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 of mixing a nickel-containing substance 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 material, and a water washing step of washing the sintered material with water, the method includes a sintering step in which a first starting material mixture is prepared, a washing step in which the sintered material obtained in the sintering step is washed to obtain a dehydrated cake, a boron addition step in which the dehydrated cake obtained in the washing step and a boron-containing substance are mixed to prepare a second starting material mixture, the boron-containing substance being at least one substance selected from a boron monomer and a boron-containing compound, and a heat treatment step in which the second starting material mixture is heat-treated.

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 demand 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 demand for the development of high-output secondary batteries. Further, in addition to the above-mentioned required characteristics, there is a high expectation for a secondary battery that is difficult to deteriorate even after repeated use and has 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 for the negative electrode and the positive electrode, materials that can release and insert 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 they can obtain a high voltage of 4V level.

[0005] As the positive electrode material of a lithium ion secondary battery, lithium cobalt composite oxide (LiCoO 2 ), lithium nickel composite oxide (LiNiO 2 ) using nickel cheaper than cobalt, lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O 2 ), lithium manganese composite oxide (LiMn 2 O 4 ), lithium nickel manganese composite oxide (LiNi 0.5 Mn 0.5 O 2 ) and other 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, research has been conducted on improvement of cycle characteristics (for example, Patent Document 1), high output, etc.

[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, an object of one aspect of the present invention 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 Problems

[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,

[0015] The positive electrode active material contains a lithium nickel composite oxide having a hexagonal layered structure and including secondary particles formed by aggregation of a plurality of primary particles, and the method includes:

[0016] A mixing step of mixing at least a nickel-containing material containing nickel and a lithium compound to prepare a first raw material mixture,

[0017] A sintering step of sintering the first raw material mixture in an oxidizing atmosphere to obtain a sintered product,

[0018] A water washing step of washing the sintered product obtained in the sintering step to obtain a dewatered cake,

[0019] A boron addition step of mixing the dewatered cake 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, and

[0020] A heat treatment step of heat treating the second raw material mixture,

[0021] 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, and 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).

[0022] Effects of the Invention

[0023] 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 that can suppress gas generation when used in a lithium ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0024]

Figure 1

[0025]

Figure 2

[0026] Hereinafter, embodiments for implementing the present invention will be described with reference to the accompanying drawings. 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.

[0027] [Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0028] 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.

[0029] 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.

[0030] (1) Regarding the positive electrode active material

[0031] (1-1) Regarding lithium nickel composite oxide

[0032] 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 or the like are not excluded.

[0033] (1-1-1) Composition

[0034] The above lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0035] 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.

[0036] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), boron (B), and element M (M) in the following ratio in terms of the molar ratio, Li:Ni:B:M = a:b:c:d.

[0037] 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, the 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.

[0038] 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 For a, b, c, d, and the 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.

[0039] (Nickel (Ni))

[0040] In the lithium nickel composite oxide, the higher the proportion of nickel, the higher the capacity when used as the positive electrode material of a lithium ion secondary battery.

[0041] In addition, in the lithium nickel composite oxide, the higher the nickel content ratio, the more likely gas generation due to the reaction with the electrolyte occurs when used in a lithium ion secondary battery. However, the positive electrode active material for a lithium ion secondary battery according to the present embodiment can suppress such gas generation and can exhibit a particularly high effect.

[0042] Therefore, as described above, b representing 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.

[0043] The upper limit value of b representing the nickel content ratio is as described above, preferably less than 1.00, and more preferably 0.97 or less.

[0044] (Boron (B))

[0045] 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.

[0046] Although the exact mechanism for suppressing gas generation is not clear, it is believed that the lithium nickel composite oxide contains boron, and this boron forms a compound with the lithium component attached to the particle surface of the lithium nickel composite oxide, which 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.

[0047] 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.

[0048] 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.

[0049] (Element M)

[0050] 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 been described, so the description is 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).

[0051] 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.

[0052] 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.

[0053] 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.

[0054] (1-1-2) Regarding the crystal structure

[0055] 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.

[0056] The crystal structure of the lithium nickel composite oxide can be analyzed by Rietveld refinement.

[0057] (1-1-3) Regarding the morphology of particles

[0058] The particles of the lithium nickel composite oxide may contain secondary particles formed by the aggregation of multiple primary particles.

[0059] 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.

[0060] (1-2) Regarding the titration curve

[0061] 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 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 is 2.0 or less.

[0062] 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, etc. 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.

[0063] According to the research of the inventors of the present invention, the amount of HCl added in the region where the 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.

[0064] 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 the 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 the pH is 8.0 or more and 11.0 or less, compared with the region where the pH is greater than 11.0, a region with a smaller change in pH with respect to the amount of HCl added appears.

[0065] 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 suppresses the gas generation caused by the decomposition of the electrolyte.

[0066] 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.

[0067] 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 produced. 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.

[0068] 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).

[0069] 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 - )".

[0070] VR1 = V(11.0 - ) ÷ V(8.0 - 11.0) ··· (1)

[0071] 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.

[0072] 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.

[0073] 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.

[0074] 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.

[0075] 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 0.3 or less, suppressing the content of lithium carbonate 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.

[0076] 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).

[0077] 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)".

[0078] VR2 = V(5.0 - 8.0) ÷ V(8.0 - 11.0) ··· (2)

[0079] 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.

[0080] 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.

[0081] (1 - 3) Regarding the particle size distribution index and volume average particle size

[0082] 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.

[0083] In this specification, D10 means the cumulative 10% particle size, which is the 10% diameter on a volume basis 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 on a volume basis 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.

[0084] 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 particle size distribution analyzer.

[0085] By making the particle size distribution index of the positive electrode active material 0.70 or more, for example, when manufacturing the positive electrode, 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.

[0086] 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.

[0087] 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, and more preferably 10 μm or more and 18 μm or less.

[0088] 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.

[0089] (2) Manufacturing method of positive electrode active material for lithium ion secondary battery

[0090] The manufacturing method of the positive electrode active material for lithium ion secondary battery of the present embodiment will be described. According to the manufacturing method of the positive electrode active material for lithium ion secondary battery of the present embodiment, the above-mentioned positive electrode active material can be manufactured. Therefore, for the matters that have been described, some descriptions will be omitted.

[0091] The manufacturing method of the positive electrode active material of the present embodiment is as Figure 2 shown in process 20, and may have the following mixing process (S1), sintering process (S2), water washing process (S3), boron addition process (S4), and heat treatment process (S5). In addition, the manufacturing method of the positive electrode active material of the present embodiment may also have a drying process after the boron addition process and before the heat treatment process as needed.

[0092] In the mixing process, a nickel-containing material containing elements other than lithium (Li), boron (B), and oxygen 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.

[0093] In the sintering process, the above-mentioned first raw material mixture is sintered in an oxidizing atmosphere to generate a sintered product.

[0094] In the water washing process, the sintered product obtained in the above sintering process is washed with water to obtain a dewatered cake.

[0095] In the boron addition process, the dewatered cake and the boron-containing material are mixed to prepare a second raw material mixture.

[0096] In the heat treatment process, the second raw material mixture can be heat-treated.

[0097] Each process will be described below.

[0098] (2-1) Mixing process

[0099] In the mixing process as described above, a nickel-containing material containing at least nickel and a lithium compound are mixed to prepare a first raw material mixture. Hereinafter, the raw materials used will be described.

[0100] (2-1-1) Nickel-containing material

[0101] The nickel-containing material 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 optionally element M. In addition, in the above nickel-containing material, element M may be an optional additive component and thus may not be contained.

[0102] The nickel-containing material 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 material may appropriately contain a nickel composite hydroxide, a nickel composite compound that is a calcined product of the nickel composite hydroxide. In addition, the nickel-containing material may also be composed of the above nickel composite compound. Examples of the calcined product of the nickel composite hydroxide include a nickel composite oxide, a mixture of a nickel composite oxide and a nickel composite hydroxide.

[0103] In addition, the nickel-containing material may 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.

[0104] 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 may also be used as the nickel-containing material. In this case, the above nickel composite compound is preferably one or more selected from a nickel composite oxide and a nickel composite hydroxide.

[0105] In addition, when 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 selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc. can be used.

[0106] 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.

[0107] When the nickel-containing material is a nickel composite oxide, the nickel-containing material can be represented by, for example, the general formula: Ni b ′ M d ′ O 1+β as shown.

[0108] When the nickel-containing material is a nickel composite hydroxide, the nickel-containing material can be represented by, for example, the general formula: Ni b ′ M d ′ (OH) 2+γ as shown.

[0109] In addition, b′ and d′ have the relationship of b′:d′ = b:d with the above-mentioned b and d, and satisfy b′ + d′ = 1. Since b, d, and element M have already been described, the description is omitted here. β and γ are preferably, for example, -0.2 ≤ β ≤ 0.2 and -0.2 ≤ γ ≤ 0.2.

[0110] When the nickel-containing material contains a nickel composite hydroxide, there are no particular limitations 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.

[0111] 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 used as the roasted product.

[0112] There are no particular limitations on the conditions for oxidative roasting of the nickel composite hydroxide. Preferably, the above-mentioned nickel composite hydroxide is subjected to oxidative roasting in an oxidizing atmosphere at a temperature of 500 °C or higher and 800 °C or lower.

[0113] 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.

[0114] There are no particular limitations on the atmosphere for 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 can be easily carried out.

[0115] (2-1-2) Lithium compound

[0116] There is no particular limitation on the lithium compound, 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, and thus lithium hydroxide is further preferably used as the lithium compound.

[0117] 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 a first raw material mixture.

[0118] There is no particular limitation on the mixing ratio of the nickel-containing material and the lithium compound, and the composition of lithium, nickel, and element M in the sintered product obtained after sintering substantially maintains the composition in the first raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0119] Here, when performing the subsequent water washing process, etc., 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).

[0120] 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 the elements other than oxygen can be the target composition.

[0121] 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.

[0122] The apparatus 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.

[0123] (2-2) Sintering process

[0124] 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.

[0125] In the sintering process, there is no particular limitation on the sintering temperature for sintering the first raw material mixture. 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.

[0126] By setting the sintering temperature at 600 °C or higher, the diffusion of lithium into the nickel-containing material can proceed sufficiently.

[0127] In addition, by setting the sintering temperature at 1000 °C or lower, the sintering between the particles of the produced sintered material can be suppressed. In addition, the generation of abnormal grain growth can be suppressed, and the coarsening of the particles of the obtained sintered material can be suppressed.

[0128] 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.

[0129] 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 vol% or more and 100 vol% or less is more preferable.

[0130] This is because by setting the oxygen concentration in the atmosphere during sintering at 18 vol% or more, the reaction between the lithium compound and the nickel-containing material can be promoted, and the crystallinity of the lithium nickel composite oxide can be improved.

[0131] 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.

[0132] 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.

[0133] In particular, the sintering step is preferably carried out in an oxygen-containing gas stream, more preferably in air or an oxygen stream. When considering battery characteristics, it is further preferred that the sintering step is carried out in an oxygen stream.

[0134] In addition, there is no particular limitation on the furnace used for sintering, and it is only necessary to sinter the first raw material mixture in a specified atmosphere. From the perspective of uniformly maintaining the atmosphere in the furnace, an electric furnace without gas generation is preferred, and both batch-type and continuous furnaces can be used.

[0135] In the method for manufacturing the positive electrode active material of the present embodiment, when the particles of the sintered material agglomerate during the sintering step, a crushing step (first crushing step) for crushing the sintered material can be provided.

[0136] Here, crushing refers to the following operation: mechanical energy is applied to the aggregate composed of multiple secondary particles generated due to sintering necks between secondary particles during sintering, 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.

[0137] 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 desired metal elements to spray pyrolysis treatment, a method of sintering after mechanically pulverizing and mixing all compounds of desired elements by a ball mill or the like.

[0138] (2-3) Water washing process

[0139] In the water washing process, the sintered product obtained in the sintering process can be washed with water to obtain a dewatered cake.

[0140] For example, the water washing process may include a slurry preparation process and a solid-liquid separation process described below.

[0141] 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.

[0142] 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 crystals 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.

[0143] In addition, the water washing is preferably carried out as follows: 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.

[0144] 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 adhered to the sintered product can be selectively and sufficiently reduced.

[0145] 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.

[0146] 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 adhered 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, it is preferable to stir the prepared slurry during the water washing.

[0147] In the water washing process, after the slurry is liquefied, the slurry is subjected to solid-liquid separation, that is, filtration and dehydration, and the dewatered cake 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.

[0148] In the water washing process, the dewatered cake containing moisture obtained after solid-liquid separation may not be dried and can be provided to the boron addition process in a water-containing state.

[0149] There are no particular limitations on the moisture content of the dewatered cake. For example, it is preferably 0.5% by mass or more and 30% by mass or less, more preferably 1% by mass or more and 20% by mass or less. The moisture content of the dewatered cake can be measured by a Karl Fischer moisture meter at a gasification temperature of 300 °C.

[0150] (2-4) Boron addition process

[0151] In the boron addition process, the dewatered cake and the boron-containing substance are mixed to prepare a second raw material mixture.

[0152] There are no particular limitations on the added boron-containing substance. It can be, for example, 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, orthoboric acid (H 3 BO 3 ), boron oxide (B 2 O 3 ), boron nitride (BN), etc. The components other than B are compounds selected from one or more of hydrogen, oxygen, and nitrogen.

[0153] There are no particular limitations on the mixing ratio of the dewatered cake and the boron-containing substance. In order to make the lithium nickel composite oxide obtained after heat treatment the target composition, experiments, etc. are carried out in advance, and the mixing ratio can be selected.

[0154] Here, generally, the composition in the lithium nickel composite oxide obtained after heat treatment is roughly maintained as 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.

[0155] Here, in the subsequent heat treatment process, in order to achieve a uniform reaction, it is preferable to finely pulverize the added boron-containing substance. Specifically, the average diameter in the long axis direction of the secondary particles of the boron-containing substance 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 as follows: arbitrarily extract 30 or more secondary particles of the boron-containing substance 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, there are no particular limitations on the upper limit value of the number of secondary particles for which the particle diameter in the long axis direction is measured. From the viewpoint of suppressing the time required for evaluation, it is preferably 100 or less.

[0156] The device and method for mixing the dewatered cake and the boron-containing substance are not particularly limited as long as they can mix the two evenly. For example, a dry mixer such as a V-type mixer or a mixing granulation device can be used.

[0157] (2-5) Heat treatment process

[0158] In the heat treatment process, the second raw material mixture can be heat-treated.

[0159] It is considered that by carrying out 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 particle surface of the washed powder contained in the dewatered cake can be promoted.

[0160] 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 substance, etc. In the heat treatment process, for example, it is preferably heat-treated at 100 °C or higher and 500 °C or lower, and more preferably at 200 °C or higher and 400 °C or lower.

[0161] By making the heat treatment temperature 100 °C or higher, the reaction between the above-mentioned boron and lithium components can be particularly carried out.

[0162] In addition, by making the heat treatment temperature 500 °C or lower, it is possible to prevent boron from flying into the atmosphere, etc. before reacting with the lithium component.

[0163] The atmosphere during heat treatment in the heat treatment process is not particularly limited. For example, it can be carried out in an oxidizing atmosphere or an inert gas atmosphere.

[0164] 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% by volume or higher and 100% by volume or lower is preferred.

[0165] 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.

[0166] 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 a specified atmosphere. From the viewpoint of uniformly maintaining the furnace atmosphere, an electric furnace without gas generation is preferred, and both batch-type and continuous-type furnaces can be used.

[0167] When agglomeration occurs in the particles of the lithium nickel composite oxide after the heat treatment process in the manufacturing method of the positive electrode active material of the present embodiment, a crushing process (second crushing process) for crushing the lithium nickel composite oxide may also be provided. Regarding crushing, it can be carried out in the same manner as in the above-mentioned first crushing process, and thus the description is omitted.

[0168] (2-6) Drying process

[0169] The method for manufacturing the positive electrode active material of the present embodiment may further include a drying step of drying the second raw material mixture after the boron addition step and before the heat treatment step.

[0170] By performing the drying step before the heat treatment step, the efficiency of the heat treatment step can be improved.

[0171] There are no particular restrictions on the drying conditions in the drying step.

[0172] The drying step is preferably carried out, for example, in an oxidizing atmosphere or a vacuum atmosphere at a temperature of 100°C or higher and 250°C or lower. By setting the drying temperature to 100°C or higher, the moisture in the second raw material mixture can be sufficiently evaporated. In addition, by setting the drying temperature to 250°C or lower, the energy required for drying can be suppressed, and the cost can be reduced.

[0173] In addition, the drying step is preferably carried out at a lower temperature than the heat treatment step.

[0174] In order to avoid the reaction of moisture and carbon dioxide in the atmosphere with the second raw material mixture, 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 add an exhaust mechanism to the drying device.

[0175] There are no particular restrictions on the drying time. For example, it is preferably 0.5 hours or more and 48 hours or less. By setting the drying time, that is, the holding time at the maximum temperature reached during drying, to 0.5 hours or more, the moisture in the second raw material mixture can be sufficiently reduced and removed. In addition, by setting the drying time to 48 hours or less, the productivity can be improved.

[0176] The second raw material mixture after the drying step can be provided to the above-mentioned heat treatment step.

[0177] [Lithium-ion secondary battery]

[0178] 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 positive electrode active material for the lithium-ion secondary battery described above.

[0179] Hereinafter, regarding a structural example of the secondary battery of the present embodiment, each structural element will be described separately. The secondary battery of the present embodiment, for example, contains 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 only 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.

[0180] (Positive electrode)

[0181] The positive electrode of the secondary battery according to this embodiment may contain the above positive electrode active material.

[0182] An example of the method for manufacturing the positive electrode will be described below. First, the above positive electrode active material (powder form), conductive material, and binder (adhesive) may be mixed to form a positive electrode composite material. Furthermore, a solvent for purposes such as adding activated carbon and viscosity adjustment may be added as needed, and it may be kneaded to produce a positive electrode composite material slurry.

[0183] The mixing ratio of each material in the positive electrode composite material, since it is an element that determines the performance of the lithium-ion secondary battery, can be adjusted according to the application. 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, it may contain 60% by mass or more and 95% by mass or less of the positive electrode active material, 1% by mass or more and 20% by mass or less of the conductive material, and 1% by mass or more and 20% by mass or less of the binder.

[0184] The obtained positive electrode composite material slurry is coated on the surface of a current collector made of, for example, aluminum foil, dried to disperse the solvent, and a sheet-shaped positive electrode is produced. If necessary, in order to increase the electrode density, it may also be pressed by roll pressing or the like. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size, etc., according to the target battery, and provided for the production of the battery.

[0185] As the conductive material, for example, carbon black-based materials such as graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, and Ketjen black (registered trademark) can be used.

[0186] As the binder (adhesive), since it serves to connect and fix 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 resins, and polyacrylic acid can be used.

[0187] If necessary, the positive electrode active material, conductive material, etc. are dispersed, and a solvent for dissolving the binder may also be added to the positive electrode composite material. Specifically, as the solvent, an organic solvent such as N-methyl-2-pyrrolidone can be used. In addition, in the positive electrode composite material, activated carbon may also be added in order to increase the electric double layer capacitance.

[0188] The method for manufacturing the positive electrode is not limited to the above example, and other methods may also be used. For example, it may also be manufactured by pressing and molding the positive electrode composite material and then drying it in a vacuum atmosphere.

[0189] (Negative electrode)

[0190] The negative electrode can use metallic lithium, lithium alloys, etc. In addition, the negative electrode can be formed as follows: a negative electrode active material capable of adsorbing and desorbing lithium ions is mixed with a binder, an appropriate solvent is added to make it into a slurry state, and this negative electrode composite material is coated on the surface of a metal foil current collector such as copper, dried, and compressed as needed to increase the electrode density.

[0191] 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.

[0192] (Separator)

[0193] 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, and known ones can be used, for example, films such as polyethylene and polypropylene, and membranes with a large number of micropores.

[0194] (Non-aqueous electrolyte)

[0195] As the non-aqueous electrolyte, for example, non-aqueous electrolytic solutions can be used.

[0196] As the non-aqueous electrolytic solution, 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 electrolytic solution. In addition, an ionic liquid refers to a salt composed of cations and anions other than lithium ions and is liquid at room temperature.

[0197] As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and trifluoropropylene carbonate, 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 butane sultone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. can be used alone, or two or more of them can be mixed and used.

[0198] As the supporting salt, LiPF 6 、LiBF 4 、LiClO 4 、LiAsF 6 、LiN(CF 3 SO 2 ) 2 And their composite salts, etc. Further, the non-aqueous electrolytic solution can contain radical scavengers, surfactants, flame retardants, etc.

[0199] 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. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0200] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0201] There is no particular limitation on the oxide-based solid electrolyte. 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, those selected from lithium phosphate (Li 3 PO 4 ), Li 3 PO 4 N X , LiBO 2 N X , LiNbO 3 , LiTaO 3 , Li 2 SiO 3 , Li 4 SiO 4 -Li 3 PO 4 , Li 4 SiO 4 -Li 3 VO 4 , Li 2 O-B 2 O 3 -P 2 O 5 , Li 2 O-SiO 2 , Li 2 O-B 2 O 3 -ZnO, Li 1+X Al X Ti 2-X (PO 4 ) 3 (0 ≤ X ≤ 1), Li 1+ X Al X Ge 2-X (PO 4 ) 3 (0 ≤ X ≤ 1), LiTi 2 (PO 4 ) 3 , Li 3X La 2 / 3-X TiO 3 (0 ≤ X ≤ 2 / 3), Li5 La 3 Ta 2 O 12 、Li 7 La 3 Zr 2 O 12 、Li 6 BaLa 2 Ta 2 O 12 、Li 3.6 Si 0.6 P 0.4 O 4 and more than one selected from the following:

[0202] As the sulfide solid electrolyte, there is no particular limitation, and a sulfide solid electrolyte containing sulfur (S) and having lithium ion conductivity and electron insulation can be appropriately used. As the sulfide solid electrolyte, for example, one or more selected from Li 2 S-P 2 S 5 、Li 2 S-SiS 2 、LiI-Li 2 S-SiS 2 、LiI-Li 2 S-P 2 S 5 、LiI-Li 2 S-B 2 S 3 、Li 3 PO 4 -Li 2 S-Si 2 S、Li 3 PO 4 -Li 2 S-SiS 2 、LiPO 4 -Li 2 S-SiS、LiI-Li 2 S-P 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 and more than one selected from the following:

[0203] In addition, as the inorganic solid electrolyte, those other than the above can be used. For example, Li 3 N、LiI、Li 3 N-LiI-LiOH etc. can be used.

[0204] As an organic solid electrolyte, there is no particular limitation on the polymer compound that exhibits ionic conductivity, and for example, polyethylene oxide, polypropylene oxide, their copolymers, etc. can be used. In addition, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0205] (Shape and structure of the secondary battery)

[0206] 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 secondary battery of the present embodiment uses a non-aqueous electrolyte solution, the structure can be as follows: 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 electrode terminal connected to the outside, and between the negative electrode current collector and the negative electrode terminal connected to the outside, a current collecting lead or the like is used for connection, and it is sealed in a battery case.

[0207] 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.

[0208] 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 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.

[0209] 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 purely 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.

[0210]

Examples

[0211] 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.

[0212] Here, first, the evaluation methods of the positive electrode active material and the secondary battery obtained in the following examples and comparative examples will be described.

[0213] (Evaluation of the positive electrode active material)

[0214] Regarding the obtained positive electrode active material, the following evaluations will be carried out.

[0215] (a) Evaluation of composition, crystal structure, and particle structure

[0216] The composition analysis was performed using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation, ICPE-9000).

[0217] In addition, regarding the obtained positive electrode active material, the powder X-ray diffraction pattern was measured, and the crystal structure was determined by Rietveld refinement analysis. As a result, it was confirmed that the positive electrode active materials produced in the following Examples and Comparative Examples were composed of lithium nickel composite oxides, and the lithium nickel composite oxides had a hexagonal layered structure.

[0218] Furthermore, when observing the particles of the positive electrode active material using a scanning electron microscope, it was confirmed that the positive electrode active materials produced in the following Examples and Comparative Examples included secondary particles formed by aggregation of a plurality of primary particles.

[0219] (b) Titration curve

[0220] 10 g of the positive electrode active material obtained in the following Examples and Comparative Examples was stirred in 50 mL of pure water for 5 minutes, and the filtered filtrate was neutralized and titrated with 1.0 M HCl to measure the titration curve. In addition, distilled water was used as the pure water.

[0221] From the obtained titration curve, the amount of HCl added in each pH region shown in the "HCl addition amount for neutralization titration" column of Table 1 was determined. In addition, VR1 and VR2 as the ratio of the HCl addition amount were calculated by the above formulas (1) and (2).

[0222] (c) Particle size distribution index

[0223] The volume-based particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (manufactured by Microtrac·BEL Corporation, Microtrac MT3300EXII). D10, D90, and the volume average particle size Mv were calculated from the particle size distribution.

[0224] Then, [(D90 - D10) / volume average particle size Mv] as the particle size distribution index was calculated.

[0225] (Evaluation of battery characteristics)

[0226] (a) Charge capacity and gas generation amount

[0227] After measuring the volume of the laminated battery produced in the following Examples and Comparative Examples by the Archimedes method, it was placed in a constant temperature bath maintained at 25°C for about 12 hours. After the open circuit voltage OCV (open circuit voltage) was stabilized, with a cut-off voltage of 2.5 - 4.3 V and a current density of 23 mA / cm 2, the adjustment process of repeating 5 charge-discharge cycles is carried out.

[0228] Next, at a temperature of 25 °C, constant current constant voltage (CCCV) charging is carried out until 4.2V. The capacity at this time is used as the charging capacity.

[0229] After charging, it is stored in a constant temperature bath set at 60 °C for 12 days. After 12 days, discharge is carried out until 2.5V. After discharge, the volume of the laminated battery is measured by the Archimedes method, and the amount of gas generated in the unit is evaluated from the difference in the volume of the laminated battery measured before the adjustment process, as the gas generation amount.

[0230] [Example 1]

[0231] (1) Manufacture of the positive electrode active material

[0232] According to Figure 2 the process 20 shown, the positive electrode active material is manufactured.

[0233] (1-1) Mixing process

[0234] (Nickel-containing material)

[0235] First, prepare the following nickel composite oxide. The nickel composite hydroxide prepared by the neutralization crystallization method is subjected to oxidative roasting at a temperature of 600 °C for 3 hours in an air 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.

[0236] Then, the mixture of the above nickel composite oxide and TiO 2 is used as the nickel-containing material. The nickel composite oxide and TiO 2 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.

[0237] (Lithium compound)

[0238] As the lithium compound, lithium hydroxide is used. In addition, as the lithium hydroxide, anhydrous lithium hydroxide is used.

[0239] The above nickel-containing material and lithium hydroxide are weighed and mixed so that Li / (Ni + Mn + Co + Ti) is 1.02, to obtain the first raw material mixture.

[0240] (1-2) Sintering process

[0241] The obtained first raw material mixture is heated to 840 °C in an oxygen atmosphere using an electric furnace, held at 840 °C for 2 hours, and sintered. Then, it is cooled to room temperature in the furnace. The obtained sintered product is subjected to a crushing treatment.

[0242] (1-3) Water washing process

[0243] Next, pure water at 20 °C is added to the obtained sintered product to form a slurry containing 1250 g of the sintered product per 1 L of water (slurry chemical process). After stirring the slurry for 20 minutes, it is filtered under pressure to conduct liquid, and dehydration is performed to produce a dewatered cake containing washed powder (solid-liquid separation process). In addition, as the pure water, water with a conductivity of 1 μS / cm or less is used.

[0244] When the moisture content of the obtained dewatered cake is measured using a Karl Fischer moisture meter at a vaporization temperature of 300 °C, it is 7% by mass. In addition, the moisture content of the dewatered cake in the following other examples is the same. This dewatered cake is provided to the boron addition process without drying.

[0245] (1-4) Boron addition process

[0246] The dewatered cake and orthoboric acid (H 3 BO 3 ) as a boron-containing substance are mixed to prepare a second raw material mixture. Here, 40 secondary particles of orthoboric acid arbitrarily extracted from the surface SEM image have an average diameter in the long axis direction of 3 μm.

[0247] The dewatered cake and orthoboric acid are mixed so that the molar ratio of the following elements contained in the lithium nickel composite oxide obtained after the heat treatment process is the ratio shown in Table 1, that is, Li:Ni:Mn:Co:Ti:B = 1.00:0.825:0.097:0.049:0.024:0.005.

[0248] (1-5) Drying process

[0249] The obtained second raw material mixture is dried at 190 °C for 10 hours in a vacuum atmosphere.

[0250] (1-6) Heat treatment process

[0251] In the heat treatment process, the second raw material mixture is heat-treated at 305 °C for 10 hours under an air flow.

[0252] Regarding the lithium nickel composite oxide obtained as the positive electrode active material, the above evaluation is performed. The evaluation results are shown in Table 1.

[0253] (2) Fabrication of secondary battery

[0254] Through the following procedure, fabricate as Figure 1The laminated battery having the structure shown above is evaluated as described above. The evaluation results are shown in Table 1.

[0255] As Figure 1 shown, 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 a positive electrode tab 15, and the negative electrode film 13 is connected to a negative electrode tab 16. The positive electrode tab 15 and the negative electrode tab 16 protrude outside the laminate 14.

[0256] 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 there is 16.5 mg of the positive electrode active material per 1 cm 2 Next, the product coated with the slurry containing the positive electrode active material 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 roll-pressed under a load of 4 t to produce the positive electrode film. Then, the positive electrode film is cut into a rectangle of 50 mm × 30 mm and dried in a vacuum dryer at 120 °C for 12 hours, and it is used as the positive electrode film 11 of the laminated battery 10.

[0257] In addition, a negative electrode film 13 prepared by the following method is prepared: artificial graphite as a negative electrode active material and PVDF as a binder are mixed at the following mass ratio, negative electrode active material: binder is 97:3, and it is dispersed and slurried in NMP. The obtained negative electrode slurry is coated on a copper foil (negative electrode current collector) with a thickness of 18 μm at a rate of 4 mg / cm 2 per unit area, and then dried and roll-pressed.

[0258] The separator 12 uses a polyethylene porous membrane with a film thickness of 20 μm, and the electrolytic solution 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) in a ratio of 20:5:25:50 as a supporting electrolyte (manufactured by Ube Industries, Ltd.). 6 In a drying chamber with a dew point management of -60 °C, the laminate of the positive electrode film 11, the separator 12, and the negative electrode film 13 is impregnated with the electrolytic solution and encapsulated by the laminate 14 to produce the laminated battery 10.

[0259] In a drying chamber with a dew point management of -60 °C, the laminate of the positive electrode film 11, the separator 12, and the negative electrode film 13 is impregnated with the electrolytic solution and encapsulated by the laminate 14 to produce the laminated battery 10.

[0260] [Examples 2 to 4]

[0261] In the boron addition step, the dehydrated cake and orthoboric acid are mixed in such a manner that the molar ratio of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment step 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.

[0262] [Examples 5 and 6]

[0263] In the heat treatment step, 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.

[0264] [Example 7]

[0265] After the boron addition step and before the heat treatment step, the drying step is not performed. 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.

[0266] [Comparative Example 1]

[0267] The sintered product obtained after the sintering step is used as the positive electrode active material. That is, when manufacturing the positive electrode active material, the steps after the water washing step are not performed. 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]

Table 1

[0269]

[0270] From the results shown in Table 1, it can be confirmed that the positive electrode active materials of Examples 1 to 7 manufactured by the method for manufacturing a positive electrode active material according to the present invention can suppress the gas generation amount.

[0271] This application claims priority based on Japanese Patent Application No. 2022-175169 filed with the Japan Patent Office on October 31, 2022, and the entire contents of Japanese Patent Application No. 2022-175169 are incorporated herein by reference.

[0272]

Reference Signs

[0273] 10 Stacked battery

[0274] 11 Positive electrode film

[0275] 12 Separator

[0276] 13 Negative electrode film

[0277] 14 Stack

[0278] 15 Positive Electrode Tab

[0279] 16 Negative Electrode Tab

[0280] 20 Process

[0281] S1 Mixing Process

[0282] S2 Sintering Process

[0283] S3 Water Washing Process

[0284] S4 Boron Addition Process

[0285] S5 Heat Treatment 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 hexagonal layered structure, and comprises secondary particles formed by aggregation of a plurality of primary particles, and the manufacturing method includes: a mixing step of mixing at least a nickel-containing material containing 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 dewatered cake, a boron addition step of mixing the dewatered cake 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 monomer and boron-containing compounds, and a heat treatment step of heat treating the second raw material mixture, the lithium nickel composite oxide contains lithium Li, nickel Ni, boron B, and an element M represented by 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, and 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.

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 a temperature of 100°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 dewatered cake.

4. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, after the boron addition step and before the heat treatment step, there is also a drying step of drying the second raw material mixture.

5. 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 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 thereby, 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 less.

6. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 5, 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 less.

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