Method for producing positive electrode active material

Abstract

The invention relates to a method for producing a positive electrode active material. A method for producing a positive electrode active material includes a first step and a second step. In the first step, a mixture obtained by mixing a lithium compound and a transition metal-containing compound containing a transition metal is fired using a heater in an oxygen atmosphere at 750-1000 DEG C to obtain a lithium transition metal composite oxide. In the second step, the lithium transition metal composite oxide is irradiated with microwaves when the temperature of the lithium transition metal composite oxide after the first step is at least 400 DEG C and less than the firing temperature in the first step.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing a positive electrode active material. Background Technology

[0002] Japanese Patent Application Publication No. 2011-210463 discloses the following: In the manufacture of the positive electrode active material of a lithium-ion battery, lithium-containing carbonate is calcined by heating with a heater and microwave heating. Summary of the Invention

[0003] This disclosure provides a method for manufacturing a positive electrode active material having a small Li site occupancy rate while improving the resistance of a non-aqueous electrolyte secondary battery.

[0004] [1] A method for manufacturing a positive electrode active material, comprising: a first step, wherein a mixture of a lithium compound and a compound containing a transition metal is calcined in an oxygen atmosphere at 750–1000°C using a heater to obtain a lithium transition metal composite oxide; and a second step, wherein the lithium transition metal composite oxide is irradiated with microwaves at a temperature above 400°C and below the calcination temperature in the first step.

[0005] [2] According to the method for manufacturing the positive electrode active material described in [1], the compound containing the transition metal is at least one of a nickel hydroxide and a nickel oxide.

[0006] [3] The method for manufacturing the positive electrode active material according to [1] or [2], wherein the compound containing the transition metal comprises at least one of Mn and Co.

[0007] [4] The method for manufacturing the positive electrode active material according to any one of [1] to [3], wherein the lithium compound is at least one of lithium hydroxide and lithium carbonate.

[0008] [5] A method for manufacturing a positive electrode active material according to any one of [1] to [4], wherein the positive electrode active material comprises Li, Ni, Mn, Co, and M, M is one or more metallic elements selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y, and the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M=a:x:y:z:t, where a, x, y, z, and t are 1.0≤a≤1.3, x+y+z+t=1, 0.25≤x≤0.9, 0<y≤0.6, 0<z≤0.6, and 0≤t≤0.1.

[0009] [6] A method for manufacturing a positive electrode active material according to any one of [1] to [5], wherein the positive electrode active material comprises secondary particles.

[0010] [7] The method for manufacturing a positive electrode active material according to any one of [1] to [6], wherein the first step is performed using a continuous firing furnace that carries the mixture while firing.

[0011] [8] The method for manufacturing the positive electrode active material according to [7], wherein the second step is performed on the lithium transition metal composite oxide taken out from the continuous sintering furnace.

[0012] [9] The method for manufacturing the positive electrode active material according to [7] or [8], wherein the continuous firing furnace is a heater-heated kiln, and in the first step, the mixture is fired in the kiln while a sagger containing the mixture is transported.

[0013]

[10] The method for manufacturing the positive electrode active material according to any one of [1] to [9], wherein the microwave irradiation amount in the second step is 200 to 1500 Wh per 1 kg of the lithium transition metal composite oxide.

[0014]

[11] The method for manufacturing a positive electrode active material according to any one of [1] to

[10] , wherein, in the second step, the output power of the microwave is 4 kW or less, and the irradiation time of the microwave is 15 to 90 minutes.

[0015] The above and other objects, features, aspects and advantages of the present invention will become clear from the following detailed description in relation to the invention, which is understood in conjunction with the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a flowchart illustrating an example of a method for manufacturing a positive electrode active material according to an embodiment. Detailed Implementation

[0017] In this specification, unless otherwise specified, the numerical ranges "m~n" include both upper and lower limits. That is, "m~n" represents a numerical range "above m and below n". Any value selected from the numerical range can be set as a new upper or lower limit. For example, a new numerical range can be set by arbitrarily combining values ​​within the numerical range with values ​​recorded in other parts of this specification, tables, or figures.

[0018] (Manufacturing method of positive electrode active material)

[0019] Figure 1This is a flowchart illustrating an example of a method for manufacturing a positive electrode active material according to an embodiment. The positive electrode active material manufactured using the method for manufacturing a positive electrode active material according to this embodiment (hereinafter also referred to as "this method") is used as the positive electrode plate of a non-aqueous electrolyte secondary battery (hereinafter also referred to as "secondary battery") such as a lithium-ion battery.

[0020] The positive electrode active material manufactured using this method is a lithium-transition metal composite oxide (hereinafter also referred to as "composite oxide") containing lithium and a transition metal. The positive electrode active material can be of the layered rock salt type, spinel type, or olivine type. The layered rock salt type is preferred. The crystal structure of the positive electrode active material can be confirmed by X-ray diffraction (hereinafter also referred to as "XRD").

[0021] There are no particular restrictions on the composition of the positive electrode active material, but it is preferred to contain Ni, and more preferably Ni, Mn, and Co. The positive electrode active material preferably contains Li, Ni, Mn, Co, and M [M is one or more metallic elements selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y]. The molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t [a, x, y, z, and t are 1.0≤a≤1.3, x+y+z+t=1, 0.25≤x≤0.9, 0<y≤0.6, 0<z≤0.6, and 0≤t≤0.1].

[0022] The molar ratio of Li is 1.0≤a≤1.3, which can be 1.0≤a≤1.25, 1.01≤a≤1.2, 1.03≤a≤1.15, or 1.04≤a≤1.1. The molar ratio of Ni is 0.25≤x≤0.9, which can be 0.3≤x≤0.9, 0.4≤x≤0.88, or 0.5≤x≤0.85. The molar ratio of Mn is 0<y≤0.6, which can be 0.05≤y≤0.5, 0.08≤y≤0.3, or 0.10≤y≤0.2. The molar ratio of Co is 0<z≤0.6, which can be 0<z≤0.5, 0.01≤z≤0.3, or 0.02≤z≤0.1. The molar ratio of M is 0 ≤ t ≤ 0.1, which can be 0 < t ≤ 0.08, 0.001 ≤ t ≤ 0.05, or 0.002 ≤ t ≤ 0.01. When the positive electrode active material contains two or more metal elements M, the molar ratio of M refers to the total amount of the two or more metal elements.

[0023] The composition of the positive electrode active material can be adjusted by the types and amounts of raw materials used in its manufacture. The composition of the positive electrode active material can be determined using ICP (inductively coupled plasma) luminescence spectrophotometry (ICP-AES).

[0024] The positive electrode active material can be a single particle or a secondary particle. Secondary particles are aggregated particles formed by the aggregation of primary particles. The positive electrode active material preferably contains secondary particles. The number of primary particles aggregated in the secondary particles is preferably 50 or more, but can be 100 or more, or even 1000 or more, typically 5 × 10⁻⁶. 6 If less than one, it can be 5×10 5 The number of primary particles in the positive electrode active material may be less than 10. In addition to the aforementioned number of secondary particles, the positive electrode active material may further include at least one of secondary particles formed by the aggregation of 2 to 10 primary particles and single particles. The content of secondary particles formed by the aggregation of 50 or more primary particles in the positive electrode active material, when the total amount of the positive electrode active material is set to 100% by mass, is, for example, 70 to 100% by mass, 85 to 98% by mass, or 90 to 95% by mass. The number of primary particles can be adjusted using manufacturing conditions such as firing conditions (firing temperature, number of firings, firing time, etc.) during the manufacture of the positive electrode active material. The number of primary particles contained in the secondary particles can be confirmed using, for example, SEM images obtained using a scanning electron microscope (hereinafter also referred to as "SEM").

[0025] The occupancy of Li sites at the 3b site of the positive electrode active material is, for example, 2-4%, 2.15-3.95%, 2.18-3.9%, or 2.2-3.8%. Regarding the Li site occupancy [%], as explained in the examples described later, it is calculated as the amount of Li present at the site represented by 3b, using Wyckoff notation, based on measurement data obtained by XRD of the positive electrode active material. The Li site occupancy of the positive electrode active material can be adjusted by adjusting the firing conditions in the first process and the microwave irradiation conditions in the second process, etc.

[0026] This method is as follows: Figure 1 As shown, the method includes the following first and second steps. In this method, a positive electrode active material can be manufactured through the first and second steps.

[0027] The first step involves calcining a mixture of a lithium compound and a transition metal-containing compound in an oxygen atmosphere at 750–1000°C using a heater to obtain a composite oxide.

[0028] The second process is a process of irradiating the composite oxide with microwaves when the temperature of the composite oxide after the first process is above 400°C but below the firing temperature in the first process.

[0029] It is believed that by irradiating a composite oxide obtained by calcining a mixture of lithium compounds and compounds containing transition metals with microwaves, at least one of the electronic arrangement and crystal distortion of the composite oxide can be adjusted. This allows for the production of a positive electrode active material with a low Li site occupancy rate while simultaneously improving the resistance of the secondary battery. Conversely, without microwave irradiation, even with a low Li site occupancy rate, it is difficult to improve the resistance of the secondary battery. Furthermore, in the first step, by using both heater heating and microwave heating, the raw materials can be heated rapidly, thus shortening the heating time. However, it is believed that this does not lead to adjustments in the electronic arrangement and crystal distortion of the composite oxide, making it difficult to improve both the Li site occupancy rate and the resistance of the secondary battery.

[0030] The following details each step of this method.

[0031] (First process)

[0032] The first step involves calcining a mixture of a lithium compound and a transition metal-containing compound to obtain a composite oxide. Calcination is performed using a heater. The first step may include the step of obtaining the mixture. The lithium compound and the transition metal-containing compound are the raw materials for the composite oxide. The mixture is typically in powder or particulate form.

[0033] As lithium compounds, one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate can be mentioned. The lithium compound is preferably at least one of lithium hydroxide and lithium carbonate, more preferably lithium hydroxide. The lithium compound can be anhydrous or a hydrate. When the lithium compound is lithium hydroxide, the lithium hydroxide can be anhydrous lithium hydroxide or lithium hydroxide hydrate. For example, lithium hydroxide monohydrate can be listed as a lithium hydroxide hydrate.

[0034] The compound containing a transition metal preferably contains one or more selected from Ni, Mn, and Co, and may contain Ni and at least one of Mn and Co, or may contain Ni, Mn, and Co. The compound containing a transition metal is preferably at least one of a nickel hydroxide and a nickel oxide, more preferably containing a nickel oxide, or is a nickel oxide. The nickel-containing compound may contain metal elements other than Ni, preferably a transition metal element other than Ni, more preferably containing at least one of Mn and Co, or may contain Mn and Co.

[0035] Nickel-containing hydroxides are preferably nickel complex hydroxides containing Ni and metal elements other than Ni. Nickel-containing oxides are preferably nickel complex oxides containing Ni and metal elements other than Ni. The metal elements other than Ni contained in nickel complex hydroxides and nickel complex oxides are preferably transition metal elements other than Ni, more preferably at least one of Mn and Co, and may be Mn and Co. Nickel-containing compounds are preferably nickel complex oxides.

[0036] The mixture may further contain a compound containing M, where M has the same meaning as described above. Examples of compounds containing M include one or more selected from oxides containing M, hydroxides containing M, sulfides containing M, oxyhydroxides containing M, and halides containing M.

[0037] The amounts of lithium compounds, transition metal compounds, and compounds containing M in the mixture can be set in a way that yields a composite oxide with the desired composition.

[0038] In cases where the first step includes obtaining a mixture, this step may, for example, use a mixer to mix a lithium compound, a compound containing a transition metal, and a compound containing M as needed. The mixer can be a general-purpose mixer, such as a jet mill, ball mill, rocker mixer, vibrating mixer, V-type mixer, belt mixer, Julia mixer, or Loedige mixer, etc.

[0039] The firing of the mixture in the first step is carried out in an oxygen atmosphere at 750–1000°C using a heater. The firing of the mixture is usually carried out in a firing furnace. The firing furnace is preferably a continuous firing furnace in which the mixture is transported and fired simultaneously. Examples of continuous firing furnaces include heater-heated kilns, such as roller kilns, shuttle kilns, pusher kilns, tunnel kilns, and externally heated rotary kilns.

[0040] The mixture can be fired either by directly feeding it into the firing furnace or by introducing a sagger containing the mixture into the firing furnace. For example, when using a heater-heated kiln as a continuous firing furnace, in the first step, the mixture can be fired while the sagger containing the mixture is being transported inside the kiln.

[0041] The saggar is made of ceramic. Materials used to form the saggar may include, for example, one or more selected from alumina, magnesium oxide, zircon, mullite, silicon dioxide, carbon, and cordierite.

[0042] The oxygen atmosphere for firing the mixture can be formed, for example, by supplying oxygen into the firing furnace. In the first step, it is preferable to perform the process while continuously supplying oxygen into the firing furnace.

[0043] The firing temperature of the mixture is 750–1000°C, specifically 760–950°C, 770–900°C, 780–880°C, or 790–850°C. Within the above firing temperature range, the firing time maintained at the target firing temperature (hereinafter also referred to as "firing time") is, for example, 1–20 hours, specifically 3–15 hours, 4–12 hours, or 5–10 hours. This firing time does not include the time required to heat to the target firing temperature. By adjusting the firing temperature and firing time to the above ranges, it is easy to obtain a positive electrode active material with a low Li site occupancy rate that can improve the resistance of the secondary battery.

[0044] Regarding the firing process in the first step, the mixture, after being heated and held at a temperature below 750°C, can be fired at 750–1000°C. For example, the mixture can be held at a holding temperature of 300–700°C for 1–5 hours, and then fired at 750–1000°C. The aforementioned holding temperature can be 400–600°C, or 450–550°C. The holding time can be 2–4 hours, or 2.5–3.5 hours.

[0045] (Second process)

[0046] The second step involves irradiating the composite oxide with microwaves. The microwave irradiation is performed at a temperature above 400°C but below the firing temperature of the composite oxide obtained in the first step. Through this microwave irradiation, at least one of the electronic arrangement and crystal deformation of the composite oxide obtained in the first step can be adjusted, making it easier to obtain a positive electrode active material with a small Li site occupancy rate that can improve the resistance of the secondary battery.

[0047] Microwave irradiation is performed after the temperature of the composite oxide following the first process is lower than the firing temperature, but under conditions where the temperature of the composite oxide above 400°C is not excessively reduced. For microwave irradiation, the composite oxide fired in the first process is cooled, but before it cools to below 400°C. The irradiation temperature only needs to be above 400°C and below the firing temperature; it can be above 400°C and below (firing temperature - 50)°C, above 420°C and below (firing temperature - 100)°C, or above 450°C and below (firing temperature - 150)°C. If microwave irradiation is performed at a temperature above the firing temperature, oxygen is released from the composite oxide due to overheating, sometimes resulting in flames. If the temperature of the composite oxide is excessively reduced, it becomes difficult to adjust the electronic arrangement and crystal deformation of the composite oxide through microwave irradiation, making it difficult to improve the Li site occupancy and the resistance of the secondary battery.

[0048] There are no particular limitations on the method for cooling the composite oxide. The composite oxide can be cooled naturally or by blowing cold air onto it. When performing the first step using a continuous firing furnace, it is preferable to irradiate the composite oxide removed from the continuous firing furnace with microwaves in the second step. The external temperature of the continuous firing furnace is typically lower than the internal temperature (e.g., 30–100°C), therefore, the composite oxide can be cooled by utilizing the temperature difference between the inside and outside of the continuous firing furnace. This suppresses overheating of the composite oxide and adjusts its electronic arrangement and crystal deformation, thereby reducing the Li site occupancy and improving the resistance of the secondary battery.

[0049] There are no particular limitations on the method of irradiating the composite oxides taken from the continuous firing furnace with microwaves. As described above, it is preferable that in the first step, the mixture is fired in a furnace heated by a heater while a sagger containing the mixture is being transported, and the composite oxides in the saggers discharged from the furnace are irradiated with microwaves. This allows the composite oxides in the saggers discharged from the furnace to be easily cooled. Therefore, irradiating the cooled composite oxides with microwaves can suppress overheating of the composite oxides caused by microwave irradiation and suppress the generation of flames caused by oxygen release from the composite oxides. The temperature of the composite oxides during microwave irradiation can be adjusted by holding the saggers discharged from the furnace for a certain period of time, and can be adjusted by adjusting the distance between the furnace and the microwave irradiation position, i.e., the transport distance of the saggers discharged from the furnace.

[0050] The method of irradiating with microwaves is not limited to the above. For example, the composite oxide discharged from the continuous firing furnace can be collected in a container and microwaves can be irradiated into the composite oxide in the container. Alternatively, the composite oxide can be discharged from the continuous firing furnace while being irradiated with microwaves.

[0051] Microwave irradiation can be performed using a microwave irradiation device, which can be done by placing the composite oxide into the device. Microwaves can be applied to the composite oxide by introducing a container or a sagger containing the composite oxide into the microwave irradiation device.

[0052] Regarding the microwave irradiation amount in the second process, the amount per 1 kg of composite oxide is preferably 200–1500 Wh, but can be 300–1200 Wh, 400–1100 Wh, or 500–1000 Wh. The microwave output power is preferably below 4 kW, but can be 0.01–4 kW, 0.05–3.5 kW, 0.1–3 kW, 1–2.5 kW, or 1.2–2 kW. The microwave irradiation time is preferably 15–90 minutes, but can be 20–80 minutes, 25–70 minutes, or 30–60 minutes.

[0053] Microwave irradiation can be carried out in an oxygen atmosphere. An oxygen atmosphere can be formed by supplying oxygen into the space where microwave irradiation is performed; for example, microwaves can be irradiated while oxygen is being supplied.

[0054] The positive electrode active material obtained by this method can be used in positive electrode plates. In the manufacturing method of positive electrode plates, the positive electrode active material produced by this method can be used to manufacture the positive electrode plate.

[0055] The positive electrode plate can have a positive electrode current collector foil and a positive electrode active material layer formed on one or both sides of the positive electrode current collector foil. The positive electrode active material is contained in the positive electrode active material layer, and the positive electrode active material layer can further contain at least one of a binder and a conductive additive. The positive electrode active material layer can be formed by adding a solvent such as N-methyl-2-pyrrolidone (NMP) to the materials forming the positive electrode active material layer, such as the positive electrode active material, binder, and conductive additive, to obtain a positive electrode slurry, coating the positive electrode slurry onto the positive electrode current collector foil, drying, and compressing.

[0056] The positive electrode current collector foil may be a metal foil made of Al materials such as Al and Al alloys. As a binder material, examples include fluoropolymers such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; cellulose resins such as carboxymethyl cellulose (CMC), methyl cellulose, and hydroxypropyl cellulose; and styrene-butadiene rubber, etc., and one or more of these can be used. As a conductive additive, carbon materials may be used. Examples of carbon materials include fibrous carbon such as carbon nanotubes and carbon black, and one or more of these can be used.

[0057] The positive electrode plate obtained as described above can be used in a secondary battery. In the manufacturing method of a secondary battery, the positive electrode plate manufactured using the above-described positive electrode plate manufacturing method can be used to manufacture the secondary battery.

[0058] The secondary battery can have an electrode body including a positive electrode plate and a non-aqueous electrolyte, and can have a battery casing that houses the electrode body and the non-aqueous electrolyte. The battery casing and non-aqueous electrolyte can be well-known battery casings and non-aqueous electrolytes used in secondary batteries.

[0059] The electrode body may include the aforementioned positive electrode plate, negative electrode plate, and separator (membrane). In the electrode body, the positive active material layer of the positive electrode plate and the negative active material layer of the negative electrode plate are separated by the separator. The electrode body may be a stacked type, consisting of positive electrode plates, negative electrode plates, and separators, or a wound type, consisting of a strip-shaped stack of positive electrode plates, negative electrode plates, and separators wound together. The wound type electrode body may have a flat shape, formed by pressing the stacked body after winding.

[0060] A negative electrode plate typically comprises a negative electrode current collector foil and a negative electrode active material layer. The negative electrode current collector foil is, for example, a metal foil made of copper or copper alloys. The negative electrode active material layer contains the negative electrode active material and may further contain conductive additives and binders. The negative electrode active material layer can be formed by adding a solvent such as water to the materials forming the negative electrode active material layer, such as the negative electrode active material, binder, and conductive additives, to obtain a negative electrode slurry. This slurry is then coated onto the negative electrode current collector foil, dried, and compressed.

[0061] Examples of anode active materials include carbon-based active materials such as graphite, as well as metal-based active materials such as Si, SiOx (x = 0.5–1.5), Si and C composites, and Sn, and at least one of these can be used. Examples of binder materials include the aforementioned cellulose-based resins, polyacrylic acid, and styrene-butadiene rubber, and at least one of these can be used. Examples of conductive additives include the aforementioned conductive additives.

[0062] The separator has a substrate, and at least one side of the substrate may have a functional layer. The substrate can be a porous sheet such as a membrane made of polyolefins such as polyethylene and polypropylene, polyester, cellulose, polyamide, etc., or a nonwoven fabric. The substrate can be a single-layer structure or a multi-layer structure. In the case of a multi-layer structure, the materials of each layer can be the same or different. Examples of functional layers include an adhesive layer formed by an adhesive and a heat-resistant layer containing inorganic fillers and adhesives.

[0063] The non-aqueous electrolyte preferably contains an electrolyte in a non-aqueous solvent such as an organic solvent. Examples of electrolytes include LiPF6, LiBF4, LiClO4, LiFSO3, and LiBOB, and at least one of these can be used. Examples of non-aqueous solvents include ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, propylene carbonate, butyl carbonate, and diethyl carbonate, and at least one of these can be used.

[0064] Example

[0065] The following examples and comparative examples illustrate this disclosure in more detail.

[0066] [Examples 1 and 2]

[0067] (Preparation of positive electrode active material)

[0068] As a transition metal compound, a nickel-containing oxide comprising Ni, Co, and Mn in a molar ratio of Ni:Co:Mn = 83:5:12 was prepared, and as a lithium compound, lithium hydroxide monohydrate (average particle size (D50): 10 μm) was prepared. The transition metal compound and the lithium compound were mixed in a molar ratio of Li:Ni:Co:Mn = 1.06:0.83:0.05:0.12 to obtain a mixture. The mixture was filled into an alumina crucible, which served as a sagger, and then placed in an electric furnace to calcify the mixture, thereby obtaining a lithium transition metal composite oxide (first step). The firing of the mixture was carried out as follows: the K thermocouple coated with alumina was inserted into the mixture in the crucible, and while measuring the temperature, it was first heated to 500°C at an oxygen flow rate of 4 L / min and a heating rate of 5°C / min. After holding at 500°C for 3 hours, it was heated to 805°C at a heating rate of 5°C / min and fired at this temperature for the times shown in Table 1.

[0069] The crucible was removed from the electric furnace and kept outside the furnace for a certain period of time. 50g of the lithium transition metal composite oxide was then removed from the crucible and placed into a microwave irradiation device. Under an oxygen atmosphere, the crucible was irradiated with microwaves of 100W output power for the irradiation times shown in Table 1, yielding the positive electrode active material. The temperature of the lithium transition metal composite oxide during microwave irradiation was above 400℃ but below 805℃. The positive electrode active material consisted of secondary particles with a layered rock salt-like structure, formed by the aggregation of more than 50 primary particles.

[0070] (Making the positive electrode plate)

[0071] A positive electrode plate was fabricated using the positive electrode active material obtained above. The positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder were prepared such that the ratio of positive electrode active material:AB:PVdF = 100:1:1 (mass ratio). These were mixed with N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode slurry. The positive electrode slurry was coated onto aluminum foil, which served as the positive electrode current collector, dried, compressed, and cut to the specified dimensions to obtain the positive electrode plate.

[0072] (Making the negative electrode plate)

[0073] A negative electrode active material, a mixture of graphite and SiO, was prepared. Styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were prepared as binders. The negative electrode active material, SBR, and CMC were prepared at a mass ratio of 100:1:1 (sigma ratio), and mixed with water to create a negative electrode slurry. This slurry was coated onto copper foil, which served as the negative electrode current collector. After drying and compression, the foil was cut to the specified dimensions to obtain the negative electrode plate.

[0074] (Fabrication of a non-aqueous electrolyte secondary battery)

[0075] A separator with a three-layer structure of polypropylene / polyethylene / polypropylene was prepared. Positive and negative electrode plates were stacked using the separator to obtain an electrode body. At both ends of the electrode body, a positive electrode sheet formed from aluminum foil in the region of the positive current collector foil where no positive active material layer has formed, and a negative electrode sheet formed from copper foil in the region of the negative current collector foil where no negative active material layer has formed, are exposed. The positive electrode sheet is welded to the aluminum plate serving as the external positive current collector, and the negative electrode sheet is welded to the copper plate serving as the external negative current collector. Then, an outer packaging body with an aluminum laminate film is inserted to form an injection port, thus fusing the film. After injecting a non-aqueous electrolyte into the injection port, the injection port is sealed, resulting in a battery.

[0076] The non-aqueous electrolyte was prepared by dissolving lithium hexafluorophosphate (LiPF6) as the electrolyte in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of EC:EMC = 1:3.

[0077] [Comparative Example 1]

[0078] Except for the absence of microwave irradiation, the positive electrode active material was obtained in the same order as described in Examples 1 and 2. The positive electrode active material is a secondary particle consisting of more than 50 primary particles condensed together, having a layered rock salt-type structure. A positive electrode plate and a non-aqueous electrolyte secondary battery were obtained, except that the positive electrode active material was used, following the same steps as described in Examples 1 and 2.

[0079] [Comparative Example 2]

[0080] Except that the firing time at 805°C for the mixture was changed to the times shown in Table 1 and microwave irradiation was not performed, the positive electrode active material was obtained in the same manner as described in Examples 1 and 2. The positive electrode active material is a secondary particle with a layered rock salt-type structure, consisting of more than 50 primary particles aggregated together. In addition to using the positive electrode active material, a positive electrode plate and a non-aqueous electrolyte secondary battery were obtained in the same manner as described in Examples 1 and 2.

[0081] [Calculation of Li site occupancy]

[0082] For the positive electrode active materials obtained in the examples and comparative examples, X-ray diffraction measurements were performed using an X-ray diffraction apparatus (Rigaku "SmartLab"). The amount of Ni present at sites denoted by 3a and 3b (hereinafter sometimes referred to as "site 3a" and "site 3b," respectively) was calculated using Rietveld analysis of the measurement data obtained from the X-ray diffraction measurements, denoted by Wyckoff notation. In this case, the Li composition of site 3a and the Ni composition of site 3b were set to be variable, while the compositions of Co and Mn were set to be constant. The amount of Li present at site 3b was calculated as the Li site occupancy [%). The results are shown in Table 1.

[0083] [Measuring Resistance]

[0084] As an example and comparative example, the rechargeable battery obtained was activated and charged to 4.2V at a current rate of 0.1C, and then discharged to 3.0V at 0.1C. Next, the rechargeable battery was charged at 25°C until the state of charge (SOC) reached 50%. After a 1-hour rest period, it was discharged for 10 seconds at a current of 1C. The open circuit voltage (OCV) immediately before discharge was set as V0 [V], and the voltage after 10 seconds was set as V1 [V]. The resistance R was calculated according to the following formula. It can be said that the smaller the resistance R, the better the resistance of the rechargeable battery. The results are shown in Table 1.

[0085] The resistance R [Ω] = (V0 - V1) [V] / 1C, and the current value [A] is given.

[0086] Table 1

[0087]

[0088] In Examples 1 and 2, the microwave irradiation dose per 1 kg of lithium transition metal composite oxide was 667 Wh and 1000 Wh, respectively.

[0089] The embodiments of the present invention have been described above. It should be considered that the embodiments disclosed herein are illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A method for manufacturing a positive electrode active material, comprising: In the first step, a mixture of a lithium compound and a transition metal-containing compound is calcined using a heater at 750–1000°C under an oxygen atmosphere to obtain a lithium transition metal composite oxide; and In the second step, the lithium transition metal composite oxide is irradiated with microwaves at a temperature above 400°C and below the firing temperature in the first step.

2. The method for manufacturing the positive electrode active material according to claim 1, wherein, The compound containing a transition metal is at least one of a nickel-containing hydroxide and a nickel-containing oxide.

3. The method for manufacturing the positive electrode active material according to claim 2, wherein, The compound containing a transition metal includes at least one of Mn and Co.

4. The method for manufacturing the positive electrode active material according to any one of claims 1 to 3, wherein, The lithium compound is at least one of lithium hydroxide and lithium carbonate.

5. The method for manufacturing the positive electrode active material according to any one of claims 1 to 3, wherein, The positive electrode active material comprises Li, Ni, Mn, Co, and M, where M is one or more metallic elements selected from Mg, Ca, Al, Ti, V, Cr, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W, and Y, and the molar ratio of Li, Ni, Mn, Co, and M is Li:Ni:Mn:Co:M = a:x:y:z:t, where a, x, y, z, and t are 1.0≤a≤1.3, x+y+z+t=1, 0.25≤x≤0.9, 0<y≤0.6, 0<z≤0.6, and 0≤t≤0.

1.

6. The method for manufacturing the positive electrode active material according to any one of claims 1 to 3, wherein, The positive electrode active material contains secondary particles.

7. The method for manufacturing the positive electrode active material according to claim 1, wherein, The first step is performed using a continuous firing furnace that carries the mixture while firing.

8. The method for manufacturing the positive electrode active material according to claim 7, wherein, The second step is performed on the lithium transition metal composite oxide removed from the continuous firing furnace.

9. The method for manufacturing the positive electrode active material according to claim 7 or 8, wherein, The continuous firing furnace is a heater-heated kiln. In the first step, the mixture is fired in the kiln while a sagger containing the mixture is being transported.

10. The method for manufacturing the positive electrode active material according to any one of claims 1 to 3, wherein, The microwave irradiation dose in the second step is 200-1500 Wh per 1 kg of the lithium transition metal composite oxide.

11. The method for manufacturing the positive electrode active material according to any one of claims 1 to 3, wherein, In the second process, the output power of the microwave is below 4kW, and the irradiation time of the microwave is 15 to 90 minutes.

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