can be adjusted according to the application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium-ion secondary battery. For example, if the total mass of the solid content of the positive electrode composite excluding the solvent is 100% by mass, the positive electrode active material can be contained in a ratio of 60% to 95% by mass, the conductive material in a ratio of 1% to 20% by mass, and the binder in a ratio of 1% to 20% by mass.

[0123] The resulting positive electrode composite paste is applied to the surface of a current collector, for example, made of aluminum foil, and dried to remove the solvent, thereby producing a sheet-like positive electrode. If necessary, it can be pressurized using a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size according to the intended battery and used in the manufacture of the battery.

[0124] As conductive materials, for example, graphite (natural graphite, artificial graphite, and expanded graphite, etc.) or carbon black-based materials such as acetylene black and Ketjenblack (registered trademark) can be used.

[0125] The binder serves to hold the active material particles together, and one or more of the following can be used: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resins, and polyacrylic acid.

[0126] If necessary, a solvent that dissolves the binder and disperses the positive electrode active material, conductive material, etc., can be added to the positive electrode mixture. Specifically, organic solvents such as N-methyl-2-pyrrolidone can be used as the solvent. In addition, activated carbon can be added to the positive electrode mixture to increase the electrical double layer capacity.

[0127] The method for manufacturing the positive electrode is not limited to the examples given above, and other methods may be used. For example, it can be manufactured by press-molding the positive electrode composite material and then drying it under a vacuum atmosphere. (Negative electrode) The negative electrode can be made of metallic lithium, lithium alloy, or the like. Alternatively, the negative electrode may be formed by mixing a binder with a negative electrode active material capable of intercalating and deintercalating lithium ions, adding a suitable solvent to make a paste, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it as needed to increase the electrode density.

[0128] As the negative electrode active material, for example, natural graphite, artificial graphite, and calcined organic compounds such as phenolic resin, and powdered carbon materials such as coke can be used. In this case, as with the positive electrode, a fluororesin such as PVDF can be used as the negative electrode binder, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing these active materials and binders. (Separator) A separator can be placed between the positive and negative electrodes as needed. The separator separates the positive and negative electrodes and holds the electrolyte. Known materials can be used, such as a thin film made of polyethylene or polypropylene with numerous micropores. (Non-aqueous electrolyte) As a non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0129] As a non-aqueous electrolyte, for example, a lithium salt dissolved in an organic solvent can be used as a supporting salt. Alternatively, a lithium salt dissolved in an ionic liquid may be used as a non-aqueous electrolyte. An ionic liquid is a salt composed of cations and anions other than lithium ions, and is liquid at room temperature.

[0130] As the organic solvent, one of the following may be used alone or in combination: cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butanesultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate.

[0131] As supporting salts, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts can be used. Furthermore, the non-aqueous electrolyte may contain radical scavengers, surfactants, and flame retardants.

[0132] Furthermore, solid electrolytes may be used as non-aqueous electrolytes. Solid electrolytes have the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0133] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0134] The oxide-based solid electrolyte is not particularly limited, and for example, one containing oxygen (O) and having lithium ion conductivity and electronic insulation properties can be suitably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4) and Li3PO4N. X LiBO2NX , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 Li7La3Zr2O 12 Li6BaLa2Ta2O 12 Li 3.6 Si 0.6 P 0.4 One or more types selected from O4, etc., can be used.

[0135] The sulfide-based solid electrolyte is not particularly limited, and for example, one or more that contain sulfur (S) and have lithium-ion conductivity and electronic insulation properties can be suitably used. For example, one or more sulfide-based solid electrolytes selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc. can be used.

[0136] Furthermore, other inorganic solid electrolytes may be used besides those mentioned above; for example, Li3N, LiI, Li3N-LiI-LiOH, etc., may be used.

[0137] The organic solid electrolyte is not particularly limited as long as it is a polymer compound exhibiting ionic conductivity; for example, polyethylene oxide, polypropylene oxide, or copolymers thereof can be used. Furthermore, the organic solid electrolyte may contain a supporting salt (lithium salt). (Shape and composition of secondary batteries) As described above, the lithium-ion secondary battery of this embodiment can be made into various shapes, such as cylindrical or stacked. Regardless of the shape adopted, if the secondary battery of this embodiment uses a non-aqueous electrolyte, the positive electrode and negative electrode can be stacked with a separator in between to form an electrode body, the resulting electrode body can be impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the positive electrode terminal that is open to the outside, and the negative electrode current collector and the negative electrode terminal that is open to the outside can be connected using current collector leads or the like, and the battery can be sealed in a battery case.

[0138] As previously described, the secondary battery of this embodiment is not limited to a form using a non-aqueous electrolyte solution as the non-aqueous electrolyte; for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery, can also be used. In the case of an all-solid-state battery, the components other than the positive electrode active material can be changed as necessary.

[0139] The secondary battery of this embodiment can be used for various applications. Because the secondary battery of this embodiment can be a high-capacity, high-output secondary battery, it is suitable for powering small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity, and is also suitable for powering electric vehicles that require high output.

[0140] Furthermore, since the secondary battery of this embodiment can be miniaturized and have a high output, it is suitable as a power source for electric vehicles where mounting space is limited. Moreover, the secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that are used in conjunction with combustion engines such as gasoline engines and diesel engines. [Examples]

[0141] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0142] First, we will explain the evaluation methods for the positive electrode active material and secondary battery obtained in the following examples and comparative examples. (Evaluation of positive electrode active material) The following evaluations were performed on the obtained positive electrode active material.

[0143] (a) Evaluation of composition, crystal structure, and particle structure The composition was analyzed using an ICP emission spectrometer (ICPE-9000, manufactured by Shimadzu Corporation).

[0144] Furthermore, the powder X-ray diffraction patterns of the obtained positive electrode active materials were measured, and the crystal structure and other properties were identified by Rietveld analysis. As a result, it was confirmed that the positive electrode active materials prepared in the following examples and comparative examples consisted of lithium nickel composite oxides, and that lithium nickel composite oxides have a hexagonal layered structure.

[0145] Furthermore, when the particles of the positive electrode active material were observed using a scanning electron microscope, it was confirmed that the positive electrode active materials prepared in the following examples and comparative examples contained secondary particles formed by the aggregation of multiple primary particles.

[0146] (b) Titration curve In the following examples and comparative examples, 10 g of the positive electrode active material was stirred in 50 mL of pure water for 5 minutes, and the titration curve was measured by neutralizing the filtered filtrate with 1.0 M HCl. Distilled water was used as the pure water.

[0147] From the obtained titration curves, the amount of HCl added in each pH range shown in the "Neutralization Titration HCl Addition Amount" column of Table 1 was determined. In addition, the HCl addition ratios VR1 and VR2 were calculated using equations (1) and (2) described above.

[0148] (c) Particle size variation index The volume-based particle size distribution was measured using a laser diffraction scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac-Bell Co., Ltd.). From the particle size distribution, D10, D90, and volume-average particle size Mv were calculated.

[0149] Then, the particle size variation index [(D90-D10) / volume-average particle size Mv] was calculated.

[0150] (Evaluation of battery characteristics) (a) Charging capacity, gas generation amount The volume of the laminate-type batteries prepared in the following examples and comparative examples was measured by the Archimedes method. After being left in a constant temperature bath maintained at 25°C for approximately 12 hours until the open circuit voltage (OCV) stabilized, the cutoff voltage was set to 2.5-4.3V and the current density to 23mA / cm². 2 The battery underwent a conditioning test involving five charge-discharge cycles.

[0151] Next, the battery was charged to 4.2V using constant current and constant voltage (CCCV) at a temperature of 25°C. The capacity at this point was defined as the charged capacity.

[0152] After charging, the batteries were stored in a constant temperature chamber set to 60°C for 12 days. After 12 days, they were discharged to 2.5V. After discharge, the volume of the laminated battery was measured using the Archimedes method, and the amount of gas generated inside the cell was evaluated from the difference between this volume and the volume measured before conditioning, and this was defined as the gas generation amount. [Example 1] (1) Manufacturing of positive electrode active material

[0153] The positive electrode active material was manufactured according to flow chart 20 shown in Figure 2. (1-1) Mixing process (Nickel-containing material)

[0154] First, nickel composite hydroxide prepared by neutralization crystallization was oxidized and roasted at 600°C for 3 hours in an air atmosphere to prepare a nickel composite oxide. The nickel composite oxide had a molar ratio of Ni:Mn:Co of 85:10:5. 0.85 Mn 0.10 Co 0.05 The answer was O.

[0155] Then, a mixture of the above-mentioned nickel composite oxide and TiO2 was used as the nickel-containing material. The nickel composite oxide and TiO2 were mixed so that the ratio of the molar amounts of Ni, Mn, Co, and Ti corresponded to the ratio shown in Table 1, i.e., Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024. (Lithium compounds) Lithium hydroxide was used as the lithium compound. Specifically, anhydrous lithium hydroxide was used.

[0156] The nickel-containing material and lithium hydroxide were weighed and mixed so that Li / (Ni+Mn+Co+Ti) was 1.02, to obtain a raw material mixture. (1-2) Firing process The obtained raw material mixture was heated to 840°C in an electric furnace under an oxygen atmosphere and maintained at 840°C for 2 hours for firing. Afterward, it was cooled in the furnace to room temperature. The resulting fired material was then subjected to a crushing treatment. (1-3)Water washing process Next, 20°C pure water was added to the obtained calcined product to create a slurry containing 1250g of calcined product per 1L of water (slurrying step). This slurry was stirred for 20 minutes, then passed through a filter press to dewater it, thereby producing a washed cake containing water-washing powder (solid-liquid separation step). As pure water, water with an electrical conductivity of 1 μS / cm or less was used.

[0157] The resulting washed cake was dried under a vacuum at 190°C for 10 hours to obtain water-washed powder (drying process). (1-4) Boron addition process A boron-containing solution, which is an aqueous solution of orthoboric acid (H3BO3), a boron-containing substance, dissolved in water, was sprayed onto the water-washed powder to prepare the treated powder. At this time, the spray amount was adjusted so that the ratio of the amount of substance of the elements contained in the lithium nickel composite oxide obtained after the heat treatment process was the ratio shown in Table 1, i.e., Li:Ni:Mn:Co:Ti:B = 1.00:0.825:0.097:0.049:0.024:0.005.

[0158] The washed powder was continuously stirred during the boron addition process. (1-5) Heat treatment process In the heat treatment process, the treated powder was heat-treated at 305°C for 10 hours under an airflow.

[0159] The lithium nickel composite oxide, which was obtained as the positive electrode active material, was evaluated as described above. The evaluation results are shown in Table 1. (2) Manufacturing of secondary batteries A laminate-type battery with the structure shown in Figure 1 was fabricated using the following procedure, and the battery was evaluated as described above. The evaluation results are shown in Table 1.

[0160] As shown in Figure 1, the laminated battery 10 has a structure in which an electrolyte is impregnated into a laminate of a positive electrode film 11, a separator 12, and a negative electrode film 13, and then sealed with a laminate 14. A positive electrode tab 15 is connected to the positive electrode film 11, and a negative electrode tab 16 is connected to the negative electrode film 13, with the positive electrode tab 15 and negative electrode tab 16 being exposed outside the laminate 14.

[0161] A slurry made by mixing 20.0 g of the obtained positive electrode active material with 0.64 g of acetylene black, 0.64 g of polyvinylidene fluoride, and N-methyl-2-pyrrolidone (NMP) was spread on an aluminum foil to a depth of 1 cm. 2 The positive electrode active material was coated so that 16.5 mg was present per Al foil. Next, the slurry containing the positive electrode active material was coated onto the Al foil and dried in air at 120°C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into strips 66 mm wide and roll-pressed with a load of 4 tons to produce a positive electrode film. The positive electrode film was then cut into a rectangle of 50 mm x 30 mm and dried in a vacuum dryer at 120°C for 12 hours, and used as the positive electrode film 11 of the laminate-type battery 10.

[0162] Furthermore, artificial graphite, which is the negative electrode active material, and PVDF, which is the binder, were mixed in a mass ratio of negative electrode active material:binder of 97:3, and dispersed in NMP to form a slurry. The resulting negative electrode slurry was then applied using an applicator at a rate of 4 mg / cm² per unit area. 2To achieve this, a negative electrode film 13 was prepared by coating an 18 μm thick copper foil (negative electrode current collector), followed by drying and roll pressing.

[0163] The separator 12 was a polyethylene porous membrane with a thickness of 20 μm, and the electrolyte was a mixture (manufactured by Ube Industries, Ltd.) consisting of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a 20:5:25:50 mixture with 1.2 M LiPF6 as the supporting electrolyte, to which 2 wt% of vinylene carbonate (VC) was added.

[0164] In a dry room controlled to a dew point of -60°C, the laminate of the positive electrode film 11, separator 12, and negative electrode film 13 was impregnated with an electrolyte, and then sealed with a laminate 14 to produce a laminate-type battery 10.

[0165] [Examples 2-4] In the boron addition process, the boron-containing solution sprayed onto the water-washed powder was sprayed such that the ratio of the amounts of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment process was as shown in Table 1. Except for the above, the positive electrode active material and lithium-ion secondary battery were manufactured and evaluated under the same conditions as in Example 1. The evaluation results are shown in Table 1.

[0166] [Examples 5 and 6] The positive electrode active material and lithium-ion secondary battery were manufactured and evaluated under the same conditions as in Example 2, except that the heat treatment temperature was changed to the temperature shown in Table 1 during the heat treatment process. The evaluation results are shown in Table 1.

[0167] [Example 7] The processed powder obtained after the boron addition step was used as the positive electrode active material. In other words, no heat treatment step was performed when manufacturing the positive electrode active material. Except for the above, the positive electrode active material and lithium-ion secondary battery were manufactured and evaluated under the same conditions as in Example 2. The evaluation results are shown in Table 1.

[0168] [Comparative Example 1] The positive electrode active material and lithium-ion secondary battery were manufactured and evaluated under the same conditions as in Example 1, except that the processes after the washing step were not performed. In other words, when manufacturing the positive electrode active material, the calcined product obtained in the calcination step was used directly as the positive electrode active material. The evaluation results are shown in Table 1.

[0169] [Table 1] As shown in Table 1, the positive electrode active materials of Examples 1 to 7, produced by the method for producing positive electrode active materials according to this disclosure, were confirmed to be able to suppress gas generation. [Explanation of symbols]

[0170] 10 Laminated batteries 11. Positive electrode film 12 Separators 13. Negative electrode film 14 Laminate 15 Positive Tab 16 Negative Electrode Tabs 20 flows S1 Mixing process S2 firing process S3 Washing process S4 Boron addition process

Claims

1. A method for producing a positive electrode active material for a lithium-ion secondary battery, which contains a lithium nickel composite oxide having a hexagonal layered structure and containing secondary particles formed by the aggregation of multiple primary particles, A mixing step of preparing a raw material mixture by mixing a nickel-containing material containing at least nickel with a lithium compound, A firing step in which the raw material mixture is fired in an oxidizing atmosphere to obtain a fired product, A washing step is performed to wash the fired product obtained in the firing step with water to obtain a water-washed powder, The process includes a boron addition step in which a boron-containing solution containing at least one boron-containing substance selected from elemental boron and boron-containing compounds is sprayed onto the water-washed powder obtained in the water-washing step, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), boron (B), and element M (M) in molar ratios such that Li:Ni:B:M = a:b:c:d (where 0.95 ≤ a ≤ 1.10, 0.50 ≤ b < 1.00, 0.00 < c ≤ 0.03, 0.00 ≤ d ≤ 0.47, b + c + d = 1, and element M is at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Ti, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al). A method for producing a positive electrode active material for a lithium-ion secondary battery, wherein 10 g of the positive electrode active material for a lithium-ion secondary battery is stirred in 50 mL of pure water for 5 minutes, and the filtrate after filtration is neutralized by titration with 1.0 M HCl, and in the titration curve obtained, the volume ratio of the amount of HCl added in the pH region greater than 11.0 to the amount of HCl added in the pH region of 8.0 to 11.0 is 2.0 or less.

2. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1, further comprising a heat treatment step of heat treating the treated powder, which is the water-washed powder to which the boron-containing solution has been sprayed, after the boron addition step.

3. The method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 2, wherein the heat treatment step involves performing a heat treatment on the treatment powder at a temperature of 100°C or higher and 500°C or lower, under an oxidizing atmosphere or an inert gas atmosphere.

4. The aforementioned washing step is A slurrying step is performed by mixing the aforementioned calcined material with water to form a slurry. A solid-liquid separation step is performed to separate the slurry into solid and liquid components and recover the water-washed powder. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1 or claim 2, comprising a drying step of drying the water-washed powder.

5. A method for producing a positive electrode active material for a lithium-ion secondary battery according to claim 1 or claim 2, wherein, in the titration curve, the volume ratio of the amount of HCl added in the region where the pH is 5.0 or more and less than 8.0 to the amount of HCl added in the region where the pH is 8.0 or more and less than 11.0 is 0.3 or less.

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