Discharge treatment method

Abstract

The purpose of the present invention is to provide a discharge processing method capable of efficiently regenerating a target battery. The discharge treatment method comprises: a discharge step for discharging a consumed lithium ion secondary battery and moving 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 proportion of lithium returning to the negative electrode is small; a measurement 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 for confirming the SOH (State Of Heath) on the basis of the measured capacity of the lithium ion secondary battery, and terminating the charging process in the charging step when the SOH of the lithium ion secondary battery reaches a recovery critical point.

Description

Technical Field

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

[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 transfer lithium from the negative electrode material.

[0003] Repeated charging degrades the positive electrode material, reducing the amount of lithium it can accept, lowering the battery capacity and increasing the resistance.

[0004] Conventionally, a technique is known in which a used positive electrode material is connected to a lithium metal battery and discharged to thereby fill the positive electrode material with lithium and reuse the positive electrode material (for example, see Patent Document 1).

[0005] [Prior art literature]

[0006] [Patent Document]

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2021-18856 Summary of the Invention

[0008] [Problems to be Solved by the Invention]

[0009] However, Patent Document 1 requires the separation of the positive electrode and the preparation of a lithium source to regenerate the positive electrode, which increases the discharge time and reduces efficiency. Furthermore, Patent Document 1 requires charging to 100%, confirming the post-charge capacity, and determining whether to terminate the discharge process. However, this method carries the risk of further battery deterioration due to charging. Such deterioration increases the discharge time and reduces efficiency.

[0010] An object of the present invention is to provide a discharge processing method capable of efficiently regenerating a battery.

[0011] [Means for solving the problem]

[0012] The discharge treatment method disclosed in the present invention comprises: a discharge step of discharging a consumed lithium-ion secondary battery to move lithium from the negative electrode of the lithium-ion secondary battery to the positive electrode; a charging step of charging the lithium-ion secondary battery at a low voltage in which a small proportion of lithium returns to the negative electrode; a measurement step of measuring the capacity of the lithium-ion secondary battery after being charged 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 terminating the charging treatment of the charging step when the SOH of the lithium-ion secondary battery reaches the critical point of recovery.

[0013] [Effects of the Invention]

[0014] According to the discharge treatment method of the present disclosure, a target battery can be efficiently regenerated. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 1 is a diagram showing the structure of a target battery 10 as an example of a battery to which the present disclosure is applied.

[0016] Figure 2 This is a flowchart showing a method for discharging a target battery.

[0017] Figure 3 It is a diagram showing the timing of charging and discharging of the target battery.

[0018] Figure 4 This is a diagram showing an example of a data set of capacity SOH, voltage, and capacity.

[0019] Figure 5 It is a graph schematically showing the transition of battery capacity. DETAILED DESCRIPTION

[0020] (Implementation Method)

[0021] [1. Structure of the target battery]

[0022] Figure 1 This figure illustrates the structure of a target battery 10, an example of a battery to which the present disclosure is applicable, and schematically shows a cross-section of the target battery 10. The target battery 10 is a secondary battery capable of both charge and discharge. The target battery 10 described in this embodiment is a laminated battery having battery materials enclosed within a laminate material 22, and has an overall flat plate shape. The target battery 10 may be a pouch-type battery, a laminate-type battery cell, a pouch-type battery cell, a lithium-ion battery cell, or a battery module.

[0023] The target battery 10 is a secondary battery known as a lithium-ion battery, which has attracted attention as a storage device with 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. In addition, examples of positive electrode active materials include ternary positive electrode materials (NCMs) containing nickel, cobalt, and manganese. Examples of negative electrode active materials for lithium-ion batteries include carbon-based materials. In addition, all-solid-state batteries using solid electrolytes as electrolytes for lithium-ion batteries are known.

[0024] like Figure 1As shown, the target battery 10 has a structure in which a stacked electrode 21 is housed in a laminate material 22. The laminate material 22 is a laminate film having a base material made of a metal material such as aluminum alloy or stainless steel. The laminate material 22 functions as a sealant that seals the outer casing of the target battery 10 and the stacked electrode 21.

[0025] The target battery 10 of this embodiment has a flat plate shape formed by laminating two laminate materials 22 . A pair of current collector tabs 23A and 23B for extracting power from the target battery 10 penetrates the outer casing and is exposed from the end of the target battery 10 .

[0026] The stacked electrode 21 is a multilayer structure composed of a stack of positive plates 11 (positive electrode) and negative plates 12 (negative electrode), with separators 13 disposed between each of the positive plates 11 and negative plates 12. The separators 13 are disposed between the positive plates 11 and negative plates 12 to prevent short circuits between the positive plates 11 and negative plates 12.

[0027] 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.

[0028] The positive electrode plate 11 includes a rectangular plate-shaped positive electrode current collector 31, with a positive electrode composite material 32 disposed 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 material 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 terminal 11A extending from an end of the positive electrode plate 11. The positive terminals 11A extending from the multiple positive electrode plates 11 that constitute the stacked electrode 21 are each connected to a current collector tab 23A.

[0029] 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. Copper foil, for example, is used for the negative electrode current collector 41. The negative electrode plate 12 includes a negative electrode terminal 12A extending from an end of the negative electrode plate 12. Each of the negative electrode terminals 12A extending from the plurality of negative electrode plates 12 that constitute the stacked electrode 21 is connected to a current collector tab 23B.

[0030] The current collector tabs 23A and 23B are formed of a thin plate-shaped metal material such as copper or aluminum, and are passed between the two laminate materials 22 to be exposed to the outside.

[0031] When the target battery 10 is a liquid lithium-ion battery, a liquid or gel electrolyte is filled inside the laminate 22. 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 carbonates such as ethylene carbonate, dimethyl carbonate, diethyl carbonate, and vinylene carbonate. These are just examples, and the electrolyte, solvent, and additive can be appropriately selected and changed.

[0032] When the target battery 10 is an all-solid-state battery, a solid electrolyte is placed within the laminate 22. Oxide-based and sulfide-based electrolytes are known as solid electrolytes, but even all-solid-state batteries using other materials can be applied to the present disclosure. For example, the solid electrolyte of an all-solid-state battery is placed 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 circuits between the positive electrode plate 11 and the negative electrode plate 12.

[0033] Furthermore, when the target battery 10 is an all-solid-state battery, the negative electrode composite material 42 of the negative electrode plate 12 may contain metallic lithium. That is, the negative electrode composite material 42 may be composed of single-element lithium. When metallic lithium is used as the negative electrode active material layer of the negative electrode composite material 42, the metallic lithium is bonded to the negative electrode current collector 41 via a cladding material or the like.

[0034] In this embodiment, a discharge treatment method particularly suitable for the case where the target battery 10 is an all-solid-state battery and the negative electrode composite material 42 contains metallic lithium is disclosed.

[0035] [2. Discharge treatment method]

[0036] Next, a method of discharging the target battery 10 will be described.

[0037] The target battery 10 is a used battery in which the discharge capacity (capacity) mAh has been depleted due to deterioration.

[0038] A battery tester 100 is connected to the target battery 10. The battery tester 100 can apply an arbitrary voltage to the target battery 10, measure the voltage and current of the target battery 10, and measure the capacity of the target battery 10 in mAh.

[0039] Figure 2 1 is a flowchart illustrating a method for discharging the target battery 10 .

[0040] First, a full discharge voltage is applied to the target battery 10 for a predetermined period of time to discharge the target battery 10 (step S1). The full discharge voltage is the voltage at which the charge rate of the target battery 10 is 0%. The charge rate is also called SOC (States of Charge).

[0041] Step S1 is an example of a discharge step.

[0042] By discharging at the full discharge voltage, lithium moves from the negative electrode plate 12 to the positive electrode plate 11 in the target battery 10 .

[0043] The transfer of lithium increases the capacity (mAh) of the target battery 10. That is, the SOH (State of Health) of the target battery 10 can be restored. SOH represents the degradation of the secondary battery's capacity (mAh) in %. The discharge in step S1 is for restoring the SOH of the target battery 10.

[0044] Next, a low voltage is applied to the target battery 10 for a predetermined period of time to charge it (step S2). The low voltage is set low so that the lithium that has moved to the positive electrode plate 11 by the discharge in step S1 only slightly returns to the negative electrode plate 12. In other words, the proportion of lithium returning to the negative electrode plate 12 is small.

[0045] Step S2 is an example of a charging step.

[0046] Figure 3 is a graph showing the timing of charging and discharging of the target battery.

[0047] Here, in the application of low voltage, as Figure 3 As shown, a full-discharge voltage V0 is applied for a predetermined time T1, followed by a low voltage V1 for a predetermined time T2, and this voltage application is repeated. Time T2 is set shorter than time T1. The application of low voltage V1 has a pulsed voltage waveform. Since the charging time of low voltage V1 is shortened, excessive lithium return to the negative electrode plate 12 is suppressed.

[0048] If the target battery 10 is charged at a high voltage, the amount of lithium that returns from the positive electrode plate 11 to the negative electrode plate 12 increases, and lithium excessively returns to the negative electrode plate 12. If lithium excessively returns to the negative electrode plate 12, when the target battery 10 is discharged again by returning from step S3 to step S1 described later, the total amount of lithium that moves from the negative electrode plate 12 to the positive electrode plate 11 may decrease.

[0049] To suppress this possibility, a low voltage is applied.

[0050] The low voltage is the voltage of a new lithium-ion battery when the charge rate is 30%. In other words, the new lithium-ion battery can be regarded as the target battery 10 with a SOH (State of Health) of 100%. 30% is an example of a low charge rate, and 20% to 30% is preferred.

[0051] Next, the capacity (mAh) of the target battery 10 charged at the low voltage V1 is measured by the battery tester 100 (step S3 ).

[0052] Step S3 is an example of a measurement step.

[0053] Next, based on the measured capacity mAh of the target battery 10, Figure 4 The SOH of the target battery 10 is checked in the shown data set (step S4).

[0054] Step S4 is an example of a confirmation step.

[0055] Figure 4 An example of a data set is shown, where the vertical axis represents voltage V and the horizontal axis represents capacity mAh.

[0056] Curve G1 is a curve of a new battery whose SOH (State of Health) is 100%. A new battery is an unused, unconsumed battery.

[0057] Curve G2 is a curve of the target battery 10 having an SOH of 95%.

[0058] Curve G3 is a curve of the target battery 10 having an SOH of 90%.

[0059] Curve G4 is a curve of the target battery 10 having an SOH of 85%.

[0060] Curve G5 is a curve of the target battery 10 having an SOH of 80%.

[0061] Curve G1 is obtained by applying voltage to a new battery and measuring the capacity in mAh. Curves G2 to G5 are obtained by applying voltage to target batteries 10 with SOH (State of Health) of 95%, 90%, 85%, and 80% and measuring the capacity in mAh.

[0062] The types of SOH (state of health) are just examples and are not limited to the five types of 100% to 80%. The curves G1 to G5 show the relationship between SOH and capacity mAh.

[0063] Reference Figure 4 When the low voltage V1 is applied to the target battery 10, if the capacity mAh measured by the battery tester 100 is the point A5 on the curve G5, it is confirmed that the SOH (State of Health) of the target battery 10 is equivalent to 80%.

[0064] Similarly, if the measured value of the capacity mAh is point A4 of curve G4, the SOH (state of health) of the target battery 10 is equivalent to 85%; if it is point A3 of curve 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 of curve G2, the SOH of the target battery 10 is equivalent to 95%; if it is point A1 of curve G1, the SOH (state of health) of the target battery 10 is equivalent to 100%.

[0065] In this embodiment, the target battery 10 is discharged by applying a full discharge voltage to move lithium from the negative electrode plate 12 to the positive electrode plate 11 (step S1 ). Therefore, a lithium source for positive electrode recovery as conventionally used is not required.

[0066] In this embodiment, since a low voltage is applied to the target battery 10 for charging (step S2), only a small amount of lithium that has moved to the positive electrode plate 11 returns to the negative electrode plate 12. Since the amount of lithium that returns to the negative electrode plate 12 is small, the total amount of lithium that has moved from the negative electrode plate 12 to the positive electrode plate 11 is unlikely to decrease when the target battery 10 is discharged again (step S1).

[0067] In this embodiment, a data set ( Figure 4 A low voltage V1 is applied to the target battery 10 to measure its capacity in mAh. The SOH is then determined based on the measured capacity in mAh, with reference to the data set. This method confirms lithium migration to the positive electrode plate 11 and restores the SOH. Compared to conventional methods of charging to 100% and then determining the SOH, this method suppresses battery degradation, shortens the discharge process, and improves efficiency.

[0068] Next, it is determined whether 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.

[0069] Step S5 is an example of a determination step.

[0070] Whether the charging termination condition is met is determined by whether the SOH (State of Health) has reached the critical point of recovery through charging at low voltage V1. Determining whether the critical point of recovery has been reached is one example of determining whether the charging termination condition is met. Reaching the critical point of recovery means that the SOH value confirmed in step S4 is at or above the critical point of recovery.

[0071] Figure 5 1 is an explanatory diagram of the recovery critical point. The vertical axis represents the SOH of the target battery 10, and the horizontal axis represents the number of repetitions of steps S1 to S5.

[0072] If the SOH confirmed in the first step S4 does not reach the recovery critical point M, return to Figure 2 Step S1 is repeated, and steps S1 to S5 are repeated. If the critical point M has not been reached in the second confirmation, a third confirmation is performed. If the critical point M has not been reached despite this, a fourth confirmation is performed. If the critical point M is reached in the fourth confirmation, it is determined that the charging end condition is met at this point.

[0073] This determination is not limited to repeating steps S1 to S5 multiple times. For example, if the recovery critical point M is reached for the first time, it may be determined that the charging end condition is satisfied at that time.

[0074] Furthermore, the charging end condition is determined to be satisfied when the recovery critical point M is reached once, but the present invention is not limited thereto. For example, the charging end condition may be determined to be satisfied when the recovery critical point M is reached multiple times.

[0075] In the present embodiment, the charging process is terminated when the SOH reaches the recovery threshold point M, thereby shortening the charging process time. The recovery threshold point M is predetermined according to the type of the target battery 10 .

[0076] In step S6, the target battery 10 is discharged by applying a full discharge voltage for a predetermined time. This allows lithium located on the negative electrode plate 12 side during charging in step S2 to move to the positive electrode plate 11. The discharge in step S6 is preferably performed before the negative electrode plate 12 of the next target battery 10 is deactivated. The discharge in step S6 is performed to deactivate the target battery 10.

[0077] Next, the target battery 10 is deactivated by water vapor (step S7). When the target battery 10 is deactivated by water vapor, the target battery 10 is preferably an all-solid-state battery.

[0078] Step S7 is an example of a deactivation step.

[0079] In step S7, the target battery 10 is cut open and placed in a high-humidity container filled with water vapor. This causes the target battery 10 to fill with water vapor, deactivating it. All-solid-state batteries contain a sulfide-based electrolyte. Therefore, sulfur-containing gases are generated and inhaled and exhausted. Exposure to water vapor converts at least a portion of the lithium contained within the all-solid-state battery into lithium compounds such as lithium hydroxide, reducing its activity and rendering it safe.

[0080] In this embodiment, the lithium content of the negative electrode plate 12 is reduced by repeating steps S1 to S5. While the lithium content of the negative electrode plate 12 of the all-solid-state battery is reduced, the target battery 10 is placed in a water vapor atmosphere, thereby enabling safer deactivation.

[0081] Furthermore, hydrogen sulfide is generated in step S7, 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 lithium content of the negative electrode plate 12 of the all-solid-state battery is reduced, shortening the time it takes to deactivate. This shortens the time the positive electrode current collector 31 and the negative electrode current collector 41 are exposed to the hydrogen sulfide atmosphere, thereby suppressing corrosion.

[0082] It should be noted that in an all-solid-state battery, since the positive electrode composite material 32 , the solid electrolyte, and the negative electrode composite material 42 are press-bonded, it is difficult to remove the positive electrode plate 11 .

[0083] In the present embodiment, the positive electrode active material contained in the positive electrode composite material 32 of the positive electrode plate 11 can be restored without disassembling the target battery 10 , and the SOH of the target battery 10 can be restored.

[0084] Furthermore, when the negative electrode plate 12 contains metallic lithium, the amount of lithium in the all-solid-state battery can be increased, thereby improving battery efficiency. However, this still leaves issues regarding safety during recycling. The discharge treatment method of this embodiment reduces the amount of active lithium in the negative electrode plate 12, thereby improving safety during recycling.

[0085] (Other embodiments)

[0086] In another embodiment, a resistance meter (not shown) is further connected to the target battery 10 .

[0087] Then, a plurality of lithium ion secondary batteries having 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 relationship between the resistance value SOH and the resistance value is prepared in advance.

[0088] In other embodiments, by referring to this data set, it is possible to confirm how much the resistance value SOH of the target battery 10 has recovered based on the resistance value when a low voltage is applied. Figure 2 The charging termination condition of step S5 shown in the figure further includes that the resistance value of the target battery 10 is equal to or less than a predetermined resistance value threshold value. This allows confirmation that the target battery 10 has recovered and the resistance value has decreased.

[0089] [Structure supported by the above-mentioned embodiment]

[0090] The above-mentioned embodiment supports the following structure.

[0091] (Structure 1) A discharge treatment method, which comprises: a discharge step of discharging a consumed lithium-ion secondary battery to move lithium from the negative electrode of the lithium-ion secondary battery to the positive electrode; a charging step of charging the lithium-ion secondary battery at a low voltage in 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 prescribed time; and a confirmation step of confirming the SOH (State Of Health) based on the measured capacity of the lithium-ion secondary battery, and terminating the charging treatment based on the charging step when the health of the lithium-ion secondary battery reaches a critical point of recovery.

[0092] According to Configuration 1, by charging with low voltage, the capacity of the target battery, which is a lithium-ion battery, can be confirmed, thereby suppressing degradation of the target battery. Furthermore, discharge processing can be performed without disassembling the target battery, thus enabling efficient regeneration of the target battery.

[0093] (Structure 2) According to the discharge treatment method of Structure 1, a data set representing the relationship between the SOH of the lithium-ion secondary battery and the capacity of the lithium-ion secondary battery is prepared, and in the confirmation step, the SOH of the lithium-ion secondary battery is confirmed with reference to the data set based on the capacity of the lithium-ion secondary battery.

[0094] According to Configuration 2, whether or not to terminate the charging process is determined based on the relationship between the SOH and the capacity. Therefore, the target battery can be regenerated with high accuracy.

[0095] (Structure 3) The discharge processing method according to Structure 1, wherein the discharge processing method includes a determination step of determining whether a charge end condition is satisfied, and when the charge end condition is not satisfied, returning to the discharge step, repeating the charge step, the measurement step, and the confirmation step.

[0096] According to Configuration 3, since the SOH can be repeatedly checked, it is possible to suppress the discharge step from being performed more than necessary, in which the SOH of the capacity is not restored, and the efficiency of the discharge process can be improved.

[0097] (Structure 4) According to the discharge processing method of Structure 3, in the determination step, when the confirmed SOH has not reached the recovery critical point, it is determined that the charge end condition is not satisfied.

[0098] According to Configuration 4, it is possible to determine the timing for ending the repetition of the discharge step and the charge step.

[0099] (Structure 5) According to the discharge processing method of Structure 3 or 4, in the measuring step, the resistance value of the lithium ion secondary battery is measured, and in the judging step, when the resistance value is below a predetermined threshold value, it is judged that the charge end condition is not satisfied.

[0100] According to Configuration 5 , not only the capacity but also the degradation state of the resistance value can be confirmed, and therefore the degree of regeneration of the target battery, which is a lithium-ion secondary battery, can be confirmed in more detail.

[0101] (Structure 6) According to the discharge treatment method of Structure 1, the lithium-ion secondary battery is an all-solid-state battery containing metallic lithium at the negative electrode, and the discharge treatment method includes a deactivation step of deactivating the all-solid-state battery using water vapor.

[0102] According to Structure 6, even in an all-solid-state battery where the positive and negative electrodes are difficult to disassemble, the SOH can be restored by discharging the battery. Furthermore, the amount of lithium in the negative electrode is reduced during the discharge step, allowing the deactivation step to be performed stably.

[0103] Description of Reference Numerals

[0104] 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…Collector sheets, 31…Positive electrode collector, 32…Positive electrode composite material, 41…Negative electrode collector, 42…Negative electrode composite material, 100…Battery tester.

Claims

1. A discharge treatment method, comprising: a discharge step of discharging the consumed lithium-ion secondary battery to move 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; as well as a confirmation step of confirming the health of the lithium-ion secondary battery based on the measured capacity; When the health of the lithium-ion secondary battery reaches a critical point for recovery, the charging process according to the charging step is terminated.

2. The discharge treatment method according to claim 1, wherein: preparing a data set representing a relationship between the health of the lithium-ion secondary battery and the capacity of the lithium-ion secondary battery, In the confirming step, the health of the lithium-ion secondary battery is confirmed based on the capacity of the lithium-ion secondary battery with reference to the data set.

3. The discharge treatment method according to claim 1, wherein: The discharge processing method includes a determination step of determining whether a charge end condition is satisfied. If the charge end condition is not satisfied, the process returns to the discharge step, and the charge step, the measurement step, and the confirmation step are repeated.

4. The discharge treatment method according to claim 3, wherein: In the determination step, if the confirmed health state has not reached the recovery critical point, it is determined that the charging end condition is not satisfied.

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

6. The discharge treatment method according to claim 1, wherein: The lithium-ion secondary battery is an all-solid-state battery, and the negative electrode contains metallic lithium. The discharge treatment method includes a deactivation step of deactivating the all-solid-state battery using water vapor.

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