How to disassemble a lithium-ion rechargeable battery

Abstract

This device suppresses heat generation inside the lithium-ion secondary battery when it is disconnected. [Solution] The method for dismantling a lithium-ion secondary battery includes a preparation step S1 in which a lithium-ion secondary battery is prepared, comprising a wound electrode body in which a positive electrode and a negative electrode are superimposed and wound together via a separator, a battery case for housing the wound electrode body, a positive electrode current collector connected to the positive electrode inside the battery case, and a negative electrode current collector connected to the negative electrode inside the battery case; a charge-discharge step S2 in which the lithium-ion secondary battery is charged at a predetermined charge rate and the lithium-ion secondary battery is discharged at a predetermined discharge rate a predetermined number of times to deposit lithium on the negative electrode; and a cutting step S3 in which, after the charge-discharge step has been performed, the connection portion between the positive electrode current collector or the negative electrode current collector and the wound electrode body of the lithium-ion secondary battery is cut.

Description

Technical Field

[0001] The present invention relates to a method for disassembling a lithium-ion secondary battery.

Background Art

[0002] For example, Japanese Patent Laid-Open No. 9-117749 discloses a method for recovering valuable materials from a secondary battery for an electric vehicle. By taking out the positive and negative electrode plates and the separator housed inside the secondary battery and performing crushing, washing, sorting, etc. on the taken-out positive and negative electrode plates and the separator, the active materials of the positive and negative electrode plates can be used as recycling raw materials. Here, in order to take out the positive and negative electrode plates and the separator, the upper part of the side surface of the case of the waste battery is cut by an electric saw. The cut waste battery is divided into a case part and a lid part, and the positive and negative electrode plates and the separator are taken out from the case part.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The inventor of the present application desires to suppress heat generation inside the lithium-ion secondary battery during cutting of the lithium-ion secondary battery.

Means for Solving the Problems

[0005] The method for disassembling a lithium-ion secondary battery disclosed herein includes a preparation step of preparing a lithium-ion secondary battery comprising a wound electrode body in which a positive electrode and a negative electrode are superimposed and wound together via a separator, a battery case for housing the wound electrode body, a positive electrode current collector connected to the positive electrode inside the battery case, and a negative electrode current collector connected to the negative electrode inside the battery case; a charge-discharge step of repeatedly charging the lithium-ion secondary battery at a predetermined charge rate and discharging the lithium-ion secondary battery at a predetermined discharge rate a predetermined number of times to deposit lithium on the negative electrode; and a cutting step of cutting the connection portion between the positive electrode current collector or the negative electrode current collector and the wound electrode body of the lithium-ion secondary battery after the charge-discharge step has been performed.

[0006] According to the method for disassembling a lithium-ion secondary battery disclosed herein, heat generation inside the lithium-ion secondary battery can be suppressed when the lithium-ion secondary battery is cut. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a perspective view of a lithium-ion secondary battery 100. [Figure 2] Figure 2 is a schematic longitudinal cross-sectional view along the line II-II in Figure 1. [Figure 3] Figure 3 is a schematic longitudinal cross-sectional view along the line III-III in Figure 1. [Figure 4] Figure 4 is a schematic cross-sectional view along the line IV-IV in Figure 1. [Figure 5] Figure 5 is a schematic perspective view showing the electrode group 20 attached to the sealing plate 14 before mating. [Figure 6] Figure 6 is a schematic perspective view of the electrode body 20a. [Figure 7] Figure 7 is a schematic diagram showing the configuration of the electrode body 20a. [Figure 8] Figure 8 shows the state in which the cutting tool CT is in contact with the positive electrode 22 and the negative electrode 24. [Figure 9]Figure 9 is a flowchart showing the procedure for disassembling the lithium-ion secondary battery 100 according to this embodiment. [Figure 10] Figure 10 is a schematic diagram of the area around the negative electrode 24 after the charge / discharge process S2. [Figure 11] Figure 11 is a graph based on the results of Examples 2, 4, and 6, with the discharge capacity until the cell voltage reaches 0V on the horizontal axis and the temperature rise on the vertical axis. [Modes for carrying out the invention]

[0008] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings. Matters other than those specifically mentioned herein but necessary for carrying out the present invention (e.g., general configuration and processes of batteries not characterizing the present invention) can be understood as design matters for those skilled in the art based on the prior art. The present invention can be carried out based on the content disclosed herein and common technical knowledge in the art. The following description is not intended to limit the technology disclosed herein to the following embodiments. Furthermore, the notation "A~B" indicating a numerical range in this specification means A or greater and B or less. Therefore, it includes cases where the value is greater than A and less than B.

[0009] In this specification, "battery" refers to all energy storage devices capable of extracting electrical energy, and is a concept that encompasses both primary and secondary batteries. Furthermore, in this specification, "secondary battery" refers to all energy storage devices capable of repeated charging and discharging.

[0010] First, the configuration of the lithium-ion secondary battery 100 according to this embodiment will be described. Figure 1 is a perspective view of the lithium-ion secondary battery 100. Figure 2 is a schematic longitudinal cross-sectional view along the line II-II in Figure 1. Figure 3 is a schematic longitudinal cross-sectional view along the line III-III in Figure 1. Figure 4 is a schematic transverse cross-sectional view along the line IV-IV in Figure 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, back, up, and down, respectively, and the symbols X, Y, and Z in the drawings represent the short side direction, the long side direction perpendicular to the short side direction (also called the longitudinal direction of the electrode body), and the up and down direction of the lithium-ion secondary battery 100, respectively. However, these are merely directions for the convenience of explanation and do not limit the installation configuration of the lithium-ion secondary battery 100 in any way.

[0011] As shown in Figure 2, the lithium-ion secondary battery 100 comprises a battery case 10 and an electrode body (here, an electrode body group 20). In addition to the battery case 10 and the electrode body group 20, the lithium-ion secondary battery 100 according to this embodiment also comprises a positive electrode terminal 30, a positive electrode external conductive member 32, a negative electrode terminal 40, a negative electrode external conductive member 42, a gasket 90, an external insulating member 92, a positive electrode current collector 50, a negative electrode current collector 60, a positive electrode internal insulating member 70, and a negative electrode internal insulating member 80. The lithium-ion secondary battery 100 further comprises an electrolyte 13. The internal resistance of the lithium-ion secondary battery 100 may be, for example, about 0.2 to 2.0 mΩ.

[0012] The battery case 10 is a housing that accommodates the electrode group 20. The battery case 10 has a flat, bottomed rectangular parallelepiped (square) shape. The material of the battery case 10 can be the same as that used conventionally, and there are no particular restrictions. The battery case 10 is preferably made of metal, and more preferably of aluminum, aluminum alloy, iron, iron alloy, etc. The battery case 10 also comprises an outer casing 12, a sealing plate 14, and a gas discharge valve 17. The outer casing 12 is a flat, square container with one side being an opening 12h. Specifically, as shown in Figure 1, the outer casing 12 comprises a substantially rectangular bottom wall 12a, a pair of first side walls 12b extending upward U from the short side of the bottom wall 12a and facing each other, and a pair of second side walls 12c extending upward U from the long side of the bottom wall 12a and facing each other. The area of ​​the first side wall 12b is larger than the area of ​​the second side wall 12c. The opening 12h (see Figure 2) is formed on the upper surface of the outer casing 12, which is surrounded by the pair of first side walls 12b and the pair of second side walls 12c. The sealing plate 14 is attached to the outer casing 12 so as to close the opening 12h of the outer casing 12. The sealing plate 14 is a plate material that is substantially rectangular in plan view. The sealing plate 14 faces the bottom wall 12a of the outer casing 12. The battery case 10 is formed by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the outer casing 12. The joining of the sealing plate 14 can be done by welding, such as laser welding.

[0013] As shown in Figures 1 and 2, the gas discharge valve 17 is formed in the sealing plate 14. The gas discharge valve 17 is configured to open when the pressure inside the battery case 10 exceeds a predetermined value, thereby discharging gas from inside the battery case 10. In addition to the gas discharge valve 17, the sealing plate 14 is also provided with an electrolyte injection hole 15 and two terminal insertion holes 18 and 19. The electrolyte injection hole 15 communicates with the internal space of the outer casing 12 and is an opening provided for injecting electrolyte 13 during the manufacturing process of the lithium-ion secondary battery 100. The electrolyte injection hole 15 is sealed by a sealing member 16. A blind rivet is a suitable example of such a sealing member 16. This allows the sealing member 16 to be firmly fixed inside the battery case 10.

[0014] FIG. 5 is a perspective view schematically showing an electrode body group 20 attached to a sealing plate 14 before fitting. In the present embodiment, a plurality (here, three) of electrode bodies 20a, 20b, and 20c are housed inside a battery case 10 (see FIG. 1). The electrode bodies 20a, 20b, and 20c are an example of a wound electrode body in the present invention. The number of electrode bodies housed inside one battery case 10 is not particularly limited, and it may be one, or two or more (plural). As shown in FIG. 2, a positive electrode current collector 50 is disposed on one side (the left side in FIG. 2) in the long side direction Y of each electrode body, and a negative electrode current collector 60 is disposed on the other side (the right side in FIG. 2) in the long side direction Y. Then, as shown in FIG. 5, each of the electrode bodies 20a, 20b, and 20c is connected in parallel. However, the electrode bodies 20a, 20b, and 20c may be connected in series. The electrode bodies 20a, 20b, and 20c are housed inside an exterior body 12 of the battery case 10 in a state covered with an electrode body holder 29 (see FIG. 3) made of a resin sheet. Further, as shown in FIG. 5, in the lithium ion secondary battery 100 according to the present embodiment, a separator 26 having a joint portion 1 is unevenly distributed in the direction where the bending of the positive electrode tab group 23 is gentle (in other words, the bent portion of the positive electrode tab group 23).

[0015] FIG. 6 is a perspective view schematically showing the electrode body 20a. FIG. 7 is a schematic diagram showing the configuration of the electrode body 20a. Hereinafter, the electrode body 20a will be described in detail as an example, but the electrode bodies 20b and 20c may have the same configuration.

[0016] As shown in FIG. 7, the electrode body 20a has a positive electrode 22, a negative electrode 24, and a separator 26. Here, the electrode body 20a is a wound electrode body in which a strip-shaped positive electrode 22 and a strip-shaped negative electrode 24 are laminated via two strip-shaped separators 26 and wound around a winding axis WL. Such a wound electrode body has a positive / negative electrode laminated structure in which the positive electrode 22 and the negative electrode 24 overlap each other with the separator 26 interposed therebetween.

[0017] The electrode body 20a has a flat shape. The electrode body 20a is disposed inside the exterior body 12 (see FIG. 1) in a direction such that the winding axis WL is substantially parallel to the long side direction Y. Specifically, as shown in FIG. 3, the electrode body 20a has a pair of curved portions (R portions) 20r facing the bottom wall 12a and the sealing plate 14 of the exterior body 12, and a flat portion 20f connecting the pair of curved portions 20r and facing the second side wall 12c (see FIG. 1) of the exterior body 12. The flat portion 20f extends along the second side wall 12c.

[0018] As shown in FIG. 2, the electrolytic solution 13 is housed inside the battery case 10 together with the electrode bodies 20a, 20b, and 20c. A part of the electrolytic solution 13 has penetrated into the electrode bodies 20a, 20b, and 20c. The electrolytic solution 13 is, for example, a non-aqueous electrolytic solution containing a non-aqueous solvent (organic solvent) and a supporting salt (electrolytic salt, such as a lithium salt or a sodium salt). Examples of the non-aqueous solvent include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of the supporting salt include fluorine-containing lithium salts such as lithium hexafluorophosphate (LiPF6). The electrolytic solution 13 is typically liquid, but may be gel-like.

[0019] As shown in FIG. 7, the positive electrode 22 has a positive electrode current collector 22c, and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed on at least one surface of the positive electrode current collector 22c. However, the positive electrode protective layer 22p is not essential and can be omitted in other embodiments. The positive electrode current collector 22c is strip-shaped. The positive electrode current collector 22c is made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. Here, the positive electrode current collector 22c is a metal foil, specifically an aluminum foil.

[0020] Multiple positive electrode tabs 22t are provided at one end 21a (the left end in Figure 7) of the positive electrode current collector 22c in the long side direction Y. The multiple positive electrode tabs 22t are provided at intervals (intermittently) along the longitudinal direction of the strip-shaped positive electrode 22. The multiple positive electrode tabs 22t protrude outward from the separator 26 toward one side in the axial direction of the winding shaft WL (the left side in Figure 7). The positive electrode tabs 22t may also be provided on the other side in the axial direction of the winding shaft WL (the right side in Figure 7), or on each of the axial sides of the winding shaft WL. The positive electrode tabs 22t are part of the positive electrode current collector 22c and are made of metal foil (aluminum foil). However, the positive electrode tabs 22t may be made of a different material from the positive electrode current collector 22c. The positive electrode tabs 22t are rectangular in shape here, but are not limited to this, and may be made of various shapes such as trapezoidal. In this embodiment, only the positive electrode protective layer 22p is formed on the positive electrode tab 22t, but the embodiment is not limited to this, and a positive electrode active material layer and a positive electrode protective layer may also be formed on the positive electrode tab.

[0021] As shown in Figure 4, multiple positive electrode tabs 22t are stacked at one end (the left end in Figure 4) in the axial direction of the winding shaft WL (see Figure 7) to form a positive electrode tab group 23. The positive electrode tab group 23 includes multiple positive electrode tabs 22t protruding from one end 21a located in the planar direction (Y direction in Figure 2) along the first side wall 12b. Each of the multiple positive electrode tabs 22t is bent so that its outer ends are aligned. This improves the ability to fit into the battery case 10 and allows for miniaturization of the lithium-ion secondary battery 100. As shown in Figure 2, the positive electrode tab group 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector 50. Specifically, the positive electrode tab group 23 is joined to the positive electrode current collector 50 in a state in which at least a portion of the tip portion of the positive electrode tab group is curved so as to be positioned along one of the pair of second side walls 12c. Therefore, the positive electrode current collector 50 is connected to the positive electrode 22 inside the battery case 10.

[0022] As shown in Figure 2, the positive electrode first current collector 51, gasket 90, and external insulating member 92 are fixed to the sealing plate 14. The positive electrode first current collector 51, gasket 90, and external insulating member 92 are fixed to the sealing plate 14 by, for example, crimping. The positive electrode second current collector 52 is electrically connected to the positive electrode terminal 30 via the positive electrode first current collector 51. The size of the multiple positive electrode tabs 22t (length along the long side direction Y and width perpendicular to the long side direction Y, see Figure 7) can be appropriately adjusted, for example, by their formation position, taking into consideration the state in which they are connected to the positive electrode current collector 50. Here, the sizes of each of the multiple positive electrode tabs 22t are different so that the outer ends align when curved.

[0023] As shown in Figure 7, the positive electrode active material layer 22a is provided in a strip shape along the longitudinal direction of the strip-shaped positive electrode current collector 22c. The positive electrode active material layer 22a contains a positive electrode active material (for example, a lithium transition metal composite oxide such as lithium nickel cobalt manganese composite oxide) that can reversibly absorb and release charge carriers. When the total solid content of the positive electrode active material layer 22a is taken as 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 22a may also contain optional components other than the positive electrode active material, such as conductive materials, binders, and various additives. As a conductive material, for example, a carbon material such as acetylene black (AB) may be used. As a binder, for example, polyvinylidene fluoride (PVdF) may be used.

[0024] As shown in Figure 7, the positive electrode protective layer 22p is provided at the boundary between the positive electrode current collector 22c and the positive electrode active material layer 22a in the long side direction Y. Here, the positive electrode protective layer 22p is provided at one end (the left end in Figure 7) in the axial direction of the winding axis WL of the positive electrode current collector 22c. However, the positive electrode protective layer 22p may also be provided at both ends in the axial direction. The positive electrode protective layer 22p is provided in a strip shape along the positive electrode active material layer 22a. The positive electrode protective layer 22p contains an inorganic filler (e.g., alumina). When the total solid content of the positive electrode protective layer 22p is considered to be 100% by mass, the inorganic filler may account for approximately 50% by mass or more, typically 70% by mass or more, for example, 80% by mass or more. The positive electrode protective layer 22p may also contain optional components other than the inorganic filler, such as conductive materials, binders, various additives, etc. The conductive material and binder may be the same as those exemplified as those that may be included in the positive electrode active material layer 22a.

[0025] As shown in Figure 7, the negative electrode 24 has a negative electrode current collector 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector 24c. A negative electrode protective layer may be further formed at the boundary between the negative electrode current collector 24c and the negative electrode active material layer 24a in the long side direction Y. The negative electrode current collector 24c is strip-shaped. The negative electrode current collector 24c is made of a conductive metal such as copper, copper alloy, nickel, or stainless steel. In this case, the negative electrode current collector 24c is a metal foil, specifically a copper foil.

[0026] Multiple negative electrode tabs 24t are provided at one axial end 21b (right end in Figure 7) of the winding shaft WL of the negative electrode current collector 24c. The multiple negative electrode tabs 24t are provided at intervals (intermittently) along the longitudinal direction of the strip-shaped negative electrode 24. Each of the multiple negative electrode tabs 24t protrudes outward from the separator 26 toward one axial side (right side in Figure 7). However, the negative electrode tabs 24t may also be provided at the other axial end (left end in Figure 7) of the winding shaft WL, or at each of the axial ends. The negative electrode tabs 24t are part of the negative electrode current collector 24c and are made of metal foil (copper foil). However, the negative electrode tabs 24t may be made of a different material from the negative electrode current collector 24c. The negative electrode tabs 24t are rectangular in shape here, but are not limited to this, and may be made of various shapes such as trapezoidal. At least a portion of the negative electrode tab 24t is provided with a region where the negative electrode active material layer 24a is not formed and the negative electrode current collector 24c is exposed.

[0027] As shown in Figure 4, the multiple negative electrode tabs 24t are stacked at one end in the axial direction (the right end in Figure 4) to form a negative electrode tab group 25. The negative electrode tab group 25 includes multiple negative electrode tabs 24t protruding from an end 21b different from the end 21a located in the planar direction along the first side wall 12b (the Y direction in Figure 2). Preferably, the negative electrode tab group 25 is provided in a position symmetrical to the positive electrode tab group 23 in the axial direction. Each of the multiple negative electrode tabs 24t is bent so that its outer end is aligned. This improves the ability to fit into the battery case 10 and allows for miniaturization of the lithium-ion secondary battery 100. As shown in Figure 2, the negative electrode tab group 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collector 60. Specifically, the negative electrode tab group 25 is joined to the negative electrode current collector 60 in a curved state such that at least a portion of the tip of the negative electrode tab group is positioned along one of the pair of second side walls 12c. Therefore, the negative electrode current collector 60 is connected to the negative electrode 24 inside the battery case 10.

[0028] As shown in Figure 2, the second negative electrode current collector 62 is electrically connected to the negative electrode terminal 40 via the first negative electrode current collector 61. Similar to the multiple positive electrode tabs 22t, the sizes of the multiple negative electrode tabs 24t are different so that their outer ends align when curved. As shown in 2, the first negative electrode current collector 61, gasket 90, and external insulating member 92 are fixed to the sealing plate 14. The first negative electrode current collector 61, gasket 90, and external insulating member 92 are fixed to the sealing plate 14, for example, by crimping. The second negative electrode current collector 62 is electrically connected to the negative electrode terminal 40 via the first negative electrode current collector 61.

[0029] As shown in Figure 7, the negative electrode active material layer 24a is provided in a strip shape along the longitudinal direction of the strip-shaped negative electrode current collector 24c. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly absorb and release charge carriers. When the total solid content of the negative electrode active material layer 24a is taken as 100% by mass, the negative electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as binders, dispersants, and various additives. As a binder, for example, rubbers such as styrene-butadiene rubber (SBR) can be used. As a dispersant, for example, celluloses such as carboxymethylcellulose (CMC) can be used.

[0030] As shown in Figure 7, the separator 26 is a component that insulates the positive electrode active material layer 22a of the positive electrode 22 and the negative electrode active material layer 24a of the negative electrode 24. For the separator 26, a porous resin sheet made of polyolefin resin such as polyethylene (PE) or polypropylene (PP) is preferred. Alternatively, the separator 26 may have a base material made of a porous resin sheet and a heat-resistant layer (HRL) containing an inorganic filler, provided on at least one surface of the base material. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titania. Alternatively, the separator 26 may have a base material made of a porous resin sheet and an adhesive layer provided on at least one surface of the base material. Examples of adhesive layers include layers containing PVdF or SBR. Furthermore, the adhesive layer may further contain other components such as inorganic fillers.

[0031] As shown in Figure 2, the positive terminal 30 is insulated from the sealing plate 14 by the positive internal insulating member 70 and the gasket 90. The positive internal insulating member 70 comprises a base portion 70a and a protruding portion 70b interposed between the positive first current collector 51 and the sealing plate 14. The positive terminal 30, exposed to the outside of the battery case 10 through the terminal insertion hole 18, is connected to the positive external conductive member 32 outside the sealing plate 14. On the other hand, the negative terminal 40 is insulated from the sealing plate 14 by the negative internal insulating member 80 and the gasket 90. Similar to the positive internal insulating member 70, the negative internal insulating member 80 also comprises a base portion 80a and a protruding portion 80b interposed between the negative first current collector 61 and the sealing plate 14. The negative electrode terminal 40, exposed to the outside of the battery case 10 through the terminal insertion hole 19, is connected to the negative electrode external conductive member 42 outside the sealing plate 14. An external insulating member 92 is interposed between the positive electrode external conductive member 32 and the negative electrode external conductive member 42 and the sealing plate 14. This external insulating member 92 provides insulation between the external conductive members 32 and 42 and the sealing plate 14.

[0032] The configuration of the lithium-ion secondary battery 100 has been described above. When disassembling the lithium-ion secondary battery 100, for example, the lithium-ion secondary battery 100 is cut at the position indicated by the dashed line F in Figure 2. The dashed line F is located in the long side direction Y between the positive electrode active material layer 22a and the negative electrode active material layer 24a (see Figure 7) and the positive electrode current collector 50 (more specifically, the positive electrode second current collector 52).

[0033] Here, when cutting the lithium-ion secondary battery 100, the actual cutting position may shift slightly from the position of the dashed line F in the long side direction Y due to the influence of the cutting device, etc. If the cutting position is shifted, the cutting tool used for cutting may come into contact with the positive electrode 22 and negative electrode 24 (see Figure 7) of the electrode group 20. Figure 8 shows the state in which the cutting tool CT is in contact with the positive electrode 22 and negative electrode 24. The cutting tool CT is a cutting tool capable of cutting the lithium-ion secondary battery 100, such as an ultrasonic cutter or an electric saw. As shown in Figure 8, when the cutting tool CT comes into contact with the positive electrode 22 and negative electrode 24, a short circuit occurs between the positive electrode 22 and the negative electrode 24. When a short circuit occurs when cutting the lithium-ion secondary battery 100, the area in question will heat up locally. In the disassembly of the lithium-ion secondary battery 100, there was a problem that the heat generated could cause a chain reaction of electrode reactions inside the electrode bodies 20a, 20b, and 20c, making temperature control impossible, resulting in so-called thermal runaway. A method to prevent thermal runaway when the cutting tool CT comes into contact with the positive electrode 22 and the negative electrode 24 has not yet been established.

[0034] Figure 9 is a flowchart showing the procedure for disassembling a lithium-ion secondary battery 100 according to this embodiment. As shown in Figure 9, the disassembly method for a lithium-ion secondary battery 100 according to this embodiment includes a preparation step S1, a charging and discharging step S2, a cutting step S3, and an extraction step S4.

[0035] Preparation step S1 is a step in which a lithium-ion secondary battery 100 is prepared, comprising electrode bodies 20a, 20b, and 20c in which a positive electrode 22 and a negative electrode 24 are superimposed and wound together via a separator 26, a battery case 10 that houses the electrode bodies 20a, 20b, and 20c, a positive electrode current collector 50 connected to the positive electrode 22 inside the battery case 10, and a negative electrode current collector 60 connected to the negative electrode 24 inside the battery case 10. The lithium-ion secondary battery 100 prepared in preparation step S1 may be, for example, a used lithium-ion secondary battery 100. However, the lithium-ion secondary battery 100 prepared in preparation step S1 may be in an unused state.

[0036] The charge-discharge process S2 is a process in which lithium is deposited on the negative electrode 24 by repeatedly charging the lithium-ion secondary battery 100 at a predetermined charge rate and discharging the lithium-ion secondary battery 100 at a predetermined discharge rate a predetermined number of times. In the charge-discharge process S2, for example, an external power supply (not shown) is connected to the lithium-ion secondary battery 100, and the lithium-ion secondary battery 100 is charged and discharged by the external power supply. In this embodiment, the charge-discharge process S2 includes a charging process S21, a first pause process S22, a discharge process S23, and a second pause process S24.

[0037] The charging process S21 is a process for charging the lithium-ion secondary battery 100. In this embodiment, the lithium-ion secondary battery 100 is charged for 25 minutes with a current that results in a C rate of 2, starting from a State of Charge (SOC) of 20%. In the charging process S21, the current is controlled to flow at a higher rate than that of the discharge process S23, which will be described later. In this embodiment, charging is performed at a C rate twice that of the discharge in the discharge process S23, which will be described later. However, the SOC at the start of charging, the C rate, and the charging time in the charging process S21 are not limited to these.

[0038] The first pause step S22 is a step in which the lithium-ion secondary battery 100 is left unattended after the charging step S21 without charging or discharging. In other words, during the first pause step S22, the supply of current to the lithium-ion secondary battery 100 is stopped. In this embodiment, during the first pause step S22, the state in which the supply of current to the lithium-ion secondary battery 100 is stopped is maintained for 30 minutes. However, the time for which the supply of current to the lithium-ion secondary battery 100 is stopped is not limited to this.

[0039] Discharge step S23 is a step in which the lithium-ion secondary battery 100 is discharged. In this embodiment, discharge is performed for 50 minutes with a current that results in a C rate of 1. Here, the C rate in discharge step S23 is half the C rate in charge step S21, and the time required for discharge is twice the charging time in charge step S21. However, the C rate and discharge time in discharge step S23 are not limited to these.

[0040] The second pause step S24 is a step in which the lithium-ion secondary battery 100 is left uncharged after the discharge step S23. That is, in the second pause step S24, the supply of current to the lithium-ion secondary battery 100 is stopped, similar to the first pause step S22. In this embodiment, the state in which the supply of current to the lithium-ion secondary battery 100 is stopped is maintained for 30 minutes during the second pause step S24. However, the duration for which the supply of current to the lithium-ion secondary battery 100 is stopped is not limited to this.

[0041] In this step, the charge / discharge process S2 involves repeatedly charging and discharging the lithium-ion secondary battery 100 when its State of Charge (SOC) is 0% until the capacity retention rate of the lithium-ion secondary battery 100 decreases by 5% or more. In this embodiment, the series of steps from the charge process S21 to the second pause process S24 is considered as one pulse, and 100 pulses of charge / discharge are performed to reduce the capacity retention rate by 5%. However, the number of pulses in the charge / discharge process S2 varies depending on the C rate during charging and / or discharging, and is not particularly limited. The capacity retention rate of the lithium-ion secondary battery 100 is the ratio of the current full charge capacity to the initial full charge capacity of the lithium-ion secondary battery 100, which is set to 100%. Here, "initial" refers to the state of the lithium-ion secondary battery 100 when it is prepared in the preparation process S1. Therefore, the initial capacity retention rate of the lithium-ion secondary battery in this embodiment may be that of a used lithium-ion secondary battery 100 or a lithium-ion secondary battery 100 in an unused state. The capacity retention rate can be measured by conventionally known methods.

[0042] The cutting process S3 is a process in which, after the charging and discharging process S2 has been performed, the connection portion between the current collector and the electrode bodies 20a, 20b, and 20c of the lithium-ion secondary battery 100 is cut. In this embodiment, the connection portion between the positive electrode current collector 50 and the electrode bodies 20a, 20b, and 20c is cut along the dashed line F shown in Figure 2. Here, the position of the dashed line F is 10 mm to the right from the left end of the battery case 10 in the long side direction Y, and passes through the positive electrode tab group 23 and the positive electrode first current collector 51. The dashed line F extends approximately parallel to the vertical direction Z. In the cutting process S3, after the connection portion between the positive electrode current collector 50 and the electrode bodies 20a, 20b, and 20c is cut, the connection portion between the negative electrode current collector 60 and the electrode bodies 20a, 20b, and 20c is also cut in the same manner. For example, the connection between the negative electrode current collector 60 and the electrode bodies 20a, 20b, and 20c (in this case, the negative electrode tab group 25 and the negative electrode first current collector) is severed along the dashed line G shown in Figure 2.

[0043] The disconnection step S3 is performed when the state of charge (SOC) of the lithium-ion secondary battery is in a predetermined low SOC state. In this embodiment, the disconnection step S3 is performed when the SOC is 0%. Therefore, if the SOC is 0% when the charge / discharge step S2 is performed, the disconnection step S3 is performed without charging. Alternatively, if the SOC is greater than 0% when the charge / discharge step S2 is performed, the lithium-ion secondary battery 100 is discharged to 0% before the disconnection step S3 is performed.

[0044] Furthermore, before the cutting process S3, there may be a step to discharge the electrolyte 13 inside the lithium-ion secondary battery 100 to the outside of the battery case 10. The electrolyte 13 can be discharged, for example, by making a hole in the bottom wall 12a of the outer casing 12 and discharging the electrolyte 13 to the outside of the battery case 10 through the hole. However, the method of discharging the electrolyte 13 is not particularly limited.

[0045] The removal step S4 is the step of removing the electrode bodies 20a, 20b, and 20c, which have been cut at the positions of the dashed lines F and G, from the battery case 10, which has also been cut at the positions of the dashed lines F and G. The removal step S4 can be achieved, for example, by pushing the cut electrode bodies 20a, 20b, and 20c to the outside of the battery case 10 using a resin extrusion rod (not shown). However, the method for removing the cut electrode bodies 20a, 20b, and 20c is not limited to this.

[0046] After the flow shown in Figure 8 is completed, the removed electrode bodies 20a, 20b, and 20c are unwound, and the desired electrode material can be recovered from the positive electrode 22 and the negative electrode 24. The method for recovering the electrode material is not particularly limited.

[0047] As described above, the disassembly method for the lithium-ion secondary battery 100 of this embodiment includes a charge / discharge process S2 before the cutting process S3. In the charge / discharge process S2, charging and discharging are repeated according to predetermined charge and discharge rates.

[0048] Here, the lithium ion concentration of the electrolyte 13 inside the battery case 10 of the lithium-ion secondary battery 100 varies depending on its location. Also, when the lithium-ion secondary battery 100 is charged, the negative electrode 24 (more specifically, the negative electrode active material layer 24a) expands, causing the entire electrode body 20a, 20b, and 20c to expand in the short-side direction X. In this embodiment, where the electrode bodies 20a, 20b, and 20c are housed inside the battery case 10 and deformation of the lithium-ion secondary battery 100 in the short-side direction X is restricted, the electrolyte 13 contained between the positive electrode 22, the negative electrode 24, and the separator 26 is pushed out during charging.

[0049] Furthermore, when the lithium-ion secondary battery 100 is discharged, the negative electrode 24 (more specifically, the negative electrode active material layer 24a) contracts, causing the entire electrode bodies 20a, 20b, and 20c to contract in the short-side direction X. At this time, the electrolyte 13 that was pushed out returns to the inside of the electrode bodies 20a, 20b, and 20c. However, if charging is started again before all of the pushed-out electrolyte 13 has returned, the electrolyte 13 is pushed out again. By repeating this process, the movement of the electrolyte 13 cannot keep up with the expansion and contraction of the electrode bodies 20a, 20b, and 20c. Consequently, a concentration gradient is created in the electrolyte 13 inside the battery case 10 (in other words, uneven salt concentration occurs). As a result, the lithium ion concentration in the electrode bodies 20a, 20b, and 20c is high on the inside in the long-side direction Y, and low on the outside in the long-side direction Y (especially at both ends in the long-side direction).

[0050] Here, in the charge-discharge process S2, the C rate of charging in the charging process S21 is 2, and the C rate of discharging in the discharge process S23 is 1. Therefore, the current when the electrolyte 13 is pushed out of the electrodes 20a, 20b, and 20c is greater than the current when the electrolyte 13 returns to the inside of the electrodes 20a, 20b, and 20c. This makes it easy for variations in lithium ion concentration to occur, and lithium deposition to occur. Therefore, when the lithium-ion secondary battery 100 is repeatedly charged and discharged in the charge-discharge process S2, lithium deposition occurs near both ends of the negative electrode 24 in the direction of the long side Y. Figure 10 is a schematic diagram of the area around the negative electrode 24 after the charge-discharge process S2. As shown in Figure 10, lithium 200 is deposited on the surface of the negative electrode 24 at the left end of the negative electrode 24. In Figure 10, only the left end of the negative electrode 24 is shown, but lithium is similarly deposited at the right end of the negative electrode 24.

[0051] As shown in Figure 10, when the cutting tool CT comes into contact with the positive electrode 22 and the negative electrode 24, a short circuit occurs between them. However, the lithium 200 deposited on the surface of the negative electrode 24 provides electrical resistance to the current generated during the short circuit. Therefore, the current flowing between the positive electrode 22 and the negative electrode 24 at this time becomes relatively small. As a result, the heat generated during the short circuit is relatively small. Thus, even if heat is generated in the cutting process S3, the generation of heat can be suppressed to the extent that a chain reaction of electrode reactions occurs inside the electrode bodies 20a, 20b, and 20c. Therefore, even when the cutting tool CT comes into contact with the positive electrode 22 and the negative electrode 24, thermal runaway does not occur, and heat generation inside the lithium-ion secondary battery 100 can be suppressed.

[0052] The following describes examples relating to the present invention, but it is not intended to limit the invention to the examples relating to the present invention.

[0053] First, a lithium-ion secondary battery was prepared for each example. In this lithium-ion secondary battery, a wound electrode body, with the positive and negative electrodes interposed by a separator, is housed in an outer casing. A sealing plate is attached to the outer casing containing the electrode body. In the following embodiments, unused lithium-ion secondary batteries were used. NCM622 was used as the nickel-cobalt-manganese composite oxide, which is the positive electrode active material. Here, the full charge capacity of the lithium-ion secondary battery is 200 Ah.

[0054] Next, charging and discharging were performed on the lithium-ion secondary batteries of Examples 2, 4, 6, 7, 8, and 9. The charging and discharging was performed for a predetermined number of pulses, each consisting of a 25-minute CC charge with a current that results in a C-rate of 2 (i.e., 400A), followed by a 30-minute rest, and a 50-minute CC discharge with a current that results in a C-rate of 1 (i.e., 200A), followed by a 30-minute rest. The predetermined number of pulses was determined so that the capacity retention rate after charging and discharging would be a predetermined value. The respective capacity retention rates are shown in Table 1 below.

[0055] [Table 1]

[0056] The lithium-ion secondary battery shown in Example 2 underwent a number of charge-discharge pulses that resulted in a capacity retention rate of 95% after charging and discharging. Similarly, in Examples 4, 6, 7, 8, and 9, the charge-discharge cycle was repeated so that the capacity retention rates after charging and discharging were 94%, 95%, 93%, and 85%, respectively. The lithium-ion secondary batteries in Examples 1, 3, and 5 did not undergo charge-discharge pulses. That is, the capacity retention rates for Examples 1, 3, and 5 are 100%.

[0057] Next, the lithium-ion secondary batteries in Examples 1, 2, 7, 8, and 9 were discharged so that their cell voltage was 3V. In this embodiment, the lithium-ion secondary batteries have a State of Charge (SOC) of 0% at 3V. Furthermore, the lithium-ion secondary batteries in Examples 3 and 4 were charged or discharged so that their cell voltage was 3.35V. In this case, the SOC at a cell voltage of 3.35V is 4%. Finally, the lithium-ion secondary batteries in Examples 5 and 6 were charged or discharged so that their cell voltage was 3.52V. The SOC at a cell voltage of 3.52V is 13%.

[0058] Subsequently, nail-piercing tests were performed on the lithium-ion secondary batteries of Examples 1 to 9. In these tests, the nail-piercing test was conducted at a position 10 mm inward from the positive terminal end on the long side of the sealing plate of the lithium-ion secondary batteries of Examples 1 to 9. The nail-piercing test forced a short circuit. The cell surface temperature of the lithium-ion secondary battery at this time was measured using a thermocouple, and the highest temperature recorded was recorded. Cell surface temperature refers to the temperature of the outer surface of the lithium-ion secondary battery. Here, the temperature was measured at a position close to the nail-piercing location across the entire outer surface of the lithium-ion secondary battery, and the highest temperature was recorded. The results are shown in Table 1. Furthermore, after the nail-piercing test, the battery case of the lithium-ion secondary battery was disassembled to check whether the electrode separator had melted. The results are shown in Table 1 below.

[0059] Comparing Examples 1 and 2 with Examples 3 and 4, Examples 2 and 4 show lower cell outer surface temperatures compared to Examples 1 and 3, respectively. In other words, in Examples 2 and 4, heat generation during the nail-piercing test (short circuit) is suppressed. In Examples 1 and 3, the capacity retention rate is 100%, so no charge / discharge pulses are performed on the lithium-ion secondary battery before the nail-piercing test. That is, lithium deposition does not occur. On the other hand, in Examples 2 and 4, the capacity retention rate is 94-95%, charge / discharge pulses are performed, and lithium deposition occurs. Therefore, the lithium deposited on the negative electrode reduces the current during a short circuit, suppressing heat generation during a short circuit. Furthermore, in Examples 2 and 4, the separator does not melt after the nail-piercing test. From this, it can be seen that heat generation during a short circuit is suppressed, thermal runaway does not occur, and heat generation inside the lithium-ion secondary battery is suppressed.

[0060] The melting point of the separator used in lithium-ion secondary batteries is approximately 130°C. Therefore, in Table 1, for those where the separator is not melted, the internal temperature of the battery case is estimated to be 140°C or lower. In Table 1, for those where the separator is melted, the internal temperature of the battery case is estimated to be 140°C or higher during the nail-piercing test.

[0061] Comparing Examples 2, 4, and 6, even if charging and discharging are performed before the nail-piercing test, the higher the cell voltage during the nail-piercing test, the higher the cell outer surface temperature. Also, in Examples 2 and 4, the separator does not melt, but in Example 6, the separator melts. Therefore, the higher the cell voltage when a short circuit occurs, the greater the amount of heat generated. Consequently, by cutting the battery case when the State of Charge (SOC) of the lithium-ion secondary battery is in a predetermined low SOC state, heat generation can be further suppressed even when a short circuit occurs. In this embodiment, since the SOC at a cell voltage of 3.35V is 4% or less, it is preferable to keep the SOC of the lithium-ion secondary battery 100 at 4% or less when cutting the battery case of the lithium-ion secondary battery.

[0062] Furthermore, comparing Examples 2, 4, and 6, the cell outer surface temperature is lowest in Example 2. Therefore, because the State of Charge (SOC) of the lithium-ion secondary battery is 0% when a short circuit occurs, heat generation can be suppressed to the greatest extent.

[0063] Figure 11 is a graph based on the results of Examples 2, 4, and 6, with the discharge capacity until the cell voltage reaches 0V on the horizontal axis and the temperature rise on the vertical axis. The temperature rise refers to the temperature rise during the nail-piercing test. The temperature rise is calculated from the difference between the cell outer surface temperature and the room temperature, as shown in Table 1. Points P1, P2, and P3 correspond to Examples 2, 4, and 6 in Table 1, respectively. Therefore, point P1 plots the relationship between the discharge capacity from a cell voltage of 3V until the cell voltage reaches 0V and the temperature rise in Example 2. The same applies to points P2 and P3. The discharge capacity until the cell voltage reaches 0V may be an estimated value or a measured value. Curve CL is an approximate curve obtained based on points P1, P2, and P3. From the general shape of curve CL, it can be considered that the temperature rise increases quadratically with respect to the discharge capacity up to 0V. Here, the amount of heat generated when current flows is proportional to the square of the current value. Therefore, the temperature rise is considered to increase quadratically with respect to the discharge capacity up to 0V. Thus, the curve CL is considered to be a quadratic curve.

[0064] Comparing Example 2 and Example 7, Example 2 has a 3% lower capacity retention rate and a 19°C lower cell outer surface temperature than Example 7. Therefore, when comparing Example 2 and Example 7, it can be said that the cell outer surface temperature decreases by approximately 6.3°C for every 1% increase in capacity retention rate. Also, in Example 2, the separator does not melt, but in Example 7, the separator does melt. Therefore, even if charging and discharging of the lithium-ion secondary battery is performed before the nail-piercing test, if the capacity retention rate is relatively high, as in Example 7 (in this case, 98% capacity retention rate), the heat generated inside the lithium-ion secondary battery remains relatively high.

[0065] Furthermore, comparing Example 2 and Example 8, Example 8 has a 2% lower capacity retention rate and a 1°C lower cell outer surface temperature compared to Example 2. Therefore, when comparing Example 2 and Example 8, the change in cell outer surface temperature per 1% of capacity retention rate is 0.5°C. Also, comparing Example 8 and Example 9, Example 9 has an 8% lower capacity retention rate and a 2°C lower cell outer surface temperature compared to Example 8. Therefore, when comparing Example 8 and Example 9, the change in cell outer surface temperature per 1% of capacity retention rate is 0.25°C. When comparing Example 2 and Example 8, or Example 2 and Example 9, the degree of decrease in cell outer surface temperature in relation to the decrease in capacity retention rate is smaller than when comparing Example 2 and Example 7. Therefore, it is considered that even if the capacity retention rate is further reduced, the change in cell outer surface temperature will be small. Accordingly, it is considered that by repeatedly charging and discharging the lithium-ion secondary battery so that the capacity retention rate decreases by 5% or more before the lithium-ion secondary battery is cut off, the heat generation inside the lithium-ion secondary battery can be sufficiently suppressed.

[0066] In the embodiment described above, unused lithium-ion secondary batteries were used. However, when recycling lithium-ion secondary batteries, it is assumed that used lithium-ion secondary batteries will be used. Used lithium-ion secondary batteries have a lower discharge capacity compared to unused lithium-ion secondary batteries. Therefore, it is expected that using used lithium-ion secondary batteries will result in less heat generation than in the embodiment described above.

[0067] In the above-described embodiment, NCM622 was used as the positive electrode active material. However, the positive electrode active material may also be NCM811 or NCM111. The reason why heat generation can be suppressed is, as mentioned above, because lithium is deposited on the surface of the negative electrode due to variations in lithium ion concentration. Therefore, even with lithium-ion secondary batteries using NCM811 or NCM111, the cell outer surface temperature during a short circuit can be similarly reduced.

[0068] The invention disclosed herein has been described in various ways. Unless otherwise specified, the embodiments and other details described herein do not limit the present invention. Furthermore, the embodiments of the invention disclosed herein can be modified in various ways, and each component and each process mentioned herein can be omitted or combined as appropriate, unless no particular problems arise.

[0069] As described above, this specification includes the disclosures set forth in the following sections.

[0070] Section 1: A preparation step for a lithium-ion secondary battery comprising: a wound electrode body in which a positive electrode and a negative electrode are superimposed and wound together via a separator; a battery case for housing the wound electrode body; a positive electrode current collector terminal connected to the positive electrode inside the battery case; and a negative electrode current collector terminal connected to the negative electrode inside the battery case; A charge-discharge process in which the lithium-ion secondary battery is charged at a predetermined charge rate and the lithium-ion secondary battery is discharged at a predetermined discharge rate, and this process is repeated a predetermined number of times to deposit lithium on the negative electrode, After the charging and discharging process is performed, a cutting process is performed to cut the connection portion between the positive electrode current collector terminal or the negative electrode current collector terminal and the wound electrode body of the lithium-ion secondary battery, This includes methods for disassembling lithium-ion rechargeable batteries.

[0071] Section 2: The method for dismantling a lithium-ion secondary battery according to item 1, wherein the cutting step is performed when the State of Charge (SOC) of the lithium-ion secondary battery is in a predetermined low SOC state.

[0072] Section 3: The method for disassembling a lithium-ion secondary battery according to item 2, wherein the low SOC state is a state in which the SOC is 0%.

[0073] Section 4: The method for disassembling a lithium-ion secondary battery according to any one of items 1 to 3, wherein the charging and discharging process is repeated when the State of Charge (SOC) of the lithium-ion secondary battery is at 0%, until the capacity retention rate of the lithium-ion secondary battery decreases by 5% or more. [Explanation of Symbols]

[0074] 1 Joint 10 Battery Case 12 Exterior 12a Bottom wall 12h opening 13 Electrolyte 14 Sealing plate 15 Liquid injection hole 16 Sealing member 17 Gas discharge valve 18, 19 Terminal insertion holes 20 Electrode group 20a,20b,20c electrode body 20f flat area 20r curved section 21a, 21b end 22 Positive electrode 22a Cathode active material layer 22c Positive electrode current collector 22p positive electrode protective layer 22t positive electrode tab 23 Positive electrode tab group 24 Negative electrode 24a Negative electrode active material layer 24c Negative electrode current collector 24t negative electrode tab 25 Negative electrode tab group 26 Separators 29 Electrode holder 30 Positive terminal 32 Positive electrode external conductive member 40 Negative terminal 42 Negative electrode external conductive member 50 Positive electrode current collector 51 Positive electrode first current collector 52 Positive electrode second current collector 60 Negative electrode current collector 61 Negative electrode first current collector 62 Negative electrode second current collector 70 Positive electrode internal insulating material 70a Base section 70b Protrusion 80 Negative electrode internal insulating material 80a Base section 80b Protrusion 90 Gasket 92 External insulating material 100 Lithium-ion rechargeable batteries 200 Lithium CL curve CT cutting tool S1 Preparation Process S2 charge / discharge process S21 Charging process S22 1st pause process S23 Discharge process S24 2nd pause process S3 cutting process S4 Extraction process WL winding shaft

Claims

1. Preparation steps for preparing a lithium-ion secondary battery comprising: a wound electrode body in which a positive electrode and a negative electrode are superimposed and wound together via a separator; a battery case for housing the wound electrode body; a positive electrode current collector connected to the positive electrode inside the battery case; and a negative electrode current collector connected to the negative electrode inside the battery case; A charge-discharge process in which the lithium-ion secondary battery is charged at a predetermined charge rate and the lithium-ion secondary battery is discharged at a predetermined discharge rate, and this process is repeated a predetermined number of times to deposit lithium on the negative electrode, After the charging and discharging process is performed, a cutting process is performed to cut the connection portion between the positive electrode current collector or the negative electrode current collector and the wound electrode body of the lithium-ion secondary battery, This includes methods for disassembling lithium-ion rechargeable batteries.

2. The method for dismantling a lithium-ion secondary battery according to claim 1, wherein the cutting step is performed when the State of Charge (SOC) of the lithium-ion secondary battery is in a predetermined low SOC state.

3. The method for disassembling a lithium-ion secondary battery according to claim 2, wherein the low SOC state is a state in which the SOC is 0%.

4. The method for disassembling a lithium-ion secondary battery according to claim 1, wherein the charging and discharging process is repeated when the State of Charge (SOC) of the lithium-ion secondary battery is at 0%, until the capacity retention rate of the lithium-ion secondary battery decreases by 5% or more.

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