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

Abstract

To provide a method for manufacturing a positive electrode active material (high Ni-containing lithium composite oxide) that can realize a lithium ion secondary battery having high energy density and excellent cycle characteristics.SOLUTION: A manufacturing method disclosed herein includes a preparation step of preparing, as a Ni source, powdered nickel hydroxide having a BET specific surface area of 10 m2 / g or more and 30 m2 / g or less and a D50 particle size of 2 μm or more and 10 μm or less, and a reaction step of mixing and firing at least the nickel hydroxide with a Li source to obtain a Ni-containing lithium composite oxide by a solid-state reaction method.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] With the spread of lithium ion secondary batteries, further increase in capacity has been demanded. Therefore, in recent years, from the viewpoint of improving the energy density, etc., a Ni-containing lithium composite oxide with a high Ni content has been used as the positive electrode active material (see Patent Documents 1 and 2). For example, Patent Document 1 includes a pulverization and mixing step of pulverizing and mixing raw materials to obtain a slurry, a granulation step of spray-drying the slurry to granulate, and a firing step of firing the obtained granulated powder (solid-phase reacting) to obtain a Ni-containing lithium composite oxide. In the pulverization and mixing step, the D 50 particle size of the pulverized raw material powder is refined to 0.1 to 1 μm, and a method for manufacturing a positive electrode active material is disclosed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] According to the newly obtained findings of the present inventor, when obtaining a product (Ni-containing lithium composite oxide) using a solid-phase reaction, the properties (particle morphology) of the raw materials greatly affect the properties of the Ni-containing lithium composite oxide, and thus also affect the characteristics of the battery. At this time, in the Ni-containing lithium composite oxide with a high Ni content, the influence of nickel hydroxide as a Ni source becomes particularly large, so its properties are important. However, as described in Patent Document 1, for example, the D 50When the particle size is refined to 0.1 to 1 μm, it has been newly found that a large amount of fine powder is mixed into the Ni-containing lithium composite oxide as a product, and as a result, the cycle characteristics (durability characteristics) of the battery are likely to deteriorate.

[0005] The present invention has been made in view of the above circumstances, and its main object is to provide a method for producing a positive electrode active material capable of realizing a lithium ion secondary battery having a high energy density and excellent cycle characteristics.

Means for Solving the Problems

[0006] According to the present invention, there is provided a method for producing a positive electrode active material including a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more. This production method uses, as a Ni source, a powdery nickel hydroxide having a BET specific surface area based on the nitrogen adsorption method of 10 m 2 / g or more and 30 m 2 / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, the D corresponding to 50% by volume from the smaller particle size side 50 particle size is 2 μm or more and 10 μm or less, and includes a preparation step of preparing the powdery nickel hydroxide, and a reaction step of obtaining a Ni-containing lithium composite oxide by solid-phase reaction by mixing and firing at least the nickel hydroxide and a Li source.

[0007] In the production method disclosed herein, the properties of nickel hydroxide, specifically, the specific surface area and D 50 particle size are set within a predetermined range. By this, mixing of fine powder into the Ni-containing lithium composite oxide can be suppressed, and a positive electrode active material suitable for use in a lithium ion secondary battery can be produced. As a result, a lithium ion secondary battery having a high energy density and relatively excellent cycle characteristics can be realized.

[0008] Further, the present invention provides a method for manufacturing a lithium-ion secondary battery, including a positive electrode manufacturing step of manufacturing a positive electrode using a positive electrode active material manufactured by the above manufacturing method. According to such a configuration, a battery with high energy density and excellent cycle characteristics can be realized.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, some preferred embodiments of the present invention will be described with reference to the drawings as appropriate. Matters other than those specifically mentioned in this specification and necessary for the implementation of the present invention (for example, the general configuration and manufacturing process of a lithium-ion secondary battery that do not characterize the present invention) can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the content disclosed in this specification and common general knowledge in the relevant field.

[0011] In this specification, the “lithium-ion secondary battery” (hereinafter sometimes simply referred to as “battery”) refers to an entire power storage device that uses lithium ions as charge carriers and can be repeatedly charged and discharged by the movement of charges associated with lithium ions between the positive and negative electrodes. Also, in this specification, the notation “A to B” indicating a range includes the meaning of “greater than A” and “less than B” in addition to the meaning of “A or more and B or less”.

[0012] 〔Positive Electrode Active Material〕 First, the positive electrode active material obtained by the manufacturing method described later will be explained. The positive electrode active material according to the present embodiment essentially contains a high-Ni-containing lithium composite oxide. The high-Ni-containing lithium composite oxide is an example of the "Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more" disclosed herein.

[0013] The high-Ni-containing lithium composite oxide contains Li, Ni, and O as essential elements, and from the viewpoint of improving the energy density of the battery, it is a compound in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more. The ratio of Ni is preferably 60 atm% or more, more preferably 70 atm% or more, and even more preferably 80 atm% or more. Specific examples of the high-Ni-containing lithium composite oxide include, for example, lithium nickel-based composite oxides, lithium nickel cobalt-based composite oxides, lithium nickel manganese-based composite oxides, lithium nickel cobalt manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, lithium iron nickel manganese-based composite oxides, and the like. These may be used alone or in combination of two or more. The high-Ni-containing lithium composite oxide preferably further contains a transition metal element other than Ni in addition to Ni, and more preferably contains at least one of Co and Mn. Among them, a lithium nickel cobalt manganese-based composite oxide containing at least Ni, Co, and Mn as transition metal elements is preferable because it has excellent battery characteristics such as a small initial resistance.

[0014] In the present specification, the term "lithium nickel cobalt manganese composite oxide" includes, in addition to oxides composed of Li, Ni, Co, Mn, and O as constituent elements, oxides containing one or more additional elements other than these. Examples of such additional elements include transition metal elements and typical metal elements such as Mg, Ba, Sr, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, K, Fe, Cu, Zn, Sn, etc. Further, the additional element may be a semi-metal element such as B, C, Si, P, etc., or a non-metal element such as S, F, Cl, Br, I, etc. This also applies to the above-mentioned lithium nickel-based composite oxides, lithium nickel cobalt-based composite oxides, lithium nickel manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, lithium iron nickel manganese-based composite oxides, etc.

[0015] The lithium nickel cobalt manganese composite oxide preferably has a composition represented by the following formula (I). Li 1+x Ni y Co z Mn (1-y-z) M α O 2-β Q β (I) In the above formula (I), x, y, z, α, and β satisfy -0.3 ≦ x ≦ 0.3, 0.5 ≦ y ≦ 0.95, 0.01 ≦ z ≦ 0.3, 0 ≦ α ≦ 0.1, and 0 ≦ β ≦ 0.5, respectively. M is at least one element selected from the group consisting of Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, and Si. Q is at least one element selected from the group consisting of F, Cl, and Br.

[0016] x preferably satisfies 0 ≦ x ≦ 0.3, more preferably satisfies 0 ≦ x ≦ 0.15, and even more preferably 0 ≦ x ≦ 0.05. From the perspective of balancing high energy density and excellent cycle characteristics, y preferably satisfies 0.6 ≦ y ≦ 0.95, for example 0.7 ≦ y ≦ 0.9, 0.8 ≦ y ≦ 0.9, and z preferably satisfies 0.03 ≦ z ≦ 0.25, more preferably satisfies 0.10 ≦ z ≦ 0.2. α preferably satisfies 0 ≦ α ≦ 0.05, and more preferably is 0. β preferably satisfies 0 ≦ β ≦ 0.1, and more preferably is 0.

[0017] The high Ni-containing lithium composite oxide preferably has a layered rock salt-type crystal structure. Examples of the lithium composite oxide having such a crystal structure include lithium nickel cobalt manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, etc. However, the crystal structure of the high Ni-containing lithium composite oxide may be a spinel structure or the like. The crystal structure can be confirmed by an X-ray diffraction method or the like.

[0018] The high Ni-containing lithium composite oxide is typically substantially spherical. However, it may be irregularly shaped or the like. In this specification, "substantially spherical" means a form that can be generally regarded as a sphere as a whole, and the average aspect ratio (major axis / minor axis ratio) based on the cross-sectional observation image of the electron microscope is generally 1 to 2, for example 1 to 1.5. The high Ni-containing lithium composite oxide is typically in the form of secondary particles formed by aggregation of a plurality of primary particles by physical or chemical bonding forces. In other words, the high Ni-containing lithium composite oxide (i.e., secondary particles) is an aggregate of primary particles in which a large number of primary particles are assembled to form one particle.

[0019] The high Ni-containing lithium composite oxide is typically in powder form. The D 50 particle size (average particle diameter) is not particularly limited, but from the perspective of improving battery characteristics (such as energy density and output characteristics), it is preferably about 25 μm or less. In one embodiment, it is 0.05 to 25 μm, and preferably 10 to 20 μm. In this specification, "D50 "Particle size (average particle diameter)" means the particle diameter (median diameter) corresponding to 50% by volume in cumulative terms from the side with smaller particle sizes (fine particle side) in the volume-based particle size distribution (cumulative distribution) based on the laser diffraction / scattering method.

[0020] D of high Ni-containing lithium composite oxide 20 The particle size is not particularly limited, but is preferably about 20 μm or less, and in one embodiment, it is 5 to 15 μm, preferably 6 to 14 μm. D of high Ni-containing lithium composite oxide 10 The particle size is not particularly limited, but is preferably about 3 μm or less, and in one embodiment, it is 0.1 to 2 μm, preferably 0.6 to 1.4 μm. By suppressing the mixing of fine powder in this way, a battery with excellent cycle characteristics can be realized. In this specification, "D 20 particle size", "D 10 particle size" respectively mean the particle diameters corresponding to 20% by volume and 10% by volume in cumulative terms from the side with smaller particle sizes (fine particle side) in the volume-based particle size distribution (cumulative distribution) based on the laser diffraction / scattering method.

[0021] 〔Manufacturing method of positive electrode active material〕 Next, the manufacturing method of the positive electrode active material as described above will be explained. The manufacturing method of the positive electrode active material according to this embodiment includes, in this order, a preparation step S1 of preparing nickel hydroxide and a reaction step S2 of obtaining a high Ni-containing lithium composite oxide (product). The manufacturing method disclosed herein may further include other steps at any stage.

[0022] The preparation step S1 is a step of preparing nickel hydroxide which serves as a Ni source for the high-Ni-containing lithium composite oxide. The nickel hydroxide is in powder form. According to the newly obtained findings of the present inventor, when obtaining a product by using a solid-phase reaction, the properties (particle morphology) of nickel hydroxide as a Ni source affect the properties of the high-Ni-containing lithium composite oxide, and thus also affect the cycle characteristics of the battery. In the case of a high-Ni-containing lithium composite oxide with a high Ni content of 50 atm% or more, the influence of nickel hydroxide as a Ni source becomes particularly large. Therefore, in order to produce a high-Ni-containing lithium composite oxide suitable for use in a battery, it is important to adjust the properties of nickel hydroxide.

[0023] Therefore, in the manufacturing method disclosed herein, as nickel hydroxide, the following conditions: (1) the BET specific surface area is 10 to 30 m 2 / g; (2) the D 50 particle size is 2 to 10 μm; are both satisfied. By this, as will also be described in the examples below, for example, compared with the case of using nickel hydroxide that does not satisfy the above BET specific surface area range or nickel hydroxide that does not satisfy the above D 50 particle size range, the incorporation of fine powder into the high-Ni-containing lithium composite oxide can be suppressed, and a battery with relatively excellent cycle characteristics can be realized. Note that nickel hydroxide having the above properties can be prepared, for example, by purchasing a commercially available reagent, or by appropriately pulverizing and classifying a commercially available reagent. For pulverization, for example, a ball mill can be used.

[0024] (1) The BET specific surface area of nickel hydroxide is 10 to 30 m 2 / g is appropriate. When the BET specific surface area is lower than this, the particles of nickel hydroxide become too large, and the particles may not adhere or attach to each other well in the reaction step S2 described later. As a result, a large amount of fine powder may be mixed in the obtained high-Ni-containing lithium composite oxide. Consequently, the cycle characteristics tend to deteriorate. On the other hand, when the BET specific surface area is higher than this, for example, the particles of nickel hydroxide become too small, and a large amount of fine powder may also remain in the obtained high-Ni-containing lithium composite oxide. Also in this case, the cycle characteristics of the battery tend to deteriorate.

[0025] The BET specific surface area of nickel hydroxide may be, for example, 15 m 2 / g or more, or may be 25 m 2 / g or less, or may be 20 m 2 / g or less. In the present specification, the "BET specific surface area" refers to a value obtained by analyzing the surface area measured by the nitrogen adsorption method by the BET method.

[0026] (2) The D 50 particle size of nickel hydroxide is appropriately 2 to 10 μm. When the D 50 particle size is smaller than this (for example, when it is 0.1 to 1 μm as disclosed in Patent Document 1), a large amount of fine powder may also remain in the obtained high-Ni-containing lithium composite oxide. As a result, the cycle characteristics tend to deteriorate. On the other hand, when the D 50 particle size is larger than this, the particles may not adhere or attach to each other well in the reaction step S2 described later. Also in this case, the cycle characteristics tend to deteriorate.

[0027] The D 50 particle size of nickel hydroxide may be, for example, 3 μm or more, or may be 8 μm or less, or may be 5 μm or less. Note that the "D 50The "particle size" refers to the particle size (median diameter) corresponding to 50% by volume in the volume-based particle size distribution (cumulative distribution) based on the laser diffraction / scattering method, as described above. The cumulative distribution is represented by a graph with the horizontal axis representing the particle size (μm) and the vertical axis representing the cumulative frequency (volume %), as shown in FIG. 2B, for example.

[0028] In a preferred embodiment, as nickel hydroxide, (3) the mode diameter is D 50 larger than the particle size (i.e., D 50 particle size < mode diameter); is used. Thereby, as described in the examples below, for example, compared with the case of using nickel hydroxide that does not satisfy the above size relationship, a battery with more excellent cycle characteristics can be realized. The mode diameter of nickel hydroxide is preferably 1.9 to 10 μm, more preferably 5 to 8 μm.

[0029] In this specification, the "mode diameter" refers to the particle size (most frequent particle size) with the highest frequency in the volume-based particle size distribution (frequency distribution) based on the laser diffraction / scattering method. The frequency distribution is represented by a graph with the horizontal axis representing the particle size (μm) and the vertical axis representing the frequency (volume %), as shown in FIG. 2A, for example. Note that since the frequency distribution represents the ratio of the amount of particles per particle size range, it has a width in the case of histogram display. In that case, the median of the width is used as the mode diameter.

[0030] In another preferred embodiment, as nickel hydroxide, the following conditions: (4) the frequency of the mode diameter is 10 to 20% by volume; (5) the ratio of D 20 to the particle size of D 50 is 1.1 to 1.9; are all satisfied. In this specification, the "ratio (D 50 particle size / D 20 particle size)" refers to the ratio of D 20 to the particle size of D 50 in the volume-based particle size distribution (cumulative distribution) based on the laser diffraction / scattering method. The frequency of the mode diameter and the above ratio (D 50 particle size / D 20 particle size) can be one index representing the spread of the particle size distribution. The frequency of the mode diameter being below a predetermined value, and the above ratio (D 50Particle size / D 20 The particle size being equal to or greater than a predetermined value may mean that the particle size distribution has a predetermined width.

[0031] By using nickel hydroxide that satisfies both of the above (4) and (5), the generation of fine powder and the adhesion balance can be optimized, and the mixing of fine powder into the high Ni-containing lithium composite oxide can be further suppressed. As a result, as described in the examples to be described later, for example, nickel hydroxide that does not satisfy the range of the above mode diameter, or the above ratio (D 50 Particle size / D 20 When compared with the case of using nickel hydroxide that does not satisfy the range of the particle size), a battery having more excellent cycle characteristics can be realized. The frequency of the mode diameter is more preferably 12% by volume or more, and more preferably 17% by volume or less. The above ratio (D 50 Particle size / D 20 The particle size) is more preferably 1.3 or more, and more preferably 1.5 or less.

[0032] Nickel hydroxide is typically in the form of secondary particles formed by aggregation of a plurality of primary particles by physical or chemical bonding forces. In other words, nickel hydroxide (i.e., secondary particles) is an aggregate of primary particles in which a large number of primary particles are assembled to form one particle.

[0033] The reaction step S2 utilizes the solid-phase reaction method, and is a step of obtaining a Ni-containing lithium composite oxide by mixing at least the powdery nickel hydroxide (Ni source) and the Li source prepared in the above preparation step S1 and firing them. The solid-phase reaction method is a method of synthesizing a target substance by weighing and mixing powder raw materials of compounds containing necessary elements (for example, carbonates, hydroxides, etc.) so as to have a predetermined composition ratio, and then firing them.

[0034] The mixing method is not particularly limited, and a conventionally known dry mixing method or wet mixing method can be adopted. Mixing can be performed, for example, using a ball mill, a jet mill, a planetary mixer, a disperser, a mortar, or the like.

[0035] In the first embodiment, the reaction step S2 includes, in this order, a mixture preparation step of obtaining a mixture by a dry mixing method, and a firing step of firing the mixture to obtain a high-Ni-containing lithium composite oxide. The dry mixing method that does not use a solvent is simple, can suppress the manufacturing cost, and can also reduce the environmental load. Hereinafter, the case of obtaining a lithium nickel cobalt manganese composite oxide as the Ni-containing lithium composite oxide will be specifically described as an example.

[0036] The mixture preparation step is a step of dry mixing at least nickel hydroxide serving as a Ni source and a Li source as metal element sources to obtain a mixture. Here, it is a step of dry mixing at least nickel hydroxide serving as a Ni source, a Li source, a Co source, and a Mn source to obtain a mixture. The order of mixing is not particularly limited. For example, first, a preliminary mixture may be prepared by mixing transition metal element sources (Ni source, Co source, Mn source), and then, a Li source may be added to and mixed with the preliminary mixture to prepare the mixture in two steps.

[0037] The metal element sources other than the Ni source (Li source, Co source, Mn source) may be, for example, compounds such as carbonates, hydroxides, nitrates, sulfates, and oxalates. Among them, carbonates are preferred. The metal element sources other than the Ni source (Li source, Co source, Mn source) are typically in powder form. The mixing ratio of the metal element sources including the Ni source may be determined so that x, y, and z in the above formula (I) have desired values. Thereby, a mixture containing all the metal elements contained in the high-Ni-containing lithium composite oxide (that is, Li, Ni, Co, Mn in the case of a lithium nickel cobalt manganese composite oxide) is obtained. The mixture is typically in powder form. The mixture may further contain, for example, the M element source and the Q element source in the above formula (I).

[0038] The firing step is a step of firing the mixture obtained in the above mixture preparation step. The firing conditions may be the same as those in the prior art and can be appropriately adjusted depending on, for example, the properties of the mixture. Although not particularly limited, the firing temperature is generally 650°C or higher, preferably 700°C or higher, 750°C or higher, for example 800°C or higher, and generally 1000°C or lower, for example 900°C or lower. The firing time is generally 2 to 24 hours, preferably 5 to 12 hours. The heating rate is, for example, 5 to 40°C / min. The firing atmosphere is preferably an oxygen-containing atmosphere, for example, an oxygen atmosphere or an air atmosphere. In the first embodiment, a high-Ni-containing lithium composite oxide can be obtained in this way.

[0039] In the second embodiment, the reaction step S2 includes, in this order, a slurry preparation step of preparing a slurry, a granulation step of spray-drying the slurry to obtain granulated powder, and a firing step of firing the granulated powder. By firing after once preparing the granulated powder, the dispersibility and homogeneity of the powder raw material (metal element source) are improved, and the particles are likely to adhere or attach to each other. As a result, the mixing of fine powder into the high-Ni-containing lithium composite oxide can be further suppressed. Thereby, the cycle characteristics of the battery can be further improved.

[0040] The slurry preparation step is a step of dispersing at least nickel hydroxide serving as a Ni source and a Li source in a solvent as metal element sources to prepare a slurry (suspension). Here, it is a step of dispersing at least nickel hydroxide serving as a Ni source, a Li source, a Co source, and a Mn source in a solvent to prepare a slurry. The metal element sources other than the Ni source (Li source, Co source, Mn source) and the mixing ratio may be the same as those in the mixture preparation step of the first embodiment described above. The solvent is typically water, but may also be a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, an organic solvent that can be uniformly mixed with water, for example, a lower alcohol, a lower ketone, etc. can be used. The properties (viscosity) of the slurry are preferably appropriately adjusted as described in, for example, Patent Document 1 so as to be suitable for the spray granulation method.

[0041] The granulation process is a process of obtaining granulated powder from a slurry using a spray granulation method (spray drying method). Specifically, the above slurry is sprayed into a dry atmosphere and dried to granulate (mold) a plurality of granulated particles. In this method, the particles contained in the sprayed droplets are generally granulated into one lump. According to the study of the present inventor, especially when passing through the spray granulation method, if the D 50 particle size of the raw material is too small, a large amount of fine powder is mixed in the obtained high-Ni-containing lithium composite oxide, and the cycle characteristics tend to deteriorate. Therefore, it is particularly effective to apply the technology disclosed herein. The granulation conditions and the D 50 particle size of the granulated powder may be the same as those in the prior art, and can be appropriately adjusted according to the properties of the slurry and the like. Thereby, typically, a granulated powder in which all the metal elements contained in the high-Ni-containing lithium composite oxide (that is, in the case of lithium nickel cobalt manganese composite oxide, Li, Ni, Co, Mn) are contained in each granulated particle can be preferably obtained.

[0042] In addition, in the second embodiment, the spray granulation method is adopted as the granulation method. However, in other embodiments, other conventionally known granulation methods, such as tumbling granulation method, fluidized bed granulation method, stirring granulation method, compression granulation method, extrusion granulation method, crushing granulation method, etc. can also be adopted.

[0043] The firing process is a process of firing the granulated powder obtained in the above granulation process. The firing conditions may be the same as those in the mixture preparation process of the first embodiment described above, and can be appropriately adjusted according to the properties of the granulated powder and the like. In the second embodiment, a high-Ni-containing lithium composite oxide can be obtained in this way.

[0044] 〔Lithium Ion Secondary Battery〕 The cathode active material obtained by the above manufacturing method has less fine powder mixed in and is suitable for use in a lithium ion secondary battery. Therefore, a lithium ion secondary battery containing the cathode active material has excellent cycle characteristics and can maintain a high energy density over a long period of time.

[0045] FIG. 1 is a longitudinal sectional view schematically showing the internal structure of a lithium ion secondary battery 100 according to an embodiment. In the following drawings, members and parts having the same function are denoted by the same reference numerals, and duplicate explanations may be omitted or simplified. The lithium ion secondary battery 100 shown in FIG. 1 is a rectangular battery in which a flat electrode body 20 and a non-aqueous electrolyte 80 are housed and sealed in a flat rectangular battery case 30. Note that FIG. 1 is an example and is not limited to what is shown. The lithium ion secondary battery may be a coin type, button type, cylindrical type, laminate case type, or the like in other embodiments.

[0046] The battery case 30 is an exterior container that houses the electrode body 20 and the non-aqueous electrolyte 80. As the material of the battery case 30, for example, a lightweight and highly thermally conductive metal material such as aluminum is used. On the outer surface of the battery case 30, a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin safety valve 36 set to release the internal pressure when the internal pressure of the battery case 30 rises above a predetermined level are provided. The positive electrode terminal 42 is electrically connected to the positive electrode current collector plate 42a, and the negative electrode terminal 44 is electrically connected to the negative electrode current collector plate 44a.

[0047] Here, the electrode body 20 is a wound electrode body in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped via two strip-shaped separator sheets 70 and wound in the longitudinal direction. However, in other embodiments, the electrode body may be a laminated electrode body in which a rectangular positive electrode and a rectangular negative electrode are laminated via a rectangular separator. As shown partially broken in FIG. 1, the positive electrode sheet 50 has a configuration in which a positive electrode active material layer 54 is formed along the longitudinal direction on one or both sides (both sides here) of the strip-shaped positive electrode current collector 52. The negative electrode sheet 60 has a configuration in which a negative electrode active material layer 64 is formed along the longitudinal direction on one or both sides (both sides here) of the strip-shaped negative electrode current collector 62.

[0048] At both ends of the electrode body 20 in the winding axis direction (width direction orthogonal to the longitudinal direction), there are formed a positive electrode current collector 52 exposed without forming a positive electrode active material layer 54, and a negative electrode current collector 62 exposed without forming a negative electrode active material layer 64, which are formed so as to protrude outward. The positive electrode active material layer non-formation part 52a and the negative electrode active material layer non-formation part 62a each function as a current collection part. A positive electrode current collecting plate 42a is provided on the positive electrode active material layer non-formation part 52a, and a negative electrode current collecting plate 44a is provided on the negative electrode active material layer non-formation part 62a. Note that the shapes of the positive electrode active material layer non-formation part 52a and the negative electrode active material layer non-formation part 62a are not limited to those in the illustrated example. The positive electrode active material layer non-formation part 52a and the negative electrode active material layer non-formation part 62a may be formed as current collection tabs processed into a predetermined shape.

[0049] The positive electrode current collector 52 is strip-shaped here. The positive electrode current collector 52 is preferably made of metal, and more preferably made of a metal foil. The positive electrode current collector 52 is aluminum foil here. The positive electrode active material layer 54 contains at least a positive electrode active material (high Ni-containing lithium composite oxide) manufactured by the manufacturing method disclosed herein. The positive electrode active material layer 54 may further contain other types of positive electrode active materials other than the positive electrode active material manufactured by the manufacturing method disclosed herein. When the total positive electrode active material contained in the positive electrode active material layer 54 is 100% by mass, the proportion of the positive electrode active material manufactured by the manufacturing method disclosed herein is generally 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, for example, 85 to 100% by mass. Thereby, the effects of the technology disclosed herein can be exhibited at a high level.

[0050] The positive electrode active material layer 54 may further contain additive components other than the positive electrode active material. Examples of the additive components include a conductive material, a binder, trilithium phosphate, and the like. Examples of the conductive material include carbon blacks such as acetylene black (AB) and carbon materials such as graphite. Examples of the binder include fluorine-based resins such as polyvinylidene fluoride (PVdF).

[0051] Although not particularly limited, when the entire positive electrode active material layer 54 is taken as 100% by mass, the proportion of the positive electrode active material is preferably 70% by mass or more, more preferably 80 to 99% by mass, and still more preferably 85 to 98% by mass. The proportion of the conductive material is preferably 0.5 to 15% by mass, for example, 1 to 10% by mass, and still more preferably 1 to 5% by mass. The proportion of the binder is preferably 0.5 to 15% by mass, for example, 0.8 to 10% by mass, and still more preferably 1 to 5% by mass.

[0052] The negative electrode current collector 62 is strip-shaped here. The negative electrode current collector 62 is preferably made of metal, and more preferably made of a metal foil. The negative electrode current collector 62 is a copper foil here. The negative electrode active material layer 64 contains a negative electrode active material. As the negative electrode active material, for example, carbon materials such as graphite, hard carbon, and soft carbon can be used. The negative electrode active material layer 64 may contain additive components other than the negative electrode active material. Examples of the additive components include a binder, a thickener, and the like. Examples of the binder include rubbers such as styrene-butadiene rubber (SBR), and fluorine-based resins such as polyvinylidene fluoride (PVdF). Examples of the thickener include celluloses such as carboxymethyl cellulose (CMC).

[0053] The separator sheet 70 is strip-shaped here. Examples of the separator sheet 70 include porous sheets (films) made of resins such as polyethylene (PE), polypropylene (PP), and polyester. Such a porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure in which PP layers are laminated on both sides of a PE layer). A heat-resistant layer (HRL) may be provided on the surface of the separator sheet 70.

[0054] The non-aqueous electrolyte 80 is typically a non-aqueous electrolyte solution containing a non-aqueous solvent and a supporting salt (electrolyte salt). However, in other embodiments, it may be a polymer electrolyte. As the non-aqueous solvent, various carbonate, ether, ester and other organic solvents used in the electrolyte of general lithium-ion secondary batteries can be used alone or in appropriate combinations of two or more. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), etc. Examples of the supporting salt include lithium salts such as LiPF6 and LiBF4.

[0055] Such a lithium-ion secondary battery 100 can be manufactured by a manufacturing method including a positive electrode manufacturing step of manufacturing a positive electrode sheet 50 using the positive electrode active material (high-Ni-containing lithium composite oxide) manufactured by the above manufacturing method.

[0056] The lithium-ion secondary battery 100 can be used for various applications. Since it has a high energy density and excellent cycle characteristics, it can be suitably used, for example, as a power source (driving power source) for a motor mounted on vehicles such as passenger cars and trucks. The type of vehicle is not particularly limited, and examples include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), battery electric vehicles (BEVs), etc.

[0057] Hereinafter, examples related to the present invention will be described, but the present invention is not intended to be limited to those shown in such examples.

[0058] <Preparation of Nickel Hydroxide> In Comparative Examples 1 to 4 and Examples 1 to 24, first, commercially available nickel hydroxide (secondary particle form) was prepared as a pulverized raw material. This was pulverized using a ball mill, and by varying the ball diameter, rotation speed, and pulverization time of the ball mill at this time, the properties of nickel hydroxide (particularly the BET specific surface area and particle size distribution) were adjusted. Specifically, when increasing the BET specific surface area or decreasing the particle diameter, the rotation speed was increased, the pulverization time was lengthened, or the ball diameter was decreased. Also, when widening the particle size distribution, the rotation speed was decreased or the pulverization time was shortened. Furthermore, a dry classifier was used, and by adjusting the classification point, the particle size distribution (specifically, the maximum particle diameter) was adjusted, and nickel hydroxides with different properties (Comparative Examples 1 to 4, Examples 1 to 24) were prepared. 50 When increasing the rotation speed, lengthening the pulverization time, or decreasing the ball diameter, the BET specific surface area was increased or the particle diameter was decreased. Also, when decreasing the rotation speed or shortening the pulverization time, the particle size distribution was widened. Furthermore, a dry classifier was used, and by adjusting the classification point, the particle size distribution (specifically, the maximum particle diameter) was adjusted, and nickel hydroxides with different properties (Comparative Examples 1 to 4, Examples 1 to 24) were prepared.

[0059] <Measurement of properties of nickel hydroxide> ·BET specific surface area Using nitrogen as the adsorbed gas and a commercially available specific surface area and pore size analyzer, the BET specific surface area of nickel hydroxide in each example was measured by the volumetric adsorption method. The results are shown in Table 1. ·Particle size distribution First, a commercially available laser diffraction / scattering type particle size distribution measuring device (model "LA-950" manufactured by Horiba, Ltd.) was prepared, and a sample (nickel hydroxide) and pure water (solvent) were put into the measurement cell. Next, after subjecting the measurement cell to ultrasonic irradiation for 4 minutes for pretreatment, measurement was performed in the transmission mode using an aqueous solvent with a refractive index of 1.240 - 0 (refractive index 1.333). Then, using the attached analysis software, the D 50 particle diameter (median diameter), mode diameter and its frequency, and the D 20 ratio of the particle diameter to the D 50 particle diameter (D 50 particle diameter / D 20 particle diameter) were calculated. The results are shown in Table 1. Also, as a representative example, Fig. 2A shows the frequency distribution of Example 16, and Fig. 2B shows the cumulative distribution of Example 16. Here, the particle diameter width is set to 1 μm for the frequency distribution.

[0060] <Preparation of cathode active material> In Comparative Examples 1 to 4 and Examples 1 to 23, a mixture was prepared by a dry mixing method, and the obtained mixture was reacted by a solid-phase reaction method. Specifically, first, powdered nickel hydroxide (Ni source) after particle size adjustment, CoCO3 (Co source), and MnCO3 (Mn source) were preliminarily mixed, Li2CO3 (Li source) was added to the obtained preliminary mixture, and further mixed to obtain a mixture. The atomic weight ratio of Ni to the total atomic weight of metal elements other than Li (Ni + Co + Mn) was set to the value shown in Table 1. Also, the ratio of the atomic weight of Li to the total atomic weight of transition metal elements (Ni + Co + Mn) (Li / transition metal ratio) was set to 1.05 atm%. Then, the obtained mixture was fired at 900 °C for 10 hours in an oxygen atmosphere. Thereby, a high-Ni-containing lithium composite oxide (cathode active material) was obtained.

[0061] In Example 24, granulated powder was obtained using a spray granulation method, and the obtained granulated powder was reacted by a solid-phase reaction method. Specifically, first, powdered nickel hydroxide (Ni source) after particle size adjustment, CoCO3 (Co source), and MnCO3 (Mn source) were preliminarily mixed, Li2CO3 (Li source) was added to the obtained preliminary mixture, and further mixed to obtain a mixture. The atomic weight ratio of Ni to the total atomic weight of metal elements other than Li (Ni + Co + Mn) was set to the value shown in Table 1. Also, the ratio of the atomic weight of Li to the total atomic weight of transition metal elements (Ni + Co + Mn) (Li / transition metal ratio) was set to 1.05 atm%. Next, the obtained mixture was dispersed in water to prepare a slurry. This slurry was sprayed and dried in a drying atmosphere to granulate the granulated powder. Then, the obtained granulated powder was fired at 900 °C for 10 hours in an oxygen atmosphere. Thereby, a high-Ni-containing lithium composite oxide (cathode active material) was obtained.

[0062] <Fabrication of Lithium-Ion Secondary Battery for Evaluation> The obtained positive electrode active material (high-Ni-containing lithium composite oxide), acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder were mixed at a mass ratio of positive electrode active material:AB:PVdF = 85:10:5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare a slurry for forming a positive electrode active material layer. Next, this slurry for forming a positive electrode active material layer was applied to the surface of an aluminum foil (positive electrode current collector) and dried to produce a positive electrode sheet.

[0063] Also, graphite (C) as a negative electrode active material, styrene-butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener were mixed at a mass ratio of C:SBR:CMC = 98:1:1, and an appropriate amount of ion-exchanged water was added to prepare a slurry for forming a negative electrode active material layer. This slurry for forming a negative electrode active material layer was applied to the surface of a copper foil (negative electrode current collector) and dried to produce a negative electrode sheet.

[0064] Also, a porous polyolefin sheet having a three-layer structure of PP / PE / PP was prepared as a separator. Next, the positive electrode sheet and the negative electrode sheet were overlapped with a separator interposed therebetween to produce an electrode assembly. Next, electrode terminals were attached to the electrode assembly, which was inserted into a battery case, and a non-aqueous electrolyte was injected. Note that as the non-aqueous electrolyte, a mixture solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) at a volume ratio of EC:DMC:EMC = 30:40:30 and in which LiPF6 as a supporting salt was dissolved at a concentration of 1 mol / L was used. Thereafter, the battery case was sealed to produce a lithium-ion secondary battery for evaluation according to each example.

[0065] <Activation Treatment of Lithium-Ion Secondary Battery> First, the lithium-ion secondary batteries for evaluation according to each example were subjected to an activation treatment. Specifically, each lithium-ion secondary battery for evaluation was charged at a constant current up to 4.2 V at a charging rate of 0.1C, and then charged at a constant voltage until the current value reached 1 / 50C to obtain a fully charged state (SOC 100% state). Thereafter, each lithium-ion secondary battery for evaluation was discharged at a constant current up to 3.0 V at a discharging rate of 0.1C.

[0066] <Measurement of initial resistance> Each of the above-activated lithium-ion secondary batteries for evaluation was adjusted to a state of SOC 50%. Then, in an environment at 25°C, it was discharged at a current value of 100 mA for 10 seconds, and the voltage drop amount ΔV was determined. The battery resistance was calculated by dividing the voltage drop amount ΔV by the discharge current value (100 mA), and this was taken as the initial resistance.

[0067] <Measurement of resistance increase rate> Each lithium-ion secondary battery for evaluation was placed in an environment at 60°C, charged at a constant current up to 4.1 V at a charging rate of 1C, and then discharged at a constant current up to 3.0 V at a discharging rate of 1C. One charge-discharge cycle was defined as one cycle, and this was repeated 200 times. Then, the battery resistance after 200 cycles was measured in the same manner as the initial resistance, and the resistance increase rate (%) after the cycle was calculated from the following formula: (battery resistance after 200 cycles / initial resistance) × 100. The results are shown in Table 1.

[0068]

Table 1

[0069] From the results in Table 1, in the preparation process, in Comparative Examples 2 and 3 where nickel hydroxide with a BET specific surface area of less than 10 m 2 / g or more than 30 m 2 / g was used, and in Comparative Examples 4 and 5 where nickel hydroxide with a D 50 particle size of less than 2 μm or more than 10 μm was used, the resistance increase rate after the cycle was relatively high. For this reason, when the BET specific surface area of nickel hydroxide is less than 10 m 2 / g (specifically 5 m 2Comparative Example 2 which is (g), and D of nickel hydroxide 50 In Comparative Example 5 where the particle size exceeds 10 μm (specifically 13 μm), the particles did not adhere or attach well to each other during the solid-phase reaction, and due to a large amount of fine powder being mixed in the high Ni-containing lithium composite oxide, it is considered that the reactivity at the solid-liquid interface increased or a large amount of coating was formed on the surface of the positive electrode active material. Also, the BET specific surface area of nickel hydroxide is 30 m 2 Exceeding / g (specifically 40 m 2 / g) is Comparative Example 3, and D of nickel hydroxide 50 In Comparative Example 4 where the particle size is less than 2 μm (specifically 1 μm), it is considered that due to a large amount of fine powder remaining in the obtained high Ni-containing lithium composite oxide, the reactivity at the solid-liquid interface increased or a large amount of coating was formed on the surface of the positive electrode active material.

[0070] Also, in Comparative Example 1 where the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is less than 50 atm% (specifically 45 atm%), the effects of the technology disclosed herein were not fully exhibited.

[0071] For these comparative examples, the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more, and in the preparation process, (1) the BET specific surface area is 10 - 30 m 2 / g, and (2) D 50 In Examples 1 to 24 using nickel hydroxide with a particle size of 2 - 10 μm, it can be seen that the increase rate of resistance after cycling is relatively suppressed and the cycle characteristics are improved. Such results indicate the technical significance of the invention disclosed herein.

[0072] Among them, in Examples 9 to 24 using nickel hydroxide with (3) a mode diameter larger than the D50 particle size in the preparation process, the increase rate of resistance after cycling was suppressed to 200% or less. Also, in the preparation process, (4) the frequency of the mode diameter is 10 - 20% by volume, and (5) D 20 With respect to the particle size 50In Examples 12 to 20 and 24 where nickel hydroxide with a particle size ratio of 1.1 to 1.9 was used, the resistance increase rate after cycling was suppressed to 180% or less. Further, in Example 24 where the positive electrode active material was produced using the spray granulation method, the resistance increase rate after cycling was suppressed to the lowest level.

[0073] As described above, specific embodiments of the technology disclosed herein include those described in the following respective items. Item 1: A method for producing a positive electrode active material containing a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more. As the Ni source, the BET specific surface area based on the nitrogen adsorption method is 10 m 2 / g or more and 30 m 2 / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, the D corresponding to 50% by volume cumulative from the smaller particle size side 50 A preparation step of preparing powdery nickel hydroxide having a particle size of 2 μm or more and 10 μm or less, and a reaction step of obtaining a Ni-containing lithium composite oxide by the solid-phase reaction method by mixing and firing at least the nickel hydroxide and a Li source. Item 2: The production method according to Item 1, wherein the mode diameter in the particle size distribution of the nickel hydroxide is larger than the D 50 particle size. Item 3: The nickel hydroxide has a mode diameter frequency in the particle size distribution of 10% by volume or more and 20% by volume or less, and the ratio of the D 20 particle size to the D 50 particle size (D 50 particle size / D 20 particle size) is 1.1 or more and 1.9 or less. The production method according to Item 1 or Item 2. Item 4: The reaction step includes a mixture preparation step of dry-mixing at least the nickel hydroxide and the Li source to obtain a mixture, and a firing step of firing the mixture. The production method according to any one of Items 1 to 3. Item 5: The above reaction process includes at least a slurry preparation process of dispersing the above nickel hydroxide and the above Li source in a solvent to prepare a slurry, a granulation process of spray-drying the above slurry by a spray granulation method to obtain granulated powder, and a firing process of firing the above granulated powder, and is the manufacturing method according to any one of Items 1 to 3. Item 6: The above Ni-containing lithium composite oxide further contains a transition metal other than Ni, and in the above reaction process, the above nickel hydroxide, the Li source, and the transition metal source other than Ni are mixed, and it is the manufacturing method according to any one of Items 1 to 5. Item 7: A manufacturing method of a lithium ion secondary battery, including a positive electrode manufacturing process of manufacturing a positive electrode using the positive electrode active material manufactured by the manufacturing method according to any one of Items 1 to 6.

[0074] As described above, specific examples of the present invention have been described in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples exemplified above. Also, if its technical features are not described as essential, they can be appropriately deleted.

Explanation of Reference Numerals

[0075] 20 Electrode body 30 Battery case 50 Positive electrode sheet (positive electrode) 54 Positive electrode active material layer 60 Negative electrode sheet (negative electrode) 64 Negative electrode active material layer 80 Non-aqueous electrolyte 100 Lithium ion secondary battery S1 Preparation process S2 Reaction process

Claims

1. A method for manufacturing a positive electrode active material including a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more, comprising: As the Ni source, the BET specific surface area based on the nitrogen adsorption method is 10 m ２ / g or more and 30 m ２ / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, D corresponding to 50% by volume from the smaller particle size side ５０ The particle size is 2 μm or more and 10 μm or less, and the mode diameter in the particle size distribution is larger than the D50 particle size. A preparation step of preparing powdery nickel hydroxide is provided, a reaction step of obtaining a Ni-containing lithium composite oxide by a solid-phase reaction method by mixing and firing at least the nickel hydroxide and a Li source; A method for manufacturing a positive electrode active material, including:

2. The reaction step includes: a mixture preparation step of dry-mixing at least the nickel hydroxide and the Li source to obtain a mixture; a firing step of firing the mixture; The manufacturing method according to Claim 1, including: The manufacturing method according to Claim 1.

3. A method for manufacturing a positive electrode active material including a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more, comprising: As the Ni source, a powdery nickel hydroxide having a BET specific surface area based on the nitrogen adsorption method of 10 m ２ / g or more and 30 m ２ / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, the D ５０ particle size corresponding to 50% by volume from the smaller particle size side is 2 μm or more and 10 μm or less, a preparation step of preparing the powdery nickel hydroxide a reaction step of obtaining a Ni-containing lithium composite oxide by a solid-phase reaction method by mixing and firing at least the nickel hydroxide and a Li source; including, The nickel hydroxide has, in the particle size distribution, a frequency of the mode diameter of 10% by volume or more and 20% by volume or less, and a ratio (D50 particle size / D20 particle size) of the D50 particle size to the D20 particle size corresponding to 20% by volume cumulative from the smaller particle size is 1.1 or more and 1.9 or less. A method for manufacturing a positive electrode active material.

4. A method for manufacturing a positive electrode active material including a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more, comprising: As the Ni source, a powdery nickel hydroxide having a BET specific surface area based on the nitrogen adsorption method of 10 m ２ / g or more and 30 m ２ / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, the D ５０ particle size corresponding to 50% by volume from the smaller particle size side is 2 μm or more and 10 μm or less, and a preparation step of preparing the powdery nickel hydroxide a reaction step of obtaining a Ni-containing lithium composite oxide by a solid-phase reaction method by mixing and firing at least the nickel hydroxide and a Li source; including, The reaction step includes: a slurry preparation step of dispersing at least the nickel hydroxide and the Li source in a solvent to prepare a slurry; a granulation step of spray-drying the slurry by a spray granulation method to obtain granulated powder; a firing step of firing the granulated powder; A method for manufacturing a positive electrode active material, including:

5. A method for manufacturing a positive electrode active material including a Ni-containing lithium composite oxide in which the ratio of the atomic weight of Ni to the total atomic weight of metal elements other than Li is 50 atm% or more, comprising: As the Ni source, a powdery nickel hydroxide having a BET specific surface area based on the nitrogen adsorption method of 10 m ２ / g or more and 30 m ２ / g or less, and in the volume-based particle size distribution based on the laser diffraction / scattering method, the D ５０ particle size corresponding to 50% by volume from the smaller particle size side is 2 μm or more and 10 μm or less, and a preparation step of preparing the powdery nickel hydroxide a reaction step of obtaining a Ni-containing lithium composite oxide by a solid-phase reaction method by mixing and firing at least the nickel hydroxide and a Li source; including, The Ni-containing lithium composite oxide further contains a transition metal other than Ni. A method for manufacturing a positive electrode active material, comprising mixing nickel hydroxide, an Li source, and a transition metal source other than Ni in the reaction step.

6. A method for manufacturing a lithium-ion secondary battery, comprising a positive electrode manufacturing step of manufacturing a positive electrode using the positive electrode active material manufactured by the manufacturing method according to any one of Claims 1 to 5. A method for manufacturing a lithium-ion secondary battery.

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