Method and system for processing waste lithium ion battery

Abstract

This method for processing a waste lithium ion battery for recovering lithium from a waste lithium ion battery that contains fluorine includes: introducing a roasted material that is obtained by roasting the waste lithium ion battery into a first dissolution tank so as to immerse the roasted material in water; performing first solid-liquid separation on the aqueous solution after immersion in the first dissolution tank; recovering the lithium from the aqueous solution that is separated by the first solid-liquid separation; introducing the residue after immersion in the first dissolution tank into a second dissolution tank, which is different from the first dissolution tank, so as to immerse the residue in water; adding calcium hydroxide to water in the second dissolution tank; performing second solid-liquid separation on the aqueous solution after immersion in the second dissolution tank; and separating excess calcium, which is derived from calcium hydroxide, and lithium from the aqueous solution that is separated by the second solid-liquid separation.

Description

Method and system for treating waste lithium-ion batteries

[0001] The present disclosure relates to a method and system for treating waste lithium-ion batteries.

[0002] In order to recover the lithium contained in lithium-ion batteries, the waste lithium-ion batteries are roasted, and the roasted material is immersed in water to dissolve the lithium ions in the water, thereby separating the lithium from impurities.

[0003] However, lithium-ion batteries contain a large amount of fluorine in the electrolyte, binder, etc., and there is a concern that lithium ions and fluorine ions may combine to produce lithium fluoride when waste lithium-ion batteries are roasted, etc. Because lithium fluoride is poorly soluble in water, if lithium fluoride is discarded as residue, the lithium recovery rate will decrease.

[0004] The following Patent Document 1 describes the addition of calcium hydroxide to a lithium solution containing fluorine and lithium in order to separate lithium from the lithium solution.

[0005] International Publication No. 2021 / 090571

[0006] However, even if calcium hydroxide is added to a dissolution tank in which the roasted product is immersed in water, lithium fluoride does not actually dissolve, and fluorine and lithium cannot be separated.

[0007] The present disclosure has been made in consideration of the above-mentioned problems, and aims to provide a method and system for treating waste lithium-ion batteries that can promote the dissolution of lithium fluoride and increase the lithium recovery rate.

[0008] A method for treating used lithium-ion batteries according to one aspect of the present disclosure is a method for recovering lithium from used lithium-ion batteries containing fluorine, the method comprising the steps of: roasting the used lithium-ion batteries to obtain a roasted product, introducing the roasted product into a first dissolving tank and immersing it in water; performing a first solid-liquid separation on the aqueous solution obtained after immersion in the first dissolving tank; recovering the lithium from the aqueous solution separated by the first solid-liquid separation; introducing the residue obtained after immersion in the first dissolving tank into a second dissolving tank different from the first dissolving tank and immersing it in water; adding calcium hydroxide to the water in the second dissolving tank; performing a second solid-liquid separation on the aqueous solution obtained after immersion in the second dissolving tank; and separating excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation.

[0009] Furthermore, a treatment system for waste lithium-ion batteries according to another aspect of the present disclosure is a treatment system for waste lithium-ion batteries for recovering lithium from waste lithium-ion batteries containing fluorine, the treatment system including: a first dissolving tank into which a roasted product obtained by roasting the waste lithium-ion batteries is introduced and immersed in water; a first separator that performs a first solid-liquid separation on the aqueous solution after immersion in the first dissolving tank; a lithium recovery device that recovers the lithium from the aqueous solution separated by the first separator; a second dissolving tank different from the first dissolving tank, into which a residue after immersion in the first dissolving tank is introduced and immersed in water to which calcium hydroxide is added; a second separator that performs a second solid-liquid separation on the aqueous solution after immersion in the second dissolving tank; and a calcium separation device that separates excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation.

[0010] According to the present disclosure, the dissolution of lithium fluoride can be promoted, thereby increasing the recovery rate of lithium.

[0011] Fig. 1 is a schematic process diagram showing the processing steps in a processing system for waste lithium ion batteries according to one embodiment of the present invention. Fig. 2 is a schematic configuration diagram of a pyrolysis system that performs the pyrolysis step shown in Fig. 1. Fig. 3 is a schematic configuration diagram of a recovery system that performs the recovery step shown in Fig. 1.

[0012] Hereinafter, one embodiment will be described with reference to the drawings. Fig. 1 is a schematic process diagram showing the processing steps in a processing system for used lithium-ion batteries according to one embodiment of the present disclosure. Note that hereinafter, lithium-ion batteries may be abbreviated as LIB.

[0013] The waste LIB to be treated by the treatment system of this embodiment is, for example, an NCM-type lithium-ion battery containing nickel, cobalt, and manganese as the positive electrode active material. However, lithium-ion batteries other than the NCM-type may also be treated. The lithium-ion battery contains graphite as the negative electrode active material, aluminum foil as the positive electrode current collector, and copper foil as the negative electrode current collector. Furthermore, the lithium-ion battery contains a fluorine compound as an electrolyte or binder.

[0014] This processing system targets large waste LIBs, i.e., battery modules made up of multiple waste LIB battery cells, and battery units made up of multiple battery modules. A battery unit is, for example, configured by housing multiple electrically connected battery modules, a control device, and a cooling device. This processing system is intended to remove waste LIBs from electric vehicles or hybrid vehicles, for example, and process the removed waste LIBs, i.e., battery units or battery modules, without disassembling them.

[0015] As shown in FIG. 1 , the treatment system of the present embodiment includes, in its treatment steps, a pyrolysis step P1 in which waste LIB is pyrolyzed and the resulting powder containing an active material is roasted, and a recovery step P2 in which the roasted active material is immersed in water to elute lithium, and then the lithium is recovered.

[0016] First, the pyrolysis process P1 will be described. The pyrolysis process P1 includes a pretreatment process P11, a crushing and sorting process P12, and a roasting process P13. Figure 2 is a schematic diagram of a pyrolysis system that performs the pyrolysis process shown in Figure 1. The pyrolysis system 1 includes a supply device 10, a pretreatment device 11, a crushing and sorting device 12, and a roasting device 13.

[0017] In the pre-treatment process P11, the waste LIB is roasted at a second temperature lower than the first temperature in the roasting process P13 (described later), i.e., pre-roasted, in order to decompose and remove the electrolyte contained in the waste LIB. For this purpose, the waste LIB is supplied from a supply device 10 to a pre-treatment device 11. The supply device 10 is, for example, a belt conveyor. The pre-treatment device 11 is, for example, a grate preheater.

[0018] The second temperature in the pretreatment step P11 is set to a temperature at which the electrolyte contained in the waste LIB can be decomposed and removed. For example, the second temperature is 150° C. or higher and lower than 400° C., and may be 150° C. or higher and 250° C. or lower.

[0019] The crushing and sorting process P12 crushes the waste LIBs processed in the pretreatment process P11, and separates the active materials from the current collectors of the crushed waste LIBs to separate the active materials. To this end, the crushing and sorting device 12 includes a crusher 12a and a sorter 12b. The crusher 12a is, for example, a roll crusher. The crusher 12a crushes large waste LIBs (battery units or battery modules) into pieces roughly the size of battery cells or smaller.

[0020] The sorter 12b is configured to separate the active material from the current collectors of the waste LIBs crushed by the crusher 12a, and sort and extract the active material. The sorter 12b is configured, for example, by a sieve shaker or the like. In reality, the sorter 12b extracts not only the positive electrode active material but also a small amount of impurities other than the active material, such as the negative electrode active material, and supplies them to the roasting device 13. The packaging materials, current collectors, and other impurities of the waste LIBs other than these are sent to a separate processing facility.

[0021] In the roasting process P13, the waste LIB sorted in the crushing and sorting process P12 is roasted at a predetermined first temperature. The mixed waste LIB is a mixture containing the active material of the waste LIB and an alkali metal salt. The roasting device 13 is, for example, an externally heated rotary kiln. The externally heated rotary kiln includes a cylinder 13a that rotates around its central axis and a heating jacket 13b that is provided to surround the outer periphery of the cylinder 13a.

[0022] The cylindrical body 13a has an inlet 13c at one end and an outlet 13d at the other end, and is supported rotatably around its central axis with the central axis inclined at a predetermined angle so as to slope downward from the inlet 13c to the outlet 13d. The waste LIB supplied from the sorter 12b to the inlet 13c of the cylindrical body 13a is transported toward the outlet 13d by the rotation of the cylindrical body 13a.

[0023] The interior of the cylinder 13a is an air atmosphere. Alternatively, the interior of the cylinder 13a may be a reducing atmosphere or a low-oxygen atmosphere with an oxygen concentration of, for example, 10% or less. A heating gas is supplied to a heating jacket 13b surrounding the outer periphery of the cylinder 13a, thereby heating the outer wall of the cylinder 13a, and the waste LIB transported inside the cylinder 13a is heated and discharged as a roasted product from a discharge port 13d. The first temperature, which is the roasting temperature in the roasting step P13, is 400°C or higher and may be, for example, 800°C.

[0024] Next, the recovery step P2 will be described. Fig. 3 is a schematic diagram of a recovery system that performs the recovery step shown in Fig. 1. The recovery step P2 includes a first dissolution step P21, a first separation step P22, and a lithium recovery step P24. Correspondingly, the recovery system 2 includes a first dissolution tank 21, a first separator 22, and a lithium recovery device 24.

[0025] In the first dissolving step P21, the roasted material is immersed in water. To this end, water is stored in the first dissolving tank 21, and the roasted material is introduced into the first dissolving tank 21. The roasted material is supplied to the first dissolving tank 21 in predetermined amounts via a hopper 20. As a result, the aqueous solution in the first dissolving tank 21 becomes a mixture of water and the roasted material. The first dissolving tank 21 is equipped with a stirring mechanism that stirs the aqueous solution in the first dissolving tank 21.

[0026] Most of the lithium component contained in the roasted product is lithium carbonate (Li2CO3) produced in the roasting step P13. The lithium carbonate dissolves in the water in the first dissolution tank 21.

[0027] In the first separation step P22, a first solid-liquid separation is performed on the aqueous solution treated in the first dissolution step P21. For this purpose, the first separator 22 is configured as a solid-liquid separator. By performing solid-liquid separation in the first separator 22, solid residues are removed from the aqueous solution. In the lithium recovery step P24, lithium is recovered from the aqueous solution separated in the first solid-liquid separation.

[0028] More specifically, the lithium recovery step P24 concentrates the aqueous solution separated in the first separation step P22. For this purpose, the lithium recovery device 24 may be equipped with a concentrator. The concentrator is configured, for example, by an evaporative concentration device or a crystallization device that heats the aqueous solution to 80°C or higher and evaporates the water content of the aqueous solution. By concentrating the aqueous solution, the concentration of lithium contained in the aqueous solution increases, and a slurry containing lithium carbonate is produced.

[0029] Furthermore, in the lithium recovery step P24, solid-liquid separation is performed on the produced slurry. For this purpose, the lithium recovery device 24 may be equipped with a solid-liquid separator. In the lithium recovery step P24, solid-liquid separation is performed, thereby precipitating lithium carbonate from the slurry. As a result, lithium is recovered as lithium carbonate. The remaining aqueous solution is subjected to waste liquid treatment. The remaining aqueous solution may be returned again to the first dissolution tank 21 or the buffer tank 23 described below.

[0030] Here, lithium fluoride is contained in the roasted product introduced into the first dissolving tank 21. As described above, waste LIB contains fluorine, and the fluorine combines with lithium during roasting, etc., to produce lithium fluoride (LiF). Lithium fluoride does not dissolve in water in the first dissolving tank 21 and is contained in the residue.

[0031] In this embodiment, the recovery process P2 includes a second dissolution process P25, a second separation process P26, and a calcium separation process P27. Correspondingly, the recovery system 2 includes a second dissolution tank 25, a second separator 26, and a calcium separation device 27.

[0032] In the second dissolution process P25, the residue remaining after immersion in the first dissolution tank 21 is introduced into a second dissolution tank 25, which is different from the first dissolution tank 21, and immersed in water. For this purpose, the second dissolution tank 25 is configured to store new water and to receive the residue. The residue is supplied to the second dissolution tank 25 in predetermined amounts via a hopper 30. Furthermore, calcium hydroxide (Ca(OH)2) is added to the water in the second dissolution tank 25. As a result, the aqueous solution in the second dissolution tank 25 becomes a mixture of new water, the residue, and calcium hydroxide. The second dissolution tank 25 is equipped with a stirring mechanism for stirring the aqueous solution in the second dissolution tank 25.

[0033] In the second dissolution tank 25 where water, residue, and calcium hydroxide are introduced, the following three reactions occur: Ca(OH)2 → Ca 2+ +2OH - ... (1) LiF → Li + +F - ... (2) Ca 2+ +2F - →CaF2 ... (3)

[0034] That is, when calcium hydroxide is added to the water in the second dissolution tank 25, the calcium hydroxide dissolves in the water, generating calcium ions and hydroxide ions, as shown in reaction formula (1). When lithium fluoride contained in the residue in the second dissolution tank 25 dissolves in the water, lithium ions and fluorine ions are generated, as shown in reaction formula (2). At this time, the calcium ions and fluorine ions combine to generate calcium fluoride (CaF2), as shown in reaction formula (3). When the fluorine ion concentration in the aqueous solution decreases due to the generation of calcium fluoride, the ionization of lithium fluoride, i.e., its dissolution, is promoted. As a result of the promotion of the dissolution of lithium fluoride, the lithium ions in the aqueous solution increase.

[0035] The residue remaining after immersion in the first dissolving tank 21 may contain a small amount of lithium carbonate that was not dissolved in the first dissolving step P21. The lithium carbonate contained in the residue is dissolved in the second dissolving tank 25. However, even in this case, the amount of lithium carbonate introduced into the second dissolving tank 25 is smaller than the amount of lithium carbonate introduced into the first dissolving tank 21, and furthermore, the second dissolving tank 25 has a higher solid-liquid ratio than the first dissolving tank 21, so the lithium concentration is diluted. Therefore, the effect of this on the dissolution of lithium fluoride in the second dissolving tank 25 is considered to be sufficiently small.

[0036] Lithium fluoride has a lower solubility than lithium carbonate, so the weight ratio of water to the residue in the second dissolving tank 25 is set to be greater than the weight ratio of water to the roasted material in the first dissolving tank 21. For example, the weight ratio of the amount of water in the second dissolving tank 25 to the residue introduced into the second dissolving tank 25 is set to be 20 to 40 times.

[0037] If the weight ratio is less than 20 times, the lithium concentration will not be sufficiently dilute, and lithium fluoride may not be sufficiently dissolved. On the other hand, if the weight ratio exceeds 40 times, the second dissolving tank 25 will become too large, and the amount of water consumed will increase, resulting in increased costs. In contrast, by setting the weight ratio of the amount of water in the second dissolving tank 25 to the residue introduced into the second dissolving tank 25 at 20 times or more and 40 times or less, lithium fluoride contained in the residue can be sufficiently dissolved in the second dissolving tank and costs can be suppressed. Note that the weight ratio is more preferably 25 times or more and 35 times or less. The weight ratio is even more preferably about 28 times.

[0038] In the second separation step P26, a second solid-liquid separation is performed on the aqueous solution treated in the second dissolution step P25. For this purpose, the second separator 26 is configured as a solid-liquid separator. By performing solid-liquid separation in the second separator 26, solid residues containing calcium fluoride and other impurities are removed from the aqueous solution. In the calcium separation step P27, excess calcium derived from calcium hydroxide and lithium are separated from the aqueous solution separated in the second solid-liquid separation.

[0039] The calcium separation step P27 includes a precipitation step P28 and a third separation step P29. Correspondingly, the calcium separation device 27 includes a precipitation tank 28 and a third separator 29. In the precipitation step P28, carbon dioxide gas is bubbled into the aqueous solution separated in the second solid-liquid separation. For this purpose, the precipitation tank 28 is configured to be able to introduce carbon dioxide gas. By bubbling carbon dioxide gas into the aqueous solution in the precipitation tank 28, excess calcium derived from the calcium hydroxide introduced in the second dissolution step P25 is precipitated as solid calcium carbonate (CaCO3). Therefore, lithium and calcium contained in the aqueous solution separated in the second solid-liquid separation can be easily separated. This makes it possible to prevent the purity of the recovered lithium carbonate from being reduced by the added calcium.

[0040] In this embodiment, the carbon dioxide gas is bubbled so that the pH of the aqueous solution separated in the second solid-liquid separation is within the range of 8 to 10. If the pH of the aqueous solution after bubbling is less than 8, the precipitated calcium carbonate may redissolve as calcium bicarbonate (Ca(HCO3)2), making it impossible to separate calcium from lithium. Furthermore, since the pH of the aqueous solution before bubbling is around 12, if the pH of the aqueous solution after bubbling is greater than 10, excess calcium cannot be sufficiently precipitated. In contrast, by bubbling carbon dioxide gas so that the pH of the aqueous solution separated in the second solid-liquid separation is within the range of 8 to 10, calcium in the aqueous solution can be appropriately separated from lithium. The pH of the aqueous solution after bubbling is more preferably set to 8.5.

[0041] In the third separation step P29, the aqueous solution after bubbling is subjected to a third solid-liquid separation. For this purpose, the third separator 29 is configured as a solid-liquid separator. By performing solid-liquid separation in the third separator 29, solid residues such as calcium carbonate are removed from the aqueous solution. The aqueous solution separated by the third solid-liquid separation is introduced into the lithium recovery device 24.

[0042] In this embodiment, the recovery step P2 includes a storage step P23 in which the aqueous solution separated in the first solid-liquid separation and the aqueous solution separated in the third solid-liquid separation are temporarily stored. For this purpose, the recovery system 2 is provided with a buffer tank 23 into which the aqueous solution discharged from the first separator 22 and the aqueous solution discharged from the third separator 29 are introduced. As a result, lithium in the aqueous solution separated in the third solid-liquid separation is also recovered in the lithium recovery step P24.

[0043] As described above, according to the present embodiment, the roasted product obtained by roasting waste lithium-ion batteries is immersed in water in the first dissolving tank 21, and the resulting residue is then immersed in water again in the second dissolving tank 25, which is different from the first dissolving tank 21. At this time, calcium hydroxide is added to the second dissolving tank 25. This promotes dissolution of lithium fluoride contained in the residue, allowing the lithium contained in the residue to be recovered. This therefore increases the lithium recovery rate.

[0044] Here, the reason why calcium hydroxide is not added to the first dissolving tank 21 will be explained. As described above, the roasted product of waste LIB is introduced into the first dissolving tank 21. This roasted product contains at least lithium carbonate and lithium fluoride as lithium compounds. The solubility of lithium carbonate in water is greater than the solubility of lithium fluoride in water. Therefore, in the first dissolving tank 21, dissolution of lithium carbonate predominates, and dissolution of lithium fluoride hardly occurs. Furthermore, the fact that the amount of lithium carbonate in the roasted product is greater than the amount of lithium fluoride is also cited as one of the reasons why lithium fluoride is difficult to dissolve.

[0045] Therefore, it is thought that adding calcium hydroxide to such an aqueous solution in first dissolving tank 21 would saturate the lithium ions due to the dissolution of lithium carbonate, and would not promote the dissolution of lithium fluoride. Based on this finding, the inventors came up with the idea of ​​immersing the residue containing lithium fluoride in new water, i.e., water not saturated with lithium ions, in second dissolving tank 25, which is different from first dissolving tank 21, in order to dissolve lithium fluoride in water.

[0046] Lithium fluoride that does not dissolve in the first dissolving tank 21 and is separated as a residue is again immersed in water in the second dissolving tank 25, whereby the lithium fluoride dissolves and the lithium component contained in the lithium fluoride can be recovered.

[0047] From the above description, many improvements and other embodiments of the present disclosure will be apparent to those skilled in the art. Therefore, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. Details of the structure or function thereof can be substantially changed without departing from the spirit of the present disclosure.

[0048] [Other Embodiments] For example, in the above embodiment, a processing system in which one or more devices or equipment correspond to each process is exemplified, but the processing system may be configured so that one device or equipment performs multiple processes.

[0049] In the above embodiment, the aqueous solution separated in the calcium separator 27 is mixed with the aqueous solution separated in the first separator 22 and introduced into the lithium recovery device 24. However, these aqueous solutions may be treated separately. For example, the calcium separator 27 may have the same function as the lithium recovery device 24, i.e., the function of performing the concentration and solid-liquid separation steps, after the third separation step P29.

[0050] [Summary of the Disclosure] [Item 1] A method for treating used lithium ion batteries according to one embodiment of the disclosure is a method for recovering lithium from used lithium ion batteries containing fluorine, comprising the steps of: roasting the used lithium ion batteries to obtain a roasted product, introducing the roasted product into a first dissolving tank and immersing it in water; performing a first solid-liquid separation on the aqueous solution after immersion in the first dissolving tank; recovering the lithium from the aqueous solution separated by the first solid-liquid separation; introducing the residue after immersion in the first dissolving tank into a second dissolving tank different from the first dissolving tank and immersing it in water; adding calcium hydroxide to the water in the second dissolving tank; performing a second solid-liquid separation on the aqueous solution after immersion in the second dissolving tank; and separating excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation.

[0051] According to the above method, the roasted product obtained by roasting waste lithium-ion batteries is immersed in water in a first dissolving tank, and the resulting residue is then immersed in water again in a second dissolving tank different from the first dissolving tank. At this time, calcium hydroxide is added to the second dissolving tank. This promotes dissolution of lithium fluoride contained in the residue, allowing the lithium contained in the residue to be recovered. Therefore, the lithium recovery rate can be increased.

[0052] [Item 2] In the method for treating waste lithium-ion batteries according to Item 1, the weight ratio of the amount of water in the second dissolving tank to the amount of the residue introduced into the second dissolving tank may be 20 to 40 times, thereby making it possible to sufficiently dissolve lithium fluoride contained in the residue in the second dissolving tank and suppressing an increase in costs.

[0053] [Item 3] In the method for treating waste lithium-ion batteries according to Item 1 or 2, the aqueous solution separated in the second solid-liquid separation may be bubbled with carbon dioxide gas, and the aqueous solution after the bubbling may be subjected to a third solid-liquid separation to remove the excess calcium as a solid. By performing the bubbling with carbon dioxide gas, the excess calcium derived from the calcium hydroxide added in the second dissolution tank can be precipitated. Therefore, lithium and calcium contained in the aqueous solution separated in the second solid-liquid separation can be easily separated. This makes it possible to prevent the purity of the recovered lithium carbonate from being reduced by the added calcium.

[0054] [Item 4] In the method for treating waste lithium-ion batteries according to Item 3, the bubbling with carbon dioxide gas may be carried out so that the pH of the aqueous solution separated in the second solid-liquid separation falls within a range of 8 to 10. This allows calcium in the aqueous solution to be appropriately separated from lithium.

[0055] [Item 5] A treatment system for waste lithium-ion batteries according to another aspect of the present disclosure is a treatment system for waste lithium-ion batteries for recovering lithium from waste lithium-ion batteries containing fluorine, the treatment system including: a first dissolving tank into which a roasted product obtained by roasting the waste lithium-ion batteries is introduced and immersed in water; a first separator that performs a first solid-liquid separation on the aqueous solution after immersion in the first dissolving tank; a lithium recovery device that recovers the lithium from the aqueous solution separated by the first separator; a second dissolving tank different from the first dissolving tank, into which a residue after immersion in the first dissolving tank is introduced and immersed in water to which calcium hydroxide is added; a second separator that performs a second solid-liquid separation on the aqueous solution after immersion in the second dissolving tank; and a calcium separation device that separates excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation, wherein calcium hydroxide is added to the water in the second dissolving tank.

[0056] 2 Recovery system (treatment system) 21 First dissolution tank 22 First separator 24 Lithium recovery device 25 Second dissolution tank 26 Second separator 27 Calcium separation device

Claims

1. A method for treating used lithium-ion batteries to recover lithium from used lithium-ion batteries containing fluorine, comprising: introducing a roasted product obtained by roasting the used lithium-ion batteries into a first dissolving tank and immersing it in water; performing a first solid-liquid separation on the aqueous solution after immersion in the first dissolving tank; recovering the lithium from the aqueous solution separated by the first solid-liquid separation; introducing a residue after immersion in the first dissolving tank into a second dissolving tank different from the first dissolving tank and immersing it in water; adding calcium hydroxide to the water in the second dissolving tank; performing a second solid-liquid separation on the aqueous solution after immersion in the second dissolving tank; and separating excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation.

2. A method for treating waste lithium-ion batteries as described in claim 1, wherein the weight ratio of the amount of water in the second dissolution tank to the amount of the residue introduced into the second dissolution tank is 20 times or more and 40 times or less.

3. The method for treating waste lithium-ion batteries according to claim 1 or 2, further comprising bubbling carbon dioxide gas through the aqueous solution separated in the second solid-liquid separation, and then subjecting the aqueous solution after the bubbling to a third solid-liquid separation, thereby removing the excess calcium as a solid.

4. A method for treating waste lithium-ion batteries as described in claim 3, wherein the bubbling with carbon dioxide gas is carried out so that the pH of the aqueous solution separated in the second solid-liquid separation is within the range of 8 to 10.

5. A treatment system for waste lithium-ion batteries for recovering lithium from waste lithium-ion batteries containing fluorine, comprising: a first dissolving tank into which a roasted product obtained by roasting the waste lithium-ion batteries is introduced and immersed in water; a first separator that performs a first solid-liquid separation on the aqueous solution after immersion in the first dissolving tank; a lithium recovery device that recovers the lithium from the aqueous solution separated in the first separator; a second dissolving tank different from the first dissolving tank, into which the residue after immersion in the first dissolving tank is introduced and immersed in water to which calcium hydroxide is added; a second separator that performs a second solid-liquid separation on the aqueous solution after immersion in the second dissolving tank; and a calcium separation device that separates excess calcium derived from the calcium hydroxide and the lithium from the aqueous solution separated by the second solid-liquid separation.

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