Method for producing a positive electrode active material for a sodium-ion secondary battery, method for producing a raw material for a positive electrode active material for a sodium-ion secondary battery, and method for producing a sodium-ion secondary battery

Abstract

This invention provides a method for efficiently recycling lithium-ion secondary batteries and for manufacturing positive electrode active materials for sodium-ion secondary batteries, raw materials for positive electrode active materials for sodium-ion secondary batteries, and sodium-ion secondary batteries. [Solution] A method for producing a positive electrode active material for a sodium-ion secondary battery according to one aspect of the present invention comprises producing a black mass containing the transition metal element and the iron element by processing a workpiece that includes a lithium-ion secondary battery equipped with a positive electrode having a positive electrode active material for a lithium-ion secondary battery containing a transition metal element other than iron, or a module or pack equipped with the lithium-ion secondary battery, and which includes a component containing iron; and producing a positive electrode active material for a sodium-ion secondary battery containing the transition metal element and the iron element by using the black mass as part of the raw materials.

Description

[Technical Field]

[0001] The present invention relates to a method for producing a positive electrode active material for a sodium-ion secondary battery, a method for producing a raw material for a positive electrode active material for a sodium-ion secondary battery, and a method for producing a sodium-ion secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, such as lithium-ion batteries, are widely used in electronic devices such as personal computers and communication terminals, as well as in automobiles, due to their high energy density. With the expansion of the lithium-ion battery market, the development of recycling methods for used lithium-ion batteries is progressing (see Patent Document 1). In particular, many lithium-ion batteries use oxides containing transition metal elements such as cobalt and nickel as positive electrode active materials, making recycling important from the perspective of resource conservation.

[0003] Lithium-ion secondary batteries (especially positive electrode active materials for lithium-ion secondary batteries) are recycled, for example, by the following procedure: Used lithium-ion secondary batteries are subjected to calcination, crushing, etc., to produce powder to obtain black mass. Impurities such as iron, aluminum, and copper are removed from the black mass by sieving, magnetic separation, etc. By wet refining, etc., the black mass from which impurities have been removed is recovered in the form of compounds such as hydroxides, metal salts such as sulfates, and oxides. By mixing the recovered compounds containing cobalt and nickel with a lithium source containing lithium and calcining, a lithium transition metal composite oxide is obtained. The obtained lithium transition metal composite oxide can be used as a positive electrode active material for lithium-ion secondary batteries to manufacture lithium-ion secondary batteries.

[0004] On the other hand, in recent years, various sodium-ion secondary batteries have been developed as non-aqueous electrolyte secondary batteries, using sodium ions as charge transport ions. As positive electrode active materials for sodium-ion secondary batteries, composite oxides containing sodium, manganese, and iron elements are known (see Patent Document 2). [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Special Publication No. 2021-504885 [Patent Document 2] Japanese Patent Publication No. 2012-201588 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] When recycling lithium-ion secondary batteries using the procedure described above, it is difficult to completely remove impurities from the black mass. Therefore, the recovered compounds containing cobalt, nickel, etc., may also contain impurities such as iron, aluminum, and copper. When lithium transition metal composite oxides are manufactured using compounds containing such impurities as raw materials, the resulting lithium transition metal composite oxide may also contain impurities, resulting in insufficient quality as a positive electrode active material for lithium-ion secondary batteries. Iron, in particular, is widely used as a constituent element in lithium-ion secondary batteries and in components such as containers, restraints, and housings of modules and packs containing lithium-ion secondary batteries. Therefore, it is present in large quantities in the black mass and is extremely difficult to remove completely. Consequently, obtaining positive electrode active materials for lithium-ion secondary batteries by recycling lithium-ion secondary batteries requires processes to remove impurities such as iron with high precision. On the other hand, sodium-ion secondary batteries use sodium instead of expensive lithium, and the market for sodium-ion secondary batteries is expected to expand in the future.

[0007] The present invention has been made based on the above circumstances, and an object of the present invention is to efficiently recycle a lithium-ion secondary battery and provide a cathode active material for a sodium-ion secondary battery, a raw material for a cathode active material for a sodium-ion secondary battery, and a method for manufacturing a sodium-ion secondary battery.

Means for Solving the Problems

[0008] A method for manufacturing a cathode active material for a sodium-ion secondary battery according to one aspect of the present invention includes treating a workpiece including a member containing iron element, the workpiece being a lithium-ion secondary battery including a cathode having a cathode active material for a lithium-ion secondary battery containing a transition metal element other than iron element, or a module or a pack including the lithium-ion secondary battery, to produce a black mass containing the transition metal element and the iron element, and using the black mass as a part of a raw material to produce a cathode active material for a sodium-ion secondary battery containing the transition metal element and the iron element.

[0009] A method for manufacturing a cathode active material for a sodium-ion secondary battery according to another aspect of the present invention includes using, as a part of a raw material, a black mass containing a transition metal element other than lithium element and iron element and the iron element, and producing a cathode active material for a sodium-ion secondary battery containing the transition metal element and the iron element.

[0010] A method for manufacturing a raw material for a cathode active material for a sodium-ion secondary battery according to another aspect of the present invention includes treating a workpiece including a member containing iron element, the workpiece being a lithium-ion secondary battery including a cathode having a cathode active material for a lithium-ion secondary battery containing a transition metal element other than iron element, or a module or a pack including the lithium-ion secondary battery, to produce a black mass containing the transition metal element and the iron element.

[0011] A method for manufacturing a sodium-ion secondary battery according to another aspect of the present invention includes the method for manufacturing a cathode active material for a sodium-ion secondary battery according to one aspect of the present invention. [Effect of the Invention]

[0012] According to any one aspect of the present invention, a lithium-ion secondary battery can be efficiently recycled to produce a positive electrode active material for a sodium-ion secondary battery, a raw material for a positive electrode active material for a sodium-ion secondary battery, and a sodium-ion secondary battery. [Brief Description of the Drawings]

[0013] [Figure 1] FIG. 1 is a flowchart showing an embodiment of a method for manufacturing a positive electrode active material for a sodium-ion secondary battery. [Figure 2] FIG. 2 is a perspective view showing an embodiment of a non-aqueous electrolyte secondary battery. [Figure 3] FIG. 3 is a schematic view showing an embodiment of a pack (power storage device) formed by assembling a plurality of non-aqueous electrolyte secondary batteries. [Modes for Carrying Out the Invention]

[0014] First, an overview of a method for manufacturing a positive electrode active material for a sodium-ion secondary battery, a method for manufacturing a raw material for a positive electrode active material for a sodium-ion secondary battery, and a method for manufacturing a sodium-ion secondary battery disclosed in this specification will be described.

[0015] (1) The method for manufacturing a positive electrode active material for a sodium-ion secondary battery according to one aspect of the present invention includes a lithium-ion secondary battery including a positive electrode having a positive electrode active material for a lithium-ion secondary battery containing a transition metal element other than iron element, or a module or a pack including the lithium-ion secondary battery, and treating an object to be treated including a member containing an iron element to produce a black mass containing the transition metal element and the iron element, and using the black mass as a part of a raw material to produce a positive electrode active material for a sodium-ion secondary battery containing the transition metal element and the iron element.

[0016] According to the method for producing positive electrode active material for sodium-ion secondary batteries described in (1) above, lithium-ion secondary batteries can be efficiently recycled and positive electrode active material for sodium-ion secondary batteries can be produced. The reason for this is as follows: Various forms of oxides containing iron and other transition metal elements have been developed for positive electrode active material for sodium-ion secondary batteries. For this reason, if black mass produced by processing lithium-ion secondary batteries, or modules or packs equipped with lithium-ion secondary batteries (hereinafter also referred to as "lithium-ion secondary batteries, etc.") is used for producing positive electrode active material for sodium-ion secondary batteries instead of for producing positive electrode active material for lithium-ion secondary batteries, the iron elements in the black mass will not become impurities and can be reused as elements constituting the positive electrode active material for sodium-ion secondary batteries. For this reason, according to the method for producing positive electrode active material for sodium-ion secondary batteries described in (1) above, iron elements may be left in the process of producing black mass by processing lithium-ion secondary batteries, etc., that is, there is no need to completely remove the iron elements, and recycling can be carried out efficiently, and positive electrode active material for sodium-ion secondary batteries can be produced using this black mass.

[0017] (2) In the method for producing a positive electrode active material for a sodium-ion secondary battery described in (1) above, the positive electrode active material for a sodium-ion secondary battery may be a transition metal composite oxide containing sodium, the transition metal element and the iron element.

[0018] A transition metal composite oxide containing sodium, a transition metal element other than iron, and iron can be obtained by calcining a mixture of a compound obtained from black mass containing the transition metal element other than iron and iron, and a sodium source containing sodium. Therefore, according to the method for producing a positive electrode active material for sodium-ion secondary batteries described in (2) above, a positive electrode active material for sodium-ion secondary batteries can be obtained more efficiently from black mass produced by processing lithium-ion secondary batteries, etc.

[0019] (3) In the method for producing a positive electrode active material for a sodium-ion secondary battery described in (1) or (2) above, the production of the positive electrode active material for a sodium-ion secondary battery may include obtaining one or more compounds containing the transition metal element and the iron element from the black mass, and calcining a mixture of the one or more compounds and a sodium source containing the sodium element.

[0020] According to the method for producing a positive electrode active material for sodium-ion secondary batteries described in (3) above, a positive electrode active material for sodium-ion secondary batteries can be obtained more efficiently from black mass produced by processing lithium-ion secondary batteries, etc.

[0021] (4) In the method for producing a positive electrode active material for a sodium-ion secondary battery described in any one of (1) to (3) above, the positive electrode active material for a lithium-ion secondary battery may contain manganese as the transition metal element.

[0022] When manufacturing positive electrode active material for lithium-ion secondary batteries by recycling lithium-ion secondary batteries, etc., it is necessary to sufficiently remove iron elements, which are impurities, from the black mass by magnetic separation or the like, as described above. However, since manganese elements are also easily removed along with iron elements during magnetic separation, it is difficult to recycle manganese elements at a sufficiently high recycling rate when manufacturing positive electrode active material for lithium-ion secondary batteries from lithium-ion secondary batteries, etc. In contrast, in the method for manufacturing positive electrode active material for sodium-ion secondary batteries described in (4) above, it is not necessary to completely remove iron elements from the black mass, and as a result, manganese elements can be easily retained in the black mass, thereby increasing the recycling rate of manganese elements.

[0023] (5) In the method for producing a positive electrode active material for a sodium-ion secondary battery described in any one of (1) to (4) above, the positive electrode active material for a lithium-ion secondary battery may contain manganese as the transition metal element, the workpiece may comprise a member containing copper, and the black mass may further contain copper.

[0024] In the method for producing a positive electrode active material for sodium-ion secondary batteries described in (5) above, since the black mass contains iron, copper, and manganese derived from the positive electrode active material for lithium-ion secondary batteries, it is possible to recover these elements and produce a composite oxide further containing copper as a positive electrode active material for sodium-ion secondary batteries.

[0025] (6) Another aspect of the present invention relates to a method for producing a positive electrode active material for a sodium-ion secondary battery, which involves using black mass containing lithium, a transition metal element other than iron, and iron as part of the raw materials to produce a positive electrode active material for a sodium-ion secondary battery containing the above-mentioned transition metal element and iron.

[0026] Since the black mass used in the method for producing positive electrode active material for sodium-ion secondary batteries described in (6) above contains lithium, black mass produced by processing lithium-ion secondary batteries, etc., can be used as this black mass. For this reason, the method for producing positive electrode active material for sodium-ion secondary batteries described in (6) above allows for the efficient recycling of lithium-ion secondary batteries and the production of positive electrode active material for sodium-ion secondary batteries, similar to the method for producing positive electrode active material for sodium-ion secondary batteries described in (1) above.

[0027] (7) A method for producing a positive electrode active material raw material for a sodium-ion secondary battery according to another aspect of the present invention comprises producing a black mass containing the transition metal element and the iron element by processing a workpiece that includes a lithium-ion secondary battery equipped with a positive electrode having a positive electrode active material for a lithium-ion secondary battery containing a transition metal element other than iron, or a module or pack equipped with the above lithium-ion secondary battery, which includes a component containing iron.

[0028] Black mass containing transition metal elements other than iron and iron can be suitably used as a raw material for positive electrode active material for sodium-ion secondary batteries, as described above. Therefore, according to the method for producing a raw material for positive electrode active material for sodium-ion secondary batteries described in (7) above, lithium-ion secondary batteries can be efficiently recycled and a raw material for positive electrode active material for sodium-ion secondary batteries can be produced.

[0029] (8) A method for producing a sodium-ion secondary battery according to another aspect of the present invention includes a method for producing a positive electrode active material for a sodium-ion secondary battery described in any one of (1) to (6) above, or a method for producing a raw material for a positive electrode active material for a sodium-ion secondary battery described in (7) above.

[0030] According to the method for manufacturing sodium-ion secondary batteries described in (8) above, lithium-ion secondary batteries can be efficiently recycled and sodium-ion secondary batteries can be manufactured.

[0031] A method for producing a positive electrode active material for a sodium-ion secondary battery, a method for producing a raw material for a positive electrode active material for a sodium-ion secondary battery, a method for producing a sodium-ion secondary battery, and other embodiments related to one embodiment of the present invention will be described in detail.

[0032] Furthermore, the lower and upper limits of each numerical range described in the embodiments of the present invention can be combined in any way.

[0033] <Method for manufacturing positive electrode active material for sodium-ion secondary batteries> A method for producing a positive electrode active material for a sodium-ion secondary battery according to one embodiment of the present invention comprises producing black mass (production of black mass S1) and producing a positive electrode active material for a sodium-ion secondary battery using black mass as part of the raw materials (production of positive electrode active material S2) (see Figure 1). Each step will be described below.

[0034] (Black Mass Production S1) In this process, black mass is obtained by processing the materials to be processed, which are lithium-ion secondary batteries, modules equipped with lithium-ion secondary batteries, or packs equipped with lithium-ion secondary batteries. Black mass refers to the powder obtained by firing, crushing, or otherwise processing the recovered lithium-ion secondary batteries. The recovered lithium-ion secondary batteries subject to processing include those recovered as used products, those recovered as unused products after shipment, and those recovered as defective products during manufacturing.

[0035] The lithium-ion secondary battery to be processed has a positive electrode having a positive electrode active material for lithium-ion secondary batteries that contains transition metal elements other than iron. Furthermore, the lithium-ion secondary battery, the module containing the lithium-ion secondary battery, or the pack containing the lithium-ion secondary battery to be processed includes a component containing iron. Apart from the points mentioned above, the objects to be processed, such as lithium-ion secondary batteries, may have the same configuration as conventionally known lithium-ion secondary batteries.

[0036] A lithium-ion secondary battery typically comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container housing these components. A lithium-ion secondary battery may further include a separator interposed between the positive and negative electrodes to electrically insulate them. The positive electrode, negative electrode, and any separator typically constitute the electrode body. A lithium-ion secondary battery may have a structure similar to that of a general non-aqueous electrolyte secondary battery. For example, the non-aqueous electrolyte secondary battery 1 (lithium-ion secondary battery) shown in Figure 2 comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 housing these components. The non-aqueous electrolyte secondary battery 1 (lithium-ion secondary battery) in Figure 2 further includes a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and negative electrode lead 6 are housed within the container 3 together with the electrode body 2, etc. The positive electrode external terminal 5 and negative electrode external terminal 7 are located outside the container 3. The positive electrode constituting electrode body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0037] The specific forms of the positive electrode, negative electrode, separator, non-aqueous electrolyte, container, etc. that constitute a lithium-ion secondary battery can adopt the description of the specific forms of a sodium-ion secondary battery described later, except that the positive electrode active material and negative electrode active material are made of materials that can intercept and release lithium ions, and the electrolyte salt is a lithium salt. The positive electrode active material used in a lithium-ion secondary battery (positive electrode active material for lithium-ion secondary batteries) is as described later. Examples of negative electrode active materials used in a lithium-ion secondary battery include those similar to the negative electrode active material used in a sodium-ion secondary battery described later. Metallic lithium can also be used as the negative electrode active material in a lithium-ion secondary battery. Examples of lithium salts used as electrolytes in lithium-ion secondary batteries include inorganic lithium salts such as LiPF6, LiPO2F2, LiBF4, and LiClO4; imide salts such as LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, and LiN(SO2CF3)(SO2C4F9); and lithium oxalate salts such as LiB(C2O4)2, LiBF2(C2O4), and LiPF2(C2O4)2. Lithium-ion secondary batteries may also be all-solid-state secondary batteries.

[0038] Transition metal elements other than iron that can be included in the positive electrode active material for lithium-ion secondary batteries used in lithium-ion secondary batteries that are the target of processing include nickel, cobalt, manganese, titanium, molybdenum, and vanadium. Nickel, cobalt, and manganese are preferred among the transition metal elements other than iron that can be included in the positive electrode active material for lithium-ion secondary batteries, with nickel and manganese being more preferred. These transition metal elements are useful because they are expensive elements and are also frequently used in positive electrode active materials for sodium-ion secondary batteries.

[0039] In one embodiment of the present invention, the positive electrode active material for lithium-ion secondary batteries may contain manganese as a transition metal element other than iron. Manganese is an element that is easily removed along with iron by magnetic separation. In the method for producing a positive electrode active material for sodium-ion secondary batteries according to one embodiment of the present invention, it is not necessary to completely remove iron from the black mass. Therefore, even when processing lithium-ion secondary batteries and the like using a positive electrode active material for lithium-ion secondary batteries containing manganese, it is easy to leave manganese in the black mass, and the recycling rate of manganese can be increased.

[0040] Examples of positive electrode active materials for lithium-ion secondary batteries containing transition metal elements other than iron include lithium transition metal composite oxides, polyanion compounds, chalcogen compounds, etc., with lithium transition metal composite oxides being preferred.

[0041] Examples of transition metal elements included in lithium transition metal composite oxides include nickel, cobalt, and manganese. Lithium transition metal composite oxides may also contain typical metal elements such as aluminum. Examples of lithium transition metal composite oxides include those having an α-NaFeO2 crystal structure and those having a spinel crystal structure.

[0042] Li 1+α Ma 1-α Examples include O2 (where Ma is a metallic element other than lithium, containing one or more transition metal elements, and including transition metal elements other than iron. 0 ≤ α < 1). It is preferable that Ma contains one or more of Ni, Co, and Mn. The total content of Ni, Co, and Mn relative to Ma ((Ni + Co + Mn) / Ma) is preferably 90 mol% or more, and more preferably 98 mol% or more.

[0043] Liβ Those represented by Mb2O4 (where Mb is a metal element other than lithium element, including one or more transition metal elements and including a transition metal element other than iron element, and 0 < β ≤ 1.2) may be mentioned. It is preferable that Mb contains Mn.

[0044] A polyanion compound is a compound composed of a polyanion (that is, a polyvalent oxoacid anion) and a cation. The polyanion compound preferably contains a transition metal cation other than lithium cation and iron cation as the cation. Examples of the polyanion compound include LiMnPO4, LiMn x Fe 1-x PO4 (0 < x < 1), LiNiPO4, LiCoPO4, Li3V2(PO4)3, Li2MnSiO4, Li2CoPO4F, etc. The surface of the particles of the polyanion compound may be coated with another material (such as a carbon material, etc.).

[0045] Examples of the chalcogen compound include titanium disulfide, molybdenum disulfide, molybdenum dioxide, etc.

[0046] The positive electrode active material for the lithium ion secondary battery may be lithium manganate. Lithium manganate is an example of the lithium transition metal composite oxide having the spinel-type crystal structure described above, and Li β Those represented by Mb2O4 (where Mb is a metal element other than lithium element, including a manganese element, and 0 < β ≤ 1.2) may be mentioned. The content of Mn in Mb (Mn / Mb) is preferably 50 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more. Lithium manganate may be a compound represented by LiMn2O4.

[0047] The iron-containing components in the material to be processed may be components of the lithium-ion secondary battery itself (the lithium-ion secondary battery cell), or components of a module or pack containing a lithium-ion secondary battery. A module containing a lithium-ion secondary battery comprises multiple electrically connected lithium-ion secondary batteries. A pack containing a lithium-ion secondary battery comprises one or more lithium-ion secondary batteries (cells) or one or more modules, and may further include a condition monitoring device, etc. Examples of iron-containing components in a lithium-ion secondary battery (cell) include iron containers (including stainless steel; the same applies hereinafter), iron lids, iron positive electrode substrates and negative electrode substrates, iron leads, iron terminals, etc. Examples of iron-containing components in a module or pack containing a lithium-ion secondary battery include iron restraint members (restraint bands, end plates, etc.) for restraining one or more lithium-ion secondary batteries, iron housings for housing one or more lithium-ion secondary batteries, etc.

[0048] Lithium-ion secondary batteries and the like may include components containing copper. That is, the workpiece may include components containing copper in addition to components containing iron. The workpiece may include components containing iron and components containing copper as separate components. Alternatively, the components containing iron and components containing copper may be the same component. That is, the component containing iron may further contain copper. Examples of components containing copper include copper negative electrode substrates, copper negative electrode leads, copper terminals, and wires containing copper wire. Components (restraining members, housings, etc.) included in a module or pack containing a lithium-ion secondary battery may also contain copper.

[0049] The black mass obtained in this process contains transition metal elements other than iron and iron. The transition metal elements other than iron contained in the black mass include those derived from positive electrode active materials for lithium-ion secondary batteries, but may also include transition metal elements other than iron derived from sources other than positive electrode active materials for lithium-ion secondary batteries. Nickel, cobalt, and manganese are preferred as transition metal elements other than iron contained in the black mass, with nickel and manganese being more preferred. The iron contained in the black mass is derived from iron-containing materials, but may also include iron derived from sources other than iron-containing materials. In addition, the black mass may contain elements (transition metal elements and other elements) that constituted the processed material such as a lithium-ion secondary battery, such as lithium, copper, aluminum, carbon, and oxygen.

[0050] The black mass described above can be obtained by processing materials such as lithium-ion secondary batteries using conventionally known methods. For example, black mass can be obtained by processing recovered lithium-ion secondary batteries, etc., through calcination, crushing, etc., to pulverize (powder) them. Modules or packs containing lithium-ion secondary batteries may be processed by calcination, crushing, etc., while they are still in module or pack form. During these processes, relatively large components such as containers, terminals, electrode base materials, restraint members, housings, etc., which are elements such as aluminum and copper, may be removed from the black mass by sieving or other methods to separate the components containing aluminum and copper. However, since copper can be used as an element constituting the positive electrode active material for sodium secondary batteries, it does not have to be removed from the black mass, and only a portion may be removed. In addition, iron is left in the obtained black mass, but some iron may be removed from the black mass. Means for removing iron from the black mass include sieving or magnetic separation of components containing iron.

[0051] One embodiment of the present invention is a method in which magnetic separation is not performed during the production of black mass. By not performing magnetic separation, iron elements are actively retained in the black mass, making it possible to obtain black mass suitable as a raw material for positive electrode active material for sodium secondary batteries. Furthermore, not performing magnetic separation has advantages such as increasing the recycling rate of elements that are easily removed by magnetic separation along with iron elements, such as manganese, and improving work efficiency by omitting the magnetic separation process.

[0052] (Manufacturing of positive electrode active material for sodium-ion secondary batteries S2) In this process, the black mass obtained in the black mass production S1 described above, which contains transition metal elements other than iron and iron, is used as part of the raw materials to produce a positive electrode active material for sodium secondary batteries that contains transition metal elements other than iron and iron. The black mass used in this process may contain various elements other than transition metal elements (including iron), such as lithium, copper, aluminum, carbon, and oxygen. Black mass obtained by recovering lithium-ion secondary batteries usually contains lithium.

[0053] The positive electrode active material for sodium-ion secondary batteries can be manufactured, for example, by obtaining one or more compounds containing transition metal elements other than iron and iron from black mass containing transition metal elements other than iron and iron (compound manufacturing S2-1), and by calcining a mixture of the above one or more compounds and a sodium source containing sodium (calcination S2-2).

[0054] (Compound production S2-1) In this process, one or more compounds containing transition metal elements other than iron and iron are obtained from black mass containing transition metal elements other than iron and iron. The production of compounds from black mass can be carried out using the same procedure as when producing positive electrode active material for lithium-ion secondary batteries from black mass obtained by processing lithium-ion secondary batteries, and conventionally known methods such as wet smelting and dry smelting can be employed.

[0055] The compounds to be produced are preferably oxides or compounds that can be converted to oxides by calcination (e.g., hydroxides, sulfates, nitrates, oxalates, carbonates, etc.), and oxides are more preferred. Examples of oxides include iron oxide, manganese oxide, nickel oxide, and copper oxide. These compounds may be isolated individually or obtained as a mixture. In one embodiment of the present invention, it is preferable to isolate and recover each compound. On the other hand, even if recovered as a mixture, if, for example, the content ratio of the constituent elements contained in the mixture can be determined, it can be used without any particular problem as a raw material for positive electrode active material for sodium secondary batteries.

[0056] The following are examples of specific procedures for obtaining one or more compounds containing transition metal elements other than iron and iron from black mass. For example, metal salts of each transition metal element can be obtained by treating black mass with a suitable acidic solution to dissolve the transition metal elements (including iron) in the black mass and performing solvent extraction. Alternatively, hydroxides of each transition metal element can be obtained by separating insoluble matter from a solution containing transition metal elements (including iron) obtained by treatment with an acidic solution and then reacting it with hydroxides of alkali metal elements (such as lithium hydroxide). Oxides of each transition metal element can be obtained by calcining the metal salts or hydroxides of each transition metal element obtained in this way. Each of the one or more compounds obtained may contain only one transition metal element or may contain multiple transition metal elements.

[0057] Black mass may contain various elements other than transition metal elements (including iron), such as lithium, copper, aluminum, carbon, and oxygen. Therefore, this process may also produce components other than one or more compounds containing transition metal elements other than iron and iron. The other components will vary depending on the processing method, but examples include lithium compounds such as lithium carbonate. These other components may be recovered as appropriate and reused for various purposes, or they may not be reused. Lithium compounds can be reused, for example, as raw materials for positive electrode active materials in lithium-ion secondary batteries.

[0058] For example, the production of a positive electrode active material for a sodium-ion secondary battery according to one embodiment of the present invention may include extracting lithium from black mass containing lithium, a transition metal element other than iron, and iron. The extraction of lithium from black mass containing lithium can be carried out, for example, by immersing the black mass in an aqueous solution to dissolve the lithium into the aqueous solution. The positive electrode active material for a sodium-ion secondary battery can also be produced using black mass from which lithium has been extracted. Thus, the extraction of lithium from black mass may be performed before obtaining one or more compounds containing a transition metal element other than iron and iron. For example, one preferred embodiment of the present invention involves producing a positive electrode active material for a sodium-ion secondary battery in the following order: extracting lithium from black mass containing lithium, transition metal elements other than iron, and iron (lithium element extraction S2-0); obtaining one or more compounds containing transition metal elements other than iron and iron from black mass containing transition metal elements other than iron and iron (compound production S2-1); and calcining a mixture of the above one or more compounds and a sodium source containing sodium (calcination S2-2).

[0059] (Firing S2-2) In this process, a mixture of one or more compounds obtained in the above process (compound production S2-1) and a sodium source containing the element sodium is calcined.

[0060] Examples of sodium sources containing the element sodium include sodium carbonate, sodium bicarbonate, sodium oxide, and sodium peroxide. From the standpoint of ease of handling, sodium carbonate or sodium bicarbonate is preferred, and sodium carbonate is more preferred. One or more types of sodium sources containing the element sodium can be used.

[0061] One or more compounds containing transition metal elements other than iron and iron used in this process may include a compound containing iron and a compound containing a transition metal element other than iron. In the case of a compound containing both iron and a transition metal element other than iron, only one of these compounds may be used.

[0062] In this process, one or more compounds containing transition metal elements other than iron and iron may be used in part, but some may be those not obtained from the black mass described above. By using at least a portion of one or more compounds containing transition metal elements other than iron and iron in this process, the objective of efficiently recycling lithium-ion secondary batteries and producing positive electrode active materials for sodium-ion secondary batteries can be achieved.

[0063] In this process, each component (one or more compounds containing transition metal elements other than iron and iron, a sodium source containing sodium, and other components as needed) is mixed and calcined to correspond to the elemental composition of the target positive electrode active material for sodium-ion secondary batteries. For example, a composite metal oxide having a metal element ratio expressed as Na:Fe:Mn = 1:1 / 2:1 / 2 can be produced by weighing sodium carbonate, iron oxide, and manganese oxide so that the molar ratio of Na:Fe:Mn is 1:1 / 2:1 / 2, mixing them, and calcining the resulting mixture. At this time, in order to increase the certainty that the sodium element ratio in the positive electrode active material for sodium-ion secondary batteries is as intended, the mixing ratio of the sodium source containing sodium in the mixture may be greater than the sodium element ratio in the target positive electrode active material for sodium-ion secondary batteries.

[0064] In this process, for example, compounds of each element corresponding to the elemental composition of the target positive electrode active material for sodium-ion secondary batteries may be mixed directly with a sodium source containing sodium and then calcined. Alternatively, a compound containing multiple transition metal elements corresponding to the target positive electrode active material for sodium-ion secondary batteries may be synthesized first, and then such a compound may be mixed with a sodium source containing sodium and then calcined. For example, when using metal salts such as sulfates or nitrates as one or more compounds containing transition metal elements other than iron and iron, a compound containing multiple transition metal elements (such as a transition metal composite hydroxide) can be synthesized by dissolving multiple of these metal salts in an aqueous solution and adding an alkaline aqueous solution dropwise. The compound containing multiple transition metal elements obtained in this way (such as a transition metal composite hydroxide) can then be mixed with a sodium source containing sodium, such as sodium carbonate, and then calcined.

[0065] Mixing one or more compounds containing transition metal elements other than iron and iron with a sodium source containing sodium can be carried out using known equipment such as a ball mill or a stirrer. The mixing may be done by dry mixing or wet mixing.

[0066] The firing conditions for the mixture are not particularly limited, but the firing temperature may be, for example, 600°C to 1,200°C, or 800°C to 1,000°C. The firing time may be, for example, 1 hour to 48 hours, or 2 hours to 24 hours. Examples of the atmosphere during firing include an inert atmosphere (nitrogen, argon, etc.) and an oxidizing atmosphere (air, oxygen, oxygen-containing nitrogen, oxygen-containing argon, etc.), but an oxidizing atmosphere is preferred.

[0067] The positive electrode active material for sodium-ion secondary batteries obtained after firing may be subjected to grinding, classification, etc., to adjust the particle size. Preferably, the average particle size of the positive electrode active material for sodium-ion secondary batteries is, for example, 0.1 μm or more and 20 μm or less. Setting the average particle size of the positive electrode active material for sodium-ion secondary batteries to be above the lower limit makes it easier to manufacture or handle the positive electrode active material for sodium-ion secondary batteries. Setting the average particle size of the positive electrode active material for sodium-ion secondary batteries to be below the upper limit improves the electronic conductivity of the positive electrode active material layer containing such a positive electrode active material for sodium-ion secondary batteries. "Average particle size" refers to the value (D50) at which the volume-based integrated distribution calculated in accordance with JIS-Z-8819-2 (2001), based on the particle size distribution measured by laser diffraction / scattering method on a dilution solution obtained by diluting particles with a solvent, in accordance with JIS-Z-8825 (2013), becomes 50%.

[0068] The resulting positive electrode active material for sodium-ion secondary batteries is preferably a transition metal composite oxide containing sodium, a transition metal element other than iron, and iron. Such a transition metal composite oxide can be effectively obtained by the methods described in "Compound Production S2-1" and "Castration S2-2" above, and is useful as a positive electrode active material for sodium-ion secondary batteries. The above transition metal composite oxide is preferably a layered oxide (an oxide having a layered crystalline structure).

[0069] The above transition metal composite oxide may also be represented by the following formula (A). Na x Me y O2···(A) In equation (A), Me is a metallic element other than sodium, including iron and transition metal elements other than iron. 0.5 ≤ x ≤ 1.2. 0.8 ≤ y ≤ 1.2 or less.

[0070] In formula (A), the transition metal element other than iron in Me is preferably at least one selected from the group consisting of nickel, manganese, and copper. The content of transition metal elements (including iron) in Me is preferably 90 mol% or more, more preferably 99 mol% or more, and may be 100 mol%. The content of iron in Me is preferably 10 mol% or more and 90 mol% or less, and more preferably 20 mol% or more and 60 mol% or less. x may be less than 1.0. y may be 1.0. x+y may be, for example, 1.5 or more and 2.2 or 1.5 or more and less than 2.0.

[0071] Examples of transition metal elements that make up Me in formula (A), and other combinations of transition metal elements contained in the resulting positive electrode active material for sodium-ion secondary batteries, include combinations of Fe, Mn, and Ni; combinations of Fe, Mn, and Cu; and combinations of Fe, Mn, Ni, and Cu. Furthermore, if the positive electrode active material for lithium-ion secondary batteries to be reused contains manganese as a transition metal element, such as lithium manganate, and the processed object such as a lithium-ion secondary battery includes components containing copper, then by not completely removing the copper, it is possible to produce black mass containing copper in addition to transition metal elements other than iron and iron. By using such black mass as part of the raw materials, it is possible to efficiently produce positive electrode active material for sodium-ion secondary batteries containing transition metal elements other than iron, iron, and copper.

[0072] Another embodiment of the present invention provides a method for producing a positive electrode active material for a sodium-ion secondary battery, comprising using black mass containing lithium, transition metal elements other than iron, and iron as part of the raw materials to produce a positive electrode active material for a sodium-ion secondary battery containing the transition metal elements and iron. Since this production method substantially comprises the steps of "Production of positive electrode active material S2" described above, the specific form is as described in "Production of positive electrode active material S2" described above.

[0073] According to a method for producing a positive electrode active material for sodium-ion secondary batteries according to one embodiment of the present invention, lithium-ion secondary batteries can be efficiently recycled and a positive electrode active material for sodium-ion secondary batteries can be produced.

[0074] <Method for producing raw materials for positive electrode active materials for sodium-ion secondary batteries> A method for producing a positive electrode active material raw material for a sodium-ion secondary battery according to one embodiment of the present invention comprises producing a black mass containing the transition metal element and the iron element by processing a workpiece that includes a lithium-ion secondary battery equipped with a positive electrode having a positive electrode active material for a lithium-ion secondary battery containing a transition metal element other than iron, or a module or pack equipped with the above lithium-ion secondary battery, which includes a component containing iron. Since this production method substantially comprises the steps of "Black Mass Production S1" described above, the specific form is as described in "Black Mass Production S1" above.

[0075] The black mass obtained by this manufacturing method is useful as a raw material for positive electrode active material in sodium-ion secondary batteries. Therefore, according to the method for manufacturing a raw material for positive electrode active material in sodium-ion secondary batteries according to one embodiment of the present invention, lithium-ion secondary batteries can be efficiently recycled and a raw material for positive electrode active material in sodium-ion secondary batteries can be manufactured.

[0076] <Manufacturing method for sodium-ion secondary batteries> A method for manufacturing a sodium-ion secondary battery according to one embodiment of the present invention includes a method for manufacturing a positive electrode active material for a sodium-ion secondary battery according to one embodiment of the present invention, or a method for manufacturing a raw material for a positive electrode active material for a sodium-ion secondary battery according to one embodiment of the present invention. The method for manufacturing a sodium-ion secondary battery may use, as at least a part of the positive electrode active material, a positive electrode active material for a sodium-ion secondary battery obtained by the method for manufacturing a positive electrode active material for a sodium-ion secondary battery according to one embodiment of the present invention. The method for manufacturing a sodium-ion secondary battery may employ conventionally known methods for manufacturing sodium-ion secondary batteries, except for using a positive electrode active material recycled from a lithium-ion secondary battery in this manner.

[0077] The method for manufacturing the sodium-ion secondary battery includes, for example, manufacturing a positive electrode, preparing a negative electrode, preparing a non-aqueous electrolyte, and housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container. The manufacturing method may also include preparing a separator, and manufacturing an electrode body using the positive electrode, negative electrode, and separator. Housing the positive electrode, negative electrode, and non-aqueous electrolyte in a container may be equivalent to housing the electrode body and non-aqueous electrolyte in a container.

[0078] The positive electrode can be manufactured by, for example, applying a positive electrode mixture paste directly to a positive electrode substrate or via an intermediate layer, and then drying it. The positive electrode mixture paste contains the positive electrode active material for sodium-ion secondary batteries obtained by the manufacturing method described above, and other components that constitute the positive electrode active material layer. The positive electrode mixture paste usually also contains a dispersion medium. By applying the positive electrode mixture paste, drying it, and pressing it as necessary, a positive electrode active material layer is formed on the positive electrode substrate, and a positive electrode is obtained. In manufacturing the positive electrode, the positive electrode active material obtained by the manufacturing method for sodium-ion secondary batteries according to one embodiment of the present invention may be mixed with other positive electrode active materials.

[0079] According to a method for manufacturing a sodium-ion secondary battery according to one embodiment of the present invention, lithium-ion secondary batteries can be efficiently recycled and sodium-ion secondary batteries can be manufactured.

[0080] (Sodium-ion secondary battery) The following describes a specific form of a sodium-ion secondary battery obtained by a method for manufacturing a sodium-ion secondary battery according to one embodiment of the present invention. The sodium-ion secondary battery comprises a positive electrode, a negative electrode, a non-aqueous electrolyte, and a container housing these. The sodium-ion secondary battery may further include a separator interposed between the positive electrode and the negative electrode to electrically insulate them. The positive electrode, the negative electrode, and any separator usually constitute an electrode body. At least a portion of the non-aqueous electrolyte usually exists in a state of permeating the electrode body. The sodium-ion secondary battery may further include other components.

[0081] A sodium-ion secondary battery may have the structure of the non-aqueous electrolyte secondary battery 1 shown in Figure 2 above. The non-aqueous electrolyte secondary battery 1 (sodium-ion secondary battery) comprises an electrode body 2, a non-aqueous electrolyte (not shown), and a rectangular parallelepiped container 3 that houses them. The non-aqueous electrolyte secondary battery 1 (sodium-ion secondary battery) in Figure 2 further comprises a positive electrode lead 4, a positive electrode external terminal 5, a negative electrode lead 6, and a negative electrode external terminal 7. The positive electrode lead 4 and the negative electrode lead 6 are housed together with the electrode body 2, etc., inside the container 3. The positive electrode external terminal 5 and the negative electrode external terminal 7 are provided outside the container 3. The positive electrode constituting the electrode body 2 is electrically connected to the positive electrode external terminal 5 via the positive electrode lead 4. The negative electrode constituting the electrode body 2 is electrically connected to the negative electrode external terminal 7 via the negative electrode lead 6.

[0082] The following will provide a detailed explanation of the main components that make up the sodium-ion secondary battery, but this is not intended to limit the application of the present invention to the following forms.

[0083] (positive electrode) The positive electrode has a positive electrode substrate and a positive electrode active material layer laminated directly or via an intermediate layer on the positive electrode substrate. Usually, the positive electrode has a portion where the positive electrode substrate is exposed. This exposed portion of the positive electrode substrate is usually connected to the above-mentioned positive electrode lead. The positive electrode may have a shape such as sheet-like, plate-like or strip-like, for example.

[0084] The thickness of the positive electrode is appropriately set according to the use of the sodium ion secondary battery and the like. The average thickness of the positive electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the positive electrode may be 50 μm, 100 μm or 200 μm. The upper limit of the average thickness of the positive electrode may be 500 μm, 400 μm, 300 μm, 200 μm or 100 μm. The average thickness of the positive electrode is the average thickness of the portion where the positive electrode active material layer is laminated directly or via an intermediate layer on the positive electrode substrate. When there are both a portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate and a portion where the positive electrode active material layer is laminated on only one side of the positive electrode substrate, it is the average thickness of the portion where the positive electrode active material layer is laminated on both sides of the positive electrode substrate. Also, in this specification, "average thickness" means the average value of the thicknesses measured at any five locations.

[0085] The positive electrode substrate has conductivity. In this specification, "having conductivity" means that the volume resistivity is 10 -2 Ω·cm or less. The volume resistivity is a value measured in accordance with JIS-H-0505 (1975). On the other hand, in this specification, "not having conductivity" or "(electric) insulating" means that the above volume resistivity is 10 7 Ω·cm or more.

[0086] Examples of the material of the positive electrode substrate include metals such as aluminum, titanium, iron, and their alloys (such as stainless steel). Among these, aluminum or an aluminum alloy is preferable from the viewpoints of potential resistance, high electron conductivity and cost.

[0087] The positive electrode substrate has a shape such as a sheet, plate, or strip. Examples of positive electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The positive electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0088] The average thickness of the positive electrode substrate may be, for example, 3 μm or more and 50 μm or less. The lower limit of the average thickness of the positive electrode substrate may be 5 μm, 8 μm, 10 μm, or 15 μm. The upper limit of the average thickness of the positive electrode substrate may be 40 μm, 30 μm, 20 μm, or 15 μm.

[0089] The intermediate layer is a layer placed between the positive electrode substrate and the positive electrode active material layer. The intermediate layer includes, for example, a conductive agent and a binder. When the intermediate layer contains a conductive agent, the contact resistance between the positive electrode substrate and the positive electrode active material layer can be reduced. Examples of conductive agents and binders used in the intermediate layer are the same as those used in the positive electrode active material layer, which will be described later.

[0090] The positive electrode active material layer contains a positive electrode active material for sodium-ion secondary batteries. The positive electrode active material layer may optionally contain conductive agents, binders, thickeners, fillers, and other optional components. The positive electrode active material layer may be formed from a positive electrode mixture containing the positive electrode active material for sodium-ion secondary batteries and other optional components. The positive electrode active material layer may be provided on only one side of a positive electrode substrate having a shape such as a sheet, or on both sides.

[0091] For the positive electrode active material for sodium-ion secondary batteries, a positive electrode active material for sodium-ion secondary batteries obtained by a method for producing a positive electrode active material for sodium-ion secondary batteries according to one embodiment of the present invention is used. As the positive electrode active material for sodium-ion secondary batteries, a mixture of the positive electrode active material for sodium-ion secondary batteries obtained by a method for producing a positive electrode active material for sodium-ion secondary batteries according to one embodiment of the present invention and other positive electrode active materials for sodium-ion secondary batteries may be used.

[0092] The content of the positive electrode active material for sodium-ion secondary batteries in the positive electrode active material layer is preferably 50% to 99% by mass, more preferably 70% to 98% by mass, and may also be 80% to 95% by mass. By setting the content of the positive electrode active material for sodium-ion secondary batteries within the above range, it is possible to achieve both high energy density and manufacturability in the positive electrode active material layer.

[0093] Conductive agents are typically components made of conductive materials. Even if the volume resistivity of a conductive agent cannot be directly measured, if the volume resistivity is 10 -2 Materials whose conductivity is known to be Ω·cm or less are classified as conductive agents. Examples of conductive agents include carbon materials, metals, and conductive ceramics. A carbon material is a material whose main constituent element is carbon. The main constituent element is the element that is present in the largest quantity by mass. For example, the carbon content in a carbon material may be 80% by mass or more, 90% by mass or more, 95% by mass, 99% by mass, or 99.9% by mass or more. It is preferable that the carbon material is a carbon material other than a non-carbonized polymer compound. Examples of carbon materials include graphite, non-graphitic carbon, and graphene-based carbon. Examples of non-graphitic carbon include carbon nanofibers, pitch-based carbon fibers, and carbon black. Examples of carbon black include furnace black, acetylene black, and Ketjen black. Examples of graphene-based carbon include graphene, carbon nanotubes (CNTs), and fullerenes. Conductive agents can take the form of powder or fibers. One or more types of conductive agents can be used. These materials may also be used as a composite of conductive agents. For example, a composite material of carbon black and CNTs may be used.

[0094] The conductive agent content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the conductive agent content may be 5% by mass, 4% by mass, or 3% by mass. By setting the conductive agent content within the above range, it is possible to increase the energy density of the sodium-ion secondary battery.

[0095] Examples of binders include water-based binders and organic solvent-based binders.

[0096] A water-based binder is a binder that dissolves or disperses in water. A water-based binder may be one that dissolves or disperses in 100 parts by mass or more of water at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is water or a mixed solvent mainly composed of water, a water-based binder (water-soluble or water-dispersible polymer material) can be used. Examples of water-based binders include polyethylene oxide, polypropylene oxide, polyvinyl alcohol, polyacrylic acid, polymethacrylic acid, polytetrafluoroethylene, styrene-butadiene rubber, polyethylene, polypropylene, nitrile-butadiene rubber, and cellulose.

[0097] An organic solvent-based binder is a binder that dissolves or disperses in an organic solvent (e.g., N-methylpyrrolidone). An organic solvent-based binder may be a binder that dissolves or disperses at 1 part by mass or more per 100 parts by mass of an organic solvent (e.g., N-methylpyrrolidone) at 20°C. When forming a positive electrode active material layer using a positive electrode mixture paste in which the dispersion medium is an organic solvent or a mixed solvent mainly composed of an organic solvent, an organic solvent-based binder (a polymer material having solubility or dispersibility in an organic solvent) can be used. Examples of organic solvent-based binders include polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, copolymers of ethylene and vinyl alcohol, polyacrylonitrile, polyphosphazene, polysiloxane, polyvinyl acetate, polymethyl methacrylate, polystyrene, polycarbonate, polyamide, polyimide, polyamideimide, crosslinked polymers of cellulose and chitosan pyrrolidone carboxylate, and derivatives of chitosan.

[0098] The binder may be a fluororesin (polytetrafluoroethylene, polyvinylidene fluoride, etc.), a polyolefin (polyethylene, polypropylene, etc.), an elastomer (ethylene propylene diene rubber, styrene butadiene rubber, fluororubber, etc.), a polysaccharide polymer (cellulose, chitosan derivatives, etc.), etc. One or more types of binders may be used.

[0099] The binder content in the positive electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, more preferably 1% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less. The upper limit of the binder content may be 5% by mass, 4% by mass, or 3% by mass. By setting the binder content within the above range, it is possible to stably maintain the positive electrode active material for sodium-ion secondary batteries.

[0100] Examples of thickening agents include polysaccharide polymers such as carboxymethylcellulose and methylcellulose. If the thickening agent has a functional group that reacts with sodium, etc., this functional group may be deactivated beforehand by methylation or the like. The thickening agent may also function as a binder. One or more types of thickening agents can be used. When the positive electrode active material layer contains a thickening agent, the content of the thickening agent in the positive electrode active material layer is preferably 0.1% by mass or more and 8% by mass or less, more preferably 5% by mass or less, and even more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a thickening agent.

[0101] The filler is not particularly limited. The filler may be a component other than the positive electrode active material, conductive agent, binder, and thickener for sodium-ion secondary batteries, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the positive electrode active material layer, or it may be included for other purposes. The filler may be an organic substance such as a polyolefin, or an inorganic substance such as an inorganic oxide, hydroxide, or carbonate. One or more types of fillers may be used. When the positive electrode active material layer contains a filler, the filler content in the positive electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the positive electrode active material layer does not contain a filler.

[0102] The positive electrode active material layer may further contain other components besides the positive electrode active material for sodium-ion secondary batteries, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the positive electrode active material layer. Furthermore, the positive electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the positive electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0103] The thickness of the positive electrode active material layer is set appropriately according to the type of positive electrode active material for sodium-ion secondary batteries, the application of the sodium-ion secondary battery, etc. The average thickness of one positive electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one positive electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one positive electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one positive electrode active material layer may be, for example, 4 mg / cm². 2 More than 100mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one positive electrode active material layer is 6 mg / cm². 2 , 8 mg / cm³ 2 or 10 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one positive electrode active material layer is 50 mg / cm². 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0104] The porosity of the positive electrode active material layer may be, for example, 20% or more and 50% or less. The lower limit of the porosity of the positive electrode active material layer may be 25%, 30%, or 35%. The upper limit of the porosity of the positive electrode active material layer may be 45%, 40%, or 35%. The "porosity (%)" of the positive electrode active material layer and the negative electrode active material layer described later is calculated using the formula (1-V2 / V1)×100, where V1 is the apparent volume (volume including voids) of the positive (negative) electrode active material layer and V2 is the sum of the actual volumes of each material constituting the positive (negative) electrode active material layer. The sum of the actual volumes V2 of each material constituting the positive (negative) electrode active material layer can be calculated from the content of each material in the positive (negative) electrode active material layer and the true density of each material.

[0105] (Negative electrode) The negative electrode comprises a negative electrode substrate and a negative electrode active material layer laminated directly to the negative electrode substrate or via an intermediate layer. Typically, the negative electrode has a portion where the negative electrode substrate is exposed. This exposed portion of the negative electrode substrate is usually connected to the negative electrode lead described above. The negative electrode may have a shape such as a sheet, plate, or strip.

[0106] The thickness of the negative electrode is set appropriately according to the application of the sodium-ion secondary battery. The average thickness of the negative electrode may be, for example, 30 μm or more and 1,000 μm or less. The lower limit of the average thickness of the negative electrode may be 50 μm, 100 μm, or 200 μm. The upper limit of the average thickness of the negative electrode may be 500 μm, 400 μm, 300 μm, 200 μm, or 100 μm. The average thickness of the negative electrode is the average thickness of the portion in which the negative electrode active material layer is laminated directly to the negative electrode substrate or via an intermediate layer. If there are portions in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate and portions in which the negative electrode active material layer is laminated on only one side of the negative electrode substrate, then the average thickness of the portion in which the negative electrode active material layer is laminated on both sides of the negative electrode substrate shall be used.

[0107] The negative electrode substrate is electrically conductive. Examples of materials for the negative electrode substrate include metals such as aluminum, copper, nickel, iron, and their alloys (such as stainless steel), as well as carbon materials. Among these, aluminum or aluminum alloys are preferred.

[0108] The negative electrode substrate has a shape such as a sheet, plate, or strip. Examples of negative electrode substrate forms include foil, vapor-deposited film, mesh, and porous material, with foil being preferred. The negative electrode substrate may also be, for example, aluminum foil or aluminum alloy foil.

[0109] The average thickness of the negative electrode substrate may be, for example, 2 μm or more and 35 μm or less. The lower limit of the average thickness of the negative electrode substrate may be 3 μm, 4 μm, 5 μm, or 10 μm. The upper limit of the average thickness of the negative electrode substrate may be 30 μm, 20 μm, 15 μm, or 10 μm.

[0110] The configuration of the negative electrode intermediate layer is not particularly limited; for example, it can be selected from the configurations exemplified for the positive electrode intermediate layer.

[0111] The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer optionally contains optional components such as a conductive agent, binder, thickener, and filler. The optional components such as the conductive agent, binder, thickener, and filler can be selected from the materials exemplified above for the positive electrode. The negative electrode active material layer may be formed from a negative electrode mixture containing the negative electrode active material and other optional components. The negative electrode active material layer may be provided on only one side of a negative electrode substrate having a shape such as a sheet, or on both sides.

[0112] For the negative electrode active material, known materials capable of intercalating and releasing sodium ions are used as negative electrode active materials for sodium-ion secondary batteries. Examples of negative electrode active materials include carbon materials such as non-graphitic carbon. Examples of non-graphitic carbon include poorly graphitizable carbon and easily graphitizable carbon, with poorly graphitizable carbon being preferred. One or more types of negative electrode active materials can be used.

[0113] "Non-graphite carbon" refers to the average lattice plane spacing (d) of the (002) plane, which is determined by X-ray diffraction before charging / discharging or during the discharge state. 002) refers to carbon materials with a nautical index of 0.34 nm to 0.42 nm. Non-graphitic carbons include poorly graphitizable carbons and easily graphitizable carbons. "Potentially graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.36 nm or more and 0.42 nm or less. "Easily graphitizable carbon" refers to the above d 002 This refers to carbon materials with a wavelength of 0.34 nm or more and less than 0.36 nm.

[0114] Here, the "discharge state" of the carbon material refers to a state in which the carbon material, which is the negative electrode active material, is discharged in such a way that sufficient sodium ions that can be absorbed and released during charging and discharging are released.

[0115] The negative electrode active material may be in particulate form. The average particle size of the negative electrode active material can be, for example, 1 nm to 100 μm, or 1 μm to 100 μm. Setting the average particle size of the negative electrode active material above the lower limit makes it easier to manufacture or handle. Setting the average particle size of the negative electrode active material below the upper limit improves the electronic conductivity of the negative electrode active material layer.

[0116] The content of the negative electrode active material in the negative electrode active material layer is preferably, for example, 60% to 99% by mass, and more preferably 90% to 98% by mass. By setting the content of the negative electrode active material within the above range, it is possible to achieve both high energy density and manufacturability in the negative electrode active material layer.

[0117] When the negative electrode active material layer contains a conductive agent, the content of the conductive agent in the negative electrode active material layer is preferably 1% by mass or more and 10% by mass or less, and more preferably 3% by mass or more and 9% by mass or less. The content of the conductive agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a conductive agent.

[0118] When the negative electrode active material layer contains a binder, the binder content in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The binder content in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a binder.

[0119] When the negative electrode active material layer contains a thickening agent, the content of the thickening agent in the negative electrode active material layer is preferably 0.1% by mass or more and 10% by mass or less, and more preferably 0.5% by mass or more and 8% by mass or less. The content of the thickening agent in the negative electrode active material layer may be 5% by mass or less, or 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a thickening agent.

[0120] The filler in the negative electrode active material layer is a component other than the negative electrode active material, conductive agent, binder, and thickener, and may be a component that is intentionally included. The filler may be included as a component that fills gaps in the negative electrode active material layer, or it may be included for other purposes. When the negative electrode active material layer contains a filler, the filler content in the negative electrode active material layer can be 0.1% by mass or more and 8% by mass or less, usually preferably 5% by mass or less, and more preferably 2% by mass or less. The technology disclosed herein can also be carried out in a form in which the negative electrode active material layer does not contain a filler.

[0121] The negative electrode active material layer may further contain other components besides the negative electrode active material, conductive agent, binder, thickener, and filler. These other components may include those unintentionally present in the negative electrode active material layer. Furthermore, the negative electrode active material layer may contain impurities unintentionally present as these other components, insofar as they achieve the effects of the present invention. The upper limit of the content of these other components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present components in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass. The upper limit of the content of unintentionally present impurities in the negative electrode active material layer may be 10% by mass, 5% by mass, 2% by mass, 1% by mass, 0.1% by mass, or 0.01% by mass.

[0122] The thickness of the negative electrode active material layer is set appropriately according to the type of negative electrode active material, the application of the sodium-ion secondary battery, etc. The average thickness of one negative electrode active material layer may be, for example, 5 μm or more and 1,000 μm or less. The lower limit of the average thickness of one negative electrode active material layer may be 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, or 100 μm. The upper limit of the average thickness of one negative electrode active material layer may be 800 μm, 500 μm, 200 μm, 100 μm, 80 μm, 60 μm, or 40 μm. The mass per unit area of ​​one negative electrode active material layer may be, for example, 2 mg / cm². 2 More than 50mg / cm 2 The following is also acceptable: The lower limit of the mass per unit area of ​​one negative electrode active material layer is 3 mg / cm². 2 , 4 mg / cm³ 2 , 5 mg / cm³ 2 or 6 mg / cm³ 2 It may also be the case that the upper limit of the mass per unit area of ​​one negative electrode active material layer is 30 mg / cm³. 2 , 20 mg / cm³ 2 , 15 mg / cm³ 2 , 12 mg / cm³ 2 or 10 mg / cm³ 2 That's fine.

[0123] The porosity of the negative electrode active material layer may be, for example, 30% to 70%. The lower limit of the porosity of the negative electrode active material layer may be 35%, 40%, or 45%. The upper limit of the porosity of the negative electrode active material layer may be 60%, 50%, or 40%. In cases where the negative electrode active material layer is foil-like, the porosity of the negative electrode active material layer may be 0%.

[0124] (Separator) A known separator can be used. Examples of separators include a separator consisting only of a substrate layer, or a separator in which an inorganic layer containing inorganic particles and a binder is formed on one or both sides of the substrate layer.

[0125] Examples of the substrate layer form of the separator include woven fabric, nonwoven fabric, and porous resin film. Among these forms, porous resin film is preferred from the viewpoint of strength, and nonwoven fabric is preferred from the viewpoint of liquid retention of non-aqueous electrolytes. The material of the substrate layer of the separator is not particularly limited as long as it has insulating properties, but resins such as polyolefins (polyethylene, polypropylene, etc.), polyimide, and aramid are preferred.

[0126] Examples of inorganic compounds constituting inorganic particles include oxides such as iron oxide, silicon oxide, aluminum oxide, titanium oxide, zirconium oxide, calcium oxide, and magnesium oxide; nitrides such as aluminum nitride and silicon nitride; carbonates such as calcium carbonate; sulfates such as barium sulfate; sparingly soluble ionic crystals such as calcium fluoride, barium fluoride, and barium titanate; covalent crystals such as silicon; mineral resource-derived materials such as talc, zeolite, kaolin, bentonite, and mica, or their artificial counterparts. One or more types of inorganic particles can be used. The average particle size of the inorganic particles is preferably, for example, 0.5 μm to 10 μm. The inorganic particle content in the inorganic layer is preferably 50% to 99% by mass, and more preferably 80% to 98% by mass.

[0127] Examples of binders used in the inorganic layer include those similar to those exemplified in the positive electrode active material layer.

[0128] The porosity of the separator may be, for example, 20% or more and 80% or less. The lower limit of the separator's porosity may be 30%, 40%, or 50% from the viewpoint of discharge performance, etc. The upper limit of the separator's porosity may be 70%, 60%, or 50% from the viewpoint of strength, etc. In this specification, "porosity" refers to a volume-based value and means a measurement value obtained with a mercury porosimeter.

[0129] The average thickness of the separator may be, for example, 10 μm to 40 μm, or 15 μm to 30 μm.

[0130] A polymer gel composed of a polymer and a non-aqueous electrolyte may be used as a separator. A polymer gel may also be used in combination with a porous resin film, nonwoven fabric, etc., as described above, as a separator.

[0131] (electrode body) As the electrode body, known structures such as wound electrode bodies and laminated electrode bodies can be used.

[0132] A wound electrode has a structure in which the positive electrode and negative electrode are wound together while being insulated. The wound electrode may be cylindrical or flattened. The electrode 2 in the non-aqueous electrolyte secondary battery 1 (sodium-ion secondary battery) shown in Figure 2 is a flattened wound electrode. A wound electrode can be manufactured, for example, by the following procedure. First, a laminate is obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a strip shape. A wound electrode is obtained by winding this laminate.

[0133] A laminated electrode body has a structure in which one or more positive electrodes and one or more negative electrodes are stacked in an insulated state. For example, a laminated electrode body can be obtained by stacking a positive electrode, a separator, and a negative electrode, each formed in a rectangular shape.

[0134] Other electrode structures can also be used, such as those in which at least one of the positive and negative electrodes is folded in a bellows-like manner and stacked.

[0135] (Non-aqueous electrolytes) A known non-aqueous electrolyte can be used. A non-aqueous electrolyte is a medium that carries charge transport ions (sodium ions) between the positive and negative electrodes and contains substantially no water. The water content in a non-aqueous electrolyte may be, for example, 10,000 ppm or less, or 5,000 ppm or less. Examples of non-aqueous electrolytes include non-aqueous electrolyte solutions and solid electrolytes. Non-aqueous electrolyte solutions and solid electrolytes may be used in combination.

[0136] (Non-aqueous electrolyte) A non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in this non-aqueous solvent.

[0137] Any known non-aqueous solvent can be used. Examples of non-aqueous solvents include carbonates, esters, ethers, amides, and nitriles. Examples of carbonates include cyclic carbonates and linear carbonates. Examples of esters include carboxylic acid esters, phosphate esters, and sulfonic acid esters. As non-aqueous solvents, compounds in which some of the hydrogen atoms contained in these compounds are substituted with halogen atoms may also be used. One or more non-aqueous solvents can be used.

[0138] A cyclic carbonate refers to a carbonate having a ring structure containing a carbonate group (-OC(=O)-O-). Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, vinylethylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, styrene carbonate, 1-phenylvinylene carbonate, and 1,2-diphenylvinylene carbonate. A cyclic carbonate may be a saturated cyclic carbonate such as ethylene carbonate, or an unsaturated cyclic carbonate such as vinylene carbonate. "Saturated" means not having carbon-carbon unsaturated bonds (carbon-carbon double bonds and carbon-carbon triple bonds). "Unsaturated" means having carbon-carbon unsaturated bonds. As a cyclic carbonate, a saturated cyclic carbonate is preferred, and ethylene carbonate is more preferred.

[0139] A chain-like carbonate refers to a carbonate that does not have a ring structure containing a carbonate group. Examples of chain-like carbonates include diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, diphenyl carbonate, trifluoroethyl methyl carbonate, and bis(trifluoroethyl) carbonate. The chain-like carbonate may be a saturated chain-like carbonate such as dimethyl carbonate, or an unsaturated chain-like carbonate such as diphenyl carbonate. A saturated chain-like carbonate is preferred as the chain-like carbonate, and ethyl methyl carbonate is more preferred.

[0140] The non-aqueous solvent preferably contains carbonate, and more preferably contains both cyclic carbonate and linear carbonate. The carbonate content in the non-aqueous solvent is preferably 80% to 100% by volume, may be 99% to 100% by volume, or 100% by volume. Using cyclic carbonate can promote the dissociation of the electrolyte salt and increase the ionic conductivity of the non-aqueous electrolyte. Using linear carbonate can keep the viscosity of the non-aqueous electrolyte low. When using both cyclic carbonate and linear carbonate, the volume ratio of cyclic carbonate to linear carbonate (cyclic carbonate:linear carbonate) is preferably in the range of 5:95 to 50:50.

[0141] Any known electrolyte salt can be used. Sodium salts are used as the electrolyte salt. One or more types of electrolyte salts may be used.

[0142] Examples of sodium salts include NaClO4, NaPF6, NaBF4, CF3SO3Na, NaAsF6, NaB(C6H5)4, CH3SO3Na, CF3SO3Na, NaN(SO2CF3)2, NaN(SO2C2F5)2, NaC(SO2CF3)3, and NaN(SO2F)2.

[0143] The electrolyte salt content in the non-aqueous electrolyte is 0.1 mol / dm³ at 20°C and 1 atm. 3 More than 2.5mol / dm 3 The following is preferred: 0.3 mol / dm 3 More than 2.0mol / dm 3 The following is more preferable: 0.5 mol / dm 3 More than 1.7mol / dm 3 The following is even more preferable: 0.7 mol / dm 3 More than 1.5mol / dm 3 The following is particularly preferable. By setting the electrolyte salt content within the above range, the ionic conductivity of the non-aqueous electrolyte can be increased.

[0144] The non-aqueous electrolyte may contain additives in addition to the non-aqueous solvent and electrolyte salt. One or more types of additives may be used. When additives are used in the non-aqueous electrolyte, the additive content in the non-aqueous electrolyte is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.1% by mass or more and 7% by mass or less, even more preferably 0.2% by mass or more and 5% by mass or less, and particularly preferably 0.3% by mass or more and 3% by mass or less.

[0145] (solid electrolyte) The solid electrolyte can be selected from any material that has sodium ion conductivity and is solid at room temperature (e.g., 20°C). Examples of solid electrolytes include sulfide solid electrolytes, oxide solid electrolytes, nitride solid electrolytes, halide solid electrolytes, and polymer solid electrolytes. One or more types of solid electrolytes can be used.

[0146] (container) The container houses the electrode body and non-aqueous electrolyte within its internal space. The container material can be a metal material such as aluminum or stainless steel, or a resin material; metal materials are preferred from the viewpoint of strength, etc. Composite materials of metal and resin materials can also be used.

[0147] The shape of the container is not particularly limited, but it can be cylindrical, rectangular (square), disc-shaped, etc. The container may also be in the form of a sheet or other shape formed from a metal-resin composite film.

[0148] (Shape, uses, etc. of sodium-ion secondary batteries) The shape of the sodium-ion secondary battery is not particularly limited. Sodium-ion secondary batteries may be cylindrical, prismatic, flat, coin-type, button-type, etc.

[0149] The applications of sodium-ion secondary batteries are not particularly limited. For example, sodium-ion secondary batteries can be used as power sources for automobiles such as electric vehicles, hybrid vehicles, and plug-in hybrid vehicles, as power sources for electronic devices such as personal computers and communication terminals, and as power storage power sources.

[0150] Sodium-ion secondary batteries are used individually or in combination. When the required output and voltage are small, a single sodium-ion secondary battery may be used. On the other hand, when at least one of the required output and voltage is large, a module (energy storage unit) or pack (energy storage device) comprising multiple sodium-ion secondary batteries may be used. Modules (energy storage units) and packs (energy storage devices) will be described in detail later.

[0151] A sodium-ion secondary battery may be constrained to maintain a constant thickness, or it may not be. Alternatively, it may be constrained to have a constant load applied to it. When the container is constrained, expansion of the container due to charge-discharge cycles may be suppressed, thus preventing a decrease in charge-discharge performance. When the container is constrained, the electrodes inside the container may or may not have a load applied to them. For example, a sodium-ion secondary battery, module (energy storage unit), or pack (energy storage device) may be provided with a constraining member to perform such a constraining.

[0152] <Pack (energy storage device)> As a pack comprising a lithium-ion secondary battery used in the method for producing a positive electrode active material for a sodium-ion secondary battery of the present invention, and a pack comprising a sodium-ion secondary battery produced by the method for producing a sodium-ion secondary battery of the present invention, for example, the pack (energy storage device) 30 shown in Figure 3 comprises a plurality of modules (energy storage units) 20. Each module (energy storage unit) 20 comprises a plurality of electrically connected non-aqueous electrolyte secondary batteries 1 (lithium-ion secondary batteries or sodium-ion secondary batteries). The pack (energy storage device) 30 may also include busbars (not shown) that electrically connect the plurality of non-aqueous electrolyte secondary batteries 1 (lithium-ion secondary batteries or sodium-ion secondary batteries), busbars (not shown) that electrically connect the plurality of modules (energy storage units) 20, etc. The module (energy storage unit) 20 or the pack (energy storage device) 30 may also include a condition monitoring device (not shown) that monitors the state of one or more non-aqueous electrolyte secondary batteries 1 (lithium-ion secondary batteries or sodium-ion secondary batteries).

[0153] <Other Embodiments> The method for producing a positive electrode active material for a sodium-ion secondary battery, the method for producing a raw material for a positive electrode active material for a sodium-ion secondary battery, and the method for producing a sodium-ion secondary battery of the present invention are not limited to the embodiments described above, and various modifications may be made without departing from the spirit of the present invention. For example, the configuration of one embodiment may be added to the configuration of another embodiment, and a part of the configuration of one embodiment may be replaced with the configuration of another embodiment or with well-known technology. Furthermore, a part of the configuration of one embodiment may be deleted. Also, well-known technology may be added to the configuration of one embodiment.

[0154] In the above embodiment, an electrode body in which a separator is interposed between the positive electrode and the negative electrode was described, but the electrode body does not need to have a separator. For example, the positive electrode and the negative electrode may be in direct contact with each other, with a non-conductive layer formed on the active material layer of either the positive electrode or the negative electrode. Thus, the positive electrode and the negative electrode may further have layers other than the base material, intermediate layer, and active material layer.

[0155] The positive electrode active material for sodium-ion secondary batteries obtained by the method for producing the positive electrode active material for sodium-ion secondary batteries of the present invention may be a compound other than a transition metal composite oxide. Furthermore, the positive electrode active material for sodium-ion secondary batteries may be produced by a method other than calcination. [Industrial applicability]

[0156] This invention is useful as a technology for recycling non-aqueous electrolyte secondary batteries. [Explanation of Symbols]

[0157] 1. Non-aqueous electrolyte secondary battery (lithium-ion secondary battery or sodium-ion secondary battery) 2 Electrode body 3 containers 4 Positive lead 5. Positive external terminal 6 Negative lead 7. Negative external terminal 20 modules (energy storage units) 30 packs (energy storage devices)

Claims

1. A lithium-ion secondary battery having a positive electrode having a positive electrode active material containing transition metal elements other than iron, or a module or pack equipped with the above lithium-ion secondary battery, wherein a workpiece containing an iron-containing component is processed to produce black mass containing the above transition metal elements and the above iron elements, and Using the above-mentioned black mass as part of the raw materials, a positive electrode active material for a sodium-ion secondary battery containing the above-mentioned transition metal element and the above-mentioned iron element is produced. A method for producing a positive electrode active material for a sodium-ion secondary battery, comprising the features described above.

2. The method for producing a positive electrode active material for a sodium-ion secondary battery according to claim 1, wherein the positive electrode active material for a sodium-ion secondary battery is a transition metal composite oxide containing sodium, the transition metal element, and the iron element.

3. The production of the above-mentioned positive electrode active material for sodium-ion secondary batteries is From the above black mass, obtain one or more compounds containing the above transition metal element and the above iron element, and Calcining a mixture of one or more of the above compounds and a sodium source containing the element sodium. A method for producing a positive electrode active material for a sodium ion secondary battery according to claim 1 or claim 2, comprising:

4. A method for producing a positive electrode active material for a sodium-ion secondary battery according to claim 1 or 2, wherein the positive electrode active material for a lithium-ion secondary battery contains manganese as the transition metal element.

5. A method for producing a positive electrode active material for a sodium-ion secondary battery according to claim 1 or 2, wherein the positive electrode active material for a lithium-ion secondary battery contains manganese as the transition metal element, the workpiece comprises a member containing copper, and the black mass further contains copper.

6. To manufacture a positive electrode active material for a sodium-ion secondary battery containing the above-mentioned transition metal elements and iron elements, using black mass containing lithium and iron elements as part of the raw materials. A method for producing a positive electrode active material for a sodium-ion secondary battery, comprising the features described above.

7. A lithium-ion secondary battery having a positive electrode having a positive electrode active material containing transition metal elements other than iron, or a module or pack equipped with the above lithium-ion secondary battery, wherein a workpiece containing an iron element is processed to produce black mass containing the above transition metal elements and the above iron element. A method for producing a positive electrode active material raw material for sodium-ion secondary batteries, comprising the features described above.

8. A method for producing a sodium-ion secondary battery, comprising the method for producing a positive electrode active material for a sodium-ion secondary battery according to claim 1, claim 2, or claim 6.

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