Method for producing positive electrode active material

Abstract

To provide a method that enables production of a positive electrode active material having a high nickel content and capable of imparting high output to a lithium ion secondary battery without using an oxygen atmosphere.SOLUTION: A method for producing a positive electrode active material disclosed here includes the steps of: performing a heat treatment on a hydroxide in which a ratio of a nickel content to a total content of all the metal elements is 60% by mole or more, in an air atmosphere to thereby obtain an oxide having primarily a spinel structure; mixing the oxide with a Li-containing compound; and firing an obtained mixture in an air atmosphere to thereby convert the mixture to a lithium composite oxide with a layered rock salt structure. In the oxide having primarily a spinel structure, a peak integrated intensity ratio of a (003) plane to a (440) plane is 1.5 or less, and a peak integrated intensity ratio of the (440) plane to a (311) plane is 4.5 or more, the peak integrated intensity ratios being obtained by powder X-ray diffraction measurement using CuKα rays.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material. [Background technology]

[0002] In recent years, lithium ion secondary batteries have been suitably used as portable power sources for personal computers, mobile terminals, and the like, and as power sources for driving vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs).

[0003] In order to extend the driving range of vehicles, lithium-ion secondary batteries are required to have a higher capacity. One of the typical positive electrode active materials for lithium-ion secondary batteries is a lithium composite oxide containing nickel, and it is known that the capacity of lithium-ion secondary batteries can be increased by using a lithium composite oxide with a high nickel content (see, for example, Patent Document 1).

[0004] When producing a lithium composite oxide with a high nickel content, a precursor of the lithium composite oxide (particularly a composite hydroxide) and a lithium source are usually fired in an oxygen atmosphere (i.e., an atmosphere with a higher oxygen concentration than the air) to suppress cation mixing of divalent nickel. Patent Document 1 proposes that in order to reduce oxygen consumption from the standpoint of reducing production costs, a nickel-cobalt-manganese composite hydroxide and a lithium source are subjected to primary calcination in an oxygen atmosphere, and then the primary calcined product is subjected to main calcination in an air atmosphere. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2022-517078 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 still requires an oxygen atmosphere in the primary calcination. Therefore, there is still room for reducing production costs, and providing an oxygen atmosphere reduces productivity. Furthermore, excess oxygen inhibits the crystal growth of the lithium composite oxide, necessitating a higher calcination temperature, which also reduces productivity. For these reasons, there is a need to develop a method for producing a lithium composite oxide (i.e., a positive electrode active material) with a high nickel content without using an oxygen atmosphere. Furthermore, high output is desired for lithium-ion secondary batteries, particularly when used as a power source for driving vehicles.

[0007] Therefore, an object of the present invention is to provide a method for producing a positive electrode active material that can impart high output to a lithium ion secondary battery and has a high nickel content, without using an oxygen atmosphere. [Means for solving the problem]

[0008] The method for producing a positive electrode active material disclosed herein includes the steps of: heat-treating, in an air atmosphere, a hydroxide having a nickel content of 60 mol % or more relative to the total content of all metal elements to obtain an oxide having a spinel structure as a main component; mixing the oxide with a Li-containing compound; and calcining the resulting mixture in an air atmosphere to convert it into a lithium composite oxide having a layered rock salt structure. In the oxide having a spinel structure as a main component, the peak integrated intensity ratio of the (003) plane to the (440) plane is 1.5 or less, and the peak integrated intensity ratio of the (440) plane to the (311) plane is 4.5 or more, as determined by powder X-ray diffraction measurement using CuKα radiation.

[0009] According to this configuration, a positive electrode active material that can impart high output to a lithium ion secondary battery and has a high nickel content can be produced without using an oxygen atmosphere. [Brief explanation of the drawings]

[0010] [Figure 1]1 is a flowchart showing each step of a method for producing a positive electrode active material according to one embodiment of the present invention. [Figure 2] 1 is a cross-sectional view schematically illustrating the configuration of a lithium ion secondary battery constructed using a positive electrode active material obtained by a manufacturing method according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic exploded view showing the configuration of the wound electrode body of FIG. 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Matters not mentioned in this specification but necessary for implementing the present invention can be understood as design matters for a person skilled in the art based on the prior art in the relevant field. The present invention can be implemented based on the contents disclosed in this specification and the technical common sense in the relevant field. Furthermore, in the following drawings, components and parts that perform the same function are denoted by the same reference numerals. Furthermore, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect the actual dimensional relationships. In this specification, a numerical range expressed as "A to B" includes A and B.

[0012] In this specification, the term "secondary battery" refers to an electricity storage device that can be repeatedly charged and discharged. In addition, in this specification, the term "lithium ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging by the transfer of charge associated with the lithium ions between the positive and negative electrodes.

[0013] As shown in FIG. 1 , the method for producing a cathode active material according to this embodiment includes the steps of heat-treating a hydroxide having a nickel content of 60 mol % or more relative to the total content of all metal elements in an air atmosphere to obtain a spinel-based oxide (hereinafter also referred to as the "heat-treatment step") S101, mixing the oxide with a Li-containing compound (hereinafter also referred to as the "mixing step") S102, and calcining the resulting mixture in an air atmosphere to convert it into a layered rock-salt lithium composite oxide (hereinafter also referred to as the "calcination step") S103. Here, the spinel-based oxide has a peak integrated intensity ratio of the (003) plane to the (440) plane of 1.5 or less and a peak integrated intensity ratio of the (440) plane to the (311) plane of 4.5 or more, as determined by powder X-ray diffraction measurement. Each step in the method for producing a cathode active material according to this embodiment is described in detail below.

[0014] In the heat treatment step S101, a hydroxide having a nickel content ratio of 60 mol % or more relative to the total content of all metal elements is heat treated in an air atmosphere to obtain an oxide mainly having a spinel structure.

[0015] The hydroxide used as the raw material is a nickel-containing hydroxide, and is typically a hydroxide conventionally used as a precursor when producing a lithium composite oxide (hence, hereinafter, this hydroxide is also referred to as a "precursor hydroxide"). Since the higher the nickel content, the higher the capacity of the lithium ion secondary battery can be, in this hydroxide, the ratio of the nickel content to the total content of all metal elements is preferably 80 mol % or more.

[0016] The precursor hydroxide is typically Ni a Me b(OH)2 (where Me is a metal element or a metalloid element other than Ni (e.g., Co, Mn, Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, B, Si, etc.), a + b = 1, a satisfies 0.60 ≦ a ≦ 1.00 (preferably 0.80 ≦ a ≦ 1.00), and b satisfies 0 ≦ b ≦ 0.40 (preferably 0 ≦ b ≦ 0.20)). The precursor hydroxide is, for example, a nickel cobalt manganese composite hydroxide, a nickel cobalt aluminum composite hydroxide, etc., and preferably a nickel cobalt manganese composite hydroxide. In this specification, the nickel cobalt manganese composite hydroxide may be doped with elements other than Ni, Co, Mn, O, and H (particularly, metal elements, metalloid elements), and for example, has a composition represented by the following formula (I). Ni x Co y [[ID=​​​​​​​​​​​​​​​The precursor hydroxide can be prepared according to a known method (e.g., a crystallization method). Specifically, for example, an aqueous solution of a nickel source compound (e.g., nickel sulfate) and another metal source compound (e.g., a sulfate of another metal) is prepared, and a crystallization reaction is carried out according to a known method using an aqueous solution containing an ammonium ion donor (e.g., ammonia water) and an alkaline aqueous solution (e.g., sodium hydroxide aqueous solution), thereby obtaining the precursor hydroxide.

[0020] In the heat treatment step S101, the precursor hydroxide is heat treated in an air atmosphere to obtain an oxide mainly having a spinel structure (hereinafter also referred to as "precursor oxide"). Therefore, in the heat treatment step S101, the precursor hydroxide is converted into the precursor oxide by heat treatment in an air atmosphere.

[0021] Here, the crystalline structure of the precursor oxide is mainly a spinel structure. When powder X-ray diffraction (XRD) measurement using CuKα radiation is performed, a peak for the (440) plane appears in the Miller index (hlk) for the spinel structure, and peaks for the (003) and (311) planes appear in the Miller index (hlk) for the layered rock salt structure. Therefore, regarding the crystalline structure of the precursor oxide being mainly a spinel structure, in this embodiment, the crystalline structure of the precursor oxide, as determined by powder X-ray diffraction (XRD) measurement using CuKα radiation, has a peak integrated intensity ratio of the (003) plane to the (440) plane [(003) plane / (440) plane] of 1.5 or less, and a peak integrated intensity ratio of the (440) plane to the (311) plane [(440) plane / (311) plane] of 4.5 or more.

[0022] If the peak integrated intensity ratio [(003) plane / (440) plane] exceeds 1.5, the lithium ion secondary battery will not be able to provide sufficient output characteristics. The peak integrated intensity ratio [(003) plane / (440) plane] is preferably 1.2 or less, and more preferably 1.0 or less.

[0023] If the peak integrated intensity ratio [(440) plane / (311) plane] is less than 4.5, the lithium ion secondary battery will not be able to achieve sufficient output characteristics. From the viewpoint of a higher output improvement effect, the peak integrated intensity ratio [(003) plane / (440) plane] is preferably 5.0 or more, more preferably 10 or more, even more preferably 50 or more, particularly preferably 100 or more, and most preferably 200 or more.

[0024] In the precursor oxide, the crystallite diameter of the (440) plane determined by powder X-ray diffraction (XRD) measurement using CuKα radiation is not particularly limited, but is preferably 40 Å or more.

[0025] The powder (XRD) measurement can be performed according to a known method. Specifically, the powder (XRD) measurement can be performed using CuKα radiation and a known powder X-ray diffractometer. The peak integrated intensity ratio can be calculated according to a known method. Specifically, the peak integrated intensity ratio can be calculated using software attached to the device.

[0026] The heat treatment conditions in the heat treatment step S101 are selected so that the precursor oxide satisfies these peak integrated intensity ratios determined by powder XRD measurement.

[0027] As an index of heat treatment conditions, the lower the heat treatment temperature, the larger the peak integrated intensity ratio [(003) plane / (440) plane] tends to be, and the larger the peak integrated intensity ratio [(440) plane / (311) plane] tends to be. The longer the heat treatment time, the larger the peak integrated intensity ratio [(440) plane / (311) plane] tends to be. The heat treatment temperature is preferably 400°C to 580°C, more preferably 480°C to 550°C. The heat treatment time is preferably 0.1 to 120 hours, more preferably 0.5 to 48 hours.

[0028] The heat treatment can be carried out according to a known method. For example, the heat treatment can be carried out using a continuous or batch type electric furnace. A precursor oxide mainly having a spinel structure can be obtained by the heat treatment. In this embodiment, the heat treatment step S101 is carried out in an air atmosphere, so there is no need to use an oxygen atmosphere.

[0029] The resulting precursor oxide, mainly composed of a spinel structure, has a higher tap density than the precursor hydroxide. This is due to the effect of moisture being released from the precursor hydroxide. Therefore, a larger amount of precursor oxide can be supplied to the calcination step S103, and the production method according to this embodiment is advantageous in terms of high yield.

[0030] Next, the mixing step S102 will be described. In the mixing step S102, the obtained precursor oxide is mixed with a Li-containing compound. The mixing step S102 is usually performed in an air atmosphere, as in conventional methods. Therefore, an oxygen atmosphere does not need to be used. The mixing step S102 may also be performed in a nitrogen atmosphere or an argon atmosphere.

[0031] The Li-containing compound can be a known lithium source compound used in the production of positive electrode active materials, and specific examples thereof include lithium carbonate, lithium hydroxide, lithium nitrate, lithium acetate, lithium oxalate, and lithium chloride. These can be used alone or in combination of two or more. Lithium hydroxide is preferred as the Li-containing compound.

[0032] The mixing ratio of the precursor oxide and the Li-containing compound may be determined according to the desired composition of the positive electrode active material, i.e., the mixing ratio of the precursor oxide and the Li-containing compound may be selected so that the molar ratio of the metal element contained in the precursor oxide to the Li element contained in the Li-containing compound is the same as the molar ratio of the metal element other than Li to the Li element in the desired composition of the positive electrode active material.

[0033] The mixing can be carried out according to a known method. For example, the mixing can be carried out using a known stirring or mixing device such as a shaker mixer, a Loedige mixer, a Julia mixer, a V-type mixer, or a ball mill. A mixture can be prepared by this mixing.

[0034] Next, the calcination step S103 will be described. In the calcination step S103, the mixture is calcined in an air atmosphere to convert it into a lithium composite oxide having a layered rock salt structure.

[0035] Here, in the production of the positive electrode active material, when the precursor is a hydroxide having a layered rock salt structure and the lithium source is sodium hydroxide, the reaction formula in the baking step is represented by the following formula (1) (in the following formula, M 1 is a metallic element containing Ni). M 1 (OH)2+LiOH+1 / 4O2→LiM 1 O2+3 / 2H2O (1)

[0036] On the other hand, when the precursor is an oxide having a layered rock salt structure, the reaction formula in the firing step is represented by the following formula (2) (where M 1 has the same meaning as above). M 1 O+LiOH+1 / 4O2→LiM 1 O2+1 / 2H2O (2)

[0037] On the other hand, when the precursor is an oxide having a spinel crystal structure, the reaction in the firing step is represented by the following formula (3) (wherein M 1 has the same meaning as above). 1 / 3M 1 3O4+LiOH+1 / 12O2→LiM 1 O2+1 / 2H2O (3)

[0038] As can be seen from the above formulas (1) to (3), the precursor oxide having a spinel crystal structure has a high oxygen content, and therefore the amount of oxygen required for the reaction is small (it will be understood by those skilled in the art that the same applies when the lithium source is other than sodium hydroxide). Comparing formulas (1) and (3), the amount of oxygen required when using a precursor oxide having a spinel crystal structure is one-third. Therefore, according to this embodiment, the synthesis reaction of the positive electrode active material can be carried out at the oxygen concentration contained in the air atmosphere. Therefore, in this embodiment, it is not necessary to use an oxygen atmosphere (i.e., an atmosphere with a higher oxygen concentration than the air). Furthermore, since a large amount of Ni is present in the precursor oxide in a trivalent state, ion mixing can be suppressed, and the resulting positive electrode active material can provide high output to lithium-ion secondary batteries.

[0039] The calcination temperature and calcination time are not particularly limited as long as a lithium composite oxide having a layered rock salt structure is obtained. The calcination temperature is, for example, 700°C to 1000°C, preferably 750°C to 900°C, and more preferably 790°C to 900°C. The calcination time is, for example, 3 to 72 hours, preferably 4 to 24 hours, and more preferably 5 to 12 hours. Furthermore, calcination is preferably carried out under conditions such that the crystallite diameter of the (003) plane of the resulting lithium composite oxide, as determined by powder X-ray diffraction measurement using CuKα radiation, is 600 Å to 1000 Å. Note that, if the calcination time is long, the crystallite diameter of the (003) plane tends to increase. Furthermore, if the calcination time is long, the crystallite diameter of the (003) plane tends to increase.

[0040] The mixture can be calcined according to a known method, for example, by using a continuous or batch electric furnace, etc. By calcining, a lithium composite oxide having a layered rock salt structure can be obtained as a positive electrode active material.

[0041] The resulting positive electrode active material (i.e., a lithium composite oxide having a layered rock salt structure) typically contains Li 1+c Ni a Meb O₂ (where Me represents a metal element or a metalloid element other than Ni (e.g., Co, Mn, Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, B, Si, etc.), a + b = 1, c satisfies -0.05 ≤ c ≤ 0.30, a satisfies 0.60 ≤ a ≤ 1.00 (preferably 0.80 ≤ a ≤ 1.00), and b satisfies 0 ≤ b ≤ 0.40 (preferably 0 ≤ b ≤ 0.20)). It has a composition represented by this formula.

[0042] The positive electrode active material is, for example, a lithium nickel cobalt manganese composite oxide or a lithium nickel cobalt aluminum composite oxide, and preferably a lithium nickel cobalt manganese composite oxide. In this specification, the lithium nickel cobalt manganese composite oxide may be doped with elements other than Li, Ni, Co, Mn, and O (particularly, metal elements, metalloid elements). For example, it has a composition represented by the following formula (II). Li 1+t Ni x Co y Mn z M α O₂ (II)

[0043] In formula (I), t, x, y, z, and α respectively satisfy -0.05 ≤ t ≤ 0.30, 0.60 ≤ x < 1.00, 0 < y < 0.40, 0 < z < 0.40, 0 ≤ α ≤ 0.10, and x + y + z = 1. M is at least one element selected from the group consisting of Zr, Mo, W, Mg, Ca, Na, Fe, Cr, Zn, Sn, B, and Al. t preferably satisfies 0 ≤ t ≤ 0.30. x preferably satisfies 0.80 ≤ x < 1.00, and more preferably satisfies 0.80 ≤ x ≤ 0.90. y preferably satisfies 0.05 ≤ y ≤ 0.15. z preferably satisfies 0.05 ≤ z ≤ 0.15. α preferably satisfies 0 ≤ α ≤ 0.05.

[0044] From the viewpoint of a higher output improvement effect, the positive electrode active material preferably has a crystallite diameter of the (003) plane determined by powder X-ray diffraction measurement using CuKα radiation of 600 Å to 1000 Å, more preferably 600 Å to 800 Å. The crystallite diameter of the (003) plane can be determined by a known method. Specifically, for example, powder X-ray diffraction measurement is performed by the above method, and the crystallite diameter can be determined using the half-width (FWHM) of the (003) plane, the 2θ value, and the Scherrer formula.

[0045] The average particle diameter of the positive electrode active material is not particularly limited, but is, for example, 0.05 μm to 20 μm, and preferably 2 μm to 10 μm. The average particle diameter of the positive electrode active material can be determined by taking a scanning electron microscope (SEM) photograph of the particles of the positive electrode active material and averaging the particle diameters of 100 particles selected arbitrarily.

[0046] The positive electrode active material obtained by the manufacturing method according to this embodiment has a high nickel content. Therefore, when a lithium ion secondary battery is constructed using this positive electrode active material, the capacity of the lithium ion secondary battery is high. Furthermore, a lithium ion secondary battery using this positive electrode active material also has excellent output characteristics. Therefore, the positive electrode active material according to this embodiment is preferably used as a positive electrode active material for a lithium ion secondary battery.

[0047] Therefore, a specific example of the configuration of a lithium ion secondary battery using the positive electrode active material obtained by the manufacturing method according to the present embodiment described above will be described with reference to the drawings.

[0048] The lithium-ion secondary battery 100 shown in FIG. 1 is a sealed battery constructed by housing a flat wound electrode assembly 20 and a nonaqueous electrolyte (not shown) in a flat, rectangular battery case (i.e., outer container) 30. The battery case 30 is provided with a positive electrode terminal 42 and a negative electrode terminal 44 for external connection, and a thin-walled safety valve 36 that is designed to release internal pressure when the internal pressure of the battery case 30 rises to a predetermined level or higher. The battery case 30 also has an injection port (not shown) for injecting a nonaqueous electrolyte 80. The positive electrode terminal 42 is electrically connected to a positive electrode current collector plate 42a. The negative electrode terminal 44 is electrically connected to a negative electrode current collector plate 44a. The battery case 30 is made of a lightweight metal material with good thermal conductivity, such as aluminum.

[0049] As shown in Figures 1 and 2, the wound electrode body 20 has a configuration in which a positive electrode sheet 50 and a negative electrode sheet 60 are overlapped with two long separator sheets 70 interposed therebetween and wound in the longitudinal direction. 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 in this case) of a long 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 in this case) of a long negative electrode current collector 62. The positive electrode active material layer-free portion 52a (i.e., a portion where the positive electrode active material layer 54 is not formed and the positive electrode current collector 52 is exposed) and the negative electrode active material layer-free portion 62a (i.e., a portion where the negative electrode active material layer 64 is not formed and the negative electrode current collector 62 is exposed) are formed so as to protrude outward from both ends in the winding axis direction (i.e., the sheet width direction perpendicular to the longitudinal direction) of the wound electrode body 20. The positive electrode active material layer-free portion 52a and the negative electrode active material layer-free portion 62a are joined to the positive electrode current collector 42a and the negative electrode current collector 44a, respectively.

[0050] The positive electrode current collector 52 constituting the positive electrode sheet 50 may be a known positive electrode current collector used in lithium ion secondary batteries, and examples thereof include a sheet or foil made of a metal with good conductivity (e.g., aluminum, nickel, titanium, stainless steel, etc.). Aluminum foil is preferred as the positive electrode current collector 52.

[0051] The dimensions of the positive electrode current collector 52 are not particularly limited and may be determined appropriately depending on the battery design. When an aluminum foil is used as the positive electrode current collector 52, the thickness thereof is not particularly limited, but is, for example, 5 μm to 35 μm, and preferably 7 μm to 20 μm.

[0052] The positive electrode active material layer 54 contains a positive electrode active material. At least the positive electrode active material obtained by the manufacturing method according to the present embodiment described above is used as the positive electrode active material. The content of the positive electrode active material in the positive electrode active material layer 54 (i.e., relative to the total mass of the positive electrode active material) is not particularly limited, but is preferably 70 mass% or more, more preferably 80 mass% or more, and even more preferably 85 mass% or more.

[0053] The positive electrode active material layer 54 may contain components other than the positive electrode active material, such as lithium phosphate (Li3PO4), a conductive material, and a binder.

[0054] The content of lithium phosphate in the positive electrode active material layer 54 is not particularly limited, but is preferably from 1% to 15% by mass, and more preferably from 2% to 12% by mass.

[0055] Suitable conductive materials include, for example, carbon black such as acetylene black (AB) and other carbon materials (e.g., graphite). The content of the conductive material in the positive electrode active material layer 54 is not particularly limited, but is, for example, 0.1% by mass to 20% by mass, preferably 1% by mass to 15% by mass, and more preferably 2% by mass to 10% by mass.

[0056] The binder may be, for example, polyvinylidene fluoride (PVdF), etc. The content of the binder in the positive electrode active material layer 54 is not particularly limited, but is, for example, 0.5% by mass to 15% by mass, preferably 1% by mass to 10% by mass, and more preferably 1.5% by mass to 8% by mass.

[0057] The thickness of the positive electrode active material layer 54 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0058] The negative electrode current collector 62 constituting the negative electrode sheet 60 may be a known negative electrode current collector used in lithium ion secondary batteries, and examples thereof include a sheet or foil made of a metal with good conductivity (e.g., copper, nickel, titanium, stainless steel, etc.). Copper foil is preferred as the negative electrode current collector 62.

[0059] The dimensions of the negative electrode current collector 62 are not particularly limited and may be determined appropriately depending on the battery design. When a copper foil is used as the negative electrode current collector 62, the thickness thereof is not particularly limited, but is, for example, 5 μm to 35 μm, and preferably 7 μm to 20 μm.

[0060] The negative electrode active material layer 64 contains a negative electrode active material. Examples of the negative electrode active material that can be used include carbon materials such as graphite, hard carbon, and soft carbon. The graphite may be natural graphite or artificial graphite, or may be amorphous carbon-coated graphite in which graphite is coated with an amorphous carbon material.

[0061] The average particle size (median size D50) of the negative electrode active material is not particularly limited, but is, for example, 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less.

[0062] The content of the negative electrode active material in the negative electrode active material layer is not particularly limited, but is preferably 90% by mass or more, and more preferably 95% by mass or more.

[0063] The negative electrode active material layer 64 may contain components other than the negative electrode active material, such as a binder or a thickener.

[0064] Examples of binders that can be used include styrene butadiene rubber (SBR) and modified products thereof, acrylonitrile butadiene rubber and modified products thereof, acrylic rubber and modified products thereof, and fluororubber. Among these, SBR is preferred. The content of the binder in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.1% by mass or more and 8% by mass or less, and more preferably 0.2% by mass or more and 3% by mass or less.

[0065] Examples of thickeners that can be used include cellulose-based polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA); and the like. Among these, CMC is preferred. The content of the thickener in the negative electrode active material layer 64 is not particularly limited, but is preferably 0.3% by mass or more and 3% by mass or less, and more preferably 0.4% by mass or more and 2% by mass or less.

[0066] The thickness of the negative electrode active material layer 64 is not particularly limited, but is, for example, 10 μm or more and 300 μm or less, and preferably 20 μm or more and 200 μm or less.

[0067] The separator 70 may be a porous sheet (film) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. 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 70.

[0068] The thickness of the separator 70 is not particularly limited, but is, for example, 5 μm or more and 50 μm or less, and preferably 10 μm or more and 30 μm or less.

[0069] The nonaqueous electrolyte typically contains a nonaqueous solvent and an electrolyte salt (in other words, a supporting salt). As the nonaqueous solvent, various organic solvents such as carbonates, ethers, esters, nitriles, sulfones, and lactones commonly used in electrolyte solutions for lithium-ion secondary batteries can be used without any particular limitation. Among these, carbonates are preferred, and specific examples thereof include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), monofluoroethylene carbonate (MFEC), difluoroethylene carbonate (DFEC), monofluoromethyl difluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). These nonaqueous solvents can be used alone or in appropriate combinations of two or more.

[0070] As the electrolyte salt, for example, lithium salts such as LiPF, LiBF, and lithium bis(fluorosulfonyl)imide (LiFSI) can be used, and among them, LiPF is preferred. The concentration of the electrolyte salt is not particularly limited, but is preferably 0.7 mol / L or more and 1.3 mol / L or less.

[0071] The nonaqueous electrolyte may contain various additives other than the above-mentioned components, such as a film-forming agent such as an oxalato complex, a gas generating agent such as biphenyl (BP) or cyclohexylbenzene (CHB), a thickener, etc., as long as the effects of the present invention are not significantly impaired.

[0072] The lithium ion secondary battery 100 has a high capacity and excellent output characteristics. The lithium ion secondary battery 100 can be used for a variety of purposes. Suitable applications include a driving power source mounted on vehicles such as electric vehicles (EVs), hybrid vehicles (HVs), and plug-in hybrid vehicles (PHVs). The lithium ion secondary battery 100 can also be used as a storage battery for small power storage devices and the like. The lithium ion secondary battery 100 can also be used in the form of a battery pack, typically consisting of a plurality of batteries connected in series and / or parallel.

[0073] The above describes a prismatic lithium ion secondary battery having a flat wound electrode assembly as an example. However, the positive electrode active material obtained by the manufacturing method according to this embodiment can also be used in other types of lithium ion secondary batteries according to known methods. For example, a lithium ion secondary battery having a stacked electrode assembly (i.e., an electrode assembly in which multiple positive electrodes and multiple negative electrodes are alternately stacked) can be constructed using the positive electrode active material obtained by the manufacturing method according to this embodiment. Furthermore, a cylindrical lithium ion secondary battery, a coin-type lithium ion secondary battery, a laminated lithium ion secondary battery, etc. can also be constructed using the positive electrode active material obtained by the manufacturing method according to this embodiment. Furthermore, an all-solid-state secondary battery using a solid electrolyte as the electrolyte can also be constructed using the positive electrode active material obtained by the manufacturing method according to this embodiment.

[0074] Examples of the present invention will be described below, but it is not intended that the present invention be limited to those shown in these examples.

[0075] Example 1 A composite hydroxide containing nickel, cobalt, and manganese in a molar ratio of 8:1:1 (i.e., Ni 0.8 Co 0.1 Mn 0.1(OH)2) was obtained as the precursor hydroxide. This precursor hydroxide was heat-treated at 550°C for 0.5 hours in an air atmosphere. This resulted in the precursor oxide. The crystal structure of this precursor oxide was analyzed using the method described below.

[0076] The obtained precursor oxide was mixed with lithium hydroxide so that the molar ratio of the metal element in the precursor oxide to the lithium element in the lithium hydroxide was 1:1. The obtained mixture was fired in an electric furnace at 850°C for 10 hours in an air atmosphere to obtain a lithium composite oxide as a positive electrode active material.

[0077] Examples 2 to 18 A composite hydroxide having the composition shown in Table 1 was used and heat-treated in an air atmosphere at the temperature and time shown in Table 1 to obtain a precursor oxide. The crystal structure of this precursor oxide was analyzed by the method described below. The precursor oxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor oxide and the lithium element in the lithium hydroxide were in a 1:1 molar ratio. The resulting mixture was fired in an electric furnace in an air atmosphere at the firing temperature and firing time shown in Table 2 to obtain a lithium composite oxide as a positive electrode active material.

[0078] Comparative Example 1 As raw materials, Ni 0.8 Co 0.1 Mn 0.1 A precursor hydroxide having a composition represented by (OH)2 was prepared. The precursor hydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor hydroxide and the lithium element in the lithium hydroxide were in a molar ratio of 1:1. The resulting mixture was fired in an electric furnace at 850°C for 10 hours in an air atmosphere to obtain a lithium composite oxide.

[0079] Comparative Example 2 As raw materials, Ni 0.8 Co 0.1 Mn 0.1A precursor hydroxide having a composition represented by (OH)2 was prepared. The precursor hydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor hydroxide and the lithium element in the lithium hydroxide were in a molar ratio of 1:1. The resulting mixture was fired in an electric furnace in an oxygen atmosphere at 860°C for 10 hours to obtain a lithium composite oxide.

[0080] Comparative Examples 3 to 5 Ni 0.8 Co 0.1 Mn 0.1 A precursor oxide was obtained by heat-treating (OH)2 in an air atmosphere at the temperature and time shown in Table 1. The crystal structure of this precursor oxide was analyzed using the method described below. The precursor oxide was mixed with lithium hydroxide. The mixture was adjusted so that the metal element in the precursor oxide and the lithium element in the lithium hydroxide were in a 1:1 molar ratio. The resulting mixture was fired in an electric furnace at the firing temperature and time shown in Table 2 under the atmosphere shown in Table 2 to obtain a lithium composite oxide, which is a positive electrode active material.

[0081] Comparative Example 6 As raw materials, Ni 0.6 Co 0.2 Mn 0.2 A precursor hydroxide having a composition represented by (OH)2 was prepared. The precursor hydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor hydroxide and the lithium element in the lithium hydroxide were in a molar ratio of 1:1. The resulting mixture was fired in an electric furnace at 890°C for 10 hours in an air atmosphere to obtain a lithium composite oxide.

[0082] Comparative Example 7 As raw materials, Ni 0.6 Co 0.2 Mn 0.2A precursor hydroxide having a composition represented by (OH)2 was prepared. The precursor hydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor hydroxide and the lithium element in the lithium hydroxide were in a molar ratio of 1:1. The resulting mixture was fired in an electric furnace in an oxygen atmosphere at 900°C for 10 hours to obtain a lithium composite oxide.

[0083] Comparative Example 8 As raw materials, Ni 0.8 Co 0.1 Mn 0.1 A precursor hydroxide having a composition represented by (OH)2 was prepared. The precursor hydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor hydroxide and the lithium element in the lithium hydroxide were in a 1:1 molar ratio. The resulting mixture was pre-baked in an electric furnace under an oxygen atmosphere at 500°C for 5 hours, and then switched to an air atmosphere and baked at 850°C for 10 hours to obtain a lithium composite oxide.

[0084] Comparative Example 9 When preparing the precursor by crystallization using nickel sulfate, cobalt sulfate, and manganese sulfate, sodium persulfate and sodium peroxide were added to form Ni 0.6 Co 0.2 Mn 0.2 O(OH) was obtained as a precursor oxyhydroxide, which was the raw material. The precursor oxyhydroxide was mixed with lithium hydroxide. The mixture was mixed so that the metal element in the precursor oxyhydroxide and the lithium element in the lithium hydroxide were in a 1:1 molar ratio. The resulting mixture was fired in an electric furnace at 890°C for 10 hours in an air atmosphere to obtain a lithium composite oxide.

[0085] [Powder X-ray diffraction measurement of precursor oxide] Powder XRD measurements were performed on the precursor oxide obtained by the heat treatment described above using an XRD device called "smart Lab" (manufactured by Rigaku). Using the analytical software "PDXL2" (manufactured by Rigaku), the peak integrated intensity ratio of the (003) plane to the (440) plane ((003) plane / (440) plane) and the peak integrated intensity ratio of the (440) plane to the (311) plane ((440) plane / (311) plane) were calculated using Miller indices hlk. The results are shown in Table 1.

[0086] [Powder X-ray diffraction measurement of positive electrode active material] Powder XRD measurement was performed on the positive electrode active material obtained above using an XRD device "smart Lab" (manufactured by Rigaku). Using the analytical software "PDXL2" (manufactured by Rigaku), the crystallite diameter of the (003) plane was calculated using the half-width and 2θ value of the (003) plane and the Scherrer equation. The results are shown in Table 2.

[0087] [Measurement of tap density of precursor oxide and precursor hydroxide] The precursor hydroxide (Ni 0.8 Co 0.1 Mn 0.1 The tap densities of the precursor oxides (Ni(OH)2) and the precursor oxides prepared in Examples 1 to 6 and 9 to 18 were measured using a commercially available tapping machine "KRS-409 Model" (manufactured by Kuramochi Scientific Instruments Manufacturing Co., Ltd.) according to the method specified in JIS K1469:2003. As a result, the precursor oxides had higher tap densities than the precursor hydroxides. Similarly, the precursor hydroxides (Ni(OH)2) used in Example 6 and Comparative Examples 6 and 7 0.6 Co 0.2 Mn 0.2 The tap densities of (OH)2) and the precursor oxide prepared in Example 6 were measured, and the precursor oxide had a higher tap density than the precursor hydroxide.

[0088] <Preparation of Lithium-ion Secondary Batteries for Evaluation> The positive electrode active materials of each of the examples and comparative examples prepared above, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were mixed in N-methylpyrrolidone (NMP) in a mass ratio of positive electrode active material:AB:PVDF = 85:10:5 to prepare a paste for forming a positive electrode active material layer. This paste was applied to a 15 μm thick aluminum foil and dried to prepare a positive electrode sheet.

[0089] A paste for forming a negative electrode active material layer was prepared by mixing natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener in a mass ratio of C:SBR:CMC = 98:1:1 in ion-exchanged water. This paste was applied to a copper foil with a thickness of 10 μm and dried to prepare a negative electrode sheet.

[0090] In addition, a porous polyolefin sheet having a thickness of 20 μm and a three-layer structure of PP / PE / PP was prepared as a separator sheet.

[0091] The positive electrode sheet, negative electrode sheet, and separator sheet were stacked together, and electrode terminals were attached and housed in a laminate case. A nonaqueous electrolyte was then poured into the laminate case, which was then airtightly sealed. The nonaqueous electrolyte used was a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3:4:3, with LiPF6 dissolved as a supporting electrolyte at a concentration of 1.0 mol / L. In this manner, a lithium-ion secondary battery for evaluation was obtained.

[0092] <Output characteristic evaluation> After activation treatment, each evaluation lithium-ion secondary battery was adjusted to an SOC of 60% and placed in an environment at -10°C. Each evaluation lithium-ion secondary battery was discharged for 2 seconds at a current value of 15 C. The output (W) was calculated based on the voltage and current value at this time. The output ratio of the evaluation lithium-ion secondary battery using the positive electrode active material obtained in Comparative Example 1 was determined as 100, and the output ratio of the evaluation lithium-ion secondary battery using the positive electrode active material obtained in the other Comparative Examples and Examples was calculated. The results are shown in Table 2.

[0093] [Table 1]

[0094] [Table 2]

[0095] The results in Tables 1 and 2 show that by heat-treating a hydroxide containing 60 mol% or more of nickel in an air atmosphere to convert it into an oxide mainly having a spinel structure with a peak integrated intensity ratio [(003) plane / (440) plane] of 1.5 or less and a peak integrated intensity ratio [(440) plane / (311) plane] of 4.5 or more, a positive electrode active material capable of imparting high power to a lithium-ion secondary battery can be produced without using an oxygen atmosphere. Therefore, it is clear that the method for producing a positive electrode active material disclosed herein can produce a positive electrode active material with a high nickel content that can impart high power to a lithium-ion secondary battery without using an oxygen atmosphere.

[0096] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific examples exemplified above.

[0097] That is, the method for producing a positive electrode active material disclosed herein includes the following items [1] to [5]. [1] A step of heat-treating a hydroxide having a nickel content of 60 mol% or more relative to the total content of all metal elements in an air atmosphere to obtain an oxide mainly having a spinel structure; mixing the oxide with a Li-containing compound; a step of calcining the obtained mixture in an air atmosphere to convert it into a lithium composite oxide having a layered rock salt structure; It encompasses In the oxide mainly having a spinel structure, the peak integrated intensity ratio of the (003) plane to the (440) plane is 1.5 or less, and the peak integrated intensity ratio of the (440) plane to the (311) plane is 4.5 or more, as determined by powder X-ray diffraction measurement using CuKα radiation. A method for producing a positive electrode active material. [2] The manufacturing method according to item [1], wherein the ratio of the nickel content to the total content of all metal elements in the hydroxide is 80 mol% or more. [3] The manufacturing method according to item [1] or [2], wherein the hydroxide is a nickel-cobalt-manganese composite hydroxide, and the lithium composite oxide having a layered rock salt structure is a lithium-nickel-cobalt-manganese composite oxide. [4] The method according to any one of items [1] to [3], wherein the peak integrated intensity ratio of the (440) plane to the (311) plane is 10 or more. [5] The method according to any one of items [1] to [4], wherein the lithium composite oxide having a layered rock salt structure has a crystallite diameter of 600 Å to 1000 Å in the (003) plane as determined by powder X-ray diffraction measurement using CuKα radiation. [Explanation of symbols]

[0098] 20 Wound electrode body 30 Battery case 36 Safety valve 42 Positive terminal 42a Positive current collector plate 44 Negative terminal 44a Negative current collector plate 50 Positive electrode sheet (positive electrode) 52 Positive electrode current collector 52a Portion where positive electrode active material layer is not formed 54 Cathode active material layer 60 Negative electrode sheet (negative electrode) 62 Negative electrode current collector 62a Part where negative electrode active material layer is not formed 64 Negative electrode active material layer 70 Separator sheet (separator) 100 Lithium-ion secondary battery

Claims

1. a step of heat-treating a hydroxide having a nickel content of 60 mol% or more relative to the total content of all metal elements alone at 400°C to 580°C in an air atmosphere to obtain an oxide mainly having a spinel structure; mixing the oxide with a Li-containing compound; a step of calcining the obtained mixture in an air atmosphere to convert it into a lithium composite oxide having a layered rock salt structure; It encompasses In the oxide mainly having a spinel structure, a peak integrated intensity ratio of a (003) plane to a (440) plane is 1.5 or less, and a peak integrated intensity ratio of a (440) plane to a (311) plane is 4.5 or more, as determined by powder X-ray diffraction measurement using CuKα radiation. A method for producing a positive electrode active material.

2. 2. The method according to claim 1, wherein the ratio of the content of nickel to the total content of all metal elements in the hydroxide is 80 mol % or more.

3. 2. The method according to claim 1, wherein the hydroxide is a nickel-cobalt-manganese composite hydroxide, and the lithium composite oxide having a layered rock salt structure is a lithium-nickel-cobalt-manganese composite oxide.

4. The manufacturing method according to claim 1 , wherein the peak integrated intensity ratio of the (440) plane to the (311) plane is 10 or more.

5. 2. The method according to claim 1, wherein the lithium composite oxide having a layered rock salt structure has a crystallite diameter of the (003) plane determined by powder X-ray diffraction measurement using CuKα radiation of 600 Å to 1000 Å.

Images