Lithium-ion battery recovery processing method, charging / discharging device, and program

Abstract

To provide a recovery processing method for a lithium-ion battery, a charge and discharge device, and a program that give an excellent effect for recovering performance of a lithium-ion battery.SOLUTION: A recovery processing method for a lithium-ion battery is a recovery processing method for a lithium-ion battery that has positive and negative electrodes and whose performance is reduced due to lithium-ion residue in the negative electrode. In the recovery processing method for a lithium-ion battery, a cycle including a first step and a second step is repeated a plurality of times. In the first step, the SOC of the lithium-ion battery is set to a first value S1 that is equal to or less than such a SOC value that the inclination of a SOC-voltage curve becomes the minimum value and equal to or more than such a SOC value that the inclination of the SOC-voltage curve becomes twice the minimum value, by charging. In the second step, the SOC of the lithium-ion battery is set to a second value S2 smaller than the first value, by discharging.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a recovery processing method, a charge / discharge device, and a program for a lithium-ion battery. [Background technology]

[0002] In recent years, the CO 2 In order to reduce CO2 emissions, there is growing interest in electric vehicles, and the use of lithium-ion batteries for in-vehicle use is also being considered. The performance of lithium-ion batteries can deteriorate due to repeated charging and discharging. As a method for recovering the performance of lithium-ion batteries, a method of placing the lithium-ion battery under certain conditions has been proposed (see, for example, Patent Document 1 and Patent Document 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-277164 A [Patent Document 2] JP 2014-127283 A Summary of the Invention [Problem to be solved by the invention]

[0004] The above-mentioned techniques have not been found to be sufficiently effective in restoring the performance of lithium-ion batteries.

[0005] An object of the present invention is to provide a recovery processing method, a charge / discharge device, and a program for a lithium ion battery that are highly effective in recovering the performance of the lithium ion battery. [Means for solving the problem]

[0006] The recovery processing method, charge / discharge device, and program of the present invention are configured as follows. (1): A method for recovering a lithium-ion battery according to one embodiment of the present invention is a method for recovering a lithium-ion battery having a positive electrode and a negative electrode, the performance of which has been reduced due to residual lithium ions in the negative electrode, the method comprising: a first step of charging the lithium-ion battery to a first value that is less than or equal to the SOC value at which the slope of the SOC-voltage curve is a minimum value and is greater than or equal to the SOC value at which the slope of the SOC-voltage curve is twice the minimum value; and a second step of discharging the lithium-ion battery to a second value that is less than the first value,

[0007] (2): In the above aspect (1), the first value is 30% or less.

[0008] (3): In the above embodiment (1) or (2), the second value is less than 10%.

[0009] (4): In any one of the embodiments (1) to (3), prior to the first step and the second step, it is determined whether or not there is a performance degradation of the lithium ion battery, and only if the performance degradation is confirmed, the first step and the second step are carried out.

[0010] (5): A charge / discharge device according to one embodiment of the present invention has a positive electrode and a negative electrode and is electrically connected to a lithium-ion battery whose performance has been reduced due to residual lithium ions in the negative electrode, and includes a control unit which charges and discharges the lithium-ion battery, and the control unit repeats a cycle including a first step of charging the lithium-ion battery to a first value that is less than or equal to the SOC value at which the slope of the SOC-voltage curve is a minimum value and is greater than or equal to the SOC value at which the slope of the SOC-voltage curve is twice the minimum value, and a second step of discharging the lithium-ion battery to a second value less than the first value, multiple times.

[0011] (6): A program according to one embodiment of the present invention causes a charge / discharge device electrically connected to a lithium ion battery having a positive electrode and a negative electrode and whose performance has been reduced due to residual lithium ions in the negative electrode to repeat a cycle including a first step of charging the lithium ion battery to a first value that is less than or equal to an SOC value at which a slope of an SOC-voltage curve becomes a minimum value and is greater than or equal to an SOC value at which a slope of the SOC-voltage curve becomes twice the minimum value, and a second step of discharging the lithium ion battery to a second value that is less than the first value. Effect of the Invention

[0012] According to the aspects (1) to (6), there are provided a recovery processing method, a charge / discharge device, and a program for a lithium ion battery, which are highly effective in recovering the performance of the lithium ion battery. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of an example of a lithium ion battery. [Diagram 2] FIG. 2 is a configuration diagram of a charge / discharge device. [Diagram 3] A schematic diagram of the movement of lithium ions in the negative electrode. (A) shows the movement during charging. (B) shows the movement during discharging. [Figure 4] 1 is a graph showing an example of a change in discharge capacity in a charge / discharge test. [Diagram 5] FIG. 2 is an explanatory diagram showing an example of a recovery processing method for a lithium ion battery according to an embodiment; [Figure 6] 1 is an example of an SOC-voltage curve. [Figure 7] 1 is a graph showing test results. [Figure 8] 1 is a graph showing test results. [Figure 9] 1 is a graph showing test results. [Figure 10] 1 is a graph showing test results. [Figure 11] 1 is a graph showing test results. [Figure 12]1 is a graph showing test results. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a recovery processing method for a lithium ion battery, a charge / discharge device, and a program according to the present invention will be described with reference to the drawings.

[0015] [Lithium-ion battery] FIG. 1 is a perspective view of an example of a lithium ion battery. As shown in Fig. 1, the lithium ion battery 1 includes a laminate 2 including electrodes, an exterior body 4 that houses the laminate 2, and a lid body 5 that seals the exterior body 4. The exterior body 4 is, for example, a metal housing. The exterior body 4 or the lid body 5 is provided with a positive electrode terminal 6 and a negative electrode terminal 7 (see Fig. 2).

[0016] The laminate 2 includes a positive electrode 21, a negative electrode 22, and a separator 23. The separator 23 is interposed between the positive electrode 21 and the negative electrode 22. The positive electrode 21, the negative electrode 22, and the separator 23 are impregnated with an electrolyte.

[0017] The positive electrode 21 has a positive electrode current collector and a positive electrode active material layer. The positive electrode active material is, for example, a lithium composite oxide containing nickel, cobalt, etc. The lithium composite oxide is, for example, a lithium nickel composite oxide, a lithium cobalt composite oxide, a lithium manganese composite oxide, a lithium nickel cobalt composite oxide, a lithium nickel manganese composite oxide, a lithium nickel cobalt manganese composite oxide, etc.

[0018] The negative electrode 22 includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material is, for example, a carbon material such as graphite. The separator 23 is formed of a resin such as polyethylene (PE) or polypropylene (PP).

[0019] The electrolytic solution contains, for example, a non-aqueous solvent and a lithium salt (electrolyte). Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC). Examples of the electrolyte include lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ) etc.

[0020] The lithium ion battery 1 is mounted on, for example, a vehicle.

[0021] [Charge / discharge device] FIG. 2 is a configuration diagram of the charge / discharge device 10 according to the embodiment. As shown in FIG. 2, the charging / discharging device 10 is electrically connected to a positive terminal 6 and a negative terminal 7 of the lithium ion battery 1. The charging / discharging device 10 includes a control unit 11. The control unit 11 can charge and discharge the lithium ion battery 1 according to a recovery processing method described later. The charging / discharging device 10 may include a power source for charging the lithium ion battery 1. If the charging / discharging device 10 does not include a power source, an external power source is used. The charging / discharging device 10 is mounted on, for example, a vehicle. The charging / discharging device 10 may also be mounted on a battery exchange device.

[0022] The control unit 11 is realized by, for example, a hardware processor such as a CPU (Central Processing Unit) executing a program (software). Some or all of these components may be realized by hardware (including circuitry) such as an LSI (Large Scale Integration), an ASIC (Application Specific Integrated Circuit), an FPGA (Field-Programmable Gate Array), or a GPU (Graphics Processing Unit), or may be realized by a combination of software and hardware. The program may be stored in advance in a storage device (storage device having a non-transient storage medium) such as an HDD or flash memory of the control unit 11, or may be stored in a removable storage medium such as a DVD or CD-ROM, and installed in the HDD or flash memory of the control unit 11 by mounting the storage medium (non-transient storage medium) in a drive device.

[0023] [Lithium-ion battery performance degradation due to repeated charging and discharging] Lithium-ion batteries can experience performance degradation, such as capacity drift, due to repeated charging and discharging. According to "Kentaro Kaji and four others, 'Research on Modeling the Degradation of Lithium-ion Batteries,' Proceedings of the Society of Automotive Engineers of Japan, Society of Automotive Engineers of Japan, Vol. 44 (2013), No. 2, pp. 429-434," three factors are cited as the degradation mechanism of lithium-ion batteries. (1) Lithium ions remain inside the negative electrode material and cannot come out, reducing the total number of active lithium ions. (2) Lithium ions are reduced (i.e., gain electrons) on the negative electrode surface and react with the electrolyte, decreasing the total amount of active lithium ions. (3) The electrolyte reacts with the surface of the negative electrode to form a resin coating, making it difficult for lithium ions to pass through, increasing the battery's internal resistance.

[0024] (1) is called "lithium ion retention deep inside the negative electrode" (lithium ion retention in the negative electrode). (2) is called "lithium precipitation". (3) is called "formation of SEI". The precipitation of needle-shaped crystals of lithium precipitation is called dendritic precipitation. Lithium deposition is likely to occur at low temperatures (for example, 0°C or lower). In contrast, lithium ions are likely to remain deep inside the negative electrode at temperatures above room temperature (for example, temperatures above 0°C. Specifically, 10°C to 65°C).

[0025] We will now explain in detail about the residual lithium ions deep inside the negative electrode. Figures 3(A) and 3(B) are schematic diagrams showing the movement of lithium ions in the negative electrode. Figure 3(A) shows the state during charging. Figure 3(B) shows the state during discharging. 34 is the electrolyte. As shown in Fig. 3(A), during charging, the negative electrode 32 is filled with lithium ions 30. As shown in Fig. 3(B), during discharging, the amount of lithium ions 30 in the negative electrode 32 decreases. When charging and discharging are repeated, the amount of lithium ions 30 that remain deep in the negative electrode 32 increases even during discharging. This is called residual lithium ions deep in the negative electrode. If the amount of residual lithium ions deep in the negative electrode increases, the amount of active lithium ions decreases, leading to a decrease in capacity.

[0026] Figure 4 is a graph showing an example of the change in discharge capacity in a charge-discharge test. Figure 4 shows the change in discharge capacity based on the capacity retention rate. The capacity retention rate is expressed as "current capacity / initial capacity x 100 (%)". As shown in FIG. 4, the discharge capacity of the lithium-ion battery in this example gradually decreases as the number of charge / discharge cycles (repetitions) increases.

[0027] [How to recover a lithium-ion battery] A lithium ion battery whose performance has deteriorated can have its performance restored by the following method. The recovery treatment method described below can be performed by a charge / discharge device 10 (see FIG. 2).

[0028] 5 is an explanatory diagram showing an example of a recovery processing method according to an embodiment. Note that the recovery processing method for a lithium ion battery is also simply called a "recovery processing method."

[0029] As shown in FIG. 5, the recovery method of this embodiment repeats a cycle including the following two steps multiple times. First step: The SOC of the lithium ion battery is set to an upper limit value S1 through charging. The upper limit value S1 is an example of a "first value." Second step: The SOC of the lithium ion battery is set to a lower limit value S2 by discharging. The lower limit value S2 is an example of a "second value". Prior to the first step, a preparation step may be performed in which the lithium ion battery is discharged to an end-of-discharge voltage.

[0030] SOC (State Of Charge) is the charging rate (%) of a lithium ion battery. In the recovery processing method of this embodiment, a first step in which the SOC is set to an upper limit value S1 and a second step in which the SOC is set to a lower limit value S2 are repeated, so that the SOC repeatedly increases and decreases. In the recovery processing method of this embodiment, the SOC increases linearly in the first step. In the second step, the SOC decreases linearly. In the example shown in FIG. 5, the first step is the first step, but either the first step or the second step may be performed first.

[0031] FIG. 6 is an example of an "SOC-voltage curve" showing the relationship between SOC and voltage. The horizontal axis of FIG. 6 indicates SOC (%). The vertical axis of FIG. 6 indicates voltage (V). The SOC-voltage curve can be obtained as follows.

[0032] The capacity of a lithium ion battery is calculated, for example, as follows. Take as an example a lithium-ion battery that uses a ternary lithium composite oxide containing cobalt, nickel, and manganese as the positive electrode active material. The rated voltage is 3.6V. The capacity is 3Ah. The upper limit voltage is 4.2V. The lower limit voltage is 2.5V.

[0033] The lithium ion battery is placed in a thermostatic chamber at 25°C and left there for 4 hours, after which the following operations are carried out in the thermostatic chamber at a temperature of 25°C. (1) Discharge the lithium-ion battery to 2.5V at a current of 3A (equivalent to 1C at rated capacity) and leave it for 10 seconds. (2) Charge the lithium-ion battery at a constant current of 3A up to 4.2V. (3) Charge the lithium-ion battery at a constant voltage of 4.2 V and a current of 0.6 A (equivalent to 0.2 C at rated capacity). (4) Discharge the lithium-ion battery at a constant current of 3 A down to 2.5 V. Measure the capacity during this discharge.

[0034] During discharge (operation (4)), the voltage is measured every second. The SOC is calculated by (capacity - current - time) / capacity x 100(%). The obtained SOC and voltage can be used to generate the SOC-voltage curve shown in FIG.

[0035] The slope of the SOC-voltage curve is the slope of a straight line obtained by linearly approximating the range of SOC corresponding to 30 seconds before to 30 seconds after the point in time using the least squares method for SOC and voltage. The slope of the SOC-voltage curve is the ratio (V / %) of the change in voltage (V) to the change in SOC (%).

[0036] The upper limit S1 of the SOC (see FIG. 5) is set to be equal to or less than the SOC value at point M1 in FIG. 6, where the slope of the SOC-voltage curve is at a minimum. In the example shown in FIG. 6, the slope of the SOC-voltage curve is at a minimum value of 0.0031 at point M1. The SOC at this time is 34%. Therefore, the upper limit S1 of the SOC is set to be equal to or less than 34%. It is preferable that the upper limit S1 is equal to or less than 50% (e.g., equal to or less than 30%). By setting the upper limit S1 of the SOC to be equal to or lower than the SOC value at point M1, the amount of residual lithium ions in the negative electrode can be reduced, and performance degradation such as capacity deviation can be suppressed.

[0037] The upper limit S1 of the SOC (see FIG. 5) is preferably equal to or greater than the SOC at point M2 in FIG. 6, where the slope of the SOC-voltage curve is twice the minimum value. The SOC at point M2 is smaller than the SOC at point M1. In the example shown in FIG. 6, the slope of the SOC-voltage curve is 0.0062, which is twice the minimum value 0.0031, at point M2. The SOC at this time is 10%. Therefore, the upper limit S1 of the SOC is preferably equal to or greater than 10%. By setting the upper limit S1 of the SOC to be equal to or greater than the SOC value at point M2, the amount of residual lithium ions in the negative electrode can be reduced, and performance degradation such as capacity deviation can be suppressed.

[0038] The lower limit value S2 of the SOC (see FIG. 5) is equal to or greater than 0% and is smaller than the upper limit value S1. The lower limit value S2 may be 0%. The lower limit value S2 is, for example, less than 10%. The lower limit value S2 may be equal to or greater than the SOC value at point M2 in FIG. 6 where the slope of the SOC-voltage curve is twice the minimum value, and equal to or less than the SOC value at point M1 where the slope of the SOC-voltage curve is the minimum value.

[0039] In the recovery processing method of this embodiment, prior to the recovery processing including the above-mentioned first and second steps, it may be determined whether or not the performance of the lithium ion battery has deteriorated, and the recovery processing may be executed only if the deterioration in performance is confirmed. The deterioration in performance may be determined, for example, based on the capacity recovery rate. By determining the deterioration in performance, the non-operational period of the lithium ion battery may be shortened.

[0040] [Effects of the recovery processing method according to the embodiment] According to the recovery method of this embodiment, a cycle including a first step of setting the SOC to an upper limit value S1 by charging and a second step of setting the SOC to a lower limit value S2 by discharging is repeated multiple times. The upper limit value S1 is set to be equal to or lower than the SOC value at point M1 where the slope of the SOC-voltage curve is at a minimum value. The upper limit value S1 is set to be equal to or higher than the SOC value at point M2. This reduces the amount of lithium ions remaining in the negative electrode, and suppresses performance degradation such as capacity deviation. This makes it possible to recover the performance of the lithium ion battery.

[0041] By restoring the performance of lithium-ion batteries, it is possible to extend the lifespan of the lithium-ion batteries and thereby improve their energy efficiency.

[0042] The above describes the form for carrying out the present invention using an embodiment, but the present invention is not limited to such an embodiment, and various modifications and substitutions can be made within the scope that does not deviate from the gist of the present invention.

[0043] The present invention will be described in detail below based on specific examples, but the present invention is not limited to the following examples.

[0044] <Example 1> A lithium-ion battery was prepared using a ternary lithium composite oxide containing cobalt, nickel, and manganese as the positive electrode active material. The rated voltage is 3.6V. The capacity is 3Ah. The upper limit voltage is 4.2V. The lower limit voltage is 2.5V.

[0045] (Preparation of samples with reduced performance) The lithium ion battery was subjected to the following charge / discharge test. The lithium ion battery was placed in a thermostatic chamber at 25° C. and left for 4 hours, after which the following operations (A) and (B) were repeated for 269 cycles in the thermostatic chamber at a temperature of 25° C. (A) Discharge the lithium-ion battery to 2.5V at a current of 9A and leave it for 10 seconds. (B) Charge the lithium-ion battery to 4.2 V at a current of 9 A and leave it for 10 seconds. This resulted in a sample with reduced (degraded) performance.

[0046] (Recovery process) As shown in FIG. 5, the cycle of the first and second steps was repeated multiple times (120 times) for the above-mentioned samples using a charge / discharge device 10 (see FIG. 2). The treatment time was 20 hours. The temperature was 25° C. The number of samples was five. The SOC-voltage curve is shown in FIG. 6. Preparation step: The lithium ion battery was discharged at a current of 9 A down to 2.5 V (lower limit S2: SOC 0%) (discharge end voltage). First step: Charge the lithium-ion battery to 0.75 Ah (upper limit S1: SOC 25%) at a current of 9 A. The charging time was 5 minutes. Second step: The lithium ion battery was discharged to 2.5 V (lower limit S2: SOC 0%) (discharge end voltage) at a current of 9 A. The discharge time was 5 minutes.

[0047] Using the above-mentioned capacity measurement method, the initial capacity of the lithium ion battery, the capacity after performance degradation (after deterioration), and the capacity after recovery were measured.

[0048] The recovery rate was calculated by the following formula: The results are shown in Table 1. Recovery rate = (Capacity after recovery - Capacity after degradation) / (Initial capacity - Capacity after degradation)

[0049] [Table 1]

[0050] As shown in Table 1, the above-mentioned recovery treatment resulted in a high recovery rate.

[0051] <Example 2> A recovery treatment test was carried out in the same manner as in Example 1, except for the upper limit S1 of SOC. The results are shown in Table 2 and FIG. For comparison, the results when the upper limit value S1 and the lower limit value S2 are set to 0% (that is, when charging and discharging were not performed) are also shown.

[0052] [Table 2]

[0053] As shown in Table 2 and FIG. 7, the recovery rate was high when the upper limit value S1 was 10% or more and 30% or less.

[0054] <Example 3> A recovery treatment test was carried out in the same manner as in Example 1, except for the upper limit S1 and the lower limit S2. The results are shown in Table 3 and FIG.

[0055] [Table 3]

[0056] As shown in Table 3 and FIG. 8, the recovery rate was high when the lower limit S2 was less than 10%.

[0057] <Example 4> A recovery treatment test was carried out in the same manner as in Example 1, except for the number of repetitions (number of cycles) of the cycle consisting of the first and second steps. The results are shown in Table 4 and Fig. 9. The horizontal axis of Fig. 9 is the treatment time. The treatment time is approximately proportional to the number of cycles. For comparison, Table 4 and FIG. 9 also show the results when the number of cycles was zero.

[0058] [Table 4]

[0059] As shown in Table 4 and Figure 9, a higher recovery rate was obtained with a higher number of cycles.

[0060] <Example 5> A recovery treatment test was carried out in the same manner as in Example 2, except that the current was 3 A. Because the current was 3 A, the charge time and discharge time were three times longer than those in Example 2. Because the treatment time was 20 hours, the same as in Example 2, the number of repeated cycles was about 1 / 3 of the number of repeated cycles in Example 2 (120 times). The results are shown in Table 5 and FIG. 10.

[0061] [Table 5]

[0062] As shown in Table 5 and FIG. 10, the tendency of the recovery rate did not change much even when the current was changed, as compared with Example 2 (see FIG. 7).

[0063] <Example 6> A performance-degraded sample was obtained in the same manner as in Example 2, except that the temperature condition in producing the performance-degraded sample was 50°C instead of 25°C. This sample was subjected to a recovery treatment test in the same manner as in Example 2. The results are shown in Table 6 and FIG.

[0064] [Table 6]

[0065] As shown in Table 6 and FIG. 11, the tendency of the recovery rate was not significantly different from that when the temperature condition was 25° C. (see FIG. 7).

[0066] <Comparative Example 1> A performance-degraded sample was obtained in the same manner as in Example 1, except that the temperature condition for producing the performance-degraded sample was -10°C instead of 25°C. This sample was subjected to a recovery treatment test in the same manner as in Example 1. The results are shown in Table 7 and FIG.

[0067] [Table 7]

[0068] As shown in Table 7 and FIG. 12, the samples whose performance deteriorated at low temperatures had lower recovery rates than the samples whose performance deteriorated at room temperature. This shows that the recovery treatment method of the present embodiment is effective for lithium ion batteries whose performance has deteriorated at room temperature.

[0069] <Comparative Example 2> A performance-degraded sample (the temperature at which the performance was reduced was 25° C.) was obtained in the same manner as in Example 1 (a performance-degraded sample in which the performance was reduced at room temperature). A performance-degraded sample was obtained in the same manner as in Example 1 except that the temperature condition in producing the performance-degraded sample was set to -10°C (a performance-degraded sample in which the performance-degrading condition was a low temperature). For these samples, a cycle including the following two steps was repeated multiple times for a treatment time of 72 hours. First step: The SOC of the lithium-ion battery was set to 1.1% by charging for 10 seconds. Second step: The SOC of the lithium-ion battery was set to 0% by discharging for 10 seconds.

[0070] [Table 8]

[0071] As shown in Table 8, in Comparative Example 2, in which the SOC (upper limit value S1) in the first step was smaller than that in Comparative Example 1, the recovery rate was higher when performance decreased at low temperatures than when performance decreased at room temperature. This shows that the effectiveness of the recovery process varies depending on the conditions under which performance degrades.

[0072] <Example 7> A recovery treatment test was carried out in the same manner as in Example 1, except for the current during charging and discharging and the treatment time. The results are shown in Table 9.

[0073] [Table 9]

[0074] As shown in Table 9, the number of cycles and current did not significantly affect the recovery rate.

[0075] The SOC range (see Figure 6) that is equal to or greater than the SOC value at point M2 where the slope of the SOC-voltage curve is twice the minimum value and is equal to or less than the SOC value at point M1 where the slope of the SOC-voltage curve is the minimum value is called the "specific range." A sample whose performance has been degraded at room temperature (e.g., 25°C) is called a "sample whose performance has been degraded at room temperature." A sample whose performance has been degraded at a low temperature (e.g., -10°C) is called a "sample whose performance has been degraded at low temperature."

[0076] The recovery treatment in which the upper limit S1 of SOC was set to a value within a specific range achieved a higher recovery rate in the samples with reduced performance at room temperature (Examples 1 and 2) compared to the sample with reduced performance at low temperature (Comparative Example 1). In contrast, the recovery process in which the upper limit S1 is below the lower limit of the specific range was not particularly effective for samples with reduced performance at room temperature (see Comparative Example 2).

[0077] The recovery processing method of this embodiment is useful when the following condition [1] is satisfied, or when both the following conditions [1] and [2] are satisfied. [1] When the recovery process (described above) was performed on a sample with reduced performance at room temperature and a sample with reduced performance at low temperature, with the upper limit S1 of the SOC set to a value within a specific range, the recovery rate in the case of reduced performance at room temperature was higher than the recovery rate in the case of reduced performance at low temperature (see Table 7). [2] When the recovery process (described above) is performed on a sample with reduced performance at room temperature and a sample with reduced performance at low temperature in such a way that the upper limit value S1 of the SOC falls below the lower limit value of the specific range, the recovery rate in the case of reduced performance at room temperature is lower than the recovery rate in the case of reduced performance at low temperature (see Table 8).

[0078] When condition [1] is met, or when both conditions [1] and [2] are met, it can be assumed that the cause of the performance degradation is the residual lithium ions deep inside the negative electrode (residual lithium ions in the negative electrode). The recovery processing method of this embodiment may be performed when the condition [1] is satisfied. The recovery processing method of this embodiment may be performed when both the condition [1] and the condition [2] are satisfied. [Explanation of symbols]

[0079] 1 Lithium-ion battery S1 Upper limit (first value) S2 Lower limit (second value)

Claims

1. A method for recovering the capacity of a lithium ion battery having a positive electrode and a negative electrode, the capacity of which has been reduced due to residual lithium ions in the negative electrode, comprising: a first step of charging the lithium ion battery to a first value that is equal to or lower than an SOC value at which a slope of an SOC-voltage curve becomes a minimum value and is equal to or higher than an SOC value at which a slope of the SOC-voltage curve becomes twice the minimum value; a second step of discharging the lithium ion battery to a second value that is smaller than the first value; A capacity recovery method for a lithium-ion battery, comprising repeating a cycle including the steps of:

2. 2. The method for recovering capacity of a lithium ion battery according to claim 1, wherein the first value is 30% or less.

3. The second value is less than 10%. The capacity recovery method for a lithium ion battery according to claim 1 or 2.

4. 3. The method for recovering the capacity of a lithium ion battery according to claim 1, further comprising the steps of: determining whether or not a capacity reduction has occurred in the lithium ion battery prior to the first step and the second step; and carrying out the first step and the second step only if the capacity reduction is confirmed.

5. Prior to the first step and the second step, the presence or absence of a capacity reduction in the lithium ion battery is determined, and the first step and the second step are carried out only if the capacity reduction is confirmed. The capacity recovery method for a lithium ion battery according to claim 3.

6. A charge / discharge device having a positive electrode and a negative electrode, electrically connected to a lithium ion battery whose capacity has been reduced due to residual lithium ions in the negative electrode, and configured to recover the capacity of the lithium ion battery, A control unit that charges and discharges the lithium ion battery, The control unit is a first step of charging the lithium ion battery to a first value that is equal to or lower than an SOC value at which a slope of an SOC-voltage curve becomes a minimum value and is equal to or higher than an SOC value at which a slope of the SOC-voltage curve becomes twice the minimum value; a second step of discharging the lithium ion battery to a second value that is smaller than the first value; A charging and discharging device that repeats a cycle including the above multiple times.

7. A program for recovering the capacity of a lithium ion battery, comprising: A charging / discharging device having a positive electrode and a negative electrode, the charging / discharging device being electrically connected to the lithium ion battery whose capacity has been reduced due to residual lithium ions in the negative electrode, a first step of charging the lithium ion battery to a first value that is equal to or lower than an SOC value at which a slope of an SOC-voltage curve becomes a minimum value and is equal to or higher than an SOC value at which a slope of the SOC-voltage curve becomes twice the minimum value; a second step of discharging the lithium ion battery to a second value that is smaller than the first value; A program that repeats a cycle including multiple times.

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