JP7825669B2 - How to recycle lithium-ion secondary batteries - Google Patents

Description

The present invention relates to a method for recycling lithium-ion secondary batteries.

In recent years, efforts to significantly reduce waste generation through waste prevention, reduction, recycling, and reuse have become more active. Toward this goal, research and development is being conducted on methods for recycling used lithium-ion secondary batteries. Known methods for recycling lithium-ion secondary batteries include dismantling used lithium-ion secondary batteries and separating and recovering battery materials. One known method involves connecting used lithium-ion secondary batteries to a resistor to discharge them, roasting the discharged batteries to decompose and burn organic materials such as the separator and electrolyte, and then pulverizing and sieving the resulting roasted material to separate and recover valuable metals contained in the electrodes, such as nickel, cobalt, and copper. However, when used lithium-ion secondary batteries are connected to a resistor to discharge them, metals contained in the negative electrode current collector migrate to the positive electrode as impurities below a certain voltage, reducing the recovery rate of the valuable metals due to these impurities.

As a method for reducing the above-mentioned impurities contained in the positive electrode, for example, Patent Document 1 discloses a method in which used lithium-ion secondary batteries are discharged, then dismantled to separate and recover the battery materials. In this method, the lithium-ion secondary battery is discharged, and dismantling begins while the battery is still discharging when the cell voltage drops below a level at which no sparks occur, and dismantling ends when the amount of copper eluted into the positive electrode reaches 10 ppm or less.

Patent No. 7234485

However, the method described in Patent Document 1 requires that the dismantling work be started and ended within a specific voltage range, which makes process management complicated.

To solve the above problems, the present application aims to provide a method for recycling lithium-ion secondary batteries that does not require discharge through a resistor, thereby reducing the amount of impurities contained in the positive electrode that originate from the negative electrode. This will ultimately contribute to a significant reduction in waste generation.

In order to solve the above problems, the present invention has the following aspects.
[1] A method for recycling a used lithium ion secondary battery comprising: a laminate having a positive electrode, a separator, and a negative electrode; an exterior body that houses the laminate; and an electrolyte solution,
a first step of exposing the laminate to a gas containing water vapor via the electrolytic solution;
a second step of converting the lithium ions contained in the negative electrode into a lithium compound.

According to the above aspect, by exposing the laminate to a gas containing water vapor via the electrolytic solution, the moisture in the gas containing water vapor, the electrolyte contained in the electrolytic solution, and the lithium ions contained in the negative electrode react with each other to produce lithium-containing compounds (e.g., LiF, _LiPF2O2 , _LiyPOx , _{LiySOx , etc. )} , which reduces the voltage of the lithium-ion secondary battery and makes discharge through a resistor unnecessary. As a result, the impurities contained in the positive electrode and derived from the negative electrode can be reduced. Therefore, the recovery rate of valuable metals can be improved.

[2] The method for recycling a lithium ion secondary battery described in [1], wherein the increase rate (A2/A1 x 100) of the content A2 of halogen elements contained in the negative electrode after the second step relative to the content A1 of halogen elements contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol%.

In this embodiment, the laminate is exposed to a gas containing water vapor via the electrolyte solution, increasing the content of halogen atoms contained in the negative electrode. In other words, a reaction occurs between the moisture in the gas containing water vapor, the halogen elements in the electrolyte contained in the electrolyte solution, and the lithium ions contained in the negative electrode, reducing the voltage of the lithium-ion secondary battery and eliminating the need for discharge via a resistor. As a result, the amount of impurities originating from the negative electrode contained in the positive electrode can be reduced. This can improve the recovery rate of valuable metals.

[3] The method for recycling a lithium ion secondary battery described in [1] or [2], wherein the increase rate (B2/B1) x 100 of the phosphorus content B2 contained in the negative electrode after the second step relative to the phosphorus content B1 contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol%.

According to the above aspect, the laminate is exposed to a gas containing water vapor via the electrolyte solution, increasing the phosphorus content in the negative electrode. That is, a reaction occurs between the moisture in the gas containing water vapor, the phosphorus in the electrolyte contained in the electrolyte solution, and the lithium ions contained in the negative electrode, reducing the voltage of the lithium-ion secondary battery and eliminating the need for discharge via a resistor. As a result, the amount of impurities originating from the negative electrode contained in the positive electrode can be reduced. Therefore, the recovery rate of valuable metals can be improved.

[4] A method for recycling a lithium ion secondary battery according to any one of [1] to [3], wherein the increase rate (C2/C1) x 100 of the sulfur content C2 contained in the negative electrode after the second step relative to the sulfur content C1 contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol%.

In this embodiment, the laminate is exposed to a gas containing water vapor via the electrolyte solution, increasing the sulfur content of the negative electrode. That is, a reaction occurs between the moisture in the gas containing water vapor, the sulfur in the electrolyte contained in the electrolyte solution, and the lithium ions contained in the negative electrode, reducing the voltage of the lithium-ion secondary battery and eliminating the need for discharge via a resistor. As a result, the amount of impurities originating from the negative electrode contained in the positive electrode can be reduced. Therefore, the recovery rate of valuable metals can be improved.

[5] A method for recycling a lithium-ion secondary battery according to any one of [1] to [4], wherein the rate of decrease ((V1-V2)/V1 x 100%) of the voltage V2 of the laminate after the second step relative to the voltage V1 of the laminate before the first step is 50% or more.

According to the above aspect, by setting the voltage reduction rate of the laminate to be equal to or greater than the above lower limit, the laminate can be safely recycled.

[6] The method for recycling a lithium-ion secondary battery described in any one of [1] to [5], wherein the voltage of the laminate after the second step is 0.8 V or less.

According to the above aspect, by setting the voltage of the laminate below the lower limit, the laminate can be safely recycled.

[7] The exterior body has a main body and a sealing body that seals an opening of the main body,
The method for recycling a lithium ion secondary battery according to any one of [1] to [6], wherein in the first step, a part of the joint where the main body and the sealing body are joined is opened.

According to the above aspect, discharge can proceed while preventing contact between the laminate and the joint and causing a short circuit.

The present invention provides a method for recycling lithium-ion secondary batteries that does not require discharge through a resistor, thereby reducing the amount of impurities contained in the positive electrode that originate from the negative electrode. This, in turn, contributes to a significant reduction in waste generation.

1 is a schematic cross-sectional view showing an example of a layer structure of a laminate in a lithium ion secondary battery according to one embodiment of the present invention. 1 is a flowchart of a method for recycling a lithium ion secondary battery according to one embodiment of the present invention. FIG. 10 is a diagram showing the relationship between the amount of opening of the joint where the main body of the outer casing and the sealing body are joined and the change over time in the voltage of the wound body exposed to the atmosphere due to the opening of the joint in Example 2.

The following describes in detail the embodiments of the present invention. However, the following description is merely an example of an embodiment of the present invention, and the present invention is not limited to these details and can be modified and implemented within the scope of its essence.

The lithium-ion secondary battery recycling method of this embodiment is a method for recycling used lithium-ion secondary batteries that include a laminate having a positive electrode, a separator, and a negative electrode, an exterior housing that houses the laminate, and an electrolyte. In other words, the lithium-ion secondary battery of this embodiment is a lithium-ion secondary battery with a liquid electrolyte (hereinafter also referred to as a "liquid electrolyte lithium-ion secondary battery").

The recycling method for lithium-ion secondary batteries of this embodiment includes a first step of exposing the laminate to a gas containing water vapor via the electrolyte solution, and a second step of converting the lithium ions contained in the negative electrode into lithium compounds. The first step initiates the second step.

<Lithium-ion secondary battery>
FIG. 1 is a schematic cross-sectional view showing an example of the layer structure of a laminate in a lithium ion secondary battery (liquid electrolyte lithium ion secondary battery) according to one embodiment of the present invention.

The lithium-ion secondary battery 10 (LIB) comprises a positive electrode 13, a separator 17, and a negative electrode 16 stacked in this order. The positive electrode 13 comprises a positive electrode current collector 11 and a positive electrode active material layer 12 disposed on the surface of the positive electrode current collector 11. While the positive electrode active material layer 12 is shown on only one side of the positive electrode current collector 11 in FIG. 1, it may be disposed on both sides. The negative electrode 16 comprises a negative electrode current collector 14 and a negative electrode active material layer 15 disposed on the surface of the negative electrode current collector 14. While the negative electrode active material layer 15 is shown on only one side of the negative electrode current collector 14 in FIG. 1, it may be disposed on both sides. While FIG. 1 shows only one positive electrode 13 and one negative electrode 16, it may also be an electrode group in which multiple positive electrodes 13 and negative electrodes 16 are alternately stacked. In this case, a separator 17 is disposed between the positive electrode 13 and the negative electrode 16.

(Positive electrode active material layer)
The positive electrode active material layer 12 contains a positive electrode active material, a conductive additive, and a binder. When the positive electrode active material has conductivity, the positive electrode active material layer does not need to contain the conductive additive.

The positive electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium ions. Examples of the positive electrode active material include lithium nickel oxide (e.g., LiNiO ₂ ), lithium cobalt oxide (e.g., LiCoO ₂ ), lithium nickel cobalt oxide, lithium nickel cobalt manganese oxide, LiFePO ₄ , LiMn _1-x Fe _{x PO 4} , LiMnPO ₄ , LiCoPO 4 , and LiNiPO _4. The positive electrode active material preferably contains one or more elements selected from the group consisting of manganese, nickel, and cobalt.

The conductive additive assists in forming a conductive path between the positive electrode active material and the positive electrode current collector 11. There are no particular limitations on the conductive additive as long as it is conductive, and examples include carbon black such as acetylene black, carbon nanotubes, and graphite such as artificial graphite.

The binder binds the positive electrode active material, conductive additive, and positive electrode current collector 11 together. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyamide (PA), polyimide (PI), polyacrylic acid and its copolymers, polyamideimide (PAI), polybenzimidazole, polyethersulfone (PES), maleic anhydride-modified polypropylene, and mixtures thereof. The binder preferably contains a crystalline polymer with a melting point. The binder is preferably a polymer containing fluorine. Examples of fluorine-containing polymers include PVDF and PTFE.

(Positive electrode current collector)
The positive electrode current collector 11 may be, for example, a metal foil such as an aluminum foil, a stainless steel foil, or a nickel foil.

(Negative electrode active material layer)
The negative electrode active material layer 15 contains a negative electrode active material, a conductive additive, and a binder. When the negative electrode active material has conductivity, the negative electrode active material layer does not necessarily contain the conductive additive.

There are no particular limitations on the negative electrode active material, as long as it is capable of absorbing and releasing lithium ions. Examples of negative electrode active materials include graphite (artificial graphite, natural graphite), amorphous carbon (hard carbon), mesocarbon microbeads, carbon fiber, and silicon materials (silicon, silicon alloys, silicon oxides).

The conductive additive assists in forming a conductive path between the negative electrode active material and the negative electrode current collector 14. There are no particular limitations on the conductive additive as long as it is conductive, and examples include carbon black such as acetylene black, carbon nanotubes, and graphite such as artificial graphite.

The binder binds the negative electrode active material, conductive additive, and negative electrode current collector 14 together. Examples of binders include carboxymethyl cellulose, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, fluororubber, and diene rubbers such as styrene-butadiene rubber. The binder preferably contains a crystalline polymer with a melting point. The binder is preferably a polymer containing fluorine. Examples of fluorine-containing polymers include PVDF, PTFE, and fluororubber.

The negative electrode current collector 14 may be, for example, a metal foil such as copper foil, stainless steel foil, or nickel foil. A carbon coating layer may be formed on the negative electrode current collector 14. The negative electrode current collector 14 may also be processed into a mesh shape.

(electrode tab)
In order to extract current to the outside of the battery, the positive electrode current collector 11 and the negative electrode current collector 14 may each be connected to an electrode tab (not shown). The electrode tab is electrically connected to these current collectors and is taken out to, for example, the exterior of the lithium-ion secondary battery.

The material from which the electrode tab is made is not particularly limited, and well-known highly conductive materials conventionally used for electrode tabs are preferably used. Metallic materials such as aluminum, copper, titanium, nickel, stainless steel, and alloys of these are preferred as materials from which the electrode tab is made, with aluminum and copper being more preferred from the standpoints of light weight, corrosion resistance, and high conductivity.

(Exterior body)
The laminate is housed in an exterior body (not shown). The exterior body has a main body and a sealing body that seals the opening of the main body. In the case of a liquid electrolyte lithium-ion secondary battery, the exterior body is filled with an electrolyte. As the exterior body, a known metal can case can be used, or a bag-shaped case using an aluminum-containing laminate film that can cover the power generating element can also be used. As the laminate film, for example, a three-layer laminate film formed by laminating polypropylene, aluminum, and nylon in this order can be used. From the viewpoint of high output and excellent cooling performance, and being suitable for use in batteries for large equipment such as EVs and HEVs, a laminate film is desirable as the exterior body.

Positive and negative electrode terminal leads (not shown) connected to the electrode tabs may also be used as needed. Known materials can be used for the positive and negative electrode terminal leads. The portions removed from the outer casing are preferably covered with heat-resistant, insulating heat-shrinkable tubing to prevent contact with peripheral devices or wiring, resulting in electrical leakage and affecting the product (e.g., automotive parts, particularly electronic devices). In addition, in wound-type lithium-ion secondary batteries, terminals may be formed using, for example, a cylindrical can (metal can) instead of electrode tabs.

(electrolyte)
The electrolytic solution contains an electrolyte and an organic solvent.
The electrolyte can be selected from those known in the art, and examples thereof include lithium salts such as _LiClO4 , _LiPF6 , _LiAsF6 , LiSbF6, _LiBF4 , _LiCF3SO3 , LiN _{( SO2CF3} ) ₂ , LiN( _SO2C2F5 ) _{2 ,} LiN( _SO2CF3 )( _{COCF3 )} , _Li ( _C4F9SO3 ), LiC( _SO2CF3 ) _{3 , and Li2B10Cl10} . The electrolyte preferably contains at least one element selected from _the group consisting of a halogen element, _{a phosphorus} element, and _a sulfur element _.
The electrolytes may be used alone or in combination of two or more.

The organic solvent can be selected from organic solvents known in the art, and examples thereof include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; esters such as methyl formate, methyl acetate, and γ-butyrolactone; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; nitriles such as acetonitrile and butyronitrile; carbamates such as 3-methyl-2-oxazolidone; and sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone.
The organic solvents may be used alone or in combination of two or more.

(separator)
Examples of the separator 17 include separators formed from olefin resins such as polyethylene and polypropylene, fluororesins, aromatic resins containing nitrogen atoms, etc. Examples of the form of the separator 17 include a porous film, a nonwoven fabric, and a woven fabric.

(Form of laminate)
The form of the laminate of the lithium ion secondary battery according to this embodiment can be any of the conventionally known forms and structures, such as a wound (cylindrical) battery, a laminated (flat) battery, a flat-wound (prismatic) battery, etc. Of these, a wound (cylindrical) battery and a flat-wound (prismatic) battery are preferred, and a wound (cylindrical) battery is more preferred.

<How to recycle lithium-ion secondary batteries>
The method for recycling a lithium-ion secondary battery of this embodiment includes a first step of exposing the laminate to a gas containing water vapor via the electrolytic solution, and a second step of converting the lithium ions contained in the negative electrode into a lithium compound. Figure 2 is a flowchart of the method for recycling a lithium-ion secondary battery of this embodiment. The lithium ions contained in the negative electrode refer to lithium ions absorbed in the negative electrode.

<First step>
In the first step S1, the laminate is exposed to a gas containing water vapor via the electrolytic solution. That is, in the recycling method for a lithium-ion secondary battery according to the present embodiment, the outer casing is opened, and the laminate is exposed to a gas containing water vapor via the electrolytic solution within the outer casing.

In the first step S1, it is preferable to open a part of the joint where the main body and the sealing body in the exterior body are joined, so that discharge can proceed while preventing contact between the laminate and the joint and causing a short circuit.
In the first step S1, it is preferable to open at least ¼ of the total length of the joint portion where the main body and the sealing body in the outer package are joined, more preferably at least ½, even more preferably at least 5/8, and particularly preferably at least ¾. By opening at least ¼ of the total length of the joint portion, discharge can proceed efficiently.

The relative humidity of the water vapor-containing gas at any temperature in the first step S1 is preferably 40% or higher, more preferably 60% or higher, and more preferably 90% or higher. If the relative humidity is above the lower limit, discharge is more likely to proceed.

An example of a gas containing water vapor is a mixed gas obtained by mixing water vapor with any gas other than water vapor. The arbitrary gas is not particularly limited, and examples include inert gases such as nitrogen and argon, oxygen, and carbon dioxide. Air is a particularly preferred gas containing water vapor.

The temperature of the water vapor-containing gas in the first step S1 is not particularly limited, but may be, for example, -20 to 70°C. It may also be near room temperature (10 to 40°C).

The time for which the laminate is exposed to the gas containing water vapor in the first step is not particularly limited, and exposure is continued until the desired voltage is reached.

<Second step>
In the second step S2, the lithium ions contained in the negative electrode are converted into lithium compounds by reacting the water in the gas containing water vapor, the electrolyte contained in the electrolytic solution, and the lithium ions contained in the negative electrode.

In the second step S2, discharging proceeds by converting the lithium ions contained in the negative electrode into lithium compounds. That is, a reaction occurs between the moisture in the gas containing water vapor, the electrolyte contained in the electrolytic solution, and the lithium ions contained in the negative electrode, reducing the voltage of the lithium-ion secondary battery and eliminating the need for discharge via resistance. As a result, the amount of impurities originating from the negative electrode contained in the positive electrode can be reduced. This can improve the recovery rate of valuable metals.

The increase rate (A2/A1 × 100) of the halogen element content A2 (mol%) contained in the negative electrode after the second step relative to the halogen element content A1 (mol%) contained in the negative electrode in the used lithium ion secondary battery is preferably greater than 100 mol%, more preferably 110 mol% or more, even more preferably 120 mol% or more, even more preferably 125 mol% or more, particularly preferably 135 mol% or more, and most preferably 200 mol% or more. It is believed that a compound containing a halogen element and lithium is produced by reacting moisture in a gas containing water vapor, an electrolyte contained in the electrolytic solution, and lithium ions contained in the negative electrode. Therefore, it is believed that the increase rate of the halogen element in the negative electrode essentially indicates the increase rate of the lithium compound produced in the negative electrode. In other words, it is believed that the increase rate of the halogen element indicates the degree of progress of discharge. When the increase rate is equal to or greater than the lower limit, it is believed that discharge is progressing well. As the halogen element, chlorine or fluorine is preferred, and fluorine is more preferred.
The content of each element, such as a halogen element, contained in the negative electrode can be measured by XPS analysis. Note that the content of the halogen element may vary slightly depending on the location of the negative electrode. When measuring the halogen element contents A1 and A2, the measurement is performed at the same location on the negative electrode. The same applies to phosphorus and sulfur, which will be described later.

The increase rate (B2/B1 x 100) of the phosphorus content B2 (mol%) in the negative electrode after the second step relative to the phosphorus content B1 (mol%) in the negative electrode of a used lithium-ion secondary battery is preferably greater than 100 mol%, more preferably 110 mol% or greater, even more preferably 115 mol% or greater, particularly preferably 140 mol% or greater, and most preferably 200 mol% or greater. It is believed that compounds containing phosphorus and lithium are produced by the reaction of moisture in the gas containing water vapor, the electrolyte in the electrolyte solution, and the lithium ions in the negative electrode. Therefore, it is believed that the increase rate of phosphorus in the negative electrode essentially represents the increase rate of lithium compounds produced in the negative electrode. In other words, it is believed that the increase rate of phosphorus represents the degree of discharge progress. When the increase rate is equal to or greater than the lower limit, it is believed that discharge is progressing satisfactorily.

The increase rate (C2/C1 x 100) of the sulfur content C2 (mol%) in the negative electrode after the second step relative to the sulfur content C1 (mol%) in the negative electrode of a used lithium-ion secondary battery is preferably greater than 100 mol%, more preferably 110 mol% or greater, even more preferably 120 mol% or greater, and particularly preferably 130 mol% or greater. It is believed that compounds containing sulfur and lithium are produced by the reaction of moisture in the gas containing water vapor, the electrolyte in the electrolytic solution, and the lithium ions in the negative electrode. Therefore, it is believed that the increase rate of sulfur in the negative electrode essentially represents the increase rate of lithium compounds produced in the negative electrode. In other words, it is believed that the increase rate of sulfur indicates the progress of discharge. When the increase rate is equal to or greater than the lower limit, it is believed that discharge is progressing satisfactorily.

In the lithium-ion secondary battery recycling method of this embodiment, the reduction rate ((V1 - V2)/V1 x 100%) of the voltage V2 of the laminate after discharge (after the second step) relative to the voltage V1 of the laminate before discharge (before the first step) is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. If the reduction rate of the voltage of the laminate is equal to or greater than the above-mentioned lower limit, the laminate can be safely recycled.

In the lithium-ion secondary battery recycling method of this embodiment, the voltage of the laminate after discharge (after the second step) is preferably 0.8 V or less, more preferably 0.7 V or less, and even more preferably 0.5 V or less. If the voltage of the laminate is below the upper limit, the laminate can be safely recycled.

In the lithium-ion secondary battery recycling method of this embodiment, it is preferable to measure the voltage of the laminate and terminate the second step S2 if the voltage of the laminate is 0.8 V or less. If the voltage of the laminate is 0.8 V or less, the laminate can be safely recycled, and the second step S2 is terminated. This eliminates unnecessary work.

The lithium-ion secondary battery recycling method of this embodiment may include, after completing the second step S2, a third step of recovering the laminate, and a fourth step of disassembling the recovered laminate to recover the electrode active material, etc.

<Mechanism of action>
In the lithium-ion secondary battery recycling method of this embodiment, the laminate is exposed to a gas containing water vapor via the electrolytic solution, causing a reaction between the moisture in the gas containing water vapor, the electrolyte contained in the electrolytic solution, and the lithium ions contained in the negative electrode, thereby promoting _the production of lithium-containing compounds (e.g., the production of LiF, _LiPF2O2 , _LiyPOx , _{LiySOx , etc.} ), which reduces the voltage of the lithium-ion secondary battery and therefore eliminates the need for discharge through a resistor. As a result, the amount of impurities contained in the positive electrode that originate from the negative electrode can be reduced. Therefore, the recovery rate of valuable metals can be improved.

The present invention will be explained in more detail below using examples, but the present invention is not limited to the following examples.

[Example 1]
A laminate was prepared by winding a laminate in which a positive electrode, a separator, and a negative electrode were stacked in this order. Aluminum was used as the positive electrode current collector, NCMA as the positive electrode active material, carbon as the conductive additive, and polyvinylidene fluoride (PCDF) as the binder. Copper foil was used as the negative electrode current collector, natural graphite as the negative electrode active material, and styrene butadiene rubber (SBR) as the binder. PE was used as the separator. The laminate was housed in an exterior body consisting of a main body and a seal, filled with an electrolyte, and then sealed with a seal to form a lithium-ion secondary battery. LiFSI and LiPF ₆ were used as the electrolyte for the electrolyte, and a mixed solvent of dimethyl carbonate, ethyl methyl carbonate, and ethylene carbonate was used as the organic solvent. The resulting lithium-ion secondary battery was repeatedly charged and discharged to obtain a used lithium-ion secondary battery.

The negative electrode was removed from a used lithium-ion secondary battery, washed with dimethyl carbonate (DMC), and then dried. Elemental analysis (F, P, S) of the surface of the negative electrode was performed by X-ray photoelectron spectroscopy (XPS). The negative electrode was removed and transferred to the XPS device in an argon atmosphere. The XPS measurement conditions were as follows. The results are shown in Table 1 (referred to as "no deactivation" in Table 1). In Table 1, the start of winding refers to the vicinity of the center of the wound body, the end of winding refers to the vicinity of the outer side of the wound body, and the middle of winding refers to the area between the start of winding and the end of winding.
・Equipment: Quantera SXM (Ulvac-PHI)
Excitation X-ray: monochromatic AlKα ray (1486 eV)
・X-ray diameter: 200 μm
Photoelectron detection angle: 45°

The entire length of the joint between the body and the sealing body in the exterior packaging of a used lithium-ion secondary battery was completely opened, and the stack was exposed to the atmosphere via the electrolyte. The atmospheric temperature was 22-25°C, and the relative humidity was 60-75%. After the voltage reached 0.6V or less, the stack was exposed for an additional 24 hours. The negative electrode was then removed from the used lithium-ion secondary battery, and elemental analysis (F, P, S) of the negative electrode surface was performed using XPS. The measurement conditions were as described above. The results are shown in Table 1 (deactivated in Table 1). The rate of decrease ((V1-V2)/V1 x 100%) of the voltage V2 of the stack after discharge (after the second step) relative to the voltage V1 of the stack before discharge (before the first step) was 50% or more, and the voltage V2 of the stack after discharge (after the second step) was 0.7V or less.

In addition, the positive electrode active material was scraped off from the undeactivated positive electrodes at the beginning, middle, and end of the roll, and from the deactivated positive electrodes at the beginning, middle, and end of the roll, and then thermally decomposed using sulfuric acid, nitric acid, and perchloric acid. Then, the material was dissolved in dilute nitric acid and dilute hydrogen peroxide to obtain a solution. This solution was analyzed using ICP spectrometry to measure the copper content.

When comparing the same locations on the negative electrode (beginning, middle, end of winding) with and without deactivation, it was found that the fluorine, phosphorus, and sulfur contents increased, and lithium compounds were formed. In other words, it is believed that lithium compounds were formed in proportion to the rate of increase in the fluorine, phosphorus, and sulfur contents, and that the formation of these lithium compounds caused the voltage to decrease (discharge progressed).

Furthermore, the copper content of the positive electrodes at the beginning, middle, and end of the winding without deactivation, and the positive electrodes at the beginning, middle, and end of the winding with deactivation, was all less than 10 ppm by mass, and no migration of copper from the copper foil of the negative electrode current collector to the positive electrode was confirmed.

[Example 2]
A deactivation treatment was carried out in the same manner as in Example 1, except that the opening length of the joint where the main body and the sealed body in the exterior packaging of the used lithium-ion secondary battery were joined was set to ¾ of the total length. The voltage change over time immediately after opening was measured and output using a data logger. The results are shown in Figure 3. Figure 3 also shows the voltage change over time immediately after opening when the entire length (full cut) of the joint in Example 1 was completely opened.
The results shown in FIG. 3 reveal that when three-quarters of the total length of the joint is opened, and when the entire joint is opened, the laminate is deactivated in a short period of time.

10 Lithium ion secondary battery 11 Positive electrode current collector 12 Positive electrode active material layer 13 Positive electrode 14 Negative electrode current collector 15 Negative electrode active material layer 16 Negative electrode 17 Separator

Claims (6)

A method for recycling a used lithium ion secondary battery comprising: a laminate having a positive electrode, a separator, and a negative electrode; an exterior body that houses and seals the laminate; and an electrolyte solution,
a method for recycling a lithium ion secondary battery, the method including: opening the exterior housing; exposing the laminate to a gas containing water vapor through the electrolytic solution; and reacting the moisture in the gas containing water vapor with an electrolyte contained in the electrolytic solution and lithium ions contained in the negative electrode , thereby producing a lithium compound. 2. The method for recycling a lithium ion secondary battery according to claim 1, wherein an increase rate (A2/A1×100) of a content A2 of halogen elements contained in the negative electrode after producing the lithium compound relative to a content A1 of halogen elements contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol %. 3. The method for recycling a lithium ion secondary battery according to claim 1, wherein an increase rate (B2/B1)×100 of a phosphorus content B2 contained in the negative electrode after producing the lithium compound relative to a phosphorus content B1 contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol%. 3. The method for recycling a lithium ion secondary battery according to claim 1, wherein an increase rate (C2/C1)×100 of a sulfur content C2 contained in the negative electrode after producing the lithium compound relative to a sulfur content C1 contained in the negative electrode of the used lithium ion secondary battery exceeds 100 mol%. 3. The method for recycling a lithium ion secondary battery according to claim 1, wherein a voltage of the laminate after producing the lithium compound is 0.8 V or less. 3. The method for recycling a lithium ion secondary battery according to claim 1, wherein the exterior body has a main body and a sealing body that seals an opening of the main body.