How to disassemble a lithium-ion rechargeable battery

Abstract

To improve recovery property of an active material contained in an electrode by easily separating a separator from the electrode in disassembly of a lithium ion secondary battery.SOLUTION: A disassembly method for a lithium ion secondary battery includes a discharging step S10, a primary crushing step S20, a drying step S30 and a secondary crushing step S40. In the discharging step S10, the lithium ion secondary battery is discharged in such a manner that a voltage of the lithium ion secondary battery is not below 0.8 V, preferably, becomes equal to or lower than 3.0 V. In the primary crushing step S20, a case is crushed and an electrode body is exposed. In the drying step S30, the electrode body is dried until a high boiling point solvent contained in an electrolyte is evaporated. In the secondary crushing step S40, the dried electrode body is crushed and a separator is peeled from the electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0005]

[0001] The present disclosure relates to a method for disassembling a lithium-ion secondary battery in which an electrode body in which an electrode and a separator are laminated is housed in a case in a state of being impregnated with an electrolytic solution containing a low-boiling-point solvent and a high-boiling-point solvent.

Background Art

[0002] Patent Document 1 discloses a method for discharging and disassembling a used lithium-ion secondary battery to separate and recover battery materials containing an active material. The method disclosed in Patent Document 1 includes starting the disassembly operation when the voltage has dropped to a level at which no spark is generated during discharging, and ending the disassembly operation at a stage where there is no contamination due to elution of copper or the contamination is minor.

[0003] In the recycling of lithium-ion secondary batteries, it is required to improve the recoverability of expensive active materials while ensuring safety. In enhancing the recoverability of the active material, it is important to facilitate the separation of the separator from the electrode. The electrode and the separator are adhered with an adhesive to form an electrode body. When the electrode body is pulverized, if the separator cannot be separated from the electrode, the active material will adhere to the separator. It is not easy to remove the active material adhering to the separator.

[0004] The method disclosed in Patent Document 1 has room for improvement in the recoverability of the active material. One of the reasons is that in the method disclosed in Patent Document 1, the voltage is reduced to 0.6 V or less during the disassembly of the lithium-ion secondary battery. Experiments related to the present disclosure have revealed that when the voltage is excessively reduced, the active material tends to adhere to the separator. Also, although the electrode body is impregnated with an electrolytic solution containing a solvent, it has been found that the ease of separating the separator from the electrode varies depending on the method of treating the electrolytic solution. However, in the method disclosed in Patent Document 1, the treatment of the electrolytic solution is not particularly considered. <​​In addition to Patent Document 1, Patent Document 2 can also be cited as an example of a document illustrating the state of the art in the field related to this disclosure. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2021-072157 [Patent Document 2] Japanese Patent Publication No. 2012-195073 [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure has been made in view of the above-mentioned issues. One of the purposes of this disclosure is to improve the recovery of active material contained in electrodes by enabling easy separation of the separator from the electrodes during the dismantling of lithium-ion secondary batteries. [Means for solving the problem]

[0008] This disclosure provides a method for disassembling a lithium-ion secondary battery to achieve the above objective. The method for disassembling a lithium-ion secondary battery according to this disclosure is a method for disassembling a lithium-ion secondary battery in which an electrode body, in which electrodes and separators are stacked, is housed in a case while impregnated in an electrolyte containing a low-boiling point solvent and a high-boiling point solvent. The method for disassembling a lithium-ion secondary battery according to this disclosure comprises a discharge step, a primary crushing step, a drying step, and a secondary crushing step. The discharge step is a step of discharging the lithium-ion secondary battery so that the voltage of the lithium-ion secondary battery does not fall below 0.8V. The primary crushing step is a step of crushing the case to expose the electrode body. The drying step is a step of drying the exposed electrode body until the high-boiling point solvent evaporates. The secondary crushing step is a step of crushing the dried electrode body to separate the separator from the electrodes. [Effects of the Invention]

[0009] According to the lithium-ion secondary battery disassembly method of this disclosure, by discharging the lithium-ion secondary battery so that the voltage does not fall below 0.8V, the adhesion of the active material to the separator can be suppressed. Then, by exposing the electrode body and drying it, and evaporating the high-boiling point solvent contained in the electrolyte, the active material can be easily detached from the separator. Therefore, after drying, the electrode body is in a state where the separator can be easily separated from the electrode, and the active material contained in the electrode can be recovered with a high recovery rate. [Brief explanation of the drawing]

[0010] [Figure 1] This figure shows the dismantling process of a lithium-ion secondary battery according to the embodiment of this disclosure. [Figure 2] This figure shows the results of verifying the relationship between voltage and the heat generated during a nail-piercing test. [Figure 3] This figure shows the results of confirming preferred discharge conditions from the viewpoint of recoverability of the positive electrode active material. [Figure 4] This figure shows the results of confirming the relationship between the dry state of the electrode body, the peelability of the separator, and the recoverability of the electrolyte. [Figure 5] This figure shows the results of a peel test of the electrode body after discharge under appropriate discharge conditions and evaporation of the electrolyte. [Modes for carrying out the invention]

[0011] 1. Lithium-ion rechargeable battery Lithium-ion secondary batteries are used by connecting multiple cells together. In this embodiment, the lithium-ion secondary battery to be disassembled is a cell. Hereafter, the lithium-ion secondary battery to be disassembled may be referred to as a cell.

[0012] The cell comprises an electrode body consisting of a laminated electrode and a separator. The electrode consists of a positive electrode and a negative electrode. The separator is a resin film that separates the positive and negative electrodes. The electrode body is housed in a case while impregnated with an electrolyte. For the case, for example, an aluminum laminate material in which resin is bonded to both sides of aluminum is used.

[0013] The positive electrode comprises a current collector made of aluminum foil and a positive electrode active material coated on the surface of the current collector. The positive electrode active material is typically lithium oxide such as lithium cobaltate, lithium manganeseate, or ternary lithium oxide. The negative electrode comprises a current collector made of copper foil and a negative electrode active material coated on the surface of the current collector. The negative electrode active material is typically carbon-based material such as graphite or hard carbon.

[0014] The electrolyte is a solution of lithium-containing salt dissolved in a solvent. The solvent consists of a low-boiling point solvent and a high-boiling point solvent. Examples of low-boiling point solvents include dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). Examples of high-boiling point solvents include ethylene carbonate (EC) and propylene carbonate (PC). In this embodiment, DMC and EMC are used as low-boiling point solvents, and EC is used as the high-boiling point solvent.

[0015] 2. Cell dismantling process Cell dismantling is performed with the aim of extracting recyclable materials from the various materials that make up the cell, and safely recovering hazardous materials. The recycled material is the expensive positive electrode active material, which is recovered in the form of black mass. Iron, copper, and aluminum are also recovered for recycling. The resin film that makes up the separator is recovered as waste. DMC, EMC, and EC are recovered as hazardous materials. The lithium-ion secondary battery dismantling method of this disclosure is applied to the cell dismantling process for separating and recovering these materials.

[0016] Figure 1 shows the disassembly process of the cell according to this embodiment. The disassembly process of the cell according to this embodiment consists of a discharging process S10, a primary crushing process S20, a drying process S30, a secondary crushing process S40, a dust collection and screening process S50, a screening process S60, and a mechanical sorting process S70. Hereinafter, the disassembly process of the cell according to this embodiment will be described.

[0017] In the discharging process S10, the cell is discharged so that the voltage of the cell becomes 0.8 V or more and 3.0 V or less. The reason for discharging the cell is to prevent the separator from melting due to heat generation caused by a short circuit when the cell is crushed in a subsequent process. The welding of the melted separator to the positive electrode deteriorates the recyclability. The 3.0 V set as the criterion for the completion of discharging is approximately the voltage corresponding to 0% SOC of the cell. The range of 0% to 100% of SOC corresponds approximately to the range of 3.0 V to 4.1 V of the voltage.

[0018] In the discharging process S10, it is allowed to over-discharge the cell as long as the voltage does not fall below 0.8 V. The reason for preventing the voltage of the discharged cell from falling below 0.8 V is to suppress the adhesion of the positive electrode active material to the separator. It is not easy to remove the positive electrode active material attached to the separator in a subsequent process. However, preventing the voltage from falling below 0.8 V means preventing the voltage from falling below 0.8 V continuously for a certain period of time, and it is allowed for the voltage to momentarily fall below 0.8 V.

[0019] In the primary crushing process S20, the case is crushed to expose the internal electrode body. By exposing the electrode body, it becomes possible to evaporate the electrolytic solution adhering to the electrode body and dry the electrode body. As a method for crushing the case, for example, a method of cutting the case with a shredder is used.

[0020] In the drying process S30, the exposed electrode body is dried, and in this process, the electrolytic solution is recovered. The drying process S30 includes a first distillation process for recovering DMC and EMC, which are low-boiling-point solvents, and a second distillation process for recovering EC, which is a high-boiling-point solvent. In the first distillation process implemented first, DMC and EMC are evaporated and recovered at a temperature lower than the boiling point of EC. When DMC and EMC are no longer detected by the gas sensor, it may be determined that DMC and EMC have completely evaporated. In the second distillation process implemented next, the remaining EC is evaporated and recovered. When EC is no longer detected by the gas sensor, it may be determined that EC has completely evaporated.

[0021] Thus, in the drying process S30, DMC, EMC, and EC are separately distilled and recovered. However, if it is not necessary to separately recover DMC, EMC, and EC, or if they are to be separated by distillation in a subsequent process, the electrode body may be dried from the beginning at a temperature higher than the boiling point of EC. In any case, in the drying process S30, the electrode body is dried until the high-boiling-point solvent EC evaporates.

[0022] In the secondary crushing process S40, the dried electrode body is crushed to peel the separator from the electrode and to peel the positive electrode active material from the current collector of the positive electrode. The reason for drying the electrode body until EC evaporates in the drying process S30 is to suppress the adhesion of the positive electrode active material to the separator and to facilitate the peeling of the positive electrode active material. In the secondary crushing process S40, the electrode body may be crushed while being heated. As a method for crushing the dried electrode body, for example, a method of crushing the electrode body with a crusher such as a hammer crusher or a chain crusher is used.

[0023] The dust collection and sieving process S50 and the sieving process S60 are processes for sorting the material that has been crushed in the secondary crushing process S40. In the dust collection and sieving process S50, only light and small objects such as dust are sorted. In the sieving process S60, relatively heavy and large objects that have been crushed to a size below a certain value are sorted. Sieves with different mesh sizes are used in the dust collection and sieving process S50 and the sieving process S60. A fine-mesh sieve is used in the dust collection and sieving process S50, and a coarse-mesh sieve is used in the sieving process S60.

[0024] In the dust collection and sieving process S50, black mass and resin film are separated from the crushed material. The black mass and resin film are further separated by substance. In the sieving process S60, materials such as aluminum, copper, and iron are separated from the crushed material. However, since black mass and resin film are also mixed in, these are sieved separately to separate them by substance. The remaining large materials, such as resin lumps, iron, aluminum (foil and lumps), and copper (foil and lumps), are mechanically separated by substance in the mechanical sorting process S70.

[0025] 3. Test Results 3-1. Test to determine the target voltage in the discharge process Figure 2 shows the results of verifying the relationship between the cell voltage and the heat generated in the nail-piercing test. The results of measuring the heat generated when a nail was driven into the cell to short-circuit it under various voltage conditions are shown in Figure 2. Since the melting temperature of the separator is 120°C, in the discharge process S10, it is necessary to lower the voltage to a level where the cell temperature does not rise above 120°C when the cell is crushed in the primary crushing process S20. According to Figure 2, the voltage at which the cell temperature reaches 120°C is in the range of 3.0V to 3.6V. However, adjusting the voltage in the range of 3.0V to 3.6V is difficult and unstable due to the large voltage decrease gradient. Therefore, in order to reliably prevent the separator from melting, it is preferable to adjust the cell voltage to 3.0V or less in the discharge process S10.

[0026] Figure 3 shows the results of confirming preferred discharge conditions from the viewpoint of positive electrode active material recovery. In Figure 3, voltages marked with circles represent voltages where preferred results were obtained, and voltages marked with X represent voltages where problems occurred. In the tests that formed the basis of the confirmation results shown in Figure 3, significant adhesion of positive electrode active material to the separator was observed at 0.3V and 0.5V. This is presumed to be due to the anchoring effect influenced by the deposition of positive electrode active material on the positive electrode surface. At 0.8V and above, no problematic adhesion of positive electrode active material to the separator was observed. However, at 3.6V, 3.7V, and 3.9V, welding of the separator to the positive electrode occurred due to heat generation. From the above confirmation results, it can be concluded that the preferred target voltage for the cell in discharge process S10 is a voltage between 0.8V and 3.0V.

[0027] 3-2. Tests to determine the target drying state in the drying process Figure 4 shows the results of the relationship between the dry state of the electrode body, the detachability of the separator, and the recoverability of the electrolyte. "Wet" in the dry state of the electrode body means that the electrode body is not completely dry. In this state, not only the high-boiling point solvent EC, but also the low-boiling point solvents DMC and EMC have not evaporated. In other words, the electrode body is moistened by the electrolyte. The separator detachability test confirmed that if the electrode body is moistened by the electrolyte, the separator can be easily detached from the electrode. However, this method has the disadvantage that the electrolyte cannot be recovered.

[0028] "DMC and EMC evaporation" in the dry state of the electrode body refers to a state where the electrode body has been dried to the extent that DMC and EMC have evaporated. In this state, only the low-boiling point solvents DMC and EMC evaporate, while the high-boiling point solvent EC does not. Tests of the separator's peelability confirmed that in the semi-dry state where EC has not evaporated, the positive electrode active material adheres more easily to the separator. This is presumed to be because the evaporation of the low-viscosity DMC and EMC leaves only EC deposited at the interface between the separator and the active material, creating an anchoring effect that facilitates adhesion between the separator and the active material. Furthermore, in this method, DMC and EMC are recovered from the electrolyte, but EC cannot be recovered.

[0029] In the dry state of the electrode body, "EC evaporation" refers to a state in which the electrode body is dried to the extent that EC evaporates. In this state, not only the low-boiling point solvents DMC and EMC, but also the high-boiling point solvent EC evaporates. Tests of the separator's detachability confirmed that the separator can be easily detached from the electrode when it is dried to the extent that EC has evaporated. Furthermore, this method allows for the recovery of EC in addition to DMC and EMC. Based on these findings, it can be concluded that the preferred target drying state for the electrode body in drying step S30 is a state in which it is dried to the extent that EC has evaporated.

[0030] 3-3. Test to confirm the peeling rate of the positive electrode active material. Figure 5 shows the results of an electrode peel test after discharge under appropriate discharge conditions and evaporation of the electrolyte. Discharging under appropriate discharge conditions means discharging so that the cell voltage is between 0.8V and 3.0V. Evaporating the electrolyte means evaporating not only the DMC and EMC but also the EC.

[0031] In the delamination test, the electrode body was crushed using a pulverizer to delaminate the positive electrode active material from the current collector, and the delamination rate was investigated. The cells used in the delamination test were a high-power lithium-ion secondary battery (Li2.1) and a medium-capacity lithium-ion secondary battery (Li3.A). The horizontal axis of the graph of the test results represents the particle size of the crushed electrode body. The test results show that a delamination rate exceeding the target value of 95% was obtained in all samples. In other words, the test results confirmed that the demolition process according to this embodiment, that is, the demolition process to which the lithium-ion secondary battery demolition method of this disclosure is applied, can recover the positive electrode active material with a high recovery rate. [Explanation of symbols]

[0032] S10 Discharge process, S20 Primary crushing process, S30 Drying process, S40 Secondary crushing process, S50 Dust collection and sieving process, S60 Sieving process, S70 Mechanical sorting process

Claims

1. A method for disassembling a lithium-ion secondary battery, wherein the electrode body, in which electrodes and separators are stacked, is impregnated in an electrolyte containing a low-boiling point solvent and a high-boiling point solvent, and housed in a case made of aluminum laminate material with resin bonded to both sides of aluminum, A discharge step in which the lithium-ion secondary battery is discharged so that the voltage of the lithium-ion secondary battery is 3.0V or less and does not fall below 0.8V, A primary shredding step involves shredding the case by cutting it with a shredder to expose the electrode body, A drying step in which the exposed electrode body is dried until the high-boiling point solvent evaporates, The process includes a secondary crushing step in which the dried electrode body is crushed to separate the separator from the electrode. A method for disassembling a lithium-ion secondary battery, characterized by the following features.

2. In the method for dismantling a lithium-ion secondary battery according to claim 1, The drying step includes a first distillation step of evaporating and recovering the low-boiling point solvent at a temperature lower than the boiling point of the high-boiling point solvent, and a second distillation step of evaporating and recovering the high-boiling point solvent remaining after the first distillation step. A method for disassembling a lithium-ion secondary battery, characterized by the following features.

3. In the method for dismantling a lithium-ion secondary battery according to claim 1, The secondary crushing step includes crushing the dried electrode body to separate the active material constituting the electrode from the current collector constituting the electrode. A method for disassembling a lithium-ion secondary battery, characterized by the following features.

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