Method for separating electrode body

Abstract

To improve the recovery rate of an electrode material.SOLUTION: The step of separating the electrodes 20 includes an immersion step S2 and an ultrasonic application step S3. In the immersing step S2, the stacked body 20 is immersed in a hydrofluoric acid-containing liquid SL. Thereafter, in the ultrasonic application step S3, ultrasonic waves are applied to the solutions SL. In the ultrasonic application step S3, ultrasonic waves are applied in a state where the positive electrode tab 23 and the negative electrode tab 25 are held.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for separating an electrode assembly. [Background technology]

[0002] JP 2021-073375 A discloses a method for recycling lithium-ion secondary batteries to recover usable materials such as nickel from used lithium-ion secondary batteries. The method involves shredding discharged lithium-ion secondary batteries into small pieces, immersing the pieces in a polar solvent to form a heterogeneous mixture, and then agitating, sieving, separating, and otherwise processing the heterogeneous mixture to recover usable electrode materials. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-073375 Summary of the Invention [Problem to be solved by the invention]

[0004] The inventors of the present invention would like to improve the recovery rate of electrode materials. [Means for solving the problem]

[0005] The electrode assembly separation method disclosed herein includes a preparation step of preparing an electrode assembly, an immersion step of immersing the electrode assembly in a solution containing hydrofluoric acid, and an ultrasonic application step of applying ultrasonic waves to the solution. The electrode assembly prepared in the preparation step includes a positive electrode sheet including a positive electrode active material layer provided on a positive electrode current collector foil, and a negative electrode sheet including a negative electrode active material layer provided on a negative electrode current collector foil. The positive electrode sheet and the negative electrode sheet are overlapped so that the positive electrode active material layer and the negative electrode active material layer face each other in a state of being insulated from each other, the positive electrode sheet has a positive electrode tab in which the positive electrode current collector foil protrudes from a region where the positive electrode active material layer and the negative electrode active material layer are overlapped, and the negative electrode sheet has a negative electrode tab in which the negative electrode current collector foil protrudes from a region where the positive electrode active material layer and the negative electrode active material layer are overlapped, and in the ultrasonic wave application step, the ultrasonic wave is applied to the solution containing hydrofluoric acid in a state where the positive electrode tab and the negative electrode tab of the electrode body are each held.

[0006] According to this method for separating the electrode assembly, the recovery rate of the electrode material can be improved. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a perspective view of an electricity storage device 100 according to one embodiment. [Figure 2] FIG. 2 is a schematic vertical cross-sectional view taken along the line AA in FIG. [Figure 3] FIG. 3 is a vertical cross-sectional view of the laminated electrode body 20. As shown in FIG. [Figure 4] FIG. 4 is a schematic diagram showing the positive electrode sheet 22 and the negative electrode sheet 24. As shown in FIG. [Figure 5] FIG. 5 is a schematic diagram showing an electrode assembly separating device 200 according to this embodiment. [Figure 6] FIG. 6 is a view taken along the arrow B in FIG. [Figure 7] FIG. 7 is a flow chart showing a method for separating the laminated electrode body 20. As shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0008] Preferred embodiments of the technology disclosed herein will be described below with reference to the drawings as appropriate. Matters necessary for implementing the technology disclosed herein other than those specifically mentioned in this specification (e.g., the general configuration and manufacturing process of an electricity storage device that do not characterize the technology disclosed herein) can be understood as design matters of a person skilled in the art based on prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. In addition, in the following drawings, components and parts that perform the same function are designated by the same reference numerals, and redundant explanations may be omitted or simplified. In addition, in this specification, the notation "A to B" indicating a range is intended to include not only the meaning of A or more and not more than B, but also the meanings of "greater than A" and "smaller than B."

[0009] <Electricity storage device 100> FIG. 1 is a perspective view of an electricity storage device 100 according to one embodiment. FIG. 2 is a schematic longitudinal cross-sectional view taken along line AA in FIG. 1, illustrating the internal structure of the electricity storage device 100. As shown in FIG. 1, the electricity storage device 100 has a polygonal shape (more specifically, a rectangular parallelepiped shape) formed of hexahedrons. The electricity storage device 100 is installed as shown in FIG. 1 when actually used. In the following description, the symbols F, Rr, L, R, U, and D in the drawings represent front, rear, left, right, top, and bottom, and the symbols X, Y, and Z in the drawings represent the thickness direction of the electricity storage device 100, the width direction perpendicular to the thickness direction, and the up-down direction perpendicular to the thickness direction and width direction, respectively.

[0010] As shown in FIG. 2, the electricity storage device 100 includes a case 10, a stacked electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, and an electrolyte solution 15. Here, the electricity storage device 100 is a non-aqueous electrolyte secondary battery, such as a lithium-ion secondary battery. The electricity storage device 100 is configured by accommodating the stacked electrode assembly 20 and the electrolyte solution 15 in a case 10 to which the positive electrode terminal 30 and the negative electrode terminal 40 are attached. In this specification, the term "electricity storage device" refers to a general device that can be repeatedly charged and discharged, and is a concept that encompasses secondary batteries such as lithium-ion secondary batteries and nickel-metal hydride batteries, and capacitors such as lithium-ion capacitors and electric double layer capacitors.

[0011] The case 10 is a housing that houses the stacked electrode assembly 20 and the electrolyte solution 15. As shown in FIG. 1, the case 10 has a flat, bottomed, rectangular parallelepiped (square) outer shape. The material of the case 10 may be the same as that conventionally used, and is not particularly limited. The case 10 is preferably made of metal, more preferably aluminum, aluminum alloy, iron, iron alloy, or the like. As shown in FIG. 2, the case 10 includes a rectangular cylindrical case body 12 having a pair of openings 12h, and two sealing plates 14 that close the pair of openings 12h. The case 10 is integrated by joining (e.g., welding) the sealing plates 14 to the peripheries of the pair of openings 12h of the case body 12. The case 10 is hermetically sealed (sealed).

[0012] As shown in FIG. 1 , the case body 12 has a bottom surface 12a, a pair of long side surfaces 12b, and a top surface 12c facing the bottom surface 12a. The bottom surface 12a and the top surface 12c each have a substantially rectangular shape with a pair of short sides and a pair of long sides. The pair of long side surfaces 12b extend from the pair of long sides of the bottom surface 12a and face each other. Here, the long side surfaces 12b have a larger area than the bottom surface 12a and the top surface 12c. Here, the long side surfaces 12b have a larger area than the sealing plate 14. The top surface 12c extends from each of the long sides of the pair of long side surfaces 12b and connects the upper ends of the pair of long side surfaces 12b to each other. The case body 12 is formed, for example, by bending a single metal plate into a rectangular tube shape and joining (for example, welding) the seams.

[0013] In this specification, the term "approximately rectangular" refers not only to a perfect rectangular shape (rectangular shape), but also to shapes such as those in which the corners connecting the long and short sides of the rectangle are rounded, or those in which the corners have notches.

[0014] As shown in Fig. 2, the pair of sealing plates 14 are plate-like members that seal the pair of openings 12h, respectively. The sealing plates 14 have a substantially rectangular shape. The area of ​​the sealing plates 14 is smaller than the area of ​​the bottom surface 12a and the top surface 12c. The pair of sealing plates 14 face each other. A positive electrode terminal 30 and a negative electrode terminal 40 are provided on each of the pair of sealing plates 14.

[0015] The positive electrode terminal 30 is attached to the sealing plate 14 located on the right side in the width direction Y of the pair of sealing plates 14. The positive electrode terminal 30 is preferably made of metal, and more preferably made of aluminum or an aluminum alloy, for example. Inside the case 10, the positive electrode terminal 30 is electrically connected to the positive electrode sheet 22 (see also FIG. 3 ) of the laminated electrode body 20 via a positive electrode current collector 32.

[0016] The negative electrode terminal 40 is attached to the sealing plate 14 located on the left side in the width direction Y of the pair of sealing plates 14. The negative electrode terminal 40 is preferably made of metal, and more preferably made of copper or a copper alloy, for example. Inside the case 10, the negative electrode terminal 40 is electrically connected to the negative electrode sheet 24 (see also FIG. 3 ) of the laminated electrode body 20 via a negative electrode current collector 42.

[0017] In this embodiment, the positive electrode terminal 30 and the negative electrode terminal 40 are provided on the pair of sealing plates 14 (opposing surfaces of the case 10), respectively, but this is not limiting. The positive electrode terminal 30 and the negative electrode terminal 40 may be provided on the same sealing plate 14, or may be provided on the case body 12.

[0018] The electrolyte solution 15 is accommodated inside the case 10 together with the laminated electrode assembly 20. A portion of the electrolyte solution 15 is impregnated into the laminated electrode assembly 20. The electrolyte solution 15 is, for example, a non-aqueous electrolyte solution containing a non-aqueous solvent (organic solvent) and a supporting salt (electrolyte salt, such as a lithium salt or a sodium salt). Examples of non-aqueous solvents include carbonates such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. Examples of supporting salts include fluorine-containing lithium salts such as lithium hexafluorophosphate (LiPF6). The electrolyte solution 15 is typically liquid, but may also be gel-like. In this embodiment, the electrolyte solution 15 contains lithium hexafluorophosphate (LiPF6). Although not particularly limited, it is preferable that an excess of the electrolyte solution 15 exists between the case 10 and the laminated electrode assembly 20.

[0019] <Laminated electrode body 20> The laminated electrode body 20 is housed inside the case 10. The number of laminated electrode bodies 20 arranged inside one case 10 may be one, or two or more (plural). The laminated electrode body 20 may be housed inside the case 10 in a state where it is covered with a resin insulating sheet (electrode body holder).

[0020] FIG. 3 is a longitudinal cross-sectional view of a laminated electrode body 20. As shown in FIG. 3, the laminated electrode body 20 includes a plurality of positive electrode sheets 22, a plurality of negative electrode sheets 24, a plurality of separators 26, and adhesive layers 28 interposed between the positive electrode sheets 22 and the separators 26 and between the negative electrode sheets 24 and the separators 26 in the lamination direction X. However, the adhesive layer 28 may be provided between either the positive electrode sheet 22 or the negative electrode sheet 24 and the separator 26. The laminated electrode body 20 is stacked with the separator 26 sandwiched between the positive electrode sheet 22 and the negative electrode sheet 24. The positive electrode sheets 22, the negative electrode sheets 24, and the separators 26 are stacked in a direction intersecting the vertical direction Z. The stacking direction of the positive electrode sheets 22, the negative electrode sheets 24, and the separators 26 is the thickness direction X. In the following description, the thickness direction X will also be referred to as the stacking direction X. FIG. 4 is a schematic diagram showing a positive electrode sheet 22 and a negative electrode sheet 24. Note that the separator 26 is not shown in FIG. 4. As shown in FIG. 4, a positive electrode active material layer 22b is formed on the positive electrode sheet 22, and a negative electrode active material layer 24b is formed on the negative electrode sheet 24. Therefore, in the stacked electrode body 20, the positive electrode sheet 22 and the negative electrode sheet 24 are stacked such that the positive electrode active material layer 22b and the negative electrode active material layer 24b face each other while being insulated from each other. The positive electrode active material layer 22b and the negative electrode active material layer 24b are insulated from each other by the separator 26 (see FIG. 3). Note that the stacked electrode body 20 may be one in which multiple positive electrode sheets 22 and multiple negative electrode sheets 24 are sandwiched between a single separator folded zigzag.

[0021] The positive electrode sheet 22 typically includes a positive electrode current collector foil 22a and a positive electrode active material layer 22b fixed to at least one surface (both surfaces in this example) of the positive electrode current collector foil 22a. The positive electrode current collector foil 22a is preferably a metal foil. In this embodiment, the positive electrode current collector foil 22a is made of, for example, aluminum or an aluminum alloy. The positive electrode active material layer 22b contains a positive electrode active material capable of reversibly absorbing and releasing charge carriers. The positive electrode active material may be a conventional material and is not particularly limited. An example of the positive electrode active material is a lithium transition metal composite oxide containing nickel, cobalt, and manganese. The positive electrode active material layer 22b may contain optional components other than the positive electrode active material, such as a binder or a conductive material. As shown in FIG. 3 , both surfaces of the positive electrode sheet 22 in the stacking direction X are bonded to separators 26 via adhesive layers 28. 4, in this embodiment, the positive electrode sheet 22 has a substantially rectangular shape when viewed in the thickness direction X. An uncoated portion 22c that does not have the positive electrode active material layer 22b is formed at one end portion in the width direction Y of the positive electrode current collector foil 22a (here, the right side in the width direction Y).

[0022] The negative electrode sheet 24 typically includes a negative electrode current collector foil 24a and a negative electrode active material layer 24b fixed to at least one surface (here, both surfaces) of the negative electrode current collector foil 24a. The negative electrode current collector foil 24a is preferably a metal foil. In this embodiment, the negative electrode current collector foil 24a is made of, for example, copper or a copper alloy. The negative electrode active material layer 24b contains a negative electrode active material capable of reversibly absorbing and releasing charge carriers. The negative electrode active material may be a conventional material and is not particularly limited. Examples of negative electrode active materials include carbon materials such as graphite and silicon-based materials. The negative electrode active material layer 24b may contain optional components other than the negative electrode active material, such as a binder, a thickener, and a dispersant. As shown in FIG. 3 , both surfaces of the negative electrode sheet 24 in the stacking direction X are bonded to separators 26 via adhesive layers 28. As shown in FIG. 4 , in this embodiment, the negative electrode sheet 24 has a substantially rectangular shape when viewed in the thickness direction X. An uncoated portion 24c that does not have the negative electrode active material layer 24b is formed at one end in the width direction Y of the negative electrode current collector foil 24a (here, the left side in the width direction Y).

[0023] 3 is an insulating sheet having a plurality of fine through-holes through which charge carriers can pass. By interposing the separator 26 between the positive electrode sheet 22 and the negative electrode sheet 24, contact between the positive electrode sheet 22 and the negative electrode sheet 24 is prevented, and charge carriers (e.g., lithium ions) can be transferred between the positive electrode sheet 22 and the negative electrode sheet 24.

[0024] The separator 26 includes a resin separator substrate and one or more heat-resistant layers (HRLs) 26a containing a metal oxide such as alumina (Al2O3). In this embodiment, the separator 26 has the heat-resistant layer 26a formed on at least one surface. The heat-resistant layer 26a may be provided on only one surface of the separator 26, or may be provided on both surfaces. In this example, the separator 26 includes the heat-resistant layer 26a on one surface, specifically, on the surface facing the positive electrode sheet 22.

[0025] The heat-resistant layer 26a typically contains an inorganic filler and a heat-resistant layer binder. The heat-resistant layer 26a suppresses thermal shrinkage of the separator 26, contributing to improved safety of the electricity storage device 100 (see FIG. 1). As the inorganic filler, ceramic particles such as alumina, zirconia, boehmite, aluminum hydroxide, silica, and titania are preferred, and from the viewpoint of suppressing thermal shrinkage of the separator 26, compounds containing aluminum are particularly preferred. As the heat-resistant layer binder, acrylic resins, fluorine-based resins, urethane resins, ethylene vinyl acetate resins, epoxy resins, and the like can be mentioned.

[0026] As shown in FIG. 2, the positive electrode sheet 22 has a positive electrode tab 23. The positive electrode tab 23 is a portion of the positive electrode current collector foil 22a (see FIG. 4) that protrudes from the region where the positive electrode active material layer 22b (see FIG. 4) and the negative electrode active material layer 24b (see FIG. 4) are overlapped. The positive electrode tab 23 is formed by overlapping the uncoated portion 22c (see FIG. 4). The positive electrode tab 23 is electrically connected to the positive electrode terminal 30 via the positive electrode current collector portion 32. The negative electrode sheet 24 has a negative electrode tab 25. The negative electrode tab 25 is a portion of the negative electrode current collector foil 24a (see FIG. 4) that protrudes from the region where the negative electrode active material layer 24b (see FIG. 4) and the negative electrode active material layer 24b (see FIG. 4) are overlapped. The negative electrode tab 25 is formed by overlapping the uncoated portion 24c (see FIG. 4). The negative electrode tab 25 is electrically connected to the negative electrode terminal 40 via the negative electrode current collecting portion 42 .

[0027] The adhesive layer 28 shown in Fig. 3 is interposed between at least one of the positive electrode sheet 22 and the negative electrode sheet 24 and the separator 26, bonding them together. This prevents misalignment of the positive electrode sheet 22 and the negative electrode sheet 24, thereby preventing misalignment of the stacked electrode body 20. In Fig. 3, both surfaces of the positive electrode sheet 22 and both surfaces of the negative electrode sheet 24 are bonded to the opposing separators 26 via the adhesive layer 28 in the stacking direction X.

[0028] The adhesive layer 28 is typically the layer containing the adhesive layer binder at the highest mass ratio. Examples of adhesive layer binders include fluorine-based resins, acrylic resins, urethane resins, ethylene vinyl acetate resins, and epoxy resins. The adhesive layer binder may be the same type as the heat-resistant layer binder described above, or may be a different type. The adhesive layer 28 may further contain other materials (e.g., inorganic fillers, etc.).

[0029] The configuration of the electricity storage device 100 having the stacked electrode body 20 has been described above. Meanwhile, in the process of recycling used secondary batteries, there is a strong demand for recovering metals such as nickel, cobalt, and manganese (so-called rare metals). When a secondary battery is crushed during recycling, the metals to be recovered are mixed with metals other than the metals to be recovered, resulting in a relatively low recovery rate of the metals to be recovered. Therefore, the inventors of the present application thought that if the positive electrode and negative electrode of the electrode body could be separated from each other without crushing them, the recovery rate of the metals to be recovered could be relatively high.

[0030] In a secondary battery, multiple positive electrode sheets and negative electrode sheets are stacked and immersed in an electrolyte. The positive electrode sheets and negative electrode sheets are relatively thin. Therefore, if the positive electrode sheets and negative electrode sheets are separated by pulling the electrode assembly, there is a risk that the positive electrode sheets and negative electrode sheets will be damaged. The present inventors have investigated how to separate the positive electrode sheets and negative electrode sheets without damaging them during the process of recycling a secondary battery.

[0031] <Electrode body separation device 200> 5 is a schematic diagram showing an electrode assembly separation device 200 according to this embodiment. As shown in FIG. 5, the electrode assembly separation device 200 includes a water tank 210, a gripping tool 220, an ultrasonic vibrator 230, and a high-frequency power supply 240.

[0032] The water tank 210 is a water tank having a substantially rectangular parallelepiped shape with an opening (not shown) formed in part of the top surface. Water WA is filled inside the water tank 210. The shape of the water tank 210 is not particularly limited. The upper end of the water WA reaches near the upper end of the water tank 210. The material from which the water tank 210 is made is not particularly limited, and the water tank 210 may be made of glass, acrylic, or the like. Although not shown, the water tank 210 may also be provided with a supply path for supplying liquid (water WA or solution SL, described below) from inside the water tank 210, a discharge path for discharging the liquid from inside the water tank 210, and the like.

[0033] The gripping tool 220 is placed inside the water tank 210 and grips the stacked electrode assembly 20. The gripping tool 220 is placed in the water WA. In this embodiment, the gripping tool 220 has a substantially U-shape. The gripping tool 220 includes a clip portion 220a. As shown in FIG. 5, a pair of gripping tools 220 are provided along the width direction Y of the stacked electrode assembly 20. Although not shown, the clip portion 220a can clamp an object by the biasing force of a spring or the like. The pair of clip portions 220a grip the positive electrode tab 23 and the negative electrode tab 25 of the stacked electrode assembly 20, respectively. When the gripping tool 220 grips the positive electrode tab 23 and the negative electrode tab 25, the stacked electrode assembly 20 is placed in the water WA. As shown in FIG. 5, in this embodiment, the up-down direction Z of the stacked electrode assembly 20 in the water WA coincides with the up-down direction as viewed in the drawing. However, there is no particular limitation on the direction in which the laminated electrode body 20 is arranged. For example, the laminated electrode body 20 may be arranged so that the stacking direction X (see FIG. 3) coincides with the up-down direction in the view of FIG.

[0034] The ultrasonic vibrator 230 is a vibrator that emits ultrasonic waves that vibrate the water WA. The configuration of the ultrasonic vibrator 230 is not particularly limited, but it can be realized, for example, by a bolt-clamped Langevin vibrator in which PZT (lead zirconate titanate) is sandwiched between metal blocks and the PZT and the blocks are fastened together with a bolt. PZT is a metal that vibrates when subjected to an AC voltage. FIG. 6 is a view taken along arrow B in FIG. 5. Note that the gripping tool 220 is not shown in FIG. 6. In FIG. 6, the left-right direction in the drawing corresponds to the stacking direction X of the stacked electrode body 20. As shown in FIG. 6, in this embodiment, the ultrasonic vibrator 230 is disposed in the water tank 210 at a position facing the positive electrode sheet 22 and the negative electrode sheet 24 in the stacking direction X of the stacked electrode body 20. Therefore, the ultrasonic vibrator 230 is disposed so that the ultrasonic waves emitted by the ultrasonic vibrator 230 travel in the stacking direction X. However, there are no particular limitations on the configuration and position of the ultrasonic transducer 230. The ultrasonic transducer 230 may be, for example, a so-called throw-in type ultrasonic transducer that is placed in the water WA.

[0035] The high-frequency power supply 240 is connected to the ultrasonic vibrator 230. The high-frequency power supply 240 has an oscillator (not shown) and a power amplifier (not shown) therein. The oscillator generates an AC signal of a predetermined frequency. The high-frequency power supply 240 may also have a switch for setting the frequency, a display screen, and the like. The power amplifier included in the high-frequency power supply 240 amplifies the AC signal generated by the oscillator to generate an ultrasonic signal. The generated ultrasonic signal is transmitted to the ultrasonic vibrator 230. This causes the ultrasonic vibrator 230 to vibrate at a predetermined frequency. However, the frequency at which the ultrasonic vibrator 230 vibrates due to the signal from the high-frequency power supply 240 is not particularly limited. The frequency may be constant, or may increase or decrease (sweep) over time.

[0036] The above has described the electrode assembly separation device 200. Next, a method for separating the stacked electrode assembly 20 will be described. Fig. 7 is a flow diagram showing the method for separating the stacked electrode assembly 20. The method for separating the stacked electrode assembly 20 disclosed here includes a preparation step S1, an immersion step S2, and an ultrasonic wave application step S3.

[0037] The preparation step S1 is a step of preparing an electrode body. In this embodiment, a stacked electrode body 20 is prepared in the preparation step S1. In the preparation step S1, first, a used electricity storage device 100 (see FIG. 2) is prepared. Next, holes are made in the case 10 of the electricity storage device 100 shown in FIG. 2, and the electrolyte solution 15 is discharged. For example, a plurality of holes are formed. By blowing air through some of the formed holes and sucking the air through the other holes, the electrolyte solution 15 inside the case 10 can be sucked. Note that in this embodiment, the electrolyte solution 15 inside the case 10 is sucked to an extent that the electrolyte solution 15 impregnated in the stacked electrode body 20 is not completely sucked. In other words, a portion of the electrolyte solution 15 is not sucked out of the case 10 and remains impregnated in the stacked electrode body 20. Therefore, the stacked electrode body 20 prepared in this embodiment is impregnated with the electrolyte solution 15 containing lithium hexafluorophosphate (LiPF6).

[0038] After the electrolyte solution 15 inside the case 10 has been sucked out, the connection between the case 10 and the sealing plate 14 is cut, and the sealing plate 14 is separated from the case 10. When drilling a hole in the case 10 and when cutting the connection between the case 10 and the sealing plate 14, for example, a tool with a cutting blade (e.g., an electric saw), an electric cutting tool (e.g., a grinder or a router), a water cutter, a laser cutter, or the like is used. After the sealing plate 14 has been separated, the stacked electrode body 20 is removed from the inside of the case 10. The stacked electrode body 20 is removed by a conventionally known method, such as extrusion using a push rod. In the removed stacked electrode body 20, the positive electrode sheet 22, the negative electrode sheet 24, and the separator 26, which are wet with the electrolyte solution 15, are stuck to each other due to surface tension.

[0039] The immersion step S2 is a step of immersing the electrode body in a solution containing hydrofluoric acid. In this embodiment, in the immersion step S2, the stacked electrode body 20 is immersed in water WA and hydrofluoric acid is added, thereby immersing the stacked electrode body 20 in the solution containing hydrofluoric acid. The stacked electrode body 20 removed in the preparation step S1 is placed inside a water tank 210 shown in FIG. 5. At this time, the stacked electrode body 20 is placed so that the positive electrode tab 23 and the negative electrode tab 25 of the stacked electrode body 20 are respectively held by the clip portions 220a of the holder 220. In this way, the stacked electrode body 20 is immersed in the water WA. At this time, it is preferable that the entire stacked electrode body 20 is placed in the water WA.

[0040] As described above, the water tank 210 is filled with water WA. The stacked electrode body 20 is impregnated with an electrolyte solution 15 containing lithium hexafluorophosphate (LiPF6). Therefore, when the stacked electrode body 20 is placed in the water WA, hydrogen fluoride (HF) is generated according to the following formulas (1), (2), and (3). LiPF6⇔LiF+PF5 (1) PF5 + H2O → POF3 + 2HF (2) POF3+H2O→POF2(OH)+HF···(3)

[0041] The hydrogen fluoride (HF) generated by the above formulas (1) to (3) dissolves in the water WA in the water tank 210. Therefore, the inside of the water tank 210 is filled with a solution SL containing hydrofluoric acid (hydrofluoric acid). Therefore, in the immersion step S2 in this embodiment, the stacked electrode body 20 impregnated with the electrolyte solution 15 containing lithium hexafluorophosphate (LiPF6) is immersed in the water WA to cause the reactions of formulas (1) to (3), thereby immersing the stacked electrode body 20 in the solution SL containing hydrofluoric acid. However, the immersion step S2 may also be performed by immersing the stacked electrode body 20 in the solution SL, which is prepared in advance. In this embodiment, the concentration of hydrofluoric acid is preferably 1.5 wt % to 5%. For example, the amount of water WA may be adjusted based on the amount of electrolyte 15 impregnated in the stacked electrode body 20, the amount of water WA in the water tank 210, and formulas (1) to (3) so that the concentration of hydrofluoric acid is 1.5 wt % to 5%.

[0042] Furthermore, when the laminated electrode body 20 is immersed in a solution SL containing hydrofluoric acid, the oxide film formed on the surface of the positive electrode current collector foil 22a (see FIG. 4) of the positive electrode sheet 22 reacts with the hydrofluoric acid and dissolves. Similarly, the oxide film formed on the surface of the negative electrode current collector foil 24a (see FIG. 4) of the negative electrode sheet 24 also dissolves. Furthermore, the heat-resistant layer 26a of the separator 26 is also dissolved by the hydrofluoric acid.

[0043] The ultrasonic wave application step S3 is a step of applying ultrasonic waves to the solution SL. In the ultrasonic wave application step S3, ultrasonic waves are applied to the solution SL containing hydrofluoric acid while the positive electrode tab 23 and the negative electrode tab 25 of the stacked electrode body 20 are each held. In this embodiment, as shown in FIG. 5, the positive electrode tab 23 and the negative electrode tab 25 are held by the clip portion 220a of the holder 220. In this state, as shown in FIG. 6, the high-frequency power supply 240 is driven and an ultrasonic signal is transmitted to the ultrasonic vibrator 230, thereby applying ultrasonic waves to the solution SL. In this embodiment, 200 kHz ultrasonic waves are continuously irradiated by the ultrasonic vibrator 230 for 10 minutes. However, the frequency and irradiation time of the ultrasonic waves are not particularly limited.

[0044] In the ultrasonic wave application step S3, ultrasonic waves are applied toward the laminated electrode body 20 in the direction in which the positive electrode sheet 22 and the negative electrode sheet 24 are stacked (stacking direction X). In this embodiment, the ultrasonic vibrator 230 is disposed at a position facing the positive electrode sheet 22 and the negative electrode sheet 24 in the stacking direction X. Therefore, the ultrasonic waves emitted by the ultrasonic vibrator 230 travel in the stacking direction X of the positive electrode sheet 22 and the negative electrode sheet 24. In other words, the ultrasonic waves travel toward the surface of the positive electrode current collector foil 22a on which the positive electrode active material layer 22b is formed and the surface of the negative electrode current collector foil 24a on which the negative electrode active material layer 24b is formed. At this time, a pressing force is generated in the propagation direction of the ultrasonic waves (here, the stacking direction X) due to the radiation pressure of the ultrasonic waves propagating through the solution SL. As a result, the solution SL and the laminated electrode body 20 are pressed in the stacking direction X. When the solution SL is pressed in the stacking direction X, a flow is formed in the solution SL, and the flow causes the laminated electrode body 20 to vibrate. Furthermore, when ultrasonic waves are applied to the solution SL, cavitation occurs in the solution SL. Therefore, bubbles BB are generated and disappear in the solution SL. At this time, the bubbles BB mainly move along the flow formed in the solution SL. Therefore, near the ultrasonic vibrator 230, the bubbles BB mainly move in the stacking direction X, and gradually spread throughout the solution SL as they move away from the ultrasonic vibrator 230.

[0045] The positive electrode sheet 22 and the negative electrode sheet 24 vibrate, and the impact generated when the air bubbles BB disappear causes the positive electrode sheet 22, the negative electrode sheet 24, and the separator 26 to gradually peel off. Thereafter, the positive electrode active material layer 22b gradually peels off from the positive electrode current collector foil 22a. Similarly, the negative electrode active material layer 24b peels off from the negative electrode current collector foil 24a. When the positive electrode active material layer 22b and the negative electrode active material layer 24b peel off, the positive electrode active material and the negative electrode active material dissolve, disperse, or precipitate in the solution SL. Because the positive electrode tab 23 and the negative electrode tab 25 are respectively held by the holding tool 220, the positive electrode current collector foil 22a and the negative electrode current collector foil 24a do not disperse in the solution SL, and remain held by the holding tool 220.

[0046] After the flow shown in FIG. 7 is completed, the worker can recover the positive electrode active material (positive electrode active material layer 22b) and the negative electrode active material (negative electrode active material layer 24b) from the solution SL, and recover the desired electrode material, such as nickel. The method for recovering the desired electrode material from the solution SL can be realized by a conventionally known method. The worker can also recover the positive electrode current collector foil 22a and the negative electrode current collector foil 24a held by the holding tool 220. This separates the stacked electrode body 20.

[0047] As described above, in the embodiment described above, in the immersion step S2, the laminated electrode body 20 is immersed in a solution SL containing hydrofluoric acid. This dissolves the surface oxide films of the positive electrode current collector foil 22a and the negative electrode current collector foil 24a. Then, in the ultrasonic wave application step S3, ultrasonic waves are applied to the solution SL while the positive electrode tab 23 and the negative electrode tab 25 are held. At this time, the laminated electrode body 20 is swung in the stacking direction X while both ends in the width direction Y are held. As the laminated electrode body 20 sways, the positive electrode active material layer 22b and the negative electrode active material layer 24b gradually peel off from the positive electrode current collector foil 22a and the negative electrode current collector foil 24a. Note that, because the positive electrode tab 23 and the negative electrode tab 25 are held, the positive electrode current collector foil 22a and the negative electrode current collector foil 24a are prevented from dispersing in the solution SL. This allows the positive electrode current collector foil 22a and the negative electrode current collector foil 24a to be separated from the positive electrode active material layer 22b and the negative electrode active material layer 24b. The desired electrode material can be obtained from the separated positive electrode active material layer 22b and negative electrode active material layer 24b. This prevents the positive electrode current collector foil 22a and the like from mixing with the positive electrode active material layer 22b and the negative electrode active material layer 24b, and allows the laminated electrode body 20 to be separated. This increases the recovery rate of the desired electrode material.

[0048] In the above-described embodiment, the electrolyte solution 15 contained in the case 10 contains lithium hexafluorophosphate (LiPF), and in the immersion step S2, the stacked electrode body 20 is immersed in water WA. The lithium hexafluorophosphate (LiPF) contained in the electrolyte solution 15 reacts with the water WA to generate hydrogen fluoride (HF). At this time, a solution SL containing hydrofluoric acid is filled in the water tank 210. Therefore, by immersing the stacked electrode body 20 impregnated with the electrolyte solution 15 in water WA, the stacked electrode body 20 can be immersed in the solution SL containing hydrofluoric acid. This allows the stacked electrode body 20 to be immersed in the solution SL containing hydrofluoric acid without having to prepare the solution SL containing hydrofluoric acid in the water tank 210 in advance. Therefore, in the step of separating the stacked electrode body 20, it is not necessary to prepare the solution SL containing hydrofluoric acid in advance. This reduces the preparation burden in the step of separating the stacked electrode body 20.

[0049] In the above-described embodiment, the stacked electrode body 20 includes a separator 26 on which a heat-resistant layer 26a is formed. The separator 26 is sandwiched between a positive electrode sheet 22 and a negative electrode sheet 24. When the stacked electrode body 20 is immersed in the immersion step S2, the heat-resistant layer 26a of the separator 26 is dissolved by the hydrofluoric acid contained in the solution SL. This makes it relatively easy to separate the positive electrode sheet 22 or the negative electrode sheet 24 from the separator 26. Therefore, even in a stacked electrode body 20 having a separator 26 on which a heat-resistant layer 26a is formed, the stacked electrode body 20 can be separated.

[0050] In the above-described embodiment, the positive electrode sheet 22 and the negative electrode sheet 24 have a substantially rectangular shape when viewed from the stacking direction X. Furthermore, in the ultrasonic wave application step S3, ultrasonic waves are applied toward the stacked electrode body 20 in the stacking direction X. Accordingly, at this time, the stacked electrode body 20 oscillates in the stacking direction X. For example, the movement of the stacked electrode body 20 can be made larger than when the stacked electrode body 20 oscillates in the up-and-down direction Z. Furthermore, the air bubbles BB generated by cavitation hit the surface of the positive electrode current collector foil 22a on which the positive electrode active material layer 22b is formed and the surface of the negative electrode current collector foil 24a on which the negative electrode active material layer 24b is formed relatively frequently. As a result, the impact of the air bubbles BB disappearing makes it easier for the positive electrode active material layer 22b and the negative electrode active material layer 24b to peel off. Therefore, the stacked electrode body 20 can be separated more efficiently.

[0051] As described above, this specification includes the disclosures set forth in the following sections.

[0052] Section 1: a preparation step of preparing an electrode body; an immersion step of immersing the electrode body in a solution containing hydrofluoric acid; an ultrasonic wave application step of applying ultrasonic waves to the solution; Including, The electrode body prepared in the preparation step is a positive electrode sheet including a positive electrode active material layer provided on a positive electrode current collector foil; a negative electrode sheet including a negative electrode active material layer provided on a negative electrode current collector foil; Equipped with the positive electrode sheet and the negative electrode sheet are stacked so that the positive electrode active material layer and the negative electrode active material layer face each other in an insulated state, the positive electrode sheet has a positive electrode tab formed by the positive electrode current collector foil protruding from a region where the positive electrode active material layer and the negative electrode active material layer are superposed, the negative electrode sheet has a negative electrode tab formed by the negative electrode current collector foil protruding from a region where the positive electrode active material layer and the negative electrode active material layer are superposed, In the ultrasonic wave application step, the ultrasonic wave is applied to the solution containing the hydrofluoric acid in a state in which the positive electrode tab and the negative electrode tab of the electrode body are respectively held. Method for separating the electrode body.

[0053] Section 2: The electrode body prepared in the preparation step is impregnated with an electrolyte solution containing LiPF6, The immersion step includes immersing the electrode body in water to generate the hydrofluoric acid, thereby immersing the electrode body in the solution containing the hydrofluoric acid. Item 1. A method for separating an electrode assembly according to item 1.

[0054] Section 3: The electrode assembly includes a separator having a heat-resistant layer (HRL) formed on at least one surface thereof, The electrode body is stacked with the separator sandwiched between the positive electrode sheet and the negative electrode sheet. Item 1 or 2. The electrode assembly separation method.

[0055] Section 4: the positive electrode sheet and the negative electrode sheet have a substantially rectangular shape when viewed from a direction in which the positive electrode sheet and the negative electrode sheet are stacked, 4. The electrode assembly separation method according to any one of items 1 to 3, wherein the ultrasonic wave application step applies the ultrasonic wave toward the electrode assembly in a direction in which the positive electrode sheet and the negative electrode sheet are stacked. [Explanation of symbols]

[0056] 10 cases 12 Case body 12a Bottom 12b long side 12c Top 12h opening 14 Sealing plate 15 Electrolyte 20. Laminated electrode body 22 Positive electrode sheet 22a Positive electrode current collector foil 22b Positive electrode active material layer 22c Uncoated area 23 Positive electrode tab 24 Negative electrode sheet 24a Negative current collector foil 24b Negative electrode active material layer 24c Uncoated area 25 Negative electrode tab 26 Separator 26a Heat-resistant layer 26e Termination 28 Adhesive layer 29 Tape 30 Positive terminal 32 Positive electrode current collector 40 Negative terminal 42 Negative electrode current collector 100 Energy storage device 200 Electrode body separation device 210 Aquarium 220 Gripping tool 220a Clip part 230 Ultrasonic vibrator 240 High frequency power supply BB bubbles S1 Preparation process S2 Soaking process S3 Ultrasonic impression process SL solution WA Water

Claims

1. a preparation step of preparing an electrode body; an immersion step of immersing the electrode body in a solution containing hydrofluoric acid; an ultrasonic wave application step of applying ultrasonic waves to the solution; Including, The electrode body prepared in the preparation step is a positive electrode sheet including a positive electrode active material layer provided on a positive electrode current collector foil; a negative electrode sheet including a negative electrode active material layer provided on a negative electrode current collector foil; Equipped with the positive electrode sheet and the negative electrode sheet are stacked so that the positive electrode active material layer and the negative electrode active material layer face each other in an insulated state, the positive electrode sheet has a positive electrode tab formed by the positive electrode current collector foil protruding from a region where the positive electrode active material layer and the negative electrode active material layer are superposed, the negative electrode sheet has a negative electrode tab formed by the negative electrode current collector foil protruding from a region where the positive electrode active material layer and the negative electrode active material layer are superposed, In the ultrasonic wave application step, the ultrasonic wave is applied to the solution containing the hydrofluoric acid in a state in which the positive electrode tab and the negative electrode tab of the electrode body are respectively held. Method for separating the electrode body.

2. The electrode body prepared in the preparation step is LiPF ６ The electrolyte solution containing The immersion step includes immersing the electrode body in water to generate the hydrofluoric acid, thereby immersing the electrode body in the solution containing the hydrofluoric acid. The electrode assembly separation method according to claim 1 .

3. The electrode assembly includes a separator having a heat-resistant layer (HRL) formed on at least one surface thereof, The electrode body is stacked with the separator sandwiched between the positive electrode sheet and the negative electrode sheet. The electrode assembly separation method according to claim 1 .

4. the positive electrode sheet and the negative electrode sheet have a substantially rectangular shape when viewed from a direction in which the positive electrode sheet and the negative electrode sheet are stacked, The electrode assembly separation method according to claim 1 , wherein the ultrasonic wave applying step applies the ultrasonic wave toward the electrode assembly in a direction in which the positive electrode sheet and the negative electrode sheet are stacked.

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