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 for mixing a lithium compound and a nickel-containing material containing at least nickel to prepare a raw material mixture, a sintering step for sintering the raw material mixture in an oxidizing atmosphere to obtain a sintered material, and a boron addition step for adding boron to the sintered material, and spraying a boron-containing solution containing a boron-containing substance, which is at least one substance selected from a boron monomer and a boron-containing compound, onto the sintered product obtained in the sintering step.

Description

Technical Field

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

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

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

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

[0005] As the positive electrode material of a lithium ion secondary battery, lithium cobalt composite oxide (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, and research has been conducted on, for example, improvement of cycle characteristics (for example, Patent Document 1) and high output.

[0007]

Prior Art Documents

[0008]

Patent Documents

[0009]

Patent Document 1

[0010] Problems to be Solved by the Invention

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

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

[0013] Means for Solving the Problems

[0014] To solve the above problems, according to one aspect of the present invention,

[0015] There is provided a method for manufacturing a positive electrode active material for a lithium ion secondary battery, the positive electrode active material containing a lithium nickel composite oxide having a hexagonal layered structure and including secondary particles formed by aggregation of a plurality of primary particles, the method comprising:

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

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

[0018] A boron addition step of spraying a boron-containing solution containing a boron-containing substance onto the sintered product obtained in the sintering step, the boron-containing substance being at least one selected from boron monomers and boron-containing compounds,

[0019] 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).

[0020] Effects of the Invention

[0021] According to one aspect of the present invention, there can be 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

[0022] ​Figure 1 】 Figure 1 It is an explanatory diagram of the laminated battery fabricated in the examples and comparative examples.

[0023]

Figure 2

[0024] Hereinafter, a 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.

[0025] [Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0026] 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.

[0027] 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.

[0028] (1) Regarding the positive electrode active material

[0029] (1-1) Regarding the lithium nickel composite oxide

[0030] The positive electrode active material of the present embodiment contains a lithium nickel composite oxide. The positive electrode active material of the present embodiment may be composed only of the lithium nickel composite oxide, and in this case, unavoidable impurities mixed in the manufacturing process or the like are not excluded.

[0031] (1-1-1) Composition

[0032] The above lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0033] 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.

[0034] 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.

[0035] Preferably, 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. Further, 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.

[0036] 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 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.

[0037] (Nickel (Ni))

[0038] 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.

[0039] Further, 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, according to the positive electrode active material for a lithium ion secondary battery of the present embodiment, the gas generation can be suppressed, and a particularly high effect can be exhibited.

[0040] Therefore, as described above, b representing the nickel content ratio is preferably 0.50 or more, more preferably 0.60 or more, still more preferably 0.70 or more, and particularly preferably 0.80 or more.

[0041] 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.

[0042] (Boron (B))

[0043] 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.

[0044] 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 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 considered that the compound further suppresses gas generation due to the decomposition of the electrolyte.

[0045] As described above, for c representing the content ratio of boron, 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.

[0046] There is no particular limitation on the upper limit value of c representing the content ratio of boron. 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.

[0047] (Element M)

[0048] As described above, in the lithium nickel composite oxide of the present embodiment, as an optional component, element M may also be contained. The element group applicable to element M has already been described, 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).

[0049] Element M is an optional component, and thus 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.

[0050] 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.

[0051] 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.

[0052] (1-1-2) Regarding the crystal structure

[0053] The lithium nickel composite oxide preferably has a hexagonal layered structure. By containing a hexagonal layered structure, lithium can be easily inserted and detached between the layers, and when used in a lithium ion secondary battery, the output characteristics and cycle characteristics can be particularly improved.

[0054] The crystal structure of the lithium nickel composite oxide can be analyzed by Rietveld refinement.

[0055] (1-1-3) Regarding the particle morphology

[0056] The particles of the lithium nickel composite oxide may contain secondary particles formed by aggregation of multiple primary particles.

[0057] In addition, in addition to the secondary particles, the lithium nickel composite oxide may contain non-aggregated primary particles. That is, the lithium nickel composite oxide may contain both primary particles and secondary particles.

[0058] (1-2) Regarding the titration curve

[0059] Regarding the filtrate obtained by mixing the positive electrode active material of the present embodiment with pure water and then filtering, in the titration curve obtained by neutralization titration, preferably, the volume ratio of the amount of HCl added in the region where pH is greater than 11.0 to the amount of HCl added in the region where pH is 8.0 or more and 11.0 or less is 3.0 or less.

[0060] The filtrate used for plotting 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.

[0061] According to the research of the inventors of the present invention, the amount of HCl added in the region where pH is greater than 11.0 in the above titration curve mainly means the HCl consumed in the reaction with lithium hydroxide contained in the positive electrode active material.

[0062] In addition, when performing neutralization titration on the above filtrate of the positive electrode active material of the present embodiment, in the titration curve, in the region where pH is 8.0 or more and 11.0 or less, compared with other pH regions, the change in pH is suppressed, and a nearly flat region appears. Specifically, for example, in the above titration curve, in the region where pH is 8.0 or more and 11.0 or less, compared with the region where pH is greater than 11.0, there is a region where the change in pH with respect to the amount of HCl added is small.

[0063] 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.

[0064] Then, it is presumed that in the above titration curve, the amount of HCl added in the region where 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.

[0065] 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 3.0 or less, the content of lithium hydroxide is suppressed, which means that the above-mentioned lithium-boron-containing compound can be sufficiently generated. Therefore, it is considered that when this positive electrode active material is applied to a lithium ion secondary battery, the reaction with the electrolyte is suppressed, and gas generation can be suppressed.

[0066] 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).

[0067] 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 - )".

[0068] VR1 = V(11.0 - ) ÷ V(8.0 - 11.0) ··· (1)

[0069] As described above, the above VR1 is preferably 3.0 or less, more preferably 2.6 or less.

[0070] 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.

[0071] 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 0.5 or less.

[0072] 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.

[0073] 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 0.5 or less, the content of lithium carbonate is suppressed, which means that the above-mentioned lithium-boron-containing compound can be sufficiently generated. Therefore, it is considered that when this positive electrode active material is applied to a lithium ion secondary battery, the reaction with the electrolyte is particularly suppressed, and gas generation can be further suppressed.

[0074] 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).

[0075] In the following formula (2), the amount of HCl added in the region where the pH is 8.0 or higher and 11.0 or lower is denoted as "V(8.0 - 11.0)", and the amount of HCl added in the region where the pH is 5.0 or higher and less than 8.0 is denoted as "V(5.0 - 8.0)".

[0076] VR2 = V(5.0 - 8.0) ÷ V(8.0 - 11.0) ··· (2)

[0077] As described above, the above VR2 is preferably 0.5 or less, more preferably 0.4 or less.

[0078] 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, more preferably 0.05 or more.

[0079] (1 - 3) Regarding the particle size distribution index and volume average particle size

[0080] 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.

[0081] In this specification, D10 means the cumulative 10% particle size, that is, the 10% diameter on a volume basis in the particle size distribution obtained by the laser diffraction scattering method, namely the particle size at a volume cumulative value of 10%. D90 means the cumulative 90% particle size, that is, the 90% diameter on a volume basis in the particle size distribution obtained by the laser diffraction scattering method, namely the particle size at a volume cumulative value of 90%. In other parts of this specification, D10 and D90 also have the same meaning.

[0082] 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 analyzer.

[0083] By making the particle size distribution index of the positive electrode active material 0.70 or more, for example, when manufacturing a positive electrode, smaller particle size particles are arranged between larger particle size particles, and the packing density of the positive electrode active material can be increased.

[0084] 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.

[0085] The volume-average particle diameter 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.

[0086] By setting 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 of the positive electrode is achieved. Specifically, by setting the volume-average particle diameter Mv of the positive electrode active material of the present embodiment to 8 μm or more, the fillability of the positive electrode can be improved. In addition, by setting the volume-average particle diameter Mv of the positive electrode active material of the present embodiment to 20 μm or less, the output characteristics and battery capacity can be particularly improved.

[0087] (2) Method for manufacturing positive electrode active material for lithium ion secondary battery

[0088] The method for manufacturing the positive electrode active material for a lithium ion secondary battery of the present embodiment will be described. According to the method for manufacturing the positive electrode active material for a lithium ion secondary battery of the present embodiment, the above positive electrode active material can be manufactured. Therefore, regarding the matters already described, some descriptions will be omitted.

[0089] The manufacturing method of the positive electrode active material of the present embodiment, as Figure 2 shown in the process 20 shown, may have the following mixing step (S1), sintering step (S2), and boron addition step (S3). In addition, as described later, a heat treatment step may also be included.

[0090] In the mixing step, a nickel-containing material containing elements other than lithium (Li), boron (B), and oxygen among the elements contained in the lithium nickel composite oxide, such as nickel (Ni), and, if necessary, an element M (M), and a lithium compound are mixed to prepare a raw material mixture.

[0091] In the sintering step, the above raw material mixture is sintered in an oxidizing atmosphere to obtain a sintered product.

[0092] In the boron addition step, a boron-containing solution containing a boron-containing material may be sprayed onto the sintered product obtained in the sintering step.

[0093] Each step will be described below.

[0094] (2-1) Mixing step

[0095] In the mixing step, as described above, a nickel-containing material containing at least nickel and a lithium compound are mixed to prepare a raw material mixture. Hereinafter, the raw materials used will be described.

[0096] (2-1-1) Nickel-containing material

[0097] The nickel-containing material provided to the mixing process is as described above and may contain elements other than lithium, boron, and oxygen among the elements contained in the target lithium nickel composite oxide, namely nickel and, as required, element M. In addition, in the above nickel-containing material, element M may be an optional additive component and thus may also be absent.

[0098] 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 nickel composite hydroxide and nickel composite compound which 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 nickel composite oxide and a mixture of nickel composite oxide and nickel composite hydroxide.

[0099] 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.

[0100] When the lithium nickel composite oxide contains a plurality of element Ms, 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 nickel composite oxide and nickel composite hydroxide.

[0101] 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.

[0102] 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 the same appropriate ranges and materials as described in “(1-1-1) Regarding the composition” of “(1-1) Regarding the lithium nickel composite oxide” of the positive electrode active material, and thus the description is omitted here.

[0103] 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.

[0104] 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 represented.

[0105] In addition, b′ and d′ have a relationship of b′:d′ = b:d with b and d described above, and satisfy b′ + d′ = 1. Since b, d, and element M have already been described, the description thereof is omitted here. β and γ are preferably, for example, -0.2 ≤ β ≤ 0.2 and -0.2 ≤ γ ≤ 0.2.

[0106] When the nickel-containing material contains nickel composite hydroxide, there are no particular limitations 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.

[0107] 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 after being a roasted product.

[0108] 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.

[0109] When using a roasted product of a nickel composite hydroxide as the nickel composite compound, when sintering a raw material mixture mixed with a 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 particularly stabilized.

[0110] 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 flow that can be easily carried out.

[0111] (2-1-2) Lithium compound

[0112] There are no particular limitations 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 high reactivity with the nickel composite compound and a low reaction temperature, so lithium hydroxide is further preferably used as the lithium compound.

[0113] 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 a raw material mixture.

[0114] There are no particular limitations 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 generally maintains the composition in the raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0115] 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) relative to the total amount (Me) of, for example, nickel and element M in the nickel-containing material.

[0116] By making the above Li / Me 1.005 or more, the crystallinity of the obtained lithium nickel composite oxide can be improved, and the content ratio of lithium in the obtained lithium nickel composite oxide relative to elements other than oxygen can be made the target composition.

[0117] 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.

[0118] 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.

[0119] (2-2) Sintering process

[0120] In the sintering process, the raw material mixture can be sintered in an oxidizing atmosphere to obtain a sintered product. In the sintering process, when sintering the raw material mixture, a sintered product in which lithium in the lithium compound diffuses and reacts in the nickel-containing material is obtained.

[0121] In the sintering process, the sintering temperature of the raw material mixture is not particularly limited. For example, it is preferably 600 °C or more and 1000 °C or less, more preferably 650 °C or more and 950 °C or less, and further preferably 680 °C or more and 900 °C or less.

[0122] By making the sintering temperature 600 °C or more, the diffusion of lithium into the nickel-containing material can proceed sufficiently.

[0123] 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.

[0124] 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 used lithium compound to the sintering temperature, for example, in the 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.

[0125] 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 vol% or more and 100 vol% or less is more preferred.

[0126] This is because, by making the oxygen concentration in the atmosphere during sintering 18% by volume or more, the reaction between the lithium compound and the nickel-containing substance can be promoted, and the crystallinity of the lithium nickel composite oxide can be improved.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] In addition, the furnace used for sintering is not particularly limited, and it is sufficient to sinter the raw material mixture in a specified atmosphere. From the viewpoint of uniformly maintaining the atmosphere in the furnace, an electric furnace without gas generation is preferred, and both batch-type and continuous-type furnaces can be used.

[0131] In the method for manufacturing the positive electrode active material of the present embodiment, when the particles of the sintered product agglomerate during the sintering step, there may be a crushing step (first crushing step) for crushing the sintered product.

[0132] Here, crushing refers to the following operation: mechanical energy is applied 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 sufficient to crush to a degree that does not damage the secondary particles.

[0133] In addition, the method for manufacturing the sintered product prepared in the sintering step 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 all compounds of desired elements by a ball mill and then sintering, etc.

[0134] (2-3) Boron addition step

[0135] In the boron addition step, a boron-containing solution containing a boron-containing substance can be sprayed onto the sintered product.

[0136] The boron-containing substance is not particularly limited. 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, for example, orthoboric acid (H 3 BO 3 ), boron oxide (B 2O 3 ) boron nitride (BN), etc.

[0137] There is no particular limitation on the solvent for the boron-containing solution. As the solvent, a solvent capable of dissolving or dispersing the above boron-containing substances can be appropriately used. As such a solvent, for example, one or more selected from water, ethanol, methanol, etc. can be cited. As the solvent, a mixture of two or more solvents can also be used. In particular, due to easy operability and suppression of carbon incorporation, water is more preferably used as the solvent.

[0138] In addition, the boron-containing solution can also be a solution in which the boron-containing substances are not dissolved but dispersed, so the above solvent can also be referred to as a dispersion medium.

[0139] There is no particular limitation on the amount of the boron-containing substance contained in the boron-containing solution sprayed on the sintered product. After the boron addition step, it can be selected according to the target composition of the obtained lithium nickel composite oxide. Therefore, in order to make the lithium nickel composite oxide obtained after the boron addition step the target composition, experiments, etc. can be carried out in advance, and the spraying amount (addition amount) can be selected.

[0140] In order to spray the boron-containing solution uniformly on the sintered product, it is preferable to stir the sintered product during the boron addition step. In addition, in order to spray the boron-containing solution on the particle surface of the sintered product, it is preferable to carry out the above-mentioned crushing step (first crushing step) after the sintering step to crush the sintered product. Therefore, the sintered product is preferably in powder form (powder state).

[0141] It is considered that in the boron addition step, by spraying the boron-containing solution on the sintered product, boron reacts with the lithium component attached to the particle surface of the sintered product, and a lithium-boron-containing compound can be formed.

[0142] In the method for manufacturing the positive electrode active material of the present embodiment, the treated powder obtained in the boron addition step can be used as the positive electrode active material. Here, in the method for manufacturing the positive electrode active material of the present embodiment, if necessary, the following heat treatment step can be further carried out on the treated powder.

[0143] (2-4) Heat treatment step

[0144] The method for manufacturing the positive electrode active material of the present embodiment may, if necessary, have a heat treatment step after the boron addition step. The heat treatment step can heat-treat the treated powder of the above sintered product sprayed with the boron-containing solution after the boron addition step.

[0145] By carrying out the heat treatment step, the reaction between the boron contained in the treated powder and the lithium component attached to the particle surface of the sintered product can be promoted. In addition, by carrying out the heat treatment step, the solvent contained in the boron-containing solution added in the boron addition step can be removed.

[0146] In the heat treatment step, the heat treatment temperature for heat-treating the treatment powder is not particularly limited and can be selected according to the boron-containing substance added, etc. In the heat treatment step, for example, it is preferable to perform heat treatment of the treatment powder at 100°C or higher and 500°C or lower, and more preferably at 200°C or higher and 400°C or lower.

[0147] By setting the heat treatment temperature at 100°C or higher, the reaction between the above-mentioned boron and lithium components can be particularly promoted.

[0148] In addition, by setting the heat treatment temperature at 500°C or lower, it is possible to prevent boron from flying off in the atmosphere before reacting with the lithium component, etc.

[0149] The atmosphere during heat treatment in the heat treatment step is not particularly limited, and for example, it can be carried out in an oxidizing atmosphere or an inert gas atmosphere.

[0150] 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 preferable.

[0151] 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.

[0152] In addition, the furnace used for heat treatment is not particularly limited, and it is only necessary to perform heat treatment on the treatment powder in a specified atmosphere. From the viewpoint of uniformly maintaining the atmosphere in the furnace, an electric furnace that does not generate gas is preferable, and both batch-type and continuous-type furnaces can be used.

[0153] In the method for manufacturing a positive electrode active material of the present embodiment, when agglomeration occurs in the lithium nickel composite oxide particles after the boron addition step or the heat treatment step, there may also be a crushing step (second crushing step) for crushing the lithium nickel composite oxide. Regarding crushing, it can be carried out in the same manner as in the above-mentioned first crushing step, and thus the description is omitted.

[0154] [Lithium-ion secondary battery]

[0155] 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 a lithium-ion secondary battery described above.

[0156] 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 only examples, and the lithium-ion secondary battery of the present embodiment can be implemented in various modified and improved forms starting from the following embodiments based on the knowledge of those skilled in the art. In addition, the use of the secondary battery is not particularly limited.

[0157] (Positive electrode)

[0158] The positive electrode of the secondary battery according to this embodiment may contain the above positive electrode active material.

[0159] 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) can be mixed to form a positive electrode composite material. Furthermore, a solvent for purposes such as adding activated carbon and adjusting viscosity can be added as needed, and it can be kneaded to produce a positive electrode composite material slurry.

[0160] 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 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, it can 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.

[0161] 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 can also be pressed by roll pressing or the like. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the target battery and provided for the manufacture of the battery.

[0162] As the conductive material, for example, carbon black-based materials such as graphite (natural graphite, artificial graphite, and expanded graphite, etc.), acetylene black, and Ketjen black (registered trademark) can be used.

[0163] As the binder (adhesive), since it plays a role in connecting and fixing the active material particles, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resins, and polyacrylic acid can be used.

[0164] If necessary, to disperse the positive electrode active material, conductive material, etc., a solvent that dissolves 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 to increase the electric double layer capacitance.

[0165] The method for manufacturing the positive electrode is not limited to the above example, 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.

[0166] (Negative electrode)

[0167] 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.

[0168] 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, fluororesins 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.

[0169] (Separator)

[0170] Between the positive electrode and the negative electrode, a separator can be interposed and arranged 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.

[0171] (Non-aqueous electrolyte)

[0172] As the non-aqueous electrolyte, for example, non-aqueous electrolytic solutions can be used.

[0173] As the non-aqueous electrolytic solution, for example, those in which a lithium salt as a supporting salt is dissolved in an organic solvent can be used. In addition, as the non-aqueous electrolytic solution, ionic liquids in which a lithium salt is dissolved can be used. In addition, an ionic liquid refers to a salt composed of cations and anions other than lithium ions and being in a liquid state at room temperature.

[0174] 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.

[0175] 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.

[0176] 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.

[0177] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0178] 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, one 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 or more selected from the following.

[0179] 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 or more selected from the following.

[0180] 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.

[0181] As the organic solid electrolyte, there is no particular limitation on the polymer compound showing 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).

[0182] (Shape and structure of the secondary battery)

[0183] 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 used in the secondary battery of the present embodiment is 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 communicating with the outside, and between the negative electrode current collector and the negative electrode terminal communicating with the outside, a current collecting lead or the like is used for connection, and it is sealed in a battery case.

[0184] 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.

[0185] 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 notebook 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.

[0186] 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 that are used in combination with combustion mechanisms such as gasoline engines and diesel engines.

[0187]

Examples

[0188] 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.

[0189] 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.

[0190] (Evaluation of the positive electrode active material)

[0191] Regarding the obtained positive electrode active material, the following evaluations are carried out.

[0192] (a) Evaluation of composition, crystal structure, and particle structure

[0193] The composition analysis was carried out using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation, ICPE-9000).

[0194] In addition, regarding the obtained positive electrode active material, the powder X-ray diffraction pattern was measured, and the crystal structure and the like were 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.

[0195] 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.

[0196] (b) Titration curve

[0197] 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.

[0198] 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).

[0199] (c) Particle size distribution index

[0200] 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.

[0201] Then, [(D90 - D10) / volume average particle size Mv] as the particle size distribution index was calculated.

[0202] (Evaluation of battery characteristics)

[0203] (a) Charge capacity and gas generation amount

[0204] 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 thermostat maintained at 25°C for about 12 hours. After the open circuit voltage OCV (open circuit voltage) became stable, with a cut-off voltage of 2.5 - 4.3 V and a current density of 23 mA / cm 2, perform an adjustment process of repeating charge and discharge 5 cycles.

[0205] Next, at a temperature of 25 °C, charge at constant current and constant voltage (CCCV) to 4.2 V. Take the capacity at this time as the charging capacity.

[0206] After charging, store it in a thermostat set at 60 °C for 12 days. After 12 days, perform discharge until 2.5 V. After discharge, measure the volume of the laminated battery by the Archimedes method, and evaluate the amount of gas generated in the unit from the difference in the volume of the laminated battery measured before the adjustment process as the gas generation amount.

[0207] [Example 1]

[0208] (1) Manufacture of the positive electrode active material

[0209] According to Figure 2 the process 20 shown, manufacture the positive electrode active material.

[0210] (1-1) Mixing process

[0211] (Nickel-containing material)

[0212] 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.

[0213] Then, use the mixture of the above nickel composite oxide and TiO 2 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

[0214] Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024.

[0215] (Lithium compound)

[0216] As the lithium compound, lithium hydroxide is used. In addition, as the lithium hydroxide, anhydrous lithium hydroxide is used.

[0217] Weigh and mix the above nickel-containing material and lithium hydroxide so that Li / (Ni + Mn + Co + Ti) is 1.02 to obtain a raw material mixture.

[0218] (1-2) Sintering process

[0219] The obtained 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.

[0220] (1-3) Boron addition process

[0221] An aqueous solution in which orthoboric acid (H 3 BO 3 ) as a boron-containing substance is dissolved in water is used as a boron-containing solution, which is sprayed onto the sintered product to prepare a treated powder. At this time, the spraying amount is adjusted so that the molar ratio of the elements contained in the lithium nickel composite oxide obtained after the boron addition process and the heat treatment process is the ratio shown in Table 1, that is, Li:Ni:Mn:Co:Ti:B = 1.02:0.825:0.097:0.049:0.024:0.005.

[0222] During the boron addition process, the sintered product is continuously stirred.

[0223] (1-4) Heat treatment process

[0224] In the heat treatment process, the treated powder obtained after the boron addition process is heat-treated at 305 °C for 10 hours under an air stream.

[0225] Regarding the lithium nickel composite oxide obtained as the positive electrode active material, the above evaluation is carried out. The evaluation results are shown in Table 1.

[0226] (2) Fabrication of secondary battery

[0227] 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.

[0228] As shown in Figure 1 , the laminated battery 10 has the following structure: a laminate of a positive electrode film 11, a separator 12, and a negative electrode film 13 is impregnated with an electrolytic solution and encapsulated by a laminate 14. In addition, the positive electrode film 11 is connected to a positive electrode tab 15, and the negative electrode film 13 is connected to a negative electrode tab 16, and the positive electrode tab 15 and the negative electrode tab 16 are exposed outside the laminate 14.

[0229] 20.0 g of the obtained positive electrode active material, 0.64 g of acetylene black, 0.64 g of polyvinylidene fluoride, and N-methyl-2-pyrrolidone (NMP) are mixed, and the slurry is coated on an Al foil so that per 1 cm 2There is 16.5 mg of the positive electrode active material. Next, the product with the slurry containing the positive electrode active material coated on the Al foil is dried in the air at 120 °C for 30 minutes to remove NMP. The Al foil coated with the positive electrode active material is cut into short strips with a width of 66 mm, and a positive electrode film is produced by roll pressing with a load of 4 t. Then, the positive electrode film is cut into rectangles of 50 mm × 30 mm and dried in a vacuum dryer at 120 °C for 12 hours, and it is used as the positive electrode film 11 of the laminated battery 10.

[0230] In addition, a negative electrode film 13 prepared by the following method is prepared. Artificial graphite as the negative electrode active material and PVDF as the binder are mixed in 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 by a coater, and then dried and roll pressed.

[0231] The separator 12 uses a polyethylene porous membrane with a film thickness of 20 μm, and the electrolytic solution used is as follows: To a mixed solution of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) with a ratio of 20:5:25:50 as a supporting electrolyte, 2 wt% of vinylene carbonate (VC) is added (manufactured by Ube Industries, Ltd.). 6 In a drying chamber with a dew point management of -60 °C, the laminate of the above positive electrode film 11, separator 12 and negative electrode film 13 is impregnated with the electrolytic solution and encapsulated by the laminate 14 to manufacture the laminated battery 10.

[0232] In the boron addition process, the spray amount of the boron-containing solution is adjusted so that the molar ratio of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment process is the value shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0233] [Examples 2 to 4]

[0234] In the boron addition process, the spray amount of the boron-containing solution is adjusted so that the molar ratio of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment process is the value shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0235] [Examples 5, 6]

[0236] In the heat treatment process, the heat treatment temperature is changed to the temperature shown in Table 1. Except for this point, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 2 and evaluated. The evaluation results are shown in Table 1.

[0237] [Example 7]

[0238] The processed powder obtained after the boron addition step is used as the positive electrode active material. That is, when manufacturing the positive electrode active material, the heat treatment step is 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 2 and evaluated. The evaluation results are shown in Table 1.

[0239] [Comparative Example 1]

[0240] Except for the point that the sintering step is not performed after the boron addition step, the positive electrode active material and the lithium-ion secondary battery are manufactured under the same conditions as in Example 1 and evaluated. That is, when manufacturing the positive electrode active material, the sintered product obtained in the sintering step is directly used as the positive electrode active material. The evaluation results are shown in Table 1.

[0241]

Table 1

[0242]

[0243] 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 amount of gas generation.

[0244] This application claims priority based on Japanese Patent Application No. 2022-175170 filed with the Japan Patent Office on October 31, 2022, and incorporates the entire contents of Japanese Patent Application No. 2022-175170 into this international application.

[0245]

Reference Signs

[0246] 10 Stacked battery

[0247] 11 Positive electrode film

[0248] 12 Separator

[0249] 13 Negative electrode film

[0250] 14 Laminate

[0251] 15 Positive electrode tab

[0252] 16 Negative electrode tab

[0253] 20 Process

[0254] S1 Mixing step

[0255] S2 Sintering step

[0256] S3 Boron addition step

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 a nickel-containing material containing at least nickel and a lithium compound to prepare a raw material mixture, a sintering step of sintering the raw material mixture in an oxidizing atmosphere to obtain a sintered product, and a boron addition step of spraying a boron-containing solution containing a boron-containing material onto the sintered product obtained in the sintering step, the boron-containing material being at least one selected from boron monomers and boron-containing compounds, the lithium nickel composite oxide contains lithium Li, nickel Ni, boron B, and an element M represented by M in the following ratio. In terms of the molar ratio, Li:Ni:B:M = a:b:c:d, where 0.95 ≤ a ≤ 1.10, 0.50 ≤ b < 1.00, 0.00 < c ≤ 0.03, 0.00 ≤ d ≤ 0.47, and b + c + d = 1. The element M is at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Ti, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al.

2. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1, further comprising a heat treatment step of heat-treating the treated powder after the boron addition step, the treated powder being the sintered product sprayed with the boron-containing solution.

3. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 2, in the heat treatment step, the heat treatment of the treated powder is carried out at 100°C or higher and 500°C or lower in an oxidizing atmosphere or an inert gas atmosphere.

4. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, by stirring 10 g of the positive electrode active material for a lithium ion secondary battery in 50 mL of pure water for 5 minutes, 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 3.0 or less.

5. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 4, in the titration curve, the volume ratio of the amount of HCl added in the region where pH is 5.0 or higher and less than 8.0 to the amount of HCl added in the region where pH is 8.0 or higher and 11.0 or lower is 0.5 or less.

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