Method for producing electrolyte for secondary battery, method for manufacturing secondary battery, and secondary battery

Abstract

To provide a method for producing an electrolyte for a secondary battery which can reduce consumption of rare resources by efficiently recovering and effectively utilizing a used electrolyte contained in a used secondary battery.SOLUTION: The method for producing the electrolyte for the secondary battery includes: a step (step S1) of disassembling a used secondary battery and taking out contents; and a step (step S2) of immersing the contents in a solvent for extraction, extracting or expelling the used electrolyte which adheres to or permeates through the contents, and obtaining an extracted liquid.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an electrolyte for a secondary battery, a method for producing a secondary battery, and a secondary battery. More specifically, the present invention relates to a method for efficiently recovering used electrolyte contained in a used secondary battery to produce a reusable electrolyte, a method for producing a secondary battery using the electrolyte, and a secondary battery including the electrolyte. [Background technology]

[0002] The EU and other countries are working to establish laws and regulations regarding the recycling of secondary batteries such as lithium-ion secondary batteries. Specifically, laws and regulations are being established that require that a specified percentage or more of the materials used in secondary batteries be reused in secondary batteries.

[0003] JP 2010-34021 A describes a method for recovering oxide-containing battery material from battery waste. This recovery method includes a step of immersing a substrate to which an oxide-containing battery material is attached in a solvent in which the oxide is substantially insoluble to peel the battery material from the substrate, and a step of separating the peeled battery material from the substrate.

[0004] Japanese Patent No. 5141970 describes a method for recovering a positive electrode active material from the positive electrode of a lithium battery. The lithium battery to which this recovery method is applied has a positive electrode active material layer formed by applying a material containing a positive electrode active material dispersed in an aqueous solvent, a conductive material, and a binder to the surface of a positive electrode current collector. This recovery method includes a step of immersing the positive electrode in an alkaline aqueous solution to peel the positive electrode active material layer from the positive electrode current collector, a step of adding an organic solvent to the peeled positive electrode active material layer peeled material to extract the binder from the peeled material, and a step of separating a supernatant containing the conductive material from a precipitate containing the positive electrode active material from the extracted material after the extraction step.

[0005] JP 2017-16941 A describes a method of removing electrolyte from battery components including a battery case, disassembling a lithium ion battery, and removing and recovering the battery components including the battery case without waste. This method of removing electrolyte from the inside of a battery case filled with electrolyte includes an opening forming step of forming an opening in the battery case, an electrolyte suction step of sucking the electrolyte from the inside of the battery case through the opening into a sealed and depressurized electrolyte recovery trap, a solvent injection step of injecting a solvent not containing electrolyte from a solvent tank into the inside of the battery case through the opening, and a mixed liquid suction step of sucking a mixed liquid containing the solvent injected into the inside of the battery case in the solvent injection step and the electrolyte remaining inside the battery case from the inside of the battery case through the opening into a sealed and depressurized electrolyte recovery trap. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2010-34021 A [Patent Document 2] Patent No. 5141970 [Patent Document 3] JP 2017-16941 A Summary of the Invention [Problem to be solved by the invention]

[0007] Among the materials contained in used secondary batteries, various methods such as horizontal recycling, wet recycling, and dry recycling have been considered for the metals of electrodes (active materials and current collecting foils) and exterior materials. These methods are mainly aimed at recovering valuable metals and metal oxides used as active materials.

[0008] On the other hand, as shown in Patent Document 3, other materials contained in secondary batteries (electrolyte and separator) are mainly incinerated, although some recovery is being considered. However, electrolyte may contain elements with high resource value such as fluorine and phosphorus. There is a risk of resource depletion of fluorine, the raw material of fluorine, and the risk of resource depletion of phosphorus has exceeded the planetary boundary, and the situation is already tight. Currently, most phosphorus is consumed in fertilizer and steelmaking, and recycling is being implemented in these fields. In the future, as electric vehicles become more widespread, it is expected that the consumption of fluorine and phosphorus by secondary batteries will also increase dramatically, so resource recovery and reuse from secondary batteries are important issues.

[0009] Furthermore, in secondary batteries where the charge / discharge cycle has progressed, the amount of electrolyte decreases due to decomposition or the like, and it is often impossible to extract the electrolyte as is, and there is a concern that the process shown in Patent Document 3 will not lead to efficient recovery.

[0010] An object of the present invention is to provide a method for producing an electrolyte for a secondary battery that can reduce the consumption of scarce resources by efficiently recovering and effectively utilizing the used electrolyte contained in a used secondary battery. Another object of the present invention is to provide a method for producing a secondary battery that can reduce the consumption of scarce resources, and to provide a secondary battery in which the consumption of scarce resources is reduced. [Means for solving the problem]

[0011] A method for producing an electrolyte solution for a secondary battery according to one embodiment of the present invention includes the steps of dismantling a used secondary battery and removing the contents, and immersing the contents in an extraction solvent to extract or expel the used electrolyte solution adhering to or permeating the contents, thereby obtaining an extract.

[0012] A method for manufacturing a secondary battery according to an embodiment of the present invention includes a step of manufacturing a secondary battery using the electrolyte solution manufactured by the above-mentioned method for manufacturing an electrolyte solution for a secondary battery.

[0013] A secondary battery according to an embodiment of the present invention includes an electrolyte solution manufactured by the above-mentioned method for manufacturing an electrolyte solution for a secondary battery. Effect of the Invention

[0014] According to the present invention, the consumption of scarce resources can be reduced by efficiently recovering and effectively utilizing the spent electrolyte contained in a secondary battery after use. [Brief description of the drawings]

[0015] [Figure 1] FIG. 1 is a flow diagram of a method for producing an electrolyte for a secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] [Electrolyte solution manufacturing method] 1 is a flow diagram of a method for producing an electrolyte for a secondary battery according to one embodiment of the present invention. This method includes a step of dismantling a used secondary battery and removing the contents (step S1), a step of immersing the contents in an extraction solvent to extract or drive off the used electrolyte adhering to or permeating the contents to obtain an extract (step S2), a step of concentrating the extract (step S3), and a step of adding another solvent to the extract (step S4).

[0017] The method for producing an electrolyte for a secondary battery according to the present embodiment is a method for producing a reusable electrolyte by recovering used electrolyte contained in a used secondary battery. The "used secondary battery" is, but is not limited to, a secondary battery that is recovered because its discharge capacity has decreased due to repeated charging and discharging and it is no longer suitable for reuse. The secondary battery is, for example, a lithium ion secondary battery.

[0018] The electrolyte solution to be recovered in this embodiment and the electrolyte solution to be produced in this embodiment are preferably non-aqueous electrolyte solutions obtained by dissolving an electrolyte in a non-aqueous solvent. The electrolyte solution to be recovered and the electrolyte solution to be produced do not need to have the same composition. The electrolyte solution to be produced in this embodiment may be any electrolyte solution that can be used as an electrolyte solution (preferably a non-aqueous electrolyte solution) for a secondary battery (preferably a non-aqueous secondary battery).

[0019] The electrolyte of the electrolytic solution is a dissociable salt, and a metal salt, particularly a lithium salt, is preferably used. Examples of the lithium salt include, but are not limited to, lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bis(trifluoromethanesulfonyl)imide (LiN(SO 2 CF 3 ) 2 ) and lithium bis(fluorosulfonyl)imide (LiN(SO 2 F) 2 ) is preferably used, and LiPF 6 and LiN(SO 2 F) 2 is particularly preferably used.

[0020] The solvent for the electrolytic solution is preferably a non-aqueous solvent, and among them, an organic solvent, particularly an organic polar solvent, is preferably used. Specific examples of the solvent that can be used as the solvent for the electrolytic solution will be described later.

[0021] [Step of removing the contents (Step S1)] First, a used secondary battery is disassembled and the contents are removed (step S1). The contents of a secondary battery are mainly positive and negative electrodes, a separator, and an electrolyte. These contents are generally housed in an exterior body made of a metal or a laminate film. In addition to these, a secondary battery may contain parts such as lead wires, current collecting tabs, and spacers for electrical insulation. Parts other than the positive and negative electrodes, separators, and electrolyte (parts with little electrolyte adhesion, such as spacers) may or may not be included in the targets to be immersed in the extraction solvent in the next extraction step (step S2).

[0022] The electrodes and separators are generally stored in the exterior body in the form of an electrode laminate in which a sheet-shaped electrode and a sheet-shaped separator are laminated, or in the form of an electrode winding in which a strip-shaped electrode and a strip-shaped separator are stacked and wound. In the case of an electrode laminate, the electrodes may be stored in a bag-shaped separator. Hereinafter, such a structure consisting of an electrode and a separator is referred to as an "electrode body." In secondary batteries such as lithium-ion secondary batteries, the amount of electrolyte used is usually kept to a minimum, and most of the electrolyte exists in a state of adhering to or permeating the contents of the electrode body, etc.

[0023] The step of dismantling a used secondary battery and removing the contents (step S1) may involve only removing the exterior body. From the viewpoint of reusing or recycling the electrode body after recovering the used electrolyte, it is preferable to remove the electrode body as it is without disassembling it.

[0024] [Step S2 of extracting electrolyte] Next, the contents removed in step S1 are immersed in an extraction solvent to extract or expel the used electrolyte adhering to or penetrating the contents (step S2). More specifically, the extraction solvent (hereinafter referred to as "extraction solvent") is poured into a solvent-resistant container or the like, and the contents removed in step S1 are immersed in this extraction solvent. Note that it is not necessary to immerse all of the contents removed in step S1 in the extraction solvent, and only a portion of the contents removed in step S1 (for example, only the positive electrode, only the negative electrode, or only the separator) may be immersed.

[0025] As described above, most of the used electrolyte contained in a used secondary battery exists in a state of adhering to or permeating the contents such as the electrode body, and is often not present in a state that can be recovered as free droplets. In this embodiment, the contents are immersed in an extraction solvent, and the electrolyte adhering to or permeating the contents is dissolved in the extraction solvent or expelled, thereby recovering the electrolyte. Hereinafter, the liquid obtained by this process, in which the used electrolyte is dissolved in the extraction solvent (or expelled), is referred to as the "extraction liquid."

[0026] The extraction solvent is preferably mainly composed of a solvent that can be used as a solvent for the electrolyte of a secondary battery. In other words, the extraction solvent is preferably free of solvents that are not suitable as a solvent for the electrolyte of a secondary battery. Examples of solvents that are not suitable as a solvent for the electrolyte of a secondary battery include solvents that become unstable at the temperature at which the secondary battery is used, solvents that significantly reduce the properties of the electrolyte (such as ion mobility), solvents that electrochemically decompose by oxidation or reduction, solvents with extremely high viscosity, and solvents that corrode the components of the secondary battery (such as electrodes, separators, and exterior bodies).

[0027] If the extraction solvent contains a solvent that is not suitable as a solvent for the electrolyte of a secondary battery, the extraction liquid will also contain this solvent. This solvent may be separated from the extraction liquid by chemical or physical operations, but it may be difficult to completely remove. In addition, the need for a separation operation complicates the process and causes increased costs. By using a solvent that can be used as a solvent for the electrolyte of a secondary battery as the extraction solvent, the extraction liquid can be used as an electrolyte as is, or by adding a relatively simple operation.

[0028] Specific examples of solvents that can be used as the solvent for the electrolyte of a secondary battery include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC), and cyclic esters such as γ-butyrolactone (γ-BL).

[0029] The extraction solvent is not particularly limited to the above solvents, but it is preferable that the main component is one or more selected from the group consisting of the above solvents. In this case, the ratio of components other than the main component in the extraction solvent is preferably 40% by volume or less. The ratio of components other than the main component is more preferably 20% by volume or less, even more preferably 5% by volume or less, and most preferably 0% by volume.

[0030] Among the above solvents, DMC, DEC and EMC are particularly preferred. Therefore, the total ratio of one or more selected from the group consisting of these particularly preferred solvents in the extraction solvent is preferably 60% by volume or more. The total ratio of one or more selected from the group consisting of these particularly preferred solvents is more preferably 80% by volume or more, even more preferably 95% by volume or more, and most preferably 100% by volume.

[0031] The extraction solvent is preferably a solvent with low viscosity. This is because the lower the viscosity of the solvent, the easier it is to extract the electrolyte. For example, it is preferable to select DEC or DMC rather than PC or EC. The viscosity of the extraction solvent is preferably 5.0 cP or less at 25°C, more preferably 2.0 cP or less at 25°C, and even more preferably 1.0 cP or less at 25°C.

[0032] The extraction solvent does not have to be the same as the solvent contained in the electrolyte to be recovered. However, when an electrolyte similar to the electrolyte to be recovered is to be produced, it is preferable to use a solvent selected from the solvents contained in the electrolyte to be recovered (the electrolyte contained in the secondary battery after use). For example, when the solvent of the electrolyte to be recovered is a mixed solvent of EC and DEC, it is preferable to use EC or DEC, or a mixed solvent thereof. Note that since the ratio of the solvents (mixing ratio) can be adjusted in a later process, even when an electrolyte similar to the electrolyte to be recovered is to be produced, it is not necessary to make the ratio of the solvents constituting the extraction solvent the same as the ratio of the solvent of the electrolyte to be recovered.

[0033] It is difficult to directly analyze and obtain information such as the composition of the electrolyte solution to be recovered. In order to analyze the electrolyte solution, it is necessary to recover the electrolyte solution by other methods such as centrifugation, which makes the method of the present embodiment aimed at reuse inapplicable. Therefore, when an electrolyte solution similar to the electrolyte solution to be recovered is to be produced, it is preferable to obtain information on the electrolyte solution to be recovered (type of electrolyte, type of solvent, etc.) from product information of the secondary battery to be recovered.

[0034] The immersion time in the extraction solvent is not limited to this, but is, for example, 1 to 24 hours. The longer the immersion time, the more electrolyte can be recovered. On the other hand, the increase in the recovery amount slows down as the immersion time becomes longer. The relationship between the immersion time and the recovery amount of the electrolyte depends on various conditions, but in an experiment under certain conditions, 60% by volume of the electrolyte could be recovered by immersion for 5 to 6 hours, and 70% by volume of the electrolyte could be recovered by immersion for 12 hours. On the other hand, it took about 36 hours to recover 80% by volume of the electrolyte. The lower limit of the immersion time is preferably 3 hours, and more preferably 5 hours. The upper limit of the immersion time is not particularly limited, but is preferably 18 hours, and more preferably 12 hours, from the viewpoint of efficiency.

[0035] The immersion conditions are such that the contents are simply immersed in the extraction solvent at room temperature, but if necessary, the temperature of the extraction solvent may be adjusted by heating, the container (immersion tank) may be rocked, the extraction solvent may be stirred, etc. When the extraction solvent is heated, the temperature is preferably 70°C or less, more preferably 50°C or less, and particularly preferably 40°C or less, in order to prevent the solvent from volatilizing.

[0036] Alternatively, fresh extraction solvent may be continuously injected into the container and the extracted liquid removed from the container for a certain period of time, so that the electrolyte is extracted while fresh extraction solvent is passed around the contents of the container for a certain period of time.

[0037] [Step S3: Concentrating the extract] After the electrolyte is extracted, the extract is separated from the contents (electrode body, etc.), and the extract is concentrated (step S3). The extract immediately after the step of extracting the electrolyte (step S2) has a low concentration of electrolyte (lithium salt, etc.) because the extraction solvent has been added. By concentrating the extract, the electrolyte concentration can be adjusted to a predetermined concentration. For example, reduced pressure distillation can be used as a concentration method.

[0038] [Step S4: Adding Solvent] If necessary, another solvent is added to the extract (step S4). The extract immediately after the step of extracting the electrolyte (step S2) or the extract immediately after the step of concentrating the extract (step S3) has a high ratio of the extraction solvent, so another solvent is added to adjust the ratio of the solvent in the extract. For example, when DEC is used as the extraction solvent to recover an electrolyte containing a mixed solvent of EC and DEC, the ratio of the solvent in the extract can be made closer to that of the original electrolyte by adding EC to the extract (or its concentrate).

[0039] As described above, the manufacturing method of the electrolyte solution for the secondary battery according to the present embodiment is not intended only to manufacture an electrolyte solution having the same composition as the electrolyte solution to be recovered. Therefore, in the step of adding another solvent to the extraction solution (step S4), a solvent different from the solvent contained in the electrolyte solution to be recovered may be added. As in the case of the extraction solvent, the solvent to be added is preferably mainly composed of a solvent that can be used as a solvent for the electrolyte solution for the secondary battery.

[0040] This step (step S4) is an optional step, and the extract can function as an electrolyte for the secondary battery even without performing this step. However, by performing this step, the solvent ratio can be optimized, and the performance of the electrolyte can be further improved.

[0041] Through the above steps, an electrolyte solution for a secondary battery is produced. The concentration of the electrolyte in the electrolyte solution may be adjusted as appropriate depending on the specifications and applications of the secondary battery, but for example, when the secondary battery is a lithium ion secondary battery, it is preferable that the electrolyte concentration in the electrolyte solution (extraction solution) after all steps is completed is within the range of 0.3 to 3.0 M. When a solvent addition step (step S4) is performed, it is preferable to adjust the concentration level in the extraction solution concentration step (step S3) taking into consideration the amount of the solvent to be added.

[0042] In one or more of the steps of extracting the electrolyte (step S2), concentrating the extract (step S3), and adding a solvent (step S4), it is preferable to add metallic lithium pieces to the extraction solvent or the extraction solution. This makes it possible to remove impurities from the extraction solvent and the extraction solution. There is no particular limit to the weight or size of the metallic lithium pieces, but adding too many pieces will waste lithium resources, so it is sufficient to add the minimum number of small pieces. The size of the metallic lithium pieces varies depending on the amount of electrolyte to be treated and is not particularly limited. For example, it is about 10 mm x 10 mm x 0.25 mm.

[0043] Since the contents (electrode body, etc.) after the treatment still contain unrecovered electrolyte, the electrolyte may be recovered by immersing the contents again in a new extraction solvent. This operation may be repeated. However, it is practically difficult to recover 100% of the electrolyte physically adsorbed on the electrode body, etc., and the extraction concentration decreases with each repetition, which increases the cost of concentration. Therefore, it is practical to carry out the process multiple times, but only about two times.

[0044] If necessary, any additive (for example, vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, adiponitrile, etc.) may be further added to the produced electrolyte solution (extraction solution).

[0045] The produced electrolyte solution (extract) may be mixed with another electrolyte solution for use. For example, an electrolyte solution (new electrolyte solution) produced by a normal method may be mixed with an electrolyte solution (regenerated electrolyte solution) produced by the production method according to the present embodiment at a predetermined ratio for use. In this case, the ratio of the electrolyte solution (regenerated electrolyte solution) produced by the production method according to the present embodiment to the total electrolyte solution is preferably 10 to 50 volume %.

[0046] [Secondary battery manufacturing method and secondary battery] A method for manufacturing a secondary battery according to an embodiment of the present invention includes a step of manufacturing a secondary battery using the electrolyte solution manufactured by the above-mentioned method for manufacturing the electrolyte solution. The secondary battery according to an embodiment of the present invention includes the electrolyte solution manufactured by the above-mentioned method for manufacturing the electrolyte solution.

[0047] [Effects of this embodiment] The present invention relates to a method for producing an electrolyte for a secondary battery, a method for producing a secondary battery, and a secondary battery according to an embodiment of the present invention. According to the present invention, the consumption of scarce resources can be reduced by efficiently recovering and effectively utilizing the used electrolyte contained in a secondary battery after use.

[0048] In this embodiment, rare resources such as fluorine and phosphorus are not separated and recovered, but are recovered and reused while retaining their function as an "electrolyte". When separating and recovering fluorine and phosphorus, CaF and PO 4 However, in order to reuse them as an electrolyte, it is necessary to synthesize an electrolyte from these substances. According to the present embodiment, the substances are recovered while retaining their function as an "electrolytic solution", so that the substances can be recovered and reused at low cost.

[0049] Another method for recovering used electrolyte from a used secondary battery, for example for recovering electrolyte for analysis, is to make a small hole in the exterior body of the secondary battery and then recover the electrolyte by centrifuging it. This method is a batch type process in which secondary batteries are treated one by one, so it is not suitable for large-scale processing. If multiple secondary batteries are to be treated at the same time, a correspondingly large device is required.

[0050] Although the purpose is different from that of the method according to the present embodiment, a solvent extraction method is also used to recover lithium from an electrolyte solution. This method uses a solvent that is not compatible with the electrolyte solution and has high lithium solubility to extract lithium into the solvent. In this method, the elements or ions to be extracted can be extracted separately, but when the lithium is to be reused as an electrolyte solution, it is necessary to synthesize lithium salts again and mix them into the solvent.

[0051] In contrast, according to the method for producing an electrolyte for a secondary battery according to the present embodiment, the used electrolyte can be collected and reused while retaining its function as an "electrolytic solution." In addition, by placing multiple electrode bodies in one container (immersion tank), it is possible to process a large amount of electrolyte at once. EXAMPLES

[0052] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0053] A small laminated secondary battery (card cell) was fabricated using electrolyte recovered from a used secondary battery (deteriorated cell), and the battery was evaluated.

[0054] The electrolyte used in the degraded cells is LiPF 6 The contents contained EC, DEC, and EMC as solvents. The ratio of the solvents at the time of disassembly was not confirmed. The deteriorated cell was disassembled and the contents were immersed in an extraction solvent. DMC was used as the extraction solvent. After immersion for 24 hours, the recovery rate was approximately 60-70% by volume.

[0055] The composition of the extract before concentration was as follows: LiPF 6 Concentration of 0.027M Solvent ratio (volume%) EC / DEC / DMC / EMC = 0.86 / 0.73 / 97.38 / 1.03

[0056] The composition of the concentrated extract was as follows: [Recovery Example 1] LiPF 6 Concentration of 0.43M Solvent ratio (volume %) EC / DEC / DMC / EMC = 15.08 / 4.98 / 76.65 / 3.29

[0057] In the same manner, electrolytes were recovered from the same deteriorated cells, and the concentration was varied to obtain electrolytes having the following compositions. [Recovery Example 2] LiPF 6 Concentration of 0.29M Solvent ratio (volume %) EC / DEC / DMC / EMC = 11.70 / 8.97 / 66.49 / 12.84 [Recovery Example 3] LiPF 6 Concentration of 0.12M Solvent ratio (volume %) EC / DEC / DMC / EMC = 5.09 / 4.13 / 85.06 / 5.72

[0058] For reference, card cells were prepared using the following electrolytes: [Reference electrolyte] LiPF 6 Concentration of 1.0M Solvent ratio (volume%) EC / DEC=30 / 70

[0059] The card cell used for the battery evaluation contained LCO in the positive electrode and graphite in the negative electrode, and had a capacity of 18 mAh. Charge and discharge tests were conducted on the card cell using the electrolytes of Recovery Examples 1 to 3 and the reference electrolyte. The results are shown in Table 1. In Table 1, "initial efficiency" represents the ratio of the initial discharge capacity to the initial charge capacity.

[0060] [Table 1]

[0061] These results confirmed that the electrolyte recovered from the deteriorated cells can be reused as an electrolyte for secondary batteries. 6 In Recovery Example 3, where the concentration of LiPF is low, the salt concentration is somewhat insufficient and the loading characteristics tend to be low, but it was confirmed that it can be used by adjusting the concentration to the optimum salt concentration. 6 It was confirmed that when the concentration of the electrolyte was concentrated to about 0.4M, the battery characteristics were comparable to those of a new reference electrolyte.

[0062] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-mentioned embodiment, and various modifications are possible within the scope of the invention.

Claims

1. A step of dismantling a used secondary battery and removing its contents; and a step of immersing the contents in an extraction solvent and extracting or expelling the used electrolyte adhering to or permeating the contents to obtain an extract.

2. A method for producing an electrolyte solution for a secondary battery according to claim 1, comprising the steps of: The extraction solvent contains, as a main component, a solvent that can be used as a solvent for an electrolyte of a secondary battery, The method for producing an electrolyte solution for a secondary battery, wherein the ratio of components other than the main component in the extraction solvent is 5 volume % or less.

3. A method for producing an electrolyte solution for a secondary battery according to claim 1, comprising the steps of: The extraction solvent contains one or more selected from the group consisting of cyclic carbonates, chain carbonates, and cyclic esters as a main component, The method for producing an electrolyte solution for a secondary battery, wherein the ratio of components other than the main component in the extraction solvent is 5 volume % or less.

4. A method for producing an electrolyte solution for a secondary battery according to claim 1, comprising the steps of: The extraction solvent contains one or more selected from the group consisting of propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and γ-butyrolactone as a main component; The method for producing an electrolyte for a secondary battery, wherein the ratio of components other than the main component in the extraction solvent is 5 volume % or less.

5. A method for producing an electrolyte solution for a secondary battery according to claim 4, comprising the steps of: A method for producing an electrolyte for a secondary battery, wherein the total ratio of one or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate in the extraction solvent is 60 volume % or more.

6. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The method for producing an electrolyte for a secondary battery, wherein the viscosity of the extraction solvent is 1.0 cP or less at 25° C.

7. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The method for producing an electrolyte for a secondary battery, wherein the solvent for extraction is selected from the solvents contained in the used electrolyte.

8. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The method for producing an electrolyte solution for a secondary battery further comprises a step of concentrating the extract.

9. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The method for producing an electrolyte solution for a secondary battery further comprises a step of adding another solvent to the extract.

10. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The method for producing an electrolyte for a secondary battery, wherein metallic lithium pieces are added to the extraction solvent or the extraction solution.

11. A method for producing an electrolyte solution for a secondary battery according to any one of claims 1 to 5, comprising the steps of: The used electrolyte extracted from the used secondary battery contains a lithium salt and an organic solvent.

12. A method for producing a secondary battery, comprising a step of producing a secondary battery using the electrolyte produced by the method for producing an electrolyte for a secondary battery according to any one of claims 1 to 5.

13. A secondary battery comprising an electrolyte produced by the method for producing an electrolyte for a secondary battery according to any one of claims 1 to 5.

14. The secondary battery according to claim 13, A secondary battery, wherein the proportion of the electrolyte produced by the method for producing an electrolyte for a secondary battery according to any one of claims 1 to 5 in the electrolyte for the secondary battery is 10 to 50 volume %.

Images