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

Abstract

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 containing secondary particles in which a plurality of primary particles are agglomerated, the lithium nickel composite oxide containing Li, Ni, B, and an element M (M) in the following proportions: Li: Ni: B: M = a: b: c: d (0.95 < = a < = 1.10, 0.50 < = blt; 1.00, 0.00 lt, 0.00 lt; (In the formula, the element M is at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Ti, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al), and the ratio of the B content to the C content, calculated from the XPS measurement result, is 0.8-30.0 inclusive.

Description

Technical Field

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

[0002] In recent years, with the popularization of portable electronic devices such as mobile phones and laptops, there is a strong desire 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 is a strong desire for the development of high-output secondary batteries. Furthermore, in addition to the above-mentioned required characteristics, there is a high expectation for secondary batteries with high durability that are difficult to deteriorate even after repeated use.

[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, and an electrolyte, etc. As the active material of the negative electrode and the positive electrode, a material that can release and insert lithium is used. As mentioned above, a lithium-ion secondary battery has high energy density, output characteristics, and durability.

[0004] Research and development of lithium-ion secondary batteries is currently in full swing, and among them, lithium-ion secondary batteries using layered or spinel lithium metal composite oxides as positive electrode materials have been put into practical use as batteries with high energy density because they can obtain high voltages of 4V.

[0005] As a positive electrode material for lithium-ion secondary batteries, lithium cobalt composite oxide (LiCoO 2 ), lithium nickel composite oxide (LiNiO 2 ), 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.

[0006] In recent years, lithium ion secondary batteries have been required to further improve battery characteristics, and studies have been conducted on, for example, improvement of cycle characteristics (eg, Patent Document 1) and higher output.

[0007] [Prior art literature]

[0008] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2016-189320 Summary of the invention

[0010] [Problems to be solved by the invention]

[0011] In recent years, there has been a demand for a positive electrode active material for lithium ion secondary batteries that can reduce reaction resistance when used in lithium ion secondary batteries.

[0012] Therefore, in view of the above-mentioned problems of the prior art, an object of one aspect of the present invention is to provide a positive electrode active material for a lithium ion secondary battery which can reduce the reaction resistance when used in a lithium ion secondary battery.

[0013]

Methods to solve the problem

[0014] In order to solve the above-mentioned problems, according to one embodiment of the present invention, there is provided a positive electrode active material for a lithium ion secondary battery, wherein the positive electrode active material comprises a lithium nickel composite oxide having a hexagonal layered structure and including secondary particles formed by agglomeration of a plurality of primary particles.

[0015] The lithium nickel composite oxide contains lithium (Li), nickel (Ni), boron (B), and element M (M) in the following ratios, in terms of the amount of substance: Li:Ni:B:M=a:b:c:d (wherein 0.95≤a≤1.10, 0.50≤b<1.00, 0.00 <c≤0.03、0.00≤d≤0.47、b+c+d=1,所述元素M是从由Mn、Co、V、Mg、Mo、Ca、Cr、Zr、Ta、Ti、Nb、Na、W、Fe、Zn、Si、Sn、Cu、P和Al构成的组中选择的至少1种元素),

[0016] When the total amount of lithium, nickel, boron, the element M, and carbon on the surface calculated from the XPS measurement result of the positive electrode active material for the lithium ion secondary battery is the total amount of substance, the ratio of the amount of carbon to the total amount of substance is the C content ratio, and the ratio of the amount of boron to the total amount of substance is the B content ratio,

[0017] The ratio of the B content ratio to the C content ratio is 0.8 or more and 30.0 or less.

[0018] [Effects of the Invention]

[0019] According to one embodiment of the present invention, a positive electrode active material for a lithium ion secondary battery can be provided which can reduce reaction resistance when used in a lithium ion secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0020]

Figure 1

[0021]

Figure 2A

[0022]

Figure 2B

[0023] Hereinafter, a mode for carrying out the present invention will be described with reference to the drawings, but the present invention is not limited to the following embodiments, and various modifications and substitutions may be made to the following embodiments without departing from the scope of the present invention.

[0024] [Positive electrode active material for lithium ion secondary batteries]

[0025] Next, the positive electrode active material for lithium ion secondary battery (hereinafter, simply referred to as “positive electrode active material”) according to the present embodiment will be described.

[0026] (1) About lithium nickel composite oxide

[0027] The positive electrode active material of this embodiment contains a lithium nickel composite oxide. The positive electrode active material of this embodiment may be composed of only a lithium nickel composite oxide, but in this case, it is not excluded that the positive electrode active material contains inevitable impurities mixed in during the production process.

[0028] (1-1) Composition

[0029] The lithium nickel composite oxide may contain lithium (Li), nickel (Ni), and boron (B).

[0030] The lithium nickel composite oxide may contain elements other than lithium, nickel and boron, and may contain, for example, the element M described below.

[0031] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), boron (B), and element M (M) in the following ratios, Li:Ni:B:M=a:b:c:d, in terms of the molar ratio of substances.

[0032] The above a, b, c, and d preferably satisfy 0.95≤a≤1.10, 0.50≤b<1.00, 0.00 <c≤0.03、0.00≤d≤0.47、b+c+d=1。此外,元素M优选从由Mn、Co、V、Mg、Mo、Ca、Cr、Zr、Ta、Ti、Nb、Na、W、Fe、Zn、Si、Sn、Cu、P和Al构成的组中选择的至少1种元素。

[0033] Lithium nickel composite oxides can be represented by the general formula: Li a Nib B c M d O 2+α As a, b, c, d and the element M in the above general formula have been described, their description is omitted here. α preferably satisfies, for example, -0.2≤α≤0.2.

[0034] (Nickel (Ni))

[0035] The higher the nickel content in the lithium nickel composite oxide, the higher the capacity can be when used as a positive electrode material for a lithium ion secondary battery.

[0036] Therefore, as described above, b indicating the content ratio of nickel is preferably 0.50 or more, more preferably 0.60 or more, further preferably 0.70 or more, and particularly preferably 0.80 or more.

[0037] The upper limit value of b indicating the content ratio of nickel is as described above, and is preferably less than 1.00, and more preferably 0.97 or less.

[0038] (Boron (B))

[0039] As described above, the lithium nickel composite oxide of the present embodiment may contain boron. According to the research of the present inventors, the lithium nickel composite oxide can reduce the reaction resistance when used in a lithium ion secondary battery by containing boron.

[0040] Although the exact mechanism for reducing the reaction resistance is not clear, it is believed that the lithium nickel composite oxide contains boron, and the boron and the lithium component attached to the surface of the lithium nickel composite oxide particles form a low-resistance reaction product. Therefore, it is believed that the resistance on the surface of the lithium nickel composite oxide particles decreases with the insertion and removal of lithium, thereby reducing the reaction resistance.

[0041] As described above, c, which represents the content ratio of boron, is preferably greater than 0.00, more preferably 0.001 or more, further preferably 0.002 or more, and particularly preferably 0.003 or more.

[0042] The upper limit of c indicating the content ratio of boron is not particularly limited, but is preferably 0.03 or less, more preferably 0.025 or less, and particularly preferably 0.02 or less, in consideration of saturation of the effect due to excessive addition.

[0043] (Element M)

[0044] As described above, the lithium nickel composite oxide of the present embodiment may contain an element M as an optional component. The element group applicable to the element M has been described, and the description thereof is omitted here. In particular, from the viewpoint of improving the thermal stability of the lithium nickel composite oxide, for example, suppressing the thermal decomposition of the lithium nickel composite oxide, it is preferred that the element M contain at least one selected from cobalt (Co), manganese (Mn), and titanium (Ti).

[0045] The element M is an optional component, and thus d indicating the content ratio of the element M is, as described above, preferably 0.00 or more, more preferably 0.05 or more, and further preferably 0.10 or more.

[0046] The upper limit value of d indicating the content ratio of the element M is, as described above, preferably 0.47 or less, more preferably 0.25 or less, and further preferably 0.20 or less.

[0047] When the lithium nickel composite oxide contains a plurality of types of elements M, the total content ratio of the plurality of types of elements M preferably satisfies the above range.

[0048] As described later, the lithium nickel composite oxide also contains carbon. However, the lithium nickel composite oxide contains carbon as an inevitable impurity in a very small amount, and therefore, the carbon is not included in the general formula of the lithium nickel composite oxide.

[0049] (1-2) Crystal structure

[0050] The lithium nickel composite oxide preferably has a hexagonal layered structure. The lithium nickel composite oxide has a hexagonal layered structure, which allows lithium to be easily inserted and removed between layers, and when used in a lithium ion secondary battery, the output characteristics and cycle characteristics can be particularly improved.

[0051] The crystal structure of the lithium nickel composite oxide can be analyzed by performing Rietveld layer analysis.

[0052] (1-3) About the particle shape

[0053] The lithium nickel composite oxide particles may include secondary particles formed by agglomeration of a plurality of primary particles.

[0054] Furthermore, the lithium nickel composite oxide may contain non-aggregated primary particles in addition to the secondary particles. In other words, the lithium nickel composite oxide may contain both primary particles and secondary particles.

[0055] (2) Proportion of B and proportion of C

[0056] As described above, the lithium nickel composite oxide contains boron, and thus, when used in a lithium ion secondary battery, the reaction resistance can be reduced.

[0057] It is believed that the boron contained in the lithium nickel composite oxide forms a low-resistance reaction product with the lithium component attached to the surface of the lithium nickel composite oxide particles. Therefore, it is presumed that the generation of impurities such as lithium carbonate that increase resistance is suppressed on the surface of the lithium nickel composite oxide particles, thereby reducing the reaction resistance.

[0058] When the positive electrode active material of the present embodiment is subjected to XPS (X-ray photoelectron spectroscopy) measurement, the type and amount of elements present in the surface layer of the lithium nickel composite oxide particles contained in the positive electrode active material can be evaluated.

[0059] Then, from the viewpoint of improving the effect of reducing the above-mentioned reaction resistance, when the positive electrode active material of this embodiment is subjected to XPS measurement, it is preferred that the content of boron (B) is high and the content of carbon (C) derived from lithium carbonate or the like, which causes an increase in resistance, is suppressed.

[0060] Here, the total amount of lithium (Li), nickel (Ni), boron (B), element M, and carbon (C) on the surface calculated from the XPS measurement results of the positive electrode active material of the present embodiment is the total amount of substance, and the ratio of the amount of carbon (C) relative to the total amount of substance is the C-containing ratio. In addition, the ratio of the amount of boron (B) relative to the above-mentioned total amount of substance calculated from the XPS measurement results of the positive electrode active material of the present embodiment is the B-containing ratio.

[0061] In the above case, the ratio of the B content ratio to the C content ratio is preferably 0.8 or more, more preferably 1.0 or more, further preferably 2.0 or more, particularly preferably 2.5 or more.

[0062] It is believed that by making the ratio of the above-mentioned B-containing ratio to the C-containing ratio 0.8 or more, the ratio of components such as lithium carbonate that are the cause of resistance increase is suppressed, and the ratio of compounds containing boron that contribute to low resistance is increased. Therefore, when used in lithium ion secondary batteries, the reaction resistance can be particularly reduced.

[0063] Here, since the ratio of the B content to the C content is excessively increased, the boron content in the lithium nickel composite oxide is increased, and the content of other nickel and element M needs to be suppressed. In addition, in order to suppress the mixing of lithium carbonate and the like, it is necessary to perform long-term water washing and precise control of the atmosphere during heat treatment, which causes the reduction of battery characteristics and the increase of costs.

[0064] Therefore, the ratio of the B content ratio to the C content ratio is preferably 30.0 or less, more preferably 15.0 or less, further preferably 10.0 or less, and particularly preferably 8.0 or less.

[0065] The above-mentioned C content is preferably small, for example, preferably 30% or less, more preferably 20% or less. By making the C content less than 30%, the content of compounds such as lithium carbonate contained in the surface layer of the particles of the lithium nickel composite oxide, which is the cause of the increase in resistance, can be fully suppressed. Therefore, when used in lithium ion secondary batteries, the reaction resistance can be particularly reduced.

[0066] The lower limit of the C content is not particularly limited, but is preferably 0% or more, more preferably 5% or more, and further preferably 10% or more.

[0067] The above-mentioned B-containing ratio and C-containing ratio can be measured and calculated in the following order. First, the positive electrode active material is measured by XPS. Then, the semi-quantitative value is calculated from the peak area of ​​the spectrum of lithium (Li), nickel (Ni), boron (B), element M, and carbon (C) obtained by XPS measurement, and the amount ratio of each component on the surface of the positive electrode active material is obtained therefrom. The peak used when calculating the amount ratio of each component can be selected according to the element, etc. For example, after the peak separation of the measured XPS spectrum, the peak with the highest intensity can be used.

[0068] Next, using the results of the above composition analysis, the C content ratio, the B content ratio, and the ratio of the B content ratio to the C content ratio can be calculated by the following formulas (1), (2), and (3). In the formulas, MLi, MC, MNi, MB, and MM respectively refer to the molar ratio of lithium, the molar ratio of carbon, the molar ratio of nickel, the molar ratio of boron, and the molar ratio of element M, calculated from the results of XPS measurement.

[0069] (C content ratio) = [MC÷(MLi+MNi+MB+MM+MC)]×100···(1)

[0070] (B content ratio) = [MB÷(MLi+MNi+MB+MM+MC)]×100···(2)

[0071] (Ratio of B content to C content) = (B content) ÷ (C content) (3)

[0072] (3) About titration curve

[0073] Regarding the filtrate obtained by mixing the positive electrode active material of this embodiment with pure water and then filtering, in the titration curve obtained by neutralization titration, preferably, the volume ratio of the HCl drop amount in the region where the pH is greater than 5.0 and less than 8.0 to the HCl drop amount in the region where the pH is greater than 8.0 and less than 11.0 is less than 0.5.

[0074] The filtrate provided for drawing the titration curve can be a filtrate obtained by adding 10 g of the positive electrode active material of this embodiment to 50 mL of pure water, stirring the pure water for 5 minutes, and filtering to separate the solid and liquid. Pure water is preferably water that has been used to remove components that affect the neutralization titration as much as possible, and distilled water can be used appropriately. In addition, when making the titration curve, as the acid for neutralizing and titrating the filtered filtrate, that is, hydrochloric acid (HCl), 1.0 M, i.e., 1.0 mol / dm 3 (1.0mol / L) of hydrochloric acid.

[0075] According to the study by the present inventors, the amount of HCl added in the region of pH 5.0 or more and less than 8.0 in the titration curve mainly means HCl consumed in the reaction with lithium carbonate contained in the positive electrode active material.

[0076] In addition, when the filtrate of the positive electrode active material of the present embodiment is subjected to neutralization titration, in the titration curve, in the region where the pH is 8.0 or more and 11.0 or less, the pH change is suppressed compared to other pH regions, and a nearly flat region appears. Specifically, for example, in the titration curve, in the region where the pH is 8.0 or more and 11.0 or less, a region where the pH change is small relative to the amount of HCl added appears compared to the region where the pH is 5.0 or more and less than 8.0.

[0077] As described above, it is believed that the lithium nickel composite oxide contains a trace amount of boron, and the boron forms a lithium-boron containing compound as a low-resistance reaction product with the lithium component attached to the surface of the lithium nickel composite oxide particles. It is also believed that the lithium-boron containing compound reduces the reaction resistance of the positive electrode active material.

[0078] It is estimated that the amount of HCl added in the region of pH 8.0 to 11.0 in the titration curve mainly means the HCl consumed in the reaction with the lithium-boron containing compound.

[0079] Therefore, it is believed that the volume ratio of the HCl dripping amount in the region where the pH is more than 5.0 and less than 8.0 and the HCl dripping amount in the region where the pH is more than 8.0 and less than 11.0 is less than 0.5, suppressing the content of lithium carbonate means that the above-mentioned lithium-boron containing compound can be fully generated. Therefore, it is believed that the positive electrode active material is applicable to lithium ion secondary batteries, and the reaction resistance of the positive electrode active material can be particularly reduced.

[0080] The volume ratio VR of the amount of HCl added dropwise in the pH range of 5.0 to less than 8.0 to the amount of HCl added dropwise in the pH range of 8.0 to 11.0 can be calculated by the following formula (4).

[0081] In the following formula (4), the amount of HCl added in the pH range of 8.0 to 11.0 is represented as “V(8.0 to 11.0)”, and the amount of HCl added in the pH range of 5.0 to less than 8.0 is represented as “V(5.0 to 8.0)”.

[0082] VR=V(5.0~8.0)÷V(8.0~11.0)···(4)

[0083] The VR is as described above, and is preferably 0.5 or less, more preferably 0.25 or less, and further preferably 0.2 or less.

[0084] The lower limit of VR is not particularly limited, but is preferably 0.01 or more, more preferably 0.05 or more, because it is difficult to completely remove lithium carbonate.

[0085] (4) Particle size distribution index and volume average particle size

[0086] The positive electrode active material of the present embodiment preferably has a particle size distribution index of [(D90-D10) / volume average particle size Mv] of 0.70 to 1.20, more preferably 0.80 to 1.00.

[0087] In this specification, D10 means cumulative 10% particle diameter, which is the 10% diameter of the volume basis in the particle size distribution obtained by laser diffraction scattering method, i.e., the particle diameter at 10% of the volume cumulative value. D90 means cumulative 90% particle diameter, which is the 90% diameter of the volume basis in the particle size distribution obtained by laser diffraction scattering method, i.e., the particle diameter at 90% of the volume cumulative value. In other parts of this specification, D10 and D90 have the same meaning.

[0088] The volume average particle size Mv is the average particle size weighted by the particle volume, and the sum of the diameters of each particle in the collection of particles multiplied by the volume of the particle is divided by the total volume of the particles. The volume average particle size can be measured and calculated by a laser diffraction scattering method using a laser diffraction particle size distribution meter.

[0089] When the particle size distribution index of the positive electrode active material is 0.70 or more, for example, when preparing the positive electrode, particles with smaller particle sizes are arranged between particles with larger particle sizes, thereby increasing the packing density of the positive electrode active material.

[0090] By setting the particle size distribution index of the positive electrode active material to 1.20 or less, mixing of excessively coarse particles and fine particles can be suppressed, and when such a positive electrode active material is used in a lithium ion secondary battery, the output characteristics can be particularly improved.

[0091] The volume average particle size Mv of the positive electrode active material of the present embodiment is not particularly limited, but is preferably, for example, 8 μm or more and 20 μm or less, and more preferably 10 μm or more and 18 μm or less.

[0092] By making the volume average particle size Mv of the positive electrode active material of the present embodiment within the above range, when the positive electrode active material of the present embodiment is used for the positive electrode of a lithium-ion secondary battery, the output characteristics and battery capacity are particularly improved, and the high filling property of the positive electrode is also achieved. Specifically, by making the volume average particle size Mv of the positive electrode active material of the present embodiment greater than 8 μm, the filling property of the positive electrode can be improved. In addition, by making the volume average particle size Mv of the positive electrode active material of the present embodiment less than 20 μm, the output characteristics and battery capacity can be particularly improved.

[0093] [Method for producing positive electrode active material for lithium ion secondary battery]

[0094] The method for manufacturing the positive electrode active material for lithium ion secondary battery of the present embodiment is described. According to the method for manufacturing the positive electrode active material for lithium ion secondary battery of the present embodiment, the above-mentioned positive electrode active material can be manufactured. Therefore, with respect to the matters already described, part of the description is omitted. In addition, the method for manufacturing the above-mentioned positive electrode active material is not limited to the following method for manufacturing the positive electrode active material.

[0095] The method for producing the positive electrode active material of the present embodiment may include the following mixing step, sintering step, water washing step, boron adding step, heat treatment step, and cooling step.

[0096] In the mixing step, elements other than lithium (Li), boron (B) and oxygen (O) contained in the lithium nickel composite oxide, such as nickel (Ni) and a nickel-containing material of the required element M (M), are mixed with a lithium compound to prepare a first raw material mixture.

[0097] In the sintering step, the first raw material mixture is sintered in an oxidizing atmosphere to produce a sintered product.

[0098] In the water washing step, the sintered product obtained in the sintering step is washed with water to obtain a water-washed powder.

[0099] In the boron adding step, the water-washed powder and the boron-containing material are mixed to prepare a second raw material mixture.

[0100] In the heat treatment step, the second raw material mixture may be heat treated.

[0101] Each step is described below.

[0102] (1) Mixing process

[0103] In the mixing step, as described above, the nickel-containing material containing at least nickel and the lithium compound are mixed to prepare the first raw material mixture. The raw materials used are described below.

[0104] (1-1) Nickel-containing substances

[0105] As described above, the nickel-containing material provided in the mixing step may contain elements other than lithium, boron and oxygen contained in the target lithium nickel composite oxide, namely nickel, and an optional element M. In the nickel-containing material, the element M may be an optional additive and may not be contained.

[0106] The nickel-containing material may contain elements corresponding to the target composition of the lithium nickel composite oxide, and its composition is not particularly limited. For example, the nickel-containing material may appropriately contain a nickel composite hydroxide, a nickel composite compound as a calcined product of the nickel composite hydroxide. In addition, the nickel-containing material may also be composed of the above-mentioned nickel composite compound. As the calcined product of the nickel composite hydroxide, a nickel composite oxide, a mixture of a nickel composite oxide and a nickel composite hydroxide may be cited.

[0107] In addition, the nickel-containing material may be, for example, a material having a coating layer containing element M on the surface of nickel oxide, nickel hydroxide, etc., and one or more selected from a mixture of a compound of nickel oxide, nickel hydroxide, etc. and element M.

[0108] When the lithium nickel composite oxide contains a plurality of elements M, the nickel-containing material may be a mixture of a nickel composite compound containing part of the element M and a compound of the remaining element M. In this case, the nickel composite compound is preferably one or more selected from nickel composite oxides and nickel composite hydroxides.

[0109] When the nickel-containing material contains a compound of the element M, the form of the compound of the element M is not particularly limited, and one or more selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc. can be used.

[0110] The nickel-containing material preferably contains nickel (Ni) and element M (M) in a ratio of Ni:M=b:d in terms of the amount of substance. Regarding b, d, and element M in the above formula, they can be the same suitable ranges and materials as described in "(1-1) Regarding composition" of "(1) Regarding lithium nickel composite oxide" of the positive electrode active material, and therefore the description is omitted here.

[0111] When the nickel-containing material is a nickel composite oxide, the nickel-containing material can be represented by, for example, the general formula: Ni b′ M d′ O 1+β express.

[0112] When the nickel-containing material is a nickel composite hydroxide, the nickel-containing material can be represented by, for example, the general formula: Ni b′ M d′ (OH) 2+γ express.

[0113] In addition, b', d' and the above-mentioned b, d have the relationship of b':d'=b:d, and b'+d'=1. Since b, d and the element M have been described, the description is omitted here. β, γ are preferably -0.2≤β≤0.2, -0.2≤γ≤0.2, for example.

[0114] When the nickel-containing material includes a nickel composite hydroxide, the method for producing the nickel composite hydroxide is not particularly limited, and for example, a nickel composite hydroxide obtained by a crystallization method such as a coprecipitation method or a homogeneous precipitation method can be used.

[0115] In the mixing step, as part or all of the nickel-containing material, the above-mentioned nickel composite hydroxide may be used as it is, or the nickel composite hydroxide may be oxidatively calcined and used as a calcined product.

[0116] The conditions for oxidatively calcining the nickel composite hydroxide are not particularly limited. The nickel composite hydroxide is preferably oxidatively calcined in an oxidizing atmosphere at a temperature of 500° C. to 800° C.

[0117] When a calcined nickel composite hydroxide is used as the nickel composite compound, the first raw material mixture mixed with a lithium compound is sintered to obtain a lithium nickel composite oxide, and the composition ratio of Li, Ni and element M in the lithium nickel composite oxide can be particularly stabilized.

[0118] The atmosphere during the oxidation calcination is not particularly limited. As described above, it is preferably carried out in an oxidizing atmosphere, and more preferably carried out in an air atmosphere (air atmosphere) or an air stream, which can be easily carried out.

[0119] (1-2) Lithium compounds

[0120] There is no particular limitation on the lithium compound, and preferably, for example, one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride and lithium oxide can be used. More preferably, the lithium compound can be one or more selected from lithium hydroxide and lithium carbonate. Lithium hydroxide has high reactivity with nickel composite compounds and low reaction temperature, so lithium hydroxide is more preferably used as the lithium compound.

[0121] Next, in the method for producing a positive electrode active material according to the present embodiment, the nickel-containing material and the lithium compound may be mixed to prepare a first raw material mixture as described above.

[0122] The mixing ratio of the nickel-containing material and the lithium compound is not particularly limited. The compositions of lithium, nickel and element M in the sintered material obtained after sintering substantially maintain the compositions in the first raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0123] Here, when the water washing step described later is implemented, the lithium may sometimes be reduced to a certain extent. Therefore, the amount of lithium (Li) in the lithium compound is preferably adjusted to be greater than 1.005 and less than 1.100 in terms of the ratio of the amount of substance (Li / Me) relative to the total amount (Me) of, for example, nickel and element M in the nickel-containing material.

[0124] By setting the Li / Me ratio to 1.005 or more, the crystallinity of the obtained lithium nickel composite oxide can be improved, and the content ratio of lithium to elements other than oxygen in the obtained lithium nickel composite oxide can be adjusted to a target composition.

[0125] Furthermore, by setting the Li / Me ratio to 1.100 or less, excessive sintering, for example, sintering of secondary particles in the obtained lithium nickel composite oxide, can be suppressed.

[0126] 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 blender or a mixing granulator can be used.

[0127] (2) Sintering process

[0128] In the sintering step, the first raw material mixture may be sintered in an oxidizing atmosphere to obtain a sintered product. In the sintering step, when the first raw material mixture is sintered, a sintered product is obtained in which lithium in the lithium compound is diffused and reacted in the nickel-containing material.

[0129] In the sintering step, the sintering temperature for sintering the first raw material mixture is not particularly limited, and may be, for example, 600° C. or higher and 1000° C. or lower.

[0130] By setting the sintering temperature to 600° C. or higher, diffusion of lithium into the nickel-containing material can be sufficiently performed.

[0131] Furthermore, by setting the sintering temperature to 1000° C. or less, the sintering between particles of the generated sintered product can be suppressed from proceeding. Furthermore, the occurrence of abnormal grain growth can be suppressed, and the coarsening of particles of the obtained sintered product can be suppressed.

[0132] During the process of raising the temperature to the sintering temperature, the temperature may be maintained in a temperature range from the melting point of the lithium compound to the sintering temperature, for example, in a temperature range of 400° C. to 550° C., for about 1 hour to 5 hours. By maintaining the temperature in the above-mentioned temperature range, the reaction can be carried out particularly uniformly.

[0133] The sintering atmosphere is preferably an oxidizing atmosphere. The oxidizing atmosphere is not particularly limited, and an oxygen-containing gas atmosphere can be used, and for example, an atmosphere having an oxygen concentration of 18 volume % or more and 100 volume % or less is more preferable.

[0134] This is because the reaction between the lithium compound and the nickel-containing material is promoted by setting the oxygen concentration in the atmosphere during sintering to 18% by volume or more, thereby improving the crystallinity of the lithium nickel composite oxide.

[0135] In the case of an oxygen-containing gas atmosphere, as the gas constituting the atmosphere, for example, air, oxygen, a mixed gas of oxygen and an inert gas, or the like can be used.

[0136] When a mixed gas of oxygen and an inert gas as described above is used as the gas constituting the oxygen-containing gas atmosphere, for example, the oxygen concentration in the mixed gas preferably satisfies the above-described range.

[0137] In particular, the sintering step is preferably carried out in an oxygen-containing gas flow, more preferably in the atmosphere or an oxygen flow. In consideration of battery characteristics, it is further preferred that the sintering step be carried out in an oxygen flow.

[0138] The furnace used for sintering is not particularly limited as long as it can sinter the first raw material mixture in a specified atmosphere. From the perspective of maintaining a uniform atmosphere in the furnace, an electric furnace without gas generation is preferred. Either a batch type or a continuous type furnace can be used.

[0139] The method for producing a positive electrode active material according to the present embodiment may include a crushing step (first crushing step) of crushing the sintered material when particles of the sintered material are aggregated in the sintering step.

[0140] Here, crushing refers to the following operation, which is to apply mechanical energy to the agglomerates composed of multiple secondary particles generated by sintering necks between secondary particles during sintering, so as to separate the secondary particles and break up the agglomerates without destroying the secondary particles themselves. For example, a pin mill, hammer mill, pulverizer, etc. is used, and the crushing can be done to the extent that the secondary particles are not destroyed.

[0141] In addition, the manufacturing method of the sintered product prepared in the sintering step is not limited to the above method. For example, it can also be prepared by the following methods: a method of spraying pyrolysis treatment on a liquid mixed with all aqueous solutions containing the desired metal elements, a method of pulverizing all compounds of the desired elements by mechanical pulverization such as a ball mill, and then sintering.

[0142] (3) Washing process

[0143] In the water washing step, the sintered product obtained in the sintering step can be washed with water to obtain a water-washed powder. In the water washing step, the sintered product obtained in the sintering step can be mixed with water and washed with water as a slurry (slurrying step). There is no particular limitation on the slurry concentration when washing the sintered product, and for example, it can be 200 g / L or more and 5000 g / L or less. By making the slurry concentration 5000 g / L or less, the slurry can be easily stirred and the dissolution rate of the attached matter can be increased.

[0144] On the other hand, by making the slurry concentration be more than 200g / L, the separation of lithium from the lattice of the sintered product can be prevented, and the collapse of crystallization can be suppressed. In addition, by making the slurry concentration be below 5000g / L, the re-precipitation of lithium carbonate caused by the high pH aqueous solution absorbing the carbon dioxide in the atmosphere can be prevented.

[0145] The water washing can be performed by controlling the temperature of the slurry to be in the range of 10°C to 40°C and making the conductivity of the liquid portion of the slurry to be in the range of 30 mS / cm to 90 mS / cm.

[0146] By setting the electrical conductivity of the slurry prepared in the water washing step to be within the above range, the excess components such as excess lithium adhering to the surface of the particles of the sintered product can be selectively and sufficiently reduced.

[0147] The water used in the water washing step is not particularly limited, and for example, water having an electrical conductivity of less than 10 μS / cm, preferably 1 μS / cm or less can be used.

[0148] There is no particular limitation on the water washing time, but it may be, for example, 3 minutes to 2 hours in order to sufficiently remove the excess components attached to the surface of the particles of the sintered product and to improve productivity.

[0149] In the water washing step, the slurry can be separated into solid and liquid after slurrying, that is, filtered and dehydrated to obtain a water-washed powder (solid-liquid separation step). Filtration and dehydration are not particularly limited, and for example, a filter press type solid-liquid separation device can be used.

[0150] In the water washing step, the water-containing water washing powder obtained after solid-liquid separation is preferably dried before being provided to the boron adding step. Therefore, the water washing powder may be dried (drying step). The drying conditions are not particularly limited.

[0151] Drying is preferably carried out in an oxidizing atmosphere or a vacuum atmosphere at a temperature of 100° C. to 250° C. or less. By setting the drying temperature to 100° C. or more, the water in the water-washed powder can be fully evaporated. In addition, by setting the drying temperature to 250° C. or less, the energy required for drying can be suppressed, and the cost can be reduced.

[0152] In order to avoid the reaction between the moisture and carbon dioxide in the atmosphere and the washing powder, the atmosphere during drying is preferably an atmosphere that suppresses or does not contain water vapor and carbon dioxide. Specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. In addition, from the viewpoint of quickly exhausting the water vapor generated by drying, it is preferred to add an exhaust mechanism to the drying device.

[0153] There is no particular restriction on the drying time, but it is preferably 0.5 hours or more and 48 hours or less. By making the drying time, i.e. the holding time of the highest reaching temperature during drying, be 0.5 hours or more, the moisture in the water-washed powder can be fully reduced and removed. In addition, by making the drying time be 48 hours or less, productivity can be improved.

[0154] (4) Boron Addition Process

[0155] In the boron adding step, the water-washed powder and the boron-containing material are mixed to prepare a second raw material mixture.

[0156] The boron-containing substance to be added is not particularly limited, and may be, for example, a boron monomer or a boron-containing compound containing boron. That is, the boron-containing substance is preferably at least one selected from a boron monomer and a boron-containing compound. As the boron-containing compound, components other than boron are preferably components that can be discharged outside the system in the heat treatment step described later, and for example, orthoboric acid (H 3 BO 3 ), boron oxide (B 2 O 3 ), boron nitride (BN) and other components other than B are one or more compounds selected from hydrogen, oxygen and nitrogen.

[0157] The mixing ratio of the water-washed powder and the boron-containing substance is not particularly limited, and the mixing ratio can be selected by conducting preliminary tests or the like so that the lithium nickel composite oxide obtained after the heat treatment has a target composition.

[0158] Here, the composition of the lithium nickel composite oxide obtained after heat treatment generally maintains the composition of the second raw material mixture. Therefore, the second raw material mixture is preferably prepared so that the composition of the second raw material mixture is the same as the composition of the target lithium nickel composite oxide.

[0159] Here, in the subsequent heat treatment process, in order to make the boron and the washed powder react evenly, the added boron-containing material is preferably finely crushed. Specifically, the average diameter of the long axis of the secondary particles of the boron-containing material observed in the surface SEM image is preferably more than 0.1μm and less than 100μm. The average diameter in the long axis is calculated as follows: arbitrarily extract more than 30 secondary particles of the boron-containing material observed by the surface SEM image, and take the average value of the particle size in the long axis measured for each secondary particle. In addition, there is no particular limit on the upper limit of the number of secondary particles for measuring the particle size in the long axis. From the perspective of suppressing the time required for evaluation, it is preferably less than 100.

[0160] The device and method for mixing the water-washed 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 blender or a mixing granulator can be used.

[0161] Here, in order to avoid water-washed powder etc. and moisture, carbon dioxide reaction in the atmosphere, the container during mixing is preferably cleaned with inert gas. In addition, in order to suppress the inhomogenization caused by the agglomeration of boron-containing material, preferably after the boron-containing material mixes, the 2nd raw material mixture is sieved several times, untie agglomeration.

[0162] (5) Heat treatment process

[0163] In the heat treatment step, the second raw material mixture may be heat treated.

[0164] It is considered that the heat treatment step promotes the production of a lithium-boron containing compound caused by the reaction between boron and the lithium component attached to the surface of the water-washed powder.

[0165] In the heat treatment step, the heat treatment temperature of the second raw material mixture is not particularly limited and can be selected according to the added boron-containing material, etc. In the heat treatment step, for example, the heat treatment is preferably performed at 200°C to 500°C, and more preferably at 200°C to 400°C.

[0166] By setting the heat treatment temperature to 200° C. or higher, the reaction between the boron and lithium components can be sufficiently advanced.

[0167] Furthermore, by setting the heat treatment temperature to 500° C. or lower, it is possible to prevent boron and lithium components from scattering in the atmosphere before reacting.

[0168] The atmosphere during the heat treatment in the heat treatment step is not particularly limited, and the heat treatment may be performed, for example, in an oxidizing atmosphere or an inert gas atmosphere.

[0169] The oxidizing atmosphere is not particularly limited, and an oxygen-containing gas atmosphere can be used. For example, an atmosphere having an oxygen concentration of 18 volume % to 100 volume % is preferred.

[0170] In the case of an oxygen-containing gas atmosphere, as the gas constituting the atmosphere, for example, air, oxygen, a mixed gas of oxygen and an inert gas, or the like can be used.

[0171] The heat treatment step is preferably performed in an atmosphere such as a decarbonated atmosphere in which the carbon dioxide concentration is suppressed. Therefore, it is preferable that the carbon dioxide concentration is suppressed, for example, in the above-mentioned oxidizing atmosphere or inert gas atmosphere.

[0172] The carbon dioxide concentration in the heat treatment atmosphere is not particularly limited, and the carbon dioxide concentration can be reduced compared to the usual atmosphere. Therefore, the carbon dioxide concentration in the heat treatment atmosphere is preferably less than 0.03 volume %, more preferably below 0.02 volume %, further preferably below 0.01 volume %, and particularly preferably below 0.008 volume %.

[0173] By performing heat treatment in an atmosphere with a suppressed carbon dioxide concentration, the generation of carbon-containing compounds such as lithium carbonate can be suppressed, thereby suppressing the above-mentioned C content ratio and increasing the B content ratio relative to the C content ratio. After the heat treatment, it is preferred that the atmosphere with a suppressed carbon dioxide concentration is also used during cooling.

[0174] In addition, the furnace used for heat treatment is not particularly limited. The second raw material mixture can be heat treated in a specified atmosphere. From the perspective of maintaining a uniform atmosphere in the furnace, an electric furnace without gas generation is preferred. Batch or continuous furnaces can be used.

[0175] The method for producing the positive electrode active material of this embodiment may also include a crushing step (second crushing step) of crushing the lithium nickel composite oxide when agglomeration occurs in the particles of the lithium nickel composite oxide after the heat treatment step. The crushing can be carried out in the same manner as in the first crushing step described above, and thus the description thereof is omitted.

[0176] [Lithium-ion secondary battery]

[0177] The lithium ion secondary battery (hereinafter also referred to as “secondary battery”) of this embodiment includes at least a positive electrode, a negative electrode, and a non-aqueous electrolyte, and the positive electrode may contain the above-mentioned positive electrode active material for lithium ion secondary batteries.

[0178] Hereinafter, each structural element will be described separately with respect to an example of a configuration of a secondary battery of the present embodiment. The secondary battery of the present embodiment, for example, contains a positive electrode, a negative electrode and a non-aqueous electrolyte, and is composed of the same structural elements as a general lithium-ion secondary battery. In addition, the embodiments described below are only examples, and the lithium-ion secondary battery of the present embodiment can be implemented starting with the following embodiments, based on the knowledge of practitioners, in various modified and improved forms. In addition, the use of the secondary battery is not particularly limited.

[0179] (positive electrode)

[0180] The positive electrode included in the secondary battery of this embodiment may contain the above-mentioned positive electrode active material.

[0181] An example of a method for manufacturing a positive electrode is described below: First, the positive electrode active material (powder), conductive material and binder (adhesive) mentioned above can be mixed into a positive electrode composite material, and activated carbon, a solvent for viscosity adjustment, etc. can be added as needed, and the mixture is kneaded to prepare a positive electrode composite slurry.

[0182] The mixing ratio of each material in the positive electrode composite material can be adjusted according to the application because it is a component that determines the performance of the lithium ion secondary battery. The mixing ratio of the materials can be the same as that of the positive electrode of the 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 mass%, it can be in accordance with the following ratios: 60 mass% to 95 mass% of the positive electrode active material, 1 mass% to 20 mass% of the conductive material, and 1 mass% to 20 mass% of the binder.

[0183] The obtained positive electrode composite slurry is applied to the surface of a current collector such as aluminum foil, dried, and the solvent is dispersed to produce a sheet-like positive electrode. If necessary, in order to increase the electrode density, pressure can also be applied by roller pressing or the like. The sheet-like positive electrode obtained in this way can be cut into appropriate sizes according to the target battery, and provided for the production of the battery.

[0184] As the conductive material, for example, graphite (natural graphite, artificial graphite, expanded graphite, etc.), acetylene black, Ketjen Black (registered trademark), and other carbon black materials can be used.

[0185] As a binder (adhesive), the function of connecting and fixing the active material particles is achieved, and therefore, for example, one or more selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose resin and polyacrylic acid can be used.

[0186] As required, the positive electrode active material, the conductive material, etc. are dispersed, and a solvent for dissolving the binder can also be added to the positive electrode composite material. As the solvent, specifically, 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 double electric layer capacitance.

[0187] The method for producing the positive electrode is not limited to the above example, and other methods may be used. For example, the positive electrode composite material may be pressed into a shape and then dried in a vacuum atmosphere.

[0188] (negative electrode)

[0189] The negative electrode can use metallic lithium, lithium alloy, etc. In addition, the negative electrode can be formed by mixing a negative electrode active material that can adsorb and desorb lithium ions with a binder, adding an appropriate solvent to make it into a slurry, applying the negative electrode composite material to the surface of a metal foil current collector such as copper, drying, and compressing as needed to increase the electrode density.

[0190] As the negative electrode active material, for example, a sintered body of an organic compound such as natural graphite, artificial graphite, and phenol resin, and a powder of a carbon material such as coke can be used. At this time, as the negative electrode binder, a fluorine-containing resin such as PVDF can be used as the positive electrode, and as a solvent for dispersing these active materials and the binder, an organic solvent such as N-methyl-2-pyrrolidone can be used.

[0191] (Diaphragm)

[0192] A separator may be interposed between the positive electrode and the negative electrode as required. The separator separates the positive electrode and the negative electrode and retains the electrolyte. A known film such as polyethylene, polypropylene, etc. having a large number of micropores can be used.

[0193] (Non-aqueous electrolyte)

[0194] As the nonaqueous electrolyte, for example, a nonaqueous electrolytic solution can be used.

[0195] As the non-aqueous electrolyte, for example, a lithium salt as a supporting salt dissolved in an organic solvent can be used. In addition, as the non-aqueous electrolyte, an ionic liquid in which a lithium salt is dissolved can be used. In addition, an ionic liquid refers to a salt that is composed of cations and anions other than lithium ions and is also liquid at room temperature.

[0196] 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 selected from the group consisting of these can be used in combination.

[0197] As supporting salt, LiPF can be used 6 , LiBF 4 、LiClO 4 、LiAsF 6 、LiN(CF 3 SO 2 ) 2 and complex salts thereof, etc. Furthermore, the non-aqueous electrolyte may contain a radical scavenger, a surfactant, a flame retardant, and the like.

[0198] In addition, as the non-aqueous electrolyte, a solid electrolyte can be used. Solid electrolytes have the property of being able to withstand high voltages. Examples of solid electrolytes include inorganic solid electrolytes and organic solid electrolytes.

[0199] Examples of the inorganic solid electrolyte include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0200] The oxide-based solid electrolyte is not particularly limited, and for example, an oxide-based solid electrolyte containing oxygen (O) and having lithium ion conductivity and electronic insulation can be appropriately used. As the oxide-based solid electrolyte, for example, 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 OB 2 O 3 -P 2 O 5 , Li 2 O-SiO 2 , Li 2 OB 2 O 3 -ZnO, Li 1+X Al X Ti 2-X (PO 4 ) 3 (0≤X≤1), Li 1+ X Al X Ge 2-X (PO 4 ) 3 (0≤X≤1), LiTi 2 (PO 4 ) 3 , Li 3X La 2 / 3-X TiO 3 (0≤X≤2 / 3), Li 5 La 3 Ta 2 O 12 , Li 7 La 3 Zr 2 O 12 , Li 6 BaLa 2Ta 2 O 12 , Li 3.6 Si 0.6 P 0.4 O 4 One or more selected from the group consisting of

[0201] The sulfide-based solid electrolyte is not particularly limited, and for example, a sulfide-based solid electrolyte containing sulfur (S) and having lithium ion conductivity and electronic insulation can be appropriately used. 2 SP 2 S 5 , Li 2 S-SiS 2 、LiI-Li 2 S-SiS 2 、LiI-Li 2 SP 2 S 5 、LiI-Li 2 SB 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 SP 2 O 5 、LiI-Li 3 PO 4 -P 2 S 5 One or more selected from the group consisting of

[0202] In addition, as the inorganic solid electrolyte, other than the above, for example, Li 3 N, LiI, Li 3 N-LiI-LiOH, etc.

[0203] The organic solid electrolyte is not particularly limited as long as it is a polymer compound showing ion conductivity, and for example, polyethylene oxide, polypropylene oxide, copolymers thereof, etc. can be used. In addition, the organic solid electrolyte may contain a supporting salt (lithium salt).

[0204] (Shape and structure of secondary battery)

[0205] The lithium-ion secondary battery of the present embodiment as described above can be in various shapes such as cylindrical and laminated. When any shape is adopted, the secondary battery of the present embodiment can be constructed as follows when a non-aqueous electrolyte is used as a non-aqueous electrolyte, wherein the positive electrode and the negative electrode are laminated into an electrode body via a diaphragm, the obtained electrode body is impregnated with a non-aqueous electrolyte, and the positive electrode current collector and the positive terminal connected to the outside, and the negative electrode current collector and the negative terminal connected to the outside are connected using a collector lead, etc., so that they are sealed in a battery case.

[0206] In addition, as described above, the secondary battery of this embodiment is not limited to the form of using a non-aqueous electrolyte as a non-aqueous electrolyte, and can also be a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery. In the case of an all-solid-state battery, the composition other than the positive electrode active material can be changed as needed.

[0207] The secondary battery of this embodiment can be used for various purposes. Since the secondary battery of this embodiment can be a high-capacity, high-output secondary battery, it is suitable for power supply of small portable electronic devices (laptop computers, mobile phone terminals, etc.) that often require high capacity, and is also suitable for power supply of electric vehicles that require high output.

[0208] In addition, the secondary battery of this embodiment is suitable as a power source for electric vehicles with limited carrying space because it can be miniaturized and have high output. In addition, the secondary battery of this embodiment can be used not only as a power source for electric vehicles driven by pure electric energy, but also as a power source for so-called hybrid vehicles used in conjunction with combustion mechanisms such as gasoline engines and diesel engines.

[0209] [Example]

[0210] Hereinafter, the present invention will be further described in detail by way of examples, but the present invention is not limited by these examples.

[0211] First, the positive electrode active materials obtained in the following Examples and Comparative Examples and the evaluation method of the secondary batteries will be described.

[0212] (Evaluation of positive electrode active material)

[0213] The following evaluations were performed on the obtained positive electrode active material.

[0214] (a) Evaluation of composition, crystal structure, and particle structure

[0215] The composition was analyzed using an ICP emission spectrometer (manufactured by Shimadzu Corporation, ICPE-9000).

[0216] In addition, the obtained positive electrode active material was measured by powder X-ray diffraction pattern, and the crystal structure was determined by Rietveld layer analysis, etc. As a result, it can be confirmed that the positive electrode active materials prepared 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.

[0217] Furthermore, regarding the positive electrode active material, when the particles were observed using a scanning electron microscope, it was confirmed that the positive electrode active materials prepared in the following Examples and Comparative Examples included secondary particles in which a plurality of primary particles were aggregated.

[0218] (b) Proportion of B and proportion of C

[0219] An XPS apparatus (Versa Probe II manufactured by Ulvac-phi) was used, with Al-Kα rays monochromatized by a monochromator as the irradiation X-ray source, at 1.0×10 -6 The photoelectron spectrum of the positive electrode active material was measured in a vacuum atmosphere of 10 Å or less.

[0220] Then, the amount ratio of lithium, nickel, boron, element M, and carbon is calculated from the peak area of ​​the obtained photoelectron spectrum, and the B content ratio, C content ratio, and the ratio of the B content ratio to the C content ratio are calculated by the above-mentioned formulas (1) to (3). When calculating the amount ratio of each element, the peak of the measured XPS photoelectron spectrum is separated, and the peak with the highest intensity is used for each element.

[0221] (c) Titration curve

[0222] 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 filtrate after filtration was neutralized and titrated with 1.0 M HCl to measure a titration curve. In addition, distilled water was used as pure water.

[0223] From the obtained titration curve, the amount of HCl added in each pH range shown in the column "Neutralization titration HCl added amount" in Table 1 was determined. In addition, VR, which is the HCl added amount ratio, was calculated using the above formula (4).

[0224] (d) Particle size distribution index

[0225] The volume-based particle size distribution was measured using a laser diffraction scattering particle size distribution measuring apparatus (Microtrac MT3300EXII, manufactured by Microtrac BEL Co., Ltd.) and D10, D90, and volume average particle size Mv were calculated from the particle size distribution.

[0226] Then, [(D90-D10) / volume average particle size Mv] was calculated as a particle size distribution index.

[0227] (Evaluation of battery characteristics)

[0228] (a) Reaction resistance

[0229] The button-type batteries prepared in the following examples and comparative examples were charged at a charging potential of 4.1 V, and the resistance was measured by the AC impedance method using a frequency response analyzer and a constant potential-constant current instrument (Solartron, 1255B). When the relationship between the measured structure and frequency was plotted, Figure 2A Nyquist plot shown.

[0230] The above Nyquist diagram represents the sum of the characteristic curves representing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity. Figure 2B As shown, a fitting calculation is performed using an equivalent circuit based on the Nyquist diagram to calculate the value of the positive electrode resistance, and the calculated positive electrode resistance is used as the reaction resistance.

[0231] [Example 1]

[0232] (1) Production of positive electrode active material

[0233] (1-1) Mixing process

[0234] (Nickel-containing)

[0235] First, the following nickel composite oxide was prepared: a nickel composite hydroxide prepared by a neutralization crystallization method was oxidatively calcined at 600° C. for 3 hours in an air atmosphere. The nickel composite oxide was a Ni composite oxide having a molar ratio of Ni:Mn:Co of 85:10:5. 0.85 Mn 0.10 Co 0.05 O.

[0236] Then, the nickel composite oxide and TiO 2 A mixture of nickel composite oxide and TiO 2 The mixing ratio of Ni, Mn, Co and Ti is Ni:Mn:Co:Ti=0.829:0.098:0.049:0.024.

[0237] (Lithium compounds)

[0238] As the lithium compound, lithium hydroxide was used. In addition, as the lithium hydroxide, lithium hydroxide anhydrate was used.

[0239] The nickel-containing material and lithium hydroxide were weighed and mixed so that Li / (Ni+Mn+Co+Ti) was 1.02, thereby obtaining a first raw material mixture.

[0240] (1-2) Sintering process

[0241] The obtained first raw material mixture was heated to 840°C in an electric furnace under an oxygen atmosphere, and kept at 840°C for 2 hours for sintering. Then, it was cooled to room temperature in the furnace. The obtained sintered product was crushed.

[0242] (1-3) Washing process

[0243] Next, pure water at 20° C. was added to the obtained sintered product to obtain a slurry containing 1250 g of the sintered product per 1 L of water (slurrying step), and the slurry was stirred for 20 minutes and then filtered through a filter press to dehydrate the slurry, thereby preparing a washed filter cake containing water-washed powder (solid-liquid separation step). In addition, as pure water, water with an electrical conductivity of 1 μS / cm or less was used.

[0244] The obtained washed cake was dried at 190° C. for 10 hours in a vacuum atmosphere to obtain a water-washed powder (drying step).

[0245] (1-4) Boron Addition Process

[0246] The water-washed powder and orthoboric acid (H 3 BO 3 ) were mixed to prepare a second raw material mixture. Here, 40 secondary particles of orthoboric acid observed by surface SEM were randomly extracted, and the average diameter in the long axis direction was calculated to be 3 μm.

[0247] The washed powder and orthoboric acid are put into a mixing container in the following manner. After the heat treatment step, the lithium nickel composite oxide obtained contains the following elements in a ratio as shown in Table 1:

[0248] Li:Ni:Mn:Co:Ti:B=1.00:0.825:0.097:0.049:0.024:0.005, and the container is filled with N 2 After gas cleaning, the mixture was mixed and then sieved three times to release the agglomeration of orthoboric acid.

[0249] (1-5) Heat treatment process

[0250] In the heat treatment step, the second raw material mixture is heat treated at 306° C. for 10 hours in an atmosphere subjected to a decarbonation treatment. In addition, as the decarbonation atmosphere, air having a carbon dioxide concentration of 0.01% by volume or less is used by decarbonation treatment. After heat treatment at the above heat treatment temperature, the mixture is cooled to room temperature in an atmosphere subjected to a similar decarbonation treatment.

[0251] The above-mentioned evaluation was performed on the obtained lithium nickel composite oxide as the positive electrode active material. The evaluation results are shown in Table 1.

[0252] (2) Production of secondary batteries

[0253] By following the steps below, Figure 1 The button-type battery having the structure shown was subjected to the above-mentioned evaluation. The evaluation results are shown in Table 1.

[0254] like Figure 1 As shown, the button-type battery 10 is a lithium ion secondary battery, which includes a positive electrode 11, a negative electrode 12, a separator 13, a gasket 14, a corrugated gasket 15, a positive electrode case 16, and a negative electrode case 17. The positive electrode 11, the negative electrode 12, and the separator 13 are impregnated with an electrolyte.

[0255] The button-type battery 10 is configured such that the positive electrode 11, the separator 13, the negative electrode 12 and the corrugated gasket 15 are stacked in order from the positive electrode case 16 to the negative electrode case 17. The positive electrode 11 contacts the inner surface of the positive electrode case 16, and the negative electrode 12 contacts the inner surface of the negative electrode case 17 via the corrugated gasket 15.

[0256] The positive electrode case 16 and the negative electrode case 17 each have a hollow structure with one end open, and the negative electrode case 17 is arranged on the opening of the positive electrode case 16. The button-type battery 10 accommodates the positive electrode 11, the negative electrode 12, the separator 13, the gasket 14, and the corrugated gasket 15 between the positive electrode case 16 and the negative electrode case 17 by arranging the negative electrode case 17 on the opening of the positive electrode case 16.

[0257] In addition, the gasket 14 is disposed between the positive electrode case 16 and the negative electrode case 17. The positive electrode case 16 and the negative electrode case 17 are fixed by the gasket 14 in a manner that the positive electrode case 16 and the negative electrode case 17 are kept in a non-contact state, that is, in an electrically insulated state, and the relative movement is restricted. In addition, the gasket 14 also has the function of sealing the gap between the positive electrode case 16 and the negative electrode case 17, and blocking the inside and outside of the button-type battery 10 in an airtight and liquid-tight manner.

[0258] The button-type battery 10 is manufactured as follows.

[0259] First, 52.5 mg of the prepared positive electrode active material, 15 mg of acetylene black and 7.5 mg of polytetrafluoroethylene (PTFE) were mixed and pressed into a diameter of 11 mm and a thickness of 100 μm at a pressure of 100 MPa to prepare a Figure 1 The positive electrode 11 is shown. Then, the produced positive electrode 11 was dried in a vacuum dryer at 120° C. for 12 hours.

[0260] After the positive electrode 11, the negative electrode 12 and the separator 13 were impregnated with the electrolyte, the button-type battery 10 was manufactured in a glove box with an Ar atmosphere and a dew point of -80°C. The manufactured positive electrode 11, the separator 13, the negative electrode 12 and the corrugated gasket 15 were stacked in order on the positive electrode case 16. Next, the negative electrode 12 was brought into contact with the inner surface of the negative electrode case 17 via the corrugated gasket 15, and the negative electrode case 17 was covered on the opening of the positive electrode case 16, thereby assembling the button-type battery 10.

[0261] The negative electrode 12 used a negative electrode sheet punched into a disk shape with a diameter of 14 mm. In the negative electrode sheet, graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride were coated on a copper foil.

[0262] As the separator 13 , a polyethylene porous film having a thickness of 25 μm was used.

[0263] The electrolyte used was 1M LiPF 6 The supporting electrolyte was an equal volume mixed solution of ethylene carbonate (EC) and diethyl carbonate (DEC) at a mixing ratio of 1:1 on a volume basis (manufactured by Toyama Pharmaceutical Industry Co., Ltd.).

[0264] The above-mentioned evaluation was performed on the button-type battery 10 as the obtained lithium ion secondary battery. The evaluation results are shown in Table 1.

[0265] [Example 2 to Example 4]

[0266] In the boron addition step, the water-washed powder and orthoboric acid are mixed in the following manner so that the ratio of the amount of Li, Ni, Mn, Co, Ti, and B contained in the lithium nickel composite oxide obtained after the heat treatment step is the value shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery are manufactured under the same conditions as in Example 1 and evaluated. The evaluation results are shown in Table 1.

[0267] [Example 5, Example 6]

[0268] In the heat treatment step, the heat treatment temperature was changed to the temperature shown in Table 1. The same conditions as in Example 2 were used to produce a positive electrode active material and a lithium ion secondary battery, and the evaluation was performed. The evaluation results are shown in Table 1.

[0269] [Example 7, Example 8]

[0270] No TiO is added during the mixing process 2 , the temperature raised and maintained in the sintering process was 820°C. In addition, in Example 8, the heat treatment temperature in the heat treatment process was changed to the temperature shown in Table 1. Except for the above points, the positive electrode active material and the lithium ion secondary battery were manufactured and evaluated under the same conditions as in Example 2. The evaluation results are shown in Table 1.

[0271] [Comparative Example 1]

[0272] The heat treatment step was carried out in an air atmosphere without decarbonation treatment. The positive electrode active material and lithium ion secondary battery were manufactured and evaluated under the same conditions as in Example 2, except that the heat treatment step was carried out in an air atmosphere without decarbonation treatment. In addition, the concentration of carbon dioxide in the air atmosphere without decarbonation treatment was higher than 0.03% by volume. The evaluation results are shown in Table 1.

[0273] [Comparative Example 2]

[0274] The washed powder obtained by drying in the washing process is used as the positive electrode active material. That is, when manufacturing the positive electrode active material, the process after the boron addition process is not implemented. 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. In addition, no boron is added in Comparative Example 2, so the ratio of the B content to the C content is 0.

[0275]

Table 1

[0276]

[0277] From the results shown in Table 1, it was confirmed that the positive electrode active materials of Examples 1 to 8 in which the ratio of the B content ratio to the C content ratio was 0.8 to 30.0 could reduce the reaction resistance.

[0278] This application claims the priority based on Japanese Patent Application No. 2022-175165 applied for on October 31, 2022, and all the contents of Japanese Patent Application No. 2022-175165 are cited as the present invention.

[0279] [Reference Signs]

[0280] 10Button type battery (lithium ion secondary battery)

[0281] 11 Positive electrode

[0282] 12 Negative electrode

[0283] 13 Diaphragm

[0284] 14 Gasket

[0285] 15 Corrugated gasket

[0286] 16. Positive electrode shell

[0287] 17 Negative electrode shell

Claims

1. A positive electrode active material for a lithium ion secondary battery, wherein, it contains a lithium nickel composite oxide, the lithium nickel composite oxide has a layered structure of a hexagonal crystal system, and includes secondary particles formed by aggregation of a plurality of primary particles, the lithium nickel composite oxide contains lithium Li, nickel Ni, boron B, and an element M represented by M in the following proportions. In terms of the molar ratio, Li:Ni:B:M = a:b:c:d, where 0.95 ≤ a ≤ 1.10, 0.50 ≤ b < 1.00, 0.00 < c ≤ 0.03, 0.00 ≤ d ≤ 0.47, and b + c + d = 1. 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, when the total amount of the substances of lithium, nickel, boron, the element M, and carbon in the surface calculated from the XPS measurement results of the positive electrode active material for the lithium ion secondary battery is the total amount of substances, and the ratio of the amount of carbon to the total amount of substances is the C content ratio, and the ratio of the amount of boron to the total amount of substances is the B content ratio, the ratio of the B content ratio to the C content ratio is 0.8 or more and 30.0 or less.

2. The positive electrode active material for a lithium ion secondary battery according to claim 1. In the titration curve obtained by stirring 10 g of the positive electrode active material for the lithium ion secondary battery in 50 mL of pure water for 5 minutes and then neutralizing and titrating the filtered filtrate with 1.0 M HCl, 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 0.5 or less.

3. The positive electrode active material for a lithium ion secondary battery according to claim 1 or 2, wherein the C content ratio is 30% or less.

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

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

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