Method for treating positive electrode of non-aqueous electrolyte secondary battery

Abstract

To provide a non-aqueous electrolyte secondary battery processing method capable of accelerating the reduction reaction of a positive electrode at low cost.SOLUTION: A processing method of a non-aqueous electrolyte secondary battery including a positive electrode with a foil containing Al and an active material as a metal composite oxide includes a heating step S11 of performing heat treatment to heat the positive electrode, a melting step S12 of melting the positive electrode by the heat of reaction between the foil and the active material to obtain a melt, and a separation step S13 of separating the melt into slag and a metal material containing a metal constituting a metal composite oxide. Due to heat-treating of the positive electrode, the reduction reaction of the positive electrode can be promoted at low cost.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a method for treating a non-aqueous electrolyte secondary battery. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries are used as power sources mounted on hybrid vehicles and electric vehicles. In recent years, a rapid increase in the amount of used non-aqueous electrolyte secondary batteries for automobiles is expected. Valuable materials such as nickel (Ni) and cobalt (Co) are contained in the electrodes of non-aqueous electrolyte secondary batteries, particularly in the positive electrodes. In order to make effective use of resources, methods for recovering valuable materials such as Ni and Co from non-aqueous electrolyte secondary batteries have been proposed.

[0003] For example, Patent Document 1 describes a method for recovering cobalt from waste secondary batteries, in which the waste batteries are roasted at 600° C. or higher, then chopped, sieved, magnetically separated, and dissolved in acid to recover cobalt.

[0004] Patent Document 2 describes a method for recovering valuable materials such as Ni, Co, etc. by mixing a reducing agent with recovered material containing Ni and Co obtained from secondary batteries and heating the mixture. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-46266 [Patent Document 2] JP 2019-131871 A Summary of the Invention [Problem to be solved by the invention]

[0006] The recovery method described in Patent Document 1 requires steps such as magnetic separation and acid dissolution after roasting, which increases the recycling cost. The recovery method described in Patent Document 2 requires a step of mixing a reducing agent, which increases the labor required for mixing and the cost of the reducing agent. In addition, in order to increase the reaction efficiency, a step of forming the mixture of the recovered material and the reducing agent into a briquette is also required.

[0007] The "thermit process" is one of the methods for recovering metals containing valuables from positive electrode active materials made of metal composite oxides. The thermite process generally uses powdered raw materials, and in order to use positive electrode metal foil in the thermite process, a process of pulverizing the metal foil is required. Alternatively, if the thermite reaction is to be carried out in the as-is state of the positive electrode metal foil without pulverizing it, external heating at high temperatures using a high-frequency induction melting furnace or the like is required, which is an obstacle to reducing costs.

[0008] SUMMARY OF THE PRESENT DISCLOSURE An object of the present invention is to provide a method for treating a non-aqueous electrolyte secondary battery that can promote the reduction reaction of the positive electrode at low cost. [Means for solving the problem]

[0009] The method for treating a nonaqueous electrolyte secondary battery according to the present invention is a method for treating a nonaqueous electrolyte secondary battery equipped with a positive electrode having an Al-containing foil and an active material as a metal composite oxide, and includes a heating step of performing a heat treatment to heat the positive electrode, a melting step of melting the positive electrode by the heat of reaction between the foil and the active material to obtain a molten material, and a separation step of separating the molten material into a metal material containing a metal that constitutes the metal composite oxide and slag. Effect of the Invention

[0010] According to the present invention, by subjecting the positive electrode to a heat treatment, the reduction reaction of the positive electrode active material can be promoted at low cost. [Brief description of the drawings]

[0011] [Figure 1]1 is a perspective view of a nonaqueous electrolyte secondary battery used in a method for treating a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. [Diagram 2] 3 is a flowchart illustrating a method for treating a nonaqueous electrolyte secondary battery according to the present embodiment.

[0012] 1. Embodiment Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[0013] FIG. 1 is a perspective view of a nonaqueous electrolyte secondary battery 10 used in the method for treating a nonaqueous electrolyte secondary battery according to the present embodiment. The nonaqueous electrolyte secondary battery 10 is a used lithium ion secondary battery used as a power source for automobiles such as electric vehicles and hybrid vehicles. In the following description, the nonaqueous electrolyte secondary battery 10 is a lithium ion secondary battery, but the nonaqueous electrolyte secondary battery 10 is not limited to a lithium ion secondary battery and may be a magnesium ion secondary battery, a sodium ion secondary battery, a potassium ion secondary battery, a calcium ion secondary battery, or the like. The nonaqueous electrolyte secondary battery 10 may be an unused lithium ion secondary battery or the like that has been confirmed to be defective after manufacture. It may also be process waste generated during the manufacturing process.

[0014] The nonaqueous electrolyte secondary battery 10 includes an electrode body (not shown) and a nonaqueous electrolyte (not shown) in a cell container 12. The cell container 12 is made of, for example, an aluminum alloy. The cell container 12 includes a container body 14 and a lid body 16. The container body 14 and the lid body 16 are laser welded. The container body 14 is formed in a bottomed rectangular tube shape, and contains the electrode body and the nonaqueous electrolyte inside. The lid body 16 is provided at the opening of the container body 14 and seals the container body 14. The lid body 16 is provided with a safety valve 18, a positive electrode terminal 20, and a negative electrode terminal 22. The safety valve 18 is for reducing the pressure inside the nonaqueous electrolyte secondary battery 10. The positive electrode terminal 20 is connected to a positive electrode (described later) via a positive electrode lead (not shown). The negative electrode terminal 22 is connected to a negative electrode (described later) via a negative electrode lead (not shown).

[0015] The electrode assembly includes a positive electrode (not shown) and a negative electrode (not shown) wound with a separator (not shown) interposed therebetween. The electrode assembly is not limited to the wound type as described above, and may be a laminated type in which a positive electrode, a negative electrode, and a separator are laminated.

[0016] The positive electrode has a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is a foil containing aluminum (Al) (hereinafter, also referred to as Al foil). The mass ratio of the positive electrode current collector in the positive electrode is 5 to 25 mass%. The positive electrode active material layer contains a positive electrode active material, a binder, and a conductive material. The mass ratios of the conductive material and the binder in the positive electrode active material layer are 0 to 30 mass% and 0 to 20 mass%, respectively, of the positive electrode.

[0017] As the positive electrode active material, any metal composite oxide containing nickel (Ni) and / or cobalt (Co) can be used. For example, the positive electrode active material can be selected from lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt composite oxide, lithium nickel manganese composite oxide, lithium nickel cobalt aluminum composite oxide, lithium nickel cobalt manganese composite oxide, etc. In this embodiment, the positive electrode active material is lithium nickel cobalt manganese composite oxide. In addition, as the positive electrode active material, any magnesium composite oxide can be used in the case of a magnesium ion secondary battery, any sodium composite oxide can be used in the case of a sodium ion secondary battery, any potassium composite oxide can be used in the case of a potassium ion secondary battery, and any calcium composite oxide can be used in the case of a calcium ion secondary battery.

[0018] The binder is a fluorine-based binder that contains a fluorine compound such as polyvinylidene fluoride (PVDF), etc. The conductive material is a carbon material such as graphite or carbon black.

[0019] The negative electrode has a negative electrode current collector and a negative electrode active material layer. For example, the negative electrode current collector is copper (Cu) foil, and the negative electrode active material is graphite. The separator is generally a porous film or nonwoven fabric made of a resin such as polyethylene (PE) or polypropylene (PP).

[0020] The non-aqueous electrolyte contains a non-aqueous solvent and a lithium salt (electrolyte) that can be dissolved in the non-aqueous solvent. As the non-aqueous solvent, carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), etc. can be used. These non-aqueous solvents can be used alone or in combination of two or more.

[0021] The electrolyte includes a fluorine compound, such as LiPF 6 (Lithium hexafluorophosphate), LiBF 4 (lithium tetrafluoroborate), LiTFSA (lithium trifluoromethanesulfonylamide), LiTFSI (lithium bis(trifluoromethane)sulfonimide), etc. These electrolytes can be used alone or in combination of two or more.

[0022] As shown in FIG. 2, the method for treating a nonaqueous electrolyte secondary battery 10 is a method for treating a nonaqueous electrolyte secondary battery having a positive electrode having a foil containing Al and an active material as a metal composite oxide, and includes a removal step S10 for removing the positive electrode from the nonaqueous electrolyte secondary battery 10, a heating step S11 for performing a heat treatment for heating the positive electrode, a melting step S12 for melting the positive electrode by the reaction heat between the foil and the active material to obtain a molten material, and a separation step S13 for separating the molten material into a metal material containing a metal constituting the metal composite oxide and slag. Here, the "reaction between the foil and the active material" refers to an oxidation-reduction reaction that generates high heat while reducing the metal oxide by the metal Al when a mixture of a positive electrode current collector that is metal Al and a positive electrode active material that is a metal oxide is reacted, and is also called a thermite reaction. The positive electrode generates heat by itself due to the reaction heat between the foil and the active material. "Self-heating" means that the temperature of the positive electrode itself increases due to the reaction heat between the foil and the active material even if heat energy is not applied to the positive electrode from an external heating means (for example, a high-frequency induction melting furnace). Each step will be described in detail below.

[0023] [Removal process] In the removal step S10, the cell container 12 is opened and the removed wound-type electrode body is unwound to obtain a sheet-like positive electrode. The sheet-like positive electrode is subjected to a heating step S11 and a melting step S12. Note that in the removal step S10, a discharging step in which the nonaqueous electrolyte secondary battery 10 is discharged, an inside-cell washing step in which the inside of the cell container 12 of the discharged nonaqueous electrolyte secondary battery 10 is washed with a washing solution, and the like may be performed.

[0024] [Heating process] In the heating step S11, a heat treatment is performed on the sheet-like positive electrode obtained in the removal step S10. The heat-treated positive electrode is then subjected to the next step, the melting step S12. The heat treatment promotes the thermite reaction in the melting step S12, making it possible to melt the positive electrode and reduce the active material.

[0025] The heating process will be described. The heating device used in the heating process has a heating furnace, a heating section, a thermometer, a gas supply section, a flowmeter, and a control section. The heating furnace has an internal space for accommodating a positive electrode. The heating section heats the positive electrode placed in the heating furnace. The thermometer measures the temperature in the heating furnace. The gas supply section supplies a gas containing oxygen (air in this example) into the heating furnace, and creates an atmosphere containing oxygen in the heating furnace. The flowmeter measures the flow rate of air in the heating furnace. The control section controls the heating section based on the measurement result of the thermometer, and heats the inside of the heating furnace at a predetermined heating rate, and controls the temperature to a preset heating temperature. The control section controls the gas supply section based on the measurement result of the flowmeter, and controls the flow rate of air supplied into the heating furnace. The control section controls the heating section and the gas supply section so that the heating temperature and flow rate are maintained for a predetermined time. The time for maintaining the heating temperature and flow rate is called the "keep time". The above heating device is an example. Therefore, the configuration of the heating device is not limited to the above configuration, and can be designed as appropriate.

[0026] The procedure of the heat treatment will be described. First, a sheet-shaped positive electrode is placed in a heat-resistant container. Next, the heating device is operated to raise the temperature inside the heating furnace to a preset heating temperature. The container in which the positive electrode is placed is placed in the heating furnace, and air is supplied into the heating furnace at a predetermined flow rate. The heating temperature and flow rate are maintained until a preset keep time has elapsed. Note that the container in which the positive electrode is placed may be placed in the heating furnace before the heating device is operated.

[0027] The heat treatment is preferably performed at a temperature at which the foil does not turn into powder. If the heating temperature is too high, the Al foil as the positive electrode current collector becomes embrittled. The embrittled foil crumbles and turns into powder when, for example, lightly touched with a finger, and becomes foil powder. The positive electrode active material in this state peels off from the foil and turns into active material powder. If the heating temperature is too high like this, the positive electrode becomes a powder containing foil powder and active material powder. When the Al foil turns into powder, the Al foil and the positive electrode active material are separated and not in close contact with each other compared to when the Al foil is not turned into powder, so that the thermite reaction in the melting step S12, that is, the reaction caused by the reaction heat between the foil and the active material, is inhibited. In addition, when the Al foil becomes embrittled, it is considered that a part of the Al foil is oxidized and alumina is generated. In this case, the amount of Al serving as a reducing agent is reduced. Furthermore, when alumina is generated so as to cover the surface of the Al foil, it prevents the contact between the active material and Al and inhibits the reaction. By performing the heat treatment at a temperature at which the foil does not turn into powder, oxidation of the Al foil can be suppressed, and the powdering of the Al foil is suppressed, so that the positive electrode in which the adhesion between the Al foil and the positive electrode active material is maintained can be subjected to the melting step S12.

[0028] The heat treatment is preferably performed at a temperature at which the binder is decomposed. If the heating temperature is too low, the binder is not decomposed sufficiently, and the binder remains in the positive electrode. When the positive electrode with the binder remaining therein is subjected to the melting step S12, the binder is thermally decomposed and then oxidized in the melting step S12, resulting in the formation of H 2 O, CO 2 Gases of oxides of hydrogen and carbon, such as CO, are generated, inhibiting the thermite reaction. Gases that inhibit the thermite reaction are called reaction-inhibiting gases. By carrying out the heat treatment at a temperature at which the binder is decomposed, the positive electrode from which the binder has been removed can be subjected to the melting step S12. It is more preferable to carry out the heat treatment at a temperature at which the conductive material is oxidized and removed.

[0029] The heat treatment is preferably performed at 400°C or more and 650°C or less. By setting the heating temperature to 400°C or more and 650°C or less, the binder is reliably decomposed, and the Al foil is not powdered, and the adhesion state between the Al foil and the positive electrode active material is reliably maintained. When the heat treatment of the positive electrode is performed at a heating temperature of 660°C or more, which is the melting point of aluminum, the Al foil melts and the surface of the melted aluminum is oxidized, and the Al foil becomes embrittled and powdered. If the heating temperature is too high, alumina is formed between the metal Al and the active material, the adhesion part between the Al foil and the positive electrode active material is reduced, and the thermite reaction is inhibited. In addition, if the heating temperature is too high, the Al of the positive electrode current collector may become a reducing agent and cause an unintended thermite reaction, which is dangerous. It is particularly preferable to perform the heat treatment at 450°C or more and 600°C or less.

[0030] The positive electrode to be subjected to the heat treatment may be in the form of a sheet as described above, or may be cut into thin strips using, for example, a shredder.

[0031] A combustion improver may be mixed with the positive electrode that has been subjected to the heating step S11, and the positive electrode with the combustion improver mixed therein may be subjected to the next step, the melting step S12. Examples of the combustion improver include Al and NaClO 3 (sodium chlorate) is used. By mixing a combustion improver into the positive electrode, the combustion of the positive electrode is promoted in the melting step S12, and the thermite reaction can be further promoted.

[0032] [Melting process] In the melting step S12, the positive electrode heated by the heat treatment is melted. x Co y Mn z O 2 In the melting step S12, the Al foil contained in the positive electrode acts as a reducing agent, and the following reaction occurs. As a result of the reaction, an alloy containing Ni, Co, and Mn (Ni x Co y Mn z ) is obtained. LiNi x Co y Mn z O 2 +Al → 1 / 2Li 2 O+Ni x Co y Mn z +1 / 2Al 2 O 3

[0033] The thermite reaction is a reaction that generates a large amount of heat, so once the reaction reaches a temperature at which the reaction can continue, the reaction proceeds due to self-heating (reaction heat). For example, the thermite method involves placing a positive electrode in a crucible and igniting it. Basically, the thermite reaction proceeds with just this ignition, and a metal material containing the metals that make up the metal composite oxide can be obtained. In the thermite method, a suitable combustion enhancer can be used as necessary. Alternatively, there is a method that uses a device that applies high-temperature heat from the outside, such as an arc melting or high-frequency induction melting furnace. In this case, the positive electrode melts due to self-heating (reaction heat), and also melts due to the heat from the arc melting or high-frequency induction melting.

[0034] [Separation process] In the separation step S13, the molten material is cooled to separate the metal material containing the metals that constitute the metal composite oxide from the slag.

[0035] 2. Action and Effects In the method for treating a nonaqueous electrolyte secondary battery according to this embodiment, by having the heating step S11 prior to the melting step S12, a spontaneous oxidation-reduction reaction (thermit reaction) proceeds in the melting step S12, so that the reduction reaction of the positive electrode can be promoted at low cost.

[0036] Since the process of crushing the positive electrode and the process of separating the foil from the active material are unnecessary, the yield when recycling the positive electrode is improved and the cost is reduced.

[0037] In the heating step S11, heating is performed at a temperature at which the foil does not turn into powder, so that the Al foil and the positive electrode active material are maintained in close contact with each other, and the thermite reaction in the melting step S12 is promoted.

[0038] In the heating step S11, heating is performed at a temperature at which the binder is decomposed, thereby suppressing the generation of reaction-inhibiting gases in the melting step S12 and promoting the thermite reaction.

[0039] In the heating step S11, the heating is performed at 400°C or more and 650°C or less, thereby suppressing the occurrence of the thermite reaction during the heat treatment, and improving safety. In addition, the Al foil is not powdered, and the adhesion state between the Al foil and the positive electrode active material is maintained. The binder is removed by the heat treatment, and the generation of reaction-inhibiting gas at the melting step S12 stage is suppressed. Therefore, the thermite reaction in the melting step S12 is promoted.

[0040] 3. Working Example The following describes experiments carried out to confirm the effects of the present invention.

[0041] [Example 1] to [Example 4] A used nonaqueous electrolyte secondary battery was prepared in which a wound-type electrode body and a nonaqueous electrolyte were housed in a cell container 12. The positive electrode and nonaqueous electrolyte contained in the prepared nonaqueous electrolyte secondary battery had the following configurations.

[0042] Positive electrode: Aluminum foil, thickness 15 μm, 20 mass% Active material (LiNi 1 / 6 Co 2 / 3 Mn 1 / 6 O 2 ) 72~73% by mass Binder (PVDF) 3-4% by mass Conductive material 4% by mass Nonaqueous electrolyte Nonaqueous solvent (DMC:EMC:PC) Mass ratio 28:27:28 Electrolyte (LiPF 6 ) 1M

[0043] In the experiment, the prepared nonaqueous electrolyte secondary battery was first discharged, the cell container 12 was opened, and the wound electrode body was taken out and rewound to obtain a positive electrode (removal step S10). The obtained positive electrode was then subjected to a heating step S11 and a melting step S12 in this order to perform the experiment. The experimental conditions and evaluation results are shown in Table 1.

[0044] In the heating step S11, the positive electrodes that were subjected to the heat treatment were designated as Examples 1 to 4. Examples 1 to 4 were obtained by changing the heating temperature within the range of 400°C or more and 600°C or less. Examples 1 to 3 were subjected to the heat treatment in the foil state, and the foil state was maintained even after the heat treatment. Example 4 was subjected to the heat treatment in the foil state, and after the heat treatment, the foil state and the powder state were mixed. In Table 1, the column "Temperature [°C]" indicates the heating temperature in the heat treatment. In the column "Temperature [°C]" and the column "Shape of positive electrode after heat treatment", "-" indicates that the heat treatment was not performed.

[0045] In the melting step S12, the positive electrodes of Examples 1 to 4 were placed in a crucible and ignited. Note that no combustion improver was used.

[0046] The molten material obtained in the melting step S12 was removed from the crucible, and whether or not the positive electrode had melted was visually observed, and the thermite reaction was evaluated according to the following criteria: "◎" and "◯" are pass marks, and "×" is fail marks.

[0047] "◎": The positive electrode melted, a metallic material was obtained, and a thermite reaction occurred. "Good": Part of the positive electrode melted, a metal material was obtained, and a thermite reaction occurred. "X": No metal material was obtained and thermite reaction did not occur.

[0048] [Table 1]

[0049] [Comparative Example 1] to [Comparative Example 2] A sheet-like positive electrode that was not subjected to the heating step S11 was used as Comparative Example 1. A positive electrode that was subjected to the heat treatment under the same conditions as Examples 1 to 4 except for changing the heating temperature was used as Comparative Example 2. Comparative Examples 1 and 2 were evaluated by the same methods and criteria as Examples 1 to 4.

[0050] From Table 1, comparing Examples 1 to 4, which are positive electrodes that were subjected to the heating step S11, with Comparative Example 1, which is a positive electrode that was not subjected to the heating step S11, it can be seen that in Comparative Example 1, the thermite reaction did not occur and a metal material was not obtained, whereas in Examples 1 to 4, a metal material was obtained by the thermite reaction. From the above, it was confirmed that the thermite reaction was promoted by performing the heating step S11.

[0051] Comparing Examples 1 to 4, which are positive electrodes that were heat-treated at a heating temperature in the range of 400°C to 600°C, and Comparative Example 2, which is a positive electrode that was heat-treated at a heating temperature of 750°C, it can be seen that in Comparative Example 2, the Al foil was powdered after the heat treatment, the thermite reaction was inhibited, and a metal material was not obtained, whereas in Examples 1 to 4, a metal material was obtained by the thermite reaction. From the above, it was confirmed that by setting the heating temperature in the range of 400°C to 600°C, the Al foil was not powdered, the adhesion state between the Al foil and the positive electrode active material was maintained, and the thermite reaction was promoted. In addition, when the heating temperature is in the range of more than 600°C to 650°C, it is less than 660°C, which is the melting point of aluminum, so the Al foil was not powdered, the adhesion state between the Al foil and the positive electrode active material was maintained, and it is considered that the thermite reaction is promoted as in Examples 1 to 4.

[0052] Comparing Examples 1 to 4, it is found that the thermite reaction is better in Examples 2 and 3, in which the heating temperature is within the range of 450° C. to 500° C., than in Example 1, in which the heating temperature is 400° C., and in Example 4, in which the heating temperature is 600° C. From the above, it was confirmed that a heating temperature within the range of 450° C. to 500° C. is particularly preferable.

[0053] It should be noted that no combustion improver was used in the melting step S12 in Examples 1 to 4 and Comparative Examples 1 and 2. That is, according to the present invention, as shown in Table 1, it was found that a metal material containing metals constituting a metal composite oxide can be obtained from the molten material obtained in the melting step S12 in some cases, even without using a combustion improver.

[0054] The present invention is not limited to the above-described embodiment, and can be modified as appropriate within the scope of the present invention. [Explanation of symbols]

[0055] 10 Nonaqueous electrolyte secondary battery S11 Heating process S12 Melting process S13 Separation process

Claims

1. A method for treating a positive electrode of a non-aqueous electrolyte secondary battery having a positive electrode having an Al-containing foil and an active material as a metal composite oxide, comprising: providing the positive electrode; a heating step of performing a heat treatment by heating the positive electrode with a heating device; a melting step of igniting the positive electrode removed from the heating device and melting the positive electrode by self-heating due to reaction heat between the foil and the active material to obtain a molten product; a separation step of separating the molten material into a metal material containing the metals constituting the metal composite oxide and slag; A method for treating a positive electrode of a non-aqueous electrolyte secondary battery comprising:

2. 2. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1, wherein the heat treatment is performed at a temperature at which the foil does not turn into powder.

3. The positive electrode comprises a binder, 3. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1, wherein the heat treatment is performed at a temperature at which the binder is decomposed.

4. 4. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 3, wherein the heat treatment is performed at a temperature of 400° C. or more and 650° C. or less.

5. 5. The method for treating a positive electrode of a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is a process waste generated in a manufacturing process of the non-aqueous electrolyte secondary battery.

6. 5. The method for treating a positive electrode of a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is a positive electrode of an unused non-aqueous electrolyte secondary battery.

7. 5. The method for treating a positive electrode of a non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode is a positive electrode of a used non-aqueous electrolyte secondary battery.

8. 4. The method for treating a positive electrode of a nonaqueous electrolyte secondary battery according to claim 1, wherein the heat treatment is carried out at a temperature of 600° C. or higher and 1250° C. or lower.

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