Positive electrode active material for lithium ion secondary batteries, lithium ion secondary batteries

Abstract

To provide a positive electrode active material for a lithium ion secondary battery, in which the reaction resistance can be reduced when used for a lithium ion secondary battery.SOLUTION: A positive electrode active material has a hexagonal crystal layer structure and contains a lithium nickel complex oxide including a secondary particle in which a plurality of primary particles are aggregated. The lithium nickel complex oxide contains in the following ratio of the amount of substance: Li:Ni:Ti:B:M=a:b:c:d:e (0.95≤a≤1.10, 0.50≤b<1.00, 0.00<c≤0.05, 0.00<d≤0.03, 0.00≤e≤0.47, and b+c+d+e=1). In an XRD pattern of the positive electrode active material, the ratio of the total amount of peak intensities of the strongest line of a titanium compound to the diffraction peak intensity of (003)-plane is 0.2 or less. The ratio of the B content to the C content, which is calculated from the XPS measurement results about the positive electrode active material, is 0.8 or more and 30.0 or less.SELECTED DRAWING: None

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 technology]

[0002] In recent years, with the widespread use of portable electronic devices such as mobile phones and laptop computers, there has been a strong demand for the development of small, lightweight secondary batteries with high energy density and durability. There is also a strong demand for high-power secondary batteries for use in power tools and electric vehicles, including hybrid vehicles. Furthermore, in addition to the required characteristics, there is a growing demand for secondary batteries that are highly durable and do not deteriorate even with repeated use.

[0003] Lithium-ion secondary batteries are a type of secondary battery that meets these requirements. Lithium-ion secondary batteries are composed of a negative electrode, a positive electrode, an electrolyte, etc., and materials capable of desorbing and inserting lithium are used as the active materials for the negative electrode and the positive electrode. As described above, lithium-ion secondary batteries have high energy density, output characteristics, and durability.

[0004] Research and development into lithium-ion secondary batteries is currently underway, and among these, lithium-ion secondary batteries that use layered or spinel-type lithium metal composite oxides as the positive electrode material are capable of achieving high voltages of around 4V, and are therefore being put into practical use as batteries with high energy density.

[0005] Positive electrode materials for lithium-ion secondary batteries include lithium cobalt composite oxide (LiCoO2), which is relatively easy to synthesize, lithium nickel composite oxide (LiNiO2), which uses nickel, which is cheaper than cobalt, and lithium nickel cobalt manganese composite oxide (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2), lithium manganese composite oxide (LiMn2O4), lithium nickel manganese composite oxide (LiNi 0.5 Mn0.5 Lithium metal composite oxides such as SiO2 have been proposed.

[0006] In recent years, there has been a demand for further improvements in the battery characteristics of lithium ion secondary batteries, and studies are underway to improve, for example, cycle characteristics (see, for example, Patent Document 1) and to increase power output. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-189320 Summary of the Invention [Problem to be solved by the invention]

[0008] In recent years, there has been a demand for positive electrode active materials for lithium ion secondary batteries that can reduce reaction resistance when used in lithium ion secondary batteries.

[0009] In view of the problems of the above-described conventional techniques, an object of one aspect of the present invention is to provide a positive electrode active material for a lithium ion secondary battery that can reduce reaction resistance when used in a lithium ion secondary battery. [Means for solving the problem]

[0010] In order to solve the above problem, according to one aspect of the present invention, A positive electrode active material for a lithium ion secondary battery containing a lithium nickel composite oxide having a hexagonal layer structure and including secondary particles formed by aggregation of a plurality of primary particles, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), titanium (Ti), boron (B), and element M (M) in a molar ratio of Li:Ni:Ti:B:M = a:b:c:d:e (where 0.95 ≤ a ≤ 1.10, 0.50 ≤ b < 1.00, 0.00 < c ≤ 0.05, 0.00 < d ≤ 0.03, 0.00 ≤ e ≤ 0.47, b + c + d + e = 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, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al). In the XRD pattern of the positive electrode active material for the lithium ion secondary battery, the ratio of the total peak intensity of the strongest lines of the titanium compound to the diffraction peak intensity of the (003) plane, which is the strongest line of the hexagonal layered structure, is 0.2 or less. When the ratio of the amount of carbon to the total amount of substances of lithium, nickel, titanium, boron, the element M, and carbon on the surface, calculated from the XPS measurement results of the positive electrode active material for the lithium ion secondary battery, is defined as the C content ratio, and the ratio of the amount of boron to the total amount of substances is defined as the B content ratio. There is provided a positive electrode active material for a lithium ion secondary battery in which the ratio of the B content ratio to the C content ratio is 0.8 or more and 30.0 or less.

Advantages of the Invention

[0011] According to one aspect of the present invention, there can be provided a positive electrode active material for a lithium ion secondary battery that can reduce the reaction resistance when used in a lithium ion secondary battery.

Brief Description of the Drawings

[0012] [Figure 1] FIG. 1 is an explanatory view of coin-type batteries fabricated in Examples and Comparative Examples. [Figure 2] FIG. 2 is a schematic explanatory view of an equivalent circuit used for measurement and analysis of impedance evaluation.

Modes for Carrying Out the Invention

[0013] Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments, and various modifications and substitutions can be made to the following embodiments without departing from the scope of the present invention. [Positive electrode active material for lithium-ion secondary batteries]

[0014] The positive electrode active material for a lithium ion secondary battery (hereinafter also simply referred to as "positive electrode active material") of this embodiment will be described below. (1) Lithium-nickel composite oxide

[0015] 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 only of a lithium nickel composite oxide, but even in this case, it does not exclude the inclusion of inevitable impurities that are mixed in during the manufacturing process, etc. (1-1) Composition

[0016] The lithium nickel composite oxide can contain lithium (Li), nickel (Ni), titanium (Ti), and boron (B).

[0017] The lithium nickel composite oxide may contain elements other than lithium, nickel, titanium, and boron, and may also contain, for example, the element M described below.

[0018] The lithium nickel composite oxide preferably contains lithium (Li), nickel (Ni), titanium (Ti), boron (B), and element M (M) in a ratio of Li:Ni:Ti:B:M=a:b:c:d:e in terms of the ratio of the amounts of substances.

[0019] It is preferable that a, b, c, d, and e satisfy 0.95 ≦ a ≦ 1.10, 0.50 ≦ b < 1.00, 0.00 < c ≦ 0.05, 0.00 < d ≦ 0.03, 0.00 ≦ e ≦ 0.47, and b + c + d + e = 1. Further, the element M is preferably at least one element selected from the group consisting of Mn, Co, V, Mg, Mo, Ca, Cr, Zr, Ta, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al.

[0020] The lithium nickel composite oxide can be represented, for example, by the general formula: Li a Ni b Ti c B d M e O 2+α Since a, b, c, d, e, and the element M in the above general formula have been described above, the description is omitted here. α preferably satisfies, for example, -0.2 ≦ α ≦ 0.2. (Nickel (Ni))[[ID=I19]] In the lithium nickel composite oxide, the higher the nickel content ratio, the higher the capacity can be when used as the positive electrode material of a lithium ion secondary battery. [[ID=I21]] [[ID=I22]]

[0021] [[ID=I23]] Therefore, as described above, b indicating the nickel content ratio is preferably 0.50 or more, more preferably 0.60 or more, still more preferably 0.70 or more, and particularly preferably 0.80 or more.

[0022] The upper limit value of b indicating the nickel content ratio is preferably less than 1.00, more preferably 0.97 or less, as described above. (Titanium (Ti)) In a lithium ion secondary battery, for example, when a short circuit occurs between the positive electrode and the negative electrode, heat may be generated. When the lithium ion secondary battery generates heat, the positive electrode active material is also heated. When the thermal stability of the positive electrode active material is low, decomposition occurs from a low temperature and oxygen is released. It is also known that when the positive electrode active material decomposes, the positive electrode active material and its decomposition products react with the electrolyte and further generate heat.

[0023] In contrast, the lithium nickel composite oxide containing titanium can enhance the thermal stability of the positive electrode active material containing the lithium nickel composite oxide, thereby suppressing decomposition of the positive electrode active material and suppressing the release of oxygen and further heat generation in the lithium ion secondary battery even when the lithium ion secondary battery generates heat.

[0024] Therefore, c, which indicates the titanium content, is preferably greater than 0.00, more preferably greater than 0.02, and even more preferably 0.022 or greater.

[0025] As described above, the upper limit of c, which indicates the titanium content, is preferably 0.05 or less, and more preferably 0.04 or less. (Boron (B)) As described above, the lithium nickel composite oxide of this embodiment can contain boron. According to the studies of the present inventors, the lithium nickel composite oxide containing boron can reduce reaction resistance when used in a lithium ion secondary battery.

[0026] Although the exact mechanism by which the reaction resistance can be reduced is not clear, 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 particle surface of the lithium nickel composite oxide. Therefore, it is believed that the resistance associated with the insertion and desorption of lithium on the particle surface of the lithium nickel composite oxide is reduced, thereby reducing the reaction resistance.

[0027] As described above, d, which indicates the content ratio of boron, is preferably greater than 0.00, more preferably 0.001 or more, even more preferably 0.002 or more, and particularly preferably 0.003 or more.

[0028] The upper limit of d, which indicates the content of boron, is not particularly limited, but since it is believed that the effect will saturate even if an excessive amount is added, it is preferably 0.03 or less, more preferably 0.025 or less, and particularly preferably 0.02 or less. (Element M)

[0029] As described above, the lithium nickel composite oxide of this embodiment can also contain the element M as an optional component. The group of elements that can be suitably used as the element M has already been explained, and therefore further explanation will be omitted here. In particular, from the viewpoint of increasing the thermal stability of the lithium nickel composite oxide and, for example, suppressing thermal decomposition of the lithium nickel composite oxide, it is preferable that the element M contains at least one selected from at least cobalt (Co) and manganese (Mn).

[0030] Since element M is an optional component, e, which indicates the content ratio of element M, is preferably 0.00 or more, more preferably 0.05 or more, and even more preferably 0.10 or more, as described above.

[0031] The upper limit of e, which indicates the content ratio of element M, is preferably 0.47 or less, as described above, more preferably 0.25 or less, and even more preferably 0.20 or less.

[0032] When the lithium nickel composite oxide contains a plurality of types of element M, it is preferable that the total content of the plurality of types of element M falls within the above range.

[0033] The lithium nickel composite oxide also contains carbon, as will be described later. However, because the lithium nickel composite oxide contains a trace amount of carbon as an unavoidable impurity, the carbon is not expressed in the general formula of the lithium nickel composite oxide. (1-2) Crystal structure The lithium nickel composite oxide preferably has a hexagonal layered structure, which allows lithium to be easily inserted and extracted between the layers, thereby improving the output characteristics and cycle characteristics when used in a lithium ion secondary battery.

[0034] The crystal structure of the lithium nickel composite oxide can be confirmed by Rietveld analysis. (1-3) Particle morphology The lithium nickel composite oxide particles can contain secondary particles formed by aggregation of a plurality of primary particles.

[0035] The lithium nickel composite oxide may contain non-aggregated primary particles in addition to secondary particles, i.e., the lithium nickel composite oxide may contain both primary particles and secondary particles. (2) B content ratio and C content ratio

[0036] As described above, by including boron in the lithium nickel composite oxide, reaction resistance can be reduced when the lithium nickel composite oxide is used in a lithium ion secondary battery.

[0037] 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 particle surface of the lithium nickel composite oxide, which is believed to suppress the generation of impurities such as lithium carbonate that increase resistance on the particle surface of the lithium nickel composite oxide, thereby reducing the reaction resistance.

[0038] When XPS (X-ray Photoelectron Spectroscopy) measurement is performed on the positive electrode active material of this embodiment, the types and amounts of elements present in the surface layers of the lithium nickel composite oxide particles contained in the positive electrode active material can be evaluated.

[0039] From the viewpoint of enhancing the effect of reducing the reaction resistance, when XPS measurement is performed on the positive electrode active material of the present embodiment, it is preferable 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.

[0040] Here, the ratio of the amount of substance of carbon (C) to the total amount of substance, which is the total amount of substance of lithium (Li), nickel (Ni), titanium (Ti), boron (B), element M, and carbon (C) on the surface, calculated from the XPS measurement results of the positive electrode active material of this embodiment, is referred to as the C content. Also, the ratio of the amount of substance of boron (B) to the total amount of substance, calculated from the XPS measurement results of the positive electrode active material of this embodiment, is referred to as the B content.

[0041] In the above case, the ratio of the B content to the C content is preferably 0.8 or more, more preferably 1.0 or more, even more preferably 2.0 or more, and particularly preferably 2.5 or more.

[0042] By setting the ratio of the B content to the C content at 0.8 or more, it is believed that the proportion of components that cause an increase in resistance, such as lithium carbonate, is suppressed and the proportion of compounds containing boron that contribute to lowering resistance is increased, which can particularly reduce reaction resistance when used in lithium-ion secondary batteries.

[0043] However, excessively increasing the ratio of the B content to the C content requires increasing the boron content in the lithium nickel composite oxide and suppressing the contents of other elements such as nickel, titanium, and element M. Furthermore, in order to suppress the incorporation of lithium carbonate and the like, it becomes necessary to perform long-term water washing and precise control of the atmosphere during heat treatment, which can lead to deterioration of battery characteristics and increased costs.

[0044] Therefore, the ratio of the B content to the C content is preferably 30.0 or less, more preferably 15.0 or less, even more preferably 10.0 or less, and particularly preferably 8.0 or less.

[0045] The C content is preferably small, for example, preferably 30% or less, and more preferably 20% or less. By setting the C content to 30% or less, the content of compounds that cause an increase in resistance, such as lithium carbonate, contained in the surface layer of the lithium nickel composite oxide particles can be sufficiently suppressed. Therefore, when used in a lithium ion secondary battery, the reaction resistance can be particularly reduced.

[0046] The lower limit of the C content is not particularly limited, and is preferably 0 or more, more preferably 5% or more, and even more preferably 10% or more.

[0047] The B content and C content can be measured and calculated by the following procedure. First, XPS measurement is performed on the positive electrode active material. Then, the mass ratio of each component on the surface of the positive electrode active material is obtained from semi-quantitative values ​​calculated from the peak areas of the spectra for lithium (Li), nickel (Ni), titanium (Ti), boron (B), element M, and carbon (C) obtained by the XPS measurement. The peaks used to determine the mass ratio of each component can be selected depending on the element, etc. For example, after peak separation of the measured XPS spectrum, the peak with the highest intensity can be used.

[0048] Next, using the results of the composition analysis, the C content, the B content, and the ratio of the B content to the C content can be calculated using the following formulas (1), (2), and (3). In the formulas, MLi, MC, MNi, MTi, MB, and MM respectively represent the amount of substance ratio of lithium, the amount of substance ratio of carbon, the amount of substance ratio of nickel, the amount of substance ratio of titanium, the amount of substance ratio of boron, and the amount of substance ratio of element M, calculated from the results of XPS measurement.

[0049] (C content) = [MC ÷ (MLi + MNi + MTi + MB + MM + MC)] × 100 (1) (B content ratio) = [MB ÷ (MLi + MNi + MTi + MB + MM + MC)] × 100 (2) (Ratio of B content to C content) = (B content) ÷ (C content) (3) (3) Intensity ratio of XRD pattern When the positive electrode active material of the present embodiment is subjected to XRD pattern measurement, it is preferable that the ratio of the sum of the peak intensities of the strongest lines of the titanium compound to the diffraction peak intensity of the (003) plane, which is the strongest line of the hexagonal layered structure (hereinafter referred to as the "peak intensity ratio") is 0.2 or less.

[0050] This is because, by setting the peak intensity ratio to 0.2 or less, most of the titanium added to the lithium nickel composite oxide remains within the lithium nickel composite oxide without forming a different phase, thereby particularly improving the thermal stability.

[0051] The peak intensity ratio is more preferably 0.1 or less.

[0052] When calculating the peak intensity ratio, the peak intensity of the strongest line of the titanium compound can be calculated by the following procedure. First, the titanium compound contained in the positive electrode active material, which is a different phase from the lithium-nickel composite oxide, is identified by phase identification. Next, the intensity of the strongest peak among the peaks of each identified titanium compound is determined. Then, the peak intensities of the strongest lines of each titanium compound thus determined can be added together to obtain the total peak intensity of the strongest lines of the titanium compounds.

[0053] The peak intensity ratio described above can be calculated by dividing the total peak intensity of the strongest lines of the obtained titanium compound by the diffraction peak intensity of the (003) plane, which is the strongest line of the hexagonal layer structure. (4) Titration curve The positive electrode active material of the present embodiment is mixed with pure water, and then filtered to obtain a filtrate. In the titration curve obtained by neutralization titration of the filtrate, the volume ratio of the amount of HCl dropped in a pH range of 5.0 or more and less than 8.0 to the amount of HCl dropped in a pH range of 8.0 or more and 11.0 or less is preferably 0.5 or less.

[0054] The filtrate used to prepare the titration curve can be obtained by adding 10 g of the positive electrode active material of this embodiment to 50 mL of pure water, stirring the mixture for 5 minutes, filtering, and separating the solid and liquid. The pure water is preferably water from which components that affect the neutralization titration have been removed as much as possible, and distilled water or the like can be suitably used. Furthermore, when preparing the titration curve, the filtered filtrate is used with 1.0 M, i.e., 1.0 mol / dm HCl, which is the acid used for the neutralization titration. 3 (1.0 mol / L) hydrochloric acid can be used.

[0055] According to studies by the present inventors, the amount of HCl added dropwise in the pH region of 5.0 or higher and lower than 8.0 on the titration curve mainly represents the HCl consumed in the reaction with lithium carbonate contained in the positive electrode active material.

[0056] Furthermore, when the filtrate of the positive electrode active material of this embodiment is subjected to neutralization titration, the titration curve shows a region in the pH range of 8.0 to 11.0 inclusive where the pH fluctuation is suppressed and the curve is nearly flat compared to other pH ranges. Specifically, for example, the titration curve shows a region in the pH range of 8.0 to 11.0 inclusive where the pH fluctuation with respect to the amount of HCl added is smaller than in the pH range of 5.0 to less than 8.0.

[0057] As described above, it is believed that the trace amount of boron contained in the lithium nickel composite oxide causes the boron to form a low-resistance reaction product, a lithium-boron-containing compound, with the lithium component attached to the particle surfaces of the lithium nickel composite oxide. It is also believed that the lithium-boron-containing compound reduces the reaction resistance of the positive electrode active material.

[0058] In the titration curve, the amount of HCl added dropwise in the pH range of 8.0 to 11.0 is presumed to represent the HCl consumed mainly in the reaction with the lithium-boron-containing compound.

[0059] Therefore, by setting the volume ratio of the amount of HCl dropped in the pH range of 5.0 or higher and lower than 8.0 to the amount of HCl dropped in the pH range of 8.0 or higher and 11.0 or lower to 0.5 or less, it is thought that the lithium carbonate content can be suppressed and the lithium-boron-containing compound can be sufficiently produced. Therefore, when this positive electrode active material is applied to a lithium ion secondary battery, it is thought that the reaction resistance of the positive electrode active material can be particularly reduced.

[0060] The volume ratio VR of the amount of HCl dropped in the pH range of 5.0 or more and less than 8.0 to the amount of HCl dropped in the pH range of 8.0 or more and 11.0 or less can be calculated by the following formula (4).

[0061] In the following formula (4), the amount of HCl added dropwise in the pH range of 8.0 to 11.0 is expressed as "V(8.0-11.0)", and the amount of HCl added dropwise in the pH range of 5.0 to less than 8.0 is expressed as "V(5.0-8.0)".

[0062] VR=V(5.0~8.0)÷V(8.0~11.0) ···(4) As mentioned above, the VR is preferably 0.5 or less, more preferably 0.25 or less, and even more preferably 0.2 or less.

[0063] The lower limit of the VR is not particularly limited, but since it is difficult to completely remove lithium carbonate, it is preferably 0.01 or more, and more preferably 0.05 or more. (5) Particle size variation index and volume average particle size In the positive electrode active material of this embodiment, the particle size variation index [(D90-D10) / volume average particle size Mv] is preferably 0.70 or more and 1.20 or less, and more preferably 0.80 or more and 1.00 or less.

[0064] In this specification, D10 is the cumulative 10% particle diameter, which means the 10% diameter on a volume basis in the particle size distribution determined by laser diffraction / scattering, i.e., the particle size at 10% of the volume cumulative value. D90 is the cumulative 90% particle diameter, which means the 90% diameter on a volume basis in the particle size distribution determined by laser diffraction / scattering, i.e., the particle size at 90% of the volume cumulative value. D10 and D90 have the same meanings in other parts of this specification.

[0065] The volume average particle size Mv is the average particle size weighted by particle volume, and is calculated by multiplying the diameter of each particle by its volume and dividing the sum by the total volume of the particles. The volume average particle size can also be measured and calculated by the laser diffraction / scattering method using a laser diffraction particle size analyzer.

[0066] By setting the particle size variation index of the positive electrode active material to 0.70 or more, for example, when fabricating a positive electrode, particles with relatively small particle sizes are arranged between particles with relatively large particle sizes, thereby making it possible to increase the packing density of the positive electrode active material.

[0067] By setting the particle size variation index of the positive electrode active material to 1.20 or less, it is possible to prevent excessively coarse particles or very small particles from being mixed in, and when such a positive electrode active material is used in a lithium ion secondary battery, it is possible to particularly improve the output characteristics.

[0068] The volume average particle size Mv of the positive electrode active material of this 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.

[0069] By setting the volume average particle diameter Mv of the positive electrode active material of this embodiment within the above range, when the positive electrode active material of this embodiment is used in the positive electrode of a lithium ion secondary battery, it is possible to particularly improve the output characteristics and battery capacity, and also to achieve high packability into the positive electrode. Specifically, by setting the volume average particle diameter Mv of the positive electrode active material of this embodiment to 8 μm or more, it is possible to improve the packability into the positive electrode. Furthermore, by setting the volume average particle diameter Mv of the positive electrode active material of this embodiment to 20 μm or less, it is possible to particularly improve the output characteristics and battery capacity. [Method of manufacturing a positive electrode active material for lithium ion secondary batteries] A method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment will be described. According to the method for producing a positive electrode active material for a lithium ion secondary battery according to this embodiment, the previously described positive electrode active material can be produced. Therefore, some of the matters already described will not be described again. Note that the method for producing the previously described positive electrode active material is not limited to the following method for producing a positive electrode active material.

[0070] The method for producing the positive electrode active material of this embodiment may include the following mixing step, firing step, water washing step, boron addition step, heat treatment step, and cooling step.

[0071] In the mixing step, a nickel-containing material containing elements other than lithium (Li), boron (B), and oxygen (O) contained in the lithium nickel composite oxide, such as nickel (Ni) or titanium (Ti), and optionally the element M (M), is mixed with a lithium compound to prepare a first raw material mixture.

[0072] In the firing step, the first raw material mixture is fired in an oxidizing atmosphere to produce a fired product.

[0073] In the water washing step, the fired product obtained in the firing step is washed with water to obtain water-washed powder.

[0074] In the boron addition step, the water-washed powder and a boron-containing substance can be mixed to prepare a second raw material mixture.

[0075] In the heat treatment step, the second raw material mixture can be heat treated.

[0076] Each step will be explained below. (1)Mixing process In the mixing step, as described above, the nickel-containing material containing at least nickel and titanium and the lithium compound are mixed together to prepare the first raw material mixture. The raw materials used will be described below. (1-1) Nickel-containing materials The nickel-containing material to be subjected to the mixing step can contain nickel, which is an element other than lithium, boron, and oxygen among the elements contained in the target lithium-nickel composite oxide as described above, as well as titanium and, if necessary, the element M. Note that, in the nickel-containing material, the element M is an optional added component and therefore does not necessarily need to be contained.

[0077] The nickel-containing material is not particularly limited as long as it contains elements corresponding to the target composition of the lithium-nickel composite oxide. For example, the nickel-containing material can suitably contain a nickel composite hydroxide or a nickel composite compound that is a roasted product of the nickel composite hydroxide. The nickel-containing material can also be composed of the above-mentioned nickel composite compound. Examples of the roasted product of the nickel composite hydroxide include a nickel composite oxide and a mixture of a nickel composite oxide and a nickel composite hydroxide.

[0078] The nickel-containing material may also be a material having a coating layer containing titanium or the element M on the surface of nickel oxide or nickel hydroxide, or a mixture of nickel oxide, nickel hydroxide, or the like with a titanium compound or a compound of the element M.

[0079] When the lithium nickel composite oxide contains multiple types of element M, the nickel-containing substance can be a mixture of nickel composite compounds containing some of the elements M and compounds of the remaining elements M. In this case, the nickel composite compound is preferably one or more types selected from nickel composite oxides and nickel composite hydroxides.

[0080] When the nickel-containing material contains a titanium compound, the form of the titanium compound is not particularly limited, and one or more types selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc. can be used.

[0081] 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 types selected from hydroxides, oxides, chlorides, nitrates, sulfates, carbonates, etc. can be used.

[0082] The nickel-containing material preferably contains nickel (Ni), titanium (Ti), and element M (M) in a ratio of Ni:Ti:M=b:c:e in terms of the amount of substance. The b, c, e, and element M in the above formula can be in the same preferred ranges and materials as those explained in "(1-1) Regarding the composition" of "(1) Regarding the lithium nickel composite oxide" in the positive electrode active material, and therefore further explanation is omitted here.

[0083] When the nickel-containing material is a nickel composite oxide, the nickel-containing material may be, for example, a material represented by the general formula: Ni b´ Ti c´ M e´ O 1+β It can be expressed as:

[0084] When the nickel-containing material is a nickel composite hydroxide, the nickel-containing material may be, for example, a material represented by the general formula: Ni b´ Ti c´ M e´ (OH) 2+γ It can be expressed as:

[0085] Note that b', c', and e' have the relationship b':c':e'=b:c:e with the already-described b, c, and e, and satisfy b'+c'+e'=1. Since b, c, e, and the element M have already been explained, further explanation will be omitted here. It is preferable that β and γ satisfy, for example, -0.2≦β≦0.2 and -0.2≦γ≦0.2.

[0086] When the nickel-containing material contains 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.

[0087] In the mixing step, the above-mentioned nickel composite hydroxide can be used as it is as part or all of the nickel-containing material, but the nickel composite hydroxide may be oxidatively roasted to form a roasted product, which can then be used.

[0088] The conditions for oxidizing roasting the nickel composite hydroxide are not particularly limited, but it is preferable to oxidizing roast the above-described nickel composite hydroxide in an oxidizing atmosphere at a temperature of 500° C. or higher and 800° C. or lower.

[0089] When a roasted nickel composite hydroxide is used as the nickel composite compound, when the first raw material mixture mixed with a lithium compound is fired to obtain a lithium nickel composite oxide, the composition ratio of Li to Ni, Ti, and the element M in the lithium nickel composite oxide can be particularly stabilized.

[0090] The atmosphere in which oxidizing roasting is carried out is not particularly limited, and it is preferably carried out in an oxidizing atmosphere as described above, and more preferably in an air atmosphere (air atmosphere) or in an air stream, which can be carried out easily. (1-2) Lithium compounds The lithium compound is not particularly limited, but for example, one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, lithium sulfate, lithium chloride, and lithium oxide can be preferably used. As the lithium compound, more preferably, one or more selected from lithium hydroxide and lithium carbonate can be used. Because lithium hydroxide has high reactivity with the nickel composite compound and a low reaction temperature, it is more preferable to use lithium hydroxide as the lithium compound.

[0091] In the method for producing a positive electrode active material of this embodiment, the nickel-containing material and the lithium compound are mixed together as described above to prepare the first raw material mixture.

[0092] The mixing ratio of the nickel-containing material and the lithium compound is not particularly limited, but the composition of lithium, nickel, and element M in the fired product obtained after firing is substantially the same as the composition in the first raw material mixture obtained by mixing the nickel-containing material and the lithium compound.

[0093] However, since lithium may be slightly reduced when performing the water washing step described below, it is preferable to adjust the ratio of the amount of lithium (Li) in the lithium compound to the total amount (Me) of, for example, nickel, titanium, and element M in the nickel-containing material so that the ratio of the amount of substance (Li / Me) is 1.005 or more and 1.100 or less.

[0094] By making the Li / Me ratio 1.005 or more, the crystallinity of the resulting lithium nickel composite oxide can be improved, and the content ratio of lithium to elements other than oxygen in the resulting lithium nickel composite oxide can be adjusted to the target composition.

[0095] Furthermore, by setting the Li / Me ratio to 1.100 or less, it is possible to prevent excessive firing and, for example, sintering of secondary particles in the resulting lithium nickel composite oxide.

[0096] The device and method for mixing the nickel-containing material and the lithium compound are not particularly limited as long as they can be uniformly mixed. For example, a dry mixer such as a V blender or a mixing granulator can be used. (2) Firing process In the calcination step, the first raw material mixture is calcined in an oxidizing atmosphere to obtain a calcined product. When the first raw material mixture is calcined in the calcination step, lithium in the lithium compound is diffused into and reacted with the nickel-containing material to obtain a calcined product.

[0097] In the firing step, the firing temperature at which the first raw material mixture is fired is not particularly limited, but can be, for example, 600°C or higher and 1000°C or lower.

[0098] By setting the firing temperature to 600° C. or higher, it is possible to sufficiently promote the diffusion of lithium into the nickel-containing material.

[0099] Furthermore, by setting the firing temperature to 1000°C or less, it is possible to suppress the progression of sintering between particles of the fired product to be produced, and also to suppress the occurrence of abnormal grain growth, thereby suppressing the coarsening of particles of the fired product to be obtained.

[0100] In the process of increasing the temperature to the calcination temperature, the mixture may be maintained in a temperature range from near the melting point of the lithium compound used to the calcination temperature, for example, in a temperature range of 400° C. to 550° C. for 1 hour to 5 hours. Maintaining the mixture in this temperature range allows the reaction to proceed particularly uniformly.

[0101] The firing atmosphere is preferably an oxidizing atmosphere. The oxidizing atmosphere is not particularly limited, but an oxygen-containing gas atmosphere can be used, and more preferably, the atmosphere has an oxygen concentration of 18% by volume or more and 100% by volume or less.

[0102] This is because by setting the oxygen concentration in the atmosphere during firing to 18% by volume or more, the reaction between the lithium compound and the nickel-containing material can be promoted, and the crystallinity of the lithium nickel composite oxide can be increased.

[0103] When an oxygen-containing gas atmosphere is used, the gas constituting the atmosphere may be, for example, air, oxygen, or a mixed gas of oxygen and an inert gas.

[0104] When a mixed gas of oxygen and an inert gas is used as the gas constituting the oxygen-containing gas atmosphere, as described above, the oxygen concentration in the mixed gas preferably satisfies the above range.

[0105] In particular, the firing step is preferably carried out in an oxygen-containing gas stream, more preferably in the air or in an oxygen stream, and even more preferably in an oxygen stream in consideration of the battery characteristics.

[0106] The furnace used for firing is not particularly limited as long as it can fire the first raw material mixture in a predetermined atmosphere. From the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferred, and either a batch type or a continuous type furnace can be used.

[0107] In the method for producing a positive electrode active material of this embodiment, if particles of the fired product have aggregated in the firing step, a crushing step (first crushing step) of crushing the fired product can be included.

[0108] Here, "crushing" refers to a process of applying mechanical energy to agglomerates of multiple secondary particles formed by sintering necking between secondary particles during firing, thereby separating the secondary particles without substantially destroying the secondary particles themselves, and breaking up the agglomerates. For example, a pin mill, hammer mill, pulverizer, or the like may be used to crush the secondary particles to an extent that they are not destroyed.

[0109] The method for producing the fired product prepared in the firing step is not limited to the above-mentioned method. For example, the fired product can be prepared by subjecting a mixture of aqueous solutions containing the desired metal elements to spray pyrolysis treatment, or by mechanically grinding the compounds of the desired elements by a ball mill or the like, followed by firing. (3)Water washing process In the water washing process, the fired product obtained in the firing process is washed with water to obtain a water-washed powder. In the water washing process, the fired product obtained in the firing process is mixed with water to form a slurry and washed with water (slurrying process). The slurry concentration when washing the fired product with water is not particularly limited, and can be, for example, 200 g / L or more and 5000 g / L or less. By setting the slurry concentration to 5000 g / L or less, stirring of the slurry can be facilitated and the dissolution rate of the attached matter can be improved.

[0110] On the other hand, by setting the slurry concentration to 200 g / L or more, it is possible to prevent lithium from being released from the crystal lattice of the fired product and suppress the collapse of the crystals, and by setting the slurry concentration to 5000 g / L or less, it is possible to prevent the reprecipitation of lithium carbonate due to the absorption of carbon dioxide gas from the atmosphere by the high pH aqueous solution.

[0111] The water washing can be carried out by controlling the temperature of the slurry to be in the range of 10°C to 40°C and the electrical conductivity of the liquid part of the slurry to be 30 mS / cm to 90 mS / cm.

[0112] By adjusting the electrical conductivity of the slurry prepared in the water washing step to fall within the above range, excess components, such as excess lithium, adhering to the surfaces of the particles of the fired product can be selectively and sufficiently reduced.

[0113] The water used in the washing step is not particularly limited, but for example, water having an electrical conductivity of less than 10 μS / cm, preferably 1 μS / cm or less can be used.

[0114] The washing time is not particularly limited, but can be, for example, 3 minutes to 2 hours from the viewpoint of sufficiently removing excess components adhering to the surface of the fired particle while also increasing productivity. It is preferable to stir the prepared slurry during washing with water.

[0115] After the water-washing step, the slurry is subjected to solid-liquid separation, i.e., filtration and dehydration to obtain a water-washed powder (solid-liquid separation step). The filtration and dehydration are not particularly limited, and for example, a filter press type solid-liquid separator can be used.

[0116] In the water washing step, the water-washed powder containing moisture obtained after solid-liquid separation is preferably dried before being subjected to the boron addition step. Therefore, the water-washed powder can be dried (drying step). The drying conditions are not particularly limited.

[0117] Drying is preferably carried out, for example, in an oxidizing atmosphere or a vacuum atmosphere at a temperature of 100°C or higher and 250°C or lower. By setting the drying temperature to 100°C or higher, the moisture in the water-washed powder can be sufficiently evaporated. Furthermore, by setting the drying temperature to 250°C or lower, the energy required for drying can be suppressed, thereby reducing costs.

[0118] The atmosphere during drying is preferably one that contains little or no water vapor or carbon dioxide to avoid reaction between the water-washed powder and moisture or carbon dioxide in the atmosphere, and more specifically, an oxidizing atmosphere such as an oxygen atmosphere or a vacuum atmosphere is preferred. In addition, from the viewpoint of being able to quickly exhaust water vapor generated by drying, it is preferred to add an exhaust mechanism to the drying apparatus.

[0119] The drying time is not particularly limited, but is preferably, for example, 0.5 hours or more and 48 hours or less. By setting the drying time, i.e., the holding time at the maximum temperature during drying, to 0.5 hours or more, the moisture in the water-washed powder can be sufficiently reduced and removed. Furthermore, by setting the drying time to 48 hours or less, productivity can be increased. (4) Boron addition process In the boron addition step, the water-washed powder and a boron-containing substance can be mixed to prepare a second raw material mixture.

[0120] The boron-containing substance to be added is not particularly limited, and may be, for example, boron alone or a boron-containing compound containing boron. That is, the boron-containing substance is preferably at least one selected from boron alone and a boron-containing compound. The boron-containing compound is preferably one in which components other than boron can be discharged outside the system in the heat treatment step described below. For example, compounds such as orthoboric acid (H3BO3), boron oxide (BO3), and boron nitride (BN) in which components other than B are one or more selected from hydrogen, oxygen, and nitrogen can be suitably used.

[0121] The mixing ratio of the water-washed powder and the boron-containing material is not particularly limited, and can be selected by conducting a test or the like in advance so that the lithium nickel composite oxide obtained after the heat treatment has the target composition.

[0122] However, since the composition of the lithium nickel composite oxide obtained after the heat treatment usually remains substantially the same as that in the second raw material mixture, it is preferable to prepare the second raw material mixture so that the composition of the second raw material mixture is the same as that of the target lithium nickel composite oxide.

[0123] Here, to ensure uniform reaction between boron and the water-washed powder in the subsequent heat treatment step, it is preferable to finely pulverize the boron-containing material to be added. Specifically, the average diameter in the long axis direction of secondary particles of the boron-containing material observed in a surface SEM image is preferably 0.1 μm or more and 100 μm or less. This average diameter in the long axis direction is calculated by randomly selecting 30 or more secondary particles of the boron-containing material observed in the surface SEM image and averaging the long axis diameters measured for each secondary particle. Note that there is no particular upper limit on the number of secondary particles whose long axis diameter is measured, but it is preferable to set it to 100 or less in order to reduce the time required for evaluation.

[0124] The apparatus and method for mixing the water-washed powder and the boron-containing material are not particularly limited as long as they can be uniformly mixed. For example, a dry mixer such as a V blender or a mixing granulator can be used.

[0125] However, to prevent the water-washed powder from reacting with moisture or carbon dioxide in the atmosphere, it is preferable to purge the container with an inert gas during mixing. Also, to prevent non-uniformity due to aggregation of the boron-containing material, it is preferable to sieve the second raw material mixture several times after mixing the boron-containing material to break up the aggregates. (5) Heat treatment process In the heat treatment step, the second raw material mixture can be heat treated.

[0126] It is believed that the heat treatment step can promote the production of lithium-boron compounds due to the reaction between boron and the lithium component attached to the surface of the water-washed powder.

[0127] In the heat treatment step, the heat treatment temperature for heat treating the second raw material mixture is not particularly limited and can be selected depending on the added boron-containing material, etc. In the heat treatment step, the heat treatment is preferably performed at 200°C or higher and 500°C or lower, and more preferably at 200°C or higher and 400°C or lower.

[0128] By setting the heat treatment temperature to 200° C. or higher, the reaction between the boron and the lithium component can be sufficiently promoted.

[0129] Furthermore, by setting the heat treatment temperature to 500° C. or less, it is possible to prevent boron from scattering into the atmosphere before it reacts with the lithium component.

[0130] The atmosphere during the heat treatment in the heat treatment step is not particularly limited, and the heat treatment can be carried out, for example, in an oxidizing atmosphere or an inert gas atmosphere.

[0131] The oxidizing atmosphere is not particularly limited, but an oxygen-containing gas atmosphere can be used, and for example, an atmosphere with an oxygen concentration of 18% by volume or more and 100% by volume or less is preferable.

[0132] When an oxygen-containing gas atmosphere is used, the gas constituting the atmosphere may be, for example, air, oxygen, or a mixed gas of oxygen and an inert gas.

[0133] The heat treatment step is preferably carried out in an atmosphere in which the carbon dioxide gas concentration is suppressed, such as a decarbonated gas atmosphere. Therefore, even in the case of the above-mentioned oxidizing atmosphere or an inert gas atmosphere, it is preferable that the carbon dioxide gas concentration is suppressed.

[0134] The carbon dioxide concentration in the heat treatment atmosphere is not particularly limited, as long as it is lower than that of normal air. Therefore, the carbon dioxide concentration in the heat treatment atmosphere is preferably less than 0.03% by volume, more preferably 0.02% by volume or less, even more preferably 0.01% by volume or less, and particularly preferably 0.008% by volume or less.

[0135] By performing the heat treatment in an atmosphere with a reduced carbon dioxide concentration, it is possible to suppress the generation of carbon-containing compounds such as lithium carbonate, 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 preferable to perform cooling in an atmosphere with a reduced carbon dioxide concentration.

[0136] The furnace used for the heat treatment is not particularly limited as long as it can heat-treat the second raw material mixture in a predetermined atmosphere. From the viewpoint of maintaining a uniform atmosphere in the furnace, an electric furnace that does not generate gas is preferred, and either a batch-type or continuous-type furnace can be used.

[0137] The method for producing a positive electrode active material of this embodiment may also include a crushing step (second crushing step) for crushing the lithium nickel composite oxide if the lithium nickel composite oxide particles have aggregated after the heat treatment step. The crushing step can be carried out in the same manner as in the first crushing step described above, and therefore a description thereof will be omitted. [Lithium-ion secondary battery] 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 can include the above-described positive electrode active material for lithium ion secondary batteries.

[0138] Below, one example of the configuration of the secondary battery of this embodiment will be described for each component. The secondary battery of this embodiment includes, for example, a positive electrode, a negative electrode, and a non-aqueous electrolyte, and is composed of the same components as a general lithium-ion secondary battery. Note that the embodiment described below is merely an example, and the lithium-ion secondary battery of this embodiment can be implemented in various forms, including the following embodiment, with various modifications and improvements based on the knowledge of those skilled in the art. Furthermore, the use of the secondary battery is not particularly limited. (positive electrode) The positive electrode of the secondary battery of this embodiment can contain the positive electrode active material described above.

[0139] An example of a method for manufacturing a positive electrode is described below. First, the above-mentioned positive electrode active material (powder), conductive material, and binder are mixed to form a positive electrode mixture, and activated carbon and a solvent for viscosity adjustment, etc., are added as needed, and the mixture is kneaded to form a positive electrode mixture paste.

[0140] The mixing ratio of each material in the positive electrode mixture is a factor that determines the performance of the lithium-ion secondary battery, and can be adjusted depending on the application. The mixing ratio of the materials can be the same as that of the positive electrodes of known lithium-ion secondary batteries, and for example, when the total mass of the solid content of the positive electrode mixture excluding the solvent is taken as 100 mass%, the positive electrode active material can be contained in proportions of 60 mass% to 95 mass% inclusive, the conductive material can be 1 mass% to 20 mass% inclusive, and the binder can be 1 mass% to 20 mass% inclusive.

[0141] The resulting positive electrode composite paste is applied to the surface of, for example, an aluminum foil current collector, and dried to remove the solvent, producing a sheet-like positive electrode. If necessary, pressure can be applied using a roll press or the like to increase the electrode density. The sheet-like positive electrode thus obtained can be cut to an appropriate size depending on the desired battery and used to produce the battery.

[0142] Examples of the conductive material that can be used include graphite (natural graphite, artificial graphite, expanded graphite, etc.) and carbon black materials such as acetylene black and Ketjen Black (registered trademark).

[0143] The binder serves to bind the active material particles together, and may be one or more selected from the group consisting of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, styrene butadiene, cellulose-based resin, and polyacrylic acid.

[0144] If necessary, a solvent for dispersing the positive electrode active material, conductive material, etc. and dissolving the binder can be added to the positive electrode mixture. Specifically, an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent. Activated carbon can also be added to the positive electrode mixture to increase the electric double layer capacity.

[0145] The method for producing the positive electrode is not limited to the above-mentioned example, and other methods may be used. For example, the positive electrode may be produced by press-molding the positive electrode mixture and then drying it in a vacuum atmosphere. (Negative electrode) The negative electrode can be made of metallic lithium, a lithium alloy, etc. Alternatively, the negative electrode can be made by mixing a binder with a negative electrode active material capable of absorbing and desorbing lithium ions, adding an appropriate solvent to form a paste of the negative electrode mixture, applying the paste to the surface of a metal foil current collector such as copper, drying it, and compressing it to increase the electrode density as needed.

[0146] Examples of the negative electrode active material include natural graphite, artificial graphite, and sintered organic compounds such as phenolic resin, and powders of carbonaceous materials such as coke. In this case, a fluorine-containing resin such as PVDF can be used as the negative electrode binder, as in the positive electrode, and an organic solvent such as N-methyl-2-pyrrolidone can be used as the solvent for dispersing the active material and binder. (separator) A separator can be sandwiched between the positive electrode and the negative electrode as needed. The separator separates the positive electrode and the negative electrode and retains the electrolyte. Any known separator can be used, for example, a thin membrane made of polyethylene, polypropylene, or the like, having many minute pores. (Non-aqueous electrolyte) As the non-aqueous electrolyte, for example, a non-aqueous electrolytic solution can be used.

[0147] The non-aqueous electrolyte may be, for example, a solution of a lithium salt as a supporting salt dissolved in an organic solvent. Alternatively, the non-aqueous electrolyte may be a solution of a lithium salt dissolved in an ionic liquid. The ionic liquid is a salt that is liquid even at room temperature and is composed of cations and anions other than lithium ions.

[0148] The organic solvent may be one selected from the group consisting of 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; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethyl methyl sulfone and butane sultone; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. These organic solvents may be used alone or in combination of two or more.

[0149] Examples of the supporting salt that can be used include LiPF, LiBF, LiClO, LiAsF, LiN(CFSO), and composite salts thereof. The non-aqueous electrolyte may further contain a radical scavenger, a surfactant, and a flame retardant.

[0150] Alternatively, the non-aqueous electrolyte may be a solid electrolyte, which has the property of being able to withstand high voltages. Examples of the solid electrolyte include inorganic solid electrolytes and organic solid electrolytes.

[0151] Examples of inorganic solid electrolytes include oxide-based solid electrolytes and sulfide-based solid electrolytes.

[0152] 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 suitably used. Examples of oxide-based solid electrolytes include lithium phosphate (Li3PO4), Li3PO4N X , LiBON X , LiNbO3, LiTaO3, Li2SiO3, Li4SiO4-Li3PO4, Li4SiO4-Li3VO4, Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3-ZnO, Li 1+X Al X Ti 2-X (PO4)3(0≦X≦1), Li 1+X Al X Ge 2-X (PO4)3(0≦X≦1), LiTi2(PO4)3, Li 3X La 2 / 3-X TiO3(0≦X≦2 / 3), Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 One or more types selected from O4 and the like can be used.

[0153] The sulfide-based solid electrolyte is not particularly limited, and for example, one containing sulfur (S) and having lithium ion conductivity and electronic insulation can be suitably used. Examples of sulfide-based solid electrolytes that can be used include one or more selected from Li2S-P2S5, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2S-B2S3, Li3PO4-Li2S-Si2S, Li3PO4-Li2S-SiS2, LiPO4-Li2S-SiS, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, etc.

[0154] As the inorganic solid electrolyte, materials other than those mentioned above may be used, for example, Li3N, LiI, Li3N-LiI-LiOH, etc.

[0155] The organic solid electrolyte is not particularly limited as long as it is a polymer compound that exhibits ion conductivity, and examples thereof include polyethylene oxide, polypropylene oxide, copolymers thereof, etc. The organic solid electrolyte may also contain a supporting salt (lithium salt). (Shape and structure of secondary battery) The lithium ion secondary battery of the present embodiment described above can be formed into various shapes such as a cylindrical shape, a laminated shape, etc. Regardless of the shape, if the secondary battery of the present embodiment uses a nonaqueous electrolytic solution as the nonaqueous electrolyte, the positive electrode and the negative electrode are laminated with a separator interposed therebetween to form an electrode assembly, the obtained electrode assembly is impregnated with a nonaqueous electrolytic solution, and the positive electrode current collector and the positive electrode terminal connected to the outside, and the negative electrode current collector and the negative electrode terminal connected to the outside are connected using current collecting leads or the like, and the battery can be sealed in a battery case.

[0156] As described above, the secondary battery of this embodiment is not limited to a battery using a non-aqueous electrolytic solution as the non-aqueous electrolyte, and may be, for example, a secondary battery using a solid non-aqueous electrolyte, i.e., an all-solid-state battery. When an all-solid-state battery is used, the components other than the positive electrode active material may be changed as necessary.

[0157] 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 example, as a power source for small portable electronic devices (such as notebook personal computers and mobile phone terminals) that always require high capacity, and is also suitable as a power source for electric vehicles that require high output.

[0158] Furthermore, since the secondary battery of this embodiment can be made smaller and have higher output, it is suitable as a power source for electric vehicles, which are subject to space restrictions. The secondary battery of this embodiment can be used not only as a power source for electric vehicles that are driven purely by electrical energy, but also as a power source for so-called hybrid vehicles that use the secondary battery in combination with a combustion engine such as a gasoline engine or a diesel engine. [Example]

[0159] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0160] First, the evaluation methods for the positive electrode active materials and secondary batteries obtained in the following examples and comparative examples will be described. (Evaluation of positive electrode active material) The resulting positive electrode active material was evaluated as follows.

[0161] (a) Evaluation of composition, crystal structure, and particle structure The composition was analyzed using an ICP emission spectrometer (Shimadzu Corporation, ICPE-9000).

[0162] Furthermore, the powder X-ray diffraction patterns of the obtained positive electrode active materials were measured, and the crystal structures, etc. were identified by Rietveld analysis. As a result, it was confirmed that the positive electrode active materials prepared in the following examples and comparative examples were made of lithium nickel composite oxides, and that the lithium nickel composite oxides had a hexagonal layer structure.

[0163] Furthermore, when the particles of the positive electrode active material were observed using a scanning electron microscope, it was confirmed that the positive electrode active materials prepared in the following examples and comparative examples contained secondary particles formed by aggregation of multiple primary particles.

[0164] (b) B content ratio, C content ratio An XPS device (ULVAC-PHI, Versa Probe II) was used, and Al-Kα rays monochromated by a monochromator were used as the irradiation X-ray source.-6 The photoelectron spectrum of the positive electrode active material was measured in a vacuum atmosphere of 0.1 Pa or less.

[0165] Then, the substance amount ratios of lithium, nickel, titanium, boron, element M, and carbon on the surface were calculated from the peak areas of the obtained photoelectron spectrum, and the B content, C content, and ratio of the B content to the C content were calculated using the above-mentioned formulas (1) to (3). When calculating the substance amount ratios of each element, peak separation was performed on the measured XPS photoelectron spectrum, and the peak with the highest intensity for each element was used.

[0166] (c) Peak intensity ratio The XRD diffraction pattern of the positive electrode active material was measured using an XRD diffractometer (X'Pert PRO, manufactured by PANalytical) using Cu-Kα radiation as the radiation source. The measurement conditions were an output of 45 kV, 40 mA, a step size of 0.0168°, and a scan speed of 0.0508° / sec.

[0167] The titanium compounds contained in the positive electrode active materials were identified by phase identification from the obtained XRD patterns. The identified titanium compound phases are shown in the column of different phases in Table 1. Note that no titanium compound phases were confirmed except in Comparative Example 2.

[0168] Next, the peak intensity of the strongest line among the peaks of each identified titanium compound was determined, and the peak intensities of the strongest lines of each titanium compound thus determined were summed to obtain the total peak intensity of the strongest lines of the titanium compounds.

[0169] Furthermore, from the obtained XRD pattern, the diffraction peak intensity of the (003) plane, which is the strongest line of the hexagonal layer structure, was determined.

[0170] The total peak intensity of the strongest line of the titanium compound is then divided by the diffraction peak intensity of the (003) plane, which is the strongest line of the hexagonal layer structure, to obtain the peak intensity ratio (I Ti化合物 / I (003) ) was calculated. Ti化合物 / I(003) In the "" column, the notation "-" indicates that no titanium compound phase was observed in the XRD diffraction pattern, that is, the peak intensity ratio was 0.

[0171] (d) Titration curve 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 with 1.0 M HCl to measure the titration curve. Distilled water was used as the pure water.

[0172] From the obtained titration curve, the amount of HCl added was determined for each pH range shown in the "Neutralization titration HCl added amount" column in Table 1. In addition, the HCl added amount ratio, VR, was calculated using the above-mentioned formula (4).

[0173] (e) Particle size variation index The volumetric particle size distribution was measured using a laser diffraction / scattering particle size distribution analyzer (Microtrac MT3300EXII, manufactured by Microtrac Bell Co., Ltd.). D10, D90, and volume average particle size Mv were calculated from the particle size distribution.

[0174] Then, the particle size variation index [(D90-D10) / volume average particle size Mv] was calculated.

[0175] (Evaluation of battery characteristics) (a) Reaction resistance The coin-type batteries prepared in the following Examples and Comparative Examples were charged at a charging potential of 4.1 V, and their electrical resistance was measured by the AC impedance method using a frequency response analyzer and a potentiogalvanostat (Solartron, 1255B). The relationship between the measured mechanism and frequency was plotted as a graph, resulting in the Nyquist plot shown in Figure 2(A).

[0176] The Nyquist plot is expressed as the sum of characteristic curves showing the solution resistance, the negative electrode resistance and its capacity, and the positive electrode resistance and its capacity. Therefore, as shown in FIG. 2(B), a fitting calculation was performed using an equivalent circuit based on this Nyquist plot to calculate the value of the positive electrode resistance, and the calculated positive electrode resistance was used as the reaction resistance.

[0177] (b) Thermal stability The thermal stability of the positive electrode active material was evaluated by quantifying the amount of oxygen released by heating the positive electrode active material in an overcharged state. The coin-type batteries fabricated in the following examples and comparative examples were CC-charged (constant current-constant voltage) at a 0.05 C rate to a cutoff voltage of 4.3 V. The coin-type batteries were then disassembled, and the positive electrode was carefully removed to avoid short-circuiting. It was then washed with DMC (dimethyl carbonate) and dried. Approximately 2 mg of the dried positive electrode was weighed and heated from room temperature to 450 °C at a heating rate of 10 °C / min using a gas chromatograph mass spectrometer (GCMS, Shimadzu Corporation, QP-2010plus). Helium was used as the carrier gas. The evolution behavior of oxygen (m / z = 32) generated during heating was measured, and the maximum oxygen evolution peak intensity (peak height) was determined.

[0178] The evaluation results for each Example and Comparative Example are shown in the "Thermal Stability" column of Table 1 as a relative ratio, with the maximum oxygen generation peak intensity in Comparative Example 1 set as the reference, 1.00. The smaller the value, the more oxygen generation is suppressed, indicating superior thermal stability. [Example 1] (1) Manufacturing of positive electrode active material (1-1) Mixing process (nickel-containing material) First, nickel composite hydroxide prepared by the neutralization crystallization method was oxidized and roasted in air at a temperature of 600°C for 3 hours to prepare a nickel composite oxide. The nickel composite oxide was a Ni composite with a mass ratio of Ni:Mn:Co of 85:10:5. 0.85 Mn 0.10 Co 0.05 It was O.

[0179] A mixture of the nickel composite oxide and TiO2 was used as the nickel-containing material. The nickel composite oxide and TiO2 were mixed so that the mass ratio of Ni, Mn, Co, and Ti was Ni:Mn:Co:Ti = 0.829:0.098:0.049:0.024. (lithium compounds) The lithium compound used was lithium hydroxide, in the form of anhydrous lithium hydroxide.

[0180] The nickel-containing material and lithium hydroxide were weighed and mixed so that the substance amount of each element, Li / (Ni+Mn+Co+Ti), was 1.055, to obtain a first raw material mixture. (1-2) Firing process The obtained first raw material mixture was heated to 840°C in an oxygen atmosphere using an electric furnace and fired by holding at 840°C for 2 hours. Thereafter, it was cooled to room temperature in the furnace. The fired product was subjected to a crushing treatment. (1-3)Water washing process Next, pure water at 20°C was added to the obtained calcined product to prepare a slurry containing 1250 g of calcined product per 1 L of water (slurrying step). After stirring this slurry for 20 minutes, it was passed through a filter press and dehydrated to produce a washed cake containing water-washed powder (solid-liquid separation step). The pure water used had an electrical conductivity of 1 μS / cm or less.

[0181] The washed cake obtained was dried in a vacuum atmosphere at 190°C for 10 hours to obtain a water-washed powder (drying step). (1-4) Boron addition process The water-washed powder was mixed with orthoboric acid (H3BO3), a boron-containing substance, to prepare a second raw material mixture. The average diameter of the major axis direction of 40 orthoboric acid secondary particles randomly selected from surface SEM images was calculated to be 3 μm.

[0182] The water-washed powder and orthoboric acid were placed in a mixing vessel so that the lithium nickel composite oxide obtained after the heat treatment step would have the ratio of the amounts of the following elements contained therein shown in Table 1, i.e., Li:Ni:Mn:Co:Ti:B=1.03:0.825:0.097:0.049:0.024:0.005, and the vessel was purged with N2 gas before mixing. After mixing, the mixture was sieved three times to break up any agglomerations of orthoboric acid. (1-5) Heat treatment process In the heat treatment step, the second raw material mixture was heat treated at 304°C for 10 hours in an air atmosphere that had been subjected to a decarbonation treatment. Note that the decarbonation air atmosphere used was air that had been subjected to a decarbonation treatment to reduce the carbon dioxide concentration to 0.01% by volume or less. After heat treatment at the above heat treatment temperature, the mixture was cooled to room temperature in the same air atmosphere that had been subjected to the same decarbonation treatment.

[0183] The lithium nickel composite oxide thus obtained as the positive electrode active material was evaluated as described above. The evaluation results are shown in Table 1. (2) Fabrication of secondary batteries A coin-type battery having the structure shown in Figure 1 was fabricated by the following procedure, and the battery was evaluated as described above. The evaluation results are shown in Table 1.

[0184] 1, the coin-type battery 10 is a lithium-ion secondary battery including a positive electrode 11, a negative electrode 12, a separator 13, a gasket 14, a wave washer 15, a positive electrode can 16, and a negative electrode can 17. The positive electrode 11, the negative electrode 12, and the separator 13 are impregnated with an electrolyte solution.

[0185] In coin battery 10, positive electrode 11, separator 13, negative electrode 12, and wave washer 15 are arranged in this order, stacked from positive electrode can 16 toward negative electrode can 17. Positive electrode 11 contacts the inner surface of positive electrode can 16, and negative electrode 12 contacts the inner surface of negative electrode can 17 via wave washer 15.

[0186] Positive electrode can 16 and negative electrode can 17 are each hollow and open at one end, with negative electrode can 17 placed in the opening of positive electrode can 16. By placing negative electrode can 17 in the opening of positive electrode can 16, coin-type battery 10 accommodates positive electrode 11, negative electrode 12, separator 13, gasket 14, and wave washer 15 between positive electrode can 16 and negative electrode can 17.

[0187] In addition, a gasket 14 is disposed between the positive electrode can 16 and the negative electrode can 17, and this gasket 14 restricts relative movement between the positive electrode can 16 and the negative electrode can 17 so that they are kept in a non-contact state, i.e., electrically insulated, and fixes them in place. The gasket 14 also seals the gap between the positive electrode can 16 and the negative electrode can 17, thereby providing an airtight and liquid-tight barrier between the inside of the coin battery 10 and the outside.

[0188] The coin battery 10 was fabricated as follows.

[0189] 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 under a pressure of 100 MPa to form a positive electrode 11 having a diameter of 11 mm and a thickness of 100 μm, as shown in Fig. 1. The prepared positive electrode 11 was then dried in a vacuum dryer at 120°C for 12 hours.

[0190] After the positive electrode 11, negative electrode 12, and separator 13 were impregnated with the electrolyte, a coin-type battery 10 was fabricated in a glove box with an Ar atmosphere and a dew point controlled at -80°C. The fabricated positive electrode 11, separator 13, negative electrode 12, and wave washer 15 were stacked in this order on a positive electrode can 16. Next, the negative electrode can 17 was placed over the opening of the positive electrode can 16 so that the negative electrode 12 was in contact with the inner surface of the negative electrode can 17 via the wave washer 15, thereby assembling the coin-type battery 10.

[0191] For the negative electrode 12, a negative electrode sheet was used, which was punched into a disk shape with a diameter of 14 mm and was made by applying graphite powder with an average particle size of about 20 μm and polyvinylidene fluoride to copper foil.

[0192] The separator 13 was a porous polyethylene film having a thickness of 25 μm.

[0193] The electrolyte used was an equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 (manufactured by Toyama Pharmaceutical Co., Ltd.) with 1M LiPF6 as the supporting electrolyte.

[0194] In order to evaluate the reaction resistance and thermal stability described above, a total of two coin-type batteries were fabricated under the same conditions for each evaluation.

[0195] [Examples 2 to 4] In the boron addition step, the water-washed powder and orthoboric acid were mixed so that the lithium nickel composite oxide obtained after the heat treatment step had a mass ratio of Li, Ni, Mn, Co, Ti, and B as shown in Table 1. Except for the above, a positive electrode active material and a lithium ion secondary battery were produced and evaluated under the same conditions as in Example 1. The evaluation results are shown in Table 1.

[0196] [Examples 5 and 6] A positive electrode active material and a lithium ion secondary battery were produced and evaluated under the same conditions as in Example 2, except that in the heat treatment step, the heat treatment temperature was changed to the temperature shown in Table 1. The evaluation results are shown in Table 1.

[0197] [Comparative Example 1] A positive electrode active material and a lithium ion secondary battery were manufactured and evaluated under the same conditions as in Example 1, except that TiO2 was not added in the mixing step and the boron addition step and subsequent steps were not performed. That is, the water-washed powder obtained after the water-washing step was used as the positive electrode active material. The evaluation results are shown in Table 1.

[0198] Comparative Example 2 The amount of TiO2 added in the mixing step was increased, and the lithium nickel composite oxide obtained after the water washing step was mixed so that the ratio of the amounts of Li, Ni, Mn, Co, and Ti contained therein was the value shown in Table 1. Furthermore, the boron addition step and subsequent steps were not performed. In other words, the water-washed powder obtained after the water washing step was used as the positive electrode active material. Aside from the above, a positive electrode active material and a lithium ion secondary battery were produced and evaluated under the same conditions as in Example 1. The evaluation results are shown in Table 1.

[0199] Comparative Example 3 The heat treatment step was carried out in an air atmosphere that had not undergone decarbonation treatment. That is, the carbon dioxide concentration in the air atmosphere was 0.03% by volume or more. Except for the above, a positive electrode active material and a lithium ion secondary battery were produced and evaluated under the same conditions as in Example 2. The evaluation results are shown in Table 1.

[0200] [Table 1]

[0201] According to the results shown in Table 1, it was confirmed that the positive electrode active materials of Examples 1 to 6 contain boron at a predetermined ratio, have a peak intensity ratio of 0.2 or less, and have a ratio of the B content to the C content of 0.8 or more and 30.0 or less. It was also confirmed that when the positive electrode active materials of Examples 1 to 6 are used in secondary batteries, the reaction resistance can be reduced compared to the positive electrode active materials of Comparative Examples 1 to 3, which do not satisfy the above-mentioned requirements.

[0202] It was also confirmed that when the positive electrode active materials of Examples 1 to 6 were used in secondary batteries, they had superior thermal stability compared to the positive electrode active material of Comparative Example 1. [Explanation of symbols]

[0203] 10 Coin-type battery (lithium-ion secondary battery) 11 Positive electrode 12 Negative electrode 13 Separator 14 Gasket 15 Wave Washer 16 Positive electrode can 17 Anode can

Claims

1. A positive electrode active material for a lithium ion secondary battery containing a lithium nickel composite oxide having a hexagonal layer structure and including secondary particles formed by aggregation of a plurality of primary particles, The lithium nickel composite oxide contains lithium (Li), nickel (Ni), titanium (Ti), boron (B), and an element M (M) in a ratio of amounts of substance of Li:Ni:Ti:B:M=a:b:c:d:e (where 0.95≦a≦1.10, 0.50≦b<1.00, 0.00<c≦0.05, 0.00<d≦0.03, 0.00≦e≦0.47, and b+c+d+e=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, Nb, Na, W, Fe, Zn, Si, Sn, Cu, P, and Al), In an XRD pattern of the positive electrode active material for a lithium ion secondary battery, the ratio of the total amount of peak intensities of the strongest lines of a titanium compound to the diffraction peak intensity of the (003) plane, which is the strongest line of a hexagonal layered structure, is 0.2 or less; When the ratio of the amount of substance of carbon to the total amount of substance, which is the total amount of substance of lithium, nickel, titanium, boron, the element M, and carbon on the surface, calculated from the XPS measurement results of the positive electrode active material for a lithium ion secondary battery, is defined as the C content ratio, and the ratio of the amount of substance of boron to the total amount of substance is defined as the B content ratio, A positive electrode active material for a lithium ion secondary battery, wherein the ratio of the B content to the C content is 0.8 or more and 30.0 or less.

2. 2. The positive electrode active material for a lithium ion secondary battery according to claim 1, wherein in a titration curve obtained by stirring 10 g of the positive electrode active material for a lithium ion secondary battery in 50 mL of pure water for 5 minutes and neutralizing titrating the filtrate after filtration with 1.0 M HCl, the volume ratio of the amount of HCl dropped in a pH range of 5.0 or more and less than 8.0 to the amount of HCl dropped in a pH range of 8.0 or more and 11.0 or less is 0.5 or less.

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

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

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

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