Positive electrode active material for lithium ion secondary battery, and lithium ion secondary battery

Abstract

The present invention is a positive electrode active material containing a lithium-nickel composite oxide having a hexagonal layered structure and containing secondary particles in which a plurality of primary particles are aggregated, the lithium-nickel composite oxide containing the following proportions in the amount of substance ratio: Li: Ni: B: M = a: b: c: d (0.95 < = a < = 1.10, 0.50 < = blt, 0.50 < = blt, 0.20 < = blt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.20 < = bt, 0.30 < = bt, 0.20 < = bt, 0.20 < = bt, 0.30 < = bt 1.00, 0.00 lt, 0.00 lt; the positive electrode active material is characterized in that 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), and the volume ratio of the dropping amount of HCl in a region having a pH greater than 11.0 to the dropping amount of HCl in a region having a pH of 8.0 to 11.0 (inclusive) in a titration curve obtained by neutralization titration of the positive electrode active material is 2.0 or less.

Description

Technical Field

[0001] The present invention relates to a positive electrode active material for a lithium ion secondary battery and 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 currently 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, 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, an object of one aspect of the present invention is to provide 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 positive electrode active material for a lithium ion secondary battery, which contains a lithium nickel composite oxide having a hexagonal layered structure and including secondary particles formed by aggregation of a plurality of primary particles.

[0015] 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).

[0016] 10 g of the positive electrode active material for a lithium ion secondary battery is stirred in 50 mL of pure water for 5 minutes, and the filtered filtrate is neutralized and titrated 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 more and 11.0 or less is 2.0 or less.

[0017]

Effects of the Invention

[0018] According to one aspect of the present invention, there can be provided 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

[0019]

Figure 1

[0020]

Figure 2

[0021] Hereinafter, the mode for carrying out the present invention will be described with reference to the accompanying 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.

[0022] [Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0023] The positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described below (hereinafter, simply referred to as "positive electrode active material").

[0024] (1) Regarding lithium nickel composite oxide

[0025] 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.

[0026] (1-1) Composition

[0027] The above lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0028] The lithium nickel composite oxide may also contain elements other than lithium, nickel, and boron. For example, it may also contain the element M described below.

[0029] 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.

[0030] The above a, b, c, and d preferably 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.

[0031] 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.

[0032] (Nickel (Ni))

[0033] In lithium nickel composite oxides, the higher the nickel content ratio, the higher the capacity can be achieved when used as the positive electrode material of a lithium ion secondary battery.

[0034] In addition, in lithium nickel composite oxides, the higher the nickel content ratio, the more likely gas generation due to the reaction with the electrolyte occurs when used in lithium ion secondary batteries. 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.

[0035] 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.

[0036] The upper limit value of b representing the nickel content ratio is as described above, preferably less than 1.00, more preferably 0.97 or less.

[0037] (Boron (B))

[0038] 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.

[0039] Although the exact mechanism for suppressing gas generation is not clear, it is considered that when the lithium nickel composite oxide contains boron, the boron forms a compound with the lithium component attached to the surface of the particles of the lithium nickel composite oxide, which is difficult to react with the electrolyte. Therefore, it is presumed that on the surface of the particles 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 considered that this compound further suppresses gas generation due to the decomposition of the electrolyte.

[0040] As described above, c representing the boron content ratio is preferably greater than 0.00, more preferably 0.001 or more, further preferably 0.002 or more, and particularly preferably 0.003 or more.

[0041] The upper limit value of c representing the boron content ratio is not particularly limited. Considering that the effect will saturate with excessive addition, it is preferably 0.03 or less, more preferably 0.025 or less, and particularly preferably 0.02 or less.

[0042] (Element M)

[0043] As described above, in the lithium nickel composite oxide of the present embodiment, as an optional component, element M may also be contained. The group of elements applicable to element M has already been described, and thus the description thereof 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).

[0044] Since element M is an optional component, d representing the content ratio of element M is preferably 0.00 or more, more preferably 0.05 or more, and further preferably 0.10 or more, as described above.

[0045] The upper limit value of d representing the content ratio of element M is preferably 0.47 or less, more preferably 0.25 or less, and further preferably 0.20 or less, as described above.

[0046] 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.

[0047] (1-2) Regarding the crystal structure

[0048] The lithium nickel composite oxide preferably has a hexagonal layered structure. By containing the hexagonal layered structure, lithium can be easily inserted into and removed from the interlayer, and when used in a lithium ion secondary battery, the output characteristics and cycle characteristics can be particularly improved.

[0049] The crystal structure of the lithium nickel composite oxide can be analyzed by Rietveld refinement.

[0050] (1-3) Regarding the particle morphology

[0051] The particles of the lithium nickel composite oxide may contain secondary particles formed by aggregation of multiple primary particles.

[0052] In addition, the lithium nickel composite oxide may contain non-aggregated primary particles in addition to the secondary particles. That is, the lithium nickel composite oxide may contain both primary particles and secondary particles.

[0053] (2) Regarding the titration curve

[0054] Regarding the filtrate obtained by filtering the positive electrode active material of the present embodiment after mixing with pure water, 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.

[0055] The filtrate used for plotting the above titration curve can be the filtrate obtained by adding 10 g of the positive electrode active material of this embodiment to 50 mL of pure water, stirring in this pure water for 5 minutes, and then filtering to separate the solid from the liquid. The pure water preferably has components that affect neutralization titration removed as much as possible, 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 filtrate after the above filtration, that is, hydrochloric acid (HCl), 1.0 M, that is, 1.0 mol / dm 3 (1.0 mol / L) hydrochloric acid can be used.

[0056] According to the research of the inventors of the present invention, the amount of HCl added in the region where the pH in the above titration curve is greater than 11.0 mainly means the HCl consumed in the reaction with lithium hydroxide contained in the positive electrode active material.

[0057] In addition, when performing neutralization titration on the above filtrate of the positive electrode active material of this 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 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, there is a region where the change in pH with respect to the amount of HCl added is small.

[0058] As described above, it is considered that by slightly containing boron in the lithium nickel composite oxide, the boron forms a lithium-boron-containing compound that is difficult to react with the electrolyte with the lithium component attached to the particle surface 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.

[0059] 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.

[0060] 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.

[0061] 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).

[0062] 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 more than 11.0 is denoted as "V(11.0 - )".

[0063] VR1 = V(11.0 - ) ÷ V(8.0 - 11.0) ··· (1)

[0064] 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.

[0065] 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, more preferably 0.1 or more.

[0066] 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.

[0067] 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.

[0068] 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 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.

[0069] 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 in the above titration curve can be calculated by the following formula (2).

[0070] 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)".

[0071] VR2 = V(5.0 - 8.0) ÷ V(8.0 - 11.0) ··· (2)

[0072] As described above, the above VR2 is preferably 0.3 or less, more preferably 0.25 or less, still more preferably 0.2 or less.

[0073] The lower limit value of the above-mentioned VR2 is not particularly limited, but since it is difficult to completely remove lithium carbonate, it is preferably 0.01 or more, more preferably 0.05 or more.

[0074] (3) Regarding the particle size distribution index and volume average particle size

[0075] 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, more preferably 0.80 or more and 1.00 or less.

[0076] In this specification, D10 means the cumulative 10% particle size, 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, 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.

[0077] 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.

[0078] By making the particle size distribution index of the positive electrode active material 0.70 or more, when manufacturing a positive electrode, for example, smaller particle size particles are arranged between larger particle size particles, and the packing density of the positive electrode active material can be increased.

[0079] By making the particle size distribution index of the positive electrode active material 1.20 or less, the mixing of overly large 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.

[0080] 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.

[0081] By making the volume-average particle diameter 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 battery capacity are particularly improved, and furthermore, high fillability for the positive electrode is achieved. Specifically, by making the volume-average particle diameter Mv of the positive electrode active material of the present embodiment 8 μm or more, the fillability for the positive electrode can be improved. In addition, by making the volume-average particle diameter Mv of the positive electrode active material of the present embodiment 20 μm or less, the output characteristics and battery capacity can be particularly improved.

[0082] [Manufacturing Method of Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0083] 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 positive electrode active material can be manufactured. Therefore, for the matters already described, some descriptions are omitted. In addition, the method for manufacturing the above positive electrode active material is not limited to the following manufacturing method of the positive electrode active material.

[0084] The manufacturing method of the positive electrode active material of the present embodiment may include the following mixing step, sintering step, water washing step, boron addition step, heat treatment step, and cooling step.

[0085] 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 required, and a lithium compound are mixed to prepare a first raw material mixture.

[0086] In the sintering step, the above first raw material mixture is sintered in an oxidizing atmosphere to form a sintered product.

[0087] In the water washing step, the sintered product obtained in the above sintering step is washed with water to obtain a water-washed powder.

[0088] In the boron addition step, the water-washed powder and a boron-containing material are mixed to prepare a second raw material mixture.

[0089] In the heat treatment step, the second raw material mixture can be heat-treated.

[0090] In the cooling step, after cooling in the above heat treatment step, the heat-treated lithium nickel composite oxide is taken out of the sintering furnace at a temperature of 200 °C or more and 300 °C or less.

[0091] Each step will be described below.

[0092] (1) Mixing step

[0093] In the mixing step 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.

[0094] (1-1) Nickel-containing material

[0095] As described above, the nickel-containing material supplied to the mixing step may contain: elements other than lithium, boron, and oxygen among the elements contained in the target lithium nickel composite oxide, namely nickel and, if necessary, element M. In addition, in the above nickel-containing material, element M may be an optional additive component and thus may not be contained.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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. may be used.

[0100] 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 may be the same appropriate ranges and materials as described in “(1) Regarding the lithium nickel composite oxide” and “(1-1) Regarding the composition” of the positive electrode active material, and thus the description is omitted here.

[0101] 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 represented.

[0102] 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 representation

[0103] In addition, b′, d′ have the relationship of b′:d′ = b:d with b, d described above, 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.

[0104] When the nickel-containing material contains nickel composite hydroxide, there are no particular restrictions on the manufacturing method of the nickel composite hydroxide, etc. For example, a nickel composite hydroxide obtained by a crystallization method such as a coprecipitation method or a homogeneous precipitation method can be used.

[0105] 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 oxidized and roasted and then used as the roasted product.

[0106] There are no particular restrictions on the conditions for oxidizing and roasting the nickel composite hydroxide. It is preferable to oxidize and roast the above-mentioned nickel composite hydroxide in an oxidizing atmosphere at a temperature of 500°C or higher and 800°C or lower.

[0107] When using the roasted product of 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.

[0108] There are no particular restrictions on the atmosphere during the oxidation 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.

[0109] (1-2) Lithium compound

[0110] There are no particular restrictions 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, the lithium compound can be one or more selected from lithium hydroxide and lithium carbonate. 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.

[0111] Then, in the manufacturing method of 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.

[0112] There are no particular restrictions on the mixing ratio of the nickel-containing material and the lithium compound. 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.

[0113] Here, when performing the subsequent water washing step 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).

[0114] 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 with respect to elements other than oxygen can be made the target composition.

[0115] 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.

[0116] 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.

[0117] (2) Sintering step

[0118] In the sintering step, the first raw material mixture can be sintered in an oxidizing atmosphere to obtain a sintered product. In the sintering step, 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.

[0119] In the sintering step, the sintering temperature for sintering the first raw material mixture is not particularly limited and can be, for example, 600°C or more and 1000°C or less.

[0120] By making the sintering temperature 600°C or more, the diffusion of lithium into the nickel-containing material can proceed sufficiently.

[0121] In addition, by making the sintering temperature 1000°C or less, the sintering between the particles of the generated 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.

[0122] 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 a temperature range from near the melting point of the used lithium compound to the sintering temperature, for example, in a temperature range of 400°C or more and 550°C or less. By maintaining in the above temperature range, the reaction can proceed particularly uniformly.

[0123] The atmosphere during sintering is preferably an oxidizing atmosphere. 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 more and 100% by volume or less is more preferable.

[0124] 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 material can be promoted, and the crystallinity of the lithium nickel composite oxide can be improved.

[0125] 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.

[0126] 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.

[0127] In particular, the sintering process 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 process is carried out in an oxygen stream.

[0128] In addition, the furnace used for sintering is not particularly limited, as long as the first raw material mixture can be sintered 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.

[0129] 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 process, a crushing process (first crushing process) for crushing the sintered product may be provided.

[0130] Here, crushing refers to the following operation: mechanical energy is input to an aggregate composed of a plurality of 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.

[0131] 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 a method of subjecting a liquid obtained by mixing all aqueous solutions containing desired metal elements to spray pyrolysis treatment, a method of mechanically pulverizing and mixing compounds of desired elements by a ball mill, etc. and then sintering.

[0132] (3) Water washing process

[0133] In the water washing process, the sintered product obtained in the sintering process can be washed with water to obtain a washed powder. In the water washing process, the sintered product obtained in the sintering process and water can be mixed and washed as a slurry (slurry process). The slurry concentration when washing the sintered product is not particularly limited. For example, it can be 200 g / L or more and 5000 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 matter can be increased.

[0134] 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.

[0135] In addition, the water washing can be 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.

[0136] By making the conductivity of the slurry prepared in the water washing process within the above range, the remaining components, such as remaining lithium, etc., on the surface of the particles attached to the sintered product can be selectively and sufficiently reduced.

[0137] The water used in the water washing process is not particularly limited. For example, water with a conductivity of less than 10 μS / cm, preferably 1 μS / cm or less, can be used.

[0138] 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, for example, it can be 3 minutes or more and 2 hours or less. In addition, it is preferable to stir the prepared slurry during the water washing period.

[0139] In the water washing process, after the slurry is liquefied, the slurry can be solid-liquid separated, that is, filtered and dehydrated, to obtain the water-washed powder (solid-liquid separation process). The filtration and dehydration are not particularly limited. For example, a pressure filtration type solid-liquid separation device can be used.

[0140] In the water washing process, the water-washed powder containing moisture obtained after solid-liquid separation is preferably dried and then provided to the boron addition process. Therefore, the water-washed powder can be dried (drying process). The drying conditions are not particularly limited.

[0141] The drying is preferably carried out at a temperature of 100°C or more and 250°C or less in, for example, an oxidizing atmosphere or a vacuum atmosphere. By making the drying temperature 100°C or more, the moisture in the water-washed powder can be sufficiently evaporated. In addition, by making the drying temperature 250°C or less, the energy required for drying can be suppressed, and the cost can be reduced.

[0142] In order to avoid the reaction of moisture, carbon dioxide in the atmosphere and the water-washed powder during drying, the atmosphere during drying preferably 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 generated water vapor through drying, it is preferable to attach an exhaust mechanism to the drying device.

[0143] Regarding the drying time, there is no particular limitation, and it is preferably, for example, 0.5 hours or more and 48 hours or less. By making the drying time, that is, the holding time at the maximum temperature reached during drying, 0.5 hours or more, the moisture in the washed powder can be sufficiently reduced and removed. In addition, by making the drying time 48 hours or less, productivity can be improved.

[0144] (4) Boron addition step

[0145] In the boron addition step, the washed powder and the boron-containing substance are mixed to prepare the second raw material mixture.

[0146] As the added boron-containing substance, there is no particular limitation. 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 step. 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.

[0147] There is no particular limitation on the mixing ratio of the washed powder and the boron-containing substance. In order to make the lithium nickel composite oxide obtained after heat treatment the target composition, preliminary tests, etc. can be carried out to select the mixing ratio.

[0148] Here, generally, the composition in the lithium nickel composite oxide obtained after heat treatment will basically maintain 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 of the target lithium nickel composite oxide.

[0149] Here, in the subsequent heat treatment step, in order to make boron and the washed powder react uniformly, 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 with 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 is no particular limitation 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.

[0150] For the device and method of mixing the washed powder and the boron-containing substance, as long as the two can be uniformly mixed, there is no particular limitation. For example, a dry mixer such as a V-type mixer or a mixing granulation device can be used.

[0151] Here, in order to prevent the reaction of the washed powder and the like with moisture and carbon dioxide in the atmosphere, the container during mixing is preferably cleaned with an inert gas. In addition, in order to suppress the non-uniformity caused by the aggregation of boron-containing substances, it is preferable to sieve the second raw material mixture several times after mixing the boron-containing substances to break up the aggregation.

[0152] (5) Heat treatment process

[0153] In the heat treatment process, the second raw material mixture can be heat-treated.

[0154] It is considered that by performing the heat treatment process, the formation of a lithium-boron-containing compound caused by the reaction of boron and the lithium component attached to the surface of the washed powder can be promoted.

[0155] 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 substances, 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 at 200°C or higher and 400°C or lower.

[0156] By making the heat treatment temperature 200°C or higher, the reaction between the above-mentioned boron and lithium components can proceed sufficiently.

[0157] In addition, by making the heat treatment temperature 500°C or lower, it is possible to prevent the boron and lithium components from flying in the atmosphere before the reaction.

[0158] 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 that does not generate gas is preferred, and both batch-type and continuous-type furnaces can be used.

[0159] (6) Cooling process

[0160] In the cooling process, the cooling after the heat treatment process is carried out. The heat-treated lithium nickel composite oxide can be taken out from the furnace used for heat treatment at a temperature (take-out temperature) of 200°C or higher and 300°C or lower.

[0161] At the take-out temperature in the above temperature range, by taking out the lithium nickel composite oxide from the furnace used for heat treatment, compared with the case where the heat source temperature is still high during cooling and cooling in the furnace used for heat treatment, the cooling rate can be increased. Therefore, it is considered that changes in the state of the lithium-boron-containing compound obtained in the heat treatment process can be suppressed.

[0162] In addition, by taking out from the furnace at a take-out temperature of 200°C or higher, the influence of the atmosphere (especially moisture) during take-out can be suppressed, and the battery characteristics can be improved when the lithium nickel composite oxide is used in a lithium ion secondary battery. Here, if the take-out temperature exceeds 300°C, it may be difficult to take out due to the high temperature. Therefore, as described above, the take-out temperature in the cooling process is preferably 300°C or lower.

[0163] In addition, the lithium nickel composite oxide taken out from the furnace used for heat treatment can be naturally cooled at a place where the mixing of impurities and the like can be suppressed.

[0164] In the method for manufacturing a positive electrode active material of the present embodiment, when agglomeration occurs in the particles of the lithium nickel composite oxide after the heat treatment step, a crushing step (second crushing step) 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-described first crushing step, and thus the description thereof is omitted.

[0165] [Lithium ion secondary battery]

[0166] 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.

[0167] 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 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 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.

[0168] (Positive electrode)

[0169] The positive electrode included in the secondary battery of the present embodiment may contain the above-described positive electrode active material.

[0170] Hereinafter, an example of the method for manufacturing a positive electrode will be described. First, the above-described positive electrode active material (powder form), a conductive material, and a binder (adhesive) can be mixed to form a positive electrode composite material, and then a solvent for purposes such as adding activated carbon and adjusting viscosity can be added as needed, and the mixture can be kneaded to produce a positive electrode composite material slurry.

[0171] 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 application. The mixing ratio of the materials can be the same as that of the positive electrode of a known lithium-ion secondary battery. For example, 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 can be contained in an amount of 60% by mass or more and 95% by mass or less, the conductive material in an amount of 1% by mass or more and 20% by mass or less, and the binder in an amount of 1% by mass or more and 20% by mass or less.

[0172] 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-like positive electrode is produced. If necessary, in order to increase the electrode density, pressing such as by rolling can also be performed. The sheet-like positive electrode thus obtained can be cut into an appropriate size according to the target battery and provided for the production of the battery.

[0173] 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.

[0174] As the binder (adhesive), which 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.

[0175] If necessary, the positive electrode active material, conductive material, etc. are dispersed, and a solvent for dissolving the binder can 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 can also be added in order to increase the electric double layer capacitance.

[0176] The method for producing 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.

[0177] (Negative electrode)

[0178] As the negative electrode, metallic lithium, lithium alloy, etc. can be used. 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 the negative electrode composite material is coated on the surface of a metal foil current collector such as copper, dried, and compressed if necessary to increase the electrode density.

[0179] As the negative electrode active material, a sintered body of an organic compound such as natural graphite, artificial graphite, and phenolic resin, and a powder of a carbon material such as coke can be used. At this time, as the negative electrode binder, similar to the positive electrode, a fluororesin such as PVDF can be used, and as the solvent for dispersing these active materials and binders, an organic solvent such as N-methyl-2-pyrrolidone can be used.

[0180] (Separator)

[0181] 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 a known one can be used. For example, a film such as polyethylene or polypropylene, a film having a large number of micropores can be used.

[0182] (Non-aqueous electrolyte)

[0183] As the non-aqueous electrolyte, for example, a non-aqueous electrolyte solution can be used.

[0184] As the non-aqueous electrolyte solution, for example, a lithium salt as a supporting salt dissolved in an organic solvent can be used. In addition, as the non-aqueous electrolyte solution, an ionic liquid in which a lithium salt is dissolved can be used. In addition, 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.

[0185] 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 thereof can be mixed and used.

[0186] As the supporting salt, LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiN(CF 3 SO 2 ) 2 and their complex salts, etc. Further, the non-aqueous electrolyte solution may contain a radical scavenger, a surfactant, a flame retardant, etc.

[0187] 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 voltage. As the solid electrolyte, an inorganic solid electrolyte and an organic solid electrolyte can be cited.

[0188] As the inorganic solid electrolyte, an oxide-based solid electrolyte, a sulfide-based solid electrolyte, etc. can be cited.

[0189] 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, 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), Li 5 La 3 Ta 2 O 12 , Li 7 La 3 Zr 2 O 12 , Li 6 BaLa 2Ta 2 O 12 、Li 3.6 Si 0.6 P 0.4 O 4 or more selected from the following:

[0190] There is no particular limitation on the sulfide solid electrolyte, 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, those 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 or more selected from the following:

[0191] 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.

[0192] There is no particular limitation on the organic solid electrolyte as long as it is a polymer compound showing ion conductivity. 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).

[0193] (Shape and Structure of Secondary Battery)

[0194] The lithium-ion secondary battery of the present embodiment described above can have various shapes such as cylindrical and laminated. When adopting any of these shapes, when the non-aqueous electrolyte used in the present embodiment is a non-aqueous electrolyte solution, the secondary battery can have the following structure: the positive electrode and the negative electrode are laminated via a separator to form an electrode body, 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, they are connected using current collecting leads or the like, and it is sealed in a battery case.

[0195] 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.

[0196] 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.

[0197] 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 where the mounting space is limited. 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 used in combination with combustion mechanisms such as gasoline engines and diesel engines.

[0198]

Examples

[0199] 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.

[0200] First, the evaluation methods for the positive electrode active material and the secondary battery obtained in the following examples and comparative examples will be described here.

[0201] (Evaluation of positive electrode active material)

[0202] Regarding the obtained positive electrode active material, the following evaluations are carried out.

[0203] (a) Evaluation of composition, crystal structure, and particle structure

[0204] The composition is analyzed using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation, ICPE-9000).

[0205] In addition, regarding the obtained positive electrode active material, a 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.

[0206] Furthermore, regarding the positive electrode active material, when observing the particles using a scanning electron microscope, it was confirmed that the positive electrode active materials produced in the following Examples and Comparative Examples contained secondary particles formed by aggregation of a plurality of primary particles.

[0207] (b) Titration curve

[0208] 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.

[0209] From the obtained titration curve, the amount of HCl added in each pH region shown in the "HCl addition amount in 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).

[0210] Figure 2 The titration curves of the positive electrode active materials obtained in Example 2 and Comparative Example 1 are shown.

[0211] (c) Particle size distribution index

[0212] 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.

[0213] Then, [(D90 - D10) / volume average particle size Mv] as the particle size distribution index was calculated.

[0214] (Evaluation of battery characteristics)

[0215] (a) Charge capacity, gas generation amount

[0216] 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 thermostatic bath maintained at 25 °C for about 12 hours. After the open circuit voltage OCV (open circuit voltage) became stable, charge and discharge were repeated 5 times at a cut-off voltage of 2.5 - 4.3 V and a current density of 23 mA / cm 2 , and an adjustment process was performed.

[0217] Next, at a temperature of 25°C, it is charged at a constant current and constant voltage (CCCV) to 4.2V. The capacity at this time is taken as the charging capacity.

[0218] After charging, it is stored in a thermostat set at 60°C for 12 days. After 12 days, it is discharged until 2.5V. After discharging, 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 volume from the laminated battery measured before the conditioning treatment, and taken as the gas generation amount.

[0219] [Example 1]

[0220] (1) Manufacture of the positive electrode active material

[0221] (1-1) Mixing process

[0222] (Nickel-containing material)

[0223] 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.

[0224] 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 Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024.

[0225] (Lithium compound)

[0226] As the lithium compound, lithium hydroxide is used. In addition, as the lithium hydroxide, anhydrous lithium hydroxide is used.

[0227] The above nickel-containing material and lithium hydroxide are weighed and mixed so that Li / (Ni+Mn+Co+Ti) is 1.06 to obtain the first raw material mixture.

[0228] (1-2) Sintering process

[0229] 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.

[0230] (1-3) Water washing process

[0231] 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 allow the liquid to pass through and dehydration is carried out. 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.

[0232] The obtained washed filter cake is dried at 190°C for 10 hours in a vacuum atmosphere to obtain washed powder (drying process).

[0233] (1-4) Boron addition process

[0234] The washed powder and orthoboric acid (H 3 BO 3 ) as the boron-containing substance are mixed to prepare a second raw material mixture. Here, 40 secondary particles of orthoboric acid observed by surface SEM image are arbitrarily extracted, and the average diameter in the long axis direction calculated is 3 μm.

[0235] The washed powder and orthoboric acid are put into a mixing container 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

[0236] Li:Ni:Mn:Co:Ti:B = 1.04:0.825:0.097:0.049:0.024:0.005. Based on cleaning the container with N 2 gas, they are mixed. After mixing, sieving is repeated 3 times to break up the agglomeration of orthoboric acid.

[0237] (1-5) Heat treatment process

[0238] In the heat treatment process, the second raw material mixture is heat-treated at 305°C for 10 hours under an atmospheric gas flow.

[0239] (1-6) Cooling process

[0240] After the heat treatment process, cooling is carried out. The heat-treated lithium nickel composite oxide is taken out from the sintering furnace at a take-out temperature of 250°C and naturally cooled to room temperature outside the furnace.

[0241] Regarding the obtained lithium nickel composite oxide as the positive electrode active material, the above evaluation is carried out. The evaluation results are shown in Table 1.

[0242] (2) Fabrication of secondary battery

[0243] 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.

[0244] AsFigure 1 As shown, the laminated battery 10 has the following structure: the laminate of the positive electrode film 11, the separator 12, and the negative electrode film 13 is impregnated with the electrolyte solution, and it is encapsulated by the 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.

[0245] 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) were mixed, and the slurry was coated on an Al foil so that there was 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 was dried in the air at 120°C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material was cut into short strips with a width of 66 mm, and roll-pressed with a load of 4 t to produce the positive electrode film. Then, the positive electrode film was cut into a rectangle of 50 mm × 30 mm and dried in a vacuum dryer at 120°C for 12 hours, and it was used as the positive electrode film 11 of the laminated battery 10.

[0246] In addition, a negative electrode film 13 prepared by the following method was prepared: artificial graphite as the negative electrode active material and PVDF as the binder were mixed at the following mass ratio, negative electrode active material: binder = 97:3, and it was dispersed and slurried in NMP. The obtained negative electrode slurry was coated on a copper foil (negative electrode current collector) with a thickness of 18 μm at a rate of 4 mg / cm per unit area by a coater, and then dried and roll-pressed. 2 After that, drying and roll-pressing were carried out.

[0247] The separator 12 used a polyethylene porous membrane with a film thickness of 20 μm, and the electrolyte solution used the following: 2 wt% of vinylene carbonate (VC) was added to a 20:5:25:50 mixture of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as a supporting electrolyte (manufactured by Ube Industries, Ltd.). 6

[0248] 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 was impregnated with the electrolyte solution and encapsulated by the laminate 14 to produce the laminated battery 10. Regarding the laminated battery 10 as the obtained lithium ion secondary battery, the above evaluation was carried out. The evaluation results are shown in Table 1.

[0249] [Examples 2 to 4]

[0250] ​In the boron addition step, the washed powder and orthoboric acid are mixed in the following manner so that the molar ratios of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment step are the values 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.

[0251] [Examples 5 and 6]

[0252] 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.

[0253] [Comparative Example 1]

[0254] 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 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.

[0255] [Comparative Example 2]

[0256] Except for not performing the washing step, the positive electrode active material and the lithium ion secondary battery are 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 step is directly supplied to the boron addition step. The evaluation results are shown in Table 1.

[0257]

Table 1

[0258]

[0259] From the results shown in Table 1, it can be confirmed that for the positive electrode active materials of Examples 1 to 6 in which 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 in the titration curve is 2.0 or less, the gas generation amount can be suppressed.

[0260] This application claims priority based on Japanese Patent Application No. 2022-175163 filed with the Japan Patent Office on October 31, 2022, and incorporates the entire contents of Japanese Patent Application No. 2022-175163 into this international application.

[0261]

Reference Signs

[0262] 10 Stacked battery

[0263] 11 Positive electrode film

[0264] 12 Separator

[0265] 13 Negative electrode film

[0266] 14 Laminated body

[0267] 15 Positive electrode tab

[0268] 16 Negative electrode tab

Claims

1. A positive electrode active material for a lithium-ion secondary battery, wherein, it contains a lithium nickel composite oxide having a layered structure of a hexagonal system, and includes secondary particles formed by aggregation of a plurality of primary particles, 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, by stirring 10 g of the positive electrode active material for the lithium-ion secondary battery in 50 mL of pure water for 5 minutes, and subjecting the filtered filtrate to neutralization titration 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 more and 11.0 or less is 2.0 or less.

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

3. The positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2, [(D90 - D10) / Mv], which is calculated from the 90% diameter D90 based on volume in the particle size distribution, the 10% diameter D10 based on volume in the particle size distribution, and the volume average particle diameter Mv, and represents the particle size distribution index, is 0.70 or more and 1.20 or less. The particle size distribution is based on the laser diffraction scattering method, the volume average particle diameter Mv is 8 μm or more and 20 μm or less.

4. A lithium-ion secondary battery, comprising at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, the positive electrode contains the positive electrode active material for a lithium-ion secondary battery according to claim 1 or 2.

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