Method for producing positive electrode active material for lithium ion secondary battery

Abstract

A method for producing a positive electrode active material for a lithium ion secondary battery, the method comprising a mixing step in which a nickel-containing material containing at least nickel and a lithium compound are mixed to prepare a first starting material mixture, a sintering step in which the first starting material mixture is sintered in an oxidizing atmosphere to obtain a sintered material, and a step in which the sintered material obtained in the sintering step is washed with water to obtain a positive electrode active material for a lithium ion secondary battery. A boron addition step for preparing a second starting material mixture by mixing the water-washed powder obtained in the water-washing step with a boron-containing substance, which is at least one substance selected from a boron monomer and a boron compound; a heat treatment step for heat-treating the second starting material mixture; and a cooling step in which at least an atmosphere in a temperature region equal to or lower than the boundary temperature is used as a carbon dioxide removal atmosphere and cooling is performed.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a positive electrode active material for a lithium ion secondary battery. Background Art

[0002] In recent years, with the popularization of portable electronic devices such as mobile phones and laptop computers, there has been a strong expectation for the development of small and lightweight secondary batteries with high energy density and durability. In addition, as batteries for electric vehicles such as power tools and hybrid vehicles, there has been a strong expectation for the development of high-output secondary batteries. Furthermore, in addition to the above-mentioned required characteristics, there is a high expectation for secondary batteries that are difficult to deteriorate even after repeated use and have high durability.

[0003] As a secondary battery that meets such requirements, there is a lithium ion secondary battery. A lithium ion secondary battery is composed of a negative electrode, a positive electrode, an electrolyte, etc., and as the active materials of the negative electrode and the positive electrode, materials that can release and intercalate lithium are used. As described above, a lithium ion secondary battery has high energy density, output characteristics, and durability.

[0004] Regarding lithium ion secondary batteries, research and development are now in full swing. Among them, lithium ion secondary batteries using layered or spinel-type lithium metal composite oxides as the positive electrode material have been put into practical use as batteries with high energy density because a high voltage of 4V level can be obtained.

[0005] As the positive electrode material of a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO2) that is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2) using nickel that is cheaper than cobalt, lithium nickel cobalt manganese composite oxide (LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2), lithium manganese composite oxide (LiMn2O4) using manganese, lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O2), etc. of lithium metal composite oxides have been proposed.

[0006] In recent years, regarding lithium ion secondary batteries, further improvement of battery characteristics has been required, for example, improvement of cycle characteristics (for example, Patent Document 1), high output, etc. have been studied.

[0007]

Prior Art Documents

[0008]

Patent Documents

[0009]

Patent Document 1

[0010]

Problems to be Solved by the Invention

[0011] In recent years, there has also been a need for a positive electrode active material for a lithium ion secondary battery that can suppress gas generation when used in a lithium ion secondary battery.

[0012] Therefore, in view of the problems of the above-mentioned prior art, in one aspect of the present invention, an object is to provide a method for manufacturing a positive electrode active material for a lithium ion secondary battery that can suppress gas generation when used in a lithium ion secondary battery.

[0013]

Means for Solving the Problem

[0014] To solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material containing a lithium nickel composite oxide having a hexagonal layered structure and including secondary particles formed by aggregation of a plurality of primary particles, the manufacturing method including:

[0015] A mixing step of mixing at least a nickel-containing material containing nickel and a lithium compound to prepare a first raw material mixture,

[0016] A sintering step of sintering the first raw material mixture in an oxidizing atmosphere to obtain a sintered product,

[0017] A water washing step of washing the sintered product obtained in the sintering step to obtain a water-washed powder,

[0018] A boron addition step of mixing the water-washed powder obtained in the water washing step and a boron-containing material to prepare a second raw material mixture, the boron-containing material being at least one selected from boron monomers and boron-containing compounds,

[0019] A heat treatment step of heat-treating the second raw material mixture, and

[0020] A cooling step of, after the heat treatment step, cooling with at least the atmosphere in a temperature region below a demarcation temperature as a carbon dioxide removal atmosphere,

[0021] The demarcation temperature is 200°C or higher and 300°C or lower,

[0022] The lithium nickel composite oxide contains lithium (Li), nickel (Ni), boron (B), and element M (M) in the following proportions. In terms of the molar ratio, 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).

[0023]

Effects of the Invention

[0024] According to one aspect of the present invention, there is provided a method for manufacturing a positive electrode active material for a lithium ion secondary battery, which can suppress gas generation when used in a lithium ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025]

Figure 1

[0026]

Figure 2

[0027]

Figure 3

[0028] Hereinafter, with respect to the mode for carrying out the present invention, it will be described with reference to the drawings. The present invention is not limited by the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.

[0029] [Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0030] Hereinafter, a method for manufacturing a positive electrode active material for a lithium ion secondary battery (hereinafter, simply referred to as "positive electrode active material") according to the present embodiment will be described.

[0031] First, the positive electrode active material obtained by the method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described, and then, the details of the method for manufacturing the positive electrode active material according to the present embodiment will be described.

[0032] (1) Regarding the positive electrode active material

[0033] (1-1) Regarding lithium nickel composite oxide

[0034] 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 a lithium nickel composite oxide, and in this case, unavoidable impurities mixed in the manufacturing process and the like are not excluded.

[0035] (1-1-1) Composition

[0036] The above lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0037] The lithium nickel composite oxide may also contain elements other than lithium, nickel, and boron. For example, it may also contain element M described below.

[0038] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), boron (B) and element M (M) in the following proportions in terms of molar ratio, Li:Ni:B:M = a:b:c:d.

[0039] Preferably, 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. In addition, 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.

[0040] The lithium nickel composite oxide can be represented, for example, by the general formula: Li a Ni b B c M d O 2+α Regarding a, b, c, d, and element M in the above general formula, since they have been described, the description is omitted here. α preferably satisfies, for example, -0.2 ≤ α ≤ 0.2.

[0041] (Nickel (Ni))

[0042] In the lithium nickel composite oxide, the higher the proportion of nickel contained, the higher the capacity can be when used as the positive electrode material of a lithium ion secondary battery.

[0043] In addition, in the lithium nickel composite oxide, the higher the content ratio of nickel, the more likely gas generation due to the 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, the gas generation can be suppressed, and a particularly high effect can be exhibited.

[0044] Therefore, as described above, b representing the content ratio of nickel 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.

[0045] The upper limit value of b representing the content ratio of nickel is as described above, preferably less than 1.00, more preferably 0.97 or less.

[0046] (Boron (B))

[0047] As described above, the lithium nickel composite oxide of the present embodiment may contain boron. According to the research of 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.

[0048] Although the exact mechanism for suppressing gas generation is not clear, it is believed that the lithium nickel composite oxide contains boron, which forms a compound with the lithium component attached to the particle surface of the lithium nickel composite oxide and is difficult to react with the electrolyte. Therefore, it is presumed that on the particle surface of the lithium nickel composite oxide, the proportion of components such as lithium hydroxide and lithium carbonate that react with the electrolyte and cause gas generation can be suppressed. It is also believed that this compound further suppresses gas generation caused by the decomposition of the electrolyte.

[0049] As described above, for c representing the boron content ratio, it is preferably more than 0.00, more preferably 0.001 or more, further preferably 0.002 or more, and particularly preferably 0.003 or more.

[0050] There is no particular limitation on the upper limit value of c representing the boron content ratio. Considering that the effect of excessive addition will saturate, it is preferably 0.03 or less, more preferably 0.025 or less, and particularly preferably 0.02 or less.

[0051] (Element M)

[0052] As described above, in the lithium nickel composite oxide of the present embodiment, as an optional component, element M may also be contained. The element group applicable to element M has already been described and will be omitted here. In particular, from the viewpoint of improving the thermal stability of the lithium nickel composite oxide, for example, suppressing the thermal decomposition of the lithium nickel composite oxide, as element M, it is preferably at least one selected from cobalt (Co), manganese (Mn), and titanium (Ti).

[0053] Since element M is an optional component, for d representing the content ratio of element M, as described above, it is preferably 0.00 or more, more preferably 0.05 or more, and further preferably 0.10 or more.

[0054] The upper limit value of d representing the content ratio of element M, as described above, is preferably 0.47 or less, more preferably 0.25 or less, and further preferably 0.20 or less.

[0055] In addition, when the lithium nickel composite oxide contains multiple types of element M, the total of the content ratios of the multiple types of element M preferably satisfies the above range.

[0056] (1-1-2) Regarding the crystal structure

[0057] The lithium nickel composite oxide preferably has a hexagonal layered structure. By containing a hexagonal layered structure, the lithium nickel composite oxide can easily insert and detach lithium between the layers, and when used in a lithium ion secondary battery, it can particularly improve the output characteristics and cycle characteristics.

[0058] The crystal structure of the lithium nickel composite oxide can be analyzed by Rietveld refinement.

[0059] (1-1-3) Regarding the morphology of particles

[0060] The particles of the lithium nickel composite oxide may contain secondary particles formed by the aggregation of multiple primary particles.

[0061] In addition, the lithium nickel composite oxide may contain unaggregated primary particles in addition to the secondary particles. That is, the lithium nickel composite oxide may contain both primary particles and secondary particles.

[0062] (1-2) Regarding the titration curve

[0063] Regarding the filtrate obtained by mixing the positive electrode active material of the present embodiment with pure water and then filtering, in the titration curve obtained by neutralization titration, preferably, the volume ratio of the amount of HCl added in the region where pH is greater than 11.0 to the amount of HCl added in the region where pH is 8.0 or more and 11.0 or less is 2.0 or less.

[0064] The filtrate used for drawing the above titration curve can be the filtrate obtained by the following method: Add 10 g of the positive electrode active material of the present embodiment to 50 mL of pure water, stir in this pure water for 5 minutes, and then filter to perform solid-liquid separation. The pure water preferably removes as much as possible the components that affect the neutralization titration, and distilled water or the like can be appropriately used. In addition, when preparing the above titration curve, as the acid for neutralization titration of the above filtered filtrate, that is, hydrochloric acid (HCl), 1.0 M, that is, 1.0 mol / dm 3 (1.0 mol / L) hydrochloric acid can be used.

[0065] According to the research of the inventors of the present invention, the amount of HCl added in the region where pH is greater than 11.0 in the above titration curve mainly means the HCl consumed in the reaction with lithium hydroxide contained in the positive electrode active material.

[0066] In addition, when performing neutralization titration on the above filtrate of the positive electrode active material of the present embodiment, in the titration curve, in the region where pH is 8.0 or more and 11.0 or less, compared with other pH regions, the change in pH is suppressed, and a nearly flat region appears. Specifically, for example, in the above titration curve, in the region where pH is 8.0 or more and 11.0 or less, compared with the region where pH is greater than 11.0, a region with a smaller change in pH with respect to the amount of HCl added appears.

[0067] As described above, it is considered that the lithium nickel composite oxide contains a trace amount of boron, and this boron forms a lithium-boron-containing compound that is difficult to react with the electrolyte with the lithium component attached to the surface of the particles of the lithium nickel composite oxide. It is also considered that this lithium-boron-containing compound further inhibits the gas generation caused by the decomposition of the electrolyte.

[0068] Then, it is presumed that in the above titration curve, the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less mainly means the HCl consumed in the reaction with the above lithium-boron-containing compound.

[0069] Therefore, it is considered that by making the volume ratio (VR1) of the amount of HCl added in the region where the pH is greater than 11.0 to the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less be 2.0 or less, the content of lithium hydroxide is suppressed, which means that the above lithium-boron-containing compound can be sufficiently generated. Therefore, it is considered that when this positive electrode active material is applied to a lithium ion secondary battery, the reaction with the electrolyte is suppressed, and gas generation can be suppressed.

[0070] In addition, the volume ratio VR1 of the amount of HCl added in the region where the pH is greater than 11.0 to the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less can be calculated by the following formula (1).

[0071] In the following formula (1), the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less is denoted as "V(8.0 - 11.0)", and the amount of HCl added in the region where the pH is greater than 11.0 is denoted as "V(11.0 - )".

[0072] VR1 = V(11.0 - ) ÷ V(8.0 - 11.0) ··· (1)

[0073] As described above, the above VR1 is preferably 2.0 or less, more preferably 1.5 or less, still more preferably 1.0 or less, and particularly preferably 0.75 or less.

[0074] The lower limit value of the above VR1 is not particularly limited, but since it is difficult to completely remove lithium hydroxide, it is preferably 0.05 or more, and more preferably 0.1 or more.

[0075] In addition, in the above 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 11.0 or less is preferably 0.3 or less.

[0076] According to the research of the inventors of the present invention, the amount of HCl added in the region where the pH is 5.0 or more and less than 8.0 in the above titration curve mainly means the HCl consumed in the reaction with lithium carbonate contained in the positive electrode active material.

[0077] Therefore, it is considered that by making 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 11.0 or less be 0.3 or less, the content of lithium carbonate is suppressed, which means that the above-mentioned lithium-boron-containing compound can be sufficiently generated. Therefore, it is considered that when this positive electrode active material is applied to a lithium ion secondary battery, the reaction with the electrolyte is particularly suppressed, and gas generation can be further suppressed.

[0078] The volume ratio VR2 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 11.0 or less can be calculated by the following formula (2).

[0079] In the following formula (2), the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less is denoted as "V(8.0 - 11.0)", and the amount of HCl added in the region where the pH is 5.0 or more and less than 8.0 is denoted as "V(5.0 - 8.0)".

[0080] VR2 = V(5.0 - 8.0) ÷ V(8.0 - 11.0) ··· (2)

[0081] As described above, the above VR2 is preferably 0.3 or less, more preferably 0.25 or less, and still more preferably 0.2 or less.

[0082] The lower limit value of the above VR2 is not particularly limited, but since it is difficult to completely remove lithium carbonate, it is preferably 0.01 or more, and more preferably 0.05 or more.

[0083] (1 - 3) Regarding the particle size distribution index and the volume average particle size

[0084] The positive electrode active material of the present embodiment preferably has [(D90 - D10) / volume average particle size Mv] representing the particle size distribution index of 0.70 or more and 1.20 or less, and more preferably 0.80 or more and 1.00 or less.

[0085] In this specification, D10 means the cumulative 10% particle size, which is the 10% diameter based on volume in the particle size distribution obtained by the laser diffraction scattering method, that is, the particle size at a volume cumulative value of 10%. D90 means the cumulative 90% particle size, which is the 90% diameter based on volume in the particle size distribution obtained by the laser diffraction scattering method, that is, the particle size at a volume cumulative value of 90%. In other parts of this specification, D10 and D90 also have the same meaning.

[0086] The volume average particle size Mv is the average particle size weighted by the particle volume. In a collection of particles, the sum of the product of the diameter of each particle and the volume of that particle is divided by the total volume of the particles. Regarding the volume average particle size, it can be measured and calculated by the laser diffraction scattering method using a laser diffraction type particle size distribution meter.

[0087] By making the particle size distribution index of the positive electrode active material 0.70 or more, when manufacturing the positive electrode, for example, particles with a smaller particle size are arranged between particles with a larger particle size, and the packing density of the positive electrode active material can be increased.

[0088] By making the particle size distribution index of the positive electrode active material 1.20 or less, the mixing of overly coarse particles and tiny particles can be suppressed. When such a positive electrode active material is used in a lithium-ion secondary battery, the output characteristics can be particularly improved.

[0089] The volume average particle size Mv of the positive electrode active material of the present embodiment is not particularly limited, and is preferably, for example, 8 μm or more and 20 μm or less, more preferably 10 μm or more and 18 μm or less.

[0090] By making the volume average particle size Mv of the positive electrode active material of the present embodiment within the above range, when the positive electrode active material of the present embodiment is used for the positive electrode of a lithium-ion secondary battery, the output characteristics and the battery capacity will be particularly improved, and furthermore, high packing property for the positive electrode will be achieved. Specifically, by making the volume average particle size Mv of the positive electrode active material of the present embodiment 8 μm or more, the packing property for the positive electrode can be improved. In addition, by making the volume average particle size Mv of the positive electrode active material of the present embodiment 20 μm or less, the output characteristics and the battery capacity can be particularly improved.

[0091] (2) Manufacturing method of positive electrode active material for lithium-ion secondary battery

[0092] The manufacturing method of the positive electrode active material for the lithium-ion secondary battery of the present embodiment will be described. According to the manufacturing method of the positive electrode active material for the lithium-ion secondary battery of the present embodiment, the above-mentioned positive electrode active material can be manufactured. Therefore, some descriptions of the matters that have been described will be omitted.

[0093] The manufacturing method of the positive electrode active material of the present embodiment, as Figure 3 shown in the process 30 shown, may have the following mixing step (S1), sintering step (S2), water washing step (S3), boron addition step (S4), heat treatment step (S5), and cooling step (S6).

[0094] In the mixing step, a nickel-containing material containing elements other than lithium (Li), boron (B), and oxygen (O) in the lithium nickel composite oxide, such as nickel (Ni), and an element M (M) as needed, and a lithium compound are mixed to prepare a first raw material mixture.

[0095] In the sintering step, the above-mentioned first raw material mixture is sintered in an oxidizing atmosphere to generate a sintered product.

[0096] In the water washing process, the sintered product obtained in the above sintering process is washed with water to obtain washed powder.

[0097] In the boron addition process, the washed powder and boron-containing substance are mixed to prepare the second raw material mixture.

[0098] In the heat treatment process, the second raw material mixture can be heat treated.

[0099] In the cooling process, after the heat treatment process, at least the atmosphere in the temperature region below the demarcation temperature can be used as the carbon dioxide removal atmosphere for cooling.

[0100] The following describes each process.

[0101] (2-1) Mixing process

[0102] In the mixing process as described above, a nickel-containing substance containing at least nickel and a lithium compound are mixed to prepare the first raw material mixture. Hereinafter, the raw materials used will be described.

[0103] (2-1-1) Nickel-containing substance

[0104] The nickel-containing substance provided to the mixing process as described above may contain: elements other than lithium, boron, and oxygen among the elements contained in the target lithium nickel composite oxide, namely nickel, and element M as required. In addition, in the above nickel-containing substance, element M can be an optional additive component and thus may not be contained.

[0105] The nickel-containing substance may contain elements corresponding to the target composition of the lithium nickel composite oxide, and its composition and the like are not particularly limited. For example, the nickel-containing substance may appropriately contain nickel composite hydroxide, nickel composite compound which is a calcined product of nickel composite hydroxide. In addition, the nickel-containing substance may also be composed of the above nickel composite compound. As the calcined product of nickel composite hydroxide, nickel composite oxide, a mixture of nickel composite oxide and nickel composite hydroxide can be cited.

[0106] In addition, the nickel-containing substance can be, for example, a material having a coating containing element M on the surface of nickel oxide, nickel hydroxide, etc., and one or more selected from a mixture of nickel oxide, nickel hydroxide, etc. and a compound of element M.

[0107] When the lithium nickel composite oxide contains a plurality of element M, a mixture of a nickel composite compound containing a part of element M and a compound of the remaining element M can also be used as the nickel-containing substance. At this time, the above nickel composite compound is preferably one or more selected from nickel composite oxide and nickel composite hydroxide.

[0108] In addition, when the nickel-containing substance contains a compound of element M, the form of the compound of element M is not particularly limited, and one or more selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc. can be used.

[0109] The nickel-containing material preferably contains nickel (Ni) and element M (M) in a molar ratio of Ni:M = b:d. Regarding b, d, and element M in the above formula, they can be within the same suitable ranges and materials as described in "(1-1-1) Regarding the composition" of "(1-1) Regarding lithium nickel composite oxides" of the positive electrode active material, and thus the description is omitted here.

[0110] When the nickel-containing material is a nickel composite oxide, the nickel-containing material can be represented, for example, by the general formula: Ni b′ M d′ O 1+β as shown.

[0111] When the nickel-containing material is a nickel composite hydroxide, the nickel-containing material can be represented, for example, by the general formula: Ni b′ M d′ (OH) 2+γ as shown.

[0112] In addition, b′, d′ have a relationship of b′:d′ = b:d with the above-mentioned b, d, and satisfy b′ + d′ = 1. Since b, d, and element M have already been described, the description is omitted here. β, γ are preferably, for example, -0.2 ≤ β ≤ 0.2, -0.2 ≤ γ ≤ 0.2.

[0113] When the nickel-containing material contains a nickel composite hydroxide, there are no particular restrictions on the manufacturing method, etc. of the nickel composite hydroxide. For example, a nickel composite hydroxide obtained by a crystallization method such as a coprecipitation method or a homogeneous precipitation method can be used.

[0114] In the mixing step, as part or all of the nickel-containing material, the above-mentioned nickel composite hydroxide can be used as it is, or the nickel composite hydroxide can be subjected to oxidative roasting and then used as the roasted product.

[0115] There are no particular restrictions on the conditions for oxidative roasting of the nickel composite hydroxide. It is preferably subjected to oxidative roasting at a temperature of 500 °C or higher and 800 °C or lower in an oxidizing atmosphere.

[0116] When using the roasted product of the nickel composite hydroxide as the nickel composite compound, when sintering the first raw material mixture mixed with the lithium compound to obtain a lithium nickel composite oxide, the composition ratios of Li, Ni, and element M in the lithium nickel composite oxide can be made particularly stable.

[0117] There are no particular restrictions on the atmosphere during oxidative roasting. As described above, it is preferably carried out in an oxidizing atmosphere, and more preferably carried out in an atmospheric atmosphere (air atmosphere) or an air stream that is easy to carry out.

[0118] (2-1-2) Lithium compound

[0119] The lithium compound is not particularly limited, and one or more selected from, for example, lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride, and lithium oxide can be preferably used. More preferably, one or more selected from lithium hydroxide and lithium carbonate can be used as the lithium compound. Lithium hydroxide has a high reactivity with the nickel composite compound and a low reaction temperature, so lithium hydroxide is further preferably used as the lithium compound.

[0120] Then, in the method for manufacturing the positive electrode active material of the present embodiment, as described above, the nickel-containing material and the lithium compound can be mixed to prepare the first raw material mixture.

[0121] The mixing ratio of the nickel-containing material and the lithium compound is not particularly limited, and the composition of lithium, nickel, and element M in the sintered product obtained after sintering basically maintains the composition in the first raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0122] Here, when performing the subsequent water washing process or the like, the amount of lithium sometimes decreases slightly. Therefore, with respect to the total amount (Me) of, for example, nickel and element M in the nickel-containing material, the amount of lithium (Li) in the lithium compound is preferably adjusted to be 1.005 or more and 1.100 or less in terms of the molar ratio (Li / Me).

[0123] By making the above Li / Me 1.005 or more, the crystallinity of the obtained lithium nickel composite oxide can be improved, and the content ratio of lithium in the obtained lithium nickel composite oxide relative to elements other than oxygen can be the target composition.

[0124] In addition, by making the above Li / Me 1.100 or less, excessive sintering can be suppressed, for example, the sintering between secondary particles in the obtained lithium nickel composite oxide can be suppressed.

[0125] The device and method for mixing the nickel-containing material and the lithium compound are not particularly limited as long as the two can be uniformly mixed. For example, a dry mixer such as a V-type mixer or a mixing granulation device can be used.

[0126] (2-2) Sintering process

[0127] In the sintering process, the first raw material mixture can be sintered in an oxidizing atmosphere to obtain a sintered product. In the sintering process, when sintering the first raw material mixture, a sintered product in which lithium in the lithium compound diffuses and reacts in the nickel-containing material is obtained.

[0128] In the sintering process, the sintering temperature for sintering the first raw material mixture is not particularly limited. For example, it is preferably 600 °C or higher and 1000 °C or lower, more preferably 650 °C or higher and 950 °C or lower, and further preferably 680 °C or higher and 900 °C or lower.

[0129] By making the sintering temperature 600 °C or higher, the diffusion of lithium into the nickel-containing material can be sufficiently carried out.

[0130] In addition, by making the sintering temperature 1000°C or lower, the sintering between the particles of the produced sintered product can be suppressed. In addition, the generation of abnormal grain growth can be suppressed, and the coarsening of the particles of the obtained sintered product can be suppressed.

[0131] During the process of heating up to the sintering temperature, it can be maintained for about 1 hour or more and 5 hours or less in the temperature range from near the melting point of the lithium compound used to the sintering temperature, for example, in the temperature range of 400°C or higher and 550°C or lower. By maintaining in the above temperature range, the reaction can proceed particularly uniformly.

[0132] The atmosphere during sintering is preferably an oxidizing atmosphere. There is no particular limitation on the oxidizing atmosphere, and an oxygen-containing gas atmosphere can be used. For example, an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less is more preferable.

[0133] This is because by making the oxygen concentration in the atmosphere during sintering 18% by volume or more, the reaction between the lithium compound and the nickel-containing substance can be promoted, and the crystallinity of the lithium nickel composite oxide can be improved.

[0134] When it is an oxygen-containing gas atmosphere, as the gas constituting the atmosphere, for example, air, oxygen, a mixed gas of oxygen and an inert gas, etc. can be used.

[0135] In addition, when using, for example, a mixed gas of oxygen and an inert gas as the gas constituting the oxygen-containing gas atmosphere, the oxygen concentration in the mixed gas preferably satisfies the above range.

[0136] In particular, the sintering step is preferably carried out in an oxygen-containing gas stream, more preferably in air or an oxygen stream. Considering the battery characteristics, it is further preferred that the sintering step is carried out in an oxygen stream.

[0137] In addition, there is no particular limitation on the furnace used for sintering, and it is only necessary to be able to sinter the first raw material mixture in a specified atmosphere. From the viewpoint of uniformly maintaining the atmosphere in the furnace, an electric furnace without gas generation is preferred, and both batch-type and continuous-type furnaces can be used.

[0138] In the method for manufacturing the positive electrode active material of the present embodiment, when the particles of the sintered product agglomerate during the sintering step, a crushing step (first crushing step) for crushing the sintered product may be provided.

[0139] Here, crushing refers to the following operation: mechanical energy is applied to the aggregate composed of multiple secondary particles generated during sintering due to sintering necks between secondary particles, etc., and the secondary particles themselves are hardly damaged, and the secondary particles are separated to break the aggregate. For example, a needle mill, a hammer mill, a crusher, etc. can be used, and it is only necessary to crush to a degree that does not damage the secondary particles.

[0140] In addition, the method for manufacturing the sintered product prepared in the sintering process is not limited to the above method. For example, it can also be prepared by the following methods: a method of subjecting a liquid obtained by mixing all aqueous solutions containing the desired metal elements to spray pyrolysis treatment, a method of sintering after mechanically pulverizing and mixing all compounds of the desired elements using a ball mill, etc.

[0141] (2-3) Water washing process

[0142] In the water washing process, the sintered product obtained in the sintering process can be washed with water to obtain washed powder.

[0143] For example, the water washing process may include a slurry preparation process, a solid-liquid separation process, and a drying process described below.

[0144] Specifically, in the water washing process, the sintered product obtained in the sintering process can be mixed with water and washed as a slurry (slurry preparation process). There is no particular limitation on the slurry concentration when washing the sintered product. For example, it is preferably 200 g / L or more and 5000 g / L or less, more preferably 500 g / L or more and 2000 g / L or less. By making the slurry concentration 5000 g / L or less, the stirring of the slurry can be facilitated, and the dissolution rate of the adhered substances can be increased.

[0145] On the other hand, by making the slurry concentration 200 g / L or more, the detachment of lithium from the lattice of the sintered product can be prevented, and the breakdown of the crystal can be suppressed. In addition, by making the slurry concentration 5000 g / L or less, the re-precipitation of lithium carbonate caused by the absorption of carbon dioxide in the atmosphere by the high-pH aqueous solution can be prevented.

[0146] In addition, water washing can be carried out as follows, for example, controlling the temperature of the slurry in the temperature range of 10 °C or more and 40 °C or less, and making the conductivity of the liquid part of the slurry 30 mS / cm or more and 90 mS / cm or less.

[0147] By making the conductivity of the slurry prepared in the water washing process within the above range, the remaining components, such as remaining lithium, on the surface of the particles attached to the sintered product can be selectively and sufficiently reduced.

[0148] There is no particular limitation on the water used in the water washing process. For example, water with a conductivity of less than 10 μS / cm, preferably 1 μS / cm or less, can be used.

[0149] There is no particular limitation on the water washing time. From the viewpoint of sufficiently removing the remaining components on the surface of the particles attached to the sintered product and improving productivity at the same time, it can be, for example, 3 minutes or more and 2 hours or less. In addition, the prepared slurry is preferably stirred during the water washing period.

[0150] In the water washing process, after the slurry is liquefied, the solid-liquid separation of the slurry is carried out, that is, filtration and dehydration are carried out, and the water washing powder can be recovered (solid-liquid separation process). There are no particular limitations on filtration and dehydration. For example, a pressure filtration type solid-liquid separation device can be used.

[0151] In the water washing process, the water washing powder containing moisture obtained after solid-liquid separation is preferably dried and then supplied to the boron addition process. Therefore, the water washing powder can be dried (drying process). There are no particular limitations on the drying conditions.

[0152] Drying is preferably carried out at a temperature of 100 °C or higher and 250 °C or lower in, for example, an oxidizing atmosphere or a vacuum atmosphere. By setting the drying temperature at 100 °C or higher, the moisture in the water washing powder can be sufficiently evaporated. In addition, by setting the drying temperature at 250 °C or lower, the energy required for drying can be suppressed, and the cost can be reduced.

[0153] In order to avoid the reaction of moisture and carbon dioxide in the atmosphere with the water washing powder during drying, the atmosphere during drying is preferably an atmosphere that suppresses or does not contain water vapor and carbon dioxide. Specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. In addition, from the viewpoint of quickly discharging the water vapor generated by drying, it is preferable to attach an exhaust mechanism to the drying device.

[0154] Regarding the drying time, there are no particular limitations, and it is preferably 0.5 hours or more and 48 hours or less, for example. By setting the drying time, that is, the holding time at the maximum temperature reached during drying, at 0.5 hours or more, the moisture in the water washing powder can be sufficiently reduced and removed. In addition, by setting the drying time at 48 hours or less, the productivity can be improved.

[0155] (2-4) Boron addition process

[0156] In the boron addition process, the water washing powder and the boron-containing substance are mixed to prepare the second raw material mixture.

[0157] There are no particular limitations on the added boron-containing substance. For example, it can be boron monomer or a boron-containing compound containing boron. That is, the boron-containing substance is preferably at least one selected from boron monomer and boron-containing compounds. As the boron-containing compound, the components other than boron are preferably components that can be discharged out of the system in the subsequent heat treatment process. For example, compounds in which the components other than B such as orthoboric acid (H3BO3), boron oxide (B2O3), boron nitride (BN), etc. are selected from one or more of hydrogen, oxygen, and nitrogen can be appropriately used.

[0158] There are no particular limitations on the mixing ratio of the water washing powder and the boron-containing substance. In order to make the lithium nickel composite oxide obtained after heat treatment the target composition, pre-tests, etc. can be carried out to select the mixing ratio.

[0159] Here, generally, the composition in the lithium nickel composite oxide obtained after heat treatment basically maintains the composition in the second raw material mixture. Therefore, it is preferable to prepare the second raw material mixture in such a way that the composition of the second raw material mixture is the same as the composition in the target lithium nickel composite oxide.

[0160] Here, in the subsequent heat treatment process, in order to make boron and the water-washed powder react uniformly, it is preferable to finely pulverize the added boron-containing material. Specifically, the average diameter in the long axis direction of the secondary particles of the boron-containing material observed in the surface SEM image is preferably 0.1 μm or more and 100 μm or less. The average diameter in the long axis direction is calculated by the following method: arbitrarily extract 30 or more secondary particles of the boron-containing material observed in the surface SEM image, and take the average value of the particle diameters in the long axis direction measured for each secondary particle. In addition, the upper limit value of the number of secondary particles for which the particle diameter in the long axis direction is measured is not particularly limited, and from the viewpoint of suppressing the time required for evaluation, it is preferably 100 or less.

[0161] The device and method for mixing the water-washed powder and the boron-containing material are not particularly limited as long as the two can be uniformly mixed. For example, a dry mixer such as a V-type mixer or a mixing granulation device can be used.

[0162] (2-5) Heat treatment process

[0163] In the heat treatment process, the second raw material mixture can be heat-treated.

[0164] It is considered that by implementing the heat treatment process, the formation of a lithium-boron-containing compound caused by the reaction between boron and the lithium component attached to the surface of the water-washed powder can be promoted.

[0165] In the heat treatment process, the heat treatment temperature for heat-treating the second raw material mixture is not particularly limited and can be selected according to the added boron-containing material, etc. In the heat treatment process, for example, it is preferably heat-treated at 200 °C or higher and 500 °C or lower, and more preferably heat-treated at 200 °C or higher and 400 °C or lower.

[0166] By making the heat treatment temperature 200 °C or higher, the reaction between the above-mentioned boron and lithium component can proceed sufficiently.

[0167] In addition, by making the heat treatment temperature 500 °C or lower, it is possible to prevent the boron and lithium component from flying in the atmosphere before the reaction.

[0168] The atmosphere during heat treatment in the heat treatment process is not particularly limited, and for example, it can be carried out in an oxidizing atmosphere or an inert gas atmosphere.

[0169] As the oxidizing atmosphere, there is no particular limitation, and an oxygen-containing gas atmosphere can be used. For example, an atmosphere with an oxygen concentration of 18 vol% or more and 100 vol% or less is preferably used.

[0170] When it is an oxygen-containing gas atmosphere, as the gas constituting the atmosphere, for example, air, oxygen, a mixed gas of oxygen and an inert gas, etc. can be used.

[0171] In addition, the furnace used for heat treatment is not particularly limited, and it is only necessary to heat-treat the second raw material mixture in the specified atmosphere. From the viewpoint of uniformly maintaining the atmosphere in the furnace, an electric furnace without gas generation is preferred, and both batch-type and continuous-type furnaces can be used.

[0172] (2-6) Cooling process

[0173] In the cooling process, after the heat treatment process, at least the atmosphere in the temperature region below the demarcation temperature can be used as a decarburized atmosphere for cooling.

[0174] After the heat treatment process, during the process of cooling to near room temperature, the obtained lithium nickel composite oxide may be carbonated due to the carbon dioxide contained in the heat treatment atmosphere. Due to carbonation, there are concerns such as lithium carbonate being generated on the particle surface of the lithium nickel composite oxide and the specific surface area decreasing. Therefore, in the cooling process, it is preferred that at least the atmosphere in the temperature region below the demarcation temperature where the reaction with carbon dioxide occurs is a decarburized atmosphere.

[0175] For example, when an atmosphere that cannot be sufficiently reduced by carbon dioxide is used in the heat treatment process, it is preferred that after reaching the maximum temperature, the product is taken out during the temperature drop process and cooled in a decarburized atmosphere. In the above case, at the demarcation temperature, the product is taken out from the heat treatment furnace and can be cooled in a decarburized atmosphere. In addition, when the temperature of the heat treatment furnace drops to near the demarcation temperature, the atmosphere in the heat treatment furnace is replaced, and it can be cooled in a decarburized atmosphere.

[0176] The demarcation temperature can be selected according to the manufactured lithium nickel composite oxide, etc., and there is no particular limitation. It is preferably 200 °C or higher and 300 °C or lower. That is, the demarcation temperature can be selected from the temperature range of 200 °C or higher and 300 °C or lower.

[0177] When a decarburized atmosphere is used in the heat treatment process, it can be directly cooled without switching the atmosphere at the demarcation temperature.

[0178] The carbon dioxide concentration in the decarburized atmosphere is not particularly limited, and it is only necessary to reduce the carbon dioxide concentration compared to normal air. Therefore, the carbon dioxide concentration in the decarburized atmosphere is preferably less than 0.03 vol%, more preferably 0.02 vol% or less, further preferably 0.01 vol% or less, and particularly preferably 0.008 vol% or less.

[0179] In addition, it is only necessary to suppress the carbon dioxide concentration in the decarburized atmosphere, and there is no particular limitation on other components therein. For example, similar to the heat treatment process, it can be an oxidizing atmosphere or an inert gas atmosphere.

[0180] In the manufacturing method of the positive electrode active material of the present embodiment, when aggregation occurs in the particles of the lithium nickel composite oxide after the heat treatment step and the cooling step, a crushing step (second crushing step) for crushing the lithium nickel composite oxide may also be provided. Regarding the crushing, it can be carried out in the same manner as in the above-described first crushing step, and thus the description thereof is omitted.

[0181] [Lithium ion secondary battery]

[0182] The lithium ion secondary battery of the present embodiment (hereinafter also referred to as "secondary battery") includes at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode may contain the above-described positive electrode active material for a lithium ion secondary battery.

[0183] Hereinafter, regarding a configuration example of the secondary battery of the present embodiment, each structural element will be described separately. The secondary battery of the present embodiment contains, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same structural elements as a general lithium ion secondary battery. In addition, the embodiments described below are merely examples, and the lithium ion secondary battery of the present embodiment can be implemented in various modified and improved forms based on the knowledge of those skilled in the art starting from the following embodiments. In addition, the use of the secondary battery is not particularly limited.

[0184] (Positive electrode)

[0185] The positive electrode included in the secondary battery of the present embodiment may contain the above-described positive electrode active material.

[0186] Hereinafter, an example of the manufacturing method of the positive electrode will be described. First, the above-described positive electrode active material (powder form), a conductive material, and a binder (adhesive) may be mixed to form a positive electrode composite material, and then a solvent for the purpose of adding activated carbon, viscosity adjustment, etc. may be added as needed, and the mixture may be kneaded to produce a positive electrode composite material slurry.

[0187] The mixing ratio of each material in the positive electrode composite material, which is an element that determines the performance of the lithium ion secondary battery, can be adjusted according to the use. The mixing ratio of the materials may be the same as that of the positive electrode of a known lithium ion secondary battery. For example, when the total mass of the solid components of the positive electrode composite material excluding the solvent is 100% by mass, the positive electrode active material may be contained in an amount of 60% by mass or more and 95% by mass or less, the conductive material may be contained in an amount of 1% by mass or more and 20% by mass or less, and the binder may be contained in an amount of 1% by mass or more and 20% by mass or less.

[0188] The obtained positive electrode composite material slurry is coated on the surface of a current collector made of, for example, aluminum foil, dried to remove the solvent, and a sheet-shaped positive electrode is produced. If necessary, in order to increase the electrode density, pressure may be applied by roll pressing or the like. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the target battery and provided for the production of the battery.

[0189] As the conductive material, carbon black-based materials such as graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen black (registered trademark), etc. can be used.

[0190] As the binder, to achieve the function of connecting and fixing the active material particles, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc. can be used.

[0191] As needed, to disperse the positive electrode active material, conductive material, etc., a solvent for dissolving the binder can also be added to the positive electrode composite material. Specifically, as the solvent, organic solvents such as N-methyl-2-pyrrolidone can be used. In addition, in the positive electrode composite material, activated carbon can also be added to increase the electric double layer capacitance.

[0192] The manufacturing method of the positive electrode is not limited to the above examples, and other methods can also be used. For example, it can also be manufactured by pressing and molding the positive electrode composite material and then drying it in a vacuum atmosphere.

[0193] (Negative electrode)

[0194] For the negative electrode, metallic lithium, lithium alloy, etc. can be used. In addition, the negative electrode can be formed as follows: mix a negative electrode active material capable of adsorbing and desorbing lithium ions with a binder, add an appropriate solvent to make it into a slurry state, coat the surface of a metal foil current collector such as copper with this negative electrode composite material, dry it, and compress it as needed to increase the electrode density.

[0195] As the negative electrode active material, for example, sintered bodies of organic compounds such as natural graphite, artificial graphite, and phenolic resin, and powder bodies of carbon materials such as coke can be used. At this time, as the negative electrode binder, similar to the positive electrode, fluorine-containing resins such as PVDF can be used, and as the solvent for dispersing these active materials and binders, organic solvents such as N-methyl-2-pyrrolidone can be used.

[0196] (Separator)

[0197] Between the positive electrode and the negative electrode, a separator can be interposed as needed. The separator separates the positive electrode and the negative electrode and holds the electrolyte. Well-known ones can be used, for example, films such as polyethylene and polypropylene, and membranes with a large number of micropores can be used.

[0198] (Non-aqueous electrolyte)

[0199] As the non-aqueous electrolyte, for example, non-aqueous electrolytic solutions can be used.

[0200] As a non-aqueous electrolyte, for example, a lithium salt as a supporting salt dissolved in an organic solvent can be used. In addition, an ionic liquid in which a lithium salt is dissolved can be used as the non-aqueous electrolyte. Further, an ionic liquid refers to a salt composed of a cation and an anion other than a lithium ion and being in a liquid state at room temperature.

[0201] As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and propyl trifluorocarbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, further, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butyrolactone sulfone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. can be used alone, or two or more thereof can be mixed and used.

[0202] As the supporting salt, LiPF6, LiBF4, LiClO4, LiAsF6, LiN(CF3SO2)2, and their composite salts, etc. can be used. Further, the non-aqueous electrolyte can contain a radical scavenger, a surfactant, a flame retardant, etc.

[0203] In addition, as the non-aqueous electrolyte, a solid electrolyte can be used. The solid electrolyte has the property of being able to withstand high voltages. As the solid electrolyte, inorganic solid electrolytes and organic solid electrolytes can be cited.

[0204] As the inorganic solid electrolyte, oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. can be cited.

[0205] As the oxide-based solid electrolyte, there is no particular limitation. For example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electron insulation can be appropriately used. As the oxide-based solid electrolyte, for example, one selected from lithium phosphate (Li3PO4), Li3PO4N X , LiBO2N X , 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-XTiO3(0 ≤ X ≤ 2 / 3), Li5La3Ta2O 12 、Li7La3Zr2O 12 、Li6BaLa2Ta2O 12 、Li 3.6 Si 0.6 P 0.4 O4, etc., and one or more selected therefrom.

[0206] As the sulfide-based solid electrolyte, there is no particular limitation, and a sulfide-based solid electrolyte containing sulfur (S) and having lithium ion conductivity and electron insulation can be appropriately used, for example. As the sulfide-based solid electrolyte, one or more selected from, for example, 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.

[0207] In addition, as the inorganic solid electrolyte, those other than the above can be used, for example, Li3N, LiI, Li3N-LiI-LiOH, etc. can be used.

[0208] As the organic solid electrolyte, there is no particular limitation as long as it is a polymer compound showing ion conductivity, and for example, polyethylene oxide, polypropylene oxide, their copolymers, etc. can be used. In addition, the organic solid electrolyte can contain a supporting salt (lithium salt).

[0209] (Shape and structure of the secondary battery)

[0210] The lithium ion secondary battery of the present embodiment described above can have various shapes such as cylindrical and laminated. When adopting any shape, when the non-aqueous electrolyte of the present embodiment uses a non-aqueous electrolyte solution, the following structure can be adopted. The positive electrode and the negative electrode are laminated as an electrode body through a separator, the obtained electrode body is impregnated with the non-aqueous electrolyte solution, and between the positive electrode current collector and the positive terminal connected to the outside, and between the negative electrode current collector and the negative terminal connected to the outside, a current collecting lead, etc. are used for connection, and it is made to be sealed in a battery case.

[0211] In addition, as described above, the secondary battery of the present embodiment is not limited to the form of using a non-aqueous electrolyte solution as the non-aqueous electrolyte. For example, it can also be a secondary battery using a solid non-aqueous electrolyte, that is, an all-solid-state battery. When it is an all-solid-state battery, the constitution other than the positive electrode active material can be changed as needed.

[0212] The secondary battery of the present embodiment can be used for various purposes. Since the secondary battery of the present embodiment can be a high-capacity and high-output secondary battery, it is suitable as a power source for, for example, small portable electronic devices (such as laptop computers and mobile phone terminals) that often require high capacity, and is also suitable as a power source for electric vehicles that require high output.

[0213] In addition, since the secondary battery of the present embodiment can be miniaturized and have high output, it is suitable as a power source for electric vehicles with limited mounting space. In addition, not only as a power source for electric vehicles driven solely by electric energy, the secondary battery of the present embodiment can also be used as a power source for so-called hybrid vehicles that are used in combination with combustion mechanisms such as gasoline engines and diesel engines.

[0214]

Examples

[0215] Hereinafter, the present invention will be further described in detail by way of examples, and the present invention is not limited by any of these examples.

[0216] First, the evaluation methods for the positive electrode active materials and secondary batteries obtained in the following examples and comparative examples will be described here.

[0217] (Evaluation of positive electrode active material)

[0218] Regarding the obtained positive electrode active material, the following evaluations are carried out.

[0219] (a) Evaluation of composition, crystal structure, and particle structure

[0220] The composition is analyzed using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation, ICPE-9000).

[0221] In addition, regarding the obtained positive electrode active material, the powder X-ray diffraction pattern is measured, and the crystal structure, etc. are determined by Rietveld refinement analysis. As a result, it can be confirmed that the positive electrode active materials produced in the following examples and comparative examples are composed of lithium nickel composite oxides, and the lithium nickel composite oxides have a hexagonal layered structure.

[0222] Furthermore, when observing the particles of the positive electrode active material using a scanning electron microscope, it can be confirmed that the positive electrode active materials produced in the following examples and comparative examples contain secondary particles formed by the aggregation of a plurality of primary particles.

[0223] (b) Titration curve

[0224] 10 g of the positive electrode active material obtained in the following examples and comparative examples is stirred in 50 mL of pure water for 5 minutes, and the filtered filtrate is neutralized and titrated with 1.0 M HCl to measure the titration curve. In addition, distilled water is used as the pure water.

[0225] From the obtained titration curve, determine the amount of HCl added in each pH region shown in the "HCl addition amount in neutralization titration" column of Table 1. In addition, calculate VR1 and VR2 as the ratio of the HCl addition amount using the above formulas (1) and (2).

[0226] Figure 2 The titration curves of the positive electrode active materials obtained in Example 2 and Comparative Example 1 are shown in.

[0227] (c) Particle size distribution index

[0228] Using a laser diffraction scattering type particle size distribution measuring device (manufactured by Microtrac·BEL Co., Ltd., Microtrac MT3300EXII), measure the volume-based particle size distribution. Calculate D10, D90, and the volume average particle size Mv from the particle size distribution.

[0229] Then, calculate [(D90 - D10) / volume average particle size Mv] as the particle size distribution index.

[0230] (Evaluation of battery characteristics)

[0231] (a) Charge capacity, gas generation amount

[0232] After measuring the volume of the laminated batteries fabricated in the following Examples and Comparative Examples by the Archimedes method, place them in a thermostat maintained at 25°C for about 12 hours. After the open circuit voltage OCV (open circuit voltage) stabilizes, perform a conditioning process of repeating 5 charge-discharge cycles at a cut-off voltage of 2.5 - 4.3V and a current density of 23 mA / cm 2 , and perform a conditioning process of repeating 5 charge-discharge cycles.

[0233] Next, at a temperature of 25°C, charge at a constant current and constant voltage (CCCV) up to 4.2V. Take the capacity at this time as the charge capacity.

[0234] After charging, store in a thermostat set at 60°C for 12 days. After 12 days, perform discharge until 2.5V. After discharge, measure the volume of the laminated battery by the Archimedes method, and evaluate the amount of gas generated in the cell as the gas generation amount from the difference from the volume of the laminated battery measured before the conditioning process.

[0235] [Example 1]

[0236] (1) Manufacture of positive electrode active material

[0237] According to Figure 3 the process 30 shown, manufacture the positive electrode active material.

[0238] (1-1) Mixing process

[0239] (Nickel-containing substance)

[0240] First, prepare the following nickel composite oxide. The nickel composite hydroxide prepared by the neutralization crystallization method is subjected to oxidative calcination at a temperature of 600 °C for 3 hours in an atmospheric atmosphere. In addition, the nickel composite oxide is Ni with a molar ratio of Ni:Mn:Co of 85:10:5 0.85 Mn 0.10 Co 0.05 O.

[0241] Then, use the mixture of the above nickel composite oxide and TiO2 as the nickel-containing substance. The nickel composite oxide and TiO2 are mixed so that the molar ratio of Ni, Mn, Co, and Ti is the ratio shown in Table 1, that is, the value corresponding to Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024.

[0242] (Lithium compound)

[0243] As the lithium compound, anhydrous lithium hydroxide is used.

[0244] Weigh and mix the above nickel-containing substance and lithium hydroxide in such a way that Li / (Ni + Mn + Co + Ti) is 1.06 to obtain the first raw material mixture.

[0245] (1-2) Sintering process

[0246] Heat the obtained first raw material mixture to 840 °C in an oxygen atmosphere using an electric furnace, hold it at 840 °C for 2 hours, and sinter it. Then, cool it to room temperature in the furnace. Crush the obtained sintered product.

[0247] (1-3) Water washing process

[0248] Next, add pure water at 20 °C to the obtained sintered product to make a slurry containing 1250 g of the sintered product per 1 L of water (slurry chemical process). After stirring the slurry for 20 minutes, filter it under pressure to pass the liquid and dehydrate it. Thus, a washed filter cake containing washed powder is produced (solid-liquid separation process). In addition, as the pure water, water with a conductivity of 1 μS / cm or less is used.

[0249] Dry the obtained washed filter cake at 190 °C for 10 hours in a vacuum atmosphere to obtain washed powder (drying process).

[0250] (1-4) Boron addition process

[0251] Mix the washed powder and orthoboric acid (H3BO3) as the boron-containing substance to prepare the second raw material mixture. Here, 40 secondary particles of orthoboric acid observed by surface SEM images are randomly extracted, and the average diameter in the long axis direction is calculated to be 3 μm.

[0252] The washing powder and orthoboric acid are mixed in such a way that in the lithium nickel composite oxide obtained after the heat treatment process, the molar ratio of the following elements contained is the ratio shown in Table 1, that is

[0253] Li:Ni:Mn:Co:Ti:B = 1.04:0.825:0.097:0.049:0.024:0.005.

[0254] (1-5) Heat treatment process

[0255] In the heat treatment process, the second raw material mixture is heat-treated at 305 °C for 10 hours under an air stream.

[0256] (1-6) Cooling process

[0257] In addition, after maintaining at 305 °C for 10 hours, at the time point when the temperature is lowered to 200 °C as the demarcation temperature, it is taken out from the heat treatment furnace and cooled in a decarbonized air atmosphere with the carbon dioxide concentration controlled to 0.008 vol% or less.

[0258] Regarding the lithium nickel composite oxide as the obtained positive electrode active material, the above evaluation is carried out. The evaluation results are shown in Table 1.

[0259] (2) Fabrication of secondary battery

[0260] A laminated battery having the structure shown in Figure 1 is fabricated through the following procedure, and the above evaluation is carried out on this battery. The evaluation results are shown in Table 1.

[0261] As shown in Figure 1 , the laminated battery 10 has the following structure: a laminate of a positive electrode film 11, a separator 12, and a negative electrode film 13 is impregnated with an electrolytic solution and encapsulated by a laminate 14. In addition, the positive electrode film 11 is connected to the positive electrode tab 15, and the negative electrode film 13 is connected to the negative electrode tab 16, and the positive electrode tab 15 and the negative electrode tab 16 are exposed outside the laminate 14.

[0262] 20.0 g of the obtained positive electrode active material, 0.64 g of acetylene black, 0.64 g of polyvinylidene fluoride, and N-methyl-2-pyrrolidone (NMP) are mixed, and the slurry is coated on an Al foil so that per 1 cm 2There is 16.5 mg of the positive electrode active material. Next, the product with the slurry containing the positive electrode active material coated on the Al foil is dried in the air at 120 °C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material is cut into short strips with a width of 66 mm, and a positive electrode film is produced by rolling under a load of 4 t. Then, the positive electrode film is cut into rectangles of 50 mm × 30 mm and dried in a vacuum dryer at 120 °C for 12 hours, which is used as the positive electrode film 11 of the laminated battery 10.

[0263] In addition, a negative electrode film 13 prepared by mixing artificial graphite as the negative electrode active material and PVDF as the binder in the following mass ratio, negative electrode active material: binder = 97:3, is dispersed and slurried in NMP. The obtained negative electrode slurry is coated onto a copper foil (negative electrode current collector) with a thickness of 18 μm by a coater at a rate of 4 mg / cm per unit area 2 and then dried and rolled.

[0264] The separator 12 uses a polyethylene porous membrane with a film thickness of 20 μm, and the electrolyte used is as follows: 2 wt% of vinylene carbonate (VC) is added to a mixed solution of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) with a ratio of 20:5:25:50, which contains 1.2 M of LiPF6 as the supporting electrolyte (manufactured by Ube Industries, Ltd.).

[0265] In a drying chamber with a dew point management of -60 °C, the laminate of the above positive electrode film 11, separator 12, and negative electrode film 13 is impregnated with the electrolyte and encapsulated by the laminate 14 to manufacture the laminated battery 10. Regarding the laminated battery 10 as the obtained lithium ion secondary battery, the above evaluation is carried out. The evaluation results are shown in Table 1.

[0266] [Examples 2 to 4]

[0267] In the boron addition process, the washed powder and orthoboric acid are mixed in the following manner so that the molar ratio of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment process is the value shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0268] [Examples 5 and 6]

[0269] In the heat treatment process, the heat treatment temperature is changed to the temperature shown in Table 1. Except for this point, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 2 and evaluated. The evaluation results are shown in Table 1.

[0270] [Comparative Example 1]

[0271] The sintered product obtained after the sintering process was used as the positive electrode active material. That is, when manufacturing the positive electrode active material, the processes after the water washing process were not carried out. Except for the above points, the positive electrode active material and the lithium-ion secondary battery were manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0272] [Comparative Example 2]

[0273] Except for not carrying out the water washing process, the positive electrode active material and the lithium-ion secondary battery were manufactured under the same conditions as in Example 2 and evaluated. That is, when manufacturing the positive electrode active material, the sintered product obtained in the sintering process was directly supplied to the boron addition process. The evaluation results are shown in Table 1.

[0274]

Table 1

[0275]

[0276] From the results shown in Table 1, it was confirmed that the positive electrode active materials of Examples 1 to 6 manufactured by the manufacturing method of the positive electrode active material according to the present invention could suppress the gas generation amount.

[0277] This application claims the priority based on Japanese Patent Application No. 2022-175164 filed with the Japan Patent Office on October 31, 2022, and incorporates the entire contents of Japanese Patent Application No. 2022-175164 into this international application.

[0278]

Reference Signs

[0279] 10 Stacked battery

[0280] 11 Positive electrode film

[0281] 12 Separator

[0282] 13 Negative electrode film

[0283] 14 Laminate

[0284] 15 Positive electrode tab

[0285] 16 Negative electrode tab

[0286] 30 Process

[0287] S1 Mixing process

[0288] S2 Sintering process

[0289] S3 Water washing process

[0290] S4 Boron addition process

[0291] S5 Heat treatment process

[0292] S6 Cooling process

Claims

1. A method for manufacturing a positive electrode active material for a lithium ion secondary battery, wherein, The positive electrode active material contains a lithium nickel composite oxide, the lithium nickel composite oxide has a layered structure of a hexagonal crystal system, and includes secondary particles formed by aggregation of a plurality of primary particles. The manufacturing method includes: a mixing step of mixing a nickel-containing material containing at least nickel and a lithium compound to prepare a first raw material mixture, a sintering step of sintering the first raw material mixture in an oxidizing atmosphere to obtain a sintered product, a water washing step of washing the sintered product obtained in the sintering step to obtain a water-washed powder, a boron addition step of mixing the water-washed powder obtained in the water washing step and a boron-containing material to prepare a second raw material mixture, the boron-containing material being at least one selected from boron monomers and boron-containing compounds, a heat treatment step of heat-treating the second raw material mixture, and a cooling step of, after the heat treatment step, cooling with at least the atmosphere in a temperature region below the demarcation temperature as a carbon dioxide removal atmosphere, the demarcation temperature is 200°C or higher and 300°C or lower, the lithium nickel composite oxide contains lithium Li, nickel Ni, boron B, and an element M represented by M in the following ratio. In terms of the molar ratio, 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, and b + c + d = 1. 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.

2. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1, in the heat treatment step, the second raw material mixture is heat-treated at 200°C or higher and 500°C or lower in an oxidizing atmosphere or an inert gas atmosphere.

3. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, the water washing step includes: a slurrying step of mixing the sintered product and water into a slurry, a solid-liquid separation step of performing solid-liquid separation on the slurry to recover the water-washed powder, and a drying step of drying the water-washed powder.

4. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, by stirring 10 g of the positive electrode active material for a lithium ion secondary battery obtained after the cooling step in 50 mL of pure water for 5 minutes, and neutralizing and titrating the filtered filtrate with 1.0 M HCl, in the titration curve obtained, the volume ratio of the amount of HCl added in the region where pH is greater than 11.0 to the amount of HCl added in the region where pH is 8.0 or higher and 11.0 or lower is 2.0 or lower.

5. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 4, in the titration curve, the volume ratio of the amount of HCl added in the region where pH is 5.0 or higher and less than 8.0 to the amount of HCl added in the region where pH is 8.0 or higher and 11.0 or lower is 0.3 or lower.

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