Method for estimating internal deterioration state of deteriorated battery and measurement system

Abstract

Provided is a method for estimating an internal deterioration state of a deteriorated battery and a measuring system. The measuring system has a charger and an estimation device, and implements the method for estimating the internal deterioration state of the deteriorated battery. The estimation device calculates a reference capacity characteristic curve from a differential of a reference charging curve, sets a reference capacity characteristic curve smaller than a division point as a negative electrode characteristic curve, and sets a reference capacity characteristic curve equal to or larger than the division point as a positive electrode characteristic curve. Further, the estimation device calculates an object capacity characteristic curve from a differential of an object charging curve, and fits the object capacity characteristic curve to each of the negative electrode characteristic curve and the positive electrode characteristic curve to obtain a change in a plurality of parameters. Accordingly, even without destructive inspection of the secondary battery, reference data can be simply obtained, and thus the capacity deterioration of the secondary battery can be well estimated from the reference data.

Description

TECHNICAL FIELD

[0001] The present application relates to a method of estimating an internal deterioration state of a deteriorated battery that estimates capacity deterioration of a secondary battery and a measurement system. BACKGROUND

[0002] A half cell fitting method (a method of estimating an internal deterioration state of a deteriorated battery) that estimates capacity deterioration of a secondary battery from electromotive force curves of a positive electrode and a negative electrode of the secondary battery is disclosed in Japanese Patent Application Publication No. 2015-87344. In the method of estimating an internal deterioration state of a deteriorated battery, a position and a shape in a capacity direction of an electromotive force curve of one of the electromotive force curves of a new battery and a deteriorated battery are changed, and capacity deterioration is estimated from a change in fitting parameters when the electromotive force curve is fitted to the electromotive force curve of the other. SUMMARY

[0003] In the method of estimating an internal deterioration state of a deteriorated battery disclosed in Japanese Patent Application Publication No. 2015-87344, electromotive force curves of each half cell (positive electrode and negative electrode) are required to be obtained in advance as reference data for comparison with a deteriorated battery. In other words, for a secondary battery for which reference data is not available, the method of estimating an internal deterioration state of a deteriorated battery cannot be implemented.

[0004] In the related art, reference data of a half cell is obtained by a destructive inspection that separates (destroys) a secondary battery into a positive electrode and a negative electrode and measures the separated positive electrode and negative electrode. However, implementing a destructive inspection in order to estimate capacity deterioration of a secondary battery causes various undesirable situations such as deterioration of efficiency, increase in cost, and the like.

[0005] The present application was made in view of the above circumstances, and has an object to provide a method of estimating an internal deterioration state of a deteriorated battery and a measurement system that can simply obtain reference data even without a destructive inspection of a secondary battery and can estimate capacity deterioration of the secondary battery well from the reference data.

[0006] To achieve the above object, a first aspect of the present application is a method of estimating an internal deterioration state of a deteriorated battery, which obtains, for a target battery before deterioration or a battery of the same kind as the target battery, a reference charge curve represented by a current-carrying capacity and a voltage, calculates, for the reference charge curve, a reference capacity characteristic curve represented by the current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage, divides the reference capacity characteristic curve by a division point in the direction of the current-carrying capacity, sets the reference capacity characteristic curve smaller than the division point as a negative electrode component, and sets the reference capacity characteristic curve equal to or larger than the division point as a positive electrode component, obtains, for the target battery after deterioration, a target charge curve represented by a current-carrying capacity and a voltage, calculates, for the target charge curve, a target capacity characteristic curve represented by the current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage, obtains a change in a plurality of parameters from a fitting operation of fitting each of the set negative electrode component and the positive electrode component of the reference capacity characteristic curve to the target capacity characteristic curve, and thereby estimates a capacity deterioration of the target battery.

[0007] In addition, to achieve the above object, a second aspect of the present application is a measurement system that implements a method of estimating an internal deterioration state of a deteriorated battery, which has a charger that charges a target battery or a battery of the same kind as the target battery, and an estimation device connected to the charger, the estimation device being configured to obtain, from a charging current and a charging voltage supplied to the target battery or the battery of the same kind as the target battery, a reference charge curve represented by a current-carrying capacity and a voltage, calculate, for the reference charge curve, a reference capacity characteristic curve represented by the current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage, divide the reference capacity characteristic curve by a division point in the direction of the current-carrying capacity, set the reference capacity characteristic curve smaller than the division point as a negative electrode component, and set the reference capacity characteristic curve equal to or larger than the division point as a positive electrode component, obtain, from a charging current and a charging voltage supplied to the target battery after deterioration, a target charge curve represented by a current-carrying capacity and a voltage, calculate, for the target charge curve, a target capacity characteristic curve represented by the current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage, obtain a change in a plurality of parameters from a fitting operation of fitting each of the set negative electrode component and the positive electrode component of the reference capacity characteristic curve to the target capacity characteristic curve, and thereby estimate a capacity deterioration of the target battery.

[0008] According to the internal deterioration state estimation method of a deteriorated battery and the measurement system described above, reference data can be easily obtained without destructive inspection of the secondary battery, and thus the capacity deterioration of the secondary battery can be well estimated based on the reference data.

[0009] The above objects, features and advantages will be more apparent from the following description taken in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is a diagram showing a measurement system for an internal deterioration state estimation method of a deteriorated battery according to an embodiment of the present application.

[0011] Figure 2 is a graph showing an object charge curve and a reference charge curve of a deteriorated object battery in terms of a load capacity and a voltage.

[0012] Figure 3 is a graph for explaining a main factor of battery capacity deterioration.

[0013] Figure 4 the left graph of is a graph showing a charge curve, Figure 4 the right graph of is a graph showing a characteristic curve obtained by differentiating a load capacity with respect to a voltage with respect to a charge curve in terms of a voltage and a differential value.

[0014] Figure 5 is a graph showing a reference capacity characteristic curve in which a division point is set in terms of a load capacity and a differential value.

[0015] Figure 6 the left graph of is a graph showing a reference charge curve in terms of a load capacity and a voltage. Figure 6 the right graph of is a graph for explaining generation of a positive electrode QV curve and a negative electrode QV curve from the reference charge curve.

[0016] Figure 7 the left graph of is a graph showing a charge curve, Figure 7 the right graph of is a graph showing a characteristic curve obtained by differentiating a load capacity with respect to a voltage with respect to a charge curve in terms of a voltage and a differential value.

[0017] Figure 8A is a flowchart showing a processing flow of an internal deterioration state estimation method of a deteriorated battery. Figure 8B is a flowchart showing a processing flow of generation of reference data.

[0018] Figure 9 is a flowchart showing an actual estimation processing of an internal deterioration state estimation method of a deteriorated battery. DETAILED DESCRIPTION

[0019] Hereinafter, the present application will be described in detail with reference to the preferred embodiments illustrated in the drawings.

[0020] As Figure 1 indicated, an internal deterioration state estimation method of a deteriorated battery according to an embodiment of the present application estimates capacity deterioration of a battery as an estimation target (hereinafter, referred to as a target battery OB) using a measurement system 100. The measurement system 100 has a placement section 110 for placing the target battery OB, a charger 120 that charges the placed target battery OB, and an estimation device 140 that actually estimates capacity deterioration of the target battery OB in a communicable manner with the charger 120.

[0021] The target battery OB is a secondary battery having a positive electrode and a negative electrode capable of outputting appropriate electric power (current, voltage) and capable of charging via the positive electrode and the negative electrode. The kind of the secondary battery is not particularly limited, and is, for example, a lithium ion secondary battery, a lithium ion polymer secondary battery, a lead-acid storage battery, a nickel-based storage battery, or the like. In the present embodiment, a case where a lithium ion secondary battery is exemplified as the target battery OB. The number of target batteries OB measured by the measurement system 100 is not limited to one, and a plurality of target batteries can be measured.

[0022] The charger 120 includes a housing 122 and a pair of terminals 124 (a positive terminal 124a and a negative terminal 124b) provided on the housing 122. The pair of terminals 124 are electrically connected to the target battery OB placed in the placement section 110 via an electric wiring 126. Inside the housing 122 of the charger 120, a power supply section 128 capable of outputting electric power to the pair of terminals 124, a current meter 130 that detects a charging current supplied from the power supply section 128 to the target battery OB, and a voltage meter 132 that detects a charging voltage supplied from the power supply section 128 to the target battery OB are provided.

[0023] The power supply section 128 outputs appropriate direct current (direct current, direct voltage) according to the state of the target battery OB. The power supply section 128 can use a storage direct current power supply capable of outputting direct current, or can use a structure that converts alternating current power supplied from the outside of the charger 120 into direct current. The current meter 130 is connected in series with the power supply section 128, and detects a charging current output from the power supply section 128. The voltage meter 132 is connected in parallel with the power supply section 128 and the current meter 130, and detects a charging voltage (inter-terminal voltage) of the target battery OB.

[0024] The estimation device 140 has a data recorder 142 (storage device) connected to the charger 120 and an information processing device 144 connected to the data recorder 142. The data recorder 142 is a storage device that acquires and stores the charging current detected by the ammeter 130 and the charging voltage detected by the voltmeter 132 in a manner capable of signal communication with the charger 120. The data recorder 142 can employ a publicly known hard disk drive (HDD), a solid state drive (SSD), or other off-line storage device, and the like. In addition, the data recorder 142 has an input-output interface capable of communicatively connecting with the ammeter 130, the voltmeter 132, and the information processing device 144 via the communication line 134, a processor that controls writing, reading, and deletion of the charging current and the charging voltage, a timer, and the like (all not shown). Furthermore, the data recorder 142 can be configured to be provided in the charger 120 or configured to receive the charging current and the charging voltage from the charger 120 by wireless communication.

[0025] The data recorder 142 acquires the charging current and the charging voltage from the charger 120 periodically and continuously while measuring time by the timer, and stores the time in association with the charging current and the charging voltage. This is to form a charging curve (charging characteristic, QV curve) represented by the current-carrying capacity (mAh) and the charging voltage (V) of the subject battery OB in the implementation of the internal deterioration state estimation method of the deteriorated battery.

[0026] The information processing device 144 has one or more processors, memories, input-output interfaces, and electronic circuits. The memories can employ various drives (HDD, SSD, and the like) or can include memories attached to the processors, integrated circuits, and the like. By executing a program not shown in the memories by the one or more processors, a plurality of functional modules that perform information processing are formed in the information processing device 144. Furthermore, at least a part of each functional module can also be constituted by electronic circuits including ASICs (Application Specific Integrated Circuits), FPGAs (Field-Programmable Gate Arrays), and the like, discrete devices.

[0027] Specifically, in the information processing device 144, a charging curve acquisition section 146, a storage section 148, a fitting section 150, and a reference data generation section 152 are formed as functional modules. The charging curve acquisition section 146 acquires the charging current, the charging voltage, the time, and the like stored in the data recorder 142, and calculates the charging curve of the subject battery OB (hereinafter referred to as the subject charging curve 10) (refer to FIG. 2).Figure 2 The object charging curve 10 is the change in voltage relative to current carrying capacity when the object battery OB is charged, and it can be represented by a graph with current carrying capacity on the horizontal axis and voltage on the vertical axis.

[0028] like Figure 1 and Figure 2 As shown, the calculation of the target charging curve 10 can be performed using known methods. For example, the charging curve acquisition unit 146 calculates the cumulative charging current based on the charging current and time until the target battery OB, with a state of charge (SOC) of 0%, is fully charged (SOC = 100%) by the charger 120. Since this cumulative charging current corresponds to the current carrying capacity, the charging curve acquisition unit 146 can obtain the target charging curve 10 by plotting a charging voltage corresponding to the increase in the cumulative charging current. When the charging curve acquisition unit 146 acquires the target charging curve 10 (or multiple curves that establish a correspondence between the charging voltage and the current carrying capacity constituting the target charging curve 10), it stores the target charging curve 10 in the storage unit 148. Furthermore, the measurement system 100 can be configured to calculate the target charging curve 10 using the data logger 142 and send the target charging curve 10 to the information processing device 144.

[0029] In addition to storing the target charging curve 10 acquired by the charging curve acquisition unit 146, the storage unit 148 also stores reference data for implementing the internal degradation state estimation method for a degraded battery. In this embodiment, the reference data is the reference charging curve 20 obtained by the measurement system 100 through reference data acquisition processing on the target battery OB before degradation or a battery of the same type as the target battery OB (a battery manufactured using the same manufacturing method).

[0030] The fitting unit 150 estimates the capacity degradation of the target battery OB by performing a fitting operation on the information related to the target charging curve 10 stored in the storage unit 148 and fitting it with reference data (reference charging curve 20). The main factors contributing to battery capacity degradation and the content of the fitting operation will be explained below.

[0031] Secondary batteries (lithium-ion secondary batteries) such as Figure 3the left side of FIG. 1, each of the positive electrode PE and the negative electrode NE has a QV curve (hereinafter, referred to as a positive electrode QV curve 22, a negative electrode QV curve 24). The positive electrode QV curve 22, in a graph in which an abscissa axis is set as a charge capacity (Q) and an ordinate axis is set as a voltage (V), after a voltage sharply rises at a low charge capacity, even if the charge capacity increases, the voltage is substantially constantly shifted, and when a high charge capacity is approached, a rate of rise of the voltage increases. On the other hand, the negative electrode QV curve 24, after a voltage sharply falls at a low charge capacity, even if the charge capacity increases, the voltage is substantially constantly shifted, and when a high charge capacity is approached, a rate of fall of the voltage gradually increases. Also, as shown in a graph on the right side of FIG. 1, a difference between the above-described positive electrode QV curve 22 and the negative electrode QV curve 24 becomes a charging curve between the unlike electrodes of the secondary battery (hereinafter, this charging curve is referred to as a full cell QV curve 26 based on a curve of the positive electrode PE and the negative electrode NE which are combined as a half cell). Figure 3

[0032] Here, the capacity deterioration of the secondary battery can be cited as the following four main factors, and each of the main factors appears in the positive electrode QV curve 22, the negative electrode QV curve 24, and the full cell QV curve 26. Figure 3 The changes of the positive electrode QV curve 22, the negative electrode QV curve 24, and the full cell QV curve 26 in the deteriorated secondary battery are indicated by a double-dot chain line.

[0033] (1) Capacity decrease of the positive electrode PE → narrowing in the charge capacity direction in the positive electrode QV curve 22

[0034] (2) Capacity decrease of the negative electrode NE → narrowing in the charge capacity direction in the negative electrode QV curve 24

[0035] (3) Decrease of lithium ions → shift in the charge capacity direction between the positive electrode QV curve 22 and the negative electrode QV curve 24

[0036] (4) Increase of resistance → separation in the voltage direction between the positive electrode QV curve 22 and the negative electrode QV curve 24 = voltage shift of the full cell QV curve 26

[0037] That is, the capacity deterioration of the secondary battery has four parameters (capacity decrease of the positive electrode PE, capacity decrease of the negative electrode NE, decrease of lithium ions, increase of resistance).

[0038] In the half cell fitting method in the related art, the separator SP of the secondary battery which becomes a reference is divided (destroyed) into the positive electrode PE and the negative electrode NE, and after the Li foil is attached to the division surface of the positive electrode PE and the negative electrode NE, charging is performed, and the positive electrode QV curve 22 and the negative electrode QV curve 24 which are reference data are obtained by monitoring a charging current and a charging voltage at this time. However, the operation of the destructive inspection is a main factor of the decrease of efficiency of the internal deterioration state estimation method of the deteriorated battery.​

[0039] Therefore, the internal deterioration state estimation method of the deteriorated battery according to the present embodiment performs a reference data acquisition process for acquiring reference data using the subject battery OB itself before deterioration or a battery of the same kind as the subject battery OB before the measurement of the subject battery OB after deterioration (actual estimation process). In the reference data acquisition process, the measurement system 100 charges the subject battery OB itself before deterioration or a battery of the same kind as the subject battery OB, and stores the charging current and the charging voltage at the time of charging in the data logger 142. Then, the information processing device 144 calculates the reference charging curve 20 (full-cell QV curve 26) as reference data from the charging current and the charging voltage stored in the data logger 142 (see also Figure 2 ).

[0040] In addition, in the reference data acquisition process, the reference data generation section 152 of the information processing device 144 divides the reference charging curve 20 into a region indicating the characteristics of the positive electrode PE and a region indicating the characteristics of the negative electrode NE. The division of the reference charging curve 20 is described in detail later.

[0041] Further, the actual estimation process performs a fitting operation to make the reference charging curve 20 (including the divided curve) acquired by the reference data acquisition process coincide with the subject charging curve 10, and analyzes the capacity deterioration of the subject battery OB from the variation amount of each parameter in the fitting operation. As described above, from the relationship between the charging curve (positive electrode QV curve 22, negative electrode QV curve 24, full-cell QV curve 26) and the four parameters, each parameter is interlocked on the charging curve.

[0042] Therefore, in the internal deterioration state estimation method of the deteriorated battery according to the present embodiment, the fitting section 150 extracts a characteristic point of the shape of the subject charging curve 10 by differentiating the voltage with respect to the charge-carrying capacity with respect to the subject charging curve 10. That is, as shown in the left side graph of FIG. 10, the subject charging curve 10 represented by the charge-carrying capacity and the voltage is converted into a characteristic curve (hereinafter referred to as a subject capacity characteristic curve 12) represented by the charge-carrying capacity and the differential value (dQ / dV) as shown in the right side graph of FIG. 10. In addition, Figure 4 Figure 4 the right side graph of FIG. 10 represents the subject capacity characteristic curve 12 when the horizontal axis is the charge-carrying capacity and the vertical axis is the differential value. Figure 4

[0043] In addition, the fitting section 150 differentiates the voltage with respect to the charge-carrying capacity with respect to the reference charging curve 20 (full-cell QV curve 26) as well as the differentiation of the subject charging curve 10, and converts it into a characteristic curve (hereinafter referred to as a reference capacity characteristic curve 22) represented by the charge-carrying capacity and the differential value (dQ / dV) as shown in the left side graph of FIG. 11. In addition, Figure 5 ​​The characteristic curve (hereinafter referred to as a reference capacity characteristic curve 30) expressed by the current capacity and the differential value as shown in the graph. Then, the fitting section 150 performs a fitting operation on the converted subject capacity characteristic curve 12 and the reference capacity characteristic curve 30. According to this, in the fitting operation, the parameter of the resistance rise (voltage shift) can be temporarily ignored.

[0044] In Figure 5 The differential value of the subject capacity characteristic curve 12 is configured to have two peak values pi, p2 on the low current capacity (low SOC) side, and gradually decrease as the current capacity increases when exceeding the two peak values pi, p2 along the increasing direction of the current capacity. Here, the correlation of the shape of the subject capacity characteristic curve 12 with the shape of the positive electrode PE and the negative electrode NE that the battery has is investigated.

[0045] Regarding the positive electrode QV curve 22, the characteristic curve (hereinafter referred to as a positive electrode characteristic curve 32) after differentiating the voltage with respect to the current capacity becomes a shape indicated by a single-dot chain line in the right side graph of Figure 4 In addition, regarding the negative electrode QV curve 24, the characteristic curve (hereinafter referred to as a negative electrode characteristic curve 34) after differentiating the voltage with respect to the current capacity becomes a shape indicated by a double-dot chain line in the right side graph of Figure 4

[0046] When comparing the subject capacity characteristic curve 12, the positive electrode characteristic curve 32, and the negative electrode characteristic curve 34, it is known that on the low current capacity side, the shape of the subject capacity characteristic curve 12 is similar to the shape of the negative electrode characteristic curve 34. That is, on the low current capacity side, the subject capacity characteristic curve 12 shows a strong correlation with the negative electrode characteristic curve 34. On the contrary, it is known that on the high current capacity (high SOC) side, the shape of the subject capacity characteristic curve 12 is similar to the shape of the positive electrode characteristic curve 32. That is, on the high current capacity side, the subject capacity characteristic curve 12 shows a strong correlation with the positive electrode characteristic curve 32.

[0047] In addition, in the lithium ion secondary battery, the correlation of the subject capacity characteristic curve 12 on the low current capacity side and the negative electrode characteristic curve 34 is stronger than the correlation of the subject capacity characteristic curve 12 on the high current capacity side and the positive electrode characteristic curve 32. The subject capacity characteristic curve 12 on the low current capacity side and the negative electrode characteristic curve 34 have two peak values pi, p2, and it can be said that the parameter of the capacity decrease of the positive electrode PE hardly affects the two peak values pi, p2 from each other. In other words, on the low current capacity side, the parameter of the capacity decrease of the negative electrode NE is more independent than other parameters. On the other hand, the subject capacity characteristic curve 12 on the high current capacity side and the positive electrode characteristic curve 32 do not have clear peak values, and are slightly affected by the parameter of the capacity decrease of the negative electrode NE.

[0048] ​In the reference data acquisition processing, the reference charge curve 20 is acquired as described above, and on the other hand, the positive electrode QV curve 22 which is a charge curve of the positive electrode PE, and the negative electrode QV curve 24 which is a charge curve of the negative electrode NE are not acquired. Therefore, as shown in Figure 5 the reference data generating section 152 calculates the reference capacity characteristic curve 30 from the reference charge curve 20, and further divides the reference capacity characteristic curve 30 at the division point DP, thereby using as the approximate positive electrode characteristic curve 32 and the negative electrode characteristic curve 34.

[0049] Specifically, the reference data generating section 152 sets the division point DP at a prescribed position in the direction in which the load capacity of the reference capacity characteristic curve 30 increases (X axis direction) beyond 2 peaks pi, p2. For example, the division point DP is set at the inflection point CP which is a point of inclination at which the reference capacity characteristic curve 30 gradually decreases from the peak p2 of the 2 peaks pi, p2 of the reference capacity characteristic curve 30 in which the load capacity is higher. The prescribed position of the division point DP is not particularly limited, but in the case where the direction of the load capacity of the battery is converted into the SOC, for example, it is preferable that the SOC be in the range of about 30% to 50%. More preferably, the division point DP can be set at a position deviated from the peak p2 of the higher load capacity in the direction in which the load capacity increases by about 5% to 20% of the SOC. Alternatively, the division point DP can also be set at the peak p2 of the higher load capacity of the reference capacity characteristic curve 30.

[0050] The division point DP set as described above can reliably suppress the portions of the 2 peaks pi, p2 of the characteristics of the negative electrode NE in the capacity direction of the reference capacity characteristic curve 30. That is, the reference capacity characteristic curve 30a of the load capacity smaller than the division point DP can reproduce the characteristics of the negative electrode characteristic curve 34, and on the other hand, the reference capacity characteristic curve 30b of the load capacity equal to or greater than the division point DP can reproduce the characteristics of the positive electrode characteristic curve 32.

[0051] Next, the principle of dividing the reference charge curve 20 obtained as the reference data will be described. As shown in Figure 6 the reference charge curve 20 can set the positive and negative electrode division point DP' which distinguishes the characteristics of the positive electrode PE and the negative electrode NE at a prescribed position in the direction of the load capacity (a position corresponding to the division point DP of the characteristic curve graph of the load capacity and the differential value) in the QV curve graph. When reversed in the voltage direction, it is understood that the reference charge curve 20a smaller than the positive and negative electrode division point DP' (low load capacity side) is the negative electrode QV curve 24 (refer to FIG. 6) described above, and the reference charge curve 20b equal to or greater than the positive and negative electrode division point DP' is the positive electrode QV curve 22 (refer to FIG. 5) described above. Figure 3) is similar in shape. This is because the low current capacity side of the reference charge curve 20 is influenced by the structure of the negative electrode NE (graphite structure in lithium ion batteries). Likewise, the reference charge curve 20b above the positive-negative electrode dividing point DP' (high current capacity side) is similar in shape to the above-mentioned positive electrode QV curve 22 (refer to Figure 3 ). This is because the high current capacity side of the reference charge curve 20 is influenced by the structure of the positive electrode PE.

[0052] For the above-mentioned reversed reference charge curve 20a smaller than the positive-negative electrode dividing point DP', by differentiating the voltage with respect to the current capacity, the same shape as the reference capacity characteristic curve 30a (refer to Figure 5 ) smaller than the dividing point DP is obtained. Likewise, for the reference charge curve 20b above the positive-negative electrode dividing point DP', by differentiating the voltage with respect to the current capacity, the same shape as the reference capacity characteristic curve 30b (refer to Figure 5 ) above the dividing point DP is obtained.

[0053] According to the above, as shown in Figure 5 , the fitting section 150 uses the reference capacity characteristic curve 30a smaller than the dividing point DP as the negative electrode characteristic curve 34 for the fitting operation of the low current capacity side of the target capacity characteristic curve 12. On the other hand, the fitting section 150 uses the reference capacity characteristic curve 30b above the dividing point DP as the positive electrode characteristic curve 32 for the fitting operation of the high current capacity side of the target capacity characteristic curve 12.

[0054] Returning to Figure 4 , the fitting section 150 sequentially fits the target capacity characteristic curve 12 of the target battery OB, the positive electrode characteristic curve 32 (reference capacity characteristic curve 30b) and the negative electrode characteristic curve 34 (reference capacity characteristic curve 30a) to each other at the parts where the correlation is strong in the fitting operation. Specifically, the fitting section 150 first performs a low current capacity side fitting operation of fitting the target capacity characteristic curve 12 to the negative electrode characteristic curve 34 (reference capacity characteristic curve 30a) on the low current capacity side. The low current capacity side fitting operation moves one of the target capacity characteristic curve 12 and the negative electrode characteristic curve 34 in the voltage direction, eliminating the shift in the voltage direction. Thereby, the parameters of the capacity drop of the negative electrode NE are roughly adjusted.

[0055] Next, the fitting section 150 performs a high current capacity side fitting operation of fitting the object capacity characteristic curve 12 and the positive electrode characteristic curve 32 (the reference capacity characteristic curve 30b obtained by differentiating the reference charge curve 20) on the high current capacity side. In the high current capacity side fitting operation, the curves in the object capacity characteristic curve 12 and the reference charge curve 20 that are moved by the low current capacity side fitting operation are moved in the voltage direction, thereby eliminating the deviation in the voltage direction. Accordingly, the parameters of the capacity decrease of the positive electrode PE are roughly adjusted. In addition, in the high current capacity side fitting operation, the curves in the object capacity characteristic curve 12 and the reference charge curve 20 that are moved by the low current capacity side fitting operation are moved in the current capacity direction, thereby eliminating the deviation in the current capacity direction. Accordingly, the parameters of the decrease of lithium ions are roughly adjusted.

[0056] That is, in the internal deterioration state estimation method of the deteriorated battery, the low current capacity side fitting operation is performed before the high current capacity fitting operation, thereby being able to temporarily fix the parameters of the capacity decrease of the negative electrode NE first. Then, the internal deterioration state estimation method of the deteriorated battery is able to stably adjust both the parameters of the capacity decrease of the positive electrode PE and the parameters of the decrease of lithium ions in a state where the parameters of the capacity decrease of the negative electrode NE are temporarily fixed by performing the high current capacity side fitting operation.

[0057] Also, the fitting section 150 performs a voltage fitting operation to adjust the parameters of the resistance rise (voltage deviation) that are ignored in the above-described low current capacity side fitting operation and the high current capacity side fitting operation. In this case, as shown in FIG. 6, the fitting section 150 differentiates the object charge curve 10 of the object battery OB with respect to the voltage and converts into a characteristic curve represented by the voltage and the differentiated value (hereinafter referred to as an object voltage characteristic curve 14). In correspondence thereto, the fitting section 150 differentiates the full battery QV curve 26 that is the reference charge curve 20 with respect to the voltage and converts into a characteristic curve represented by the voltage and the differentiated value (hereinafter referred to as a full battery characteristic curve 42). Figure 7

[0058] In other words, the fitting section 150 extracts the characteristic points of the shape by differentiating the parameters of the resistance rise that vary in the Y-axis direction (voltage direction) in the object voltage characteristic curve 14 and the full battery characteristic curve 42, and adjusts the parameters of the resistance rise in the voltage direction as shown in FIG. 7. Figure 7 ​the object voltage characteristic curve 14 and the full-cell characteristic curve 42 is weaker than the correlation of the object capacity characteristic curve 12 and the negative electrode characteristic curve 34 and the correlation of the object capacity characteristic curve 12 and the positive electrode characteristic curve 32. As described above, the full-cell QV curve 26 is calculated from the difference between the positive electrode QV curve 22 and the negative electrode QV curve 24, and the reason for this is that it is easily affected by the parameters of the capacity decrease of the positive electrode PE, the capacity decrease of the negative electrode NE, and the decrease of lithium ions.

[0059] Therefore, in the voltage fitting operation, the curves moved in the object voltage characteristic curve 14 and the full-cell characteristic curve 42 (reference charge curve 20) by the high current capacity side fitting operation are moved in the voltage direction (X-axis direction), and thus the deviation in the voltage direction is eliminated. Accordingly, the parameter of the resistance rise is roughly adjusted. That is, the internal deterioration state estimation method of the deteriorated battery first adjusts the parameter of the resistance rise in a state in which the parameters of the capacity decrease of the negative electrode NE, the capacity decrease of the positive electrode PE, and the decrease of lithium ions are temporarily fixed. Therefore, the fitting section 150 can set the changes of all the parameters that are the main factors of the capacity deterioration.

[0060] After the voltage fitting operation, the fitting section 150 performs a fine fitting operation, that is, fine adjustment of the deviation between the object charge curve 10 of the object battery OB and the reference charge curve 20 (positive electrode QV curve 22, negative electrode QV curve 24, full-cell QV curve 26). As described above, even if the characteristic curves obtained by differentiating the voltage with respect to the current capacity are fitted to each other, a slight deviation can occur in the charge curve (object charge curve 10 and reference charge curve 20) represented by the current capacity and the voltage. Therefore, the fitting section 150 eliminates the slight deviation by finally performing the fine fitting operation on the charge curve.

[0061] The full-cell QV curve 26 can apply the data itself acquired by the reference data acquisition process. The positive electrode QV curve 22 and the negative electrode QV curve 24 are obtained by dividing the reference charge curve 20 by applying the division point DP (positive-negative electrode division point DP') of the characteristic curve to the QV curve graph. That is, as shown in the right side graph of FIG. 6, the reference charge curve 20a smaller than the positive-negative electrode division point DP' becomes the negative electrode QV curve 24, and the reference charge curve 20b equal to or larger than the positive-negative electrode division point DP' becomes the positive electrode QV curve 22. In addition, in the negative electrode QV curve 24, the voltage corresponding to the current capacity equal to or larger than the positive-negative electrode division point DP' can be a value obtained by extending the voltage of the positive-negative electrode division point DP' by a certain value in this state (refer to FIG. 6). Figure 6 Figure 6 ​the fine line). Also, in the positive electrode QV curve 22, the voltage corresponding to the charge capacity smaller than the positive and negative electrode dividing point DP' can be a value obtained by extending the voltage of the positive and negative electrode dividing point DP' by a certain value in this state (see Figure 6 the fine line (one-dot chain line).

[0062] In the fine adjustment fitting operation, the fitting section 150 can set upper and lower limit values for each parameter of the capacity degradation. Also, the fitting section 150 can use the entire charge capacity = 0 to 100% for the region of the charge curve used in the fine adjustment fitting operation, or can divide into a low charge capacity region used in the low charge capacity side fitting operation and a high charge capacity region used in the high charge capacity side fitting operation.

[0063] The fitting section 150 completes the entire fitting operation by the end of the fine adjustment fitting operation. At the time of completion, the fitting section 150 stores each parameter of the capacity degradation (capacity drop of the positive electrode PE, capacity drop of the negative electrode NE, decrease of lithium ions, resistance rise) changed by each fitting operation in the storage section 148. In addition, the information processing device 144 also notifies the user of each parameter of the analyzed capacity degradation through a notification mechanism (monitor or the like) not shown. Thereby, the user can recognize the state of the capacity degradation of the object battery OB.

[0064] The measurement system 100 according to the present embodiment is basically configured as described above, and the following describes the flow of the internal degradation state estimation method of the degraded battery with reference to Figures 8A-9 to the internal degradation state estimation method of the degraded battery.

[0065] The internal degradation state estimation method of the degraded battery first performs a reference data acquisition process. Specifically, as shown in Figure 8A the measurement system 100 acquires the reference charge curve 20 with respect to the object battery OB before degradation or a battery of the same kind as the object battery OB, and stores the reference charge curve 20 in the storage section 148 (step S10). For example, the measurement system 100 charges the object battery OB before degradation by the charger 120, stores the charge current and the charge voltage at the time of charging in the data recorder 142, and calculates the reference charge curve 20 from the charge current and the charge voltage stored by the charge curve acquisition section 146.

[0066] Thereafter, the reference data generation section 152 of the information processing device 144 generates the positive electrode characteristic curve 32 and the negative electrode characteristic curve 34 used as the reference data of the fitting operation from the acquired reference charge curve 20 (step S20). In addition, at this time, the fitting section 150 can also generate the positive electrode QV curve 22 and the negative electrode QV curve 24.

[0067] Specifically, as shown in Figure 8BAs shown, the reference data generation unit 152 differentiates the current carrying capacity with respect to the reference charging curve 20 using voltage, and calculates a reference capacity characteristic curve 30 expressed as the current carrying capacity and the differential value (step S21). After this, the reference data generation unit 152 sets a dividing point DP on the reference capacity characteristic curve 30 to divide the curve (step S22). As described above, the dividing point DP is set at a predetermined position in the direction of increasing current carrying capacity, exceeding the two peaks p1 and p2 of the reference capacity characteristic curve 30 (such as the inflection point CP, where the curve drops after exceeding the higher peak p2). Then, the reference data generation unit 152 stores the reference capacity characteristic curve 30a, which is smaller than the dividing point DP, as the negative electrode characteristic curve 34 in the storage unit 148, and stores the reference capacity characteristic curve 30b, which is larger than the dividing point DP, as the positive electrode characteristic curve 32 in the storage unit 148 (step S23).

[0068] Furthermore, the reference data generation unit 152 sets the dividing point DP set on the reference capacity characteristic curve 30 as the positive and negative electrode dividing point DP' on the reference charging curve 20 before differentiation (step S24). The reference data generation unit 152 generates the negative electrode QV curve 24 by reversing the reference charging curve 20a, which is smaller than the positive and negative electrode dividing point DP', in the voltage direction, and generates the positive electrode QV curve 22 based on the reference charging curve 20b above the positive and negative electrode dividing point DP', and stores these curves in the storage unit 148 (step S25).

[0069] Then, the internal degradation state estimation method performs actual estimation processing on the degraded target battery OB to estimate the estimated capacity degradation (step S30). For example... Figure 9 As shown, in the actual estimation process, the measurement system 100 charges the degraded target battery OB using the charger 120, and stores the charging current and charging voltage during charging in the data logger 142 (step S31). Then, the charging curve acquisition unit 146 of the information processing device 144 acquires the target charging curve 10 based on the stored charging current and charging voltage (step S32). After this, the fitting unit 150 of the information processing device 144 performs a fitting operation between the target charging curve 10 and the reference data.

[0070] In the fitting operation, the fitting unit 150 differentiates the current carrying capacity of the target charging curve 10 with respect to voltage, and converts the target charging curve 10 into the target capacity characteristic curve 12 (step S33). Then, the fitting unit 150 sequentially extracts highly correlated regions from the target capacity characteristic curve 12, the positive electrode characteristic curve 32 (reference capacity characteristic curve 30b), and the negative electrode characteristic curve 34 (reference capacity characteristic curve 30a), and performs the fitting operation in order of high to low correlation.

[0071] Specifically, the fitting section 150 first performs a low load capacity fitting operation of fitting the object capacity characteristic curve 12 on the low load capacity side (a range of 0% to about 30% of the load capacity) with the negative electrode characteristic curve 34 (step S34). Thereby, one of the object capacity characteristic curve 12 and the negative electrode characteristic curve 34 (for example, the negative electrode characteristic curve 34) is moved in the differential value direction, and the shift in the differential value direction is made uniform. Then, by the low load capacity fitting operation, the parameter of the capacity drop of the negative electrode NE is changed.

[0072] Next, the fitting section 150 performs a high load capacity fitting operation of fitting the object capacity characteristic curve 12 on the high load capacity side (a range of 80% to about 100% of the load capacity) with the positive electrode characteristic curve 32 (step S35). Thereby, one of the object capacity characteristic curve 12 and the positive electrode characteristic curve 32 (for example, the positive electrode characteristic curve 32) is moved in the differential value direction and the load capacity direction, and the shift in the differential value direction and the load capacity direction is made uniform. Also, by the high load capacity fitting operation, the parameters of the capacity drop of the positive electrode PE and the reduction of lithium ions are changed respectively.

[0073] Then, the fitting section 150 converts the object charge curve 10 to an object voltage characteristic curve 14, and also converts the reference charge curve 20 (full cell QV curve 26) to a reference voltage characteristic curve 40 (full cell characteristic curve 42) (step S36). Also, the fitting section 150 performs a voltage fitting operation to fit the object voltage characteristic curve 14 with the full cell characteristic curve 42 (step S37). Thereby, one of the object voltage characteristic curve 14 and the full cell characteristic curve 42 (for example, the full cell characteristic curve 42) is moved in the voltage direction to make the shift in the voltage direction uniform. Also, by the voltage fitting operation, the parameter of the resistance rise is changed.

[0074] At the end of the fitting operations, the fitting section 150 performs a fine adjustment fitting operation (step S38). Thereby, the fitting section 150 can eliminate slight deviations on the charge curves (the object charge curve 10 and the reference charge curve 20 (the positive electrode QV curve 22, the negative electrode QV curve 24, the full cell QV curve 26)) to fit the object charge curve 10 and the reference charge curve 20 well.

[0075] When the processing of the above-described actual estimation processing ends, the information processing device 144 estimates the deterioration state of the object battery OB from the respective parameters of the capacity deterioration obtained in the actual estimation processing, and notifies the deterioration state through an appropriate notification mechanism (step S40). As a result, a user who sees the estimation result notified by the information processing device 144 can recognize the deterioration state of the deteriorated object battery OB with high accuracy.

[0076] The present application is not limited to the above-described embodiments, and various changes can be made in accordance with the gist of the application. For example, in the internal deterioration state estimation method for the deteriorated battery according to the present embodiment, the fitting operation on the low current capacity side having a strong correlation on the characteristic curve is performed first. However, in a case where the correlation on the high current capacity side is stronger than the correlation on the low current capacity side on the characteristic curve, the fitting operation on the high current capacity side is performed first in the internal deterioration state estimation method, of course.

[0077] In addition, in the fitting operation, the fitting section 150 is not limited to the method of fitting the characteristic curves after differentiating the charge curves (the target charge curve 10, the reference charge curve 20) to each other, and a method of fitting the charge curves to each other can also be employed. At this time, the positive electrode QV curve 22 and the negative electrode QV curve 24 as the reference data of the fitting can employ the above-described generation method. Alternatively, the positive electrode QV curve 22 can be obtained by integrating the reference capacity characteristic curve 30b on or above the division point DP, and similarly, the negative electrode QV curve 24 can be obtained by integrating the reference capacity characteristic curve 30a less than the division point DP.

[0078] Further, the low current capacity fitting operation (fitting of the target capacity characteristic curve 12 and the negative electrode characteristic curve 34) and the high current capacity fitting operation (fitting of the target capacity characteristic curve 12 and the positive electrode characteristic curve 32) are not limited to be performed once, respectively. For example, after the low current capacity fitting operation, the high current capacity fitting operation can be performed, and then the low current capacity fitting operation is performed again. Alternatively, the low current capacity fitting operation can be performed after the high current capacity fitting operation, and then the high current capacity fitting operation is performed again. In this way, by alternately performing the low current capacity fitting operation and the high current capacity fitting operation a plurality of times, the fitting accuracy can be improved.

[0079] The following description can grasp the technical idea and effects that can be understood from the above-described embodiments.

[0080] The first aspect of the present application is a method for estimating an internal deterioration state of a deteriorated battery, which obtains a reference charge curve 20 represented by a current-carrying capacity and a voltage for a target battery OB before deterioration or a battery of the same kind as the target battery OB, calculates a reference capacity characteristic curve 30 represented by a current-carrying capacity and a differential value by differentiating the voltage with respect to the current-carrying capacity for the reference charge curve 20, divides the reference capacity characteristic curve 30 by a division point DP in the direction of the current-carrying capacity, sets a reference capacity characteristic curve 30a smaller than the division point DP as a negative electrode component (negative electrode characteristic curve 34), and sets a reference capacity characteristic curve 30b equal to or larger than the division point DP as a positive electrode component (positive electrode characteristic curve 32), obtains a target charge curve 10 represented by a current-carrying capacity and a voltage for the target battery OB after deterioration, calculates a target capacity characteristic curve 12 represented by a current-carrying capacity and a differential value by differentiating the voltage with respect to the current-carrying capacity for the target charge curve 10, obtains changes in a plurality of parameters from a fitting operation of fitting each component of the set negative electrode component and positive electrode component of the reference capacity characteristic curve 30 to the target capacity characteristic curve 12, and thereby estimates a capacity deterioration of the target battery.

[0081] According to the above, in the method for estimating an internal deterioration state of a deteriorated battery, even if a destructive inspection is not performed on the secondary battery, reference data (a negative electrode component (negative electrode characteristic curve 34) and a positive electrode component (positive electrode characteristic curve 32) of the reference capacity characteristic curve 30) for estimating a capacity deterioration of the target battery OB can be easily obtained. Also, the method for estimating an internal deterioration state can well estimate a capacity deterioration of the target battery OB by performing a fitting operation between the target capacity characteristic curve 12 of the target battery OB and the reference data.

[0082] Further, the low current-carrying capacity side of the reference capacity characteristic curve 30 has a plurality of peaks pi, p2 in the increasing direction of the differential value, and the division point DP is set within a prescribed range of a peak p2 higher toward the increasing direction of the current-carrying capacity or beyond the peak p2. In the method for estimating an internal deterioration state, by thus setting the division point DP, the negative electrode component (negative electrode characteristic curve 34) having a plurality of peaks p2 on the low current-carrying capacity side of the reference capacity characteristic curve 30 can be extracted with high accuracy.

[0083] Further, the differential value of the reference capacity characteristic curve 30 decreases toward the increasing direction of the current-carrying capacity from the peak p2 higher, and the division point DP is set at an inflection point CP at which a change rate of the differential value changes. According to this, in the method for estimating an internal deterioration state, the negative electrode component (negative electrode characteristic curve 34) and the positive electrode component (positive electrode characteristic curve 32) of the reference capacity characteristic curve 30 can be reliably divided.

[0084] In addition, in the fitting operation, first, a low-load capacity fitting operation of fitting the negative electrode component (negative electrode characteristic curve 34) of the reference capacity characteristic curve 30, which has a strong correlation with the object capacity characteristic curve 12, to the object capacity characteristic curve 12 is performed, and then a high-load capacity fitting operation of fitting the positive electrode component (positive electrode characteristic curve 32) of the reference capacity characteristic curve 30, which has a weak correlation with the object capacity characteristic curve 12, to the object capacity characteristic curve 12 is performed. In this way, in the internal deterioration state estimation method, by performing the fitting operation in the order of the low-load capacity side and the high-load capacity side, the changes in each of the parameters of the capacity decrease of the negative electrode NE, the capacity decrease of the positive electrode PE, and the decrease in lithium ions among the plurality of parameters can be appropriately extracted.

[0085] In addition, with respect to the object charge curve 10, the object voltage characteristic curve 14 expressed by voltage and a differential value is calculated by differentiating the voltage with respect to the load capacity, and in the fitting operation, after the reference capacity characteristic curve 30 is fitted to the object capacity characteristic curve 12, a voltage fitting operation of fitting the reference voltage characteristic curve 40, which is obtained by differentiating the voltage with respect to the load capacity, to the object voltage characteristic curve 14 is performed with respect to the reference charge curve 20. According to this, by the internal deterioration state estimation method, the parameter of the voltage shift based on the resistance rise can be stably extracted.

[0086] In addition, by applying the division point DP set on the reference capacity characteristic curve 30 to the positive and negative division points DP' of the reference charge curve 20, according to this, the negative electrode QV curve 24 is generated from the reference charge curve 20a less than the positive and negative division points DP', and the positive electrode QV curve 22 is generated from the reference charge curve 20b equal to or greater than the positive and negative division points DP'. According to this, by the internal deterioration state estimation method, the positive electrode QV curve 22 and the negative electrode QV curve 24 can be used as reference data.

[0087] In addition, in the fitting operation, after the voltage fitting operation, a fine adjustment fitting operation of fitting the negative electrode QV curve 24 and the positive electrode QV curve 22 to the object charge curve 10 by fine adjustment is performed. According to this, by the internal deterioration state estimation method, even if a slight deviation occurs due to the fitting operation of the characteristic curve, the deviation can be eliminated by the fine adjustment fitting operation. Therefore, by the internal deterioration state estimation method, the capacity deterioration of the object battery OB can be estimated with higher accuracy.

[0088] In addition, a second aspect of the present application is a measurement system 100 that implements an internal deterioration state estimation method for a deteriorated battery, the measurement system 100 including a charger 120 that charges a target battery OB or a battery of the same kind as the target battery OB, and an estimation device 140 connected to the charger 120, the estimation device 140 acquiring a reference charge curve 20 represented by a current-carrying capacity and a voltage from a charge current and a charge voltage supplied to the target battery OB or the battery of the same kind as the target battery OB, calculating a reference capacity characteristic curve 30 represented by a current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage for the reference charge curve 20, dividing the reference capacity characteristic curve 30 by a division point DP in the direction of the current-carrying capacity, setting a reference capacity characteristic curve 30a smaller than the division point DP as a negative electrode component (a negative electrode characteristic curve 34), and setting a reference capacity characteristic curve 30b equal to or larger than the division point DP as a positive electrode component (a positive electrode characteristic curve 32), acquiring a target charge curve 10 represented by a current-carrying capacity and a voltage from a charge current and a charge voltage supplied to the target battery OB after deterioration, calculating a target capacity characteristic curve 12 represented by a current-carrying capacity and a differential value by differentiating the current-carrying capacity with respect to the voltage for the target charge curve 10, acquiring changes in a plurality of parameters from a fitting operation that fits each component of the set reference capacity characteristic curve 30 and the target capacity characteristic curve 12, and thereby estimating a capacity deterioration of the target battery OB. According to this, the measurement system 100 can easily obtain reference data without performing a destructive inspection on the secondary battery, and thereby can estimate the capacity deterioration of the target battery OB using the reference data.

Claims

1. A method for estimating the internal degradation state of a degraded battery, characterized in that, For the target battery (OB) before degradation or a battery of the same type as the target battery, a reference charging curve (20) expressed in terms of current carrying capacity and voltage is obtained. For the reference charging curve, the reference capacity characteristic curve (30) is calculated by differentiating the current carrying capacity with respect to the voltage, and representing the current carrying capacity and the differential value. The reference capacity characteristic curve is divided by a dividing point (DP) in the current-carrying capacity direction. The reference capacity characteristic curve smaller than the dividing point is set as the negative component, and the reference capacity characteristic curve above the dividing point is set as the positive component. For the degraded battery, a charging curve representing the current carrying capacity and voltage is obtained. For the object charging curve, the object capacity characteristic curve (12) is calculated by differentiating the current carrying capacity with respect to the voltage, and representing the current carrying capacity and the differential value. By fitting the negative and positive components of the established reference capacity characteristic curve to the target capacity characteristic curve, changes in various parameters are obtained, thereby inferring the capacity degradation of the target battery. In the fitting operation, First, a low-current-carrying-capacity fitting operation is performed to fit the negative component of the reference capacity characteristic curve, which has a strong correlation with the object's capacity characteristic curve, to the object's capacity characteristic curve. Next, a high-current-carrying-capacity fitting operation is performed to fit the positive component of the reference capacity characteristic curve, which has a weak correlation with the target capacity characteristic curve, to the target capacity characteristic curve.

2. The method for estimating the internal degradation state of a degraded battery according to claim 1, characterized in that, The low current-carrying capacity side of the reference capacity characteristic curve has multiple peaks (p1, p2) in the direction of increasing differential value. The dividing point is set at a higher peak among the plurality of peaks that increases in the direction of increasing current carrying capacity, or within a specified range exceeding that higher peak.

3. The method for estimating the internal degradation state of a degraded battery according to claim 2, characterized in that, The differential value of the reference capacity characteristic curve decreases as it moves from the higher peak toward the direction of increasing current carrying capacity. The dividing point is set at the inflection point (CP) of the rate of decrease of the differential value.

4. The method for estimating the internal degradation state of a degraded battery according to claim 1, characterized in that, For the charging curve of the object, the voltage characteristic curve of the object, expressed in terms of the voltage and the differential value, is calculated by differentiating the current carrying capacity with respect to the voltage (14). In the fitting operation, after fitting the reference capacity characteristic curve to the target capacity characteristic curve, a voltage fitting operation is performed on the reference charging curve to fit the reference voltage characteristic curve (40) to the target voltage characteristic curve, wherein the reference voltage characteristic curve is obtained by differentiating the current carrying capacity with respect to the voltage.

5. The method for estimating the internal degradation state of a degraded battery according to claim 4, characterized in that, The dividing point set on the reference capacity characteristic curve is used to divide the positive and negative electrode dividing points (DP') of the reference charging curve. Accordingly, a negative electrode QV curve (24) is generated from the reference charging curve smaller than the positive and negative electrode dividing point, and a positive electrode QV curve (22) is generated from the reference charging curve above the positive and negative electrode dividing point.

6. The method for estimating the internal degradation state of a degraded battery according to claim 5, characterized in that, In the fitting operation, after the voltage fitting operation, a fine-tuning fitting operation is performed to fit the negative electrode QV curve and the positive electrode QV curve to the target charging curve by fine-tuning.

7. A measurement system (100) for implementing a method for estimating the internal degradation state of a degraded battery, characterized in that, It includes: a charger (120) for charging the target battery or a battery of the same type as the target battery; and a estimation device (140) connected to the charger. The estimation device is configured such that, A reference charging curve, expressed in terms of current carrying capacity and voltage, is obtained based on the charging current and charging voltage supplied to the target battery or a battery of the same type as the target battery. For the reference charging curve, a reference capacity characteristic curve, represented by the current carrying capacity and the differential value, is calculated by differentiating the current carrying capacity with respect to the voltage. The reference capacity characteristic curve is divided by a dividing point in the current-carrying capacity direction. The reference capacity characteristic curve smaller than the dividing point is set as the negative component, and the reference capacity characteristic curve above the dividing point is set as the positive component. Based on the charging current and charging voltage supplied to the degraded target battery, a target charging curve, expressed in terms of current carrying capacity and voltage, is obtained. For the charging curve of the object, the capacity characteristic curve of the object, represented by the current carrying capacity and the differential value, is calculated by differentiating the current carrying capacity with respect to the voltage. By fitting the negative and positive components of the established reference capacity characteristic curve to the target capacity characteristic curve, changes in various parameters are obtained, thereby inferring the capacity degradation of the target battery. In the fitting operation, First, a low-current-carrying-capacity fitting operation is performed to fit the negative component of the reference capacity characteristic curve, which has a strong correlation with the object's capacity characteristic curve, to the object's capacity characteristic curve. Next, a high-current-carrying-capacity fitting operation is performed to fit the positive component of the reference capacity characteristic curve, which has a weak correlation with the target capacity characteristic curve, to the target capacity characteristic curve.

Images