Method for producing positive electrode active material, method for producing positive electrode plate, and method for producing non-aqueous electrolyte secondary battery

Abstract

The invention relates to a method for manufacturing a positive electrode active material, a method for manufacturing a positive electrode plate, and a method for manufacturing a non-aqueous electrolyte secondary battery. This method for producing a positive electrode active material comprises a step in which a mixture of a nickel-containing compound and a lithium compound, which have been put into a rotary kiln, is fired at 750-1000 DEG C in an oxygen atmosphere. The nickel-containing compound is at least one of a nickel-containing hydroxide and a nickel-containing oxide. A yttrium-chromium composite oxide layer is formed on the outermost surface of the inner wall of the furnace.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a positive electrode active material, a method for manufacturing a positive electrode plate, and a method for manufacturing a non-aqueous electrolyte secondary battery. Background Technology

[0002] The positive electrode active material used in lithium secondary batteries is manufactured by sintering in a sintering furnace. For example, Japanese Patent Application Publication No. 2022-146357 discloses that if an alloy core tube is used for a long period of time, metal components may mix into the raw materials, thus forming aluminum oxide on the outermost layer of the inner wall of the core tube. Summary of the Invention

[0003] This disclosure provides a method for manufacturing a positive electrode active material that can suppress the mixing of Cr as an impurity even when using a rotary kiln in which the material of the forming furnace contains an alloy containing Cr.

[0004] [1] A method for manufacturing a positive electrode active material, which is a method for manufacturing a positive electrode active material containing a lithium transition metal composite oxide, includes a step of firing a mixture of a nickel-containing compound and a lithium compound in an oxygen atmosphere at 750 to 1000°C in a rotary kiln.

[0005] The nickel-containing compound is at least one of a nickel-containing hydroxide and a nickel-containing oxide.

[0006] A layer of yttrium-chromium composite oxide is formed on the outermost surface of the inner wall of the furnace.

[0007] [2] According to the method for manufacturing the positive electrode active material described in [1], wherein the layer covers the base material layer of the furnace, the base material layer being formed of an alloy containing Cr.

[0008] [3] According to the method for manufacturing the positive electrode active material described in [2], the layer is formed by sputtering yttrium oxide onto the base material layer.

[0009] [4] The method for manufacturing the positive electrode active material according to [2] or [3], wherein the Cr-containing alloy further comprises Fe and Ni.

[0010] [5] The method for manufacturing the positive electrode active material according to any one of [1] to [4] further includes a step of molding the mixture to obtain a molded body.

[0011] In the firing process, the molded body is fired.

[0012] [6] The method for manufacturing a positive electrode active material according to any one of [1] to [5], wherein the lithium compound is at least one of lithium hydroxide and lithium carbonate.

[0013] [7] The method for manufacturing the positive electrode active material according to any one of [1] to [6], wherein the Cr content of the lithium transition metal composite oxide is less than 1 ppm.

[0014] [8] The method for manufacturing the positive electrode active material according to any one of [1] to [7], wherein the lithium transition metal composite oxide comprises Li, Ni and Mn.

[0015] [9] The method for manufacturing the positive electrode active material according to any one of [1] to [8], wherein the lithium transition metal composite oxide comprises Li, Ni, Mn, Co and M, wherein 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

[0016] 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.

[0017]

[10] A method for manufacturing a positive electrode plate, wherein the positive electrode active material is manufactured by a method for manufacturing a positive electrode active material according to any one of [1] to [9].

[0018]

[11] A method for manufacturing a non-aqueous electrolyte secondary battery, which is a method for manufacturing a non-aqueous electrolyte secondary battery including a positive electrode plate, wherein the positive electrode plate is manufactured using the method for manufacturing a positive electrode plate according to

[10] .

[0019] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description relating to the invention, which is understood in conjunction with the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating an example of a method for manufacturing a positive electrode active material according to an embodiment.

[0021] Figure 2 A flowchart illustrating another example of a method for manufacturing a positive electrode active material according to an embodiment. Detailed Implementation

[0022] 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". A value arbitrarily 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.

[0023] (Method for manufacturing positive electrode active material (1))

[0024] Figure 1 and Figure 2 This 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.

[0025] The positive electrode active material manufactured using this method comprises a first lithium transition metal complex oxide (lithium transition metal complex oxide) (hereinafter also referred to as "first complex oxide"). The Cr content of the first complex oxide is preferably 50 ppm or less, but can be 25 ppm or less, 10 ppm or less, 5 ppm, more preferably 1 ppm or less, and can be 0.9 ppm or less. The Cr content of the first complex oxide refers to its mass ratio relative to the total mass of the first complex oxide. The Cr content of the first complex oxide can be adjusted by manufacturing the positive electrode active material using, for example, the method described later.

[0026] There are no particular limitations on the composition of the first composite oxide, but it is preferable that, in addition to Li, the first composite oxide also contains Ni and Mn as transition metals. More preferably, the first composite oxide 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], and 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].

[0027] The molar ratio of Li is 1.0≤a≤1.3, which can be 1.00≤a≤1.25, 1.01≤a≤1.20, 1.03≤a≤1.15, or 1.04≤a≤1.10. The molar ratio of Ni is 0.25≤x≤0.9, which can be 0.25≤x≤0.90, 0.30≤x≤0.90, 0.40≤x≤0.88, or 0.50≤x≤0.85. The molar ratio of Mn is 0<y≤0.6, which can be 0.00<y≤0.60, 0.05≤y≤0.50, 0.08≤y≤0.30, or 0.10≤y≤0.20. The molar ratio of Co is 0 < z ≤ 0.6, which can be 0.00 < z ≤ 0.60, 0.00 < z ≤ 0.50, 0.01 ≤ z ≤ 0.30, or 0.02 ≤ z ≤ 0.10. The molar ratio of M is 0 < t ≤ 0.1, which can be 0 < t ≤ 0.08, 0.001 ≤ t ≤ 0.05, 0.000 < t ≤ 0.100, or 0.002 ≤ t ≤ 0.010. When the first composite oxide contains two or more metallic elements M, the molar ratio of M refers to the total amount of the two or more metallic elements.

[0028] The composition of the first composite oxide can be adjusted by the types and amounts of raw materials used in its manufacture. The composition of the first composite oxide can be determined using ICP (inductively coupled plasma) luminescence spectrophotometry (ICP-AES).

[0029] The positive electrode active material may contain only the first composite oxide, or it may contain active materials other than the first composite oxide. The content of the first composite oxide in the positive electrode active material relative to the total amount of the positive electrode active material may be 85-100% by mass, 90-100% by mass, 92-99% by mass, or 95-98% by mass.

[0030] This method is as follows: Figure 1 As shown, the process includes a step of firing a mixture of nickel-containing compounds and lithium compounds in an oxygen atmosphere at 750–1000°C (hereinafter also referred to as the "firing step"). In this method, the nickel-containing compound is at least one of nickel-containing hydroxide and nickel-containing oxide, and a layer of yttrium-chromium composite oxide (hereinafter also referred to as "YCrO3") is formed on the outermost surface of the inner wall of the furnace (hereinafter also referred to as the "YCrO3 layer").

[0031] In this method, a rotary kiln with a YCrO3 layer formed on the outermost surface of the inner wall is used to fire a mixture containing nickel and lithium compounds. Because YCrO3 has low reactivity with lithium compounds, the reaction between lithium compounds and the YCrO3 on the outermost surface of the inner wall is suppressed, thus inhibiting corrosion of the inner wall. Consequently, the inclusion of Cr as an impurity in the inner wall of the furnace into the first composite oxide is suppressed, making it easier to obtain a first composite oxide with the aforementioned Cr content range. Furthermore, the YCrO3 layer is difficult to crack even within the firing temperature range of the mixture, resulting in excellent furnace durability of the rotary kiln used in this method.

[0032] In this method, the nickel-containing and lithium-containing compounds in the calcination mixture are raw materials for the composite oxide. The mixture is usually in powder or particle form.

[0033] The nickel-containing compound is at least one of a nickel-containing hydroxide and a nickel-containing oxide, more preferably containing a nickel-containing oxide or a nickel-containing oxide. In addition to Ni, the nickel-containing compound may contain metallic elements other than Ni, preferably a transition metal element other than Ni, more preferably containing at least one of Mn and Co, and may contain both Mn and Co. The Cr content in the nickel-containing compound is preferably 0.001% by mass or less, and may be 0.0001% by mass or less.

[0034] 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.

[0035] As lithium compounds, one or more selected from lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate can be cited. The Cr content in the lithium compound is preferably 0.001% by mass or less, and may be 0.0001% by mass or less. The lithium compound is preferably at least one of lithium hydroxide and lithium carbonate, more preferably lithium hydroxide. The lithium compound may be anhydrous or a hydrate. When the lithium compound is lithium hydroxide, the lithium hydroxide may be anhydrous lithium hydroxide or lithium hydroxide hydrate. Examples of lithium hydroxide hydrates include, for instance, lithium hydroxide monohydrate.

[0036] The average particle size (D50) of the lithium compound is, for example, 3–20 μm, 5–18 μm, or 8–15 μm. In this specification, the average particle size is the particle size (D50) that represents the cumulative frequency of the smallest particle size in the volume-based particle size distribution, which is the 50% of the total particle size. The volume-based particle size distribution can be measured using a laser diffraction particle size distribution measuring device.

[0037] The content of nickel-containing compounds and lithium compounds in the mixture can be set in a manner that yields the first composite oxide with the desired composition.

[0038] The rotary kiln used in this method can be an externally heated type. The entire rotary kiln can be formed of YCrO3 as long as a YCrO3 layer is formed on the outermost surface of its inner wall, and the portion of the kiln outside the YCrO3 layer can be formed of materials other than YCrO3. For example, the kiln can have a base material layer formed of an alloy containing Cr, and a YCrO3 layer formed on the outermost surface of the inner wall side of the kiln covering the base material layer. When the YCrO3 layer covers the base material layer, the thickness of the YCrO3 layer can be, for example, 10–1000 nm, 50–900 nm, or 100–800 nm. Preferably, the YCrO3 layer covers the entire surface of the inner wall side of the kiln, but it can cover more than 80%, more than 90%, or more than 95% of the entire surface of the inner wall side of the kiln. By ensuring that the YCrO3 layer coverage ratio is within the range described above, it is easy to suppress the incorporation of Cr as an impurity into the first composite oxide.

[0039] The base layer is preferably formed of an alloy containing Cr. In addition to Cr, the Cr-containing alloy may contain one or more metals selected from Fe, Ni, Mn, and Mo, with Fe and Ni being preferred. The Cr-containing alloy may also contain non-metallic elements such as Si, P, S, and C, provided it functions as an alloy. Examples of Cr-containing alloys include at least one of SUS310S and SUS316L.

[0040] There are no particular limitations on the method for forming the YCrO3 layer. When the inner wall of the furnace has a base material layer formed of a Cr-containing alloy and a YCrO3 layer covering the base material layer, the YCrO3 layer can be formed by spraying yttrium oxide (hereinafter also referred to as "Y2O3") onto the base material layer. By spraying Y2O3 onto the base material layer, the Cr in the base material layer is composited with the sprayed Y2O3, thus forming the outermost layer of the inner wall of the furnace. Because the Cr in the base material layer is composited with the sprayed Y2O3, the YCrO3 layer is difficult to peel off from the base material layer.

[0041] The YCrO3 layer can be formed, for example, as described below. First, Y2O3 powder is sprayed onto a base material layer to form a Y2O3 layer, resulting in a laminate of the base material layer and the Y2O3 layer. The thickness of the Y2O3 layer is, for example, 50–200 μm, and can be 80–150 μm. Second, after firing the laminate, it is cooled to allow Y2O3 to diffuse into the chromium oxide layer precipitated on the base material, forming the YCrO3 layer. This firing and cooling process is repeated more than twice to cause the Y2O3 film present on the YCrO3 layer to expand and peel off, thereby forming the YCrO3 layer on the outermost surface. The firing of the laminate can be carried out, for example, at atmospheric pressure and a temperature of 800–1200°C for 1–20 hours, and the number of firing and cooling cycles can be, for example, 2–5 times, 2–4 times, or 2–3 times.

[0042] The firing of the mixture is carried out in an oxygen atmosphere. An oxygen atmosphere can be formed, for example, by supplying oxygen into the furnace of a rotary kiln. The firing of the mixture is preferably carried out while oxygen is continuously supplied into the furnace.

[0043] The firing temperature of the mixture is 750–1000℃, or 760–950℃, or 770–900℃, or 780–880℃, or 790–850℃. The firing time at the above firing temperatures is, for example, 1–20 hours, or 5–15 hours, or 8–12 hours.

[0044] (Method for manufacturing positive electrode active material (2))

[0045] The firing process of this method is as follows: Figure 2 As shown, it may include: a first step of obtaining a mixture containing a nickel compound and a lithium compound, a second step of molding the mixture to obtain a molded body, and a third step of firing the molded body using a rotary kiln.

[0046] The first step of obtaining the mixture can be carried out by mixing a nickel-containing compound and a lithium compound. The nickel-containing compound and lithium compound can be the substances described above. The mixing ratio of the nickel-containing compound and the lithium compound can be set in a manner that yields the first composite oxide with the desired composition.

[0047] The mixing of nickel-containing compounds with lithium compounds can be carried out using, for example, a mixer. The mixer can be a general mixer, such as a jet mill, ball mill, rocking mixer, vibratory mixer, V-type mixer, ribbon mixer, Julia mixer, or Loedige mixer.

[0048] The second step is to mold the mixture obtained in the first step to obtain a molded body. As for the molding method of the mixture, there is no limitation as long as a molded body with the density described later can be obtained, compression molding is preferred.

[0049] The maximum diameter of the molded body obtained in the second process is, for example, 18–50 mm, 20–48 mm, 21–45 mm, or 22–40 mm. If the maximum diameter of the molded body is within the above range, the contact area between the lithium compound and the inner wall of the rotary kiln can be reduced, thus reducing the amount of Cr mixed into the first composite oxide. Furthermore, the molded body can be fired effectively. On the other hand, if the maximum diameter of the molded body decreases, the contact area between the lithium compound and the inner wall of the kiln tends to increase. If the maximum diameter of the molded body increases, it becomes difficult to fire sufficiently into the interior of the molded body, or firing takes longer, making it difficult to fire the molded body effectively. In this specification, the maximum diameter of the molded body refers to the longest length among the lengths connecting any two points on the outer periphery of the molded body (the length when connecting the two points through the interior of the molded body).

[0050] The density of the molded body obtained in the second process is, for example, 1.5–4 g / cm³. 3 It can be 1.5–4.0 g / cm³. 3 Preferably, it is 1.6–3.5 g / cm³. 3 It can be 1.8–3.0 g / cm³. 3 It can be 2.0–2.8 g / cm³. 3 It can be 2.0–2.5 g / cm³. 3 If the density of the molded body is within the aforementioned range, cracking during firing is suppressed, and firing can be carried out effectively. On the other hand, if the density of the molded body is small, it becomes prone to cracking during firing in the third process. If the density of the molded body is large, oxygen becomes difficult to penetrate into the interior of the molded body, making it difficult to fire sufficiently into the interior, or requiring more time for firing, thus making it difficult to fire the molded body effectively.

[0051] There are no particular limitations on the shape of the molded body obtained in the second process, but a spherical, ellipsoidal, or cylindrical shape is preferred, with an ellipsoidal or cylindrical shape being more desirable. By shaping the molded body as described above, the contact area with the inner wall of the rotary kiln can be reduced, thereby reducing the amount of Cr mixed into the first composite oxide. Furthermore, the molded body with the above-described shape has fewer corners compared to a prism or similar shape, thus suppressing powdering of the molded body due to the corners being shaved during firing in the rotary kiln in the third process. Regarding ellipsoidal or cylindrical molded bodies, they are preferred because they are easier to move at a suitable firing speed within the rotary kiln used in the third process compared to spherical molded bodies.

[0052] The molded body can have a single-layer structure formed by molding a mixture, or a multi-layer structure containing a core layer formed by molding the mixture and a cover layer covering the core layer. The core layer can be formed by compressing the mixture. In a molded body having a core layer and a cover layer (hereinafter also referred to as a "multi-layer molded body"), the cover layer can cover the entire surface of the core layer or a portion of the core layer. Preferably, the cover layer covers more than 70%, more than 80%, and more than 90% of the entire surface of the core layer. For example, a multi-layer molded body can have a three-layer structure in which a cover layer, a core layer, and a cover layer are stacked sequentially.

[0053] The coating preferably comprises a second lithium transition metal composite oxide (hereinafter also referred to as "second composite oxide"), more preferably comprising the second composite oxide and a binder. By including the second composite oxide in the coating, the core layer formed using a mixture containing lithium compounds becomes difficult to expose. Therefore, during the firing process in the third step, the inner wall of the rotary kiln becomes less likely to come into direct contact with the lithium compounds, further suppressing the incorporation of Cr as an impurity into the first composite oxide.

[0054] The second composite oxide is not particularly limited as long as it contains an oxide of lithium and a transition metal. Preferably, the second composite oxide has the composition described in the first composite oxide, and more preferably, it is the first composite oxide manufactured in this method. The second composite oxide may have the same composition as the first composite oxide contained in the molded body, or it may have a different composition. The coating layer may, for example, contain the positive electrode active material manufactured in this method, i.e., the positive electrode active material containing the first composite oxide. The composition of the second composite oxide, as described for the first composite oxide, can be obtained using ICP-AES.

[0055] Regarding the coating layer, an adhesive may be included to improve the coating properties of the core layer. If the second composite oxide is mixed with the adhesive, the granulation properties of the second composite oxide can be improved, thereby improving the coating properties of the core layer using the coating layer.

[0056] The binder comprises one or more selected from polyvinylidene fluoride (PVdF), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA), and polyacrylamide (PAM), preferably PVdF. The binder is used to improve the granulation properties of the second composite oxide, and therefore, relative to the total amount of the second composite oxide, it can be 0.1–5.0% by mass, 0.5–3.0% by mass, or 0.8–2.0% by mass.

[0057] The molded body can be obtained by shaping the mixture using a molding machine, for example, by compressing the mixture using a powder molding machine. The powder molding machine can be any type of powder molding machine, such as a hydraulic press, hydrostatic press, briquetting machine, single-punch tablet press, or rotary tablet press.

[0058] There are no particular limitations on the method for forming the multilayer molded article. For example, it can be obtained by simultaneously molding the material forming the coating layer and the mixture forming the core layer. For example, a multilayer molded article can be obtained by laminating a layer of material containing a second composite oxide with a layer of the mixture and then molding the laminate. When the coating layer contains an adhesive, a multilayer molded article can be obtained, for example, as described below. First, the second composite oxide and the adhesive are mixed and dispersed in a solvent such as N-methyl-2-pyrrolidone (NMP). The NMP is then evaporated by heating, thereby obtaining granules containing the second composite oxide and the adhesive. Next, the granules are loaded into a mold, the mixture is loaded onto it, and then the granules are loaded again. The molded article is then compressed to obtain a multilayer molded article. The above molding process for forming the multilayer molded article can be compression molding.

[0059] The third step is to fire the molded body obtained in the second step using a rotary kiln. The rotary kiln described above can be used. The firing conditions for the molded body are listed in the firing conditions for the mixture described above.

[0060] (Manufacturing method of positive electrode plate)

[0061] The positive electrode plate manufacturing method of this embodiment is a method for manufacturing a positive electrode plate using a positive electrode active material, and the positive electrode active material is manufactured using this manufacturing method.

[0062] 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 material and a conductive material. As for the positive electrode active material layer, it can be formed by coating a positive electrode slurry, obtained 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 material, and conductive material, onto the positive electrode current collector foil, and then drying and compressing it.

[0063] The positive electrode current collector foil may be a metal foil made of Al materials such as Al and Al alloys. Examples of binder materials 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, among others. Carbon materials may be used as conductive materials. Examples of carbon materials include fibrous carbon such as carbon nanotubes and carbon black, among others.

[0064] (Manufacturing method of non-aqueous electrolyte secondary battery)

[0065] The manufacturing method of the non-aqueous electrolyte secondary battery (secondary battery) in this embodiment is the manufacturing method of the secondary battery using the above-described positive electrode plate, and the positive electrode plate is manufactured using the above-described positive electrode plate manufacturing method.

[0066] A secondary battery may include: an electrode body containing a positive electrode plate and a non-aqueous electrolyte, and may have a battery casing that houses the electrode body and the non-aqueous electrolyte. The battery casing and the non-aqueous electrolyte may be of known types used in secondary batteries.

[0067] The electrode body may include the aforementioned positive electrode plate, negative electrode plate, and separator. 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 a positive electrode plate, a negative electrode plate, and a separator, or a wound type, formed by winding a strip-shaped stack of positive electrode plates, negative electrode plates, and separators. The wound type electrode body may have a flat shape formed by pressing the stacked material after winding. The negative electrode plate typically has a negative current-collecting foil and a negative active material layer. The negative current-collecting foil, negative active material layer, and separator may use known negative current-collecting foils, negative active material layers, and separators used in secondary batteries.

[0068] (Disclosures related to rotary kilns)

[0069] The rotary kiln for manufacturing positive electrode active materials has been described above, but rotary kilns can also be used for other purposes besides manufacturing positive electrode active materials. As shown below, this disclosure discloses rotary kilns that can be used for manufacturing positive electrode active materials and other applications. The rotary kiln of this disclosure can be of the external heating type.

[0070] The rotary kiln disclosed herein has a furnace in which a layer of yttrium-chromium composite oxide (YCrO3 layer) is formed on the outermost surface of the inner wall. As long as the YCrO3 layer is formed on the outermost surface of the inner wall, the entire furnace can be formed of YCrO3, and the parts of the furnace outside the YCrO3 layer can be formed of materials other than YCrO3.

[0071] The rotary kiln disclosed herein has a furnace, which may have: a base material layer formed of an alloy containing Cr, and a YCrO3 layer formed on the outermost surface of the inner wall side of the furnace, covering the base material layer. The YCrO3 layer covering the base material layer, and the material forming the base material layer, can be set as described in the manufacturing method of the positive electrode active material.

[0072] For rotary kilns including furnaces with a base material layer and a YCrO3 layer, a process can be included to form a YCrO3 layer by spraying yttrium oxide (Y2O3) onto a base material layer formed of an alloy containing Cr. Methods for forming a YCrO3 layer on the base material layer can be exemplified by methods described in the manufacturing methods of positive electrode active materials.

[0073] Example

[0074] The following examples and comparative examples illustrate this disclosure in more detail.

[0075] [Example 1]

[0076] (Preparation of the mixture)

[0077] A nickel composite oxide containing Ni, Co, and Mn in a molar ratio of Ni:Co:Mn = 83:5:12 is prepared, along with lithium hydroxide monohydrate (average particle size (D50): 10 μm) as a lithium compound. The nickel-containing compound and the lithium compound are mixed in a molar ratio of Li:Ni:Co:Mn = 1.06:0.83:0.05:0.12 to obtain a mixture (first step).

[0078] (Making the molded object)

[0079] 5.0 g of the mixture was loaded into a powder molding die ("DT6025A-2025" manufactured by NPa SYSTEM). The mixture in the die was then compressed into a cylinder with a diameter of 20 mm and a height of 10 mm using a hydraulic press (manufactured by Riken Machinery) at 20 MPa, resulting in a density of 2.2 g / cm³. 3 The molded body (second process). The maximum diameter of the molded body is 22.4 mm.

[0080] (Preparation of a metal plate with a YCrO3 layer)

[0081] As a material for the base layer of a furnace containing Cr alloys, simulating a rotary kiln, a 100mm × 100mm SUS310S plate was prepared. Yttrium (Y2O3) powder was sprayed onto the SUS310S plate to form a 100μm thick Y2O3 layer, resulting in a laminate of the SUS310S plate and the Y2O3 layer. Next, the laminate was fired at 1000°C under atmospheric pressure for 10 hours, followed by cooling, allowing Y2O3 to diffuse into the chromium oxide layer precipitated on the SUS310S plate, forming a yttrium-chromium composite oxide layer (YCrO3 layer). The firing and cooling process was repeated twice, causing the Y2O3 film on the YCrO3 layer to thermally expand and peel off. Thus, a SUS310S plate with a YCrO3 layer formed on its outermost surface (hereinafter also referred to as "metal plate with a YCrO3 layer") was obtained.

[0082] (Sintering process)

[0083] A molded body was placed on the YCrO3 layer of a metal plate with a YCrO3 layer, and then placed in an electric furnace and fired at 805°C for 10 hours in an oxygen atmosphere (third step) to obtain a lithium transition metal composite oxide as the positive electrode active material. The Cr content in the positive electrode active material was determined using ICP (inductively coupled plasma) luminescence spectrophotometry (ICP-AES). Specifically, the determination was performed according to JIS K 0116:2014 General Rules for Luminescence Spectrophotometry, using a high-resolution ICP luminescence spectrophotometer (Hitachi High-Tech Co., Ltd. "PS3500DDII"). The lithium transition metal composite oxide was dissolved using an alkaline melting method, diluted with ultrapure water, tartaric acid, or hydrochloric acid to a specified volume, and then analyzed. The results are shown in Table 1.

[0084] [Comparative Example 1]

[0085] (Preparation of a metal plate with a chromium oxide coating)

[0086] As a material for the base layer of a furnace containing Cr alloys, a 100mm × 100mm SUS310S plate was prepared. The SUS310S plate was fired at 1000°C for 10 hours under atmospheric pressure to obtain an SUS310S plate with a chromium oxide film formed on the outermost surface (hereinafter also referred to as "metal plate with chromium oxide film").

[0087] (Firing process)

[0088] Except for using a metal plate with a chromium oxide film instead of a metal plate with a YCrO3 layer, the molded body was fired according to the steps described in Example 1 to obtain a lithium transition metal composite oxide as the positive electrode active material. As described in Example 1, the Cr content in the positive electrode active material was determined by ICP-AES. The results are shown in Table 1.

[0089] [Comparative Example 2]

[0090] A metal plate with a chromium oxide film prepared according to the steps of Comparative Example 1 was placed on a mixture prepared according to the steps of Example 1, and then placed in an electric furnace and calcined at 805°C for 10 hours under an oxygen atmosphere to obtain a lithium transition metal composite oxide as the positive electrode active material. As described in Example 1, the Cr content in the positive electrode active material was determined by ICP-AES. The results are shown in Table 1.

[0091] Table 1

[0092] Types of metal sheets Materials fired through a firing process Cr content [ppm] Example 1 <![CDATA[Metal plate with YCr03 layer]]> Molded body 0.7 Comparative Example 1 Metal plate with chromium oxide film Molded body 19.2 Comparative Example 2 Metal plate with chromium oxide film mixture 143

[0093] Embodiments of the present invention have been described, and should be considered as illustrative in all respects and not as limiting. The scope of the invention is defined by the claims and is intended to include all modifications within the meaning and scope of the claims.

Claims

1. A method for manufacturing a positive electrode active material, comprising a method for manufacturing a positive electrode active material containing a lithium transition metal composite oxide, including a step of firing a mixture of a nickel-containing compound and a lithium compound in an oxygen atmosphere at 750–1000°C. The nickel-containing compound is at least one of a nickel-containing hydroxide and a nickel-containing oxide. A layer of yttrium-chromium composite oxide is formed on the outermost surface of the inner wall of the furnace.

2. The method for manufacturing the positive electrode active material according to claim 1, wherein, The layer covers the base material layer of the furnace, which is formed of an alloy containing Cr.

3. The method for manufacturing the positive electrode active material according to claim 2, wherein, The layer is formed by spraying yttrium oxide onto the base material layer.

4. The method for manufacturing the positive electrode active material according to claim 2 or 3, wherein, The Cr-containing alloy also contains Fe and Ni.

5. The method for manufacturing the positive electrode active material according to claim 1 or 2, further comprising the step of molding the mixture to obtain a molded article. In the firing process, the molded body is fired.

6. The method for manufacturing the positive electrode active material according to claim 1 or 2, wherein, The lithium compound is at least one of lithium hydroxide and lithium carbonate.

7. The method for manufacturing the positive electrode active material according to claim 1 or 2, wherein, The Cr content of the lithium transition metal composite oxide is less than 1 ppm.

8. The method for manufacturing the positive electrode active material according to claim 1 or 2, wherein, The lithium transition metal composite oxide comprises Li, Ni, and Mn.

9. The method for manufacturing the positive electrode active material according to claim 1 or 2, wherein, The lithium transition metal composite oxide comprises Li, Ni, Mn, Co, and M, wherein 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, 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.

10. A method for manufacturing a positive electrode plate, wherein, The positive electrode active material is manufactured using the manufacturing method of any one of claims 1 to 9.

11. A method for manufacturing a non-aqueous electrolyte secondary battery, comprising a positive electrode plate, wherein... The positive electrode plate is manufactured using the manufacturing method of the positive electrode plate according to claim 10.

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