How to dismantle an energy storage device

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 charge-discharge step S2 in which the lithium-ion secondary battery is repeatedly charged and discharged in a predetermined low voltage range to break down the crystal structure of the nickel-cobalt-manganese composite oxide, and a cutting step S3 after the charge-discharge step S2 in which the connection portion between the positive electrode terminal or negative electrode terminal and the electrode body is cut.

Description

[Technical Field]

[0001] The present invention relates to a method for dismantling an energy storage device. [Background technology]

[0002] Japanese Patent Publication No. 2016-46209 discloses a battery equipped with a structure for discharging used batteries. This discharge is performed as a pretreatment for recycling used batteries. In such a battery, a metal member is embedded in the battery case. By bringing a coil connected to an AC power source close to the metal member, the coil is inductively heated, and the battery case melts. When the battery case melts, an opening is formed in the battery case. By injecting saltwater through this opening, the battery can be completely discharged. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-46209 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] Incidentally, the inventor of this application is considering cutting the battery case, removing the electrode body, disassembling it, and recycling it. According to the inventor's knowledge, they want to suppress the heat generated inside the energy storage device when it is cut. [Means for solving the problem]

[0005] A method for disassembling a lithium-ion secondary battery disclosed herein includes a preparation step of preparing an energy storage device comprising an electrode body having a positive electrode, a negative electrode, and a separator, having a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide; a battery case housing the 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 and discharging the energy storage device in a predetermined low voltage range to break the crystal structure of the nickel-cobalt-manganese composite oxide; and a cutting step of cutting the connection portion between the positive electrode current collector or the negative electrode current collector and the electrode body of the energy storage device after the charge-discharge step has been performed.

[0006] According to the method for disassembling an energy storage device disclosed herein, heat generation of the energy storage device can be suppressed when the energy storage device is disconnected. [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 graph showing the relationship between the reaction resistance of the positive electrode and the positive electrode potential. [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, "energy storage device" refers to a device in which charging and discharging occur through the movement of a charge carrier between a pair of electrodes (positive electrode and negative electrode) via an electrolyte. Energy storage devices include secondary batteries such as lithium-ion secondary batteries, nickel-metal hydride batteries, and nickel-cadmium batteries; and capacitors such as lithium-ion capacitors and electric double-layer capacitors. The following describes embodiments in which the energy storage device is a lithium-ion secondary battery.

[0010] 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.

[0011] First, the configuration of the lithium-ion secondary battery 100 according to this embodiment will be described. FIG. 1 is a perspective view of the lithium-ion secondary battery 100. FIG. 2 is a schematic longitudinal sectional view taken along line II-II of FIG. 1. FIG. 3 is a schematic longitudinal sectional view taken along line III-III of FIG. 1. FIG. 4 is a schematic cross-sectional view taken along line IV-IV of FIG. 1. In the following description, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom, respectively, and the symbols X, Y, and Z in the drawings represent the short-side direction, the long-side direction orthogonal to the short-side direction (also referred to as the longitudinal direction of the electrode body), and the vertical direction of the lithium-ion secondary battery 100, respectively. However, these are merely directions for convenience of explanation and do not limit the installation form of the lithium-ion secondary battery 100 in any way.

[0012] As shown in FIG. 2, the lithium-ion secondary battery 100 includes 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 further includes 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 includes an electrolytic solution 13. The internal resistance of the lithium-ion secondary battery 100 can be, for example, about 0.2 to 2.0 mΩ.

[0013] The battery case 10 is a housing that houses the electrode body group 20. Here, the battery case 10 has an outer shape of a flat and bottomed rectangular parallelepiped shape (rectangular). The material of the battery case 10 may be the same as that conventionally used, and there is no particular limitation. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. Further, the battery case 10 includes an exterior body 12, a sealing plate 14, and a gas discharge valve 17. The exterior body 12 is a flat rectangular container with one surface being an opening 12h. Specifically, as shown in FIG. 1, the exterior body 12 includes a substantially rectangular bottom wall 12a, a pair of first side walls 12b that extend upward U from the short sides of the bottom wall 12a and face each other, and a pair of second side walls 12c that extend upward U from the long sides of the bottom wall 12a and face each other. The area of the first side wall 12b is larger than the area of the second side wall 12c. And the opening 12h (see FIG. 2) is formed on the upper surface of the exterior body 12 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 exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 is a plate material having a substantially rectangular shape in plan view. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The battery case 10 is formed by joining (for example, welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12. The joining of the sealing plate 14 can be performed by welding such as laser welding.

[0014] As shown in FIGS. 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 becomes a predetermined value or more and discharge the gas inside the battery case 10. Further, in addition to the gas discharge valve 17, a liquid injection hole 15 and two terminal insertion holes 18 and 19 are provided in the sealing plate 14. The liquid injection hole 15 communicates with the internal space of the exterior body 12 and is an opening provided for injecting the electrolytic solution 13 in the manufacturing process of the lithium ion secondary battery 100. The liquid injection hole 15 is sealed by a sealing member 16. As such a sealing member 16, for example, a blind rivet is suitable. Thereby, the sealing member 16 can be firmly fixed inside the battery case 10.

[0015] Figure 5 is a schematic perspective view showing the electrode group 20 attached to the sealing plate 14 before mating. In this embodiment, multiple (in this case, three) electrode bodies 20a, 20b, and 20c are housed inside the battery case 10 (see Figure 1). The number of electrode bodies housed inside one battery case 10 is not particularly limited; there may be one or two or more. As shown in Figure 2, a positive electrode current collector 50 is located on one side of the long side direction Y (left side in Figure 2) of each electrode body, and a negative electrode current collector 60 is located on the other side of the long side direction Y (right side in Figure 2). As shown in Figure 5, each of the electrode bodies 20a, 20b, and 20c is connected in parallel. However, the electrode bodies 20a, 20b, and 20c may also be connected in series. The electrode bodies 20a, 20b, and 20c are housed inside the outer casing 12 of the battery case 10, covered by an electrode body holder 29 (see Figure 3) made of a resin sheet. Furthermore, as shown in Figure 5, in the lithium-ion secondary battery 100 according to this embodiment, the separator 26 on which the junction portion 1 is formed is located predominantly on the side of the positive electrode tab group 23 where the curvature is gentler (in other words, the bent portion of the positive electrode tab group 23).

[0016] Figure 6 is a schematic perspective view of electrode body 20a. Figure 7 is a schematic diagram showing the configuration of electrode body 20a. In the following, electrode body 20a will be used as an example to explain in detail, but electrodes 20b and 20c can be configured similarly.

[0017] As shown in Figure 7, the electrode body 20a has a positive electrode 22, a negative electrode 24, and a separator 26. In this case, 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 stacked with two strip-shaped separators 26 in between, and wound around a winding axis WL. Such a wound electrode body has a positive-negative electrode stacked structure in which multiple positive electrodes 22 and negative electrodes 24 are stacked with separators 26 in between. However, the structure of the electrode body 20a is not particularly limited and may be other conventionally known structures (such as a stacked electrode body).

[0018] The electrode body 20a has a flattened shape. The electrode body 20a is positioned inside the outer casing 12 (see Figure 1) with the winding axis WL oriented substantially parallel to the long side direction Y. Specifically, as shown in Figure 3, the electrode body 20a has a pair of curved portions (R portions) 20r facing the bottom wall 12a and sealing plate 14 of the outer casing 12, and a flat portion 20f connecting the pair of curved portions 20r and facing the second side wall 12c (see Figure 1) of the outer casing 12. The flat portion 20f extends along the second side wall 12c.

[0019] As shown in Figure 2, the electrolyte 13 is housed inside the battery case 10 together with the electrodes 20a, 20b, and 20c. A portion of the electrolyte 13 impregnates the electrodes 20a, 20b, and 20c. The electrolyte 13 is a non-aqueous electrolyte containing, for example, a non-aqueous solvent (organic solvent) and a supporting salt (electrolyte salt, such as a lithium salt or sodium salt). Examples of non-aqueous solvents include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. An example of a supporting salt is a fluorine-containing lithium salt such as lithium hexafluoride phosphate (LiPF6). The electrolyte 13 is typically liquid, but may also be gel-like.

[0020] As shown in Figure 7, the positive electrode 22 includes a positive electrode current collector 22c and a positive electrode active material layer 22a and a positive electrode protective layer 22p fixed to 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, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode current collector 22c is a metal foil, specifically an aluminum foil.

[0021] 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.

[0022] 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.

[0023] As shown in FIG. 2, the first positive electrode current collector 51, the gasket 90, and the external insulating member 92 are fixed to the sealing plate 14. The first positive electrode current collector 51, the gasket 90, and the external insulating member 92 are fixed to the sealing plate 14 by, for example, caulking. The second positive electrode current collector 52 is electrically connected to the positive electrode terminal 30 via the first positive electrode current collector 51. Note that the sizes of the plurality of positive electrode tabs 22t (the length along the long side direction Y and the width orthogonal to the long side direction Y, see FIG. 7) can be appropriately adjusted depending on, for example, the formation position and the like in consideration of the state of being connected to the positive electrode current collector portion 50. Here, the sizes of the plurality of positive electrode tabs 22t are different from each other so that the outer ends are aligned when curved.

[0024] As shown in FIG. 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 capable of reversibly occluding and releasing charge carriers. Here, the positive electrode active material is a nickel cobalt manganese-based composite oxide. The crystal structure of the positive electrode active material is, for example, a layered structure. In the present specification, the "nickel cobalt manganese-based composite oxide" is a term that includes, in addition to oxides having Ni, Co, Mn, and O as constituent elements, oxides containing one or more additional elements other than these. Examples of the additional elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, and typical metal elements. The additional elements may be semi-metal elements such as B, C, Si, P; non-metal elements such as S, F, Cl, Br, I. In the present embodiment, from the viewpoints of energy density and capacity retention rate, as the nickel cobalt manganese-based composite oxide, LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), or LiNi 0.33 Co 0.33 Mn 0.33 O2 (NCM111) can be preferably used. Note that as the nickel cobalt manganese-based composite oxide, LiNi0.5 Co 0.2 Mn 0.3 O2 or similar substances may also be used.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] In this embodiment, the positive electrode 22 and the negative electrode 24 are formed such that the opposing capacitance ratio between the positive electrode 22 and the negative electrode 24 is in the range of 1.0 or more and 1.2 or less. Here, the opposing capacitance ratio is the theoretical capacity per unit area (mAh / cm²) of the positive electrode 22. 2 The theoretical capacity per unit area of ​​the negative electrode 24 (mAh / cm²) 2 This is the ratio (theoretical capacity of the negative electrode / theoretical capacity of the positive electrode), and typically, for the opposing portion where the positive electrode active material layer 22a and the negative electrode active material layer 24a face each other, the following formula applies: Opposing capacity ratio = {Mass of negative electrode active material per unit area of ​​negative electrode 24 (g / cm³) 2 ) × Theoretical capacitance of the negative electrode active material (mAh / g) / {Mass of the positive electrode active material per unit area of ​​the positive electrode (g / cm²) 2This value is obtained by {) × theoretical capacitance of positive electrode active material (mAh / g)}. Note that the theoretical capacitance (or method for calculating it) of the positive electrode active material and the negative electrode active material are publicly known; for example, the theoretical capacitance of graphite is 372 mAh / g. Furthermore, it is preferable that the mass of the positive electrode active material and the mass of the negative electrode active material per unit area are the average values ​​in the region where the positive electrode 22 and the negative electrode 24 face each other.

[0033] 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.

[0034] 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.

[0035] 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).

[0036] 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.

[0037] 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.

[0038] Preparation step S1 is a step in which a lithium-ion secondary battery 100 is prepared, comprising electrode bodies 20a, 20b, and 20c having a positive electrode 22, a negative electrode 24, and a separator 26, each having a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide; a battery case 10 housing 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, for example, be 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.

[0039] The charge-discharge process S2 is a process in which the lithium-ion secondary battery 100 is repeatedly charged and discharged in a predetermined low voltage range to break down the crystalline structure of the nickel-cobalt-manganese composite oxide. 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 this external power supply. The positive electrode 22 has a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide. Therefore, when charging and discharging are repeatedly performed in a low voltage range and the surface of the positive electrode 22 becomes lithium-rich, crystals with a rock salt-type structure of NiO and MnO are formed, and the crystalline structure of the nickel-cobalt-manganese composite oxide is broken down. The charge-discharge process S2 may be carried out in a room temperature environment (for example, around 25°C ± 10°C or 25°C ± 5°C) or in a high temperature environment (for example, around 45°C).

[0040] In this embodiment, one cycle consists of charging until the cell voltage reaches 3.5V, followed by discharging until the cell voltage reaches 0.9V. This cycle is repeated multiple times. That is, the low voltage range in this embodiment is 0.9V to 3.5V. The charge / discharge process S2 is repeated until the capacity retention rate of the lithium-ion secondary battery 100 is 97% or less. In this embodiment, when the cell voltage is 3.5V, the positive electrode potential is 3.7V (vsLi+ / Li). That is, the voltage at which the positive electrode potential is 3.7V (vsLi+ / Li) is set as the upper limit of the charging voltage.

[0041] The capacity retention rate of the lithium-ion secondary battery 100 is the ratio of the current discharge capacity to the initial discharge 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 preparation step 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 charge / discharge process S2 is terminated when the discharge capacity of the lithium-ion secondary battery 100 during the above cycle execution falls below 97% of the discharge capacity of the lithium-ion secondary battery 100 when it is prepared in preparation step S1. The C rate during charging and discharging in the charge / discharge process S2 is not particularly limited, but is, for example, about 0.5C. 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] 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.

[0044] 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.

[0045] After the flow shown in Figure 9 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.

[0046] 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, the lithium-ion secondary battery 100 is repeatedly charged and discharged in a predetermined low voltage range. In this embodiment, in the charge / discharge process S2, charging and discharging are repeated in a low voltage range of cell voltage from 0.9 to 3.5V.

[0047] Incidentally, the inventors of this invention investigated the relationship between the reaction resistance of the positive electrode and the positive electrode potential in a lithium-ion secondary battery. The results are shown in Figure 10. Figure 10 is a graph showing the relationship between the reaction resistance of the positive electrode and the positive electrode potential. The vertical axis of the graph in Figure 10 shows "reaction resistance (%)", and shows the relative value when the reaction resistance at a positive electrode potential of 3.8V (vs. Li+ / Li) is set to 100%. The horizontal axis of the graph in Figure 10 shows "positive electrode potential (V (vs. Li+ / Li))". Figure 10 shows that the reaction resistance of the positive electrode increases as the positive electrode potential decreases. It is shown that the reaction resistance at the positive electrode is even higher when the positive electrode potential is below 3.7V (vs. Li+ / Li) than when the positive electrode potential is 3.7V (vs. Li+ / Li) or higher.

[0048] In this embodiment, during the charge-discharge process S2, charging and discharging are repeated in a low-voltage region of 0.9 to 3.5V. At this time, the positive electrode potential is less than 3.7V (vs. Li+ / Li). When the positive electrode potential is less than 3.7V (vs. Li+ / Li), there is an excess of lithium on the surface of the positive electrode 22. According to the inventors' findings, the positive electrode 22 has a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide, and when the positive electrode battery becomes low-potential, as described above, rock salt-type crystals of NiO and MnO are formed. For example, when the positive electrode potential falls below 2V, rock salt-type crystals of NiO and MnO are formed on the surface of the positive electrode. The formed rock salt-type crystals are poorly reversible. As a result, the discharge capacity of the lithium-ion secondary battery 100 decreases and the reaction resistance increases. In this embodiment, during the charge-discharge process S2, charging and discharging are performed in the cell voltage range of 0.9 to 3.5V. At this point, the positive electrode potential is less than 3.7V (vs. Li+ / Li).

[0049] As shown in Figure 8, when the cutting tool CT comes into contact with the positive electrode 22 and the negative electrode 24, a short circuit occurs between the positive electrode 22 and the negative electrode 24. However, as described above, the charging and discharging process S2 generates rock salt-type crystals on the surface of the positive electrode 22, increasing the reaction resistance of the lithium-ion secondary battery 100. This makes it possible to relatively reduce the heat generated during a short circuit. Therefore, even if heat is generated in the cutting process S3, the generation of such heat can be suppressed to the extent that a chain reaction of electrode reactions occurs inside the electrode bodies 20a, 20b, and 20c. Consequently, thermal runaway does not occur even when the cutting tool CT comes into contact with the positive electrode 22 and the negative electrode 24, and heat generation inside the lithium-ion secondary battery 100 can be suppressed.

[0050] 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.

[0051] First, lithium-ion secondary batteries were prepared for Examples 1 to 11. In these lithium-ion secondary batteries, a wound electrode body, in which the positive and negative electrodes are wound with a separator in between, 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 prepared. Here, the full charge capacity of the lithium-ion secondary battery is 200 Ah. NCM622 was used as the nickel-cobalt-manganese composite oxide, which is the positive electrode active material. Furthermore, in each example of the lithium-ion secondary battery, the positive and negative electrodes are formed such that the opposing capacity ratio is between 1.0 and 1.2.

[0052] Next, a cycle test was performed on the lithium-ion secondary batteries of Examples 2, 3, 5, 6, 8, 9, 10, and 11, involving repeated charging and discharging. The cycle test voltages, which are the lower and upper limits of the cell voltage during the cycle test, are shown in Table 1 below.

[0053] [Table 1]

[0054] As shown in Table 1, for lithium-ion secondary batteries in Examples 2, 5, and 8, a cycle test was performed in which a charge-discharge operation was performed in which CC charging was performed until the voltage between the positive and negative electrodes reached 4.25V, and then CC discharging was performed in which the voltage between the positive and negative electrodes reached 3.5V, and this cycle of CC charging and CC discharging was repeated. For lithium-ion secondary batteries in Examples 3, 6, 9, 10, and 11, a cycle test was performed in which a charge-discharge operation was performed in which a charge-discharge operation was performed in which the voltage between the positive and negative electrodes reached 3.5V, and then CC discharging was performed in which the voltage between the positive and negative electrodes reached 0.9V, and this cycle of CC charging and CC discharging was repeated. Note that no cycle test was performed on lithium-ion secondary batteries in Examples 1, 4, and 7. The above cycle test was repeated in Examples 2, 3, 5, 6, 8, and 9 until it was confirmed that the capacity retention rate of the lithium-ion secondary battery was 97% or less. The capacity retention rate is the ratio of the discharge capacity after the cycle test to the discharge capacity of the lithium-ion secondary battery before the cycle test, which is set to 100%. In Examples 2, 3, 5, 6, 8, and 9, the lithium-ion secondary batteries have a capacity retention rate of 97% or 96%. In Example 10, the cycle test was repeated until the lithium-ion secondary battery's capacity retention rate reached 93%. In Example 11, the cycle test was repeated until the lithium-ion secondary battery's capacity retention rate reached 99%.

[0055] Next, the short-circuit starting cell voltage of the lithium-ion secondary batteries was adjusted. The short-circuit starting cell voltage is the cell voltage when performing the nail-piercing test described later. The lithium-ion secondary batteries in Examples 1, 2, and 3 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. The lithium-ion secondary batteries in Examples 4, 5, and 6 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%. The lithium-ion secondary batteries in Examples 7, 8, 9, 10, and 11 were charged or discharged so that their cell voltage was 3.52V. The SOC at a cell voltage of 3.52V is 18%.

[0056] Subsequently, nail-piercing tests were performed on the lithium-ion secondary batteries of Examples 1 to 11. 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 11. The nail-piercing action 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.

[0057] Comparing Examples 1, 2, and 3, the cell outer surface temperature decreases in the order of Example 3, Example 2, and Example 1. This indicates that the reaction resistance is greater in the order of Example 3, Example 2, and Example 1, and that heat generation during the nail-piercing test (short circuit) is suppressed in Examples 2 and 3 compared to Example 1. Therefore, it is considered that the crystal structure on the positive electrode surface changes in Examples 2 and 3 due to the cycle test performed before the nail-piercing test. Here, in Examples 2 and 3, the cycle test was performed at a lower voltage in Example 3. Therefore, it is considered that more changes in the crystal structure occurred in Example 3 compared to Example 2, resulting in a greater decrease in the cell outer surface temperature. Thus, by repeatedly charging and discharging in the low voltage range, heat generation during lithium-ion secondary battery disconnection can be suppressed.

[0058] Similarly, when comparing Examples 4, 5, and 6, the cell outer surface temperature is lowest in Example 6, which was cycled at a low voltage. Similarly, when comparing Examples 7, 8, and 9, the cell outer surface temperature is lowest in Example 9, which was cycled at a low voltage. Furthermore, when comparing Examples 3, 6, and 9, the cell outer surface temperature decreases in the order of Example 3, Example 6, and Example 9. This is thought to be because a lower short-circuit initiation cell voltage results in a smaller current during a short circuit.

[0059] Comparing Example 9 and Example 10, Example 9 has a capacity retention rate of 97%, while Example 10 has a capacity retention rate of 93%. Therefore, Example 10 has a 4% lower capacity retention rate than Example 9. The difference in cell outer surface temperature between Example 9 and Example 10 is 5°C. On the other hand, comparing Example 9 and Example 11, Example 9 has a capacity retention rate of 97%, while Example 11 has a capacity retention rate of 99%. Therefore, Example 11 has a 2% lower capacity retention rate than Example 9. The difference in cell outer surface temperature between Example 9 and Example 11 is 73°C. Therefore, it is considered that by performing cycle tests so that the capacity retention rate of the lithium-ion secondary battery is 97% or less, the degree of decrease in the cell outer surface temperature is relatively large, and the effects of the present invention can be more favorably obtained.

[0060] In the above-described embodiment, 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 above-described embodiment.

[0061] 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 that, as described above, there is an excess of lithium on the surface of the positive electrode, and a rock salt-type crystal structure is formed. Therefore, even with lithium-ion secondary batteries using NCM811 or NCM111, the cell outer surface temperature during a short circuit can be similarly reduced.

[0062] 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.

[0063] As described above, this specification includes the disclosures set forth in the following sections.

[0064] Section 1: Preparation steps for preparing an energy storage device comprising: an electrode body having a positive electrode, a negative electrode, and a separator, each having a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide; a battery case housing the 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 energy storage device is repeatedly charged and the lithium-ion secondary battery is discharged in a predetermined low voltage range, thereby breaking down the crystal structure of the nickel-cobalt-manganese composite oxide, A method for dismantling an energy storage device, which includes a cutting step of cutting the connection portion between the positive electrode current collector or the negative electrode current collector and the electrode body after the charging and discharging step has been performed.

[0065] Section 2: The method for dismantling an energy storage device according to item 1, wherein the nickel-cobalt-manganese composite oxide is NCM811, NCM622, or NCM111.

[0066] Section 3: The method for dismantling an energy storage device according to item 1 or 2, wherein the opposing capacitance ratio, which is the ratio of the capacitance of the negative electrode to the capacitance of the positive electrode, is in the range of 1.0 or more and 1.2 or less. [Explanation of Symbols]

[0067] 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 CT cutting tool S1 Preparation Process S2 charge / discharge process S3 cutting process S4 Extraction process WL winding shaft

Claims

1. Preparation steps for preparing an energy storage device comprising: an electrode body having a positive electrode, a negative electrode, and a separator, each having a positive electrode active material layer containing a nickel-cobalt-manganese composite oxide; a battery case housing the 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 energy storage device is repeatedly charged and discharged in a predetermined low voltage range, thereby breaking down the crystal structure of the nickel-cobalt-manganese composite oxide, A method for dismantling an energy storage device, which includes a cutting step of cutting the connection portion between the positive electrode current collector or the negative electrode current collector and the electrode body after the charging and discharging step has been performed.

2. The method for dismantling an energy storage device according to claim 1, wherein the nickel-cobalt-manganese composite oxide is NCM811, NCM622, or NCM111.

3. The method for dismantling an energy storage device according to claim 1, wherein the opposing capacitance ratio, which is the ratio of the electrical capacitance of the negative electrode to the electrical capacitance of the positive electrode, is in the range of 1.0 or more and 1.2 or less.

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