Electric discharge processing method

Abstract

To provide an electric discharge processing method with which it is possible to efficiently reproduce the battery subject to processing.SOLUTION: The electric discharge processing method comprises: a discharge step in which a depleted lithium-ion secondary battery is discharged, and lithium is moved from the anode to the cathode of the lithium-ion secondary battery; a charge step in which the lithium-ion secondary battery is charged with a low voltage at which the proportion of lithium returning to the anode is small; a measurement step in which the capacity of the lithium-ion secondary battery is measured after being charged with the low voltage for a prescribed duration; and a confirmation step in which the state of health (SOH) is confirmed on the basis of the measured capacity of the lithium-ion secondary battery. Charge processing by the charge step is finished when the SOH of the lithium-ion secondary battery reaches a recovery critical point.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a discharge treatment method. [Background technology]

[0002] Lithium-ion secondary batteries include liquid lithium-ion secondary batteries and all-solid-state batteries. Lithium-ion secondary batteries consist of a positive electrode material, a negative electrode material, and a separator. The positive electrode material can reversibly exchange lithium from the negative electrode material. Repeated charging causes the cathode material to deteriorate, reducing the amount of lithium it can accept, reducing the battery's capacity and increasing its resistance. Conventionally, a technique for recycling a used positive electrode material is known in which the positive electrode material is electrically connected to metallic lithium and subjected to a discharge treatment to fill the positive electrode material with lithium (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-18856 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the positive electrode must be separated and a lithium source must be prepared to regenerate the positive electrode, which increases the time required for the discharge process and reduces efficiency. Furthermore, in Patent Document 1, the battery must be charged to a 100% charge rate, the capacity after charging must be checked, and then a decision must be made as to whether or not to terminate the discharge process. However, this method may cause the battery to deteriorate again due to charging. If this deterioration occurs, the time required for the discharge process increases and efficiency decreases. An object of the present invention is to provide a discharge treatment method that can efficiently regenerate a battery. [Means for solving the problem]

[0005] The discharge treatment method of the present disclosure includes a discharging step of discharging a depleted lithium ion secondary battery and transferring lithium from the negative electrode to the positive electrode of the lithium ion secondary battery; a charging step of charging the lithium ion secondary battery at a low voltage at which a small proportion of lithium returns to the negative electrode; a measuring step of measuring the capacity of the lithium ion secondary battery after charging at the low voltage for a predetermined time; and a confirmation step of confirming the SOH (State Of Health) based on the measured capacity of the lithium ion secondary battery, and the charging treatment in the charging step is terminated when the SOH of the lithium ion secondary battery reaches a recovery limit point. [Effects of the Invention]

[0006] According to the discharge treatment method of the present disclosure, the target battery can be efficiently regenerated. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a diagram showing the configuration of a target battery 10 as an example of a battery to which the present disclosure is applied. [Figure 2] 10 is a flowchart showing a method for discharging a target battery. [Figure 3] 1 is a chart showing the timing of charging and discharging a target battery. [Figure 4] FIG. 10 is a diagram showing an example of a data set of capacitance SOH, voltage, and capacitance. [Figure 5] 1 is a graph schematically showing the change in battery capacity; DETAILED DESCRIPTION OF THE INVENTION

[0008] (Embodiment) [1. Target battery configuration] FIG. 1 is a diagram showing the configuration of a target battery 10 as an example of a battery to which the present disclosure is applied, and schematically shows a cross section of the target battery 10. The target battery 10 is a secondary battery capable of charging and discharging. The target battery 10 described in this embodiment is a laminated battery in which battery materials are encapsulated in a laminate material 22, and has an overall flat plate shape. The target battery 10 can be referred to as a pouch-type battery, a laminated battery cell, a pouch-type battery cell, a lithium-ion battery cell, a battery module, or the like.

[0009] The subject battery 10 is a secondary battery known as a lithium-ion battery, which has attracted attention as an electricity storage device with a high energy density. Examples of positive electrode active materials for lithium-ion batteries include lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, and lithium iron phosphate. Examples of positive electrode active materials include ternary cathode materials (NCMs) containing nickel, cobalt, and manganese. Examples of negative electrode active materials for lithium-ion batteries include carbon-based materials. All-solid-state batteries, which use a solid electrolyte as the electrolyte for lithium-ion batteries, are also known.

[0010] 1, the target battery 10 has a configuration in which a laminated electrode 21 is housed in a laminate material 22. The laminate material 22 is a laminate film whose base material is a metal material such as an aluminum alloy or stainless steel. The laminate material 22 functions as an exterior body of the target battery 10 and as a seal that seals the laminated electrode 21.

[0011] The target battery 10 of this embodiment has a flat plate shape formed by bonding two sheets of laminate material 22 together, and a pair of current collecting tabs 23A, 23B for extracting power from the target battery 10 penetrate the outer casing and are exposed from the end of the target battery 10.

[0012] The laminated electrode 21 is a multilayer body in which positive electrode plates 11 (positive electrode) and negative electrode plates 12 (negative electrode) are laminated, and a separator 13 is disposed between each positive electrode plate 11 and negative electrode plate 12. The separator 13 is disposed between the positive electrode plate 11 and the negative electrode plate 12 to prevent a short circuit between the positive electrode plate 11 and the negative electrode plate 12.

[0013] The positive electrode plates 11 and the negative electrode plates 12 are alternately arranged, and one positive electrode plate 11 and one negative electrode plate 12 facing each other constitute one electrode plate pair. A stacked electrode 21 is formed by stacking a plurality of electrode plate pairs.

[0014] The positive electrode plate 11 includes a rectangular plate-shaped positive electrode current collector 31, and a positive electrode composite 32 is provided on both sides of the positive electrode current collector 31. The positive electrode current collector 31 is an aluminum material formed into a foil or plate shape. The positive electrode composite 32 includes, for example, a positive electrode active material, a conductive material, a conductive additive, and a binder. The positive electrode plate 11 has a positive electrode terminal 11A extending from an end of the positive electrode plate 11. The positive electrode terminals 11A extending from the multiple positive electrode plates 11 constituting the stacked electrode 21 are each connected to a current collecting tab 23A.

[0015] The negative electrode plate 12 includes a rectangular negative electrode current collector 41. A negative electrode composite material 42 is provided on the surface of the negative electrode current collector 41 that faces the positive electrode plate 11. The negative electrode current collector 41 is made of, for example, copper foil. The negative electrode plate 12 has a negative electrode terminal 12A that extends from an end of the negative electrode plate 12. The negative electrode terminals 12A that extend from the multiple negative electrode plates 12 that make up the stacked electrode 21 are each connected to a current collecting tab 23B.

[0016] The current collecting tabs 23A and 23B are formed from a thin metal plate such as copper or aluminum, and pass between the two laminate materials 22 and are exposed to the outside.

[0017] If the target battery 10 is a liquid lithium-ion battery, the inside of the laminate material 22 is filled with a liquid or gel electrolyte. The electrolyte includes, for example, an electrolyte, a solvent, and an additive. Examples of the electrolyte include lithium salts such as lithium hexafluorophosphate (LiPF6). Examples of the solvent and additive include carbonate esters such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, and vinylene carbonate. These are just some examples, and the electrolyte, solvent, and additive can be selected and changed as appropriate.

[0018] When the target battery 10 is an all-solid-state battery, a solid electrolyte is disposed inside the laminate material 22. Although oxide-based electrolytes and sulfide-based electrolytes are known as solid electrolytes, the present disclosure may also be applicable to all-solid-state batteries using other materials. The solid electrolyte of the all-solid-state battery is disposed, for example, between the positive electrode plate 11 and the negative electrode plate 12 in place of the separator 13. In this case, the solid electrolyte not only functions as an electrolyte but also prevents short-circuiting between the positive electrode plate 11 and the negative electrode plate 12. Furthermore, when the subject battery 10 is an all-solid-state battery, the negative electrode composite 42 of the negative electrode plate 12 may contain metallic lithium. That is, the negative electrode composite 42 may be composed of elemental lithium. When metallic lithium is used as the negative electrode active material layer of the negative electrode composite 42, the metallic lithium and the negative electrode current collector 41 are bonded together by a clad material or the like. In this embodiment, a discharge treatment method is disclosed that is particularly suitable when the subject battery 10 is an all-solid-state battery and the negative electrode composite material 42 contains metallic lithium.

[0019] [2. Discharge treatment method] Next, a method for discharging the target battery 10 will be described. The subject battery 10 is a used battery, and is a battery in a state where the discharge capacity (capacity) mAh has been consumed due to deterioration.

[0020] A battery tester 100 is connected to the target battery 10. The battery tester 100 can apply any voltage to the target battery 10, measure the voltage and current of the target battery 10, and measure the capacity (mAh) of the target battery 10.

[0021] FIG. 2 is a flowchart showing a method for discharging the target battery 10. First, a full discharge voltage is applied to the target battery 10 for a predetermined time to discharge it (step S1). The full discharge voltage is a voltage at which the charge rate of the target battery 10 becomes 0%. The charge rate can also be referred to as SOC (States Of Charge). Step S1 is an example of a discharging step.

[0022] By discharging at the full discharge voltage, lithium moves from the negative electrode plate 12 to the positive electrode plate 11 in the subject battery 10 . The movement of lithium increases the capacity (mAh) of the target battery 10. In other words, the SOH (State of Health) of the target battery 10 can be restored. The SOH is a percentage of the deterioration state of the capacity (mAh) of a secondary battery. The discharge in step S1 is a discharge for restoring the SOH of the target battery 10.

[0023] Next, a low voltage is applied to the target battery 10 for a predetermined time to charge it (step S2). The low voltage is set so low that only a small amount of the lithium that has moved to the positive electrode plate 11 due to the discharge in step S1 returns to the negative electrode plate 12, in other words, the proportion of lithium that returns to the negative electrode plate 12 is small. Step S2 is an example of a charging step.

[0024] FIG. 3 is a chart showing the timing of charging and discharging the subject battery. Here, in the application of the low voltage, as shown in FIG. 3, a full discharge voltage V0 is applied for a predetermined time T1, and then a low voltage V1 is applied for a predetermined time T2, and this voltage application is repeated. The time T2 is set to be shorter than the time T1. The low voltage V1 is applied with a pulsed voltage waveform. Since the charging time by the low voltage V1 is reduced, excessive return of lithium to the negative electrode plate 12 is suppressed.

[0025] When the target battery 10 is charged at a high voltage, a large amount of lithium returns from the positive electrode plate 11 to the negative electrode plate 12, and too much lithium returns to the negative electrode plate 12. If too much lithium returns to the negative electrode plate 12, there is a risk that the total amount of lithium that moves from the negative electrode plate 12 to the positive electrode plate 11 will decrease when the process returns from step S3 to step S1 (described below) and the target battery 10 is discharged again. To reduce this risk, a lower voltage is applied.

[0026] Low voltage is the voltage when a new lithium-ion battery is at a 30% state of health. In other words, a new lithium-ion battery is a target battery 10 with a SOH (State of Health) of 100%. 30% is an example of a low state of health, and a state of health between 20% and 30% is preferable.

[0027] Next, the capacity (mAh) of the target battery 10 after charging at the low voltage V1 is measured by the battery tester 100 (step S3). Step S3 is an example of a measurement step.

[0028] Next, based on the measured capacity mAh of the target battery 10, the SOH of the target battery 10 is confirmed in the data set shown in FIG. 4 (step S4). Step S4 is an example of a confirmation step.

[0029] FIG. 4 shows an example of a data set, where the vertical axis represents voltage (V) and the horizontal axis represents capacity (mAh). Graph G1 is the curve for a new battery, which is the standard for a SOH (state of health) of 100%. A new battery is an unused, unconsumed battery. Graph G2 is the curve for the subject battery 10 with an SOH of 95%. Graph G3 is the curve for the subject battery 10 with an SOH of 90%. Graph G4 is the curve for the subject battery 10 with an SOH of 85%. Graph G5 is the curve for the subject battery 10 with an SOH of 80%.

[0030] Graph G1 is a curve obtained by applying a voltage to a new battery and measuring the capacity (mAh). Graphs G2 to G5 are curves obtained by applying a voltage to target batteries 10 with SOH (State of Health) of 95%, 90%, 85%, and 80% and measuring the capacity (mAh).

[0031] The types of SOH (health level) are just an example and are not limited to the five from 100% to 80%. Each of the graphs G1 to G5 shows the correlation between SOH and capacity mAh.

[0032] Referring to FIG. 4, when a low voltage V1 is applied to the target battery 10, if the capacity mAh measured by the battery tester 100 is point A5 on graph G5, the SOH (State of Health) of the target battery 10 is confirmed to be equivalent to 80%. Similarly, if the measured value of the capacity mAh is point A4 on graph G4, the SOH (state of health) of the target battery 10 is equivalent to 85%; if it is point A3 on graph G3, the SOH (state of health) of the target battery 10 is equivalent to 90%; if the measured value of the capacity mAh is point A2 on graph G2, the SOH of the target battery 10 is equivalent to 95%; and if it is point A1 on graph G1, the SOH (state of health) of the target battery 10 is equivalent to 100%.

[0033] In this embodiment, a full discharge voltage is applied to the target battery 10 to discharge it, thereby transferring lithium from the negative electrode plate 12 to the positive electrode plate 11 (step S1), thereby eliminating the need for a lithium source for positive electrode recovery as in the conventional case.

[0034] In this embodiment, the target battery 10 is charged by applying a low voltage (step S2), so that only a small amount of the lithium that has moved to the positive electrode plate 11 returns to the negative electrode plate 12. Because the amount of lithium that returns to the negative electrode plate 12 is small, when the target battery 10 is discharged again (step S1), the total amount of lithium that moves from the negative electrode plate 12 to the positive electrode plate 11 is unlikely to decrease.

[0035] In this embodiment, a data set (FIG. 4) is prepared that shows the correlation between the SOH and capacity mAh of the target battery 10. A low voltage V1 is applied to the target battery 10 to measure the capacity mAh, and the data set is referenced to confirm the SOH from the measured capacity mAh. This confirms that lithium has migrated to the positive electrode plate 11 and the SOH has recovered. Compared to the conventional method of charging the battery to 100% charge and then confirming the SOH, this method suppresses battery degradation, shortens the time required for the discharge process, and improves efficiency.

[0036] Next, it is determined whether or not the charging end condition is satisfied (step S5). If the charging end condition is satisfied, the process proceeds to step S6, and if not, the process returns to step S1. Step S5 is an example of a determination step. Whether the charge termination condition is met is determined by whether the SOH (State of Health) reaches the recovery limit point due to charging at low voltage V1. Determining whether the recovery limit point is reached is an example of determining whether the charge termination condition is met. Reaching the recovery limit point means that the SOH value confirmed in step S4 is equal to or greater than the recovery limit point.

[0037] 5 is an explanatory diagram of the recovery limit point, where the vertical axis represents the SOH of the subject battery 10 and the horizontal axis represents the number of times steps S1 to S5 are repeated. If the SOH confirmed in step S4 the first time has not reached the recovery limit point M, the process returns to step S1 in FIG. 2, and steps S1 to S5 are repeated. If the recovery limit point M has not yet been reached in the second check, a third check is performed, and if the recovery limit point M has still not been reached, a fourth check is performed. In the fourth check, the recovery limit point M is reached, and at this point it is determined that the charge termination condition has been met.

[0038] This determination is not limited to repeating steps S1 to S5 multiple times. For example, if the recovery limit point M is reached the first time, it may be determined that the charge termination condition is met at that point. In addition, although it is determined that the charge termination condition is satisfied when the recovery limit point M is reached once, this is not limiting. For example, it may be determined that the charge termination condition is satisfied when the recovery limit point M is reached multiple times.

[0039] In this embodiment, the charging process time can be shortened because the charging process is terminated when the SOH reaches the recovery limit point M. The recovery limit point M is predetermined depending on the type of the target battery 10.

[0040] In step S6, the target battery 10 is discharged by applying a full discharge voltage for a predetermined time. This allows the lithium on the negative electrode plate 12 side due to the charging in step S2 to be moved to the positive electrode plate 11. The discharge in step S6 is preferably performed before the deactivation of the negative electrode plate 12 of the next target battery 10. The discharge in step S6 is a discharge for deactivating the target battery 10.

[0041] Next, the target battery 10 is deactivated with water vapor (step S7). When the target battery 10 is deactivated with water vapor, the target battery 10 is preferably an all-solid-state battery. Step S7 is an example of a deactivation step.

[0042] In step S7, the target battery 10 is cut open and placed in a humid container filled with water vapor. This causes the target battery 10 to fill with water vapor, deactivating the battery. All-solid-state batteries contain a sulfide-based electrolyte. This generates sulfur-containing compound gas, which is then absorbed and exhausted. By placing the battery in water vapor, at least a portion of the lithium contained in the battery's contents is converted into lithium compounds such as lithium hydroxide, reducing its activity and making it safe.

[0043] In this embodiment, the lithium content of the negative electrode plate 12 is reduced by repeating steps S1 to S5. With the lithium content of the negative electrode plate 12 of the all-solid-state battery reduced, the target battery 10 is placed in a water vapor atmosphere, so that the battery can be deactivated more safely. Furthermore, in step S7, hydrogen sulfide is generated, causing corrosion of the aluminum of the positive electrode current collector 31 and the copper of the negative electrode current collector 41. In step S7, the amount of lithium in the negative electrode plate 12 of the all-solid-state battery is reduced, so the time required for deactivation is shortened and the time that the positive electrode current collector 31 and the negative electrode current collector 41 are exposed to a hydrogen sulfide atmosphere is shortened, thereby suppressing corrosion.

[0044] In addition, in the all-solid-state battery, the positive electrode mixture 32, the solid electrolyte, and the negative electrode mixture 42 are pressure-bonded together, so that it is difficult to remove the positive electrode plate 11. In this embodiment, the positive electrode active material contained in the positive electrode mixture 32 of the positive electrode plate 11 can be recovered without disassembling the subject battery 10, and the SOH of the subject battery 10 can be recovered as a result. Furthermore, when the negative electrode plate 12 contains metallic lithium, the amount of lithium in the all-solid-state battery can be increased, which improves the efficiency of the battery, but leaves issues with safety in recycling. According to the discharge treatment method of the present embodiment, the amount of active lithium in the negative electrode plate 12 can be reduced, which improves safety in recycling.

[0045] (Other embodiments) In another embodiment, a resistance meter (not shown) is further connected to the target battery 10. Then, a plurality of lithium ion secondary batteries with different resistance values ​​SOH are prepared, a low voltage is applied to each lithium ion secondary battery, the resistance value when the low voltage is applied is measured, and a data set showing the correlation with the resistance value SOH is prepared in advance.

[0046] In another embodiment, by referencing this data set, it is possible to confirm the extent to which the resistance value SOH of the target battery 10 has recovered from the resistance value when a low voltage is applied. In this case, the charge termination condition of step S5 shown in Fig. 2 is further supplemented with the requirement that the resistance value of the target battery 10 be equal to or less than a predetermined resistance threshold value. This makes it possible to confirm that the target battery 10 has recovered and its resistance value has decreased.

[0047] [Configuration supported by the above embodiment] The above embodiment supports the following configurations.

[0048] (Configuration 1) A discharge treatment method comprising: a discharging step of discharging a depleted lithium ion secondary battery and transferring lithium from the negative electrode to the positive electrode of the lithium ion secondary battery; a charging step of charging the lithium ion secondary battery at a low voltage at which the rate at which lithium returns to the negative electrode is low; a measuring step of measuring the capacity of the lithium ion secondary battery after charging at the low voltage for a predetermined time; and a confirmation step of confirming the SOH (State Of Health) based on the measured capacity of the lithium ion secondary battery, wherein the charging treatment by the charging step is terminated when the SOH of the lithium ion secondary battery reaches a recovery limit point. According to the first aspect, by charging the target battery by applying a low voltage, the capacity of the target battery, which is a lithium-ion battery, can be confirmed, thereby preventing the target battery from deteriorating. Furthermore, the target battery can be discharged without being disassembled. Therefore, the target battery can be efficiently regenerated.

[0049] (Configuration 2) The discharge treatment method according to Configuration 1, wherein a data set representing a correlation between the SOH of the lithium ion secondary battery and the capacity of the lithium ion secondary battery is prepared, and the confirmation step confirms the SOH of the lithium ion secondary battery by referring to the data set based on the capacity of the lithium ion secondary battery. According to the second aspect, it is possible to determine whether or not to terminate the charging process based on the correlation between the SOH and the capacity, thereby enabling the target battery to be regenerated with high accuracy.

[0050] (Configuration 3) The discharge treatment method according to Configuration 1, further comprising a determination step of determining whether a charge termination condition is satisfied, and if the charge termination condition is not satisfied, returning to the discharge step, and repeating the charge step, the measurement step, and the confirmation step. According to the third aspect, since the SOH can be checked repeatedly, it is possible to prevent the discharge step from being performed more than necessary so that the SOH of the capacity does not recover, and it is possible to improve the efficiency of the discharge process.

[0051] (Configuration 4) The discharge treatment method according to Configuration 3, wherein the determining step determines that the charge termination condition is not satisfied if the confirmed SOH has not reached the recovery limit point. According to the fourth aspect, it is possible to determine the timing to end the repetition of the discharging step and the charging step.

[0052] (Configuration 5) The discharge treatment method according to Configuration 3 or 4, wherein the measuring step measures a resistance value of the lithium ion secondary battery, and the determining step determines that the charge termination condition is not satisfied if the resistance value is equal to or less than a predetermined threshold value. According to configuration 5, since it is possible to check not only the capacity but also the deterioration state of the resistance value, it is possible to check the degree of regeneration of the target battery, which is a lithium ion secondary battery, in more detail.

[0053] (Configuration 6) The discharge treatment method according to Configuration 1, wherein the lithium ion secondary battery is an all-solid-state battery containing metallic lithium in a negative electrode, and further comprising a deactivation step of deactivating the all-solid-state battery with water vapor. According to configuration 6, even in an all-solid-state battery in which it is difficult to disassemble and extract the positive and negative electrodes, the SOH can be restored by performing a discharge treatment. In addition, since the amount of lithium in the negative electrode is reduced by the discharge step, the deactivation step can be performed stably. [Explanation of symbols]

[0054] 10...target battery, 11...positive electrode plate (positive electrode), 12...negative electrode plate (negative electrode), 13...separator, 21...laminated electrode, 22...laminate material, 22A, 22B...current collecting tabs, 31...positive electrode current collector, 32...positive electrode composite, 41...negative electrode current collector, 42...negative electrode composite, 100...charging / discharging device.

Claims

1. a discharging step of discharging the exhausted lithium ion secondary battery and transferring lithium from the negative electrode to the positive electrode of the lithium ion secondary battery; a charging step of charging the lithium ion secondary battery at a low voltage at which a proportion of lithium returning to the negative electrode is small; a measuring step of measuring the capacity of the lithium ion secondary battery after charging at the low voltage for a predetermined time; a confirmation step of confirming a State of Health (SOH) based on the measured capacity of the lithium ion secondary battery; Equipped with When the SOH of the lithium ion secondary battery reaches a recovery limit point, the charging process in the charging step is terminated. Discharge treatment method.

2. preparing a data set representing a correlation between the SOH of the lithium ion secondary battery and the capacity of the lithium ion secondary battery; The confirmation step includes: confirming the SOH of the lithium ion secondary battery based on the capacity of the lithium ion secondary battery by referring to the data set; The discharge treatment method according to claim 1 .

3. a determination step of determining whether a charging termination condition is satisfied; If the charging termination condition is not satisfied, the process returns to the discharging step, and the charging step, the measuring step, and the checking step are repeated. The discharge treatment method according to claim 1 .

4. The determining step If the confirmed SOH has not reached the recovery limit point, it is determined that the charge termination condition is not satisfied. The discharge treatment method according to claim 3 .

5. the measuring step measures a resistance value of the lithium ion secondary battery; In the determining step, it is determined that the charge termination condition is not satisfied when the resistance value is equal to or less than a predetermined threshold value. The discharge treatment method according to claim 3 or 4.

6. the lithium ion secondary battery is an all-solid-state battery, and the negative electrode contains metallic lithium; A deactivation step of deactivating the all-solid-state battery with water vapor is provided. The discharge treatment method according to claim 1 .

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