Stabilization method for used lithium-ion batteries

Abstract

To provide a stabilization processing method of waste lithium ion battery performing discharge treatment safely.SOLUTION: In a stabilization processing method of waste lithium ion battery performing heating treatment of the waste lithium ion battery between a temperature (upper limit temperature) lower than both the decomposition temperature of the separator of the waste lithium ion battery and the SEI breaking temperature, and the gasification start temperature (lower limit temperature) of the electrolyte of the waste lithium ion battery, and causing internal short circuit of an electrode in the waste lithium ion battery, the upper limit temperature is about 280°C, the lower limit temperature is about 90°C, the waste lithium ion battery is heat treated in a substance which is liquid at the lower limit temperature, and having a boiling point or a demarcation point below the upper limit temperature, the substance is water (H2O) or triacyl glycerine, and after the heat treatment, plastics of the waste lithium ion battery are subjected to carbonization or decomposition processing in a roasting device or a super heat steam device while being placed in the substance.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a stabilization process for recycling used lithium ion batteries. [Background technology]

[0002] Secondary batteries are used to store electricity in portable devices such as smartphones and electric vehicles. Demand for these devices is growing rapidly, resulting in a corresponding increase in the amount of discarded secondary batteries, and increased demand for the disposal and recycling of storage batteries. These secondary batteries must have performance tailored to the devices they are used in, and lithium-ion batteries are the most commonly used. Lithium-ion batteries are housed in a metal (e.g., aluminum) housing. The battery contains a negative electrode material (e.g., graphite) attached to a negative electrode substrate (e.g., copper foil), a positive electrode material (e.g., aluminum foil), a positive electrode substrate (e.g., aluminum foil), a current collector (e.g., aluminum or copper), a separator (e.g., polyolefin (e.g., polypropylene, polyethylene)), and an electrolyte (e.g., lithium hexafluorophosphate (LiPF6)). Used lithium-ion batteries (also referred to as waste lithium-ion batteries, or simply referred to as waste LiBs) cannot be disposed of or buried as they are because they contain hazardous substances such as the fluorides and phosphoric acids mentioned above. They also contain many rare and valuable metals, such as lithium (Li), cobalt (Co), and nickel (Ni), and there is a need to recover these valuable metals to conserve resources. Therefore, many methods have been proposed for treating the hazardous substances contained in waste lithium-ion batteries and recovering the valuable metals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2017-131795 [Patent Document 2] Patent Publication No. 2016-22395 Summary of the Invention [Problem to be solved by the invention]

[0004] When recycling used lithium-ion batteries, the active lithium in a charged or partially charged state exists in a high-energy state. This high-energy state is released (discharged) during the recycling process. However, this release can cause heat generation, fire, or explosion due to the flammable electrolytic materials contained within the battery, making safe disposal generally difficult. For this reason, some manual discharge or electrolyte cleaning is performed as a preliminary step to the recycling process, but safe disposal is still difficult and contributes to the high cost of recycling. Therefore, if disposal must be performed in a high-temperature furnace where fire is not a problem, metal components such as aluminum and compound components such as cobalt oxide mix at high temperatures, placing a heavy burden on subsequent extraction processes. Heat treatment at temperatures below the melting point of aluminum has also been proposed, but due to the potential discharge issue, it has also been proposed to seal used lithium-ion batteries in a heat-resistant container and place them in a heat treatment furnace to prevent damage to the furnace even if heat is generated by discharge during the heat treatment. (Patent Document 1) [Means for solving the problem]

[0005] The method described in Patent Document 1 requires an expensive heat-resistant container, and it is unclear whether it will actually be used without problems. In other words, to effectively and inexpensively recycle used lithium-ion batteries, a method for safely discharging used lithium-ion batteries without incurring significant costs is needed. Furthermore, previous patent documents and information suggest that prior to metal extraction, used lithium-ion batteries must be treated in a manner that (A) separates organic components such as plastics by carbonization or combustion, or that allows for subsequent crushing, and (B) stabilizes lithium, which has a high energy storage capacity, such as an oxide. Furthermore, (C) performing the reaction below the melting point of aluminum facilitates subsequent metal extraction. (Patent Document 2)

[0006] Among these, condition (B) above corresponds to the electrical energy stored in a lithium-ion battery, and it is necessary to convert this Li into a stable state. Li exists as lithium carbide (LiC6) at the anode and as a composite oxide such as Li(NiMnCo)O2 at the cathode. Although the cathode material is a stable composite oxide, it must be stabilized in the form of 4LiC6 + O2 → 2Li2O + 24C, which requires an oxidizing atmosphere with sufficient oxygen potential. Patent Document 2 describes a "reducing or non-oxidizing" atmosphere, which does not fall under this definition. However, a high oxygen potential causes the exothermic carbon combustion reaction C + O2 → CO2, making it difficult to suppress the reaction below the melting point of aluminum (approximately 660°C) as described in condition (C). In other words, a weakly oxidizing atmosphere is required that oxidizes Li but does not cause the carbon combustion reaction C + O2 → CO2.

[0007] The present invention provides a safe and secure stabilization method for waste lithium ion batteries that satisfies the above-mentioned requirements (A), (B), and (C), and an associated stabilization method for waste lithium ion batteries, and in particular, a stabilization method for waste lithium ion batteries that safely discharges the batteries, and has the following characteristics. (1) The present invention is a stabilization method for used lithium ion batteries, characterized in that the used lithium ion battery is heat-treated at a temperature (upper limit temperature) lower than both the decomposition temperature of the separator and the collapse temperature of the SEI (Solid Electrolyte Interface) of the used lithium ion battery, and at or above the gasification start temperature (lower limit temperature) of the electrolyte of the used lithium ion battery, to cause the used lithium ion battery to become inactivated (for example, cause an internal short circuit of the electrodes), wherein the upper limit temperature is about 280°C and the lower limit temperature is about 90°C, the lithium ion battery is heat-treated in a substance that is liquid at the lower limit temperature and has a boiling point or demarcation point below the upper limit temperature, and the substance is water (HO) or triacylglycerin.

[0008] (2) In addition to (1), the present invention is characterized in that the electrode layer of the used lithium ion battery is perforated before the heat treatment, and after the heat treatment, the used lithium ion battery is placed in the substance and then carbonized or decomposed in a roasting device or superheated steam device, or the used lithium ion battery is placed in the substance and then carbonized or decomposed in a superheated steam device, or the used lithium ion battery is placed in the substance and then carbonized or decomposed in a superheated steam device, or the heat treatment described in (1) is achieved by placing the used lithium ion battery in a superheated steam device and then carbonizing or decomposing in a superheated steam device.

[0009] (3) The present invention is a stabilization method for used lithium ion batteries, characterized by including a step of placing used lithium ion batteries in a carbonizing, weakly oxidizing environment to carbonize or decompose plastics, wherein the weakly oxidizing environment is a combination of an atmosphere and a temperature that does not allow the reaction C + O2 → CO2 to proceed and has an oxygen potential that can oxidize lithium.

[0010] (4) In addition to (1), the present invention is characterized in that the atmosphere of the weakly oxidizing environment is MxO (M is an element or a reactive group), the temperature of the weakly oxidizing environment is not more than the temperature where the oxygen potential according to the Ellingham diagram of 2XM + O2 = 2MxO is higher than the oxygen potential for the oxidation of lithium (Li) and lower than the oxygen potential of C + O2 = CO2, and is not less than the decomposition temperature of plastics, the atmosphere of the weakly oxidizing environment is water vapor, and the temperature condition of the weakly oxidizing environment is not more than about 650°C, which is the temperature at the point where the oxygen potential diagrams of 2H2O + O2 = 2H2O and C + O2 = CO2 intersect based on the Ellingham diagram, and is not less than the decomposition temperature of plastics. (5) The present invention is characterized in that after carrying out the stabilization treatment method for used lithium ion batteries described in (1) or (2), the stabilization treatment method for used lithium ion batteries described in (3) or (4) is carried out.

[0011] (6) The present invention is a stabilization method for used lithium ion batteries, which is characterized in that used lithium ion batteries are discharged in a conductive aqueous solution of a salt having a cation that fixes fluorine and sulfur and an anion that decomposes by a carbonization reaction, and then separated into metal components, compound components, and carbide components by superheated steam treatment at 650°C or less, and further characterized in that after the used lithium ion batteries are discharged in the conductive aqueous solution, the used lithium ion batteries are placed in the conductive aqueous solution and then subjected to superheated steam treatment, and the conductive aqueous solution is an aqueous solution of calcium carbonate.

[0012] (7) In addition to (6), the present invention is characterized in that the discharge treatment is carried out by cutting the used lithium-ion battery in a conductive aqueous solution using ultrasonic ceramic cutting and allowing the conductive aqueous solution to seep into the used lithium-ion battery from the cut parts, or by perforating the used lithium-ion battery in a conductive aqueous solution using a cutting tool (tool) and allowing the conductive aqueous solution to seep into the used lithium-ion battery from the perforated parts, the cutting tool (tool) being a good conductor of electricity and a good conductor wire being passed through the perforated parts, or by discharging the used lithium-ion battery in a conductive aqueous solution by applying external deformation to cause strain on the used lithium-ion battery in the conductive aqueous solution and allowing the conductive aqueous solution to seep into the used lithium-ion battery from the strain, and the method of applying external deformation to cause strain on the used lithium-ion battery is a method of applying external deformation to cause strain on the used lithium-ion battery using a rotating press roller or a press machine.

[0013] (8) In addition to (6) or (7), the present invention is characterized in that a conductive filler or a conductive powder is mixed into the conductive aqueous solution, the conductive filler or the conductive powder is conductive carbon black, conductive tin oxide, conductive titanium oxide, or various metal powders, and the temperature of the superheated steam treatment is about 300°C to about 650°C. [Effects of the Invention]

[0014] The present invention relates to a method for stabilizing used lithium-ion batteries. The method involves heat-treating used lithium-ion batteries at a temperature (upper limit temperature) lower than both the separator decomposition temperature and the SEI (Solid Electrolyte Interface) collapse temperature, but above the electrolyte gasification start temperature (lower limit temperature). This prevents the separator from decomposing or carbonizing, resulting in deformation, partial short-circuiting of the positive and negative electrodes, or changes in the internal electrolyte, or damage to the electrodes, wiring, and other electrical systems, preventing rapid discharge (referred to as a deactivated state in the present invention). This allows for gradual discharge without sudden heat generation. Additionally, the present invention involves heat-treating used lithium-ion batteries in a substance that is liquid at the lower limit temperature and has a boiling point or demarcation point below the upper limit temperature. The heat generated during the discharge process is absorbed by a substance with a large heat capacity, completely preventing problems such as fire or explosion that could damage the device. When this liquid is water, it is cost-effective and does not burden the environment. The present invention also relates to a stabilization method for used lithium-ion batteries, which includes a step of placing used lithium-ion batteries in a weakly oxidizing environment such as superheated steam at 650°C or less to carbonize them. This allows for carbonization of only organic materials such as plastics without causing sudden heat generation, making it easy to separate the valuable metal components contained in the lithium-ion batteries. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a diagram showing a superheated steam device for performing heat treatment on waste lithium ion batteries according to the present invention. [Figure 2] Figure 2 is an Ellingham diagram. [Figure 3] FIG. 3 is a graph showing the decomposition temperatures of plastics. [Figure 4] FIG. 4 is a graph showing the experimental results of boiling water treatment of used storage batteries. [Figure 5] FIG. 5 is a diagram showing the flow of the processing method of the present invention. [Figure 6] FIG. 6 illustrates a method for damaging a lithium ion battery in a conductive aqueous solution in a small container containing the conductive aqueous solution. [Figure 7] FIG. 7 illustrates another method of damaging a lithium-ion battery. [Figure 8] FIG. 8 is a diagram showing a state in which a lithium ion battery immersed in a large container containing a conductive aqueous solution and a small container containing a conductive aqueous solution are arranged. [Figure 9] FIG. 9 is a diagram showing a superheated steam device in which a waste lithium ion battery and a small container containing a conductive aqueous solution are placed. [Figure 10] FIG. 10 is a table showing the evaluation results of the deactivation state of lithium batteries due to heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0016] This invention is a stabilization treatment for used (waste) lithium-ion batteries, a safe method for facilitating the separation of lithium-ion battery components prior to metal extraction. Specifically, as a preliminary step to metal extraction from waste lithium-ion batteries (LiBs), this treatment carbonizes or decomposes organic materials such as plastics in a carbonizing, weakly oxidizing environment to facilitate separation from valuable metal components and stabilize highly reactive lithium (Li). Here, a carbonizing or decomposing, weakly oxidizing atmosphere refers to a combination of atmosphere and temperature that does not promote the C + O → CO reaction and has an oxygen potential that can oxidize Li.

[0017] Prior to metal extraction, spent LiBs must be treated in two ways: (A) to separate organic components such as plastics by carbonization or combustion, or to a state that can be separated by subsequent crushing, and (B) to stabilize Li, which has a high energy storage capacity, such as an oxide. Furthermore, (C) conducting the reaction below the melting point of aluminum facilitates subsequent metal extraction. Among these, (B) corresponds to the chemical storage of electrical energy held by LiBs, and it is necessary to convert this Li to a stable state. Li exists as LiC6 at the anode and as a complex oxide such as Li(NiMnCo)O2 at the cathode. While the cathode material is a stable complex oxide, it must be stabilized in the reaction system 4LiC6 + O2 → 2Li2O + 24C, which requires an oxidizing atmosphere with oxygen potential. Patent Document 2, which describes a "reducing or non-oxidizing" atmosphere, does not fall under this definition. However, if the oxygen potential is high, the exothermic reaction of carbon combustion (C + O2 → CO2) occurs, making it difficult to suppress the reaction below the melting point of aluminum (C). In other words, it is necessary to treat the material in a weakly oxidizing atmosphere that oxidizes Li but does not cause carbon combustion (C + O2 → CO2).

[0018] FIG. 1 is a diagram showing a roasting apparatus for thermally treating waste lithium-ion batteries according to the present invention, and shows a superheated steam apparatus 100 as an example of a roasting apparatus. Waste lithium-ion batteries 107 are placed on a support shelf 106 inside the superheated steam apparatus 100. A superheated steam generator 102 is attached to the superheated steam apparatus 100, and temperature-controlled superheated steam is introduced into the superheated steam apparatus 100. A temperature sensor 103 is attached to detect the temperature inside the superheated steam apparatus 100, and the temperature inside the superheated steam apparatus 100 is sent to a controller 104. Steam is heated to an appropriate temperature in a boiler 101 and sent to the superheated steam generator 102, and superheated steam at a predetermined temperature is introduced into the superheated steam apparatus 100. Therefore, the temperature inside the superheated steam apparatus 100 is always controlled to a predetermined temperature. The superheated steam introduced into the superheated steam device 100 and the gases (waste gas, pyrolysis gas, etc.) generated by the heating treatment of the waste lithium ion batteries 107 are discharged to the outside through an exhaust line 105.

[0019] Since the superheated steam device 100 contains air and the like when the waste lithium-ion batteries 107 are placed inside the superheated steam device 100, a pump or the like (for example, to a separate line or the exhaust line 105) may be attached to exhaust the air to the outside before the superheated steam is introduced into the superheated steam device 100. Normally, the air and the like are exhausted from the exhaust line 105 together with the superheated steam at an initial stage, so that the inside of the superheated steam device 100 is filled with superheated steam when the actual heating process is performed, and the waste lithium-ion batteries 107 are heated by the superheated steam.

[0020] Superheated steam generators provide a weakly oxidizing atmosphere because the atmosphere is superheated steam (H2O). In other words, the steam provides an oxygen potential that equilibrates the reaction 2H2O → 2H2 + O2. This oxygen potential, as seen in the Ellingham diagram in Figure 2, oxidizes lithium (Li) throughout the entire temperature range below several thousand degrees. However, while the oxygen potential is insufficient to promote the C + O2 → CO2 reaction at low temperatures, it provides sufficient oxygen potential to promote the carbon combustion reaction at high temperatures. The transition temperature is known to be the temperature at the point where the oxygen potential diagrams for 2H2 + O2 = 2H2O and C + O2 = CO2 intersect on the Ellingham diagram, which is approximately 650°C, as shown in Figure 2. Above this temperature, the exothermic carbon combustion reaction C + O2 → CO2 occurs, causing the temperature to rise rapidly, making it difficult to suppress the reaction below the melting point of aluminum (660°C).

[0021] Specifically, if the temperature of superheated steam is set to approximately 650°C or less, a weakly oxidizing environment is created that oxidizes lithium (Li) and prevents carbon combustion (C + O2 → CO2). Furthermore, because plastics decompose when subjected to high-temperature heat treatment, the temperature must be above the decomposition onset temperature of the plastic. For example, Figure 3 shows a graph showing the decomposition temperatures of plastics. For example, the decomposition onset temperature of polyethylene is approximately 350°C. Therefore, if the target plastic is polyethylene, a temperature between approximately 350°C and approximately 650°C constitutes the weakly oxidizing environment described above, and also allows decomposition or carbonization of the plastic. In this invention, the term "decomposition" is sometimes used instead of "carbonization," but it should be noted that these terms have different meanings. In other words, carbonization can be considered to be included in decomposition. Furthermore, as mentioned above, a weakly oxidizing environment (atmosphere) is a combination of atmosphere and temperature that has an oxygen potential that prevents the C + O2 → CO2 reaction from proceeding and allows lithium to be oxidized.

[0022] MxO (M is an element or reactive group) is also commonly used to provide a weakly oxidizing atmosphere. When MxO is used, objectives (A) and (B) are achieved by treating the atmosphere at a temperature where the oxygen potential according to the Ellingham diagram (2XM + O2 = 2MxO) is higher than the oxygen potential for the oxidation of Li, but lower than the oxygen potential for C + O2 → CO2. The aforementioned water (H2O) is also a type of MxO, but other examples include CsO2, N2O, and NO2.

[0023] If waste lithium-ion batteries are directly decomposed or carbonized using a superheated steam device or a roasting device, the separator may be decomposed or carbonized, causing discharge between the positive and negative electrodes, resulting in heat generation or, in the worst case, explosion, which may damage the device. Furthermore, when discharge treatment is performed using such partial contact, it is difficult to control the partial contact, which can increase the short-circuit current and cause a chain reaction of heat generation. The resulting temperature rise can melt metals such as aluminum, making it difficult to recover valuable metals. The weakly oxidizing environment of the present invention may also become unsustainable due to the heat generated.

[0024] Lithium-ion batteries have a separator between the positive and negative electrodes that prevents discharge, so removing the separator will cause discharge. However, if the separator is completely removed through carbonization or other means, a sudden discharge will occur, causing damage to the device due to sudden heat generation or explosion. Therefore, it is possible to achieve a partial short circuit between the positive and negative electrodes by partially damaging or destroying the separator, which will allow discharge to occur quietly.

[0025] Decomposition of polyolefins, the main components of separators, begins at approximately 350°C for polyethylene, 320°C for polypropylene, and 320°C for polystyrene (not shown in Figure 3), as shown in Figure 3. Above this temperature, the separator decomposes or carbonizes, becoming electrically conductive and becoming a conductor, short-circuiting and potentially causing rapid fire. To achieve safe energy release, discharge by partial short-circuiting must occur below this temperature. It has also been reported that at 280°C, just below this temperature, the solid electrolyte interphase (SEI) formed by the partial reduction reaction between Li and the electrolyte in the LiB anode breaks down, generating heat due to a direct reaction between Li and the electrolyte. This heat generates a separator decomposition reaction, so discharge must be performed at a temperature (below 280°C) at which the solid electrolyte interphase (SEI) breaks down and heat is not generated due to a direct reaction between Li and the electrolyte. Alternatively, heat treatment at this temperature range may chemically change the electrolyte or damage the electrical system, such as the electrodes and wiring, so that sudden discharge does not occur. In chemical terms, deactivation means that a chemical substance loses its activity and no longer reacts, i.e., is inactivated. In the present invention, deactivation refers to the state in which sudden discharge does not occur. Furthermore, a deactivated state is called a deactivated state, and the treatment that brings about the deactivated state (for example, the heat treatment described above) is called a deactivation treatment.

[0026] To achieve a partial short circuit, the separator must be deformed without decomposing or carbonizing, creating a localized contact between the positive and negative electrodes. To deform the separator, it must soften or melt, making it deformable, and a force must be applied to deform it. Polyolefins used for separators include polyethylene (PE), polystyrene (PS), and polypropylene (PP). PE has a melting point of 95°C to 140°C, while PS has a melting point of 100°C. The glass transition temperature of PS is 90°C, and that of PP is 0°C. Therefore, separators can be easily deformed when force is applied at temperatures around 100°C.

[0027] The deformation forces include stress due to differences in the coefficient of thermal expansion, and pressure due to vaporization and gas generation caused by chemical reactions. The difference in the coefficient of thermal expansion between metal and plastic is about 0.01% / ℃, so the higher the temperature at which the treatment is performed, the more effective it is. A greater effect is the pressure generated by vaporization and gas generation, which has also been observed in cases where degraded lithium-ion batteries swell.

[0028] The electrolyte used for LiBs is a 1M solution of a lithium salt such as LiPF6 dissolved in an organic solvent. The organic solvent is a mixture of volatile solvents such as EC (ethylene carbonate), PC (propylene carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate). DMC in particular is used in many LiBs, but its boiling point is 90°C, and heating above that temperature causes evaporation, which can lead to deformation.

[0029] PC (boiling point 242°C) is sometimes used without mixing with DMC, but its degradation mechanism during use is known to be decomposition into acetone and propanal, and acetone is present in used LiBs. The boiling point of acetone is 56°C, lower than that of DMC (90°C). In other words, acetone evaporates when heated to temperatures above the boiling point of DMC. EMC (boiling point 107°C) is also sometimes used without mixing with DMC, but it is known that the degradation reaction during use is 2EMC → DMC + DEC. In this case, used LiBs also contain DMC, which has a boiling point of 90°C. Heating the LiB to above 90°C, the boiling point of the DMC contained in the organic solvent, makes it possible to apply pressure that deforms the softened separator, resulting in localized short circuits.

[0030] As described above, the temperature is set below the separator's decomposition or carbonization temperature, below the temperature at which an internal short circuit would occur due to the decomposition or carbonization of the separator. This decomposition or carbonization temperature causes the separator inside the LiB to deform, resulting in a partial short circuit between the positive and negative electrodes. The SEI coating is set at a temperature below the separator's decomposition or carbonization temperature, below the temperature at which heat generation due to a direct reaction between Li and the electrolyte does not occur, and above the electrolyte's gasification initiation temperature. Specifically, the present invention provides an energy release method that heats used lithium-ion batteries at a temperature between 90°C and 280°C, allowing for gradual discharge. This method can also be used in the same superheated steam furnace or roasting furnace to subsequently decompose or carbonize the batteries (either continuously or after discharge). This means that continuous discharge and decomposition or carbonization processes are possible.

[0031] However, even with the partial discharge treatment described above, the discharge process can sometimes proceed rapidly. Specifically, when discharge treatment is performed by partial contact, the partial contact area is difficult to control, which can increase the short-circuit current and lead to chain reactions of heat generation. Therefore, taking into account the worst-case scenario, the present invention further absorbs such rapid heat generation using a substance with a large heat capacity. Because liquids often have a large heat capacity, the subject of this invention is a liquid. Specifically, the discharge treatment is performed by immersing used lithium-ion batteries in a liquid. Because the liquid is in a liquid state, the discharge treatment is performed below the boiling point or decomposition point of the liquid, and the heat generated by the discharge is absorbed by the liquid. Specifically, the above objective can be achieved by treating the batteries in a substance that is liquid at the aforementioned temperature of 90°C and has a boiling point or decomposition point between 100°C and 280°C. Furthermore, it is desirable that this liquid does not generate complex oxides or sulfides during subsequent decomposition, carbonization, or roasting processes. Examples of liquids that satisfy these conditions include triacylglycerol and water. That is, used lithium-ion batteries are immersed in boiling water at about 90°C or higher (water at about 90°C to about 100°C) or in triacylglycerol at about 90°C to about 280°C, and then discharged. Triacylglycerol is, for example, various edible oils, and the decomposition points of peanut oil and olive oil are 220°C and 210°C, respectively.

[0032] This discharge treatment can be performed alone, or it can be performed using a superheated steam device or roasting furnace, and the same device can be used to perform decomposition, carbonization, or conventional roasting treatments consecutively. When performing discharge treatment using a superheated steam device, naturally, superheated steam is not introduced and heat treatment is performed under the above-mentioned conditions. Alternatively, a container containing waste lithium batteries can be placed in the above-mentioned treatment solution (e.g., triacylglycerol or water) in the carbonization or roasting device, and discharge treatment is performed during the temperature rise process, followed by continuous carbonization or roasting. In this case, the container can be recycled if it is made of a material that does not deform or chemically react during the heat treatment. For example, stainless steel or titanium is used. The treatment solution in the container is evaporated and released during the decomposition, carbonization, or roasting treatment. If the container is not to be recycled, it can be made of plastic, which also decomposes or carbonizes, so there is no problem. Furthermore, since the conditions for this discharge treatment may vary depending on the size and type of waste lithium batteries, it is possible to investigate in advance the conditions (e.g., heat treatment temperature and heat treatment time) that will completely deactivate the waste lithium batteries to be treated (a state in which the deactivated state cannot be restored), and then perform the deactivation treatment under those conditions. For example, there are methods that involve a single long-term heat treatment or multiple (two or more) heat treatments. In this case, too, the heat treatment may be performed alone, or it may be performed using a superheated steam device or a roasting furnace, and decomposition treatment, carbonization treatment, or conventional roasting treatment may be performed consecutively using the same device.

[0033] When this treatment is performed during the decomposition or carbonization process using superheated steam, a water film (which can also be called a boundary film) covering the LiB is formed on the LiB surface in the initial stage, automatically satisfying the above-mentioned condition (the LiB reaches a temperature of 90°C to 100°C). In other words, superheated steam provides a weakly oxidizing environment, and if the temperature is set to a temperature above the decomposition or carbonization temperature of plastic, discharge treatment will also occur automatically. Alternatively, if the only purpose is to simply cause discharge in the LiB, it is sufficient to subject the LiB to superheated steam treatment at 100°C or higher. In other words, even if the LiB is not immersed in water and treated at 90°C to 100°C, discharge treatment of the LiB will occur in the initial stage if the superheated steam treatment is performed in a superheated steam device under conditions that provide a weakly oxidizing environment with superheated steam and at a temperature above the decomposition or carbonization temperature of plastic. In order to perform the above-mentioned discharge treatment more effectively, the electrode layer of the waste lithium battery may be perforated in advance. This perforation treatment damages the separator (e.g., creates holes), so that the discharge treatment works effectively.

[0034] Example 1 Figure 4 is a graph showing the experimental results of boiling water treatment of used storage batteries. The voltage of a used LiB was measured after it was placed in boiling tap water from a charged state and removed after one minute, and again after being placed in boiling tap water for 30 minutes. In addition, to verify the effect of different electrolytes, the voltage of a nickel-metal hydride (Ni-HM) battery, which uses KOH as the electrolyte and does not undergo any reactions in this temperature range, was compared with that after 30 minutes of boiling tap water treatment. The voltage of the LiB dropped to less than half after one minute of treatment, and was almost zero after 30 minutes of treatment, confirming the effect of discharge. On the other hand, the voltage of the Ni-HM, which has a stable electrolyte, remained unchanged even after 30 minutes. <Example 2> Figure 10 shows the results of measuring the potential difference (electromotive force) between the positive (+) and negative (-) electrodes of a CR1616 coin-type lithium battery (LiB) at room temperature after immersion in a salad oil bath maintained at 120°C for a predetermined time and then removal from the oil bath. This table shows the results of evaluating the deactivation state of the lithium battery due to heat treatment. The LiB can be determined to be deactivated when the electromotive force reaches nearly 0 V (approximately 0.2 V or less). The data at 170 min in the first treatment (held at 120°C) was measured after immersion for 150 min and then holding it at room temperature for 20 min. The data at the second treatment was measured after immersion for 170 min for 21 hours at room temperature and then immersion in the salad oil bath for a predetermined time. The data at 130 min in the second treatment was measured after immersion for 120 min and then holding it at room temperature for 10 min. The data at 360 min and 1000 min are also the electromotive force of the LiB when held at room temperature. This shows that even LiB that appears to have been deactivated after a single long heat treatment (approximately 150 min) can be restored (returned to its original state) by leaving it at room temperature for a short time. Furthermore, a second long heat treatment (approximately 60 to 120 min) completely deactivates it. This suggests that performing two deactivation heat treatments is effective. Alternatively, it indicates the need for a continuous heat treatment longer than the above heat treatment (for example, approximately +60 to 120 min), and such a long heat treatment (for example, approximately 210 to 270 min) can achieve a completely deactivated state with a single heat treatment. 10, if the heat treatment (e.g., temperature, time) is insufficient and the battery separator is not completely destroyed, the separator may return to its original state to some extent by leaving it at room temperature, or the electrolyte inside the battery may change due to the heat treatment, causing the battery to lose its electromotive force, but leaving it at room temperature may cause the altered electrolyte to partially return to its original state and restore the battery, or the electrodes or wiring may be damaged by the heat treatment and cause the battery to lose its electromotive force, but leaving it at room temperature may cause the damaged electrodes or wiring to be partially repaired and restored. However, if the battery is subjected to heat treatment multiple times (two or more times) or to a continuous, long-term heat treatment (one time), the above state becomes irreversible and the battery becomes completely deactivated.

[0035] This invention relates to a method for recovering rare elements (Li, Co, Ni, etc.) used in lithium-ion batteries for mobile phones and automobiles, i.e., a method for recycling used (waste) lithium-ion batteries. Next, we describe another method (the second invention) that allows for discharge treatment before decomposition or carbonization of waste lithium-ion batteries. When recycling used lithium-ion batteries, charged lithium-ion batteries contain active lithium (Li) in a high-energy state. When this high-energy state is released, the flammable electrolyte material generates heat and ignites, making safe disposal generally difficult. While some manual discharge and electrolyte cleaning have been attempted, most involve high-temperature furnaces where ignition is not a problem. This results in the mixing of metal components such as aluminum and compound components such as cobalt oxide at high temperatures, placing a heavy burden on subsequent extraction processes. Therefore, this invention features a superheated steam treatment at temperatures below 650°C, which allows metals and compounds to be easily physically separated, as a preliminary step to metal extraction. For this purpose, the high-energy Li, which is at risk of reacting with the steam, is discharged using an aqueous solution of electrolytic salts. Instead of using salts containing halogens or other substances in the anions, organic anions consisting of carbon, hydrogen, and oxygen that decompose and carbonize during superheated steam treatment are used, and cations such as calcium (Ca) that adsorb fluorine and other substances contained in lithium-ion batteries are used to prevent the release of harmful substances during the superheated steam treatment stage.

[0036] The second invention is a treatment method for separating lithium-ion batteries, which have been discharged using an electrolyte solution containing a salt having cations that fix fluorine and sulfur and anions that decompose through a carbonization reaction, into metal components, compound components, and carbides using superheated steam treatment. During the discharge treatment, ultrasonic ceramic cutting is used to damage the lithium-ion battery, causing discharge between the electrodes; during the discharge treatment, a cutting tool such as a drill made of a good conductor that is electrically insulated from earth is used to promote short-term discharge; or during the discharge treatment, external deformation is applied to distort the cell package, causing the electrolyte solution to leach out from the distortion.

[0037] FIG. 5 shows an example of the processing method of the present invention. A used lithium-ion battery (sometimes referred to as LiB) is immersed in a container containing a conductive aqueous solution (also called an electrolytic aqueous solution or electrolyte aqueous solution). Alternatively, the used lithium-ion battery is placed in a container, and the conductive aqueous solution is poured into the container, immersing the lithium-ion battery in the conductive aqueous solution. The conductive aqueous solution is a salt containing a cation that fixes and adsorbs fluorine or sulfur and an anion that decomposes by a carbonization reaction. For example, the cation is calcium (Ca) ion, and the anion is an organic anion such as carbonate, acetate, oxalate, or formate, and the salt is, for example, calcium carbonate salt. Conventionally, discharge processing of used lithium-ion batteries has been commonly performed for safety reasons, and involves immersing the battery in inexpensive salt water or an aqueous solution of a chloride such as sodium chloride to discharge the battery. However, the anion in salt water is chlorine, and when processed with superheated steam, it oxidizes to chloride, damaging the furnace and the environment. Furthermore, the chlorine may corrode the furnace during subsequent roasting or superheated steam treatment, or may be released into the atmosphere, damaging the furnace and the environment. Furthermore, because chloride solutions are highly conductive, they may short-circuit lithium-ion batteries, causing a sudden change in voltage and the sudden explosion of the solution.

[0038] In contrast, the organic anions used in the present invention, such as carbonate, decompose and carbonize during the subsequent heating process (superheated steam treatment), and contain no chlorine, so there is little risk of damage to the heating furnace or the environment. On the other hand, the conductive aqueous solution (organic acid salt) of calcium carbonate, etc., used in the present invention has a low ionization coefficient, which makes the discharge process ineffective. Therefore, since it is necessary to shorten the distance between the discharge electrodes, in the present invention, the lithium-ion battery casing is damaged by cutting or perforating, etc., to facilitate discharge between the output electrodes (positive and negative electrodes separated by a separator) inside the lithium-ion battery, which are located at a short distance from each other. In other words, the conductive aqueous solution penetrates the lithium-ion battery through the damage, such as the cut or perforation, and causes a short circuit (discharge) between the positive and negative electrodes.

[0039] In this invention, a lithium-ion battery is damaged in a container (small container) containing a conductive aqueous solution. Figure 6 shows an example of a method for damaging a lithium-ion battery in a small container 11 containing a conductive aqueous solution. Figure 6(a) shows how presses 14 and 15 press the lithium-ion battery 12 from both sides (in the direction of the arrows) to damage the battery. Specifically, the presses 14 and 15 press and crush the battery 12, deforming the battery's casing, and allowing the conductive aqueous solution to penetrate into the casing through the gaps created by the deformation. This method may also be called the lateral pressure method. The conductive aqueous solution inside the casing causes discharge between the electrodes. The pressure applied to deform the casing may be uniform across the casing side, or may be concentrated in a specific area, as long as it creates gaps in the casing. Because the press used in the lateral pressure method is also immersed in the conductive aqueous solution, it is made of a highly resistant material that is resistant to deterioration by the conductive aqueous solution, such as stainless steel or ceramic.

[0040] Figure 6(b) shows how the lithium-ion battery 13 is deformed by rotary rolls 16 and 17 to create gaps. The rotary rolls 16 and 17 rotate in the direction of the arrows, and the lithium-ion battery 13 is transported in the direction of the arrows between the rotary rolls 16 and 17, which are spaced apart enough to damage the battery's casing. A conductive aqueous solution is then allowed to penetrate the casing through the gaps created by the damage, and the conductive aqueous solution inside the casing discharges electricity between the electrodes. The example shown in Figure 6(b) deforms the casing of the lithium-ion battery 12 by varying the pressure over time, which may be called a continuous roll method. The rotary (rolling) rolls used in the continuous roll method are also immersed in the conductive aqueous solution, and are therefore made of a highly resistant material that is resistant to degradation by the conductive aqueous solution. For example, they are made of stainless steel or ceramics.

[0041] FIG. 7 illustrates another method for damaging a lithium-ion battery. The lithium-ion battery 21 is immersed in a small container 11 containing a conductive aqueous solution, and a drill 22 is used to drill a hole in the side of the battery's housing. The external electrodes of the lithium-ion battery are indicated by A and B, allowing the front and back sides to be clearly identified. In FIG. 7(a), the tip of the drill 22 is placed against the front side of the housing of the lithium-ion battery 21. The positive electrode surface, separator surface, and negative electrode surface (collectively referred to as the electrode surfaces) are arranged approximately parallel to this side. Therefore, drilling a hole in the approximate center of the front side of the lithium-ion battery 21 with the drill 22 creates a hole penetrating the electrode surface. FIG. 7(b) illustrates the state in which the drill 22 has penetrated the side of the housing of the lithium-ion battery 21, showing the back side of the housing. Even in this state, if the drill 22 is made of a material with good electrical conductivity (e.g., various metals), a short circuit will occur between the electrodes (positive and negative electrodes), resulting in a discharge. And / or, the conductive aqueous solution penetrates through the formed holes into the lithium ion battery 21, thereby starting discharge. That is, the drill bit acts as an external discharge body to assist discharge by the conductive aqueous solution.

[0042] However, if the electrical conductivity of the drill 22 is low, discharge is unlikely to occur, and discharge is unlikely to occur when drilling, and if the conductivity of the conductive aqueous solution is also low and discharge occurs gradually, as shown in Figure 7(c), a hole is drilled into the housing of the lithium-ion battery 21 with the drill 22, and after the tip of the drill 22 emerges from the back side of the housing, a metal wire 23 (which can be in the form of a string or tape) with extremely good electrical conductivity is attached near the tip of the drill 22, and then, as shown in Figure 7(d), the drill 22 is pulled out, leaving the metal wire 23 passing through the through hole. After the metal wire 23 has passed through the through hole, the metal wire 23 is removed from the drill (blade) 22, leaving the metal wire 23 in the through hole, as shown in Figure 7(e). FIG. 7(e) is a see-through plan (top) view of a lithium-ion battery 21. The positive electrode, separator, and negative electrode layers are arranged in layers parallel to the side of the housing. A hole drilled with a drill bit 22 runs through the center of the battery, through which a metal wire 23 passes. The metal wire 23 directly shorts the electrodes (positive and negative electrodes), causing a discharge, and / or the conductive aqueous solution that penetrates the hole rapidly accelerates the discharge. If the metal wire 23 is in direct contact with the electrodes (positive and negative electrodes), a discharge occurs immediately. However, even if there is no direct contact, the distance between the electrodes and the metal wire 22 is extremely small (much smaller than the distance between the electrodes), so a discharge can occur quickly due to the conductive aqueous solution that penetrates between them. Note that various electrically good conductors (wires) other than metal wires may also be used. Examples include carbon wires, silicides, and conductive plastics. Although the term "wire" is used, it is acceptable to use string- or tape-shaped wires as long as they fit into the through-hole (including perforations). Therefore, the term "wire" encompasses these various types.

[0043] In addition to the aforementioned method of damaging used lithium-ion batteries using a drill or other tool to inject a conductive solution into the batteries and allow discharge between the electrodes, another method involves cutting or drilling using an ultrasonic ceramic cutter. That is, similar to the method shown in Figures 6 and 7, the used lithium-ion battery (or its casing) is placed in a conductive solution, and the casing is then cut or drilled with an ultrasonic ceramic cutter to allow the conductive solution to penetrate into the casing. If the cutter is a good conductor, when cutting the electrically isolated structure inside the battery by the separator during drilling, the cutter may penetrate the separator, causing a partial short circuit between the electrodes (positive and negative electrodes), resulting in an internal short circuit and impairing the generation of external discharge current. In contrast, when using a ceramic cutter, the ceramic cutter is an insulator, so this short circuit does not occur, preventing the generation of external discharge current. Furthermore, ultrasound not only enhances drilling and cutting performance, but also promotes the penetration of the conductive solution into the battery. When discharge treatment is carried out in a conductive aqueous solution with a large heat capacity as in the present invention, even if the discharge treatment occurs rapidly, no sudden temperature rise, explosion, or sudden outbreak occurs due to heat generation, so it can be said to be an extremely safe discharge treatment method.

[0044] If the conductivity of a conductive aqueous solution is not high enough, discharge is unlikely to occur. Therefore, to increase the conductivity of the conductive aqueous solution, the present invention mixes a conductive filler or conductive fine powder into the conductive aqueous solution. The conductive filler or conductive fine powder is dispersed and suspended in the conductive aqueous solution. When the conductive aqueous solution penetrates the vicinity of the battery cell electrodes through a damaged portion of a used lithium-ion battery, discharge occurs through the conductive aqueous solution whose conductivity has been increased by the dispersed conductive filler. Examples of conductive (dispersed) fillers or conductive (dispersed) fine powders include carbon black, graphite, various metal powders such as silver, nickel, and copper, conductive tin oxide, and conductive titanium oxide. These remain as carbonized materials, metal compounds, or elemental metals after superheated steam treatment or roasting, making them harmless and recyclable.

[0045] Next, the lithium-ion battery is immersed in the conductive aqueous solution in the small container, which is then immersed in a large container containing the same solution. The conductive aqueous solution in both the small and large containers is the same. Although the previous step damaged the lithium-ion battery to promote discharge, it is desirable to fully discharge it by leaving it in the conductive aqueous solution for a certain period of time. For example, it may be left for half a day to about a week. Figure 8 shows the arrangement of the lithium-ion battery immersed in the large container 31 containing the conductive aqueous solution and the small container 11 containing the conductive aqueous solution. Arranging multiple small containers 11 reduces running costs. While Figure 8 shows the small containers 11 arranged in a single row on the bottom of the large container 31, creating shelves or stacking them in multiple layers allows for mass processing.

[0046] The small container containing fully discharged waste lithium-ion batteries is removed from the large container, placed in a conductive aqueous solution, and then placed in a superheated steam furnace after the batteries have been saturated with the conductive aqueous solution. Figure 9 shows a superheated steam generator 100 in which a small container 108 containing waste lithium-ion batteries and the conductive aqueous solution is placed on a support shelf 106 provided within the device. The superheated steam generator 100 includes a superheated steam generator 102 and a temperature sensor 103 for detecting the temperature inside the device. A signal from the temperature sensor 103 is sent to a controller 104, which controls the operation of a boiler 101 to maintain the temperature inside the device at a predetermined temperature. Superheated steam at an appropriate temperature is sent to the superheated steam generator 102, and the superheated steam generator 102 sends steam at a predetermined temperature and in a predetermined amount into the superheated steam device 100, maintaining the temperature and amount of steam inside the superheated steam device 100 at a predetermined level. In particular, the small container 108 and its surroundings are brought into a predetermined state. The pressure inside the superheated steam device 100 may be set to a high pressure state equal to or higher than atmospheric pressure. The gas inside the superheated steam device is discharged to the outside through the exhaust line 105. When the small container 108 is placed inside the superheated steam device 100, air is present inside the device, but once superheated steam enters the device, the air is discharged to the outside through the exhaust line 105, and the inside of the device is filled with superheated steam and no oxygen is present.

[0047] The conductive aqueous solution in the small container 108 is maintained at its evaporation temperature (approximately 100°C, depending on the type of aqueous solution) until it evaporates. After evaporation, the temperature reaches approximately the same as the superheated steam temperature (approximately 300°C to 650°C), carbonizing or decomposing the plastics that make up the waste lithium-ion batteries. Rare metals contained in the electrodes are also oxidized, forming their oxide compounds. The small container 108 may be made of metals that do not react at this temperature (e.g., stainless steel) or plastics that do carbonize (e.g., polypropylene or polycarbonate). Metals can be reused, while plastics are carbonized or decomposed, eliminating the need for recovery. A removal system may be installed in the exhaust line 105. The waste lithium-ion batteries are placed in the small container 108 in their casings. However, removing metals, such as screws and other accessories, beforehand facilitates recycling after the superheated steam carbonization process. The temperature inside the superheater is kept below the melting point of Al (approximately 660°C) (preferably not exceeding 650°C) and the treatment is carried out in an oxygen-free environment. Therefore, although the surfaces of Al and various metals other than lithium are partially oxidized, they remain largely unoxidized overall, making recycling easy.

[0048] The reason for placing the waste lithium-ion batteries in the conductive aqueous solution in the superheated steam generator is to prevent sudden heat generation or explosion due to discharge during heating in the superheated steam generator. While sufficient discharge has already occurred in the large container, there is little need for concern. However, just to be safe, the waste lithium-ion batteries are placed in a small container 108 containing the conductive aqueous solution and placed in the superheated steam generator 100. Furthermore, waste lithium-ion batteries contain fluorine (such as the electrolyte LiPF6), and if fluorine is released in the form of hydrogen fluoride (HF), it could damage the equipment or pollute the environment. Installing exhaust gas removal equipment to prevent environmental pollution would increase both equipment and running costs. However, cations in the conductive aqueous solution combine with the generated HF to form harmless fluorides. For example, if the conductive aqueous solution contains calcium carbonate, calcium fluoride (CaF2) is formed, rendering the waste harmless. The anionic compounds are CO2 and HO, so there is no risk if the waste is released to the outside, eliminating the need for special removal equipment. The temperature inside the superheated steam device is maintained at 300°C to 650°C, which increases the temperature of the conductive aqueous solution and its electrical conductivity, thereby promoting the remaining discharge. The conductive aqueous solution eventually evaporates completely, leaving calcium (Ca) as a single substance or in the form of a compound in a small container. This can be recovered through post-processing along with carbonized waste lithium-ion batteries. The superheated steam treatment method used in this invention is a heat treatment at 650°C or below, which is lower than the melting point of aluminum, so there is no risk of aluminum melting. Furthermore, although plastics are decomposed or carbonized, this method does not emit CO2. Furthermore, since no chlorine-based substances are used, no chlorine-based compounds are generated, resulting in a low environmental impact.

[0049] After superheated steam treatment, remaining materials include carbonized plastics, oxidized compounds of metals that reacted with steam, and unreacted metals. These materials are removed and used as raw materials for the extraction process following physical separation. If small containers are present, these materials remain in the small containers, which are then removed from the superheated steam furnace. If the small containers are also carbonized and no longer remain, placing the inner container containing the small containers in the superheated steam furnace before treatment with the superheated steam device makes it easier to recover the remaining materials. After crushing the remaining materials in a crushing device, they are separated into metals and other substances, and metals (e.g., lithium (Li), cobalt (Co), nickel (Ni), copper (Cu), aluminum (Al), and iron (Fe)) are recovered from the separated materials via an extraction process. The remaining materials after superheated steam treatment can be subjected to various conventional methods for recovering valuable metals, such as physical separation and subsequent extraction processes. When the discharge treatment in the liquid described above is performed, the waste lithium batteries can be completely deactivated by the long-term heat treatment (single heat treatment) or multiple heat treatments (for example, the heat treatment methods described in Figure 10 and the related sections) in the liquid in which the waste lithium batteries are immersed, and then removed from the liquid and placed in a superheated steam device for decomposition and carbonization treatment (the process starting from the middle shown in Figure 5). Alternatively, the liquid container in which the waste lithium batteries are immersed can be placed in the superheated steam device to perform the discharge treatment (for example, the long-term heat treatment (single heat treatment) or multiple heat treatments) in the superheated steam device, and then the deactivated waste lithium batteries can be continuously decomposed and carbonized while still in the container and placed in the superheated steam device (similar to the method shown in Figure 5).

[0050] As described in detail above, the present invention provides a stabilization method for waste (used) lithium-ion batteries that safely discharges them. By using the present invention, waste lithium-ion batteries can be safely discharged, significantly reducing the adverse effects on the treatment equipment and the environment. Furthermore, the stabilization process cost of the present invention is low, and the recycling cost of lithium-ion batteries can be reduced. It goes without saying that, in this specification, when the content described in a certain part of the specification can be consistently applied to other parts not described, the content can also be applied to the other parts. Furthermore, it goes without saying that the content of the examples and embodiments described in this application document can be used in combination with the content of other examples and embodiments. Furthermore, the above-described embodiment is merely an example, and various modifications can be made within the scope of the present invention, and the scope of the present invention is not limited to the above-described embodiment. [Industrial Applicability]

[0051] The stabilization treatment method for used lithium ion batteries of the present invention may also be applicable to the recycling treatment of other ion batteries. [Explanation of symbols]

[0052] 11... Small container, 12... Lithium ion battery, 13... Lithium ion battery, 14···Press, 15···Press, 16···Rotary rolling roll, 17···Rotary rolling roll, 21. Lithium ion battery, 22. Drill, 23. Metal wire, 31. Large container, 100... Superheated steam device, 101... Boiler, 102... Superheated steam generator, 103: Temperature sensor; 104: Controller; 105: Exhaust line; 106···Support shelf, 107···Lithium ion battery, 108···Small container

Claims

1. A method for stabilizing used lithium ion batteries, characterized in that a substance has a boiling point or demarcation point at or below a temperature (upper limit temperature) that is lower than both the decomposition temperature of the separator of the used lithium ion battery and the collapse temperature of the SEI (Solid Electrolyte interface), and is liquid at the gasification start temperature (lower limit temperature) of the electrolyte of the used lithium ion battery, is subjected to heat treatment in a liquid between the lower limit temperature and the upper limit temperature, thereby causing the used lithium ion battery to become inactivated.

2. The substance is water (H ２ 0), and the lithium ion battery is immersed in water at 90°C to 100°C to cause discharge.

3. 2. The stabilization treatment method for used lithium ion batteries according to claim 1, wherein the substance is triacylglycerol, and the lithium ion battery is immersed in triacylglycerol at 90°C to 280°C to cause discharge.

4. The stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 3, characterized in that a perforation treatment is performed on the electrode layer of the used lithium ion battery before the heat treatment.

5. The used lithium ion battery is placed in the above-mentioned substance and then placed in a superheated steam device to carbonize or decompose the plastics of the used lithium ion battery. The stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 4, characterized in that the heat treatment is carried out by placing the used lithium ion batteries in the substance at an early stage of the heat treatment, which is the carbonization treatment or the decomposition treatment.

6. The stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 4, characterized in that after the heat treatment, plastics of the used lithium ion batteries are carbonized or decomposed in a roasting device or a superheated steam device while being placed in the substance.

7. The stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 4, characterized in that the used lithium ion batteries are placed in the substance and then placed in a roasting device or a superheated steam device to carry out the heat treatment, and then plastics in the used lithium ion batteries are carbonized or decomposed.

8. The stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 4, characterized in that the used lithium ion batteries are placed in the substance and then placed in a superheated steam device, and plastics in the used lithium ion batteries are carbonized or decomposed.

9. A stabilization method for used lithium ion batteries, characterized by carrying out the stabilization method for used lithium ion batteries according to any one of claims 1 to 4, followed by a step of placing the used lithium ion batteries in a weakly oxidizing environment and carbonizing or decomposing plastics, wherein the weakly oxidizing environment is a combination of an atmosphere and a temperature that does not allow the reaction C + O2 → CO2 to proceed and has an oxygen potential that can oxidize lithium.

10. The weakly oxidizing atmosphere is MxO (M is an element or a reactive group), The temperature of the weakly oxidizing environment is 2×M+O ２ The oxygen potential according to the Ellingham diagram of 2MxO is higher than the oxygen potential for the oxidation of lithium (Li), and C + O ２ =CO ２ 10. The stabilization treatment method for used lithium ion batteries according to claim 9, wherein the temperature is lower than the oxygen potential of the battery and higher than the decomposition temperature of plastics.

11. the weakly oxidizing atmosphere is water vapor; The temperature condition of the weakly oxidizing environment is based on the Ellingham diagram, and is set to 2H ２ O+O ２ =2H ２ O and C+O ２ =CO ２ The stabilization treatment method for used lithium ion batteries according to claim 9, characterized in that the temperature is about 650°C or less, which is the temperature at the point where the oxygen potential diagrams of the above intersect, and is higher than the decomposition temperature of plastics.

12. After carrying out the stabilization treatment method for used lithium ion batteries according to any one of claims 1 to 5, The used lithium ion battery is discharged in a conductive aqueous solution of a salt having a cation that fixes fluorine and sulfur and an anion that decomposes by a carbonization reaction, and further A stabilization treatment method for used lithium ion batteries, which enables separation of the used lithium ion batteries into metal components, compound components, and carbide components by superheated steam treatment at 650°C or less.

13. 13. The stabilization treatment method for used lithium ion batteries according to claim 12, wherein the conductive aqueous solution is a calcium carbonate aqueous solution.

14. 14. The stabilization treatment method for used lithium ion batteries according to claim 12 or 13, characterized in that the discharge treatment using the conductive aqueous solution is carried out by cutting the used lithium ion batteries in the conductive aqueous solution using ultrasonic ceramic cutting and allowing the conductive aqueous solution to seep into the used lithium ion batteries from the cut parts.

15. A method for stabilizing a used lithium ion battery as described in claim 14, characterized in that a good electrical conductor wire is passed through the cut portion.

16. 14. The stabilization treatment method for used lithium ion batteries according to claim 12 or 13, characterized in that the discharge treatment using the conductive aqueous solution is carried out by drilling holes in the used lithium ion battery using a cutting instrument (tool) in the conductive aqueous solution and allowing the conductive aqueous solution to seep into the used lithium ion battery through the drilled holes.

17. A method for stabilizing a used lithium ion battery as described in claim 16, characterized in that a good electrical conductor wire is passed through the perforated portion.

18. 14. The stabilization treatment method for used lithium ion batteries according to claim 12 or 13, characterized in that the discharge treatment using the conductive aqueous solution is carried out by applying external deformation to the used lithium ion battery in the conductive aqueous solution to cause distortion, and causing the conductive aqueous solution to leach into the used lithium ion battery due to the distortion.

19. 19. The stabilization treatment method for used lithium ion batteries according to claim 18, wherein the method of applying external deformation to impart strain to the used lithium ion battery is a method of applying external deformation to impart strain to the used lithium ion battery using a rotary press roller or a press machine.

20. The stabilization treatment method for used lithium ion batteries according to any one of claims 12 to 19, characterized in that a conductive filler or a conductive powder is mixed into the conductive aqueous solution.

21. The stabilization treatment method for used lithium ion batteries according to any one of claims 12 to 20, characterized in that after the used lithium ion battery is discharged using the conductive aqueous solution, the used lithium ion battery is subjected to a superheated steam treatment while being placed in the conductive aqueous solution.

22. The stabilization treatment method for used lithium ion batteries according to claim 21, wherein the temperature of the superheated steam treatment is about 300°C to about 650°C.

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