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

Abstract

A method for producing a positive electrode active material for a lithium ion secondary battery, the method comprising a mixing step of mixing a nickel-containing 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 material, and a heat treatment step of heat treating the sintered material, and a boron addition step for mixing the heat-treated powder obtained in the heat treatment step with a boron-containing substance, the boron-containing substance being at least one substance selected from among a boron monomer and a boron-containing compound, and a heat-treating step for heat-treating the sintered material obtained in the sintering step, and a boron addition step for mixing the heat-treated powder obtained in the heat treatment step with the boron-containing substance.

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 insert lithium are used. As described above, a lithium ion secondary battery has high energy density, output characteristics, and durability.

[0004] Regarding lithium ion secondary batteries, research and development are now in full swing. Among them, lithium ion secondary batteries using layered or spinel-type lithium metal composite oxides as the positive electrode material have been put into practical use as batteries with high energy density because 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, 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 method for manufacturing a positive electrode active material for a lithium-ion secondary battery that can suppress gas generation when used in a lithium-ion secondary battery.

[0013] Means for Solving the Problems

[0014] To solve the above problems, according to one aspect of the present invention, there is provided a method for manufacturing a positive electrode active material for a lithium-ion secondary battery,

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

[0016] A mixing step of mixing at least a nickel-containing 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,

[0018] A heat treatment step of heat-treating the sintered product obtained in the sintering step, and

[0019] A boron addition step of mixing the heat-treated powder obtained in the heat treatment step and a boron-containing substance, where the boron-containing substance is at least one selected from boron monomers and boron-containing compounds,

[0020] 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).

[0021] Effects of the Invention

[0022] 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. Description of the Drawings

[0023]

Figure 1

[0024]

Figure 2

[0025] Hereinafter, a mode for carrying out the present invention will be described with reference to the drawings. The present invention is not limited by the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention.

[0026] [Method for Manufacturing Positive Electrode Active Material for Lithium Ion Secondary Battery]

[0027] 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.

[0028] 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 of the present embodiment will be described.

[0029] (1) Regarding the positive electrode active material

[0030] (1-1) Regarding the lithium nickel composite oxide

[0031] 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 and the like are not excluded.

[0032] (1-1-1) Composition

[0033] The above lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0034] 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.

[0035] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), boron (B), and the element M (M) in the following ratio in terms of the molar ratio, Li:Ni:B:M = a:b:c:d.

[0036] 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. 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.

[0037] 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.

[0038] (Nickel (Ni))

[0039] 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.

[0040] In addition, in the lithium nickel composite oxide, the higher the nickel content ratio, the more likely gas generation due to the reaction with the electrolyte occurs when used in a lithium ion secondary battery. However, 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.

[0041] 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.

[0042] The upper limit value of b representing the nickel content ratio is as described above, preferably less than 1.00, and more preferably 0.97 or less.

[0043] (Boron (B))

[0044] 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.

[0045] 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 this compound further suppresses gas generation caused by the decomposition of the electrolyte.

[0046] As described above, c representing the content ratio of boron is preferably more than 0.00, more preferably 0.001 or more, still more preferably 0.002 or more, and particularly preferably 0.003 or more.

[0047] The upper limit value of c representing the content ratio of boron is not particularly limited. In consideration of the saturation of the effect due to excessive addition, it is preferably 0.03 or less, more preferably 0.025 or less, and particularly preferably 0.02 or less.

[0048] (Element M)

[0049] As described above, in the lithium nickel composite oxide of the present embodiment, as an optional component, element M may also be contained. The element group applicable to element M has already been described and will be omitted here. In particular, from the viewpoint of improving the thermal stability of the lithium nickel composite oxide, for example, suppressing the thermal decomposition of the lithium nickel composite oxide, as element M, it is preferably at least one selected from cobalt (Co), manganese (Mn), and titanium (Ti).

[0050] 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 still more preferably 0.10 or more as described above.

[0051] 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 still more preferably 0.20 or less as described above.

[0052] 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.

[0053] (1-1-2) Regarding the crystal structure

[0054] The lithium nickel composite oxide preferably has a hexagonal layered structure. By containing the 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.

[0055] The crystal structure of the lithium nickel composite oxide can be analyzed by Rietveld refinement.

[0056] (1-1-3) Regarding the particle morphology

[0057] The particles of the lithium nickel composite oxide may contain secondary particles formed by aggregation of multiple primary particles.

[0058] In addition, the lithium nickel composite oxide may contain unaggregated primary particles in addition to the secondary particles. That is, the lithium nickel composite oxide may contain both primary particles and secondary particles.

[0059] (1-2)Regarding the titration curve

[0060] Regarding the filtrate obtained by mixing the positive electrode active material of the present embodiment with pure water and then filtering, in the titration curve obtained by neutralization titration, preferably, the volume ratio of the amount of HCl added in the region where the pH is greater than 11.0 to the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less is 3.0 or less.

[0061] The filtrate used for drawing the above titration curve can be the filtrate obtained by the following method: Add 10 g of the positive electrode active material of the present embodiment to 50 mL of pure water, stir in this pure water for 5 minutes, and then filter to perform solid-liquid separation. The pure water preferably removes as much as possible the components that affect the neutralization titration, and distilled water or the like can be appropriately used. In addition, when preparing the above titration curve, as the acid for neutralization titration of the above filtered filtrate, that is, hydrochloric acid (HCl), 1.0 M, that is, 1.0 mol / dm 3 (1.0 mol / L) hydrochloric acid can be used.

[0062] According to the research of the inventors of the present invention, the amount of HCl added in the region where the pH is greater than 11.0 in the above titration curve mainly means the HCl consumed in the reaction with lithium hydroxide contained in the positive electrode active material.

[0063] In addition, when performing neutralization titration on the above filtrate of the positive electrode active material of the present embodiment, in the titration curve, in the region where the pH is 8.0 or more and 11.0 or less, compared with other pH regions, the change in pH is suppressed, and a nearly flat region appears. Specifically, for example, in the above titration curve, in the region where the pH is 8.0 or more and 11.0 or less, compared with the region where the pH is greater than 11.0, a region where the change in pH with respect to the amount of HCl added is small appears.

[0064] As described above, it is considered that the lithium nickel composite oxide contains a trace amount of boron, and this boron forms a lithium-boron-containing compound that is difficult to react with the electrolyte with the lithium component attached to the surface of the particles of the lithium nickel composite oxide. It is also considered that this lithium-boron-containing compound further suppresses the gas generation caused by the decomposition of the electrolyte.

[0065] 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.

[0066] 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 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.

[0067] 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).

[0068] 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 to 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 to)".

[0069] VR1 = V(11.0 to) ÷ V(8.0 to 11.0) ··· (1)

[0070] As described above, the above VR1 is preferably 3.0 or less, more preferably 2.6 or less.

[0071] 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.

[0072] 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.

[0073] 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.

[0074] Therefore, it is considered that by making the volume ratio of the amount of HCl added in the region where the pH is 5.0 or more and less than 8.0 to the amount of HCl added in the region where the pH is 8.0 or more and 11.0 or less be 0.5 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.

[0075] 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).

[0076] 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 to 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 to 8.0)".

[0077] VR2 = V(5.0 to 8.0) ÷ V(8.0 to 11.0) ··· (2)

[0078] As described above, VR2 is preferably 0.5 or less, more preferably 0.4 or less.

[0079] There is no particular limitation on the lower limit value of VR2 described above. However, since it is difficult to completely remove lithium carbonate, it is preferably 0.01 or more, more preferably 0.05 or more.

[0080] (1-3) Regarding the particle size distribution index and volume average particle size

[0081] The positive electrode active material of the present embodiment is preferably such that [(D90 - D10) / volume average particle size Mv] representing the particle size distribution index is 0.70 or more and 1.20 or less, more preferably 0.80 or more and 1.00 or less.

[0082] In this specification, D10 means the cumulative 10% particle size, which is the 10% diameter on a volume basis in the particle size distribution obtained by the laser diffraction scattering method, that is, the particle size at a volume cumulative value of 10%. D90 means the cumulative 90% particle size, which is the 90% diameter on a volume basis in the particle size distribution obtained by the laser diffraction scattering method, that is, the particle size at a volume cumulative value of 90%. In other parts of this specification, D10 and D90 have the same meaning.

[0083] 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.

[0084] 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.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] (2) Method for manufacturing a positive electrode active material for a lithium ion secondary battery

[0089] The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to the present embodiment will be described. According to the method for manufacturing a positive electrode active material for a lithium ion secondary battery of the present embodiment, the above positive electrode active material can be manufactured. Therefore, some descriptions of the matters already described will be omitted.

[0090] The manufacturing method of the positive electrode active material of the present embodiment is as Figure 2 shown in Process 20, and may include the following mixing step (S1), sintering step (S2), heat treatment step (S3), and boron addition step (S4).

[0091] In the mixing step, a nickel-containing material containing elements other than lithium (Li), boron (B), and oxygen in the lithium nickel composite oxide, such as nickel (Ni), and a nickel-containing material of an element M (M) as needed, and a lithium compound are mixed to prepare a raw material mixture.

[0092] In the sintering step, the above raw material mixture is sintered in an oxidizing atmosphere to form a sintered product.

[0093] In the heat treatment step, the sintered product can be heat treated.

[0094] In the boron addition step, the heat treated powder and a boron-containing material can be mixed.

[0095] Each step will be described below.

[0096] (2-1) Mixing step

[0097] 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.

[0098] (2-1-1) Nickel-containing material

[0099] 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, 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.

[0100] 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.

[0101] 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 the mixture of nickel oxide, nickel hydroxide, etc. and a compound of element M.

[0102] 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. At this time, the above nickel composite compound is preferably one or more selected from nickel composite oxide and nickel composite hydroxide.

[0103] 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.

[0104] The nickel-containing material preferably contains nickel (Ni) and element M (M) in a molar ratio of Ni:M = b:d. Regarding b and d in the above formula and element M, they can be the same appropriate ranges and materials as described in “(1-1) Regarding lithium nickel composite oxide” and “(1-1-1) Regarding composition” of the positive electrode active material, so the description is omitted here.

[0105] 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 to represent.

[0106] 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 to represent.

[0107] In addition, b′ and d′ have the 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 is omitted here. β and γ are preferably, for example, -0.2 ≤ β ≤ 0.2 and -0.2 ≤ γ ≤ 0.2.

[0108] 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.

[0109] In the mixing step, as part or all of the nickel-containing material, the above-mentioned nickel composite hydroxide can be used as it is, or the nickel composite hydroxide can be subjected to oxidative roasting and used as a roasted product.

[0110] There are no particular limitations on the conditions for oxidative roasting of the nickel composite hydroxide. It is preferable to subject the above-mentioned nickel composite hydroxide to oxidative roasting in an oxidizing atmosphere at a temperature of 500°C or higher and 800°C or lower.

[0111] When using a roasted product of nickel composite hydroxide as the nickel composite compound, when sintering the 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 particularly stabilized.

[0112] 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.

[0113] (2-1-2) Lithium compound

[0114] 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.

[0115] 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.

[0116] There are no particular limitations 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 generally maintains the composition in the raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0117] 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.

[0118] By making the above Li / Me 1.005 or more, the crystallinity of the obtained lithium nickel composite oxide can be improved, and the content ratio of lithium in the obtained lithium nickel composite oxide relative to elements other than oxygen can be the target composition.

[0119] 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.

[0120] 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.

[0121] (2-2) Sintering process

[0122] 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.

[0123] 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.

[0124] By making the sintering temperature 600 °C or more, the diffusion of lithium into the nickel-containing material can be sufficiently carried out.

[0125] 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.

[0126] 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.

[0127] 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.

[0128] 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.

[0129] 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.

[0130] 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.

[0131] 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.

[0132] In addition, there is no particular limitation on the furnace used for sintering, and it is sufficient that the raw material mixture can be sintered in the specified atmosphere. From the viewpoint of uniformly maintaining the atmosphere in the furnace, an electric furnace without gas generation is preferred, and both batch-type and continuous furnaces can be used.

[0133] 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.

[0134] Here, crushing refers to the following operation: mechanical energy is input to the aggregate composed of multiple secondary particles generated due to sintering necks between secondary particles during sintering, and the secondary particles themselves are hardly damaged, and the secondary particles are separated to break the aggregate. For example, a needle mill, a hammer mill, a crusher, etc. can be used, and it is sufficient to crush to a degree that does not damage the secondary particles.

[0135] 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 spray pyrolysis treatment of a liquid in which an aqueous solution containing the desired metal element is all mixed, a method of mechanically pulverizing and mixing compounds of the desired elements by a ball mill and then sintering, etc.

[0136] (2-3) Heat treatment step

[0137] In the heat treatment step, the sintered product can be heat-treated.

[0138] It is considered that by carrying out the heat treatment step, the lithium component arranged on the particle surface of the sintered product is activated, and when the subsequent boron addition step is carried out, the formation of a lithium-boron-containing compound can be promoted. In addition, by carrying out the heat treatment step, the composition of the sintered product can be made uniform.

[0139] In the heat treatment process, the heat treatment temperature of the heat-treated sintered material is not particularly limited and can be selected according to the type and addition form of the boron-containing substance added in the boron addition process described below. In the heat treatment process, for example, it is preferably heat-treated at 100°C or higher and 500°C or lower, and more preferably heat-treated at 200°C or higher and 400°C or lower.

[0140] By setting the heat treatment temperature at 100°C or higher, the lithium component disposed on the particle surface of the sintered material can be sufficiently activated, and in the boron addition process, the reaction between the above boron and lithium components can proceed sufficiently.

[0141] In addition, by setting the heat treatment temperature at 500°C or lower, a reduction such as the scattering of the lithium component disposed on the particle surface of the sintered material can be prevented.

[0142] The atmosphere during heat treatment in the heat treatment process is not particularly limited, and for example, it can be carried out in an oxidizing atmosphere or an inert gas atmosphere.

[0143] 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 preferred.

[0144] 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.

[0145] In addition, the furnace used for heat treatment is not particularly limited, and it is only necessary to heat-treat the sintered material 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.

[0146] (2-4) Boron addition process

[0147] In the boron addition process, the heat-treated powder and the boron-containing substance can be mixed.

[0148] As the added boron-containing substance, there is no particular limitation, and it can be, for example, boron monomer or a boron-containing compound containing boron. That is, the boron-containing substance is preferably at least one selected from boron monomer and boron-containing compounds. As the boron-containing compound, for example, orthoboric acid (H 3 BO 3 ), boron oxide (B 2 O 3 ), boron nitride (BN), etc. can be appropriately used.

[0149] In the boron addition process, by adding and mixing the boron-containing substance to the heat-treated powder, the boron-containing substance can be disposed on the surface of the particles of the heat-treated powder. It is considered that at this time, boron reacts with the lithium component attached to the surface of the heat-treated powder to form a lithium-boron-containing compound.

[0150] There is no particular limitation on the mixing ratio of the heat-treated powder and the boron-containing substance. In order to obtain a lithium nickel composite oxide with a target composition after the boron addition step, experiments, etc. are carried out in advance, and the mixing ratio can be selected.

[0151] Specifically, it is preferable to add and mix the boron-containing substance in such a manner that the composition of the mixture obtained in the boron addition step is the same as the composition in the target lithium nickel composite oxide.

[0152] Here, in the boron addition step, in order to 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.

[0153] The apparatus and method for mixing the heat-treated powder and the boron-containing substance 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.

[0154] The boron-containing substance is not limited to the form added in a solid state, and it can also be in a liquid state and added and mixed to the heat-treated powder.

[0155] Specifically, for example, in the boron addition step, a boron-containing solution containing the boron-containing substance can be sprayed onto the heat-treated powder.

[0156] By using the boron-containing substance as a boron-containing solution and spraying it onto the heat-treated powder, the boron-containing substance can be uniformly supplied on the particle surface of the heat-treated powder. In addition, by spraying the boron-containing solution onto the particle surface of the heat-treated powder, the reaction between boron and the lithium component attached to the surface of the heat-treated powder can be particularly promoted.

[0157] In order to uniformly spray the boron-containing solution onto the heat-treated powder, it is preferable to stir the heat-treated powder during the boron addition step.

[0158] There is no particular limitation on the solvent when it is a boron-containing solution. As the solvent, a solvent that can dissolve or disperse the above-mentioned boron-containing substance 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, since the operability is easy and the incorporation of carbon can be suppressed, water is more preferably used as the solvent.

[0159] In addition, since the boron-containing solution can also be a solution in which the boron-containing substance is not dissolved but dispersed, the above-mentioned solvent can also be referred to as a dispersion medium.

[0160] The mixture obtained in the boron addition step can be used as the positive electrode active material.

[0161] In the method for manufacturing the positive electrode active material of the present embodiment, when aggregation occurs in the particles of the lithium nickel composite oxide after the boron addition step, a crushing step (second crushing step) for crushing the lithium nickel composite oxide may also be provided. Crushing can be carried out in the same manner as in the above-described first crushing step, and thus the description thereof is omitted.

[0162] [Lithium ion secondary battery]

[0163] 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.

[0164] Hereinafter, a configuration example of the secondary battery of the present embodiment will be described, and 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.

[0165] (Positive electrode)

[0166] The positive electrode included in the secondary battery of the present embodiment may contain the above-described positive electrode active material.

[0167] An example of the method for manufacturing the positive electrode will be described below. First, the above-described positive electrode active material (powder form), a conductive material, and a binder (adhesive) may be mixed to form a positive electrode composite material, and then a solvent for the purpose of adding activated carbon, viscosity adjustment, etc. may be added as needed, and the mixture may be kneaded to produce a positive electrode composite material slurry.

[0168] 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 use. The mixing ratio of the materials may be the same as that of the positive electrode of a known lithium ion secondary battery. For example, when the total mass of the solid components of the positive electrode composite material excluding the solvent is 100% by mass, the positive electrode active material may be contained in an amount of 60% by mass or more and 95% by mass or less, the conductive material may be contained in an amount of 1% by mass or more and 20% by mass or less, and the binder may be contained in an amount of 1% by mass or more and 20% by mass or less.

[0169] The obtained positive electrode composite material slurry is coated on the surface of a current collector made of, for example, aluminum foil, dried to evaporate the solvent, and a sheet-shaped positive electrode is produced. If necessary, in order to increase the electrode density, pressure may be applied by roll pressing or the like. The sheet-shaped positive electrode thus obtained can be cut into an appropriate size according to the target battery and provided for the production of the battery.

[0170] As the conductive material, carbon black-based materials such as graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen black (registered trademark), etc. can be used.

[0171] As the binder, it plays a role in connecting and fixing the active material particles. Therefore, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, polyacrylic acid, etc. can be used.

[0172] If necessary, the positive electrode active material, conductive material, etc. are dispersed, and a solvent dissolving the binder can also be added to the positive electrode composite material. Specifically, as the solvent, organic solvents such as N-methyl-2-pyrrolidone can be used. In addition, in the positive electrode composite material, activated carbon can also be added to increase the electric double layer capacitance.

[0173] The manufacturing method of the positive electrode is not limited to the above examples, and other methods can also be used. For example, it can also be manufactured by pressing and molding the positive electrode composite material and then drying it in a vacuum atmosphere.

[0174] (Negative electrode)

[0175] For 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 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.

[0176] As the negative electrode active material, for example, sintered bodies of organic compounds such as natural graphite, artificial graphite, and phenolic resin, and powder bodies of carbon materials such as coke can be used. At this time, as the negative electrode binder, similar to the positive electrode, fluorine-containing resins such as PVDF can be used, and as the solvent for dispersing these active materials and binders, organic solvents such as N-methyl-2-pyrrolidone can be used.

[0177] (Separator)

[0178] 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. Known ones can be used, for example, films such as polyethylene and polypropylene, and membranes with a large number of micropores can be used.

[0179] (Non-aqueous electrolyte)

[0180] As the non-aqueous electrolyte, for example, non-aqueous electrolytic solutions can be used.

[0181] As the non-aqueous electrolyte, for example, a lithium salt as a supporting salt dissolved in an organic solvent can be used. In addition, an ionic liquid in which a lithium salt is dissolved can be used as the non-aqueous electrolyte. Further, an ionic liquid refers to a salt composed of a cation other than a lithium ion and an anion and being in a liquid state even at room temperature.

[0182] As the organic solvent, one selected from cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, and propyl trifluorocarbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate, further, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane, sulfur compounds such as ethyl methyl sulfone and butyrolactone sulfone, phosphorus compounds such as triethyl phosphate and trioctyl phosphate, etc. can be used alone, or two or more thereof can be mixed and used.

[0183] 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 may contain a radical scavenger, a surfactant, a flame retardant, etc.

[0184] In addition, as the non-aqueous electrolyte, a solid electrolyte can be used. The solid electrolyte has the property of being able to withstand high voltages. As the solid electrolyte, inorganic solid electrolytes and organic solid electrolytes can be cited.

[0185] As the inorganic solid electrolyte, oxide-based solid electrolytes, sulfide-based solid electrolytes, etc. can be cited.

[0186] As for the oxide-based solid electrolyte, there is no particular limitation. For example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electron insulation can be appropriately used. As the oxide-based solid electrolyte, for example, one selected from lithium phosphate (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 、Li4 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 2 Ta 2 O 12 、Li 3.6 Si 0.6 P 0.4 O 4 etc., more than one selected from the following.

[0187] As for 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, for example. 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-P2 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 etc. One or more selected from the above.

[0188] 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.

[0189] As the organic solid electrolyte, there is no particular limitation as long as it is a polymer compound showing ionic conductivity. For example, polyethylene oxide, polypropylene oxide, their copolymers, etc. can be used. In addition, the organic solid electrolyte can contain a supporting salt (lithium salt).

[0190] (Shape and structure of the secondary battery)

[0191] The lithium - ion secondary battery of the present embodiment described above can have various shapes such as cylindrical and laminated. When adopting any one of the shapes, when the non - aqueous electrolyte of the secondary battery of the present embodiment uses a non - aqueous electrolyte solution, the structure can be as follows: the positive electrode and the negative electrode are laminated as an electrode body through a separator, the obtained electrode body is impregnated with the non - aqueous electrolyte solution, and between the positive electrode current collector and the positive 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, etc., and it is sealed in a battery case.

[0192] 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.

[0193] 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.

[0194] In addition, since the secondary battery of the present embodiment can be miniaturized and have high output, it is suitable as a power source for electric vehicles with limited mounting space. In addition, not only as a power source for electric vehicles driven purely by electric energy, the secondary battery of the present embodiment can also be used as a power source for so-called hybrid vehicles that are used in combination with combustion mechanisms such as gasoline engines and diesel engines.

[0195]

Examples

[0196] 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.

[0197] 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.

[0198] (Evaluation of positive electrode active material)

[0199] Regarding the obtained positive electrode active material, the following evaluations are carried out.

[0200] (a) Evaluation of composition, crystal structure, and particle structure

[0201] The composition is analyzed using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000).

[0202] In addition, regarding the obtained positive electrode active material, the powder X-ray diffraction pattern is measured, and the crystal structure and the like are determined by Rietveld refinement analysis. As a result, it can be confirmed that the positive electrode active materials produced in the following examples and comparative examples are composed of lithium nickel composite oxides, and the lithium nickel composite oxides have a hexagonal layered structure.

[0203] Furthermore, when observing the particles of the positive electrode active material using a scanning electron microscope, it can be confirmed that the positive electrode active materials produced in the following examples and comparative examples contain secondary particles formed by the aggregation of a plurality of primary particles.

[0204] (b) Titration curve

[0205] 10 g of the positive electrode active material obtained in the following examples and comparative examples is stirred in 50 mL of pure water for 5 minutes, and the filtered filtrate is neutralized and titrated with 1.0 M HCl to measure the titration curve. In addition, distilled water is used as the pure water.

[0206] From the obtained titration curve, determine the amount of HCl added in each pH region shown in the "HCl addition amount in neutralization titration" column of Table 1. In addition, calculate VR1 and VR2 as the ratio of the HCl addition amount using the above formulas (1) and (2).

[0207] (c) Particle size distribution index

[0208] Measure the volume-based particle size distribution using a laser diffraction scattering particle size distribution analyzer (manufactured by Microtrac·BEL Corporation, Microtrac MT3300EXII). Calculate D10, D90, and the volume average particle size Mv from the particle size distribution.

[0209] Then, calculate [(D90 - D10) / volume average particle size Mv] as the particle size distribution index.

[0210] (Evaluation of battery characteristics)

[0211] (a) Charge capacity, gas generation amount

[0212] After measuring the volume of the laminated battery fabricated in the following Examples and Comparative Examples by the Archimedes method, place it in a constant temperature bath maintained at 25°C for about 12 hours. After the open circuit voltage OCV (open circuit voltage) stabilizes, perform a conditioning process of repeating 5 charge-discharge cycles at a cut-off voltage of 2.5 - 4.3V and a current density of 23 mA / cm 2 ,

[0213] Next, at a temperature of 25°C, charge at a constant current and constant voltage (CCCV) up to 4.2V. Take the capacity at this time as the charge capacity.

[0214] After charging, store it in a constant temperature bath set at 60°C for 12 days. After 12 days, perform discharge until 2.5V. After discharge, measure the volume of the laminated battery by the Archimedes method, and evaluate the amount of gas generated in the cell as the gas generation amount from the difference in volume from the laminated battery measured before the conditioning process.

[0215] [Example 1]

[0216] (1) Manufacture of positive electrode active material

[0217] According to Figure 2 the process flow 20 shown, manufacture the positive electrode active material.

[0218] (1-1) Mixing process

[0219] (Nickel-containing material)

[0220] First, prepare the following nickel composite oxide. The nickel composite hydroxide prepared by the neutralization crystallization method is subjected to oxidative calcination at a temperature of 600 °C for 3 hours in an 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.

[0221] Then, use the above-mentioned mixture of 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

[0222] Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024.

[0223] (Lithium compound)

[0224] As the lithium compound, lithium hydroxide is used. In addition, as the lithium hydroxide, anhydrous lithium hydroxide is used.

[0225] Weigh and mix the above-mentioned nickel-containing material and lithium hydroxide in such a way that Li / (Ni + Mn + Co + Ti) is 1.02 to obtain a raw material mixture.

[0226] (1-2) Sintering process

[0227] Heat the obtained raw material mixture in an electric furnace in an oxygen atmosphere to 840 °C, hold it at 840 °C for 2 hours, and sinter. Then, cool it to room temperature in the furnace. Crush the obtained sintered product.

[0228] (1-3) Heat treatment process

[0229] In the heat treatment process, heat the sintered product in an air stream at 305 °C for 10 hours.

[0230] (1-4) Boron addition process

[0231] Mix the heat-treated powder obtained in the heat treatment process and orthoboric acid (H 3 BO 3 ) as the boron-containing material to obtain lithium nickel composite oxide as the positive electrode active material. Here, 40 secondary particles of orthoboric acid observed by the surface SEM image are randomly extracted, and the average diameter in the long axis direction is calculated to be 3 μm.

[0232] In addition, in the boron addition process, the heat-treated powder and orthoboric acid are mixed so that the molar ratio of the elements contained in the obtained lithium nickel composite oxide after mixing is the ratio shown in Table 1, that is,

[0233] Li:Ni:Mn:Co:Ti:B = 1.02:0.825:0.097:0.049:0.024:0.005.

[0234] Regarding the lithium nickel composite oxide as the obtained positive electrode active material, the above evaluation was carried out. The evaluation results are shown in Table 1.

[0235] (2) Fabrication of secondary battery

[0236] Through the following procedure, a laminated battery with the structure as Figure 1 shown was fabricated, and the above evaluation was carried out on this battery. The evaluation results are shown in Table 1.

[0237] As Figure 1 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 an electrolytic solution and encapsulated by a laminate 14. In addition, the positive electrode film 11 is connected to the positive electrode tab 15, and the negative electrode film 13 is connected to the negative electrode tab 16, and the positive electrode tab 15 and the negative electrode tab 16 are exposed outside the laminate 14.

[0238] 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 such that there was 16.5 mg of the positive electrode active material per 1 cm 2 Next, the product with the slurry containing the positive electrode active material coated 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 rectangles 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.

[0239] 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 in 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 onto a copper foil (negative electrode current collector) with a thickness of 18 μm by a coater at a rate of 4 mg / cm 2 per unit area, and then dried and roll-pressed.

[0240] The separator 12 used a polyethylene porous membrane with a film thickness of 20 μm, and the electrolytic solution used the following: 1.2 M LiPF 6A mixture of ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) at a ratio of 20:5:25:50 as a supporting electrolyte, with 2 wt% of vinylene carbonate (VC) added (manufactured by Ube Industries, Ltd.).

[0241] 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 an electrolytic solution and encapsulated by the laminate 14 to fabricate the laminated battery 10.

[0242] [Examples 2 to 4]

[0243] In the boron addition process, the heat-treated powder and orthoboric acid were mixed in such a way that the molar ratio of Li, Ni, Mn, Co, Ti, and B contained in the resulting lithium nickel composite oxide after mixing was the value shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery were manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0244] [Examples 5 and 6]

[0245] In the heat treatment process, the heat treatment temperature was changed to the temperature shown in Table 1. Except for this point, the positive electrode active material and the lithium ion secondary battery were manufactured under the same conditions as in Example 2 and evaluated. The evaluation results are shown in Table 1.

[0246] [Example 7]

[0247] In the boron addition process, the heat-treated powder was supplied by spraying a boron-containing solution, and the two were mixed. The boron-containing solution is an aqueous solution in which orthoboric acid (H 3 BO 3 ) is dissolved in water.

[0248] During the boron addition process, the heat-treated powder was continuously stirred.

[0249] Except for the above points, the positive electrode active material and the lithium ion secondary battery were manufactured under the same conditions as in Example 2 and evaluated. The evaluation results are shown in Table 1.

[0250] [Comparative Example 1]

[0251] The sintered product obtained after the sintering process was used as the positive electrode active material. That is, when manufacturing the positive electrode active material, the processes after the heat treatment process were not carried out. Except for the above points, the positive electrode active material and the lithium ion secondary battery were manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0252]

Table 1

[0253]

[0254] Based on 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.

[0255] This application claims priority based on Japanese Patent Application No. 2022-175171 filed with the Japan Patent Office on October 31, 2022, and incorporates the entire contents of Japanese Patent Application No. 2022-175171 into this international application.

[0256]

Reference Signs

[0257] 10 Stacked battery

[0258] 11 Positive electrode film

[0259] 12 Separator

[0260] 13 Negative electrode film

[0261] 14 Laminate

[0262] 15 Positive electrode tab

[0263] 16 Negative electrode tab

[0264] 20 Process

[0265] S1 Mixing process

[0266] S2 Sintering process

[0267] S3 Heat treatment process

[0268] S4 Boron addition process

Claims

1. 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 having a hexagonal layered structure, including 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, a heat treatment step of heat treating the sintered product obtained in the sintering step, and a boron addition step of mixing the heat treated powder obtained in the heat treatment step and a boron-containing material, the boron-containing material being at least one selected from boron monomer 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, in the boron addition step, spraying a boron-containing solution containing the boron-containing material onto the heat treated powder.

3. The method for manufacturing a positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, in the heat treatment step, heat treating the sintered product in an oxidizing atmosphere or an inert gas atmosphere at a temperature of 100°C or higher and 500°C or lower.

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, filtering the filtrate, and neutralizing and titrating it 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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