Method for producing regenerated carbon material

Abstract

The present invention relates to a method for producing a regenerated carbon material. Provided is a method for easily removing more Li from a carbon-based negative electrode active material containing Li to obtain a regenerated carbon material. This method for producing a regenerated carbon material comprises: a first heat treatment step in which a carbon-based negative electrode active material containing Li is heat-treated together with ethylene carbonate at a temperature less than the boiling point of ethylene carbonate to obtain a heat-treated product containing lithium ethylene dicarbonate; and a second heat treatment step for converting lithium ethylene dicarbonate into lithium carbonate by heat-treating the heat-treated product at a temperature equal to or higher than the boiling point of ethylene carbonate.

Description

Technical Field

[0001] This disclosure relates to a method for manufacturing recycled carbon materials. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used in various fields, such as vehicle power supplies and portable power sources. In recent years, from the perspective of SDGs (Safety, Government, and Goods Administration), there is a need to promote the reuse of used lithium-ion rechargeable batteries. As an example of this reuse, used lithium-ion rechargeable batteries have been recycled by classifying them into various materials (see, for example, Patent Documents 1 and 2).

[0003] On the other hand, as described in Patent Documents 1 and 2, carbon-based negative electrode active materials such as graphite are known as negative electrode active materials for lithium-ion secondary batteries.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2019-169309

[0007] Patent Document 2: Japanese Patent Publication No. 2022-547698 Summary of the Invention

[0008] In the aforementioned conventional technologies, sintering and acid leaching processes are performed to reuse used lithium-ion secondary batteries. However, the carbon-based negative electrode active material of used lithium-ion secondary batteries contains lithium (Li). During sintering and acid leaching, it is impossible to completely separate the carbon-based negative electrode active material from the lithium, leaving most of the Li within the material. Therefore, the presence of lithium limits the applicability of the recovered carbon-based negative electrode active material as a recycled carbon material. Due to this problem, there is a need to develop a technology that can easily remove Li from the carbon-based negative electrode active material.

[0009] Therefore, the purpose of this disclosure is to provide a method for easily removing more Li from Li-containing carbon-based anode active materials to obtain regenerated carbon materials.

[0010] The method for manufacturing recycled carbon materials disclosed herein includes: a first heat treatment step, wherein a carbon-based negative electrode active material containing Li is heat-treated together with ethylene carbonate at a temperature below the boiling point of ethylene carbonate to obtain a heat-treated product containing lithium diethylene carbonate; and a second heat treatment step, wherein the heat-treated product is heat-treated at a temperature above the boiling point of ethylene carbonate to convert lithium diethylene carbonate into lithium carbonate.

[0011] Based on this composition, it is easy to remove more Li from the Li-containing carbon-based negative electrode active material, thus obtaining recycled carbon material. Attached Figure Description

[0012] Figure 1 A flowchart illustrating the steps of the method for manufacturing the recycled carbon material of this disclosure.

[0013] Figure 2 The image shows a longitudinal cross-sectional view illustrating an example of the internal structure of a lithium-ion secondary battery containing a carbon-based negative electrode active material containing Li, used in the method for manufacturing the recycled carbon material of this disclosure.

[0014] Figure 3 To show Figure 2 The diagram shows an exploded view of the electrode structure of a lithium-ion secondary battery.

[0015] Figure 4 for Figure 2 The diagram shows a schematic cross-sectional view of the negative electrode of a lithium-ion secondary battery. Detailed Implementation

[0016] The embodiments disclosed herein will be described below with reference to the accompanying drawings. It should be noted that matters not mentioned in this specification and necessary for the implementation of this disclosure can be understood by those skilled in the art based on prior art. This disclosure can be implemented based on the content disclosed in this specification and common technical knowledge in the field. Furthermore, in the following drawings, components and parts that perform the same function are labeled with the same reference numerals. Additionally, the dimensional relationships (length, width, thickness, etc.) in the drawings do not reflect actual dimensional relationships. It should be noted that in this specification, the numerical range denoted as "A to B" includes both A and B.

[0017] It should be noted that in this specification, the term "secondary battery" refers to an energy storage device that can be repeatedly charged and discharged. Furthermore, in this specification, the term "lithium-ion secondary battery" refers to a secondary battery that uses lithium ions as charge carriers and achieves charging and discharging through the movement of charges accompanying lithium ions between the positive and negative electrodes.

[0018] The method for manufacturing recycled carbon materials disclosed herein is as follows: Figure 1As shown, the process includes the following steps as necessary steps: a first heat treatment step S101, in which a carbon-based negative electrode active material containing Li is heat-treated together with ethylene carbonate (hereinafter sometimes abbreviated as "EC") at a temperature below the boiling point of ethylene carbonate to obtain a heat-treated product containing lithium ethylene dicarbonate; and a second heat treatment step S102, in which the heat-treated product is heat-treated at a temperature above the boiling point of ethylene carbonate to convert lithium ethylene dicarbonate into lithium carbonate. Each step is described in detail below.

[0019] <First Heat Treatment Process>

[0020] First, the first heat treatment step S101 will be explained. The Li-containing carbon-based negative electrode active material is typically a carbon-based negative electrode active material recovered from a used lithium-ion secondary battery. That is, the Li-containing carbon-based negative electrode active material is typically the negative electrode active material of a used lithium-ion secondary battery. Since a large amount of active material is used, the requirements for reuse are particularly high; therefore, the Li-containing carbon-based negative electrode active material is preferably the negative electrode active material of a used lithium-ion secondary battery that was used as a power source for vehicle propulsion. However, the Li-containing carbon-based negative electrode active material is not limited to this. For example, the Li-containing carbon-based negative electrode active material could be the negative electrode active material of a lithium-ion secondary battery that was not shipped due to manufacturing defects.

[0021] When a lithium-ion secondary battery is charged, lithium ions are adsorbed onto the carbon-based negative electrode active material. Furthermore, during repeated charge-discharge cycles, lithium ions may deposit as metallic lithium on the surface of the carbon-based negative electrode active material. Alternatively, when recovering the carbon-based negative electrode active material from a lithium-ion secondary battery, lithium ions contained in the electrolyte may adhere to the surface of the carbon-based negative electrode active material. Therefore, the carbon-based negative electrode active material recovered from a lithium-ion secondary battery may contain Li. That is, the Li contained in the carbon-based negative electrode active material may be Li adsorbed in the carbon-based negative electrode active material, Li deposited on the surface of the carbon-based negative electrode active material, or Li adhered to the surface of the carbon-based negative electrode active material, etc.

[0022] Examples of carbon-based anode active materials include graphite, hard carbon, and soft carbon. Among these, graphite is preferred. Graphite can be natural graphite, artificial graphite, or amorphous carbon-coated graphite, where graphite is coated with an amorphous carbon material.

[0023] Carbon-based anode active materials typically have a median diameter (D50) of, for example, 0.1 μm or more and 50 μm or less, preferably 1 μm or more and 25 μm or less, and more preferably 5 μm or more and 20 μm or less, but are not limited thereto. The median diameter (D50) of carbon-based anode active materials can be obtained, for example, by laser diffraction scattering.

[0024] In the first heat treatment step S101, the carbon-based negative electrode active material containing Li is heat-treated together with EC at a temperature below the boiling point of EC. The boiling point of EC is 244°C, therefore, the heat treatment temperature in the first heat treatment step S101 is below 244°C.

[0025] Through this heat treatment, Li and EC contained in the carbon-based negative electrode active material undergo a reaction represented by the following formula (I) to obtain a heat-treated product containing lithium diethylene carbonate ((CH2OCO2Li)2).

[0026] 2(CH2O)2CO+2Li→(CH2OCO2Li)2+C2H4···(I)

[0027] From the viewpoint of efficiently carrying out the reaction represented by the above formula (I), the heat treatment temperature in the first heat treatment step S101 is preferably 90°C or higher, more preferably 100°C or higher, and even more preferably 110°C or higher. Furthermore, from the viewpoint of suppressing the reaction between Li and EC contained in the carbon-based negative electrode active material and ensuring sufficient pre-EC volatilization, the heat treatment temperature in the first heat treatment step S101 is preferably 220°C or lower, more preferably 170°C or lower, and even more preferably 140°C or lower.

[0028] The heat treatment time in the first heat treatment step S101 can be appropriately determined according to the heat treatment temperature. The heat treatment time in the first heat treatment step S101 is, for example, 30 minutes to 72 hours, preferably 40 minutes to 24 hours, and more preferably 50 minutes to 6 hours.

[0029] The heat treatment in the first heat treatment step S101 is preferably carried out at 90°C to 220°C for 30 minutes to 72 hours, more preferably at 100°C to 170°C for 40 minutes to 24 hours, and even more preferably at 110°C to 140°C for 50 minutes to 6 hours.

[0030] It should be noted that the presence of water in the atmosphere can lead to side reactions such as the reaction between Li and water. Therefore, the first heat treatment step S101 is preferably performed in a dry atmosphere (e.g., a dry air atmosphere, an inert gas atmosphere, etc.). The first heat treatment step S101 can be performed using a known heating device.

[0031] <Second heat treatment process S102>

[0032] In the second heat treatment step S102, the heat-treated product obtained in the first heat treatment step is heat-treated at a temperature above the boiling point of ethylene carbonate. Since the boiling point of ethylene carbonate is 244°C, the heat treatment temperature in the second heat treatment step S102 is above 244°C.

[0033] Through this heat treatment, the lithium diethylene carbonate contained in the heat-treated product obtained in the first heat treatment process reacts with the Li contained in the carbon-based negative electrode active material in a reaction represented by the following formula (II), thereby converting the lithium diethylene carbonate into lithium carbonate.

[0034] (CH2OCO2Li)2+2Li→2Li2CO3+C2H4···(II)

[0035] From the viewpoint of efficiently carrying out the reaction represented by the above formula (II), the heat treatment temperature in the second heat treatment step S102 is preferably 250°C or higher, more preferably 255°C or higher, and even more preferably 260°C or higher. Furthermore, the heat treatment temperature in the second heat treatment step S102 is preferably 350°C or lower, more preferably 320°C or lower, and even more preferably 290°C or lower.

[0036] The heat treatment time in the second heat treatment step S102 can be appropriately determined according to the heat treatment temperature. The heat treatment time in the second heat treatment step S102 is, for example, 30 minutes to 72 hours, preferably 40 minutes to 24 hours, and more preferably 50 minutes to 6 hours.

[0037] The heat treatment in the second heat treatment step S102 is preferably carried out at 250°C to 350°C for 30 minutes to 72 hours, more preferably at 255°C to 320°C for 40 minutes to 24 hours, and even more preferably at 260°C to 290°C for 50 minutes to 6 hours.

[0038] It should be noted that the presence of water in the atmosphere can lead to side reactions such as the reaction between Li and water. Therefore, the second heat treatment step S102 is preferably performed in a dry atmosphere (e.g., a dry air atmosphere or an inert gas atmosphere). The second heat treatment step S102 can be performed using a known heating device.

[0039] The specific implementation methods of the first heat treatment step S101 and the second heat treatment step S102 will be described below using the first embodiment to the third embodiment as examples.

[0040] First, an example of the structure of a lithium-ion secondary battery is shown. Figure 2 and Figure 3 . Figure 2 The image shows a longitudinal cross-sectional view illustrating an example of the internal structure of a lithium-ion secondary battery containing a carbon-based negative electrode active material including Li, used in the method for manufacturing the recycled carbon material of this disclosure.

[0041] Figure 3 To illustrate Figure 2 An exploded view of the electrode body of a lithium-ion secondary battery is shown.

[0042] Figure 4 For along Figure 2 The diagram shows a cross-sectional view of the negative electrode of a lithium-ion secondary battery along its thickness direction.

[0043] like Figure 2 As shown, the lithium-ion secondary battery 100 is a sealed battery in which a flat electrode 20 and a non-aqueous electrolyte 80 are housed inside the battery casing 30. Figure 2 As shown, the battery casing 30 consists of an outer packaging body 32 that houses the electrode body 20 and a cover 34 that seals the opening of the outer packaging body 32. The outer packaging body 32 and the cover 34 are sealed by welding, such as laser welding. Materials used for the battery casing 30 include, for example, aluminum, aluminum alloy, and resin.

[0044] In the example shown, the battery casing 30 is square. However, the shape of the battery casing 30 is not limited to this; for example, it can be cylindrical. Alternatively, the battery casing 30 can be a laminated casing, for example, having a gas barrier layer such as an aluminum layer and a sealant layer containing a thermoplastic resin.

[0045] The battery casing 30 includes a positive terminal 42 and a negative terminal 44 for external connection. Additionally, a safety valve 36 is provided in the battery casing 30, configured to release internal pressure when the internal pressure of the battery casing 30 rises above a predetermined level. An injection port (not shown) for injecting a non-aqueous electrolyte is provided in the battery casing 30. The positive terminal 42 is electrically connected to the positive current collector 42a. The negative terminal 44 is electrically connected to the negative current collector 44a.

[0046] like Figure 2 and Figure 3 As shown, the electrode body 20 has a form in which a strip-shaped positive electrode 50 and a strip-shaped negative electrode 60 are overlapped and wound in the longitudinal direction by two strip-shaped separators 70. Therefore, in this embodiment, the electrode body 20 is a wound electrode body. However, the electrode body 20 is not limited to this, and can be a stacked electrode body in which multiple positive electrodes and multiple negative electrodes are stacked together by separators.

[0047] like Figure 3 and Figure 4 As shown, in the negative electrode sheet 60, a negative electrode active material layer 64 is formed on one or both sides (in this case, both sides) of the negative electrode current collector 62 along the longitudinal direction. The negative electrode sheet 60 has a portion where the negative electrode active material layer 64 is not formed, thus exposing the negative electrode current collector 62, namely, the non-formed portion 62a of the negative electrode active material layer. A negative electrode current collector plate 44a is bonded to the non-formed portion 62a of the negative electrode active material layer.

[0048] As an example of the negative current collector 62 constituting the negative electrode sheet 60, copper foil can be cited. The negative electrode active material layer 64 contains a carbon-based negative electrode active material containing Li. The negative electrode active material layer 64 may contain components other than carbon-based negative electrode active materials, such as adhesives (e.g., styrene-butadiene rubber (SBR), etc.), tackifiers (e.g., carboxymethyl cellulose (CMC), etc.).

[0049] The content of carbon-based negative electrode active material in the negative electrode active material layer 64 is preferably 90% by mass or more, more preferably 95% by mass or more and 99% by mass or less. The content of binder in the negative electrode active material layer 64 is preferably 0.1% by mass or more and 8% by mass or less, more preferably 0.5% by mass or more and 3% by mass or less. The content of tackifier in the negative electrode active material layer 64 is preferably 0.3% by mass or more and 3% by mass or less, more preferably 0.5% by mass or more and 2% by mass or less.

[0050] In the positive electrode 50, a positive active material layer 54 is formed on one or both (in this case, both) sides of the positive current collector 52 along the longitudinal direction. The positive electrode 50 has a portion where the positive active material layer 54 is not formed, thus exposing the positive current collector 52, namely, the non-formed portion 52a of the positive active material layer. A positive current collector plate 42a is bonded to the non-formed portion 52a of the positive active material layer.

[0051] Examples of positive current collector 52 constituting positive electrode sheet 50 include aluminum foil. The positive electrode active material layer 54 contains a positive electrode active material. Examples of positive electrode active materials include lithium metal composite oxides and lithium transition metal phosphate compounds. The positive electrode active material layer 54 may include conductive materials (e.g., carbon black, carbon nanotubes), binders (e.g., polyvinylidene fluoride (PVDF)), etc.

[0052] Examples of diaphragm 70 include porous resin sheets such as polyethylene and polypropylene. The porous sheet can be a single-layer or multi-layer structure. A heat-resistant layer (HRL) may be provided on the surface of diaphragm 70.

[0053] The non-aqueous electrolyte 80 typically contains a non-aqueous solvent and a supporting salt (in other words, an electrolyte salt). Examples of non-aqueous solvents include carbonates (e.g., EC, ethyl methyl carbonate, dimethyl carbonate, etc.), esters, ethers, etc. Examples of supporting salts include lithium salts such as LiPF6. The concentration of the supporting salt is not particularly limited, but is preferably 0.7 mol / L to 1.3 mol / L. The non-aqueous electrolyte 80 may contain various additives such as gas generators and film-forming agents. It should be noted that in this embodiment, a non-aqueous electrolyte is used as the electrolyte, but the electrolyte may also be a solid electrolyte.

[0054] The lithium-ion secondary battery 100 is preferably used for vehicle applications (i.e., as a drive power source for vehicles such as battery electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs), but is not limited thereto. The lithium-ion secondary battery 100 can also be used as a power source for electronic devices, etc.

[0055] (First Implementation)

[0056] In the first embodiment, the used lithium-ion secondary battery 100 is subjected to heat treatment in a first heat treatment step S101 and a second heat treatment step S102.

[0057] When the non-aqueous electrolyte 80 of the lithium-ion secondary battery 100 contains EC, the carbon-based negative electrode active material coexists with EC in the lithium-ion secondary battery 100. In this case, it can be directly supplied for heat treatment. Generally, EC, as a cyclic carbonate, is often used in combination with chain carbonates such as dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC) as a non-aqueous solvent in the non-aqueous electrolyte 80. DMC has a boiling point of 90°C, and EMC has a boiling point of 107°C. Therefore, even when EC is used in combination with DMC and EMC in the non-aqueous electrolyte 80, DMC and EMC volatilize preferentially compared to EC, thus enabling the reaction between EC and Li contained in the carbon-based negative electrode active material to proceed with high efficiency.

[0058] In the absence of EC in the non-aqueous electrolyte 80 of the lithium-ion secondary battery 100, the non-aqueous electrolyte 80 is extracted from the lithium-ion secondary battery 100, and EC is injected into the battery casing 30. Thus, in the lithium-ion secondary battery 100, the carbon-based negative electrode active material and EC coexist.

[0059] The lithium-ion secondary battery 100 in which the carbon-based negative electrode active material and EC coexist is subjected to heat treatment. Specifically, for example, the lithium-ion secondary battery 100 is placed in a heating device such as a constant temperature dryer, heater, or electric furnace, and heated at a temperature below the boiling point of EC by a reaction represented by the above formula (I) to generate lithium diethylene carbonate. Thus, the first heat treatment step S101 can be performed.

[0060] Then, the temperature of the heating device is set to a temperature above the boiling point of EC, thereby enabling the second heat treatment step S102 to be performed. It can also be explained that after the first heat treatment step S101, the heat-treated material can be removed from the heating device and transferred to another heating device for the second heat treatment step S102.

[0061] (Second Implementation)

[0062] In the second embodiment, the negative electrode 60 recovered from the used lithium-ion secondary battery 100 is subjected to heat treatment in the first heat treatment step S101 and heat treatment in the second heat treatment step S102.

[0063] Therefore, in the second embodiment, firstly, the negative electrode 60 is removed from the used lithium-ion secondary battery 100. This can be done according to known methods. Specifically, for example, the battery casing 30 of the lithium-ion secondary battery 100 is opened to expose the electrode body 20. The opening of the battery casing 30 can be performed, for example, by cutting the portion slightly below the cover 34 of the outer packaging 32 using a tool with a cutting edge (e.g., an electric saw), an electric cutting tool (e.g., a grinder, a Leutor cutter), a water jet cutter, a laser cutter, or other cutting means.

[0064] Before disassembling the used lithium-ion secondary battery 100, it can be discharged. This reduces the amount of Li contained in the carbon-based negative electrode active material and allows for safer disassembly.

[0065] Next, the exposed electrode body 20 is removed, and the negative electrode 60 is taken out from the electrode body 20. For example, first, the non-formed portion 52a of the positive electrode active material layer and the non-formed portion 62a of the negative electrode active material layer of the electrode body 20 are detached from the positive electrode current collector 42a and the negative electrode current collector 44a, respectively. Next, for example, if the electrode body 20 is a wound electrode body as shown in the example, the wound electrode body 20 is unwound, separating it into the positive electrode 50, the negative electrode 60, and the separator 70. If the electrode body 20 is a stacked electrode body, it is separated into the positive electrode 50, the separator 70, and the negative electrode 60.

[0066] In the case where the non-aqueous electrolyte 80 contains EC and the negative electrode 60 is attached to the non-aqueous electrolyte 80, the carbon-based negative electrode active material and EC coexist in the negative electrode 60.

[0067] In the absence of EC in the non-aqueous electrolyte 80, the carbon-based negative electrode active material contained in the negative electrode active material layer 64 of the negative electrode 60 is brought into contact with the EC. Specifically, for example, the negative electrode 60 is immersed in EC and then lifted. Alternatively, for example, EC is coated onto the negative electrode active material layer 64 by spraying. In this way, the carbon-based negative electrode active material contained in the negative electrode active material layer 64 coexists with the EC.

[0068] A negative electrode 60, in which carbon-based negative electrode active material and EC coexist, is placed in a heating device such as a constant temperature dryer, heater, or electric furnace. The electrode is heated at a temperature below the boiling point of EC to generate lithium diethylene carbonate via a reaction represented by the above formula (I). This allows for the first heat treatment step S101 to be performed.

[0069] Then, the temperature of the heating device is set to a temperature above the boiling point of EC, thereby enabling the second heat treatment step S102 to be performed. It can also be explained that after the first heat treatment step S101, the heat-treated material can be removed from the heating device and transferred to another heating device for the second heat treatment step S102.

[0070] (Third Implementation)

[0071] In the third embodiment, the carbon-based negative electrode active material recovered from the used lithium-ion secondary battery 100 is subjected to heat treatment in the first heat treatment step S101 and heat treatment in the second heat treatment step S102.

[0072] Therefore, firstly, the negative electrode 60 is removed from the lithium-ion secondary battery 100 in the same order as in the second embodiment. The carbon-based negative electrode active material is recovered from the negative electrode active material layer 64 of the removed negative electrode 60. This can be performed using known methods. Specifically, for example, the negative electrode active material layer 64 is peeled off from the negative electrode 60, and the binder and thickener contained in the negative electrode active material layer 64 are removed using a solvent or the like. For example, if CMC is used as a thickener, the negative electrode active material layer 64 is washed with water to dissolve and remove the CMC. If SBR is used as a binder, the negative electrode active material layer 64 is washed with an organic solvent (e.g., toluene, benzene, etc.) with a solubility parameter of 7.7 to 9.5 to dissolve and remove the SBR.

[0073] The recovered carbon-based negative electrode active material is brought into contact with EC (electrochemical polymerase). Specifically, for example, the carbon-based negative electrode active material is impregnated with EC and then lifted. Alternatively, for example, EC is coated onto the carbon-based negative electrode active material by spraying or the like. In this way, the carbon-based negative electrode active material and EC coexist.

[0074] The carbon-based negative electrode active material coexisting with EC is placed in a heating device such as an electric furnace, hot air dryer, or high-temperature dryer, and heated at a temperature below the boiling point of EC to generate lithium diethylene carbonate through a reaction represented by the above formula (I). This allows for the first heat treatment step S101 to be performed.

[0075] Then, the temperature of the heating device is set to a temperature above the boiling point of EC, thereby enabling the second heat treatment step S102 to be performed. It can also be explained that after the first heat treatment step S101, the heat-treated material can be removed from the heating device and transferred to another heating device for the second heat treatment step S102.

[0076] In the first and second embodiments, since EC and carbon-based negative electrode active material coexist beforehand, it is advantageous for the non-aqueous electrolyte 80 of the lithium-ion secondary battery 100 to contain EC. In the method for manufacturing the recycled carbon material disclosed herein, it is particularly preferred that the carbon-based negative electrode active material be used together with an electrolyte containing EC, and that the first and second heat treatment steps be performed in a dry atmosphere.

[0077] As described in the first to third embodiments above, the Li contained in the carbon-based negative electrode active material is converted into lithium carbonate through heat treatment in the first heat treatment step S101 and the second heat treatment step S102. Therefore, the method for manufacturing recycled carbon material according to this disclosure may further include a step of removing lithium carbonate from the heat-treated product obtained from the second heat treatment step S102. Lithium carbonate can be easily removed from the carbon-based negative electrode active material by washing with water.

[0078] Therefore, the method for manufacturing recycled carbon materials disclosed herein preferably includes a process of washing the heat-treated material obtained from the second heat treatment process S102 with water and removing lithium carbonate from the carbon-based negative electrode active material (lithium carbonate removal process).

[0079] The lithium carbonate removal process can be carried out according to known methods. After washing with water, it can be dried according to known methods.

[0080] In the case of a lithium carbonate removal process, a further step can be taken to recover the washing water generated by the water washing process, and to evaporate the water from the washing water to recover the lithium carbonate. This process can be carried out according to known methods. Lithium carbonate can be used for various applications, for example, as a lithium source for lithium composite oxides used as positive electrode active materials in lithium-ion secondary batteries.

[0081] As in the first or second embodiment, when the first heat treatment step S101 and the second heat treatment step S102 are performed on the lithium-ion secondary battery 100 or the negative electrode 60, for example, the methods described in the second and third embodiments can be used to recover the carbon-based negative electrode active material from which more Li has been removed, thereby obtaining a recycled carbon material. The recycled carbon material can be used not only as a negative electrode active material but also for various other applications.

[0082] As described above, according to the method for manufacturing recycled carbon materials of this disclosure, it is easy to remove more Li from Li-containing carbon-based anode active materials to obtain recycled carbon materials. The method for manufacturing recycled carbon materials disclosed herein is useful in terms of material reuse.

[0083] The following describes in detail test examples related to this disclosure, but it is not intended to limit this disclosure to the implementation shown in the embodiments.

[0084] [Evaluation of battery manufacturing]

[0085] Used lithium-ion secondary batteries were prepared. These batteries consist of wound electrodes housed in an aluminum battery casing. The positive electrode comprises aluminum foil and a positive electrode active material layer, which contains lithium nickel cobalt manganese composite oxide, acetylene black, and polyvinylidene fluoride in a mass ratio of 92:5:3. The negative electrode comprises copper foil and a negative electrode active material layer, which contains graphite, styrene-butadiene rubber, and carboxymethyl cellulose as carbon-based negative electrode active materials in a mass ratio of 99:0.5:0.5. The non-aqueous electrolyte contains ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate as non-aqueous solvents in a volume ratio of 3:3:4, and contains LiPF6 as a supporting salt at a concentration of approximately 1.1 mol / L.

[0086] After discharging the used lithium-ion secondary battery, the battery casing is opened under an argon atmosphere. The wound electrode body is unwound, and the negative electrode is removed. The negative electrode active material layer contains a non-aqueous electrolyte. Therefore, the EC contained in the non-aqueous electrolyte adheres to the graphite.

[0087] Under an argon atmosphere, with a non-aqueous electrolyte impregnated in the negative electrode active material layer, the negative electrode was placed in a constant-temperature dryer. The negative electrode was heat-treated under the conditions shown in Table 1. After heat treatment, the negative electrode was washed with water and dried to remove the water. However, for Comparative Example 1, washing and drying were performed without heat treatment. A portion of the negative electrode active material layer was shaved off, and the residue obtained from carbon combustion was prepared as a test sample. Using this test sample and a commercially available ICP-based spectrophotometer, the Li content (mass %) in the negative electrode active material layer was determined. The results are shown in Table 1.

[0088] Table 1

[0089]

[0090] As shown in Table 1, it can be seen that by subjecting the carbon-based anode active material containing Li to two stages of heat treatment—heat treatment at a temperature below the boiling point of EC and heat treatment at a temperature above the boiling point of EC—the efficient removal of Li contained in the carbon-based anode active material becomes easy.

[0091] The specific examples of this disclosure have been described in detail above, but these are merely illustrative and do not limit the scope of the claims. The technology described in the claims includes embodiments with various modifications and alterations to the specific examples described above.

[0092] That is, the method for manufacturing the recycled carbon material disclosed herein is as follows [1] to

[10] .

[0093] [1] A method for manufacturing recycled carbon materials, comprising: a first heat treatment step, wherein a carbon-based negative electrode active material containing Li is heat-treated together with ethylene carbonate at a temperature below the boiling point of ethylene carbonate to obtain a heat-treated material containing lithium diethylene carbonate; and a second heat treatment step, wherein the heat-treated material is heat-treated at a temperature above the boiling point of ethylene carbonate to convert lithium diethylene carbonate into lithium carbonate.

[0094] [2] The manufacturing method according to item [1], wherein the heat treatment of the first heat treatment step is carried out at 90°C to 220°C for 30 minutes to 72 hours.

[0095] [3] The manufacturing method according to item [1], wherein the heat treatment of the first heat treatment step is carried out at 110°C to 140°C for 50 minutes to 6 hours.

[0096] [4] The manufacturing method according to any one of items [1] to [3], wherein the heat treatment of the second heat treatment step is carried out at 250°C to 350°C for 30 minutes to 72 hours.

[0097] [5] The manufacturing method according to any one of items [1] to [3], wherein the heat treatment of the second heat treatment step is performed at 260°C to 290°C for 50 minutes to 6 hours.

[0098] [6] The manufacturing method according to any one of items [1] to [5] further includes the steps of washing the heat-treated material obtained in the second heat treatment step with water and removing lithium carbonate from the carbon-based negative electrode active material.

[0099] [7] The manufacturing method according to item [6] further includes the steps of recovering the cleaning water generated by the washing and evaporating the water from the cleaning water to recover the lithium carbonate.

[0100] [8] The manufacturing method according to any one of items [1] to [7], wherein the carbon-based negative electrode active material is used with a non-aqueous electrolyte containing ethylene carbonate, and the first heat treatment step and the second heat treatment step are carried out in a dry atmosphere.

[0101] [9] The manufacturing method according to any one of items [1] to [8], wherein the carbon-based negative electrode active material is graphite.

[0102]

[10] The manufacturing method according to any one of items [1] to [9], wherein the carbon-based negative electrode active material is the negative electrode active material of a used lithium-ion secondary battery.

Claims

1. A method for producing a regenerated carbon material, comprising: a first heat treatment step in which a carbon-based negative electrode active material containing Li is heat-treated with ethylene carbonate at a temperature lower than the boiling point of ethylene carbonate to obtain a heat-treated product containing lithium ethylene dicarbonate; and a second heat treatment step in which the heat-treated product is heat-treated at a temperature higher than the boiling point of ethylene carbonate to convert lithium ethylene dicarbonate into lithium carbonate.

2. The manufacturing method according to claim 1, wherein, The heat treatment of the first heat treatment step is performed at 90°C to 220°C for 30 minutes to 72 hours.

3. The manufacturing method according to claim 1, wherein, The heat treatment of the first heat treatment step is performed at 110°C to 140°C for 50 minutes to 6 hours.

4. The manufacturing method according to claim 1, wherein, The heat treatment of the second heat treatment step is performed at 250°C to 350°C for 30 minutes to 72 hours.

5. The manufacturing method according to claim 1, wherein, The heat treatment of the second heat treatment step is performed at 260°C to 290°C for 50 minutes to 6 hours.

6. The method according to claim 1, further comprising a step of washing the heat-treated product obtained in the second heat treatment step with water to remove lithium carbonate from the carbon-based negative electrode active material.

7. The method according to claim 6, further comprising a step of recovering washing water produced by the washing with water and evaporating water from the washing water to recover lithium carbonate.

8. The manufacturing method according to claim 1, wherein, The carbon-based negative electrode active material is used with a nonaqueous electrolyte containing ethylene carbonate, and the first heat treatment step and the second heat treatment step are performed in a dry atmosphere.

9. The production method according to claim 1, wherein The carbon-based negative electrode active material is graphite.

10. The manufacturing method of claim 1, wherein, The carbon-based negative electrode active material is a negative electrode active material of a used lithium ion secondary battery.

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